Method for preparation of organoalkoxysilanes

Abstract: Disclosed is a one reactor, continuous system for the manufacture of organoalkoxysilanes. The reactor consists of a fractionating means that allows for completion of the reaction and separation of the HCl formed as a by-product. Also disclosed is a means for removing or reducing any residual hydrolyzable chloride or other acids in the organoalkoxysilanes using ion exchange resins.

Description: This invention relates to a continuous process for producing organoalkoxysilanes in which the simultaneous reaction and removal of by products results in the reduction of unwanted side reactions and elimination of gel formation. This invention also relates to a method for reduction of acid in the resulting organoalkoxysilane. US-A-4,642,363 discloses a method for the continuous or batch preparation of trialkyl organo-oxysilanes by reaction of organic hydroxy compounds with trialkyl halogen silanes in the absence of acid-binding substances. The organic hydroxy compound is added directly to the trialkoxy halogen silane in an amount which corresponds to no more than the stoichiometrically necessary amount. The trialkyl halogen silane, or the resultant mixture is always at the boiling temperature or above the boiling temperature in the gaseous state. The reaction mixture is subjected, no later than toward the end of the reaction, to a column distillation in which the column temperature is held such that the reaction is carried to the end within the column. In continuous operation, the trialkyl halogen silane is introduced in gaseous form into the bottom of a column and either kept under reflux or introduced into a reactor into which corresponding stoichiometric amounts of organic hydroxy compound are simultaneously introduced. In the column, either a raw product or freshly introduced organic hydroxy compound in liquid form flows against the gaseous trialkyl halogen silane, and the desired trialkyl organooxysilane collects at ebullition on the floor of the column and is continuously removed. US-A-4,421,926 discloses a process for converting a mixture of at least two different halosilanes having the general formula R n SiX 4-n , which are difficult to separate, to at least two different alkoxysilanes having the formula, R n Si(OR') 4-n , where R and R' are saturated or unsaturated alkyl groups of 1 to about 8 carbon atoms or aromatic; X is halogen; and n is 0-3; and separating the alkoxysilanes. The co-alkoxylation of the halosilanes is carried out by charging a reboiler equipped with a reflux column with an alkoxylating agent, such as, an aliphatic alcohol, and, optionally, at least one of the halosilanes being alkoxylated; feeding at least two halosilanes to be co-alkoxylated into the upper section of the column; introducing the alkoxylating agent, such as, an aliphatic alcohol, into the upper section of the column to react with the halosilanes in a reaction zone in the column and thereby form alkoxysilanes and hydrogen halide; removing the hydrogen halide; collecting at least two alkoxysilanes formed in the column and separating the alkoxysilanes. In one preferred embodiment, the alkoxysilanes are separated and collected at two different points in the column in a distillation zone below the reaction zone. Two halosilanes, which are co-methoxylated and thereafter separated, are dimethyldichlorosilane and methyltrichlorosilane which form dimethyldimethoxysilane and methyltrimethoxysilane, respectively, when heated in the presence of the alkoxylating agent, methanol. US-A-3,792,071 discloses an improved continuous process for the manufacture of substituted or unsubstituted alkoxysilanes and alkoxypolysiloxanes by reacting a chlorosilane with a substituted or unsubstituted alcohol in a column provided with a reflux condenser at an elevated temperature, the improvement comprising (a) introducing a chlorosilane of the formula R n SiCl 4-n wherein R is selected from the group consisting of hydrogen, hydrocarbon radicals and substituted hydrocarbon radicals in which the substituted groups are inert under the reaction conditions and n is a number of from 0 to 3, at the head of the column, a substituted or unsubstituted aliphatic alcohol having up to 6 carbon atoms in which the substituted groups are inert to the chlorosilane under the reaction conditions being introduced in a gaseous state at a point below the point of introduction of the chlorosilane or in the lowest one-third of the length of the column, (b) removing the reaction product from the column at a point below the point of introduction of the alcohol, (c) maintaining the temperature over the entire internal cross-section of at least two-thirds of the zone between the inlet of the alcohol and the inlet of the silane above the boiling point of