Monday, April 30, 2007

Microbial conditioning and pretreatment for lignin co-products

Swetha Mahalaxmi1, Clint Williford1, Ashwini Thakre1, Charles Burandt1, and James Rawlins2. (1) Chemical Engineering, University of Mississippi, P.O. Box 1848, University, MS 38677, (2) School of Polymers and High Performance Materials, The University of Southern Mississippi, 118 College Drive #10037, Hattiesburg, MS 39406

Cellulosic ethanol continues to develop as a potential alternative transportation fuel. For its production, major process steps involve pretreatment to degrade or disengage lignin, saccharification to depolymerize cellulose to sugars, and fermentation of sugars to ethanol. Through DOE-supported projects, Novozymes and Genencor have dramatically reduced the enzymatic hydrolysis costs, leaving pretreatment as a significant remaining cost challenge to cellulosic ethanol commercialization. Aggressive research and development is pursuing alternative pretreatments to meet this challenge. In this matter, lignin plays a key role. It inhibits enzymatic hydrolysis of cellulose, and process designs typically consign its recalcitrant, low-value forms to boilers. However, lignin, in appropriate molecular weight ranges, is a suitable component of phenolic resin plastics.

Our objective is to combine microbial conditioning to improve pretreatment performance, allowing reductions in severity and complexity, reduced costs, and improved economics for the biomass grower. Furthermore, we aim to obtain a more useable lignin co-product.

In this work, we applied bacterial and fungal inoculua to corn stover, switchgrass, sorghum, and giant miscanthus. Using enzymatic hydrolysis, we determined sugar yields.  In parallel, we have performed ammonia fiber expansion (AFEX) and expansion centrifugation pretreatments on the four feedstocks and assessed the impact on enzymatic hydrolysis. (In ongoing work we are combining conditioning with pretreatment, including dilute acid hydrolysis.) We extracted lignin from conditioned, pretreated, and enzymatically hydrolyzed biomass. We assessed hydrolyzed biomass for the amount of lipophilic extractives and Klason lignin content, among other properties. We then assessed the extracted lignin for suitability as an adhesive.