JP2008184409A - Distillation method of alkylamine-containing mixture and method for producing alkylamines - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a distillation method of an alkylamine-containing mixture by which the cooling cost of a refrigerant required for the top condensation in an alcohol-recovering step in an alkylamine production process is reduced. <P>SOLUTION: The condensation temperature at the second condenser is heightened by adding an aqueous solution of an alcohol to a gas inlet of the second condenser to reduce the cooling cost at the condensation in a step for condensing the top gas at the first condenser to afford a liquid rich in the alcohol, and condensing the noncondensed gas at the second condenser to afford a liquid rich in the alkylamine, in an alcohol-recovering distillation column for recovering the unreacted alcohol in an alkylamine reaction product. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for distillation of an alkylamine-containing mixture and a method for producing an alkylamine using the same. More particularly, the present invention relates to a method for distilling and separating an alkylamine from a mixture containing an alkylamine, an alcohol and water in an economically advantageous manner, and a method for producing an alkylamine from alcohol and ammonia using the same as a part of the purification process. Yes, the economic efficiency was improved by reducing the cooling energy cost of the distillation process. Alkylamine is an important chemical intermediate as a raw material for various solvents, pharmaceuticals, rubber chemicals, surfactants and the like.

  Alkylamines such as methylamine are generally reacted at high temperature (around 400 ° C.) in the gas phase with an alcohol such as methanol and ammonia in the presence of a solid acid catalyst having dehydration and amination effects such as alumina, silica alumina, and zeolite. Manufactured by. This reaction usually produces a mixture of dialkylamine, monoalkylamine, and trialkylamine. Among the alkylamines, methylamines, which are industrially important, are much less demanding than dimethylamine. Therefore, after separating dimethylamine from the reaction mixture, other methylamines are recycled to the reaction system and reused. ing.

  Distillation is commonly used to separate each alkylamine from the reaction mixture. Since the alkylamine synthesis reaction from alcohol and ammonia is an equilibrium reaction, the reaction mixture contains the starting alcohol and ammonia in addition to each alkylamine, and ammonia and methylamines form a complex azeotropic system. Therefore, separating this requires a very complicated distillation operation and a large apparatus, and the energy consumption cost of the production process becomes very large. This recovery process is disclosed in detail in Non-Patent Document 1, for example.

In particular, in the case of a process for producing methylamine using a zeolite catalyst, the methanol conversion is usually suppressed to 80 to 98% in order to improve the dimethylamine selectivity. For this reason, in many cases, unreacted methanol is separated and recovered and recycled to the reaction process or purification process for reuse.
With respect to this methanol recovery step, prior art relating to a method for removing aldehydes, which are trace by-products that become catalyst poisons, has been disclosed (Patent Document 1).
That is, it has been proposed that an aldehyde compound in methanol can be easily and easily removed by reacting with monomethylamine and / or ammonia to raise the boiling point and distilling and separating in a methanol recovery distillation column. However, since this method introduces monomethylamine or ammonia, which is a low-boiling component, into the distillation column, the condensation temperature at the top of the column is lowered, leading to an increase in the cooling cost of the condensing refrigerant.
"Revision manufacturing process complete works" (published on April 25, 1978 by Chemical Industry Co., Ltd.) JP 2003-146945 A

  The object of the present invention is to reduce the energy consumption cost and to construct an economically advantageous alkylamine production process in the step of separating and recovering unreacted alcohol in a recovery distillation column in the alkylamine production process. is there.

  As a result of intensive studies to achieve the above object, the present inventors condensate the top gas in two stages in the alcohol recovery distillation column, particularly for the second condenser introduced gas rich in low-boiling components, It has been found that the cooling temperature in the second condenser can be increased by adding an aqueous alcohol solution, that is, the cooling cost for condensing the top of the tower can be reduced, and the present invention has been achieved.

