Layered nano silicon-aluminum molecular sieve catalyst as well as preparation method and application thereof

Abstract

The invention discloses a layered nano silicon-aluminum molecular sieve catalyst as well as a preparation method and application thereof, and relates to the technical field of catalysts. According to the technical scheme, the preparation method comprises the following steps: mixing, heating and uniformly stirring a silicon source, an alkali source, deionized water, a structure-directing agent, a surfactant and a peptizing aid to obtain silicon pre-hydrolysate; the preparation method comprises the following steps: mixing an aluminum source, an alkali source, deionized water, a structure-directing agent, a surfactant and a peptizing aid, heating and uniformly stirring to obtain aluminum pre-hydrolysate; adding the silicon pre-hydrolysate and the aluminum pre-hydrolysate into the crystallization mother liquor in a stirring state in a parallel flow manner, and completing pre-crystallization; and transferring the pre-crystallized feed liquid into a crystallization kettle, crystallizing, curing, filtering, washing, drying and roasting to obtain the layered nano silicon-aluminum molecular sieve catalyst. The layered nano silicon-aluminum molecular sieve catalyst is used for acrolein hydration reaction, the reaction mass space velocity can reach 5h <-1 >, the reaction condition requirement is mild, the acrolein conversion rate is greater than 55%, and the 3-hydroxypropionaldehyde selectivity is greater than or equal to 92%.

Description

Technical Field

[0001] The present invention relates to the technical field of catalysts, and in particular to a layered nano-silicon-aluminum molecular sieve catalyst and a preparation method and application thereof. Background Art

[0002] 1,3-Propanediol (1,3-PDO) is a colorless, odorless, viscous liquid soluble in a variety of solvents, including water, alcohol, and ether. A key chemical raw material, 1,3-Propanediol is widely used in polyesters, polyurethanes, cosmetics, biodegradable plastics, pharmaceutical intermediates, inks, printing and dyeing, lubricants, and other fields. However, its primary use is as a polymer monomer, replacing ethylene glycol and butanediol in the production of polyol polyesters. This is used to manufacture high-performance new polyester fibers (PTT), which are then used in the apparel, carpet, electronics, and automotive markets. In recent years, 1,3-Propanediol has experienced rapid growth, primarily driven by the downstream PTT consumer market.

[0003] With the development of domestic PTT and the continuous maturity of the downstream market, the cost of 1,3-propylene glycol largely determines the market competitiveness of PTT. Optimizing and improving 1,3-propylene glycol production technology is the only way to reduce PTT production costs and accelerate the future market development of PTT. Therefore, the development of low-cost 1,3-propylene glycol products has become a research and development hotspot for scientific research institutes and enterprises.

[0004] The main technologies for synthesizing 1,3-propylene glycol include biological, propylene, and ethylene oxide methods. The production cost of biological methods for synthesizing 1,3-propylene glycol in China is high, while the propylene and ethylene oxide methods have yet to be commercialized. The propylene method involves oxidizing propylene to acrolein, which is then hydrated to produce 3-hydroxypropionaldehyde (3-HPA). This is then hydrogenated in two stages to produce 1,3-propylene glycol. The propylene method offers advantages such as a simple process, a well-defined catalyst system, and minimal equipment requirements.

[0005] The hydration of acrolein to 3-hydroxypropionaldehyde is a key step in the propylene-based process for producing 1,3-propylene glycol. Initially, inorganic acids were used as catalysts, but the reaction's selectivity and yield were low, and acrolein and 3-hydroxypropionaldehyde were prone to condensation or polymerization. To address these issues, weakly acidic ion exchange resins were employed as catalysts. However, these catalysts suffer from slow reaction rates, low space-time yields, and difficulty regenerating the catalyst after deactivation.

[0006] Degussa and Hoechst have successively researched and developed acidic catalysts with inorganic supports. Degussa used a catalyst with a surface area of 50m 2 / g TiO2 or γ-Al2O3 as a carrier, after impregnation treatment with H3PO4 or NaH2PO4 solution, a Ti-OP structure active catalyst was obtained. The acrolein hydration conversion rate obtained by the reaction was 50%, and the selectivity of 3-hydroxypropionaldehyde could reach 81%. Hoechst used ZSM-5 molecular sieve as the active component to prepare a catalyst. When the acrolein mass fraction was 18-19%, the reaction temperature was 80℃, and it was continuously operated for 1500h in a fixed bed reactor, the catalyst activity hardly changed, and the average acrolein conversion rate was about 44.3%, and the average selectivity of 3-hydroxypropionaldehyde was about 87.7%. DuPont used a pyridinium ion hydration catalyst, the reaction temperature was 45-60℃, and the reaction mass space velocity was 0.5-0.6h -1 The average conversion rate of acrolein per pass was 51%, and the average selectivity of 3-hydroxypropionaldehyde was 83%.

