FR2989073A1 - Preparing a silane compound, comprises mixing silicide or silicon alloy with an aqueous solvent, fluidizing the mixture, and reacting the fluidized alloy with hydrochloric acid, which is pre-dissolved in aqueous solution - Google Patents

Abstract

Preparing a silane compound or its mixture, comprises mixing silicide or silicon alloy with an aqueous solvent, fluidizing the mixture, and reacting the fluidized alloy with hydrochloric acid, which is pre-dissolved in aqueous solution. Preparing a silane compound of formula (Si nH 2 n + 2) (I) or its mixture, comprises mixing silicide or silicon alloy having a structure of formula (M 1> xM 2> ySi z) (II) with an aqueous solvent, fluidizing the mixture, and reacting the fluidized alloy with hydrochloric acid, which is pre-dissolved in aqueous solution. M 1>a reducing metal; M2 : an alkali or alkaline earth metal; x-z : 0-1; and n : 1-3.

Description

Production of silanes from fluidized alloys of silicon and alkaline earth metals or silicides of alkaline earth metals. The present invention relates to the production of silicon hydrides or silanes from silicon alloys or silicides. Certain silanes and more particularly monosilane, or silicon tetrahydride (SiH4) and disilane (Si2H6) are used as a silicon vector in deposition techniques of amorphous silicon, polycrystalline silicon, nanocrystalline silicon or microcrystalline silicon also called nano or micromorph, of silica, silicon nitride, or other silicon compound for example in vapor deposition techniques. Thin film deposition of amorphous silicon, and microcrystalline silicon obtained from silane and / or disilane, make it possible to manufacture solar cells.

It is also possible to obtain coatings resistant to acid corrosion, by cracking silane and to manufacture compounds such as silicon carbide. Finally, the silane is capable of adding to the single or multiple bonds of the unsaturated hydrocarbons to give organosilanes.

