Title of Invention

PREPARATION OF A SILICATE OR OF GLASS IN A SUBMERGED-BURNER FURNACE IN A REDUCING ENVIRONMENT

Abstract

The invention relates to a process for preparing a silicate of an element chosen from alkali metals, alkaline-earth metal a or rate earths, comprising a reaction between silica end a sulfate of said element in a reactor equipped with at least one submerged burner within a molten mass, said submerged burner being fed with a gas containing oxygen, an excess of fuel/ reducing agent being introduced into the reactor relative to the oxygen effectively consumed. The process allows the reaction, to be earried out satisfactorily and at relatively fow temperature.

Full Text

PREPARATION OF A SILICATE OR OF GLASS IN A SUBMERGED- BURNER FURNACE IN A REDUCING ENVIRONMENT The present invention relates to a process for 5 preparing glass or a silicate, such as sodium silicate, that can be used to manufacture glass or silica in the form of particles iprecipitated silical. Within the context ot the present invention, the term 10 "batch materials" is understood to mean all materials, vitrifiable substances, natural ores or synthesized products, materials resulting from cullet tecycling, etc. that can be incorporated into the composition feeding a giass furnace. The term "glass" is understood 15 to mean glass in the broad sense, that is to say encompassing any material with a glass. glass-ceramic of ceramic matrix, the main constituent of which is silica. The term "manufacture" includes the indispensable step of melting the batch materials and 20 possibly all the subsequent/supplementary steps for the purpose of refining/cenditioning the molten glass for the purpose of its final forming operation, especially in the form of flat glass (glazing), hollow-ware (flasks, bottles), glass in the form of mineral (glass 25 or rock) wool used for its thermal or acoustic insulation properties, or even possibly glass in the form of yarns referred to as textile yarns used in reinforcement. 30 The invention relates most particularly to the batch materiels needed to manufacture glasses having a significant content of ajkali metals, especially sodium, for example glasses of the silica-soda-lime type used to make flat giess. The batch material 35 currently used most often for providing sodium or potassium is soflium carbonate Na2CO3 or potassium carbonate K2CO3, which choice is not without its drawbacks since, on the one hand, this compound provides only sodium as constituent element of the - 2 - glass, the entire carbonate part decomposing in the form of evolution of CO; during melting. On the other hand, this is an expensive batch material, compared with the ethers, since it is a synthetic product 5 obtained by the Solvay process from sodium chloride and lime, which process involves a number of manufacturing steps and consumes a great deal of energy. This is the reason why it has been proposed to use as 10 sodium source not a carbonate but a silicate, possibly in the form of a mixed alkali metal (Na)/alKaline-earth metal (Ca) silicate prepared beforehand. The use of this type of intermediate product has the advantage of jointly ptoviding several of the constituenes of the 15 glass, of eliminating the decarbonatization phase and of reducing CO2 emissions from the melting furnace. It also makes it possible to speed up the melting of the batch materials in their entirety and of favoring their homogenization during melting as indicated, for 20 example, in the patents FR 1 211 098 and FR 1 469 109. However, this approacn poses the problem of the manufacture of this silicate. A first method of Synthesis was described in the patent 25 WO 00/46161; this involves the conversion of a halide, for example NaCl, and silica into a silicate at high temperature, the heat supply being provided by submerged burners. Combustion by submerged burners is already known, for example from the patents US-3 627 30 504, US-3 260 587 or US-4 539 034, for melting virrifiable materials to make glass. To use this technoclogy in a content different form the synthesis of silicates, and therefore upstream of the actual glass manufacture, indeed offers many advantages: this method 35 of combustion causes, within the materials undergoing reaction, strong turbulence and vigorous convection motion around the gas jets or flames from the submerged burners. This promotes very effective stirring of the reaetants, Furthermore, submerged burners provide the - 3 - heat idirerctly at the point where it is needed, into the mass of the products undergoing reaction. It is also an environmentally friendly method of combustion. Direct conversion of. NaCl and silica carried out in this way 5 is therefore very attractive for more than one reason. However, it turns out that this direct conversion is not easy to implement on a large scale. WO 03/031357 teaches the manufacture of a silicate in 10 two separate steps, the overall reaction involving a halide (such as NaCl) and silica in order to make a silicate, this overall reaction passing via the manufacture of a sulfate. The above document teaches that carbon or sulfur may be used as solid fuel, 15 The object of the invention is firstly to develop a method of manufacturing a silicate that is particularly productive and easy to use on an industrial scale. Furthermore, this novel type of manufacture may also be 20 environmentally friendly insofar as all the reaction products. involved can be urilized or recycled. The term "submerged burners" is understood to mean burners configured so that the "flames" that they 25 generate or the combustion gases emanating from these flames develop in the reactor where the conversion takes place, within the very mass of the materials being converted (the reaction