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-stage oxidation reactors which are connected in series, cyclohexane and oxygen-containing gas are equally divided into m strands for feeding and are respectively used as feeding materials of the m-stage oxidation reactors, in addition, the first-stage oxidation reactor to the (m-1) th-stage oxidation reactor are respectively and independently provided with respective product external circulation, carrying out heat exchange heating on the mth-stage reaction product and the first-stage reaction product to the (m-1) th-stage reaction product respectively, then carrying out flash evaporation, cooling the obtained flash evaporation gas phase, then carrying out water-oil separation, taking the oil phase as an external circulation material of the mth-stage oxidation reactor, and discharging the water phase; and carrying out liquid-liquid separation on the obtained flash evaporation liquid phase, taking the upper liquid phase as a circulating material, taking the lower liquid phase as an adipic acid crude product, and separating and refining to obtain the adipic acid product. According to the method, the conversion rate of total cyclohexane can be increased, the risk of liquid-liquid layering of a reaction system is avoided, and the process separation energy consumption is reduced.

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 ranks second among all dicarboxylic acids in terms of production volume. It is an important basic petrochemical raw material, mainly used as a raw material for nylon 66 and engineering plastics. The production processes of adipic acid mainly include phenol method, cyclohexane method, cyclohexene method, butadiene method and biological method. The cyclohexane method is currently the most important production method for adipic acid.

[0003] The cyclohexane method is divided into a one-step method and a two-step method. The two-step method is currently the most widely used method in industry, accounting for more than 80% of the total output of adipic acid. The two-step process is relatively complicated, with more by-products, a large amount of nitric acid, severe corrosion of the reaction equipment, and a large amount of nitrogen oxides emitted into the atmosphere, 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 considered to be one of the technologies with the most promising industrial applications. According to the different catalytic systems, it can be divided into homogeneous catalysis and heterogeneous catalysis.

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

[0005] CN104549520B discloses a method for preparing adipic acid by direct oxidation of cyclohexane, which uses an ferromagnetic ferrite catalyst to directly oxidize cyclohexane to prepare cyclohexane. The catalyst is recovered by a method of attracting a magnet, which solves the problem that homogeneous catalysts are difficult to recover without loading. The method requires the catalyst to have ferromagnetism, and the selection is relatively limited. The method of recovering the catalyst by attracting a magnet is difficult to implement industrially.

[0006] CN202688236U discloses a device for preparing adipic acid by reaction / concentration coupling. The device removes water generated during the reaction by setting a condenser on the top of the reactor. A large amount of water is generated during the reaction, the conversion rate of the reaction intermediate is limited, the reaction rate is reduced, the reaction time is prolonged, and it is not conducive to the generation of adipic acid. The above method increases the conversion rate of the intermediate product, shortens the reaction time, and improves the yield of adipic acid. Cyclohexene, cyclohexanol, and water in the reaction system form three binary azeotropes, and it is difficult to effectively separate the generated water by simply setting a condensation separator on the top of the reactor.

[0007] The one-step reaction time is relatively long, usually 4 to 20 hours, and acetic acid is often used as a solvent. In order to reduce the volume of a single reactor during industrial amplification, a multi-reactor series process is often used. The reaction of cyclohexane with molecular oxygen is a highly exothermic reaction. As the scale of the device increases, the built-in coils and jackets cannot meet the needs of rapid heat removal from the reactor, and each reactor needs to be equipped with an external circulation heat remover. The oxidation temperature of cyclohexane is generally low, mostly between 90 and 160°C. This part of the low-temperature reaction heat is difficult to recycle, and circulating water and other media are often used for cooling and heat exchange, resulting in energy waste.

