Method for separating m-cresol and p-cresol based on beta-cyclodextrin

Abstract

The invention discloses a method for separating m-cresol and p-cresol based on beta-cyclodextrin, which comprises the following steps: by taking a m-cresol and p-cresol mixture obtained by vacuum distillation of crude phenol as a raw material, heating, stirring and mixing the m-cresol and p-cresol mixture and a beta-cyclodextrin aqueous solution, cooling to low temperature, carrying out vacuum filtration, soaking and washing filter residues with ethanol, and drying to obtain the m-cresol and p-cresol. And distilling the obtained washing liquid to recover ethanol to obtain m-cresol, extracting the filtrate with diethyl ether, evaporating diethyl ether from the extract to obtain p-cresol, and the purity of the m-cresol and the purity of the p-cresol are both 96% or above. According to the method, beta-cyclodextrin can form a more stable inclusion compound with a substituent group position of m-cresol so as to separate the m-cresol in a precipitation form, and p-cresol is left in a mother solution and can be further purified, so that the separation efficiency is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of separation of coal chemical fine chemicals, and in particular relates to a method for separating m-p-cresol. Background Art

[0002] Meta-p-cresol is an important extract of crude phenol vacuum distillation of coal tar. Since the boiling points of meta-cresol and p-cresol are similar (only 0.4°C difference), it is difficult to separate them by conventional distillation methods in industry. At present, the more conventional methods for separating cresol isomers include crystallization separation method, complex addition method, alkylation separation method and molecular sieve adsorption method, but these methods often have problems such as high energy consumption, low yield or insufficient purity. Therefore, it is of great significance to develop an efficient, low-energy consumption, high-purity meta-p-cresol separation method.

[0003] The separation of m-cresol is mainly carried out according to two principles: chemical method and physical method. The chemical method, for example, uses urea complexation and alkane substitution to separate the two, and the physical method uses extraction and melting point differences to perform crystallization separation. For example, CN111909004A discloses a method for separating m-cresol, which uses m-cresol obtained by vacuum distillation of crude phenol as a raw material, uses common urea and oxalic acid as complexing agents, and obtains m-cresol and p-cresol through two-step complexation crystallization, and controls the temperature and reaction time during the complexation and crystallization process. In this separation method, the wastewater generated in the subsequent treatment process of the urea complex reaction will contain urea, oxalic acid and other possible harmful substances, which need to be strictly treated before discharge, increasing the cost and difficulty of wastewater treatment, and the process is complicated and energy consumption is high. CN118993850A discloses a method for separating m-p-cresol, wherein the mixed phenol is separated by column chromatography, the eluent is a mixed solvent of n-hexane and dichloromethane in a volume ratio of 1 to 3:1, the filler of the chromatography column is glucose gel, and the mixed phenol is separated by silica gel chromatography. The selectivity of the glucose gel in the separation method is relatively poor, thereby affecting the separation purity of m-p-cresol, and when the mixed solvent is used as the eluent, the recovery of the solvent is relatively difficult, the operation is complicated and the cost is high. CN116239451A discloses a method for separating and purifying m-p-cresol, wherein the m-p-cresol solution and the desorbent are respectively introduced into an adsorption separation device, based on the molecular sieve adsorption chromatography separation principle, a p-cresol extract and a m-cresol residual liquid are obtained, the p-cresol extract and the m-cresol residual liquid are respectively distilled and separated to obtain crude p-cresol and crude m-cresol, and the crude p-cresol and the crude m-cresol are respectively subjected to secondary distillation and separation to obtain refined p-cresol and refined m-cresol. The secondary distillation process in this separation method consumes a lot of energy, and the energy consumption and cost are relatively high. The process is relatively complicated and requires precise control of process parameters such as temperature and pressure. The boiling points of m-cresol and p-cresol are similar, and it is difficult to achieve efficient separation using conventional distillation methods. Even if secondary distillation is used, it needs to be repeated many times, thereby reducing the overall separation efficiency. Summary of the invention

[0004] The invention provides a method for separating m-cresol based on beta-cyclodextrin. The method utilizes the selective inclusion action of beta-cyclodextrin to achieve efficient separation of m-cresol and p-cresol.

[0005] The method for separating m-p-cresol based on β-cyclodextrin provided by the present invention comprises the following steps:

[0006] Step 1: Add β-cyclodextrin into deionized water, heat and stir to dissolve, and obtain a β-cyclodextrin solution.

[0007] Step 2: Add the m-para-cresol mixture to the β-cyclodextrin solution, stir at a constant temperature of 30-50° C. for 1-3 hours, cool to 4-10° C., and separate by vacuum filtration.