mass). Generally speaking, the burner are placed so as rc be flush with 30 on slightly proud of the side walls or the floor of the reactor used. The XXX the invention is firstly a method of meterials compounds based on one or more silicates 35 of alkali metais, such as Na and K, and/or of alkaline- earth metals, such as Ca and Mg, and/or of rare earths, such as Ce, possibly in the form of mixed silicates combining at least two of these elements. This method involves a conversion reaction in which said sulfates - 4 - with silica are converted into the corresponding silicates, the heat supply needed for this conversion being provided, at least in part, by a combustion reaction using one or more submerged burners. Thermal 5 energy is injected into the submerged-burner furnace sufficient to form the silicate and for the latter to remain liquid and of low enough viscosity to flow sufficiently rapidly out of the furnace. The advantage of submerged burners is that they inject the necessary 10 heat directly into the liquid reaction mass, this injection also causing effective stirring of the various materials in the furnace owing to the turbulence generated by the gases stirring them. According to the invention, it is preferable to inject 15 most of the energy via the submerged burners, but it is not excluded either to inject some of this by another means, such as resistance heating elements, although the coexistence of resistance heating elements and submerged burners is not recommended (corrosion of the 20 resistance elements). In general, a heat supply of between 500 and. 2500 kwh per ton of silicate produced is suitable. Combustion by submerged burners requires an injection 25 of oxygen, either in the form of pure oxygen or in the form of a mixture of oxygen with at least one other gas, sueh as air. This oxygen is intended to react with the fuel in order no generate the necessary heat, Depending on the nature of the fuel and the way it is 30 introduced, the fuel can react relatively rapidly with the oxygen. Thus, if the fuel is s gas (a hydrocarbon, such as methane, propane or butane, or a sulfuir- containing gas, such as H;Sl fed directly into the submerged burner already supplied with oxygen, the 35 combustion is rapid and estimated to be complete lit should be understood here. of course, that the fuel and the oxygen arrive at the same point in the submerged burner, for example via a premixing cell. This means that if the submerged burner is supplied stoichio- - 5 - metrically with oxygen and with combustible gas, all the combustible gas and all the oxygen react together. On the other hand, if the oxygen is in excess relative to this stoichiometry, a measurable amount of oxygen 5 will escape with the flue gases. If the combustible gas is in excess with respect to this stoichiometry, this fuel will aiso have a tendency to escape, but there will be a risk of relatively explosive postcombustion, a situation that cannot therefore be recommended. 10 It is also possible to introduce solid fuel such as, for example. solid sulfur or solid carbon (coal). In this case, the solid fuel is generally introduced into the reaction vessel as batch materials, that is to say 15 independently of the submerged burners, but in any cast as close as possible to said burners if it is desired for the solid fuel to react effectively with the oxygen flowing in via said burners. However, even if this solid fuel is introduced very close to the submerged 20 burners, it is difficult to have perfect combustion efficiency, which means that oxygen may generally pass through the reaction mass without ccmpletely reacting with the fuel and be found (in measurable amount) in the flue gases, even if the fuel is in scoichiometry or 25 even in excess with respect to oxygen. According to the invention, an excess of fuel (or reducing agent) is introduced relative to the oxygen actually consumed [and not relative to the oxygen only 30 introduced). This is because the Applicant has discovered than if the reaction medium has exctss fuel, the silicate formation reaction is activated and can even be carried out at a lower temperature than in the absence of this excess, which also amounts to stating 35 that the silicete formation reaction is activated at lower temperatures than in the absence of this excess. It seems that the excess fuel, not consumed by the oxygen from the submerged burners, plays in fact in this case a direct role in the silicate formatlon - 6 - reaction, this role being of the reducing type. Without the present explanation being in any way limiting, at least one of the following reactions might then be involved: 5 SiO2 + Na2SO4 + 4C -> Na2SiO3 + SO2 + 4 C02 (1) SiO2 + Na2SO4 + 4 S-> Na2SiO3 + 3/2 SO2 (2) reaction (1) rating place in the presence of a carbon fuel or a fuel that generates carbon, such as coal, coke or a carbon-containing plastic (a polymer such as 10 polyethylene, polypropylene or the like) and reaction (2) taking place in the presence of a fuel containing or generating sulfur. It is also possible to use a fuel containing both carbon and sulfur such as, for example, a vulcanized rubber (such as from motor vehicle tires). 