Octane blending

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). 

Fig. 4. Octane blending behavior where (--) represents the measured octane response curve, (-) the tangent to the curve, and (-) the linear...

Most of the octane blending values reported ia the Hterature use a slight variation on this theoretically sound approach. The composition and octane of the base fuel are assumed to be fixed and the second component is assumed to be added. Using the same nomenclature, the blending octane number (BON) of component 2 is defined as... 

Most refineries develop iadividual octane blending equations which do a good job of predicting that refinery s blending behavior. In order to use these equations ia refinery planning and operations, these may be linearized ia a piecewise fashion. 

Oxirane Process. In Arco s Oxirane process, tert-huty alcohol is a by-product in the production of propylene oxide from a propjiene—isobutane mixture. Polymer-grade isobutylene can be obtained by dehydration of the alcohol. / fZ-Butyl alcohol [75-65-0] competes directly with methyl-/ fZ-butyl ether as a gasoline additive, but its potential is limited by its partial miscibility with gasoline. Current surplus dehydration capacity can be utilized to produce isobutylene as more methyl-/ fZ-butyl ether is diverted as high octane blending component. 

Through the 19.30s, Ipatieff led UOP in its effort to develop two catalytic processes for the production of high-octane fuel alkylation and polymerization— the first, a reaction of a hydrocarbon with an olefin (double-bonded compound) the second, the formation of long molecules from smaller ones. Both processes produce high-octane blending compounds that increase the quality of cracked gasoline. 

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. 

After bauxite treatment the product was fractionated to produce C3-C4 and naphtha (C5-204°C) fractions. The C3-C4 olefin-rich gas was oligomerized over a solid phosphoric acid (SPA) catalyst to produce an unhydrogenated polymer gasoline with a research octane number (RON) of 95 and MON of 82.21 The bauxite-treated FT motor gasoline (RON of 87, MON of 76) was mixed with the polymer gasoline and some natural gas condensates (and crude-oil-derived naphtha) to produce the final motor gasoline product. In this respect it is noteworthy that the Fe-HTFT-derived material was the high-octane-blend stock. 

Octane blending debit/bonus, 72 411 Octane number, 18 665 Octane number requirement (ONR), 12 392, 393-394... 

Butane isomerization is usually carried out to have a source of isobutane which is often reacted with C3-C5 olefins to produce alkylate, a high octane blending gasoline [13]. An additional use for isobutane was to feed dehydrogenation units to make isobutene for methyl tert-butyl ether (MTBE) production, but since the phaseout of MTBE as an oxygenate additive for gasoline, this process has decHned in importance. Zeolitic catalysts have not yet been used industriaUy for this transformation though they have been heavily studied (Table 12.1). 

Butane isomerization and pentane-hexane isomerization are the two most important isomerization processes. Isobutane is utilized primarily as alkylate feedstock. Isopentanes and isohexanes have become valuable high-octane blending components in gasoline. 

The process involves reacting butenes and mixtures of propenes and butenes with either a phosphoric acid type catalyst (UOP Process) or a nickel complex-alkyl aluminum type catalyst (IFP Dimersol Process) to produce primarily hexene, heptene, and octene olefins. The reaction first proceeds through the formation of a carbocation which then combines with an olefin to form a new carbocation species. The acid proton donated to the olefin initially is then released and the new olefin forms. Hydrotreatment of the newly formed olefin species results in stable, high-octane blending components. 

Toluene is used as a high-octane blending stock in gasoline as a solvent for paints and coatings, gums, resins, oils, rubber and adhesives and as an intermediate in the preparation of many chemicals, dyes, pharmaceuticals, detergents and explosives (Lewis, 1993). 

Hydrogenation—A refinery process in which hydrogen is added to the molecules of unsaturated (hydrogen-deficient) hydrocarbon tractions. It plays an important part in the manufacture of high-octane blending stocks for aviation gasoline and in the quality improvement of various petroleum products. 

Isomerate process a fixed-bed isomerization process to convert pentane, heptane, and heptane to high-octane blending stocks. 

The liquids output represents a combination of transportation and utility fuels as summarized in Table III. All of the naphtha is to be reformed on site to produce a very high aromatic stock. With an exceptional octane blending value, this stream will find ready application as a gasoline component, but perhaps more important, it is also a source of substantial quantities of petrochemical raw materials as noted in Table IV. The potential yield of BTX and phenolics along with the low boiling paraffins should make such a plant an important factor in the future supply picture for these materials. 

Durene Formation - An aromatic compound, durene (1, 2, 4, 5-tetramethylbenzene) is produced in the MTG process. Durene has excellent research octane blending quality (110 RON clear) and boils within the gasoline distillation range (197°C) however, its freezing point is relatively high at 79°C. 

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