Effects of finely divided solids on mass transfer between a gas and an organic liquid

Abstract

Global gas-liquid mass transfer parameters, k,a and a were determined in an organic liquid in which finely divided solid particles were suspended in a mechanically stirred vessel. The product kLa and a both decreased linearly with solids loading; both were independent of particle size and particle density. Gas holdup was independent of solids loading. SCOPEThree-phase slurry reactors, in which a gas, a liquid, and a finely-divided solid are contacted, are widely used in industry. Gas-liquid mass transfer often presents a major resistance to the rate of reaction and it can affect product selectivity. If present, this resistance is usually much more important than that of mass transfer from liquid to the outside surface of solid particles. The prediction of gas-liquid mass transfer in these systems is still highly uncertain, partly because most laboratory or pilot plant studies have been conducted with water. Water is safe and cheap, and aqueous systems are of intrinsic interest for some applications. However, aqueous systems often behave substantially differently than organic systems. The latter are of primary interest in the chemical and petroleum industry and much less is known about them.Interfacial area, a, was determined here by the socalled chemical method (unsteady state absorption with simultaneous chemical reaction in the fast-reaction regime) using the reaction of COP with cyclohexylamine (CHA) in a solution of 90% toluene and 10% isopropanol. The overall mass transfer coefficient, kLa, was determined by the unsteady state desorption of helium from the same liquid into a nitrogen purge stream. The solid properties investigated were particle concentration (0-45 vol.%), size (35-200 pm), density (0.7-4.5 g / mL), and composition (glass, polytetrafluoroethylene, polypropylene). The effect of gas phase mixing upon the calculation of these parameters was also evaluated. Studies were made in a 1 L aerated and mechanically agitated reactor. CONCLUSIONS AND SIGNIFICANCEThe overall mass transfer coefficient and the interfacial area decreased linearly with inert solids loading. The decrease in kLa can be attributed to the decrease in a: kL was independent of solids loading for the conditions of this study. Gas holdup did not vary with inert solids loading, indicating that the decrease in a was due to bubble coalescence.Correspondence concerning this paper should be addressed to C.N. Satterfield Both kLa and a were independent of particle size for particle sizes below 200 pm. Both were also independent of particle density. Stirring speed was shown to be an appropriate basis for comparison of mass transfer parameters. At high solids loadings kLa and a were lower when the solids were relatively nonwetting. A mechanism for enhanced bubble coalescence was postulated.The use of an apparent viscosity for prediction of AIChE JournalMay 1986 Vol. 32, No. 5 773 mass transfer can be misleading because results differ depending upon whether a viscosity increase is caused by addition of solids or, e.g., by addition of a high-vi...

Interfacial areas and gas hold‐ups at elevated pressures in a mechanically agitated gas‐liquid reactor

“…The main advantage of this reaction is the possibility of varying the rate constant over a wide range by changing the Co2 + catalyst concentration. However, the reaction is restricted to aqueous solutions and, furthermore, the noncoalescing behaviour of this ionic system also limits its use, see Bartos and Satterfield [21].…”

“…In recent years, amines have been used to determine mass transfer parameters in different reactors, see e.g. Metha and Sharma [24], Midoux et al [25], Versteeg [26] and Bartos and Satterfield [21]. The advantages of reactions between CO, and amines are: the possibility of setting up different regimes of the chemical method by selecting different amines and different concentrations.…”