15 According to the invention, the situation may therefore be especially as in one of the following a) submerged burners supplied with oxygen (which may include air) and with combustible gas, the combustible 20 gas being in short supply relative to the oxygen and being completely consumed by the oxygen, a solid or liquid fuel being also added to the reaction mass, which partially reacts with the oxygen but is present in a sufficiently large amount not to be completely 25 consumed by the oxygen and to act as a reducing aqent within the meaning of the invention in order to promote silicate formation, it being possible for some oxygen to escape with the flue gases; b) submerqed burners supplied with oxygen. (which may 30 include air) and with combustible gas, the combustible gas and the oxygen being in stoichiometric ratio, the oxygen and the combustible gas reacting completely together, a solid or liquid fuel or gaseous fuel (such as HZS) also being added to the reaction mass, and 35 acting as a reducing agent within the meaning of the invention in order to promote silicate formation; c\ sulmerged burners supplied, with oxygen. (which may include air) without combustible gas, a solid or liquid fuel also being added to the reaction mixture, reacting - 7 - with, at least part of the oxygen but being present in a sufficiently large amount to also act as a reducing agent within the meaning of the invention in order to promote silicate formation, some of the oxygen 5 generally escaping with the flue gases; and d) submerged burners supplied with oxygen (which may include air) and with combustible H2S gas, the combustible gas being in excess relative to the oxygen and acting as a reducing agent relative to the sulfate, 10 promoting silicate forfmation. In all these situations, it may be seen that there is excess fuel in the reaction mixture relative to the effectively reacting oxygen. The effectively reacting 15 oxygen can be easily determined by measuring the oxygen escaping in the flue gases. A person skilled, in the art is able,, by routine tests, knowing the amounts of oxygen not reacting, to determine the necessary amounts of fuel to be introduced in order to be in excess fuel 20 mode within the context of the invention. It should be pointed out that the "fuel" materials or the "reducing" materials are merely the same and can fulfill both roles the fuel role being played by 25 reaction with the oxygen, the reducing role being played in the silicate formation reaction, within the context of the invention, the excess fuel allows this combustible material to play a larger reducing role, 30 Thus, the subject of the invention is firstly a process for preparing a silicate of an element chosen from alkali metals, alkaline-earch metais or rare earths, comprising a reaction between silica and a sulfate of said element in a reactor equipped with at least one 35 submerged burner within a molten mass, said submerged burner being supplied with an oxyqen-coataining gas, an excess of reducing fuel being introduced into the reactor relative to tne effectively consumed oxygen. - 8 - Within the context of the present invention, tne excess fuel plays a reducing role thanks to the carbon or sulfur that it contains and it combines with the sodium sulfate. For each fuel, it is possible to define a 5 carbon equivalent or a sulfur equivalent corresponding to the mass of pure carbon or sulfur that the fuel in fact provides as reducing agent. To give aa example, a hydrocarbon polymer has a higher mass than the carbon that it contains and it actually acts as a reducing 10 agent. Within the context of the present invention, the excess fuel preferably represents 0.1 to 2 mol, and more preferably 0.3 to 1 mol, of carbon or sulfur equivalent per mole of sulfate. Thus, the excess reducing fuel may be a solid or a liquid acting as a 15 source of carbon of sulfur, or both as a source of carbon and sulfur. The following materials may be mentioned as examples of solid or liquid fuel supplying sulfur and/or carbon: vulcanized rubbers, tires, wood, board, paper, animal flour, crude oil-contaminated sand 20 (the latter material being both a source of fuel/reducing agent and of silical and fuel oil. The fuel that can be in excess may also be a sulfur- containing gas such as H2S. 25 A silica/sulfate molar ratio is used that corresponds to the silicate that it is desired to obtain. This silicate may be represented by the formula MyOy n(Si02) , in which M represents an alkali or alkaline-earth metal or a rare earth, x and y represent positive integers or 30 non-integers, and n represents a positive integer or non-integer. M20y can in particular be Na2o, K20, CeO2- In general, n (the SiO2/M2O2 molar ratiol is between. L and 4 and more particularly between 1-3 and 4, especially when M represents an alkali or alkaline- 35 earth, metal. For the use in which M is Na, n is more particularly between 1.5 and 3,B. For the case in which M is a rare earth, such as Ce, n may generally be greater than 5 and generally less than 1000. - 9 - In the reaction mass there are at least the following separate phases: - solid silica; - liquid sulfate; 5 - liquid silicate; and - gases emanating from the submerged burners and from the silicate formation reaction (which may contain, depending on the case, So2, SO3, CO2, H2, H2O, O2, etc,). 10 The reaction medium therefore contains many separate phases and the a submerged-burner technology is particularly effective for vigorously stirring them and for making the reaction proceed. 15 The liquid sulfate and the liquid silicate form two separate phases. Reaction conditions (temperature, stirring induced by the submerged burners, residence time, excess reducing agent) art sought such that the liquid sultate phase disappears before exit from the 20 reactor, and in any case is present in the smallest: auount possible doring manufacture. This residua1 amount of sulfate is usually expressed as the amount of SO3. The absence of sulfate at the exit of the reactor shows that the sulfate has indeed reacted. If this is 25 not the case, undesirable sulfate inclusions may be seen with the naked eye in the final silicate. In addition, when hot, there may be splashes of relatively explosive liquid sulfate downstream of manufacture. In general, this drawpack may be remedied by increasing 30 the excess amount of reducing agent. The minimum amount of excess reducing agent can therefore be determined by the disappearance of the sulfate phase in the final silicate. It is unnecessary to introduce an excessively large excess amount of reducing agent as this may lead 35 to a yellaw-brown coloration (due to the formation of sulfide ions s2) visible to the naked eye in the final silicate, which coloration is undesirable. In genera), the excess reducing agent is between one and two times the excess amount necessary for disappearance of the - 10 - sulfate phase. Thus, it is preferred to introduce an excess of fuel in an amount sufficient for the Silicate to contain no sulfate inclusion. 