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http://www.mhg114.com/forum.php?mod=viewthread&tid=106584 Coal contains volatile substances such as tar and gas. The differentiated use of coal involves separating the various components within coal through pyrolysis, including methane, hydrogen, tar, and semi-coke. Tar hydrogenation can also produce gasoline and diesel. The differentiated use of coal has two practical advantages: first, it enables more efficient and thorough utilization of resources; second, semi-coke is effectively purified through pyrolysis to become a clean fuel with low volatile matter and low sulfur content. Replacing bulk coal with semi-coke can help reduce air pollution. Therefore, the differentiated utilization of coal is regarded by many experts as an effective way to achieve clean and efficient use of coal; it represents the most ideal approach for coal processing and utilization, and it is also a key development direction for coal chemical industry during the 13th Five-Year Plan period. The image shows Honghui Energy Chemical Company’s project for the differentiated utilization of 10 million tons of coal. (Photographed by Wang Hong) However, in an era of low oil prices, despite the good performance shown by enterprises engaged in the selective use of coal in recent years, which has been recognized by the industry, the downstream products derived from coal utilization, such as diesel and naphtha, have experienced significant price drops ； On the other hand, semi-coke, an important product of coal utilization based on different quality levels, is facing both overproduction and a lack of cost-effective utilization methods; as a result, the economic viability of the product chain resulting from such differentiated coal utilization is under scrutiny. In the interviews, industry experts believe that as the use of coal in a differentiated manner is gaining momentum at present, if the industry is to develop further and better, careful consideration must be given to the downstream product pathways resulting from such differentiated use of coal. Diesel: It is feasible to produce diesel that meets national standards. One of the key advantages of the differentiated use of coal lies in its use for producing diesel. Coal pyrolysis produces coal tar, and diesel can be manufactured by hydrogenating coal tar; this approach requires less investment compared to direct or indirect methods of converting coal into oil. However, the diesel produced falls short of the national standards; although it has a low freezing point, low sulfur content, and low nitrogen content, its cetane number and levels of polycyclic aromatic hydrocarbons are on the low side. “The comprehensive performance of diesel produced by the hydrogenation of coal tar does not meet the standards for National III vehicle diesel. ”Zhang Jianqiang, deputy general manager of Gansu Honghui Energy Chemical Co., Ltd., said that the cetane number of diesel produced by the hydrogenation of coal tar is less than 40, while the cetane number required for diesel used in vehicles meeting National Standard III is at least 49. Therefore, it can only be used as a component in diesel blending and cannot be directly used as fuel in motor vehicles. In the future, coal will continue to play a dominant role in China’s energy consumption for a long time, and its utilization must follow a path of clean and efficient conversion. The image shows the Yanchang Petroleum coal, oil, and gas resource comprehensive conversion project. (Photographed by Guohua) Zhang Jianqiang said that in an era of high oil prices, diesel produced through the hydrogenation of coal tar has no trouble finding buyers, and the enterprises that have started producing it have achieved good economic returns. Affected by the sharp drop in international crude oil prices and the continuous reduction in domestic refined oil prices, the price of diesel produced through coal tar hydrogenation has fallen to around 4,000 yuan per ton, which is half of its peak price. When fuel consumption tax is taken into account, companies that produce diesel via coal tar hydrogenation essentially earn no profit and may even incur losses. Meanwhile, the pace of upgrading refined oil in our country is accelerating. Starting from January 1, 2016, key cities in the eastern region began to supply regular diesel with the same sulfur content as that required for vehicles meeting National IV standards. On July 1, 2017, regular diesel meeting National IV standards was supplied nationwide, while the sale of regular diesel that did not meet these standards was halted in the country. Against the backdrop of falling international oil prices and the upgrading of refined petroleum products, China raised the consumption tax on refined petroleum products three times in a row over the past two years. Therefore, the general manager of a company that is developing a project for the differentiated utilization of coal