JP2013063965A - Process for production of dialkyl oxalate or/and dialkyl carbonate, and production apparatus therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an effective process for production of a dialkyl oxalate or/and a dialkyl carbonate, and an apparatus for production thereof.SOLUTION: The process for production of the dialkyl oxalate or/and the dialkyl carbonate includes a first step to produce a reaction gas including the dialkyl oxalate or/and the dialkyl carbonate and nitrogen monoxide by reacting a gas including carbon monoxide and an alkyl nitrite in a first reaction vessel 1 in the presence of a catalyst; a second step to give a condensed solution including the dialkyl oxalate or/and the dialkyl carbonate, and a non-condensed gas including nitrogen monoxide by contacting the reaction gas and an absorbing solution in an absorbing apparatus 2; a third step to disperse and supply a molecular oxygen to the non-condensed gas using one or plural nozzles and supplying the mixed gas to the second reaction vessel while oxidizing the nitrogen monoxide in piping to react the mixed gas and an alkanol to thereby give an alkyl nitrite-containing gas in a second reaction vessel 3, and to circulate and supply the alkyl nitrite-containing gas to the first step; and a fourth step to give the dialkyl oxalate or/and the dialkyl carbonate by distillation of the condensed solution with a distillation apparatus. There is also provided the apparatus for production thereof.

Description

  The present invention relates to a method of obtaining dialkyl oxalate or / and dialkyl carbonate by reacting carbon monoxide and alkyl nitrite in the presence of a catalyst, or reacting carbon monoxide and alkyl nitrite in the presence of a catalyst to produce dialkyl carbonate. The present invention relates to a method for efficiently producing dialkyl oxalate and / or dialkyl carbonate by converting nitric oxide produced together with dialkyl oxalate and / or dialkyl carbonate to alkyl nitrite, and a production apparatus therefor.

  Conventionally, as shown by the following formulas (1), (1) ′, and (2), carbon monoxide and alkyl nitrite are reacted in the presence of a catalyst to produce dialkyl oxalate and / or dialkyl carbonate. Then, the nitric oxide produced in the reaction is reacted with oxygen and alkanol to generate (regenerate) alkyl nitrite, and the alkyl nitrite is reused in the dialkyl oxalate formation reaction and / or the dialkyl carbonate formation reaction. However, methods for continuously producing dialkyl oxalate and / or dialkyl carbonate are known (for example, Patent Documents 1, 2, and 3).

2 CO + 2 RONO → (COOR) ₂ + 2 NO (1)
CO + 2 RONO → ROCOOR + 2 NO (1) '
2 NO + 2 ROH + 1/2 O ₂ → NO + NO ₂ + 2 ROH → N ₂ O ₃ + 2 ROH → 2 RONO + H ₂ O (2)
(In the formula, R represents an alkyl group.)

  However, it is known that the reaction of the following formula (3) occurs as a side reaction of the above formula (2), and nitric acid is by-produced.

2 NO + ROH + O ₂ → 2 NO ₂ + ROH → N ₂ O ₄ + ROH → RONO + HNO ₃ (3)
(In the formula, R represents an alkyl group.)

  The side reaction represented by the above formula (3) is often seen to increase when the production facility is enlarged, causing a reduction in the yield of alkyl nitrite.

Moreover, the dissociation degree of dinitrogen tetroxide to nitrogen dioxide produced in the side reaction represented by the above formula (3) is as low as about 20% at 1 atm and 27 ° C. Therefore, in order to suppress the side reactions, NO ₂ concentration it is necessary to suppress the occurrence of locally high space.

Japanese Patent Laid-Open No. 2004-2336 JP 2004-107336 A JP 7-145108 A

  The present invention suppresses a side reaction in producing alkyl nitrite from nitric oxide in a method for producing dialkyl oxalate and / or dialkyl carbonate in which carbon monoxide and alkyl nitrite are reacted in the presence of a catalyst. It is an object of the present invention to provide a method for producing dialkyl oxalate and / or dialkyl carbonate efficiently by producing alkyl nitrite.

As a result of intensive studies to solve the above problems, the present inventors have completed the present invention.
That is, the present invention has the following configuration.
[1] a first step of reacting carbon monoxide and an alkyl nitrite-containing gas in the first reactor in the presence of a catalyst to produce a reaction gas containing dialkyl oxalate or / and dialkyl carbonate and nitric oxide; ,
A second step of contacting the reaction gas with a dialkyl oxalate absorbent or / and a dialkyl carbonate absorbent to obtain a condensate containing dialkyl oxalate or / and dialkyl carbonate, and a non-condensable gas containing nitric oxide;
While mixing molecular oxygen with non-condensable gas and oxidizing nitric oxide in the piping, the mixed gas is supplied to the second reactor and reacted with alkanol to obtain an alkyl nitrite-containing gas. A third step for circulatingly supplying an alkyl nitrate-containing gas to the first step;
A fourth step of distilling the condensate to obtain dialkyl oxalate or / and dialkyl carbonate;
It is a continuous production method of dialkyl oxalate and / or dialkyl carbonate characterized in that molecular oxygen in the third step is dispersedly supplied using one or a plurality of nozzles.
[2] The continuous production method of dialkyl oxalate and / or dialkyl carbonate according to [1] above, wherein the mixed gas in the third step is dispersedly supplied to the second reactor using one or a plurality of nozzles.
[3] The continuous production method of dialkyl oxalate and / or dialkyl carbonate according to [1] or [2] above, wherein the nozzle includes a plurality of outlets.
[4] a first reactor (1) for reacting carbon monoxide with an alkyl nitrite-containing gas to produce a reaction gas containing dialkyl oxalate or / and dialkyl carbonate;
A carbon monoxide supply line (11) for supplying carbon monoxide to the first reactor (1);
A reaction gas extraction line (12) for extracting a reaction gas containing dialkyl oxalate and / or dialkyl carbonate from the first reactor;
A non-condensable gas containing nitric oxide and a condensate containing dialkyl oxalate or / and dialkyl carbonate in contact with a dialkyl oxalate or / and dialkyl carbonate and a dialkyl oxalate absorbent or / and a dialkyl carbonate absorbent. A dialkyl oxalate or / and dialkyl carbonate absorber (2) that produces
A condensate extraction line (14) for extracting the condensate containing dialkyl oxalate or / and dialkyl carbonate from the dialkyl oxalate or / and dialkyl carbonate absorber (2);
A non-condensed gas extraction line (15) for extracting non-condensed gas containing nitric oxide from a dialkyl oxalate or / and dialkyl carbonate absorber;
An oxygen supply line (16) having one or more nozzles for supplying molecular oxygen to the non-condensable gas flowing through the non-condensable gas extraction line (15);
A second reaction in which a mixed gas of non-condensable gas and oxygen is introduced from the bottom, alkanol is introduced from the top, and nitrogen monoxide, oxygen, and alkanol in the mixed gas are reacted to produce a gas containing alkyl nitrite. Vessel (3),
An alkanol supply line (19) for supplying alkanol to the second reactor (3);
A gas circulation line (22) of the alkyl nitrite-containing gas withdrawn from the upper part of the second reactor (3) and supplying the alkyl nitrite-containing gas to the first reactor (1);
A dialkyl oxalate and / or dialkyl carbonate production apparatus having a distillation apparatus for distilling the condensate extracted from the condensate extraction line (14) to obtain dialkyl oxalate and / or dialkyl carbonate.
The numerical values in parentheses in the above [4] and the following [5] to [9] are the numerical values of the symbols described in FIG. Indicates. In FIG. 1, the distillation apparatus is not shown.
[5] The dialkyl oxalate according to the above [4], wherein the non-condensable gas extraction line (15) is provided with one or a plurality of nozzles for dispersing and supplying the mixed gas to the lower part of the second reactor (3). / And an apparatus for producing dialkyl carbonate.
[6] The apparatus for producing dialkyl oxalate and / or dialkyl carbonate according to [4] or [5] above, wherein the nozzle includes a plurality of outlets.
[7] Production of dialkyl oxalate and / or dialkyl carbonate according to any one of the above [4] to [6], wherein the nozzle includes a blowout port for supplying molecular oxygen to the tip and / or side Device.
[8] The dialkyl oxalate according to any one of the above [4] to [7], wherein the nozzle of the oxygen supply line (16) is disposed on substantially the same plane as the cross section of the pipe constituting the non-condensable gas extraction line. / And an apparatus for producing dialkyl carbonate.
[9] Any of the above-mentioned [4] to [8], wherein a stirrer for stirring the mixed gas is provided on the downstream side of the connecting portion between the non-condensable gas extraction line (15) and the oxygen supply line (16). For producing dialkyl oxalate and / or dialkyl carbonate.

