Preparation method and application of catalyst for preparing anhydrous formaldehyde through anaerobic dehydrogenation of methanol

Abstract

The invention belongs to the field of chemical technology innovation, and relates to a preparation method and application of a catalyst for preparing anhydrous formaldehyde through anaerobic dehydrogenation of methanol. The dehydrogenation catalyst is prepared by modifying a molecular sieve with alkali metal ions and transition metal ions, and the high-temperature catalytic activity of the molecular sieve can be adjusted by combining the low-temperature catalytic performance of transition metals Ag, Cu and Zn, the strong adsorption effect of oxygen-enriched vacancies on the surface of reducible metal oxide on methoxyl of methanol and the acidity of Li doping. The AgCeLi-USY modified molecular sieve catalyst realizes excellent catalytic activity in a wide temperature range of 350-700 DEG C, the methanol conversion rate reaches 80-99%, the formaldehyde yield reaches 54-65%, and the catalyst can be recycled for more than 6 times.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical industry, and specifically relates to a preparation method and application of a catalyst for preparing anhydrous formaldehyde through oxygen-free dehydrogenation of methanol. Background Art

[0002] As an important organic chemical raw material, formaldehyde is mainly used to produce chemical products such as urea-formaldehyde resin, phenolic resin, melamine formaldehyde resin, urotropine, polyols, polyoxymethylene, nylon-4 and vinylon. It is also widely used in medicine, pesticides, dyes, disinfectants, fungicides, preservatives, wood processing and chemical fiber. In recent years, the demand for high-performance engineering plastics, electronic chemicals and urotropine has increased, which has led to an increasing demand for high-concentration formaldehyde. At present, the industry mainly uses a two-step method to prepare high-concentration formaldehyde: (1) Ag or Cu catalyst oxidative dehydrogenation at 597~697 °C or iron molybdate catalyst at 297~397 °C with excess air oxidation to prepare an aqueous solution containing 35~45% formaldehyde; (2) formaldehyde aqueous solution is concentrated by vacuum distillation or solvent azeotropy. However, the vapor pressure of formaldehyde aqueous solution is very low and formaldehyde and water easily form azeotropes, so the separation and purification of formaldehyde aqueous solution is very difficult and expensive.

[0003] The oxygen-free dehydrogenation of methanol to produce anhydrous formaldehyde is a new process with potential industrial prospects. It can avoid the shortcomings of high energy consumption, high cost and environmental pollution caused by the traditional oxidation-dehydration method. Directly converting methanol into anhydrous formaldehyde simplifies the process flow, reduces energy consumption and cost, reduces the emission of wastewater and exhaust gas, and avoids the problem of equipment corrosion caused by the oxidation of methanol to formic acid. However, this process needs to be carried out at a high temperature of 400~800 ℃, facing the problems of the generation of thermodynamically favorable by-products at high temperature, the decomposition of formaldehyde at high temperature, and self-polymerization and oxidation at low temperature. Therefore, the difficulty of this technology lies in the development of a catalyst with high activity, high selectivity and high stability at high temperature. Commonly used catalysts for the oxygen-free dehydrogenation of methanol include alkali metal carbonates, metals and metal oxides, and molecular sieve catalysts. Among them, alkali metal carbonates such as sodium bicarbonate have high selectivity, but have low activity and high reaction temperature (700~900 ℃), easy to melt and lose and form methyl carbonate or formate with the catalyst, etc., and it is necessary to add additives or carriers to improve their activity and stability (CN101147872A, CN102941112A); metals and metal oxides mainly include metals such as Cu, Ag, Zn, Zr, V and their oxides. Such catalysts have high activity, but have problems such as low high temperature selectivity and catalyst deactivation due to metal reduction, volatilization or sintering (CN1390639A, CN1537673A, CN1544 147A, CN102274722A, CN101961650A, CN105712857A); molecular sieve catalysts and composite catalysts formed with other metals or non-metals have high stability at high temperatures, but they also have problems such as poor low-temperature activity, low high-temperature selectivity, excessive catalyst acidity leading to the occurrence of side reactions such as dehydration and polycondensation, and small pores that are prone to large diffusion resistance and easy clogging (CN107162884A, CN105732350A, CN104447248A). Therefore, it is of great significance to develop a dehydrogenation catalyst with significant and stable formaldehyde yield in a wide reaction temperature range, which also lays the foundation for the industrialization of methanol oxygen-free dehydrogenation technology. Summary of the invention

