JPH0227335B2 - - Google Patents

Description

[Detailed description of the invention]

[] BACKGROUND TECHNICAL FIELD OF THE INVENTION The present invention relates to a method for producing dimethylamine by gas phase catalytic reaction of methanol and ammonia. More specifically, the present invention relates to a method for vapor phase catalytic synthesis of dimethylamine, which is characterized by the catalyst used. Methylamine is usually produced by reacting methanol and ammonia in the gas phase at high temperature in the presence of a solid acid catalyst (hereinafter referred to as conventional catalyst) such as alumina or silica. In this reaction, some or all of the hydrogen atoms of ammonia are replaced, resulting in monomethylamine (hereinafter referred to as MMA) and dimethylamine (hereinafter referred to as DMA).
and trimethylamino (hereinafter referred to as TMA)
Three types of methylamines are produced simultaneously. Each amine is separated from the reaction product, and DMA, which has overwhelming commercial demand among the three, is used as a final product, while MMA and less demand are used as final products.
Most of the TMA is transferred to the reaction system and reused. Distillation is used to separate DMA from the methylamine reaction product, but distillation of DMA is not easy. This is because coexisting TMA forms azeotropes with water, other amines, and water-reacted methanol, respectively, so DMA or DMA-
Recovery of TMA azeotrope and recovery of DMA from DMA-TMA azeotrope and MMA and
Operations become more complicated due to the need to collect TMA, etc.
This is because an increase in the size of the device and an increase in energy consumption are unavoidable. Therefore, promoting the production of DMA and suppressing the production of TMA in the synthetic reaction system is
This directly leads to a reduction in the utility cost of the DMA purification process and a reduction in the size of the equipment. However, the final production ratio of the three types of methylamines is determined thermodynamically, and the higher the temperature, the more
In addition, the higher the ratio N/C of the number of nitrogen atoms to the number of carbon atoms in the reaction mixture, the higher the DMA production ratio and
TMA production ratio is low. For example, reaction temperature =
At 400°C and N/C = 2.0, the thermodynamically calculated equilibrium formation of each amine is MMA =
0.288, DMA=0.279 and TMA=0.433.
With conventional catalysts, the TMA production reaction is relatively fast, so
Throughout the reaction zone, the DMA production ratio or DMA production ratio/TMA production ratio never exceeds this equilibrium value, and therefore, as mentioned above, a large amount of TMA and MMA must always be recycled to the reaction system after separation. This is the translation. Although it is possible to shift the reaction equilibrium itself and improve DMA production by increasing the reaction temperature or N/C ratio,
As the reaction temperature increases, the amount of impurities produced increases,
Furthermore, this method is not necessarily economically advantageous because the increased amount of unreacted ammonia circulation increases the size of the apparatus. Another problem with conventional catalysts is that they contain a large amount of by-product impurities. Amine yield of conventional catalyst (reacted methanol is MMA, DMA and
The rate of conversion to TMA) was 96.5-97.5%,
The remaining 2.5-3.5% methanol is converted into _C2 - _C6 olefins, dimethylmonoethylamine, monomethylmonoethylamine, carbon dioxide, formaldehyde, dimethyl ether, etc., but the by-products of these impurities reduce the amine yield. Not only does it reduce the amount of methylamine, but it also has a large impact on the separation and production process of methylamine. For example, certain liquid impurities in the system can significantly impair the separation efficiency of the storage column. Gaseous impurities also accumulate in the condenser, reducing heat transfer efficiency. Prior Art A certain type of zeolite synthesized by a special manufacturing method has been proposed as a catalyst to be used in the gas phase catalytic reaction between methanol and ammonia (Japanese Patent Application Laid-open Nos. 54-148708 and 55-104234). ). [] Summary of the Invention The present invention aims to provide a solution to the above-mentioned problems, and attempts to achieve this object by using a specific zeolite as a dimethylamine synthesis catalyst. Therefore, the method for producing methylamine according to the present invention involves reacting methanol and ammonia in the presence of naturally produced mordenite to produce dimethylamine with a selectivity higher than the theoretical equilibrium value calculated thermodynamically. This is a characteristic feature. Effects Mordenite-based zeolite has the ability to significantly suppress TMA formation, and by using it as a catalyst, it is possible to increase the composition above the equilibrium composition under normal conditions.
