Preparation method of (methyl) acrylonitrile

Abstract

The present application provides a method for preparing (meth) acrylonitrile, the method comprising: a catalytic reaction step of reacting (meth) acrolein with ammonia in a reactor containing a catalyst to produce a crude product comprising (meth) acrylonitrile, unreacted ammonia, unreacted (meth) acrolein, and one or more by-products; and a purification step: separating (methyl) acrylonitrile from the crude product. According to the method, synthesis of (methyl) acrylonitrile can be realized by using a low-cost catalyst through safe, environment-friendly and mild process steps, and effective recycling of materials and heat is realized while generation of toxic impurities is avoided.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of fine chemical industry, in particular to a method for synthesizing (methyl) acrylonitrile, and more particularly to a continuous process for synthesizing (methyl) acrylonitrile. BACKGROUND

[0002] (methyl) acrylonitrile includes acrylonitrile and methacrylonitrile (referred to as "MAN"), which is an important intermediate product of fine chemical synthesis process, and is mainly used as an intermediate to produce poly(methyl) acrylimide and (methyl) methacrylate products, etc., and has a very high demand in the global market. For example, the global market sales of methacrylonitrile in 2024 is about 197 million US dollars, and the global market size of methacrylonitrile is still showing a trend of continuous expansion. With the vigorous development of aerospace, vehicles, ships and other industries, the core layer made of poly(methyl) acrylimide foam as the main material is favored by the market, becoming an important driving force for the development of (methyl) acrylonitrile industry. The progress of organic glass, paint and other industries has to some extent promoted the development of (methyl) methacrylate industry, thereby significantly promoting the development of (methyl) acrylonitrile industry as an intermediate product.

[0003] However, in contradiction to the growing huge market demand for (methyl) acrylonitrile, the existing technology for synthesizing (methyl) acrylonitrile has always had serious defects. Specifically, the existing main production technologies include acetone cyanohydrin method, mixed C4 direct ammoxidation method, isobutene ammoxidation method, and methacrylamide method, etc. Among them, the isobutene ammoxidation method has become the mainstream process for industrial production of methacrylonitrile due to its lower investment cost, easy availability of raw materials and other advantages. The isobutene ammoxidation method mainly uses high-purity isobutene obtained by processing C4 byproduct of catalytic cracking of petroleum chemical industry as raw material, and synthesizes MAN product with ammonia and air mixture under the action of catalyst. However, even this optimal process still has the problems of low selectivity of product, many by-products, and the highest yield of target product can only reach 70%-80% level; secondly, the unreacted ammonia gas in the reaction process is difficult to recover, which will cause waste of raw materials; thirdly, the process will inevitably produce toxic and harmful substances such as hydrogen cyanide, and the post-processing process needs additional complex purification unit, which brings great environmental pressure; fourthly, the heat control and heat recovery of the process are poor, causing a large amount of energy waste; fifthly, the mixture of ammonia and oxygen used in the catalytic reaction process of the process is difficult to control, and there is a great risk of explosion; sixthly, the process mainly uses Mo-Bi-Fe catalyst, and often needs to use expensive metal additives such as Mn, V, Ni, Ce, Sb for modification, and the catalyst type and structure are complex, and the catalyst preparation process cost is high.

[0004] In recent years, in order to solve the above problems, researchers have invested a lot of manpower and funds for research and development, trying to improve the above existing process, and trying to develop a new synthesis process, such as isobutene step-by-step ammoxidation method and methacrolein ammoxidation method, etc. However, it is frustrating to find that although the newly developed synthesis process has slightly improved the yield of the target product (for example, the isobutene step-by-step ammoxidation method can achieve a yield of 80-85% under optimal conditions, and the methacrolein ammoxidation process can achieve a yield of 85-90% under optimal conditions), but these processes still have the above various problems of the prior art, sometimes even causing the above various problems of the prior art to be further worsened (for example, the mixture of ammonia and oxygen is difficult to control and easy to explode, the toxic by-product hydrogen cyanide is difficult to handle, the catalyst preparation is complex and the cost is high, the temperature is difficult to control and the energy is wasted seriously, the raw materials are difficult to recover, etc.), so these newly developed processes are still only in the laboratory stage, and further industrialization is not seen.

[0005] Therefore, it is urgent to develop a new process for producing methacrylonitrile in order to achieve excellent yield of the target product while overcoming the above defects of the prior art. SUMMARY

[0006] The present application provides a method for preparing (meth)acrylonitrile, the method comprising:

[0007] a catalytic reaction step of reacting (meth)acrolein with ammonia in a reactor containing a catalyst to produce a crude product comprising (meth)acrylonitrile, unreacted ammonia, unreacted (meth)acrolein, and one or more by-products;

[0008] a purification step of separating (meth)acrylonitrile from the crude product.

[0009] According to one embodiment of the present application, the catalytic reaction step does not add oxygen.

[0010] According to another embodiment of the present application, the catalytic reaction step does not add the following substances: oxygen, air, ozone, H2O2, water vapor, nitrogen.

[0011] According to another embodiment of the present application, the catalyst comprises a first metal element and a second metal element supported on a carrier; wherein the first metal element is nickel; the second metal element is selected from one or more of: Cu, Fe, Co, Ce, Mn, Zn; the carrier comprises one or more selected from: alumina, zirconia, silica, magnesium-aluminum composite oxide, magnesium oxide, silicon-aluminum composite oxide, magnesium-zirconium composite oxide, silicon-aluminum-zirconium composite oxide, magnesium-aluminum-zirconium composite oxide.

