10-20: Post steam explosion refining to increase cellulose conversion during enzymatic hydrolysis

A limited yield of fermentable sugars from enzymatic hydrolysis has been a barrier in the biomass-to-fuel industry. In an effort to increase the overall sugar recovery, refining, a mature process in pulping paper industry, was introduced and proved to have great potential in the biofuels field. Refining is a mechanical process that subjects fibers to a shearing action, exposing more microfibrils on the fiber surface.

In this study, hybrid poplar chips were steam exploded using 6 different conditions with or without the addition of SO₂. The steaming temperature ranged from 190 °C to 212 °C, and the residence time ranged from 5 min to 10 min. After each pretreatment, half of the solid fractions were refined using a Valley Beater. Then, all 12 samples, including both refined and unrefined solids, were enzymatically hydrolyzed at 5 % consistency and 5 FPU/g cellulose cellulase enzyme loading. The extent of cellulose conversion highlighted the difference in digestibility between refined and unrefined solids. Refining improved the cellulose to glucose conversion as much as 20 % for steam pretreated samples without SO₂, whereas little digestibility improvements were observed for SO₂ catalyzed steam pretreated samples. In addition, in this paper we will discuss the effects of refining on particle size distribution and available surface area.