[0008] As the one-step oxidation reaction of cyclohexane proceeds, the water content in the product will continue to increase. When the water content exceeds a certain value, liquid-liquid stratification will inevitably occur. Acetate transition metal catalysts are easily soluble in polar solutions, that is, the lower water layer in the liquid-liquid stratification, and are almost insoluble in the upper cyclohexane layer. Once liquid-liquid stratification occurs, it will cause an imbalance in the distribution of the catalyst and a sharp drop in the reaction efficiency. The experiment found that once the stirring in the reactor stops, only simple air bubbling remains, and the reaction conversion rate and selectivity will 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 compounds. The complexity of the system is the main reason for the difficulty in subsequent separation and catalyst recovery. Liquid-liquid stratification is prone to occur during the reaction process, and the separation process of water separation in the reaction process is complicated and energy-intensive. 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 conversion rate of cyclohexane per pass, insufficient utilization of reaction heat, 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, on the one hand, improve the conversion rate of total cyclohexane and avoid the risk of liquid-liquid stratification in the reaction system, and on the other hand, can not only recycle the low-temperature heat of the reaction entering and exiting the reactor, but also be used for dehydration of flash products and recycling of cyclohexane, simplifying the subsequent separation process, reducing process separation energy consumption, and further controlling the water content to avoid liquid-liquid stratification, and can be used in one-step industrial production of cyclohexane, achieving 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 first-stage oxidation reactor to the m-1-stage oxidation reactor are respectively independently provided with respective product external circulations, the method comprising 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 first stage reaction product, the second stream of cyclohexane and the second stream of oxygen-containing gas enter into a second stage oxidation reactor for reaction to obtain a second stage reaction product;

[0014] c) each oxidation reactor after the second stage oxidation reactor is fed and reacted in the same manner as in step b), i.e., the product of the previous stage reaction and the corresponding cyclohexane and oxygen-containing gas of the current stage enter the current stage oxidation reactor for reaction to obtain the current stage reaction product;

[0015] d) The m-th stage reaction product and the first stage reaction product to the m-1-th stage reaction product are respectively subjected to heat exchange and temperature increase, and then flash evaporation is performed. 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, and 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 then separated and refined to obtain the adipic acid product.

[0016] Furthermore, each of the first-stage oxidation reactor to the (m-1)-th-stage oxidation reactor is separately provided with an external circulation of its own product for removing heat from the reactor.

[0017] Furthermore, the m-stage oxidation reactor is at least a three-stage oxidation reactor, and preferably, m is 3-8.

[0018] 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.

[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 product external circulation is cooled by heat exchange. More preferably, the first-stage reaction product to the m-1-th stage reaction product are all subjected to heat exchange with the m-th stage reaction product before external circulation.

[0021] Furthermore, the m-th stage reaction product is the reaction product of the m-th stage oxidation reactor (ie, the final stage oxidation reactor).

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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, wherein the mass ratio of manganese to cobalt to copper is (0.1 to 5):1:(0.1 to 10).

[0026] Furthermore, the amount of catalyst used in step a) is 0.03% to 0.08% of the total liquid feed mass.

[0027] Furthermore, the premix in step a) is stirred to avoid liquid-liquid stratification.

[0028] 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.

[0029] 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%.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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 .

[0034] Furthermore, the flash evaporation conditions are as follows: temperature 69-75° C., pressure 0-1 MPaG.

[0035] 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 (cyclohexane, acetic acid, etc.) 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, and there is no dehydration function.

[0036] Furthermore, the M-stage reactor is an M-stage series bubbling reactor.

[0037] 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.

[0038] 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.

[0039] 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, designing the reactors in series, feeding cyclohexane and oxygen-containing gas in parallel, controlling the situation where the total cyclohexane / acetic acid ratio is relatively high, and also reducing the cyclohexane / acetic acid ratio of each stage of the reactor, breaking through the upper limit of the single-pass conversion rate of the process, while increasing the upper limit of the maximum water content of each stage of the reaction, thereby better solving the above-mentioned problems.

