Dimethyl Ether What is dimethyl ether? Dimethyl ether is also called methoxymethane, dme gas or Dimethylaether, is an organic compound, a colorless and odorous flammable gas in the standard state, and its chemical formula is C2H6O or CH3-O-CH3. Relative vapor density (air is 1) 1.62, explosion range: 3.4鈥?7.0% (V/V), ignition temperature: 350掳C, dimethyl ether is easily soluble in water, alcohol and ether. DME is inert, non-corrosive, non-carcinogenic, and almost non-toxic. Dimethyl ether does not form peroxides on long-term exposure to air. It is a colorless gas under normal pressure and has a characteristic odor of ethers. As a substitute for freon, dimethyl ether is rapidly increasing in use in the aerosol and refrigerant industries. Dimethyl ether contains oxygen atoms, high thermal efficiency, complete combustion, clean tail gas without black smoke, and is an environmentally friendly fuel. With the rising price of petroleum and the environmental protection issues of vehicle and civil fuels, dimethyl ether, as a clean and environmentally friendly fuel, has attracted increasing attention from all walks of life. DME may become an important fuel in the near future. The price of petroleum products has been rising year after year, while the cost of coal-based dimethyl ether is low. DME will completely replace liquefied petroleum gas and partially replace diesel. Dimethyl ether fuel properties: (1) DME is an environmentally friendly non-pollutant, soluble in water and degradable. DME molecules are soluble in water, and can be degraded and soluble in water in the troposphere: rain and snow can absorb DME from the atmosphere, and it will not remain in the atmosphere forever. Degradation: In the atmosphere, large molecules become smaller molecules, long carbon chains become shorter carbon chains, and finally decompose into carbon dioxide and water. (2) DME has high combustion efficiency and low oxygen demand. Oxygen atoms are contained in the molecule of dimethyl ether, and the amount of air required for combustion is small: CH3OCH3+3O2=3H20+2CO2, the oxygen demand per kg of dimethyl ether is 1.46Nm3 Liquefied petroleum gas: C3H8+5O2=4H20+3CO2, the oxygen demand per kg of liquefied petroleum gas is 2.55Nm3 (3) DME is a clean fuel - clean, no black smoke. DME fuel has simple components and contains oxygen atoms, requires low air mixing, complete combustion, clean and no black smoke. (4) The economic benefits of dimethyl ether blending are the most obvious - the substitution ratio of blending is 1:1. When blending with liquefied gas, when the ratio does not exceed 25%, the substitution ratio with liquefied gas is 1:1. Reason: less oxygen demand, high thermal efficiency, when burning completely as fuel alone, the substitution ratio with liquefied petroleum gas is about 1.3:1. (5) At present, it is more reasonable to blend dimethyl ether - burner selection. When blending with liquefied gas, if the proportion of dimethyl ether does not exceed 25%, the liquefied gas burner can be used; when it is used as fuel alone, the natural gas burner can be used; it is best to use a special burner. Reason: The difference between oxygen demand and Wobbe index Wobbe index: Calorific value per unit volume/(relative specific gravity) 1/2 (6) DME has simple requirements for transportation and sealing鈥攕ealing materials. When blending with liquefied gas, the ratio does not exceed 25%, and the seals and hoses of liquefied gas storage, transportation, and burner can be used; when used as fuel alone, oil-resistant rubber (such as nitrile rubber) cannot be used for seals and hoses , seals and hoses need to be replaced. It can be changed to polytetrafluoroethylene, etc., and the O-ring can be changed to special rubber. 聽 What is the difference between dimethyl ether, diesel and liquefied petroleum gas? Physical PropertiesUnitDimethyl EtherDiesel FuelLiquefied Petroleum Gas Molecular Formula聽Ch3och3CxhyC3h8~ 4h10 Molecular Weight聽47190~22044~56 Boiling Point鈩?/p 锛?4.9180~360锛?2.1 Liquid DensityG/Cm30.6680.840.501 Stoichiometric Air/Fuel RatioKg/ Kg9.014.612.72 Octane Number聽55~6040~55聽 Latent Heat Of VaporizationKj/Kg460(-20鈩?270聽 Low Calorific ValueMj/Kg28.4342.546.36 Ignition Point鈩?/p 235250470 Liquid Viscosity聽0.154.4~5.4聽 Carbon Content Percentage%52.28681.8 Hydrogen Percentage%13.01418.2~17.9 Oxygen Percentage%34.800 Gas Pressure At 20掳CBar5.108.4 聽 It can be seen from the table that the properties of dimethyl ether are very similar to liquefied petroleum gas (LPG), and it is liquid at a lower pressure (5.1bar), so the infrastructure of liquefied petroleum gas can be used for DME completely, and oil tanks can be used for long-distance transportation , Oil tank trucks, can also be transported by low-pressure pipelines, or distributed to users with 15kg tanks. 