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New process could reduce cost of biofuel production from plant waste

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Researchers led by Rutgers University in the US state of New Jersey have developed a new process that could reduce the cost of producing biofuels such ethanol from plant waste.

The process, which features an ammonia-salt based solvent that quickly turns plant fibres into sugars needed to make ethanol, works effectively at near-room temperature, unlike conventional processes.

“Our pretreatment system can slash – by up to 50-fold – the use of enzymes to turn solvent-treated cellulose (plant fibre) into glucose (a sugar) 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. “Similar processes could greatly reduce the cost of producing biofuels from waste biomass like corn stalks and leaves.”

The solvent is able to extract over 80% of the lignin in plant waste, which could be used to help upgrade valuable aromatic chemicals in the future, according to Chundawat.

The research benefitted from collaborative efforts and access to a high-tech Bio-SANS instrument at Oak Ridge National Laboratory for analysis of how complex biological systems such as plant waste respond during processing to better understand how cellulose is dissolved at a molecular level.

Corn stalks, leaves and stover, as well as switchgrass, for example, have tightly packed cellulose microfibrils, which are difficult to break down using enzymes or microbes, making it harder to turn many plant-based materials in biomass into biofuels.

Speeding up the conversion of cellulose into sugars such as glucose with enzymes requires suitable solvents or heat- and/or chemical-based pretreatments. While several solvents able to break down cellulose fibres have been explored, most remain expensive or require extreme ranges of operating pressures or temperatures to be effective.

The ammonia-salt based solvent system speeds up the conversion of cellulose into sugars using enzymes. This can reduce the cost of biofuels production, as enzymes can account for approximately 15-20% of the cost of making biofuels.

The team’s next steps will be to optimise the pretreatment process for biomass, municipal solid wastes and bioenergy crops, such as switchgrass and poplar, which could be turned into fuels, at the same time as developing more robust enzymes to further reduce costs.

Co-authors include former post-doctoral fellow Shyamal Roy; doctoral student Shashwat Gupta; Ramendra Pal, a post-doctoral associate; and Chao Zhao, a former post-doctoral fellow.

The study, ‘Ammonia-salt solvent promotes cellulosic biomass deconstruction under ambient pretreatment conditions to enable rapid soluble sugar production at ultra-low enzyme loadings’, was published in the journal Green Chemistry.