JPH07206778A - Continuous production of dimethyl carbonate - Google Patents

Abstract

PURPOSE:To efficiently and continuously obtain dimethyl carbonate useful as a solvent, etc., in high yield without increasing loss of carbon monoxide by carrying out vapor phase catalytic reaction of carbon monoxide with methyl nitrite to produce dimethyl carbonate and treating dimethyl carbonate under specific conditions. CONSTITUTION:Vapor phase catalytic reaction of carbon monoxide with methyl nitrite is carried out in a reactor 1 in the presence of a solid catalyst to produce dimethyl carbonate and dimethyl carbonate is absorbed in dimethyl oxalate which is an absorbing solvent in a dimethyl carbonate absorption tower 2. Nitrogen monoxide in an uncondensing gas is brought into contact with molecular oxygen and methanol in a methyl nitrite regeneration tower 3 to produce methyl nitrite and dimethyl carbonate in the absorbing liquid is separated by distillation. Further, a purge gas from a gas circulation system and an oxidized gas of ammonia are fed to a methyl nitrite recovery tower 4 and nitrogen oxide in the gas is brought into contact with methanol so as to produce methyl nitrite to continuously provide the objective dimethyl carbonate.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for industrially producing dimethyl carbonate by subjecting carbon monoxide and methyl nitrite to a gas phase catalytic reaction in the presence of a solid catalyst, and particularly to producing dimethyl carbonate on a large scale. A method for continuously producing dimethyl carbonate by effectively replenishing nitrogen oxides required to regenerate methyl nitrite. Dimethyl carbonate is a compound useful as a synthetic raw material for aromatic polycarbonates, pharmaceuticals and agricultural chemicals, and as a solvent.

[0002]

2. Description of the Related Art A method for continuously producing dimethyl carbonate by subjecting carbon monoxide and methyl nitrite to a gas phase catalytic reaction in the presence of a solid catalyst is disclosed, for example, in Japanese Patent Application No. 3-269950. , A first step in which carbon monoxide and methyl nitrite are subjected to a gas phase catalytic reaction in a reactor in the presence of a solid catalyst to produce dimethyl carbonate, and the dimethyl carbonate produced in the first step is a dimethyl carbonate absorption tower (absorption tower) In the second step of absorbing with dimethyl oxalate as an absorption solvent in step 2, the nitric oxide in the non-condensed gas in the second step is contacted with molecular oxygen and methanol in a methyl nitrite regeneration tower (regeneration tower) to remove methyl nitrite. It comprises a third step of producing and a fourth step of distilling and separating the dimethyl carbonate absorbed and separated into dimethyl oxalate in the extractive distillation column and the dimethyl carbonate distillation column.

In this process, methyl nitrite and nitric oxide are catalytically present and are not substantially consumed in the entire reaction as shown in the following reaction formula. Gas dissolved in the can solution and circulated between the first step, the second step, and the third step (circulation gas)
Inevitably, the loss due to the purging of Mn is unavoidable, and methyl nitrite or nitrogen oxides (NO _x ) are being replenished.

[0004]

[Chemical 1]

To replenish methyl nitrite or NO _x ,
NO _X generated by the reaction between sodium nitrite and an inorganic acid such as nitric acid or sulfuric acid is mixed with the non-condensable gas and the molecular oxygen-containing gas in the second step and introduced into the regeneration tower in the third step. However, although this method is a simple and excellent method for generating NO _x , it has a problem that sodium nitrite as a raw material is special, and sodium nitrate is further produced as a by-product. It is not the preferred method in the process of producing dimethyl carbonate on a large scale for use in production.

[0006] Further, a method of air-oxidizing ammonia is also known as a method for producing NO _x . However, in this method, a large amount of nitrogen gas in the air is entrained in NO _x , so that in the above-mentioned process for producing dimethyl carbonate. When applied (that is, the oxidizing gas of ammonia is introduced into the regeneration tower of the third step), it is necessary to purge a large amount of gas (circulation gas). In this case, although methyl nitrite and nitric oxide in the purge gas can be recovered by, for example, the method described in JP-A-1-121250, it is difficult to recover carbon monoxide, and the loss thereof is very large. There's a problem.

