Synthesis of Phenol by Means of Benzene Hydroxylation and Its Recovery in Membrane Contactors- Pres orale O 08-

AICIng 2014. Atti del IX Convegno Nazionale dell'Associazione di Chimica per l'Ingegneria Lecce 14-17 Settembre 2014 25 Synthesis of Phenol by Means of Benzene Hydroxylation and Its Recovery in Membrane Contactors Raffaele Molinari1, Pietro Argurio1, Teresa Poerio2 1 Department of Environmental and Chemical Engineering, University of Calabria, Via P. Bucci, 44/A, 87036, Arcavacata di Rende (CS), Italy 2 Institute on Membrane Technologies ITM-CNR, c/o University of Calabria, Via P. Bucci,17/C, 87036 Arcavacata di Rende (CS), Italia Email: pietro.argurio@unical.it ABSTRACT Two different three-compartment membrane contactors were tested in the synthesis and separation of phenol produced by direct hydroxylation of benzene using a Fenton reaction. Phenol produced in the aqueous reacting phase was extracted in the organic phase and simultaneously stripped in the basic aqueous phase. It was evidenced that the use of a third compartment containing an alkaline aqueous stripping phase permitted one to recover phenol at 100% purity. Keywords: Phenol production, benzene hydroxylation, membrane contactors Phenol is a very prominent chemical intermediate in industry. Nowadays it is industrially synthesized mainly by the cumene process, which presents many drawbacks, such as high energy consumption, because of multistep reactions, and the production of a large amount of acetone as by-product. On these bases, the search for new routes for phenol synthesis, as the direct hydroxylation of benzene, became more intensive in the past decade. Such a process presents various potential advantages compared to the traditional cumene process, but its selectivity is usually rather poor since phenol can be oxidized easier than benzene. The prompt removal of the produced phenol from the reacting environment represents a key point for developing such a method. On this regard, membranes can play an important role. In our previous works [1, 2] we proposed the use of a biphasic membrane reactor, for the direct hydroxylation of benzene to phenol. A flat-sheet membrane separates an acidic aqueous phase (containing a Fe or V based catalyst and H2O2) and an organic phase (benzene). Benzene permeates across the membrane and reacts at the aqueous interface, while produced phenol permeates back and it is extracted into the organic phase, where it is protected by subsequent oxidations. Despite the high phenol selectivity (98%) in the organic phase, this system possesses some important drawbacks: over-oxidations with production of by-products (benzoquinone, biphenyl and tar in the reacting phase) by using Fe based catalyst or low system productivity by using V based catalysts. Considering these results, in the present work the use of three phase membrane contactors has been tested in the one-step benzene hydroxylation to phenol. Two solid (SMC, Figure 1) or liquid (LMC, Figure 2) membranes separate three immiscible phases: the aqueous reacting phase and the organic (only benzene) phase (as in our previous work), plus a third basic aqueous phase acting as a stripping agent. Operating in this way, phenol extracted in the organic phase is simultaneously stripped in the alkaline aqueous phase [3], thus performing the process of product recovery. AICIng 2014. Atti del IX Convegno Nazionale dell'Associazione di Chimica per l'Ingegneria 26 Lecce 14-17 Settembre 2014 Figure 1: Scheme of the three phases SMC. Figure 2: Scheme of the three phases LMC. Preliminarily, mass-transport tests were carried out at 25 and 35 °C to determine the mass permeation flux of the two membrane contactor and the influence of salts dissolved in the aqueous feed phase. The obtained results evidenced better performances (86.5% of phenol recovered in the strip phase) using the SMC with 0.1 M Na2SO4 in the aqueous feed phase at 35 °C. Probably the worst condition of agitation of the organic phase in the case of LMC (to avoid phase mixing) is the principal cause of the observed performance. In the catalytic tests, better results (phenol productivity 0.62 gph gcat−1 h−1) were obtained using the SMC containing 0.1 M Na2SO4 in the aqueous reacting phase (Table 1). These results can be explained thanks to the high phenol flux away from the reacting phase which permitted to extract a high amount of phenol in the organic and aqueous (strip) phases. The results evidenced that use of a third compartment, containing an alkaline aqueous stripping phase, permitted to perform simultaneously the process of phenol synthesis, recovery, purification (100% purity) and concentration. Table 1. Summary of the results obtained in the catalytic tests (aqueous feed phase: pH 2.8 (0.19 mL acetic acid), 0.095 g iron(II) sulphate, NaCl or Na2SO4 0.1 M; organic phase: benzene; aqueous stripping phase: NaOH 0.1 M; T = 35°C; time = 240 minutes). NaCl Na2SO4 SMC LMC SMC LMC Sph,org (%) 78.7 88.4 81.3 100 Sph,strip (%) 100 100 100 100 Pph (gph gcat -1 h-1) 0.32 0.06 0.62 0.21 Sph,org: phenol selectivity in the organic phase; Sph,strip: phenol selectivity in the strip phase; Pph: phenol productivity. References [1] R. Molinari, T. Poerio, P. Argurio, Catalysis Today, 118, 52-56, (2006). [2] R. Molinari, P. Argurio, T. Poerio, Applied Catalysis A: General, 437−438, 131-138, (2012). [3] R. Molinari, P. Argurio, T. Poerio, Industrial & Engineering Chemistry Research, 52, 10540- 10548, (2013).