JP2022156940A - Production method and production apparatus of dialkyl carbonate and/or dialkyl oxalate - Google Patents

Abstract

To provide a production method of dialkyl carbonate and/or dialkyl oxalate, which enables measurement of a nitric acid concentration of a solution safely, suppressing corrosion of a reaction apparatus made of SUS, and continuous production over a long time by decreasing a nitrogen source in waste water.SOLUTION: A production method of dialkyl carbonate and/or dialkyl oxalate comprises: a third step of reacting a noncondensable gas including nitrogen monoxide, molecular oxygen, and an alcohol to obtain an alkyl nitrite and nitric acid; a fourth step of reacting carbon monoxide and/or nitrogen monoxide, an alcohol, and nitric acid obtained in the third step to produce an alkyl nitrite. The third and/or fourth step comprise a sub-step of: measuring a nitric acid concentration of an arbitrary solution in the step from UV absorbance; judging whether the measured nitric acid concentration is in a target range; and, when the concentration is outside the target range, adjusting an amount of nitric acid in the solution to adjust the concentration into the target range.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for producing dialkyl carbonate and/or dialkyl oxalate.

Dialkyl carbonate is a useful compound as a raw material for synthesizing aromatic polycarbonates, medicines and agricultural chemicals, and the like. Dialkyl oxalates are also useful compounds as synthetic starting materials for glycols, dye intermediates, and pharmaceuticals (see Patent Document 1).

Conventionally, as shown in the following formula, carbon monoxide and alkyl nitrite are reacted in the presence of a catalyst to produce dialkyl carbonate and/or dialkyl oxalate (see Patent Document 2). Nitrogen oxide is reacted with oxygen and alcohol to produce (regenerate) alkyl nitrite, and the alkyl nitrite is reused in the reaction to produce dialkyl carbonate and/or dialkyl oxalate while continuously producing dialkyl carbonate and/or dialkyl oxalate. Or a method for producing a dialkyl oxalate is known.

CO + 2RONO → CO(OR) ₂ + 2NO
2CO + 2RONO → (COOR) ₂ + 2NO
2NO + 2ROH + 1/ _2O2 → 2RONO + _H2O
(In the formula, R represents an alkyl group.)

Such a method for continuously producing dialkyl carbonate and/or dialkyl oxalate while regenerating and reusing alkyl nitrite is disclosed in Patent Document 3 and the like. In addition, methods for producing alkyl nitrites from nitric oxide, oxygen and alcohol are disclosed in Patent Documents 4 to 6.

Further, Patent Document 7 discloses a treatment apparatus and treatment method for waste water containing nitric acid and nitrous acid. In the apparatus and method, the concentration of nitric acid and nitrite in the wastewater is determined from the concentration of nitric acid and nitrite measured by the ultraviolet absorbance method and the concentration of nitric acid measured by the ion electrode method. and nitrite concentrations can be measured rapidly.

JP 2014-162746 A JP-A-11-189570 JP-A-6-298706 Japanese Unexamined Patent Application Publication No. 2004-2336 JP 2004-91484 A WO2018/179808 JP 2014-113547 A

In the processes for producing dialkyl carbonate and/or dialkyl oxalate in which carbon monoxide and alkyl nitrite are reacted in the presence of a catalyst in Patent Documents 2 to 6, the loss of nitrogen components, which are the sources of alkyl nitrite, especially from nitrous oxide to nitrous acid. Nitric acid is produced as a by-product when the alkyl nitrate is regenerated. Therefore, the reuse of nitric acid as a nitrogen source has been considered, but when the concentration of nitric acid is high, the corrosion of stainless steel (hereinafter sometimes referred to as SUS) reaction equipment progresses, leading to long-term continuous operation. However, there is a problem that the nitrogen source in the waste liquid increases as well as the production becomes difficult. Also, contact with alcohol in a solution with a high concentration of nitric acid may result in the formation of alkyl nitrates.

On the other hand, as a method for measuring the concentration of nitric acid in an aqueous solution, a method using an ultraviolet absorbance method is known. could not be measured. In the apparatus and method of Patent Document 7, it is possible to measure the concentration of nitric acid and nitrous acid in wastewater in real time. A simpler method was desired.

The present invention can safely measure the nitric acid concentration in the solution, suppresses corrosion of the SUS reactor, and reduces the nitrogen source in the waste liquid, enabling continuous production over a long period of time. An object of the present invention is to provide a method and apparatus for producing dialkyl carbonate and/or dialkyl oxalate. Another object of the present invention is to efficiently produce a dialkyl carbonate and/or a dialkyl oxalate while maintaining the reaction activity while solving the above problems.

