GB2105363A

GB2105363A - A process for producing branched paraffinic hydrocarbons

Info

Publication number: GB2105363A
Application number: GB08224727A
Authority: GB
Inventors: George Mortimer Kramer
Original assignee: Exxon Research and Engineering Co
Current assignee: ExxonMobil Technology and Engineering Co
Priority date: 1981-08-31
Filing date: 1982-08-27
Publication date: 1983-03-23
Also published as: NL8203408A; GB2105363B; IT8223048A0; IT1153723B

Abstract

Branched paraffinic hydrocarbons are produced by a process wherein a C4-C6 paraffinic compound is contacted at a temperature of -100 to +150 DEG C with a strong acid system. The reaction zone is characterized by the additional presence of a reagent which comprises an adamantane hydrocarbon or an aminoalkyladamantane either containing at least one unsubstituted bridgehead position, e.g., 4-amino- butyl-1-adamantane. The reactions referred to are isomerization of the non-cyclic C4-C6 compound or addition thereto of a C2-C5 olefin.

Description

SPECIFICATION A process for producing branched paraffinic hydrocarbons This invention relates to a catalytic process for producing branched paraffins under strong acid catalyzed conditions in the presence of adamantane hydrocarbons and aminoalkyladamantanes as hydride transfer catalysts.

Alkylation of olefins by carbonium ions or isomerization of paraffins under strong acid conditions are well-known processes for producing a wide variety of useful hydrocarbon materials and particularly gasoline additives. For example, 2,2,4-trimethylpentane is a common blending agent used for gasoline octane improvement which can be produced by alkylating isobutylene with isobutane in sulfuric acid or liquid HF.

An example of an acid-catalyzed reaction process is described in U.S. Patent No. 3,231 633.

Hydrocarbon conversion processes employing novel Lewis acid systems are disclosed in U.S.

Patent No. 4,229,611 and U.S. Patent No. 4,162,233, both assigned to Exxon Research and Engineering Company.

U.S. Patent No. 3,671,598 describes a process for isomerizing saturated cyclic hydrocarbons under strong acid conditions in the presence of an adamantane hydrocarbon. However, no suggestion is made that an adamantane compound might be useful in paraffin-olefin alkylation under strong acid conditions or that other specifically substituted adamantanes, particularly those with aminoalkyl substituents, might be more effective in increasing the rate of isomerization of paraffins to branched isomers.

New methods for producing such branched paraffinic hydrocarbons useful as octane improvement agents are constantly being searched for in an effort to improve isomerization and paraffin-olefin alkylation process efficiency. More active catalysts enable these rearrangements to be conducted at lower temperature where thermodynamic equilibria are more favorable to branched structures, an important factor in butane, pentane and hexane isomerization.

We have unexpectedly found that the presence of an adamantane hydrocarbon or an aminoalkyladamantane hydrocarbon in a strong acid system containing a paraffinic hydrocarbon rapidly increases the rate of a paraffin-olefin alkylation reaction or of the isomerization of said hydrocarbon, presumably through increased intermolecular hydride transfer that the paraffin undergoes in the system. Since intermolecular hydride transfer is generally the rate determining step in paraffinolefin alkylation and in paraffin isomerization (see "lndustrial Laboratory Alkylation", edited by Lyle F.

Albright and Arthur R. Goldsby, ACS Symposium Series 55, Published Washington, D.C., 1977, Chapter One, "Alkylation Studies" by G. M. Kramer), then the presence of the adamantane hydrocarbon or the aminoalkyladamantane will significantly increase the reaction rate of these processes. In the production of octane-increasing agents, this should lead to the utilization of smaller and more efficient reactors, which enhances the economics of the process.

More specifically, by this invention, there is provided a process comprising contacting a C4-C6 paraffinic hydrocarbon with a strong acid system and in the presence of an adamantane hydrocarbon or an aminoalkyladamantane, containing at least one unsubstituted bridgehead position, at a temperature of about -100 to 1 500 C, thereby producing a branched paraffinic hydrocarbon where only the C4-C6 paraffinic hydrocarbon is used as the feed to the process, a branched isomer of said hydrocarbon having the same number of carbon atoms is produced.In that embodiment of the invention where a C2-C5 olefin is co-present with the C4-C6 paraffinic hydrocarbon in the reactor, the product of the resulting paraffin-olefin alkylation process will be a C6-C11 branched paraffinic hydrocarbon.

In the process, the total described range of applicable paraffins and olefins (for alkylation) can be used in the subject process, under very strong acid conditions, e.g., AlBr3. However, in the slightly weaker acid systems, such as H2SO4 and HF, n-paraffins like n-butane do not generally undergo the isomerization process and n-butane and ethylene do not generally undergo the alkylation process and they require the stronger acid systems, as described herein.

