Process and product and system for cyclohexane oxidation with tail gas recycle

Abstract

The application relates to the chemical industry field and discloses a tail gas recycling cyclohexane oxidation method, a product and a system. The tail gas recycling cyclohexane oxidation method comprises the following steps: in the presence of a solvent and a catalyst, a gas containing free oxygen is contacted with cyclohexane to perform an oxidation reaction, and mixed tail gas and liquid-phase products containing adipic acid are obtained; wherein, in the initial reaction stage, the gas containing free oxygen is obtained from external oxygen-containing gas; after the initial reaction, at least part of the mixed tail gas is returned to the oxidation reaction stage, and the gas containing free oxygen contains the mixed tail gas and the external oxygen-containing gas. The method has the advantages of low content of by-product glutaric acid and high selectivity of adipic acid. Moreover, the application has the advantages of small equipment investment, simple operation process, low cost, environmental protection and the like in the continuous industrial production of adipic acid prepared by the one-step oxidation method of cyclohexane.

Description

Technical Field

[0001] This invention relates to the field of chemical engineering, and specifically to a method, product, and system for the oxidation of cyclohexane for the reuse of tail gas. Background Technology

[0002] Adipic acid is an important basic organic chemical raw material. Its main use is in the production of nylon 66 salt, and it can also be used in the production of polyurethane, plasticizers, polyamides, synthetic leather, lubricants, etc. Adipic acid is usually derived from the catalytic oxidation of cyclohexane. In particular, the one-step oxidation method of cyclohexane to produce adipic acid is receiving increasing attention. For example, using cyclohexane as a raw material and air or oxygen as an oxidant to synthesize adipic acid, most existing technologies optimize this method from the perspective of developing new catalysts. For example, biomimetic catalysis and free radical oxidation are used to convert cyclohexane into adipic acid. For instance, CN 1231449C (Invention title: Method for preparing adipic acid by biomimetic catalytic oxidation of cyclohexane with oxygen) discloses a method for preparing adipic acid by oxidizing cyclohexane with air using metalloporphyrin as a catalyst.

[0003] While the one-step oxidation of cyclohexane to adipic acid in the existing technology achieves efficient conversion of cyclohexane to adipic acid, the numerous side reactions during the oxidation process, especially the presence of a large amount of glutaric acid in the product, affect the economic efficiency of this synthesis reaction.

[0004] Furthermore, the existing one-step molecular oxygen oxidation process for producing adipic acid from cyclohexane generates a large amount of tail gas. The main components of the tail gas are oxygen, nitrogen (or other inert gases), carbon monoxide, carbon dioxide, and small amounts of cyclohexane, acetic acid, etc. The release of tail gas into the atmosphere will cause environmental problems such as increased VOCs, resulting in low environmental benefits.

[0005] Therefore, how to provide a simple, efficient, green and environmentally friendly method for synthesizing adipic acid, and solve the problems of large amounts of tail gas emissions and large amounts of glutaric acid byproducts in the adipic acid synthesis solution of the one-step oxidation of cyclohexane to produce adipic acid in the existing technology, is the research direction in this field. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a method, product, and system for cyclohexane oxidation with waste gas recovery. This method effectively solves the problems mentioned above, offering advantages such as low glutaric acid content as a byproduct and high selectivity for adipic acid. Furthermore, this invention requires minimal equipment investment and involves a simple operation process. When used in the continuous industrial production of adipic acid from cyclohexane via one-step oxidation, it offers advantages such as low cost and a more environmentally friendly process.

[0007] The first aspect of the present invention is to provide a method for cyclohexane oxidation for tail gas recycling, comprising: contacting a gas containing free oxygen with cyclohexane in the presence of a solvent and a catalyst to carry out an oxidation reaction, thereby obtaining a mixed tail gas and a liquid-phase product containing adipic acid; wherein, in the initial reaction stage, the gas containing free oxygen is derived from an external oxygen-containing gas; and after the initial reaction, at least a portion of the mixed tail gas is returned to the oxidation reaction stage, wherein the gas containing free oxygen contains the mixed tail gas and the external oxygen-containing gas.

[0008] In a preferred embodiment of the present invention, before returning the mixed tail gas to the oxidation reaction stage, the mixed tail gas is contacted with an alkaline material. Verification has shown that contacting the mixed tail gas with an alkaline material before returning it to the oxidation reaction stage for reuse can significantly reduce the content of the byproduct glutaric acid in the resulting reaction solution, and further improve the selectivity of adipic acid.

[0009] The alkaline material can be selected from a wide range. In a preferred embodiment of the present invention, the alkaline material is preferably a solid material; more preferably, the alkaline material contains at least one of alkaline hydroxide and alkaline oxide.