the alcohol at the pressure prevailing in the column and (d) maintaining at the head of the column an excess of the alcohol boiling under reflux during the reaction. US-A-4 298 753 describes a continuous process for preparing silanes and siloxanes having SiOC groups. In a first reactor a chlorosilane is reacted with a deficit of hydroxyl-containing aliphatic compound, and the reaction is completed in a second reactor with addition of further hydroxyl-containing aliphatic compound as a gas. It is an object of this invention to provide a method for producing organoalkoxysilanes by the alkoxylation of organochlorosilanes. It is further an object of this invention to provide a method for producing organoalkoxysilanes in which the formation of gels and undesirable impurities is minimized through raw materials, process conditions and process equipment. It is further an object of this invention to provide a continuous method for producing organoalkoxysilanes in which only one reactor is required. It is further an object of this invention to provide a method for removing or reducing hydrolysable chloride and other acids in the organoalkoxysilanes. The chemistry of alkoxylation of organochlorosilanes is very complex, being dependent on the purity of the organochlorosilane, the conditions under which the reaction takes place and the ease of removal of the HCl formed in the reaction process. The objects of this invention are achieved by a combination of raw materials, process conditions and process equipment. The present invention provides a process for making organoalkoxysilanes using fractionation means consisting essentially of (i) a column comprised of contacting devices (ii) means for providing heat to and partially containing the contents at a sump portion and (iii) means for providing cooling to the contents at a head of the column; wherein the process comprises A) feeding simultaneously into the column a) a liquid organochlorosilane, b) liquid alcohol and c) vaporized alcohol, such that the alcohol contacts the organochlorosilane, and is continuously supplied in an excess, in an amount up to 125% of the theoretical amount required to obtain a complete reaction; B) maintaining a temperature within said column such that at least the lower 1/3 of the column is above the boiling point of the alcohol within 20°C of the boiling point of the alcohol and no reflux of alcohol is present in the head of the column; C) recovering any organoalkoxysilane formed from the sump portion of the column; and D) recovering HCl at the head of the column. The organochlorosilanes and organoalkoxysilanes of this invention are exemplified by the formula wherein R 1 is selected from an saturated or unsaturated alkylene group containing 1 to 10 carbons, an arylene group containing 6 to 10 carbons; any of said groups containing one or more ether oxygen atoms within aliphatic segments thereof; R 2 is selected from the hydrogen atom, a halide atom, the nitrogen atom and an alkyl group consisting of 1 to 6 carbons optionally containing one or more of acryloxy, methacryloxy, carboxy or ester functional groups; R 3 is independently selected from the hydrogen atom and an alkyl group containing 1 to 6 carbons and an aryl group containing 6 to 10 carbons; R 4 is independently selected from the chlorine atom or the alkoxy group; a has the value of 0 to 3 and b has the value of 0 to 1 such that the sum of a + b does not exceed 3. Completion of reaction is defined as when substantially all R 4 present on the molecule are represented by the alkoxy group. Alcohols useful in this invention are of the general formula HOR 5 wherein R 5 is selected from a straight or branched chain alkyl group containing 1 to 6 carbons. The alkoxy group is produced when the hydrogen atom is removed from the molecule and is substituted by -OR 5 . Alcohols useful in this invention should boil at a temperature lower than the organoalkoxysilane formed from them. Alcohols most commonly employed by the method of this invention are methanol and ethanol. Some side reactions and formation of some by-products can be initially decreased by the use of a organochlorosilane which has been distilled. Distillation of the organochlorosilane is applied to remove impurities that include lower or higher boiling matter or unreacted raw materials, impurities from the starting materials and residual platinum. Distillation will result in a material essentially free of reactants that could result in or possibly catalyze some of the side reactions. The function of using a distilled material is also to remove higher molecular weight molecules that could precipitate out during the alkoxylation process. The use of distilled organochlorosilanes is preferred, especially when acrylate containing materials are used. The distillation of