Metal oxide catalysts for the oxidation of methanol to synthesize polymethoxy dimethyl ether and methods of making and using the same

Abstract

The application discloses a metal oxide catalyst for synthesizing polymethoxy dimethyl ether by methanol oxidation and a preparation method and application thereof, and belongs to the technical field of catalyst preparation and application. The catalyst is prepared from an active metal precursor and an acidic component, wherein the active metal is composed of any two components in Ti, Ni, Fe, Co, Mo, V, Cu and Mn; the acidic component is introduced into the catalyst system in a co-dissolution manner with the metal precursor, and the acidic component includes inorganic acid or organic acid; the inorganic acid includes one of hydrochloric acid, phosphoric acid and sulfuric acid; and the organic acid includes one of oxalic acid, citric acid, chlorosulfonic acid, tartaric acid, trifluoromethane sulfonic acid, methane sulfonic acid and ethylenediaminetetraacetic acid. The application precisely regulates the strength and quantity of the acid center on the catalyst surface by introducing the acidic component, simultaneously regulates the types and molar ratio of the active metal, and directionally constructs the catalyst with a specific lattice structure; and high efficient dual-function synergy of the acid site and the oxidation active site can be realized.

Description

Technical Field

[0001] This invention belongs to the field of catalyst preparation and application technology, specifically relating to a metal oxide catalyst for the synthesis of polyoxymethylene dimethyl ether by methanol oxidation, its preparation method and application. Background Technology

[0002] Polymethoxydimethyl ether (DMM) x The general formula is CH3O-(CH2O). x -CH3, x=1~8, is a polymer composed of CH2O- units, each end-capped by a methyl group and a methoxy group. Its physicochemical properties can be flexibly adjusted by controlling the chain length of the methyleneoxy group. DMM x Characterized by high oxygen content and high cetane number, DMMs with different carbon chain lengths x The physicochemical properties of these materials determine their unique application values. Among them, medium-chain-length DMMs... 3-5 With performance similar to diesel fuel, adding it to diesel can significantly improve combustion performance and reduce emissions of nitrogen oxides and particulate matter, making it an internationally recognized and highly attractive clean diesel oxygenated additive. Low-polymerization degree DMM x (x=1~2) is a green and environmentally friendly specialty organic solvent that can replace toxic benzene-based solvents and has application potential in the field of electronic-grade solvents; meanwhile, DMM x It can also serve as a potential solvent for CO2 absorption. Existing DMM x The current production process primarily utilizes an acid-catalyzed aldehyde condensation route, employing catalysts such as ion exchange resins, solid superacids, ionic liquids, and molecular sieves (Chinese patents CN120757441A, CN116836045A, CN112495427A). This process involves sequential steps including methanol oxidation to formaldehyde, formaldehyde condensation to polyoxymethylene, and aldehyde condensation, resulting in a long reaction time, high energy consumption, and difficulties in product separation. Therefore, there is an urgent need to develop more efficient synthesis technologies.

[0003] Methanol, as an important oxygen-containing platform compound, serves as a crucial link between resources such as coal, natural gas, and biomass and downstream high-value-added chemicals. Currently, industrially, methanol is mainly produced from coal and natural gas via syngas. Technologies for producing olefins (MTO), gasoline (MTG), and aromatics (MTA) from methanol have been industrialized. The oxidation of methanol to produce high-value-added oxygen-containing chemicals and clean diesel additives has become an important development direction for the high-quality utilization of methanol. This route, using methanol as a raw material, involves catalytic oxidation under mild conditions to produce a series of products such as formaldehyde, methyl formate, methyl acetal, and polyoxymethylene dimethyl ether, offering advantages such as high atom economy, low carbon emissions, a wide variety of downstream products, and a green and flexible process route.

[0004] Among them, methanol is directly oxidized to synthesize polyoxymethylene dimethyl ether (DMM). x This is an important research direction in the field: Chinese patent CN102030621A reports the preparation of DMM by methanol gas-phase method on catalysts with transition metals and acidic molecular sieves as active components. x The core focus of the reaction process is the control of reactor temperature; Chinese patent CN117599839A focuses on the design and construction of bifunctional catalysts with metal oxide-molecular sieve core-shell structures. However, the above work suffers from problems such as multiple steps in catalyst preparation and relatively complex composition. Current research mainly focuses on short-chain products (mainly DMM with x=1). x The synthesis of the first CO chain product, while the medium-length DMM has greater industrial application value. x The selectivity and yield of (x=3~5) still fall short of practical requirements. The core of this problem lies in the extremely high requirements of the bifunctional synergy of the catalyst itself. To achieve the controllable synthesis of longer CO chain products, it is necessary to construct acidic sites and redox active sites with gradient distribution on the catalyst surface to ensure that the two form an efficient synergistic effect, which can both promote the formation of intermediates and chain growth, and inhibit the occurrence of side reactions such as methanol dehydration to dimethyl ether.