[0010] In a more preferred embodiment of the present invention, the alkaline material contains calcium oxide, preferably a mixture of calcium oxide and calcium chloride, and more preferably, the mass ratio of calcium chloride to calcium oxide is (0.1-1):1.

[0011] According to the present invention, the proportion of the mixed exhaust gas returned to the oxidation reaction stage can be selected within a wide range. In a preferred embodiment of the present invention, taking the total volume of the mixed exhaust gas obtained after the oxidation reaction as 100%, 10%-100%, preferably 45%-75%, of the mixed exhaust gas obtained after the oxidation reaction is returned to the oxidation reaction stage. For example, 45%, 55%, 65%, 75%, and any two values ​​or any range of any two values.

[0012] According to the present invention, the volume content of oxygen in the oxygen-containing gas during the initial reaction stage and after the initial reaction can be selected within a wide range. In a preferred embodiment of the present invention, the volume content of oxygen in the oxygen-containing gas during the initial reaction stage and after the initial reaction is 15-50%, preferably 20%-30%; for example, 20%, 24%, 28%, 30%, and any two values ​​or any range of any two values.

[0013] In a more preferred embodiment of the present invention, the oxygen-containing gas also contains CO, preferably with a volume content of 0.1%-5%, more preferably 0.3%-3%, in the oxygen-containing gas. In this more preferred embodiment, the inventors of the present invention have found that the content of the byproduct glutaric acid in the reaction solution obtained from the reaction can be significantly further reduced, and the selectivity of adipic acid is also further improved.

[0014] In a preferred embodiment of the present invention, after the oxidation reaction, the mixed exhaust gas obtained from the oxidation reaction is further subjected to post-treatment to remove at least some organic matter, and the post-treated mixed exhaust gas is then returned to the oxidation reaction stage.

[0015] More preferably, when the method includes contacting the mixed exhaust gas with an alkaline material, the post-treatment step is performed first, and then the post-treated mixed exhaust gas is contacted with the alkaline material.

[0016] More preferably, the post-treatment method includes, but is not limited to, condensation. More preferably, the condensation temperature is 6-25°C, and preferably the liquid obtained from condensation is returned to the oxidation reaction stage.

[0017] According to the present invention, the solvent can be selected from a wide range. In a preferred embodiment of the present invention, the solvent is selected from at least one of polar protic solvents, preferably an organic polar protic solvent with 6 or fewer carbon atoms, more preferably an acidic compound with pKa ≥ 3, and even more preferably acetic acid and / or propionic acid.

[0018] According to the present invention, the mass ratio of cyclohexane to solvent can be selected within a wide range. In a preferred embodiment of the present invention, the mass ratio of cyclohexane to solvent is (0.4-1.5):1, preferably (0.6-1):1.

[0019] According to the present invention, the mass ratio of cyclohexane to the catalyst can be selected within a wide range. In a preferred embodiment of the present invention, the mass ratio of cyclohexane to the catalyst is (600-20000):1, preferably (1500-10000):1; for example, 1500, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 10000, and any two values ​​or any range of two values ​​in any ratio to 1.

[0020] According to the present invention, the catalyst can be a conventional catalyst used in the art for the oxidation of cyclohexane to adipic acid. This includes, but is not limited to, cases where the catalyst contains at least one of the fourth-period transition metal elements.

[0021] In a more preferred embodiment of the present invention, the catalyst contains at least one of copper, manganese and cobalt.

[0022] In a more preferred embodiment of the present invention, the catalyst contains a copper compound and / or a manganese compound, as well as a rare earth compound, preferably in a mass ratio of rare earth elements to the total mass of copper and manganese elements of (0.5-10):1, more preferably (1-5):1.

[0023] According to the present invention, the feeding method before the reaction can adopt conventional feeding methods in the art. In a preferred embodiment of the present invention, the method includes first mixing the catalyst and cyclohexane with the solvent to obtain a cyclohexane-containing mixture, and then contacting the cyclohexane in the mixture with the gas containing free oxygen under continuous injection.

[0024] In a more preferred embodiment of the present invention, the ratio of the mass flow rate of the oxygen-containing gas to the flow rate of the reaction mixture based on the mass of the solvent during the reaction process is (10-100):1, preferably (20-50):1.

[0025] According to the present invention, the conditions of the oxidation reaction can be selected within a wide range. In a preferred embodiment of the present invention, the conditions of the oxidation reaction include: a reaction temperature of 90-120°C; and / or a reaction pressure of 2-5 MPa; and / or a reaction time of 1-4 h.

[0026] A second aspect of the present invention is to provide a liquid-phase product containing adipic acid prepared according to the method of the first aspect. The content of glutaric acid in the liquid-phase product containing adipic acid obtained by the present invention is significantly lower than the content of the product in the prior art.

