Water vapor treatment method for improving stability of molecular sieve framework

Abstract

The invention discloses a water vapor treatment method for improving the stability of a molecular sieve framework, and belongs to the technical field of molecular sieve material modification. The method aims at solving the problems that the structure of an existing molecular sieve carrier is easy to collapse in a hydrothermal environment, and an acid center is easy to lose. The core of the method is that the molecular sieve carrier is subjected to multi-stage treatment by adopting water vapor at different temperatures and different time. The method comprises the following steps: firstly, carrying out preliminary hydrothermal treatment under relatively mild conditions, and inducing migration and preliminary condensation of part of silicon hydroxyl in a molecular sieve framework; and then deep treatment is carried out under the harsh condition, framework silicon atoms are promoted to be rearranged and migrated more sufficiently, structural defects are filled up, and a more stable Si-O-Si network structure is formed. Through the gradient type hydrothermal activation process, the hydrothermal stability and mechanical strength of the molecular sieve framework are remarkably enhanced on the premise of not remarkably losing the specific surface area and acidity. The method is simple in process, low in cost and suitable for pretreatment of molecular sieve catalyst carriers with high hydrothermal stability requirements in reactions of petrochemical engineering, fine chemical engineering and the like.

Description

A steam treatment method to improve the stability of molecular sieve framework Technical Field

[0001] This invention belongs to the field of molecular sieve material modification technology, specifically relating to a water steam treatment method for improving the stability of the molecular sieve framework. Background Technology

[0002] Molecular sieves are crystalline aluminosilicate materials with regular pore structures. Due to their excellent shape-selective catalytic performance, high specific surface area, and tunable acidity, they are widely used in petrochemical, fine chemical, and environmental protection fields as catalysts, adsorbents, and ion exchangers.

[0003] However, in many industrial catalytic processes, the framework structure of molecular sieves is easily damaged. Specifically, this manifests in two ways: 1) framework aluminum is easily removed, leading to the loss of acidic centers and a decrease in catalyst activity; 2) silicon-oxygen bonds break, the framework collapses, the pore structure is destroyed, the specific surface area decreases sharply, and ultimately, the catalyst is completely deactivated. Therefore, improving the hydrothermal stability of molecular sieves is a key technical challenge for extending catalyst life and improving process economy.

[0004] Currently, the main methods for improving the stability of molecular sieves include heteroatom doping: introducing heteroatoms into the molecular sieve through ion exchange to block pores and stabilize the aluminum framework. However, this method is costly and may partially block the pores, affecting reactant diffusion. CN116354362B reports a method for introducing Cu ions into ZSM-5 molecular sieves, which significantly improves stability.

[0005] Phosphorus modification: CN116477638B reports a method for modifying molecular sieves with phosphate compounds. By treating the molecular sieves with phosphorus-containing compounds, PO-Al bonds are formed on the framework, stabilizing the aluminum framework.

[0006] The methods described above all have certain limitations. Therefore, developing a new method that is simple in process, low in cost, and can effectively improve the intrinsic framework stability of molecular sieves is of great industrial significance. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a water vapor treatment method to improve the stability of molecular sieve frameworks. By precisely controlling the gradient and process of water vapor treatment, the directional migration and rearrangement of silicon atoms in the molecular sieve framework are achieved, thereby fundamentally strengthening its framework structure without introducing foreign elements. The technical solution of this invention is as follows: Pretreatment: The molecular sieve support to be treated is dried at 100-150℃ for 2-12 hours to remove physically adsorbed water.

[0008] First-stage hydrothermal treatment: The dried molecular sieve is placed in a water vapor atmosphere and treated for 0.5-3 hours at a temperature of 300-550℃ and normal pressure. The water vapor atmosphere is a mixture of water vapor and nitrogen or air with a volume fraction of 20%-80%.

