JP4214858B2 - Production method of dialkyl oxalate - Google Patents

Description

  The present invention provides a dialkyl oxalate production method in which carbon monoxide and alkyl nitrite are reacted in the presence of a catalyst to produce a dialkyl oxalate, which efficiently suppresses the loss of the nitrogen component as the alkyl nitrite source. The invention relates to a process for producing dialkyl acids.

  Conventionally, as shown in the following formula, carbon monoxide and alkyl nitrite are reacted (preferably in a gas phase) to form dialkyl oxalate, and then nitric oxide produced in the reaction is reacted with oxygen and alkanol. There is known a method for continuously producing dialkyl oxalate while producing (regenerating) alkyl nitrite and reusing the alkyl nitrite in a dialkyl oxalate production reaction.

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

  Thus, methods for continuously producing dialkyl oxalate while regenerating and reusing alkyl nitrite are disclosed in, for example, Patent Documents 1 to 3 and the like. In addition, methods for producing alkyl nitrite from nitric oxide, oxygen and alkanol are disclosed in detail in Patent Documents 4 and 5, etc.

  However, in the above method, when dialkyl oxalate is produced, loss of nitrogen components (alkyl nitrite and nitric oxide) due to purging of the circulating gas is unavoidable, and from nitric oxide, oxygen and alkanol. When alkyl nitrite was produced (regenerated), nitric acid was by-produced as in the following formula, causing further loss of nitrogen components. For this reason, it was necessary to replenish the reaction system with a nitrogen component (nitrogen oxide such as nitric oxide, nitrogen dioxide, dinitrogen trioxide, dinitrogen tetroxide, etc.) that becomes an alkyl nitrite source.

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

  On the other hand, as a method for producing nitric oxide from concentrated nitric acid, a method of reducing with metal such as bismuth, copper, lead, mercury, iron oxide (II), or diarsenic trioxide is known (non-patent) Literature 1) and these methods use a stoichiometric reaction and require a large amount of the above-mentioned metals and oxides thereof, which is not preferable as an industrial method.

Japanese Patent Publication No.57-30095 Japanese Patent Publication No. 61-6057 Japanese Patent Laid-Open No. 11-246477 JP-A-11-189570 JP-A-6-298706 Chemical Dictionary 1 reduced edition 32nd edition, page 665

  The present invention relates to a process for producing dialkyl oxalate by reacting carbon monoxide with alkyl nitrite in the presence of a catalyst. In the process for producing dialkyl oxalate, loss of a nitrogen component as an alkyl nitrite source, particularly from nitric oxide to nitrite. It is an object of the present invention to provide a method for efficiently producing dialkyl oxalate by suppressing loss of nitrogen component due to by-product of nitric acid when regenerating alkyl.

  As a result of intensive studies to solve the above problems, the present inventors have completed the present invention. That is, the present invention is (1) in the first step, carbon monoxide and alkyl nitrite are supplied to a reactor for producing dialkyl oxalate and reacted in the presence of a catalyst to produce dialkyl oxalate and nitric oxide. (2) In the second step, the reaction gas of the first step is supplied to the dialkyl oxalate absorber and brought into contact with the dialkyl oxalate absorption solution, and contains the condensate containing dialkyl oxalate and nitric oxide. A non-condensable gas is obtained, and (3) in the third step, the non-condensed gas and molecular oxygen of the second step are supplied to the lower portion of the alkyl nitrite regeneration reaction tower, and the alkanol is supplied to the alkyl nitrite regeneration reaction tower. The nitrogen nitrite reacts with nitric oxide, oxygen, and alkanol while flowing down from the upper part of the reaction tower to the lower part of the reaction column to produce alkyl nitrite, and the resulting alkyl nitrite-containing gas is supplied to the first step. Together to perform the reaction by ring supplied, (4) in the fourth step, to obtain a dialkyl oxalate was distilled condensate of the second step, the preparation of the dialkyl oxalate,

(5) A column bottom liquid containing nitric acid and alkanol is extracted from the bottom of the third step alkyl nitrite regeneration reactor and introduced into the nitric acid conversion reactor, and carbon monoxide is supplied to the reactor. In the presence of a platinum group metal catalyst, the bottom liquid of the introduction column and the carbon monoxide are brought into contact with each other to produce alkyl nitrite, and the resulting alkyl nitrite-containing gas is supplied to the reaction tower for alkyl nitrite regeneration. To a process for producing dialkyl oxalate.

  According to the present invention, in the process for producing a dialkyl oxalate by reacting carbon monoxide with an alkyl nitrite in the presence of a catalyst, the loss of the alkyl nitrite source, particularly the regeneration of the alkyl nitrite from nitric oxide. Method to continuously and efficiently produce dialkyl oxalate with high space-time yield and high selectivity by suppressing the loss of nitrogen components due to the by-product of nitric acid (resulting in higher alkyl nitrite production rate) Can be provided.

  That is, conventionally, since a considerable amount of nitric acid is produced when regenerating alkyl nitrite from nitric oxide in the regeneration tower, the production rate of alkyl nitrite was reduced due to loss of nitrogen content. Therefore, this nitric acid can be efficiently converted to alkyl nitrite and reused for the production of dialkyl oxalate. Further, by-product nitric oxide can be recycled and converted to alkyl nitrite. Therefore, it is possible to construct a highly efficient process for producing dialkyl oxalate with reduced loss of nitrogen component.

Further, according to the present invention, in the production of dialkyl oxalate, the loss of the nitrogen component can be suppressed (the nitric acid can be regenerated and reused as the alkyl nitrite), and the replenishment amount of the nitrogen component can also be reduced. Furthermore, as necessary, a simple method of replenishing nitric acid can be used as a means to compensate for loss of nitrogen components (alkyl nitrite, nitric oxide) due to purging of the regeneration tower discharge gas (circulation gas). become.
Note that the present invention can constitute an efficient process because the recovery loss of the platinum group metal or the compound thereof used as a catalyst when converting nitric acid into alkyl nitrite can be suppressed to a very low level.