The reason that an adamantane hydrocarbon or an aminoalkyladamantane hydrocarbon increases the rate of intermol-ecular hydride transfer during branched paraffin isomerization or during paraffin-olefin alkylation is not clearly understood. One theory that we do not wish to be bound by is that reversible hydride transfer from the adamantyl group to a carbonium ion in solution is enhanced due to lack of steric repulsions in the transition state involving the adamantyl group when compared to that involving a paraffin.

In the process, C4-C6 paraffinic hydrocarbons are isomerized and C2C5 olefins are alkylated by C4-C6 linear or branched paraffinic compounds. As is well-known, the extent of the rearrangement and the possibility of changing the branchiness of the paraffin, depends primarily on the acid system.

The adamantane hydrocarbon or the aminoalkyladamantane compound catalyzes the process appropriate to the acid employed. Examples of operable paraffins include n-butane, isobutane; isopentane, n-pentane, 2-methylpentane, 3-methylpentane, n-hexane, mixtures thereof, and the like.

In the isomerization process embodiment of the invention, preferred paraffins in the process are 2- and 3-methylpentane, n-hexane, n-pentane and n-butane, or refinery streams containing mixtures of these components.

The product paraffins of the isomerization embodiment of the process are C4-C6 branched paraffinic hydrocarbons. Representative examples include isobutane, isopentane, 2-methylpentane, 3 methylpentane, 2,3-dimethylbutane, 2,2-dimethylbutane, and the like. The preferred product paraffinic hydrocarbons in the process are the most highly branched isomers in each of the C4, C5 and C6 product streams. The product paraffins are useful as gasoline blending agents for octane improvement and/or hydrocarbon solvents.

In the paraffin-olefin alkylation process embodiment of the invention, it is preferred that the starting paraffinic compound used is branched, since branching facilitates reaction and results in a higher octane number product for combustion purposes. A preferred paraffin hydrocarbon in this embodiment of the process is isobutane.

Linear or branched C2-C5 olefins useful in the alkylation embodiment of the process include ethylene, propylene, butene-1, cis or trans butene-2, isobutylene, pentene-1, pentene-2, methylbutenes, mixtures thereof, and the like. Preferred olefins are butylenes.

Weight ratio of paraffin-olefin used in the process is generally about 5 to 1 and preferably about lotto 1.

The product hydrocarbons in the reaction of isobutane with butylenes are mainly C8 branched paraffins. Representative examples include 2,2,4-, 2,3,4-, 2,3,3- and 2,2,3-trimethylpentanes, 2,4-, 2,3- and 2,5-dimethylhexanes, and the like. Preferred products in the alkylation process are the trimethylpentanes.

Carbonium ions in the process can be generated in various ways; most often by protonation of an olefin, but also by oxidation of a paraffin or in situ from their respective halides, e.g., t-butyl chloride, in the acid system, or they can be generated from the free hydrocarbon by undergoing intermolecular hydride transfer with in situ generated adamantyl cation. The preferred method depends on the acid system, but in H2SO4 or HF, they are readily formed by protonation of olefins.

The phrase "a strong acid system", as used herein, refers to the acid system capable of assisting in generating carbonium ions in the process and includes an "acid component" and a solvent, or one material that can function in both capacities, such as concentrated sulfuric acid or liquid HF. The acid system can be solid, liquid, gaseous or in the vapor phase. Preferably, the acid system is a liquid.

The strong acid components in the acid system are conventional erotic, aprotic, or Lewis acids and include Al Br3, AICI3, GaCI3, TaF5, SbF5, AsF5, BF3, HF, HCI, HBr, H2SO4, HSO3F, CF3SO3H, and the like and mixtures thereof. A preferred acid component in the process, when aimed at preparing most highly branched products, is AlBr3, GaCI3, orTa F5. If a rapid but limited rearrangement is desired, H2SO4 or HF would be the preferred acids. An example of the former is the isomerization of n-hexane to dimethylbutanes and an example of the iatter is the isomerization of 2-methylpentane to 3methylpentane. Also, HCI and HBr are preferably not used alone, but are used in combination with other Lewis acids, e.g., AICI3 or Al Br3.

Also a component of the "acid system", if required, is a solvent for the acid component. For Lewis acids, halogenated paraffins and aromatics are generally used; representative examples include CH3Br, CH2Br2, CH2C 12,1 ,2-dichloroethane, 1 ,2,3-trichlorobenzene, 1 ,2,3,4-tetrachlorobenzene, pentafluorobenzene, HF, H2SO4, CF3SO3H, HSO3F and the like, and mixtures thereof.

The molar concentration of acid component in the solvent, if they are different materials, is generally between 0.1 and 8.OM, and preferably 0.5 to 4.OM (moles/liter).

The volume ratio of the acid system to the paraffinic hydrocarbon to be isomerized is generally about 5/1 to 1/5, and preferably about 3/1 to 1/3 parts by volume. However, larger and smaller ratios can be effectively employed.

