Downstream products of dimethyl ether

1 Overview Dimethyl ether is an important coal chemical product that has found wide application in the fields of new energy and fine chemicals11l. The large-scale production of dimethyl ether began in Germany in 1966, mainly for use in the hair gel industry; subsequently, Europe and Japan also started producing dimethyl ether. China started producing dimethyl ether relatively late; large-scale production only began in 1955. The main domestic manufacturers and their production capacities are shown in Table 1. Table 1: Major dimethyl ether manufacturers and their production capacities in China
Manufacturer | Production capacity/t·a-1 | Production method
Shandong Jiutai Chemical Co., Ltd. | 35.5 | Liquid-phase dehydration
Guangdong Zhongshan Fine Chemical Co., Ltd. | 5.0 | Gas-phase dehydration
Chengdu Huayang Weiyuan Natural Gas Chemical Plant | 2.0 | Gas-phase dehydration
Guangdong Jiangmen Nitrogen Fertilizer Factory | 2.5 | Gas-phase dehydration
Zhejiang Zhuji Xinya Chemical Co., Ltd. | 1.0 | Gas-phase dehydration
Anhui Mengcheng County Fertilizer Factory | 3.0 | Gas-phase dehydration
Jiangsu Kunshan Chemical Raw Materials Factory | 1.0 | Liquid-phase dehydration
Zhejiang Yiwu Guangming Chemical Co., Ltd. | 2.5 | Gas-phase dehydration
Hubei Tianli Industrial Company | 1.5 | One-step gas-phase process
Shaanxi New Type Fuel and Appliance Co., Ltd. | 5.0 | One-step gas-phase process
Ningxia Yinchuan China National Coal Energy Group Corporation | 830.0 | Gas-phase dehydration
Luzhou Natural Gas Chemical Company | 100.0 | Gas-phase dehydration
The main products of China’s small-scale fertilizer industry in the past, namely ammonium carbonate and urea, are now facing dual pressures from market and product structure adjustments. As the production technology of DME becomes more mature and the number of its downstream products increases, it is necessary for the small fertilizer industry to take advantage of this development. This paper discusses and analyzes the development and application of dimethyl ether and its downstream products, in order to provide decision-making references for the structural adjustment of the small-scale fertilizer industry. 2 Applications of dimethyl ether 2.1 Use as a new energy source Energy is the material foundation for the sustainable development of the national economy. The overall characteristics of China’s energy resources are \"abundant coal, scarce oil, and limited gas.\" At present, our country has become the third largest oil importer after the United States and Japan ； Furthermore, China’s total coal reserves amount to 114.5 billion tons, and 80% of this coal is burned directly, resulting in annual sulfur dioxide emissions of 19 million tons. This leads to acid rain and the greenhouse effect, causing severe pollution of the atmospheric environment. Therefore, the research and application of environmentally friendly and energy-saving new energy sources have become an important factor in China’s economic development. As a substitute fuel for diesel, dimethyl ether features cleanliness, low pollution levels, good power performance, and easy storage; its overall performance is far superior to that of liquefied gas, natural gas, methanol, ethanol, and others. Compared to methanol fuel and alcohol-ether fuels, dimethyl ether has the following advantages: ① At the same temperature, its saturated vapor pressure is lower than that of liquefied gas, making it safer for storage and transportation ； ②The lower explosion limit of dimethyl ether in air is twice that of liquefied gas, making it safer ； ③Dimethyl ether contains oxygen in itself, has a single component, short carbon bonds, high thermal efficiency, and good combustion properties; no residues or black smoke are produced during combustion, and its exhaust emissions meet ** standards ； ④Using dimethyl ether as a clean fuel for household use in place of liquefied gas is largely compatible with existing liquefied gas filling equipment, cylinders, and stoves, making it easy to promote its use. At present, China’s automobile industry is developing rapidly, and it is estimated that the annual consumption of diesel will reach around 120 million tons by 2010. Based on a 5% substitution of diesel with dimethyl ether, the domestic demand for dimethyl ether by 2010 would be approximately 6.74 million tons. Experts predict that within the next 3 years, the demand for fuel-grade dimethyl ether as a fuel for domestic use and in vehicles will increase significantly; by 2010, the demand for dimethyl ether is expected to exceed 100,075 tons, indicating very promising market prospects. 