Separation technique could improve biofuel production
10 May 2013
A new technique for pre-treating cellulosic biomass with ionic liquids could bring down the cost of biofuels.
The team at the US Department of Energy (DOE)’s Joint BioEnergy Institute (JBEI) claim that the new technique could bring the cost processing biofuels down to competitive levels.
The process removes the need for expensive enzymes, which are used in ionic liquid pretreatments, and makes it easier to recover fuel sugars.
The separation of sugars and ionic liquids can be a difficult and expensive problem
“We’re able to separate the pretreatment solution into two phases, a sugar-rich water phase for recovery and a lignin-rich ionic liquid phase for recycling. As an added bonus, our new pretreatment technique uses a lot less water than previous pretreatments,” said Blake Simmons, a chemical engineer at JBEI.
Recent studies have shown that acid catalysts can replace enzyme-based hydrolysis, but the subsequent separation of sugars and ionic liquids becomes a difficult and expensive problem.
Simmons and his colleagues solved this by deploying the ionic liquid imidazolium chloride in tandem with an acid catalyst.
“Imidazolium is the most effective known ionic liquid for breaking down lignocellulose and the chloride anion is amenable with the acid catalyst,” Simmons said.
“The combination makes it easy to extract fermentable sugars that have been liberated from biomass and also easy to recover the ionic liquid for recycling.”
Complete separation of the pretreatment solution was achieved by adding sodium hydroxide.
The optimised sodium hydroxide concentration for both phase separation and sugar extraction was 15-percent, resulting in the recovery of maximum yields of 54-percent glucose and 88-percent xylose.
The JBEI researchers believe these sugar yields can be increased by optimising the process conditions and using more advanced methods of phase separation and sugar recovery.
“After optimising the process conditions, our next step will be to scale the process up to 100 liters,” Simmons said. “For that work we will use the facilities at the Advanced Biofuels Process Demonstration Unit.”
A burning problem
With the burning of fossil fuels continuing to add 9 billion metric tons of excess carbon dioxide to the atmosphere each year, the need for carbon neutral, cost-competitive renewable alternative fuels has never been greater.
Advanced biofuels, produced from the microbial fermentation of sugars in lignocellulosic biomass, could displace gasoline, diesel and jet fuel on a gallon-for-gallon basis and be directly dropped into today’s engines and infrastructures without impacting performance. If done correctly, the use of advanced biofuels would not add excess carbon to the atmosphere.
Environmentally benign ionic liquids are used as green chemistry substitutes for volatile organic solvents. While showing great potential as a biomass pretreatment for dissolving lignocellulose and helping to hydrolyse the resulting aqueous solution into fuel sugars, the best of these ionic liquids so far have required the use of expensive enzymes.