[0012] According to another embodiment of the present application, the mass percentage of the first metal element is 30-50%, the mass percentage of the second metal element is 5-30%, and the mass percentage of the carrier is 20-65%, based on the total mass of the catalyst.

[0013] According to another embodiment of the present application, the first metal element is nickel; the second metal element is copper; and the carrier comprises a mixture of alumina and zirconia, and in the mixture, the mass ratio of alumina to zirconia is 1:3 to 1:1.

[0014] According to another embodiment of the present application, the method further comprises a pretreatment step before the catalytic reaction step: preheating the vaporized (methyl)acrolein and ammonia to 150-300°C, and feeding them into the reactor of the catalytic reaction step at a molar ratio of (methyl)acrolein:ammonia = 1:6 to 2:1.

[0015] According to another embodiment of the present application, the purification step comprises the following sub-steps:

[0016] Sub-step (i): separating the crude product into a gas phase material and a first liquid phase material by heat recovery operation and gas-liquid separation, the gas phase material comprising unreacted ammonia, and recycling the gas phase material to the catalytic reaction step and / or the pretreatment step; and performing oil phase / water phase separation on the first liquid phase material, the separated water phase comprising unreacted (methyl)acrolein and one or more by-products, and the separated first oil phase comprising (methyl)acrylonitrile;

[0017] Sub-step (ii): performing one or more rectification processes on the first oil phase;

[0018] Sub-step (iii): performing one or more rectification processes on the separated one or more by-products.

[0019] According to another embodiment of the present application, at least part of the by-products and / or waste materials obtained in sub-step (iii) are catalytically incinerated to generate heat, and at least part of the heat is used in the catalytic reaction step and / or the pretreatment step.

[0020] According to another embodiment of the present application, heat is recovered from the crude product by heat recovery operation in sub-step (i), and at least part of the heat is used in the catalytic reaction step and / or the pretreatment step.

[0021] According to another embodiment of the present application, the catalytic reaction step does not produce hydrogen cyanide.

[0022] According to another embodiment of the present application, the catalytic reaction step, the pre-treatment step and the sub-steps (i)-(iii) of the purification step are all carried out in a continuous manner.

[0023] In the detailed description section below, the method of the present application is further described in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 A schematic diagram of the method for preparing (meth)acrylonitrile according to one embodiment of the present application is shown;

[0025] Figure 2 A schematic diagram of the process flow for preparing (meth)acrylonitrile in a continuous manner according to one embodiment of the present application is shown;

[0026] Figure 3 A catalyst prepared according to one embodiment of the present application is shown;

[0027] Figure 4 A gas chromatography apparatus used in the embodiments of the present application is shown;

[0028] Figures 5A-5C A gas chromatogram of the target product and by-products prepared according to one embodiment of the present application is shown.

[0029] Figure 2 The meanings of the reference numerals in the accompanying drawings are as follows:

[0030] A: pre-treatment step / section; B: catalytic reaction step / section; C: purification step / section; D: post-treatment step / section;

[0031] 1: methacrolein; 2: liquid ammonia; 3: pre-heated mixed gas; 4: post-reaction product; 5: post-primary cooling product; 6: post-secondary cooling product; 7: unreacted ammonia gas; 8: liquid product; 9: aqueous product; 10: evaporated organic matter; 11: waste water; 12: crude methacrylonitrile product; 13: main product post-primary distillation overhead; 14: unreacted methacrolein; 15: methacrylonitrile; 16: by-product crude product; 17: isobutyronitrile; 18: by-product post-primary distillation column bottom product; 19: 3,5-dimethylpyridine; 20: high-boiling polymer; 21: incineration exhaust gas; 22: exhaust gas; cl: cooling water; el: heat recovery steam; e2: outgoing pipe network steam;

[0032] E1: methacrolein vaporizer; E2: liquid ammonia vaporizer; E3: methacrolein preheater; E4: ammonia preheater; E5: main product primary rectifier overhead exchanger; E6: methacrylonitrile product exchanger; E7: isobutyronitrile product exchanger; E8: 3,5-dimethylpyridine product exchanger; E9: waste heat boiler; R101: catalytic reactor; F101: falling film evaporator; S101: gas-liquid separator; S102: oil-water separator; S103: main product primary rectifier overhead gas-liquid separator; T101: main product primary rectifier; T102: main product secondary rectifier; T103: by-product primary rectifier; T104: by-product secondary rectifier; V101: methacrylonitrile product tank; V102: isobutyronitrile product tank; V103: 3,5-dimethylpyridine product tank; CTO: catalytic incinerator; SCR: selective catalytic reduction reactor. DETAILED DESCRIPTION

[0033] "Ranges" are disclosed herein in terms of both a lower limit and an upper limit. Each lower limit can be combined with each upper limit to create a range. A given range is defined by selecting a lower limit and an upper limit. The selected lower limit and upper limit define the boundaries of a particular range. All ranges created in this manner are inclusive and combinable, i.e., any lower limit can be combined with any upper limit to create a range. For example, where ranges of 60-120 and 80-110 are listed for a particular parameter, it is understood that ranges of 60-110 and 80-120 are also contemplated. Additionally, if a minimum range value of 1 and 2 is listed, and if a maximum range value of 3, 4, and 5 is listed, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5.

[0034] In this application, the use of "about" or "approximately" with respect to a given numerical value x means that the exact value of the numerical value used in place of x is "within an acceptable limit of error" for the numerical value being used in place of x. For example, if the exact value is not known or is difficult to determine, and a value within 10% of the exact value is determined to satisfy the needs of the application, then the "about" or "approximately" language includes the value that is within 10% of the exact value.