That is, the present invention relates to the following [1] to [9].
[1] a first step of reacting carbon monoxide with an alkyl nitrite to produce a dialkyl carbonate and/or a dialkyl oxalate and nitric oxide;
The product obtained in the first step is brought into contact with an absorption liquid that absorbs dialkyl carbonate and/or dialkyl oxalate to obtain a condensate containing dialkyl carbonate and/or dialkyl oxalate and a non-nitrogen monoxide containing condensate. a second step of obtaining a condensed gas;
A third step of reacting the non-condensable gas containing nitrogen monoxide obtained in the second step, molecular oxygen and alcohol to obtain alkyl nitrite and water as main products and nitric acid as a by-product. When,
a fourth step of reacting carbon monoxide and/or nitrogen monoxide, alcohol and nitric acid obtained in the third step to produce an alkyl nitrite;
A method for producing a dialkyl carbonate and/or a dialkyl oxalate having
The third and / or fourth step is a sub-step of measuring the concentration of nitric acid in any solution in the step from UV absorbance and determining whether the measured concentration of nitric acid is within the target range. and adjusting the amount of nitric acid in the solution to bring the concentration within the target range when the concentration is outside the target range. Method.
[2] A first gas containing carbon monoxide, an alkyl nitrite, and nitrogen monoxide is introduced into a first reactor, and the carbon monoxide and the alkyl nitrite are reacted in the presence of a catalyst to produce a dialkyl carbonate. and/or a first step of producing a second gas containing dialkyl oxalate and nitric oxide;
Contacting the second gas with an absorbing liquid that absorbs the dialkyl carbonate and/or the dialkyl oxalate to obtain a condensed liquid containing the dialkyl carbonate and/or the dialkyl oxalate and a non-condensable gas containing nitrogen monoxide. process and
A mixed gas obtained by mixing a non-condensable gas and molecular oxygen and alcohol are introduced into a second reactor to react nitrogen monoxide, molecular oxygen and alcohol to produce alkyl nitrite as the main product. and water, and nitric acid as a by-product to obtain a third gas containing alkyl nitrite together with unreacted nitric oxide, and a bottom liquid containing unreacted alcohol, nitric acid and water. process and
Carbon monoxide and/or nitrogen monoxide and the column bottom liquid are introduced into a third reactor and mixed to obtain a mixed liquid, and carbon monoxide and/or nitrogen monoxide in the mixed liquid are reacted with alcohol and nitric acid. , a fourth step to produce an alkyl nitrite, wherein the alkyl nitrite is recycled to the second reactor of the third step along with unreacted carbon monoxide and/or nitrogen monoxide, and unreacted alcohol and nitric acid and water are transferred to a liquid waste collection tank;
a fifth step of circulating the first gas obtained by mixing the third gas obtained in the third step and carbon monoxide to the first step;
A method for producing a dialkyl carbonate and/or a dialkyl oxalate having
The third and / or fourth step includes the bottom liquid in the second reactor and the piping between the second reactor and the third reactor, the mixed liquid in the third reactor, and the third reactor and waste liquid recovery The concentration of nitric acid in at least one selected from the group consisting of the pipes to the tank and the waste liquid in the waste liquid collection tank is measured from the UV absorbance, and the control unit determines whether the measured concentration of nitric acid is within the target range. In the sub-step of determining whether or not the concentration is outside the target range, adjusting the amount of nitric acid in the bottom liquid, the mixed liquid, or the waste liquid to bring the concentration within the target range The method for producing dialkyl carbonate and/or dialkyl oxalate according to [1], comprising substeps.
[3] The method for producing dialkyl carbonate and/or dialkyl oxalate according to [1] or [2], wherein the UV absorbance is measured at a wavelength of 280 nm to 330 nm.
[4] The method for producing dialkyl carbonate and/or dialkyl oxalate according to any one of [1] to [3], wherein the concentration of nitric acid after adjustment is 0.001% by mass to 10% by mass.
[5] Any one of [1] to [4], wherein the alcohol is methanol, the alkyl nitrite is methyl nitrite, and the dialkyl carbonate and/or dialkyl oxalate is dimethyl carbonate and/or dimethyl oxalate The manufacturing method described in 1.
[6] having a catalyst for reacting carbon monoxide and alkyl nitrite to produce dialkyl carbonate and/or dialkyl oxalate and nitrogen monoxide, wherein carbon monoxide, alkyl nitrite and nitrogen monoxide are produced; a first reactor for producing a second gas containing dialkyl carbonate and/or dialkyl oxalate and nitric oxide from the first gas containing;
The second gas is brought into contact with an absorption liquid that absorbs dialkyl carbonate and/or dialkyl oxalate, and the condensate containing dialkyl carbonate and/or dialkyl oxalate and the non-condensable gas containing nitrogen monoxide are mixed. a separating absorption tower;
a third gas containing an alkyl nitrite together with unreacted nitric oxide by introducing a mixed gas of said non-condensable gas and molecular oxygen and alcohol, and reacting said nitric oxide, molecular oxygen and alcohol; and a second reactor producing a bottom liquid containing unreacted alcohol, nitric acid and water;
Carbon monoxide and/or nitrogen monoxide and the bottom liquid are introduced and mixed to obtain a mixture, and the carbon monoxide and/or nitrogen monoxide, alcohol and nitric acid are reacted to produce alkyl nitrite. a third reactor;
a waste liquid recovery tank for recovering a waste liquid containing unreacted alcohol and nitric acid and water in the third reactor;
a pipe for transferring the second gas produced in the first reactor to the absorption tower;
a pipe for transferring the non-condensable gas separated in the absorption tower to the second reactor;
a pipe for transferring the third gas generated in the second reactor to the first reactor;
A pipe for transferring the bottom liquid produced in the second reactor to the third reactor;
piping for transferring the alkyl nitrite produced in the third reactor to the second reactor together with unreacted carbon monoxide and/or nitrogen monoxide;
A pipe for transferring the waste liquid generated in the third reactor to the waste liquid recovery tank;
a pipe installed at the outlet of the waste liquid recovery tank;
a UV detector for detecting the concentration of nitric acid in the bottom liquid, mixed liquid in the third reactor, or waste liquid;
Determine whether the concentration of nitric acid detected by the UV detector is within the target range, and when the concentration is outside the target range, the amount of nitric acid in the bottom liquid, mixed liquid, or waste liquid and a control unit that adjusts the concentration to be within a target range;
A device for producing dialkyl carbonate and/or dialkyl oxalate, comprising
The UV detector is installed in the pipe that transfers the bottom liquid generated in the second reactor to the third reactor, the pipe that transfers the waste liquid generated in the third reactor to the waste liquid collection tank, and the outlet of the waste liquid collection tank. A device for producing dialkyl carbonate and/or dialkyl oxalate, which is installed in at least one of the pipes.
[7] The dialkyl carbonate and/or dialkyl oxalate according to [6], wherein the bottom liquid, mixed liquid or waste liquid in the third reactor contains nitric acid, alcohol, nitrogen monoxide and alkyl nitrite. manufacturing device.
[8] The carbonate according to [6] or [7], wherein the alcohol is methanol, the alkyl nitrite is methyl nitrite, and the dialkyl carbonate and/or dialkyl oxalate is dimethyl carbonate and/or dimethyl oxalate. An apparatus for producing dialkyl and/or dialkyl oxalate.
[9] The concentration of nitric acid in the column bottom liquid, the mixed liquid in the third reactor, or the waste liquid is measured in real time using the absorbance by a UV detector and the calibration curve, [6] to [ 8], the apparatus for producing dialkyl carbonate and/or dialkyl oxalate according to any one of

According to the present invention, the nitric acid concentration in the solution can be safely measured, the corrosion of the SUS reactor can be suppressed, and the nitrogen source in the waste liquid can be reduced, thereby enabling continuous production over a long period of time. It is possible to provide a method and an apparatus for producing dialkyl carbonate and/or dialkyl oxalate that enable In addition, it is possible to efficiently produce a dialkyl carbonate and/or a dialkyl oxalate while maintaining the reaction activity while solving the above problems.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing an example of the schematic configuration of an alkyl nitrite production apparatus used in the method for producing dialkyl carbonate and/or dialkyl oxalate of the present invention; 1 is a schematic diagram showing an example of a reactor 2 used in the method for producing dialkyl carbonate and/or dialkyl oxalate of the present invention; FIG. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a diagram showing a schematic configuration of a production apparatus to which one embodiment of the method for producing dialkyl carbonate and/or dialkyl oxalate of the present invention is applied; 1 is a calibration curve showing the relationship between absorbance at 303 nm and nitric acid concentration, prepared for calculating nitric acid concentration in Examples 1-1 and 1-2. 2 is a graph showing the correlation between the nitric acid concentration calculated from the absorbance at 303 nm and the nitric acid concentration by titration in Example 1-2. 4 is a graph showing the relationship between nitric acid concentration and absorbance at each wavelength in Example 2. FIG. In Example 4-2, the nitric acid concentration calculated from the absorbance at 303 nm and the nitric acid concentration by ion chromatography analysis for several samples taken from the nitric acid reduction tank reaction liquid and the mixture of the regeneration tower bottom liquid and the nitric acid reduction tank reaction liquid. is a graph showing the correlation of

Preferred embodiments of the invention are described below, optionally with reference to the drawings. In each drawing, the same or equivalent elements are denoted by the same reference numerals, and overlapping descriptions are omitted as the case may be. In addition, the following embodiments are examples of embodiments of the present invention, and the present invention is not limited to the following embodiments.

In the method for producing dialkyl carbonate and/or dialkyl oxalate of the present invention, nitric oxide, oxygen, and alcohol are reacted to regenerate raw material alkyl nitrite, and the concentration of nitric acid produced as a by-product is measured in real time, By controlling within a predetermined numerical range, it is possible to suppress corrosion of the SUS reactor and reduce the nitrogen source in the waste liquid, thereby enabling continuous production over a long period of time. In addition, when the alkyl of the dialkyl carbonate and/or the dialkyl oxalate is methyl, the production of methyl nitrate is suppressed, making it possible to safely measure the concentration of nitric acid in the solution.

[Method for producing dialkyl carbonate and/or dialkyl oxalate]
Each step of the present invention will be described below.

(First step)
The first step is a step of reacting carbon monoxide with alkyl nitrite to produce dialkyl carbonate and/or dialkyl oxalate and nitric oxide. In the first step, a first gas containing carbon monoxide, an alkyl nitrite, and nitrogen monoxide is introduced into a first reactor, and the carbon monoxide and the alkyl nitrite are reacted in the presence of a catalyst, The step of generating the second gas containing dialkyl carbonate and/or dialkyl oxalate and nitrogen monoxide is preferred. Specifically, the first gas can be introduced into a first reactor filled with a catalyst, and carbon monoxide and alkyl nitrite can be catalytically reacted in the gas phase. A single-tubular or multi-tubular catalyst packed tower is effective as the reactor.