聽 Dimethyl ether production process: At present, the production methods of DME at home and abroad mainly include one-step synthesis gas method and methanol method (two-step method). The methanol method is further divided into a methanol gas phase method and a methanol liquid phase method. The industrialization technology of the one-step process of syngas is not yet mature. 聽 The reasons are: 鈶?The existing technology has not been tested by the device; 鈶?Even according to the existing technology, its production cost is higher than that of the methanol gas phase method. 聽 One step method: The one-step synthesis gas method takes synthesis gas (CO + H2) as the raw material, and the methanol synthesis reaction and methanol dehydration reaction are completed in one reactor, accompanied by the CO shift reaction. The reaction formula is as follows: 2CO+4H2 = 2CH3OH CO+H2O =CO2 +H2 2CH3OH =CH3OCH3 +H2O Total reaction: 3CO + 3H2 =H3COCH3 +CO2 聽 The main feature of the one-step synthesis gas method lies in the advantages of the reaction, the methanol synthesis reaction and the methanol dehydration reaction are completed in one reactor. The reaction equilibrium constant is large, and the one-way conversion rate of synthesis gas is high, reaching 40.0% ~75.0%. Since the methanol generated by the reaction immediately undergoes dehydration reaction to generate dimethyl ether, the weakness of the low conversion rate of the synthetic methanol reaction is overcome. 聽 Two-step method: 1. Methanol liquid phase method Methanol dehydration reaction is carried out in liquid phase, under normal pressure or slight positive pressure, at 130掳C. Its chemical reaction formula is as follows: 2CH3OH =H3COCH3 +H2O The methanol liquid phase method is developed from the sulfuric acid method, and the production of dimethyl ether by the sulfuric acid method is the first half of the production process in the production process of dimethyl sulfate by the sulfuric acid method. Methanol dehydration reaction is carried out in liquid phase, under normal pressure or slight positive pressure, at 130掳C. Methanol enters the reactor after preheating, and undergoes dehydration reaction under the catalysis of inorganic acid. By heating, the dimethyl ether, water and phase equilibrium methanol produced by the reaction are vaporized and sent out of the reactor. The reaction product is condensed and separated, and the uncondensed gas phase is compressed and liquefied to obtain the product dimethyl ether. The condensate is separated by rectification, water is discharged from the tower kettle, and methanol is returned as raw material. 聽 2. Methanol gas phase method The chemical reaction formula of methanol dehydration reaction is as follows. Main reaction: 2CH3OH =H3COCH3 +H2O Main side reactions: CH3OH =CO + 2H2 H3COCH3 =CH4 +H2 +CO CO +H2O =CO2 +H2 Gas-phase catalytic dehydration of methanol is the most widely used industrial production method of dimethyl ether at home and abroad. It is characterized by mature and reliable technology, low investment, flexible product adjustment, simple process and low production cost. The reaction pressure is 0.5~1.5MPa, and the temperature is 230~400掳C. Methanol is vaporized in the heat exchanger to exchange heat with the reaction product from the reactor, and then enters the reactor for gas-phase catalytic dehydration reaction, and the reaction product is cooled and condensed by circulating water after heat exchange. Reactor structures include adiabatic fixed bed, heat exchange fixed bed, multi-stage chilled fixed bed and isothermal tubular fixed bed. The material after cooling and condensing is subjected to gas-liquid separation in the intermediate tank of crude methyl ether. The gas phase is the non-condensable gas produced by the side reaction and the saturated vapor of dimethyl ether and methanol, which is sent to the washing tower to absorb and recover the dimethyl ether in methanol or methanol-water solution. The absorption liquid is returned to the intermediate tank of crude methyl ether, and the absorption tail gas is sent out to the device. The crude dimethyl ether in the intermediate tank of crude methyl ether is separated by rectification with a rectification tower. The dimethyl ether vapor from the top of the rectification tower is condensed by the rectification tower condenser, and part of it flows back into the tower, and part of it is sent to the product storage tank as a product. . The methanol-water solution obtained from the dimethyl ether rectification tower is sent to the methanol concentration tower to rectify and concentrate the methanol, and the concentrated methanol is returned as the reaction raw material. Alcohol-containing wastewater is discharged from the tank of the methanol concentration tower. 聽 3. Storage and transportation Store in a cool, ventilated warehouse dedicated to flammable gases. Keep away from fire and heat sources. Storage temperature should not exceed 30掳C. It should be stored separately from oxidants, acids, and halogens, and should not be mixed. Explosion-proof lighting and ventilation facilities are adopted. Prohibit the use of mechanical equipment and tools that are prone to sparks. The storage area should be equipped with leakage emergency treatment equipment. 