A method for selectively adsorbing m-cresol and p-cresol

Abstract

The present invention discloses a method for selectively adsorbing p-cresol and m-cresol. Using a mixture containing p-cresol and m-cresol as the adsorption liquid, an adsorbent is used to selectively adsorb the adsorption liquid. The adsorbent is a flaky ZSM-5 zeolite molecular sieve, and the mass of p-cresol adsorbed by the adsorbent accounts for more than 97% of the total mass of m-cresol and p-cresol adsorbed by it. The flaky ZSM-5 zeolite molecular sieve can also be modified with organic bases, inorganic bases, inorganic salts, or a silica layer can be coated on its surface for modification. By using this method, p-cresol and m-cresol can be efficiently adsorbed and separated in a single time, and the adsorption selectivity of p-cresol can reach more than 97%. The best selective adsorption effect can achieve only the adsorption of p-cresol without the adsorption of m-cresol.

Description

Technical Field

[0001] The present invention relates to a method for selectively adsorbing m-cresol and p-cresol. Background Art

[0002] Coal tar and direct coal liquefied oil are important intermediate products of coal conversion. However, the presence of phenolic compounds in the composition not only affects the storage stability of oil products, but also reacts with hydrogen during further upgrading to generate water, increasing the hydrogen consumption and forming an oil-water mixture that is difficult to separate. Therefore, phenolic compounds need to be separated before hydrofining.

[0003] Phenolic monomers (such as phenol, m-cresol, and p-cresol, etc.) can be used as chemical raw materials or intermediates in organic chemical synthesis, and can be used to synthesize products such as pesticides, dyes, fragrances, medicines, antioxidants, etc. Therefore, high-purity m-cresol and p-cresol both have good market prospects and great development potential.

[0004] Currently, the existing methods for separating p-cresol and m-cresol are mainly divided into two categories: physical methods and chemical methods. Chemical methods include complexation separation method, chelating-like method, alkylation method, etc.; physical methods include extraction method, crystallization separation method, molecular sieve adsorption separation method, and membrane permeation separation method. Among them, the complexation separation method, extraction method, and crystallization method, etc., are hindered from industrial utilization due to many problems such as complex processes, high pollution, and high energy consumption; the membrane permeation separation method is only applicable to gas state, and the main problem is low separation efficiency, making it difficult to achieve large-scale application; the alkylation method is the most mature and has been studied the most, but usually cannot achieve continuous operation. The molecular sieve adsorption separation method has the best application prospect due to its simple process, high separation efficiency, and the adsorbent can usually be regenerated.

[0005] Chinese Patent CN104815612A discloses a preparation method of a molecular sieve adsorbent for separating m-cresol and p-cresol, including steps of molecular sieve forming, chemical liquid phase deposition treatment, high-temperature water vapor treatment, and calcination modification. Although this adsorbent can highly selectively adsorb p-cresol, the processes of preparing and modifying the molecular sieve are very complex and energy-consuming.

[0006] Chinese Patent CN107879900A discloses a method for separating and purifying a mixture of cresol isomers. This method uses ion-exchanged X molecular sieve, ion-exchanged Y molecular sieve, ZSM-5 molecular sieve, etc. as the active components of the adsorbent. Although high-purity p-cresol or m-cresol can be finally obtained, this method relies on a sequential simulated moving bed for separation, with complex separation steps, expensive separation equipment, and the separation effect mainly depending on the use of the sequential simulated moving bed and repeated separation. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a method for selectively adsorbing p-cresol and m-cresol in view of the disadvantages and deficiencies of the prior art. This separation method can selectively adsorb p-cresol with high efficiency in a single time, and the selectivity can reach more than 97%. The best selective adsorption effect can achieve only adsorbing p-cresol without adsorbing m-cresol, which can effectively reduce the equipment investment in the p-cresol and m-cresol adsorption separation process.

[0008] To solve the above technical problems, a technical solution adopted by the present invention is as follows:

[0009] A method for selectively adsorbing p-cresol and m-cresol, using a mixture containing p-cresol and m-cresol as the adsorption liquid, and selectively adsorbing the adsorption liquid with an adsorbent. The adsorbent is a flaky ZSM-5 zeolite molecular sieve, and the mass of p-cresol adsorbed by the adsorbent accounts for more than 97% of the total mass of p-cresol and m-cresol adsorbed by it.

[0010] In some embodiments, the mass of p-cresol adsorbed by the adsorbent accounts for 100% of the total mass of p-cresol and m-cresol adsorbed by it, that is, the adsorbent only adsorbs p-cresol without adsorbing m-cresol.

