Characterization and evaluation of guayule processing residues as potential feedstock for biofuel and chemical production

In the processing of guayule (Parthenium argentatum) for bulk rubber production using solvent extraction, two residue streams are produced: a complex resin-rich liquid and a ground, dry woody bagasse. In order to enhance the economic viability of guayule as an industrial crop, value-added use of the residues is needed and has the potential to reduce gross rubber production costs. The main objective of this research is the characterization of these two residues using analytical techniques to identify potential value-added components and applications. Here, guayule bagasse and resin were characterized by CNHS/O elemental analysis, bomb calorimetry, thermogravimetric analysis, Fourier-transform infrared spectrometry (FT-IR), X-ray diffractometry (XRD), gas chromatography-mass spectrometry (GC-MS), and high-resolution Fourier transform ion cyclotron resonance mass spectroscopy (FT-ICR MS). Guayule bagasse has high energy content (22-24 MJ/kg), less moisture (0.5-1.5 wt.%) and ash (3.7-4.1 wt.%), low cellulose crystallinity (29-34 %), and abundant carbohydrates (36-38 wt.%) and lignin (22-23 wt.%) relative to plenty of other lignocellulosic biomass, indicating bagasse's potential for thermochemical conversion to fuels. By FT-ICR MS with negative ionization mode, the most abundant classes among the 7200 heteroatom-containing compounds detected in guayule resin were O-3, followed by O-4 and O-2. Identified compounds included fatty acids, steroids, triterpenoids, and sesquiterpene esters, some of which have never been reported, as potential precursors of industrial chemicals. Characterization of guayule bagasse and resin guides exploring potential applications of waste streams, beneficial for enhancing techno-economic feasibility of guayule rubber-derived tires manufacturing industry.