JPH0459307B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for producing esters, and more particularly to a method for producing esters with high yield using a gas separation membrane having water vapor selective permeability. (Prior art) Methods for synthesizing esters include the reaction of a carboxylic acid with an alkyl halide in the presence of an acid catalyst;
Although several reactions are known, such as the reaction of acid chlorides or acid anhydrides with alcohols or phenols, the most common is the Fischer method, in which a carboxylic acid and alcohol are heated under reflux under an acid catalyst. Although this reaction is an equilibrium reaction, the equilibrium constant is relatively small, and in order to make this reaction useful in synthetic chemistry, methods must be used to increase the amount of ester produced. This can be done by using an excess of one of the reactants in the equilibrium reaction, or by removing water as the reaction progresses. In the synthesis of esters, attempts are generally made to increase the yield of esters by using an excess of alcohol;
The yield of ester cannot be said to be sufficient, and if water, which is a product, can be efficiently removed from the reaction system,
Great advantages can be obtained in the production of esters. As a method for removing water from the system, a method using azeotropic distillation is conventionally known. This method involves adding a third component such as benzene or toluene to the reaction system, and
This is a method in which an azeotropic mixture of components is formed, a vapor phase of the azeotropic composition is condensed, and then an alcohol layer containing water and an organic layer are separated. However, according to this method, it is necessary to recover and recycle the entraining agent added as the third component, and the cost increase in this step poses a major obstacle in practical use. Further, in U.S. Pat. No. 2,956,070, Jennings et al. attached a vinyl acetate membrane to the reaction solution in the esterification reaction of acetic acid and n-butanol, and removed the generated water by pervaporation. discloses a method to do so. In the pervaporation method, a liquid mixture is placed on one side of the membrane, and the pressure on the other side is reduced or an inert gas is flowed to maintain a low vapor pressure, and the pressure difference allows the liquid to permeate. This method performs separation by evaporation, and many studies have been conducted to obtain membranes with excellent separation coefficients and permeation rates as a separation and condensation method for liquid mixtures. It has not yet been put into practical use. Regarding application to esterification reactions, the pervaporation method is disadvantageous in terms of energy because it is a separation operation that involves phase changes. However, there are major problems such as the durability of the membrane and the regeneration of the membrane due to the adhesion of the produced ester to the membrane, so it has not been put to practical use on an industrial scale. The purpose of the present invention is to provide a method for producing esters in high yield and in a short time by selectively separating water vapor from the water-alcohol mixed vapor produced during the synthesis of esters from carboxylic acids and alcohols. There is a particular thing. Another object of the present invention is to provide a method that enables an esterification reaction without a catalyst. Furthermore, another object of the present invention is to provide a method that enables the reduction of alcohol usage and the recovery and reuse of alcohol. (Means for solving the problem) The method for producing an ester of the present invention is a method for producing an ester in which a carboxylic acid and a water-soluble alcohol are reacted.
This method is characterized by separating water vapor from alcohol mixed vapor. The carboxylic acid used in the present invention is not particularly limited as long as it is generally known; for example,
Examples include aliphatic carboxylic acids, aromatic carboxylic acids, and alicyclic carboxylic acids having a carbon number of _C2 to _C45 . Also,
The number of carboxyl groups contained in these does not need to be one, and two or more polycarboxylic acids can also be used. These may be used alone or in a mixed system of two or more. Furthermore, oxidized paraffin and petrolatum oxide may be used together, if necessary. The water-soluble alcohol used in the present invention is not particularly limited as long as it is generally known;
For example, methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, allyl alcohol, ethyl cellosolve, methyl cellosolve, ethanolamine, ethylethanolamine, ethylene glycol, propylene glycol, glycerin, furfuryl alcohol. These can be used singly or in a mixed system of two or more. The molar ratio of carboxylic acid to alcohol can vary over a wide range. Preferably (former/latter) 1/1 to 1/1
It is 0. As the catalyst, a strong acid such as p-toluenesulfonic acid or an ion exchange resin having a sulfonic acid group is used. The separation membrane used in the present invention exhibits high permeability to water vapor, alcohol, carboxylic acid,
It is necessary to be as impermeable to esters as possible. Furthermore, since the water-alcohol mixed vapor produced in the esterification reaction is at a high temperature, heat resistance is required. Examples of the material for the separation membrane include inorganic porous membranes having micropore diameters of 20 to 10 Å that can effectively separate water and alcohol. Methods for producing such inorganic porous membranes include porous glass produced by utilizing the phase separation phenomenon of sodium borosilicate glass, porous silica produced by the sol-gel method produced by hydrolysis of metal alkoxide, or Examples include films such as alumina. These membranes can be used alone or supported on porous ceramics with larger pore diameters. As the organic polymer material, cellulose, chitin, alginic acid, or polyimide-based polymers are used. Although these are conventionally known, for the purpose of further increasing water vapor permeability, for example,
The polymer may have a functional group such as a hydroxyl group, a carboxyl group, or a sulfone group as it is, or may be modified by introducing a compound having these functional groups into the main chain, side chain, or end of the polymer. These membranes are used in the form of a flat membrane, a tubular shape, or a hollow fiber, but they may also be in the form of a composite membrane with the above-mentioned inorganic material, for example, an organic polymer membrane supported on an inorganic layer. (Effects of the Invention) According to the present invention, in addition to being able to synthesize esters with a yield that greatly exceeds the equilibrium value of the esterification reaction, the present invention has various advantages not found in conventional techniques. For example, it becomes possible to reduce the amount of alcohol used, use hydrous alcohol, reuse alcohol, etc. Furthermore, since the reaction time can be significantly shortened, coloring of the ester can be prevented, and high-quality products can be manufactured. EXAMPLES Below, the present invention will be explained in more detail with reference to Examples and Comparative Examples. (Example) The acids used in the esterification reaction were oleic acid (manufactured by Wako Pure Chemical Industries, Ltd., acid value: 205.2), NPS-L-70 (trade name, manufactured by Nippon Seiwa Co., Ltd., oxidized paraffin, acid value: 74). ),
There were three types: OX-1749 (trade name, manufactured by Nippon Seiro Co., Ltd., betrolatum oxide, acid value: 33), and the alcohol was ethanol. The yield of the esterification reaction is determined by the determination of carboxylic acid by JIS method (acid value test method: JIS K-3504) and the determination of the produced ester (saponification value test method: standard oil and fat analysis test method).
I asked for it from. As a catalyst, P-toluenesulfonic acid was used in an amount of 1% by weight based on the weight of ethanol. In the separation experiment, an acid and alcohol mixture was used as the feed liquid, esterification was carried out at 85°C, the downstream side was reduced in pressure with a vacuum pump, and the permeate was trapped in liquid nitrogen to determine its weight and composition. The permeation composition was determined by gas chromatography. FIG. 1 shows an outline of a vapor separation apparatus equipped with a gas separation membrane used in the present invention. The vapor separation membrane is a cylindrical multi-pore AVD (trade name: Ceramic Porous Tube, manufactured by Mitsui Kentoishi Co., Ltd., average pore diameter: approximately 1 μm) with a length of 10 cm and a diameter of 1 cm.The outer surface of the membrane is coated with alumina gel porous material using the sol-gel method. A membrane (average pore size: approximately 50 Å) was attached as a support, and various separation membranes were attached on top of this by the dip method. Note that a flat membrane reactor was used for pervaporation separation conducted as a comparative experiment. Example 1 A mixture of oleic acid, ethanol and P-toluenesulfonic acid was charged into a reaction vessel and esterification was carried out at 85°C while pervaporation separation as a comparative example or vapor separation as an example under the same conditions. I performed the operation. As a separation membrane, 0.8 of chitosan acetate (Flownatsuk #250 manufactured by Kyowa Yushi Co., Ltd.) was used.
A chitosan membrane that was deacetylated with a 4% sodium hydroxide aqueous solution after air-drying the wt% aqueous solution was used. Figure 2 shows the change in reaction rate over time, and the values of permeation rate and separation coefficient in each separation experiment are shown in the table.
The molar ratio in the figure indicates the molar ratio of oleic acid:ethanol.

