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1 Overview: Currently, international and domestic oil and gas prices are rising sharply. In the context of global energy shortages, a significant drop in oil and gas prices is no longer possible. Looking at the global trends in energy development, hydrogen and solar energy will be the main sources of energy in the future. Before hydrogen and solar energy can be widely commercialized, alternative energy sources are necessary. “\"Abundant coal, limited oil, and scarce gas\" is the current energy situation in China. There is increasing interest in using coal as a raw material to produce dimethyl ether, a new type of clean energy source that can serve as an alternative fuel. **The National Development and Reform Commission has begun to advance a strategy for replacing petroleum, with multiple large-scale dimethyl ether production facilities under construction or in the planning stage, in order to alleviate the shortage of petroleum supply. Dimethyl ether (DME) is a colorless and non-toxic gas or compressed liquid with a boiling point of –24 °C and a freezing point of –140 °C. It has a slight ether-like odor, and its vapor pressure at room temperature is approximately 0.5 MPa. Its saturated vapor pressure is lower than that of liquefied petroleum gas, making it safer to store and transport compared to liquefied petroleum gas ； It also has good combustion performance and high thermal efficiency; there are no residues or black smoke during combustion, and the emissions of CO and NO are low ； Dimethyl ether can also be blended with liquefied petroleum gas, city gas, or natural gas for mixed combustion, thereby increasing the heat output. Dimethyl ether with a purity of ≥95% can be used directly as a fuel alternative to liquefied petroleum gas. DME has a high cetane number and excellent compressibility, making it very suitable for compression-ignition engines; it is an ideal alternative fuel for diesel engines. As the pace of modern urban development accelerates, the demand for clean fuels will continue to increase. From the perspectives of **energy strategy, economic security, and sustainable development, giving due attention to the technological research and development, commercial application, and large-scale development of alternative fuels such as dimethyl ether is a top priority in our current energy strategy.** Continuously summarizing production experience, optimizing the manufacturing process, and reducing the cost of dimethyl ether are the top priorities in the dimethyl ether industry at present. Over the years, relying on the province’s abundant coal resources and with the goal of developing alternative energy sources, we have consistently worked to research production technologies for dimethyl ether. Through years of exploration and experimentation, we succeeded in developing a new method for producing dimethyl ether – the super-strong acid liquid-phase synthesis method. In November 2005, we were granted a **patent (patent number: ZL200410022599.5) for this method. Patent applications are also in progress for other technologies such as the method for producing super-strong acid catalysts, various methods for producing dimethyl ether through high-pressure liquid-phase synthesis, methods for using dimethyl ether as a refrigerant, and techniques for producing dimethyl ether as a substitute for acetylene additives. The company is at the forefront in China in terms of the production and application of dimethyl ether. Companies and experts from the United States, Japan, Canada, Taiwan, China, as well as many domestic peers have visited the company on numerous occasions for inspections and guidance. Our company’s technology for the liquid-phase synthesis of dimethyl ether using superacidic solutions has been improved and optimized on numerous occasions; it features advanced processes, low energy consumption, minimal investment requirements, high yields, excellent product quality, and no pollutant emissions during production. As a result, its production costs are **lower than those of competitors in the same industry. This process technology has solved the global challenge of scaling up dimethyl ether production facilities, reaching an advanced level in the industry. Using this technology to build dimethyl ether plants can save 30%–50% in investment compared to conventional methods currently used in China, such as the vapor-phase method and the composite acid method. The China Council for the Promotion of International Exchange and the China Patent Technology Promotion Center have listed this project as a recommended candidate for international exchanges of scientific and technological achievements and patent technologies in 2005. In May 2005, the UK International Science Centre gave the following evaluation of our company’s “Method for the Liquid-Phase Synthesis of Dimethyl Ether using Superacidic Solutions”: “(1) Patent achievements with independent intellectual property rights” ； (2) High-tech achievements in cutting-edge fields ； (3) The project has a wide range of applications ； (4) The product market has broad prospects, high profit margins, and low investment risks. After thorough consideration by the expert panel, and through scientific evaluations such as systematic assessment, feasibility analysis, and market research, it was unanimously agreed that this project possesses significant commercial value and potential. 