USHY zeolite

The experimental methods used to recover the compounds retained in the USHY zeolite after reaction ("coke") as well as to analyze them have already been described (ref. 9). It has been shown that the treatment of solubilization of the zeolite by hydrofluoric acid did not cause any transformation of the coke constituents (ref. 10). 

Kinetic Parameters for Reaction of 2-Methylpentane on USHY Zeolites at 400 C... 

Other Reactions on Zeolites. - Coke deposits on USHY, H-OFF, and HZSM-5 zeolites were characterized by EELS. The EELS spectra were taken on small areas during a short period of time to minimize specimen drift and electron beam-induced damages. Because of this, the spectra were too noisy to proceed with a data reduction, and therefore no quantitative treatment of the EELS spectra was attempted. A qualitative analysis was carried out, comparing the spectra taken on the coked zeolite (or on the insoluble coke) with the EELS spectra taken on reference carbon compounds of known structure. Figure 5 shows the results. It was found that in HZSM-5 and H-OFF the coke forms an external envelope around the zeolite crystal and stands as an empty mold after zeolite extraction. Its structure is similar to that of coronene (polyaromatic-pregraphitic). In USHY zeolite, the coke has a structure more like pentacene (linear polyaromatic). 

The coke deposited during the cracking of n-nonane on USHY zeolite was also characterized with this technique ". The CP/MAS - NMR spectra were recorded after 15,30,60 and 450 sec of reaction. Figure 8 shows these spectra. It was found that the coke contained both aliphatic and aromatic components. As time on stream increased, the intensity of the signal that corresponds to the sp region at 13 ppm (methyl groups) and at 30 ppm (tertiary carbon groups)... 

USHY- zeolite, coked with n-nonane. From Ref 84... 

We show here that a deep change in the composition of coke and on its effect on the zeolite acidity and activity can occur even for treatment under nitrogen flow at relatively low temperatures (250°C). A USHY zeolite was chosen for this study, coke being formed during m-xylene transformation through isomerization and disproportionation at 250 C. 

Figure 1 shows that there is a very rapid deactivation of the USHY zeolite m-xylene conversion passes from 55% at 2 minutes to 3% at 75 minutes. This deactivation can be related to the retention of carbonaceous compounds on the zeolite ( coke ). The coke content of the zeolite first increases very rapidly with time-on-stream then more slowly. 

Fig. 3. Percentage of the various coke families deposited after 18 minutes reaction at 250°C on the USHY zeolite as a function of the ageing time under nitrogen flow at the reaction temperature. (I) Insoluble part of coke.

Catalyst deactivation during catalytic cracking of n-octane, isooctane and 1-octene over USHY zeolite at mild conditions and short times on stream... 

Aim of this work is to study the influence of the reactant on the coking process and the catalyst deactivation, as well as the product distributions. Therefore, the cracking of n-octane, isooctane and 1-octene was investigated in a fixed bed reactor, over USHY zeolite (0.5gr), at a range of temperatures, with two different reactant mole fi actions in the feed stream, and 20 min. time on stream. 

USHY zeolite was kindly provided by GRACE DAVISON (Germany) in a calcinated powder size of 1pm. The catalyst was pressed into a large pellet using an infrared tableting press, crushed, and then sieved to 1.0-1.7 mm. Before the experiment, 0.5gr of the resulting catalyst were placed in an oven and heated to 200 "C for 2 hr, to remove humidity and ensure the desirable performance. 

The product distribution and the deactivation of USHY zeolite during n-octane, isooctane and 1-octene reactions were studied and the results showed that reactant feed composition influences the final coke content, but not the reaction mechanism resulting in similar product distributions. Isobutane was found in all reactants to be the dominant product. 1-octene only showed a high tendency towards oligomerisation, and that is the reason for the higher coke amounts measured than the other two reactants. At lower isooctane and 1-octene compositions the coke content decreased with increasing temperature. An analysis of coke composition is essential to be carried out in future work and will provide us with better understanding of the mechanisms involved in coke formation. 

Coking, aging and regeneration of zeolites. XIII- Composition of the carbonaceous compounds responsible for the deactivation of a USHY zeolite during toluene disproportionation, submitted for publication. 

Groten W.A., Wojciechowski, B.W. and Hunter, B.K. (1990), Coke and deactivation. II- Formation of coke and minor products in the catalytic cracking of n-hexane on USHY zeolite, J. Catal. 125, 311-324. 

Oxidation of 1-MN (900 ppm) was carried out at various temperatures (300 to 450" C), at high GHSV (18,000h ) and in wet air (50% relative humidity) over a USHY zeolite, which is a readily available and thermally stable zeolite. 

Figure 5.12. Influence of the time of reaction on the global conversion of 1-MN (a) and on the carbon dioxide yield (b) over a USHY zeolite at 300°C ( ), 400°C (A) and 450°C ( ).

MN is transformed into CxHyOz compounds before its complete oxidation into carbon dioxide. At a low temperature (300 C), the reaction rate V2 is very low and only CxHyOz compounds are formed and retained initially in the pores of the zeolite. When the temperature increases, the reaction rate increases since the USHY zeolite possesses active acid sites able to transform CxHyOz into carbon dioxide. These sites, which are able to transform aromatic compounds into carbon dioxide, were specifically attributed to strong acid sites. 

Figure 5.13. 1-MN conversion (a) and carbon dioxide yield (b) taken after 7h of reaction as a function of temperature over USHY zeolite in the absence (A) and presence ( ) of NH3.

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