Technique aims to reduce the cost of biofuel production

Lignin, which protects plant cell walls, is difficult to break down or remove from plant materials called biomass, such as the non-edible parts of the corn plant. However, lignin needs to be extracted in order to reach the energy-rich cellulose that is used to make biofuels.

‘Finding inexpensive ways to remove lignin is one of the largest barriers to producing cost-effective biofuels… And our approach is very promising’ said Ezinne Achinivu, a Ph.D. student in chemical and biomolecular engineering at NC State and lead author of a study describing the new technique.

According to NCSU, the researchers began by making a number of liquid salts called protic ionic liquids (PILs). PILs are fairly inexpensive to prepare, because they are made by mixing together an acid, such as acetic acid, and a base. As part of the pre-treatment process, one of the PILs is mixed with biomass and then heated and stirred. The lignin dissolves into the PIL, leaving the cellulose behind as a solid. The cellulose, which is now much easier to process, is then easily filtered from the mixture for use in the next biofuel production steps.

The remaining PIL-lignin liquid mixture can then be heated to distil the PIL, leaving the lignin behind as a black powder. The vapours from the PIL are collected and cooled to recover the liquid PIL so that it can be re-used. The lignin is also valuable, because it can be used to manufacture polymers or other chemical products which could supplement the cost of running the biofuel production facility.

‘This PIL-based technique can be easily scaled up and is likely to be both more energy efficient and less expensive than existing biomass pre-treatment techniques for removing lignin,’ Achinivu said in a statement.

The researchers are reportedly working to apply the technique to wood and other biomass feedstock materials, as well as to better understand and fine-tune the interactions between the PILs and lignin.

‘If we can better understand how the PIL dissolves the lignin, we can make the process even more efficient by using less energy while extracting more lignin,’ Achinivu said.

The paper, ‘Lignin Extraction from Biomass with Protic Ionic Liquids,’ is published online in Green Chemistry.