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1 Overview? Dimethyl ether and dimethyl carbonate are hot topics in domestic chemical literature in recent years. Dimethyl ether is an important green industrial product. Its main uses are: Clean fuels, aerosols, refrigerants, foaming agents, organic synthetic raw materials, etc. Especially when it is used as a diesel blending agent and a substitute for liquefied petroleum gas as a civilian fuel, its voice is increasing day by day. The industry for producing dimethyl ether is transforming from fine chemicals to basic chemicals, and domestic research on the synthesis of dimethyl ether is in full swing. Thousand-ton-level test equipment has been constructed in many places, and preparations have begun for 10,000-ton-level production equipment. The largest dimethyl ether production project in China has begun operation in Ningxia. 1.1 Properties of dimethyl ether? Dimethyl ether (DME) is a relatively inert, non-corrosive organic substance. Its main physical and chemical properties are shown in Table 1 [1]. Dimethyl ether is a colorless flammable gas at normal temperature and pressure, and the allowable concentration in the air is 400×10-6. It has the properties of general ethers. Dimethyl ether is non-corrosive to metals, does not irritate the skin of the human body, does not cause cancer, has no destructive effect on the atmospheric ozone layer, is easily degraded in the troposphere, and will not form peroxides when exposed to the air for a long time. Therefore, it is an excellent green chemical product. http://www.nmtech.com.cn/jishuwang/upload/0601261043352492.jpg Table 2 is a comparison of dimethyl ether and liquefied petroleum gas [1]. It can be seen from the data in the table: Under the same temperature conditions, the saturated vapor pressure of dimethyl ether is lower than that of liquefied petroleum gas, and its storage and transportation are safer than liquefied petroleum gas. The lower explosion limit of dimethyl ether in air is twice as high as that of liquefied petroleum gas. Therefore, during use, dimethyl ether is safer than liquefied petroleum gas as a fuel. Although the calorific value of dimethyl ether is lower than that of liquefied petroleum gas, because dimethyl ether itself contains oxygen, the amount of air required during the combustion process is much lower than that of liquefied petroleum gas, so that the theoretical combustion temperature of dimethyl ether's premixed gas calorific value is higher than that of liquefied petroleum gas. Table 3 is a comparison of the physical properties of dimethyl ether and other fuels [2]. http://www.nmtech.com.cn/jishuwang/upload/0601261044231565.jpg 1.2 Uses? The future of dimethyl ether as a bulk industrial product depends on whether it can be used as a raw material for the fuel and ethylene industries. ? 1.2.1 Chemical raw materials? Dimethyl ether is also an organic intermediate. It can be carbonylated to produce methyl acetate and acetic anhydride, and can also be used as a methylation reagent for the synthesis of medicines, pesticides and fuels, and can be reacted with fuming sulfuric acid or sulfur trioxide to produce dimethyl sulfate. In addition, dimethyl ether is also an excellent organic solvent. ? The cracking of dimethyl ether to generate ethylene is the mainstream process of the three-step process of producing ethylene from natural gas and belongs to the Fischer-Tropsch synthetic fuel process route. Therefore, it is an excellent raw material for the future ethylene industry. 1.2.2 Vehicle fuel and civilian fuel? Dimethyl ether has a high cetane number and can be directly used as vehicle fuel after liquefaction. Its combustion effect is better than methanol fuel. It not only has all the advantages of methanol fuel, but also overcomes its shortcomings of low-temperature startability and poor acceleration performance. Since dimethyl ether itself contains oxygen, has a single component and a short carbon chain, it can achieve smokeless and efficient combustion and reduce noise. Automobile exhaust does not require catalytic conversion treatment to meet California's ultra-low emission standards for automobiles. Moreover, existing diesel vehicle engines can burn dimethyl ether fuel with only slight modifications, and the operating performance will not be damaged [3]. ? Dimethyl ether is easy to compress, and its storage pressure is 1.35MPa, which is less than 1.92MPa of liquefied petroleum gas, so it can replace coal gas and liquefied petroleum gas as civil fuel. If dimethyl ether is used as fuel alone, its pressure level meets the requirements of liquefied gas, and it can be filled with current liquefied gas cans. The stove can also be basically used with liquefied gas stoves, and the combustion exhaust gas fully meets the requirements. * * Hygienic standards only need to solve the problem of swelling of pipe fittings. Canned liquid dimethyl ether will be the clean fuel for homes of the future. Dimethyl ether can also be mixed into city gas or natural gas in a certain proportion for peak adjustment, and can improve gas quality and increase calorific value. 