Process method for selective oxidation separation of m-cresol / p-cresol mixture

Abstract

The invention provides a process method for selective oxidation separation of a m-cresol / p-cresol mixture by using a metal chelating ionic liquid as a catalyst, and relates to the field of separation of fine chemicals in the coal chemical industry. According to the method, a m-cresol / p-cresol mixture is used as a raw material, a metal chelating ionic liquid is used as a catalyst, oxygen or air is used as an oxidant, p-cresol is selectively oxidized into 3, 3-dimethoxybiphenyl, then the m-cresol and the 3, 3-dimethoxybiphenyl are separated through phase splitting and rectification, and separation and high-value utilization of the m-cresol / p-cresol mixture are achieved. The method is simple and efficient to operate, mild in reaction condition and low in separation cost.

Description

Technical Field

[0001] The present invention relates to the field of separation of fine chemicals in coal chemical industry, and particularly to a method for separating a m-cresol / p-cresol mixture. Background Art

[0002] Coal tar is an important coal chemical product, and a series of crude phenol products can be obtained through rectification and other means. The m-cresol / p-cresol mixture is one of them. Due to its limited application fields, the m-cresol / p-cresol mixture is mostly circulated as a low-value-added raw material, while high-purity m-cresol and p-cresol monomers have important application values in the fields of medicine, pesticides, and polymer materials. Since the boiling points of m-cresol and p-cresol differ by only 0.4 °C, it is difficult to separate and purify the two by conventional rectification. Therefore, developing a simple and efficient method for separating m-cresol / p-cresol is of great significance for the high-value utilization of the m-cresol / p-cresol mixture.

[0003] Currently, there are some relatively mature industrial process methods for separating the m-cresol / p-cresol mixture, mainly including complexation separation method, alkylation separation method, crystallization separation method, and adsorption separation method.

[0004] The complexation separation method is to add a complexing agent to the m-cresol / p-cresol mixture so that it can react with the selected single cresol to form a complex that is easy to separate, thereby achieving the separation of the single cresol. This method uses oxalic acid, urea, etc. as complexing agents, and usually goes through processes such as heating to form a complex, cooling and crystallizing to separate the complex, and decomposing the complex. The complexation separation method has cheap and easily available raw materials and can be recycled, but the reaction temperature is high, the crystallization temperature is low, the process is relatively cumbersome, the efficiency is low, and the energy consumption is high.

[0005] The alkylation separation method is to react m-cresol and p-cresol with isobutene respectively under an acid catalyst to obtain alkylation derivatives, and then through operations such as rectification, recrystallization, solvent extraction, and dehydrocarbonation, m-cresol and p-cresol products are obtained. This method has a relatively simple process and can obtain high-purity products, and it is the mainstream separation process in industrial applications, but there are still problems such as low recovery rate and recycling rate of the catalyst, high energy consumption, and environmental pollution.

[0006] The crystallization separation method is a method of separating by using the difference in solubility of the cresol mixture in a solvent at different temperatures and the difference in melting point of the mixture. This method can obtain high-purity cresol isomer monomers, but the production capacity is limited, it is not suitable for large-scale production, and the energy consumption is high due to repeated heating and cooling.

[0007] The adsorption separation method utilizes the different adsorption capacities of adsorbents for meta / p-cresol to selectively adsorb one of the cresols on the adsorbent and then desorb it in a specific solvent, thereby separating the meta / p-cresol mixture. As a new separation method, it has high application prospects. However, the adsorption capacity is small, and the development of adsorbents and desorbents remains a difficult point hindering its development.