  According to the present invention, in a method for producing dialkyl oxalate and / or dialkyl carbonate by reacting carbon monoxide with alkyl nitrite in the presence of a catalyst, and in the production apparatus thereof, the reaction between carbon monoxide and alkyl nitrite is carried out. The produced nitric oxide reacts with oxygen and alkanol to produce alkyl nitrite, which suppresses side reactions when producing alkyl nitrite from this nitric oxide and efficiently produces high-selectivity alkyl nitrite. And dialkyl oxalate or / and dialkyl carbonate can be obtained efficiently.

It is a figure explaining schematic structure of one Embodiment of the dialkyl oxalate or / and dialkyl carbonate manufacturing apparatus used for a dialkyl oxalate or / and dialkyl carbonate manufacturing process. It is a figure explaining schematic structure of one embodiment of a plurality of nozzles which supply molecular oxygen provided in an oxygen supply line. It is a figure explaining schematic structure of other embodiments of a plurality of nozzles which supply molecular oxygen provided in an oxygen supply line. It is a figure explaining the schematic structure of embodiment of the cyclic | annular nozzle containing the several blower outlet which supplies the molecular oxygen provided in the oxygen supply line. (A) It is VV 'sectional drawing explaining the schematic structure inside the 2nd reactor of a dialkyl oxalate or / and dialkyl carbonate manufacturing apparatus, (B) Of the several nozzle provided in the non-condensable gas extraction line It is a figure explaining a schematic structure. It is a top view explaining schematic structure of a plurality of nozzles provided in a non-condensable gas extraction line.

In the present invention, two alkyl groups in the dialkyl oxalate molecule may be the same or different. Similarly, in dialkyl carbonate, two alkyl groups in the molecule may be the same or different. That is, the dialkyl oxalate in the present invention is meant to contain dimethyl oxalate, diethyl oxalate, methyl ethyl oxalate and the like. Moreover, the dialkyl carbonate in the present invention is meant to include dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate and the like.
Hereinafter, the method for producing dialkyl oxalate and / or dialkyl carbonate of the present invention will be described. The method for producing dialkyl oxalate and / or dialkyl carbonate of the present invention is roughly divided into four steps.

(First step)
In the first step, carbon monoxide and an alkyl nitrite-containing gas are reacted in the presence of a catalyst in the first reactor, and the generated dialkyl oxalate or / and dialkyl carbonate and nitrogen monoxide are contained. Is a step of generating.

(Second step)
In the second step, the reaction gas containing dialkyl oxalate or / and dialkyl carbonate and nitric oxide obtained in the first step is brought into contact with the dialkyl oxalate absorbing solution or / and the dialkyl carbonate absorbing solution, This is a step of dividing into a condensate containing a dialkyl oxalate or / and dialkyl carbonate and a dialkyl oxalate absorbent or / and a dialkyl carbonate absorbent and a non-condensable gas containing nitric oxide.

(Third process)
In the third step, molecular oxygen is dispersed and supplied to the non-condensed gas obtained in the second step to obtain a mixed gas, and the first step is performed using one or a plurality of nozzles while oxidizing the contained nitric oxide. Dispersed and fed into the two reactors, the mixed gas and alkanol are uniformly reacted (gas-liquid contact reaction) to obtain an alkyl nitrite-containing gas, and the obtained alkyl nitrite-containing gas is circulated and supplied to the first step It is a process to do. In the third step, molecular oxygen is distributed and supplied to the non-condensed gas using one or a plurality of nozzles. In the case where the nozzle is a nozzle including one outlet, it is preferable to use a plurality of nozzles, and in the case of a nozzle including a plurality of outlets, it is preferable to use one or a plurality of nozzles.

(Fourth process)
The fourth step is a step of obtaining the dialkyl oxalate or / and dialkyl carbonate by distilling the condensate obtained in the second step (including dialkyl oxalate or / and dialkyl carbonate).

  In the third step, as shown in the following formula (2), a small amount of molecular oxygen is mixed with a non-condensed gas containing nitric oxide, and nitrogen monoxide, oxygen, and alkanol in the obtained mixed gas are mixed. Reaction (gas-liquid contact reaction) is carried out to produce a small amount of nitrogen dioxide. Nitrogen dioxide reacts with nitrogen monoxide present around this nitrogen dioxide molecule to generate dinitrogen trioxide, which reacts with alkanol to produce alkyl nitrite and water. .

2 NO + 2 ROH + 1/2 O ₂ → NO + NO ₂ + 2 ROH → N ₂ O ₃ + 2 ROH → 2 RONO + H ₂ O (2)
(In the formula, R represents an alkyl group, preferably an alkyl group having 1 to 3 carbon atoms.)

  However, when a heterogeneous and inappropriate amount of molecular oxygen is supplied to a non-condensable gas containing nitrogen monoxide, a reaction of the following formula (3) occurs as a side reaction of the above formula (2), and nitrogen dioxide When an atmosphere having a high concentration is generated, nitrogen dioxide reacts to produce dinitrogen tetroxide, and dinitrogen tetroxide and alkanol react to produce nitric acid as a by-product.

2 NO + ROH + O ₂ → 2 NO ₂ + ROH → N ₂ O ₄ + ROH → RONO + HNO ₃ (3)
(In the formula, R represents an alkyl group, preferably an alkyl group having 1 to 3 carbon atoms.)

The side reaction represented by the above formula (3) is more likely to occur as the production apparatus becomes larger and the production amount increases. When the side reaction represented by the above formula (3) occurs, the yield of the intermediate alkyl nitrite decreases and the yield of the final product dialkyl oxalate and / or dialkyl carbonate decreases. In order to suppress the side reaction, it is necessary to suppress the generation of a space where the NO ₂ concentration is locally high.

In the method for producing dialkyl oxalate and / or dialkyl carbonate of the present invention, in the third step, molecular oxygen is used in the non-condensed gas containing nitric oxide obtained in the second step, using one or more nozzles. By supplying in a dispersed manner, generation of an atmosphere having a locally high NO ₂ concentration is suppressed, generation of dinitrogen tetroxide (N ₂ O ₄ ) is suppressed, and the side reaction represented by the above formula (3) is performed. Generation of nitric acid can be suppressed. The present invention is particularly effective when the apparatus is enlarged and the piping constituting the non-condensed gas extraction line is enlarged.

  Furthermore, in the method for producing dialkyl oxalate and / or dialkyl carbonate according to the present invention, in the third step, molecular oxygen is dispersedly supplied to the non-condensed gas and mixed while oxidizing nitric oxide in the pipe. It is preferable that the mixed gas is dispersedly supplied to the second reactor using one or a plurality of nozzles to react nitrogen monoxide, oxygen and alkanol in the mixed gas. Nitrogen monoxide, oxygen, and alkanol react uniformly by supplying the mixed gas into the second reactor using one or a plurality of nozzles, and nitric acid is generated by the side reaction represented by the above formula (3). Can be suppressed. The present invention is particularly effective when the apparatus is enlarged and the reactor for reacting nitric oxide, oxygen, and alkanol in the mixed gas is enlarged. In the case where the nozzle is a nozzle including one outlet, it is preferable to use a plurality of nozzles, and in the case of a nozzle including a plurality of outlets, it is preferable to use one or a plurality of nozzles.

  Next, the dialkyl oxalate and / or dialkyl carbonate production apparatus of the present invention will be described with reference to the drawings. FIG. 1 is a diagram illustrating a schematic configuration of an embodiment of a dialkyl oxalate and / or dialkyl carbonate production apparatus used in the dialkyl oxalate and / or dialkyl carbonate production method of the present invention.