[0005] Therefore, designing and synthesizing bifunctional catalysts that combine precise structural regulation with efficient synergistic effects has become a promising approach for the methanol oxidation synthesis of long-chain DMMs. x The main challenges we face. Summary of the Invention

[0006] This invention aims to provide a metal oxide catalyst for the oxidative synthesis of polyoxymethylene dimethyl ether (POMME) from methanol and its preparation method. The invention also provides the application of the above catalyst in the direct oxidative synthesis of POMME from methanol, specifically in the catalytic reaction involving DMM. x High selectivity and high methanol conversion rate.

[0007] This invention discloses a method for preparing a metal oxide catalyst and its application in the methanol oxidation to polyoxymethylene dimethyl ether (DME) reaction. The preparation method is characterized by its simplicity and high operability. Specifically, this invention uses a metal salt as a precursor, which is calcined to form a metal oxide active phase, and then combined with an in-situ modification strategy using acidic groups to construct the catalyst. During the preparation process, by controlling the type and molar ratio of the metal salt precursor, the pH value of the precursor solution, and the type and amount of acidic groups introduced, and then coordinating with programmed temperature calcination, a metal oxide catalyst possessing both Brønsted and Lewis acid sites, and matching with redox active sites, can be constructed. While existing related patents have already used metal oxides combined with molecular sieves for the methanol oxidation to DMM... xHowever, the direct application of metal oxide-based catalysts to this reaction system has not been reported in the literature. The metal oxide catalyst provided by this invention, on the one hand, adjusts the number of redox active sites by controlling the type and molar ratio of the metal oxide; on the other hand, it achieves precise control of the catalyst's acid strength and acid distribution through the in-situ introduction of acidic groups, thereby enhancing the synergistic efficiency of the two types of active sites. Simultaneously, this catalyst also possesses significant energy-saving advantages. Compared to existing catalysts, it can catalyze the direct oxidation and conversion of methanol under normal atmospheric pressure and mild reaction conditions in the gas phase, providing a solution for DMM. x This provides a new technological path for green and efficient synthesis.

[0008] This invention provides a metal oxide catalyst for the synthesis of polyoxymethylene dimethyl ether from methanol oxidation. The catalyst is prepared from an active metal precursor and an acid solution. The active metal is composed of two of the following: Ti, Ni, Fe, Co, Mo, V, Cu, and Mn. The first metal includes any one of Ti, Ni, Fe, Mn, and Co, and the second metal includes any one of V, Mo, and Cu. The acidic component is introduced into the catalyst system via co-dissolution with the metal precursor. The acidic component includes an inorganic acid or an organic acid. The inorganic acid includes one of hydrochloric acid, phosphoric acid, and sulfuric acid, and the organic acid includes one of oxalic acid, citric acid, chlorosulfonic acid, tartaric acid, trifluoromethanesulfonic acid, methanesulfonic acid, and ethylenediaminetetraacetic acid. The catalyst system comprises a metal oxide and an acidic component, wherein the mass fraction of the acidic component in the catalyst is 0.1%–10%.

[0009] The catalyst comprises two metal oxides, with a suitable molar ratio of the first metal to the second metal ranging from 0.2 to 1. Preferably, the metal oxides are selected from combinations of the following two metals: Ti-V, Ni-Mo, Fe-V, Mn-Cu, Fe-Mo, and Co-Cu. The metal precursor is selected from (NH4)6Mo7O. 24 •4H2O, NH4VO3, Co(NO3)2•6H2O, Fe(NO3)3•9H2O, FeCl3•6H2O, Cu(NO3)2•3H2O, Ti(OC4H9)4, Mn(NO3)2•4H2O or Ni(NO3)2•6H2O.