聽 Dimethyl ether application fields 1. In terms of civilian use: Dimethyl ether is a colorless, non-toxic, non-carcinogenic, and less corrosive product. It has good combustion performance, high thermal efficiency, no residue, no black smoke during combustion, and low CO and NO emissions. It can also be mixed with liquefied petroleum gas, coal gas or natural gas to increase heat, and 鈮?5% dimethyl ether can be directly used as a fuel to replace liquefied gas. Therefore, it may be an ideal clean fuel to replace liquefied gas. DME can replace coal gas and liquefied petroleum gas for domestic fuel. The vapor pressure of dimethyl ether at normal temperature is 0.5MPa. At the same temperature, the saturated vapor pressure of dimethyl ether is lower than that of liquefied petroleum gas, and its storage and transportation are safer than that of liquefied petroleum gas. If dimethyl ether is used alone as a fuel, its pressure level is in line with that of liquefied petroleum gas. Requirements, existing liquefied gas tanks can be used for centralized and unified canning, and the cooker can also be used in common with the liquefied gas cooker. Dimethyl ether can also be mixed into city gas or natural gas in a certain proportion for peak regulation, and can improve gas quality and heat value. At the same temperature, the saturated vapor pressure of dimethyl ether is lower than that of liquefied petroleum gas, so its storage and transportation are safer than liquefied petroleum gas; the lower explosion limit of dimethyl ether in air is twice that of liquefied petroleum gas, so it is also Safer than liquefied petroleum gas; although the calorific value of dimethyl ether is lower than that of liquefied petroleum gas, because dimethyl ether itself contains oxygen, the air required in the combustion process is much lower than that of liquefied petroleum gas, so the calorific value of dimethyl ether premixed gas and its theoretical The combustion temperature is higher than that of liquefied petroleum gas. In addition to being used alone, the mixture of dimethyl ether, methanol, water (not added, from the reaction of raw material methanol and methanol to dimethyl ether) and other components can be formulated into a stable fuel-alcohol ether fuel. 聽 2. As an alternative fuel to fuel oil: Since petroleum resources are non-renewable, research and development of alternative fuels for future vehicles are being conducted worldwide. The biggest potential market for future DME applications is as an alternative fuel for diesel. In contrast, the cetane number of conventional engine alternative fuels such as liquefied petroleum gas, natural gas, methanol, etc. is less than 10, which is only suitable for ignition engines. The cetane number content is an important indicator of diesel combustion performance. The cetane number of dimethyl ether is higher than that of diesel oil, which has excellent compressibility and is very suitable for compression ignition engines. DME can reduce nitrogen oxide emissions by replacing diesel oil. Realizing smokeless combustion, it is an ideal clean fuel for diesel engines. Using dimethyl ether, the tail gas does not need catalytic conversion treatment, and the emission of nitrogen oxides and black smoke particles can meet the requirements of ultra-low emission tail gas of California fuel vehicles, and can reduce engine noise. Studies have shown that existing car engines can use DME fuel with only a slight modification. Although DME costs more than diesel, it is less expensive and less polluting than low-polluting alternatives such as liquid propane. Using dimethyl ether as fuel requires only a slight improvement to the fuel system of the original diesel engine. Under the premise of maintaining the efficiency of the original diesel engine, the same output power, torque and fuel economy, without any exhaust gas recirculation system and exhaust gas treatment device, the nitrogen oxides can be greatly reduced to below 2.5g/(kW路h) , At the same time, the contradiction between controlling nitrogen oxides and particulate emissions no longer exists, soot emissions are zero, there is no accelerated smoke, and particulate emissions are also greatly reduced. 聽 3. Dimethyl ether power generation: DME can also be used as a fuel for combined cycle power plants. Power generation systems generally use syngas as fuel. When the power generation load is low, the syngas can be converted into DME products, which can be conveniently stored for re-use or export at high load. The effect is similar to using methanol as fuel for combined cycle power generation. 聽Dimethyl Ether website:http://www.julychem.com/dimethyl-ether/