JP2962454B2 - Continuous production method of dimethyl carbonate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a process for producing dimethyl carbonate by reacting carbon monoxide and methyl nitrite in the gas phase in the presence of a solid catalyst. The present invention relates to a method for industrially producing dimethyl carbonate by effectively circulating gas by installing a circulator for circulating water at an optimum position. Dimethyl carbonate is a useful compound as a raw material for synthesizing aromatic polycarbonate and various chemicals, and as a solvent.

[0002]

2. Description of the Related Art A method for industrially producing dimethyl carbonate by subjecting carbon monoxide and methyl nitrite to gas phase contact reaction in the presence of a solid catalyst is disclosed in, for example, Japanese Patent Application No. 3-269950. , A first step in which carbon monoxide and methyl nitrite are subjected to a gas phase contact reaction in the presence of a solid catalyst in a reactor to form dimethyl carbonate. A second step in which dimethyl acid is absorbed, and a third step in which nitric oxide in the non-condensed gas in the second step is brought into contact with molecular oxygen and methanol in a methyl nitrite regeneration tower (regeneration tower) to produce methyl nitrite. Consists of processes. The gas containing carbon monoxide and methyl nitrite is supplied to a gas circulator in a conduit between the regeneration tower in the third step and the reactor in the first step, and the gas in the reactor in the first step and the second It is circulated between the absorption tower in the step and the regeneration tower in the third step.

[0003] However, in this method, when the reaction is carried out with the pressure in the reactor set to an optimum condition, a pressure loss occurs in each device when the gas circulates through the above three steps, so that the absorption tower and Operating conditions for the regeneration tower were not always optimal. That is, in the absorption tower, the higher the pressure, the higher the efficiency of absorption of dimethyl carbonate, and
In the regenerator, the higher the pressure, the faster the rate of methyl nitrite regeneration (the rate of oxidation of nitric oxide), and at the same time, the easier it is to remove water in the tower. As a result, carbon dioxide from carbon monoxide in the reactor is reduced. While the by-product of gas is suppressed and the selectivity of dimethyl carbonate is improved, the performance of the apparatus has not been sufficiently improved because the pressure has been reduced due to pressure loss.

[0004]

DISCLOSURE OF THE INVENTION The present invention solves the problems derived from the circulation of a gas containing carbon monoxide and methyl nitrite in the production of dimethyl carbonate as described above.
It is an object of the present invention to provide an industrially suitable method for continuously producing dimethyl carbonate.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a first step in which carbon monoxide and methyl nitrite are reacted in a gas phase in the presence of a solid catalyst in a reactor to form dimethyl carbonate. In a dimethyl oxalate absorption solvent in a dimethyl carbonate absorption tower, and nitric oxide in the non-condensed gas in the second step is brought into contact with molecular oxygen and methanol in a methyl nitrite regeneration tower to produce nitrous acid. In the method for producing dimethyl carbonate comprising the third step of producing methyl, a circulator for circulating a gas containing carbon monoxide and methyl nitrite comprises a reactor in the first step and a dimethyl carbonate absorption in the second step. A continuous flow of dimethyl carbonate, wherein the gas is circulated by being installed in a conduit between the towers or a conduit between the dimethyl carbonate absorption tower in the second step and the methyl nitrite regeneration tower in the third step. It is achieved by the granulation method.

First, each step in the present invention will be described step by step. In the first step of the present invention, a raw material gas containing carbon monoxide and methyl nitrite is introduced into a reactor filled with a solid catalyst supporting a platinum group metal and / or a compound thereof and a cocatalyst. Is a dimethyl carbonate synthesis step of obtaining a reaction gas containing dimethyl carbonate. In the second step, the reaction gas in the first step was led to a dimethyl carbonate absorption tower (hereinafter, referred to as an absorption tower), and brought into contact with dimethyl oxalate added as an absorption solvent, to thereby generate the reaction gas in the first step. This is a dimethyl carbonate absorption / separation step of separating into a non-condensable gas containing nitric oxide and an absorbing solution absorbing the generated dimethyl carbonate. In the third step, the non-condensable gas in the second step is led to a methyl nitrite regenerating tower (hereinafter, referred to as a regenerating tower), brought into contact with the supplied molecular oxygen-containing gas and methanol, and Is a nitrite regenerating step of regenerating nitric oxide into methyl nitrite and circulating it to the reactor of the first step.

