Hydrothermal treatment method for improving stability of Beta molecular sieve framework

Abstract

The invention discloses a hydrothermal treatment method for improving the stability of a Beta molecular sieve framework, and belongs to the technical field of material preparation. According to the method, the dealumination Beta molecular sieve is subjected to hydro-thermal treatment twice or multiple times, and re-dealumination and silicon atom rearrangement are realized through hydro-thermal treatment, so that a skeleton structure is more stable, and the stability of a catalyst constructed by taking the molecular sieve as a carrier is improved. The temperature range of the hydrothermal treatment is 80-160 DEG C, and the treatment time range is 5 minutes to 10 hours. The method is simple in process and convenient to operate, can effectively improve the stability of the Beta molecular sieve carrier and prolong the service life of the Beta molecular sieve carrier, and can be widely applied to the fields of petrochemical engineering, fine chemical engineering, environmental protection and the like.

Description

Technical Field

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

[0002] Molecular sieves are a class of microporous crystalline materials with regular pore structures. Due to their unique physicochemical properties, they are widely used in catalysis, adsorption separation, and other fields. Among them, Beta molecular sieves, with their three-dimensional twelve-membered ring pore structure and excellent catalytic performance, have important applications in petrochemicals and fine chemicals. However, native Beta molecular sieves have a high framework aluminum content (SiO2 / Al2O3 is usually 20-50). Under harsh reaction conditions such as high temperature (>300℃) and steam, framework aluminum is easily removed, forming non-framework aluminum species, leading to the following problems: ① Increased nesting defects of framework silanol groups, causing crystal structure collapse; ② Pore blockage or deformation, resulting in a sharp decrease in mass transfer efficiency; ③ Disordered distribution of acidic sites, accelerating the rate of coking and deactivation. Therefore, dealumination modification of Beta molecular sieves and simultaneous enhancement of framework stability are key to solving their industrial application bottlenecks.

[0003] Currently, the main methods for dealumination modification of molecular sieves include hydrothermal treatment, acid treatment, and chemical treatment. Among them, hydrothermal treatment is a commonly used dealumination method. It removes aluminum atoms from the molecular sieve framework through high-temperature steam treatment, forming silanol nests. Then, silicon atoms migrate to fill the defects, thereby achieving the reconstruction and stabilization of the molecular sieve framework.

[0004] In the prior art, CN100406383C discloses a method for preparing deeply dealuded Y zeolite. This method employs a combination of two hydrothermal treatments, ammonium salt exchange, and acid treatment. The second hydrothermal treatment temperature is higher than the first, resulting in Y zeolite products with high crystallinity, high silica-to-alumina ratio, and abundant secondary pores. CN1170634C describes a method for preparing high-silica Y zeolite, including subjecting NaY zeolite or Y-type zeolite that has undergone ultrastabilization treatment to one or more ammonium exchange, hydrothermal treatment, and / or chemical dealuding. Its key feature is the use of low-temperature selective ammonium exchange. CN100408477C proposes a method for preparing highly crystallinity modified Y zeolite. This method includes steps such as ammonium exchange, hydrothermal treatment, secondary exchange dealuding under pH control, secondary hydrothermal treatment, and chemical dealuding, yielding Y zeolite with a cell parameter of 2.425–2.435 nm and a relative crystallinity ≥95%. CN1031500C discloses a novel method for preparing high-silica Y zeolite, which combines chemical dealuding and hydrothermal treatment processes, using them alternately to treat NaY zeolite. CN100572275C describes a method for modifying Y molecular sieves, in which a surfactant is added during acid dealuding to achieve a high SiO2 / Al2O3 ratio while maintaining high crystallinity.

