Sorption selectivity

Several selective interactions by MIP membrane systems have been reported. For example, an L-phenylalanine imprinted membrane prepared by in-situ crosslinking polymerization showed different fluxes for various amino acids [44]. Yoshikawa et al. [51] have prepared molecular imprinted membranes from a membrane material which bears a tetrapeptide residue (DIDE resin (7)), using the dry phase inversion procedure. It was found that a membrane which contains an oligopeptide residue from an L-amino acid and is imprinted with an L-amino acid derivative, recognizes the L-isomer in preference to the corresponding D-isomer, and vice versa. Exceptional difference in sorption selectivity between theophylline and caffeine was observed for poly(acrylonitrile-co-acrylic acid) blend membranes prepared by the wet phase inversion technique [53]. 

Sorption Selectivity of Organic Biologically Active Ions by Crosslinked Polyelectrolytes... 

The selectivity of ion exchange Ks can easily be determined experimentally for the simplest systems of exchange between monovalent ions. The value of Ks may be used for analysis of thermodynamic functions AG°, AH0 and AS0, of sorption selectivity... 

The sorption selectivity for more complex ions (e.g., ions of antibiotics) in competition with small ions increases to a still greater extent [59]. Particularly high constants for selective bonding (up to some hundreds and thousand) have... 

Since the mechanism of interaction between proteins polyfunctional with respect to ionogenic groups and CP is complex, an approximate method of calculation of sorption selectivity constants according to the inverse form of Langmuir isoterm should be used. Hence, the approximate values of AG, AH and AS obtained from Eq. (3.5) should be applied (Table 7). 

Other reservoir properties being similar, high-rank coals are more favorable for C02 storage because of their methane displacement efficiency (related to lower sorption selectivity for C02 compared to methane and higher absolute sorption of methane with increasing rank see Figs 1 and 3). Higher ranks of coal are also more... 

In comparison with adsorptive/absorptive techniques for aroma recovery from bioconversions, the disadvantage of pervaporation is the fact that both sorption and diffusion determine the overall selectivity. While the sorption selectivity is very high (equal to that of adsorptive/absorption), the diffusion selectivity favours water owing to the simple fact that water is a smaller molecule than aroma compounds and thus sterically less hindered during diffusion (Table 19.1). The overall (perm)selectivity P=SD) is therefore lower than in strictly sorption controlled processes, although it is still favourable compared with that for evaporation. This shortcoming compares, however, with operational advantages of pervaporation as outlined before. 

Compound Sorption coefficient S (mg-mg ) Diffusion coefficient D (m -s ) Sorption selectivity Diffusion selectivity Overall permselectivity... 

Consideration of the framework models strongly suggests that not only are the pore systems different but it is likely that the cation positions will be different. A possible consequence would be an alteration of ion exchange or sorption selectivities. 

Polyamide-polyether block copolymers (Pebax , Elf Atochem, Inc., Philadelphia, PA) have been used successfully with polar organics such as phenol and aniline [32-34], The separation factors obtained with these organics are greater than 100, far higher than the separation factors obtained with silicone rubber. The improved selectivity reflects the greater sorption selectivity obtained with the polar organic in the relatively polar polyamide-polyether membrane. On the other hand, toluene separation factors obtained with polyamide-polyether membranes are below those measured with silicone rubber. 

Chandrakumar, K.R.S., and Pal, S., DFT and local reactivity descriptor studies on the nitrogen sorption selectivity from air by sodium and calcium exchanged zeolite-A, Colloids Surf. A - Physicochemical Eng. Aspects, 205, 127-138, 2002a. 

In the following section, an example is discussed to illustrate how the most important stationary phase properties - namely, sorption selectivity, sorption capacity, and catalytic activity - affect the SMBR performance. 

The sorption selectivity has little influence on the separation when molecular sieving is considered. An Arrhenius type of equation is still valid for the activated transport, but attention should be drawn to the pre-exponential term, Dq (see Equation 4.7). From transition state theory this factor may be expressed as shown in Equation 4.15 [32] ... 

Sorption selectivity, as, can be defined as the ratio of the sorption coefficient for solutes A and B in a binary mixture ... 

Amongst these the choice of the polymer is the most important since it decides the sorption selectivity for the solute of interest. The methods adopted to prepare PV membranes can be broadly classified into three types ... 

Removal of VOCs from water Silicalite-fllled polyfsiloxane imide) membranes The sorption selectivity of the PS I membranes for chloroform/water solutions was investigated. The silicalite-filled membrane with 120 p.m thickness exhibit a high total permeation flux of 280 gm /h with separation factor of 52.2 for 1.2 wt% of the chloroform/water mixture [109]... 

Samdani AR, Mandal S, and Pangarkar VG. Role of and criterion for sorption selectivity in pervaporative removal of trace organics from aqueous solutions. Sep. Sci. Tech. 2003 38(5) 1069-1092. 

The permselectivity of hydrocarbon vapors, p, is dominated by the sorption component, and sorption of hydrocarbon vapors by rubbery polymers is determined by the condensability of their vapors. It can be seen from Table 9.3, that in organosilicon polymers the propane/methane sorption selectivity, is 10.5-16.2, whereas diffusion selectivity, is only 0.16-0.41. Refs. [39 3] report values of permselectivity of hydrocarbon mixtures with nitrogen for organosilicon membranes produced by GKSS (see Figure 9.10). It can be seen that separation selectivity increases with rising boiling temperature of the hydrocarbon, which points to domination of the sorption component of selectivity. 

In the study of adsorptive desulfurization of a model diesel fuel over a nickel-based sorbent in a fixed-bed adsorption system at ambient temperature and atmosphere pressure, Kim et al.123 found that the direct interaction between the sulfur atom in the sulfur compounds and the surface nickel plays an important role, indicating that the supported nickel adsorbent is good for the selective removal of the sulfur compounds, which have no alkyl steric hindrance, from hydrocarbon streams. However, the sorption affinity of the alkyl DBTs with alkyl groups at 4- and/or 6-positions is reduced due to the steric hindrance. The sorption selectivity of the nickel-based sorbent for various compounds at room temperature increases in the order of Nap 1-MNap < 4,6-DMDBT < DBT < quinoline < indole, as shown in Figure 5.14.123... 

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