DMA is obtained. That is, this catalyst exhibits specific DMA selectivity not seen in conventional solid acid catalysts during the methylamine synthesis reaction. Another major feature of the mordenite-based zeelite catalyst is that the amount of by-products of the above-mentioned impurities is extremely small. That is, when mordenite is used under the same reaction conditions as in the case of a conventional solid acid catalyst, the amine yield is improved by 2-3% compared to the case of the conventional catalyst, and the amount of impurities is about 1 /3 to 1/5. As a result, the methanol consumption rate is further improved, and the operability and efficiency of the separation and purification process are significantly improved. In particular, naturally produced mordenite has high DMA selectivity and produces a small amount of impurities. [] Detailed description of the invention 1 Catalytic ability of zeolite From experiments using various zeolites as catalysts (Comparative Examples 2 to 4), it was found that zeolite generally exhibits catalytic activity as a solid acid catalyst in the methylamine synthesis reaction, and is particularly effective. It has been found that zeolite with a molecular sieving effect and a pore diameter of around 5 Å has a certain degree of high DMA selectivity. This is because the steric hindrance at the entrance to the zeolite's pores prevents large-sized TMA molecules in the reactants and products from leaving the pores, and as a result, the TMA production reaction is suppressed. This is thought to be due to improved DMA selectivity. There are various types of zeolite with a molecular sieving action with a pore diameter of around 5 Å, such as zeolite A, gmelinite, siyabasai, and mordenite, but each zeolite has differences in external surface activity, effective pore size distribution, solid acid properties, etc. be. That is, in some cases, the effect of improving DMA selectivity is small, and in others, the dehydration reaction between methanol and ammonia or amine is the reaction between amine and ammonia (disproportionation reaction).
Therefore, even if the DMA selectivity is high in the region where the methanol conversion rate is low, the reaction between the amine and ammonia proceeds to equilibrium in the region where the methanol conversion rate is high, and the overall reaction rate is therefore slow. There are only a limited number of catalysts that are large and can ultimately significantly increase the DMA production ratio. Under these circumstances, mordenite-based zeolite with an effective fine diameter of about 1 to about 5 Å exhibits high catalytic activity in the synthesis of methylamine through a gas-phase catalytic reaction between methanol and ammonia.
In particular, it shows a specific effect of increasing the selectivity of DMA beyond the thermodynamic equilibrium. 2 Mordenite Zeolite Mordenite is an orthorhombic crystalline aluminosilicate represented by the following formula. Me _1/o (AiSi ₅ O ₁₂ )・3H ₂ O (Here, Me represents an n-valent alkali or alkaline earth metal atom or hydrogen) Me has ion exchange properties, and the effective pore diameter of mordenite is influenced by the size of the exchanged cation. Generally, those exchanged with larger cations give those with smaller effective pore sizes. The exchanged cations also affect the solid acid properties of the zeolite and may themselves promote or inhibit catalytic activity, thereby changing the reaction rate. Therefore, the activity and selectivity of the mordenite-based zeolite catalyst will vary depending on the type and amount of exchanged cations. Any mordenite, even one in which all metal cations are exchanged with hydrogen ions, exhibits high DMA selectivity compared to conventional catalysts, but the appropriate type must be used to obtain the highest degree of activity and selectivity. It is necessary to exchange an appropriate amount of cations. Experimental results show that the composition of naturally occurring mordenite gives particularly high DMA selectivity. Naturally produced mordenite is represented by the following formula and contains some quartz crystal or montmorillonite as impurities. (Ca _x/z , K _y , Na _z ) (AlSi ₅ O ₁₂ )・3H ₂ O (where x+y+z=1, x/z, y and z are each 0.1 to 0.6) Values of x to z and Although the type and amount of impurities differ somewhat depending on the production area, they all have an effective fine diameter of about 5 Å and have similar effects on DMA selectivity. Examples of X-ray patterns characterizing these mordenites are shown in the table below.

