Zeolite catalyst ZSM

FIGURE 13.38 The structure of the ZSM-5 zeolite catalyst. Reactants diffuse through the channels, which are narrow enough to hold intermediates in positions favorable for reaction. 

FIGURE 9.2 This high-resolution electron micrograph shows the unique pore structure of the ZSM-5 zeolite catalyst. Molecules such as methanol and hydrocarbons can he catalytically converted within the pores to valuable fuels and lubricant products. Courtesy, Mobil Research and Development Corporation. 

The aromatization of liquefied petroleum gases (LPG) has been investigated for more than a decade due to its economical and strategic importance for the exploitation of natural gas reserves and valorization of light hydrocarbons obtained from petroleum refining. Commercially, these reactions using gallium modified ZSM-5 zeolite catalysts are known as Cyclar process, developed jointly by UOP and BP [1]. 

Initial activity (TOF) was measured on fresh catalysts and EB conversion was also followed with time on stream (table 1). ZSM-5 zeolite catalyst is respectively 40, 25 and 2 times initially more active for the EB conversion than the Ferrierite, ZSM-22 and EU-1 catalysts (table 1). Except for ZSM-5, high deactivation occurs on zeolite catalysts as shown by EB conversion drop at different contact time (table 1). 

Methanol can be used directly as a transportation fuel, or it can be converted into gasoline with catalysts such as the ZSM-5 zeolite catalyst. 

M., Mukai, S.R., Kawase, M., and Hashimoto, K. (2003) Methanol to olefins using ZSM-5 zeolite catalyst membrane reactor. Chem. Eng. Sci.,... 

D.Y. (2006) Isomerization of n-butane to isobutane over Pt-modified beta and ZSM-5 zeolite catalyst catalyst deactivation and regeneration. Chem. Eng. ]., 120, 83-89. 

Mobil ZSM-5 zeolite catalysts can be modified to reduce the effective pore and channel dimensions. These modified zeolites allow discrimination between molecules of slightly different dimensions. Because of this shape-selective action, p-ethyltoluene is able to diffuse out of the catalyst pores at a rate about three orders of magnitude greater than the two regioisomers. As a result, p-ethyltoluene is formed with very high (97%) selectivity.333... 

A completely new approach for BTX production has emerged in recent years. It converts C2 to C6 paraffins into aromatics using a modified ZSM-5 zeolite catalyst which contains gallium (19). An example of this approach, the Cydar process, has been in commercial operation by British Petroleum at Grangemouth, Scodand since August 1990 (20). It uses C3 C4 feed and employs UOP s CCR technology to compensate for rapid catalyst coking. 

Mobil s High Temperature Isomerization (MHTI) process, which was introduced in 1981, uses Pt on an acidic ZSM-5 zeolite catalyst to isomerize the xylenes and hydrodealkylate EB to benzene and ethane (126). This process is particularly suited for unextracted feeds containing Cg+ aliphatics, because this catalyst is capable of cracking them to light paraffins. Reaction occurs in the vapor phase to produce a PX concentration slightly higher than equilibrium, ie, 102—104% of equilibrium. EB conversion is about 40—65%, with xylene losses of about 2%. Reaction conditions are temperature of 427—460°C, pressure of 1480—1825 kPa, WHSV of 10—12, and a H2/hydrocarbon molar ratio of 1.5—2 1. Compared to the MVPI process, the MHTI process has lower xylene losses and lower formation of heavy aromatics. 

Heterogeneous catalysts activate C—H bonds at significantly higher temperatures. For example, a Fe/Co modified Mo-supported acidic ZSM-5 zeolite catalyst dehydrogenates methane under non-oxidizing conditions at 700°C to a mixture of Q-C4 alkanes/alkenes and Q-Q2 aromatics such as benzene and naphthalene.140... 

