Polymethoxy dimethyl ether synthesis process based on high-load acidic catalyst

Abstract

The invention discloses a polyoxymethylene dimethyl ether synthesis process based on a high-load acidic catalyst, and belongs to the technical field of chemical production processes. The process comprises the following steps: by taking methanol or dimethyl ether as a raw material, carrying out molecular sieve dehydration pretreatment, carrying out one-step oxidative condensation in a fixed bed reactor by adopting a high-load acid catalyst, standing for liquid separation, carrying out double-tower rectification, carrying out molecular sieve dehydration and filtering by a filter membrane to finish product refining. Wherein a high-load acidic catalyst mesoporous silica is used as a carrier, a Mo-V / W composite oxidation active center is constructed, gradient acidic sites of strong acid in a pore channel-strong acid in a pore channel inlet / surface are matched, and the outer surface is subjected to hydrophobic passivation treatment, so that multifunctional synergistic catalysis is realized. According to the process, the traditional complex process is simplified, the selectivity and the product purity of the target product are greatly improved, the catalyst structure is stable, the service life is long, the obtained product meets the diesel oil mixing requirement, effective combustion supporting and emission reduction can be achieved under high altitude and other scenes, and the good industrial application prospect is achieved.

Description

Technical Field

[0001] This invention relates to the field of chemical production process technology, and in particular to a process for synthesizing polyoxymethylene dimethyl ether based on a highly loaded acidic catalyst. Background Technology

[0002] Polyoxymethylene dimethyl ether (PODE) n As a new type of clean fuel additive, it features high oxygen content, excellent cetane number, and good miscibility with diesel fuel. It can significantly improve diesel combustion efficiency and reduce carbon monoxide (CO) and nitrogen oxides (NOx). x The study of particulate matter (PM) emissions has significant application value in the field of fuel optimization under special environments such as high altitude and low oxygen, and has become a research hotspot in the chemical and energy fields.

[0003] Currently, the synthesis of PODE mainly focuses on oxidative condensation reactions using methanol or dimethyl ether as raw materials. However, existing technologies still have many key problems that urgently need to be solved. First, in terms of the synthesis route, traditional processes often adopt a "two-step method": first, formaldehyde intermediate is prepared by methanol oxidation, and then formaldehyde is condensed with methanol / dimethyl ether to generate PODE. This route has drawbacks such as a lengthy process, high energy consumption for intermediate product separation, and low overall production efficiency, making it difficult to meet the needs of continuous industrial production. Second, insufficient catalyst performance is the core bottleneck restricting product quality: existing catalysts mostly adopt a single acidic site or a single metal active center design. Their acidic site distribution is disordered, and the active centers are prone to aggregation, resulting in low activation efficiency of raw materials and an inability to precisely control the chain growth process, leading to low selectivity of the target product and low degree of polymerization PODE. 1-2 and high degree of polymerization PODE 7+ Excessive proportion of byproducts severely impacts the combustion performance of blended fuels. Furthermore, traditional catalysts lack effective control over the depth of oxidation, easily leading to over-oxidation of feedstocks and the generation of CO. x Byproducts not only reduce raw material utilization but also increase subsequent separation costs. In addition, existing catalysts have insufficient structural stability, and active centers are prone to deactivation due to sintering and carbon buildup, resulting in a large-scale decline in activity after long-term operation, making it difficult to meet the requirements of long-term industrial applications.

[0004] Furthermore, the product suffers from a wide degree of polymerization distribution and high impurity content. Due to the lack of a directional control structure design for chain growth in the catalyst, the PODE product obtained by the existing process has a scattered degree of polymerization distribution and high levels of impurities such as residual moisture and paraformaldehyde. When mixed with diesel, it is prone to problems such as poor atomization and injector clogging. Especially in high-altitude, low-oxygen environments, it cannot fully exert its combustion-supporting and emission-reduction effects. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by proposing a polyoxymethylene dimethyl ether synthesis process based on a highly loaded acidic catalyst.

[0006] To achieve the above objectives, the present invention employs the following technical solution: a polyoxymethylene dimethyl ether synthesis process based on a highly supported acidic catalyst, comprising the following steps: (1) The raw material is dehydrated by molecular sieve to a moisture content of ≤0.1wt% to obtain pretreated raw material; (2) The highly loaded acid catalyst is mixed with an equal volume of ceramic rings and packed in the middle of the fixed bed reactor, with both ends filled with quartz sand; (3) Purge the reactor with nitrogen for 30-60 minutes, raise the temperature to 200-240℃, adjust the pressure to 0.5-1.5MPa, introduce the raw material and oxygen, and control the feed space velocity to 0.8-2.0h. -1 Meanwhile, nitrogen gas is introduced as a carrier gas to continuously react and collect the condensed liquid products. (4) The liquid product is allowed to stand at room temperature to separate into layers, and the aqueous phase is removed by separation. A double-tower distillation process is adopted. The pressure at the top of the light component removal tower is 0.08-0.12 MPa and the temperature is 38-50℃ to remove the light component. The pressure at the top of the product distillation tower is 0.04-0.06 MPa, and the fraction at 130-160℃ is collected. The fraction at 130-160℃ is passed through a 3A molecular sieve column to dehydrate to ≤0.05wt% water content, and then filtered through a 0.22μm filter membrane to obtain polyoxymethylene dimethyl ether.

[0007] Preferably, the raw material in (1) refers to methanol or dimethyl ether.

[0008] Preferably, the loading amount of the highly loaded acidic catalyst in (2) is 30%-40% of the effective volume of the fixed-bed reactor.

[0009] Preferably, the volume hourly space velocity (VHSV) of nitrogen purging in step (3) is 600-1200 h⁻¹ based on the effective volume of the fixed-bed reactor. -1 .

[0010] Preferably, the heating to 200-240℃ in (3) refers to heating to 200-230℃ when the raw material is methanol, and heating to 210-240℃ when the raw material is dimethyl ether.

[0011] Preferably, adjusting the pressure to 0.5-1.5 MPa in (3) means adjusting the pressure to 0.5-1.0 MPa when the raw material is methanol and adjusting the pressure to 0.8-1.5 MPa when the raw material is dimethyl ether.

[0012] Preferably, the molar ratio of raw materials and oxygen in (3) is: methanol: oxygen = 1:0.5-1, dimethyl ether: oxygen = 1:0.8-1.5.

[0013] Preferably, the volume fraction of nitrogen introduced in (3) is 20%-35% of the total feed gas volume, wherein the total feed gas volume is the sum of the feed volumes of raw materials, oxygen and nitrogen.

[0014] Preferably, the theoretical number of plates in the light-light distillation tower in (4) is 18-22, and the theoretical number of plates in the product distillation tower is 28-32.

[0015] Preferably, the preparation method of the highly supported acidic catalyst is as follows: S1. Add mesoporous silica to dilute nitric acid solution, stir at room temperature for 1-3 hours, filter, wash with deionized water until the pH of the filtrate is neutral, and dry to obtain the pretreated carrier. Although silanol groups (-Si-OH) naturally exist on the surface of mesoporous silica (SBA-15), their quantity is limited and their distribution is uneven, making it difficult to meet the requirements for efficient anchoring of subsequent active components. In this step, 5-10 wt% dilute nitric acid is used for room temperature stirring treatment. The protonation effect of nitric acid breaks some of the silicon-oxygen bonds (Si-O-Si) on the surface of the support and promotes the participation of water molecules in the reaction, generating a large number of uniformly distributed silanol groups (-Si-OH) on the surface of the support. These hydroxyl groups serve as anchoring points for subsequent active components and acidic sites, significantly improving the uniformity and binding strength of the subsequent loading process. S2. Add one of ammonium molybdate and ammonium metavanadate or ammonium tungstate to deionized water and stir until dissolved to obtain a precursor aqueous solution. Add the precursor aqueous solution dropwise to the pretreated support until the liquid level just covers the pretreated support. At room temperature, sonicate and stir for 2-3 hours, let stand for 12-24 hours, filter, dry, and then place in a tube furnace. Introduce a nitrogen-hydrogen mixed gas and heat to 400-600℃ at a rate of 3-7℃ / min. Hold at this temperature for 3-5 hours and cool to room temperature to obtain a support loaded with oxidative active centers. In this step, ammonium molybdate and ammonium metavanadate (or ammonium tungstate) are first dissolved in deionized water to form Mo. 6+ V 5+ (or W) 6+The precursor aqueous solution was added dropwise to the pretreated support. Ultrasonic and stirring actions accelerated the diffusion of metal ions into the mesopores of the support. The metal ions underwent coordination adsorption with the silanol groups (-Si-OH) on the support surface, forming a stable surface adsorption state through -O- bonds. After standing for 12-24 hours, adsorption equilibrium was further promoted. After filtration and drying, a nitrogen-hydrogen mixture was introduced into a tube furnace, and reduction was carried out at 400-600℃. During the reduction process, high-valence metal ions were partially reduced by hydrogen, forming metal oxides (MoO3, V2O5, WO3) with both oxidizing and reducing capabilities. Furthermore, composite oxide solid solutions (such as Mo-VO, Mo-WO) were formed between the metal ions, serving as the oxidizing active centers for the catalytic reaction. Their redox pairs (Mo... 6+ / Mo 4+ V 5+ / V 4+ It can provide lattice oxygen to achieve the oxidative activation of raw materials. The key chemical reaction equations are as follows: (NH4)6Mo7O 24 ·4H₂O→7MoO₃+6NH₃↑+7H₂O↑ (drying and roasting stage) MoO3 + H2 → MoO2 + H2O (reduction stage, forming Mo) 6+ / Mo 4+ redox (to) 2NH4VO3→V2O5+2NH3↑+H2O↑ (drying and roasting stage) V₂O₅ + H₂ → 2VO₂ + H₂O (reduction stage, forming V₂O) 5+ / V 4+ redox (to) (NH4) 10 W 12 O 41 xH2O→12WO3 +10NH3↑ + (x+5)H2O↑ (drying and roasting stage) WO3 + H2 → WO2 + H2O (reduction stage, forming W) 6+ / W 5+ redox (to) S3. Place the support with oxygen-loaded active centers in a quartz boat, put it in the isothermal zone of a horizontal tube furnace, introduce nitrogen as a carrier gas, heat to 120-140℃, then introduce SO3 vapor, and deposit at the isothermal temperature for 1-2 hours. After deposition, stop the SO3 vapor introduction, raise the furnace temperature to 180-220℃, treat at this temperature for 30-60 minutes, cool to room temperature, add an ethanol solution of p-toluenesulfonic acid, stir at room temperature for 3-5 hours, filter, dry, and then transfer to a muffle furnace. Heat to 200-240℃ in an air atmosphere for 1.5-2.5 hours, and cool to room temperature to obtain a highly loaded acidic catalyst precursor. The support for the oxidizing active centers in this step has a one-dimensional ordered mesoporous structure. A large number of unoccupied silanol groups (-Si-OH) remain on the inner surface of the pores and in the interstices between the oxidizing active centers. At 120-140℃, SO3 is introduced in vapor form. With the help of nitrogen as a carrier gas, the small SO3 molecules can rapidly diffuse into the depth and middle of the pores of the support, undergoing nucleophilic substitution reactions with the silanol groups within the pores to directionally generate strongly acidic -SO3H sites anchored inside the pores. Due to the spatial confinement within the pores, physically adsorbed SO3 is difficult to retain. Subsequent heat treatment at 180-220℃ further removes the residual physically adsorbed SO3 and strengthens the stability of the -Si-O-SO3H bonds through thermal vibration, preventing the acid sites from detaching. These strongly acidic sites within the pores can be activated and diffused into the pores to methanol / dimethyl ether, efficiently generating initial C1 active species such as formaldehyde and methoxy groups, providing raw materials for chain growth reactions. The chemical reaction equation is as follows: Si-OH (support) + SO3 → Si-O-SO3H (strong acid site); After SO3 deposition, the pores of the support are occupied by strong acid sites of -SO3H. As an organic macromolecule, the pores of the support already contain oxidative active centers and strong acid sites, significantly increasing the diffusion resistance of p-toluenesulfonic acid (p-CH3C6H4SO3H). It is difficult for p-toluenesulfonic acid to penetrate deep into the pores, and it can only diffuse to the pore entrance region and the outer surface of the support. The sulfonic acid group (-SO3H) in the p-toluenesulfonic acid molecule undergoes a dehydration condensation reaction with the silanol groups at the pore entrance and the hydroxyl groups at the interface of the oxidative active centers on the support surface and the pore entrance. It is directionally anchored through covalent bonds (-Si-O-SO2-), forming medium-strong acid sites distributed at the pore entrance and the support surface. Heat treatment in air at 200-240℃ can further consolidate the covalent bond and prevent the acid sites from falling off during the reaction. These medium-strong acid sites are located on the diffusion path of C1 active species from the pores, which can specifically capture and stabilize "secondary carbon-like active intermediates", promoting their directional chain growth with subsequent C1 species, and finally generating high-polymerization-degree PODE. The chemical reaction equation is as follows: Si-OH (support surface / pore inlet) + p-CH3C6H4SO3H → Si-O-SO2C6H4CH3 + H2O; S4. Disperse the highly supported acidic catalyst precursor in ethanol, add dimethyldichlorosilane, stir at room temperature for 4-8 hours, filter, wash with anhydrous toluene 2-3 times, and dry to obtain the highly supported acidic catalyst. In this step, the highly loaded acidic catalyst precursor is dispersed in ethanol, and dimethyldichlorosilane is added. The mixture is stirred at room temperature for 4-8 hours. Dimethyldichlorosilane ((CH3)2SiCl2) first undergoes a hydrolysis reaction in ethanol to generate an intermediate containing silanol groups (-Si(CH3)2-OH). This intermediate rapidly undergoes a dehydration condensation reaction with the silanol groups (-Si-OH) on the outer surface of the catalyst to form a dense hydrophobic passivation layer (-Si-O-Si(CH3)2-). This passivation layer can block the acidic sites on the outer surface of the catalyst, inhibit random oxidation and disordered condensation side reactions on the outer surface, and force the reaction to take place inside the pores with a nano-confined effect. At the same time, it does not affect the synergistic effect between the gradient acidic sites and the oxidation active centers within the pores. The chemical reaction equation is as follows: (CH3)2SiCl2 + 2C2H5OH → (CH3)2Si(OH)2 + 2C2H5Cl (hydrolysis reaction) Si-OH (catalyst outer surface) + (CH3)2Si(OH)2 → Si-O-Si(CH3)2-OH + H2O Si-O-Si (CH3)2-OH + HO-Si (catalyst outer surface) → Si-O-Si (CH3)2-O-Si (catalyst outer surface) + H2O.

[0016] Preferably, the S1 mesoporous silica has a pore size of 2-5 nm and a specific surface area ≥600 m². 2 / g.

[0017] More preferably, the specific type of the S1 mesoporous silica is SBA-15.

[0018] Preferably, the ratio of the amount of S1 mesoporous silica to dilute nitric acid solution is 1g:5-10ml.

[0019] Preferably, the S1 mesoporous silica is specifically of type SBA-15. Preferably, the concentration of the dilute nitric acid solution in S1 is 5-10 wt%.

[0020] Preferably, the molar ratio of ammonium molybdate to ammonium metavanadate or ammonium tungstate in S2 is 3-5:1.

[0021] Preferably, the total mass fraction of solute in the precursor aqueous solution in S2 is 5-8 wt%.

[0022] Preferably, the nitrogen-hydrogen mixed gas introduction rate in S2 is based on the effective volume of the tubular furnace, with a volume hourly space velocity of 1000-2000 h⁻¹. -1 The volume ratio of nitrogen to hydrogen in the nitrogen-hydrogen mixture is 95:5.

[0023] Preferably, the nitrogen introduction rate in S3 is based on the effective volume of the horizontal tube furnace, with a volumetric space velocity of 800-1500 h⁻¹. -1 .

[0024] Preferably, the SO3 vapor in step S3 is introduced at a rate of 0.3-1.0 ml / min·10 g of carrier loaded with oxygen active centers.

[0025] Preferably, in step S3, the ratio of the carrier carrying the oxygen active center to the ethanol solution of p-toluenesulfonic acid is 1g:4-8ml, and the concentration of p-toluenesulfonic acid in the ethanol solution of p-toluenesulfonic acid is 8-15wt%.

[0026] Preferably, the ratio of the highly loaded acidic catalyst precursor, ethanol and dimethyldichlorosilane in S4 is 1g:8-12ml:0.06-0.15g.

[0027] Preferably, the synthesis mechanism of the polyoxymethylene dimethyl ether synthesis process based on a highly supported acidic catalyst in this invention is explained as follows: The synthesis mechanism of this invention is based on the one-step oxidative condensation of methanol or dimethyl ether to produce polyoxymethylene dimethyl ether. Through the synergistic effect of the oxidative active center and gradient acidic sites in a highly loaded acidic catalyst, the generation of C1 active species, intermediate stabilization, and chain growth are directionally regulated, ultimately achieving the efficient synthesis of the target product with a high degree of polymerization. The basic reaction mechanisms of methanol and dimethyl ether are first described below, followed by a detailed explanation of the catalytic synthesis mechanism of this invention: I. Basic Reaction Mechanism of One-Step Oxidative Synthesis of PODE from Methanol / Dimethyl Ether 1. Basic reaction mechanism using methanol as a raw material Methanol is first oxidized to formaldehyde (HCHO) by the active oxidation site. Formaldehyde, as the core C1 active species, undergoes a nucleophilic addition reaction with unoxidized methanol to form methyl hemiacetal (CH3OCH2OH). The methyl hemiacetal further undergoes dehydration to form methoxymethyl ether (PODE1). Subsequently, the formaldehyde molecule continues to insert into PODE1. n Chain growth is achieved through the CO bonds, ultimately forming PODEs with different degrees of polymerization via methoxy terminology end-capping. n The key basic reaction equations are as follows: Oxidation reaction: CH3OH + [O] (catalyst lattice oxygen) → HCHO + H2O Addition reaction: CH3OH + HCHO → CH3OCH2OH (methyl hemiacetal) Dehydration condensation reaction: CH3OCH2OH + CH3OH → CH3OCH2OCH3(PODE1) + H2O Chain propagation reaction: CH3O(CH2O) nCH3 (PODE) n +HCHO→CH3O(CH2O) n+1 CH3 (PODE) n+1 ); 2. Basic reaction mechanism using dimethyl ether as a raw material Dimethyl ether first breaks the CO bond at a strong acid site to generate a methoxy group (-OCH3) and a methyl radical (·CH3). The methoxy group is then oxidized to formaldehyde at the active oxidizing center. Subsequently, formaldehyde undergoes a condensation reaction with the methoxy group to generate PODE1. Chain growth is achieved through the continuous insertion of formaldehyde molecules, ultimately leading to end capping and the formation of PODE1. n The key basic reaction equations are as follows: Bond breaking reaction: CH3OCH3 + H + (Strong acid site) → CH3 - +·CH3+ H2O Oxidation reaction: CH3O - + [O] (catalyst lattice oxygen) → HCHO + OH - Condensation reaction: CH3O - + HCHO→CH3OCH2O - (PODE1 intermediate) End-capping reaction: CH3O(CH2O) n O - +·CH3→CH3O(CH2O) n CH3 (PODE) n ).