[0007]

DISCLOSURE OF THE INVENTION The present invention relates to a preferable method for replenishing nitrogen oxides (NO _x ) required for regenerating methyl nitrite in a process for producing dimethyl carbonate on a large scale, and particularly, PROBLEM TO BE SOLVED: To provide an industrially preferable continuous production method of dimethyl carbonate capable of regenerating methyl nitrite to produce dimethyl carbonate by a preferable NO _x supplementing method without increasing carbon monoxide loss. The purpose is.

[0008]

The object of the present invention is to carry out a gas phase catalytic reaction of carbon monoxide and methyl nitrite in the presence of a solid catalyst in a reactor to produce dimethyl carbonate. In the dimethyl carbonate absorption tower to absorb the dimethyl carbonate produced in step 2), contacting the nitric oxide in the non-condensed gas in the second step with molecular oxygen and methanol in the methyl nitrite regeneration tower To supply methyl nitrite recovery column with purge gas from the gas circulation system and ammonia oxidizing gas. And contacting the nitrogen oxides in the gas with methanol to produce methyl nitrite
It is achieved by a continuous process for the production of dimethyl carbonate, characterized in that it consists of individual steps.

First, the outline of each step of the present invention will be described.
The first step is to introduce a raw material gas containing carbon monoxide and methyl nitrite into a reactor filled with a solid catalyst carrying a platinum group metal and / or its compound and a co-catalyst to carry out a gas phase catalytic reaction. This is a dimethyl carbonate synthesis step in which dimethyl carbonate is produced to obtain a reaction gas containing dimethyl carbonate. In the second step, the reaction gas in the first step was introduced into a dimethyl carbonate absorption tower (hereinafter referred to as an absorption tower), brought into contact with dimethyl oxalate added as an absorption solvent, and produced in the catalytic reaction of the first step. It is a dimethyl carbonate absorption step in which a non-condensed gas containing nitric oxide and an absorption liquid absorbing the generated dimethyl carbonate are separated.

In the third step, the non-condensed gas in the second step is introduced into a methyl nitrite regenerator (hereinafter referred to as a regenerator), brought into contact with the molecular oxygen and methanol supplied, and the non-condensed gas in the non-condensed gas is introduced. This is a methyl nitrite regeneration step in which nitric oxide is regenerated to methyl nitrite and is circulated and fed to the reactor in the first step. The fourth step is a dimethyl carbonate purification step in which methanol is removed from the dimethyl carbonate absorbed and separated into dimethyl oxalate in the second step by extractive distillation, and then dimethyl carbonate is separated by distillation.

The gas containing carbon monoxide and methyl nitrite is circulated between the first step, the second step and the third step (hereinafter, referred to as the first step, the second step and the third step). The gas that circulates between the steps is referred to as a circulation gas, and this system is referred to as a gas circulation system.) Carbon dioxide produced as a by-product of the catalytic reaction accumulates, so that the circulation gas is purged from the gas circulation system. It The circulation gas is purged by purging a part of the gas (regeneration gas) derived from the regeneration tower of the third step, and the purge amount is at least the amount of the by-product gas accumulated in the circulation gas. .

An active ingredient for producing dimethyl carbonate
Some carbon monoxide, methyl nitrite and nitric oxide are
Lost due to circulating gas purge, methyl nitrite and monoacid
Nitrogen nitride is further absorbed by the absorption liquid of the absorption tower of the second step and the recycle of the third step.
It is also lost by dissolution in the can of the raw tower. For this reason, the book
In the invention, nitrogen oxide of methyl nitrite source (hereinafter referred to as NO _X
The purge amount of the circulating gas is as follows.
Control and increase carbon monoxide loss without increasing
The required amount of ammonia gas is supplied.

In the fifth step, the oxidizing gas of ammonia and the purge gas from the gas circulation system are led to a methyl nitrite recovery tower (hereinafter referred to as a recovery tower) for recovering methyl nitrite and nitric oxide. , NO _x in the gas is contacted with methanol to be regenerated into methyl nitrite, and the regenerated methyl nitrite is also absorbed into methanol together with methyl nitrite in the purge gas, which is used in the regeneration tower of the third step. This is a process for recovering and supplying methyl nitrite.

