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1 Properties and uses of dimethyl ether Dimethyl ether, abbreviated as DME, has the chemical formula CH3OCH3. It is a colorless compound with a slight ether-like odor, and it has been widely used in the chemical and pharmaceutical industries as a solvent, in aerosols, as a refrigerant, and as a raw material for various organic syntheses. Dimethyl ether can be used directly as an engine fuel and a domestic fuel. Due to the continuous rise in oil prices, dimethyl ether has become a hot topic as a coal-based fuel to replace petroleum products. Thanks to its resource advantages and environmental benefits, and considering China’s energy profile characterized by a lack of oil and gas but an abundance of coal, dimethyl ether holds great prospects in the field of clean fuels. Dimethyl ether is hailed as a \"green product of the 21st century\" abroad, while in China it is referred to as a \"second-generation civilian liquid fuel\". For a long time, due to high production costs and sales prices, dimethyl ether has struggled to be widely adopted as an energy source, aside from its use in the fine chemical industry. With new breakthroughs in dimethyl ether production technology in our country, some experts suggest that we should vigorously develop and promote this clean new energy source as a supplement to and alternative to petroleum resources. By making use of our abundant coal resources, we can address the issue of energy security at its root, and achieve progress in our energy technology so that it can rival the world’s advanced levels. Given the advantages of dimethyl ether that no other alternative fuel can match, if its price drops to a level competitive with that of diesel or LPG, it will become a major alternative to diesel, gasoline, and liquefied gas, offering immeasurable market prospects. 2 Production technology of dimethyl ether: With the continuous improvement of dimethyl ether production technology, its production costs have been significantly reduced. Coupled with the development of the civilian fuel and automotive fuel markets, there is a strong enthusiasm for domestic production of dimethyl ether, with an increasing number of enterprises entering this field. The production capacity is usually between 10 and 100 kt. There are two methods for producing dimethyl ether: the syngas one-step method and the methanol dehydration two-step method; the methanol dehydration method is further divided into gas-phase catalytic dehydration of methanol and liquid-phase catalytic dehydration of methanol. 2.1 Process for producing dimethyl ether from syngas in one step: The process of producing dimethyl ether from syngas in one step involves carrying out both the synthesis of methanol and the dehydration of methanol within the same reactor. Compared with the methanol dehydration method, it offers advantages such as a shorter process flow and lower energy consumption; it also enables higher single-pass conversion rates, facilitating large-scale production to reduce costs. The product is primarily used as an alcohol-ether fuel. The one-step production of dimethyl ether from syngas is a new technical field; numerous research institutions and patent holders both at home and abroad are paying close attention to this technology. However, there are few industrial projects, and no plants with a capacity of ten thousand tons have been built yet, either domestically or internationally. 2.2 Methanol liquid-phase dehydration production process: Technical improvements were made to the sulfuric acid-based process by adding phosphoric acid to the reactor, thereby changing the relative composition of the materials evaporated in the reactor and enabling continuous operation of the facility; this approach solved the problem of emissions of inorganic acids from the reactor. The advantage of the liquid-phase method is its low reaction temperature. Since the dehydration of methanol is an exothermic reaction, the lower the reaction temperature, the higher the equilibrium conversion rate. As a result, the one-pass conversion rate of methanol in the reactor using this method is higher than that in the gas-phase method, reaching over 90%. Disadvantages of the liquid-phase method: low product purity and high electricity consumption per ton of product ； The production medium is highly corrosive and does not meet environmental protection requirements ； The equipment requires high-quality materials and involves large investment. The reactor has a large volume, making it difficult to scale up the equipment; the diameter of the reactor in a 10kt plant is over Ф4000mm. 2.3 Advanced vapor-phase dehydration of methanol: The process of producing dimethyl ether through the vapor-phase dehydration of methanol involves using catalysts such as crystalline aluminum silicate to carry out this dehydration reaction. This method features high conversion efficiency and good selectivity, enabling the production of high-purity dimethyl ether suitable for use in aerosols, as well as dimethyl ether suitable for use as fuel. This process has advantages such as a simple production workflow, low equipment investment, and easy dimethyl ether purification. To date, the gas-phase dehydration of methanol is the main method for dimethyl ether production both domestically and internationally. 