Analysis of Coal Chemical Technology and Its Current Development Status

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Over the past few decades, fossil fuels have accounted for over 90% of China’s primary energy consumption structure. Coal is the main energy source in our country, as well as the primary raw material for many important chemical products. With the continuous and rapid development of China’s society and economy, demand for energy and chemical products has also seen a high growth rate in recent years. Coal chemistry plays an important role in China’s energy and chemical industries. The development of coal chemical industry in our country is of practical and long-term significance for leveraging the advantages of abundant coal resources, compensating for the shortage of domestic oil and gas resources, meeting the demand for chemical products, ensuring energy security, and promoting sustainable economic development. Economic growth, social progress, and environmental protection are the three key aspects of sustainable development. Properly handling the relationship between economic development and environmental protection is a core issue in China’s pursuit of sustainable development; by adhering to sustainable, safe, and clean development approaches, it is possible to achieve sustainable development. I. The coal chemical technology route is an industry in which coal is used as a raw material and transformed into gaseous, liquid, and solid products or semi-finished goods through chemical methods; these products are then further processed into a range of chemical products or petroleum fuels. This industry is known as the coal chemical industry, or simply coal chemistry. From a technical perspective, coal chemical industry includes three technical routes: coal coking, coal gasification, and coal liquefaction. The coking of coal is a process in which coal is heated under air-free conditions to be decomposed into coke, coal tar, coke oven gas, and crude benzene. Coke can be used to produce calcium carbide, which in turn is used to make acetylene; acetylene can then be used to manufacture important basic chemical raw materials such as PVC, PVA, and BDO. Coal gasification is the process of reacting coal with steam and oxygen at high temperatures to produce syngas (H2+CO), which can be used to manufacture synthetic ammonia and methanol, among other things. Methanol is an important chemical raw material that can be used to produce a variety of C1 chemical products. Coal liquefaction is the process of converting coal into liquid fuel through chemical processing. Coal liquefaction is divided into two main processes: direct liquefaction and indirect liquefaction. Direct liquefaction is a process that converts coal into liquid hydrocarbons through direct hydrogenation, producing fuels such as gasoline, kerosene, and diesel. Indirect liquefaction involves first producing syngas, which is then converted into hydrocarbon fuels and oxygen-containing compound fuels (such as low-carbon mixed alcohols, dimethyl ether, etc.) through catalytic action. Coal coking is a traditional field in coal chemical industry. With the emergence of new technologies and processes, coal gasification and coal liquefaction have become important directions for the development of modern coal chemistry. II. Industrial characteristics of coal chemical industry: The main features of the new type of coal chemical industry are the rational utilization of coal resources and the full realization of the value of coal ； The co-production of various coal chemical products is achieved through the optimized integration of multiple coal conversion technologies ； Advanced and reliable technology, market-ready products ； High production efficiency, low environmental pollution, and good economic benefits. 1. Make effective use of coal resources. Coal is not only an essential industrial fuel but also a highly valuable raw material for the chemical industry. Generally speaking, the utility of coal as a chemical raw material is far greater than its utility merely as an industrial fuel. Since the rate of exploitation and utilization of coal far exceeds its rate of formation through natural processes, coal can be considered a non-renewable primary energy source. Therefore, from the perspective of efficient utilization of coal resources, priority should be given to using coal to produce products with high utility value and added value. The new type of coal chemical industry achieves a hierarchical utilization of coal resources, from higher-value to lower-value applications, by optimizing and integrating various coal conversion technologies to produce both coal chemical products and clean energy. 2. Maximize economic benefits. Although any coal conversion technology focuses on maximizing the economic efficiency of the process, optimizing the economic efficiency of each subsystem does not necessarily result in the optimal economic efficiency for the overall system composed of multiple subsystems. By optimizing and integrating various coal conversion technologies, the new type of coal chemical industry not only enables better realization of economies of scale across the entire system, but also reduces the capital investment required for construction and the total cost of the products produced, through the optimal allocation and sharing of resources such as various process flows, key equipment, auxiliary facilities, and utility systems. This improves the efficiency of the entire process, thereby maximizing the economic benefits associated with the utilization of coal resources to produce various chemical and energy products. 3. Make it more environmentally friendly. Every coal conversion technology results in pollutant emissions. To meet the increasingly stringent environmental protection requirements, appropriate environmental measures must be taken to treat the pollutants generated through proper processing, conversion, recycling, or safe disposal, in order to achieve reduction, resource utilization, and harmlessness, ultimately resulting in near-zero emissions or emissions that meet regulatory standards. The new type of coal chemical industry integrates various coal conversion technologies optimally; this not only facilitates the centralized and comprehensive treatment of pollutants, **reducing environmental protection costs**, but also makes it possible to turn waste into resources, or even to transform waste into something valuable. III. Core technologies of coal chemical industry 1. Direct coal liquefaction. Direct coal liquefaction is a high-tech advancement in the field of coal chemistry. This technology converts coal into oil-coal slurry, which is then subjected to catalytic hydrogenation at around 450°C and a pressure of 10–30 MPa to produce liquefied oil, which can be further processed into gasoline, diesel, and other chemical products. 