The catalyst is preferably a platinum group metal solid catalyst, and includes palladium-based, platinum-based, rhodium-based, ruthenium-based, iridium-based catalysts, etc. Among them, palladium-based catalysts are preferred. Nitrates, sulfates, phosphates, halides and salts of these metals such as acetates, oxalates and benzoates can also be used. The platinum group metal solid catalyst can be, for example, in the form of being carried on an inert carrier such as activated carbon, alumina, silica, diatomaceous earth, pumice, zeolite, molecular sieve and the like. In this case, the supported amount of the platinum group metal is 0.01 to 10% by mass, preferably 0.2 to 2% by mass, based on the carrier in terms of the platinum group metal.

The first gas contains carbon monoxide, alkyl nitrite and nitric oxide. The first gas can be used by diluting it with a gas that is inert to the reaction, such as nitrogen gas or carbon dioxide gas.

Although the concentration of the alkyl nitrite in the first gas can be varied over a wide range, it is preferred that the concentration be 1% by volume or more in order to obtain a satisfactory reaction rate. The higher the concentration of the alkyl nitrite, the faster the reaction proceeds. It can be in the range of ~30% by volume. When the alkyl nitrite is methyl nitrite, the amount is preferably 3 to 25% by volume from the viewpoint of suppressing the production of by-product methyl nitrate.

The concentration of carbon monoxide in the first gas can vary widely and can be chosen in the range of 10-90% by volume.

The concentration of nitric oxide in the first gas can vary widely and can be chosen in the range of 1-20% by volume.

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

The reaction pressure can be normal pressure to 0.98 MPa (gauge pressure), preferably normal pressure to 0.49 MPa (gauge pressure), but in some cases the pressure is slightly lower than normal pressure. good too.

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

(Second step)
In the second step, the product obtained in the first step is brought into contact with an absorption liquid that absorbs dialkyl carbonate and/or dialkyl oxalate, and a condensate containing dialkyl carbonate and/or dialkyl oxalate and monoxidation and a non-condensable gas containing nitrogen.
In the second step, a second gas containing dialkyl carbonate and/or dialkyl oxalate and nitrogen monoxide is brought into contact with an absorption liquid that absorbs dialkyl carbonate and/or dialkyl oxalate to obtain dialkyl carbonate and/or dialkyl oxalate. It is preferred to obtain a condensate containing dialkyl acid and a non-condensable gas containing nitric oxide. Here, the non-condensable gas can be divided into non-condensable gas 1 and non-condensable gas 2 and introduced into the second and third reactors respectively.
Specifically, the dialkyl carbonate and/or dialkyl oxalate, which are reaction products, are introduced into a condenser and cooled to a temperature below the temperature at which the dialkyl carbonate and/or dialkyl oxalate condense while being brought into contact with the absorbing liquid. It can be separated into non-condensable gas.

The condensate generally contains alkyl formate and the like in addition to the target dialkyl carbonate and/or dialkyl oxalate. On the other hand, the non-condensable gas contains unreacted carbon monoxide, alkyl nitrite, etc., in addition to the nitrogen monoxide generated in the reaction in the first step.

In the second step, there is a problem that part of the target dialkyl carbonate and/or dialkyl oxalate is entrained in the non-condensable gas, and when the target has a relatively high melting point such as dimethyl oxalate, The reaction product is brought into contact with the absorption liquid in order to avoid the problem of the object solidifying and adhering to the walls of the condenser and the like, which can lead to blockage thereof. The contact method is not particularly limited, and examples thereof include a countercurrent contact method and a bubbling contact method.

The absorption liquid is not limited as long as it easily dissolves the target dialkyl carbonate and/or dialkyl oxalate, but it is preferably an alcohol, more preferably the same as the alkyl portion of the dialkyl carbonate and/or dialkyl oxalate. It is an alcohol with an alkyl group. That is, when the target is dimethyl carbonate and/or dimethyl oxalate, the absorbing liquid is preferably methanol.

The supply amount of the absorbing liquid is not particularly limited, and when the object is dimethyl carbonate and/or dimethyl oxalate, the absorbing liquid, preferably methanol, is added to 100 parts by volume of the object to be treated, that is, the second gas. It is preferably 0.01 to 0.1 parts by volume. For example, cooling condensation can be performed at a temperature of 0 to 60° C. while flowing 0.01 to 0.1 volume part of methanol with respect to 100 volume parts of the second gas.

(Third step)
In the third step, the non-condensable gas containing nitrogen monoxide obtained in the second step, molecular oxygen and alcohol are reacted to produce alkyl nitrite and water as main products and nitric acid as a by-product. is the process of obtaining
In the third step, a mixed gas obtained by mixing non-condensable gas and molecular oxygen and alcohol are introduced into the second reactor, and nitrogen monoxide, molecular oxygen and alcohol are reacted to produce a main product and water as a by-product, and a third gas containing the alkyl nitrite together with unreacted nitric oxide, and the bottom containing unreacted alcohol, nitric acid and water. It is preferably a step of obtaining a liquid.

FIG. 1 is a diagram showing an alkyl nitrite production apparatus. In the alkyl nitrite production apparatus 100 of FIG. 1, liquid alcohol is supplied from an alcohol supply line 11 (hereinafter also referred to as "pipe 11") to an alkyl nitrite production reaction tower 1 (hereinafter also referred to as "reaction tower 1"). supplied to the top of the Reactor 1 corresponds to the second reactor.
The upper part of the reaction tower 1 in this specification refers to a portion above the middle part of the reaction tower 1 in the vertical direction. The intermediate portion of the reaction tower 1 in the present specification refers to a section with a height of 40 to 60 when the height of the reaction tower 1 is 100. The lower part of the reaction tower 1 in this specification refers to a portion below the middle part of the reaction tower 1 in the vertical direction.

The upper part of the reaction tower 1 is provided with a supply port for supplying alcohol. A pipe 11 is connected to the supply port. The alcohol that flows through the pipe 11 and is supplied to the upper part of the reaction tower 1 from this supply port flows downward from the upper part of the reaction tower 1 .

A supply port for supplying the non-condensable gas 1 containing nitrogen monoxide to the reaction tower 1 is provided below the middle part of the reaction tower 1 . A source gas supply line 12 (hereinafter also referred to as "pipe 12") is connected to this supply port. The non-condensable gas 1 flowing through the pipe 12 is supplied to the lower part of the reaction tower 1 from this supply port. The non-condensable gas 1 supplied to the lower part of the reaction tower 1 rises upward from the lower part of the reaction tower 1 .

In FIG. 1 , an oxygen supply line 15 (hereinafter also referred to as “pipe 15 ”) is connected to pipe 12 . The pipe 15 may be connected directly to the lower part of the reaction tower 1 without passing through the pipe 12, or may be connected to both the lower part of the reaction tower 1 and the pipe 12. Oxygen is molecular oxygen. Oxygen is supplied to the lower part of the pipe 12 and/or the reactor 1 through the pipe 15 . Among these, oxygen is preferably supplied to the pipe 12 in terms of reaction efficiency. In this case, a mixed gas containing at least nitrogen monoxide and oxygen is supplied to the lower part of the reaction column 1 .

The alcohol, nitrogen monoxide and oxygen supplied to the reaction tower 1 react inside the reaction tower 1 to produce alkyl nitrite. The main reaction at this time is described by the following formula (1). At this time, in the reaction tower 1, a side reaction represented by the following formula (2) proceeds and nitric acid is produced as a by-product. In formulas (1) and (2), R ¹ represents an alkyl group, preferably an alkyl group having 1 to 4 carbon atoms, more preferably a methyl group or an ethyl group, particularly preferably a methyl group. That is, the alcohol is preferably methanol. That is, it is preferred that the alcohol is methanol, the alkyl nitrite is methyl nitrite, and the dialkyl carbonate and/or dialkyl oxalate is dimethyl carbonate and/or dimethyl oxalate.
2NO + 2R ¹ OH + 1/2O ₂ → 2R ¹ ONO + H ₂ O (1)
NO + 3/4O ₂ + 1/2H ₂ O → HNO ₃ (2)

The alkyl nitrite produced in the reaction of (1) forms a third gas together with unreacted nitrogen monoxide, and the third gas is further introduced into the first gas and used as a raw material in the first step to produce dialkyl carbonate and / or produce a dialkyl oxalate. The dialkyl carbonate and/or dialkyl oxalate are recovered in the condensed liquid in the second step, but partly mixed with the non-condensed gas and further mixed into the reaction tower 1 . When the alcohol in the third step is methanol, the reaction in (1) above produces methyl nitrite, and the first step produces dimethyl carbonate and/or dimethyl oxalate. / Or dimethyl oxalate will be mixed.