the organochlorosilane need not be achieved by complicated or novel methods nor is the separation critical. Distillation can be achieved by such techniques such as thin film evaporation, flash evaporation, batch or continuous distillation and other such methods employed in the art. The addition of a compound that inhibits polymerization or stabilizes the organofunctional silane may be required during the alkoxylation process especially when acryloxy or methacryloxy (herein referred to only as acryloxy) groups are present. The acryloxy groups may undergo polymerization even at the mildest conditions achieved during the alkoxylation. Examples of inhibitors useful for preventing polymerization of acryloxy functional silanes are diphenylphenylenediamine, phenothiazine, monomethyl ether of hydroquinone or anilinophenol or other phenolic inhibitors. The preferred inhibitor for this invention is phenothiazine. Phenothiazine may already be present in the acryloxyorganochlorosilane (depending on the process used to produce it) or may be added to the acryloxyorganochlorosilane at any point prior to its introduction into the column. Levels of 50 to 2500 parts per million parts organochlorosilane should be added with the preferred level being 100 to 1000 parts per million parts organochlorosilane. The alkoxylation reaction should be carried out in equipment which can simultaneously provide for the reaction between the organochlorosilane and alcohol and the removal of the hydrochloric acid. One such example, and that which is preferred for this invention, is a column suitable for fractionation. The column should be designed to allow for proper separation of the HCl away from the organoalkoxysilane and to provide enough residence time for the reaction to go to completion. The column should be equipped with a means of providing heat to the material at a sump portion of the column and a means of cooling and more preferably condensing the material at the head of the column. Multiple column systems that simulate a one column system are also useful in this invention. Means for providing heat can be exemplified by such means as a reboiler. Types of reboilers useful and known in the art are a kettle reboiler, vertical and horizontal thermosiphon reboiler, forced recirculation reboiler or others. Partial, single and multi-component reboiler systems can be used. The medium for providing the heat in the heat means can be steam, electric or other depending on the temperature desired. Means for cooling can be exemplified by single or multi-component cooling systems comprising air cooled overhead condensers, horizontal and vertical in-shell condensers, horizontal or vertical in-tube condensers and others. The medium for providing the cooling in the condenser can be air, water, glycol, known refrigerants and others. The column should be equipped with vapor/liquid contacting devices suitable for the separation and reaction needs and also for preventing the formation and collection of gels. These contacting devices may be further exemplified by trays or packing which are known in the art and are commercially available. The preferred contacting devices of this invention are those relating to trays however packing has been found suitable for this invention. Columns that contain a combination of packing and trays are also suitable. The preferred type of tray for this invention is that of the bubble cap. Operation of the column and design of the contacting devices should prevent the allowance of non-wetted surfaces (dry spots) as it is believed that undesired reactions will be enhanced on those surfaces. This can be achieved by maintaining a constant liquid flow in the column and ensuring that the column temperatures do not become too hot. Start-up of the process can be aided by the use of a heel, consisting of the organoalkoxysilane, in the heating means so that the desired operation temperature can be achieved in the heating means at the start of the operation. The use of the organoalkoxysilane is not necessary, however, it is preferred. Other materials which are non-reactive with the organochlorosilane, organoalkoxysilane, methanol or hydrochloric acid can also be used in the heat means during the start-up. These materials should boil at a temperature above the desired operating temperature. If a material other than the organoalkoxysilane is used it may be desirable to separate that material from the final product through distillation means or by disposing of the product contaminated with the heel material. If the organochlorosilane is used as the heel, material from the bottom of the column should be recycled with the feed until complete reaction has been achieved. Materials suitable for the heel can be exemplified by the organoalkoxysilane, similar organoalkoxysilanes, the