A Continuous Membrane Reactor for Benzene Hydroxylation to Phenol

Phenol production from direct hydroxylation of benzene with H2O2 carried out in a membrane reactor operating in a continuous mode was studied for the first time. The performance was compared also with those of another membrane reactor operating in semi-batch configuration. In these systems the phenol produced was recovered by using water on the stripping side of the membrane reactor, where the membrane was always in contact with a "fresh" stripping stream, promoting a more efficient removal of phenol present in the retentate side. The influence of the hydrophilic and hydrophobic character of the membrane material on the phenol recovery was investigated at different flow rates of the feed and the stripping phases. The results indicated that the better performance was achieved using a hydrophilic membrane, with a total feed flow rate of 2 mL min-1 and a stripping flow rate of 1 mL min-1, in terms of phenol recovery (25%) and selectivity (94%). In addition the continuous removal of phenol from the reaction side reduces the possible formation of by-products such as benzoquinone, avoiding completely biphenyl formation that was not detected in all the tests carried out in the continuous mode.