Methylamine synthesis method

Abstract

The present invention relates to the field of catalytic synthesis, and discloses a methylamine synthesis method, which comprises: in the presence of a zeolite catalyst obtained through organic alkali treatment, carrying out a reaction on methanol and ammonia to generate a methylamine-containing material flow, and the acid content of the zeolite catalyst obtained through organic alkali treatment is 200-400 [mu] mol.g <-1 >. According to the methylamine synthesis method provided by the invention, the selectivity of trimethylamine in a reaction product can be reduced, the content of trimethylamine in the product is reduced, and meanwhile, the high methanol conversion rate is ensured.

Description

Technical Field

[0001] The invention relates to the field of catalytic synthesis, and in particular to a method for synthesizing methylamine. Background Art

[0002] The production of methylamine from methanol and liquid ammonia usually needs to be carried out in the presence of a solid acid catalyst, and the reaction produces a mixture of monomethylamine (MMA), dimethylamine (DMA) and trimethylamine (TMA). Monomethylamine is usually used in pesticides, explosives, surfactants, industrial solvent N-methylpyrrolidone and gas purifiers, dimethylamine is mainly used in medicine, rubber accelerators, industrial solvents dimethylformamide and dimethylacetamide, etc., and trimethylamine is used in choline chloride, odor additives for natural gas, etc.

[0003] This process uses a traditional equilibrium methylamine catalyst, and the distribution of methylamine products is determined by thermodynamics. Under current industrial conditions, the production of trimethylamine is about 50%. Since the current market demand for trimethylamine is relatively low, too high trimethylamine selectivity does not meet market demand. The output of trimethylamine can be reduced by the return process, but the process energy consumption will increase. Therefore, it is of practical significance to study catalysts with low trimethylamine and high monomethylamine selectivity.

[0004] Patent CN1572785B of Mitsubishi Rayon Co., Ltd. proposes to use mordenite with a crystallinity greater than or equal to 60%, and at the same time control the catalyst particle size, preferably a catalyst of 2-5mm can increase the selectivity of dimethylamine; US5137854 discloses a mordenite catalyst treated with silicon tetrachloride. CN1618786A uses molecular sieves such as mordenite, and after modification with alkali metals, alkaline earth metals, rare earth metals or phosphorus, the catalytic performance can reach more than 30% of dimethylamine selectivity when the methanol conversion rate is greater than 98%. CN1657167A discloses a catalyst modified with silicon on molecular sieves such as mordenite and HZSM-5, and uses a variety of silicone oils and solvents. The final dimethylamine selectivity can reach more than 50%, and the methanol conversion rate reaches more than 98%.

[0005] Currently, the selectivity of dimethylamine can be improved to a certain extent by modification, but there is no clear method to significantly reduce the selectivity of trimethylamine after modifying the catalyst. Summary of the invention

[0006] The purpose of the present invention is to overcome the problem of high selectivity of trimethylamine in the reaction product in the methylamine synthesis process in the prior art, and to provide a methylamine synthesis method, which can reduce the selectivity of trimethylamine in the reaction product, reduce the content of trimethylamine in the product, and ensure a high methanol conversion rate.

[0007] In order to achieve the above object, the present invention provides a method for synthesizing methylamine, which comprises: reacting methanol and ammonia in the presence of a zeolite catalyst obtained by treatment with an organic base to generate a stream containing methylamine;

[0008] The acid content of the zeolite catalyst obtained by organic base treatment is 200-400 μmol·g -1 .

[0009] Preferably, the acid content of the zeolite catalyst obtained by the organic base treatment is 210-380 μmol·g -1 .

[0010] Preferably, the concentration of the organic base in the organic base solution is 0.1-2 mol / L, preferably 0.2-0.8 mol / L.

[0011] Preferably, based on the mass of zeolite raw powder being 1 g, the amount of the organic base solution used is 3-20 mL, preferably 5-18 mL.

