JP6048135B2 - Process for producing dialkyl oxalate - Google Patents

Description

  The present invention relates to a method for producing a dialkyl oxalate.

  Conventionally, a process for producing dialkyl carbonate and / or oxalate oxalate by reacting carbon monoxide and alkyl nitrite in the presence of a catalyst is known. The object of these methods is useful as a raw material for the synthesis of chemical products, and since it is applied industrially and produces the object on an industrial scale, improvement of the process is always required. Especially, in the manufacturing method of dialkyl oxalate, there is a high need for a method that can be obtained by efficiently separating the target product.

JP 2007-238522 A JP 2006-169211 A JP 2006-089417 A JP 2004-323470 A JP 2004-323371 A JP 2004-107336 JP JP 2004-091484 A JP 11-279125 A Japanese Patent Laid-Open No. 11-279116 Japanese Patent Laid-Open No. 11-140028 Japanese Patent Laid-Open No. 10-330324 Japanese Patent Laid-Open No. 10-330323 Japanese Patent Laid-Open No. 10-287626 Japanese Patent Laid-Open No. 10-156180 Japanese Patent Laid-Open No. 10-045676 JP 09-020727 A JP 09-012512 A Japanese Patent Laid-Open No. 08-301818 Japanese Unexamined Patent Publication No. 08-253443 Japanese Unexamined Patent Publication No. 08-253442 Japanese Patent Laid-Open No. 08-020561 Japanese Patent Laid-Open No. 07-238062 JP 07-206779 A Japanese Unexamined Patent Publication No. 07-206778 JP 07-196581 A JP 07-145108 A JP 07-126220 A JP 07-118210 A JP 07-041457 A Japanese Patent Laid-Open No. 06-329596 Japanese Patent Laid-Open No. 06-306018 Japanese Patent Laid-Open No. 06-239807 Japanese Unexamined Patent Publication No. 06-192181 Japanese Patent Laid-Open No. 06-116209 Japanese Unexamined Patent Publication No. 06-092910 Japanese Unexamined Patent Publication No. 06-072966 Japanese Patent Laid-Open No. 06-025104 JP 05-339213 A JP 05-043517 A JP 05-025096 A JP 04-297445 A JP 04-297444 A Japanese Unexamined Patent Publication No. 04-297443 Japanese Patent Laid-Open No. 04-290849 JP 04-290848 A JP 04-270249 A Japanese Patent Laid-Open No. 04-139153 Japanese Patent Laid-Open No. 04-139152 JP 04-089458 A Japanese Unexamined Patent Publication No. 03-141243 Japanese Unexamined Patent Publication No. 01-216958 Japanese Unexamined Patent Publication No. 60-056937 JP 59-080630 JP 58-126836 A JP 58-021646 JP 57-123142 A JP 57-123141 A JP 57-122043 Japanese Unexamined Patent Publication No. 57-122042 JP 57-042656 A JP 57-042655 A JP 57-042654 A Japanese Unexamined Patent Publication No. 56-164145 JP 56-081536 JP JP-A-55-164655 JP 54-106429 A JP-A-54-103817 JP 54-100312 A JP 54-084517 A JP 54-084516 A JP 54-084515 A JP 54-084514 A JP 54-084513 A JP 54-041813 A JP-A-53-015313 Japanese Patent Laid-Open No. 52-031015 JP 52-017415 A JP-A-51-105008 Japanese Patent Laid-Open No. 51-095013 Japanese Patent Laid-Open No. 51-029428 Japanese Patent Laid-Open No. 51-006916 Japanese Patent Laid-Open No. 50-131917

  The present invention relates to a method for efficiently separating a target product in a method for producing a dialkyl oxalate.