1.2.3 Fine chemical products? Currently, most self-spraying daily chemical products such as aerosols and hair sprays still use chlorofluorocarbons as propellants. Chlorofluorocarbons have a destructive effect on the ozone layer, so environmentally friendly propellants must be used instead of chlorofluorocarbons. Since the solubility properties of dimethyl ether are similar to those of chlorofluorocarbons, it is imperative to use dimethyl ether or its mixture with propane or butane as propellant to replace chlorofluorocarbons. ?Nowadays, many domestic manufacturers of aerosol insecticides and plastic spray coatings have gradually switched to using dimethyl ether as aerosol propellant. 1.3 What is the market prospect of dimethyl ether? According to recent domestic research, adding 10% dimethyl ether to diesel can change the performance of diesel. Xi'an Jiaotong University has developed a diesel prototype using dimethyl ether. At present, the annual consumption of diesel in the country is about 80Mt. If dimethyl ether is added according to the above proportion, the consumption will be very considerable. Using dimethyl ether as a household fuel is ideal for residents in towns far away from natural gas pipelines and refineries. Near coal-producing areas, the synthesis gas produced by pit coal gasification, underground coal gasification, coal bed methane, etc. is used to produce dimethyl ether and bottled instead of liquefied gas, which is superior to liquefied gas. Near natural gas pipelines, the conversion method is used to obtain synthesis gas to produce dimethyl ether, which can form a powerful ethylene and post-processing industry. In overseas gas fields, natural gas is made into dimethyl ether and then transported back to China, which is much more convenient than natural gas liquefaction. ? 2. Production method of dimethyl ether? The current main production methods are methanol dehydration to produce dimethyl ether and synthesis gas to produce dimethyl ether in one step. ? 2.1 Dehydration of methanol to dimethyl ether? It is divided into liquid phase method and gas phase method. At present, all domestic production equipment adopts this method. ? The liquid phase method is to heat a mixture of sulfuric acid and methanol, and dehydrate the methanol to produce dimethyl ether. Due to the strong corrosiveness and serious pollution of sulfuric acid, it has been gradually eliminated. In recent years, Shandong Luming Chemical Co., Ltd. has improved the liquid phase method, changed the composition of the acidic medium, obtained its own intellectual property rights, and is building a large-scale dimethyl ether production device. ? The gas phase method is to pass methanol vapor through a molecular sieve catalyst and catalytically dehydrate it to obtain dimethyl ether. This method is a gas-solid phase catalytic reaction plus distillation process. There are domestic studies in this area, and a kiloton-level production process has been developed based on these studies. ? 2.2 One-step synthesis of dimethyl ether from synthesis gas is divided into gas phase method and three-phase method, which are methods under research and development. ? The gas phase method is that the synthesis gas reacts on the surface of the solid catalyst ； The three-phase method is the slurry method, in which the synthesis gas diffuses to the surface of the catalyst suspended in an inert solvent for reaction. In the gas phase method, the conversion rate of synthesis gas in the reactor is low, the circulation volume of unreacted synthesis gas is large, and the use of hydrogen-rich synthesis gas (H2/CO is greater than 2) is required. The single-pass conversion rate of the three-phase method is higher than that of the gas-phase method, and it has high selectivity and low energy consumption. It can increase the output of DME and reduce costs. It is a new method worthy of development and has important economic and social benefits. Therefore, the research on the one-step production of dimethyl ether from synthesis gas is the current direction of dimethyl ether technology development. 3. Domestic and foreign device construction status? Because dimethyl ether has the above-mentioned major uses, it determines that it has a broad market and demand. The world's dimethyl ether production capacity is about 300kt, and the output is about 200kt. The main manufacturers include American Dupout and Air Products, Dutch AKEO, Danish Topsφe and Mitsubishi Heavy Industries. The production of dimethyl ether in my country has just started, and the current annual output is less than 20kt. ? 3.1 Domestic situation? At present, dimethyl ether is mainly produced by dehydration of methanol in China, which is a fine chemical product, which is commonly known as the two-step method. The process is technically mature, but the scale is small and lacks the practice of large-scale and formalized design. The one-step device is a kiloton-level test device and is technically prepared for large-scale production. The production equipment is shown in Table 4 and Table 5. The current test data does not indicate that the processes and process conditions of the above two devices are mature, so large-scale amplification and formalized design on this basis are difficult. 