Zeolite particle size

In the present study the effect of zeolite particle size (micro- vs. nano-particles) and N20 concentrations on ODHP is studied over Fe modified BEA zeolites. The feasibility of periodic reactivation over Fe-BEA catalysts by oxygen pulses for continuous C3H6 production has been also evaluated. 

The development of a successful zeolite/polymer mixed-matrix membrane with properties superior to the corresponding polymer membrane depends upon good performance match and good compatibility between zeolite and polymer materials, as well as small enough zeolite particle size for membrane manufacturing on a large scale. 

C., Tatlier, M., Erdem-Senatalar, A., Schoeman, B., and Sterte, J. (2000) Effect of zeolite particle size on the performance of polymer-zeolite mixed matrix membranes./. Membr. Sci., 175 (2), 285-288. 

The characteristics of the solid particles of catalyst (size, mechanical resistance, etc.) have to be adapted to the reactor. In many organic reactions catalysed by acid zeolites, the catalytic act is concentrated in the outer rim of the crystals and decreasing the zeolite particle size generates a significant gain in activity. However, the use of small particles in batch reactors causes serious drawbacks in the separation of the zeolite from the reaction mixture for the recovery of reaction products and the eventual reuse of the catalyst. Also, small particles cannot be used in fixed bed reactors because of excessive pressure drops. 

A method for determining the effect of particle size on the effective permeability values of zeolite-polymer mixed matrix membranes has been developed in this study. The model presented is a modified form of the effective medium theory, including the permeability and thickness of an additional phase, the interphase, which is assumed to surround the zeolite particles in the polymer environment. The interphase thickness and permeability values were determined by taking into consideration the assumptions that in case the size of the zeolite particles is held constant, the interphase thickness should be equal for different gases and in case the zeolite particle size is varied, the interphase permeability should remain constant for the same gas. The model seems to fit the experimental permeability data for O2, N2 and CO2 in the silicalite-PDMS mixed matrix membranes well. 

The zeolite particle size can be toned to minimize mass transport resistance into the particle and thus increase activity. 

The relationship between cation radius and hydrated cation radius, at 298 K, is depicted in Fig. 2 [59N1, OlPl]. The radius of a fully hydrated ion is proportional to the ionic charge, but not proportional to the ionic radius without H2O shell. Cs rm- 1-69 A, rhyd= 3.29 A) is exchanged more easily thanUE (rion= 0.60 A, rhyd= 3.82 A) or Be = 0.31 A, rhyd = 4.59 A) [59N1, 88M2]. The elevated temperatures normally enhance the ion-exchange reactions, while the pH is also critical, particularly in the case of acidic solutions, because small H" cations are very mobile and reactive over many other cations. Other factors concern the solid/liquid ratio, the zeolite particle sizes, and the treatment time. As mentioned above, this discussion is valid in case of alkali or alkaline-earth element cations which are practically stable in aqueous solutions. 

In pharmaceutical preparations and fruit juices, ascorbic acid is readily separated from other compounds by TLC on silica gel and quantified directly by absorption at 254 nm. Serum and plasma may be deproteinized with twice its volume of methanol or ethanol. Various ascorbic acid compounds in plant extracts and foods have been separated on cellulose layers and detected by spraying with 2,S dichlorophenol indophenol (36). Heulandite, a natural zeolite (particle size 45 p) has successfully been employed as an adsorbent and ascorbic acid and other hydrophilic vitamins have separated within 5 cm by ascending chromatography in dimethylformamide (37). HPTLC and OPLC methods have been developed to improve the separation of ascorbic acid from other water soluble vitamins, with mixed success (11). 

Rajagopalan, K., Peters, A.W. and Edwards, G.C., "Influence of zeolite particle size on selectivity during fluid catalytic cracking". Applied Catalysis, 23, 69-80 (1986). 

Besides the position of the Pt clusters, the zeolite particle size is another important parameter for selective hydrogenation of the trans fatty acid methyl ester isomer. Larger crystals have a higher ratio of internal to external surface and consequently a lower ratio of external to internal Pt clusters, which induce an improving hydrogenation selectivity. Also the Si/Al ratio influences the catalytic system. A Pt/ZSM-5 catalyst with an Si/Al ratio up to 80-150 results in further improvement of the reaction selectivity based on shape selectivity of diffusional origin. 

In particular, emphasis will be placed on the use of chemisorption to measure the metal dispersion, metal area, or particle size of catalytically active metals supported on nonreducible oxides such as the refractory oxides, silica, alumina, silica-alumina, and zeolites. In contrast to physical adsorption, there are no complete books devoted to this aspect of catalyst characterization however, there is a chapter in Anderson that discusses the subject. 

The functions of the filler and the binder are to provide physical integrity (density, attrition resistance, particle size distribution, etc.), a heat transfer medium, and a fluidizing medium in which the more important and expensive zeolite component is incorporated. 

