Does crude methanol contain benzene?

If it is synthesized from methanol, the presence of toluene is almost impossible; methanol aromatization requires a selective catalyst, and the reaction temperature is also different from that used in methanol synthesis. It is recommended to check whether it has been mixed in from subsequent processes

The methanol synthesis unit of this enterprise is designed for a pressure of 6.0 MPa; a total of 73 cubic meters of catalyst are installed in the two towers, and the methane content in the feed gas is 11%. It was put into operation in March 2013; due to the small heat exchange area of the gas heat exchanger at the inlet of the synthesis tower, the temperature of the gas entering the tower was low. Currently, the exit temperature from the tower is 235°C, while the inlet temperatures are 188°C and 191°C. At the beginning of operation, the tower exit temperature was 215°C, with an even lower inlet temperature. Gas-to-gas heat exchangers often suffer from wax formation, and even gel-like substances may appear; high-pressure steam is required for cleaning during shutdown.

The company’s designed methanol production capacity is 200,000 tons per year, and the current production level is satisfactory. The current operating pressure is 5.9 MPa. The composition of the gas fed into the tower is as follows: hydrogen 43.29%, carbon monoxide 17.22%, carbon dioxide 2.74%, methane 34.11%, nitrogen 2.63%; hydrogen 55.59%, carbon monoxide 29.54%, carbon dioxide 2%. 17%, methane 10.02%, nitrogen 2.57%

The Shanxi Institute of Coal Chemistry, Chinese Academy of Sciences, has collaborated with Saiding Engineering Company on the fixed-bed methanol-to-aromatics technology. Using methanol as the raw material and a modified ZSM-5 molecular sieve as the catalyst, this process facilitates the catalytic conversion into products primarily consisting of aromatics under conditions of an operating pressure of 0.1–5.0 MPa, an operating temperature of 300–460°C, and a liquid feed rate of 0.1–6.0 h^-1； The gaseous product, low-carbon hydrocarbons, is separated from the liquid product, C5+ hydrocarbons, through cooling and separation ； The liquid-phase product C5+ hydrocarbons are separated by extraction to yield aromatic and non-aromatic compounds. This invention features high overall selectivity for aromatics and flexible process operation. This technology belongs to large-scale downstream conversion technologies for methanol, with aromatic compounds primarily consisting of BTX as the target products. Using MoHZSM-5 (ion-exchange) molecular sieve as a catalyst and methanol as the feedstock, at T = 380–420°C, atmospheric pressure, and an LHSV of 1 h^-1, the methanol conversion rate exceeds 99%, the selectivity of the liquid-phase products is greater than 33% (on a mass basis of methanol), while the selectivity of the gas-phase products is less than 10%. The aromatic content in the liquid-phase product is greater than 60%. The laboratory catalyst screening and evaluation as well as repeated regeneration tests have been completed; the single-pass lifetime of the catalyst is over 20 days, with an estimated total lifetime of more than 8,000 hours. The collaborative development of this technology has entered the industrial demonstration phase, and the engineering design and construction of the industrial demonstration plant (10,000–100,000 tons/year of methanol) have been completed. At the end of February 2012, the 100,000-ton/year methanol-to-aromatics plant built by Saiding Company for Inner Mongolia Qinghua Group completed its initial commissioning successfully, and the project was put into operation smoothly. This is China’s first methanol-to-aromatics plant, designed using the patented technology of \"a process for producing hydrocarbon products from methanol in one step,\" which Saiding developed in collaboration with the Shanxi Institute of Coal Chemistry, Chinese Academy of Sciences. On July 5, 2012, the second phase of Qinghua Group’s projects involving the lightweight processing of 500,000 tons of coal tar, the production of aromatics from 100,000 tons of methanol, and logistics facilities capable of handling 10 million tons, began construction in the development zone of Alxa League in Inner Mongolia. The Qinghua Group’s project for the lightening of 500,000 tons of coal tar per year requires a total investment of 4.28 billion yuan. The construction includes a raw material pre-distillation unit, dehydration and tailing removal units, reaction units, and distillation units. It also encompasses facilities for producing hydrogen from coke oven gas, storage and transportation systems, 2×75 tons/hour circulating fluidized bed boilers, as well as supporting facilities for power supply, water supply, and environmental protection. Once completed, the project will be able to produce 122,200 tons of Light Coal Tar No. 1, 285,000 tons of Light Coal Tar No. 2, and 80,380 tons of coal tar pitch per year. Once the project for producing 100,000 tons of aromatic compounds per year from methanol is put into operation, it will be able to produce 75,000 tons of aromatic compounds, 22,500 tons of liquefied gas, and 3,400 tons of dry gas per year. This project has advantages such as abundant raw material sources, mature technology, adjustable ratios of ethylene and propylene in the products, and low emissions of waste gases, wastewater, and solid waste.

