Direct synthesis of alkoxysilanes using copper-aluminum alloy catalysts

Abstract

An improved catalytic reaction between metallic silicon and alcohol is provided for the formation of alkoxysilanes, particularly trialkoxysilanes. The direct synthesis of metallic silicon and alcohol utilizes a catalytically effective amount of copper-aluminum alloy as a catalyst precursor and further benefits from a catalyst-promoting effective amount of catalyst accelerator.

Description

[Technical Field]

[0001] This application claims the benefit and priority of U.S. Provisional Application No. 63 / 460,488, filed on 19 April 2023, the entire contents of which are incorporated herein by reference. This application relates to the direct synthesis of alkoxysilanes by the reaction of copper-catalyzed metallic silicon with alcohols. [Background technology]

[0002] Trialkoxysilanes, particularly trimethoxysilane, triethoxysilane, and tri(isopropoxy)silane, are used in the production of silane coupling agents. One method for synthesizing trialkoxysilanes is to proceed directly from metallic silicon and alcohol in the presence of copper or a copper compound. This method is known in the art as direct synthesis, direct reaction, direct process, or Rochow reaction. For trialkoxysilanes, this method is most preferably carried out in a slurry reactor.

[0003] In the direct synthesis of trialkoxysilanes, the copper source used as a catalyst is preferably anhydrous and free from corrosive substances such as chloride ions. While a wide variety of copper-containing catalysts useful for the direct synthesis of alkoxysilanes have been disclosed in the literature, none have been found to be sufficiently satisfactory in achieving the desired selectivity, reaction rate, and stability. For example, U.S. Patent No. 5,362,897 discloses a direct process for producing trialkoxysilanes, in which the reaction is carried out using "wet" CuCl instead of commercially available "dry" CuCl, and high reaction rates and silicon conversion rates are obtained in the presence of CuCl, silicon containing 0.30-0.37 wt% aluminum, and aluminum or an aluminum compound. "Wet" CuCl is defined as "prepared through the steps of crystallization, separation, and drying" (Column 2, Lines 62-65). Dry CuCl is prepared from metallic copper and chlorine gas (Column 2, Lines 62-65). The specification further discloses that aluminum alloys of Si, Ca, and Mg are suitable, and that the aluminum alloy used must contain more than 50% by weight (>50 wt%) Al (column 3, lines 46-48).

[0004] When examining the cutting edge technologies for the direct synthesis of alkoxysilanes, it is clear that there remains a need for improved processes that possess the desired high reaction rate, selectivity, and silicon conversion rate, reduce the generation of unwanted by-products, and overcome other shortcomings of conventional processes. [Overview of the project]

[0005] Overall, the present invention provides an improved catalytic reaction between metallic silicon and alcohol for the formation of alkoxysilanes, particularly trialkoxysilanes. The direct synthesis reaction of metallic silicon and alcohol according to a preferred embodiment of the present invention utilizes a catalytically effective amount of copper-aluminum alloy as a catalytic precursor and optionally obtains advantages from a catalytically effective amount of a catalyst accelerator, which is an organic or inorganic compound having at least one phosphorus-oxygen bond if the desired trialkoxysilane is trimethoxysilane, and copper(I) cyanide and / or an organic nitrile if the target product is triethoxysilane. These copper-aluminum alloys can enhance selectivity for trialkoxysilanes, control the formation of tetraalkoxysilanes, and / or improve reaction stability in batch, semi-continuous, or continuous operations.

[0006] One aspect of the present invention provides a direct synthesis process for producing alkoxysilanes, particularly trialkoxysilanes, from metallic silicon and alcohols, such as methanol, ethanol, and higher alcohols, while reducing the co-produced tetraalkoxysilanes. These advantages are illustrated by the use of a copper-aluminum (Cu-Al) alloy as a copper source for catalytically activating the metallic silicon.

[0007] Another aspect of the present invention provides an improved direct synthesis process that includes using an anhydrous non-halogenated copper-aluminum alloy as a catalyst precursor to obtain desired reaction rate and selectivity and high silicon conversion rate. These alloys preferably contain less than 50 wt% (<50 wt%) of aluminum to obtain desired reaction rate and selectivity and high silicon conversion rate.

[0008] Water has been found to react with trialkoxysilanes and tetraalkoxysilanes to produce soluble, gel-like and / or resinous organosilicates. The formation of such silicates represents inefficiencies in the direct synthesis process. In addition, as disclosed in U.S. Patent Nos. 5,783,720 and 6,090,965, which are incorporated herein by reference in their entirety, silicates cause undesirable foaming of the reaction solvent and incomplete recovery. Accordingly, a further aspect of the present invention uses anhydrous catalyst precursors or catalyst precursors that do not produce water upon pyrolysis.

[0009] A further aspect of the present invention provides for the direct synthesis of trialkoxysilanes, where silicate condensation, gel and resin formation are prevented or substantially reduced.

[0010] In view of the above, the present invention provides for the production of trialkoxysilanes with greatly reduced levels of tetraalkoxysilane by-products, while at the same time providing a reaction rate selected at a desired value, avoiding or reducing deactivation, reducing the formation of condensed silicates, gels and resins, increasing the silicon conversion rate, and maintaining a high level of selectivity, particularly in continuous and semi-continuous operations.

[0011] In a preferred embodiment, the present invention provides a process for the direct synthesis of alkoxysilanes, which comprises: (a) forming a reaction slurry comprising a thermally stable solvent, metallic silicon, a catalytically effective amount of a Cu-Al catalyst precursor, and optionally a catalyst promoter; (b) stirring and heating the reaction slurry to form copper-activated silicon in situ, supplying alcohol to the reaction slurry to react with the copper-activated silicon to produce an alkoxysilane; and optionally, (c) recovering the alkoxysilane. **DETAILED DESCRIPTION OF THE INVENTION**

[0012] The present invention relates to the synthesis of alkoxysilanes from metallic silicon and alcohols. This process in which metallic silicon and alcohols are converted into alkoxysilanes, such as trialkoxysilanes, and co-products encompasses physical and chemical phenomena that occur simultaneously and sequentially. In order to meet certain economic and process engineering requirements, appropriate chemical activity (reaction rate) and selectivity over a specific period (conversion period) are necessary. If the activity and selectivity drop sharply after reaching the desired values, thereby restricting the conversion of raw materials into trialkoxysilanes, the process is inefficient and unstable. Stability means that the desired rate and selectivity are maintained until all raw materials are consumed or until consumption exceeds a preset criterion. Thus, the period of steady state during which the values of rate and selectivity are relatively constant will contribute to effective process control and efficient utilization of raw materials.

[0013] Unless otherwise specified, all technical and scientific terms used in this application have the same meaning as commonly understood by those skilled in the art to which this invention belongs. In general, the nomenclature used in this application and the experimental procedures described are well known and commonly used in the art. When a term is presented in the singular form, the inventors also consider the plural form of that term to be applicable. "Direct process", "direct synthesis", and "direct reaction" refer to the process of Rochow and Richard Müller, which is the most common technique for preparing organosilicon compounds on an industrial scale. This encompasses the copper-catalyzed reaction of alkyl halides and metallic silicon and generally takes place in a fluidized bed reactor.

[0014] In a slurry reactor for the direct synthesis of trialkoxysilanes, catalyst-activated silicon particles are suspended in a thermally stable, high-boiling solvent and reacted with an alcohol at high temperatures. The product stream exiting the reaction region typically contains a mixture of unreacted alcohol, trialkoxysilane, tetraalkoxysilane, alkyldialkoxysilane, alkyltrialkoxysilane, and condensed silicate. Trialkoxysilane is usually the desired product. It is desirable to improve the production of the most desirable product for which the synthesis method is known.

