Method for preparing adipic acid through one-step oxidation of cyclohexane

Abstract

The invention discloses a method for preparing adipic acid through one-step oxidation of cyclohexane. The method comprises at least three stages of m stages of oxidation reactors which are connected in series, cyclohexane and oxygen-containing gas are equally divided into m strands for feeding, and the m strands are used as feeding materials of the m stages of oxidation reactors respectively. Enabling the obtained premixed material and a first stream of oxygen-containing gas to enter a first-stage oxidation reactor for reaction to obtain a first-stage reaction product; the second-stage oxidation reactor and the subsequent stages of oxidation reactors enter the current-stage oxidation reactor for reaction according to the mode that the previous-stage reaction product, the cyclohexane and the oxygen-containing gas of the current-stage corresponding stream enter the current-stage oxidation reactor for reaction to obtain the current-stage reaction product, and the mth-stage reaction product is separated and refined to obtain the adipic acid product. According to the method provided by the invention, the conversion rate of total cyclohexane and the selectivity of adipic acid can be improved, and the risk of performance reduction caused by liquid-liquid layering of a reaction system is avoided.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical industry, and particularly relates to a method for preparing adipic acid by one-step oxidation of cyclohexane. Background Art

[0002] Adipic acid is the main basic petrochemical raw material for synthesizing nylon 66, and its output ranks second among all dicarboxylic acids. In industry, there are three process routes for the production of adipic acid: cyclohexane process, cyclohexene process and phenol process, among which the production of adipic acid by air oxidation of cyclohexane via cyclohexanone and cyclohexanol (KA oil) is the mainstream process.

[0003] The cyclohexane method uses benzene as raw material and obtains cyclohexane through selective hydrogenation. It can be specifically divided into a one-step method and a two-step method. The two-step method, also known as the KA oil method, is currently the most widely used method in industry, accounting for more than 80% of the total output of adipic acid. This method has a complex process, many by-products, produces a large amount of nitrogen oxides, and the reaction equipment is severely corroded, causing great harm to the environment. Compared with the two-step method, the one-step method has the advantages of stronger atomic economy, shorter process route, and less environmental pollution. It is the technology with the most promising industrial application prospects. According to the type of catalyst, it can be divided into homogeneous catalysis and heterogeneous catalysis.

[0004] In the one-step process, the heterogeneous catalytic method uses a solid catalyst and molecular oxygen as an oxidant to directly synthesize adipic acid. It has the advantages of short process flow, low investment cost, easy catalyst separation, and green environmental protection. The disadvantages are low catalytic activity, complex catalyst, high preparation and use costs, low reaction efficiency, and many by-products. The homogeneous catalytic method has high reaction activity, high cyclohexane single-pass conversion rate and high selectivity for adipic acid. The disadvantage is that it requires the use of polar solvents such as acetic acid, and subsequent product separation and catalyst recycling are more difficult. Developing highly active and highly selective catalysts and supporting reaction processes, reducing solvent ratios, simplifying separation processes, reducing energy consumption, and realizing catalyst and solvent recycling are the keys to achieving the industrialization of the one-step process.

[0005] CN1270578A discloses a method and device for removing acetic acid from cyclohexane in the production of adipic acid, which proposes a process scheme for separating oxidation products by using washing water to remove the solvent acetic acid, adding cyclohexane to precipitate the catalyst, and realizing the recycling of the catalyst by solid-liquid separation. CN1530358A discloses a process for catalytic oxidation of cyclohexane by direct oxidation of cyclohexane with air in a three-pot series stirred reactor using tetraphenylporphyrin iron or tetraphenylporphyrin cobalt as a catalyst.

[0006] CN1157605A, CN104109083B, CN105665010B and the like disclose methods for directly producing adipic acid using transition metal homogeneous catalysts. The cyclohexane conversion rate is generally high, between 40% and 85%, and the adipic acid selectivity is 60% to 85%. In the above methods, the reaction time is usually more than 5 hours, the oxygen content in the tail gas is usually not controlled, and the process is an intermittent reaction. The oxygen content in the tail gas of this type of reaction should be controlled below 5% in order to ensure the safety of the process. The transition metal catalyst is one or more combinations of cobalt, manganese, copper, iron, etc.

