Abstract
Biochemical conversion of wheat straw was investigated using hydrothermal pretreatment, enzymatic saccharification, and microbial fermentation. Pretreatment conditions that were compared included autocatalyzed hydrothermal pretreatment at 160, 175, 190, and 205 °C and sulfuric-acid-catalyzed hydrothermal pretreatment at 160 and 190 °C. The effects of using different pretreatment conditions were investigated with regard to (i) chemical composition and enzymatic digestibility of pretreated solids, (ii) carbohydrate composition of pretreatment liquids, (iii) inhibitory byproducts in pretreatment liquids, (iv) furfural in condensates, and (v) fermentability using yeast. The methods used included two-step analytical acid hydrolysis combined with high-performance anion-exchange chromatography (HPAEC), HPLC, ultra-high performance liquid chromatography-electrospray ionization-triple quadrupole-mass spectrometry (UHPLC-ESI-QqQ-MS), and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). Lignin recoveries in the range of 108–119% for autocatalyzed hydrothermal pretreatment at 205 °C and sulfuric-acid-catalyzed hydrothermal pretreatment were attributed to pseudolignin formation. Xylose concentration in the pretreatment liquid increased with temperature up to 190 °C and then decreased. Enzymatic digestibility was correlated with the removal of hemicelluloses, which was almost quantitative for the autocatalyzed hydrothermal pretreatment at 205 °C. Except for the pretreatment liquid from the autocatalyzed hydrothermal pretreatment at 205 °C, the inhibitory effects on Saccharomyces cerevisiae yeast were low. The highest combined yield of glucose and xylose was achieved for autocatalyzed hydrothermal pretreatment at 190 °C and the subsequent enzymatic saccharification that resulted in approximately 480 kg/ton (dry weight) raw wheat straw.
Highlights
Growing global energy demand and the need to replace fossil fuels with renewable fuels are the major challenges of modern society [1]
A portion of the filter cake was stored frozen for analytical enzymatic saccharification assay, and the rest was air-dried for around one week; the yield of pretreated solids was determined gravimetrically based on DW
The yield of pretreated solids resulting from the most severe autocatalyzed pretreatment was 27% lower than that of the least severe one
Summary
Growing global energy demand and the need to replace fossil fuels with renewable fuels are the major challenges of modern society [1]. The current production of liquid biofuels, such as bioethanol, is dominated by biochemical conversion routes mainly based on food-related feedstocks, such as corn starch and sugarcane sugar. Agricultural and agroindustrial residues, e.g., wheat straw, corn stover, and sugarcane bagasse, are lignocellulosic materials of interest in many countries due to their availability [3,4]. Co-utilization of lignocellulosic residues with starch or sugar can further boost bioethanol production through integration into 1.5 G processes [5]. Biochemical conversion of agricultural residues, such as corn stover and wheat straw, has been significantly improved [7,10], but further research is still required for designing highly competitive and sustainable processes for the production of biofuels and other bio-based commodities
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