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

Abstract

Abstract 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.