Process for producing benzyl alcohol

Abstract: A process for producing benzyl alcohol of high purity by hydrolysis of benzyl acetate in the presense of a solid acid catalyst, comprising steps of feeding benzyl acetate, water, and acetic acid to a hydrolysis reactor packed with a solid acid catalyst to cause reaction to obtain a liquid reaction mixture containing benzyl acetate, water, benzyl alcohol, and acetic acid; introducing the liquid reaction mixture to an acetic acid-water recovery column to separate the liquid reaction mixture by distillation into a column top distillate composed of acetic acid and water and a column bottom liquid composed mainly of benzyl alcohol and benzyl acetate; recycling the column top distillate of the acetic acid-water recovery column, after removing most of the acetic acid by an acetic acid-water separation column, to the hydrolysis reactor.

Description: The present invention relates to a process for producing benzyl alcohol. Benzyl acetate itself is useful as a solvent and a perfume. Benzyl alcohol which is derived from the benzyl acetate by hydrolysis or by transesterification with methanol is an important compound useful as a powerful solvent, a nontoxic medical additive, and an intermediate compound for agricultural chemicals and medicines. For industrial production of benzyl acetate, a process is known in which benzyl chloride produced by chlorination of toluene is hydrolyzed by alkali, and the resulting benzyl alcohol is esterified with acetic acid. This process comprises multistage reactions, and includes many steps of separation and purification after the respective reactions. Therefore, the process is complex and is not advantageous economically. Moreover, in the hydrolysis reaction of the second step, an alkali such as sodium hydroxide is required in an equivalent amount or more, and a large amount of a salt containing organic compounds is formed as the by-product, which involves problems in after-treatment thereof. In a process not industrially conducted, benzyl acetate is produced by reaction of toluene, acetic acid, and oxygen in the presence of a catalyst for oxyacetoxylation. This process produces benzyl acetate in one step reaction without formation of a by-product salt, so that it is advantageous economically and can be of low environmental load. Many techniques of benzyl acetate production have been disclosed, for example, in JP-B-42-13081, JP-A-52-151135, JP-A-52-151136, JP-B-50-28947, JP-B-52-16101, and JP-A-63-174950 (The term "JP-A" herein means an "unexamined published Japanese patent application", and the term "JP-B" herein means an "examined Japanese patent publication"). However, in these techniques, detailed studies are not made on industrial production process including separation and purification of benzyl acetate. Therefore, known techniques are not satisfactory for production of high-purity benzyl acetate. On the other hand, benzyl alcohol can be produced by the known processes below. Of these, the processes (1) and (3) are practiced industrially: (1) Hydrolysis of benzyl chloride by sodium hydroxide, (2) Hydrolysis of benzyl acetate in the presence of a catalyst, and (3) Reduction of benzaldehyde by hydrogen in the presence of a catalyst. The above processes (1) and (2) both produces benzyl alcohol by hydrolysis. The process (1) consumes an equivalent amount or more of sodium hydroxide for stoichiometric reaction of benzyl chloride, involving a problem of after-treatment of a large amount of an aqueous solution of organic compound-containing sodium chloride formed as a by-product. The process (3) employs relatively expensive benzaldehyde as the starting material, and is disadvantageous economically. The process (2) of hydrolysis of benzyl acetate to produce benzyl alcohol forms useful acetic acid as the by-product without discharging waste water, thus being economical and of low environmental load. Regarding this hydrolysis process, a method is disclosed in which a mixture of water and benzyl acetate in a volume ratio of water/benzyl acetate of 25 is hydrolyzed at a temperature of 20-30°C in the presence of Amberlite IR-100, a sulfonic acid type cation-exchange resin (J. Chem. Soc., No.5, 1952, 1607). However, in this process, the catalyst activity is low, and an extremely large amount of water is required, so that the starting material concentration is lowered. Therefore, this process is not industrially advantageous in consideration of the energy for removal of unreacted water from the liquid reaction mixture. Further, the above disclosure does not specifically disclose the method for isolation and purification of the resulting benzyl alcohol. In another process (Russian Patent: SU1077875), benzyl alcohol of high purity (98%) is obtained at an improved yield by hydrolysis of benzyl acetate in a flow system at a temperature of 90-98°C at water/benzyl acetate ratio of 3 (by weight) through a porous sulfonic acid type cation-exchange resin containing 2.2-4.0 m-equivalent/g of nitro group by replacing acetic acid with water during the reaction. However, this process, which requires use of a special nitro group-containing resin as the catalyst, is not practical as an industrial process in view of the catalyst cost. As discussed above, the benzyl alcohol production process has not yet been investigated sufficiently for industrialization including the separation and purification steps, and no process is satisfactory as the process for producing high-purity benzyl alcohol. SU-A-1 077 875 describes a method for producing benzyl alcohol, wherein the proposed method comprises hydrolysis of benzyl acetate at 90-98 deg. C in the presence of porous sulphocationite contg. nitro-groups in the amount of 2.2-4.0 mg-equiv./g. The yield of benzyl alcohol is increased to 78-98% in comparison to 44-47% in previously used method. An object of the present invention is to provide a process for economical production of benzyl alcohol of high purity. As a solution of the above-described problems, it has been found that benzyl alcohol, which cannot readily be isolated and purified from the hydrolysis product of benzyl acetate, can be produced