[0007] The one-step reaction takes a long time, usually 4 to 20 hours, and polar solvents such as acetic acid are often used to dissolve high-melting-point products such as adipic acid generated by the reaction, and a multi-reactor series process is often used. The reaction of cyclohexane and molecular oxygen is a highly exothermic reaction, and the built-in coil and jacket alone cannot meet the needs of rapid heat removal from the reactor, so the reactor is often equipped with an external circulation heat remover.

[0008] As the reaction proceeds, the water content in the oxidation product will continue to increase. When the water content exceeds a certain value, liquid-liquid stratification will inevitably occur. Transition metal catalysts are mostly soluble in polar solutions, that is, the polar layer in the liquid-liquid stratification is the water layer, and are almost insoluble in the upper cyclohexane layer. Once liquid-liquid stratification occurs, the heavy metal elements in the catalyst will cause the proportion of metal elements in the catalyst in different liquid layers to change due to different distribution coefficients, and the reaction performance will drop sharply. In the small test, it was found that once the stirring in the reactor stopped, the reaction conversion rate and selectivity would drop significantly. Controlling the water content in the reactor can effectively avoid the risk of liquid-liquid stratification.

[0009] The reaction products of the one-step oxidation reaction of cyclohexane include cyclohexane, acetic acid, water, cyclohexanone, cyclohexanol, adipic acid, glutaric acid, succinic acid, catalysts, initiators and other substances. Among them, water and cyclohexane, water and cyclohexanone, water and cyclohexanol, cyclohexane and acetic acid will form binary azeotropes, and water and acetic acid will form association complexes. The complexity of the oxidation products is the main reason for the difficulty in subsequent separation and catalyst recovery. Controlling the water content during the reaction process can effectively avoid the liquid-liquid stratification phenomenon, greatly simplify the subsequent separation process, and reduce the energy consumption of the separation process. Both simulation calculations and experimental results show that simple separation methods cannot achieve effective removal of water, and will impose certain restrictions on the reaction process conditions, affecting the reaction efficiency. Summary of the invention

[0010] In view of the problems existing in the prior art such as low cyclohexane per-pass conversion rate, insufficient reaction heat utilization, risk of liquid-liquid stratification of reaction products and uneven distribution of catalysts in the reaction process, and high separation energy consumption in the reaction process, the present invention provides a method for preparing adipic acid by one-step oxidation of cyclohexane. The method provided by the present invention can improve the conversion rate of total cyclohexane and adipic acid selectivity, avoid the risk of liquid-liquid stratification in the reaction system, can be used in the one-step industrial production of cyclohexane, and has achieved good technical effects.

[0011] The present invention provides a method for preparing adipic acid by one-step oxidation of cyclohexane, the method comprising at least three M-stage oxidation reactors arranged in series, cyclohexane and oxygen-containing gas are divided into M feeds, which are respectively used as feeds for the M-stage oxidation reactors, and the method comprises the following steps:

[0012] a) premixing the first stream of cyclohexane, acetic acid and catalyst, and the obtained premixed material and the first stream of oxygen-containing gas enter the first stage oxidation reactor for reaction to obtain a first stage reaction product;

[0013] b) The second-stage oxidation reactor and subsequent oxidation reactors are operated in a manner that the product of the previous stage reaction reacts with the cyclohexane and oxygen-containing gas of the corresponding stage into the oxidation reactor of the current stage to obtain the product of the current stage reaction;

[0014] c) The m-th stage reaction product is separated and refined to obtain adipic acid product.

[0015] Furthermore, the m-stage oxidation reactor is at least a three-stage oxidation reactor, and preferably, m is 3-8.

[0016] Furthermore, cyclohexane and oxygen-containing gas are divided into m feeds, which are respectively used as feeds for m-stage oxidation reactors, that is, cyclohexane is divided into m feeds according to the m-stage oxidation reactors, and each stage oxidation reactor is provided with cyclohexane feed; the oxygen-containing gas is divided into m feeds according to the m-stage oxidation reactors, and each stage oxidation reactor is provided with oxygen-containing gas feed.