[0010] This invention provides a method for preparing the above-mentioned metal oxide catalyst for the methanol oxidation synthesis of polyoxymethylene dimethyl ether, comprising the following steps: (1) Select two precursors corresponding to the metals, prepare metal salt solutions respectively and stir them thoroughly until the system is homogeneous and stable; adjust the pH of the metal salt solution corresponding to the second metal to 1-6 using acid solution; under continuous stirring, add the first metal salt solution dropwise to the above pH-adjusted solution at a constant dropping rate of 2-10 mL / min.

[0011] (2) Stir the solution in step (1) until it is uniform and let it stand for 3-8 hours.

[0012] (3) Heat the sample obtained in step (2) at 100-150°C. o The metal oxide catalyst is dried at C and then placed in a tube furnace. Under a protective atmosphere, it is heated to 200-500°C at a heating rate of 1-4°C / min for 4-8 hours and then naturally cooled to room temperature to obtain the catalyst.

[0013] Furthermore, the concentrations of the first metal salt solution and the second metal salt solution prepared are both 0.2~2.5 mol / L, and the molar ratio of the first to the second active metal in the prepared catalyst is 0.2~1.

[0014] The acid solution includes inorganic or organic acids. The inorganic acid includes one of hydrochloric acid, phosphoric acid, and sulfuric acid, and the organic acid includes one of oxalic acid, citric acid, chlorosulfonic acid, tartaric acid, trifluoromethanesulfonic acid, methanesulfonic acid, and ethylenediaminetetraacetic acid. The concentration of the inorganic acid is 1-7 mol / L, and the concentration of the organic acid is 1-5 mol / L.

[0015] The protective atmosphere during roasting is one of oxygen, air, nitrogen, or argon.

[0016] This invention provides the application of the above-mentioned metal oxide catalyst in the direct oxidation of methanol to synthesize polyoxymethylene dimethyl ether, the steps of which are as follows: Methanol and a reaction gas are mixed at a molar ratio of 1:2 to 1:20. The reaction gas is a mixture of oxygen and nitrogen, with oxygen comprising 10% to 100% by volume. The mixture is then fed into a fixed-bed reactor for reaction under the following conditions: gas space velocity of 1000 to 10000 h⁻¹. -1 The reaction temperature is 150~300℃, and the reaction pressure is 0.1~1.0MPa. Compared with existing technologies, the catalyst preparation process of this invention is simple, allowing for convenient control of active sites, matching of acid sites with redox sites, suppression of side reactions, and ultimately achieving a methanol conversion rate of over 70%. x Selectivity increases to over 60%, and the proportion of high-value-added products (x=2~8) can reach over 45%, with overall catalytic performance superior to conventional catalysts.

[0017] The beneficial effects of this invention are: (1) This invention develops a method for preparing a highly selective and highly active catalyst for the direct oxidation of methanol to synthesize polyoxymethylene dimethyl ether. By controlling the type and molar ratio of metals, the pH value of the precursor solution, the type and amount of acidic groups, a metal oxide catalyst with Brønsted acid sites, Lewis acid sites and redox active sites can be constructed, thereby improving the activity of methanol oxidation reaction.

[0018] (2) The method for preparing metal oxide catalysts of the present invention adopts an in-situ introduction strategy of acidic groups, which directly constructs functionalized active centers during the preparation of the catalyst. The steps are simple and convenient, and the preparation parameters (such as metal molar ratio, calcination temperature, modification time, pH, etc.) are easy to control.

[0019] (3) The metal oxide catalyst of the present invention, under mild conditions, has high methanol conversion rate and DMM. x It boasts advantages such as high selectivity, good stability, and easy separation and recovery. Furthermore, key process parameters such as the molar ratio of methanol to reactant gas, reaction temperature, and space velocity have been optimized, effectively suppressing side reactions such as excessive methanol oxidation. Attached Figure Description

[0020] Figure 1 The image shows a TEM image of the catalyst prepared in Example 5. Detailed Implementation

[0021] The present invention will be further illustrated by the following embodiments, but is not limited to the following embodiments. Example 1