[0007] my country has also conducted extensive research and development on the reaction technology for hydrating acrolein to produce 3-hydroxypropionaldehyde in the propylene process for the preparation of 1,3-propylene glycol. CNOOC Tianjin Chemical Research and Design Institute uses modified molecular sieve catalysts and a fixed-bed reactor for the hydration reaction. Under low temperature and slightly positive pressure conditions, the average single-pass conversion rate of acrolein is >50%, and the average selectivity of 3-hydroxypropionaldehyde is >90%. Shanghai Petrochemical Co., Ltd. uses a mercaptocarboxylic acid resin catalyst and a fixed-bed hydration reactor. The reaction temperature is 45-55°C and the reaction mass space velocity is 0.5-0.75h. -1 The average conversion rate of acrolein per pass was 45%, and the average selectivity of 3-hydroxypropionaldehyde was 89%. PetroChina Lanzhou Chemical Research Institute used aminocarboxylic acid / aminophosphoric acid resin catalysts and a fixed bed reactor for the hydration reaction. The reaction temperature was 50-55°C and the reaction mass space velocity was 0.1-0.5h -1 The average conversion rate of acrolein per pass is ≥50%, the selectivity of 3-hydroxypropanal is ≥95%, and the overall yield is ≥47.5%. Shanghai Normal University uses aminocarboxylic acid / aminophosphoric acid resin catalyst and a fixed bed reactor for hydration reaction. The reaction temperature is 40-70℃ and the reaction mass space velocity is 0.5-1h -1 The average conversion rate of acrolein per pass was 53%, and the average selectivity of 3-hydroxypropionaldehyde was 89%. Heilongjiang Petrochemical Science Research Institute used modified cation exchange resin as a catalyst for acrolein hydration reaction, with an average conversion rate of acrolein per pass of >45% and a selectivity of 3-hydroxypropionaldehyde >85%. Shanghai Jiaotong University used a fixed-bed continuous flow reactor to investigate the stability of acrolein hydration reaction of chelated ion exchange resin, with a reaction mass space velocity of 1h -1 , the mass fraction of acrolein is 10-12%, the acrolein conversion rate is maintained at around 50%, and the 3-hydroxypropanal selectivity is maintained at 89%. The above acrolein hydration catalysts still have disadvantages such as low reaction mass space velocity, low processing capacity, low acrolein conversion rate, and low overall 3-hydroxypropionaldehyde product yield. Acrolein recovery and 3-hydroxypropionaldehyde purification steps need to be added at the end of the intermediate output, which cannot effectively balance material and energy consumption. The main reason is the insufficient stability of the catalyst. Taking resin catalysts as an example, during the reaction, the surface active groups fall off or H + The metal ions in the aqueous solution are exchanged away, which reduces the number of active centers and reduces the activity. Secondly, any catalyst with a porous structure, such as resin-type or molecular sieve-type catalysts, has the problem of surface active centers being covered by polymers generated during the reaction, which leads to a decrease in the number of active centers or an increase in internal diffusion resistance, and ultimately causes a rapid decline in catalytic activity, a decrease in the effective processing capacity of the device, and an increase in the pressure of the intermediate distillation separation and purification module, which brings technical limitations to pilot scale-up and industrial design. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a layered nano-silicon-aluminum molecular sieve catalyst and its preparation method and application, which can achieve a mass space velocity of 5h when used in the hydration reaction of acrolein. -1 , the reaction conditions are required to be milder, the acrolein conversion rate is greater than 55%, and the 3-hydroxypropionaldehyde selectivity is ≥92%.

[0009] The technical solution of the present invention is: In a first aspect, the present invention provides a method for preparing a layered nano-silicon-aluminum molecular sieve catalyst, comprising the following steps: S1: preparing silicon pre-hydrolysis solution: mixing silicon source, alkali source, deionized water, structure directing agent, surfactant, and peptization aid, heating and stirring uniformly to obtain silicon pre-hydrolysis solution; S2: preparing an aluminum pre-hydrolysis solution: mixing an aluminum source, an alkali source, deionized water, a structure directing agent, a surfactant, and a peptizing agent, heating and stirring the mixture to obtain an aluminum pre-hydrolysis solution; S3 parallel pre-crystallization: adding the silicon pre-hydrolyzed liquid and the aluminum pre-hydrolyzed liquid to the crystallization mother liquor in a stirred state in parallel to complete the pre-crystallization; S4 post-maturation treatment: the pre-crystallization liquid is transferred to a crystallization kettle for crystallization and aging, and a layered nano-silica-alumina molecular sieve catalyst is obtained after filtering, washing, drying and calcining.

[0010] Preferably, in step S1, the silicon source is silica sol, tetramethyl orthosilicate or tetraethyl orthosilicate; the silicon source accounts for 5-12 wt.% of all raw materials, calculated on the mass of silicon oxide, the alkali source accounts for 7.5-65 wt.%, the structure directing agent accounts for 0.5-15 wt.%, the surfactant accounts for 0.5-10 wt.%, and the peptization aid accounts for 0.2-12 wt.%.

[0011] Preferably, in step S2, the aluminum source is pseudo-boehmite, boehmite or alumina; the aluminum source accounts for 0.2-0.4 wt.% of all raw materials, calculated on the mass of alumina, the alkali source accounts for 5-20 wt.%, the structure directing agent accounts for 3-15 wt.%, the surfactant accounts for 0.5-10 wt.%, and the peptizing agent accounts for 0.2-12 wt.%.

[0012] Preferably, in step S1, the alkali source is tetraethylammonium chloride, tetraethylammonium bromide or tetraethylammonium hydroxide, the structure-directing agent is polydiallyldimethylammonium chloride, coconut shell cellulose or piperidine, and the peptizing agent is polyethylene glycol (PEG), polyvinyl pyrrolidone (PVP) or polyvinyl alcohol (PVA); in step S2, the alkali source is sodium hydroxide, potassium hydroxide or triethanolamine, the structure-directing agent is lignin, coconut shell cellulose or homopiperazine, and the peptizing agent is alkyl sulfonate (SAS), polyethylene glycol (PEG) or carboxymethyl cellulose (CMC); in steps S1 and S2, the surfactant is tetrabutylammonium bromide (TBAB), hexadecyltrimethylammonium bromide (CTAB) or polyvinyl butyral (PVB).

[0013] Preferably, in steps S1 and S2, the heating temperature is 30-60°C.

[0014] Preferably, in step S3, the molar ratio of silicon element to aluminum element in the silicon pre-hydrolysis solution and the aluminum pre-hydrolysis solution is (10-100):1; the stirring speed is 200-1000 r / min, and the pre-crystallization temperature is 50-100°C.

