Title of Invention

"METHOD OF TREATING A MATERIAL CONTAINED IN A VESSEL"

Abstract

The present invention relates to a method of treating a material contained in a vessel. This method involves a fluid present in the vessel and comprises at least one pressurisation step in which the pressure in the vessel is increased and at least one depressurisation step in which the pressure in the vessel is decreased. The invention further relates to an apparatus for executing this method and the products obtained by this method.

Full Text

A METHOD AND PROCESS FOR CONTROLLING THE TEMPERATURE-, PRES­SURE- AND DENSITY PROFILES IN DENSE FLUID PROCESSES The present invention relates to a method and appara­tus for controlling the temperature-, pressure- and density profiles within a vessel operating under high pressure con­ditions, in particular with a dense fluid under supercriti­cal conditions. More in particular the invention relates to measures and procedures, and an apparatus for controlling the temperature-, pressure- and density profile within pres­sure vessels for dense fluid treatment processes in order to improve the efficiency of such processes. BACKGROUND Fluids under high pressure, and in particular under supercritical conditions have attractive properties for many applications. The diffusivity, viscosity and surface tension are gas-like, while properties such as density and solubil­ity are liquid- like. Furthermore, the solubility is tune­able by simple means such as temperature and pressure. These attractive properties of such dense fluids at sub- or supercritical conditions have attracted increasing interest, and many applications are under development in re­search laboratories all over the world. Examples of applica­tions include impregnation (coating), extraction, reactions, synthesis of particles in the micrometer and nanometer range, synthesis of new advanced materials etc. The solubility in a dense fluid is a function of the fluid density, and the operating window for most appli­cations is typically selected from solubility considera­tions. The density of a dense fluid is a unique function of the temperature and pressure. Further, many applications in- volve processing of thermosensitive compounds or materials, where temperature or pressure gradients affects the me­chanical integrity of the end product or lead to unaccept­able large variations in the quality. This is particularly true for applications involving high pressure treatment of a porous media e.g. an impregnation (coating) or an extraction process. Such applications generally involves a pressurisation step, a step at a substantially constant pressure and a depres-surisation step. If e.g. the operating pressure is approxi­mately 150 bar, an adiabatic temperature increase of ap­proximately 40 C will occur during pressurisation if the free volume in vessel is 75 % and even more if the free vol­ume is higher. Likewise, a similar temperature decrease oc­curs during depressurization. If the free volumes not occu­pied by the material to being treated is present within the vessel, considerable higher temperatures may be present lo­cally. Such uncontrolled temperature increases are undesir­able in most applications as the temperature has a signifi­cant impact on the fluid density and pressure. For example, in a process utilizing supercritical CO2 operating at 145 bar and 45 °C, a temperature drop of only 6 °C will result in a pressure decrease of 20 bar in order to maintain a con­stant density. In practise, the temperature drop will be compensated by a change in density and not in pressure. As the solubility properties of a dense fluid is related to the density, temperature effects have a very strong influence on the performance of dense fluid processes and need to be con­trolled accurately. Most dense fluid applications are still only performed in laboratory to pilot scale in small diameter vessels in the milliliter to liter scale. In such dense fluid applications, temperature control is generally performed by using a jack­eted (double walled) vessel with a thermostated cooling or heating fluid to remove or add heat from the process, and a control of the inlet fluid temperature. However, when scaling up such processes to large scale in­dustrial vessels, it has been found that the heat transfer area of the vessel is not large enough to ensure sufficient heat transfer through the vessel walls. It has further been found that significant temperature- and density gradients may exist within the vessel, which lead to less efficient processes and may result in unacceptable high variations of the quality of the final product. DESCRIPTION OF THE INVENTION An objective of the present invention is to provide a method for improved control of temperature-, pressure- and density profiles within a pressure vessel for dense fluid treatment processes in order to improve the efficiency of such processes. Another objective of the present invention is to provide a method for improving the mixing of the fluid within the vessel. Further objectives includes providing method(s) for reducing energy consumption, and equipment size of such processes. Furthermore, it is an objective of the present inven­tion to provide an apparatus for use in treating a material by the method mentioned above. Additionally, it is an objec­tive to provide a product obtained by the above mentioned method. These objectives and the advantages that will be evi­dent from the following description is obtained by the fol- lowing preferred embodiments of the invention. In one embodiment of the method may involve a fluid present in the vessel and comprising at least one pressurisation step in which the pressure in the vessel may be increased and at least one depressurisation step in which the pressure in the vessel may be decreased. In another embodiment the method may further comprise recir-culating in at least part time of the method at least a part of the fluid, the re-circulating comprising: withdrawing from the vessel at least a part of the fluid contained within the vessel and feeding it to a re-circulation loop and subsequently feeding the fluid to the vessel. Furthermore, the method according to the invention may fur­ther comprise a holding step in which the pressure in the vessel may substantially be constant and/or in which the pressure of the fluid in the vessel may be varied according to a pre-selected schedule during a holding period of prede­termined length, the fluid may preferably be at supercriti­cal conditions during the holding period. Additionally, the method according may further comprise the step of controlling the temperature of the fluid in the re-circulation loop according to the present invention. In another preferred embodiment the heat may be added to and/or extracted from the fluid in the recirculation loop. Advantageously, the method may control temperature-, pres­sure- and/or density profiles within the vessel according to invention. Furthermore, the fluid after the pressurisation step may be in a supercritical state according to a preferred embodiment of the present invention. In a preferred embodiment the fluid may be selected from the group consisting of carbon dioxide, alcohol, water, eth­ane, ethylene, propane, butane, sulfur-hexafluoride, nitrou-soxide, chlorotrifluoromethane, monofluoromethane, methanol, ethanol, DMSO, isopropanol, acetone, THF, acetic acid, ethyleneglycol, polyethyleneglycol, N,N-dimethylaniline etc. and mixtures thereof. In another preferred embodiment the fluid may furthermore be selected from the group consisting of methane, pentane, hexane, cyclohexane, toluene, heptane, benzene, ammonia, propanol etc. and mixtures thereof. Additionally, the fluid according to the invention may be carbon dioxide. The fluid may furthermore comprise at least one cosolvent according to a preferred embodiment of the present inven­tion. Advantageously, the cosolvent may according to a preferred embodiment of the invention be selected from the group con­sisting of alcohol(s), water, ethane, ethylene, propane, bu­tane, sulfurhexafluoride, nitrousoxide, chlorotrifluoro­methane, monofluoromethane, methanol, ethanol, DMSO, isopro­panol, acetone, THF, acetic acid, ethyleneglycol, polyethyl­eneglycol, N,N-dimethylaniline etc. and mixtures thereoff. Furthermore, the cosolvent may according to a preferred em­bodiment of the invention be selected from the group con- sisting of methane, pentane, hexane, heptane, ammonia, ben­zene, etc. and mixtures thereof. The fluid may in another preferred embodiment further com­prise one or more surfactants, said surfactants being pref­erably selected from the group consisting of hydrocarbons and fluorocarbons preferably having a hydrophilic/lipophilic balance value of less than 15, where the HLB value is deter­mined according to the following formula: HLB = 7 + sum(hydrophilic group numbers)-sum(lipophilic group num­bers) . Advantageously, the fluid after the depressurisation step may be in a gas and/or liquid and/or solid state according to invention. In yet another preferred embodiments the fluid present in the re-circulation loop may have substantially the same thermodynamical properties as the fluid within the vessel, such as the fluid does not undergo a phase change to a liq­uid or solid state Furthermore, the re-circulation according to the invention may be performed during the pressurisation step and/or dur­ing the depressurisation step and/or, when appendant on claims 3-14, during the holding step. In another embodiment part of the fluid in the pressure ves­sel may be withdrawn to the re-circulation loop from/to a pressure in the pressure vessel below 70 bar, such as from/to a pressure below 60 bars, preferably from/to a pres­sure below 40 bars, and advantageously from/to a pressure below 2 bar. Furthermore, in preferred embodiment of the present inven­tion the fluid volume withdrawn from the vessel may corre­spond to the exchange of at least one vessel volume per hour, such as at least two vessel volume exchanges per hour, preferably at least 5 vessel volume exchanges per hour, and advantageously at least 10 vessel volume exchanges per hour, and preferably in the range of 10 to 20 vessel volume ex­changes per hour. Advantageously, the pressure in the vessel after pressurisa­tion step may be in the range 85-500 bar, preferably in the range 85-300 bar such as 100-200 bar according to the inven­tion. In another preferred embodiment the temperature in the ves­sel may be maintained in the range 20-300 °C, such as a 30-150 °C, preferable as 35-100 °C, such as 40-60 C Additionally, the rate of (de)pressurisation is controlled in a predefined manner in specific pressure intervals during the (de)pressurisation period according to the present in­vention. In an additional embodiment of the present invention the rate of pressure increase in at least part of the pressure range from 40 to 120 bars may at the most be one half of the maximum rate of pressurisation outside this range, such as one third of the maximum rate of pressurisation, and pref­erably at the most one fifth of the maximum rate of pres­surisation, and more preferably at the most one tenth of maximum rate of pressurisation outside this pressure range. In another preferred embodiment the rate of depressurisation rate in at least part of the pressure interval below 110 bars may at the most be one half of the maximum rate of de­pressurisation outside this range, such as one third of the maximum rate of depressurisation, and preferably at the most one fifth of the maximum rate of depressurisation, and more preferably at the most one tenth of maximum rate of depres­surisation outside this pressure range. When controlling the rate of the (de) pressurisation in the predefined manner the processed material, such as whole cork stoppers, wood and the like thermosensitive material, is not destroyed or damaged. Furthermore, the temperature of the fluid being fed into vessel during depressurisation may be increased by up to 10 °C, such as up to 25 °C compared to the inlet temperature during the holding period according to the invention. Advantageously, the temperature of the fluid being fed to the vessel during depressurisation may be maintained in the range 35-70 C at pressures above 40 bars according to an em­bodiment of the invention. In an embodiment of the present invention the pressure of the fluid in the vessel may be reduced during the holding period prior to being fed to means for separation. In another embodiment of the invention the rate of pressure increase during the pressurisation step may be typically in the range of 0,05-100 bar/min, such 0,1-20 bar/min, and preferably in the range of 0,1-15 bar/min, such as in the range of 0,2-10 bar/min. Furthermore, the pressure increase during the holding period or pressurisation step may be obtained at least partially by increasing the temperature of the fluid fed to the vessel, said temperature increase being preferably obtained by add­ing heat to the fluid before being fed to the vessel accord­ing to the invention. In yet another embodiment of the invention the rate of pres­sure increase during the pressurisation step and/or rate of pressure decrease during the depressurisation step may be controlled at least partially by adding or subtracting heat from the fluid, preferably the fluid being present in the re-circulation loop. According to an embodiment of the present invention the tem­perature of the fluid fed to the vessel during all or some of the holding period may vary according to a predefined schedule in order to introduce pressure variations corre­sponding to the temperature variations in the vessel. In another embodiment of the invention the temperature of the fluid fed to the vessel during all or some of the hold­ing period may vary according to a predefined schedule, and the pressure may be maintained at a substantially constant level by adding or extracting fluid to/from the vessel in order to introduce density variations corresponding to the temperature variations in the vessel. Additionally, the uppermost and lowermost levels of the tem­perature may according to an embodiment of the invention se­lected so as to provide a density change between the upper­most and lowermost level of up to 75 %, such as 50 % and preferable up to 30 %. Advantageously, the diameter of the vessel according to the invention may be at least 10 cm, such as at 25 cm, prefera- bly at least 40 cm, more preferably at least 60 cm, even more preferably at least 80 cm, and advantageously above 120 cm. Furthermore, the pressure vessel