Conversion over Zeolitic Catalysts

1 Conversion over Zeolitic Catalysts - The examined starting material was dipentene provided by Arizona Chemical, Florida, USA. This vendor offers a large product spectrum of several dipentenes. For the present work dipentene Sylvapine DP-738 (formerly named Acintene DP-738) was used. Its components 

The experiments were conducted with the following catalysts (Table 9)  

Catalyst Si02tAl20j Acid strength Acid strength Ce content Pd content BET area A o(pAa) TPD(iO nNH3/g) (wt%) (wt%) (m /g) 

The monocyclic terpenes are easily disproportionated to the dehydrogenated p-cymene and the hydrogenated /7-menthane. For a short time on stream TOS ( 2 h), cracking of /)-cymene to toluene and propane/propene on the strongly acidic sites is the dominant reaction. With increasing TOS, these strong acid sites of the catalysts deactivate and, thus, the formation of products obtained by cracking decreases. 

The conversion of a-pinene over the Ce-promoted, zeolite-supported Pd catalysts proceeds via an acid-catalysed ring opening of the bicyclic terpene to a monocyclic terpene, e.g. a-limonene. This is followed by dehydrogenation, possibly via isomerization to a-terpinene or y-terpinene. 1,8-Cineole is dehydrated on the acid sites to p-menthadiene prior to dehydrogenation to p-cymene on the Pd sites of the catalyst. The conversion of all reactants is complete during the test run of 8 h. The results are quite similar to a-limonene conversion, as expected from the reaction pathway via p-menthenes and p-menthadienes. 

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In hydrocarbon conversion over zeolite catalysts, the formation and retention of heavy products (carbonaceous compounds often called coke ) is the main cause of catalyst deactivation. 5X 77 XI1 These carbonaceous compounds may poison or block the access of reactant molecules to the active sites. Moreover, their removal, carried out through oxidation treatment at high temperature, often causes a decrease in the number of accessible acid sites due to, e.g., zeolite dealumination or sintering of supported metals. 

The goal of the molecular-beam, mass-spectrometry (MBMS) studies of biomass pyrolysis product conversion over zeolite catalysts is to provide rapid characterization, in real time, of the fate of the complex reactants as a function of reaction parameters. This technique allows the qualitative observation of transient, reactive and high molecular weight reactants and products that might otherwise escape detection by conventional collection and analysis methods. The goal is to optimize gasoline yields from biomass, at this small scale, by evaluating a typical Mobil HZSM-5 zeolite in its ability... 

Mole s reaction path for olefin formation via toluene. Adapted from Mole T, Bett G, Seddon D. Conversion of methanol to hydrocarbons overZSM-5 zeolite an examination of the role of aromatic hydrocarbons using IScarbon- and deuterium-labeled feeds.] Catal 1983 84 435—45 Mole T, WhitesideJA, Seddon D. Aromatic co-catalysis of methanol conversion over zeolite catalysts.] Catal 1983 82 261-6. 

Mole T, Whiteside JA, Seddon D. Aromatic co-catalysis of methanol conversion over zeolite catalysts. 

Chang, C.D. and Silvestri, A.J. (1977) The conversion of methanol and other 0-compounds to hydrocarbons over zeolite catalysts. J. Catal., 47, 249. 

The pyrolysis gas chromatogram of ABS at 550°C changes considerably when the pyrolysis products are passed over zeolite catalysts. The specific activity towards certain reactions, e.g., cycliza-tion, aromatization, or chain cleavage is somewhat dependent on the nature of the individual zeolite. In general, enhanced benzene, toluene, ethylbenzene at the cost of dimer, trimer formation is observed. Nitrogen containing compounds do not appear in the pyrolysis oil after catalytic conversion. However, the product gas is rich in nitriles (132). 

The vapor-phase acylation of pyrrole was carried out over zeolite catalysts such as HZSM-5(19.7), HZSM-5(30), HZSM-5(280), HY, and cation-promoted modified zeolites like CeHZSM-5(30), LaHZSM-5(30), and CeHY, in a fixed-bed reactor at atmospheric pressure using acetic anhydride as an acylating agent <1998CAL95>. The catalytic activity of the zeolite catalysts was dependent on the reaction temperature and the type of cation polymer used in the modification of the zeolite surface. The acylation was found to be more active on Br0nsted acidic sites available over zeolite systems. The yield of l-(l//-pyrrol-2-yl)-l-ethanone 376 with respect to the conversion of pyrrole on HZSM-5(280) at 250 °C was 75.5% (Equation 87). 

With increasing temperatures the NO conversion over most catalysts of this group passes throu a maximum (33). Cu/ZSM-5 has the highest maximum at the lowest temperature, namely, 500°C. The activity of Cu in other zeolites, e.g., mordenite, ferrierite, faujasite, /3 and L, is distinctly lower (33,35). A rough correlation seems to exist between activity and Si/Al ratio of these zeolites (33) Li and Hall state, however, that the Si/Al cannot be the sole controlling factor, because Cu/Y and dealuminated Cu/Y have very similar activities (i5). 