[0040] In addition, the present invention arranges an external circulation heat removal on the m-stage oxidation reactor. After the product of the last-stage oxidation reactor is heat-exchanged and heated with the first-stage reaction products to the m-1-th reaction products respectively, flash evaporation and dehydration are performed using the low-temperature heat of the reaction. This not only further controls the water content and avoids liquid-liquid stratification, but also greatly simplifies the subsequent separation process and significantly reduces the energy consumption of the separation process. It can be used in the one-step industrial production of cyclohexane and has achieved good technical effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] 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;

[0042] 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

[0043] The scheme of the present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0044] The method for preparing adipic acid by one-step oxidation of cyclohexane of the present invention is as follows: Figure 1 Process, including:

[0045] 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 can be arranged inside each stage of the oxidation reactor; the oxygen-containing gas, the discharge of the premixing kettle 1 and the cyclohexane in the reactors of each stage undergo oxidation reaction in the first oxidation reactor 3, the second oxidation reactor 6, ..., and the m-th stage oxidation reactor 9 under the condition of the presence of a catalyst; condensers 10, 11, ..., and the condenser 12 are arranged on the top of the first oxidation reactor 3, the second oxidation reactor 6, ..., and the m-th stage 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 in 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-th stage reaction product obtained by connecting to the m-1-th stage oxidation reactor is fed into the feed port of the m-th stage oxidation reactor 9 through the external circulation pump. The material is discharged at a constant flow rate at the bottom of the m-th oxidation reactor 9, passes through the flash heat exchanger 13, and then sequentially enters the external circulation heat exchanger arranged outside the m-1-th oxidation reactor, the external circulation heat exchanger 8 arranged outside the second-stage oxidation reactor 6, and the external circulation heat exchanger 4 arranged outside the first-stage oxidation reactor 3, and then flows into the flash tank 15. The return temperature of the external circulation material is controlled by controlling the bypass flow of the external circulation heat exchangers 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.

[0046] 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.

[0047] 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 mth stage 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 the oxygen-containing gas enters the gas distributor arranged in the reactor. The flash tank 15 is provided with an agitator to avoid liquid-liquid stratification during the flash evaporation process.

[0048] The present invention is further described below by way of examples. To facilitate comparison of process and technical effects, the catalysts in Examples 1-5 and Comparative Examples all use transition metal acetate catalysts containing manganese, cobalt and copper, and the mass ratio of manganese, cobalt and copper in the catalyst is 1.5:1:2. The mass ratio of manganese, cobalt and copper in the catalyst in Example 6 is 4.5:1:8. The amount of catalyst used 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.

[0049] [Example 1]

[0050] Adipic acid synthesis device and process flow Figure 1 As shown, 5 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 provided with an external circulation heat exchanger to remove heat, and the product after the 5th stage reactor is flashed, the flash temperature is 69-72°C, the pressure is normal pressure, the total feed cyclohexane / acetic acid mass ratio is 0.6, and each stage of the reactor reacts under the condition of a cyclohexane / acetic acid mass ratio of 0.23, the reaction temperature is 105°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%.

[0051] Reaction part: total conversion of cyclohexane 89.0%, selectivity of adipic acid 81.3%, energy consumption 4.5 kg standard oil / ton adipic acid, 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.

[0052] [Example 2]

[0053] Adipic acid synthesis device and process flow Figure 1As shown, four stages of bubbling bed reactors are connected in series, and the oxygen-containing gas is air. Cyclohexane and air are divided into four streams, all of which are fed in parallel. The 1-3 stage reactors are provided with an external circulation heat exchanger to remove heat, and the product after the 4th stage reactor is flash evaporated, the flash temperature is 69-72°C, the pressure is normal pressure, the total feed cyclohexane / acetic acid ratio is 0.6, and each stage of the reactor reacts under the condition of a cyclohexane / acetic acid mass ratio of 0.28, the reaction temperature is 105°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%.

[0054] Reaction part: total conversion of cyclohexane 79.0%, selectivity of adipic acid 81.2%, energy consumption 5.0 kg standard oil / ton adipic acid, 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.