according to 'the present invention may either be horizontally or vertically posi­tioned. Additionally, the re-circulation loop according to the pre­sent invention may comprise at least one heat exchanger for addition or extraction of heat to/from said fluid. In another embodiment of the invention the re-circulation loop may comprise means for withdrawing and recirculating said fluid and wherein said means has/have a head of a mag­ nitude substantially similar to the dynamic pressure loss in the recirculation loop. In yet another embodiment said means may comprise a cen­trifugal pump, a centrifugal compressor, a piston pump and/or a piston compressor. Furthermore, the total head of the means according to the invention may substantially be the same as the dynamic pres­sure loss in the re-circulation loop, thereby providing a high volumetric throughput rather than a large pressure head. In an embodiment of the invention the pressure of the fluid present in any part of the external re-circulation loop may substantially be constant and in the same order magnitude as the pressure in the vessel at the specific stage in the cy­cle . Advantageously, a coating or an impregnation treatment may according to an embodiment of the present invention be per­formed in the pressure vessel. The re-circulation loop according to a preferred embodiment of the invention may further comprise a mixer vessel for mixing the fluid with chemicals and being arranged down­stream of a heat exchanger. Furthermore, the mixer vessel containing chemical (s) to may according to an embodiment of the invention be used for coating or impregnation. Advantageously, an extraction treatment may be or may addi­tionally be performed in the pressure vessel according to the present invention. In another embodiment of the invention the re-circulation loop may comprise means for separating the supercritical fluid from extracted components. Said means for separating the supercritical fluid from ex­tracted components may furthermore according to the inven­tion comprise one or more cyclone stages. Furthermore, the pressure of said cyclones may be decreasing between each stage according to the invention. In an embodiment of the invention the temperature of said cyclones may be decreasing between each stage. In another embodiment of the invention the operating pres­sure and temperature of at least the last cyclone may be be- low the critical point of said supercritical fluid. Additionally, the means for separating the supercritical fluid from extracted components may comprise or further com­prise an activated carbon filter according to an preferred embodiment of the invention. Furthermore, the separation may according to the invention be performed in a vessel comprising said supercritical fluid in both gaseous state and liquid state, the liquid phase be­ing preferably controlled to a specific level in the vessel. According to the present invention the separation may be performed in a gravimetric settling chamber comprising said supercritical fluid in both gaseous state and liquid state, the liquid phase being preferably controlled to a specific level in the vessel. I an embodiment of the invention the method may further com­prise at least one step of extraction of components from the material contained in the vessel, wherein said extraction comprising controlling the thermodynamical state in the ves­sel so as to obtain a pre-selected state in which extraction of components occur. According to an embodiment of the invention said extraction of components may be performed at a temperature of maximum 25 °C less than the boiling point of said components being extracted, preferably at a temperature of maximum 15 °C less than the boiling point of said components being extracted, more preferably at a temperature of maximum 10 °C less than the boiling point of said components being extracted and most preferably at a temperature substantially at or above the boiling point of said components being extracted. According to another embodiment of the invention said ex­traction of components from the material in the vessel may be performed at a temperature in vessel, which is close the maximum continuous operating temperature of the material contained in the vessel such as in the range -25 °C to + 25 °C of the maximum continuous operating temperature of the ma­terial to be treated, such as in the range -10 °C to + 10 °C of the maximum continuous operating temperature of the mate­rial to be treated. Furthermore, said extraction of components from the material in the vessel may be performed at a temperature in the ves­sel, which is below the thermal decomposition temperature of said material in the vessel, according to the invention. Additionally, the temperature in the vessel during said ex­ tracting of components from the material contained in the vessel, may according to the present invention be in the range 70-140 C. According to an embodiment of the invention the pressure in the vessel during said extraction of components from the ma­terial contained in the vessel, may be in the range 100-500 bar, such as in the range 120-300 bar. According to another embodiment of the invention the ratio of the amount of CO2 used to extract said components from the material contained in the vessel to the amount of material contained in the vessel may be in the range 1 kg/kg to 80 kg/kg, such as in the range 1 kg/kg to 60 kg/kg, and pref­erably in the range 1 kg/kg to 40 kg/kg such as in the range 5 kg/kg to 20 kg/kg. Advantageously, the components being extracted may according to the invention be components resulting in an undesired smell in the material to be treated. Additionally, the components being extracted from the mate­rial in the vessel may in another embodiment of the present invention may comprise extraction of organics such as or­ganic solvents, monomers, aromatic oils such as extender oil and organic acids. In an embodiment of the invention the potential allerghenes may be reduced by at least 10 %, such as reduced by at least 25 %, and preferable reduced by at least 50 %. Furthermore, the content of Zn may according to the present invention be reduced by at least 10 %, such as reduced by at least 25 %, and preferable reduced by at least 50 %. In embodiment of the invention inorganic species such as heavy metals such as Zn may substantially be maintained in the material after the treatment. Additionally, the thermodynamic state in the vessel may ac­cording to the present invention be controlled so as to ob­tain a selective extraction of components from the material contained in the vessel, while substantially maintaining other extractable components in the material. Advantageously, said selective extraction may according to the present invention further be controlled by substantially saturating the extraction fluid with components desired to be maintained in the material in the vessel. According to the invention said method may comprise subse­quent extraction steps, wherein the thermodynamic state in each step is controlled so as to obtain a pre-selected state in which a pre-selected extraction of components from the material in the vessel occur. Furthermore, the thermodynamic state in the first step may according to the present invention be selected so as to ob­tain a pre-selected state in which a pre-selected extraction resulting in an undesired smell in the material to be treated is substantially removed, while maintaining the ma­jority of other extractable compounds such as extender oils, aromatic oils, antioxidants and antiozonants within the ma­terial to be treated. In another embodiment of the present invention the thermody­namic state in the first step may be selected so as the to­tal amount of extract being removed in the first step com­pared to the total amount of extractables is in the range 10-35 %. The total amount of extractables being determined by e.g. the SOXLETH method (ASTM D1416) using pentane as solvent. In yet another embodiment of the invention the residual amount of aromatic oils, organic acids, antioxidants and an­tiozonants in the product may be at least 0.5 weight %, such as at least 1 weight %, and preferably at least 2 weight % such as at least 3 weight %, and the treated material being substantially free of smell. Furthermore, the thermodynamic state in the first step may according to the present invention be controlled so as the temperature in the vessel may be in the range 65-100 C such as in the range 70-90 C, and is controlled so as the pres­sure in the vessel may be in the range 100-200 bar such as in the range 140 -170 bar. Additionally, the thermodynamic state in the second extrac­tion step may according to the present invention be con­trolled so as the temperature in the vessel is in the range 80-140 C, and is controlled so as the pressure in vessel is in the range 200-300 bar. In a preferred embodiment of the invention said method may further comprise at least one step of extraction of compo­nents from the material contained in the vessel, wherein said extraction comprising: controlling the thermodynamical state in the vessel so as to obtain a pre-selected state in which extraction of components occur, withdrawing from said vessel at least a part of the fluid contained within the vessel during said step(s) of extraction of components from the material contained in the vessel,and feeding it to a re-circulation loop for separation of extracted components from said fluid, separating at least partly said extracted components from said fluid at a pressure above the critical pressure of said fluid feeding said separated fluid to the vessel. Furthermore, the pressure in the vessel for said extraction of components may according to the present invention be at least 150 bars, such as at least 200 bar, such as at least 300 bars. According to the present invention the pressure for said separation of said extracted components from said fluid may at least be 1/2 of the of the pressure in the vessel for said extraction of components, such as at least 2/3 of the pressure in the vessel for said extraction of components, such as at least 3/4 of the pressure in the vessel for said extraction of components. Advantageously, the thermodynamic state for separation of may according to the present invention be controlled so as the solubility of the extracted components in said fluid is maximum 20 % of the solubility of the extracted components at the pressure in the vessel for said extraction of compo­nents, such as is maximum 10 % of the solubility of the ex­tracted components at the pressure in the vessel for said extraction of components, and preferable maximum 5 % of the solubility of the extracted components at the pressure in the vessel for said extraction of components. Furthermore, said method further may according to the pre­sent invention be comprise at least at least one impregna­tion or coating step for impregnating the material contained in the vessel, wherein said impregnation or coating step comprising controlling the thermodynamically state in the vessel so as to obtain a pre-selected state in which impreg­nation components, such as one or more reactant contained in the vessel, impregnates or coates the material contained in the vessel. According to the invention said impregnation or coating step may involve a chemical reaction. Additionally, the chemical (s) used in said impregnation or coating step may according to the present invention be pre­cursors for a chemical reaction. Advantageously, said chemical reaction may according to the present invention be a silylation. In a preferred embodiment of the present invention said chemical(s) may be impregnated or coated in substantially a monolayer on said material contained in the vessel. In another embodiment of the present invention the surface coverage of said chemical(s) on said material contained in the vessel, may be at least 5 molecules/nm2, such as at least 6 molecules/nm2. Furthermore, the holding period may according to the present invention be comprise one or more extraction steps, and wherein the extraction step is followed by one or more im­ pregnation steps. Additionally, the holding period may according to the pre­sent invention be comprise one or more extraction step(s), and followed by one or more impregnation step(s), and wherein the impregnation may be followed by one or more step(s) of increasing the temperature, and wherein the one or more steps of increasing the temperature may be followed by one or more steps of decreasing the temperature. According to an embodiment of the invention the last step(s) of the holding period may comprise one or more extraction step(s). According to another embodiment of the invention excess im­pregnation chemical (s) from the one or more impregnation step(s) may be extracted from said material contained in the vessel in said last one or more extraction step(s) . In a preferred embodiment of the invention a supercritical thermodynamical state may be maintained in the vessel during all of the steps in the holding period. In another preferred embodiment of the invention the holding period may comprise one or more extraction steps, wherein the pressure in the vessel may be kept constant, and wherein the extraction step may be followed by one or more impregna­tion steps during which the pressure in the vessel may be kept substantially at the same level as during the impregna­tion step, and wherein no substantially pressure change oc­cur in the vessel during change over from the extraction to the impregnation step. According to the invention the method may further comprise a further impregnation step following the first impregnation step, and wherein the pressure during further impregnation step may be higher or lower than the pressure during the first impregnation step. Additionally, the impregnation step or the further impregna­tion step may according to the present invention be followed by one or more steps of increasing the temperature, prefera­bly while keeping the pressure constant, one or more of the one or more steps of increasing the temperature may prefera­bly be followed by one or more steps of decreasing the tem­perature, preferably while keeping the pressure constant. In an embodiment of the present invention said method may further comprise agitating the fluid and/or the material present in the vessel at least part time during the treat­ment of the material. In another embodiment of the invention the vessel may be an agitated vessel, such as a fluidised bed, and/or preferably an expanded bed, and/or such as a motor