Browsing by Author "Barrer, Richard M."

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Diffusion of Some n-Paraffins in Zeolite A
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1974, 70 (1-6), 1974) Barrer, Richard M.; Clarke, David J.
A study has been made of the sorption kinetics of n-C4H10, n-C6H14 and n-C9H20 at each of three temperatures in four samples of Linde Sieve A with 30.55, 32.54, 34.10 and 35.48 % of Na+ replaced by Ca2+. Over the earlier stages good straight lines were obtained when the fractional uptake was plotted against time½. The kinetics have been analysed in terms of the slopes k of these lines. The coefficients k/A(A= surface area) are independent of state of sub-division and distributions of shape and size of crystallites. They therefore characterise the sortion kinetics. Their dependences upon chain length of paraffin, amounts sorbed, temperature and % exchange of Na+ by Ca2+ have been evaluated. From k diffusion coefficients have been estimated and their dependence and that of the activation energies for diffusion upon the paraffin, and the extent of exchange have been found. The intrinsic mobility coefficient of n-C4H10 has been derived and found to decrease with the amount sorbed.
Ion Exchange in Mordenite
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1974, 70 (12), 1974) Barrer, Richard M.; Klinowski, Jacek
Ion-exchange isotherms have been measured for synthetic mordenite involving the cation pairs Na+⇌Cs+, NH+4⇌K+, NH+4⇌Na+, NH+4⇌Li+, 2NH+4⇌Ca2+, 2NH+4⇌Sr2+ and 2NH+4⇌Ba2+. In all cases except those involving Ca2+ and Sr2+ reversible exchange was effected. The values of the thermodynamic equilibrium constant, Ka, and the standard free energy of exchange, ΔG⊖, were calculated for the reversible pairs. For additional combinations of the reversible ionic pairs, Ka and ΔG⊖ were obtained using the triangle rule. The thermodynamic affinity sequence is Cs+ > K+ > NH+4 > Na+ > Ba2+ > Li+. The thermodynamic affinity sequence among monovalent alkali metal ions established in this work for mordenite was found to be repeated for other zeolites, provided exchanges which do not go to completion are normalised by considering the equilibrium only in terms of the exchangeable fraction of the ions.
Ion-exchange Selectivity and Electrolyte Concentration
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1974, 70 (11), 1974) Barrer, Richard M.; Klinowski, Jacek
It is shown how, from a given exchange isotherm at a given total solution normality, one may calculate isotherms and exchange selectivity coefficients at other total normalities. When the exchange ions have different valences the isotherms depend strongly upon the total normality, and the selectivity of the exchanger, for the ion of higher valence increases without limit with increasing dilution. Also when the ions have different valences isotherms without inflexion points can become sigmoid with increasing dilution and sigmoid isotherms can loose their inflexions. In these circumstances sigmoid isotherms, for example in zeolites, cannot provide evidence that there is more than one kind of exchange site in the exchanger. However, the changes in isotherm shape or position with dilution are very small when the ions have the same valence. A way of diagrammatic representation of isotherms has been described which is independent of electrolyte concentration.
Modified Zeolites Part 1.—Dealuminated Mordenites and their Silanation
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (09-12), 1978) Barrer, Richard M.; Trombe, Jean-Christian
A series of partially dealuminated H-mordenites having different ratios SiO2/Al2O3 has been prepared from Na-mordenite by various treatments with acid. From these a series of dealuminated Na-mordenites has been made by treating the corresponding H-mordenites with dilute NaOH. The loss of water, including that from the groups [graphic omitted] and the “nests” of hydroxyls, H4O4, has been investigated as a function of temperature for the dealuminated forms. This showed at 360°C the existence of some OH groups not originating from [graphic omitted]. Such groups were attributed to —OH originating from nests. The silanation of the dealuminated H- and Na-mordenites was investigated quantitatively. In the mordenites free of zeolitic water the ratios H2(evolved)/SiH4(chemisorbed) were always between 1.5 and 2 and each ratio usually remained reasonably constant over the course of a run. This suggested a rather constant ratio of primary chemisorption to secondary reaction during many runs. The ratio increased above 2 only if zeolitic water was also present. No evidence was found for a significant amount of the reaction [graphic omitted] in which SiH4 interacts with intact “nests”, H4O4, to regenerate defect-free framework. The Elovich equation appeared able to represent the kinetics of chemisorption of SiH4.
Modified zeolites. Part 2.—Sorption by dealuminated, silanated mordenites
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (09-12), 1978) Barrer, Richard M.; Trombe, Jean-Christian
A comparison has been made of sorption isotherms and kinetics of O2, N2 and Ar in each of a series of partially dealuminated mordenites before and after different extents of silanation. Before silanation partially dealuminated mordenites sorbed each gas freely but after silanation some very selective sorbents were obtained which at 77 K imbibed O2 much more copiously than either N2 or Ar. This selectivity was further improved when acidic H was replaced by Na in the dealuminated H-mordenites before silanation. In many of the sorbents a rapid initial uptake was followed by a slow diffusion at rates in the sequence O2 > N2 > Ar, which is the inverse order of their van der Waals cross-sectional diameters. The results provide evidence that after silanation the intracrystalline channels are not uniformly accessible to a given sorbate.