[0004] In view of this, the present invention provides a preparation method and application of a catalyst for the production of anhydrous formaldehyde by oxygen-free dehydrogenation of methanol, aiming to overcome the problems of narrow reaction temperature range and low formaldehyde yield faced by existing catalysts for oxygen-free dehydrogenation of methanol. This patent modifies the molecular sieve to obtain a modified molecular sieve catalyst doped with alkali metals and transition metals, which not only adjusts the acidity of the molecular sieve surface, but also combines the reaction activity of the molecular sieve high temperature reaction range (600~900 ℃) and the transition metal low temperature reaction range (350~650 ℃) defined in this case, as well as the adsorption of methanol by oxygen vacancies on the surface of reducible metal oxides, thereby achieving excellent catalytic activity and formaldehyde yield in a wide reaction window from 350~700 ℃.

[0005] To achieve the above purpose, the technical scheme of the present invention is as follows: the modified molecular sieve catalyst is prepared by ion exchange-electrostatic adsorption method. First, the molecular sieve is placed in an alkali metal salt solution for ion exchange for 2 to 5 hours and then centrifuged. After repeated exchange 2 to 4 times, it is placed in an oven to dry overnight, and then calcined at 350 to 700 ° C for 3 to 12 hours to obtain an alkali metal-modified molecular sieve catalyst; secondly, the obtained alkali metal-modified molecular sieve catalyst is placed in a transition metal salt solution and stirred for 2 to 8 hours for electrostatic adsorption, and then centrifuged, washed, dried overnight and placed in a muffle furnace at 300 to 600 ° C for 3 to 6 hours to obtain a transition metal and alkali metal modified molecular sieve catalyst.

[0006] Wherein, the modified molecular sieve is one of USY, ZSM-5, Beta and HY molecular sieves, preferably USY and Beta molecular sieves.

[0007] The alkali metal salt is selected from any one or more of water-soluble lithium salts, potassium salts and sodium salts; the anion of the alkali metal salt is selected from any one of carbonates, nitrates, acetates and oxalates.

[0008] In some embodiments, the alkali metal salt is one or more of Li2CO3, LiNO3, CH3COOLi, Li2C2O4, K2CO3, CH3COOK, K2C2O4, KNO3, Na2CO3, CH3COONa, and Na2C2O4, wherein the alkali metal ion concentration is 0.02~1.0 mol / L.

[0009] Wherein, the transition metal salt comprises one or more of AgNO3, Zn(NO3)2, Cu(NO3)2, Ce(NO3)2, and Al(NO3)3, and the transition metal concentration thereof is 0.02~5.0 mol / L.

[0010] The modified molecular sieve catalyst uses methanol as a raw material and performs an oxygen-free dehydrogenation reaction in a fixed bed quartz tube reactor in a N2 atmosphere. The reaction temperature is 400-800 °C, the methanol volume content is 5-40%, and the mass space velocity of the bed is 1.5-10 ml∙g cat. -1 ∙s -1 .

