Acetophenone hydrogenation in photocatalytic membrane reactor under UV and visible light - Pres Poster P2 -

AICIng 2014. Atti del IX Convegno Nazionale dell'Associazione di Chimica per l'Ingegneria 48 Lecce 14-17 Settembre 2014 Acetophenone hydrogenation in photocatalytic membrane reactor under UV and visible light Raffaele Molinari, Pietro Argurio, Cristina Lavorato Department of Environmental and Chemical Engineering, University of Calabria, Via P. Bucci, 44/A, 87036, Arcavacata di Rende (CS), Italy Email: pietro.argurio@unical.it ABSTRACT The hydrogenation of acetophenone to phenylethanol was carried out in a photocatalytic membrane reactor (PMR) by using water as solvent and formic acid as electron donor under UV and visible light irradiation. The use of a membrane reactor was found to improve the efficiency of the photocatalytic reaction compared to a batch reactor. Doping TiO2 photocatalyst with Pd improved five times its photocatalytic activity under visible light irradiation. The results evidenced that performing the photocatalytic hydrogenation in membrane reactors represents a promising green method of chemical production. Keywords: Photocatalysis, membrane reactor, acetophenone hydrogenation, phenylethanol, TiO2 doping, visible light. The reduction of carbonyl compounds in the corresponding alcohols is an important transformation in organic synthesis. The reduction of acetophenone to phenylethanol, which is used as a building block for the synthesis of bioactive compounds (e.g. agrochemicals, pharmaceuticals, natural products) is an important reaction due to the limited natural resources of the reduced product [1]. Photocatalytic transfer hydrogenation, using sacrificial chemicals as hydrogen and electron donor, is an alternative and more sustainable method to synthesize organic compounds operating under mild conditions and using cheaper catalysts. The most widely used photocatalyst is titanium dioxide (TiO2), but its use presents some important drawbacks: the electron/hole recombination and the spectrum of absorbance mainly in the UV region. Noble metal doping has been reported to be very effective in limiting these restrictions [2]. Alcohol are sacrificial reagents largely used for photocatalytic reductions, used in large excess to shift the reaction to the desired product. Formic acid is an interesting alternative since it is converted into carbon dioxide (CO2) and hydrogen (H2) making the reaction irreversible. In view of large scale applications, photocatalytic membrane reactors (PMRs) can be proposed because they combine the advantage of classical photoreactors and those of membrane processes with a synergy of both technologies [3]. On the basis of this, in the present work the hydrogenation of acetophenone to phenylethanol was carried out in PMRs using water as solvent, formic acid as hydrogen and electron donor and commercial TiO2 and homemade Pd/TiO2 as photocatalyst under UV and visible light, respectively. Preliminary tests were carried out in batch to investigate the influence of some operating conditions on system performances. Better results in terms of phenylethanol yield (4.7%) were obtained in the following conditions: i) 1.5 g L-1 of TiO2; ii) pH = 7.5; iii) [HCOOH] = 1.97 M. These conditions were used in the following photocatalytic tests in PMRs. The use of a PMR, obtained by coupling the batch photoreactor with a membrane contactor (Figure 1), was found to improve the efficiency of the photocatalytic reaction compared to a batch reactor (Table 1). This behaviour is due to the extraction of produced phenylethanol in the organic extracting phase, shifting the hydrogenation reaction forward to the product and allowing to limit over hydrogenations. The most efficient system was found to be the PMR in which acetophenone was used as both extracting organic phase and substrate reservoir.