3.2 Overseas situation? The current annual production capacity of dimethyl ether in the world is about 150kt. Dimethyl ether production is basically produced through a methanol dehydration process, the so-called two-step process. The technology is mature, but the production scale is not large enough. The main devices used to generate dimethyl ether by the two-step method abroad are shown in Table 6[4]. http://www.nmtech.com.cn/jishuwang/upload/0601261048059204.jpg At present, foreign countries have begun to construct one-step large-scale equipment [5] and are making technical preparations for ultra-large-scale production, see Table 7. http://www.nmtech.com.cn/jishuwang/upload/0601261049026426.jpg 4. What is the progress of domestic research on dimethyl ether synthesis technology? Domestic scientific research units focus on the synthesis of dimethyl ether, mainly in two aspects.: Catalyst screening, reactor bed format. ? Theoretically, the one-step synthesis of DME from synthesis gas has advantages in chemical thermodynamics over the two-step method. Under certain conditions (for example, 250°C and 5.0MPa, H2/CO=2.0), the conversion rate of synthesis gas reaction to DME is higher than that of CH3OH [7]. The process undergoes three independent reactions on the catalyst surface: ? Methanol synthesis reaction CO+2H2→2CH3OH-90.4kJ/mol (1)? Methanol dehydration to DME reaction? 2CH3OH→CH3OCH3+H2O-23.4kJ/mol (2)? Water gas conversion reaction? CO+H2O→CO2+H2-41.0kJ/mol (3)? The reactants and products (CO, H2, CH3OH, CH3OCH3, H2O, CO2) reach dynamic equilibrium according to the above three reactions. The temperature distance at which the three reactions deviate from equilibrium is called the equilibrium temperature distance. ? One-step synthesis of DME can be divided into two categories: fixed bed and slurry bed according to the form of catalytic reactor. The catalysts used in both processes are the same type. Since the temperature distribution of the slurry bed reactor is uniform, the heat balance is easier to control, the operation is simple and the stability is good. Therefore, most reactor studies for the one-step synthesis of dimethyl ether use slurry bed reactors. ? 4.1 Catalysts In order to take advantage of the chemical thermodynamics advantages of the one-step method over the two-step method, a catalyst suitable for the one-step method must be prepared, and chemical kinetic factors such as temperature, pressure, space velocity, and H2/CO suitable for the synthesis reaction must be selected. Currently, the catalysts used in the one-step DME synthesis process are composed of two catalysts, namely a metal catalyst for synthesizing methanol and a solid acid catalyst for dehydrating methanol to produce DME. It is commonly referred to as a bifunctional catalyst. ? The traditional process of synthesizing methanol catalyst mainly uses Cu/Zn series. Methanol dehydration catalyst mainly uses zeolite molecular sieves such as γ-Al2O3 or HZSM-5. ? At present, research on catalysts for the one-step synthesis of dimethyl ether is mainly focused on the following aspects:: ? (1) Research on preparation methods and composite formulas of bifunctional catalysts ； ? (2) Research on catalyst usage conditions in different reactors ； ? (3) The impact of adding different additives to the methanol synthesis catalyst on the catalyst performance and usage conditions. ? Table 8 [8] lists the composition and performance of several catalysts. ? In order to adjust the acidic function of the catalyst, some use metal ions such as calcium, magnesium, tungsten, and vanadium as modifiers to modify HZSM-5 in order to adjust the synergistic effect of the two catalysts. ? The main methods of compounding the two catalysts include dry mixing, wet mixing and co-precipitation impregnation. It is generally believed that the catalyst prepared by the co-precipitation impregnation method has better performance and is conducive to exerting the synergistic effect of metal/acidic dual-functional catalysts to improve the conversion rate of CO and the selectivity of DME. ? Literature [9] believes that the ratio of CuO/ZnO/Al2O3 and HZSM-5 molecular sieve is 1:4. 