[0005] However, the aforementioned methods mainly target the modification of Y-type molecular sieves, with relatively little research on the modification of dealubilized Beta molecular sieves. Compared to Y-type molecular sieves, dealubilized Beta molecular sieves have different structural characteristics and stability issues. Existing modification methods applied to dealubilized Beta molecular sieves often encounter the following problems: First, a single hydrothermal treatment is insufficient to achieve effective removal of framework aluminum and sufficient rearrangement of silicon atoms, resulting in insufficient stability of the dealubilized Beta molecular sieve framework; second, improper control of hydrothermal treatment conditions, such as excessively high temperatures or prolonged treatment times, can easily lead to excessive destruction of the molecular sieve structure and a significant decrease in crystallinity; third, when dealubilized Beta molecular sieves are used as catalyst supports, their stability is still not ideal, and structural collapse easily occurs during catalytic reactions, leading to catalyst deactivation. Summary of the Invention The purpose of this invention is to overcome the shortcomings of the prior art and provide a hydrothermal treatment method to improve the stability of the Beta molecular sieve framework, solve the problem of poor stability of catalysts prepared using dealusized Beta molecular sieves as supports, improve the stability of catalysts prepared using dealusized Beta molecular sieves as supports, and provide a method to stabilize the framework by using hydrothermal treatment to rearrange silicon atoms.

[0006] The technical solution of this invention: A hydrothermal treatment method for improving the stability of a Beta molecular sieve framework is disclosed. The method involves performing secondary or multiple hydrothermal treatments on the dealuded Beta molecular sieve framework material to achieve secondary dealuding and silicon atom rearrangement, thereby obtaining a catalyst support with higher stability.

[0007] Preferably, the dealuated Beta molecular sieve is added to an aqueous mixture, heated to a certain temperature, kept at that temperature, and then cooled to room temperature. It is then washed with deionized water, and the above heating and holding process is repeated two or more times by adding an organic amine and a deionized water mixture.

[0008] More preferably, the hydrothermal treatment involves at least two gradient heating hydrothermal treatments, with the second treatment temperature being higher than the first.

[0009] More preferably, the temperature range is 80-160℃.

[0010] More preferably, the time range is from 5 minutes to 10 hours.

[0011] More preferably, the water treatment solution is a mixture of organic amine and deionized water, wherein the mass concentration of organic amine is 0.01~20%.

[0012] More preferably, the organic amine used includes one or more of n-butylamine, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide. More preferably, the organic amine and deionized mixture used also contains additives, including a silicon source and a fluoride; the silicon source has a mass concentration of 0.05%-5% based on SiO2, the fluoride has a mass concentration of 0.01%-1.0%, and tetraethylammonium bromide has a mass concentration of 0.1-1.0%.

[0013] More preferably, the silicon source is orthosilicic acid or orthosilicate; the fluoride is ammonium fluoride or ammonium hydrogen fluoride.

[0014] More preferably, the water treatment solution comprises the following components by mass fraction: 0.3%-0.8% tetrabutylphosphine bromide, 2-6% starch, 0.2-0.5% sodium silicate, 0.1-1.0% ammonium fluoride, and the balance being water. Beneficial effects of the present invention By employing secondary or multiple hydrothermal treatments to process dealugenized Beta molecular sieves, the rearrangement of silicon atoms within the sieve framework can be promoted, effectively repairing framework defects generated during dealumination and resulting in a more stable molecular sieve framework structure. Compared to existing technologies, the dealugenized Beta molecular sieves treated using this method exhibit significantly improved stability when used as catalyst supports, maintaining good structural integrity during catalytic reactions and extending catalyst lifespan. Furthermore, by controlling the hydrothermal treatment temperature within the range of 80-160℃ and the treatment time within the range of 5 minutes to 10 hours, optimal treatment conditions can be adjusted according to different degrees of dealumination in the Beta molecular sieves to obtain the best framework stabilization effect, thus providing a stable and reliable support material for the preparation of high-performance catalysts.

[0015] The first step achieves mild dealumination and framework activation through an organic amine-tetraethylammonium bromide system. Tetraethylammonium bromide and organic amines are structurally homologous, which reduces the mass transfer resistance of the treatment solution within the micropores, guiding the silicon source and fluoride to precisely target dealumination defects. The second step achieves deep silicon replenishment and mesoporous construction through a tetrabutylphosphine bromide-starch system. Starch acts as a soft template to form hierarchical channels, while tetrabutylphosphine bromide enhances stability through phosphorus-oxygen bonds with the framework silicon. This mechanism resulted in a crystallinity retention rate of 69.5-73.1% after aging in steam at 300℃ for 120 hours.