Accordingly, the gas containing carbon monoxide and methyl nitrite of the present invention is led out of the reactor in the first step as a reaction gas containing dimethyl carbonate, as described above,
Next, dimethyl carbonate is led out of the absorption tower in the second step as a non-condensed gas that has been absorbed and separated, and finally, from the regeneration tower in the third step as a gas in which methyl nitrite has been regenerated (hereinafter, referred to as regeneration gas). After being led out, it is again circulated to the reactor of the first step and reused as a source gas.

A gas circulator is used to circulate the gas containing carbon monoxide and methyl nitrite as described above. The feature of the present invention is that the gas circulator is used for the reaction in the first step. To introduce a reaction gas derived from the vessel into the absorption tower in the second step or a conduit introducing non-condensable gas derived from the absorption tower in the second step into the regeneration tower in the third step. . The gas circulator used in the present invention, depending on the scale of the device, includes ordinary compressors used industrially, for example, a rotary type, a centrifugal type, an axial type is preferable. Used for

In accordance with one embodiment of the present invention, a gas circulator is installed in a conduit between the reactor of the first step and the absorption tower of the second step so that the gas circulator is conventionally in the third step. When the load on the circulator is the same, the pressures in the absorption tower and the regeneration tower can be maintained higher than when installed in the conduit between the regeneration tower and the reactor in the first step. This makes it possible to increase the absorption efficiency of dimethyl carbonate in the absorption tower, the regeneration rate of methyl nitrite (oxidation rate of nitric oxide), and the removal efficiency of water in the regeneration tower. And, by improving the efficiency of removing water, it is also possible to suppress the by-product of carbon dioxide from carbon monoxide in the reactor.

According to another embodiment of the present invention, a gas circulator is installed in a conduit between an absorption tower in the second step and a regeneration tower in the third step, so that the gas circulator can be used in a conventional manner. The pressure in the regeneration tower can be maintained higher than when installed in a conduit between the regeneration tower in the three steps and the reactor in the first step. This makes it possible to increase the regeneration rate of methyl nitrite (oxidation rate of nitric oxide) and the efficiency of removing moisture in the regeneration tower. And in a reactor, it becomes possible to suppress by-product of carbon dioxide gas similarly to the above-mentioned case. Therefore, according to the present invention, even if the apparatus is downsized, the same performance as the conventional one can be obtained in the regeneration tower.
Further, the present invention is more suitable for large-scale industrial dimethyl carbonate production, since the above-mentioned effects become more significant as the apparatus becomes larger.

The synthesis of dimethyl carbonate in the first step of the present invention comprises, as described above, a gas circulator for circulating a gas containing carbon monoxide and methyl nitrite, and a conduit between the reactor and the absorption tower. Or installed in the conduit between the absorption tower and the regeneration tower,
By introducing a raw material gas containing carbon monoxide and methyl nitrite into a reactor filled with a solid catalyst in which a platinum group metal and / or its compound and a cocatalyst are supported on a carrier, and performing a gas phase contact reaction Will be implemented.

As the above-mentioned solid catalyst, for example, those in which a platinum group metal and / or a compound thereof and a cocatalyst described in JP-A-3-141243 and the like are supported on a carrier are effective. Examples of the platinum group metal supported on the carrier as a platinum group metal and / or a compound thereof with these solid catalysts include palladium, platinum, iridium, ruthenium and rhodium, with palladium being most preferred. In addition to the platinum group metals, compounds of metals such as copper, iron, bismuth, and cerium may be supported as co-catalysts. As the carrier, activated carbon, alumina, silica, diatomaceous earth, zeolite, clay mineral and the like can be used.

[0013] Carbon monoxide and methyl nitrite are usually diluted with a gas inert to the reaction such as nitrogen or carbon dioxide gas.
It is preferable that the raw material gas is fed to the reactor so that the contact time with the solid catalyst is usually 10 seconds or less, preferably 0.2 to 5 seconds. In addition, as a reactor filled with a solid catalyst, a single-tube or multi-tube catalyst packed tower is suitable.