economically by constructing an isolation-purification process in consideration of the azeotropy of the components including benzyl alcohol and acetic acid as hydrolysis products, unreacted benzyl acetate and water, and recycling the process fractions to the specified process, and by using, as the catalyst, a sulfonated styrene-divinylbenzene copolymer having divinylbenzene units in a specified content range, and by reacting the starting materials in a specific ratio as disclosed in claim 1. Fig. 1 is a flow sheet showing specifically an example of a process of hydrolysis in the production process of benzyl alcohol of the present invention. Fig. 2 is a flow sheet showing specifically an example of a process of hydrolysis utilizing liquid-liquid separation in the production process of benzyl alcohol of the present invention. Fig. 3 is a flow sheet showing specifically an example of a process of azeotropic distillation employing water in the production process of benzyl alcohol of the present invention. Fig. 4 is a flow sheet showing specifically an example of a process of extractive distillation employing glycerin in the production process of benzyl alcohol of the present invention. Fig. 5 is a diagram showing compositions of a ternary component system composed of benzyl acetate, acetic acid, and water in the process of production of benzyl alcohol of the present invention. The process for producing benzyl alcohol by hydrolysis of benzyl acetate according to the present invention is described below. The process of the present invention includes various modifications, and is not limited to the examples of the embodiment shown by the drawings. Fig. 1 shows an example a hydrolysis reaction process according to the present invention. In this process of the present invention, benzyl alcohol is produced by hydrolysis of benzyl acetate by use of a reactor 9 packed with a solid-acid catalyst. The solid-acid catalyst is not specially limited, and includes inorganic solid-acid catalysts such as silica-alumina, alumina, zirconia, titania, and silica; and organic solid acid-catalyst such as strong acidic cation exchange resin. Of these, preferred are sulfonated styrene-divinylbenzene copolymers as the strongly acidic cation exchange resin. The sulfonated styrene-divinylbenzene copolymer as the solid-acid catalyst is not specially limited in the divinylbenzene unit content. In consideration of the catalyst life and the reaction activity, the divinylbenzene unit content is lower than 8% by weight. The sulfonated styrene-divinylbenzene copolymer is not specially limited provided that the vinylbenzene unit content is in the aforementioned range, and commercial copolymers are useful. The structure of the copolymer may be either of a gel type or of an MR type (macroreticular type). The gel type copolymer includes simple gel type copolymers and macroporous (MP) copolymers, both being useful. The MR type copolymer is a porous copolymer, and is not limited in the surface area, the porosity, and the average pore diameter. The amount of the acid of the copolymer is not specially limited, but the copolymer has preferably a total ion exchange capacity in the range of from 3.0 to 6.5 m-equivalent/g based on the dry resin. Benzyl acetate as the starting material is not specially limited, and may be the one produced by oxyacetoxylation reaction from toluene, acetic acid, and oxygen by use of a palladium type catalyst. As the composition of the starting material, a higher content of benzyl acetate is undesirable since by-products such as dibenzyl ether is increased and the equilibrium conversion and the reaction rate are lower in the higher content of benzyl acetate. On the other hand, at a higher content of water in the liquid mixture of the starting materials, remarkably larger amount of water remains in the reaction mixture after the reaction, which requires a larger amount of energy (latent evaporation heat) for separation and recovery of benzyl acetate from the reaction mixture. Furthermore, at the higher content of water, since the strongly ion-exchange resin is extremely affinitive to water, the fed starting materials tends to form a heterogeneous phase to prevent the adsorption of benzyl acetate onto the catalyst, which lowers the reaction rate and is disadvantageous in industrial production. Therefore, the ratio of water/benzyl acetate is selected usually in the range of from 1/9 to 3/2, preferably from 1/9 to 2/3. At a higher content of acetic acid in the starting material liquid mixture, the acetic acid content becomes higher to decrease the equilibrium conversion, and the decreased benzyl acetate content reduces the reaction rate, since the hydrolysis reaction of benzyl acetate is an equilibrium reaction and the acetic acid is one of the reaction products. Therefore, the content of acetic acid in the starting material liquid mixture is selected to be not higher than 30% by weight, preferably not higher than 20% by weight. As mentioned above, the composition of the starting material mixture is important in the present invention. It is particularly preferred to conduct the reaction in a specified three-component system of benzyl acetate/acetic acid/water as shown later. A useful type of the reactor is a fixed bed continuous reaction system in which the starting materials including benzyl acetate and water, and acetic acid as necessary, are continuously fed. However; the type of the reactor is not limited thereto, and any solid-liquid contact systems may be employed irrespectively of continuous systems or batch systems. The hydrolysis of benzyl acetate is an equilibrium reaction shown by the reaction equation (1) below. C 6 H 5 CH 2 OCOCH 3 + H 2 O = C 6 H 5 CH 2 OH + CH 3 COOH Therefore, the conversion in a single step reaction is limited thermodynamically even if the reaction is conducted in the aforementioned composition range. More specifically, the equilibrium constant K shown by the equation (2) is 0.40 at 80°C according to the investigation by the inventors of the present invention. Therefore, with an equimolar material feed composition of benzyl acetate and water (for example, Benzyl acetate/Water/Acetic acid = 89.3/10.7/0 % by weight), the equilibrium conversion is as low as 38.7%. The conversion of benzyl acetate can be raised by removing at least part of the produced acetic acid in a multi-stage reaction system or reaction distillation system during the reaction. K = [BzOH] [AcOH] / [BzOAc] [H 2 O] where [BzOH] is the concentration of benzyl alcohol, [AcOH] is the concentration of acetic acid, [BzoAc] is the concentration of benzyl acetate, and [H 2 O] is the concentration of water. The reaction temperature is selected in the range usually of from 40 to 150°C, preferably from 60 to 120°C. At the reaction temperature of lower than 40°C, the reaction rate is low, whereas at the reaction temperature of higher than 150°C, formation of benzyl ether as the by-product increases to lower the reaction selectivity, and may decompose or deteriorate the catalyst cation-exchange resin. The reaction pressure is not specifically limited. The pressure may be applied to prevent boiling of the reaction liquid or to prevent significant evolution of bubbles caused by dissolved gas. Usually the pressure is selected in the range of from an atmospheric pressure to 981 kPa (10 kg/cm 2 G). The liquid space velocity (LHSV) is selected in the range of usually from 0.1 to 30 h -1 , preferably from 0.2 to 6 h -1 . To the hydrolysis reactor 9, are introduced mixedly the benzyl acetate fed freshly as the starting material, recycled benzyl acetate from an alcohol concentration column 11, and a recycled aqueous acetic acid solution from an acetic acid-water separation column 12. The method of mixing is not specially limited. For example, the mixing is conducted in a mixing vessel provided before the reactor for sufficient agitation and mixing, or by an inactive packed bed provided at the upstream side to the catalyst layer in the reactor. At the outlet of the hydrolysis reactor 9, the composition of the liquid corresponds preferably at least to. 70% equilibrium conversion. At the composition of lower than 70% equilibrium conversion, a larger amount of energy is required for recovery of the unreacted benzyl acetate, which can be disadvantageous in industrial production. The reaction, mixture discharged from the hydrolysis reactor 9, which is composed of benzyl acetate, benzyl alcohol, water, and acetic acid, is introduced to an acetic acid-water recovery column 10. From the top of the acetic acid-water recovery column 10, acetic acid and water is recovered, and is introduced to an acetic acid-water separation column 12. Acetic acid is recovered from the bottom of the acetic acid-water separation column 12, and the fraction mainly composed of water is removed from the top thereof, and is recycled to the hydrolysis reactor 9. In operation of the acetic acid-water recovery column 10, the concentration of acetic acid is very important since the acetic acid as an extracting agent destroys the azeotrope composed of water and benzyl alcohol to bring benzyl acetate and benzyl alcohol to the column bottom. The concentration of the acetic acid should be controlled to be not less than 10 mol% based on the water. At the acetic acid concentration of lower than 10 mol% relative to water, azeotropes composed of water and benzyl acetate, and of water and benzyl alcohol are formed in the acetic acid-water recovery column 10, thereby benzyl acetate and benzyl alcohol being distilled out from the column top, which may make the intended separation impossible. With the aforementioned material composition, no problem is caused in the operation of the column. However, when the reaction is conducted at a higher concentration of water or at a lower hydrolysis conversion ratio, the acetic acid concentration at the inlet of the acetic acid-water recovery column becomes lower, so that acetic acid should be replenished to increase the acetic acid concentration up to 10 mol% relative to water. The benzyl alcohol and benzyl acetate discharged from the bottom of the acetic acid-water recovery column 10 is introduced to an alcohol concentration column 11 to obtain an azeotropic mixture composed of benzyl alcohol and benzyl acetate from the column top, and benzyl acetate from the column bottom. The benzyl acetate obtained from the column bottom is recycled to the hydrolysis reactor 9. Since the bottom liquid contains a small amount of high-boiling impurities including dibenzyl ether, a part of the bottom liquid is generally introduced to a heavy separation column 13 to remove high-boiling components mainly composed of dibenzyl ether. Thereby the concentration of impurities is decreased in the recycled benzyl acetate recycled to the hydrolysis reactor 9. Fig. 2 shows an example of the hydrolysis reaction process utilizing liquid-liquid separation. In this process, water is removed from the reaction liquid mixture by utilizing the low solubilities of benzyl alcohol and benzyl acetate in water. The reaction mixture discharged from the hydrolysis reactor 9 is introduced to a liquid-liquid separator 14 to separate it into an aqueous phase and an organic phase. The separated aqueous phase is recycled to the hydrolysis reactor 9, and the separated organic phase is introduced to the acetic acid-water recovery column 10. By this simple operation,. water and a part of the acetic acid are removed, and the large energy consumption by the acetic acid-water recovery column is saved, whereby the production cost can be reduced. The liquid-liquid separation is conducted in principle at a temperature where the liquid-liquid separation occurs. In consideration of partition coefficients of the respective components, separation time, and separation cost, the temperature is preferably in the range of from 10 to 60°C. In the case where the reaction liquid mixture contains an extremely large amount of water or acetic acid, and the liquid-liquid separation does not occur or takes a long time, the process of Fig. 1 in which liquid-liquid separation is not conducted is preferably employed for the production of benzyl alcohol. In the hydrolysis process shown in Fig. 1 or Fig. 2, benzyl alcohol having a purity of 99% or higher can be obtained from the top of the alcohol concentration