ZSM-5 molecular sieve catalyst as well as preparation method and application thereof

Abstract

The invention provides a ZSM-5 molecular sieve catalyst and a preparation method and application thereof, the preparation method comprises the following steps: pretreatment: soaking agricultural waste biomass in a hydrochloric acid solution, mixing with alkali, calcining to obtain a calcined product, and dissolving the calcined product in a recycled crystallization mother solution to obtain a sodium silicate solution; adjusting the pH value of the sodium silicate solution to a first alkaline range for primary hydrolysis; then adjusting the pH value of the material subjected to primary hydrolysis to be within a second alkaline range, and carrying out secondary hydrolysis; wherein the minimum value of the second alkaline range is greater than the maximum value of the first alkaline range, and both the first alkaline range and the second alkaline range are greater than 7; adding an aluminum source for hydrothermal crystallization to obtain a catalyst precursor, collecting to obtain a crystallization mother solution, and recycling the crystallization mother solution; and carrying out ion exchange on the catalyst precursor to obtain the ZSM-5 molecular sieve catalyst. The preparation method disclosed by the invention is low in cost, simple in process, green and environment-friendly, and realizes zero emission of the crystallization mother liquor.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of catalyst preparation, in particular to a ZSM-5 molecular sieve catalyst, a preparation method and application thereof. BACKGROUND

[0002] ZSM-5 molecular sieve has excellent performance in the hydration of cyclohexene to cyclohexanol due to its unique pore structure, excellent thermal stability and shape-selective catalytic performance, and can make the selectivity of cyclohexanol reach more than 99%, significantly improving the industrial benefit. However, the traditional preparation of ZSM-5 molecular sieve often uses organic template agents, which is high in cost and easy to cause environmental pollution due to direct discharge of mother liquor. The mother liquor contains unreacted raw materials and additives, and if the mother liquor can be effectively recycled, it can not only reduce the cost, but also reduce the environmental pressure, which is in line with the concept of green chemistry.

[0003] For example, patent CN1715186A provides a preparation method of small-grained ZSM-5 molecular sieve suitable for cyclohexene hydration reaction, which mixes silica-alumina gel particles with an aqueous solution of an organic template agent, and then performs hydrothermal crystallization in the presence or absence of ZSM-5 seeds, and then filters, dries and calcines to obtain the product. The patent has high preparation cost due to the use of organic template agent. Patent CN101041442A discloses a preparation method of small-grained strong acid type ZSM-5 molecular sieve, which uses a silicon source, an aluminum source and an inorganic acid as raw materials, and is prepared by ultrasonic pretreatment, hydrothermal crystallization, filtration, exchange, washing and drying. The synthesis process does not use organic template agent and does not require high temperature calcination, simplifying the traditional production process and reducing production cost. However, the crystallization mother liquor in the production process is not recycled, which still causes certain environmental pollution. Patent CN101468805A discloses the effective utilization of the mother liquor produced in the preparation of titanium silicate molecular sieve to synthesize ZSM-5 molecular sieve. The method comprises mixing a silicon source, an aluminum source, a base and water to obtain a reaction mixture, and hydrothermally crystallizing the reaction mixture. The silicon source, the base and part or all of the water are derived from the mother liquor produced in the preparation of titanium silicate molecular sieve. Although the reduction of mother liquor discharge reduces the environmental pollution, the patent still adds organic amine or quaternary ammonium salt as a template agent in the preparation process.

[0004] Using low-cost silicon source to prepare ZSM-5 molecular sieve can significantly reduce raw material cost, realize high value-added utilization of solid waste, and has many advantages such as resource recycling and environmental friendliness. However, there are still some problems in the existing preparation methods, such as the need to use template agent, long crystallization time, low crystallinity, low product purity, etc., which limit its large-scale application and performance improvement.

[0005] For example, CN107640775A utilizes a solvent-free method to mix a silicon source, an aluminum source, Na2CO3·10H2O, and a template agent, and then directly places them into a reaction kettle for constant temperature crystallization to obtain ZSM-5 molecular sieve. This method has a simple synthesis process and no secondary pollution, but the cost is high due to the use of an organic template agent, and the crystallization time is long. SUMMARY

[0006] In view of the deficiencies in the prior art, the present application discloses a ZSM-5 molecular sieve catalyst and a preparation method thereof. The preparation method of the catalyst uses agricultural waste as a raw material and does not use a template agent. The mother liquor is collected and reused, which is green and efficient. A ZSM-5 molecular sieve catalyst with high crystallinity is prepared.