[0011] In some embodiments, the lengths of the flaky ZSM-5 zeolite molecular sieve in the a-axis and b-axis directions are La and Lb respectively, and the ratio of Lb to La is 0.3 or less. The a-axis direction is the direction corresponding to the sinusoidal pore channels of the flaky ZSM-5 zeolite molecular sieve, and the b-axis direction is the direction corresponding to the straight pore channels of the flaky ZSM-5 zeolite molecular sieve. Preferably, the ratio of Lb to La is 0.25 or less.

[0012] In some embodiments, the silica-alumina ratio of the flaky ZSM-5 zeolite molecular sieve is 10 or more. Preferably, the silica-alumina ratio of the flaky ZSM-5 zeolite molecular sieve is 20 - 280; more preferably, the silica-alumina ratio of the flaky ZSM-5 zeolite molecular sieve is 25 - 100.

[0013] In some embodiments, the flaky ZSM-5 zeolite molecular sieve is prepared by a preparation method including the following steps: mixing tetraalkyl orthosilicate, trialkyl aluminate, tetraalkyl ammonium hydroxide, water and urea uniformly in a reaction kettle to obtain a first reaction mixture, and then reacting the first reaction mixture at 160 - 220 °C. After the reaction is completed, separation, purification and calcination are carried out. The alkyl group is independently an alkyl group of C1 - C6.

[0014] Preferably, the tetraalkyl orthosilicate is tetraethyl orthosilicate.

[0015] Preferably, the trialkyl aluminate is triisopropyl aluminate (aluminum isopropoxide).

[0016] Preferably, the tetraalkyl ammonium hydroxide is tetrapropyl ammonium hydroxide.

[0017] In some embodiments, the molar ratio of the tetraalkyl orthosilicate, alkyl titanate, tetraalkylammonium hydroxide, water and urea is 1:0.01 - 0.001:0.2 - 0.5:20 - 40:0.5 - 1.4.

[0018] In some embodiments, the reaction time is 3 - 10 days.

[0019] In some embodiments, the separation and purification include filtration, washing and drying.

[0020] The inventors have found through research that, compared with ordinary ZSM-5 zeolite molecular sieves or flaky zeolite molecular sieves of other types, when using flaky ZSM-5 zeolite molecular sieves as adsorbents, the pore size of the flaky ZSM-5 zeolite molecular sieve is close to the molecular kinetic diameter of p-cresol. At the same time, the sinusoidal pore channels along the a-axis are conducive to the diffusion of p-cresol. The length of the a-axis of the flaky structure is much higher than the length of the b-axis, which can well adsorb p-cresol and reduce the adsorption of m-cresol. Furthermore, it can significantly improve the adsorption selectivity of the adsorbent for p-cresol, effectively separate p-cresol and m-cresol in the liquid phase, and high-purity separation products can be obtained after post-treatment.

[0021] In addition to flaky ZSM-5 zeolite molecular sieves, various modified flaky ZSM-5 zeolite molecular sieves can also be selected as adsorbents. As adsorbents, these modified flaky ZSM-5 zeolite molecular sieves can also effectively separate p-cresol.

[0022] In some embodiments, the flaky ZSM-5 zeolite molecular sieve is a flaky ZSM-5 zeolite molecular sieve modified with an organic base, a flaky ZSM-5 zeolite molecular sieve modified with an inorganic base, a flaky ZSM-5 zeolite molecular sieve modified with an inorganic salt, or a flaky ZSM-5 zeolite molecular sieve with an amorphous silica layer coated on its surface; the organic base is selected from one or more combinations of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide and tetrabutylammonium hydroxide; the inorganic base is selected from sodium hydroxide and / or potassium hydroxide; the inorganic salt is selected from one or more combinations of potassium nitrate, sodium nitrate, calcium nitrate, barium nitrate, potassium chloride, sodium chloride, calcium chloride and barium chloride.

[0023] In some embodiments, the flaky ZSM-5 zeolite molecular sieve modified with an organic base is prepared by a preparation method including the following steps: uniformly mixing the flaky ZSM-5 zeolite molecular sieve, the organic base and water to obtain a second reaction mixture, and then reacting the second reaction mixture at 140 - 200 °C. After the reaction, separation, purification and calcination are carried out.

[0024] Further, the molar ratio of the flaky ZSM-5 zeolite molecular sieve to the organic base is 2-10, preferably 3-8, and particularly preferably 4-6.

