China team’s super-efficient catalyst turns coal to plastic and other synthetics
Plastics, detergents, adhesives, solvents and synthetic rubbers could be produced without need for petroleum, study finds
The iron-based nanoparticle catalyst converts syngas, or synthesis gas, into hydrogen and carbon-based compounds called olefins by coupling two reactions that separately have limitations but together have synergistic effects.
This process produces olefins with a large variety of uses – including as chemical intermediates for pharmaceuticals, plastics, packaging materials, car parts and clothing – without the need for petroleum.
“This study represents a substantial breakthrough in enhancing hydrogen atom economy for syngas conversion,” the team said in a paper published in the peer-reviewed journal Science on October 30.
Olefins are a class of hydrocarbon compounds – such as ethylene and propylene – that are key building blocks in the production of plastics, detergents, adhesives, solvents and synthetic rubber.
They are mainly produced by breaking down petroleum using high heat or converting methanol using catalysts, which can have limited efficiency and produce substantial waste by-products, including carbon dioxide.
Syngas is mainly composed of hydrogen and carbon monoxide and is derived from heating carbon-rich materials such as biomass, waste, natural gas or coal.
“Direct synthesis of olefins from syngas can enable the production of value-added chemicals from versatile resources that substitute for petroleum oil, such as coal, biomass or natural gas,” the scientists said in the paper.
However, the hydrogen atom economy – a measure of how efficiently a reaction uses its hydrogen atoms to make a desired product – of the direct conversion of syngas to olefins is typically low, meaning a lot of hydrogen is wasted as by-products.
“This limitation not only increases production costs but also raises environmental concerns, prompting the need for innovative catalytic solutions in the emerging technology of direct syngas to olefins,” the team wrote.
Using a novel iron-based catalyst, the team was able to convert syngas to olefins with an improved hydrogen atom economy, with by-products being fed back into the reaction for more efficient olefin production.
This allowed for a hydrogen atom economy of 66 to 86 per cent, far surpassing the 43 to 47 per cent in the traditional methanol-to-olefins conversion pathway. There was a 46 per cent reduction in waste emissions compared with the traditional method.
“It also provides a sustainable alternative to existing olefin production technologies, offering great potential for the resource-efficient transformation of the olefin industry and contributing to the achievement of carbon neutrality goals,” the team said.
According to the paper, the catalyst achieves this by coupling two important reactions – one that converts carbon monoxide and steam into hydrogen, along with another that builds olefins.
This turns a multi-step process into a more hydrogen-efficient single step that requires less steam and produces less waste water and carbon dioxide, despite the syngas having a lower-than-ideal hydrogen ratio to start with, according to the paper.
The catalyst achieved a carbon monoxide conversion rate of around 95 per cent, while olefin selectivity – the proportion of olefins produced relative to total hydrocarbon products – exceeded 75 per cent. Performance was also stable over 500 hours of testing.
“Starting from syngas with low hydrogen/carbon monoxide ratios, the authors achieved high olefin selectivity and hydrocarbon yield, along with a reduction in CO2 and water by-products that led to high hydrogen atom economy,” Phil Szuromi, deputy editor of Science, said in an editor’s note for the paper.
The team said that the catalyst with a superior hydrogen atom economy for the syngas-to-olefin reaction would provide a sustainable olefin production route compared with present methanol-to-olefin technology.