2 Main Technologies and Performance Indicators for the Liquid-Phase Synthesis of Dimethyl Ether Using Superacidic Agents The method we have invented for the liquid-phase synthesis of dimethyl ether using superacidic agents combines the advantages of the gas-phase method, the composite acid method, and the sulfuric acid method. It features a simple process, low investment costs, no wastewater pollution. The production temperature is maintained at 120 ℃, the gas pressure in the production line ranges from 0.1 to 0.8 MPa, there is minimal equipment maintenance required, energy consumption is low, water usage is minimal, the catalyst exhibits high catalytic efficiency, a long service life, high conversion rates, and good selectivity. This approach enables an effective increase in production efficiency, resulting in high product purity. Compared with other processes, it offers significant technical advantages. Key technical and performance specifications: (1) Dimethyl ether purity: 99.9% ； (2) Methanol consumption index: 1.44 t ； (3) Catalyst loss: 40 g, more than 200 times lower than the sulfuric acid method or the composite acid method ； (4) Coal consumption for heating: 50 kg ； (5) Production efficiency: 14 t/24 h (based on a single 3000L reactor) ； (6) Depreciation of reaction equipment: 30 yuan ； (7) Power consumption: 50 kW·h ； (8) Conversion rate 96% ； (9) Selectivity 99%. (Note: The consumption and depreciation metrics are all based on per ton of dimethyl ether; the same applies hereafter.) Production facilities for synthesizing dimethyl ether using fluorine-containing superacid catalysts, which employ difluoromethyldisulfonic acid catalysts with exceptional catalytic capabilities, reduce the production cost of dimethyl ether significantly compared to existing domestic processes. The main advantages in terms of production costs are as follows: (1) A substantial reduction in equipment investment and depreciation costs; the depreciation cost of equipment used in this fluorine-containing superacid catalysis process is only 16%–17% of that in the methanol gas-phase dehydration method, and 60% of that in the composite acid catalysis method. (2) It reduces heating energy consumption and maintenance costs, and the entire production process can basically achieve an energy balance on its own. (3) It increased the methanol conversion rate and significantly reduced the specific consumption of methanol. 3 Process Flow and Technical Features The main technical flow of the industrial plant for the synthesis of dimethyl ether from methanol via dehydration catalyzed by fluorinated superacid is as follows: Liquid methanol delivered by a metering pump is preheated to 90–120 °C, and then introduced into the catalyst consisting of difluoromethyldisulfonic acid in the main reaction tower. Through a distributor, methanol comes into full counter-current contact with the fluorinated superacid catalyst; at a temperature of 100–120 °C, methanol is rapidly catalyzed to undergo dehydration and form dimethyl ether. The resulting dimethyl ether gas stream passes through the middle and upper sections of the reaction tower where it is separated and purified. After that, it is sent to a condenser where it is cooled to 50–60 °C, followed by entry into a buffer tank. Further separation takes place in this tank before the material enters a drying vessel. The dried dimethyl ether exiting the drying vessel is cooled to 20–25 °C in another condenser, after which it is stored in a product tank in liquid form. During this process, compared to conventional processes, the compressor is eliminated, resulting in significant savings in equipment investment and operating costs. This production process possesses the following technical features: (1) The super-strong acid catalyst has greater acidity than sulfuric acid and composite acids, allowing the reaction temperature to remain below 120 ℃ with a heating temperature of ≤100 ℃, thereby significantly reducing the energy costs associated with heating ； (2) The boiling point of superacid catalysts is much higher than that of sulfuric acid, resulting in significantly reduced volatilization losses and thereby **less equipment corrosion ； (3) Superacid catalysts possess a stronger acidity than concentrated sulfuric acid and composite acids, being 4 to 5 times more acidic than them, thereby significantly increasing the catalytic rate and the production capacity of manufacturing facilities ； (4) Superacid catalysts have no oxidizing properties, do not generate black wastewater, are environmentally friendly; the water produced is clear and transparent, and can be treated simply to meet discharge standards ； (5) Production equipment is simplified, equipment investment is significantly reduced, equipment depreciation costs **decrease**, and floor space is **saved**. Due to the extreme acidity and low volatility of superacid catalysts, they exhibit the following technical properties in catalyzing the dehydration of methanol to produce dimethyl ether. (1) Significantly reducing the reaction temperature lowers heating energy consumption: Due to the extremely high acidity of difluoromethyldisulfonic acid, the monomethyl ester of difluoromethyldisulfonic acid exhibits strong methyl cation activity at room temperature, allowing it to react rapidly with methanol to form dimethyl ether. To increase the reaction rate and ensure continuous evaporation of the water vapor produced, a temperature of 100–130 °C is required. The reaction temperature is reduced by 20–40 °C compared to the sulfuric acid method and the composite acid method. (2) The production capacity of the device increases significantly: due to the greatly enhanced catalytic rate, the production capacity is 2–4 times higher than that of the composite acid method under the same reaction conditions. (3) The production equipment is simplified, resulting in a significant reduction in equipment investment; the depreciation costs associated with the equipment used in production are also greatly reduced. Due to the extremely fast catalytic rate of difluoromethyldisulfonic acid, the methanol fed into the system is rapidly reacted. With the help of distributors