  That is, according to the first aspect of the present invention, in the operation of distilling a mixture containing alkylamine, alcohol and water, distilling alcohol and alkylamine from the top of the column, and drawing water from the bottom of the column, the top gas is removed from the first stage. It is condensed by a condenser and separated into an alcohol-rich condensate and an alkylamine-rich gas, a part of the alcohol-rich condensate is refluxed to the distillation column, and an alkylamine-rich gas is condensed in a second-stage condenser. And a method for distillation of an alkylamine-containing mixture. Furthermore, the alcohol concentration in the condensate in the first stage condenser is adjusted to 80% by mass or more and 99% by mass or less, the aqueous alcohol solution is introduced into the gas inlet of the second stage condenser, The effect can be improved by using a refrigerant having an operating pressure of 95 kPa abs or more and 202 kPa abs or less and a temperature of 20 ° C. or more and 35 ° C. or less in the second condenser.

  The second aspect of the present invention is a method for producing an alkylamine comprising a synthesis step of synthesizing an alkylamine by reacting alcohol and ammonia as raw materials in the presence of a catalyst, and a purification step of distilling and separating the resulting reaction mixture. It is related with the manufacturing method of the alkylamine which includes the distillation method of the alkylamine containing mixture as described in any one of Claims 1-4 as a part of purification process. Furthermore, a part of the alcohol-rich condensate condensed by the first stage condenser is recycled to the synthesis process as an alkylamine synthesis raw material, and part or all of the condensate condensed by the second stage condenser is synthesized. The effect can be improved by recycling to the process and / or the purification process.

  By carrying out the present invention, it is possible to increase the tower top condensation temperature in the alcohol recovery step in the alkylamine production process. As a result, it is possible to reduce the refrigerant cooling refrigerator and its associated equipment, and the cost required for its introduction and maintenance. Can be reduced.

The alkylamine-containing mixture distillation method according to the first aspect of the present invention relates to distillation of a mixture containing an alkylamine, an alcohol, and water (hereinafter also referred to as alcohol recovery distillation). The mixture containing the alkylamine, alcohol and water is advantageously applied to the mixture containing the alkylamine, alcohol and water obtained from the alkylamine production process from alcohol and ammonia.
Examples of the alkylamine include methylamine, ethylamine, propylamine, butylamine and the like, but application to methylamine is most preferable. Each alkylamine may be a mixture of monoalkylamine, dialkylamine and / or trialkylamine.
Examples of the alcohol include methanol, ethanol, propanol, butanol, etc. In the case of a mixture containing an alkylamine, alcohol and water obtained from the alkylamine production process as described above, the alkyl group of the alkylamine and the alkyl of the alcohol The groups are the same. The most preferred alcohol is methanol.

  As the alcohol recovery distillation column used in the present invention, a packed column or a plate column having a theoretical plate number of about 20 to 40 is usually used, a reflux ratio of 0.5 to 10, and a column top pressure of 0.1 to 2.0 MPa. Distill under moderate conditions. A mixture containing alkylamine, alcohol and water is fed to the middle stage of the alcohol recovery distillation column. In the operation of performing two-stage condensation at the top of the column and extracting alcohol and alkylamine (preferably methanol and methylamine) from the top of the column, the column operating pressure is 95 kPa to 202 kPa, preferably 95 kPa to 150 kPa, more preferably 95 kPa. The refrigerant flow rate is adjusted so that the condensation temperature of the first condenser is 35 ° C. or higher and 85 ° C. or lower, preferably 35 ° C. or higher and 75 ° C. or lower, more preferably 35 ° C. or higher and 70 ° C. or lower. In the first condenser, it is preferable to obtain a condensate having an alcohol concentration (preferably methanol concentration) of 80% by mass to 99% by mass in the condensate. Uncondensed gas from the first condenser is sent to the second condenser to be condensed. The refrigerant temperature of the second condenser is preferably 20 ° C. or higher and 35 ° C. or lower. Since the condensation temperature of the uncondensed gas is usually lower than the condensation temperature of the first condenser, the second condenser does not condense completely, so the pressure increases, so an alcohol aqueous solution is added to the second condenser gas inlet and the pressure is increased. It is preferable to prevent the rise. When the alcohol aqueous solution is a 99 mass% methanol aqueous solution, the methanol concentration in the composition after the addition is 55 mass% or more and 99 mass% or less if the distillation column operating pressure is 202 kPa or more, and if the methanol concentration is 150 kPa or more. Add from 67 to 99% by mass, 75 to 99% by mass if distillation tower operating pressure is 120 kPa or more, and 81 to 99% by mass if distillation tower operating pressure is 100 kPa or more It is preferable to do this.

