Hydrodeoxygenation of bio-oil model compounds using alumina, zirconia and carbon supported metal catalysts

Bio-oil is an attractive alternative to petroleum oil and important renewable source of energy and chemicals. Through hydrodeoxygenation (HDO) it can be transformed into transportation fuel by removal of oxygen. Because of bio-oil complex composition, HDO of its model compounds is of high interest. In the current work, mainly HDO of isoeugenol (not previously studied) as a model compound was investigated over a range of metals on mildly acidic (Al2O3 and ZrO2) and a neutral support (carbon), with dodecane as a solvent. The fresh and spent catalysts were characterized using different physico-chemical methods. Several catalysts allowed higher selectivity towards propylcyclohexane and complete conversion of dihydroeugenol. Gas samples taken after isoeugenol and guaiacol HDO were investigated using GC and GC-MS techniques, demonstrating high abundance of ethane and methane. First influence of reaction temperatures (150, 200 and 250℃) was investigated with the most suitable one being 250℃. Bimetallic catalysts containing iridium-rhenium and platinum-rhenium over alumina and carbon supports resulted in higher molar concentration of propylcyclohexane in comparison with monometallic ones. Low gas chromatography based sum of the reactants and products in the liquid phase analysis (GCLPA) was obtained in isoeugenol HDO at 250℃ and 30 bar. The effect of pressure was investigated in isoeugenol HDO over two alumina supported catalysts, showing that high pressure of hydrogen favored high selectivity towards propylcyclohexane. Optimization tests were done with different substrate to catalyst ratio illustrating that HDO was not effective in terms of propylcyclohexane selectivity in the presence of too high isoeugenol concentration. Solventless isoeugenol HDO was performed over Ir-C catalyst at 150℃ (a semi-batch mode) and 200℃ (a batch mode) and the total pressure of 11 bar giving a complete conversion of isoeugenol to dihydroeugenol. Iridium and nickel catalysts over zirconia support applied in HDO of isoeugenol and guaiacol at 250℃ and 30 bar and vanillin HDO at 100℃ and 30 bar demonstrated different distribution of products, the two latter ones giving mainly different alcohols, while isoeugenol HDO resulted in propylcyclohexane as the main product. However, low GCLPA was observed indicating high formation of gaseous products and adsorption of compounds