The coal route focuses on upgrading methanol-to-aromatics – An analysis of the aromatic compounds production technology route (Part 2)

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The coal route focuses on upgrading methanol-to-aromatics – An analysis of the aromatic compounds production technology (Part 2). Author/Source: China Chemical Industry News. Date: 2016-08-25. Clicks: 9. Source: Methanol-based production of aromatic compounds is regarded by the industry as an inevitable option for reducing dependence on external sources of these compounds and diversifying the raw material supply. Reporters from China Chemical Industry News learned at the 2016 China Aromatic Hydrocarbons Industry Chain Development Conference that in the production of aromatic hydrocarbons via the coal route, the coal-to-methanol stage is already relatively mature, while research efforts are primarily focused on the methanol-to-aromatic hydrocarbons stage. Our country was among the first to conduct research on the production of aromatics from methanol, and its related technologies are at the world’s leading level. Currently, the domestic technologies that possess independent intellectual property rights include fixed-bed methanol-to-aromatics technology, fluidized-bed methanol-to-aromatics technology, and toluene-methanol methylation-based aromatics production technology, among others. Fixed-bed process: It boasts the highest energy efficiency level in China. Methanol-to-aromatics is a process in which methanol, under the action of catalysts, undergoes a series of reactions to be converted into aromatics, with benzene, toluene, and xylene being the main products. The fixed-bed methanol to aromatics technology developed by the Shanxi Institute of Coal Chemistry, Chinese Academy of Sciences, and other institutions belongs to the category of large-scale downstream conversion technologies for methanol. Using MoHZSM-5 (ion-exchange) molecular sieves as catalysts and methanol as the raw material, the target product is aromatics; this technology has enabled the one-step conversion of methanol into high-quality aromatics under fixed-bed conditions for the first time in China. This technology was successfully tested for the first time in February 2012 at the 100,000 tons per year methanol-to-aromatics plant of Qinghua Group in Inner Mongolia, which was designed by Saiding Company. This is China’s first one-step methanol-to-aromatics plant, designed by Saiding using a process developed in collaboration with the Shanxi Coal Chemical Research Institute. According to Dr. Liu Ping from the Key Laboratory of Coal Conversion at the Shanxi Coal Chemistry Institute, this technology has since been put into use in places such as Yunnan Xianfeng, Tangshan in Hebei, and Xinjiang Xinye, with a total production capacity of 800,000 tons per year. In February this year, the 100,000 tons per year methanol-to-aromatics plant built by Shaanxi Baonit Chemical Group was put into operation successfully, producing 300 tons of aromatics per day, which is close to the designed capacity. 2.46–2.48 tons of methanol are consumed per ton of product, achieving the best energy efficiency among similar domestic installations. Fluidized bed process: Products are superior to those produced via the petroleum route. The circulating fluidized bed methanol-to-aromatics technology (FMTA) is a highly notable technology developed by Tsinghua University. At the 2016 China Aromatic Hydrocarbons Industry Chain Development Conference, Professor Qian Weizhong from Tsinghua University presented the development progress and latest advancements of this technology. The series of engineering challenges they overcame included the rapid deactivation of catalysts, which necessitated the use of fluidized bed continuous reaction regeneration technology ； For the one-way conversion of methanol, a separate reactor is required for the cyclic conversion to aromatics ； Due to complexities such as the reaction and regeneration process under pressure, catalysts for the conversion of methanol into aromatics were first developed internationally, along with a fluidized-bed continuous reaction and regeneration technology suitable for large-scale industrial production. In January 2013, the world’s first industrial pilot plant for producing aromatics from methanol on a scale of 10,000 tons using this technology was successfully commissioned at the Huadian Coal Industry’s coal chemical complex in Yulin, Shaanxi. The methanol conversion rate of this technology is >99.99%; 1 ton of aromatics can be produced from 3.07 tons of methanol. The entire process has a short technical flow, and the products obtained are superior to those produced via the petroleum route. Huadian Coal Industry Group recently revealed that the preliminary work for its industrial demonstration project for producing aromatics from coal-based methanol using this technology is progressing smoothly. The process package for converting methanol into aromatics, which is the core component of this project, has been developed jointly by Huadian Coal Industry Group, Tsinghua University, and CNPC East China Design Institute. The environmental impact assessment report for this project will be submitted to the Ministry of Environmental Protection for approval in the near future, and its water resource assessment report has also been submitted for approval. A 10,000-ton methanol-to-aromatics plant consumes less than 3 tons of methanol to produce 1 ton of aromatics; in