[0007] To achieve the above technical purposes, in one aspect, the present application provides a preparation method of a ZSM-5 molecular sieve catalyst, which comprises the following steps:

[0008] (1) pretreatment, which comprises:

[0009] S1, soaking the agricultural waste biomass ash in a first inorganic acid solution, and washing the solid phase material to neutral after solid-liquid separation;

[0010] S2, mixing the solid phase material with an alkali and calcining;

[0011] S3, dissolving the calcination product obtained in step S2 in the recovered crystallization mother liquor to obtain a sodium silicate solution after removing the residue;

[0012] (2) adjusting the pH value of the sodium silicate solution to a first alkaline range for primary hydrolysis; then adjusting the pH value of the material after primary hydrolysis to a second alkaline range for secondary hydrolysis; wherein the minimum value of the second alkaline range is greater than the maximum value of the first alkaline range, and both the first alkaline range and the second alkaline range are greater than 7;

[0013] (3) adding an aluminum source to the material after secondary hydrolysis for hydrothermal crystallization;

[0014] (4) after the hydrothermal crystallization is completed, the material is subjected to solid-liquid separation to obtain a catalyst precursor and collect a crystallization mother liquor; the crystallization mother liquor is transported to step (1);

[0015] (5) the catalyst precursor is contacted with a second inorganic acid solution for ion exchange to obtain the ZSM-5 molecular sieve catalyst.

[0016] In the technical solution, the biomass ash from agricultural waste is used as raw material, impurities are removed by soaking in acid solution, and the calcined product containing soluble sodium silicate is obtained after mixing with alkali and calcination; the calcined product is dissolved in the recovered crystallization mother liquor, and after removing the residue, a clear sodium silicate solution is obtained, thereby realizing the recycling of the crystallization mother liquor. Further, in the technical solution, the sodium silicate solution is subjected to dynamic pH value control in stages, nucleation is carried out in a relatively acidic first alkaline range, and crystal growth is carried out in a relatively alkaline second alkaline range, thereby affecting the distribution of active species of silicon source by adjusting the pH value, and further optimizing the balance between nucleation and crystal growth, combined with hydrothermal crystallization and ion exchange, to prepare a high-crystallinity ZSM-5 molecular sieve catalyst.

[0017] The embodiments and comparative examples of the present application show the influence of dynamic pH value control of the sodium silicate solution on the relative crystallinity and catalytic performance of the ZSM-5 molecular sieve catalyst.

[0018] It should be noted that washing to neutral in the present application means washing the material to a state where the pH value does not change. The present application is not limited to the method of solid-liquid separation in step S1, and those skilled in the art can select an operation that can separate the solid material from the liquid material, such as filtration separation, centrifugal separation, gravity sedimentation separation, etc. The present application is not limited to the operation of removing residue in step S2, and those skilled in the art can select an operation that can separate the undissolved residue from the dissolved solution according to the need, such as filtration separation, centrifugal separation, gravity sedimentation separation, etc. Understandably, the preparation method of the ZSM-5 molecular sieve catalyst of the present application can realize the recycling of the recovered crystallization mother liquor in the process, and deionized water can be used to dissolve the calcined product in step S3 at the beginning of the process, and the recovered crystallization mother liquor can be used to dissolve the calcined product in the subsequent process.

[0019] Further, the pH value of the first alkaline range is 9-10; further, the temperature of the first hydrolysis is 30-60℃, and the time is 30-90min.

[0020] Further, the pH value of the second alkaline range is 10-12; further, the temperature of the second hydrolysis is 70-90℃, and the time is 90-120min.

[0021] The embodiments of the present application show the process of preparing ZSM-5 molecular sieve catalysts with different first alkaline ranges and second alkaline ranges.

[0022] Further, in step S2, alkali solution is added to the material after the first hydrolysis to adjust the pH value; the solutes of the alkali solution include one or both of sodium hydroxide and ammonia.

[0023] Further, in the step S1, the first inorganic acid includes at least one of hydrochloric acid, sulfuric acid and nitric acid. Preferably, when the first inorganic acid is hydrochloric acid, the concentration of the hydrochloric acid solution is 1-6 mol / L, preferably 3 mol / L; further, in the step S1, the solid-liquid ratio of the biomass ash and the first inorganic acid solution is 1:(3-12), preferably 1:5. Preferably, in the step S1, the soaking temperature is 60-90℃, preferably 70℃. Through the soaking of the acid solution, the metal oxides (such as K, Ca, Mg, etc.) and acid-soluble impurities in the biomass ash can be removed, and the purity of the subsequent silicon source is improved. By selecting a suitable concentration of the first inorganic acid solution, a suitable solid-liquid ratio of the biomass ash and the acid solution, and a soaking temperature, the efficiency of impurity removal can be improved.

