Alkali lignin, a recalcitrant biomass material produced as a waste product of paper and biofuel industries, also has potential as a sustainable source of phenolic derivatives, which may have applications in chemical, agricultural and manufacturing industries. Our study focused on the characterization of lignin subjected to subcritical water (SW) treatment in comparison to untreated alkali lignin. The investigation served as a baseline study of lignin SW treatment, of use as a comparison for studies combining SW treatment with additional reagents or catalysts. Mass distribution of breakdown products by thermal desorption and pyrolytic processes, and identification of major organic and gas components were determined using a “lignomics tool-kit”, which included thermal carbon analysis (TCA), liquid-liquid extraction gas chromatography-mass spectrometry (LLE-GC-MS), thermal desorption-pyrolysis-gas chromatography-mass spectrometry (TD-pyr-GC-MS), and gel permeation chromatography (GPC) analyses. Analytical data from TCA, TD-pyr and LLE-GC-MS showed good mass balance closure for SW treated samples. SW treatment at 300 °C resulted in maximum mass of monomeric species in the liquid fraction (6.0 wt.% compared to initial lignin for unfiltered samples), although total liquid fraction species' mass decreased, showing repolymerization trends with increased temperature. Dimeric species were scant in the liquid fractions of SW treated samples although untreated lignin showed that one-fourth of organic species were dimers. Unexpectedly, a significant fraction of lignin following the TD-pyr appeared in GC-MS analysis as converted to CO2 and smaller gas species. Corroboration of lignin breakdown by GPC showed numerical-average molecular weights (Mn) for the liquid fractions of unfiltered/untreated lignin as well as unfiltered and filtered SW treated (300 °C) samples at 1630, 810, and 460 g/mol, respectively.

Lignomics toolkit analysis of subcritical water treated alkali lignin

2019 Spring National Meeting

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