[0028] II. Catalytic synthesis mechanism of the present invention (synergistic catalytic effect of highly supported acidic catalyst) The synthesis mechanism of this invention is essentially a synergistic catalytic process involving "oxidation active center - gradient acidic sites - nano-confined space - outer surface passivation layer" in a highly supported acidic catalyst. By matching the spatial distribution and performance of each functional site, the selectivity of the basic reaction is directionally regulated, side reactions are suppressed, and PODE is preferentially generated. 3-6 The specific process is as follows: 1. Raw material adsorption and activation (synergistic effect of oxidative active centers and strong acid sites within pores) Pretreated methanol or dimethyl ether is transported to a fixed-bed reactor via nitrogen carrier gas. Under conditions of 200-240℃ and 0.5-1.5 MPa, the feed molecules diffuse into the mesoporous channels of the catalyst. Firstly, the -SO3H strong acid sites within the channels provide protons (H... + Protonation activation of raw material molecules: methanol is protonated to generate CH3OH2. + After protonation, dimethyl ether breaks the CO bond to generate CH3O. -and CH3; simultaneously, oxidative active centers (Mo) dispersed within the channels 6+ / Mo 6+ V 5+ / V 4+ W 6+ / W 4+ Redox releases lattice oxygen, oxidizing the activated methoxy or methanol molecules to formaldehyde, while the oxidative active center itself is reduced (e.g., Mo). 6+ →Mo 4+ Subsequently, O2 in the gas phase re-oxidizes and regenerates the reduced active sites (Mo). 4+ →Mo 6+ This completes the oxidation cycle, during which the raw materials are directionally converted into formaldehyde, the core C1 active species, avoiding excessive oxidation that generates CO. x The key reaction equations are as follows: Protonation activation (methanol):

[0029] Protonation activation (dimethyl ether):

[0030] ; 2. Formation and stabilization of secondary carbon intermediates Formaldehyde molecules generated within the pores diffuse outwards, reaching the medium-strong acid sites (Si-O-SO2C6H4CH3 anchored by p-toluenesulfonic acid) at the pore inlet and on the carrier surface. These sites possess moderate acid strength and can specifically adsorb the reaction product of formaldehyde and methoxy groups, methyl hemiacetal (CH3OCH2OH), and catalyze its dehydration to form a "secondary carbon-like active intermediate" (CH3O-CH2-O·). The structure of this intermediate is similar to the secondary carbon sites in highly polymerizable PODE molecules. The medium-strong acid sites stabilize its conformation through hydrogen bonding, preventing intermediate decomposition or disordered polymerization, thus laying the foundation for directional chain growth. The key reaction equations are as follows: ; 3. Targeted Chain Growth The catalyst support, SBA-15, with its one-dimensional ordered mesopores (pore size 2-5 nm), provides a nano-confined space, restricting the movement freedom of the secondary carbon intermediate and forcing formaldehyde molecules to linearly insert along the CO bonds of the intermediate, thus achieving directional chain growth. Formaldehyde molecules are continuously generated from within the pores and diffuse to the moderately strong acid sites, undergoing addition reactions with the secondary carbon intermediate, gradually increasing the degree of polymerization by 3-6: as the chain grows... 3-6 At this point, the steric hindrance of the intermediate reaches equilibrium with the adsorption strength of the moderately strong acid site, and no further insertion of formaldehyde molecules occurs; while low degree of polymerization (PODE) 1-2 Due to its low steric hindrance, the intermediate will continue to react with formaldehyde and grow to PODE.3-6 High degree of polymerization (PODE) 7+ The intermediates, due to excessive steric hindrance, are difficult to exist stably within the mesopores. This process results in the product distribution being concentrated within the target degree of polymerization range. The critical chain growth reaction equation is as follows: CH3O-(CH2O) x -O·(x=1-2, secondary carbon intermediate)+HCHO→CH3O-(CH2O) x+1 -O·(x=2-5, chain growth intermediate) CH3O-(CH2O)5-O·(PODE6 intermediate)+·CH3→CH3O(CH2O)5CH3(PODE6); 4. Suppression of side reactions and desorption of products The dimethyldichlorosilane passivation layer (-Si-O-Si(CH3)2-) on the outer surface of the catalyst blocks the acidic sites on the outer surface, preventing random oxidation of the raw material or formaldehyde on the outer surface of the support (generating CO). x ) or disordered condensation (generating byproducts such as dimethyl ether and paraformaldehyde); simultaneously, the hydrophobic properties of the passivation layer reduce the adsorption strength between the product and the support surface, when PODE 3-6 After formation, the material desorbs from the catalyst surface under the action of airflow and enters the subsequent separation and purification process. Unreacted species such as formaldehyde and methoxyl remain in the pores and continue to participate in the reaction, thereby improving the utilization rate of raw materials.

[0031] In summary, the synthesis mechanism of this invention integrates the oxidation, condensation, chain growth, and end-capping steps of methanol / dimethyl ether into a one-step reaction through the synergistic effect of multifunctional sites on a highly loaded acidic catalyst. Simultaneously, it utilizes gradient acidity distribution and nano-confinement effects to directionally regulate the degree of polymerization of the product, ultimately achieving PODE. 3-6 The core advantage of this highly efficient synthesis lies in the spatial matching and performance synergy of various functional sites, which solves the technical bottlenecks of low product selectivity and uncontrolled chain growth in traditional processes.

[0032] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention employs a one-step oxidative condensation method using methanol or dimethyl ether to synthesize polyoxymethylene dimethyl ether. This eliminates the need for additional preparation and separation of formaldehyde intermediates, significantly simplifying the traditional two-step synthesis process. It reduces energy consumption and equipment investment for intermediate product transfer and separation, thereby significantly improving production efficiency. Furthermore, the process utilizes a fixed-bed reactor for continuous reaction, with precisely controlled temperature, pressure, and feed parameters ensuring a stable and controllable reaction process. This avoids material losses and process fluctuations that are common in stepwise reactions, providing an efficient and feasible technical path for large-scale industrial production.

[0033] 2. The highly loaded acidic catalyst designed in this invention constructs a gradient acidic site distribution of "strong acid within the pores - medium-strong acid at the pore inlet / surface," combined with Mo-V / W composite oxidation active centers, achieving targeted regulation of feedstock activation, intermediate stabilization, and chain growth. The strong acid sites efficiently protonate the feedstock to generate C1 active species, the medium-strong acid sites specifically stabilize secondary carbon-like intermediates, and the composite active centers precisely control oxygen to avoid over-oxidation. The synergistic effect of these three factors significantly enhances the target product PODE. 3-6 Its selectivity effectively inhibits low-polymerization-degree byproducts, high-polymerization-degree byproducts, and CO. x The generation of this catalyst solves the problems of scattered product distribution and severe side reactions in traditional catalysts.

[0034] 3. The high-loaded acidic catalyst of this invention uses SBA-15, which has a high specific surface area and high stability, as a support. By anchoring the active center and acidic sites with silanol groups and combining the anti-sintering properties of the composite oxide solid solution, the dispersibility and structural stability of the active components are significantly improved. The hydrophobic passivation layer on the outer surface effectively reduces carbon deposition and blockage of active sites, extending the service life of the catalyst. Compared with the problems of easy agglomeration and rapid deactivation of traditional catalysts, the catalyst of this invention can maintain high efficiency catalytic performance for a long time, reducing the frequency and cost of catalyst replacement in industrial production, and improving the economic feasibility and sustainability of the process.

