Glucose production from anhydrosugars by acid hydrolysis

The thermal processing of lignocellulosic material, for example by fast-pyrolysis, results in the formation of three fractions namely char, gases, and pyrolysis oil, the latter also referred to as bio-oil. The bio-oil composition depends upon the type of lignocellulosic material as well as pyrolysis conditions used, but in general is a mixture of acids, aldehydes, furans, phenols, water, and anhydrosugars. Among the anhydrosugars, 1, 6-anhydro-β-D-glucopyranose, commonly known as levoglucosan (LG), might be present in the bio-oil in major concentrations. LG can be converted via hydrolysis into monomeric sugar units such as glucose, which is a valuable chemical platform; for example it can be fermented to produce biofuels (ethanol and butanol). However the hydrolysis of LG into glucose is not a straightforward process, as it involves several parameters including temperature, residence time, catalyst type and acid catalyst to LG ratio. Normally liquid or solid acid catalysts are used to enhance the hydrolysis process and therefore to improve the glucose yield. The use of liquid acid catalysts such as sulfuric acid (H2SO4), encompasses several drawbacks as these liquid catalysts are difficult to recover and recycle, are environmentally unfriendly, represent a potential corrosion hazard, and might also promote the formation of by-products such as 5-hydroxymethyl furfural (5-HMF) and levulinic acid. On the other hand solid acid catalysts can be recovered by phase separation, are environmentally friendly and there are a wide range of catalysts available including acid zeolites, heteropolyacids (HPAs), polymer-based resins and, carbon-based.

This research work will collate and evaluate information about research into existing solid acid catalysts to enhance the acid hydrolysis of anhydrosugars including LG and cellobiose into glucose. The results will lead to the selection of preferred catalysts based on their properties and influence during the hydrolysis process. The variation of the process parameters such as reaction time, temperature and type of catalyst, will be also considered and analysed for their impact in the glucose yield. Future studies will also include the influence of the substrate to catalyst ratio as well as other catalytic properties. This overview will form the basis of an experimental programme.