Method and system for synthesizing N-methylaniline and co-producing N, N-dimethylaniline by gas phase method

Abstract

The invention relates to a method and a system for synthesizing N-methylaniline and co-producing N, N-dimethylaniline by a gas phase method, and belongs to the technical field of chemical engineering. The system comprises a raw material gasification unit, a reaction unit, a separation and rectification unit and a hydrogen recovery unit which are connected through pipelines. The method comprises the following steps of: firstly, mainly synthesizing N-methylaniline from raw materials aniline and part of methanol in a first-methylaniline reactor, then partially or completely feeding first-methylaniline reaction gas into a second-methylaniline reactor, adding methanol steam, and further reacting to generate N, N-dimethylaniline. And after the product gas is subjected to heat exchange energy recovery, a liquid phase and a gas phase respectively enter the separation and rectification unit and the hydrogen recovery unit. The purification of N-methylaniline and N, N-dimethylaniline and the recovery of byproduct hydrogen are realized. The yield of N, N-dimethylaniline (in terms of aniline) can be adjusted in a range of 5-30% by adjusting reaction conditions and a feeding ratio.

Description

Technical Field

[0001] The present invention belongs to the technical field of chemical alkylation reactions, and specifically relates to a method and system for synthesizing N-methylaniline and co-producing N,N-dimethylaniline by a gas-phase method. Background Art

[0002] N-methylaniline is a fine chemical product with wide applications, mainly used in the production of pesticides, dyes, dye intermediates, rubber additives, and explosives stabilizers, and can also be used as a solvent and acid acceptor, serving as an environmentally friendly intermediate for organic synthesis, acid absorbent, and solvent. N,N-dimethylaniline is the main raw material for the anti-inflammatory analgesic "mefenamic acid", and can also be used as an intermediate raw material for dyes, pesticides, and other chemical products. It is used in the production of vanillin, azo dyes, triphenylmethane dyes, and can also be used as a solvent, stabilizer, analytical reagent, etc. Both N-methylaniline and N,N-dimethylaniline are important dyes and dye intermediates. However, in the market competition, there are price fluctuations and a certain degree of market demand that rises and falls reciprocally.

[0003] Whether it is N-methylaniline or N,N-dimethylaniline, the synthesis methods are mainly two methods: liquid-phase kettle reaction and gas-phase fixed-bed reaction. The liquid-phase method mainly uses strong acids as catalysts, which can cause equipment corrosion, and adopts batch production, with a general automation level of the device. The current main synthesis process is the gas-phase method. Different solid catalysts are used, and methanol is used as the alkylating agent to synthesize N-methylaniline and N,N-dimethylaniline respectively under gas-phase conditions in a fixed-bed reactor. Since the reaction raw materials for the two are highly consistent and the reaction conditions are extremely close, in order to achieve a single set of devices, diverse products, meet market demands, and increase the enterprise's anti-risk ability, it is necessary to develop a co-production technology.

[0004] In the existing patented technologies, Patent 202410095002.7 discloses a method for synthesizing N-methylaniline and N,N-dimethylaniline using a copper silicate catalyst. In this method, the selective regulation range of N-methylaniline and N,N-dimethylaniline is not large, and the reaction requires the addition of carrier gases such as nitrogen, resulting in an increase in raw material costs and separation costs. In addition, to achieve a high aniline conversion rate, a very high methanol-aniline molar ratio is required, resulting in an increase in subsequent separation costs. Therefore, providing a process for co-producing N-methylaniline and N,N-dimethylaniline, realizing continuous and stable operation, maximizing energy utilization, and achieving a high single-pass conversion rate and selectivity of aniline has become an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0005] The object of the present invention is to provide a method for synthesizing N-methylaniline by gas phase method with co-production of N,N-dimethylaniline, which can achieve continuous and stable operation, a relatively high single-pass conversion rate of aniline, and adjustable selectivities of N-methylaniline and N,N-dimethylaniline within a certain range. By adjusting the reaction conditions and feed ratios, the yield of N,N-dimethylaniline (calculated based on aniline) can be adjusted within the range of 5-30%.

[0006] The second object of the present invention is to provide a system for synthesizing N-methylaniline by gas phase method with co-production of N,N-dimethylaniline. The system has a simple structure and reasonable design, and can achieve the purification of N-methylaniline and N,N-dimethylaniline and the recovery of by-product hydrogen.

[0007] To achieve the above objects, the technical solutions adopted by the present invention are as follows:

[0008] A method and system for synthesizing N-methylaniline by gas phase method with co-production of N,N-dimethylaniline. The system includes a raw material gasification unit, a reaction unit, a separation and rectification unit, and a hydrogen recovery unit connected in sequence through pipelines.

[0009] Further, the raw material gasification unit includes an aniline storage tank, an aniline delivery pump, an aniline preheater, an aniline vaporization and superheater, a methanol storage tank, a methanol delivery pump, a methanol preheater, and a methanol vaporization and superheater;

[0010] The aniline storage tank is connected to the aniline delivery pump, and then to the tube side of the aniline preheater. The other end of the tube side of the aniline preheater is connected to the tube side of the aniline vaporization and superheater, and the other end of the tube side of the aniline vaporization and superheater is connected to the aniline flowmeter F21 in the reaction unit.

[0011] The methanol storage tank is connected to the methanol delivery pump, and then to the tube side of the methanol preheater. The other end of the tube side of the methanol preheater is connected to the tube side of the methanol vaporization and superheater, and the other end of the tube side of the methanol vaporization and superheater is respectively connected to the mono-methyl reaction methanol flowmeter F22 and the di-methyl reaction methanol flowmeter F23 in the reaction unit.