column 11 by controlling the operation conditions of the alcohol concentration column 11. Benzyl alcohol of a higher purity containing less benzyl acetate can be obtained by further conducting azeotropic distillation or extractive distillation. Fig. 3 shows an example of the azeotropic distillation employing water. The column top distillate of the alcohol concentration column 11 is introduced to a first alcohol purification column 15, in which benzyl acetate is separated from benzyl alcohol by utilizing water as the azetrope. The distillate from the column top is introduced to a liquid-liquid separator 17 to separate the two liquid phases. A part of the separated aqueous phase is returned to the first alcohol purification column 15 as the recycle. The organic phase which contains benzyl acetate, benzyl alcohol, and a small amount of water is recycled to the acetic acid-water recovery column 10 or the hydrolysis reactor 9. The bottom liquid, which contains a small amount of water in addition to benzyl alcohol, of the first alcohol purification column 15 is introduced to a second alcohol purification column 16. In the second alcohol purification column 16, the water in the benzyl alcohol is completely removed from the column top by utilizing azeotrope of benzyl alcohol and water to obtain high purity benzyl alcohol from the column bottom. The column top distillate is recycled to the first alcohol purification column 15. Benzyl alcohol of higher quality can be obtained by distillation and purification by use of another distillation column. In the above process, benzyl alcohol is purified by means of two purification columns: the first column for separation only of benzyl acetate, and the second column for separation of water. This process is advantageous in comparison with the purification by means of one purification column in points below. (1) The operation temperature can be lowered, and the first column can be operated at an atmospheric pressure, which reduces the equipment cost. (2) The lower operation temperature prevents deterioration of the product quality. (3) A less expensive heating source (low pressure steam) can be used to.reduce the energy cost. (4) The operation of the distillation columns is stabilized more. Fig. 4 shows an example of extractive distillation process employing glycerin. The column top distillate of the alcohol concentration column 11 is introduced to an extractive distillation column 18. In the extractive distillation column 18, glycerin is used as the extracting agent, and the introduced distillation fraction is further separated into a column top distillate composed mainly of benzyl alcohol and benzyl acetate and a column bottom liquid composed of benzyl alcohol and glycerin. To the distillate from the column top, water is added, and then the distillate is introduced to a liquid-liquid separator 20 to separate into two liquid phases. Of the two phases, the aqueous layer composed of water and glycerin is recycles to the extractive distillation column 18, and the organic phase is recycled to the hydrolysis reactor 9. Otherwise, the aqueous phase in.the liquid-liquid separator 20 may be recycled, after removal of water, to the extractive distillation column 18. The organic phase in the liquid-liquid separator 20, which contains a small amount of glycerin, is recycled to the hydrolysis reactor 9, preferably after removal of glycerin. The column bottom liquid containing benzyl alcohol and glycerin of the extractive distillation column 18 is introduced to a product column 19, and benzyl alcohol of high purity can be obtained from the top of the column. The column bottom liquid composed mainly of glycerin is recycled to the extractive distillation column 18. Benzyl alcohol of higher quality can be obtained by distillation and purification by use of another distillation column. In the present invention, the aforementioned columns of the acetic acid-water recovery column 10, the alcohol concentration column 11, the acetic acid-water separation column 12, the heavy separation column 13, the first alcohol purification column 15, the second alcohol purification column 16, the extractive distillation column 18, and the product columns 19 are usual continuous multi-stage distillation columns such as packed columns and plate columns. The liquid-liquid separators 14, 17, 20 are usual settling vessels.. As described above, benzyl acetate and water, and benzyl alcohol and water which are not readily separable owing to the azeotropy can be separated readily by utilizing the acetic acid in the reaction liquid of the hydrolysis reaction as the extracting agent. Thereby, water and acetic acid can be completely separated from the reaction liquid mixture to obtain high-purity benzyl alcohol at remarkably reduced production cost. The water separated by the acetic acid-water separation column is recycled to the hydrolysis reactor, and the acetic acid is useful as an industrial chemical. Therefore, the process does not discharge waste water and causes less environmental load. A still higher purity of benzyl alcohol can be produced efficiently by concentrating the benzyl alcohol by the alcohol concentration column, and subsequently subjecting the concentrated benzyl alcohol to azeotropic distillation with water or extractive distillation with glycerin. The preferred hydrolysis catalyst of the present invention is explained below. In the hydrolysis reaction of benzyl acetate of the present invention, the preferred catalyst is a sulfonated styrene-vinylbenzene copolymer which is a strongly acidic cation exchange resin. The sulfonated styrene-vinylbenzene copolymer should contain the divinylbenzene units at a content of less than 8% by weight. The copolymer of the divinylbenzene content of 8% by weight or higher is less reactive and does not achieve the object of the present invention. The content of the divinylbenzene units is preferably not lower than 1% by weight in consideration of the catalyst strength, and is preferably not higher than 7% by weight in consideration of the catalyst life. The sulfonated styrene-divinylbenzene copolymer employed in the present invention is not specially