Tsinghua University’s circulating fluidized bed methanol-to-aromatics technology (FMTA); Datang International is building a 1 million tons per year purified terephthalic acid (PTA) plant in Dolun, Inner Mongolia. The core technology of this project is Tsinghua University’s Methanol to Aromatics (FMTA) technology. It utilizes a fluidized-bed reactor, and the pilot plant with an annual capacity of 10,000 tons of aromatics (xylene) produces these aromatics from methanol sourced from the first phase of the Tolon Coal Chemicals project. Tsinghua University has also joined forces with Hualu Company to build an industrial pilot plant for the production of aromatics from methanol, with a capacity of 30,000 tons per year. China Huaneng Group plans to build the first pilot-scale and industrial-scale coal-to-aromatics facility in the Yuheng Coal Chemical Industry Zone of the Northern Shaanxi Energy and Chemical Industry Base, thereby establishing a completely new technology route for the production of aromatics. In accordance with the project development plan, China Huaneng will first construct a pilot plant for coal-to-aromatics production on a ten-thousand-ton scale, while simultaneously launching an industrial demonstration project on a million-ton scale, comprising facilities for coal-to-methanol production at 3 million tons per year and aromatic compounds production at 1 million tons per year. The circulating fluidized bed coal-to-aromatics (FMTA) technology, developed by Tsinghua University and featuring independent intellectual property rights, uses methanol as its raw material. The experimental plant with a capacity of 100 tons per year has been operating stably for over a thousand hours, meeting the requirements for industrial pilot-scale production. 　 At the end of March 2011, the HuanDian Yuheng coal-to-aromatics demonstration project began construction in Yulin, Shaanxi. The total investment in this project is approximately 38.1 billion yuan. It utilizes the flow-bed methanol-to-aromatics technology, which was developed by Tsinghua University and holds independent intellectual property rights, to build a plant capable of producing millions of tons of methanol-to-aromatics products from coal. In 2011, an investment of 100 million yuan was made first for a 10,000-ton industrial pilot project. In mid-January 2013, Donghua Technology Company issued a announcement stating that the world’s first pilot-scale coal-to-aromatics plant, built by Shaanxi Huadian Yuheng Coal Chemical Co., Ltd. in the Northern Shaanxi Energy and Chemical Industry Base and under the general contracting of this company, had produced aromatics; the initial trial run was successful, completing the entire production process. It is reported that the Huadian project plans to build a plant for producing aromatics from coal-based methanol on a scale of one million tons; this pilot plant is part of the first-phase industrial trial project for producing aromatics from methanol on a scale of 10,000 tons. In early February 2013, the 10,000-ton-per-year fluidized-bed methanol-to-aromatics industrial pilot project, funded by Huadian Coal Industry Group and developed through a collaboration between Huadian Coal Industry and Tsinghua University, was successfully implemented in the Yulin-Yuheng Coal Chemical Industrial Park in Shaanxi Province. In the first batch of feed, the conversion rate of methanol was higher than 99.99%, and the content of ** (primarily toluene, xylene, and trimethylbenzene) in the oil-phase products exceeded 90%. As of January 15, approximately 100 tons of methanol raw material had been fed in total. The plant operated steadily for 54 hours, and the industrial test unit achieved successful ignition on the first attempt as well as a successful trial run with feedstock, thereby establishing the key processes.

