Nick Carne
A Sino-Dutch research team claims to have made an important breakthrough it says improves the financial and environmental viability of coal to liquid (CTL) fuels.
There has been considerable debate for more than a decade about the potential to use CTL as an alternative to oil and gas, particularly in countries with plenty of coal. In recent years, China has shown significant interest.
Technical issues aside, one of the main stumbling blocks to date has been the large amount of carbon dioxide released during the CTL process.
And that is where the researchers from the National Institute of Clean-and-Low-Carbon Energy in Beijing, China, and Eindhoven University of Technology in the Netherlands come in. Writing in the journal Science Advances, the team, led by Beijing’s Peng Wang, says it has found a way to capture the carbon dioxide as well as substantially reduce operating costs.{%recommended 8006%}
The key is a new type of catalyst to be used in the Fischer-Tropsch reactor, the part of the process in which carbon monoxide and hydrogen are converted into liquid hydrocarbons.
The CTL process is complicated, requiring coal to be converted first to syngas – a mixture of carbon monoxide (CO) and hydrogen – and then to a liquid. Some of the CO is taken out of the syngas by converting it to CO2, in a process called water-gas shift.
The researchers discovered that the carbon dioxide release is triggered because the iron-based catalysts in the reactor are not pure. They have developed an alternative catalyst using a type of iron carbide, called epsilon iron carbide, which they say generates almost no CO2 at all. Any that is been produced can be easily removed at the water-gas shift stage.
“We are aware that our new technology facilitates the use of coal-derived fossil fuels,” says Eindhoven’s Emiel Hensen.
“However, it is very likely that coal-rich countries will keep on exploiting their coal reserves in the decades ahead. We want to help them do this in the most sustainable way.”
Hensen says the results are likely to reduce efforts to develop CTL catalysts based on cobalt. While these do not have carbon dioxide problems, they are expensive and cobalt is in high demand for use in batteries.
Hensen also expects the new catalysts will play a role in the future energy and basic chemicals industry. The feedstock will not be coal or gas, but waste and biomass. Syngas will continue to be the central element, as it is also the intermediate product in the conversion of these new feedstocks.
