Multi-criteria analysis of a biorefinery for co-production of lactic acid and ethanol from sugarcane lignocellulose

Biorefineries are regarded as a key enabler to facilitate the transition toward a sustainable and low carbon bioeconomy. In this study, alternative lignocellulose biorefineries annexed to a typical sugar mill were investigated to co-produce ethanol (EtOH), lactic acid (LA), and/or electricity, utilizing bagasse and a component of harvesting residues (brown leaves) as feedstock. Studied scenarios included EtOH as the sole product from glucose and xylose (Scenario 1), LA as the sole product from these two sugars (Scenario 2), EtOH from glucose and LA from xylose (Scenario 3), and EtOH from xylose and LA from glucose (Scenario 4), all of which were associated with some level of export electricity production. Aspen Plus (R) simulations of the scenarios were developed considering all supplementary units, such as evaporation, water treatment, boiler, and steam/power generation in addition to the process units required for the main product streams. Economic evaluation, energy assessment, and environmental life cycle assessment (LCA) were carried out on the developed simulations, in a multi-criteria analysis of the desirability of each scenario. To service the combined energy demands of a sugar mill and annexed biorefinery, a 35 to 40% bypass of lignocellulose directly to the boiler section was required to achieve integrated scenarios that were energy self-sufficient, i.e., not dependent on external (fossil) energy sources. Scenario 2 was economically most attractive with the highest internal rate of return (IRR) of 31.1%, whereas Scenario 1 had the lowest IRR of 10.0%. Scenarios 2 and 4 were economically the most robust, with the least sensitivity to variations in the key economic drivers, i.e., EtOH, LA and enzymes. The LCA suggested that LA producing scenarios introduced environmental burdens that were marginally higher than Scenario 1, due to higher consumption of processing chemicals. Overall, Scenario 4 was found to be the most desirable biorefinery scenario, by balancing financial and environmental considerations. (c) 2017 Society of Chemical Industry and John Wiley & Sons, Ltd