[0012] Through the above technical solution, the beneficial technical effects obtained are as follows:

[0013] The methylamine synthesis method provided by the present invention treats a zeolite catalyst with an organic base under a high-temperature hydrothermal reaction, thereby specifically changing the acid position of the zeolite catalyst, reducing the acid amount, inhibiting the generation of trimethylamine during the methylamine synthesis process, and ensuring a high reaction activity. DETAILED DESCRIPTION

[0014] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0015] In one aspect, the present invention provides a method for synthesizing methylamine, the method comprising: reacting methanol and ammonia in the presence of a zeolite catalyst obtained by treatment with an organic base to generate a stream containing methylamine;

[0016] The acid content of the zeolite catalyst obtained by organic base treatment is 200-400 μmol·g -1 .

[0017] In the present invention, the inventors have found through research that targeted changes in acidic properties and reductions in acidity can reduce the generation of trimethylamine. Further research has found that weakening the acidity of the zeolite catalyst through organic base treatment and inhibiting the generation of trimethylamine can not only improve the selectivity of the methylamine synthesis reaction, but also ensure high reaction activity.

[0018] According to the present invention, preferably, the acid amount of the zeolite catalyst obtained by the organic base treatment is 200-400 μmol·g -1 , for example, 200 μmol·g -1 , 210μmol·g -1 , 220μmol·g -1 , 240 μmol·g -1 , 260μmol·g -1 , 280μmol·g -1 , 300 μmol·g -1 、320μmol·g -1 、340μmol·g -1 、360μmol·g -1 、380μmol·g -1 , 400 μmol·g -1 , and any range between any two values, preferably 210-380 μmol·g -1 The use of this preferred embodiment is more conducive to further reducing the generation of trimethylamine and maintaining the activity of the zeolite catalyst.

[0019] In the present invention, the acid content of the zeolite catalyst is measured by Fourier transform infrared spectroscopy, the instrument is Nicolet Nexus 4700, the sample is placed in a vacuum system, treated at 400°C for two hours, and the sample background is measured. Next, pyridine is introduced, adsorbed at 200°C for 10 minutes, desorbed for 40 minutes, and finally measured by infrared testing.

[0020] In the present invention, the acid amount of the zeolite catalyst refers to the acid amount of the entire zeolite catalyst at 200°C.

[0021] In the present invention, the acid content of the zeolite catalyst obtained by the organic base treatment is significantly reduced, and the generation of trimethylamine in the methylamine synthesis reaction is further inhibited.

[0022] In the present invention, preferably, the pore volume of the zeolite catalyst is 0.4-0.6 cm 3 ·g -1 , preferably 0.45-0.57cm 3 ·g -1 The appropriate pore structure is conducive to the methylamine synthesis reaction.

[0023] In the present invention, the pore volume of the zeolite catalyst is measured by conducting a nitrogen adsorption and desorption experiment in a liquid nitrogen atmosphere at a relative pressure of 0.99. Before the nitrogen adsorption and desorption experiment, the zeolite catalyst also includes a pretreatment process of vacuuming and heating to remove impurities, and the heating temperature is 300°C.

[0024] According to the present invention, preferably, the organic base is selected from at least one of tetrapropylammonium hydroxide, tetramethylammonium hydroxide, triethanolamine, tetraethylammonium hydroxide, N,N-diisopropylethylamine and tetrabutylammonium hydroxide, preferably selected from at least one of tetrapropylammonium hydroxide, tetramethylammonium hydroxide, tetraethylammonium hydroxide, N,N-diisopropylethylamine and tetrabutylammonium hydroxide.

[0025] In the present invention, the above preferred template-like organic base is selected for alkali treatment to avoid the destruction of the zeolite catalyst structure by the inorganic base, thereby ensuring a high reaction activity and further reducing the generation of trimethylamine.

[0026] According to the present invention, preferably, the process of organic base treatment comprises: subjecting a mixture containing an organic base solution, zeolite raw powder and an optional surfactant to a hydrothermal reaction, and calcining a solid product obtained by the hydrothermal reaction to obtain a zeolite catalyst.