【table】

[Table] The mordenite used as a catalyst in the present invention is particularly preferably one having an effective pore diameter of about 5 Å, but in general, mordenite having an effective pore diameter of about 4 to 10 Å can be used in the present invention. In addition, in mordenite, which has an effective pore diameter of approximately 5 Å, each molecule of ammonia, methanol, MMA, DMA, and water can pass through the entrance of the pore, whereas TMA molecules with a large molecular diameter prevent them from passing through. As a result, TMA generation is suppressed and DMA
This is understood to improve selectivity. Mordenite zeolite as a catalyst is
It should be in any convenient form, eg tablets, granules, etc. 3. Reaction between methanol and ammonia The method for producing methylamine according to the present invention is based on a gas phase catalytic reaction between methanol and ammonia using a conventional catalyst, if it is noted that the catalyst used is mordenite zeolite. There is essentially no difference. The reaction temperature is about 300 to 500℃, preferably 350℃
-about 450℃, reaction pressure is normal pressure - about 30 atm (gauge), preferably about 15 - 25 atm (gauge), supply ammonia/methanol weight ratio 0.3 -
1.9 (or N/C=0.5~3.5) preferably
A condition of approximately 0.8 to 1.5 (or N/C = 1.5 to 2.8) is normal. Under these conditions, the rate of dehydration reaction between methanol and ammonia or amine is almost the same as when using conventional catalysts, and the methanol conversion rate is 97-99% and the amount of TMA produced is higher than when using conventional catalysts. decreased by about 30%,
DMA production increases by approximately 30%. Mordenite catalyst differs from conventional catalysts in that
The lower the reaction rate, the higher the DMA selectivity. Therefore, it is possible to further improve DMA selectivity by sacrificing methanol conversion. However, in that case, recovery or treatment of residual methanol becomes a problem, and therefore, industrially, it is preferable to operate at a methanol conversion rate of 95% or higher. 4 Experimental Example Comparison Example 1 15ml of silica alumina, a conventional catalyst, with an inner diameter of 16mm
Ammonia/
Methanol mixture (weight ratio 50/50 or 60/40)
was passed at a flow rate of 0.4 to 1.6 g/min, and the reaction products shown in Table 3 were obtained after 2 to 3 hours. Comparative Example 2 A reaction test was conducted under the same conditions as in Comparative Example 1 using chabasite as a catalyst, and the results shown in Table 3 were obtained. Comparative Example 3 A reaction test was conducted using zeolite 4a as a catalyst under the same conditions as in Comparative Example 1, and the results shown in Table 3 were obtained. Comparative Example 4 A reaction test was conducted under the same conditions as in Comparative Example 1 using Houjasite as a catalyst, and the results shown in Table 3 were obtained. Example 1 A reaction test was conducted under the same conditions as in Comparative Example 1 using naturally produced mordenite exhibiting the X-ray diffraction pattern shown in Table 1 as a catalyst, and the results shown in Table 3 were obtained. Example 2 A reaction test was conducted under the same conditions as in Comparative Example 1 using naturally produced mordenite exhibiting the X-ray diffraction pattern shown in Table 2 as a catalyst, and the results shown in Table 3 were obtained. Comparative Example 5 A reaction test was conducted under the same conditions as in Comparative Example 1 using Na-type synthetic mordenite (small port mordenite) in which some of the Na ions were replaced with Ca ions as a catalyst, and the results in Table 3 were obtained. Obtained. Comparative Example 6 A reaction test was conducted under the same conditions as in Comparative Example 1 using Na-type synthetic mordenite (small port mordenite) in which Na ions were exchanged with hydrogen ions as a catalyst, and the results shown in Table 3 were obtained.

【table】

[Table] Table 4 was created based on the results of Example 1, Example 2, Comparative Example 5, and Comparative Example 6 shown in Table 3.
DMA selectivity, TMA selectivity, amine yield, and impurity production rate are shown. From this Table 4, the natural mordenite catalysts (Example 1 and Example 2) have higher DMA selectivity and amine yield than the synthetic mordenite catalysts (Comparative Example 5 and Comparative Example 6), and TMA selectivity and It can be seen that the impurity production rate is low.

【table】

Claims (1)

[Claims] 1. A method for producing methylamine, which comprises reacting methanol and ammonia in the presence of naturally occurring mordenite to produce dimethylamine at a selectivity higher than the theoretical equilibrium value calculated thermodynamically.