Alkylation is a reaction in which an alkyl group is added to an organic molecule. Thus an isoparaffin can be reacted with an olefin to provide an isoparaffin of higher molecular weight. Industrially, the concept depends on the reaction of a C.sub.2 to C.sub.5 olefin with isobutane in the presence of an acidic catalyst producing a so-called alkylate. This alkylate is a valuable blending component in the manufacture of gasolines due not only to its high octane rating but also to its sensitivity to octane-enhancing additives.
Industrial alkylation processes have historically used hydrofluoric or sulfuric acid catalysts under relatively low temperature conditions. The sulfuric acid alkylation reaction is particularly sensitive to temperature, with low temperatures being favored to minimize the side reaction of olefin polymerization. Acid strength in these liquid acid catalyzed alkylation processes is preferably maintained at 88 to 94 weight percent by the continuous addition of fresh acid and the continuous withdrawal of spent acid. The hydrofluoric acid process is less temperature sensitive and the acid is easily recovered and purified.
Both sulfuric acid and hydrofluoric acid alkylation share inherent drawbacks including environmental and safety concerns, acid consumption, and sludge disposal. Research efforts have been directed to developing alkylation catalysts which are equally as effective as sulfuric or hydrofluoric acids but which avoid many of the problems associated with these two acids. For a general discussion of sulfuric acid alkylation, see the series of three articles by L. F. Albright et al., "Alkylation of Isobutane with C.sub.4 Olefins", 27 Ind. Eng. Chem. Res., 381-397, (1988). For a survey of hydrofluoric acid catalyzed alkylation, see 1 Handbook of Petroleum Refining Processes 23-28 (R. A. Meyers, ed., 1986).
With the increasing demands for octane and the increasing environmental concerns, it has been desirable to develop an alkylation process employing safer, more environmentally acceptable catalyst systems. Specifically, it is desirable to provide an industrially viable alternative to the currently used hydrofluoric and sulfuric acid alkylation processes. Consequently, substantial efforts have been made to develop a viable isoparaffin-olefin alkylation process which avoids the environmental and safety problems associated with sulfuric and hydrofluoric acid alkylation while retaining the alkylate quality and reliability characteristic of these well-known processes. Research efforts have been directed toward solid as well as liquid alkylation catalyst systems, as reflected in the following references.
U.S. Pat. No. 3,862,258 teaches an alkylation process using a catalyst comprising a macroreticular acid cation exchange resin and boron trifluoride. According to the patent, the life of such a catalyst can be extended by the presence in the reaction mixture of closely controlled amounts of water which can be added to the feed as water or as water-forming compound.
U.S. Pat. No. 3,450,644 discloses a method for regenerating a zeolite catalyst used in hydrocarbon conversion processes involving carbonium ion intermediates.
U.S. Pat. No. 3,549,557 describes alkylation of isobutane with C.sub.2 -C.sub.3 olefins using certain crystalline aluminosilicate zeolite catalysts in a fixed-, moving- or fluidized bed system.
U.S. Pat. No. 3,644,565 discloses alkylation of a paraffin with an olefin in the presence of a catalyst comprising a Group VIII noble metal present on a crystalline aluminosilicate zeolite. The catalyst is pretreated with hydrogen to promote selectivity.
U.S. Pat. No. 3,647,916 describes an isoparaffin-olefin alkylation process featuring use of an ion-exchanged crystalline aluminosilicate, isoparaffin/olefin molar ratios below 3:1 and regeneration of the catalyst.
U.S. Pat. No. 3,655,813 discloses a process for alkylating C.sub.4 -C.sub.5 isoparaffins with C.sub.3 -C.sub.9 olefins using a crystalline aluminosilicate zeolite catalyst wherein a halide adjuvant is used in the alkylation reactor. The isoparaffin and olefin are introduced into the alkylation reactor at specified concentrations and catalyst is continuously regenerated outside the alkylation reactor.
U.S. Pat. No. 3,706,814 discloses another zeolite-catalyzed isoparaffin-olefin alkylation process and further provides for the addition of C.sub.5 + paraffins such as Udex raffinate or C.sub.5 + olefins to the alkylation reactor feed and the use of specific reactant proportions, halide adjuvants, etc.
U.S. Pat. No. 3,236,671 discloses an alkylation reaction wherein crystalline aluminosilicate zeolites having silica to alumina mole ratios above 3 are used. The reference also discloses the use of various metals exchanged and/or impregnated on such zeolites.