[0008] Step 3: The filter residue obtained in step 2 is soaked and washed with ethanol, and the obtained washing liquid is distilled to recover the ethanol to obtain m-cresol; the filtrate obtained in step 2 is extracted with ether, and the extract is evaporated to obtain p-cresol.

[0009] Furthermore, in the above step 1, it is preferred to heat and stir to dissolve at 30 to 40°C.

[0010] Furthermore, in the above step 1, the mass fraction of β-cyclodextrin in the β-cyclodextrin solution is preferably 1% to 3%.

[0011] Furthermore, in the above step 2, the volume ratio of the m-p-cresol mixture to the β-cyclodextrin solution is preferably 1:4-8.

[0012] Furthermore, in the above step 2, the mixture is preferably stirred at a constant temperature of 40° C. for 2 hours.

[0013] Furthermore, in the above step 3, the filter residue is preferably washed by soaking in ethanol for 20 to 40 minutes.

[0014] Furthermore, in the above step 3, the washing liquid is preferably distilled at 60-70° C. to recover ethanol.

[0015] Furthermore, in the above step 3, the ether is preferably evaporated from the extract at 30-40°C.

[0016] The beneficial effects of the present invention are as follows:

[0017] 1. Efficient separation: The selectivity of β-cyclodextrin inclusion complex for guest molecules mainly depends on the size and shape of the cyclodextrin cavity and the size, shape and polarity of the guest molecules. Due to the differences in molecular structure and properties between m-cresol and p-cresol, their binding ability with β-cyclodextrin and the stability of the formed inclusion complex are different. β-cyclodextrin can form a more stable inclusion complex with the substituent position of m-cresol, thereby separating it in the form of precipitation, and p-cresol remains in the mother liquor, achieving highly selective separation of the m-cresol mixture.

[0018] 2. Low energy consumption: Compared with traditional separation methods, β-cyclodextrin inclusion reaction does not require the use of large amounts of organic solvents and high temperature and high pressure conditions, so it has lower energy consumption and less environmental pollution. At the same time, β-cyclodextrin, as a natural polymer compound, has good biocompatibility and degradability, and will not cause long-term impact on the environment and ecosystem.

[0019] 3. High yield: The process of separating the m-cresol mixture by β-cyclodextrin inclusion complexation is simple, the reaction conditions are mild, the reaction time is short, the separation efficiency is high, and the purity of m-cresol and p-cresol is both above 96%. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is the GC-MS chart of crude phenol.

[0021] Figure 2 This is the GC-MS graph of m-cresol obtained after separation with β-cyclodextrin.

[0022] Figure 3 This is the GC-MS graph of p-cresol obtained after separation with β-cyclodextrin. DETAILED DESCRIPTION

[0023] The present invention is further described in detail below in conjunction with embodiments and drawings, but the protection scope of the present invention is not limited to these embodiments.

[0024] The method for obtaining the meta-p-cresol mixture used in the following examples is as follows: crude phenol is added to a round-bottom flask for distillation, the initial temperature is set to 50°C, and after the temperature is reached, the temperature is increased by 5°C every 5 minutes. When the temperature in the flask reaches the range of 200-205°C, the fractions are collected to obtain the meta-p-cresol mixture. Figure 1 It can be seen that the content of intermediate cresol in crude phenol accounts for 20.93%, and p-cresol accounts for 20.86%.

[0025] Example 1

[0026] Step 1: Add 4.625 g of β-cyclodextrin to 250 mL of deionized water, heat to 30-40° C. under stirring, and stir at a constant temperature to completely dissolve the β-cyclodextrin to obtain a β-cyclodextrin solution with a mass fraction of 1.85%.

[0027] Step 2: Add 41.8 mL of the m-p-cresol mixture to 250 mL of the β-cyclodextrin solution, stir at 40° C. for 2 hours, then cool to 4-10° C. and separate by vacuum filtration.

[0028] Step 3: Add 50 mL of ethanol to the filter residue obtained in step 2, soak and wash for 30 minutes to release the m-cresol contained in β-cyclodextrin into the ethanol, and then heat the obtained washing liquid to 60-70° C. to distill and recover the ethanol to obtain 25 mL of m-cresol. Add 50 mL of ether to the filtrate obtained in step 2 for extraction, and evaporate the ether from the extract at 30-40° C. to obtain 15 g of p-cresol.

[0029] Depend on Figure 2 It can be seen that after β-cyclodextrin inclusion separation, the purity of m-cresol obtained is 100%. Figure 3 It can be seen that after the β-cyclodextrin inclusion separation, the purity of the obtained p-cresol is 100%, indicating that the selective inclusion effect of β-cyclodextrin is used to achieve efficient separation of m-cresol and p-cresol.