driven mixer such as a rotating drum and/or an impeller. According to a preferred embodiment of the invention the vessel may be a fluidised bed. Furthermore, the material being fluidised may according to the present invention be the material to be treated. According to another preferred embodiment of the invention the material being fluidised may be a bed material not being the material to be treated. Additionally, the fluidisation may according to the present invention be obtained by the flow of the fluid being fed to the vessel. Advantageously, said method may according to the present in­vention be further comprise spraying of coating or impregna­tion chemical(s) into said agitated vessel in at least part time of said depressurisation step. According to the present invention said coating or impregna­tion chemical(s) may be sprayed into said agitated vessel as a slurry. In a preferred embodiment of the present invention said coating or impregnation chemical(s) may be substantially in­soluble in the fluid contained ion the vessel. In another preferred embodiment of the present invention at least a first part of the fluid withdrawn from the vessel during depressurisation may be fed to a buffer tank having an outlet connected to the vessel either directly or via the re-circulation loop, wherein it is condensed, preferably by direct spraying into the liquid phase of said fluid. By spraying the fluid direct into the buffer tank and thereby obtaining a condensation direct at the inside walls of the buffer tank in stead of using a condenser, such con­densing equipment is no longer needed and it is thereby ob­tained to save cost and energy. According to the invention at least a second part of fluid withdrawn from the vessel may be fed to a condenser wherein it is condensed, the condensed fluid being subsequently fed into a buffer tank having an outlet connected to the vessel either directly or via the recirculation loop. By implementing the mentioned re-circulation or re-circulation loop in an embodiment of the present invention the method of treating a material contained in a vessel may be executed without mixing extractants and impregnation chemicals, or without the need to depressurise before im­pregnation of the material. An efficient process is hereby obtained since the treatment of extracting and impregnating the material may be executed in turns in a continues process without depressurise the vessel all the way down the start­ing pressure for then again pressurise the vessel for the subsequent treatment. The re-circulation thereby is time and energy saving. It further has the advantage of being able of extracting ex­cess reactants such as monomers for a polymerisation reac­tion in a single stage process. In an embodiment of the present invention the temperature in the buffer tank may be controlled so as to maintain substan­tially constant, said controlling being obtained at least partially by splitting the first and the second part of fluid being withdrawn from the vessel and fed to the buffer tank, thereby balancing the heat consumed by the evaporative cooling generated from the fluid being withdrawn from the buffer tank through the outlet thereof. In another preferred embodiment if the invention the con­trolling of the temperature in the buffer tank may further comprise controlling the liquid level in the buffer tank by adding make-up fluid from a fluid make-up tank. Furthermore, said method may according to the present inven­tion comprise several treatment lines operating in parallel and in different states in the cyclic method, and wherein said several treatment lines are connected to said buffer tank and have: common feeding system(s) for pressurisation, common lines for depressurization including compressors, common condenser(s), - common line(s) for spraying said fluid into the liquid phase - common make-up system(s) According to an embodiment of the invention said several treatment lines may comprise 2 to 6 lines, such as 3-4 lines. Additionally, the pressure in said buffer tank may according to the present invention be in the range 55-70 bars, and preferably in the range 60-70 bars. In an preferred embodiment of the invention the temperature in said buffer tank is in the range 12-30 C, and preferably in the range 15-25 C. In another preferred embodiment of the invention the volume of the buffer tank compared to the total system volume of all treatment lines (excluding the buffer tank) may be in the range of 50-300%, such as in the range of 100-150%. The present invention may further comprise a method of pro­ducing particles, preferably comprising nanocrystallites, said method utilises a method according to any of the pre­ceding claims, wherein chemicals, such as reactants to form the particles by chemical reactions, are introduced into the fluid to participate in a particle formation process. Said particle formation process may according to the present invention be selected among the following particle formation processes: RESS (rapid expansion of supercritical solu­tions) , GAS (Gas Antisolvent) , SAS (solvent Anti Solvent) , SEDS (Solution Enhanced Dispersion by supercritical fluid), PCA (Precipitation with Compressed Antisolvent), PGSS (Pre­cipitation from Gas-saturated Solutions) and variations thereoff. Furthermore, additional nucleation sites in the vessel may according to the present invention be provided by addition of seed particles or filling material. According to the present invention the number of nucleation sites may further be increased by introducing ultrasound or vibrating surface effect. Additionally, the particles formed may according to the pre- sent invention have a crystallite size in the nanometer range. Furthermore, said particles may according to the present in­vention comprise oxide(s) such as metal oxide(s) . In a preferred embodiment of the present invention said par­ticle process may be a modified sol-gel process using a metal alkoxide as precursor. In yet another embodiment of the invention said oxides is selected among silica, alumina, zirconia, titania, and mix­tures thereof. In a further embodiment of the invention said oxides is se­lected among ceria, yttria, zinc, iron, nickel, gerraania, barium, antimonia, and mixtures thereof. Advantageously, said oxides may according to the present in­vention be a thermoelectrical material or a precursor for a thermoelectric material. Additionally, said oxides may according to the present in­vention comprise a semi-conducting material. Furthermore, said oxides may according to the present inven­tion comprise a piezoelectric material. According to a preferred embodiment of the present invention said thermoelectrical material may comprise Bi2Te3 or Bi2Te3 doped with semimetals and/or metals. According to another preferred embodiment of the present in­vention said particles comprises carbide(s), nitride(s) or boride(s). Additionally, said particles may according to the present invention comprise one or more pharmaceutical or biological material(s). Furthermore, the material to be treated may according to the present invention be wood. In a preferred embodiment of the invention the treatment may be an extraction and the components being extracted com­prises terpenes and resins. In another embodiment of the invention the wood may be im­pregnated with an organic fungicide or an organic insecti­cide . Advantageously, the wood may according to the present inven­tion be impregnated with chemical(s) comprising propicona-zole. Furthermore, the wood according to an embodiment of the in­vention may be impregnated with a chemical(s) comprising te-buconazole. According to the present invention the wood may furthermore be impregnated with chemicals comprising IPBC. In an embodiment of the invention the material treated may be cork. In another embodiment of the invention the material to be treated may be a porous sorbent. Additionally, said porous sorbent may according to the pre­sent invention be selected among aerogels, zeolites, sili-cagel, activated carbons, silicas, aluminas, zirconias, ti-tanias. Furthermore, said porous sorbent may according to the pre­sent invention have a pore size in the range 5-100 nm, such as in the range 5-50 nm and preferably in the range 5-20 nm. According to an embodiment of the present invention said po­rous sorbent may be impregnated with a silane compound. Advantageously, the chemical (s) for said impregnation or coating step may according to the present invention be se­lected among organosilanes, alkoxysilanes, chlorosilanes, fluorosilanes, such as octadecyl silanes, n-octadecyltriethoxysilane, n-octadecyldimethylmethoxysilane, perfluorooctyltriethoxysilane, hexamethyldisilazane, tri-chlorooctadecylsilane, mercaptopropylsilane, mercaptopropyl-trimethoxysilane, ethylenedimaine, trimethoxysilane, tri-methylchlorosilane, ODDMS, tetraethoxysilane. Furthermore, said porous sorbent may according to the pre­sent invention be a functionalized porous sorbent for use for chromatographic separations. Additionally, said functionalized porous sorbent may accord­ing to the present invention be used as stationary phase for liquid chromatography. In a preferred embodiment of the present invention said po­rous sorbent may be used in a chromatographic column for the purification or analysis of pharmaceutical or biotechnologi-cal compounds. Additionally, in an embodiment of the present invention said porous sorbent may be used in a chromatographic column for the purification or analysis of insuline. Furthermore, the material being treated may according to the present invention be wool, preferably the method comprises extraction of lanoline. In another embodiment of the present invention the material to be treated may be a polymer. In yet another embodiment of the present invention the mate­rial to be treated may be a rubber. Additionally, the material in the vessel may according to the present invention be a polymer or elastomer such as se­lected from the group consisting of polyethylene, polypro­pylene, polystyrene, polyesters, polyethylene terephtalate, polyvinyl chloride, polyvinyl acetates, polyoxymethylene, polyacryloamide, polycarbonate, polyamides, polyurethane, copolymers thereof, chlorinated products thereof, rubbers and chlorinated rubber, silicone rubbers, butadiene rubbers, styrene-budiene-rubbers, isoprene polymers, vulcanised fluororubbers, silicone rubbers. In a preferred embodiment of the invention said material may be a recycled material. In another preferred embodiment of the invention said mate­rial may be vulcanised rubber. In yet a preferred embodiment of the invention said material to be treated may comprise vulcanised rubber. Furthermore, the material to be treated may according to the present invention be a silicone rubber. Advantageously, the material to be treated may according to the present invention be a particulate material such as a granulate, a powder or a fine powder. According to an embodiment of the present invention said im­pregnation chemical(s) may comprise ethylene, propylene, styrene, acrylic esters, acrylic acids, urethanes, epoxides, epoxy resins. Additionally, according to the invention said chemical(s) may comprise a radical initiator such as AIBN. In a preferred embodiment of the present invention the im­pregnation chemical may be a pharmaceutical drug. The invention further comprise an apparatus for use in treating a material, said apparatus comprising a vessel adapted to contain material to be treated and a fluid taking part in the treatment, said apparatus further comprising pressure means for increasing / decreasing the pressure in the vessel so as to perform at least one pressurisation step in which the pressure in the vessel in increased and at least one depressurisation step in which the pressure in the vessel is decreased and a recirculating loop for recirculating at least a part of the fluid, the recirculation loop being adapted to withdrawing from the vessel at least a part of the fluid contained within the vessel and feeding it to the re-circulation loop and subsequently feeding the fluid to the vessel. Additionally, said apparatus may according to the invention further comprise agitating means for agitating, such as fluidise, the fluid and the material present in the vessel at least part time during treatment of the material. Furthermore, said apparatus may in another preferred embodi­ment of the invention further comprise a fluid recovery device, preferably being condenser, in fluid communication with the vessel. Advantageously, said fluid recovery device may according to the invention further comprise: means for withdrawing gaseous fluid from said fluid re­covery device and feeding it to the vessel, means for withdrawing liquid fluid from said fluid re­covery device and feeding it to the vessel, means for condensing fluid from the vessel by cooling means for condensing fluid by direct spraying into the liquid phase of said fluid recovery device, a heat exchanger immersed in said liquid phase of said fluid recovery device. In an additional embodiment of the invention said fluid re­covery device maycommunicate with several vessels such as 2-6 vessels. Said apparatus may according to the invention further mans according to the above mentioned thereby being adapted to carry out the method according to any of the preceding claims. The present invention may further relate to a product ob­tainable from any of the above mentioned method. Additionally, the present invention may further relate to a treated wood product comprising impregnation chemical(s) such as propiconazole, tebuconazole, IPBC and mixtures thereof. In a preferred embodiment of the invention said impregnation chemical (s) may be present in a concentration in the range 0,05-1,0 g/m3, such as in the range 0,1-0,5 g/m3 and pref­erably in the range 0,1-0,3 g/m3, such as in the range 0,15-0,25 g/m3. In another embodiment of the present invention the wood product may be a preservation effect against fungis. In yet another embodiment the wood product may have a pres­ervation effect against insects such termites. Furthermore, the concentration of components resulting in cork taint in wine such as Tri-Chloro-Anisole (TCA) may ac­cording to the invention be reduced with more than 95 %, such as more than 97,5 %, such as more than 99 %. The present invention may further relate to a porous chroma-tographic material obtainable from any of the above men­tioned method, wherein said material functionalized by a silylation impregnation and wherein said impregnation chemi­cal (s) may be deposited substantially in a monolayer. Additionally, said material may comprise a surface coverage of said impregnation chemical(s) of at least 5 molecules/nm2 such as at least 6 molecules/nm2. The present invention may further relate to an odourless polymer product obtainable from any of the above mentioned method, wherein said product may be substantially free of adversely smelling compounds. The present invention may further relate to a polymer prod­uct obtainable from any of the above mentioned method, wherein said material may be substantially free of excess monomers and volatile organic solvents. In a preferred embodiment of the present invention said polymer product may comprise a rubber. In another preferred embodiment of the present invention said rubber may comprise vulcanised rubber. In yet another preferred embodiment of the present invention said non-smelling effect may be stable at least up to a tem­perature of 50 C, such as up 70 C, and preferably up to 90 C or more. Furthermore, said non-smelling effect may according to an embodiment of the present invention be stable at least up to a temperature of 50 C, such as up 70 C, and preferably up to 90 C or more. Advantageously, the rubber may according to an embodiment of the present invention comprise antioxidants and antiozonants in an amount of at least 0,25 weight %, such as at least 0,5 wt %. Additionally, the residual amount of aromatic oils, organic acids and antiozonants in the product may according to an- other embodiment of the present invention be at least 0,5 weight %, such as at least 1 weight %, and preferable at least 2 weight %. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a typical pressure-time curve for a cyclic process for a supercritical treatment. FIG. 2 shows a diagrammatic representation of the recircula-tion principle according to the present invention. Fig: 3 shows an example of the effect of pulsation in an im­pregnation process according to the present invention. FIG. 4 shows an example of a prior art cyclic supercritical extraction process. FIG. 5 shows diagrammatic representation of an extraction process according to the present invention Fig. 6 shows a diagrammatic representation of a process lay­out suitable for operating any combination of a supercriti­cal extraction process, a supercritical impregnation step, a particle formation step and a curing step at an elevated temperature. DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODI­MENTS The present invention is further illustrated by the draw­ings . In FIG. 1, a pressure-time curve for a cyclic supercritical treatment process is shown. Initially, the material to be treated is loaded into a pressure vessel. After a certain material handling and purging time, the cyclic supercritical treatment process may be divided in to three consecutive steps: a pressurisation period a holding period for supercritical treatment at ele­ vated pressure a depressurisation period In the pressurisation period the pressure vessel is pressur­ised by adding a fluid to the vessel until the pressure in the vessel exceeds the desired treatment pressure. The tem­perature in the vessel may be controlled by conventional means such as controlling the inlet temperature to the ves­sel in a heat exchanger before introducing the fluid into the pressure vessel and the temperature of the walls in the vessel, e.g. by using a jacketed pressure vessel with a heating or cooling fluid, electrical heating etc. The rate of pressure increase is shown to be constant, but may have any shape. The holding period for treatment starts, when the desired pressure and temperature have been established. The treat­ment process may be an extraction or impregnation process, but may also be a particle formation process. During the holding period for treatment the pressure may be maintained substantially constant, or may be varied according to a pre­defined schedule as described in the examples. After the holding period the pressure vessel is depressur- ised in a controlled manner as further described in the ex­amples . Fig. 2 is a diagrammatic representation of a re-circulation principle according to the present invention. The material to be treated is loaded into the pressure treatment vessel. The pressure treatment vessel is pressurised up to the de­sired operating pressure by feeding CO2 to the pressure ves­sel by the CO2 feed pump. The temperature of the feed is con­trolled by the feed heat exchanger. The pressure treatment vessel is depressurised by withdrawing CO2 from the vessel to the CO2 outlet in a controlled manner. From/to a pressure below 70 bars such as below 60 bars, preferable below 40 bars, and advantageously from a pressure below 2 bars, part of the C02 in the pressure treatment vessel is withdrawn from the vessel to a re-circulation loop by the re-circulation pump, and returned to the pressure vessel after optionally passing a re-circulation heat exchanger for controlling the temperature in the vessel. Fig. 3 shows results from a supercritical wood impregnation process, which is further exemplified in the examples 1 and 2 . A porous item to be impregnated is divided into two identi­cal pieces so as to eliminate any effect of variations in the material to be treated. In the experiment the reference items is first impregnated with an impregnation chemical at a substantially constant pressure of 150 bar and a temperature of 50 °C. The effi­ciency of the impregnation process is evaluated by the im­pregnation efficiency defined as the amount of the impregna­tion chemical present in the C02 phase compared to the amount of the impregnation chemical deposited in the items after treatment. In the first experiment, the pressure vessel is first pres­surised up to the reference conditions of approximately 150 bars and 50 °C, whereafter the vessel is depressurised to 130 bars under substantially constant temperature, whereaf­ter the pressure vessel is pressurised again to 150 bars us­ing the approximately the same concentration of the impreg­nation chemical in the CO2 in the vessel. After the pressuri-sation, the pressure vessel is depressurised in a controlled manner. As seen from the left figure no significant effect on the impregnation efficiency is observed. A second experiment is conducted in a similar manner, wherein the pressure level after the first depressurisation is reduced to 120 bars instead of 130 bars. As seen from the figure a significant improvement of the impregnation effi­ciency is obtained. The results given in this figure is applicable for impregna­tion of porous materials in general, and in particular for impregnation of materials like rubber and cork. Fig. 4 shows a typical industrial multi vessel process i.e where several extraction vessels are used sequentially in parallel. However, for simplificity only 2 vessels (8, 18) are shown. The operating procedure is only described for the extraction vessel.(8), and the procedure will be similar for the extraction vessel (18). The extraction vessel (8) is loaded with the material to be extracted. Liquid carbon di­oxide is stored in the storage tank (1) . Liquid CO2 is trans­ferred from the storage tank (1) via the pump (2) and the valve (3) to the intermediate storage tank (4). When the plant is started up, liquid C02 from the intermedi­ate storage tank (4) is transferred by the pump (6) to the extraction vessel (8), if the valve (5) is open. In the heat exchanger (7) the liquid COS is evaporated and the tempera­ture of the gaseous C02 is controlled. The pressurization of the extraction vessel (8) by means of the pump (6) and the evaporator (7) is continued until the operating pressure in the supercritical region is reached. The cyclic supercritical extraction process is now performed by expanding CO2 through the control valve (9), adjusting the temperature in the heat exchanger (10) and further expanding the C02 through the valve (11) and subsequently separating the extracted material in the separation units (12, 13). Subsequently the CO2 is liquefied in the condenser (14) and returned to the intermediate storage (4), from where it is transferred back into the extraction vessel via the pump (6) and the evaporator (7). Supercritical C02 is thus continuously circulated through the extraction vessel (8) for the required amount of time to reach the required extraction yield. After the extraction process has been finalized the vessel (8) are depressurized. This is in the prior art process ac­complished by opening valves (15, 16) . The pressure in ves­sel (18) is substantial ambient pressure and by opening the valves (15, 16) the pressures between vessels (8, 18) are equalized. By the expansion of the CO2 from vessel (8) to vessel (18) the CO2 is cooled and to avoid formation of liq­uid CO2 or dry ice, heat has to be added in the heat exchang­ers (7, 17) . Further emptying of vessel (8) is accomplished by extracting CO2 from vessel (8) via the valves (9, 19) and the compressor (20). As the temperature of the CO2 is increased during com­pression, the CO2 gas stream has to be cooled in heat ex­changer (17) before entering the vessel (18). As the pressure in vessel (8) reaches a level of typically 2-5 bar the emptying operation will stop. The residual CO2 in vessel (8) is vented to the atmosphere and additional CO2 is added to vessel (18) from liquid intermediate storage (4) through the pump (20) and heat exchanger (17) until the op­erating pressure of vessel (18) is reached. The cyclic ex­traction process can now be performed with vessel (18) in the same manner as described for vessel (8) . A disadvantage of such prior art process is that the energy consumption is high due to the liquefaction of the fluid and due to the need for re-heating the fluid before entering the pressure vessel. Further equipment costs is increased due to a high heat transfer area required in the condenser and in the heating/cooling system compared to the present inven­tion. A further disadvantage of such prior art process is the fact that the rate of pressurization and depressurization of the vessels cannot be controlled independently as two vessels at all times are interconnected. Generally by transferring CO2 directly from one vessel to the next, the possibility of op­timizing both pressurization and depressurization rates in­dependently are lost. Fig. 5 illustrates the principles of an industrial scale su­percritical process for the extraction of Tri-Chloro-Anisole (TCA) from cork according to the present invention. TCA represents a major quality problem for wines stored in bot­ tles with cork stoppers due to the development of the so- called "cork taste". Development of cork taste may destroy the wine and make it undrinkable. It should be understood that process comprises several ex­traction lines operating in parallel as indicated in the figure. Typically a process according to the present inven­tion comprises 2-6 lines operating sequentially in different stages of the cyclic process. The various lines share some major components, such as the buffer tank (1), the control valves (17), (18), the condenser (19), the heat exchanger (2), and the compressors (21), (23). These shared components are described in details below. For simplification only one vessel is shown in the figure. A typical cyclic supercritical extraction process is per­formed as follows: C02 is stored/recovered in a common buffer tank (1) shared between several extraction lines as indicated on the figure. The pressure in the buffer tank (1) will typically be in the range 50-70 bars, and preferably at a pressure of approxi­mately 60 bars. The level of the liquid CO2 in the buffer tank (1) is controlled by pumping liquid CO2 from a make up tank (not shown in the drawing) , and the pressure is con­trolled by controlling the temperature in the buffer tank (1). When starting the pressurisation of vessel (6) gaseous C02 is drawn from buffer tank (1) and piped at a predeter­mined rate through a heat exchanger (2), valve (3), heat ex­changer (4), and valve (5). Optionally liquid C02 may also be withdrawn from the buffer tank through the valve (26), the pump (27) and the valve (28) . Withdrawing gaseous CO2 from the buffer tank (1) generates an evaporative cooling in the buffer tank (1), which is further described below. From a pressure of about 2 bar part of the C02 in the vessel is withdrawn and re-circulated by the compressor (9) . The CO2 from the compressor (9) is mixed with the C02 from the buffer tank (1) after the valve (3) . When the vessel (6) has reached a pressure slightly below the pressure in the buffer tank, then valve (3) is closed and valve (8) is opened and the compressor (9) is used to compress the gaseous CO2 from approx. 60 bar to the final supercritical pressure for the extraction, which typically is 120 bar. Throughout the pres-surisation process the compressor (9) operates and provides a large re-circulation rate through the vessel (6). This al­lows for optimum control of temperature and heat and mass transfer throughout the vessel. The extraction process is accomplished by purging typically 10-100 kg C02 per kg cork granulate through the vessel (6) at a temperature of typi­cally 60° C. The CO2 exiting vessel (6) is expanded through the valve (7) reheated in the heat exchanger (10) and ex­panded through the valve (11) . Subsequently TCA and other components like waxes are removed in the separators (12, 13) whereupon the C02 is cleaned for residual content of TCA in an active carbon filter (14). The C02 exiting the carbon fil­ter (14) is recompressed in the compressor (9) and the tem­perature controlled in the heat exchanger (4) to provide the required pressure and temperature for the extraction in the vessel (6). When depressurising the vessel (6) vapour phase C02 is piped in a controlled manner through valve (15), valve (16). The major part of the CO2 is generally entering the buffer tank (1) through valve (17) , from where it is con­densed by direct spraying into the liquid C02 phase in the buffer tank (1). Part of the C02 pass through the valve (18) into the condenser (19) , where the CO2 gas is liquefied be­fore entering the buffer tank (1). As heat is generated from the direct condensation in the buffer tank (1) , the heat need to be removed in order maintain a substantially con­stant temperature in the buffer tank (1) . This is done by balancing the heat consumed by the evaporative cooling gen­erated from the gas being withdrawn from the buffer tank (1). This balancing of the temperature in the buffer tank is performed by Controlling the split between the amount of CO2 enter­ ing the buffer tank (1) as a liquid through the valve (18) and the condenser (19), and the amount of C02 be­ ing introduced directly into the liquid phase in the buffer tank (1) through the valve (17), Pine tuning of the temperature in the buffer tank by extracting or adding heat through the heat exchanger (25) immersed in the liquid phase in the buffer tank (1) and/or optionally withdrawing liquid CO2 from the buffer tank (1) to an external heat exchanger (not shown) and re-circulating the liquid C02 to the buffer tank (1), c) Controlling the liquid level in the buffer tank (1) by adding make up C02 from a C02 make-up tank (not shown) It should be noticed that the buffer tank (1) needs to have a certain volume in order to work properly as a buffer tank, and in order to damp potential fluctuations of the tempera­ture and pressure in the tank. The volume of the buffer tank compared to the total system volume of all lines (excluding the buffer tank (1) ) is generally in the range 50-300 %, and preferably in the range 100-150 %. The further depressurisation of extraction vessel (6) from approx. 