Strong-acidity composite metal oxide catalyst as well as preparation and application thereof

Abstract

The invention discloses a method for synthesizing methylal through acetalation by using a strongly acidic composite metal oxide, and particularly relates to preparation of a strongly acidic composite metal oxide catalyst and a method for preparing methylal through condensation of methanol and formaldehyde by using the strongly acidic composite metal oxide catalyst. The preparation method comprises the following steps: preparing a ZrO2-SiO2 composite oxide precursor by adopting a coprecipitation method, dipping and loading active metal and an auxiliary agent on the composite oxide precursor, and applying the active metal and the auxiliary agent to a process of preparing methylal through acetalation. The method has the advantages of simple synthesis, no corrosion to equipment, mild reaction conditions, capability of improving the activity and stability of the catalyst, and the like.

Description

Technical Field

[0001] The present invention discloses a method for synthesizing dimethoxymethane by acetalization using a strongly acidic composite metal oxide catalyst, specifically relating to a method for modifying an acidic catalyst with a metal oxide and then using the modified catalyst for the condensation of methanol and formaldehyde to prepare dimethoxymethane. Background Art

[0002] Methanol is an important chemical raw material, which can be obtained from coal, natural gas, biomass, etc. through the syngas route. Due to the maturity of the syngas-to-methanol technology in recent years, the methanol production capacity has been severely excessive, and the development of downstream products of methanol has received extensive attention. Methanol can be used to produce organic chemical products such as olefins and alkanes, and can also be oxidized to prepare oxygen-containing compounds such as aldehydes or esters. The oxidation path of methanol has good atom economy and low energy consumption.

[0003] Dimethoxymethane (DMM), commonly known as dimethoxymethane, is one of the important chemical materials. Therefore, it has low toxicity, low boiling point, high oxygen content, and at the same time, it has hydrophilicity and lipophilicity, good solubility, small surface tension, and low heat of vaporization. It is widely used in industries such as medicine, cosmetics, daily necessities, pesticides, automotive manufacturing supplies, cotton, rubber industry, detergents, paints, inks, and diesel additives. Also, due to its excellent volatility and no damage to atmospheric ozone, it can be used as a refrigerant to replace Freon. Among the numerous processes for synthesizing dimethoxymethane (DMM), the process of reacting methanol and formaldehyde to produce DMM is the most mature and is also the main method for synthesizing DMM in industry currently. In this method, the reaction is carried out on an acidic catalyst, such as liquid acids (concentrated sulfuric acid, p-toluenesulfonic acid, ionic liquids), solid acids (strongly acidic cation exchange resin, HZSM-5 zeolite, crystalline aluminosilicate), etc.

[0004] In recent years, researchers have conducted extensive research on the catalytic condensation of methanol and formaldehyde to prepare dimethoxymethane using solid acid catalysts. For example, the invention patents EP 0327343, JP2000109443A, etc. publicly disclosed by Asahi Kasei Corporation of Japan use solid acids such as cation exchange resin and crystalline aluminosilicate as catalysts and have been applied industrially; Jin Mingshan et al. (Fudan University Journal (Natural Science Edition), 2003, 42(3): 280-284.) prepared supported phosphotungstic heteropolyacid catalysts and Cs x H 3-x PW 12 O 40(X = 1, 1.5, 2, 2.5, 3) Cesium salt of phosphotungstic heteropolyacid catalyst; Acidic molecular sieve catalysts studied by Wang Shujuan et al. (Journal of Jilin University (Science Edition), 2002, 40(3): 320 - 323.); Compared with liquid acid catalysts and acidic ionic liquid catalysts, solid acids (strong acidic cation exchange resin, crystalline aluminosilicate, HZSM-5 molecular sieve) etc. have the advantages of high activity, no corrosion, and easy separation, and are a kind of green and environmentally friendly catalyst, which has attracted extensive attention in recent years. Summary of the Invention

[0005] The main technical problem to be solved by the present invention is to provide a method for modifying a strong acidic catalyst and using the modified catalyst for the synthesis of methylal by acetalization. By modifying and modifying the acidic catalyst with composite metal oxides, the acid strength and the number of acid centers of the catalyst are effectively changed, and by-products such as DMC are inhibited, thereby improving the selectivity of methylal.

[0006] A method for synthesizing methylal by acetalization using a strong acidic composite metal oxide catalyst, specifically as follows:

[0007] (1) Prepare a ZrO2 - SiO2 composite oxide precursor by the co - precipitation method: Load tetraethyl orthosilicate and ethanol into a flask in sequence and stir. The volume ratio of tetraethyl orthosilicate to ethanol is 1:1 - 1:5 (the preferred range is 1:1.5 - 1:5); Then weigh an aqueous solution of a zirconium precursor salt and add it dropwise to the flask, and add ammonia water (mass concentration of 5 - 20%) dropwise to the above - mentioned mixed solution until pH = 8 - 11, reflux and stir at 80 - 120 °C for 2 - 10 h; After stirring, carry out solid - liquid separation, dry the solid and then calcine to obtain the composite metal oxide precursor.