[0024] Understandably, the present application is not limited to the amount of biomass ash and the first inorganic acid in the step S1 and the soaking time, and the biomass ash and the first inorganic acid solution can be contacted for sufficient reaction. Understandably, in the actual process, the biomass ash is immersed in the first inorganic acid solution for a sufficient time; in the optional example of the present application, the first inorganic acid solution can be recycled.

[0025] Further, in the step S2, the base is sodium hydroxide; further, in the step S2, the mass ratio of the solid-phase material (based on the mass of SiO2) to the base is 1:(1.5-4), preferably 1:2; further, in the step S2, the calcination temperature is 700-900℃, and the calcination time is 1-3h. Through the mixing and calcination with the base, the amorphous SiO2 in the solid-phase material can be converted into soluble sodium silicate (water glass), thereby efficiently extracting the silicon element.

[0026] Further, in the step S3, the solid-liquid ratio of the calcined product to the crystallization mother liquor is 1:(2-8), preferably 1:5, thereby recycling the recovered crystallization mother liquor, achieving zero discharge of the crystallization mother liquor, and obtaining a sodium silicate solution with a suitable concentration range of silicon element. In addition, the recovered crystallization mother liquor in the present application only contains inorganic base (for adjusting the pH of the system), silicon source and aluminum source, without other impurities, and all of them are needed for the preparation of catalysts, so the crystallization mother liquor can be directly reused in the entire catalyst preparation system without additional post-treatment. Moreover, the addition of the recovered crystallization mother liquor can effectively reduce the additional amount of silicon source and aluminum source in the synthesis process, thereby saving costs.

[0027] Further, the silicon source content in the sodium silicate solution is 5wt%-10wt% based on SiO2.

[0028] Further, the content of the silicon source in the crystallization mother liquor is 5wt%-10wt% based on SiO2. Still further, the content of the aluminum source (based on Al2O3) in the crystallization mother liquor is less than 1wt%, which can be ignored in the actual process.

[0029] Further, the biomass ash includes one or more of rice husk ash, bagasse ash, wheat straw ash, corn cob ash, and coconut shell ash. The embodiments of the present application show the process of preparing ZSM-5 molecular sieve catalysts using different biomass ashes as raw materials.

[0030] Further, in the step (1), when the biomass ash includes bagasse ash, wheat straw ash, corn cob ash, and coconut shell ash, the step (1) further includes first calcining the biomass ash at 450-600°C for 1-5h, so as to completely carbonize the organic matter and avoid interference in the subsequent acid / alkali treatment.

[0031] Further, the aluminum source includes at least one of aluminum sulfate, aluminum chloride, and aluminum nitrate.

[0032] Further, the silicon / aluminum ratio of the aluminum source (based on Al2O3) to the sodium silicate solution (based on SiO2) is 20-60, preferably 30-50. By optimizing the dosage ratio of the aluminum source to the sodium silicate solution, the silicon / aluminum ratio in the hydrothermal crystallization material can be controlled, and thus the hydrothermal stability and selectivity of the prepared ZSM-5 molecular sieve can be controlled.

[0033] Further, the hydrothermal crystallization operation includes pre-crystallization at 80-100°C for 4-8h, and then temperature rising to 150-190°C for further crystallization for 12-24h. By gradient hydrothermal crystallization, the crystal growth can be controlled, and the crystallinity of the molecular sieve is improved.

[0034] Further, the second inorganic acid for ion exchange includes at least one of hydrochloric acid, nitric acid, and sulfuric acid. Still further, the concentration of the second inorganic acid solution is 0.5-2mol / L. Still further, the temperature for ion exchange is 60-90°C, and the time is 2-8h. The ion exchange process is used to improve the acidity, thermal stability, pore structure, and surface properties of the ZSM-5 molecular sieve. By optimizing the type of the second inorganic acid, the concentration of the second inorganic acid, and the ion exchange control conditions, the efficiency of ion exchange can be improved, and the catalytic performance of the prepared ZSM-5 molecular sieve catalyst can be improved.

