A Novel Solid-acid Catalyst Using Sulfonated Crosslinked Chitosan Resin

Sulfonated crosslinked chitosan resins (SCCRs) were prepared by firstly crosslinking chitosan to crosslinked chitosan resins (CCRs) using a reverse emulsion crosslinking method, followed by sulfonating CCRs with concentrated H2SO4 as the sulfonation agent. The properties and application of SCCRs as solid acid catalysts were studied. The acidic sites in SCCRs, including C-6-O and C-2-N sulfate groups, are all weak acidic sites. SCCRs of higher crosslinking degrees have a higher sulfonation rate of the C-6 primary hydroxyl groups, thus more C-6-O sulfate groups. High-temperature treatment and TG analysis verified that the crosslinking can improve the thermostability of both SCCR backbone and its acidic groups, and a higher crosslinking degree leads to better thermostability. Catalytic esterification of citric acid with butanol and propionic acid with n-butyl alcohol demonstrated that SCCRs have good catalytic activity and can be repetitively used as efficient solid acid catalysts.