limited provided that divinylbenzene unit content is in the aforementioned range, and may be a commercial product. The structure may be either of a gel type or a macroreticular type (MR type). The gel type copolymer includes simple gel type copolymers and macroporous (MP) copolymers, both being useful. The MR type copolymer is a porous copolymer, and' is not limited in the surface area, the porosity, and the average pore diameter. The total ion exchange capacity is preferably in the range of from 3 to 6.5 m-equivalent/g based on the dry resin. In the present invention, the hydrolysis reaction is conducted by a continuous fixed bed reaction system in which benzyl acetate and water as the starting materials are fed continuously to a reactor packed with a catalyst composed of the aforementioned sulfonated styrene-vinylbenzene copolymer. The starting materials may further contain, as desired, acetic acid in addition to the benzyl acetate and water to improve mixing of the starting materials. The water and the benzyl acetate are used in a water/benzyl acetate mole ratio ranging usually from 0.5 to 30, preferably from 1 to 15. At the mole ratio of less than 0.5, the conversion of benzyl acetate may be lower, whereas at the mole ratio of higher than 30, the reaction rate may be lower and be disadvantageous in industrial production. The concentration of acetic acid in the entire starting material is controlled to be in the range of usually from 0 to 30% by weight, preferably from 3 to 20% by weight. At the acetic acid concentration of higher than 30% by weight, the amount of acetic acid which is a reaction product is larger and the equilibrium deviates to the starting material side disadvantageously because the hydrolysis reaction of benzyl acetate is an equilibrium reaction. The reaction temperature is controlled in the range of usually from 40 to 150°C, preferably from 60 to 120°C. At the reaction temperature of lower than 40°C, the reaction rate is lower, whereas at the reaction temperature of 150°C, the by-product dibenzyl ether increases to lower the selectivity, and further the catalyst cation exchange resin may be decomposed or deteriorated. The reaction pressure is not specially limited, and.the reaction may be conducted under pressure, as desired. The liquid space velocity (LHSV) is controlled to be in the range of usually from 0.1 to 30 h -1 , preferably from 0.2 to 6 h -1 . The reaction mixture.discharged from the reactor is subjected to after-treatment according to a conventional process or the aforementioned process to obtain benzyl alcohol. As described above, benzyl alcohol can be produced efficiently and economically by use of the sulfonated styrene-divinylbenzene copolymer having divinylbenzene unit content in the specified range according to the present invention. The starting material composition specified for the hydrolysis reaction in the present invention is explained below. The composition of the starting material liquid is explained by reference to the composition diagram (Fig. 5) for the starting materials of ternary system of benzyl acetate/acetic acid/water. Table 1 shows the starting material compositions at the indicated points in Fig. 5. The composition of the starting material in the present invention should be in the closed region surrounded by the line segments derived.by bonding the points A, B, C, and D in Fig. 5 Specifically, when the material contains y% by weight of water, x% by weight of benzyl acetate, and z% by weight of acetic acid (where x + y + z = 100), the compositions of the starting materials are in the ranges: 1/9 ≤ y/x ≤ 3/2, and 0 ≤ z ≤ 30 At the starting material composition having the acetic acid content higher than the line A-D in Fig. 5 (z>30), the produced acetic acid increases, thereby lowering the equilibrium conversion and lowering the benzyl acetate content to decrease the reaction rate. At the starting material composition having the benzyl acetate content higher than the line A-B in Fig. 5 (y/x < 1/9), by-products such as dibenzyl ether increase, and the equilibrium conversion and the reaction rate become lower undesirably. At the starting material composition having the water content higher than the line C-B in Fig. 5 (3/2 < y/x), a larger amount of water remains after the reaction, and a large amount of energy (latent evaporation heat) is required for separation and recovery of benzyl acetate from the reaction liquid mixture. Moreover, the strongly acidic ion exchange resin generally is extremely affinitive to water, and in the above region, where the supplied starting material becomes heterogeneous, the adsorption of benzyl acetate to the catalyst is prevented to lower the reaction rate disadvantageously in industrial production. As described above, the starting material composition in the present invention is in the closed region surrounded by the lines bonding the points A, B, C, and D successively. For obtaining a higher purity of benzyl alcohol, the composition is preferably in the closed region surrounded by the lines bonding the points E, B, F, and G successively, namely in the range of 1/9 ≤ y/x ≤ 2/3, and 0 ≤ z ≤ 20. A reactor useful in the present invention is a fixed-bed continuous reaction type reactor which is fed continuously with benzyl acetate and water as the starting materials, and acetic acid as necessary, and reacts them. However, the type of the reactor is not limited thereto, but may be any usual method for solid-liquid contact. For improving the conversion of benzyl acetate, a multi-stage reaction type, a reaction distillation type, may be employed in which at least a part of the formed acetic acid is removed during the reaction. The reaction temperature in the present invention is controlled in the range of usually from 40 to 150°C, preferably from 60 to 120°C. At the reaction temperature of lower than 40°C, the reaction rate is lower, whereas at the reaction temperature of higher than 150°C, the by-product dibenzyl ether produced more to lower the selectivity, and may decompose or deteriorate the catalyst cation exchange resin. The reaction pressure is not specially limited, but is controlled to be at such a pressure