More efficient process for sugar extraction from biomass

Scientists have developed a more efficient process for extracting sugars from wood chips, corn cobs and other organic waste from forests and farms, creating a renewable feedstock which could serve as a cheaper, sustainable substitute for petroleum in the production of chemicals and fuels.

"To make greener chemicals and fuel, we're working with plant material, but we don't want to compete with its food value," said Basudeb Saja, associate director for research at the University of Delaware’s (UD) Catalysis Center for Energy Innovation.

"So instead of taking corn and extracting its sugars to make ethanol, we're making use of the stalks and cobs left over after the corn is harvested, as well as other kinds of waste like wood chips and rice hulls." Saha, the leader of the research project, continued.

Recent years have seen a growing trend towards using organic waste, known as lignocellulosic biomass, to create chemicals for producing biofuels, biodegradeable plastics, pharmaceuticals and cosmetics, but biorefineries have struggled with both finding a steady supply of feedstocks and with keeping processing costs down.

The heart of the problem is the difficulty in breaking down waste such as wood chips and corn cobs.

"The lignin that makes their cell walls so tough and sturdy acts like superglue, holding tightly to the sugars," Saha said.

 

Two steps into one

At present, industry generally separates out the sugars from the lignin using a two-step process, relying on harsh chemicals and reaction conditions in the first step, and an expensive enzyme in the second step.

The process developed at UD uses just one step, bypassing the pretreatment step commonly used in biorefineries to disintegrate the lignin from the sugar polymers cellulose and hemicellulose. The single-step technology integrates the pretreatment step and the hydrolysis of cellulose and hemicellulose in one pot and operates at considerably lower temperature (85°C) and a shorter reaction time (one hour), making the method more water and energy efficient.

A concentrated solution of an inorganic salt in the presence of a small amount of mineral acid is the key to the new process. Filed as an international patent application by UD, the solution swells the particles of wood or other biomass, allowing the solution to interact with the fibres.

According to Saha, the solution is efficient enough to deliver theoretical 95% sugar yields.

Significantly, the team have integrated this step with the dehydration reaction, which converts the sugars to furans in the same pot and enables the salt solution to be recycled.

"Our process enables -- for the first time -- the economical production of feed streams that could profoundly improve the economics of cellulosic bioproducts manufactured downstream, not to mention the environmental benefits of replacing petroleum," Saha says. "More than 10,000 million metric tons of carbon emissions were reported in 2010 from conventional fossil fuels and chemicals, which has a long-term catastrophic effect on our environment."