Fractionation: an essential tool for lignin valorization

Lignin is a hydrophobic three-dimensional polymer that acts as a binder accounting for the plants structural integrity and as a regulator for the water flux inside the cell wall. Lignin utilization as a potential feedstock for chemical products has attracted more and more attention. Being one of the three main constituents in biomass, it represents a very attractive low-cost, renewable and largely available starting material. However, lignin is difficult to decompose due to its structural complexity and its high stability and up to now most of lignin is burned as a source of energy. Nowadays valorization of lignin and its transformation into small high value chemicals represent a real challenge and is fully linked to the complexity and the heterogeneity of the starting material. Such variability originates from the source of the biomass, the growing parameters and the extraction conditions. One of the best ways to degrade lignin is by using oxidative depolymerization processes. The main drawback of these methods is the possibility of a fast recombination of the small molecules which are already part of the raw material performed by oxygen-based radical species [1]. In order to obtain more homogeneous starting material for the following oxidative treatments, we set-up an industrial fractionation method. The starting material which has been used in this work has been the Lignin ProtobindTM1000 which is an agricultural fiber soda pulp. The fractionation step is a necessary tool to obtain different fractions which appear much more consistent in terms of average molecular weight, polydispersity and solubility. In this work ProtobindTM1000 has been dissolved in an aqueous/ethanol solution and submitted firstly to a microfiltration under vacuum in order to eliminate the insoluble residue. Then it undergoes the cross-flow filtration process using two subsequent membranes with a cut-off of 3 kDa and 1 kDa. All the retentate and permeate fractions of the fractionation process have been fully characterized in terms of composition, chemical and physical properties. This strategy has offered an essential tool for a more efficient lignin valorization allowing to identify specific applications for all the different fractions, spanning from the material science [2] to the preparative organic chemistry. Acknowledgements This work has been performed as part of the ValorPlus Project that has received funding from the European Union's Seventh Framework Programme for research, technological development and demonstration under grant agreement no FP7-KBBE-2013-7-613802.