JPH0625104A - Continuous production of dimethyl carbonate - Google Patents

Abstract

PURPOSE:To obtain a new process capable of industrially and advantageously performing production of dimethyl carbonate by a vapor-phase reaction by using carbon monoxide and methyl nitrite as raw materials in the presence of a platinum group metal-based solid catalyst. CONSTITUTION:A new process for continuously producing dimethyl carbonate consists of (A) a reaction process wherein carbon monoxide and a methyl nitrite-containing gas are introduced to a reactor packed with a solid catalyst carrying a platinum group metal (compound) or the platinum group metal (compound) and a cocatalyst and catalytically reacted in a vapor phase to give a reactional product comprising dimethyl carbonate, (B) the reaction product is fed to an absorption column, dimethyl oxalate is used as an absorption solvent and the reactional product is separated into a nitrogen monoxide-containing concondensed gas and an absorption solution having absorbed dimethyl carbonate, (C) the noncondensed gas is sent to a recovering column, nitrogen monoxide is recovered as methyl nitrite and methyl nitrite is circulatively fed to the reactor, (D) dimethyl carbonate is separated from methanol by extractive distillation while adding further dimethyl oxalate to the absorption solution and (E) dimethyl carbonate is separated from a mixture of the separated dimethyl carbonate and dimethyl oxalate by distillation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel method for producing dimethyl carbonate, which comprises using carbon monoxide and methyl nitrite as raw materials to produce dimethyl carbonate by a gas phase reaction in the presence of a platinum group metal-based solid catalyst. , A novel process which can be industrially advantageously carried out. Dimethyl carbonate is a compound useful as a raw material for synthesizing aromatic polycarbonate, medicines and agricultural chemicals, and as a solvent.

[0002]

2. Description of the Related Art Conventionally, the present inventors have already disclosed a method for producing dimethyl carbonate by bringing carbon monoxide and methyl nitrite into contact with a platinum group metal-based solid catalyst in a vapor phase.
No. 141243 and Japanese Patent Application No. 2-257042. This reaction itself is an extremely excellent reaction as a method for producing dimethyl carbonate. However, industrial application of this reaction and production of dimethyl carbonate on an industrial scale requires a process capable of continuously and efficiently carrying out the reaction and separation and purification.

[0003]

DISCLOSURE OF THE INVENTION The present inventors have proposed an industrially novel continuous method for producing dimethyl carbonate by bringing carbon monoxide and methyl nitrite into vapor phase contact with a platinum group metal-based solid catalyst. For the purpose of establishing the process, earnest study was conducted.

Regarding the method for producing dimethyl carbonate from carbon monoxide and methyl nitrite, there is a method disclosed in JP-A-60-181051, in addition to the method proposed by the present inventors. As a continuous process,
It was not fully disclosed. The present invention provides a novel and industrial continuous process as a continuous production method of dimethyl carbonate.

[0005]

[Means for Solving the Problems]

1. Introducing a gas containing carbon monoxide and methyl nitrite into a reactor loaded with a platinum group metal and / or a compound thereof or a solid catalyst loaded with a platinum group metal and / or a compound thereof and a cocatalyst, 1. The first step of obtaining a reaction product containing dimethyl carbonate by catalytically reacting in the gas phase. The reaction product in the first step was introduced into an absorption tower, dimethyl oxalate was added as an absorption solvent, and the non-condensed gas containing carbon monoxide produced in the catalytic reaction in the first step and the produced dimethyl carbonate were absorbed. 2. The second step of separating into an absorption liquid, The non-condensed gas in the second step is introduced into the regeneration tower and brought into contact with the supplied molecular oxygen-containing gas and methanol,
A third step of regenerating the nitric oxide in the non-absorbing gas into methyl nitrite so that the nitric oxide in the tower outlet gas is 2 to 7% by volume, and circulatingly supplying it to the reactor in the first step.

