Introduction to the production technology of dimethyl ether via methanol gas-phase method

Thread Content

1. Dimethyl ether industry: Dimethyl ether is a clean and environmentally friendly fuel, and it is an alternative energy source that is **recognized and encouraged for development**. In an era of high oil prices, the coal-based dimethyl ether industry will become a key force in effectively reducing China’s dependence on imported oil. The use of dimethyl ether as a substitute for liquefied petroleum gas (LPG) has been accepted by consumers, and the National Development and Reform Commission, the Ministry of Construction, and the Ministry of Agriculture have each issued relevant standards. Dimethyl ether replacing liquefied petroleum gas (LPG) is used not only as a fuel for household use, but also in industrial applications such as ceramic and glass firing, as well as metal cutting and welding, where its consumption is significant. A greater future use of dimethyl ether is to replace diesel as a fuel for engines in vehicles, ships, and power generation. China’s diesel consumption has exceeded 120 million tons per year, and its liquefied petroleum gas consumption is around 20 million tons per year; therefore, the industrial prospects for dimethyl ether are quite promising. The methanol-to-dimethyl ether production plant is characterized by low investment costs, high output value, and rapid returns on investment; for example, a profit of around 200 yuan per ton of product can be generated, allowing the initial investment to be recovered within 1–3 years. In order to promote the use of dimethyl ether, the Ministry of Finance and the **State Taxation Administration issued the \"Notice on the VAT Rate Applicable to Dimethyl Ether\" (Caishui No. 72). It stipulates that, as a measure to encourage the use of dimethyl ether, starting from July 1, 2008, VAT will be levied on dimethyl ether at a rate of 13%. 2. Production methods of dimethyl ether: Currently, there are mainly two types of methods for producing dimethyl ether both domestically and internationally: the syngas one-step method and the methanol method, with the latter further divided into the gas-phase methanol method and the liquid-phase methanol method. The industrialization technology for the one-step synthesis gas process is not yet fully mature. At the current level of technology, the production cost is higher than that of the methanol method; technical deficiencies need to be addressed, and key technical aspects require further exploration and breakthroughs. The existing and planned dimethyl ether production plants all use the methanol method. The liquid-phase production process, due to its low operating pressure, low capacity per reactor, and certain level of pollution, results in high investment costs and high power consumption, making it unsuitable for widespread adoption. The gas-phase methanol method is the most economical and reasonable approach for producing dimethyl ether at present. Currently, all large-scale dimethyl ether production plants under planning or construction at home and abroad use the methanol gas-phase method. 3. The company’s new technology for methanol production via the gas phase method ※Development history: The company’s technology for producing dimethyl ether from methanol using the gas phase method was first developed in China in the 1980s; it was designated as a key scientific and technological project under the \"Eighth Five-Year Plan,\" and industrial production of this technology began in 1994. In the 1990s, 3 sets of aerosol-grade and 7 sets of fuel-grade plants were built and put into operation, and the production of fuel-grade dimethyl ether using crude methanol as raw material was successfully implemented. Subsequent continuous innovation and improvement have led to the development of advanced new technologies for the methanol vapor phase process. Two Chinese invention patents were applied for in 1995 and 2003 respectively and granted; the key technical aspects of the new methanol gas-phase process are included in the claims of these two patents. In December 2005, the first dimethyl ether fuel production facility to utilize the company’s new methanol vapor-phase technology was put into operation at Bengbu New Ao Gas Company, marking a new advancement in dimethyl ether production technology. The production cost of dimethyl ether was significantly reduced, and the technical level reached world-class standards. Due to the demonstration effect of the commissioning of this facility, domestic companies have begun to plan and construct dimethyl ether fuel production plants, giving rise to a \"dimethyl ether craze\" within the industry. Adhering to the principles of \"striving for excellence\" and \"continuous improvement,\" the company’s R&D and design professionals have, over the years, focused on reducing energy consumption, lowering costs, and optimizing operations. The results of these ongoing technological innovations have been significant, with the technology used in dimethyl ether production continually being improved. Based on the production performance