Abstract:
The use of bio-oil from fast pyrolysis of biomass as a substitute for conventional fossil fuels is being examined, but there is scepticism surrounding its feasibility due to its acidity, instability, and low calorific value. These characteristics are caused primarily by the high elemental oxygen content in the oil. An active catalyst which is of interest due to its reported ability to facilitate certain mechanisms favourable in oxygen reduction, is a nanostructured material called layered double hydroxide (LDH). A catalyst support was made by synthesising mesoporous silica containing pre-made MgAl-LDH and CaAl-LDH. High surface areas (up to 600 m2/g) and mesopores (3.3 to 4.8 nm) were produced by accurate control of the synthesis pH. MgAl-LDH significantly reduced the oxygen and water contents and increased calorific values of the lighter pyro-oil fractions (16.2 to 22.5 MJ/kg), while CaAl-LDH increased the oxygen contents of these oils. The catalysts had little effect on the oxygen contents of the heavier pyro-oil fractions, suggesting that there was greater catalytic action on the lighter compounds as a result of the catalyst support pore size. The optimal catalyst support was that which was synthesized at an intermediate pH of 7. Understanding the synthesis conditions required for improved silica catalyst supports will be helpful to examine the effects of future powdered catalysts in similar processes.
