Method for synthesizing phenol and cyclohexanone by using lignin monomer biphenyl as raw material

Abstract

The invention discloses a method for synthesizing phenol and cyclohexanone by taking lignin monomer biphenyl as a raw material. The method comprises the following steps: firstly, by taking acetonitrile or isopropanol as a solvent, catalyzing selective hydrogenation of biphenyl by using a supported metal catalyst to obtain cyclohexylbenzene; and then adding a free radical initiator into the reaction liquid, oxidizing cyclohexylbenzene in an oxygen atmosphere, and then adding an acid catalyst to react to obtain phenol and cyclohexanone. The invention realizes a phenol / cyclohexanone synthesis method capable of replacing petroleum energy as a source, and accords with the basic idea of sustainable development; according to the method disclosed by the invention, the C-C bond in the lignin monomer biphenyl is broken under a mild reaction condition, so that the overall utilization of lignocellulose is promoted.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical synthesis, and particularly relates to a method for converting lignin monomer biphenyl into phenol and cyclohexanone. Background Art

[0002] Petrochemicals are an important part of the chemical industry. They play a pivotal role in people's daily life and production, and also have a profound impact on the development of countries around the world. It is a double-edged sword. While it has brought great progress and convenience to society, it has also brought a series of serious environmental problems, such as greenhouse effect, acid rain and haze. Therefore, chemical production based on green resources such as biomass instead of fossil resources is of great significance to the sustainable development of human society and the natural environment. Lignocellulose is a kind of biomass energy. It mainly exists in agricultural and forestry wood and is a material carrier for storing solar energy. According to the different chemical structures, it is divided into cellulose, hemicellulose and lignin. Lignin gives plants and trees a rigid structure. Compared with the first two components, its structure is more complex and its conversion and utilization are more difficult. On the one hand, the traditional method of treating lignin is to burn it to generate heat. However, the extremely low energy utilization rate determines that this method of treating lignin is not a good solution. On the other hand, lignin accounts for about 15-40% of plant components. Improving the utilization rate of lignin is a key link in improving the overall utilization rate of lignocellulose. Converting lignin to obtain monocyclic compounds as commodity chemicals and fuels is one of the goals of biorefining.

[0003] However, the stable CC bonds in the lignin structure are difficult to cleave, which seriously hinders its conversion into small molecule compounds. Among them, the 5-5' bond accounts for the highest proportion in lignin and has the largest bond dissociation energy (481-494 kJ mol -1 ). For example, guaiacyl is a basic unit in lignin. When two molecules of guaiacyl undergo dehydrogenation coupling, a 5-5' bond between benzene rings is formed. The classic method of nitrobenzene oxidation can only break the CO bond, but not the CC bond, which also shows that it is very difficult to break the CC bond. (Science, 2016, 354, 329-333) In response to the problem that the CC bond of lignin is difficult to break, Wang Yanqin et al. prepared mesoporous Ru / NbOPO4 materials, which achieved simultaneous breaking of CC bonds and CO bonds in a one-pot reaction, and decomposed sulfate lignin to obtain monocyclic hydrocarbon compounds, with a yield 1.5 times that of previous nitrobenzene oxidation. (Chem, 2019, 5, 1521-1536) That is, under the catalytic conditions of Ru / NbOPO4, the most harvested monocyclic hydrocarbon compounds are obtained by breaking the CC bond of lignin. However, when biphenyl is used as the reaction substrate, the yield of monocycloalkanes is less than 50%, and the yield of benzene is only 24%; that is, the efficiency of CC bond breaking is very low, and most CC bonds are retained.

