The aim of this project was to determine a fundamental understanding of the parameters affecting a microwave pyrolysis and microwave hydrolysis process of microcrystalline cellulose, providing a fundamental insight into the processes of cellulose degradation.
A systematic investigation into the microwave pyrolysis of cellulose was performed in which the fundamental parameters of microwave power, microwave duration, sample density, sample pre-heating and maximum pyrolysis temperature were studied. About 65wt.% decomposition of microcrystalline cellulose could be achieved, resulting in the formation of ~44wt.% bio-oil or ~26wt.% gas under their optimum microwave pyrolysis conditions. The maximum temperature/heating rate attained during the microwave pyrolysis processes and moisture content played a critical role in the overall extent of decomposition.
The temperature of decomposition under microwave activation was ~120oC lower than that of the thermal decomposition, with initiation of the decomposition process occurring at ~180oC. This coincides with the phase change of cellulose structure.
However, the resulting pyrolysis bio-oil largely consisted of levoglucosenone, 1,4:3,6-dianhydro-α-D-glucopyranose, levoglucosan and 1,6-anhydro-β-D-glucofuranose. Due to limitations in use of these products, a hydrolysis process to produce simple fermentable sugars was developed.
It proved possible to achieve ~80wt.% decomposition of cellulose with ~30-40wt.% fermentable sugars formed. Further to this, the new microwave specific reaction pathway of cellulose decomposition was determined and the degree of freedom of the cellulose enclosed -CH2OH groups were found to be crucial. This mechanism helped explain the key experimental observations such as: high efficiency of microwave treatment; the dependence of the selectivity yield of glucose on the applied microwave density; the observed high glucose to HMF ratio and the influence of the degree of cellulose crystallinity on the results of the hydrolysis.
