WO1993000316A1

WO1993000316A1 - Improved liquid acid alkylation catalyst and isoparaffin:olefin alkylation process

Info

Publication number: WO1993000316A1
Application number: PCT/US1992/005201
Authority: WO
Inventors: Kenneth Joseph Del Rossi; Albin Huss, Jr.
Original assignee: Mobil Oil Corporation
Priority date: 1991-06-21
Filing date: 1992-06-18
Publication date: 1993-01-07
Also published as: AU2252992A

Abstract

The invention provides an isoparaffin:olefin alkylation catalyst composition comprising from about 10 to about 90 weight percent of at least one selected from the group consisting of hydrofluoric acid and the halogenated sulfonic acids together with from about 10 to about 90 weight percent of a solvent having a donor number of less than about 40 in the absence of intentionally added metal halide. An isoparaffin:olefin alkylation process employing the catalyst composition of the invention is also disclosed.

Description

IMPROVED LIQUID ACID ALKYLATION CATALYST AND ISOPARAFFIN:OLEFIN ALKYLATION PROCESS

The present invention relates to the art of catalytic alkylation. More specifically, the invention relates to a liquid alkylation catalyst and an isoparaffin:olefin alkylation process. Particularly, the invention provides a liquid alkylation catalyst composition which avoids many of the safety and environmental concerns associated with hydrofluoric acid while retaining a commercially useful level of isoparaffinrolefin alkylation catalytic activity. 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_ to C_ 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 concentrated hydrofluoric or sulfuric acid catalysts under relatively low temperature conditions. Acid strength is preferably maintained at 88 to 94 weight percent by the continuous addition of fresh acid and the continuous withdrawal of spent acid. As used herein, the term "concentrated hydrofluoric acid" refers to an essentially anhydrous liquid containing at least about 85 weight percent HF.

Hydrofluoric and sulfuric acid catalyzed alkylation processes share inherent drawbacks including environmental and safety concerns, acid consumption, and sludge disposal. 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. 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).

Hydrogen fluoride, or hydrofluoric acid (HF) is highly toxic and corrosive. However, it is used as a catalyst in isomerization, condensation, polymerization ^• and hydrolysis reactions. The petroleum industry used anhydrous hydrogen fluoride primarily as a liquid catalyst for alkylation of olefinic hydrocarbons to produce alkylate for increasing the octane number of gasoline. Years of experience in its manufacture and use have shown that HF can be handled safely, provided the hazards are recognized and precautions taken. Though many safety precautions are taken to prevent leaks, massive or catastrophic leaks are feared primarily because the anhydrous acid will fume on escape creating a vapor cloud that can be spread for some distance. Previous workers in this field approached this problem from the standpoint of containing or neutralizing the HF cloud after its release.

U.S. Patent Nos. 4,938,935, 4,985,220 and 4,938,936 teach various methods for containing and/or neutralizing HF acid clouds following accidental releases.

But it would be particularly desirable to provide composition which avoids the cloud forming problems associated with HF while providing commercially useful activity as an isoparaffin:olefin alkylation catalyst. Diluents and complexing agents for hydrofluoric acid have, in the past, been disclosed for various purposes as noted in the following references.

U.S. Patent No. 2,615,908 teaches thioether-HF-copper complex compounds and a method for preparing the same. Potential uses for the thioether-HF-copper composition compounds are listed from column 6, line 55 through column 8 at line 3. The method is said to be useful for purifying HF-containing vent gases from an industrial HF alkylation plant. See column 7, lines 10-24.

U.S. Patent No. 3,531,546 discloses a HF-CO, catalyst composition which is said to be useful for alkylation as well as olefin isomerization.

U.S. Patent No. 3,795,712 relates to acid catalysts comprising a Lewis acid, a Bronsted acid, and a sulfone of the formula R-SO^-R', where R and R' are each separately a monovalent radical containing from 1 to 8 carbon atoms or form together a divalent radical having from 3 to 12 carbon atoms.

