Mass transfer and kinetics of H 2 O 2 direct synthesis in a batch slurry reactor Nicola Gemo a , Pierdomenico Biasi b , Paolo Canu a,⇑ , Tapio O. Salmi b a Dipartimento di Ingegneria Industriale, University of Padova, via Marzolo 9, 35131 Padova, Italy b Process Chemistry Centre (PCC), Laboratory of Industrial Chemistry and Reaction Engineering, Åbo Akademi, Biskopsgatan 8, 20500 Turku, Finland highlights " Modeling of H 2 O 2 direct synthesis, decomposition and hydrogenation experiments. " Gas to liquid and liquid to solid mass transfer limitation analysis. " Estimation of activation energies and pre-exponential factors. graphical abstract article info Article history: Available online 20 July 2012 Keywords: Batch reactor modeling Hydrogen peroxide Direct synthesis Green chemistry Palladium abstract A model of a gas bubbling, batch slurry reactor for H 2 O 2 direct synthesis is presented. Experimental mea- surements were carried out in the absence of halides and acids at temperatures between 258 and 297 K (pressures 14–20 bar, depending on temperature) with H 2 and O 2 diluted in CO 2 outside flammability limits (gas phase composition of CO 2 ,O 2 and H 2 was 77%, 21% and 2%, respectively). Kinetic experiments performed on a commercial 5% Pd/C catalyst (0.15 g in 400 ml methanolic solution) have been used to identify the intrinsic kinetics and assess the influence of mass transfer. The simplest rate equations com- patible with the acknowledged reaction network has been included in a reactor model, which accounts for mass transfer resistances between gas and liquid and bulk of the liquid-catalyst surface. The corresponding Arrhenius parameters were estimated from direct synthesis experiments for all the reactions. Comparable temperature dependence was observed for H 2 O production, hydrogenation and decomposition (activation energies close to 45 kJ mol 1 ), while H 2 O 2 synthesis has a much lower activa- tion energy (close to 24 kJ mol 1 ), suggesting that a higher selectivity is achievable at low temperature. Decomposition had a very limited influence on the overall peroxide production rate, being quite slow (its rate is approx. 40% the direct synthesis rate at H 2 full conversion). Hydrogenation was the most rapid side reaction, depressing H 2 O 2 production as H 2 conversion increased. Independent investigation on the H 2 O 2 hydrogenation in the absence of O 2 highlighted significant difference in the kinetics, apparently due to a different oxidation state of the catalyst. A sensitivity analysis on the mass transfer coefficients to allow for uncertainties in the correlations proved that no resistances in the liquid occur, while gas–liquid H 2 transfer rate may be limiting, although unlikely, requiring that literature coefficients overestimates the real transfer rate by an order of magnitude. Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction Hydrogen peroxide is the simplest peroxide and is commer- cially available in aqueous solution over a wide concentration range. The main uses of hydrogen peroxide are in the preparation 1385-8947/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.cej.2012.07.015 ⇑ Corresponding author. E-mail address: paolo.canu@unipd.it (P. Canu). Chemical Engineering Journal 207–208 (2012) 539–551 Contents lists available at SciVerse ScienceDirect Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej