Alkylate in gasoline

The primary source of lead in the environment has historically been anthropogenic emissions to the atmosphere. In 1984, combustion of leaded gasoline was responsible for approximately 90% of all anthropogenic lead emissions. EPA phased out the use of lead alkyls in gasoline, however, and by 1990, auto emissions accounted for only 33% of the annual lead emissions (EPA 1996h). Use of lead additives in motor fuels was totally banned after December 31, 1995 (EPA 1996f). The ban went into effect on February 2, 1996. Atmospheric deposition is the largest source of lead found in soils. Lead is transferred... 

Parker, W. W., Hudson, R. L. A simplified chromatographic method for separation and identification of mixed lead alkyls in gasoline. Anal. Chem. 35, 1334 (1963). 

R. MacKinven, Search for Ash-Free Compounds to Replace Lead Alkyls in Gasoline, Dtsch. Ges. fuer Mineraloelwiss und Kohlechem, 24th Symp. Compend. 74/75, Hamburg, Sep. 30-Oct. 3, 2 (1974) p. 687. 

Propene is used as a chemical intermediate in the production of polypropylene, acrylonitrile, propylene oxide, isopropanol, and cumene. Refineries use much of their production of propene internally as a refinery heating gas, to produce alkylates in gasoline, and to produce liquefied petroleum gas. 

Some heavy ends in gasoline affected the elution time of tetraethyllead in the gasoline, so that a longer collection time was required for this substance. However, none of the other lead alkyls were affected appreciably. Table 121 shows the analysis of a typical sample of mixed lead alkyls in gasoline containing about 15 ml per gallon. 

Table 121. Triplicate Analysis of a 5-Component Mixture of Lead Alkyls in Gasoline...

Fig. 150. Gas chromatographic separation of mixed methyl-ethyl lead alkyls in gasoline.

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. 

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). 

Polymerization - Polymerization is occasionally used to convert propene and butene to high octane gasoline blending components. The process is similar to alkylation in its feed and products, but is often used as a less expensive... 

Seasonal chances in gasoline sales and heating oil sales compel some modifications to be made in conversion level. Therefore, the conversion pattern of a given catalytic cracking unit can vary from season to season. In summer operations, for instance, higher yields of motor gasoline are desired, both from direct production of 5/430° FVT catalytic naphtha and also from conversion of butylenes and isobutane to alkylate. 

Figure 11.4-2 shows process flows for an HF alkylation unit. The three sections are 1) reaction, 2). settling and 3) fractionation. In the reaction section isobutane feed is mixed with the olefin feed (usually propylene and butylene) in approximately a 10 or 15 to 1 ratio. In the presence of the HF acid catalyst the olefins react to form alkylate for gasoline blending. The exothermic reaction requires water cooling. The hydrocarbon/HF mixture goes to the settling... 

Alkylation in petroleum processing produces larger hydrocarbon molecules in the gasoline range from smaller molecules. The products are branched hydrocarbons having high octane ratings. 

As the gasoline Reid vapor pressure (RVP) is reduced, the operation ol the debutanizer becomes more critical. The allowable vapor pressure in gasoline makes it difficult to prevent heavy ends in the alkylation feed. This can limit the production of gasoline without sacrificing alkylation. This limitation is often from insufficient overhead cooling and reboiling ... 

Other major components in gasoline come from catalytic reforming, alkylation and the addition of an oxygenated octane booster, methyl tertiary-butyl ether (MTB E). 

Samples for determination of ionic alky Head species in marine fauna were homogenized in the presence of salts and the alkyllead component was extracted with toluene and oxidized with HN03. Determination was by DPASV115. A method based on oxidation on Hg electrode has been described116 for analysis of alkylleads in gasoline. Alkylation of Hg is involved, of course, but as an oxidation the method does not suffer from the background of atmospheric oxygen. The peak potentials Ev for oxidation of tetramethyllead and tetraethyllead on various cathodes are well resolved (Table 5). 

Sulfuric acid alkylation an alkylation process in which olefins (C3, C4, and C5) combine with isobutane in the presence of a catalyst (sulfuric acid) to form branched-chain hydrocarbons used especially in gasoline blending stock. 

The isobutylene in the C4 stream generally ends up in one of four places a refinery alkylation plant (covered further below), an MTBE plant, a polymerization process, or in gasoline. The first three are methods of removing isobutylene from the C4 stream the fourth is the default—the isobutylene just follows the other butanes and butylenes to the gasoline blending pool. 

Benzene and para-xylene are the most sought after components from reformate and pygas, followed by ortho-xylene and meta-xylene. While there is petrochemical demand for toluene and ethylbenzene, the consumption of these carmot be discussed in the same way as the other four. Toluene is used in such a large quantity in gasoline blending that its demand as a petrochemical pales in comparison. Fthylbenzene from reformate and pygas is typically dealkylated to make benzene or isomerized to make xylenes. On-purpose production of petrochemical ethylbenzene (via ethylene alkylation of benzene) is primarily for use as an intermediate in the production of another petrochemical, styrene monomer. Ethylbenzene plants are typically built close coupled with styrene plants. 

The ASTM-EFA standard method of analyzing lead In gasoline requires extraction of alkyl lead Iodide complexes Into methyllsobutylketone and a subsequent flame atomic absorption analysis of the extract A more direct method has been proposed ( ) which uses Zeeman atomic absorption analysis after sample dilution. Both methods were used to analyze a set of five field collected samples. The results showed a bias (average difference between method results) of 0.0012 g/gal with the standard flame results higher. The correlation coefficient between the results was 0.9998 0.0009, and a pairwise t-test showed no difference between the methods (6). 

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