INTERNAL DIFFUSION COUPLED TO HYDROGENATION KINETICS IN SUPPORTED IONIC LIQUID CATALYSTS (SILCAs)
Advancing the chemical engineering fundamentals
Chemical Reaction Engineering: Advanced Concepts (T2-2b)
Keywords: Catalysis, Ionic Liquids, Diffusion, Reaction Kinetics, Simulation
Kinetics and mass transfer studies for supported ionic liquid catalysts (SILCAs)(1) were studied for complex catalytic hydrogenations of unsaturated aldehydes as an important class of reactions in the production of fine and specialty chemicals. The hydrogenation products are often employed as e.g. components for perfumes and insect repellents, flavors and pharmaceuticals (2-6). The factors affecting the hydrogenation selectivity of α,β-unsaturated aldehydes are multitude and have been reviewed by e.g. Gallezot and Richard (7) as well as Claus et al (8). Importantly, internal mass-transfer (inside the catalytic material) as well as coupled diffusion and reaction that can have major influence on the performance of, especially, an industrial process, are often not studied in detail and, consequently, misleading conclusions can be drawn about the limiting phenomena involved. The interaction of complex reactions and diffusion in porous catalysts have been experimentally studied and modeled by ee.g. Julcour et al. (9) and Aumo et al. (6) in which more complex hydrogenation systems were addressed and reaction-diffusion phenomena were quantitatively modeled.
To our best knowledge, combined reaction and diffusion in ionic liquids has so far been almost neglected in open literature (10), partially due to the lack of relevant physico-chemical data. The system can be characterized as a gas-liquid-liquid-solid system, where gaseous hydrogen and an unsaturated aldehyde diffuse from molecular solvent to a thin layer of ionic liquid containing the catalytically active species, metallic palladium nanoparticles. In order to obtain more understanding about the importance of mass-transfer and diffusion limitations for these kinds of processes, a model describing the concentration profiles of the reactants in the catalysts was developed. In our first attempt (10), only limited amount of physico-chemical data was available. Hereby we report evolved modeling results with experimentally determined diffusion coefficients of the involved species in ionic liquids, coupled to measured densities and viscosities of them. The results agree nicely with our previous simulations describing the concentration profiles in the thin ionic liquid layer comprising the catalytically active species.
(1) Mikkola, J.-P, Virtanen, P., Karhu, H., Murzin, D. Yu and Salmi, T., Supported Ionic Liquids Catalysts for Fine Chemicals: citral hydrogenation, Green Chem., 2006, 8, 197-205
(2) De Simone, R.s., Gradeff, P.S., Process for the hydrogenation of citral to citronellal and of citronellal to citronellol suing chromium-promoted Raeny-nickel catalyst, 1977, US Patent 4,029,709
(3) Marin, A.B., Butler, J.F., Method for repelling fire ants and horn flies and compositions for repelling fire ants and horn flies and acting as anti-feedants for fire ants and horn flies, 1998, US Patent 5,753,686
(4) Mohammadi, F., Vargas, A., Cosmetic composition for stressed skin under extreme conditions, 2003, US Patent 6,649,178
(5) Warren, C .B., Butler, J.F., Wilson, R.A., Mookherjee, B.D., Smith, L.C., Marin, A.B., Narula, A.P.S., and Boden R.M., Insect repellent compositions and methods for using same, 1997, US Patent 5,633,236
(6) Aumo, J., Structured Catalysts in Complex Three-Phase Hydrogenations, Doctoral thesis, Åbo Akademi, 2005, ISBN 952-12-1503-8
(7) Gazellot, P. and Richard, D., Selective hydrogenation of α,β –unsaturated aldehydes, Catalysis Reviews – Science Engineering, 1998, 40, 81-126
(8) Claus, P., Schimpf, S. and Gaube, J., Selective hydrogenation of multiple unsaturated compounds in: Baerns, M. (Ed.), Basic principles in applied catalysis, 2004, Springer Verlag Berlin, Germany, p.85
(9) Julcour, C., Le Lann, J.M., Wilhelm, A.M. and Delmas, H., Dynamics of internal diffusion during the hydrogenation of 1,5,9-cyclododecatriene on Pd/Al2O3, Cat.Tod., 1999, 48, 147-159
(10) Mikkola, J.-P., Wärnå, J., Virtanen, P. and Salmi, T., The effect of internal diffusion in supported ionic liquid catalysts (SILCAs): interaction with kinetics, J.Moulijn Festschrift Special Issue of Ind.Eng.Chem.Res. 2007 (in press)
Presented Monday 17, 16:40 to 17:00, in session Chemical Reaction Engineering: Advanced Concepts (T2-2b).