[0017] Furthermore, each of the first-stage oxidation reactor to the m-1-th-stage oxidation reactor is separately provided with a respective product external circulation for removing heat from the reactor; preferably, the product external circulation is cooled by heat exchange.

[0018] Furthermore, in step (c), the m-th stage reaction product is flash evaporated. Preferably, the obtained flash gas phase is first cooled and then subjected to water-oil separation, the oil phase is used as the external circulation material of the m-th stage oxidation reactor, and the water phase is discharged; the obtained flash liquid phase is subjected to liquid-liquid separation, the upper liquid phase is circulated back to step a) as the circulating material for premixing, and the lower liquid phase is used as the crude adipic acid product, which is then separated and refined to obtain the adipic acid product.

[0019] Furthermore, condensers are separately arranged at the top of each stage of oxidation reactor to recover the condensed and entrained liquid in the tail gas.

[0020] Furthermore, the m-th stage reaction product is the reaction product of the m-th stage oxidation reactor (ie, the final stage oxidation reactor).

[0021] Furthermore, in the method, the mass ratio of the total feed amount of m cyclohexane to the feed amount of acetic acid is 0.40 to 0.80, preferably 0.45 to 0.65, and more preferably 0.50 to 0.65.

[0022] Furthermore, in the method, the mass ratio of cyclohexane to acetic acid in each stage of the oxidation reactor is reacted at 0.20 to 0.50, preferably 0.20 to 0.40.

[0023] Furthermore, in the method, the feed amount of each cyclohexane in the m cyclohexane strands accounts for at least 5% of the total cyclohexane feed.

[0024] Furthermore, the catalyst described in step a) is a transition metal acetate homogeneous catalyst, and a conventional transition metal acetate homogeneous catalyst in the art can be used, wherein the transition metal can be selected from at least one of manganese, cobalt, iron, and copper, preferably manganese and cobalt, manganese and copper, or cobalt and copper, more preferably manganese, cobalt and copper, and the mass ratio of manganese, cobalt, and copper is (0.1-5):1:(0.1-10).

[0025] Furthermore, the amount of catalyst used in step a) is 0.03% to 0.08% of the total liquid feed mass.

[0026] Furthermore, the premix in step a) is stirred to avoid liquid-liquid stratification.

[0027] Furthermore, in step a), the oxygen content in the oxygen-containing gas is 10 vol% to 100 vol%. The oxygen-containing gas is preferably air.

[0028] Furthermore, in step a), to ensure the safety of the reaction system, the volume content of oxygen in each stage of reaction tail gas is controlled to be 2 vol% to 5 vol%.

[0029] Furthermore, the feed amount of each oxygen-containing gas in step a) is a fixed value for controlling the oxygen content of the tail gas, and the flow rate of the oxygen-containing gas can be adjusted by the length-to-diameter ratio of the reactor.

[0030] Furthermore, a gas distributor is provided inside the reactor to adjust the distribution of the oxygen-containing gas in the reactor. The oxygen-containing gas first passes through the gas distributor and then contacts and reacts with other materials.

[0031] Furthermore, the products of the oxidation reaction carried out in the M-stage reactor include at least adipic acid, glutaric acid, succinic acid, cyclohexanol, cyclohexene, water, carbon monoxide, and carbon dioxide.

[0032] Furthermore, the reaction temperature in the M-stage reactor is 90-150°C, preferably 100-120°C, the reaction pressure is 0.3-2.0 MPaG, preferably 1.0-1.6 MPaG, and the liquid volume space velocity is 0.1-0.4 h -1 , preferably 0.2 to 0.3h -1 .

[0033] Furthermore, the flash evaporation conditions are as follows: temperature 69-75° C., pressure 0-1 MPaG.

[0034] Furthermore, the reaction temperature in the M-stage reactor is lower than the boiling point of each combined azeotrope, and the tail gas of the reactor will carry a portion of liquid and organic components (acetic acid, cyclohexane) that enter the gas phase due to the saturated vapor pressure, which are recovered and utilized through condensers separately arranged at the top of each stage of oxidation reactor, without dehydration function.

[0035] Furthermore, the M-stage reactor is an M-stage series bubbling reactor.