[0008] (2) Preparation of the composite metal oxide catalyst: Weigh a certain amount of tungsten precursor salt and prepare an aqueous solution with a concentration of 5% - 50%, and then weigh a transition metal precursor salt relative to 0.5% - 10% (calculated as transition metal oxide) of WO3 and add it to the aqueous solution of the tungsten precursor salt. Add the above - mentioned solution to the composite metal oxide precursor prepared in step (1) for equal - volume impregnation, and finally carry out drying and calcination.

[0009] The zirconium precursor salt includes one or more of zirconium nitrate, zirconium sulfate, zirconium acetate, and zirconium oxychloride octahydrate. The content of ZrO2 in the ZrO2 - SiO2 composite oxide precursor is 0.5 - 20%, preferably 0.5 - 10%.

[0010] The tungsten precursor salt includes one or more of ammonium tungstate, ammonium metatungstate, and ammonium paratungstate.

[0011] The transition metal includes one or more of Pt, Co, Ni, Mn, Fe, Mo, V, and Ce, and the precursor salts of the transition metal include one or more of H2PtCl6·6H2O, Pt(NO3)2, Co(NO3)2·6H2O, Ni(NO3)2·6H2O, Mn(NO3)2·6H2O, NH4MnO4, MnC2O4·2H2O, Fe(NO3)3·9H2O, (NH4)2MoO4, NH4VO3, VO2(C2O4)·2H2O, Ce(NO3)3, and Ce(Ac)3·3H2O.

[0012] In step (1), after the solid-liquid separation of the ZrO2-SiO2 composite oxide precursor, the drying temperature of the solid is 80-120 °C, and the time is 2-12 h. After drying, the solid is calcined at 350-750 °C (preferably 450-600 °C) for 3-12 h (preferably 3-6 h); in step (2), the drying temperature of the composite metal oxide catalyst is 100-120 °C, and the time is 2-12 h. After drying, it is calcined at 350-750 °C (preferably 450-600 °C) for 5-12 h (preferably 5-8 h). The content of the mixture of the transition metal and WO3 relative to the ZrO2-SiO2 composite is 1%-50%, preferably 5%-30%.

[0013] The strongly acidic composite metal oxide catalyst is applied to catalyze the acetalization of methanol and formaldehyde to synthesize methylal.

[0014] The formaldehyde includes one or more of aqueous formaldehyde solution (mass fraction 30%-70%), trioxane, and paraformaldehyde.

[0015] Using a fixed-bed reactor, the middle section of the bed is filled with the strongly acidic composite metal oxide catalyst (the formed catalyst is 20-60 mesh), and the upper and lower sections are filled with quartz sand; the raw materials are a mixed solution of methanol and formaldehyde, and the molar ratio of methanol to formaldehyde is 2:1-10:1, preferably 2:1-4:1; the reaction temperature is 40-150 °C (preferably 50-120 °C), and the reaction is carried out at atmospheric pressure. The WHSV during the reaction process is 1-10 h -1 (preferably 1-5 h -1 ). The reaction involved in the present invention can be represented by the following reaction equation:

[0016]

[0017] The advantages of the present invention are simple synthesis, no corrosion to equipment, mild reaction conditions, and can improve the activity and stability of the catalyst, etc.

[0018] The beneficial technical effects of the present invention:

[0019] 1. The surface of ZrO2 has both acidic sites, basic sites, and abundant oxygen vacancies on the surface. On the one hand, it can adjust the acidity and basicity of the catalyst surface, and under certain conditions, it can also have an oxidation function to oxidize alcohols into aldehydes, further promoting the forward movement of the acetal reaction.

[0020] 2. The obtained catalyst is used in the process of preparing dimethoxymethane by acetalization, which has a simple process, convenient operation, and effectively reduces costs. It is a green synthesis route with good application prospects. Specific Embodiments

[0021] The following elaborates on the preferred embodiments of the present invention in detail, so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making a clearer and more definite definition of the protection scope of the present invention.

[0022] Using a fixed-bed reactor, the middle section of the bed is filled with the strongly acidic composite metal oxide catalyst (the formed catalyst is 20 - 60 mesh), and the upper and lower sections are filled with quartz sand;

[0023] Example 1

[0024] Take 29.5 ml of tetraethyl orthosilicate and add it to 45 ml of ethanol, denoted as solution 1; weigh 5.51 g of zirconium nitrate and add it to 20 ml of water, denoted as solution 2; add solution 2 dropwise to solution 1 and stir for 2 h; then add 10% ammonia water by mass dropwise to the above mixed solution until pH = 9; reflux and stir at 100 °C for 2 h, then perform solid-liquid separation, dry at 80 °C for 12 h, and finally calcine at 450 °C for 8 h to obtain 20% ZrO2 - SiO2 composite oxide.