The % aniline conversions as a function of time on stream at three reaction temperatures show for the two zeolite catalysts (Figure 2) an increase as the temperature increases. The aniline conversion over LiY catalyst is higher than that over NaY at any reaction temperature. It was reported that both acid and basic... 

Eecently a study was made of the intracrystalline catalytic dehydro-halogenation patterns of two-carbon haloalkanes over zeolite catalysts in continuous flow systems (108). At 260°, REX, NaX, NiX, AgX, HY, metal-hydrogen Y, and Linde 5A zeolites all converted substantial amounts of ethyl chloride to ethylene in gas phase reactions, while amorphous silica-alumina was considerably less reactive. Catalysts such as y—AI2O3 or CaCl2 require temperatures of 360-420° for comparable conversions (109). With REX, conversion increased rapidly from about 5% at 150° to nearly 100% at 316° and higher. 

Results in Fig. 3 show a strong influence of space velocity on the initial propane conversion activity and product selectivity in the propane aromatization over zeolite catalyst without and with silica binder (50 wt%). Results showing a comparison of the zeolite catalysts with and without silica binder (50 wt%) for their product selectivity, dehydrogenation/ cracking (D/C) and aromatization/cracking (A/C) activity ratios and also p-X/m-X ratio (or shape selectivity) in the propane aromatization at two different iso-conversions (5 and 25%) of propane are presented in Table 4. The comparison brings out following important effects of... 

Aromatization of paraffins is one of the most important conversion process for the production of the aromatics which is of great interest in both petroleum (as gasoline blender) and petrochemical industries. The conversion of lower alkanes to higher value products like benzene, toluene and xylenes over zeolite catalysts is well studied reaction [1-4]. A process for the transformation of propane and butane to aromatics has been developed and commercialized jointly by UOP and BP [5]. The technical feasibility of C3-C4 stream aromatization has been demonstrated by 1000 bbl/day Cyclar process at Grangemouth, U.K. and 200 bbl/day Z-forming pilot plant at Kawasaki Refinery of Mitsubishi Oil, Japan. Both these processes employ high silica, medium pore ZSM-5 zeolite based catalysts for aromatization. 

Conversion and selectivity of ethylbenzene dehydrogenation over zeolite catalysts... 

Figure 8. Proposed reaction mechanism for the conversion of allyl alcohol over zeolite catalysts.

Taking into account the investigation results of propane interaction with one of aromatization reaction products, i.e. with benzene [6-7], the study of C6H6 C3Hg mixture conversion over mixed catalysts (MC) containing zeolite H-form and PRAC was carried out. Table 4 shows the influence of mole ratio on the conversion of C6H6 C3Hg mixtures. 

C.D. Chang and A.J. Silvestri. The Conversion of Methanol and Other O-Com-pounds to Hydrocarbons over Zeolite Catalysts. J. Catal. 47 249 (1977). 

Recently, selective synthesis of / -cymene from toluene and propane or isopropanol over zeolite catalysts has been thoroughly investigated. Zeolite-based processes avoid the disposal of spent catalyst, product contamination by the catalyst, separation of the catalyst from the product and corrosion of the reactor and tubes. The results using various zeolite types were promising. However, the formation of undesired -propyl toluene is observed particularly in the presence of MFI type zeolites, whereas large pore zeolites yield significant amounts of m-and o-cymene besides the desired / -cymene. However, low conversion and relatively low selectivity are the drawbacks of these investigations. 

P. V. Menacherry, G. L. Haller, Neopentane conversion over zeolite-supported platinum and palladium catalysts, J. Catal, 1997, 167, 4254-37. 

Conversion of alkylbenzenes over zeolite catalysts. I-Dealkylation and disproportionation of ethylbenzene over... 

Fig. 19.7 NOx conversion in NH3-SCR over zeolite catalysts after hydrothermal ageing for 64 h at 670 °C. Reaction conditions ...

Experiments with conversion of MeOH in the presence of benzene [109,123], alkylation of ethylene with toluene [124], and alkylation of ethylene with ethylbenzene [125], over zeolite catalysts, show high yields and conversions to the corresponding ethylated analogs. This suggests that ethylene oligomerization and methylation (alkylation of ethylene by methanol) reactions are not very important under MTO conditions. So, the ethylene is relatively inert compared to other olefins under MTO conditions. 

Chang CD, Lang WH, Smith RL. The conversion of methanol and other O-componnds to hydrocarbons over zeolite catalysts II. Pressure effects. J Catal 1979 56 169-73. 

The process which was developed hy DOW involves cyclodimerization of hutadiene over a proprietary copper-loaded zeolite catalyst at moderate temperature and pressure (100°C and 250 psig). To increase the yield, the cyclodimerization step takes place in a liquid phase process over the catalyst. Selectivity for vinylcyclohexene (VCH) was over 99%. In the second step VCH is oxidized with oxygen over a proprietary oxide catalyst in presence of steam. Conversion over 90% and selectivity to styrene of 92% could he achieved. ... 

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