5 A sufficiently high temperature is chosen in order to make the reaction proceed, resulting in a suitable viscosity of the reaction mixture. This is because, if the viscosity is too high, the reaction mass solidifies and the reaction does not proceed. If the viscosity is 10 too low, there will be excessive splashing, which tends to erode the walls and the roof and can therefore result in undesirable foreign particles in the product of manufacture. In addition, material going onto the walls and the roof is no longer available to react with 15 the material introduced. In fact, these two extremes both result in particularly insufficient stirring of the reactants, thereby reducing the efficiency. Correct stircing of the mixture also results in temperature uniformity throughout the reaction mass. The aim is for 20 the silicate phase to have a viscosity of between 50 and 3000 poise, and more particularly between 100 and 1000 poise, at the temperature of the reaction mixture. In general, a temperature between 1000 and 1500°C, and more particularly between 1200 and l400ºC, is suitable. 25 The final silicate is a solid translucent at room temperature. Preferably, it contains no batch stones, that is to say particles of the initial silica that have not participated in the reaction. The presence of 30 batch stones may be remedied by increasing the residence time in the reactor, Preferably the reactor for preparing the silicate is followed by a refining vessel. This vessel is separate 35 from the reactor so as to prevent any silicate from the vessel slipping back into the reactor and to prevent the silicate undergoing refining from being contaminated by raw silicate from the reactor. This refining operation affords the following Advantages: - 11 - - the last batch stones (silica partides) are eliminated; - the maximum amount of sulfur is eliminated from the final silicate (sulfur released in H2S by the final 5 silicate is toxic and produces undesirable smells); - the redox is lowered - in practice the aim is to have, at exit from the vessel, a redox (equal to the total FeO/Fe201 mass ratio in the final silicate) of less than 0,5, or even less than 0.4; and 10 - the excess reducing agent still in the silicate is consumed, which amounts to improving the efficiency of the silicate formation reaction (the reducing agent that is not reacted with the sulfate in the reactor is consumed). 15 The refining vessel is generally equipped with heating means, such as at least one submerged burner. Such a burner generates a flame of greater or lesser oxidizing power depending on the intended redox at exit. Such 20 burners may be supplied with combustible gas and with air or with oxygen with oxygen being in excess relative to the combustible gas. During this refining operation, the raw silicate becomes clearer, even becoming colorless and translucent. The temperature of the 25 silicate in the refining vessel is generally between the same temperature as in the reactor and 150°C below the temperatute in the reactor, and preferably between 50ºC below the temperature in the reactor and l50ºC below the temperature in the reactor, 30 The separation, between the melting reactor and the refining vessel may be a channel or a spillway or partitions along the sides. 35 The "silica" may be introduced into the reaction mixture as any compound containing predominantly silica (silicon oxids) SiO2, even if it may also contain other elements or other minority compounds, which is very particularly the. cast when natural materials, such as -.12 – sand, are used. The effectiveness of the burners in all aspects (quality of the mixing, excellent heat transfer) means 5 that the conversion via the reaction is greatly favored, and is so without there being a need to attain extremely high temperatures. Another advantage of submerged burners is the 10 following: they allow the introduction of liquid/solid fuels in the same way as the vitrifiable batch materials. This consequently results in varied redox ratios of tne molten silicate, in the reactor, possibly ranging from 0.1 to 0-9 depending on the residence time 15 (a longer residence time results in a lower redox ration , In fact, at the inlet ot the reactor, at the point where the various batch materials are charged, it is necessary for the redox ratio to be relatively high (between 0.35 ana 0.9), this being favorable to the 20 sulfate decomposition reaction. After the refining vessel, the redox ratio is generally in the 0.1 to 0.5 range. The chosen oxidizer for feeding the submerged burner(s) 25 (reactor or refining vessel) may simply be air. However, it is preferential to use an oxidizer in the form of oxygen-enriched air, and ever an oxidizer substantially in the form of oxygen alone. A high oxygen concentration is advantageous for various 30 ceasons: the volume, of combustion flue gas is thus reduced, this being favorable from the energy standpoint and avoids any risk of excessive fluidization of the materials undergoing the reaction, that may cause spiashing against the superstructures, 35 especially the roof of the reactor where the conversion takes place. Furthermore, the "flames" obtained are shorter and more emissive, thereby allowing their energy to be transferred more rapidly to the materials undergoing melting/conversion. In addition, where - 13 - appropriate, the sulfur oxide concentration in the flue gases is higher, facilitating the subsequent conversion to sulfuric acid. 5 As regards the choice of fuel for the submerged burner(s), three approaches are possible, as alternatives or in combination: it is possible to choose a liquid fuel, a gaseous fuel or a fuel in solid form. 10 If it is at least partly in gaseous form, it may feed the submerged burners directly. If it is in liquid or solid form, It may be injected close to the submerged burnars. 