[0035] 4. This invention, through the directional regulation of a gradient catalytic system and a refining process involving dual-tower distillation and molecular sieve dehydration, yields a product with a polymerization degree concentrated in PODE. 3-6 The product is of high purity, extremely low moisture content, and minimal impurities. It exhibits excellent miscibility with diesel fuel, with superior cetane number and oxygen content compatibility. In special environments such as high altitudes and low oxygen levels, it effectively improves diesel fuel combustion completeness, shortens ignition delay, and significantly reduces fuel consumption and CO and NO emissions. x It reduces emissions of pollutants such as particulate matter, solves the problems of poor atomization and excessive emissions that easily occur when existing products are mixed, and expands the application scenarios of polyoxymethylene dimethyl ether in the field of clean fuels. Detailed Implementation

[0036] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with existing known technologies. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0037] Preparation Example 1: A specific method for preparing a highly supported acidic catalyst, including the following steps: S1. Take 10g of SBA-15 and add it to 50ml of 5wt% dilute nitric acid solution. Stir at room temperature for 1h, filter, wash with deionized water until the pH of the filtrate is neutral, and dry to obtain the pretreated carrier. S2. Add ammonium molybdate and ammonium metavanadate to deionized water at a molar ratio of 3:1 and stir until dissolved to obtain a precursor aqueous solution with a total solute mass fraction of 5 wt%. Add the precursor aqueous solution dropwise to the pretreated carrier until the liquid level just covers the pretreated carrier. Sonicate and stir at room temperature for 2 hours, let stand for 12 hours, filter, dry, and then place in a tube furnace. Based on the effective volume of the tube furnace, calculate the volumetric hourly space velocity (VHSV) at 1000 h⁻¹. -1 A nitrogen-hydrogen mixed gas (nitrogen and hydrogen in volume ratio of 95:5) was introduced, and the temperature was increased to 400℃ at a rate of 3℃ / min, held at that temperature for 3h, and then cooled to room temperature to obtain a support for loading oxidative active centers. S3. Place 10g of oxygen-loaded active center carrier in a quartz boat and put it in the isothermal zone of a horizontal tube furnace. Based on the effective volume of the horizontal tube furnace, the volume hourly space velocity is 800 h⁻¹. -1 Nitrogen gas was introduced as a carrier gas, and the temperature was raised to 120°C. Then, SO3 vapor was introduced at a rate of 0.3 ml / min·10 g of oxygen-loaded active center support, and deposition was carried out at a constant temperature for 1 h. After deposition, the SO3 vapor introduction was stopped, the furnace temperature was raised to 180°C, and the treatment was carried out at this temperature for 30 min. After cooling to room temperature, 40 ml of 8 wt% p-toluenesulfonic acid ethanol solution was added, and the mixture was stirred at room temperature for 3 h. After filtration and drying, the mixture was transferred to a muffle furnace and heat-treated at 200°C for 1.5 h in an air atmosphere. After cooling to room temperature, a highly loaded acidic catalyst precursor was obtained. S4. Disperse 10g of the highly loaded acidic catalyst precursor in 80ml of ethanol, add 0.6g of dimethyldichlorosilane, stir at room temperature for 4h, filter, wash twice with anhydrous toluene, and dry to obtain the highly loaded acidic catalyst.

[0038] Preparation Example 2: A specific method for preparing a highly supported acidic catalyst, including the following steps: S1. Take 10g of SBA-15 and add it to 80ml of 8wt% dilute nitric acid solution. Stir at room temperature for 2h, filter, wash with deionized water until the pH of the filtrate is neutral, and dry to obtain the pretreated carrier. S2. Ammonium molybdate and ammonium metavanadate were added to deionized water at a molar ratio of 4:1 and stirred until dissolved to obtain a precursor aqueous solution with a total solute mass fraction of 6 wt%. The precursor aqueous solution was added dropwise to the pretreated carrier until the liquid level just covered the pretreated carrier. The mixture was sonicated and stirred at room temperature for 2.5 h, allowed to stand for 18 h, filtered, dried, and then placed in a tube furnace. Based on the effective volume of the tube furnace, a volume hourly space velocity (VHSV) of 1500 h⁻¹ was measured. -1 A nitrogen-hydrogen mixed gas (nitrogen and hydrogen in volume ratio of 95:5) was introduced, and the temperature was increased to 500℃ at a rate of 5℃ / min, held at that temperature for 4 hours, and then cooled to room temperature to obtain a support for loading oxidative active centers. S3. Place 10g of oxygen-loaded active center carrier in a quartz boat and put it in the isothermal zone of a horizontal tube furnace. Based on the effective volume of the horizontal tube furnace, the volume hourly space velocity is 1200 h⁻¹. -1 Nitrogen gas was introduced as a carrier gas, and the temperature was raised to 130℃. Then, SO3 vapor was introduced at a rate of 0.6 ml / min·10 g of oxygen-loaded active center support, and deposition was carried out at a constant temperature for 1.5 h. After deposition, the SO3 vapor introduction was stopped, the furnace temperature was raised to 200℃, and the treatment was carried out at this temperature for 45 min. After cooling to room temperature, 60 ml of 12 wt% p-toluenesulfonic acid ethanol solution was added, and the mixture was stirred at room temperature for 4 h. After filtration and drying, the mixture was transferred to a muffle furnace and heat-treated at 220℃ in an air atmosphere for 2 h. After cooling to room temperature, a highly loaded acidic catalyst precursor was obtained. S4. Disperse 10g of the highly loaded acidic catalyst precursor in 100ml of ethanol, add 1.2g of dimethyldichlorosilane, stir at room temperature for 6h, filter, wash twice with anhydrous toluene, and dry to obtain the highly loaded acidic catalyst.

[0039] Preparation Example 3: A specific preparation method for a highly supported acidic catalyst, including the following steps: S1. Take 10g of SBA-15 and add it to 100ml of 10wt% dilute nitric acid solution. Stir at room temperature for 3h, filter, wash with deionized water until the pH of the filtrate is neutral, and dry to obtain the pretreated carrier. S2. Add ammonium molybdate and ammonium tungstate to deionized water at a molar ratio of 5:1 and stir until dissolved to obtain a precursor aqueous solution with a total solute mass fraction of 8 wt%. Add the precursor aqueous solution dropwise to the pretreated carrier until the liquid level just covers the pretreated carrier. Sonicate and stir at room temperature for 3 hours, let stand for 24 hours, filter, dry, and then place in a tube furnace. Based on the effective volume of the tube furnace, use a volumetric hourly space velocity (VHSV) of 2000 h⁻¹. -1 A nitrogen-hydrogen mixed gas (nitrogen and hydrogen in volume ratio of 95:5) was introduced, and the temperature was increased to 600℃ at a rate of 7℃ / min, held at that temperature for 5h, and then cooled to room temperature to obtain a support for loading oxidative active centers. S3. Place 10g of oxygen-loaded active center carrier in a quartz boat and put it in the isothermal zone of a horizontal tube furnace. Based on the effective volume of the horizontal tube furnace, the volume hourly space velocity is 1500 h⁻¹. -1Nitrogen gas was introduced as a carrier gas, and the temperature was raised to 140℃. Then, SO3 vapor was introduced at a rate of 1.0 ml / min·10 g of oxygen-loaded active center support, and deposition was carried out at a constant temperature for 2 h. After deposition, the SO3 vapor introduction was stopped, the furnace temperature was raised to 220℃, and the treatment was carried out at this temperature for 60 min. After cooling to room temperature, 80 ml of 15 wt% p-toluenesulfonic acid ethanol solution was added, and the mixture was stirred at room temperature for 5 h. After filtration and drying, the mixture was transferred to a muffle furnace and heat-treated at 240℃ for 2.5 h in an air atmosphere. After cooling to room temperature, a highly loaded acidic catalyst precursor was obtained. S4. Disperse 10g of the highly loaded acidic catalyst precursor in 120ml of ethanol, add 1.5g of dimethyldichlorosilane, stir at room temperature for 8h, filter, wash three times with anhydrous toluene, and dry to obtain the highly loaded acidic catalyst.

[0040] Comparative Preparation Example 1: The difference between Comparative Preparation Example 1 and Preparation Example 2 is that step S4 is omitted, and the highly loaded acidic catalyst precursor obtained in step S3 is the highly loaded acidic catalyst.

[0041] Comparative Preparation Example 2: The difference between Comparative Preparation Example 2 and Preparation Example 2 is that in step S3, after SO3 deposition is completed, the SO3 vapor is stopped, the furnace temperature is raised to 220°C, and the furnace is treated at this temperature for 60 minutes. After cooling to room temperature, a highly loaded acidic catalyst precursor is obtained.

[0042] Comparative Preparation Example 3: The difference between Comparative Preparation Example 3 and Preparation Example 2 is as follows: Step S3: 10g of the support with oxygen active center was added to 80ml of ethanol solution of p-toluenesulfonic acid with a concentration of 15wt%, stirred at room temperature for 5h, filtered, dried, and then transferred to a muffle furnace. The mixture was then heated to 240℃ in air atmosphere for 2.5h and cooled to room temperature to obtain a highly loaded acidic catalyst precursor.

[0043] Comparative Preparation Example 4: The difference between Comparative Preparation Example 4 and Preparation Example 2 is that ammonium metavanadate is not added in step S2.

[0044] Comparative Preparation Example 5: The difference between Comparative Preparation Example 5 and Preparation Example 2 is that SBA-15 in S1 is replaced with silicon dioxide.

[0045] Example 1: The specific synthesis process of polyoxymethylene dimethyl ether based on a highly supported acidic catalyst includes the following steps: (1) Methanol is dehydrated through a molecular sieve until the moisture content is ≤0.1wt% to obtain a pretreated raw material; (2) The highly loaded acid catalyst prepared in Preparation Example 1 was mixed with an equal volume of ceramic rings and packed into the middle of a fixed-bed reactor. The packing volume was 30% of the effective volume of the fixed-bed reactor, and both ends were filled with quartz sand. (3) Based on the effective volume of the fixed-bed reactor, with a capacity of 600 h⁻¹ -1 The reactor was purged with nitrogen at a volume hourly space velocity (VHSV) for 30 min, the temperature was raised to 200℃, the pressure was adjusted to 0.5 MPa, and methanol and oxygen were introduced at a molar ratio of 1:0.5, with the feed space velocity controlled at 0.8 h⁻¹. -1 Meanwhile, nitrogen, which accounts for 20% of the total volume of the feed gas (methanol, oxygen and nitrogen), is introduced as a carrier gas to continuously react and collect the condensed liquid products. (4) The liquid product is allowed to stand at room temperature to separate into layers, and the aqueous phase is removed by separation. A double-tower distillation process is adopted. The light component is removed by a light component removal tower (theoretical plate number 18-22) with a top pressure of 0.08-0.12 MPa and a temperature of 38-50℃. The product distillation tower (theoretical plate number 28-32) has a top pressure of 0.04-0.06 MPa and collects the 130-160℃ fraction. The 130-160℃ fraction is passed through a 3A molecular sieve column to dehydrate to a water content of ≤0.05wt%, and then filtered through a 0.22μm filter membrane to obtain polyoxymethylene dimethyl ether.

