GB2059429A

GB2059429A - Improvements in the Production of Alkyl Silicates

Info

Publication number: GB2059429A
Application number: GB8023100A
Authority: GB
Original assignee: Zirconal Processes Ltd
Current assignee: Zirconal Processes Ltd
Priority date: 1979-10-02
Filing date: 1980-07-15
Publication date: 1981-04-23

Abstract

An alkoxysilane of the general formula (RO)nSi(OA)4-n where R is C1-C6 alkyl A is -C2H4OCH3; -C2H4OC2H5; -C2H4OC6H5, -C2H4OC2H4OCH3; -C2H4OC2H4OC2H5; -C2H4NR1R2 where R1 and R2 are C1-C4 alkyl and n is 1, 2, 3 or 4, is made by the reaction of the mixture of ROH and AOH and a silicon or a silicide in a large volume of a solution containing as catalyst the metal alkoxide corresponding to the alcohol AOH.

Description

SPECIFICATION Improvements in the Production of Alkyl Silicates This invention relates to the manufacture of alkyl silicates by the catalysed reaction of silicon or silicides with an alcohol and is a development of the invention, hereinafter called the previous invention, set out in EPC Application No. 79 300 542 published under the number 0,004,41 8 on 17th October 1 979. This published specification is primarily concerned with the production of ethyl silicate.

We have discovered that, when a metal alkoxide corresponding to the alcohol AOH is used as a catalytic agent, substituted alkoxysilanes containing the group SiOA are produced. The present invention proposes a method of increasing the yield of the substituted alkoxysilanes which products have industrial applications.

Thus according to the present invention there is provided a method of manufacturing alkoxysilanes of the type (RO)nSi(OA)4~n where R is C1-C6 alkyl, preferably ethyl, A is -C2H4OCH -C2H4OC2H -C2H40C6H5; -C2H4OC2H4OCH3; --C,H,OC,H,OC,H,; -C2H4N R1R2 where R1 and R2 are C1-C4 alkyl and n is 1, 2, 3 or 4, by reacting together the alcohol ROH in a catalytic solution containing a metal alkoxide corresponding to the alcohol AOH, there being preferably at least 500 ml of catalytic solution for each mole of silicon or silicide, thereby having sufficient thermal capacity effectively to maintain a temperature to catalyse the reaction and to discharge as a product alkoxysilanes as vapour together with the alcohol vapour and hydrogen gas.

The method of the invention is characterised by the step of mixing with the alcohol ROH a quantity of the alcohol AOH. This mixing step significantly increases the yield of the substituted alkoxysilane in the product which also contains the unsubstituted tetraalkoxysilane Si(OR)4. It should be noted that the use of 100% AOH as the starting alcohol would not produce a 100% yield of the alkoxysilane Si(OA)4 but a mixed product. In fact approximately 5% AOH, 95% (molar ratios) ROH provides a notably increased yield of substituted product as compared to a 100% ROH starting material. Up to about 50% AOH can in certain circumstances be used.

The reaction between the alcohol and silicon or a silicide is carried out at high temperature in a catalytic solution which has sufficient thermal capacity to maintain the reaction temperature and to catalyse the reaction and to discharge the alkoxysilane products as a vapour together with the alcohol vapour and hydrogen gas. The thermal capacity of the catalytic solution can be maintained and indeed increased by stepwise additions of the alcohol and silicon or a silicide, then the alkoxysilane products are removed as vapour and the sequence repeated.

The term silicide is intended to cover additionally to the metallic silicides carbon silicide more usually called silicon carbide.

The necessary thermal capacity is achieved by: (a) carrying out the reaction at as high a temperature as is practicable, (b) maintaining a relatively large volume of catalytic solution, that is metal alkoxide in a solvent, at least 500 ml per mole of silicon, (c) selecting an appropriate solvent.

Preferred solvents are linear oligomers of the following general formula

Formula I where n is 1 or a whole number greater than 1 or cyclic compounds of the general formula II:

Formula II where n is 3 or a whole number greater than 3 A is CH3; OR where R is C1-C4 alkyl preferably ethyl; O(CH2CH20)mD where D is methyl, ethyl or phenyl and m is 1 or 2. Preferably all the A groups are the same in each compound. B is the same as A and when A is CH3, B can also be C6H5.When A is OR or O(CH2CH20)mD, the solvent may also contain SiA4 and/or A3Si-O-SiA3 species, provided that there is not more than 20% by weight of SiA4 and 40% by weight of A3Si-0-SiA3. When A is Cm3, the solvent may also contain not more than 20% by weight of Si(OR)4 and/or Si[O(CH2CH20)mD]4 species. When A is CH3 and B is C6H5 the solvent may also contain not more than 60% of Si(OR)4 species, R being preferably ethyl.

The solvent may also comprise a mixture of components having different A groups and it may also be a mixture of cyclic and linear polymers.

Examples of suitable solvents are the methyl polysiloxanes and the methyl phenyl polysiloxanes, which may be linear or cyclic, also the ethoxypolysiloxanes. Tetraethoxysilane and technical ethyl silicate are other suitable solvents, one example of the latter being described in British Patent No.

674,137. Another suitable solvent is the alkoxysilane reaction product.

The catalyst comprises at least one metal alkoxide corresponding to the alcohol AOH in solution in a solvent defined as above. The preferred metal alkoxides are the alkali metal alkoxides. A mixture of the sodium alkoxide and the potassium alkoxide is advantageous. We have now discovered that the metal alkoxide, preferred in the previous invention, is essential to produce the substituted alkoxysilanes. It will be appreciated that the alkoxide has a reaction function as well as a catalytic and is consumed to a certain extent.