2. Indirect coal liquefaction. Coal indirect liquefaction is a process in which coal is gasified to produce syngas (CO, H2), which is then used in the F-T synthesis to obtain engine fuel oils and other chemical products. ?3. Large-scale advanced gasification. Gasification is an important unit technology for the development of new coal chemical industries. Although there is still a certain gap between China’s advanced large-scale coal gasification technologies and those abroad, the pace of development has accelerated in recent years. “During the 15th Five-Year Plan period, industrial demonstration development and scale-up research were carried out respectively on the multi-nozzle water-coal slurry gasification technology and the dry coal powder fluidized bed gasification technology, both of which possess independent intellectual property rights. Given the diversity of coal types and qualities, there is an urgent need to research and develop gasification technologies suitable for coal types with high ash melting points and moderate to strong cohesion. ?4. Coal-to-methanol technology. Methanol is a flammable and volatile colorless liquid with combustion properties very similar to those of liquid fuels used in practice. It has a high octane rating and good anti-knock properties. Its raw materials are widely available, and its transportation, storage, packaging, filling, and use bear a great deal of similarity to the characteristics of gasoline and diesel fuels used in internal combustion engines currently available on the market. At the same time, methanol can also serve as an important raw material for fuel cells. Currently, methanol serving as a substitute for petroleum has become a reality. In the long term, methanol can also become one of the main alternatives to oil. Research on the production of ethylene and propylene from methanol is showing promise; at current oil and olefin prices, the expected economic benefits of producing olefins from methanol are roughly comparable to those of producing them from naphtha and light diesel. Therefore, from the perspective of China’s alternative oil resources, the moderate development of the methanol industry holds significant strategic importance. 5. Two-step synthesis technology for dimethyl ether. Dimethyl ether can replace diesel as an engine fuel, and it can also serve as a civilian fuel alternative to LPG. Compared with the one-step synthesis of dimethyl ether using syngas as a raw material, the two-step method for producing dimethyl ether offers advantages such as higher efficiency, fewer process steps, and lower production costs. Research and development of a two-step process for the synthesis of dimethyl ether are underway in the country. ?6. Coal chemical co-production system. The coal chemical co-production system represents an important direction in the development of new coal chemical technologies. The basic principle of co-production is to take advantage of the strengths and complementarities of different technical approaches, optimize and integrate various processes, thereby achieving comprehensive utilization of resources and energy, reducing investment in infrastructure construction, lowering production costs, and minimizing the emission of pollutants or waste. Such as the co-production of F-T synthesis and methanol synthesis, and the co-production of coal coking and direct liquefaction. ?7. A cogeneration system centered on gasification. The cogeneration system centered on coal gasification is a key aspect of the development of new coal chemical industries, and it comes in various forms. The core idea is to use coal (or petroleum coke, residue oil, etc.) as the raw material for gasification; the resulting gas is then used as a raw material or fuel for producing liquid fuels, chemical products, and electricity. By optimizing and integrating the production processes of these various products, it is possible to reduce construction costs and operating expenses, thereby contributing to environmental protection. Currently, in China, research is being carried out on the development of simulation software for the optimized integration of cogeneration systems, as well as on the key technologies involved. ?8. Other advanced coal chemical technologies. The development of new coal chemical industries also involves the research and application of other unit process technologies, such as efficient gas purification and separation technologies, large-scale and high-efficiency synthesis technologies, and gas turbine power generation technologies suitable for different calorific values. IV. Main products of coal chemical industry 1. Coal-to-oil. The overall energy characteristics of our country are \"abundant coal, limited oil, and gas available.\" Our country possesses abundant coal resources, and due to its large reserves and relatively stable price, coal has become the preferred fuel for power generation in our country. The shortage of oil resources has brought the use of coal as a substitute for oil back onto the agenda, and converting coal into oil has become an important trend in China’s energy strategy. At present, coal-to-oil technology and its industrialization in China are still in the initial stages of development, with progress being driven through both technology imports and independent research and development. 2. Coal-to-methanol and downstream products. Methanol production in our country began in 1957; in the 1950s, facilities for producing methanol from coal or coke were established in places such as Jilin, Lanzhou, and Taiyuan. A number of small and medium-sized plants were built in the 1960s, and a co-production process for methanol was developed based on the ammonia synthesis industry. In the 1970s, the Sichuan Vinylon Plant introduced a 95,000-ton/year low-pressure process unit that used acetylene off-gases as raw material, based on British ICI technology. In December 1995, the 200,000 tons per year methanol production plant, jointly designed by the Eighth Design Institute of the Ministry of Chemical Industry and the Shanghai Chemical Engineering Design Institute, was successfully put into operation at Shanghai Pacific Chemical Company. This marked a new step forward in China’s methanol production technology toward larger scale and greater reliance on domestic capabilities. In 2000, Hangzhou Linda Company developed the JW low-pressure homogeneous methanol synthesis tower technology, which possesses complete independent intellectual property rights, thereby breaking the long-standing monopoly held by a few foreign companies such as ICI and Lurgi. In 2004, this technology was awarded the Second Prize for Technical Invention. In 2005, this technology was successfully applied to China’s first methanol plant powered by coke oven gas. Developing downstream products of methanol will be the direction for future development. Methanol is an important basic chemical raw material, and its downstream products include organic acids such as acetic acid and formic acid, various oxygen-containing compounds such as ethers and esters, olefins such as ethylene and propylene, and fuels such as dimethyl ether and synthetic gasoline. In line with market demands, developing downstream products of methanol that are in short supply in the domestic market – especially those that can replace petrochemical products – is an important direction for the large-scale expansion of methanol production and the enhancement of competitive strength in the market. 