[0025] Weigh 0.097 g of ammonium tungstate and prepare an aqueous solution with a concentration of 5%, weigh 0.046 g of H2PtCl6·6H2O and add it to the above aqueous solution, then add the prepared 20% ZrO2 - SiO2 composite oxide to this solution for equal-volume impregnation for 5 h. Finally, dry at 100 °C for 6 h and then calcine at 500 °C for 6 h to obtain a 20% PtO2 - WO3 / 20% ZrO2 - SiO2 composite metal oxide catalyst.

[0026] Press the obtained sample into tablets of 20 - 60 mesh, and then load it into a stainless steel tube fixed-bed reactor (the inner diameter of the fixed bed is 8 mm) for evaluation. Using a 37% aqueous formaldehyde solution by mass as the formaldehyde source, n 甲醇 :n 甲醛 = 7:3 (molar ratio), reaction temperature 120 °C, WHSV = 3 h -1 . Finally, through analysis, the formaldehyde conversion rate is 90.5%, and the selectivity of dimethoxymethane is 92.4%.

[0027] Example 2

[0028] Take 33.2 ml of tetraethyl orthosilicate and add it to 66.4 ml of ethanol, denoted as Solution 1; weigh 2.30 g of zirconium sulfate and add it to 20 ml of water, denoted as Solution 2; add Solution 2 dropwise to Solution 1 and stir for 2 h; then add 5% ammonia water by drops to the above mixed solution until pH = 8; carry out solid-liquid separation after refluxing and stirring at 120 °C for 10 h, dry at 120 °C for 2 h, and finally calcine at 600 °C for 3 h to obtain 10% ZrO2-SiO2 composite oxide.

[0029] Weigh 2.998 g of ammonium metatungstate and prepare an aqueous solution with a concentration of 30%; weigh 0.762 g of Co(NO3)2·6H2O and add it to the above aqueous solution, then add the prepared 10% ZrO2-SiO2 composite oxide to this solution for isovolumetric impregnation for 2 h. Finally, dry at 120 °C for 4 h and then calcine at 450 °C for 12 h to obtain a 7% CoO-WO3 / 10% ZrO2-SiO2 composite metal oxide catalyst.

[0030] Press the obtained sample into tablets with a mesh size of 20 - 60, and then load it into a stainless steel tube fixed-bed reactor (inner diameter of the fixed bed is 8 mm) for evaluation. Using a 70% aqueous formaldehyde solution by mass as the formaldehyde source, n 甲醇 :n 甲醛 = 2:1 (molar ratio), reaction temperature 40 °C, WHSV = 1 h -1 . Finally, through analysis, the formaldehyde conversion rate is 88.1% and the selectivity of methylal is 89.4%.

[0031] Example 3

[0032] Take 36.7 ml of tetraethyl orthosilicate and add it to 183.51 ml of ethanol, denoted as Solution 1; weigh 0.13 g of zirconium acetate and add it to 20 ml of water, denoted as Solution 2; add Solution 2 dropwise to Solution 1 and stir for 2 h; then add 20% ammonia water by drops to the above mixed solution until pH = 11; carry out solid-liquid separation after refluxing and stirring at 90 °C for 5 h, dry at 100 °C for 5 h, and finally calcine at 550 °C for 6 h to obtain 0.5% ZrO2-SiO2 composite oxide.

[0033] Weigh 1.535 g of ammonium paratungstate and prepare an aqueous solution with a concentration of 10%; weigh 0.531 g of Ni(NO3)2·6H2O and add it to the above aqueous solution, then add the prepared 0.5% ZrO2-SiO2 composite oxide to this solution for isovolumetric impregnation for 4 h. Finally, dry at 110 °C for 4 h and then calcine at 500 °C for 6 h to obtain a 10% NiO-WO3 / 0.5% ZrO2-SiO2 composite metal oxide catalyst.

[0034] The obtained sample was tableted into 20 - 60 mesh, and then loaded into a stainless - steel tube fixed - bed reactor (inner diameter of the fixed - bed: 8 mm) for evaluation. Using a 50% aqueous formaldehyde solution by mass concentration as the formaldehyde source, n 甲醇 :n 甲醛 = 5:1 (molar ratio), reaction temperature 80 °C, WHSV = 10 h -1 . Finally, through analysis, the formaldehyde conversion rate was 80.1% and the selectivity of methylal was 92.3%.

[0035] Example 4

[0036] 31.4 ml of tetraethyl orthosilicate was pipetted and added to 94.06 ml of ethanol, denoted as solution 1; 3.92 g of zirconium oxychloride octahydrate was weighed and added to 20 ml of water, denoted as solution 2; solution 2 was added dropwise to solution 1 and stirred for 2 h; then 15% aqueous ammonia by mass concentration was added dropwise to the above - mentioned mixed solution until pH = 10; after refluxing and stirring at 100 °C for 3 h, solid - liquid separation was carried out, dried at 80 °C for 8 h, and finally calcined at 550 °C for 5 h to obtain 15% ZrO₂ - SiO₂ composite oxide.