[0027] In the present invention, the organic base solution, zeolite raw powder and optional surfactant are mixed uniformly to obtain the mixture. There is no particular limitation on the mixing method. According to a preferred embodiment of the present invention, the mixture can be mixed uniformly by stirring at room temperature. The stirring rate can be adaptively adjusted by those skilled in the art according to the mixing conditions.

[0028] In the present invention, the method of adding the organic alkali solution, zeolite powder and optional surfactant is not particularly limited, and they can be added separately or together.

[0029] According to a preferred embodiment of the present invention, an organic base solution of a certain concentration is prepared first, a surfactant is added thereto and stirred to dissolve, and then zeolite raw powder is added thereto and mixed evenly.

[0030] According to the present invention, preferably, the concentration of the organic base in the organic base solution is 0.1-2mol / L, such as 0.1mol / L, 0.2mol / L, 0.3mol / L, 0.4mol / L, 0.5mol / L, 0.6mol / L, 0.7mol / L, 0.8mol / L, 0.9mol / L, 1mol / L, 1.1mol / L, 1.2mol / L, 1.3mol / L, 1.4mol / L, 1.5mol / L, 1.6mol / L, 1.7mol / L, 1.8mol / L, 1.9mol / L, 2mol / L, and any range composed of any two values, preferably 0.2-0.8mol / L. In the present invention, the concentration of the organic base in the organic base solution is controlled within an appropriate range. If the concentration is too high, the original zeolite powder is over-treated, so that the methanol conversion rate is reduced; if the concentration is too low, the original zeolite powder is not treated enough, and the formation of trimethylamine cannot be effectively suppressed.

[0031] In the present invention, the solvent of the organic alkaline solution is water, preferably deionized water.

[0032] According to the present invention, preferably, based on the mass of the zeolite raw powder as 1g, the amount of the organic alkali solution is 3-20mL, for example, 3mL, 4mL, 5mL, 6mL, 7mL, 8mL, 9mL, 10mL, 11mL, 12mL, 13mL, 14mL, 15mL, 16mL, 17mL, 18mL, 19mL, 20mL, and any range composed of any two values, preferably 5-18mL. The organic alkali solution is mixed with the zeolite raw powder according to the above-mentioned liquid-solid ratio, and the alkali treatment obtains a zeolite catalyst without destroying the crystallinity of the zeolite raw powder, thereby reducing the content of trimethylamine in the product.

[0033] According to the present invention, preferably, the zeolite raw powder is selected from at least one of ZSM-5 molecular sieve, β molecular sieve and mordenite. Preferably, it is selected from at least one of hydrogen-type ZSM-5 molecular sieve, hydrogen-type β molecular sieve and hydrogen-type mordenite. The zeolite catalyst is obtained by mixing the above-mentioned specific zeolite raw powder with an organic base and performing alkali treatment, which can ensure that the catalyst has high reactivity during the methylamine synthesis process while inhibiting the formation of trimethylamine.

[0034] According to the present invention, preferably, the silicon-aluminum molar ratio SiO2 / Al2O3 of the zeolite raw powder is 5-500, for example, 5, 10, 20, 30, 40, 50, 100, 150, 200, 250, 300, 350, 400, 450, 500, and any range between any two values, preferably 10- 100. In the present invention, the silicon-aluminum molar ratio SiO2 / Al2O3 of the zeolite raw powder is measured by X-ray fluorescence spectrometer.

[0035] In the present invention, the source of the zeolite raw powder is not particularly limited, and it can be commercially available or prepared by an existing method. The zeolite raw powder is prepared by an existing method, and the specific method is well known to those skilled in the art, and the prepared zeolite raw powder meets the above parameter limitations. The organic base treatment using the zeolite raw powder that meets the above parameter limitations can effectively inhibit the formation of trimethylamine in the methylamine synthesis reaction.

