Friedel-Crafts alkylation properties of aluminosilica SBA-15 meso/macroporous monoliths and mesoporous powders

The catalytic activities of SBA-15 aluminosilica meso/macroporous monoliths (Si/Al=72) and mesoporous powders (Si/Al=70) have been investigated using batch Friedel-Crafts alkylation of single-ring aromatic compounds, including toluene, ethylbenzene, cumene, and styrene, with benzyl alcohol. The toluene alkylation activities of the meso/macroporous monolith catalysts were compared with nanoporous zeolite Beta (Si/Al=75, average particle size ∼10 μm) and mesoporous SBA-15 aluminosilica (average particle size ∼25 μm), as powders and pellets (0.5 cm thick x 1 cm diameter) to study the effects of framework crystallinity, particle size, pore size, and pore structure on the overall conversion. Apparent reaction rate coefficients were quantified based on a model for the alkylation of toluene with benzyl alcohol via two parallel reaction schemes to benzyl toluene. Moderate toluene alkylation rates (∼10^-4 s^-1) and high selectivities (>90%) for benzyl toluene were observed for meso/macroporous aluminosilica SBA-15 monoliths, compared to the mesoporous SBA-15 and zeolite Beta powders, which displayed faster alkylation rates (∼10^-3 s^-1), though were less selective (79 and 59%, respectively). In pellet form, both the mesoporous SBA-15 and the zeolite Beta materials yielded lower rates of alkylation (∼10^-4 s^-1), due to slower internal diffusion of reactants and products within the smaller pellet macropores, compared to the meso/macroporous monoliths. Diffusive resistances to mass transfer were quantified by estimating Thiele moduli and effectiveness factors for the different catalysts, based on benzyl alcohol diffusivities measured by PFG NMR. The aluminosilica meso/macroporous SBA-15 monoliths deactivated more slowly, retaining 92% of their original activities after one use, compared to 75, 76, and 0.6% for SBA-15 powder, SBA-15 pellet, and zeolite Beta powder catalysts, respectively.