The concentration of methyl nitrite in the raw material gas is determined from the viewpoint of reaction rate and safety. That is, in order to obtain a satisfactory reaction rate, the concentration of methyl nitrite is preferably 1
It is necessary that the concentration be at least 10% by volume, but since methyl nitrite is an explosive compound, it is not preferable that the concentration is too high. In the present invention, a concentration of 3 to 25% by volume is generally suitable.

The concentration of carbon monoxide in the raw material gas can be varied over a wide range. However, in a continuous process, if a high concentration is used to purge a part of the circulating gas, loss to the outside of the system increases, which is economically undesirable. Therefore, a suitable concentration of carbon monoxide is industrially usually 1 to 50% by volume, preferably 5 to 30% by volume.

The reaction temperature is preferably relatively low as long as a desired reaction rate can be obtained.
0 ° C, more preferably 80 to 150 ° C, is suitable. The reaction pressure is usually from normal pressure to 10 kg / c.
m ² (gauge pressure), preferably 1 to 6 kg / cm ² (gauge pressure) is suitable.

The synthesis reaction of dimethyl carbonate is performed in this manner, and dimethyl carbonate, dimethyl oxalate, nitric oxide, carbon dioxide, unreacted carbon monoxide and methyl nitrite,
A reaction gas containing an inert gas or the like is led out of the reactor. The desired dimethyl carbonate is converted into the second gas by the second gas.
It is separated by leading to the absorption tower of the process and absorbing it in dimethyl oxalate fed from the top of the absorption tower,
It is further purified by distillation.

The absorption and separation of dimethyl carbonate by dimethyl oxalate in the second step of the present invention is performed as follows. The feed amount of dimethyl oxalate in the absorption tower depends on the amount of dimethyl carbonate in the reaction gas introduced into the absorption tower, but is usually 3 to 10 times by weight, more preferably 4 to 6 times by weight, of dimethyl carbonate. Is preferred. Also, a small amount of dimethyl carbonate and dimethyl oxalate are entrained in the reaction gas into which dimethyl carbonate has been absorbed, and this is hydrolyzed in the next third step, resulting in complete loss. It is preferable to feed a small amount of methanol from the top of the absorption tower in order to recover dimethyl oxalate. The feed amount of methanol is usually 5 to 30% by weight, more preferably 10 to 20% by weight, based on dimethyl carbonate in the reaction gas.

The operating temperature of the absorption tower is preferably a low temperature in order to efficiently absorb dimethyl carbonate, but if the operating temperature is too low, dimethyl oxalate solidifies and is disadvantageous in energy. Therefore, preferably 0 to 80
C, more preferably 10 to 50C. The dimethyl carbonate absorbed by the dimethyl oxalate in this manner is separated and purified by distillation after removing low boiling compounds such as methanol and trace amounts of methyl formate by-produced in the reaction.

On the other hand, the non-condensed gas separated in the above-mentioned absorption tower includes first unreacted carbon monoxide and methyl nitrite in addition to unreacted carbon monoxide and methyl nitrite.
Because it contains a large amount of nitric oxide generated in the process,
In the regeneration tower in the third step, the non-absorbed gas is brought into contact with molecular oxygen and methanol to regenerate nitric oxide in the gas into methyl nitrite as follows. At this time, as the regeneration tower, a usual gas-liquid contacting device such as a packed tower, a bubble tower, a spray tower, and a step tower is used.

As the molecular oxygen-containing gas, pure oxygen or oxygen diluted with an inert gas is used, and the gas is fed such that the concentration of nitric oxide in the regeneration gas is usually 2 to 7% by volume. This is because when the recycled gas is recycled to the reactor for dimethyl carbonate synthesis, the concentration of nitric oxide is 8% by volume.
When the amount is more than the above, the effect of inhibiting the reaction becomes remarkable, and when the amount is less than 2% by volume, a considerable amount of oxygen and nitrogen dioxide is contained in the regenerating gas, which reduces the activity of the catalyst. Because it becomes.