[0011] The ion exchange-electrostatic adsorption method developed in the present invention is used to prepare a modified molecular sieve catalyst. Alkali metal salts, especially alkali metal carbonates, are used to exchange ions with molecular sieves to obtain modified molecular sieves with adjustable surface acidity. The modified alkali metal ions are also used to adjust the charge distribution on the surface of the molecular sieve, and the transition metal cations are uniformly dispersed on the surface or in the pores of the molecular sieve through electrostatic adsorption. Compared with pure molecular sieve catalysts, alkali metal-modified molecular sieves can promote the desorption of hydrogen produced by the reaction on the surface of the molecular sieve and inhibit the formation of carbon deposits, but the reaction still needs to be at 600~800℃ to obtain a certain formaldehyde yield. Transition metals such as Cu, Ag and their oxide catalysts can achieve higher methanol conversion rates and formaldehyde selectivity at relatively low temperatures (350~650℃), but they face problems such as metal oxides being reduced by product hydrogen and sintering themselves, resulting in decreased activity. Therefore, active components such as Cu and Ag are anchored on the surface or in the pores of the modified molecular sieve by electrostatic adsorption, and during the anaerobic dehydrogenation of methanol, the intermediate formed by the metal and the methoxy group migrates to the silanol nest in the molecular sieve and stabilizes, thereby effectively avoiding the rapid sintering process of the metal. The advantages of the present invention are reflected in that the modified molecular sieve catalyst not only exhibits excellent methanol conversion rate and formaldehyde yield in a wide reaction temperature range, but also can improve the service life of the catalyst through chemical cycle regeneration. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is the cyclic regeneration activity of AgLi-USY molecular sieve catalyst. DETAILED DESCRIPTION

[0013] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below through embodiments.

[0014] Example 1: Preparation of AgCeLi-USY molecular sieve catalyst.

[0015] 50 g of USY molecular sieve with a silicon-aluminum ratio of 5.4 was weighed, ion exchanged in 0.1 M lithium carbonate solution for 3 times, then centrifuged and washed 3 times, dried in an oven at 80 °C overnight, and calcined at 650 °C for 4 h in an air atmosphere to obtain Li-USY molecular sieve.

[0016] The prepared Li-USY molecular sieve was further placed in a 0.1M mixed solution of silver nitrate and cerium nitrate, stirred at room temperature for 6 h, filtered and dried, and then heated to 500 °C for calcination for 3 h in an air atmosphere. The calcined AgCeLi-USY molecular sieve catalyst was formed and filled into a reaction tube, filling a 2 cm bed layer, and nitrogen was introduced as a carrier gas under normal pressure. Methanol was sampled by a micro pump with a volume content of 5-20%. The reaction was carried out at 350-700 °C, and the feed space velocity was 3-10 ml∙g cat. -1 ∙s -1 The product is detected online by gas chromatography dual-channel TCD.

[0017] Example 2: Preparation of AgCeNa-USY molecular sieve catalyst.

[0018] Weigh 50 g of USY molecular sieve with a silicon-aluminum ratio of 5.4, carry out ion exchange three times in 0.1 M sodium carbonate solution, then centrifuge and wash three times, place in an oven to dry overnight at 80 °C, and calcine at 650 °C for 4 h in air atmosphere to obtain Na-USY molecular sieve. The prepared Na-USY molecular sieve is further placed in a 0.1 M mixed solution of silver nitrate and cerium nitrate, stirred at room temperature for 6 h, filtered and dried, and then heated to 500 °C for calcination for 3 h in air atmosphere. The calcined AgCeNa-USY molecular sieve catalyst is formed and filled into a reaction tube, filling a 2 cm bed layer, and nitrogen is introduced as a carrier gas under normal pressure. Methanol is sampled by a micro pump with a volume content of 5-20%. The reaction is carried out at 350-700 °C, and the feed space velocity is 3-10 ml∙g cat. -1 ∙s -1 The product is detected online by gas chromatography dual-channel TCD.

[0019] Example 3: Preparation of AgCeK-USY molecular sieve catalyst.

[0020] Weigh 50 g of USY molecular sieve with a silicon-aluminum ratio of 5.4, carry out ion exchange three times in 0.1 M potassium carbonate solution, then centrifuge and wash three times, place in an oven to dry overnight at 80 °C, and calcine at 650 °C for 4 h in air atmosphere to obtain K-USY molecular sieve. The prepared K-USY molecular sieve is further placed in a 0.1 M mixed solution of silver nitrate and cerium nitrate, stirred at room temperature for 6 h, filtered and dried, and then heated to 500 °C for calcination for 3 h in air atmosphere. The calcined AgCeK-USY molecular sieve catalyst is formed and filled into a reaction tube, filling a 2 cm bed layer, and nitrogen is introduced as a carrier gas under normal pressure. Methanol is sampled by a micro pump with a volume content of 5-20%. The reaction is carried out at 350-700 °C, and the feed space velocity is 3-10 ml∙gcat. -1 ∙s -1 The product is detected online by gas chromatography dual-channel TCD.