[0015] Preferably, in step S3, the crystallization mother liquor is a suspension of microcrystalline powder particles of an incompletely crystallized silica-alumina molecular sieve, and the preparation method is as follows: after mixing pseudo-boehmite, silica sol, deionized water and a peptization aid, heating and stirring at 60-80° C. to form a suspended emulsion; wherein, the pseudo-boehmite is 0.5-2 wt.% based on alumina, the silica sol is 1-3 wt.% based on silicon oxide, and the peptization aid is 5-10 wt.%; the peptization aid is polyvinyl pyrrolidone (PVP), polyethylene Then, dilute nitric acid or dilute hydrochloric acid is added dropwise to adjust the pH to 4-4.5. After constant reflux stirring for 60-100 minutes, it becomes a uniform colloidal white turbid liquid. No obvious solid particles are deposited by the naked eye. After cooling to room temperature, the colloidal white turbid liquid is transferred to a centrifuge and centrifuged at 2000-4500 r / min for 1-5 minutes. The upper layer of colloidal white turbid liquid with no solid particle deposition is collected, which is the crystallization mother liquor.

[0016] The crystallization mother liquor is a suspension of microcrystalline powder particles of silica-alumina molecular sieve that has not re-crystallized to maturity after peptization separation and crystallization. The presence of the crystallization mother liquor causes the structure-directing agent and surfactant to cluster around the highly dispersed microcrystals. The silicon pre-hydrolyzed solution and the aluminum pre-hydrolyzed solution continue to hydrolyze, crystallize, and grow on the microcrystal surfaces in a quantitative ratio, controlling the uniformity of crystal growth and the silicon-aluminum ratio within the framework, enhancing the effects of the structure-directing agent and surfactant, and promoting the stable formation of a layered nanostructure. However, if mature crystallized seed particles are added, the size of the mature crystallized particles and the exposed area of the crystal faces cannot be controlled. The silicon pre-hydrolyzed solution and the aluminum pre-hydrolyzed solution continue to hydrolyze, crystallize, and grow on the seed crystal surfaces, thereby losing the guiding effect of the structure-directing agent and surfactant. Controlling the system temperature and crystallization concentration will hardly change the crystal growth trend. Ultimately, the desired layered nanostructure will not be formed, and only a conventional disordered silica-alumina molecular sieve will be formed, which will affect its performance in catalyzing the acrolein hydration reaction.

[0017] Preferably, in step S4, the aging temperature is 80-200°C, and the aging time is 1-48h; forward and reverse bidirectional stirring is performed during the crystallization aging process, and the stirring speed is 10-200r / min; the drying temperature is 80-150°C, and the drying time is 1-24h; the roasting temperature is 350-850°C, and the roasting time is 1-12h.

[0018] In a second aspect, the present invention provides a layered nano-silica-alumina molecular sieve catalyst, which is prepared by the above-mentioned preparation method of the layered nano-silica-alumina molecular sieve catalyst.

[0019] In a third aspect, the present invention provides an application of the layered nano-silica-alumina molecular sieve catalyst, which is used for the hydration of acrolein to produce 3-hydroxypropionaldehyde, with a reaction mass space velocity of 1-5h -1 , the reaction temperature is 30-60°C, and the concentration of acrolein solution is 10-25wt.%.

[0020] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention provides a method for preparing a layered nano-silicon-aluminum molecular sieve catalyst. By preparing silicon and aluminum pre-hydrolyzed solutions of specific concentrations and formulations, and using a crystallization mother liquor as the base liquid, a co-current pre-crystallization method is employed. This method effectively controls the concentration balance of the two components during the synthesis of the silicon-aluminum molecular sieve, effectively ensuring the silicon-aluminum ratio embedded in the molecular sieve main structure during the pre-crystallization process. Simultaneously, dynamic pre-crystallization is employed to assist in ensuring uniform dispersion of fine seed crystals within the pre-crystallization feed solution, while also providing a favorable crystallization and maturation environment for the nano-layered molecular sieve structure.

[0021] 2. The preparation method of the layered nano-silicon-aluminum molecular sieve catalyst of the present invention selects a specific crystallization and maturation temperature and forward and reverse bidirectional rotation crystallization during the dynamic crystallization and maturation process of the pre-crystallization liquid, and the micro-crystallites grow uniformly to form layered crystal walls. The crystal walls are orderly stacked and combined into crystal barriers under the action of structure-directing agents and surfactants, and finally a layered nano-molecular sieve morphology is constructed.

[0022] 3. The preparation method of the layered nano-silica-alumina molecular sieve catalyst of the present invention is to obtain a typical MFI structure molecular sieve catalyst through post-aging treatment. The MFI structure belongs to a two-dimensional ten-membered ring pore system, which is composed of Z-shaped pores along the a-axis and straight pores along the b-axis. It has a uniform and adjustable pore system and has an enhancing effect on the selectivity of the acrolein hydration reaction. It has high crystallinity, large specific surface area and large pore volume. In addition, the structure has high hydrophobicity and excellent thermal stability. It can maintain high conversion rate and high selectivity under extreme reaction conditions, and there is no polymer aggregation and accumulation on the catalyst surface, which affects the catalyst life. After the MFI structure molecular sieve catalyst is formed and activated, it is used for the acrolein hydration reaction, and the reaction mass space velocity can reach 5h -1 , the reaction conditions require milder, higher raw material conversion rate (acrolein conversion rate > 55%) and higher product selectivity (3-hydroxypropionaldehyde selectivity ≥ 92%). BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is an SEM image of the layered nano-silica-alumina molecular sieve catalyst of Example 1 of the present invention.

[0024] Figure 2 This is an SEM image of the layered nano-silica-alumina molecular sieve catalyst of Example 2 of the present invention.