2.4 Ningbo Yuandong’s DME production technology: Ningbo Yuandong Company employs the most widely used and mature industrial method for DME production both domestically and internationally, namely the gas-phase dehydration of methanol. By leveraging its advantages in terms of reactors and catalysts, as well as through process optimization, the company has managed to achieve leading levels in China in terms of methanol conversion rate and DME selectivity. Additionally, by fully recovering the heat generated during the DME production reaction and reducing steam usage, the company is able to lower production costs, thereby giving its products a strong competitive edge in the market. 2.4.1 Technical features (1) Simple process, convenient for production operations. The process mainly includes methanol vaporization, dimethyl ether distillation, and methanol recovery; it is simple to operate and the production process is easy to control. If a methanol synthesis unit is available, the methanol and water obtained from the bottom of the DME distillation column can also be sent to the methanol synthesis process for methanol recovery, thereby reducing steam consumption. (2) The catalyst layer has a small footprint, resulting in fewer by-products. The cold-tube uniform-temperature dimethyl ether reactor utilizes continuous heat exchange, serving both reaction and heat transfer functions; gas flows inside the reactor tubes while catalysts are filled outside them, resulting in a high catalyst loading factor. The catalyst layer has a small temperature difference, making overheating less likely, and thus it has a long service life ； It features a high methanol conversion rate, few by-products, and low methanol consumption per ton of product. (3) With a low temperature at the inlet of the tower and a high temperature at the outlet, the reaction heat generated in the production of fuel-grade dimethyl ether can be used in place of steam for heating the dimethyl ether reboiler, requiring a lower steam pressure level. The inlet temperature of the isothermal reactor is around 170°C, which is much lower than that of cold-shock and adiabatic reactors, while the outlet temperature of the reactor is above 300°C. The gas exiting the reactor can first be used to produce high-quality steam as a by-product or directly to heat the bottom of the separation tower, before being used to preheat the gas entering the dimethyl ether reactor. (4) Heat recovery from the reaction is efficient, resulting in low steam consumption. The reaction heat is used not only to heat the gas entering the tower and preheat the methanol feedstock, but also for heating the DME or methanol reboilers. This efficient utilization of heat reduces the consumption of steam and cooling water (see Table 1). http://www.nmtech.com.cn/jishuwang/upload1/0807141645214663.jpg 2.4.2 Reactor Technology The reactor is the core equipment of the entire production facility. The main types of reactors used for the gas-phase dehydration to produce dimethyl ether include: adiabatic type, multi-stage cooling type, inter-stage heat exchange type, shell-and-tube type, and Far East cold-tube uniform temperature type. The dehydration of methanol to dimethyl ether is an exothermic reaction; reducing the temperature rise in the catalyst layer and maintaining a lower temperature in the lower part of the catalyst can increase the equilibrium conversion rate of methanol dehydration as well as the dimethyl ether concentration at the reaction outlet, and it also helps to extend the service life of the catalyst. Using the catalyst at too high a temperature results not only in a low methanol conversion rate and a low space-time yield of the catalyst, but also leads to an increase in side reactions, higher consumption of methanol as a raw material, and accelerated coking and deactivation of the catalyst. (1) Adiabatic, inter-stage heat exchange, or multi-stage quench reactors: Adiabatic, inter-stage heat exchange, or multi-stage quench reactors have a simple structure; however, no heat exchange occurs within the catalyst, which leads to large temperature differences across the catalyst layer, resulting in low synthesis efficiency and high levels of by-products. The cold gas is mixed with the reaction gas to lower the temperature, thereby diluting the DME concentration; only a portion of the gas flow passes through the entire catalyst layer, resulting in low catalyst efficiency and a higher amount of catalyst being required to achieve the same production capacity. The inlet temperature of such reactors is 260–270°C; in some plants, the initial temperature at the bottom layer of the catalyst reaches over 370°C. The range for temperature adjustment is limited, which makes it easy for the catalyst layer to overheat. As a result, it is difficult to improve the overall activity of the catalyst, and its service life is short. (2) Shell-and-tube reactor: Its structure is similar to that of a shell-and-tube heat exchanger, with continuous heat exchange inside the catalyst. It shows significant effects in methanol synthesis units: a catalyst is installed inside the tubes, and heat transfer oil is used for forced circulation to remove the reaction heat; high-quality steam cannot be produced as a by-product. Forced circulation of heat transfer oil not only increases equipment and operating costs, but it is also difficult to achieve an isothermal condition in the catalyst layer through counterflow heat exchange outside the tubes. Although its reaction efficiency is better than that of cold-quenching