CN116062771A - Modified ZSM-23 molecular sieve and preparation method and application thereof - Google Patents

Abstract

The invention provides a modified ZSM-23 molecular sieve, and a preparation method and application thereof. The external surface SiO of the modified ZSM-23 molecular sieve of the invention ₂ /Al ₂ O ₃ The molar ratio is 500-1500, bulk phase SiO ₂ /Al ₂ O ₃ The molar ratio is 60-200, the total infrared acid amount of pyridine is 0.02-0.35 mmol/g, and the total infrared acid amount of di-tert-butylpyridine is 0.001-0.015 mmol/g. The catalyst prepared by the modified ZSM-23 molecular sieve is used for normal paraffin isomerization reaction, and can obviously improve the selectivity of isoparaffin while ensuring higher normal paraffin conversion rate.

Description

A kind of modified ZSM-23 molecular sieve and its preparation method and application

technical field

The invention relates to the field of molecular sieves and preparation thereof, in particular to a modified ZSM-23 molecular sieve and a preparation method thereof.

Background technique

In 1978, Plank et al. of Mobile Company used pyrrolidine as a template agent to synthesize a medium-porous high-silica zeolite molecular sieve by hydrothermal synthesis, named ZSM-23, and its topological structure was MTT configuration. ZSM-23 molecular sieve has a one-dimensional ten-membered ring straight pore structure with a pore size of 0.45×0.52nm. The unique pore structure and acidic properties make it exhibit high catalytic activity and selective.

The isomerization reaction of n-alkanes catalyzed by molecular sieves follows the pore mechanism and the lock-and-key mechanism, but because there are some acidic sites on the outer surface of molecular sieves that do not have shape-selective isomerization catalytic performance, it is easy to cause side reactions such as cracking, so the external surface of molecular sieves Surface modification to reduce the acidity of the outer surface while retaining the acidity in the pores is of great significance for improving the selectivity of the isomerization reaction.

CN102794193A discloses a method for modifying the outer surface of a microporous molecular sieve. The method is to mix silica sol and microporous molecular sieve, and physically adsorb the molecular sieve and silica sol by liquid deposition method, and the silica sol colloidal ions are attached to the outer surface of the molecular sieve, and then filtered, dried, and roasted to prepare the acid content of the outer surface. Reduced molecular sieves. However, due to the low force between the surface of the molecular sieve and the attachment, this silanization method needs to be repeated many times and cyclically impregnated to achieve the purpose of eliminating the acidity of the outer surface, resulting in a large waste of silicon ester and greatly reducing the efficiency of the modification process. .

CN109529923A discloses a method for preparing an oxide-modified microporous molecular sieve shape-selective catalyst. The method is to add the microporous molecular sieve without removing the template into the metal nitrate solution, stir evenly, and then filter, dry and roast to obtain the metal oxide modified microporous molecular sieve shape-selective catalyst. However, although this nitride or metal oxide modification method can better cover the acidity of the outer surface of the molecular sieve, the degree of dispersion of the attachments during the modification process is not uniform, which easily leads to blockage of the molecular sieve channels and affects the catalytic performance of the molecular sieve. .

Contents of the invention

Aiming at the deficiencies of the prior art, the invention provides a modified ZSM-23 molecular sieve and its preparation method and application. When the catalyst prepared by the modified ZSM-23 molecular sieve is used in the isomerization reaction of normal paraffins, the selectivity of isoparaffins can be significantly improved while ensuring a relatively high conversion rate of normal paraffins.

The first aspect of the present invention provides a modified ZSM-23 molecular sieve, the molar ratio of SiO ₂ /Al ₂ O ₃ on the outer surface of the modified ZSM-23 molecular sieve is 500-1500, and the bulk SiO ₂ /Al ₂ O ₃ The molar ratio is 60-200, the total pyridine infrared acid content is 0.02-0.35 mmol/g, and the di-tert-butyl pyridine infrared total acid content is 0.001-0.015 mmol/g.

Further, preferably, the molar ratio of SiO ₂ /Al ₂ O ₃ on the outer surface of the modified ZSM-23 molecular sieve is 600-1000, and the molar ratio of SiO ₂ /Al ₂ O ₃ on the bulk phase is 80-150.

Further, preferably, the total pyridine infrared acid content of the modified ZSM-23 molecular sieve is 0.10-0.25 mmol/g, and the total infrared acid content of di-tert-butylpyridine is 0.005-0.012 mmol/g.