[0036] According to the present invention, preferably, the conditions of the hydrothermal reaction include: a reaction temperature of 60-280°C, for example, 60°C, 70°C, 80°C, 90°C, 100°C, 120°C, 140°C, 160°C, 180°C, 200°C, 220°C, 240°C, 260°C, 280°C, and any range between any two values, preferably 80-240°C, further preferably 100-180°C; and / or a reaction time of 3-170 hours, for example, 3h, 5h, 10h, 15h, 20h, 30h, 40h, 50h, 60h, 70h, 80h, 90h, 100h, 110h, 120h, 130h, 140h, 150h, 160h, 170h, and any range between any two values, preferably 20-150 hours.

[0037] In the present invention, the hydrothermal reaction is carried out under the above conditions, which can avoid excessive treatment results due to the hydrothermal reaction temperature being too high and the reaction time being too long, thereby reducing the catalyst reaction activity; if the temperature is too low and the hydrothermal reaction time is too short, the catalyst will not change much after treatment and the effect will not be obvious.

[0038] In the present invention, the equipment for the hydrothermal reaction is not particularly limited, as long as it can achieve the hydrothermal reaction. Preferably, the hydrothermal reaction is carried out in a hydrothermal kettle, and after the hydrothermal reaction is completed, the product is taken out after cooling.

[0039] The present invention also includes filtering, washing and drying the solid product obtained by the hydrothermal reaction and then performing the roasting. The present invention does not particularly limit the conditions of the filtration, washing and drying. Those skilled in the art can make appropriate selections according to the specific circumstances, as long as the purposes of filtration, washing and drying can be achieved.

[0040] In the present invention, the calcination conditions include: a calcination temperature of 300-600°C, preferably 350-550°C; a calcination time of 1-5h, preferably 2-3h. Calcination under the above conditions can change the acidity of the catalyst without destroying the structure of the zeolite catalyst, thereby ensuring a high reaction activity of the methylamine synthesis reaction.

[0041] In the present invention, the surfactant is not particularly limited, as long as it can play a role in improving the compatibility of two different substances. According to the present invention, preferably, the surfactant is selected from at least one of hexadecyltrimethylammonium bromide, dodecyltrimethylammonium bromide and dodecyltrimethylammonium chloride. This preferred embodiment is more conducive to improving the treatment effect of the organic base.

[0042] In the present invention, the addition amount of the surfactant is not particularly limited, and those skilled in the art can perform adaptive adjustment according to the treatment effect of organic base. Preferably, in the volume of organic base solution as 100mL, the addition amount of the surfactant is 0.01-10g, such as 0.01g, 0.05g, 0.1g, 0.2g, 0.5g, 1g, 2g, 3g, 4g, 5g, 6g, 7g, 8g, 9g, 10g, and any range of composition between any two values, preferably 0.1-5g. Adding the above-mentioned surfactant to coordinate with the organic base solution can effectively reduce the acid amount of the catalyst after the organic base treatment, and reduce the content of trimethylamine in the product.

[0043] According to the present invention, preferably, the reaction conditions include: reaction temperature of 300-400°C, preferably 320-390°C; reaction pressure of 0.5-5MPa, preferably 1-4MPa; methanol gas hourly space velocity of 500-5000h -1 , preferably 1000-4000h -1 The molar ratio of ammonia to methanol is 0.5-5, preferably 1-3. The zeolite catalyst treated with an organic base is reacted under the above conditions to ensure a high reaction activity while inhibiting the formation of trimethylamine. In the present invention, the methanol conversion rate can be maintained at more than 96%, more preferably more than 98%.

[0044] In the present invention, the methylamine synthesis product includes monomethylamine, dimethylamine and trimethylamine, and the molar contents of monomethylamine, dimethylamine and trimethylamine are measured by passing the product into a gas chromatograph for analysis.

[0045] According to the present invention, preferably, in the methylamine-containing stream, the trimethylamine selectivity is not higher than 25%, preferably not higher than 20%, and more preferably not higher than 16%.

[0046] In the present invention, the monomethylamine selectivity, dimethylamine selectivity and trimethylamine selectivity refer to the molar content percentages of monomethylamine, dimethylamine and trimethylamine in the methylamine-containing logistics.