[0016] All added components (C, H, O, N, Si, F, P) can be completely decomposed or volatilized during subsequent calcination at 550-600℃, leaving no metal or heteroatom residues on the final support. The stepwise treatment forms a microporous-mesoporous hierarchical pore structure, achieving a BET specific surface area retention rate of 76.9-80.5%, which is 49.9-57.2% higher than that of the one-step mixing treatment. This process retains the shape-selective catalytic properties of Beta molecular sieves while overcoming the diffusion limitations of macromolecular reactants, making the support suitable for reactions that traditional supports struggle with, such as heavy oil cracking and macromolecular oxidation.

[0017] The dealuminolized Beta molecular sieve treated by the method of this invention exhibits a fundamentally enhanced skeletal integrity. After aging with steam at 300°C for 120 hours, its crystallinity retention rate can reach over 73%. Its microporous structure is perfectly restored and maintained. Attached Figure Description

[0018] Figure 1 The nitrogen adsorption-desorption curve of the modified molecular sieve obtained in Example 1 is shown below. Figure 2 The nitrogen adsorption-desorption curves after hydrothermal treatment of the molecular sieve obtained in Example 1 are shown. Detailed Implementation

[0019] 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.

[0020] Example 1 (Composite treatment solution, gradient temperature treatment) Step 1: Prepare composite treatment solution 1: Take 50 ml of deionized water, add 2.5 g of tetraethylammonium hydroxide (40% aqueous solution, equivalent to a pure product concentration of about 2%), 0.1 g of sodium silicate (concentration of about 0.2%), 0.025 g of ammonium fluoride (concentration of 0.05%) and 0.05 g of tetraethylammonium bromide (concentration of 0.1%), and stir until homogeneous; Prepare composite treatment solution 2: 50mL deionized water + 0.15g tetrabutylphosphine bromide (concentration 0.3%) + 1g starch (concentration 2%) + 0.1g sodium silicate (concentration 0.2% based on SiO2) + 0.05g ammonium fluoride (concentration 0.1%), stir until the starch is evenly dispersed.

[0021] Step 2: Add 1.0 g of dealuminized Beta molecular sieve (SiO2 / Al2O3 molar ratio = 150) to composite treatment solution 1, disperse it by ultrasonication, and then transfer it to a 100 ml stainless steel reactor lined with polytetrafluoroethylene and seal it.

[0022] Step 3, First hydrothermal treatment: The temperature is raised to 100℃ and held at that temperature for 3 hours. After cooling naturally to room temperature, the mixture is centrifuged, washed with deionized water until neutral, and then dried at 100℃ for 2 hours.

[0023] Step 4, Second hydrothermal treatment: The dried intermediate is redispersed in composite treatment solution 2 and transferred to a sealed reactor. The reactor is heated to 140°C and kept at that temperature for 4 hours, followed by cooling and washing.

[0024] Step 5: Dry the final product at 100°C for 12 hours to obtain a highly stable dealuminated Beta molecular sieve support S1.

[0025] Example 2 (composite treatment solution, multiple treatments at constant temperature) Based on Example 1, the difference is that the temperature in steps 3 and 4 is 120°C, resulting in carrier S2.

[0026] Example 3 (Investigating the effect of surfactant concentration): The treatment steps were exactly the same as in Example 1, except that the amount of tetraethylammonium bromide in the composite treatment solution 1 was adjusted to 0.25 g (concentration of 0.5%), and the carrier S3 was obtained.

[0027] Example 4 (Investigating the effect of fluoride concentration): The treatment steps were exactly the same as in Example 1, except that the amount of ammonium fluoride in the composite treatment solution 1 was adjusted to 0.005 g (concentration of 0.01%), and the carrier S4 was obtained.