The second aspect of the present invention provides a kind of preparation method of modified ZSM-23 molecular sieve, comprises the following steps:

(1) prepare the ZSM-23 molecular sieve that does not remove template;

(2) mixing the ZSM-23 molecular sieve obtained in step (1) with the dealumination and silicon supplementation reagent to carry out dealumination and silicon supplementation;

(3) the material obtained in step (2) is subjected to steam treatment;

(4) Treating the material obtained in step (3) with a buffer solution to obtain a modified ZSM-23 molecular sieve.

Further, in step (1), the ZSM-23 molecular sieve without template removal can be prepared by hydrothermal synthesis. For example: feed silicon source, aluminum source, template agent, alkali source, and water into SiO ₂ in the following molar ratio: (0.003～0.02)Al ₂ O ₃ : (0.4～2.0)R (template agent):(0.01～10) Na ₂ O: (10~200)H ₂ O, crystallize the mixed material at 150~180°C for 2~5 days, wash the product until the pH value is 7~8, and then filter and store at 80~120°C Drying to obtain ZSM-23 molecular sieve without template removal.

Further, in the preparation process of the ZSM-23 molecular sieve, the silicon source is selected from one or more of silica sol, white carbon black, tetraethyl orthosilicate, etc., and the aluminum source is selected from octadecadecanoate One or more of aluminum sulfate, pseudoboehmite, sodium metaaluminate, etc., the template agent is selected from one or more of isopropylamine, dimethylamine, pyrrolidine, and the alkali source is selected from One or more of sodium hydroxide, potassium hydroxide, etc., the water is deionized water.

Further, in step (2), the dealumination and silicon supplementation reagent is at least one of ammonium hexafluorosilicate solution, ethyl tetrasilicate solution and the like.

Further, in step (2), the molar concentration of the dealumination and silicon supplementation reagent is 0.5-1.5 mol/L. Wherein the mass ratio of the ZSM-23 molecular sieve obtained in step (1) to the dealumination silicon replenishing reagent is 1:2-1:8.

Further, in step (2), the specific operation process of the dealumination and silicon supplementation is: mix the ZSM-23 molecular sieve obtained in step (1) with water evenly, then raise the temperature to 60-100°C, keep stirring, add the dealuminum sieve dropwise. Aluminum supplementation silicon reagent, continue to stir for 60-120 minutes after the dropwise addition, filter while hot, wash the obtained filter cake with water, filter again and dry. Wherein, the liquid-solid volume ratio of water to the ZSM-23 molecular sieve obtained in step (1) is 2:1-8:1.

Further, in step (3), the conditions for the steam treatment are as follows: the temperature is 400-700°C, preferably 500-600°C, the pressure is 0.01-0.3MPa, preferably 0.1-0.2MPa, and the time is 0.5- 6h, preferably 1-4h.

Further, in step (4), the buffer solution is one or more of oxalic acid-ammonium oxalate solution and acetic acid-ammonium acetate solution. The pH value of the buffer solution is 4.5-6.5, preferably 5.0-6.0. In the buffer solution, the molar concentration of organic acid radicals is 0.1-1.0 mol/L. The liquid-solid volume ratio of the buffer solution to the material obtained in step (3) is 3:1˜10:1.

Further, in step (4), the specific treatment process is: mixing and stirring the material obtained in step (3) with the buffer solution, the treatment temperature is 40-80° C., and the treatment time is 0.5-3 hours.

Further, in step (4), solid-liquid separation (such as suction filtration) is performed; and the above operation is repeated 2 to 4 times, and the final obtained material is dried to obtain the modified ZSM-23 molecular sieve.

The third aspect of the present invention provides an application of the above-mentioned modified ZSM-23 molecular sieve in a catalyst for shape-selective isomerization of n-paraffins.

Further, the n-paraffin isomerization catalyst includes the modified ZSM-23 molecular sieve and Group VIII noble metal components, wherein the content of the Group VIII noble metal components is 0.01% to 10% by metal weight , preferably 0.1% to 3%.

Further, the Group VIII noble metal is platinum and/or palladium.

Further, the normal alkanes include at least one of n-dodecane, n-tetradecane, n-hexadecane, n-octadecane and the like.

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

1. The modified ZSM-23 molecular sieve of the present invention has a low total amount of di-tert-butylpyridine infrared acid, eliminates the acid sites on the outer surface and has an open and smooth pore structure. The catalyst prepared by the modified ZSM-23 molecular sieve of the present invention, The selectivity of isoparaffins is significantly improved while ensuring a relatively high conversion rate of normal paraffins.

