JP2003342236A - Method for producing dimethyl carbonate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an industrially advantageous method for producing dimethyl carbonate enabling an ordinary refining process to be adopted because of taking no third component in the system from the outside and also enabling unreacted raw materials to be efficiently reused. <P>SOLUTION: The method for producing dimethyl carbonate comprises the 1st step of carrying out a transesterification reaction between ethylene carbonate and methanol to obtain a reaction mixture comprising methanol, the dimethyl carbonate, ethylene glycol and ethylene carbonate, the 2nd step of carrying out an extractive distillation of the reaction mixture in the presence of the ethylene carbonate as extraction solvent to separate the methanol which is then recycled as a reaction material to the 1st step, the 3rd step of distilling and isolating the dimethyl carbonate from a high-boiling fraction recovered in the 2nd step, and the 4th step of separating the ethylene carbonate from the high-boiling fraction recovered in the 3rd step and then recycling the ethylene carbonate thus separated to the 1st step as another reaction material and concurrently recycling it as the extraction solvent to the 2nd step. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing dimethyl carbonate, and more particularly to an industrially advantageous method for producing dimethyl carbonate which employs a transesterification reaction.

[0002]

2. Description of the Related Art In the production of dimethyl carbonate by the transesterification reaction of ethylene carbonate and methanol, unreacted raw materials remain in the reaction solution because the reaction is an equilibrium reaction. Therefore, in an industrial process,
It is important how efficiently the unreacted raw materials are recovered from the reaction mixture and recycled.

[0003]

The present invention has been made in view of the above circumstances, and an object thereof is to provide an industrially advantageous method for producing dimethyl carbonate by a transesterification reaction between ethylene carbonate and methanol. Especially.

[0004]

As a result of intensive studies, the present inventor has obtained the following findings. That is, by skillfully utilizing the recovered unreacted ethylene carbonate, a part of it is utilized as an extraction solvent for the extractive distillation of unreacted methanol, which is difficult to separate because it forms a minimum azeotropic mixture with dimethyl carbonate, Then, if the residual ethylene carbonate is recycled together with the recovered unreacted methanol as a raw material for the transesterification reaction, a normal purification process can be adopted because there is no external incorporation of the third component, and The unreacted raw material can be efficiently reused, which is industrially advantageous.

The present invention has been completed based on the above findings, and its gist resides in a method for producing dimethyl carbonate, which is characterized by sequentially including the following first to fourth steps.

<First Step> Ethylene carbonate and methanol are transesterified to obtain a reaction mixture containing methanol, dimethyl carbonate, ethylene glycol and ethylene carbonate.

<Second Step> In the presence of ethylene carbonate as an extraction solvent, the reaction mixture obtained in the first step is subjected to extractive distillation to separate methanol, which is circulated as a reaction raw material in the first step.

<Third step> Dimethyl carbonate is separated by distillation from the high boiling point fraction recovered in the second step.

<Fourth Step> Ethylene carbonate is separated from the high boiling point fraction recovered in the third step and circulated as a reaction raw material in the first step and as an extraction solvent in the second step.

[0010]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a process conceptual diagram showing an example of a preferred embodiment of the present invention.

The manufacturing method of the present invention sequentially includes the following first to fourth steps. In the following description, the abbreviations shown in Table 1 below may be used.

[0012]

[Table 1]

<First Step (A)> First, EC and MeOH
And are transesterified to obtain a reaction mixture containing MeOH, DMC, EG and EC. The transesterification reaction between EC and MeOH is represented by the following chemical reaction formula (1).

[0014]

[Chemical 1]

The above transesterification reaction is an equilibrium reaction, and unreacted raw material components always exist in the reaction solution. That is, in the reaction liquid, in addition to the products DMC and EG, the raw materials EC and MeOH are contained, and further, by-produced DME and the like are contained.

Usually, the above transesterification reaction is carried out in the presence of a catalyst. As the catalyst, those generally used as ester exchange catalysts for carbonates can be used without limitation. Specifically, examples of homogeneous catalysts include amines such as triethylamine, alkali metals such as sodium, alkali metal compounds such as sodium chloroacetate and sodium methylate, and thallium compounds. Examples of the ion-exchange resin modified by, an amorphous silicas impregnated with a silicate of an alkali metal or an alkaline earth metal, an ammonium-exchanged Y-type zeolite, a mixed oxide of cobalt and nickel, and the like.

The type of reactor is not particularly limited, but it is preferable to use a fixed bed reactor (specifically, a tubular reactor). The reaction is preferably carried out continuously, E
The usage ratio (molar ratio) of MeOH to C is usually 2 to 2.
0, the reaction temperature is usually 50 to 180 ° C., and the reaction time is usually 0.5 to 5 hours.

In the illustrated example, EC and MeOH are
First from line (L1) and line (L2), respectively
The reaction liquid supplied to the step (A) is taken out from the line (L3).

