Guayule Stems Fractionation and Sugars Recovery by Different Pretreatment Technologies

The bagasse of guayule, obtained after extraction of natural rubber and resins, can be used to produce 2nd generation fermentable sugars and lignin. For this purpose, four pretreatment technologies were applied to deconstruct the guayule bagasse: diluted acid (DA), steam explosion (SE), organosolv (OS), and the steam explosion followed by alkaline washing (AW). The obtained lignocellulosic pulp underwent enzymatic hydrolysis (EH) to produce glucose. The conditions that gave the highest hydrolysis yield were assessed. A mass balance was elaborated for all processes which were compared on the basis of sugars yield, water and chemical consumption, and energy expenditure footprint. The greatest amount of glucose (133 g kgxe213; 1 of dry guayule bagasse, corresponding to 71% enzymatic hydrolysis yield) was obtained using SE followed by AW, whereas SE and OS had lower yields (104 g and 106 g kgxe213; 1, respectively). The highest overall monomeric sugars yield, including xylose, was obtained by DA (317 g kgxe213; 1) followed by OS (243 g kgxe213; 1) pretreatment, although the sugar streams must be purified in both processes by removing the acid and the solvent, respectively. SE is a process with a limited requirement of chemicals and energy input, which are significantly higher for AW and for OS, respectively.