In the regeneration tower, a molecular oxygen-containing gas is usually supplied in an amount of 0.08 to 0.2 mol based on oxygen with respect to 1 mol of nitrogen monoxide in the raw material gas introduced into the reactor in the first step. These gases are preferably contacted with methanol at a temperature of 60 ° C. or lower, and the contact time is preferably 0.5 to 2 seconds. The above-mentioned methanol is used in an amount required to completely absorb and react with the generated nitrogen dioxide and almost the same mole of nitric oxide, and usually, the amount of nitrogen monoxide in the raw material gas introduced into the reactor is increased. It is preferable to use 2 to 5 parts by volume for 1 part by volume.

Since the liquid led out of the regeneration tower is a methanol solution containing water produced by the above-mentioned regeneration reaction, the water content in methanol is preferably 2% by volume or less, preferably by operation such as distillation. It is industrially advantageous to reuse it in the second and third steps after purifying it to 0.2% by volume or less.

Next, the process of the present invention will be specifically described with reference to a flow sheet drawing showing one embodiment of the present invention.
A raw material gas containing carbon monoxide, methyl nitrite and nitrogen monoxide is introduced through a conduit 22 into the upper part of the multitubular reactor 1 in which a platinum group metal-based solid catalyst is filled in a reaction tube. The catalytic reaction is performed in the gas phase in the reactor 1, and the reaction gas that has passed through the catalyst layer is taken out from the lower part of the reactor, is pressurized by a gas circulator installed in the conduit 11, and is introduced into the absorption tower 2. .

In the absorption tower 2, the reaction gas and the conduit 13,
By contact with methanol and dimethyl oxalate introduced from 14, dimethyl carbonate in the reaction gas is absorbed by dimethyl oxalate and separated. The liquid consisting of dimethyl carbonate, dimethyl oxalate and methanol is supplied from the bottom to conduit 15
And separated and purified. On the other hand, a non-condensable gas containing unreacted carbon monoxide, methyl nitrite, and by-produced nitric oxide is passed through the conduit 12 from the top through the regeneration tower 3.
Introduced at the bottom. When a gas circulator is not installed in the above-mentioned conduit 11, a gas circulator is installed in this conduit 12, and the non-condensable gas taken out of the absorption tower is pressurized and introduced into the regeneration tower 3.

In the regenerator 3, countercurrent contact between the non-condensable gas and the molecular oxygen-containing gas introduced through the conduit 16 and methanol introduced from above through the conduit 19 is carried out, whereby methyl nitrite is regenerated. . In addition, when the nitrogen source required for the regeneration of methyl nitrite is insufficient, nitrogen oxide may be introduced through the conduit 17.

The regeneration gas generated in the regeneration tower 3 is supplied to the conduit 2
0 and 22 are supplied to the reactor 1 together with freshly supplied carbon monoxide from the conduit 21. On the other hand, water by-produced in the regenerator 3 is supplied from the lower part to the conduit 18 in the form of an aqueous methanol solution.
Taken out through. After the water in the liquid is removed by an operation such as distillation, the methanol aqueous solution is circulated and reused as methanol supplied to the absorption tower 2 or the regeneration tower 3 through the conduits 13 and 19.

[0028]

Next, the method of the present invention will be specifically described with reference to examples and comparative examples. The space-time yield of dimethyl carbonate (DMC) (STY) (k
g / m ³ · hr) is the contact reaction time between carbon monoxide and methyl nitrite as θ (hr), the amount of dimethyl carbonate generated during that time as a (kg), and the amount of catalyst charged into the reaction tube. Was determined as b (m ³ ) by the following equation.

[0029]

(Equation 1)

The selectivity (X) (%) of carbon dioxide based on carbon monoxide in each of the Examples and Comparative Examples is the above θ.
(Hr) generated dimethyl carbonate, dimethyl oxalate,
The amounts of carbon dioxide gas were determined as c (mol), d (mol), and e (mol) by the following formulas.

[0031]

(Equation 2)

Example 1 A dimethyl carbonate was produced by installing a diaphragm type gas circulation pump in a conduit between the following reactor and a regeneration tower. In a tube of a stainless steel multi-tube reactor consisting of six tubes having an inner diameter of 27 mm and a height of 500 mm, Japanese Patent Laid-Open No.
Activated carbon (Shirasagi: manufactured by Takeda) as disclosed in Japanese Patent No. 41243 was filled with 1.71 l of a solid catalyst (4 mmφ × 6 mm) supporting palladium chloride and cupric chloride.