[0021] Example 4: Preparation of CuCeLi-USY molecular sieve catalyst.

[0022] Weigh 50 g of USY molecular sieve with a silicon-aluminum ratio of 5.4, carry out ion exchange three times in 0.1 M lithium carbonate solution, then centrifuge and wash three times, place in an oven to dry overnight at 80 °C, and calcine at 650 °C for 4 h in air atmosphere to obtain Li-USY molecular sieve. The prepared Li-USY molecular sieve is further placed in a 0.1 M mixed solution of copper nitrate and cerium nitrate, stirred at room temperature for 6 h, filtered and dried, and then heated to 500 °C for calcination for 3 h in air atmosphere. The calcined CuCeLi-USY molecular sieve catalyst is formed and filled into a reaction tube, filling a 2 cm bed layer, and nitrogen is introduced as a carrier gas under normal pressure. Methanol is sampled by a micro pump with a volume content of 5-20%. The reaction is carried out at 350-700 °C, and the feed space velocity is 3-10 ml∙g cat. -1 ∙s -1 The product is detected online by gas chromatography dual-channel TCD.

[0023] Example 5: Preparation of ZnCeLi-USY molecular sieve catalyst.

[0024] Weigh 50 g of USY molecular sieve with a silicon-aluminum ratio of 5.4, carry out ion exchange three times in 0.1 M lithium carbonate solution, then centrifuge and wash three times, place in an oven to dry overnight at 80 °C, and calcine at 650 °C for 4 h in air atmosphere to obtain Li-USY molecular sieve. The prepared Li-USY molecular sieve is further placed in a 0.1 M mixed solution of zinc nitrate and cerium nitrate, stirred at room temperature for 6 h, filtered and dried, and then heated to 500 °C for calcination for 3 h in air atmosphere. The calcined ZnCeK-USY molecular sieve catalyst is formed and filled into a reaction tube, filling a 2 cm bed layer, and nitrogen is introduced as a carrier gas under normal pressure. Methanol is sampled by a micro pump with a volume content of 5-20%. The reaction is carried out at 350-700 °C, and the feed space velocity is 3-10 ml∙g cat. -1 ∙s -1 The product is detected online by gas chromatography dual-channel TCD.

[0025] Example 6: Preparation of AgCeLi-ZSM-5 molecular sieve catalyst.

[0026] Weigh 50 g of ZSM-5 molecular sieve with a silicon-aluminum ratio of 60, carry out ion exchange three times in 0.1 M lithium carbonate solution, then centrifuge and wash three times, place in an oven to dry overnight at 80 °C, and calcine at 650 °C for 4 h in air atmosphere. The prepared Li-ZSM-5 molecular sieve is placed in a 0.1 M mixed solution of silver nitrate and cerium nitrate, stirred at room temperature for 6 h, filtered and dried, and then heated to 500 °C for 3 h in air atmosphere. The calcined AgCeLi-ZSM-5 molecular sieve catalyst is formed and filled into the reaction tube, filling a 2 cm bed layer, and nitrogen is introduced as a carrier gas under normal pressure. Methanol is sampled by a micro pump with a volume content of 5-20%. The reaction is carried out at 350-700 °C, and the feed space velocity is 3-10 ml∙g cat. -1 ∙s -1 The product is detected online by gas chromatography dual-channel TCD.

[0027] Example 7: Preparation of AgCeLi-Beta molecular sieve catalyst.

[0028] Weigh 50 g of Beta molecular sieve with a silicon-aluminum ratio of 25, carry out ion exchange three times in 0.1 M lithium carbonate solution, then centrifuge and wash three times, place in an oven to dry overnight at 80 °C, and calcine at 650 °C for 4 h in air atmosphere. The prepared Li-Beta molecular sieve is placed in a 0.1 M mixed solution of silver nitrate and cerium nitrate, stirred at room temperature for 6 h, filtered and dried, and then heated to 500 °C for calcination for 3 h in air atmosphere. The calcined AgCeLi-Beta molecular sieve catalyst is formed and filled into the reaction tube, filling a 2 cm bed layer, and nitrogen is introduced as a carrier gas under normal pressure. Methanol is sampled by a micro pump with a volume content of 5-20%. The reaction is carried out at 350-700 °C, and the feed space velocity is 3-10 ml∙g cat. -1 ∙s -1 The product is detected online by gas chromatography dual-channel TCD.