The present invention 1 includes a first step of obtaining a reaction product by reacting carbon monoxide and an alkyl nitrite in the presence of a catalyst;
A second step of contacting the reaction product with an alcohol to obtain a condensate containing dialkyl oxalate and a non-condensable gas containing nitric oxide;
A third step of distilling the condensate to distill the dialkyl carbonate-containing alcohol to obtain a dialkyl oxalate;
A fourth step of adding a dialkyl oxalate to the dialkyl carbonate-containing alcohol distilled in the third step to distill the alcohol to obtain a mixture of dialkyl oxalate and dialkyl carbonate;
The present invention relates to a method for producing dialkyl oxalate (also referred to as a first embodiment), which includes a fifth step of distilling the mixture obtained in the fourth step to obtain dialkyl oxalate.
The present invention 2 further includes a sixth step in which the non-condensable gas obtained in the second step is brought into contact with a molecular oxygen-containing gas and alcohol, and the obtained alkyl nitrite-containing gas is circulated to the first step. The present invention relates to a method for producing a dialkyl oxalate according to the first aspect of the present invention.
The present invention 3 relates to the method for producing dialkyl oxalate of the present invention 1 or 2, wherein the alcohol distilled in the third step is reused in the first step and / or the sixth step.
The present invention 4 is a first step for obtaining a reaction product by reacting carbon monoxide and alkyl nitrite in the presence of a catalyst;
A 2 ′ step in which the reaction product is contacted with an alcohol to obtain a condensate containing dialkyl oxalate and a non-condensable gas containing nitric oxide;
A third step for distilling the condensate to distill alcohol to obtain a mixture of dialkyl oxalate and dialkyl carbonate;
The present invention relates to a method for producing dialkyl oxalate (also referred to as a second embodiment), which includes a fourth step of obtaining a dialkyl oxalate by distilling the mixture obtained in the third 3 step.
The present invention 5 includes a 5 ′ step in which the non-condensed gas obtained in the 2 ′ step is brought into contact with a molecular oxygen-containing gas and an alcohol, and the resulting alkyl nitrite-containing gas is circulated to the 1 ′ step. Furthermore, it is related with the manufacturing method of the dialkyl oxalate of this invention 4 which is a continuous manufacturing method.
The present invention 6 relates to the method for producing dialkyl oxalate of the present invention 4 or 5, wherein the alcohol distilled in the 3 ′ step is reused in the 1 ′ step and / or the 5 ′ step.
Invention 7 is the oxalic acid according to any one of Inventions 1 to 6, wherein the alkyl nitrite is methyl nitrite, the dialkyl oxalate is dimethyl oxalate, the dialkyl carbonate is dimethyl carbonate, and the alcohol is methanol. The present invention relates to a method for producing dialkyl.

  ADVANTAGE OF THE INVENTION According to this invention, the target object can be efficiently isolate | separated and obtained in the manufacturing method of a dialkyl oxalate. The dialkyl oxalate of the present invention can be a continuous production method and is highly useful.

It is a flow sheet which shows an example of the 1st mode of the present invention. It is a flow sheet which shows an example of the 2nd mode of the present invention.

  Examples of the dialkyl oxalate in the present invention include C1-C4 dialkyl esters of oxalic acid, such as dimethyl oxalate, diethyl oxalate, and methyl ethyl oxalate. Especially, the usefulness of the manufacturing method of dimethyl oxalate is high.

  The nitrite as a raw material is a nitrite corresponding to dialkyl oxalate, and examples thereof include alkyl esters having 1 to 4 carbon atoms of nitrous acid, such as methyl nitrite and ethyl nitrite. Methyl nitrate. Dialkyl carbonate is a by-product and is a dialkyl carbonate corresponding to dialkyl oxalate, and examples thereof include dialkyl esters having 1 to 4 carbon atoms of carbonic acid, such as dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. .

Hereafter, each process of the 1st aspect of this invention is demonstrated.
(First step)
The first step is a step of obtaining a reaction product by reacting carbon monoxide and alkyl nitrite in the presence of a catalyst. Specifically, a raw material gas containing carbon monoxide and alkyl nitrite is introduced into a reactor filled with a catalyst, and a catalytic reaction can be performed in a gas phase. As the reactor, a single-tube type or multi-tube type catalyst packed tower is effective.

  As the catalyst, a platinum group metal solid catalyst is preferable, and examples thereof include palladium-based, platinum-based, rhodium-based, ruthenium-based, and iridium-based catalysts. Of these, palladium-based catalysts are preferable. These metal nitrates, sulfates, phosphates, halides and salts such as acetates, oxalates and benzoates can also be used. The platinum group metal solid catalyst may be in the form of being supported on an inert carrier such as activated carbon, alumina, silica, diatomaceous earth, pumice, zeolite, or molecular sieve. In this case, the supported amount of the platinum group metal is 0.01 to 10% by weight, preferably 0.2 to 2% by weight, based on the support in terms of platinum group metal.

  The raw material gas containing carbon monoxide and alkyl nitrite can be diluted with a gas inert to the reaction such as nitrogen gas and carbon dioxide gas.

  The concentration of alkyl nitrite in the raw material gas can be varied over a wide range, but it is preferable that the concentration be 1 vol% or more from the viewpoint of obtaining a satisfactory reaction rate. The higher the alkyl nitrite concentration, the faster the reaction proceeds. However, the concentration used is preferably selected so that a liquid phase of dialkyl oxalate does not form in the reaction zone. It can be a range. When the alkyl nitrite is methyl nitrite, considering that methyl nitrite is an explosive compound, it can be preferably 3 to 25% by volume.

  The concentration of carbon monoxide in the raw material gas can be varied in a wide range and can be selected in the range of 10 to 90% by volume.

  Since the reaction proceeds sufficiently rapidly even at a low temperature, and the side reaction is smaller as the reaction temperature is lower, it is advantageous to carry out the reaction at a relatively low temperature as long as the desired space-time yield is maintained. Specifically, it can be set to 50 to 200 ° C, and preferably 80 to 150 ° C.

