A method for preparing regenerated molecular sieves

Abstract

This invention relates to the field of regenerated molecular sieves. A method for preparing regenerated molecular sieves includes: preparing aqueous solution A, which is a mixed aqueous solution of sulfuric acid and aluminum sulfate; preparing aqueous solution B, which is a mixed aqueous solution of water glass, n-butylamine, and sodium hydroxide; preparing regenerated molecular sieve seed crystals; mixing equal volumes of aqueous solution A and aqueous solution B evenly, then adding the regenerated molecular sieve seed crystals; stirring under sealed conditions for 36-48 hours; filtering and washing the product until neutral, drying it, and then immersing it in an ammonium nitrate aqueous solution with a concentration of 6-9 g•ml⁻¹; performing ion exchange under sealed conditions at 110-130°C; removing and drying the product; and then calcining it at 500-600°C for 4-6 hours to obtain regenerated ZSM-5 molecular sieves. The beneficial effects of this invention are: fully utilizing the molecular sieve after the reaction as seed crystals, realizing the resource utilization and high-value utilization of waste.

Description

Technical Field

[0001] This invention relates to the field of regenerated molecular sieves. Background Technology

[0002] Molecular sieves are an important class of inorganic porous materials that are widely used in adsorption and catalysis. They play an irreplaceable role in catalytic reactions such as cracking, hydrogenation, reforming, disproportionation, dehydrogenation, cyclization, and aromatization.

[0003] The catalytic effect of molecular sieves is inseparable from their regular and ordered pore structure. In the catalytic process, the pore structure of molecular sieves not only provides space for acidic sites, but also achieves shape selection through the confinement effect of pore size, thereby obtaining the desired catalytic products with high selectivity.

[0004] However, during the reaction process, molecular sieves accumulate intermediate and byproducts in their pores, eventually forming carbon deposits that hinder mass transfer of reactants and isolate active sites. While high-temperature calcination can remove these carbon deposits, the high temperature and oxidizing environment also damage the molecular sieve structure. After multiple reaction-regeneration cycles, repeated carbon deposition and oxidation significantly affect the structural order of the molecular sieve, destroying its structure and ultimately leading to deactivation. Deactivated molecular sieves are often only treated as solid waste, or even hazardous solid waste, wasting valuable molecular sieve resources and increasing environmental pollution. Therefore, finding a method to achieve high-value utilization of waste molecular sieves after reactions is of great significance to the field of molecular sieve catalysis. Summary of the Invention

[0005] The technical problem to be solved by the present invention is: how to provide a method for preparing regenerated molecular sieves.

[0006] To achieve the objective of this invention, a molecular sieve that has undergone carbon removal treatment after participating in a catalytic reaction is used as a seed crystal for regenerated molecular sieves. The regenerated molecular sieve is synthesized by reacting it with an aluminum source and a silicon source.

[0007] The technical solution adopted in this invention is: a method for preparing regenerated molecular sieves, which is carried out according to the following steps.

[0008] Step 1: Prepare aqueous solution A, which is a mixed aqueous solution of sulfuric acid and aluminum sulfate, wherein the mass ratio of water, sulfuric acid and aluminum sulfate is 1:0.035~0.038:0.011~0.012; Prepare aqueous solution B, which is a mixed aqueous solution of water glass, n-butylamine and sodium hydroxide, wherein the mass ratio of water, water glass, n-butylamine and sodium hydroxide is 1:0.457~0.459:0.045~0.048:0.008~0.012.

[0009] Step 2: Prepare regenerated molecular sieve seed crystals. The used ZSM-5 molecular sieve is calcined in air to prepare regenerated molecular sieve seed crystals with a carbon content of less than 0.01 wt% and a particle size of 300-400 mesh. The molecular sieve structure integrity of the regenerated molecular sieve seed crystals is 50%-80% of that of the fresh molecular sieve.

[0010] Step 3: Mix equal volumes of aqueous solution A and aqueous solution B thoroughly, then add the regenerated molecular sieve seed crystals. Under sealed conditions, heat to 170-190℃ and stir for 36-48 hours. After filtering and washing until neutral, dry the product and then immerse it in an ammonium nitrate aqueous solution with a concentration of 6-9 g•ml-1. Let it stand for 4-10 hours under sealed conditions at 110-130℃ for ion exchange. After drying, calcine it at 500-600℃ for 4-6 hours to obtain the regenerated ZSM-5 molecular sieve.

