Low-carbon coal extraction seen as game-changer
New synthesis technique doubles the yield of raw materials used in a range of industrial products
Chinese scientists claim to have made significant advancements in the production of low-carbon compounds derived from coal, which could yield substantial economic benefits, and have far-reaching implications for the country’s energy and resource security.
The research has centred on olefins – also known as alkenes – a class of chemical compounds that serve as important raw materials in the production of various industrial products such as plastics, pharmaceuticals, cosmetics, and even spacecraft.
Olefin production has traditionally relied on petroleum, but synthesising them from coal involves a far more complex process.
In endeavouring to produce olefins from coal, the researchers said they were able to double the yield of the previous international record, according to a paper published in the peer-reviewed journal, Science, on May 19.
By harnessing a new synthesis technique, the research team said it was able to produce a light-olefin yield of 48 per cent, much more than the previously confirmed yield of less than 27 per cent.
Light olefins refer to olefins with fewer carbon atoms, such as ethylene, propylene and butenes.
The traditional synthesis method, known as the FischerTropsch process, believed to date back to the early 1920s, begins with converting coal into a mix of carbon monoxide and hydrogen. The gas mixture, called syngas, is then transformed into olefins. The conversion happens with the help of a specific catalyst – the key element in the process. However, the efficiency of such reactions has always been limited.
In 2016, a research team led by Professor Pan Xiulian and academic Bao Xinhe from the Dalian Institute of Chemical Physics (DICP) first proposed a new synthesis technique known as OXZEO. This method used a composite catalyst system that separated the decomposition of the reactants from the formation of products. By separating these two processes, the reaction efficiency was significantly increased.
For the first time, OXZEO managed to shatter the classical limit of the Fischer-Tropsch synthesis, raising the selectivity of light olefins from 58 to 80 per cent when the conversion rate of carbon monoxide was 17 per cent.
The method also consumed less water and emitted fewer exhaust gases because of its higher conversion rate.
Still, the reaction had its limitations – it was not possible to simultaneously increase the conversion rate and selectivity. Achieving a higher conversion rate of carbon monoxide meant that the proportion of olefins in the product would decrease.
Conversely, achieving a highly pure product meant that the conversion rate of reactants would decrease.
After another seven years of research, the team was able to improve the catalyst system, which not only promoted the reaction rate, but also suppressed the occurrence of side reactions.
While maintaining a selectivity of more than 80 per cent for light olefins, the catalyst has now achieved a conversion rate of 85 per cent for carbon monoxide.
China’s ethylene industry has seen booming development in recent years, while further establishing a global reputation.
In 2019, China’s ethylene production capacity surpassed Europe’s for the first time. In 2021, it eclipsed the Middle East.
Last year, China’s ethylene production capacity of 49.33 million tonnes surpassed that of the United States, which recorded 43.3 million tonnes for the year. The milestone made China the world’s largest producer of ethylene.
“Most ethylene production has used petroleum as a direct raw material. But for China, which is rich in coal but lacks petroleum resources, technology that converts coal to ethylene is strategically significant,” said an analyst with the China National Petroleum Corporation in the Chinese journal International Petroleum Economics.
“Once scaled up, the technology could reduce China’s dependence on petroleum in chemical production,” he said.
In 2020, the technology behind OXZEO – Nano-confined Catalysis – took top prize at the State Natural Science Awards, one of the highest awards for scientists in China.
“In 2020, in collaboration with industry partners, the DICP completed an industrial pilot test that could produce 1,000 tonnes of olefins per year. Now that the reaction yield has been doubled, it’s expected that industrial applications will be further accelerated,” said an official report on the DICP’s website.
Pan said: “The design idea behind OXZEO should have universal applicability for similar catalyst systems and will fundamentally promote further development in the field of molecular catalysis research.”