The market for monosilane and disilane will experience a very strong expansion for the manufacture of integrated semiconductors and the manufacture of solar cells (photovoltaic), as well as for semiconductor components and the manufacture of flat screens. Several types of methods described below have been used up to now. First, the reduction of SiCl 4 by LiH in a KCl / LiCl bath at temperatures between 450 ° C and 550 ° C is known. The yield of the reaction is interesting, but the method is based, on the one hand, on the availability of LiH while the lithium resources are very limited and on the other hand on the possibility of recycling the lithium metal by electrolysis. The reaction medium is very corrosive and uses particular materials. This process has been used to produce small amounts of silane. The reduction of SiF4 by NaAIH4 in organic solvent medium is another example. This process is industrially viable only when there is SiF4, a by-product of another chemical production and sodium to make sodium aluminum hydride. This method is not easily usable, especially for these two reasons. Another known reaction is the acid attack in liquid NH 3 medium of a stoichiometric Mg 2 Si alloy. The balance of the reaction is as follows: Mg 2 Si + 4 HCl SiH 4 + 2 MgCl 2 NH 3 Liq. This process is carried out at a temperature close to ambient temperature at atmospheric pressure. Magnesium silicide (Mg2Si) has been extensively tested in aqueous media and ammonia. Although sufficiently acceptable to lead to industrial production units, the process has the following major drawbacks: industrial magnesium silicide due to the volatility of magnesium only contains 70% to 80% of the stoichiometric compound. The conditions of manufacture of the stoichiometric compound make it a product too expensive for this industry, in parallel with the production of monosilane by this route, many higher silanes including polychlorosilanes, siloxanes and silicone gums are manufactured, making the balance of monosilane material unattractive and inducing significant difficulties in the management of the process. This process is not satisfactory because of the difficulty of controlling the process and the implementation of highly regulated liquid ammonia. Another known reaction is the disproportionation of SiHCI 3 on resins containing grafted amino groups or the like. The complete process is described as follows: a) 4 Si Metal. +12 HCl 4 SiHCI3 + 4H2 (temperature between about 300 ° C and about 1000 ° C) b) 4 SiHCI3 SiH4 + 3 SiCl4 (near ambient temperature) c) 3 SiCl4 + 3H2 3 SiHCI3 + 3HCl ( temperature of about 1000 ° C), ie the following reaction balance: 4 Si Metal + 9 HCl 3 SiH4 + 3 SiHCI3 + H2 A variant of the above reaction is described as follows: a) 4 Si Metal + 16 HCl 4 SiCl 4 + 8 H2 (temperature between about 1000 ° C. and about 1100 ° C.) 2 9890 73 3 b) 4 SiCl 4 + 4H 2 SiHC13 + 4HCl (temperature of about 1000 ° C.) 4 SiHCI 3 SiH 4 + 3 SiCl 4, ie the reaction balance next: 4 Si metal + 12 HCI SiH4 + 3 SiCI4 + 4 H2. This process requires high temperatures in an extremely corrosive environment and consumes a lot of energy (about 50 kWh / kg for step b)). To achieve maximum efficiency, step b) requires many recirculation loops of chlorosilane mixtures. In addition to the use of highly corrosive, toxic and flammable products, such a type of process is very expensive in energy and presents many industrial risks. The generation of monosilane and higher silanes has been described in the Handbook of Inorganic Chemistry Gmelin Si-Silicon, by reacting silicon silicides and alloys in an acidic or basic medium in the aqueous phase. In patent applications EP146456 and WO2006 / 041272, the synthesis of monosilane in aqueous phase by dropping a powder of Alx Siy Caz, x, y and z representing the percentages respectively of aluminum, silicon and calcium, in a solution of HCI, is described. The composition of the gases produced was about 80% monosilane, 10% disilane and 5% trisilane as well as traces of disiloxane. A disadvantage of such a process is the formation in abundance of a foam in the reaction medium, which decreases the yield of the reaction and requires the presence of an anti-foaming agent. Such a reaction is very exothermic and temperatures above 100 ° C are achieved quite rapidly if the rate of introduction of the alloy powder is not significantly reduced. All these works described above do not guarantee the conditions necessary for the realization of a profitable process for an industrial development. The development of processes involving less difficult reaction conditions and / or which can be used for small and medium units in almost all environments and near the use of monosilane is a major challenge for industries mentioned above. Thus, there is a need to implement a new silane supply route allowing: - a reduction in the transport of hazardous materials; - less stringent operating conditions; - modular unit size and customized; to avoid the presence of air in the reactor. One of the objectives achieved by the applicant through the present invention is to allow to refine the operating conditions and thus to increase the conversion efficiency of the alloy to monosilane and disilane.

It has been found a simple process, using inexpensive raw materials and producing silicon hydrides with an industrial yield and not having all the disadvantages seen above. An object of the present invention is to overcome all or part of the disadvantages of the prior art noted above. The object of the invention described hereinafter is to propose additional optimizations of the process starting from the alloys AISiCa while minimizing the disadvantages mentioned above. To this end, the subject of the invention is a process for preparing a compound or a mixture of compounds of formula Sin1-12, + 2 in which n is an integer greater than or equal to 1 and less than or equal to 3 , comprising at least the following steps: step a) of mixing at least one silicide or silicon alloy in the form of a powder of formula M1xM2ySiz in which M1 is a reducing metal, M2 an alkaline or alkaline earth metal, x, y and z ranges from 0 to 1, z being different from 0 and the sum x + y different from 0, with an aqueous solvent and fluidizing said mixture; step b) reaction of the fluidized alloy from step a) with hydrochloric acid previously dissolved in aqueous solution. The reducing metals are, for example, Al, B, Ga, In. The alkali metals are, for example, Li, Na, K, Cs. The alkaline earth metals are, for example, Mg, Ca, Sr, Ba.

Furthermore, embodiments of the invention may include one or more of the following features: Process as defined above, characterized in that said solvent is selected from water or a crown ether.