[0025] Further, the molar ratio of the water to the flaky ZSM-5 zeolite molecular sieve is 3-20, preferably 4-15, and particularly preferably 6-10.

[0026] Further, the reaction time is 0.5-2 days.

[0027] Further, the separation and purification include filtration, washing, and drying.

[0028] The aforementioned organic base-modified flaky ZSM-5 zeolite molecular sieve is a hollow-structured flaky ZSM-5 zeolite molecular sieve.

[0029] In some embodiments, the inorganic base-modified flaky ZSM-5 zeolite molecular sieve is prepared by a preparation method including the following steps: uniformly mixing the flaky ZSM-5 zeolite molecular sieve, the inorganic base, and water to obtain a third reaction mixture, and then reacting the third reaction mixture at 50-120 °C. After the reaction, separation, purification, and calcination are carried out.

[0030] Further, the molar ratio of the flaky ZSM-5 zeolite molecular sieve to the inorganic base is 3-15, preferably 5-10, and particularly preferably 6-8.

[0031] Further, the molar ratio of the water to the flaky ZSM-5 zeolite molecular sieve is 1-8, preferably 2-5, and particularly preferably 2-4.

[0032] Further, the reaction time is 1-4 h.

[0033] Further, the separation and purification include filtration, washing, and drying.

[0034] The aforementioned inorganic base-modified flaky ZSM-5 zeolite molecular sieve is a hierarchical pore flaky ZSM-5 zeolite molecular sieve.

[0035] In some embodiments, the inorganic salt-modified flaky ZSM-5 zeolite molecular sieve is prepared by a preparation method including the following steps: uniformly mixing the flaky ZSM-5 zeolite molecular sieve and the inorganic salt aqueous solution to obtain a fourth reaction mixture, and then reacting the fourth reaction mixture at 50-100 °C. After the reaction, separation, purification, and calcination are carried out.

[0036] Further, the mass ratio of the inorganic salt aqueous solution to the flaky ZSM-5 zeolite molecular sieve is 5-20, preferably 6-15, and particularly preferably 8-12.

[0037] Further, the molar concentration of the inorganic salt aqueous solution is 0.1 - 3 mol / L, preferably 0.5 - 2 mol / L, and particularly preferably 0.8 - 1.5 mol / L.

[0038] Further, the reaction time is 2 - 6 h.

[0039] Further, the separation and purification include filtration, washing, and drying.

[0040] The aforementioned inorganic salt-modified flaky ZSM-5 zeolite molecular sieve is a flaky ZSM-5 zeolite molecular sieve after cation exchange.

[0041] In some embodiments, the flaky ZSM-5 zeolite molecular sieve coated with an amorphous silica layer is prepared by a preparation method including the following steps: uniformly mixing the flaky ZSM-5 zeolite molecular sieve, tetraalkyl orthosilicate, and an organic solvent to obtain a fifth reaction mixture, and then reacting the fifth reaction mixture at 80 - 140 °C, and performing separation, purification, and calcination after the reaction ends.

[0042] Further, the tetraalkyl orthosilicate is tetraethyl orthosilicate.

[0043] Further, the organic solvent is cyclohexane.

[0044] Further, the mass ratio of the flaky ZSM-5 zeolite molecular sieve to the tetraalkyl orthosilicate is 5 - 15, preferably 8 - 13, and particularly preferably 9 - 11.

[0045] Further, the mass ratio of the organic solvent to the flaky ZSM-5 zeolite molecular sieve is 1 - 10, preferably 2 - 8, and particularly preferably 4 - 6.

[0046] Further, the reaction time is 1 - 12 h.

[0047] Further, the separation and purification include filtration, washing, and drying.

[0048] In some embodiments, the adsorption separation method includes the following steps: 1) dissolving p-cresol and m-cresol in a solvent to obtain an adsorption solution; 2) adding the adsorbent to the adsorption solution for selective adsorption; 3) separating the adsorbent and the adsorption solution, and analyzing the contents of p-cresol and m-cresol in the separated adsorption solution.

[0049] In some embodiments, the solvent is selected from one or a combination of more of 1,3,5-trimethylbenzene, toluene, xylene, ethylbenzene, or diethylbenzene.

[0050] In some embodiments, the mass concentration of p-cresol in the adsorption solution is 1% - 10%.

[0051] In some embodiments, the mass concentration of m-cresol in the adsorption liquid is 1%-10%.

[0052] In some embodiments, the mass-volume ratio of the adsorbent to the adsorption liquid is 1 g: 1-20 mL.

[0053] In some embodiments, the adsorption time is 10 min-120 min.

