Lawrence Berkeley National Laboratory

A pilot-scale continuous tubular reactor (PCTR) was employed for the isothermal pretreatment of agave bagasse (AG), corn stover (CS), sugarcane bagasse (SC), and wheat straw (WS) with three residence times. The objective was to evaluate the impact of this technology on enzymatic saccharification at low solid loadings (4% w/v) and on sequential saccharification and glucose fermentation (SSF) at high solid loading (20% w/v) for bioethanol production. Deformation in cellulose and hemicellulose linkages and xylan removal of up to 60% were achieved after pretreatment. The shortest residence time tested (20 min) resulted in the highest glucan to glucose conversion in the low solid loading (4% w/v) enzymatic saccharification step for AG (83.3%), WS (82.8%), CS (76.1%) and SC (51.8%). Final ethanol concentrations after SSF from PCTR-pretreated biomass were in the range of 38 to 42 g L^-1 (11.0-11.3 kg of ethanol per 100 kg of untreated biomass). Additionally, PCTR performance in terms of xylan removal and sugar release were compared with those from a batch lab-scale autohydrolysis reactor (BLR) under the same process conditions. BLR removed higher xylan amounts than those achieved in the PCTR. However, higher sugar concentrations were obtained with PCTR for SC (13.2 g L^-1 vs. 10.5 g L^-1) and WS (21.7 g L^-1 vs. 18.8 g L^-1), whilst differences were not significant (p < 0.05) with BLR for AG (16.0 g L^-1 vs. 16.3 g L^-1) and CS (18.7 g L^-1 vs. 18.4 g L^-1).