Process as defined above, characterized in that step b) is carried out in the presence of CaCl 2 in an amount of between 0.1% and 2% by weight of all the alloys introduced into the reaction medium. Process as defined above, characterized in that M1 is aluminum and M2 is calcium or magnesium.

Process as defined above, characterized in that the silicon alloy has the formula CaAl2Si2. Process as defined above, characterized in that step a) is carried out under an inert atmosphere of hydrogen or nitrogen. Process as defined above, characterized in that step b) is carried out at a temperature between 20 ° C and 100 ° C and at a pressure between 1 bar and 10 bar. Process as defined above, characterized in that the particle size of the silicon alloy is between 50 μm and 0.9 mm and preferably between 0.1 mm and 0.4 mm. Process as defined above, characterized in that the compounds of formula Sin1-12, + 2: silane, disilane and trisilane are condensed in liquid form and then separated by fractional evaporation, each fraction then being subjected to purification. Process as defined above, characterized in that the first fraction corresponding to the monosilane is isolated by evaporation at -78 ° C. at 3. 104 pascals, the second fraction corresponding to disilane is isolated by evaporation at 0 ° C. under 5.104 pascals. A process as defined above for the preparation of a gaseous mixture comprising up to 90% monosilane and at least 10% disilane, preferably comprising 80% monosilane and 20% disilane. Process as defined above for the preparation of disilane

The silicon alloy is selected from CaAl 2 Si 2, SiMg 2, SiCa 2, AlSiCa, CaSi, CaSi 2, MgSi, AisiNa, AlSiMg, SiNa, AlSiLi, SiK, CaMgSi, CaMgSiSi4, Ca0, 5SiO, 33 and Ca0, 5Si, 75, or a mixture thereof, preferably SiO, 5Mg, AISiNa, SiNa, SiO, 25Li, SiO, 25Na, SiO, 25K, or SiK. Other silicon alloys that are suitable for the present invention are ferosilicon-type alloys, for example FeSi, FeSiMg, FeSiCa. Preferably, the alloy used in the process that is the subject of the present invention is the CaAl 2 Si 2 composition, which is the most active phase giving the best yields.

By higher silanes, the compounds of formulas Sir, H 2, 2, n 2, including disilane, trisilane or tetrasilane, are understood. The alloys or silicides used in the implementation of the process according to the invention are alloys or silicides also used to control the foaming and deoxygenation of slags in steel foundries. These are low-cost, easily produced industrial products. One of the advantages of the process that is the subject of the invention is that it can conduct the reactions under conditions close to ambient conditions (temperature and pressure) in materials that are common in the mineral chemical industry, such as glass-reinforced reactors, for example. Processes involving these alloys or silicides can make it possible to produce silane in small and medium size units closest to the markets. Regardless of the alloys and silicides available and the operating and environmental constraints, the same unit can be used by adjusting the operating parameters. In all cases, the by-products are valuable or reusable mineral products.

It has also been found that the particle size of the alloy powder has an influence on the kinetics of the reaction and therefore on the reaction efficiency. The kinetics increase when the particle size decreases. Foaming during the reaction is the limiting factor for particle size. All other conditions being equal, when the particle size is divided by 10, the quantity of silane produced at the same time is multiplied by about 15. According to a preferred embodiment of the present invention, the alloy used is CaAl 2 Si 2. The inventors have found that surprisingly and unexpectedly, it was the alloy providing the best results.

