Economic and Environmental Sustainability Analysis of Guayule Rubber

J.C. Quinn, E. Sproul, H.M. Summers, C. Seavert, J. Robbs, S. Khanal, V. Mealing, A.E. Landis, N. Fan, O. Sun
Colorado State University,
United States

Keywords: natural rubber, techno-economics, life cycle assessment

Summary:

The increasing probability of drought in the American southwest represents a significant risk to rural farmers who depend upon supplemental irrigation. Introducing high-value drought tolerant crops has the potential to mitigate this risk and provide consistent revenue to farmers. While a range of crops may meet these criteria, one that has received considerable attention in the past is guayule (Parthenium argentatum). Guayule is a desert shrub native to arid regions of northern Mexico and southern Texas. It has long been known for its high natural rubber content, which can be extracted and used in industrial products such as tires and medical equipment. In addition to rubber, guayule also contains a resin and leftover biomass (bagasse) which can be sold as coproducts for other industrial applications. While the physical characteristics of guayule have long been studied, the economic viability and environmental impact of guayule’s products remain largely unknown. Previous studies have attempted to estimate production costs and environmental impacts of guayule rubber. However, these studies represent isolated analyses with their own disconnected assumptions largely due to limited data. As a result, there is a need for an improved analysis in which economic and environmental factors are considered within a single integrated framework. In addition, this analysis should be informed by up-to-date data resulting from recent developments in agricultural and biorefining methods. This work addresses the need for an integrated environmental and economic analysis of guayule that includes up-to-date production data. At the center of this analysis is a detailed systems model that tracks all of the energy and materials required to cultivate, harvest, transport, and refine guayule. This systems model is used to inform a thirty-year economic analysis that tracks production costs at the farm and biorefinery. These costs are used to determine the minimum selling price of guayule rubber that is required to recover all production costs with a 10% internal rate of return. In addition to the economic analysis, the systems model also informs an environmental analysis that determines the cradle-to-gate impacts of guayule rubber, resin, and bagasse. The baseline result of the integrated analysis is a minimum rubber selling price of $3.31 per kilogram, with resin sold at $1.00 per kilogram and bagasse sold at $0.10 per kilogram. Production costs are split across agriculture and biorefining. Within agriculture, high cost contributors include agricultural equipment and irrigation. Within biorefining, the largest cost contributors are capital equipment and solvents. Environmental results in the baseline scenario show that irrigation, solvents, and natural gas are major contributors across multiple impact categories. Furthermore, this analysis highlights significant variation across environmental results due to mass and economic allocation methods. Tradeoffs of the baseline and other scenarios will be further analyzed in the future to provide guidance to experimental teams in hopes that methods can be further improved to simultaneously reduce production costs and environmental impacts.