Influence Of Axial Dispersion Research Articles

Breakthrough dynamics of nitrogen, oxygen, and argon on silver exchanged titanosilicates (Ag-ETS-10)

Breakthrough curves of N2, O2, and Ar on Silver exchanged titanosilicates (Ag-ETS-10) extrudates and granules were measured using a laboratory scale dynamic column breakthrough (DCB) apparatus. In order to investigate the dynamics of the mass transfer, effect of flow rate, temperature and pressure on the composition and temperature curves were studied. In a separate attempt, N2 breakthrough curves on two columns filled with Ag-ETS-10 extrudates and granules with two different sizes were obtained. Influence of axial-dispersion, macropore, and film resistance within the column was investigated using fundamentals of mass transfer and fluid dynamics which assisted in classifying the dynamics of this separation. The experimental results indicated the rapid mass transfer and the potential for rapid cycles using Ag-ETS-10 for high-purity O2 production. A fully predictive mathematical model was shown to describe the experimental curves to a high level of precision.

Advantage of the single pellet string reactor for testing real-size industrial pellets of potassium-doped CoMnAl catalyst for the decomposition of N2O

Two tubular laboratory reactors, the single pellet string reactor (i.d. = 0.55 cm) and the fixed bed reactor (i.d. = 5 cm) were compared on the basis of laboratory experiments of N2O catalytic decomposition and measurements of residence time distribution curves. K/Co4MnAlOx mixed oxide in the form of cylinders (5.1 mm × 5.1 mm) was used as a catalyst. The influence of external diffusion, deviation from plug flow and influence of axial dispersion on N2O conversion obtained in both reactors were discussed. The influence of macroscopic phenomena on the rate of catalytic reaction was significantly lower in the single pellet string reactor, which predetermined it as a suitable laboratory reactor for testing of real-size industrial catalysts. Experimentally obtained results were confirmed by mathematical modeling.

Description of the dynamics of vapor adsorption in a fixed bed of an adsorbent using various approximations of the mixed-diffusion model

The use of the mixed-diffusion model for calculating the dynamics of adsorption of the vapors of volatile organic compounds in a fixed bed of a porous adsorbent is considered. The V2O5/Al2O3 system is used as an example. It is shown that a simplified version of the mixed-diffusion model in which the influence of axial dispersion is neglected and the establishment of equilibrium on the external boundary of a grain is assumed gives distorted knowledge of the real dynamics of the process. The complete mixed-diffusion model adequately reflects the influence of the contributions of axial dispersion and external and internal mass transfer in the smearing of the sorption front, but diversions from the assumptions of the model that manifest themselves in the concentration dependence of an apparent internal-diffusion coefficient are also observed in this case. The considerable advantage of the model is that using a single-fitting parameter allows experimental data to be approximated with a satisfactory accuracy.

Modeling of Protein Adsorption in Membrane Affinity Chromatography

For the design of affinity membranes protein adsorption in membrane affinity chromatography (MAC) was studied by frontal analysis. According to fast mass transfer, small thickness of affinity membranes and high affinity between the protein and the ligand, an ideal adsorption (IA) model was proposed for MAC and was used together with equilibrium‐dispersive (E‐D) model to describe the adsorption of bovine serum albumin (BSA) onto cellulose diacetate/polyethyleneimine (CA/PEI) blend membranes with and without Cu2+ chelating. E‐D model was found to better describe the initial region of experimental breakthrough curves. The influence of axial dispersion was revealed and it showed the importance of design of the module to homogenously distribute feed solution. IA model was found to be better for the whole experimental breakthrough curve. According to it, the capacity of affinity membranes and the specificity of the interaction are of equal importance for the design of affinity membranes. An optimum feed concentration was also found in the operation of MAC. The discrepancy between experimental optimum feed concentrations and predicted ones from IA model may be due to the ignorance of some experimental effects such as axial dispersion.

Pseudostationary Pulsed Laser Polymerization: A Simple Method for the Direct Determination of Axial Dispersion as Occurring in Size Exclusion Chromatography

AbstractTheoretical distribution curves were calculated for several values of pulse separation t0 and concentrations of initiating radicals ρ formed by each pulse for both types of termination (disproportionation and combination). The absolute and relative peak widths of the additional peaks for the number, molar mass, and hyperdistribution were determined and compared. In all cases, the peak widths of these different distributions became the same with increasing values of C = ktρt0 and/or L0 = kp[M]t0, with [M] = monomer concentration and kt and kp are the rate constants of termination and propagation, respectively. This is similar to the behavior of Poisson distributions if only the degrees of polymerization are fairly high (P̄n ≥ 50). The analogy is further supported by the finding that under the same conditions the peak widths themselves approach the theoretical ones for Poisson distributions. Thus, the fulfilment of these two criteria suggests that the various peaks in multimodal distributions should be treated in the same formal way as Poissonian peaks although they clearly originate from a superposition of adjacent Poissonian peaks of different amplitude and, on the whole have a peak width somewhat in excess of the theoretical one of true Poisson peaks of the same P̄n. The point of inflection can be used as a measure of L0 without reservation only if the first criterion is not fulfilled. The influence of axial dispersion on the location of the extrema was calculated by use of standard deviations σad,k (0.05 and 0.025) to give “experimental curves” for which a pronounced increase in the absolute and relative peak widths was observed. Based on an assumed additivity of the peak variances, a simple procedure was tested for the direct determination of σad,k. The accuracy increased with increasing peak chain lengths and C values for those values determined from the first peak. The values determined from the second peak in the chain length region between 400–700 were closest to the input value.The points of inflection on the low and high molecular weight side of the additional first three peaks are given as a function of the peak maximum. The lower and upper lines were calculated with Equation (11) and (12), respectively.imageThe points of inflection on the low and high molecular weight side of the additional first three peaks are given as a function of the peak maximum. The lower and upper lines were calculated with Equation (11) and (12), respectively.

