Interactions of Torrefaction and Alkaline Pretreatment with Respect to Glucose Yield of Hydrolyzed Wheat Straw

Abstract

Torrefaction is known to reduce the logistical costs of biomass. Torrefied biomass’ prospects as feedstock for fermentation to liquid biofuel are largely unknown. This study investigated the interactions of torrefaction and alkaline pretreatment of wheat straw on glucose yields from enzymatic hydrolysis, including treatment order and the potential for pH to play a role in the process. Across a range of torrefaction severities with temperatures of 200 °C, 220 °C, and 240 °C and durations of 20, 40, and 60 min, torrefaction had a negative impact on glucose yield of wheat straw with or without alkaline pretreatment and regardless of the order of alkaline pretreatment. Alkaline pretreatment after torrefaction results in higher glucose yield than alkaline pretreatment before torrefaction, or by torrefaction alone. Hence, there is the prospect for adding logistical benefits of torrefaction to the bioethanol system if alkaline pretreatment is coupled with torrefaction. Decreasing trend in pH with increase in torrefaction severities was observed for trials without buffer, indicating chemical changes causing the decrease in pH might be associated with the reduction in yield.

Synergistic Effects of Torrefaction and Alkaline Pretreatment on Sugar and Bioethanol Production from Wood Waste

“…The release of volatile matter at higher temperatures results in the condensation of solid materials, which eventually increases the ash content, similar to the earlier report of Cahyanti et al [16]. In addition, the increase in mass loss with increased torrefaction temperature is also in accordance with Tripathi et al [27] for torrefaction and alkaline pretreatment of wheat straw.…”

“…TB exhibited an increasing trend in polysaccharide retention and reduced mass loss compared to RWW, demonstrating the synergistic effect of alkali pretreatment on polysaccharide extraction. A similar observation was made by Tripathi et al [27], where the impact of alkaline pretreatment on the torrefaction of wheat straw significantly enhanced the polysaccharide yield. However, their research typically involved the alkaline pretreatment of grassy biomass followed by torrefaction.…”

“…The glucose concentratio in the RWW was 2.74%, whereas that in the TWW was 1.39% (T225) and 0.85% (T275) an decreased to 0.64% (T300). These results are in comparison with those of Tripathi et al [27 where the glucose concentration in the hydrolysate was reduced from 27.7% (raw bi mass) to 2.4% and 1.5% for wheat straw torrefied at 220 °C and 240 °C, respectively. contrast, the mannose and xylose concentrations in the hydrolysate from the T225 bioma (0.38% and 0.8%, respectively) were slightly higher than those in the raw biomass (0.62 and 0.41%, respectively), which can be attributed to the degradation of polysaccharide…”

“…The reduction in monosaccharides occurred because of the degradation of cellulose and hemicellulose as sources of glucose, mannose, and xylose. Furthermore, the higher cellulose crystallinity and hydrophobicity attained at higher torrefaction temperatures severely inhibit hydrolytic enzyme access to cellulose, resulting in reduced saccharification [7,27].…”

“…The reduction in monosaccharides occurred because of the degradation of cellulose and hemicellulose as sources of glucose, mannose, and xylose. Furthermore, the higher cellulose crystallinity and hydrophobicity attained at higher torrefaction temperatures severely inhibit hydrolytic enzyme access to cellulose, resulting in reduced saccharification [7,27]. However, alkaline pretreatment significantly improved the glucose concentration in both the RWW and TWW (T225), whereas the glucose concentration was not detected at higher temperatures (T275 and T300).…”