Physical Property Issues In Simulation: Gas Solubility

Published December 2003

The engineering aspects of process design attempt to optimize the performance to maximize the economics and define the best possible process. However, the most under-rated aspect of such efforts is the determination of the underlying physical properties used to define the process. This review examines the impact of gas solubility on process design. Early stage simulation tends to start with the most simplistic assumption. For gas solubility, this generally results in the assumption of ideal gas behavior and ignores gas solubility. The consequences are illustrated using an ammoximation process employing ammonia gas and hydrogen peroxide to convert cyclohexanone to cyclohexanone oxime. Simulation improvements require deviation from ideal gas assumptions, which means using Henry's Law. The typical problem with that assumption is the lack of suitable Henry's Law parameters in the property data files of the simulation software. Implementation without known parameters typically results in crude estimation based on simple knowledge, such as approximate known concentration in the liquid mixture. The same ammoximation process is used to show the pitfalls of such an approach, along with a kludge approach to make things work. Finally, literature searches to gather data and estimation techniques to fill in the blanks are required to provide more realistic simulation results. The impact on the ammoximation process is demonstrated, and the limitations of this approach are discussed. This review is intended to show the problems and limitations with physical property data and the impact on simulation results, as well as the subsequent process design.