Mechanistic Model for Kinetics of Propene Hydroformylation with Rh Catalyst Dmitry Yu. Murzin, Andreas Bernas, and Tapio Salmi Dept. of Chemical Engineering, A ˚ bo Akademi University, Process Chemistry Centre, FI-20500 A ˚ bo/Turku, Finland DOI 10.1002/aic.12746 Published online in Wiley Online Library (wileyonlinelibrary.com). Hydroformylation of propene to isobutyraldehyde and n-butyraldehyde was studied in the kinetic regime in a semibatch stainless steel reactor at 85–115C and 1–15 bar pressure in 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate solvent with rhodium catalyst cyclohexyl diphenylphosphine as a ligand, which showed lower normal/isometric aldehyde ratio (n/i) than previously studied triphenylphosphine. The rate was pressure and Rh concentration dependent. The regioselectivity was conversion independent; however, dependent on the ligand concentration, as higher ligand concentration promoted isobutyraldehyde formation. The influence of ligand concentration on regioselectivity was investigated. A kinetic model was proposed based on the mechanism of alkene hydroformylation and compared with experimental observations. Numerical data fitting was performed showing good agreement of reaction rates and regioselectivity with experimental data. V V C 2011 American Institute of Chemical Engineers AIChE J, 00: 000–000, 2011 Keywords: hydroformylation, propene, rhodium, cyclohexyl diphenylphosphine, kinetic modeling Introduction Hydroformylation is the oldest and in production volume the largest homogeneously catalyzed industrial process. The hydroformylation reaction was discovered by Otto Roelen in 1938, and the reaction is also called oxosynthesis and Roelen’s reaction. 1–4 Hydroformylation of alkenes with carbon monoxide and hydrogen is a homogeneously catalyzed gas–liquid (G–L) reaction, which is used for the production of linear and branched aldehydes, as demonstrated in Figure 1. A wide range of aldehydes having applications in perfumes, surfactants, plasticizers, and solvents is produced by this reac- tion, which is a typical case of simultaneous absorption of two or more gases, with reaction in a liquid medium or in an interfacial regime in the presence of a homogeneous cata- lyst. 5–12 The catalyst used in hydroformylation is typically an organometallic complex. Cobalt-based catalysts dominated hydroformylation until 1970s, after which rhodium-based cat- alysts were commercialized. The main part of the aldehydes formed is hydrogenated to alcohols or oxidized to carboxylic acids. Furthermore, the alcohols obtained can undergo further reactions, such as esterification. Thus, the aldehydes are typi- cal intermediates for chemical industry. 13 In recent years, a lot of effort has been put on the ligand chemistry, to find new ligands for tailored processes. 14,15 In spite of intensive research on hydroformylation in the last 50 years, both the reaction mechanisms and kinetics are not clear in most cases. Both associative and dissociative mechanisms have been proposed. 13,16 The discrepancies in mechanistic speculations have also lead to a variety of rate equations for hydroformylation processes. The concentrations of the reactant (substrate) alkene, the catalyst, as well as H 2 and CO are included in the kinetic expressions, but very little quantitative information on the effect of the ligands is available. Typically, the effects of the alkene, the catalyst, and H 2 are positive on the reaction kinetics, whereas an inhibitory effect of CO is characteristic for many rate equations proposed hitherto. 17 The general feature of previous studies has been that the partial pressures of H 2 and CO have not been screened systematically, thus the exact form of the rate equation remains obscured; for instance, the effect of CO cannot always be p 1 CO , as proposed in some rate equations, but a zero-order or higher order behav- ior might become visible at lower CO pressures. 17 A lot of research has been published on hydroformylation of alkenes, but the vast majority of the effort has been focused on the chemistry of various metal–ligand systems. In alkene hydroformylation with triphenylphosphine (TPP) ligand, the mechanism of hydrogen activation has been stud- ied through in situ high-pressure Fourier transform infrared spectroscopy (FTIR). 18 NMR spectroscopy is also a useful tool for in situ studies. 19 Quantitative kinetic studies including modeling of rates and selectivities, that is n/i ratio, are much scarcer. In this work, we present the approach to modeling of hydroformyla- tion kinetics. Hydroformylation of propene with a rhodium- based catalyst was selected as a case study. The aim of this work is to discuss the mechanism of hydroformylation and to compare the kinetics, which corresponds to the mecha- nism, with experimental observations, focusing mainly on regioselectivity and using the theory of complex reactions. 20 Experimental In a typical experiment, the catalyst precursor (acetylace- tonato)dicarbonylrhodium(I) (99%, Alfa Aesar) and the Correspondence concerning this article should be addressed to D. Y. Murzin at dmurzin@abo.fi. V V C 2011 American Institute of Chemical Engineers AIChE Journal 1 2011 Vol. 00, No. 0