JPH08311000A - Production of methylamine - Google Patents

Abstract

PURPOSE: To provide a production method for methylamine simplified in production process with no need of the operation for separating trimethylamine. CONSTITUTION: In this method for producing methylamine by vapor phase catalytic reaction among methanol, ammonia and a methylamine mixture, the following processes or operations are interrelatively linked: disproportionation process designed to subject both the ammonia and methylamine mixture to catalytic reaction in the presence of a solid acid catalyst <=15Å in average pore diameter to reduce trimethylamine quantity; main reaction process designed to subject the methanol, ammonia and part or the whole of a methylamine-contg. mixture from the disproportionation process in the presence of a silylated solid acid catalyst while suppressing the maximum temperature in the catalyst bed to <=350 deg.C; and the operation of a 1st distillation column designed to distillate a methylamine mixture from the main reaction process (and part of the methylamine mixture from the disproportionation process) under a pressure of 10-25kg/cm<2> G, distill off virtually the whole trimethylamine in the above mixture in the form of an azeotropic mixture with the ammonia from the column head, and feed this whole trimethylamine to the disproportionation process.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing methylamine by reacting methanol with ammonia.
More specifically, it relates to a method for producing methylamine that does not produce trimethylamine, which is in low demand.

[0002]

Methylamine is generally used in the presence of a solid acid catalyst in the gas phase of methanol and ammonia at 300 ° C to 300 ° C.
By reacting at 400 ° C, the following (1) to (3)
It is produced according to the reaction formula (1), and three kinds of mono, di, and tri are mixed and produced due to the difference in the number of substitution of methyl groups.

NH ₃ + CH ₃ OH → CH ₃ NH ₂ + H ₂ O (1) CH ₃ NH ₂ + CH ₃ OH → (CH ₃ ) ₂ NH + H ₂ O (2) (CH ₃ ) ₂ NH + CH ₃ OH → (CH ₃ ) ₃ N + H ₂ O (3) CH ₃ NH ₂ : monomethylamine (hereinafter abbreviated as MMA) (CH ₃ ) ₂ NH: dimethylamine (hereinafter abbreviated as DMA) (CH ₃ ) ₃ N: trimethylamine (hereinafter TMA) Abbreviated)

The methylamine-containing mixture obtained by the reaction is
It is separated and refined in the subsequent refining process, and is widely used as a raw material for chemicals, agricultural chemicals, medicines, feeds, and the like. However, the demand for these methylamines is not uniform, and MMA and DMA occupy 95% or more of the market, and TMA accounts for only about 5%. The separation and purification of the methylamine mixture is generally carried out by distillation.
Small difference in boiling point between A and DMA and TMA, and TMA
It is not easy to efficiently separate three kinds of methylamines because they azeotrope with MMA and DMA, so it is necessary to consider these points in order to establish a rational methylamine production process. There is.

According to the conventional general method for producing methylamine, methylamine produced in the presence of a solid acid catalyst in the main reaction step, ammonia supplied in excess, unreacted methanol, and by-products. In the first distillation operation of the water-containing mixture, ammonia or a part of ammonia and methylamine is distilled, and the distillate is recycled to the main reaction step or the disproportionation step. In the second distillation column, the boiling point difference between MMA, DMA and TMA is small as described above.
Since TMA is azeotropically distilled with MMA and DMA, TMA is distilled by extractive distillation with water, the bottom liquid is supplied to a third distillation column to distill a mixture of MMA and DMA, and this distillate is removed. (4) Supply to the distillation column, and from the top of the tower, add MMA to the bottom of the tower.
Follow the process of separating the MA.

[0006]

The problem with the conventional production method is that the production ratio of each methylamine produced in the main reaction step is close to that determined thermodynamically,
It is not possible to control it freely depending on the reaction conditions, more specifically, TMA rather than market demand.
The TMA produced in excess is required to be circulated again in the reaction step because the production ratio of MMA and DMA is high, and the extractive distillation performed in the second distillation column (not shown in the drawings after the second distillation column) is performed by MMA and DMA. Since it requires several times the amount of extracted water, it causes an increase in the amount of drainage, and since the liquid containing the large amount of extracted water is distilled in the third distillation column, enormous recovery energy is required. The point is to do.

