(433e) Effect of Gas-Liquid Mass Transfer Rates on the Palladium Catalysed Phenylacetylene Oxidative Carbonylation Reaction

To date, the study of chemical systems with nonlinear dynamics has been a relatively pure science with few applications that are of practical importance1. Most of the work in the area of oscillatory chemical reactions has focused on inorganic reactions. There is little existing work on organic chemical oscillators as these are rarely encountered in the laboratory environment. The oscillatory nature of the phenylacetylene carbonylation reaction in the catalytic system (PdI2?KI?O2?NaOAc in methanol solution) has been previously reported.2-8 The products resulting from this reaction have been isolated.8 Experiments reported by Novakovic et al.6 performed in a reaction calorimeter using power compensation reaction calorimetry9 demonstrate simultaneous oscillations of both pH and Qr (reaction exotherm). Recently Novakovic et al.7 reported influence of oscillations on product selectivity as well as the dynamics of product formation. When operating in an oscillatory pH regime product formation is suppressed until oscillations occur after which there is selective formation (>90%) of Z-2-phenyl-but-2-enedioic acid dimethyl ester. When operating in non-oscillatory pH mode selectivity is poor and several other products are formed.

This reaction system consumes two gasses, CO and Air (used as a source of O2). Novakovic et al.6 reported the influence of stirrer agitation speed on occurrence of oscillations suggesting that gas liquid mass transfer rates are significant. To achieve robust prediction of chemical behaviour and product selectivity control will require a fundamental understanding of both the chemical and physical phenomena involved.

Gas liquid mass transfer rates in this system are dependent on a number of factors some of which are interacting: the mass transfer coefficient due to agitation; the solubility of the individual gases; the partial pressures of the gases and solvent vapour in the head space which themselves are dependent on the operating temperature and individual gas flow rates.

This paper reports on a combined experimental and modelling study of CO and Air (O2) gas liquid mass transfer rates on the palladium catalysed phenylacetylene oxidative carbonylation reaction. Simulation work revealed that at the previously reported operating conditions6,7 CO is mass transfer limited due to its poor solubility in methanol. This study includes varying agitation rate, individual gas and vapour partial pressure variation and operating reaction system at elevated pressure. Experiments are performed in HEL SIMULARTM reaction calorimeter and HEL AutoMATE autoclave. Variables recorded on-line include reaction temperature, pH, Qr, turbidity, stirrer agitation speed, gas flow rates and pressure while concentration?time profiles are measured off-line using GC-MS. The results quantify the influence of gas liquid mass transfer rates on reactant conversion and the dynamics and selectivity of product formation as well as the occurrence of oscillatory behaviour in this reaction system.

1. Sagues, F. and Epstein, I.R., Nonlinear chemical dynamics. The royal society of chemistry, Dalton Transactions, 2003, 7, 1201-1217.

2. Malashkevich, A.V., Bruk, L.G. and Temkin, O.N., New Oscillation Reaction in Catalysis by Metal Complexes: A Mechanism of Alkyne Oxidative Carbonylation. The Journal of Physical Chemistry A, 1997, 101, 9825-9827.

3. Gorodskii, S.N., Zakharov, A.N., Kulik, A.V., Bruk, L.G. and Temkin, O.N., Oxidative Carbonylation of Alkynes in an Oscillation Mode: I. Concentration Limits for Oscillations in the Course of Phenylacetylene Carbonylation and Possible Mechanism of the Process. Kinetics and Catalysis, 2001, 42, 2, 251-263.

4. Gorodskii, S.N., Kalenova, E.S., Bruk, L.G. and Temkin, O.N., Oxidative carbonylation of alkynes in self-oscillating mode. Effect of the nature of substrates on the dynamic behaviour of reaction system. Russian Chemical Bulletin, International Edition, 2003, 52, 7, 1534-1543.

5. Temkin, O.N. and Bruk, L.G., Palladium (II, I, 0) Complexes in Catalytic Reactions of Oxidative Carbonylation. Kinetics and Catalysis, 2003, 44, 5, 601-617.

6. Novakovic, K., Grosjean, C., Scott, S.K., Whiting, A., Willis, M. J. and Wright, A.R., Achieving pH and Qr Oscillations in a Palladium Catalysed Phenylacetylene Oxidative Carbonylation Reaction Using an Automated Reactor System. Chemical Physics Letters, 2007, 435, 142?147.

7. Novakovic, K., Grosjean, C., Scott, S.K., Whiting, A., Willis, M. J. and Wright, A.R., The influence of oscillations on product selectivity during the palladium-catalysed phenylacetylene oxidative carbonylation reaction. Physical Chemistry Chemical Physics, 2008, 10, 749-753.

8. Grosjean, C., Novakovic, K., Scott, S.K., Whiting, A., Willis, M. J. and Wright, A.R., Product Identification and Distribution from the Oscillatory versus Non-Oscillatory Palladium(II) Iodide-Catalysed Oxidative Carbonylation of Phenylacetylene. Journal of Molecular Catalysis A, 2008, 284, 33-39.

9. Barton, J. and Rogers, R., Chemical Reaction Hazards, Institute of Chemical Engineering, Rugby, Warwickshire, UK, 1993.