  As shown in FIG. 1, one embodiment of an apparatus for producing dialkyl oxalate and / or dialkyl carbonate comprises reacting a carbon monoxide supply line 11 with carbon monoxide and an alkyl nitrite-containing gas to produce dialkyl oxalate or A first reactor 1 for generating a reaction gas containing / and / or dialkyl carbonate, a reaction gas extraction line 12 for extracting a reaction gas containing dialkyl oxalate or / and dialkyl carbonate from the first reactor 1, and a dialkyl oxalate Or / and a dialkyl carbonate and a dialkyl oxalate absorbent or / and a dialkyl carbonate absorbent are brought into contact with each other to form a noncondensable gas containing nitric oxide and a condensate containing dialkyl oxalate and / or dialkyl carbonate. The produced dialkyl oxalate or / and dialkyl carbonate absorber 2 (hereinafter also referred to as “absorber”); A condensate extraction line 14 for extracting a condensate containing dialkyl oxalate and / or dialkyl carbonate from the absorber 2 and a non-condensable gas containing nitric oxide from the dialkyl oxalate or / and dialkyl carbonate absorber 2 are extracted. A condensed gas extraction line 15, an oxygen supply line 16 having one or a plurality of nozzles (not shown in FIG. 1) for supplying molecular oxygen to the non-condensed gas flowing through the non-condensed gas extraction line 15, and the second reactor 3 An alkanol supply line 19 for supplying alkanol to the gas, a mixed gas of non-condensable gas and oxygen is introduced from the lower part, an alkanol is introduced from the upper part, and nitrogen monoxide, oxygen and alkanol in the mixed gas are reacted, A second reactor 3 for producing an alkyl nitrite-containing gas; and an alkyl nitrite-containing gas at the top of the second reactor 3 An alkyl nitrite-containing gas circulation line 22 (hereinafter also referred to as “gas circulation line”) to be extracted and supplied to the first reactor 1 and the condensate introduced from the condensate extraction line 14 are distilled to dialkyl oxalate or / And a distillation apparatus (not shown in FIG. 1) for obtaining dialkyl carbonate. Next, a method for producing dialkyl oxalate and / or dialkyl carbonate will be described by using a dialkyl oxalate or / and dialkyl carbonate production apparatus, divided into first to fourth steps, with reference to FIG.

(First step)
The first step is mainly performed in the first reactor 1, and carbon monoxide and an alkyl nitrite-containing gas are reacted in the presence of a catalyst to produce dialkyl oxalate and / or dialkyl carbonate. The reaction gas containing the dialkyl oxalate and / or dialkyl carbonate and the nitric oxide produced by the reaction is withdrawn from the first reactor 1 by the reaction gas withdrawal line 12. As the first reactor 1, a single-tube or multi-tube heat exchanger reactor can be used effectively.

  Carbon monoxide is supplied to the first reactor 1 through a carbon monoxide supply line 11. In the case of a continuous reaction, carbon monoxide is supplied from the carbon monoxide supply line 11 to compensate for consumption due to the reaction and loss due to the purge of the circulating gas. It is preferable that the supply amount of carbon monoxide is 0.5 to 2 times the mole of the supply amount (number of moles) of alkyl nitrite per unit time in the alkyl nitrite-containing gas. Moreover, it is preferable that the carbon monoxide density | concentration in source gas is 1-50 volume%.

  For example, the alkyl nitrite-containing gas is preferably supplied to the first reactor 1 through the gas circulation line 22 from the second reactor 3 used in the third step. In the case of continuous reaction, an alkyl nitrite-containing gas (circulation gas) extracted from the upper part of the second reactor 3 is circulated and supplied to the first reactor 1 as a raw material gas by the gas circulation line 22. The alkyl nitrite concentration in the raw material gas is preferably 1 to 35% by volume, more preferably 2 to 20% by volume, and still more preferably 5 to 15% by volume. The source gas may contain an inert gas such as nitrogen or carbon dioxide, and may contain a small amount of nitric oxide or alkanol (steam).

  Examples of the alkyl nitrite in the alkyl nitrite-containing gas include alkyl nitrites having 1 to 3 carbon atoms such as methyl nitrite, ethyl nitrite, n-propyl nitrite and i-propyl nitrite. Of these, methyl nitrite is preferred.

  The catalyst used in the first step is preferably a platinum group metal catalyst, that is, a solid catalyst in which a platinum group metal is supported on a carrier (see Japanese Patent Publication No. 57-30095, Japanese Patent No. 2937292, etc.). The supported amount of the platinum group metal is preferably 0.01 to 10% by mass and more preferably about 0.2 to 2% by mass with respect to the carrier. Examples of the carrier include inert carriers such as activated carbon, alumina (α-alumina, γ-alumina, etc.), silica, diatomaceous earth, pumice, zeolite, molecular sieve and the like. As the platinum group metal, palladium is particularly preferable.

  The solid catalyst is, for example, a platinum group metal compound (particularly a palladium compound) supported on a support by a known method (impregnation method, evaporation to dryness method, etc.), and then the platinum group metal compound is reduced to a reducing substance (hydrazine, formaldehyde). , Sodium formate, hydrogen, carbon monoxide, etc.) to a platinum group metal (particularly palladium metal). Reduction to the platinum group metal can also be performed using hydrogen or carbon monoxide in the reactor before the reaction. The platinum group metal catalyst can contain other metals or compounds thereof as a promoter component, if necessary.

  The palladium compound is not particularly limited as long as it is reduced to palladium metal. For example, as a palladium compound, palladium inorganic acid salts (palladium nitrate, palladium sulfate, palladium phosphate, etc.), palladium halides (palladium chloride, palladium bromide), palladium organic acid salts (palladium acetate, palladium oxalate, Palladium benzoate and the like) and various complexes of palladium can be used.

  In the first step, the reaction temperature is preferably 50 to 200 ° C, more preferably 80 to 150 ° C. The pressure is preferably normal pressure to 1 MPaG, more preferably normal pressure to 0.6 MPaG, and still more preferably 0.2 to 0.6 MPaG. The contact time between the source gas and the platinum group metal catalyst is preferably 0.2 to 10 seconds, more preferably 0.2 to 5 seconds.

(Second step)
The second step is performed in the dialkyl oxalate or / and dialkyl carbonate absorber 2 and the reaction gas containing dialkyl oxalate or / and dialkyl carbonate and nitrogen monoxide extracted from the first reactor 1 and oxalic acid A liquid containing dialkyl oxalate or / and dialkyl carbonate (hereinafter referred to as “condensate”) by directly contacting and condensing with a dialkyl absorbent or / and dialkyl carbonate absorption liquid (hereinafter referred to as “absorbing liquid”). ) And a gas containing nitric oxide (hereinafter referred to as “non-condensable gas”).

  The absorbing liquid is not particularly limited as long as it is a liquid in which dialkyl oxalate or / and dialkyl carbonate is easily dissolved, but is preferably a polar solvent, and is the same as the alkyl group portion of dialkyl oxalate or / and dialkyl carbonate to be produced. An alkanol having an alkyl group or a dialkyl oxalate is more preferable. That is, when producing dimethyl oxalate and / or dimethyl carbonate, methanol is preferred, and when producing diethyl oxalate or / and diethyl carbonate, ethanol is preferred, and dialkyl oxalate or / and It is preferable that it is an alkanol which has the same C1-C3 alkyl group as the alkyl group part of dialkyl carbonate. This is because when the alkanol is used as the absorbent, the absorbent and the dialkyl oxalate or / and the dialkyl carbonate undergo a transesterification reaction. Dialkyl oxalate or / and carbonic acid having the same chemical structure even when a transesterification occurs by using an alkanol having the same alkyl group as the alkyl group part of dialkyl oxalate or / and dialkyl carbonate as the absorbing solution. Dialkyl is obtained.