[0015] Selectivity can be calculated as a preference for the formation of trialkoxysilane under reaction conditions. In this application, this is expressed as the weight ratio of trialkoxysilane to tetraalkoxysilane. Alternatively, selectivity can be expressed as a molar percentage, i.e., 100 moles of trialkoxysilane / the molar sum of all silicon-containing products. It is desirable to improve the selectivity of known synthesis methods.

[0016] The rate of direct synthesis of trialkoxysilanes can be calculated as the time-based consumption of raw materials, i.e., alcohol or metallic silicon, or as the time-based formation of the product, e.g., trialkoxysilane or optionally, the product including by-products. The unit of reaction rate is generally the weight percentage of silicon conversion per unit time, e.g., kilograms of product per kilogram of metallic silicon consumed per unit time. It is desirable to improve the reaction rates of known synthesis methods.

[0017] Stability can be considered as the maintenance of the desired rate and selectivity until all raw materials are consumed, or until consumption exceeds a predetermined threshold. The progress of direct synthesis can be monitored by determining the composition of the product and / or the reaction rate as a function of time or the conversion of metallic silicon. In batch operations, the reaction profile typically shows an initial period (referred to as the introductory period) in which the reaction rate and the concentration of trialkoxysilane in the reaction mixture increase, after which the reaction settles into a steady state. In this state, the composition of the reaction mixture is approximately constant. A period of decreasing reaction rate and a decrease in the trialkoxysilane content in the product mixture typically follows the steady state. Improving the stability of known synthetic methods is desirable.

[0018] The actual catalysts in the direct synthesis of alkoxysilanes are considered to be copper-silicon alloys, or intermetallic compounds and solid solutions formed by the diffusion of copper into metallic silicon, or by the reaction of copper compounds with metallic silicon. Thus, all copper-containing raw materials that are effective in activating silicon for direct synthesis with alcohols should be considered catalyst precursors and are referred to as such in this application.

[0019] The following equation represents the basic chemical reaction that occurs during the direct synthesis of trialkoxysilane and alcohol (ROH): Si + 3ROH → HSi(OR)3 + H2(1) HSi(OR)3+ROH → Si(OR)4+H2(2) ROH + H2 → RH + H2O (3) 2ROH → ROR + H2O (4) RCH2OH → R'CH=CH2+H2O (5) 2Si(OR)4+H2O → (RO)3SiOSi(OR)3+2ROH (6) 2HSi(OR)3+H2O → H(RO)2SiOSi(OR)2H+2ROH (7) 2HSi(OR)3+Si(OR)4+H2O → HSi(RO)2SiOSi(OR)2OSi(OR)2H+2ROH (8) RCH2OH → RCHO+H2(9) RCHO+2RCH2OH → RCH(OCH2R)2+H2O (10) RR"CHOH" → RR"CO+H2(11)

[0020] The desired products of the direct synthesis of this invention are alkoxysilanes, particularly trialkoxysilanes of general formula HSi(OR)3 and alkyldialkoxysilanes of general formula RSiH(OR)2, where R is an alkyl group having 1 to 6 carbon atoms. R is preferably methyl, ethyl, propyl, or isopropyl. By-products of this synthesis include Si(OR)4, RSi(OR)3, linear, branched, and cyclic silicates, such as (RO)3SiOSi(OR)3, H(RO)2SiOSi(OR)2H, HSi(RO)2SiOSi(OR)3, (RO)3SiOSi(OR)2R, (RO)3SiOSi(RO)2OSi(RO)3, (RO)3SiOSi(OR)HOSi(OR)3, (RO)3SiOSi(OR)ROSi(OR)3, (RO)Si[OSi(OR)3]3, (RO)3SiOSi(OR)(OSi(RO)3)OSi(OR)3, and [OSi(OR)2] n Here, n is at least 4, and R in the formula is as previously defined and includes hydrogen gas, hydrocarbons such as methane and ethane, alkenes such as ethylene, ethers such as dimethyl ether and diethyl ether, aldehydes such as acetaldehyde, acetals such as 1,1-diethoxyethane, and ketones such as acetone.

[0021] Hydrogen gas, hydrocarbons, volatile aldehydes, ketones, and ethers are typically not recovered with the liquid reaction products but are discharged from the reactor vessel as gaseous streams. Some silicates evaporate from the reactor and remain soluble in the liquid reaction products. Others remain dissolved in the solvent or precipitate as insoluble gels and resins. Linear, branched, and cyclic silicates, gels, and resins are formed via the hydrolysis and condensation of trialkoxysilanes and tetraalkoxysilanes.

[0022] It is important to prevent or minimize the generation of water (see Equations 4, 5, and 10). For example, water reacts with trialkoxysilanes and tetraalkoxysilanes to produce soluble, gelled, and / or resinous organic silicates. The formation of such silicates represents an inefficiency in the direct synthesis process. Acetals and less volatile aldehydes and ketones are present in the liquid reaction mixture.

[0023] In addition to alkoxysilanes, the gaseous product stream may contain hydrogen gas, hydrocarbons, ethers, volatile aldehydes and ketones, and deactivators such as nitrogen and argon. These components in the gaseous effluent can be identified and quantified using analytical methods based on gas chromatography, Fourier transform infrared spectroscopy (FTIR), or mass spectrometry. Assuming that the reaction in formula [1] produces most of the hydrogen gas in the effluent, the amount of hydrogen produced in the direct synthesis can be used as a rough measure of the reaction rate and silicon conversion rate. The formation of hydrocarbons and ethers shown in formulas [3]-[5], and the formation of aldehydes, acetals, and ketones in formulas [9]-

[11] can be used as a measure of the inefficiency of the alcohol conversion. It is desirable that less than 2% by weight of the alcohol supplied to the reaction is converted to hydrocarbons, ethers, aldehydes, acetals, and ketones, and most preferably nothing is converted.

[0024] Gas chromatography (GC) analysis has proven to be a reliable and accurate technique for determining the composition of liquid reaction products. Other methods, such as nuclear magnetic resonance (NMR) and mass spectrometry (MS), are also available. These are particularly useful for identifying and quantifying high molecular weight silicates contained in the reaction products and reaction solvents. Data on the composition and weight of the reaction products, as well as the silicon content of each component, are used to calculate the silicon conversion rate.

[0025] Gravimetric analysis, atomic absorption spectroscopy, and inductively coupled plasma (ICP) spectroscopy are suitable methods for quantifying the silicon content of the reaction solvent. Appropriate analytical procedures include those described in Chapter 8 of "Analytical Chemistry of Silicones," edited by ALSmith, Willie & Sons, New York, 1991. The soluble silicates retained in the reaction solvent are an indicator of the degree to which side reactions such as those shown in Equations 6-8 occur. All of these reactions depend on the presence of water formed, for example, by the reactions in Equations 3-5 and 10. The gels and soluble silicates contained in the reaction solvent can be removed according to the methods disclosed in U.S. Patents 5,166,384; 6,090,965, and 6,166,237. The contents of these patents and references, as well as the contents of the patents and references referred to herein and thereafter, are incorporated in their entirety by reference.