[0009] Secondary hydrothermal treatment: The molecular sieve after primary treatment is treated at a temperature of 500-800℃ and at normal pressure for 1-6 hours. The water vapor atmosphere is a mixture of water vapor and nitrogen or air with a volume fraction of 60%-100%.

[0010] Post-treatment: The molecular sieve after secondary treatment is calcined in dry air at 400-550℃ for 2-6 hours to remove any possible residual carbon deposits and other impurities, thereby obtaining a highly stable molecular sieve support.

[0011] Preferably, the molecular sieve is one of Y-type, ZSM-5, Beta, MCM-22 or MOR-type molecular sieves.

[0012] Preferably, the temperature of the first-stage steam treatment is 450-500℃, the time is 1-2 hours, and the volume fraction of steam is 30%-50%.

[0013] Preferably, the temperature of the secondary steam treatment is 650-700℃, the time is 2-4 hours, and the volume fraction of steam is 80%-100%.

[0014] The highly stable dealuded Beta molecular sieve carrier obtained by this invention can be applied to, but is not limited to, petroleum reforming and biomass conversion.

[0015] The beneficial effects of this invention: This invention employs a two-stage hydrothermal treatment strategy of "mild first, then vigorous." The first stage, acting as a "preheating" and "induction" phase, allows unstable silanol groups in the molecular sieve framework to migrate and undergo initial condensation reactions under relatively mild conditions, preparing for subsequent deeper treatments and avoiding structural damage caused by abrupt changes in conditions. The second stage, conducted at a higher temperature, provides sufficient energy for the long-range migration and rearrangement of silicon atoms, enabling them to effectively fill vacancies left by dealumination or lattice defects, forming a more complete and stable Si-O-Si network structure, thereby significantly improving the overall stability of the framework. This method does not introduce any foreign metal or non-metal elements, and the treated molecular sieve maintains a high specific surface area and pore volume while significantly improving its stability. The entire process involves only the control of water vapor and temperature, making it simple to operate, easy to scale up for industrial production, and highly economical. Attached Figure Description

[0016] Figure 1 shows the nitrogen adsorption-desorption curve of the modified molecular sieve obtained in Example 1; Figure 2 shows the nitrogen adsorption-desorption curve of the molecular sieve obtained in Example 1 after hydrothermal treatment. Detailed Implementation

[0017] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments and accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0018] Example 1: 10 g of commercially available NaY molecular sieve (SiO2 / Al2O3 molar ratio of 5.1) was dried at 120°C for 4 hours.

[0019] Primary treatment: The dried NaY molecular sieve was placed in a tube furnace and a mixed gas consisting of 40% water vapor and 60% nitrogen (volume fraction) was introduced and treated at 480°C for 1.5 hours.

[0020] Secondary treatment: Subsequently, the system temperature was raised to 680°C, and 100% water vapor was introduced. The system was then treated for 3 hours under the same atmosphere.

[0021] Post-processing: After the processing is completed, the sample is calcined in dry air at 500℃ for 4 hours to obtain the final modified molecular sieve sample, denoted as Sample-1.

[0022] The obtained carrier was impregnated with the active metal Sn using a common method. Specifically, 0.1 g of SnCl4 was weighed and dissolved in 5 mL of deionized water, and 1 g of Sample-1 was weighed and added to the above solution. The mixture was stirred, dried, and calcined at 600 °C for 2 h to obtain Cat.-1.

[0023] Example 2: Take 10 grams of NaY molecular sieve from the same batch as in Example 1 and dry it at 120°C for 4 hours.

[0024] Primary treatment: A mixture of 30% water vapor and 70% air is introduced and treated at 460°C for 2 hours.

[0025] Secondary treatment: Raise the temperature to 700℃, switch to a mixture of 90% water vapor and 10% air, and treat for 2 hours.

[0026] Post-processing: After the processing is completed, the sample is calcined in dry air at 500℃ for 4 hours to obtain the final modified molecular sieve sample, denoted as Sample-2.