4.2 Fixed bed http://www.nmtech.com.cn/jishuwang/upload/0601261050213590.jpg The fixed bed is a reactor in which solid catalyst particles are loaded, and the reactants (gas phase) contact it through the catalyst bed to perform chemical reactions, so it is also called a gas-solid phase reactor. The fixed bed is a conventional reactor. To dissipate the heat of the reaction, the fixed bed can use a multi-stage cold shock type or a tube waste heat boiler, which has sufficient practical experience in the chemical industry. ? Pilot research reports on the one-step fixed-bed DME synthesis process have been reported abroad. The Danish Holdo Topsoe Company completed 12,000 hours of operation on a 50kg/d DME pilot plant in Linbai. ? There are two main fixed bed process flows. One is to recycle the syngas, and the other is to pass the syngas through once, and a large amount of the tail gas is used for combined cycle power generation (IGCC) or co-production of pipeline gas. Domestic institutions such as Tsinghua University, Lanzhou Institute of Chemical Physics, Dalian Institute of Chemical Physics, and Zhejiang University have also successively developed catalyst technology for the one-step synthesis of DME, and almost all have completed single-tube expansion tests. The 1500t/a industrial test device built by Zhejiang University at Hubei Tianli Company uses a fixed-bed catalytic synthesis reactor. ? Zhang Haitao et al. [10] used the kinetic data obtained from experiments to establish a one-dimensional mathematical model of a tubular fixed-bed reactor. By calculating the 5000t/a dimethyl ether reactor under typical working conditions, the process and equipment design parameters of the reactor were obtained. ? In the process of dimethyl ether synthesis, fixed bed is easy to succeed. However, because the conversion rate is not high, the amount of gas circulation after the reaction is large. In addition, the separation of CO2 and dimethyl ether is difficult, so it is difficult to scale up the process (above 300kt level). This is why more people are willing to work on slurry beds in dimethyl ether synthesis research. ? 4.3 Slurry bed? Slurry bed is a solid catalyst particle (solid phase) suspended in an inert solvent (liquid phase). The reactants (gas phase) dissolve into the solvent and pass through the solvent layer to the catalyst surface for chemical reaction. During the reaction process, the three phases of gas, liquid and solid are in contact, so it is also called a three-phase bed, as shown in Figure 1. ? Due to the simple structure of the slurry bed reactor and the large solvent heat capacity, the catalyst particles and inert mineral oil form a slurry, and the high-pressure synthesis gas enters and bubbles from the bottom of the tower, making the feed and catalyst more fully mixed. The heat of reaction is easily removed, isothermal operation is easily achieved for strongly exothermic reactions, and thermal deactivation of the catalyst and by-products are not easily produced. The temperature throughout the reactor is relatively uniform and easy to control, preventing local overheating of the catalyst and reducing the catalyst deactivation rate. ? Research shows that the CO conversion rate of slurry bed is higher than that of fixed bed, while the H2/CO ratio of syngas is lower, which is conducive to using CO-rich coal-based syngas as raw material, opening up a new way for coal-saving technology. Therefore, domestic and foreign scholars have conducted extensive research on slurry bed technology in recent years and have achieved a series of meaningful results. http://www.nmtech.com.cn/jishuwang/upload/0601261051164633.jpg Figure 1 Schematic diagram of the slurry bed DME synthesis reactor of NKK Company. Japan Steel Pipe Company (NKK), Air Products Chemical Company of the United States [14,16], Shanxi Taiyuan Coal Chemistry Institute of the Chinese Academy of Sciences [11,12], East China University of Science and Technology [13] and other units have done a lot of research work on the slurry bed technology. ? Table 9 lists the progress of the DME slurry bed synthesis process developed by Steel Pipe Company and Air Products Chemicals. The two companies have different test plans. NKK produces DME, while Air Products Chemicals produces DME and co-produces methanol. http://www.nmtech.com.cn/jishuwang/upload/0601261052143831.jpg? 5. Development status of process research on dimethyl ether plant construction in China. Currently, process research on one-step dimethyl ether plant is still in the development stage in my country. ? The process of producing dimethyl ether from synthesis gas proposed by a domestic scientific research unit is basically a one-unit, two-tower process, that is, a reactor, an absorption tower, and a distillation tower. At present, with the cooperation of some design institutes, it is being vigorously promoted in China. However, the construction of a one-step synthesis gas dimethyl ether plant has not been smooth sailing. Some kiloton-level devices did not continue production after commissioning and qualification, and some devices were not constructed after the design was completed. ? In 2004, Tsinghua University built a 3000/a one-step device in Chongqing and it has been put into operation. The purity of the product is not high, less than 98%. ? To date, there is insufficient evidence that this technology has matured. In particular, simulation technology has not been fully applied, and it has not been closely integrated with production test data. There has been insufficient research on the process, and the separation problem has been simplified. Although 10,000-ton project