[0035] In this application, all embodiments and preferred embodiments mentioned herein can be combined with each other to form new technical solutions, unless otherwise specified.

[0036] In this application, all technical features and preferred features mentioned herein can be combined with each other to form new technical solutions, unless otherwise specified.

[0037] In this application, the term "comprising" mentioned herein means open-ended and can also be closed-ended. For example, the term "comprising" can mean that other components not listed can also be included, or only the listed components can be included.

[0038] In the present application, (methyl)acrylonitrile means acrylonitrile, methacrylonitrile or a mixture thereof; (methyl)acrylaldehyde means acrylaldehyde, methacrylaldehyde or a mixture thereof.

[0039] According to one embodiment of the present application, as shown in Figure 1 According to one embodiment of the present application, as shown in

[0040] Specifically, the pre-treatment step (also referred to as pre-treatment section) comprises a raw material gasification section and a raw material pre-heating section. The raw material gasification section comprises a preliminary heating of the (methyl)acrylaldehyde and liquid ammonia raw materials, for example to a temperature of 80-120°C, so that the (methyl)acrylaldehyde and liquid ammonia raw materials are converted into gaseous substances. The raw material pre-heating section comprises a (methyl)acrylaldehyde pre-heater and an ammonia gas pre-heater, for further heating of the preliminary heated materials to a temperature of 150-300°C, for example to a temperature of 220-270°C. Subsequently, the pre-treated (methyl)acrylaldehyde and ammonia raw materials are fed into a reactor containing a catalyst, for carrying out the catalytic reaction step / section.

[0041] According to one embodiment of the present application, after the pre-treatment step, the (methyl)acrylaldehyde and ammonia raw materials are fed into a reactor containing a catalyst in a molar ratio of 1 :6 to 2: 1, for example in a molar ratio of 1 :5 to 1 : 1.

[0042] According to one embodiment of the present application, as shown in Figure 1 According to one embodiment of the present application, as shown in

[0043] According to one embodiment of the present application, no oxygen is fed into the reactor during the catalytic reaction step. According to another embodiment of the present application, no water vapor is fed into the reactor during the catalytic reaction step. According to one embodiment of the present application, no oxidizing agent, such as oxygen, air, ozone, H2O2, etc., is fed into the reactor during the catalytic reaction step. According to one embodiment of the present application, no nitrogen is fed into the reactor during the catalytic reaction step. According to one preferred embodiment of the present application, only (methyl)acrylaldehyde and ammonia as raw materials are fed into the reactor containing the catalyst during the catalytic reaction step, without feeding any other reagent. This is a technical progress of the present application, which can use only (methyl)acrylaldehyde and ammonia as raw materials, and make them catalytically react in the reactor containing the catalyst, without adding oxygen, water vapor and any other oxidizing agent into the catalytic reaction system, thereby avoiding the risk of explosion in the reactor in the prior art, while achieving the desired catalytic reaction performance.

[0044] It should be noted that the solid catalyst pre-loaded in the reactor and the treatment of the catalyst before the start of the catalytic reaction do not affect the operation of "no other components are fed during the reaction" described above.

[0045] According to one embodiment of the present application, the reactor herein is a fixed bed reactor or a fluidized bed reactor, such as a tubular fixed bed reactor, preferably a packed tubular fixed bed reactor. According to another embodiment of the present application, the reaction temperature in the reactor is 250-450°C, such as 280-400°C, or 300-380°C, or 330-350°C. According to another embodiment of the present application, the reaction is carried out under normal pressure.

[0046] According to one preferred embodiment of the present application, the process of the present application is carried out in a continuous manner. Specifically, the raw materials (methyl)acrylaldehyde and ammonia are continuously pretreated in the pretreatment step, and after the pretreatment, the raw materials are continuously fed into the reactor for catalytic reaction, and after the catalytic reaction, the formed crude product is continuously output from the reactor and transported to the downstream purification step.

[0047] Another technical progress of the present application is that the catalyst used in the catalytic reaction step of the present application has a very simple composition design, and the active component therein is inexpensive, without using expensive elements (especially noble metals such as silver, platinum, rhodium, palladium, etc.). Using this simple and inexpensive catalyst in the synthesis process can achieve excellent raw material conversion rate, target product selectivity and yield, avoid the formation of toxic and harmful hydrocyanic acid by-product, and effectively avoid the increase in cost and complexity caused by complex catalyst composition design.

[0048] According to one embodiment of the present application, the catalyst comprises a first metal element and a second metal element supported on a carrier; wherein the first metal element is nickel; and the second metal element is selected from one or more of Cu, Fe, Co, Ce, Mn, Zn, preferably the second metal element is copper.

[0049] According to another embodiment of the present application, the carrier comprises one or more selected from alumina, zirconia, silica, magnesium-aluminum composite oxide (e.g. hercynite), magnesium oxide, silica-aluminum composite oxide, magnesium-zirconium composite oxide, silica-aluminum-zirconium composite oxide, magnesium-aluminum-zirconium composite oxide. Preferably, the carrier comprises a mixture of alumina and zirconia, and in the mixture, the mass ratio of alumina to zirconia is 1:3 to 1:1.

[0050] According to one embodiment of the present application, the mass percentage of the first metal element in the catalyst is 30-50%, preferably 35-48%, more preferably 40-45%. According to another embodiment of the present application, the mass percentage of the second metal element in the catalyst is 5-30%, preferably 10-25%, more preferably 12-20%, more preferably 15-18%. According to another embodiment of the present application, the mass percentage of the carrier in the catalyst is 20-65%, or 30-60%, or 35-55%, or 40-50%.

