Preparation method and application of modified ZSM-5 molecular sieve

Abstract

The invention belongs to the technical field of chemical product synthesis, and discloses a preparation method and application of a modified ZSM-5 molecular sieve. A metal heteroatom component is introduced into a ZSM-5 molecular sieve framework, so that the pore structure and active sites of the molecular sieve can be effectively improved, the carbon deposition resistance of the catalyst is improved, the activity and stability of the catalyst are enhanced, and the service life of the catalyst is greatly prolonged.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical product synthesis, and specifically relates to a preparation method and application of a modified ZSM-5 molecular sieve. Background Art

[0002] Both m-cresol and p-cresol are important fine chemical intermediates with high product added value. m-cresol is a raw material for pesticides, medicines, antioxidants, and spices, while p-cresol is mainly used in the synthesis of antioxidants, fluorescent brighteners, medicines, dyes, pesticides and other fields. At present, the main ways to obtain m-cresol in industry are natural separation and chemical synthesis. The natural separation method is to separate and purify m-cresol from coal tar. The main methods of chemical synthesis include p-chlorotoluene hydrolysis, isopropyl toluene oxidation, o-cresol isomerization, phenol alkylation, etc. Among them, the m-cresol product produced by o-cresol isomerization has the advantages of high meta position (m-cresol content greater than 75%) and good product quality. Compared with other synthesis methods, the production of m-cresol by o-cresol isomerization is a new green and environmentally friendly process.

[0003] There are many reports on the isomerization of o-cresol. U.S. Patent No. 4503269 discloses the use of ZSM-5 molecular sieve for the isomerization reaction of o-cresol to synthesize m-cresol. The process uses a high-pressure reactor and a fixed-bed reactor. However, the m-cresol selectivity of the process is less than 90%, and the catalyst deactivates quickly with a life of only 40 hours.

[0004] Patent CN103341363A discloses a fluidized catalytic method for isomerizing o-cresol to produce m- and p-cresol. The catalyst involved includes a series of molecular sieve materials. However, this type of catalyst has a short life and is not suitable for fixed bed reactors. Only fluidized bed processes can be used. The equipment is complex, the operation is difficult, and the production cost is high.

[0005] Patent CN201510334647.2 discloses an MCM-41 / ZSM-5 composite molecular sieve for the isomerization reaction of o-cresol. The catalyst has a lifespan of up to 1,000 hours in a fixed bed reactor, with an o-cresol conversion rate of about 45% and a m-cresol selectivity of about 95%.

[0006] Patent CN202210918350.0 discloses a molecular sieve catalyst modified by metal phosphate and heteropolyacid. When the catalyst is used for the isomerization of o-cresol, the o-cresol conversion rate can reach about 50% and the selectivity can reach more than 95%, but the life of the catalyst is only 400 hours.

[0007] In summary, the currently reported catalysts for the isomerization of o-cresol to m-cresol still have the problem of short lifespan. If they are to be suitable for fixed bed devices, it is necessary to find catalysts with better activity and stability. Summary of the invention

[0008] In order to overcome the shortcomings of the prior art, the present invention provides a preparation method and application of a modified ZSM-5 molecular sieve. By introducing metal heteroatom components into the ZSM-5 molecular sieve framework, the pore structure and active sites of the molecular sieve can be effectively improved, the anti-carbon deposition ability of the catalyst is improved, the activity and stability of the catalyst are enhanced, and the life of the catalyst is greatly extended.

[0009] The above object of the present invention is achieved by the following technical solution: A method for preparing a modified ZSM-5 molecular sieve, the steps are as follows: The silicon source aqueous solution, the aluminum source aqueous solution and the template agent aqueous solution are mixed uniformly to obtain an initial gel; The initial gel prepared in step 1 is mixed with a germanium source aqueous solution and an iron source aqueous solution, the pH value of the solution is adjusted, and the mixture is aged to obtain a mixed gel; The mixed gel prepared in step 2 is placed in a crystallization kettle for hydrothermal crystallization to obtain a Fe / Ge isomorphously substituted ZSM-5 molecular sieve; The molecular sieve prepared in step 3 is filtered, washed, dried and calcined to remove the template agent to obtain molecular sieve raw powder; The molecular sieve raw powder obtained in step 4 is subjected to ion exchange, filtration, washing, drying and calcination to obtain a hydrogen-type Fe-Ge-ZSM-5 molecular sieve.

[0010] Furthermore, the silicon source described in step 1 is one or more of silica sol, water glass, tetraethyl orthosilicate and white carbon black, the aluminum source is one or more of aluminum sulfate, aluminum nitrate, aluminum hydroxide, sodium aluminate and aluminum isopropoxide, and the template is an organic amine template.

[0011] In a further preferred embodiment of the present invention, the organic amine template is one or more of tetrapropylammonium hydroxide, tetrapropylammonium bromide, di-n-propylamine, and cyclohexylamine.