[0028] Example 5: Three-Step Heating Treatment Based on Example 1, the hydrothermal treatment conditions were changed: First treatment: 80℃, 2 hours, compound treatment solution 1.

[0029] Second treatment: 120℃, 2 hours, compound treatment solution 2.

[0030] Third treatment: 140℃, 2 hours, compound treatment solution 2.

[0031] (The treatment solution was replaced with fresh solution each time, and washing and drying were performed in between). The rest was the same as in Example 1, and the carrier S5 was obtained.

[0032] Example 6 Two High-Temperature Short-Time Treatments Based on Example 1, the hydrothermal treatment conditions were changed: First treatment: 140℃, 2 hours.

[0033] Second treatment: 160℃, 1 hour. Other steps are the same as in Example 1, yielding carrier S6.

[0034] Comparative Example 1 (Ternary system, without surfactant) The processing steps are exactly the same as in Example 1, but with composite treatment liquid 1 but without the addition of tetraethylammonium bromide, to obtain carrier D1.

[0035] Comparative Example 2 only involved organic amine treatment (corresponding to the original scheme). The processing steps are exactly the same as in Example 1, except that the composite treatment solution 1 is only a 5% tetraethylammonium hydroxide aqueous solution, without silicon source, fluorine source, or surfactant. Carrier D2 is obtained.

[0036] Comparative Example 3 (Comparison with Common Surfactants) The processing steps were exactly the same as in Example 1, except that the tetraethylammonium bromide of the composite treatment solution 1 was replaced with an equal mass (0.05 g) of sodium dodecyl sulfate (SDS) to obtain carrier D3.

[0037] Comparative Example 4 (Pure Water Heat Treatment) One gram of dealuated Beta molecular sieve was placed in 50 ml of deionized water, heated to 160°C under sealed conditions, kept at that temperature for 1 hour, and then cooled to room temperature. The mixture was washed three times with deionized water and dried to obtain carrier D4.

[0038] Comparative Example 5 (New system without biological template) The processing steps are exactly the same as in Example 1, but no starch is added to the composite treatment liquid 2 to obtain carrier D5. Comparative Example 6 (Starch Replacement) The processing steps were exactly the same as in Example 1, except that the starch in the composite treatment solution 2 was replaced with an equal mass of a conventional polymer (such as polyethylene glycol PEG-20000). Carrier D6 was obtained.

[0039] Comparative Example 7 (without tetrabutylphosphine bromide) The processing steps were exactly the same as in Example 1, except that tetrabutylphosphine bromide was removed from the composite treatment solution 2. This yielded carrier D7.

[0040] Comparative Example 8 (order reversed) The first step involves heat treatment with composite treatment solution 2, followed by a second step heat treatment with composite treatment solution 1. This yields carrier D8.

[0041] Comparative Example 9 The first step is omitted: the original dealuated Beta molecular sieve is directly subjected to a hydrothermal treatment (140°C, 4 hours) using treatment solution 2. Other treatment steps are exactly the same as in Example 1, resulting in carrier D9.

[0042] Comparative Example 10 One-step mixing method: Mix all components of composite treatment liquid 1 and composite treatment liquid 2 at one time, and perform hydrothermal treatment on the molecular sieve once (e.g., 120°C, 5 hours). Other steps are the same as in Example 1 to obtain carrier D10.

[0043] Comparative Example 11 (without any post-processing) One gram of dealuated Beta molecular sieve was washed three times with deionized water without any hydrothermal treatment and dried at 100°C to obtain carrier D11. Catalytic performance evaluation: All the supports obtained above were loaded with 5 wt% of the active component Sn using an equal-volume impregnation method, and then dried and calcined to prepare the catalyst. Its stability was evaluated in the reaction of fructose dehydration to prepare 5-hydroxymethylfurfural (5-HMF), and the key data are compared in Table 1 below: Method for preparing the catalyst: Weigh 0.11 g SnCl4, dissolve it in 5 mL of deionized water, then weigh 1 g of the dealuated Beta molecular sieve support obtained above, add it to the above solution, stir, dry, and calcine at 600℃ for 2 h to obtain the catalyst.