The reaction pressure can be normal pressure to 10 kg / cm ² (gauge pressure), preferably normal pressure to 5 kg / cm ² (gauge pressure), but in some cases, the pressure is slightly lower than normal pressure. There may be.

  The reaction time can be 10 seconds or less, preferably 0.2 to 5 seconds.

(Second step)
The second step is a step of bringing the reaction product obtained in the first step into contact with alcohol to obtain a condensate containing dialkyl oxalate and a non-condensable gas containing nitric oxide. Specifically, the reaction product is guided to a condenser, and while the reaction product is brought into contact with alcohol, the reaction product is cooled to a temperature below which the dialkyl oxalate is condensed, and can be separated into a condensate and a non-condensable gas.

  In general, the alcohol solution as the condensate contains dialkyl carbonate, formate, and the like in addition to the target dialkyl oxalate. On the other hand, the non-condensable gas contains unreacted carbon monoxide, alkyl nitrite, and the like in addition to nitrogen monoxide generated by the reaction in the first step.

  In the second step, there is a problem that part of the target dialkyl oxalate is entrained in the non-condensable gas, and when the target has a relatively high melting point such as dimethyl oxalate, the target is condensed. In order to avoid problems such as solidification and adhesion to the walls of the vessel, which can lead to their blockage, the reaction product is brought into contact with alcohol. The method for contacting is not particularly limited, and examples thereof include a countercurrent contact method and a bubbling contact method.

  The alcohol is not limited as long as the target dialkyl oxalate can be easily dissolved, and is preferably an alcohol having the same alkyl group as the alkyl portion of the dialkyl oxalate. That is, when the target product is dimethyl oxalate, it is preferably methanol.

  The supply amount of alcohol is not particularly limited, and when the target product is dimethyl oxalate, methanol is preferably 0.01 to 0.1 part by volume with respect to 100 parts by volume of the object to be processed. For example, it is possible to cool and condense at a temperature of 0 to 60 ° C. while flowing 0.01 to 0.1 part by volume of methanol with respect to 100 parts by volume of the processed product.

(Third step)
The third step is a step of distilling the condensate obtained in the second step to distill the dialkyl carbonate-containing alcohol to obtain dialkyl oxalate. Specifically, the condensate obtained in the second step is led to the distillation column (1), and dialkyl oxalate can be obtained as a distillation residue by distillation.

  The distillation can be carried out at a normal pressure of 64 to 200 ° C., preferably 90 to 190 ° C. at normal pressure. The distillate is a dialkyl carbonate-containing alcohol containing dialkyl carbonate by-produced in the first step in addition to the alcohol.

  When the target product is dimethyl oxalate and methanol is used as the alcohol in the second step, it is possible to use methanol and the first by adopting conditions of 64 to 200 ° C. at normal pressure, preferably 65 to 180 ° C. at normal pressure. Dimethyl oxalate can be efficiently obtained by distilling dimethyl carbonate by-produced in the process by azeotropic distillation.

(4th process)
The dialkyl carbonate-containing alcohol distilled in the third step contains an alcohol that can be reused in the production of dialkyl oxalate and a dialkyl carbonate that is useful as a fuel additive. In the first aspect of the present invention, first, dialkyl oxalate and dialkyl carbonate-containing alcohol, which are main products, are separated, and then dialkyl oxalate is added to the dialkyl carbonate-containing alcohol, and the alcohol and dialkyl carbonate are extracted by distillation. The separation is also targeted. The step for that is the fourth step, and the fifth step that follows. Specifically, in the fourth step, the dialkyl carbonate-containing alcohol distilled in the third step is led to the distillation column (2), the dialkyl oxalate is added, the alcohol is separated by extractive distillation, the dialkyl oxalate and A mixture of dialkyl carbonates can be obtained as a distillation residue. The addition of the dialkyl oxalate is carried out so that the dialkyl oxalate contained in the dialkyl carbonate-containing alcohol is not entrained during the separation of the alcohol by distillation. Preferably, the alcohol is distilled while adding the dialkyl oxalate.
Thereby, in the production of dialkyl oxalate, it is possible to suppress the accumulation of dialkyl carbonate in the system even when alcohol is reused, and to obtain dialkyl carbonate useful as a fuel additive or the like. it can.
The alcohol obtained in the fourth step can be reused as the alcohol used in the first step and / or the sixth step. At that time, after the alcohol obtained in the fourth step is distilled again, it may be reused in the first step and / or the sixth step.

  The amount of dialkyl oxalate added is 0.1 to 2 times the weight of the dialkyl carbonate-containing alcohol, preferably 0.5 to 1 from the viewpoint that the dialkyl carbonate and the alcohol can be easily separated. .5 times the weight.