[0051] According to one embodiment, the catalyst of the present application is prepared by using a metal-soluble salt solution (e.g. aqueous solution) as a precursor solution of the first metal and the second metal, mixing the precursor solution of the metal salt with a precipitant and a solid form of the carrier raw material or a suspension of the carrier raw material to cause a precipitation reaction, washing, drying, grinding and first firing the obtained precipitate to obtain a raw powder, and then granulating and second firing the raw powder. The thus-prepared catalyst can be a long strip-shaped particle (e.g. the size of the long strip-shaped particle catalyst can be 1-10 mm, preferably 2-8 mm, more preferably 3-7 mm, most preferably 4-6 mm in length; 0.1-1 mm, or 0.4-0.8 mm in diameter), a spherical particle, a flat particle, an irregular particle, etc.

[0052] According to a further embodiment, the granulation comprises mixing the raw powder with a binder, water and a pore former, and then extrusion granulation using a granulator, such as a screw extrusion granulator. Examples of the binder include aluminum sol, silicon sol, zirconium sol, etc., and examples of the pore former include carbon black powder, polymer powder, bio-based pore former, etc. The pore former will be burned out during the subsequent sintering process, leaving a porous structure in the catalyst, while the binder will be converted into aluminum oxide, silicon oxide, zirconium oxide, etc. during the sintering process, together with the carrier raw material added as described above, to form part of the carrier in the catalyst.

[0053] According to another embodiment of the present application, the first sintering can be performed in an air atmosphere, at a temperature of 250-450°C, such as 300-400°C, for a duration of 1-6 hours, such as 3-4 hours.

[0054] According to another embodiment of the present application, the second sintering can be performed in an air atmosphere, at a temperature of 500-750°C, such as 550-700°C, or 600-650°C, for a duration of 1-6 hours, such as 3-4 hours.

[0055] According to an embodiment of the present application, the crude product output from the reactor in the catalytic reaction step described above comprises the target product (the (meth)acrylonitrile), unreacted raw materials (ammonia and / or (meth)acrolein), and by-products.

[0056] Another inventive point of the present application is that, through the raw material design and catalyst design described above, the catalytic reaction not only achieves excellent raw material conversion, target product ((meth)acrylonitrile) selectivity and yield, but also the by-products inevitably generated in the catalytic reaction are mainly high-value compounds (such as isobutyronitrile and 3,5-dimethylpyridine), and the generation of toxic and harmful by-products is avoided to the greatest extent.

[0057] According to an embodiment of the present application, the crude product obtained in the catalytic reaction step is completely free of toxic hydrocyanic acid by-products, specifically, free of detectable hydrocyanic acid by-products.

[0058] According to another embodiment of the present application, the by-products contained in the crude product obtained in the catalytic reaction step are mostly (such as more than 50 mol%, or more than 70 mol%, or more than 80 mol%, or more than 90%, or more than 95 mol%, based on the total moles of all by-products) compounds with application prospects and commercial value, such as isobutyronitrile and 3,5-dimethylpyridine, both of which have high market value and can be co-produced with (meth)acrylonitrile, thereby further improving the economic value of the method of the present application.

[0059] Another inventive point of the present application is that through the design of the purification steps, the separation, purification and recovery of the target product and high value by-products can be achieved in a simple and low-cost manner, the unreacted raw materials are efficiently recycled, and the content of toxic and harmful substances in waste water and waste gas is effectively reduced, thereby achieving significant improvement in environmental value.

[0060] As shown in Figure 1 The purification steps of the method of the present application can include the following three sub-steps: (i) product separation (primary separation); (ii) main product rectification ((methyl) acrylonitrile rectification); and (iii) by-product rectification.

[0061] According to one embodiment of the present application, in the sub-step (i), the crude product stream prepared in the catalytic reaction step is subjected to one or more heat recovery operations, and at least a part of the recovered heat can be used for heating the raw materials in the pretreatment step. According to one exemplary embodiment of the present application, the crude product stream is subjected to at least two heat recovery operations, wherein in the first heat recovery operation, the crude product stream output from the catalytic reaction step is passed through the (methyl) acrolein preheater and the ammonia gas preheater as described above, and at least a part of the energy required for preheating the raw materials for the pretreatment section is supplied by heat exchange. The second heat recovery operation can be carried out in a falling film evaporator.

[0062] After the above-mentioned heat recovery operation, the crude product is subjected to gas-liquid separation, and the crude product is separated into a gaseous material and a first liquid material, the gaseous material contains unreacted ammonia, and the gaseous material is recycled to the catalytic reaction step and / or the pretreatment step; then the first liquid material is subjected to oil phase / water phase separation, the separated water phase contains unreacted (methyl) acrolein and one or more by-products, and the separated first oil phase contains (methyl) acrylonitrile and one or more by-products. According to one exemplary embodiment of the present application, the water phase can be sent back to the falling film evaporator as described above for further separation treatment. For example, in the falling film evaporator, unreacted methyl acrylonitrile and various by-products are evaporated from the water phase, and the (methyl) acrolein gas after heating in the pretreatment step, ammonia gas and ammonia gas discharged from the gas-liquid separator are combined and enter the reactor to participate in the catalytic reaction again, and the remaining waste water is discharged to a waste water treatment station for treatment, and is discharged after reaching the standard. According to another embodiment of the present application, at least a part of the heat required for the separation and purification treatment of the water phase in the falling film evaporator can come from the second heat recovery operation of the crude product in the falling film evaporator as described above.