[0027] The obtained support was impregnated with the active metal Sn using a common method. Specifically, 0.1 g of SnCl4 was weighed and dissolved in 5 mL of deionized water, and then 1 g of Sample-2 was weighed and added to the above solution. The mixture was stirred, dried, and calcined at 600 °C for 2 h to obtain Cat.-2. In Example 3, 10 g of NaY molecular sieve from the same batch as in Example 1 was dried at 120 °C for 4 hours.

[0028] Primary treatment: The dried NaY molecular sieve was placed in a tube furnace and a mixed gas consisting of 40% water vapor and 60% nitrogen (volume fraction) was introduced and treated at 300°C for 1.5 hours.

[0029] Secondary treatment: Subsequently, the system temperature was raised to 680°C, and 100% water vapor was introduced. The system was then treated for 3 hours under the same atmosphere.

[0030] Post-processing: After the processing is completed, the sample is calcined in dry air at 500℃ for 4 hours to obtain the final modified molecular sieve sample, denoted as Sample-3.

[0031] The obtained support was impregnated with the active metal Sn using a common method. Specifically, 0.1 g of SnCl4 was weighed and dissolved in 5 mL of deionized water, and then 1 g of Sample-3 was weighed and added to the above solution. The mixture was stirred, dried, and calcined at 600 °C for 2 h to obtain Cat.-3. In Example 4, 10 g of NaY molecular sieve from the same batch as in Example 1 was dried at 120 °C for 4 hours.

[0032] Primary treatment: The dried NaY molecular sieve was placed in a tube furnace and a mixed gas consisting of 40% water vapor and 60% nitrogen (volume fraction) was introduced and treated at 480°C for 1.5 hours.

[0033] Secondary treatment: Subsequently, the system temperature was raised to 800℃, and 100% water vapor was introduced for treatment under the same atmosphere for 3 hours.

[0034] Post-processing: After the processing is completed, the sample is calcined in dry air at 500℃ for 4 hours to obtain the final modified molecular sieve sample, denoted as Sample-4.

[0035] The obtained support was impregnated with the active metal Sn using a common method. Specifically, 0.1 g of SnCl4 was weighed and dissolved in 5 mL of deionized water, and then 1 g of Sample-4 was weighed and added to the above solution. The mixture was stirred, dried, and calcined at 600 °C for 2 h to obtain Cat.-4. In Example 5, 10 g of NaY molecular sieve from the same batch as in Example 1 was dried at 120 °C for 4 hours.

[0036] Primary treatment: The dried NaY molecular sieve was placed in a tube furnace and a mixed gas consisting of 40% water vapor and 60% nitrogen (volume fraction) was introduced and treated at 400°C for 1.5 hours.

[0037] Secondary treatment: Subsequently, the system temperature was raised to 500°C, and 100% water vapor was introduced. The system was then treated for 3 hours under the same atmosphere.

[0038] Post-processing: After the processing is completed, the sample is calcined in dry air at 500℃ for 4 hours to obtain the final modified molecular sieve sample, denoted as Sample-5.

[0039] The obtained support was impregnated with the active metal Sn using a common method. Specifically, 0.1 g of SnCl4 was weighed and dissolved in 5 mL of deionized water, and then 1 g of Sample-5 was weighed and added to the above solution. The mixture was stirred, dried, and calcined at 600 °C for 2 h to obtain Cat.-5. For Comparative Example 1, 10 g of NaY molecular sieve from the same batch as in Example 1 was subjected to a first-stage hydrothermal treatment under the same conditions as in Example 1 (480 °C, a mixed gas consisting of 40% water vapor and 60% nitrogen (volume fraction), for 1.5 h), and then directly calcined at 500 °C for 4 h to obtain the sample, denoted as Comparative-1.

[0040] The obtained support was impregnated with the active metal Sn using a common method. Specifically, 0.1 g of SnCl4 was weighed and dissolved in 5 mL of deionized water, and 1 g of Comparative-1 was weighed and added to the above solution. The mixture was stirred, dried, and calcined at 600 °C for 2 h to obtain Cat.-6.

