High-value propylene glycol from low-value biodiesel glycerol: A techno-economic and environmental assessment under uncertainty

Abstract

Recent governmental policies that promote a biobased economy have led to an increasing production of biodiesel, resulting in large amounts of waste glycerol being generated as low-cost and readily available feedstock. Here, the production of high-value biobased propylene glycol as an alternative chemical route to valorize biodiesel glycerol was studied and assessed considering economic and life cycle environmental criteria. To this end, the conventional industrial process for propylene glycol production, which uses petroleum-based propylene oxide as feedstock, was compared against three different hydrogenolysis routes based on biodiesel glycerol using process modeling and optimization tools. The environmental impact of each alternative was evaluated following Life Cycle Assessment principles, whereas the main uncertainties were explicitly accounted for via stochastic modeling. Comparison among the various cases reveals that there are process alternatives based on biodiesel glycerol that outperform the current propylene glycol production scheme simultaneously in profit and environmental impact (i.e., 90% increment in profit and 74% reduction in environmental impact under optimum process conditions). Overall, this work demonstrates the viability to develop sustainable biorefinery schemes that convert waste glycerol into high-value commodity chemicals, like propylene glycol, thereby promoting holistic bioeconomy frameworks.