and specialized reaction towers, the conversion rate of methanol can reach 96%. The dimethyl ether gas emerging from the main reactor contains very little methanol, allowing fuel-grade dimethyl ether to be obtained at 95% purity without the need for distillation. (4) Significant reduction in catalyst volatilization loss: Compared with the composite acid method, the volatilization loss of the difluoromethylbisulfonic acid catalyst is greatly reduced. The main difference lies in the reaction mechanism; the composite acid method requires a high temperature of 135 °C to produce active monomethyl sulfate and dimethyl sulfate. Dimethyl sulfate has a boiling point of only 188 °C, and it volatilizes rapidly along with the dimethyl ether gas stream at a reaction temperature of 140 °C. Difluoromethyldisulfonic acid has no boiling point at atmospheric pressure. Due to the high reactivity of the monomethyl ester of difluoromethyldisulfonic acid, it reacts rapidly with the methanol introduced, making it difficult to form the dimethyl ester. Moreover, at a reaction temperature of 120 °C, the volatilization loss of difluoromethyldisulfonic acid during the catalytic synthesis of dimethyl ether can be reduced to 40 g. The alkali washing process hardly consumes caustic soda. In the composite acid method, the sulfuric acid loss due to volatilization ranges from 5 to 20 kg, requiring a large amount of caustic soda for alkaline washing and neutralization. (5) Clean and environmentally friendly: Difluoromethyldisulfonic acid shows almost no oxidizing properties at a reaction temperature of 130 °C, and it does not oxidize methanol to produce black substances. Because concentrated sulfuric acid has strong oxidizing properties, both the sulfuric acid method and the mixed acid method generate large amounts of black, toxic wastewater. The superacid method does not generate the black wastewater associated with the composite acid method; the resulting water is clear and transparent, and can meet discharge standards after simple treatment, making it a clean production process for dimethyl ether. (6) Equipment corrosion is **reduced**, and the amount of maintenance required for the equipment is significantly decreased: since difluoromethyldisulfonic acid hardly volatilizes to the dimethyl ether production equipment located downstream of the main reactor, corrosion is confined to within the main reactor. 4 Technical principle of this patent: This patent relates to the synthesis of dimethyl ether from methanol through dehydration, catalyzed by fluorine-containing superacids. Due to differences in the acid strength of catalysts, the catalytic rates and reaction conditions of various strong acid catalysts vary greatly. The fluorinated superacid used in this project is the inexpensive and readily available difluoromethyldisulfonic acid (HO3S-CF2-SO3H). Methanol and this fluorinated superacid catalyst first produce a methyl ester product – difluoromethyldisulfonic acid monomethyl ester. This product exhibits a highly electrophilic methyl cation state at room temperature, and it reacts rapidly with methanol to form dimethyl ether. The reaction conditions required for different catalysts to produce methyl ester products with methyl cation activity vary significantly. Fluorine-containing superacids possess a stronger superacidic strength than 100% sulfuric acid; they are able to generate reactive methyl cations under milder reaction conditions than sulfuric acid, and they significantly accelerate catalytic reactions. The chemical reaction equation for the catalytic dehydration synthesis of dimethyl ether using difluoromethyldisulfonic acid is as follows: The key catalyst for the synthesis of dimethyl ether via sulfuric acid-catalyzed dehydration or composite acid catalysis is sulfuric acid; the monomethyl sulfate formed by the reaction between sulfuric acid and methanol requires a temperature of 135 °C to exhibit methyl cation activity. Therefore, the reaction temperature during production must be 140 ℃. Due to its strong oxidizing properties, concentrated sulfuric acid oxidizes methanol at high temperatures of 140 °C, producing large amounts of black oxidation products and sulfur dioxide gas. If the pH value is below 10 during alkaline cleaning, an unpleasant odor will appear in the dimethyl ether product, caused by sulfur dioxide. Difluoromethyldisulfonic acid has almost no oxidizing property at 130 °C and does not produce the pungent sulfur dioxide. 5 Some views on dimethyl ether production in China (1) On the progress of dimethyl ether production methods: Considering the original methods for producing dimethyl ether, such as the dehydration using concentrated sulfuric acid and the high-temperature reaction using aluminum phosphate, as well as the current mainstream production routes—the one-step and two-step methods—it can be seen that the dehydration method using concentrated sulfuric acid features mild reaction conditions (130–160 °C), a high conversion rate of methanol (>85%), and allows for either batch or continuous production. However, the equipment is severely corroded, residual liquids and wastewater cause serious environmental pollution, the operating conditions are harsh, and product post-treatment is relatively difficult ； The methanol conversion rate and dimethyl ether selectivity using the aluminum phosphate high-temperature reaction method are both low. Therefore, all these production methods were phased out. The one-step method for producing DME breaks the thermodynamic equilibrium of methanol yield, thereby increasing the reaction rate and conversion rate. The main problem is that the heat generated during this one-step process is substantial; a slurry bed can be used to remove this heat, but a series of technical issues still need to be addressed. An adiabatic