Retention behavior of dilute

This study investigates the retention behavior of dilute polymer solutions in oil sands. Results indicate that the presence of a large amount of fines and/or a variety of minerals in the sand may result in high adsorption and retention causing excessive loss of polymer and high injection pressures. Injection of a surfactant with the polymer leads to increased oil recoveries because the dilute polymer may selectively adsorb on mineral grain surfaces leaving the surfactant to act at liquid/iiquid contacts. 

KIKANI AND SOMERTON Retention Behavior of Dilute Polymers... 

The principles of IGC, as a gas-phase technique used to characterize the surface and bulk properties of solid materials, are very simple as the process is the reverse of conventional gas chromatography. Typically, an empty cylindrical column is uniformly packed with the solid material of interest, normally a powder, fiber, or film. A pulse or constant concentration of gas is then injected down the column at a fixed carrier gas flow rate, and the retention behavior of the pulse or concentration front is measured with a detector (Figure 10.1). The retention of a solvent or probe molecule on the material is recorded and the measurement is made effectively at an inflnite dilution of the probe. A range of thermodynamic parameters can then be calculated. A major advantage of IGC is that it is readily applicable to mixtures of two or more polymers. 

Additional modes of HPTC include normal phase, where the stationary phase is relatively polar and the mobile phase is relatively nonpolar. Silica, diol, cyano, or amino bonded phases are typically used as the stationary phase and hexane (weak solvent) in combination with ethyl acetate, propanol, or butanol (strong solvent) as the mobile phase. The retention and separation of solutes are achieved through adsorp-tion/desorption. Normal phase systems usually show better selectivity for positional isomers and can provide orthogonal selectivity compared with classical RPLC. Hydrophilic interaction chromatography (HILIC), first reported by Alpert in 1990, is potentially another viable approach for developing separations that are orthogonal to RPLC. In the HILIC mode, an aqueous-organic mobile phase is used with a polar stationary phase to provide normal phase retention behavior. Typical stationary phases include silica, diol, or amino phases. Diluted acid or a buffer usually is needed in the mobile phase to control the pH and ensure the reproducibility of retention times. The use of HILIC is currently limited to the separation of very polar small molecules. Examples of applications... 

An interesting behavior of the retention/inversion ratio in dl- and meso-(CH3CHCl)2 was observed upon dilution with several compounds (Fig. 1) (91). This effect was assigned to the relative concentrations of... 

The hypothesis of linear behavior of the equilibrium isotherm in analytical chromatography has three important consequences. First, the different components contained in a sample of a mixture behave independently of each other. They do not compete for interaction with the stationary phase because the sample size is small and the solutions are dilute. Therefore, the elution profiles and the retention times of the various components of a mixture are independent of the presence of other solutes and of their relative concentrations. Each band profile is the same as if the corresponding solute were alone, pure. As a consequence and in contrast with nonlinear chromatography, there is only one problem to solve in linear chromatography, the determination of the peak profile of a single component. 

For infinite dilution operation the carrier gas flows directly to the column which is inserted into a thermostated oil bath (to get a more precise temperature control than in a conventional GLC oven). The output of the column is measured with a flame ionization detector or alternately with a thermal conductivity detector. Helium is used today as carrier gas (nitrogen in earlier work). From the difference between the retention time of the injected solvent sample and the retention time of a non-interacting gas (marker gas), the thermodynamic equilibrium behavior can be obtained (equations see below). Most experiments were made up to now with packed columns, but capillary columns were used, too. The experimental conditions must be chosen so that real thermodynamic data can be obtained, i.e., equilibrium bulk absorption conditions. Errors caused by unsuitable gas flow rates, unsuitable polymer loading percentages on the solid support material and support surface effects as well as any interactions between the injected sample and the solid support in packed columns, unsuitable sample size of the injected probes, carrier gas effects, and imprecise knowledge of the real amount of polymer in the column, can be sources of problems, whether data are nominally measured under real thermodynamic equilibrium conditions or not, and have to be eliminated. The sizeable pressure drop through the column must be measured and accounted for. 

Cesium and iodine atoms which are released from fuel specimens into a high-temperature steam-hydrogen environment are thermodynamically unstable and will be rapidly converted into species that are stable under these conditions. Since the chemical form of iodine in particular will considerably influence its transport and retention behavior within the reactor pressure vessel and the primary system, it is important to know the kinetics of these conversion reactions. A kinetics assessment of the most essential reactions (Cronenberg and Osetek, 1988) has shown that for extremely low concentrations of iodine and cesium in steam (e. g. mole ratio I H2O < 10" ), the predominant form of iodine is HI and that of cesium is CsOH. This is due to the fact that because the concentrations of iodine and cesium are so dilute, the elements are much more likely to collide and react with H2O and H2 than with each other. Low concentrations of iodine and cesium increase the time for thermochemical equilibrium to be established for their reaction products. For mixtures which are so dilute in fission products, the reaction times may approach tens of seconds or longer, so that for high effluent rates the environmental conditions may change (e. g. by transport into the next control volume showing other conditions) before thermochemical equilibrium has been achieved. Under such conditions, certain limitations caused by reaction kinetics may exist. 

The interaction between particle and applied field determines the concentration profile distribution inside the channel. Theory assumes that the particles do not interact with each other, that is, the particle concentration is so low that they can be considered in a condition of infinite dilution and thus with an ideal behavior. Under these assumptions, the field-particle interaction has been classified into three major elution modes Brownian (or normal), steric, and hyperlayer (or focusing). These elution modes, which are limiting cases, correspond to different mechanisms of separation and, theoretically, they can explain FFF retention on the basis of particle properties such as the... 

The complexation properties of PEI were investigated in the aqueous phase for Co, Ni, Zn, Cd, and Cu ions using membrane filtration [35, 39, 40]. According to the elution behavior, which was measured for each metal at different pH values, PEI is an effective polymeric complexing agent suitable for the retention and separation of metals in aqueous diluted solutions. 

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