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With the rapid development of my country's national economy, energy tension has become increasingly serious. In 2007, my country imported 163.17 million tons of crude oil and 33.8 million tons of refined oil products. Oil import dependence reached 47.1%. At present, the international crude oil price has exceeded 100 US dollars/bbl, which has greatly affected our country's economic construction and development, forcing * * Adjust the energy structure, accelerate the development of clean alternative energy, and ease the contradiction between oil supply and demand. 1 Current situation and development trend of dimethyl ether market 1.1 Liquefied petroleum gas replaces dimethyl ether (DME). The properties of liquefied petroleum gas (DME) are very similar to liquefied petroleum gas (LPG) and can be used as civil fuel and power fuel. A comparison of the properties of liquefied petroleum gas and dimethyl ether is shown in Table 1. http://www.nmtech.com.cn/jishuwang/upload1/0808191038182455.jpg August 27, 2007 * * The Ministry of Construction issued Bulletin No. 691 "Construction Standards for Dimethyl Ether for Urban Gas" (numbered CJ/T259-2007), which will be implemented on January 1, 2008. The more mature method at present is to mix dimethyl ether into LPG at a ratio of 20% to 25% for use as civil fuel. In 2007, my country's urban LPG consumption was approximately 22 million tons (10 million tons imported). Based on this dosage and adding 20% dimethyl ether, 4.4 million tons of dimethyl ether will be needed per year. ； With the advancement of technology and the improvement of stoves, if dimethyl ether completely replaces LPG, the annual domestic demand for dimethyl ether for gas will reach about 15 million tons. 1.2 The comparison of the properties of diesel instead of dimethyl ether and diesel is shown in Table 2. Dimethyl ether has many similar properties to diesel, and the domestic research and development of dimethyl ether vehicles has achieved great success. A team composed of Shanghai Jiao Tong University, Shanghai Diesel Engine Co., Ltd., Shanghai Automotive Industry (Group) Corporation and other units successfully developed 10 dimethyl ether buses and put them on Shanghai No. 147 bus line for demonstration operation in September 2007. At the same time, the first vehicle dimethyl ether filling station in China was built. It is planned that the number of demonstration vehicles will reach 100 in 2008, and the scale of use will be more than 1,000 before the 2010 World Expo. In October 2007, Linyi, Shandong Province also decided to pilot the application of dimethyl ether in the automotive field to optimize the energy structure and reduce environmental pollution. In addition, Beijing, Wuhan and other places also intend to introduce dimethyl ether buses. Xi'an Jiaotong University has developed a dimethyl ether bus, and the prototype has been completed. It is understood that the use of dimethyl ether fuel for vehicles * * The standard is being developed and is expected to be released in 2008. Based on the fact that my country's diesel consumption exceeded 124 million tons in 2007, if 5% is replaced by dimethyl ether, a market demand of 6 million tons/a will be generated. http://www.nmtech.com.cn/jishuwang/upload1/0808191039599332.jpg 1.3 Total Demand Dimethyl Ether is also continuously expanding its market share in other consumer fields, such as propellants, refrigerants, foaming agents, etc. After 2010, the total demand for dimethyl ether in the domestic market should be around 22 million t/a. 1.4 Production Capacity Before 2002, only a few domestic enterprises such as Guangzhou Zhongshan Fine Chemical Factory produced dimethyl ether, with a total production capacity of approximately 32,000 t/a and an annual output of 20,000 t. In 2006, there were more than 30 manufacturing enterprises, mainly including Shandong Jiutai 150,000 t/a, Shandong Yuhuang 50,000 t/a, Inner Mongolia Yigao 20,000 t/a, Sichuan Lutianhua 110,000 t/a, etc., with a total production capacity of 300,000 t/a. In 2007, the new production capacity exceeded 2 million tons and the output exceeded 1 million tons. It is estimated that another 2 million tons of new production capacity will be added in 2008. Including the devices under construction and planned, the total production capacity in 2010 will be about 10 million t/a. The growth rate is relatively fast, but it still cannot meet the market demand. 2. Production process of dimethyl ether. The earliest dimethyl ether was produced in the side reaction of high-pressure synthesis of methanol and then separated. With the advancement of science and technology, the dimethyl ether generated in the side reaction of methanol synthesis is far from meeting people's demand for dimethyl ether as a new generation of clean alternative energy. Countries around the world have successively developed a series of new processes with low investment, good operating conditions and less pollution, which are basically divided into two categories: one-step method and two-step method. One-step method includes gas phase one-step method, three-phase slurry bed one-step method and direct synthesis of dimethyl ether from natural gas. ； The two-step method first synthesizes methanol from synthesis gas, and then dehydrates methanol to produce dimethyl ether, including a liquid phase two-step method and a gas phase two-step method. 