[0029] Example 8: Preparation of AgCeLi-HY molecular sieve catalyst.

[0030] Weigh 50 g of HY molecular sieve with a silicon-aluminum ratio of 40, carry out ion exchange three times in 0.1 M lithium carbonate solution, then centrifuge and wash three times, place in an oven to dry overnight at 80 °C, and calcine at 650 °C for 4 h in air atmosphere. The prepared Li-HY molecular sieve is placed in a 0.1 M mixed solution of silver nitrate and cerium nitrate, stirred at room temperature for 6 h, filtered and dried, and then heated to 500 °C for 3 h in air atmosphere. The calcined AgCeLi-HY molecular sieve catalyst is formed and filled into the reaction tube, filling a 2 cm bed layer, and nitrogen is introduced as a carrier gas under normal pressure. Methanol is sampled by a micro pump with a volume content of 5-20%. The reaction is carried out at 350-700 °C, and the feed space velocity is 3-10 ml∙g cat. -1 ∙s -1 The product is detected online by gas chromatography dual-channel TCD.

[0031] Example 9: The catalyst after the reaction in Example 1 was purged with N2 for 30 min, then calcined at 500°C for 1 h in situ with air, and then purged under N2 atmosphere for another 30 min before conducting an oxygen-free dehydrogenation experiment of methanol. The cyclic oxidation regeneration experiment showed that the catalyst had good stability and recyclability (see Figure 1 ).

[0032] Comparative Example 1: USY, Beta, TS-1 and MCM-22 molecular sieves were formed and filled into a reaction tube to fill a 2 cm bed. Nitrogen was introduced as a carrier gas under normal pressure. Methanol was injected by a micro pump with a volume content of 5-20%. The reaction was carried out at 600-800°C and the feed space velocity was 3-10 ml∙g cat. -1 ∙s -1 The product was detected online by gas chromatography dual-channel TCD.

[0033] Comparative Example 2: Preparation of Li-USY, Na-USY, K-USY and Cs-USY molecular sieve catalysts.

[0034] Weigh 50 g of USY molecular sieve with a silicon-aluminum ratio of 5.4, and perform ion exchange three times in 0.1 M lithium carbonate, sodium carbonate, potassium carbonate, and cesium carbonate solutions, then centrifuge and wash three times, place in an oven to dry overnight at 80 °C, and calcine at 650 °C for 4 h in an air atmosphere. The calcined Li-USY, Na-USY, and K-USY molecular sieve catalysts are formed and filled into a reaction tube, filling a 2 cm bed layer, and nitrogen is introduced as a carrier gas under normal pressure. Methanol is sampled by a micro pump with a volume content of 5-20%. The reaction is carried out at 600-800 °C, and the feed space velocity is 3-10 ml∙g cat. -1 ∙s-1 The product is detected online by gas chromatography dual-channel TCD.

[0035] Comparative Example 3: Preparation of Li-MCM-22, Li-Beta and Li-TS-1 catalysts.

[0036] 50 g of MCM-22 with a silicon-aluminum ratio of 28, 50 g of Beta with a silicon-aluminum ratio of 25, and 50 g of TS-1 molecular sieve with a titanium-silicon ratio of 30 were weighed respectively, and ion exchange was carried out three times in a 0.1 M lithium carbonate solution, and then centrifuged and washed three times, and then placed in an oven to dry overnight at 80 °C, and calcined at 650 °C for 4 h in an air atmosphere. The calcined Li-SAPO-11, Li-Beta, and Li-TS-1 molecular sieve catalysts were formed and filled into a reaction tube, filling a 2 cm bed layer, and nitrogen was introduced as a carrier gas under normal pressure. Methanol was sampled by a micro pump with a volume content of 5-20%. The reaction was carried out at 600-800 °C, and the feed space velocity was 3-10 ml∙g cat. -1 ∙s -1 The product is detected online by gas chromatography dual-channel TCD.

