Parallel adsorption

Modern SMR plants (Figure 2.5b) incorporate a PSA unit for purifying hydrogen from C02, CO, and CH4 impurities (moisture is preliminarily removed from the process gas). The PSA unit consists of multiple (parallel) adsorption beds, most commonly filled with molecular sieves of suitable pore size it operates at the pressure of about 20 atm. The PSA off-gas is composed of (mol%) C02—55, H2—27, CH4—14, CO—3, N2—0.4, and some water vapor [11] and is burned as a fuel in the primary reformer furnace. Generally, SMR plants with PSA need only a HT-WGS stage, which may somewhat simplify the process. 

It follows that in the adsorption state, the O—O bond length varies from 0.121 to 0.135 and 0.137 nm for vertical and parallel adsorption forms, respectively. This bond length is close to the 0—0 bond length in peroxides (0.149 nm). It means that after adsorbed by the FeS2 surface, the oxygen is more like peroxides rather than O2. It is clearly in line with the works reported by Ahlberg and Broo (1996a,b,c). 

Figure 8.3 Fixture for comparing filter materials using parallel adsorption filters.

APOPO uses a polyester fiber wad for their rats to smell so we ran a parallel adsorption filter configuration (Fig. 8.3) and let the rats smell both the MEDDS and the APOPO filter. Figure 8.3 is a picture of the parallel filter system. 

Since the same mechanisms are involved, aggregation times are generally similar to adsorption times. As a consequence, ffoc growth rates typically parallel adsorption rates or, for continuous polymer addition, the rate of polymer addition. Furthermore, ffoc growth continues only so long as fresh polymer is... 

The interaction of N2 with transition metals is quite complex. The dissociation is generally very exothermic, with many molecular adsorption wells, both oriented normal and parallel to the surface and at different sites on the surface existing prior to dissociation. Most of these, however, are only metastable. Both vertically adsorbed (y+) and parallel adsorption states (y) have been observed in vibrational spectroscopy for N2 adsorbed on W(100), and the parallel states are the ones known to ultimately dissociate [335]. The dissociation of N2 on W(100) has been well studied by molecular beam techniques [336-339] and these studies exemplify the complexity of the interaction. S(Et. 0n Ts) for this system [339] in Figure 3.36 (a) is interpreted as evidence for two distinct dissociation mechanisms a precursor-mediated one at low E and Ts and a direct activated process at higher These results are similar to those of Figure 3.35 for 02/ Pt(lll), except that there is no Ts... 

For the infrared spectra there is, of course, no impact mechanism available for exciting additional features from not completely symmetrical modes, and none of the in-plane ca. 1395 (pi3), 1275 (v9), or 1147 cm 1 (vU) or vv) modes would be allowed if the MSSR applied strictly to parallel adsorption on (111) or (100) facets. They would, however, all become allowed on a Cs site, such as would arise from adsorption on twofold bridges. The infrared spectra of alternative monosubstituted or ortho-disubstituted benzenes (the most likely dissociatively adsorbed species) would give rise to two additional strong bands between 1400 and 1620 cm-1, and so the observed spectrum is again seen to be consistent with nondissociative adsorption. 

This is an adsorption mechanism (we call it a "parallel adsorption mechanism, since the adsorption of reactants follows two independent routes in what follows we will consider one more adsorption mechanism that is "consecutive ). 

A simple model approach to the heterogeneity of surface reactivity in soils can be developed by assuming that Eq. 4.3 [without the dissociable species Q(aq)] applies to each member of a set of parallel adsorption-desorption react ions involving the same reactant aqueous species, but with differing ail sorbent and adsorbate species. A rate law for each of the parallel reactions can be postulated in the following form (cf. Eq. 1.34) ... 

