Methods for producing adipic acid with low N2O tail gas emissions

Abstract

This invention relates to the field of adipic acid synthesis technology and discloses a method for producing adipic acid with low N2O tail gas emissions. The method includes: Step S1. A first contact reaction is carried out between cyclohexene, hydrogen peroxide, and a first catalyst, wherein the first catalyst is a solid catalyst comprising a tungsten-doped titanium-containing molecular sieve; the liquid phase material from the contact reaction is subjected to oil-water separation to obtain an aqueous phase containing cyclohexane oxide and an oil phase containing cyclohexene; Step S2. A second contact reaction is carried out between the aqueous phase containing cyclohexane oxide and nitric acid and a second catalyst, wherein the second catalyst is a Cu-containing... 2+ V 5+ and Mo 6+ The method utilizes ionic liquid catalysts. It results in low N2O emissions, high exhaust gas absorption rate, low production cost, and is environmentally friendly, showing promising prospects for industrial application.

Description

Technical Field

[0001] This invention relates to the field of adipic acid synthesis technology, specifically to a method for producing adipic acid with low N2O tail gas emissions. Background Technology

[0002] Adipic acid, as an important chemical raw material, can be used to synthesize nylon 66 and polyurethane raw materials, as well as novel biodegradable plastics PBAT (polybutylene terephthalate) and PBSA (polybutylene succinate). In recent years, many new adipic acid production facilities have been built in my country, resulting in a significant increase in adipic acid production. Since current domestic and international adipic acid production capacity can meet the consumption demand, the future development goals of the adipic acid industry are to improve product efficiency, reduce production costs, and minimize environmental pollution. Currently, there are two main industrial production processes for adipic acid: one is the cyclohexane process developed by DuPont, where cyclohexane is oxidized in air to obtain KA oil (a mixture of cyclohexanol and cyclohexanone), which is then oxidized with nitric acid to synthesize adipic acid; the other is the improved process by Asahi Kasei Corporation—the cyclohexene process, where cyclohexene is hydrated to obtain cyclohexanol, which is then oxidized with nitric acid to synthesize adipic acid. DuPont's air oxidation process for cyclohexane suffers from poor safety, low atom utilization, and high production costs. Asahi Kasei's improved process offers enhanced safety and atom utilization, but the cyclohexene hydration reaction suffers from low single-pass yields due to reaction equilibrium and miscibility limitations. Furthermore, both processes require nitric acid as an oxidant to oxidize cyclohexanol (ketones), a process that releases large amounts of N2O waste gas (0.3 tons / 1 ton of adipic acid), causing irreversible damage to the ozone layer and the environment.

[0003] The hydrogen peroxide oxidation of cyclohexene to synthesize adipic acid is a novel, clean process for synthesizing adipic acid. This method offers high adipic acid yield, eliminates organic solvents and harmful phase-transfer catalysts, and produces no N2O emissions. Using cyclohexene as a raw material, 30 wt% H2O2 as an oxidant, and peroxytungstic acid as a catalyst, the yield of adipic acid can reach 94.7% in a 4*5000L pilot-scale unit (GreenChemistry, 2012, 14, 2868). However, this process involves a relatively long oxidation reaction pathway, requiring 3-4 reactors in series. Trace impurities in the reactors have a significant impact on hydrogen peroxide, resulting in a high rate of ineffective decomposition of hydrogen peroxide. Summary of the Invention

[0004] The purpose of this invention is to provide a method for producing adipic acid with low N2O emissions. This method has low N2O emissions, high absorption rate, low production cost, and is environmentally friendly, with good prospects for industrial application.

[0005] This invention provides a method for producing adipic acid with low N2O emissions. The method includes: Step S1. A first contact reaction is carried out between cyclohexene, hydrogen peroxide, and a first catalyst, wherein the first catalyst is a solid catalyst comprising a tungsten-doped titanium-containing molecular sieve; the liquid phase material of the contact reaction is subjected to oil-water separation to obtain an aqueous phase containing cyclohexane oxide and an oil phase containing cyclohexene; Step S2. A second contact reaction is carried out between the aqueous phase containing cyclohexane oxide and nitric acid and a second catalyst, wherein the second catalyst is a Cu-containing... 2+ V 5+ and Mo 6+ Ionic liquid catalysts.