First, characteristic portions of the present invention will be described with reference to the drawings. FIG. 1 is a schematic process diagram illustrating the steps of producing a dialkyl oxalate according to the present invention.
As shown schematically in FIG. 1, the present invention is a process for producing a dialkyl oxalate by reacting carbon monoxide and an alkyl nitrite in the presence of a catalyst, and in the third step, a liquid alkanol is produced. Is supplied to the upper part of the alkyl nitrite regeneration reactor (hereinafter abbreviated as regeneration tower) 3 through the alkanol supply line 17 and flows down from the upper part of the regeneration tower 3 to the dialkyl oxalate absorber (hereinafter referred to as “regeneration tower”). While a non-condensable gas from the absorption tower 2 is supplied to the lower part of the regeneration tower 3 through a non-condensed gas extraction line 15 and oxygen through an oxygen supply line 16, nitrogen monoxide, oxygen and alkanol are reacted (gas). Liquid contact reaction) to produce alkyl nitrite,

  The resulting gas containing alkyl nitrite is withdrawn from the top of the regeneration tower 3 by the gas circulation line 19 and the bottom liquid containing nitric acid and alkanol is withdrawn from the bottom of the regeneration tower 3 by the tower bottom liquid withdrawal line 18. A part of the bottom liquid (outlet bottom liquid) is introduced into a nitric acid conversion reactor 4 (hereinafter abbreviated as reactor 4), and nitric acid (regeneration tower 3) in the introduced tower bottom liquid (introduced tower bottom liquid). (By-product) is converted into alkyl nitrite, and the alkyl nitrite is supplied to the regeneration tower 3 (that is, nitric acid is recovered as alkyl nitrite).

  That is, according to the present invention, when the alkyl nitrite is produced in the regeneration tower 3 as described above in the third step, the lead-out bottom liquid (part thereof) is introduced into the reactor 4 through the tower bottom liquid extraction line 18. Then, carbon monoxide is supplied to the reactor 4 through the CO supply line 20, and in the presence of the platinum group metal catalyst, the introduction tower bottom liquid and the carbon monoxide are brought into contact to produce alkyl nitrite (introduction tower bottom). The nitric acid and alkanol in the liquid are reacted with carbon monoxide to convert nitric acid to alkyl nitrite), and the resulting alkyl nitrite-containing gas is extracted by a conversion gas extraction line 22 and supplied to the regeneration tower 3. To do.

Hereinafter, the present invention will be described in more detail with reference to the drawings.
In the first step of the present invention, carbon monoxide and alkyl nitrite are supplied to a dialkyl oxalate production reactor 1 (hereinafter also referred to as main reactor 1) through a raw material gas supply line 11 and reacted in the presence of a catalyst ( Gas phase contact reaction) to generate dialkyl oxalate and nitric oxide (hereinafter, this reaction is also referred to as a main reaction). At this time, a single-tube or multi-tube heat exchanger reactor is effective for the reactor.

  Preferred examples of the alkyl nitrite include alkyl nitrites having 1 to 3 carbon atoms such as methyl nitrite, ethyl nitrite, n-propyl nitrite, and i-propyl nitrite. Among them, methyl nitrite is particularly preferable. preferable. Carbon monoxide may be pure gas or diluted with an inert gas such as nitrogen.

  In the first step, the catalyst is preferably a platinum group metal catalyst, particularly a solid catalyst in which a platinum group metal is supported on a carrier (Patent Document 1, etc.). In that case, the supported amount of the platinum group metal is preferably about 0.01 to 10% by weight, more preferably about 0.2 to 2% by weight with respect to the carrier. Examples of the carrier include inert carriers such as activated carbon, alumina (such as α-alumina), silica, diatomaceous earth, pumice, zeolite, and molecular sieve. 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, It can be prepared by reducing to a platinum group metal (particularly palladium metal) with formaldehyde, sodium formate, hydrogen, carbon monoxide and the like. Reduction to the platinum group metal can also be performed using carbon monoxide in the reactor before the reaction. The platinum group metal-based 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 palladium compounds, palladium inorganic acid salts (palladium nitrate, palladium sulfate, palladium phosphate, etc.), palladium halides (palladium chloride, palladium bromide, etc.), palladium organic acid salts (palladium acetate, palladium oxalate) , Palladium benzoate, etc.) and various complexes of palladium can be used.

  For example, the reaction in the first step is performed by introducing a raw material gas containing carbon monoxide and alkyl nitrite into the upper portion of the dialkyl oxalate production reactor 1 through a raw gas supply line 11 as shown in FIG. It is carried out by a method of contacting with a metal catalyst in a gas phase (Patent Document 2 etc.). In the case of continuous reaction, an alkyl nitrite-containing gas (circulation gas) extracted from the regeneration tower 3 is circulated and supplied as a raw material gas through the gas circulation line 19 to compensate for losses due to consumption due to the reaction and purging of the circulation gas. Carbon monoxide is supplied by the source gas supply line 11 or the CO supply line 20.

  The carbon monoxide concentration in the source gas is preferably 1 to 50% by volume, and the alkyl nitrite concentration is 1 to 35% by volume, more preferably 2 to 20% by volume, and particularly 3 to 15% by volume. preferable. The remainder of the source gas contains an inert gas such as nitrogen or carbon dioxide, but may contain a small amount of nitric oxide or alkanol (steam).

In the first step, the reaction temperature is preferably 50 to 200 ° C., more preferably 80 to 150 ° C., and the pressure is from normal pressure to 10 kg / cm ² G (about 1 MPaG), and further from normal pressure to 5 kg / cm ² G. (About 0.5 MPaG), particularly 2 to 5 kg / cm ² G (about 0.2 to about 0.5 MPaG) is preferable. The contact time between the source gas and the platinum group metal catalyst is preferably about 0.2 to 10 seconds, more preferably about 0.2 to 5 seconds.