The reaction mechanism of the reaction between the alloy and the hydrochloric acid, for the production of monosilane is written as follows: (1) Al2CaSi2 + HC1AlCl3 + CaCl2 + SiH2 + H2 (2) 2S / H2 + H2O SIH4 [S11120 ] 72 (3) 3S / H2 + H2O S / 2H6 [SIH2O] n (4) 2S / H2 2H2 2S / H4 The first reaction reveals a reaction intermediate, SiH2, which recombines with the water of the aqueous solution. By this recombination, two molecules of SiH2 intermediates produce a silane molecule SiH4 and a silica molecule [SiH20], which precipitates. The maximum conversion efficiency of the ternary alloy is therefore reduced. A solution object of an embodiment of the method of the present invention proposed to overcome this limitation is to reduce the activity of the water by adding in the system a third additive which, once hydrated, has the potential to create a complex with the water molecules and thus reduces the chemical activity of the water. The addition of anhydrous CaCl 2 in solution is preferred: the CaCl 2 is highly soluble in water (750 g / L at 20 ° C); CaCl 2 forms in water a CaCl 2 complex, 6H 2 O (up to 30 ° C.), then CaCl 2, 2H 2 O; - CaCl2 is already a product of the reaction and does not introduce any third product to separate; - The reaction mechanism shows a reaction intermediate SiH2 partially consumed by the aqueous solvent, the addition of a third body thus reduces the chemical reactivity of the water and promotes the production of silane.

In addition, remaining at a temperature well below 200 ° C, the risk of formation of chlorosilanes by reaction between light silanes and HCl are very low. Other features and advantages will appear on reading the following description, made with reference to Figures 1 and 2. Figure 1 shows a diagram of an installation for implementing the method according to the invention. FIG. 2 represents a diagram of a feed installation located upstream of the reactor of FIG. 1.

The production unit 1 comprises at least four parts containing a reactor 2, a feed system 7 of the silane generator, a purification system 3 and a recycling system 4 of the solvent from the reactor 2. The production reaction silanes takes place in a reactor 2 provided with a mixing means 40 (such as a scraper or a kneader). The reactor 2 is filled with a silicon alloy, such as CaAl 2 Si 2, from a source 5 on the one hand and with the aid of an additive such as CaCl 2, derived from a source 20 and on the other hand, from a source 6, a solution containing an acid, such as HCl for example, premixed with an aqueous solvent to reach a concentration defined by the user, for example 10% by weight . The additive will preferably be mixed with the acid solution before introduction into the reactor. The proportions of the mixture are chosen prior to the reaction by the user in order to obtain the best possible yield given the problems to be solved identified above. The reactor 2 may for example be secured to a removable cover at the top fixed by arches. The lid has a sealed opening for connecting a sealed hopper. Preferably, the reactor is surrounded by a thermal insulation sheath. In the vicinity of the reactor 2, a means 7 for the flow of the silicon alloy is present. Such a flow means comprises, for example, a hopper initially filled with a silicon alloy in the form of a powder of formula M1xM2ySiz in which M1 is a reducing metal, M2 an alkaline or alkaline earth metal, x, y and z varying from 0 to 1, z being different from 0. Preferably, the alloy is CaAl 2 Si 2. For example, the hopper comprises a worm and a constriction hose for isolating the hopper of the reactor 2. The design of the hopper is for example similar to the hoppers used to pour the calcium carbide into the acetylene reactors. The alloy is fed into drums similar to the drums used to transport the calcium carbide in the acetylene production units.

According to a particular embodiment of the invention, above the reactor cover 2 are arranged two sealed valves in series ensuring the isolation of the reactor. An integrated lateral stitching between these two valves makes it possible to purge the reactor 2 before disconnection. An analogous device 8 equips the outlet of the bottom of the reactor 2 to evacuate the liquids. The bottom of the reactor 2 is closed by means 9, for example a dome, preventing the liquid products from stagnating in the bottom channel. This dome is raised by actuating the bottom valve 8. The liquids are stored temporarily in a buffer capacity, then pass through the filtration system and are finally sent to a crystallizer system 10 via line 11.

