Methane synthesis process

Abstract

The application relates to the field of catalytic synthesis, and discloses a methylamine synthesis method, which comprises the following steps: reacting methanol and ammonia in the presence of a zeolite catalyst treated by an organic alkali to generate a methylamine-containing stream; the acid amount of the zeolite catalyst treated by the organic alkali is 200-400 mu mol.g ‑1 The methylamine synthesis method can reduce the selectivity of trimethylamine in the reaction product, reduce the content of trimethylamine in the product, and ensure high methanol conversion rate.

Description

Technical Field

[0001] This invention relates to the field of catalytic synthesis, and more specifically to a method for synthesizing methylamine. Background Technology

[0002] The production of methylamine from methanol and liquid ammonia typically requires the presence of a solid acid catalyst, yielding a mixture of monomethylamine (MMA), dimethylamine (DMA), and trimethylamine (TMA). Monomethylamine is commonly used in pesticides, explosives, surfactants, the industrial solvent N-methylpyrrolidone, and as a gas purifier. Dimethylamine is primarily used in pharmaceuticals, rubber accelerators, and as industrial solvents such as dimethylformamide and dimethylacetamide. Trimethylamine is used in choline chloride and as an odor additive in natural gas.

[0003] This process uses a traditional equilibrium methylamine catalyst, and the distribution of methylamine products is thermodynamically determined. Under current industrial conditions, trimethylamine production is approximately 50%. Since current market demand for trimethylamine is relatively low, excessively high trimethylamine selectivity does not meet market requirements. A recycle process can reduce trimethylamine production, but this will increase energy consumption. Therefore, researching catalysts with low trimethylamine and high dimethylamine selectivity is of practical significance.

[0004] Mitsubishi Rayon Corporation's patent CN1572785B proposes using mordenite with a crystallinity of ≥60%, while controlling the catalyst particle size, preferably 2-5 mm, to increase dimethylamine selectivity. US5137854 discloses a mordenite catalyst treated with silicon tetrachloride. CN1618786A uses molecular sieves such as mordenite, modified with alkali metals, alkaline earth metals, rare earth metals, or phosphorus, achieving a dimethylamine selectivity of over 30% at a methanol conversion rate greater than 98%. CN1657167A discloses a silicon-modified catalyst on molecular sieves such as mordenite and HZSM-5, using various silicone oils and solvents, ultimately achieving a dimethylamine selectivity of over 50% and a methanol conversion rate of over 98%.

[0005] Currently, modification can improve the selectivity of dimethylamine to some extent, but there is no clear method to significantly reduce the selectivity of trimethylamine after catalyst modification. Summary of the Invention

[0006] The purpose of this invention is to overcome the problem of high trimethylamine selectivity in the reaction products during the synthesis of methylamine in the existing technology, and to provide a method for synthesizing methylamine that can reduce the selectivity of trimethylamine in the reaction products, reduce the content of trimethylamine in the products, and at the same time ensure a high methanol conversion rate.

[0007] To achieve the above objectives, 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;

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

[0009] Preferably, the acidity of the zeolite catalyst obtained by treatment with organic base 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, more preferably 0.2-0.8 mol / L.

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

[0012] The beneficial technical effects obtained through the above technical solution are as follows:

[0013] The methylamine synthesis method provided by this invention involves treating a zeolite catalyst with an organic base under a high-temperature hydrothermal reaction. This process specifically alters the acidic sites of the zeolite catalyst, reduces the acid content, inhibits the formation of trimethylamine during the methylamine synthesis process, and simultaneously ensures high reactivity. Detailed Implementation

[0014] The endpoints and any values ​​of the ranges disclosed herein 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 the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0015] 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 acidity of the zeolite catalyst obtained by treatment with organic base is 200-400 μmol·g. -1 .

[0017] In this invention, the inventors discovered through research that targeted modification of acidity properties and reduction of acidity can decrease the formation of trimethylamine. Further research revealed that treating the zeolite catalyst with an organic base weakens its acidity and inhibits the formation of trimethylamine, which not only improves the selectivity of the methylamine synthesis reaction but also ensures high reaction activity.

