JPH0859566A - Production of methylamines - Google Patents

Abstract

PURPOSE: To provide a method for efficiently producing a methylamine, capable of maintaining methanol conversion ratio high even after operation for a long period of time. CONSTITUTION: In a method for producing a methylamine by reacting methanol with ammonia in the presence of a zeolite catalyst, the amount of sodium chloride contained as an impurity in reaction raw materials to be supplied to the catalyst is limited to <=0.1 millimol per hour based on 1kg of the catalyst to provide the method for producing a methylamine.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing methylamines, and more particularly to a method for producing methylamines in which the formation of trimethylamine from methanol and ammonia is sufficiently suppressed. The present invention relates to a method for producing methylamines while maintaining high activity for a long period of time.

[0002]

BACKGROUND ART Methylamines, that is, monomethylamine, dimethylamine and trimethylamine are produced by a method of reacting methanol or a mixture of methanol and dimethyl ether with ammonia, a method of catalytic reduction of hydrocyanic acid and the like. Thus, these methylamines are produced as a mixture of mono-, di-, and trimethylamines and have corresponding uses. On the other hand, the demand for these methylamines is biased toward dimethylamine or monomethylamine, and the demand for trimethylamine is small at present. Methylamines obtained by the reaction of methanol and ammonia using ordinary amorphous silica-alumina as a catalyst have trimethylamine as a main product, and there is a problem that dimethylamine, which is in great demand, is small in amount to be obtained. In order to overcome these difficulties, when dehydrated crystalline aluminosilicate (zeolite) having a pore size of 5 to 10 angstrom is used as a catalyst for the reaction between alcohol having 1 to 18 carbon atoms and ammonia, mono and diamines are used. Is preferentially produced over triamine.
Further, natural zeolite and synthetic zeolite are shown as types of zeolite suitable for the above-mentioned reaction. As natural zeolites, faujasite, analsite, clinoptyllite, ferrierite, chabazite, gmelinite, levinite, erionite and mordenite are disclosed as suitable. It is disclosed that X-type, Y-type, A-type and the like are suitable as the synthetic zeolite (USP., 3,384, 66).
7; 1968).

A method in which methanol and ammonia are mixed at a specific ratio and reacted in the presence of a catalyst such as mordenite to obtain a large amount of monomethylamine (JP-A-56-11).
3747) and a crystalline aluminosilicate selected from Na mordenite to disproportionate monomethylamine to obtain dimethylamine with high selectivity (JP-A-56-468).
46) A method is also disclosed. The above USP. , 3, 3
A method of using a naturally occurring mineral for mordenite used in the same manner as in 84,667 (JP-A-57-16944).
4), a method of using mordenite ion-exchanged with lanthanum ions as a catalyst (JP-A-58-49340), and a method of using mordenite having an ion exchange amount of an alkali metal within a specific range (JP-A-59). -21005
0), a method of using steam-treated mordenite as a catalyst (JP-A-59-227841), a method of using A-type zeolite having a low binder content as a catalyst (JP-A-58-69846), or a Rho type (ZK). -5) A method of using zeolite as a catalyst is also disclosed.

When the zeolite type catalyst is used by the above method, the amount of trimethylamine produced can be suppressed. Furthermore, in order to make the amount of trimethylamine produced zero or substantially zero, the pores of mordenite are formed into silicon tetrachloride. There is also known a method of using a catalyst modified by the CVD treatment of JP-A No. 03-262540; J. Ca.
tal. 131, 482 (1991). ). A method in which a compound obtained by precipitating and modifying a compound of silicon, aluminum, phosphorus or boron on chabazite, erionite, ZK-5 and Rho type zeolite is used as a catalyst (Japanese Patent Laid-Open Publication No. 6-58242).
1-254256) to reduce the production of trimethylamine. Further, a method of reacting alcohol and ammonia with a non-zeolitic molecular sieve SAPO as a catalyst to obtain an alkylamine (Japanese Patent Laid-Open No. 2-73).
4) is also known.

[0005]

As described above, by using various conventionally disclosed zeolite-based catalysts for the reaction of methanol and ammonia, the production amount of trimethylamine, which is in low demand, can be suppressed to a low level, and It is possible to increase the acquisition amount of a large amount of dimethylamine. However, when these zeolite-based compounds are used as a catalyst, the shape of the catalyst micropores is almost the same as the size of the product molecule in order to express the shape selectivity that suppresses the formation of trimethylamine. When a substance or carbonaceous material is deposited or deposited on the micropores of the catalyst, the activity of the catalyst is lowered, and the production amount of the target substance is gradually reduced, making practical production impossible.