[0063] The oil phase obtained in the above sub-step (i) is a crude (meth)acrylonitrile product, mainly comprising (meth)acrylonitrile, high-value by-product isobutyronitrile and 3,5-dimethylpyridine, a small amount of unreacted methacrolein, and high-boiling polymer substances as low-value by-products. According to an exemplary embodiment, the (meth)acrylonitrile content is 80-90% by mass, the isobutyronitrile content is 3-5% by mass, the 3,5-dimethylpyridine content is 5-12% by mass, the (meth)acrylonitrile content is 0.1-1% by mass, and the high-boiling polymer substance content is 1-2% by mass, based on the total mass of the oil phase. The oil phase is subjected to one or more rectification operations, for example, two rectification operations, in sub-step (ii).

[0064] According to an exemplary embodiment of the present application, the oil phase is subjected to rectification in sub-step (ii) using two main product rectification columns. Specifically, the oil phase is first subjected to rectification in a main product primary rectification column, and a by-product mixture having a higher boiling point than (meth)acrylonitrile is obtained at the bottom of the column. The overheads are subjected to heat exchange and then enter a gas-liquid separator, and a portion of unreacted (meth)acrylonitrile gas is returned to the inlet of the catalytic reactor to continue participating in the catalytic reaction. 20-30% by mass of the condensed liquid is returned to the main product primary rectification column for further processing, and the remaining liquid material is subjected to processing in a main product secondary rectification column. The column bottom material is subjected to heat exchange and then enters a product tank, and a high-purity (meth)acrylonitrile product can be obtained. The overheads of the main product secondary rectification column mainly comprise unreacted (meth)acrylonitrile, which is returned to the inlet of the catalytic reactor to continue participating in the catalytic reaction. Through the above main product rectification operation, a (meth)acrylonitrile product having a purity of >99% by weight can be obtained.

[0065] According to another embodiment of the present application, heat is also recovered in the above sub-step (ii). For example, heat is recovered from the overheads of the main product primary rectification column and the column bottom product of the main product secondary rectification column, and is transported to a heat collection pipe network for further optimized utilization.

[0066] In sub-step (iii), the column bottom material of the main product primary rectification column of sub-step (ii) is subjected to at least one rectification, preferably two or more rectifications. Specifically, the column bottom material of the main product primary rectification column (hereinafter referred to as “column bottom mixture”) is a by-product mixture having a lower boiling point than (meth)acrylonitrile, mainly comprising by-products such as isobutyronitrile, 3,5-dimethylpyridine, and high-boiling polymer substances.

[0067] According to one embodiment of the present application, the mixture in the kettle is transported to a primary distillation column of by-products to produce overhead material and kettle material, the overhead material is heated and then enters a product tank, and a by-product of isobutyronitrile with a purity of >98wt% can be obtained; the kettle material is further processed by a secondary distillation column of by-products to further produce overhead material and kettle material, the overhead material is heated and then enters a product tank, and a by-product of 3,5-dimethylpyridine with a purity of >98wt% can be obtained, and the kettle material is mainly high-boiling polymer substances and is transported to a post-processing section.

[0068] According to another embodiment of the present application, heat recovery is also performed in the sub-step (iii). For example, heat is recovered from the overhead distillate of the primary distillation column of by-products and the overhead effluent of the secondary distillation column of by-products, and is transported to a heat collection pipe network for further optimized utilization.

[0069] According to another embodiment of the present application, as shown in Figure 1 the method of the present application further comprises post-processing of the separated by-products (specifically, high-boiling polymer substances). Specifically, the kettle material of the secondary distillation column of by-products obtained in the above-mentioned sub-step (iii) is mainly high-boiling polymer substances, which is transported to a catalytic incinerator for processing, flue gas generated therefrom is further introduced into a selective catalytic reduction reactor for denitration reaction to obtain denitration gas, which is then introduced into a waste heat boiler to recover heat and is finally discharged after detection. The reaction temperature of the catalytic incinerator is 300-400°C, and the reaction temperature of the selective catalytic reduction reactor is 280-320°C. According to one exemplary embodiment of the present application, the catalyst used in the catalytic incinerator is Cu-Cr / Al2O3, and the mass percentage of Cu is 5-15 mass%, the mass percentage of Cr is 3-8 mass%, and the rest is an alumina carrier. According to another embodiment of the present application, the catalyst used in the catalytic reduction reactor is V2O5-WO3 / TiO2, and the mass percentage of V is 2-10 mass%, the mass percentage of W is 3-7 mass%, and the rest is a titanium oxide carrier; the oxygen content of the denitration gas is 2-5wt%, and the content of nitrogen oxides is less than 100ppm.

[0070] According to another embodiment of the present application, heat recovery is also performed in the post-processing step. For example, at least part of the heat recovered from the waste heat boiler can be used to provide heat for the sub-steps (i)-(iii) of the preheating step, the catalytic reaction step and / or the purification step, and part of these heat can be transported to a heat collection pipe network for further optimized utilization.

[0071] The method of the present application can achieve the following advantages:

[0072] (1)Saving raw materials: The process can realize the recycling of unreacted ammonia gas at the outlet of the reactor and unreacted methacrolein in the separation section, which can effectively avoid resource waste.

[0073] (2)Reducing energy consumption: The process can realize heat recovery of high-temperature gas at the outlet of the reactor, which can effectively reduce energy consumption. In addition, through heat recovery in the purification section and the post-treatment section, the energy utilization efficiency can be improved.

