Kinetics of carbonyl sulfide hydrolysis.: 2.: Effect of n-alkanes in mixtures of water plus hydrocarbon

Carbonyl sulfide (COS), which occurs as an impurity in commercial sources of propane, can hydrolyze in the presence of water to form hydrogen sulfide (H2S) and carbon dioxide (CO2). Whereas COS is not itself corrosive, the hydrolysis product H2S is corrosive, especially in the presence of water. This hydrolysis is thought to be a major problem in the liquefied petroleum gas industry. In this paper, we summarize the results from studies that address the issue of COS hydrolysis in the presence of various n-alkanes. A series of kinetics measurements were made of COS in aqueous systems containing methane, ethane, propane, n-butane, or n-hexane at 85 degreesC. Reaction rates were determined from chromatographic monitoring of the decrease in COS and the appearance of H2S in the vapor phase as a function of time. The hydrolysis rates varied for each of the hydrocarbon systems, and all rates were several orders of magnitude lower than those previously reported for pure water. Furthermore, we found the rate of COS hydrolysis to be correlated with the binary interaction diffusion coefficient, D-12, for the alkanes in water. This suggests that the diffusion of larger organic molecules into the aqueous phase impedes the ability of COS to react with water.