  Distillation can be carried out under normal pressure conditions, or under pressure or reduced pressure. In the case of performing under pressure or reduced pressure, the temperature can be changed according to the pressure change.

  When the target product is dimethyl oxalate, methanol is used as the alcohol, and the conditions of 64 to 120 ° C. at normal pressure, preferably 65 to 100 ° C. at normal pressure, particularly preferably 65 to 75 ° C. at normal pressure are adopted. Accordingly, methanol can be distilled from dimethyl carbonate-containing methanol to efficiently obtain a mixture of dimethyl oxalate and dimethyl carbonate.

(5th process)
The fifth step is a step in which the mixture obtained in the fourth step is distilled to obtain dialkyl oxalate. Specifically, in the fifth step, a mixture of dialkyl oxalate and dialkyl carbonate, which is the distillation residue of the fourth step, is led to the distillation column (3), and the dialkyl carbonate is separated by distillation, and the dialkyl oxalate is distilled off. It can be obtained as a liquid.
The dialkyl carbonate obtained in the fifth step can also be distilled again.

  Distillation can be carried out under conditions of 90 to 200 ° C. at normal pressure, preferably 90 to 190 ° C. at normal pressure.

When the target substance is dimethyl oxalate, dimethyl oxalate can be obtained by separating dimethyl carbonate by adopting conditions of 90 to 200 ° C. at normal pressure, preferably 90 to 180 ° C. at normal pressure.
Distillation can be carried out under normal pressure conditions, or under pressure or reduced pressure. In the case of performing under pressure or reduced pressure, the temperature can be changed according to the pressure change.

(6th process)
The first aspect of the present invention includes a step of bringing the non-condensable gas obtained in the second step into contact with a molecular oxygen-containing gas and alcohol, and circulating the obtained alkyl nitrite-containing gas to the first step. Thus, it can be a continuous production method. Specifically, the non-condensed gas obtained in the second step can be guided to a regeneration tower and brought into contact with a molecular oxygen-containing gas and alcohol to regenerate nitrogen monoxide in the gas to alkyl nitrite.

  Examples of the regeneration tower include ordinary gas-liquid contact devices such as a packed tower, a bubble tower, a spray tower, and a plate tower.

  Non-condensable gas and molecular oxygen gas can be introduced into the regeneration tower individually or in a mixed state. In the regeneration tower, a part of nitric oxide can be oxidized to nitrogen dioxide with a molecular oxygen-containing gas, and these can be regenerated to alkyl nitrite by absorption reaction with alcohol.

  As the molecular oxygen-containing gas, pure oxygen or oxygen diluted with an inert gas can be used, and feed is preferably performed so that the concentration of nitric oxide in the regeneration gas is 2 to 7% by volume. . Within this range, the inhibition of the reaction due to the high concentration of nitric oxide is suppressed, and the activity of the catalyst can be maintained.

  The molecular oxygen-containing gas can be supplied in an amount of 0.08 to 0.2 mol on an oxygen basis with respect to 1 mol of nitric oxide in the gas introduced into the regeneration tower, and these gases are used for use. It is preferable to make it contact with alcohol at the temperature below the boiling point of this alcohol, and the contact time can be 0.5 to 20 second. The amount of alcohol used can be more than the necessary amount for completely absorbing and reacting the generated nitrogen dioxide and this with approximately equimolar nitric oxide, and the nitrogen monoxide in the gas introduced into the regeneration tower. It is preferable that alcohol is 2-5 volume parts with respect to 1 volume part.

  When the target product is dimethyl oxalate, the non-condensable gas and the molecular oxygen-containing gas are preferably brought into contact with methanol at a temperature of 60 ° C. or less, and the contact time is preferably 0.5 to 2 seconds. Methanol can be 2 to 5 parts by volume with respect to 1 part by volume of nitric oxide in the gas introduced into the regeneration tower.

  In the case of adding a sixth step to obtain a continuous production method, alkyl nitrite dissolves in a small amount in the absorption liquid of the absorption tower or the can liquid of the regeneration tower and is accompanied outside the system, or a part of the circulating gas is purged. As a result, the nitrogen oxide content is lost. Therefore, the replenishment is performed by supplying alkyl nitrite to the reactor of the first step, or by supplying nitric oxide, nitrogen dioxide, dinitrogen trioxide, It can also be carried out by introducing nitrogen oxides such as dinitrogen tetroxide or nitric acid.

  When the content of nitric oxide in the non-condensable gas in the second step is large and when regenerating nitric oxide to alkyl nitrite in the sixth step, more than the required amount of alkyl nitrite is obtained, non-condensation A part of the gas may be directly circulated and supplied to the reactor in the first step without introducing the entire amount of gas into the regeneration tower. Since the liquid derived from the regeneration tower is an alcohol solution containing water produced as a by-product in the regeneration reaction, the water in the alcohol is suitably 2% by volume or less, preferably 0.2% by distillation or the like. It is industrially advantageous to reuse it in the second step or the third step after purification to a volume% or less.

