Adsorption equilibrium, countercurrent

Activation energy, stability in trickle-bed reactors, 76 Activation overpotential, cross-flow monolith fuel cell reactor, 182 Activity balance, deactivation of non-adiabatic packed-bed reactors, 394 Adiabatic reactors stability, 337-58 trickle-bed, safe operation, 61-81 Adsorption equilibrium, countercurrent moving-bed catalytic reactor, 273 Adsorption isotherms, countercurrent moving-bed catalytic reactor, 278,279f... 

The countercurrent column is considered as a cascade of cells in series. The adsorption equilibrium is assumed to be reached in each cell or equilibrium stage or plate. The broadening effects, linked to the mass transfer kinetics and to the hydrodynamics, are lumped together and are quantified by the number of theoretical plates N, which can be derived from an analytical pulse injection. 

For adsorption from dilute liquid solutions in stagewise countercurrent operations, uiiere the Freundlich equation describes the adsorption equilibrium, derive aiudytical expressions in terms of R, iR, Iq, and Yff for the minimum adsorbent/solvent ratio when fresh adsorbent is used. 

Continuous Countercurrent Systems Most adsorption systems use fixed-bed adsorbers. However, if the fluid to be separated and that used for desorption can be countercurrently contacted by a moving bed of the adsorbent, there are significant efficiencies to be realized. Because the adsorbent leaves the adsorption section essentially in equilibrium with the feed composition, the inefficiency of the... 

A simultaneous countercurrent movement of solid and gaseous phases makes it possible to enhance the efficiency of an equilibrium limited reaction with only one product (Fig. 4(a)) [34]. A positive effect can be obtained for the reaction A B if the catalyst has a higher adsorption capacity for B than for A. In this case, the product B will be collected mainly in the upper part of the reactor, while some fraction of the reactant A will move down with the catalyst. Better performance is achieved when the reactants are fed at some side port of the column inert carrier gas comes to the bottom and the component B is stripped off the catalyst leaving the column (Fig 4(a)). The technique was verified experimentally for the hydrogenation of 1,3,5-trimethylbenzene to 1,3,5-trimethylcyclohexane over a supported platinum catalyst [34]. High purity product can be extracted after the catalytic reactor, and overequilibrium conversion can be obtained at certain operating conditions. 

Description Aromatics are produced from naphtha in the Aromizing section (1), and separated by conventional distillation. The xylene fraction is sent to the Eluxyl unit (2), which produces 99.9% paraxylene via simulated countercurrent adsorption. The PX-depleted raffinate is isomerized back to equilibrium in the isomerization section (3) with either EB dealkylation-type (XyMax) processes or EB isomerization-type (Oparis) catalysts. High-purity benzene and toluene are separated from non-aromatic compounds with extractive distillation (Morphylane ) processes (4). Toluene and C9 to Cn aromatics are converted to more valued benzene and mixed xylenes in the TransPlus process (5), leading to incremental paraxylene production. 

In this study, the binary (02/Ar, 9S S vol.%) mixture assumed as the composition of the products of equilibrium-controlled PSA process was used as a feed gas and CMS as adsorbent. Also, four different PSA processes which have two-stage countercurrent blowdown and one-stage cocurrent purge (or PE) steps with a different cycle sequence are compared to confirm and develop both the high purity and high recovery oxygen producing adsorption processes. 

All processes are modeled as series of countercurrent equilibrium cells. Parameters were determined experimentally (section 3). A liquid-phase reaction is accounted for by Da = (rate constant)x(cell volume)/(solid flow rate). Adsorption is described by the bi-Langmuir model. All equations were implemented in the simulation environment DIVA [3] details on the implementation of a largely analogous model can be found in [1,4]. The following set of performance parameters were used to evaluate each process ... 

The attention of many workers has been given to the equilibrium-limited case (proportionate-pattern) of multiple adsorption (D2, Wl, W3, W7, among others). In the constant-pattern case, Fujita s work has already been discussed (Section III, B, 2b). Also, using the theoretical-plate approximation to a packed column, plate-by-plate calculations can be carried out in the constant-pattern case exactly as for continuous (countercurrent) distillation this treatment is suggested from work on chromatographic and displacement problems by Mair (M2), Spedding (S6), and Glueckauf (G3). Moreover the linear-equilibrium result can be extended, in a nearly trivial fashion, to any number of components. 

Nitrogen dioxide, N02, produced by a thermal process for fixation of nitrogen, is to be removed from a dilute mixture with air by adsorption on silica gel in a continuous countercurrent adsorber. The mass flow rate of the gas entering the adsorber is 0.50 kg/s it contains 1.5% N02 by volume, and 85% of the N02 is to be removed. Operation is to be isothermal at 298 K and 1 atm. The entering gel will be free of N02. If twice the minimum gel rate is to be used, calculate the gel mass flow rate and the composition of the gel leaving the process. The equilibrium adsorption data at this temperature are (Treybal, 1980) ... 

The bulk separation of mixtures (in contrast to the removal of trace components) into high-purity products by adsorption requires a countercurrent flow of phases as in other equilibrium-based separations. The moving-bed adsorber, which offers the eountercurrent flow of the phases, was used for the separation of a gaseous mixture of hydrocarbons using activated carbon as adsorbent.lt is known as a hypersorber. Though it performed well, it... 

Acetone can be removed from acetone-air mixtures using simple countercurrent cascades, by adsorption onto charcoal (Foust et al. 1980). We wish to find the required number of equilibrium stages to reduce a gas stream carrying 0.222 kg acetone per kg air to a value 0.0202 kg acetone per kg air. Qean charcoal = 0) enters the system at 2.5 kg/sec, and the air rate is constant at 3.5 kg/sec. Equilibrium between the solid and gas can be taken to obey the Langmuir-type relationship... 

With a favorable equilibrium and a high adsorption rate, the adsorption may be carried out in a single stage adsorber with packing. If, in a single stage, the desired concentration is not reached, two or more adsorption stages are connected in series. This is realized by cross or countercurrent flow of the adsorbent and the fed carrier phase. 

We wish to estimate the height of a continuous countercurrent isothermal adsorber for drying air at 26.7 C, standard atmospheric pressure, from an initial humidity 0.003 to a final humidity 0.0001 kg H20/kg dry air. The entering gel will be dry. Note-. So-called "dry silica gel must contain a minimum of about 5% water if it is to retain its adsorptive capacity. Moisture measurements as ordinarily reported do not include this.) A gel rate 0.680 kg/m s (500 Ib/ft h) and an air rate 1.36 kg/m s (1000 Ib/ft h) will be used. For the moisture contents expected here, the equilibrium adsorption isotherm at 26.7 C, std atm (see Illustration 11.9), can be taken as substantially straight and described by the expression Y 0.018SJf. 

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