New lignin-solvent process harvests biofuel, paper and chemicals from plant material
In order to improve the sustainability credentials of biofuels, experts have been trying to figure out ways to produce them from non-food sources, such as cellulose – the material that makes up the cell walls of plants. Now, researchers from the Wisconsin Institute for Sustainable Technology (WIST) at the University of Wisconsin-Stevens Point have patented a process that they say paves the way for the creation of biofuels from cellulosic plant material.
WIST’s first patent is for a process that makes biofuels and other products from such material, including agricultural left-overs such as corn stover, or plants grown specifically for fuel production, such as hardwood and softwood trees. The method they’ve patented involves an aqueous solvent that separates cellulosic material into pure cellulose and lignin, the substance that gives woody biomass its rigidity. The lignin-solvent mixture can then be separated from the water and becomes a high-energy-density fuel that can be used independently or in combination with biodiesel.
But it’s not just cellulosic ethanol that can come out of this process. Pure cellulose can be used to make paper or can be converted into fermentable sugars. Besides biofuels, the sugars can also be used to make other renewable chemicals for industry including isoprene. It's a material used to make rubber, plastics and pharmaceuticals, but which comes mostly from petroleum.
The patent is an improvement on traditional processes for separating lignin from cellulose employed by the paper industry, which make it more difficult to convert the cellulose to sugars. Also, the lignin that's produced contains chemicals that cannot be easily or economically separated. The new lignin-solvent process results in a purified lignin and pure cellulose, which can be readily used to produce other renewable chemicals. This saves the lignin from being burned, which is the process conventional paper plants typically adopt to recover inorganic chemicals from the pulping process and to produce energy as well.
WIST is working with UW’s WiSys Technology Foundation to license the intellectual property to private industry for development. The researchers envisage several applications for the lignin, including carbon fiber.
Besides the lignin-solvent process, WIST hopes to develop a biorefinery that could be fitted to existing paper mills or to revive idle ones. They have performed the process in the lab and now are looking to develop it into a demonstration-scale plant.