2. The preparation method of the modified ZSM-23 molecular sieve of the present invention, firstly, the molecular sieve obtained by hydrothermal synthesis is not treated with a template release agent, and the organic template molecule in the channel acts as a channel protective agent, and the method of dealumination and silicon supplementation is used for fixed-point removal The acid center on the outer surface of the molecular sieve reduces the non-shape-selective cracking reaction of normal alkanes on the outer surface of the molecular sieve. The aluminum on the outer surface of the molecular sieve is replaced by a non-acidic silicon atom under the action of the dealumination and silicon replenishing reagent, and the acidic center in the channel is protected due to the presence of the template molecule. Subsequent treatment with constant pressure and high temperature water vapor reduces the total acid content of the molecular sieve, and also removes the template agent molecules in the pores. Finally, a buffer solution is used to remove the non-skeleton aluminum produced in the hydrothermal treatment process, so that the pores of the molecular sieve are more open and smooth, and it is easy to diffuse the intermediate product in the shape-selective isomerization reaction process of n-alkanes. The modified ZSM-23 prepared by the present invention The catalyst can significantly improve the selectivity of isoparaffins while ensuring a relatively high conversion rate of normal paraffins.

Description of drawings

Figure 1 is the XRD pattern of the modified molecular sieve obtained in Example 1.

Detailed ways

The action and effect of the technical solution of the present invention will be further described below in conjunction with examples and comparative examples, but the following examples do not constitute limitations to the protection scope of the present invention.

In the present invention, the % involved in the examples and comparative examples are mass fractions unless otherwise specified.

In the present invention, the outer surface SiO ₂ /Al ₂ O _The molar ratio is measured by X-ray photoelectron spectroscopy (XPS), and the elemental composition and state of the surface of the catalyst are measured on the Multilab2000 type electron spectrometer of the American Thermofisher company, and the excitation source is Mg Kα, cathode voltage and current were 13kV and 20mA, respectively. The electron binding energy is calibrated by C1s (284.6eV).

In the present invention, the bulk phase SiO ₂ /Al ₂ O ₃ molar ratio is analyzed by X-ray fluorescence spectroscopy (XRF), using a ZSX100e X-ray fluorescence spectrometer, the spectral line is Kα, the crystal is Li F1, the target is Rh, and the detector It is SC flashing, the timing is 20s, and the light path atmosphere is vacuum.

In the present invention, the pyridine infrared determination method is as follows: the powdered ZSM-23 molecular sieve is compressed into tablets, and then degassed at 450° C. for 2 hours after vacuuming. When the temperature dropped to room temperature, pyridine molecules were used as probe molecules, and the infrared spectrum of chemical desorption was measured, and the adsorption amount was calculated.

的2,6-二叔丁基吡啶分子能够接触到的质子酸。2，6-二叔丁基吡啶红外测定方法如下：将粉末状ZSM-23分子筛进行压片，抽真空后，于450℃下脱气2h。当温度降到室温后用2，6-二叔丁基吡啶分子作探针分子，测定其化学脱附的红外谱图，并计算吸附量。In the present invention, the total acid amount of di-tert-butylpyridine infrared means that the kinetic diameter is

The 2,6-di-tert-butylpyridine molecule is able to access the protonic acid. The infrared determination method of 2,6-di-tert-butylpyridine is as follows: the powdered ZSM-23 molecular sieve is pressed into tablets, and then degassed at 450°C for 2 hours after vacuuming. When the temperature drops to room temperature, 2,6-di-tert-butylpyridine molecules are used as probe molecules, and the infrared spectrum of its chemical desorption is measured, and the adsorption amount is calculated.

Example 1

Weigh 8g of sodium hydroxide and dissolve it in 810mL of water, add 6.66g of aluminum sulfate octadecahydrate, 150g of silica sol (40% by mass fraction), and 35.4g of isopropylamine (iPA) successively during the stirring process to form a material molar ratio of _SiO2 : 0.01Al ₂ O ₃ : 0.6iPA: 0.1Na ₂ O: 50H ₂ O mixed gel, put the mixed initial gel into a closed reactor and carry out crystallization at 160°C for 3 days, and the obtained mixture The product was washed until the pH value was 7, then filtered and dried at 120°C to obtain ZSM-23 powder without template removal. Take 30g of the above-mentioned ZSM-23 powder, add 180mL of water and mix evenly, stir and heat to 60°C, use a peristaltic pump to add 90mL of 0.5mol/L ammonium hexafluorosilicate solution dropwise at a constant speed, keep the temperature at 60°C and continue stirring for 90min. Suction filtration while hot, add 240mL water to the obtained filter cake, heat to 60°C and keep for 20min, suction filtration while hot, dry the filter cake at 120°C for 24h, then place the dried product in a hydrothermal treatment furnace, heat at 500°C , treated under 0.1MPa pressure for 2h, the obtained material was placed in 300mL of oxalic acid-ammonium oxalate solution with a pH value of 6.0, in which the molar concentration of oxalate was 0.3mol/L, stirred and heated to 60°C, kept for 30min while hot Suction filtration, this process was repeated 3 times, the obtained filter cake was dried at 120°C for 24 hours, and the obtained modified molecular sieve was named ZSM-23-1. The XRD pattern of the modified molecular sieve is shown in FIG. 1 .