[0018] According to the present invention, preferably, the acidity of the zeolite catalyst obtained by treatment with organic base is 200-400 μmol·g. -1 For example, 200 μmol·g -1 210 μmol·g -1 220 μmol·g -1 240 μmol·g -1 260 μmol·g -1 280 μmol·g -1 300 μmol·g -1 320 μmol·g -1 340 μmol·g -1 360 μmol·g -1 380 μmol·g -1 400 μmol·g -1 And any range between any two values, preferably 210-380 μmol·g -1 This preferred embodiment is more conducive to further reducing the formation of trimethylamine while maintaining the activity of the zeolite catalyst.

[0019] In this invention, the acidity of the zeolite catalyst was determined by Fourier transform infrared spectroscopy using a Nicolet Nexus 4700 instrument. The sample was placed in a vacuum system and treated at 400°C for two hours, after which the sample background was measured. Next, pyridine was introduced, and adsorption was performed at 200°C for 10 minutes, followed by desorption for 40 minutes. Finally, infrared spectroscopy was used to determine the acidity.

[0020] In this invention, the acid content of the zeolite catalyst refers to the total acid content of the zeolite catalyst at 200°C.

[0021] In this invention, the acid content of the zeolite catalyst obtained by treatment with organic base is significantly reduced, which further inhibits the formation of trimethylamine in the methylamine synthesis reaction.

[0022] In this invention, preferably, the pore volume of the zeolite catalyst is 0.4-0.6 cm³. 3 ·g -1 The preferred size is 0.45-0.57cm. 3 ·g -1 A suitable pore structure facilitates the synthesis of methylamine.

[0023] In this invention, the pore volume of the zeolite catalyst is measured by performing a nitrogen adsorption-desorption experiment in a liquid nitrogen atmosphere at a relative pressure of 0.99. Before performing the nitrogen adsorption-desorption experiment, the zeolite catalyst also includes a pretreatment process of vacuuming and heating to remove impurities, with the heating temperature being 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, and more preferably selected from at least one of tetrapropylammonium hydroxide, tetramethylammonium hydroxide, tetraethylammonium hydroxide, N,N-diisopropylethylamine and tetrabutylammonium hydroxide.

[0025] In this invention, the preferred template-like organic base is selected for alkali treatment to avoid the destruction of the zeolite catalyst structure by using inorganic base, thus ensuring high reactivity while further reducing the formation of trimethylamine.

[0026] According to the present invention, preferably, the organic alkali treatment process includes: subjecting a mixture containing an organic alkali solution, zeolite powder, and optionally a surfactant to a hydrothermal reaction, and calcining the solid product obtained from the hydrothermal reaction to obtain a zeolite catalyst.

[0027] In this invention, the mixture is obtained by uniformly mixing an organic alkali solution, zeolite powder, and optional surfactant. There is no particular limitation on the mixing method. According to a preferred embodiment of the invention, the mixture can be stirred at room temperature until uniform. The stirring rate can be adjusted by those skilled in the art according to the mixing conditions.

[0028] In this invention, there are no particular limitations on the method of adding the organic alkali solution, zeolite powder, and optional surfactant; they can be added separately or together.

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

[0030] According to the present invention, preferably, the concentration of the organic base in the organic base solution is 0.1-2 mol / L, for example, 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L, 2 mol / L, and any range between any two values, preferably 0.2-0.8 mol / L. In this invention, controlling the concentration of the organic base in the organic base solution within an appropriate range is crucial. If the concentration is too high, the zeolite powder is over-treated, resulting in a decrease in methanol conversion; if the concentration is too low, the zeolite powder is under-treated, and the formation of trimethylamine cannot be effectively inhibited.

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

[0032] According to the present invention, preferably, based on 1g of zeolite powder, the amount of the organic alkali solution used 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 between any two values, preferably 5-18mL. The organic alkali solution is mixed with the zeolite powder according to the above liquid-solid ratio, and the alkali treatment yields a zeolite catalyst while reducing the trimethylamine content in the product, without destroying the crystallinity of the zeolite powder.

[0033] According to the present invention, preferably, the zeolite powder is selected from at least one of ZSM-5 molecular sieve, β molecular sieve, and mordenite. More preferably, it is selected from at least one of hydrogen-form ZSM-5 molecular sieve, hydrogen-form β molecular sieve, and hydrogen-form mordenite. By mixing the above-mentioned specific zeolite powder with an organic base and subjecting it to alkali treatment to obtain a zeolite catalyst, the formation of trimethylamine can be suppressed while ensuring high reactivity of the catalyst during the synthesis of methylamine.

[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, or 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 spectrometry.