[0011] The molecular sieve structure integrity of the regenerated molecular sieve seed crystals is 50% to 80% of that of the fresh molecular sieve. In step three, when adding the regenerated molecular sieve seed crystals, the amount of regenerated molecular sieve seed crystals added is 5% to 30% of the weight of the final regenerated ZSM-5 molecular sieve.

[0012] The beneficial effects of this invention are: it fully utilizes the reacted molecular sieve as a seed crystal, realizing the resource utilization and high-value utilization of waste; it saves raw material consumption in the preparation process of regenerated molecular sieves, achieving high efficiency and low consumption in molecular sieve synthesis; and it utilizes the defect sites formed by the structural destruction of the reacted molecular sieve to achieve pore-expanding modification of the regenerated molecular sieve. Detailed Implementation

[0013] The specific embodiments of the present invention will be further described in detail below through specific examples. Example 1

[0014] A method for preparing regenerated molecular sieves, comprising the following steps:

[0015] Step 1: Prepare aqueous solution A, which is a mixed aqueous solution of sulfuric acid and aluminum sulfate, wherein the mass ratio of water, sulfuric acid and aluminum sulfate is 1:0.036:0.011, and concentrated sulfuric acid and aluminum sulfate are used for preparation; Prepare aqueous solution B, which is a mixed aqueous solution of water glass, n-butylamine and sodium hydroxide, wherein the mass ratio of water, water glass, n-butylamine and sodium hydroxide is 1:0.458:0.046:0.011.

[0016] Step 2: Prepare regenerated molecular sieve seed crystals. The used ZSM-5 molecular sieve is calcined in air to prepare regenerated molecular sieve seed crystals with a carbon content of less than 0.01 wt% and a particle size of 350 mesh. The molecular sieve structure integrity of the regenerated molecular sieve seed crystals is 60% of that of the fresh molecular sieve.

[0017] Step 3: After thoroughly mixing equal volumes of aqueous solution A and aqueous solution B, add the regenerated molecular sieve seed crystals (ensuring the solution after mixing A and B completely submerges the regenerated molecular sieve seed crystals). The amount of regenerated molecular sieve seed crystals added should be controlled at 15% of the final molecular sieve weight (add the regenerated molecular sieve seed crystals according to the requirements of the final molecular sieve). Under sealed conditions, heat to 180℃ and stir for 36 hours. After filtering and washing until neutral, dry the product and then immerse it in an 8 g·ml solution. -1 An aqueous solution of ammonium nitrate was allowed to stand for 6 hours at 120°C under sealed conditions for ion exchange. After being removed and dried, it was then calcined at 550°C for 5 hours to obtain regenerated ZSM-5 molecular sieve.

[0018] The crystallinity of the regenerated molecular sieve reached 94% of that of the fresh ZSM-5 molecular sieve, the average pore size was 121% of that of the fresh ZSM-5 molecular sieve, the aromatic selectivity in the propane aromatization reaction was 92%, and the stable reaction time reached 31 days. Example 2

[0019] A method for preparing regenerated molecular sieves, comprising the following steps:

[0020] Step 1: Prepare aqueous solution A, which is a mixed aqueous solution of sulfuric acid and aluminum sulfate, wherein the mass ratio of water, sulfuric acid and aluminum sulfate is 1:0.035:0.011; Prepare aqueous solution B, which is a mixed aqueous solution of water glass, n-butylamine and sodium hydroxide, wherein the mass ratio of water, water glass, n-butylamine and sodium hydroxide is 1:0.457:0.046:0.008.

[0021] Step 2: Prepare regenerated molecular sieve seed crystals. The used ZSM-5 molecular sieve is calcined in air to prepare regenerated molecular sieve seed crystals with a carbon content of less than 0.01 wt% and a particle size of 300 mesh. The molecular sieve structure integrity of the regenerated molecular sieve seed crystals is 70% of that of the fresh molecular sieve.

[0022] Step 3: Mix equal volumes of aqueous solution A and aqueous solution B thoroughly, then add the regenerated molecular sieve seed crystals. Under sealed conditions, heat to 170℃ and stir for 36 hours. The product is filtered, washed until neutral, and dried. Then, it is immersed in an ammonium nitrate aqueous solution with a concentration of 9 g•ml-1 and allowed to stand for 5 hours under sealed conditions at 110℃ for ion exchange. After removal and drying, it is calcined at 500℃ for 4 hours to obtain the regenerated ZSM-5 molecular sieve.