  Next, an example of the process of the first aspect of the present invention will be specifically described according to the flow sheet of FIG. In the figure, 1 is a reactor, 2 is a condenser, 3 is a regeneration column, 4 is a distillation column (1), 5 is a distillation column (2), and 6 is a distillation column (3). 35 is a conduit.

  A gas circulator (not shown) in which a gas containing carbon monoxide, alkyl nitrite, and nitric oxide is installed in the conduit 20 at the top of the multi-tube reactor 1 in which a reaction tube is filled with a platinum group metal solid catalyst. To be introduced through the conduit 21. A reaction reaction is performed in the gas phase in the reactor 1, and the reaction product gas that has passed through the catalyst layer is taken out from the lower part and introduced into the condenser 2 through the conduit 11.

  In the condenser 2, the reaction product gas is condensed while contacting with the alcohol introduced from the conduit 13. The condensate containing the dialkyl oxalate is led from the lower part through the conduit 14 to the distillation column (1) 4.

  On the other hand, non-condensed gas containing unreacted carbon monoxide, alkyl nitrite, and by-produced nitric oxide is introduced into the lower part of the regeneration tower 3 through the conduit 12 from the upper part.

  In the regeneration tower 3, the non-condensed gas is mixed with the molecular oxygen-containing gas introduced through the conduit 16 at the bottom, and reacted with the alcohol introduced through the conduit 18 at the top by countercurrent contact to regenerate the alkyl nitrite. . In the regeneration tower 3, an absorption reaction to methanol occurs following an oxidation reaction of nitric oxide to nitrogen dioxide, and alkyl nitrite can be generated. When a sufficient nitrogen source is insufficient to produce alkyl nitrite, nitrogen oxides may be mixed through the conduit 15.

  The alkyl nitrite-containing gas generated in the regeneration tower 3 is circulated and supplied to the reactor 1 through the conduits 19 and 21 together with the carbon monoxide newly supplied from the conduit 20. On the other hand, the water produced as a by-product in the regeneration tower 3 is taken out through the conduit 17 from the bottom in the form of an aqueous alcohol solution. This alcohol aqueous solution can be recycled and reused as alcohol supplied to the condenser 2 or the regeneration tower 3 through the conduits 18 and 13 after removing water in the liquid by an operation such as distillation.

  In the distillation column (1) 4, alcohol containing dialkyl carbonate and the like is distilled, and the target dialkyl oxalate solution is obtained through the conduit 22.

  The dialkyl carbonate-containing alcohol distilled in the distillation column (1) 4 is introduced into the distillation column (2) 5 through the conduit 23. Distillation tower (2) 5 is fed with dialkyl oxalate through conduit 31 and distills alcohol through conduit 32 to obtain a mixture of dialkyl oxalate and dialkyl carbonate.

  A mixture of dialkyl oxalate and dialkyl carbonate, which is a distillation residue of the distillation column (2) 5, is introduced into the distillation column (3) 6 through a conduit 33. Distillate dimethyl carbonate is distilled in the distillation column (3) 6, and the target dialkyl oxalate is obtained through the conduit 35.

Hereafter, each process of the 2nd aspect of this invention is demonstrated.
(1 'and 2' steps)
The first and second steps are the same as the first and second steps of the first aspect, and the descriptions and preferred forms of the first and second steps relating to the first aspect are applied.

(3rd step)
The 3 ′ step is a step of distilling the condensate obtained in the 2 ′ step to distill alcohol to obtain a mixture of dialkyl oxalate and dialkyl carbonate. Specifically, the condensate obtained in the 2 ′ step is introduced into a distillation column (1 ′), and the alcohol is distilled by distillation to obtain a mixture of dialkyl oxalate and dialkyl carbonate as a distillation residue. it can.
At this time, it is preferable to introduce dialkyl oxalate into the upper part of the distillation column (1 ′) and let the inside of the distillation column flow down.

Distillation can be carried out under conditions of 64 to 200 ° C. at normal pressure, preferably 65 to 190 ° C. at normal pressure. The distillate is substantially alcohol.
Distillation can be carried out under normal pressure conditions, or under pressure or reduced pressure. In the case of performing under pressure or reduced pressure, the temperature can be changed according to the pressure change.
The alcohol obtained in the 3 ′ step can be reused as the alcohol used in the 1 ′ step and / or the 5 ′ step. At that time, the alcohol obtained in the 3 ′ step can be distilled again and reused in the 1 ′ step and / or the 5 ′ step.

  When the target product is dimethyl oxalate and methanol is used as the alcohol in the second step, methanol is efficiently used by adopting conditions of 64 to 200 ° C. at normal pressure, preferably 65 to 190 ° C. at normal pressure. And a mixture of dimethyl oxalate and dimethyl carbonate can be obtained as a distillation residue.

