Mild-Temperature hydrodeoxygenation of vanillin a typical bio-oil model compound to Creosol a potential future biofuel

Abstract

This study reports mild temperature hydrodeoxygenation (HDO) of vanillin an oxygenated phenolic compound found in bio-oil to creosol. It investigates the sensitivity of vanillin HDO reaction to changes in solvent, catalyst support and active metal type, and processing parameters using 100 ml batch reactor. The processing parameters considered include temperature (318 K – 338 K), hydrogen gas pressure (1 MPa – 3 MPa), catalyst loading (0.1 kg/m3 – 0.5 kg/m3), and agitation speed (500 rpm–900 rpm). As expected, significant variation in conversion and product selectivity was displayed in the results. Among the solvents considered, 2-propanol and ethyl acetate produced the best performance with conversion close to 100 % and selectivity toward creosol above 90 %. Remarkable differences were found in the H2 uptake during VL HDO reaction under different catalyst. The hierarchy in H2 uptake of the catalysts include: Pd/C > PdRh/Al2O3 > Pd/Al2O3 = Pt/C > Pt/SiO2 >> Rh/Al2O3. This was correlated to catalytic performance; Pd/C emerged as the best among the monometallic catalysts with 71 % selectivity toward creosol, but consumed 9 mmol of hydrogen per mol of vanillin converted. While the prepared bimetallic PdRh/Al2O3 catalyst consumed slightly lower amount of hydrogen (8 mmol), and produced significantly higher selectivity toward creosol (99 %). Even after three cycles the prepared catalyst demonstrated superior performance over the monometallic catalysts with selectivity toward creosol above 80 %. The reaction condition that maximises the degree of deoxygenation to creosol derived via Taguchi analysis includes temperature 338 K, hydrogen gas partial pressure 3.0 MPa, catalyst loading 0.5 kg/m3, and agitation speed 500 rpm.