From the top of the catalyst layer, 4.02 kg / c
Raw material gas (composition: carbon monoxide 20.0% by volume, methyl nitrite 10.0% by volume, nitrogen monoxide 4.0% by volume, methanol 7.0% by volume, carbonic acid pressurized to m ² (gauge pressure) Gas (1.0% by volume, nitrogen: 58.0% by volume) is preheated to about 90 ° C. in a heat exchanger and then supplied at a rate of 6.80 Nm ³ / hr, and hot water is passed through the shell side of the reactor. The reaction was carried out while maintaining the temperature at the center of the catalyst layer at about 120 ° C.
At this time, the space-time yield (STY) of dimethyl carbonate was 338.
kg / m ³ · hr.

The gas passing through the catalyst layer has a pressure of 3.
Since the pressure was reduced to 71 kg / cm ² (gauge pressure), it was 4.28 kg / cm by a diaphragm type gas circulation pump.
² (gauge pressure). This is the inner diameter 100mm,
It was led to the bottom of a 1300 mm high absorption tower (Raschig-filled gas-liquid contact absorber), and methanol 0.18
1 / hr, and 2.50 kg / hr of dimethyl oxalate from a position 200 mm below the top of the column, the mixture was brought into countercurrent contact at a top temperature of 35 ° C. and a bottom temperature of 40 ° C. As a result, the composition of 3.29 kg / hr of the absorbing solution obtained from the bottom of the column was 77.7% by weight of dimethyl oxalate and 1% of dimethyl carbonate.
7.3% by weight, 4.3% by weight of methanol and 0.04% by weight of methyl formate. The pressure of the non-condensable gas taken out from the top of the column is 4.18 kg / cm ² (gauge pressure).
Met.

Since the concentration of methyl nitrite in 6.63 Nm ³ / hr of the non-condensable gas (gas introduced into the regeneration tower) obtained from the top of the column is lower than that in the raw material gas,
Methyl nitrite was regenerated in the next regeneration tower. Since a part of methyl nitrite was dissolved in the absorbing solution in the absorption tower, nitric oxide was also supplied at the same time. That is, a gas containing 79 Nl / hr of oxygen and 14.0% by volume of nitrogen monoxide was mixed with 7.5 Nl / hr of a non-condensable gas, and then mixed with an inner diameter of 158 m.
m, a gas-liquid contact type regeneration tower having a height of 1400 mm, methanol 5.0 l / hr was introduced from the top of the tower, and the top temperature was 30
C. and the bottom temperature was 40 ° C., and the mixture was brought into countercurrent contact to regenerate methyl nitrite.

Regeneration gas 6.65 N derived from the regeneration tower
The pressure of m ³ / hr is 4.02 kg / cm ² (gauge pressure).
Then, 0.15 Nm ³ / hr of carbon monoxide is additionally supplied,
Composition of 20.0% by volume of carbon monoxide, 10.0% by volume of methyl nitrite, 4.0% by volume of nitric oxide, 7.0% by volume of methanol, 1.0% by volume of carbon dioxide and 58.0% by volume of nitrogen At the reactor.

On the other hand, 2.1% by weight derived from the regeneration tower
The methanol containing 3.8 l / hr was reused as a methanol source in the regeneration tower after removing water by distillation. Note that dimethyl carbonate was distilled from 3.29 kg / hr of the absorption liquid derived from the absorption tower by distillation to obtain 0.55 g of dimethyl carbonate.
It was obtained continuously at 7 kg / hr. Further, as described above, the selectivity of the generated carbon dioxide contained in the reaction gas led out of the reactor by performing the gas circulation was 1.6%.