[0037] 5.321 g of ammonium metatungstate was weighed and prepared into an aqueous solution with a concentration of 40%, 0.102 g of Mn(NO₃)₂·6H₂O was added to the above - mentioned aqueous solution, and then the prepared 15% ZrO₂ - SiO₂ composite oxide was added to this solution for equal - volume impregnation for 6 h. Finally, after drying at 110 °C for 3 h and calcining at 600 °C for 6 h, a 0.5% MnO - WO₃ / 15% ZrO₂ - SiO₂ composite metal oxide catalyst could be prepared.

[0038] The obtained sample was tableted into 20 - 60 mesh, and then loaded into a stainless - steel tube fixed - bed reactor (inner diameter of the fixed - bed: 8 mm) for evaluation. Using trioxane as the formaldehyde source, n 甲醇 :n 甲醛 = 4:1 (molar ratio), reaction temperature 80 °C, WHSV = 2 h -1 . Finally, through analysis, the formaldehyde conversion rate was 90.9% and the selectivity of methylal was 92.0%.

[0039] Example 5

[0040] Take 34.7 ml of tetraethyl orthosilicate and add it to 173.4 ml of ethanol, denoted as Solution 1; weigh 1.59 g of zirconium acetate and add it to 20 ml of water, denoted as Solution 2; add Solution 2 dropwise to Solution 1 and stir for 2 h; then add 18% ammonia water by drops to the above mixed solution until pH = 9.5; carry out solid-liquid separation after refluxing and stirring at 120 °C for 3 h, dry at 100 °C for 8 h, and finally calcine at 550 °C for 5 h to obtain 6% ZrO2-SiO2 composite oxide.

[0041] Weigh 2.879 g of ammonium tungstate and prepare an aqueous solution with a concentration of 50%; weigh 0.056 g of MnC2O4·2H2O and add it to the above aqueous solution, then add the prepared 6% ZrO2-SiO2 composite oxide to this solution for isovolumetric impregnation for 8 h. Finally, dry at 120 °C for 3 h and then calcine at 550 °C for 6 h to obtain 1% MnO-WO3 / 6% ZrO2-SiO2 composite metal oxide catalyst.

[0042] Press the obtained sample into tablets with a size of 20-60 mesh, and then load it into a stainless steel tube fixed-bed reactor (the inner diameter of the fixed bed is 8 mm) for evaluation. Using paraformaldehyde as the formaldehyde source, n 甲醇 :n 甲醛 = 6:1 (molar ratio), reaction temperature 120 °C, WHSV = 9 h -1 Finally, after analysis, the formaldehyde conversion rate is 89.7% and the selectivity of methylal is 87.8%.

[0043] Example 6

[0044] Take 30.3 ml of tetraethyl orthosilicate and add it to 60.5 ml of ethanol, denoted as Solution 1; weigh 4.96 g of zirconium acetate and add it to 20 ml of water, denoted as Solution 2; add Solution 2 dropwise to Solution 1 and stir for 2 h; then add 7% ammonia water by drops to the above mixed solution until pH = 9; carry out solid-liquid separation after refluxing and stirring at 80 °C for 2 h, dry at 80 °C for 12 h, and finally calcine at 550 °C for 3 h to obtain 18% ZrO2-SiO2 composite oxide.

[0045] Weigh 1.949 g of ammonium paratungstate and prepare an aqueous solution with a concentration of 5%; weigh 0.352 g of Fe(NO3)3·9H2O and add it to the above aqueous solution, then add the prepared 18% ZrO2-SiO2 composite oxide to this solution for isovolumetric impregnation for 8 h. Finally, dry at 120 °C for 2 h and then calcine at 550 °C for 6 h to obtain 4% Fe2O3-WO3 / 18% ZrO2-SiO2 composite metal oxide catalyst.

[0046] The obtained sample was pressed into tablets of 20 - 60 mesh, and then loaded into a stainless steel tube fixed - bed reactor (inner diameter of the fixed bed: 8 mm) for evaluation. Using an aqueous formaldehyde solution with a mass concentration of 30% as the formaldehyde source, n 甲醇 :n 甲醛 = 6:1 (molar ratio), reaction temperature 150 °C, WHSV = 1 h -1 . Finally, through analysis, the formaldehyde conversion rate was 92.4%, and the selectivity of methylal was 85.2%.

[0047] Example 7

[0048] 35.4 ml of tetraethyl orthosilicate was pipetted and added to 35.4 ml of ethanol, denoted as solution 1; 0.92 g of zirconium sulfate was weighed and added to 20 ml of water, denoted as solution 2; solution 2 was added dropwise to solution 1 and stirred for 6 h; then an aqueous ammonia solution with a mass concentration of 12% was added dropwise to the above - mentioned mixed solution until pH = 10.5; after refluxing and stirring at 90 °C for 5 h, solid - liquid separation was carried out, dried at 120 °C for 2 h, and finally calcined at 500 °C for 6 h to obtain 4% ZrO2 - SiO2 composite oxide.