As mentioned above, the demand for TMA is low,
It is not a rational method to carry out a bad operation of energy intensity such as extractive distillation to separate this. Considering these, the rational methylamine production process is to suppress the production amount of TMA,
It can be said that it is a process of increasing the production ratio of and DMA, and a process of efficiently purifying and separating the reaction product. Here, the efficient purification separation means that the process is simplified, the energy consumption rate is improved, and the purification is performed at low cost. Specifically, it is a method aimed at improving the energy intensity and reducing the amount of wastewater by eliminating the TMA separation operation.

However, regarding the suppression of the amount of TMA produced, as described above, the production ratio of each methylamine is close to that which is determined thermodynamically, and for example, from ammonia and methanol to methylamine. When the production reaction is carried out, the production ratio of TMA depends on the reaction temperature and the nitrogen / carbon molar ratio of the raw material at the reactor inlet (hereinafter simply referred to as N /
It is approximately 40-
It is in the range of 60% by weight. That is, it cannot be freely controlled depending on the conditions.

On the other hand, in Japanese Patent Publication No. 62-47172, the first step of reducing the amount of TMA in the presence of a porous solid acid catalyst having an average pore diameter of 20 Å or more, and a pore having an effective pore diameter of 10 Å or less. Disclosed is a method for producing methylamine by combining with a second step of carrying out a reaction for producing methylamine in the presence of a solid acid catalyst.

According to this method, steric hindrance of the catalyst used in the second step prevents the TMA having the largest molecular diameter in the product from leaving the pores, and as a result, suppresses the TMA forming reaction. , MMA and DMA can be obtained in high yield. Therefore, it is possible to improve the energy consumption rate in the DMA refining process and downsize the device. In addition, TMA, which is in low demand, is recycled to the first step, where it reacts with the methylamine mixture and ammonia to reduce the amount and re-apply it as a raw material to the second step. Is a method for producing each methylamine.

However, even in this method, the production ratio of TMA in the main reaction step can only be reduced to about 20 to 30% by weight, and the details of the reason will be described later, but as described in the publication. , TMA requires extractive distillation with water to separate it, and therefore problems such as deterioration of energy intensity and increase of wastewater cannot be solved. Here, the production ratio of TMA in the main reaction step means T in total methylamine increased by the reaction in the main reaction step.
It is defined as the weight ratio of MA.

After that, the catalyst for forming methylamine was further limited, and the TMA was more than the equilibrium value calculated thermodynamically.
Various methods have been disclosed in which MMA and DMA are obtained in a high yield by significantly reducing the production amount of. For example, a method using natural mordenite as a catalyst (Japanese Patent Publication No. 2-273).
No. 35), a method of using mordenite ion-exchanged with lanthanum ions as a catalyst (Japanese Patent Publication No. 3237/1990).
No. 8), a method of using mordenite with the content of alkali metal limited to a specific range as a catalyst (Japanese Patent Publication No. 2).
No. 16743), a method of steam-treating a zeolite catalyst (JP-B-2-2876), and a method of using an A-type zeolite substantially containing no binder as a catalyst (JP-B-3-8331). ) And the like.

By using these catalysts, the amount of TMA produced can be reduced. However, even in these methods, the production ratio of TMA in the main reaction step can only be reduced to about 10% by weight. Further, JP-A-3-262540 discloses a method of modifying mordenite by a gas phase chemical reaction of carbon tetrachloride. According to this method, the amount of TMA produced can be further reduced, but it is difficult to industrially prepare a catalyst at low cost, and in any of these methods, the reaction product can be efficiently produced from the reaction product. It did not mention the method for purifying methylamine.