4. 4. A fourth step in which dimethyl carbonate is extracted and distilled from methanol while adding dimethyl oxalate to the mixed solution of dimethyl carbonate, methanol and dimethyl oxalate obtained in the second step. Dimethyl carbonate is distilled off from the mixture of dimethyl carbonate and dimethyl oxalate separated from methanol in the fourth step to obtain dimethyl carbonate as a product. In addition, it was found that if a process consisting of the fifth step of supplying dimethyl oxalate to the fourth step in a circulating manner is adopted, dimethyl carbonate that is extremely industrially advantageous can be obtained, and the continuous production method was developed. Came to.

Next, each step of the present invention will be described in detail below. First step A raw material gas containing carbon monoxide and methyl nitrite in a reactor loaded with a platinum group metal and / or a compound thereof or a solid catalyst loaded with a platinum group metal and / or compound and a co-catalyst Is introduced and the catalytic reaction is carried out in the gas phase. As the reactor, a single-tube type or multi-tube type catalyst packed column is effective, and the contact time between the platinum group metal-based solid catalyst and the raw material gas is suitably 10 seconds or less, preferably 0.2 to 5
Set to be seconds. As the platinum group metal-based solid catalyst, Japanese Patent Application No. 3-141243 and Japanese Patent Application No. 1-201114 are available.
A catalyst in which a platinum group metal compound described in No. 6 is supported on a carrier, a catalyst in which a platinum group metal cation is supported on a carrier, and a salt of copper or iron added as a cocatalyst is effective.

As the simple substance, activated carbon, alumina, silica, diatomaceous earth, zeolite, clay mineral and the like are used. The gas containing carbon monoxide and methyl nitrite, which is a raw material gas, is usually diluted with a reaction-inert gas such as nitrogen or carbon dioxide.

Regarding the reaction temperature, the reaction proceeds sufficiently quickly even at low temperature, and the lower the reaction temperature is, the less side reactions occur. Therefore, the reaction temperature is relatively low as long as the desired space-time yield is maintained.
That is, it is preferably 50 to 200 ° C., preferably 80 to 1
It is 50 ° C. The reaction pressure is suitably atmospheric pressure to 10 kg / cm ² (gauge pressure), preferably atmospheric pressure to 5 kg / cm ² (gauge pressure).
In some cases, the pressure may be slightly lower than normal pressure.

The concentration of methyl nitrite in the raw material gas can be varied over a wide range, but in order to obtain a satisfactory reaction rate, the concentration should preferably be 1 vol% or more. On the contrary, since methyl nitrite is an explosive compound, it is not preferable to increase the concentration of methyl nitrite from the viewpoint of safety. Therefore, it is preferably 3 to 25% by volume. The concentration of carbon monoxide in the raw material gas may vary over a wide range and can be suitably selected in the range of 10 to 90% by volume, but in the continuous process, it is circulated to keep the concentration of the inert gas constant. To purge some of the gas,
Since the loss increases outside the system when the concentration is increased, it is economically preferable to perform the treatment at 5 to 30% by volume.

Second step The reaction product in the first step is led to the lower part of the absorption tower for gas separation, and at the same time, dimethyl oxalate is fed from the upper part of the absorption tower, and dimethyl carbonate in the reaction gas is absorbed and separated by dimethyl oxalate. To do. A small amount of dimethyl carbonate and dimethyl oxalate are entrained in the gas from which dimethyl carbonate is separated, and this is hydrolyzed to a complete loss during the regeneration of nitric oxide in the third step. In order to recover dimethyl oxalate, it is preferable to feed a small amount of methanol from the top of the absorption tower.

The flow rate of dimethyl oxalate depends on the amount of dimethyl carbonate entering the absorption tower, but it is preferably 3 to 10 times by weight, and more preferably 4 times the weight of dimethyl carbonate.
~ 6 times weight is required. Further, as the amount of methanol fed from the top of the column, it is preferable that the amount of methanol itself be separated in the fourth step because it is to be separated, but if it is too small, the loss of dimethyl carbonate and dimethyl oxalate increases, so the reaction The amount is preferably 5 to 30% by weight, more preferably 10 to 20% by weight, based on dimethyl carbonate in the gas.

