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At present, the existing production methods of dimethyl ether at home and abroad include methanol dehydration, one-step synthesis gas method and carbon dioxide hydrogenation method. Carbon dioxide hydrogenation is still in the exploratory stage. Methanol dehydration (two-step method) and synthesis gas one-step method have high production costs due to low reaction yield, large equipment investment, low product purity, and high energy consumption, and cannot compete with liquefied petroleum gas, gasoline and diesel, etc. In view of the above situation, our company has invested in scientific research to focus on key problems and developed a new process for the production of dimethyl ether by composite acid catalytic dehydration. Achieved high efficiency, low consumption and clean production of dimethyl ether. The introduction is as follows. 1. Process: Coal is gasified to produce water gas. The water gas undergoes purification processes such as desulfurization and decarbonization. The resulting methanol synthesis gas (main component H2+CO) catalyzes the synthesis of crude methanol. The crude methanol generates dimethyl ether under the condition of a composite acid catalyst. The specific process is as follows. (1) Crude methanol is continuously added to the methanol distributor by a pump and evenly atomized, and is catalytically dehydrated under the condition of liquid composite acid. The reaction is a liquid-liquid contact reaction. Due to the action of the composite acid, the azeotropic phenomenon of water and acid is destroyed, so that the water can evaporate stably and evenly, achieving the purpose of continuous production of dimethyl ether. (2) Catalytic reaction conditions: The reaction temperature is 110-160°C, the reaction pressure is below 0.1MPa, the one-time reaction yield is greater than 93%, and the total reaction yield is greater than 99.5%. (3) The dimethyl ether gas generated by the catalytic reaction, the water vapor generated by dehydration, and the unreacted methanol gas are condensed and dried through a heat exchanger. After removing moisture and methanol, they are pressurized and liquefied into 99.9% liquid dimethyl ether finished product. (4) The water vapor and part of the unreacted methanol generated during the reaction dehydration process enter the distillation tower after condensation. The recovered methanol is returned to the reactor to continue the reaction. The tail gas with a methanol content of <0.5% is discharged from the top of the tower and sent to the coal gasifier for incineration. There is no waste water discharge, and the entire process realizes clean production. 2 Technical Features (1) This technology uses low-cost composite acid as a catalyst. The catalyst is basically consumed. The reaction is carried out at low temperature and low pressure. The post-treatment process is simple, there are few side reactions, and the yield is high (total yield reaches 99.5%). Therefore, the production cost is only 50% to 70% of the cost of other methods at home and abroad. The production cost of our company's current 35kt/a dimethyl ether production unit is 2,200 yuan/t. Compared with gasoline, diesel, and liquefied petroleum gas, it has strong cost advantages and competitiveness. (2) Short process flow and low equipment investment. Except for the reactor, which requires acid-resistant materials, carbon steel equipment can be used for all other equipment, and the equipment investment is only about 1/4 of other investments of the same production scale. (3) Product purity is high. Using original condensation separation technology, trace amounts of methanol and moisture entrained in dimethyl ether gas can be removed in one go, and the product purity is as high as 99.9% or more. (4) Continuous closed and clean production. This process is a continuous and closed production process. The reaction and regeneration of the catalyst are carried out simultaneously. There is no emission of three wastes. It is an environmentally friendly and clean production process. 3 Technology and product application situation Our company’s dimethyl ether production unit with an annual output of 5,000 tons has been in continuous operation since August 2001, and the catalyst has not been replaced. ； The device with an annual output of 30kt was officially put into production on December 21, 2003. This method has low energy consumption, low equipment corrosion, short production process, low equipment investment, low production cost, total product yield as high as 99.5%, and purity as high as 99.9%. At present, our company's DME products are exported to Guangdong, Shanghai, Zhejiang, Jiangsu, Liaoning, Hubei and other places, and replace liquefied petroleum gas in Linyi City and its counties and townships, sold as bottled gas, and as pipeline gas in small and medium-sized towns ； In the field of refrigerants, our company has signed a cooperation agreement with the Refrigerant Research Institute of Shanghai Jiao Tong University to conduct comprehensive basic tests on the use of dimethyl ether as a refrigerant. ； As a clean fuel to replace gasoline and diesel in automobiles, our company has done a lot of fruitful experiments and cooperated with Xi'an Jiaotong University, Shanghai Jiaotong University, China Tianjin Automotive Research Center, Shanghai CNPC and other units. The modified 18 cars and 6 motorcycles have been running for two years, with good power performance and exhaust emissions reaching Euro III standards. We plan to modify 2,000 taxis and buses in 2004 to reduce urban automobile exhaust pollution. The exhaust emission test results of DME used in diesel automobile engines are shown in Table 1. The combustion test results of DME replacing city gas in civil gas stoves are shown in Table 2. 4 Prospects http://www.nmtech.com.cn/jishuwang/upload/0601261002497816.jpg The development of dimethyl ether clean fuel has great strategic significance for changing my country's energy structure. At the same time, it is also a useful supplement to petrochemical industry and downstream products. Therefore, the dimethyl ether industry has broad development prospects in our country. Because dimethyl ether fuel is environmentally friendly and * * The importance of energy security has attracted great attention from relevant departments. Our company's annual 30kt dimethyl ether production line was officially put into production in December 2003 ； The second phase of the 70kt dimethyl ether project with an annual output has started construction and will be completed and put into operation in October this year. ； The design of the third phase of the 1Mt annual dimethyl ether project planned to be constructed in Ordos City, Inner Mongolia has begun and is planned to be completed within 5 years. It is expected that after the project is completed and put into operation, the production cost of dimethyl ether is expected to drop to 1,300 to 1,500 yuan per ton. Currently, Linyi City, Shandong Province, where our company is located, is implementing the "Blue Sky Project" and has started to build 10 to 20 gas stations in the city. At the same time, the city's buses and taxis will be transformed into dimethyl ether fuel vehicles within three years, striving to become the first demonstration city in my country to promote dimethyl ether fuel vehicles.