Example 2

Weigh 8g of sodium hydroxide and dissolve it in 810mL of water. During the stirring process, add 6.66g of aluminum sulfate octadecahydrate, 150g of silica sol (40% by mass fraction), and 35.4g of isopropylamine to form a material molar ratio of SiO ₂ : 0.01Al ₂ O ₃ : 0.6iPA: 0.1Na ₂ O: 50H ₂ O mixed gel, put the mixed initial gel into a closed reactor for crystallization at 160°C for 3 days, and wash the obtained mixture product to The pH value is 7, and then filtered and dried at 120°C to obtain ZSM-23 powder without template removal. Take 30g of the above-mentioned ZSM-23 powder, add 180mL of water and mix evenly, stir and heat to 60°C, use a peristaltic pump to add 90mL of 0.8mol/L ammonium hexafluorosilicate solution dropwise at a constant speed, keep the temperature at 60°C and continue stirring for 90min. Suction filtration while hot, add 240mL water to the obtained filter cake, heat to 60°C and keep for 20min, suction filtration while hot, dry the filter cake at 120°C for 24h, then place the dried product in a hydrothermal treatment furnace, heat at 530°C , treated under 0.1MPa pressure for 2h, the obtained material was placed in 300mL of acetic acid-ammonium acetate solution with a pH value of 6.0, wherein the molar concentration of acetate was 0.4mol/L, stirred and heated to 60°C, kept for 30min while hot Suction filtration, this process was repeated 3 times, the obtained filter cake was dried at 120°C for 24 hours, and the obtained modified molecular sieve was named ZSM-23-2.

Example 3

Weigh 8g of sodium hydroxide and dissolve it in 810mL of water. During the stirring process, add 6.66g of aluminum sulfate octadecahydrate, 150g of silica sol (40% by mass fraction), and 35.4g of isopropylamine to form a material molar ratio of SiO ₂ : 0.01Al ₂ O ₃ : 0.6iPA: 0.1Na ₂ O: 50H ₂ O mixed gel, put the mixed initial gel into a closed reactor for crystallization at 160°C for 3 days, and wash the obtained mixture product to The pH value is 7, and then filtered and dried at 120°C to obtain ZSM-23 powder without template removal. Take 30g of the above-mentioned ZSM-23 powder, add 180mL of water and mix evenly, stir and heat to 60°C, use a peristaltic pump to add 90mL of 0.8mol/L tetraethyl orthosilicate solution dropwise at a constant speed, keep the temperature at 60°C and continue stirring for 90min. Suction filtration while hot, add 240mL water to the obtained filter cake, heat to 60°C and keep for 20min, suction filtration while hot, dry the filter cake at 120°C for 24h, then place the dried product in a hydrothermal treatment furnace, heat at 550°C , treated under 0.1MPa pressure for 2h, the obtained material was placed in 300mL of acetic acid-ammonium acetate solution with a pH value of 5.5, wherein the molar concentration of acetate was 0.4mol/L, stirred and heated to 60°C, kept for 30min while hot Suction filtration, this process was repeated 3 times, the obtained filter cake was dried at 120°C for 24 hours, and the obtained modified molecular sieve was named ZSM-23-3.

