Absorption equilibria

Fig. 21. Single absorption equilibrium-stage diagram where the equiUbrium curve is for 8% SO2, 12.9% the diagonal lines represent the adiabatic temperature rise of the process gas within each converter pass the horizontal lines represent gas cooling between passes, where no appreciable conversion...

Figure 8-62. Absorption equilibrium curve. Used by permission, Hutchison, A. J. L., Petroleum Refiner, V. 29 (1950), p. 100, Gulf Pub. Co., all rights reserved.

Sing-around method, 11 674 Single absorption equilibrium-stage diagram, 23 777... 

Mass transfer controlled by diffusion in the gas phase (ammonia in water) has been studied by Anderson et al. (A5) for horizontal annular flow. In spite of the obvious analogy of this case with countercurrent wetted-wall towers, gas velocities in the cocurrent case exceed these used in any reported wetted-wall-tower investigations. In cocurrent annular flow, smooth liquid films free of ripples are not attainable, and entrainment and deposition of liquid droplets presents an additional transfer mechanism. By measuring solute concentrations of liquid in the film and in entrained drops, as well as flow rates, and by assuming absorption equilibrium between droplets and gas, Anderson et al. were able to separate the two contributing mechanisms of transfer. The agreement of their entrainment values (based on the assumption of transfer equilibrium in the droplets) with those of Wicks and Dukler (W2) was taken as supporting evidence for this supposition. 

We can write the absorption equilibrium coefficients for A and B in terms of their partial pressures (PA and PB) and the concentration of open sites (Cs) ... 

As for distillation, the thermodynamic data form the basis for the design for absorption and the absorption equilibrium data can be found either tabulated, from correlations or from commercial software. Again, good data is vital to ensure good design. 

The height of an absorption column depends on the feed conditions, the product purity specifications, the solvent used and the extent of separation through the absorption equilibrium relationship, but also on the rate of separation. If the rate of mass transfer of the gaseous component from the gas phase into the liquid phase is slow, then the column needs to be longer to ensure that the required amount is removed. The rate of mass transfer depends on the mass-transfer coefficient, normally denoted kG or k. The value of the mass-transfer coefficient depends on the components in the gas feed and on the solvent used and is often determined experimentally. The type of packing used in the column will also have an impact on the column height as for distillation. 

Fig. 6. Time dependence of film thicknesses of polyelectrolytes adsorbed on dendrimer SAMs. Concentrations of polyelectrolytes are 0.04wt.% for NaPGA and NaHA and 0.02wt.% for DNA. Numerical values in blankets after pH values denote the film thicknesses at absorption equilibrium. Reprinted from Ref. [111].

When dissolved S(IV)aq Is oxidized in the droplets, the absorption equilibrium between the S(IV)aq-concentration and the (S02)g concentra-tion is disturbed. It is continuously re-established following Henry s law and the well-known dissolution equilibria of S(IV) in the liquid phase. Thus a (S02)g concentration-gradient between the inlet and the outlet of the reactor is formed, which is related to the travel time of the mixture. 

The vertical portions of the isotherms for the 25 weight % alloy, representing hydrogen uptake at constant pressure, show no variation of pressure with composition, indicating that in this slower hydrogen absorption, equilibrium of three solid phases has been reached. 

Material Formula Density gem Flam- mability Limiting oxygen index % Optical transmission % Radia- tion resis- tance Refrac- tive index Resistance to Ultra violet Water absorption % Water absorption equilibrium % Water absorption - over 24 hours %... 

Sakurai, Ikeda and Okabe reported values of equivalent to 30-50 layers of FeS [12], which makes the modeling of the reaction step via an absorption equilibrium somewhat strained. As an alternative, semi-empirical approach we can adopt the parabolic rate hypothesis used in the oxidation of metals [15] and apply it to the formation of reaction product on the surface,... 

This principle can be, and has been, applied to hi temperature gas mixtures. Specifically, the removal of H,S from fuel gas streams (natural gas and coal gasification product streams). Since the membrane is exposed to the same pressure on both sides, there is no theoretical limit to the pressure at which the process operates. Also, since there is no reaction or absorption equilibrium, there is no theoretical limit to removal. 

Case 2. The rate of decomposition is very small compared with the rate of absorption and desorption. In this case, /c2 is very small so that the denominator of Eqs. (34.4) and (34.5) is k Ca + k. Introducing the absorption equilibrium constant K =... 

Kx,Kq absorption equilibrium constants in Langmuir-Hinshelwood rate equation, volume/mol... 

Upon reaching absorption equilibrium any component / is distributed so that its partial pressure in the interacting media is the same value or p. (in conditions of low pressure). That is why saturation pressures in interacting media are equal... 

The hydrogenation of ethylene on copper is inhibited by excess ethylene at low temperatures, whereas at high temperatures both reactants are weakly absorbed and the reaction becomes second order. The apparent energy of activation was found to be constant between 0 arid 100°C, but to decrease strongly at higher temperatures. The effect can be explained on the lines described above. The authors used a slightly different approach which does not involve the simplifying assumption that the absorptive equilibrium is rapid (122). 

J. V. Sinisterra, J. M. Marinas, and A. Llobura [Can. J. Chem., 61, 230 (1983)] employed an extended form of the Hammett equation to correlate data for esterification of ethanol with substituted benzoic acids in the gas phase over a solid AIPO4 catalyst. The focus of their efforts was correlation of values of the adsorption equilibrium constants and apparent rate constants. Use the information tabulated below to prepare a Hammett plot of experimental absorption equilibrium constants versus the corresponding values of the a parameters for the substituted benzoic acids indicated. Employ the a values in Table 7.2 of the text. In principle the intercept of the best straight line through these data should correspond to the adsorption equilibrium constant for benzoic acid. By how much does this value differ from the experimental value below What value of the parameter p characterizes the chemisorption of substituted benzoic acids ... 

Absorption equilibrium is preferably described by Henry s law since often, but not always, the absorptives are above their critical temperatures ... 

When the forces between a particle and another condensed species are treated, thermodynamics and statistical mechanics of the aerosol (particles plus gas) enter through temperature dependence of the interaction forces. However, actual aerosol particle interaction forces may be altered in a fundamental way if one or both of the particles or surfaces absorb molecules from the suspending gas. ASH et al. [5.4] considered nonionic systems in which the relative velocity of the particle and surface or other particle is "sufficiently small, in relation to the rates of absorption and desorption, that absorption equilibrium is maintained as the particles move together, collide and then either adhere or separate." They, therefore, assume constant temperature for the entire aerosol system implying at least several nonabsorbing gas molecular collisions with the sorbent species between each sorbate interaction that is to say, the sorbate must be a minority (< 10 percent) species in the gas. By use of conventional equilibrium thermodynamics they derive the expression for the excess force (beyond van der Waals and electrostatic) between two bodies due to sorption as... 

For graphical representation of the gas-liquid equilibrium, the absorption equilibrium , the partial pressure diagram (p,(x,) diagram), and also the equilibrium diagram y,( r,) or i (X,), are used. 

Sufficiently good solubility of the key (gas to be absorbed) component (favorable absorption equilibrium properties). 

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