Acid catalyzed cellulose hydrolysis involves interactions at the solvent-solid interface as protons attach to the surface to permit solvent molecules to break the glycosidic bonds required to convert cellulose into glucose. For many years, researchers have known that amorphous cellulose is more reactive than crystalline varieties. The reactivity of amorphous cellulose has motivated many studies to exploit its reactivity for unlocking the potential of biomass for production of renewable fuels and chemicals. In parallel, researchers showed that amorphous cellulose spontaneously crystallizes in the presence of water. We performed a series of careful tests on cellulose amorphized to different extents, both before and after exposure to liquid water. Amorphous cellulose is indeed more reactive than crystalline cellulose, but that exposure to water promotes spontaneous collapse of the amorphous cellulose to crystalline cellulose II, a form of crystalline cellulose that is less common than the familiar cellulose I. The reactivity of cellulose II is intermediate to cellulose I and amorphous cellulose, explaining the observation that amorphization treatments increased cellulose hydrolysis reactivity; however, the mechanism for the increased reactivity is not the original explanation and instead involves formation of cellulose II. Interestingly, exposure to non-aqueous solvents under non-reactive conditions does not promote conversion of amorphous to crystalline cellulose, encouraging evaluation of alcoholysis conditions. Here, we found that amorphized cellulose rapidly depolymerizes in the presence of ethanol at mild conditions. A multi-step process involving amorphization-ethanolysis-amorphization-ethanolysis achieved &gt;60% cellulose conversion at 140 °C and after several hours. Interestingly, we found that ethanolyzed cellulose recovered crystallinity, suggesting the presence of both solvent-induced and reaction induced recrystallization routes. Hypothesizing a role for the hydrophobic effect, we then studied the effect of salting in and salting out additives on the reactivity of amorphous cellulose. These tests showed that addition of the strongly salting in salt, guanidinium chloride, greatly increased cellulose hydrolysis reactivity, consistent with a hydrophobic effect. Lastly, we generalized this finding to bamboo.

Chemistry at the cellulose-solvent interface

ACS Spring Meeting 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.