[0054] The present invention also provides the aforementioned adsorbent.

[0055] Compared with the prior art, the present invention has the following advantages:

[0056] By using the method for selectively adsorbing p-cresol and m-cresol of the present invention, p-cresol and m-cresol can be highly selectively separated. The flaky ZSM-5 zeolite molecular sieve used in the present invention can achieve an adsorption selectivity for p-cresol of more than 97%. The best selective adsorption effect can achieve only the adsorption of p-cresol without the adsorption of m-cresol. Description of the Drawings

[0057] Figure 1 SEM image of the flaky ZSM-5 zeolite molecular sieve prepared in Example 1;

[0058] Figure 2 SEM image of the organically base-modified flaky ZSM-5 zeolite molecular sieve prepared in Example 2;

[0059] Figure 3 SEM image of the inorganically base-modified flaky ZSM-5 zeolite molecular sieve prepared in Example 3;

[0060] Figure 4 SEM image of the flaky ZSM-5 zeolite molecular sieve with a silica layer coated on the surface prepared in Example 5. Detailed Embodiments

[0061] The present invention will be further described below in conjunction with the embodiments. However, the present invention is not limited to the following embodiments. The implementation conditions adopted in the embodiments can be further adjusted according to different requirements of specific use, and the implementation conditions not specified are conventional conditions in the industry. The technical features involved in various embodiments of the present invention can be combined with each other as long as they do not conflict with each other.

[0062] All kinds of reagent raw materials used in the following embodiments are purchased from aladdin reagent company, and the mass percentages of the solutes in the aqueous solutions of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide are all 25%.

[0063] Example 1

[0064] This embodiment provides a method for selectively adsorbing m - and p - cresol, and the specific steps are as follows:

[0065] 1) Synthesize flaky ZSM - 5 zeolite molecular sieve: Mix 5.5 g of tetrapropylammonium hydroxide aqueous solution (mass concentration of 25%) with 4.1 g of water evenly, then add 2.8 g of tetraethyl orthosilicate. After stirring evenly to obtain a mixed solution, add 0.056 g of aluminum isopropoxide to the mixed solution, continue stirring for 8 h, then add 0.65 g of urea, and continue stirring for 2 h. After that, transfer it to a reaction kettle and react at 200 °C for 48 h. After the reaction is completed, obtain a white product through filtration, washing, and drying at 80 °C for 12 h. Calcinate the obtained product at 550 °C for 4 h to obtain flaky ZSM - 5 zeolite molecular sieve. Its SEM image is as Figure 1 shown. It can be seen that it has a flaky structure, and the ratio of Lb to La of the flaky ZSM - 5 zeolite molecular sieve is about 0.25. The silicon - aluminum ratio measured by inductively coupled plasma atomic emission spectrometry (ICP) is 40.

[0066] 2) Separation: Use 1 g of the flaky ZSM - 5 zeolite molecular sieve prepared in step 1) as an adsorbent and place it in 5 ml of a 1,3,5 - trimethylbenzene solution of p - cresol and m - cresol. In this solution, the mass concentrations of p - cresol and m - cresol are both 3%. Use the static liquid - phase adsorption method to measure the static liquid - phase adsorption and separation performance of this adsorbent for m - cresol and p - cresol. Through the analysis of the chromatographic results of the adsorption liquid before and after adsorption, the amount of p - cresol adsorbed by the adsorbent accounts for 100% of its total adsorption amount, and it does not adsorb m - cresol, that is, this adsorbent can achieve the adsorption and separation of m - cresol and p - cresol.

[0067] Example 2

[0068] This embodiment provides a method for selectively adsorbing m - and p - cresol, and the specific steps are as follows:

[0069] 1) Synthesize flaky ZSM - 5 zeolite molecular sieve: Mix 4.4 g of tetrapropylammonium hydroxide aqueous solution (mass concentration of 25%) with 4.1 g of water evenly, then add 2.8 g of tetraethyl orthosilicate. After stirring evenly to obtain a mixed solution, add 0.028 g of aluminum isopropoxide to the mixed solution, continue stirring for 8 h, then add 0.81 g of urea, and continue stirring for 2 h. After that, transfer it to a reaction kettle and react at 200 °C for 48 h. After the reaction is completed, obtain a white product through filtration, washing, and drying at 80 °C for 12 h. Calcinate the obtained product at 550 °C for 4 h to obtain flaky ZSM - 5 zeolite molecular sieve.

