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Abstract: The kinetics of 1-octene hydroformylation catalyzed by triphenylphosphine modified rhodium in carbon dioxide have been explored at 90°C and pressures up to 48MPa. The apparent catalyst solubility was determined by evaluating the reaction rate for different rhodium amounts. The kinetics follow a first order in 1-octene, a negative order of −1.2 in carbon monoxide, an order of 0.25 in hydrogen, and a negative order of −0.2 in triphenylphosphine, which is to a great extent in agreement with studies on the hydroformylation of linear 1-alkenes in organic solvents. The observed apparent turnover frequencies range from 1900 to 7000molaldehyde molRh −1 h−1. These turnover frequencies are of the same order of magnitude as observed for hydroformylations in organic solvents, indicating that rhodium modified with triphenylphosphine can be used with high efficiency in supercritical carbon dioxide rich mixtures. [Copyright &y& Elsevier]

Abstract: 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 0.5molL−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. [Copyright &y& Elsevier]

Abstract: For the hydroformylation of 1-octene in supercritical carbon dioxide the relationship between the change in pressure and the change in reaction mixture composition as a function of time has been investigated. The activity and selectivity has been studied for the catalyst based on tris(3,5-bis(trifluoromethyl)phenyl)phosphine and rhodium(I) dicarbonyl acetylacetonate. The influence of the ligand to rhodium ratio on the hydroformylation has been used to demonstrate how the pressure can be correlated to the conversion and yield. The initial rate of reaction is in good agreement with the initial pressure change in the batch reactor. Up to an aldehyde yield of 80%, the pressure drop appears to be independent of the reaction rate and selectivity. The highest average reaction rate, , has been obtained for a ligand to rhodium ratio of 50 and an initial concentration of 1-octene of 0.5molL−1. Both the reaction rate and the selectivity increase when the ligand to rhodium ratio is increased. The Peng–Robinson equation of state has been used to describe the pressure as a function of the concentration of the reactants and products. The calculated pressure corresponds reasonably well with the observed reactor pressure. Following the progress of the reaction by monitoring the pressure is a good alternative to reaction mixture sampling, especially for fast reactions. [Copyright &y& Elsevier]