Method for synthesizing adipic acid by one-step direct oxidation of cyclohexane

文档序号：354310 发布日期：2021-12-07 浏览：29次中文

阅读说明：本技术 环己烷一步直接氧化合成己二酸的方法 (Method for synthesizing adipic acid by one-step direct oxidation of cyclohexane ) 是由干丰丰陈燕鑫杨运信于 2020-06-02 设计创作，主要内容包括：本发明涉及环己烷一步直接氧化合成己二酸的方法,主要解决现有技术中存在的环己烷直接氧化制己二酸均相反应过程中需要用到醋酸等有机溶剂,造成后续产物分离困难,并对设备造成严重的腐蚀,以及可溶性金属催化剂难以回收造成重金属污染,难以实现己二酸工业化连续生产的问题。通过采用环己烷一步直接氧化合成己二酸的方法,包括在催化剂存在下环己烷与含氧气气体反应生成己二酸,所述催化剂具有如下所示的结构；其中,R-(1)、R-(2)、R-(3)、R-(4)和R-(5)中至少一个是连接有酸性基团的脂肪链,所述脂肪链的碳数至少为9。。(The invention relates to a method for synthesizing adipic acid by one-step direct oxidation of cyclohexane, which mainly solves the problems that in the prior art, organic solvents such as acetic acid and the like are required in the homogeneous reaction process for preparing adipic acid by direct oxidation of cyclohexane, so that subsequent products are difficult to separate, equipment is seriously corroded, a soluble metal catalyst is difficult to recover, heavy metal pollution is caused, and industrial continuous production of adipic acid is difficult to realize. A method for synthesizing adipic acid by adopting cyclohexane through one-step direct oxidation, which comprises the steps of reacting cyclohexane with oxygen-containing gas in the presence of a catalyst to generate adipic acid, wherein the catalyst has a structure shown as the following formula; wherein R is 1 、R 2 、R 3 、R 4 And R 5 At least one is a fatty chain having an acidic group attached thereto, said fatty chain having a carbon number of at least 9.)

1. A method for synthesizing adipic acid by one-step direct oxidation of cyclohexane comprises reacting cyclohexane with an oxygen-containing gas in the presence of a catalyst to produce adipic acid, wherein the catalyst has a structure shown in formula 1 below:

wherein R is₁、R₂、R₃、R₄And R₅At least one is a fatty chain having an acidic group attached thereto, said fatty chain having a carbon number of at least 9.

2. The method according to claim 1, wherein the acidic group is a carboxyl group or a sulfonic acid group.

3. The method according to claim 1, wherein the aliphatic chain has at least one kind selected from the group consisting of a straight chain carbon atom, a branched chain carbon atom and a cyclic carbon atom.

4. The method according to claim 1, wherein the aliphatic chain elements are composed of carbon atoms, hydrogen atoms and optional hetero atoms, and the ratio of the number of hetero atoms to the number of carbon atoms is 0 to 0.6. The heteroatom is preferably an O atom.

5. The method of claim 1, wherein the aliphatic chain is an alkylene group.

6. The process as set forth in claim 1, wherein said fatty chain is a polyoxyalkylene chain.

7. The method as set forth in claim 1, wherein the molar ratio of the catalyst to cyclohexane is 0.002 to 0.02.

8. The method according to claim 1, wherein the oxygen containing gas is selected from gases having an oxygen content of 5 to 100% by volume.

9. The process as claimed in claim 1, wherein the reaction temperature is from 80 ℃ to 130 ℃.

10. The method according to claim 1, wherein the reaction pressure is 1.0 to 3.0 MPa. And/or the reaction time is preferably 1 to 8 hours. And/or the oxygen-containing gas is measured by air, and the feeding speed of the oxygen-containing gas is 3-10 liters/minute on the basis of every 10 moles of cyclohexane.

Technical Field

The invention relates to a method for synthesizing adipic acid by one-step direct oxidation of cyclohexane.