2.2 Use as a substitute for chlorofluorocarbons The need to protect the atmospheric ozone layer has forced a complete halt to the production and use of chlorofluorocarbons. As a substitute for chlorofluorocarbons, dimethyl ether exhibits excellent properties in aerosols: it does not pollute the environment, has low toxicity, and helps to prevent spray products from becoming damp. It is thus an ideal propellant for next-generation aerosols. In Europe and the United States, a large amount of DME is used in aerosols; approximately 25% of aerosols use DME as a propellant ； If half of the aerosol products in our country use DME as a propellant, 25,000 tons of DME would be required annually. Furthermore, the easy liquefaction property of dimethyl ether has also drawn attention; many studies are being conducted to use dimethyl ether as a substitute for chlorofluorocarbons as a refrigerant, taking advantage of its low pollution level and excellent cooling performance. As a blowing agent, dimethyl ether enables products such as foam plastics to have uniform pore sizes, as well as improved flexibility and pressure resistance, offering very promising application prospects. 2.3 Fuel for use in fuel cells Fuel cells typically use hydrogen or hydrogen-rich gases as fuel, but due to its low density and flammability, hydrogen is difficult to transport and store, which limits its practical application. Therefore, finding a hydrogen carrier that can store hydrogen within a compound and release it at the desired location is a viable option. Dimethyl ether has attracted attention due to its non-toxicity, non-corrosiveness, and lack of carcinogenic properties. The challenge lies in how to release the hydrogen from dimethyl ether efficiently; generally, two methods are employed: ① Partial oxidation of dimethyl ether to produce CO and H2, followed by a water-gas shift reaction – a process with great potential. Zhang et al. studied catalysts for the hydrogen production via high-temperature partial oxidation reforming of dimethyl ether, and found that the Pt/Al2O3 + Ni-MgO dual-bed catalyst could effectively catalyze this reaction, achieving a 100% conversion rate of dimethyl ether at 700°C and a 90% H2 yield. Among them, Pt/A12O3 can inhibit the homogeneous decomposition of dimethyl ether, while Ni-MgO can produce more H2 through reforming reactions ； ②Hydrogen production via dimethyl ether steam reforming consists of the hydrolysis of dimethyl ether to produce methanol, followed by the steam reforming of methanol. Takeishi et al. investigated Cu- and Al-containing catalysts for this reaction, which are active in the hydrogen production via dimethyl ether steam reforming. Adding Pd to it can significantly improve the low-temperature catalytic activity of this catalyst and increase the hydrogen yield. Matsumoto et al. combined a dimethyl ether dehydration catalyst with a methanol steam reforming catalyst, and investigated the effect of various combination schemes on reaction activity. The results showed that a combination of H-mordenite and CuO/CeO2 yielded a high H2 yield; in particular, at 250°C, when the mass ratio of H-mordenite to 80% CuO/CeO2 was 21.5, the H2 production rate was 71 mol(kgcath)-1. Overall, however, there are not many studies currently on producing hydrogen using dimethyl ether as a raw material, so it holds great potential for development. 2.4 Development of downstream products from DME: Dimethyl ether is an important chemical raw material, and it can be used to develop a range of fine chemical products with broad applications and good market prospects. Many scholars abroad are working on research related to the production of mixtures such as ethylene, propylene, and butenes from methanol and dimethyl ether. The Dalian Institute of Chemical Physics under the Chinese Academy of Sciences has also achieved good results in its research on producing ethylene from syngas using dimethyl ether. Furthermore, the use of the dimethyl ether carbonylation method to produce methyl acetate, the synthesis of dimethyl carbonate from dimethyl ether, and the production of dialkoxyl hydrocarbons from dimethyl ether all possess significant industrial importance and potential for development. 