[0035] It should be noted that the amount of the second inorganic acid is not limited in the present application. The catalyst precursor can be contacted with the second inorganic acid solution to sufficiently perform ion exchange. Understandably, in the actual process, the catalyst precursor is immersed in the inorganic acid solution as a whole. In the optional examples of the present application, the second inorganic acid solution can be recycled.

[0036] In another aspect, the present application provides a ZSM-5 molecular sieve catalyst prepared by the above method.

[0037] In another aspect, the present application provides the use of the above ZSM-5 molecular sieve catalyst in the hydration of cyclohexene to cyclohexanol.

[0038] Compared with the prior art, the present application has the following beneficial effects:

[0039] The preparation method of the ZSM-5 molecular sieve catalyst of the present application uses agricultural waste biomass ash as raw material, and after acid soaking and alkali mixed calcination, a sodium silicate solution is obtained by dissolving in the recovered crystallization mother liquor. Through the recycling of the crystallization mother liquor, the problems of resource waste and environmental pollution caused by direct discharge are avoided. Through the stage-by-stage dynamic pH value control of the sodium silicate solution, the balance of nucleation and crystal growth can be optimized, and combined with subsequent hydrothermal crystallization and ion exchange, a ZSM-5 molecular sieve catalyst with high crystallinity can be obtained. The preparation method of the present application is low in cost, simple in process, green and environmentally friendly, and realizes zero discharge of the crystallization mother liquor.

[0040] The ZSM-5 molecular sieve catalyst prepared by the present application has high relative crystallinity, can efficiently and selectively catalyze the hydration reaction of cyclohexene, and has important application value. BRIEF DESCRIPTION OF DRAWINGS

[0041] The drawings accompanying the specification of this application are used to provide a further understanding of the present application, the illustrative embodiments of the present application and the description thereof serve to explain the present application, and do not constitute an improper limitation on the present application. In the drawings:

[0042] Figure 1 The XRD patterns of the ZSM-5 molecular sieves prepared in Examples 1-4 of the present application, Comparative Example 1, Comparative Example 2.1, and Comparative Example 3 are shown. DETAILED DESCRIPTION

[0043] In order to facilitate the understanding of the present application, the present application will be described more fully below, and preferred embodiments of the present application are given. It should be understood that these embodiments are only used for more detailed description, and should not be understood as limiting the present application in any form, i.e. not intended to limit the scope of protection of the present application.

[0044] Unless otherwise defined, the technical terms used in the following examples have the same meaning as generally understood by those skilled in the art to which the present application belongs. The test reagents used in the following examples, unless otherwise specified, are conventional biochemical reagents; the experimental methods, unless otherwise specified, are conventional methods.

[0045] In the examples and comparative examples of the present application, the preparation method of the calcined product is as follows:

[0046] S1, calcining the agricultural waste biomass ash at 450-600℃ for 1-5h; then soaking the biomass ash in 0.05-1.5mol / L hydrochloric acid solution, stirring at about 80℃ for 1-3h; then performing solid-liquid separation (filtration), and washing the separated solid phase to neutral. The solid-liquid ratio of the biomass ash to the hydrochloric acid solution is 1:(3-12), preferably 1:5.

[0047] S2, mixing the solid phase material obtained in step S1 with alkali and grinding uniformly; then calcining at 700-900℃ for 1-3h, and cooling to obtain the calcined product. The alkali is sodium hydroxide; the mass ratio of the solid phase material to the alkali is 1:(1.5-4), preferably 1:2.

[0048] Example 1

[0049] A preparation method of a ZSM-5 molecular sieve catalyst, comprising: adding 50g of a calcined product (obtained by pretreating rice husk ash, with a sodium silicate content of 95%) and 250g of recovered ZSM-5 crystallization mother liquor into a hydration reactor, stirring and dissolving, then adding 0.1mol / L HCl into the reactor at 45℃, adjusting the pH of the system to 9.5, and stirring for 30min. Then, adding 10wt% NaOH solution into the reactor, adjusting the pH of the system to 12, and increasing the temperature to 90℃ and stirring for 120min. The content of the silicon source in the recovered crystallization mother liquor is 5wt% based on SiO2; aluminum sulfate solution (prepared by dissolving 13g of aluminum sulfate octadecahydrate into 100g of deionized water) is added into the reactor for gradient crystallization: crystallization at 100℃ for 4h, and crystallization at 170℃ for 12h. After hydrothermal crystallization, centrifugal separation is performed to obtain a solid catalyst precursor, and the recovered crystallization mother liquor is collected, which can be directly recycled. The obtained catalyst precursor is washed with deionized water to neutral and dried. Ion exchange is performed on the catalyst precursor using 0.5mol / L HNO3 solution at 60℃ for 4h; then, ZSM-5 molecular sieve is prepared after washing and drying. The XRD pattern of the product is shown in Figure 1 , and the relative crystallinity of the product is shown in Table 1.

