Methanol conversion into gasoline, zeolites

Figure 8. NMR spin diffusion spectrum of products of methanol conversion into gasoline over zeolite ZSM-5 with the projection onto the F2 axis (corresponding to a conventional spectrum) at the top [51]. Carbon atoms to which individual resonances are assigned are highlighted. For signal assignment see Table 2.

The phenomenon of shape selectivity in the reactions performed on zeolites arises from the fact that the probabilities of forming various products in the narrow intracrystalline cavities and channels are largely determined by the dimension and configuration of the zeolite pores [163], Although there was extensive indirect evidence of the shape selectivity of catalysis by zeolites [164,165], there was no direct observation of this effect based on analysis of the reaction products inside the pores. The ability of MAS NMR to identify the structure of organic molecules directly in the intracrystalline voids of zeolites allowed direct observation of the shape selectivity effect. Anderson and Klinowski analyzed the products of methanol conversion into gasoline on zeolite ZSM-5 by in situ C MAS NMR and reliably established the formation in zeolite pores of a number of methyl-substituted benzenes that had never been observed at the reactor outlet [166], The origin of this effect was obvious (Scheme 6) different trimethylbenzenes are formed in the zeolite pores, however, the bulkiest isomers cannot leave the pore interior because of the limited pore exit size in the zeolite structure. Thus, the... 

The theoretical modeling of the activation and reaction of methanol by Brpnsted acid sites within zeolites has attracted a wide interest. This is in part a consequence of the industrial importance of the interaction—as the first step of the conversion of methanol into gasoline in the MTG process (213). However, a great deal of the theoretical interest has arisen because of the possibility of proton transfer from the zeolite lattice to methanol. An early investigation was that of Vetrivel et al. (214), who employed ab... 

Afterwards, the synthesis of various new zeolites, especially ZSM5 (MFI, 1967), the discovery of new shape selective transformations such as the (accidental) discovery of the remarkably stable and selective conversion of methanol into gasoline range hydrocarbons over HZSM5 (7), the development of post-synthesis treatments of zeolites,. .. combined to make them the single most important family of catalysts used all other the world. 

Another synthesis process proposed to receive benefits from operating with monolith catalysts is the conversion of methanol for gasoline production [16,17J. The catalyst used was the ZSM-5 zeolite. However, rather than binding the catalyst onto the wall by use of a washcoat, it was uniformly crystallized on the cordierite honeycomb (62 cells/cm ) wall surfaces (up to 30% by weight), similar to the method described in the patent assigned to Lachman and Patil [18]. The effects of methanol partial pressure on conversion and temperature on hydrocarbon selectivity were determined. Three regimes of mass transfer resistances are experienced in this reaction reactant transfer to the reactor walls within the monolith channels through the laminar flow, diffusion resistance at the surface between zeolite crystals on the walls, and diffusion into the zeolite molecular-size pores to the active sites within the crystals, where the reaction rate limit is anticipated. 

The expected return of oil price increases over the next decade will again spur investigation into conversion processes for alternative fuel sources such as coal. Coal gasification will produce substantial amounts of carbon dioxide as a by-product. If this carbon dioxide could be converted economically to methanol or methane, established zeolite catalytic processes could convert these intermediates to gasoline. Furthermore, concern about providing a substitute for natural gas to the established gas pipelines has led the Gas Research Institute to sponsor investigation of carbon dioxide conversion selectively to methane (2). 

These catalysts provide three-dimensional microscopic media for reaction. The most important are the zeolites (see 14.2.2.2). Faujasites are used to crack petroleum for the manufacture of gasoline, and HZSM-5 to convert methanol into gasoline and in other petrochemical conversion processes including xylene isomerization and toluene di sproportionation. ... 

Anderson MW, Klinowski J. Solid-state NMR studies of the shape-selective catalytic conversion of methanol into gasoline on zeolite ZSM-5. J Am Chem Soc 1990 112 10-6. 

The Mobil methanol-to-olefins (MTO) process may seem to be an abridged version of the MTG process, but the distribution of olefins is governed not only by the process conditions, but largely by the architecture of the zeolite, with ZSM-5 being the best option for the modification. In this case, smaller-pore zeolites (ZSM-34, SAPO-34) show excellent results so far as the olefins formed should not be transformed into gasoline. The latter zeolite-like material developed and commercialized by UOP jointly with Norsk Hydro provides the selectivities to ethylene and propylene above 85% at the 100% methanol conversion [113]. 

Molecular sieve catalysts that have been used for the conversion of methanol to hydrocarbons fall into two general classifications. Most of the initial research was done using ZSM-5 (MFI), a medium-pore size zeolite with a three dimensional pore system consisting of straight (5.6 x 5.3 A) and sinusoidal channels (5.5 x 5.1 A). While most of this work was directed at the conversion of methanol to liquid hydrocarbons for addition to gasoline, it was found that the product slate could be shifted toward light olefins by the use of low pressure and short contact times. 

Methanol has been studied as a possible precursor of gasoline. For example, certain zeolite catalysts (Section 3-3) allow the conversion of methanol into a mixture of hydrocarbons. 

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