[0046] Example 2: The specific synthesis process of polyoxymethylene dimethyl ether based on a highly supported acidic catalyst includes the following steps: (1) Methanol is dehydrated through a molecular sieve until the moisture content is ≤0.1wt% to obtain a pretreated raw material; (2) The highly loaded acid catalyst prepared in Preparation Example 2 was mixed with an equal volume of ceramic rings and packed into the middle of a fixed-bed reactor. The packing volume was 35% of the effective volume of the fixed-bed reactor, and both ends were filled with quartz sand. (3) Based on the effective volume of the fixed-bed reactor, with a capacity of 1000 h⁻¹ -1 The reactor was purged with nitrogen at a volume hourly space velocity (VHSV) for 45 min, the temperature was raised to 220℃, the pressure was adjusted to 0.8 MPa, and methanol and oxygen were introduced at a molar ratio of 1:0.8, with the feed space velocity controlled at 1.5 h⁻¹. -1 Meanwhile, nitrogen, which accounts for 30% of the total volume of the feed gas (methanol, oxygen and nitrogen), is introduced as a carrier gas to continuously react and collect the condensed liquid products. (4) The liquid product is allowed to stand at room temperature to separate into layers, and the aqueous phase is removed by separation. A double-tower distillation process is adopted. The light component is removed by a light component removal tower (theoretical plate number 18-22) with a top pressure of 0.08-0.12 MPa and a temperature of 38-50℃. The product distillation tower (theoretical plate number 28-32) has a top pressure of 0.04-0.06 MPa and collects the 130-160℃ fraction. The 130-160℃ fraction is passed through a 3A molecular sieve column to dehydrate to a water content of ≤0.05wt%, and then filtered through a 0.22μm filter membrane to obtain polyoxymethylene dimethyl ether.

[0047] Example 3: The specific synthesis process of polyoxymethylene dimethyl ether based on a highly supported acidic catalyst includes the following steps: (1) Methanol is dehydrated through a molecular sieve until the moisture content is ≤0.1wt% to obtain a pretreated raw material; (2) The highly loaded acid catalyst prepared in Preparation Example 3 was mixed with an equal volume of ceramic rings and packed into the middle of a fixed-bed reactor. The packing volume was 40% of the effective volume of the fixed-bed reactor, and both ends were filled with quartz sand. (3) Based on the effective volume of the fixed-bed reactor, with a capacity of 1200 h⁻¹ -1 The reactor was purged with nitrogen at a volume hourly space velocity (VHSV) for 60 min, the temperature was raised to 230℃, the pressure was adjusted to 0.10 MPa, and methanol and oxygen were introduced at a molar ratio of 1:1, with the feed hourly space velocity controlled at 2.0 h⁻¹. -1 Meanwhile, nitrogen, which accounts for 35% of the total volume of the feed gas (methanol, oxygen and nitrogen), is introduced as a carrier gas to continuously react and collect the condensed liquid products. (4) The liquid product is allowed to stand at room temperature to separate into layers, and the aqueous phase is removed by separation. A double-tower distillation process is adopted. The light component is removed by a light component removal tower (theoretical plate number 18-22) with a top pressure of 0.08-0.12 MPa and a temperature of 38-50℃. The product distillation tower (theoretical plate number 28-32) has a top pressure of 0.04-0.06 MPa and collects the 130-160℃ fraction. The 130-160℃ fraction is passed through a 3A molecular sieve column to dehydrate to a water content of ≤0.05wt%, and then filtered through a 0.22μm filter membrane to obtain polyoxymethylene dimethyl ether.

[0048] Example 4: The specific synthesis process of polyoxymethylene dimethyl ether based on a highly supported acidic catalyst includes the following steps: (1) Dimethyl ether is dehydrated through a molecular sieve until the moisture content is ≤0.1wt% to obtain a pretreated raw material; (2) The highly loaded acid catalyst prepared in Preparation Example 2 was mixed with an equal volume of ceramic rings and packed into the middle of a fixed-bed reactor. The packing volume was 35% of the effective volume of the fixed-bed reactor, and both ends were filled with quartz sand. (3) Based on the effective volume of the fixed-bed reactor, with a capacity of 1000 h⁻¹ -1 The reactor was purged with nitrogen at a volume hourly space velocity (VHSV) for 45 min, the temperature was raised to 230℃, the pressure was adjusted to 1.2 MPa, and dimethyl ether and oxygen were introduced at a molar ratio of 1:1.2, with the feed hourly velocity controlled at 1.5 h⁻¹. -1 Meanwhile, nitrogen, which accounts for 30% of the total volume of the feed gas (dimethyl ether, oxygen and nitrogen), is introduced as a carrier gas to continuously react and collect the condensed liquid products. (4) The liquid product is allowed to stand at room temperature to separate into layers, and the aqueous phase is removed by separation. A double-tower distillation process is adopted. The light component is removed by a light component removal tower (theoretical plate number 18-22) with a top pressure of 0.08-0.12 MPa and a temperature of 38-50℃. The product distillation tower (theoretical plate number 28-32) has a top pressure of 0.04-0.06 MPa and collects the 130-160℃ fraction. The 130-160℃ fraction is passed through a 3A molecular sieve column to dehydrate to a water content of ≤0.05wt%, and then filtered through a 0.22μm filter membrane to obtain polyoxymethylene dimethyl ether.

[0049] Comparative Example 1: The difference between Comparative Example 1 and Example 2 is that the highly loaded acidic catalyst prepared according to Preparation Example 2 is replaced with the highly loaded acidic catalyst prepared according to Comparative Preparation Example 1.

[0050] Comparative Example 2: The difference between Comparative Example 2 and Example 2 is that the highly loaded acidic catalyst prepared according to Preparation Example 2 is replaced with the highly loaded acidic catalyst prepared according to Comparative Preparation Example 2.

[0051] Comparative Example 3: The difference between Comparative Example 3 and Example 2 is that the highly loaded acidic catalyst prepared according to Preparation Example 2 is replaced with the highly loaded acidic catalyst prepared according to Comparative Preparation Example 3.

[0052] Comparative Example 4: The difference between Comparative Example 4 and Example 2 is that the highly loaded acidic catalyst prepared according to Preparation Example 2 is replaced with the highly loaded acidic catalyst prepared according to Comparative Preparation Example 4.

[0053] Comparative Example 5: The difference between Comparative Example 5 and Example 2 is that the highly loaded acidic catalyst prepared according to Preparation Example 2 is replaced with the highly loaded acidic catalyst prepared according to Comparative Preparation Example 5.

[0054] Comparative Example 6: The difference between Comparative Example 6 and Example 2 is that in step (3), methanol and oxygen are introduced at a molar ratio of 1:0.3.

[0055] Comparative Example 7: The difference between Comparative Example 7 and Example 2 is that in step (3), methanol and oxygen are introduced at a molar ratio of 1:1.5.

[0056] Comparative Example 8: The difference between Comparative Example 8 and Example 2 is that in step (3), the temperature is raised to 180°C and the pressure is adjusted to 0.3 MPa.

[0057] Comparative Example 9: The difference between Comparative Example 9 and Example 2 is that in step (3), the temperature is raised to 260°C and the pressure is adjusted to 2.0 MPa.

[0058] Performance testing: 1. Catalytic activity and selectivity testing: Liquid phase products from Examples 1-4 and Comparative Examples 1-9 after 24 hours of continuous reaction were analyzed using a gas chromatograph (GC, model: Agilent 7890B) equipped with a flame ionization detector (FID). The chromatographic column used was an HP-5 capillary column (30m × 0.32mm × 0.25μm). The column temperature program was: initial temperature 40℃, held for 2 min, then increased to 200℃ at 10℃ / min and held for 5 min. The carrier gas was nitrogen, flow rate 1.0 mL / min, injection port temperature 250℃, detector temperature 280℃, and injection volume 1 μL. The conversion rate of reactants was calculated using the external standard method: (amount of reactants - amount of unreacted reactants) / amount of reactants × 100%. PODE was also calculated. n (n=3-6) Selectivity of each degree of polymerization = Number of PODEs generated at the target degree of polymerization / Total number of PODEs n (Total production × 100%) and CO x The percentage of (CO+CO2) byproducts is shown in Table 1.

[0059] 2. Polyoxymethylene dimethyl ether (PODE) 3-6 Product purity and impurity content testing: The final products of Examples 1-4 and Comparative Examples 1-9 after distillation and purification were collected. The purity was determined using the gas chromatograph combined with a mass spectrometer (GC-MS, model: Agilent 7890B-5977A). The types of impurities were qualitatively analyzed by matching the NIST spectral library, and the PODE was quantitatively calculated using the external standard method. 3-6 Purity: The moisture content of the product was determined using a Karl Fischer moisture analyzer (model: Metrohm 831), and the experimental results are shown in Table 1.

