Gasoline pool

The conventional leaded premium gasoline is characterized by minimum RON and MON values of 97 and 86, respectively. In 1993, it was the principal product in the gasoline pool in France having 60% of the sales, but its share is diminishing and, in 2000, it will play mostly a minor role. 

The potential advantages of LPG concern essentially the environmental aspects. LPG s are simple mixtures of 3- and 4-carbon-atom hydrocarbons with few contaminants (very low sulfur content). LPG s contain no noxious additives such as lead and their exhaust emissions have little or no toxicity because aromatics are absent. This type of fuel also benefits often enough from a lower taxation. In spite of that, the use of LPG motor fuel remains static in France, if not on a slightly downward trend. There are several reasons for this situation little interest from automobile manufacturers, reluctance on the part of automobile customers, competition in the refining industry for other uses of and fractions, (alkylation, etherification, direct addition into the gasoline pool). However, in 1993 this subject seems to have received more interest (Hublin et al., 1993). 

U.S. petroleum benzene prices since 1974 are Hsted in Table 6 (64). Until 1978, benzene prices were relatively stable and through 1985 they increased considerably, peaking in 1981 because of the increased demand for aromatics in the gasoline pool. At that time, there was also a large surplus of low priced imported benzene and a softening of the ethylbenzene—styrene market. The decline of cmde oil prices in 1986 caused a dramatic drop in domestic benzene prices. In 1987, U.S. benzene production increased 13.9% over 1986, and this rise was largely ascribed to a favorable export market for benzene derivatives... 

All of the benzoic acid producers in the United States employ the Hquid-phase toluene air oxidation process. As toluene becomes more important in the gasoline pool as an octane booster, the benzoic acid producers have to compete with gasoline marketers for the available toluene. If the attractiveness of toluene as an octane booster continues, the cost of producing benzoic acid will most likely increase. 

Di- and Triisobutylcncs. Diisobutylene [18923-87-0] and tnisobutylenes are prepared by heating the sulfuric acid extract of isobutylene from a separation process to about 90°C. A 90% yield containing 80% dimers and 20% trimers results. Use centers on the dimer, CgH, a mixture of 2,4,4-trimethylpentene-1 and -2. Most of the dimer-trimer mixture is added to the gasoline pool as an octane improver. The balance is used for alkylation of phenols to yield octylphenol, which in turn is ethoxylated or condensed with formaldehyde. The water-soluble ethoxylated phenols are used as surface-active agents in textiles, paints, caulks, and sealants (see Alkylphenols). 

It competes direedy with MTBE as an octane enhancer in the gasoline pool. Since MTBE is more desirable than tert-huty alcohol because of its total miscibility with gasoline, tert-huty alcohol wiU be an important source of isobutylene used in the manufacture of MTBE. High purity isobutylene, C Hg, can be obtained by dehydration of tert-huty alcohol, C H qO. 

Depending upon the refinery needs, the raw C5 plus steam cracked naphtha may be sent to isoprene extraction, treated to remove gum forming diolefins and sent to the refinery gasoline pool, or else completely hydrogenated and then fed to an aromatics extraction unit. 

When high purity isobutylene is not required, the acid extract from the rich stage may be heated for a few minutes to 250-300°F, and then quickly cooled. Under these conditions the isobutylene dimerizes to form largely 2,4,4, trimethyl pentene-1. This is known as the dimer process and may be used to concentrate i-butenes for dehydrogenation feed, the isobutylene dimer being added to the motor gasoline pool. Trimers, as well as codimers with normal butenes are also produced. 

An alternative method for separating the hutenes is hy extracting isobutene (due to its higher reactivity) in cold sulfuric acid, which polymerizes it to di- and triisohutylene. The dimer and trimer of isobutene have high octane ratings and are added to the gasoline pool. 

Upgrade lower-value materials such as heavy residues to more valuable products such as naphtha and LPG. Naphtha is mainly used to supplement the gasoline pool, while LPG is used as a fuel or as a petrochemical feedstock. 

As has been mentioned in Chapter 3, isobutane is mainly used as an alkylating agent to produce different compounds (alkylates) with a high octane number to supplement the gasoline pool. Isobutane is in high... 

Isobutylene (CH2=C(CH3)2) is a reactive C4 olefin. Until recently, almost all isobutylene was obtained as a by-product with other C4 hydrocarbons from different cracking processes. It was mainly used to produce alkylates for the gasoline pool. A small portion was used to produce chemicals such as isoprene and diisobutylene. However, increasing demand for oxygenates from isobutylene has called for other sources. 

The debutanized gasoline is cooled, first by supplying heat to the stripper reboiler or preheating the debutanizer feed. This is followed by a set of air or water coolers. A portion of the debutanizer bottoms is pumped back to the presaturator or to the primary absorber as lean oil. The balance is treated for sulfur and blended into the refinery gasoline pool. 

A number of refiners split the debutanized gasoline into light and heavy gasoline. This optimizes the refinery gasoline pool when blending is constrained by sulfur and aromatics. In a few gasoline splitters, a third heart cut is withdrawn. This intermediate cut is low in octane and it is processed in another unit for further upgrading. 

FCC gasoline has always been the most valuable product of a cat cracker unit. FCC gasoline accounts for about 35 vol% of the total U.S. gasoline pool. Historically, the FCC has been run for maximum gasoline yield with the highest octane. 

Benzene. Most of the benzene in the gasoline pool comes from reformate. Reformate, the high-octane blending component from a reformer unit, comprises about 30 vol% of the gasoline pool. Depending on the reformer feedstock and severity, reformate contains 3 vol to 5 voFf benzene. 

FCC gasoline contains 0.5 to 1.3 vol% benzene. Since it accounts for about 35 vol% of the gasoline pool, it is important to know what affects the cat cracker gasoline benzene levels. The benzene content in the FCC gasoline can be reduced by ... 

Most of the benzene in the gasoline pool comes from the reformer unit (reformate). To reduce the reformate s benzene, one must modify the feedstock quality and/or operating conditions. Benzene s precursors in the reformer feed (C, and C ) can be prefractionated and sent to an isomerization unit. The reformer operating pressure can be reduced... 

Light olefins, particularly tertiary olefins, are very reactive in forming ozone and also increase gasoline pool RVP. However, the future trend of most FCC operations is projected to produce more olefin feed, but little will reach the gasoline pool. This is because olefins, particularly the C4 and Cg olefins, can either be alkylated and/or etherified, or used for petrochemical feedstock. 

Altering the refinery process to put more aromatics into the gasoline pool. This would increase the crude oil requirement per litre of fuel it would also increase exposure of the general public to higher levels of toxic benzene. This was not viewed as a significant problem. 

Adding ethanol to the gasoline pool this had already been done for many years in Brazil. 

Adding methyl -butyl ether (MTBE) to the gasoline pool. Of all the (cost-effective) organic fuel supplements tested, MTBE had the highest octane number. 

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