[0049] 1.028 g of ammonium tungstate was weighed and prepared into an aqueous solution with a concentration of 20%, 0.022 g of (NH4)2·MoO4 was added to the above - mentioned aqueous solution, and then the prepared 4% ZrO2 - SiO2 composite oxide was added to this solution for equal - volume impregnation for 2 h. Finally, after drying at 120 °C for 2 h and calcining at 450 °C for 6 h, a 1.8% MoO - WO3 / 4% ZrO2 - SiO2 composite metal oxide catalyst was prepared.

[0050] The obtained sample was pressed into tablets of 20 - 60 mesh, and then loaded into a stainless steel tube fixed - bed reactor (inner diameter of the fixed bed: 8 mm) for evaluation. Using an aqueous formaldehyde solution with a mass concentration of 37% as the formaldehyde source, n 甲醇 :n 甲醛 = 10:1 (molar ratio), reaction temperature 60 °C, WHSV = 1 h -1 . Finally, through analysis, the formaldehyde conversion rate was 91.5%, and the selectivity of methylal was 91.4%.

[0051] Example 8

[0052] 32.5 ml of tetraethyl orthosilicate was pipetted and added to 129.84 ml of ethanol, denoted as solution 1; 3.19 g of zirconium acetate was weighed and added to 20 ml of water, denoted as solution 2; solution 2 was added dropwise to solution 1 and stirred for 6 h; then an aqueous ammonia solution with a mass concentration of 10% was added dropwise to the above - mentioned mixed solution until pH = 9; after refluxing and stirring at 110 °C for 2 h, solid - liquid separation was carried out, dried at 100 °C for 10 h, and finally calcined at 500 °C for 4 h to obtain 12% ZrO2 - SiO2 composite oxide.

[0053] Weigh 2.039 g of ammonium metatungstate and prepare an aqueous solution with a concentration of 30%. Weigh 0.119 g of (NH4)2·VO3 and add it to the above aqueous solution. Then add the prepared 12% ZrO2-SiO2 composite oxide to this solution for equal-volume impregnation for 5 h. Finally, dry it at 100 °C for 5 h and then calcine it at 500 °C for 6.5 h to obtain a 4.9% V2O3-WO3 / 12% ZrO2-SiO2 composite metal oxide catalyst.

[0054] Press the obtained sample into tablets with a size of 20 - 60 mesh, and then load it into a stainless steel tube fixed-bed reactor (the inner diameter of the fixed bed is 8 mm) for evaluation. Using an aqueous formaldehyde solution with a mass concentration of 37% as the formaldehyde source, n 甲醇 :n 甲醛 = 10:1 (molar ratio), the reaction temperature is 60 °C, and WHSV = 1 h -1 . Finally, through analysis, the formaldehyde conversion rate is 85.2%, and the selectivity of methylal is 92.4%.

[0055] Example 9

[0056] Transfer 33.6 ml of tetraethyl orthosilicate and add it to 167.83 ml of ethanol, denoted as solution 1; weigh 2.35 g of zirconium oxychloride octahydrate and add it to 20 ml of water, denoted as solution 2; add solution 2 dropwise to solution 1 and stir for 2 h; then add aqueous ammonia with a mass concentration of 8% dropwise to the above mixed solution until pH = 11; reflux and stir at 80 °C for 10 h and then perform solid-liquid separation, dry at 120 °C for 4.5 h, and finally calcine at 500 °C for 6.5 h to obtain 9% ZrO2-SiO2 composite oxide.

[0057] Weigh 2.384 g of ammonium paratungstate and prepare an aqueous solution with a concentration of 18%. Weigh 0.385 g of CeNO3 and add it to the above aqueous solution. Then add the prepared 9% ZrO2-SiO2 composite oxide to this solution for equal-volume impregnation for 5 h. Finally, dry it at 100 °C for 5 h and then calcine it at 500 °C for 6.5 h to obtain a 7.2% CeO2-WO3 / 9% ZrO2-SiO2 composite metal oxide catalyst.

[0058] Press the obtained sample into tablets with a size of 20 - 60 mesh, and then load it into a stainless steel tube fixed-bed reactor (the inner diameter of the fixed bed is 8 mm) for evaluation. Using trioxane as the formaldehyde source, n 甲醇 :n 甲醛 = 2:1 (molar ratio), the reaction temperature is 80 °C, and WHSV = 5 h -1 . Finally, through analysis, the formaldehyde conversion rate is 83.1%, and the selectivity of methylal is 88.9%.

[0059] Example 10

[0060] Take 33.2 ml of tetraethyl orthosilicate and add it to 66.4 ml of ethanol, denoted as solution 1; weigh 2.30 g of zirconium sulfate and add it to 20 ml of water, denoted as solution 2; add solution 2 dropwise to solution 1 and stir for 2 h; then add 10% ammonia water dropwise to the above mixed solution until pH = 9; reflux and stir at 80 °C for 4 h, then perform solid-liquid separation, dry at 100 °C for 6 h, and finally calcine at 500 °C for 6.5 h to obtain 10% ZrO2-SiO2 composite oxide.