[0004] Phenol is an important chemical raw material. It can be used to make resins, synthetic fibers, plastics, and can also be used in the production of medicines and pesticides. Recently, researchers have been committed to converting lignin into phenolic chemicals. (ACS Sustainable Chemistry & Engineering, 2023, 11, 3170-3181) The experiment used a Ti-doped nickel metal catalyst loaded on mesoporous alumina (NiTiMA). Under the conditions of 400°C and 100MPa H2, the researchers converted lignin into oils and phenolic compounds under solvent-free conditions, including chain hydrocarbons, cycloalkanes, naphthalene, aromatics, catechol, guaiacol, etc. Among them, alkylphenols include p-benzoylphenol, ethylphenol, etc., with a total yield of about 10wt%. The shortcomings of the experiment are that the reaction temperature is high, the reaction conditions are harsh, and no pure phenol is produced, that is, the alkylphenol does not break the CC bond. Cyclohexanone is also an important chemical raw material. In the early days, it was produced using phenol as raw material. Now there are synthesis methods such as cyclohexane oxidation and benzene hydrogenation. Its preparation source is also mainly non-renewable petroleum. Summary of the invention

[0005] The present invention aims to provide a new method for preparing phenol and cyclohexanone by using biphenyl, a monomer in lignin, as a raw material. The present invention uses biphenyl, a monomer in lignin, as a reaction raw material to prepare phenol and cyclohexanone by a two-step method.

[0006] The method for preparing phenol and cyclohexanone provided by the present invention comprises: subjecting biphenyl to a hydrogenation reaction to obtain cyclohexylbenzene; and subjecting the cyclohexylbenzene to an oxidation-hydrolysis reaction to obtain phenol and cyclohexanone.

[0007] Specifically, the method for preparing phenol and cyclohexanone comprises the following steps:

[0008] 1) dissolving biphenyl in an organic solvent, using hydrogen as a hydrogen source, and causing a hydrogenation reaction under the catalytic action of a supported metal catalyst to obtain a solution containing cyclohexylbenzene;

[0009] 2) adding a free radical initiator to the solution obtained in step 1), introducing oxygen to carry out oxidation reaction for t1 time, adding an acid catalyst to react for t2 time, and obtaining phenol and cyclohexanone.

[0010] In step 1) of the above method, the supported metal catalyst is selected from at least one of Ni / SiO2, Ni / TiO2, Ni / Nb2O5 or Ni / C, and specifically can be at least one of Ni / SiO2 and Ni / C.

[0011] The metal (Ni) loading of the supported metal catalyst is 1-10wt%, preferably 2-10wt%;

[0012] The mass ratio of the supported metal catalyst to biphenyl is 1:80-1:1, and the preferred mass ratio is 1:20-1:1.

[0013] The organic solvent may be at least one of isopropanol, acetonitrile, and cyclohexane, and specifically may be acetonitrile or isopropanol;

[0014] The hydrogenation reaction is carried out in a tank reactor.

[0015] The concentration of biphenyl is 0.005-0.4 g / ml, preferably 0.005-0.1 g / ml, more preferably 0.005-0.04 g / ml;

[0016] The hydrogen pressure is 0.1-3Mpa, preferably 1-3Mpa;

[0017] The reaction temperature is 80-300°C, preferably 100-300°C, more preferably 140-180°C,

[0018] The reaction time is 1-48 h, preferably 6-48 h, more preferably 12-48 h.

[0019] In step 2) of the above method, the free radical initiator is one or more of N-hydroxyphthalimide (NHPI), azobisisobutyronitrile (AIBN), azobisisoheptanenitrile (ABVN), dibenzoyl peroxide (BPO), H2O2, preferably NHPI+AIBN;

[0020] The acid catalyst is one of H2SO4, HCl, CH3COOH, Nafion-H or Ambelyst-36; preferably sulfuric acid (H2SO4), perfluorosulfonic acid resin (Nafion-H) or solid acid catalyst Ambelyst-36;

[0021] The concentration of the free radical initiator is 0.001-1 g / ml, preferably 0.02-1 g / ml; the amount of the acid catalyst is 0.001-0.1 g / ml, preferably 0.005-0.1 g / ml, more preferably 0.02-0.1 g / ml;

[0022] The operation of step 2) of the above method is: adding a free radical initiator to the solution obtained in step 1), introducing oxygen, reacting for t1 time, then adding an acid catalyst and a reaction solvent, and obtaining phenol and cyclohexanone after t2 time;

[0023] The reaction temperature is 30-150°C, preferably 50-130°C;

[0024] The reaction time t1 is 0.5-35h, and the preferred reaction time is 3-20h;

[0025] The t2 time is 3-30h, preferably the reaction time is 5-30h, more preferably 10-30h;

[0026] The oxygen pressure is 0-10 atm, and the preferred reaction oxygen pressure is 2-10 atm.

