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When used in town gas, dimethyl ether is gaseous at normal temperature and pressure, and turns into liquid under a certain pressure, which is similar to liquefied petroleum gas. A comparison of the properties of liquefied petroleum gas and dimethyl ether is shown in Table 1. Table 1 Comparison of properties of liquefied petroleum gas and dimethyl ether m3/kg category vapor pressure (60℃)/MPa average calorific value/kJ·kg-1 lower explosion limit/% theoretical air volume theoretical smoke volume premixed gas calorific value/kJ·m-3 theoretical combustion Burning temperature/℃ Liquefied petroleum gas 1.92457601.711.3212.0239092055 Dimethyl ether 1.35315903.56.967.4642192250 It can be seen from Table 1: ①At the same temperature, the saturated vapor pressure of dimethyl ether is lower than that of liquefied petroleum gas, and storage and transportation are safer than liquefied petroleum gas. ； ②The lower explosion limit of dimethyl ether in air is 1 times higher than that of liquefied petroleum gas, so dimethyl ether is safer during use ； ③Although the calorific value of dimethyl ether is lower than that of liquefied petroleum gas, because dimethyl ether itself contains oxygen, the theoretical amount of air required during the combustion process is much lower than that of liquefied petroleum gas. As a result, the calorific value and theoretical combustion temperature of dimethyl ether's premixed gas are higher than that of liquefied petroleum gas. Dimethyl ether has a single component, short carbon chain, good combustion performance, high thermal efficiency, and no residual liquid and black smoke during the combustion process. It is a high-quality, clean fuel. On the other hand, dimethyl ether, like liquefied petroleum gas, is a gas after decompression, so the burner can be used universally without much modification. There are two ways to use dimethyl ether as fuel in China:: One is to blend 20% dimethyl ether into liquefied petroleum gas, which is also the main sales method of dimethyl ether in China. This method can be used normally without changing the existing stove. It can be used not only for bottled gas but also for pipeline gas supply. The second is the application of pure dimethyl ether gas. The leading company is Shandong Jiutai Company. In order to cooperate with the promotion of pure dimethyl ether gas, the company jointly developed a special gas stove for dimethyl ether with well-known domestic stove brand manufacturers. According to users’ feedback after long-term use: Dimethyl ether gas burns fully without residual liquid, and the stove has no carbon deposits after use, which has obvious advantages. At present, the company has established a sales network across the country and developed more than 50 regional agents. The product standard for the construction industry of dimethyl ether for urban gas was approved on August 21, 2007. Approval No.: CJ/T259-2007, effective from January 1, 2008. Dimethyl ether for town gas * * Standards are in the process of being developed. In view of the overlap with the construction industry standards, in accordance with the relevant regulations on standard management in my country, there are * * Standards will cover issues covered by industry standards. Therefore, the standards development group is drafting a report recommending that this * * The standard was renamed "Dimethyl Ether Mixture for Town Gas"” ； When liquefied petroleum gas is mixed with dimethyl ether, the dimethyl ether content is ≤20%, and there is no lower limit. As a diesel engine fuel, dimethyl ether has the following characteristics:: (1) There are no CC bonds in the molecular structure of dimethyl ether, only CO and CH bonds, and it contains 34.8% oxygen. It produces few soot particles after combustion, and NOx emissions are only 20% of diesel emissions. (2) The cetane number of dimethyl ether is higher than that of diesel, its auto-ignition temperature is lower, its ignition delay period is shorter than that of diesel, and its combustion noise is lower than that of diesel. (3) The low calorific value of dimethyl ether is lower than that of diesel, only 64.7% of diesel. However, the theoretical mixture calorific value of dimethyl ether and air is 5% higher than that of diesel (dimethyl ether is 3066kJ/kg, diesel is 3911kJ/kg), so the power of dimethyl ether engine can be higher than that of diesel engine. (4) Dimethyl ether has a large latent heat of vaporization, which is 1.64 times that of diesel. The use of direct injection combustion can greatly reduce the maximum combustion temperature in the diesel engine cylinder and improve NOx emissions. (5) Dimethyl ether vaporizes into gas at 24.9°C under normal pressure. In order to ensure that dimethyl ether does not vaporize in the fuel system and cause air blockage in the delivery pipeline, the fuel must be pressurized. (6) Dimethyl ether is non-corrosive to metals, so there are no special requirements for fuel system materials. However, natural rubber will swell and age in long-term contact with dimethyl ether, so the sealing material must be appropriately selected. At present, my country has Shanghai Jiao Tong University, Xi'an Jiao Tong University, Jilin University and other scientific research institutions studying the application of dimethyl ether vehicle fuel. ； SAIC Motor Corporation undertook the trial operation of DME buses and passed the regulations on October 10, 2007. * * Acceptance organized by the National Development and Reform Commission, Clean Vehicle Center, and Shanghai Municipal Development