CN115636735B - A process for extracting and separating a mixture of m-p-cresol - Google Patents

Abstract

The invention provides a process method for extracting and separating m-cresol and p-cresol mixtures, and relates to the field of separation of coal chemical fine chemicals. The method takes a m-cresol mixture as a raw material, dissolves the m-cresol mixture in normal hexane or toluene solvent, adopts 4-pyridine formamide, urea or oxalic acid as a solid extractant, separates one of the cresols through solid phase extraction, and then obtains single cresols with purity of more than 98% through back extraction. The method is simple and efficient in operation, the extractant can be recycled after back extraction, and the solvent and the back extractant can be recycled.

Description

A process for extracting and separating a mixture of m-p-cresol

Technical Field

The invention relates to the field of separation of coal chemical fine chemicals, and in particular to a method for separating a m-p-cresol mixture.

Background technique

Coal tar is an important coal chemical product. After vacuum distillation, a series of crude phenol products can be obtained. Among them, m-cresol mixture is one of the common crude phenol products. Since the boiling point difference between m-cresol and p-cresol is less than 1°C, they cannot be separated by conventional distillation. Therefore, the development of an efficient and low-energy method for separating m-cresol mixtures has high application value.

There are some mature process methods in industry for separating m-p-cresol mixtures, mainly including complex separation, alkylation separation, crystallization separation and adsorption separation.

The complex separation method is to add a complexing agent to the m-cresol mixture so that it can react with the selected single cresol to form an easily separable complex, 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 to crystallize and separate the complex, and decomplexing the complex. The raw materials of the complex separation method are cheap and easy to obtain, 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.

The process flow of the alkylation separation method is as follows: in the presence of an acid catalyst, m-cresol and p-cresol react with isobutylene to obtain their respective alkylated derivatives. The boiling points of the two products differ greatly and can be separated by distillation, followed by recrystallization, solvent extraction, dehydrogenation and other operations to obtain m-cresol and p-cresol products. This method is relatively simple and can obtain high-purity products. It is the mainstream separation process for industrial applications, but it still has problems such as low catalyst recovery and recycling rates, high energy consumption, and environmental pollution.

The crystallization separation method is a method of crystallization separation using the difference in solubility of cresol mixtures in solvents at different temperatures and the difference in melting points of the mixtures. This method can obtain high-purity cresol isomer monomers, but the production capacity is limited and it is not suitable for large-scale production. In addition, the repeated heating and cooling consumes a lot of energy.

Adsorption separation method is to use the different adsorption capacity of adsorbents for m-cresol to selectively adsorb a certain cresol on the adsorbent, and then desorb it in a specific solvent to separate the m-cresol mixture. As a new separation method, it has a good prospect, but the adsorption capacity is small, and the development of adsorbents and desorbents is still a difficulty that plagues its development.

Based on the above analysis, the complex separation process and high energy consumption are common problems of existing methods. Therefore, it is urgent to develop a new method for separating m-p-cresol mixtures that is simple to operate, highly efficient, energy-saving, and environmentally friendly.

Summary of the invention

The present invention aims at the common problems in the traditional process of separating meta-p-cresol mixture, and provides a method for efficiently separating the meta-p-cresol mixture by solid phase extraction. The method is based on solid phase extraction technology, dissolving the meta-p-cresol mixture in a solvent to form a solution, then adding a solid extractant to the solution, extracting and separating the single cresol in the solution, and realizing efficient separation of the meta-p-cresol mixture under mild conditions. The method uses the meta-p-cresol mixture as a raw material, n-hexane or toluene as a solvent, and 4-pyridinecarboxamide, urea or oxalic acid as an extractant, and can separate a single cresol with a purity greater than 98% from the meta-p-cresol mixture. The method is simple and efficient to operate, and the extractant, solvent and stripping agent can be recycled, providing a new path for the separation of the meta-p-cresol mixture.

The present invention provides a process for extracting and separating a m-p-cresol mixture, which is characterized by comprising the following steps:

S1: dissolving the m-para-cresol mixture in a solvent to prepare a solution, placing the solution in a separator, adding a solid extractant in proportion, controlling the temperature of the solution, stirring and extracting, and separating the liquid and solid phases by centrifugation or filtration after the extraction time is reached to obtain a raffinate and an extract solid;

S2: Take the solid extract in step S1, add a stripping agent, stir and strip at room temperature, and after the stripping time is reached, separate the liquid and solid phases by centrifugation or filtration: the solid phase after stripping is the solid extractant, which can be reused; the liquid phase after stripping can be distilled at atmospheric pressure to obtain a single cresol with a purity greater than 98%, and the stripping agent can be reused;

S3: taking the raffinate from step S1, and recovering the solvent and the remaining m-p-cresol mixture by atmospheric distillation.