  In the second step of the present invention, the reaction gas of the first step (main reaction gas; containing dialkyl oxalate and nitric oxide) is supplied to the absorption tower 2 to absorb the dialkyl oxalate absorption liquid (hereinafter referred to as absorption liquid). And a non-condensable gas containing nitric oxide and a condensate containing dialkyl oxalate. That is, in the second step, the reaction gas (main reaction gas) in the first step is extracted from the lower part of the main reactor 1 through the main reaction gas extraction line 12 and supplied to the lower part of the absorption tower 2, and the absorption liquid is absorbed. The main reaction gas and the absorption liquid are brought into gas-liquid contact while being supplied to the upper part of the absorption tower 2 by the supply line 13 and flowing down from the upper part to the lower part of the absorption tower, thereby converting the dialkyl oxalate in the main reaction gas into the absorption liquid. It is condensed and dissolved to obtain a condensate containing dialkyl oxalate and a non-condensable gas containing nitric oxide. The condensate is extracted from the bottom of the absorption tower 2 by a condensate extraction line 14, and the non-condensable gas is extracted from the top of the absorption tower 2 by a non-condensable gas extraction line 15.

  Preferred examples of the absorbing liquid include alkanols having 1 to 3 carbon atoms such as methanol and ethanol. Among them, alkanols (particularly methanol) having the same alkyl group as the alkyl nitrite are preferable. The absorption tower only needs to be capable of gas-liquid contact, for example, a shelf type such as a sheave tray, a bubble bell tray, or a valve tray, or a packed tower type filled with a packing material such as a pole ring or a Raschig ring. Any absorption tower may be used.

In the absorption tower 2, the operation temperature is preferably not higher than the temperature at which the dialkyl oxalate is condensed. For example, when the target product is dimethyl oxalate, it may be in the range of 0 to 80 ° C., more preferably 20 to 60 ° C. preferable. The operation pressure is from normal pressure to 10 kg / cm ² G (about 1 MPaG), further from normal pressure to 5 kg / cm ² G (about 0.5 MPaG), particularly from 2 to 5 kg / cm ² G (about 0.2 to The range is preferably about 0.5 MPaG). The supply amount of the absorbing liquid is preferably about 1 to 100 parts by weight, more preferably about 2 to 20 parts by weight with respect to 100 parts by weight of dialkyl oxalate in the main reaction gas, and the temperature at the time of supply is 0 to 50 parts. It is preferable that it is about degreeC.

  In the third step of the present invention, the non-condensed gas (including nitrogen monoxide) and molecular oxygen of the second step are supplied to the regeneration tower 3 and alkanol is supplied to react nitrogen monoxide, oxygen and alkanol. (Gas-liquid contact reaction) to generate alkyl nitrite (regenerate nitric oxide into alkyl nitrite) (hereinafter, this reaction is referred to as a regeneration reaction, and the product is also referred to as regenerated alkyl nitrite).

  That is, in the third step, the non-condensable gas (including nitrogen monoxide) in the second step is combined with molecular oxygen (supplied by the oxygen supply line 16) together with the non-condensed gas extraction line 15 at the bottom of the regeneration tower 3 ( In particular, it is supplied between the lower zone 3B and the bottom and above the bottom liquid; the same applies hereinafter, and at the same time, liquid alkanol is fed to the upper part of the regeneration tower 3 (between the upper zone 3A and the top; Gas-liquid contact (reaction of nitric oxide and oxygen with alkanol; liquid gas alkanol flowing from the upper part of the regeneration tower 3 to the lower part) and a mixed gas of non-condensed gas and molecular oxygen; According to the above reaction formula), alkyl nitrite is generated (regenerated), and the resulting alkyl nitrite-containing gas (regenerated alkyl nitrite-containing gas) is used as a circulation gas in the gas circulation line 19. It is circulated and supplied to the first step in a more withdrawn from the top of the regenerator 3.

  At this time, the molecular oxygen can be separately supplied directly to the lower part of the regeneration tower 3. Further, if necessary, in order to compensate for loss of nitrogen components (alkyl nitrite, nitric oxide) due to purge of the circulating gas from the purge line 24, etc., nitric oxide (nitrogen monoxide, nitrogen dioxide, dinitrogen trioxide, Dinitrogen tetroxide or the like) may be replenished to the non-condensable gas extraction line 15 (preferably upstream of the connecting portion of the oxygen supply line 16) or the lower portion of the regeneration tower 3 by a nitrogen oxide supply line (not shown). .

  Preferred examples of the alkanol supplied to the upper portion of the regeneration tower 3 include alkanols having 1 to 3 carbon atoms such as methanol and ethanol, and alkanols having the same alkyl group as the alkyl nitrite used in the first step (particularly Methanol) is preferred. The molecular oxygen may be a pure gas, diluted with an inert gas such as nitrogen, or supplied as air.

  In the third step, the regeneration reaction is controlled so that the concentration of nitric oxide in the gas withdrawn from the regeneration tower 3 is in the range of 2 to 7% by volume. That is, molecular oxygen is preferably supplied in a range of 0.08 to 0.2 mol per mol of nitric oxide in the non-condensable gas, and alkanol is −15 to 50 ° C., more preferably −10. At -30 ° C (cooling as necessary), 0.2-3 mol, more preferably 0.3-2, per 1 mol of nitric oxide in the non-condensable gas supplied to the lower part of the regeneration tower 3 It is preferable to supply to the upper part of the regeneration tower 3 in a molar range. However, nitric oxide in this case means the amount of nitric oxide contained in the non-condensed gas before oxygen mixing.

In the third step, the reaction temperature is not higher than the boiling point of the alkanol at the pressure at that time (particularly from 0 ° C. to the boiling point of the alkanol; for example, in the case of methanol, 0 to 60 ° C., more preferably 5 to 60 ° C., particularly The reaction pressure is preferably from normal pressure to 10 kg / cm ² G (about 1 MPaG), further from normal pressure to 6 kg / cm ² G (about 0.6 MPaG), particularly from ² to 6 kg / It is preferably in the range of cm ² G (about 0.2 to about 0.6 MPaG). The gas-liquid contact time is preferably about 0.5 to 20 seconds.

