Isotherm measurement single-component isotherms

Pressure Swing Adsorption (PSA) unit is a dynamic separation process. In order to create a precise model of the process and thus an accurate design, it is necessary to have a good knowledge of the mixture s adsorption behaviour. Consequently, the dilAision rates in the adsorbent particles and the mixture isotherms are extremely vital data. This article intends to present a new approach to study the adsorption behaviour of isomer mixtures on zeolites. In a combined simulation and experimental project we set out to assess the sorption properties of a series of zeolites. The simulations are based on the configurational-bias Monte Carlo technique. The sorption data are measured in a volumetric set-up coupled with an online Near Infra-Red (NIR) spectroscopy, to monitor the bulk composition. Single component isotherms of butane and iso-butane were measured to validate the equipment, and transient volumetric up-take experiments were also performed to access the adsorption kinetics. 

To measure a point of the single component isotherm, pure gas is admitted to the setup with valve 2 closed (figure 1). By closing valve 1 and opening valve 2 the pressure... 

Single-component isotherm parameters cannot always predict elution profiles with satisfied accuracy [122, 123], Therefore, to be able to predict accurate overloaded multi-component elution profiles where competition occurs competitive adsorption isotherm parameters are often necessary. Measurement of isotherms from a mixture is also often necessary because the pure enantiomers are not always accessible in large quantities. However, there exist only a small number of reports on the determination of multi-component adsorption isotherm parameters. FA can be used to determine binary isotherm data but it is time-consuming. The PP method is an alternative method to determine isotherm parameters from binary mixtures. It has been reported that the PP method works well up to weakly non-linear conditions [118, 119],... 

IAS (etc.) Thermo-dynamics Multi-component Measurements for single component isotherms only... 

Figure 6.28 compares measured and simulated profiles for the batch separation of EMD53986. Very good agreement between theory (solid lines) and experiment (symbols) is achieved using the multi-component modified-Langmuir isotherm (Fig. 6.21). Also shown are the simulation results neglecting component interaction by using only the single-component isotherms (dashed line), which deviate strongly from the observed mixture behavior. Typical for competitive adsorption is the displacement of the weaker retained R-enantiomer and the peak expansion of the stronger adsorbed S-enantiomer.

Similar results were obtained with the enantiomers of methyl mandelate separated on 4-methylcellulose tribenzoate immobilized on silica [30]. Figure 4.4a shows the experimental adsorption data for the two pure enantiomers (symbols), the best bi-Langmuir isotherms (solid lines) and the best LeVan-Vermeulen isotherms [33]. The data (symbols) were obtained by ECP. Figures 4.4b-d compare the competitive isotherm data measured with three mixtures of different composition and the isotherms calculated from the single component isotherms (Figure 4.4a) using the competitive bi-Langmuir model (Eq. 4.10). Results obtained... 

If we apply one of these equations to single-component isotherm data, we see that Eqs. 4.54 and 4.55 can be applied to the competitive adsorption data for a binary mixtiue only if Eq. 3.31 applies to the single-component data for each component. Then the six parameters can be derived from the single-component isotherms and only the coefficient b has to be measured with the mixture. Using more complicated models, Lin et al. [70] and Moreau et al. [71] have derived similar isotherms. Attempts at reducing the number of independent parameters as well as at determining these parameters from sets of experimental data have had limited success so far. 0onsiderable attention is required to clarify this issue. 

Zhou et al. measured by FA the single-component isotherms of two related peptides, bradykinin and kallidin (MW 1060 and 1188, respectively) on a Zorbax SB Ci8 microbore column (Agilent Technologies), using a 20% aqueous solution of ACN (with 0.1% TFA) as the mobile phase [81]. The isotherm data were fitted to the Langmuir, the bi-Langmuir, the Langmuir-Frermdlich and the Toth isotherm... 