3. Coal-based methanol to olefins (MTO). In recent years, our country has been the region in the world with the fastest growth in polyolefin production and consumption; the production, consumption, and imports of polyethylene and polypropylene have all increased at a rapid pace. At present, ethylene production in China’s petrochemical industry relies primarily on the naphtha route. The domestic polyethylene industry is facing a demand that exceeds supply and continues to develop; therefore, developing a production pathway based on coal-derived methanol–ethylene–polyethylene has various advantages and significance. Since 2003, many domestic enterprises have paid attention to the development of technologies for producing olefins (mainly ethylene and propylene) from methanol, and have incorporated olefin co-production into the design of new methanol projects. While continuing to monitor the research progress in foreign MTO processes and catalyst technologies, China also needs to strengthen its own research and development efforts, improve existing technologies, and carry out preparatory work for the adoption and localization of such technologies in the future. 4. Coal-to-natural gas. With tight energy supplies, the domestic energy market has currently become quite active. Affected by various factors such as **policies and domestic demand for natural gas, many energy companies in China are currently competing to invest in coal-to-natural gas projects. Although there are high expectations for the development of natural gas, coal-to-natural gas is after all a type of coal chemical project; in its actual operation, it must overcome challenges related to raw material costs, energy conservation and emission reduction, as well as transportation issues. The traditional coal-to-natural gas process involves gasification of coal to produce syngas, which is then converted into methane – synthetic natural gas – through a methanation reaction. The second technology is Catalytic gasification, developed by EXXON in the 1970s; it uses potassium carbonate (an alkali supermetal oxide or alkaline earth metal) as a catalyst to react coal with steam to produce methane. The third technology is hydrogasification technology. The first technology for converting natural gas through gasification is a mature industrial technology, while the latter two coal-to-natural-gas conversion technologies are new technologies in the research and development stage. Currently, all coal-to-natural gas projects under construction or in the preliminary research phase in China employ the first mature process technology, which involves coal gasification and methane conversion. V. Directions for the Development of the Coal Chemical Industry 1. At present, the development of coal chemistry in China is showing signs of overheating. Low-level repetitive construction, which involves expanding the production capacity of various coal chemical products without taking into account environmental carrying capacity, ecological balance, carbon dioxide emissions, or resource consumption, is not the right direction for the development of the coal chemical industry. 2. Given China’s energy structure, which is characterized by a shortage of oil and gas but an abundance of coal, in order to meet the needs of various sectors of the national economy, the production of some key basic chemical products in China (such as synthetic ammonia, PVC, and methanol) will continue to rely on coal as the main raw material for a considerable period of time. The aforementioned traditional coal chemical industry should not pursue capacity expansion in a one-sided manner, but rather should take energy conservation, consumption reduction, and emission cuts as the direction for its development. 3. The total volume of basic chemical products produced from coal as raw material should be aimed at meeting domestic demand, with exports not being encouraged. 4. Develop the modern coal chemical industry by taking technological progress as the main driving force and the clean utilization of coal as the key focus. Modern coal chemical industry should be a resource-saving and environment-friendly industry. 5. Coal-to-oil projects are an important part of the energy security strategy, as well as a significant endeavor in terms of technological innovation. It is necessary to respect scientific and economic laws, carry out pilot projects first, and avoid hasty action. **When deploying coal-to-oil projects, equal emphasis should be placed on introducing foreign technologies and using domestic technologies, with priority given to supporting domestic technologies. Given the three major risks of investment, cost, and technology associated with coal-to-oil production, it is not advisable to establish too many facilities. 6. Converting coal into liquid fuels (gasoline, diesel, methanol); the energy utilization efficiency of coal is too low, which does not conform to the principle of efficient use of coal resources. The extensive development of coal-to-oil and coal-to-methanol processes has had little effect in reducing China’s high dependence on imported oil; instead, it has led to excessive consumption and waste of coal resources. Numerous coal-to-oil projects have temporarily alleviated the dual pressures related to oil and coal supply security, but they have significantly reduced China’s energy security levels, resulting in irreversible and catastrophic consequences. 7. By adopting advanced coal gasification technology to produce gas from low-quality coal, and through an optimized combination of electricity, gas, and chemical products – that is, a cogeneration approach – efficient and clean utilization of coal is achieved.