An object of the present invention is not only to obtain MMA and DMA, which are in high demand, in high yield, but also to provide a method for efficiently and inexpensively producing methylamine. More specifically, it is an object of the present invention to provide a method for producing methylamine that simplifies the steps by omitting the TMA separation operation that causes problems such as deterioration in energy consumption rate and increase in wastewater amount.

[0015]

[Means for Solving the Problems] The inventors of the present invention reasonably reduce the amount of TMA produced in the main reaction step, omit the TMA separation operation, and improve the energy consumption rate. We have been earnestly studying to establish the amine production process. As a result, the solid acid catalyst having a specific pore size is used in the disproportionation step, the solid acid catalyst subjected to the silylation treatment is used in the main reaction step, and the reaction is performed while suppressing the maximum temperature in the catalyst layer to 350 ° C or less. It has been found that the above object can be achieved by further performing a distillation operation at a specific pressure.

That is, the present invention provides a method for producing methylamine by subjecting a mixture of methanol, ammonia and methylamine to a gas phase catalytic reaction, wherein the mixture of ammonia and methylamine is a solid acid catalyst having an average pore diameter of 15 Å or less. In the presence of methane, a disproportionation step for reducing the amount of trimethylamine, and a solid obtained by silylating methanol or ammonia with all or part of the methylamine-containing mixture obtained from the disproportionation step. Subjected to catalytic reaction in the presence of an acid catalyst, and the maximum temperature in the catalyst layer is 350 ° C.
One of the main reaction step in which the reaction is carried out while suppressing the following, and the methylamine-containing mixture obtained from the main reaction step, or the methylamine-containing mixture obtained from the main reaction step and the methylamine-containing mixture obtained from the disproportionation step 10 to 25 parts
Distillation at Kg / cm ² G to distill substantially all of the trimethylamine in the mixture as an azeotrope with ammonia from the top of the column, and feed it to the disproportionation step. And a method for producing methylamine.

The present invention will be described in detail. The skeleton of the method for producing methylamine according to the present invention comprises a main reaction step for carrying out a synthetic reaction of methylamine, and ammonia and TMA in a methylamine-containing mixture obtained from the main reaction step, which are recovered from the top of a distillation operation. The bottom is composed of a first distillation column for obtaining a liquid containing substantially no TMA, and a disproportionation step of consuming the recovered TMA by a disproportionation reaction.

The term "methylamine mixture" as used herein means a mixture of MMA, DMA and TMA, and the term "methylamine-containing mixture" means a methylamine mixture containing components other than methylamine such as ammonia and methanol. It is defined as The raw material methanol is supplied to the inlet of the main reaction step, and the ammonia is supplied to the inlet of the disproportionation step and / or the main reaction step. The synthesis reaction of methylamine is generally carried out in the presence of a solid acid catalyst, but in the present invention, the solid acid catalyst used in the main reaction step is limited to the silylated solid acid catalyst.

The silylation treatment referred to in the present invention is Japanese Patent Application No.
The method disclosed in Japanese Patent Laid-Open No. 185908 is used. That is, the solid acid catalyst treated with acid, washed and dried is once calcined at several hundreds of degrees Celsius and then conditioned to contain 3 to 40% by weight of water.
This is a method of treating this in a liquid phase in which alkoxide of silicon such as tetramethoxyorthosilicate or trimethylchlorosilane is dissolved in a solvent and modifying the surface with silicon oxide.

The prior art has shown that the steric hindrance added to the catalyst suppresses the TMA formation reaction, but the object of the present invention is to minimize the amount of TMA formation in the main reaction step. However, in the first distillation operation, the TM
By distilling the entire amount of A as an azeotrope with ammonia from the top of the column, a complicated TMA separation operation is omitted. This is because in the catalyst layer under the solid acid catalyst subjected to the silylation treatment. It is achieved by carrying out the reaction while suppressing the maximum temperature of 3 to 350 ° C. or lower and suppressing the amount of TMA generated to a predetermined amount or lower. The reason for this is that the silylation treatment controls the inlet diameter of the pores and the steric hindrance suppresses the TMA formation reaction, and the surface of the solid acid catalyst is poisoned by the silylation active sites. It is considered that this is because the TMA generation reaction on the catalyst surface is also suppressed, and these effects are sufficiently exhibited by suppressing the maximum temperature in the catalyst layer to 350 ° C. or lower. .

