The two-step method firstly produces methanol from synthesis gas, and then the methanol is dehydrated under the action of catalyst to produce dimethyl ether. In the past, sulfuric acid was mainly used as catalyst, but now ZSM-5 molecular sieve made of γ-Al2O3/SiO _ 2 is mostly used as catalyst, which has excellent performance and good selectivity, and can produce high-purity dimethyl ether and avoid pollution.
One-step direct preparation of dimethyl ether from synthesis gas includes that synthesis gas enters the reactor, and methanol synthesis, methanol dehydration and water gas shift reaction are completed at the same time. The product is a mixture of methanol and dimethyl ether, which is obtained by distillation and separation, and unreacted methanol is returned to the reactor. One-step method mostly adopts bifunctional catalyst, which generally consists of two kinds of catalysts, one is methanol synthesis catalyst and the other is methanol dehydration catalyst. Catalysts for methanol synthesis include Cu-Zn-Al (O)-based catalysts, such as BASF, S3-85 and I-CI-5 12. Methanol dehydration catalysts include alumina, porous SiO _ 2-Al _ 2O _ 3, Y-type molecular sieve, ZSM-5 molecular sieve and mordenite. According to the type of reactor, one-step process can be divided into fixed bed and slurry bed.
According to the phase state and process characteristics of the reaction process, there are two-phase method and three-phase method to synthesize dimethyl ether from syngas in one step. Two-phase method is also called gas phase method (GPDME), and three-phase method is also called liquid phase method (LPDME).
Two-phase method is also called gas phase method (GPDME) to vaporize dimethyl ether.
Three-phase method is also called liquid phase method (LPDME).
Dimethyl ether and its production method 2008-05-09 Source: Baidu Post Bar
Core Tip: Dimethyl ether (DME) is a colorless gas with slight ether smell, and its vapor pressure is about 0.5 MPa at room temperature, which is very similar to the physical properties of liquefied petroleum gas. 1. Properties and uses of dimethyl ether
Dimethyl ether (DME) is a colorless gas with a slight ether smell. The vapor pressure at room temperature is about 0.5 MPa, which is very similar to the physical properties of liquefied petroleum gas. Dimethyl ether is inert, non-corrosive, non-carcinogenic and almost non-toxic. Unlike diethyl ether, dimethyl ether will not form peroxide when exposed to air for a long time. The saturated vapor pressure of dimethyl ether is lower than that of liquefied petroleum gas, and it is safer to store and transport, with good combustion performance, high thermal efficiency, NO residue and black smoke during combustion, and low CO and NO emissions. Dimethyl ether can also be mixed with liquefied petroleum gas, coal gas or natural gas to improve heat. More than 95% of dimethyl ether can be directly used as a fuel to replace liquefied petroleum gas. Therefore, it may be an ideal clean fuel to replace liquefied gas. In addition, dimethyl ether can also be used as a chemical raw material, mainly used to make spray paint, pesticides, air fresheners, hair gels, rust inhibitors and lubricants.
2. Development progress of dimethyl ether at home and abroad
The production method of dimethyl ether was originally obtained by rectifying the by-products in the production of high-pressure methanol. With the wide application of low-pressure methanol synthesis technology, the side reactions are greatly reduced, and the industrial production technology of dimethyl ether is rapidly developed into methanol dehydration or direct synthesis gas. Methanol dehydration method includes liquid phase methanol method and gas phase methanol method. The former reaction is carried out in liquid phase, and methanol is obtained by dehydration with concentrated sulfuric acid. However, this method is gradually eliminated due to the problems of small equipment scale, easy corrosion, environmental pollution and poor operating conditions. In recent years, the demand for dimethyl ether has increased greatly, and countries have successively developed new technologies with low investment, good operating conditions and no pollution, mainly including two-step method and one-step method.
The two-step method firstly produces methanol from synthesis gas, and then the methanol is dehydrated under the action of catalyst to produce dimethyl ether. In the past, sulfuric acid was mainly used as catalyst, but now ZSM-5 molecular sieve made of γ-Al2O3/SiO _ 2 is mostly used as catalyst, which has excellent performance and good selectivity, and can produce high-purity dimethyl ether and avoid pollution.