A third gas extraction line 13 (hereinafter also referred to as “pipe 13”) is connected to the top of the reaction tower 1 . The third gas contains unreacted nitric oxide and alkyl nitrite. The third gas containing alkyl nitrite produced by the above formula (1) or the like can be extracted from the reaction tower 1 using the pipe 13 .

At the bottom of the reaction tower 1, a tower bottom liquid containing nitric acid and water produced in the above (1) and (2), unreacted alcohol and the like remains.

(Fourth step)
The fourth step is a step of reacting carbon monoxide and/or nitrogen monoxide, alcohol and nitric acid obtained in the third step to produce alkyl nitrite.
In the fourth step, carbon monoxide and / or nitrogen monoxide and the column bottom liquid are introduced into the third reactor and mixed to obtain a mixed liquid, carbon monoxide and / or nitrogen monoxide in the mixed liquid, alcohol and The step of reacting nitric acid to produce an alkyl nitrite is preferred. The alkyl nitrite produced in this step is circulated to the second reactor of the third step together with unreacted carbon monoxide and/or nitrogen monoxide, and unreacted alcohol, nitric acid and water are transferred to the waste liquid recovery tank. be done. Moreover, the alcohol used in the fourth step is unreacted alcohol or newly added alcohol in the third step. The alcohol used in the fourth step may be a mixture of unreacted alcohol and newly added alcohol in the third step.

In FIG. 1, the bottom liquid of reaction tower 1 contains at least water, unreacted alcohol and nitric acid. This bottom liquid is extracted from the lower part of the reaction tower 1 using a bottom liquid extraction line 14 (hereinafter also referred to as "pipe 14"), and is transferred to a nitric acid conversion reactor 2 (hereinafter referred to as "reactor 2"). (also called). Reactor 2 corresponds to the third reactor. The pipe 14 may be connected to a position at the bottom of the reaction tower 1 from which the bottom liquid can be extracted. Specifically, it is preferably connected to the bottom of the reaction tower 1. The position where the pipe 14 is connected to the reactor 2 is not particularly limited, and it is preferably connected to the upper part of the reactor 2 from the viewpoint of easiness of supplying the bottom liquid to the reactor 2 .

The bottom liquid supplied to the reactor 2 through the pipe 14 contacts and mixes with carbon monoxide and/or nitrogen monoxide to form a mixed liquid. Carbon monoxide and nitrogen monoxide are respectively supplied to the nitrogen monoxide or carbon monoxide supply line 16 (hereinafter also referred to as "pipe 16"), or the nitrogen monoxide and carbon monoxide mixed gas supply line 17 (hereinafter referred to as " It is supplied to the reactor 2 via a pipe 17"). Alkyl nitrites are produced in the mixture, for example, by reactions represented by formulas (3) and (4). That is, nitric acid, alcohol, carbon monoxide and/or nitrogen monoxide react to produce alkyl nitrite. In formulas (3) and (4), R ¹ has the same definition as above.
_HNO3 + CO + ^R1OH → ^R1ONO + _H2O + _CO2 (3)
_HNO3 + 2NO + ^3R1OH → ^3R1ONO ₊ 2H2O (4)

A fourth gas containing alkyl nitrite produced in the reactor 2 and unreacted carbon monoxide and/or nitrogen monoxide is extracted from a fourth gas extraction line 18 (hereinafter also referred to as “pipe 18”). and supplied to the reaction tower 1. The pipe 18 is preferably connected to a supply port provided above the intermediate portion of the reaction tower 1 in the vertical direction. Thereby, the fourth gas is supplied to the upper part of the reaction tower 1 . Unreacted alcohol, nitric acid and water in the reactor 2 are transferred to the waste liquid recovery tank.

In the reactor 2, when carbon monoxide is used as the gas to be brought into contact with the bottom liquid, it is preferable to bring the bottom liquid and carbon monoxide into contact in the presence of a catalyst in order to improve the reaction efficiency. . As the catalyst used here, a catalyst containing a platinum group metal is preferable, and a catalyst containing palladium is more preferable. As the catalyst containing a platinum group metal, a catalyst in which a platinum group metal is supported on a carrier is preferable. Moreover, the reaction liquid in the reactor 2 is preferably controlled at 10 to 60°C.

The amount of the platinum group metal supported in such a catalyst is preferably 0.01 to 10% by mass, more preferably 0.2 to 2% by mass, relative to the carrier. Examples of the carrier that constitutes the catalyst include inert carriers such as activated carbon, alumina, silica, diatomaceous earth, pumice, zeolite, and molecular sieves. Among these, alumina is preferred, and α-alumina is particularly preferred.

When supplying carbon monoxide to the reactor 2, as shown in FIG. be. From the viewpoint of reaction efficiency of carbon monoxide, the pipe 16 is preferably connected to the lower portion of the reactor 2 . That is, the pipe 16 is preferably connected to a supply port provided below the middle portion of the reactor 2 in the vertical direction. Moreover, when supplying carbon monoxide to the reactor 2, it is preferable that the pipe 18 is connected to the middle portion of the reactor 1 in the height direction, as shown in FIG. Thereby, oxidation of carbon monoxide in the fourth gas can be reduced.

The upper part of the reactor 2 in this specification means a part above the middle part in the vertical direction of the reactor 2 . The intermediate portion of the reactor 2 in this specification refers to a section with a height of 40 to 60 when the height of the reactor 2 is 100. The lower part of the reactor 2 in this specification refers to a portion below the middle part of the reactor 2 in the vertical direction.

The carbon monoxide supplied to the reactor 2 via the pipe 16 and the carbon monoxide supplied using the carbon monoxide supply line 32 described later are supplied from the same carbon monoxide source. may be supplied from different carbon monoxide sources.

Reactor 2 may be partitioned into a plurality of reaction sections. The reactor 2 may be partitioned into a plurality of reaction sections (reaction tanks) by piping, or may be partitioned into a plurality by inner walls, weirs, or the like. The number of reaction sections formed by partitioning the reactor 2 may be 2 to 5 or 2 to 3 from the viewpoint of reaction control and economy. The plurality of reaction sections formed in the reactor 2 are preferably arranged in series along the flow direction of the raw material solution or reaction liquid, as shown in FIG. 2, for example. From the viewpoint of improving throughput, the reactors may be arranged in parallel, or the reactors arranged in series may be arranged in parallel. The method of arrangement can also be appropriately adjusted according to the purpose of production, production volume, equipment, and the like.

FIG. 2 shows an example of a reactor 2 in which reaction vessels A to C are arranged in series. The reactor 2 having a plurality of reaction vessels arranged in series includes a reaction vessel A having a reaction temperature of 60° C. to 80° C., and a reaction vessel downstream of the reaction vessel A having a reaction temperature of 80° C. to 100° C. A tank C may be provided. The reaction temperature in reactor A may be 65°C to 75°C. The reaction temperature in the reactor C may be 85°C to 95°C. The reaction temperature in the reaction vessel B is preferably higher than the reaction temperature in the reaction vessel A and lower than the reaction temperature in the reaction vessel C. A multi-stage reaction vessel having two or more stages may be used as the reaction vessel.

In the reactor 2, the gas superficial velocity may be 20 mm/sec to 100 mm/sec or 30 mm/sec to 80 mm/sec in the reactor (reaction section) having a nitric acid concentration of 1% by mass or more. In a reactor (reaction section) having a nitric acid concentration of less than 1% by mass, the gas superficial velocity may be 1 mm/sec to 20 mm/sec, or may be 5 mm/sec to 15 mm/sec. By setting the gas superficial velocity as such, it may be possible to produce the alkyl nitrite more efficiently. The gas superficial velocity in the present disclosure indicates the gas velocity based on the cross section of the reactor (reaction section) when the reactor (reaction section) is tubular. If the cross section is not constant, the gas superficial velocity can be obtained from the average value.

