Ana Toledano

Heterogeneously Catalysed Mild Hydrogenolytic Depolymerisation of Lignin Under Microwave Irradiation with Hydrogen‐Donating Solvents

A series of hydrogen‐donating solvents have been investigated in lignin depolymerisation practices by using a mild, microwave‐assisted, hydrogen‐free, hydrogenolytic approach promoted by the use of in situ hydrogen generating reagents with Ni 10 % Al‐SBA‐15 as a heterogeneous catalyst. Selected solvents were tetralin, isopropanol, glycerol and formic acid. Final identified products, namely bio‐oil, biochar and residual lignin were characterised by using GC–MS, matrix‐assisted laser desorption/ionisation time‐of‐flight mass spectrometry and high‐performance size‐exclusion chromatography to evaluate the extension of the hydrogenolytic process. Interestingly, the obtained phenolic monomeric products were found to be remarkably affected by the type of hydrogen‐donating solvent, with the best results obtained with formic acid, a potentially renewable derived solvent, which unexpectedly provided no biochar as compared to a maximum of 38 % obtained for tetralin. The reported protocol constitutes another step towards the development of fully sustainable and “green” methodologies of low environmental impact for lignin depolymerisation.

Fractionation of organosolv lignin from olive tree clippings and its valorization to simple phenolic compounds.

Lignin valorization practices have attracted a great deal of interest in recent years due to the large excess of lignin produced by the pulp and paper industry, together with second-generation bioethanol plants. In this work, a new lignin valorization approach is proposed. It involves ultrafiltration as a fractionation process to separate different molecular weight lignin fractions followed by a hydrogen-free, mild, hydrogenolytic, heterogeneously catalyzed methodology assisted by microwave irradiation to obtain simple phenolic, monomeric products by depolymerization using a nickel-based catalyst. The main products obtained were desaspidinol, syringaldehyde, and syringol; this proves the efficiency of the depolymerization conditions applied. The concentration of these observed compounds increased when the molecular weights of the lignin fractions increased. The applied depolymerization conditions, which take advantage of the use of formic acid as a hydrogen-donating solvent, did not generate any biochar in the systems.