[0027] A third aspect of the present invention is to provide a system for the oxidation of cyclohexane for tail gas recycling, comprising at least:

[0028] A reactor, comprising an inlet, an outlet, a gas outlet, and a gas inlet, wherein the reactor has at least one inlet for feeding one or more of cyclohexane, a solvent, and a catalyst, either separately or simultaneously; the reactor outlet is used for discharging the synthesis liquid; a gas supply device, wherein the outlet of the gas supply device is connected to the gas inlet of the reactor for introducing oxygen-containing gas into the reactor; and a tail gas purifier, wherein the inlet of the tail gas purifier is connected to the gas outlet of the reactor, and the outlet of the tail gas purifier is connected to the gas inlet of the reactor.

[0029] In a preferred embodiment of the present invention, an alkaline material is provided in the gas passage of the exhaust gas purifier; preferably, the alkaline material is a solid material; more preferably, the alkaline material contains at least one of alkaline hydroxide and alkaline oxide; even more preferably, the alkaline material contains calcium oxide, preferably a mixture of calcium oxide and calcium chloride, and even more preferably, the mass ratio of calcium chloride to calcium oxide is (0.1-1):1.

[0030] In a preferred embodiment of the present invention, the system further includes a gas mixer, the inlet of which is connected to the outlet of the exhaust gas purifier and the outlet of the gas supply device, respectively, and the outlet of the gas mixer is connected to the inlet of the reactor; and / or, a condenser is further provided between the outlet of the reactor and the exhaust gas purifier; preferably, the condenser includes at least two outlets, one outlet is connected to the inlet of the exhaust gas purifier, and the other outlet is used to discharge part of the exhaust gas.

[0031] In a preferred embodiment of the present invention, the system further includes: a raw material storage tank, the outlet of which is connected to the inlet of the reactor; and / or,

[0032] A synthesis liquid collection tank, wherein the inlet of the synthesis liquid collection tank is connected to the outlet of the reactor; and / or,

[0033] The gas supply device includes at least two gas sources: a gas source capable of supplying oxygen-containing gas and a gas source capable of supplying carbon monoxide.

[0034] Preferably, the gas supply device further includes a gas source for supplying nitrogen.

[0035] According to the present invention, the components in the above-described system, such as reactors, gas supply devices, exhaust gas purifiers, gas mixers, condensers, raw material storage tanks, synthesis liquid collection tanks, and gas sources, are conventional components in the art. The present invention does not have any special requirements, as long as they can achieve their respective functions and meet the specific connection relationships in the system of the present invention. For example, reactors include, but are not limited to, reaction vessels.

[0036] In a more preferred embodiment of the present invention, the system is as follows: Figure 1 As shown, the system for cyclohexane oxidation and tail gas reuse includes:

[0037] The reactor 1 is provided with a feed inlet, a discharge outlet, a gas outlet, and a gas inlet (7 containing free oxygen gas). The reactor 1 has at least one feed inlet for feeding one or more of cyclohexane, solvent, and catalyst, either separately or simultaneously. The discharge outlet of the reactor 1 is used for discharging the synthesis liquid.

[0038] Gas supply device 9, the outlet of which is connected to the inlet of the reaction vessel 1, for introducing oxygen-containing gas into the reaction vessel 1;

[0039] The exhaust gas purifier 3 has an inlet that can be connected to the outlet of the reaction vessel 1, and the outlet of the exhaust gas purifier 3 can be connected to the inlet of the reaction vessel 1.

[0040] The exhaust gas purifier 3 has an alkaline material in its gas passage; preferably, the alkaline material is a solid material; more preferably, the alkaline material contains at least one of alkaline hydroxide and alkaline oxide; even more preferably, the alkaline material contains calcium oxide, preferably a mixture of calcium oxide and calcium chloride, and even more preferably, the mass ratio of calcium chloride to calcium oxide is (0.1-1):1.

[0041] A gas mixer 5 is provided, the inlet of which can be connected to the outlet of the exhaust gas purifier 3 and the outlet of the gas supply device 9 respectively, and the outlet of the gas mixer 5 can be connected to the inlet of the reaction vessel 1; a condenser 8 is also provided between the outlet of the reaction vessel 1 and the exhaust gas purifier 3; preferably, the condenser 8 includes at least two outlets, one outlet is connected to the inlet of the exhaust gas purifier 3, and the other outlet (exhaust gas vent outlet 6) is used to discharge part of the exhaust gas.