[0036] Furthermore, after the discharge of the final oxidation reactor, flash dehydration is carried out to control the water content of the 1 to m-1 level, avoiding the risk of liquid-liquid stratification and uneven catalyst distribution in the reaction part, while achieving the purpose of dehydration of the reaction part. The subsequent separation unit does not need to be strictly separated, which simplifies the separation process and reduces the separation energy consumption. The flash oxidation product passes through the flash heat exchanger and the external circulation heat exchangers at various levels in turn, which increases the gasification separation of the oxidation product. While controlling the reaction temperature at each level, the utilization of low-temperature reaction heat is achieved, reducing the energy consumption of the reaction part.

[0037] Furthermore, a flash tank is provided in the flash process, gas phase material is discharged from the top of the flash tank, and the flash pressure is controlled by the gas phase pressure.

[0038] In the reaction of preparing adipic acid by cyclohexane oxidation, conventional series connection process is adopted. As the number of reactors increases, the cyclohexane conversion rate will be improved, but the water content in the outlet product will also increase. When the reaction order exceeds a certain number, the cyclohexane conversion rate reaches the limit and no longer increases. As the water content increases, liquid-liquid stratification occurs, which limits the reaction and thus causes performance degradation. Improving process conversion rate and avoiding liquid-liquid stratification are key issues that need to be solved in this area using homogeneous catalysts. Those skilled in the art only realize that the series connection process is simple, solves the problem of reactor single volume limitation, and is easy to industrial amplification, but in the series connection process, the higher the cyclohexane / acetic acid ratio, the smaller the energy consumption of the process, and the higher the economy, but the conversion rate is low, and the limit water content will also be significantly reduced, and the risk of liquid-liquid stratification is prone to occur. If its ratio is reduced, that is, the lower the cyclohexane / acetic acid, the cyclohexane conversion rate is significantly increased, but the energy consumption and economy are worse. In view of the above-mentioned contradictions and difficulties, the present invention proposes for the first time to adopt a process scheme combining series and parallel connection, design the reactors in series, feed cyclohexane and oxygen-containing gas in parallel, control the situation where the total cyclohexane / acetic acid ratio is high, and also reduce the cyclohexane / acetic acid ratio of each stage of the reactor, break through the upper limit of the single-pass conversion rate of the process, improve the product selectivity, and at the same time increase the upper limit of the maximum water content of each stage of the reaction, so as to avoid the risk of performance degradation caused by premature liquid-liquid stratification in the reaction system as much as possible, thereby better solving the above-mentioned problems.

[0039] In addition, the present invention sets an external circulation heat removal on the M-stage oxidation reactor to reduce the heat of the reaction. Preferably, the product of the last-stage oxidation reactor is flash-evaporated and dehydrated, which not only further controls the water content and avoids liquid-liquid stratification, but also can be used in the one-step industrial production of cyclohexane oxygen-containing gas, achieving better technical effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 A schematic flow diagram of a method for preparing adipic acid by a one-step process using cyclohexane provided by the present invention;

[0041] Figure 1 In the figure, 1 is a premixing kettle, 2 is a feed pump, 3 is a first oxidation reactor, 4 is an external circulation heat exchanger, 5 is an external circulation pump, 6 is a second oxidation reactor, 7 is an external circulation pump, 8 is an external circulation heat exchanger, 9 is an m-th oxidation reactor, 10 is a condenser, 11 is a condenser, 12 is a condenser, 13 is a flash heat exchanger, 14 is an external circulation heat exchanger, 15 is a flash tank, 16 is a discharge pump, 17 is a condensation cooler, 18 is a liquid-liquid separator, 19 is an oil-water separator, and 20 is an external circulation pump. DETAILED DESCRIPTION

[0042] The scheme of the present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0043] The method for preparing adipic acid by one-step oxidation of cyclohexane of the present invention is as follows: Figure 1Process, including:

[0044] m-stage oxidation reactors are arranged in series, cyclohexane and oxygen-containing gas are divided into m feed streams, the first stream of cyclohexane, acetic acid and catalyst are stirred and premixed in a premixing kettle 1, the feed is discharged from the discharge port of the premixing kettle 1, and is fed into a first oxidation reactor 3 through a feed pump 2 and the first stream of oxygen-containing gas, the first-stage reaction product, the second stream of cyclohexane and the second stream of oxygen-containing gas enter a second-stage oxidation reactor 6 for reaction to obtain a second-stage reaction product ..., according to the above feeding sequence, the reaction product of the m-1th stage, the mth stream of cyclohexane and the mth stream of oxygen-containing gas are fed into an m-stage oxidation reactor 9 for reaction. An oxygen-containing gas feed distributor may be provided inside each oxidation reactor; the oxygen-containing gas, the discharge of the premixing kettle 1 and the cyclohexane in each reactor undergo oxidation reaction in the first oxidation reactor 3, the second oxidation reactor 6, ..., and the m-th oxidation reactor 9 under the condition of the presence of a catalyst; condensers 10, 11, ..., and condensers 12 are provided on the top of the first oxidation reactor 3, the second oxidation reactor 6, ..., and the m-th oxidation reactor 9 to recover the condensed and entrained liquid in the tail gas; wherein the first-stage reaction product of the first-stage oxidation reactor 3 is fed into the feed port of the second-stage oxidation reactor 6 through the external circulation pump 5, and the second-stage reaction product obtained by the second-stage oxidation reactor 6 is fed into the feed port of the next-stage oxidation reactor through the external circulation pump 7 ... and the m-1-stage reaction product obtained by connecting to the m-1-stage oxidation reactor is fed into the feed port of the m-th oxidation reactor 9 through the external circulation pump. The discharge at the bottom of the m-th oxidation reactor 9 is controlled to flow into the flash tank 15 at a constant flow rate. The return temperature of the external circulation material is controlled by controlling the bypass flow of the external circulation heat exchanger 4, 8, ... to control the temperature of each oxidation reactor. The flash pressure of the gas phase discharged from the top of the flash tank 15 is controlled by pressure; the gas phase at the top of the flash tank 15 is cooled by the condenser cooler 17 and then enters the oil-water separator 19 to achieve oil-water separation, the lower water phase in the oil-water separator 19 is discharged outside the boundary, and the upper oil phase is returned to the m-th stage oxidation reactor 9 through the external circulation pump 20 and the external circulation heat exchanger 14 in sequence, and the oil phase return temperature is controlled by the bypass flow of the external circulation heat exchanger 14; the bottom discharge of the flash tank 15 enters the liquid-liquid separator 18 through the discharge pump 16, the upper liquid layer returns to the premixing kettle 1, and the lower liquid layer is sent to the subsequent refining unit.

[0045] in Figure 1 The "circulating material" shown in the figure refers to the return material obtained after being sent to the subsequent refining unit and separated, such as cyclohexane, acetic acid, cyclohexanone, cyclohexanol, etc.; the function of the flash heat exchanger 13 is to exchange heat with steam to control the gasification rate and supplement the heat required for dehydration.

[0046] By adopting the above process flow, the separation part is no longer designed with a water separation function, and some intermediate materials no longer need to be strictly separated, so the separation process can be greatly simplified. The return material contains water, and the premixing kettle 1 is stirred to avoid liquid-liquid stratification. The first oxidation reactor 3, the second oxidation reactor 6, the final oxidation reactor 9 and other reaction equipment are bubbling reactors. The feed amount of the oxygen-containing gas is a fixed value because the oxygen content of the tail gas is controlled. The flow rate of the oxygen-containing gas can be adjusted by the length-to-diameter ratio of the reactor, and a gas distributor is set when the oxygen-containing gas enters the reactor. The flash tank 15 is provided with an agitator to avoid liquid-liquid stratification during the flash evaporation process.

[0047] The present invention is further described below by way of examples. To facilitate comparison of process technology effects, the catalysts in Examples 1-5 and Comparative Examples all use transition metal acetate catalysts containing manganese, cobalt and copper, the mass ratio of manganese, cobalt and copper in the catalyst is 1.5:1:2, and the amount of catalyst is 0.056% of the total liquid mass. The device scale is the same, and the volume content of tail gas oxygen is controlled to 3% to ensure the safety of the device. The mass ratio of manganese, cobalt and copper in the catalyst in Example 6 is 4.5:1:8.