When producing methylamines from methanol and ammonia using zeolite, especially mordenite, as a catalyst, the catalytic activity can be changed over time even at an operation at a relatively low reaction temperature of 300 ° C. or lower in order to suppress the formation of carbonaceous matter. It is described that the decrease is extremely large, the catalyst life is about 2 to 3 months in the industrial operation, and it is very difficult to use the zeolite catalyst efficiently (Japanese Patent Laid-Open No. 2-6355).
4, USP. , 5,068,442). Further, in the above specification, when synthesizing methylamine with a zeolite catalyst such as mordenite, hydrocarbons such as methane and ethane, hydrogen, dimethyl ether, and aldehydes such as formaldehyde are by-produced. In particular, it is described that aldehydes such as formaldehyde cause precipitation of carbonaceous matter and cause a temporary decrease in catalytic activity. Therefore, in order to extend the life of the zeolite catalyst, the amount of formaldehyde in the reaction raw material supplied to the catalyst layer is 0.15 g /
h. kg-cat. It is disclosed below that it is important to suppress. Further, it is also disclosed that these aldehydes are mainly mixed in the unreacted methanol fraction, and when unreacted methanol is recycled to the catalyst layer, the life of the catalyst is remarkably shortened (Japanese Patent Laid-Open No. Hei 2). -6355
4, USP. , 5,068, 442, Chemical Engineering Volume 56 4
21., 1990). For the above reasons, a complex synthesis route is used in which a normal silica-alumina catalyst is combined with a zeolite catalyst having shape selectivity and recycled methanol is supplied to a normal silica-alumina catalyst having no shape selectivity to decompose and remove mixed formaldehydes. A method for producing methylamines having is also proposed.

Even when a reaction method in which measures against deterioration of the catalyst as described above are taken or a catalyst showing durability against formaldehyde (Japanese Patent Application No. 06-068478) is used,
In the reaction over a long period of time, there is a problem that the conversion rate of methanol gradually decreases. An object of the present invention is a method for producing methylamines from methanol and ammonia in the presence of a zeolite catalyst, which does not have the above-mentioned problems, that is, the conversion of methanol is kept high for a long period of time, and efficient methylation is achieved. It is intended to provide a method for producing amines.

[0008]

Means for Solving the Problems The present inventors have proposed a method for producing methylamines in which the formation of trimethylamine is suppressed from ammonia and methanol in the presence of a zeolite catalyst, and the conversion rate of methanol even during long-term operation. Various studies were conducted on an efficient method for producing methylamines that keeps the temperature high. As a result, in the method of producing methylamines by reacting methanol and ammonia in the presence of a zeolite catalyst, the amount of sodium chloride contained as an impurity in the reaction raw material supplied to the catalyst is adjusted to 1
By limiting the concentration to 0.1 mmol / kg or less per hour, more preferably 0.05 mmol / hr or less, it is possible to maintain the conversion rate of methanol at a high value even during long-term operation and to efficiently produce methylamine. The present invention has been completed and the present invention has been completed.

That is, the present invention provides a method for producing methylamines by reacting methanol and ammonia in the presence of a zeolite catalyst, wherein the amount of sodium chloride contained as an impurity in the reaction raw material supplied to the catalyst is used as a catalyst. This is a method for producing methylamines, which is characterized in that it is limited to 0.1 mmol / hr or less per kg.

Further, in the present invention, it is preferable that the amount of sodium chloride contained as an impurity in the reaction raw material supplied to the catalyst is 0.05 mmol or less per 1 kg of the catalyst per hour.

When methylamines are produced from methanol and ammonia in the presence of a zeolite catalyst, unreacted methanol is recovered from the reaction mixture after completion of the reaction and is recycled again as a reaction raw material to the catalyst layer to deteriorate the catalytic activity. It is said that the methanol conversion rate is lowered (Japanese Patent Laid-Open No. 2-63554, Chemical Engineering 1996, 56).
Vol. 421). Further, it is said that the deterioration of the catalytic activity is caused by the mixing of aldehydes into the catalytic layer.