[0027] Compared with the prior art, the present invention has the following advantages:

[0028] 1. Replace the phenol / cyclohexanone synthesis route based on traditional fossil energy and use lignin monomer biphenyl as the reaction raw material, which is beneficial to the sustainable development of human beings and the natural environment;

[0029] 2. Through hydrogenation reaction and oxidation-hydrolysis method, the breaking effect of CC bond in biphenyl is improved to obtain nearly pure phenol and cyclohexanone;

[0030] 3. The entire reaction route has mild conditions and low requirements for experimental equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is the reaction route for preparing phenol and cyclohexanone from biphenyl in the present invention.

[0032] Figure 2 This is the GC spectrum of the biphenyl hydrogenation reaction product in Example 1.

[0033] Figure 3 This is the GC spectrum of the oxidation-hydrolysis reaction of cyclohexylbenzene in Example 65. DETAILED DESCRIPTION

[0034] The present invention is further described in detail below in conjunction with specific embodiments, and the examples provided are only for illustrating the present invention, rather than for limiting the scope of the present invention. The examples provided below can be used as a guide for further improvements by those of ordinary skill in the art, and do not constitute a limitation of the present invention in any way.

[0035] The experimental methods in the following examples, unless otherwise specified, are all conventional methods, and are performed according to the techniques or conditions described in the literature in the field or according to the product instructions. The materials, reagents, etc. used in the following examples, unless otherwise specified, can all be obtained from commercial channels.

[0036] Examples 1-29

[0037] The first step of hydrogenation reaction is carried out in a kettle reactor. After 0.1 g of biphenyl and 10 ml of reaction solvent acetonitrile are added to the reactor, 0.01 g of a 3 wt% loaded metal catalyst is added, 1.2 MPa of H2 is filled, and the reaction is carried out at a certain temperature for a specific time under magnetic stirring.

[0038] Table 1. Hydrogenation activity of different catalysts

[0039]

[0040]

[0041] As can be seen from the results in Table 1, Ni / SiO2, Ni / TiO2, Ni / Nb2O5 or Ni / C catalysts are all active in biphenyl hydrogenation. Reaction conditions have a certain influence on catalytic activity. Ni / SiO2 and Ni / C were used as catalysts and the reaction conditions (temperature, time, catalyst dosage) were optimized. With the optimization of reaction conditions, Ni / SiO2 and Ni / C were used as catalysts, yields of more than 50% were obtained.

[0042] Examples 30-50

[0043] The first step of hydrogenation reaction was carried out in a kettle reactor. After a certain amount of biphenyl and 10 ml of reaction solvent were added to the reactor, a certain amount of 3wt% Ni / SiO2 was added, 1.2Mpa H2 was charged, and the reaction was carried out at 140°C for 12 hours under magnetic stirring.

[0044] Table 2. Effect of different solvents on reaction activity

[0045]

[0046]

[0047] From the results in Table 2, it can be seen that the concentration of the reaction substrate and catalyst used will affect the reaction results. When the reaction substrate concentration exceeds 0.04 g / ml, the product yield decreases significantly, which may be because the substrate is not fully dissolved in the solvent; acetonitrile or isopropanol as a solvent is more conducive to the reaction than cyclohexane.

