Comparative techno-economic and life cycle assessment of electrocatalytic processes for lignin valorization

Abstract

This study explores the potential of using electrochemical (EC) methods for valorizing lignin, a lignocellulosic biomass cell wall component, into biofuels and high-value compounds. Traditional direct electroreduction as well as oxidation of lignin have faced challenges in efficiency and selectivity due to the requirement of high oxidation potentials and expensive, toxic electrodes, leading to uncontrolled degradation. We propose using a hydrogen atom transfer (HAT) mediator to achieve benzylic oxidation, enhancing efficiency and selectivity under milder conditions. The research employs the NREL model for producing ethanol to evaluate the commercial viability of EC lignin conversion. We carried out a techno-economic analysis (TEA) and a life cycle assessment (LCA) using BioSTEAM and GREET® 2022, respectively, to evaluate the process's economic and environmental impacts over 20 years. Sensitivity analysis has been conducted to examine base case values extracted from the catalytic performance of phthalimide-N-oxyl type HAT mediators. Our findings suggest that a 2000 metric tonnes per day biorefinery using this method could produce approximately 49.56 tpd of chemicals, with the EC unit consuming 3.5% of the input energy. The TEA operating cost for chemical production was estimated at $16.86 per kg, with a total capital expenditure of $403 769 MM. The LCA revealed that producing by-products in ethanol production can lead to around 10 to 46% reduction in total CO₂ emissions, depending on the employed allocation methods. The study indicates that integrating an EC unit using a HAT mediator into second-generation biorefineries for lignin oxidation followed by a reduction in chemicals could offer additional revenue streams and lower environmental impacts compared to conventional methods.