The residence time in the reactor 2 (reaction section) may be appropriately changed according to the reaction conditions and the volume of the reactor 2 (reaction section). The total residence time in the reactor 2 may be about 1 hour to 20 hours, or about 2 hours to 10 hours. The residence time of the reaction solution in each reaction section depends on the reaction temperature and conversion rate in each reaction section, but from the viewpoint of yield and quality, the residence time in the downstream reaction section (second reaction section) is It may be set longer than the residence time of the upstream reaction section (first reaction section).

<Measurement of nitric acid concentration>
The third and / or fourth step is a sub-step of measuring the concentration of nitric acid in any solution in the step from UV absorbance and determining whether the measured concentration of nitric acid is within the target range. and adjusting the amount of nitric acid in the solution when the concentration is outside the target range to bring the concentration within the target range.
Preferably, the third and / or fourth step includes the bottom liquid in the second reactor and the piping between the second reactor and the third reactor, the mixed liquid in the third reactor, and the third reactor The concentration of nitric acid in at least one selected from the group consisting of the pipes between and the waste liquid recovery tank and the waste liquid in the waste liquid recovery tank is measured from the UV absorbance, and the control unit determines that the measured nitric acid concentration is within the target range. wherein, when the concentration is outside the target range, adjusting the amount of nitric acid in the bottom liquid, the mixed liquid, or the waste liquid to bring the concentration within the target range It has a sub-step to be within.
By providing such a sub-process, it is possible to adjust the concentration of nitric acid in the bottom liquid, mixed liquid, or waste liquid to an appropriate range, suppress corrosion of the SUS reactor, and reduce nitrogen in the waste liquid. By reducing the source, continuous and efficient production of dialkyl carbonate and/or dialkyl oxalate can be achieved over a long period of time. The bottom liquid, mixed liquid or waste liquid may contain alcohol and/or water together with nitric acid, and may be referred to as a solution.

As used herein, the term "waste liquid recovery tank" refers to tanks, equipment, and the like installed in the rear stage of the reactor 2, and includes, for example, the nitric acid concentration tower 3 in FIG. Moreover, the waste liquid refers to the aqueous solution in general discharged from the reactor 2, and specifically refers to the aqueous solution in general flowing after the waste liquid recovery line 21 in FIG.
From the viewpoint of reducing the nitrogen source in the waste liquid and effectively utilizing it, it is preferable to measure the concentration of nitric acid in the waste liquid recovery line 21 and determine whether or not the concentration is within the target range.

In order to measure the UV absorbance in the bottom liquid, mixed liquid or waste liquid in real time, a UV detector is installed in the second reactor, the third reactor, the waste liquid recovery tank, and the piping connecting these, and the UV absorbance The concentration of nitric acid in the column bottom liquid, mixed liquid, or waste liquid is measured. UV absorbance measurements can be made continuously or intermittently. The UV absorbance referred to here is obtained by irradiating a target sample with light in the ultraviolet region (200 to 380 nm) and measuring the intensity of the light transmitted through the sample with a UV detector. good.

It is known that the higher the concentration of nitric acid in the mixture in the third reactor, the more advantageous it is for the production of alkyl nitrite, but the corrosion of the SUS reactor progresses. Chemical Equipment Material Corrosion Resistance Table p75 According to FIG. 52, it is known that when the concentration of nitric acid exceeds 10% by mass, the corrosion of the SUS surface progresses at 0.0025 mm/year. Therefore, in order to perform long-term continuous production, the nitric acid concentration of the column bottom liquid, mixed liquid or waste liquid is preferably controlled at 0.001% by mass or more and 10% by mass or less, more preferably 0.002% by mass or more. 9% by mass or less is preferable, and 0.003% by mass or more and 8% by mass or less is particularly preferable.

The nitrate concentration UV measurement method is based on the continuous flow analysis method in which the sample solution is adjusted and the absorbance is measured while the sample solution is flowing through the pipeline. In this method, the wavelength of the measurement light is selected according to the nitric acid concentration of the sample liquid, the absorbance is measured, and the nitric acid concentration is measured from this absorbance.
In order to measure the UV absorbance in real time, a sample loop may be provided in the second reactor, the third reactor, the waste liquid collection tank, and the piping connecting these. For example, a switching valve is installed in the second reactor, the third reactor, the waste liquid recovery tank, and the piping connecting them, and when measuring the UV absorbance, the valve is switched to the sample loop side, a sample is collected, and the UV absorbance is measured. can be measured in real time. Before measuring the UV absorbance, it is desirable to prepare a calibration curve from the UV absorbance and the nitric acid concentration by another measurement method. As another measuring method, known analytical methods such as titration and chromatography can be used.

In FIG. 1, a UV detector may be attached to the column bottom liquid extraction line 14 (hereinafter also referred to as "pipe 14"), a waste liquid recovery line 21 (hereinafter also referred to as "pipe 21"), a concentrated liquid extraction line 22 (hereinafter also referred to as "piping 22") and/or a waste liquid extraction line 25 (hereinafter also referred to as "piping 25"). If installed in the pipe 14 , it can be used to control the concentration of nitric acid introduced into the reactor 2 . If installed in the pipe 21, 22 or 25, the nitrogen content in the waste liquid can be estimated. In the case of FIG. 2, when attached to the pipe 34, it can be used to control the nitric acid concentration introduced into the reactor 2, and when attached to the pipe 37, the nitrogen content in the waste liquid can be estimated. At least one UV detector may be installed, or a plurality of UV detectors may be installed.

When the nitric acid concentration level of the sample liquid is known in advance, the wavelength of the measurement light is selected according to the nitric acid concentration level, and the absorbance is measured using the measurement light of an appropriate wavelength. Specifically, the absorbance of nitric acid becomes maximum near 300 nm. The absorbance can also be adjusted by adjusting the optical path length. The longer the optical path length, the higher the absorbance. The wavelength is preferably 280 nm to 330 nm, more preferably 280 nm to 320 nm, even more preferably 280 nm to 315 nm. Within this wavelength range, nitric acid concentration can be measured with high accuracy.

A spectrophotometer used to detect nitrate ions generally has an absorbance of -0.5 to 3 Abs. (Abs. is an arbitrary unit), it is necessary to adjust the sample injection amount and the measurement wavelength so that the absorbance falls within this measurement range. With a commonly used spectrophotometer, if the nitric acid concentration is up to 10M, the nitric acid concentration of the sample can be measured simply by changing the measurement wavelength to the long wavelength side without changing the injection amount of the sample. When the nitric acid concentration exceeds 10M, it is necessary to change the measurement wavelength to the long wavelength side and adjust the sample injection amount. Unless the injection amount of the sample is adjusted, a general spectrophotometer cannot measure within the measurable range (absorbance of -0.5 to 3 Abs.). Since the measurable range varies depending on the spectrophotometer used, the reference nitric acid concentration for switching the measurement wavelength may be determined according to the spectrophotometer used in the measurement system.

A calibration curve can be used to determine the nitric acid concentration from the measured absorbance. The calibration curve is prepared by using nitrate ion standard solutions of various concentrations (0 to 14 M), taking the maximum absorbance obtained by actually measuring this as the absorbance of the concentration, and creating a graph connecting the absorbance of each concentration. . In addition, in order to change the measurement wavelength and the sample injection amount, a calibration curve that takes these conditions into consideration is used.