  The method for bringing the reaction gas into contact with the absorbing liquid is not particularly limited, and examples thereof include a countercurrent contact method in which an ascending gas and a descending liquid are brought into contact with each other, and a bubbling contact method. One of these methods may be used alone, or a plurality of methods may be used in combination. As shown in FIG. 1, when the countercurrent contact method is used, for example, the reaction gas extracted from the bottom of the first reactor 1 is supplied between the lower part and the middle part of the absorber 2 by the reaction gas extraction line 12. Circulate from below to above. On the other hand, the absorption liquid is supplied to the upper part of the absorption device 2 through the absorption liquid supply line 13 and circulates from above to below. In this manner, the reaction gas and the absorbing liquid are brought into countercurrent contact in the absorption device 2. When the bubbling contact method is used, for example, the reaction gas is blown into the absorption liquid stored inside the absorption device 2, and the reaction gas and the absorption liquid are brought into contact with each other at the interface between the bubble and the absorption liquid.

  The absorption device 2 only needs to have an absorption tower that can efficiently make gas-liquid contact between a reaction gas containing dialkyl oxalate or / and dialkyl carbonate and nitric oxide and an absorption liquid. . Examples of the absorption tower include a tray type such as a sieve tray, a bubble tray, and a valve tray, or a packed tower type absorption tower packed with irregular packing such as a pole ring and Raschig ring or regular packing.

  The operating temperature of the absorption tower in the absorption device 2 is preferably not higher than the temperature at which dialkyl oxalate or / and dialkyl carbonate is condensed. For example, when the target product is dimethyl oxalate or / and dimethyl carbonate, preferably 0 to 80 degreeC, More preferably, it is 20-60 degreeC. The operating pressure is preferably normal pressure to 1 MPaG, more preferably normal pressure to 0.6 MPaG, and still more preferably 0.2 to 0.6 MPaG. The supply amount of the absorbent is preferably 1 to 100 parts by mass, more preferably about 2 to 20 parts by mass with respect to 100 parts by mass of the dialkyl oxalate and / or dialkyl carbonate contained in the reaction gas. Is preferably about 0 to 50 ° C.

  As shown in FIG. 1, the condensate containing dialkyl oxalate or / and dialkyl carbonate and absorption liquid produced in the absorption device 2 is extracted from the lower part of the absorption device 2 and by a condensate extraction line 14. The non-condensable gas containing nitrogen monoxide is extracted from the upper part of the absorber 2 by the non-condensed gas extraction line 15.

(Third process)
The third step is mainly performed in the second reactor 3, and molecular oxygen is mixed with the non-condensed gas obtained in the second step to obtain a mixed gas, and this mixed gas is supplied to the second reactor 3. In addition to supplying to the lower part, alkanol is supplied to the upper part of the second reactor 3 to react nitrogen monoxide, oxygen and alkanol to obtain an alkyl nitrite-containing gas, and to obtain the obtained alkyl nitrite-containing gas. The first reactor 1 is circulated and supplied.

As shown in FIG. 1, in the second reactor 3, the non-condensable gas extraction line 15 is at the bottom (between the lower region 3B and the bottom of the second reactor 3 in FIG. 5B and above the bottom liquid). The alkanol supply line 19 for supplying alkanol is connected to the upper part (between the upper region 3A and the top of the second reactor 3 in FIG. 5B). A gas circulation line 22 for extracting the alkyl nitrite-containing gas produced in the second reactor 3 and supplying it to the first reactor 1 is connected to the top of the second reactor 3. It is preferable that a gas purge line 23 for purging a part of the circulating gas is further connected to the gas circulation line 22 or the top of the second reactor 3. It is preferable that a non-condensable gas extraction line 15 is branched from an NO supply line 18 that extracts non-condensable gas and supplies it to the third reactor 4 for nitric acid conversion. When the NO supply line 18 is branched, an oxygen supply line 16 for supplying molecular oxygen is connected to the non-condensable gas extraction line 15 downstream of the NO supply line 18. A nitrogen oxide (NO _x ) supply line 17 for replenishing nitrogen oxides may be further connected to the non-condensable gas extraction line 15 between the connecting portion and the branch portion of the NO supply line 18.

In the production apparatus of the present invention, one or a plurality of nozzles for uniformly dispersing and supplying molecular oxygen to the non-condensable gas are provided in the oxygen supply line 16. By uniformly dispersing and supplying molecular oxygen to the non-condensable gas from the nozzle or nozzles, a mixed gas in which the non-condensable gas and molecular oxygen are uniformly mixed can be obtained, and the concentration of NO ₂ is locally increased. Generation of a high atmosphere can be suppressed, and generation of dinitrogen tetroxide (N ₂ O ₄ ) can be suppressed. When the nozzle includes a single outlet, it is preferable to provide a plurality of nozzles so that molecular oxygen can be uniformly distributed and supplied to the non-condensed gas. In the case where the nozzle includes a plurality of outlets, it is preferable to provide one or a plurality of nozzles so that molecular oxygen can be uniformly supplied to the non-condensed gas.

  The nozzle for supplying molecular oxygen is preferably a nozzle including an outlet (hole) for supplying molecular oxygen at the tip and / or side of the tube, for example. For example, in the case of a nozzle including an air outlet for supplying molecular oxygen to the side of the tube, it is more preferable to arrange a plurality of air outlets at substantially equal intervals. By using a multi-hole nozzle including a plurality of outlets, molecular oxygen is uniformly distributed and supplied into a pipe in which the multi-hole nozzle is arranged (in FIGS. 1 and 2, the pipe 15a of the non-condensable gas extraction line 15). be able to. Examples of such a porous nozzle include a metal porous sintered tube nozzle, a ceramic porous tube nozzle, and a porous tube nozzle provided with a large number of pores serving as outlets at the tip and side surfaces. For example, the nozzle is not limited to a mode in which an outlet having a uniform size is arranged at the tip and / or side surface of the tube, and the nozzle, for example, toward the tip of the tube in consideration of the pressure of molecular oxygen or the like. A nozzle provided with a plurality of air outlets may be used so that the number of nozzles gradually increases. For example, a nozzle provided with a plurality of air outlets gradually increasing in diameter toward the tip of the tube may be used. Good.

  It is preferable that the nozzle for supplying molecular oxygen to the non-condensed gas is arranged on substantially the same plane as the cross section of the pipe 15 a constituting the non-condensed gas extraction line 15. In the present specification, the arrangement on substantially the same plane naturally includes the case where the nozzle itself or the nozzle outlet is arranged on the same plane of the cross section of the pipe (or the second reaction vessel), and further includes the nozzle itself or the nozzle. This includes the case where the air outlet is located at a position slightly upstream or downstream from the same plane of the cross section. Here, “slightly upstream or downstream position” means on the same plane of the cross section of the pipe (or the second reaction vessel), although it depends on the diameter of the pipe (or the second reaction vessel). From the above, it is preferable that the nozzle itself or the nozzle outlet is located upstream or downstream from the same plane of the cross section in a distance range of 3 cm or less, more preferably 2 cm or less, further preferably 1 cm or less, and particularly preferably 5 mm or less. Says being in position. In the present specification, the plurality of nozzles may be two or more nozzles, and the number of nozzles to be arranged in the pipe depends on the size of the pipe on which the nozzles are arranged and the diameter and number of the outlets provided on the nozzles. Is not limited. The number of the plurality of nozzles is preferably 2 or more, more preferably 3 or more, still more preferably 4 or more, and particularly preferably 3 to 10. For example, as shown in FIG. 2, on the substantially same plane as the cross section of the pipe 15a through which the non-condensable gas flows, at substantially equal intervals from the entire circumference of the pipe 15a, toward the center on the same plane as the cross section of the pipe 15a. It is preferable to insert and arrange a plurality of nozzles 16a having outlets that open. For example, as shown in FIG. 2, a plurality of nozzles 16a connected to a pipe 16 that is a molecular oxygen supply line (preferably, for example, a porous material including one or a plurality of air outlets at the tip and / or side of the pipe). The molecular oxygen is supplied from the nozzle. The molecular oxygen is uniformly distributed and supplied from the plurality of nozzles 16a to the non-condensable gas flowing in the pipe 15a, and the second mixed gas is oxidized while oxidizing nitrogen monoxide contained in the non-condensed gas in the pipe 15a. It is supplied to the reactor 3. The molecular oxygen supply line only needs to have one or a plurality of nozzles for dispersing and supplying molecular oxygen, and the molecular oxygen supply source (for example, an oxygen cylinder) is 1 There may be one or more.

