Dehydration and Condensation of Furfuryl Alcohol to Light Oligomer over Molybdenum Oxide Catalysts: Effect of Loading and Reaction Time

The conversion of renewable biomass into bio-fuels and bio-chemicals has been investigated as a result of increasing demand for petroleum oil and increasing concern of greenhouse gas emissions. Lignocellulosic biomass (non-edible biomass) is second generation biomass composed from the residues of agriculture and forest, which prevent competition with producing biomass for food and as a feedstock as renewable biomass. The abundance of lignocellulosic materials resulted in the synthesis of large amounts of furfurals through acidic hydrolysis which is an important raw material for the synthesis of valuable chemicals. Furfuryl alcohol (FA), which is produced from furfural derived from a selective dehydration of xylose, is an attractive intermediate chemical for the production of various chemicals, such as levulinic acid and polymerized FA (PFA). PFA can be easily produced from FA monomers using a strong mineral acid, such as H₂SO₄, and can produce ordered carbons through the pyrolysis, vapor deposition and carbonization methods. Although homogeneous catalysts show a higher conversion of FA monomer to FA oligomers/ polymers without hydrothermal treatment, they should be replaced by heterogeneous catalysts for separation and recycling issues. Molybdenum Oxide (MoO₃), a metal oxide catalyst was investigated in a batch reactor system for the FA dehydration reaction under mild experimental conditions, at 100^oC and ambient pressure. Five dimers (2,2â??-Difurylmethane, 2-(2-furylmethyl)-5-methylfuran, Difurfuryl ether, 4-Furfuryl-2-pentenoic acid γ-lactone, 5-Fufuryl-furfuryl alcohol), and two trimmers (2,5-Difurfurylfuran and 2,2â??-(Furylmethylene)bis(5-methylfuran)) were observed through GC and GC/MS. Various catalyst loading of MoO₃ ranging from 0.05g to 1.2 g with 3.00g of FA for 6 hours were compared and the highest conversion ~36wt% was obtained with a catalysts loading of 1.2g. Two different catalyst loadings (0.3g and 1.2g) were chosen to determine the optimal reaction time. It was observed that the FA conversion rate gradually increased when reaction time increased from 2hrs to 8hrs, while the selectivity to the observed C₉-C₁₅ oligomers decreased with increase of reaction time. The highest yield to C₉-C₁₅ oligomers (~21wt%) were obtained by using 1.2g MoO₃ for 8 hours. Reaction mechanism for FA dehydration over MoO3 is also proposed. FA oligomers made from the Molybdenum Oxide catalyst can be upgraded using a hydrodeoxygenation (HDO) reaction to produce alternative biofuels C₉-C₁₅ in the future.