Specifically, as an example, a calibration curve obtained by the following equation is used.
X=(A−b)/a (5)
X: nitrate ion concentration (M)
A: measured absorbance (maximum absorbance, Abs.)
a: Detection sensitivity per 1 M nitrate ion concentration (Abs./M)
b: blank absorbance (absorbance when measuring nitric acid concentration 0M, Abs.)
Here, the detection sensitivity a varies depending on the measurement wavelength and sample injection amount. Therefore, detection sensitivity for nitrate ions at each measurement wavelength used for measurement in advance (Tλ: molar extinction coefficient at a certain wavelength, set according to wavelength), sample injection amount V (μl: carrier flow rate C (μl/sec) and sample injection time The product of t (sec)) and the detection sensitivity relationship K (K = V x f, f: the rate of change in detection sensitivity when the sample injection amount is changed) is experimentally detected based on the following formula: The sensitivity a is obtained in advance, and the optimum value is set to be used when the measurement conditions are changed.
a=Τλ×K, that is, X=(A−b)/(Τλ×K) (6)

By using this equation as a calibration curve, for example, if a calibration curve is created for nitric acid concentrations up to 1 M using a wavelength of 280 nm, even if the measurement wavelength and sample injection amount are changed, the nitric acid concentration accompanying changes in the measurement conditions The nitrate ion concentration can be obtained by calculating the change in detection sensitivity for ions. By storing this calibration curve data in the central control unit of the measuring apparatus, real-time automatic measurement is possible.

The installation location of the UV detector for measuring the column bottom liquid is not limited. You can install multiple. In order to grasp the initial concentration of nitric acid, it is preferable to measure the concentration of nitric acid in the bottom liquid drawing line 14 from the lower part of the reaction column 1 to the reactor 2 . Further, in FIG. 2, the nitric acid concentration in each reaction section may be measured, or the nitric acid concentration in a line connecting each reaction section may be measured. Finally, the nitric acid concentration in the mixed liquid in the reactor 2 may be measured.

When the range of nitric acid concentration in the column bottom liquid, mixed liquid or waste liquid is 10% by mass or less, the column bottom liquid, mixed liquid or waste liquid is used as it is as a sample liquid, and the absorbance is measured with respect to the measurement light of a single wavelength. Then, it is preferable to measure the nitric acid concentration from this absorbance. By using this method, the nitric acid concentration can be measured simply and accurately. In this case, the single wavelength is preferably 280-320 nm, more preferably 290-315 nm, and particularly preferably 300-305 nm.

In the third and/or fourth step, the control unit determines whether the measured nitric acid concentration is within the target range, and when the concentration is outside the target range, the bottom liquid , adjusting the amount of nitric acid in the mixed liquid or waste liquid to bring the concentration within the target range. Through this process, the nitric acid concentration in the bottom liquid, mixed liquid, or waste liquid can be kept within the target range, preventing the progress of corrosion in the reactor, and reducing the nitrogen source in the waste liquid. Continuous production over The target range of nitric acid concentration is, for example, preferably 0.001% by mass to 10% by mass, more preferably 0.002% by mass to 9% by mass, and particularly preferably 0.003% by mass to 8% by mass. be.

The adjustment of the amount of nitric acid in the bottom liquid, the mixed liquid, or the waste liquid is to control the nitric acid concentration in the bottom liquid, the mixed liquid, or the waste liquid within the target range when it is out of the target range. be. The nitric acid concentration in the reactor may be increased by increasing the feeding amount of the nitric acid-containing solution or lowering the reaction temperature. In addition, reduce the feed amount of the solution containing nitric acid, stop feeding the solution containing nitric acid, feed the nitric acid containing solution diluted by adding water etc. to the solution containing nitric acid, raise the reaction temperature, etc. to reduce the concentration of nitric acid in the reactor. Specific examples include, but are not limited to, the operations described above. The progress of corrosion in the reactor can be prevented by the measures described above.

When the alkyl of the dialkyl carbonate and/or dialkyl oxalate is methyl, by controlling the concentration of nitric acid in the column bottom liquid, mixed liquid or waste liquid in the third or fourth step, corrosion of SUS containers and methyl nitrate production should be suppressed. Therefore, setting the upper limit of the nitric acid concentration for operation leads to long-term continuous production. A drop test requires less than 2% by weight of methyl nitrate in solution.

Methyl nitrate may reach a production amount of 2% by mass when the nitric acid concentration is 40% by mass, the methanol is 30% by mass, the reaction time is 10 hours, and the reaction temperature is 80 ° C., and the nitric acid concentration is Controlling to less than 40% by mass is required.

When the nitric acid concentration exceeds 40% by mass, the amount of nitric acid fed to the reaction tower 1 or the reactor 2 is reduced to lower the nitric acid concentration in the reactor, or the feed amount of methanol is reduced to reduce the feed amount of the reaction tower 1. Alternatively, the methanol concentration in the reactor 2 is lowered, or the reaction temperature is lowered. With the measures described above, the production amount of methyl nitrate in the reactor 1 or reactor 2 can be suppressed to 2% by mass or less. For nitric acid feed, for example, the bottom liquid circulation line 19 can be used.

The alkyl nitrite production apparatus 100 includes a nitric acid concentration column 3 for distilling off low-boiling components from the reaction liquid from the reactor 2 to concentrate nitric acid. By maintaining the alcohol concentration in the nitric acid concentrate from the nitric acid concentration column 3 at 4% by mass or less, the nitric acid content such as alkyl nitrate mixed in the low boiling point components can be sufficiently reduced. As a result, the amount of nitric acid to be treated as waste liquid can be sufficiently reduced. By circulating the nitric acid concentrate to the reactor 2 through the concentrated liquid circulation line 23, the nitric acid component can be effectively used. Therefore, nitrogen monoxide used as a raw material can be sufficiently reduced.

If the concentration of nitric acid in the concentrated liquid in the nitric acid concentration column 3 can be reduced, the neutralization process can be shortened, resulting in a method for producing dialkyl carbonate and/or dialkyl oxalate with less burden on the environment. From the viewpoint of suppressing corrosion of SUS pipes, the concentration of nitric acid in the concentrate is preferably 10% by mass or less, more preferably 8% by mass or less, and particularly preferably 5% by mass or less.

The alkyl nitrite manufacturing apparatus 100 includes a waste liquid extraction line 25 . If the concentration of nitric acid in the waste liquid cannot be accurately determined, an error will occur in the amount of alkali to be added for neutralization, and the waste liquid will flow out before the neutralization process is completed. The production method of the present invention may comprise a step of online measuring the concentration of nitric acid in the waste liquid from the UV absorbance. By providing this step, it becomes possible to accurately measure the concentration of nitric acid in the waste liquid, and appropriate waste liquid treatment becomes possible.

(Fifth step)
The fifth step is a step of circulating the first gas obtained by mixing the third gas obtained in the third step and carbon monoxide to the first step. Carbon monoxide is supplied to the third gas via a carbon monoxide supply line 32 . The third gas contains alkyl nitrite together with unreacted nitrogen monoxide, and this step enables effective utilization of alkyl nitrite, which is a raw material for dialkyl carbonate and/or dialkyl oxalate.

[Device for producing dialkyl carbonate and/or dialkyl oxalate]
FIG. 3 shows a schematic configuration of an apparatus for producing dialkyl carbonate and/or dialkyl oxalate to which the method for producing dialkyl carbonate and/or dialkyl oxalate of the present invention is applied. The symbols used in FIG. 3 have the meanings described above. FIG. 3 shows an example of a dialkyl carbonate and/or dialkyl oxalate production apparatus, and the present invention is not limited to this.

The present invention is by no means limited to the above embodiments. For example, the reactor 2 is not limited to a stirred tank type as shown in FIG. For example, reactor 2 may be of the multistage column type with trays such as packed columns or sieve trays. Since the reaction is a gas-liquid contact reaction, it preferably has a stirring function. Moreover, the reactor 2 may be, for example, a gas-liquid mixing reactor, a packed column, a plate column, a bubble column, or the like. The type of reactor is not limited to these, and generally known reactors other than those described above may be used. When a stirred tank reactor is used, it is preferable to use a reactor with high gas-liquid contact efficiency, which has a blade-shaped stirrer and a rotating device, etc., from the viewpoint of improving the stirring performance and gas dispersibility. When the reactor is of a multistage column type, the reactor preferably has a packing material with high gas-liquid contact efficiency. The produced alkyl nitrite may be accompanied by a gas and led out of the reaction system (purified by washing or the like as necessary) and used for other reactions.