[0012] Further, the reaction unit includes an aniline flowmeter F21, a mono-methyl reaction methanol flowmeter F22, a di-methyl reaction methanol flowmeter F23, a di-methyl reaction flowmeter F24, a di-methyl reaction methanol flow regulating valve V21, a mono-methyl reaction gas shunt valve V22, a di-methyl reaction gas control valve V23, a di-methyl reaction gas on-off valve V24, a mono-methyl reactor, a di-methyl reactor, a first mixer, and a second mixer.

[0013] Further, the tube passes of the mono-methyl reactor and the di-methyl reactor are filled with an alkylation catalyst produced by Southwest Research and Design Institute of Chemical Industry Co., Ltd.

[0014] One end of the aniline flowmeter F21 is connected to the raw material gasification unit, and the other end is connected to the first mixer; one end of the monomethyl reaction methanol flowmeter F22 is connected to the raw material gasification unit, and the other end is connected to the first mixer. The ratio of aniline to methanol is controlled and enters the first mixer, and the first mixer is connected to the top inlet of the monomethyl reactor. The bottom outlet of the monomethyl reactor is respectively connected to the monomethyl reaction gas shunt valve V22 and the dimethyl reaction flowmeter F24, and the other end of the dimethyl reaction flowmeter F24 is connected to the dimethyl reaction gas control valve V23.

[0015] One end of the dimethyl reaction methanol flowmeter F23 is connected to the methanol gasification and superheater of the raw material gasification unit, and the other end is connected to the dimethyl reaction methanol flow regulating valve V21. The dimethyl reaction methanol flow regulating valve V21 and the dimethyl reaction gas control valve V23 are connected to the second mixer, and the other end of the second mixer is connected to the top inlet of the dimethyl reactor. The bottom outlet of the dimethyl reactor is connected to the dimethyl reaction gas on-off valve V24.

[0016] After the dimethyl reaction gas on-off valve V24 is connected to the monomethyl reaction gas shunt valve V22, it is then connected to the shell side of the aniline preheater of the raw material gasification unit. The other end of the shell side of the aniline preheater is connected to the shell side of the methanol preheater, and the other end of the shell side of the methanol preheater is connected to the gas-liquid separator of the separation and rectification unit.

[0017] Furthermore, the separation and rectification unit includes a gas-liquid separator, a rectification pump, and a rectification column;

[0018] The gas-liquid separator, the rectification pump, and the rectification column are sequentially connected by pipelines for sending the liquid phase in the gas-liquid separator into the rectification column for rectification. The rectification column is connected with a light component extraction pipeline, an N,N-dimethylaniline extraction pipeline, an N-methylaniline extraction pipeline, and a heavy component extraction pipeline.

[0019] The gas phase in the gas-liquid separator is sent to the hydrogen recovery unit.

[0020] Furthermore, the hydrogen recovery unit includes a cryogenic cooler, a compressor, a drying tower, and a pressure swing adsorption tower.

[0021] The inlet of the cryogenic cooler is connected to the gas phase port of the gas-liquid separator through a pipeline, the outlet is connected to the inlet of the compressor through a pipeline, the outlet of the compressor is connected to the inlet of the drying tower, and the outlet of the drying tower is connected to the inlet of the pressure swing adsorption tower.

[0022] The pressure swing adsorption tower is connected with a by-product hydrogen extraction pipeline and a tail gas pipeline.

[0023] Another object of the present invention is to protect a method for synthesizing N-methylaniline by gas phase method with co-production of N,N-dimethylaniline, which is carried out by using the above system.

[0024] In some embodiments of the present invention, in the synthesis process, methanol and aniline are used as raw materials, and an alkylation reaction occurs under the action of an alkylation catalyst produced by Southwest Research and Design Institute of Chemical Industry Co., Ltd., successively generating N-methylaniline and N,N-dimethylaniline. The process method includes the following steps:

[0025] S1. The methanol transfer pump sends the raw material methanol in the methanol storage tank to the methanol preheater, methanol vaporizer and superheater for preheating, vaporization and superheating. After that, the methanol vapor flows to the monomethyl reaction methanol flowmeter F22 and the dimethyl reaction methanol flowmeter F23 respectively.

[0026] S2. The aniline transfer pump sends the raw material aniline in the aniline storage tank to the aniline preheater, aniline vaporizer and superheater for preheating, vaporization and superheating. After the aniline vapor is metered by the aniline flowmeter F21, it flows into the first mixer in proportion to the methanol vapor metered by the monomethyl reaction methanol flowmeter F22, and then flows into the monomethyl reactor to synthesize N-methylaniline.

[0027] S3. Part or all of the monomethyl reaction gas flowing out of the monomethyl reactor is metered by the dimethyl reaction flowmeter F24, and then flows into the second mixer in proportion to the methanol vapor metered by the dimethyl reaction methanol flowmeter F23, and then enters the dimethyl reactor to synthesize N,N-dimethylaniline.

[0028] S4. The heat generated in the monomethyl reactor and the dimethyl reactor is removed by the heat transfer oil, and the reaction temperature is regulated by it.

[0029] S5. After the reaction gas flowing out of the monomethyl reactor is mixed with the reaction gas flowing out of the dimethyl reactor, it preheats the raw material aniline and the raw material methanol in turn, and then enters the gas-liquid separator. Its liquid phase is sent to the distillation column by the distillation pump for product refining; the gas phase is first cooled by the cryogenic cooler, then processed by the drying tower, sent to the compressor for pressurization, and then the by-product hydrogen is recovered by the pressure swing adsorption tower.

[0030] S5. After the reaction gas flowing out of the monomethyl reactor is mixed with the reaction gas flowing out of the dimethyl reactor, it preheats the raw material aniline and the raw material methanol in turn, and then enters the gas-liquid separator. Its liquid phase is refined by the separation and distillation unit; the gas phase is recycled by the hydrogen recovery unit to recover the by-product hydrogen.

