Hybrid Thermal Biological Conversion to Industrial Chemicals

Grant # 98-05
Principal Investigator: Robert C. Brown
Co-Principal Investigators: Tonya Peeples, Curtis Hanson
Organizations: Iowa State University, University of Iowa, University of Northern Iowa
Subgrantees/Consultants: University of Iowa, University of Northern Iowa
Co-Sponsors: Council of Great Lakes Governors, Great Lakes Regional Biomass Energy Program – DOE, Iowa Biotechnology Byproducts Consortium – USDA
Participants: Daren Daugaard, David Falkowski
Technical Area: Renewable Energy

Background and Significance:

Lignocellulosic plant materials are underutilized by the agricultural processing industry. Indeed, lignocellulose, in the form of oat hulls, corn stover, wheat straw, and similar materials, are usually considered as wastes. However, it has long been recognized that cellulose can be converted to sugars followed by fermentation to alcohol or organic acids. If agricultural wastes such as corn stover could be economically converted to industrial chemicals, it would represent an important new source of income for farmers or profit centers for agricultural businesses.

The major stumbling block toward such an enterprise has been fractionation of lignocellulose into its constituents, lignin and cellulose. Research for the past decade has focused on acid pretreatments and enzymatic hydrolysis, which have proven too costly for commercial operations. Recently, researchers at the University of Waterloo in Ontario, Canada, developed an alternative route for “cracking” lignocellulose based on fast pyrolysis, a process by which lignocellulose is thermally degraded. Fast pyrolysis consists of rapid heating of lignocellulose to moderately high temperatures (about 400°C) to form a mixture of solids, liquids, and gases. The Waterloo researchers showed that under appropriate process conditions, pyrolysis will delignify biomass and yield levoglucosan, an anhydrosugar that can be hydrolyzed to fermentable sugars. Thus, fast pyrolysis combined with fermentation can circumvent the slow and costly acid and enzymatic hydrolysis processes that currently stand in the way of converting low-value lignocellulose into high-value chemical products.

Further improvements in the process could be achieved by using microorganisms that directly ferment complex sugars in the extreme acidic and reactive environment found in pyrolysis liquids. Another approach is to identify chemical pathways for converting levoglucosan into commercially important products. For example, hydrogenolysis is being investigated as a method for converting the pyrolysis liquids to polyols such as ethylene glycol.

This project has five major elements: evaluate depolymerization potential of corn stover and switchgrass as lignocellulosic feedstock; determine the fermentation potential of pyrolysis sugars using conventional microorganisms; screen and select extremophilic microorganisms suitable for direct fermentation of pyrolysis sugars; perform laboratory tests on hydrogenolysis of pyrolysis liquids, and estimate the cost of an integrated pyrolysis / fermentation / distillation process for a corn stover-to-ethanol plant.

Project Objectives:

The objective of this project is to investigate the feasibility of converting lignocellulosic wastes into high value chemical products by a hybrid thermal/biological process. In particular, we will investigate thermal depolymerization of corn stover into complex sugars and their subsequent hydrolysis and fermentation to ethanol.