1. Field of the Disclosure
Embodiments disclosed herein relate generally to the alkylation of paraffinic hydrocarbon feedstocks. More particularly, embodiments disclosed herein relate to a process for the preparation of an olefin-containing feed and an alkylation process using the prepared feed.
2. Background
Alkylation is the reaction of paraffins, usually isoparaffins, with an olefin in the presence of a strong acid which produces paraffins, e.g., of higher octane number than the starting materials and which boils in the range of gasolines. In petroleum refining, the alkylation reaction is generally the reaction of a C3 to C5 olefin with isobutane.
In refining alkylations, hydrofluoric or sulfuric acid catalysts are commonly used. For sulfuric acid catalyzed alkylation, low temperature or cold acid processes are favored, minimizing side reactions. In a typical process, the reaction is carried out in a reactor where the hydrocarbon reactants are dispersed into a continuous acid phase.
For example, U.S. Pat. No. 2,762,853 discloses an alkylation process including feeding isoparaffins, such as isobutane or isopentane and C2-C5 monoolefins to an alkylation reactor. The alkylation reaction is catalyzed with sulfuric acid in excess of 88 percent preferably in excess of 96 percent. The alkylation products are then separated into gasoline range components and heavier alkylate products among other finishing processes.
As another example, U.S. Pat. No. 2,859,260 discloses an alkylation process including reacting isoparaffins with olefins in the presence of a sulfuric acid catalyst. The reaction product is then separated to recover a hydrocarbon-rich phase and an acid-rich phase. The hydrocarbon-rich phase is further treated to remove catalyst esters from the hydrocarbon phase, among other downstream operations. Another example of a prior art alkylation process is disclosed in U.S. Pat. No. 3,013,092.
Whereas the above alkylation reactions may occur in a single reactor, Albright et al. disclose a two-step alkylation process in which butyl sulfates or butyl fluorides are formed in the first step and alkylate is produced in the second step. See, for example, “Alkylation of Isobutane with C4 Olefins. 1. First-Step Reactions Using Sulfuric Acid Catalyst,” Lyle F. Albright et al., Ind. Eng. Chem. Res. 1988, 27, 381-386 and “Alkylation of Isobutane with C4 Olefins. 3. Two-Step Process Using Sulfuric Acid Catalyst,” Lyle F. Albright et al., Ind. Eng. Chem. Res. 1988, 27, 391-397.
Cold acid alkylation feedstocks generally contain both olefins and paraffins, typically in the C3-C5 range. The propane and n-butane in the feed are non-reactive, and build up in the alkylation process, requiring considerable fractionation energy to remove them. In addition, some C4 olefin feeds, such as those produced by dehydration of butanes, may contain aromatic compounds.
Accordingly, there exists a need for a process for decreasing the concentration of inert alkanes in alkylation feedstocks.