[0031] Furthermore, in some embodiments of the present invention:

[0032] (1) In the N-methylaniline synthesis reaction occurring in the monomethyl reactor, the feed molar ratio of raw material methanol to aniline is 1-3:1, the reaction temperature is 190-320 °C, and the reaction pressure is 0.1 MPaA-0.6 MPaA.

[0033] (2) The feed mass ratio of methanol to the mono-methylamine reaction gas for the N,N-dimethylaniline synthesis reaction occurring in the dimethyl reactor (22) is 0 to 1:1, preferably 0.5 to 0.75:1, the reaction temperature is 200 to 330 °C, and the reaction pressure is 0.1 MPaA to 0.6 MPaA.

[0034] Further, in some embodiments of the present invention, the process method further includes a separation and rectification unit. The liquid-phase product in the gas-liquid separator is sent to the rectification of the rectification column by a rectification pump, and the light and heavy components are separated according to the boiling point to obtain two products, N-methylaniline and N,N-dimethylaniline.

[0035] Further, in some embodiments of the present invention, the process method further includes a hydrogen recovery unit. The gas phase in the gas-liquid separator is first cooled by a cryogenic cooler, then pressurized by a compressor and dehydrated by a drying tower, and the by-product hydrogen is recovered by a pressure swing adsorption tower.

[0036] The present invention can realize the co-production of N-methylaniline and N,N-dimethylaniline, thus realizing product diversification.

[0037] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0038] (1) The present invention uses methanol and aniline as raw materials, and the process characteristics of synthesizing N-methylaniline and N,N-dimethylaniline realize a single set of devices and diversified products, which helps enterprises improve their ability to resist market risks.

[0039] (2) The present invention realizes the continuous operation of co-producing N-methylaniline and N,N-dimethylaniline and optimizes the utilization of heat.

[0040] (3) The present invention realizes the recovery of hydrogen in the gas phase, which helps to improve the comprehensive benefits.

[0041] (4) The present invention can preferably realize continuous and stable operation, a relatively high single-pass conversion rate of aniline, and adjustable selectivities of N-methylaniline and N,N-dimethylaniline within a certain range. By adjusting the reaction conditions and feed ratio, the yield of N,N-dimethylaniline (calculated based on aniline) can be adjusted within the range of 5 to 30%. Description of the Drawings

[0042] Figure 1 It is a schematic structural diagram of a method and system for synthesizing N-methylaniline and co-producing N,N-dimethylaniline by a gas-phase method according to the present invention.

[0043] In the figure, 11 - aniline storage tank, 12 - aniline transfer pump, 13 - aniline preheater, 14 - aniline vaporization and superheater, 15 - methanol storage tank, 16 - methanol transfer pump, 17 - methanol preheater, 18 - methanol gasification and superheater, 21 - monomethyl reactor, 22 - dimethyl reactor, 23 - first mixer, 24 - second mixer, 31 - gas - liquid separator, 32 - rectification pump, 33 - rectification column, 41 - cryogenic cooler, 42 - compressor, 43 - drying tower, 44 - pressure swing adsorption tower;

[0044] Aniline flowmeter F21, monomethyl reaction methanol flowmeter F22, dimethyl reaction methanol flowmeter F23, dimethyl reaction flowmeter F24, dimethyl reaction methanol flow regulating valve V21, monomethyl reaction gas shunt valve V22, dimethyl reaction gas control valve V23, dimethyl reaction gas on - off valve V24;

[0045] 301 - light component extraction pipeline, 302 - N, N - dimethylaniline extraction pipeline, 303 - N - methylaniline extraction pipeline, 304 - heavy component extraction pipeline, 401 - by - product hydrogen extraction pipeline, 402 - tail gas pipeline. Detailed implementation mode

[0046] As Figure 1 shown, this embodiment discloses a system for synthesizing N - methylaniline and co - producing N, N - dimethylaniline by gas - phase method, which includes a raw material gasification unit, a reaction unit, a separation and rectification unit, and a hydrogen recovery unit connected by pipelines.

[0047] Furthermore, the raw material gasification unit includes an aniline storage tank, an aniline transfer pump, an aniline preheater, an aniline vaporization and superheater, a methanol storage tank, a methanol transfer pump, a methanol preheater, and a methanol gasification and superheater;

[0048] The aniline storage tank is connected to the aniline transfer pump, and then to the tube side of the aniline preheater. The other end of the tube side of the aniline preheater is connected to the tube side of the aniline vaporization and superheater, and the other end of the tube side of the aniline vaporization and superheater is connected to the aniline flowmeter F21 in the reaction unit.

[0049] The methanol storage tank is connected to the methanol transfer pump, and then to the tube side of the methanol preheater. The other end of the tube side of the methanol preheater is connected to the tube side of the methanol vaporization and superheater, and the other end of the tube side of the methanol vaporization and superheater is respectively connected to the monomethyl reaction methanol flowmeter F22 and the dimethyl reaction methanol flowmeter F23 in the reaction unit.

[0050] Further, the reaction unit includes a monomethylamine reactor, a dimethylamine reactor, a first mixer, a second mixer, an aniline flowmeter F21, a methanol flowmeter F22 for monomethylamine reaction, a methanol flowmeter F23 for dimethylamine reaction, a flowmeter F24 for dimethylamine reaction, a methanol flow control valve V21 for dimethylamine reaction, a gas shunt valve V22 for monomethylamine reaction gas, a control valve V23 for dimethylamine reaction gas, and a shut-off valve V24 for dimethylamine reaction gas. The tube sides of the monomethylamine reactor and the dimethylamine reactor are both filled with an alkylation catalyst produced by Southwest Research and Design Institute of Chemical Industry Co., Ltd.