[0061] Weigh 1.988 g of ammonium tungstate and prepare an aqueous solution with a concentration of 5%; weigh 0.175 g of NH4MnO4 and add it to the above aqueous solution, then add the prepared 10% ZrO2-SiO2 composite oxide to this solution for isovolumetric impregnation for 5 h. Finally, dry at 120 °C for 5 h and then calcine at 650 °C for 5 h to obtain the 5.3% MnO-WO3 / 10% ZrO2-SiO2 composite metal oxide catalyst.

[0062] Press the obtained sample into tablets with a size of 20 - 60 mesh, then load it into a stainless steel tube fixed-bed reactor (the inner diameter of the fixed bed is 8 mm) for evaluation. Using trioxymethylene as the formaldehyde source, n 甲醇 :n 甲醛 = 10:1 (molar ratio), the reaction temperature is 120 °C, and WHSV = 9 h -1 . Finally, after analysis, the formaldehyde conversion rate is 86.2% and the selectivity of methylal is 89.3%.

[0063] Example 11

[0064] Take 31.4 ml of tetraethyl orthosilicate and add it to 94 ml of ethanol, denoted as solution 1; weigh 3.9 g of zirconium oxychloride octahydrate and add it to 20 ml of water, denoted as solution 2; add solution 2 dropwise to solution 1 and stir for 3 h; then add 15% ammonia water dropwise to the above mixed solution until pH = 11; reflux and stir at 80 °C for 4 h, then perform solid-liquid separation, dry at 120 °C for 4 h, and finally calcine at 600 °C for 6.5 h to obtain 15% ZrO2-SiO2 composite oxide.

[0065] Weigh 0.876 g of ammonium paratungstate and prepare an aqueous solution with a concentration of 5%; weigh 0.154 g of Ce(Ac)3·3H2O and add it to the above aqueous solution, then add the prepared 15% ZrO2-SiO2 composite oxide to this solution for isovolumetric impregnation for 5 h. Finally, dry at 120 °C for 5 h and then calcine at 650 °C for 5 h to obtain the 15.7% CeO2-WO3 / 15% ZrO2-SiO2 composite metal oxide catalyst.

[0066] The obtained sample was tableted into 20 - 60 mesh, and then loaded into a stainless - steel tube fixed - bed reactor (inner diameter of the fixed - bed is 8 mm) for evaluation. Using paraformaldehyde as the formaldehyde source, n 甲醇 :n 甲醛 = 6:1 (molar ratio), reaction temperature 60 °C, WHSV = 2 h -1 . Finally, through analysis, the formaldehyde conversion rate was 92.5%, and the selectivity of methylal was 90.4%.

[0067] Example 12

[0068] 34.7 ml of tetraethyl orthosilicate was pipetted and added to 173.4 ml of ethanol, denoted as solution 1; 3.9 g of zirconium acetate was weighed and added to 20 ml of water, denoted as solution 2; solution 2 was added dropwise to solution 1 and stirred for 3 h; then 20% ammonia water by mass concentration was added dropwise to the above - mentioned mixed solution until pH = 11; after refluxing and stirring at 100 °C for 4 h, solid - liquid separation was carried out, dried at 100 °C for 6 h, and finally calcined at 500 °C for 8 h to obtain 6% ZrO2 - SiO2 composite oxide.

[0069] 1.895 g of ammonium metatungstate was weighed and prepared into an aqueous solution with a concentration of 30%, 0.308 g of VO2(C2O4)·2H2O was added to the above - mentioned aqueous solution, and then the prepared 6% ZrO2 - SiO2 composite oxide was added to this solution for equal - volume impregnation for 5 h. Finally, after drying at 120 °C for 5 h and calcining at 650 °C for 5 h, a 12.9% V2O5 - WO3 / 6% ZrO2 - SiO2 composite metal oxide catalyst could be prepared.

[0070] The obtained sample was tableted into 20 - 60 mesh, and then loaded into a stainless - steel tube fixed - bed reactor (inner diameter of the fixed - bed is 8 mm) for evaluation. Using 55% formaldehyde by mass concentration as the formaldehyde source, n 甲醇 :n 甲醛 = 3:1 (molar ratio), reaction temperature 40 °C, WHSV = 1 h -1 . Finally, through analysis, the formaldehyde conversion rate was 85.5%, and the selectivity of methylal was 92.1%.

[0071] Example 13

[0072] 31.4 ml of tetraethyl orthosilicate was taken and added to 62.7 ml of ethanol, denoted as Solution 1; 3.9 g of zirconium nitrate was weighed and added to 20 ml of water, denoted as Solution 2; Solution 2 was added dropwise to Solution 1 and stirred for 3 h; then 10% ammonia water by mass concentration was added dropwise to the above mixed solution until pH = 9; after refluxing and stirring at 100 °C for 6 h, solid-liquid separation was carried out, dried at 100 °C for 3 h, and finally calcined at 650 °C for 4 h to obtain 16% ZrO2-SiO2 composite oxide.