proposals, feasibility studies, preliminary designs, etc. are already common, actual engineering implementation is rare. ? With the project support of Sinopec Group, Lanzhou Design Institute cooperated with East China University of Science and Technology and Tsinghua University to develop a one-step dimethyl ether production project from syngas based on slurry bed in 2000, which appeared in the face of chemical engineering research with a new look. This technology strives to achieve low investment, high efficiency, and stable and reliable technology. In order to achieve this goal, the development unit has completed a general basic process package for the production of dimethyl ether from coal-based synthesis gas with an annual output of 30kt [6], proposed a general process package, and proposed a new process of "syngas-slurry bed-fine separation" of "one bed, two returns and three towers". After inquiry, we found that this process does not exist at home and abroad, so we created it. Among them, the separation process has been applied for * * Invention patent, patent application number is 03134277.9. “"One bed" refers to the slurry bed or fixed bed, "double return" refers to the two return streams in the process, and "three towers" refers to the absorption tower, product separation tower, and methanol recovery tower. ? The process data proposed by the new process using simulation technology are based on phase equilibrium test data and have scientific basis. For a newly built dimethyl ether production unit using natural gas or coal-to-syngas as raw material, this report can be used as a basis, other parts can be added, and an actual process package design can be compiled to meet the needs of users. A design institute with rich experience should be able to do this. ? If natural gas-based synthesis gas is to be used as raw material, the process data needs to be modified appropriately. ? 6 New process for one-step synthesis of dimethyl ether from syngas? Currently, the scientific research and engineering progress of one-step synthesis of DME from syngas is very active [1~2], indicating that this is a very promising new process. But objectively speaking, large-scale industrial production with real significance has not yet been realized and is still in its infancy. The following introduces several new processes for the one-step synthesis of dimethyl ether from synthesis gas proposed at home and abroad. ? 6.1 Sinopec Group’s new “one-bed, two-return, three-tower” process [6] ? A brief description of the main process is shown in Figure 2. http://www.nmtech.com.cn/jishuwang/upload/0601261052586284.jpg Figure 2 Schematic diagram of Sinopec Group’s “one bed, two returns and three towers” process (1) Dimethyl ether synthesis process? The main task of this process is to synthesize dimethyl ether and separate dimethyl ether and methanol from the gas phase. The main equipment includes dimethyl ether reactor, intermediate heat exchanger, final cooler, gas-liquid separator, absorption tower, flash tank, circulating gas compressor, flash gas compressor, and steam drum. ? There are two return streams in this process, which is the core part of the one-bed, double-return and three-tower process. (2) Dimethyl ether distillation process? The purpose of setting up this process is to obtain product dimethyl ether and product methanol. ? The dimethyl ether distillation part includes dimethyl ether distillation and methanol distillation. The main equipment includes dimethyl ether product tower and methanol distillation tower. ? The process parameters of this process are relatively conventional. The dimethyl ether product tower is a pressurized tower, and the methanol distillation tower is an atmospheric tower. ? 6.2 Dalian Institute of Chemical Physics’ new solid-phase process??? In recent years, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, has developed a dual-functional catalyst for the one-step synthesis of dimethyl ether from synthesis gas, and based on this, a new one-step synthesis of dimethyl ether from synthesis gas has been developed. The process flow is shown in Figure 3. ? http://www.nmtech.com.cn/jishuwang/upload/0601261053376078.jpg? Figure 3 Flowchart of solid-phase synthesis of dimethyl ether at Dalian Institute of Chemical Physics. The synthesis gas is compressed and mixed with circulating gas, and then exchanges heat with the reaction product to increase the temperature before entering the reactor. Under the action of the catalyst, the synthesis gas reacts to generate dimethyl ether, methanol, water, etc. The reaction products and unreacted synthesis gas enter the separation tank after cooling down by heat exchange with the raw materials, and are separated into liquid water and gas phase mixture. The liquid phase water is sent to the sewage treatment device, and the gas phase mixture enters the absorption tower. After removing the methanol, it is sent to the extraction tower (the extraction agent can be ethanol or water). In the extraction tower, the product dimethyl ether is extracted by the