came up with the idea of adjusting the product lines derived from coal tar hydrogenation. He proposed two options for such adjustments: one was to convert the diesel produced through coal tar hydrogenation into regular diesel that meets National IV standards, as well as diesel suitable for use in vehicles under those same standards, so that it could be sold directly in the market ； Secondly, diesel or coal tar is used to produce chemical products, thereby avoiding consumption taxes in a reasonable manner. Liu Huantian, a senior engineer at Qilu Petrochemical, believes that it is feasible to adjust diesel produced from coal tar to meet the National IV standards for regular diesel as well as the National IV standards for vehicle diesel. The diesel produced by Fischer-Tropsch synthesis has a cetane number of 65, and it is free of sulfur, nitrogen, phosphorus, and heavy metal ions; its aromatic hydrocarbon content is also low. However, its drawback is a relatively high freezing point, and its density is lower than that of ordinary diesel, at only a little over 0.7 kilograms per cubic decimeter. The cetane number of polydimethyl methoxypolyethylene averages over 76; when added to diesel, it can lower the dew point of the diesel. With an oxygen content of over 40%, it enables more complete combustion of diesel, thereby significantly reducing emissions of pollutants such as carbon smoke and particles. Diesel produced by the hydrogenation of coal tar, when blended with FTO diesel and polyoxydimethyl ether, can meet the national IV and V standards for vehicle diesel and can be directly supplied to the end market. At present, about 2/3 of China’s diesel consumption is concentrated in areas such as non-road machinery and watercraft, resulting in strong market demand. Li Baoming, deputy chief engineer at Shanxi Danfeng Chemical Co., Ltd., said that it is indeed a feasible approach for the diesel produced via coal tar hydrogenation to be directly sold in the end market after being blended with Fischer-Tropsch diesel and polyoxymethylene dimethyl ethers to meet standards. However, the specific blending methods and proportions still need to be verified. In diesel produced by the hydrogenation of coal tar, a low cetane number indicates a low content of alkanes in the components, along with a high content of naphthenes and aromatics. Therefore, some companies have proposed whether it is possible to extract chemical products from it, as this would not only increase the value of the products but also allow them to avoid consumption taxes. However, from what the journalists have learned, there is still a lack of robust technical support for extracting chemical products from the diesel obtained through coal tar hydrogenation. The reporter learned from experts at relevant design institutes that the total cycloalkanes in diesel produced by coal tar hydrogenation amount to about 54.67%. It is theoretically feasible to produce aromatics through diesel cracking. However, the cycloalkane structure in diesel is complex and difficult to determine. It is challenging to separate and extract diesel into chemical products with a purity of over 99.5%, and it is difficult to quantify the selectivity of the resulting chemical products. Ensuring complete conversion into monocyclic aromatics is problematic from both process and catalyst perspectives, and it is not guaranteed that all of them will be effective single aromatics. According to investigations by reporters, Sinopec has not yet made any breakthroughs in the technology for producing aromatics from diesel; it currently only uses hydrogenation of diesel to produce high-octane gasoline components, rather than extracting aromatics. Naphtha: Industrial validation is still needed for its use in producing aromatics. Besides diesel, the products of coal tar hydrogenation also include naphtha. By adjusting the catalyst and operating conditions, the proportion of naphtha obtained can reach up to 35%–40%. According to the reporter’s understanding, the price of naphtha obtained through the hydrogenation of coal tar is currently around 3,800 yuan per ton, which represents only a slight profit. If an additional consumption tax of 2,300 to 2,400 yuan per ton is imposed, the companies will incur losses. Naphtha is an important raw material for the production of ethylene and aromatics. So, can naphtha produced by the hydrogenation of coal tar also be used to produce ethylene and aromatics? Or can aromatics be directly produced from coal tar? This has also become an issue of concern for industry professionals at present. Some industry experts believe that the route of producing aromatics directly from coal tar is not feasible. Zhu Fangming, deputy general manager of Hunan Changling Petrochemical Technology Development Co., Ltd., told reporters that coal tar contains a high amount of aromatics. In theory, it is possible to obtain aromatics through hydrocracking, but the aromatics obtained