One-step direct preparation of dimethyl ether from synthesis gas includes that synthesis gas enters the reactor, and methanol synthesis, methanol dehydration and water gas shift reaction are completed at the same time. The product is a mixture of methanol and dimethyl ether, which is obtained by distillation and separation, and unreacted methanol is returned to the reactor. One-step method mostly adopts bifunctional catalyst, which generally consists of two kinds of catalysts, one is methanol synthesis catalyst and the other is methanol dehydration catalyst. Catalysts for methanol synthesis include Cu-Zn-Al (O)-based catalysts, such as BASF, S3-85 and I-CI-5 12. Methanol dehydration catalysts include alumina, porous SiO _ 2-Al _ 2O _ 3, Y-type molecular sieve, ZSM-5 molecular sieve and mordenite. According to the type of reactor, one-step process can be divided into fixed bed and slurry bed.
The reaction of preparing dimethyl ether by one-step method can be divided into the following steps:
Carbon monoxide+H2-> ch3oh-δ h = 90.7kj/mol (1)
2ch2 oh-& gt； CH3 och 3+H2O-δH = 23.5 kj/mol(2)
Carbon monoxide+H2O-> carbon dioxide +H2-δH = 4 1.2 kj/mol (3)
Total reaction formula: 3co+3h2—>; ch 3 och 3+CO2-δH = 246. 1kJ/mol(4)
Compared with the two-step method, the one-step method has its own advantages. The conversion rate of CO in the one-step method is much higher than that in the two-step method, but in the one-step method, because three reactions must occur at the same time, and all three reactions are exothermic, the catalyst used is required to have good heat resistance and high selectivity at high temperature. Dimethyl ether produced by one-step method is generally used as alcohol ether fuel. If high purity is to be produced, it needs further separation and purification. Although the conversion rate of two-step method is not as high as that of one-step method, it has the characteristics of mature production technology, wide equipment adaptability and simple post-treatment. It can be built directly in methanol production plants or in other non-methanol production plants with good public facilities. Compared with the one-step method, the two-step synthesis process is slightly longer, but the two catalysts are installed in different reactors without interference. Judging from the current technical development trend, the one-step method has the characteristics of short process, high equipment efficiency, low operating pressure and high one-way conversion rate of CO, which greatly reduces the equipment investment and operating costs, and the production cost of dimethyl ether synthesis is greatly reduced compared with the two-step method. Therefore, one-step method is more reasonable in economy, more competitive in the market, and has more technical advantages on the whole.
According to the phase state and process characteristics of the reaction process, there are two-phase method and three-phase method to synthesize dimethyl ether from syngas in one step. Two-phase method is also called gas phase method (GPDME), and three-phase method is also called liquid phase method (LPDME). The gas phase method is mainly carried out in a fixed bed reactor, and the synthesis gas reacts on the surface of a solid catalyst. If carbon-rich syngas is used, the catalyst surface will coke quickly and become inactive. Therefore, the gas phase process can only use hydrogen-rich syngas (H2/ carbon monoxide is much greater than 2) and operate at a low conversion rate (unreacted syngas circulates in large quantities). The main technological processes of gas phase method include TIGAS method of Topso Company of Denmark and ASMTG method jointly developed by Mitsubishi Heavy Industries Company of Japan and COSMO Oil Company. The liquid phase method is mainly carried out in a slurry reactor, in which CO, H2 and dimethyl ether are gas phases, inert solvent is liquid phase, and catalyst powder suspended in the solvent is solid phase. Because of the large heat capacity of liquid phase, the liquid phase method is easy to operate at constant temperature, and the surface of catalyst particles is surrounded by solvent, which greatly alleviates the coking phenomenon, so carbon-rich syngas can be used as raw material. At present, China Tsinghua University, American Air Chemical Company and Japanese NKK Company are all committed to developing the industrial technology of one-step synthesis of dimethyl ether from syngas in slurry bed, and they conducted pilot tests at the end of last century and the beginning of this century respectively, which laid the foundation for the large-scale production of dimethyl ether.
At present, domestic DME technology research and development units mainly include Shandong Jiutai Chemical Technology Co., Ltd., Tsinghua University Ministry of Chemical Industry, Blue Flower Research Institute, Zhejiang University, Hangzhou University Catalytic Research Institute, Dalian Institute of Chemical Industry of Chinese Academy of Sciences, Taiyuan University of Technology, School of Chemical Engineering of East China University of Science and Technology, Southwest Research Institute of Chemical Industry of the Ministry of Chemical Industry, etc.