U.S. Patent No. 3,856,764 teaches an olefin polymerization catalyst comprising (1) at least one organoaluminum compound, (2) at least one nickel compound selected from the class consisting of nickel salts of carboxylic acids, organic complex compounds of nickel, or nickel tetracarbonyl and (3) at least one hydrogen fluoride complex prepared by complexing hydrogen fluoride with a member of the class consisting of ketones, ethers, esters, alcohols, nitriles, and water.

U.S. Patent No. 4,636,488 discloses an anhydrous nonalcoholic alkylation catalyst comprising a mixture of a mineral acid and an ether in proportions of from about 50 to about 99 weight percent of mineral acid and from about 1 to about 50 weight percent of ether. Useful mineral acids include HF; see column 4 at lines 56-60.

Promoters such as alcohols, thiols, water, ethers, thioethers, sulfonic acids, and carboxylic acids are disclosed in combination with strong Bronsted acids such as HF, fluorosulfonic and trihalomethanesulfonic acids in U.S. Patent No. 3,778,489. The promoters are said to modify the activity of the strong Bronsted acids for alkylation. U.S. Patent No. 3,795,712 teaches hydrocarbon alkylation in the presence of a sulfone and from 10 -5 to 5 moles of hydrofluoric acid per liter of sulfone.

U.S. Patent Nos. 4,025,577 and 4,094,924 teach isoparaffin:olefin alkylation catalysts comprising a hydrogen halide and a metal fluoride, and, optionally, a suitable diluent.

The preceding references demonstrate the desirability of a liquid Bronsted acid catalyst (such as HF) for isoparaffin:olefin alkylation, as well the utility of liquid Bronsted acids in combination with metal halides, particularly metal fluorides. However, metal fluorides have been found to cause operational problems in two principal areas. First, the corrosovity of metal halides toward materials of process unit construction is of a character sufficiently distinct from that of the strong Bronsted acids that more costly preventive measures (including alloy selection, coating, and additive treatment) are required. Second, the presence of a metal halide in a liquid alkylation catalyst composition complicates process design and increases capital and operating costs for the catalyst recovery, treatment, and recycle facilities. Thus, it would be highly desirable both from the standpoint of initial process design and unit construction, as well as from the standpoint of operational simplicity and reliability, to provide an alkylation catalyst composition and process which avoids both the safety and environmental concerns associated with concentrated HF while also overcoming the design and operational difficulties attendant to the use of intentionally added metal halides.

This invention provides a catalyst composition for alkylation of an isoparaffin with an olefin comprising from about 10 to about 90 weight percent of at least one selected from the group consisting of hydrofluoric acid and the halogenated sulfonic acids together with from about 10 to about 90 weight percent of a solvent having a Donor Number of less than about 40 in the absence of intentionally added metal halide.

This invention also provides the catalyst composition of claim 1 wherein said solvent is characterized by a Donor Number of less than about 30.

In accordance with the present invention, it has been found that a group of solvents having Donor

Numbers less than about 40 in admixture with certain strong Bronsted acids surprisingly exhibit commercially useful levels of isoparaffin:olefin alkylation activity, and, at the same time, overcome major drawbacks of both concentrated HF and metal halides.

The invention further provides, in a first aspect, an alkylation catalyst complex comprising from about 10 to about 90 weight percent of at least one selected from the group consisting of hydrofluoric acid and the halogenated sulfonic acids together with from about 10 to about 90 weight percent of a solvent having a Donor Number of less than about 40 in the absence of intentionally added metal halide.

The invention also provides, in a second aspect, a process for alkylating an isoparaffin with an olefin comprising effecting reaction of isoparaffin and olefin with an alkylation catalyst composition comprising from about 10 to about 90 weight percent of at least one selected from the group consisting of hydrofluoric acid and the halogen-substituted sulfonic acids, together with from about 10 to about 90 weight percent of a solvent having a Donor Number of less than about 40, in the absence of intentionally added metal halide.

The invention provides a liquid isoparaffin:olefin alkylation catalyst composition which provides commercially useful levels of isoparaffin:olefin alkylation activity while avoiding safety and environmental concerns attendant to the storage, transfer, and processing of concentrated HF. Feedstocks useful in the present alkylation process include at least one isoparaffin and at least one olefin. The isoparaffin reactant used in the present alkylation process has from about 4 to about 8 carbon atoms. Representative examples of such isoparaffins include isobutane, isopentane,

3-methylhexane, 2-methylhexane, 2,3-dimethylbutane and 2,4-dimethylhexane.