[0042] Raw material storage tank 2, the outlet of which is connected to the inlet of the reaction vessel 1;

[0043] Synthesis liquid collection tank 4, the inlet of which is connected to the outlet of the reaction vessel 1;

[0044] The gas supply device 9 includes at least the following two gas sources: a gas source capable of supplying oxygen-containing gas and a gas source capable of supplying carbon monoxide.

[0045] Preferably, the gas supply device 9 further includes a gas source for supplying nitrogen.

[0046] Based on the above technical solution, this invention relates to a method for producing adipic acid via a one-step oxidation of cyclohexane, mainly solving the problems of large-scale tail gas emissions and the presence of a large amount of glutaric acid as a byproduct in the adipic acid synthesis solution in existing one-step oxidation methods. This invention employs a one-step oxidation method for producing adipic acid, in which at least a portion of the reaction tail gas is mixed with an oxygen-containing gas from the outside environment and recycled to the oxidation reaction stage. This tail gas reuse not only reduces the environmental pressure caused by tail gas emissions but also unexpectedly achieves the beneficial effect of reducing the content of the byproduct glutaric acid and improving the selectivity of the target product, adipic acid.

[0047] Moreover, the equipment investment of this invention is small and the operation process is simple. When used in the continuous industrial production of adipic acid by one-step oxidation of cyclohexane, it has the advantages of low cost and more environmentally friendly process. Attached Figure Description

[0048] Figure 1 This is a schematic diagram of the reaction path and the cyclohexane oxidation system for tail gas recycling in a preferred embodiment of the present invention.

[0049] 1. Reactor; 2. Raw material storage tank; 3. Tail gas purifier; 4. Synthesis liquid collection tank; 5. Gas mixer; 6. Tail gas exhaust outlet; 7. Gas inlet containing free oxygen; 8. Condenser; 9. Gas supply device Detailed Implementation

[0050] The present invention will now be described in detail with reference to specific embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0051] Unless otherwise specified, other raw materials and equipment are all commercially available products or equipment in this field.

[0052] In the following examples and comparative examples, high performance liquid chromatography was used to analyze the mass concentrations of adipic acid and glutaric acid in the reaction solution.

[0053] The method for calculating the selectivity of adipic acid is as follows:

[0054] Adipic acid selectivity = (Moles of adipic acid produced / Moles of cyclohexane consumed) * 100%

[0055] The conversion rate of cyclohexane is calculated as follows:

[0056] Cyclohexane conversion rate = (Moles of cyclohexane consumed in the reaction) / (Moles of cyclohexane in the feed) * 100%

[0057] The following examples are combined Figure 1 To explain, the fresh oxygen-containing gas is the oxygen-containing gas from the outside environment mentioned above, and the different gases in the fresh oxygen-containing gas in the embodiments come from different gas sources.

[0058] The process conditions for some of the examples and comparative examples are listed in Table 1, and the results analysis is listed in Table 2.

[0059]

Example 1

[0060] 1) Prepare 100 kg of Co-Mn-Cu catalyst acetic acid solution, wherein the concentration of Co element is 40 ppm, the concentration of Mn element is 60 ppm, and the concentration of Cu element is 80 ppm. Add 20 kg of cyclohexane as a reaction raw material. Mix the above materials to prepare acetic acid solution and add it to reaction vessel 1 through raw material storage tank 2.

[0061] 2) Fresh oxygen-containing gas (oxygen volume content 21%, carbon monoxide volume content 1%, the remainder is nitrogen) is continuously introduced into the reactor 1 through the free oxygen gas inlet 7. The gas flow rate is 20 kg / h. The reactor 1 is heated to the reaction temperature of 100℃, the reaction pressure is 3.0 MPa, and the condenser temperature is 10℃.

[0062] 3) Acetic acid solution and oxygen-containing gas are continuously fed into reactor 1. The feed flow rate of acetic acid solution is 1 kg / h (calculated based on the amount of acetic acid in the solution), and the flow rate of oxygen-containing gas is 20 kg / h.

[0063] 4) The reaction tail gas is condensed by condenser 8, the liquid is returned to reactor 1, 30% of the tail gas is discharged, and the remaining 70% of the tail gas volume is purified in tail gas purifier 3 with a mixture of calcium oxide and calcium chloride (calcium oxide 80% mass fraction) and then mixed with fresh oxygen-containing gas in gas mixer 5. The mixed gas continuously enters reactor 1 at a gas flow rate of 20 kg / h.

[0064] 5) After 40 hours of reaction, the feed was stopped and the reaction was terminated. The reaction residence time was calculated to be 4 hours. A sample of the adipic acid oxidation reaction solution was taken from the synthesis liquid collection tank 4 and the composition was analyzed. The cyclohexane conversion rate was calculated to be 22.6%, the adipic acid selectivity was 95.0%, and the concentration of the byproduct glutaric acid in the reaction solution was 826 ppm.