that prevents boiling of the reaction liquid or remarkable bubble formation caused by a dissolved gas. The pressure is usually in the range of from an atmospheric pressure to 981 kPa (10 kg/cm 2 G). The liquid space velocity (LHSV) is controlled to be in the range of usually from 0.1 to 30 h -1 , preferably from 0.2 to 6 h -1 . The reaction mixture discharged form the reactor is subjected to after-treatment by a known process or the aforementioned process to obtain benzyl alcohol. As described above, according to the present invention, benzyl alcohol can be produced efficiently and economically by hydrolysis reaction of benzyl acetate in the specified range of the starting material composition. The present invention is described in more detail by reference to examples. In the description below, "%" is based on weight, benzyl alcohol is denoted by "BzOH", and benzyl acetate is denoted by "BzOAc". Example 1 Benzyl alcohol was produced by the hydrolysis reaction process shown in Fig. 1. 1,080 Milliliters of Amberlist 31 Wet (Japan Organo Co., Ltd.), a sulfonated acid type cation exchange resin (styrene-divinylbenzene copolymer of divinylbenzene unit content of 4%) was packed to a hydrolysis reactor 9. To this reactor 9, a starting material mixture (composed of BzOAc: 72.2%, water: 18.3%, BzOH: 6.6%, and acetic acid: 2.8%) at an LHSV of 0.27 h -1 to allow the reaction to proceed at 90°C. Thereby, a liquid reaction mixture (composed of BzOH: 32.6%, BzOAc: 36.1%, acetic acid: 17.2%, and water: 14.0%) was obtained at a rate of 241.3 g/h. This liquid reaction mixture was introduced to an acetic acid-water recovery column 10, and distillation was conducted at a pressure of 6.7 kPa (50 Torr) to obtain an aqueous acetic acid solution from the column top at a rate of 75.4 g/h. The bottom liquid of the acetic acid-water recovery column 10 (composed of BzOH: 47.4%, and BzOAc: 52.5%) was continuously introduced to an alcohol concentration column 11, and the distillation was conducted at an ordinary pressure to obtain 21.7 g/h of BzOH from the column top with a purity of 99.0%, and 144.3 g/h of a column bottom liquid (composed of BzOAc: 60.3%, and BzOH: 39.6%). Example 2 Benzyl alcohol was produced by the hydrolysis reaction process shown in Fig. 2. The reaction was conducted in the same manner as in Examples 1 by use of the hydrolysis reactor 9. The obtained liquid reaction mixture (composed of BzOH: 32.6%, BzOAc: 36.1%, acetic acid: 17.2%, water: 14.0%) was introduced to a liquid-liquid separator 14 to allow the mixture to separate at 30°C into an organic phase (composed of BzOH: 34.3%, BzOAc: 38.4%, acetic acid: 16.7%, and water: 10.4%) and an aqueous phase (composed of BzOH: 6.3%, BzOAc: 1.1%, acetic acid: 25.0%, and water: 67.5%). The aqueous phase was recycled to the hydrolysis reactor 9. The organic phase separated by the liquid-liquid separator 14 was introduced to an acetic acid-water recovery column 10, and distillation was conducted at a pressure of 6.7 kPa (50 Torr) to obtain an aqueous acetic acid solution from the column top at a rate of 61.5 g/h. The bottom liquid of the acetic acid-water recovery column 10 (composed of BzOH: 47.2%, and BzOAc: 52.8%) was continuously introduced to an alcohol concentration column 11, and the distillation was conducted at an ordinary pressure to obtain 21.7 g/h of BzOH of 99.0% purity from the column top, and 143.1 g/h of a column bottom liquid (composed of BzOAc: 60.6%, and BzOH: 39.3%). Example 3 The hydrolysis reactor 9 and the acetic acid-water recovery column 10 were conducted in the same manner as in Example 1, and the resulting benzyl alcohol was purified by azeotropic distillation with water as shown in Fig. 3. The bottom liquid discharged from the acetic acid-water recovery column 10 (composed of BzOH: 47.7%, and BzOAc: 52.5%) was continuously introduced to.the alcohol concentration column 11 and distilled at an ordinary pressure. The bottom liquid composed mainly of BzOAc and containing a small amount of BzOH was discharged at a rate of 97.6 g/h. The column top distillate of the alcohol concentration column 11 (composed of BzOH: 92.9%, BzOAc: 7.1%) was introduced continuously to the first alcohol purification column 15 and was distilled with introduction of water (43.2 g/h) at atmospheric pressure. Thereby, an organic phase composed mainly of BzOAc and.containing a small amount of BzOH and water, and an aqueous phase composed mainly of water were distilled out at a rate respectively of 13.0 g/h and 42.1 g/h from the liquid-liquid separator 17 equipped at the column top portion. The bottom liquid (composed of BzOH: 96.1%, and water: 3.7%) of the first alcohol purification column 15 was introduced continuously to the second alcohol purification column 16, and was distilled at a pressure of 13.3 kPa (100 Torr) to obtain BzOH of purity of 99.8% from the column bottom at a rate of 54.1 g/h and a column top distillate composed mainly of water from the column top at a rate of 2.4 g/h. Example 4 The hydrolysis reactor 9, the acetic acid-water recovery column 10, and the alcohol concentration column 11 were conducted driven in the same manner as in Example 1, and the resulting benzyl alcohol was purified by extractive distillation with glycerin as shown in Fig. 4. The column top liquid of the alcohol concentration column 11 (composed of BzOH: 92.9%, and BzOAc: 7.1%) was introduced continuously to the extractive distillation column 18, and glycerin is introduced to the upper portion of the extractive distillation column 18 at a rate of 176.6 g/h. Extractive distillation was conducted at a pressure of 6.7 kPa (50 Torr) to obtain a distillate (composed of BzOAc: 68.7%, BzOH: 29.7%, and glycerin 1.4%) from the column top at a rate of 6.9 g/h. Water was added to the distillate, and the mixture was separated by the liquid-liquid separator 20 to obtain an organic phase composed mainly of BzOAc and containing a small amount of BzOH and water, and an aqueous phase composed mainly of water at a rate respectively of 6.9 g/h, and 3.6 g/h. The bottom liquid of the extractive distillation column 18 (composed of BzOH: 25.8%, and glycerin: 74.1%) was introduced to the