Methanol, conversion to gasoline

M. G. Block, R. B. Callen and J. H. Stockinger, The analysis of hydrocar bon products obtained from methanol conversion to gasoline using open tubular GC columns and selective olefin absorption , ]. Chromatogr. Sci. 15 504-512 (1977). 

The reaction scheme of MTO is similar to that which describes methanol conversion to gasoline (MTG) (4,5) ... 

The selectivity of a novel kind of zeolite was investigated for methanol conversion to gasoline-range hydrocarbons by Le Van MaO and McLaughlin (1989) [72]. Two new categories of ZSM-5 zeolites were prepared nontoxic zeolites derived from chrysotile asbestos fibers, and Zn- and Zn-Mn-modified ZSM-5 zeolites. Feeds in this study included methanol, 1—butanol, 2- nethyl-... 

From the point of view of catalysis the interesting feature of these materials is the possibility of sulfonation of the aromatic rings, producing Brdnsted acidity [67,68], which is active for reactions such as isobutanc/butene alkylation, Fricdel-Crafts alkylation, alcohol dehydration, methanol conversion to gasoline, hydrolysis of esters, and so on. Some drawbacks associated with these materials are diffusional restrictions for bulkier molecules, and reaction and regeneration temperature limitations. 

Mobil Oil Corporation has developed a process on a pilot scale that can successfully convert methanol into 96 octane gasoline. Although methanol can be used directiy as a transportation fuel, conversion to gasoline would eliminate the need to modify engines and would also eliminate some of the problems encountered using gasoline—methanol blends (see Alcohol fuels Gasoline and other motor fuels). 

This section discusses the production of methanol and ammonia from wood. Methanol is a clean-burning material that may find widespread future use as an automotive fuel (directly or for conversion to gasoline by the Mobil process) as a fuel for industrial or utility boilers, gas turbines, or fuel cells as a chemical intermediate or as a biological feedstock for protein. 

Various catalysts can be used for converting methanol to DME and water (ref. 11). The fixed-bed MTG process uses a 7-alumina catalyst which has high selectivity for methanol conversion to DME and water and low selectivity for methanol decomposition and coke. These properties are important as any loss of methanol to byproducts directly affects gasoline yield. Commercially, it is preferred to have one DME reactor per ZSM-5 train. Thus, high coke formation in the DME catalyst would necessitate the additional expense of multiple DME reactors. 

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... 

Mobil MTG and MTO Process. Methanol from any source can be converted to gasoline range hydrocarbons using the Mobil MTG process. This process takes advantage of the shape selective activity of ZSM-5 zeoHte catalyst to limit the size of hydrocarbons in the product. The pore size and cavity dimensions favor the production of C-5—C-10 hydrocarbons. The first step in the conversion is the acid-catalyzed dehydration of methanol to form dimethyl ether. The ether subsequendy is converted to light olefins, then heavier olefins, paraffins, and aromatics. In practice the ether formation and hydrocarbon formation reactions may be performed in separate stages to faciHtate heat removal. 

Shape-selective zeolites can also be used to discriminate among potential products of a chemical reaction, a property called product shape selectivity. In this case, the product produced is the one capable of escaping from the zeolite pore structure. This is the basis of the selective conversion of methanol to gasoline over... 

Avidan and Edwards (1986) successfully scaled up from bench scale to demonstration plant from 0.04 m to 0.6 m diameter while maintaining nearly 100% conversion for a fluid bed methanol to gasoline process. In this case, they ran at a superficial gas velocity which was high enough to be in the turbulent flow regime suppressing bubbles. By this technique they eliminated the losses associated with gas bypassing in bubbles. 

The catalyst used for the conversion of methanol to gasoline is based on a new class of shape-selective zeolites (105-108), known as ZSM-5 zeolites, with structures distinctly different from other well-known zeolites. Apparently, the pore dimensions of the ZSM-5 zeolites are intermediate between those of wide-pore faujasites (ca. 10 A) and very narrow-pore zeolites such as Zeolite A and erionite (ca. 5 A) (109). The available structural data indicate a lattice of interconnecting pores all having approximately the same diameter (101). Hydrocarbon formation... 

MTG [Methanol to gasoline] A common abbreviation for any process achieving this conversion, notably the Mobil process. This uses as a catalyst the synthetic zeolite ZSM-5, invented at the Mobil Research Laboratory in 1972. The process was first disclosed in 1976 and commercialized in 1985 by New Zealand Synfuels, a joint venture of Mobil Corporation and Petrocorp. In 1990, this process was providing one third of New Zealand s gasoline requirements. 

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