  In the third step, when reacting nitrogen monoxide, oxygen and alkanol, the bottom liquid of the regeneration tower 3 is extracted by a tower bottom liquid extraction line 18 via a liquid transporting means (not shown) such as a pump. "A majority of the column bottom liquid (outflow column bottom liquid) is taken out by the column bottom liquid circulation line 23 branched from the middle of the column bottom liquid extraction line 18, guided to the cooler 5, and cooled. The liquid (cooling tower bottom liquid) is circulated and supplied to an intermediate part of the regeneration tower 3 (between an upper region 3A and a lower region 3B described later and preferably below a connecting portion of a converted gas extraction line 22 described later), It is more preferable that the bottom liquid circulation operation of “flowing down from the middle part of the regeneration tower 3” is performed under the conditions described later. This column 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 regeneration tower 3 to perform the regeneration reaction. Most of the column bottom liquid (derived column bottom liquid) is preferably subjected to this column bottom liquid circulation operation.

  In the column bottom liquid circulation operation, (a) the circulation supply amount of the column bottom liquid (that is, the supply amount of the cooling tower bottom liquid to the intermediate portion of the regeneration tower 3) is set to 50 to 300 of the alkanol supply amount to the regeneration tower 3. (B) The alkanol supply amount to the regeneration tower 3 and the column bottom liquid circulated and fed to the intermediate part of the regeneration tower 3 (that is, The total amount of alkanol in the cooling tower bottom liquid) is 20 to 150 times mol, more preferably 30 to 120 times the amount of nitric oxide in the non-condensable gas (before oxygen mixing) supplied to the lower part of the regeneration tower 3. (C) Further, the alkanol concentration in the bottom liquid is preferably 15 to 60% by weight, more preferably 20 to 55% by weight. In the column bottom liquid circulation operation, the outlet column bottom liquid is in the range of 0 to 60 ° C., and is 1 to 20 ° C. (particularly 3 to 10 ° C.) lower than the temperature of the column bottom liquid at the bottom of the regeneration tower 3. It is preferable to cool it. In the present invention, the reaction heat generated in the lower region of the regeneration tower can be effectively removed and the by-product nitric acid can be reduced to a low level by performing the column bottom liquid circulation operation particularly under the conditions (a) to (c). The gas-liquid contact reaction can be performed efficiently.

The supply amount of alkanol to the regeneration tower 3 is the total amount of liquid and vapor (and / or mist) alkanol newly supplied to the regeneration tower 3 from the outside. For example, in FIG. The liquid alkanol supplied to the upper part of the regeneration tower 3 by the line 17 and the vapor (and / or mist) alkanol accompanying the non-condensable gas supplied to the lower part of the regeneration tower 3 by the non-condensable gas extraction line 15. Is the total amount. The liquid alkanol in the circulation tower bottom liquid (cooling tower bottom liquid) circulated and supplied to the intermediate part of the regeneration tower by the tower bottom liquid circulation line 23 and the intermediate part of the regeneration tower 3 by the conversion gas extraction line 22 are supplied. Vapor (and / or mist) alkanol accompanying the converted alkyl nitrite (described later) is not included in the amount of alkanol supplied to the regeneration tower 3.

  The regeneration tower 3 only needs to have an upper region 3A capable of performing absorption such as to remove water generated by the regeneration reaction and a lower region 3B capable of performing the regeneration reaction. However, it is preferable that the upper region 3A and the lower region 3B are installed with an appropriate interval (that is, an intermediate portion). 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 structure having a plurality of shelves such as sheave trays and valve trays, or a packed column structure that is filled with packing materials such as Raschig rings and pole rings. Further, the lower zone 3B may be of any type as long as it has a function capable of effectively performing the regeneration reaction. For example, a multistage distillation column format similar to that of the upper zone 3A Or what is necessary is just to have the structure of a packed tower form.

  As the regeneration tower 3, for example, as shown in FIG. 1, the upper area 3A of the regeneration tower 3 has a multistage distillation tower type or packed tower structure, and the lower area 3B has a packed tower structure. Further, 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 preferably mentioned.

  Further, as shown in FIG. 1, the regeneration tower 3 has a non-condensed gas extraction line 15 for supplying non-condensed gas from the absorption tower 2 at the lower part (particularly between the lower region 3B and the bottom part, An alkanol supply line 17 for supplying alkanol to the upper part (between the upper zone 3A and the top), and to extract the regenerated nitrite-containing nitrite-containing gas and supply it to the main reactor 1 as a circulating gas. The gas circulation lines 19 are preferably connected to the top. It is preferable that an oxygen supply line 16 for supplying molecular oxygen is connected to the non-condensed gas extraction line 15, and a nitrogen oxide supply line (not shown) is further upstream of the connecting portion of the oxygen supply line 16. May be connected. It is preferable that a gas purge line 24 for purging a part of the circulating gas is further connected to the gas circulation line 19.

  Further, as shown in FIG. 1, the regeneration tower 3 draws column bottom liquid and introduces it into the column bottom liquid extraction line 18 for introducing it into the nitric acid conversion reactor 4 (described later). Branching from the middle of the conversion gas extraction line 22 and the column bottom liquid extraction line 18 for extracting the contained gas (described later) and supplying it to the regeneration tower 3 (especially the area where the alkanol is flowing down, especially the middle part of the regeneration tower 3). The tower bottom liquid circulation lines 23 for supplying the tower bottom liquid to the intermediate portion of the regeneration tower 3 (particularly below the connecting portion of the line 18) are preferably connected. A liquid transporting means (not shown) such as a circulation pump is installed in the tower bottom liquid extraction line 18 between the branch point of the tower bottom liquid circulation line 23 and the regeneration tower 3. The cooler 5 is preferably installed.

  In the fourth step of the present invention, the condensate (including dialkyl oxalate) in the second step is extracted from the absorption tower 2 through the condensate extraction line 14 and distilled by a distillation apparatus (not shown) to obtain dialkyl oxalate. Is. This distillation is performed by a conventional method, for example, a method in which an alkanol as an absorption solution or a dialkyl carbonate as a by-product is distilled from the top of the column and a target dialkyl oxalate is extracted from the middle or bottom of the column. Can be performed.