In the dialkyl carbonate and/or dialkyl oxalate production equipment, the bottom liquid in the second reactor or piping, the mixed liquid in the third reactor or piping, or the waste liquid in the waste liquid recovery tank or piping contains nitric acid, alcohol , nitric oxide and alkyl nitrite.

In the apparatus for producing dialkyl carbonate and/or dialkyl oxalate, the alcohol introduced into the second reactor and the third reactor is methanol; It is preferable that the alkyl nitrite to be produced is methyl nitrite; and that the target compound dialkyl carbonate and/or dialkyl oxalate is dimethyl carbonate and/or dimethyl oxalate.

In the dialkyl carbonate and/or dialkyl oxalate production apparatus, a UV detector measures the absorbance of the column bottom liquid, the mixed liquid in the third reactor, or the waste liquid, and uses a calibration curve to determine the column bottom liquid, It is preferable to measure the concentration of nitric acid in the mixed liquid or waste liquid in the third reactor in real time.

Preparation of calibration curve (1)
A 10% by mass sodium nitrate aqueous solution was passed through a UV detector (SPD-10A manufactured by Shimadzu Corporation), and the absorbance at 303 nm was measured to be 0.438. The nitrate ion concentration at this time was converted into nitric acid concentration, and a calibration curve of nitric acid concentration and absorbance was prepared as shown in FIG.

Example 1-1
800 ml of a liquid containing 10% by mass of nitric acid, 30% by mass of methanol, and 60% by mass of water was introduced into a 1 L autoclave equipped with a stirring blade. 10% by volume of NO—N ₂ was blown at 1000 ml/min under normal pressure while stirring, and the mixture was reacted at a temperature of 30° C. for 4 hours. The obtained reaction solution in the nitric acid reduction tank (corresponding to reactor 2) was passed through an HPLC UV detector (manufactured by Shimadzu Corporation, SPD-10A), and the nitric acid concentration was calculated from the absorbance (303 nm). The calibration curve shown in FIG. 4 was used to calculate the nitric acid concentration. The nitric acid concentration calculated by the UV detector was 9.22 mass %. When the nitric acid concentration of the same reaction liquid was measured by neutralization titration, it was 10.06% by mass.

Example 1-2
A nitric acid reduction tank reaction solution was obtained by changing the methanol concentration, nitric acid concentration, reaction pressure, reaction temperature, and blown NO concentration of Example 1-1. Each reaction solution was analyzed in the same manner as in Example 1-1, and the nitric acid concentration was calculated from the absorbance. In addition, the nitric acid concentration of the same reaction solution was measured by neutralization titration. FIG. 5 shows a graph plotting the nitric acid concentration by titration on the horizontal axis and the nitric acid concentration by absorbance on the vertical axis. As shown in FIG. 5, the slope was approximately 1, R ² =0.977, and the nitric acid concentrations from the two measurements were highly correlated.

Example 2
Methyl nitrite was regenerated from nitric acid using methanol as the alcohol in the configuration of the alkyl nitrite production apparatus shown in FIG. To the bottom liquid (regeneration tower bottom liquid) of the reaction tower 1 in FIG. A total of 5 types of nitric acid aqueous solutions were prepared, including the respective added aqueous solutions and a simulated solution. When the nitric acid concentrations of these aqueous solutions were determined by neutralization titration, they were 13.10, 7.49, 5.26, 9.60 and 10.01% by mass, respectively.
Table 1 shows the results of measuring the absorbance at a wavelength of 280 to 380 nm for the same aqueous solution. For example, in Table 1, the absorbance at a wavelength of 302 nm of the aqueous solution adjusted to 5.26% by mass by adding a 60% by mass nitric acid aqueous solution to the reaction solution having a nitric acid concentration of 2.99% by mass obtained in Example 1-2 is , 1.1426. A spectrophotometer U-2010 (cell length: 2 mm) manufactured by Hitachi, Ltd. was used for the measurement.

Based on Table 1, a graph plotting the relationship between absorbance at 280, 302, 303, 313 and 334 nm and nitric acid concentration by neutralization titration is shown in FIG. As shown in FIG. 6, the absorbance at 302 nm and 303 nm shows a good correlation with the nitric acid concentration by neutralization titration, and it was confirmed that the nitric acid concentration can be calculated by measuring the absorbance using this wavelength. .

Example 3
Methyl nitrite was regenerated from nitric acid with the configuration of the alkyl nitrite production apparatus shown in FIG. For the mixed solution (reaction solution in the nitric acid reduction tank) (pilot 100 L) in the reactor 2 in FIG. 1, the nitric acid concentration was measured from the absorbance at 303 nm using an HPLC UV detector (manufactured by Shimadzu Corporation, SPD-10A). As a result, it was 3.92% by mass. The nitric acid concentration of the same reaction solution was calculated by neutralization titration and found to be 3.42% by mass.
For calculation of nitric acid concentration using a UV detector, a calibration curve prepared from absorbance at 303 nm using an aqueous solution of HNO ₃ /MeOH/H ₂ O = 5% by mass/30% by mass/65% by mass was used. board.

Creation of calibration curve (2)
Methyl nitrite was regenerated from nitric acid using methanol as the alcohol in the configuration of the alkyl nitrite production apparatus shown in FIG. The bottom liquid of the reaction tower 1 (regeneration tower bottom liquid) in FIG. AF46-VB-EX), and the absorbance measured at 300 nm was 2.066 cu. The nitric acid concentration at this time was 1.63% by mass by ion chromatography analysis. The slope was calculated from the relationship between the absorbance on the horizontal axis and the nitric acid concentration on the vertical axis, and used as a calibration curve. The slope was 0.7882.

Example 4-1
Dimethyl oxalate was produced with the configuration of the dialkyl oxalate production apparatus shown in FIG. The mixed solution (reaction solution in nitric acid reduction tank) in reactor 2 in FIG. .159. The nitric acid concentration calculated from the absorbance using the calibration curve obtained in preparation of the calibration curve (2) was 0.91% by mass. Further, the concentration of nitric acid was 0.67% by mass and the concentration of methyl nitrate was 6.8 ppm by mass by ion chromatography analysis.

Example 4-2
Dimethyl oxalate was produced in the same manner as in Example 4-1. The solution obtained by mixing the mixed liquid of the reactor 2 (reaction liquid of the nitric acid reduction tank), the bottom liquid of the reaction tower 1 (regeneration tower bottom liquid), and the mixed liquid was sampled over time, and As in 4-1, the nitric acid concentration was calculated from the absorbance at a wavelength of 303 nm and ion chromatography analysis. The correlation of nitrate concentrations obtained from the two measurements is shown in FIG. The nitrate concentrations obtained from the two measurements showed good correlation.

1: Reactor for alkyl nitrite production (second reactor)
2: Reactor for nitric acid conversion (third reactor)
3: Nitric acid concentration tower 4: Cooler 5: Reactor for producing dialkyl carbonate and/or dialkyl oxalate (first reactor)
6: Absorption tower 11: Alcohol supply line 12: Source gas supply line 13: Third gas extraction line 14: Column bottom liquid extraction line 15: Oxygen supply line 16: Nitrogen monoxide or carbon monoxide supply line 17: Monoxide Nitrogen and carbon monoxide mixed gas supply line 18: fourth gas extraction line 19: column bottom liquid circulation line 20: purge line 21: waste liquid recovery line 22: concentrated liquid extraction line 23: concentrated liquid circulation line 24: distillate Extraction line 25: Waste liquid extraction line 26: Second gas extraction line 27: Absorbing liquid supply line 28: Condensate extraction line 32: Carbon monoxide supply line 100: Alkyl nitrite production device 200: Dialkyl carbonate and/or dialkyl oxalate manufacturing device.
A, B, C: reaction tank 34: liquid supply nozzle 35: gas supply nozzle 36: gas extraction nozzle 37: liquid extraction nozzle 38: first connection part 39: second connection part 30: reactor for nitric acid conversion ( third reactor)
M:: Stirrer.