<Second Step (B)> Next, in the presence of EC as an extraction solvent, the reaction mixture obtained in the first step is subjected to extractive distillation to separate MeOH, which is circulated as a reaction raw material in the first step. MeOH and DMC in the reaction mixture form the lowest azeotrope. The azeotropic composition at normal pressure is MeOH
Is about 65% by weight. Therefore, in the present invention, EC is added as an extraction solvent, and the azeotropic composition is distilled while shifting to the rich side corresponding to the desired purity of MeOH.

The purity of MeOH separated and recovered in the second step (B) is usually 85% by weight or more, preferably 90% by weight or more. Therefore, the number of concentration stages and recovery stages of the distillation column in the second step (B) and the operating conditions (temperature, pressure, reflux ratio, etc.) are appropriately selected so that the above-mentioned component separation is carried out.

When the raw materials are removed from the reaction solution, the product DM
C and EG may cause a reverse reaction of transesterification. Therefore, the processing temperature of the second step is usually 15
It is set to 0 to 180 ° C, preferably 150 to 170 ° C.
Also, the residence time should be as short as possible.
The residence time maintained at a temperature of not less than 0 ° C is preferably 1 hour or less.

In the case of the illustrated example, the reaction mixture obtained in the first step is fed from the line (L3) to the second step (B),
The EC collected in the below-mentioned fourth step (D) is the line (L8
It is supplied from b) to the second step (B). Then, the separated and recovered MeOH is circulated to the first step (A) through the line (L4), and the residual high boiling point fraction from which the MeOH has been separated is recovered through the line (L5).

<Third Step (C)> Next, the target component DMC is separated by distillation from the high boiling point fraction recovered in the second step. The purity of DMC separated and recovered in the third step (C) is
It is usually 95% by weight or more, preferably 98% by weight or more. The number of concentration stages and recovery stages of the distillation column and the operating conditions (temperature, pressure, reflux ratio, etc.) in the third step (C) are appropriately selected so that the above-mentioned component separation is carried out.

The high boiling point fraction recovered in the second step contains EG
, Which may cause the reverse reaction of the transesterification reaction in the first step with DMC. Therefore,
The treatment temperature in the third step is usually 150 to 180 ° C, preferably 150 to 170 ° C. In addition, the residence time should be as short as possible, and the residence time at which the temperature is maintained at 150 ° C. or higher is preferably 1 hour or less.

Although MeOH is mixed in DMC as the above-mentioned reverse reaction proceeds, when DMC is transesterified with phenol to produce diphenyl carbonate as a polycarbonate raw material, MeOH is produced by the reaction. Therefore, a small amount of MeOH contained in the recovered DMC can be treated together with MeOH by-produced in the diphenyl carbonate (DPC) generation reaction by the transesterification reaction of DMC and phenol, and thus the DMC obtained by the production method of the present invention is It can be used as a raw material for DPC.

In the case of the illustrated example, the high boiling point fraction recovered in the second step is supplied from the line (L5) to the third step (C), the separated DMC is recovered through the line (L6), and the DMC is recovered. The residual high-boiling fraction separated from the
Collected through 7).

<Fourth step (D)> Next, EC is separated from the high boiling point fraction recovered in the third step, and circulated as a reaction raw material in the first step and as an extraction solvent in the second step. The purity of EC separated and collected in the fourth step (D) is usually 85% by weight or more, preferably 90% by weight or more.
The above circulating EC is usually recovered as a side cut from the side of the distillation column. That is, the above-mentioned EC for circulation
Separates the EG fraction from the top of the tower and TEG, PE from the bottom of the tower.
It is recovered by separating the high boiling point product fraction such as G. Therefore, the number of concentration stages and recovery stages of the distillation column in the fourth step (D) and the operating conditions (temperature, pressure, reflux ratio, etc.) are appropriately selected so that the above-mentioned component separation is carried out.

Although EG and EC form an azeotrope, they do not show a definite minimum boiling point in the range of atmospheric pressure to a reduced pressure of about 7 KPa, and the minimum boiling point matches the boiling point of ethylene glycol. Therefore, by normal distillation separation, EG
EC is obtained from the bottom of the mixture of EC and EC.

In the case of the illustrated example, the high boiling point fraction recovered in the third step is supplied from the line (L7) to the fourth step (D), and the EC for circulation is the branch line from the line (L8). It is circulated through (L8a) and (L8b) to the first step (A) and the second step (B), respectively. And E
G fraction is collected through line (L9), and TEG, P
The high boiling point product fraction such as EG is recovered through a line (L10).

In the present invention, the EC separated in the fourth step
The ratio of recycling in the first step and the second step of the first step is 30 to 80% by weight (preferably 50 to 70% by weight),
The second step is preferably 20 to 70% by weight (preferably 30 to 50% by weight) (total of 100% by weight in both steps).
According to such a material balance, the above-mentioned extractive distillation using EC and the reuse of EC for the transesterification reaction can be well balanced. If the EC distribution ratio to the second step is less than 20%, the function of extractive distillation cannot be fulfilled, and if it exceeds 70%, the EC separation energy in the fourth step increases and energy loss occurs.