[0050] Example 2

[0051] A preparation method of a ZSM-5 molecular sieve catalyst, comprising: adding 50 g of a calcined product (obtained by pretreatment of coconut shell ash, with a sodium silicate content of 95%) and 100 g of recovered ZSM-5 crystallization mother liquor into a hydration reactor, adding 0.3 mol / L H2SO4 into the reactor at 30℃, adjusting the pH of the system to 9, and stirring for 90 min. Subsequently, 5 wt% NaOH solution is added into the reactor, the pH of the system is adjusted to 11, and the temperature is raised to 70℃ and stirred for 90 min. In the recovered crystallization mother liquor, the content of the silicon source in the crystallization mother liquor is 5 wt% based on SiO2;

[0052] An aluminum nitrate solution (prepared by dissolving 5 g of aluminum nitrate nonahydrate in 100 g of deionized water) is added into the reactor, and gradient crystallization is performed: crystallization at 80℃ for 5 h, and crystallization at 180℃ for 24 h. After hydrothermal crystallization, the solid catalyst precursor is separated by centrifugation, and the recovered crystallization mother liquor is collected, which can be directly recycled. The obtained catalyst precursor is washed with deionized water until neutral and dried. Ion exchange of the catalyst precursor is performed using 1 mol / L HCl solution at 70℃ for 6 h; and then ZSM-5 molecular sieve is prepared through washing and drying. The XRD pattern of the product is shown in Figure 1 , and the relative crystallinity of the product is shown in Table 1.

[0053] Example 3

[0054] A preparation method of a ZSM-5 molecular sieve catalyst, comprising: adding 50 g of a calcined product (obtained by pretreatment of coconut shell ash, with a sodium silicate content of 95%) and 100 g of recovered ZSM-5 crystallization mother liquor into a hydration reactor, adding 0.3 mol / L H2SO4 into the reactor at 30℃, adjusting the pH of the system to 9, and stirring for 90 min. Subsequently, 5 wt% NaOH solution is added into the reactor, the pH of the system is adjusted to 11, and the temperature is raised to 70℃ and stirred for 90 min. In the recovered crystallization mother liquor, the content of the silicon source in the crystallization mother liquor is 5 wt% based on SiO2; Figure 1 , and the relative crystallinity of the product is shown in Table 1.

[0055] Example 4

[0056] A method for preparing a ZSM-5 molecular sieve catalyst, comprising: adding 50 g of a calcined product (obtained by pretreating corn cob ash, with a sodium silicate content of 95%) and 200 g of a recovered ZSM-5 crystallization mother liquor into a hydration reactor, adding 0.2 mol / L of HNO3 into the reactor at -50°C, adjusting the pH of the system to 10.2, and stirring for 45 min. Subsequently, adding a 10 wt% ammonia water solution into the reactor, adjusting the pH of the system to 11.4, and stirring at 70°C for 100 min. In the recovered crystallization mother liquor, the content of a silicon source is 5 wt% based on SiO2. An aluminum chloride solution (prepared by dissolving 7 g of aluminum chloride hexahydrate into 100 g of deionized water) is added into the reactor, and gradient crystallization is performed: crystallization at 85°C for 6 h, and crystallization at 190°C for 14 h. After hydrothermal crystallization, the solid catalyst precursor is separated by centrifugation, and the recovered crystallization mother liquor is collected. The part of the crystallization mother liquor can be directly recycled. The obtained catalyst precursor is washed with deionized water until neutral and dried. Ion exchange is performed on the catalyst precursor by using 1 mol / L of an H2SO4 solution, heating at 90°C for 2 h, and then washing and drying to obtain the ZSM-5 molecular sieve. The XRD pattern of the product is shown in FIG. 1, and the relative crystallinity of the product is shown in Table 1. Figure 1

[0057] Comparative Example 1

[0058] A method for preparing a ZSM-5 molecular sieve catalyst, comprising: adding 58 g of a calcined product (obtained by pretreating rice husk ash, with a sodium silicate content of 95%) and 250 g of deionized water into a hydration reactor, adding 0.1 mol / L of HCl into the reactor at 45°C, adjusting the pH of the system to 9.5, and stirring for 30 min. A 10 wt% NaOH solution is added into the reactor, the pH of the system is adjusted to 12, and the temperature is increased to 90°C for stirring for 120 min.