[0074] (3)Green and environmentally friendly: In the method of the application, the generation of toxic and harmful substances such as hydrocyanic acid in the traditional ammoxidation process can be effectively avoided, thereby reducing the risk of environmental pollution and reducing the post-treatment cost. In addition, through the re-purification of wastewater by falling film evaporator, the content of residual organic matter in wastewater can be effectively reduced, and the wastewater treatment cost can be reduced. Through the denitration treatment of waste gas in the post-treatment section, the environmental pollution is also reduced.

[0075] (4)High safety in operation process: In the method of the application, there is no oxygen gas participating in the reaction throughout the process, which can effectively avoid the risk of ammonia / oxygen mixture explosion compared with the traditional ammoxidation preparation process, and the safety in operation process is high.

[0076] (5)Excellent market economy: The continuous production process of the application can obtain high yield of methacrylonitrile, and also by-product high value-added products isobutyronitrile and 3,5-dimethylpyridine, and the catalyst can achieve excellent catalytic performance with simple and cheap design, which has high market value.

[0077] (6)Easy to scale up production: Since the method of the application has high methacrolein conversion rate and methacrylonitrile mass yield, and the reaction belongs to a gas phase continuous reaction process, it is suitable for industrial production. Compared with the catalyst used in the existing ammoxidation method, the catalyst has the characteristics of high methacrolein conversion rate, simple catalyst composition and low cost, which is suitable for industrial large-scale production.

[0078] In the following examples, the method of the application is specifically illustrated by specific examples, which aims to better understand the content of the application. It should be understood that these examples are only illustrative and not limiting. The reagents used in the examples are commercially available unless otherwise specified. The methods and conditions used in the examples are conventional methods and conditions unless otherwise specified.

[0079] Example

[0080] All reagents used in the following examples are of analytical purity, so deionized water is used, and the solvent is used Figure 4The product was characterized using a Trace 1310 gas chromatograph (equipped with a WAX column) produced by Thermo Fisher Scientific. The purity of the product was determined using the internal standard method with cyclohexanone as the internal standard.

[0081] Example 1

[0082] In this embodiment, according to Figure 2 The process flow diagram shown is designed to implement the method of the present application. The process for continuously producing methacrylonitrile includes a pretreatment section (A), a catalytic reaction section (B), a product purification section (C) and a post-treatment section (D) in the direction of material flow.

[0083] The raw material pretreatment section (A) includes a raw material gasification section and a raw material preheating section. The raw material gasification section includes a methacrolein gasifier E1 and a liquid ammonia gasifier E2, respectively, for heating the methacrolein (material 1) and the liquid ammonia (stream 2) to 120°C, converting them into gaseous state. The raw material preheating section includes a methacrolein preheater E3 and an ammonia preheater E4, respectively, for further heating the gaseous methacrolein (material 1) and the ammonia (stream 2) to 250°C. The molar ratio of methacrolein (material 1) to liquid ammonia (material 2) is 1:3, the flow rate of methacrolein (material 1) is 1 L / h, and the flow rate of liquid ammonia (material 2) is 3 L / h.

[0084] The catalytic reaction section (B) includes a fixed-bed tubular reactor R101, with the tubular interior filled with a supported, elongated catalyst. The catalyst is a Ni-Cu / Al2O3-ZrO2 supported catalyst, prepared by the following steps: 13 grams of Al2O3 powder and 24 grams of ZrO2 powder are weighed, dispersed in 100 milliliters of deionized water, and stirred thoroughly to form a suspension. 228 grams of Ni(NO3)2·6H2O and 93 grams of Cu(NO3)2·6H2O are weighed, dissolved in 100 milliliters of deionized water, and stirred thoroughly to form a precursor solution. Ammonia water with a concentration of 13.38 mol / L is also prepared as a precipitant. While stirring, the precursor solution and precipitant are simultaneously added dropwise to the Al2O3-ZrO2 suspension. The pH of the mixed system is maintained at pH = 10. After the additions are complete, the mixture is heated at 50°C for 180 minutes to initiate a precipitation reaction.

[0085] The resulting precipitate was filtered, and the filter cake was washed with deionized water until the filtrate was neutral. The filter cake was then dried in a 120°C oven for 12 hours. After grinding, the powder sample was placed in a muffle furnace and calcined at 400°C for 3 hours in an air atmosphere to obtain the granulated raw powder.

[0086] The granulation raw powder, binder (aluminum sol), deionized water, pore expanding agent (carbon black powder) are mixed in a mass ratio of 1:0.3:0.1:0.03 and uniformly kneaded, then granulated by a screw extruder and sheared into long strip-shaped particles with a length of 5 mm and a diameter of 0.5 mm, which are placed in a muffle furnace and calcined at 600°C for 3 hours in an air atmosphere to obtain a catalyst, as shown in Figure 3 .

[0087] The catalyst is characterized by using an Optima 7000DV type plasma emission spectrometer (ICP) of American PE Company, and the content of Ni element in the catalyst is 43% by mass, the content of Cu element is 17% by mass, and the balance is the carrier, and the mass ratio of Al2O3 / ZrO2 in the carrier is 2:3.

[0088] The above-mentioned catalyst is loaded into the tubes of the reactor R101, and the pretreated methacrolein and ammonia are input into the reactor, and the reaction temperature of the reactor is 330°C, and the reaction pressure is normal pressure.

