Optimization of processing conditions for dilute acid and alkaline pretreatment of agave bagasse at high solids loading by response surface methodology

Utilization of lignocellulosic materials for the production of value-added chemicals or biofuels generally requires a pretreatment process to overcome the recalcitrance of the plant biomass for further enzymatic hydrolysis and fermentation stages. Two of the most employed pretreatment processes are the ones that used dilute acid (DA) and alkaline (AL) catalyst providing specific effects on the physicochemical structure of the biomass such as high xylan and lignin removal for DA and AL, respectively. Another important effect that need to be studied is the use of a high solids pretreatment (15%) since offers many advantaged over lower solids loadings, including increased sugar and ethanol concentrations (in combination with a high solids saccharification) which will be reflected in lower capital costs, however this data is currently limited. In this study, several variables such as catalyst loading, retention time and solids loading, were studied using Response Surface Methodology (RSM) based on a factorial Central Composite Design (CCD) of DA and AL pretreatment on agave bagasse using a range of solids from 3 to 30% (w/w) to obtain optimal process conditions for each pretreatment. In order to minimize possible formation of degradation byproducts lower temperatures were used in DA at 130 °C while AL used autoclave conditions (121 °C). Furthemore, subsequent enzymatic hydrolysis were performed using Novozymes Cellic CTec2 and HTec2. Pretreated biomass were characterized by wet-chemistry techniques and selected samples were analyzed by powder X-ray diffraction (XRD), and scanning electron microscopy (SEM).