[0060] Table 1 Catalytic activity and selectivity tests of catalysts and polyoxymethylene dimethyl ether (PODE) 3-6 Product purity and impurity content test results

[0061] 3. Catalyst Continuous Operation Stability Test: The catalysts used in Examples 1-4 and Comparative Examples 1-5 were selected and operated continuously for 100 hours under their respective process conditions. Samples were taken every 25 hours, and the feed conversion rate and PODE were tested according to the "Catalyst Activity and Selectivity Test" method. 3-6 Selectivity was determined by recording the activity decline rate as (initial selectivity - xh subsequent selectivity) / initial selectivity × 100%), where x = 25, 50, 75, and 100. The experimental results are shown in Table 2.

[0062] Table 2. Results of catalyst continuous operation stability test

[0063] 4. Performance test of diesel blending at high altitude (above 2000m): The final products of Examples 2 and 4 and the products of Comparative Examples 1-9 were selected and mixed with 0# diesel at a volume fraction of 15% to prepare diesel-PODE blended fuel; at the same time, pure 0# diesel was set as a blank control group. At the plateau test site at an altitude of 2500m, a diesel engine (model: Weichai WP10H) with a China VI emission standard was selected and connected to the engine bench test system. Test Procedure: The engine was first warmed up by idling for 30 minutes. Then, it was continuously run under urban-suburban combined driving conditions (including starting, acceleration, constant speed, and deceleration stages) according to GB / T 12545.2-2021 "Test Method for Fuel Consumption of Passenger Cars" for a total test mileage of 500km. The total fuel consumption was recorded in real time using the fuel consumption metering device (accuracy ±0.1L) on the dynamometer. After the test, the fuel consumption rate (L / 100km) was calculated using the formula: Fuel Consumption Rate (L / 100km) = Total Consumption (L) ÷ Total Mileage (km) × 100. An exhaust gas analyzer (model: Horiba MEXA-7100DEGR) was used to detect CO and NO in the exhaust gas. x The concentration of particulate matter (PM) emissions was measured; the experimental results are shown in Table 3.

[0064] Table 3. Test results of diesel fuel blending performance at high altitudes (above 2000m)

[0065] Data Analysis: As can be seen from the experimental data in Table 1, the raw material conversion rate and PODE of Examples 1-4 were... 3-6 Selectivity, CO x The byproduct ratio and product purity were significantly better than those of the comparative example. This may be because the catalyst used in the examples provided a directional distribution of gradient acidic sites: during the catalyst preparation process, SO3 vapor diffused into the interior of the SBA-15 mesopores with the help of nitrogen carrier gas, reacting with the silanol groups in the pores to generate -SO3H strong acid sites, which can efficiently protonate methanol / dimethyl ether and directionally generate C1 active species; subsequently, the p-toluenesulfonic acid ethanol solution could only diffuse to the pore inlet and the surface of the support, forming medium-strong acid sites (Si-O-SO2C6H4CH3) through dehydration condensation, which can specifically stabilize the "secondary carbon-like active intermediate (CH3O-CH2-O·)", avoiding chain growth termination at PODE. 1-2 This drives a targeted increase in the degree of aggregation to 3-6, which is PODE 3-6 The key to high selectivity; Precise oxygen control in Mo-V / W composite oxidation active centers: During catalyst preparation, ammonium molybdate forms a composite oxide solid solution (such as Mo-VO) with ammonium metavanadate / ammonium tungstate, whose redox pairs (Mo...6+ / Mo 4+ V 5+ / V 4+ Active oxygen can be precisely provided through a "release lattice oxygen - oxygen regeneration" cycle: ensuring that methanol / methoxygen is oxidized to formaldehyde without excessive oxidation to generate CO. x Therefore, CO x By-products account for only 6.89%-8.12%, and the raw material conversion rate remains above 83%; The support used is SBA-15, utilizing the synergistic effect of mesoporous confinement and external surface passivation: during the catalyst preparation process, the selected SBA-15 provides nanoscale confinement space, constraining the intermediate conformation and avoiding high-polymerization-degree PODEs. 7+ The formation of a dimethyl dichlorosilane passivation layer (-Si-O-Si(CH3)2-) blocks acidic sites on the outer surface, inhibiting random condensation of raw materials on the outer surface of the carrier (such as the formation of dimethyl ether and paraformaldehyde), further improving the selectivity of the target product. At the same time, dual-tower distillation (18-22 trays in the light removal tower and 28-32 trays in the product distillation tower) and dehydration with 3A molecular sieve ensure high product purity and extremely low moisture content. In comparison: Comparative Example 1 (without passivation layer): Step S4 is omitted, leaving acidic sites on the catalyst's outer surface, leading to random condensation of the raw materials on the surface (e.g., formaldehyde self-polymerization into paraformaldehyde, methanol dehydration into dimethyl ether), PODE 3-6 Selectivity decreased to 61.35%, CO x The byproduct content increased to 12.87% due to excessive surface oxidation, and the product purity decreased to 98.76% due to byproduct residue, highlighting the necessity of the passivation layer to "inhibit side reactions on the outer surface". Comparative Example 2 (without medium-strong acid sites): In step S3, no p-toluenesulfonic acid ethanol solution was added, only the strong acid sites within the pores were retained, which could not stabilize the secondary carbon intermediate, and chain growth easily terminated at PODE. 1-3 PODE 3-6 With a selectivity of only 31.56%, the core role of "directed chain growth" at moderately strong acid sites is verified. Comparative Example 3 (without strong acid sites): In step S3, SO3 vapor was not introduced. Relying solely on the moderately strong acid sites of p-toluenesulfonic acid, the feedstock could not be efficiently protonated, resulting in insufficient C1 active species and a feedstock conversion rate of 67.24%. PODE 3-6 The selectivity of 28.79% indicates that strong acid sites are a prerequisite for "raw material activation to formaldehyde generation"; Comparative Example 4 (Single Mo active center, without V / W assistance): Lacking ammonium metavanadate / ammonium tungstate in step S2, and using only ammonium molybdate as the active center precursor, it is impossible to form Mo-VO or Mo-WO composite oxide solid solutions. The composite solid solution formed by Mo and V / W in the examples can pass through Mo... 6+ / Mo 4+ With V 5+ / V 4+ (or W) 6+ / W 4+ The redox mechanism of Mo synergistically regulates the oxidation depth, ensuring both formaldehyde formation efficiency and preventing over-oxidation; while single Mo active sites lack this synergy, resulting in high-priced Mo... 6+ It easily releases excessive lattice oxygen, directly oxidizing methoxy groups to CO. x Simultaneously, without the dispersion effect of V / W, the active centers of Mo tend to aggregate, leading to a reduction in the activation sites of the raw materials, resulting in a final conversion rate of 77.35% and PODE. 3-6 The selectivity of 58.62% fully demonstrates the key role of the complex active center in regulating the oxidation depth and the dispersibility of the active center; Comparative Example 5 (Ordinary silica support, without SBA-15 mesoporous structure): Comparative Example 5 uses ordinary silica to replace SBA-15, thus losing the advantages of "one-dimensional ordered mesoporous structure + high specific surface area" of SBA-15 in the examples. On the one hand, ordinary silica lacks mesoporous confinement space and cannot constrain the conformation of secondary carbon intermediates, making chain growth prone to branching or termination at PODE. 1-2 PODE 3-6 The selectivity was only 45.39%; on the other hand, ordinary silica has few and unevenly distributed silanol groups on its surface, and the active centers (Mo-VO) are prone to agglomeration, making it impossible to efficiently adsorb and activate the raw materials, resulting in a conversion rate of only 58.18%. Furthermore, the lack of mesopores leads to a disordered distribution of acidic sites, exacerbating side reactions and increasing CO content. x The by-product ratio was 15.74%, and the product purity was 97.32%, both significantly worse than the example. Comparative Example 6 (Oxygen Insufficient): Oxidative Active Center (Mo) 6+ / Mo 4+ Unable to be regenerated by O2, lattice oxygen is rapidly depleted, formaldehyde production drops sharply, and the raw material conversion rate is 54.83%. PODE 3-6 The selectivity of 22.47% confirms the supporting role of the "oxygen cycle" of the complex active center in the reaction; Comparative Example 7 (Excess Oxygen): Excess O2 enhances the oxidizing capacity of the active sites, further oxidizing formaldehyde to CO. x At the same time, it disrupts the stability of secondary carbon intermediates, PODE 3-6With a selectivity of only 28.79%, and product purity reduced to 96.78% due to paraformaldehyde residue, the importance of precise oxygen control is highlighted. Comparative Example 8 (low temperature and low pressure, deviating from process parameters): disrupted the kinetic equilibrium of "protonation activation - oxidation to formaldehyde - chain growth": at low temperature, the proton transfer efficiency of the -SO3H strong acid sites in the pores of the examples dropped sharply, and methanol was protonated to generate CH3OH2. + The conversion rate slowed significantly, the proportion of unactivated methanol increased, and the conversion rate was only 63.45%. Simultaneously, the low temperature increased the energy barrier for the formation of secondary carbon intermediates, making them easily decomposed into methanol and formaldehyde, which could not undergo the subsequent insertion reaction with formaldehyde. PODE 3-6 The selectivity is only 17.62%; low pressure reduces the amount of raw material adsorbed in the mesopores, shortens the gas residence time, and reduces the probability of collision between active sites and raw materials, further lowering the reaction efficiency. x Although the byproduct percentage of 5.37% is low, it stems from insufficient reaction kinetics rather than oxidation control, which contradicts the "low CO" figure of the example. x There is a fundamental difference between "high selectivity" and "high selectivity"; Comparative Example 9 (High Temperature and High Pressure, Deviating from Process Parameters): Over-enhancing the reaction intensity disrupts the "oxidation-condensation equilibrium" of the examples: At high temperature, the oxidation capacity of the Mo-V / W composite active center becomes uncontrolled, the lattice oxygen release rate far exceeds the formaldehyde generation rate, and a large amount of formaldehyde is further oxidized to CO. x High pressure prolongs the residence time of the product within the mesopores, allowing PODE6 to continuously insert into formaldehyde to generate PODE6. 7+ Furthermore, excessive condensation leads to the formation of paraformaldehyde, PODE 3-6 The selectivity is only 24.31%; more seriously, it may also cause the SBA-15 mesoporous structure to collapse, the active center to agglomerate, the catalyst structure to be destroyed, and the product purity to be only 95.94%. This fully demonstrates that the "200-230℃, 0.5-1.0MPa" range specified in the examples is the optimal range for matching the characteristics of the catalyst. Deviation from this range will cause side reactions to runaway.

