The past, present and future of heterogeneous catalysis

The kaleidoscopic applications of zeolite catalysts (zeo-catalysts) in petrochemical processes has been considered as one of the major accomplishments in recent decades. About twenty types of zeolite have been industrially applied so far, and their versatile porous architectures have contributed their most essential features to affect the catalytic efficiency. This review depicts the evolution of pore models in zeolite catalysts accompanied by the increase in industrial and environmental demands. The indispensable roles of modulating pore models are outlined for zeo-catalysts for the enhancement of their catalytic performances in various industrial processes. The zeolites and related industrial processes discussed range from the uni-modal micropore system of zeolite Y (12-ring micropore, 12-R) in fluid catalytic cracking (FCC), zeolite ZSM-5 (10-R) in xylene isomerization and SAPO-34 (8-R) in olefin production to the multi-modal micropore system of MCM-22 (10-R and 12-R pocket) in aromatic alkylation and the hierarchical pores in FCC and catalytic cracking of C4 olefins. The rational construction of pore models, especially hierarchical features, is highlighted with a careful classification from an industrial perspective accompanied by a detailed analysis of the theoretical mechanisms.

Recent advances of pore system construction in zeolite-catalyzed chemical industry processes

Development of an universal group contribution equation of state

Alkylbenzenes form an important segment of petrochemical industry for the manufacture of widely used commodities and specialty products. Since the last review on this topic (8), numerous new zeolite-based catalysts have been synthesized, characterized and evaluated in various transformations of aromatic hydrocarbons. This comprehensive review covers major reactions of mono-, di-, and tri-alkylbenzenes such as disproportionation, alkylation, transalkylation, isomerization, etc., over different zeolite-based acid catalysts. During the last decade, significant progress was made in the synthesis and structure determination of novel zeolites, mesoporous single crystals, hierarchic zeolites and two-dimensional zeolites. These developments have enhanced the understanding of the role of zeolites (effects of structural type, morphology, acid sites, accessibility of acid sites, shape selectivity factors) in transformations of aromatics. In this review, the emphasis is on the influence of the type of acid sites, zeo...

Recent Advances in Reactions of Alkylbenzenes Over Novel Zeolites: The Effects of Zeolite Structure and Morphology

A descriptor for the relative propagation of the aromatic- and olefin-based cycles in methanol-to-hydrocarbons conversion on H-ZSM-5

Comparison studies of xylene isomerization and disproportionation reactions between SSZ-33, TNU-9, mordenite and ZSM-5 zeolite catalysts

The results of measurements of saturated liquid densities using a high-pressure stainless steel pycnometer system over a wide variation of temperature from 298.15 to 473.15 K are presented for benzene, cyclohexane, and hexane. Experimental densities were compared with those predicted by the Spencer-Danner-modified Rackett equation (SDR) and the Hankinson-Brobst-Thompson correlation (HBT). The SDR showed an average deviation of 0.22% while the HBT predicted the densities of the three organic solvents with an average deviation of 0.28%. The data obtained have also been compared with the available data reported in the literature.

Saturated liquid densities of benzene, cyclohexane, and hexane from 298. 15 to 473. 15 K

Catalytic transformation of three methyl benzenes (toluene, m -xylene, and 1,2,4-trimethyl benzene) has been investigated over ZSM-5, TNU-9, mordenite and SSZ-33 catalysts in a novel riser simulator at different operating conditions. Catalytic experiments were carried out in the temperature range of 300–400 °C to understand the transformation of these alkyl benzenes over large pore (mordenite and SSZ-33) in contrast to medium-pore (ZSM-5 and TNU-9) zeolite-based catalysts. The effect of reaction conditions on the isomerization to disproportionation product ratio, distribution of trimethylbenzene (TMB) isomers, and p -xylene/ o -xylene ratios are reported. The sequence of reactivity of the three alkyl benzenes depends upon the pore structure of zeolites. The zeolite structure controls primarily the diffusion of reactants and products while the acidity of these zeolites is of a secondary importance. In the case of medium pore zeolites, the order of conversion was m -xylene > 1,2,4-TMB > toluene. Over large pore zeolites the order of reactivity was 1,2,4-TMB >  m -xylene > toluene for SSZ-33 catalyst, and m -xylene ∼ 1,2,4-TMB > toluene over mordenite. Significant effect of pore size between ZSM-5 and TNU-9 was observed; although TNU-9 is also 3D 10-ring channel system, its slightly larger pores compared with ZSM-5 provide sufficient reaction space to behave like large-pore zeolites in transformation of aromatic hydrocarbons. We have also carried out kinetic studies for these reactions and activation energies for all three reactants over all zeolite catalysts under study have been calculated.

Catalytic transformation of methyl benzenes over zeolite catalysts

Catalytic transformation of three methyl benzenes (toluene, m -xylene, and 1,2,4-trimethylbenzene) has been investigated over USY-based FCC zeolite catalyst in a novel Riser Simulator at different operating conditions. The effect of reaction conditions on the variation of isomerization to disproportionation products ratio (I/D), distribution of trimethylbenzene (TMB) isomers (1,3,5-to-1,2,3-) and values of p -xylene/ o -xylene (P/O) ratios are reported. The sequence of reactivity of the three alkyl benzenes was found to decrease as the number of methyl group per benzene ring decreases, as follows: 1,2,4-trimethylbenzene >  m -xylene > toluene . This is true at all temperatures investigated over the USY zeolite. Toluene was found unreactive in our reaction condition. Effectiveness factor ( η ss ) of both 1,2,4-TMB and m -xylene have been estimated. While m -xylene's η ss was close to unity at all condition, 1,2,4-TMB's η ss was less than that of m -xylene. The effectiveness factor was estimated from the quasi-steady state approximation modeling of the experimental data involving a decay function based on “Time on Stream” (TOS). Based on the present study, it was found that the number of methyl groups has the most important role on the reactivity of 1,2,4-TMB, m -xylene and toluene over Y-based catalyst.

Catalytic transformation of C7–C9 methyl benzenes over USY-based FCC zeolite catalyst

Xylene transformation reactions have been investigated over ZSM-5 zeolite in a riser simulator that mimics closely the operation of commercial fluidized-bed reactors. Two reaction schemes have been used to model the transformation reactions. The first is based on a triangular reaction path which assumes a direct interconversion between o- and p-xylene isomers (1,3-methyl shift), and a second scheme assumes the reactions proceed via 1,2-methyl shift only (o-xylene ⇄ m-xylene ⇄ p-xylene). The rate constants and activation energies are obtained from simplified kinetic models based on the isomerization of the pure xylene isomers using the “time on stream” decay model. The results provide ample evidence to suggest that direct interconversion between o- and p-xylene isomers (a 1,3-methyl shift) occurs with the same rate as the conversion of m- to o-xylene (a 1,2-methyl shift) over ZSM-5 zeolite catalyst, and the 1,3-methyl shift reaction path is a better representation of the xylene isomerization mechanism in Z...

N. M. Tukur

Papers

Comparison studies of xylene isomerization and disproportionation reactions between SSZ-33, TNU-9, mordenite and ZSM-5 zeolite catalysts

Saturated liquid densities of benzene, cyclohexane, and hexane from 298. 15 to 473. 15 K

Catalytic transformation of methyl benzenes over zeolite catalysts

Catalytic transformation of C7–C9 methyl benzenes over USY-based FCC zeolite catalyst

Modeling Xylene Reactions over ZSM-5 Zeolite in a Riser Simulator: 1,3- versus 1,2-Methyl Shift