Ammonia oxidizing gas can be conveniently obtained at low cost by air oxidation of ammonia, and is particularly suitable when a large amount of NO _x is required. This gas is produced using a large excess of air with respect to ammonia, it contains a large amount of nitrogen gas together with NO _X. For this reason, when this gas is directly supplied to the gas circulation system, a large amount of nitrogen gas is brought into the gas circulation system, and it becomes necessary to purge a large amount of the circulation gas. There will be a loss. Therefore, in the present invention, in order to prevent this, the oxidizing gas of ammonia is supplied to the recovery tower outside the gas circulation system, and the accompanying nitrogen gas is discharged as waste gas. Then, NO _X in the oxidizing gas ammonia is converted and reproduced together with NO _X in the purge gas to methyl nitrite, only methanol generated methyl nitrite is to be supplied to the regeneration tower.

The method for producing the oxidizing gas of ammonia is as follows:
For example, the method used industrially in the nitric acid production process may be used, and ammonia and air may be used as O ₂ / NH ₃ = 0.5.
˜5, preferably 0.8 to 3 are mixed, and a gas phase catalytic reaction is carried out on a catalyst such as platinum or iron-bismuth. As the reactor, a single tube reactor filled with these solid catalysts is suitable.

Next, the first to third steps and the fifth step of the present invention will be described in more detail. First Step The synthesis of dimethyl carbonate in the first step is carried out by using a raw material containing carbon monoxide and methyl nitrite in a reactor filled with a platinum group metal and / or a compound thereof and a solid catalyst in which a co-catalyst is supported on a carrier. It is carried out by introducing a gas to carry out a gas phase catalytic reaction.

Examples of the solid catalyst include, for example, Japanese Patent Laid-Open No. Hei 3
It is effective to use a platinum group metal and / or a compound thereof and a co-catalyst supported on a carrier as described in JP-A-1411243. Examples of the platinum group metal supported on the carrier as a platinum group metal and / or a compound thereof by these solid catalysts include palladium, platinum, iridium, ruthenium and rhodium, with palladium being most preferred. As the palladium compound, palladium chloride,
Palladium halides such as palladium bromide, palladium nitrate, palladium inorganic acid salts such as palladium sulfate,
Examples thereof include organic acid salts of palladium such as palladium acetate and palladium benzoate, halide-containing complexes of palladium such as lithium tetrachloropalladate, and paramine ammine complexes such as tetraamminepalladium chloride and tetraamminepalladium nitrate. Of these palladium compounds, palladium chloride is most preferred.

In the solid catalyst, a compound of a metal such as copper, iron, bismuth or cerium may be supported on the carrier as a co-catalyst in addition to the platinum group metal. In the solid catalyst, activated carbon, alumina, silica, diatomaceous earth, zeolite, clay mineral, or the like can be used as a carrier.

Carbon monoxide and methyl nitrite are usually diluted with a reaction-inert gas such as nitrogen or carbon dioxide,
The raw material gas is supplied 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 for filling the solid catalyst,
Single-tube or multi-tube reactors are preferred.

The concentration of methyl nitrite in the raw material gas is determined in terms of reaction rate and safety. That is, the concentration of methyl nitrite is preferably 1 to obtain a satisfactory reaction rate.
It is necessary that the concentration is not less than volume%, but it is not preferable that the concentration is too high because methyl nitrite is an explosive compound. In the present invention, a concentration of 3 to 25 volume% is usually preferable. Further, the concentration of carbon monoxide in the raw material gas can be varied over a wide range, but in the continuous process, a portion of the circulating gas is purged as described above, so if the concentration becomes high, loss to the outside of the system increases and it is economical. Not good for Therefore, a suitable concentration of carbon monoxide is industrially usually 1 to 50% by volume,
It is preferably 5 to 30% by volume.

The reaction temperature is preferably a relatively low temperature as long as a desired reaction rate can be obtained, and is usually 50 to 200 ° C., more preferably 80 to 150 ° C. The reaction pressure is usually from normal pressure to 10 kg / cm ² (gauge pressure),
It is preferably 1 to 6 kg / cm ² (gauge pressure).