product column 19, and distillation was conducted at a pressure of 6.7 kPa (50 Torr) to obtain BzOH of 99.9% purity from the column top at a rate of 61.5 g/h, and a column bottom liquid mainly composed of glycerin at a rate of 176.5 g/h. Example 5 Benzyl alcohol was produced by the hydrolysis reaction process as shown in Fig. 3. Into the hydrolysis reactor 9, was packed 1,080 mL of Amberlist 31 Wet (Japan Organo Co., Ltd.) which is a sulfonated acid type cation exchange resin based on a styrene-vinylbenzene copolymer of divinylbenzene unit content of 4%. To this reactor, were fed fresh BzOAc (88.2 g/h), an aqueous 19.5% acetic acid solution obtained as a side stream from the top portion of the acetic acid-water separation column 12 (56.7 g/h), and a bottom liquid of the alcohol concentration column 11 (142.8 g/h, composed of BzOAc: 94.0% and BzOH: 6.0%), and the reaction was allowed to proceed at 80°C. Thereby, a reaction liquid (composed of BzOH: 24.3%, BzOAc: 46.8%, acetic acid: 16.7%, and water: 12.2%) was obtained at a rate of 287.7 g/h. The reaction liquid was introduced to the acetic acid-water recovery column 10, and distillation was conducted at a pressure of 6.7 kPa (50 Torr) to obtain an aqueous acetic acid solution from the column top at a rate of 83.8 g/h. The bottom liquid of the acetic acid-water recovery column 10 (composed of BzOH: 33.8%, and BzOAc: 66.2%) was introduced continuously to the alcohol concentration column 11, and distillation was conducted at a pressure of 12.7 kPa (95 Torr) to obtain a bottom liquid composed mainly of BzOAc and a small amount of BzOH at a rate of 142.8 g/h. The column top distillate of the alcohol concentration column 11 (composed of BzOH: 75.8%, and BzOAc: 24.2%) was introduced continuously to the first alcohol purification column 15, and was distilled with introduction of water (0.8 g/h) at atmospheric pressure. Thereby, an organic phase composed mainly of BzOAc and containing a small amount of BzOH and water, and an aqueous phase composed mainly of water were discharged at a rate respectively of 32.0 g/h and 81.3 g/h from the liquid-liquid separator 17 equipped'at the column top portion. The organic phase was recycled to the acetic acid-water recovery column 10, and the aqueous phase was recycled to the first alcohol purification column 15. The bottom liquid of the first alcohol purification column 15 (composed of BzOH: 92.7%, and water: 7.3%) was introduced continuously to the second alcohol purification column 16, and distillation was' conducted at a pressure of 13.3 kPa (100 Torr) to obtain BzOH of 99.9% purity from the column bottom at a rate of 63.4 g/h and a distillate composed mainly of water from the column top at a rate of 5.1 g/h. This distillate was recycled to the first alcohol concentration column 15. Example 6 Into a flow reactor equipped with a temperature controller, was packed a sulfonic acid type cation exchange resin (based on a styrene-divinylbenzene copolymer) having a divinylbenzene content (DVB content) shown in Table 2. To this reactor, benzyl acetate and water as the starting materials (mole ratio of water/benzyl acetate = 63/37) was fed at 80°C at LHSV of 0.45 h -1 to cause reaction. The conversion of the benzyl acetate (BC) and the selectivity of the benzyl alcohol (BS) were measured by gas chromatography. The results are shown in Table 2. The reaction was continued for 1,000 hours under the above conditions, and the activity deterioration coefficient (rate of drop of benzyl acetate conversion per hour) was measured, but no activity deterioration was observed. Examples 7-8 and Comparative Examples 1-4 Into a flow reactor equipped with a temperature controller, was packed a sulfonic acid type cation exchange resin (based on a styrene-divinylbenzene copolymer) having a divinylbenzene content (DVB content) shown in Table 2 such that the amount of the sulfonic acid group is the same as in Example 6. The reaction was conducted in the same manner as in Example 6. The conversion ratio of the benzyl acetate (BC) and the selectivity of the benzyl alcohol (BS) were measured by gas chromatography in the same manner as in Example 6. The results are shown collectively in Table 2. In Comparative Example 4, the activity deterioration coefficient was measured by continuing the reaction for 1,000 hours under the same reaction as in Example 6, and was found to be 0.002% per hour. Example 9 Into a flow reactor equipped with a temperature controller, was packed 22.07 g of Amberlist 31 Wet (Japan Organo Co., Ltd.) which is a sulfonic acid type cation exchange resin based on a styrene-vinylbenzene copolymer of divinylbenzene unit content of 4%. To this reactor, the starting materials shown in Tablet 3 were fed at 80°C at LHSV of 0.45 h -1 to cause reaction. The reaction product was analyzed quantitatively by gas chromatography, from which were calculated the conversion (BC) of the benzyl acetate (BzOAc), the selectivity (BS) of the benzyl alcohol, and the reaction productivity (STY; space time yield) represented by grams of benzyl alcohol per liter of the wet resin per hour. Table 3 shows the results. Table 3 also shows the mole ratio of dibenzyl ether (BzOBz), a reaction by-product, to the benzyl alcohol, the weight ratio (W/B) of water to benzyl alcohol in the produced liquid which is an index of the load in the benzyl alcohol separation-recovery process, and the estimated equilibrium conversion. Examples 10-12 and Comparative Examples 5-7 The hydrolysis reaction was conducted in the same manner as in Example 9 except that the composition of the starting materials fed to the reactor was changed as shown in Table 3. The results are shown in Table 3 collectively. Example 13 The hydrolysis reaction was conducted in the same manner as in Example 9 except that the cation exchange resin was replaced by XT-2071 (Japan Organo Co., Ltd.) which is a sulfonated acid type cation exchange resin based on a styrene-vinylbenzene copolymer of divinylbenzene unit content of 7% in an equivalent amount of the sulfonated acid group; the composition of the starting materials was as shown in Table 3; and LHSV was 0.39 h -1 . The results are shown in Table 3.