Example 2 A dimethyl carbonate was produced by installing a diaphragm type gas circulation pump in a conduit between the following regeneration tower and absorption tower. In a tube of a stainless steel multi-tube reactor consisting of six tubes having an inner diameter of 27 mm and a height of 500 mm, Japanese Patent Laid-Open No.
Activated carbon (Shirasagi: manufactured by Takeda) as described in JP-A-41243 was filled with 1.71 l of a solid catalyst (4 mmφ × 6 mm) supporting palladium chloride and cupric chloride.
The reaction was carried out in the same manner as described above. At this time, the space-time yield (STY) of dimethyl carbonate was 338 kg / m ³ · hr, and the pressure of the gas passed through the catalyst layer was 3.71 kg / cm ² (gauge pressure).

The gas that has passed through the catalyst layer is passed through an inner diameter of 100
to the bottom of an absorption tower (Raschig ring-filled gas-liquid contact absorber) with a height of 1300 mm and methanol 0.18 l / hr from the top, and 2.50 kg of dimethyl oxalate from 200 mm below the top. While introducing / hr, countercurrent contact was performed at a tower top temperature of 35 ° C and a tower bottom temperature of 40 ° C. As a result, 3.28 kg of the absorbing solution obtained from the bottom of the column /
The composition of hr was 78.1% by weight of dimethyl oxalate, 16.8% by weight of dimethyl carbonate, 4.2% by weight of methanol, and 0.03% by weight of methyl formate. The pressure of non-condensable gas withdrawn from the top of the column so was 3.60kg / cm ² (gauge pressure), pressurized to 4.18kg / cm ² with a diaphragm type gas circulating pump (gauge pressure).

Since the concentration of methyl nitrite in 6.64 Nm ³ / hr of the non-condensable gas (gas introduced into the regeneration tower) obtained from the top of the column is lower than in the raw material gas,
Methyl nitrite was regenerated in the next regeneration tower. Since a part of methyl nitrite was dissolved in the absorbing solution in the absorption tower, nitric oxide was also supplied at the same time. That is, a gas containing 79 Nl / hr of oxygen and 14.0% by volume of nitrogen monoxide was mixed with 7.5 Nl / hr of a non-condensable gas, and then mixed with an inner diameter of 158 m.
m, a gas-liquid contact type regeneration tower having a height of 1400 mm, methanol 5.0 l / hr was introduced from the top of the tower, and the top temperature was 30
C. and the bottom temperature was 40 ° C., and the mixture was brought into countercurrent contact to regenerate methyl nitrite.

6.66 N of regeneration gas derived from the regeneration tower
The pressure of m ³ / hr is 4.02 kg / cm ² (gauge pressure).
Then, 0.15 Nm ³ / hr of carbon monoxide is additionally supplied,
Composition of 20.0% by volume of carbon monoxide, 10.0% by volume of methyl nitrite, 4.0% by volume of nitric oxide, 7.0% by volume of methanol, 1.0% by volume of carbon dioxide and 58.0% by volume of nitrogen At the reactor.

On the other hand, 2.1% by weight derived from the regeneration tower
3.8 l / hr of water-containing methanol was reused as a methanol source in the regeneration tower after removing water by distillation. In addition, dimethyl carbonate was distilled from 3.28 kg / hr of the absorption liquid derived from the absorption tower by distillation.
It was obtained continuously at 40 kg / hr. Further, as described above, the selectivity of the generated carbon dioxide contained in the reaction gas led out of the reactor by performing the gas circulation was 1.6%.

Comparative Example 1 A diaphragm type gas circulation pump was installed in a conduit between the following regeneration tower and reactor to produce dimethyl carbonate. In a tube of a stainless steel multi-tube reactor consisting of six tubes having an inner diameter of 27 mm and a height of 500 mm, Japanese Patent Laid-Open No.
Activated carbon (Shirasagi: manufactured by Takeda) as described in JP-A-41243 was filled with 1.71 l of a solid catalyst (4 mmφ × 6 mm) supporting palladium chloride and cupric chloride.
The reaction was carried out in the same manner as described above. At this time, the space-time yield (STY) of dimethyl carbonate was 338 kg / m ³ · hr, and the pressure of the gas passed through the catalyst layer was 3.71 kg / cm ² (gauge pressure).