By carrying out the synthesis reaction of dimethyl carbonate in this manner, dimethyl carbonate, dimethyl oxalate, nitric oxide, carbon dioxide gas, unreacted carbon monoxide and methyl nitrite,
A reaction gas containing an inert gas or the like is discharged from the reactor. The target dimethyl carbonate is separated by introducing this reaction gas into the absorption tower of the second step and absorbing it by dimethyl oxalate supplied from the upper part of the absorption tower.

Second Step The absorption of dimethyl carbonate in the second step is carried out by bringing the above-mentioned reaction gas into contact with dimethyl oxalate as an absorption solvent in an absorption tower as follows. The supply 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 relative to dimethyl carbonate.
A weight times, preferably 4 to 6 times by weight is suitable. The operating temperature of the absorption tower is preferably low in order to efficiently absorb dimethyl carbonate, but if the temperature is too low, solidification of dimethyl oxalate occurs, and it is also disadvantageous in terms of energy. 0 to 100 ° C, preferably 30 to
80 ° C is good.

A small amount of dimethyl carbonate and dimethyl oxalate are entrained in the non-condensed gas in the absorption tower, but they are completely lost when they are brought into the next third step, and therefore a small amount of methanol from the top of the absorption tower. It is preferable to recover dimethyl carbonate and dimethyl oxalate accompanied by feeding. At this time, the amount of methanol supplied is usually 5 to 30% by weight, preferably 10 to 20% by weight, based on dimethyl carbonate in the reaction gas. In addition to the unreacted carbon monoxide and methyl nitrite, a large amount of nitric oxide produced in the first step is contained in the non-condensed gas. Is regenerated to methyl nitrite in the regeneration tower. It should be noted that the dimethyl carbonate absorbed in the dimethyl oxalate in this manner is the known low-boiling compound such as methanol or a trace amount of methyl formate by-produced in the reaction due to dimethyl oxalate in the fourth step. After being separated by extractive distillation,
Further, it is separated and purified by distillation.

Third Step Regeneration of methyl nitrite in the third step is carried out by contacting the non-condensed gas with the molecular oxygen-containing gas and methanol in the regeneration tower as follows. At this time, as the regeneration tower, a usual gas-liquid contact device such as a packed tower, a bubble tower, a spray tower, or a plate tower is used.

As the molecular oxygen-containing gas, pure oxygen gas, oxygen gas diluted with an inert gas such as nitrogen, or air is used individually or in a mixed state with the non-condensed gas. In the regeneration tower, the molecular oxygen-containing gas is usually supplied in an amount of 0.08 to 0.2 mole based on oxygen with respect to 1 mole of nitric oxide in the gas introduced into the regeneration tower. These gases are 6
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. Methanol is used in an amount equal to or more than that required for completely absorbing and reacting nitrogen dioxide produced from nitric oxide and molecular oxygen and almost equimolar amount of nitric oxide, and is usually introduced into a regeneration tower. 2 to 1 mol of nitric oxide in the gas
5 mol is used.

The methanol used in the regenerator is directly supplied to the upper part of the regenerator, or it is supplied to the middle stage of the regenerator after contacting with purge gas in the recovery column to absorb methyl nitrite. . The ratio of both used depends on the purge amount of the circulating gas, but usually 30 to 90%, preferably 50 to 80% of the total methanol used in the regeneration tower is directly supplied to the regeneration tower from the upper part of the regeneration tower.

Since the liquid discharged from the regeneration tower is a methanol solution containing water produced by the methyl nitrite regeneration reaction, the water content in methanol is usually 2% by volume or less, preferably 0.2% by an operation such as distillation. It is industrially advantageous to reuse it in the second step, the third step, and the recovery column after purifying it so that the content is less than or equal to volume%. Further, the gas (regenerated gas) discharged from the regeneration tower is the first gas according to the gas circulation system.
It is purely used in the process reactor and reused in the dimethyl carbonate synthesis reaction. At this time, a required amount of carbon monoxide is replenished to the gas circulation system in accordance with the amount consumed in the reaction and the amount reduced by purging the circulating gas.