2.4.1 Synthesis of dimethyl carbonate Dimethyl carbonate is an important raw material and intermediate in organic synthesis; it is a highly useful non-toxic chemical and is regarded as a green chemical product for the 21st century. Dimethyl carbonate is a solvent with excellent properties; it is insoluble in water, can be mixed with alcohols and esters, is flammable, non-corrosive, and highly reactive. It can be used in the synthesis of polycarbonates as well as in the production of intermediates for pharmaceuticals and pesticides. The market prospects are very broad. Currently, the methanol oxidation carbonylation method is commonly used to synthesize dimethyl carbonate, with halides of copper and palladium as catalysts. The formation of water during the reaction reduces the equilibrium yield, causes severe equipment corrosion, and makes product separation difficult. If DME is used as a raw material, dimethyl carbonate can be prepared via oxidative carbonylation. The reaction is as follows: CH3OCH3 + CO + 1/2 O2 → (CH3O)2CO. 2.4.2 Synthesis of dimethyl sulfate Dimethyl sulfate is an important alkylating agent that is widely used in organic synthesis fields such as pesticides, pharmaceuticals, fragrances, and dyes; it can also be used as a solvent. In our country, dimethyl sulfate is typically produced using methanol and sulfuric acid as raw materials. This process not only involves a long sequence of steps but also causes equipment corrosion; moreover, the intermediate product, methyl hydrogen sulfate, is highly toxic. As a result, the production environment is harsh. Yet many companies still use this method today. In the 1970s, Sadilak proposed a method for preparing dimethyl sulfate from DME and SO3, namely a gas-phase reaction between DME and fuming sulfuric acid or SO3, carried out at 35–45°C for 10–15 minutes to yield dimethyl sulfate. This method features mild reaction conditions, avoids the formation of the highly toxic substance methyl hydrogen sulfate, results in low pollution, and achieves a product selectivity of 94%-96%, making it one of the methods with great potential for development. Compared with other synthesis methods, the DME method features a single reaction product and good selectivity. At present, Wuhan Qingjiang Chemical Co., Ltd. uses methanol etherification to produce dimethyl ether, which is then combined with SO3 in a methyl ester mother liquor for synthesis; subsequent vacuum distillation yields a pure product with a purity of over 98.5%. 2.4.3 Synthesis of ethylene Ethylene is one of the most fundamental and important chemical raw materials, and it serves as an important indicator for measuring a country’s industrial capacity. Our country is short of oil; therefore, how to produce important chemical raw materials such as ethylene and propylene from syngas has increasingly become a focus of attention for scientists in our country. Currently, many researchers are actively working on the synthesis of ethylene from methanol and dimethyl ether. Good progress has been made at the Dalian Institute of Chemical Physics, Chinese Academy of Sciences, in the research on producing ethylene from syngas via dimethyl ether. Dimethyl ether at 450°C ； Using zeolite as a catalyst, a dehydration reaction takes place to produce ethylene and propylene, with yields of 65% and 25% respectively, while the conversion rate of dimethyl ether is 87%. The reaction equation is: CH3OCH3 → CH2=CH2 + H2O. 2.4.4 Synthesis of dimethyl sulfide Dimethyl sulfide serves as an intermediate in the production of pesticides, dyes, and fragrances; it is also a raw material for the manufacture of dimethyl sulfoxide. Additionally, it can be used as a solvent in organic synthesis, polymerization reactions, and cyanation reactions, as well as a spinning solvent for synthetic fibers. It finds applications as an industrial cleaning agent, a drug penetration enhancer, a solvent for hydraulic oils, and a corrosion inhibitor for batteries at low temperatures. Dimethyl sulfide can be synthesized from DME and H2S, or it can be prepared by reacting DME with CS2. Both reactions use γ-Al2O3 as a catalyst, and they exhibit high selectivity in the production of dimethyl sulfide, with the product purity exceeding 90%. 