The coal-based methanol to aromatics technology, developed through a collaboration between the Research Institute of Henan Coal Chemical Group and Beijing University of Chemical Technology, passed its mid-term evaluation at the end of August 2011. This technology enables the production of aromatics to shift from the traditional petroleum-based approach to a coal-based one. Since its launch in June 2010, the Research Institute of Henan Coal Chemical Group and Beijing University of Chemical Technology have carried out extensive research on topics related to this project, including the improvement of the performance of methanol aromatization catalysts, the development of xylene isomerization and benzene serta toluene alkylation processes, as well as the design of processes for producing aromatics from coal-based methanol. Significant progress has been achieved so far. This project identified the optimal catalyst and suitable process conditions for the reaction, specified the plant scale, the preliminary design of the reactor, and the parameters of key equipment, thereby establishing a relatively complete technology for producing aromatics from coal-based methanol. All technical specifications have met the expected goals; indicators such as the catalyst’s single-pass lifetime and the benzene alkylation conversion rate have exceeded expectations and reached high levels. Next, the researchers will accelerate the design of the 10,000-ton-scale process package to lay a solid foundation for the subsequent pilot-scale production of aromatics from methanol. In addition, China Five Rings Engineering Co., Ltd. has also carried out a pilot-scale design for the catalytic conversion of methanol to aromatics.

In a certain company’s synthetic oil production process, the pure methanol coming from the methanol storage tank is pressurized to 2.0 Mpa by a methanol pump, with a flow rate of 38.8 m3/h. It then enters the tube side of the methanol preheater, where it exchanges heat with the reaction gas on the shell side to reach a temperature of 160°C and a pressure of 1.95 Mpa. Next, it goes into the shell side of the methanol evaporator, where it vaporizes and exchanges heat with the reaction gas again to reach a temperature of around 162°C and a pressure of 1.9 Mpa. Finally, it passes through the tube side of the methanol superheater, where it exchanges heat with the reaction gas once more to be superheated to 340°C before joining the recycled gas and entering the synthetic oil reactor. Under the action of a catalyst, it is synthesized into a mixture of water, hydrocarbons, and hydrogen. After leaving the tower, the reaction mixture enters the subsequent system in two streams: the first stream goes to the methanol superheater for heat exchange (a small portion goes to the steam generator to produce steam) ； The second stream goes to the tube side of the circulating gas heat exchanger for heat exchange (a portion of it enters the sampling system for data analysis) ； The most important aspect is to ensure that, after the gas exiting the tube side of the methanol superheater and the gas that has been heated in the recycle gas exchanger are combined, their temperature remains above 320°C before entering the synthetic oil reactor; the remaining gas is then used to generate steam in the steam generator. The gas mixture, formed at the outlet of the methanol preheater shell side, the outlet of the methanol superheater shell side, and the main pipe outlet of the synthetic oil reactor, is combined at a temperature of around 110°C. It then enters the syngas air cooler where its temperature is reduced to 80°C, and further cooled to 40°C in the syngas cooler shell side. Finally, gas, liquid, and water are separated in the oil-water separator. The crude gasoline is pumped by a feed pump to the oil separation unit for fractional distillation, thereby yielding the final product. Most of the gas is pressurized to 2.0 Mpa by the recycle gas compressor, then enters the shell side of the recycle gas heat exchanger where it is heated to above 320°C before merging with superheated methanol and entering the synthetic oil reactor. A portion is sent as bleed gas to the feed tank of the absorption tower in the oil separation unit to absorb hydrocarbons, thereby maintaining a certain level of inert gas in the system to facilitate the synthesis reaction. Process water is sent to biological treatment via process pumps.

Based on the above analysis, no benzene should be produced during the methanol synthesis process; however, the gas-to-gas heat exchanger in the company’s methanol synthesis tower became clogged with gel-like substances, and high-pressure steam was used to clean it during shutdowns. It is worth in-depth study.

It mainly depends on the benzene content. Trace amounts of benzene are present in the CO2 removed from syngas