[0026] The reaction can be carried out in batch, semi-continuous, or continuous mode. In batch operation, metallic silicon, copper catalyst precursor, and accelerator are first added to the reactor in a single step, and then alcohol is added continuously or intermittently until the metallic silicon is completely reacted or until the desired degree of conversion is reached. In continuous operation, metallic silicon, copper catalyst precursor, and accelerator are first added to the reactor, and then the solids content of the slurry is maintained within the desired limit. The batch mode is described in U.S. Patent No. 4,727,173, and the continuous mode is described in U.S. Patent No. 5,084,590.

[0027] In semi-continuous mode, additional metallic silicon, copper catalyst precursors, and accelerators are introduced into the reactor during or upon completion of a batch reaction. This results in multiple additions of silicon, copper catalyst, and accelerators for a single charge of the solvent (see Examples 6 and 7 of U.S. Patent No. 4,727,173). Additions are typically made towards the end of each steady-state period of the charge. If the copper source is hydrated or produces water during thermal decomposition, the alcohol flow is usually interrupted while additions are being made. After these multiple additions, the tetraalkoxysilane content of the crude product typically increases to over approximately 6% by weight, and may even increase to about 12% by weight. Due to the accumulation of condensation silicates in the solvent, both the viscosity and foaming properties of the solvent generally increase.

[0028] When a hydrated copper catalyst precursor is used, measures must be taken during the design of the reaction system to prevent any water formed during the dehydration and thermal decomposition of the catalyst precursor from coming into contact with the trialkoxysilane reaction product. Additionally, the introduction of the reactants into the reaction slurry must be delayed until the dehydration and thermal decomposition are complete. This can be achieved at ambient pressure at temperatures above 150°C, preferably 150-180°C. The advantages of the present invention can be achieved by a catalytically effective, halogen-free, anhydrous copper supply source that does not generate water in the reactor and promotes the continuous direct synthesis of trialkoxysilane.

[0029] It is desirable that the tetraalkoxysilane content remain below approximately 6% by weight until at least three additions of metallic silicon are completed, and preferably at least six additions. Furthermore, it is desirable that the addition of metallic silicon, copper catalyst precursor, and accelerator to the reaction be carried out without interrupting the alcohol flow. Both of these desired objectives can be achieved by embodiments that include the use of copper-aluminum alloys as copper catalyst precursors. These alloys must be halide-free and anhydrous.

[0030] When the direct synthesis is carried out using a copper-aluminum alloy according to the present invention, the trialkoxysilane generally contains at least about 70% by weight, preferably at least about 80% by weight, of liquid reaction products. The typical level of tetraalkoxysilane Si(OR)4 is less than 7% by weight, preferably less than about 6% by weight. Compounds (RO)2SiH2, RSiH(OR)2, and RSi(OR)3 are each less than about 4% by weight, preferably less than about 2% by weight. The condensed silicate is at most about 5% by weight, preferably less than about 1% by weight.

[0031] In addition to the percentage ranges described above, the selectivity for a desired trialkoxysilane can also be expressed as a weight ratio HSi(OR)3 / Si(OR)4. According to the process of the present invention, when calculated throughout the entire reaction, this ratio is at least about 16. This overall value is also referred to herein as product selectivity and is distinct from the selectivity of individual samples taken during the reaction steps. This is preferably at least about 18, and values ​​exceeding 30 can be achieved during the steady-state phase of the reaction.

[0032] The reaction rate is typically expressed as the rate of metallic silicon conversion per unit time, but it can also be expressed as the rate of alcohol conversion per unit time or the space-time yield (product yield per unit time by weight of raw materials). It is desirable to have a reaction rate that provides a good balance between product formation and heat removal from the reactor (temperature control). Rates exceeding a silicon conversion rate of about 4 wt% per hour, preferably about 5-20% per hour, are achievable in the process of the present invention. It is also achievable to shorten the introduction time, i.e., the interval between the start of the reaction and the achievement of steady states in both rate and product composition, preferably less than about 4 hours, more preferably less than about 1 hour. During that time, the maximum amount of metallic silicon consumed is usually about 15 wt%, and advantageously less than about 10 wt%.

[0033] Reaction stability refers to maintaining the desired rate and selectivity until all metallic silicon is consumed or until a predetermined threshold is reached. Thus, the degree of silicon conversion is a quantitative measure of reaction stability. A silicon conversion rate exceeding approximately 70% by weight, preferably exceeding approximately 85% by weight, and more preferably exceeding approximately 90% by weight, is reliably achievable by the process of this invention.

[0034] The present invention also involves using organophosphates and inorganic phosphates to obtain a reaction profile of Si(OR)4 (a plot of reaction time, alcohol supply, or silicon conversion rate against the concentration of Si(OR)4 in the product mixture) that remains at a minimum value for a longer period compared to a control. When ethanol is the reactant, copper(I) cyanide (CuCN) and / or organic nitriles can be advantageously used to improve reaction stability. The use of organophosphates and inorganic phosphates as accelerators is disclosed in U.S. Patent No. 7,652,164. The use of CuCN and / or organic tolyl is disclosed in U.S. Patent No. 7,429,672. Copper-aluminum alloy catalyst precursor

[0035] While we do not wish to be bound by theory, copper-aluminum alloys, which are useful as starting materials for activating metallic silicon for direct reaction with alcohols, are not considered to be actual catalysts for the direct synthesis process themselves. When a slurry containing copper-aluminum alloy, metallic silicon, and a thermally stable reaction solvent is heated, copper and silicon interact to produce what is considered to be the actual catalytic phase that reacts with the alcohol. The actual catalyst is considered to be a copper-silicon intermetallic compound and / or a solid solution formed by the diffusion of copper into silicon or the reaction of the copper compound with metallic silicon. Thus, the raw material of copper-aluminum alloy is a copper catalyst precursor, and is described as such in this application.

[0036] The copper-aluminum alloy of the present invention is a two-component composition, but trace amounts of other metals may be present that do not directly impair or inhibit the process. Cu-Al alloy compositions range from compositions containing about 4 wt% copper to compositions containing about 4 wt% aluminum. Preferred compositional ranges are from about 20 wt% copper to about 85 wt% copper, i.e., 80 to 15 percent aluminum. More preferably, alloys have a composition in the range of 33 to 80 wt% copper. Particularly effective Cu-Al alloys contain less than 50% aluminum, preferably about 15 to 50% aluminum, and more preferably about 35 to 45% aluminum, with the remainder being copper.

[0037] The Cu-Al alloy catalyst precursor is advantageously used in powder form. The powder may include Al-Cu solid solutions and stoichiometrically formulated Al-Cu phases, such as Al2Cu, Al3Cu4, and Al4Cu9, as disclosed in Zobac et al., Metallurgical and Materials Transactions A, 50 (2019), pp. 3805-3815. The composition of the copper-aluminum alloy can be determined by wet chemical analysis, atomic absorption spectroscopy, inductively coupled plasma (ICP) spectroscopy, energy-dispersive X-ray (EDX) analysis, or equivalent methods. The bulk structure can be established by XRD (X-ray diffraction). If the surface composition of the copper-aluminum alloy is of interest, X-ray photoelectron spectroscopy (XPS) can be used.

[0038] The process of the present invention is effective with copper-aluminum catalyst precursors having a particle size distribution in the range of about 0.1 to about 100 micrometers, preferably in the range of about 0.1 to about 50 micrometers. However, nano-sized precursors may be even more effective. Nanometer-sized particles are about 1 nanometer (10 -9 From meters to approximately 100 nanometers (10 -7The particle size distribution is in the range of 10 to 60 nanometers. Particularly preferred are catalyst precursor particles having a particle size distribution in the range of 20 to 60 nanometers. These nano-sized materials are also described in the art as nanostructures, nanocrystals, nanosize, nanoscale, ultrafine, or extremely fine. The structure and high surface-to-volume ratio of nanomaterials make them particularly desirable in catalytic, electronic, magnetic, and coating (pigment) applications. Compared to conventional copper catalyst precursors for the direct synthesis of trialkoxysilanes, nanometer-sized particles are 10 to 100 times smaller.

