The depletion of fossil fuels alongside an increase in carbon footprint, and the growing need for utilizing sustainable sources of energy has led to advancements in deconstruction of lignocellulosic biomass for economic production of biofuels and bioproducts. Co-solvent enhanced lignocellulosic fractionation (CELF) with tetrahydrofuran(THF)-water has shown to significantly improve delignification and cellulose deconstruction by increased solubilization of cellulose for acid-based hydrolysis. While atomistic molecular dynamics (MD) simulations have provided insights on the preferential aggregation behavior of THF-water and decrystallization of cellulose fibrils, little is known about the local solvent structure around hydrolyzed sites and how it facilitates the disintegration of fibril into simple sugars. In this work, we perform all-atom replica-exchange umbrella sampling (REUS) simulations of hydrolyzed (reducing end) cellulose fibril composed of 18 chains with degree of polymerization (N) = 20 in two systems, (1) 1:1 THF: water by volume and (2) pure water at 443 K. We investigate the effects of preferential co-solvent interactions around the hydrolyzed sites on decrystallization of cellulose fibril by calculating free energy cost from potential mean force (PMF) profiles. Contact number defined between heavy atoms of hydrolyzed units and remaining fibril are used as reaction coordinates for estimation of free energy. Furthermore, we examine the local solvent structure around the hydrolyzed sites through radial distribution functions (RDFs) and hydrogen bonding analysis. The results are compared with the solvent structure from acid-based hydrolysis experiments and reactive MD ReaxFF simulations. The coupling of physical (solvent organization) and chemical (catalysis of bond cleavage) processes emerges as a key principle behind optimal pretreatment design.

Effect of co-solvent pretreatment on acid-based hydrolysis and decrystallization of cellulose: A mole dynamics study

ACS Spring Meeting 2021

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