[0048] Examples 51-64

[0049] The first step of hydrogenation reaction was carried out in a kettle reactor. After 0.4 g of biphenyl and 10 ml of acetonitrile were added to the reactor, 0.1 g of a certain loading amount of Ni / SiO2 was added, and a certain amount of H2 was charged. Under magnetic stirring, the reaction was carried out at 140°C for 12 hours.

[0050] Table 3. Effect of different solvents on reaction activity

[0051]

[0052] It can be seen from Table 3 that the hydrogen pressure has an effect on the reaction results. When the hydrogen pressure is less than 0.5 MPa, the yield of the product is low. The metal loading of the catalyst has a catalytic effect on the product yield. The yield of cyclohexylbenzene first increases with the metal loading and then remains unchanged. This may be because the surface metal of the catalyst is the main site for catalytic hydrogenation reactions.

[0053] Examples 65-86

[0054] After obtaining cyclohexylbenzene through the first step of reaction, without changing the reaction device, a certain amount of free radical initiator is added after opening the kettle, 1atm O2 is charged, and 0.1g of 98% sulfuric acid solution (mass fraction) is added at 60°C after 3 hours, and then phenol and cyclohexanone are obtained after 4 hours. Sodium hydroxide is added to the solution after the reaction, and dichloromethane: water (volume ratio is 5mL:15mL) is used for liquid separation and extraction. The obtained aqueous phase is a sodium phenol salt solution, and the organic phase contains cyclohexanone. The aqueous phase is neutralized with dilute hydrochloric acid to obtain phenol.

[0055] Table 4. Effect of free radical initiator concentration on reaction activity

[0056]

[0057] It can be seen from the data in Table 4 that the catalytic effect is better when the free radical initiators NHPI and AIBN are used together. At the same time, the concentration of the free radical initiator also affects the catalytic effect, which may be because it is difficult to produce enough peroxyl radicals at a low concentration, and by-products are generated when the concentration is too high.

[0058] Examples 87-104

[0059] After cyclohexylbenzene is obtained through the first step of reaction, there is no need to change the reaction apparatus. After opening the kettle, 0.1 g / ml of NHPI+AIBN is added as a free radical initiator, 1 atm O2 is filled, and after a period of time at a certain reaction temperature, 0.1 g of 98% sulfuric acid solution (mass fraction) is added at room temperature, and then phenol and cyclohexanone are obtained after 4 hours.

[0060] Table 5. Effect of temperature and time on reaction activity

[0061]

[0062]

[0063] As can be seen from Table 5, the reaction temperature and reaction time have a certain influence on the yield of the product. As the reaction temperature and reaction time increase or extend, the product yield first increases and then decreases, which may be because the reaction temperature is too high or the reaction time is too long, which may cause side reactions.

[0064] Examples 105-110

[0065] After cyclohexylbenzene is obtained through the first step of reaction, there is no need to change the reaction apparatus. After opening the kettle, 0.1 g / ml of NHPI+AIBN is added as a free radical initiator, a certain pressure of O2 is filled in, and after 15 hours at 70°C, 0.1 g of 98% sulfuric acid solution (mass fraction) is added at room temperature, and then phenol and cyclohexanone are obtained after 4 hours.

[0066] Table 6. Effect of O2 on reaction activity

[0067]

[0068] From the results in Table 6, it can be seen that the oxygen pressure has an effect on the reaction results, but after reaching 2 atm, the effect on the reaction activity is small.

[0069] Examples 111-129

[0070] After cyclohexylbenzene is obtained through the first step of reaction, there is no need to change the reaction apparatus. After opening the kettle, 0.1 g / ml of NHPI+AIBN is added as a free radical initiator, 2 atm of O2 is filled in, and after 15 hours at 70°C, 0.1 g of acid catalyst is added at room temperature, and then phenol and cyclohexanone are obtained after a certain period of time.

[0071] Table 7. Effect of acid catalyst on reaction activity

[0072]

[0073]

[0074] It can be seen from Table 7 that the type of acid catalyst has a significant effect on the reaction activity, among which Nafion-H and Ambelyst-36 have a better catalytic effect on the reaction. The reaction time also has a certain effect on the product yield, and a better yield can be obtained when the reaction is more than 10 hours.

