Abstract
AbstractSix 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 1H 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.
Highlights
The acid catalyzed alkylation of aromatic hydrocarbons represent one of the most fundamental and strategic synthetic methodologies leading to fine or bulk chemicals on an industrial scale [1,2,3,4]
The present study demonstrates that the application of silica supported PTA under flow conditions offers a reliable methodology for liquid phase Friedel–Crafts alkylation reactions compared to the use of immobilized heteropolyacids in batch systems
The present study demonstrates the beneficial use of silica supported phosphotungstic acid catalysts in a continuous flow system under mild reaction conditions for the Friedel–Crafts alkylation of toluene with 1-octene as a model reaction
Summary
The acid catalyzed alkylation of aromatic hydrocarbons represent one of the most fundamental and strategic synthetic methodologies leading to fine or bulk chemicals on an industrial scale [1,2,3,4]. Heteropolyacids (HPAs) are a unique class of compounds due to their high Brönsted-acidity, relatively high thermal stability, low corrosivity and high structural modularity as well as the ease of their preparation [11, 12]. Since the first successful utilization of silica supported heteropolyacids in the liquid phase Friedel–Crafts alkylation of aromatic compounds by alkenes [47], great efforts have been devoted to fine tune the structural characteristics of the catalyst and the support for these types of reactions [48,49,50,51]. To the best of our knowledge, there are no experimental data available in the literature focusing on the practical application of these catalytic systems in continuous flow liquid phase alkylation reactions
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