Effluent profiles

Figure 3. Effluent Profiles for brine saturated Wilmington sand...

Figure 6. Effluent profiles in coarse grained fraction of Wilmington sand...

For the case where perturbations from a cyclic steady are moderate in magnitude, it is convenient to employ a linearized process model when designing a regulatory system. In particular, if the effluent profiles are linearized locally about the upstream and downstream cut points, and if the yield is maximized by enforcing the restriction Puic = P Equations 1-5 lead to the following result ... 

Figure 4. Reactor effluent profiles at 204°C. Conditions Qhe — 23 L/min Qcyciohexane — S3 mL/min. Key. /, benzene , unknown compound O, cyclohexane and-----------------, simulation.

Adenosine 5 -phosphosulfate was separated from ATP and other adenine nucleotides by chromatography on a Synchropak AX-100 column (4.1 mm x 250 mm). The mobile phase contained 0.1 M sodium phosphate buffer (pH 7.3) and 0.8 M NaHC03. The effluent profile was obtained by monitoring at 254 nm. 

Figure 13 shows that the core permeability drops over many injected pore volumes and ultimately levels off. The effluent profile (dashed lines) shows that the oil droplets appear after some time, and their concentration rises slowly and levels off at the inlet value of 0.5%. The time at which the permeability reduction stops is about the same time at which the oil droplets approach their inlet concentration. 

A core-flood for adsorption determination consists of injecting a measured volume of surfactant solution containing a nonadsorbing tracer into a brine-saturated core and collecting effluent fractions at the core outlet. Chemical analysis of the effluent samples allows the calculation of an adsorption level based on material balance considerations and also results in a set of effluent profiles for the surfactant and the tracer. In addition to the material balance, adsorption is evaluated by matching experimental effluent concentrations from the core-floods with a convection—dispersion—adsorption numerical model. The model parameters then allow calculation of a complete adsorption isotherm. 

Examples of experimental and simulated effluent profiles and the adsorption isotherm based on the simulated surfactant profile are shown in Figure 10. For the data discussed in this chapter, adsorption was modeled using the surface excess formalism (8—10, 115), or in some cases, the Langmuir adsorption model (8, 9, 34, 82) as discussed in detail in these references. The model used to calculate the adsorption isotherm in Figure 10 assumes that surfactant adsorption takes place from the monomer... 

Effluent profiles obtained from a core-flood performed with a mixture of two surface-active components (C12 and C18) separated from a commercially available sulfobetaine are shown in Figure 24 (115). The points represent experimental data, and the lines were obtained by simulating the core-flood with a convection—dispersion—adsorption model that is based on the surface excess concept and takes into account monomer—micelle equilibrium (115). Because the mixture contains different homologues of the same surfactant, the ideal mixed micelle model... 

Figure 24. Effluent profiles of tracer and C12 and C18 components of a sulfobetaine from Berea sandstone. (Reproduced with permission from reference 134. Copyright 1991 Pergamon Press Ltd.)...

Figure 26 also shows the effluent profile of a nonionic surfactant (alkylphenylethoxy alcohol) that was injected into the core containing the preadsorbed anionic surfactant. Material balance calculations indicated that the nonionic surfactant adsorbs as much as it would in a clean core despite the presence of the anionic surfactant on the solid surfaces. The anionic surfactant that was adsorbed during the first two floods is recovered completely. 

Figure 26. Effluent profiles obtained during sequential core-floods with an anionic and a nonionic surfactant.

Experimental interest lies in the value of q that depends on the applied concentration, that is, where q =/(c), which thus describes the isotherm-of the adsorbate. Application of protein solution to the column produced an effluent profile of the type shown in Figure 5. The amount of protein adsorbed may be calculated by integrating the area between the void volume and the actual effluent profile (lateral diffusion, DM, does not modify the integrated area). A series of runs using different cG values thus establishes a dynamic isotherm. 

Aside from the relative position of the profile, the shape of the effluent profile contains information concerning the kinetics of the adsorption process. All concentrations of protein from zero to cQ are brought into contact with the column surface as the protein solution flows through the column, as a function of the position of the profile, and therefore as a function of time. Working with small molecules, previous researchers have shown that compounds exhibiting Langmuir isotherms produce sharp fronts, and diffuse tails, if pure solvent is used to desorb the column (21,22). However, Equation 7 shows that both diffusional and adsorption effects can alter the shape of the effluent profile. The former effect includes both normal molecular diffusion, and also diffusion due to flow properties in the column (eddy diffusion), which broadens (decreases the slope) the affluent profiles. To examine the adsorption processes, apart from the diffusional effects, the following technique can be applied. 

Alternatively, the saturated substrate may not be inert to new solution-borne protein molecules, but may exchange with such molecules (23). The result of such a process, which does indeed occur as will be shown later, does not appear to alter adsorption effluent profiles. 

Initial experiments had indicated that the monomer standard BSA powder used in our experiments contained 13% dimer. Previous studies have shown that the different molecular weight species of human serum albumin exhibit varied affinities for surfaces (24). We were interested in elucidating the effect of dimer species in our adsorption experiments. The molecular weight differences of the monomer and dimer allowed us to follow the relative concentrations of each species in the effluent profile. Figure 8 illustrates the data obtained from a run in which 1.0 mg/mL BSA was applied to a... 

A design feature of these systems is separate effluent ports for each layer This allows us to demonstrate one of the key features of a non-unit mobility flood namely the change in the local flow rates in each of the layers, and the altered effluent profiles from the layers ... 

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