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Thermal Carbon Analysis Enabling Comprehensive Characterization of Lignin and Its Degradation Products

Voeller, Keith, Bílek, Honza, Kreft, Jasmine, Dostálková, Alžběta, Kozliak, Evguenii, Kubátová, Alena
ACS sustainable chemistry 2017 v.5 no.11 pp. 10334-10341
carbon, chemical speciation, feedstocks, fractionation, gas chromatography-mass spectrometry, lignin, models, oxygen, screening, solvents, temperature, thermogravimetry
We have developed a novel thermal carbon analysis (TCA) method that provides both carbon mass balance and thermal fractionation profiles. Though not providing chemical structural information, this method enables a comprehensive characterization of both lignin and its degradation products, potential renewable and sustainable feedstocks. TCA is essential as a complement to a qualitative chemical speciation by thermal desorption–pyrolysis gas chromatography–mass spectrometry (TD–Py–GC–MS). Mono- and diaromatic oxygenated compounds were used as model compounds to optimize the method. The influence of various parameters such as solvents, amounts of sample loaded, and temperature ramp configuration, were investigated. A multistep temperature program with TD and pyrolytic temperatures with and without oxygen was employed for analysis of untreated lignin, where up to 55 wt % evolved in the presence of oxygen only, this fraction being unaccounted for by currently used methods. The TCA results were supported by thermogravimetric analysis with a matching heating ramp resulting in a similar mass distribution; however, TCA has the advantage of being selective for carbon. For lignin degradation products, the TD steps of TCA yielded similar recoveries as a solvent extraction followed by GC–MS. Thus, TCA may be used for screening significant product fractions to quantify the previously uncharacterized oligomer/polymer and char fractions.