60 bars to a pressure in the range 20-30 bars is performed through valve (15), valve (20) and compressor (21) . The valve (24) is closed during this operation to en­sure that no back flow occur. The compressor (21) will gen- erally be a one-stage compressor. After the compressor the CO2 is discharged to the buffer tank (1) through the valves (17) and/or (18) and heat exchanger (19) as described above for the pressure range 120-60 bars. It should be noticed that depressurisation from 60 to a pressure in the range 20-30 bars also could be performed us­ing the re-circulation compressor (9), but a system of two compressors is generally preferred due to capacity and re­dundancy considerations. The depressurisation of the vessel from a pressure in the range 20-30 bars to a pressure in the range 2-6 bars (6) is performed through the valve (22) by the compressor (23). Af­ter the compressor the C02 is again discharged to the buffer tank (1) through the valves (17) and/or (18) and heat ex­changer (19) as described above. The final depressurisation is performed by venting off the fluid vessel to the atmos­phere (not shown) . The pressure for this depressurisation step is set by the desired recovery of the CO2. If a high COZ recovery is desired, the pressure for the final stage will typically be in the range 1-3 bars above ambient pressure. In this case the compressor (23) will comprise a three stage compressor. If a lower C02 recovery is desired, the compres­sor (23) may comprise a 2 stage compressor. It should be noticed that the compressors (21, 23) are gen­erally only in used in a limited part of cyclic process, such as 10-35 % of the total cycle time. As such compressors are relatively expensive the compressors (21, 23) are pref­erably shared between several extraction lines as indicated in the figure. It should further be noticed that the com­pressors (21, 23) may comprise more than one compressor op­erating in the same pressure range in order to fulfil redun­dancy or economical demands. Fig. 6 shows a diagrammatic representation of a process lay­out suitable for operating any combination of steps of a su­percritical extraction step, a supercritical impregnation step, a particle formation step, and/or a curing step at an elevated temperature. Compared to the extraction process ac­cording to the present invention shown in Fig. 5. this proc­ess diagram further comprise a mixer vessel (29) in the re-circulation loop for addition of chemical(s), and/or cosol-vent(s)and/or surfactants. The mixer is preferably contain­ing a high surface area packing material so as to provide a high contact area for addition of said chemical(s), and/or cosolvent(s), and/or surfactant(s). It should be understood that said chemical(s) , cosolvent(s) and/or surfactant(s) may be added to the same vessel but said re-circulation loop may comprise more than one mixer for addition of said chemi­cal (s), and/or cosolvent(s) and/or surfactants separately. Preferred combinations of said supercritical extraction step(s), supercritical impregnation step(s) and curing step(s) at elevated temperature step are: a) An extraction process, wherein the holding period for ex- i traction is followed by a holding period for impregnation at substantially the same pressure level as for the hold­ing period for extraction. An extraction process, wherein the holding period for ex­ traction is followed by a holding period for impregnation at substantially the same pressure level as for the hold­ ing period for extraction, and further followed by a fi­ nal extraction process to remove excess impregnation chemicals. An extraction process, wherein the holding period for ex- traction is followed by a holding period for impregnation at substantially the same pressure level and wherein said impregnation period is followed by a curing step at ele­vated temperature, and optionally finalised by a final extraction step before depressurisation. d) A process as described in d) , wherein the impregnation step and subsequent curing step at elevated temperature is repeated multiple times so as to the control the im­pregnation level. EXAMPLES ILLUSTRATIVE EXAMPLE 1: CYCLIC PROCESS FOR SUPERCRITICAL IMPREGNATION The conventional supercritical impregnation process includes 3 consecutive steps: The material to be treated is introduced into a pressure vessel. In the first step the vessel is pressurized by adding a fluid to the reactor, until the pressure in the vessel ex­ceeds the desired pressure of said fluid. The temperature of the fluid may be controlled by conventional means before the introduction into the vessel, and the temperature in the re­actor is further controlled by controlling the wall tempera­ture, to a level exceeding the desired temperature of the fluid. At the established temperature and pressure the en­closed fluid in the vessel enters the supercritical state, and the impregnation compounds become soluble in the fluid. As pressurisation of the vessel is achieved by introducing fluid, and as the fluid by definition is compressible, fur- ther compression of the fluid takes place in the vessel. The derived heat of compression is dissipated in the materials enclosed in the reactor, and finally removed through the re­actor walls. The heat of compression may lead to a signifi­cant temperature increase. If for example carbon dioxide is compressed from 1 bar to 200, which is a normal impregnation pressure, the corresponding adiabatic temperature increase exceeds 100 °C. It is obvious to one skilled in the art, that the presence of a solid porous material filling most of the internal vessel volume is hindering the dissipation of heat through the walls, as convective heat transport is hindered, and that the effect of the hindrance is proportional to the distance from the vessel center to the wall, i.e. increasing with increasing vessel diameter. Therefore large-scale su­percritical impregnation in conventional equipment is accom­panied by an unwanted heating of the material being impreg­nated, which might lead to crucial damage of thermo sensi­tive materials like wood. Furthermore, the flow of the su­percritical fluid into the porous material to be impregnated creates a force acting on the material, which might cause further damage, particularly as the mechanical strength of the material is reduced at increasing temperature. The second step is a treatment at practically constant tem­perature and pressure, during which impregnation compounds are distributed throughout the material to be impregnated. Furthermore, during this step the heat of compression is dissipated to the vessel walls, if sufficient residence time is allowed, establishing the intended temperature throughout the reactor. Upon the treatment, depressurisation is conducted in the third step, by controlled evacuation of the fluid from the vessel. The expansion of the fluid leads to reduced solubil­ity of the impregnation compounds, which therefore precipi- tate at the internal surfaces of. the porous material, pro­viding the intended impregnation. The energy required to ex­pand the fluid is taken from the remaining fluid, and the other materials in the reactor, and finally balanced by heat introduced through the reactor walls. During the depressuri-sation the expanding fluid is flowing from the inside to the outside of the porous material to be impregnated. As heat is supplied through the reactor walls and required inside the porous material, heat and mass fluxes are oppositely di­rected, causing a very poor heat conductance. Therefore lo­cal cold spots are formed inside the porous material, at which condensation of the expanding fluid might occur, once the critical pressure and temperature is passed. Formation of liquid in the pores of the material dramatically in­creases the flow resistance, leading to formation of very large forces acting on the porous structure, which therefore shows tendency to cracking or bursting. Once again, the im­pact of the heat transfer hindrance is increased at increas­ing vessel diameter. In order to avoid structural damage to the impregnated material, a very slow depressurisation rate have to be applied. ILLUSTRATIVE EXAMPLE 2 CYCLIC PULSATION PROCESS FOR SUPERCRITICAL IMPREGNATION During the holding period for impregnation period of the su­percritical impregnation, as described in the example 1, the pressure and temperature are maintained practically con­stant. Consequently distribution of the impregnation com­pounds in the porous material to be impregnated is mainly due to diffusion, as no convective supercritical solvent flow exist inside the porous material. To enhance and accel­erate the impregnation compound distribution, a pressure pulsation may be induced during the impregnation period, creating a convective flow inside the porous structures. In order to preserve the dissolved impregnation compounds in­side the vessel, the pressure pulsation is preferably in­duced by a pulsation of the supercritical solvent inlet tem­perature, i.e. by alternating in a cyclic pattern the set point of the heat exchanger in the re-circulation loop. By pulsating the pressure, a pumping effect is created in the porous material, which very efficiently equals out any gra­dients in temperature or solute concentrations existing in the material. A further benefit from the pressure pulsation during the im­pregnation period may be derived in the case where the lower limit of the cyclic pressure pulsation is below the solubil­ity limit of the impregnation compounds at the applied tem­perature and intended concentration of impregnation com­pounds in the supercritical solvent. The solubility of a substance in a supercritical solvent is to a first approxi­mation determined by the solvent temperature and density, i.e. by reactor temperature and pressure. The solubility limit is defined as the lower pressure at a certain tempera­ture, at which the intended amount of a substance is solu­ble. If the pressure is reduced below this limit, precipita­tion takes place. If a supercritical impregnation is executed at an impregna­tion pressure above the solubility limit, but with pressure pulsation reducing the reactor pressure below the solubility limit during the impregnation period, the following is tak­ing place; during the last part of the pressurization and the first part of the impregnation period, the porous struc­ture will be filled with supercritical solvent containing dissolved impregnation compounds. During the pressure reduc- tion part of the pulse the solubility limit is broken, and precipitation of the dissolved compounds on the interior surfaces of the porous material takes place. During the pressurization part of the pulse, supercritical solvent is introduced into the porous structure from the reactor bulk, carrying in more dissolved impregnation compounds, which are precipitated during the next pulse. The net result is an ac­tive transport of impregnation compounds into the material to be impregnated caused by the pressure pulsation. The effect of such pulsation is verified in experiments, im­pregnating spruce cut in pieces. Every log is parted in two identical pieces, with one serving as reference, i.e. being impregnated according to the method described in example 2, and the other being impregnated with pulsation, and other­wise identical process parameters. The wood is impregnated at a pressure of 150 bar and a temperature of 50 °C, with an impregnation compound addition corresponding to a solubility limit of approximately 125 bar. The concentration of impreg­nation compound precipitated in the wood is determined by chemical analysis. The expected deposition of the compound is calculated as the concentration dissolved in the bulk solvent phase, multiplied with the solvent volume entrapped in the wood at impregnation conditions, i.e. the deposition achieved if the total amount of solvent introduced into the wood was carrying a full load of impregnation compound. The impregnation efficiency is defined as the ratio of the meas­ured deposition to the expected deposition. The impregnation efficiency derived from pulsating impregna­tion above the solubility limit is described in the left part of the figure, and denoted "20 bar peak". The effect of pulsation above the solubility limit is rather limited, as no significant increase in impregnation efficiency is found, when compared to the reference pieces. Impregnation with pulsation below the solubility limit is shown in the right part of the figure, and denoted "30 bar peak". The effect of pulsation below the solubility limit is significant. The impregnation efficiency is doubled, when compared to the reference logs. ILLUSTRATIVE EXAMPLE 3 CYCLIC SUPERCRITICAL EXTRACTION PROCESS WITH RECIRCULATION One aspect of the present invention involves a cyclic proc­ess for supercritical extraction treatment of materials. Hence, in a preferred embodiment of the present invention the material to be treated by the supercritical extraction process is initially loaded in to a pressure vessel. In many applications, the cyclic process is initiated by purging the vessel with the specific fluid used in the cy­clic process in order to minimize contamination of the fluid. This purging may be conducted by applying a vacuum (pressure below ambient pressure) to the vessel, while feed­ing the specific fluid to the vessel for a certain period of time. Typically this purging time will be in the range 1-20 minutes. In other cases this purging may be performed by