Before materials like grass, wood, or leaves can be converted into ethanol for biofuels, they must undergo a pretreatment step. The pretreatment step separates or destroys lignin to make cellulose more accessible for conversion into fermentable sugars. The separated lignin is treated as waste, but lignin can be burned as an alternative to coal and natural gas or used as a chemical feedstock for polymers. The cost of purifying the lignin from these streams is generally considered to be too high.
Steven Sherman and co-workers, Savannah River National Laboratory, South Carolina, USA, report a method for recovering lignin from the liquid solutions generated by pretreatment with ammonium hydroxide. By using acidification, evaporation, and precipitation or centrifugation, the team shows that 66–95 % of dissolved lignin can be recovered as a precipitated solid. They estimate to breakeven on the process, the lignin price would be $2.36/kg for pilot-scale and $0.78/kg for industrial-scale plants.
- A new process developed for separation of lignin from ammonium hydroxide pretreatment solutions
S. R. Sherman, J. J. Goodell, C. E. Milliken, J. A. Morris, M. B. Gorensek,
Environ. Prog. Sustainable Energy 2011.