[0070] 2) Organic base modification: 1 g of the flaky ZSM-5 zeolite molecular sieve prepared in step 1), 0.2 g of tetrapropylammonium hydroxide aqueous solution (mass concentration of 25%) and 8 g of water were mixed evenly. The evenly mixed solution was transferred to a reaction kettle and crystallized in an oven at 160 °C for 1 day. After crystallization, it was filtered, washed, dried at 80 °C for 12 h, and then calcined at 550 °C for 4 h to obtain a flaky ZSM-5 zeolite molecular sieve modified with an organic base and having a hollow structure. Its SEM image is as shown in Figure 2 shown. It can be seen that it is also a flaky structure. The ratio of Lb to La of the flaky ZSM-5 zeolite molecular sieve is about 0.17. The silicon-aluminum ratio of the molecular sieve measured by ICP is 80.

[0071] 3) Separation: 1 g of the flaky ZSM-5 zeolite molecular sieve modified with an organic base prepared in step 2) was used as an adsorbent and placed in 5 ml of a diethylbenzene solution of p-cresol and m-cresol. In this solution, the mass concentrations of p-cresol and m-cresol were both 5%. The static liquid-phase adsorption separation performance of this adsorbent for m-cresol and p-cresol was measured by the static liquid-phase adsorption method. Through the analysis of the chromatographic results of the adsorption liquid before and after adsorption, the amount of p-cresol adsorbed by the adsorbent accounted for 100% of its total adsorption amount, and it did not adsorb m-cresol, that is, this adsorbent could achieve the adsorption separation of m-cresol and p-cresol.

[0072] Example 3

[0073] This example provides a method for selectively adsorbing m- and p-cresol, and the specific steps are as follows:

[0074] 1) Synthesis of flaky ZSM-5 zeolite molecular sieve: 3.3 g of tetrapropylammonium hydroxide aqueous solution (mass concentration of 25%) and 4.1 g of water were mixed evenly, then 2.8 g of tetraethyl orthosilicate was added, and after stirring evenly, a mixed solution was obtained. 0.056 g of aluminum isopropoxide was added to the mixed solution, and after continuing to stir for 8 h, 0.65 g of urea was added, and then stirring was continued for 2 h. Then it was transferred to a reaction kettle and reacted at 200 °C for 48 h. After the reaction, a white product was obtained through filtration, washing, and drying at 80 °C for 12 h. The obtained product was calcined at 550 °C for 4 h to obtain a flaky ZSM-5 zeolite molecular sieve.

[0075] 2) Inorganic base modification: 1 g of the flaky ZSM-5 zeolite molecular sieve prepared in step 1), 0.24 g of sodium hydroxide and 5 g of water were mixed evenly. The evenly mixed solution was transferred to a reaction kettle and reacted at 65 °C for 2 h. After the reaction, it was filtered, washed, dried at 80 °C for 12 h, and then calcined at 550 °C for 4 h to obtain a multi-porous, inorganic-base-modified flaky ZSM-5 molecular sieve. Its SEM image is as shown in Figure 3 shown. It can be seen that it is also a flaky structure. The ratio of Lb to La of the flaky ZSM-5 zeolite molecular sieve is about 0.25. The silicon-aluminum ratio of the molecular sieve measured by ICP is 40.

[0076] 3) Separation: Take 1 g of the inorganic base-modified flaky ZSM-5 zeolite molecular sieve prepared in step 2) as an adsorbent and place it in 5 ml of a 1,3,5-trimethylbenzene solution of p-cresol and m-cresol. In this solution, the mass concentrations of p-cresol and m-cresol are both 3%. Use the static liquid-phase adsorption method to measure the static liquid-phase adsorption and separation performance of this adsorbent for m-cresol and p-cresol. By analyzing the chromatographic results of the adsorption liquid before and after adsorption, the amount of p-cresol adsorbed by the adsorbent accounts for 100% of its total adsorption amount, and it does not adsorb m-cresol, that is, this adsorbent can achieve the adsorption and separation of m-cresol and p-cresol.

[0077] Example 4

[0078] This example provides a method for selectively adsorbing m- and p-cresol, and the specific steps are as follows:

[0079] 1) Synthesis of flaky ZSM-5 zeolite molecular sieve: Mix 5.5 g of tetrapropylammonium hydroxide aqueous solution (mass concentration of 25%) with 4.1 g of water evenly, then add 2.8 g of tetraethyl orthosilicate, and stir evenly to obtain a mixed solution. Add 0.056 g of aluminum isopropoxide to the mixed solution, continue to stir for 8 h, then add 0.65 g of urea, and continue to stir for 2 h. Then transfer it to a reaction kettle and react at 200 °C for 48 h. After the reaction is completed, obtain a white product through filtration, washing, and drying at 80 °C for 12 h. Calcinate the obtained product at 550 °C for 4 h to obtain the flaky ZSM-5 zeolite molecular sieve.