The reaction may be carried out using batches of reagents or may be started with batches of reagents and then maintained by continuous additions of the alcohol and silicon or silicide to a relatively large volume of the catalytic solution. A preferred expedient is to introduce the reagents below the surface of the solution preferably near the bottom of the reaction vessel. When the reagents are not preheated, on entry they initially lower the temperature of the solution and then commence their catalysed reaction. As the reagents rise through the catalytic solution the reaction proceeds until the mixture of alcohol and products is vapourised with a considerable loss of heat. The large thermal capacity of the volume of the catalytic solution at elevated temperature readily provides that heat. The rate of reaction can be monitored by measuring the rate of evolution of hydrogen.Alternatively, the alcohol (or mixture of alcohols) can be introduced as a vapour.

The product of the process is an alkoxy-silane (a silicon ester) of the formula (RO)nSi(OA)4~n, where n is 1, 2, 3 or 4. The unsubstituted tetraalkoxysilane Si(OR)4 which inevitably forms part of the reaction product is, of course, the case when n=4. The present invention also proposes converting the product to a mixture of alkoxypolysiloxanes by controlled hydrolysis and condensation-polymerisation, thereby increasing the silica equivalent. Thus when the product is tetraethoxysilane it can be converted by controlled hydrolysis and condensation-polymerisation to technical ethyl silicate, which is a mixture of tetraethoxysilane and ethoxypolysiloxane oligomers. The preferred technical ethyl silicate contains silicon equivalent to approximately 40% by weight SiO2.

The substituted alkoxysilane products which characterise the present invention can be used in the binding of refractory powders and paint pigments. On hydrolysis, the products form a hydrolysate which gels, usually with the aid of a catalyst, to provide a rigid and coherent gel. Slurries of refractory powder and a gellable hydrolysate can thus be formed to the required shape either by cavity or pattern moulding and thereafter set in this shape by gelling of the hydrolysate. A paint for anti-corrosion applications can be made by dispersing zinc dust in the hydrolysate. For this use the hydrolysate is preferably prepared from an alkoxysilane product rich in the (RO)n Si(OA)4~n species according to the invention where n is 1, 2 or 3.The reason for this is that the hydrolysis products are less volatile due to their higher molecular weight.

The invention will now be described by way of the following specific examples:- General Notes to Examples Moisture must be rigorously excluded. Reactions are commenced in an atmosphere of dry nitrogen. Dry alcohol must be used, the procedures for drying are given in Example 1. The rate of reaction may be followed by measuring the rate of hydrogen evolution. This is used to control the rate of addition of reactants to maintain optimum reaction rate. Usually silicon (or silicide) is added in batches and alcohol added dropwise, or a silicon/alcohol slurry added, when the observed rate of hydrogen evolution diminishes to a low value. The reaction temperature is maintained as constant as possible.

A-Metal Alkoxide Preparation Method 1 2-Ethoxyethanol (290 ml, 2.96 mole) was introduced into a flask fitted with a reflux condenser and nitrogen inlet. The vessel was flushed with nitrogen and potassium ( 1 9g, 0.5 mole) was slowly added over a 3 hour period, followed by sodium (1 1.5g, 0.5 mole). The mixture was refiuxed for 4 hours until hydrogen evolution ceased. The initial solution was pale yellow but turned deep red after 2 hours.

Method 2 Using the apparatus and procedure of Method 1, to 2-ethoxyethanol (180 ml, 1.76 mole) sodium (5.58g, 0.254 mole) was slowly added, followed by potassium (9.429, 0.242 mole) and the resulting mixture refluxed for two hours.

Method 3 Sodium (7.4g, 0.311 mole) was slowly added to 2-ethoxyethanol (170 ml, 1.75 mole) and the resulting mixture refluxed for 1 hour. In a separate vessel, potassium (139, 0.33 mole) was slowly added to 2-ethoxyethanol (160 ml, 1.65 mole) and the resulting mixture refluxed for 1 hour. The two solutions may be combined for use, or used individually.

Method 4 Toluene (40-50 ml) was placed in a flask fitted with a reflux condenser, nitrogen inlet and dropping funnel, whose lower end was under the toluene. The flask was flushed with dry nitrogen which was passed through the flask throughout the course of the reaction. Potassium (1 9g, 0.5 mole) was added, then 2-ethoxyethanol (160 ml, 1.7 mole) was slowly added dropwise. When the potassium had reacted, sodium (11 .5g, 0.5 mole) was added, then further 2-ethoxyethanol added dropwise until a total volume of 300 ml was added. The solution was warmed and toluene distilled off at 121 OC. The remaining solution was refluxed for 4 hours. The 2-ethoxyethanol can also be added to sodium and potassium metals concurrently.

Method 5 Using the apparatus and procedure of Method 1, dry ethanol (100 ml, 1.77 mole) was used to dissolve sodium (4.75g, 0.207 mole) and potassium (9.299, 0.238 mole) which were slowly added in the order given. The mixture was refluxed for two hours, then used immediately. Sodium and potassium may be dissolved in ethanol individually.

Method 6 A 2 litre, 5 necked flask, fitted with a partial take-off head, mechanical stirrer, dropping funnel, thermometer and nitrogen inlet was flushed with nitrogen after introducing a solution comprising technical ethyl silicate (40% 8iO2 w/w-1 10 ml) and dry ethanol (46g-1 mole). To this solution was added potassium (5.5g, 0.14 mole), then sodium (3.29, 0.16 mole). The mixture was warmed for 3 hours to give the catalytic solution.

Method 7 Using the procedure of Method 1, methyl-digol (200 ml, 1.70 mole) was used as solvent for sodium (5.67g, 0.247 mole), then for potassium (9.659, 0.247 mole).

Method 8 Using the procedure of Method 1,2-phenoxyethanol (250 ml, 1.99 mole) was used as solvent for sodium (5.669. 0.246 mole) and for potassium (9.829, 0.252 mole).