Fig. 33. Perspective views from the top-layer side (Panel a) and from the bottom-layer side (Panel b) of the representative, nearly-stoichiometric surface cluster V360 98- The geometric structure of the V205 (010)- surface cluster (see Fig. 26) involves the SINDOl optimized intra-layer bond lengths [28] and the crystallographic values of the bond angles and the inter-layer V-O bond length. The surface layer views of alternative perpendicular adsorptions of toluene on the bridging oxygen 0(2) from the top layer side (c) and from the bottom layer side (d), and two alternative parallel adsorptions (Panels e, f) on the bottom layer. In Panel d the same adsorbate-substrate separation as in Figs. 7a, 9 and 25e has been adopted, while in the remaining panels this separation has been increased by 1 A relative to those shown in Fig. 25...

Many different forms of loop have been reported in the literature, but the major types are represented in the IUPAC classification (1985) given in Figure 7.3. Types HI, H2 and H3 were included in the first classification proposed by de Boer (1958). Type HI (originally known as Type A) is a fairly narrow loop with very steep and nearly parallel adsorption and desorption branches. In contrast, the Type H2 loop (formerly Type E) is broad with a long and almost flat plateau and a steep desorption branch. Types H3 (formerly Type B) and H4 do not terminate in a plateau at high p/p° and the limiting desorption boundary curve is therefore more difficult to establish. 

Temperature-swing adsorption processes have to identical, parallel adsorption beds. One of the beds is in the adsorption cycle while the other bed is being regenerated by heating with a regenerating gas. The two beds generally operate 180 degrees out of phase (Knaebel, 1999). 

For small inert molecules it can be difficult to assess directly the monolayer, as the heat of adsorption is so small that it approaches the heat of condensation. This leads to parallel adsorption in the first and subsequent layers and therefore does not allow definition of the monolayer capacity. A way to circumvent this difficulty is to determine the adsorption in the presence of multilayers and to relate the sorbed amount to the monolayer capacity. This approach was first... 

The point is that the lamella [429] has a complex multilayer structure (see Figure 7.2). It consists of two boundaries of foam cells, two direct plate micellae [413], and a liquid film, which is a part of the continuous phase of the foam. All in all, the lamella has six parallel adsorption layers. Hence, its modulus of elasticity must be many times larger than that of a simple adsorption layer. 

SCHEME 2.5 Wroblowa s oxygen electroreduction mechanism with electrochemical rate constants k3 forthe direct reduction to water, k2 and k 2 for the parallel electrochemical reduction and oxidation of adsorbed hydrogen peroxide, k3 for the electrochemical decomposition of hydrogen peroxide to water, k4 for the chemical catalytic decomposition of hydrogen peroxide to oxygen, and ks and fc 5 for the parallel adsorption/desorption of the adsorbed hydrogen peroxide. The species with the super index and ° are located at the interface and in the bulk of the solution, respectively. The sub index ads refers to the adsorbed state, and the term dif symbolizes the diffusion to the bulk of the solution and vice versa. 

The mechanism of aromatic hydrogenation is still the subject of extensive research. Most of the work presented describes hydrogenation as proceeding through parallel adsorption of the aromatic ring on the metallic surface, by interaction of the r-electrons of the aromatic ring with empty <7-orbitals of the metal... 

From the maximum surface concentration of neq(ma )=0.4 x 10 mol g found for 2,5-DHF and the maximum number of Cd surface sites as calculated for cubic CdS [174], 1.54x10 mol g, it is estimated that 2,5-DHF is adsorbed at about every fourth Cd center, in agreement with a parallel adsorption however, the presence of perpendicular adsorption cannot be excluded. Contrary to this, when 2,5-DHF is adsorbed onto ZnS from aqueous suspension, it occupies each Zn site and a matches the calculated molecular area [107]. The difference can be rationalized by comparing the polarities of the two sulfides with those of 2,5-DHF and the solvents employed. Because the surface polarity parameter Ej of CdS (0.68 0.06) is comparable with the value of methanol (Ej = 0.762) [175], but is much higher than that of 2,5-DHF (E = 0.366)... 

In continuous processes at least two adsorbers are used in parallel (adsorption, desorption). Because of the complicated operation, fully automatic apparatus is preferred (Figure 2.3.6-1). 

Figure 21.25) the isotherm shows the characteristic type IV shape. The almost parallel adsorption and desorption branches (subtype Hi) indicate a narrow pore size distribution. 

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