2.1 One-step process technology for producing dimethyl ether. The one-step process uses natural gas or synthesis gas generated by coal gasification as raw material, and simultaneously completes the two reaction processes of methanol synthesis and methanol dehydration and the shift reaction in the reactor. The product is a mixture of methanol and dimethyl ether. ； Dimethyl ether is separated through the fractionation device, and methanol is returned to the reactor to continue participating in the dehydration reaction. The process is as follows: CO+H2=CH3OH, 2CH3OH=CH3OCH3+H2O, CO+H2O—→CO2+H2. The total reaction equation is: 3CO+3H2=CH3OCH3+CO2. The one-step method uses a bifunctional catalyst. The catalyst is generally made of a physical mixture of two types of catalysts, one of which is a methanol synthesis catalyst, such as Cu-Zn-Al(O) based catalyst, BASFS3-85 and ICI-512, etc. ； The other type is methanol dehydration catalysts, such as Al2O3, porous SiO2, Y-type molecular sieve, ZSM-5 molecular sieve, mordenite, etc. This process does not require a dedicated methanol synthesis unit. Compared with the two-step method, the process is simple, requires less equipment, requires less investment, and has low operating costs, and can maximize economic benefits. Therefore, it has become a hot topic in domestic and foreign development and is the main direction of future development. The most representative technologies are: Danish Topsoe process, American Air Products process, Japanese NKK process, Tsinghua University process, and Dalian Institute of Chemical Physics process of Chinese Academy of Sciences. The one-step synthesis of dimethyl ether technology is divided into fixed-bed gas-phase one-step method and three-phase sedimentation bed gas-phase one-step method. The status of domestic completed and proposed gas phase one-step process devices is listed in Table 3. http://www.nmtech.com.cn/jishuwang/upload1/0808191040293324.jpg 2.1.1 Fixed bed gas phase one-step method This process is that synthesis gas reacts on the surface of a dual-functional solid catalyst in a fixed bed to directly prepare dimethyl ether. It consists of two processes: synthesizing methanol and dehydrating methanol to produce dimethyl ether. Due to the synergistic effect of the catalyst and the coupling effect of the reaction, the generated methanol is continuously converted into dimethyl ether, and the methanol synthesis reaction is no longer restricted by thermodynamics, so the single-pass conversion rate of CO can be greatly improved. In recent years, my country has done a lot of work on the one-step production of dimethyl ether from synthesis gas. The Lanzhou Institute of Chemical Physics, Lanzhou Institute of Chemical Physics, Dalian Institute of Chemical Physics, Tsinghua University, Zhejiang University, Hangzhou University, Shanxi Coal Chemistry Institute, Southwest Research Institute of Chemical Industry, East China University of Science and Technology, etc. are all committed to the research of one-step production of dimethyl ether from fixed-bed synthesis gas. Great progress has been made in research on catalyst types, activity, life, CO conversion rate, dimethyl ether yield, etc. The development status of the one-step production of dimethyl ether from synthesis gas in a fixed bed is shown in Table 4. In my country, the fixed-bed gas phase one-step process for producing dimethyl ether has been established by Mitsubishi Heavy Industries of Japan (1986), Topsoe Company of Denmark (1993), Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Zhejiang University and other units, and successful pilot tests have been conducted. The results are shown in Table 4. http://www.nmtech.com.cn/jishuwang/upload1/0808191040515384.jpg (1) Danish Topsoe process. After the desulfurized natural gas is mixed with water vapor, it enters the autothermal reformer (composed of three parts: a high-pressure reactor (ATR), a combustion chamber and a catalyst bed) to generate dimethyl ether. The company has built a 50 kg/d pilot plant and completed 1,200 hours of continuous operation. The catalyst used is a mixture of a water gas shift catalyst, a Cu-based methanol synthesis catalyst, and a methanol dehydration (alumina and aluminum silicate) catalyst. When the reaction temperature is 240-290°C and the pressure is 4.2MPa, the single-pass conversion rate of CO reaches 60%-70%. (2) Dalian Institute of Chemical Physics technology. This process uses a metal-zeolite dual-functional catalyst system and selects the SD219-III catalyst to convert synthesis gas into dimethyl ether with high selectivity. Small-scale test results show that the conversion rate of CO is as high as more than 90%, and the selectivity of dimethyl ether in oxygen-containing organic matter is about 95%. (3)Zhejiang University. In 1993, a single-tube test for the one-step synthesis of dimethyl ether from industrial synthesis gas was completed at the Tongxiang Fertilizer Factory in Zhejiang. On this basis, in 1997, a 1500 t/a one-step industrial demonstration device for the synthesis of dimethyl ether was established in Hubei. 