[0080] 2) Inorganic salt modification: Add 1 g of the flaky ZSM-5 zeolite molecular sieve prepared in step 1) to 10 g of a 1 mol / L potassium chloride aqueous solution and mix evenly. Then carry out an ion exchange reaction at 80 °C in an oil bath for 4 h. After centrifugal separation, continue with ion exchange, and repeat the ion exchange three times. After the ion exchange is completed, obtain the potassium-type inorganic salt-modified flaky ZSM-5 molecular sieve through filtration, washing, drying at 80 °C for 12 h, and then calcining at 550 °C for 4 h. The ratio of Lb to La of this inorganic salt-modified flaky ZSM-5 zeolite molecular sieve is about 0.25. The silicon-aluminum ratio of the molecular sieve measured by ICP is 40.

[0081] 3) Separation: Take 1 g of the potassium-type flaky ZSM-5 molecular sieve prepared in step 2) as an adsorbent and place it in 5 ml of a 1,3,5-trimethylbenzene solution of p-cresol and m-cresol. In this solution, the mass concentrations of p-cresol and m-cresol are both 1%. Use the static liquid-phase adsorption method to measure the static liquid-phase adsorption and separation performance of this adsorbent for m-cresol and p-cresol. By analyzing the chromatographic results of the adsorption liquid before and after adsorption, the amount of p-cresol adsorbed by the adsorbent accounts for 100% of its total adsorption amount, and it does not adsorb m-cresol, that is, this adsorbent can achieve the adsorption and separation of m-cresol and p-cresol.

[0082] Example 5

[0083] This example provides a method for selectively adsorbing m - and p - cresol, and the specific steps are as follows:

[0084] 1) Synthesize flaky ZSM - 5 zeolite molecular sieve: Mix 5.5 g of tetrapropylammonium hydroxide aqueous solution (mass concentration of 25%) with 4.1 g of water evenly, then add 2.8 g of tetraethyl orthosilicate, and stir evenly to obtain a mixed solution. Add 0.084 g of aluminum isopropoxide to the mixed solution, continue stirring for 8 h, then add 0.65 g of urea, and continue stirring for 2 h. Then transfer it to a reaction kettle and react at 200 °C for 48 h. After the reaction is completed, obtain a white product through filtration, washing, and drying at 80 °C for 12 h. Calcinate the obtained product at 550 °C for 4 h to obtain flaky ZSM - 5 zeolite molecular sieve.

[0085] 2) Coating with a silica layer: Mix 1 g of the flaky ZSM - 5 zeolite molecular sieve prepared in step 1) with 10 g of tetraethyl orthosilicate and 6 g of cyclohexane evenly, transfer the evenly - mixed solution to a reaction kettle, and crystallize at 100 °C for 10 h. After the crystallization is completed, obtain a flaky ZSM - 5 zeolite molecular sieve with an amorphous silica layer on its surface through filtration, washing, drying at 80 °C for 12 h, and then calcining at 550 °C for 4 h. Its SEM image is as Figure 4 shown. It can be seen that it has a flaky structure, and the ratio of Lb to La of the flaky adsorbent is about 0.1. The silicon - aluminum ratio of the molecular sieve measured by ICP is 45.

[0086] 3) Separation: Use 1 g of the flaky ZSM - 5 zeolite molecular sieve with an amorphous silica layer on its surface prepared in step 2) as an adsorbent, and place it in a 5 - ml 1,3,5 - trimethylbenzene solution of p - cresol and m - cresol. In this solution, the mass concentrations of p - cresol and m - cresol are both 3%. Use the static liquid - phase adsorption method to measure the static liquid - phase adsorption and separation performance of this adsorbent for m - cresol and p - cresol. Through the chromatographic result analysis of the adsorption liquid before and after adsorption, the amount of p - cresol adsorbed by the adsorbent accounts for 97% of its total adsorption amount, and the amount of m - cresol adsorbed accounts for 3% of its total adsorption amount.

