Abstract
Bagasse, a major by-product of sugarcane-processing industries, has potential to play a significant role as feedstock for production of cellulosic ethanol, platform chemicals, and bio-based commodities. Pretreatment is essential for efficient processing of lignocellulosic feedstocks by biochemical conversion. In this work, auto-catalyzed (A-HTP) and dilute sulfuric-acid-catalyzed (SA-HTP) hydrothermal pretreatment of sugarcane bagasse was investigated, setting the temperature (175−205 °C) and the time (4−51 min) in such a way that the severity factor (SF) was always maintained at one of three predetermined values (2.8, 3.8, and 4.8). The investigation covered the effects of different operational pretreatment conditions on (i) the formation of sugars and water-soluble bioconversion inhibitors, including newly discovered inhibitors such as formaldehyde and p-benzoquinone, in the pretreatment liquid, (ii) the chemical composition and recovery of constituents in the solid phase, as determined using two-step treatment with sulfuric acid, Py-GC/MS, and solid-state NMR, (iii) pseudo-lignin formation, (iv) furan aldehydes in condensates from the gas phase, (v) enzymatic digestibility of pretreated solids, (vi) enzyme inhibition by pretreatment liquids, and (vii) fermentability of pretreatment liquids using Saccharomyces cerevisiae yeast. Glucose and xylose were the predominant sugars in pretreatment liquids from SA-HTP and A-HTP, respectively. For A-HTP, the enzymatic digestibility of the pretreated solids was proportional to the SF, while for SA-HTP no clear trend was observed. The best enzymatic digestibility (above 80%) was achieved for A-HTP performed at SF 4.8. The highest total yields of glucose and xylose, the predominant sugars, were achieved for A-HTP at SF 3.8 and temperatures of 190 °C and 205 °C. The fermentability of the pretreatment liquids by Saccharomyces cerevisiae was lower for SA-HTP than for A-HTP. The investigation suggests that hydrothermal pretreatment of sugarcane bagasse can be performed with good results without addition of sulfuric acid, but that the conditions must be just harsh enough to almost quantitatively solubilize the hemicelluloses.
Highlights
Lignocellulosic residues have potential as feedstocks for bio-based fuels, chemicals, and materials
The hydrothermal pretreatment performed without addition of acid catalyst resulted in higher pretreatment yields, i.e. gravimetric yields of pretreatment solids, than the one cata lyzed with sulfuric acid
A wide array of chemical, biochemical, and microbial analyses pro vided detailed information about positive and negative aspects of different operational conditions used for hydrothermal pretreatment of sugarcane bagasse
Summary
Lignocellulosic residues have potential as feedstocks for bio-based fuels, chemicals, and materials. For producing advanced biofuels and other bio-based commodities from lignocellulosic biomass, it is required to deconstruct the feedstock into sugars that could further be converted into end-products of interest (Chundawat et al, 2011). Numerous pretreatment methods can be used for improving bioconversion to fermentable sugars. Their effects on the susceptibility of substrates to enzymes are achieved by removal of hemicelluloses or disruption of lignin, among other mechanisms (Zhao et al, 2012). For setting-up efficient bioconversion processes, it is crucial to develop cost-effective and energy-efficient pretreatment methods resulting in high yields of sugars from cellulose and hemicelluloses
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