Example 4

Weigh 8g of sodium hydroxide and dissolve it in 810mL of water. During the stirring process, add 6.66g of aluminum sulfate octadecahydrate, 150g of silica sol (40% by mass fraction), and 35.4g of isopropylamine to form a material molar ratio of SiO ₂ : 0.01Al ₂ O ₃ : 0.6iPA: 0.1Na ₂ O: 50H ₂ O mixed gel, put the mixed initial gel into a closed reactor for crystallization at 160°C for 3 days, and wash the obtained mixture product to The pH value is 7, and then filtered and dried at 120°C to obtain ZSM-23 powder without template removal. Take 30g of the above-mentioned ZSM-23 powder, add 180mL of water and mix evenly, stir and heat to 60°C, use a peristaltic pump to add 90mL of 0.8mol/L ammonium hexafluorosilicate solution dropwise at a constant speed, keep the temperature at 60°C and continue stirring for 90min. Suction filtration while hot, add 240mL water to the obtained filter cake, heat to 60°C and keep for 20min, suction filtration while hot, dry the filter cake at 120°C for 24h, then place the dried product in a hydrothermal treatment furnace, heat at 500°C , treated under 0.15MPa pressure for 2h, the obtained material was placed in 300mL of oxalic acid-ammonium oxalate solution with a pH value of 5.5, in which the molar concentration of oxalate was 0.3mol/L, stirred and heated to 60°C, kept for 30min while hot Suction filtration, this process was repeated 3 times, the obtained filter cake was dried at 120°C for 24 hours, and the obtained modified molecular sieve was named ZSM-23-4.

Example 5

Weigh 8g of sodium hydroxide and dissolve it in 810mL of water. During the stirring process, add 6.66g of aluminum sulfate octadecahydrate, 150g of silica sol (40% by mass fraction), and 35.4g of isopropylamine to form a material molar ratio of SiO ₂ : 0.01Al ₂ O ₃ : 0.6iPA: 0.1Na ₂ O: 50H ₂ O mixed gel, put the mixed initial gel into a closed reactor for crystallization at 160°C for 3 days, and wash the obtained mixture product to The pH value is 7, and then filtered and dried at 120°C to obtain ZSM-23 powder without template removal. Take 30g of the above-mentioned ZSM-23 powder, add 180mL of water and mix evenly, stir and heat to 60°C, use a peristaltic pump to add 90mL of 1.0mol/L tetraethyl orthosilicate solution dropwise at a constant speed, keep the temperature at 60°C and continue stirring for 90min. Suction filtration while hot, add 240mL water to the obtained filter cake, heat to 60°C and keep for 20min, suction filtration while hot, dry the filter cake at 120°C for 24h, then place the dried product in a hydrothermal treatment furnace, heat at 530°C , treated under 0.15MPa pressure for 2h, the obtained material was placed in 300mL of oxalic acid-ammonium oxalate solution with a pH value of 5.5, and the molar concentration of oxalate was 0.6mol/L, stirred and heated to 60°C, kept for 30min while hot Suction filtration, this process was repeated 3 times, the resulting filter cake was dried at 120°C for 24 hours, and the obtained modified molecular sieve was named ZSM-23-5.

Example 6

Weigh 8g of sodium hydroxide and dissolve it in 810mL of water. During the stirring process, add 6.66g of aluminum sulfate octadecahydrate, 150g of silica sol (40% by mass fraction), and 35.4g of isopropylamine to form a material molar ratio of SiO ₂ : 0.01Al ₂ O ₃ : 0.6iPA: 0.1Na ₂ O: 50H ₂ O mixed gel, put the mixed initial gel into a closed reactor for crystallization at 160°C for 3 days, and wash the obtained mixture product to The pH value is 7, and then filtered and dried at 120°C to obtain ZSM-23 powder without template removal. Take 30g of the above ZSM-23 powder, add 180mL of water and mix evenly, stir and heat to 60°C, use a peristaltic pump to add 90mL of 1.0mol/L ammonium hexafluorosilicate solution dropwise at a constant speed, keep the temperature at 60°C and continue stirring for 90min. Suction filtration while hot, add 240mL water to the obtained filter cake, heat to 60°C and keep for 20min, suction filtration while hot, dry the filter cake at 120°C for 24h, then place the dried product in a hydrothermal treatment furnace, heat at 550°C , treated under 0.15MPa pressure for 2h, the obtained material was placed in 300mL of oxalic acid-ammonium oxalate solution with a pH value of 5.0, in which the molar concentration of oxalate was 0.3mol/L, stirred and heated to 60°C, kept for 30min while hot Suction filtration, this process was repeated 3 times, the obtained filter cake was dried at 120°C for 24 hours, and the obtained modified molecular sieve was named ZSM-23-6.

