Adsorption cross-flow systems

Polymeric membranes modified through the dynamic single layer of polyelectrolyte adsorption method, as reported by Ba et al. (2010), provided some useful information about the membrane performance stability. In this study, a cross-flow system was... 

Howell and Velicangil (jj.) described three phases in flux loss with time. The gel layer of retained species forms on the membrane in seconds and, as discussed earlier, its restriction on filtration rate can be reduced by increasing the cross flow. Over a period of minutes adsorption of constituents from the media on the membrane takes place. In the time frame of hours, the gel layer on the membrane may become unstable resulting in a less permeable layer. These effects of adsorption and gel layer instability are the principle causes of fouling. They result in lower system output than would be expected based on the solution and operating conditions. The filtration rate of a badly fouled system is dependent on pressure and independent of cross flow. 

Total smface areas were measured by nitrogen adsorption at -196 C, using an automated instrument (Omnisorp lOOCX, Coulter Electronics Limited). The cross sectional area of the nitrogen molecule was assumed to be 16.2 x 10 m. Pore type and volume data were also obtained by this method, using t-plot analysis. Metal areas were measured by selective chemisorption of hydrogen at 30 °C in the same instrument. Copper surface areas were measured in a flow system by nitrous oxide chemisorption at 60 C. 

We recognize here the cross-flow model for packed-beds discussed earlier in Section 5.2 (104-107). This represents its generalization for K 1. Let us consider for the moment our system to be a tube packed with nonporous catalyst particles with plug flow of gas. Then A represents the ratio of the combined maximum volumetric mass transfer rate to the catalyst surface and adsorption rate at the surface to the flow through the tube. If we know the true rate constant, for surface reaction and the partition... 

A detailed analysis of the recovery mechanism in this system has been carried out (Clifford and Sorbie, 1984, 1985), and the cross-flow mechanisms mentioned in the previous section have been shown to apply. However, the analysis is quite lengthy and the reader is referred to this earlier work. Also, the mechanisms will be illustrated much more clearly using results from the calculations presented in the following subsection. This example is presented here as a suitable real-field illustration of the effects of polymer flooding in stratified systems. This example will be considered again when discussing the effects of polymer adsorption and degradation. 

A flow injection optical fibre biosensor for choline was also developed55. Choline oxidase (ChOX) was immobilized by physical entrapment in a photo-cross-linkable poly(vinyl alcohol) polymer (PVA-SbQ) after adsorption on weak anion-exchanger beads (DEAE-Sepharose). In this way, the sensing layer was directly created at the surface of the working glassy carbon electrode. The optimization of the reaction conditions and of the physicochemical parameters influencing the FIA biosensor response allows the measurement of choline concentration with a detection limit of 10 pmol. The DEAE-based system also exhibited a good operational stability since 160 repeated measurements of 3 nmol of choline could be performed with a variation coefficient of 4.5%. 

Despite the importance of mixtures containing steam as a component there is a shortage of thermodynamic data for such systems. At low densities the solubility of water in compressed gases has been used (J, 2 to obtain cross term second virial coefficients Bj2- At high densities the phase boundaries of several water + hydrocarbon systems have been determined (3,4). Data which would be of greatest value, pVT measurements, do not exist. Adsorption on the walls of a pVT apparatus causes such large errors that it has been a difficult task to determine the equation of state of pure steam, particularly at low densities. Flow calorimetric measurements, which are free from adsorption errors, offer an alternative route to thermodynamic information. Flow calorimetric measurements of the isothermal enthalpy-pressure coefficient pressure yield the quantity 4>c = B - TdB/dT where B is the second virial coefficient. From values of obtain values of B without recourse to pVT measurements. 

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