The impact of process parameters on the purity and chemical properties of lignin extracted from miscanthus x giganteus using a modified organosolv method

This work evaluates the purity and chemical properties of lignin extracted directly from Miscanthus x giganteus using a modified organosolv method (direct extraction) with lignin obtained from Miscanthus x giganteus which had been subjected to sequential sub-critical water mediated hydrolysis of increasing severity (sequential extraction). The data obtained were subjected to statistical analysis to ensure significant difference (p < 0.05) unless stated otherwise. The percentage of biomass solubilisation from sequential extraction was 45.5% and greater than the value of 35.6% obtained by direct extraction. The percentage of delignification from sequential and direct extraction was 58.0% and 81.5%, respectively. An assessment of percentage of lignin recovery after precipitation from direct extraction was 69.3% whereas the sequential extraction yielded 70.3%; the results were not significantly different (p=0.38) suggesting there was no negative impact of repeatedly processing biomass prior to lignin recovery using the same experimental conditions. The purity of the precipitated lignin and lignin derived from dried supernatant by sequential extraction was 91.5% and 23.7%, respectively, of higher purity than from direct extraction (88.4% and 14.1%, respectively). The chemical properties of precipitated lignin were further characterised by Fourier Transform Infrared Spectroscopy (FTIR). This showed that the Miscanthus x giganteus which is subjected to sequential extraction yielded high purity lignin than from direct extraction. Overall, the conceptual design of this work to sequentially process biomass is a promising method for recovery of multiple naturally occurring building blocks including hemicellulose, cellulose and lignin, which then become the feedstock for various applications.