(4th process)
The 4 ′ step is a step in which the mixture obtained in the 3 ′ step is distilled to obtain a dialkyl oxalate. Specifically, the mixture obtained in the 3 ′ step is introduced into a distillation column (2 ′), and dialkyl carbonate can be distilled by distillation to obtain dialkyl oxalate as a distillation residue.

The distillation can be carried out at 90 to 200 ° C. at normal pressure, preferably 90 to 180 ° C. at normal pressure.
Distillation can be carried out under normal pressure conditions, or under pressure or reduced pressure. In the case of performing under pressure or reduced pressure, the temperature can be changed according to the pressure change.

  When the target product is dimethyl oxalate, dimethyl carbonate can be efficiently distilled by adopting conditions of 90 to 200 ° C. at normal pressure, preferably 90 to 190 ° C. at normal pressure. As a liquid, dimethyl oxalate can be obtained.

(5th step)
In the second aspect of the invention, the step of bringing the non-condensed gas obtained in the 2 ′ step into contact with the molecular oxygen-containing gas and alcohol, and circulating the obtained alkyl nitrite-containing gas to the 1 ′ step. In addition, it can be set as a continuous manufacturing method. Specifically, the non-condensable gas obtained in the 2 ′ step can be guided to a regeneration tower and brought into contact with a molecular oxygen-containing gas and alcohol to regenerate nitrogen monoxide in the gas to alkyl nitrite. . The 5 ′ step is the same as the sixth step of the first embodiment, and the description and preferred form of the sixth step relating to the first embodiment are applied.

  Next, an example of the process of the second aspect of the present invention will be specifically described according to the flow sheet of FIG. In the figure, 1 is a reactor, 2 is a condenser, 3 is a regeneration column, 7 is a distillation column (1 '), 8 is a distillation column (2'), and 11 to 21, 41 to 45 are conduits.

  A gas circulator (not shown) in which a gas containing carbon monoxide, alkyl nitrite, and nitric oxide is installed in the conduit 20 at the top of the multi-tube reactor 1 in which a reaction tube is filled with a platinum group metal solid catalyst. To be introduced through the conduit 21. A reaction reaction is performed in the gas phase in the reactor 1, and the reaction product gas that has passed through the catalyst layer is taken out from the lower part and introduced into the condenser 2 through the conduit 11.

  In the condenser 2, the reaction product gas is condensed while being brought into contact with the alcohol introduced from the conduit 13, and the condensate containing dialkyl oxalate is led from the lower portion through the conduit 14 to the distillation column (1 ′) 7.

  On the other hand, non-condensed gas containing unreacted carbon monoxide, alkyl nitrite, and by-produced nitric oxide is introduced into the lower part of the regeneration tower 3 through the conduit 12 from the upper part.

  In the regeneration tower 3, the non-condensed gas is mixed with the molecular oxygen-containing gas introduced through the conduit 16 at the bottom, and reacted with the alcohol introduced through the conduit 18 at the top by countercurrent contact to regenerate the alkyl nitrite. . In the regeneration tower 3, an absorption reaction to methanol occurs following an oxidation reaction of nitric oxide to nitrogen dioxide, and alkyl nitrite can be generated. When a sufficient nitrogen source is insufficient to produce alkyl nitrite, nitrogen oxides may be mixed through the conduit 15.

  The alkyl nitrite-containing gas generated in the regeneration tower 3 is circulated and supplied to the reactor 1 through the conduits 19 and 21 together with the carbon monoxide newly supplied from the conduit 20. On the other hand, the water produced as a by-product in the regeneration tower 3 is taken out through the conduit 17 from the bottom in the form of an aqueous alcohol solution. This alcohol aqueous solution can be recycled and reused as alcohol supplied to the condenser 2 or the regeneration tower 3 through the conduits 18 and 13 after removing water in the liquid by an operation such as distillation.

  In the distillation column (1 ') 7, the alcohol is distilled through the conduit 41, and a mixture of dialkyl oxalate and dialkyl carbonate is obtained as a distillation residue. The distilled alcohol can be recycled and reused as the alcohol supplied to the condenser 2 or the regeneration tower 3 through the conduits 18 and 13.

  The mixture of dialkyl oxalate and dialkyl carbonate obtained in the distillation column (1 ') 7 is introduced into the distillation column (2') 8 through a conduit. The distillation column (2 ') 8 distills the alkyl carbonate, and the target dialkyl oxalate is obtained through the conduit 44. Dialkyl oxalate is introduced into the upper part of the distillation column (1 ') 7 through a conduit 45, and flows down inside the distillation column.

  Next, specific examples will be described.