[0055] [Example 3]

[0056] Adipic acid synthesis device and process flow Figure 1 As shown, three stages of 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 provided with an external circulation heat exchanger to remove heat, and the product after the 3rd stage reactor is flashed, the flash temperature is 71-75°C, the pressure is 0.1MPaG, the total feed cyclohexane / acetic acid ratio is 0.6, and each stage of the reactor reacts under the condition of a cyclohexane / acetic acid mass ratio of 0.36, the reaction temperature is 105°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%.

[0057] Reaction part: total conversion of cyclohexane 65.0%, selectivity of adipic acid 81.3%, energy consumption 6.0 kg standard oil / ton adipic acid, 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.

[0058] [Example 4]

[0059] 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 the product after the 5th stage reactor is flashed, the flash temperature is 69-72°C, the pressure is normal pressure, the total feed cyclohexane / acetic acid ratio is 0.6, and each stage of the reactor reacts under the condition of a cyclohexane / acetic acid mass ratio of 0.2, the reaction temperature is 120°C, the reaction pressure is 1.6MPaG, 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%.

[0060] Reaction part: total conversion of cyclohexane 93.4%, selectivity of adipic acid 80.0%, energy consumption 3.0 kg standard oil / ton adipic acid, 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.

[0061] [Example 5]

[0062] 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 the product after the 5th stage reactor is flashed, the flash temperature is 69-72°C, the pressure is normal pressure, the total feed cyclohexane / acetic acid ratio is 0.45, and each stage of the reactor reacts under the condition of a cyclohexane / acetic acid mass ratio of 0.24, the reaction temperature is 100°C, the reaction pressure is 1.0 MPaG, 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%.

[0063] Reaction part: cyclohexane total conversion rate 78.3%, adipic acid selectivity 83.0%, energy consumption 8.0 kg standard oil / ton adipic acid, no liquid-liquid stratification risk in the reactor. For easy comparison, the process conditions and main technical indicators are listed in Table 1 and Table 2.

[0064] [Example 6]

[0065] 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. The product after the 5th stage reactor is flashed, the flash temperature is 69-72°C, the pressure is normal pressure, the total feed cyclohexane / acetic acid mass ratio is 0.75, and each stage of the reactor reacts under the condition of a cyclohexane / acetic acid mass ratio of 0.45, the reaction temperature is 105°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%.

[0066] Reaction part: total conversion of cyclohexane 85.2%, selectivity of adipic acid 79.1%, energy consumption 6.0 kg standard oil / ton adipic acid, 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.

[0067] [Comparative Example 1]

[0068] Adipic acid synthesis device and process flow Figure 1As shown, five stages of bubbling bed reactors are connected in series. The difference compared with Example 1 is that no flash dehydration function is set (that is, the product after the fifth stage reactor directly enters the separation and refining unit), and cyclohexane is not divided into strands and is fed once through the premixing kettle. Figure 1 Set up external circulation to remove heat. The total feed cyclohexane / acetic acid ratio is 0.6, and the cyclohexane / acetic acid ratios of the 2nd to 5th stages are not controlled and decrease in sequence as the reaction proceeds. The reaction temperature is 105°C, the reaction pressure is 1.2MPaG, and the liquid volume space velocity is 0.25h -1 .

[0069] Reaction part: total conversion of cyclohexane 58.5%, selectivity of adipic acid 78.2%, energy consumption 25 kg standard oil / ton adipic acid, liquid-liquid stratification in stages 4 and 5. For easy comparison, the process conditions and main technical indicators are listed in Tables 1 and 2.

[0070] [Comparative Example 2]

[0071] Adipic acid synthesis device and process flow Figure 1 As shown, five stages of bubbling bed reactors are connected in series. The difference compared with Example 1 is that no flash dehydration function is set (that is, the product after the fifth stage reactor directly enters the separation and refining unit), and cyclohexane is not divided into strands and is fed once through the premixing kettle. Figure 1 Set up external circulation to remove heat. The total feed cyclohexane / acetic acid ratio is 0.8, and the cyclohexane / acetic acid ratios of the 2nd to 5th stages are not controlled and decrease in sequence as the reaction proceeds. The reaction temperature is 105°C, the reaction pressure is 1.2MPaG, and the liquid volume space velocity is 0.25h -1 .

