Title of Invention

A PROCESS AND AN APPARATUS FOR EXTRACTING A COMPONENT FROM LIQUID

Abstract

A process for extracting a desired fraction from liquids comprising the steps of: a) providing a liquid containing a desired fraction of the kind such as herein described to be extracted; b) providing a dense phase solvent for extraction of said desired fraction, said dense phase solvent being chosen from the group consisting of supercritical fluids and liquefied gases, said dense phase solvent having a different density than said liquid; c) contacting said liquid and said dense phase solvent in a rotating mixer (18) to dissolve said desired fraction into said dense phase solvent by forming a loaded solvent and to separate said loaded solvent from remaining raffinate by centrifugal force, said rotating mixer operating with sufficient internal pressure of at least 5MPa to maintain said desired fraction dissolved in said dense phase solvent; d) discharging said loaded solvent and raffinate from said rotating mixer; and e) decreasing pressure on said loaded solvent to convert said loaded solvent into a gas and said desired fraction and to liberate desired fraction from said gas.

Full Text

FORM 2 THE PATENTS ACT, 1970 [39 OF 1970] COMPLETE SPECIFICATION [See Section 10; Rule 13] "A PROCESS AND AN APPARATUS FOR EXTRACTING A DESIRED FRACTION FROM LIQUID" PRAXAIR TECHNOLOGY, INC., Technology Licensors, a corporation organised and existing under the laws of the State of Delaware, United States of America, having an Office at 39 old Ridgebury Road, Danbury, State of Connecticut 06810-5113, United States of America, The following specification particularly describes the nature of the invention and the manner in which it is to be performed:- ORIGINAL GRANTED 2-3-2005 FIELD OF THE INVENTION The present invention relates to. a process for extracting a desired fraction from liquids and more particularly to a process and system for removing a desired fraction from a liquid using a centrifugal extractor. DESCRIPTION OF RELATED ART Extraction processes using dense phase (i.e., a supercritical fluid or a liquefied gas) solvents have been in commercial operation for 50 years. Extraction from solid materials has been done in a batch manner, periodically stopping the extraction process to depressurize, unload, reload, and repressurize the "extraction vessel prior to resuming extraction. Multiple batch extraction, vessels in series, with the periodic removal of a single vessel from the extraction train, have reduced but not eliminated the lost processing time. For example, U.S. Pat. Nos. 5,288,511 and 5,312,635 to Kazlas et al. disclose using supercritical carbon dioxide in batch processes to decaffeinate acidified coffee and to remove oil from fried food products, respectively. The processing equipment used in continuous extractions consists of vertical cylindrical columns similar to that used for low-pressure distillation or liquid-liquid extraction. This equipment operates in either a batch or continuous manner to extract components from a variety of sources. Prior art solutions to the problem of increasing production rates in the extraction of liquids with dense phase solvents have been limited to the application of various distributors in vertical cylindrical columns. More recent attempts have been described in U.S. Pat. No. 4,956,052 to Hirata et al. As in liquid-liquid extraction, the use of different distributors reduces the vertical circulation of the continuous phase and promotes high interfacial contact 10 between the dispersed and continuous phases. All of these solutions, however, are limited by the force of gravity to effect the counterflow of liquids of different density. Notwithstanding prior art solutions, a problem l5 associated with the commercial utilization of dense phase solvent extraction processes continues to be the high processing cost, relative to alternate extraction methods. This high processing cost, due principally to limited production rates in capital intensive process 20 equipment, has limited the application of dense phase extraction processes to high-value products. These products are typically produced in small volumes and by a small number of processors, inherently limiting the wide-scale utility of this technology. An 25 extraction process that results in reduced processing costs due to increased production rates would facilitate extending the utilization of this technology to a greater range of products. Centrifugal extractors, such as Podbielniak and 3) Westfalia extractors, increase production capacity in liquid-liquid extraction systems and overcome the limitations of gravity as the driving force for separation. For example, U.S. Pat. No. 2,044,996 to Podbielniak, combines the advantages of multi-stage countercurrent contact of two fluid phases with the ability of a centrifuge to process large volumes of material quickly in a small compact device. Similarly, Wem, in U.S. Pat. No. 4,382,900, discloses a centrifugal gas-liquid apparatus that relies upon an annular packing of gas/liquid permeable material in the 10 extractor. The extractor rotates to force liquid radially outward through the permeable material with centrifugal force where it encounters a gas before exiting through a separate chamber. Similarly, the gas passes through the liquid and permeable material and 15 exits through a gas outlet. These centrifugal extractors only operate with liquid-liquid or gas-liquid systems. Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present 20 invention to provide an extraction process and apparatus that result in reduced processing costs due to increased production rates. It is another object of the present invention to provide a process and apparatus that will permit the 25 continuous processing of large volumes of liquids with dense phase fluids in a smaller, more compact device. Still other objects and advantages of the invention will be apparent from the specification. SUMMARY OF THE- INVENTION The above and other objects and advantages, which will be apparent to one of skill in the art, are. achieved in the present invention, which is directed to, in a first aspect, a process for extracting a component from liquids. First it provides a liquid containing a desired fraction to "be extracted and a dense phase solvent for extraction of the desired fraction. The dense phase solvent is chosen from the group consisting of supercritical fluids and liquefied gases. This solvent has a different density than the liquid. Then contacting the liquid and the dense phase solvent in a rotating mixer dissolves. the desired fraction into the dense phase solvent by forming a loaded solvent. Furthermore, the mixer separates the loaded solvent from the remaining raffinate with centrifugal force. The mixer operates with sufficient internal pressure to maintain the desired fraction dissolved in the dense phase solvent. Then the rotating mixer discharges the loaded solvent and raffinate. Finally, decreasing pressure on the loaded solvent converts the loaded solvent into a gas and the desired fraction and. liberates the desired fraction from the gas. Accordingly, there is provided a process for extracting a desired fraction from liquids comprising the steps of: a) providing a liquid containing a desired fraction of the kind such as herein described to be extracted; b) providing a dense phase solvent for extraction of said desired fraction, said dense phase solvent being chosen from the group consisting of supercritical fluids and liquefied gases, said dense phase solvent having a different density than said liquid; c) contacting said liquid and said dense phase solvent in a rotating mixer to dissolve said desired fraction into said dense phase solvent by forming a loaded solvent and to separate said loaded solvent from remaining raffinate by centrifugal force, said rotating mixer operating with sufficient internal pressure of at least 5MPa to maintain said desired fraction dissolved in said dense phase solvent; d) discharging said loaded solvent and raffinate from said rotating mixer; and e) decreasing pressure on said loaded solvent to convert said loaded solvent into a gas and said desired fraction and to liberate desired fraction from said gas. Accordingly, there is also provided a process for extracting a desired fraction from liquids comprising the steps of: a) providing a liquid containing a desired fraction to be extracted therefrom; b) providing supercritical carbon dioxide solvent for extraction of said desired fraction, said supercritical solvent having a different density than said liquid; c) contacting said liquid and said supercritical solvent in a rotating mixer to dissolve said desired fraction into said supercritical solvent by forming a loaded solvent, and to separate said loaded solvent from remaining raffinate by centrifugal force, said rotating mixer operating with sufficient internal pressure to maintain said desired fraction dissolved in said dense phase solvent; d) discharging said loaded solvent and raffinate from said rotating mixer; and e) decreasing pressure on said loaded solvent to convert said loaded solvent into carbon dioxide gas and said desired fraction and to liberate said desired fraction from said carbon dioxide gas. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS The features of the invention believed to be novel and the elements characteristic of the invention are set forth with particularly in the appended claims. The figures are for illustration purposes only and are not drawn to scale. The invention itself, however, - For example, the various liquids that the dense phase extraction process and apparatus of the present invention may be applied include: plasticizer recovery, monomer purification, fine chemical production, flavor extraction and fragrance extraction. These liquids generally have a density of about 0.6 to 1.6 g/cc. The various dense phase solvents that serve as extractants for the aforementioned fractions or l0 impurities in the product liquids may for example include: liquefied carbon dioxide, supercritical carbon dioxide, ammonia, ethane, ethylene, propane, propylene, butane, other hydrocarbon gases, nitrous oxide, CFC13, CF3C1, other halogenated hydrocarbons and mixtures thereof. These solvents generally have a density of about 0.3 to 1.0 g/cc. The preferred dense phase solvent for several systems is supercritical carbon dioxide. Liquid carbon dioxide exists at any temperature between the triple point temperature of -56.6°C and the critical point temperature of 31°C by compressing the carbon dioxide to the liquefaction pressure. At a temperature of from about 0°C to 30°C, the liquefaction pressure is 5.5 MPa (505 psia) to 7.2 MPa (1046 psia). Advantageously, the carbon dioxide solvents operate with a liquefaction pressure of at least about 5 MPa (750 psia). Most advantageously, carbon dioxide solvents operate as a supercritical fluid. Supercritical carbon dioxide exists at a temperature at or above 31°C and a pressure 30 at or above 7.4 MPa (1070.16 psia). Supercritical carbon dioxide (like other supercritical solvents) is neither liquid nor vapor, but combines some of the solvent and transport properties of each. Figure 1 illustrates a modified centrifugal extractor found to have particular advantages in the preferred mode of operation of the present invention. The body of a centrifugal extractor 10 consists of a cylindrical housing 12 supported by legs 14 and 16. Inside the housing 12, a rotatable mixer or centrifuge l0 18 rotates about its horizontal axis 20. The centrifuge 18 contains a number of spaced concentric cylinders 22 having perforations or openings therein. Between the cylinders, and formed thereby, are a plurality of discrete mixing regions or chambers 25 l5 that serially interconnect from near the axis 20 to near the periphery of the housing 12. For most extraction processes, a