[0048] [Example 1]

[0049] Adipic acid synthesis device and process flow Figure 1 As shown, the difference is that the flash dehydration function is not set. Five stages of bubbling bed oxidation reactors are connected in series, and the oxygen-containing gas is air. Cyclohexane and air are divided into 5 streams, all of which are fed in parallel. The 1-4 stage reactors are equipped with an external circulation heat exchanger to remove heat, and the refrigerant is cooling water. The product after the 5th stage reactor directly enters the separation and refining unit to obtain adipic acid product. The total feed cyclohexane / acetic acid mass ratio is 0.45, and each stage of the reactor reacts under the condition of a cyclohexane / acetic acid mass ratio of 0.20, the reaction temperature is 120°C, the reaction pressure is 1.6MPaG, and the liquid volume space velocity is 0.3h -1 The oxygen volume content in each stage of reaction tail gas is controlled to be 3 vol%.

[0050] Reaction part: cyclohexane total conversion rate 91.0%, adipic acid selectivity 79.5%, no risk of liquid-liquid stratification in the reactor. For easy comparison, the process conditions and main technical indicators are listed in Table 1 and Table 2.

[0051] [Example 2]

[0052] Adipic acid synthesis device and process flow Figure 1As shown, the difference is that the flash dehydration function is not set. Four-stage bubbling bed reactors are connected in series, and the oxygen-containing gas is air. Cyclohexane and air are divided into 4 streams, all of which are fed in parallel. The 1-3 reactors are equipped with an external circulation heat exchanger to remove heat, and the refrigerant is cooling water. The product after the 4th reactor directly enters the separation and refining unit to obtain adipic acid product. The total feed cyclohexane / acetic acid ratio is 0.45. Each reactor reacts under the condition of a cyclohexane / acetic acid mass ratio of 0.25, the reaction temperature is 120°C, the reaction pressure is 1.6MPaG, and the liquid volume space velocity is 0.3h -1 The oxygen volume content in each stage of reaction tail gas is controlled to be 3 vol%.

[0053] Reaction part: cyclohexane total conversion rate 80.5%, selectivity 79.3% and no risk of liquid-liquid stratification in the reactor. For the convenience of comparison, the process conditions and main technical indicators are listed in Table 1 and Table 2.

[0054] [Example 3]

[0055] Adipic acid synthesis device and process flow Figure 1 As shown, the difference is that the flash dehydration function is not set. Three-stage bubbling bed reactors are connected in series, and the oxygen-containing gas is air. Cyclohexane and air are divided into three streams, all of which are fed in parallel. The 1-2 stage reactors are equipped with an external circulation heat exchanger to remove heat, and the refrigerant is cooling water. The product after the third stage reactor directly enters the separation and refining unit to obtain adipic acid product. The total feed cyclohexane / acetic acid ratio is 0.45. Each stage of the reactor reacts under the condition of a cyclohexane / acetic acid mass ratio of 0.32, the reaction temperature is 120°C, the reaction pressure is 1.6MPaG, and the liquid volume space velocity is 0.3h -1 The oxygen volume content in each stage of reaction tail gas is controlled to be 3 vol%.

[0056] Reaction part: cyclohexane total conversion rate 68.5%, selectivity 79.2%, no risk of liquid-liquid stratification in the reactor. For easy comparison, the process conditions and main technical indicators are listed in Table 1 and Table 2.

[0057] [Example 4]

[0058] Adipic acid synthesis device and process flow Figure 1 As shown, 5 stages of bubbling bed reactors are connected in series, and the oxygen-containing gas is air. Cyclohexane and air are divided into 5 streams, all of which are fed in parallel. The 1-4 stage reactors are provided with an external circulation heat exchanger to remove heat, and cooling water is used as the refrigerant. The product after the 5th stage reactor is flashed at a temperature of 69-72°C and a pressure of normal pressure. The insufficient heat source required for dehydration is supplemented by low-pressure steam, and a steam heater is provided in front of the flash tank 15. The total feed cyclohexane / acetic acid ratio is 0.65, and each stage of the reactor reacts under the condition that the cyclohexane / acetic acid mass ratio is controlled to be 0.2, the reaction temperature is 100°C, the reaction pressure is 1.2MPaG, and the liquid volume space velocity is 0.2h-1 The oxygen volume content in each stage of reaction tail gas is controlled to be 3 vol%.