[0059] An aluminum sulfate solution (prepared by dissolving 13 g of aluminum sulfate octadecahydrate into 100 g of deionized water) is added into the reactor, and gradient crystallization is performed: crystallization at 100°C for 4 h, and crystallization at 170°C for 12 h. After hydrothermal crystallization, the solid product is separated by centrifugation, and the recovered crystallization mother liquor is collected. The obtained solid product is washed with deionized water until neutral and dried. Ion exchange is performed on the solid product by using 0.5 mol / L of an HNO3 solution, heating at 60°C for 4 h, and then washing and drying to obtain the ZSM-5 molecular sieve. The XRD pattern of the product is shown in FIG. 2, and the relative crystallinity of the product is shown in Table 1. Figure 1

[0060] Comparative Example 2

[0061] Comparative Example 2.1 ​​

[0062] A method for preparing a ZSM-5 molecular sieve catalyst, the method comprising: adding 50 g of a calcined product (obtained by pretreating rice husk ash, with a sodium silicate content of 95%) and 250 g of a recovered ZSM-5 crystallization mother liquor into a hydration reactor, and stirring at 45 °C for 120 min. Subsequently, an aluminum sulfate solution (obtained by dissolving 13 g of aluminum sulfate octadecahydrate into 100 g of deionized water) is added to the system, and gradient crystallization is performed: crystallization at 100 °C for 4 h, and crystallization at 170 °C for 12 h. After the crystallization is completed, the solid product is centrifugally separated, and the recovered crystallization mother liquor is collected. The obtained solid is washed with deionized water until neutral, and dried. Ion exchange is performed using a 0.5 mol / L HNO3 solution, heated at 60 °C for 4 h, and the ZSM-5 molecular sieve is finally obtained after washing, drying. The XRD pattern of the product is shown in FIG. 1, and the relative crystallinity of the product is shown in Table 1. Figure 1

[0063] Comparative Example 2.2

[0064] A method for preparing a ZSM-5 molecular sieve catalyst, the method is the same as in Example 1, except that after the calcined product is dissolved in the recovered ZSM-5 crystallization mother liquor, the pH in the reactor is first adjusted to 9.5, and stirring is performed at 45 °C for 30 min, and then an aluminum sulfate solution is added to the reactor for hydrothermal crystallization. The ZSM-5 molecular sieve is obtained in this comparative example, and the relative crystallinity of the product is shown in Table 1.

[0065] Comparative Example 2.3

[0066] A method for preparing a ZSM-5 molecular sieve catalyst, the method is the same as in Example 1, except that after the calcined product is dissolved in the recovered ZSM-5 crystallization mother liquor, the pH in the reactor is first adjusted to 12, and stirring is performed at 90 °C for 120 min, and then an aluminum sulfate solution is added to the reactor for hydrothermal crystallization. The ZSM-5 molecular sieve is obtained in this comparative example, and the relative crystallinity of the product is shown in Table 1.

[0067] Comparative Example 2.4

[0068] A method for preparing a ZSM-5 molecular sieve catalyst, the method is the same as in Example 1, except that after the calcined product is dissolved in the recovered ZSM-5 crystallization mother liquor, the pH in the reactor is first adjusted to 12, and stirring is performed at 45 °C for 30 min; then 0.1 mol / L HCl is added dropwise to adjust the pH in the reactor to 9.5, and the temperature is raised to 90 °C for stirring for 120 min.

[0069] Comparative Example 3

[0070] ​A preparation method of a ZSM-5 molecular sieve catalyst, the method comprising: adding 50 g of a calcination product (obtained by pretreating rice husk ash, with a sodium silicate content of 95%) and 250 g of a recovered ZSM-5 crystallization mother liquor into a hydration reactor, continuously adding 0.1 mol / L of HCl into the reactor at room temperature, adjusting the pH of the system to 9.5, and stirring for 30 min; adding a 10 wt% NaOH solution into the reactor, adjusting the pH of the system to 12, and stirring at 90°C for 120 min.