The recovery of methyl nitrite in the fifth step fifth step, by supplying the purge gas from the oxidizing gas and the gas circulation system of ammonia to be supplied for replenishing the NO _X in the recovery column, these gases N
The O _X as well as conversion and playback methyl nitrite is contacted with methanol, the generated and methyl nitrite in methyl nitrite and in the purge gas is done by absorption in methanol. The oxidizing gas of ammonia is obtained by air oxidation of ammonia as described above, and the purge gas is obtained by withdrawing a part of the regenerating gas discharged from the regenerating tower.

The recovery column is preferably a gas-liquid contact type column type absorption device which is usually used such as a packed column, a plate column, a bubble column column, and the oxidizing gas of ammonia is supplied to the bottom of this column together with a purge gas. At this time, the oxidizing gas of ammonia and the purge gas may be directly supplied to the recovery tower, but it is more preferable to supply both to the recovery tower after mixing the both. The amount of purge gas depends on the amount of accumulated by-product gas such as carbon dioxide gas in the circulating gas, but is usually 0.1% of the volume of the gas phase portion of the circulation system including the reactor, the absorption tower and the regeneration tower. -30% by volume / hr, preferably 0.1-20%
Capacity / hr. The supply amount of the oxidizing gas of ammonia is usually 0.1 to 30 mol% / hr of the total number of moles of methyl nitrite and nitric oxide contained in the gas phase portion.
Is an amount containing NO _X corresponding to. If necessary, the molecular oxygen-containing gas is introduced according to the amount of nitric oxide in the purge gas as in the regeneration tower.

The methanol used in the recovery column is the regeneration of methyl nitrite from nitric oxide in the purge gas, the conversion of NO _{x in} the oxidizing gas of ammonia to methyl nitrite, and the absorption of the produced methyl nitrite. Is fed from the top of this tower to The supply amount thereof is usually 5 to 200 times mol, particularly 20 to 50 times mol, based on the total number of moles of nitric oxide and methyl nitrite in the purge gas and NO _x in the ammonia oxidizing gas. preferable. This methanol is cooled in order to increase the absorption efficiency of the produced methyl nitrite, preferably 20%.
It is preferable to use one having a temperature of not higher than 0 ° C, particularly 10 ° C or lower.

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 in which a raw material gas containing carbon monoxide, methyl nitrite and nitric oxide is installed in a conduit 20 above a multi-tube reactor 1 having a reaction tube filled with a platinum group metal-based solid catalyst (Fig. It is pressurized with (not shown) and introduced through conduit 22. In the reactor 1, the catalytic reaction is carried out in the gas phase, the reaction gas passing through the catalyst layer is taken out from the lower part of the reactor,
It is introduced into the absorption tower 2 through the conduit 11.

In the absorption tower 2, the reaction gas and the conduit 13,
Upon contact with methanol and dimethyl oxalate introduced from 14, dimethyl carbonate in the reaction gas is absorbed by dimethyl oxalate and separated. Dimethyl carbonate,
A liquid consisting of dimethyl oxalate and methanol is taken out from the lower part through a conduit 15 and separated and purified by a known purification process (not shown). On the other hand, the non-condensed gas containing unreacted carbon monoxide, methyl nitrite, and nitric oxide produced by the above catalytic reaction is passed through the conduit 12 from the upper part to the regeneration tower 3
Will be introduced at the bottom of.

In the regeneration tower 3, the non-condensing gas and the molecular oxygen-containing gas introduced through the conduit 16 are brought into countercurrent contact with methanol introduced from the upper portion through the conduit 19 to regenerate methyl nitrite. . The gas discharged from the regeneration tower 3 (regeneration gas) is supplied 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 lower portion through the conduit 18 in the form of a methanol solution. This methanol solution is reused as methanol to be supplied to the absorption tower 2, the regeneration tower 3 or the recovery tower 4 through the conduits 13, 19 and 25 after water in the liquid is removed by an operation such as distillation.