[0039] Nano-sized copper sources are particularly advantageous for use in this application. In embodiments of the present invention, nano-sized precursors have a particle size distribution of about 0.1 to about 600 nanometers. In a second embodiment, the particle size distribution is in the range of about 0.1 to about 500 nanometers. And in a third embodiment, it is about 0.1 to about 100 nanometers. The particle size can be determined by transmission electron microscopy (TEM), high-resolution scanning electron microscopy (HRSEM), or an equivalent method.

[0040] Various physical and chemical methods are technically known for preparing nano-sized copper-aluminum alloys. These include high-energy milling (see Yadav et al., Nanoscience and Nanotechnology 2, (2012), pp. 22-48), laser ablation (see N. Patra et al., IOP Conference Proceedings Series: Mater.Sci.Eng. 390 (2018) 012046), and electrical explosions (see NVSvarovskaya et al., Progress in Natural Science: Materials International 25 (2015), pp. 1-5).

[0041] The copper-aluminum catalyst precursor used in this invention is preferably anhydrous, but materials containing adhering water can also be used. In addition to particle size and water content, various other criteria can be used to characterize the copper-aluminum catalyst precursor of this invention. The BET specific surface area of ​​the precursor is as low as about 0.1 m². 2 It can be around / g. Approximately 10m 2 A BET specific surface area exceeding 15 m² is preferable. 2 Values ​​exceeding / g are particularly preferred.

[0042] Depending on their preparation methods and conditions, nano-sized copper catalyst precursors may contain trace amounts of impurities and foreign substances. Thus, trace amounts of barium, calcium, chromium, iron, lead, magnesium, manganese, nickel, phosphorus, sodium, tin, and zinc may be present in commercially available copper-aluminum alloys.

[0043] The zinc content of the copper catalyst precursor is preferably less than about 2500 ppm, more preferably less than about 1500 ppm, and more preferably less than about 750 ppm. Based on the initial weight of metallic silicon charged into the reactor, the zinc content of the reaction slurry should typically be less than about 100 ppm, and preferably less than about 50 ppm. Another element that may be present in trace amounts in the catalyst precursor is lead (Pb). Its concentration in the slurry should typically be less than about 50 ppm, and preferably less than 10 ppm.

[0044] The copper-aluminum catalyst precursor used in the direct synthesis process of this invention is used in a level effective for catalyzing the reaction. Generally, the effective amount is in the range of about 0.01 to about 5 parts by weight of catalyst precursor per 100 parts by weight of metallic silicon. The small particle size and large surface area of ​​the nano-sized copper-aluminum catalyst precursor preferred for use in this invention result in high dispersion of the actual catalyst phase on the silicon surface. Therefore, using the nano-sized copper-aluminum catalyst precursor in the lower end of this broad range is very effective in initiating and maintaining the selective synthesis of trialkoxysilane. Thus, about 0.05 to about 2 parts by weight of nano-sized copper-aluminum catalyst precursor per 100 parts by weight of metallic silicon is preferred, and about 0.08 to about 1 part by weight per 100 parts by weight of silicon is particularly preferred. Expressed in terms of parts by weight of copper per 100 parts by weight of silicon, the effective range is about 0.008 to 4.5 parts of copper, the preferred range is about 0.03 to 1.8 parts of copper, and the more preferred range is about 0.05 to 0.9 parts of copper.

[0045] Combinations of Cu-Al with copper formate, copper chloride, and / or copper hydroxide can also be used to activate metallic silicon for the direct synthesis of alkoxysilanes. However, it has been found that the copper source used as a catalyst in the direct synthesis of trialkoxysilanes preferably does not contain or substantially contains chloride ions or other halogen ions. In embodiments, "substantially free" means that the copper source contains less than 100 ppm, preferably less than 50 ppm, of chlorine or other halogen ions. Halogen ions can be corrosive and may affect the selection of materials for reactors, vessels, and piping. Furthermore, their presence may adversely affect the final use of the reaction product. Thus, the use of chlorides and other halides should be avoided. silicon

[0046] The metallic silicon reactant used in the process of this invention can be any commercially available grade of metallic silicon in particulate form. It may be manufactured by any currently practiced method, such as casting, wet granulation, spraying, and acid leaching. These methods are described in detail in “Silicon for the Chemical Industry” (H. Oye et al., eds.), vol. I (pp. 39-52), vol. II (pp. 55-80), vol. III (pp. 33-56, 87-94), Tapir, published by the Norwegian University of Science and Technology, and are also described in U.S. Patents Nos. 5,258,053, 5,015,751, 5,094,832, 5,128,116, 4,539,194, 3,809,548, and 4,539,194, and German Patents Nos. 3,403,091 and 3,343,406. Special types of chemically graded silicon containing controlled concentrations of alloying elements are also preferred, provided that copper is not one of the alloying elements and that the alloying elements are not detrimental to the rate, selectivity, and stability of the direct synthesis process of trialkoxysilane. These types of special silicon are described in U.S. Patents 5,059,343, 5,714,131, 5,334,738, and 5,973,177, and European Patent Applications 0494837 and 0893448.

[0047] A typical composition of commercially available metallic silicon useful in this invention, expressed in weight percent, is Si ~ 98.5%, Fe < 1%, Al ~ 0.05 to 0.7%, Ca ~ 0.001 to 0.1%; Pb < 0.001%, Water < 0.1%. Generally, smaller particle sizes are preferred for ease of dispersion in slurry, faster reaction, and minimization of corrosion in the reactor. Preferably, no particles larger than about 500 micrometers are included so as to minimize corrosion in the reactor. Adjusting the particle size by sieving the pulverized metallic silicon is optional. A particle size distribution in which at least about 90% by weight are between about 1 and 300 micrometers is preferred. Particularly preferred is a distribution in which at least about 90% by weight of metallic silicon particles are between about 20 and 200 micrometers. alcohol

[0048] The alcohol reactant useful in the process of this invention is of the formula ROH, where R is an alkyl group containing 1 to 6 carbon atoms. Preferably, R is an alkyl group containing 1 to 3 carbon atoms. More preferred alcohols are methanol and ethanol. While it is customary to use a single alcohol directly in the synthesis process, it is also possible to use mixtures of two or more alcohols to prepare trialkoxysilanes with different alkoxy groups, or to accelerate the reaction of less reactive alcohols. For example, up to about 5% by weight of methanol may be added to ethanol to improve the rate and stability of the direct synthesis of triethoxysilane. Alternatively, the reaction can be initiated with one alcohol and continued with another alcohol or mixture. Thus, copper-activated silicon prepared with the nano-sized copper-aluminum catalyst precursor according to the present invention can be reacted first with methanol and then with ethanol. The alcohol is preferably anhydrous. However, some content, for example up to about 0.1% by weight of water, is usually acceptable without significantly impairing selectivity, reactivity, and stability.

