JPS60197639A - Preparation of dimethyl carbonate - Google Patents

Abstract

PURPOSE:In preparation of dimethyl carbonate through methyl formate by reacting phosgene with methanol, to carry out the reaction in a short time in high purity, by circulating the unreacted alcohol and methyl chloroformate by distillation operation, using them. CONSTITUTION:Excess methanol is reacted with phosgene at a temperature <= the boiling point of phosgene, to obtain a reaction product comprising methyl chloroformate as a main product. The unreacted alcohol and methyl chloroformate, distillates at the top of column at the final stage, are recycled, mixed with the reaction product, a molar ratio of methanol to methyl chloroformate is made into 1.1-1.3:1, the temperature is raised to 50-65 deg.C, and they are mixed, to obtain dimethyl carbonate. The reaction product is further distilled, high- purity dimethyl carbonate is obtained from the bottom of column, an azeotropic mixture of methanol and dimethyl carbonate and methyl chloroformate are recovered from the top of column, and they are circulated to the previous stage. EFFECT:Since the reaction time of the second process can be shortened, a small- sized reactor will suffice.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the production of dimethyl carbonate using phosgene and methanol as raw materials, and provides a novel process that can obtain highly pure dimethyl carbonate in a short time and can be carried out industrially advantageously. It is something.

Dimethyl carbonate is an industrially very useful substance that is used as a solvent for the synthesis of agricultural chemicals and pharmaceutical raw materials, and for natural resins.

Several methods have been proposed for producing dimethyl carbonate, including synthesis using carbon oxide, methanol, and oxygen, but these have problems such as high reaction pressure and extremely slow reaction rate, making them industrially unsuitable. It is difficult to say that it is a manufacturing method.

It is also well known that dimethyl carbonate is synthesized via methyl chloroformate by the reaction of phosgene and alcohol (for example, RlQ, Brewster,
Written by W, E, Mc, Ewen, Koji Nakanishi Blue Star Organic Chemistry (1st) P, 28B Tokyo Kagaku Doujin).

However, this method also has the following problems. In other words, it is relatively easy to synthesize methyl chloroformate from phosgene and methanol, but in the reaction of methyl chloroformate and methanol, the reaction rate is fast at the beginning of the reaction, but
As the reaction progresses, it slows down exponentially, and an extremely long reaction time is required to achieve a conversion rate of 95% or more of methyl chloroformate.

To address this difficulty, 1 Japanese Patent Application Laid-Open No. 50-85528
He proposes a strategy of adding methanol once the reaction has progressed to a certain extent. However, although this method slightly improves the reaction time, it still requires a long reaction time to achieve a conversion rate of 95% or more of methyl coolformate. Furthermore, although the unreacted amount of methyl coolformate was reduced, a large amount of unreacted methanol coexisted in dimethyl carbonate, and if 1 was used as it was, it could not be said that highly pure dimethyl carbonate was obtained.

In order to overcome these conventional difficulties and establish a method for industrially advantageous production of highly pure dimethyl carbonate in a short period of time, the present invention was achieved as a result of intensive studies.

To explain the present invention in detail, as the raw material methanol, industrial methanol is usually used, but in consideration of the utilization rate of phosgene, methanol with a low water content is preferable. As the phosgene, ordinary phosgene obtained by reacting -carbon oxide and chlorine in the presence of an activated carbon catalyst is used.

In the present invention, dimethyl carbonate is produced via methyl formate through the reaction of phosgene and methanol, and highly purified dimethyl carbonate is obtained by distillation. Each step of the present invention will be explained in detail.

1st step Phosgene is introduced into the methanol present in the reactor.

At this time, in order to increase the utilization rate of phosgene for the reaction, it is preferable that phosgene be introduced in liquid form, that methanol be constantly in molar excess relative to phosgene, and that the reaction temperature be below the boiling point of phosgene.

Second Step The product from the first step and the overhead effluent from the sixth step are mixed. At this time, the molar ratio of methyl chloroformate and methanol is such that the conversion rate of methyl chloroformate is 85 to 9596.
It is preferable to set the ratio to be 1:1.1 to 1.6 in view of the need to shorten the reaction time as much as possible and to minimize the amount of excess methanol.