  Further, for example, as shown in FIG. 3, a plurality of nozzles 16a for supplying molecular oxygen may be arranged in parallel on substantially the same plane as the cross section of the pipe 15a through which the non-condensed gas flows. FIG. 3 shows a mode in which three tubular nozzles 16a including one or a plurality of air outlets on the side of the tube are arranged in parallel on substantially the same plane.

  When one nozzle including a plurality of air outlets is arranged, a nozzle having a form in which a plurality of air outlets are arranged on substantially the same plane as the cross section of the pipe 15a constituting the non-condensable gas extraction line 15 may be provided. preferable. For example, as shown in FIG. 4, a plurality of air outlets for supplying molecular oxygen are arranged on the side portion as a form of a nozzle capable of arranging a plurality of air outlets on substantially the same plane as the cross section of the pipe 15 a. An annular nozzle 26 in which the pipe provided for is configured in an annular shape is illustrated. The annular nozzle 26 shown in FIG. 4 includes a communication passage 26a connected to a molecular oxygen supply source. Other nozzle forms include, for example, a spiral nozzle that includes a plurality of air outlets on the side of the tube and the tube is formed in a spiral shape, and a plurality of air outlets on the side of the tube, and a tube An example of a meandering nozzle is shown in FIG. In addition, the arrow in FIG. 4 shows the supply direction of molecular oxygen.

  As the molecular oxygen, pure oxygen gas may be supplied as it is, pure oxygen gas may be diluted with an inert gas such as nitrogen, or air may be supplied as molecular oxygen. In the third step, the obtained alkyl nitrite-containing gas is controlled so that the concentration of nitric oxide in the alkyl nitrite-containing gas is 2 to 7% by volume. That is, molecular oxygen is preferably supplied in an amount of 0.08 to 0.2 mol of oxygen with respect to 1 mol of nitric oxide in the non-condensed gas.

  In the production apparatus of the present invention, it is preferable to further provide a stirring device for stirring and mixing the mixed gas uniformly on the downstream side of the connecting portion between the non-condensable gas extraction line 15 and the molecular oxygen supply line 16. The stirring device is not particularly limited as long as the mixed gas can be mixed uniformly. For example, a rotating blade, a shielding plate that stirs the mixed gas by preventing a part of the mixed gas from flowing and causing turbulent flow. Can be provided. As a rotary blade, a rotary blade of a mode that operates continuously or intermittently by power, or a mode in which a shaft rotates by at least one blade of a rotary blade having a plurality of blades due to the flow of mixed gas being subjected to stress. Rotor blades can be used. The shielding plate is not particularly limited as long as the shielding plate is disposed so as to block a part of the flow of the mixed gas and cause a turbulent flow.

Further, as shown in FIG. 1, the NO _x supply line 17 may be connected to the non-condensed gas extraction line 15 as described above. By connecting the NO _x supply line 17 to the non-condensable gas extraction line 15, nitrogen oxides (NO, NO ₂ , N ₂ O ₃ , N ₂ O _4, etc.) are supplied to the non-condensed gas. Nitrogen loss due to dissolution or purging of alkyl nitrate or nitric oxide is compensated. Further, nitrogen content may be supplemented with nitric acid instead of nitrogen oxide (NO _x ) (see Japanese Patent Application Laid-Open Nos. 2003-71283 and 2003-79622).

  The mixed gas may contain nitrogen dioxide, dinitrogen trioxide, dinitrogen tetroxide, etc. in addition to nitrogen monoxide by supplying molecular oxygen or nitrogen oxides. The number of moles of is preferably equal to or more than (more than) the total number of moles of nitrogen dioxide and dinitrogen tetroxide in the mixed gas in terms of grams of nitrogen atoms.

  The mixed gas is supplied to the lower part of the second reactor 3 through a non-condensable gas extraction line 15. In order to suppress the side reaction represented by the above formula (3), when the mixed gas is supplied to the second reactor 3, the mixed gas is uniformly distributed to the lower part of the second reactor 3. It is preferable to introduce.

  In the production apparatus of the present invention, at the introduction portion of the second reactor 3 of the non-condensable gas extraction line 15, one or a plurality of nozzles for uniformly supplying the mixed gas to the lower portion of the second reactor 3 is provided. It is preferable. When a nozzle having a single outlet is used, a plurality of nozzles for supplying the mixed gas to the lower part of the second reactor 3 are provided so that the mixed gas can be uniformly distributed to the lower part of the second reactor 3. It is preferable to provide a nozzle. When a nozzle including a plurality of outlets is used, it is preferable to provide one or a plurality of nozzles so that the mixed gas can be uniformly supplied to the lower part of the second reactor 3.

  FIG. 5A is a VV ′ cross-sectional view showing a schematic configuration inside the second reactor 3, and FIG. 5B illustrates a schematic configuration of a plurality of nozzles provided in the non-condensed gas extraction line. It is a figure to do. FIGS. 5A and 5B show a preferred embodiment of a plurality of nozzles provided in the non-condensed gas extraction line 15 for supplying the mixed gas to the lower part of the second reactor 3 in a distributed manner. For example, as shown in FIGS. 5 (A) and 5 (B), as a preferred embodiment of a nozzle for supplying a mixed gas to the lower part of the second reactor 3, a non-condensable gas withdrawn inserted into the second reactor 3 is extracted. A plane H-shaped pipe 15b is connected to the downstream side of one pipe 15a constituting the line 15, and, for example, the tip of the pipe is connected to four tip ends and two intersections of the H-shaped pipe 15b. The mode which arrange | positions the six blowing nozzles 15c which have a blower outlet in a part each facing the opening of a blower outlet below is mentioned. As described above, by providing the plurality of nozzles 15 c on the downstream side of the non-condensable gas extraction line 15 inserted into the second reactor 3, the mixed gas is uniformly distributed and supplied to the lower part of the second reactor 3. Nitric oxide in the mixed gas reacts quickly with the alkanol, thereby suppressing side reactions and suppressing by-products of nitric acid. When a plurality of nozzles 15 c are provided in the non-condensed gas extraction line 15 and the mixed gas is supplied to the second reactor 3 as in the preferred embodiment shown in FIGS. 5 (A) and 5 (B), the non-condensed gas is extracted. This is particularly effective when the piping 15a constituting the line 15 is large and the dialkyl oxalate or / and dialkyl carbonate production apparatus itself is enlarged as in the case where the second reactor 3 is large. For example, the non-condensable gas extraction line inserted into the second reactor 3 when the diameter of the pipe constituting the non-condensable gas extraction line is 20 cm or more and the size of the lower part of the second reactor 3 is 2 m or more. It is preferable to provide a plurality of nozzles 15 c on the downstream side of 15 and uniformly distribute and supply the lower part of the second reactor 3. As described above, by providing the plurality of nozzles 15 c in the non-condensable gas extraction line 15 inserted into the second reactor 3, the mixed gas is uniformly distributed from the plurality of nozzles 15 c to the lower part of the second reactor 3. It can be supplied and reacted with alkanol promptly to suppress the side reaction represented by the above formula (3) and to efficiently produce alkyl nitrite and water.

  In the production apparatus of the present invention, when the nozzle for uniformly supplying the mixed gas to the lower part of the second reactor 3 is a nozzle including a plurality of outlets, the number of nozzles is one. There may be more than one. When one nozzle including a plurality of air outlets is arranged, it is preferable to use a nozzle having a form in which a plurality of air outlets are arranged on substantially the same plane as the cross section of the second reactor 3. As an example of providing a nozzle having a configuration in which a plurality of outlets can be arranged on substantially the same plane as the cross section of the second reactor 3, for example, a plurality of outlets as shown in FIG. In addition, for example, a spiral nozzle that includes a plurality of air outlets on the side of the tube and the tube is configured in a spiral shape, or a side of the tube. A meandering nozzle may be provided which includes a plurality of outlets and has a pipe configured in a meandering manner.