[0089] The material 4 output from the reactor is characterized by using a gas chromatograph as shown in Figure 4 , and the conversion rate of methacrolein is 98.6%, the selectivity of the main product methacrylonitrile is 86.4%, the selectivity of the by-product isobutyronitrile is 4.2%, and the selectivity of the by-product 3,5-dimethylpyridine is 8.8%.

[0090] As shown in Figure 2 , the reactor outlet material 4 is divided into two (in a ratio of 1:1), and is respectively input into the methacrolein preheater E3 and the ammonia gas preheater E4 for heat exchange (primary cooling), so as to realize heat exchange and provide energy for the pretreatment section to realize energy recycling.

[0091] The two streams after the above-mentioned primary cooling are combined into one stream 5, which is transported to the falling film evaporator F101 for secondary heat exchange, and then the stream 6 after the secondary heat exchange is transported to the gas-liquid separator S101 (condensing gas-liquid separator, with a pressure of 0.1 MPa and a temperature controlled at 20°C, and with a built-in cyclone guide blade structure), in which gas-liquid separation is carried out by centrifugal force. The gas discharged from the top of the gas-liquid separator S101 is mainly ammonia, which is combined with the ammonia / methacrylonitrile mixture 3 after pretreatment to participate in the catalytic reaction again. The liquid product 8 discharged from the gas-liquid separator S101 is the crude product after ammonia removal, which is input into the oil-water separator S102 (normal pressure horizontal gravity type separator, with a temperature controlled at 20°C), in which oil-water phase separation is realized by using the density difference between oil and water and the gravitational force.

[0092] The oil phase and water phase separated in the oil-water separator S102 have a mass ratio of about 1:0.33, and the lower water phase product 9 (mainly containing 95.4wt% water, 2.9wt% methacrolein, and 1.7wt% imine intermediate) is output and transported to the falling film evaporator F101. The water phase product 9 is purified by using the secondary cooling of the material 5 to recover heat, and the evaporated organic matter 10 (mixture of methacrolein and imine intermediate) evaporated from the falling film evaporator F101 is added to the heated mixture 3 in the pretreatment step to participate in the reaction again. The waste water 11 discharged from the falling film evaporator F101 after purification is sent to a waste water treatment station for treatment and discharged after reaching the standard.

[0093] The upper oil phase (methyl acrylate crude product 12) output from the oil-water separator S102 is characterized by using gas chromatography, and it is measured that it contains 85.8wt% methyl acrylate, 3.8wt% isobutyronitrile, 8.2wt% 3,5-dimethylpyridine, 1.4wt% high-boiling polymer, and 0.8wt% methacrolein.

[0094] The methyl acrylate crude product 12 is transported to the main product primary rectification tower T101 for rectification. The main product primary rectification tower T101 has a bottom temperature of 105°C, a top temperature of 95°C, a pressure of 0.1 MPa, and a plate number of 10. The top effluent 13 is a crude methyl acrylate product, which is heated by the heat exchanger E5 and then enters the gas-liquid separator S103. The S103 is a condensing gas-liquid separator with a pressure of 0.1 MPa and a temperature controlled at 75°C. It has a built-in cyclone guide vane structure to separate gas and liquid by centrifugal force. The gas output from the top of the gas-liquid separator S103 is characterized by gas chromatography and determined as methacrolein gas, which is transported to the reactor R101 inlet for recycling. 30% of the mass fraction of the condensed liquid input into the gas-liquid separator is returned to the main product primary rectification tower T101 for further treatment, and the remaining liquid material enters the main product secondary rectification tower T102 for treatment. The main product secondary rectification tower T102 has a bottom temperature of 85°C, a top temperature of 75°C, a pressure of 0.1 MPa, and a plate number of 10. The tower kettle material 15 output from the bottom of the main product secondary rectification tower T102 is heated by the heat exchanger E6 to recover heat and then enters the product tank V101. The product is characterized by gas chromatography, as shown in FIG. 1C, and determined as a high-purity methyl acrylate product with a purity of 99.2wt%. The top material 14 of the main product secondary rectification tower T102 is unreacted methacrolein, which is transported back to the reactor R101 inlet in the form of gas for recycling. Figure 5A The oil phase and water phase separated in the oil-water separator S102 have a mass ratio of about 1:0.33, and the lower water phase product 9 (mainly containing 95.4wt% water, 2.9wt% methacrolein, and 1.7wt% imine intermediate) is output and transported to the falling film evaporator F101. The water phase product 9 is purified by using the secondary cooling of the material 5 to recover heat, and the evaporated organic matter 10 (mixture of methacrolein and imine intermediate) evaporated from the falling film evaporator F101 is added to the heated mixture 3 in the pretreatment step to participate in the reaction again. The waste water 11 discharged from the falling film evaporator F101 after purification is sent to a waste water treatment station for treatment and discharged after reaching the standard.

[0095] The tower bottom material output from the main product primary rectification tower T101 is the by-product crude product, which is transported to the by-product primary rectification tower T103 for rectification. The tower bottom temperature of the by-product primary rectification tower T103 is 130°C, the tower top temperature is 120°C, the pressure is 0.1 MPa, and the number of plates is 3. The material 17 flowing out from the top of the by-product secondary rectification tower T103 is sent to the product tank V102 after heat recovery through the heat exchanger E7, and is characterized by gas chromatography, as shown in Table 2. Figure 5B As shown in Table 2, it is determined to be high-purity isobutyronitrile (high-value by-product) with a purity of 98.3wt%.