[0051] One end of the aniline flowmeter F21 is connected to the raw material gasification unit, and the other end is connected to the first mixer; one end of the methanol flowmeter F22 for monomethylamine reaction is connected to the raw material gasification unit, and the other end is connected to the first mixer. The ratio of aniline to methanol is controlled and enters the first mixer, which is connected to the top inlet of the monomethylamine reactor. The bottom outlet of the monomethylamine reactor is respectively connected to the gas shunt valve V22 for monomethylamine reaction gas and the flowmeter F24 for dimethylamine reaction, and the other end of the flowmeter F24 for dimethylamine reaction is connected to the control valve V23 for dimethylamine reaction gas.

[0052] One end of the methanol flowmeter F23 for dimethylamine reaction is connected to the methanol gasification and superheater of the raw material gasification unit, and the other end is connected to the methanol flow control valve V21 for dimethylamine reaction. The methanol flow control valve V21 for dimethylamine reaction and the control valve V23 for dimethylamine reaction gas are connected to the second mixer, and the other end of the second mixer is connected to the top inlet of the dimethylamine reactor. The bottom outlet of the dimethylamine reactor is connected to the shut-off valve V24 for dimethylamine reaction gas.

[0053] After the shut-off valve V24 for dimethylamine reaction gas is connected to the gas shunt valve V22 for monomethylamine reaction gas, it is then connected to the shell side of the aniline preheater of the raw material gasification unit. The other end of the shell side of the aniline preheater is connected to the shell side of the methanol preheater, and the other end of the shell side of the methanol preheater is connected to the gas-liquid separator of the separation and rectification unit.

[0054] Further, the separation and rectification unit includes a gas-liquid separator, a rectification pump, and a rectification column;

[0055] The gas-liquid separator, the rectification pump, and the rectification column are connected in sequence through pipelines to send the liquid phase in the gas-liquid separator into the rectification column for rectification. The rectification column is connected with a light component extraction pipeline, an N,N-dimethylaniline extraction pipeline, an N-methylaniline extraction pipeline, and a heavy component extraction pipeline.

[0056] The gas phase in the gas-liquid separator is sent to the hydrogen recovery unit.

[0057] Further, the hydrogen recovery unit includes a cryogenic cooler, a compressor, a drying tower, and a pressure swing adsorption tower.

[0058] The inlet of the cryogenic cooler is connected to the gas-phase port of the gas-liquid separator through a pipeline, the outlet is connected to the inlet of the compressor through a pipeline, the outlet of the compressor is connected to the inlet of the drying tower, and the outlet of the drying tower is connected to the inlet of the pressure swing adsorption tower.

[0059] A by-product hydrogen extraction pipeline and a tail gas pipeline are connected to the pressure swing adsorption tower.

[0060] A method for synthesizing N-methylaniline by gas phase method with co-production of N,N-dimethylaniline disclosed in the present invention is carried out by using the above system.

[0061] In some embodiments of the present invention, the synthesis process uses methanol and aniline as raw materials, and under the action of an alkylation catalyst of Southwest Research and Design Institute of Chemical Industry Co., Ltd., an alkylation reaction occurs to successively produce N-methylaniline and N,N-dimethylaniline. The process includes the following steps:

[0062] S1. The methanol transfer pump sends the raw material methanol in the methanol storage tank to the methanol preheater, methanol vaporization and superheater for preheating, vaporization and superheating. After that, the methanol vapor flows to the monomethyl reaction methanol flowmeter F22 and the dimethyl reaction methanol flowmeter F23 respectively.

[0063] S2. The aniline transfer pump sends the raw material aniline in the aniline storage tank to the aniline preheater, aniline vaporization and superheater for preheating, vaporization and superheating. After that, the aniline vapor is metered by the aniline flowmeter F21 and then flows into the first mixer in proportion with the methanol vapor metered by the monomethyl reaction methanol flowmeter F22, and then flows into the monomethyl reactor to synthesize N-methylaniline.

[0064] S3. Part or all of the monomethyl reaction gas flowing out of the monomethyl reactor is metered by the dimethyl reaction flowmeter F24 and then flows into the second mixer in proportion with the methanol vapor metered by the dimethyl reaction methanol flowmeter F23, and then enters the dimethyl reactor to synthesize N,N-dimethylaniline.

[0065] S4. The heat generated in the monomethyl reactor and the dimethyl reactor is removed by the heat transfer oil, and the reaction temperature is regulated by it.

[0066] S5. After the reaction gas flowing out of the monomethyl reactor is mixed with the reaction gas flowing out of the dimethyl reactor, it preheats the raw material aniline and the raw material methanol in turn, and then enters the gas-liquid separator. Its liquid phase is sent to the distillation column by the distillation pump for product purification; the gas phase is first cooled by the cryogenic cooler, then pressurized by the compressor, sent to the drying tower for treatment, and then the by-product hydrogen is recovered by the pressure swing adsorption tower.

[0067] S5. After the reaction gas flowing out of the monomethyl reactor is mixed with the reaction gas flowing out of the dimethyl reactor, it preheats the raw material aniline and the raw material methanol in turn, and then enters the gas-liquid separator. Its liquid phase is refined by the separation and distillation unit to realize product purification; the gas phase is recycled by the hydrogen recovery unit to realize the recovery of by-product hydrogen.

[0068] In the solution implemented by the present invention, (1) in the mono-methyl aniline reactor, for the synthesis reaction of N-methyl aniline, the feed molar ratio of raw material methanol to aniline is 1-3:1, the reaction temperature is 190-320 °C, and the reaction pressure is 0.1 MPaA-0.6 MPaA. (2) In the dimethyl aniline reactor, for the synthesis reaction of N,N-dimethyl aniline, the feed mass ratio of raw material methanol to the mono-methyl reaction gas is 0-1:1, preferably 0.5-0.75:1, the reaction temperature is 200-330 °C, and the reaction pressure is 0.1 MPaA-0.6 MPaA.