Based on the above findings, a reaction method not including a recycle system of unreacted methanol, and 10 pp of aldehyde compounds flowing into the catalyst layer together with the reaction raw materials are used.
The synthesis of methylamine was tested in the presence of a zeolite catalyst, keeping below m. As a result, in some cases, the catalyst was not deteriorated even after a long-term synthetic reaction test was carried out, and no reduction in the conversion of methanol was substantially observed. However, in some cases, when the same batch catalyst was used and the same long-term methylamine synthesis test was conducted, it was found that the methanol conversion rate was lowered and the catalyst activity was deteriorated. This is a methylamine synthesis catalyst that is durable against aldehyde compounds (Japanese Patent Application No. 06-068478).
Similarly, it was revealed that in the case of the test using, the decrease in the methanol conversion rate may or may not be observed.

As a result of analyzing the zeolite catalyst subjected to a methylamine synthesis reaction test for a long period of time for the purpose of knowing the cause of the above-mentioned decrease in methanol conversion rate, it was found that the carbonaceous substances deposited on the zeolite catalyst were irrespective of whether the methanol conversion rate was decreased or not. Since the amount was the same, it was estimated that the deposition of carbonaceous material on the zeolite catalyst was not the main cause of the decrease in methanol conversion. Then, the amount of acid points of the zeolite catalyst was measured by ammonia temperature programmed desorption of the catalyst after the above-mentioned long-term methylamine synthesis test. It was found that the amount of acid sites was decreased as compared with the catalyst that was not available, and it was found that the decrease of the amount of acid sites was mainly due to neutralization of acid sites by sodium.

As a result of various studies on the cause of sodium contamination in the reaction raw material used for the zeolite catalyst for the synthesis of methylamines, it was found that sodium is incorporated as sodium chloride from methanol. Methanol is practically produced in oil producing areas or large-scale producing areas of natural gas, and is transported by tankers to the consuming areas for use. Sodium chloride in methanol is mixed when the tank of a methanol carrier is washed with seawater, and not when it is washed with fresh water. Therefore, during the methylamines synthesis reaction, the difference between the case where the methanol conversion rate decreases and the case where it does not decrease depends on the difference in the amount of sodium chloride as an impurity mixed in the reaction raw material supplied to the catalyst layer. Became clear.

The amount of sodium chloride in methanol that is transported and imported by a tanker is usually in the range of 1 to 2 ppm and there is no problem, but 20 to 30 ppm may be mixed in, so long-term operation is not possible. At this time, sufficient care must be taken to maintain a high methanol conversion rate.
Also, in the recovered methanol from various manufacturing processes,
Since a large amount of sodium chloride may be mixed in during the salting-out operation or the like, caution should be exercised when using recovered methanol as a raw material for producing methylamine.

In order to keep the amount of sodium chloride mixed as an impurity in the zeolite catalyst layer for the synthesis of methylamine at 0.1 mmol / hr or less per 1 kg of the catalyst of the method of the present invention, the amount of sodium chloride in methanol to be used is changed. Just keep it low enough. In order to remove sodium chloride, it may be possible to achieve the purpose by using a conventional method such as ion exchange or adsorption operation, or by selecting the shape of the methanol evaporator or the shape of the mist separator in the methylamine production process. is there. Further, by eliminating the mixture of sodium chloride in the reaction system, it is possible to obtain the effect of preventing the corrosion due to the halogen in the methylamine production apparatus.

The zeolite that can be used as a catalyst in the method of the present invention is not particularly limited and various zeolites can be exemplified.
For example, mordenite, clinoptyl light, chabazite and the like are frequently used. Conventional mordenite, which has been frequently used in the reaction for obtaining methylamines from methanol and ammonia, is a crystalline aluminosilicate represented by Na ₈ (Al ₈ Si ₄₀ O ₉₆ ) / 24H ₂ O (ATL
AS OF ZEOLITE STRUCTURE TY
PES, W.A. M. Meier and D.M. H. Ol
Son, 1987, Butterworths).

Me1 / n (AlSi ₅ O ₁₂ ) .3H
₂ O, (Me represents an n-valent alkali or alkaline earth atom or hydrogen) (JP-A-57).
169444; JP-A-59-21050).

In either case, normal mordenite is a natural or synthetic product (Zeol from Norton).
on, UCC LZM-8, La Grande Pa
Roisse CM-180, etc.)
/ Al ratio is 5, (silica / alumina) ratio (SiO ₂ / A
L ₂ O ₃ ) is in the vicinity of 10 and its (silica / alumina) ratio exceeds 11 is not known except for a special synthetic product.