The olefin component of the feedstock includes at least one olefin having from 2 to 12 carbon atoms. Representative examples of such olefins include butene-2, isobutylene, butene-1, propylene, ethylene, hexene, octene, and heptene, merely to name a few. The preferred olefins include the C. olefins, for example, butene-l, butene-2, isobutylene, or a mixture of one or more of these C. olefins, with butene-2 being the most preferred. Suitable feedstocks for the process of the present invention are described in U.S. Patent 3,862,258 at column 3, lines 44-56, the disclosure of which is incorporated by reference as if set forth at length herein. The molar ratio of isoparaffin to olefin is generally from about 1:1 to about 100:1, preferably from about 1:1 to about 50:1, and more preferably from about 5:1 to about 20:1. The term "donicity" describes the propensity of a solvent to donate electron pairs to acceptor solutes. The term "Donor Number" (DN) as used herein is a measure of donicity, and is defined as the negative of the enthalpy change, measured in Kcal-mol- , for the reaction of the solvent with SbCl.. to form a 1:1 adduct, where both reactants are in dilute solution in 1,2-dichloroethane (DCE) . For a discussion of donicity and Donor Numbers, see Y. Marcus, "The Effectivity of Solvents as Electron Pair Donors", 13 Journal of Solution Chemistry 599 (1984) . The Table below, reports donor numbers listed in the Marcus article for various solvents.

Additives useful in the present invention include nitroalkanes, carbonates, perhalogenated alkanes, halogenated alcohols, sulfonic acids, sulfones, acetyl halides, benzoyl halides, phosphorous oxychloride, alkyl sulfites, anhydrides, esters, and sulfuryl halides. Nonlimiting examples of these additives include nitromethane, 1-nitropropane, propylene carbonate, perfluorodecalin, 2,2,2-trifluoroethanol, methanesulfonic acid, sulfolane, acetyl chloride, benzoyl fluoride, methyl propionate, sulfuryl chloride, and sulfuryl chloride fluoride.

Table

Solvent DN Solvent DN

1,2-dichloroethane (0)

Acetyl Chloride 0.7

Benzoyl Chloride 2.3

Sulfuryl Chloride 0.1 Thionyl Chloride 0.4

Selenoyl Chloride 12.2 Phosphoryl Chloride 11.7 Tetrachloroethy1ene

Carbonate 0.8 Dichloroethylene

Carbonate 2.7

Nitromethane 2.7

Nitrobenzene 4.4

Acetic Anhydride 10.5 Methyl Acetate 16.4

Ethyl Acetate 17.1

2-Propyl Acetate 17.5

Ethyl Propanoate 17.1

Ethyl Butanoate 16.8 Ethyl Isobutanoate 16.4

Ethyl t-Pentanoate 12.9

Diethylcarbonate 16.0

Ethylene Carbonate 16.4

1,2-Propylene Carbonate 15.1

Acetone 17.0

2-Butanone 17.4

Methylisopropyl- ketone 17.1

Thus additives useful in the present invention are characterized by Donor Numbers of less than about 40, preferably less than about 30, more preferably less than about 16. The catalyst composition of the present invention may be readily substituted for the concentrated hydrofluoric acid catalyst in an existing hydrofluoric acid alkylatior arocess without substantial equipment modifications. Accordingly, the conversion conditions for the process of the present invention resemble those of typical commercial hydrofluoric acid alkylation processes.

The present alkylation process is suitably conducted at temperatures of from about 10 to about 500^βC, preferably from about 10 to about 200°C, and more preferably from about 20^βC to about βCC. Pressure is maintained to ensure a liquid phase in the alkylation reaction zone. Pressures typically range from from about 20 to about 1200 psig, preferably from about 50 to about 500 psig. Olefin feed rates generally range from about 0.01 to about 10 HSV and more preferably from about 0.05 to about 5 hr WHSV. The mixed isoparaffin:olefin reactants may be contacted with the catalyst composition of the invention in any suitable reaction vessel, examples of which include stirred-tank reactors as well as riser-type reactors. Contact time for the mixed isoparaffin:olefin feed and the catalyst composition of the invention typically are within the range of from about 0.1 second to about 100 minutes, and more preferably from about 10 seconds to about 20 minutes.