The operating temperature of the absorption tower is preferably low in order to efficiently absorb dimethyl carbonate, but if it is too low, solidification of dimethyl oxalate occurs and it is also disadvantageous in terms of energy. Suitably 0 ° C to 80
C., preferably 10 to 50.degree. C. The mixed solution of dimethyl carbonate and dimethyl oxalate absorbed and separated by dimethyl oxalate is sent to the fourth step in order to remove methanol and a small amount of low boiling point compounds such as methyl formate produced in the reaction. On the other hand, the non-condensed gas contains unreacted carbon monoxide, methyl nitrite, etc. in addition to the nitric oxide produced in the contact reaction in the first step, and is sent to the third step.

Third Step The non-absorption gas separated in the second step is introduced into a regeneration tower and brought into contact with the molecular oxygen-containing gas and methanol to regenerate nitrogen monoxide in the gas to methyl nitrite. As the regeneration tower in this step, a usual gas-liquid contact device such as a packed tower, a bubble tower, a spray tower or a plate tower is used.

The non-absorbed gas and the molecular oxygen-containing gas which are brought into contact with methanol can be introduced into the regeneration column individually or in a mixed state. In this regeneration tower, a part of nitric oxide is oxidized to nitrogen dioxide by a molecular oxygen-containing gas, and at the same time, these are absorbed in methanol to be reacted to regenerate methyl nitrite. As the molecular oxygen-containing gas, pure oxygen or oxygen diluted with an inert gas is used and is fed so that the concentration of nitric oxide in the regeneration gas is 2 to 7% by volume. This means that when the gas is recycled to the reactor of the first step, the concentration of nitric oxide is 8
If it is more than volume%, the reaction inhibiting effect becomes remarkable, and if it is less than 2 volume%, a considerable amount of oxygen and nitrogen dioxide will be contained in the regeneration gas, which reduces the activity of the catalyst. It will be a factor to cause.

For this purpose, 0.08 to 0.2 mol of a molecular oxygen-containing gas based on oxygen is supplied to 1 mol of nitric oxide in the gas introduced into the regeneration tower, and these gases are mixed at 6 mol.
It is preferable to contact with methanol at a temperature of 0 ° C. or lower, and the contact time is preferably 0.5 to 2 seconds. The amount of methanol used is at least the amount required to completely absorb and react the produced nitrogen dioxide and almost equimolar amount of nitric oxide, and usually 1 volume of nitric oxide in the gas introduced into the regeneration tower. It is preferable to use 2 to 5 parts by volume of methanol per part.

Since the present invention is a continuous process, a small amount of methyl nitrite is dissolved in the absorption liquid of the absorption tower or the bottom liquid of the regeneration tower and is entrained outside the system, or part of the circulating gas is purged. Nitric oxide content is lost due to
To supply it, methyl nitrite is supplied to the reactor in the first step, or nitrogen oxide such as nitric oxide, nitrogen dioxide, dinitrogen trioxide, and dinitrogen tetraoxide or nitric acid is supplied to the regeneration tower in the third step. It can also be done by introducing it.

Further, when the content of nitric oxide in the non-absorbed gas in the second step is large, and more than the necessary amount of methyl nitrite is obtained when the nitric oxide is combined with the nitrite ester in the third step. In addition, a part of the non-absorption gas may be directly circulated to the reactor in the first step without being guided to the regeneration column. Since the liquid discharged from the regeneration tower is a methanol solution containing water by-produced in the regeneration reaction, the water content in methanol is suitably 2% by volume or less, preferably 0.2% by an operation such as distillation. It is industrially advantageous to refine the product to a volume% or less and then reuse it in the third official determination or in the second step.