Claims: A process for producing benzyl alcohol of high purity by hydrolysis of benzyl acetate in the presence of a solid acid catalyst, comprising steps of feeding benzyl acetate, water, and acetic acid to a hydrolysis reactor packed with a solid acid catalyst to cause reaction to obtain a liquid reaction mixture containing benzyl acetate, water, benzyl alcohol, and acetic acid; introducing the liquid reaction mixture to an acetic acid-water recovery column to separate the liquid reaction mixture by distillation into a column top distillate composed of acetic acid and water and a column bottom liquid composed mainly of benzyl alcohol and benzyl acetate; recycling the column top distillate of the acetic acid-water recovery column, after removing most of the acetic acid by an acetic acid-water separation column; to the hydrolysis reactor, wherein the solid acid catalyst is a sulfonated styrene-divinylbenzene copolymer having a divinylbenzene unit content of less than 8% by weight, and wherein the starting material comprises benzyl acetate (x% by weight), water (y% by weight), and acetic acid (z% by weight) in the range: 1/9 ≤ y/x ≤ 3/2, and 0 ≤ z ≤ 30 (x + y + z = 100). The process according to claim 1, wherein the column bottom liquid of the acetic acid-water recovery column is distilled in an alcohol concentration column to obtain a column top fraction composed of benzyl alcohol and benzyl acetate and a column bottom fraction composed of benzyl acetate, and the column bottom fraction of the alcohol concentration column is recycled to the hydrolysis reactor. The process according to claim 2, wherein benzyl alcohol is obtained from the column top fraction of the alcohol concentration column. The process according to claim 2, wherein the column top fraction of the alcohol concentration column is mixed with additional water, and the mixture is distilled by a first alcohol purification column to obtain a column top distillate composed of benzyl acetate, benzyl alcohol, and water, and a column bottom liquid composed of water-containing benzyl alcohol; the column top distillate of the first alcohol. concentration is separated by a liquid-liquid separator into an organic phase composed of benzyl acetate and benzyl alcohol and an aqueous phase; the organic phase is recycled to the acetic acid-water recovery column or the hydrolysis reactor; and the aqueous phase is recycled to the first alcohol purification column. The process according to claim 4, wherein the column bottom liquid of the first alcohol purification column is distilled by a second alcohol purification column to obtain benzyl alcohol from the column bottom; and the column top distillate composed of water and benzyl alcohol is recycled to the first alcohol purification column. The process according to claim 2, wherein the column top distillate of the alcohol concentration column is distilled with glycerin by an extractive distillation column to obtain a column top fraction composed of benzyl acetate and benzyl alcohol, and a column bottom fraction composed of glycerin-containing benzyl alcohol; the column top fraction of the extractive distillation column is mixed with additional water, and is separated by a liquid-liquid separator into an organic phase composed of benzyl acetate and benzyl alcohol and an aqueous phase; the organic phase is recycled to the hydrolysis reactor; and the aqueous phase is recycled to the extractive distillation column. The process according to claim 6, wherein the column bottom fraction obtained by the extractive distillation column is distilled by a product column to obtain benzyl alcohol from the column top; and a column bottom fraction mainly composed of glycerin is recycled to the extractive distillation column. The process according to claim 1, wherein the starting material has a composition in the range: 1/9 ≤ y/x ≤ 2/3, and 0 ≤ z ≤ 20.

Inventors: HANAYA MAKOTO, HATTORI AKITAKA, HORI TAKASHI, IKUMI SHUNYA, MIYAKE TAKANORI, MIZUI NORIMASA, NAGIRA NOBUO, OKADA TAKASHI, HANAYA, MAKOTO, HATTORI, AKITAKA, HORI, TAKASHI, IKUMI, SHUNYA, MIYAKE, TAKANORI, MIZUI, NORIMASA, NAGIRA, NOBUO, OKADA, TAKASHI
Applicants: TOSOH CORP, TOSOH CORPORATION
Application year: 1996
Main classification: C07C67
IPC codes: C07C69, C07C67, C07C27, C07C29