  In the present invention, when producing dialkyl oxalate by the first to fourth steps, as described above, the column bottom liquid containing nitric acid and alkanol is extracted from the bottom of the regeneration tower 3 by the column bottom liquid extraction line 18. A part of the column bottom liquid (outflow column bottom liquid) is introduced into the nitric acid conversion reactor 4 (hereinafter also referred to as the reactor 4), and carbon monoxide is supplied to the reactor 4 so that a platinum group metal catalyst is obtained. In the presence of the reaction solution, the bottom liquid of the introduction column and the carbon monoxide were brought into contact with each other (that is, nitric acid in the bottom liquid of the introduction tower was reacted with carbon monoxide and alkanol), and by-produced in the regeneration reaction in the third step. Nitric acid is converted to alkyl nitrite (this reaction is hereinafter referred to as a conversion reaction, and the resulting alkyl nitrite is also referred to as converted alkyl nitrite), and the resulting alkyl nitrite-containing gas (converted alkyl nitrite-containing gas) is extracted from the converted gas. On line 22 Ri supplied to the regenerator 3 is extracted from the reactor 4 (i.e., recovered by converting nitrate to nitrite alkyl) it is characterized in.

  At this time, the introduction amount of the outlet column bottom liquid into the reactor 4 (the amount of the introduced column bottom liquid) is set so that the level of the bottom liquid in the regeneration tower 3 is constant or in a certain range, and It is preferable to adjust the column bottom liquid circulation operation to a range where it can be performed under the above conditions. Carbon monoxide may be used as it is or diluted with an inert gas (nitrogen or the like), and is 1 to 20 mol, more preferably 1.5 to 10 mol with respect to 1 mol of nitric acid in the bottom liquid of the introduction tower. It is preferable to use at a mole ratio, particularly 2-5 mole ratio.

  In the introduction tower bottom liquid, the alkanol concentration is preferably 15 to 60% by weight, since the alkanol concentration in the bottom liquid of the regeneration tower 3 is preferably controlled as described above in the tower bottom liquid circulation operation. Preferably, it is 20 to 55% by weight. The concentration of nitric acid is not particularly limited from the conversion reaction itself (for example, it may be 60% by weight or less), but the regeneration tower 3 can efficiently generate alkyl nitrite by a column bottom liquid circulation operation or the like. Is preferably 20% by weight or less, more preferably 1 to 20% by weight, and particularly preferably about 2 to 15% by weight. The tower bottom liquid also contains water generated by the regeneration reaction and a small amount of alkyl nitrite.

  In the reactor 4, the conversion reaction is continuously performed by continuously extracting the bottom liquid of the regeneration tower 3 through the column bottom liquid extraction line 18 and storing a part thereof (if necessary, storing it in an intermediate tank (not shown)). After introducing the platinum group metal catalyst into the reactor 4 periodically or intermittently, the CO supply line 20 is used to stir the solution under normal pressure or pressure while circulating carbon monoxide in the liquid. Alternatively, carbon monoxide is introduced into the reactor 4 and the solution is stirred under pressure. Alternatively, the reactor 4 can be filled with a platinum group metal catalyst as a fixed bed, and the tower bottom liquid extracted from the regeneration tower 3 and carbon monoxide can be circulated countercurrently or in parallel. The reaction is carried out in the liquid phase, and can be performed batchwise or continuously.

In the conversion reaction, the reaction temperature is preferably in the range of 0 to 300 ° C, more preferably 20 to 100 ° C. Further, 200 kg / cm ² (about 20 MPa) from the partial pressure atmospheric pressure of carbon monoxide, even 30kg / cm ² (about 3 MPa) from atmospheric pressure, in particular 3~10kg / cm ² (about 0.3 to about 1MPa ) Is preferable. Further, the conversion reaction is carried out until the nitric acid concentration (residual nitric acid concentration) of the column bottom liquid (introduced column bottom liquid) introduced into the reactor 4 is 1 wt% or less, further 0.5 wt% or less, It is preferable for suppressing a recovery loss of the platinum group metal due to elution or dissolution of the platinum group metal or a compound thereof.

  In the conversion reaction, the platinum group metal catalyst can be used by dissolving or suspending the platinum group metal or a compound thereof as it is, but in general, the platinum group metal is supported on a support in consideration of catalyst recovery. The catalyst is preferably used in a fixed bed or a suspended bed. In that case, the supported amount of the platinum group metal is preferably 0.01 to 20% by weight, more preferably 0.1 to 15% by weight in terms of metal with respect to the support. Examples of the carrier include activated carbon and alumina, and activated carbon is preferable. The shape of the carrier is not particularly limited as long as it can be applied to a fixed bed or a suspended bed (powder, granules, pulverized product, etc.). The size of the carrier is not limited as long as it can be applied to a fixed bed or a suspended bed.

  Examples of the platinum group metal include palladium, platinum, ruthenium, rhodium and osmium. Palladium and platinum are preferable, and palladium is particularly preferable. Examples of the platinum group metal compound include inorganic acid salts (nitrate, sulfate, hydrochloride, etc.) and organic acid salts (acetate, etc.) of the platinum group metal, such as palladium nitrate, palladium sulfate, palladium chloride, palladium acetate. Etc.

  The platinum group metal catalyst is used in an amount of 0.0001 to 0.2% by weight, more preferably 0.0005 to 0.1% in terms of metal with respect to the column bottom liquid (introduced column bottom liquid) introduced into the reactor 4. It is preferable that it is weight%, especially 0.005-0.05 weight%. Specifically, for example, when 10% by weight of palladium metal supported on activated carbon (10% by weight Pd / C) is used, the amount used is 0 in terms of platinum group metal with respect to the introduction tower bottom liquid. 0.001 to 2% by weight, more preferably 0.005 to 1% by weight, and particularly preferably 0.05 to 0.5% by weight.

  The white metal metal catalyst is a alkanol solution or suspension in the reactor 4 from the middle of the column bottom liquid extraction line 18 (between the branch point of the column bottom liquid circulation line 23 and the reactor 4; not shown). Or may be supplied directly (not shown) directly to the reactor 4. Further, the reactor 4 may be filled in advance as a solid catalyst (fixed bed or suspension bed).