Fourth Step The mixed liquid of dimethyl carbonate, methanol and dimethyl oxalate derived from the second step is fed to the lower part of the extractive distillation column for removing methanol. At the same time, dimethyl oxalate is newly fed to the extractive distillation column at the bottom of the tower to prevent azeotropic distillation of methanol and dimethyl carbonate. The amount of dimethyl oxalate fed is preferably 0.1 to 2 times, and preferably 0.5 to 1. 1 times the total number of moles of dimethyl carbonate and methanol fed to the column.
Five times the molar amount is required. The amount of dimethyl oxalate serves as an important absorbent to prevent substantial loss of dimethyl carbonate to the distillate side, and the number of distillation column plates for separation to separate the process for recycling. It depends on the amount of energy used when increasing and separating. That is, when the flow rate of dimethyl oxalate is too low, the loss of dimethyl carbonate to the distilling side becomes large and the yield is deteriorated, and the absorption tower for absorption and separation requires a high number of stages. On the contrary, if the amount is more than a certain amount, the loss of dimethyl carbonate to the distilling side is practically eliminated, so that flowing more than that is not effective and is wasted in terms of energy.

The operating pressure is not particularly limited, but it can be carried out in a wide range from depressurization to pressurization.
It is preferable to operate in the range of ² kg / cm ² G. Methanol distilled from the extractive distillation column is preferably reused as an industrial process in the second and third steps, but methyl formate and methylal, which are produced in small amounts as by-products in the reaction of the first step, are the distillate methanol. Since it is included in the
It is desirable to reuse methanol after distilling them off. The separated distillation residues, methyl formate and methylal, are discarded by incineration or the like, but can be further recovered as methanol from these by alkaline decomposition or the like. The bottom liquid of the extractive distillation column is supplied to the fifth step in the state of a binary solution of dimethyl carbonate and dimethyl oxalate.

Fifth step In the fifth step, the liquid from which methanol and other low-boiling products have been separated is subjected to high-quality carbon dioxide by distilling and separating dimethyl carbonate in a distillation column for obtaining dimethyl carbonate as a product. Dimethyl is continuously taken out. The operating pressure is not particularly limited, and it can be performed in a wide range from pressurization to depressurization. On the other hand, the bottom liquid of this distillation column gives dimethyl oxalate having a considerably high purity and is supplied to the second step and the third step as it is. The amount produced as a by-product in the reaction of the first step is a by-product. Is extracted as. Since dimethyl oxalate itself is a compound with various uses, it is highly pure even in the state of a can, but if necessary, it is further purified by distillation. As the distillation column in the fourth step and the fifth step, a usual device such as a packed column or a plate column is used.

Next, the process of the present invention will be specifically described with reference to the flow sheet drawings showing one embodiment of the present invention. A gas circulator (not shown) in which a gas containing carbon monoxide, methyl nitrite, and nitric oxide is installed in a conduit 20 above the multitubular reactor 1 having a reaction tube filled with a platinum group metal-based solid catalyst. (No.) and introduced through conduit 22. The reaction reaction gas is carried out in the gas phase in the reactor 1, and the reaction product gas that has passed through the catalyst layer is taken out from the lower part and introduced into the absorption tower 2 through the conduit 11.

In the absorption tower 2, dimethyl carbonate in the reaction product gas is absorbed and separated into dimethyl oxalate while contacting with methanol and dimethyl oxalate introduced from the conduits 13 and 14, and dimethyl carbonate, dimethyl oxalate and methanol are separated. The liquid consisting of is introduced into the extractive distillation column 4 through the conduit 15 from the lower part. On the other hand, the non-absorbed gas containing unreacted carbon monoxide, methyl nitrite, and by-produced nitric oxide, etc. is introduced into the lower part of the regeneration tower 3 from the upper part through the conduit 12.

In the regenerator 3, the non-absorption gas is mixed with the molecular oxygen-containing gas introduced through the conduit 16 in the lower portion and reacted with the methanol introduced through the conduit 19 in the upper portion by countercurrent contact to generate methyl nitrite. To play.
In the regeneration tower 3, the oxidation reaction of nitric oxide to nitrogen dioxide is followed by the absorption reaction to methanol, and methyl nitrite is produced. If there is insufficient nitrogen source to generate methyl nitrite, nitrogen oxide may be mixed through the conduit 17.