[0008] Based on the above analysis, the complex separation process and high energy consumption are common problems in existing methods. Therefore, there is an urgent need to develop a new method for separating meta / p-cresol mixtures that is simple to operate, energy-efficient, and environmentally friendly. Summary of the Invention

[0009] In view of the common problems in the traditional separation process of meta / p-cresol mixtures, the present invention provides a process method for selectively oxidizing and separating meta / p-cresol mixtures using a metal chelating ionic liquid as a catalyst. This method first prepares a metal chelating ionic liquid from an ionic liquid and a metal chloride, and then uses the metal chelating ionic liquid as a catalyst to catalytically oxidize p-cresol in the meta / p-cresol mixture with oxygen in a high-pressure reactor. After the reaction, water is added to the mother liquor to form two phases. The aqueous phase contains the catalyst and trace amounts of reactants and products, and the oil phase contains m-cresol and the product 3,3-dimethoxybiphenyl. The aqueous phase is recycled by simple evaporation to recover the catalyst and trace reactants and products for use in the catalytic reaction of the raw materials, and the water is recycled for phase separation of the mother liquor. The oil phase is separated by distillation to obtain m-cresol and the p-methyl product 3,3-dimethoxybiphenyl. This method is simple and efficient to operate, has mild reaction conditions, is environmentally friendly, and the metal chelating ionic liquid can be regenerated and recycled, providing a new path for the separation of meta / p-cresol mixtures.

[0010] A process method for selectively oxidizing and separating meta / p-cresol mixtures, characterized by comprising the following steps:

[0011] S1: Add an ionic liquid and a metal chloride to a reaction kettle in a certain proportion, react at 80 °C for 2 hours, and then cool to obtain a metal chelating ionic liquid;

[0012] S2: Place the meta / p-cresol mixture in a high-pressure reaction kettle, add a certain amount of the metal chelating ionic liquid obtained in step S1 as a catalyst, fill in oxygen or air at a certain pressure, heat up and react for a period of time, and then cool to obtain a mother liquor;

[0013] S3: Take the mother liquor in step S2, add deionized water to make it divide into upper and lower phases. The lower phase is recovered by atmospheric distillation to obtain the metal chelating ionic liquid and deionized water, and the upper phase is separated by distillation to obtain m-cresol with a purity of 99% and 3,3-dimethoxybiphenyl with a purity of 99%.

[0014] The method according to claim 1, characterized in that, in step S1, the ionic liquid is selected from 1-ethyl-3-methylimidazolium chloride and 1-butyl-3-methylimidazolium chloride.

[0015] The method according to claim 1, characterized in that, in step S1, the metal chloride is selected from copper chloride, cuprous chloride, ferric chloride, ferrous chloride, and aluminum chloride.

[0016] The method according to claim 1, characterized in that, in step S1, the molar ratio of the ionic liquid to the metal chloride is from 10:1 to 1:10.

[0017] The method according to claim 1, characterized in that, in step S2, the molar ratio of m-cresol to p-cresol is from 3:7 to 7:3.

[0018] The method according to claim 1, characterized in that, in step S2, the oxygen pressure is from 1.0 MPa to 3.0 MPa, and oxygen can also be replaced by air, and the air pressure is from 2 MPa to 5.0 MPa.

[0019] The method according to claim 1, characterized in that, in step S2, the oxidation reaction temperature is 50 °C to 100 °C.

[0020] The method according to claim 1, characterized in that, in step S2, the oxidation reaction time is 20 min to 180 min.

[0021] The method according to claim 1, characterized in that, in step S2, the mass fraction of the catalyst is 3 wt% to 6 wt%.

[0022] The method according to claim 1, characterized in that, in step S3, the volume ratio of the amount of deionized water used to the amount of catalyst used is 10:1.

[0023] This method utilizes the fact that metal chelating ionic liquids can selectively catalyze the oxidation of p-cresol by oxygen under certain conditions, and realizes the separation and high-value utilization of m / p-cresol by using the boiling point difference between the oxidation product of p-cresol and m-cresol. Compared with the existing methods for separating m / p-cresol mixtures, the method for selectively oxidizing and separating m / p-cresol mixtures provided by the present invention has the following advantages: (1) The process flow is simple, and the m / p-cresol mixture is separated by selective oxidation; (2) The oxidation conditions are mild, the temperature is between 50 °C and 100 °C, and the energy consumption is low; (3) The catalyst in the oxidation process and the deionized water used for phase separation can both be reused, and no phenolic wastewater is generated, which is environmentally friendly. Detailed implementation manners

[0024] The present invention is further illustrated by the following examples, but the protection scope of the present invention is not limited to the following examples.