[0065]

Example 2

[0066] 1) Prepare 100 kg of Co-Mn-Cu catalyst acetic acid solution, wherein the concentration of Co element is 40 ppm, the concentration of Mn element is 60 ppm, and the concentration of Cu element is 80 ppm. Add 20 kg of cyclohexane as a reaction raw material. Mix the above materials to prepare acetic acid solution and add it to reaction vessel 1 through raw material storage tank 2.

[0067] 2) Fresh oxygen-containing gas (oxygen volume content 21%, the remainder is nitrogen) is continuously introduced into the reactor 1 through the free oxygen gas inlet 7. The gas flow rate is 20 kg / h. The reactor 1 is heated to the reaction temperature of 100℃, the reaction pressure is 3.0 MPa, and the condenser temperature is 10℃.

[0068] 3) Acetic acid solution and oxygen-containing gas are continuously fed into reactor 1. The feed flow rate of acetic acid solution is 1 kg / h (calculated based on the amount of acetic acid in the solution), and the flow rate of oxygen-containing gas is 20 kg / h.

[0069] 4) The reaction tail gas is condensed by condenser 8, the liquid is returned to reactor 1, 30% of the tail gas is discharged, and the remaining 70% of the tail gas volume is purified in tail gas purifier 3 with a mixture of calcium oxide and calcium chloride (calcium oxide 80% mass fraction) and then mixed with fresh gas in gas mixer 5. The mixed gas continuously enters reactor 1 with a gas flow rate of 20 kg / h.

[0070] 5) After 40 hours of reaction, the feed was stopped and the reaction was terminated. The reaction residence time was calculated to be 4 hours. A sample of the adipic acid oxidation reaction solution was taken from the synthesis liquid collection tank 4 and the composition was analyzed. The cyclohexane conversion rate was calculated to be 22.3%, the adipic acid selectivity was 94.1%, and the concentration of the byproduct glutaric acid in the reaction solution was 1036 ppm.

[0071]

Example 3

[0072] 1) Prepare 100 kg of Co-Mn-Cu catalyst acetic acid solution, wherein the concentration of Co element is 40 ppm, the concentration of Mn element is 60 ppm, and the concentration of Cu element is 80 ppm. Add 20 kg of cyclohexane as a reaction raw material. Mix the above materials to prepare acetic acid solution and add it to reaction vessel 1 through raw material storage tank 2.

[0073] 2) Fresh oxygen-containing gas (oxygen volume content 21%, the remainder is nitrogen) is continuously introduced into the reactor 1 through the free oxygen gas inlet 7. The gas flow rate is 20 kg / h. The reactor 1 is heated to the reaction temperature of 100℃, the reaction pressure is 3.0 MPa, and the condenser temperature is 10℃.

[0074] 3) Acetic acid solution and oxygen-containing gas are continuously fed into reactor 1. The feed flow rate of acetic acid solution is 1 kg / h (calculated based on the amount of acetic acid in the solution), and the flow rate of oxygen-containing gas is 20 kg / h.

[0075] 4) The reaction tail gas is condensed by condenser 8, the liquid is returned to reactor 1, 30% of the tail gas is discharged, and the remaining 70% of the tail gas volume is purified with calcium oxide (100% mass fraction of calcium oxide) in tail gas purifier 3 and then mixed with fresh gas in gas mixer 5. The mixed gas continuously enters reactor 1 with a gas flow rate of 20 kg / h.

[0076] 5) After 40 hours of reaction, the feed was stopped and the reaction was terminated. The reaction residence time was calculated to be 4 hours. A sample of the adipic acid oxidation reaction solution was taken from the synthesis liquid collection tank 4 and the composition was analyzed. The cyclohexane conversion rate was calculated to be 21.9%, the adipic acid selectivity was 93.4%, and the concentration of the byproduct glutaric acid in the reaction solution was 1977 ppm.

[0077]

Example 4

[0078] 1) Prepare 100 kg of Co-Mn-Cu catalyst acetic acid solution, wherein the concentration of Co element is 40 ppm, the concentration of Mn element is 60 ppm, and the concentration of Cu element is 80 ppm. Add 20 kg of cyclohexane as a reaction raw material. Mix the above materials to prepare acetic acid solution and add it to reaction vessel 1 through raw material storage tank 2.

[0079] 2) Fresh oxygen-containing gas (oxygen volume content 21%, the remainder is nitrogen) is continuously introduced into the reactor 1 through the free oxygen gas inlet 7. The gas flow rate is 20 kg / h. The reactor 1 is heated to the reaction temperature of 100℃, the reaction pressure is 3.0 MPa, and the condenser temperature is 10℃.