[0096] The tower bottom material 18 flowing out from the bottom of the by-product primary rectification tower T103 is transported to the by-product secondary rectification tower T104 for rectification. The tower bottom temperature of the by-product secondary rectification tower T104 is 190°C, the tower top temperature is 180°C, the pressure is 0.1 MPa, and the number of plates is 5. The material 19 flowing out from the top of the by-product secondary rectification tower T104 is sent to the product tank V103 after heat recovery through the heat exchanger E8, and is characterized by gas chromatography, as shown in Table 2. Figure 5C As shown in Table 2, it is determined to be high-purity 3,5-dimethylpyridine (high-value by-product) with a purity of 98.6wt%.

[0097] The tower top material of the main product primary rectification tower T101, the tower bottom material of the main product secondary rectification tower T102, the tower top material of the by-product primary rectification tower T103, and the tower top material of the by-product secondary rectification tower T104 are respectively subjected to heat recovery through the heat exchangers E5, E6, E7, and E8 to generate steam, which is transported to the heat collection pipe network to realize energy recycling.

[0098] The post-treatment section (D) includes a catalytic incinerator CTO, a selective catalytic reduction reactor SCR, and a waste heat boiler E9. The material 20 flowing out from the bottom of the by-product secondary rectification tower T104 is a high-boiling polymer substance, which is transported to the catalytic incinerator CTO (which is filled with a Cu-Cr / Al2O3 catalyst with a Cu content of about 10 mass% and a Cr content of 5 mass%). The waste gas 21 generated by incineration at a temperature of 380°C is transported to the selective catalytic reduction reactor SCR (which is filled with a V2O5-WO3 / TiO2 catalyst with a V content of 4 mass% and a W content of 6 mass%). The temperature is 315°C, and the denitration (removal of nitrogen oxides) is performed thereon. The treated denitration gas is measured by the ISQ-7000 gas chromatograph-mass spectrometer (GC-MS) of Thermo Fisher Corporation to have an oxygen content of 3.3wt% and a nitrogen oxide content of less than 100ppm. The gas is transported into the waste heat boiler E9, water c1 is supplied to the boiler at the same time, heat exchange is performed, and steam e1 is produced. After the steam e1 provides heat for the methylacrolein gasifier E1 and the liquid ammonia gasifier E2 in the pretreatment section (A), the remaining steam e2 is transported to the heat collection pipe network to realize energy recycling.

Claims

1. A method for preparing (meth)acrylonitrile, comprising: a catalytic reaction step of reacting (meth)acrolein with ammonia in a reactor containing a catalyst to generate a crude product comprising (meth)acrylonitrile, unreacted ammonia, unreacted (meth)acrolein, and one or more by-products; Purification step: separating (meth)acrylonitrile from the crude product.

2. The method according to claim 1, wherein The catalytic reaction step is performed without adding oxygen.

3. The method according to claim 1, wherein The catalytic reaction step does not add the following substances: oxygen, air, ozone, H2O2, water vapor, and nitrogen.

4. The method according to claim 1, wherein The catalyst comprises a first metal element and a second metal element supported on a carrier; The first metal element is nickel; The second metal element is selected from one or more of the following: Cu, Fe, Co, Ce, Mn, Zn; The support comprises one or more selected from the group consisting of: alumina, zirconia, silicon oxide, magnesium-aluminum composite oxide, magnesium oxide, silicon-aluminum composite oxide, magnesium-zirconium composite oxide, silicon-aluminum-zirconium composite oxide, and magnesium-aluminum-zirconium composite oxide; Based on the weight of the catalyst, the mass percentage of the first metal element is 30-50%, the mass percentage of the second metal element is 5-30%, and the mass percentage of the carrier is 20-65%.

5. The method according to claim 4, wherein The first metal element is nickel; the second metal element is copper; the support comprises a mixture of aluminum oxide and zirconium oxide, and in the mixture, the mass ratio of aluminum oxide to zirconium oxide is 1:3 to 1:

1.

6. The method according to claim 1, wherein The method further comprises a pretreatment step before the catalytic reaction step: preheating the gasified (meth)acrolein and ammonia to 150-300° C. and conveying the gasified (meth)acrolein and ammonia to the reactor of the catalytic reaction step at a molar ratio of (meth)acrolein:ammonia of 1:6 to 2:

1.

7. The method according to claim 6, wherein The purification step comprises the following sub-steps: Sub-step (i): separating the crude product into a gas phase material and a first liquid phase material through heat recovery and gas-liquid separation, wherein the gas phase material contains unreacted ammonia, and the gas phase material is recycled to the catalytic reaction step and / or the pretreatment step; and performing oil phase / water phase separation on the first liquid phase material, wherein the separated water phase contains unreacted (meth)acrolein and one or more by-products, and the separated first oil phase contains (meth)acrylonitrile; Sub-step (ii): performing one or more distillation treatments on the first oil phase; Sub-step (iii): performing one or more distillation treatments on the separated one or more by-products.

8. The method according to claim 7, wherein At least a portion of the by-products and / or waste materials obtained in sub-step (iii) is catalytically incinerated to generate heat, and at least a portion of the heat is used in the catalytic reaction step and / or pretreatment step.

9. The method according to claim 7, wherein Heat is recovered from the crude product by the heat recovery operation in sub-step (i), and at least a portion of the heat is used in the catalytic reaction step and / or the pretreatment step.

10. The method according to any one of claims 1 to 9, wherein The catalytic reaction step does not produce hydrocyanic acid; The catalytic reaction step, the pretreatment step, and sub-steps (i) to (iii) of the purification step are all performed in a continuous manner.

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