[0025] Example 1

[0026] A metal chelating ionic liquid was obtained by mixing 1-ethyl-3-methylimidazolium chloride and copper chloride in a molar ratio of 1:1 and adding them to a reaction kettle. After reacting at 80 °C for 2 hours, it was cooled to room temperature. A m-cresol / p-cresol mixture with a m-cresol mole fraction of 60% was added to a high-pressure reaction kettle, and 3 wt% of the metal chelating ionic liquid was added. After filling with 1.0 MPa of oxygen, the reaction kettle was closed and stirring was started. After heating to 70 °C and maintaining for 60 min, after the reaction was completed, it was cooled to room temperature, the gas was discharged, and the reaction kettle was opened to collect the mother liquor. Deionized water with a volume ratio of 10:1 to the catalyst dosage was added to phase-separate the mother liquor. The lower phase was subjected to atmospheric distillation to recover the metal chelating ionic liquid and deionized water, and the upper phase was rectified in a rectification column. The light component was m-cresol with a purity of 99%, and the heavy component was 3,3-dimethoxybiphenyl with a purity of 99%.

[0027] Example 2

[0028] A metal chelating ionic liquid was obtained by mixing 1-ethyl-3-methylimidazolium chloride and ferric chloride in a molar ratio of 4:1 and adding them to a reaction kettle. After reacting at 80 °C for 2 hours, it was cooled to room temperature. A m-cresol / p-cresol mixture with a m-cresol mole fraction of 50% was added to a high-pressure reaction kettle, and 3 wt% of the metal chelating ionic liquid was added. After filling with 2.0 MPa of oxygen, the reaction kettle was closed and stirring was started. After heating to 60 °C and maintaining for 40 min, after the reaction was completed, it was cooled to room temperature, the gas was discharged, and the reaction kettle was opened to collect the mother liquor. Deionized water with a volume ratio of 10:1 to the catalyst dosage was added to phase-separate the mother liquor. The lower phase was subjected to atmospheric distillation to recover the metal chelating ionic liquid and deionized water, and the upper phase was rectified in a rectification column. The light component was m-cresol with a purity of 99%, and the heavy component was 3,3-dimethoxybiphenyl with a purity of 99%.

[0029] Example 3

[0030] A metal chelating ionic liquid was obtained by mixing 1-ethyl-3-methylimidazolium chloride and cuprous chloride in a molar ratio of 7:1 and adding them to a reaction kettle. After reacting at 80 °C for 2 hours, it was cooled to room temperature. A m-cresol / p-cresol mixture with a m-cresol mole fraction of 30% was added to a high-pressure reaction kettle, and 4 wt% of the metal chelating ionic liquid was added. After filling with 3.0 MPa of oxygen, the reaction kettle was closed and stirring was started. After heating to 60 °C and maintaining for 20 min, after the reaction was completed, it was cooled to room temperature, the gas was discharged, and the reaction kettle was opened to collect the mother liquor. Deionized water with a volume ratio of 10:1 to the catalyst dosage was added to phase-separate the mother liquor. The lower phase was subjected to atmospheric distillation to recover the metal chelating ionic liquid and deionized water, and the upper phase was rectified in a rectification column. The light component was m-cresol with a purity of 99%, and the heavy component was 3,3-dimethoxybiphenyl with a purity of 99%.

