Selectivity equilibrium

Some factors which may retard the wetting and preclude attainment of equilibrium are a combination of low capillary pressures and high fluid viscosities, metastable equilibria, selective adsorption, and coacervation. 

Phases and Phase Equilibria Selected phase diagrams are shown in Figs. 3.1-193-... 

Phases and Phase Equilibria. Selected phase diagrams are shown in Figs. 3.1-252-3.1-257 [1.219]. Pd forms continuous solid solutions with all other noble metals and with Co, Cu, Fe, and Ni. Miscibility gaps exist in alloys with C, Co, Ir, Pt, Rh, and ternary Pd—Ag—Cu alloys (Fig. 3.1-257) [1.220]. All platinum-group metals (PGM) lower the y-a transition temperature in Fe-alloys considerably (Fig. 3.1-343). Thermodynamic data are given in Tables 3.1-190-3.1-194. Numerous intermediate phases exist also in alloys with rare earth metals [1.216,217,217,222]. The solubility of... 

Phases and Phase Equilibria. Selected phase diagrams are shown in Figs. 3.1-277-3.1-281 [1.219]. Thermodynamic data are given in Tables 3.1-190-3.1-193 and... 

Phases and Phase Equilibria. Selected phase diagrams of Rh are shown in Fig. 3.1-301a-c. Rhodium forms continuous solid solutions with Fe, Co, Ni, Ir, Pd, and Pt. Miscibility gaps exist in alloys with Fe, Co, Ni, Cu, Ag, Au, Pd, Pt, Ru, and Os. Thermo-d3mamic data are given in Table 3.1-236 (see also... 

Phases and Phase Equilibria. Selected phase diagrams are shown in Figs. 3.1-339-3.1-342 [1.216]. Continuous series of solid solution are formed with Re and Ru. Miscibility gaps exist with Ir, Pd and Pt. The solid solubility in the Os—W system are 48.5 at.% for W and 5 at.% for Os. Osmium alloyed to Fe lowers the y-a transition temperature considerably (Fig. 3.1-343 [1.297]). Thermodynamic data are given in Table 3.1-267 [1.216] and molar heat capacities in Table 3.1-190. Table 3.1-268 gives structures and lattice parameters of intermediate compounds with Ir, Ru, Pt, and W [1.216]. 

Both cases can be solved by any of the methods described for calculating isothermic chemical equilibria, selecting the ratio of input constituents by trial and error until the condition of zero overall enthalpy according to relation (5.147) is satisfied. This procedure, however, is laborious, although the use of the above-described procedures is a certain advantage. 

This term is analogous to relative volatility or its reciprocal (or to an equilibrium selectivity). Similarly, the assumption of a constant sepa-... 

Such esterifications and acetal formations are achieved through enzyme catalyses. However, such reactions are relatively rare in aqueous conditions chemically. This is because the reversed reactions, hydrolysis, are much more favorable entropically. Kobayashi and co-workers found that the same surfactant (DBSA) that can catalyze the ether formation in water (5.2 above) can also catalyze the esterification and acetal formations reactions in water.52 Thus, various alkanecarboxylic acids can be converted to the esters with alcohols under the DBSA-catalyzed conditions in water (Eq. 5.6). Carboxylic acid with a longer alkyl chain afforded the corresponding ester better than one with a shorter chain at equilibrium. Selective esterification between two carboxylic acids with different alkyl chain lengths is therefore possible. 

This term is analogous to relative volatility or its reciprocal (or to an equilibrium selectivity). Similarly, the assumption of a constant separation factor is a useful assumption in many sorptive operations. [It is constant for the Langmuir isotherm, as described below, and for mass-action equilibrium with za = zh in Eq. (16-24).] This gives the constant separation factor isotherm... 

When developing a liquid phase adsorptive separation process, a laboratory pulse test is typically used as a tool to search for a suitable adsorbent and desorbent combination for a particular separation. The properties of the suitable adsorbent, such as type of zeolite, exchange cation and adsorbent water content, are a critical part of the study. The desorbent, temperature and liquid flow circulation are also critical parameters that can be obtained from the pulse test. The pulse test is not only a critical tool for developing the equilibrium-selective adsorption process it is also an essential tool for other separation process developments such as rate-selective adsorption, shape-selective adsorption, ion exchange and reactive adsorption. 

The foundation of equilibrium-selective adsorption is based on differences in the equilibrium selectivity of the various adsorbates with the adsorbent While all the adsorbates have access to the adsorbent sites, the specific adsorbate is selectively adsorbed based on differences in the adsorbate-adsorbent interaction. This in turn results in higher adsorbent selectivity for one component than the others. One important parameter that affects the equilibrium-selective adsorption mechanism is the interaction between the acidic sites of the zeolite and basic sites of the adsorbate. Specific physical properties of zeolites, such as framework structure, choice of exchanged metal cations, Si02/Al203 ratio and water content can be... 

One of the parameters in the broad class of equilibrium-selective adsorption mechanisms is the interaction between the acidic and basic sites of the adsorbent and the adsorbate. ZeoUtes can be ion-exchanged with a variety of metal cations... 