the case of a million-ton plant, the methanol consumption per ton of aromatics is expected to drop to 2.5–2.8 tons, while high-value products such as liquefied gas and hydrogen are also produced. Among them, the by-produced hydrogen, when returned to the methanol plant, can increase methanol production by 12%, thereby significantly reducing the overall cost of aromatics. By then, coal-based aromatics will not only have a significant cost advantage over the petroleum-based route, but will also be more advantageous compared to DMTO, as the price of aromatics is generally higher than that of olefins, while the consumption of methanol as a raw material remains similar to that in DMTO. Methylation process: A new process route that integrates coal chemical industry and petrochemical industry to produce p-xylene (PX) through the methylation of toluene and methanol. Currently, the price of methanol in the market is less than 2,000 yuan per ton, while toluene costs around 5,000 yuan per ton. Therefore, the greatest advantage of this process technology is that it uses toluene and low-cost methanol as raw materials to produce high-concentration PX. Some representatives at the meeting argued that the promotion of this technology can not only effectively alleviate the issue of overcapacity in domestic methanol production, but also provide strong technical support for future capacity expansions of aromatic compounds production facilities, as well as for adjusting the structure of raw materials and products used in aromatic compound production, thereby achieving diversification of aromatic compound raw materials. 　 On October 23, 2012, the technology for producing PX and low-carbon olefins from toluene and methanol, developed by the Dalian Institute of Chemical Physics of the Chinese Academy of Sciences, passed evaluation. This technology employs a circulating fluidized bed process to simultaneously produce PX and low-carbon olefins such as ethylene and propylene with high selectivity, all within a single reaction system using one catalyst. This technology can be used as a technical upgrade for existing aromatic compound plants to increase PX production and reduce the energy consumption of these plants ； It can also be applied to newly built aromatic compound complexes; compared with traditional PX production technologies, it reduces the investment and operating costs associated with units for processes such as disproportionation and isomerization ； If a separate unit for producing PX and low-carbon olefins from toluene and methanol is built, expensive adsorption separation units can be replaced with simple crystallization separation units, **thereby reducing the production cost of PX. According to the reporter’s understanding, Sinopec is also an active adopter of the process route for producing PX via toluene methanol methylation. In March 2015, the world’s only industrial demonstration plant capable of producing 200,000 tons per year of xylene through toluene-methanol methylation using Sinopec’s process was put into operation at Yangzi Petrochemical. This plant not only produced high-concentration PX but also generated only minimal amounts of by-products in the form of benzene and C9. In the new process, the introduction of methanol improves the utilization rate of toluene; theoretically, only 1 ton of toluene is required to produce 1 ton of PX, whereas in the traditional toluene disproportionation process, about 2.5 tons of toluene are needed per ton of PX produced, with more benzene as a by-product. Therefore, the new process features high yield and low cost, linking petrochemicals and coal chemicals. Other processes: Refining details for industrialization. In addition to the aforementioned technologies, the Research Institute of Henan Coal Chemical Group is also working together with Beijing University of Chemical Technology to develop technologies for producing aromatics from coal-based methanol, and a relatively complete set of such technologies has been established so far ； The Shanghai Research Institute of Petrochemical Technology, Sinopec, uses molecular sieve (ZSM-5) catalysts loaded with dehydroxide species. Laboratory scale tests of these catalysts have been completed, showing an aromatic yield of over 50% for a single conversion process, with a selectivity of more than 80%. Currently, they are working with relevant organizations on pilot-scale studies of the methanol-to-aromatics technology. Although significant progress has been made in the research and development of coal-based aromatic compounds, their current industrialization is not entirely satisfactory. At the meeting, some representatives told reporters that this is mainly due to current low oil prices, which enhance the competitiveness of aromatic compounds produced through oil-based routes, while the development of coal-based routes is hindered. However, some experts believe that China’s resource endowments and its high external dependence on PX, at 57%, determine the strategic significance of coal-based aromatics. Meanwhile, compared to the petroleum-based route for producing aromatics, the methanol-based route can reduce costs by about 20%, and the resulting aromatics have a high xylene content; they are free of impurity elements such as sulfur and nitrogen, making them more suitable for PX production. Therefore, it is imperative for researchers to improve the relevant process details as soon as possible and make comprehensive preparations for industrialization.