Background

Adipic Acid (AA) also known as adipic acid, formula C₆H₁₀O₄Is an organic dibasic acid of great significance produced in all dicarboxylic acidsThe amount is second only to terephthalic acid, and is second. It has wide application, is an important monomer for synthesizing nylon 66 and engineering plastics, can be used for producing various ester products, spices and the like, and has important functions in the aspects of chemical production, organic synthesis industry, medicine, lubricant manufacturing and the like.

The main method for industrially producing adipic acid at present is the cyclohexane method, which accounts for more than 90% of the total production capacity of adipic acid. The method adopts cyclohexane as a raw material, and synthesizes adipic acid by oxidation in two steps, wherein in the first step, in the presence of a metal catalyst, cyclohexane is oxidized by taking air as an oxygen source to generate cyclohexanol and cyclohexanone (commonly known as KA oil); and in the second step, nitric acid is adopted to further oxidize the generated KA oil to obtain adipic acid. The cyclohexane method is characterized in that: although the production technology is mature and dominates in the production of adipic acid, the process is complex, the reaction is severe, the energy consumption is high, the single-pass conversion rate of cyclohexane is very low, generally only 3-6%, and the method is praised as one of the lowest efficiency processes in the production technology; in addition, the use of a large amount of nitric acid causes severe corrosion of equipment, and a large amount of nitrogen oxide gas is generated, causing severe environmental pollution.

In order to solve the problem, scientists develop a great deal of new clean and harmless adipic acid green synthesis process research. Mainly comprises a molecular sieve catalysis method, nano metal loaded catalysis, biomimetic catalysis, a free radical catalysis method and the like.

For example, the documents Catalysis Communications,2015,58: 46-52. The author dopes Mn in a titanium silicalite molecular sieve material with a hollow structure to synthesize a Mn-Ti-Si catalyst, and can directly perform O reaction without an initiator or a solvent₂The cyclohexane was oxidized to give adipic acid with a cyclohexane conversion of 13.4% and an adipic acid selectivity of 57.5%.

For example, the documents Reaction Kinetics, Mechanisms and Catalysis,2011,102(1):143- "154. The authors used nano Au/SiO₂The catalyst does not need a promoter or a solvent, takes air as an oxygen source, oxidizes cyclohexane to synthesize adipic acid, the cyclohexane conversion rate is about 10 percent, the KA oil selectivity is 92 percent, and the adipic acid selectivity is very low.

For example, the document Canadian Journal of Chemistry,2015,93(7):696-^ⅢT(p-Cl)PP]Cl as catalyst, with O₂Cyclohexane and cyclohexanone are oxidized to directly obtain adipic acid.

For example, Organic Process Research & Development 1998,2,255-260. the authors directly obtained adipic acid by oxidizing cyclohexane with oxygen using N-hydroxyphthalimide (NHPI for short) as a free-radical catalyst, promoted with a small amount of transition metal, with a cyclohexane conversion of 73% and an adipic acid yield of 53%.

For example, the structure of a free radical catalyst is optimized by a group of documents J.org.chem.2001,66,7889-7891.Ishii, and a novel free radical catalyst is synthesized by introducing lipophilic dodecyloxycarbonyl on a benzene ring structure of NHPI, so that the solubility and the reaction activity of the catalyst in a solvent-free reaction system are greatly enhanced, and the conversion rate is far higher than that of the NHPI catalyst under the synergistic action of Co and Mn promoters and the solvent-free reaction condition.

These cases all achieve green synthesis of adipic acid, but also have some drawbacks and disadvantages. For example, although the molecular sieve catalysis method realizes the advantages of no solvent or initiator in the reaction process, repeated reuse of the catalyst and the like, the yield of adipic acid is low, and the molecular sieve preparation process is complex and has high cost. The nano metal catalysis method has similar problems, although the recycling of the catalyst can be well realized, the reaction without solvent or promoter can also be realized, but the reaction activity is lower, the reaction yield is low, the energy consumption is high, and the method is not suitable for industrial application. The biomimetic catalysis and free radical catalysis methods have the characteristics of high selectivity, high conversion rate, low energy consumption and the like and have certain industrial application prospect, but because most of the catalysis methods adopt a homogeneous system and use a large amount of organic solvents such as acetic acid and the like, the subsequent products are easy to separate and the equipment is seriously corroded. Even if the solvent-free reaction is adopted, the synergistic promotion is mostly needed by virtue of a metal catalyst, so that the problems of difficult recovery of the soluble metal catalyst, heavy metal pollution and the like are caused.

