Life Cycle Assessment of Catechols from Lignin Depolymerization

Lignin is the second most abundant natural polymer on Earth. The aromatic structure of lignin makes it a promising platform for biobased chemicals. Catalytic depolymerization of lignin has been demonstrated with high yields and selectivity, resulting in efficient conversion to target products. In this study, we performed a comparative process simulation and life cycle assessment (LCA) of catechol-derived products from lignin contained in candlenut shells with those conventionally derived from petrochemical phenol. The modeled biobased production pathway includes candlenut cultivation, nutshell separation and preparation, lignin extraction and purification, catalytic depolymerization of lignin, and catalyst synthesis. Commercial-scale process modeling was done in ASPEN Plus based on experimental data, while life cycle environmental burdens were modeled using the U.S. EPA's TRACI 2.1 impact assessment method, covering 10 categories of resource use and impact. Comparison of biobased and fossil-based results showed an overall reduction in environmental impacts for the lignin route of 2%, 7%, and 59% in global warming potential, ecotoxic effects, and fossil fuel depletion, respectively. In other environmental impact categories, particularly ozone depletion, the fossil-based route was shown to be preferable. Dichloromethane, used as a solvent in purification of extracted lignin, and electricity use during depolymerization of lignin are the dominant contributors in total environmental burdens of the biobased route. A complementary analysis was conducted to consider the relative impacts of an alternate extraction method. The overall results emphasize the need for further work in developing conversion processes and also considering several parallel scenarios to find the most beneficial use of lignin on a life cycle basis.