[0041] Comparative Example 2: 10 grams of NaY molecular sieve from the same batch as in Example 1 were directly subjected to a second-stage hydrothermal treatment (680°C, 100% steam, 3 hours) under the same conditions as in Example 1, without the first-stage hydrothermal treatment. Then, the sample was calcined at 500°C for 4 hours to obtain the sample, which was denoted as Comparative-2.

[0042] The obtained support was impregnated with the active metal Sn using a common method. Specifically, 0.1 g of SnCl4 was weighed and dissolved in 5 mL of deionized water, and then 1 g of Comparative-2 was weighed and added to the above solution. The mixture was stirred, dried, and calcined at 600°C for 2 h to obtain Cat.-7. For Comparative Example 3, 10 g of NaY molecular sieve from the same batch as in Example 1 was subjected to a single-stage hydrothermal treatment (480°C, 100% steam, 1.5 h), followed by direct calcination at 500°C for 4 h to obtain the sample, designated Comparative-3.

[0043] The obtained support was impregnated with the active metal Sn using a common method. Specifically, 0.1 g of SnCl4 was weighed and dissolved in 5 mL of deionized water, and 1 g of Comparative-3 was weighed and added to the above solution. The mixture was stirred, dried, and calcined at 600 °C for 2 h to obtain Cat.-8.

[0044] The molecular sieve samples obtained in Examples 1 to 5 and Comparative Examples 1 to 3, as well as the original NaY molecular sieve (denoted as Original), were subjected to accelerated aging experiments at 800°C and 100% water vapor atmosphere for 4 hours to simulate a harsh hydrothermal environment. X-ray diffraction (XRD) crystallinity analysis and specific surface area (BET) determination were performed on the samples before and after aging. The results are shown in Table 1 below: Table 1

[0045] The catalysts obtained in Examples 1 to 5 and Comparative Examples 1 to 3 were applied to the fructose dehydration reaction to produce 5-HMF. The reaction conditions were as follows: a mixture of deionized water and acetone with a mass ratio of 1:9 was prepared, and fructose with a mass fraction of 10% was added to prepare the reaction solution. The solution was pumped into a reactor containing the catalyst at a certain flow rate and reacted continuously at 180°C. Samples were taken for HPLC analysis to determine the conversion rate and yield.

[0046] The changes in conversion rate and selectivity before and after 180 h of reaction are shown in Table 2 below: Table 2

[0047] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for improving the stability of molecular sieve supports, characterized in that, Includes the following steps: a) Pre-treat and dry the molecular sieve support; b) subject the dried molecular sieve support to a first heat treatment at 300-550℃ for 0.5-3 hours under a primary steam atmosphere; c) subject the molecular sieve support treated in step b) to a second heat treatment at 500-800℃ for 1-6 hours under a secondary steam atmosphere, wherein the steam concentration in the secondary steam atmosphere is higher than that in the primary steam atmosphere; d) calcine the molecular sieve support treated in step c) to obtain a highly stable molecular sieve support.

2. The method according to claim 1, characterized in that, The primary water vapor atmosphere is a mixture of nitrogen or air containing 20%-80% water vapor by volume.

3. The method according to claim 1 or 2, characterized in that, The secondary water vapor atmosphere is a mixture of nitrogen or air containing 60%-100% water vapor by volume.

4. The method according to claim 1, characterized in that, The temperature of the first-stage steam treatment is 450-500℃, and the time is 1-2 hours.

5. The method according to claim 1, characterized in that, The secondary steam treatment is carried out at a temperature of 650-700℃ for 2-4 hours.

6. The method according to claim 1, characterized in that, The molecular sieve carrier is a Y-type, ZSM-5, Beta, MCM-22, or MOR-type molecular sieve.

7. The method according to claim 1, characterized in that, The calcination described in step d) is carried out in dry air at 400-550°C for 2-6 hours.

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