  FIG. 6 is a cross-sectional view below the second reactor 3 showing another preferred embodiment of a plurality of nozzles provided in the non-condensable gas extraction line. As shown in FIG. 6, as a preferred embodiment of the nozzle provided on the downstream side of the non-condensable gas extraction line 15 a for supplying the mixed gas to the inside of the second reactor 3, downstream of the pipe 15 a constituting the non-condensed gas extraction line 15. A plurality of sides are branched (in FIG. 6, it is branched into three. The number of branches is not limited.) A plurality of branches (15 in FIG. 6) are provided in each branch portion 15d of the branched pipe 15a. For example, the aspect which arrange | positions the several blowing nozzle 15c which has a blower outlet in the front-end | tip part of a pipe | tube with the opening of each blower outlet facing downward is mentioned.

  The alkanol was supplied from the upper part of the second reactor 3 through the alkanol supply line 19, the alkanol flowed from the upper part to the lower part of the second reactor 3 (reaction tower), and dispersedly supplied at the lower part of the second reactor 3. Nitric oxide and alkanol contained in the mixed gas react (gas-liquid contact reaction) to obtain an alkyl nitrite-containing gas. The obtained alkyl nitrite-containing gas is circulated and supplied to the first reactor 1 through the gas circulation line 22 from the upper part of the second reactor 3.

  The alkanol is preferably an alkanol having an alkyl group having 1 to 3 carbon atoms, more preferably an alkanol having the same alkyl group as the alkanol used in the dialkyl oxalate absorbing solution or / and the dialkyl carbonate absorbing solution. . For example, when producing dimethyl oxalate and / or dimethyl carbonate, if methanol is used as the dialkyl oxalate absorbent or / and dialkyl carbonate absorbent in the second step, methanol is used as the alkanol in the third step. It is preferable. The temperature of the alkanol supplied to the upper part of the second reactor 3 by the alkanol supply line 19 is preferably 0 to 50 ° C., more preferably 0 to 30 ° C., in the non-condensed gas before mixing the molecular oxygen. It is preferable to supply alkanol 0.2-3 mol with respect to 1 mol of nitric oxide, and it is more preferable to supply 0.3-2 mol.

The second reactor 3 reacts (gas-liquid contact reaction) the upper region 3A for absorbing and removing water generated by the reaction of nitric oxide, oxygen and alkanol, and nitrogen monoxide, oxygen and alkanol. It has a lower region 3B where a reaction for generating alkyl nitrite can be performed. It is preferable that the upper region 3A and the lower region 3B are arranged at an appropriate interval (that is, an intermediate portion). The bottom liquid 3a of the second reactor 3 can be cooled and circulated in the intermediate portion between the upper area 3A and the lower area 3B by the above-mentioned bottom liquid circulation operation. The upper region 3A may be of any type as long as it has a function of allowing alkanol to flow down and absorbing water in the upward flow by the alkanol. For example, it may have a multi-stage distillation column type structure having a plurality of shelves such as a sheave tray and a valve tray, or a packed column type structure filled with packing materials such as Raschig rings and pole rings. Further, the lower region 3B is of any type as long as it has a function capable of reacting nitrogen monoxide, oxygen and alkanol to efficiently produce alkyl nitrite. For example, it is only necessary to have a multistage distillation column type or packed column type structure similar to the upper region 3A.
In order to suppress the movement of the filler, it is preferable to provide a pressing member having a porous structure or a network structure on the top of the filler. By providing the pressing member, generation of a large gap due to the movement of the filler can be suppressed, and gas-liquid contact can be performed efficiently.
Examples of the presser include hold down grating and hold down plate.

  As the second reactor 3, for example, as shown in FIG. 1, the upper region 3A of the second reactor 3 has a multi-stage distillation column type structure having a plurality of shelves, and the lower region 3B has a packed column type. A structure having a structure in which the upper region 3A and the lower region 3B are connected continuously at an appropriate interval (that is, provided with an intermediate portion) is preferable.

  Further, for example, as shown in FIG. 1, a column bottom liquid extraction line 20 for extracting the bottom liquid 3 a and introducing it into the nitric acid conversion reactor 4 is connected to the bottom of the second reactor 3. Then, at the intermediate portion of the second reactor 3 (particularly below the connecting portion of the conversion gas extraction line 25), the column bottom liquid is branched from the middle of the column bottom liquid extraction line 20 and circulated and supplied to the second reactor 3. It is preferable that the column bottom liquid circulation line 21 for connecting is connected. In the bottom liquid extraction line 20, liquid transport means such as a circulation pump is installed between the branch portion of the tower bottom liquid circulation line 21 and the second reactor 3 (not shown). 21 is preferably provided with a cooler 5.

  Furthermore, in the second reactor 3 (particularly, the area where the alkanol is flowing down, particularly the middle part thereof), a converted alkyl nitrite-containing gas (described later) is withdrawn from the nitric acid conversion reactor 4, and the second reactor 3 The conversion gas extraction line 25 to be supplied to is connected.

  In the third step, the reaction temperature is preferably a temperature not higher than the boiling point of the alkanol under the pressure in the second reactor 3 (particularly from 0 ° C. to the boiling point of the alkanol). For example, when methanol is used as the alkanol, the reaction temperature in the third step is preferably 0 to 80 ° C, more preferably 5 to 80 ° C, and still more preferably 10 to 80 ° C. The reaction pressure is preferably normal pressure to 1 MPaG, more preferably normal pressure to 0.6 MPaG, and still more preferably 0.2 to 0.6 MPaG. The gas-liquid contact time between the mixed gas and the alkanol is preferably about 0.5 to 20 seconds.

  In the third step, when reacting nitrogen monoxide, oxygen, and alkanol, the bottom liquid extraction line is fed to the bottom liquid 3a of the second reactor 3 via a liquid transporting means (not shown) such as a pump. 20, the most of the bottom liquid 3 a of the reactor 3 is taken out by a bottom liquid circulation line 21 branched from the middle of the bottom liquid extraction line 20, led to the cooler 5 to be cooled, and the cooled bottom liquid 3 a is cooled. The second reactor 3 is circulated and fed to an intermediate portion of the second reactor 3 (between the upper region 3A and the lower region 3B of the second reactor 3 and preferably below the connecting portion of the conversion gas extraction line 25 described later). It is preferable to flow down from the middle part of the vessel 3 to the lower part. The circulation operation of the bottom liquid 3a of the second reactor 3 is more preferably performed under the following conditions. This bottom liquid circulation operation is preferably performed simultaneously and continuously with the operation of supplying the non-condensable gas, molecular oxygen and alkanol to the second reactor 3 to cause the regeneration reaction.

  In this bottom liquid circulation operation, the condition (a) the circulation supply amount of the bottom liquid (that is, the supply amount of the cooled bottom liquid 3a to the intermediate part of the second reactor 3) is the alkanol supply to the second reactor 3. The amount is preferably 50 to 300 times, more preferably 60 to 180 times, and still more preferably 70 to 160 times. Condition (b) Total of the amount of alkanol supplied to the second reactor 3 and the amount of alkanol in the bottom liquid 3a (that is, the bottom liquid cooled by the cooler 5) circulated and supplied to the intermediate part of the second reactor 3 Is preferably 20 to 150 times mol, more preferably 30 to 120 times mol of the amount of nitrogen oxide supplied to the second reactor 3. Condition (c) Furthermore, the alkanol concentration in the bottom liquid is preferably 15 to 60% by mass, and more preferably 20 to 55% by mass. In the bottom liquid circulation operation, the temperature of the bottom liquid is in the temperature range of about 0 to 60 ° C., and 1 to 20 ° C. (particularly from the temperature of the bottom liquid 3a (see FIG. 5) at the bottom of the second reactor 3). It is preferable to cool to a low temperature (2-10 ° C.). By performing the bottom liquid circulation operation of the second reactor 3 under the above conditions (a) to (c), the heat of reaction generated in the lower part of the second reactor 3 can be effectively removed, and by-product nitric acid is produced. The gas-liquid contact reaction between the mixed gas containing nitric oxide and oxygen and the alkanol can be efficiently performed.