In order to recover the desired silanes, the products from the reactor 2 that are not sent to the crystallizer system 10 are directed to a purification system 3 via a pipe 12 or pipe 19. Said purification system 3 comprises at least a fractionation column present to separate the silanes from the other products present, and finally a double distillation column used to recover the pure monosilane, which is then used for the desired applications. There is also provided a fractionation system capable of delivering a silane / disilane mixture. Indeed, the use of a mixture containing up to 90% of SiH 4 and at least 10% of Si 2 H 6 can be envisaged in silicon deposition techniques. Thus, according to one particular embodiment, the subject of the invention is a process and a production unit making it possible to continuously produce mixtures of gaseous silanes, including monosilane / disilane mixtures. These mixtures can be used directly for the manufacture of thin-film solar cells. The process makes it possible to produce mixtures with a composition of 80% monosilane and 20% disilane by volume. The process according to the invention also makes it possible to continuously produce a stream of disilane (Si 2 H 6). The powder of the compound (the silicon alloy, for example CaAl2Si2) is introduced into the reactor 2 continuously through the hopper. The reactor 2 may consist of a first slightly frustoconical bottom 13 consisting of a metal filtering medium 15 to which is added an organic filter media 14, for example a filter paper, the purpose of which is to retain the particles that do not have reacted. The frustoconical bottom 13 contains in its center a hole closed by a bung 5 mechanically removable from the outside. The reactor 2 also contains an agitation system 40 whose function is to stir the powder of the compound. Acid, for example hydrochloric acid (HCl), is injected by diffusers 16 above the maximum level 17 provided for the level of solid contained in the frustoconical bottom. The solvent entrained with the gas is liquefied in the condenser (s) 18 and is then re-injected into the reactor 2. The additional solvent is provided by the recycling of the water contained in the liquid effluents. FIG. 2 represents an exemplary implementation of a reactor supply system 7, said supply system 7 serving to implement step a) of the method that is the subject of the present invention. The role of this sub-assembly 7 is to carry out the introduction of the alloy powder into the reactor 2, excluding any contact between the reaction gas and the air. These contacts can just as easily take place in the reactor (for example following an air inlet with the alloy) or outside the reactor (for example following a rise in the reaction gas in the reactor system. supply of the reactor). The process consists of the following steps: Introduction of the alloy into a storage hopper 21. The alloy can then be stirred or not to facilitate its flow. The alloy is then driven by a worm 22 to an insulated tank and agitated 23. The solvent of the process, here water is also injected into this tank 23. The agitation of the mixture will allow to fluidize and maintain fluidization of the alloy in the liquid. The insulated and stirred tank 23 will be under an inert atmosphere (eg, nitrogen or hydrogen) to prevent dissolution of oxygen in the liquid. The stirred solvent-alloy mixture is then driven by a metering screw for direct injection into the reactor 2 shown in FIG. 1. A glass reactor 23 with a volume of 2.5 liters is used to carry out the reaction. This reactor 23 has a mechanical stirrer 24 with straight blades. The stirrer 24 is inserted through the removable lid of the reactor 23, the latter sealing the system. The reactor 23 is also equipped with a jacket supplied with water in order to apply a set temperature within the reactor. A thermocouple immersed in the reactor makes it possible to measure the temperature of the reactive medium and the water of the jacket is thermostatically controlled by means of a water bath. An injection device 25 of aqueous solution is integrated in the lid and a solid injection device 26. The liquid solution is derived from a solution tank previously created and then transferred via a pump. The injected solid comes from a tank 21 initially charged then passes through an airlock which is evacuated to prevent any entry of air through this. A gas outlet is also integrated in the reactor lid to collect the generated gases. These gases are then sampled and analyzed. A safety valve set at a pressure of 1.7 bar is connected to this gas circuit to ensure the safe operation of the system. The outlet of this valve is connected to a detoxification cartridge. All the gases generated are stored in a bottle initially purged at near vacuum pressure. The control of the pressure at the end of the reaction in the bottle and the precise knowledge of its volume makes it possible to determine the quantity of material thus captured. A valve is integrated at the bottom of the reactor to collect residual liquids and solids at the end of the reaction. The course of a test is as follows: An initial solution of silicon alloy as defined above mixed with water is prepared. An example of this solution is: 20 g of alloy mixed with 50 ml. This solution can be prepared immediately before the test or several hours in advance. An example of the previous duration of the preparation is: 100 hours. The alloy-water solution is injected into the reactor prior to any other step. The reactor as well as the gas lines are purged of any presence of oxygen by inerting the system with nitrogen. A temperature setpoint is supplied to the water circulating in the jacket. An example of a given instruction is: 50 ° C. The agitator in the reactor is started. An example of a stirring speed is: 365 rpm. ^ The system is evacuated. An example of pressure in the system is: 200mbar. The total volume of liquid in the reactor will eventually be 1 L for a fixed average concentration. An example of concentration is: 3.7M. A solution of hydrochloric acid is then prepared at a precise concentration, taking into account the dilution generated by the addition of water with the alloy. An example of concentration is: 3.9M. The hydrochloric acid solution is gradually injected into the reactor to reach the required volume (1L). The reaction then takes place. An example of injection speed is: 100mL / min. The pressure in the reactor and the storage bottle being measured, the progress of the reaction is monitored by the pressure profile in the gaseous atmosphere. The reaction is considered complete when the pressure profile in the storage bottle shows a stable plateau. The diagram in FIG. 3 shows the results of various tests: The quantities of gas generated (H2, SiH4, Si2H6) The quantities of solid waste generated.