[Table] As is clear from Figure 2, when a membrane was attached, an improvement in the reaction rate was observed compared to a blank experiment in which no membrane was attached, and the effect was particularly remarkable in steam separation. However, after the chitosan membrane was used for pervaporation, it became brittle and could not be reused. Example 2 A vapor separation experiment in an oleic acid-ethanol esterification reaction was conducted using a polyimide membrane as a separation membrane. The polyimide membrane was obtained by using a dichloroethane solution of Ultem (trade name, manufactured by General Electric Company), immersing the support in this solution, and air-drying it. Figures 3 and 4 show changes over time in the reaction rate and the amount of water produced and permeated. The molar ratio in the figure indicates the molar ratio of oleic acid:ethanol. The equilibrium constant and reaction rate constant of oleic acid and ethanol at 85°C, determined from a blank experiment, are as follows. Equilibrium constant: 2.54, reaction rate constant: k ₁ =
1.20×10 ^-2 M ^-1・h ^-1 , k ² =4.73×10 ^-2 M ^-1 , h ^-1 . According to water vapor selective separation using a polyimide membrane,
A reaction rate far exceeding the equilibrium value of the ester reaction was obtained. The membrane separation effect was observed both when the molar ratio of oleic acid and ethanol was 1:3 and 1:2, and the reaction rate reached almost 100%. Figures 5 and 6 show the results when OX-1749 and NPS-L-70 were used. As in the case of oleic acid, the reaction rate can be improved by simultaneously using membrane separation using a water vapor selective permeation membrane in the ester reaction. Example 3 A vapor separation experiment in an olefinic acid-ethanol esterification reaction was conducted using a water glass membrane as a separation membrane. The water glass membrane was obtained by immersing the support in an 8% by weight water glass (sodium silicate) solution and air drying. Figure 7 shows the change in reaction rate over time. Similar to the case of chitosan membrane or polyimide membrane, the effect of improving the ester reaction yield was observed.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of a vapor separation device equipped with a gas separation membrane used in the present invention, Figure 2 is a diagram showing changes in reaction rate over time, and Figure 3 is a diagram showing changes in reaction rate over time. Figure 4 is a diagram showing the amount of permeation and production of water, Figure 5 is a diagram showing similar results when using OX-1749, and Figure 6 is a diagram showing the same results when using OX-1749.
FIG. 7 is a diagram showing similar results when NSP-L-70 was used, and FIG. 7 is a diagram showing changes in reaction rate over time. 1... Esterification reaction container, 2... Mantle heater, 3... Band heater, 4... Thermometer,
5... Separation membrane, 6... Condenser, 7... Cold trap, 8... Vacuum pump, 9... Vacuum gauge.

Claims (1)

[Claims] 1. A method for producing an ester by reacting a carboxylic acid with a water-soluble alcohol, the method comprising: separating water vapor from the generated water/alcohol mixed vapor using a gas separation membrane. . 2. The method according to claim 1, wherein the gas separation membrane is a water vapor selectively permeable membrane. 3. The method according to claim 1, wherein the gas separation membrane is an inorganic porous membrane or a cellulose, chitin, alginic acid, or polyimide polymer membrane.