U.S. Pat. No. 3,738,977 discloses alkylation of paraffins with ethylene using a zeolite catalyst which possesses a Group VII metal component. The catalyst is pretreated with hydrogen.
U.S. Pat. No. 3,917,738 describes a process for alkylating an isoparaffin with an olefin using a solid, particulate catalyst capable of absorbing the olefin. The isoparaffin and the olefin are admixed to form a reactant stream in contact with catalyst particles at the upstream end of an adsorption zone. Thereafter, the reactants are passed concurrently with the catalyst so that a controlled amount of olefin is adsorbed into the catalyst before the combination of reactants and catalyst is introduced into an alkylation zone. This controlled olefin adsorption is thought to prevent polymerization of the olefin during alkylation.
U.S. Pat. No. 4,384,161 describes a process of alkylating isoparaffins with olefins to provide alkylate using a large-pore zeolite catalyst capable of absorbing 2,2,4-trimethylpentane, for example, ZSM-4, ZSM-20, ZSM-3, ZSM-18, zeolite Beta, faujasite, mordenite, zeolite Y and the rare earth metal-containing forms thereof, and a Lewis acid such as boron trifluoride, antimony pentafluoride or aluminum trichloride. The use of a large-pore zeolite with a Lewis acid is reported to increase the activity and selectivity of the zeolite, thereby effecting alkylation with high olefin space velocity and low isoparaffin/olefin ratio. According to the patent, problems arise in the use of solid catalyst in that they appear to age rapidly and cannot perform effectively at high olefin space velocity and the patent teaches the above solution to rectify the problem utilizing a zeolite alkylation catalyst.
The article entitled "Fixed Bed Catalytic Process to Produce Synthetic Lubricants from Decene-1", IND. ENG. CHEM. PROD. RES. DEV., Vol. 22, No. 4 (1983) teaches oligomerizing olefin to produce fluids with lubricating properties using a silica-BF.sub.3 -water catalyst. The authors further teach that with this system much of the BF.sub.3 can be recycled to minimize BF.sub.3 consumption and disposal problems. The reference teaches that water is a necessary component of the system and that in its absence a BF.sub.3 -silica catalyst rapidly deactivates.
In U.S. Pat. No. 4,308,414, an olefin, such as 1-decene, is oligomerized in the presence of a three-component catalyst comprising boron trichloride, a minute amount of water and a particulate absorbent material such as silica to a lubricating product predominating in those oligomer fractions having viscosities within the lubricating oil range such as the trimer and tetramer.
U.S. Pat. No. 4,429,177 further relates to a method for making lubricating oil utilizing a catalyst comprising boron trifluoride, a minute amount of elemental oxygen and a particulate absorbent material such as silica.
U.S. Pat. No. 3,977,621 relates to oligomerization of olefins catalyzed by boron trifluoride which is controlled to yield desired trimer as a dominant lubricant product by adding small amounts of ester together with water or alcohol promoter.
U.S. Pat. No. 4,365,105 also relates to oligomerizing an olefin in the presence of three-component catalyst used in making lubricating oils which comprises a particular silica absorbent with boron trifluoride and water absorbed on the silica.
U.S. Pat. No. 4,394,296 relates to a three-component catalyst used in making lubricating oils which comprises a particular silica absorbent with boron trifluoride and water absorbed on the silica.
U.S. Pat. No. 2,939,890 discloses a process for alkylating an aromatic hydrocarbon with an olefin-acting compound at alkylation conditions in the presence of an alkylation catalyst comprising boron trifluoride-modified alumina. Subsequently, U.S. Pat. No. 3,131,230 discloses the importance of the presence of small amounts of water for maintaining catalyst activity. Both of these patents are limited to aromatic alkylation processes.
U.S. Pat. No. 2,804,491 relates to an isoparaffin-olefin alkylation to make gasoline at temperatures between -20.degree. and 150.degree. F. utilizing a two-component catalyst comprising essentially excess BF.sub.3 with a "silica stabilized gel alumina." No activators are taught.
U.S. Pat. Nos. 3,251,902 and 3,893,942, as well as French Patent 1,593,716 and the article by Kirsh and Potts, DIV. OF PET. CHEM. A.C.S. 15, A109 (1970) address alkylation in the presence of zeolite-based catalyst systems.
U.S. Pat. No. 3,467,728 relates to a process for isomerizing olefinic hydrocarbon, such as 1-butene or 1-pentene by contacting the hydrocarbon with a catalyst comprising a crystalline alumina silicate combined with a substantially anhydrous boron halide.