fixed bed not only requires a large amount of catalyst but also risks catalyst deactivation due to overheating if not operated properly. Currently, research on the one-step production of DME from syngas is still in the experimental stage, and no large-scale industrial plants have been successfully developed. Therefore, the current technology of producing dimethyl ether via a two-step gas-phase fixed-bed catalytic process is the main method for developing large-scale dimethyl ether production facilities. (2) On the scaling up and localization of dimethyl ether plants: China’s dimethyl ether production started relatively late; in the early 1990s, only a few manufacturers were operating in the country. Compared with the new plants built in recent years, these existing plants had small scales, outdated production technologies, and high production costs, which made them uncompetitive. As a result, most of them are now shut down or operating at reduced capacity. In recent years, given the promising prospects for the dimethyl ether market and the advancement of production technologies for this substance, many regions in China have established or plan to establish dimethyl ether production projects. From a development trend perspective, the scale of dimethyl ether production facilities is moving toward larger sizes, with capacities upgrading from the current 10,000-ton level to 100,000 tons, or even millions of tons ； Production technology is evolving toward one-step processes, especially the one-step liquid-phase slurry bed process ； As for raw materials, the use of both coal and natural gas will continue, with regions choosing appropriate raw materials based on local conditions. By the end of 2007, China’s dimethyl ether production capacity had reached over 1 million tons, but the utilization rate of these facilities was low, resulting in limited domestic production. Sichuan Lutianhua Group Co., Ltd. and Shandong Jiutai Chemical Technology Co., Ltd. were the two largest dimethyl ether producers in terms of capacity and output in 2007. The currently under construction dimethyl ether projects mostly have a capacity of over 100,000 tons, while those with a capacity of millions of tons account for a significant proportion of the projects in the planning stage. In Inner Mongolia alone, there are plans to build dimethyl ether production facilities with a capacity of over 10 million tons. It is evident that the enlargement and localization of dimethyl ether production facilities represent an inevitable trend in the development of this industry, with coal serving as the primary raw material in dimethyl ether production in the future. In the face of the trend toward larger-scale and more regionalized dimethyl ether plants, some existing problems have also come to light. Resource advantages lead to a relative concentration of projects, and excessive concentration in production poses challenges to local resources and sales networks. Most of the existing dimethyl ether production facilities produce dimethyl ether as a by-product, locating the dimethyl ether production units near the methanol synthesis plants and utilizing crude alcohol in the production process to reduce costs. However, dimethyl ether is gaseous at normal pressure and becomes liquid under pressure; it is transported to the customer’s location using pressure-resistant tank trucks, and the additional transportation costs reduce its cost advantage. Some companies adopt a more flexible production approach, focusing on the production of methanol while decentralizing the production of dimethyl ether. They take advantage of geographical and policy benefits by building large-scale methanol plants in western regions. Utilizing the fact that methanol remains in liquid state at normal pressure, they transport it to the eastern regions where there is high demand for dimethyl ether, either via train cars or long-distance pipelines. Alternatively, they purchase methanol locally and then establish plants in various locations based on the consumption levels in those areas. This approach requires less investment and faster construction times. Given China’s current situation of excess methanol production, limited use of dimethyl ether, and a lack of experience in designing and constructing very large dimethyl ether plants, this production and sales method not only helps to reduce transportation costs but also allows the production capacity of these plants to be adjusted according to regional demand, thereby increasing their operational efficiency and reducing investment risks. (3) China should develop diversified dimethyl ether production technologies. At present, dimethyl ether projects in China exhibit a characteristic of technological homogeneity. Many domestic enterprises and research institutions are engaged in research on dimethyl ether, including Shandong Jiutai Chemical Technology Co., Ltd., Tsinghua University, Zhejiang University, the Dalian Institute of Chemical Physics of the Chinese Academy of Sciences, Taiyuan University of Technology, the Southwest Chemical Engineering Research and Design Institute, and the Shanxi Coal Chemistry Institute of the Chinese Academy of Sciences. Among the numerous dimethyl ether projects, aside from Shandong Jiutai Chemical Technology Co., Ltd. which uses its own technology and a few companies that have adopted foreign technology, most projects make use of the methanol-to-dimethyl ether technology developed by the Southwest Chemical Research and Design Institute. Moreover, these various technologies also have many shortcomings. Therefore, our country should also promote the application and research of dimethyl ether technology by other enterprises and research institutions, and develop diversified dimethyl ether production technologies suited to local conditions.