Gas discharged from the regeneration tower 3 (regeneration gas)
Is purged from the gas circulation system through conduit 23. This purge gas is introduced into the lower part of the recovery column 4 together with the gas containing NO _x obtained by air-oxidizing the ammonia supplied through the conduit 17. At this time, if necessary, the molecular oxygen-containing gas is introduced from the conduit 27. In the recovery tower 4, these mixed gases introduced from the lower part are brought into countercurrent contact with methanol introduced from the upper part through the conduit 25 to regenerate and convert NO _X into methyl nitrite.

The methyl nitrite obtained in the recovery tower 4 is taken out from the lower part in the form of a methanol solution and supplied to the middle stage of the regeneration tower 3 through the conduit 24. The purge gas supplied to the stripping column 4, nitrogen gas or a small amount of by-product gas contained in the NO _X containing gas and molecular oxygen-containing gas is discharged out of the system through the conduit 26.

[0037]

EXAMPLES Next, the method of the present invention will be specifically described with reference to Examples and Comparative Examples. The space-time yield (STY) of dimethyl carbonate (kg / m ³ · h in Examples and Comparative Examples)
r) is the contact reaction time between carbon monoxide and methyl nitrite, θ (hr), and the amount of dimethyl carbonate formed during that time is a (hr).
(Kg), and the amount of catalyst packed in the reaction tube is b (m ³ ).
Was calculated by the following equation.

[0038]

[Equation 1]

Example 1 [Production of dimethyl carbonate] In a tube of a stainless multi-tube reactor composed of 20 tubes having an inner diameter of 27 mm and a height of 3.0 m, as shown in JP-A-3-141243. Solid catalyst (4 mmφ × 6 mm) in which palladium chloride and cupric chloride are supported on activated carbon (Shirasagi: manufactured by Takeda) 34.
0 l was filled. With a gas compressor from the top to this catalyst layer,
Raw material gas pressurized to 4.02 kg / cm ² (gauge pressure) (composition: carbon monoxide 20.0% by volume, methyl nitrite 1
0.0% by volume, 4.0% by volume of nitric oxide, 7.0% by volume of methanol, 1.0% by volume of carbon dioxide, 58.0% by volume of nitrogen) were preheated to about 90 ° C. by a heat exchanger, 136 Nm
^It was supplied at a rate of ³ / hr and hot water was passed through the shell side of the reactor to keep the temperature of the central portion of the catalyst layer at about 125 ° C. to carry out the reaction. At this time, the space-time yield (STY) of dimethyl carbonate was 342 kg / m ³ · hr.

The gas which has passed through the above catalyst layer has an inner diameter of 300
mm, height 5.0 m, led to the bottom of a pole-ring-filled gas-liquid contact absorber (absorption tower), and methanol from the top of the tower 3.
Countercurrent contact was carried out at a column top temperature of 35 ° C. and a column bottom temperature of 55 ° C. while introducing 6 l / hr and dimethyl oxalate 50.0 kg / hr from a position 1000 mm below the column top. As a result, the composition of the absorption liquid 65.8 kg / hr obtained from the bottom of the tower was as follows: dimethyl oxalate 77.6% by weight, dimethyl carbonate 17.3% by weight, methanol 4.2% by weight, methyl formate 0.1% by weight. %, And methyl nitrite was 0.3% by weight.

On the other hand, the concentration of methyl nitrite in the non-condensed gas (gas introduced into the regeneration tower) 132.6 Nm ³ / hr obtained from the top of the absorption tower is lower than that in the raw material gas. , Methyl nitrite was regenerated in the next regeneration tower. That is, the non-condensable gas contains oxygen gas of 1.54 Nm ³ / hr.
After being mixed, the mixture was introduced into a gas-liquid contact absorption device (regeneration tower) having an inner diameter of 300 mm and a height of 6.4 m, and 20 l / hr of methanol introduced from the top of the tower, a top temperature of 30 ° C., and a bottom temperature of 4
The methyl nitrite was regenerated by contacting it in countercurrent at 0 ° C. Further, 14 l / hr of a methanol solution having absorbed methyl nitrite in the methyl nitrite recovery tower was simultaneously supplied to the middle stage of the regeneration tower.

