Process for continuously producing dialkyl carbonate and diol

Details Process for continuously producing dialkyl carbonate and diol Process for continuously producing dialkyl carbonate and diol

2001-06-11

2002-11-12

Solola, T. A. (Department: 1626)

Organic compounds -- part of the class 532-570 series

Organic compounds

Carbonate esters

C568S619000, C568S852000

Reexamination Certificate

active

06479689

ABSTRACT:

BACKGROUND OF THE INVENTION
The instant application is a 371 of PCT/JP00/01284 filed Mar. 3, 2000.
1. Field of the Invention
The present invention relates to a method for continuously producing a dialkyl carbonate and a diol. More particularly, the present invention is concerned with a method for continuously producing a dialkyl carbonate and a diol from a cyclic carbonate and an aliphatic monohydric alcohol, comprising: (1) continuously feeding a cyclic carbonate and an aliphatic monohydric alcohol to a continuous multi-stage distillation column, and continuously effecting a transesterification between the cyclic carbonate and the aliphatic monohydric alcohol in the presence of a transesterification catalyst in the multi-stage distillation column, while continuously withdrawing a low boiling point mixture in a gaseous form containing the produced dialkyl carbonate and the unreacted aliphatic monohydric alcohol from an upper portion of the multi-stage distillation column and continuously withdrawing a high boiling point mixture in a liquid form containing the produced diol and the unreacted cyclic carbonate from a lower portion of the multi-stage distillation column, and (2) continuously feeding the high boiling point mixture withdrawn from the lower portion of the multi-stage distillation column to a continuous etherification reactor, to thereby effect a continuous etherification reaction between the unreacted cyclic carbonate and a part of the produced diol and produce a chain ether and carbon dioxide, while continuously withdrawing the resultant etherification reaction mixture containing the remainder of the diol produced in step (1) and the produced chain ether from the continuous etherification reactor, wherein the etherification reaction mixture has a cyclic carbonate content of from 0 to 10
−2
in terms of the weight ratio of the cyclic carbonate to the diol. By the method of the present invention, in a continuous process for producing a dialkyl carbonate and a diol from a cyclic carbonate and an aliphatic monohydric alcohol, a high purity diol can be easily obtained.
2. Prior Art
With respect to the method for producing a dialkyl carbonate and a diol by reacting a cyclic carbonate with an aliphatic monohydric alcohol, various proposals have been made. Most of those proposals relate to the development of catalysts for the above reaction. Examples of such catalysts include alkali metals or basic compounds containing alkali metals (see U.S. Pat. No. 3,642,858, Unexamined Japanese Patent Application Laid-Open Specification No. 54-48715 (corresponding to U.S. Pat. No. 4,181,676)), tertiary aliphatic amines (see Unexamined Japanese Patent Application Laid-Open Specification No. 51-122025 (corresponding to U.S. Pat. No. 4,062,884)), thallium compounds (see Unexamined Japanese Patent Application Laid-Open Specification No. 54-48716 (corresponding to U.S. Pat. No. 4,307,032)), tin alkoxides (see Unexamined Japanese Patent Application Laid-Open Specification No. 54-63023), alkoxides of zinc, aluminum and titanium (see Unexamined Japanese Patent Application Laid-Open Specification No. 54-148726), a mixture of a Lewis acid with a nitrogen-containing organic base (see Unexamined Japanese Patent Application Laid-Open Specification No. 55-64550), phosphine compounds (see Unexamined Japanese Patent Application Laid-Open Specification No. 55-64551), quaternary phosphonium salts (see Unexamined Japanese Patent Application Laid-Open Specification No. 56-10144), cyclic amidines (see Unexamined Japanese Patent Application Laid-Open Specification No. 59-106436 (corresponding to U.S. Pat. No. 4,681,967, EP 110629, and DE 3366133G)), compounds of zirconium, titanium and tin (see Unexamined Japanese Patent Application Laid-Open Specification No. 63-41432 (corresponding to U.S. Pat. No. 4,661,609, EP 255252 and DE 3781742G)), a