[0087] Comparative Example 1

[0088] This comparative example provides a method for selectively adsorbing m - and p - cresol, and the specific steps are as follows:

[0089] 1 g of directly purchased ZSM-5 zeolite molecular sieve (spherical structure, silica-alumina ratio of 50) was used as the adsorbent and placed in 5 ml of a 1,3,5-trimethylbenzene solution of p-cresol and m-cresol. In this solution, the mass concentrations of p-cresol and m-cresol were both 3%. The static liquid-phase adsorption method was used to measure the static liquid-phase adsorption separation performance of this adsorbent for m-cresol and p-cresol. Through the analysis of the chromatographic results of the adsorption liquid before and after adsorption, the amount of p-cresol adsorbed by the adsorbent accounted for 60% of its total adsorption amount, and the amount of m-cresol adsorbed accounted for 40% of its total adsorption amount. That is, a single adsorption separation could not separate m-cresol and p-cresol, and multiple adsorption separations were required to obtain high-purity m-cresol and p-cresol.

[0090] Comparative Example 2

[0091] This comparative example provides a method for selectively adsorbing m- and p-cresols, and the specific steps are as follows:

[0092] 1 g of directly purchased flake-structured MWW molecular sieve (silica-alumina ratio of 50) was used as the adsorbent and placed in 5 ml of a 1,3,5-trimethylbenzene solution of p-cresol and m-cresol. In this solution, the mass concentrations of p-cresol and m-cresol were both 3%. The static liquid-phase adsorption method was used to measure the static liquid-phase adsorption separation performance of this adsorbent for m-cresol and p-cresol. Through the analysis of the chromatographic results of the adsorption liquid before and after adsorption, the amount of p-cresol adsorbed by the adsorbent accounted for 45% of its total adsorption amount, and the amount of m-cresol adsorbed accounted for 55% of its total adsorption amount. That is, this adsorbent did not show obvious adsorption selectivity for p-cresol.

[0093] Comparative Example 3

[0094] This comparative example provides a method for selectively adsorbing m- and p-cresols, and the specific steps are as follows:

[0095] 1 g of directly purchased adsorbent X for separating xylene in industry (Ca-K ion-exchanged X zeolite molecular sieve) was used as the adsorbent and placed in 5 ml of a 1,3,5-trimethylbenzene solution of p-cresol and m-cresol. In this solution, the mass concentrations of p-cresol and m-cresol were both 3%. The static liquid-phase adsorption method was used to measure the static liquid-phase adsorption separation performance of this adsorbent for m-cresol and p-cresol. Through the analysis of the chromatographic results of the adsorption liquid before and after adsorption, the amount of p-cresol adsorbed by the adsorbent accounted for 55% of its total adsorption amount, and the amount of m-cresol adsorbed accounted for 45% of its total adsorption amount. That is, this adsorbent did not show obvious adsorption selectivity for p-cresol.

[0096] It can be seen that in the present invention, a flake-structured ZSM-5 zeolite molecular sieve is used as the adsorbent for adsorbing and separating p-cresol and m-cresol, which can selectively adsorb p-cresol with high selectivity and achieve the effective separation of the two.

[0097] The endpoints and any values in the ranges disclosed herein are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

Claims

1. A method for selectively adsorbing m - cresol and p - cresol, using a mixture containing p - cresol and m - cresol as the adsorption liquid, and selectively adsorbing the adsorption liquid with an adsorbent, characterized in that: The adsorbent is a flaky ZSM-5 zeolite molecular sieve, and the mass of p-cresol adsorbed by the adsorbent accounts for more than 97% of the total mass of m,p-cresol adsorbed by it; the lengths of the flaky ZSM-5 zeolite molecular sieve in the a-axis and b-axis directions are La and Lb respectively, and the ratio of Lb to La is 0.3 or less. The a-axis direction is the direction corresponding to the sinusoidal pore channels of the flaky ZSM-5 zeolite molecular sieve, and the b-axis direction is the direction corresponding to the straight pore channels of the flaky ZSM-5 zeolite molecular sieve.

2. The method for selectively adsorbing m - cresol and p - cresol according to claim 1, characterized in that: The silicon-aluminum ratio of the flaky ZSM-5 zeolite molecular sieve is 10 or more.

3. The method for selectively adsorbing m - cresol and p - cresol according to claim 1, characterized in that: The flaky ZSM-5 zeolite molecular sieve is prepared by a preparation method including the following steps: mixing tetraalkyl orthosilicate, trialkyl aluminate, tetraalkyl ammonium hydroxide, water and urea uniformly in a reaction kettle to obtain a first reaction mixture, and then reacting the first reaction mixture at 160-220 °C. After the reaction is completed, separation, purification and calcination are carried out. The alkyl group is independently a C1-C6 alkyl group.

4. The method for selectively adsorbing m - cresol and p - cresol according to claim 3, characterized in that: The tetraalkyl orthosilicate is tetraethyl orthosilicate; and / or the trialkyl aluminate is triisopropyl aluminate.