2.4.5 Synthesis of alkyl halides Alkyl halides can be synthesized using DME. Among these alkyl halides, CH3Cl is the most widely used chemical reagent; it serves as an important methylating agent in organic synthesis, and can be used as a solvent for rubber, resins, and organic compounds, as well as a raw material for polychloromethanes. The Japanese company Soda uses γ-Al2O3 as a catalyst to react DME with HCl to produce CH,Cl. Additionally, Germany has also reported that using solid ZnCl2 as a catalyst and a reaction temperature of 129–350°C, the reaction of DME with HCl can yield CH3Cl in high yields and with high selectivity ； In addition, some people have also used the reaction of DME with HF to synthesize CH3F. 2.4.6 Synthesis of N,N-diamines N,N-diamines are one of the basic raw materials used in the production of basic dyes and alkaline dyes. The reaction of DME with aniline can yield N,N-diamine, and compared to other production methods (such as the synthesis of N,N-diamine using aniline and methanol over a zeolite catalyst), the dimethyl ether-based method offers advantages such as fewer side reactions, lower reaction temperatures, and higher product selectivity. Therefore, the dimethyl ether method will become one of the most valuable and promising production methods for amine alkylation. 2.4.7 Synthesis of acetic acid and acetic anhydride Acetic acid and acetic anhydride are important basic organic chemical raw materials that are widely used in the synthesis of various fine organic chemicals in fields such as pharmaceuticals, pesticides, leather processing, textiles, light industry, rubber, synthetic fibers, as well as metal processing and food industry. At present, the demand for acetic acid and acetic anhydride in our country is on the rise. The reaction of DME with CO enables the carbonylation synthesis of methyl acetate and acetic anhydride, which yield acetic acid upon hydrolysis. The reaction equations are as follows: CH3OCH3 + CO → CH3COOCH3; CH3COOCH3 + H2O → CH3COOH + CH3OH; CH3OCH3 + 2CO → (CH3CO)2O. In these reactions, rhodium carbonyl-iodide is commonly used as a catalyst, the reaction temperature is around 200°C, and the reaction pressure is in the range of several dozen MPa. Although rhodium catalysts have high activity, their high cost limits their development to some extent. As can be seen from the above reaction equations, the synthesis of acetic anhydride from DME is an atom-economical reaction, as it is more advantageous than synthesizing acetic anhydride directly from methanol. 2.4.8 Other reactions: DME can act as a coupling agent to form siloxanes with silicon at high temperatures in sealed systems. DME can react with soluble silanes, aluminum trichloride, and ammonia to produce aluminum nitride-alumina-silica ceramic materials with high strength and corrosion resistance. This ceramic material possesses excellent heat resistance, corrosion resistance, and oxidation resistance, as well as high strength; it is particularly suitable for manufacturing cutting tools, engine components, and turbine parts. DME reacts with O2 and NH3 to produce hydrocyanic acid, and when mixed with air it reacts to form formaldehyde and other substances ； The reaction of DME with ethylene oxide produces a mixture of dimethyl ethylene glycol, dimethyl diethylene glycol, dimethyl triethylene glycol, and dimethyl tetraethylene glycol. Under the action of the solid catalyst SnO2/MgO, DME can be oxidized and dimerized to produce dimethoxyethane ； DME reacts with ammonia on modified acidic molecular sieves to produce dimethylamine ； DME reacts with P2O5 to produce alkyl polyphosphates. 3 Conclusion Dimethyl ether is readily available and has a wide range of applications; it holds great potential as a fuel and for the production of olefins, and has thus become a focus of research in the fields of energy, environment, and chemical engineering. Our province is rich in coal resources, providing an ample supply of raw materials for DME production. Relevant enterprises can take advantage of this to vigorously develop DME and its downstream products, as well as promote the use of DME as a new type of clean energy. This not only helps to optimize China’s energy structure and reduce dependence on oil, a strategic resource, but also holds great significance for the coordinated development of resource utilization and environmental protection in our country.

Downstream products that can be developed: low-carbon alcohols； Ethylene and propylene ； Olefin mixtures, etc ； Methyl acetate ； Dimethyl carbonate ； Dialkoxyl hydrocarbon compounds ； Some people are still thinking about developing ethylene oxide.

It’s just that the manufacturing process isn’t very mature.

How to liquefy dimethyl ether at normal temperature and pressure, or how to liquefy the downstream products of dimethyl ether