[0022] 12.48g (NH4)6Mo7O 24 • 4H₂O was dissolved in deionized water to prepare a molybdenum ion concentration of 1.4 mol / L. The solution was stirred for 10 min until completely dissolved, and the pH of the molybdenum solution was adjusted to 3 using 3 mol / L sulfuric acid solution. Subsequently, Ni(NO₃)₂•6H₂O was accurately weighed in another beaker according to a nickel-molybdenum molar ratio of 0.6, and dissolved in 50 mL of deionized water to prepare a nickel salt solution. This nickel salt solution was added dropwise to the pH-adjusted molybdenum salt solution at a rate of 5.0 mL / min using a constant flow pump, with magnetic stirring maintained during the addition. After the addition was completed, stirring was continued for 30 min, and the solution was allowed to stand at room temperature for 4 h. Then, it was transferred to a constant temperature oven and dried at 120 °C for 12 h. The dried solid product was placed in a tube furnace and heated to 300°C with air at a heating rate of 2°C / min. It was then calcined at this temperature for 4 hours and allowed to cool naturally to room temperature. The calcined product was then pulverized to 20-40 mesh and pressed into tablets to obtain a metal oxide catalyst with a nickel-molybdenum ratio of 0.6. The chemical composition of the catalyst was determined by elemental analysis, and the S content was 0.76%.

[0023] The reaction was carried out in a continuous flow fixed-bed reactor. The catalyst was placed in the middle of the reactor. The feedstock was methanol and 20% oxygen, with a methanol-to-oxygen ratio of 1:8. The reaction temperature was 220°C. o C, reaction space velocity 4000 h⁻¹ -1 The reaction pressure was 0.1 MPa, and the reaction time was 10 hours. The methanol conversion rate was 83.7%, DMM. x The selectivity was 86.5%, of which DMM 2-8 It is 56.1%. Example 2

[0024] 11.7 g of NH4VO3 was weighed into deionized water to prepare a vanadium ion concentration of 1.4 mol / L. The solution was stirred for 10 min until completely dissolved, and the pH of the vanadium solution was adjusted to 3 with 4 mol / L phosphoric acid solution. Then, Fe(NO3)3•9H2O was accurately weighed into another beaker according to an iron-vanadium molar ratio of 0.4, and dissolved in deionized water to prepare an iron salt solution. This iron salt solution was added dropwise to the pH-adjusted vanadium salt solution at a rate of 7.0 mL / min using a constant flow pump, with magnetic stirring maintained during the addition. After the addition was complete, stirring was continued for 30 min. The solution was allowed to stand at room temperature for 4 h, and then transferred to a constant temperature oven and dried at 120 °C for 12 h. The dried solid product was placed in a tube furnace and heated to 300°C with air at a heating rate of 2°C / min. It was then calcined at this temperature for 4 hours and allowed to cool naturally to room temperature. The calcined product was then pulverized to 20-40 mesh and pressed into tablets to obtain a metal oxide catalyst with an iron-vanadium ratio of 0.4. The chemical composition of the catalyst was determined by elemental analysis, and the P content was 2.34%.

[0025] The reaction was carried out in a continuous flow fixed-bed reactor. The catalyst was placed in the middle of the reactor. The feedstock was methanol and 20% oxygen, with a methanol to oxygen ratio of 1:6. The reaction temperature was 210°C. o C, reaction space velocity 3000 h⁻¹ -1 The reaction pressure was 0.1 MPa, and the reaction time was 10 hours. The methanol conversion rate was 74.8%, DMM. x The selectivity was 70.6%, of which DMM 2-8 It is 54.2%. Example 3

[0026] 24.2 g of Cu(NO3)2•3H2O was dissolved in deionized water to prepare a copper ion concentration of 2.3 mol / L. The solution was stirred for 10 min until completely dissolved, and the pH of the copper solution was adjusted to 2 with 2 mol / L sulfuric acid solution. Subsequently, Mn(NO3)2•4H2O was accurately weighed in another beaker according to a manganese-copper molar ratio of 0.3 and dissolved in deionized water to prepare a manganese salt solution. This manganese salt solution was added dropwise to the pH-adjusted copper salt solution at a rate of 7.0 mL / min using a constant flow pump, with magnetic stirring maintained during the addition. After the addition was completed, stirring was continued for 30 min. The solution was allowed to stand at room temperature for 4 h, and then transferred to a constant temperature oven and dried at 120 °C for 12 h. The dried solid product was placed in a tube furnace and heated to 300°C with air at a heating rate of 2°C / min. It was then calcined at this temperature for 4 hours and allowed to cool naturally to room temperature. The calcined product was then pulverized to 20-40 mesh and pressed into tablets to obtain a metal oxide catalyst with a manganese-copper ratio of 0.3. The chemical composition of the catalyst was determined by elemental analysis, and the S content was found to be 0.88%.