15 Aa gaseous fuel, mention may be made of natural gas (predominantly methane), propane, hydrogen or any other hydrocarbon compound and/or sulfur compound, espectally H2S (the advantage of H2S is there is no discharge of 20 C02 into the atmosphere) . As solid or liquid fuel, mention may be made of any compound predominantly in carbon compound and/or hydrocarbon compound and/or sulfur compound, (including 25 sulfur and carbon) : as in the previous case, these may be byproducts of the oil industry (heavy fuel oil, asphalt, etc.). They may be polymer-based meterials that can thus be recycled (any plastics, tires, vulcanized rubber, etc.), and even hydrocarbon- 30 contaminared xxx both the silica xxx way of dealing xxx beaches after an oil spillage for example. 35 According to the invention, it is xxx to use sulfur-containing fuels such as sulfur - 14 - compounds, like worn tires (which may contain, for example, 0,5 to 48 sulfur), or even pure sulfur, There are traces of sulfur in all vulcanized polymers [tires] and. sulfur is also found in hyproducts ot the oll 5 industry, and the invention allows them to be beneficially utilized: this is because the sulfur contained in the fuel provided for carrying out combustion reaction will be oxidized. Specifically, these sulfur OXides (SO2 and/or SO3) can be converted 10 into sulfuric acid, by recovering them from the flue gases and treating them appropriately. There are therefore two choices (alternative or cumulative in fact, especially depending on the quantity of H3S04 manufactured, which depends intimately on the chosen S 15 content of the fuell either the H2SO4 is utilized, as a reactant widely used in the chemical industry, independently of the process according to the invention, or it is reused in a variant of the process of the invention specifically, the combustion product 20 of the silicate formation reaction is used, in a "feedback" process, as reactant for. reacting with, the silicate and resulting in precipitated silica. Thus, the invention also relates to a process for preparing a precipitated silica, comprising a step a) of preparing 25 a silicate as claimed in one of the preceding claims, the reactor being equipped with 5 stack, this being fitted with a system for recovering the sulfur oxide, resulting in sulfuric acid, a step b) for the acid treatment of the silicate produced at a) with the 30 sulfuric acid produced at a), resulting in, on the one hand, precipitated silica, and on the other hand, the sulfate of said element feeing recycled at a). There is another way, as an alternative to or in 35 combination with the previous one, of manufacturing - 15 - H2SO4 from the process according to the invention: the reaction of converting sulfate to silicate itself produces sulfur oxides so4 and/or 50. Here again, these sulfur oxides may therefore be recovered and made to 5 undergo a conversion reaction, converting them to sulfurie acid. As in the previous case, this sulfutic acid may be reused as reactant with silicate and/or it. may be utilized as a reactant for the chemical industry. 10 As A result, If the fuel contains a significant amount of sulfur, these two reactions of converting sulfur oxides to sulfuric acid may produce more, and even significantly more, sulturic acid than is needed for 15 reaccion of converting the halides to sulfates, resulting in the beneficiation of the process according to the invention in its entirety. A first outlet for the silicates manufactured according 20 to the invention is in the glass industry: they may substitute, at least in part, for the conventional batch materials that provide alkali metals or rare eaxths, with, very particularly as regards sodium, at least partial substitution of Na2CO3 and of sand with 25 the silicate. The silicates of the invention can therefore be, employed for feeding a glass furnace. Before subsequent conversion, for example in a glass furnace, the silicate may be converted into granales, for temporary storage. The glass furnace may be of 30 conventional design (for example, an electric melting furnace using submerqed electrodes, a crown-fired furnace operating with lateral regenerators, a horseshoe-fired furnace and any type of furnace known in the glass industry thus including submerged-barner 35 furnaces), possibly with a design and an operating - 16 - method chat are slightly modified so as to be suitable for a melting process with no carbonace or with less carbonate than for standard melting operations. 5 It should be noted that certain silicates other than sodium silicate are also very useful to manufacture according to the invention. Thus, the invention allows potassium silicate to be manufactured from K2SO4, which is at least economically, very advantageous as batch 10 material containing Si and K for the manufacture of what is referred to as "mixed-alKali" glass, that is to say glass containing both Na and K. Such glass is used especially for producing tactile screens, glass for television screens and gloss for plasma display penels. 