The process has been demonstrated on a pilot scale by Lurgi and Statoil. Sufficient propylene has been produced to make polypropylene resin product by Borealis. This process appears to use an oxide doped ZSM-5 zeolite catalyst in fixed bed reactors. The oxide doping promotes the methanol conversion to olefins. All olefins, other than propylene, are recycled to extinction or purged as fuel gas or produced as naphtha. The flow sheet is illustrated in the Figure 11.8. 

Calculating the space-time for parallel reactions. m-Xylene is reacted over a ZSM-5 zeolite catalyst. The following parallel elementary reactions were found to occur [Ind. En, Chem Res., 27, 942 (1988)] ... 

Synthesis of Ga- and Zn-H-ZSM-5 zeolite catalysts using Ga- and Zn-impregnated for the transformation of n-butane to aromatic... 

The synthesized catalysts were analysed for phase purity and structure identification by an X-ray powder diffiactometer (Philips pw 1830) using CuKa radiation. The X-ray difffactograms of Ga-H-ZSM-5 and Zn-H-ZSM-5 zeolite catalysts are given in Figures 1 and 2. The morphology of the zeolite catalysts was investigated by a scanning electron microscope... 

ZSM-5 zeolites have been widely used in selective conversion of hydrocarbons through various modification methods. It is well known that Zn- or Ga-containing ZSM-5 zeolites are excellent catalysts for C2-C4 paraffin aromatization called as Cyclar process. Moreover, light olefins of C2""-C4 can be produced from saturated hydrocarbons on modified ZSM-5 zeolite catalysts [1]. Lately a catalyst for CH4 aromatization, that can be regarded as an extension of the Cyclar process, has been derived from ZSM-5 zeolite modified with Mo(VI) species [2-3], In this presentation, the aromatization of CH4 and C2H6 over Mo(VI)/HZSM-5 and W( VI) /HZSM- 5 zeolite catalysts and their mechanistic features are investigated. 

The results of C2H5 conversion over Mo(VI)/HZSM-5 and W(VI)/HZSM-5 catalysts are summarized in Table 7. It appears that both of the reaction routes for the catalytic conversion of C2H5 can proceed over Mo or W modified ZSM-5 zeolite catalysts respectively. 

The C2H6 conversion over W(VI) and Mo(VI) modified ZSM-5 zeolite catalysts... 

Angelescu E, Gurau P, Pogonaru G, et al. 1990. Conversion of alkanes into gasoline on ZSM-5 zeolite catalysts. Revue Roumaine de Chimie 35 229-237. 

C. Berger, A. Raichle, R.A. Rakoczy, Y. Traa, and J. Weitkamp, Hydroconversion of Methylcyclohexane on TEOS-modified H-ZSM-5 Zeolite Catalysts Production of a High-quality Synthetic Steamcracker Feedstock. Microporous Mesoporous Mater., 2003, 59, 1-12. 

This paper will review by means of selected examples the information that can be obtained from spectroscopic studies of the ZSM-5 zeolite catalyst and the many different reactions occurring during the conversion of methanol to gasoline. With a process as chemically complex as MTG it is hardly necessary to emphasize that all possible means of investigation must be employed to achieve a complete understanding of all aspects of the process at the molecular level. Spectroscopic studies do not replace but rather complement the traditional methods for catalyst characterization and determination of reaction mechanisms by for example analysis of reaction products and use of isotopic tracers. 

The exceptional activity exhibited by ion-exchanged copper ZSM-5 zeolite catalysts for nitric oxide (NO) decomposition, and for the selective catalytic reduction (SCR) of nitrogen oxides (NOx) in the presence of excess oxygen is well documented [1-10]. The nature of the active copper species in the SCR reaction however still remains uncertain. We and others have recognised that there are two different types of copper species within the ZSM-5 zeolite channels [11]. Isolated copper ions exist in low symmetry environments, and small clusters, where the copper atoms are linked by extra-lattice oxygen species such as [Cu(II)-0-Cu(n)] dimers, are also present. Recent studies have also suggested that the isolated copper ions in ZSM-5 occupy two types of sites [11], which may have different SCR reactivity. It is likely... 

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