[0066] As can be seen from the performance test data in Table 2, after 100 hours of continuous operation in Examples 1-4, the raw material conversion rate remained at 81.26%-83.27%, and the activity decrease rate was only 2.88%-3.34%. This is mainly due to the long-term stability of the catalyst structure. SBA-15 mesoporous structural support: The mesoporous silica of the S1 step has a high specific surface area and mechanical stability. It can anchor the Mo-V / W active centers and acidic sites through the silanol groups on the pore walls, thus preventing the aggregation of active components. Anti-sintering ability of composite active centers: The solid solution formed by Mo and V / W can inhibit the migration and sintering of metal oxides at high temperature. After 100h, the ratio of redox pairs did not change significantly and can still provide lattice oxygen efficiently. The anti-carbon deposition effect of the passivation layer: The hydrophobic passivation layer in step S4 can reduce the adhesion of carbon deposits on the catalyst surface during the reaction, avoid the blockage of active sites, and ensure long-term catalytic efficiency. In comparison: Comparative Example 1 (without passivation layer): Without passivation protection on the outer surface, carbon deposits quickly adhere to the acidic sites on the surface, and the raw material conversion rate drops from 80.41% to 71.89%, with an activity decrease rate of 10.59%, demonstrating the key role of the passivation layer in "anti-carbon deposition". Comparative Example 2 (no medium-strong acid sites, only strong acid sites): The p-toluenesulfonic acid impregnation process, lacking step S3, only forms strong acid sites through SO3 vapor deposition, failing to construct the "strong acid (inside the pores) - medium-strong acid (pore entrance / surface)" gradient distribution as in the examples. In the examples, the core function of the medium-strong acid sites is to stabilize the "secondary carbon-like active intermediate" through hydrogen bonding, preventing intermediate decomposition or disordered polymerization. However, Comparative Example 2 relies solely on strong acid sites. After intermediate formation, the lack of stable sites makes it prone to rapid decomposition into methanol and formaldehyde. The decomposition products adhere to the catalyst surface, forming light carbon deposits that block the contact channels between the strong acid sites and the oxidation active centers. Simultaneously, disordered decomposition leads to a continuous decline in the raw material activation efficiency, with the raw material conversion rate decreasing from the initial 76.68% to 65.43% after 100 hours, and the activity decrease rate reaching 14.67%. This fully demonstrates the crucial role of medium-strong acid sites in stabilizing intermediates and preventing carbon deposition. Comparative Example 3 (no strong acid sites, only medium-strong acid sites): The SO3 vapor deposition in step S3 was omitted, and medium-strong acid sites were constructed solely through p-toluenesulfonic acid, completely eliminating the strong acid sites within the pores of the previous example. In this example, the strong acid sites are the core of the protonation activation of the raw material, while the acid strength of the medium-strong acid sites is insufficient to efficiently break the OH / CO bonds of the raw material, resulting in insufficient activation efficiency. Unactivated raw materials are prone to slow dehydration reactions on the support surface, generating dimethyl ether and gradually forming heavy carbon deposits. Simultaneously, without strong acid sites to anchor the oxidation active centers, the Mo-V active centers easily aggregate, significantly reducing oxidation capacity. Ultimately, the raw material conversion rate decreased from 67.24% to 55.78%, with an activity decrease rate of 17.04%. This indicates that strong acid sites are a prerequisite for the "directed conversion of raw materials to formaldehyde," and their absence prevents the initiation of an efficient catalytic cycle. Comparative Example 4 (Single Mo Active Center): In step S2, ammonium metavanadate was not added. The single Mo active center was prone to sintering at high temperature, resulting in a decrease in oxidation capacity. The raw material conversion rate decreased from 77.35% to 67.35%, and the activity decrease rate was 12.93%, which verified the "anti-sintering synergistic effect" of the Mo-V / W composite active center. Comparative Example 5 (Ordinary silica carrier): In step S1, ordinary silica was used, which could not anchor the active components. Within 100 hours, the active centers agglomerated, and the raw material conversion rate dropped from 58.18% to 45.76%, with an activity decrease rate of 21.35%.

[0067] Based on the experimental data in Table 3, the PODE in Examples 2 and 4... 3-6 When the product is mixed with #0 diesel, the fuel consumption rate, CO, and NO at high altitudes (2500m) are reduced. x PM emissions were significantly lower than those of the control group and the blank group, mainly due to the following reasons: High oxygen content improves combustion completeness: Example product PODE 3-6 With a purity of ≥99.32%, the product has a lower oxygen content and higher purity. In high-altitude, low-oxygen environments, it can supplement the oxygen required for combustion, reduce incomplete combustion of diesel fuel, and therefore has low PM emissions. Excellent cetane number and solubility: PODE 3-6 A cetane number ≥75 can improve the ignition performance of diesel fuel, shorten the ignition delay time, and reduce NO. x It is generated and is completely miscible with diesel fuel, ensuring stable combustion and reducing fuel consumption. Low impurities reduce combustion interference: The product in the example has a moisture content of ≤0.03wt% and low impurity content, which will not interfere with the diesel combustion process. In contrast, the product in the comparative example has more impurities, which can easily lead to uneven combustion, increased fuel consumption and emissions. In comparison: Comparative Example 1 (without external surface passivation layer): The dimethyl dichlorosilane passivation treatment in step S4 was omitted, leaving a large number of acidic sites on the catalyst's external surface. This caused random condensation of the raw materials on the surface during the reaction (such as formaldehyde self-polymerization into paraformaldehyde and methanol dehydration into dimethyl ether). These byproducts were mixed into the final product. When mixed with diesel, paraformaldehyde was easily precipitated in high-altitude and low-temperature environments, clogging the engine fuel injectors and causing poor fuel atomization. At the same time, the residual dimethyl ether diluted the diesel concentration, reduced the cetane number of the mixed fuel, and further aggravated incomplete combustion. Comparative Example 2 (PODE) 3-6 Low selectivity): PODE in the product 3-6 The selectivity was 31.56%, and its oxygen content and cetane number were lower than those of the example, resulting in poor combustion performance. The mixed fuel consumption rate was 39.85 L / 100km, and the PM emission was 71.59 mg / m³. 3 Because low-polymerization-degree PODE cannot effectively supplement oxygen, diesel fuel still burns incompletely. Comparative Example 3 (No Strong Acid Sites): Due to the absence of strong acid sites, PODE in the product... 3-6The extremely low oxygen content results in low oxygen content and cetane number in the product. In high-altitude, low-oxygen environments, this means that the oxygen required for combustion cannot be effectively replenished, and the ignition performance of diesel fuel is difficult to improve. This leads to low diesel combustion efficiency, and the unburned diesel fuel forms a large amount of soot (PM). At the same time, local oxygen deficiency leads to increased CO emissions. The final fuel consumption rate is 40.67L / 100km, and PM emissions are 75.38mg / m³. 3 NO x The emissions of 889.64 ppm confirm that strong acid sites indirectly affect high-altitude combustion performance by regulating the degree of product polymerization. Comparative Example 4 (Single Mo Active Center): Due to the lack of V / W auxiliary active components, the oxidation depth of the single M active center was out of control, resulting in a small amount of residual CO in the product. x , and PODE 3-6 With a purity of only 98.57%, when mixed with diesel, CO... x It dilutes the concentration of the combustible mixture in the cylinder, and Mo oxide impurities adhere to the spark plug surface, affecting ignition efficiency. Both factors combined lead to increased combustion fluctuations. At high altitudes, these fluctuations are further aggravated, resulting in a fuel consumption rate of 38.42 L / 100km and NO... x Emissions were 791.37 ppm, and PM emissions were 65.82 mg / m³. 3 This illustrates the importance of the composite active center to product purity and combustion stability; Comparative Example 5 (Ordinary Silica Carrier): Replacing SBA-15 with ordinary silica resulted in no mesoporous confinement effect, and the PODE content in the product was reduced. 1-2 with PODE 7+ When coexisting with diesel, PODE 7+ Due to its high viscosity, it easily leads to clogging of the fuel injection system; at high altitudes and low air pressure, poorly atomized fuel is even more difficult to burn completely, resulting in a final fuel consumption rate of 39.26L / 100km, CO emissions of 789.54ppm, and PM emissions of 69.41mg / m³. 3 This highlights the crucial role of SBA-15 mesoporous structure in the product's degree of polymerization distribution and impurity control; Comparative Example 6 (Insufficient Oxygen): With a methanol to oxygen molar ratio of only 1:0.3, the redox cycle at the oxidative active center is interrupted, resulting in a sharp decrease in formaldehyde production and reduced PODE in the product. 1-2 The conversion rate is high, but the raw material conversion rate is only 54.83%. When mixed with diesel, the low molecular weight products will lower the flash point of the mixed fuel, and PODE... 1-2 The low oxygen content at high altitudes cannot compensate for the lack of oxygen, resulting in low combustion efficiency, with a final fuel consumption rate of 41.35L / 100km and PM emissions of 78.64mg / m³. 3The CO emission was 876.32 ppm, indicating that the amount of oxygen directly determines product quality and the combustion-supporting effect at high altitudes by affecting the amount of formaldehyde generated. Comparative Example 7 (product with many impurities): The product purity is only 96.78%, which easily forms carbon deposits during combustion, clogging the fuel injectors and resulting in poor fuel atomization, demonstrating the impact of product purity on high-altitude performance. Comparative Example 8 (Low Temperature and Low Pressure): Insufficient kinetics in the protonation and oxidation reactions of the raw materials resulted in a high proportion of low molecular weight products. These low molecular weight products have low oxygen content and low boiling points, making them prone to vaporization in the fuel line at high altitudes, leading to vapor lock and unstable fuel supply. Simultaneously, the low oxygen content failed to improve diesel combustion, resulting in a final fuel consumption rate of 41.89 L / 100km, CO emissions of 903.45 ppm, and PM emissions of 81.26 mg / m³. 3 This confirms that the reaction parameters must be matched with the catalyst activity; otherwise, product defects will lead to a complete deterioration of high-altitude performance. Comparative Example 9 (High Temperature and High Pressure): Excessive oxidation and excessive condensation coexist, CO in the product x High residue levels and the presence of high-polymerization-degree byproducts mean that when mixed with diesel fuel, these byproducts, due to their high viscosity, are difficult to uniformly dissolve in the diesel. (CO) x This will reduce the oxygen concentration in the cylinder, further exacerbating incomplete combustion. At high altitudes, the combustion fluctuations of stratified fuels are even greater, resulting in a fuel consumption rate of 40.98 L / 100km and NO... x Emissions: 904.69 ppm; PM emissions: 77.42 mg / m³ 3 This indicates that excessive process parameters can disrupt the "oxidation-condensation balance," resulting in defective products that cannot meet the requirements for high-altitude use. The blank control group (without PODE): pure diesel fuel had a combustion efficiency of only 65%-70% in the high-altitude, low-oxygen environment, with a large amount of fuel not completely burned due to lack of oxygen. Fuel consumption was 35.27L / 100km, and emission concentrations were significantly higher than those in the example, confirming the PODE. 3-6 It greatly helps reduce emissions from diesel fuel combustion at high altitudes.

