A Methodology to Evaluate Solvent Extraction-Based Processes Considering Techno-Economic and Environmental Sustainability Criteria for Biorefinery Applications

Extraction processes are widely used in biorefinery applications to recover target products from biomass, and their comprehensive evaluation is key to improving their economic and environmental sustainability. This paper applies a systematic methodology that combines a rigorous process design, techno-economic analysis, and life cycle assessment to evaluate the sustainability performance of solvent extraction-based processes, with a focus on downstream activities. The methodology, which consists of seven iterative steps that combine process simulation and economic and environmental sustainability assessment tools, is demonstrated using a biodiesel production process from algae biomass, with hexane as the lipid extraction solvent. The minimum biodiesel selling price is estimated at U.S. $8.95 per U.S. gal, using the discounted cash flow rate of return. This is 3.5 times the average price of fossil diesel, mostly due to the cost of algae biomass and lipid recovery capacity of the solvent. Eighteen environmental impact categories are estimated from cradle to grave using the ReCiPe v1.1 method. For example, the climate change and primary energy demand are calculated at 95 g CO2 eq./MJ and 1.52 MJ/MJ biodiesel, which are 5 and 24% higher compared to fossil diesel, respectively. Lipid extraction is identified as the hotspot of the downstream processing stages for all impact categories (52-97%) and an opportunity for improving the overall sustainability performance of algae biodiesel, e.g., solvent selection. These findings provide a benchmark for future improvements to biodiesel production from algae biomass, with focus on the interactions between biomass and the solvent, e.g., phase equilibrium thermodynamics.