Fe-zeolites filled in PVDF membranes in the selective oxidation of benzene to phenol

Benzene conversion to phenol has been studied in liquid-phase in a flow-trough ultrafiltration membrane reactor in mild conditions using Fe-zeolite catalysts filled in a PVDF (polyvinylidenefluoride) polymeric matrix. The catalysts and the catalytic membranes were prepared, morphologically characterized and catalytically tested. The affinity between the membrane system and reagents and/or products was evidenced by contact angles, sorption and permeation flux measurements. From sorption measurements it was found a greater affinity of benzene reagent for the membrane material (sorption = 0.37g benzenel/g membrane) with respect to a negligible sorption of phenol. Permeations flux measurements evidenced an increased permeate flux for the membrane filled with the zeolite catalysts: the enhanced flux allowed to get contact times between products and/or reagents with the catalyst in the range 0.4–12 s. Reactivity tests, performed at various contact time, showed the highest phenol yield (5.5%) in a single pass using the PVDF membrane filled with Na–Fe-Silicalite-1 at 35 °C. The use of different catalyst forms (free or entrapped in the polymeric matrix) in an open batch reactor evidenced the best performance in terms of selectivity for the entrapped catalyst (97% vs. 69%).