and segmented adiabatic reactions, it is still far inferior to its performance when used in methanol synthesis units. Shell-and-tube reactors still suffer from issues such as a small catalyst loading volume, difficulty in loading and unloading, and complex structure. (3) Single-tube baffled methanol dehydration reactor with a gas distribution box in the Far East type. The advantages of this reactor are: ① An insulating layer can be installed on the bed, resulting in a more uniform temperature distribution within the bed, especially when it is necessary to raise the temperature rapidly in the upper part of the bed. ②The cold tube structure is more reliable. In this structure, the cold tube bundles are divided into several separate clusters, with no interaction between these clusters. Thermal compensation is achieved between the upper and lower cold tubes within each cluster through upper elbows; its design is much more reliable than the configuration in which a single tube with double-loop structure and an upper loop tube buried within the catalyst is used. ③It eliminates the air introduction pipe of the double-loop tubular single-tube baffle cold tube shell, as well as the related cover gasket box, resulting in a simpler structure. It reduces the requirements for manufacturing and installing the internal components, effectively prevents accidents caused by filler leakage from the catalyst basket cover that lead to large temperature differences across the bed layer, and also makes it easier to replace the internal components. ④The catalyst is easy to load and unload, and the pressure drop across the bed is low. 2.4.3 Modified Catalysts: Our company, in collaboration with Jiangsu University, has developed a specialized modified alumina catalyst for the synthesis of dimethyl ether. This catalyst is obtained by modifying ordinary γ-Al2O3 by adding sulfates; such modified γ-Al2O3 catalyst possesses an appropriate level of acidity, which enables high conversion rates and selectivity in the reaction of methanol dehydration to produce dimethyl ether at lower temperatures. Moreover, it helps to prevent carbon deposition at higher temperatures. Its advantages: ① Methanol dehydration conversion rate of 385% ； ②The catalyst has a long service life of over 1 year ； ⑧Dimethyl ether selectivity 397%. 2.4.4 Dimethyl ether distillation technology: The internal components of the distillation tower utilize wire mesh corrugated packing and liquid distributors produced using the company’s proprietary technology; these components feature a large specific surface area, excellent ability to distribute liquid evenly, low pressure loss in the tower, and high efficiency in mass and heat transfer. 3 Equipment investment (see Table 2) http://www.nmtech.com.cn/jishuwang/upload1/0807141645429056.jpg 4 Raw material requirements: The requirements for methanol as a raw material in the production of dimethyl ether depend on the performance of the catalyst. This device requires that the raw material methanol be high-purity methanol, but crude methanol with a purity of over 93% can also be used directly depending on the actual conditions of the operator. 5 Site requirements: Since the raw material methanol and the product dimethyl ether are flammable and explosive substances, strict regulations exist regarding the safety distances between the production units, the tank areas, and the control rooms. For a production facility with a capacity of 20 kt/year, the required area is at least 15,000 m2. The tank areas should be located in relatively remote locations, with a safety distance of at least 50 m on all sides; moreover, there should be no residential areas within 500 m of these areas. 6 Economic analysis (taking 10 kt/a of dimethyl ether as an example: raw material methanol costs 3,400 yuan per ton, while the price of dimethyl ether is 5,800 yuan per ton before taxes; prices may vary in different regions). The investment required for construction is approximately 7.5 million yuan ； Annual increase in sales revenue: approximately 58 million yuan ； After-tax profit: approximately 21 million yuan ； The payback period for investment is less than 2 years (including a 1-year construction period). The gas-phase dehydration method for methanol is currently the primary approach for dimethyl ether production, thanks to its advantages such as a simple production process, low equipment investment, and easy purification of dimethyl ether. Through years of innovation and improvement, Far East Company has developed an advanced and unique production process for synthesizing dimethyl ether from methanol through dehydration. Compared with existing gas-phase catalytic dehydration methods for methanol both at home and abroad, this new process represents significant improvements and innovations; it is at the advanced level in China. It features lower investment costs and shorter construction times, making it the most ideal method for producing dimethyl ether at present. 7 Technical services available from our company: Depending on the owner’s requirements, our company can provide turnkey projects that include overall project management, complete engineering design, as well as the supply, installation, and commissioning of all equipment. Alternatively, we can offer only related technical services such as process package development and engineering design, with the owner being responsible for equipment procurement and installation.