Pretreatment Processes for Cellulosic Ethanol Production: Processes Integration and Modeling for the Utilization of Lignocellulosics Such as Sugarcane Straw

Abstract

Pretreatment is the key step for a viable and efficient cellulosic ethanol production process and, for this reason, it must be very selective in avoiding polysaccharide degradation and inhibitors formation. This work provides a brief overview of the leading pretreatment technologies available to date, with emphasis on those that are already closed to or eventually reached commercial scale such as steam explosion and/or dilute acid hydrolysis. Details are also given with regard to the fundamental effects of pretreatment on the chemical composition and organizational structure of the plant cell wall. Furthermore, the impact of steam explosion and enzymatic hydrolysis on the overall capital cost of cellulosic ethanol production has been determined in light of the following process integration approaches using sugarcane straw as the reference material: simultaneous saccharification and co-fermentation (SSCF), separated hydrolysis and co-fermentation (SHCF) and separated hydrolysis and fermentation (SHF). As a result, cellulosic ethanol produced from SSCF, SHCF, and SHF processes resulted in capital cost estimates of $1.66, $1.75, and $2.23 per liter of ethanol produced. The difference among these values is related to the easiness with which different unit operations are harmonized in a sustainable and fully operational biorefinery unit.