Date of Award

1996

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemical Engineering

First Advisor

Louis J. Thibodeaux

Abstract

Solvent sublation is a nonfoaming adsorptive bubble process which exploits the surface active nature of organic compounds in their removal from aqueous systems. Gas bubbles are introduced into an aqueous media and are buoyed upward to an immiscible organic solvent. As the bubbles rise, organic materials are selectively adsorbed from the aqueous phase and transported to the overlying, quiescent solvent layer. This dissertation studied three-phase, continuous solvent sublation of pyrene and pentachlorophenol from simulated wastewater at the pilot-scale. Steady-state removal efficiencies as high as 96% for pyrene and 94% for pentachlorophenol were demonstrated and were significantly greater than the corresponding 67% removal efficiencies observed in bubble fractionation. Moreover, experimentally determined separation factors, which are measures of the solvent utility, were as high as 300 demonstrating the superiority of solvent sublation over solvent extraction. Based on correlations and observations in the bubble column literature, it was determined that the upper limit of the homogeneous flow regime is the appropriate operating regime for solvent sublation. This is in contrast to previous sublation studies which indicated that the lower limit was preferred. Additionally, hydrodynamic data were collected from two different types of gas spargers: namely a porous frit and an annular shear sparger. The shear sparger differs from the frit in that bubbles are generated in the presence of a shear field which tends to produce smaller bubbles. It is shown that the use of the annular shear sparger delays the transition from the homogeneous flow regime to the heterogeneous flow regime. Thus, for applications requiring homogeneous flow, column capacity is improved by 25%. Two equivalent models (SCM and ADM2) were developed for predicting sublation performance. The transport mechanisms considered, in the order of their relative importance, were (i) sorptive mass transport, (ii) bubble-wake entrainment (solvent extraction of the aqueous boundary layer surrounding a bubble), and (iii) solvent-water molecular mass transfer. It was shown that the Henry enhancement factor, which accounts for surface adsorption at the gas-liquid interface is a good predictor of a compound's susceptibility to adsorptive mass transfer.

ISBN

9780591035353

Pages

224

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