Zeolite conversion over

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. ... 

The results in Table 3 show that H-mordenite has a high selectivity and activity for dehydration of methanol to dimethylether. At 150°C, 1.66 mol/kg catal/hr or 95% of the methanol had been converted to dimethylether. This rate is consistent with that foimd by Bandiera and Naccache [10] for dehydration of methanol only over H-mordenite, 1.4 mol/kg catal/hr, when extrt lat to 150°C. At the same time, only 0.076 mol/kg catal/hr or 4% of the isobutanol present has been converted. In contrast, over the HZSM-5 zeolite, both methanol and isobutanol are converted. In fact, at 175 X, isobutanol conversion was higher than methanol conversion over HZSM-5. This presents a seemingly paradoxical case of shape selectivity. H-Mordenite, the zeolite with the larger channels, selectively dehydrates the smaller alcohol in the 1/1 methanol/ isobutanol mixture. HZSM-5, with smaller diameter pores, shows no such selectivity. In the absence of methanol, under the same conditions at 15(fC, isobutanol reacted over H-mordenite at the rate of 0.13 mol/kg catal/hr, higher than in the presence of methanol, but still far less than over H M-5 or other catalysts in this study. 

Figure 3 Comparison of decal in conversion over proton-form zeolites (filled) and Pt-zeolites (open). H-Beta-25 ( , ), H-Beta-75 (, O), H-Y-l 2 (A, A).

The initial conversions of toluene in toluene disproportionation carried out at 500 °C follow the order ZSM-5 < SSZ-35 = Beta < SSZ-33 (Fig. 1). This order cannot be directly related to the increasing pore size or connectivity of individual zeolites. In such case SSZ-35 should exhibit a lower conversion compared with ZSM-5 and toluene conversion over zeolite Beta should be higher or comparable with that over SSZ-33. 

Toluene alkylation with isopropyl alcohol was chosen as the test reaction as we can follow in a detail the effect of zeolite structural parameters on the toluene conversion, selectivity to cymenes, selectivity to para-cymene, and isopropyl/n-propyl ratio. It should be stressed that toluene/isopropyl alcohol molar ratio used in the feed was 9.6, which indicates the theoretical toluene conversion around 10.4 %. As you can see from Fig. 2 conversion of toluene over SSZ-33 after 15 min of T-O-S is 21 %, which is almost two times higher than the theoretical toluene conversion for alkylation reaction. The value of toluene conversion over SSZ-33 is influenced by a high rate of toluene disproportionation. About 50 % of toluene converted is transformed into benzene and xylenes. Toluene conversion over zeolites Beta and SSZ-35 is around 12 %, which is due to a much smaller contribution of toluene disproportionation to the overall toluene conversion. A slight increase in toluene conversion over ZSM-5 zeolite is connected with the fact that desorption and transport of products in toluene alkylation with isopropyl alcohol is the rate controlling step of this reaction [9]... 

In toluene disproportionation the highest toluene conversion was achieved over SSZ-33 due to a high acidity combined with 3-D channel system. High toluene conversion over SSZ-35 results from its strong acidity and large reaction volumes in 18-MR cavities. Toluene conversion in the alkylation with isopropyl alcohol is influenced by a high rate of competitive toluene disproportionation over SSZ-33. ZSM-5 exhibits a high p-selectivity for /7-isopropyl toluene, which seems to be connected with diffusion constraints in the channel system of this zeolite. 

SYNGAS CONVERSION OVER RUTHENIUM/ZEOLITE CATALYSTS AT 51 atm,... 

The bi-functional conversion of 2,2,4-trimethylpentane over Pt/DAY has been recently reported by Jacobs et al. (104). It was compared to the corresponding conversion over Pt/H-ZSM-5 and Pt/H-ZSM-11. All three zeolites had the same chemical composition. The authors found that 2,2,4-trime-thylpentane underwent 3-scission over Pt/DAY, while the formation of feed isomers was favored over the other two catalysts. The differences in reaction products were related to differences in the pore geometry of the zeolites. A similar study was carried out with n-decane. 

A.B. "Shape Selective Conversion Over Intermediate Pore Size Zeolite Catalysts" Am. Inst, of Chem. Eng. 72,... 

Elementarf Steps of Hydrocarbon Conversion over Zeolites 429... 

The third and last part of the book (Chapters 12-16) deals with zeolite catalysis. Chapter 12 gives an overview of the various reactions which have been catalyzed by zeolites, serving to set the reader up for in-depth discussions on individual topics in Chapters 13-16. The main focus is on reactions of hydrocarbons catalyzed by zeolites, with some sections on oxidation catalysis. The literature review is drawn from both the patent and open literature and is presented primarily in table format. Brief notes about commonly used zeolites are provided prior to each table for each reaction type. Zeolite catalysis mechanisms are postulated in Chapter 13. The discussion includes the governing principles of performance parameters like adsorption, diffusion, acidity and how these parameters fundamentally influence zeolite catalysis. Brief descriptions of the elementary steps of hydrocarbon conversion over zeolites are also given. The intent is not to have an extensive review of the field of zeolite catalysis, but to select a sufficiently large subset of published literature through which key points can be made about reaction mechanisms and zeolitic requirements. 