Example 7

Weigh 8g of sodium hydroxide and dissolve it in 810mL of water. During the stirring process, add 6.66g of aluminum sulfate octadecahydrate, 150g of silica sol (40% by mass fraction), and 35.4g of isopropylamine to form a material molar ratio of SiO ₂ : 0.01Al ₂ O ₃ : 0.6iPA: 0.1Na ₂ O: 50H ₂ O mixed gel, put the mixed initial gel into a closed reactor for crystallization at 160°C for 3 days, and wash the obtained mixture product to The pH value is 7, and then filtered and dried at 120°C to obtain ZSM-23 powder without template removal. Take 30g of the above ZSM-23 powder, add 180mL of water and mix evenly, stir and heat to 60°C, use a peristaltic pump to add 90mL of 1.2mol/L tetraethyl orthosilicate solution dropwise at a constant speed, keep the temperature at 60°C and continue stirring for 90min. Suction filtration while hot, add 240mL water to the obtained filter cake, heat to 60°C and keep for 20min, suction filtration while hot, dry the filter cake at 120°C for 24h, then place the dried product in a hydrothermal treatment furnace, heat at 570°C , treated under 0.15MPa pressure for 2h, the obtained material was placed in 300mL of oxalic acid-ammonium oxalate solution with a pH value of 4.5, in which the molar concentration of oxalate was 0.4mol/L, stirred and heated to 60°C, kept for 30min and then hot Suction filtration, this process was repeated 3 times, the obtained filter cake was dried at 120°C for 24 hours, and the obtained modified molecular sieve was named ZSM-23-7.

Example 8

Weigh 8g of sodium hydroxide and dissolve it in 810mL of water. During the stirring process, add 6.66g of aluminum sulfate octadecahydrate, 150g of silica sol (40% by mass fraction), and 35.4g of isopropylamine to form a material molar ratio of SiO ₂ : 0.01Al ₂ O ₃ : 0.6iPA: 0.1Na ₂ O: 50H ₂ O mixed gel, put the mixed initial gel into a closed reactor for crystallization at 160°C for 3 days, and wash the obtained mixture product to The pH value is 7, and then filtered and dried at 120°C to obtain ZSM-23 powder without template removal. Take 30g of the above ZSM-23 powder, add 180mL of water and mix evenly, stir and heat to 60°C, add 90mL of 1.5mol/L ammonium hexafluorosilicate solution dropwise at a constant speed with a peristaltic pump, keep the temperature at 60°C and continue stirring for 90min. Suction filtration while hot, add 240mL water to the obtained filter cake, heat to 60°C and keep for 20min, suction filtration while hot, dry the filter cake at 120°C for 24h, then place the dried product in a hydrothermal treatment furnace, heat at 570°C , treated under 0.2MPa pressure for 2h, the obtained material was placed in 300mL of acetic acid-ammonium acetate solution with a pH value of 4.5, wherein the molar concentration of acetate was 0.4mol/L, stirred and heated to 60°C, kept for 30min while hot Suction filtration, this process was repeated 3 times, the obtained filter cake was dried at 120°C for 24 hours, and the obtained modified molecular sieve was named ZSM-23-8.

Comparative example 1

Weigh 8g of sodium hydroxide and dissolve it in 810mL of water. During the stirring process, add 6.66g of aluminum sulfate octadecahydrate, 150g of silica sol (40% by mass fraction), and 35.4g of isopropylamine to form a material molar ratio of SiO ₂ : 0.01Al ₂ O ₃ : 0.6iPA: 0.1Na ₂ O: 50H ₂ O mixed gel, put the mixed initial gel into a closed reactor for crystallization at 160°C for 3 days, and wash the obtained mixture product to The pH value was 7, then filtered, dried at 120°C, and then calcined at 550°C for 6 hours to obtain the ZSM-23 powder from which the template agent was removed. Take 30g of the above-mentioned ZSM-23 powder, add 180mL of water and mix evenly, stir and heat to 60°C, use a peristaltic pump to add 90mL of 0.5mol/L ammonium hexafluorosilicate solution dropwise at a constant speed, keep the temperature at 60°C and continue stirring for 90min. Suction filtration while hot, add 240mL water to the obtained filter cake, heat to 60°C and keep for 20min, suction filtration while hot, dry the filter cake at 120°C for 24h, then place the dried product in a hydrothermal treatment furnace, heat at 500°C , treated under 0.1MPa pressure for 2h, the obtained material was placed in 300mL of oxalic acid-ammonium oxalate solution with a pH value of 6.0, in which the molar concentration of oxalate was 0.3mol/L, stirred and heated to 60°C, kept for 30min while hot Suction filtration, this process was repeated 3 times, the obtained filter cake was dried at 120°C for 24 hours, and the obtained modified molecular sieve was named ZSM-23-B.

