Degradation of cellulose into glucose is interesting for the production of biofuels and platform chemicals. In contrast to the common degradation routes with aqueous systems, we have recently introduced a system that functions with HCl gas.<sup>1</sup> Similar to harsh acid hydrolysis in aqueous medium, the cellulosic fibres were discolored within a prolonged HCl (g) hydrolysis, allegedly because of the formation of humins from furfural precursors. Here, we introduce a modified hydrolytic process where the cellulosic fibres have been impregnated with chlorite prior to the hydrolysis within HCl gas reactor. Evidently, formation of humins decreases with the chlorite addition.<br/>In this realm, different cellulose polymorphs were hydrolyzed by HCl gas with chlorite addition to examine the effect of the crystal structure on the degradation rate of cellulose while simultaneously blocking the discoloration. Furthermore, we followed the effect of the water content within the fibers on the degradation and humin formation. The hydrolysis was monitored with various methods, e.g., oligosaccharide and monosaccharide analysis of filtrates by chromatography as well as in situ video monitoring of the possible discoloration. X-ray diffraction was conducted to determine the possible crystallinity change and the degree of polymerzation was analyzed by viscometry from the remaining, hydrolyzed cellulose. It was found that the cellulose crystallites started to degrade during hydrolysis process at 50% water content and with an excess of HCl gas. Also, the degradation rate of cellulose expectedly depended on the chosen polymorph. HCl gas hydrolyzed cellulose samples were washed with water and filtrated prior to the analyzes. Interestingly, we found that the combination of HCl (g) and chlorite disintegrated the cellulosic fibres first into small colloidal particles which could be fully degraded into glucose by 4% posthydrolysis with sulphuric acid.

Degradation of cellulose polymorphs with modified HCl gas hydrolysis

ACS Spring 2022

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