Claims (9)

a first step of reacting carbon monoxide with an alkyl nitrite to produce a dialkyl carbonate and/or a dialkyl oxalate and nitric oxide;
The product obtained in the first step is brought into contact with an absorption liquid that absorbs dialkyl carbonate and/or dialkyl oxalate to obtain a condensate containing dialkyl carbonate and/or dialkyl oxalate and a non-nitrogen monoxide containing condensate. a second step of obtaining a condensed gas;
A third step of reacting the non-condensable gas containing nitrogen monoxide obtained in the second step, molecular oxygen and alcohol to obtain alkyl nitrite and water as main products and nitric acid as a by-product. When,
a fourth step of reacting carbon monoxide and/or nitrogen monoxide, alcohol and nitric acid obtained in the third step to produce an alkyl nitrite;
A method for producing a dialkyl carbonate and/or a dialkyl oxalate having
The third and / or fourth step is a sub-step of measuring the concentration of nitric acid in any solution in the step from UV absorbance and determining whether the measured concentration of nitric acid is within the target range. and adjusting the amount of nitric acid in the solution to bring the concentration within the target range when the concentration is outside the target range. Method. A first gas containing carbon monoxide, an alkyl nitrite and nitrogen monoxide is introduced into a first reactor, and the carbon monoxide and the alkyl nitrite are reacted in the presence of a catalyst to produce a dialkyl carbonate and/or a first step of producing a second gas containing dialkyl oxalate and nitric oxide;
Contacting the second gas with an absorbing liquid that absorbs the dialkyl carbonate and/or the dialkyl oxalate to obtain a condensed liquid containing the dialkyl carbonate and/or the dialkyl oxalate and a non-condensable gas containing nitrogen monoxide. process and
A mixed gas obtained by mixing a non-condensable gas and molecular oxygen and alcohol are introduced into a second reactor to react nitrogen monoxide, molecular oxygen and alcohol to produce alkyl nitrite as the main product. and water, and nitric acid as a by-product to obtain a third gas containing alkyl nitrite together with unreacted nitric oxide, and a bottom liquid containing unreacted alcohol, nitric acid and water. process and
Carbon monoxide and/or nitrogen monoxide and the column bottom liquid are introduced into a third reactor and mixed to obtain a mixed liquid, and carbon monoxide and/or nitrogen monoxide in the mixed liquid are reacted with alcohol and nitric acid. , a fourth step to produce an alkyl nitrite, wherein the alkyl nitrite is recycled to the second reactor of the third step along with unreacted carbon monoxide and/or nitrogen monoxide, and unreacted alcohol and nitric acid and water are transferred to a liquid waste collection tank;
a fifth step of circulating the first gas obtained by mixing the third gas obtained in the third step and carbon monoxide to the first step;
A method for producing a dialkyl carbonate and/or a dialkyl oxalate having
The third and / or fourth step includes the bottom liquid in the second reactor and the piping between the second reactor and the third reactor, the mixed liquid in the third reactor, and the third reactor and waste liquid recovery The concentration of nitric acid in at least one selected from the group consisting of the pipes to the tank and the waste liquid in the waste liquid collection tank is measured from the UV absorbance, and the control unit determines whether the measured concentration of nitric acid is within the target range. In the sub-step of determining whether or not the concentration is outside the target range, adjusting the amount of nitric acid in the bottom liquid, the mixed liquid, or the waste liquid to bring the concentration within the target range 2. The method for producing dialkyl carbonate and/or dialkyl oxalate according to claim 1, comprising substeps. 3. The method for producing dialkyl carbonate and/or dialkyl oxalate according to claim 1, wherein the UV absorbance is measured at a wavelength of 280 nm to 330 nm. The method for producing dialkyl carbonate and/or dialkyl oxalate according to any one of claims 1 to 3, wherein the concentration of nitric acid after adjustment is 0.001% by mass to 10% by mass. Carbonic acid according to any one of claims 1 to 4, wherein the alcohol is methanol, the alkyl nitrite is methyl nitrite, and the dialkyl carbonate and/or dialkyl oxalate is dimethyl carbonate and/or dimethyl oxalate. A method for producing a dialkyl and/or a dialkyl oxalate. A first catalyst containing carbon monoxide, alkyl nitrite and nitrogen monoxide, which has a catalyst for reacting carbon monoxide and alkyl nitrite to produce dialkyl carbonate and/or dialkyl oxalate and nitrogen monoxide; a first reactor for producing a second gas containing dialkyl carbonate and/or dialkyl oxalate and nitric oxide from one gas;
The second gas is brought into contact with an absorption liquid that absorbs dialkyl carbonate and/or dialkyl oxalate, and the condensate containing dialkyl carbonate and/or dialkyl oxalate and the non-condensable gas containing nitrogen monoxide are mixed. a separating absorption tower;
a third gas containing an alkyl nitrite together with unreacted nitric oxide by introducing a mixed gas of said non-condensable gas and molecular oxygen and alcohol, and reacting said nitric oxide, molecular oxygen and alcohol; and a second reactor producing a bottom liquid containing unreacted alcohol, nitric acid and water;
Carbon monoxide and/or nitrogen monoxide and the bottom liquid are introduced and mixed to obtain a mixture, and the carbon monoxide and/or nitrogen monoxide, alcohol and nitric acid are reacted to produce alkyl nitrite. a third reactor;
a waste liquid recovery tank for recovering a waste liquid containing unreacted alcohol and nitric acid and water in the third reactor;
a pipe for transferring the second gas produced in the first reactor to the absorption tower;
a pipe for transferring the non-condensable gas separated in the absorption tower to the second reactor;
a pipe for transferring the third gas generated in the second reactor to the first reactor;
A pipe for transferring the bottom liquid produced in the second reactor to the third reactor;
piping for transferring the alkyl nitrite produced in the third reactor to the second reactor together with unreacted carbon monoxide and/or nitrogen monoxide;
A pipe for transferring the waste liquid generated in the third reactor to the waste liquid recovery tank;
a pipe installed at the outlet of the waste liquid recovery tank;
a UV detector for detecting the concentration of nitric acid in the bottom liquid, mixed liquid in the third reactor, or waste liquid;
Determine whether the concentration of nitric acid detected by the UV detector is within the target range, and when the concentration is outside the target range, the amount of nitric acid in the bottom liquid, mixed liquid, or waste liquid and a control unit that adjusts the concentration to be within a target range;
A device for producing dialkyl carbonate and/or dialkyl oxalate, comprising
The UV detector is installed in the pipe that transfers the bottom liquid generated in the second reactor to the third reactor, the pipe that transfers the waste liquid generated in the third reactor to the waste liquid collection tank, and the outlet of the waste liquid collection tank. A device for producing dialkyl carbonate and/or dialkyl oxalate, which is installed in at least one of the pipes. 7. The apparatus for producing dialkyl carbonate and/or dialkyl oxalate according to claim 6, wherein the bottom liquid, mixed liquid or waste liquid in the third reactor contains nitric acid, alcohol, nitrogen monoxide and alkyl nitrite. 8. The dialkyl carbonate and/or oxalate according to claim 6 or 7, wherein the alcohol is methanol, the alkyl nitrite is methyl nitrite, and the dialkyl carbonate and/or dialkyl oxalate is dimethyl carbonate and/or dimethyl oxalate. Equipment for producing dialkyl acid. Any one of claims 6 to 8, characterized in that the concentration of nitric acid in the column bottom liquid, the mixed liquid in the third reactor, or the waste liquid is measured in real time using the absorbance by a UV detector and a calibration curve. The apparatus for producing dialkyl carbonate and/or dialkyl oxalate according to item 1.

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