The method according to claim 1, characterized in that the solvent in step S1 is n-hexane or toluene.

The method according to claim 1, characterized in that the concentration of the solution prepared by the m-p-cresol mixture in step S1 is 100 g/L to 200 g/L.

The method according to claim 1, characterized in that the solid extractant in step S1 is selected from 4-pyridinecarboxamide, urea, and oxalic acid.

The method according to claim 1 is characterized in that the molar ratio of the amount of solid extractant added in step S1 to the total amount of phenol is 0.3 to 0.9.

The method according to claim 1, characterized in that the extraction temperature in step S1 is 15°C to 45°C.

The method according to claim 1, characterized in that the extraction time described in step S1 is 10 min to 60 min.

The method according to claim 1, characterized in that the stripping agent in step S2 is selected from ethyl acetate, dichloromethane, and diethyl ether.

The method according to claim 1 is characterized in that, in step S2, the volume ratio of the added amount of the stripping agent to the solution is 0.3 to 1.0.

The method according to claim 1 is characterized in that the back extraction time in step S2 is 10 min to 30 min.

The extractant of the present invention separates meta-cresol through hydrogen bonding, and the selection of the extractant is based on the following principles: (1) the interaction energy between the extractant and meta-cresol is greater than the solvent free energy of meta-cresol in n-hexane or toluene solvent, so that the extractant can extract and separate meta-cresol from the solution; (2) the interaction energy between the extractant and meta-cresol and p-cresol is greatly different, so that the extractant has greater selectivity for the two cresols in the solution, and preferentially extracts the cresol with greater interaction energy with the extractant in the solution. Combined with molecular simulation calculations, 4-pyridinecarboxamide, urea, and oxalic acid are selected as extractants.

Compared with the traditional method for separating a meta-cresol mixture, the method for extracting and separating a meta-cresol mixture provided by the present invention has the following advantages: (1) the process flow is simple, the extractant and the solution are added to the reaction at one time, and the operation of repeatedly dropping the meta-cresol mixture and the solution in the traditional process is avoided; (2) the separation conditions are mild, the temperature of the separation process is between 15°C and 45°C, and no high-temperature complexation or low-temperature crystallization processes are required, and the energy consumption is low; (3) an organic solvent is used for back extraction during separation, the separation is easy, the solvent can be reused, and no phenol-containing wastewater is generated; (4) the operation is continuous, and the product quality is good.

Detailed ways

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.

Example 1

A mixture of m-cresol with a mass fraction of 70% m-cresol is used as a raw material, dissolved in n-hexane to prepare a 200 g/L solution. 1 L of the solution is placed in a separator with a stirrer, urea is used as an extractant, 66.7 g of urea is added (the molar ratio of urea to the total phenol content in the solution is 0.6), stirred at 15°C for 60 minutes, and then filtered to separate the liquid and solid phases to obtain a raffinate and an extract solid.

After the solid extract was taken out, ethyl acetate was used as a stripping agent, and the amount added was 0.3 L (the volume ratio to the solution was 0.3). After stirring at room temperature for 30 minutes, the liquid and solid phases were separated by filtration. For the liquid phase solution after stripping, 97.4 g of meta-cresol was obtained by atmospheric distillation, the purity of meta-cresol was 98.6%, and the yield was 68.6%. The solid phase after stripping was urea, which could be reused.

The raffinate was distilled at normal pressure to recover n-hexane, and 102.6 g of a m-p-cresol mixture was obtained, with a mass fraction of m-cresol of 43%.

Example 2

A mixture of m-cresol with a mass fraction of 70% m-cresol is used as a raw material, dissolved in n-hexane to prepare a 200 g/L solution. 1 L of the solution is placed in a separator with a stirrer, urea is used as an extractant, 100.0 g of urea is added (the molar ratio of urea to the total phenol content in the solution is 0.9), stirred at 25°C for 60 minutes, and then centrifuged to separate the liquid and solid phases to obtain a raffinate and an extract solid.

After the solid extract is taken out, ethyl acetate is used as a stripping agent, and the amount added is 1L (the volume ratio to the solution is 1.0). After stirring at room temperature for 10 minutes, the liquid and solid phases are separated by centrifugation. For the liquid phase solution after stripping, 102.5g of meta-cresol is obtained by atmospheric distillation, and the purity of meta-cresol is 98.1%, and the yield is 71.8%. The solid phase after stripping is urea, which can be reused.

The raffinate was distilled at normal pressure to recover n-hexane, and 97.5 g of a m-p-cresol mixture was obtained, wherein the mass fraction of m-cresol was 40%.