[0006] The reaction process for synthesizing adipic acid in this invention has a low N2O volume content in the reaction tail gas and a high adipic acid yield, because NO and NO2 can enter the NO... X The absorption tower absorbs the nitric acid for reuse, greatly improving atom utilization and reducing nitric acid consumption. Compared with the technology of producing adipic acid by oxidizing cyclohexene with hydrogen peroxide alone, this invention uses less hydrogen peroxide and consumes less nitric acid, resulting in better economic benefits. It has the advantages of low production cost and environmental friendliness, and has good prospects for industrial application. Detailed Implementation

[0007] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. 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.

[0008] This invention provides a method for producing adipic acid with low N2O emissions. The method includes: Step S1. A first contact reaction is carried out between cyclohexene, hydrogen peroxide, and a first catalyst, wherein the first catalyst is a solid catalyst comprising a tungsten-doped titanium-containing molecular sieve; the liquid phase material of the contact reaction is subjected to oil-water separation to obtain an aqueous phase containing cyclohexane oxide and an oil phase containing cyclohexene; Step S2. A second contact reaction is carried out between the aqueous phase containing cyclohexane oxide and nitric acid and a second catalyst, wherein the second catalyst is a Cu-containing... 2+ V 5+ and Mo 6+ Ionic liquid catalysts.

[0009] According to a preferred embodiment of the present invention, the method further includes returning the separated oil phase containing cyclohexene to step S1 for the first contact reaction.

[0010] In this invention, in step S1, there are no special requirements for the tungsten content in the tungsten-doped titanium-containing molecular sieve. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the tungsten content in the tungsten-doped titanium-containing molecular sieve, calculated as oxide, is 0.1-0.35 wt%, preferably 0.2-0.3 wt%.

[0011] In this invention, the specific type of titanium-containing molecular sieve in step S1 is not specifically limited. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the titanium-containing molecular sieve is selected from TS-1 molecular sieve and / or Ti-MWW molecular sieve.

[0012] In this invention, there is no special limitation on the silicon-to-titanium ratio of the titanium-containing molecular sieve. For example, the silicon-to-titanium molar ratio is 32-35 when calculated as oxides.

[0013] In this invention, there are no special requirements for the ratio of hydrogen peroxide to cyclohexene in the first contact reaction. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the molar ratio of hydrogen peroxide to cyclohexene is 1-2:1, preferably 1.1-1.5:1.

[0014] In this invention, the ratio of solid catalyst to cyclohexene in the first contact reaction can be selected from a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the molar ratio of solid catalyst (based on tungsten oxide) to cyclohexene is 0.02-0.12:1.

[0015] In this invention, there are no special requirements for the concentration of hydrogen peroxide in the first contact reaction. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the concentration of hydrogen peroxide is 10-30 wt%, preferably 20-25 wt%.

[0016] In this invention, the temperature of the first contact reaction is not particularly limited. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the temperature of the reaction is 50-95°C, preferably 70-75°C.

[0017] In this invention, there are no special requirements for the residence time of the first contact reaction, but sufficient contact reaction is preferred. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the residence time is 0.5-48h, preferably 0.5-10h.

[0018] In this invention, there are no special requirements for the reaction site of the first contact reaction. For example, it can be carried out in a batch reactor, in which a solid filter is provided. When the reaction liquid of the first contact reaction is discharged, the solid catalyst is left in the batch reactor by the solid filter.

[0019] In this invention, in order to make the contact reaction more complete, the first contact reaction is carried out under stirring conditions, and there are no special requirements for the stirring rate, for example, it can be 100-160 rpm.

[0020] In this invention, there are no special requirements for the solvent of the first contact reaction, such as water, and the amount of solvent is not specifically limited, but can be adjusted according to the specific working conditions.

[0021] In this invention, the liquid phase material after the first contact reaction needs to be separated into oil and water. There are no special requirements for the specific operation of oil-water separation. For example, the liquid phase material after the first contact reaction can be separated by an oil-water separator.