[0049] Generally, the direct synthesis process is carried out in batches in a slurry, and the alcohol is supplied to the slurry as a gas or liquid. Introduction in gaseous form is preferred. An introduction period lasting from a few minutes to about 5 hours may be observed. The initial alcohol supply is optionally controlled to a low level and then increased following the introduction period. Similarly, the alcohol supply is optionally reduced after a silicon conversion rate of about 70% by weight is achieved to minimize the formation of tetraalkoxysilane. Generally, once the reaction has begun, the alcohol supply can be adjusted to bring about the desired level of alcohol conversion. Those skilled in the art can easily adjust the supply in a given reaction by monitoring the composition of the product. If the supply is too high, the product flow will contain a large proportion of tetraalkoxysilane and unreacted alcohol. reaction solvent

[0050] The solvent for the direct synthesis process of trialkoxysilane slurry phases maintains a well-dispersed state of copper-activated silicon and facilitates both mass transfer of alcohol to the catalytic site and heat transfer between the reactive solid and reactants. The solvents useful in the process of this invention are thermally stable compounds or mixtures that do not degrade under activation and reaction conditions. Structurally, such solvents can be linear or branched paraffins, naphthenes, alkylated benzenes, aromatic ethers, polyaromatic hydrocarbons, and others. In the latter case, aromatic rings can be fused to each other, as in naphthalene, phenanthrene, anthracene, and fluorene derivatives. They can be linked by a single carbon-carbon bond, as in biphenyl and terphenyl derivatives, or by a cross-linked alkyl group, as in diphenylethane and tetraphenylbutane.

[0051] One preferred type of solvent is a high-temperature stable organic solvent, typically used as a heat exchange medium. An example of a heat exchange solvent is THERMINOL. 登録商標 59. THERMINOL 登録商標 60, THERMINOL登録商標 66, DOWTHERM 登録商標 HT, MARLOTHERM 登録商標 S, MARLOTHERM 登録商標 LH, JARYTHERM 登録商標 BT06, diphenyl ether, diphenyl and terphenyl and their alkylated derivatives are included, and the normal boiling point is higher than about 250 °C.

[0052] THERMINOL 登録商標 is a trade name for the heat transfer fluid of Eastman Chemical. THERMINOL 登録商標 59 is a mixture of alkyl-substituted aromatic compounds and is recommended for use between -45 and 315 °C. THERMINOL 登録商標 60 is a mixture of polyaromatic compounds and has an average molecular weight of 250. Its optimal temperature range is from -45 °C to 315 °C. THERMINOL 登録商標 66 and DOWTHERM 登録商標 HT is a mixture of hydrogenated terphenyls and has an average molecular weight of 240. The maximum temperature limit is about 370 °C. THERMINOL 登録商標 59, THERMINOL 登録商標 66 and DOWTHERM 登録商標 HT is a preferred solvent of the present invention. DOWTHERM 登録商標 The fluid is manufactured by Dow Chemical. MARLOTHERM 登録商標 is a trade name for the heat transfer fluid of Eastman Chemical. MARLOTHERM 登録商標 S is a mixture of isomers of dibenzylbenzene. MARLOTHERM 登録商標 LH is a mixture of isomers of benzyltoluene. Both can be used at temperatures up to about 350 °C. Both are preferred solvents for the present invention. JARYTHERM 登録商標 is a trade name for the heat transfer fluid of Arkema Chemicals. JARYTHERM 登録商標BT06 is one such heat-conducting fluid. It contains a mixture of benzyltoluene isomers, dibenzyltoluene isomers, and ditylphenylmethane.

[0053] Suitable alkylated benzenes for carrying out the direct synthesis process in this case are dodecylbenzene, tridecylbenzene, tetradecylbenzene, and mixtures thereof, for example, NALKYLENE from Vista Chemical. 登録商標 It is sold under the name ISORCHEM by Condea Augusta. 登録商標 and SIRENE 登録商標 It is sold under NALKYLENE. 登録商標 550BL, NALKYLENE 登録商標 550L, NALKYLENE 登録商標 500, NALKYLENE 登録商標 501, NALKYLENE 登録商標 600L, and NALKYLENE 登録商標 V-7050 is a particularly preferred reaction solvent for use with nano-sized copper-aluminum precursors. Alkylated benzene solvents typically provide good reaction stability and selectivity for trialkoxysilanes when used with nano-sized catalyst precursors at temperatures between 180 and 220°C.

[0054] Naphthenes are cyclic paraffins. They are components of white mineral oil, petroleum distillates, and certain fuels. White mineral oil and petroleum distillates also contain linear or branched paraffins (see A. Debska-Chwaja et al., "Soaps, Cosmetics and Specialty Chemicals" (November 1994), pp. 48-52; ibid. (March 1995), pp. 64-70). Suitable examples of commercially available products containing naphthenes and paraffins that are useful as reaction solvents for the present invention are the white mineral oils CARNATION 70, KAYDOL, LP-100 and LP-350, and the petroleum distillates PD-23, PD-25 and PD-28, all of which are sold by Crompton under the trade name WITCO. Other examples of naphthenes useful as reaction solvents include butylcyclohexane, decahydronaphthalene, perhydroanthracene, perhydrophenanthrene, perhydrofluorene, and their alkylated derivatives, bicyclohexyl, perhydroterphenyl, perhydrobinaphthyl, and their alkylated derivatives.

[0055] Alkylated benzenes, naphthenes, and mixtures of linear and branched paraffins with polyaromatic hydrocarbons are also useful as reaction solvents for the present invention.

[0056] The used solvent can be treated with boric acid or borate as described in U.S. Patent No. 5,166,384, or with formic acid as disclosed in U.S. Patent No. 6,090,965, or by thermal hydrolysis as disclosed in U.S. Patent No. 6,166,237, and can be reused in subsequent trialkoxysilane direct synthesis reactions.

[0057] Metallic silicon, copper-aluminum catalyst precursor, accelerator, and solvent can be added to each other in any order within the reactor. However, to facilitate stirring, it is preferable to add the solid to the solvent. The solvent must be present in an amount sufficient to uniformly disperse the solid and gaseous reactants. Generally, the reaction is initiated with a solvent-to-solid weight ratio between about 1:2 and about 4:1, preferably about 1:1 to about 2:1. However, since metallic silicon is consumed during batch-type direct synthesis, the solvent-to-solid ratio increases. For continuous reactions, this ratio can be maintained within a preferred narrow range. Copper-silicon activation conditions

[0058] Activation is the process of incorporating a catalyst (or precursor) and, if desired, other auxiliary agents into metallic silicon to make it reactive with alcohols. Activation may be carried out in the same reactor used for direct synthesis, or in a separate reactor. In the latter case, the activated silicon is typically, and preferably, transferred to the synthesis reactor in an anhydrous, non-oxidizing atmosphere by known methods. It is particularly preferable to transfer the activated silicon as a slurry in the reaction solvent.

[0059] Activation of the copper catalyst precursor and metallic silicon in a slurry reactor can generally be carried out at a temperature between about 20 and 400°C, preferably between about 150 and 300°C, and the mixture contains about 0.01 to about 50% by weight of copper relative to silicon.

[0060] For activation, an accelerator containing phosphates is optionally present. In one embodiment of the present invention, prior to the injection of the alcohol reactant, the stirred slurry is heated to about 200 to 300°C for about 0.01 to 24 hours in an inert gas atmosphere (e.g., nitrogen or argon). The time and temperature must be sufficient to result in effective copper-silicon activation and to avoid significant loss of trialkoxysilane selectivity and / or formation of hydrocarbons and water during direct synthesis. It is not necessary for all metallic silicon to be present during the activation step. For example, some of the silicon used and all of the copper-aluminum catalyst precursor can be activated in the reaction solvent, and the remaining metallic silicon can be added later.

