Process model and comparative life cycle assessment (LCA) of a biorefinery concept based on fractionated subcritical water hydrolysis for sugar cane trash valorization

Abstract

Subcritical water hydrolysis, which incorporates depolymerization, reaction and separation of sugars from biomass, has been proposed as an alternative to conventional hydrolysis. Since this process does not require chemicals, it could potentially lead to simpler biorefinery schemes. Yet, high water to biomass (S/F) mass ratios reported in experimental studies could limit technical feasibility for scaling-up purposes, as well as resulting in an inferior environmental performance due to the production of highly diluted sugar fractions. Therefore, in this study a biorefinery model based on fractionated subcritical water hydrolysis of sugar cane trash was proposed and simulated for (S/F) ratios in the range 7.5–24, based on previously reported experimental results and simulation studies, to assess the effect of mass and energy inputs in the environmental performance when compared to the conventional acid-enzymatic process by means of a gate-to-gate LCA assessment. LCA results showed inferior environmental performance of the proposed process with (S/F) of 12 and 24, ratios considerably lower than those usually employed in experimental studies, which is mainly the result of the energy requirements as steam production. Yet, a (S/F) ratio of 7.5 showed an improved environmental performance in 12 out of 18 categories assessed, which was attributed not only to the decreased energy consumption but also to the elimination of additional environmental burdens such as the production of chemicals and enzymes. These results suggest further experimental research should focus on reducing (S/F) ratios in experimental studies in order to advance the technical feasibility of the proposed process.