[0025] Figure 3 This is an SEM image of the layered nano-silica-alumina molecular sieve catalyst of Example 3 of the present invention. DETAILED DESCRIPTION

[0026] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention.

[0027] Example 1 The preparation method of the layered nano-silicon-aluminum molecular sieve catalyst of this embodiment comprises the following steps: S1 Preparation of silicon pre-hydrolyzed solution Tetraethyl orthosilicate, tetraethylammonium hydroxide, deionized water, coconut shell cellulose, TBAB, and PEG were mixed, heated to 60° C., and stirred evenly to obtain a silicon pre-hydrolyzed solution; wherein, tetraethyl orthosilicate accounted for 5 wt.% of all raw materials, and the amount of tetraethylammonium hydroxide added was 65 wt.%, the amount of coconut shell cellulose added was 8.5 wt.%, the amount of TBAB added was 3.2 wt.%, and the amount of PEG added was 2.5 wt.%, based on the mass of silicon oxide.

[0028] S2 Preparation of aluminum pre-hydrolysis solution Pseudoboehmite, sodium hydroxide, deionized water, coconut shell cellulose, CTAB, and CMC are mixed, heated to 60° C., and stirred evenly to obtain an aluminum pre-hydrolysis solution; wherein, pseudoboehmite accounts for 0.2 wt.% of all raw materials, and the addition amount of sodium hydroxide is 10 wt.%, the addition amount of coconut shell cellulose is 3 wt.%, the addition amount of CTAB is 4.6 wt.%, and the addition amount of CMC is 1.5 wt.%, calculated on the mass of alumina.

[0029] S3 co-current pre-crystallization Silicon pre-hydrolysis solution and aluminum pre-hydrolysis solution with a molar ratio of silicon to aluminum of 40:1 were added to the crystallization mother liquor in a stirring state respectively, with a stirring speed of 300 r / min, and pre-crystallization was completed at a pre-crystallization temperature of 60°C.

[0030] The crystallization mother liquor is prepared by mixing pseudo-boehmite, silica sol, deionized water, and polyvinyl pyrrolidone, heating and stirring at 60°C to form a suspension emulsion. The pseudo-boehmite is present at 0.5 wt.% (based on alumina), the silica sol is present at 1 wt.% (based on silica), and the peptizing agent is present at 5 wt.%. 5 wt.% dilute nitric acid is then added dropwise to adjust the pH to 4.5. After constant reflux and stirring for 60 minutes, the mixture becomes a uniform colloidal white turbid liquid. No solid particles are visible to the naked eye. After cooling to room temperature, the colloidal white turbid liquid is transferred to a centrifuge and centrifuged at 2000 rpm for 1 minute. The upper layer of colloidal white turbid liquid free of solid particle deposition is collected as the crystallization mother liquor.

[0031] S4 post-curing treatment The pre-crystallization liquid was transferred to a crystallization kettle and crystallized and matured at 80°C for 48 hours. During the crystallization and maturation process, forward and reverse bidirectional stirring was performed at a stirring speed of 50 r / min. After filtration and washing, it was dried at 100°C for 8 hours and finally calcined at 550°C for 6 hours to obtain a layered nano-silica-alumina molecular sieve catalyst.

[0032] from Figure 1It can be clearly seen from the SEM image that the layered nano-silica-alumina molecular sieve catalyst prepared in this embodiment is distributed in a layered plate-like shape, and the stacking and growth size of the plate particles are uniform, which indirectly indicates that during the pre-hydrolysis pre-treatment of the silicon source and aluminum source, the dynamic pre-crystallization assistance and the aging crystallization post-treatment, the growth and shaping of the crystals are induced in the expected direction to achieve the optimal catalytic morphology.

[0033] The layered nano-silica-alumina molecular sieve catalyst of this embodiment was evaluated: the layered nano-silica-alumina molecular sieve catalyst was heated to 550°C at a rate of 2°C / min in an air environment and calcined for 6 hours. After activation, it was used for the hydration of acrolein to 3-hydroxypropionaldehyde in a fixed-bed reactor with a mass space velocity of 2h. -1 The reaction temperature was 40° C., and the concentration of the acrolein solution was 15 wt %. Using the layered nano-silica-alumina molecular sieve catalyst of this example, the acrolein conversion rate was 56%, and the 3-hydroxypropionaldehyde selectivity was 92.2%.

[0034] Example 2 The preparation method of the layered nano-silicon-aluminum molecular sieve catalyst of this embodiment comprises the following steps: S1 Preparation of silicon pre-hydrolyzed solution Silica sol, tetraethylammonium bromide, deionized water, piperidine, CTAB, and PVA were mixed, heated to 30° C., and stirred evenly to obtain a silicon pre-hydrolysis solution; wherein, the silica sol accounts for 10 wt.% of all raw materials, and based on the mass of silicon oxide, the added amount of tetraethylammonium bromide is 45 wt.%, the added amount of piperidine is 15 wt.%, the added amount of CTAB is 10 wt.%, and the added amount of PVA is 12 wt.%.

[0035] S2 Preparation of aluminum pre-hydrolysis solution Aluminum oxide, potassium hydroxide, deionized water, homopiperazine, PVB, and PEG are mixed, heated to 30° C., and stirred evenly to obtain an aluminum pre-hydrolysis solution; wherein, aluminum oxide accounts for 0.4 wt.% of all raw materials, and based on the mass of alumina, the addition amount of potassium hydroxide is 20 wt.%, the addition amount of homopiperazine is 15 wt.%, the addition amount of PVB is 10 wt.%, and the addition amount of PEG is 12 wt.%.

[0036] S3 co-current pre-crystallization The silicon pre-hydrolysis solution and the aluminum pre-hydrolysis solution with a molar ratio of silicon element to aluminum element of 100:1 were added to the crystallization mother liquor in a stirring state respectively, the stirring speed was 1000r / min, and the pre-crystallization was completed at a pre-crystallization temperature of 100°C.

