Process increases viability of biofuels from plant waste

A new process developed on the US could make it more economical to produce biofuels from plant waste, an advance that could eventually reduce reliance on fossil fuels.

plant waste
Image by Andrew Martin from Pixabay

The approach is said to feature an ammonia-salt based solvent that rapidly turns plant fibres into sugars needed to make ethanol. Unlike conventional processes, the new method works well at close to room temperature, according to a Rutgers-led study in the journal Green Chemistry.

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"Our pre-treatment system can slash - by up to 50-fold - the use of enzymes to turn solvent-treated cellulose into glucose used to make bioproducts like ethanol," said lead author Shishir P. S. Chundawat, an assistant professor in the Department of Chemical and Biochemical Engineering in the School of Engineering at Rutgers University-New Brunswick in New Jersey. "Similar processes could greatly reduce the cost of producing biofuels from waste biomass like corn stalks and leaves."

The solvent can also extract more than 80 per cent of the lignin in plant waste. Lignin, which binds to and fortifies plant fibres, could be used to help upgrade valuable aromatic chemicals in the future, according to Chundawat.

The research benefited from collaborative efforts and access to a Bio-SANS (Biological Small-Angle Neutron Scattering Instrument) instrument at Oak Ridge National Laboratory, Tennessee, for analysis of how complex biological systems like plant waste respond during processing to better understand how cellulose is dissolved at a molecular level.

Corn (maize) stalks, leaves and other residue (corn stover) and switchgrass, for example, have tightly packed cellulose microfibrils, which are tiny strands thinner than fibres. Microfibrils are difficult to break down using enzymes or microbes, making it hard to turn many plant-based materials in biomass into biofuels or biochemicals.

Speeding up the conversion of cellulose into sugars like glucose with enzymes requires suitable solvents or heat- and/or chemical-based pre-treatments. According to Rutgers, several solvents that can break down cellulose fibres have been explored, but many are costly or require extreme ranges of operating pressures or temperatures to be effective.

The ammonia-salt based solvent system quickens the conversion of cellulose into sugars using enzymes. It can greatly reduce the cost of biofuels production because enzymes can account for about 15 per cent to 20 per cent of the cost of making biofuels like ethanol from biomass.

Next steps will be to optimise the pre-treatment process for biomass like corn stover, municipal solid wastes and bioenergy crops like switchgrass and poplar that could be turned into fuels, while also developing more robust enzymes to further reduce costs, according to Chundawat.