The second aspect of the present invention is a method for producing an alkylamine comprising a synthesis step of synthesizing an alkylamine by reacting alcohol and ammonia as raw materials in the presence of a catalyst, and a purification step of distilling and separating the resulting reaction mixture. The present invention relates to a method for producing an alkylamine comprising a distillation method of an alkylamine-containing mixture of
In addition to alcohol ammonia, an alkylamine mixture recycled from the purification process (a mixture of mono-, di- and / or tri-forms) may be used as a raw material used in the synthesis process. As the catalyst used in the synthesis step, silica, silica alumina, alumina, zeolite, and the like are used, and zeolite with high selectivity of dialkylamine such as dimethylamine, which is highly demanded, is preferably used. As the zeolite, mordenite, chabazite, erionite, zeolite rho and the like and modified products thereof are used.
The reaction temperature for producing the alkylamine according to the present invention is preferably 200 to 350 ° C, particularly preferably 250 to 330 ° C. The reaction pressure is preferably in the range of 0.1 to 5 MPaG, particularly preferably in the range of 0.5 to 3 MPaG, and the N / C ratio (molar ratio of the number of nitrogen atoms to carbon atoms in the reaction system) is 1 to 2.5. It is good to implement in the range.

The present invention is applied to a process for separating and purifying alkylamines from a reaction mixture obtained by subjecting alcohol and ammonia to a gas phase catalytic reaction in the presence of a catalyst. As an example of a preferred purification step, unreacted ammonia is separated from the reaction mixture in an ammonia separation tower, trialkylamine is separated in a trialkylamine separation tower, and water is separated in a dehydration tower, and then monoalkylamine and dialkyl containing ammonia are separated. The amine mixture is supplied to the monoalkylamine separation tower, the monoalkylamine and dialkylamine are recovered, the distillate obtained from the bottom of the dehydration tower is supplied to the alcohol recovery distillation tower, and the waste water is supplied from the bottom to the top of the tower. Examples of the purification process for alkylamines include a process of extracting alcohol and alkylamine and recycling the overhead product to the reaction step or the purification step.
The present invention is intended to reduce the energy cost and the equipment cost by improving the condensation method at the top of the alcohol recovery distillation column.

  The ammonia separation column used in the present invention is usually a packed column or a plate column having a theoretical plate number of about 20 to 40, a reflux ratio of 1 to 10, and a column top pressure of about 1.2 to 3.0 MPa. Distill under conditions. The reaction mixture is supplied to the middle stage of the distillation column. Here, almost all of the unreacted ammonia and a part of the monoalkylamine, dialkylamine and trialkylamine are withdrawn from the top of the column and recycled to the reaction system. Monoalkylamine, dialkylamine, trialkylamine, unreacted alcohol, reaction by-product water and a small amount of ammonia are extracted from the bottom of the column. The ammonia concentration at the bottom of the column varies depending on the amount of steam heated in the ammonia separation column. At this time, the heating amount is adjusted so that the tower bottom ammonia concentration is preferably 200 ppm or less, more preferably 150 ppm or less.

  As the trialkylamine separation column used in the present invention, a packed column or a plate column having a theoretical plate number of about 20 to 40 is usually used, a reflux ratio of 5 to 10, and a column top pressure of 0.5 to 2.0 MPa. Distill under moderate conditions. The bottom liquid of the ammonia separation tower is supplied to the middle stage of the distillation tower, and water is supplied to the vicinity of the top of the tower to perform extractive distillation. Trialkylamine is distilled from the top of the column, and monoalkylamine, dialkylamine, unreacted alcohol, water and a small amount of ammonia are extracted from the bottom of the column.