[0037] Comparative Example 4: Preparation of AgCe-USY catalyst.

[0038] Weigh 50 g of USY molecular sieve with a silicon-aluminum ratio of 5.4 and place it in a 0.1 M mixed solution of silver nitrate and cerium nitrate. Stir at room temperature for 6 h, filter and dry, and then heat to 500 °C for calcination for 3 h in an air atmosphere. The calcined AgCe-USY molecular sieve catalyst is formed and filled into a reaction tube with a 2 cm bed. Nitrogen is introduced as a carrier gas under normal pressure, and methanol is sampled by a micro pump with a volume content of 5-20%. The reaction is carried out at 350-700 °C, and the feed space velocity is 3-10 ml∙g cat. -1 ∙s -1 The product is detected online by gas chromatography dual-channel TCD.

[0039] Comparative Example 5: Preparation of ZrCeLi-USY molecular sieve catalyst.

[0040] Weigh 50 g of USY molecular sieve with a silicon-aluminum ratio of 5.4, carry out ion exchange three times in 0.1 M lithium carbonate solution, then centrifuge and wash three times, place in an oven to dry overnight at 80 °C, and calcine at 650 °C for 4 h in air atmosphere to obtain Li-USY molecular sieve. The prepared Li-USY molecular sieve is further placed in a 0.1 M mixed solution of zirconyl nitrate and cerium nitrate, stirred at room temperature for 6 h, filtered and dried, and then heated to 500 °C for calcination for 3 h in air atmosphere. The calcined ZrCeLi-USY molecular sieve catalyst is formed and filled into a reaction tube, filling a 2 cm bed layer, and nitrogen is introduced as a carrier gas under normal pressure. Methanol is sampled by a micro pump with a volume content of 5-20%. The reaction is carried out at 350-700 °C, and the feed space velocity is 3-10 ml∙g cat. -1 ∙s -1 The product is detected online by gas chromatography dual-channel TCD.

[0041] Comparative Example 6: Preparation of AgMgLi-USY molecular sieve catalyst.

[0042] Weigh 50 g of USY molecular sieve with a silicon-aluminum ratio of 5.4, carry out ion exchange three times in 0.1 M lithium carbonate solution, then centrifuge and wash three times, place in an oven to dry overnight at 80 °C, and calcine at 650 °C for 4 h in air atmosphere to obtain Li-USY molecular sieve. The prepared Li-USY molecular sieve is further placed in a 0.1 M mixed solution of magnesium nitrate and silver nitrate, stirred at room temperature for 6 h, filtered and dried, and then heated to 500 °C for calcination for 3 h in air atmosphere. The calcined AgMgLi-USY molecular sieve catalyst is formed and filled into a reaction tube, filling a 2 cm bed layer, and nitrogen is introduced as a carrier gas under normal pressure. Methanol is sampled by a micro pump with a volume content of 5-20%. The reaction is carried out at 350-700 °C, and the feed space velocity is 3-10 ml∙g cat. -1 ∙s -1 The product is detected online by gas chromatography dual-channel TCD.

[0043] Comparative Example 7: Preparation of AgCeLi-TS-1 molecular sieve catalyst.

[0044] Weigh 50 g of TS-1 molecular sieve with a titanium-silicon ratio of 30, perform ion exchange three times in a 0.1 M lithium carbonate solution, then centrifuge and wash three times, place in an oven to dry overnight at 80 °C, and calcine at 650 °C for 4 h in an air atmosphere. The prepared Li-TS-1 molecular sieve is placed in a 0.1 M mixed solution of silver nitrate and cerium nitrate, stirred at room temperature for 6 h, filtered and dried, and then heated to 500 °C for 3 h in an air atmosphere. The calcined AgCeLi-TS-1 molecular sieve catalyst is formed and filled into a reaction tube, filling a 2 cm bed layer, and nitrogen is introduced as a carrier gas under normal pressure. Methanol is sampled by a micro pump with a volume content of 5-20%. The reaction is carried out at 350-700 °C, and the feed space velocity is 3-10 ml∙g cat. -1 ∙s -1 The product is detected online by gas chromatography dual-channel TCD.