[0047] According to a particularly preferred embodiment of the present invention, a method for synthesizing methylamine, wherein the method comprises: reacting methanol and ammonia in the presence of a zeolite catalyst obtained by treatment with an organic base to generate a stream containing methylamine;

[0048] The acid content of the zeolite catalyst obtained by treatment with an organic base is 210-380 μmol·g -1 ;

[0049] The organic base treatment process comprises: subjecting a mixture containing an organic base solution, zeolite raw powder and an optional surfactant to a hydrothermal reaction, and calcining a solid product obtained by the hydrothermal reaction to obtain a zeolite catalyst;

[0050] The organic base is selected from at least one of tetrapropylammonium hydroxide, tetramethylammonium hydroxide, tetraethylammonium hydroxide, N,N-diisopropylethylamine and tetrabutylammonium hydroxide;

[0051] The concentration of the organic base in the organic base solution is 0.1-2 mol / L, preferably 0.2-0.8 mol / L;

[0052] Based on the mass of zeolite raw powder as 1g, the amount of the organic base solution is 3-20mL, preferably 5-18mL;

[0053] The conditions of the hydrothermal reaction include: a reaction temperature of 100-180° C. and a reaction time of 20-150 hours;

[0054] The conditions for the reaction of methanol and ammonia include: a reaction temperature of 320-390°C; a reaction pressure of 1-4 MPa; a methanol gas hourly space velocity of 1000-4000 h -1 ; The molar ratio of ammonia to methanol is 1-3.

[0055] The present invention will be described in detail below through examples and comparative examples. In the following examples and comparative examples, the molar contents of methanol, monomethylamine, dimethylamine and trimethylamine in the reactants and products are measured by gas chromatography;

[0056] Methanol conversion rate (%) = molar content of methanol reacted / molar content of methanol in raw material × 100%.

[0057] The test methods for the acid content and pore volume of the zeolite catalyst are described in the aforementioned specification and will not be repeated here; unless otherwise specified, the reagents and materials used can be obtained commercially, and the room temperature is 25°C.

[0058] Preparation Example of Z-1 Molecular Sieve

[0059] 21.5 g of sodium silicate nonahydrate, 0.2 g of sodium hydroxide and 5.7 g of tetrapropylammonium bromide were dissolved in 100 mL of deionized water to obtain a mixed solution, 2.5 g of aluminum sulfate was weighed and dissolved in 50 mL of deionized water to prepare an aluminum sulfate solution, the aluminum sulfate solution was added to the mixed solution under stirring, and the mixture was evenly mixed before being transferred into a reactor. After crystallization at 170° C. for 48 hours, the mixture was taken out for filtration, washed and dried. After calcination at 550° C. for 4 hours, 1 mol / L ammonium chloride solution was used for exchange three times to obtain a hydrogen-type ZSM-5 molecular sieve with a silicon-aluminum molar ratio SiO2 / Al2O3 of 10, which was recorded as Z-1.

[0060] Preparation Example of Z-2 Molecular Sieve

[0061] 69.8 g of sodium silicate nonahydrate, 0.3 g of sodium hydroxide and 16 g of tetrapropylammonium bromide were dissolved in 150 mL of deionized water to obtain a mixed solution, 2.1 g of aluminum sulfate was weighed and dissolved in 28 mL of deionized water to prepare an aluminum sulfate solution, the aluminum sulfate solution was added to the mixed solution under stirring, and the mixture was evenly mixed before being transferred into a reactor. After crystallization at 170° C. for 48 h, the mixture was taken out for filtration, washed and dried, calcined at 550° C. for 4 h, and exchanged three times with 1 mol / L ammonium chloride solution to obtain a hydrogen-type ZSM-5 molecular sieve with a silicon-aluminum molar ratio SiO2 / Al2O3 of 40, which was recorded as Z-2.