[0073] 1.479 g of ammonium tungstate was weighed and prepared into an aqueous solution with a concentration of 5%; 0.322 g of Pt(NO3)2 was added to the above aqueous solution, and then the prepared 15% ZrO2-SiO2 composite oxide was added to this solution for isovolumetric impregnation for 4 h. Finally, after drying at 100 °C for 5 h and calcining at 450 °C for 8 h, 18% PtO2-WO3 / 15% ZrO2-SiO2 composite metal oxide catalyst could be prepared.

[0074] The obtained sample was tableted into 20 - 60 mesh, and then loaded into a stainless steel tube fixed-bed reactor (inner diameter of the fixed bed is 8 mm) for evaluation. Using 62.5% formaldehyde by mass concentration as the formaldehyde source, n 甲醇 :n 甲醛 = 4:1 (molar ratio), reaction temperature 80 °C, WHSV = 3 h -1 Finally, after analysis, the formaldehyde conversion rate was 91.5% and the selectivity of methylal was 88.3%.

[0075] Comparative Example 1

[0076] 5.51 g of zirconium nitrate was weighed and added to 20 ml of water, and 10% ammonia water by mass concentration was added dropwise to the above solution until pH = 9; after refluxing and stirring at 100 °C for 2 h, solid-liquid separation was carried out, dried at 80 °C for 12 h, and finally calcined at 450 °C for 8 h to obtain ZrO2.

[0077] 0.097 g of ammonium tungstate was weighed and prepared into an aqueous solution with a concentration of 5%; 0.046 g of H2PtCl6·6H2O was added to the above aqueous solution, and then the prepared ZrO2 was added to this solution for isovolumetric impregnation for 5 h. Finally, after drying at 100 °C for 6 h and calcining at 500 °C for 6 h, 20% PtO2-WO3 / ZrO2 composite metal oxide catalyst could be prepared.

[0078] The obtained sample was tableted into 20 - 60 mesh, and then loaded into a stainless steel tube fixed-bed reactor (inner diameter of the fixed bed is 8 mm) for evaluation. Using 37% aqueous formaldehyde solution as the formaldehyde source, n 甲醇 :n 甲醛= 7:3 (molar ratio), reaction temperature 120 °C, WHSV = 3 h -1 Finally, through analysis, the formaldehyde conversion rate was 80.9% and the selectivity for methylal was 78.2%.

[0079] Comparative Example 2

[0080] 31.4 ml of tetraethyl orthosilicate was taken and added to 94.06 ml of ethanol. Aqueous ammonia with a mass concentration of 15% was added dropwise to the above mixed solution until pH = 10; after refluxing and stirring at 100 °C for 3 h, solid-liquid separation was carried out, dried at 80 °C for 8 h, and finally calcined at 550 °C for 5 h to obtain the oxide SiO2.

[0081] 5.321 g of ammonium metatungstate was weighed and prepared into an aqueous solution with a concentration of 40%. 0.102 g of Mn(NO3)2·6H2O was weighed and added to the above aqueous solution, and then the prepared 15% ZrO2-SiO2 composite oxide was added to this solution for equal-volume impregnation for 6 h. Finally, after drying at 110 °C for 3 h and calcining at 600 °C for 6 h, the 0.5% MnO-WO3 / SiO2 composite metal oxide catalyst could be prepared.

[0082] The obtained sample was tableted into 20 - 60 mesh, and then loaded into a stainless-steel tube fixed-bed reactor (inner diameter of the fixed bed is 8 mm) for evaluation. Using trioxane as the formaldehyde source, n 甲醇 :n 甲醛 = 4:1 (molar ratio), reaction temperature 80 °C, WHSV = 2 h -1 Finally, through analysis, the formaldehyde conversion rate was 80.3% and the selectivity for methylal was 83.3%.

[0083] Comparative Example 3

[0084] 1.028 g of ammonium tungstate was weighed and prepared into an aqueous solution with a concentration of 20%. 0.022 g of (NH4)2·MoO4 was weighed and added to the above aqueous solution, and Aldrich nano SiO2 was added to this solution for equal-volume impregnation for 2 h. Finally, after drying at 120 °C for 2 h and calcining at 450 °C for 6 h, the 1.8% MoO-WO3 / SiO2 composite metal oxide catalyst could be prepared.

[0085] The obtained sample was tableted into 20 - 60 mesh, and then loaded into a stainless-steel tube fixed-bed reactor (inner diameter of the fixed bed is 8 mm) for evaluation. Using an aqueous formaldehyde solution with a mass concentration of 37% as the formaldehyde source, n 甲醇 :n 甲醛 = 10:1 (molar ratio), reaction temperature 60 °C, WHSV = 1 h -1 Finally, through analysis, the formaldehyde conversion rate was 83.4% and the selectivity for methylal was 78.6%.