5. The method for selectively adsorbing m - cresol and p - cresol according to claim 3, characterized in that: The tetraalkyl ammonium hydroxide is tetrapropyl ammonium hydroxide.

6. The method for selectively adsorbing m - cresol and p - cresol according to claim 3, characterized in that: The molar ratio of the tetraalkyl orthosilicate, alkyl titanate, tetraalkyl ammonium hydroxide, water and urea is 1:0.01-0.001:0.2-0.5:20-40:0.5-1.

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7. The method for selectively adsorbing m - cresol and p - cresol according to claim 3, characterized in that: The reaction time is 3-10 days; and / or the separation and purification includes filtration, washing and drying.

8. The method for selectively adsorbing m - cresol and p - cresol according to claim 1, characterized in that: The flaky ZSM-5 zeolite molecular sieve is an organically base-modified flaky ZSM-5 zeolite molecular sieve, an inorganically base-modified flaky ZSM-5 zeolite molecular sieve, an inorganic salt-modified flaky ZSM-5 zeolite molecular sieve or a flaky ZSM-5 zeolite molecular sieve with an amorphous silica layer coated on its surface; the organic base is selected from one or a combination of more than one of tetramethyl ammonium hydroxide, tetraethyl ammonium hydroxide, tetrapropyl ammonium hydroxide and tetrabutyl ammonium hydroxide; the inorganic base is selected from sodium hydroxide and / or potassium hydroxide; the inorganic salt is selected from one or a combination of more than one of potassium nitrate, sodium nitrate, calcium nitrate, barium nitrate, potassium chloride, sodium chloride, calcium chloride and barium chloride.

9. The method for selectively adsorbing m - cresol and p - cresol according to claim 8, characterized in that: The organically base-modified flaky ZSM-5 zeolite molecular sieve is prepared by a preparation method including the following steps: mixing the flaky ZSM-5 zeolite molecular sieve, the organic base and water uniformly to obtain a second reaction mixture, and then reacting the second reaction mixture at 140-200 °C. After the reaction is completed, separation, purification and calcination are carried out.

10. The method for selectively adsorbing m - cresol and p - cresol according to claim 8, characterized in that: The inorganically base-modified flaky ZSM-5 zeolite molecular sieve is prepared by a preparation method including the following steps: mixing the flaky ZSM-5 zeolite molecular sieve, the inorganic base and water uniformly to obtain a third reaction mixture, and then reacting the third reaction mixture at 50-120 °C. After the reaction is completed, separation, purification and calcination are carried out.

11. The method for selectively adsorbing m - cresol and p - cresol according to claim 8, characterized in that: The flaky ZSM-5 zeolite molecular sieve modified by inorganic salts is prepared by a preparation method including the following steps: uniformly mixing the flaky ZSM-5 zeolite molecular sieve and an inorganic salt aqueous solution to obtain a fourth reaction mixture, and then reacting the fourth reaction mixture at 50-100 °C, followed by separation, purification and calcination after the reaction ends.

12. The method for selectively adsorbing m - cresol and p - cresol according to claim 8, characterized in that: The flaky ZSM-5 zeolite molecular sieve with an amorphous silica layer coated on the surface is prepared by a preparation method including the following steps: uniformly mixing the flaky ZSM-5 zeolite molecular sieve, tetraalkyl orthosilicate and an organic solvent to obtain a fifth reaction mixture, and then reacting the fifth reaction mixture at 80-140 °C, followed by separation, purification and calcination after the reaction ends.

13. The method for selectively adsorbing m - cresol and p - cresol according to claim 1, characterized in that: The method includes the following steps: 1) dissolving p-cresol and m-cresol in a solvent to obtain an adsorption solution; 2) adding the adsorbent to the adsorption solution for selective adsorption; 3) separating the adsorbent and the adsorption solution, and analyzing the contents of p-cresol and m-cresol in the separated adsorption solution.

14. The method for selectively adsorbing m - cresol and p - cresol according to claim 13, characterized in that: The solvent is selected from one or a combination of more than one of 1,3,5-trimethylbenzene, toluene, xylene, ethylbenzene or diethylbenzene; and / or, the mass concentration of p-cresol in the adsorption solution is 1-10%; and / or, the mass concentration of m-cresol in the adsorption solution is 1-10%; and / or, the mass-volume ratio of the adsorbent to the adsorption solution is 1 g:1-20 mL; and / or, the adsorption time is 10 min-120 min.

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