15 Likewise, the invention allows more economical manufacture of special glasses containing additives, for which chlorides are less expensive than oxides. This is the case with rare earths such as cerium – the 20 presence of cerium oxide giving the glasses UV- screening properties - and rare earths of this type are also found in the composition of special glasses of high elastic modulus for hard disks. The invention thus makes it possible to have a batch material containing 25 Si and Ce, namely cerium silicate, for a moderate cost. A second outlet for the silicates manufactured according to the invention (apart from those used as batch materials for a glass furnace) , more particularly 30 sodium silicate, is in the detergents industry, sodium silicate frequently being incorporated into the composition of washing poweters/detergents. A third outlet for the silicates formed according to 35 the invention is in the preparation of special silicas -17- commonly referred to as "precipitated silicas" that are incorporated for example its the composition of concretes. This is because the silicates formed according to the invention may undergo acid attack, 5 adventageously by sulfuric acid, so as to precipitate. silica in the form of particles having a particular particle size: the intended particles are generally of nanoscale dimensions (0.5 to 300 mn and 1 to 100 mn for example) . 10 To carry out the reaction of converting the sulfates to silicates, it is possible to use, as described in the patent WO-OO/46161, a reactor equipped with one or more submerged burners and with at least one means of 15 introducing the silica and/or the sulfatea below the level of the molten materials, especially in the form of one or more feed-screw botch chargers. Preferably, the same applies in the case of the solid or liquid fuels possibly used, such as the carbon and/or 20 hydrocarbon and/or sulfur compounds (including solid sulfur and solid carbon) mentioned above. It is thus possible to introduce, directly, into the mass of products undergoing melting/reaction, at least those of the starting reactants that can vaporize before having 25 the time to react. The process according to the invention described above therefore has many advantages, among which: > a reduction in CO2 emissions in glass furnaces which 30 completely or partly substitute sodium carboonate with sodium silicate - these furnaces consume less energy since the decarbonatization reactions are reduced or eliminated; > a possibility of turning the process into a feedback - 18 - process, with the H2SO4 hyproduct manufactured being reused, and > a possibility of utilizion xxx derivatives as fuel. 5 Figuce 1 shew 3 a silicate manufacturing plant comprising a reactor followed by a refining vessel. Figure 2 is a diagram of a preferred version of the 10 method according to the invention, operating in a feedback loop and resulting in a precipitated silica. Figure 1 shows a reactor 1 equipped with submerged burners 2 and including a system 3 for introducing 15 solid materials (sand, sulfate, coal, sulfur, etc.) below the level of the reaction mass 4, the flue gases escaping via the stack 5. The raw silicate passes via channel 6 into the refining vessel J, which is equipped with at least one suhmerged burner with a more 20 oxidizing flame than those of the reactor. The flue qsaes generated in the refining vessel escape via the stack 8. The refined silicate 9 is recovered via the spillway 10. 25 Figure 2 shows how the silicate manufactured according to the invention can be retreated with the suifuric acid produced in the melting reactor in order to prepare precipitated silica of calibrated particle size. The silicace on the one hand and the sulfate on 30 the other are fed back into this psocess. The sulfuric acid is also fed back, an excess amount possibly being created depending on the nature of the fuel and/or of the reducing agent used. - 19 – EXAMPLE 1 A melting furnace equipped with a submerged burner followed by a refining vessel equipped with a submerged 5 burner were used. The furnace and the vessel were both cylindrical (of vertical axis) and both had a floor area of 0.07 m2. The submerged burners (furnace and vessel) both operated stoichiometrically with methano and pure oxygen (the oxygen was therefore entirely 10 consumed in each burner flame)sand and sodium sulfate were introduced into the furnace in a ratio allowing a sodium silicate to be obtained having an sio;/Na20 molar ratio of 3,5. Also introduced was coke, acting as excess fuel/reducing agent, in an amount of 0.5 mol of 15 carbon per mole of sulfate introduced. The output was 3 metric tons per day per m2. The furnace and the vessel both operated at 1300°C. The redox ratio (weight ratio of FeO to total Fe2O3) on exiting the furnace was 0.7 and the residual so3 (so3 dissolved by the silicate) was 20 0.428 by weight (measured by x-ray fluorescence or by carbon/sulfur analysis), indicating that the efficiency of the reaction in the furnace was around 98%. In the refining vessel, the residual sulfate reacted with the residual reducing agent. Obtained ar the exit of the 25 vessel was a silicate of formula NazO-3.5(SiOz) which was translucent and colorless, the residual SO3 (SO3 evolution from the residual sulfate) was less than 0.05%. The redox ratio here was 0.20, 30 EXAMPLE 2 This example is the same as the previous one, except that the submerged burner of the refining vessel operated with an insufficiency of oxygen (reducing 35 flame with an oxygen flow rate 15% below - 20 - stoichiometry) . Obtained at the exit, of the vesssl was a translucent and colorless 5; xxx Na2O-3.5(5iO2), the residual SO2xxxwas less than 0.05%. In this case redxxx 5 EXAMPLE 3 (comparative example) This example is as in Example 1 except that there was no excess addition in the form of coke. Inclusions of 10 sodium sulfate visible to the naked eye were found in the final silicate, The residual SO3 was greater than 11. This indicates a reaction efficiency much lower than that of Example 1. The sulface introduced did not decompose sufficiently. Enrichment with silica is too 15 greet, the reaction mass rapidly becoming too viscose, and the reactor had to be stopped. EXAMPLE 4 20 This example is as in Example 1 except that the excess reducing agent in the form of coke was replaced with an excess of reducing agent, in, the form of spent tires, the composition of which was approximately 28 sulfur by weight, 80% carbon by weight and 18% hydrogen by 25 weight. This reducing agent was introduced in an amount representing 51 of the mass of sodium sulfate introduced. A silicate containing O.l% residual 50, was obtained, the redox ratio of which was 0-5. The presence of sulfur in the reducing agent allowed 30 additional sulfuric acid to be produced. - 21 – CLAIMS 1. A process for preparing a silicate of an element chosen from alkali metals, alkaline-earth metals 5 or rare earths, comprising a reaction between silica and a sulfate of said element in a reactor equipped with at least one submerged burner within a molten mass, said submerged burner being supplied with an oxygen-containing gas, an excess 10 of reducing fuel being introduced into the reactor relative to the effectively consumed oxygen. 2. The process as claimed in the preceding claim, characterised in that the excess fuel/reducing 15 agent is a solid or liquid acting as a source of carbon. 3. The process as claimed in either of the preceding claims, characterized in that the excess 20 fuel/reducing agent is a solid or liquid acting as a source of sulfur. 4. The process as claimed in one of the preceding claims, characterized in that the excess 25 fuel/reducing agent is a gas acting as source of sulfur. 5. The process as claimed in one of the preceding claims, characterized in that the silicate pnase 30 in the reaction maSS has a viscosity of between 50 and 3000 poise. 6. The process as claimed in the preceding claim, characterized in that the silicate phase in the 35 reaction mass has a viscosity of between 100 and - 22 – 1030 poise. 7. The process as claimed in one of the preceding claims, characterized in that the reaction mass 5 has a temperature of between 1000 and 1500oC. 8. The process as claimed in the preceding claim, characterized in that the reaction mass has a temperature of between 1200 and 1400°C, 10 9. The process as claimed in one of the preceding claims, characterised in that the excess fuel is sufficient for the silicate not to contain any sulfate inclusion. 15 10. The process as claimed in one of the preceding claims, characterized in that the excess fuel represents from 0.1 to 2 mol of carbon equivalent and/or sulfur equivalent per mole of sulfate. 20 11. The process as claimed in the preceding claim, characterised in that the excess fuel represents from 0.3 to 1 mol of carbon equivalent and/or sulfur equivalent per mole of sulfate, 25 12. The process as claimed in one of the preceding claims, characterised in that the reactor is followed by a vessel for refining the silicate output by the reactor. 30 13. The process as claimed in the preceding claim, characterised in that the temperature of the silicate in the refining vessel is between the same temperature as in the reactor and 150°C below 35 the temperature in the reactot. - 23 - 14. The process as claimed in xxx characterized in that the tempereture of the silicate in the refining vessel is between 50ºC below the temperature in the reactor and 150ºC 5 below the temperature in the reactor, 15. The process as claimed in one of claims 12 to 14, characterized in that the vessel is equipped with at least one submerged burner. 10 16. The process as claimed in one of claims 12 to 15, characterized in that the Iron redox ratio in the silicate leaving the vessel is less than 0.5. 15 17. The process as claimed in one of the preceding claims, characterized in that the silicate is of formula MROyn (SiO2) in which MR0y represents Na2O or K2O and n represents a number of males between 1 and 4. 20 18. The process as claimed in the preceding claim, characterised in that n is between 1.3 and 4, 19. A process for preparing a precipitated silica, 25 comprising: - a step a) of prepayxxxclaimed in one of the precedingxxx for being equipped with a stack when as zizued with a. system for recovering the sulfur oxides, resulting 30 in sulfurie acid; and - a step b) for the acid treatment of the silicate produced at a) with the sulfuric acid produced at a), resulting in, on the one hand, precipitated silica and, on the othet hand, the sulfate of said 35 element, said sulfate being recycled at a). - 24 - 20. The process as claimed in the preceding claim characterized in that the precipitated silica has a size of between 0.5 and 300 mn. 5 21. Precipitated silica obtained by the process of either of the two preceding claims. 22. Use of the precipitated silica of the preceding 10 claim in tires or food products. The invention relates to a process for preparing a silicate of an element chosen from alkali metals, alkaline-earth metal a or rate earths, comprising a reaction between silica end a sulfate of said element in a reactor equipped with at least one submerged burner within a molten mass, said submerged burner being fed with a gas containing oxygen, an excess of fuel/ reducing agent being introduced into the reactor relative to the oxygen effectively consumed. The process allows the reaction, to be earried out satisfactorily and at relatively fow temperature.

