Adsorption and separation processes

18-0-01 - An experimental adsorbent screening study for CO2 removal from flue gas 

Department of Chemical Engineering, University of Ottawa, Ottawa, Ontario, Canada -tezel eng. uottawa. ca 

The selection of a suitable zeolite adsorbent for CO2 removal from flue gas (mixture of CO2 and N2) has been carried out. The limiting heats of adsorption, Henry s Law constants for CO2 and N2, CO2 pure component adsorption isotherms and expected working capacity curves for Pressure Swing Adsorption (PSA) separation application were determined. The results show that the most promising adsorbent characteristics are a near linear CO2 isotherm and a low Si02/Al203 ratio with a cation in the zeolite structure that has strong electrostatic interaction. 

Adsorption isotherms of amino acids in BEA type zeolites (Si02/Al203 = 25. ..300, ionic form H, Na, K, Ca ) have been analyzed. Phenylalanine, leucine, isolecine, methionine, and arginine were found to form dimers in the zeolite pores (Si02/Al203 = 25, H, Na ). In case of higher content of silicium the dimerization was less pronounced. The adsorption was rather selective, depending on the pH and ionic form. Sorbate-zeolite interaction was essentially interpreted in terms of hydrophobic forces. 

18-0-03 - Kinetic separation of binary mixtures of carbon dioxide and C2 hydrocarbons on modified LTA-type zeolites 

---

Activated carbon is commonly acknowledged to be very efficient as a VOC adsorbent. However, in the last decade, interests arose to develop new materials, such as alumni-silicate molecular sieve, towards operating conditions for which activated carbon was inappropriate due to its inflammability and adsorption capacity dependence on effluent relative humidity. Apart from hydrophobicity, the advantages of High Silica Zeolites (HSZ) are notably a thermal and chemical stability, a high steric selectivity and a complete regeneration at low temperatures [11]. Yet, for adsorption and separation processes development, organic compounds properties impact on adsorption and crystalline framework influence on selectivity are to be clarified and efficiently modeled. 

The rewards for being able to understand and control the process of carbonization to give a particular pore structure are potentially enormous, with applications which include catalysis, carbon-in-pulp metal adsorption and separation processing, molecular sieves and bioethical applications. 

When performing the studies summarized here, also the principle of structural chemical modelling [10] was extensively used, which imply the comparison of the results of chromatographic experiments on the adsorbents possessing predicted separation centres with those on the adsorbents which have only a small number of such centres, if any. The identification of the portions of chromatographic materials, on which the adsorption and separation processes take place, had formed a scientific background for the development... 

Adsorption and separation processes involve also the active sites existing on the external surface of (CH3)4N - montmorillonite, their role being more important in the case of adsorption of isoparaffins and cyclohexane molecules. This is indicated by a significantly smaller differences between the specific retention volumes of iso- and cycloparaffins on natural and tetramethylammonium samples than the difference in Vm values characteristic for n-paraffines on the same adsorbents. Thus, the tetramethylammonium montmorillonite adsorbs n-alkanes selectively from the mixtures containing iso- and cycloparaffines, which is confirmed by the values of relative retention volumes for such hydrocarbon pairs as, for instance, n-heptane / 2,4- dimethylpentane. These can be easily calculated from the data presented in Table 5. 

A. Selective Adsorption and Separation Processes Using Organoclays... 

Physisorption-based adsorption and separation processes are of primary interest for various applications, including H2 storage, carbon capture and sequestration, and hydrocarbon separations. Physisorption based separation of adsorbate mixtures can occur through a variety of mechanisms, including equilibrium, steric, kinetic, or some combination of these in more complex systems. 

General Reeebences Lemlich (ed.). Adsorptive Bubble Separation Techniques, Academic, New York, 1972. Garleson, Adsorptive Buhhle Separation Processes in Scamehom and Harwell (eds.), Surfactant-Based Separation Processes, Marcel Dekker, New York, 1989. 

Wang, L.K. and Wang, M.H.S., Removal of organic pollutants by adsorptive bubble separation processes, 1974 Earth Environment arid Resources Conference Digest of Technical Papers, Vol. 1, IEEE Cat. No. 74 CH0876-3EQC, pp. 56-57, September 1974. 

Krofta, M. and Wang, L.K., Flotation and Related Adsorptive Bubble Separation Processes, Lenox Institute of Water Technology, Lenox, MA, Report No. LIR-0681/1, 150pp., June 1981. 

Liquid-solid distributions are involved in ion-exchange and other adsorption-based separation processes, separation processes based on crystallization or precipitation, flotation processes for ore dressing, and smelting processes. 

Mangani et al. [13] used Carbopack B columns to recover chlorinated insecticides in soil samples. These workers noted that, although the principles governing the adsorption and extraction process in the extraction in soil analysis are the same as those that govern liquid-solid chromatography, the main feature of a chromatographic column, i.e. separation efficiency, is almost completely absent. 

In the chromatographic liquid adsorptive separation process, the adsorption and desorption processes must occur simultaneously. After the desorption step, both the rejected product (product with lower selectivity, resulting in less adsorption by adsorbent) and the extracted product (product with higher selectivity, resulting in strong adsorption by adsorbent) contain desorbent In general, the desorbent is recovered by fractionation or evaporation and recycled back into the system. 

Consequently, they are distributed on the surface randomly even if there is no surface migration. Therefore, in contrast to the discussion of adsorption and desorption processes in Section X, the mechanism (188) needs no assumed rapid surface migration (it is evident, of course, that if the migration occurs, it does not affect the results). The analysis of adsorption and desorption rates given in Section X needs only minor alterations to its application to stage 1 namely, products kbPb> would be substituted for rate constants of desorption on separate surface sites, k, and the fugacity of adsorbed particles I, px for p. Therefore, in analogy to (148) and (157), we obtain... 

This natural process by which dissolved and/or particulate surface-active materials end up in the atmosphere has been modeled and studied in the laboratory. As summarized by Detwiler and Blanchard (ref. 46), tests in suspensions of bacteria (ref. 76,96,97), latex spheres (ref. 98), dyes (ref. 99), and in sea water and river water (ref. 96,100,101) have demonstrated successful transfer of all manner of surface-active material from the bulk fluid, or the bulk interface, to the droplets ejected when bubbles burst. (This situation can be pictured as an extension of the common industrial adsorptive-bubble-separation process (ref. 102) into a third dimension or phase — the atmosphere.) Further laboratory tests with various tap waters, distilled waters, and salt solutions have shown that no water sample was ever encountered that did not contain at least traces of surface-active material (ref. 46). 

There is a synergism between adsorption and chromatographic processes which is clearly demonstrated in the supercritical fluid literature. Research in supercritical fluid chromatography can usually be divided into analytical applications and the measurement of physicochemical data. Early analytical separations methodology performed at pressures close to ambient conditions... 

C02 is recoverable by physical adsorptions of active carbons or zeolites, or a chemical sorption by carbonation of calcium oxide (CaO) at the C02 recovery and separation process. CaO is absorbable chemically C02 at temperatures of 500-800°C [Eq. (5)]. CaO can remove C02 from hydrocarbon reaction system at the reaction temperature for C02 production with small sensible heat loss, and also enhance reaction rate and yield of the C02 production reaction (Kato, 2003). 

---