[0069] In the solution implemented by the present invention, it further includes a separation and rectification step. The liquid-phase product in the gas-liquid separator is sent to the rectification column for purification by a rectification pump, and the light and heavy components are separated according to the boiling point to obtain two products of N-methyl aniline and N,N-dimethyl aniline.

[0070] In the solution implemented by the present invention, it further includes a hydrogen recovery step. The gas phase in the gas-liquid separator is first cooled by a cryogenic cooler, then pressurized by a compressor and dehydrated by a drying tower, and then the by-product hydrogen is recovered by a pressure swing adsorption tower.

[0071] To make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with specific embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. For those not specified in the embodiments, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. For reagents or instruments not specified in the manufacturer, they are all conventional products that can be obtained through commercial purchase. For example, the tube sides of the mono-methyl aniline reactor and the dimethyl aniline reactor are both filled with alkylation catalysts (commercially available products) produced by Southwest Research and Design Institute of Chemical Industry Co., Ltd.

[0072] The examples of the embodiments are shown in the drawings, where the same or similar reference numerals represent the same or similar elements or elements with the same or similar functions from beginning to end. The embodiments described below with reference to the drawings are exemplary and are intended to explain the present invention, and should not be construed as a limitation of the present invention.

[0073] Example 1:

[0074] As Figure 1 shown, a method and system for synthesizing N-methyl aniline and co-producing N,N-dimethyl aniline by gas phase method, taking the production capacity of 10,000 tons / year of N-methyl aniline and co-producing N,N-dimethyl aniline as an example, its structure description is shown in the specific implementation manner; the specific process steps are as follows:

[0075] The raw material aniline is heated, vaporized, and superheated to 230°C, and the value of aniline flowmeter F21 is 1200 kg / h; the raw material methanol is heated, vaporized, and superheated to 230°C, and the value of methanol flowmeter F22 for the first methylation reaction is 825 kg / h. After the aniline and methanol vapors are mixed, they enter the first methylation reactor, and under the action of an alkylation catalyst, N-methylaniline is mainly produced. The reaction pressure is controlled at 0.2 MPaA, and the reaction temperature is controlled at 235°C through heat transfer oil.

[0076] The value of methanol flowmeter F23 for the second methylation reaction is 620 kg / h, and the value of flowmeter F24 for the second methylation reaction is 1012.5 kg / h. After the two are mixed, they enter the second methylation reactor, and under the action of an alkylation catalyst, N,N-dimethylaniline is mainly produced. The reaction pressure is controlled at 0.15 MPaA, and the reaction temperature is controlled at 245°C through heat transfer oil.

[0077] After the reaction gas recovers heat, its temperature is reduced to 70°C. The liquid phase is sent to distillation to obtain 1150 kg / h of N-methylaniline product and 210 kg / h of N,N-dimethylaniline product; the gas phase is sent to the hydrogen recovery unit, and the recoverable hydrogen volume is about 335 Nm 3 / h.

[0078] Example 2:

[0079] As Figure 1 shown, a system for synthesizing N-methylaniline and co-producing N,N-dimethylaniline by gas phase method, taking the production capacity of 10,000 tons / year of N-methylaniline and co-producing N,N-dimethylaniline as an example, its structure description is shown in the specific implementation manner; the specific process steps are as follows:

[0080] The raw material aniline is heated, vaporized, and superheated to 230°C, and the value of aniline flowmeter F21 is 1200 kg / h; the raw material methanol is heated, vaporized, and superheated to 230°C, and the value of methanol flowmeter F22 for the first methylation reaction is 825 kg / h. After the aniline and methanol vapors are mixed, they enter the first methylation reactor, and under the action of an alkylation catalyst, N-methylaniline is mainly produced. The reaction pressure is controlled at 0.3 MPaA, and the reaction temperature is controlled at 235°C through heat transfer oil.

[0081] The value of methanol flowmeter F23 for the second methylation reaction is 620 kg / h, and the value of flowmeter F24 for the second methylation reaction is 1012.5 kg / h. After the two are mixed, they enter the second methylation reactor, and under the action of an alkylation catalyst, N,N-dimethylaniline is mainly produced. The reaction pressure is controlled at 0.25 MPaA, and the reaction temperature is controlled at 245°C through heat transfer oil.

[0082] After the reaction gas recovers heat, its temperature drops to 70°C. The liquid phase is sent to distillation to obtain 1,090 kg / h of N-methylaniline product and 280 kg / h of N,N-dimethylaniline. The gas phase is sent to the hydrogen recovery unit, and the recoverable hydrogen volume is approximately 305 Nm 3 / h.

[0083] Example 3:

[0084] As Figure 1 shown, a method and system for synthesizing N-methylaniline and co-producing N,N-dimethylaniline by gas phase method. Taking the production capacity of 10,000 tons / year of N-methylaniline and co-producing N,N-dimethylaniline as an example, its structural description is shown in the specific implementation manner. The specific process steps are as follows:

[0085] The raw material aniline is heated, vaporized and superheated to 230°C, and the value of the aniline flowmeter F21 is 1,200 kg / h. The raw material methanol is heated, vaporized and superheated to 230°C, and the value of the methanol flowmeter F22 for the first methylation reaction is 825 kg / h. After the aniline and methanol vapor are mixed, they enter the first methylation reactor. Under the action of the alkylation catalyst, N-methylaniline is mainly produced. The reaction pressure is controlled at 0.4 MPaA, and the reaction temperature is controlled at 235°C through heat transfer oil.