[0075] Examples 130-136

[0076] After cyclohexylbenzene is obtained through the first step of reaction, there is no need to change the reaction apparatus. After opening the kettle, 0.1 g / ml of NHPI+AIBN is added as a free radical initiator, 2 atm of O2 is filled in, and it is reacted at 70°C for 15 hours; a certain amount of Nafion-H is added at room temperature, and then phenol and cyclohexanone are obtained after 5 hours.

[0077] Table 8. Effect of acid catalyst dosage on reaction activity

[0078]

[0079] It can be seen from the above examples that phenol and cyclohexanone can be prepared from lignin monomer biphenyl through hydrogenation, oxidation-hydrolysis reaction, and this process can be used as an alternative to the phenol / cyclohexanone preparation route using fossil energy as the source. This process improves the breaking effect of the CC bond in biphenyl, and obtains nearly pure phenol and cyclohexanone; and the reaction conditions are mild and the requirements for experimental equipment are low.

[0080] The present invention has been described in detail above. For those skilled in the art, without departing from the purpose and scope of the present invention, and without the need to carry out unnecessary experimental conditions, the present invention can be implemented in a wide range under equivalent parameters, concentrations and conditions. Although the present invention provides specific embodiments, it should be understood that the present invention can be further improved. In a word, according to the principles of the present invention, the application is intended to include any changes, uses or improvements to the present invention, including departure from the disclosed scope in the application, and changes made with conventional techniques known in the art.

Claims

1. A method for preparing phenol and cyclohexanone, comprising: subjecting biphenyl to a hydrogenation reaction to obtain cyclohexylbenzene; and subjecting the cyclohexylbenzene to an oxidation-hydrolysis reaction to obtain phenol and cyclohexanone.

2. The method according to claim 1, characterized in that: The method comprises the following steps: 1) dissolving biphenyl in an organic solvent, using hydrogen as a hydrogen source, and carrying out a hydrogenation reaction under the catalytic action of a supported metal catalyst to obtain a solution containing cyclohexylbenzene; 2) adding a free radical initiator to the solution obtained in step 1), introducing oxygen to carry out oxidation reaction for t1 time, adding an acid catalyst, and reacting for t2 time to obtain phenol and cyclohexanone.

3. The method according to claim 2, characterized in that: In step 1), the biphenyl is derived from lignin; The supported metal catalyst is selected from at least one of Ni / SiO2, Ni / TiO2, Ni / Nb2O5 or Ni / C; The metal loading of the supported metal catalyst is 1-10wt%; The mass ratio of the supported metal catalyst to biphenyl is 1:80-1:

1.

4. The method according to claim 2, characterized in that: The organic solvent is at least one of isopropanol, acetonitrile and cyclohexane; The hydrogenation reaction is carried out in a tank reactor; The concentration of biphenyl is 0.005-0.4 g / ml; The pressure of hydrogen is 0.1-3Mpa; The reaction temperature is 80-300°C; The reaction time is 1-48h.

5. The method according to claim 2, characterized in that: In step 2), the free radical initiator is one or more of NHPI, AIBN, ABVN, BPO, and H2O2; The acid catalyst is one of H2SO4, HCl, CH3COOH, Nafion-H or Ambelyst-36; The concentration of the free radical initiator is 0.001-1g / ml; The amount of acid catalyst used is 0.001-0.1 g / ml.

6. The method according to claim 2, characterized in that: The operation of step 2) is: adding a free radical initiator to the solution obtained in step 1), introducing oxygen, reacting for t1 time, then adding an acid catalyst and a reaction solvent, and obtaining phenol and cyclohexanone after t2 time; Among them, the reaction temperature for reaction time t1 is 30-150oC; Reaction time t1 is 0.5-35h; T2 time is 3-30h; The pressure of oxygen is 0-10atm.

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