Desorption displacement fluid

However, ia some cases, the answer is not clear. A variety of factors need to be taken iato consideration before a clear choice emerges. Eor example, UOP s Molex and IsoSiv processes are used to separate normal paraffins from non-normals and aromatics ia feedstocks containing C —C2Q hydrocarbons, and both processes use molecular sieve adsorbents. However, Molex operates ia simulated moving-bed mode ia Hquid phase, and IsoSiv operates ia gas phase, with temperature swiag desorption by a displacement fluid. The foUowiag comparison of UOP s Molex and IsoSiv processes iadicates some of the primary factors that are often used ia decision making ... 

Adsorption and Desorption Adsorbents may be used to recover solutes from supercritical fluid extracts for example, activated carbon and polymeric sorbents may be used to recover caffeine from CO9. This approach may be used to improve the selectivity of a supercritical fluid extraction process. SCF extraction may be used to regenerate adsorbents such as activated carbon and to remove contaminants from soil. In many cases the chemisorption is sufficiently strong that regeneration with CO9 is limited, even if the pure solute is quite soluble in CO9. In some cases a cosolvent can be added to the SCF to displace the sorbate from the sorbent. Another approach is to use water at elevated or even supercritical temperatures to facilitate desorption. Many of the principles for desorption are also relevant to extraction of substances from other substrates such as natural products and polymers. 

The first case considered is solute desorption during unconfined compression. We consider a two dimensional plane strain problem, see Fig. 1. A sinusoidal strain between 0 and 15 % is applied at 0.001 Hz, 0.01 Hz, 0.1 Hz and 1 Hz. To account for microscopic solute spreading due to fluid flow a dispersion parameter is introduced. Against the background of the release of newly synthesized matrix molecules the diffusion parameter is set to the value for chondroitin sulfate in dilute solution Dcs = 4 x 10 7 cm2 s-1 [4] The dispersion parameter Dd is varied in the range from 0 mm to 1 x 10 1 mm. The fluid volume fraction is set to v = 0.9, the bulk modulus k = 8.1 kPa, the shear modulus G = 8.9 kPa and the permeability K = lx 10-13m4 N-1 s-1 [14], The initial concentration is normalized to 1 and the evolution of the concentration is followed for a total time period of 4000 s. for the displacement and linear discontinuous. For displacement and fluid velocity a 9 noded quadrilateral is used, the pressure is taken linear discontinuous. 

In contrast with two-phase bubble-containing fluids, aerosols, and emulsions, foam has a least three phases. Along with gas and the free continuous liquid phase, foam contains the so-called skeleton phase, which includes adsorption layers of surfactants and the liquid between these layers inside the capsule envelope. The volume fraction of the skeleton phase is extremely small even compared with the volume fraction of the free liquid. Nevertheless, this phase determines the foam individuality and its structure and rheological properties. It is the frame of reference with respect to which the diffusion motion of gas and the hydrodynamic motion of the free liquid can occur under the action of external forces and internal inhomogeneities. At the same time, the elements of the skeleton phase themselves can undergo strain and relative displacements as well as mass exchange with the other phases (solvent evaporation and condensation and surfactant adsorption and desorption). 

This cycle. Ihoogh soma what similar to the inert-purge cycle, differs from it in dial a gas or liquid that adsorbs a bom as strongly as the adsorbate is used to remove the ndsorbate (sse Fig. 12.4-3). Desorption is thus facilitated both by adsorbate partial-pressure or concentration reduction in (he fluid around the particles and by competitive adsorption of the displacement medium. As with the inert-purge cycle, iha maximum della loading is X,. 

Because the measurement of a contact angle must involve some movement of the wetting line, it is possible, or even probable, that the act of spreading of the hquid will displace certain surface equilibria that will not be reestablished over the time frame of the experiment. For example, the displacement of a second fluid may result in the estabhshment of a nonequilibrium situation in terms of the adsorption of the various components at the solid-liquid, solid-fluid 2, and liquid-fluid 2 interfaces. Time will be required for adsorption equilibrium to be attained, and it may not be attained during the time of the contact angle measurement if the transport and adsorption-desorption phenomena involved are slow. The kinetic effect may be especially significant for solutions containing surfactants, polymers, or other dissolved adsorbates. 

Lopez-Avila et al. [86] have considered validation of analytical supercritical fluid extraction methods. When developing an SEE method, various critical factors need to be considered (i) solubility of the analyte in the supercritical fluid (SF) (ii) diffusion of the analyte from the solid matrix into the bulk fluid or displacement of the analyte by the SF that diffused into the matrix and (Hi) the matrix itself, which can be very adsorptive. Poor SEE recoveries may be attributed to matrix effects (e.g., not all of the analyte may be extractable), to inefficient retention of the analyte in the collection solvent or on the sorbent trap, or to inefficient desorption from the sorbent trap. Once an SEE procedure has been developed and tested with real matrices, the next step... 

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