Disclosure of Invention

The invention aims to solve the technical problems that in the prior art, organic solvents such as acetic acid and the like are required to be used in the homogeneous reaction for preparing adipic acid by directly oxidizing cyclohexane, so that subsequent products are difficult to separate, equipment is seriously corroded, a soluble metal catalyst is difficult to recover, heavy metal pollution is caused, and the like.

In order to solve the technical problems, the technical scheme of the invention is as follows:

a method for synthesizing adipic acid by one-step direct oxidation of cyclohexane comprises reacting cyclohexane with an oxygen-containing gas in the presence of a catalyst to produce adipic acid, wherein the catalyst has a structure shown in formula 1 below:

wherein R is₁、R₂、R₃、R₄And R₅At least one is a fatty chain having an acidic group attached thereto, said fatty chain having a carbon number of at least 9.

The NHPI molecular structure matrix has high selectivity for carboxyl connected with a long aliphatic chain.

On the other hand, the selectivity was significantly low in both cases where only the aliphatic chain was bonded to the parent substance (comparative example 2) and where the aliphatic chain had too few carbon atoms although the parent substance had a carboxyl group bonded to the aliphatic chain (comparative example 3). In the prior art, the substance which is consistent with the structural formula 1 is used for synthesizing an intermediate of a thiol phosphate derivative and the like, and no report is found for synthesizing adipic acid.

The process of the invention can be carried out in the absence of a solvent (cyclohexane is the reactant and is not considered as a solvent). Since the present invention is carried out in the absence of a solvent, there is an advantage in the product separation and purification process at least in saving the energy consumption for separation required for removing the solvent, and the absence of a solvent is preferred from this viewpoint.

In the above technical scheme, when the acidic group connected to the aliphatic chain contains a carbon atom, the carbon atom is not counted in the carbon number of the aliphatic chain.

In the above technical solution, the carbon number of the aliphatic chain may be 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, etc., as non-limiting examples.

In the above technical scheme, R can be selected₁、R₂、R₃And R₄Is H and R₅Is an aliphatic chain to which an acidic group is attached.

In the above technical scheme, the fatty chain connected with an acidic group may optionally conform to the structure shown in formula 2:

-R₆-A₇formula 2;

wherein R is₆Is said aliphatic chain, A₇Is an acidic group.

In the above technical solution, the acidic group is preferably a carboxyl group or a sulfonic acid group.

In the above-mentioned embodiment, the aliphatic chain may have at least one selected from the group consisting of a straight chain carbon atom, a branched chain carbon atom and a cyclic carbon atom.

In the technical scheme, the aliphatic chain elements comprise carbon atoms, hydrogen atoms and optional heteroatoms, and the ratio of the number of the heteroatoms to the number of the carbon atoms is 0-0.6. Such as, but not limited to, a ratio of number of heteroatoms to number of carbon atoms of 0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, and the like.

In the above technical scheme, the heteroatom is preferably an O atom.

In the above technical solution, the aliphatic chain structure may include at least one of a ketone group, an ether group, and an ester group.

In the above technical solution, the aliphatic chain may be an alkylene group. For example, it may be a straight or branched chain alkylene group.

In the above technical scheme, when the aliphatic chain is a linear alkylene group, R6 may be, but is not limited to, according to the following structural formula 3:

-(CH₂)_n-, structural formula 3;

wherein n is the carbon number of the aliphatic chain.

In the above technical scheme, the fatty chain may be a polyoxyalkylene chain.

In the above technical scheme, when the fatty chain is a polyoxyalkylene chain, R₆May be, but is not limited to, according to formula 4 below:

-(R₇O)_mR₈-, structural formula 4;

wherein R is₇And R₈Independently selected from C2 or C3 alkylene groups, and m is the number of repeating units required to satisfy the carbon number of the aliphatic chain.