The gas having passed through the catalyst layer is passed through an inner diameter of 100
to the bottom of an absorption tower (Raschig ring-filled gas-liquid contact absorber) with a height of 1300 mm and methanol 0.18 l / hr from the top, and 2.50 kg of dimethyl oxalate from 200 mm below the top. While introducing / hr, countercurrent contact was performed at a tower top temperature of 35 ° C. and a tower bottom temperature of 20 ° C. As a result, 3.28 kg of the absorbing solution obtained from the bottom of the column /
The composition of hr was 78.1% by weight of dimethyl oxalate, 16.8% by weight of dimethyl carbonate, 4.2% by weight of methanol, and 0.1% by weight of methyl formate. The pressure of the non-condensable gas taken out from the top was 3.60 kg / cm ² (gauge pressure).

Since the concentration of methyl nitrite in 6.64 Nm ³ / hr of the non-condensable gas (gas introduced into the regeneration tower) obtained from the top of the column is lower than that in the raw material gas,
Methyl nitrite was regenerated in the next regeneration tower. Since a part of methyl nitrite was dissolved in the absorbing solution in the absorption tower, nitric oxide was also supplied at the same time. That is, after mixing 7.5 Nl / hr of a gas containing 78 Nl / hr of oxygen and 14.0% by volume of nitrogen monoxide into a non-condensable gas, the mixture is 158 m in inner diameter.
m, a gas-liquid contact type regeneration tower having a height of 1400 mm, methanol 5.0 l / hr was introduced from the top of the tower, and the top temperature was 30
C. and the bottom temperature was 40 ° C., and the mixture was brought into countercurrent contact to regenerate methyl nitrite.

Regeneration gas 6.66 N derived from the regeneration tower
The pressure of m ³ / hr is 3.49 kg / cm ² (gauge pressure)
After pressurizing with a diaphragm gas circulation pump, 0.15 Nm ³ / hr of carbon monoxide was additionally supplied, and 20.0% by volume of carbon monoxide and 10.0% of methyl nitrite were added.
The reactor was led to the reactor at a composition of% by volume, 4.0% by volume of nitric oxide, 7.0% by volume of methanol, 1.0% by volume of carbon dioxide and 58.0% by volume of nitrogen.

On the other hand, 2.0% by weight derived from the regeneration tower
4.5 l / hr of methanol containing water was reused as a methanol source in the regeneration tower after removing water by distillation. In addition, dimethyl carbonate was distilled from 3.28 kg / hr of the absorption liquid derived from the absorption tower by distillation.
It was obtained continuously at 40 kg / hr. Further, as described above, the selectivity of the generated carbon dioxide contained in the reaction gas led out of the reactor by performing the gas circulation was 2.2%.

[0048]

[0049]

[Table 1]

According to the method of the present invention, dimethyl carbonate is produced by reacting carbon monoxide and methyl nitrite in the presence of a solid catalyst. It is possible to improve the regeneration rate of methyl nitrate (oxidation rate of nitric oxide) and the efficiency of removing water, and to suppress the by-product of carbon dioxide in the reactor. A manufacturing method can be provided.

[Brief description of the drawings]

FIG. 1 is a flow sheet showing one embodiment of the present invention.

[Description of References] 1 is a reactor, 2 is an absorption tower, 3 is a regeneration tower, and 11 to 22 are conduits.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-141243 (JP, A) JP-A-5-25096 (JP, A) JP-A-6-25104 (JP, A) JP-A-7- 69995 (JP, A) JP-A-62-190146 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C07C 69/96 C07C 68/00 C07C 68/08 CAPLUS (STN) REGISTRY (STN) WPIDS (STN)

Claims (1)

(57) [Claims] 1. A first step of reacting carbon monoxide and methyl nitrite in a gas phase in the presence of a solid catalyst in a reactor to form dimethyl carbonate. The second absorbed by dimethyl acid
A method for producing dimethyl carbonate comprising the step of contacting nitric oxide in the non-condensed gas with molecular oxygen and methanol in a methyl nitrite regeneration tower in the second step to produce methyl nitrite. A circulator for circulating a gas containing carbon oxide and methyl nitrite may be provided as a conduit between the reactor in the first step and the dimethyl carbonate absorption tower in the second step or the dimethyl carbonate absorption tower in the second step. A continuous method for producing dimethyl carbonate, comprising circulating the gas by installing the gas in a conduit between three steps of methyl nitrite regeneration tower.