[0086] The value of the methanol flowmeter F23 for the second methylation reaction is 620 kg / h, and the value of the flowmeter F24 for the second methylation reaction is 1,012.5 kg / h. After the two are mixed, they enter the second methylation reactor. Under the action of the alkylation catalyst, N,N-dimethylaniline is mainly produced. The reaction pressure is controlled at 0.35 MPaA, and the reaction temperature is controlled at 245°C through heat transfer oil.

[0087] After the reaction gas recovers heat, its temperature drops to 70°C. The liquid phase is sent to distillation to obtain 1,050 kg / h of N-methylaniline product and 320 kg / h of N,N-dimethylaniline. The gas phase is sent to the hydrogen recovery unit, and the recoverable hydrogen volume is approximately 290 Nm 3 / h.

[0088] Example 4:

[0089] As Figure 1 shown, a method and system for synthesizing N-methylaniline and co-producing N,N-dimethylaniline by gas phase method. Taking the production capacity of 10,000 tons / year of N-methylaniline and co-producing N,N-dimethylaniline as an example, its structural description is shown in the specific implementation manner. The specific process steps are as follows:

[0090] The raw material aniline is heated, vaporized, and superheated to 230°C, and the value of the aniline flowmeter F21 is 1200 kg / h; the raw material methanol is heated, vaporized, and superheated to 230°C, and the value of the methanol flowmeter F22 for the first methylation reaction is 825 kg / h. After the aniline and methanol vapors are mixed, they enter the first methylation reactor, and under the action of an alkylation catalyst, N-methylaniline is mainly produced. The reaction pressure is controlled at 0.3 MPaA, and the reaction temperature is controlled at 235°C through heat transfer oil.

[0091] The value of the methanol flowmeter F23 for the second methylation reaction is 310 kg / h, and the value of the flowmeter F24 for the second methylation reaction is 506.25 kg / h. After the two are mixed, they enter the second methylation reactor, and under the action of an alkylation catalyst, N,N-dimethylaniline is mainly produced. The reaction pressure is controlled at 0.25 MPaA, and the reaction temperature is controlled at 245°C through heat transfer oil.

[0092] After the reaction gas recovers heat, its temperature is reduced to 70°C. The liquid phase is sent to distillation to obtain 1155 kg / h of N-methylaniline product and 200 kg / h of N,N-dimethylaniline; the gas phase is sent to the hydrogen recovery unit, and the recoverable hydrogen volume is approximately 280 Nm 3 / h.

[0093] Example 5:

[0094] As Figure 1 shown, a method and system for synthesizing N-methylaniline and co-producing N,N-dimethylaniline by gas phase method, taking the production capacity of 10,000 tons / year of N-methylaniline and co-producing N,N-dimethylaniline as an example, its structure description is shown in the specific implementation manner; the specific process steps are as follows:

[0095] The raw material aniline is heated, vaporized, and superheated to 230°C, and the value of the aniline flowmeter F21 is 1200 kg / h; the raw material methanol is heated, vaporized, and superheated to 230°C, and the value of the methanol flowmeter F22 for the first methylation reaction is 825 kg / h. After the aniline and methanol vapors are mixed, they enter the first methylation reactor, and under the action of an alkylation catalyst, N-methylaniline is mainly produced. The reaction pressure is controlled at 0.3 MPaA, and the reaction temperature is controlled at 235°C through heat transfer oil.

[0096] The value of the methanol flowmeter F23 for the second methylation reaction is 930 kg / h, and the value of the flowmeter F24 for the second methylation reaction is 1518.75 kg / h. After the two are mixed, they enter the second methylation reactor, and under the action of an alkylation catalyst, N,N-dimethylaniline is mainly produced. The reaction pressure is controlled at 0.25 MPaA, and the reaction temperature is controlled at 245°C through heat transfer oil.

[0097] After the reaction gas recovers heat, its temperature drops to 70°C. The liquid phase is sent to distillation to obtain 1020 kg / h of N-methylaniline product and 350 kg / h of N,N-dimethylaniline; the gas phase is sent to the hydrogen recovery unit, and the recoverable hydrogen volume is about 328 Nm 3 / h.

[0098] Comparative Example 1:

[0099] As Figure 1 shown, a method and system for synthesizing N-methylaniline and co-producing N,N-dimethylaniline by gas phase method. Taking the production capacity of 10,000 tons / year of N-methylaniline and co-producing N,N-dimethylaniline as an example, its structural description is shown in the specific implementation manner; the specific process steps are as follows:

[0100] The raw material aniline is heated, vaporized and superheated to 230°C, and the value of aniline flowmeter F21 is 1200 kg / h; the raw material methanol is heated, vaporized and superheated to 230°C, and the value of monomethyl reaction methanol flowmeter F22 is 825 kg / h. After the aniline and methanol vapor are mixed, they enter the monomethyl reactor. Under the action of an alkylation catalyst, N-methylaniline is mainly produced. The reaction pressure is controlled at 0.3 MPaA, and the reaction temperature is controlled at 235°C through heat transfer oil.

[0101] The methanol vapor does not pass through the dimethyl reaction methanol flowmeter F23 to the dimethyl reactor, and the monomethyl reaction gas does not enter the dimethyl reactor either. Instead, it directly goes to heat exchange and separation. After the reaction gas recovers heat, its temperature drops to 70°C. The liquid phase is sent to distillation to obtain 1250 kg / h of N-methylaniline product and 100 kg / h of N,N-dimethylaniline; the gas phase is sent to the hydrogen recovery unit, and the recoverable hydrogen volume is about 250 Nm 3 / h.