U.S. Pat. No. 3,800,003 relates to a process for producing an alkylation reaction product from an isoparaffinic reactant and an olefinic reactant containing 1-butene, 2-butene and isobutene which includes passing the olefinic reactant through an isomerization zone. The isomerization catalyst comprises a crystalline aluminosilicate combined with a substantially anhydrous boron halide which can be boron trifluoride. Conventional catalysts are utilized for the alkylation reaction and include sulfuric acid and hydrogen fluoride catalyst which have the disadvantages set forth above.
Catalyst complexes comprising BF.sub.3 as well as BF.sub.3 :H.sub.3 PO.sub.4 adducts have been proposed, and are discussed in greater detail below. While these catalysts effectively overcome many of the safety and environmental drawbacks of sulfuric and hydrofluoric acid alkylation systems, the volume and quality of BF.sub.3 alkylates have not, in the past, proven comparable to that of sulfuric or hydrofluoric acid alkylates. Further, the BF.sub.3 -catalyzed isobutane:butene alkylation processes typically require high isoparaffin:olefin feed ratios of at least about 5:1 to produce an alkylate gasoline product of acceptable quality.
U.K. Patent 545,441, assigned to Standard Oil Development Company, teaches a BF.sub.3 :H.sub.3 PO.sub.4 catalyzed isoparaffin-olefin alkylation process.
U.S. Pat. No. 2,345,095 to Bruner teaches a paraffin-olefin alkylation process catalyzed by a boron trifluoride-water complex, represented by the formula BF.sub.3 :nH.sub.2 O, where n is preferably from 1 to 1.5
U.S. Pat. Nos. 2,296,370 and 2,296,371 to Slotterbeck disclose a BF.sub.3 :H.sub.2 O:HF catalyst system and an isoparaffin-olefin alkylation process employing the same. The catalyst system is said to avoid yield loss due to oxidation of the resulting alkylate product.
U.K. Patent 550,711 teaches a process for increasing the activity of at least partially spent BF.sub.3 :H.sub.2 O catalyst systems for reuse in an organic condensation reaction. Briefly, the process volatilizes BF.sub.3 from the liquid catalyst mass to the extent required to promote separation of a distinct hydrocarbon phase from the catalyst mass. This hydrocarbon phase is then decanted off and fresh BF.sub.3 is added to restore catalytic activity.
Canadian Patent 424,000 teaches a process for producing gasoline boiling range hydrocarbons from isobutane and a normally gaseous olefin by absorbing the olefin in phosphoric acid of at least 75 weight percent concentration with an amount of isobutane equal to at least three moles of isobutane per mole of alkyl phosphate in the presence of a catalytic mixture of phosphoric acid and boron halide at temperature between 20.degree. C. and 60.degree. C.
U.S. Pat. No. 3,873,634 to Hoffman teaches a method of increasing the rate of ethylene alkylation by isobutane by carrying out the reaction simultaneously with the alkylation of a small amount of a higher weight olefin with isobutane in the presence of a BF.sub.3 :H.sub.3 PO.sub.4 catalyst complex at low temperature and pressure.
U.S. Pat. No. 3,925,500 to Wentzheimer discloses a combined acid alkylation and thermal cracking process employing a BF.sub.3 :H.sub.3 PO.sub.4 acid catalyst in which unconverted propane and ethane from the alkylation process are converted, for example, to propylene and ethylene which are subsequently alkylated with isobutane to evolve a valuable liquid fuel.
U.S. Pat. No. 4,795,728 to Kocal teaches a hydrofluoric acid catalyzed alkylation process for producing motor fuel. The hydrofluoric acid catalyst complex includes from 0.5 to 5 weight percent of a cationic or anionic surfactant component enabling the process to be operated at an olefin:acid volumetric feed ratio of greater than 1.0 while maintaining acceptable alkylate quality.
Finally, the two-part article "Modern Alkylation", by Lyle F. Albright, published in the Nov. 12 and 26, 1990 issues of the Oil and Gas Journal summarizes the present state of H.sub.2 SO.sub.4 and HF alkylation technology.
Both the liquid-catalyzed and solid-catalyzed alkylation reactions described above share certain essential features, including the need for excess isoparaffin and the criticality of effective catalyst/reactant mixing. But recycling unreacted isoparaffin at the high isoparaffin:olefin ratios required for maximum alkylate quality detracts from the economic benefit of producing the improved alkylate. Clearly, then, it would be highly desirable to provide a catalytic isoparaffin:olefin alkylation process which produces high quality alkylate at relatively low fresh feed isoparaffin:olefin ratios.