Method 9 Using a flask fitted with a reflux condenser and dropping funnel, sodium ethoxide solid (NaOEt.2EtOH, 83.6g (0.54 mole) was dissolved in 2-ethoxyethanol (250 ml, 2.58 mole), which was added dropwise over a period of 2 hours. There was a very exothermic reaction, giving a liquid mixture.

The dropping funnel and reflux condenser were removed and replaced by a distillation head and condenser. The mixture was heated under reduced pressure (100 mm Hg) and 102 grams distillate collected over 2 hours. This distillate comprised ethanol 41 parts and 2-ethoxyethanol 59 parts. The residue was used in the preparation of mixed alkoxysilanes (EtO)nSi(OCH2CH2OEt)4~n, n=4, 3, 2, 1.

Method 10 Using the procedure of Method 2, ethyldigol (190 ml, 1.4 mole) was used as solvent for sodium (5.809, 0.252 mole) and for potassium (9.839, 0.252 mole).

Method 11 Using the procedure of Method 2, 2-dimethylaminoethanol (125 ml, 1.21 mole) was used as solvent for sodium (4.849. 0.21 mole) and for potassium (9.70g, 0.25 mole).

B-Production of Alkoxysilanes Example 1 A 2 litre, 5 necked flask fitted with a partial take-off head, mechanical stirrer, dropping funnel and nitrogen gas inlet was flushed with nitrogen. Then 1 70 ml of metal alkoxide solution prepared as described in Method 2 was added, together with 340 ml of tetraethoxysilane to form the catalytic solution. 1 4g of silicon powder, average particle size 50-80 microns, composition 97% Si, 3% Fe, were added, i.e. 510 ml catalytic solution/mole silicon. Then 30 ml dry ethanol were added. The ethanol must be dried prior to use either by treatment with a molecular sieve (e.g. Linde type 3A) or by distillation over sodium or magnesium. The mixture was heated by an electric heating mantle.When the reactor temperature reached 1 200C, the distillation head temperature rose to 900 C. After 80 ml distillate (mixture of ethanol and alkoxysiiane) was collected, the distillation head temperature fell to ambient and the reactor temperature rose to 1 500C, at which temperature it was maintained for the remainder of the reaction period. The reaction was monitored by measuring the rate of hydrogen evolution. Further reactants were added when the rate fell to less than 30 ml/min. Silicon was added in batches of 7 or 14 grams, ethanol (dry) being added dropwise at a rate such that the reactor temperature remained at 1 500C. The reaction was run in this way for 26 hours.A total of 709 (2.14 mole) silicon was added, 93% being converted to alkoxysilane. The average rate of production of alkoxysilane was 18g/hour. The final reaction mixture was distilled at atmospheric pressure to recover pure alkoxysilane.

Example 2 180 ml of metal alkoxide solution prepared by Method 1 was added to 500 ml of technical ethyl silicate to form the catalytic solution. To this was added 12 grams of silicon (i.e. 1 587 ml catalytic solution/mole silicon) and 303.5 grams (6.6 mole) dry ethanol. The mixture was heated for 3 hours at 70-800C then the temperature was raised to 1 200C, 580 ml of distillate (b.82-900C) being collected. The temperature was raised to 1 45 OC and a 4:1 molar ratio slurry of ethanol:silicon added.

The reaction temperature rose and was maintained in the temperature range 1 65-1 900C by adjusting the rate of addition of the slurry. Distillate (b.1 15-1 300C) was collected at the rate of about 90 ml/hour during the 40 hours which the reaction was run, a total of 3500 ml being collected.

Fractionation at atmospheric pressure gave 750g pure tetraethoxysilane b. 1 68-1 700C. The purity was confirmed by the IR spectrum.

Example 3 To the catalytic solution prepared in Method 6, silicon (6g, 0.21 mole, i.e. 798 ml catalytic solution/molesilicon) was added. Distillate was removed until the reactor temperature reached 1 450C, then a slurry of ethanol/silicon (molar ratio 4:1) was added. The reactor temperature rose to 1 650C and was maintained in the range 165--190"C by adjusting the rate of addition of the ethanol/silicon slurry.

The reaction was carried out for 5 hours, during which time 225 ml of distillate (b. 1 30-1 560C) was collected. Fractionation of this mixture gave 1259 pure tetraethoxysilane The purity was confirmed by the IR spectrum.

Example 4 To the metal alkoxide solution prepared as in Method 5 was added 450 ml of the alkoxysilane product of Example 2 to give the catalytic solution. Then 1 4g silicon powder, average particle size 50-60 microns were added, i.e. 1100 ml catalytic solution/mole silicon. Following the procedure of Example 1, 56g (2.0 mole) silicon and 425 ml (7.5 mole) dry ethanol were added over a period of 22- hours, the reactor temperature being maintained between 1 50-1 600C. The percentage conversion of silicon to product was greater than 95% and the production rate was 20.5 grams/hour. The product was purified as described in Example 1.

Example 5 To 170 ml of the metal alkoxide solution prepared as described in Method 7,340 ml of tetraethoxysilane were added to prepare the catalytic solution. To this was added 1 6 grams of silicon powder, average particle size 50-60 microns, i.e. 893 ml catalytic solution/mole silicon, then 30 ml dry ethanol. The mixture was heated to 1 500C and maintained in the temperature range 150--1600C during 23+ hours, in which time 44g (1.7 mole) silicon and 330 ml (5.85 mole) dry ethanol were added. The percentage conversion of silicon to product was greater than 95% and the production rate was 16.1 grams/hour.

Example 6 To 250 ml of the metal alkoxide solution prepared as described in Method 8,340 ml of tetraethoxysilane were added to prepare the catalytic solution. To this was added 1 6 grams of silicon powder, average particle size 50-60 microns, i.e. 1 033 ml catalytic solution/mole silicon, then 30 ml dry ethanol. The mixture was heated as described in Example 1 and maintained at a temperature of 150-1 900C during 13- hours. In this time 1 89 (0.64 mole) of silicon and 130 ml (2.3 mole) dry ethanol were added. The percentage conversion of silicon to product was 66% and the production rate was 6.5 grams/hour.

