Total: $0.00Close Cart
eBook & Document Store
Excerpt From this Document
- Alkylation is any reaction in which an alkyl group is added to a compound; in petroleum refining, it normally means reaction of an olefin with an i-paraffin to produce a larger i-paraffin.
- Alkylation processes combine light olefins (primarily propylene and butylene) with isobutane in the presence of a highly acidic catalyst, either sulfuric acid or hydrofluoric acid. The product (alkylate) contains a mixture of high-octane, branched-chain paraffinic hydrocarbons. Figure 1 illustrates the reaction between isobutane and trans-2-butene. Alkylate is a highly desirable gasoline blend stock because, in addition to its high octane, it has a low vapor pressure. The octane of the product depends on the operating condition and the kinds of olefins used.
22.214.171.124 Cascade Sulfuric Acid Alkylation
- This is a low-temperature process (Figure.2) employing concentrated sulfuric acid catalyst to react olefins with iso -butane to pro duce high-octane aviation or mo tor fuel blending stock. The olefin feed is split into equal streams and charged to the individual reaction zones of the cascade reactor. Iso-butane-rich recycle and refrigerant streams are introduced in the front of the reactor and passed through the reaction zones. The olefin is contacted with the iso-butane and acid in the reaction zones, which operate at 28C to 78C (358F to 458F) and 5 to 15 psi, after which vapors are withdrawn from the top of the reactor, compressed, and condensed. Part of this stream is sent to a de-propanizer to control propane concentration in the unit. De-propanizer bottoms and the remainder of the stream are combined and returned to the reactor. Spent acid is withdrawn from the bottom of the settling zone; hydrocarbons spill over a baffle into a special withdrawal section and are hot-water washed with caustic addition for pH control before being successively de-propanized, de-iso-butanized, and de-butanized. Alkylate can then be taken directly to motor fuel blending or be rerun to produce aviation grade blending stock. Isobutane is recycled.
- The effluent refrigeration process (Stratco) uses a single-stage reactor in which the temperature is maintained by cooling coils (Fig.3). The reactor contains an impeller that emulsifies the acid–hydrocarbon mixture and recirculates it in the reactor. Average residence time in the reactor is on the order of 20 to 25 minutes. Emulsion removed from the reactor is sent to a settler for phase separation. The acid is recirculated and the pressure of the hydrocarbon phase is lowered to flash vaporize a portion of the stream and reduce the liquid temperature to about 30°F. The cold liquid is used as coolant in the reactor tube bundle. The flashed gases are compressed and liquefied, then sent to the depropanizer where LPG grade propane and recycle isobutane are separated. The hydrocarbon liquid from the reactor tube bundle is separated into isobutane, n-butane, and alkylate streams in the deisobutanizer column. The isobutane is recycled and n-butane and alkylate are product streams.
- A separate distillation column can be used to separate the n-butane from the mixture or it can be removed as a sidestream from the deisobutanizing column. The choice is a matter of economics because including a separate column to remove the n-butane increases the capital and operating costs. Separating nbutane as a sidestream from the deisobutanizing can be restricted because the pentane content is usually too high to meet butane sales specifications. The sidestream n-butane can be used for gasoline blending.
About this Document
alkylation process invloved in petroleum industry