Kinetic study of carbonylation of ethanol using homogeneous Rh complex catalyst

Carbonylation of ethanol using homogeneous rhodium complex catalysts is an essential route for the manufacture of propionic acid, as carbonylation of methanol to acetic acid is a large-scale commercial process that could provide critical insights for the ethanol carbonylation process. The reaction mechanism of ethanol has not been well understood yet, and the high cost of downstream separation due to high water content is still worrying. Consequently, propionic acid was used as solvent to reduce water content in the kinetic experiments carried out in a semibatch autoclave reactor. Homogeneous rhodium was used as complex catalyst with HI as a promoter and propionic acid as solvent. The effects of ethanol, hydroiodic acid, rhodium, and the pressure of carbon monoxide on reaction rate and selectivity of propionic acid were investigated. The reaction mechanism was determined through these batches in the meantime. A kinetic model for ethanol carbonylation was deduced based upon the observations and reaction mechanism. The parameters of the model were regressed and verified with the experimental data. The activation energy was found to be 75.6 kJ center dot mol(-1). Residual error distribution and a statistical test showed that the kinetic model is reasonable and acceptable.