Roger Dean Whitley

A versatile model for simulation of reaction and nonequilibrium dynamics in multicomponent fixed-bed adsorption processes

Abstract Mixtures of large biochemicals can exhibit complex chromatographic behavior. In addition to mass transfer mechanisms, the presence of nonequilibrium ad

High purity oxygen production by pressure swing adsorption

The oxygen purity produced by pressure swing adsorption (PSA) processes is limited to 95%, with the rest being essentially argon. This oxygen grade is suitable for many industrial applications. However, medical applications, cylinder filling, oxyfuel cutting in metal fabrications, and fuel cells technology with recirculation loop, among others, require oxygen with a higher purity (99% or above). In this paper, a study of high-purity oxygen production by a PSA unit using a silver exchanged zeolite from Air Products and Chemicals, Inc., with oxygen/argon adsorption selectivity is presented. This study comprehends the determination of adsorption equilibrium isotherms of oxygen, nitrogen, and argon as well as the simulation and optimization of a PSA experimental unit and the corresponding experimental validation.

Non-linear waves in chromatography II. Wave interference and coherence in multicomponent systems

This second instalment on non-linear waves examines in detail the effects caused by interactions between different solutes in multicomponent systems. Emphasis is on concepts and qualitative insight, and mathematics is kept at a minimum. To avoid unnecessary complications, the assumption of ideal theory are taken for granted. In the discussion, no restrictions are imposed on the nature of equilibria between the moving and sorbent phases and on the number of components. However, all examples are of two- and three-component systems with competitive sorption equilibria.

Effects of temperature and flow rate on frontal and elution chromatography of aggregating systems

Abstract During chromatography, β-lactoglobulin A can aggregate into tetramers, octamers, and dodecamers. Increasing temperature changes relative peak heights and results in peak merging. In the literature, temperature-induced shifts in equilibrium distributions were hypothesized to cause these changes. Using a reaction-separation model, we have shown that an increase in reaction rates in accordance with the Arrhenius relationship also explains the literature data well. When aggregation rates are fast relative to mass transfer rates, there is a loss of resolution between individual aggregates; breakthrough times and retention times of concentration wave fronts and peaks are averaged, resulting in a single front or peak. Conversely, when reaction rates are relatively slow, wave fronts and peaks of individual aggregates are distinct. Scaling up a complex reacting system is difficult because changes in apparently unrelated parameters, such as particle size, flow rate, concentration, and temperature, can all alter effective reaction rates. This study shows that a dimensionless group approach provides a simple method to predict surprising results. Most surprising is that at low temperatures (slow reaction rates) a decrease in flow rate results in a loss of resolution between the aggregates, whereas at high temperatures (fast reaction rates) an increase in flow rate can enhance resolution.

Determination of ion-exchange equilibrium parameters of amino acid and protein systems by an impulse response technique

Abstract The application of an impulse technique to determine the Langmuir isotherm parameters of amino acids and proteins in ion-exchange chromatography is described. The ion-exchange column is approximated as many stages in series. Within each stage. the mass transfer rate of a given solute between mobile and stationary phases is finite. Responses to pulse and step changes are calculated using a fast and stable algorithm. The equilibrium parameters are estimated by comparing the responses with the experimental data. The sensitivity of the response with respect to equilibrium and mass transfer parameters was studied. The accuracy of estimation of the equilibrium parameters depends strongly on the pulse volume and pulse concentration. A methodology for selecting the proper pulse parameters was developed and successfully used to determine the equilibrium parameters of phenylalanine and bovine serum albumin. The stage model represents pulse data as closely as a more detailed rate equation model while requiring two orders of magnitude less computation time. This technique offers a fast alternative to the conventional batch equilibrium and frontal analysis methods for determining equilibrium isotherms. The impulse technique requires fewer laboratory manipulations than the batch method and, as a result, the data are less scattered. More important, it requires only 1% as much substrate as batch methods and is of value in estimating the equilibrium parameters of costly biochemicals.