of the factory, compared with existing technologies at home and abroad, it consumes the least amount of methanol and water vapor, thereby effectively reducing the production cost of dimethyl ether. The advancement and reliability of new technologies have been proven through more than 30 units put into operation in recent years. **The Ministry of Science and Technology has designated the Southwest Chemical Engineering Research and Design Institute and Sichuan Tianyi Technology Co., Ltd. as the entities responsible for carrying out the tasks related to the “Development of Large-scale Projects for the Production of Dimethyl Ether from Methanol”, which is part of the “Key Technologies for the Production of Oxides via Non-petroleum Routes” under the science and technology support program. ※Industrial achievements: As of June 2008, more than 70 units with a dimethyl ether production capacity of 10 kt/a to 400 kt/a had been built, thanks to the technology transferred by the Southwest Chemical Engineering Research and Design Institute and Sichuan Tianyi Technology Co., Ltd. along with the engineering design provided. Of these, there are 18 units with a capacity of 100 kt/a and 9 units with a capacity of 200 kt/a; 9 of the 100 kt/a units and 2 of the 200 kt/a units are already in operation. ※Technical Features: The company’s gas-phase methanol-to-dimethyl ether production technology features a unique process design, low investment costs, and low production expenses. The main technical advantages are as follows: 1) When produced in conjunction with methanol plants, crude methanol can be used as the raw material, which significantly reduces production costs (primarily by reducing steam consumption; using crude methanol as a raw material can cut steam usage by about 1.5 tons per ton of dimethyl ether produced). This technology for producing dimethyl ether from crude methanol has been tested in several plants with a capacity of 100 kt/a each. 2) The reactor uses a multi-stage quench-type fixed-bed design; it has a large catalyst loading capacity, low investment costs, an appropriate reaction temperature, few side reactions, and is suitable for scale-up. It not only avoids the drawbacks of adiabatic fixed-bed reactors, such as excessive temperature rise leading to increased side reactions and a low single-pass conversion rate of methanol, but also overcomes the disadvantages of heat-exchange fixed-bed and isothermal tubular fixed-bed reactors, namely large size and limited catalyst loading capacity (a key technology protected by patents). 3) A unique vaporization distillation tower structure and separation process are employed; there is no methanol concentration tower for recovering unreacted methanol. The vaporization distillation tower performs three functions: vaporizing the feed methanol, concentrating the recovered methanol, and separating out the water from the feed material as well as the water generated during the reaction. It simplifies the process, reduces investment, and effectively cuts steam consumption. The steam consumption per ton of dimethyl ether produced is more than 0.5 tons lower than that of similar technologies at home and abroad. It also prevents methanol loss during the operation of the methanol concentration tower (which operates at atmospheric pressure), thereby ensuring low methanol consumption effectively (a key technology protected by patent). Without adopting this patented technology, it is difficult to keep the water vapor consumption below 1.6 t/tDME. 4) A specially developed catalyst of our own is used for large-scale production; it features good activity, excellent thermal stability, and a dehydration reaction selectivity of over 99.5%. Furthermore, thanks to the advanced and rational design of the separation process, the separation losses of methanol and dimethyl ether are low, effectively ensuring the methanol consumption, which is a key indicator of consumption. Methanol consumption is lower than that of similar technologies at home and abroad. 5) Compared with similar technologies at home and abroad, it not only features advanced technology but is also mature and reliable, with the lowest production costs. 4. Product quality: The product quality meets the standards of the chemical industry, HG/T3934-2007 (see table below).
Items: Type I, Type II
Mass fraction of dimethyl ether/%: ≥ 99.9, ≥ 90.0
Mass fraction of methanol/%: ≤ 0.05, ≤ 0.5
Mass fraction of water/%: ≤ 0.03, ≤ 0.3
Copper sheet corrosion test: ≤ – – Grade I
Acidity (based on H2SO4)/%/: ≤ 0.0003, ---
Note: Acidity is tested for Type I products when used as refrigerants.

5. Main consumptions (per ton of dimethyl ether produced):
Serial number, Name, Specification, Unit, Consumption, Remarks
1. Methanol, Purified crude methanol, t, 1.395–1.41; varies depending on scale and raw material purity
2. Water vapor, ≥1.0 MPa, t, 1.05–1.25; varies depending on scale and raw material purity
3. Circulating cooling water, ≥0.3 MPa, ≤32°C, t/h, 70–80; depends on circulation rate
4. Electricity, 380/220 V, 50 Hz, kWh, 6–15; varies depending on scale and raw material purity