are mixtures with a very complex and varied composition; it is difficult to determine the proportions of benzene, toluene, xylene, and p-xylene. The processes of separation and purification are complex and cumbersome. It is only meaningful to produce benzene, toluene, xylene from coal tar for the manufacture of aromatics, with high selectivity for p-xylene, which has the highest market value, and a purity level of 99.95%. Zhu Fangming pointed out that if such standards cannot be met, the production of aromatics from coal tar can only remain a concept. Wan Xuebing, general manager of Shandong Zibo Tailong Catalysis Technology Co., Ltd., also believes that coal tar contains a high level of aromatics and has a very complex composition; therefore, the separation and purification processes aimed at obtaining aromatics such as benzene, toluene, xylene, and p-xylene do not hold any economic value. The higher the content of alkanes in naphtha, the higher the yields of ethylene, propylene, and butadiene obtained from its cracking. According to the standards set by Sinopec and CNPC for naphtha used as raw material in ethylene cracking, the alkane content is required to be at least 55%. According to investigations by reporters, the alkane content in refined naphtha produced through the hydrogenation of coal tar is around 38%, while that in cracked naphtha is about 50% – levels that are difficult to meet the requirements for use as raw material in ethylene cracking. The level of aromatic potential in naphtha directly determines the amount of aromatics that can be produced, as well as the economic efficiency of the plant. The aromatic potential content, also known as the potential content of aromatics, refers to the sum of the content of C6–C10 naphthenes and the content of C6–C10 aromatics in naphtha. Through catalytic reforming, C6 naphthenes are converted into C6 aromatics (benzene), C7 naphthenes are converted into C7 aromatics (toluene), and so on. Meanwhile, C7 aromatics, C9 aromatics, and C10 aromatics are converted into high-value C8 aromatics (mixed xylene) and benzene through disproportionation reactions. At present, the aromatic potential of naphtha produced by coal tar hydrogenation ranges from 45% to 60%, which is higher than that of conventional reforming feedstocks. Naphtha reforming can yield benzene, toluene, xylene, and heavy aromatics with a molecular weight of C9 or higher; the remaining components can be used as blending components for high-octane gasoline. These high-octane gasoline blending components can be sold directly, or companies can use them to formulate National V gasoline by mixing them with externally purchased catalytic gasoline, straight-run gasoline, or alkylated gasoline components, thereby ensuring that the aromatic content meets the quality standards for National V gasoline. Therefore, some technology patent holders and design institutes have proposed several routes for producing finished products: one is the route for producing aromatic compounds such as benzene, toluene, and xylene from naphtha ； The second is the route for producing aromatics and high-octane gasoline products; the products are adjusted accordingly based on changes in the market prices of aromatics and gasoline. If the scale of the facility is large, it is possible to purchase some petrochemical naphtha with a low aromatic content ； Third, after naphtha is used to extract two chemical products such as cyclopentane, it is then isomerized to increase its octane rating, and used as a blending component for National V gasoline ； Fourthly, naphtha is processed through the fine chemical route; after distillation, isopentane, n-pentane, cyclopentane, n-hexane, and cyclohexane are obtained. N-pentane can be used as a foaming agent, cyclopentane can be used as a refrigerant, while n-hexane and cyclohexane serve as high-performance extraction agents. “However, these days it’s usually the case that one expert comes forward with one product route, and another expert proposes another product route; none of these have yet been tested on an industrial scale. ”said Cao Xianyong, a senior engineer at Gansu Honghui Energy Chemical Co., Ltd. In Cao Xianyong’s view, the use of naphtha reforming to produce aromatics still requires industrial-scale verification. Experts believe that the compounds capable of forming aromatics are mostly derived from theoretical calculations based on the PONA value (the composition of alkanes, olefins, cycloalkanes, and aromatics) for individual hydrocarbon components. What is the difficulty level of catalytic processing after naphtha reforming? Dry gas and liquefied gas will increase; how much of it will turn into a liquid state? It is very difficult to determine these issues, and they need to be verified. Also, what is the economic viability after verification? What is the periodicity of the project? It’s also still unknown at the moment. Semicoke: The utilization methods are still