Therefore, the mordenite used in the method of the present invention has a (silica / alumina) ratio of 10 or more. If the (silica / alumina) ratio is around 10, ordinary synthetic or natural mordenite is used. Those having a (silica / alumina) ratio of 11 or more can be obtained by subjecting ordinary mordenite to a conventional method such as acid treatment or steam treatment, or (10 + n) Na aqueous solution of sodium silicate and aqueous solution of aluminum chloride. ₂ O
(3 + n) Al ₂ O ₃ (87-n) SiO ₂ (where n
Is prepared by hydrothermally synthesizing a gel-like slurry having a composition of 0 to 4) at 130 to 250 ° C. for 10 hours to several days (Am. Mineral. Volume 65,
1012 (1972)).

Clinoptyllite is Na ₆ (Al ₆ Si ₃₀
O ₇₂ ) 24H ₂ O. As it is (silica /
Alumina) ratio may be used, or one having a higher (silica / alumina) ratio by acid treatment, steam treatment or the like may be used.

Chabazite is Ca ₆ (Al ₁₂ Si
The composition is ₂₄ O ₇₂ ) 40H ₂ O, and it may be used as it is (silica / alumina) ratio or may be used by increasing the (silica / alumina) ratio by a conventional method.

In the method of the present invention, the zeolites used are usually hydrogen ion type in many cases.
Synthetic or natural zeolites are usually obtained in the Na ion form. In the method of the present invention, sodium ions in the above zeolite are converted into hydrogen ion type by a conventional method. In order to convert to the hydrogen ion type, for example, the above zeolite to be ion-exchanged is put into an aqueous ammonium salt solution such as ammonium nitrate or ammonium chloride, and ion-exchanged. The concentration of the aqueous ammonium salt solution is frequently in the range of 0.1 to 2 N, and the ammonium salt aqueous solution is used in an amount corresponding to 2 to 10 times the amount of the cation to be ion-exchanged in the zeolite. The temperature for ion exchange is from room temperature to the boiling point of the ammonium salt aqueous solution. The time required for ion exchange is often in the range of 1 to 30 hours. The zeolite ion-exchanged with an ammonium salt is washed with deionized water, solid-liquid separated, dried and calcined at 500 to 700 ° C. to obtain a catalyst or a precursor thereof.

In order to convert the sodium ions in the above-mentioned zeolite to the hydrogen ion type, besides the method of treating with an ammonium salt aqueous solution, a method of directly performing an ion exchange treatment with an acid aqueous solution is often used. The acid used at this time is hydrochloric acid,
It is nitric acid or sulfuric acid. The concentration of the aqueous acid solution is often 6 N or less, particularly 0.5 to 4 N. The amount of acid used is between 2 and 10 of the cations in the zeolite to be exchanged.
Double dose is used. Similarly, a zeolite ion-exchanged with an aqueous acid solution is washed with deionized water, solid-liquid separated, dried and calcined at 400 to 700 ° C. to obtain a catalyst or its precursor.

Mordenite or clinoptyllite obtained by ion-exchange of sodium ion for hydrogen ion usually has a poor ability to suppress the formation of trimethylamine. In order to appropriately adjust the amount of cations in the zeolite in order to impart the trimethylamine production inhibiting ability to the zeolite, for example, the treatment is carried out by the method described in JP-A-59-21050. Alternatively, the outer surface of the zeolite is subjected to silylation treatment with a silylating agent in order to suppress the production of trimethylamine. The silylating agent used for the silylation treatment of the above-mentioned zeolite is alkoxide Si (OR) of silicon.
₄ (R represents a lower alkyl group such as methyl, ethyl or isopropyl) is convenient, and tetramethoxysilane, tetraethoxysilane and the like are frequently used in the method of the present invention. These silicon alkoxides are
It can be easily obtained as an industrial raw material and can be easily produced by the reaction of silicon tetrachloride with an alcohol such as methanol or ethanol, or the reaction of silicon metal with an alcohol.