The low donicity solvent component of the alkylation catalyst composition may be added by injection directly into the alkylation process unit, or may be mixed with the hydrocarbon charge, or may be mixed with the fresh and/or the circulating acid catalyst component, or with a stream of mixed acid/additive catalyst. Downstream from the alkylation reaction zone, the low donicity solvent is preferably separated from the alkylate product stream, mixed with fresh and/or circulating acid and/or circulating acid/additive catalyst mixture, and recycled to the alkylation reaction zone. The particular separation technique selected, however, depends upon the characteristics of the selected perhalogenated alkane.

The low donicity solvent may partition between the acid and the alkylate-containing hydrocarbon reactor effluent, or may remain in either the hydrocarbon or the acid phase, or may form a third discrete phase, depending upon the characteristics of the selected low donicity solvent. If the boiling point of the selected low donicity solvent does not overlap major hydrocarbon products, distillation is preferred to separate and recycle the solvent. Higher boiling (e.g. >200*C) solvents may require extraction (for example, liquid-liquid solvent extraction) to be efficiently recovered from alkylation byproducts such as ASO (acid soluble oil) . " Changes and modifications in the specifically described embodiments can be carried out without departing from the scope of the invention which is intended to be limited only by the scope of the appended claims.

Claims

CLAIMS:

1. A catalyst composition for alkylation of an isoparaffin with an olefin comprising from about 10 to about 90 weight percent of at least one selected from the group consisting of hydrofluoric acid and the halogenated sulfonic acids together with from about 10 to about 90 weight percent of a solvent having a Donor Number of less than about 40 in the absence of intentionally added metal halide.

2. The catalyst composition of claim 1 wherein said solvent is characterized by a Donor Number of less than about 30.

3. The catalyst composition of claim 2 wherein said solvent is characterized by a Donor Number of less than about 16.

4. The catalyst composition of claim 3 wherein said solvent is selected from the group consisting of acetyl halides, benzoyl halides, phosphorous oxyhalides, alkyl sulfites, anhydrides, esters, and sulfuryl halides.

5. The catalyst composition of claim 1. comprising from about 10 to about 80 weight percent of said solvent.

6. The catalyst composition of claim 5 comprising from about 20 to about 60 weight percent of said solvent.

7. The catalyst composition of claim 1 wherein said halogenated sulfonic acids are selected from the group consisting of chlorosulfonic, fluorosulfonic, difluoromethanesulfonic, trifluoromethanesulfonic, and perfluoroalkanesulfonic acids.

8. A process for alkylating as isoparaffin with an olefin comprising effecting reaction of isoparaffin and olefin with an alkylation catalyst composition comprising from about 10 to about 90 weight percent of at least one selected from the group consisting of hydrofluoric acid and the halogenated sulfonic acides, together with from about 10 to about 90 weight percent of a solvent characterized by a Donor Number of less than about 40 in the absence of intentionally added metal halide.

9. The process of claim 8 wherein said solvent is characterized by a Donor Number of less than about 20.

10. The process of claim 8 wherein said solvent is characterized by a Donor Number of less than about 10.

11. The process of claim 10 wherein said solvent is selected from the group consisting of acetyl halides, benzoyl halides, phosphorous oxyhalides, alkyl sulfites, anhydrides, esters, and sulfuryl halides.

12. The process of claim 8 wherein said solvent comprises from about 10 to about 80 weight percent of said catalyst composition.

13. The process of claim 12 wherein said solvent comprises from about 20 to about 60 weight percent of said catalyst composition.

14. The process of claim 8 further comprising charging said isoparaffin and said olefin to a riser reactor containing said catalyst composition.

15. The process of claim 8 wherein said halogenated sulfonic acids are selected from the group consisting of chlorosulfonic, fluorosulfonic, difluoromethanesulfonic, trifluoromethanesulfonic, and perfluoroalkanesulfonic acids.