Theodore Vermeulen

Separation by Adsorption Methods

Publisher Summary Adsorption may be considered a prototype for all fluid–solid separation operations. When it is conducted under countercurrent conditions, the calculation methods required are entirely analogous to those for countercurrent absorption or extraction. Adsorption is analogous to selective condensation of gas molecules or to selective crystallization or fusion from a liquid. It is based upon intermolecular attractive forces of the van der Waals type between a solute and the solid surface. An efficient adsorbent in contact with a gas phase may hold a volume of adsorbate equal to as much as 1.0% of the particle volume (silica gel has an even larger capacity). This chapter discusses theories and practice of adsorption methods for separation puts stress on column dynamics under linear equilibrium and column dynamics at a constant separation factor. It also describes the chromatographic separation method in which only a small amount of solution containing the components to be separated is admitted to the column. If the column is long enough, the zones will draw apart completely from one another, and may be recovered in the effluent as separate solutions of each individual solute. Finally, the chapter addresses the problems of data interpretation and apparatus design extensively, focusing on fixed-bed operations

The receding contact angle

Receding as well as advancing water contact angles have been measured on glass surfaces treated with dichlorodimethysilane and with chlorotrimethysilane. The experimental data support the theory of contact-angle hysteresis on heterogeneous surfaces as proposed by Dettre and Johnson. Among the surfaces prepared here, the Me2SiCl2-treated one is unique in showing zero hysteresis, a result attributable to homogeneous coverage and structure. The Me3SiCl-treated surface appears to possess both micro- and macroheterogeneity. In these systems, the advancing angle is believed to approximate closely the equilibrium contact angle.

Ion-exchange pretreatment for scale prevention in desalting systems

Abstract Ion exchange pretreatment can protect dependably against scaling from calcium sulfate and alkaline deposits in desalting equipment, and against acid corrosion. When a feedwater is “softened” by ion exchange to replace most of its calcium by sodium, use of the sodium-rich reject brine from desalination to regenerate the exchanger makes the treatment chemically self-sufficient. An inexpensive vessel construction using salt-resistant reinforced concrete appears suitable for large-scale use. For moderate concentration factors (up to around 5 for seawater feed), and moderately low sulfate/chloride ratios, regeneration can be carried out in fixed-bed mode, preferably counterflow (upflow). At higher sulfate levels, precipitation occurs, and regeneration must be done in fluidized- (expanded-) bed mode to keep calcium sulfate from collecting in the bed. When weak-acid cation exchange with acidified exchanger is used to eliminate bicarbonate, feedwater acidity excursions are avoided, and the total-dissolved solids level is reduced rather than increased.

Determination of Interfacial Area in Unstable Emulsions by Light Transmission

Total interfacial area can be determined in agitated mixtures of transparent immiscible liquids by calculation from photoelectric measurements of their light transmission relative to clear fluids, with a probe of new design which is inserted into the emulsion. The probe is compact and rugged, and can be assembled from a simply constructed housing together with commercially available parts. A calibration obtained by high‐speed photography of the emulsions is presented. The drop diameters measured were in the range of 0.01 to 0.10 cm, and, in this range, the specific area is found to depend only upon the light transmission and the ratio of refractive indexes of the dispersed and continuous phases.

Ion‐Exchange and Adsorption Column Kinetics with Uniform Partial Presaturation

The available mathematical solutions for fixed‐bed concentration histories apply primarily to one‐component systems in adsorption and to two‐component systems in ion exchange. Thomas has developed explicit general relations for the saturation of an adsorbent bed initially free of saturating component by a fluid phase containing only this component; as well as for the converse elution situation.These results are extended here to cases of mixed binary feeds (in ion exchange), and cases of columns that are uniformly partially saturated prior to the run under study. New definitions of the dimensionless parameters that characterize the sorption processes render the existing numerical framework applicable for evaluating this broadened range of operating conditions. From the theoretical standpoint, these new parameters clarify the mathematical interrelationships between adsorption and ion exchange, between saturation and elution, and between sorption of trace components and sorption of gross or bulk components. ...

Calcium removal from sea water by fixed-bed ion exchange

Abstract Calcium removal from sea water prior to evaporation permits increased temperature and concentration during evaporation. The results of laboratory studies on calcium removal by fixed-bed ion exchange are reported. Synthetic regenerants were employed, simulating in composition and total amount the waste brine from the evaporator. In actual practice, use of this brine eliminates the need to purchase regenerant chemicals. Commercial polystyrene sulfonate resins were used at room temperature, employing downflow for the softening step, and upflow for regeneration, without rinse. In multicyclic operation, the effects of particle size, bed depth, flow rate, and regenerant concentration on the degree of calcium removal have been studied. Relations for predicting resin volume and cycle time under given operating conditions are presented as an aid in calculations leading to economic optimization of the process.

Column Dynamics of Ternary Ion Exchange Part I: Diffusional and Mass Transfer Relations

Abstract The complete multicomponent ion-exchange diffusion equations based on irreversible thermodynamics and their approximations by the Nernst-Planck model or the Ficks law model are all put in the same algebraic form. Their differences occur only in the definition of the diffusion coefficients. Multicomponent diffusion coefficients. Multicomponent diffusion coefficients are related to those in binary systems by either the Nernst-Planck or Ficks law model. Using a linear driving force approximation for the flux equations, similar relationships are developed for estimating multicomponent (ternary) mass transfer coefficients based on the analysis of binary data. Hence from binary data and these relationships, multicomponent effluent concentration histories may be predicted numerically.

Column Dynamics of Ternary Ion Exchange Part II: Solution Mass Transfer Controlling

Abstract The nonequilibrium theory for column dynamics of multicomponent ion exchange has been evaluated using the ternary system Ag-Na-H at a total solution concentration of 0.05 N (0.05 M) so that solution mass transfer controls the exchange. Ternary mass transfer coefficients have been related to binary values by both simple (constant) and improved (concentration-dependent) Ficks law models, as well as by simple and improved Nernst-Planck models. Binary coefficients of all four types were obtained directly from constant-pattern binary breakthroughs and the individual-component Nernst-Planck coefficients were derived from the binary coefficients. Using each of the four models, ternary effluent concentration histories (ECH) were predicted using the method of characteristics. All the models predicted effluent concentration histories that matched closely the experimental ones, indicating that either model may be used satisfactorily for prediction; the simple models are preferred to the improved ones since they contain fewer parameters.

A mathematical model of the cyclic operation of desalination-feedwater softening by ion-exchange with Fluidized-bed regeneration

Abstract The goal of this work was to optimize the steady cyclic operation of an ion-exchange pretreatment of an agricultural wastewater that is fed to a desalination plant. The ion-exchange resin is exhausted to remove calcium in a fixed bed. Brine from the desalination plant regenerates the ion exchanger in a fluidized bed to prevent plugging by calcium sulfate. After the calcium sulfate precipitates, the regenerant can be reused. To predict how the plant should be operated, a mathematical model was needed. The model qualitatively agrees with experimental results. Conclusions about operating such a plant are drawn.