Comparative Performance of Leading Pretreatment Technologies for Biological Conversion of Corn Stover, Poplar Wood, and Switchgrass to Sugars

Abstract

The Biomass Refining Consortium for Applied Fundamentals and Innovation (CAFI), formed in early 2000, completed its last study in 2010 to determine comparative sugar yields from application of leading pretreatments to shared sources of cellulosic feedstocks followed by enzymatic hydrolysis of the resulting solids with a common source of enzymes. This chapter highlights key findings over the 10-year life of the CAFI team on the enzymatic hydrolysis of corn stover, poplar wood, and switchgrass that had been subjected to the following leading pretreatments: ammonia fiber expansion (AFEX), ammonia recycle percolation (ARP), dilute sulfuric acid, liquid hot water (LHW), lime, soaking in aqueous ammonia (SAA), and sulfur dioxide steam explosion. First, compositions are reported for each of the three baseline CAFI feedstocks. For all three feedstocks, the highest yields of xylose, glucose, and soluble oligomers are then reported for pretreatment coupled with subsequent enzymatic hydrolysis with baseline loadings of cellulase and β-glucosidase. In all cases, material balances were performed. Differences in yields are then reported for application of the same pretreatments to a second source of poplar and two other varieties of switchgrass. Following pretreatment of each feedstock, the compositions of the solids are compared to demonstrate that high yields can be realized even though the different pretreatments left different proportions of xylan and lignin in the pretreated solids. Temperatures, times, and catalyst types and loadings that resulted in the highest xylose and glucose yields in solution are summarized for each feedstock and pretreatment. The results show that a wide range of pretreatment conditions can realize high yields of sugars from cellulosic biomass, and that different types of biomass and even different varieties of the same biomass perform differently and can require modification of pretreatment conditions to increase yields.