solvent. The unreacted raw material synthesis gas is used as circulating gas after being pressurized by a compressor and mixed with fresh raw materials before entering the reactor for reaction. The extracted dimethyl ether enters the desorption fractionation tower with the solvent for desorption and concentration. The solvent to remove dimethyl ether is cooled and pumped into the extraction tower for recycling. The concentrated dimethyl ether product is condensed and cooled, then compressed by a compressor and then put into cylinders or sent to storage tanks. ? Reaction conditions of the process reactor: The synthesis gas raw material H2/CO=1~2, CO/CO2=15~25, the operating pressure is 2.5~4.0MPa, the reaction temperature is 230~300℃, the syngas raw material inlet air velocity is 700~1500h-1?, and the catalyst used is a metal zeolite catalyst. ? 6.3 The new liquid phase ether process of AirProduct Company in the United States [14] With the funding of the US Department of Energy, the product of the new liquid phase dimethyl ether process developed by AirProduct Company is fuel-grade dimethyl ether, which is used as a diesel alternative fuel. The process flow is shown in Figure 4. The company has tested the process in a 15t/d scale pilot plant. ? After the synthesis gas enters the device, it is mixed with the circulating gas, then exchanges heat with the reaction product to heat up, and then enters the dimethyl ether slurry bed reactor. The product from the top of the reactor is cooled by heat exchange and sent to the oil collection tank to remove the entrained oil and catalyst, and then the gas phase is cooled and sent to the separation tower. Most of the unreacted gas containing a small amount of methanol and dimethyl ether obtained from the top of the separation tower is used as circulating gas and sent to the slurry bed reactor for further reaction. A small amount of it is used as a purge gas, and is washed with methanol to recover the dimethyl ether entrained in the purge gas. The recovered liquid is mixed with the dimethyl ether product obtained from the dimethyl ether fractionating tower as a fuel grade dimethyl ether product and is discharged from the device. After the mixture of liquid methanol, dimethyl ether and water obtained from the bottom of the separation tower is separated by the dimethyl ether fractionation tower, the distillate obtained from the top of the fractionation tower is the dimethyl ether product. The distillate obtained from the bottom of the tower is sent to the methanol fractionation tower. After being separated by the methanol fractionation tower, the distillate obtained from the bottom of the tower is sewage and is sent to the wastewater treatment device. The distillate obtained from the top of the tower is methanol, which can be used as a scrubbing gas, or recycled to the slurry bed reactor for further conversion into dimethyl ether product, and can also be sold as a by-product. ? The reactor operating parameters are: The temperature is 200~350℃, the pressure is 2.76~10.3MPa, the catalyst addition amount is 10%~50% of the quality of the mineral oil used, the catalyst particle size is 140 mesh, the space velocity is 1000~15000h-1, and the catalyst is CuO-ZnO-Al2O3/γ-Al2O3. http://www.nmtech.com.cn/jishuwang/upload/0601261054178718.jpg Figure 4 AirProduct Company’s liquid-phase synthesis process of dimethyl ether? 6.4 Japan NKK Company’s new liquid-phase process [14] Japan’s NKK Company has also developed a new one-step process for the synthesis of dimethyl ether from synthesis gas based on a slurry bed reactor. The process flow is shown in Figure 5. ? This process can use natural gas, coal or liquefied petroleum gas as raw materials. After the raw materials enter the device, they are first sent to the synthesis gas converter to produce synthesis gas. The synthesis gas is cooled and compressed to 5-7MPa, enters the absorption tower to remove CO2, and then passes through the activated carbon adsorption tower to remove sulfides and then exchanges heat to 200°C before entering the bottom of the reactor. In the reactor, synthesis gas bubbles in the slurry composed of catalyst and mineral oil to generate dimethyl ether, methanol, CO2, water, etc. The mixture leaving the reactor is condensed and cooled and separated into two parts: a liquid mixture of dimethyl ether, methanol and water, and unreacted synthesis gas. The unreacted synthesis gas is recycled back to the reactor for further reaction. The mixture of dimethyl ether, methanol and water is further separated to obtain wastewater, methanol and dimethyl ether. The wastewater is sent to the wastewater treatment system, and methanol and dimethyl ether exit the device as products. The product is higher purity dimethyl ether rather than fuel grade dimethyl ether. http://www.nmtech.com.cn/jishuwang/upload/0601261054545046.jpg Figure 5 The process flow of liquid phase synthesis of dimethyl ether by Japanese NKK Company? In addition, Danish Halder Topsos Shell Oil Company, Italian Snamprigetti Company, Mobil Oil Company, etc. are also developing technology for one-step synthesis of dimethyl ether from synthesis gas. ? 