[0044] Method for dehydrating fructose to produce 5-HMF: Prepare a mixture of deionized water and acetone at a mass ratio of 1:9, then add 10% fructose to prepare the reaction solution. Pump the solution into a reactor containing a catalyst at a certain flow rate and react continuously at 180°C. Take samples for HPLC analysis to determine the conversion rate and yield.

[0045] Hydrothermal aging method: The molecular sieve is treated under 300℃ steam for 120 h.

[0046] Crystallinity analysis method: After XRD characterization, the Scherrer formula was used for calculation.

[0047] Table 1

[0048] Comparative Examples D9 (step 1 omitted) and D10 (one-step mixing method) were among the worst performing groups of all samples. Their various indicators (crystallinity retention of approximately 48%, selectivity retention of approximately 57%) were even close to the destructive effect of pure hydrothermal treatment (D4), far lower than the core Example S1 (crystallinity retention of 73.1%, selectivity retention of 91.6%). This indicates that the first step (organic amine system) is not a simple pretreatment, but rather creates an indispensable activating framework for the second step: it may achieve controllable preliminary dealumination, open the channel for subsequent deep repair, and form a surface chemical environment conducive to the action of organophosphine templates. The two-step method avoids mutual interference of key components: the failure of one-step mixing (D10) shows that if all components such as organic amines, organophosphines, and starch are mixed simultaneously, complex side reactions or competitive adsorption may occur between them, canceling out their positive effects and leading to complete repair failure. Only through sequential and isolated reaction environments can the chemical reactions of each step proceed in an orderly and efficient manner. The performance of comparative example D8 (in reverse order) (crystallization retention rate of 56.8%) was significantly lower than that of S1, indicating that the activation in the first step is a prerequisite for the deep repair in the second step, and the reverse operation cannot achieve the expected stabilization effect.

[0049] 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 hydrothermal treatment method for improving the stability of a Beta molecular sieve framework, characterized in that, The method involves performing secondary or multiple hydrothermal treatments on the dealuded Beta molecular sieve framework material. The hydrothermal treatment achieves secondary dealuding and silicon removal, thereby improving the stability of the Beta molecular sieve framework.

2. The hydrothermal treatment method for improving the stability of the Beta molecular sieve framework according to claim 1, characterized in that, The hydrothermal treatment involves at least two gradient heating processes, with the second process being at a higher temperature than the first.

3. The hydrothermal treatment method for improving the stability of the Beta molecular sieve framework according to claim 1 or 2, characterized in that, The temperature range is 80-160℃.

4. The hydrothermal treatment method for improving the stability of the Beta molecular sieve framework according to claim 1 or 2, characterized in that, The time range is 5 minutes to 10 hours.

5. The hydrothermal treatment method for improving the stability of the Beta molecular sieve framework according to claim 1, characterized in that, The water treatment solution is a mixture of organic amine and deionized water, with the organic amine mass concentration ranging from 0.01% to 20%.

6. The hydrothermal treatment method for improving the stability of the Beta molecular sieve framework according to claim 5, characterized in that, The organic amines used include one or more of n-butylamine, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide.

7. The hydrothermal treatment method for improving the stability of the Beta molecular sieve framework according to claim 5 or 6, characterized in that, The organic amine and deionized mixture used also contains additives, including a silicon source and fluorides; the silicon source has a mass concentration of 0.05%-5% based on SiO2, the fluoride has a mass concentration of 0.01%-1.0%, and tetraethylammonium bromide has a mass concentration of 0.1-1.0%; the silicon source is orthosilicic acid or orthosilicate; the fluoride is ammonium fluoride or ammonium hydrogen fluoride.

8. The hydrothermal treatment method for improving the stability of the Beta molecular sieve framework according to claim 1, characterized in that, The water treatment solution comprises the following components by mass fraction: 0.3%-0.8% tetrabutylphosphine bromide, 2-6% starch, 0.2-0.5% sodium silicate, 0.1-1.0% ammonium fluoride, with the balance being water.

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