Mobil MTG-process

By selection of appropriate operating conditions, the proportion of coproduced methanol and dimethyl ether can be varied over a wide range. The process is attractive as a method to enhance production of Hquid fuel from CO-rich synthesis gas. Dimethyl ether potentially can be used as a starting material for oxygenated hydrocarbons such as methyl acetate and higher ethers suitable for use in reformulated gasoline. Also, dimethyl ether is an intermediate in the Mobil MTG process for production of gasoline from methanol. 

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. 

Catalysts in the ZSM-5 and ZSM-11 family are used to convert methanol into high octane gasoline components in the Mobil MTG process (45). 

Hydrocarbons from Synthesis Gas and Methanol. Two very important catalytic processes in which hydrocarbons are formed from synthesis gas are the Sasol Eischer-Tropsch process, in which carbon monoxide and hydrogen obtained from coal gasification are converted to gasoline and other products over an iron catalyst, and the Mobil MTG process, which converts methanol to gasoline range hydrocarbons using ZSM-5-type 2eohte catalysts. 

If methanol can be considered to be the intermediate in a multistep reaction to form a final species, e. g., gasoline as in the Mobil MTG process [4], then a bifunctional catalyst ought markedly to increase the utilization of the syngas. Since in the MTG process dimethyl ether (DME) is a key intermediate, Sofianos et al. [9] proposed for this purpose a bifunctional catalyst, prepared by intimate mixing of finely milled samples of the methanol catalyst and of y-alumina, the acid catalyst which dehydrates methanol to DME. The results obtained show that the CO conversion using the bifunctional catalyst is nearly four times higher than that obtained with the monofunctional catalyst. 

The methanol-to-gasoline route proved in New Zealand starting in 1985 (Mobil MTG process), which includes an improved MTG fluid-bed oligomerization reactor that... 

Figure 15 shows simplified flow schemes of the two alternatives. The indirect route to methanol is based on steam reforming followed by methanol synthesis. The process consumes ca. 7 Gcal/t corresponding to a thermal efficiency of 68%. The synthesis gas route may also lead to gasoline by further conversion of methanol via the Mobil MTG-process (Yurchak, 1988) or by the Topsoe TIGAS process (Topp-Joergensen, 1988). 

Metha.nol-to-Ga.soline, The most significant development in synthetic fuels technology since the discovery of the Fischer-Tropsch process is the Mobil methanol-to-gasoline (MTG) process (47—49). Methanol is efftcientiy transformed into C2—C q hydrocarbons in a reaction catalyzed by the synthetic zeoHte ZSM-5 (50—52). The MTG reaction path is presented in Figure 5 (47). The reaction sequence can be summarized as... 

Direct fuel appHcations of methanol have not grown as anticipated (see Alcohol fuels). It is used in small quantities in California and other locations, primarily for fleet vehicle operation. Large-scale use of methanol as a direct fuel is not anticipated until after the year 2000. Methanol continues to be utilised in the production of gasoline by the Mobil methanol-to-gasoline (MTG) process in New Zealand. A variant of this process has also been proposed to produce olefins from methanol. 

Since there are many possible reaction systems for an MTG process, it was necessary to focus the development efforts. In the mid-1970fs, Mobil decided to pursue a double-pronged approach in order to ensure both short- and long-term objectives. The plan was ... 

Fig. 19.25. Schematic of Mobil s fluid-bed MTG process, which uses a unique zeolite catalyst to convert methanol to high octane, unleaded gasoline. (CourtesyThe Pace Company, Denver, CO.)...

Early attempts to convert methanol into olefins were based on the zeolite ZSM-5. The Mobil MTO process was based on the fluidised bed version of the MTG technology. Conversion took place at about 500°C allegedly producing almost complete methanol conversion. However, careful reading of the patent Uterature indicates that complete methanol conversion may not have been achieved by this means. Because of incomplete conversion, there would be a necessity to strip methanol and dimethyl ether from water and hydrocarbon products in order to recycle unconverted methanol. In this variant, the total olefin yield is less than 20% of the products of which ethylene is a minor but not insignificant product. The major product is gasoUne. Ethylene is difficult to process and has to be treated specially. Claims that it is possible that ethylene can be recycled to extinction conflict with the known behaviour of ethylene in zeolite catalyst systems and have to be viewed with some suspicion. 

Syngas conversion to methanol has been shown to take place on supported palladium catalyst [1]. Methanol can in turn be converted to gasoline over ZSM-5 via the MTG process developed by Mobil [2]. In recent work we have reported syngas (CO/H2) conversion to hydrocarbon products on bifunctional catalysts consisting of a methanol synthesis function, Pd, supported on ZSM-5 zeolites [3]. Work on syngas conversion to hydrocarbon products on Pd/SAPO molecular sieves has been published elsewhere [Thomson et. al., J. CataL. in press].Therefore, this paper will concentrate on propylene conversion. 

A are detected by Jt-ray diffraction. This behavior contrasts with that of SiOi-supported Pd, for which Fajula et al. report a decrease in particle size under syngas conversion conditions 88). In the presence of strong acid sites, methanol and dimethyl ether are converted further to branched higher hydrocarbons. This catalysis is reminiscent of that of HZSM-5 in Mobil s MTG process. A tentative reaction scheme, relating sites with products, has been given 313). 

Aromatic gasoline is now produced from methanol in MOBIL s MTG-process, which is catalyzed by the zeolite H-ZSM-5. Much attention has been paid to understanding the mechanistic pathway(s) of the chemical reactions that take place. Although there is still some controversy about the details, the main steps are generally accepted ... 

Mobil recently commercialized its fixed-bed methanol-to-gasoline (MTG) process in a 14,500 B/D (gasoline) plant, based on natural gas, which is located in New Zealand. Process development studies were carried out in a small pilot plant to define conditions for producing gasoline in good yield and with acceptable product quality while also insuring satisfactory catalyst life. The process was successfully scaled-up by a factor of 100 to a demonstration unit size of 4 B/D. The scale-up factor from the demonstration unit to the commercial plant was in excess of 3000. The characteristics of the fixed-bed MTG process, its development, scale-up to demonstration unit, and assurance of acceptable product quality are discussed. 

It has been a little over ten years since Mobil announced a process for converting methanol to high-octane gasoline from nonpetroleum sources (refs. 1-3). In 1987, a commercial plant has been in operation in New Zealand for more than one year, converting natural gas from the Maui and Kapuni fields into methanol and then into 14,500 B/D of gasoline via Mobil s fixed-bed MTG process. The gasoline produced is fully compatible with conventional gasoline. 

An overall schedule of the project is shown in Fig. 5. The total project took five years to engineer, procure and construct. This does not include the time required to develop the MTG process by Mobil Corporation, or the feasibility studies performed by the New Zealand Government. 

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