dense phase solvent enters a light phase conduit or inlet 24 and a liquid enters a heavy phase inlet 26 to supply the extractor--when the solvent has a greater density than the liquid, the solvent enters the inlet 26 and the liquid enters the inlet 24. In order for the centrifuge to effectively separate the dense phase from the liquid, the fluids must have different densities. the concentr liquid to di 25 Spinning the centrifuge causes the solvent and liquid to flow in opposite directions through the chambers 25 between the concentric cylinders 22. The high density liquid flows to the periphery and the low density solvent travels inwardly. As the fluids travel within ic cylinders, the solvent contacts the ssolve or extract a desired fraction or component from the liquid and form a loaded solvent and a raffinate.. After the loaded solvent reaches the peripheral of the centrifugal extractor 22, it exits through a 5 high density outlet 28. Similarly, the raffinate exits near the centrifuge's center through an outlet conduit 30. This completes the extraction of a fraction from the liquid. For some extraction processes, it is advantageous to connect multiple centrifuges in series 10 or to recycle the raffinate through the extractor for extraction of additional fractions not originally extracted. Since the liquid and solvent enter from a fixed shaft to a rotating shaft, these fluids each pass 15 through mechanical seals. Unfortunately, when operating the extractor at the extraction pressures necessary to maintain the desired fraction dissolved in the liquefied gases or supercritical fluids, these seals tend to leak. Therefore, these extractors 20 require special seals designed for high-pressure fluids. Furthermore, when using strong solvents such as, supercritical carbon dioxide, it is important to use silicone seals or other materials resistant to the solvent. 25 Optionally, a pressure vessel 40 houses the entire centrifugal extractor. A pump 42 pressurizes the entire housing 12 through a valve 4 4 and conduit 4 6 with any suitable gas such as air, carbon dioxide, inert gases and nitrogen. Pressurizing the entire 30 centrifuge lowers the pressure differential at the seals to allow them to operate with internal pressures above their brigiriral design capability. Furthermore, placing the entire vessel in a pressure chamber allows operators to set the pressure at different levels for different solvent. when "ramping up" pressure within the chamber it is important to increase pressure within the extractor at a similar rate to within the pressure chamber. An optional swing valve (not illustrated) between the inlet lines 24 and 26 and conduit 46 minimises pressure differentials. 10 During operation adjusting the rotational speeds of the centrifugal extractor determines the separation force between the fluids. Increasing the rotation speed however can decrease the mixing of the fluids in the chambers. Therefore, for each liquid extraction l5 system, it is important to rotate the centrifuge at a rate that maximizes extraction from the liquid. For small batch operations, it is possible to place the liquid supply and dense phase vessels within a pressure chamber for continuous and large-scale operations however supplying pressurized streams through the inlets 24 and 26 and removing pressurized streams through the outlets 28 and 30 allows effective extraction from high volumes of liquid. Referring to Figure 2, dense phase solvent, 25 advantageously in its liquid or supercritical phase, flows through a conduit 50a from a supply or storage vessel 55 to a pump 60 where the pressure is adjusted to the desired operating pressure. The compressed dense phase solvent then flows from the pump 60 outlet via a conducting 50b through a preheater 65. The preheater adjusts the solvent temperature to the desired operating desired operating temperature. The heated solvent then flows through a conduit 50c into the light liquid phase inlet located near the periphery of the centrifugal extractor 10. The liquid feed is pumped from a storage 5 vessel 70 through a conduit 50d and enters the centrifugal extractor 10 through its heavy phase inlet located near the central axis of the centrifuge. The two streams of product liquid and dense phase fluid flow in a countercurrent fashion aided by centrifugal 10 force, as described previously. Consequently, a desired fraction of the liquid is dissolved in the dense phase solvent. The liquid feed, stripped of some fraction, exits the centrifugal extractor through an outlet located near the periphery of the drum and 15 through the heavy phase outlet as a raffinate 75--for some extraction processes, the raffinate represents the desired end product.. When operating the centrifuge at high internal pressures, the raffinate advantageously flows through a pressure reduction valve 80. The dense 20 phase fluid solvent, containing a solubilized fraction from the liquid feed, exits the centrifugal extractor at an outlet located near the center of the drum and passes through the light phase outlet. The loaded dense phase solvent passes via a 25 conduit 50e across a pressure reduction valve 85 and via a conduit 50f into a separation vessel 90. This vessel decreases the pressure of the loaded dense phase solvent to convert it to a low density gas. At this separation pressure, the liberated gas separates from 3O the previously dissolved material leaving an extract. The system removes extract through a conduit 50g. The stripped solvent phase exits the separation vessel as a gas through a conduit 50h. Then a heat exchanger 95 condenses the gas to its liquefied or supercritical phase. This condensed gas then travels through a conduit 50i to the storage vessel 55 for future extraction. The pump 60 then recycles this condensed gas through the preheater 65 for repeated extraction. Thus, the present invention achieves the aforementioned objects and provides unexpected advantages in providing a