Example 7 To 350 ml of metal alkoxide solution prepared as described in Method 1 was added 500 ml technical ethyl silicate to prepare the catalytic solution. Then 21g of ferrosilicon powder, average particle size 50-60 microns was added, i.e. 850 ml catalytic solution/mole silicon, together with 50 ml dry ethanol. Following the procedure of Example 1, a further 72.59 ferrosilicon (2.5 mole) and 46.2 ml dry ethanol (12.6 mole) were added over 50 hours, the temperature being maintained at 160 1 800C. The percentage conversion of silicon to product was greater than 95% and the production rate was 10 grams/hour.

Example 8 To 290 ml of metal alkoxide solution prepared as described in Method 1 was added 700 ml tetraalkoxysilane prepared as described in Example 1, to give the catalytic solution. 21 grams of ferrosilicon (1 mole Si), average particle size 50-60 microns, were added i.e. 990 ml catalytic solution/mole silicon, together with 50 ml dry ethanol. Following the procedure of Example 1, the reaction was carried out for 34 hours at an average temperature of 1 480C. The percentage conversion of silicon to product was greater than 95% and the production rate was 34 grams/hour.

Example 9 A catalytic solution was prepared by mixing 1 50 ml of a metal alkoxide solution prepared according to Method 1 with 250 ml of a polymethylphenyl siloxane (Dow Corning 550 fluid). 7 grams (0.25 mole) of silicon, average particle size 50-60 microns, were added, i.e. 1600 ml catalytic solution/mole silicon. Dry ethanol (50 ml) was added and the mixture was gently warmed, being maintained between 900C and 1 300C during the reaction (10 hours). Alkoxysilane product was produced at rates between 11 and 56 gram/hour, depending on the reaction temperature.

Example 10 A catalytic solution was prepared by mixing 1 50 ml of a metal alkoxide solution prepared according to Method 1 with 125 ml of a polymethylphenyl siloxane (Dow Corning 550 fluid) and with 1 25 ml tetraethoxysilane. 7 grams (0.25 mole) of silicon, average particle size 50-60 microns, were added, i.e. 1 600 ml catalytic solution/mole silicon. Dry ethanol (50 ml) was added and the mixture was gently warmed, being maintained between 900C and 130"C during the reaction (10 hours).

Alkoxysilane was produced at rates between 11 and 112 grams/hour, depending on the reaction temperature.

Example 11 In the preceding Examples, the volume ratio of solvent to metal alkoxide solution, giving the catalytic solution is 2:1 or greater. In this Example, the catalytic solution used has a volume ratio of solvent to metal alkoxide solution of 1 :2.

The procedure followed is as described in Example 1. The metal alkoxide solution is prepared as described in Method 1. The catalytic solution is made by adding to 350 ml of metal alkoxide solution, prepared as described in Method 1, 1 70 ml of alkoxysilane prepared as described in Example 1. To this catalytic solution is added 149 (0.5 mole) silicon powder, average particle size 50-60 microns, i.e.

1040 ml catalytic solution/mole silicon, together with 30 ml dry ethanol. The mixture was heated to 1 50CC and the reaction was carried out for 14+ hours. During this time 43.75 grams (1.75 mole) silicon and 410 ml (7.27 mole) dry ethanol were added. The percentage conversion of silicon to product was greater than 95% and the production rate was 34 grams/hour.

Example 12 A catalytic solution was prepared by adding 350 ml of tetraethoxysilane to 175 ml of metal alkoxide solution prepared as described in Method 1. To this catalytic solution is added 149 (0.5 mole) silicon powder, particle size 5 microns or less, i.e. 1 050 ml catalytic solution/mole silicon, together with 30 ml dry ethanol. The reaction was carried out as described in Example 1, except that the dry ethanol used contained 2% v/v toluene. During 192 hours 61g (2.1 mole) silicon and 450 ml (9.27 mole) ethanol were added. The percentage conversion of silicon was greater than 95% and the production rate was 44 grams/hour.

Example 13 Alkoxysilanes were prepared following the procedure of Example 1, except that ethanol was introduced into the reactor as a 70:30 mixture by volume of ethanol and alkoxysilane.

The catalytic solution was prepared by adding 350 ml of alkoxysilane prepared as described in Example 1 to 1 90 ml of metal alkoxide solution prepared as described in Method 1. To this catalytic solution was added 14 grams (0.5 mole) silicon powder, particle size 5 microns or less, i.e. 1080 ml catalytic solution/mole silicon, together with 30 ml dry ethanol. The average reaction temperature was 1 37 OC over a 15 hour reaction period. 43.59 (1.5 mole) silicon and 275 ml (5.88 mole) dry ethanol (as the ethanol-alkoxysilane mixture) were added. The percentage conversion of silicon was greater than 95% and the production rate was 23.6 grams/hour.

Example 14 A catalytic solution was prepared by adding to 500 ml tetraethoxysilane, 290 ml of metal alkoxide solution prepared as described in Method 1. To this catalytic solution was added 1 5 grams (0.5 mole) silicon powder (95% Si:5% Fe+Mn, particle size 50-60 microns), i.e. 1 580 ml catalytic solution/mole silicon, together with 60 ml dry ethanol. The procedure of Example 1 was followed, giving a percentage conversion of silicon greater than 95% and a production rate of 35.7 grams/hour.

Example 15 Following the procedure of Example 1, silicon powder containing 0.51.5% Fe, 0.2-0.75% Ca and 0.51.5% Al was used. The catalytic solution was prepared by adding to 400 ml tetraethoxysilane, 200 ml of metal alkoxide solution prepared as described in Method 1. To this catalytic solution was added 16 grams (0.5 mole) of the silicon powder particle size 50-60 microns, i.e. 1200 ml catalytic solution/mole silicon, together with 30 ml dry ethanol. The average temperature of the reactor was 133 OC. The reaction was carried out for 12 hours, 28.5 grams of the silicon and 360 ml dry methanol being added. The percentage conversion of silicon to alkoxysilane was 66% and the production rate was 22 grams/hour.