Further, the maximum temperature in the catalyst layer in the main reaction step is set to 3
The importance of carrying out the reaction while suppressing the temperature to 50 ° C or lower will be described in detail. The methylamine formation reaction is an exothermic reaction as shown in the following formulas (4) to (6), and the temperature in the reactor rises due to the heat of reaction. When the present inventors calculated the adiabatic temperature rise in the reactor from the reaction heat of the methylamine formation, it was about 8 depending on the reaction conditions.
The amount of heat is such that it reaches 0 to 120 ° C.

NH ₃ + CH ₃ OH → CH ₃ NH ₂ + H ₂ O + 4.0 kcal / mol (4) CH ₃ NH ₂ + CH ₃ OH → (CH ₃ ) ₂ NH + H ₂ O + 8.1 kcal / mol (5) (CH ₃ ) ₂ NH + CH ₃ OH → (CH ₃ ) ₃ N + H ₂ O + 10.3 kcal / mol (6)

From the equilibrium value calculated thermodynamically,
The rise in temperature tends to decrease the amount of TMA produced,
According to the experiments conducted by the present inventors, as described above, TM
When a catalyst in which the production ratio of A is limited to a ratio lower than the thermodynamic equilibrium value is used, the production amount of TMA tends to rapidly increase as the temperature rises. Further, it has been clarified that the maximum attainable temperature is more dominant than the inlet temperature and the outlet temperature of the catalyst layer in the main reaction step in the production ratio of methylamine and the amount of by-products.

In a laboratory-scale reactor, the amount of heat released is extremely large, so that the temperature rise due to the heat of reaction does not pose a particular problem, but in the case of industrial production, this temperature rise due to the heat of reaction is sufficient. If not taken into consideration, the production ratio of each methylamine will be significantly different from that expected from the inlet temperature of the catalyst layer in the main reaction step. Further, if the temperature becomes higher than necessary, by-products such as formaldehyde, ethylamine, and acetonitrile are generated, and these are mixed in the product, so that it is not possible to obtain highly pure methylamine. Therefore, TM in the main reaction process
In order to suppress the production ratio of A and obtain highly pure methylamine, it is necessary to actively remove the reaction heat of the methylamine production reaction. In order to achieve the present invention, the catalyst of the main reaction step is used. The reaction must be carried out while controlling the maximum temperature in the layer to 350 ° C or lower, preferably 330 ° C or lower.

The temperature referred to here is a macroscopic temperature that can be measured with a thermocouple thermometer, a resistance thermometer, or the like, and is distinguished from the so-called microscopic temperature found on the surface or pores of the catalyst. In fact, the inventors have not been able to clarify what temperature the surface of the catalyst and the inside of the pores have reached microscopically during the progress of the reaction. If the maximum temperature in the catalyst layer of the raw material is suppressed to 350 ° C or lower, TM
The amount of A produced can be suppressed to such an extent that the entire amount can be distilled as an azeotropic composition with ammonia in the first distillation operation, and the amount of by-products can be suppressed to 100 ppm or less in terms of methylamine.
It is confirmed that the present invention can be achieved. Examples of the type of the main reactor that satisfies such conditions include a fixed bed reactor having a jacket, a fluidized bed reactor having an intercooler, a multitubular reactor, and the like. It is necessary to design the reactor with due consideration of heat velocity, heat transfer area, etc.

The silylation-treated solid acid catalyst is charged into the main reactor, where the synthetic reaction of methylamine is carried out. At this time, the inlet temperature of the catalyst layer is preferably 250 ° C to 340 ° C, and the N / C ratio of the inlet raw material is preferably in the range of 1.5 to 5.0. If the inlet temperature is less than 250 ° C., the catalyst activity is low and the conversion of methanol is insufficient, resulting in poor efficiency, which is not preferable. Also, if the temperature exceeds 340 ° C, the temperature rises due to the heat of reaction,
It becomes difficult to suppress the maximum temperature in the catalyst layer to 350 ° C. or less, and the object of the present invention is not achieved.