Investigation of the Peak Width of Polystyrene Prepared by Rotating‐Sector Polymerization in Microemulsion

AbstractStyrene was polymerized by intermittent photoinitiation (at a constant sector speed and a light to dark ratio of 1:5) in microemulsion. The molecular weight distribution was measured by size‐exclusion chromatography and turned out to be extremely well structured. When the points of inflection were used for the calculation of the rate constant of propagation in analogy to pulsed‐laser polymerization/size‐exclusion chromatography (PLP‐SEC), values were obtained which were lower than those accepted for bulk polymerization but good agreement was achieved with a slightly modified equation. The absolute peak width (introduced as the difference between two successive points of inflection) turned out to be an invariant quantity no matter which type of distribution curve (number, molar mass, or hyper distribution) was analyzed, thus demonstrating the Poissonian character of the peaks. Furthermore, the relative peak widths (defined as the ratio of two successive points of inflection) for the first peak scattered between 1.35–1.45, those for the second peak between 1.26–1.30. After subtracting the respective value for the theoretical peak width, the same value for the first and second peaks was obtained for all experiments over a broad range of experimental parameters. As the appearing peaks are well resolved and narrow, the influence of axial dispersion on the results is, therefore, conclusively demonstrated. A simple procedure for the direct determination of axial dispersion is presented based on the relative peak widths and the additivity of the peak variances. The invariance of the peak widths is an easily verifiable theoretical and experimental prerequisite for this procedure. Comparison of GPC traces of a microemulsion polymerization of styrene (t0 = 1.4 s, [M] = 4.326 mol · l−1; light‐to‐dark ratio 1:5; full line) and of a standard mixture (styrene, peak masses: 1 950, 89 400, 993 000; dashed line).imageComparison of GPC traces of a microemulsion polymerization of styrene (t0 = 1.4 s, [M] = 4.326 mol · l−1; light‐to‐dark ratio 1:5; full line) and of a standard mixture (styrene, peak masses: 1 950, 89 400, 993 000; dashed line).

Degradation of aromatic compounds by Pseudomonas putida

AbstractThe influence of different process kinetics on the course of phenol degradation has been studied as well as the influence of axial dispersion in the liquid phase on the reactor height with relatively large biofilm thickness in a conventional fluidized bed and air‐lift bioreactor. The object of this was to achieve a high conversion of substrate in a device of real size in real process time. For calculating the mathematical model, the method of orthogonal collocation with the STIFF integration routine has been used.

Liquid—solid mass transfer in packed beds of parallelepipedal particles: energetic correlation

Mass transfer between liquid flow and anisotropic square-base parallelepipedal particles of different height-to-side ratio is investigated with an electrochemical method. The influence of axial dispersion is studied and the results analyzed by using bed structure parameters. A comparison of mass transfer performances for beds of spherical particles is made. A single energetic correlation for all types of studied parallelepipedal particles is proposed for a large range of Reynolds numbers, including creeping flow and intertial regime: ▪ where Xe is an energetic dimensionless criterion: ▪ E is the mechanical power dissipated by unit volume of fluid.

Transfert thermique dans un réacteur catalytique à lit fixe à température de paroi constante

Three bidimensional pseudo-homogeneous models are considered for estimation of heat transfer parameters in a fixed bed catalytic reactors. The Peclet and Biot numbers are obtained by identification of experimental and calculated temperatures profiles in a pilot plant reactor. Particular attention is drawn to sensivity of identification to experimental variables. The results obtained from the one parameter model proposed by Dewash and Froment are compared with experimental data, and influence of axial dispersion in catalytic bed is studied by comparison of different models.

Determination of the aeration capacity of bubble columns by dynamic method. The influence of axial dispersion and of the start-up period

A dynamic method for the determination of volumetric mass transfer coefficient of oxygen, kLa, in bubble columns using an oxygen electrode was derived on the basis of a liquid phase axial dispersion model The influence of aeration startup was studied assuming that the kLa value is position and time dependent. The conditions are defined under which the influence of aeration startup and of axial mixing of the liquid upon the steady state kLa value is negligible. A critical assessment has been made of various methods proposed for evaluation of oxygen probe responses.