Example 16 A catalytic solution was prepared by adding 1000 ml tetraethoxysilane to 400 ml of metal alkoxide solution prepared according to Method 1. To this catalytic solution was added 28g (1 mole) silicon, particle size 50-60 microns, i.e. 1400 ml catalytic solution/mole silicon, together with 70 ml dry ethanol. Following the procedure of Example 1, 1 56.25 grams of silicon, particle size 5 microns or less were added together with 1 920 ml dry ethanol in the course of 452 hours. The reactor temperature was maintained at an average of 1 480C. The percentage conversion of silicon was greater than 95% and the production rate was 53.5 grams/hour.

Example 17 A catalytic solution was prepared by adding 600 ml tetraethoxysilane to 300 ml of metal alkoxide solution prepared according to Method 1. To this catalytic solution was added 28 grams (1 mole) silicon, particle size 50-60 microns, i.e. 900 ml catalytic solution/mole silicon together with 50 ml dry ethanol. Following the procedure of Example 16, silicon of 74 micron particle size was used. The percentage conversion of silicon was greater than 95% and the prodyction rate was 34 grams/hour.

Example 18 A catalytic solution was prepared by adding 300 ml of alkoxysilane prepared as described in Example 1 to 1 75 ml of the metal alkoxide product of Method 8. To this catalytic solution was added 14 grams (0.5 mole) silicon, particle size 50-60 microns, i.e. 950 ml catalytic solution/mole silicon together with 30 ml dry ethanol. Following the procedure of Example 1, the reaction was carried out for 20- hours, the mean reaction temperature being 1 580C. 28 grams silicon and 230 ml dry ethanol were added. The percentage conversion of silicon was greater than 95% and the production rate was 10.2 grams/hour.

Example 19 A catalytic solution was prepared by adding 340 ml of alkoxysilane prepared as described in Example 1 to 170 ml of sodium 2-ethoxyethoxide solution prepared as described in Method 3. To this catalytic solution was added 14 grams (0.5 mole) silicon powder, particle size 50-60 microns, i.e.

1020 ml catalytic solution/mole silicon, together with 40 ml dry ethanol. Following the procedure of Example 1, the reaction was carried out for 22 2 hours, the mean reaction temperature being 1 480C.

49 grams silicon and 290 ml ethanol were added. The percentage conversion of silicon to product was greater than 95% and the production rate was 1 5 grams/hour.

Example 20 The procedure of Example 1 9 was followed, except that the catalytic solution was prepared using 170 ml of potassium 2-ethoxyethoxide made as described in Method 3. The percentage conversion of silicon to alkoxysiiane was greater than 95% and the production rate was 22 grams/hour.

Example 21 A catalytic solution was prepared by adding 675 ml of tetraethoxysilane to 290 ml metal alkoxide solution prepared as described in Method 1. In this catalytic solution the volume ratio of solvent to metal alkoxide solution is 2.25:1. To the catalytic solution is added 1 4g (0.5 mole) silicon, i.e. 1930 ml catalytic solution/mole silicon, together with 60 ml dry ethanol. The mixture was warmed to 1 450C and ethanol slowly added dropwise so as to maintain the reaction temperature in the range 165 1 700C. The alkoxysilane produced was removed from the reaction system by distillation as a mixture of ethanol and product. At 1 450C the production rate of alkoxysilane was 24 grams/hour. At the end of the reaction the production rate of alkoxysilane was 14.6 grams/hour.

Example 22 In this Example, the thermal capacity of the catalytic solution is first increased by stepwise additions of ethanol and silicon, then alkoxysilane and ethanol were removed as vapour and the sequence repeated.

Starting Procedure A clean and dry reaction vessel is purged with dry nitrogen for about 1 5 minutes. The catalytic solution is made by charging the reaction vessel with 204 litres of tetraethoxysilane, followed by 204 litres of metal alkoxide solution prepared according to Method 4 and then by a further 136 litres of tetraethoxysilane. To this catalytic solution 5 kg silicon powder was added, i.e. 3046 ml catalytic solution/mole silicon, followed by 10 litres dry ethanol. The mixture was heated until the reactor temperature was 1400 C. At this stage the distillation head temperature (head temperature) was the ambient temperature.

Production of Alkoxysilane Dry and preheated ethanol was added at a rate such that the reactor temperature did not drop below 1400 C. Ethanol was added at this required rate until evolution of hydrogen ceased. Then a further 5 kg silicon was added and more ethanol was added at the required rate until evolution of hydrogen ceased. No distillate was collected in this cycle, i.e. the reaction was done under total reflux condition.

It is necessary to maintain a minimum reactor temperature of 1400 C. Although a minimum reactor temperature of 1 400C is required, the temperature is preferably in the range 155-1 650C. The ethanol addition can be replaced by a mixture of ethanol and tetraethoxysilane.

Separation of Alkoxysilane from Reaction Mixture The separation of alkoxysilane from the reaction mixture was carried out by the following procedure.

(i) The preferred reactor temperature is 1 500C.

(ii) Dry ethanol was added to the reaction mixture at a rate such that a constant head temperature is maintained.

(iii) It is preferable to remove the product as a mixture of alkoxysilane and ethanol. The product should be removed at a high head temperature (1 400 C or over) to ensure that the distillate is rich in alkoxysilane. It is important that only the amount of alkoxysilane produced is removed.

The ethanol-alkoxysilane mixture collected is distilled to separate the ethanol and the alkoxysilane. The ethanol recovered can be re-used.