[0022] In this invention, during the first contact reaction, to maintain a constant molar ratio of tungsten to cyclohexene in the solid catalyst, this can be achieved by adding solid catalyst to the reaction vessel. This is well known to those skilled in the art, and the specific operation will not be described in detail here.

[0023] In this invention, the second catalyst contains Cu 2+ With V 5+ The content relationship is not particularly limited. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, Cu 2+ With V 5+ The molar ratio is 1:0.5-2.5.

[0024] In this invention, the second catalyst contains Cu 2+ with Mo 6+ The content relationship is not particularly limited. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, Cu 2+ with Mo 6+ The molar ratio is 1:0.5-1.5, preferably 1:0.8-1.1.

[0025] In this invention, the second catalyst contains Cu. 2+ V 5+ and Mo 6+The ionic liquid catalyst has no special requirements regarding its source. Any ionic liquid that can form containing these ions can be used in this invention. For example, it can be obtained by dissolving copper oxide, vanadium oxide, or molybdenum oxide in acid. The anion in the ionic liquid catalyst is the acid radical ion of the acid. There are no special requirements regarding the specific type of the acid radical ion. For example, it can be a nitrate ion.

[0026] In this invention, in the second contact reaction, according to a preferred embodiment of the invention, the molar ratio of nitric acid (HNO3) to cyclohexane oxide and its derivatives in the aqueous phase containing cyclohexane oxide is 7-10:1, preferably 8-9:1.

[0027] In this invention, there are no special requirements regarding the ratio of nitric acid to the second catalyst in the second contact reaction. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, nitric acid, calculated as HNO3, reacts with V in the second catalyst. 5+ The molar ratio is 10⁻⁴¹⁶:1.

[0028] In this invention, the temperature of the second contact reaction is not particularly limited. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the temperature of the reaction is 60-90°C, preferably 75-80°C.

[0029] In this invention, there are no special requirements for the concentration of nitric acid in the second contact reaction. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the concentration of nitric acid is 30-70 wt%, preferably 55-65 wt%.

[0030] In this invention, there are no special requirements for the residence time of the second contact reaction, but sufficient contact reaction is preferred. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the residence time is 10-50 min, preferably 20-30 min.

[0031] In this invention, there are no special requirements for the reaction site of the second contact reaction. For example, it can be carried out in a batch reactor. In order to make the contact reaction more complete, the second contact reaction is carried out under stirring conditions. There are no special requirements for the stirring rate, for example, it can be 140-160 rpm.

[0032] According to a preferred embodiment of the present invention, the method further includes: performing gas phase composition analysis on the exhaust gas emitted in step S2, and sending the emitted exhaust gas into a NO3-precipitated nitrogen oxide generator. x The absorption tower is used for recycling.

[0033] The present invention will be described in detail below through embodiments.

[0034] In the following embodiments, The content of adipic acid was determined by liquid chromatography; Gas chromatography was used to determine the composition of the reaction tail gas and the types and contents of cyclohexane derivatives. In the following examples, the Cu-Mo-V catalyst used contains Cu 2+ V 5+ Mo 6+ NO3 - The solution is obtained by dissolving copper oxide, vanadium oxide, and molybdenum oxide in nitric acid; in the comparative example, the Cu-V catalyst used contains Cu. 2+ V 5+ NO3 - It is obtained by dissolving copper oxide and vanadium oxide in nitric acid.

[0035]

Example 1

[0036] The gas phase composition of the reaction tail gas in the second reactor was analyzed, and the tail gas was then sent to NO. X The absorption tower is used for recycling.

[0037] The content of adipic acid in the second reaction vessel was determined by liquid chromatography, and the yield of adipic acid was 91.3%. The tail gas in the second reaction vessel was collected for component analysis and detection. The components of the tail gas are shown in Table 1.

[0038]

Example 2

[0039] The gas phase composition of the reaction tail gas in the second reactor was analyzed, and the tail gas was then sent to NO. X The absorption tower is used for recycling.