[0012] Furthermore, the germanium source described in step 2 is one or more of germanium chloride, germanium nitrate, germanium hydroxide and sodium germanate, and the iron source is one or more of ferric chloride, ferric nitrate, ferric sulfate, ferric hydroxide and sodium ferrite.

[0013] Furthermore, in step 2, the pH value is adjusted to 9.0-12 using 1 mol / L sodium hydroxide solution or 1 mol / L nitric acid solution, the aging temperature is 20-80° C., and the aging time is 12-72 hours.

[0014] Furthermore, the molar ratio of silicon, aluminum, iron and germanium in steps 1 and 2 is 20-200:2:0.2-2:0.2-2:10-500:200-4000.

[0015] In the further preferred embodiment of the present invention, the silicon source is SiO2, the aluminum source is Al2O3, the iron source is Fe2O3, the germanium source is GeO2, and the molar ratio of each substance is SiO2:Al2O3:Fe2O3:GeO2:template:water=20~200:1:0.1~1:0.2~2:10~500:200~4000.

[0016] Furthermore, in step 3, the crystallization temperature is 120-200° C., and the crystallization time is 12-72 hours.

[0017] Furthermore, in steps 4 and 5, the drying temperature is 100-140° C., the drying time is 8-24 hours, the roasting temperature is 400-600° C., and the roasting time is 4-24 hours.

[0018] Furthermore, the ion exchange step in step 5 is specifically as follows: the molecular sieve and the ion exchange liquid are placed in a stirred flask and mixed thoroughly, placed in a water bath, exchanged at a constant temperature, then filtered, the molecular sieve is washed with deionized water, and the filtered molecular sieve solid is dried and calcined to obtain the molecular sieve after ion exchange.

[0019] In a further preferred embodiment of the present invention, the ion exchange liquid is an ammonium nitrate solution with a concentration of 0.5 to 1 mol / L, a mass ratio of the molecular sieve to the ammonium nitrate aqueous solution of 1:10 to 100, an exchange temperature of 50 to 90° C., and an exchange time of 2 to 12 hours.

[0020] Another object of the present invention is to protect the use of the Fe-Ge-ZSM-5 molecular sieve prepared by the above method in the isomerization reaction of o-cresol.

[0021] Furthermore, the Fe-Ge-ZSM-5 molecular sieve catalyzes the isomerization reaction of o-cresol in the following steps: The prepared catalyst is loaded into a fixed bed reactor. In the presence of a carrier gas, the temperature and pressure are raised to a preset temperature and pressure. Then, o-cresol is injected into the reactor at a certain space velocity. The reaction is continued under the set conditions, and the product is analyzed by gas chromatography.

[0022] The process conditions are: reaction temperature is 280℃-400℃, reaction pressure is 0.1~2MPa, feed space velocity of raw material o-cresol is 0.2-3h-1, and molar ratio of circulating carrier gas to o-cresol is 0.5~5.

[0023] The circulating carrier gas is one or both of nitrogen and hydrogen.

[0024] Compared with the prior art, the present invention has the following beneficial effects: by introducing metal heteroatom components into the ZSM-5 molecular sieve framework, the pore structure and active sites of the molecular sieve can be effectively improved, the anti-coking ability of the catalyst is improved, the activity and stability of the catalyst are enhanced, and the life of the catalyst is greatly prolonged. In addition, since the metal atoms introduced into the molecular sieve have moderate hydrogenation performance, when performing the hydroisomerization of o-cresol, phenols will not be excessively hydrogenated, but the carbon deposition of the catalyst can be further suppressed, thereby further prolonging the life of the catalyst. DETAILED DESCRIPTION

[0025] The present invention is described in detail below by specific examples, but the protection scope of the present invention is not limited. Unless otherwise specified, the experimental methods used in the present invention are all conventional methods, and the experimental equipment, materials, reagents, etc. used can be obtained from commercial channels.