Figure 3a is a schematic of the functionalized zeolite beta. Figure 3b plotted the catalytic conversion of HEX and PYC over 6 A zeolites as a function of time. For sulfonated zeolite (Z-S03H), more than 60 % HEX was converted in 4 hours, and nearly complete conversion was observed over 12 hours. On the other hand, PYC, which has a large molecular size and cannot enter the microporosity, showed less than 8 % conversion over extended reaction time with same Z-S03H as catalyst. Both HEX and PYC were also reacted over pure zeolite beta (Z), and the TMMPS functionalized zeolite (Z-SH) before it was treated with H202. Pure zeolite and Z-SH showed low catalytic activity, and only a small fraction of either HEX or PYC was converted. Further evidence of the size selectivity is provided when amines of different sizes are used to poison (neutralize) the acid sites (19). As shown in Figure 3c, the... 

It is proposed that the high selectivity to isomers even at high conversion is obtained because the formation of n-hydrocarbon from the monomethyl isomers, i.e. the reverse reaction, occurs at a higher rate over the molybdenum oxycarbide catalysts than the bifunctional Pt/jS-zeolite catalyst. Over the Pt/jS-zeolite catalyst this reverse reaction would involve... 

Theoretical Approaches. Computer modeling is an increasingly fruitful tool in catalysis, and several research groups have attempted to rationalize high carbon conversion over zeolites from a theoretical point of view. The main problem to be... 

Clearly the losses and gains of a particular species present in the product gasoline as compared to the parent feed gasoline can represent the balance of complex reactions. However, under the reaction conditions employed, it is not likely that there will be appreciable generation of C6+ hydrocarbons other than as intermediates, so that an examination of reactant losses in this region provides a reasonable comparison of reactant conversion over the two zeolites. 

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. 

Figure 3.1 Acetylation at 373 K with acetic anhydride of a series of aromatic compounds over HBEA-15 zeolite. Conversion (XSUB) of anisole ( ), 2-methoxynaphthalene (x), m-xylene ( ), toluene ( ), 2-methylnaphthalene (o) and fluorobenzene (a) versus time. Reprinted from Journal of Catalysis, Vol. 230, Guidotti et al. Acetylation of aromatic compounds with H-BEA zeolite the influence of the substituents on the reactivity and on the catalyst stability, pp. 375-383, Copyright (2005), with permission from Elsevier...

Acetaldehyde decomposition, reaction pathway control, 14-15 Acetylene, continuous catalytic conversion over metal-modified shape-selective zeolite catalyst, 355-370 Acid-catalyzed shape selectivity in zeolites primary shape selectivity, 209-211 secondary shape selectivity, 211-213 Acid molecular sieves, reactions of m-diisopropylbenzene, 222-230 Activation of C-H, C-C, and C-0 bonds of oxygenates on Rh(l 11) bond-activation sequences, 350-353 divergence of alcohol and aldehyde decarbonylation pathways, 347-351 experimental procedure, 347 Additives, selectivity, 7,8r Adsorption of benzene on NaX and NaY zeolites, homogeneous, See Homogeneous adsorption of benzene on NaX and NaY zeolites... 

Investigation of n-butane conversion over H-forms of the ferrierite and theta-1 zeolites demonstrated that the isobutene selectivities were similar (and low) for these catalysts. The maximum selectivities (7-8 %) were obtained at low n-butane conversions (5-10 %) and decreased with increasing conversion of n-butane due to olefin interconversion and aromatisation reactions. Isobutene was in equilibrium with the other butene isomers due to the high isomerisation activity of the parent zeolites. The maximum selectivity to butenes, which was observed at low conversions, was around 20 %. This value reflects a moderate contribution of the dehydrogenation steps in n-butane transformation over H-forms of the ferrierite and theta-1 zeolites and indicates an important role of the n-butane protolytic cracking steps over these two catalysts. 

A review of this field has been given by Haw (1999). Reactions can be followed either in sealed glass ampoules or flow-through cells constructed within the spectrometer. The formation of intermediates can be studied in real time. An elegant example of this was shown in an early study of methanol to gasoline conversion over HZSM-5 zeolites. As a result of the shape selectivity of the catalyst, spectroscopic evidence of reaction intermediates, which were not seen as reaction products, was observed (Anderson and Klinowski, 1990). 

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