Boosting biofuel efficiency

PurdueUniversity chemical engineers claim an environmentally friendly process for producing liquid fuels from biomass could provide all of the fuel needed for the entire US transportation sector.

The new approach modifies conventional methods for producing liquid fuels from biomass by adding hydrogen from a ‘carbon-free’ energy source, such as solar or nuclear power, during the gasification step. This suppresses the formation of carbon dioxide and increases the efficiency of the process, making it possible to produce three times the volume of biofuels from the same quantity of biomass, said Rakesh Agrawal, Professor of Chemical Engineering at Purdue.

The researchers are calling their approach a ‘hybrid hydrogen-carbon process,’ or H2CAR.

‘Further research is needed to make this a large-scale reality,’ Agrawal said. ‘We could use H2CAR to provide a sustainable fuel supply to meet the needs of the entire US transportation sector – all cars, trucks, trains and aeroplanes.’

A conventional method for turning biomass or coal into liquid fuels involves first breaking down the raw material with a chemical process that gasifies it into carbon dioxide, carbon monoxide and hydrogen. Then those constituents are turned into a liquid fuel with other processes.

In the H2CAR concept, hydrogen would be harvested by splitting water molecules by electrolysis. Then the hydrogen would be added during the gasification step, making the process more efficient by suppressing the formation of carbon dioxide and converting all of the carbon atoms to fuel.

When conventional methods are used to convert biomass or coal to liquid fuels, 60 per cent to 70 per cent of the carbon atoms in the starting materials are lost in the process as carbon dioxide, a greenhouse gas, whereas no carbon atoms would be lost using H2CAR, Agrawal said.

‘This waste is due to the fact that you are using energy contained in the biomass to drive the entire process,’ he said. ‘I’m saying, treat biomass predominantly as a supplier of carbon atoms, not as an energy source.’

Other researchers have estimated that the United States has a sustainable supply of about 1.4 billion tons of biomass each year that could be used specifically for the production of liquid fuels. With conventional methods, that quantity of biomass would provide 30 per cent of the fuel required for the nation’s annual transportation needs. But the same quantity of biomass would provide enough fuel to meet all transportation needs using the new H2CAR method, Agrawal said.