[0026] Example 1

[0027] Preparation of Fe-Ge-ZSM-5 molecular sieve (1) Weigh 100 g of silica sol (SiO2 ≥ 30 wt%) and mix well with 100 g of deionized water, then add 203 g of 25% tetrapropylammonium hydroxide (TPAOH) solution under stirring, and continue stirring until the solution is clear to obtain solution A; (2) Dissolve 5.7 g of aluminum sulfate in 100 g of deionized water and stir evenly to obtain solution B; (3) Slowly drip solution B into solution A while stirring to obtain initial gel C; (4) Weigh 1.4 g of Na2GeO3 and dissolve it in 20 g of deionized water. Stir evenly to obtain solution D. Then slowly drop solution D into the initial gel C while stirring to obtain gel E. (5) Weigh 3.4 g of Fe(NO3)3·9H2O and dissolve it in 5 g of deionized water. Stir evenly to obtain solution F. Then slowly drip solution F into gel E under stirring to obtain a mixed gel. Then adjust the pH of the gel solution to 10 with 1 mol / L sodium hydroxide and age it at 30°C for 24 h. The molar ratio of Si:Al:Fe:Ge:template in the obtained gel is 30:1:0.5:0.5:15. (6) placing the mixed gel in a crystallization kettle and performing hydrothermal crystallization at 180° C. under autogenous pressure for 24 h to obtain a Fe / Ge isomorphously substituted ZSM-5 molecular sieve; (7) The obtained molecular sieve was filtered, washed, dried at 120°C for 24 h and calcined at 550°C for 12 h to remove the template, thereby obtaining the molecular sieve raw powder; (8) The molecular sieve raw powder was ion exchanged three times with 1 mol / L NH4NO3 solution at 70°C, and then filtered, washed, dried at 120°C for 24 h and calcined at 550°C for 8 h to obtain the hydrogen-type Fe-Ge-ZSM-5 molecular sieve, which was recorded as CAT-1.

[0028] Example 2

[0029] The method for preparing molecular sieve is the same as that in Example 1, except that the silicon source is changed to tetraethyl orthosilicate, the molar ratio of Si:Al:Fe:Ge:template in the gel is controlled to be 30:1:0.8:0.3:15, and other conditions remain unchanged. The obtained molecular sieve is recorded as CAT-2.

[0030] Example 3

[0031] The method for preparing molecular sieve is the same as that in Example 1, except that the aluminum source is changed to aluminum isopropoxide, the template is changed to di-n-propylamine, the molar ratio of Si:Al:Fe:Ge:template in the gel is controlled to be 50:1:0.3:0.7:30, and other conditions remain unchanged. The obtained molecular sieve is recorded as CAT-3.

[0032] Example 4

[0033] The method for preparing the molecular sieve is the same as that in Example 1, except that the crystallization temperature is changed to 140° C. and other conditions remain unchanged. The obtained molecular sieve is recorded as CAT-4.

[0034] Example 5

[0035] The method for preparing molecular sieve is the same as that in Example 1, except that the calcination temperature when removing the template is changed to 450°C, the calcination time is 24 hours, the molar ratio of Si:Al:Fe:Ge:template in the gel is controlled to be 80:1:0.5:0.5:50, and other conditions remain unchanged. The obtained molecular sieve is recorded as CAT-5.

[0036] Example 6

[0037] The method for preparing the molecular sieve is the same as that in Example 1, except that the iron source is changed to iron hydroxide, the germanium source is changed to germanium hydroxide, and other conditions remain unchanged. The obtained molecular sieve is recorded as CAT-6.

[0038] Example 7

[0039] The method for preparing molecular sieve is the same as that in Example 1, except that: during ion exchange, 0.5 mol / L NH4NO3 solution is used, the exchange temperature is 85°C, and other conditions remain unchanged. The obtained molecular sieve is recorded as CAT-7.

[0040] Example 8

[0041] The method for preparing molecular sieve is the same as that in Example 1, except that the aging time is changed to 48 h, and other conditions remain unchanged. The obtained molecular sieve is recorded as CAT-8.

[0042] Example 9

[0043] 10 g each of the modified ZSM-5 molecular sieves described in Examples 1 to 8 and the commercially available HZSM-5 molecular sieve with a silicon-aluminum molar ratio of 25 were weighed, tableted, crushed, and sieved to 20-40 mesh to obtain a molded catalyst.

[0044] Example 10

[0045] The initial catalytic performance of the formed catalyst prepared in Example 9 in the isomerization reaction of o-cresol was evaluated in the following manner. 5 g of the prepared catalyst was loaded into a fixed bed reactor, and the temperature was raised to 280°C under the condition of nitrogen as carrier gas. The o-cresol feed rate was 5 g / h (space velocity 1.0 h -1 ), nitrogen flow rate 30mL / min, reaction pressure 0.2MPa, continuous reaction at a constant temperature of 280℃ for 200h, the product was analyzed by gas chromatography, and the results are shown in Table 1.

[0046] Table 1 Comparison of catalytic performance of different catalysts in the presence of nitrogen

[0047] Embodiment 11

[0048] The initial catalytic performance of the formed catalyst prepared in Example 9 in the isomerization reaction of o-cresol was evaluated in the following manner. 5 g of the prepared catalyst was loaded into a fixed bed reactor, and the temperature was raised to 280°C under the condition of hydrogen as carrier gas. The o-cresol feed rate was 5 g / h (space velocity 1.0 h -1 ), hydrogen flow rate 30mL / min, reaction pressure 0.2MPa, continuous reaction at a constant temperature of 280℃ for 200h, the product was analyzed by gas chromatography, and the results are shown in Table 2.