[0023] The crystallinity of the regenerated molecular sieve reaches 89% of that of the fresh ZSM-5 molecular sieve, the average pore size is 119% of that of the fresh ZSM-5 molecular sieve, the aromatic selectivity in the propane aromatization reaction is 91%, and the stable reaction time reaches 30 days. Example 3

[0024] A method for preparing regenerated molecular sieves, comprising the following steps:

[0025] Step 1: Prepare aqueous solution A, which is a mixed aqueous solution of sulfuric acid and aluminum sulfate, wherein the mass ratio of water, sulfuric acid and aluminum sulfate is 1:0.038:0.011; Prepare aqueous solution B, which is a mixed aqueous solution of water glass, n-butylamine and sodium hydroxide, wherein the mass ratio of water, water glass, n-butylamine and sodium hydroxide is 1:0.459:0.045:0.012.

[0026] Step 2: Prepare regenerated molecular sieve seed crystals. The used ZSM-5 molecular sieve is calcined in air to prepare regenerated molecular sieve seed crystals with a carbon content of less than 0.01 wt% and a particle size of 350 mesh. The molecular sieve structure integrity of the regenerated molecular sieve seed crystals is 80% of that of the fresh molecular sieve.

[0027] Step 3: Mix equal volumes of aqueous solution A and aqueous solution B thoroughly, then add the regenerated molecular sieve seed crystals. Under sealed conditions, heat to 190℃ and stir for 48 hours. The product is filtered, washed until neutral, dried, and then immersed in an ammonium nitrate aqueous solution with a concentration of 9 g•ml-1. Under sealed conditions at 130℃, let stand for 10 hours for ion exchange. After removal and drying, calcine at 600℃ for 4 hours to obtain the regenerated ZSM-5 molecular sieve.

[0028] The regenerated ZSM-5 molecular sieve has a molecular sieve structure integrity (crystallinity) of 91% that of the fresh molecular sieve. The average pore size is 125% of that of the fresh ZSM-5 molecular sieve. In the propane aromatization reaction, the aromatic selectivity is 91%, and the stable reaction time reaches 32 days.

[0029] Comparative Example 1

[0030] When using fresh ZSM-5 (directly purchased and unused) as a reference, its molecular sieve structure integrity (crystallization) is 100%, its average pore size is 100%, its aromatic selectivity in propane aromatization is 90%, and its stable reaction time is 27 days.

[0031] Comparative Example 2

[0032] To prepare regenerated molecular sieve seed crystals, the used ZSM-5 molecular sieve was calcined in air to prepare regenerated molecular sieve seed crystals with a carbon content of 0.005 wt% and a particle size of 350 mesh; the regenerated molecular sieve seed crystals were directly used as regenerated ZSM-5 molecular sieves.

[0033] The regenerated ZSM-5 molecular sieve has 65% of the crystallinity of the fresh molecular sieve, an average pore size of 157% of the fresh ZSM-5 molecular sieve, an aromatic selectivity of 39% in the propane aromatization reaction, and a stable reaction time of 16 days.

Claims

1. A method for preparing regenerated molecular sieves, characterized in that: Follow these steps: Step 1: Prepare aqueous solution A, which is a mixed aqueous solution of sulfuric acid and aluminum sulfate, wherein the mass ratio of water, sulfuric acid and aluminum sulfate is 1:0.035~0.038:0.011~0.012; Prepare aqueous solution B, which is a mixed aqueous solution of water glass, n-butylamine and sodium hydroxide, wherein the mass ratio of water, water glass, n-butylamine and sodium hydroxide is 1:0.457~0.459:0.045~0.048:0.008~0.

012. Step 2: Prepare regenerated molecular sieve seed crystals. The used ZSM-5 molecular sieve is calcined in air to prepare regenerated molecular sieve seed crystals with a carbon content of less than 0.01 wt% and a particle size of 300-400 mesh. The molecular sieve structure integrity of the regenerated molecular sieve seed crystals is 50%-80% of that of the fresh molecular sieve. Step 3: Mix equal volumes of aqueous solution A and aqueous solution B thoroughly, then add the regenerated molecular sieve seed crystals. Under sealed conditions, heat to 170-190°C and stir for 36-48 hours. Filter and wash the product until neutral, then dry it. Finally, immerse it in a solution with a concentration of... 6~9g·mL -1 An aqueous solution of ammonium nitrate is allowed to stand for 4-10 hours under sealed conditions at 110-130°C for ion exchange. After drying, it is calcined at 500-600°C for 4-6 hours to obtain regenerated ZSM-5 molecular sieve.

2. The method for preparing regenerated molecular sieves according to claim 1, characterized in that: In step three, when adding the regenerated molecular sieve seed crystals, the amount of regenerated molecular sieve seed crystals added is 5% to 30% of the weight of the final regenerated ZSM-5 molecular sieve.