[0068] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A process for synthesizing polyoxymethylene dimethyl ether based on a highly supported acidic catalyst, characterized in that, Includes the following steps: (1) The raw material is dehydrated by molecular sieve to a moisture content of ≤0.1wt% to obtain pretreated raw material; (2) The highly loaded acid catalyst is mixed with an equal volume of ceramic rings and packed in the middle of the fixed bed reactor, with both ends filled with quartz sand; (3) Purge the reactor with nitrogen for 30-60 minutes, raise the temperature to 200-240℃, adjust the pressure to 0.5-1.5MPa, introduce the raw material and oxygen, and control the feed space velocity to 0.8-2.0h. -1 Meanwhile, nitrogen gas is introduced as a carrier gas to continuously react and collect the condensed liquid products. (4) The liquid product is allowed to stand at room temperature to separate into layers, and the aqueous phase is removed by separation. A double-tower distillation process is adopted. The light component is removed by the pressure at the top of the light component removal tower of 0.08-0.12 MPa and the temperature of 38-50℃. The product distillation tower is pressured at the top of 0.04-0.06 MPa, and the fraction at 130-160℃ is collected. The fraction at 130-160℃ is passed through a 3A molecular sieve column to dehydrate to ≤0.05wt% water content, and then filtered through a 0.22μm filter membrane to obtain polyoxymethylene dimethyl ether.

2. The polyoxymethylene dimethyl ether synthesis process based on a highly supported acidic catalyst according to claim 1, characterized in that, The raw materials mentioned in (1) refer to methanol or dimethyl ether.

3. The polyoxymethylene dimethyl ether synthesis process based on a highly supported acidic catalyst according to claim 1, characterized in that, The loading amount of the high-loaded acidic catalyst in (2) is 30%-40% of the effective volume of the fixed-bed reactor.

4. The polyoxymethylene dimethyl ether synthesis process based on a highly supported acidic catalyst according to claim 1, characterized in that, The volume hourly space velocity (VHSV) for nitrogen purging in (3) is 600-1200 h⁻¹ based on the effective volume of the fixed-bed reactor. -1 Heating to 200-240℃ refers to heating to 200-230℃ when the feedstock is methanol, and to 210-240℃ when the feedstock is dimethyl ether; adjusting the pressure to 0.5-1.5MPa refers to adjusting the pressure to 0.5-1.0MPa when the feedstock is methanol, and to 0.8-1.5MPa when the feedstock is dimethyl ether; the molar ratio of feedstock to oxygen is: methanol:oxygen = 1:0.5-1, dimethyl ether:oxygen = 1:0.8-1.5; the volume fraction of nitrogen introduced is 20%-35% of the total feed gas volume, where the total feed gas volume is the sum of the feed volumes of feedstock, oxygen, and nitrogen.

5. The polyoxymethylene dimethyl ether synthesis process based on a highly supported acidic catalyst according to claim 1, characterized in that, The theoretical number of plates in the light-light distillation column in (4) is 18-22, and the theoretical number of plates in the product distillation column is 28-32.

6. The polyoxymethylene dimethyl ether synthesis process based on a highly supported acidic catalyst according to claim 1, characterized in that, The preparation method of the highly supported acidic catalyst is as follows: S1. Add mesoporous silica to dilute nitric acid solution, stir at room temperature for 1-3 hours, filter, wash with deionized water until the pH of the filtrate is neutral, and dry to obtain the pretreated carrier. S2. Add one of ammonium molybdate and ammonium metavanadate or ammonium tungstate to deionized water and stir until dissolved to obtain a precursor aqueous solution. Add the precursor aqueous solution dropwise to the pretreated support until the liquid level just covers the pretreated support. At room temperature, sonicate and stir for 2-3 hours, let stand for 12-24 hours, filter, dry, and then place in a tube furnace. Introduce a nitrogen-hydrogen mixed gas and heat to 400-600℃ at a rate of 3-7℃ / min. Hold at this temperature for 3-5 hours and cool to room temperature to obtain a support loaded with oxidative active centers. S3. Place the support with oxygen-loaded active centers in a quartz boat, put it in the isothermal zone of a horizontal tube furnace, introduce nitrogen as a carrier gas, heat to 120-140℃, then introduce SO3 vapor, and deposit at the isothermal temperature for 1-2 hours. After deposition, stop the SO3 vapor introduction, raise the furnace temperature to 180-220℃, treat at this temperature for 30-60 minutes, cool to room temperature, add an ethanol solution of p-toluenesulfonic acid, stir at room temperature for 3-5 hours, filter, dry, and then transfer to a muffle furnace. Heat to 200-240℃ in an air atmosphere for 1.5-2.5 hours, and cool to room temperature to obtain a highly loaded acidic catalyst precursor. S4. Disperse the highly supported acidic catalyst precursor in ethanol, add dimethyldichlorosilane, stir at room temperature for 4-8 hours, filter, wash with anhydrous toluene 2-3 times, and dry to obtain the highly supported acidic catalyst.

7. The polyoxymethylene dimethyl ether synthesis process based on a highly supported acidic catalyst according to claim 6, characterized in that, The S1 mesoporous silica has a pore size of 2-5 nm and a specific surface area ≥600 m². 2 / g; the ratio of mesoporous silica to dilute nitric acid solution is 1g:5-10ml; the concentration of dilute nitric acid solution is 5-10wt%.

8. The polyoxymethylene dimethyl ether synthesis process based on a highly supported acidic catalyst according to claim 6, characterized in that, The molar ratio of ammonium molybdate to ammonium metavanadate or ammonium tungstate in S2 is 3-5:1; the total mass fraction of solute in the precursor aqueous solution is 5-8 wt%; the introduction rate of the nitrogen-hydrogen mixed gas is based on the effective volume of the tubular furnace, with a volume hourly space velocity of 1000-2000 h⁻¹. -1 The volume ratio of nitrogen to hydrogen in the nitrogen-hydrogen mixture is 95:

5.

9. The polyoxymethylene dimethyl ether synthesis process based on a highly supported acidic catalyst according to claim 6, characterized in that, The nitrogen injection rate in S3 is based on the effective volume of the horizontal tube furnace, with a volumetric space velocity of 800-1500 h⁻¹. -1 The SO3 vapor is introduced at a rate of 0.3-1.0 ml / min·10 g of oxygen-supported active center carrier; the ratio of the oxygen-supported active center carrier to the ethanol solution of p-toluenesulfonic acid is 1 g: 4-8 ml, and the concentration of p-toluenesulfonic acid in the ethanol solution of p-toluenesulfonic acid is 8-15 wt%.

10. The polyoxymethylene dimethyl ether synthesis process based on a highly supported acidic catalyst according to claim 6, characterized in that, The ratio of the highly loaded acidic catalyst precursor, ethanol, and dimethyldichlorosilane in S4 is 1g:8-12ml:0.06-0.15g.

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