[0049] Table 2 Comparison of catalytic performance of different catalysts in the presence of hydrogen

[0050] Example 12

[0051] The stability of the catalyst CAT-1 was investigated using the evaluation method of Example 10. During the evaluation process, the activity of the catalyst was maintained by continuously increasing the reaction temperature.

[0052] Table 3 Evaluation of catalyst catalytic stability in the presence of nitrogen

[0053] Embodiment 13

[0054] The stability of catalyst CAT-1 was investigated using the evaluation method of Example 11. During the evaluation process, the activity of the catalyst was maintained by continuously increasing the reaction temperature.

[0055] Table 4 Evaluation of catalyst stability in the presence of hydrogen

[0056] The above-described embodiments are only preferred embodiments of the present invention, but not all feasible embodiments of the present invention. For those skilled in the art, any obvious changes made thereto without departing from the principles and spirit of the present invention should be considered to be included in the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a modified ZSM-5 molecular sieve, characterized in that: Here are the steps: S1. The silicon source aqueous solution, the aluminum source aqueous solution, and the template aqueous solution are mixed to obtain an initial gel; S2. The initial gel prepared in step S1 is mixed with an aqueous solution of a germanium source and an aqueous solution of an iron source, the pH value of the solution is adjusted to 9.0 to 12, and aged to obtain a mixed gel; S3. The mixed gel obtained in step S2 is placed in a crystallization reactor for hydrothermal crystallization to obtain a Fe / Ge isomorphously substituted ZSM-5 molecular sieve; S4. The molecular sieve obtained in step S3 is filtered, washed, dried and calcined to remove the template to obtain a molecular sieve raw powder; S5. The molecular sieve powder obtained in step S4 is subjected to ion exchange, filtered, washed, dried and calcined to obtain a hydrogen Fe-Ge-ZSM-5 molecular sieve; The molar ratio of silicon, aluminum, iron and germanium in steps 1 and 2 is 20-200:2:0.2-2:0.2-2:10-500:200-4000; The ion exchange step in step 5 is specifically as follows: the molecular sieve and the ion exchange liquid are placed in a stirred flask and mixed thoroughly, placed in a water bath, exchanged at a constant temperature, then filtered, the molecular sieve is washed with deionized water, and the filtered molecular sieve solid is dried and calcined to obtain the molecular sieve after ion exchange.

2. The method for preparing the modified ZSM-5 molecular sieve according to claim 1, characterized in that: The silicon source described in step 1 is one or more of silica sol, water glass, tetraethyl orthosilicate and white carbon black, the aluminum source is one or more of aluminum sulfate, aluminum nitrate, aluminum hydroxide, sodium aluminate and aluminum isopropoxide, and the template is an organic amine template, which is one or more of tetrapropylammonium hydroxide, tetrapropylammonium bromide, di-n-propylamine and cyclohexylamine.

3. The method for preparing the modified ZSM-5 molecular sieve according to claim 1, characterized in that: The germanium source described in step 2 is one or more of germanium chloride, germanium nitrate, germanium hydroxide and sodium germanate, and the iron source is one or more of ferric chloride, ferric nitrate, ferric sulfate, ferric hydroxide and sodium ferrite.

4. The method for preparing the modified ZSM-5 molecular sieve according to claim 1, characterized in that: In the step 2, the pH value is adjusted to 9.0-12 using 1 mol / L sodium hydroxide solution or 1 mol / L nitric acid solution, the aging temperature is 20-80° C., and the aging time is 12-72 hours.

5. The method for preparing the modified ZSM-5 molecular sieve according to claim 5, characterized in that: The silicon source is SiO2, the aluminum source is Al2O3, the iron source is Fe2O3, and the germanium source is GeO2. The molar ratio of each substance is SiO2:Al2O3:Fe2O3:GeO2:template:water=20~200:1:0.1~1:0.2~2:10~500:200~4000.

6. The method for preparing the modified ZSM-5 molecular sieve according to claim 1, characterized in that: In step 3, the crystallization temperature is 120-200° C., and the crystallization time is 12-72 hours.

7. The method for preparing the modified ZSM-5 molecular sieve according to claim 1, characterized in that: In the steps 4 and 5, the drying temperature is 100-140° C., the drying time is 8-24 hours, the roasting temperature is 400-600° C., and the roasting time is 4-24 hours.

8. The method for preparing the modified ZSM-5 molecular sieve according to claim 1, characterized in that: The ion exchange liquid is an ammonium nitrate solution with a concentration of 0.5-1 mol / L, a mass ratio of the molecular sieve to the ammonium nitrate aqueous solution of 1:10-100, an exchange temperature of 50-90° C., and an exchange time of 2-12 hours.

9. Application of Fe-Ge-ZSM-5 molecular sieve in the isomerization reaction of o-cresol.

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