The type of each of the above-mentioned distillation columns may be either a plate column or a packed column. As the tray tower, a known type such as a sieve tray or a bubble bell tower can be used. As the packing in the packed tower, regular packing such as Sulzer pack, Mela pack, MC pack, IMT
Irregular packings such as P and Raschig rings can be used. Incidentally, the theoretical plate number of each distillation column is usually 5 to 30 plates,
It is preferably 7 to 20 stages, and the reflux ratio is usually 0.1 to 10.
5, preferably 0.5-2. A general multi-tube heat exchanger can be used as the condenser installed in each distillation column.

[0032]

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded.

Example 1 The first step to the fourth step described below were sequentially performed.

<First Step> As a reactor, a fixed bed reactor (diameter 51 cm, height 152 cm) packed with a catalyst in which bismuth oxide was supported on porous alumina particles was used. The MeOH and EC collected by the operation described later together with MeOH: 9 kg / h and EC: 15 kg / h were heated to 140 ° C. and continuously supplied to a fixed bed reactor to carry out a transesterification reaction. Reaction pressure is 1400KP
a and LHSV were set to 0.33. The composition of the obtained reaction liquid was as follows: EC: 59% by weight, MeOH: 20% by weight, EG:
It was 10% by weight and DMC: 12% by weight.

<Second Step> A packed column having 19 theoretical plates was used as the distillation column. Then, the reaction solution was supplied to the 10th stage, and the EC recovered in the 4th step (the recovery amount of 3
(Equivalent amount of 0% by weight) was supplied, and extractive distillation was carried out at a column top pressure of 101 KPa and a reflux ratio of 0.93. The top distillate volume is 2
5 kg / h, the composition was MeOH: 93% by weight, DMC: 7% by weight, and a trace amount of EG was contained. On the other hand, the bottom bottoms flow rate was 121 kg / h, and the composition was EC: 79% by weight, EG: 11% by weight, Me.
OH: 0.2% by weight.

<Third Step> As a distillation column, a packed column having 21 theoretical plates was used. Then, the high boiling point fraction (column bottoms) recovered in the second step was supplied to the 10th stage, and distillation was performed at a column top pressure of 16 KPa and a reflux ratio of 1. The top distillate amount was 12 kg / h, and the composition was DMC: 98% by weight and MeOH: 2% by weight. On the other hand, the bottom bottom product flow rate was 109 kg / h, the composition thereof was EC: 88% by weight, EG: 12% by weight, and the DMC content was 10% by weight or less.

<Fourth Step> As a distillation column, a packed column having 19 theoretical plates was used. Then, the high boiling point fraction (column bottoms) collected in the third step was supplied to the 11th stage, and while performing the side cut from the 17th stage, the column top pressure was 8 KPa,
Distillation was carried out at a reflux ratio of 1. The overhead distillate amount was 10 kg / h, and the composition thereof was EG: 83% by weight and EC: 17% by weight. On the other hand, the bottom bottom product flow rate was 1 kg / h, and the composition was a high boiling point product such as TEG or PEG. The liquid amount of the side cut liquid was 98 kg / h, and the composition thereof was EC: 95.4 wt% and EG: 4.6 wt%. Then, 70% by weight of the side cut liquid is circulated in the first step as a reaction raw material,
30 wt% was circulated in the second step as the extraction solvent.

As a result of continuously performing the above operation, EC
Conversion of 89% DMC: 12 kh / h and EG 8 kg /
I was able to get h.

[0039]

EFFECTS OF THE INVENTION According to the present invention described above, since there is no incorporation of the third component from the outside, an ordinary purification process can be adopted, and moreover, unreacted raw materials can be efficiently reused. An industrially advantageous method for producing dimethyl carbonate is provided.

[Brief description of drawings]

FIG. 1 is a process conceptual diagram showing an example of a preferred embodiment of the present invention.

[Explanation of symbols]

A: First step B: Second step C: Third step D: Fourth step

Claims (2)

[Claims] 1. A method for producing dimethyl carbonate, which comprises sequentially the following first to fourth steps. <First Step> Ethylene carbonate and methanol are transesterified to obtain a reaction mixture containing methanol, dimethyl carbonate, ethylene glycol and ethylene carbonate. <Second Step> In the presence of ethylene carbonate as an extraction solvent, the reaction mixture obtained in the first step is subjected to extractive distillation to separate methanol, which is circulated as a reaction raw material in the first step. <Third Step> Dimethyl carbonate is separated by distillation from the high boiling fraction collected in the second step. <Fourth step> Ethylene carbonate is separated from the high-boiling fraction recovered in the third step, circulated as a reaction raw material in the first step, and circulated as an extraction solvent in the second step. 2. The ratio of ethylene carbonate separated in the fourth step, which is circulated in the first step and the second step, is the first step.
The method for producing dimethyl carbonate according to claim 1, wherein the step is 30 to 80% by weight and the second step is 20 to 70% by weight (total 100% by weight in both steps).