[0037] The crystallization mother liquor is prepared by mixing pseudo-boehmite, silica sol, deionized water, and polyvinyl alcohol, heating and stirring at 80°C to form a suspension emulsion. The pseudo-boehmite is present at 2 wt.% (based on alumina), the silica sol is present at 3 wt.% (based on silica), and the peptization aid is present at 10 wt.%. 5 wt.% dilute nitric acid is then added dropwise to adjust the pH to 4. After constant reflux and stirring for 60 minutes, the mixture becomes a uniform colloidal white turbid liquid. No solid particles are visible to the naked eye. After cooling to room temperature, the colloidal white turbid liquid is transferred to a centrifuge and centrifuged at 4500 rpm for 5 minutes. The upper layer of colloidal white turbid liquid free of solid particle deposition is collected as the crystallization mother liquor.

[0038] S4 post-curing treatment The pre-crystallization liquid was transferred to a crystallization kettle and crystallized and matured at 100°C for 8 hours. During the crystallization and maturation process, forward and reverse bidirectional stirring was performed at a stirring speed of 200 r / min. After filtration and washing, it was dried at 150°C for 1 hour and finally calcined at 850°C for 1 hour to obtain a layered nano-silica-alumina molecular sieve catalyst.

[0039] from Figure 2 It can be clearly seen from the SEM image that the layered nano-silicon-aluminum molecular sieve catalyst prepared in this example is distributed in a layered plate-like shape, and the stacking and growth size of the plate particles are uniform. However, compared with Example 1, some small-shaped particles appear. This may be because under the high silicon-aluminum ratio reaction conditions, the crystal growth process is slightly affected, resulting in faster maturation and shaping of the crystals.

[0040] The layered nano-silica-alumina molecular sieve catalyst of this embodiment was evaluated: the layered nano-silica-alumina molecular sieve catalyst was heated to 650°C at a rate of 2°C / min in an air environment and calcined for 5h. After activation, it was used for the hydration of acrolein to 3-hydroxypropionaldehyde in a fixed-bed reactor with a mass space velocity of 5h. -1 The reaction temperature was 60° C., and the concentration of the acrolein solution was 25 wt %. Using the layered nano-silica-alumina molecular sieve catalyst of this example, the acrolein conversion rate was 55.2%, and the 3-hydroxypropanal selectivity was 92%.

[0041] Example 3 The preparation method of the layered nano-silicon-aluminum molecular sieve catalyst of this embodiment comprises the following steps: S1 Preparation of silicon pre-hydrolyzed solution Tetramethyl orthosilicate, tetraethylammonium chloride, deionized water, polydiallyldimethylammonium chloride, PVB, and PVP are mixed, heated to 40° C., and stirred evenly to obtain a silicon pre-hydrolyzed solution; wherein, tetramethyl orthosilicate accounts for 12 wt.% of all raw materials, and based on the mass of silicon oxide, the addition amount of tetraethylammonium chloride is 7.5 wt.%, the addition amount of polydiallyldimethylammonium chloride is 0.5 wt.%, the addition amount of PVB is 0.5 wt.%, and the addition amount of PVP is 0.2 wt.%.

[0042] S2 Preparation of aluminum pre-hydrolysis solution Boehmite, triethanolamine, deionized water, lignin, TBAB, and SAS were mixed, heated to 40°C, and stirred evenly to obtain an aluminum pre-hydrolysis solution; wherein, boehmite accounted for 0.3wt.% of all raw materials, and based on the mass of alumina, the addition amount of triethanolamine was 5wt.%, the addition amount of lignin was 8.5wt.%, the addition amount of TBAB was 0.5wt.%, and the addition amount of SAS was 0.2wt.%.

[0043] S3 co-current pre-crystallization Silicon pre-hydrolysis solution and aluminum pre-hydrolysis solution with a molar ratio of silicon element to aluminum element of 10:1 were added to the crystallization mother liquor in a stirring state respectively, the stirring speed was 200 r / min, and pre-crystallization was completed at a pre-crystallization temperature of 50°C.

[0044] The crystallization mother liquor is prepared by mixing pseudo-boehmite, silica sol, deionized water, and polyethylene glycol, heating and stirring at 70°C to form a suspension emulsion. The pseudo-boehmite is present at 1.2 wt.% (based on alumina), the silica sol is present at 2 wt.% (based on silica), and the peptizing agent is present at 8 wt.%. 2 wt.% dilute hydrochloric acid is then added dropwise to adjust the pH to 4.5. After constant reflux and stirring for 60 minutes, the mixture becomes a uniform colloidal white turbid liquid. No solid particles are visible to the naked eye. After cooling to room temperature, the colloidal white turbid liquid is transferred to a centrifuge and centrifuged at 3000 rpm for 3 minutes. The upper layer of colloidal white turbid liquid free of solid particle deposition is collected as the crystallization mother liquor.

[0045] S4 post-curing treatment The pre-crystallization liquid was transferred to a crystallization kettle and crystallized and matured at 200°C for 1 hour. During the crystallization and maturation process, forward and reverse bidirectional stirring was performed at a stirring speed of 10 r / min. After filtering and washing, it was dried at 80°C for 24 hours and finally calcined at 350°C for 12 hours to obtain a layered nano-silica-alumina molecular sieve catalyst.

[0046] from Figure 3 It can be clearly seen from the SEM image that the layered nano-silicon-aluminum molecular sieve catalyst prepared in this example is distributed in a layered plate-like shape, and the stacking and growth size of the plate-like particles are uniform.

