RU2158729C1 - Method of preparing phthalic acid diethyl ester - Google Patents

Abstract

FIELD: organic chemistry, more particularly preparation of diethyl phthalate. SUBSTANCE: method comprises reacting phthalic anhydride and ethyl alcohol in film mode in the presence of solid aluminium γ oxide catalyst impregnated with sulfuric anhydride in amount of at least 15% at 120-130 C. EFFECT: simplified process. 3 cl, 1 dwg, 1 ex, 1 tbl

Description

 The invention relates to the field of organic chemistry, in particular to the production of carboxylic acid esters containing an esterified carboxyl group bonded to a carbon atom of a six-membered aromatic nucleus, namely to the production of phthalic acid diethyl ester - diethyl phthalate. Diethyl phthalate is widely used as a plasticizer for plastics, solvents and in various fields of perfumery, cosmetics and medicine.

 Known methods for producing diethyl phthalate by the interaction of ethyl alcohol with phthalic anhydride, or phthalic acid or its acid chloride.

A known method of producing diethyl phthalate by the interaction of phthalic anhydride with ethyl alcohol in the presence of a sulfuric acid catalyst [1]. The process is carried out by passing alcohol vapors through a reaction mixture of phthalic anhydride and sulfuric acid at a temperature of 120-130 ^o C. In this case, diethyl phthalate remains in the molten phthalic anhydride, and water vapor and vapors of unreacted ethyl alcohol are condensed and collected in the form of an aqueous solution. The resulting diethyl phthalate contains from 3 to 5% sulfuric acid. The crude diethyl phthalate is then washed from sulfuric acid and dried. The disadvantages of this method are:
high consumption of ethyl alcohol, the return of which to the process is carried out after dehydration;
washing crude diethyl phthalate from sulfuric acid;
as a waste, a large amount of wastewater.

 The objective of the present invention is to identify more optimal conditions for the esterification of phthalic anhydride with vapors of ethyl alcohol, the creation of a simpler process used in industrial production with great economic effect.

To solve this problem, it is proposed to carry out the esterification of phthalic anhydride with ethyl alcohol vapors in film mode in the presence of a solid catalyst - granular γ-alumina impregnated with sulfuric anhydride of at least 15%. The process is carried out at a temperature of 120-130 ^o C.

 The use of a solid catalyst - granular γ-alumina impregnated with sulfuric anhydride allows the use of a solid catalyst at the same time as a nozzle, which provides the interaction of phthalic anhydride with ethyl alcohol in film mode. This avoids the disadvantages that are present when using a liquid catalyst - concentrated sulfuric acid in the prototype method. The proposed technical solution allows to simplify the process of obtaining diethyl phthalate and make it more economical in industrial production while obtaining high final results of marketable products.

 The method worked out in pilot production with continuous operation.

Example
To carry out the method of producing diethyl phthalate by reacting phthalic anhydride with ethanol in the presence of a solid catalyst - granular γ-Al ₂ O ₃ impregnated with sulfuric anhydride, an esterification catalyst is preliminarily prepared.

Granular γ-Al ₂ O ₃ , previously dried and free from dust by dispersion, is placed in a cylindrical apparatus. A controlled stream of dry air containing 6-7% wt. Is passed through an apparatus containing γ-Al ₂ O ₃ . sulfuric anhydride. The amount of air flow is determined from the calculation of the total absorption of sulfuric anhydride by aluminum oxide in a mass ratio of Al ₂ O ₃ : SO ₃ = 15: 1. The catalyst thus prepared is discharged in a dry atmosphere, weighed and loaded into a column reactor for etherification, which is shown in the drawing.

The cylindrical reactor is made of stainless steel, the inner diameter of the reactor is 6.0 cm. A catalyst 60 cm high is loaded into the reactor, the volume of the catalyst located in the reactor is 1.7 dm ³ . In the reactor, in its upper part, through the nozzle A, molten phthalic anhydride is metered (T ^o = 130-140 ^o C). Ethyl rectified alcohol is dosed under a layer of molten phthalic anhydride. The required temperature in the reactor (130 ± 10 ^o C) is supported by electric heaters (windings) located on the outer wall of the reactor. The resulting vapors of ethyl alcohol interact with molten phthalic anhydride when it flows through the packed catalyst in the form of a film. The process proceeds according to the reaction:
C ₆ H ₄ (CO) ₂ O + 2C ₂ H ₅ OH ---> C ₆ H ₄ (COOC ₂ H ₅ ) ₂ + H ₂ O
The resulting diethyl phthalate flows into the lower part of the reactor and, after cooling, enters the commercial product collector, and the vaporous reaction products — water and unreacted ethyl alcohol — are removed from the reactor through the nozzle D located in the lower part of the reactor.

 The film mode in the form of a falling film on the surface of the catalyst nozzle provides the best contact of reacting components in two phases, and the free withdrawal of liquid and gaseous reaction products. For the melting of phthalic anhydride, its dosing, the dosing of ethyl anhydride, and the condensation of vaporous reaction products, standard equipment and instruments are used.

 For comparison, experiments were carried out in the same reactor on the production of diethyl phthalate by the interaction of phthalic anhydride with ethanol in the presence of a catalyst - granular γ-alumina impregnated with sulfuric anhydride in a bubbling mode.

 In the reactor (see drawing), to create a bubbling regime, the flow of reagents was changed to ascending. The molten phthalic anhydride and ethyl alcohol were metered through nozzles C and D located at the bottom of the reactor. Through the nozzle A and the nozzle B located in the upper part of the reactor, the liquid reaction mixture, water vapor and ethyl alcohol were withdrawn.

 During the esterification process, the rate and time of dosing of phthalic anhydride and ethyl alcohol was determined using a metering pump and hours. Sampling of the reaction mixtures was carried out after passing through the reactor 1.5 l of the total reaction mixture of phthalic anhydride and ethyl alcohol to ensure that the process goes to stationary mode. The content of the components of the reaction mixture was determined by gas-liquid chromatography (GLC). The technological parameters of the experiments are presented in the table.

The table shows that the esterification of phthalic anhydride with ethyl alcohol in the presence of a solid catalyst - granular γ Al ₂ O ₃ impregnated with sulfuric anhydride in the film mode has significant advantages over the bubbling mode according to the final results of the process: the yield of diethyl phthalate, its content in the finished product, as well as ethyl alcohol in the condensate.

 The proposed method for the production of diethyl phthalate is simpler, more technological and economical.

Sources:
1. Oil and fat industry, 1985, N 5 "Obtaining methyl and ethyl esters of high-boiling carboxylic acids."

Claims (3)

 1. A method of producing phthalic acid diethyl ester by esterification of phthalic anhydride with ethyl alcohol in the presence of a catalyst at an elevated temperature, characterized in that the reaction of phthalic anhydride with ethyl alcohol is carried out in film mode, granular γ-alumina impregnated with sulfuric anhydride is used as a catalyst. 2. The method according to p. 1, characterized in that the interaction of phthalic anhydride with ethyl alcohol is carried out at 120 - 130 ^o C.  3. The method according to claim 1, characterized in that the granular γ-alumina contains at least 15% sulfuric anhydride.

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