The methyl nitrite-containing gas produced in the regeneration tower 3 is circulated to the reactor 1 through the conduits 20 and 22 together with carbon monoxide newly supplied from the conduit 21. On the other hand, the water by-produced in the regeneration tower 3 is taken out from the bottom through the conduit 18 in the form of an aqueous methanol solution. This aqueous methanol solution is circulated and reused as methanol to be supplied to the absorption tower 2 or the regeneration tower 3 through the conduits 13 and 19 after removing water in the liquid by an operation such as distillation.

In the extractive distillation column 4, only dimethyl carbonate is extracted by countercurrent contact with dimethyl oxalate introduced through the conduit 25 and separated from methanol. The separated methanol is introduced from the upper portion to a distillation column 6 for purifying methanol by a conduit 24, and after purification, the conduit 1
It is recycled and reused as methanol supplied to the absorption tower 2 and the regeneration tower 3 through 3 and 19. Further, the mixed liquid of dimethyl carbonate and dimethyl oxalate from which methanol has been separated is introduced into the distillation column 5 through the conduit 23.

In the distillation column 5, dimethyl carbonate is obtained from the top through the conduit 27 as a product object. The bottom liquid is high-purity dimethyl oxalate, part of which is obtained as a by-product through the conduit 28, and the rest is contained in the conduits 26 and 14.
Through 25, it is supplied to the absorption tower 2 and the distillation tower 4.

[0027]

EXAMPLES Next, specific examples will be described. Example 1 In a tube of a stainless multi-tube reactor composed of 6 tubes having an inner diameter of 27.1 mm and a height of 500 mm, Japanese Patent Application No.
Activated carbon as indicated by No. -257042 (Takeda Corporation)
Catalyst 7 with Palladium supported on Shirasagi 4mmφ × 6mm)
80 g (1.731) were charged. 2.5kg / cm with a diaphragm type gas circulation pump from the top to this catalyst layer
Raw material gas compressed to ² (gauge pressure) (composition: carbon monoxide 15.0% by volume, methyl nitrite 15.0% by volume, nitric oxide 3.5% by volume, methanol 1.8% by volume, carbon dioxide 2 (2% by volume and 62.5% by volume of nitrogen) was preheated to about 90 ° C. in a heat exchanger and then fed at a rate of 6.9 Nm ³ / hr, and hot water was passed through the shell side of the reactor to form a catalyst. The temperature in the middle of the layer was kept at about 120 ° C. The reaction rate of dimethyl carbonate formation in this reaction is 430 kg / m for STY.
It was ³ hr.

The gas which has passed through the catalyst layer has an inner diameter of 100 m.
m, height 1300 mm, led to the bottom of a Raschig ring-filled gas-liquid contact absorber, and from the top of the tower methanol 0.2 l / h
In addition, r was introduced at a rate of 2.65 kg / hr of dimethyl oxalate from a position 200 mm below the top of the column, and the temperature at the top of the column was 5
And countercurrent contact were carried out at a column bottom temperature of 20 ° C. From the bottom of the column, 3.8 kg / hr of absorbing liquid (composition: dimethyl oxalate 76.7% by weight, dimethyl carbonate 19.6% by weight, methanol 3.7% by weight, methyl formate 0.1% by weight) was obtained. On the other hand, non-absorbed gas (composition: carbon monoxide 12.8% by volume, methyl nitrite 10.3% by volume, nitric oxide 8.7% by volume, methanol 1.9% by volume, carbon dioxide gas 2.2% by volume from the top of the tower. % And nitrogen 64.0% by volume) 6.8 Nm ³ / hr was obtained.

