Continuous Flow Friedel-Crafts Alkylation Catalyzed by Silica Supported Phosphotungstic Acid: An Environmentally Benign Process

Six silica-supported phosphotungstic acid catalysts (PTA/SiO2) of different composition (20-70 wt% PTA content) have been synthesized and characterized by elemental analysis, BET, BJH, NH3-TPD methods, FT-IR spectroscopy of adsorbed pyridine and H-1 MAS NMR techniques. The new composite catalysts were first applied in the Friedel-Crafts alkylation of toluene with 1-octene as a benchmark process under batch conditions in order to screen their activity and recyclability. The combined analytical techniques together with the catalytic studies enabled the identification of the main factors affecting the activity of the catalysts. Based on these preliminary experiments, the best performing catalyst system (50 wt% PTA/SiO2) was investigated in continuous flow mode using an in-house-made flow reactor. The thorough screening of the reaction conditions (temperature, toluene/1-octene molar ratio and flow rate) provided firm evidence that the 50 wt% PTA/SiO2 composite is highly active, selective and stable catalyst under mild reaction conditions even at elevated flow rate. Additionally, the catalyst used in the flow mode could successfully be regenerated and reused in the alkylation process.

Automated summary

Six silica-supported phosphotungstic acid catalysts with different compositions were synthesized and characterized. The best performing catalyst system (50 wt% PTA/SiO2) was found to be highly active, selective, and stable even at elevated flow rates. The catalyst could successfully be regenerated and reused in the alkylation process in a flow reactor.