The son of Li and Zhi, the chairman of Shandong Jiutai Chemical Technology Co., Ltd., has been committed to the research in the field of energy and chemical industry for a long time, actively tackling dimethyl ether technology. After repeated experimental research, 200 1 developed a low-cost and high-efficiency production method of dimethyl ether, that is, "liquid-phase compound acid dehydration and catalytic production of dimethyl ether", and they applied for a patent in China. In July, 2002, Shandong Science and Technology Department organized experts to appraise the project, and considered that the production technology reached the international leading level, which solved the worldwide problem in the process of dimethyl ether production. In May 2004, at the China International Patent and Famous Brand Expo held in China National Intellectual Property Administration, the patented technology won the gold medal, and Shandong Jiutai Chemical Technology Co., Ltd. was named "Top Ten Patent Enterprises in China".
Under the auspices of Academician Jin Yong, the Department of Chemical Engineering of Tsinghua University has developed the technology of one-step synthesis of dimethyl ether in slurry bed. The pilot test has passed the technical appraisal organized by the State Education Commission and reached the international advanced level. In 2003, Tsinghua University and Chongqing Yingli Fuel Chemical Co., Ltd. jointly invested 20 million yuan to build a 3000t/a dimethyl ether pilot plant, which was put into operation at the end of April 2004 and produced qualified dimethyl ether products. On this basis, Chongqing Yingli Fuel Chemical Co., Ltd. will carry out technical tracking and related supporting industrialization work to build a large-scale industrialized production device.
From the reaction results, the circulating slurry bed dimethyl ether production technology developed by Tsinghua University is obviously superior to the LPDMETM process of American Air Products Company and the pilot test results of Japanese NKK Company, and the one-way conversion rate of CO is greatly improved. At the same time, medium-pressure steam (2.0MPa) was also by-produced in the reaction process, and the energy utilization rate was high. The catalyst used in LPDMETM process is very sensitive to water, so methanol and dimethyl ether can only be co-produced by syngas with low H2/ CO molar ratio, and the selectivity of dimethyl ether cannot be improved. The self-developed catalyst was applied to the circulating slurry bed dimethyl ether production process developed in Tsinghua University. The selectivity of dimethyl ether reached over 94%, and no obvious catalyst deactivation was found during the trial operation, which indicated that the catalyst had good stability.
However, when dimethyl ether is produced in one step, one molecule of dimethyl ether will produce one molecule of CO2, that is, one third of CO will be produced in the production process, which not only increases the consumption of raw gas, but also makes CO2 emission unsatisfactory from the perspective of environmental protection, which is a waste from the perspective of resource protection.
According to the chemical reaction formula, the theoretical molar ratio of H2 and carbon monoxide in the process of dimethyl ether production is 1: 1. However, the commonly used gas-making methods, such as gas produced by fixed bed air gasification with coal as raw material and gas or pure oxygen produced by steam conversion with natural gas as raw material, can not meet this requirement. Therefore, it is of great significance to recover CO2.
Direct synthesis of dimethyl ether by hydrogenation of CO2, as a new method to synthesize dimethyl ether, is in the exploration stage. CO2 is the most abundant carbon resource on the earth, and its greenhouse effect has brought great losses to human ecological balance. Therefore, the synthesis of various chemicals from CO2 to realize the recycling of CO2 has attracted the interest of researchers all over the world. Because the hydrogenation of CO2 to methanol is limited by thermodynamic equilibrium, people begin to pay attention to the direct hydrogenation of CO2 to dimethyl ether. This can break the thermodynamic equilibrium of CO2 hydrogenation to methanol and improve the conversion rate of CO2. Dalian Institute of Chemical Engineering has also done a lot of work in this respect, and is preparing to build an industrial demonstration device for the production of methanol and dimethyl ether by the reaction of CO2 and H2. Researchers at home and abroad have done a lot of work and achieved some results, but the conversion rate of CO2 is only 14 ~ 29%, and the selectivity of dimethyl ether is only about 50%. Therefore, this technology needs to be further improved.
This article comes from China New Energy Information Network | New Energy. NengYuan.Net original link://2008 /2008/0509/576.html