Multi-step fractionation as a tool for enhanced valorization of technical lignins: a model study

The valorisation of lignin obtained as a by-product of the pulping and biofuel industries is one of the most promising topics in the bioresource field. Despite its potential value as the only massively available aromatic biopolymer feedstock, technical lignin is nowadays mostly burnt as low cost energy source because of its chemical recalcitrance. The high heterogeneity of this material, largely dependent on the different vegetal sources and the specific biomass recovery methods, restricts its direct use and hinders also the optimization of depolymerisation approaches. The development of effective technical lignin fractionation strategies is therefore today one of the most challenging topic in the green chemistry field. In this study, the fractionation of an industrial commercial lignin was developed by a three step procedure set-up either in aqueous or in an environmentally friendly organic solvent in order to obtain sustainable and scalable processes.1,2 The first step consisted in a microfiltration or a Soxhlet extraction, depending on the type of solvent used. Then a cascade membrane-mediated ultrafiltration allowed to obtain at the end three refined lignin fractions. The parent lignin and the different lignin fractions were fully characterized. The two-step process reported here allows accessing lignin fractions with well-defined physico-chemical properties (including mass distribution, glass transition temperature, aliphatic and phenolic hydroxyl groups concentration, syringyl/guaiacyl unit ratio) and represents a valuable approach towards the development of bio-based polymers and the preparation of key platform chemicals, thereby paving the way for an effective exploitation and valorization of this remarkable resource. [1] Allegretti, C.; Fontanay, S.; Krauke, Y.; Luebbert, M.; Strini, A.; Troquet, J.; Turri, S.; Griffini, G.; D’Arrigo, P. ACS Sustainable Chem. Eng. 2018, 6, 9056-9064; DOI: 10.1021/acssuschemeng.8b01410. [2] Allegretti, C.; Fontanay, S.; Rischka, K.; Strini, A.; Troquet, J.; Turri, S.; Griffini, G.; D’Arrigo P. ACS Omega 2019, in press; DOI: 10.1021/acsomega.8b02851.