[0040] The content of adipic acid in the second reaction vessel was determined by liquid chromatography, and the yield of adipic acid was 89.8%. The tail gas in the second reaction vessel was collected for component analysis and detection. The components of the tail gas are shown in Table 1.

[0041]

Example 3

[0042]

Example 4

Example 5

[0043]

Example 6

[0044] Comparative Example 1 The method is the same as in Example 1, except that the Cu-V catalyst (Mo-free) used in the second contact reaction is different. 6+ Cu 2+ V 5+ NO3 - The molar ratio is 1:2:12.

[0045] Comparative Example 2 The method is the same as in Example 1, except that TS-1 molecular sieve (tungsten-free, silicon-titanium molar ratio of 33) is used in the first contact reaction. Comparative Example 3 Adipic acid is prepared using the existing cyclohexene process: Nitric acid (65 wt%) and Cu-V catalyst at a molar ratio of 40:1 were added to the reactor. In the Cu-V catalyst, Cu... 2+ V 5+ NO3 -The molar ratio of nitric acid to cyclohexanol was 1:2:12. Cyclohexanol was then added to the reactor, with a molar ratio of nitric acid to cyclohexanol of 8:1. The temperature of the reactor was adjusted to 79℃, and the reaction time was 30 min. The adipic acid content was determined by liquid chromatography, and the adipic acid yield was 87.97%. The tail gas was collected for component analysis, and the components of the tail gas are shown in Table 1.

[0046] Comparative Example 4 Adipic acid was synthesized by oxidizing cyclohexene with nitric acid alone. Nitric acid (65 wt%) and Cu-V catalyst at a molar ratio of 40:1 were added to the reactor. In the Cu-V catalyst, Cu... 2+ V 5+ NO3 - The molar ratio of nitric acid to cyclohexene is 1:2:12. Cyclohexene is then added to the reactor. The molar ratio of nitric acid to cyclohexene in the reactor is 8:1. The temperature of the reactor is adjusted to 79℃ and the reaction time is 30min.

[0047] The adipic acid content was determined by liquid chromatography, with an adipic acid yield of 47.74%. The tail gas was collected for component analysis, and the components of the tail gas are shown in Table 1. This route has an excessively low adipic acid yield, and the N2O content in the tail gas remains high, making it unsuitable for practical application.

[0048] Comparative Example 5 Existing cyclohexane process: Nitric acid (65 wt%) and Cu-V catalyst at a molar ratio of 40:1 were added to the reactor. In the Cu-V catalyst, Cu... 2+ V 5+ NO3 - The molar ratio of nitric acid to cyclohexanol is 1:2:12. Then, a mixture of cyclohexanol and cyclohexanone is added to the reactor, wherein the ratio of cyclohexanol to cyclohexanone is 47:53 (mass ratio). The molar ratio of nitric acid to cyclohexanol / cyclohexanone in the reactor is 8:1. The temperature of the reactor is adjusted to 79℃ and the reaction time is 30min.

[0049] The content of adipic acid was determined by liquid chromatography, and the yield of adipic acid was 83.81%. The exhaust gas was collected for component analysis and detection. The components of the exhaust gas are shown in Table 1.

[0050] Currently used adipic acid production processes include the cyclohexane method and the cyclohexene method. To visually compare the N2O emission reduction effect and adipic acid yield in this invention, Comparative Example 3 shows the reaction process of nitric acid oxidation of cyclohexanol in the cyclohexene method for producing adipic acid; Comparative Example 5 shows the reaction process of nitric acid oxidation of KA oil (cyclohexanol to cyclohexanone mass ratio = 47:53) in the cyclohexane method for producing adipic acid; and Comparative Example 4 shows the reaction process of synthesizing adipic acid using nitric acid oxidation of cyclohexene without hydrogen peroxide assistance. The comparison shows that, compared with existing technologies, the technology of this invention has a higher adipic acid yield and a significant advantage in low N2O emissions.