[0080] 3) Acetic acid solution and oxygen-containing gas are continuously fed into reactor 1. The feed flow rate of acetic acid solution is 1 kg / h (calculated based on the amount of acetic acid in the solution), and the flow rate of oxygen-containing gas is 20 kg / h.

[0081] 4) The reaction tail gas is condensed by condenser 8, the liquid is returned to reactor 1, 30% of the tail gas is discharged, and the remaining 70% of the tail gas volume is mixed with fresh gas in gas mixer 5. The mixed gas is continuously fed into reactor 1 at a gas flow rate of 20 kg / h.

[0082] 5) After 40 hours of reaction, the feed was stopped and the reaction was terminated. The reaction residence time was calculated to be 4 hours. A sample of the adipic acid oxidation reaction solution was taken from the synthesis liquid collection tank 4 and the composition was analyzed. The cyclohexane conversion rate was calculated to be 24.5%, the adipic acid selectivity was 86.3%, and the concentration of the byproduct glutaric acid in the reaction solution was 3456 ppm.

[0083]

Example 5

[0084] The reaction was carried out according to the method of Example 1, except that some conditions were adjusted, as shown in Table 1. Conditions not listed in Table 1 are the same as those in Example 1, and an adipic acid oxidation synthesis solution was obtained.

[0085] A sample of the adipic acid oxidation reaction solution was taken from the synthesis liquid collection tank 4, and its composition was analyzed by high performance liquid chromatography. The mass concentration of adipic acid in the synthesis liquid and the mass concentration of the byproduct glutaric acid were calculated. The conversion rate of cyclohexane and the selectivity of adipic acid were also calculated. The results are shown in Table 2.

[0086]

Example 6

[0087] The reaction was carried out according to the method of Example 1, except that some conditions were adjusted, as shown in Table 1. Conditions not listed in Table 1 are the same as those in Example 1, and an adipic acid oxidation synthesis solution was obtained.

[0088] A sample of the adipic acid oxidation reaction solution was taken from the synthesis liquid collection tank 4, and its composition was analyzed by high performance liquid chromatography. The mass concentration of adipic acid in the synthesis liquid and the mass concentration of the byproduct glutaric acid were calculated. The conversion rate of cyclohexane and the selectivity of adipic acid were also calculated. The results are shown in Table 2.

[0089]

Example 7

[0090] The method of Example 1 was used to oxidize cyclohexane to produce adipic acid, except that the Co element in the catalyst was replaced with lanthanum (La), and the concentration of La element was 40 ppm, while other conditions remained unchanged.

[0091]

Example 8

[0092] The method of cyclohexane oxidation to adipic acid was carried out according to Example 1, except that the tail gas recirculation ratio was changed to 30%, while other conditions remained the same.

[0093]

Example 9

[0094] The method of cyclohexane oxidation to adipic acid was carried out according to Example 1, except that fresh oxygen-containing gas (oxygen volume content 14%, the remainder being nitrogen) was used, while everything else remained the same.

[0095] Comparative Example 1

[0096] 1) Prepare 100 kg of Co-Mn-Cu catalyst acetic acid solution, wherein the concentration of Co element is 40 ppm, the concentration of Mn element is 60 ppm, and the concentration of Cu element is 80 ppm. Add 20 kg of cyclohexane as a reaction raw material. Mix the above materials to prepare acetic acid solution and add it to reaction vessel 1 through raw material storage tank 2.

[0097] 2) Fresh oxygen-containing gas (oxygen volume content 21%, the remainder is nitrogen) is continuously introduced into the reactor 1 through the free oxygen gas inlet 7. The gas flow rate is 20 kg / h. The reactor 1 is heated to the reaction temperature of 100℃, the reaction pressure is 3.0 MPa, and the condenser temperature is 10℃.

[0098] 3) Acetic acid solution and oxygen-containing gas are continuously fed into reactor 1. The feed flow rate of acetic acid solution is 1 kg / h (calculated based on the amount of acetic acid in the solution), and the flow rate of oxygen-containing gas is 20 kg / h.

[0099] 4) The reaction tail gas is condensed by condenser 8, the liquid is returned to reactor 1, and the tail gas is 100% discharged.

[0100] 5) After 40 hours of reaction, the feed was stopped and the reaction was terminated. The reaction residence time was calculated to be 4 hours. A sample of the adipic acid oxidation reaction solution was taken from the synthesis liquid collection tank 4 and the composition was analyzed. The cyclohexane conversion rate was calculated to be 24.8%, the adipic acid selectivity was 67.7%, and the concentration of the byproduct glutaric acid in the reaction solution was 9429 ppm.