After the alkoxysilane produced has been removed, the sequence of stepwise additions of silicon and ethanol is repeated to continue the production of alkoxysilane. This in its turn is removed then the sequence of stepwise additions of silicon and ethanol is continued.

Preparation of Polysilicate Alkoxysilane 259 volumes Anhydrous ethanol 82.2 volumes Water 1 6.4 volumes must be distilled or de-ionised Acid solution 1.3 volumes The acid solution is 1% v/v of concentrated sulphuric acid (98% H2SO4 by weight) in anhydrous ethanol.

The mixture of alkoxysilane, anhydrous ethanol and acid solution is heated to reflux temperature and water added dropwise with stirring over a period of 30 minutes. Refluxing is carried out for 60 minutes when the addition is completed. The ethanol is recovered from the product by distillation under general lowering of pressure. Distillation was finished when a pot temperature of 1 400C at 100 mm Hg pressure was reached. The amount of ethanol recovered was 1 80 volumes. This can be used again in the preparation.

Product characterisation Density at 200C=1 .06 gm/ml Silica content=36.1% w/w Acidity=0.013% wv H2SO4 Example 23 A catalytic solution was prepared by mixing 125 ml of the metal alkoxide solution prepared as in Method 11 with 395 ml of tetraethoxysilane. To this solution was added 149 (0.5 mole) silicon powder average particle size 50-60 microns and 30 ml dry ethanol, i.e. 1 040ml catalytic solution per mole silicon. The procedure followed was according to Example 1 and over 29-; hours at an average reaction temperature of 1 550C, the average production rate of alkoxysilane was 1 8.9 grams/hour with a yield of 86.0% based on the weight of silicon used.

Example 24 A catalytic solution was prepared by mixing 1 90 ml of the metal alkoxide solution prepared according to Method 10 with 360 ml of tetraethoxysilane. To this solution was added 1 4g (0.5 mol) of silicon powder, average particle size 50-60 microns and 30ml dry ethanol, i.e. 11 00ml catalytic solution per mole silicon. Following the procedure of Example 1 the reaction was run for 30 hours at an average temperature of 1 480C yielding 72.8% of alkoxysilane based on the weight of silicon used, at an average production rate of 1 9.2 grams/hour.

Example 25 1 50 ml of metal alkoxide solution prepared according to Method 2 was added to 300 ml of alkoxysilane prepared according to Example 1 and to it was added 149 (0.5 mole) of silicon powder, average particle size 50-60 microns, and 30 ml dry ethanol (i.e. 900 ml catalytic solution per mole silicon). The procedure followed was similar to that of Example 1 except that the ethanol was added in the vapour state, being boiled in a 100 ml 3 necked round bottomed flask fitted with a glass delivery tube to transfer ethanol vapour to the reaction vessel, below the liquid surface and a 50ml dropping funnel to add cold ethanol dropwise to the boiling ethanol in the flask. The delivery tube was wrapped in trace heating wire in order to prevent condensation of the ethanol between the flasks.The reaction was run for 29.8 hours under these conditions and the average production rate of the product was 1 8.9 grams/hour at an average reaction temperature of 1 520 C. The yield of product based on the weight of silicon used was 86.3%.

Example 26 A catalytic solution was prepared by mixing 300 ml of tetraethoxysilane with 1 50 ml of metal alkoxide solution made according to Method 2. To this was added 149 (0.5 mole) silicon powder, average particle size 5 microns and 30 ml dry ethanol, i.e. 900 ml catalytic solution per mole silicon.

The procedure of Example 1 was followed and the reaction run for 37.8 hours at an average temperature of 1 530C. Alkoxysilane was produced at an average rate of 29.1 grams/hour in 94.2% yield based on the weight of silicon used.

Example 27 300ml tetraethoxysilane were added to 150ml of metal alkoxide solution made following Method 1 but using only sodium (11 .58g, 0.504 mole), to make the catalytic solution. To this was added 149 (0.5 mole) of silicon powder, average particle size 5 microns, and 30ml dry ethanol, to give 900ml catalytic solution per mole silicon. Following the procedure of Example 1, the reaction was run for 28.5 hours at an average temperature of 1 580C giving a 97.6% yield of aikoxysilane based on the weight silicon used, at an average production rate of 27.7 grams/hour.

Example 28 To 300my tetraethoxysilane were added 1 50 ml of metal alkoxide solution made following Method 1 but using only potassium metal (1 9.5g, 0.5 mole) to produce 450ml catalytic solution.

Silicon powder (1 4g 0.5 mole) was added together with 30ml dry ethanol to the catalytic solution, producing 900ml catalytic solution per mole silicon. Following the procedure of Example 1 the reaction was run for 34.75 hours at an average temperature of 1 520C. The yield of product based on the weight of silicon used was 94.1% and the average production rate 28.4 grams/hour.

Example 29 A metal alkoxide solution was made following the procedure of Method 5 and to 100my of this solution was added 380ml tetraethoxysilane, producing 480ml of catalytic solution. To this was added 149 (0.5 mole) of silicon powder, average particle size 5 microns, i.e. 960 ml catalytic solution per mole silicon. Following the procedure of Example 1 , the reaction was run for 32.8 hours at an average temperature of 1 490C with an average ester production rate of 1 9grams/hour and in 94.1% yield based on the weight of siilcon consumed.

Example 30 Following the procedure of Method 5, but using only potassium metal (19.479, 0.499 mole) a metal alkoxide solution was made up (110 ml) and added to 370 ml tetraethoxysilane to produce the catalytic solution. Silicon powder (1 4g 0.5 mole) of average particle size 5 microns was added to it, producing a system with 960ml catalytic solution per mole silicon. The reaction was carried out according to Example 1 and over 37.75 hours at an average temperature of 151 OC produced ester at an average rate of 22.6 grams/hour in 86.6% yield based on the weight of silicon used.