Oxygen 87.2 Nl / h was added to this non-absorption gas.
nitrogen gas containing r and 14.0% by volume of nitric oxide 7.
After mixing 5Nl / hr, inner diameter 158mm, height 14
It is led to the bottom of a gas-liquid contact type regeneration tower of 00 mm, and introduced at a rate of 5.0 l / hr of methanol from the top of the tower, and the temperature of the top of the tower is 3
Countercurrent contact was carried out at 0 ° C. and a column bottom temperature of 40 ° C. to regenerate nitrogen monoxide in the gas into methyl nitrite. Regeneration gas in the regeneration tower (composition: carbon monoxide 12.8% by volume, methyl nitrite 1
5.4 vol%, nitric oxide 3.7 vol%, methanol 1.9 vol, carbon dioxide 2.3 vol% and nitrogen 64.1
6.6 Nm ³ / hr was supplied to the gas circulation pump and compressed. Next, carbon monoxide is 0.2 Nm in the discharge gas.
³ / hr was replenished and mixed, and then introduced into the reactor. On the other hand, 4.0 l of 2.2 wt% hydrous methanol derived from this regeneration tower
/ Hr was reused as a methanol source in the column after removing water by distillation.

3.5 k of absorption liquid derived from the absorption tower
g / hr was introduced into the middle stage of the distillation column having an inner diameter of 50 mm and a height of 2500 mm, and dimethyl oxalate liquid was introduced at a rate of 1.4 kg / hr at a distance of 300 mm from the top of the column, and the top temperature was 64
Distillation was performed at a temperature of 146 ° C and a bottom temperature of 146 ° C. From the bottom of the column, dimethyl carbonate 14.3% by weight, dimethyl oxalate 87.5% by weight
A mixed solution of 4.78 kg / h was obtained. On the other hand, from the top of the column, 0.13 kg / of distillate consisting of 94.5% by weight of methanol, 5.2% by weight of methyl formate and 0.3% by weight of dimethyl carbonate.
got hr. This methanol solution was purified in a distillation tower and circulated and reused in the regeneration tower and absorption tower.

A mixed solution of dimethyl carbonate and dimethyl oxalate discharged from this distillation column was set to have an inner diameter of 65 mm and a height of 16 mm.
It is introduced into a 00 mm packed tower, the tower top temperature is 90 ° C, and the tower bottom temperature is 1.
Distilled at 63 ° C. From the top of the column, 0.68 kg / hr of dimethyl carbonate having a purity of 99.4% was obtained. Further, from the bottom of the tower, dimethyl oxalate having a purity of almost 100% 4.69 kg / hr
Was extracted and 4.05 kg / hr of this was circulated and supplied to the absorption tower and the extractive distillation tower. As a result, high-purity dimethyl carbonate could be continuously obtained from the dimethyl carbonate produced in the reaction with a production yield of 98%.

[0032]

[Brief description of drawings]

FIG. 1 is a flow sheet showing an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1 is a reactor, 2 is an absorption column, 3 is a regeneration column, 4 is an extractive distillation column, 5 and 6 are distillation columns, and 11 to 29 are conduits.

Claims (1)

[Claims] 1. Introducing a gas containing carbon monoxide and methyl nitrite into a reactor loaded with a platinum group metal and / or a compound thereof or a solid catalyst loaded with a platinum group metal and / or a compound thereof and a cocatalyst, 1. The first step of obtaining a reaction product containing dimethyl carbonate by catalytically reacting in the gas phase. The reaction product in the first step was introduced into an absorption tower, dimethyl oxalate was added as an absorption solvent, and the non-condensed gas containing nitric oxide produced in the catalytic reaction in the first step and the produced dimethyl carbonate were absorbed. 2. The second step of separating into an absorption liquid, The non-condensed gas in the second step is introduced into the regeneration tower and brought into contact with the supplied molecular oxygen-containing gas and methanol,
3. A third step in which nitric oxide in the non-absorbed gas is regenerated into methyl nitrite so that the nitric oxide in the tower outlet gas becomes 2 to 7% by volume, and is circulated and supplied to the reactor in the first step. 4. A fourth step in which dimethyl carbonate is extracted and distilled from methanol while adding dimethyl oxalate to the mixed solution of dimethyl carbonate, methanol and dimethyl oxalate obtained in the second step. Dimethyl carbonate is distilled off from the mixture of dimethyl carbonate and dimethyl oxalate separated from methanol in the fourth step to obtain dimethyl carbonate as a product. Further, dimethyl oxalate comprises a fifth step in which the dimethyl oxalate is circulated and fed into the fourth step, and a continuous process for producing dimethyl carbonate.