Mixture adsorption equilibria

Adsorption at the surface is assumed to be rapid compared to the diffusion rates. The following relationship was developed to describe the mixture adsorption equilibria (3) ... 

J. U. Keller, F. Dreisbach, H. Rave, R. Staudt, M. Tomalla Measurement of gas mixture adsorption equilibria of natural gas compounds on microporous sorbents. Adsorption 5 (1999) 199-214. 

The DA isotherm contains parameters related separately to the solid and the adsorbates. The advantage of using the potential theory for predicting gaseous mixture adsorption equilibria is that the pure component characteristic curves are generally independent of temperature. Thus having obtained isotherm information of a pure component at one temperature, the mixture equilibria at other temperatures and pressures can be predicted. The DA equation and its... 

FIGURE 4.20. Calculation of mixture adsorption equilibria from pure-component spreading pressures. ... 

Mehta, S.D., and Danner, R.P., An improved potential theory method for predicting gas-mixture adsorption equilibria, Ind. Eng. Chem. Fund., 24(3), 325-330 (1985). 

Heslop, M.J. Buffham, B.A., and Mason, G A test of the polynomial-fitting method of determining binary-gas-mixture adsorption equilibria, Ind. Eng. Chem. Res., 35(4), 1456-1466 (1996). 

Measurement of Gas Mixture Adsorption Equilibria of Natural Gas Compounds on Microporous Sorbens,... 

Figure 6.24. Experimental setup for combined dielectric-manometiic measurements of pure gas and gas mixture adsorption equilibria. IFT University of Siegen, 1990.

Today there are several experimental methods available to measure pure gas and gas mixture adsorption equilibria on porous rigid or swelling sorbent materials. All these methods have their specific advantages and disadvantages [1]. Choice of any of them depends mainly on the purpose of measurement and/or accuracy and reliability of data needed. For quick measurements of restricted accuracy gas expansion experiments or volumetric measurements are recommended. If high accuracy data are needed, weighing procedures, i. e. gravimetry should be used... 

Ideal adsorbed solution theory (lAST) [4] is a widely used engineering thermodynamic method, the equivalent to the Raoult s law for adsorption, which uses the pure-gas isotherms as inputs to predict the mixture adsorption equilibrium at the temperature of interest. Before the lAST calculation, the pure gas isotherm must be fitted with a suitable isotherm equation to an acceptable degree of accuracy we used a piece-wise fit [3]. 

Zeolite membranes show high thermal stability and chemical resistance compared with those of polymeric membranes. They are able to separate mixtures continuously on the basis of differences in the molecular size and shape [18], and/or on the basis of different adsorption properties [19], since their separation ability depends on the interplay of the mixture adsorption equilibrium and the mixture. Different types of zeolites have been studied (e.g. MFI, LTA, MOR, FAU) for the membrane separation. They are used still at laboratory level, also as catalytic membranes in membrane reactors (e.g. CO clean-up, water gas shift, methane reforming, etc.) [20,21]. The first commercial application is that of LTA zeolite membranes for solvent dehydration by pervaporation [22], Some other pervaporation plants have been installed since 2001, but no industrial applications use zeolite membranes in the GS field [23]. The reason for this limited application in industry might be due to economical feasibility (development of higher flux membranes should reduce both costs of membranes and modules) and poor reproducibility. 

Moon, H., and Tien, C., Further work on the prediction of gas-mixture adsorption equilibrium using the potential theory, Sep. Technol., 3(3), 161-167 (1993). 

The local equilibrium curve is in approximate agreement with the numerically calculated profiles except at very low concentrations when the isotherm becomes linear and near the peak apex. This occurs because band-spreading, in this case, is dominated by adsorption equilibrium, even if the number of transfer units is not very high. A similar treatment based on local eqnihbrinm for a two-component mixture is given by Golshau-Shirazi and Gniochou [J. Phys. Chem., 93, 4143(1989)]. 

The chromatographic resolution of bi-naphthol enantiomers was considered for simulation purposes [18]. The chiral stationary phase is 3,5-dinitrobenzoyl phenyl-glycine bonded to silica gel and a mixture of 72 28 (v/v) heptane/isopropanol was used as eluent. The adsorption equilibrium isotherms, measured at 25 °C, are of bi-Langmuir type and were proposed by the Separex group ... 

The separation of bi-naphthol enantiomers can be performed using a Pirkle-type stationary phase, the 3,5-dinitrobenzoyl phenylglycine covalently bonded to silica gel. Eight columns (105 mm length) were packed with particle diameter of 25 0 fiva. The solvent is a 72 28 (v/v) heptane isopropanol mixture. The feed concentration is 2.9 g for each enantiomer. The adsorption equilibrium isotherms were determined by the Separex group and already reported in Equation (28) [33]. 

Hougen- Watson Models for Cases where Adsorption and Desorption Processes are the Rate Limiting Steps. When surface reaction processes are very rapid, the overall conversion rate may be limited by the rate at which adsorption of reactants or desorption of products takes place. Usually only one of the many species in a reaction mixture will not be in adsorptive equilibrium. This generalization will be taken as a basis for developing the expressions for overall conversion rates that apply when adsorption or desorption processes are rate limiting. In this treatment we will assume that chemical reaction equilibrium exists between various adsorbed species on the catalyst surface, even though reaction equilibrium will not prevail in the fluid phase. 