[0071] An aluminum sulfate solution (prepared by dissolving 13 g of aluminum sulfate octadecahydrate into 100 g of deionized water) was added into the reactor, and crystallization was performed at 170°C for 16 h. After the crystallization was completed, the solid product was separated by centrifugation, and the crystallization mother liquor was collected for recovery. The obtained solid was washed with deionized water until neutral and dried. Ion exchange was performed using a 0.5 mol / L HNO3 solution, heating at 60°C for 4 h, and the ZSM-5 molecular sieve was finally obtained after washing and drying. The XRD pattern of the product is shown in FIG. 1, and the relative crystallinity of the product is shown in Table 1. Figure 1

[0072] Test Example: Evaluation experiment of catalytic hydration of cyclohexene

[0073] In this test example, the ZSM-5 molecular sieves prepared in Examples 1-4 and Comparative Examples 1-3 were used to catalyze the reaction of cyclohexene hydration to produce cyclohexanol, in order to characterize the effect of the technical solutions of the present application. Specifically:

[0074] 18 g of each catalyst, 36 g of cyclohexene, and 54 g of deionized water were weighed into a 250 ml high-pressure reactor in sequence, sealed and replaced with nitrogen three times, and finally filled with 0.38 MPa of nitrogen; the reaction temperature was set to 120°C, and the rotation speed was 600 r / min, and the reaction was carried out at 120°C for 1 h. After the reaction was completed, the high-pressure reactor was rapidly cooled. The upper oil phase was analyzed by gas chromatography, and the results are shown in Table 1 below.

[0075] Table 1

[0076]

[0077]

[0078] In combination with Table 1 and Figure 1 ​The average relative crystallinity of the ZSM-5 molecular sieve prepared in the application reaches 94.61%, which proves that the ZSM-5 molecular sieve has a complete crystal structure and reflects that the ZSM-5 molecular sieve prepared in the application has better catalytic activity, selectivity and water / thermal stability, and the test results in Table 1 also confirm this: the average cyclohexene conversion rate of the ZSM-5 molecular sieve prepared in the application reaches 11.42%, and the average cyclohexanol selectivity reaches 99.48% (test examples 1-4), which shows better catalytic performance advantages compared with test examples 6-11.

[0079] The relative crystallinity of the ZSM-5 molecular sieve prepared in Comparative Example 1 is similar to that of the ZSM-5 molecular sieve prepared in the application, and its catalytic performance (test example 5) is similar to that of the ZSM-5 molecular sieve catalyst (test examples 1-4) prepared in the application; but the crystallization mother liquor in Comparative Example 1 is not recycled, which consumes more raw materials and requires additional subsequent mother liquor crystallization process. Therefore, compared with Comparative Example 1, the preparation method of the ZSM-5 molecular sieve catalyst in the application can save process cost and realize green and low-energy-consumption preparation of ZSM-5 molecular sieve.

[0080] It can be proved by combining test example 1 with test examples 7-10 that in the preparation method of the ZSM-5 molecular sieve in the application, the pH value of the system is dynamically adjusted in stages in step (2), and the relative pH values of the first alkaline range and the second alkaline range are controlled, which optimizes the nucleation and crystal growth balance process, directly affects the distribution of active species of the silicon source, and then realizes the synthesis of high-crystallinity molecular sieve. As can be seen from Table 1, the average relative crystallinity (94.61%) of the ZSM-5 molecular sieve prepared in the application is significantly higher than that (85.3%) of the ZSM-5 molecular sieve prepared in Comparative Example 2. In addition, by comparing the test results of the test examples, it is further proved that in the technical scheme of the application, by dynamically controlling the pH value of the nucleation and crystal growth stage during the preparation of the catalyst, a ZSM-5 molecular sieve catalyst with high catalytic activity and better selectivity can be obtained.

[0081] It should be noted that the above content is a further detailed description of the application in combination with specific embodiments, and the specific implementation of the application cannot be limited to these descriptions. For ordinary skilled persons in the technical field to which the application belongs, some simple improvements can be made without departing from the concept of the application, and all of them should be regarded as falling within the scope of protection of the application.