The N / C ratio of the raw material at the main reactor inlet is 1.5
Below 1, TMA in the first distillation column due to lack of ammonia
Is not preferable because it becomes impossible to recover the entire amount of the above as an azeotropic mixture with ammonia. On the other hand, when it exceeds 5.0, the circulation amount of ammonia is unnecessarily high and the energy for recovering ammonia increases, which is not preferable because it is not efficient.

The methylamine-containing mixture obtained from the main reaction step is optionally mixed with a part of the methylamine-containing mixture obtained from the disproportionation step and supplied to the first distillation column for purification separation. The TMA is distilled off at the top as an azeotrope with substantially all of the ammonia.

One of the conditions required here is that in order not to produce TMA, which is in low demand, as a product, the weight ratio of TMA of the raw material supplied to the first distillation column to ammonia (here, the weight ratio of TMA to ammonia). Is defined as TMA weight / ammonia weight × 100 in the mixture, and hereinafter, abbreviated as TMA / NH ₃ ratio) is 13% by weight.
Hereafter, the amount is preferably suppressed to 10% by weight or less.

When the production ratio of TMA in the main reaction step is high, it is necessary to circulate an excessive amount of ammonia to meet this condition. However, circulating excess ammonia means that the first distillation column is upsized and the energy consumption is deteriorated due to ammonia recovery, and it is practically impossible to operate industrially.
Therefore, if a silylated solid acid catalyst is used as the catalyst in the main reaction step and the maximum temperature in the catalyst layer is controlled to 350 ° C. or lower, the TMA production ratio in the main reaction step will be 7%.
The amount can be suppressed to less than or equal to wt%, and substantially the entire amount of TMA can be distilled out as an azeotropic mixture with ammonia from the top of the first distillation column within a range where industrial operation is possible.

PEP Report 138 contains 210 psig of ammonia and TMA (about 15 Kg / cm ²
In G) it is shown that 82% by weight of ammonia (TMA / NH ₃ ratio = 22% by weight) forms an azeotropic composition. However, the distillation performed in the first distillation column is a multi-component system distillation of ammonia, MMA, DMA, TMA, methanol, water, etc. In this system, substantially all of TMA is converted into an azeotropic mixture with ammonia as a column. In order to distill from the top, the TMA / NH ₃ ratio in the raw material must be 13% by weight or less, preferably 10% by weight or less.
This is the point that the present inventors experimentally confirmed.

The second condition is to select the operating pressure of the first distillation column. Generally, when distilling a low boiling point component such as ammonia, the condition under high pressure is
Although it is advantageous in operation because it can be condensed at a high temperature, the present inventors have confirmed that TMA substantially does not form an azeotropic composition with ammonia in the range of 25 to 30 Kg / cm ² G. If the operating pressure exceeds 25 Kg / cm ² G, the total amount of TMA cannot be distilled off from the top of the first distillation column, and the present invention cannot be carried out.
If it is less than 10 kg / cm ² G, the boiling point at the top of the column will be 30 ° C. or less, which is not efficient. Therefore, it is necessary to select the condition in the range of 10 to 25 kg / cm ² G in consideration of the composition of the outlet of the main reactor and the operation efficiency. There is. Kg used here for pressure unit
/ Cm ² G indicates a gauge pressure.

When the first distillation operation is carried out after satisfying the above conditions, substantially the whole amount of TMA can be distilled off from the top of the column as an azeotropic mixture with ammonia, and the bottom liquid is substantially removed. It is possible to recover a TMA-free methylamine-containing mixture.