[0031] Example 4

[0032] A metal chelating ionic liquid was obtained by mixing 1-ethyl-3-methylimidazolium chloride and copper chloride in a molar ratio of 2:1 and adding them to a reaction kettle. After reacting at 80 °C for 2 hours, it was cooled to room temperature. A meta / para-cresol mixture with a meta-cresol mole fraction of 70% was added to a high-pressure reaction kettle, and 4 wt% of the metal chelating ionic liquid was added. After filling with 2.0 MPa of air, the reaction kettle was closed and stirring was started. After heating to 80 °C and maintaining for 120 min, after the reaction was completed, it was cooled to room temperature, the gas was discharged, and the reaction kettle was opened to collect the mother liquor. Deionized water with a volume ratio of 10:1 to the catalyst dosage was added to phase-separate the mother liquor. The lower phase was recovered by atmospheric distillation to obtain the metal chelating ionic liquid and deionized water, and the upper phase was rectified in a rectification column. The light fraction was meta-cresol with a purity of 99%, and the heavy fraction was 3,3-dimethoxybiphenyl with a purity of 99%.

[0033] Example 5

[0034] A metal chelating ionic liquid was obtained by mixing 1-ethyl-3-methylimidazolium chloride and cuprous chloride in a molar ratio of 10:1 and adding them to a reaction kettle. After reacting at 80 °C for 2 hours, it was cooled to room temperature. A meta / para-cresol mixture with a meta-cresol mole fraction of 60% was added to a high-pressure reaction kettle, and 4 wt% of the metal chelating ionic liquid was added. After filling with 5.0 MPa of air, the reaction kettle was closed and stirring was started. After heating to 90 °C and maintaining for 150 min, after the reaction was completed, it was cooled to room temperature, the gas was discharged, and the reaction kettle was opened to collect the mother liquor. Deionized water with a volume ratio of 10:1 to the catalyst dosage was added to phase-separate the mother liquor. The lower phase was recovered by atmospheric distillation to obtain the metal chelating ionic liquid and deionized water, and the upper phase was rectified in a rectification column. The light fraction was meta-cresol with a purity of 99%, and the heavy fraction was 3,3-dimethoxybiphenyl with a purity of 99%.

[0035] Example 6

[0036] A metal chelating ionic liquid was obtained by mixing 1-ethyl-3-methylimidazolium chloride and cuprous chloride in a molar ratio of 1:5 and adding them to a reaction kettle. After reacting at 80 °C for 2 hours, it was cooled to room temperature. A meta / para-cresol mixture with a meta-cresol mole fraction of 70% was added to a high-pressure reaction kettle, and 5 wt% of the metal chelating ionic liquid was added. After filling with 2.5 MPa of air, the reaction kettle was closed and stirring was started. After heating to 100 °C and maintaining for 20 min, after the reaction was completed, it was cooled to room temperature, the gas was discharged, and the reaction kettle was opened to collect the mother liquor. Deionized water with a volume ratio of 10:1 to the catalyst dosage was added to phase-separate the mother liquor. The lower phase was recovered by atmospheric distillation to obtain the metal chelating ionic liquid and deionized water, and the upper phase was rectified in a rectification column. The light fraction was meta-cresol with a purity of 99%, and the heavy fraction was 3,3-dimethoxybiphenyl with a purity of 99%.

[0037] Example 7

[0038] Mix 1-ethyl-3-methylimidazolium chloride and ferrous chloride in a molar ratio of 1:8 and add them to a reaction kettle. At 80 °C, after reacting for 2 hours, cool to room temperature to obtain a metal chelating ionic liquid. Add a m-cresol / p-cresol mixture with a molar fraction of m-cresol of 40% to a high-pressure reaction kettle, and add 5 wt% of the metal chelating ionic liquid. After filling with 2.0 MPa of air, close the reaction kettle and start stirring. After heating to 70 °C and maintaining for 180 min, cool to room temperature after the reaction ends, exhaust the gas and open the reaction kettle to collect the mother liquor. Add deionized water with a volume ratio of 10:1 to the catalyst dosage to phase-separate the mother liquor. The lower phase is recovered by atmospheric distillation to obtain the metal chelating ionic liquid and deionized water, and the upper phase is rectified in a rectification column. The light fraction is m-cresol with a purity of 99%, and the heavy fraction is 3,3-dimethoxybiphenyl with a purity of 99%.