Example 3

A mixture of m-cresol with a mass fraction of 70% m-cresol is used as a raw material, dissolved in n-hexane to prepare a 200 g/L solution. 1 L of the solution is placed in a separator with a stirrer, urea is used as an extractant, 66.7 g of urea is added (the molar ratio of urea to the total phenol content in the solution is 0.6), stirred at 20°C for 60 minutes, and then filtered to separate the liquid and solid phases to obtain a raffinate and an extract solid.

After the solid extract is taken out, ethyl acetate is used as a stripping agent, and the amount added is 0.5L (the volume ratio to the solution is 0.5). After stirring at room temperature for 20 minutes, the liquid and solid phases are separated by filtration. For the liquid phase solution after stripping, 99.9g of m-cresol is obtained by atmospheric distillation, and the purity of m-cresol is 98.5%, and the yield is 70.3%. The solid phase after stripping is urea, which can be reused.

The raffinate was distilled at normal pressure to recover n-hexane and obtain 100.1 g of a m-p-cresol mixture, wherein the mass fraction of m-cresol was 42%.

Example 4

A mixture of m-p-cresol with a mass fraction of 60% p-cresol is used as a raw material, dissolved in toluene to prepare a 100 g/L solution. 1 L of the solution is placed in a separator with a stirrer, 4-pyridinecarboxamide is used as an extractant, 45.2 g of 4-pyridinecarboxamide is added (the molar ratio of 4-pyridinecarboxamide to the total phenol content in the solution is 0.4), stirred at 25°C for 60 minutes, and then filtered to separate the liquid and solid phases to obtain a raffinate and an extract solid.

After the solid extract is taken out, ether is used as a stripping agent, and the amount added is 0.5L (the volume ratio to the solution is 0.5). After stirring at room temperature for 30 minutes, the liquid and solid phases are separated by filtration. For the liquid phase solution after stripping, 33.1g of p-cresol is obtained by atmospheric distillation, and the purity of p-cresol is 98.0%, and the yield is 54.0%. The solid phase after stripping is 4-pyridinecarboxamide, which can be reused.

The raffinate was distilled at normal pressure to recover toluene, and 66.9 g of a m-p-cresol mixture was obtained, with a mass fraction of p-cresol of 41%.

Example 5

A mixture of m-p-cresol with a mass fraction of 60% p-cresol is used as a raw material, dissolved in n-hexane to prepare a 200 g/L solution. 1 L of the solution is placed in a separator with a stirrer, oxalic acid is used as an extractant, 50.0 g of oxalic acid is added (the molar ratio of oxalic acid to the total phenol content in the solution is 0.3), stirred at 45°C for 10 minutes, and then filtered to separate the liquid and solid phases to obtain a raffinate and an extract solid.

After the solid extract is taken out, dichloromethane is used as a stripping agent, and the amount added is 0.5L (the volume ratio with the solution is 0.5), and after stirring at room temperature for 30 minutes, the liquid and solid phases are separated by filtration. For the liquid phase solution after stripping, 76.5g of p-cresol is obtained by atmospheric distillation, and the purity of p-cresol is 99.1%, and the yield is 63.2%. The solid phase after stripping is oxalic acid, which can be reused.

The raffinate was distilled at normal pressure to recover n-hexane, and 123.5 g of a m-p-cresol mixture was obtained, with a mass fraction of p-cresol of 36%.

Example 6

A mixture of m-p-cresol with a mass fraction of 60% p-cresol is used as a raw material, dissolved in n-hexane to prepare a 200 g/L solution. 1 L of the solution is placed in a separator with a stirrer, oxalic acid is used as an extractant, 66.7 g of oxalic acid is added (the molar ratio of oxalic acid to the total phenol content in the solution is 0.4), stirred at 25°C for 30 minutes, and then filtered to separate the liquid and solid phases to obtain a raffinate and an extract solid.

After the solid extract is taken out, dichloromethane is used as a stripping agent, and the amount added is 1L (the volume ratio with the solution is 1.0). After stirring at room temperature for 10 minutes, the liquid and solid phases are separated by filtration. For the liquid phase solution after stripping, 89.1g of p-cresol is obtained by atmospheric distillation, and the purity of p-cresol is 98.5%, and the yield is 73.1%. The solid phase after stripping is oxalic acid, which can be reused.

The raffinate was distilled at normal pressure to recover n-hexane, and 110.9 g of a m-p-cresol mixture was obtained, with a mass fraction of p-cresol of 29%.

Example 7

A mixture of m-cresol with a mass fraction of 70% of m-cresol is used as a raw material, dissolved in n-hexane to prepare a 200 g/L solution. 1 L of the solution is placed in a separator with a stirrer, urea is used as an extractant, 66.7 g of urea is added (the molar ratio of urea to the total phenol content in the solution is 0.6), stirred at 25°C for 40 minutes, and then filtered to separate the liquid and solid phases to obtain a raffinate A and an extract solid B.