[0101] Comparative Example 2

[0102] 1) Prepare 100 kg of Co-Mn-Cu catalyst acetic acid solution, wherein the concentration of Co element is 40 ppm, the concentration of Mn element is 60 ppm, and the concentration of Cu element is 80 ppm. Add 20 kg of cyclohexane as a reaction raw material. Mix the above materials to prepare acetic acid solution and add it to reaction vessel 1 through raw material storage tank 2.

[0103] 2) Fresh oxygen-containing gas (oxygen volume content 21% and carbon dioxide volume content 1% with the remainder being nitrogen) is continuously introduced into the reactor 1 through the free oxygen gas inlet 7. The gas flow rate is 20 kg / h. The reactor 1 is heated to the reaction temperature of 100°C, the reaction pressure is 3.0 MPa, and the condenser temperature is 10°C.

[0104] 3) Acetic acid solution and oxygen-containing gas are continuously fed into reactor 1. The feed flow rate of acetic acid solution is 1 kg / h (calculated based on the amount of acetic acid in the solution), and the flow rate of oxygen-containing gas is 20 kg / h.

[0105] 4) The reaction tail gas is condensed by condenser 8, the liquid is returned to reactor 1, and the tail gas is 100% discharged.

[0106] 5) After 40 hours of reaction, the feed was stopped and the reaction was terminated. The reaction residence time was calculated to be 4 hours. A sample of the adipic acid oxidation reaction solution was taken from the synthesis liquid collection tank 4 and the composition was analyzed. The cyclohexane conversion rate was calculated to be 24.7%, the adipic acid selectivity was 56.3%, and the concentration of the byproduct glutaric acid in the reaction solution was 43109 ppm.

[0107] Table 1

[0108]

[0109] Table 2

[0110]

[0111]

[0112] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

[0113] All publications, patent applications, patents, and other references mentioned in this specification are incorporated herein by reference. Unless otherwise defined, all technical and scientific terms used in this specification have the meanings commonly understood by those skilled in the art. In case of conflict, the definitions in this specification shall prevail.

[0114] When this specification uses the prefixes “known to those skilled in the art,” “prior art,” or similar terms to derive materials, substances, methods, steps, apparatus, or components, the objects derived from such prefixes cover those commonly used in the art at the time of this application, but also include those that are not currently commonly used but will become generally recognized in the art as suitable for similar purposes.

[0115] The endpoints and any values ​​of the ranges disclosed in this application are not limited to the precise ranges or values; such ranges or values ​​should be understood to include values ​​close to them. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. In principle, various technical solutions can be combined with each other to obtain new technical solutions, which should also be considered as specifically disclosed herein.

[0116] In the context of this specification, except where expressly stated otherwise, any matters or issues not mentioned shall apply directly to those known in the art without any modification.

[0117] Furthermore, any implementation described herein can be freely combined with one or more other implementations described herein, and the resulting technical solutions or technical ideas shall be regarded as part of the original disclosure or original record of the present invention, and should not be regarded as new content not disclosed or anticipated herein, unless those skilled in the art consider the combination to be obviously unreasonable.

Claims

1. A method for cyclohexane oxidation for tail gas recycling, comprising: In the presence of a solvent and a catalyst, a gas containing free oxygen is contacted with cyclohexane to carry out an oxidation reaction, yielding a mixed tail gas and a liquid-phase product containing adipic acid. The catalyst contains at least one of copper, manganese and cobalt. In the initial reaction stage, the free oxygen-containing gas comes from an external oxygen-containing gas. Following the oxidation reaction, the process further includes post-treatment of the mixed tail gas obtained from the oxidation reaction to remove at least some organic matter. A portion of the post-treated mixed tail gas is then returned to the oxidation reaction stage. The post-treatment method includes condensation, and the condensed liquid is returned to the oxidation reaction stage. The gas containing free oxygen contains the mixed tail gas and oxygen-containing gas from the outside. Before the mixed tail gas returns to the oxidation reaction stage, it includes contacting the mixed tail gas with an alkaline material. The alkaline material contains at least one of an alkaline hydroxide and an alkaline oxide. During and after the initial reaction, the oxygen content in the oxygen-containing gas is 20%-50% by volume. Taking the total volume of the mixed exhaust gas obtained after the oxidation reaction as 100%, 45%-100% of the mixed exhaust gas obtained after the oxidation reaction is returned to the oxidation reaction stage.

2. The method according to claim 1, characterized in that: The alkaline material contains calcium oxide.

3. The method according to claim 2, characterized in that: The alkaline material is a mixture of calcium oxide and calcium chloride.

4. The method according to claim 3, characterized in that: The mass ratio of calcium chloride to calcium oxide is (0.1-1):

1.