Example 1
In a tube of a stainless steel multi-tube reactor composed of 6 tubes with an inner diameter of 27.1 mm and a height of 500 mm, palladium is applied to activated carbon (Takeda Co., Ltd. Hakuho 4 mmφ × 6 mm) as shown in Japanese Patent Application No. 2-257042. Was loaded with 780 g of a catalyst supporting palladium (a supported amount of palladium of 1.731% by weight). A raw material gas (composition: carbon monoxide 15.0 vol%, methyl nitrite 15.0 vol%, 1 wt%, compressed to 2.5 kg / cm ² (gauge pressure) from above with a diaphragm type gas circulation pump. 6.9 Nm ³ / hr after preheating to about 90 ° C. in a heat exchanger in advance (nitrogen oxide 3.5 vol%, methanol 1.8 vol%, carbon dioxide 2.2 vol% and nitrogen 62.5 vol%) Feeding at a rate and passing hot water through the shell side of the reactor maintained the central temperature of the catalyst layer at about 120 ° C.

The gas that has passed through the catalyst layer is led to the bottom of a Raschig ring-packed gas-liquid contact condenser having an inner diameter of 100 mm and a height of 1300 mm. Methanol is introduced from the top of the tower at a rate of 0.2 l / hr. Countercurrent contact was performed at a temperature of 20 ° C. and a bottom temperature of 20 ° C. A condensate (composition: dimethyl oxalate 76.7% by weight, dimethyl carbonate 19.6% by weight, methanol 3.7% by weight, methyl formate 0.1% by weight) was obtained from the bottom of the column at 3.8 kg / hr. On the other hand, non-condensable gas from the top of the tower (composition: carbon monoxide 12.8 vol%, methyl nitrite 10.3 vol%, nitric oxide 8.7 vol%, methanol 1.9 vol%, carbon dioxide 2.2 vol. % And nitrogen 64.0% by volume) 6.8 Nm ³ / hr.

After mixing this non-condensed gas with 7.5 Nl / hr of nitrogen gas containing 87.2 Nl / hr of oxygen and 14.0% by volume of nitrogen monoxide, the tower of a gas-liquid contact type regenerative tower having an inner diameter of 158 mm and a height of 1400 mm Introduced to the bottom, introduced at a rate of 5.0 l / hr of methanol from the top of the column, brought into countercurrent contact at a top temperature of 30 ° C. and a bottom temperature of 40 ° C., and regenerated nitrogen monoxide in the gas into methyl nitrite. . Regeneration gas in the regeneration tower (composition: carbon monoxide 12.8 vol%, methyl nitrite 15.4 vol%, nitric oxide 3.7 vol%, methanol 1.9 vol, carbon dioxide 2.3 vol% and nitrogen 64.1% by volume) 6.6 Nm ³ / hr was supplied and compressed to the gas circulation pump. Subsequently, carbon monoxide 0.2 Nm ³ / hr was replenished and mixed with the discharge gas, and led to a stainless steel multi-tube reactor. On the other hand, the 2.2 wt% water-containing methanol 4.0 l / hr derived from the regeneration tower was reused as a methanol source in the tower after removing water by distillation.

  The condensate 3.5 kg / hr derived from the condenser was introduced into the middle stage of a distillation column having an inner diameter of 50 mm and a height of 2500 mm, and distilled at a column top temperature of 90 ° C. and a column bottom temperature of 170 ° C. From the column bottom, 100% by weight of dimethyl oxalate was obtained at 2.68 kg / h. On the other hand, a distillate of 0.82 kg / hr consisting of 83.8% by weight of dimethyl carbonate, 15.8% by weight of methanol and 0.4% by weight of methyl formate was obtained from the top of the column.

  The distillate obtained from the top of this distillation column is led to the middle stage of a distillation column having an inner diameter of 50 mm and a height of 2500 mm, and dimethyl oxalate solution is added at 0.3 kg / hr to the upper part of the distillation column (300 mm below the top). At a column top temperature of 64 ° C. and a column bottom temperature of 146 ° C. From the bottom of the tower, 0.99 kg / hr of a mixed solution of 69.7% by weight of dimethyl carbonate and 30.3% by weight of dimethyl oxalate was obtained. On the other hand, from the top of the tower, a methanol solution of 0.13 kg / hr consisting of 97.5% by weight of methanol and 2.5% by weight of methyl formate was obtained. This methanol solution was purified by distillation again and recycled to the regeneration tower and condenser.

  On the other hand, a mixed liquid of dimethyl carbonate and dimethyl oxalate derived from the tower bottom was introduced into a packed tower having an inner diameter of 65 mm and a height of 1600 mm, and distilled at a tower top temperature of 90 ° C. and a tower bottom temperature of 163 ° C. From the top of the column, 0.68 kg / hr of dimethyl carbonate having a purity of 99.4% was obtained. Further, 4.69 kg / hr of dimethyl oxalate having a purity of almost 100% was extracted from the bottom of the column. As a result, high-purity dimethyl oxalate was continuously obtained with a production yield of 98%.