[0027] The reaction was carried out in a continuous flow fixed-bed reactor. The catalyst was placed in the middle of the reactor. The feedstock was methanol and oxygen in a ratio of 1:4. The reaction temperature was 210°C. o C, reaction space velocity 3000 h⁻¹ -1 The reaction pressure was 0.1 MPa, and the reaction time was 10 hours. The methanol conversion rate was 76.2%, DMM. x The selectivity was 89.8%, of which DMM 2-8 It is 68.3%. Example 4

[0028] 24.2 g of Cu(NO3)2•3H2O was dissolved in deionized water to prepare a copper ion concentration of 1.4 mol / L. The solution was stirred for 10 min until completely dissolved, and the pH of the copper solution was adjusted to 2 using 2 mol / L trifluoromethanesulfonic acid solution. Co(NO3)2•6H2O was accurately weighed according to a cobalt-copper molar ratio of 0.5 and dissolved in deionized water to prepare a cobalt salt solution. The cobalt salt solution was added dropwise to the pH-adjusted copper salt solution at a rate of 10 mL / min using a constant flow pump, with magnetic stirring maintained during the addition. After the addition was completed, stirring was continued for 30 min. The solution was allowed to stand at room temperature for 6 h, and then transferred to a constant temperature oven and dried at 120 °C for 12 h. The dried solid sample was placed in a tube furnace and heated to 400℃ at a rate of 2℃ / min under an oxygen atmosphere. It was then calcined at this temperature for 6 hours and naturally cooled to room temperature. The resulting sample was then pressed into tablets to a mesh size of 20-40, ultimately yielding a metal oxide catalyst with a cobalt-copper ratio of 0.5. The chemical composition of the catalyst was determined by elemental analysis, and the S content was found to be 0.92%.

[0029] The reaction was carried out in a continuous flow fixed-bed reactor. The catalyst was placed in the middle of the reactor. The feedstock was methanol and 30% oxygen, with a methanol-to-oxygen ratio of 1:6. The reaction temperature was 240°C. o C, reaction space velocity 4000 h⁻¹ -1 The reaction pressure was 0.1 MPa, and the reaction time was 10 hours. The methanol conversion rate was 91.2%, DMM. x The selectivity was 60.5%, of which DMM 2-8 It is 45.2%.

[0030] Example 5 11.7 g of NH4VO3 was dissolved in deionized water to prepare a vanadium ion concentration of 1.5 mol / L. The solution was stirred for 10 min until completely dissolved, and the pH of the vanadium solution was adjusted to 4 using 3 mol / L chlorosulfonic acid solution. FeCl3•6H2O was accurately weighed according to an iron-vanadium molar ratio of 0.7 and dissolved in deionized water to prepare an iron salt solution. This iron salt solution was added dropwise to the pH-adjusted vanadium salt solution at a rate of 5 mL / min using a constant flow pump, with magnetic stirring maintained during the addition. After the addition was complete, stirring was continued for 30 min. The solution was allowed to stand at room temperature for 6 h, and then transferred to a constant temperature oven and dried at 140 °C for 12 h. The dried solid sample was placed in a tube furnace and heated to 400℃ at a rate of 2℃ / min under a nitrogen atmosphere. It was then calcined at this temperature for 6 hours and naturally cooled to room temperature. The resulting sample was then pressed into tablets to a mesh size of 20-40, ultimately yielding a metal oxide catalyst with an iron-vanadium ratio of 0.7. The chemical composition of the catalyst was determined by elemental analysis, and the S content was found to be 0.56%.

[0031] The reaction was carried out in a continuous flow fixed-bed reactor. The catalyst was placed in the middle of the reactor. The feedstock was methanol and 40% oxygen, with a methanol-to-oxygen ratio of 1:6. The reaction temperature was 220°C. o C, reaction space velocity 4000 h⁻¹ -1 The reaction pressure was 0.1 MPa, and the reaction time was 10 hours. The methanol conversion rate was 82.5%, DMM. x The selectivity was 83.4%, of which DMM 2-6 It is 57.8%.

[0032] Figure 1 The image shows a TEM image of the catalyst prepared in Example 5. Clear, continuous, and uniformly distributed lattice fringes can be observed, indicating that the obtained iron-vanadium catalyst has good crystallinity. Measurement of the lattice fringes shows that the spacing matches the standard interplanar spacing of the corresponding Fe-V oxide crystal planes, further confirming the successful synthesis of the target phase.