under exploration. In the process of differentiated utilization of coal, pyrolyzing 1 ton of coal can produce approximately 0.5 tons of semicoke. The use of semicoke is crucial for the differentiated utilization of coal, and it also affects the efficiency of such utilization at low oil prices. Currently, the semi-coke market is in a state of surplus; therefore, industry experts suggest that to achieve rational utilization of coal, the issue of semi-coke utilization must be addressed properly. Since last year, the Yulin region has been promoting itself as a \"clean fuel\" in order to expand sales channels for semi-coke. There is encouragement to use semi-coke as a substitute for coal used in small boilers, household heating, and the food service industry, thereby reducing various haze-forming precursors associated with coal use in domestic applications and improving urban and regional haze pollution. There is also a significant decline in the large amounts of toxic polycyclic aromatic hydrocarbons emitted indoors by residents. However, due to its lower strength, semi-coke is not tough enough after being processed into shaped coal, making it prone to breaking during long-distance transportation. Moreover, it is more expensive than regular raw coal, so it is difficult for users to give up using raw coal in favor of semi-coke; as a result, the use of semi-coke as a fuel for household heating remains rare. Generating electricity from semi-coke is also less economical than using raw coal. The market price of semi-coke has always been 200 yuan per ton higher than that of lump coal. Moreover, semi-coke has a low volatile content after carbonization, making it difficult to ignite when burned on its own. Existing pulverized coal boilers or circulating fluidized bed boilers are mostly designed for bituminous coal; if semi-coke is to be used, the existing equipment and control systems need to be modified and adjusted, which undoubtedly increases costs. Semicoke can be used as a feedstock for gasification, and combined with coal chemical processes such as Fischer-Tropsch synthesis to achieve multiple product outputs, thus realizing the selective utilization of coal. According to investigations, the partial substitution of raw coal with semi-coke in the production of water-coal slurry gasification has already been implemented on an industrial scale, with the maximum blending ratio reaching 50%. It is understood that in order to produce tar and gas on a commercial scale, the systematic utilization of coal requires larger-scale operations. Currently, the size of individual coal pyrolysis units is increasing steadily. Putting aside the issue of technical maturity, the new vertical retorting furnaces, rotary furnaces, and advanced belt-type pyrolysis units under construction allow for an annual coal pyrolysis capacity per unit that has risen from 100,000 tons with traditional vertical retorting furnaces to 300,000 tons and even 1 million tons, thus laying the foundation for the large-scale utilization of coal in a differentiated manner. Currently, pyrolysis in China can produce approximately 0.5 tons of semi-coke per ton of coal; therefore, a project for the selective utilization of 10 million tons of coal per year would generate 5 million tons of semi-coke annually. “There is too much semi-coke; it can’t be used all. ” That’s what Tang Hongqing, an advisor at Beijing Zhongke Synthetic Oil Engineering Co., Ltd., said. Liu Siming, a senior engineer in the Energy and Chemical Engineering Department of the Petrochemical Planning Institute, told reporters that if semi-coke is used alone to produce water-coal slurry for subsequent gasification, due to its high porosity and large specific surface area, the concentration of the slurry formed after combining semi-coke with water is low, and its slurry-forming properties are poor. With a fixed carbon content of 80% to 85%, it requires a high amount of oxygen. Since semi-coke has already removed the volatiles, low volatile content leads to reduced reactivity and a lower carbon conversion rate as well. Semicoke has a high ash content and high hardness; in some cases, the ash content can reach 35%. As a result, whether it is used to produce water-coal slurry or for dry powder gasification, it tends to cause blockages in the gasification furnace, and the cost of producing effective syngas is also high. “There are solutions for utilizing semi-coke, but no particularly good ones yet; to use it entirely for gasification, a process from experimentation to industrial-scale implementation is required. ” Tang Hongqing said. Some industry experts even suggest that if the gasification of semi-coke is not economical and there is no viable way to utilize it, the diesel produced by hydrogenating the coal tar obtained through pyrolysis does not meet the required standards; in such cases, it is more economical to simply gasify the coal and then use Fischer-Tropsch synthesis to produce oil