Time domain NMR spectroscopy as a fast method for probing the efficiency of biomass pretreatments for second generation ethanol production

Abstract

Herein we describe a simple and fast spectroscopy method based on the Time Domain Nuclear Magnetic Resonance (TD-NMR) method (or low field NMR) to determine the efficiency of lignocellulosic biomass pretreatments for increasing saccharification by enzymes, a key step in second generation (2G) ethanol production. Three different pretreatments (liquid hot water (LHW), steam explosion (SE) and steam-exploded and delignified (SED) process) were used as characteristic processes to reduce biomass recalcitrance, being the untreated and treated biomass (sugarcane bagasse) fully characterized before and after the treatments – using electron microscopy, structural techniques and the direct evaluation of commercial enzyme activity. The analyses in TD-NMR indicate that the binding mode of water (1. Shorter T2-water molecules of low mobility, which are adsorbed into the cell wall and around the lumens; 2. Intermediate T2 -looser water molecules and within small cellulose pores; 3. Longer T2-water inside larger cellulose pores and excess water outside the cellulose pores) as evinced by the technique are directly related to the ability of each process for increasing the enzymatic action in the saccharification of pretreated biomass. Given its low cost and fast acquisition time, the proposed method based in TD-NMR could be especially useful as a predictive technique for control routines in large-scale industrial production of 2G ethanol.