Therefore, in the conventional method for producing methylamine, the extractive distillation operation required for the separation and recovery of TMA is not necessary, and the extracted water is also unnecessary, so that the energy consumption rate is improved. It is possible to obtain various effects such as reduction of wastewater and drainage. The methylamine-containing mixture obtained from the top of the first distillation column is mixed with ammonia as necessary and supplied to a disproportionation reactor filled with a solid acid catalyst. Here, the disproportionation reaction proceeds according to the following equations (7) to (9), and the amount of TMA produced in the main reaction step is consumed in a proportionate amount.

[0035]

The solid acid catalyst used here has an average pore size of less than 15Å, and zeolite is particularly preferable. The reason for this is that when the average pore diameter exceeds 15 Å, by-products such as ethylamine and acetonitrile are likely to be generated, and the purity of methylamine is reduced. Also,
The role of the solid acid catalyst used in the disproportionation step is to consume TMA, unlike the role of the catalyst used in the main reaction step, so that the average pore size of the catalyst does not cause steric hindrance to TMA. , Preferably 5 Å or more.

Since the disproportionation reaction is a slight endothermic reaction as opposed to the main reaction step, there is no particular limitation on the type of reactor, and similarly, a fixed bed reactor or a fluidized bed reaction can be used. A container or the like can be suitably used.

In the disproportionation reaction of the present invention, the inlet temperature of the catalyst layer is preferably in the range of 280 to 450 ° C. Inlet temperature is 2
Below 80 ° C, the activity of the catalyst is insufficient, and
When the temperature exceeds 0 ° C, side reactions become significant and deterioration of the catalyst with time progresses rapidly, which is not preferable.

Generally, it is advantageous to operate at a temperature as low as possible in terms of by-products, catalyst deterioration and energy as described above, however, in the present invention, TM is used.
Since A is not manufactured as a product, it is necessary to consume the same amount of TMA newly generated in the main reaction step in the disproportionation step in terms of mass balance. That is, the reaction conditions cannot be freely selected within the above range, and a large amount of T
The formation of MA requires the consumption of that much TMA in the disproportionation process. This means that the disproportionation reaction must be carried out under higher temperature conditions. Therefore, minimizing the amount of TMA produced in the main reaction step also favors the disproportionation reaction. It will lead to advancement under certain conditions. All or part of the methylamine-containing mixture obtained from the disproportionation step is recycled to the main reaction step and used as a part of the raw material for the main reaction step.

By the series of operations as described above, a mixture of MMA not containing TMA, DMA, unreacted methanol, and water as a by-product can be recovered as a bottom product of the first distillation column. Purification and separation of these mixtures according to a known method, a mixture of MMA and DMA is distilled from the top of the second distillation column, and methanol and water are recovered from the bottom liquid,
MMA and DMA may be separated in the third distillation column and recovered as a product.

[0041]

The present invention will be described below in detail with reference to examples. Example 1 Both the main reactor (a) and the disproportionation reactor (c) are 1B reaction tubes having a 6B jacket, a reactor having a total length of 5 m is used, and a catalyst is provided inside the tubes and a jacket side is provided. A system was used in which an organic heating medium was filled and heating was performed from outside with an electric heater. The first distillation column (a) is a packed column having a length of 2 m, a total length of 5 m, and a filling height of 3 m. As shown in FIG. 1, a main reactor (a), a disproportionation reactor (c), and a first distillation column (a). Connected. All the reactors and piping used were made of stainless steel. Mordenite having an average pore diameter of 10 Å was washed with 2N hydrochloric acid by acid treatment and then conditioned to contain 10 wt% of water.
The silylation treatment was performed in a toluene solution of 1.5 mol% tetraethoxysilicate at an amount such that the ratio of tetraethoxysilicate and mordenite was 0.33 mol / kg-mordenite. This catalyst in the main reactor (a) 2.
The disproportionation reactor (c) was charged with 5 kg, and 1.5 kg of the catalyst obtained by only acid-washing the above natural mordenite with 2N hydrochloric acid was charged. Pressure in the system is 18 Kg / c
m ² G, internal heat medium internal temperature of main reactor (a) 300 to 3
05 ℃, the internal temperature of the organic heat medium of the disproportionation reactor 335-34
At 0 ° C., methanol 1 was supplied at a rate of 1000 g / h, the flow rate of ammonia 2 was adjusted so that the N / C ratio at the inlet of the main reactor was 2.5, and the reaction was continuously performed to achieve steady state. I waited for the condition. A steady state was reached about 35 hours after the reaction was started, and the temperature distribution of the catalyst layer at that time was measured. As a result, the inlet temperature was 282 ° C, and the highest temperature was at a position of about 1.2 m from the inlet. The temperature was 318 ° C.
When the fluid flow rate of each line was measured, the results shown in Table 1 were obtained. Even after 200 hours, the temperature distribution and the fluid flow rate did not change significantly, and the T
The methylamine mixture containing no MA could be recovered stably. When the composition of the bottom liquid was analyzed by gas chromatography, the content of TMA was 100 ppm.
It was below.