[0062] Example 1

[0063] Prepare 100 mL of a solution with a concentration of 0.2 mol / L of N,N-diisopropylethylamine, add 0.2 g of hexadecyltrimethylammonium bromide and stir to dissolve, then add 10 g of Z-1 molecular sieve and stir to mix evenly at room temperature, transfer to a hydrothermal kettle, perform hydrothermal reaction at 180°C for 48 hours, take out after cooling, filter, dry, and calcine at 500°C for 3 hours to obtain catalyst Z1-A.

[0064] Example 2

[0065] Prepare 100 mL of a solution with a concentration of 0.2 mol / L of tetrapropylammonium hydroxide, add 0.2 g of hexadecyltrimethylammonium bromide and stir to dissolve, then add 10 g of Z-1 molecular sieve and stir to mix evenly at room temperature, transfer to a hydrothermal kettle, perform hydrothermal reaction at 170°C for 30 hours, take out after cooling, filter, dry, and calcine at 500°C for 3 hours to obtain catalyst Z1-B.

[0066] Example 3

[0067] Prepare 100 mL of a solution with a concentration of 1.1 mol / L of tetramethylammonium hydroxide, add 0.2 g of hexadecyltrimethylammonium bromide and stir to dissolve, then add 10 g of Z-1 molecular sieve and stir to mix evenly at room temperature, transfer to a hydrothermal kettle, and perform hydrothermal reaction at 180°C for 150 h. After cooling, take out the product, filter it, dry it, and calcine it at 500°C for 3 h to obtain catalyst Z1-C.

[0068] Example 4

[0069] Prepare 100 mL of a solution with a concentration of 0.2 mol / L of tetrapropylammonium hydroxide, add 10 g of Z-1 molecular sieve and stir to mix evenly at room temperature, transfer to a hydrothermal kettle, perform hydrothermal reaction at 170°C for 30 h, take out after cooling, filter, dry, and calcine at 500°C for 3 h to obtain catalyst Z1-D.

[0070] Example 5

[0071] Prepare 100 mL of a solution with a concentration of 0.1 mol / L of tetrabutylammonium hydroxide, add 0.2 g of hexadecyltrimethylammonium bromide and stir to dissolve, then add 10 g of Z-1 molecular sieve and stir to mix evenly at room temperature, transfer to a hydrothermal kettle, perform hydrothermal reaction at 140°C for 10 h, take out after cooling, filter, dry, and calcine at 500°C for 3 h to obtain catalyst Z1-E.

[0072] Example 6

[0073] Prepare 100 mL of a solution with a concentration of 0.6 mol / L of tetraethylammonium hydroxide, add 0.2 g of hexadecyltrimethylammonium bromide and stir to dissolve, then add 10 g of Z-1 molecular sieve and stir to mix evenly at room temperature, transfer to a hydrothermal kettle, and perform hydrothermal reaction at 170°C for 20 h. After cooling, take out the product, filter it, dry it, and calcine it at 550°C for 2 h to obtain catalyst Z1-F.

[0074] Example 7

[0075] Prepare 100 mL of a solution with a concentration of 0.1 mol / L of tetraethylammonium hydroxide, add 0.2 g of hexadecyltrimethylammonium bromide and stir to dissolve, then add 10 g of Z-2 molecular sieve and stir to mix evenly at room temperature, transfer to a hydrothermal kettle, and perform hydrothermal reaction at 150°C for 10 hours. After cooling, take out the product, filter it, dry it, and calcine it at 500°C for 3 hours to obtain catalyst Z2-A.

[0076] Example 8

[0077] Prepare 100 mL of a solution with a triethanolamine concentration of 0.3 mol / L, add 0.2 g of hexadecyltrimethylammonium bromide and stir to dissolve, then add 10 g of Z-2 molecular sieve and stir to mix evenly at room temperature, transfer to a hydrothermal kettle, perform hydrothermal reaction at 160°C for 48 hours, take out after cooling, filter, dry, and calcine at 500°C for 3 hours to obtain catalyst Z2-B.