[0039] Example 8

[0040] Mix 1-ethyl-3-methylimidazolium chloride and cuprous chloride in a molar ratio of 1:10 and add them to a reaction kettle. At 80 °C, after reacting for 2 hours, cool to room temperature to obtain a metal chelating ionic liquid. Add a m-cresol / p-cresol mixture with a molar fraction of m-cresol of 50% to a high-pressure reaction kettle, and add 5 wt% of the metal chelating ionic liquid. After filling with 1.5 MPa of oxygen, close the reaction kettle and start stirring. After heating to 70 °C and maintaining for 100 min, cool to room temperature after the reaction ends, exhaust the gas and open the reaction kettle to collect the mother liquor. Add deionized water with a volume ratio of 10:1 to the catalyst dosage to phase-separate the mother liquor. The lower phase is recovered by atmospheric distillation to obtain the metal chelating ionic liquid and deionized water, and the upper phase is rectified in a rectification column. The light fraction is m-cresol with a purity of 99%, and the heavy fraction is 3,3-dimethoxybiphenyl with a purity of 99%.

[0041] Example 9

[0042] Mix 1-butyl-3-methylimidazolium chloride and cuprous chloride in a molar ratio of 1:2 and add them to a reaction kettle. At 80 °C, after reacting for 2 hours, cool to room temperature to obtain a metal chelating ionic liquid. Add a m-cresol / p-cresol mixture with a molar fraction of m-cresol of 60% to a high-pressure reaction kettle, and add 5 wt% of the metal chelating ionic liquid. After filling with 1.0 MPa of oxygen, close the reaction kettle and start stirring. After heating to 50 °C and maintaining for 180 min, cool to room temperature after the reaction ends, exhaust the gas and open the reaction kettle to collect the mother liquor. Add deionized water with a volume ratio of 10:1 to the catalyst dosage to phase-separate the mother liquor. The lower phase is recovered by atmospheric distillation to obtain the metal chelating ionic liquid and deionized water, and the upper phase is rectified in a rectification column. The light fraction is m-cresol with a purity of 99%, and the heavy fraction is 3,3-dimethoxybiphenyl with a purity of 99%.

[0043] Example 10

[0044] A mixture of 1-butyl-3-methylimidazolium chloride and aluminum chloride with a molar ratio of 1:7 was added to a reaction kettle. After reacting at 80 °C for 2 hours, it was cooled to room temperature to obtain a metal chelating ionic liquid. A mixture of m-cresol and p-cresol with a molar fraction of m-cresol of 60% was added to a high-pressure reaction kettle, and 6 wt% of the metal chelating ionic liquid was added. After filling with 2.5 MPa of oxygen, the reaction kettle was closed and stirring was started. After heating to 60 °C and maintaining for 120 min, after the reaction was completed, it was cooled to room temperature, the gas was discharged, and the reaction kettle was opened to collect the mother liquor. Deionized water with a volume ratio of 10:1 to the catalyst dosage was added to phase-separate the mother liquor. The lower phase was recovered by atmospheric distillation to obtain the metal chelating ionic liquid and deionized water, and the upper phase was rectified by a rectification column. The light component was m-cresol with a purity of 99%, and the heavy component was 3,3-dimethoxybiphenyl with a purity of 99%.