[0035] In this invention, the source of the zeolite powder is not particularly limited; it can be commercially available or prepared using existing methods. The zeolite powder is prepared using existing methods, the specific methods of which are well known to those skilled in the art, and the obtained zeolite powder only needs to meet the above-mentioned parameter limitations. Treating the zeolite powder that meets the above parameter limitations with an organic alkali can effectively inhibit the formation of trimethylamine in the methylamine synthesis reaction.

[0036] According to the present invention, preferably, the conditions for 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, more 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 this invention, hydrothermal reaction is carried out under the above conditions, which can avoid excessively high hydrothermal reaction temperature and reaction time, which would lead to over-treatment and reduce the catalyst's reaction activity; if the temperature is too low or the hydrothermal reaction time is too short, the catalyst will not change much after treatment and the effect will not be obvious.

[0038] In this invention, the equipment for the hydrothermal reaction is not particularly limited, as long as it can realize the hydrothermal reaction. Preferably, the hydrothermal reaction is carried out in a hydrothermal reactor, and the product is removed after cooling after the hydrothermal reaction is completed.

[0039] The present invention also includes calcining the solid product obtained by hydrothermal reaction after filtration, washing, and drying. The present invention does not have any particular limitation on the conditions for filtration, washing, and drying. Those skilled in the art can make appropriate selections according to the specific circumstances, as long as the purpose of filtration, washing, and drying can be achieved.

[0040] In this invention, the calcination conditions include: a calcination temperature of 300-600℃, preferably 350-550℃; and a calcination time of 1-5 hours, preferably 2-3 hours. Calcination under these conditions can alter the acidic properties of the zeolite catalyst without damaging its structure, thus ensuring high reactivity in the methylamine synthesis reaction.

[0041] In this invention, the surfactant is not particularly limited, as long as it can improve the compatibility of two different substances. According to this 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 organic bases.

[0042] In this invention, the amount of surfactant added is not particularly limited, and those skilled in the art can make adaptive adjustments based on the treatment effect of the organic alkali. Preferably, based on a volume of 100 mL of organic alkali solution, the amount of surfactant added is 0.01-10 g, for example, 0.01 g, 0.05 g, 0.1 g, 0.2 g, 0.5 g, 1 g, 2 g, 3 g, 4 g, 5 g, 6 g, 7 g, 8 g, 9 g, 10 g, and any range between any two values, preferably 0.1-5 g. Adding the above surfactant in combination with the organic alkali solution can effectively reduce the acidity of the catalyst after organic alkali treatment and reduce the trimethylamine content in the product.

[0043] According to the present invention, preferably, the reaction conditions include: a reaction temperature of 300-400°C, more preferably 320-390°C; a reaction pressure of 0.5-5 MPa, more preferably 1-4 MPa; and a methanol gas hourly space velocity of 500-5000 h⁻¹. -1 Preferably 1000-4000h -1 The molar ratio of ammonia to methanol is 0.5-5, preferably 1-3. The zeolite catalyst obtained by treatment with an organic base reacts under the above conditions, ensuring high reactivity while suppressing the formation of trimethylamine. In this invention, the methanol conversion rate can be maintained at 96% or higher, more preferably 98% or higher.

[0044] In this invention, the methylamine synthesis products include monomethylamine, dimethylamine, and trimethylamine. The molar content of monomethylamine, dimethylamine, and trimethylamine is determined by analyzing the products through gas chromatography.

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

[0046] In this invention, the selectivity of monomethylamine, dimethylamine, and trimethylamine refers to the percentage of molar content of monomethylamine, dimethylamine, and trimethylamine in a methylamine-containing stream.

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

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

[0049] The organic alkali treatment process includes: subjecting a mixture containing an organic alkali solution, zeolite powder, and optional surfactant to a hydrothermal reaction, and calcining the solid product obtained from 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 1g of zeolite powder, the amount of organic alkali solution used is 3-20mL, preferably 5-18mL;

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

[0054] The reaction conditions for methanol and ammonia include: a reaction temperature of 320-390℃; a reaction pressure of 1-4 MPa; and a methanol gas hourly space velocity of 1000-4000 h⁻¹. -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 were determined by gas chromatography;

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

[0057] The methods for testing the acidity and pore volume of zeolite catalysts are described in the aforementioned instructions 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] Z-1 Molecular Sieve Preparation Example

[0059] 21.5g of sodium silicate nonahydrate, 0.2g of sodium hydroxide, and 5.7g of tetrapropylammonium bromide were dissolved in 100mL of deionized water to obtain a mixed solution. 2.5g of aluminum sulfate was weighed and dissolved in 50mL of deionized water to prepare an aluminum sulfate solution. The aluminum sulfate solution was added to the mixed solution with stirring. After uniform mixing, the mixture was transferred to a reaction vessel and crystallized at 170℃ for 48h. The solution was then removed, filtered, washed, and dried. After calcination at 550℃ for 4h, the solution was exchanged three times with 1mol / L ammonium chloride solution to obtain a hydrogen-form ZSM-5 molecular sieve with a silicon-aluminum molar ratio of SiO2 / Al2O3 of 10, which was designated as Z-1.