7 "One bed, two returns and three towers" new process technology analysis The new one-step direct production process of dimethyl ether from synthesis gas developed by Sinopec Group is currently the smallest economic scale acceptable for a unit with an annual output of 30kt dimethyl ether and a by-product of 5610t of methanol. Its design specifications are as follows. (1) Design scale? Operation day 300d (7200h)? Annual output of dimethyl ether 30000t? Daily output of dimethyl ether 100t? Hourly output of dimethyl ether 4.17t? (2) Product specifications? Dimethyl ether ≥ 99.9% methanol < 10×10-6? Water < 50×10-6? Others <500×10-6? (3) Raw gas composition (example)? H2? 52.6% CO 38.4%? Others 9.0%? Temperature 40.0℃ Pressure 5.1MPa? (4) Ton of ether consumption quota (Table 10) http://www.nmtech.com.cn/jishuwang/upload/0601261056034380.jpg (5) Energy consumption per ton of ether 50.535GJ? (6) Investment estimate? With the support of old enterprises, starting from the raw material refined synthesis gas, the cost of the new device is estimated to be approximately RMB 28 million. See Table 11 for details. http://www.nmtech.com.cn/jishuwang/upload/0601261056469321.jpg If the price of dimethyl ether is 3,000 yuan/t and the price of methanol is 2,000 yuan/t, the annual synthesis gas consumption is approximately 1.09×108m3. The price of syngas is 0.40 yuan/m3. ? Equipment investment 28 million yuan? Sales revenue 30000×3000+5610×2000=101.22 million yuan/year? Raw material cost 1.09×108×0.4=43.6 million yuan/year? If other expenses such as consumption, management expenses, loan principal and interest repayment, taxes, etc. are taken into account, this device will still make a large profit. It is estimated that the cost of raw gas for dimethyl ether production from synthesis gas accounts for more than 60% of the total product cost. Therefore, this is a bulk chemical product with better benefits. ? 8. Investment estimate of natural gas to produce dimethyl ether equipment? The natural gas to produce dimethyl ether process mainly includes two parts: natural gas to synthesis gas and synthesis gas to produce dimethyl ether. The former is a mature process that has been industrialized, and the latter is the content described in this article. ? As we all know, the investment in natural gas to produce dimethyl ether equipment is much lower than the investment in coal to produce dimethyl ether of the same scale. The main reason is that the investment in coal gasification is higher. Table 12 lists the investment estimates for producing dimethyl ether from natural gas. It is easy to see that small-scale production is uneconomical. The price of natural gas plays a leading role, which is relatively difficult in the country. Lowering the price of natural gas is a loss for the utilization of natural gas resources. Therefore, for the production of dimethyl ether from natural gas, when dimethyl ether is used as a bulk chemical product, large equipment must be built in resource-rich areas, that is, the scale should be above 300kt/a. 9 Problems? At present, the output of dimethyl ether at home and abroad is not high. One of the reasons is that the application fields have not been effectively developed. The demand for dimethyl ether will grow rapidly after its application fields are widely explored, especially after it is developed as fuel and downstream products. ? The new one-step dimethyl ether production process from synthesis gas is a technical idea suitable for China's national conditions. The successful development of this process will occupy the commanding heights of domestic and foreign technology and reach the international advanced level. At present, although many development units claim that the one-step process for producing dimethyl ether with gas has been successful, the most critical issue, the catalyst life data, has not been responsibly announced, and this is not included in the identification conclusion. Therefore, continued testing is inevitable. ? The focus of domestic research work is on catalysts and reactor structures, with little process research. This may be related to the domestic scientific research system. Grassroots chemical companies with large financial resources do not pay enough attention to new processes and have insufficient ability to bear technical risks. They do not have test workshops for process development and research, and the fixed asset disposal system for process equipment is unfavorable. Therefore, new domestic processes are still mainly introduced. ? At present, many domestic companies have plans to build new DME devices. Some companies still plan to use methanol as raw material because the one-step synthesis gas method still lacks experience in the construction of industrial equipment. In addition, the two-step process is simple, and it is technically and economically reasonable to follow a large-scale methanol unit with a small and medium-sized dimethyl ether unit. ?