The present work aims at exploring a newhydrolysis approach using sequential combinations of organic acid [oxalic acid(OA)] andbase [tetramethylammonium hydroxide (TMAH)] toconvert lignocellulosicbiomass at mild conditions (150-215 C, 1-2h,and 1atm N2) using a spruce wood sample in a batch reactor. In the single-step tests, hydrolysiswithOAcan convert biomass to yield sugars and furanic compounds.Hydrolysis with TMAH mainly depolymerizes lignin to produce phenolic compounds but also converts some poly- saccharides in biomass possibly by the peeling reaction and/or alkaline hydrolysis.Asequential combination of OA and TMAHcan significantly increase the conversion of the biomass compared to single- or two-step reactions with either the acid or the base. The analysis of liquid products by chemical derivatization followed by gas chromatography equippedwith a flame ionization detector (GC-FID) and the characterization of the solid residues by pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) and 13Ccross-polariza- tionmagic angle spinning nuclearmagnetic resonance (CPMAS NMR) reveal strong synergetic effects from the sequential combinationof acidandbase. Insingle-step reactions,OAserves as aprotondonor tocleave the glycosidic bond between polysaccharide monomers, while TMAH reacts more selectively to lignin than polysaccharides. In two-step tests, the reaction withOAin the first step significantly enhances the conversion with TMAH in the second step by almost twice compared to the corresponding reaction with base alone. GC-FID analysis of the liquid sample shows relatively higher conversion of carbohydrates in the biomass with base in the second step.Py-GC-MSand 13CCPMASNMRanalysis also reveals that acid treatment in the first step enables base to convert more cellulose in the second step.
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