Further preferred is R₇And R₈Independently selected from- (CH)₂CH₂) -and- (CH)₂CH(CH₃))-；

Further preferred is R₇And R₈Are all- (CH)₂CH₂) In this case, m is most preferably 3 or more, and for example, but not limited to, m may be 3, 4, 5, 6,7, 8, 9, 10, and the like.

In the above technical scheme, R₆May be, but is not limited to, according to structural formula 5 below:

wherein the value of p satisfies the carbon number of the aliphatic chain.

In the technical scheme, the molar ratio of the catalyst to cyclohexane is preferably 0.002-0.02. For example, but not limited to, the catalyst to cyclohexane molar ratio is 0.0025, 0.003, 0.0035, 0.004, 0.0045, 0.005, 0.0055, 0.006, 0.0065, 0.007, 0.0075, 0.008, 0.0085, 0.009, 0.0095, 0.01, 0.011, 0.012, 0.013, 0.014, 0.015, 0.016, 0.017, 0.018, 0.019, and the like.

In the technical scheme, the oxygen-containing gas is selected from gases with the oxygen volume content of preferably 5-100%. For example, but not limited to, the oxygen content is 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, etc. by volume.

In the above technical scheme, the reaction temperature is preferably 80 ℃ to 130 ℃. For example, but not limited to, the reaction temperature is 85 ℃, 90 ℃, 95 ℃, 100 ℃, 105 ℃, 110 ℃, 115 ℃, 120 ℃, 152 ℃ and so on.

In the technical scheme, the reaction pressure is preferably 1.0-3.0 MPa. For example, but not limited to, a reaction pressure of 1.1MPa, 1.2MPa, 1.3MPa, 1.4MPa, 1.5MPa, 1.6MPa, 1.7MPa, 1.8MPa, 1.9MPa, 2.0MPa, 2.1MPa, 2.2MPa, 2.3MPa, 2.4MPa, 2.5MPa, 2.6MPa, 2.7MPa, 2.8MPa, 2.9MPa, etc.

The pressures stated in the present invention are gauge pressures.

In the above technical scheme, the reaction time is preferably 1 to 8 hours, for example, but not limited to, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, 6.5 hours, 7 hours, 7.5 hours, and the like.

In the above technical solution, the oxygen-containing gas is measured by air, and the feeding rate of the oxygen-containing gas is preferably 3 to 10 liters/minute, such as, but not limited to, 3.5 liters/minute, 4 liters/minute, 4.5 liters/minute, 5 liters/minute, 5.5 liters/minute, 6 liters/minute, 6.5 liters/minute, 7 liters/minute, 7.5 liters/minute, 8 liters/minute, 8.5 liters/minute, 9 liters/minute, 9.5 liters/minute, and the like, based on 10 moles of cyclohexane.

The selectivity of the product adipic acid is detected by liquid phase HPLC. The solid-liquid mixed product obtained by the reaction of preparing adipic acid by oxidizing cyclohexane is electromagnetically stirred and dissolved by water and methanol in a ratio of 90:10(V/V), and is filtered and diluted into a high-efficiency liquid phase for detection. Chromatographic analysis conditions: the chromatography column model is ZORBAX SAX 4.6mm X250 mm mu 5m, and the mobile phase is methanol: 50mmol/L KH₂PO₄The column temperature was 25 ℃, the flow rate was 1.0mL/min, the amount of sample was 20 μ L, and the detection wavelength was 210 nm.

The present invention will be described in detail below with reference to examples and comparative examples.

Detailed Description

[ example 1]

Adding 10mol of cyclohexane and 0.1mol of the catalyst of the embodiment 1 into a 2-liter high-pressure reaction kettle (provided with a reflux condensing device communicated with the atmosphere through a pressure-retaining valve), sealing and stirring, heating to 110 ℃, continuously introducing air at 5 liters/min, controlling the pressure in the kettle to be kept at 1.5MPa all the time, reacting for 3 hours, cooling to room temperature, taking out a reaction mixture, analyzing, and obtaining an analysis result: the cyclohexane conversion was 10.2%, the adipic acid selectivity was 85.2%, and the overall yield was 8.69%.