  The alkanol supply amount of (a) and (b) in the bottom liquid circulation operation condition in the third step is the total amount of liquid and vapor (and / or mist) alkanol newly supplied to the second reactor 3. For example, as shown in FIG. 1, it is included in the liquid alkanol introduced into the second reactor 3 through the alkanol supply line 19 and the mixed gas introduced into the second reactor 3 through the non-condensable gas extraction line 15. This is the total amount of vapor (and / or mist) alkanol. On the other hand, the liquid alkanol in the circulating bottom liquid (cooled bottom liquid) circulated and supplied to the intermediate part of the second reactor 3 by the bottom liquid circulation line 21 and the converted gas extraction line 25 (described later) are used for the second reactor. Vapor-like (and / or mist-like) alkanol entrained in the converted alkyl nitrite-containing gas (described later) introduced into 3 is not included in the supply amount of alkanol to the second reactor 3. However, when the nitric oxide-containing gas supplied to the third reactor 4 for nitric acid conversion (described later) is accompanied by a vapor-like (and / or mist-like) alkanol, the entrained alkanol is the second reactor. 3 is included in the alkanol supply amount to 3.

Further, the supply amount of nitrogen oxides to the second reactor 3 in the bottom liquid circulation operation condition (b) in the third step is the total amount of nitrogen oxides newly supplied to the second reactor 3 from the outside, Nitric oxide in the non-condensed gas supplied by the non-condensed gas extraction line 15, nitrogen oxides generated from the nitrogen monoxide and molecular oxygen supplied by the oxygen supply line 16, replenished by the NO _x supply line 17 And nitrogen monoxide contained in the converted alkyl nitrite-containing gas introduced from the nitric acid conversion reactor 4 to the second reactor 3 by the conversion gas extraction line 25.

(Fourth process)
The fourth step is performed in a distillation apparatus (not shown), and the condensed liquid (including dialkyl oxalate or / and dialkyl carbonate and absorbing liquid) extracted from the absorbing apparatus 2 by the condensed liquid extraction line 14 is distilled. Purify dialkyl oxalate or / and dialkyl carbonate. This distillation is carried out by an ordinary method, for example, by using an ordinary distillation column, distilling the alkanol of the absorbing solution or dialkyl carbonate as a by-product from the top of the column, and dialkyl oxalate or / and dialkyl carbonate of interest in the middle or It can carry out by the method of extracting from a tower bottom. If necessary, high-purity dialkyl oxalate and / or dialkyl carbonate can be obtained by further distillation.

  Further, when producing dialkyl oxalate and / or dialkyl carbonate by the first to fourth steps, the bottom liquid 3a of the second reactor 3 containing nitric acid and alkanol is extracted by the bottom liquid extraction line 20, and the bottom liquid Is introduced into the third reactor 4 for nitric acid conversion, and nitrogen monoxide (NO) is introduced into the third reactor 4 through the NO supply line 18 branched from the non-condensable gas extraction line 15. In the third reactor 4, the bottom liquid of the second reactor 3 is brought into contact with nitric oxide, and nitric acid by-produced by the reaction of nitric oxide, oxygen, and alkanol in the third step is converted to alkyl nitrite. To obtain an alkyl nitrite-containing gas. This alkyl nitrite-containing gas is extracted from the third reactor 4 through the conversion gas extraction line 25, and is an intermediate part of the second reactor 3, from the upper side of the bottom liquid circulation line 21 to the second reactor 3. Supply.

  At this time, the amount of the bottom liquid of the second reactor 3 introduced into the third reactor 4 is such that the level of the bottom liquid of the second reactor 3 is constant or within a certain range, and the second reactor 3 It is preferable to adjust the bottom liquid circulation operation to a range that can be carried out under the above conditions. Since the alkanol concentration of the bottom liquid in the second reactor 3 is controlled as shown in the condition (c) in the bottom liquid circulation operation, the alkanol concentration of the bottom liquid introduced into the third reactor 4 is preferably 15 -60 mass%, More preferably, it is 20-55 mass%. The concentration of nitric acid in the bottom liquid is not particularly limited, and may be, for example, 60% by mass or less. In order to efficiently produce alkyl nitrite in the second reactor 3 by bottom liquid circulation operation, the concentration of nitric acid in the bottom liquid is preferably 20% by mass or less, more preferably 1 to 20% by mass, and still more preferably. Is about 2 to 15% by mass. In addition, the bottom liquid contains water and a small amount of alkyl nitrite by-produced by the reaction of nitric oxide, oxygen and alkanol.

Nitric oxide (NO) supplied to the third reactor 4 by the NO supply line 18 supplies the non-condensed gas flowing through the NO supply line 18 branched from the non-condensed gas extraction line 15 as nitrogen monoxide as it is. Can do. Nitric oxide supplied to the third reactor 4 may contain a component that does not participate in the reaction, but it needs to contain no nitrogen oxides produced by the presence of molecular oxygen. Specifically, it is necessary not to contain nitrogen dioxide, dinitrogen trioxide, dinitrogen tetroxide, and molecular oxygen. Nitric oxide may be supplied from outside the system to the third reactor 4, but the non-condensable gas supplied to the lower part of the second reactor 3 is removed from the non-condensed gas extraction line 15 (particularly the connection of the oxygen supply line 16). Upstream of the unit; when the NO _x supply line 17 is connected upstream of the connection part of the oxygen supply line 16, it is extracted from the connection part of the NO _x supply line 17 by the nitrogen monoxide (NO) supply line 18 The third reactor 4 is particularly preferably supplied. Further, in FIG. 1, as indicated by a broken line, the non-condensable gas withdrawal line 15 to the NO _x to supply NO _x is branched from the supply line 17 NO _x third reactor 4 in nitric oxide from the branch line 17a (NO ) May be supplied.

  In the nitric acid conversion reaction in the third reactor 4, the supply amount of nitric oxide may be equal to or greater than 1 mol of nitric acid in the bottom liquid of the second reactor 3. When a large amount of non-condensable gas supplied to the lower part is introduced into the third reactor 4 as nitric oxide, the reaction between nitric oxide, oxygen and alkanol in the second reactor 3 and the reaction for nitric acid conversion are further performed. It is preferable to control within a range that does not interfere with the conversion reaction in the vessel 4 and the reaction in the first reactor 1 that generates a reaction gas containing dialkyl oxalate or / and dialkyl carbonate and nitric oxide. The supply amount of nitric oxide to the third reactor 4 is preferably 1 to 50 mol, more preferably 1.5 to 20 mol, still more preferably 2 to 10 mol, with respect to 1 mol of nitric acid in the bottom liquid. is there.

In the nitric acid conversion reaction, the reaction temperature is preferably 10 to 200 ° C, more preferably 20 to 100 ° C. The reaction pressure is preferably from normal pressure to 30 kg / cm ² G (about 3 MPaG), particularly ² to 10 kg / cm ² G (about 0.2 to about 1 MPaG). The conversion reaction is carried out in the liquid phase and can be performed batchwise or continuously.

  In the nitric acid conversion reaction, for example, the bottom liquid of the second reactor 3 is continuously extracted from the bottom liquid extraction line 20, and a part of the bottom liquid is continuously or intermittently introduced into the third reactor 4. It is carried out by stirring the solution under normal pressure or increased pressure while circulating nitrogen monoxide, or by introducing nitrogen monoxide into the third reactor 4 and stirring the solution under increased pressure. At this time, it is preferable that nitrogen monoxide does not substantially contain nitrogen oxides generated by the presence of molecular oxygen, and nitrogen oxides are also substantially contained in the bottom liquid to the nitric acid conversion reactor 4. More preferably, it is not contained. It is particularly preferable that the reaction system is not substantially supplied with nitrogen oxides.

