Hydrodeoxygenation of stearic acid and tall oil fatty acids over Ni-alumina catalysts: influence of reaction parameters and kinetic modelling

Kinetics in the hydrodeoxygenation of stearic acid was investigated over Ni-γ-Al₂O₃ catalyst. The main variables were catalyst prereduction mode, reaction atmosphere and hydrogen pressure in the total pressure range of 7–30 bar. The results revealed that high conversion, 99% in 360 min and high selectivity to heptadecane, 97% were achieved at 300 °C under 30 bar total pressure. The yield of an intermediate hydrogenation product, stearyl alcohol increased with increasing hydrogen pressure as expected. Higher reaction rates and conversion levels were also achieved with the prereduced catalyst and carrying out the reaction in the presence of hydrogen. As a comparison to stearic acid, hydrodeoxygenation of tall oil fatty acids, an industrial feedstock was successfully demonstrated with Ni-γ-Al₂O₃ under the same conditions. A kinetic model including the pressure effect was derived and applied for data with Ni-γ-Al₂O₃ as well as for Pd/C, Ni-H-Y-80 and Ni/SiO₂ catalysts. The model described well the kinetic data.