[0047] The layered nano-silica-alumina molecular sieve catalyst of this embodiment was evaluated: the layered nano-silica-alumina molecular sieve catalyst was heated to 750°C at a rate of 2°C / min in an air environment and calcined for 3 hours. After activation, it was used for the hydration of acrolein to 3-hydroxypropionaldehyde in a fixed-bed reactor with a mass space velocity of 1h. -1 The reaction temperature was 30° C., and the concentration of the acrolein solution was 10 wt %. Using the layered nano-silica-alumina molecular sieve catalyst of this example, the acrolein conversion rate was 55.1%, and the 3-hydroxypropanal selectivity was 92.3%.

[0048] Comparative Example 1 The difference from Example 1 is that in step S3, the aluminum pre-hydrolysis solution is first added to the crystallization mother liquor, and then the silicon pre-hydrolysis solution is added.

[0049] The catalyst of Comparative Example 1 was evaluated: under the same conditions as in Example 1, using the catalyst of Comparative Example 1, the acrolein conversion was 30% and the 3-hydroxypropionaldehyde selectivity was 83%.

[0050] By comparing Example 1 with Comparative Example 1, it can be seen that in Comparative Example 1, aluminum pre-hydrolyzate is added first and silicon pre-hydrolyzate is added later during pre-crystallization, resulting in an imbalance in the silicon and aluminum components during the crystallization process, inconsistent crystallization maturity of each component in the crystallization mother liquor, resulting in an imbalance in the silicon-aluminum ratio embedded in the main structure of the molecular sieve, affecting the distribution of active sites on the catalyst surface, and causing a decrease in catalytic activity.

[0051] Comparative Example 2 The difference from Example 2 is that in steps S1 and S2, no structure directing agent is added.

[0052] The catalyst of Comparative Example 2 was evaluated: under the same conditions as in Example 2, using the catalyst of Comparative Example 2, the acrolein conversion was 40% and the 3-hydroxypropionaldehyde selectivity was 83%.

[0053] By comparing Example 2 with Comparative Example 2, it can be seen that because no structure-directing agent is added to the silicon pre-hydrolysis solution and the aluminum pre-hydrolysis solution, although the micro-grains can grow uniformly to form layered crystal walls, the crystal walls are stacked disorderly, making it difficult to form a regular layered nanostructure, which destroys the microscopic morphology and the effective exposure of the macroscopic active crystal surfaces, resulting in a decrease in catalytic activity.

[0054] Comparative Example 3 The difference from Example 3 is that the layered nano-silica-alumina molecular sieve catalyst is used for the hydration of acrolein to 3-hydroxypropionaldehyde, and the reaction mass space velocity is 6h -1 .

[0055] The catalyst of Comparative Example 3 was evaluated: under the same conditions as in Example 3, using the catalyst of Comparative Example 3, the acrolein conversion was 53.8% and the 3-hydroxypropionaldehyde selectivity was 90%.

[0056] By comparing Example 3 with Comparative Example 3, it can be seen that although the mass space velocity is too large, the prepared catalyst has a well-ordered, uniform and firm layered nanostructure, which maintains the micromorphology and effective exposure of the macroscopic active crystal surface during the reaction. At the same time, it also suppresses the polymer coverage problem generated during the catalyst surface reaction to a certain extent, reduces the loss of active center number, and decreases the internal diffusion resistance. Therefore, the catalyst performance is not significantly affected.

[0057] Comparative Example 4 The difference from Example 1 is that in step S3, only the aluminum pre-hydrolysis solution is added to the crystallization mother liquor.

[0058] The catalyst of Comparative Example 4 was evaluated: under the same conditions as in Example 1, using the catalyst of Comparative Example 4, the acrolein conversion was 20% and the 3-hydroxypropionaldehyde selectivity was 60%.

[0059] Comparing Example 1 with Comparative Example 4, it can be seen that when no silicon pre-hydrolyzate is added, the porous aluminum molecular sieve catalyst formed has certain catalytic performance, but the acrolein conversion rate and 3-hydroxypropionaldehyde selectivity are significantly reduced. The main reason is that in the absence of a silicon skeleton, it is difficult to form a uniform and unobstructed molecular sieve pore structure during the synthesis of the catalyst, and the acrolein hydration reaction raw materials cannot penetrate deep into the catalyst system to react; secondly, the active sites on the crystal surface are significantly different from those of the silicon aluminum molecular sieve, which seriously affects the adsorption activation hydration of acrolein and the dissociation and removal of 3-hydroxypropionaldehyde.

[0060] Comparative Example 5 The difference from Example 1 is that in step S3, only silicon pre-hydrolysis liquid is added to the crystallization mother liquor.

[0061] The catalyst of Comparative Example 5 was evaluated: under the same conditions as in Example 1, using the catalyst of Comparative Example 5, the acrolein conversion was 5% and the 3-hydroxypropionaldehyde selectivity was 20%.

[0062] Comparing Example 1 with Comparative Example 5 shows that without the addition of an aluminum pre-hydrolyzate, the resulting porous silicon molecular sieve catalyst exhibits virtually no catalytic activity, significantly reducing both the acrolein conversion rate and the 3-hydroxypropionaldehyde selectivity. This is primarily due to the difficulty in forming the molecular sieve structure during catalyst synthesis in the absence of an aluminum framework. Furthermore, without an aluminum source, the silica powder catalyst is difficult to form, and once formed, it lacks sufficient strength to sustain subsequent reactions.

[0063] Comparative Example 6 The difference from Example 1 is that in steps S1 and S2, no peptizing agent is added.

[0064] The catalyst of Comparative Example 6 was evaluated: under the same conditions as in Example 1, using the catalyst of Comparative Example 6, the acrolein conversion was 45% and the 3-hydroxypropionaldehyde selectivity was 90%.

