Upgrading Process of 4-Methylanisole as a Lignin-Derived Bio-Oil Catalyzed by Pt/gamma-Al2O3: Kinetic Investigation and Reaction Network Development

摘要

This study investigated the catalytic upgrading of 4-methylanisole using Pt/gamma-Al2O3 in the presence of hydrogen with a fixed-bed tubular flow reactor at 573-673 K, 8-20 bar, and space velocities in the range of 3-120 (g of 4-methylanisole)/(g of catalyst X h). Selectivity-conversion data were used to determine an approximate reaction network. It is observed that the scission of the C-methyl-O bond is faster that the scission of the C-aromatic-O bond. So 4-methylphenol forms as a primary intermediate product via scission of the C-methyl-O bond, and then hydrogenolysis of the C-aromatic-O occurs giving toluene. Also another possible deoxygenation route involves a direct C-aromatic-O bond-breaking reaction, leading to toluene. Multiple transalkylation reactions including intramolecular and bimolecular rearrangement account for methylphenols with multiple methyl substituents. The major products were 4-methylphenol, 2,4-dimethylphenol, and 2,4,6-trimethylphenol. So we inferred that transalkylation involving methyl in methoxy groups is one of the kinetically significant reaction classes catalyzed by the acidic support. A pseudo-first-order kinetic model was found to describe well the observed product distribution and to estimate kinetic parameters such as kinetic constants and activation energy of reactions. Kinetic studies revealed that the overall conversion improves with increasing temperature, pressure, and inverse space velocity. The formation of 4-methylphenol by the hydrogenolysis reaction was about two times faster than the formation of toluene by hydrodeoxygenation. The apparent activation energy for the formation of 4-methylphenol as the main product was approximately 15.5 kJ/mol.