process and apparatus that will permit the continuous processing of large volumes of liquids with dense phase fluids in a smaller, more compact device. Additionally, the invention provides an extraction process and apparatus that results in reduced processing costs due to increased production rates. While the present invention has been particularly described, in conjunction with a specific preferred embodiment, it is evident that many alternatives, 20 modifications and variations will be apparent to those skilled in the art in light of the foregoing description. It is therefore contemplated that the appended claims will embrace any such alternatives, modifications and variations as falling within the true 25 scope and spirit of the present invention. Thus, having described the invention, what is claimed is: WE CLAIM:- 1. A process for extracting a desired fraction from liquids comprising the steps of: a) providing a liquid containing a desired fraction of the kind such as herein described to be extracted; b) providing a dense phase solvent for extraction of said desired fraction, said dense phase solvent being chosen from the group consisting of supercritical fluids and liquefied gases, said dense phase solvent having a different density than said liquid; c) contacting said liquid and said dense phase solvent in a rotating mixer (18) to dissolve said desired fraction into said dense phase solvent by forming a loaded solvent and to separate said loaded solvent from remaining raffinate by centrifugal force, said rotating mixer operating with sufficient internal pressure of at least 5MPa to maintain said desired fraction dissolved in said dense phase solvent; d) discharging said loaded solvent and raffinate from said rotating mixer; and e) decreasing pressure on said loaded solvent to convert said loaded solvent into a gas and said desired fraction and to liberate desired fraction from said gas. 2. The process as claimed in claim 1 wherein said liquid has a density between 0.6 and 1.6 g/cc. 3. The process as claimed in claim 1 wherein said dense phase solvent has a density between 0.3 to 1.0 g/cc. 4. The process as claimed in claim 1 including the additional steps of pressurizing said gas to convert it back into said dense phase solvent and recycling the converted dense phase solvent into said rotating mixer after said separating of said desired fraction from said loaded solvent. 5. The process as claimed in claim 1 wherein said rotating mixer has a plurality of interconnected chambers and said contacting occurs in said chambers. 6. A process for extracting a desired fraction from liquids comprising the steps of: a) providing a liquid containing a desired fraction to be extracted therefrom; b) providing supercritical carbon dioxide solvent for extraction of said desired fraction, said supercritical solvent having a different density than said liquid; c) contacting said liquid and said supercritical solvent in a rotating mixer to dissolve said desired fraction into said supercritical solvent by forming a loaded solvent, and to separate said loaded solvent from remaining raffinate by centrifugal force, said rotating mixer operating with sufficient internal pressure to maintain said desired fraction dissolved in said dense phase solvent; d) discharging said loaded solvent and raffinate from said rotating mixer; and e) decreasing pressure on said loaded solvent to convert said loaded solvent into carbon dioxide gas and said desired fraction and to liberate said desired fraction from said carbon dioxide gas. 7. The process as claimed in claim 6 including the additional steps of pressurizing said carbon dioxide gas to convert it back into said supercritical solvent and recycling the. converted supercritical solvent back into said rotating mixer. 8. The process as claimed in claim 6 wherein said rotating mixer has a plurality of interconnected chambers extending from near the center to near the periphery thereof and said contacting occurs in said chambers. 9. An apparatus for extracting a desired fraction from liquids comprising: an inlet conduit for supplying a liquid, said liquid containing a desired fraction to be extracted therefrom; a supply vessel for supplying a dense phase solvent for extracting said desired fraction, said dense phase solvent being chosen from the group consisting of supercritical fluids and liquefied gases; a rotatable mixer connected to said inlet conduit and said supply vessel, said rotatable mixer having a centrifuge, said centrifuge having inlets for receiving said liquid and said dense phase solvent, a mixing chamber for dissolving said desired fraction into said dense phase solvent as a loaded solvent at an into said dense phase solvent as a loaded solvent at an extraction pressure sufficient to maintain said desired fraction dissolved in said dense phase solvent and for separating loaded phase from remaining raffinate, a raffinate outlet for discharging said raffinate and a solvent outlet for discharging said loaded solvent; and a separation vessel connected to said solvent outlet of said rotatable mixer for receiving said loaded solvent, said separation vessel having a separation pressure less than said extraction pressure of said centrifugal extractor for converting said loaded solvent into a gas and said desired fraction and for liberating said desired fraction from said gas. 10. The apparatus as claimed in claim 9 wherein a pressure vessel surrounds said centrifugal extractor for operating said centrifugal extractor at pressures sufficient to maintain said dense phase solvent. 11. A process for extracting a desired fraction from liquids substantially as herein described with reference to the accompanying drawings. 12. An apparatus for extracting a desired fraction from liquids substantially as herein described with reference to the accompanying drawings. Dated this 24* day of March, 2000. [RITUSHKA NBGI] OF REMFRY & SAGAR ATTORNEY FOR THE APPLICANTS