2 9890 73 13 The first test is a reference point obtained with the aid of an airlock injection system and is to be compared to the following three tests, carried out with different preparation dates of the silicon-water alloy mixtures. . Thus, injection of the pre-mixed silicon alloy with water provides 119 g of SiH 4 per 1 kg of alloy when mixing is carried out just before the test. When the mixture is prepared 6 days in advance, it makes it possible to obtain 113 g of SiH4 per 1 kg of alloy. This injection system provides similar or even better yields than those of the vacuum airlock injection (113 g SiH4 per 1 kg of alloy).

This similarity of yield is also observed on the other gases (H2 and Si2H6) and on the quantity of waste generated.

Claims (12)

REVENDICATIONS1. A process for the preparation of a compound or a mixture of compounds of formula Sin1-12, + 2 wherein n is an integer greater than or equal to 1 and less than or equal to 3, comprising at least the following steps: step a) for mixing at least one silicide or silicon alloy in the form of a powder of formula M1xM2ySiz in which M1 is a reducing metal, M2 an alkali or alkaline earth metal, x, y and z vary from 0 to 1, z being different 0 and the sum x + y different from 0, with an aqueous solvent and fluidization of said mixture; step b) reaction of the fluidized alloy from step a) with hydrochloric acid previously dissolved in aqueous solution. 2. Method according to claim 1, characterized in that said solvent is selected from water or a crown ether. 3. Method according to one of the preceding claims, characterized in that step b) is carried out in the presence of CaCl2 in an amount of between 0.1% and 2% by weight of all the alloys introduced into the reaction medium. . 4. Method according to one of the preceding claims, characterized in that M1 is aluminum and M2 is calcium or magnesium. 5. Method according to claim 4, characterized in that the silicon alloy has the formula CaAl2Si2. 6. Method according to one of the preceding claims, characterized in that step a) is carried out under an inert atmosphere of hydrogen or nitrogen. 7. Method according to one of the preceding claims, characterized in that step b) is conducted at a temperature between 20 ° C and 100 ° C and at a pressure between 1 bar and 10 bar. 8. Method according to one of the preceding claims, characterized in that the particle size of the silicon alloy is between 50 pm and 0.9 mm and preferably between 0.1 mm and 0.4 mm. 9. Method according to one of the preceding claims, characterized in that the compounds of formula SinH2n + 2: silane, disilane and trisilane are condensed in liquid form, then separated by fractional evaporation, each fraction is then subjected to purification. 10. The method of claim 9, characterized in that the first fraction corresponding to monosilane is isolated by evaporation at -78 ° C under 3.104 pascals, the second fraction corresponding to disilane is isolated by evaporation at 0 ° C under 5.104 pascals. 11. Method according to one of the preceding claims for the preparation of a gaseous mixture comprising up to 90% of monosilane and at least 10% of disilane, preferably comprising 80% of monosilane and 20% of disilane. 12. Process according to one of the preceding claims for the preparation of disilane.