Combined Severity Factor for Predicting Sugar Recovery in Acid-Catalyzed Pretreatment Followed by Enzymatic Hydrolysis

Abstract

The severity factor developed by Chornet and Overend combines the effects of temperature and time in a single function to allow translation of sugar and oligomer release results from operation at one combination of temperature and time to realize nearly the same release at a different combination of these two variables. This factor has proven very valuable in correlating results from pretreatment of a variety of cellulosic biomass materials with just hot water or steam. The severity factor concept was subsequently extended to facilitate trading off among temperature, time, and acid concentration for pretreatments that employ dilute acid to hydrolyze hemicellulose. The resulting combined severity factor can be derived from simple first-order kinetic models that have been shown to describe sugar release from dilute acid pretreatment. In addition to describing hemicellulose sugar yields, it has been shown that the combined severity factor can provide some insights into expected sugar release yields from subsequent enzymatic hydrolysis of the solids left after dilute acid pretreatment. Furthermore, a simple adjustment in one parameter of the combined severity factor makes it possible to translate from one combination of temperature, time, and acid concentration conditions that maximizes yields from acid-catalyzed breakdown of xylooligomers released in hydrothermal pretreatment of biomass to a different set of conditions for maximum sugar release.