organochlorosilane, similar organochlorosilanes, solvents or any combination thereof. The method for introducing the feeds into the column has been found to also increase the degree of completion of the reaction. The alcohol can be fed into the column in either a liquid or a vapor phase or a combination of both. The preferred method is to feed the alcohol at levels such that 60 to 100 percent can be vapor and 0 to 40 percent can be liquid. The liquid alcohol should be fed into the upper portion of the column while the alcohol in the vapor phase should be fed into the lower portion of the column. It is preferable, but not necessary, to mix the liquid alcohol with the organochlorosilane prior to initiating it into the column or to feed them into the same location. The process for this mixing can be obtained by using the same pipe or mechanical means to feed them into the column or supplying them independently into an agitated vessel. It is preferred that the liquid alcohol and feed be introduced into the column at the head while the alcohol being fed in the vapor form be introduced into the column at a point above the heat source and below the bottom contacting device. Alcohol should be continuously supplied in excess of the theoretical amount required to complete the reaction. The amount of alcohol should not exceed 125 percent of the theoretical amount required to obtain a complete reaction. The preferred amount of alcohol of this invention is from 101 to 115 percent of the theoretical amount. The use of theoretical amounts of alcohol or a slight excess below the desired levels may result in a highly acidic product. Operating conditions have also been found to enhance the completion of the reaction. The reboiler temperature should be maintained at temperatures above the boiling point of the alcohol and below the boiling point of the organoalkoxysilane at atmospheric pressures. If the column is operated under vacuum or at pressures above that of atmospheric the temperatures should be adjusted accordingly. It is preferred that the temperature of the column be operated at a point below the boiling point of the organoalkoxysilane but at a temperature high enough to allow the reaction to proceed to completion. It is also desired that the lower 1/3 of the column be maintained at a temperature above the boiling point of the alcohol, within approximately 20°C. of the boiling point of the alcohol. The preferred temperature range in the lower 1/3 of the column when using methanol is 73°C. to 77°C. Temperatures in the remaining upper 2/3 of the column, particularly in the head of the column, may be well below the boiling point of the alcohol. By maintaining such conditions during operation, there should be no reflux of alcohol in the head of the column. The basic principles of the operation of this invention comprises feeding a liquid organochlorosilane and excess liquid/vapor alcohol into a fractionation means comprised of contacting devises, heat means and cooling means. The operating temperature in the heat means is maintained above the boiling point of the alcohol but below that of the organochlorosilane. The temperature should be such that there is no reflux of alcohol in the head of the column. The organochlorosilane may or may not have been distilled prior to its use and it may or may not contain a compound that can inhibit polymerization of the organochlorosilane or organoalkoxysilane. The organoalkoxysilanes produced by this invention sometimes contain small amounts of residual hydrolyzable chloride or other acids such as methacrylic acid. Although it is believed that these acids are in quantities low enough that the stability of the material is not affected, it may be undesirable for certain applications or for aesthetic reasons to have this acid present. A method to reduce the acid present in the organoalkoxysilane is achieved by contacting the organoalkoxysilane with an ion exchange resin. Ion exchange resins, in particular anionic exchange resins, comprised of tertiary amines and useful in non-aqueous media are preferable for this invention. In particular, Amberlyst A-21 produced by the Rohm and Haas Corp., Philadelphia, Pa. and Dowex MWA-1 produced by Dow Chemical Company, Midland, Mi., have been found to be useful. The organoalkoxysilane may be treated to reduce the acid as it directly comes off of the bottom of the reactor or the organoalkoxysilane may be collected stored and treated at a later time to reduce any acid. The ion exchange resins useful in this invention are charged into a column or other containing source to produce a bed of appropriate size for the amount of material to be processed. When the ion exchange resin is contained in a base of water, this should be displaced by first flowing methanol through the