pressurisation of the vessel up to a pressure of 0,5-5 bars above ambient pressure and venting the vessel until the pressure is substantially the same as ambient pressure. It should be understood that any combination of purging using a vacuum and venting from a pressure above ambient pressure may be applied and that this procedure may be repeated. After the purging period the vessel is pressurised by the specific fluid at a predetermined inlet temperature to the vessel and a predetermined rate of pressure increase in the vessel. In many applications the inlet temperature to the vessel will be controlled to achieve a temperature within the pres­sure vessel above the condensation temperature of the spe­cific fluid, and below a certain maximum temperature dic­tated by the material to be treated in the vessel. The inlet temperature of supercritical fluid is typically controlled in the range 0-200 °C, such as 0-150°C, and preferably in the range 15-100 °C and more preferably in the range 35-60 °C during pressurization. The set point for the inlet tem­perature may be constant during the pressurisation period, but in many applications according to the present invention the inlet temperature is increasing during the pressurisa­tion period. As described above control of temperature within the vessel is critical for many applications. In the prior art, tem­perature control is performed by control of inlet tempera­ture and/or control of the inlet and outlet temperature of a heating or cooling fluid fed to a jacketed vessel. However, applying such systems for large diameter vessels, creates temperature gradients within the vessels as the heat trans­fer area is not large enough to ensure sufficient heat transfer capacity. Hence, in a preferred embodiment of the present invention part of the fluid is withdrawn from the vessel in at least part of the pressurisation period, and fed to an external re-circulation loop comprising at least one heat exchanger for adding or extracting heat from the fluid, where after the fluid is re-circulated to the pressure vessel after con­ditioning. It is further preferred that the fluid do not un­dergo a phase change in the external re-circulation loop during the pressurisation period. The withdrawing of the fluid from the vessel to the external re-circulation loop is preferably performed from a pressure below 40 bars such as a pressure below 20 bar, and advanta­ geous at a pressure below 2 bars. In order to maximize the effect of the re-circulation the fluid flow withdrawn needs to have a certain size. Hence, in a preferred embodiment according to the present invention, the fluid flow corresponds to replacement of at least one vessel volume per hour, such as at least 5 vessel volumes per hour, and preferably at least 10 vessel volumes per hour and more preferably between 10-50 vessel volumes per hour and advantageously in the range 10-20 vessel volumes per hour. The rate of pressure increase is typically in the range 0,05-100 bar/min, such as 0,1-20 bar/min and preferably in the range 0,1-15 bar/min, such as in the range 0,2-10 bar/min. The rate of pressure increase may be constant or vary during the pressurisation period. Generally means for pressurisa­tion have a constant volumetric flow rate. Hence, the maxi­mum mass flow rate of said means increases with the density of the fluid used for pressurisation. Hence, for a constant temperature within the vessel the rate of pressure increase will vary with the fluid density if said means were operat­ing at maximum capacity during the pressurisation period. However, in addition to the increase of the mass transfer mass flow rate, the rate of pressure increase may also be obtained by increasing the temperature to the vessel or by a combination of the two. However, many materials relevant for the present invention are characterised by loosing/decreasing their mechanical strength at temperatures above a certain level and increas­ing the pressurisation rate above a certain level at spe­cific temperatures results in pressure damages of the mate­rial being treated. It has been found that certain pressure intervals exist in which the risk of such pressure damages are particularly high. Hence, one aspect of the present invention involves control­ling the rate of pressurisation and the temperature in spe­cific pressure intervals during the pressurisation period, while operating higher rates outside this interval. It has been found that the rate of pressure increase is particu­larly critical in the pressure range from 40 to 120 bars, such as in the range 60 to 110 bars, and in particular in the range 65 to 100 bars. Hence, in a preferred embodiment the rate of pressurisation in at least part of the interval 40 to 120 bars is at the most one half of the maximum rate of pressurisation outside this range, such as one third of the maximum rate of pressurisation, and preferably at the most one fifth of the maximum rate of pressurisation, and more preferably at the most one tenth of maximum rate of pressurisation outside this pressure range. In many applications, the majority of the fluid fed to the vessel is C02. However, it may also comprise other fluids such as one or more co-solvents, one or more surfactants or impurities such as air and/or water and/or traces of the ex­tracted compounds. Suitable surfactants are hydrocarbons and fluorocarbons preferably having a hydrophilic/lipophilic balance value of less than 15, where the HLB value is determined according to the following formula: HLB = 7 + sum (hydrophilic group numbers) -sumdipophilic group numbers) Examples and descriptions of surfactants can be found in the prior art e.g. W09627704 and EP0083890, which hereby with respect to disclosure concerning surfactants and their preparation are incorporated herein by reference. The temperature and pressure during the holding period for extraction depend of the specific substrate to be treated and the species to be extracted. Examples of suitable co-solvents are water, ethane, ethyl-ene, propane, butane, sulfurhexafluoride, nitousoxide, chlorotrifluoromethane, monofluoromethane, methanol, etha-nol, DMSO, isopropanol, acetone, THF, acetic acid, ethylene-glycol, polyethyleneglycol, N,N-dimethylaniline etc. and mixtures thereoff. The pressure during the holding period for extraction will typically be in the range 85-500 bar. The target temperature during the extraction period will typically be 35-200 °C such as 40-100 °C. During the holding period for extraction, part of the fluid is continuously withdrawn from the vessel. The extracted species is separated from the extraction fluid by decreasing the pressure in one or more steps. Each step comprising a separator for separating said extracted compounds from the extraction fluid. Non-limiting examples of suitable separa­tors are gravimetric settling chambers, cyclones and poly­phase separators. After separation of the extracted species from the extraction fluid, the extraction fluid may be fur­ther purified in an activated carbon filter before re-circulation to the pressure vessel. The duration of the holding period for extraction will typi­cally be in the range 5-300 minutes. As for the pressurisation period the re-circulation flow rate during the holding period needs to be of a certain size in order to enhance mass transfer and to obtain a substan­tially uniform extraction quality in the whole pressure ves­sel. Hence, in a preferred embodiment according to the pre­sent invention, the fluid flow withdrawn corresponds to re­placement of at least one vessel volume per hour, such as at least 5 vessel volumes per hour, and preferably at least 10 vessel volumes per hour and more preferably between 10-50 vessel volumes per hour and advantageously in the range 10-20 vessel volumes per hour. After the pressurisation period, the vessel is depressurised at a controlled temperature and rate of depressurisation. Hence, in another aspect of the present invention part of the fluid is withdrawn from the vessel in at least part of the depressurisation period, and fed to an external re-circulation loop comprising at least one heat exchanger for adding or extracting heat from the fluid, where after the fluid is re-circulated to the pressure vessel after condi­tioning. It is further preferred that the fluid do not un­dergo a phase change in the external re-circulation loop during the depressurisation period. For some materials the inlet temperature in at least part of the depressurisation period may advantageously be increased compared to the inlet temperature of the holding in order to compensate for the considerable cooling arising from the ex­pansion. Typically, the inlet temperature during depressurisation may be increased by up to 10 °C, such as up to 25 °C compared to the inlet temperature during the holding period. The actual inlet temperature during depressurisation will typically be maintained in the range 35-70 C at pressures above 40 bars. As for the pressurisation and holding periods, the re-circulation flow rate during the depressurisation period needs to be of a certain size in order to ensure substan­tially uniform pressure-, temperature- and density condi­tions within the vessel. Hence, in a preferred embodiment according to the present invention, the fluid flow withdrawn during the depressurisation period corresponds to replace­ment of at least one vessel volume per hour, such as at least 5 vessel volumes per hour, and preferably at least 10 vessel volumes per hour and more preferably between 10-50 vessel volumes per hour and advantageously in the range 10-20 vessel volumes per hour. According to the present invention the rate of depressurisa­tion is typically in the range 0,05-100 bar/min, such as 0,1-20 bar/min and preferably in the range 0,1-15 bar/min, such as in the range 0,2-10 bar/min. It has further been found that many materials may be damaged during depressurisation if the depresssurisation rate is too high in specific pressure regions, while operation in other regions can be performed at considerable higher depressuri-sation rates. More specifically it has been found that the rate of depressurisation is critical at pressures below 110 bars, such below 90 bars, and in particular in the range 15 to 90 bars. Outside this range operation at considerable higher depressurisation rates is possible without damaging the material. Hence, in a preferred embodiment of the present invention, the rate of depressurisation in at least part of the pres­sure interval below 110 bars is at the most one half of the maximum rate of depressurisation outside this range, such as one third of the maximum rate of depressurisation, and pref­erably at the most one fifth of the maximum rate of depres­surisation, and more preferably at the most one tenth of maximum rate of depressurisation outside this pressure range. The depressurisation period may further comprise one or more holding periods at constant pressure in which the pressure and temperature conditions inside the material is allowed to stabilise. In the pressure interval above 2-5 baro the expanded fluid is typically recovered for reuse. Below a pressure below 5 baro such as below 2 baro, the fluid is typically vented off at a controlled depressurisation rate. Before opening the pressure vessel and unloading the mate­rial, the vessel is generally purged with air in order to avoid any exposure risk by the fluid, when opening the ves­sel. This purging may be conducted by applying a vacuum (pressure below ambient pressure) to the vessel, while feed­ing air to the vessel for a certain period of time. Typi- cally this purging time will be in the range 1-20 minutes. In other cases this purging may be performed by pressurisa-tion of the vessel with air up to a pressure of 0,5-5 bars above ambient pressure and venting the vessel until the pressure is substantially the same as ambient pressure. It should be understood that any combination of purging using a vacuum and venting from a pressure above ambient pressure may be applied and that this procedure may be repeated. ILLUSTRATIVE EXAMPLE 4 CYCLIC SUPERCRITICAL EXTRACTION PROCESS WITH RECIRCULATION AND PULSATION A substantial discussion of the many uses of supercritical fluid extraction is set forth in the text "Supercritical Fluid Extraction" by Mark McHugh and Val Krukonis (Butter-worth -He inmann, 1994). Supercrical fluid extraction is often applied for materials comprising confined spaces i.e. micro-or nanoporous structures. Despite higher diffusivity than liquids, supercritical fluids still exhibit limited ability to rapidly transfer extracted material from confined spaces to a bulk supercritical phase. Lack of thorough mixing of the fluid in the bulk phase, and between the fluid in the bulk phase and the fluid in the confined spaces limits the mass transfer rate to essentially the diffusion rate of the solute(s) [see e.g. EP 1,265,683]. It should further be no­ticed that a pressure and/or temperature gradient generally exist between the bulk phase and the centre of the confined space thereby creating a convective transport of the fluid into the confined space. Thus, the diffusive transport of solutes needs to take place in the opposite direction of the convective transport, thereby reducing the efficiency of the process and thereby increasing processing costs. Various attempts have been made to by apply pressure pulses to provide a pumping effect to address this problem. Wetmore et al (US 5,514,220) teaches that cleaning of porous mate­rial can be improved by raising or spiking the extraction pressure by at least 103 bar between the uppermost and low­ermost levels of extraction pressure. Other examples of pressure pulse cleaning is given in US 5,599,381, US 4,163,580, and US 4,059,308). Common for these prior methods is that while such large pressure swings provides signifi­cant improved extraction efficiencies (up to 7 fold), they result in severe cooling of the supercritical fluid and the pressure vessel due to the Joule-Thompson effect. For in­stance, at a temperature of 50 °C a pressure drop of 103 bars results in an adiabatic drop in temperature of approxi­mately 18,5 °C. Such large pressure pulses and temperature drops are undesirable as they may induce fatigue problems of the pressure vessel, and further may cause the fluid to con­dense either in the confined spaces (capillary condensation) or even in the bulk phase. Horhota et al (EP 1,265,583) dis­closes a pressure modulation technique, where repeated pres­sure pulses of less than 30 % relative difference between the uppermost and lowermost