  The dehydration tower used in the present invention is usually a packed tower or a plate tower having a theoretical plate number of about 25 to 45, a reflux ratio of 0.5 to 5, and a top pressure of about 0.2 to 2.0 MPa. Distill under conditions. Further, the bottom liquid of the trialkylamine separation tower is supplied to the middle stage of the distillation tower. Monoalkylamine, dialkylamine and a small amount of ammonia are distilled from the top of the column, and unreacted alcohol, water and alkylamine are extracted from the bottom of the column. Alkylamine is mixed in the tower bottom liquid, but its concentration is lower than that of alcohol and water, which are the main components.

  As the monoalkylamine separation column used in the present invention, a packed column or a plate column having a theoretical plate number of about 30 to 50 is used, and distillation is performed at a reflux ratio of 3 to 20 and a column top pressure of 0.2 to 0.7 MPa. . In addition, monoalkylamine, dialkylamine and a small amount of ammonia are fed to the middle stage of the monoalkylamine separation column. A monoalkylamine containing ammonia is distilled from the top of the monoalkylamine separation tower, and the product monoalkylamine is obtained as a side-cut fraction from 2 to 10 stages, more preferably from 3 to 8 stages in theoretical stages. The product dialkylamine is extracted from the bottom. If the side cut stage is higher than the second stage, the impurity ammonia cannot be sufficiently removed, and the steam reduction effect in the ammonia tower is reduced. If the side cut stage is lower than the tenth stage, the dialkylamine concentration in the product monoalkylamine is increased. . Further, the amount of distillation for removing low boiling impurities from the top of the column is preferably 0.01 to 0.9 as a molar ratio with respect to the side cut fraction, more preferably 0.05 to 0.00. 7 or less. If it is less than 0.01, removal of low boiling impurities is not sufficient, and if it is 0.9 or more, the amount of low boiling impurities decreases, but the amount of steam used in the dehydration tower and monoalkylamine separation tower increases due to an increase in the amount of recycling. Therefore, the steam reduction effect in the ammonia removal tower is reduced. By distilling under such conditions, a high-quality product monoalkylamine having a purity of 99.9% by mass or more and impurity ammonia of 300 ppm or less can be obtained as a side cut fraction.

  As the alcohol recovery distillation column used in the present invention, a packed column or a plate column having a theoretical plate number of about 20 to 40 is usually used, a reflux ratio of 0.5 to 10, and a column top pressure of 0.1 to 2.0 MPa. Distill under moderate conditions. A dehydration tower bottom liquid containing alkylamine, alcohol and water is fed to the middle stage of the alcohol recovery distillation tower. The bottom distillate is mainly composed of reaction by-product water and water injected in the trialkylamine separation tower, and is discharged out of the system as waste water. However, the waste water contains alcohol and alkylamine, which is a wastewater treatment cost. The amount of heating is not preferable because it causes an increase or a deterioration in product yield, so the impurity concentration in the bottom wastewater is 1% by mass or less, preferably 0.5% by mass or less, more preferably 0.1% by mass or less Adjust. In the operation of carrying out two-stage condensation at the top of the tower and extracting water from the bottom of the tower and extracting alcohol and alkylamine (preferably methanol and methylamine) from the top of the tower, the operation pressure at the top of the tower is 95 kPa to 202 kPa, preferably 95 kPa to 150 kPa. Hereinafter, the refrigerant flow rate is set so that the condensation temperature of the first condenser is 35 ° C to 85 ° C, preferably 35 ° C to 75 ° C, more preferably 35 ° C to 70 ° C, more preferably 95 kPa to 120 kPa. adjust. In the first condenser, it is preferable to obtain a condensate having an alcohol concentration (preferably methanol concentration) of 80% by mass to 99% by mass in the condensate. Uncondensed gas from the first condenser is sent to the second condenser to be condensed. The refrigerant temperature of the second condenser is preferably 20 ° C. or higher and 35 ° C. or lower. Since the condensation temperature of the uncondensed gas is usually lower than the condensation temperature of the first condenser, the second condenser does not condense completely, so the pressure increases, so an alcohol aqueous solution is added to the second condenser gas inlet and the pressure is increased. It is preferable to prevent the rise. When the alcohol aqueous solution is a 99 mass% methanol aqueous solution, the methanol concentration in the composition after the addition is 55 mass% or more and 99 mass% or less if the distillation column operating pressure is 202 kPa or more, and if the methanol concentration is 150 kPa or more. Add from 67 to 99% by mass, 75 to 99% by mass if distillation tower operating pressure is 120 kPa or more, and 81 to 99% by mass if distillation tower operating pressure is 100 kPa or more It is preferable to do this. Part of the condensate in the first condenser is refluxed to the alcohol recovery distillation column, part of it is recycled to the synthesis process as an alkylamine raw material, and the condensate in the second condenser is transferred to the synthesis process as an alkylamine raw material Alternatively, the active ingredients can be recovered and recycled to the purification process to increase product yield.