Documents:

00490-kolnp-2006-abstract.pdf

00490-kolnp-2006-claims.pdf

00490-kolnp-2006-description complete.pdf

00490-kolnp-2006-drawings.pdf

00490-kolnp-2006-form 1.pdf

00490-kolnp-2006-form 2.pdf

00490-kolnp-2006-form 3.pdf

00490-kolnp-2006-form 5.pdf

00490-kolnp-2006-international publication.pdf

00490-kolnp-2006-pct others.pdf

00490-kolnp-2006-priority document.pdf

490-kolnp-2006-correspondence 1.1.pdf

490-KOLNP-2006-CORRESPONDENCE-1.1.pdf

490-KOLNP-2006-CORRESPONDENCE.pdf

490-kolnp-2006-examination report 1.1.pdf

490-kolnp-2006-form 18.1.pdf

490-KOLNP-2006-FORM 27.pdf

490-kolnp-2006-form 3.1.pdf

490-kolnp-2006-form 5.1.pdf

490-KOLNP-2006-FORM-27.pdf

490-kolnp-2006-gpa 1.1.pdf

490-kolnp-2006-granted-abstract 1.1.pdf

490-kolnp-2006-granted-claims 1.1.pdf

490-kolnp-2006-granted-description (complete) 1.1.pdf

490-kolnp-2006-granted-drawings 1.1.pdf

490-kolnp-2006-granted-form 1.1.pdf

490-kolnp-2006-granted-form 2.1.pdf

490-kolnp-2006-granted-specification 1.1.pdf

490-KOLNP-2006-OTHERS.pdf

490-kolnp-2006-others1.1.pdf

490-KOLNP-2006-PETITION UNDER RULE 137.pdf

490-kolnp-2006-reply to examination report 1.1.pdf

490-kolnp-2006-translated copy of priority document 1.1.pdf

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