pressure levels are applied in an attempt to overcome the drawbacks of the large pressure pulse techniques. Small pressure pulses according EP 1,265,583 may provide enhanced mixing in bulk phase, and may be suitable for applications such as supercritical parts cleaning. However, small pressure pulses will not create the desired significant pumping effect, when applied for low permeability materials such as micro- or nanoporous materi­als . A further objective of the present invention is to provide a method for improving the mass and heat transfer in a cyclic dense fluid extraction process not suffering the drawbacks in the prior art. Hence, according to an aspect of the present invention a cy­clic dense fluid extraction process is performed as de­scribed in example 3, wherein part of the fluid is continuously withdrawn from the pres­sure vessel during the holding period, the extracted species is separated from the extraction fluid by decreasing the pressure in one or more steps, each of said step comprises separation means for separat­ing said extracted compounds from the fluid, said separated fluid is fed to one or more heat ex­changer (s) for addition or extraction of heat, and re-circulated to the pressure vessel characterised in that the inlet temperature to the vessel is modulated between two or more temperature levels so as to provide a modulation in the fluid density within the vessel. In a preferred embodiment the uppermost and lowermost levels of the inlet temperature is selected so as to provide a den­sity change between the uppermost and the lowermost level of up 75 %, such as up to 50 %, and preferable up to 30 %. The temperature modulation is generally performed at least two times and may be repeated multiple times such as 5-100 times. In order to achieve the desired efficiency, the volume of the fluid withdrawn from the pressure vessel needs to be of a certain size such as corresponding to replacement of at least 5 vessel volumes per hour and preferably in the range 10-50 vessel volumes per hour such as replacement of 10-20 vessel volumes per hour The temperature modulation is in particular effective for enhancing mass- and heat transfer efficiency for a super­critical extraction process during the holding period. How­ever, temperature modulation also be applied in the pres-surisation and/or the depressurisation period for minimisa­tion of the temperature- and/or pressure gradients between the bulk phase and the centre of a confined space. This par­ticularly relevant in relation to the treatment of low per­meability materials containing confined spaced in a micro-or nanoporous structure. In another aspect of the present invention, the temperature modulation of the inlet temperature is performed in combina­tion with a pressure pulsation technique. In a further aspect of the present invention said tempera­ture modulation is performed during the holding period and combined with an overall pressure control loop for maintain­ing the pressure in the pressure vessel substantially con­stant by adding or extracting fluid to/from the pressure vessel. In another preferred embodiment of the present invention the temperature modulation of the inlet is combined with a pres­sure modulation or pressure pulsation technique, wherein the lowermost pressure level are obtained at substantially the same time as the uppermost temperature level and vice versa. ILLUSTRATIVE EXAMPLE 5 CYCLIC SUPERCRITICAL EXTRACTION PROCESS FOR TREATMENT OF POLYMERS Another aspect of the present invention involves supercriti­cal treatment of polymers containing impurities such as ex­cess monomers and/or solvents from the polymerisation reac­tion. Other undesired impurities may be compounds resulting in an unpleasant smell, or compounds limiting the further processing of the materials, such as reduced adhesion. Exam­ples of such components are extender oils, and/or organic acids present in recycled vulcanised rubbers. Hence, in a preferred embodiment of the present invention such treatment of polymers, which undergoes a supercritical extraction process as described in example 3 and 4 in order to remove the undesirable residues, and make the materials suitable for further processing. The removal of these compo­nents makes the polymer matrix more porous and more accessi­ble for e.g. modification by reactive impregnation or adhe­sive . ILLUSTRATIVE EXAMPLE 6 CYCLIC SUPERCRITICAL TREATMENT OF PARTICULATE MATTER Many important aspects of the present invention involve su­percritical treatment of particulate matter. In such appli­cations it is often desirable to introduce movement and/or mixing of/in the particulate phase. Hence, for such applica­tions it may further be advantageous to use an agitated ves­sel such as a fluidised bed or a motor driven mixer such as an impeller or rotating drum in addition to the re-circulation and pulsation methods described herein. ILLUSTRATIVE EXAMPLE 7 CYCLIC SUPERCRITICAL EXTRACTION AND IMPREGNATION Another aspect of the present invention involves the super­critical treatment of a material as described in the exam­ples 3-6, wherein the material subsequent to the holding pe­riod for extraction, further undergoes a holding period for impregnation prior to the depressurisation period. Said im­pregnation period is preferably performed at substantially the same average pressure as for the extraction period. During said holding period for impregnation part of the fluid is withdrawn from the pressure vessel and fed to an external re-circulation loop further comprising at least one mixer vessel for addition of impregnation chemicals and/or co-solvents and/or surfactants to the fluid before re-circulating the fluid to the pressure vessel. Said mixing vessel (s) for addition of chemicals are preferable posi­tioned after the heat exchanger(s) for adding or extracting heat and is operating at substantially the same pressure as the pressure within the pressure vessels. The chemicals may be added to the mixer vessel at the begin­ning of the cyclic process, or at any part of the cyclic process. It is further generally preferred to apply a pulsation method as described in example 2 and 4 in both the holding period for extraction and the holding period for impregna­tion in order to improve the effiency of both the extraction and impregnation process. Hence, in a preferred embodiment according to the present invention part of the fluid is con­tinuously withdrawn from the pressure vessel and fed to a re-circulation loop comprising one or more heat exchanger(s) for addition or extraction of heat, and re-circulated to the pressure vessel. The inlet temperature to the vessel is modulated between two or more temperature levels in order to provide a modulation in the fluid density within the vessel, while an overall control loop is maintaining the pressure within the pressure vessel substantially constant by adding or extracting fluid to/from the pressure vessel. After the holding period for impregnation the pressure ves­sel is depressurised according to the methods described in examples 3-6. ILLUSTRATIVE EXAMPLE 8: SUPERCRITICAL PRODUCTION OF NANOPARTICLES ACCORDING TO THE CURRENT INVENTION Supercritical fluids are excellent solvents for reactive particle formation, leading to nano-particle products with very narrow size distribution. The basis of the reactive particle formation method is a chemical system, in which reactants are soluble in the sol­vent utilized, while the reaction products are insoluble. An example of such system is metal oxides, formed from reaction between metal alcoholates and water. Due to the insolubility of the product the chemical reaction rapidly produces a su­persaturated product solution, and hence precipitation starts to take place in the reaction vessel. The precipita­tion is initiated at, and grows from, any available nuclea-tion site, i.e. vessel walls or seed particles present in the vessel. Precipitation, and accordingly particle growth, continues until the solution is no longer supersaturated. If a sufficiently high number of nucleation sites are provided in the reaction vessel, precipitation time and thereby par­ticle growth is restricted, and very small particles - in the nano-meter range - with a very narrow size distribution and high degree of crystalinity are formed. Examples of ways to introduce the nucleation sites to the reaction vessel are addition of seed particles or a filling material. In order to ensure the narrow particle size distribution, precipitation time must be controlled accurately, i.e. su­per-saturation must be achieved in all parts of the vessel at the same time. Several conditions must be fulfilled to achieve such homogenous super-saturation; the mixing of re-actants must be homogenous, the chemical reaction should be relatively fast compared to the precipitation time, and the solvent properties should be carefully controlled to ensure homogenous solubility throughout the vessel. Both reactant mixing and solvent property control are facilitated through the circulation loop of the present invention. By treatment lines mentioned is meant treatment processes or just lines. WE CLAIM: 1. A method of treating a material contained in a vessel, said treating comprising changing the composition of the material by impregnating, extracting or combinations thereof, said method involving a fluid present in the vessel and comprising at least one pressurisation step in which the pressure in the vessel is increased and at least one depressurisation step in which the pressure in the vessel is decreased, said method additionally comprising re-circulating during at least part of the method at least a part of the fluid, the re-circulating comprising: withdrawing from the vessel at least a part of the fluid contained within the vessel and feeding said fluid to a recirculation loop and subsequently feeding the fluid to the vessel, wherein the fluid after the pressurisation step is in a supercritical state, and wherein re-circulation is performed during the pressurisation step and/or during the depressurisation step characterized in that the fluid present in the re-circulation loop remains in the same phase and without undergoing a phase change to a liquid or solid state. 2. A method as claimed in claim 1, wherein, between said at least one pressurization step and at least one depressurization step, a holding step in which the pressure in the vessel is substantially constant and/or in which the pressure of the fluid in the vessel is varied according to a pre-selected schedule during a holding period of predetermined length, the fluid is preferably at supercritical conditions during the holding period, and in which, the temperature of the fluid in the recirculation loop is controlled by addition and/or extraction of heat in the recirculation loop, and in which temperature-, pressure- and/or density profiles are controlled within the vessel, is present. 3. A method as claimed in any of the preceding claims, wherein said fluid is selected from the group consisting of carbon dioxide, alcohol, water, methane, ethane, ethylene, propane, butane, pentane, hexane, cyclohexane, toluene, heptane, benzene, ammonia, sulfurhexafluoride, nitrousoxide, chlorotrifluoromethane, monofluoromethane, methanol, ethanol, DMSO, propanol, isopropanol, acetone, THF, acetic acid, ethyleneglycol, polyethyleneglycol, N,N-dimethylaniline etc. and -mixtures thereof. •4. A method as claimed in any of the preceding claims, wherein said fluid is carbon dioxide. 5. A method as claimed in any of the preceding claims, wherein said fluid comprises at least one cosolvent selected from the group consisting of alcohol (s), water, methane, ethane, ethylene, pro- pane, butane, pentane, hexane, heptane, ammonia, ben-zene, sulfurhexafluoride, nitrousoxide, chlorotri-fluoromethane, monofluoromethane, methanol, ethanol, DMSO, isopropanol, acetone, THF, acetic acid, ethyle-neglycol, polyethyleneglycol, N, N-dirnethylaniline etc. and mixtures thereof. 6.. A method as claimed in any of the preceding claims, wherein the fluid after the depressurisation step is in a gas and/or liquid and/or solid state. 7. A method as claimed in claims 1-6, wherein part of the fluid in the pressure vessel is withdrawn to the recirculation loop from/to a pressure in the pressure vessel below 70 bar, such as from/to a pressure below 60 bars, preferably from/to a pressure below 4 0 bars, and advantageously from/to a pressure below 2 bar. 8. A method as claimed in any of the preceding claims, wherein the fluid volume withdrawn from the vessel corresponds to the exchange of at least one vessel volume per hour, such as at least two vessel volume exchanges per hour, preferably at least 5 vessel volume exchanges per hour, and advantageously at least 10 vessel volume exchanges per hour, and preferably in the range of 10 to 2 0 vessel volume exchanges per hour. 9. A method as claimed in any of the preceding claims, wherein the pressure in the vessel after pressurisation step is in the range 85-500 bar, preferably in the range 85-3 0 0 bar such as 100-2 00 bar. 10. A method as claimed in any of the preceding claims, wherein the temperature in the vessel is maintained in the range 20-300 °C, such as a 30-150 °C, preferable as 35-100 °C, such as 40-60 °C 11. A method as claimed in any of the preceding claims, wherein the rate of pressurisation and/or depressurisation is controlled in a predefined manner in specific pressure intervals during the (de)pressurisation period, wherein the rate of pressure increase in at least part of the pressure range from 4 0 to 12 0 bars is at the most one half of the maximum rate of pressurisation outside this range, such as one third of the maximum rate of pressurisation, and preferably at the most one fifth of the maximum rate of pressurisation, and more preferably at the most one tenth of maximum rate of pressurisation outside this pressure range. 12. A method as claimed in any of the preceding claims, wherein the temperature of the fluid fed to the vessel during all or some of the holding period varies according to a predefined schedule in order to introduce pressure variations corresponding to the temperature variations in the vessel, wherein the uppermost and lowermost levels of the temperature is selected so as to provide a density change between the uppermost and lowermost level of up to 75 %, such as 50 % and preferable up to 30 %. 13. A method as claimed in claims 2-12, wherein the recirculation loop comprises a mixer vessel for mixing the fluid with chemicals and being arranged downstream of a heat exchanger.