[0033] Example 6 12.48g (NH4)6Mo7O 24 • 4H₂O was dissolved in deionized water to prepare a molybdenum ion concentration of 1.3 mol / L. The solution was stirred for 10 min until completely dissolved, and the pH of the molybdenum solution was adjusted to 2.5 with 4 mol / L trifluoromethanesulfonic acid solution. FeCl₃•6H₂O was accurately weighed according to an iron-molybdenum molar ratio of 0.6 and dissolved in deionized water to prepare an iron salt solution. The iron salt solution was added dropwise to the pH-adjusted molybdenum salt solution at a rate of 5 mL / min using a constant flow pump, with magnetic stirring maintained during the addition. After the addition was completed, stirring was continued for 30 min. The solution was allowed to stand at room temperature for 6 h, and then transferred to a constant temperature oven and dried at 140 °C for 12 h. The dried solid sample was placed in a tube furnace and heated to 350°C at a programmed heating rate of 2°C / min under a nitrogen atmosphere. It was then calcined at this temperature for 5 hours and allowed to cool naturally to room temperature. The resulting sample was then pressed into tablets to a mesh size of 20-40, ultimately yielding a metal oxide catalyst with an iron-molybdenum ratio of 0.6. The chemical composition of the catalyst was determined by elemental analysis, and the S content was found to be 0.80%.

[0034] The reaction was carried out in a continuous flow fixed-bed reactor. The catalyst was placed in the middle of the reactor. The feedstock was methanol and oxygen in a ratio of 1:10. The reaction temperature was 210°C. o C, reaction space velocity 7200 h⁻¹ -1 The reaction pressure was 0.1 MPa, and the reaction time was 10 hours. The methanol conversion rate was 71.8%, DMM. x Selectivity 78.4%, including DMM 2-8 It is 48.9%.

[0035] Example 7 24.2 g of Cu(NO3)2•3H2O was dissolved in deionized water to prepare a copper ion concentration of 1.3 mol / L. The solution was stirred for 10 min until completely dissolved. The pH of the copper solution was adjusted to 2.5 with 4 mol / L chlorosulfonic acid solution. Mn(NO3)2•4H2O was accurately weighed according to a manganese-copper molar ratio of 0.4 and dissolved in deionized water to prepare a manganese salt solution. The manganese salt solution was added dropwise to the pH-adjusted copper salt solution at a rate of 5 mL / min using a constant flow pump. Magnetic stirring was maintained during the addition. After the addition was completed, stirring was continued for 30 min. The solution was allowed to stand at room temperature for 6 h, and then transferred to a constant temperature oven and dried at 140 °C for 12 h. The dried solid sample was placed in a tube furnace and heated to 350°C at a rate of 2°C / min under a nitrogen atmosphere. It was then calcined at this temperature for 5 hours and allowed to cool naturally to room temperature. The resulting sample was then pressed into tablets to a mesh size of 20-40, ultimately yielding a metal oxide catalyst with a manganese-copper ratio of 0.4. The chemical composition of the catalyst was determined by elemental analysis, and the S content was found to be 0.83%.

[0036] The reaction was carried out in a continuous flow fixed-bed reactor. The catalyst was placed in the middle of the reactor. The feedstock was methanol and oxygen in a ratio of 1:10. The reaction temperature was 240°C. o C, reaction space velocity 7200 h⁻¹ -1 The reaction pressure was 0.1 MPa, and the reaction time was 10 hours. The methanol conversion rate was 93.1%, DMM. x Selectivity 64.8%, of which DMM 2-6 It is 45.8%.

[0037] Example 8 12.48g (NH4)6Mo7O 24 • 4H₂O was dissolved in deionized water to prepare a molybdenum ion concentration of 1.1 mol / L. The solution was stirred for 10 min until completely dissolved, and the pH of the molybdenum solution was adjusted to 4 using 4 mol / L sulfuric acid solution. Ni(NO₃)₂•6H₂O was accurately weighed according to a nickel-molybdenum molar ratio of 0.9 and dissolved in deionized water to prepare a nickel salt solution. This nickel salt solution was added dropwise to the pH-adjusted molybdenum salt solution at a rate of 5 mL / min using a constant flow pump, with magnetic stirring maintained during the addition. After the addition was completed, stirring was continued for 30 min. The solution was allowed to stand at room temperature for 6 h, and then transferred to a constant temperature oven and dried at 140 °C for 12 h. The dried solid sample was placed in a tube furnace and heated to 300°C at a rate of 2°C / min under a nitrogen atmosphere. It was then calcined at this temperature for 5 hours and allowed to cool naturally to room temperature. The resulting sample was then pressed into tablets to a mesh size of 20-40 mesh, ultimately yielding a metal oxide catalyst with a nickel-molybdenum ratio of 0.9. The chemical composition of the catalyst was determined by elemental analysis, and the S content was found to be 0.65%.