[0061] Alternatively, an alcohol, optionally mixed with an inert gas, is introduced during heating into a stirred slurry of the copper-aluminum catalyst precursor, accelerator, metallic silicon, and reaction solvent. The reaction continues at atmospheric pressure, typically above a minimum temperature of 180°C. Preferably, after the temperature reaches or exceeds approximately 180°C, the vapor of the alcohol is introduced into the stirred slurry. Reaction conditions

[0062] The design, description, and operating conditions related to three-phase reactors are described in the following literature, papers, and patents: ●A. Ramachandran and RV Chaudhari, "Three-Phase Catalytic Reactors," Gordon and Breach Science Press, NY, 1983. ●N. Gartsman et al., "International Chemical Engineering," vol. 17 (1977), pp. 697-702. ●H. Ying et al., “Industrial and Engineering Chemistry”, Process Design & Development, vol. 19 (1980) pp. 635-638 ●N. Satterfield et al., "Chemical Engineering Science," vol. 35 (1980), pp. 195-202. ●M. Boxall et al., "Metal Journal," (August 1984), pp. 58-61 ● U.S. Patent No. 4,328,175

[0063] The reactor may be operated in batch, semi-continuous, or continuous mode. In batch operation, a single addition of metallic silicon and copper catalyst precursors is made to the reactor first, and then alcohol is added continuously or intermittently until the metallic silicon is completely reacted or until the desired degree of conversion is reached.

[0064] In continuous operation, unlike batch operation, both metallic silicon and copper catalyst precursors are initially added to the reactor, and then the solid content of the slurry is maintained within a selected range. Alcohol is added continuously. As can be understood, during continuous operation, while maintaining a continuous mode of operation, the supply of alcohol may be optionally interrupted for a short time between additions of metallic silicon.

[0065] The batch mode is described in U.S. Patent No. 4,727,173, and the continuous mode is described in U.S. Patent No. 5,084,590. Semi-continuous (also called multiple batch) operation is performed when additional metallic silicon, copper-aluminum catalyst precursors, and phosphate accelerators are added to the reactor after the silicon conversion has achieved a desired conversion rate, and in each case alcohol is added continuously or intermittently until the silicon conversion rate achieves a desired degree of conversion.

[0066] Many such additions of metallic silicon can be made without the addition of further solvents. Typically, at least three, and up to ten, additions of solids can be made before condensed silicates, gels, and resins form in the slurry and viscosity increases. The increase in viscosity leads to a decrease in the mass transfer of alcohol to the copper-activated silicon surface and a decrease in the reaction rate.

[0067] The use of Cu-Al as a source of catalytic copper in this invention is achieved by reducing the formation of condensed silicates (also called heavy beads) and the formation of gels and resins. The heavy beads are soluble in the crude reaction product and can be quantified by gas chromatography or NMR. Gels and resins are observed on the reactor walls and impeller.

[0068] The direct synthesis of alkoxysilanes is carried out in a slurry reactor, in a preferred embodiment, containing a thermally stable solvent, metallic silicon, a copper-aluminum catalyst precursor, a phosphate-containing accelerator, and a foaming control agent, and is continuously stirred in contact with alcohol vapor. The number and type of impellers are selected to effectively result in the suspension of solids, the dispersion of gases, and the mass transfer of alcohol to copper-activated silicon. The reactor may have a single nozzle or multiple nozzles for introducing gaseous alcohol. A mechanism for continuously or intermittently adding the accelerator, copper-aluminum catalyst precursor-silicon mixture, or metallic silicon must also be provided. Preferably, a mechanism for continuously removing and recovering volatile reaction products and unreacted alcohol is also provided. Separation and purification of the trialkoxysilane product is optionally carried out in the manner disclosed in U.S. Patent No. 4,761,492 or No. 4,999,446.

[0069] According to the method of this invention, once the initial doses of metallic silicon and copper-aluminum catalyst precursor are activated, the continuous direct synthesis of the slurry phase of alkoxysilane is advantageously continued by adding silicon alone, or silicon containing less copper-aluminum catalyst and phosphate-containing accelerator than the initially added silicon. In this way, the copper concentration of the slurry is controlled to minimize the conversion of alcohols to hydrocarbons and water (formulas 3, 4, 5, and 10 above). The problems caused by water are as described above.

[0070] The reaction generally takes place at temperatures above about 150°C, but below the temperature at which the reactants, accelerators, solvents, or desired products degrade or decompose. Preferably, the reaction temperature is maintained in the range of about 200°C to about 280°C. The reaction of methanol with copper-activated silicon of the present invention preferably takes place at about 220 to 270°C, and most preferably at about 230 to 260°C. The reaction with ethanol preferably takes place at about 200 to 240°C, and most preferably at about 205 to 230°C. The pressure at which the reaction takes place can vary from below atmospheric pressure to above atmospheric pressure. Atmospheric pressure is generally used in the reaction of methanol or ethanol with copper-activated silicon. Pressures in the range of about 1 to 5 atmospheres are advantageous for increasing the reaction rate in the direct synthesis process of this application.

[0071] Preferably, the contents of the reaction mixture are stirred to maintain a well-mixed slurry of copper-activated silicon particles, accelerator, and gaseous alcohol in the solvent. In this application, the term stirring encompasses any mechanism that imparts motion to the slurry, such as turbulent stirring or flowing of the slurry, or bubbling gas into the slurry. The discharge line carrying the gaseous reaction mixture from the reactor is preferably well-insulated to ensure that the trialkoxysilane does not reflux. Reflux can consequently accelerate the reaction between the trialkoxysilane and the alcohol, resulting in the loss of the desired trialkoxysilane product through the formation of tetraalkoxysilane.

[0072] The presence of gaseous alcohol, hydrogen gas, and other gases in the reactor can cause foaming. This is undesirable because it can result in the loss of solvent, accelerator, and copper-activated silicon from the reactor. Therefore, controlling foaming during the reaction can be useful. U.S. Patent No. 5,783,720 describes a foaming control agent for reaction slurries, preferably SAG from Momentive Performance Materials. 登録商標 1000, SAG登録商標 100, SAG 登録商標 The addition of silicon-containing foam control agents such as 47 and FF-170, Wacker-Chemie's OEL AF98 / 300, and Dow Corning's FS 1265 has been shown to eliminate or control this problem. SAG 登録商標 1000, SAG 登録商標 100 and SAG 登録商標 47 is a foam control composition containing polydimethyl silicone and silica. FS1265, FF-170, and OEL AF98 / 300 contain fluorinated silicone, e.g., poly(trifluoropropylmethylsiloxane). The foam control agent must be persistent; for example, a single addition at the start of a batch reaction is sufficient to avoid or mitigate foam formation until all of the metallic silicon is consumed. The effective level of use of the foam control agent ranges from 0.000001% to 5% by weight based on the total initial weight of the reaction slurry. Higher levels may, in some cases, lead to a decrease in the reaction rate. Physical and mechanical methods for preventing or controlling foam formation can also be used. These include rakes, ultrasonic devices, and foam trappers.

[0073] At a substantially constant temperature, the reaction rate depends largely on the surface area and particle size of the metallic silicon and copper catalyst precursors, as well as the alcohol supply rate. High reaction rates are obtained with a large surface area, fine particle size, and high alcohol supply rate. These parameters are selected to ensure that a safe and economically sustainable product output is achieved without endangering people, property, and the environment. By reducing the alcohol flow rate during the direct synthesis of triethoxysilane, inactivation can be reduced or prevented, and stability can be maintained. This flow rate control not only reduces excess alcohol used for dehydrogenation and other side reactions, but also facilitates the separation of the product in the stripping column downstream of the reactor.