[0045] Table 1. Performance of a series of molecular sieve catalysts for catalytic oxygen-free dehydrogenation of methanol to anhydrous formaldehyde.

[0046]

[0047] The above experiments show that the modified zeolite catalysts based on TS-1 and MCM-22 exhibit poor formaldehyde yields, while the modified USY, Beta and HY zeolite catalysts have good catalytic activity. Compared with the catalysts modified with Zr and Mg metals, the AgCeLi-USY modified zeolite has outstanding methanol conversion rate and formaldehyde yield in a wider temperature range (350~700 ℃), which is mainly due to the synergistic effect of low-temperature high-activity Ag, reducible CeO2 rich in oxygen vacancies and acid-adjustable Li-doped high-temperature active USY zeolite.

[0048] The above-mentioned embodiments are only preferred embodiments of the present invention, but the present invention is not limited to the specific details in the above-mentioned embodiments. Within the technical concept of the present invention, several modifications and improvements can be made to the technical solution of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be based on the attached claims.

Claims

1. A method for preparing a modified molecular sieve catalyst for producing anhydrous formaldehyde by anaerobic dehydrogenation of methanol, characterized in that: The dehydrogenation modified molecular sieve catalyst is prepared by an ion exchange-electrostatic adsorption method, that is, the molecular sieve is modified by alkali metal ions and transition metal ions in sequence, and then calcined and formed for use in anhydrous methanol dehydrogenation reaction under an inert gas atmosphere.

2. The method for preparing the modified molecular sieve catalyst according to claim 1, characterized in that: (1) The molecular sieve is placed in an alkali metal salt solution for exchange for 2 to 5 hours and then centrifuged. The exchange is repeated 2 to 4 times and then placed in an oven for drying. The alkali metal-modified molecular sieve catalyst is then calcined to obtain; (2) The alkali metal-modified molecular sieve catalyst obtained in step 1 is placed in a transition metal salt solution and stirred for 2 to 8 hours, and the negative charges enriched on the surface of the alkali metal-modified molecular sieve are used to realize electrostatic adsorption of transition metal cations, and then the transition metal and alkali metal-modified molecular sieves are obtained after centrifugation, washing, drying and calcination.

3. The method for preparing the modified molecular sieve catalyst according to claim 2, characterized in that: The modified molecular sieve is one or more of USY, Beta, ZSM-5 and HY molecular sieves.

4. The method for preparing the modified molecular sieve catalyst according to claim 2, characterized in that: The alkali metal salt in step (1) is selected from any one or more of water-soluble lithium salts, potassium salts, and sodium salts; the anion of the alkali metal salt is selected from any one of carbonates, nitrates, acetates, and oxalates; and the concentration of the alkali metal ions is 0.02-1.0 mol / L.

5. The method for preparing the modified molecular sieve catalyst according to claim 2, characterized in that: In the step (1), the calcination temperature of the molecular sieve after ion exchange is 350-700°C, and the calcination time is 3-12 h.

6. The method for preparing the modified molecular sieve catalyst according to claim 2, characterized in that: The transition metal salt in step (2) comprises two or more of AgNO3, Zn(NO3)2, Cu(NO3)2, Ce(NO3)2, and Al(NO3)3, and the transition metal concentration is 0.02-5.0 mol / L.

7. The method for preparing the modified molecular sieve catalyst according to claim 2, characterized in that: In the step (2), the calcination temperature of the modified molecular sieve after the transition metal electrostatic adsorption is 300-600° C., and the calcination time is 3-6 h.

8. Use of the modified molecular sieve catalyst according to any one of claims 1 to 7 in the reaction of producing anhydrous formaldehyde by anaerobic dehydrogenation of methanol, characterized in that: The prepared catalyst was formed and loaded into a fixed bed quartz tube reactor. Methanol dehydrogenation experiments were carried out at 400-800 °C under N2 atmosphere, where the methanol volume content was 5-40% and the mass space velocity of the bed was 1.5-10 mL·g cat. -1 ·s -1 .

Images