5. The method according to claim 1, characterized in that: Taking the total volume of the mixed exhaust gas obtained after the oxidation reaction as 100%, 45%-75% of the mixed exhaust gas obtained after the oxidation reaction is returned to the oxidation reaction stage.

6. The method according to claim 1, characterized in that: During and after the initial reaction, the oxygen content in the oxygen-containing gas is 20%-30% by volume.

7. The method according to claim 1, characterized in that: The oxygen-containing gas also contains CO.

8. The method according to claim 7, characterized in that: The volume percentage of CO in the oxygen-containing gas is 0.1%-5%.

9. The method according to claim 7, characterized in that: The volume percentage of CO in the oxygen-containing gas is 0.3%-3%.

10. The method according to claim 1, characterized in that: The condensation temperature is 6-25℃.

11. The method according to claim 1, characterized in that: The solvent is selected from at least one of polar protic solvents.

12. The method according to claim 1, characterized in that: The solvent is an organic polar protic solvent with 6 or fewer carbon atoms.

13. The method according to claim 12, characterized in that: The solvent is an acidic compound with pKa ≥ 3.

14. The method according to claim 12, characterized in that: The solvent is acetic acid and / or propionic acid.

15. The method according to claim 1, characterized in that: The mass ratio of cyclohexane to solvent is (0.4-1.5):

1.

16. The method according to claim 1, characterized in that: The mass ratio of cyclohexane to solvent is (0.6-1):

1.

17. The method according to claim 1, characterized in that: The mass ratio of cyclohexane to the catalyst is (600-20000):

1.

18. The method according to claim 1, characterized in that: The mass ratio of cyclohexane to the catalyst is (1500-10000):

1.

19. The method according to claim 1, characterized in that: The catalyst contains copper and / or manganese compounds, as well as rare earth compounds.

20. The method according to claim 19, characterized in that: The ratio of the mass of rare earth elements to the total mass of copper and manganese elements is (0.5-10):

1.

21. The method according to claim 19, characterized in that: The ratio of the mass of rare earth elements to the total mass of copper and manganese elements is (1-5):

1.

22. The method according to claim 1, characterized in that: The method includes first mixing the catalyst and cyclohexane with the solvent to obtain a cyclohexane-containing mixture, and then contacting the cyclohexane in the mixture with the gas containing free oxygen under continuous injection.

23. The method according to claim 1, characterized in that: During the reaction, the ratio of the mass flow rate of the gas containing free oxygen to the flow rate of the reaction mixture (based on the mass of the solvent) is (10-100):

1.

24. The method according to claim 1, characterized in that: During the reaction, the ratio of the mass flow rate of the gas containing free oxygen to the flow rate of the reaction mixture (based on the mass of the solvent) is (20-50):

1.

25. The method according to any one of claims 1-24, characterized in that: The conditions for the oxidation reaction include: The reaction temperature is 90-120℃; and / or, The reaction pressure is 2-5 MPa; and / or, The reaction time is 1-4 hours.

26. The method according to any one of claims 1-24, characterized in that: The system used in the method includes at least: A reactor having an inlet, an outlet, an outlet, and an outlet, wherein the number of inlets is at least one for feeding one or more of cyclohexane, solvent, and catalyst, either separately or simultaneously, and the outlet is for discharging the synthesis liquid. A gas supply device, wherein the outlet of the gas supply device is connected to the inlet of the reactor for introducing oxygen-containing gas into the reactor; An exhaust gas purifier, wherein the air inlet of the exhaust gas purifier is connected to the air outlet of the reactor, and the air outlet of the exhaust gas purifier is connected to the air inlet of the reactor; an alkaline material is provided in the gas passage of the exhaust gas purifier. The alkaline material contains at least one of alkaline hydroxides and alkaline oxides; A condenser is also provided between the gas outlet of the reactor and the exhaust gas purifier, and the liquid flows back to the reactor; the condenser includes at least two gas outlets, one of which is connected to the gas inlet of the exhaust gas purifier, and the other of which is used to discharge part of the exhaust gas.

27. The method according to claim 26, characterized in that: The system also includes a gas mixer, the inlet of which can be connected to the outlet of the exhaust gas purifier and the outlet of the gas supply device, respectively, and the outlet of the gas mixer can be connected to the inlet of the reactor.

28. The method according to claim 26, characterized in that: The system also includes: A raw material storage tank, the outlet of which is connected to the inlet of the reactor; and / or, A synthesis liquid collection tank, wherein the inlet of the synthesis liquid collection tank is connected to the outlet of the reactor; and / or, The gas supply device includes at least two gas sources: a gas source capable of supplying oxygen-containing gas and a gas source capable of supplying carbon monoxide.

29. The method according to claim 26, characterized in that: The gas supply device also includes a gas source for supplying nitrogen.

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