Enhanced Biomass Hydrolysis with Hot Wash Separation

A future predicated upon bio-based fuels, chemicals, and materials is a well-recognized national goal. Bioenergy and biobased products have the potential to provide an energy efficient and environmentally sustainable economy. In addition, new biobased industries can be created that provide greater stability for rural economies. The conversion of biomass to biobased products as envisioned in thebiorefinery concept requires effective solid/liquid separation for the streams resulting from biomass pretreatment. Dilute acid pretreatment of biomass can readily solubilize the hemicellulosic fraction of biomass and increase the enzymatic hydrolysis of the residual cellulose from a wide variety of feedstocks. This pretreatment process also solubilizes some of the lignin, likely more than waspreviously realized. However, cooling of pretreated biomass solids below the lignin glass-to-liquid-transition temperature following pretreatment may allow the solubilized lignin to precipitate onto the cellulosic residue, interfering with subsequent enzymatic hydrolysis of the residual cellulose. The inhibition of enzymatic hydrolysis of cellulose decreases soluble sugar yields and increasescosts for fermentation of these sugars to other bio-based products. By keeping pretreated biomass residues above this glass-to-liquid-transition temperature and washing out the solubilized lignin and hemicellulosic sugars with hot water yields and enzymatic hydrolysis rates of the residual cellulose are increased. This is the 'hot wash' process. Previous bench-scale work demonstrated a 30-35%increase in the enzymatic hydrolysis of dilute-acid-pretreated yellow poplar sawdust and a 12-13% improvement with pretreated corn stover by employing the hot wash process. This hot wash process has been scaled up to the pilot scale with similar improvements in enzymatic hydrolysis of the residual cellulose to glucose for fermentation into other bio-based products. A 200 kg (dry) per day Sunds(now Metso) horizontal screw reactor was used for pretreatment of the biomass. The pretreated solids were discharged into a hot and pressurized 130-l Jaygo high solids paddle type reactor to keep the pretreated solids above 135?C. The two reactor systems were integrated with a Pneumapress? Model 3-C276 automatic pressure filter for performing the hot wash separation of pretreated biomass. Hotwashing of the hot filter cakes in the Pneumapress filter chamber was carried out with hot water, hot dilute ethanol (0.2 wt-% and 0.5 wt-%), and hot dilute alkali (0.1 wt-% and 0.2 wt-% NaOH) above 140?C. This paper presents pilot-scale hot wash results for pretreated yellow poplar sawdust and corn stover feedstocks. A 32% increase in the enzymatic hydrolysis of the yellow poplar and 17%increase for corn stover were found at the pilot scale, indicating scalability. Preliminary process economic and sensitivity analysis incorporating the hot wash process into a base case model for bioconversion of biomass to bioethanol will be presented.