(474d) Experimental and Modeling Results for Rich Gas Absorption of HCl in Caustic Solutions

Developing modeling capability and performance data in the area of absorbing "rich gas" fills a long-standing technical gap in separations technology. The term "rich gas" is used in this context to denote an application in which a substantial portion or a majority of the gas is absorbed from the incoming gas mixture. Closing this gap can lead to more efficient designs of scrubbers, resulting in lower cost and smaller footprints for our processes.

An experimental apparatus for rich gas absorption utilizing a 5.08 cm (2") packed tower with 0.635 cm (1/4") ceramic saddles was used to measure the absorption performance of hydrogen chloride (HCl) gas in aqueous sodium hydroxide (NaOHaq) absorbent. The system of absorbing HCl in caustic is a classic system that can be used to quantify and test correlations for gas phase mass transfer coefficients because the ionic reactions of HClaq with excess NaOHaq are extremely rapid.

Feed gas mixtures with increasing concentrations of HCl in nitrogen were absorbed across limited packed bed heights to produce meaningful data for absorption performance evaluation in the rich phase. Concentrations of HCl in the incoming feed gas were varied from 5% to 90%. The results of this experimental program are presented in this report. The results are surprising because of the very high fraction of HCl that was absorbed across very short bed depths.