Characterization and Deconstruction of Oligosaccharides in Black Liquor From Deacetylation Process of Corn Stover

Wei Wang,Rui Katahira,Xiaowen Chen,Melvin Tucker

doi:10.3389/fenrg.2019.00054

Wei Wang, Rui Katahira + Show 2 more

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https://doi.org/10.3389/fenrg.2019.00054

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Abstract

The NREL developed, atmospheric pressure, low severity Deacetylation and Mechanical Refining (DMR) process under atmospheric pressure, generates highly fermentable, low toxicity sugar syrups and highly reactive lignin streams. The dilute alkali deacetylation step saponifies acetyl groups from the hemicellulosic fraction of biomass into a black liquor waste stream that also contains solubilized acetic, ferulic, p-coumaric acids and lignin-carbohydrate complexes (LCCs), oligosaccharides, and solubilized lignin. Valorization of the soluble components in the deacetylation black liquor waste stream requires characterization of the black liquor. WeOur analyses show that glucan, xylan and lignin were three main components in black liquor and the oligosaccharides in the black liquor were mainly xylan dimers and trimers with arabinofuranose branch groups mainly on the xylooligomers. GPC chromatograms showed that the black liquor also contained oligomeric lignin moieties with molecular weights ranging between 1800 to ~10,000 Da. Enzymatic saccharification of the black liquor was conducted based on the compositional and structural information. Incorporation of Novozymes Cellic® CTec2 and HTec2 commercial cellulase and hemicellulase enzyme preparations with various accessary enzymes showed up to 57% hydrolysis of the xylooligosaccharides in the black liquor to monomeric sugars, which could be used to improve biorefinery carbon utilization in biological fermentations to improve end product fuel or bioproduct volumes per metric tonne of biomass processed. This is so far the first study about characterizing DMR black liquor and exploring breaking down the oligosaccharides in black liquor for potential use.

Highlights

The development of renewable liquid fuels from lignocellulosic biomass is considered by Environmental Protection Agency (EPA) as one of the most important strategies to cease the global climate change attributed to Green House Gas (GHG) emissions from fossil fuels combustion
In Deacetylation and Mechanical Refining (DMR) black liquor, xylo-oligomers were higher in concentration than gluco-oligomers because deacetylation targeted at removing acetyl branch groups on xylan back bone, which made xylan easier to be degraded
A fair amount of lignin was released from deacetylation process but it was much less than the lignin dissolved in kraft black liquor (Niemelä et al, 2007; Alekhina et al, 2015), indicating the deacetylation condition was pretty mild

Summary

Introduction

The development of renewable liquid fuels from lignocellulosic biomass is considered by Environmental Protection Agency (EPA) as one of the most important strategies to cease the global climate change attributed to Green House Gas (GHG) emissions from fossil fuels combustion. Among all the pre-treatment processes, the Deacetylation and Mechanical Refining (DMR) process developed by National Renewable Energy Laboratory (NREL, Golden, Colorado) is a unique atmospheric pre-treatment process that has demonstrated. Characterization and Deconstruction of Oligosaccharides in Black Liquor high sugar concentration (>270 g/L fermentable sugars) and low toxicity sugar syrup production from corn stover, which led to an ethanol product titer of 86 g/L in followed fermentation test (Chen et al, 2012, 2014, 2016). Mechanical refining further improves the digestibility of deacetylated biomass by increasing the cellulose accessibility with cutting and fibrillation The DMR pre-treated biomass has shown good digestibility and superb fermentability as reported previously (Zhang et al, 2014; Chen et al, 2016; de Assis Castro et al, 2017)

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