[0078] Example 9

[0079] Prepare 50 mL of a solution with a concentration of 0.3 mol / L of tetrapropylammonium hydroxide, add 0.2 g of hexadecyltrimethylammonium bromide and stir to dissolve, then add 10 g of Z-2 molecular sieve and stir to mix evenly at room temperature, transfer to a hydrothermal kettle, and perform hydrothermal reaction at 160°C for 48 hours. After cooling, take out and filter, dry, and calcine at 500°C for 3 hours to obtain catalyst Z2-C.

[0080] Example 10

[0081] Prepare 100 mL of a solution with a concentration of 0.3 mol / L of tetrapropylammonium hydroxide, add 0.2 g of hexadecyltrimethylammonium bromide and stir to dissolve, then add 10 g of Z-2 molecular sieve and stir to mix evenly at room temperature, transfer to a hydrothermal kettle, and perform hydrothermal reaction at 160°C for 48 hours. After cooling, take out and filter, dry, and calcine at 500°C for 3 hours to obtain catalyst Z2-D.

[0082] Embodiment 11

[0083] The organic base treatment was carried out according to the method of Example 10, except that the hydrothermal reaction was carried out at 70° C. for 10 h to obtain catalyst Z2-E.

[0084] Example 12

[0085] The organic base treatment was carried out according to the method of Example 10, except that the added surfactant was dodecyltrimethylammonium bromide with a mass of 1 g, to obtain catalyst Z2-F.

[0086] Example 13

[0087] The organic base treatment was carried out according to the method of Example 10, except that 10 g of ZSM-5 molecular sieve (NKF-5 Nanhua) with a silicon-aluminum ratio of 120 was added to obtain catalyst Z3.

[0088] Embodiment 14

[0089] The organic base treatment was carried out according to the method of Example 10, except that 10 g of MCM-22 molecular sieve (NKF-10 Nanhua) was added to obtain catalyst M1.

[0090] Embodiment 15

[0091] 45.75g of silica sol (40wt% SiO2), 0.3g of sodium hydroxide and 17.6g of triethanolamine template were dissolved in 10mL of deionized water to obtain a mixed solution, 0.5g of sodium aluminate was dissolved in 5mL of deionized water to prepare a sodium aluminate solution, the sodium aluminate solution was added to the mixed solution under stirring, the mixture was evenly mixed and then transferred into a reactor, crystallized at 150°C for 120h, filtered out, washed and dried, calcined at 550°C for 5h, and exchanged three times with 1mol / L ammonium chloride solution to obtain a hydrogen-type β molecular sieve with a silicon-aluminum ratio of 100.

[0092] Prepare 100 mL of tetraethylammonium hydroxide solution with a concentration of 0.3 mol / L, add 0.2 g of hexadecyltrimethylammonium bromide surfactant and stir to dissolve, then add 10 g of β molecular sieve and stir to mix evenly, transfer to a hydrothermal kettle, hydrothermally react at 150° C. for 48 h, cool, take out, filter, dry, and calcine at 500° C. for 3 h to obtain catalyst BA.

[0093] Comparative Example 1

[0094] Z-1 molecular sieve is used as the zeolite catalyst without organic base treatment.

[0095] Comparative Example 2

[0096] Z-2 molecular sieve is used as zeolite catalyst without organic base treatment.

[0097] Comparative Example 3

[0098] The method of Example 1 is followed, except that the N,N-diisopropylethylamine solution is replaced by a sodium hydroxide solution of the same concentration and volume to obtain a zeolite catalyst.

[0099] Test Case

[0100] 1 g of the zeolite catalysts obtained by treatment in Examples 1-15 and Comparative Examples 1-3 were respectively used to carry out methylamine synthesis reaction. The reaction conditions included: reaction temperature of 360° C., reaction pressure of 1.5 MPa, methanol gas hourly space velocity of 4000 h -1 , the molar ratio of ammonia to methanol is 1.

[0101] The results of the acid content and pore volume of the zeolite catalyst are shown in Table 1.