Regenerated gas led from the regeneration tower 132.7N
The composition of m ³ / hr was as follows: carbon monoxide 17.6% by volume, methyl nitrite 10.3% by volume, nitric oxide 4.1% by volume, methanol 7.1% by volume, carbon dioxide gas 1.1% by volume, Nitrogen 5
Since it was 9.0% by volume, of this, 400 Nl / h
r was purged. This purge gas was used as an ammonia oxidizing gas produced by the following method: 1.37 Nm ³ / hr
(Composition: 4.1% by volume of nitric oxide, 5.7% by volume of nitrogen dioxide, 1.1% by volume of oxygen, 1.5% by volume of water, 8% of nitrogen
7.6% by volume), then inner diameter 70 mm, height 12
A countercurrent contact was made with 14.0 l / hr of methanol cooled to 10 ° C. introduced from the top of the gas-liquid contactor (recovery tower) of 00 mm to convert NO _x into methyl nitrite and absorbed into methanol. . The obtained absorbing liquid contained 4.3% by weight of methyl nitrite and was withdrawn from the bottom of the tower and supplied to the middle stage of the regeneration tower. At this time, in the waste gas 1.5 Nm ³ / hr discharged from the top of the recovery tower, NO _x 530 ppm,
Methyl nitrite 1330ppm, carbon monoxide 4.7vol%
(7.5 Nl / hr) was contained.

Regenerated gas after purging 132.3 m
³ / hr after pressurizing with said gas compressor, and additionally supplied carbon monoxide 3.3 nM ³ / hr and nitrogen 0.3 Nm ³ / hr, carbon monoxide 20.0% by volume, methyl nitrite 1
0.0% by volume, 4.0% by volume nitric oxide, 7.0% by volume methanol, 1.0% by volume carbon dioxide and 58.0% nitrogen.
It was introduced into the reactor at a composition of% by volume. 1 derived from the regeneration tower
24 l / hr of methanol containing 2.6% by weight of water was reused as a methanol source in a regeneration tower or the like after removing water by distillation. Dimethyl carbonate was continuously obtained at 11.2 kg / hr by distillation from 65.8 kg / hr of the absorption liquid derived from the absorption tower.

[Production of Ammonia Oxidizing Gas] Ammonia gas 192 Nl / hr and air 14 were placed in a stainless steel reactor having an inner diameter of 30 mm containing three platinum-ruthenium mesh catalysts.
A mixed gas of 90 Nl / hr was heated to 100 ° C. by a preheater and supplied. The temperature of the reaction part of the reactor is 800 to 850 ° C.
Ammonia is oxidized in air by controlling it with an electric furnace provided outside the reactor so that the obtained oxidizing gas of ammonia is passed through a cooler to partially condense the water contained in the gas and separate it. After that, it was used for supplementing NO _{X in} Examples and Comparative Examples. The composition of the gas at the time of replenishment is 4.1% by volume of nitric oxide, 5.7% by volume of nitrogen dioxide, 1.1% by volume of oxygen, 1.5% by volume of water, and 87.6% by volume of nitrogen.
Met.

Comparative Example 1 Dimethyl carbonate was produced in the reactor in the same manner as in Example 1 (S
TY: 342 kg / m ³· Hr), oxalic acid dihydrate in the absorption tower
After absorbing dimethyl carbonate in methyl, proceed as follows.
The ammonia gas is supplied to the regeneration tower to supply methyl nitrite.
Playback operation was performed. Non-condensed gas obtained from the top of the absorption tower
Gas (gas introduced into the regeneration tower) 132.6 Nm³/ Hr
And NO_XTo replenish the above
Space 1.37 Nm³/ Hr (Composition: Nitric oxide 4.1 volume
%, Nitrogen dioxide 5.7% by volume, oxygen 1.1% by volume, moisture
(1.5% by volume, 87.6% by volume of nitrogen) and mixed with acid.
Elementary gas 1.54 Nm³/ Hr, and then mix
To the regeneration tower and pass through the methyl nitrite recovery tower
20 l / hr of methanol introduced from the column and a top temperature of 30
℃, the bottom temperature of 40 ℃ and contact with countercurrent to recycle methyl nitrite.
I went live. In the middle stage of this regeneration tower, a recovery tower is used
Simultaneously with 14 l / hr of methanol solution that absorbed methyl acid
Supplied to.