  In the nitric acid conversion reaction, a nitrate of a group 8 metal (or a group 8-10 metal or a platinum group metal) or a 1B metal (or a group 11 metal) may be present as a catalyst. Preferred examples of the group 8 metal nitrate include ferric nitrate, nickel nitrate, and cobalt nitrate. Preferred examples of the 1B metal nitrate include cupric nitrate. These catalysts are preferably present in an amount of 20% by mass or less, more preferably 10% by mass or less, in terms of metal, with respect to the bottom liquid of the second reactor 3.

  The third reactor 4 is not limited as long as it can perform the nitric acid conversion reaction, and can be a stirred tank type or a multi-stage tower type (packed tower, sieve tray tower, etc.), and may be plural. A multi-tank type may be used. Since the nitric acid conversion reaction is a gas-liquid contact reaction with nitric oxide, when using a stirred tank reactor, the gas-liquid contact efficiency has a blade shape and a rotating device capable of high stirring and high gas dispersion. It is preferable to use a high stirrer, and it is preferable to use a filler with good gas-liquid contact efficiency in a multi-stage tower type reactor. And it is preferable to connect the NO supply line 18, the bottom liquid extraction line 20, and the conversion gas extraction line 25 to the 3rd reactor 4, and also the waste liquid extraction line 24 is connected to the bottom part.

  Alkyl nitrite (converted alkyl nitrite) produced by the nitric acid conversion reaction is entrained with nitric oxide (as a converted alkyl nitrite-containing gas) and supplied to the intermediate portion of the second reactor 3 through the converted gas extraction line 25. Is done. At this time, in the case where a large amount of non-condensable gas is not introduced as nitrogen monoxide into the third reactor 4, the zone where the alkanol of the second reactor 3 flows down, particularly the middle portion of the second reactor 3, particularly the It is preferable to supply the converted alkyl nitrite-containing gas above the intermediate portion and above the connecting portion of the bottom liquid circulation line 21 (located in the intermediate portion of the regeneration tower 3). After the nitric acid conversion reaction, the reaction liquid is extracted from the bottom of the third reactor 4 through a waste liquid extraction line 24.

  In the third reactor 4 for nitric acid conversion, instead of nitrogen oxide replenishment to compensate for the loss of nitrogen (alkyl nitrite, nitrogen monoxide) due to circulation gas purging, etc., this corresponds to the replenishment An amount of nitric acid (preferably an aqueous nitric acid solution) to be supplied can be separately supplied through a nitric acid supply line (not shown), and the conversion reaction can be performed under the same conditions together with nitric acid in the bottom liquid of the second reactor 3. As a result, nitric acid by-produced in the second reactor 3 can be efficiently converted and recovered as alkyl nitrite and reused for the production of dialkyl oxalate and / or dialkyl carbonate. A simple method of replenishing nitric acid in the third reactor 4 can be used as a means for compensating for the loss of (nitric acid) and the loss of nitrogen (alkyl nitrite, nitric oxide) due to the purge of the circulating gas, The replenishment amount of nitrogen can also be reduced.

1 First reactor 2 Dialkyl oxalate or / and dialkyl carbonate absorber (absorber)
3 Second reactor 3A Upper area of the second reactor (multi-stage distillation column format with multiple shelves)
3B Lower area of second reactor (packed tower type)
3a Bottom liquid 4 Nitric acid conversion third reactor (third reactor)
DESCRIPTION OF SYMBOLS 5 Cooler 11 Carbon monoxide supply line 12 Reaction gas extraction line 13 Absorption liquid supply line 14 Condensate extraction line 15 Non-condensate gas extraction line 15a Piping 15b Planar H-shaped piping 15c Blowing nozzle 15d Branching part 16 Oxygen supply line 16a Nozzle 17 NO _x supply line 17a NO _x branch line 18 NO supply line 19 alkanol supply line 20 bottom liquid extraction line 21 bottom liquid circulation line 22 gas circulation line 23 gas purge line 24 waste liquid extraction line 25 conversion gas extraction line 26 annular nozzle 26a annular nozzle Connecting road

Claims (9)

A first step of reacting carbon monoxide and an alkyl nitrite-containing gas in a first reactor in the presence of a catalyst to produce a reaction gas containing dialkyl oxalate or / and dialkyl carbonate and nitric oxide;
A second step of contacting the reaction gas with a dialkyl oxalate absorbent or / and a dialkyl carbonate absorbent to obtain a condensate containing dialkyl oxalate or / and dialkyl carbonate, and a non-condensable gas containing nitric oxide;
While mixing molecular oxygen with non-condensable gas and oxidizing nitric oxide in the piping, the mixed gas is supplied to the second reactor and reacted with alkanol to obtain an alkyl nitrite-containing gas. A third step for circulatingly supplying an alkyl nitrate-containing gas to the first step;
A fourth step of distilling the condensate to obtain dialkyl oxalate or / and dialkyl carbonate;
A method for continuously producing dialkyl oxalate and / or dialkyl carbonate, characterized in that molecular oxygen in the third step is dispersedly supplied using one or more nozzles.   The method for continuously producing a dialkyl oxalate and / or a dialkyl carbonate according to claim 1, wherein the mixed gas in the third step is dispersedly supplied to the second reactor using one or a plurality of nozzles.   The method for continuously producing dialkyl oxalate and / or dialkyl carbonate according to claim 1 or 2, wherein the nozzle comprises a plurality of outlets. A first reactor for reacting carbon monoxide with an alkyl nitrite-containing gas to produce a reaction gas containing dialkyl oxalate or / and dialkyl carbonate;
A carbon monoxide supply line for supplying carbon monoxide to the first reactor;
A reaction gas extraction line for extracting a reaction gas containing dialkyl oxalate and / or dialkyl carbonate from the first reactor;
A non-condensable gas containing nitric oxide and a condensate containing dialkyl oxalate or / and dialkyl carbonate in contact with a dialkyl oxalate or / and dialkyl carbonate and a dialkyl oxalate absorbent or / and a dialkyl carbonate absorbent. A dialkyl oxalate or / and dialkyl carbonate absorber that produces
A condensate extraction line for extracting a condensate containing dialkyl oxalate or / and dialkyl carbonate from a dialkyl oxalate or / and dialkyl carbonate absorber;
A non-condensable gas extraction line for extracting non-condensable gas containing nitric oxide from a dialkyl oxalate or / and dialkyl carbonate absorber;
An oxygen supply line having one or more nozzles for supplying molecular oxygen to the non-condensable gas flowing through the non-condensable gas extraction line;
A second reaction in which a mixed gas of non-condensable gas and oxygen is introduced from the bottom, alkanol is introduced from the top, and nitrogen monoxide, oxygen, and alkanol in the mixed gas are reacted to produce a gas containing alkyl nitrite. And
An alkanol supply line for supplying alkanol to the second reactor;
An alkyl nitrite-containing gas circulation line withdrawing the alkyl nitrite-containing gas from the upper part of the second reactor and supplying it to the first reactor;
A dialkyl oxalate and / or dialkyl carbonate production apparatus comprising a distillation apparatus for distilling a condensate extracted from a condensate extraction line to obtain dialkyl oxalate and / or dialkyl carbonate.   The apparatus for producing dialkyl oxalate and / or dialkyl carbonate according to claim 4, wherein one or a plurality of nozzles are provided in the non-condensable gas extraction line to supply the mixed gas in a distributed manner to the lower part of the second reactor.   The dialkyl oxalate and / or dialkyl carbonate production apparatus according to claim 4 or 5, wherein the nozzle includes a plurality of outlets.   The apparatus for producing dialkyl oxalate and / or dialkyl carbonate according to any one of claims 4 to 6, wherein the nozzle includes a blow-out port at a tip portion and / or a side portion.   The apparatus for producing dialkyl oxalate and / or dialkyl carbonate according to any one of claims 4 to 7, wherein the nozzle of the oxygen supply line is arranged on substantially the same plane as a cross section of the pipe constituting the non-condensable gas extraction line.   The apparatus for producing dialkyl oxalate and / or dialkyl carbonate according to any one of claims 4 to 8, wherein a stirrer for stirring the mixed gas is provided on the downstream side of the connecting portion between the non-condensable gas extraction line and the oxygen supply line. .

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