The method of treating the above-mentioned zeolite with a silylating agent is not particularly limited, but treatment in the liquid layer or C
There are treatments in the air layer by the VD method. inside that,
When performing the silylation treatment of the zeolite in a liquid layer, when using an alcoholic solvent forming a homogeneous phase with water as a solvent for dissolving the alkoxide of silicon,
The case where benzene, toluene, etc., which form two liquid phases with water, are used as a solvent is often used. As a solvent forming a homogeneous phase with water, lower alcohols such as methanol, ethanol and isopropyl alcohol are often used. In addition, compounds such as methyl cellosolve and ethyl cellosolve may be used as a solvent. Further, if the solvent used has a large amount of water, the silicon alkoxide is hydrolyzed and wasted, so it is preferable that the amount of water in the solvent is as small as possible. The alkoxide of silicon is used by dissolving it in the alcohol solvent described above, and the amount of dissolution is often 0.1 to 50 wt%, particularly 1 to 30 wt%.

The above zeolite is suspended in the above-mentioned alcohol solution of silicon alkoxide to deposit and fix the silicon compound on the outer surface of the zeolite. Prior to the treatment with the silicon compound, the water content of the treated zeolite was adjusted to 4
It is preferable to dry so that the amount becomes not more than%. The amount of silicon alkoxide used is 0.5 with respect to the weight of mordenite.
A range of -30%, especially 1-20% is often used. The temperature at which the silylation treatment is carried out is from room temperature to the boiling point of the alcohol solution, and the treatment temperature can be further increased when the treatment is carried out under pressure, which is usually in the range of 20 to 90 ° C. The time required for the treatment mainly depends on the treatment temperature, but it is 3 to 30 hours near room temperature, and 1 to 60 at 90 to 90 ° C.
The range of 10 hours is often used.

When a solvent that forms a two-liquid phase with water, such as benzene or toluene, is used, the amount of silicon alkoxide used and the treatment conditions are the same as when using a solvent that forms a homogeneous phase with water. It is preferable to adjust the water content in the zeolite to be treated to 3 to 20 wt%. Further, a method in which a trace amount of an acid such as hydrochloric acid, nitric acid, sulfuric acid, or an organic acid is mixed together with water in the above range in zeolite and then treated with silicon alkoxide is a more preferable embodiment.

The treated zeolite is separated from the treatment solution by a conventional method such as filtration or centrifugation and heated under an atmosphere of an inert gas such as nitrogen, or heated under a reduced pressure to adhere.
Alternatively, the adsorbed organic solvent or the like is removed. Then
Heat treatment is performed at 400 to 700 ° C. in an air or oxygen atmosphere to obtain a catalyst. If the starting mordenite is in the form of granules or tablets, it is directly used as a catalyst. When it is in the form of powder, it is extruded or tableted by a conventional method to give a catalyst.

The reactants used in the process of the present invention are methanol or a mixture of methanol and dimethyl ether and ammonia. In addition to this, monomethylamine can be added to the reaction raw material. The molar ratio of ammonia to methanol is often in the range of 0.5: 1 to 5: 1. The amount of reaction gas supplied to the catalyst layer is 200 to 2000 l / h
r. l-cat. Is frequently used, and the reaction pressure is 0 to
40kg / cm ² G, particularly heavy in the range of 10~30kg / cm ² G. The temperature of the catalyst layer when carrying out the reaction is 250 to 400.
C., preferably 250 to 350.degree. C. is often used.

[0031]

EXAMPLES The present invention will be described below with reference to Examples and Comparative Examples. Example 1 500 g of mordenite hydrothermally synthesized by a usual method was subjected to ion exchange with a 1N aqueous ammonium nitrate solution, and the ion exchange operation was repeated 3 times to completely exchange sodium ions for hydrogen ions (Na <0.1%). 100 g of this mordenite was taken and brought into contact with a 0.05N aqueous solution of sodium nitrate to prepare a mordenite having a sodium content of 1%. This mordenite was tablet-molded into a size of 3 mm × 3 mm and calcined at 600 ° C. to obtain a catalyst. 50 g of this catalyst was charged into a 1-inch stainless steel reactor, and heated from outside with a sand fluidized bed to 290 ° C. 40 methanol per hour
g, 40g of ammonia per hour is pressed into the catalyst layer and 300
After reacting at 60 ° C. and a pressure of 20 kg / cm ² G for 6 hours, the reaction was stopped and steam was passed through the catalyst layer at 450 ° C. for 6 hours. After that, the circulation of methanol and ammonia was restarted again at a reaction temperature of 300 ° C. to carry out a synthesis reaction of methylamines. The amount of sodium chloride contained as an impurity in the methanol used at this time was 1 ppm, and the amount of sodium chloride flowing into the catalyst layer was 0.025 mmol / hr or less per 1 kg of the catalyst, which was included in the preferred range of the method of the present invention. ing. Under these reaction conditions, the synthetic reaction of methylamines was tested for a long time. The obtained reaction results are shown in Table 1.