Documents:

268-MUM-2000-ABSTRACT(24-3-2000).pdf

268-MUM-2000-ABSTRACT(GRANTED)-(15-2-2007).pdf

268-MUM-2000-CANCELLED PAGES(2-3-2005).pdf

268-MUM-2000-CLAIMS(24-3-2000).pdf

268-mum-2000-claims(granted)-(02-03-2005).pdf

268-mum-2000-claims(granted)-(15-2-2007).pdf

268-mum-2000-claims(granted)-(2-3-2005).doc

268-mum-2000-correspondence(30-11-2005).pdf

268-MUM-2000-CORRESPONDENCE(7-7-2004).pdf

268-mum-2000-correspondence(ipo)-(20-01-2005).pdf

268-MUM-2000-CORRESPONDENCE(IPO)-(28-3-2007).pdf

268-MUM-2000-DESCRIPTION(COMPLETE)-(24-3-2000).pdf

268-mum-2000-description(granted)-(15-2-2007).pdf

268-mum-2000-drawing(02-03-2005).pdf

268-MUM-2000-DRAWING(24-3-2000).pdf

268-mum-2000-drawing(granted)-(15-2-2007).pdf

268-MUM-2000-FORM 1(19-7-2004).pdf

268-MUM-2000-FORM 1(24-3-2000).pdf

268-mum-2000-form 13(19-07-2004).pdf

268-mum-2000-form 19(22-01-2004).pdf

268-MUM-2000-FORM 2(COMPLETE)-(24-3-2000).pdf

268-mum-2000-form 2(granted)-(02-03-2005).pdf

268-mum-2000-form 2(granted)-(15-2-2007).pdf

268-mum-2000-form 2(granted)-(2-3-2005).doc

268-MUM-2000-FORM 2(TITLE PAGE)-(24-3-2000).pdf

268-mum-2000-form 2(title page)-(granted)-(15-2-2007).pdf

268-mum-2000-form 3(24-03-2000).pdf

268-mum-2000-form 3(31-07-2000).pdf

268-mum-2000-form 5(19-07-2004).pdf

268-mum-2000-petition under rule 137(19-07-2004).pdf

268-mum-2000-petition under rule 138(19-07-2004).pdf

268-mum-2000-petition under section 138(1)-(19-07-2004).pdf

268-mum-2000-power of authority(02-03-2005).pdf

268-mum-2000-power of authority(14-09-2000).pdf

268-MUM-2000-SPECIFICATION(AMENDED)-(2-3-2005).pdf

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