[0030] Example 2

[0031] In this example, a 3% β-cyclodextrin solution was used to replace the 1.85% β-cyclodextrin solution in Example 1, and the other steps were the same as those in Example 1, thereby separating m-para-cresol.

[0032] Example 3

[0033] In this example, the β-cyclodextrin solution with a mass fraction of 1% in Example 1 is substituted with the β-cyclodextrin solution with a mass fraction of 1.85%, and the other steps are the same as those in Example 1, thereby separating m-para-cresol.

[0034] Example 4

[0035] In step 2 of this embodiment, 41.8 mL of the m-p-cresol mixture is added to 209 mL of a β-cyclodextrin solution having a mass fraction of 1.85%, and the other steps are the same as those in embodiment 1, thereby separating the m-p-cresol.

[0036] Example 5

[0037] In step 2 of this embodiment, 41.8 mL of the m-p-cresol mixture is added to 292.6 mL of a β-cyclodextrin solution having a mass fraction of 1.85%, and the other steps are the same as those in embodiment 1, thereby separating the m-p-cresol.

[0038] Comparative Example 1

[0039] In this example, α-cyclodextrin is used to replace β-cyclodextrin in Example 1, and the other steps are the same as those in Example 1, thereby separating m-para-cresol.

[0040] Comparative Example 2

[0041] In this example, γ-cyclodextrin is used to replace β-cyclodextrin in Example 1, and the other steps are the same as those in Example 1, thereby separating m-para-cresol.

[0042] The purity of the meta-cresol and p-cresol separated in the above-mentioned embodiments 1 to 5 and comparative examples 1 and 2 was tested. The specific process of the test was as follows: a gas chromatography-flame ionization detector (FID) was used to measure the concentration of meta-cresol and p-cresol using a DB-WAX strong polarity column with a length of 30 m and an inner diameter of 0.2 mm. The chromatographic conditions were: a constant temperature box at 150° C., a sample injector temperature at 230° C., a detector temperature at 280° C., and a detection time of 45 min. The internal standard method was used for quantitative analysis, with n-hexane as the solvent and o-nitrotoluene as the internal standard. The test results are shown in Table 1.

[0043] Table 1

[0044]

[0045]

[0046] As can be seen from Table 1, the purity of m-cresol and p-cresol separated by inclusion with β-cyclodextrin in Examples 1 to 5 is significantly higher than the purity of the m-p-cresol mixture separated by inclusion with α-cyclodextrin and γ-cyclodextrin in Comparative Examples 1 and 2.

Claims

1. A method for separating m-p-cresol based on β-cyclodextrin, characterized in that: The method comprises the following steps: Step 1: Add β-cyclodextrin into deionized water, heat and stir to dissolve, and obtain a β-cyclodextrin solution; Step 2: Add the m-p-cresol mixture to the β-cyclodextrin solution, stir at a constant temperature of 30-50° C. for 1-3 hours, cool to 4-10° C., and separate by vacuum filtration; Step 3: The filter residue obtained in step 2 is soaked and washed with ethanol, and the obtained washing liquid is distilled to recover the ethanol to obtain m-cresol; the filtrate obtained in step 2 is extracted with ether, and the extract is evaporated to obtain p-cresol.

2. The method for separating m-p-cresol based on β-cyclodextrin according to claim 1, characterized in that: In step 1, heat and stir at 30-40°C to dissolve.

3. The method for separating m-p-cresol based on β-cyclodextrin according to claim 1, characterized in that: In step 1, the mass fraction of β-cyclodextrin in the β-cyclodextrin solution is 1% to 3%.

4. The method for separating m-p-cresol based on β-cyclodextrin according to claim 3, characterized in that: In step 2, the volume ratio of the m-p-cresol mixture to the β-cyclodextrin solution is 1:4-8.

5. The method for separating m-p-cresol based on β-cyclodextrin according to claim 1, characterized in that: In step 2, the mixture was stirred at a constant temperature of 40° C. for 2 hours.

6. The method for separating m-p-cresol based on β-cyclodextrin according to claim 1, characterized in that: In step 3, the filter residue is soaked and washed with ethanol for 20 to 40 minutes.

7. The method for separating m-p-cresol based on β-cyclodextrin according to claim 1, characterized in that: In step 3, the obtained washing liquid is distilled at 60-70° C. to recover ethanol.

8. The method for separating m-p-cresol based on β-cyclodextrin according to claim 1, characterized in that: In step 3, the extract is evaporated from ether at 30-40°C.

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