[0045] Example 11

[0046] A mixture of 1-butyl-3-methylimidazolium chloride and cuprous chloride with a molar ratio of 1:1 was added to a reaction kettle. After reacting at 80 °C for 2 hours, it was cooled to room temperature to obtain a metal chelating ionic liquid. A mixture of m-cresol and p-cresol with a molar fraction of m-cresol of 70% was added to a high-pressure reaction kettle, and 6 wt% of the metal chelating ionic liquid was added. After filling with 2.0 MPa of air, the reaction kettle was closed and stirring was started. After heating to 70 °C and maintaining for 100 min, after the reaction was completed, it was cooled to room temperature, the gas was discharged, and the reaction kettle was opened to collect the mother liquor. Deionized water with a volume ratio of 10:1 to the catalyst dosage was added to phase-separate the mother liquor. The lower phase was recovered by atmospheric distillation to obtain the metal chelating ionic liquid and deionized water, and the upper phase was rectified by a rectification column. The light component was m-cresol with a purity of 99%, and the heavy component was 3,3-dimethoxybiphenyl with a purity of 99%.

[0047] Example 12

[0048] A mixture of 1-butyl-3-methylimidazolium chloride and cuprous chloride with a molar ratio of 6:1 was added to a reaction kettle. After reacting at 80 °C for 2 hours, it was cooled to room temperature to obtain a metal chelating ionic liquid. A mixture of m-cresol and p-cresol with a molar fraction of m-cresol of 70% was added to a high-pressure reaction kettle, and 6 wt% of the metal chelating ionic liquid was added. After filling with 4.0 MPa of air, the reaction kettle was closed and stirring was started. After heating to 90 °C and maintaining for 100 min, after the reaction was completed, it was cooled to room temperature, the gas was discharged, and the reaction kettle was opened to collect the mother liquor. Deionized water with a volume ratio of 10:1 to the catalyst dosage was added to phase-separate the mother liquor. The lower phase was recovered by atmospheric distillation to obtain the metal chelating ionic liquid and deionized water, and the upper phase was rectified by a rectification column. The light component was m-cresol with a purity of 99%, and the heavy component was 3,3-dimethoxybiphenyl with a purity of 99%.

Claims

1. A process for selectively oxidizing and separating a m - / p -cresol mixture, characterized in that, It includes the following steps: S1: Add ionic liquid and metal chloride into a reaction kettle in a certain proportion. After reacting at 80 °C for 2 hours, cool to obtain metal chelating ionic liquid; S2: Place the mixture of m- / p-cresol in a high-pressure reaction kettle, add a certain amount of the metal chelating ionic liquid obtained in step S1 as a catalyst, charge oxygen or air at a certain pressure, heat up and react for a period of time, and then cool to obtain the mother liquor; S3: Take the mother liquor in step S2, add deionized water to make it divide into upper and lower phases. The lower phase is distilled under normal pressure to recover the metal chelating ionic liquid and deionized water, and the upper phase is rectified to obtain m-cresol with a purity of 99% and 3,3-dimethoxybiphenyl with a purity of 99%.

2. The method according to claim 1, wherein The ionic liquid described in step S1 is selected from 1-ethyl-3-methylimidazolium chloride and 1-butyl-3-methylimidazolium chloride.

3. The method according to claim 1, wherein The metal chloride described in step S1 is selected from copper chloride, cuprous chloride, ferric chloride, ferrous chloride, and aluminum chloride.

4. The method according to claim 1, wherein The molar ratio of the ionic liquid to the metal chloride described in step S1 is 10:1 to 1:

10.

5. The method according to claim 1, characterized in that The molar ratio of m-cresol to p-cresol described in step S2 is 3:7 to 7:

3.

6. The method according to claim 1, wherein The oxygen pressure described in step S2 is 1.0 MPa to 3.0 MPa, and oxygen can also be replaced with air, and the air pressure is 0.5 MPa to 5.0 MPa.

7. The method according to claim 1, wherein The oxidation reaction temperature described in step S2 is 50 °C to 100 °C.

8. The method according to claim 1, wherein The oxidation reaction time described in step S2 is 20 min to 180 min.

9. The method according to claim 1, characterized in that, The mass fraction of the catalyst described in step S2 is 3 wt% to 6 wt%.

10. The method according to claim 1, wherein The volume ratio of the amount of deionized water used to the amount of catalyst used described in step S3 is 10:1.