  The present invention will be described more specifically with reference to the following examples. However, the present invention is not limited to the following examples.

Example 1
A raw material liquid consisting of 11.7% by mass of monomethylamine, 6.4% by mass of dimethylamine, 3.1% by mass of trimethylamine, 31.3% by mass of methanol, and 47.5% by mass of water is supplied to the distillation experiment apparatus at 10 kg / h. The distillation operation was performed at a pressure of 101 kPa. Two stages of condensers are installed at the top of the column, the amount of water flow is adjusted so that the condensation temperature of the first condenser is 38 ° C., uncondensed gas is introduced into the second condenser, and the second condenser gas inlet The methanol aqueous solution which consists of 99 mass% was supplied to the part at 6 kg / h. The distillation operation was continued, the liquid distillation amount from the first condenser was 3 kg / h, the column reflux amount from the first condenser was 7.5 kg / h, and the liquid distillation amount from the second condenser was 2 kg / h. h, The amount of heating at the bottom of the tower was adjusted so that the amount extracted from the bottom of the tower was 5 kg / h. In the first condenser and the second condenser, water having a temperature of 25 ° C. was used as a refrigerant.
As a result of distillation, the mixture of the uncondensed gas of the first condenser and the aqueous methanol solution introduced into the second condenser was completely condensed at a temperature of 36 ° C. The composition of the first condenser condensate was 80.9 mass% methanol, and the composition of the second condenser condensate was 79.6 mass% methanol. The material balance in this operation is shown in Table 1.

Example 2
As a result of distillation under the same conditions as in Example 1 except that the aqueous methanol solution was not supplied to the second condenser gas inlet, a condensate having a composition methanol of 80.9% by mass was obtained in the first condenser. Since the gas introduced into the two condensers was not condensed and distilled out as a whole gas, no condensate was obtained. Therefore, when the refrigerant of the second condenser was changed to an ethylene glycol aqueous solution having a temperature of −10 ° C. and the same distillation operation was performed again, the first condenser uncondensed gas introduced into the second condenser had a temperature of 3.5. The whole amount was condensed at ° C. Table 2 shows the material balance in this operation.

Comparative Example 1
Distillation was carried out under the same conditions as in Example 1 except that the second stage condensation was not performed at the top of the tower but was distilled at 5 kg / h from the top of the tower. The amount could not be obtained. Then, the refrigerant of the condenser was changed to an ethylene glycol aqueous solution having a temperature of −10 ° C., and a similar distillation operation was performed again. As a result, the target flow rate was reached at a tower top temperature of 19 ° C. Table 3 shows the material balance in this operation.