The hydroxyl-terminated polymer was then added to the dispersion and the mixture allowed to stand for 24 hr to achieve adsorption equilibrium. Further n-heptane was then added to give a 4 1 (by volume) n-heptane ethanol solvent composition, and the sample... 

If 1.6 kg carbon is added, what is relative saturation of the equilibrium mixture assuming the temperature to be unchanged The vapour pressure of acetone at 303 K is 37.9 kN/m2 and the adsorption equilibrium data for acetone on carbon at 303 K are ... 

Mixture phase equilibrium calculations, types of, 24 680-681 Mixture-process design type, 8 399 commercial experimental design software compared, 8 398t Mixtures. See also Multicomponent mixtures Nonideal liquid mixtures acetylene containing, 2 186 adsorption, 2 593-594 adsorption isotherm models,... 

EXAMPLE 9.4 Kinetic-Theory-Based Description of Binary Adsorption. Assume that two gases A and B individually follow the Langmuir isotherm in their adsorption on a particular solid. Use the logic that results in Equation (46) to derive an expression for the fraction of surface sites covered by one of the species when a mixture of the two gases is allowed to come to adsorption equilibrium with that solid. 

If gas A is being adsorbed from a mixture with gas A, the probability that at adsorption equilibrium a certain surface site is occupied by a particle A is... 

There have been few studies reported in the literature in the area of multi-component adsorption and desorption rate modeling (1, 2,3., 4,5. These have generally employed simplified modeling approaches, and the model predictions have provided qualitative comparisons to the experimental data. The purpose of this study is to develop a comprehensive model for multi-component adsorption kinetics based on the following mechanistic process (1) film diffusion of each species from the fluid phase to the solid surface (2) adsorption on the surface from the solute mixture and (3) diffusion of the individual solute species into the interior of the particle. The model is general in that diffusion rates in both fluid and solid phases are considered, and no restrictions are made regarding adsorption equilibrium relationships. However, diffusional flows due to solute-solute interactions are assumed to be zero in both fluid and solid phases. 

A mathematical model has been developed to describe the kinetics of multicomponent adsorption. The model takes into account diffusional processes in both the solid and fluid phases, and nonlinear adsorption equilibrium. Comparison of model predictions with binary rate data indicates that the model predictions are in excellent for solutes with comparable diffusion rate characteristics. For solutes with markedly different diffusion rate constants, solute-solute interactions appear to affect the diffusional flows. In all cases, the total mixture concentration profiles predicted compares well with experimental data. 

For safety reasons, the cycling operation is interrupted during the weekend. After an interruption, always happening at the end of a discharge phase, several cycles are necessary to join the continuous curve representative of the evolution of the behaviour of the tank. This phenomenon tends to demonstrate the importance of the kinetics of the multi-component adsorption equilibrium in the case of a complex mixture of gas. 

Adsorption of surfactant on solid surfaces is generally described by adsorption isotherms. For this purpose, a simple adsorption experiment can be performed at a constant temperature by dispersing known amounts of solid adsorbent into a constant volume of dilute surfactant solution at which the initial surfactant concentrations are varied and shaking the mixture until equilibrium is reached. The moles of surfactant adsorbed per unit mass of the solid (Ns) for each solution can be determined from ... 

The presulfiding pretreatment involved contacting the catalyst with an H2S/H2 mixture (without CO) at 661 K until the feed and effluent H2S concentrations were equal, indicating adsorption equilibrium, following which CO was introduced. Figure 31 shows typical activity-versus-time... 

To model the adsorption equilibrium, a suitable isotherm equation has to be chosen. For mixtures, the model equations are usually coupled to take into... 

The method of predicting the mixture adsorption isotherms is to first select the feed mole fractions of interest and to pick an adsorption level within Region II. The pure component standard states are determined from the total equilibrium concentration that occurs at that set level of adsorption for the pure surfactant component adsorption isotherms. The total equilibrium mixture concentration corresponding to the selected adsorption level is then calculated from Equation 8. This procedure is repeated at different levels of adsorption until enough points are collected to completely descibe the mixture adsorption isotherm curve. 

A solution is t3q>lcally a system of more than one component. In actual cases, there are at least two substances that can adsorb. For a binary fluid mixture, including dilute solutions, adsorption of one type of molecule (say A) involves replacement of the other (B). Thus, adsorption from solution is essentially an exchange process. If one molecule of A replaces r molecules of B at the Interface, the adsorption equilibrium can be written as... 

Adsorption equilibrium of polar/non-polar mixtures on MCM-41 experiments and Monte Carlo simulation... 

The binary mixture adsorption is simulated by assuming an ideal AB-gas at fixed T, Pa and Pb- In equilibrium there are two ways to perform a change of the system state adsorbing (desorbing) one molecule onto (from) the surfece. 

Counterdiffusion of cumene and 1-MN occurred readily in type Y zeolite, as shown by several studies. The 1-MN is selectively adsorbed relative to cumene thus, when the zeolite was initially saturated with cumene and placed in 1-MN, essentially 100% of the cumene diffused out but when the zeolite was saturated with 1-MN and placed in cumene, only about 74% of the 1-MN diffused out. The same end point was also reached when SK-500 saturated with cumene was placed in a mixture of 1-MN and cumene in the proper ratio. This selective adsorption equilibrium value was essentially independent of temperature and, except for the cerium form of type Y, was independent of the nature of the cation... 

---