Methanol in gasoline

Methanol is more soluble in aromatic than paraffinic hydrocarbons. Thus varying gasoline compositions can affect fuel blends. At room temperature, the solubiUty of methanol in gasoline is very limited in the presence of water. Generally, cosolvents are added to methanol—gasoline blends to enhance water tolerance. Methanol is practically insoluble in diesel fuel. 

The incremental cost of using methanol in gasoline is approximately equal to the incremental cost of converting the methanol to gasoline by the Mobil process. Such end-use costs must of course be included in overall fuel comparisons. 

If energy prices develop in such a way that it becomes economically attractive to use methanol in gasoline or as a fuel for power production the market potential in these areas is almost unlimited. This development, however, will be governed by political decisions and so predictions for the future are almost impossible. 

Using 5-30% Methanol in Gasoline," Intersoc. Energy Convers. Conf. Proc. 9th (Aug. 1974), 749104. 

The use of gasohol or methanol (or ethanol) with gasoline (M-85) has become the intermediate stage in the extensive use of alcohol fuels. Because of the possibility of phase separation when water is present in 10% methanol in gasoline, a cosolvent such as tertbutyl alcohol (TBA) must be added. M-85 does not require a cosolvent, though the emissions are worse than M-100. 

The tendency to separate is expressed most often by the cloud point, the temperature at which the fuei-alcohol mixture loses its clarity, the first symptom of insolubility. Figure 5.17 gives an example of how the cloud-point temperature changes with the water content for different mixtures of gasoline and methanol. It appears that for a total water content of 500 ppm, that which can be easily observed considering the hydroscopic character of methanol, instability arrives when the temperature approaches 0°C. This situation is unacceptable and is the reason that incorporating methanol in a fuel implies that it be accompanied by a cosolvent. One of the most effective in this domain is tertiary butyl alcohol, TBA. Thus a mixture of 3% methanol and 2% TBA has been used for several years in Germany without noticeable incident. 

Ethers result from the selective addition of methanol or ethanol to the isobutene contained in C4 olefin fractions. Ethers are used as components in gasoline because of their high octane blending value (RON and MON). 

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... 

The most extensive worldwide program on methanol blend gasoline was in Italy where from 1982 to 1987 a 1.9 x lO" m /yr (5 x 10 gal/yr) plant produced a mixture containing 69% methanol. The balance contained higher alcohols. This mixture was blended into gasoline at the 4.3% level and marketed successfully as a premium gasoline known as Super E (82). 

The term gasohol has come into wide usage to identify, generally, a blend of gasoline and ethanol, with the latter derived from grain. The term may also be appHed to blends of methanol or other alcohols in gasolines or other hydrocarbons, without regard to sources of components. 

Ethers, such as MTBE and methyl / fZ-amyl ether (TAME) are made by a catalytic process from methanol (qv) and the corresponding isomeric olefin. These ethers have excellent octane values and compete on an economic basis with alkylation for inclusion in gasoline. Another ether, ethyl tert-huty ether (ETBE) is made from ethanol (qv) and isobutylene (see Butylenes). The cost and economic driving forces to use ETBE vs MTBE or TAME ate a function of the raw material costs and any tax incentives that may be provided because of the ethanol that is used to produce it. 

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. 

Mesitylene can be synthesized from acetone by catalytic dehydrocyclization (17). Similarly, cyclotrimerization of acetylenes has produced PMBs such as hexamethylbenzene (18). Durene has been recovered from Methanex s methanol-to-gasoline (MTG) plant in New Zealand (19). 

Some efforts were made in the early 1980s to employ isobutyl and -butyl alcohols as octane extenders in gasoline. American Methyl Corporation in 1983, under a special waiver of the 1977 Clean Air Act (24), marketed a gasoline blend called Petrocoal containing methanol and a C-4 alcohol which was principally isobutyl alcohol. About 10,000 t of isobutyl and 5000 t of -butyl alcohol were consumed in this appHcation (10). In 1984, the EPA attempted to rescind this waiver and demand for isobutyl alcohol as a gasoline additive dropped to 136.3 t (10). Ultimately, the waiver was rescinded and no isobutyl or -butyl alcohol has been marketed for gasoline additive end use since 1984. 

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. 

Methanol to Ethylene. Methanol to ethylene economics track the economics of methane to ethylene. Methanol to gasoline has been flilly developed and, during this development, specific catalysts to produce ethylene were discovered. The economics of this process have been discussed, and a catalyst (Ni/SAPO 34) with almost 95% selectivity to ethylene has been claimed (99). Methanol is converted to dimethyl ether, which decomposes to ethylene and water the method of preparation of the catalyst rather than the active ingredient of the catalyst has made the significant improvement in yield (100). By optimizing the catalyst and process conditions, it is claimed that yields of ethylene, propylene, or both are maximized. This is still in the bench-scale stage. 

The illustrated unit can be used to study vapor-phase reforming of kerosene fractions to high octane gasoline, or hydrogenation of benzene, neat or in gasoline mixtures to cyclohexane and methylcyclopentane. In liquid phase experiments hydrotreating of distillate fractions can be studied. The so-called Solvent Methanol Process was studied in the liquid phase, where the liquid feed was a solvent only, a white oil fraction. 

By 1999, General Motors, Daimler-Clirysler, Toyota, and Nissan all had demonstration fuel cell vehicles operating on niethanol, with plans to start introducing vehicles into the market by 2005. Auto makers have shown a preference for methanol over gasoline primarily because of the likelihood of the sulfur content in gasoline poisoning some of the catalysts used in the fuel cell. 

---