[0038] The reaction was carried out in a continuous flow fixed-bed reactor. The catalyst was placed in the middle of the reactor. The feedstock was methanol and 10% oxygen, with a methanol-to-oxygen ratio of 1:9. The reaction temperature was 220°C. o C, reaction space velocity 3600 h⁻¹ -1 The reaction pressure was 0.1 MPa, and the reaction time was 10 hours. The methanol conversion rate was 76.5%, DMM. x Selectivity 78.3%, of which DMM 2-8 It is 54.2%.

[0039] Example 9 11.7 g of NH4VO3 was dissolved in deionized water to prepare a vanadium ion concentration of 1.5 mol / L. The solution was stirred for 10 min until completely dissolved, and the pH of the vanadium solution was adjusted to 4 using 3 mol / L hydrochloric acid. Ti(OC4H9)4 was accurately weighed according to a titanium-vanadium molar ratio of 0.8 and dissolved in 100 mL of ethanol. This solution was added dropwise to the pH-adjusted vanadium salt solution at a rate of 5 mL / min using a constant flow pump, with magnetic stirring maintained during the addition. After the addition was complete, stirring was continued for 30 min. The solution was allowed to stand at room temperature for 6 h, and then transferred to a constant temperature oven and dried at 140 °C for 12 h. The dried solid sample was placed in a tube furnace and heated to 400℃ at a rate of 2℃ / min under a nitrogen atmosphere. It was then calcined at this temperature for 6 hours and naturally cooled to room temperature. The resulting sample was then pressed into tablets to a mesh size of 20-40 mesh, ultimately yielding a metal oxide catalyst with a titanium-vanadium ratio of 0.8. The chemical composition of the catalyst was determined by elemental analysis, and the Cl content was 1.53%.

[0040] The reaction was carried out in a continuous flow fixed-bed reactor. The catalyst was placed in the middle of the reactor. The feedstock was methanol and 40% oxygen, with a methanol-to-oxygen ratio of 1:6. The reaction temperature was 220°C. o C, reaction space velocity 4000 h⁻¹ -1 The reaction pressure was 0.1 MPa, and the reaction time was 10 hours. The methanol conversion rate was 72.5%, DMM. x The selectivity was 88.4%, of which DMM 2-6 It is 56.8%.

[0041] Example 10 24.2 g of Cu(NO3)2•3H2O was dissolved in deionized water to prepare a copper ion concentration of 2 mol / L. The solution was stirred for 10 min until completely dissolved, and the pH of the copper salt solution was adjusted to 2 using 4 mol / L trifluoromethanesulfonic acid solution. Co(NO3)2•6H2O was accurately weighed according to a cobalt-copper molar ratio of 0.7 and dissolved in deionized water to prepare a cobalt salt solution. The cobalt salt solution was added dropwise to the pH-adjusted copper salt solution at a rate of 5 mL / min using a constant flow pump, with magnetic stirring maintained during the addition. After the addition was completed, stirring was continued for 30 min. The solution was allowed to stand at room temperature for 6 h, and then transferred to a constant temperature oven and dried at 140 °C for 12 h. The dried solid sample was placed in a tube furnace and heated to 300°C at a rate of 2°C / min under a nitrogen atmosphere. It was then calcined at this temperature for 4 hours and allowed to cool naturally to room temperature. The resulting sample was then pressed into tablets to a mesh size of 20-40, ultimately yielding a metal oxide catalyst with a cobalt-copper ratio of 0.7. The chemical composition of the catalyst was determined by elemental analysis, and the S content was found to be 0.55%.

[0042] The reaction was carried out in a continuous flow fixed-bed reactor. The catalyst was placed in the middle of the reactor. The feedstock was methanol and oxygen in a ratio of 1:8. The reaction temperature was 200°C. o C, reaction space velocity 3600 h⁻¹ -1 The reaction pressure was 0.1 MPa, and the reaction time was 10 hours. The methanol conversion rate was 71.3%, DMM. x Selectivity was 73.2%, including DMM. 2-6 It is 47.8%.