Example 2 A continuous reaction was carried out under the same conditions as in Example 1 except that the pressure in the system was changed to 13 Kg / cm ² G, and a steady state was awaited. A steady state was reached about 40 hours after the start of the reaction. At that time, the catalyst layer inlet temperature was 290 ° C, and the maximum temperature was 324 ° C, about 1.2 m from the inlet. When the fluid flow rate of each line was measured, the results shown in Table 2 were obtained. 15
The fluid flow rate did not change significantly even after 0 hour, and the methylamine mixture containing no TMA could be stably recovered from the bottom liquid 6 of the first distillation column. When the composition of the bottom liquid was analyzed by gas chromatography, the TMA content was 100 ppm or less.

Example 3 A continuous reaction was carried out under the same conditions as in Example 1 except that the pressure in the system was changed to 23 Kg / cm ² G, and a steady state was awaited. A steady state was reached about 40 hours after the start of the reaction. At that time, the catalyst layer inlet temperature was 296 ° C, and the maximum temperature was 329 ° C at about 1.2 m from the inlet. When the fluid flow rate of each line was measured, the results shown in Table 3 were obtained. 22
The fluid flow rate did not change significantly even after 0 hour, and the methylamine mixture containing no TMA could be stably recovered from the bottom liquid 6 of the first distillation column. When the composition of the bottom liquid was analyzed by gas chromatography, the TMA content was 100 ppm or less.

[0044]

[Table 1]
(Unit = g / h) Main reactor TMA production ratio = 5.3% First distillation column raw material TMA / NH ₃ × 100 = 8.3%

[0045]

[Table 2]
(Unit = g / h) Main reactor TMA production ratio = 4.9% First distillation column raw material TMA / NH ₃ × 100 = 7.9%

[0046]

[Table 3]
(Unit = g / h) Main reactor TMA production ratio = 6.2% First distillation column raw material TMA / NH ₃ × 100 = 9.5%

Comparative Example 1 Under the same conditions as in Example 1 except that the internal temperature of the organic heating medium in the main reactor (a) was changed to 340 to 345 ° C., the continuous reaction was carried out and the steady state was awaited. About 70 hours after the start of the reaction, the steady state was reached, and the catalyst layer inlet temperature at that time was 319 ° C.
The highest temperature was shown about 1.0 m from the inlet, and the temperature was 362 ° C. When the fluid flow rate of each line was measured, the results shown in Table 4 were obtained. After 180 hours, the fluid flow rate did not change significantly, and the first distilling column bottoms 6
It was not possible to eliminate the TMA in the methylamine recovered from.

Comparative Example 2 As a catalyst to be charged in the main reactor, mordenite having an average pore size of 10 Å was acid-washed with 2N hydrochloric acid, and a catalyst not subjected to silylation was charged, and the same conditions as in Example 1 were used. The continuous reaction was carried out at and the steady state was awaited. About 60 hours after the start of the reaction, a steady state was reached. At that time, the catalyst layer inlet temperature was 286 ° C, and the maximum temperature was about 1.2 from the inlet.
At m, the temperature was 328 ° C. When the fluid flow rate of each line was measured, the results shown in Table 5 were obtained. After 220 hours, there is no big change in the fluid flow rate,
T in methylamine recovered from the first distillation column bottoms liquid 6
I couldn't get rid of MA.