[0102] Comparative Example 2:

[0103] As Figure 1 shown, a method and system for synthesizing N-methylaniline and co-producing N,N-dimethylaniline by gas phase method. Taking the production capacity of 10,000 tons / year of N-methylaniline and co-producing N,N-dimethylaniline as an example, its structural description is shown in the specific implementation manner; the specific process steps are as follows:

[0104] The raw material aniline is heated, vaporized and superheated to 230°C, and the value of aniline flowmeter F21 is 1200 kg / h; the raw material methanol is heated, vaporized and superheated to 230°C, and the value of monomethyl reaction methanol flowmeter F22 is 825 kg / h. After the aniline and methanol vapor are mixed, they enter the monomethyl reactor. Under the action of an alkylation catalyst, N-methylaniline is mainly produced. The reaction pressure is controlled at 0.3 MPaA, and the reaction temperature is controlled at 235°C through heat transfer oil.

[0105] The F23 value of the methanol flowmeter in the dimethyl reaction is 1,240 kg / h, and the F24 value of the dimethyl reaction flowmeter is 2,025 kg / h. After the two are mixed, they enter the dimethyl reactor and further react to produce N,N-dimethylaniline under the action of an alkylation catalyst. The reaction pressure is controlled at 0.25 MPaA, and the reaction temperature is controlled at 245 °C through heat transfer oil.

[0106] After the reaction gas recovers heat, its temperature drops to 70 °C. The liquid phase is sent to distillation to obtain 960 kg / h of N-methylaniline product and 410 kg / h of N,N-dimethylaniline; the liquid phase is sent to the hydrogen recovery unit, and the recoverable hydrogen volume is approximately 350 Nm 3 / h.

[0107] Comparative Example 3:

[0108] As Figure 1 shown, a method and system for synthesizing N-methylaniline and co-producing N,N-dimethylaniline by gas phase method, taking the production capacity of 10,000 tons / year of N-methylaniline and co-producing N,N-dimethylaniline as an example, its structure description is shown in the specific implementation manner; the specific process steps are as follows:

[0109] The raw material aniline is heated, vaporized, and superheated to 230 °C, and the F21 value of the aniline flowmeter is 1,200 kg / h; the raw material methanol is heated, vaporized, and superheated to 230 °C, and the F22 value of the methanol flowmeter in the monomethyl reaction is 825 kg / h. After the aniline and methanol vapor are mixed, they enter the monomethyl reactor and mainly produce N-methylaniline under the action of an alkylation catalyst. The reaction pressure is controlled at 0.2 MPaA, and the reaction temperature is controlled at 235 °C through heat transfer oil.

[0110] The methanol vapor does not pass through the F23 of the dimethyl reaction methanol flowmeter to the dimethyl reactor, and the monomethyl reaction gas does not enter the dimethyl reactor either. Instead, it directly goes to heat exchange and separation. After the reaction gas recovers heat, its temperature drops to 70 °C. The liquid phase is sent to distillation to obtain 1,270 kg / h of N-methylaniline product and 67 kg / h of N,N-dimethylaniline; the gas phase is sent to the hydrogen recovery unit, and the recoverable hydrogen volume is approximately 320 Nm 3 / h.

[0111] The above embodiments only represent the specific implementation manners of the present application. The description is relatively specific and detailed, but it should not be construed as a limitation on the protection scope of the present application. It should be noted that for those of ordinary skill in the art, without departing from the concept of the technical solution of the present application, several modifications and improvements can still be made, and these all belong to the protection scope of the present application.

[0112] This Background of the Invention section is provided to generally present the context of the present invention. Work of the presently named inventors, to the extent it is described in this Background of the Invention section, and aspects of the work that are not yet prior art as of the filing of this application, are neither expressly nor impliedly admitted to be prior art to the present invention.

Claims

1. A system for synthesizing N-methylaniline and co-producing N,N-dimethylaniline by gas-phase method, characterized in that : The system includes a raw material gasification unit, a reaction unit, a separation and rectification unit, and a hydrogen recovery unit that are connected in sequence through pipelines; The raw material gasification unit includes an aniline storage tank (11), an aniline transfer pump (12), an aniline preheater (13), an aniline vaporization and superheater (14), a methanol storage tank (15), a methanol transfer pump (16), a methanol preheater (17), and a methanol vaporization and superheater (18); The aniline storage tank (11) is connected to the aniline transfer pump (12), and then to the tube side of the aniline preheater (13). The other end of the tube side of the aniline preheater (13) is connected to the tube side of the aniline vaporization and superheater (14), and the other end of the tube side of the aniline vaporization and superheater (14) is connected to the reaction unit; The methanol storage tank (15) is connected to the methanol transfer pump (16), and then to the tube side of the methanol preheater (17). The other end of the tube side of the methanol preheater (17) is connected to the tube side of the methanol vaporization and superheater (18), and the other end of the tube side of the methanol vaporization and superheater (18) is connected to the reaction unit.

2. The system according to claim 1, wherein: The reaction unit includes a monomethyl reactor (21), a dimethyl reactor (22), a first mixer (23), and a second mixer (24); The outlet end of the superheater (18) is respectively connected to the first mixer (23) and the second mixer (24); the first mixer (23) is connected to the top inlet of the monomethyl reactor (21), and the second mixer (24) is connected to the top inlet of the dimethyl reactor (22); the monomethyl reactor (21) and the dimethyl reactor (22) are connected.

3. The system according to claim 2, characterized in that: The separation and rectification unit includes a gas-liquid separator (31), a rectification pump (32), and a rectification column (33); The other end of the shell side of the methanol preheater (17) is connected to the gas-liquid separator (31) in the separation and rectification unit; the gas-liquid separator (31) is connected to the rectification pump (32) and the rectification column (33) in sequence through pipelines, and is used to send the liquid phase in the gas-liquid separator (31) into the rectification column (33) for rectification; the gas phase in the gas-liquid separator (31) is sent into the hydrogen recovery unit.