[0060] Z-2 Molecular Sieve Preparation Example

[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 with stirring. After uniform mixing, the mixture was transferred to a reaction vessel and crystallized at 170 °C for 48 h. The solution was then removed, filtered, washed, and dried. After calcination at 550 °C for 4 h, the solution was exchanged three times with 1 mol / L ammonium chloride solution to obtain a hydrogen-form ZSM-5 molecular sieve with a silicon-aluminum molar ratio of SiO2 / Al2O3 of 40, which was designated as Z-2.

[0062] Example 1

[0063] Prepare 100 mL of N,N-diisopropylethylamine solution with a concentration of 0.2 mol / L, 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 reactor and react hydrothermally at 180℃ for 48 h. After cooling, remove and filter, dry, and calcine at 500℃ for 3 h to obtain catalyst Z1-A.

[0064] Example 2

[0065] Prepare 100 mL of a 0.2 mol / L tetrapropylammonium hydroxide solution, 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 reactor and react hydrothermally at 170℃ for 30 h. After cooling, remove and filter, dry, and calcine at 500℃ for 3 h to obtain catalyst Z1-B.

[0066] Example 3

[0067] Prepare 100 mL of a tetramethylammonium hydroxide solution with a concentration of 1.1 mol / L, 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 reactor and hydrothermally react 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 0.2 mol / L tetrapropylammonium hydroxide solution, add 10 g of Z-1 molecular sieve, stir and mix evenly at room temperature, transfer to a hydrothermal reactor, and react hydrothermally at 170℃ for 30 h. After cooling, remove and filter, dry, and calcine at 500℃ for 3 h to obtain catalyst Z1-D.

[0070] Example 5

[0071] Prepare 100 mL of a 0.1 mol / L tetrabutylammonium hydroxide solution, 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 reactor and react hydrothermally at 140 °C for 10 h. After cooling, remove and filter, dry, and calcine at 500 °C for 3 h to obtain catalyst Z1-E.

[0072] Example 6

[0073] Prepare 100 mL of a tetraethylammonium hydroxide solution with a concentration of 0.6 mol / L, 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 reactor and hydrothermally react 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 tetraethylammonium hydroxide solution with a concentration of 0.1 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 reactor and hydrothermally react at 150 °C for 10 h. After cooling, take out the product, filter it, dry it, and calcine it at 500 °C for 3 h to obtain catalyst Z2-A.

[0076] Example 8

[0077] Prepare 100 mL of a 0.3 mol / L triethanolamine solution, add 0.2 g of cetyltrimethylammonium 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 reactor and react hydrothermally at 160℃ for 48 h. After cooling, remove and filter, dry, and calcine at 500℃ for 3 h to obtain catalyst Z2-B.

[0078] Example 9

[0079] Prepare 50 mL of a 0.3 mol / L tetrapropylammonium hydroxide solution, 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 reactor and hydrothermally react at 160 °C for 48 h. After cooling, remove and filter, dry, and calcine at 500 °C for 3 h to obtain catalyst Z2-C.

[0080] Example 10

[0081] Prepare 100 mL of a 0.3 mol / L tetrapropylammonium hydroxide solution, 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 reactor and hydrothermally react at 160 °C for 48 h. After cooling, remove and filter, dry, and calcine at 500 °C for 3 h to obtain catalyst Z2-D.

[0082] Example 11

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

[0084] Example 12

[0085] The organic base was treated according to the method of Example 10, except that the surfactant added was dodecyltrimethylammonium bromide, with a mass of 1g, 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 10g of ZSM-5 molecular sieve (NKF-5 Nanhua) was added, with a silicon-to-aluminum ratio of 120, to obtain catalyst Z3.

