The adsorption characteristics of cadmium ions from aqueous solutions onto two organo-ceramic adsorbents synthesized in our laboratories were studied. The main species participating in the adsorption process, determined from the chemical equilibrium, is Cd 2+ . Formation of a bidentate cadmium-thiol complex is proposed to explain the experimental isotherms. The kinetics of adsorption onto the sol-gel-synthesized adsorbent was studied in a differential batch reactor with recycle. Two kinetic models were tested with experimental data: chemical reaction and film/pore mass-transfer resistances. The results indicate that either model can be used to explain the adsorption process as observed from the AARD values and from the F-test. The values of fitted parameters are k 1 ) 0.0021 L‚g/mmol 2 ‚min, D p ) 1.4 × 10 -7 cm 2 /s, and τ ) 5.0. The last two parameters can be used to satisfactorily predict the breakthrough curve in a fixed bed by the film/pore diffusion model. A sensitivity analysis shows that pore diffusion resistances control the adsorption process.

SynopsisThe transport of gases in many glassy polymers can be described satisfactorily by means of a "dual-mode sorption" model. The transport behavior observed with a given gas/polymer system can be characterized by the model parameters, which are obtained from solubility measurements in conjunction with absorption/desorption or permeability measurements. The present study discusses the inverse problem, namely, the prediction of the absorption/desorption behavior of a gas in a glassy polymer from a specified set of dual-mode sorption parameters. Satisfactory agreement is obtained between reported absorption rates of sulfur dioxide in glassy polycarbonate and of water vapor in Kapton@+ and the rates predicted by the dual-mode sorption model. This study also confirms the consistency of the model.

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A transient technique is proposed for measuring the mean thermal conductivity of a small bed of solid particles. Such beds are used in different catalytic rate studies or for a temperature-programmed desorption apparatus. The lower bound of conductivity for a thin bed of 47% by weight nlckel/slllca catalyst was 2.6 W/(m K), In orderof-magnitude agreement with published data. If methane were produced catalytically from a CO/H2 mixture in such a catalytic bed at typical flow conditions, the calculated difference between center line and wall temperatures should not exceed 4 °C.

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