4. The system according to claim 3, characterized in that, The hydrogen recovery unit includes a cryogenic cooler (41), a compressor (42), a drying tower (43), and a pressure swing adsorption tower (44); The inlet of the cryogenic cooler (41) is connected to the gas phase port of the gas-liquid separator (31) through a pipeline, the outlet is connected to the inlet of the compressor (42) through a pipeline, the outlet of the compressor (42) is connected to the inlet of the drying tower (43), and the outlet of the drying tower (43) is connected to the inlet of the pressure swing adsorption tower (44).

5. The system according to claim 2, wherein: The tube sides of the monomethyl reactor (21) and the dimethyl reactor (22) are both filled with an alkylation catalyst; A methyl reaction methanol flowmeter F22 is provided on the pipeline between the superheater (18) and the first mixer (23); a dimethyl reaction methanol flowmeter F23 and a dimethyl reaction methanol flow regulating valve V21 are successively provided on the pipeline between the superheater (18) and the second mixer (24); an aniline flowmeter F21 is provided on the pipeline between the aniline vaporization and superheater (14) and the first mixer (23); a dimethyl reaction flowmeter F24 and a dimethyl reaction gas control valve V23 are successively provided on the pipeline between the monomethyl reactor (21) and the second mixer (24). The bottom outlet of the monomethyl reactor (21) is also connected to a monomethyl reaction gas shunt valve V22. The bottom outlet of the dimethyl reactor (22) is connected to a dimethyl reaction gas on-off valve V24. After the dimethyl reaction gas on-off valve V24 is connected to the monomethyl reaction gas shunt valve V22, it is then connected to the shell side of the aniline preheater (13) of the raw material gasification unit. The other end of the shell side of the aniline preheater (13) is connected to the shell side of the methanol preheater (17). The other end of the shell side of the methanol preheater (17) is connected to the separation and rectification unit.

6. The system according to claim 3, wherein: The rectification column (33) is respectively connected with a light component extraction pipeline (301), an N,N-dimethylaniline extraction pipeline (302), an N-methylaniline extraction pipeline (303) and a heavy component extraction pipeline (304).

7. The system according to claim 4, characterized in that: The pressure swing adsorption tower (44) is connected with a by-product hydrogen extraction pipeline (401) and a tail gas pipeline (402).

8. A method for synthesizing N-methylaniline by gas-phase method with co-production of N,N-dimethylaniline, characterized in that, Using methanol and aniline as raw materials, an alkylation reaction occurs under the action of an alkylation catalyst to produce N-methylaniline and N,N-dimethylaniline; the specific method includes the following steps: S1. The methanol transfer pump (16) sends the raw material methanol in the methanol storage tank (15) to the methanol preheater (17), the methanol gasification and superheater (18) for preheating, gasification and superheating. After that, the methanol vapor flows to the methyl reaction methanol flowmeter F22 and the dimethyl reaction methanol flowmeter F23 respectively. S2. The aniline transfer pump (12) sends the raw material aniline in the aniline storage tank (11) to the aniline preheater (13), the aniline vaporization and superheater (14) for preheating, gasification and superheating. After the aniline vapor is metered by the aniline flowmeter F21, it flows into the first mixer (23) in proportion to the methanol vapor metered by the methyl reaction methanol flowmeter F22, and then flows into the monomethyl reactor (21) to synthesize N-methylaniline. S3. Part or all of the monomethyl reaction gas flowing out of the monomethyl reactor (21) is metered by the dimethyl reaction flowmeter F24, and then flows into the second mixer (24) in proportion to the methanol vapor metered by the dimethyl reaction methanol flowmeter F23, and then enters the dimethyl reactor (22) to synthesize N,N-dimethylaniline. S4. The heat generated in the monomethyl reactor (21) and the dimethyl reactor (22) is removed by the heat transfer oil, and the reaction temperature is regulated by it. After the reaction gas flowing out of the monomethylamine reactor (21) is mixed with the reaction gas flowing out of the dimethylamine reactor (22), the raw material aniline and the raw material methanol are preheated in sequence, and then enter the gas-liquid separator (31); the liquid phase is refined by the separation and rectification unit (3) to obtain the product; the gas phase is recycled by the hydrogen recovery unit (4) to recover the by-product hydrogen.

9. The method for synthesizing N-methylaniline and co-producing N,N-dimethylaniline by gas phase according to claim 8, characterized in that: (1) In the N-methylaniline synthesis reaction occurring in the monomethylamine reactor (21), the feed molar ratio of the raw material methanol to aniline is 1-3:1, the reaction temperature is 190-320 °C, and the reaction pressure is 0.1 MPaA-0.6 MPaA; (2) In the N,N-dimethylaniline synthesis reaction occurring in the dimethylamine reactor (22), the feed mass ratio of the raw material methanol to the monomethylamine reaction gas is 0-1:1, the reaction temperature is 200-330 °C, and the reaction pressure is 0.1 MPaA-0.6 MPaA.

10. A method for synthesizing N-methylaniline and co-producing N,N-dimethylaniline by gas-phase method according to claim 8 or 9, characterized in that, The method further includes a separation and rectification step. The liquid phase product in the gas-liquid separator (31) is sent to the rectification tower (33) by the rectification pump (32) for refining. According to the boiling point, the light and heavy components are separated to obtain two products, N-methylaniline and N,N-dimethylaniline; The method further includes a hydrogen recovery step. The gas phase in the gas-liquid separator (31) is first cooled by the cryogenic cooler (41), then processed by the compressor (42), sent to the drying tower (43) for pressurization, and then the by-product hydrogen is recovered by the pressure swing adsorption tower (44).

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