Comparative example 2

Weigh 8g of sodium hydroxide and dissolve it in 810mL of water. During the stirring process, add 6.66g of aluminum sulfate octadecahydrate, 150g of silica sol (40% by mass fraction), and 35.4g of isopropylamine to form a material molar ratio of SiO ₂ : 0.01Al ₂ O ₃ : 0.6iPA: 0.1Na ₂ O: 50H ₂ O mixed gel, put the mixed initial gel into a closed reactor for crystallization at 160°C for 3 days, and wash the obtained mixture product to The pH value is 7, and then filtered and dried at 120°C to obtain ZSM-23 powder without template removal. Take 30g of the above ZSM-23 powder, add 180mL of water and mix evenly, stir and heat to 60°C, use a peristaltic pump to add 90mL of 1.0mol/L ammonium hexafluorosilicate solution dropwise at a constant speed, keep the temperature at 60°C and continue stirring for 90min. Suction filtration while hot, add 240mL water to the obtained filter cake, heat to 60°C and keep for 20min, suction filtration while hot, and dry the filter cake at 120°C for 24h. Subsequently, the obtained material was placed in a hydrothermal treatment furnace, and treated at 550° C. for 2 hours under a pressure of 0.15 MPa, and the obtained modified molecular sieve was named ZSM-23-C.

Comparative example 3

Weigh 8g of sodium hydroxide and dissolve it in 810mL of water. During the stirring process, add 6.66g of aluminum sulfate octadecahydrate, 150g of silica sol (40% by mass fraction), and 35.4g of isopropylamine to form a material molar ratio of SiO ₂ : 0.01Al ₂ O ₃ : 0.6iPA: 0.1Na ₂ O: 50H ₂ O mixed gel, put the mixed initial gel into a closed reactor for crystallization at 160°C for 3 days, and wash the obtained mixture product to The pH value is 7, and then filtered and dried at 120°C to obtain ZSM-23 powder without template removal. Take 30g of the above-mentioned ZSM-23 powder and place it in a hydrothermal treatment furnace, treat it at 550°C and a pressure of 0.15MPa for 2h, put the obtained material in 300mL of 0.3mol/L hydrochloric acid solution, stir and raise the temperature to 60°C, and keep it for 30min Suction filtration while hot, wash the filter cake twice with water, and dry the obtained material at 120°C for 24 hours. The modified molecular sieve obtained is named ZSM-23-D.

Table 1 The characterization results of the modified molecular sieves obtained in the examples and comparative examples

Example 9

Catalysts C1-C8 were prepared using the modified molecular sieves obtained in Examples 1-8 respectively. The specific steps were: take 10 g of modified ZSM-23 molecular sieves, press them into tablets to 20-40 mesh, and use 10 mL of 0.005 g/mL H ₂ PtCl ₆ The solution was impregnated, placed at room temperature for 6 hours, dried at 120°C for 4 hours, and then reduced in a hydrogen atmosphere at 500°C for 4 hours to obtain catalysts containing 0.5wt% Pt, which were named C1-C8 respectively. Take 10 mL of the catalyst prepared above and put it in a stainless steel tube reactor, raise the temperature to the reaction temperature under a hydrogen atmosphere, pass the raw material oil n-dodecane to react, and analyze the product by gas chromatography. Reaction conditions: the reaction temperature is 280°C, the reaction pressure is normal pressure, the liquid hourly volume space velocity is 1.0h ^-1 , and the volume ratio of hydrogen to oil is 15:1. The isomerization reaction results are shown in Table 2.

Comparative example 4

Catalysts C9-C11 were prepared using the modified molecular sieves obtained in Comparative Examples 1-3 respectively. The specific steps were: take 10 g of modified ZSM-23 molecular sieves, press them into tablets to 20-40 mesh, and use 10 mL of 0.005 g/mL H ₂ PtCl ₆ The solution was impregnated, placed at room temperature for 6 hours, dried at 120°C for 4 hours, and then reduced in a hydrogen atmosphere at 500°C for 4 hours to obtain catalysts containing 0.5 wt% Pt, which were named C9-C11. Take 10 mL of the catalyst prepared above and put it in a stainless steel tube reactor, raise the temperature to the reaction temperature under a hydrogen atmosphere, pass the raw material oil n-dodecane to react, and analyze the product by gas chromatography. Reaction conditions: the reaction temperature is 280°C, the reaction pressure is normal pressure, the volumetric space velocity of n-dodecane liquid is 1.0h ^-1 , the volume ratio of hydrogen to oil is 15:1, and the isomerization reaction results are shown in Table 2.

