ChemLiVal was a 3.5-year project aiming at developing new environmentally friendly pathways for the synthesis of aromatic chemicals by selective heterogeneous catalysis of lignins for bio-active molecules and technical polymers. The approach of the project consisted of 1) starting with a high purity lignin to avoid interferences of non-lignin compounds; 2) proceeding with a “deconstruction” of the lignin by coupling depolymerization and/or catalysis to access an aromatic pool; 3) addressing the problems of selectivity and purifications; 4) transforming the obtained aromatics into intermediates for fine chemicals and technical polymers. Particular attention was paid to reduce the impurities (extractives, carbohydrates and inorganics) of kraft lignin after precipitation with CO2 or H2SO4. Very high purity (up to 96 % of lignin) was obtained with successive cycles of dissolution/reprecipitation/washing. Additional purification could be achieved by removal of remaining sulfate ions, reducing the final sulfur content of the lignin. Quantitative 2D QQ-HQSC combined with 31P NMR spectroscopy analyses allowed determining the different structural moieties present in the lignins. Pre-depolymerization trials with different oxidants were tested, but unfortunately, no important reduction of the molar mass was observed. Then, different catalytic systems were tested in order to “deconstruct the lignin structure” into smaller molecules : Au/TiO2, Pt/Al2O3, Au/Ti and Ag/Ti supported on SBA-15, Fe(TAML)Li alone and supported on Si02. A complex separation protocol was developed in order to allow recovering the products after the catalyzed reactions. Three fractions were recovered in most cases: 1) monoaromatic, essntially phenolic compounds; 2) oligomers; 3) solid residue (lignin + char) recovered as precipitate in acidic medium. Although different proportions of these three fractions and the phenolic compounds were observed, for all the cases, the fraction of monoaromatic molecules obtained was very small, demonstrating a certain recalcitrance of lignin to deconstruction. Moreover, the separation of the monomers is very complex to be economically feasible, but seems interesting for partial replacement of phenol in adhesives. Fiinally, fine chemistry was approached only with lignin model molecules and the production of styrene by Cu-phenantroline and biaryles and stylbenes by Pd-catalyzed reactions are the most noticeable achievements.

Chemical valorisation of lignins toward fine chemicals and polymers: The ChemLiVal project

251st National Meeting (2016)

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