5A Zeolite

Fig. 4J Langmuir plots (a) for propane on 5A zeolite (courtesy Ruthven) (fc) for carbon monoxide on zeolite CaY-54 (courtesy Stone). In (a) the adsorption is expressed in terms of number C of molecules of adsorbate per cavity in (b), as m (stp).

The acidic character of 5A zeolite as a function of the calcium content has been explored by different techniques propylene adsorption experiments, ammonia thermodesorption followed by microgravimetry and FTIR spectroscopy. Propylene is chemisorbed and slowly transformed in carbonaceous compounds (coke) which remain trapped inside the zeolite pores. The coke quantities increase with the Ca2+ content. Olefin transformation results from an oligomerization catalytic process involving acidic adsorption sites. Ammonia thermodesorption studies as well as FTIR experiments have revealed the presence of acidic sites able to protonate NH3 molecules. This site number is also correlated to the Ca2+ ion content. As it has been observed for FAU zeolite exchanged with di- or trivalent metal cations, these sites are probably CaOH+ species whose vas(OH) mode have a spectral signature around 3567 cm"1. 

Even if 5A zeolite is widely used in iso-paraffin separation from an n/iso paraffin mixture, the adsorbent is affected by a slow deactivation mainly due to coke formation inside the molecular sieve porosity. Its aging phenomenon decreases its sorption properties. According to previous studies, 5A zeolite deactivation results essentially from heavy carbonaceous compound formation in a-cages blocking the 5A zeolite microporosity [1-2]. 

Di or trivalent cations are able to induce the dissociation of coordinated water molecules to produce acidic species such as MOH+ (or MOH2+ for trivalent metal cations) and H+. Several infrared studies concerning rare-earth or alkali-earth metal cation exchanged Y zeolites have demonstrated the existence of such species (MOH+ or MOH2+) [3, 4, 5, 6]. However, the literature is relatively poor concerning the IR characterization of these acidic sites for LTA zeolites. The aim of the present work is to characterize 5A zeolite acidity by different techniques and adsorption tests carried on 5A zeolite samples with different ion exchange. 

The 4A and 5A zeolite samples come from the French Institute of Petroleum (IFP). These samples named in the text 5A 67, 5A 73.5 and 5A 86 are exchanged at 67%, 73.5% and 86% by calcium ions, respectively. Prior each microgravimetric measurement, 20 mg of zeolite sample are outgassed at 350°C under primary vacuum... 

Propylene cokage experiments followed by gravimetry have shown that higher is the 5A zeolite calcium content, higher are the cokage kinetics and carbon content inside the pores (Fig. 1). The total carbon contents retained in the porosity after desorption at 350°C of physisorbed propylene are 14.5% and 11% for 5A 86 and 5A 67 samples respectively. These carbon contents are relatively important and probably come from the formation of heavy carbonaceous molecules (coke) as it has been observed by several authors [1-2], The coke formation requires acid protonic sites which seems to be present in both samples but in more important quantity for the highly Ca-exchanged one (5A 86). 

Fig. 3 represents the IR spectra in the hydroxyl region and in the OH bending region for the activated 4A and 5A zeolite samples. The outgassed 5A 86 sample IR spectrum exhibits a weak absorption at 3744 cm 1 which corresponds to non acidic external silanol groups and a large contribution between 3700 cm 1 and 3500 cm 1 (Fig. 3a). This... 

Adsorption Equilibrium Numerous purification and recovery processes for gases and liquids Activated carbon-based applications Desiccation using silica gels, aluminas, and zeolites Oxygen from air by PSA using LiX and 5A zeolites... 

Molecular sieving Separation on n- and isoparafins using 5A zeolite Separation of xylenes using zeolite... 

IsoSiv [Isomer separation by molecular sieves] A process for separating linear hydrocarbons from naphtha and kerosene petroleum fractions. It operates in the vapor phase and uses a modified 5A zeolite molecular sieve, which selectively adsorbs linear hydrocarbons, excluding branched ones. Developed by Union Carbide Corporation and widely licensed, now by UOP. The first plant was operated in Texas in 1961. By 1990, more than 30 units had been licensed worldwide. See also Total Isomerization. 

Molex A version of the Sorbex process, for separating linear aliphatic hydrocarbons from branched-chain and cyclic hydrocarbons in naphtha, kerosene, or gas oil. The process operates in the liquid phase and the adsorbent is a modified 5A zeolite the pores in this zeolite will admit only the linear hydrocarbons, so the separation factor is very large. First commercialized in 1964 by 1992, 33 plants had been licensed worldwide. See also Parex (2). 