The concentrations and distribution of electrolytes are not fixed, because cell membranes are permeant to ions and to water. Movement of ions and water in and out of cells is determined by the balance of thermodynamic forces, which are normally close to equilibrium. Selective changes of ion concentrations cause movement of water in or out of cells to compensate for these alterations. The kidneys are a major site where changes in salt or water are sensed. The loss of fluids due to illness or disease may alter intracellular and extracellular electrolyte concentrations, with attendant changes in fluid movement in or out of cells. Changes of extracellular or intracellular ion concentrations, particularly for potassium, sodium, and calcium, can have profound effects on neuronal excitability and contractility of the heart and other muscles. 

The high equilibrium selectivity for normal paraffins relative to aromatics observed for H-ZSM-5 and H-ZSM-11, so contrary to that reported for the lower silica/alumina ratio zeolites, may in part be due to the much higher silica/alumina ratio of these relatively hydrophobic zeolites, resulting in reduced polarity and ability to interact with polarizable molecules. However, other zeolites of comparable silica/alumina ratio, such as dealuminized H-morde-nite, exhibited no such enhanced preference for n-paraffins ] ) (see Table II). Clearly, silica/alumina ratio alone is insufficient to account for these differences. The structure of these zeolites, therefore, must play some role in the observed selectivity. 

The use of various zeolites for the separation of xylene isomers has received a considerable amount of attention. Numerous patents have been issued for such separations however, equilibrium selectivity factors tend to be relatively low (9). We found virtually no p-xylene selectivity for a dealuminized H-mordenite under equilibrium conditions. H-ZSM-5, however, did exhibit a distinct preference for p-xylene sorption even at equilibrium (Table V). 

For paraxylene separation, both kinds of selectivity can be observed. In the MFI structure, the aperture of the pores is sufficiently close to the dimensions of the molecules to make shape selectivity appear. However, the kinetic diameters of paraxylene and of ethylbenzene are identical, so that the selectivity is not effective for these two components. Moreover, the capacity of MFI zeolites is weak compared to other structures. More open structures which provide the opportunity to use equilibrium selectivity are preferred. The problem is that the selectivity is mainly due to interactions between the zeolite and the aromatic ring which are identical for all the xylenes. It will be shown in the following sections that this problem can be solved by using chosen FAU zeolites. 

In this review, the problems of complex formation in different systems of interacting macromolecules namely in polymer-polymer, polymer-alternating or statistical copolymer systems are discussed. The influence of solvent nature, the critical phenomena, equilibrium, selectivity and co-operativity in reactions are considered. The perspectives of development of this field of polymer science and the potential practical applications of interpolymer complexes are pointed out. 

Table 3 Equilibrium Selectivity Coefficients, aJJ, Measured (or ISMA-1 in Seawater Sorption Studies...

Kinetic Leakage If the anion resin is fouled in some way, for example with organics, the kinetics of exchange are impeded and detailed studies have demonstrated that the normal equilibrium selectivity of sulfate over chloride is violated leading to the preferential slip of the kinetically slower diffusing sulfate ion. 

Excellent monoalkylation selectivity has also been observed over many years of service in the JLM operation as shown in Fig. 10. Under the normal operating conditions of the unit, an equilibrium cumene selectivity of about 91 mol% is predicted. Thus, results clearly show that the beta zeolite catalyst is active enough to achieve near-equilibrium selectivity. This is an important feature of the catalyst as the amount of dialkylate that must be processed in the transalkylator and the subsequent cost of processing this material are minimized. 

Selectivity is a means by which mixture equilibria can be grasped. Several different definitions exist, but all basically are ratios of what is adsorbed to what remains in the fluid phase at equilibrium. Selectivity, therefore, provides a simple description of the nature of multicomponent equilibria, although the values are seldom employed in mathematical models. Some common definitions are... 

It is primarily the span of absolnte pressnres, conpled with differences in mole fractions (caused by pressure shifts and/or by admitting different streams to the column), that drive PSA separations. Equilibrium selectivity can canse composition shifts to occur simply by changing the pressure. To illustrate this point, consider an adsorbent bed of zeolite 5A filled with air (assnmed to be only oxygen and nitrogen) at 3 atm. The mole fractions in the gas phase of oxygen and nitrogen are... 

Most cycles exploit equilibrium selectivity differences between species. Some exploit differences in intraparticle diffusion rates. These are becoming more prevalent with advances in adsorbent modification techniques. Efficient PSA cycles result from a good adsorbent, full exploitation of the input power, and careful control. The input power is exploited fully when a gas product or byproduct is used to accomplish tasks as reversibly as possible. The shift in adsorbent loading may be 1 to 10 wt% for concentrated feeds. Generally, the energy requirements of regeneration most strongly affect overall cost. 

B-ZSM-5 samples (A and C) were observed to be inactive for the alkylation, even at 600°C, with a very low methanol conversion yielding light olefins. The SAPO-11 sample (H) gave very low alkylation conversion with thermodynamic para-xylene equilibrium selectivity. The latter result obviously arises from the pore dimensions (6 x 6.2 A), larger than for MFI samples. 

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