After the extract solid B is taken out, ethyl acetate is used as a stripping agent, and the amount added is 0.5L (the volume ratio to the solution is 0.5). After stirring at room temperature for 30 minutes, the liquid and solid phases are separated by filtration. For the liquid phase solution after stripping, 95.9g of m-cresol is obtained by atmospheric distillation, the purity of m-cresol is 98.5%, and the yield is 67.5%. The solid phase after stripping is urea, which can be reused.

The raffinate A was placed in a separator with a stirrer, and oxalic acid was used as the extractant. 26.0 g of oxalic acid was added (the molar ratio of oxalic acid to the total phenol content in the solution was 0.3). After stirring at 25°C for 30 minutes, the liquid and solid phases were separated by filtration to obtain the raffinate C and the extract solid D.

After the extract solid D is taken out, dichloromethane is used as a stripping agent, and the amount added is 0.3L (the volume ratio to the solution is 0.3). After stirring at room temperature for 30 minutes, the liquid and solid phases are separated by filtration. For the liquid phase solution after stripping, 39.8g of p-cresol is obtained by atmospheric distillation, and the purity of p-cresol is 98.1%, and the yield is 66.7%. The solid phase after stripping is oxalic acid, which can be reused.

The raffinate C was distilled at normal pressure to recover n-hexane, and 64.2 g of a m-p-cresol mixture was obtained, wherein the mass fraction of m-cresol was 70%.

Example 8

A mixture of m-cresol with a mass fraction of 70% m-cresol is used as a raw material, dissolved in n-hexane to prepare a 200 g/L solution. 1 L of the solution is placed in a separator with a stirrer, urea is used as an extractant, 66.7 g of urea (the molar ratio of urea to the total phenol content in the solution is 0.6) is added, stirred at 25°C for 60 minutes, and then filtered to separate the liquid and solid phases to obtain a raffinate and an extract solid.

After the solid extract is taken out, ethyl acetate is used as a stripping agent, and the amount added is 0.5L (the volume ratio to the solution is 0.5). After stirring at room temperature for 10 minutes, the liquid and solid phases are separated by filtration. For the liquid phase solution after stripping, 100.0g of meta-cresol is obtained by atmospheric distillation, and the purity of meta-cresol is 98.6%, and the yield is 70.4%. The solid phase after stripping is urea, which can be reused.

The raffinate was distilled at normal pressure to recover n-hexane, and 100.0 g of a m-p-cresol mixture was obtained, wherein the mass fraction of m-cresol was 41%.

The solid extractant after back extraction was used again under the above conditions to obtain m-cresol with a purity of 98.5% and a m-cresol yield of 70.1%, and the extraction separation performance did not change.

Claims (7)

1. A process for the extractive separation of a mixture of m-and p-cresol, comprising the steps of:

S1: dissolving m-cresol and p-cresol mixture in a solvent to prepare a solution, placing the solution in a separator, adding a solid extractant in proportion, controlling the temperature of the solution, stirring and extracting, and separating liquid and solid phases by a centrifugal or filtering mode after the extraction time is reached to obtain raffinate and extract solids;

S2: taking the extract solid in the step S1, adding a stripping agent, stirring at room temperature, carrying out stripping, and separating liquid-solid two phases by a centrifugal or filtering mode after the stripping time is reached: the solid phase after back extraction is a solid extractant for re-extraction; the liquid phase after back extraction is distilled under normal pressure to obtain single cresol with purity more than 98 percent, and the back extractant is recycled;

s3: taking raffinate in the step S1, and recycling a solvent and the residual m-cresol mixture by adopting normal pressure distillation;

In the step S1, the solvent is selected from n-hexane and toluene; the solid extractant is selected from 4-pyridine formamide, urea and oxalic acid;

in step S2, the stripping agent is selected from ethyl acetate, dichloromethane, diethyl ether.

2. The method according to claim 1, wherein the m-p-cresol mixture of step S1 is formulated at a solution concentration of 100g/L to 200g/L.

3. The method according to claim 1, wherein the molar ratio of the amount of the solid extractant added to the total phenol amount in step S1 is 0.3 to 0.9.

4. The process according to claim 1, wherein the extraction temperature in step S1 is 15 ℃ to 45 ℃.

5. The method according to claim 1, wherein the extraction time in step S1 is 10min to 60min.

6. The method according to claim 1, wherein the volume ratio of the stripping agent added to the solution in step S2 is 0.3-1.0.

7. The method according to claim 1, wherein the back extraction time in step S2 is 10min to 30min.