Bioconversion of lignocellulosic materials into fuel ethanol: Pretreatment and non-isothermal simultaneous saccharification and fermentation

An integrated bioprocess called non-isothermal simultaneous saccharification and fermentation (NSSF) was developed for bioconversion of lignocellulosic materials into ethanol. Pretreatment methods were developed to make the lignocellulosic biomass amenable for the direct bioconversion.; For pretreatment, two novel methods, ammonia recycled percolation (ARP) and two-stage dilute-acid (DA) process, were investigated. In the ARP process, lignocellulosic biomass was treated with aqueous ammonia at elevated temperatures and pressures inside a percolation reactor. The cellulose fraction was retained in the biomass, while lignin and hemicellulose were selectively removed from the biomass. The enzymatic digestibility of the ARP-treated samples was substantially higher than that of {dollar}alpha{dollar}-cellulose. The extent of delignification in the ARP process was in the range of 23-63% for hybrid poplar and 60-85% for switchgrass. A two-stage dilute-acid percolation (DA) process was investigated using extremely low acid (0.078 wt% sulfuric acid) under moderate temperature (145{dollar}spcirc{dollar}C-170{dollar}spcirc{dollar}C). Hemicellulose in switchgrass was completely solubilized with no sugar decomposition. The combined pretreatment of ARP and DA essentially fractionated the switchgrass into three major components. The digestibility of these samples was consistently higher than that of DA-treated samples. Further investigation of the interaction between cellulase and xylan indicated that the enzymatic hydrolysis of cellulose was inhibited by both external and internal xylan. The external xylan was found to be a noncompetitive inhibitor to cellulase enzymes.; A non-isothermal simultaneous saccharification and fermentation process (NSSF) was developed to alleviate the problem of mismatching optimal temperatures for cellulase and microorganism in SSF. The NSSF was conducted in a two-zone bioreactor that is composed of a hydrolysis column containing biomass and a fermenter. The hydrolysis column is maintained at the optimal temperature for the enzymatic hydrolysis (50{dollar}spcirc{dollar}C) and the fermenter is controlled at 20-30{dollar}spcirc{dollar}C. A cell-free cellulase enzyme solution is recirculated between them. Thus, enzymatic hydrolysis and microbial fermentation occur in separated location, yet simultaneously. The NSSF reduced the enzyme requirement by 30% to 40% in comparisons to the SSF. The effect of temperature on {dollar}beta{dollar}-glucosidase activity was the most significant among the individual cellulase compounds. Both ethanol yield and productivity were substantially higher in the NSSF than in the SSF at the enzyme loading of 5 IFPU/g glucan and 10 IFPU/g glucan. The terminal yield attainable in 4 days with the SSF was reachable in 40 hours with the NSSF.