Example 3
Unreacted ammonia was separated from the reaction mixture obtained by subjecting methanol and ammonia to a gas phase contact reaction in the presence of a zeolite catalyst in an ammonia separation tower (column diameter 0.5 m, theoretical plate 30 plates, plate column). However, a distillate was obtained at 1023 kg / h from the bottom of the column. Ammonia separation tower bottom distillate is fed to a trimethylamine separation tower (column diameter 0.3 m, theoretical plate 30 stages, packed tower), and separation operation is performed at a reflux ratio of 15 with water injection of 285 kg / h. After separation and removal, 1188 kg / h of distillate was obtained from the bottom of the column. This was supplied to a dehydration tower (column diameter 0.3 m, theoretical plate 35, packed tower) and subjected to a separation operation at a reflux ratio of 1.3. Water was separated from the top of the tower, and monomethylamine and dimethyl containing a small amount of ammonia. An amine mixture was obtained at 462 kg / h, and this was supplied to a monomethylamine separation column (column diameter 0.45 m, theoretical plate 40, plate column), and separated at a reflux ratio of 5. Monomethylamine 22 kg from the top of the column. Dimethylamine 440 kg / h was obtained from the bottom of the column. Distillate is obtained from the bottom of the dehydration tower at 804 kg / h, and this is fed to a methanol recovery tower (column diameter 0.3 m, theoretical plate 35, plate column) and separated at a reflux ratio of 2. It was. The methanol recovery tower was operated at an operating pressure of 101 kPa, the tower top gas was condensed in two stages, and a 99% aqueous methanol solution was added at 60 kg / h to the gas inlet of the second condenser. At this time, the condensation temperature of the first condenser was 43 ° C., the condensation temperature of the second condenser was 35.6 ° C., and each condenser used 28 ° C. industrial water as a refrigerant. By this operation, a distillate is obtained from the first condenser at 90 kg / h, and a distillate is obtained from the second condenser at 89 kg / h, and these are mixed with the raw material before the zeolite catalyst reaction step and recycled as a reaction raw material. .

Comparative Example 2
Except for not adding methanol at the methanol recovery tower and the second condenser gas inlet, operation was carried out under the same conditions as in Example 3. As a result, 28 ° C. industrial water was sufficient for the second methanol recovery tower condenser. As the pressure in the methanol recovery tower increased without being condensed, the second condenser supply gas was sent to the abatement equipment. By this operation, a distillate was obtained from the first condenser at 90 kg / h, mixed with the raw material before the zeolite catalyst reaction step, and recycled as a reaction raw material. Recycling from the second condenser was not possible, resulting in a product loss of 29 kg / h.

Comparative Example 3
Except that the refrigerant was changed to ethylene glycol of −10 ° C. in the methanol recovery tower and the second condenser, the operation was performed under the same conditions as in Comparative Example 2, and the methanol recovery tower first condenser collected 90 kg / h. A effluent was obtained, a distillate was obtained from the second condenser at 29 kg / h, and these were mixed with the raw material in the previous stage of the zeolite catalyst reaction step and recycled as a reaction raw material. Since the refrigerator was operated to produce ethylene glycol at −10 ° C. and the amount of power used increased, the methylamine power consumption rate deteriorated by 5 kWh / T.

  The alkylamine produced or distilled in the present invention is an important chemical intermediate as a raw material for various solvents, pharmaceuticals, rubber chemicals, surfactants and the like.

Claims (6)

  In the operation of distilling a mixture containing alkylamine, alcohol and water to distill off alcohol and alkylamine from the top of the column and drawing water from the bottom of the column, the top gas is fractionated by the first-stage condenser into alcohol. The alkylamine is characterized in that it is separated into a rich condensate and an alkylamine-rich gas, a part of the alcohol-rich condensate is refluxed to the distillation column, and the alkylamine-rich gas is condensed in a second-stage condenser. Distillation method of containing mixture.   The method for distillation of an alkylamine-containing mixture according to claim 1, wherein the alcohol concentration in the condensate is adjusted to 80% by mass or more and 99% by mass or less in the first stage condenser.   The method for distillation of an alkylamine-containing mixture according to claim 1 or 2, wherein an alcohol aqueous solution is introduced into the gas inlet of the second stage condenser.   The operating pressure of the distillation column is 95 kPa abs or more and 202 kPa abs or less, and a refrigerant of 20 ° C or more and 35 ° C or less is used for the second condenser. Distillation of alcohol and alkylamine containing mixtures.   A method for producing an alkylamine comprising: a synthesis step of synthesizing an alkylamine by reacting alcohol and ammonia in the presence of a catalyst in the presence of a catalyst; and a purification step of distilling and separating the resulting reaction mixture. The manufacturing method of the alkylamine which includes the distillation method of the alkylamine containing mixture as described in any one as a part of a refinement | purification process.   6. The production method according to claim 5, wherein a part of the alcohol-rich condensate condensed by the first stage condenser is recycled to the synthesis process as an alkylamine synthesis raw material and condensed by the second stage condenser. A method for producing an alkylamine, wherein a part or all of the liquid is recycled to a synthesis step and / or a purification step.