[0074] High selectivity for trialkoxysilane, high reaction rate, and stable performance are achievable when a copper catalyst precursor and a phosphate-containing accelerator are used in the implementation of preferred embodiments of the present invention. This is particularly true when trimethoxysilane is prepared by the direct synthesis process of the present invention. Preferably, the copper catalyst precursor is a Cu-Al alloy, and the accelerator is copper orthophosphate or copper hydroxyphosphate. According to the teachings of the present invention, the weight ratio of trialkoxysilane / tetraalkoxysilane is at least 15, preferably greater than 17, and most preferably greater than 20. At the same time, the silicon conversion rate is greater than 50 percent, preferably greater than 70 percent, and most preferably greater than 85 percent, until the reaction rate and / or trialkoxysilane selectivity drops to an unacceptable level. Examples

[0075] The following examples illustrate key features of preferred embodiments of the present invention. These examples are not intended to limit the scope of the present invention. Rather, they illustrate preferred embodiments of the present invention and are provided to facilitate the implementation of the invention by those skilled in the art. Abbreviations and units used

[0076] The abbreviations used in the presentation of the data in the exemplary examples are as follows: [Table 1] Equipment used

[0077] In the exemplary embodiment presented herein, an 8-liter three-phase stainless steel slurry reactor was used. Four 1.27 cm wide baffles spaced 90° apart were fixed to the reactor wall. Agitation was performed by two impellers mounted on an axial shaft. The reactor was heated using an electrically heated mantle controlled by a heater / temperature controller. A valved connection was available at the top of the reactor for mounting a stainless steel cylinder, which could be used to introduce additives into the reactor (under nitrogen pressure) or to sample the contents of the reactor.

[0078] Methanol or ethanol was supplied to the reactor via a calibrated laboratory pump. An alcohol vapor inlet line was inserted through the top of the reactor. The line was heat-trace and controlled to 120°C to prevent the vapor from condensing. The alcohol vapor was introduced into the reactor below the turbine level.

[0079] The reaction products and unreacted alcohol were discharged from the reactor via packed tubes, which acted as droplet separators and partial distillation columns to remove solvents and high-boiling silicates from the product flow. The packing consisted of Teflon spheres supported by stainless steel mesh. Thermocouples were dispersed along the length of the tubes to record temperature and indicate foaming. The bottom thermocouple was coplanar with the top of the reactor. Foaming was detected using FF170, FS1265, AF98 / 300, and SAG thermocouples. 登録商標 47 and SAG 登録商標 Control was achieved by using 100. A flexible stainless steel tube connects the outlet of the droplet separator / partial distillation column to a cooled heat exchanger, which is also fitted with a four-way valve to regulate the flow of sampling and crude product to the distillation column.

[0080] Two 10-plate Oldershaw distillation columns were used to separate the liquid reaction product and unreacted alcohol from the gas. The effluent from the reactor was introduced into the top tray of the lower column. A magnetically controlled reflux condenser and a distillation head equipped with a thermocouple covered the top of the upper column. The reflux condenser and another downstream condenser were cooled to -25°C. The uncondensed gas was discharged from the condenser through a liquid-sealed bubbler into a fume hood. A wide tube was used downstream of the bubbler to avoid back pressure. The effluent gas stream was diluted with nitrogen before being released into the laboratory fume hood. A thermocouple was placed in the second opening of a three-necked flask, and the inlet of an FMI laboratory pump was attached to the other opening. This pump was used to transfer the liquid product from the flask to a storage bin. All glass containers used for storing or sampling trimethoxysilane and triethoxysilane were washed with dilute hydrochloric acid, thoroughly rinsed with methanol (or ethanol), and dried in an oven at 110°C before use.

[0081] Gas chromatography analysis of the reaction products was performed as described below. General procedure for silicon activation and reaction with copper

[0082] The reactor was charged with solvent, metallic silicon, copper-aluminum catalyst precursor, and foam control agent, and then sealed. The initial weight ratio of solvent to silicon was typically 2:1. The slurry was stirred at 670-900 rpm, and nitrogen was introduced during heating to the desired reaction temperature. Simultaneously, the alcohol evaporator and feed inlet were heated to 150-170°C, and the refrigerant circulating in the reflux condenser was cooled to ~-25°C. The flow of alcohol into the reactor was started once all set temperatures were achieved. During the reaction, the nitrogen flow was reduced to ~50 ml / min.

[0083] Once the alcohol flow has started, sampling and analysis of hydrogen in the vented gas flow should be performed every 10–30 minutes until a stable composition is established. This will indicate the end of the induction period. Subsequently, gas sampling should be performed every 30 minutes to monitor hydrogen and other uncondensed by-products. During this reaction process, the total vented gas flow is used as an approximate measure of the reaction rate according to the stoichiometry of equation (1).

[0084] Samples were pre-washed with acid, rinsed with alcohol, dried in an oven, and collected for 2–5 minutes every half hour in a container attached to a sampling valve. The container was cooled with dry ice between sample collections. Samples were weighed and analyzed by gas chromatography. The majority of the liquid product was condensed in a flask acting as a reboiler and transferred to storage. All of this data was used to calculate the then composition of the product stream, the selectivity for trialkoxysilane, the reaction rate, and the overall silicon conversion rate. The reaction is generally terminated after ~50 to 70% of the silicon charged into the reactor has reacted and is still in the steady state region. The reactor is then cooled to <50°C before being opened to charge additional silicon, copper-aluminum alloy, and accelerators (copper orthophosphate or copper hydroxyphosphate). In these multi-batch experiments, typically three or four charges of raw materials are made. In some cases, termination is made at a smaller or larger silicon conversion rate, depending on the purpose of the experiment and time constraints. In some cases, the residual solids from the reaction are recovered and weighed to calculate the silicon conversion rate. In most cases, the silicon conversion rate is determined from the composition and weight of the collected sample.

[0085] Gas samples were analyzed for hydrogen, nitrogen, and hydrocarbon (e.g., methane, ethane) content using gas chromatography. Dimethyl ether was analyzed using gas chromatography-mass spectroscopy. Liquid samples containing alkoxysilanes were analyzed using gas chromatography and a thermal conductivity detector. Materials used

[0086] The industrial-grade metallic silicon samples (Si-1, Si-2, and Si-3) used in the exemplary examples are identified in Tables 2 to 4, along with their relevant analytical data. It is noteworthy that the Al concentration was less than 0.3 wt% in all samples. Particles in the 45–300 micrometer particle size range accounted for approximately 70% by weight of all three samples. MARLOTHERM 登録商標 LH was the only solvent used. FF170 (Momentive), FS1265 (Dow Corning), and Wacker-Chemie's OEL AF98 / 300 were used as foam control agents. Methanol was ACS grade (>99.9 wt%) and had a water content of <0.1 wt%.

[0087] The copper-aluminum alloy was obtained from Yamaishi Metal Co., Ltd. Its nominal composition is 60 wt% Cu and 40 wt% Al. Table 5 shows the particle size distribution. Approximately 84 wt% was smaller than 45 micrometers. This was crushed and further sieved to obtain particles smaller than 38 micrometers, and in some experiments, smaller than 20 micrometers.

[0088] Copper orthophosphate or copper hydroxyphosphate has been used as an accelerator for the direct synthesis of trimethoxysilane, as taught in U.S. Patent No. 7,652,164. [Table 2] [Table 3] [Table 4] [Table 5] Examples 1 and 2

[0089] Examples 1 and 2 demonstrate the use of a copper-aluminum alloy containing 60 wt% Cu and 40 wt% Al, with the particle size distribution shown in Table 5, as a copper source when directly synthesizing trimethoxysilane in multiple batches using two different silicon samples, Si-2 and Si-1. Based on the weight of the charged silicon, the copper concentration was 0.31 wt% and the aluminum concentration was 0.21 wt%.