bed. The methanol is then displaced by a flow of nitrogen until the bed is dry. The removal of all water, methanol or other hydroxylic materials from the ion exchange resin is important to prevent undesired reactions and/or the formation of gels. Once the ion exchange media has been prepared the organoalkoxysilane is fed so that it contacts the resin bed and flows through the bed at a rate such as to maintain a liquid level in the bed. The bed should be renewed or changed when acid levels of those greater than desired are contained in the material leaving the bed. The organoalkoxysilanes produced by this invention and treated thereafter to remove acid contamination may be further exemplified by, but not limited to, those which have unsaturated or other highly reactive sites or are sensitive to decomposition at higher temperatures. These compounds may be further exemplified by vinyltrimethoxysilane, isobutyltrimethoxysilane, chloropropyltrimethoxysilane, chloroisobutylmethyldimethoxysilane, chloropropylmethyldimethoxysilane, hexenylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, methyl-3-methyldimethoxysilyl-2-methylpropionate, cyanoethyltrimethoxysilane, phenyltrimethoxysilane, propyltrimethoxysilane, trifluoropropylmethyldimethoxysilane and others. So that those skilled in the art can understand and appreciate the invention taught herein the following examples are presented, it being understood that these examples should not be used to limit the scope of this invention over the limitations found in the claims attached hereto. Example 1 Distilled, inhibited 3-methacryloxypropyltrichlorosilane (A) was prepared according to U.S. Patent No. 4,780,555 and was found to have a GLC purity of 98.52 percent monomer. The apparatus used was a two sectioned, 29 tray, bubble cap column. The upper section contained 20 bubble caps spaced at 1 inch intervals while the bottom column contained 9 bubble caps spaced at 1 inch intervals. Seventeen inches above the top bubble cap tray was a volatile condensation unit consisting of a water condenser, Dry Ice condenser and a condensed volatile take-off mechanism. Uncondensed volatiles were scrubbed with water. The condenser was arranged such that no condensate could be returned to the column. Attached to the bottom of the column was a reboiler fitted with a thermowell, a heater well and a sink-trap-shaped glass tube outlet terminated with a stopcock. The reboiler was heated with an internal cylindrical heating element connected to a Variac (R) which was controlled by a thermoregulator. The reboiler contents were magnetically stirred. A constant level of liquid was maintained in the reboiler throughout the experiment. The reboiler was charged with 211 g of 3-methacryloxypropyltrimethoxysilane (B) containing 150 ppm of phenothiazine and heated to approximately 116°C. Methanol (MeOH) was delivered at 0.83 ml/min to the top of the premixer (a 10 turn spiral condenser) where it mixed at ambient temperature with (A) which was being delivered at a rate of 4.76 ml/min. The MeOH/(A) mix entered the top of the column at 3 inches above the top bubble cap tray. Methanol was also delivered to the vaporizer at 2.06 ml/min. The methanol vapor then entered the column below the bottom bubble cap tray but above the reboiler. The reboiler temperature was maintained at 109 to 116°C. The temperature of the bottom 9 bubble caps varied from 70° to 76°C. The temperature at 12 inches above the MeOH/(A) feed point but below the condenser varied from 16° to 23°C. during the run. In a period of 114.5 hours, a total of 39816 g (152.26 moles) of (A) and 15588 g (487.12 moles) of methanol were reacted resulting in 36928.8 grams of product. The product was analyzed by GLC to contain 93.5% 3-methacryloxypropyltrimethoxysilane and 4.69 percent methanol. The column and reboiler remained free of any gels during the entire operation. Example 2 This example is provided to show how higher reboiler temperatures can result in gellation. Distilled 3-methacryloxypropyltrichloroilane (A) containing 0.015 wt.% phenothiazine was prepared according to U.S. Patent No. 4,780,555 and was found to have a GLC purity of 98.2 percent monomer. The apparatus used was a 40 x 1 inch column packed to a height of 35 inches with 1/8" glass helices supported by ceramic saddles. Directly over the column was a volatile condensation unit comprised of a water cooled overheads condenser and a Dry Ice condenser. The water condenser contained a magnetically controlled reflux mechanism. A reboiler containing a U-tube discharge, 40 Watt heater and magnetic stirrer were attached at the bottom of the column. The reboiler was charged with 155.4 grams of 3-methacryloxypropyltrimethoxysilane (B) containing 1930 ppm of phenothiazine and heated to approximately 135°C. Methanol was