[0072] Reaction part: total conversion of cyclohexane 52.2%, selectivity of adipic acid 76.0%, energy consumption 23 kg standard oil / ton adipic acid, liquid-liquid stratification occurred in stages 3 to 5. For easy comparison, the process conditions and main technical indicators are listed in Tables 1 and 2.

[0073] [Comparative Example 3]

[0074] Adipic acid synthesis device and process flow Figure 1 As shown, five stages of bubbling bed reactors are connected in series, and the oxygen-containing gas is air. Cyclohexane and air are divided into five streams, all of which are fed in parallel. The difference compared with Example 1 is that the flash dehydration function is not set (that is, the product after the fifth stage reactor directly enters the separation and refining unit). Each reactor is the same Figure 1 Set up external circulation to remove heat. The total feed cyclohexane / acetic acid ratio is 0.6, and each reactor reacts under the condition of cyclohexane / acetic acid mass ratio of 0.23, reaction temperature is 105℃, reaction pressure is 1.2MPaG, liquid volume space velocity is 0.25h -1 .

[0075] Reaction part: total conversion of cyclohexane 66.7%, selectivity of adipic acid 79.0%, energy consumption 27 kg standard oil / ton adipic acid, liquid-liquid stratification occurred in stage 5. For easy comparison, the process conditions and main technical indicators are listed in Tables 1 and 2.

[0076] [Comparative Example 4]

[0077] Adipic acid synthesis device and process flow Figure 1 As shown, the difference compared with Example 1 is that the liquid phase discharge from the 5th stage reactor is not heat exchanged with the external circulation heat exchanger of other reactors, the product after the 5th stage reactor is flashed, and the insufficient heat source required for dehydration is supplemented by low-pressure steam, and a steam heater is arranged in front of the flash tank 15.

[0078] Reaction part: total conversion of cyclohexane 82.7%, selectivity of adipic acid 81.3%, energy consumption 30 kg standard oil / ton adipic acid, 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.

[0079] Table 1 Process conditions of various embodiments and comparative examples

[0080]

[0081] Table 2 Summary of main technical indicators of various embodiments and comparative examples

[0082]

[0083] The method for preparing adipic acid by one-step oxidation of cyclohexane provided by the present invention has been described through the above embodiments. It is obvious that those skilled in the art can modify or appropriately change and combine the structure and preparation method described in the present invention without departing from the content, spirit and scope of the present invention to implement the present invention. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art, and they are all deemed 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 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 first-stage oxidation reactor to the m-1-stage oxidation reactor are respectively independently provided with respective product external circulations, 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 first stage reaction product, the second stream of cyclohexane and the second stream of oxygen-containing gas enter into a second stage oxidation reactor for reaction to obtain a second stage reaction product; c) each oxidation reactor after the second stage oxidation reactor is fed and reacted in the same manner as in step b), i.e., the product of the previous stage reaction and the corresponding cyclohexane and oxygen-containing gas of the current stage enter the current stage oxidation reactor for reaction to obtain the current stage reaction product; d) The m-th stage reaction product and the first stage reaction product to the m-1-th stage reaction product are respectively subjected to heat exchange and temperature increase, and then flash evaporation is performed. 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, and 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 then separated and refined to obtain the 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 Condensers are separately arranged on the top of each stage of oxidation reactor to recover the condensed and entrained liquid in the tail gas.

4. The method according to claim 1, characterized in that The product external circulation is cooled by heat exchange; preferably, the first-stage reaction products to the m-1-stage reaction products are all subjected to heat exchange with the m-stage reaction products before external circulation.

5. The method according to claim 1, characterized in that 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.

6. The method according to claim 1, characterized in that In the method, the mass ratio of cyclohexane to acetic acid in each oxidation reactor is 0.20-0.50; preferably, in the method, the feed amount of each cyclohexane in the m cyclohexane strands accounts for at least 5% of the total cyclohexane feed.

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 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.

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

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

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