Documents:

3439-DELNP-2006-Absract-(24-06-2009).pdf

3439-delnp-2006-abstract.pdf

3439-DELNP-2006-Claims (6-1-2010).pdf

3439-DELNP-2006-Claims-(24-06-2009).pdf

3439-delnp-2006-claims.pdf

3439-DELNP-2006-Correspondence-Others-(17-12-2008).pdf

3439-DELNP-2006-Correspondence-Others-(24-06-2009).pdf

3439-DELNP-2006-Correspondence-Others-(6-1-2010).pdf

3439-DELNP-2006-Correspondence-Others.pdf

3439-delnp-2006-description (complete).pdf

3439-delnp-2006-drawings.pdf

3439-DELNP-2006-Form-1-(17-12-2008).pdf

3439-DELNP-2006-Form-1-(24-06-2009).pdf

3439-delnp-2006-form-1.pdf

3439-delnp-2006-form-13-(17-12-2008).pdf

3439-delnp-2006-form-13.pdf

3439-delnp-2006-form-18.pdf

3439-DELNP-2006-Form-2-(17-12-2008).pdf

3439-DELNP-2006-Form-2-(24-06-2009).pdf

3439-delnp-2006-form-2.pdf

3439-delnp-2006-form-3.pdf

3439-delnp-2006-form-5.pdf

3439-delnp-2006-gpa.pdf

3439-delnp-2006-pct-304.pdf

3439-delnp-2006-pct-306.pdf

3499-DELNP-2006-Claims-(23-12-2009).pdf

3499-DELNP-2006-Correspondence-Others-(23-12-2009).pdf