It can be seen from the evaluation results that the catalyst prepared by the invention is better than the reference catalyst in the selectivity and yield of isomeric hydrocarbons under the same process conditions.

The application result of the catalyst of table 2 embodiment and comparative example gained

Catalyst number Conversion rate of n-dodecane, % Isohydrocarbon selectivity, % Isomerized hydrocarbon yield, % C1 94.2 65.2 61.4 C2 93.8 68.4 64.2 C3 93.3 72.6 67.7 C4 92.8 78.7 73.0 C5 92.5 86.6 80.1 C6 92.2 87.3 80.5 C7 90.1 81.5 73.4 C8 88.4 76.4 67.5 C9 85.5 59.5 50.9 C10 91.3 61.8 56.4 C11 83.2 50.2 41.8

Claims (12)

1. A modified ZSM-23 molecular sieve is characterized in that SiO is arranged on the outer surface of the modified ZSM-23 molecular sieve ₂ /Al ₂ O ₃ The molar ratio is 500-1500, bulk phase SiO ₂ /Al ₂ O ₃ The molar ratio is 60-200, the total infrared acid amount of pyridine is 0.02-0.35 mmol/g, and the total infrared acid amount of di-tert-butylpyridine is 0.001-0.015 mmol/g.

2. The modified ZSM-23 molecular sieve according to claim 1, wherein: the SiO on the outer surface of the modified ZSM-23 molecular sieve ₂ /Al ₂ O ₃ The molar ratio is 600-1000, bulk phase SiO ₂ /Al ₂ O ₃ The molar ratio is 80-150.

3. The modified ZSM-23 molecular sieve according to claim 1 or 2, characterized in that: the total pyridine infrared acid amount of the modified ZSM-23 molecular sieve is 0.10-0.25 mmol/g, and the total di-tert-butylpyridine infrared acid amount is 0.005-0.012 mmol/g.

4. A preparation method of a modified ZSM-23 molecular sieve comprises the following steps:

(1) Preparing ZSM-23 molecular sieve without removing template;

(2) Mixing the ZSM-23 molecular sieve obtained in the step (1) with a dealumination silicon supplementing reagent to dealuminate silicon supplementing;

(3) Carrying out steam treatment on the material obtained in the step (2);

(4) And (3) treating the material obtained in the step (3) by adopting a buffer solution to obtain the modified ZSM-23 molecular sieve.

5. The method of claim 4, wherein: in the step (2), the dealumination and silicon supplementing reagent is at least one of ammonium hexafluorosilicate solution and tetraethoxysilane solution; the molar concentration of the dealumination silicon-supplementing reagent is 0.5-1.5 mol/L.

6. The method of claim 4, wherein: the mass ratio of the ZSM-23 molecular sieve obtained in the step (1) to the dealumination and silicon-supplementing reagent is 1:2-1:8.

7. The method of claim 4, wherein: in the step (2), the dealumination and silicon supplementing operation process comprises the following steps: uniformly mixing the ZSM-23 molecular sieve obtained in the step (1) with water, heating to 60-100 ℃, continuously stirring, dripping a dealumination silicon-supplementing reagent, continuously stirring for 60-120 min after dripping, filtering while the mixture is hot, washing the obtained filter cake with water, filtering again and drying.

8. The method of claim 4, wherein: in the step (3), the conditions of the steam treatment are as follows: the temperature is 400-700 ℃, preferably 500-600 ℃, the pressure is 0.01-0.3 MPa, preferably 0.1-0.2 MPa, and the time is 0.5-6 h, preferably 1-4 h.

9. The method of claim 4, wherein: in the step (4), the buffer solution is one or more of oxalic acid-ammonium oxalate solution and acetic acid-ammonium acetate solution.

10. The method according to claim 9, wherein: the pH value of the buffer solution is 4.5-6.5, preferably 5.0-6.0; in the buffer solution, the molar concentration of the organic acid radical is 0.1-1.0 mol/L; the liquid-solid volume ratio of the buffer solution to the material obtained in the step (3) is 3:1-10:1 mL/g.

11. The method of claim 4, wherein: in the step (4), the processing procedure is as follows: mixing and stirring the material obtained in the step (3) with a buffer solution, wherein the treatment temperature is 40-80 ℃ and the treatment time is 0.5-3 h.

12. Use of a modified ZSM-23 molecular sieve as defined in any of claims 1-3 or a modified ZSM-23 molecular sieve prepared according to the method defined in any of claims 4-11 in a normal paraffin shape selective isomerization catalyst.

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