Innovation

Bioprocess converts waste gas into liquid fuel

Researchers from the Massachusetts Institute of Technology (MIT) have discovered a form of bioconversion that could be used to convert waste gases to biodiesel for transportation.

The ‘Integrated bioprocess for conversion of gaseous substrates to liquids’ report, published in the Proceedings of the National Academy of Sciences (PNAS) journal yesterday (7 March), describes the process of converting syngas – synthetic gas that predominantly includes a mixture hydrogen, carbon monoxide and carbon dioxide – into liquid lipids that can be used as fuels.

The bioconversion involves two main steps, the first of which processes syngas into acetic acid (concentrated vinegar) in an anaerobic bioreactor using bacteria  The acetic acid is then used as a substrate for an oil-producing yeast, which aerobically converts it into lipids.

Researchers say the bioprocess has been trialled successfully at a pilot plant in China. The productivity was found to be 0.19 grammes per litre of acid per hour, although the authors claim that ‘the system can be further optimised’.

Transportation was responsible for 27 per cent of global gas emissions in 2013, according to the US Environmental Protection Agency (EPA), and biofuels have been seen as a possible replacement to fossil fuels. The discovery of this bioconversion has the potential to turn waste gases from power stations into low-carbon liquid fuels.

MIT owns the patent for the process, and licensed GTL Biofuel Inc to run the pilot plant outside Shanghai from September 2015. A larger ‘semi-commercial’ demonstration plant, 20 times the size, is now planned for construction.

Fuel ‘can replace gasoline or diesel’

Professor Gregory Stephanopoulos, of the Chemical Engineering Department at MIT, told the Guardian: “This will test if the process can be scaled up and evaluate its costs and carbon footprint. It is one thing to do it on a scale of 1-2 litres in the lab, but a different story to move up 1,000 litres and then 20,000 litres in the demonstration plant.”

Fuels from renewable resources need to be from “low-cost feed stocks”, Stephanopoulos commented. Manure and farm waste, along with other waste, is a “promising source of the syngas required”, he said.

Stephanopoulos argues that the current practice of burning the biogas that is already produced across Europe to produce electricity is ‘wasteful’, and that converting it into a liquid biofuel that could be used for transport would be better. Speaking of the practice of burning syngas for electricity, he added: “It is very costly and can only survive due to subsidies. [It is better] to use the gas to produce fuels that can replace gasoline or diesel.”

The full paper can be read at the PNAS website.