Example 2
Condensate (composition: dimethyl oxalate 76.7% by weight, dimethyl carbonate 19.6% by weight, methanol 3.7% by weight, methyl formate 0. 1% by weight) 3.8 kg / hr was obtained.
The condensate 3.5 kg / hr derived from the condenser is led to the middle stage of a distillation column having an inner diameter of 50 mm and a height of 2500 mm, and dimethyl oxalate is added to the top of the column (300 mm below the top of the column) at 1.4 kg / hr. At a column top temperature of 64 ° C. and a column bottom temperature of 146 ° C. From the tower bottom, 4.75 kg / hr of a mixed solution of 85.9% by weight of dimethyl oxalate and 14.1% by weight of dimethyl carbonate was obtained. On the other hand, a distillate of 0.15 kg / hr consisting of 97.4% by weight of methanol and 2.6% by weight of methyl formate was obtained from the top of the column.

  The mixed liquid obtained from the bottom of this distillation column was led to the middle stage of a distillation column having an inner diameter of 50 mm and a height of 2500 mm, and distilled at a column top temperature of 90 ° C. and a column bottom temperature of 170 ° C. From the bottom of the column, dimethyl oxalate having a purity of almost 100% was obtained at 4.08 kg / hr. From the top of the column, 99.6% pure dimethyl carbonate was obtained at 0.67 kg / hr.

  On the other hand, the distillate (97.4% by weight of methanol, 2.6% by weight of methyl formate) obtained from the top of the column was purified by distillation again and recycled to the regeneration tower and condenser.

  ADVANTAGE OF THE INVENTION According to this invention, the target object can be efficiently isolate | separated and obtained in the manufacturing method of a dialkyl oxalate. The dialkyl oxalate of the present invention can be a continuous production method and is highly useful.

1 Reactor 2 Condenser 3 Regeneration Tower 4 Distillation Tower (1)
5 Distillation tower (2)
6 Distillation tower (3)
7 Distillation tower (1 ')
8 Distillation tower (2 ')
11-23, 31-35, 41-45 conduit

Claims (7)

A first step of reacting carbon monoxide and alkyl nitrite in the presence of a catalyst to obtain a reaction product;
A second step of contacting the reaction product with an alcohol to obtain a condensate containing dialkyl oxalate and a non-condensable gas containing nitric oxide;
A third step of distilling the condensate to distill the dialkyl carbonate-containing alcohol to obtain a dialkyl oxalate;
Fourth step of obtaining a mixture of dialkyl oxalate and dialkyl carbonate by adding 0.1 to 2.0 times weight of dialkyl oxalate to the dialkyl carbonate-containing alcohol distilled in the third step to distill the alcohol. And a method of producing dialkyl oxalate, comprising a fifth step of distilling the mixture obtained in the fourth step using a single distillation column to obtain dialkyl oxalate. The non-condensed gas obtained in the second step is a continuous production method further comprising a sixth step of contacting the molecular oxygen-containing gas and alcohol with the obtained alkyl nitrite-containing gas in the first step. The manufacturing method of the dialkyl oxalate of Claim 1.   The method for producing dialkyl oxalate according to claim 1 or 2, wherein the alcohol distilled in the third step is reused in the first step and / or the sixth step. A first step of obtaining a reaction product by reacting carbon monoxide with alkyl nitrite in the presence of a catalyst;
A 2 ′ step in which the reaction product is contacted with an alcohol to obtain a condensate containing dialkyl oxalate and a non-condensable gas containing nitric oxide;
The condensate obtained in the second step is led to the middle stage of the distillation tower, dialkyl oxalate is introduced into the upper part of the distillation tower, and the condensate is distilled off while allowing the alcohol to distill while flowing down the inside of the distillation tower . A third step for obtaining a mixture of dialkyl oxalate and dialkyl carbonate; and a fourth step for distilling the mixture obtained in step 3 ' using a single distillation column to obtain dialkyl oxalate. Method for producing dialkyl acid. The non-condensed gas obtained in the 2 ′ step is brought into contact with a molecular oxygen-containing gas and alcohol, and the continuous production method further includes a 5 ′ step in which the obtained alkyl nitrite-containing gas is circulated to the 1 ′ step. The method for producing a dialkyl oxalate according to claim 4, wherein   The method for producing a dialkyl oxalate according to claim 4 or 5, wherein the alcohol distilled in the 3 'step is reused in the 1' step and / or the 5 'step.   The dialkyl oxalate of any one of claims 1 to 6, wherein the alkyl nitrite is methyl nitrite, the dialkyl oxalate is dimethyl oxalate, the dialkyl carbonate is dimethyl carbonate, and the alcohol is methanol. Production method.

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