[0065] Comparing Example 1 with Comparative Example 6, it can be seen that when no peptizing agent is added, the conversion of acrolein decreases, but the selectivity of 3-hydroxypropanal is not significantly affected. This is because the role of the peptizing agent is mainly reflected in the synthesis process, which can improve the uniformity of the hydrolysis of the silicon-aluminum source and assist in promoting the crystallization of the structure-directing agent in the later stage. When no peptizing agent is added, it does not affect the catalyst reaction in essence, but the uniformity of the hydrolysis of the molecular sieve decreases, the grain size is different, and the uniformity of the porous structure is affected, so the conversion rate and selectivity decrease.

[0066] Comparative Example 7 The difference from Example 1 is that in steps S1 and S2, no surfactant is added.

[0067] The catalyst of Comparative Example 7 was evaluated: under the same conditions as in Example 1, using the catalyst of Comparative Example 7, the acrolein conversion was 40% and the 3-hydroxypropionaldehyde selectivity was 85%.

[0068] Comparing Example 1 with Comparative Example 7, it can be seen that when no surfactant is added, the acrolein conversion rate and the 3-hydroxypropionaldehyde selectivity both decrease significantly. This is because the role of the surfactant is mainly reflected in the synthesis process, which can effectively promote the rapid collision and growth of high-concentration silicon source and aluminum source molecules in the silicon pre-hydrolyzate and aluminum pre-hydrolyzate during the co-current hydrolysis crystallization and dynamic crystallization processes. Therefore, when no surfactant is added, during the fusion process of the silicon pre-hydrolyzate, the aluminum pre-hydrolyzate and the crystallization mother liquor, the silicon and aluminum molecules in the crystallization area are unevenly distributed, the collision crystallization process is mostly in an unstable state, the silicon-aluminum skeleton tends to grow more irregularly, the silicon-aluminum ratio is unbalanced, and the acrolein conversion rate and the 3-hydroxypropionaldehyde selectivity both decrease.

[0069] Comparative Example 8 The difference from Example 1 is that in step S3, mature crystallized particles of silica-alumina molecular sieve are used instead of the crystallization mother liquor of Example 1. The preparation method of mature crystallized particles of silica-alumina molecular sieve is as follows: 8 wt.% silica sol, 5 wt.% tetrapropylammonium hydroxide and deionized water are pre-hydrolyzed at 60 ° C to obtain solution M; 1.2 wt.% pseudo-boehmite, 1 wt.% sodium hydroxide and deionized water are pre-hydrolyzed at 60 ° C to obtain solution N; solution N is slowly added to solution M (the mass ratio of solution M to solution N is 5:1), stirred and premixed uniformly to obtain solution X; solution X is transferred to a crystallization kettle and crystallized at 200 ° C; after crystallization is completed, the solid-liquid mixture is centrifuged, washed and dried; after drying, the catalyst is placed in a muffle furnace, calcined at 750 ° C for 3 hours, and then ground through a 200 mesh sieve to obtain mature crystallized particles of silica-alumina molecular sieve.

[0070] The catalyst of Comparative Example 8 was evaluated: under the same conditions as in Example 1, using the catalyst of Comparative Example 8, the acrolein conversion was 42.8%, and the 3-hydroxypropionaldehyde selectivity was 87.3%.

[0071] Comparing Example 1 with Comparative Example 8, it can be seen that in Comparative Example 8, mature crystallized particles of silicon-aluminum molecular sieve are selected as crystal seeds in the crystallization stage, and the acrolein conversion rate and 3-hydroxypropionaldehyde selectivity of the obtained silicon-aluminum molecular sieve catalyst are reduced to varying degrees. The main reason is that the size of the mature crystallized particles, the area of the exposed crystal surface, etc. cannot be controlled, the trend of crystal growth will be affected by the crystal seeds, and the silicon pre-hydrolyzate and the aluminum pre-hydrolyzate lose the guiding effect of the structure-directing agent and the surfactant during hydrolysis, crystallization and growth on the surface of the crystal seeds. It is difficult to adjust the structure to the expected layered nanostructure according to the established process, and only an ordinary disordered silicon-aluminum molecular sieve will be formed, which will weaken the effects of mass transfer and active site exposure, and ultimately lead to a decrease in activity.

[0072] Comparative Example 9 The difference from Example 1 is that in step S4, the crystallization aging temperature is 50°C.

[0073] The catalyst of Comparative Example 9 was evaluated: under the same conditions as in Example 1, using the catalyst of Comparative Example 9, the acrolein conversion was 30% and the 3-hydroxypropionaldehyde selectivity was 60%.

[0074] By comparing Example 1 with Comparative Example 9, it can be seen that when the crystallization ripening temperature is too low, molecular motion is restricted, and the role of surfactants and structure-directing agents in crystal ripening and skeleton growth is affected, and the formation of a regular silicon-aluminum skeleton and a balanced silicon-aluminum ratio cannot be guaranteed, resulting in a decrease in both conversion rate and selectivity.

[0075] Comparative Example 10 The difference from Example 1 is that in step S4, the crystallization aging temperature is 260°C.

[0076] The catalyst of Comparative Example 10 was evaluated: under the same conditions as in Example 1, using the catalyst of Comparative Example 10, the acrolein conversion was 47% and the 3-hydroxypropionaldehyde selectivity was 90%.

[0077] Comparing Example 1 with Comparative Example 10, it can be seen that when the crystallization and aging temperature is too high, both the acrolein conversion rate and the 3-hydroxypropionaldehyde selectivity are reduced. The main reason is that when the crystallization and aging temperature is too high, the exoskeleton grows and matures rapidly, but the endoskeleton crystal form is not yet complete. Under the continuous high temperature crystallization and aging environment, the exoskeleton and the endoskeleton grow synchronously, resulting in a deviation in the crystal form maturity and even an imbalance in the active center / face distribution. The connectivity and pore size distribution of the pore structure are also affected to a certain extent, resulting in a decrease in the acrolein conversion rate and 3-hydroxypropionaldehyde selectivity.