2.1.2 Three-phase slurry bed synthesis gas one-step process The three-phase slurry bed one-step process for producing dimethyl ether is to use a bifunctional catalyst with a particle size that is fine to a certain extent, suspending it in a liquid-phase heat carrier that is inert to the reaction and stable under reaction conditions, and forms a gas, liquid, and solid three-phase contact reaction in the reactor. The advantage is that: The bed temperature distribution is uniform, the temperature difference is small, the operation flexibility is large, the raw material adaptability is strong, and the space-time yield of dimethyl ether is high ； The heat released by the reaction is taken away by the cooling medium in the coil in the slurry bed or by the circulation of the liquid heat carrier itself, which can easily maintain the best operating conditions, protect the catalyst, and improve the selectivity of CO. The slurry bed reactor is used instead of the fixed bed reactor. Its structure is simple, and the reaction heat can be easily removed in time through the inert medium. The dimethyl ether synthesis process with a strong exothermic reaction can be easily operated at an isothermal temperature. It has fewer side reactions and a high single-pass conversion rate. It can handle hydrogen-poor synthesis gas and is more suitable for the raw material gas of coal-based synthesis gas. (1) Air Chemicals Corporation of America. The company developed a three-phase slurry bed synthetic dimethyl ether process with funding from the U.S. Department of Energy to produce fuel-grade dimethyl ether for use as a diesel alternative fuel. The scale of the pilot plant is 15 t/d, and the test results are ideal and the expected goals have been achieved. (2) Japan NKK Company. The company has also developed a new process for directly synthesizing dimethyl ether from synthesis gas using a three-phase slurry bed reactor. In 1989, a laboratory simulation test study of 1 kg/d was conducted. In 1995, a small trial of 50kg/d was conducted. From 1997 to 2000, with the funding of Japan's Agency of Natural Resources and Energy, we built a 5 t/d pilot plant in Kushiro, northern Japan, in a joint venture with Taiheiyo Coal Mining Co. Ltd. and Sumitomo Metallndustries Ltd., and completed the dimethyl ether pilot plant. In April 2003, Japan's NKK and Kawasaki Steel established JFE Company to continue research on the one-step DME method. From 2003 to 2006, a 100t/d industrial demonstration project was completed, and the industrialization process ranked among the best in the world. (3) Tsinghua University. In 1998, Tsinghua University began to cooperate with American Air Chemicals Company to conduct research on slurry bed one-step dimethyl ether production technology. Later, we cooperated with Chongqing Yingli Combustion Co., Ltd. to develop a one-step synthesis of dimethyl ether technology using a circulating slurry bed reactor, and successfully conducted a 3000t/a pilot test in Chongqing from April to September 2004. The pilot test results are: When the synthesis reaction process conditions are 250°C, 4.5 MPa, and the H2/CO volume ratio is about 1, the single-pass conversion rate of CO exceeds 60%, and the selectivity of dimethyl ether is greater than 95%. (4) Shanxi Institute of Coal Chemistry, Chinese Academy of Sciences. and Hunyuan County * * The jointly undertaken "Interim Test of Clean Fuel Synthesis of Dimethyl Ether by Coal-Based Syngas Slurry Bed One-step Method" has been implemented in Datong. 2.1.3 The problems existing in the one-step gas phase method and three-phase siltation bed production of dimethyl ether technology are first of all the serious waste of raw materials. Each molecule of dimethyl ether generated must also generate a molecule of CO2. The second is the short service life of the catalyst. Because the optimal reaction temperature ranges of the synthesis and dehydration catalysts do not match well, increasing the reaction temperature will inevitably reduce the life of the other part of the catalyst, resulting in a shortened life of the entire catalyst. The third is that CO, H2, CO2, dimethyl ether, methanol, water and other products are not easy to separate. 2.1.4 The latest process research on the one-step production of dimethyl ether - direct production of dimethyl ether from natural gas. This process mainly uses a liquid phase selective catalyst to catalytically oxidize methane to obtain dimethyl sulfate, which is then cracked into dimethyl ether in a cracking furnace. This process saves 70% of equipment investment compared with the two-step method, and the reaction temperature is only 180°C. It has the characteristics of simple process, low energy consumption, simple and convenient operation, etc. At present, this technology has completed laboratory and pilot-scale design research, and the construction of expanded pilot-scale demonstration devices is nearing completion. 2.2 Two-step process technology for producing dimethyl ether. The two-step process is accomplished by first synthesizing methanol in one reactor and dehydrating methanol in another reactor. The two-step method is also divided into two categories: gas phase two-step method and liquid phase two-step method. 