Note that dimethyl carbonate and methanol are azeotropic, so if there is a large amount of unreacted alcohol, excess dimethyl carbonate will flow out from the top of the column together with methanol and methyl chloroformate during distillation, reducing the production of dimethyl carbonate per unit time. The combination of methanol and methyl chloroformate is of great importance, since it requires additional energy and is economically disadvantageous as the amount decreases. Next, the mixed solution is heated and mixed. In order to obtain a satisfactory reaction rate at this time, the reaction temperature is preferably 50' to 70'C.

Third step: The reaction solution containing dimethyl carbonate as a main component obtained in the second step is led to a distillation column. As the distillation column, a normal distillation apparatus such as a packed column or a tray column is used. Then, unreacted methanol, methyl sulfurate, and dimethyl carbonate are separated by distillation.

Note that methanol and dimethyl carbonate form an azeotropic composition. Therefore, during distillation, an azeotropic composition of methanol and dimethyl carbonate and methyl pyroformate are condensed and recovered from the top of the column, and dimethyl carbonate is obtained from the bottom of the column. The recovered material obtained from the top of the column is recycled and supplied to the second step.

By recycling unreacted alcohol and methyl chloroformate in this way, the reaction time in the second step can be shortened compared to the conventional time, and at the same time, the reaction time of the second step can be shortened compared to the conventional time. It is difficult to obtain pure dimethyl carbonate in a short time. Therefore,
As the reaction time of the second step is shortened, the capacity of the reaction vessel is also much smaller than that of the conventional method, and it can be said that this method is extremely advantageous industrially. - The present invention will be explained in more detail below with reference to Examples. Note that % in the examples indicates weight %.

Example 3 with Dimroth, dropping funnel, thermometer and stirrer
Add methanol 59.35J to the 00d 4 flask.
I (1,855 mol) was charged, and phosgene 102.82F was added at a rate of 11/min while stirring. At this time, the reaction solution was continued to be cooled to below 0°C, and stirring was continued for 3 hours at 0°C after the addition.

After that, this liquid was collected from the top of the column during distillation.26
．． 941C composition MeOH40,996, methyl chloroformate 28.0%, dimethyl carbonate 17.596, HCJ
1 M, 5%) was added. After mixing, the total weight of the liquid is 1
81.25#, and the composition is MeOH21,196,
The molar ratio of methanol to methyl chloroformate is 1.21.

Next, while stirring, the temperature of the reaction solution was gradually raised until it reached a boiling state, and the mixture was stirred for 2 hours. 109.4 # of products containing dimethyl carbonate as the main component were obtained, and the composition of this liquid was 10,096% methanol, 6.91% methyl chloroformate,
Dimethyl carbonate 78.26';l;, HCJ 4.759
6, and the selectivity of dimethyl carbonate based on phosgene was 88°596. Furthermore, this liquid was poured into a distillation column (diameter 50 d, distillation stage height 50 degrees, recovery stage height 45 degrees,
A pot capacity of 20 filled with magnetic Raschig rings 5 x 5 in the recovery stage and magnetic Raschig rings 3111 x 5 in the distillation stage.
Rectification was performed in a glass distillation column (0d glass distillation column). And from the pot, dimethyl carbonate with a purity of 99.596 or higher 89.51
1 was obtained, and 26.94# of a mixture of methanol, methyl chloroformate, and dimethyl carbonate was recovered from the top of the column.

Patent applicant Mitsubishi Gas Chemical Co., Ltd. Representative Kazuyoshi Nagano

Claims (1)

[Claims] In producing dimethyl carbonate by reacting methanol and phosgene, (1) An excess molar amount of methanol is allowed to coexist with phosgene at a temperature below the boiling point of phosgene, and the reaction is performed to produce a product mainly containing methyl coolformate. (2) The product obtained from the first step and the overhead effluent obtained from the third step are mixed, and the molar ratio of methanol and methyl chloroformate is adjusted to 1.1 to 1.5: 1 and 50-65℃
The main component liquid of dimethyl carbonate obtained in the second step (3) $2 is distilled, and an azeotrope of methanol and dimethyl carbonate and methyl coolformate are distilled from the top of the column. 6th step (4) of collecting and obtaining dimethyl carbonate from the bottom of the column; Includes each step of circulating and supplying the azeotrope of methanol and dimethyl carbonate and methyl cool formate recovered from the top of the column to the second step. Method for producing dimethyl carbonate.