[0059] Reaction part: total conversion of cyclohexane was 90.0%, selectivity was 83.0%, and there was no risk of liquid-liquid stratification in the reactor. For the convenience of comparison, the process conditions and main technical indicators are listed in Tables 1 and 2.

[0060] [Example 5]

[0061] Adipic acid synthesis device and process flow Figure 1 As shown, 5 stages of bubbling bed reactors are connected in series, and the oxygen-containing gas is air. Cyclohexane and air are divided into 5 streams, all of which are fed in parallel. The 1-4 stage reactors are provided with an external circulation heat exchanger to remove heat, and cooling water is used as the refrigerant. The product after the 5th stage reactor is flash evaporated, and the flash evaporation temperature is 69-72°C, the pressure is normal pressure, and the insufficient heat source required for dehydration is supplemented by low-pressure steam. A steam heater is provided in front of the flash tank 15. The total feed cyclohexane / acetic acid ratio is 0.5, and each stage of the reactor reacts under the condition of a cyclohexane / acetic acid mass ratio of 0.26, the reaction temperature is 105°C, the reaction pressure is 1.0MPaG, and the liquid volume space velocity is 0.4h -1 The oxygen volume content in each stage of reaction tail gas is controlled to be 3 vol%.

[0062] Reaction part: total conversion of cyclohexane was 79.0%, selectivity was 82.5%, and there was no risk of liquid-liquid stratification in the reactor. For the convenience of comparison, the process conditions and main technical indicators are listed in Tables 1 and 2.

[0063] [Example 6]

[0064] Adipic acid synthesis device and process flow Figure 1 As shown, 5 stages of bubbling bed reactors are connected in series, and the oxygen-containing gas is air. Cyclohexane and air are divided into 5 streams, all of which are fed in parallel. The 1-4 stage reactors are provided with an external circulation heat exchanger to remove heat, and cooling water is used as the refrigerant. The product after the 5th stage reactor is flashed at a temperature of 69-72°C and a pressure of normal pressure. The insufficient heat source required for dehydration is supplemented by low-pressure steam, and a steam heater is provided in front of the flash tank 15. The total feed cyclohexane / acetic acid mass ratio is 0.65, and each stage of the reactor reacts under the condition of a cyclohexane / acetic acid mass ratio of 0.2, the reaction temperature is 100°C, the reaction pressure is 1.2MPaG, and the liquid volume space velocity is 0.25h -1 The oxygen volume content in each stage of reaction tail gas is controlled to be 3 vol%.

[0065] Reaction part: total conversion of cyclohexane was 82.0%, selectivity was 79.2%, and there was no risk of liquid-liquid stratification in the reactor. For the convenience of comparison, the process conditions and main technical indicators are listed in Tables 1 and 2.

[0066] [Comparative Example 1]

[0067] Adipic acid synthesis device and process flow Figure 1 As shown, five stages of bubbling bed reactors are connected in series. Compared with Example 1, the difference is that cyclohexane is not divided into strands and is fed once through a premixing kettle. Figure 1 An external cycle was set to remove heat, and cooling water was used as the refrigerant. The total feed cyclohexane / acetic acid ratio was 0.45. The cyclohexane / acetic acid ratios of the 2nd to 5th stages were not controlled and decreased in sequence as the reaction proceeded. The reaction temperature was 120°C, the reaction pressure was 1.6 MPaG, and the liquid volume space velocity was 0.3 h -1 .

[0068] Reaction part: total conversion of cyclohexane was 55.0%, selectivity was 75.4%, and liquid-liquid stratification occurred in stages 4 and 5. For the convenience of comparison, the process conditions and main technical indicators are listed in Tables 1 and 2.

