Benzene hydroxylation to phenol in a membrane contactor using V(III) and V(IV) catalysts and study of membrane resistance

A two phase membrane reactor has been tested in the benzene hydroxylation to phenol ant its recovery by using vanadium based catalysts. Better performances and no tar formation was observed by feeding the oxidant (hydrogen peroxide) by a micro pump by the “bulk tube” mode. Improved results in terms of yield (35.2 vs. 25.1 %), conversion of hydrogen peroxide to phenol (36.6 vs. 25.9 %), productivity (0.97 vs. 0.78 g gcat-1 h-1) were obtained by using vanadium(III) chloride with respect to vanadium(IV) acetyl acetonate, evidencing that the initial oxidation state of vanadium catalyst influences system performance. By increasing test duration from 270 to 510 minutes higher phenol extraction/recovery in the organic phase (61.1 vs. 46.3 %) and then higher selectivity (97.5 vs. 92.8 %) were obtained. A weak membrane resistance was observed after 246 hours of consecutive catalytic runs on the same membrane piece, due to the degradation of membrane material (polypropylene).