[0088] Example 14

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

[0090] Example 15

[0091] 45.75g of silica sol (40wt% SiO2), 0.3g of sodium hydroxide, and 17.6g of triethanolamine template agent 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 with stirring. After uniform mixing, the mixture was transferred to a reaction vessel and crystallized at 150℃ for 120h. After crystallization, the mixture was removed, filtered, washed, and dried. After calcination at 550℃ for 5h, the mixture was exchanged three times with 1mol / L ammonium chloride solution to obtain a hydrogen-form β-molecular sieve with a silicon-to-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 cetyltrimethylammonium bromide surfactant and stir to dissolve, then add 10 g of β molecular sieve and stir to mix evenly. Transfer to a hydrothermal reactor and react hydrothermally at 150 °C for 48 h. After cooling, remove, filter, dry, and calcine at 500 °C for 3 h to obtain catalyst BA.

[0093] Comparative Example 1

[0094] Z-1 molecular sieve was used as the zeolite catalyst, and no organic base treatment was performed.

[0095] Comparative Example 2

[0096] Z-2 molecular sieve was used as the zeolite catalyst, and no organic base treatment was performed.

[0097] Comparative Example 3

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

[0099] Test case

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

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

[0102] After the reaction stabilized for 0.5 h, the product was collected 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] As can be seen from the results in Table 1, when using the methylamine synthesis method provided by this invention, the zeolite catalyst treated with organic base is used for the methylamine synthesis reaction, and the selectivity of trimethylamine in the reaction product is significantly reduced. While ensuring the methanol conversion rate, the formation of trimethylamine is effectively suppressed.

[0106] When the catalysts of Comparative Examples 1 and 2, which were not treated with organic bases, were used in the methylamine synthesis reaction, their selectivity for monomethylamine was low, while their selectivity for trimethylamine was high, making it difficult for them to effectively inhibit the formation of trimethylamine. The catalyst of Comparative Example 3, which was treated with inorganic bases, not only failed to effectively inhibit the formation of trimethylamine, but also showed a significant decrease in methanol conversion.

[0107] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for synthesizing methylamine, characterized in that, The method includes reacting methanol and ammonia in the presence of a zeolite catalyst obtained by treatment with an organic base to generate a methylamine-containing stream; The acidity of the zeolite catalyst obtained by treatment with organic base is 260-340 μmol·g. -1 The zeolite powder is selected from at least one of ZSM-5 molecular sieve and β molecular sieve. The organic alkali treatment process includes: A mixture containing an organic alkaline solution, zeolite powder, and a surfactant is subjected to a hydrothermal reaction. The solid product obtained from the hydrothermal reaction is then calcined to obtain a zeolite catalyst. The concentration of the organic base in the organic base solution is 0.2-0.8 mol / L; The silicon-aluminum molar ratio (SiO2 / Al2O3) of the zeolite raw powder is 10-100; The conditions for the hydrothermal reaction include: The reaction temperature is 80-240℃; And / or, the reaction time is 20-150 hours.

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

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

4. The method according to claim 1, wherein, Based on 1g of zeolite powder, the amount of organic alkali solution used is 3-20mL.

5. The method according to claim 4, wherein, Based on 1g of zeolite powder, the amount of organic alkali solution used is 5-18mL.

6. The method according to claim 1, wherein, The conditions for the hydrothermal reaction include: The reaction temperature is 100-180℃.

7. The method according to claim 1, wherein, The surfactant is selected from at least one of hexadecyltrimethylammonium bromide, dodecyltrimethylammonium bromide, and dodecyltrimethylammonium chloride.

8. The method according to claim 1, wherein, The amount of surfactant added is 0.01-10g, based on a volume of 100mL of organic alkali solution.

9. The method according to claim 8, wherein, The amount of surfactant added is 0.1-5g, based on a volume of 100mL of organic alkali solution.

10. The method according to claim 1, wherein, The roasting conditions include: a roasting temperature of 300-600℃ and a roasting time of 1-5 hours.

11. The method according to claim 10, wherein, The roasting conditions include: a roasting temperature of 350-550℃ and a roasting time of 2-3 hours.

12. The method according to any one of claims 1-11, wherein, The conditions for the reaction 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. -1 The molar ratio of ammonia to methanol is 0.5-5.

13. The method according to any one of claims 1-11, wherein, In the methylamine-containing stream, the trimethylamine selectivity is no higher than 25%.

14. The method according to claim 13, wherein, In the methylamine-containing stream, the trimethylamine selectivity is no higher than 20%.

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