[0069] [Comparative Example 2]

[0070] Adipic acid synthesis device and process flow Figure 1 As shown, 5-stage bubbling bed reactors are connected in series. Compared with Example 1, the difference is that cyclohexane is not divided into shares, and the premixing kettle is fed once. Each reactor is provided with an external circulation to remove heat, and the refrigerant is cooling water. The total feed cyclohexane / acetic acid ratio is 0.65, and the cyclohexane / acetic acid ratio of the second to fifth stages is not controlled, and decreases in sequence as the reaction proceeds. The reaction temperature is 100°C, the reaction pressure is 1.2MPaG, and the liquid volume space velocity is 0.2h -1 .

[0071] Reaction part: total conversion of cyclohexane was 65.6%, selectivity was 78.3%, and liquid-liquid stratification occurred in stages 3 and 4. For the convenience of comparison, the process conditions and main technical indicators are listed in Tables 1 and 2.

[0072] Table 1 Process conditions of various embodiments and comparative examples

[0073]

[0074]

[0075] Table 2 Summary of main technical indicators of various embodiments and comparative examples

[0076]

[0077] The specific one-step oxidation method of cyclohexane to produce adipic acid proposed by the present invention has been described through the above-mentioned examples. It is obvious that those skilled in the art can modify or appropriately change and combine the structure and preparation method described herein without departing from the content, spirit and scope of the present invention to implement the technology of the present invention. It should be particularly pointed out that all similar substitutions and modifications are obvious to those skilled in the art, and they are all considered to be included in the spirit, scope and content of the present invention.

Claims

1. A method for preparing adipic acid by one-step oxidation of cyclohexane, the method comprising at least three stages of m-stage oxidation reactors arranged in series, cyclohexane and oxygen-containing gas are divided into m feeds, which are respectively used as feeds for the m-stage oxidation reactors, the method comprising the following steps: a) premixing the first stream of cyclohexane, acetic acid and catalyst, and the obtained premixed material and the first stream of oxygen-containing gas enter the first stage oxidation reactor for reaction to obtain a first stage reaction product; b) The second-stage oxidation reactor and subsequent oxidation reactors are operated in a manner that the product of the previous stage reaction reacts with the cyclohexane and oxygen-containing gas of the corresponding stage into the oxidation reactor of the current stage to obtain the product of the current stage reaction; c) The m-th stage reaction product is separated and refined to obtain adipic acid product.

2. The method according to claim 1, characterized in that The m-stage oxidation reactor is at least a three-stage oxidation reactor, and preferably, m is 3-8.

3. The method according to claim 1, characterized in that: The first-stage oxidation reactor to the m-1-th-stage oxidation reactor are respectively provided with respective product external circulation.

4. The method according to claim 1, characterized in that: In step (c), the m-th stage reaction product is flashed; preferably, the obtained flash gas phase is first cooled and then subjected to water-oil separation, the oil phase is used as the external circulation material of the m-th stage oxidation reactor, and the water phase is discharged; the obtained flash liquid phase is subjected to liquid-liquid separation, the upper liquid phase is recycled back to step a) as the circulating material for premixing, and the lower liquid phase is used as the crude adipic acid product, which is further separated and refined to obtain the adipic acid product.

5. The method according to claim 1, characterized in that Condensers are separately arranged on the top of each stage of oxidation reactor to recover the condensed and entrained liquid in the tail gas.

6. The method according to claim 1, characterized in that In the method, the mass ratio of the total feed amount of m cyclohexane and the feed amount of acetic acid is 0.40-0.80; optionally, the mass ratio of cyclohexane and acetic acid in each oxidation reactor is reacted at 0.20-0.

50.

7. The method according to claim 1, characterized in that The amount of catalyst used in step a) is 0.03% to 0.08% of the total liquid feed mass.

8. The method according to claim 1, characterized in that The oxygen content in the oxygen-containing gas in step a) is 10 vol% to 100 vol%.

9. The method according to claim 1, characterized in that: The reaction temperature in the M-stage reactor is 90-150° C., preferably 100-120° C., the reaction pressure is 0.3-2.0 MPaG, preferably 1.0-1.6 MPaG, and the liquid volume space velocity is 0.1-0.4 h -1 , preferably 0.2 to 0.3h -1 .

10. The method according to claim 4, characterized in that The flash evaporation conditions are as follows: temperature 69-75° C., pressure 0-1 MPaG.

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