solid, strongly basic anion-exchanger containing a quaternary ammonium group (see Unexamined Japanese Patent Application Laid-Open Specification No. 63-238043), a solid catalyst selected from the group consisting of a tertiary amine- or quaternary ammonium group-containing ion-exchange resin, a strongly acidic or a weakly acidic ion-exchange resin, a silica impregnated with a silicate of an alkali metal or an alkaline earth metal, and a zeolite exchanged with ammonium ion (see Unexamined Japanese Patent Application Laid-Open Specification No. 64-31737 (corresponding to U.S. Pat. No. 4,691,041)), a homogeneous catalyst selected from the group consisting of tertiary phosphine, tertiary arsine, tertiary stibine, a divalent sulfur compound and a selenium compound (see U.S. Pat. No. 4,734,518).
With respect to the method for conducting the above-mentioned reaction between a cyclic carbonate and a diol, the below-mentioned four types of methods (1) to (4) have conventionally been proposed. Hereinbelow, explanation is made with respect to such methods (1) to (4), taking as an example the production of dimethyl carbonate and ethylene glycol by the reaction between ethylene carbonate and methanol, which is a representative example of reactions between cyclic carbonates and diols.
(1) A completely batchwise method (hereinafter referred to as “method (1)”).
(2) A batchwise method using a reaction vessel provided at an upper portion thereof with a distillation column (hereinafter referred to as “method (2)”).
(3) A liquid flow method using a tubular reactor (hereinafter referred to as “method (3)”).
(4) A reactive distillation method (hereinafter referred to as “method (4)”).
The completely batchwise method (1) is a method in which ethylene carbonate, methanol and a catalyst are fed to an autoclave as a batchwise reaction vessel, and a reaction is performed at a reaction temperature higher than the boiling point of methanol under pressure for a predetermined period of time (see U.S. Pat. No. 3,642,858, Unexamined Japanese Patent Application Laid-Open Specification No. 54-48715 (corresponding to U.S. Pat. No. 4,181,676, EP 1082 and DE 2860078G), Unexamined Japanese Patent Application Laid-Open Specification No. 54-63023, Unexamined Japanese Patent Application Laid-Open Specification No. 54-148726, Unexamined Japanese Patent Application Laid-Open Specification No. 55-64550, Unexamined Japanese Patent Application Laid-Open Specification No. 55-64551 and Unexamined Japanese Patent Application Laid-Open Specification No. 56-10144).
The batchwise method (2), using an apparatus comprising a reaction vessel provided at an upper portion thereof with a distillation column, is a method in which ethylene carbonate, methanol and a catalyst are fed to the reaction vessel, and a reaction is performed by heating the contents of the reaction vessel to a predetermined temperature. In this method, the produced dimethyl carbonate and methanol form a minimum boiling point azeotropic mixture having a boiling point of 63° C./760 mmHg. The boiling point of methanol per se is 64.6° C./760 mmHg. In this method, the reaction is performed by using an excess amount of methanol in the reaction system, so that the resultant reaction products can be separated into the azeotropic mixture and methanol, due to the difference in boiling point therebetween, by means of the distillation column provided at the upper portion of the reaction vessel. Specifically, a gaseous mixture of dimethyl carbonate and methanol, which is formed in the reaction vessel, is allowed to ascend inside the distillation column, and during the ascending of the gaseous mixture, the gaseous mixture is caused to separate into a gaseous azeotropic mixture and liquid methanol. Then, the gaseous azeotropic mixture is distilled from the top of the distillation column while the liquid methanol flows down to the reaction vessel so as to be recycled to the reaction system in the reaction vessel.
The liquid flow method (3) is a method in which a solution of ethylene carbonate in methanol is continuously fed to a tubular reactor to perform a reaction at a predetermined reaction temperature in the tubular reactor, and the resultant reaction mixture i

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