Blends, gasoline

Low level blends of ethanol and and gasoline enjoyed some popularity in the United States in the 1970s. The interest persists into the 1990s, encouraged by the exemption of low level ethanol-gasoline blends from the Federal excise tax as well as from state excise taxes in many states. 

Capacity Limitations and Biofuels Markets. Large biofuels markets exist (130—133), eg, production of fermentation ethanol for use as a gasoline extender (see Alcohol fuels). Even with existing (1987) and planned additions to ethanol plant capacities, less than 10% of gasoline sales could be satisfied with ethanol—gasoline blends of 10 vol % ethanol the maximum volumetric displacement of gasoline possible is about 1%. The same condition apphes to methanol and alcohol derivatives, ie, methyl-/-butyl ether [1634-04-4] and ethyl-/-butyl ether. 

Only a small portion of motor fuel needs could be satisfied if truly large-scale alcohol—gasoline blending or fuel switching occurred via transition to fuel-flexible vehicles and ultimately to neat alcohol-fueled vehicles (132). 

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. 

Eor a considerable period, >90% of the new cars in Brazil operated on E96 fuel, or a mixture of 96% ethanol and 4% water (82). The engines have high compression ratios (ca 12 1) to utilize the high knock resistance of ethanol and deUver optimum fuel economy. In 1989 more than one-third of Brazil s 10 million automobiles operated on 96% ethanol/4% water fuel. The remainder ran on gasoline blends containing up to 20% ethanol (5). 

W. E. Morris, The Interaction Approach to Gasoline Blending, paper presented at NPRA Annual Meeting, San Antonio, Tex., Mar. 23—25,1975. 

Recoveries of 90—95% ethane have been achieved usiag the expander processes. The Hquid product from the demethanizer may contain 50 Hquid vol % ethane and usually is deHvered by a pipeline to a central fractionation faciHty for separation iato LPG products, chemical feedstocks, and gasoline-blending stocks. 

Benzene, toluene, and xylene are made mosdy from catalytic reforming of naphthas with units similar to those already discussed. As a gross mixture, these aromatics are the backbone of gasoline blending for high octane numbers. However, there are many chemicals derived from these same aromatics thus many aromatic petrochemicals have their beginning by selective extraction from naphtha or gas—oil reformate. Benzene and cyclohexane are responsible for products such as nylon and polyester fibers, polystyrene, epoxy resins (qv), phenolic resins (qv), and polyurethanes (see Fibers Styrene plastics Urethane POLYiffiRs). 

The cumene product is 99.9 wt % pure, and the heavy aromatics, which have a research octane number (RON) of 109, can either be used as high octane gasoline-blending components or combiaed with additional benzene and sent to a transalkylation section of the plant where DIPB is converted to cumene. The overall yields of cumene for this process are typically 97—98 wt % with transalkylation and 94—96 wt % without transalkylation. 

Cumene. Cumene (qv) is produced by Friedel-Crafts alkylation of benzene by propylene (103,104). The main appHcation of cumene is the production of phenol (qv) and by-product acetone (qv). Minor amounts are used in gasoline blending (105). 

Toluene demand in 1996 increased because of the new Amoco and Mobil (Chalmette) disproportionation plants as well as other capacity changes at Coastal (Eagle Point), Phillips (Sweeney), Gulf Chemicals (Arochem plant, Puerto Rico), Koch, and Texaco (Huntsman, Port Arthur). Dewitt (71) forecasts continued increase for this appHcation at the rate of about 14% between 1995 and the year 2000. These will have a significant effect on toluene price and availabiUty in the later 1990s. On the other hand, toluene demand for gasoline blending is expected to decline by about 283 million Hters by 1997-1998. 

Until the 1940s light oil obtained from the destmctive distillation of coal was the principal source of benzene. Except for part of the World War 11 period, the quantity of benzene produced by the coal carbonization industry was sufficient to supply the demand even when a large portion of benzene was used for gasoline blending. 

Extractive distillation, using similar solvents to those used in extraction, may be employed to recover aromatics from reformates which have been prefractionated to a narrow boiling range. Extractive distillation is also used to recover a mixed ben2ene—toluene stream from which high quaUty benzene can be produced by postfractionation in this case, the toluene product is less pure, but is stiU acceptable as a feedstock for dealkylation or gasoline blending. Extractive distillation processes for aromatics recovery include those Hsted in Table 4. 

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. 

In the physical separation process, a molecular sieve adsorbent is used as in the Union Carbide Olefins Siv process (88—90). Linear butenes are selectively adsorbed, and the isobutylene effluent is distilled to obtain a polymer-grade product. The adsorbent is a synthetic 2eohte, Type 5A in the calcium cation exchanged form (91). UOP also offers an adsorption process, the Sorbutene process (92). The UOP process utilizes ahquid B—B stream, and uses a proprietary rotary valve containing multiple ports, which direct the flow of Hquid to various sections of the adsorber (93,94). The cis- and trans-isomers are alkylated and used in the gasoline blending pool. 

In addition to MTBE, two other ethers commonly used as fuel additives ate /n/f-amyl methyl ether (TAME) and ethyl in/f-butyl ether [637-92-3] (ELBE). There ate a number of properties that ate important in gasoline blending (see Gasoline and OPHER MOTOR fuels) (Table 3). 

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