• Energy Research

This study aims to characterize and valorize hemp residual biomass by a slow pyrolysis process. The volatile by-products of hemp carbonization were characterized by several methods (TGA, UV-VIS, TLC, Flash Prep-LC, UHPLC, QTOF-MS) to understand the pyrolysis reaction mechanisms and to identify the chemical products produced during the process. The obtained carbon yield was 29%, generating a gaseous stream composed of phenols and furans which was collected in four temperature ranges (F1 at 20–150 °C, F2 at 150–250 °C, F3 at 250–400 °C and F4 at 400–1000 °C). The obtained liquid fractions were separated into subfractions by flash chromatography. The total phenolic content (TPC) varied depending on the fraction but did not correlate with an increase in temperature or with a decrease in pH value. Compounds present in fractions F1, F3 and F4, being mainly phenolic molecules such as guaiacyl or syringyl derivatives issued from the lignin degradation, exhibit antioxidant capacity. The temperature of the pyrolysis process was positively correlated with detectable phenolic content, which can be explained by the decomposition order of the hemp chemical constituents. A detailed understanding of the chemical composition of pyrolysis products of hemp residuals allows for an assessment of their potential valorization routes and the future economic potential of underutilized biomass.

AbstractKraft lignin valorization is the cornerstone for the establishment of biorefineries based on residual fractions from the pulping processes. From the precipitation process to depolymerization, various strategies have emerged, all focused on obtaining high yields or higher purity monomers. The strategy used in this study was to modify the structure of the precipitated Kraft lignin with different oxidative enzymatic treatments, with the purpose of facilitating subsequent catalytic depolymerization. The treatments were performed with different concentrations of lacasse and mediator, and then lignin structure and chemical composition were analyzed to find the optimal treatment for depolymerization. Chemometric methods based on infrared signals were used as fast tools to reduce the complexity of the chemical information generated from lignin characterization, and were therefore used to distinguish the most appropriate chemoenzymatic treatment. The results of the chemical catalysis showed higher conversion yields of the Kraft lignin after the enzymatic process than after using only chemical catalysis. The primary compounds obtained were catechol and its derivatives, thus validating its selection by means of infrared spectroscopy and chemometrics. In conclusion, it was possible to choose a straightforward chemoenzymatic process that improves the conversion of the Kraft lignin to aromatic compounds with the help of non‐destructive, low‐cost, and fast tools. © 2020 Society of Chemical Industry and John Wiley & Sons, Ltd