  That is, in the present invention, a solid catalyst in which a white metal metal is supported on a support (preferably using a tower bottom liquid having a nitric acid concentration of 20% by weight or less (more preferably 1 to 20% by weight, particularly 2 to 15% by weight). In the presence of powder) until the nitric acid concentration in the liquid (residual nitric acid concentration) is 1% by weight or less (particularly 0.5% by weight or less), and the bottom liquid introduced into the reactor 4 is contacted with carbon monoxide. It is particularly preferred that As a result, it is possible to resupport the white metal metal or a compound thereof dissolved or dissolved in the liquid by contact with nitric acid on the support, and a process in which the recovery loss of the platinum group metal can be suppressed to a very low level. From this viewpoint, in the case of continuous reaction, it is preferable to use a plurality of reactors 4 or multiple reactors (two or more). In order to further suppress the recovery loss, it is also preferable to treat the waste liquid of the reactor 4 (extracted by the waste liquid extraction line 21) with an adsorbent such as activated carbon or alumina (for example, pass through an adsorbent packed column). .

  The reactor 4 is not particularly limited as long as it can perform a conversion reaction, and a stirring tank, a packed tower, a trickle bed type, etc. can be used. Good. The reactor 4 is preferably connected to a CO supply line 20 for supplying carbon monoxide, the column bottom liquid extraction line 18, a conversion gas extraction line 22, and a waste liquid extraction line 21.

  The gas containing alkyl nitrite (converted alkyl nitrite) produced in the reactor 4 is supplied to the regeneration tower 3 along with the converted gas extraction line 22 along with the carbon monoxide, but the alkanol in the regeneration tower 3 flows down. In particular, it is preferable to feed the zone above the intermediate portion of the regeneration tower 3, particularly the intermediate portion above the connecting portion of the column bottom liquid circulation line 23.

  Further, in the reactor 4, instead of the conventional replenishment of nitrogen oxide to compensate for the loss of nitrogen components (alkyl nitrite, nitric oxide) due to the purge of the circulating gas, etc., an amount of nitric acid corresponding to the replenishment amount ( Nitric acid solution (preferably nitric acid aqueous solution) is supplied by a nitric acid supply line (not shown), and nitric acid and alkanol in the liquid can be reacted with carbon monoxide under the same conditions together with nitric acid in the bottom liquid of the introduction tower.

Furthermore, when starting production of dialkyl oxalate, carbon monoxide, nitric acid and alkanol are supplied to a nitric acid conversion reactor, and reacted in the presence of a platinum group metal catalyst to produce alkyl nitrite. The reaction of the first step can be started by supplying the alkyl nitrite as the alkyl nitrite used in the first step from the reactor to the first step through the reaction column for regeneration of the alkyl nitrite. That is, nitric acid (preferably nitric acid aqueous solution) is fed into the reactor 4 through a nitric acid supply line (not shown), alkanol is removed from the alkanol supply line 17 through the regeneration tower 3, and the bottom liquid drawing line 18 is used to convert carbon monoxide into CO. Each is supplied through a supply line 20, and carbon monoxide, nitric acid and alkanol are reacted in the same manner to generate alkyl nitrite, and the alkyl nitrite is extracted together with carbon monoxide from the conversion gas extraction line 22 through the regeneration tower 3 and gas circulation. It can also be introduced into the main reactor 1 via line 19.

  Next, the present invention will be specifically described with reference to an example in which the present invention is implemented by the manufacturing process illustrated in FIG. Nitric acid was analyzed by ion chromatography, palladium was analyzed by ICP (inductively coupled high-frequency plasma emission analyzer), moisture was analyzed by Karl Fischer moisture meter, and the others were analyzed by gas chromatography. Pd / C means a solid catalyst in which palladium metal (Pd) is supported on activated carbon (C).

[Comparative Example 1]
(1) 1st process The pellet of 5 mm in diameter and 3 mm in height which carry | supported 5 weight% of palladium to the alpha alumina in the tube of the stainless steel multi-tubular main reactor 1 which consists of six tubes with an internal diameter of 36.7 mm. Of solid catalyst 3.3 L (liter) was charged.
From the upper part of this reactor, a gas compression circulator (not shown) is used to mix a mixture of carbon monoxide and a regeneration tower-derived gas (pressure: 3.5 kg / cm ² G, composition: carbon monoxide 18. 6 volume%, methyl nitrite 8.5 volume%, nitric oxide 5.7 volume%, methanol 6.5 volume%, carbon dioxide 3.0 volume%, nitrogen 57.7 volume%) in a heat exchanger ( After heating to about 90 ° C. (not shown), the catalyst layer is supplied to the catalyst layer at a flow rate of 15.6 Nm ³ / hr, and hot water is passed through the shell side of the reactor to bring the temperature of the catalyst layer to 105 to 120 ° C. The carbon monoxide was reacted with methyl nitrite.

(2) Second step
The reaction gas (total amount) that has passed through the catalyst layer of the main reactor 1 is introduced from the lower part of the gas-liquid contact type absorption tower 2 filled with Raschig rings having an inner diameter of 158 mm and a height of 1400 mm, and methanol is introduced from the top of the absorption tower 2. Was supplied at a flow rate of 0.15 L / hr, and both were brought into countercurrent contact at about 35 ° C. Then, 1.74 kg of condensate (composition: dimethyl oxalate 90.9 wt%, dimethyl carbonate 2.0 wt%, methyl formate 0.1 wt%, methanol 6.5 wt%) from the bottom of the absorption tower 2. / hr with withdrawn at a flow rate of the non-condensable gas (composition from the top of the absorption tower 2: CO 15.2% by volume, methyl nitrite 4.8 volume%, nitrogen monoxide 9.9% by volume, methanol 6 0.8 vol%, carbon dioxide 3.2 vol%, nitrogen 60.0 vol%) was extracted at a flow rate of 15.0 Nm ³ / hr.