Claims

1. A method for preparing a layered nano-silicon-aluminum molecular sieve catalyst, characterized in that: The following steps are involved: S1: preparing silicon pre-hydrolysis solution: mixing silicon source, alkali source, deionized water, structure directing agent, surfactant, and peptization aid, heating and stirring uniformly to obtain silicon pre-hydrolysis solution; S2: preparing an aluminum pre-hydrolysis solution: mixing an aluminum source, an alkali source, deionized water, a structure directing agent, a surfactant, and a peptizing agent, heating and stirring the mixture to obtain an aluminum pre-hydrolysis solution; S3 parallel pre-crystallization: adding the silicon pre-hydrolyzed liquid and the aluminum pre-hydrolyzed liquid to the crystallization mother liquor in a stirred state in parallel to complete the pre-crystallization; S4 post-maturation treatment: the pre-crystallization liquid is transferred to a crystallization kettle for crystallization and aging, and a layered nano-silica-alumina molecular sieve catalyst is obtained after filtering, washing, drying and calcining.

2. The method for preparing the layered nano-silicon-aluminum molecular sieve catalyst according to claim 1, wherein: In step S1, the silicon source is silica sol, tetramethyl orthosilicate or tetraethyl orthosilicate; the silicon source accounts for 5-12 wt.% of all raw materials, calculated on the mass of silicon oxide, the alkali source accounts for 7.5-65 wt.%, the structure directing agent accounts for 0.5-15 wt.%, the surfactant accounts for 0.5-10 wt.%, and the peptizing agent accounts for 0.2-12 wt.%.

3. The method for preparing the layered nano-silicon-aluminum molecular sieve catalyst according to claim 1, wherein: In step S2, the aluminum source is pseudo-boehmite, boehmite or alumina; the aluminum source accounts for 0.2-0.4wt.% of all raw materials, calculated on the mass of alumina, the alkali source is 5-20wt.%, the structure directing agent is 3-15wt.%, the surfactant is 0.5-10wt.%, and the peptizing agent is 0.2-12wt.%.

4. The method for preparing the layered nano-silicon-aluminum molecular sieve catalyst according to claim 1, wherein: In step S1, the alkali source is tetraethylammonium chloride, tetraethylammonium bromide or tetraethylammonium hydroxide, the structure-directing agent is polydiallyldimethylammonium chloride, coconut shell cellulose or piperidine, and the peptizing agent is polyethylene glycol, polyvinyl pyrrolidone or polyvinyl alcohol; in step S2, the alkali source is sodium hydroxide, potassium hydroxide or triethanolamine, the structure-directing agent is lignin, coconut shell cellulose or homopiperazine, and the peptizing agent is alkyl sulfonate, polyethylene glycol or carboxymethyl cellulose; in steps S1 and S2, the surfactant is tetrabutylammonium bromide, hexadecyltrimethylammonium bromide or polyvinyl butyral.

5. The method for preparing the layered nano-silicon-aluminum molecular sieve catalyst according to claim 1, wherein: In steps S1 and S2, the heating temperature is 30-60°C.

6. The method for preparing the layered nano-silicon-aluminum molecular sieve catalyst according to claim 1, wherein: In step S3, the molar ratio of silicon element to aluminum element in the silicon pre-hydrolysis solution and the aluminum pre-hydrolysis solution is (10-100):1; the stirring speed is 200-1000 r / min, and the pre-crystallization temperature is 50-100°C.

7. The method for preparing the layered nano-silicon-aluminum molecular sieve catalyst according to claim 1, wherein: In step S3, the crystallization mother liquor is a suspension of microcrystalline powder particles of incompletely crystallized silica-alumina molecular sieves, and the preparation method is: after mixing pseudo-boehmite, silica sol, deionized water and a peptizing agent, heating and stirring at 60-80°C to form a suspended emulsion; wherein, the pseudo-boehmite is 0.5-2wt.% based on alumina, the silica sol is 1-3wt.%, and the peptizing agent is 5-10wt.% based on silica; the peptizing agent is polyvinyl pyrrolidone, polyvinyl alcohol, carboxymethyl cellulose or polyethylene glycol; then, dilute nitric acid or dilute hydrochloric acid is added dropwise to adjust the pH to 4-4.5, and after constant reflux stirring for 60-100 minutes, it becomes a uniform colloidal white turbid liquid; after cooling to room temperature, the colloidal white turbid liquid is transferred to a centrifuge, centrifuged at 2000-4500r / min for 1-5 minutes, and then taken out, and the colloidal white turbid liquid with no solid particle deposition on the upper layer is collected, which is the crystallization mother liquor.

8. The method for preparing the layered nano-silicon-aluminum molecular sieve catalyst according to claim 1, wherein: In step S4, the aging temperature is 80-200°C, and the aging time is 1-48 hours; forward and reverse bidirectional stirring is performed during the crystallization aging process, and the stirring speed is 10-200 r / min; the drying temperature is 80-150°C, and the drying time is 1-24 hours; the roasting temperature is 350-850°C, and the roasting time is 1-12 hours.

9. Layered nano-silicon-aluminum molecular sieve catalyst, characterized in that: The catalyst is prepared by the method for preparing the layered nano-silicon-aluminum molecular sieve catalyst according to any one of claims 1 to 8.

10. The use of the layered nano-silicon-aluminum molecular sieve catalyst according to claim 9, characterized in that: Layered nano-silica-alumina molecular sieve catalyst is used in the hydration of acrolein to 3-hydroxypropionaldehyde, with a reaction mass space velocity of 1-5h -1 , the reaction temperature is 30-60°C, and the concentration of acrolein solution is 10-25wt.%.

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