and Reform Commission ； Shandong Jiutai's dimethyl ether car is also being tested. Dimethyl ether is an important chemical raw material that can be used in the synthesis of many fine chemicals and can also be used as an intermediate for the synthesis of gasoline and olefins. Dimethyl ether has many unique uses in chemical industries such as pharmaceuticals, fuels, and pesticides. It can replace some fluorochlorohalogenated hydrocarbons as aerosol propellants and refrigerants. High-concentration dimethyl ether can be used as * * agent. The biggest potential use of dimethyl ether is as a substitute for city gas and liquefied petroleum gas. More strategically, it is as a supplement to petroleum energy and replaces diesel as motor vehicle fuel. The production process of dimethyl ether has evolved from traditional methanol dehydration under the action of concentrated sulfuric acid to gas-phase methanol catalytic dehydration and direct synthesis of synthesis gas. 1. Sulfuric acid method (liquid phase methanol dehydration method) Methanol in the presence of sulfuric acid generates methyl hydrogen sulfate and then regenerates dimethyl ether. H2SO4 + CH3OH → CH3HSO4 + H2O CH3HSO4 + CH3OH → CH3OCH3 + H2SO4 This process can produce dimethyl ether products with a purity greater than 99.6%. The main features of this process are mild reaction conditions (130-160°C), high methanol conversion rate in one pass (>85%), and can be produced intermittently or continuously. However, the equipment is severely corroded, residual liquid and wastewater seriously pollute the environment, operating conditions are harsh, and product post-processing is difficult. 2. Methanol gas-phase catalytic dehydration method The reaction equation of methanol gas-phase catalytic dehydration method is as follows: 2CH3OH → CH3OCH3 + H2O There are many types of catalysts in this process. Common ones include calcium aluminum phosphate, aluminum silicate, ZSM-5 and γ-Al2O3. The reaction conditions vary depending on the catalyst performance, and the reaction temperature is between 200 and 400°C. Since the reaction is an exothermic process, the single-pass conversion rate of methanol is 70% to 80%, and the selectivity of dimethyl ether is greater than 99%. This process can use various forms of reactors. Its main features are simple process, high degree of automation, and basically no "three wastes" pollution and equipment corrosion problems. The purity of the dimethyl ether product produced by this process can reach 99.9%, and the highest purity can reach 99.999%. 3. Direct synthesis of dimethyl ether from synthesis gas. The reaction of synthesis of dimethyl ether from synthesis gas is as follows:: 4H2 + 2CO → 2CH3OH 2CH3OH → CH3OCH3 + H2O CO + H2O → CO2 + H2 3H2 + 3CO → CH3OCH3 + CO2 The one-step synthesis of dimethyl ether from synthesis gas combines the two-step reactions of methanol synthesis and methanol dehydration in one reactor. The key is to select a bifunctional catalyst with high activity and selectivity. There has been much research on this internationally since the 1980s, and it is still in the experimental stage. 4. Direct synthesis of dimethyl ether by hydrogenation of carbon dioxide. The process of direct synthesis of dimethyl ether by hydrogenation of CO2 is a process in which CO2 and H2 directly synthesize dimethyl ether on a composite dual-functional catalyst for methanol synthesis and methanol dehydration. This process can effectively utilize CO2 and reduce environmental pollution caused by industrial emissions. ； The CO2 conversion rate and selectivity are very low, but it is still in the laboratory exploratory research stage. In summary, the one-step and two-step methods for synthesizing dimethyl ether each have their own advantages. However, because the two-step synthesis of dimethyl ether process is limited by thermodynamic equilibrium, the single-pass conversion rate of methanol is low, and the process is long, the one-step synthesis of dimethyl ether process has become a research hotspot at home and abroad. However, the process technology is not yet mature, the equipment is complex, the operating conditions are harsh, the investment is large, and the preparation and activity maintenance of the composite catalyst have not been completely solved. At present, the vast majority of large-scale dimethyl ether construction projects announced at home and abroad adopt two-step process technology, indicating that the two-step process has strong overall competitiveness. If an efficient methanol synthesis process is developed and the single-pass conversion rate of CO is increased to more than 90%, large amounts of syngas circulation can be avoided. * * To reduce compression power consumption (this technology has already made breakthroughs), the two-step synthesis of dimethyl ether process will have good development prospects. It is worth mentioning that the two-step reactive distillation liquid-phase catalytic dehydration method developed by Shandong University of Science and Technology to synthesize dimethyl ether can seal the composite super acid catalyst in the lower part of the reactive distillation tower, effectively eliminating pollution and equipment corrosion while obtaining high-quality dimethyl ether products. This technology is simple and easy to implement, has high methanol single-pass conversion rate and selectivity, low separation energy consumption, and saves equipment investment. It can solve the problem of industrial production equipment of million tons of dimethyl ether, and has good economic benefits and development prospects.