(3) Third step Packing tower (regeneration tower) having an inner diameter of 158 mm and a height of 1400 mm (having a 10 mm Raschig ring packed bed 800 mm below the tower top and a 10 mm Raschig ring packed bed 400 mm from 30 mm below this packed bed) 3 , the non-condensed gas obtained in the second step is supplied at a flow rate of 15.0 Nm ³ / hr (pressure 3.1 kg / cm ² G) through the non-condensed gas extraction line 15 , and at the oxygen gas supply line 16. Oxygen is supplied at a flow rate of 0.15 Nm ³ / hr, and nitrogen gas containing 26.8% by volume of nitrogen monoxide is further non-condensed at a flow rate of 0.157 Nm ³ / hr through a nitrogen oxide supply line (not shown). The gas was supplied through the degassing line 15 . Further, a 20 ° C. methanol solution was supplied at a flow rate of 44 L / hr from the alkanol supply line 17 at the top of the regeneration tower 3 . At this time, the pressure of the regeneration tower 3 was adjusted to 2.9 kg / cm ² G at the top of the tower. In addition, a column bottom liquid is extracted from the bottom of the regeneration tower 3 by a column bottom liquid extraction line 18, and 360 L / hr via a cooler 5 by a column bottom liquid circulation line 23 and an attached circulation pump (not shown). Was circulated and supplied between the upper region and the lower region of the regeneration tower 3 at a flow rate.

When the composition of each part was measured when the state of the regeneration tower 3 was stabilized, a regeneration tower discharge gas (circulation gas) was obtained from the gas circulation line 19 at the top of the regeneration tower 3 at a flow rate of 15.1 Nm ³ / hr. It was. The gas derived from the regeneration tower thus obtained is 15.2% by volume of carbon monoxide, 8.7% by volume of methyl nitrite, 5.9% by volume of nitric oxide, 6.8% by volume of methanol, 3. The composition was 2% by volume and 60.0% by volume of nitrogen. Further, the moisture in the derived gas was 0.05% by volume or less. A part of this gas (0.09 Nm ³ / hr) is purged, and the remainder is pressurized to 3.5 kg / cm ² G with a gas compression circulator, and carbon monoxide is further flowed at a flow rate of 0.63 Nm ³ / hr. In addition, it was supplied to the main reactor 1 in the first step. On the other hand, the composition of the bottom liquid of the regeneration tower 3 is 51.1% by weight of methanol, 41.5% by weight of water, 7.0% by weight of nitric acid, and 0.4% by weight of methyl nitrite. A part thereof was extracted from the outlet at a flow rate of 0.63 L / hr.
In this comparative example, nitric acid was produced in an amount of 0.010 mol (2.5 mol% with respect to consumed nitric oxide) with respect to 1 mol of nitric oxide supplied to the regeneration tower.

(4) Fourth Step The condensate extracted from the absorption tower 2 in the second step is introduced at a flow rate of 1.74 kg / hr into a distillation tower (packed tower; not shown) having an inner diameter of 50 mm and a height of 3 m. Distillation was carried out at a column top temperature of 64.5 ° C. and a column bottom temperature of 166 ° C., and dimethyl oxalate having a purity of 99.8 wt% was obtained from the column bottom at a flow rate of 1.57 kg / hr. From the top of the distillation column, a distillate comprising 82.2% by weight of methanol, 17.7% by weight of dimethyl carbonate and 0.1% by weight of methyl formate was obtained at a flow rate of 0.17 liter / hr.

[Example 1]
Dimethyl oxalate was produced in the same manner as in Comparative Example 1 except that the next nitric acid conversion step was provided in the third step.
(5) Nitric acid conversion step The above-mentioned regeneration tower was added to a 5 L SUS autoclave (reactor 4 ) having a stirrer, gas supply nozzle, liquid supply nozzle, gas extraction nozzle, liquid extraction nozzle (with sintered metal filter). The column bottom liquid (outflow column bottom liquid) was continuously introduced at a flow rate of 0.63 L / hr. When the introduction amount reached 3 L, 6 g of 1 wt% Pd / C was added to start stirring and heating, and carbon monoxide was blown at a flow rate of 0.63 Nm ³ / hr. At the same time, to stop the supply of new carbon monoxide by the raw material gas supply line 11 to the main reactor 1 of the first step.

The temperature of the reactor 4 is controlled to 80 ° C., and then the reaction is performed so that the liquid level is kept constant when the amount of the regenerated tower bottom liquid (introduced tower bottom liquid) reaches 3.5 L. While continuously extracting the liquid from the reactor 4 and adjusting the amount of outgas so that the pressure in the reactor becomes 6.0 kg / cm ² G, the upper and lower regions of the regeneration tower 3 are converted by the conversion gas extraction line 22. During this period, the gas discharged from the reactor 4 ( conversion gas) was supplied. The main reactor 1, the absorber 2, the regenerator 3, while continuously do the reactor 4, methyl nitrite and nitrogen monoxide in the gas supplied to the main reactor 1 of the first step The amount of nitrogen gas containing nitrogen monoxide supplied to the regeneration tower 3 through the nitrogen oxide supply line (not shown) and the non-condensed gas extraction line 15 was adjusted so that the total was the same as in Comparative Example 1. .

In a state where the whole was stable from the start of continuous operation (after 15 hours from the start), the supply amount and composition of each part were as follows.
The amount of nitrogen gas containing nitrogen monoxide supplied to the regeneration tower 3 through the nitrogen oxide supply line (not shown) and the non-condensable gas extraction line 15 is 0.029 Nm ³ / hr, and the regeneration tower derived gas (circulation gas) ) Carbon monoxide 15.2% by volume, methyl nitrite 8.7% by volume, nitrogen monoxide 5.9% by volume, methanol 6.8% by volume, carbon dioxide 9.3% by volume, nitrogen 54.%. It was 1% by volume. The composition of the extracted liquid 0.58 L / hr from the reactor 2 in the nitric acid conversion step was 46.82% by weight of water, 52.60% by weight of methanol, 0.39% by weight of nitric acid, and 0.19% by weight of methyl nitrite. %, The content of Pd (dissolved Pd) in the liquid was about 3 ppm in terms of metal. The conversion rate of nitric acid in the reactor 4 was 95%.
In addition, the dimethyl oxalate obtained in the fourth step is the same in purity and amount as in Comparative Example 1, and the composition and amount of low boilers (methanol, dimethyl carbonate, methyl formate) extracted from the top of the distillation column are also comparative examples. Same as 1.