Claims

1. A metal oxide catalyst for the oxidative synthesis of polyoxymethylene dimethyl ether from methanol, characterized in that, It is prepared by reacting an active metal precursor with an acid solution, wherein the active metal is composed of two of Ti, Ni, Fe, Co, Mo, V, Cu, and Mn. The first metal includes any one of Ti, Ni, Fe, Mn, and Co, and the second metal includes any one of V, Mo, and Cu. The acidic component is introduced into the catalyst system by co-dissolving with the metal precursor, and the acidic component includes inorganic acid or organic acid.

2. The metal oxide catalyst for the synthesis of polyoxymethylene dimethyl ether by methanol oxidation according to claim 1, characterized in that, Inorganic acids include one of hydrochloric acid, phosphoric acid, and sulfuric acid, while organic acids include one of oxalic acid, citric acid, chlorosulfonic acid, tartaric acid, trifluoromethanesulfonic acid, methanesulfonic acid, and ethylenediaminetetraacetic acid.

3. The metal oxide catalyst for the synthesis of polyoxymethylene dimethyl ether by methanol oxidation according to claim 1, characterized in that, The catalyst system includes metal oxides and acidic components, wherein the acidic components account for 0.1%–10% of the mass fraction of the catalyst.

4. The metal oxide catalyst for the synthesis of polyoxymethylene dimethyl ether by methanol oxidation according to claim 3, characterized in that, The catalyst comprises two metal oxides, with the molar ratio of the first metal to the second metal being 0.2 to 1; the metal oxides include combinations of the following two metals: Ti-V, Ni-Mo, Fe-V, Mn-Cu, Fe-Mo, and Co-Cu.

5. The metal oxide catalyst for the synthesis of polyoxymethylene dimethyl ether by methanol oxidation according to claim 1, characterized in that, The metal precursor is selected from (NH4)6Mo7O 24 •4H2O, NH4VO3, Co(NO3)2•6H2O, Fe(NO3)3•9H2O, FeCl3•6H2O, Cu(NO3)2•3H2O, Ti(OC4H9)4, Mn(NO3)2•4H2O or Ni(NO3)2•6H2O.

6. A method for preparing a metal oxide catalyst for the methanol oxidation synthesis of polyoxymethylene dimethyl ether according to any one of claims 1 to 5, characterized in that... Includes the following steps: (1) Select two metal precursors, prepare metal salt solutions respectively and stir thoroughly until the system is homogeneous and stable; The pH of the metal salt solution corresponding to the second metal was adjusted to 1-6 using an acid solution. Under continuous stirring, the first metal salt solution was added dropwise to the pH-adjusted solution at a constant dropping rate of 2-10 mL / min. (2) Stir the solution in step (1) until homogeneous and let it stand for 3-8 hours; (3) Heat the sample obtained in step (2) at 100-150°C. o The metal oxide catalyst is dried at C and then placed in a tube furnace. Under a protective atmosphere, it is heated to 200-500°C at a heating rate of 1-4°C / min for 4-8 hours and then naturally cooled to room temperature to obtain the catalyst.

7. The method for preparing the metal oxide catalyst for the methanol oxidation synthesis of polyoxymethylene dimethyl ether according to claim 6, characterized in that, In step (1), the concentrations of the first metal salt solution and the second metal salt solution are both 0.2-2.5 mol / L.

8. The method for preparing the metal oxide catalyst for the methanol oxidation synthesis of polyoxymethylene dimethyl ether according to claim 6, characterized in that, The concentration of the inorganic acid is 1-7 mol / L, and the concentration of the organic acid is 1-5 mol / L.

9. The method for preparing the metal oxide catalyst for the methanol oxidation synthesis of polyoxymethylene dimethyl ether according to claim 6, characterized in that, The protective atmosphere during roasting is one of oxygen, air, nitrogen, or argon.

10. The application of the metal oxide catalyst according to any one of claims 1 to 5 in the direct oxidation of methanol to synthesize polyoxymethylene dimethyl ether, characterized in that, Methanol and a reaction gas are mixed at a molar ratio of 1:2 to 1:

20. The reaction gas is a mixture of oxygen and nitrogen, with oxygen comprising 10% to 100% by volume. The mixture is then fed into a fixed-bed reactor for reaction, with a gas space velocity of 1000 to 10000 h⁻¹. -1 The reaction temperature is 150~300℃, and the reaction pressure is 0.1~1.0MPa; In this application, the methanol conversion rate reaches over 70%, DMM x The selectivity is over 60%, and the proportion of high value-added products with x=2~8 is over 45%.

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