Full kinetic description of 1-octene hydroformylation in a supercritical medium

The kinetics of the hydroformylation of 1-octene in a supercritical carbon dioxide medium, catalyzed by a tris(3,5-bis[trifluoromethyl]phenyl)phosphine-modified rhodium catalyst, have been investigated. The influence of the concentration of carbon dioxide, reactants, catalyst precursors, and the reaction temperature has been determined. A kinetic model was developed, which describes the concentration-time profiles of the reactants, the linear and branched aldehydes, and the internal alkenes. Using the kinetic model activation energies for hydroformylation of 1-octene to nonanal and 2-methyloctanal were determined. Throughout the concentration ranges studied an approximate first order dependence of the hydroformylation rate on the hydrogen and catalyst concentration was found which indicated that oxidative addition of hydrogen was the rate limiting step. The increase in reaction rate and regioselectivity with an increase in ligand concentration is a striking feature of the catalyst investigated here. At higher concentrations the reaction rate was found to have a strong negative order dependence on the carbon monoxide concentration. The reaction rate had a positive order in 1-octene at a concentration lower than 0.5 mol L−1 while saturation kinetics were observed at a higher concentration. The results were explained by invoking the contribution of both monophosphine and diphosphine rhodium species to the hydroformylation catalysis.

An extensive mathematical model has been developed which describes the reaction kinetics of hydroformylation of 1-octene in supercritical carbon dioxide catalyzed by Rh modified with tris(3,5-bis[trifluoromethyl]phenyl)phosphine. The model allows for an accurate prediction of the formation rates of the n-aldehydes, iso-aldehydes, and the octene isomers. Analysis of the kinetic model using the differential method results in a description of the reaction orders as a function of reactant and catalyst precursor concentration. Using supercritical carbon dioxide as a solvent and the highly active trifluoromethylated catalyst turnover frequencies with an industrial applicability have been obtained.Figure optionsDownload high-quality image (189 K)Download as PowerPoint slideHighlights
► Mathematical model of kinetics of 1-octene hydroformylation in supercritical CO2.
► The reaction is first order in hydrogen and rhodium.
► Increasing phosphine ligand concentration improves selectivity and activity.
► 1-Octene reaction order shifts from one to below zero with increasing concentration.
► Rhodium with trifluoromethylated phosphine allows for high turnover frequencies.