2.2.1 The gas phase two-step method methanol steam passes through the ZSM-5 molecular sieve made of γ-Al2O3/SiO2, etc., and is dehydrated to generate dimethyl ether at 0.5 to 0.8 MPa and 280 to 340°C. The product purity reaches 99.9%, and the process is relatively mature. Its main features are a high degree of automation, no special requirements for equipment materials, and basically no problems with three waste emissions and equipment corrosion. The most representative ones in China include Tianyi Company Technology of Southwest Research Institute of Chemical Industry and Tsinghua University Technology. As of 2007, 12 units (with a total capacity of 270,000 t/a) have been built and put into production in China using Tianyi technology. 9 units are being installed, 16 units have been designed, and 1 unit is planned to be built. The total production capacity is 2.37 million t/a. The maximum capacity of the equipment in service is 100,000 t/a. Several sets of devices have also been built using technology from Tsinghua University. Tianyi Company began to conduct technical research on the two-step synthesis of dimethyl ether in 1985. In 1991, the pilot research project of methanol gas phase dehydration to dimethyl ether was originally * * The Science and Technology Commission listed it as a key research project in the “Eighth Five-Year Plan” and passed the original plan two years later. * * Acceptance organized by the Science and Technology Commission. Since the first 10,000 t/a industrialized device was built using this technology in 1994 and put into operation, this technology has been transferred to nearly a hundred devices in China. This technology has the following characteristics: First, the reactor uses a multi-stage chilled fixed bed (patented technology) reactor, which not only avoids the shortcomings of an adiabatic fixed bed reactor that causes an increase in side reactions and a low single-pass conversion rate of methanol due to excessive temperature rise, but also overcomes the shortcomings of the heat exchange fixed bed and isothermal tubular fixed bed reactors, which are large in size and have small catalyst loading capacity. ； The second is to adopt a new vaporization tower and separation process without setting up a concentration tower for recovering unreacted methanol (patented technology), which simplifies the process and reduces investment. The steam consumption per ton of dimethyl ether products can be reduced by more than 0.5 t compared with similar foreign technologies. ； Third, the methanol-aqueous solution discharged from the bottom of the dimethyl ether distillation tower is used as the absorbent of the reaction exhaust gas scrubber, which reduces the methanol content in the exhaust exhaust gas and reduces methanol consumption. 2.2.2 Liquid-phase two-step method (1) The traditional liquid-phase two-step method uses sulfuric acid as a catalyst. Methanol first generates methyl hydrogen sulfate under the action of sulfuric acid, and then regenerates dimethyl ether. The reaction equation is: H2SO4+CH3OH=CH3HSO4+H2O CH3HSO4+CH3OH=CH3OCH3+H2SO4 This process can produce dimethyl ether products with a purity greater than 99.6%, which can be used as aerosols and dimethyl sulfate intermediates ； It has the advantages of mild reaction conditions (130~160℃) and high single-pass methanol conversion rate (about 90%). ； However, there are problems such as equipment corrosion, serious environmental pollution and high toxicity of intermediate products. This method has been basically eliminated abroad. (2) Shandong Jiutai Chemical Co., Ltd. (formerly Shandong Luming) has developed a new process for the liquid phase production of dimethyl ether through compound acid catalytic dehydration, and has solved the condensation separation technology to enable the reaction and dehydration to proceed continuously, and has independent intellectual property rights. Nearly 7 units of this technology have been built or prepared for construction in China. The units built using Jiutai technology are shown in Table 5. http://www.nmtech.com.cn/jishuwang/upload1/0808191043584423.jpg (3) The preparation of dimethyl ether by catalytic distillation developed by Dalian Institute of Chemical Physics, Chinese Academy of Sciences is also a new two-step process. This process integrates the two units of reaction and separation into one. In the reactive distillation tower, sulfuric acid or other complex acids are used as catalysts to dehydrate methanol to generate dimethyl ether and separate at the same time. Although the two-step method requires methanol synthesis, methanol distillation, methanol dehydration, dimethyl ether distillation and other processes, the process is long, the equipment investment is large, and the product cost is high, it is still the most important production method at home and abroad. 3 Conclusion (1) The domestic market capacity of dimethyl ether is very huge. (2) The one-step dimethyl ether production process has lower equipment investment and production and operation costs than the two-step method. It is the direction of future development, but there are still many problems that require further research. (3) The two-step dimethyl ether production technology is mature and stable, and is currently the most widely used in China.