[0090] The reaction was carried out at 250°C and 650 rpm in the 8-liter reactor described above, following the general procedure described above. Tables 6 to 9 show an overview of the amounts of materials used and the composition of the products. Three preparations were made in Example 1, with silicon, Cu-Al, and a phosphate accelerator; four preparations were made in Example 2. Marlotherm 登録商標 LH was initially added (Examples 1A and 2A), and even if additional solids were added in subsequent reactions, supplemental Marlotherm 登録商標 LH was not required. The amounts of silicon, Cu-Al, and copper orthophosphate accelerators added in Examples 1B, 1C, 2B, 2C, and 2D were based on the weight of silicon converted in the previous reaction. [Table 6] [Table 7] [Table 8] [Table 9]

[0091] Performance data for Examples 1 and 2 show that the Cu-Al alloy yielded excellent activation of silicon from two different sources containing less than 0.3 wt% Al, producing a TMS of 91–96 wt%, a selectivity of 29–40, and a rate of 4–7% Si / h. The copper concentration provided by Cu-Al was 0.31 wt% based on the silicon charged at the start of each batch reaction. The induction period in Examples 1A and 2A ended with a silicon conversion rate of ~11%, and <6% in Examples 1B to 1C and Examples 2B to 2D. The concentration of soluble silicate (HVS) in the reaction product was less than 1 wt% throughout the experiments in both examples, indicating that water formation is significantly suppressed when Cu-Al is used. Visual inspection of the reactor during or after the experiments in Examples 1 and 2 showed no gel or resin on the walls, baffles, or impeller. Examples 3 (0.41% Cu) and 4 (0.51 wt% Cu)

[0092] Examples 3A to 3D and 4A to 4C demonstrate the effect of increasing the amount of Cu-Al used to catalyze the direct synthesis of trimethoxysilane in silicon containing less than 0.3 wt% aluminum. The amounts of raw materials used are shown in Tables 10 and 12. As disclosed above, the reaction is carried out by Marlotherm 登録商標 The experiment was conducted in an 8-liter reactor equipped with LH at 250°C and 650 rpm. The experimental data are shown in Table 11 (Examples 3A to 3D) and Table 13 (Examples 4A to 4C). The copper concentration was 0.41 wt% in Example 3 and 0.51 wt% in Example 4. [Table 10] [Table 11] [Table 12] [Table 13]

[0093] The results of Examples 1, 2, and 3, taken together, indicate that excellent yield, reaction rate, and selectivity of the crude product were obtained at low copper concentrations (0.3–0.5 wt%). The reactor walls, impeller, and baffles remained shiny and free from silicate gels or resins. HVS was also less than 1% by weight, indicating low water production when Cu-Al is the source of catalytic copper in direct synthesis. Example 5

[0094] Example 5 demonstrates the direct synthesis of trimethoxysilane with a metallic silicon sample Si-3 and Cu-Al with a particle size distribution of less than 38 micrometers. The raw materials, as described in Table 4, were sieved to obtain two fractions: particles less than 38 micrometers and particles less than 20 micrometers. The reaction was carried out as described in the general procedure above. Four starting materials were prepared. The copper concentration was 0.41 wt%. The amounts of raw materials used are shown in Table 14. Performance data are shown in Table 15. [Table 14] [Table 15]

[0095] As already shown in Examples 1 to 4, Example 5 demonstrates that silicon containing less than 0.3 wt% Al (<3000 ppm) yields superior performance with a chlorine-free catalyst copper source (Cu-Al) containing less than 50 wt% Al. These results are in contrast to the teachings of U.S. Patent No. 5,362,897.

Claims

1. A process for the direct synthesis of alkoxysilanes: (a) Form a reaction slurry comprising a thermally stable solvent, metallic silicon, a catalytically effective amount of copper-aluminum catalyst precursor, and optionally a catalyst accelerator and optionally a foaming control agent; (b) A process comprising stirring and heating a reaction slurry to form copper-activated silicon in situ, and then supplying an alcohol to the reaction slurry to react with the copper-activated silicon to produce an alkoxysilane.

2. (c) The process of claim 1, further comprising recovering the alkoxysilane.

3. The process of claim 1 or 2, wherein the alkoxysilane comprises at least one trialkoxysilane.

4. The process according to any one of claims 1 to 3, wherein the alkoxysilane comprises at least one alkyldialkoxysilane.

5. The process of any one of claims 1 to 4, wherein the reaction in the slurry is carried out in a batch manner, in which a single addition of metallic silicon, a copper-aluminum alloy catalyst precursor, and an optional catalyst accelerator and an optional foaming control agent is first made to the reactor, and then alcohol is added continuously or intermittently until the metallic silicon has reacted to a selected degree of conversion.

6. The process of any one of claims 1 to 5, wherein the reaction in the slurry is carried out in a continuous operation, in which metallic silicon, a copper-aluminum alloy catalyst precursor, and an optional catalyst accelerator and an optional foaming control agent are first added to the reactor, thereafter the solid content of the slurry is maintained within a selected range, and then the alcohol is added continuously.

7. The process of any one of claims 1 to 6, wherein the reaction conditions in the slurry are adjusted to maintain the content of tetraalkoxysilane by-products at about 6% by weight or less.

8. The process of any one of claims 1 to 7, wherein the reaction product in the slurry is adjusted to contain about 70% by weight or more trialkoxysilane.

9. The process according to any one of claims 1 to 8, wherein the catalyst accelerator is present in the slurry throughout the reaction step and is selected from the group consisting of copper(I) cyanide, organonitriles, organophosphates, and inorganic phosphates.

10. The process of any one of claims 1 to 9, wherein the copper-aluminum alloy contains approximately 15 to 80% by weight of aluminum.

11. The process of claim 9, wherein the copper-aluminum alloy contains approximately 50% or less by weight of aluminum.

12. A process according to any one of claims 1 to 11, wherein the copper-aluminum alloy contains approximately 35 to approximately 45% by weight of aluminum.

13. The process of any one of claims 1 to 11, wherein the copper-aluminum alloy contains approximately 15 to approximately 50% by weight of aluminum.

14. The process of any one of claims 1 to 13, wherein the copper-aluminum alloy is substantially free of halides.

15. The process of any one of claims 1 to 14, wherein the copper-aluminum catalyst precursor comprises particles having a particle size distribution in the range of about 0.1 to about 50 micrometers.

16. The process according to any one of claims 1 to 14, wherein the copper-aluminum catalyst precursor comprises particles having a particle size distribution of about 600 nanometers or less.

17. The process according to any one of claims 1 to 14, wherein the copper-aluminum catalyst precursor comprises particles having a particle size distribution in the range of about 1 nanometer to about 100 nanometers.

18. The process according to any one of claims 1 to 14, wherein the copper-aluminum catalyst precursor comprises particles having a particle size distribution in the range of about 20 nanometers to about 60 nanometers.

19. The process of any one of claims 1 to 18, wherein the alcohol is one or more selected from the formula ROH, where R is an alkyl group comprising 1 to 6 carbon atoms.

20. The process according to any one of claims 1 to 19, wherein the thermally stable solvent is a high-temperature heat-conducting fluid.

21. The process according to any one of claims 1 to 20, wherein the reaction is carried out at a temperature of approximately 150 to 300°C.

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