Comparative technical, economic and environmental assessment of biomass-to-ethanol conversion technologies: biochemical and thermochemical routes integrated in a sugarcane biorefinery

The second generation ethanol production from sugarcane bagasse and straw can be produced competitively via biochemical or thermochemical conversion routes in biorefineries. Considering biomass-to-ethanol technologies, this work aims to compare technical, economic and environmental aspects of biochemical and thermochemical routes. The biochemical route considered is via steam explosion pre-treatment followed by enzymatic hydrolysis and fermentation process to ethanol production from the surplus biomass available. The thermochemical conversion route considered is via integrated direct gasification and mixed alcohols synthesis process with gas turbine in combined cycle to supply the plant energy demand. Both routes are considered integrated in an optimized annexed first generation sugarcane biorefinery with production of sugar; anhydrous ethanol and electricity. Mass and energy balances obtained from computer simulation developed in Aspen Plus^®7.3.2 platform provide information for the technical, economic and environmental assessment of each technological route. The economic evaluation impacts are determined using traditional financial metrics (e.g. internal rate of return, net present value and products production costs). The environmental assessment is carried out using the Life Cycle Assessment methodology to calculate the impact categories (e.g. acidification, climate changes, depletion of abiotic resources, ecotoxicity, eutrophication, human toxicity, land use, ozone layer depletion, and photochemical oxidation). Results show that besides the different mix of products obtained in each conversion route, booth routes present good economic and environmental impacts in comparison to the fossil alternatives. This assessment provides a comparative and critical analysis of the biomass-to-ethanol conversion technologies and elucidates critical points to be better assessed in the future studies.