Salt-assisted organic-acid-catalyzed depolymerization of cellulose

Abstract

Dicarboxylic acids (e.g. oxalic and maleic acid) are able to depolymerize cellulose, producing oligomers and glucose. However, to reach efficient organic-acid-catalyzed performances with crystalline celluloses, high temperatures (>160 °C) are needed. These energetically-demanding conditions lead to undesired sugar degradation as well. Herein it is shown that organic acid-catalyzed cellulose depolymerization can proceed efficiently in water under mild reaction conditions (100–125 °C) by the addition of inexpensive NaCl (30 wt%). The application of some pressure in the reactor (10–30 bar) also influences and improves the depolymerization outcome. It is believed that the salt solutions act in a mechanism similar to ionic liquids and disrupt the hydrogen-bond matrix among cellulose fibers. Depolymerization proceeds efficiently with amorphous cellulose, α-cellulose, as well as with microcrystalline cellulose (Avicel^®). Importantly, catalysis can be easily controlled by temperature, catalyst loading and salt concentrations, as well as by the applied pressure in the reactor, and thus sugar degradation can be diminished. Furthermore, experiments conducted using concentrated seawater as solvent and maleic acid as catalyst showed positive results in the hydrolysis of Avicel^®.