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M.Sc. (Biochemistry) / Please refer to full text to view abstract

Thesis (M.Sc.(Chemical Engineering))--University of the Witwatersrand, Faculty of Engineering, 1987. / Experimental work showed that the adsorption of the aurocyanide ion by activated carbon is under film diffusion control until the carbon reaches 70 per cent of its equilibrium loading capacity. A rate expression based on the classical film diffusion rate expression is suggested and the model for the batch test developed. The proposed model is shown to simulate batch adsorption tests at different ratios of carbon mass to solution volume. The mass transfer coefficient was linked to the carbon particle size and agitation rato by the use of dimensionless numbers. Correlations are suggested for fixed beds, fluidized beds and rolling bottles. It was determined experimentally that, at equivalent Reynolds numbers, the fixed bed provides the optimum system for mass transfer.

The search for a low cost and effective technique to control and remove volatile organic chemicals (VOCs) has gathered a great attention from the adsorption process field. Advances in manufacturing technology have enabled the creation of activated carbon monoliths (ACM) as promising substitute for traditional packed beds of granular adsorbent materials. The research described in this thesis comprises an extensive experimental study of a single component adsorption process onto square and hexagonal channel Novacarb™ ACM supplied by MAST Carbon Technology Ltd. ACM characterisation methods such as nitrogen and solvent adsorption isotherms, electron microscopy, thermo-gravimetric analysis and thermal dynamic characterization have been used. High BET surface area, high total pore volume and high total solvent mass uptakes have been found. ACM were tested by obtaining column breakthrough curves mainly using dichloromethane and acetone as the adsorbates at the bench-scale. The adsorption dynamics of the ACMs studied were also compared with those of extrudates manufactured by the same process as the ACMs. The influence of humidity on the adsorption process has been studied at the bench-scale. Finally, the adsorption system was scaled-up to about 60cm length monoliths in order to study both adsorption and electrical regeneration taking advantage of the particular electrical properties held by the Novacarb™ ACM. It has been found that ACMs are able to adsorb high levels of VOCs, up to 40% by weight of DCM, good behaviour under humidity conditions and low pressure drop. In contrast, kinetics of ACMs have been found to be somewhat inferior to those of equivalent packed beds, although the ACM performance can be improved by reducing the wall thickness. Adsorption of DCM at the pilot-scale has demonstrated that the Novacarb™ ACM could easily be used in a cyclic thermal swing adsorption process with a half cycle time of less than one hour.

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