Claims

1. A method for preparing a ZSM-5 molecular sieve catalyst, characterized in that: The following steps are involved: (1) Preprocessing, which includes: S1, soaking agricultural waste biomass ash in a first inorganic acid solution, and washing the solid phase material to neutrality after solid-liquid separation; S2, mixing the solid phase material with a sodium-containing alkali and calcining; S3, dissolving the calcined product obtained in step S2, using a dissolving solvent comprising the crystallization mother liquor recovered in step (4), and removing the residue to obtain a sodium silicate solution; (2) adjusting the pH value of the sodium silicate solution to a first alkaline range for primary hydrolysis; then adjusting the pH value of the material after the primary hydrolysis to a second alkaline range for secondary hydrolysis; wherein the minimum value of the second alkaline range is greater than the maximum value of the first alkaline range; (3) adding an aluminum source to the secondary hydrolyzed material for hydrothermal crystallization; (4) After the hydrothermal crystallization is completed, the material is subjected to solid-liquid separation to obtain a catalyst precursor and collect the crystallization mother liquor; the crystallization mother liquor is transported to S3 of step (1); (5) The catalyst precursor is contacted with a second inorganic acid solution to perform ion exchange to obtain the ZSM-5 molecular sieve catalyst.

2. The method for preparing the ZSM-5 molecular sieve catalyst according to claim 1, wherein The pH value of the first alkaline range is 9 to 10; Preferably, the temperature of the primary hydrolysis is 30-60°C and the time is 30-90 minutes; and / or, the pH value of the second alkaline range is 10 to 12; Preferably, the temperature of the secondary hydrolysis is 70-90°C and the time is 90-120 min; And / or, in step S2, after the primary hydrolysis is completed, alkali solution is added to the reacted material to adjust the pH value; the solute of the alkali solution includes one or both of sodium hydroxide and ammonia water.

3. The method for preparing the ZSM-5 molecular sieve catalyst according to claim 1, wherein In step S1, the first inorganic acid includes at least one of hydrochloric acid, sulfuric acid, and nitric acid; Preferably, when the first inorganic acid is hydrochloric acid, the concentration of the hydrochloric acid solution is 1 to 6 mol / L, preferably 3 to 5 mol / L; preferably, in step S1, the solid-liquid ratio of the biomass ash to the first inorganic acid solution is 1:(3 to 12), preferably 1:(5 to 7); Preferably, in step S1, the soaking temperature is 60-90°C, preferably 70-80°C.

4. The method for preparing the ZSM-5 molecular sieve catalyst according to claim 1, wherein The sodium-containing alkali in step S2 is sodium hydroxide; Preferably, the mass ratio of the solid phase material (in terms of SiO2 mass) to the sodium-containing alkali in step S2 is 1: (1.5-4), preferably 1:(2-3); Preferably, in step S2, the calcination temperature is 700-900° C., and the calcination time is 1-3 hours.

5. The method for preparing the ZSM-5 molecular sieve catalyst according to claim 1, wherein In step S3, the solid-liquid ratio of the calcined product to the crystallization mother liquor is 1:(2-8), preferably 1:(4-6); And / or, the content of silicon source in the crystallization mother solution is 5wt% to 10wt% calculated as SiO2.

6. The method for preparing the ZSM-5 molecular sieve catalyst according to claim 1, wherein The biomass ash includes one or more of rice husk ash, bagasse ash, wheat straw ash, corn cob ash, and coconut shell ash; Preferably, in step (1), when the biomass ash comprises bagasse ash, wheat straw ash, corn cob ash, or coconut shell ash, the step further comprises first calcining the biomass ash at 450-600° C. for 1-5 hours.

7. The method for preparing the ZSM-5 molecular sieve catalyst according to claim 1, wherein The aluminum source includes at least one of aluminum sulfate, aluminum chloride and aluminum nitrate; Preferably, the silicon-aluminum ratio of the aluminum source (calculated as Al2O3) to the sodium silicate solution (calculated as SiO2) is 20-60, preferably 30-50.

8. The method for preparing the ZSM-5 molecular sieve catalyst according to claim 1, wherein The hydrothermal crystallization operation includes: pre-crystallization at a temperature of 80-100° C. for 4-8 hours, then heating to 150-190° C. and continuing crystallization for 12-24 hours; and / or, the second inorganic acid comprises at least one of hydrochloric acid, nitric acid, and sulfuric acid; Preferably, the concentration of the second inorganic acid solution is 0.5 to 2 mol / L; Preferably, the ion exchange temperature is 60-90° C. and the time is 2-8 hours.

9. A ZSM-5 molecular sieve catalyst, characterized in that: The catalyst is prepared by the preparation method of the ZSM-5 molecular sieve catalyst according to any one of claims 1 to 9.

10. Use of the ZSM-5 molecular sieve catalyst according to claim 9 in the hydration of cyclohexene to produce cyclohexanol.

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