Zeolite nitrogen sorption

This is also true of nitrogen sorption in hydrated zeolites. 

The observed variation of nitrogen sorption capacity at atmospheric pressure with content of presorbed water is shown in Figure 2. In all cases, the nitrogen capacity is seen to fall off regularly with increasing amounts of presorbed water, the rate of fall being highest in zeolite NaA and lowest in zeolite NaY. 

Chandrakumar, K.R.S., and Pal, S., DFT and local reactivity descriptor studies on the nitrogen sorption selectivity from air by sodium and calcium exchanged zeolite-A, Colloids Surf. A - Physicochemical Eng. Aspects, 205, 127-138, 2002a. 

P. Graham, A.D. Hughes, and L.V.C. Rees, Sorption of binary gas mixtures in zeolites I. Sorption of nitrogen and carbon dioxide mixtures in silicalite. Gas Sep. A Purif. 3 56 (1989). 

Micropore volume, total and external surface data of the modified and parent zeolites determined by nitrogen sorption measurements are reported on Table 2 Micropore volumes decrease by more than 1/3 following modification of H-Y, whatever the grafting agent or the Si/Al ratio. Moreover, the modification of the amino- into 4-methoxybenzamido function further reduces the micropore accessibility. This could indicate an anchorage of the organic chain inside micropore system. 

Surface areas were determined by nitrogen sorption at -196 C using a S-point (p/pg = 0.06-0.21) BET calculation method Because KDT s can contain large ainounts of nonfromework alumina, as-measured surface areas tend to underestimate the concentration of the zeolitic constituent For this reason, surface areas are reported on both an as-nteasured m /g product) and a "m /g framework basis For the latter, framework mass computations assumed that sll silica was in the zeolite framework, and that only framework aluminum contributed to sodium ion exchange capacity The "m /g framework" data should thus be considered reasonable estimates rather than accurate values ... 

The pore volume was determined by nitrogen sorption-desorption at -196°C with the gas adsorption system ASAP 2010 (Micromeritics). All the zeolite samples present a large micropore volume (0.25 to 0.32 cm g ). NaY, NaHFAU and especially HFAU (Table 1) have also mesopores. With this latter zeolite, it is due to dealumination during thermal treatment of NH4FAU, this treatment causing the formation of extraframework aluminium species (Table 1). 

Nitrogen sorption isotherms of ZSM-5 zeolites were measured with a Micromeritics ASAP 2020 volumetric instrument at - 196 °C. In order to attain a sufficient accuracy in the accumulation of the sorption data, this instrument was equipped with pressure transducers covering the 133 Pa, 1.33 and 133 kPa ranges. Prior to the sorption measurements, all samples were degassed at 250 °C for at least 24 h until a pressure of 10 Pa was attained. 

The experiments of the sorption of propene in zeolite with preadsorbed CO (or in another series of experiments with preadsorbed NO) displays that propene replaced CO from Co2+ sites the band of Co2+-CO (at 2206 cm"1) diminishes as the bands of C=C—Co2+ (1590 and 1605 cm"1) increase (Figs. 1 A and B). On the other hand, the sorption of CO in zeolite with preadsorbed propene exhibits that CO is not able to replace propene the band of C=C Co2+ does not change upon the sorption of CO (spectra not shown). Contrary to CO, nitrogen monoxide was found to be able to remove propene from Co2+ sites - the bands of propene disappear upon NO sorption whereas Co2+(NO)2 dinitrosyls appear (Fig. 1 C). On the other hand, propene does not... 

In a sorption pump, the gas is trapped within the adsorbing material (zeolites or active charcoal) called molecular sieve. Zeolites are porous aluminium silicates which adsorb large amount of gas when cooled to low temperature (usually 77K). The pump is filled with zeolite and put in a bucket containing liquid nitrogen (see Fig. 1.11). 

The sorption pumps are clean but are one shot , that is, two pumps in parallel and connected by valves alternatively are needed for a continuous pumping. When the first pump is saturated, the second pump is started, while the first is regenerated removing the liquid nitrogen, the trapped gas is expelled through the blow-off valve. The pump (with zeolite) is heated to 200-300°C to remove water vapour. Charcoal pumps are heated to about 100°C. 

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. 

Zeolites (3 were treated with a NaBO, solution, and the porous properties of boronated samples were investigated by sorption measurements with benzene and nitrogen as adsorbate, TEM, SEM and composition analysis. It is shown that the micropores are converted into the mesopores and the mesopores are developed into larger mesopores due to the extraction of framework silicon by base. The small atom size of boron and the poor stability of boron in framework should be responsible for the silicon removal in a large amount. The dissolution of silicon also causes the corrosion of outer surface of particles and the decrease of particle size. 

Influence of Presorbed Water on the Sorption of Nitrogen by Zeolites at Ambient Temperatures... 

Figure 1. Isotherms for sorption of nitrogen on zeolites (a) NaA, (b) CaA, (c) NaX, and (d) NaY at (O) 10°C, (A) 25°C, and O 40°C. The ordinate is in units of g nitrogen/100 g dehydrated zeolite. Sorption data are shown as open symbols, desorption data, as filled symbols.

The observed sorption capacity Q for nitrogen is shown as a function of pressure p, for the dehydrated zeolites in Figure 1. Here, and throughout this paper, sorption capacities are expressed as one-hundred times the mass sorbate x per unit mass of dehydrated sorbent m,... 

Table VII. Reported Sorption Capacities for Nitrogen on Zeolite NaA at 25°C and Atmospheric Pressure...

Of particular interest in the present study is the apparent existence of an activated sorption mechanism for nitrogen in partially hydrated zeolite NaA, a further study of which is planned. The less definitely established irreversibly sorbed nitrogen on dehydrated zeolites NaA and NaX, but not on CaA and NaY, is in need of confirmation, and of further characterization. A practical utility of the results is the quantifying of nitrogen uptake from air, which persists even with appreciable sorbed water. This amount can be approximated from the isotherms as the capacity at 0.8 atm. inasmuch as the contribution due to oxygen is very small. Conversely, the isotherms can be used to assess the state of hydration of a zeolite, with the aid of a measurement of the amount of sorbed nitrogen, either by mass loss on evacuation at room temperature in a balance, or by collection of gas evolved on immersion of a sample in water. 

Sorption effects in the macroscopic scale are usually used for non-continuous pumping. They contain a highly porous sorption material like activated carbon or zeolites with a huge inner surface. The sorption material is usually cooled down by liquid nitrogen. They are regenerated by heating the sorption material to temperatures of several hundred degrees Celsius after a disconnection of pump and vacuum-chamber. 

A water pump can reach pressures of 1 Torr. An oil vacuum pump can reach 20 mTorr. A turbomolecular pump can reach pressures of 10 10 Torr (10-8 Pa). A sorption pump can reach pressures of 10-2 Torr by exposing the system to a porous zeolite cooled to liquid nitrogen temperature with a Dewar flask placed on the outside. 

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