[0051] Table 1

[0052] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for producing adipic acid with low N2O tail gas emissions, characterized in that, The method includes: Step S1. Cyclohexene, hydrogen peroxide and a first catalyst are subjected to a first contact reaction. The first catalyst is a solid catalyst, which includes a tungsten-doped titanium-containing molecular sieve. The liquid phase material of the contact reaction is separated into oil and water to obtain an aqueous phase containing cyclohexane oxide and an oil phase containing cyclohexene. Step S2. The aqueous phase containing cyclohexane oxide is subjected to a second contact reaction with nitric acid and a second catalyst, wherein the second catalyst contains Cu. 2+ V 5+ and Mo 6+ Ionic liquid catalysts.

2. The method according to claim 1, characterized in that, The method further includes returning the separated oil phase containing cyclohexene to step S1 for the first contact reaction.

3. The method according to claim 1 or 2, characterized in that, The tungsten-doped titanium-containing molecular sieve contains 0.1-0.35 wt% tungsten as oxide.

4. The method according to claim 3, characterized in that, The tungsten-doped titanium-containing molecular sieve contains 0.2-0.3 wt% tungsten as oxide.

5. The method according to claim 1 or 2, characterized in that, The titanium-containing molecular sieve is selected from TS-1 molecular sieve and / or Ti-MWW molecular sieve.

6. The method according to claim 1 or 2, characterized in that, The conditions for the first contact reaction include: The molar ratio of hydrogen peroxide (H₂O₂) to cyclohexene is 1-2:1; and / or The molar ratio of solid catalyst (based on tungsten oxide) to cyclohexene is 0.02-0.12:1; and / or The hydrogen peroxide concentration is 10-30 wt%; and / or The reaction temperature is 50-95℃; and / or Stay duration 0.5-48 hours; and / or The process is carried out in a batch reactor equipped with a solids filter; and / or The process is carried out under stirring conditions at a stirring rate of 100-160 rpm.

7. The method according to claim 6, characterized in that, The conditions for the first contact reaction include: The molar ratio of hydrogen peroxide (H₂O₂) to cyclohexene is 1.1-1.5:1; and / or The hydrogen peroxide concentration is 20-25 wt%; and / or The reaction temperature is 70-75℃; and / or The stay duration is 0.5-10 hours.

8. The method according to claim 1 or 2, characterized in that, The solvent for the first contact reaction is water.

9. The method according to claim 1 or 2, characterized in that, The aqueous phase containing cyclohexane oxide includes cyclohexane oxide and its derivatives.

10. The method according to claim 9, characterized in that, The derivatives include one or more of cyclohexanediol, cyclohexanone, and cyclohexanol.

11. The method according to claim 1 or 2, characterized in that, In the second catalyst, Cu 2+ With V 5+ The molar ratio is 1:0.5-2.5; and / or Cu 2+ with Mo 6+ The molar ratio is 1:0.5-1.

5.

12. The method according to claim 11, characterized in that, In the second catalyst, Cu 2+ with Mo 6+ The molar ratio is 1:0.8-1.

1.

13. The method according to claim 1 or 2, characterized in that, The conditions for the second contact reaction include: The molar ratio of nitric acid (HNO3) to cyclohexane oxide and its derivatives in an aqueous phase containing cyclohexane oxide is 7-10:1; and / or Nitric acid, calculated as HNO3, reacts with V in the second catalyst. 5+ The molar ratio is 10⁻⁴¹⁶:1; and / or The reaction temperature is 60-90℃; and / or The stay time is 10-50 minutes; and / or Nitric acid concentration is 30-70 wt%; and / or Carried out in a batch reactor; and / or The process is carried out under stirring conditions at a stirring rate of 140-160 rpm.

14. The method according to claim 13, characterized in that, The conditions for the second contact reaction include: The molar ratio of nitric acid (HNO3) to cyclohexane oxide and its derivatives in an aqueous phase containing cyclohexane oxide is 8-9:1; and / or The reaction temperature is 75-80℃; and / or The nitric acid concentration is 55-65 wt%; and / or The stay time is 20-30 minutes.

15. The method according to claim 1 or 2, characterized in that, The method further includes: performing gas phase composition analysis on the exhaust gas emitted in step S2, and sending the emitted exhaust gas into a NO3-precipitated nitrogen oxide generator. x The absorption tower is used for recycling.

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