To develop effective catalysts for the C02 reforming of methane, other supports were also used for nickel catalysts, including perovskite (244), Y zeolite (245,246), 5A zeolite (247), high-silica ZSM-5 zeolite (248), and AIPO4 (tridymite) (249). 

In this particular case, the adsorption process can be used to overcome the distillation limitation. This is demonstrated in Figure 6.2, which represents the relative adsorption of C5 and C(, Hnear, branched and cycHc paraffins from the liquid phase of the 5A adsorbent used in the HOP GasoHne Molex process, licensed by HOP. In this process, only Hnear paraffins can enter the pores of 5A zeolite, while branched and cyclic paraffins are completely excluded due to their large kinetic diameters. Also, the selectivity for Hnear paraffins with respect to other types of paraffins is infinite. Consequently, the separation of Hnear paraffins from branched and cyclic paraffins becomes possible. 

Tn recent experimental work in this laboratory (1-3) we have studied the kinetics and equilibria of sorption of light hydrocarbons and some other simple non-polar molecules, in 5A zeolite. The crystal structure of the A-type zeolites is among the simplest of the zeolitic lattices (4). In this paper we show that many features of the sorption kinetics and equilibria may be explained by simple theoretical considerations. 

Table I. Values of Kq and q0 Giving Temperature Dependence of Henry Constants for Sorption in 5A Zeolite and Chabazite according to Equation 2 ...

The importance of quadrupole interaction in zeolitic sorption has been pointed out by Barrer and Stuart (20). Such effects are clearly illustrated by the data for sorption of nitrogen and carbon dioxide in both H-chabazite and 5A zeolite. For these molecules, which have large quadrupole moments, the experimental values of K0 are much smaller than the theoretical values predicted from the idealized model suggesting either localized sorption at specific sites within the cavity or restricted rotational freedom. 

Figure 1. Equilibrium isotherms for sorption in 5A zeolite and H-chabadte data of Glessner and Myers (26), data of Barrer and Davies (7), O data of Derrah (3), X theoretical lines from Equation 8.

Figure 8. Temperature dependence of limiting diffusivity for sorption in 5A zeolite data for C02 from Sargent and Whitford (37), X theoretical line from Equations 14 and 16, — data of Garg (31),. ...

Table III. Critical Diameters, Activation Energies, and Values of D for Diffusion in 4A and 5A Zeolites...

Table IV. Comparison of Theoretical and Experimental Diffusivities for Simple Molecules in 5A Zeolite...

Table IV also gives values of D and E for diffusion of carbon dioxide in 5A zeolite, calculated on the assumption that /+ = 1, using the values...

Study of Mixture Equilibria of Methane and Krypton on 5A Zeolite... 

In this paper we report experimental and theoretical results on the sorption of methane and krypton on 5A zeolite. The sorption of methane in the 5A cavity is reported to be non-localized (9.), whereas that of krypton is localized at a cavity site and window site (10). The multicomponent form of the isotherm of Schirmer et al. is used to interpret the experimental data and to predict mixture equilibria at other concentrations. 

The system methane-krypton 5A was selected for study because previous pure component studies for each of these sorbates on Linde 5A zeolite indicate that the sorption mechanisms are significantly different. 

Pure component experimental data for sorption of methane and krypton on 5A zeolite at 238, 255. and 271K, and in the pressure range of 0 to 97.36 kPa were also obtained during this work (shown in Figures 3 and U). Further sorption data for methane on 5A zeolite (10, 13, 1 0, and for krypton on 5A zeolite (10. 15) are also plotted for other temperatures, all of which appear to be consistent. These experimental data were used to derive the energy and entropy parameters in equation U for the isotherm model of Schirmer et al. by a minimization of a sum of squares optimization procedure. 

The resulting optimized parameters and for sorption of methane and krypton on 5A zeolite are shown in Figure 5 and are presented in Table 1. The calculated energy parameters -22000 Joules/mole for methane and - 16,725-0 Joules/mole for krypton were independent of the amount adsorbed and agree with... 

Figure 3. Equilibrium sorption data for CHt on pure 5A zeolite parameter is temperature data of (x) Roberts, (O) Derrah, COJ Loughlin, (A) Lederman (---------) theoretical curves calculated using Equation 4 and data in Table I...

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