Furthermore, this separation problem, which is theoretically simple, is also highly relevant to the pharmaceutical industry. An example is the separation of mixtures of N-benzoyl-D- and L-alanine on immobilized BSA (see Figures 11.20). We have explained in Chapters 3 and 4 (i) that a competitive bi-Langmuir isotherm can be employed to account for the competitive behavior of these components (Figure 4.25c) and (ii) that, because the chiral selective retention mechanism involves adsorption of the enantiomers in the hydrophobic cavity of BSA, the column saturation capacity of the chiral selective mechanism is the same for the two enantiomers. This competitive bi-Langmuir isotherm model is simply derived from the parameters obtained from single-component isotherm measurements. 

In all these figures, we used the competitive Langmuir isotherm model to calculate the band profiles. However, the coefficients of the isotherms used for Figures 11.21 are the coefficients of the single-component isotherms determined by frontal analysis, while the coefficients of the isotherms used to calculate the profiles in Figure 11.22 are measured by the simple wave method (Chapter 4, Section 4.2.4). These latter coefficients are certainly empirical coefficients, and their use would not permit an accurate prediction of single-component bands. However, they permit the calculation of band profiles that are in much better agreement... 

A chromatographic method has been used to measure single component sorption isotherms of O, N / CH, ... 

Microbalances are often used to measure single component adsorption isotherms. Measurements are possible in the pressure range between 1 and lo Pa (Akgiin 2007). The partial pressure of oiganic adsorptives can be adjusted by means of a bubble flask in combination with a condenser (Scholl 1991). As a rule gas concentrations are measured by gas chromatographs equipped with special calibrated analyzers. Multicomponent adsorption equihbria can be determined by... 

Guan, H. Stanley, B. Guiochon, G. Theoretical study of the accuracy and precision of the measurement of single component isotherms by the elution by characteristic points (ECP) method. J. Chromatogr. A, 1994, 659, 27. 

Figure 4.7. Single component isotherms of (top) proteins and (bottom) synthetic tri-block copolymers measured at room temperature for Octyl-sepharose stationary phase. The affinity constants calculated from an isotherm fit according to the Langmuir model seemed to indicate that the proteins bind more strongly than the copolymers and hence could not be displaced by them [reproduced with permission from reference 14].

The working capacity of a sorbent depends on fluid concentrations and temperatures. Graphical depiction of soration equilibrium for single component adsorption or binary ion exchange (monovariance) is usually in the form of isotherms [n = /i,(cd or at constant T] or isosteres = pi(T) at constant /ij. Representative forms are shown in Fig. I6-I. An important dimensionless group dependent on adsorption equihbrium is the partition ratio (see Eq. 16-125), which is a measure of the relative affinities of the sorbea and fluid phases for solute. 

The objective of this study is to compare the strengfti of adsorptive interaction between adsorbents and thiophene/benzene. Extremely low partial pressures at less than 10 atm would be necessary to meet this objective if isotherms were measured at ambient temperature, because the isotherms at ambient temperature are fairly flat and are difficult to compare. However, it is very difficult to obtain and control such low partial pressures experimentally. Therefore, single component isothoms for benzene and thiophene were measured at 90, 120 and 180 °C using standard gravimetric methods. A Shimadzu TGA-50 automatic recording microbalance was employed. Isosteric heats of adsorption were calculated using the Clausius-Clapeyron equation from isotherms at different temperatures. 

Single-component adsorption equilibria on activated carbon of the n-alkanes Q-C4 and of the odorant tert-butyl mercaptan were measured at the operating conditions expected in a large-scale facility for adsorbed natural gas (ANG) storage. The experimental data were correlated successfully with the Adsorption Potential theory and collapsed into a single temperature-independent characteristic curve. The obtained isotherm model should prove to be very useful for predicting the adsorption capacity of an ANG storage tank and to size and optimize the operation of a carbon-based filter for ANG applications. 

Direct determination of the column saturation capacity requires measurement of the adsorption isotherm. Use of methods such as frontal analysis, elution by characteristic point are classical techniques. Frontal analysis and elution by characteri.stic point require mg or gram quantities of pure product component. It is also possible to estimate the column saturation capacity from single-component overloaded elution profiles using the retention time method or using an iterative numerical method from a binary mixture [66J. 

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