Effect of MgCl2 loading on the evolution of reaction intermediates during cellulose fast pyrolysis at 325 °C

Abstract

This study reports the effect of MgCl2 loading on the evolution of reaction intermediates during cellulose fast pyrolysis at 325°C. The loading of MgCl2 significantly changes the reaction pathways of cellulose pyrolysis and enhances the cross-linking of hydroxyl groups to release water even during the heating-up stage, as a result of the weakened hydrogen bonding networks during both the wet impregnation and the heating processes. Such a highly cross-linked cellulose strongly affects the evolution of reaction intermediates during the subsequent isothermal pyrolysis at 325°C, i.e., producing the water-soluble intermediates rich in cross-linked structures. The loading of MgCl2 may catalyse the interactions between the water-soluble and water-insoluble portions in pyrolysing cellulose, depending on the Mg distribution. Our results indicate that the water-insoluble Mg has a little effect on the pyrolysis of sugar structures in the water-insoluble portion, which still proceeds in a similar way as that of raw cellulose, i.e., dominantly via depolymerisation. Whereas the water-insoluble Mg has a strong catalytic effect on the pyrolysis of non-sugar structures in the water-insoluble portion into more condensed structures, leading to a high char yield from the pyrolysis of the MgCl2-loaded cellulose.