Example 31 A metal alkoxide solution was made up according to Method 7 (145 ml) and mixed with 290 ml tetraethoxysilane and 1 4g silicon powder (0.5 mole) of average particle size 5 microns and 30 ml of dry ethanol, i.e. 870ml catalytic solution per mole silicon. Following the procedure of Example 1 the reaction was run for 43.1 hours at an average temperature of 1 500C, giving a yield of 95.6% product based on the weight of silicon used at an average production rate of 28.1 grams/hour.

Example 32 Following Method 10 195ml of metal alkoxide solution was made and mixed with 285ml tetraethoxysilane, 1 4g (0.5 mole) silicon powder of average particle size 5 microns and 30 rnl of dry ethanol, i.e. 960 mi catalytic solution per mole silicon. The reaction was run for 41.3 hours at an average temperature of 1 550C according to Example 1 and produced a product yield of 97.2% based on the weight of silicon used at an average production rate of 27.3 grams/hour.

Example 33 170ml of metal alkoxide solution was prepared according to Method 1, but using only sodium metal (15.489 0.673 mole). To this was added 340ml alkoxysilane produced according to Example 1 and 40 ml dry ethanol and 1 4g (0.5 mole) silicon powder of average particle size 50-60 microns, i.e.

1020 ml catalytic solution per mole silicon. Following Example 1 the reaction was run for 22.5 hours at an average temperature of 148"C yielding alkoxysilane at an average rate of 15.0 grams/hour in 78.7% yield based on the weight of silicon used.

Example 34 1 75 ml of metal alkoxide solution was prepared according to Method 1 but using only potassium metal (26.69, 0.68 mole). To this was added 350ml alkoxysilane produced according to Example 1,30 ml dry ethanol and 149 (0.5 mole) silicon powder of average particle size 50-60 microns, i.e. 1050 ml catalytic solution per mole silicon. Following Example 1 the reaction was run for 21.8 hours at an average temperature of 1 550C, producing alkoxysilane at an average rate of 22.7 grams/hour in 84.4% yield based on the weight of silicon used.

Example 35 1 30 ml of metal alkoxide solution was prepared according to Method 5, but using only sodium metal (1 1.619, 0.528 mole). To this was added 420 ml alkoxysilane produced according to Example 1, and 149, (0.5 mole) silicon powder of average particle size 5060 microns, i.e. 1 100ml catalytic solution per mole silicon. Following Example 1 the reaction was run for 23.2 hours at an average temperature of 1490C, alkoxysilane was produced at an average rate of 13 grams/hour.

Example 36 100ml of metal alkoxide solution was prepared according to Method 5, but using only potassium metal (19.50g, 0.50 mole). To this was added 450 ml alkoxysilane, produced according to Example 1 and 149 (0.5 mole) silicon powder of average particle size, 50-60 microns, i.e. 1100 ml catalytic solution per mole silicon. Following Example 1 the reaction was run for 23.2 hours at an average temperature of 1 520C. Alkoxysilane was produced at an average rate of 16.2 grams/hour in 75.1% yield based on the weight of silicon used.

Example 37 A catalytic solution was prepared by dissolving sodium (4.89, 0.21 mole) in 75 ml 2dimethylaminoethanol over a two hour period. It was necessary to heat the mixture gently to faciltate solution of the sodium when about half the quantity was added. Potassium (9.70g, 0.25 mole) was now dissolved in the mixture over a six hour period, with the addition of two 25 ml portions of 2dimethylaminoethanol. The mixture was heated for two hours after all the metal dissolved. To this solution was added 395 ml alkoxysilane produced according to Example 1, then 14 grams silicon powder, average particle size 53 microns were added (i.e. 1 040 ml catalytic solution per mole silicon).

Then 30 ml of dry ethanol were added. The reaction was run for 29-; hours, the average reaction temperature being 155 C. The average rate of production of alkoxysilane was 1 8.9 grams/hour, the yield of alkoxysilane, based on the weight of silicon used, was 86.0%.

Identification of Components of the Reaction Product Ester The product collected from the various reactions detailed in the Examples was analysed by Gas Liquid Chromatography (G.L.C.) using a Pye model 204 GCD chromatograph and with SE 30 and OV17 columns. The carrier gas used was nitrogen, at a flow rate of 40 ml per minute and the oven temperature of the chromatograph was 2000C.

Peaks other than ethanol, alkali metal solvent and tetraethoxysilane were found, in quantities between 1 and 20 area %, depending upon the circumstances under which the product was-collected.

These peaks have been identified as mixed esters of the type (EtO)n Si(OA)4~n where n=1 ,2,3 by chemically equilibrating mixtures involving AOH and Si(OEt)4 also EtOH and Si(OA)4 (A=EtOCH2CH2, EtCH2CH20CH2CH2) and analysing them by G.L.C. Major peaks in these mixtures, whose proportion varies systematically with the molar ratio of equilibrants, have similar retention times to the minor product components.

Example 38 Tetraethoxysilane (58.669, 0.282 mole and 2-ethoxyethanol (25.699, 0.285 mole) were refluxed together in a three necked, 1 00 ml round bottom flask fitted with thermometer and reflux condenser, for 6 hours, the temperature of the mixture fell from 1 320C to 11 00C during this time. Similarly mixtures of tetraethoxysilane and 2-ethoxyethanol (69.759, 0.335 mole and 85.149, 0.409 mole with 1 0.06g, 0.112 mole and 102.1 0g, 1.138 mole respectively) of mole ratios 3:1 and 1:3 were refluxed for 6 hours, the temperatures of the mixtures falling as in the first case.

G.L.C. analysis of these mixtures showed peaks corresponding to ethanol, 2-ethoxyethanol and tetraethoxysilane together with the three mixed esters (EtO)nSi(OCH2CH2OEt)4 n=1,2,3. Samples of product from Examples 26, 27, 28 showed peaks with similar retention times as the mixed esters.