vaporized and delivered to the center of the column, 16 inches below the liquid (A) feed point, at a liquid rate of 2.15 g/min. (A) was delivered 4 inches from the top of the column at a rate of 5.69 g/min. The reboiler temperature was maintained at 125°C. to 126°C. The temperature of the column at the point of the 3-methacryloxypropyltrichlorosilane feed was 41° to 50°C. A reflux ratio of 16/4 was maintained during the operation. After a period of 14 hours gels were visible in the column in and below the ceramic saddles. At 24 hours the column plugged and operation was discontinued. Example 3 For this example a 20 bubble cap tray column equipped with a condenser and reboiler as in Example 1 was used. A mixture of hexenyldimethylmethoxysilane and hexenyldimethylchlorosilane was placed in the reboiler and heated to approximately 130°C. Methanol was vaporized and fed to the column at a rate of approximately 2.0 g/min above the reboiler but below the bottom tray. Liquid hexenylmethyldichlorosilane (C) was fed to the top of the column at approximately 6.03 g/min. The reboiler was maintained at a temperature of 120° to 130°C. No reflux was observed in the head of the column. The column was operated for 8 hours. Gas Chromotography (GC) of the resulting material showed 97 area% hexenylmethyldimethoxysilane (D). There was no evidence by GC of addition of HCl across the double bond or C=C isomerization. Example 4 The same apparatus used in Example 1 was used in this example. The reboiler was charged with 219.6 g of methyl-3-methyldimethoxysilyl-2-methylpropionate (E) and heated to 130°C. Methanol was vaporized and fed to the column at a rate of 1.61 g/min. below the bottom tray and above the reboiler. Liquid methanol at a rate of 0.51 g/min was mixed with the chlorosilane being fed to the top of the column. Methyl-3-methyldichlorosilyl-2-methylpropionate (F) was fed to the column at a rate of approximately 7.25 g/min. The reboiler temperature was maintained at 125° to 131°C. which allowed the temperature in the lower 1/3 of the column to be maintained at 70° to 76°C. Temperatures at the head of the column varied from 20° to 33°C. No reflux was observed in the head of the column. The column was operated until a total of 4422 g of (E) and 1295.4 g of methanol were fed. A product of 90 area% purity (GC) was obtained. No residues were observed in the system. Example 5 A 7/8 inch by 43 inch column having a volume of 415 ml. was charged with 253.9 g of Amberlyst A-21 resin purchased from Rohm and Haas Corporation containing 55 percent water. The water was displaced by downflowing methanol through the bed. The methanol was then displaced with nitrogen. 3-methacryloxypropyltrimethoxysilane produced in Example 1 having an acid number of approximately 1.2 mg KOH/g was then pumped at a rate of 6.25 to 6.9 ml/min. to the top of the bed. Acid was observed at the bottom of the column after 10 to 15 hours of operation, at which time the bed was replaced. The resulting acid content of the 3-methacryloxypropyltrimethoxysilane was 0.042 mg KOH/g.

Claims: A process for making organoalkoxysilanes using fractionation means consisting essentially of (i) a column comprised of contacting devices (ii) means for providing heat to and partially containing the contents at a sump portion and (iii) means for providing cooling to the contents at a head of the column; wherein the process comprises A) feeding simultaneously into the column a) a liquid organochlorosilane, b) liquid alcohol and c) vaporized alcohol, such that the alcohol contacts the organochlorosilane, and is continuously supplied in an excess, in an amount up to 125% of the theoretical amount required to obtain a complete reaction; B) maintaining a temperature within said column such that at least the lower 1/3 of the column is above the boiling point of the alcohol within 20°C of the boiling point of the alcohol and no reflux of alcohol is present in the head of the column; C) recovering any organoalkoxysilane formed from the sump portion of the column; and D) recovering HCl at the head of the column. A process as claimed in claim 1 wherein a reboiler is used as the means to provide heat and the temperature of the reboiler contents is maintained between 70 to 115°C. while operating under atmospheric pressure. A process as claimed in claim 1 where the organochlorosilane is distilled prior to its introduction into the column. A method as claimed in claim 1 wherein additionally the organoalkoxysilanes prepared are contacted with an ion exchange resin that is free of hydroxylic materials to remove any acid.

Inventors: BANK HOWARD MARVIN, PETRISKO ROBERT ALLAN, BANK, HOWARD MARVIN, PETRISKO, ROBERT ALLAN
Applicants: DOW CORNING, DOW CORNING CORPORATION
Application year: 1990
Main classification: C07F7
IPC codes: C07F7