Applied Catalysis A: General 393 (2011) 340–347 Contents lists available at ScienceDirect Applied Catalysis A: General journal homepage: www.elsevier.com/locate/apcata Selectivity control of benzene conversion to phenol using dissolved salts in a membrane contactor Raffaele Molinari ∗ , Teresa Poerio Department of Chemical Engineering and Materials, University of Calabria, Via P. Bucci, 44/A, I-87036 Rende (CS), Italy article info Article history: Received 5 July 2010 Received in revised form 24 November 2010 Accepted 9 December 2010 Available online 16 December 2010 Keywords: Liquid phase benzene oxidation to phenol Catalytic membrane contactor Selective oxidation Tar formation from benzene Salts and phenol extraction (from aqueous to organic) abstract Effect of salts, pH, type of acids and anion sulphate in the synthesis and separation of phenol through the hydroxylation of benzene by using a Fenton reaction in a biphasic membrane contactor has been investigated. The results indicated that sodium sulphate (1 M) increased phenol extraction in the organic phase (76.3%) but also increased reaction kinetics promoting over-oxidation products and a black solid (tar) formation. The acids delayed and in some tests avoided the tar appearance as precipitate but also gave a reduction of phenol selectivity. The sulphate absence, obtained by using iron(0), did not avoid the precipitate formation but only caused its decrease favouring a significant increase of the ratio productivity/amount of black solid from 4.6 to 62.4. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Phenol is an important raw material for the synthesis of petro- chemicals, agrochemicals, and plastics. The current worldwide capacity for phenol production is nearly 7 million metric tonnes per year [1]. Today, almost 95% of the worldwide phenol produc- tion is based on a three-step process with the so-called “cumene process”. Despite its great success, the cumene process has some disadvantages: poor ecology, an explosive intermediate (cumene hydroperoxide) and a multistep character, making difficult to achieve high phenol yields with respect to benzene [2]. The search for new routes for phenol production based on the one-step direct benzene oxidation became more intensive in the last decade [3–10] but this reaction is a little selective because phenol is more reactive than benzene and over-oxygenated by- products occur. To slow down consecutive catalytic reactions catalytic mem- brane reactors (CMRs) can be employed. These systems have attracted attention because of their advantages related to the syn- ergy of the catalyst and membrane when implemented in the same device [11–13]. Within this family, the membrane contactors also permit to combine membrane separation and catalytic reaction in one unit operation. The separation of a product from the reaction ∗ Corresponding author. Tel.: +39 0984 496699; fax: +39 0984 496655. E-mail address: r.molinari@unical.it (R. Molinari). mixture is one of the advantages in using a membrane in a reactor and permits to obtain improvements in terms of yield and selec- tivity in equilibrium-limited reactions and in consecutive catalytic reactions. A membrane contactor is a device that achieves gas/liquid or liquid/liquid mass transfer without dispersion of a phase within another [14]. As common feature of these processes the separation perfor- mance is determined by the distribution coefficient of a component in two phases. The membrane, which can be defined as a permse- lective barrier between two homogenous phases, represents only an interface. It accomplishes a particular separation transporting a component more easily than another because of differences in physical and/or chemical properties between the membrane itself and the permeating components. Membrane contactors have a number of important advantages compared to conventional dis- persed phase contactors. Some of them are: no flooding at high flow rates, no unloading at low flow rates, absence of emulsions, no density difference between fluids required. They reduce the vol- ume of equipment and offer more interfacial area in non-dispersive contact across a membrane, leading to a decrease in the value of a height transfer unit (HTU). The membrane should be accurately chosen to enable as much as possible higher values of the mass transfer coefficient. Additional advantages of this technique are a high surface area per unit volume, when hollow fibre modules are used, and the possibility of changing the hydrodynamics of both phases independently. These contactors give any wanted shape of 0926-860X/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.apcata.2010.12.018