Example 39 Using the procedure of Example 38 two mixtures of ethyldigol and tetraethoxysilane were refluxed and analysed by G.L.C. In the first case tetraethoxysilane (43.12g, 0.205 mole) and ethyldigol (27.989, 0.209 mole were refluxed for 72 hours during which time the temperature of the mixture fell from 1 640C to 1 040C. In the second case tetraethoxysilane (26.839, 0.128 mole) and ethyldigol (51.51 g, 0.38 mole) were refluxed for 8 hours during which time the temperature of the mixture fell from 170 to 1270C.

G.L.C. analysis of these two mixtures after reflux showed the presence of five components, ethanol, ethyldigol, tetraethoxysilane and two mixed esters (EtO)3SiOCH2CH20CH2CH2OEt and (EtO)2Si(OCH2CH2OCH2CH2OEt)2. Samples of product from Examples 24 and 32 which were also analysed contained components with similar retention times as the mixed esters.

Example 40 Following Example 38 two mixtures of 2-dimethylaminoalcohol and tetraethoxysilane were refluxed and analysed by G.L.C. In the first case tetraethoxysilane (42.709, 0.205 mole) and 2dimethylaminoethanol (18.279, 0.205 mole) were refluxed for 7-1/3 hours after which the mixture had reached a constant temperature of 1 OS0 C. Secondly tetraethoxysilane (29.81 g, 0.143 mole) and 2dimethylaminoethanol (38.39g, 0.431 mole) were refluxed for 6+ hours a final, constant temperature of 1 07.50C being reached.

G.L.C. analysis of the two mixtures showed the presence of ethanol, 2-dimethylaminoethanol, and tetraethoxysilane together with the mixed esters (EtO)n Si(OCH2CH2NMe2)4~n n=1, 2, 3. Samples of product from Example 23 were analysed under similar conditions and were found to have peaks corresponding to the three mixed esters.

Example 41 Following Example 38 two mixtures of methyl digol and tetraethoxysiiane were refluxed and analysed by G.L.C. Tetraethoxysilane (34.709, 0.167 mole) and methyl digol (20.01 g, 0.1 67 mole) were refluxed for 152 hours attaining a final temperature of 11 50C. A second mixture of tetraethoxysilane (20.929 0.100 mole) and methyl digol (36.05g, 0.300 mole) was refluxed for 1434 hours reaching a final, constant, temperature of 116 C.

G.LC. analysis of the two mixtures showed the presence of ethanol, methyl digol and tetraethoxysilane plus two mixed esters (EtO)n Si(OCH2CH2OCH2CH20Me)4 n=2, 3. Samples of product from Examples 5 and 31 were analysed under similar conditions and found to contain peaks corresponding to the two mixed esters.

Example 42 Following Example 38 two mixtures of tetraethoxysilane (20.839, 0.100 mole) and 1 0.42g, 0.050 mole) and 2-phenoxyethanol (14.049, 0.102 mole) and 20.239, 0.146 mole) were refluxed and analysed by G.L.C. The first mixture was refluxed for 142 hours reaching a final, constant, temperature of 11 50C and the second for 134 hours reaching 11 80C.

G.L.C. analysis for both mixtures showed the presence of ethanol,tetraethoxysiiane, 2phenoxyethanol and PhOCH2CH2OSi(OEt)3. Samples of product from Example 6 were analysed under the same conditions and found to contain PhOCH2CH20Si(OEt)3.

Example 43 Process in Accordance With the Invention With Proportion of an Alcohol AOH in Reactant Alcohol A catalytic solution was prepared by mixing 300 ml of tetraethoxysilane with 1 50 ml of metal alkoxide solution prepared according to Method 2, i.e. the catalyst was the reaction product of potassium and 2-ethoxyethanol. To this solution was added 1 4g (0.5 mole) of silicon powder of average particle size five microns and 30 ml dry ethanol, i.e. 900 ml catalytic solution per mole of silicon. The procedure followed was according to Example 1 with the exception that the alcohol added was not pure ethanol but 95% ethanol by volume and 5% 2-ethoxyethanol by volume. During a 33.5 hour period at an average reaction temperature of 1 580C the average production rate of product was 30.5 grams/hour with a yield of 98.8% based on the weight of silicon used.

G.L.C. analysis of the product collected showed that there was an increased yield of the substituted alkoxysiianes (EtO)nSi (OCH2CH2OEt) n=3, 2, 1 compared with product collected from a reaction carried out under the same conditions but with only ethanol added. The content of such substituted product was increased. Specifically the content of (EtO)3SiOCH2CH2OEt was increased from 12 to 20%, of (EtO)2Si(OCH2CH2OEt)2 from 1.5% to 3% and of (EtO)Si(OCH2CH20Et)3 from 0 to 1%.

Claims

1. A method of manufacturing alkoxysilanes of the type {RO)nSi(OA)4~n where R is C 1-C6alkyI,A is -C2H4OCH3; -C2H4OC2H5; -C2H40C6H5: -C2H4OC2H4OCH3; -C2H4OC2H4OC2H5; -C2H4NR1R2 where R1 and R2 are C1-C4 alkyl and n is 1, 2, 3 or 4, comprising reacting together a mixture of the alcohol ROH and the alcohol AOH in a catalytic solution containing an alkali metal alkoxide corresponding to the alcohol AOH and having sufficient thermal capacity effectively to maintain a temperature to catalyse the reaction and to discharge the alkoxysilane as vapour together with the alcohol vapour and hydrogen gas.

2. A method as claimed in Claim 1 wherein the said thermal capacity is achieved by having at least 500 ml of catalytic solution for each mole of silicon or silicide.

3. A method as claimed in either Claim 1 or Claim 2 wherein R is C2H5.

4. A method as claimed in any of the preceding claims wherein there is 10% or less of the alcohol AOH in the said mixture.