Exergy-based performance analysis for biojet fuel pathways in Brazil

Abstract

Increasing efforts in developing sustainable and economically viable technologies to produce transportation fuels have been made in the last decades. Particularly, the aviation industry has conceived that biojet fuels are vital to decrease 50% of the greenhouse gas emissions by 2050 and to achieve carbon-neutral growth by 2020. Thus, the goal of this study is to rank self-sufficient biorefineries for biojet fuel production in Brazil bases on an exergy-based performance analysis aiming to identify the processes irreversibilities. The production capacity assumed for this analysis covers 10% of the projected fuel demand by 2020 in São Paulo (Guarulhos) and Rio de Janeiro (Galeão) airports and considers that the biojet fuel produced is suitable for blending with fossil jet up to 50%. In this context, the base capacity analysed was 210 kton jet/year considering sugarcane (SC) and SC straw as feedstocks, largely available in Brazil. Hence, 24 scenarios were compared for lignocellulosic and lignin valorization processes. These technological pathways covers eight pre-treatment processes such as dilute acid (DA), dilute acid + alkaline treatment (DA-A), steam explosion (SE), steam explosion + alkaline treatment (SE-A), organosolv (O), wet oxidation (WO), liquid hot water (LHW) and liquid hot water + alkaline treatment (LHW-A), followed by enzymatic hydrolysis. Furthermore, three thermochemical processes for the direct conversion of bagasse and lignin upgrade to renewable jet fuel or electricity were considered (Fast pyrolysis, Gasification Fischer-Tropsch and Cogeneration). The exergy assessment evidenced that combined pretreatment processes with the alkaline treatment (DA-A, SE-A, LHW-A) have a better global exergetic performance than the lignocellulosic pre-treatments carried out standalone (DA, SE, O, WO, and LHW). In addition, the use of fast-pyrolysis as a technology for the lignin residues presented the higher performance for all the scenarios. It is shown that the CO2 equivalent index and the renewability exergy index are appropriate metrics to determinate the environmental impact/renewability performance of the technological pathways. Lastly, the environmental analysis shows that all scenarios lead to a 30% reduction of specific CO2 equivalent emissions in exergy base in comparison to the petroleum-based jet fuel impacts.