[0049]

[Table 4]
(Unit = g / h) Main reactor TMA production ratio = 20.5% First distillation column raw material TMA / NH ₃ × 100 = 19.1%

[0050]

[Table 5]
(Unit = g / h) Main reactor TMA production ratio = 21.9% First distillation column raw material TMA / NH ₃ × 100 = 18.0%

[0051]

As described in detail above, according to the present invention, by suppressing the maximum temperature in the catalyst layer to 350 ° C. or lower in the presence of the silylated solid acid catalyst,
TM in the methylamine-containing mixture that is the raw material for the first distillation column
Since a substantially total amount of A is distilled as an azeotropic mixture from the top of the first distillation column and a methylamine mixture containing substantially no TMA is recovered from the bottom liquid, a complicated operation such as the conventional method is performed. It is not necessary to perform TMA separation by performing Therefore, it is possible to simplify the process, reduce the equipment cost by omitting the TMA separation step and the TMA tank, and reducing the size of the second distillation column (dehydration column), omitting the extracted water and the accompanying second distillation column (dehydration column). There are many advantages such as reduction of variable costs by improvement of energy consumption per unit in (1) and reduction of wastewater amount in terms of environment. As a result, MMA and DMA, which are in high demand, can be efficiently recovered at a high recovery ratio at a low cost, which is a great effect.

[Brief description of drawings]

FIG. 1 is a process diagram of the production of methylamine according to the present invention.

[Explanation of symbols]

 A Main reactor a 1st distillation tower c Disproportionation reactor 1 Methanol 2 Ammonia 3 Main reaction raw material 4 Methylamine mixture 5 1st distillation tower distillate 6 1st distillation tower bottoms 7 Disproportionation reaction raw material

Claims (6)

[Claims] 1. A method for producing methylamine by subjecting a mixture of methanol, ammonia and methylamine to a gas phase catalytic reaction, wherein the mixture of ammonia and methylamine is present in the presence of a solid acid catalyst having an average pore size of 15Å or less. Of the solid acid catalyst obtained by subjecting the disproportionation step of reducing the amount of trimethylamine to a catalytic reaction in the above step, and all or a part of the methylamine-containing mixture obtained from the disproportionation step and methanol and ammonia to silylation treatment. A main reaction step in which the reaction is carried out in the presence of the catalyst while suppressing the maximum temperature in the catalyst layer to 350 ° C. or lower, and a methylamine-containing mixture obtained from the main reaction step, or a main reaction step 10 to 25 kg / cm of a portion of the methylamine-containing mixture obtained from the above and the methylamine-containing mixture obtained from the disproportionation step.
Characterized by the combined operation of the first distillation column, which is distilled at ² G to distill substantially all of the trimethylamine in the mixture as an azeotrope with ammonia from the top of the column and feed it to the disproportionation step. A method for producing methylamine. 2. The nitrogen / carbon molar ratio of the raw material at the inlet of the main reaction step is in the range of 1.5 to 5.0.
The method for producing methylamine according to 1. 3. The method for producing methylamine according to claim 1, wherein the inlet temperature of the catalyst layer in the main reaction step is in the range of 250 to 340 ° C. 4. The method for producing methylamine according to claim 1, wherein the inlet temperature of the catalyst layer in the disproportionation step is 280 to 450 ° C., and the nitrogen / carbon molar ratio of the inlet raw material is 5 or more. . 5. The method for producing methylamine according to claim 1, wherein the silylation-treated solid acid catalyst is a zeolite treated with a silylating agent in a liquid phase. 6. The silylation-treated solid acid catalyst is mordenite treated with a silylating agent in a liquid phase.
The method for producing methylamine according to 1.