| Pretreatment represents a bottleneck in the process of biologically converting cellulosic biomass to ethanol, as it affects downstream fermentation and is expensive. This thesis addressed some of these obstacles by examining both steam and liquid hot water (LHW) pretreatment of biomass—primarily sugar cane bagasse. Key performance metrics included fiber reactivity, xylan recovery, and the extent to which pretreatment hydrolyzate inhibited glucose fermentation. A thermodynamic and economic analysis was also completed. In a preliminary characterization using a 250 mL batch reactor, LHW pretreatment (220°C, 2 min) produced highly reactive fiber—≥90% conversion by simultaneous saccharification and fermentation (SSF)—over a range of solids concentrations (1–10%). At ∼10% solids, however, LHW pretreatment produced hydrolyzate that inhibited fermentation rate. A more comprehensive study using a 25 L reactor was also conducted. In this study, both LHW and steam pretreatment were capable of achieving ≥90% SSF conversion. Combined effectiveness for LHW pretreatment, however, was limited to ∼80% SSF conversion and ∼80% xylan recovery, while combined effectiveness for steam pretreatment was even lower due to poor xylan recovery. In addition, solids concentration (1–8%) significantly affected LHW pretreatment performance: xylan dissolution, hydrolyzate furfural concentration, and hydrolyzate inhibition increased, while xylan recovery and hydrolyzate pH decreased. Key conclusions are: (1) LHW pretreatment is more effective than steam pretreatment since it achieves better xylan recovery; (2) Batch LHW pretreatment produces results comparable to conventional dilute acid pretreatment (80% SSF conversion; 80% xylan recovery); (3) Achieving concurrently high (>90%) SSF conversion and xylan recovery will likely require a modified LHW pretreatment configuration that better preserves xylan; (4) Differences between LHW and steam pretreatment may result as much from the fact that the two methods operate at different solids concentration as from differences between saturated steam and liquid water; (5) LHW pretreatment performance could not be adequately correlated to the severity parameter suggesting that kinetic behavior for LHW pretreatment is different than that for steam pretreatment. |