Gas discharged from the regeneration tower 133.9 Nm ³
The composition of / hr is as follows: carbon monoxide 17.5% by volume, methyl nitrite 10.2% by volume, nitric oxide 4.1% by volume, carbon dioxide gas 1.1% by volume, methanol 7.1% by volume, nitrogen 60. ．
Since it was 0% by volume, 1.96 Nm ³ / hr was purged from this gas to maintain the nitrogen concentration. After mixing 110 Nl / hr of air with this purge gas, Example 1
1 was supplied to the recovery tower and introduced from the top of the recovery tower.
Countercurrent contact with 14 l / hr of methanol cooled to 0 ° C. was performed to convert the nitric oxide in the purge gas into methyl nitrite, and at the same time, it was absorbed in methanol together with the methyl nitrite contained in the purge gas. . The obtained absorption liquid contained 6.9% by weight of methyl nitrite and was withdrawn from the bottom of the tower and supplied to the middle stage of the regeneration tower. At this time, the waste gas 1.64 Nm ³ / hr discharged from the top of the recovery tower contains N
It contained O _x 500 ppm, methyl nitrite 1200 ppm, and carbon monoxide 20.9% by volume (324 Nl / hr).

Regeneration gas after purging 132.0 m
³ / hr was pressurized by the gas compressor, and then carbon monoxide (3.6 Nm ³ / hr) and nitrogen (0.3 Nm ³ / hr) were additionally supplied, and carbon monoxide (20.0% by volume) and methyl nitrite (1) were added.
0.0% by volume, 4.0% by volume nitric oxide, 7.0% by volume methanol, 1.0% by volume carbon dioxide and 58.0% nitrogen.
It was introduced into the reactor at a composition of% by volume. The other operations were performed in the same manner as in Example 1, and the results were the same as in Example 1. Table 1 shows the compositions of the purge gas and the gas (waste gas) discharged from the recovery tower in Examples and Comparative Examples.

[0048]

[Table 1]

[0049]

INDUSTRIAL APPLICABILITY According to the method of the present invention, carbon monoxide and methyl nitrite are reacted in the presence of a solid catalyst to industrially produce dimethyl carbonate. NO _X needed to regenerate
When replenishing the gas, a large amount of the accompanying inert gas can be purged outside the gas circulation system circulating between the reactor, the absorption tower and the regeneration tower, so that the loss of carbon monoxide as an active ingredient is reduced. In addition, it is possible to recover almost no methyl nitrite and nitric oxide in the purge gas without increasing the amount, and an industrially suitable continuous production method of dimethyl carbonate,
Particularly, it is possible to provide an excellent continuous production method of dimethyl carbonate in a process for producing dimethyl carbonate on a large scale.

[Brief description of drawings]

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

[Explanation of symbols]

1 is a reactor, 2 is an absorption tower, 3 is a regeneration tower, 4 is a recovery tower, 1
1-27 show conduits.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display area C07C 68/08 // C07B 61/00 300

Claims (1)

[Claims] 1. A first step in which carbon monoxide and methyl nitrite are subjected to a gas phase catalytic reaction in a reactor in the presence of a solid catalyst to produce dimethyl carbonate, and the dimethyl carbonate produced in the first step is a dimethyl carbonate absorption tower. Second step of absorbing with dimethyl oxalate as an absorption solvent in step 3, third step of contacting nitric oxide in the non-condensed gas in the second step with molecular oxygen and methanol in a methyl nitrite regeneration tower to produce methyl nitrite
Step, the fourth step of distilling and separating dimethyl carbonate in the absorbing solution in the second step, and the purge gas from the gas circulation system and the oxidizing gas of ammonia are supplied to the methyl nitrite recovery column to remove the nitrogen oxides in the gas from methanol. A continuous process for the production of dimethyl carbonate, which comprises the steps of the fifth step of contacting with and producing methyl nitrite.