As can be seen in the graph, the Y/TUD-1 catalyst was twice as active as the commercial Y catalyst. This is primarily due to its very high calculated diffusivity of 131x10 cm /sec, which is over 10 times the diffusivity calculated for commercial zeolite Y, 11x10 cm /sec. Extrapolation of the curve to zero particle size shows that the commercial Y zeolite is in fact intrinsically more active than the Y zeolite embedded in the TUD-1. If the Y zeolite in TUD-1 had been optimized for this reaction like the commercial Y catalyst, one should expect an even greater boost in performance. 

Table 2 Porosymmetry and Particle Size Data for Zeolites ...

In spite of such positive effects of the presence of ammonia during preparation, the particles sizes remain important on Au/FAU-2, comparable to particles previously described for similar Au/zeolites [1,2]. Noticeably, they are much bigger than expected from the insertion of the Au particles inside the pores. On the contrary, very small gold nanoparticles with a mean diameter of about 2 nm are obtained on the BEA support, that can be due to the textural properties and high external surface area of this support made... 

Testing of the catalyst was performed in the dual-fluidized bed reactor, where in the first reactor pyrolysis of the biomass and in the second upgrading of the pyrolysis vapours through catalytic de-oxygenation occurred. The bed material in the pyrolysis section was 40 g of quartz sand with a particle size distribution of 100 - 150 pm. The particle size of the catalyst was 250 - 355 pm. The amount of zeolite used in each experiment was 1.75 g. The biomass raw material used in the experiments was pine... 

The transformation of n-hexadecane was carried out in a fixed-bed reactor at 220°C under a 30 bar total pressure on bifunctional Pt-exchanged HBEA catalysts differing only by the zeolite crystallites size. The activities of the catalysts and especially the reaction scheme depended strongly on the crystallites size. Monobranched isomers were the only primary reaction products formed with the smallest crystallites, while cracking was the main reaction observed with the biggest crystallites. This was explained in terms of number of zeolite acidic sites encountered by the olefinic intermediates between two platinum particles. 

Fe-zeolites were prepared using the NH4 form of BEA Si/Al = 13.5. Parent BEA zeolite (average particle size of 300 nm or 1pm) was dried at 150 °C for 4 h and then mixed with a solution of FeCl3 in acetyl acetone. After 12 h of mixing, excess of the solution was removed, the solid was dried at room temperature and heated under vacuum at 350 °C for 4 h. A sample was washed with distilled water and dried in an air at room temperature. Then, the remaining organic species in the Fe-zeolites was removed by calcination at 450 °C in air for 10 h. The produced catalysts contain 0.6 wt% of Fe. This preparation procedure predominantly provides iron introduction into cationic sites [3], Two types of catalysts were prepared, Fe-BEA with a particle size of 1 pm (Fe/m-BEA) and Fe-BEA with particle size of 300 nm (Fe/n-BEA). 

Figures 1 shows the catalytic performance of the Fe-BEA catalysts in the temperature range of 250-550 °C. It is clear from the figure that propylene yield depends on particle size of the parent BEA zeolite. Effect of the N20 concentration has been analyzed under reaction regimes RS-1 and RS-2. Increase in N20 concentration resulted in the same propene yields but increased the N20 conversion and decreased the selectivity toward propylene. At higher temperature has been obtained increases in the formation of the molecular oxygen which further accelerates production of the undesired carbon oxides. Thus, at lower feed concentration of N20, i.e. at 1 1 feed ratio of reactants (RS-1), formation of carbon oxides is suppressed and the selectivity of ODHP reaction is...

After the catalytic runs no modification of mean particle size is observed for this last system. Conversly, Ru CO) deposited on silica-alumina is readily decomposed at 200°C to metallic particles of 1 nm mean size which are also catalysts for the F-T synthesis. The catalytic activity at 200°C is C i one tenth of the Y zeolite supported ones and methane is practically the only hydrocarbon formed. Electron microscopy examination of the catalyst after reaction reveals a drastic sintering of the... 

Fischer-Tropsch synthesis could be "tailored by the use of iron, cobalt and ruthenium carbonyl complexes deposited on faujasite Y-type zeolite as starting materials for the preparation of catalysts. Short chain hydrocarbons, i.e. in the C-j-Cq range are obtained. It appears that the formation and the stabilization of small metallic aggregates into the zeolite supercage are the prerequisite to induce a chain length limitation in the hydrocondensation of carbon monoxide. However, the control of this selectivity through either a definite particle size of the metal or a shape selectivity of the zeolite is still a matter of speculation. Further work is needed to solve this dilemna. 

Figure 9. Particle size distribution for the various (M)ZSM-5 zeolites, as computed from SEM (Reproduction with permission, from ref (26), Elsevier, Sci. Publ. Co.) ...

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