[Example 2]
Nitrogen gas containing nitrogen monoxide supplied to the regeneration tower 3 through a non-condensable gas extraction line 15 from a nitrogen oxide supply line (not shown) is replaced with nitrogen gas not containing nitrogen monoxide, and nitric acid is added to the reactor 4 . Dimethyl oxalate was produced in the same manner as in Example 1, except that 60% nitric acid was supplied at a flow rate of 0.04 kg / hr through a supply line (not shown). As a result, the composition and amount of each part were exactly the same as in Example 1, and the purity and amount of dimethyl oxalate obtained in the fourth step were also the same.

Example 3
Replace the reactor 4 in the nitric acid conversion process from a 5L autoclave to a type in which two 2.5L autoclaves are connected by an overflow pipe (overflow is the position where the amount of liquid in the first tank becomes 1.8L), 1% by weight Dimethyl oxalate was produced in the same manner as in Example 1 except that Pd / C was continuously supplied in the reactor 2 so as to be 0.17 g / L. The amount of nitrogen gas containing nitrogen monoxide supplied to the regeneration tower 3 through the nitrogen oxide supply line (not shown) and the non-condensate extraction line 15 was adjusted in the same manner as in Example 1. As a result, the composition of the extracted liquid 0.58 L / hr from the reactor 4 was 47.22% by weight of water, 52.43% by weight of methanol, 0.15% by weight of nitric acid, and 0.19% by weight of methyl nitrite, The content of Pd in the liquid was about 1 ppm in terms of metal. The conversion rate of nitric acid was 98%. In addition, the composition and amount of each part were exactly the same as in Example 1, and the purity and amount of dimethyl oxalate obtained in the fourth step were also the same.

Dialkyl oxalate is a useful compound for the production of various chemicals such as oxalic acid, oxamide, and ethylene glycol.

It is a schematic process diagram which illustrates a dialkyl oxalate manufacturing process.

Explanation of symbols

1: Reactor for production of dialkyl oxalate (main reactor)
2: Dialkyl oxalate absorber (absorption tower)
3: Reactor for regeneration of alkyl nitrite (regeneration tower)
3A: Upper area 3B: Lower area 4: Nitric acid conversion reactor 5: Cooler 11: Raw material gas supply line 12: Main reaction gas extraction line 13: Absorbed liquid supply line 14: Condensate extraction line 15: Non-condensed gas extraction Line 16: Oxygen supply line 17: Alkanol supply line 18: Tower bottom liquid extraction line 19: Gas circulation line 20: CO supply line 21: Waste liquid extraction line 22: Conversion gas extraction line 23: Tower bottom liquid circulation line 24: Purge line

Claims (5)

(1) In the first step, carbon monoxide and alkyl nitrite are supplied to a reactor for producing dialkyl oxalate and reacted in the presence of a catalyst to produce dialkyl oxalate and nitric oxide; In two steps, the reaction gas of the first step is supplied to the dialkyl oxalate absorber and brought into contact with the absorbing solution for absorbing dialkyl oxalate to obtain a condensate containing dialkyl oxalate and a non-condensable gas containing nitric oxide. (3) In the third step, the non-condensed gas and molecular oxygen of the second step are supplied to the lower part of the reaction tower for alkyl nitrite regeneration, and the alkanol is supplied to the upper part of the reaction tower for alkyl nitrite regeneration. While flowing down from the upper part to the lower part of the reaction tower, nitric oxide, oxygen, and alkanol are reacted to produce alkyl nitrite, and the resulting alkyl nitrite-containing gas is circulated and fed to the first step. Together to perform response, (4) in the fourth step, to obtain a dialkyl oxalate was distilled condensate of the second step, the preparation of the dialkyl oxalate,
(5) A column bottom liquid containing nitric acid and alkanol is extracted from the bottom of the reaction tower for alkyl nitrite regeneration in the third step and introduced into the nitric acid conversion reactor, and carbon monoxide is supplied to the reactor. In the presence of a platinum group metal catalyst, the bottom liquid of the introduction column and the carbon monoxide are brought into contact with each other to produce alkyl nitrite, and the resulting alkyl nitrite-containing gas is supplied to the reaction tower for alkyl nitrite regeneration. A process for producing a dialkyl oxalate characterized by Carbon monoxide, nitric acid, and alkanol are fed to a nitric acid conversion reactor and reacted in the presence of a platinum group metal catalyst to produce alkyl nitrite. The alkyl nitrite is used as the alkyl nitrite used in the first step. The process for producing a dialkyl oxalate according to claim 1, wherein the reaction is started from the reactor through the reaction tower for alkyl nitrite regeneration to the first step. The process for producing a dialkyl oxalate according to claim 1 or 2, wherein the platinum group metal catalyst is a solid catalyst in which a white metal metal or a compound thereof is supported on a carrier. The method for producing a dialkyl oxalate according to claim 1 or 2, wherein the bottom liquid and the carbon monoxide are brought into contact with each other until the concentration of nitric acid in the bottom liquid introduced into the nitric acid conversion reactor is 1% by weight or less. In the third step, the bottom liquid extracted from the bottom of the alkyl nitrite regeneration reaction tower is led to a cooler to be cooled, and the cooled bottom liquid is circulated and fed to the intermediate part of the alkyl nitrite regeneration reaction tower. In the column bottom liquid circulation operation, (a) the circulation supply amount of the column bottom liquid is 50 to 300 times the alkanol supply amount to the reaction column for alkyl nitrite regeneration, and (b) The total amount of alkanol supplied and the amount of alkanol in the bottom liquid circulated to the middle of the reaction tower for alkyl nitrite regeneration is the amount of nitric oxide in the non-condensable gas supplied to the reaction tower for alkyl nitrite regeneration. The sulfur of claim 1 or 2, wherein nitric oxide, oxygen, and alkanol are reacted while the reaction is carried out under the condition of 20 to 150 times mol of (c) and the alkanol concentration of the bottom liquid of 15 to 60% by weight. Dialkyl acid Law.

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