[0102] After the reaction was stable for 0.5 h, the product was taken for chromatographic analysis. The results of methanol conversion, monomethylamine selectivity, dimethylamine selectivity, and trimethylamine selectivity in the product are shown in Table 1.

[0103] Table 1

[0104]

[0105] It can be seen from the results in Table 1 that, by using the methylamine synthesis method provided by the present invention, the zeolite catalyst treated with an organic base is used for the methylamine synthesis reaction, the selectivity of trimethylamine in the reaction product is significantly reduced, and the formation of trimethylamine is effectively suppressed while ensuring the methanol conversion rate.

[0106] When the catalysts of Comparative Examples 1 and 2 that were not treated with an organic base were used in the methylamine synthesis reaction, their selectivity for monomethylamine was low and their selectivity for trimethylamine was high, and they could not effectively inhibit the formation of trimethylamine. The catalyst of Comparative Example 3 that was treated with an inorganic base not only failed to effectively inhibit the formation of trimethylamine, but also significantly reduced the methanol conversion rate.

[0107] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for synthesizing methylamine, characterized in that: The method comprises: reacting methanol and ammonia in the presence of a zeolite catalyst obtained by treatment with an organic base to generate a stream containing methylamine; The acid content of the zeolite catalyst obtained by organic base treatment is 200-400 μmol·g -1 .

2. The method according to claim 1, wherein: The acid content of the zeolite catalyst obtained by treatment with an organic base is 210-380 μmol·g -1 .

3. The method according to claim 1 or 2, wherein: The organic base is selected from at least one of tetrapropylammonium hydroxide, tetramethylammonium hydroxide, triethanolamine, tetraethylammonium hydroxide, N,N-diisopropylethylamine and tetrabutylammonium hydroxide, preferably selected from at least one of tetrapropylammonium hydroxide, tetramethylammonium hydroxide, tetraethylammonium hydroxide, N,N-diisopropylethylamine and tetrabutylammonium hydroxide.

4. The method according to any one of claims 1 to 3, wherein: The process of the organic alkali treatment comprises: A mixture containing an organic alkali solution, zeolite raw powder and an optional surfactant is subjected to a hydrothermal reaction, and a solid product obtained by the hydrothermal reaction is calcined to obtain a zeolite catalyst.

5. The method according to claim 4, wherein: The concentration of the organic base in the organic base solution is 0.1-2 mol / L, preferably 0.2-0.8 mol / L; Preferably, based on the mass of zeolite raw powder being 1 g, the amount of the organic base solution used is 3-20 mL, preferably 5-18 mL.

6. The method according to claim 4 or 5, wherein: The zeolite raw powder is selected from at least one of ZSM-5 molecular sieve, β molecular sieve and mordenite; Preferably, the silicon-aluminum molar ratio SiO2 / Al2O3 of the zeolite raw powder is 5-500, preferably 10-100.

7. The method according to any one of claims 4 to 6, wherein: The conditions of the hydrothermal reaction include: The reaction temperature is 60-280°C, preferably 80-240°C, and more preferably 100-180°C; And / or, the reaction time is 3-170 hours, preferably 20-150 hours.

8. The method according to any one of claims 4 to 7, wherein: The surfactant is at least one selected from the group consisting of hexadecyltrimethylammonium bromide, dodecyltrimethylammonium bromide and dodecyltrimethylammonium chloride; Preferably, based on the volume of the organic base solution being 100 mL, the amount of the surfactant added is 0.01-10 g, preferably 0.1-5 g; Preferably, the calcination conditions include: a calcination temperature of 300-600° C., preferably 350-550° C.; and a calcination time of 1-5 h, preferably 2-3 h.

9. The method according to any one of claims 1 to 8, wherein: The reaction conditions include: The reaction temperature is 300-400℃, the reaction pressure is 0.5-5MPa, and the methanol gas hourly space velocity is 500-5000h -1 , the molar ratio of ammonia to methanol is 0.5-5.

10. The method according to any one of claims 1 to 9, wherein: In the methylamine-containing stream, the trimethylamine selectivity is not higher than 25%, preferably not higher than 20%.

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