[0086] By comparing Comparative Example 1 with Example 1, Comparative Example 2 with Example 4, and Comparative Example 3 with Example 7, it was found that under the same active components, additives and the same evaluation conditions, the catalysts with ZrO2 or SiO2 alone as the carrier were not as excellent as the modified catalyst. The possible reason is that the surface of ZrO2 has both acidic sites and basic sites, and has characteristics such as rich oxygen vacancies on the surface. SiO2 is a neutral material. The combination of the two can, on the one hand, provide better BET properties for the catalyst and adjust the acidity and basicity of the catalyst surface, and can also have an oxidation function to oxidize alcohols into aldehydes under certain conditions, further promoting the forward movement of the acetal reaction, making the catalyst have higher activity and selectivity.

[0087] The above are only the embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent structure or equivalent process transformation made by using the content of the specification of the present invention, or directly or indirectly applied in other related technical fields, shall be equally included in the patent protection scope of the present invention.

Claims

1. A preparation method of a strongly acidic composite metal oxide catalyst, characterized in that: (1) Preparation of ZrO2-SiO2 composite oxide precursor by coprecipitation method: Tetraethyl orthosilicate and ethanol were charged into a flask and stirred, and the volume ratio of tetraethyl orthosilicate to ethanol was 1:1 - 1:5 (preferred range is 1:1.5 - 1:5); then an aqueous solution of zirconium precursor salt was weighed and added dropwise to the flask, and ammonia water (mass concentration of 5 - 20%) was added dropwise to the above mixed solution until pH = 8 - 11, and refluxed and stirred at 80 - 120 °C for 2 - 10 h; after stirring, solid-liquid separation was carried out, and the solid was dried and then calcined to obtain the composite metal oxide precursor; (2) Preparation of composite metal oxide catalyst: A tungsten precursor salt was weighed and prepared into an aqueous solution with a concentration of 5% - 50%, and a transition metal precursor salt relative to 0.5% - 10% of WO3 (calculated based on transition metal oxide) was added to the aqueous solution of tungsten precursor salt, and the above solution was added to the composite metal oxide precursor prepared in step (1) for equal-volume or over-volume impregnation, and finally dried and calcined to obtain a strongly acidic composite metal oxide catalyst.

2. The preparation method of the composite metal oxide catalyst according to claim 1, characterized in that, The zirconium precursor salt includes one or more of zirconium nitrate, zirconium sulfate, zirconium acetate, zirconium oxychloride octahydrate; among them, the mass content of ZrO2 in the ZrO2-SiO2 composite oxide precursor is 0.5 - 20%, preferably 0.5 - 10%.

3. The preparation method of the composite metal oxide catalyst according to claim 1, characterized in that, The tungsten precursor salt includes one or more of ammonium tungstate, ammonium metatungstate, ammonium paratungstate.

4. The preparation method of the composite metal oxide catalyst according to claim 1, characterized in that, The transition metal includes one or more of Pt, Co, Ni, Mn, Fe, Mo, V, Ce, and the precursor salts of the transition metal include one or more of H2PtCl6·6H2O, Pt(NO3)2, Co(NO3)2·6H2O, Ni(NO3)2·6H2O, Mn(NO3)2·6H2O, NH4MnO4, MnC2O4·2H2O, Fe(NO3)3·9H2O, (NH4)2MoO4, NH4VO3, VO2(C2O4)·2H2O, Ce(NO3)3, Ce(Ac)3·3H2O.

5. The preparation method of the composite metal oxide according to claim 1, characterized in that, In step (1), after solid-liquid separation of the ZrO2-SiO2 composite oxide precursor, the drying temperature of the solid is 80 - 120 °C, the time is 2 - 12 h, and after drying, the solid is calcined at 350 - 750 °C (preferably 450 - 600 °C) for 3 - 12 h (preferably 3 - 6 h); In step (2), the drying temperature of the composite metal oxide catalyst is 100 - 120 °C, the time is 2 - 12 h, and after drying, it is calcined at 350 - 750 °C (preferably 450 - 600 °C) for 5 - 12 h (preferably 5 - 8 h); Among them, the sum of the transition metal and WO3 mixture is 1% - 50% of the mass of the ZrO2-SiO2 composite metal oxide precursor, preferably 5% - 30%.

6. A strongly acidic composite metal oxide catalyst prepared by the preparation method according to any one of claims 1 - 5.

7. An application of the catalyst according to claim 6, characterized in that: This catalyst can be applied to the catalytic synthesis of methylal by the acetalization of methanol and formaldehyde.

8. The application of the catalyst according to claim 7, characterized in that: The formaldehyde includes one or more of aqueous formaldehyde solution (mass fraction of 30% - 70%), trioxane, and paraformaldehyde.

9. The application of the catalyst according to claim 7, characterized in that: Using a fixed-bed reactor, the raw material is a mixed solution of methanol and formaldehyde, and the molar ratio of methanol to formaldehyde is 2:1 - 10:1, preferably 2:1 - 4:1; the reaction temperature is 40 - 150 °C (preferably 50 - 120 °C), the reaction is carried out at atmospheric pressure, and the WHSV during the reaction process is 1 - 10 h -1 (preferably 1 - 5 h -1 ).

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