Economic and environmental sustainability assessment of guayule bagasse to fuel pathways

Abstract

Guayule (Parthenium argentatum A. Gray) is a desert-dwelling crop that can produce hard rubber for tires and has the potential to help meet the water conservation needs of arid regions such as the Southwest U.S. Previous work has quantified the cost and environmental impact from guayule rubber production. However, establishing the economic viability of a domestic guayule industry requires identifying value-added products from the residual non-rubber guayule biomass, referred to as bagasse. Using guayule bagasse for bioenergy production is one potential solution, but the best pathway for thermochemical conversion of bagasse to fuels has yet to be defined. In this work, process models of pyrolysis and pelletization of bagasse are developed to inform a path to commercialization. A facility processing 200 tonnes of guayule bagasse per day is considered with a system boundary defined from biomass cultivation to fuel combustion. The materials and energy inventory results enabled the first comparative assessment of bagasse to fuels by concurrently performing techno-economic analysis and well-to-wheels life cycle assessment on both pathways. The minimum fuel selling price for the bagasse to fuels pathway was $0.076 per MJ ($9.26 per gallon of gasoline equivalent) and the minimum selling price of pellets from bagasse was $176 per tonne. This work compares the economic and life cycle results of both processes to make conclusions about the economic potential of bagasse and environmental impact of its conversion, areas to reduce production cost of biofuels, and potential for greenhouse gas emissions reduction compared with conventional fuels. In addition, the work identifies areas where future research may optimize production costs such that these fuels can be integrated alongside guayule rubber into a successful bioeconomy for the Southwest United States.