Zeolites pelletization

Zeolite Pellets or granules of aluminum silicate, used in water treatment or aircleaning applications. 

Fig. 5.3.3 (A) NMR spectrum of hyperpolarized 129Xe in NaX zeolites. (B) 2D slice in the flow direction of a 3D chemical shift selective MRI of gas in the zeolite pellets. (C) 2D slice perpendicular to the flow direction of the same 3D chemical shift selective MRI as in (A). Adapted from Ref. [14].

Fig. 5.3.8 Photograph of the detection region of the NMR probe with radiofrequency coil. A methane—air mixture was ignited above the zeolite pellets. The mixture also contained xenon for NMR detection. Hp-129Xe NMR spectra with 30% xenon (from high-density xenon optical pumping) in 70% methane is depicted. (1) The spectrum in the absence of combustion and (2) the spectrum during combustion. Adapted from Ref. [2],...

Alkylation of benzene with propylene was carried out with the acid zeolites, pelletized, crushed, and sieved at 0.25-0.42 mm diameter. The reaction was performed in an automated high pressure stainless steel reactor, at 3.5 MPa, temperatures ranging from 125 to 200°C, WF1SV from 12 to 18 h"1 referred to the olefin, and benzene to propylene (B/P) molar ratio of 3.5. More details can be found in [7]. 

Hydrated Zeolites. The zeolitic pellets are hydrated by equilibration at atmospheric moisture content. The cell is immersed in liquid air, and a minimum equilibrium temperature of — 120°C was obtained. At that temperature the conductivity and capacity of the samples are measured over the frequency range 200-107 Hz. After eliminating the cooling liquid, the temperature rises slowly (0.5°C/min). Measurements are performed continuously in the same frequency range during the. temperature rise up to room temperature. The results are near-equilibrium values, and the errors are assumed to be the same over the complete temperature range. The same procedure was applied by Mamy for dielectric measurements on montmorillonite 11). 

Early work was done with a sized fraction (about 0.1 mm) obtained by grinding zeolite pellets which contained a significant amount of binder. Subsequently, the pure zeolite powder was used. In all cases the zeolite was washed with a large volume of dilute salt solution, sometimes containing a small amount of acetate buffer at about pH 5.5, and precautions were taken to avoid hydrolytic precipitation of the metals. 

Cells 1 and 2 of the barrier frame were filled with 8-14 SMZ while Cell 3, adjacent to the pilot-test tank wall, was filled with iron/surfactant-modified zeolite pellets (Fe/SMZ pellets, see below). During refilling, sheets of plywood were temporarily placed against the inner faces of the barrier frame to retain the fill material. The SMZ was transferred using a conveyor belt that ran from the outside the pilot-test tank to the appropriate cell. While the SMZ was loaded in the barrier frame the samplers were reinstalled in their original positions. The annular space between the plywood and the outer perforated metal of the frame was filled with aquifer sand. The plywood was then pulled out of the cell using a jack and appropriate blocking. 

In order to study the catalyst deactivation phenomenon under supercritical conditions and the difference between the liquid phase (LP) and supercritical fluid phase (SCFP) reactions, experiments were carried out in an isothermal tubular reactor (D=I2 mm, L=600 mm) packed with grounded Y-type zeolite pellets of 60 mesh. The experimental equipment for the LP and SCF reaction processes is illustrated in Figure 1. 

A Mossbauer transmission cell similar to that prepared by Delgass and coworkers (20) was used for all Mossbauer experiments. Zeolite pellets between 200 mg and 300 mg were used as samples. 

A gaseous mixture of CO ( C/ C = 0.011, natural abundance) and helium as a carrier gas was introduced into a small column of zeolite pellets for a selected time, then desorbed by evacuation of the column. 

The gas chromatograph (GC 9-A Shimadzu Co., Ltd.) was used with helium carrier. Siliceous zeolite pellets (with binder) were crashed and screened to obtain particle size between 4.95 x 10" to 8.33 x 10" m (an average particle radius of 6.64 x 10" m) and packed to the column (length, 30cm, diameter, 3mm). The experimental column pressure was kept 200 kPa, Ae experimental column temperature was kept at 393, 423 and 453 K, respectively. Pulse responses of vaporized chloroform with helium were detected by TCD. Response data were stored and processed by a personal computer. 

C. Application of Pulsed-Pield Gradient NMR to Zeolite Pellets... 

Fig. 2. Mass transport parameters in zeolite pellets as determined by PFG NMR and TD NMR (42).

T iffusion in porous pellets is often the rate-limiting process in industrial adsorption or catalytic processes. Much useful work in this field has been done by Smith and coworkers (3, 5), but for molecular sieve pellets the situation is complicated by diffusion in the zeolite crystal itself, as well as through the pores formed between the crystals. Few studies have been made of zeolite crystal diffusion, but Barrer and Brook (1) reported some results on diffusion of simple gases in various cation-substituted mordenites, and Wilson (7) gives some indirect results from the study of separation of CO2 from air using a fixed bed of type 4A zeolite pellets. In the present work, results have been obtained by studying self-diffusion of CO2 in a single pellet of type 5A zeolite under controlled conditions. The experimental results were fitted satisfactorily by a very simplified model of the pellet structure, which made it possible to deduce approximate values of the self-diffusion coefficients for both pore and crystal diffusion. 

Catalyst Preparation. Catalyst preparation consisted of the exchange of nickel or cobalt nitrate for the sodium cation. Ratios of nickel or cobalt to sodium of 20 1 were used for maximum exchange and the ion exchanged zeolite pellets were leached with deionized water. Catalyst preparations were reduced for 16 hours at 400°C in a stream of hydrogen. Similar procedures have been reported (5, 6). 

Study of the Deactivation of an HY Zeolite Pellet using Xe NMR Spectroscopy and NMR Imaging... 

Combined use of Xe NMR and H-imaging NMR shows that coking of an HY zeolite pellet results in a heterogeneous distribution both at the nanometric and macroscopic scales. This distribution depends upon the direction of the flow of reactant. It was also observed how diffusion of dimethylpentane occurs through both uncoked and coked sections of the pellet. 

Xe NMR is particularly helpfiil to study the coking of HY zeolite pellets. The presence of two signals in the spectra clearly shows the heterogeneous distribution of coke at the nanometric scale. This heterogeneity depends on the direction of the flow of the reactant. 

It is well known that water adsorption in zeolites releases heat while water desorption absorbs heat. This phenomenon has been exploited for the design of a heat pump for cooling applications using waste heat or solar energy. Currently, zeolite pellets are used, and the heat and mass transfer are inefficient, leading to bulky pumps. Recently, there have been renewed interests in zeolite coating heat pumps. A new in situ... 

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