Biomass pretreatment generally aims to increase accessibility to plant cell wall polysaccharides for carbohydrate-active enzymes to produce sugars for biological or catalytic upgrading to ethanol or advanced biofuels. Significant research has been conducted on a suite of pretreatment processes for bioethanol processes. An alternative option, which has received less attention in the biofuels community, is the use of alkaline pretreatment for the partial depolymerization of lignin from intact biomass. A known issue with alkaline pretreatment is the loss of polysaccharides from peeling reactions, but this loss can be mitigated with anthraquinone, as commonly practiced in pulping. Here, we conduct a comprehensive bench-scale evaluation of alkaline pretreatment using corn stover at temperatures of 100, 130, and 160 °C and sodium hydroxide loadings from 35 to 660 mg NaOH/g dry biomass with anthraquinone. Compositional analysis is conducted on the starting material and residual solids after pretreatment, and mass balance is inferred in the liquor by difference. The residual solids after alkaline pretreatment are characterized for crystallinity and imaged by scanning and transmission electron microscopy to reveal the physical changes in the carbohydrate portions of the biomass remaining after pretreatment, which demonstrate dramatic modifications to biomass cell wall architecture with lignin removal but rather insignificant changes in cellulose crystallinity. Our results show that alkaline pretreatment at relatively mild conditions is able to remove substantial amounts of lignin from biomass. Going forward, to be an economically feasibile process, technologies will be required to upgrade the resulting lignin-rich liquor stream.

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Furfural is an important fuel precursor which can be converted to hydrocarbon fuels and fuel intermediates. In this work, the production of furfural by dehydration of process-relevant pentose rich corn stover hydrolyzate using a biphasic batch reaction system has been investigated. Methyl isobutyl ketone (MIBK) and toluene have been used to extract furfural and enhance overall furfural yield by limiting its degradation to humins. The effects of reaction time, temperature, and acid concentration (H 2 SO 4 ) on pentose conversion and furfural yield were investigated. For the dehydration of 8 wt % pentose-rich corn stover hydrolyzate under optimum reaction conditions, 0.05 M H 2 SO 4 , 170 °C for 20 min with MIBK as the solvent, complete conversion of xylose (98−100%) and a furfural yield of 80% were obtained. Under these same conditions, except with toluene as the solvent, the furfural yield was 77%. Additionally, dehydration of process-relevant pentose rich corn stover hydrolyzate using solid acid ion-exchange resins under optimum reaction conditions has shown that Purolite CT275 is as effective as H 2 SO 4 for obtaining furfural yields approaching 80% using a biphasic batch reaction system. This work has demonstrated that a biphasic reaction system can be used to process biomass-derived pentose rich sugar hydrolyzates to furfural in yields approaching 80%.

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BackgroundIndustrial biotechnology that is able to provide environmentally friendly bio-based products has attracted more attention in replacing petroleum-based industries. Currently, most of the carbon sources used for fermentation-based bioprocesses are obtained from agricultural commodities that are used as foodstuff for human beings. Lignocellulose-derived sugars as the non-food, green, and sustainable alternative carbon sources have great potential to avoid this dilemma for producing the renewable, bio-based hydrocarbon fuel precursors, such as microbial lipid. Efficient bioconversion of lignocellulose-based sugars into lipids is one of the critical parameters for industrial application. Therefore, the fed-batch cultivation, which is a common method used in industrial applications, was investigated to achieve a high cell density culture along with high lipid yield and productivity.ResultsIn this study, several fed-batch strategies were explored to improve lipid production using lignocellulosic hydrolysates derived from corn stover. Compared to the batch culture giving a lipid yield of 0.19 g/g, the dissolved-oxygen-stat feeding mode increased the lipid yield to 0.23 g/g and the lipid productivity to 0.33 g/L/h. The pulse feeding mode further improved lipid productivity to 0.35 g/L/h and the yield to 0.24 g/g. However, the highest lipid yield (0.29 g/g) and productivity (0.4 g/L/h) were achieved using an automated online sugar control feeding mode, which gave a dry cell weight of 54 g/L and lipid content of 59 % (w/w). The major fatty acids of the lipid derived from lignocellulosic hydrolysates were predominately palmitic acid and oleic acid, which are similar to those of conventional oilseed plants.ConclusionsOur results suggest that the fed-batch feeding strategy can strongly influence the lipid production. The online sugar control feeding mode was the most appealing strategy for high cell density, lipid yield, and lipid productivity using lignocellulosic hydrolysates as the sole carbon source.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-016-0542-x) contains supplementary material, which is available to authorized users.