Comparative Example 1 The same catalyst as in Example 1 was used, and the synthesis of methylamine was tested in the same reactor and reaction conditions. The amount of sodium chloride contained as impurities in the methanol used at this time was 20 ppm, and the amount of sodium chloride flowing into the catalyst layer was 0.5 mmol / kg of catalyst per hour. Table 1 shows the results of testing the long-term synthetic reaction of methylamines under these reaction conditions.

Example 2 50 g of mordenite (Na <0.1%) completely exchanged with hydrogen ions in Example 1 was taken and treated with a solution of tetraethoxysilane dissolved in toluene to silylate the catalyst surface. did. This was tablet-molded and baked at 600 ° C. to prepare a catalyst. This was tested for the synthesis reaction of methylamine under the same apparatus and reaction conditions as in Example 1, and the content of sodium chloride in methanol was 1 ppm. Sodium chloride flowing into the catalyst layer per hour was 0.
It is not more than 025 mmol, which is a preferable range of the present invention. Long-term methylamine synthesis was tested under these conditions.
The results obtained are shown in Table 1.

Comparative Example 2 The synthesis of methylamine was tested using the same catalyst as in Example 2 and the same equipment and reaction conditions as in Example 1. The amount of sodium chloride contained as an impurity in the methanol used at this time was 20 ppm, and the amount of sodium chloride flowing into the catalyst layer was 0.5 mmol / kg of catalyst per hour. The long-term synthesis of methylamines was tested under these reaction conditions, and the results obtained are shown in Table 1.

Example 3 The same test as in Example 1 was carried out by replacing the catalyst used with hydrogen ion type chabazite. The obtained results are also shown in Table 1.

Example 4 The same test as in Example 1 was conducted except that the catalyst used was changed to silylated hydrogen ion type clinoptyllite. The obtained results are also shown in Table 1.

[0037]

[Table 1] Table 1 ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ MeOH conversion rate Selection to methylamines Rate (%)% Monolith ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ Example 1 (A) 86 36 54 10 (B) 84 40 51 9 ─────────────────────────────────── Comparative Example 1 (A ) 86 36 54 10 (B) 79 44 49 7 ─────────────────────────────────── Example 2 (A) 91 35 62 3 (B) 89 36 61 3 ─────────────────────────────────── Comparison Example 2 (A) 91 35 62 3 (B) 82 42 55 3 ───────── ────────────────────────── Example 3 (A) 88 35 56 11 (B) 85 39 39 51 10 ─────── ──────────────────────────── Example 4 (A) 87 39 57 5 (B) 84 42 54 54 4 ━━━━━━ ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ Note (A) is the measured value 200 hours after the start of the reaction, and (B) is the measured value after 2200 hours. Indicates.

[0038]

INDUSTRIAL APPLICABILITY According to the method of the present invention, in a method for producing methylamines from methanol and ammonia in the presence of a zeolite catalyst, the methanol conversion rate can be maintained at a high value even after a long-term reaction, and the efficiency of A good plant operation is possible.

Claims (6)

[Claims] 1. A method for producing methylamines by reacting methanol and ammonia in the presence of a zeolite catalyst, wherein the amount of sodium chloride contained as an impurity in a reaction raw material supplied to the catalyst is 0 per hour per 1 kg of the catalyst. A method for producing methylamines, which is limited to 1 mmol or less. 2. The method according to claim 1, wherein the amount of sodium chloride contained as an impurity in the reaction raw material supplied to the catalyst is 0.05 mmol or less per 1 kg of the catalyst per hour. 3. The method according to claim 1, wherein the zeolite catalyst is mordenite. 4. The method according to claim 1 or 2, wherein the zeolite catalyst is obtained by subjecting the outer surface of mordenite to a silylation treatment with a silylating agent. 5. The method according to claim 1 or 2, wherein the zeolite catalyst is clinoptyllite. 6. The method according to claim 1, wherein the zeolite catalyst is chabazite.