The adamantane hydrocarbon useful in the process contains from zero to four linear or branched alkyl groups and contains at least one unsubstituted bridgehead position and can be prepared by conventional methods in the art. It is believed that at least one bridgehead adamantane position must be unsubstituted in order for an increase in intermolecular hydride transfer to occur. The adamantyl ring can be substituted with alkyl groups which are generally linear or branched C1-C4 alkyl moieties, being methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, and the like. A preferred alkyl substitute, if present, is methyl.

Representative adamantane hydrocarbons in the process are adamantane, 1-methyl- adamantane, 2-methyl-adamantane, 1,3-dimethyl adamantane, and the like. Preferably unsubstituted adamantane is used.

The molar concentration of adamantane hydrocarbon in solution in the paraffinic hydrocarbon in the process ranges from about 0.1 to 1 .OM (moles/liter). However, larger and smaller ratios can also be used effectively.

The aminoalkyladamantane hydrocarbon useful in the process contains at least one aminoalkyl group and at least one unsubstituted bridgehead position, is surface active and can be prepared by conventional methods in the art. By the term "surface active", is meant that the aminoalkyladamantane depresses the surface tension of the acid system when used at low concentration.

The aminoalkyladamantane is preferably of the formula:

where n=0--10 and wherein the adamantane ring, the alkyl bridge and the amino group can be further modified and substituted with groups which are inert under the process conditions and include C1-C4 alkyl groups for the amine protons and NO2 and CF3 or CnF2n+, (n=1-1 0) replacements for the remaining protons provided that at least one bridgehead hydrogen remains.

Representative examples include 4-aminobutyl-[1-adamantane],3-aminopropyl-[1-adamantane], 2-aminoethyl-[1 -adamantane], 1 -aminomethyl-adamantane, 1 0-aminodecyl-[1 -adamantane], and the corresponding aminoalkyl-2-adamantane derivatives, and the like. Preferred aminoalkyladamantane in the process is 4-aminobutyl-1-adamantane.

The molar concentration of aminoalkyladamantane in the acid solution varies from about 10-8 to 10-1 moles/liter, and preferably about 10-4 to 10-2 moles/liter. However, larger and smaller ratios can also be used effectively.

Temperatures in the process are conducted in the range of about -100 to 1 500 C. The isomerization embodiment of the invention is carried out preferably at about -50 to 1000C, depending primarily on the temperature required to obtain a liquid-phase catalyst. The paraffin-olefin alkylation embodiment of the process is carried out preferably at about -65 to 650C.

The process is normally carried out at atmospheric pressure but may also be conducted at higher pressures up to about 20 atmospheres.

Yields of isomeric hydrocarbons in the process are only limited by the thermodynamic equilibrium at the process temperature, and it is within the scope of this invention to separate undesirable isomers from the mixed product and recycle them for further conversion to the more desirable isomers.

A particularly preferred embodiment of the process is where n-butane is isomerized to isobutane, n-pentane is isomerized to isopentane, and n-hexane is isomerized to a mixture of methylpentanes and dimethylbutanes.

Yields of alkylate in the process range from about 1 50 to 204 percent of theory based on starting olefin (butylenes).

weight of product Yield=( ) x 100 weight of olefin feed Particularly preferred embodiments of the alkylation process are where isobutylene is reacted with isobutane to produce predominantly a mixture of 224, 234, 233 and 223 trimethylpentanes.

Propylene is reacted with isobutane cation to produce a C7 product comprising 2,3- and 2,4dimethylpentanes; where isobutane is reacted with a mixture of butenes, as obtained from a petroleum feedstream, to produce a mixture comprising branched C5 paraffinic hydrocarbons of which at least 80 percent are trimethylpentanes; and wherein isobutane is reacted with a mixture of amylenes, as obtained from a petroleum feedstream, to produce a mixture comprising predominantly branched C5 and branched C9 paraffinic hydrocarbons.

Apparatus for carrying out the subject process is conventional, either in a laboratory, pilot plant, or full industrial scale, and the process can be conducted in a batch-type operation or in a continuoustype operation and in slurry, liquid, gaseous, or vapor phase. Preferred is a continuous-type operation.

Generally, the process is conducted by contacting a liquid mixture of paraffin and an adamantane or an amino-alkyladamantane hydrocarbon with the acid system described herein. In the paraffin-olefin alkylation embodiment of the invention, an olefin is a component of the mixture. If the hydrocarbon mixture is miscible with said acid system, then the reaction takes place in a one-phase homogeneous manner. If the acid system is, for example, H2SO4, then the process is conducted in a two-phase manner, the acid system being the lower phase. The entire system is preferably at reaction temperature at time of mixing during which the entire system is adequately mixed, stirred and agitated to ensure good contact between the acid system and the hydrocarbon system. The reaction is allowed to progress until a desired or substantial quantity of former product is obtained.This can be monitored by analytical methods such as gas chromatography and mass spectrometry. After the desired paraffinic product has been formed, the phases can be separated and the hydrocarbon phase treated by extraction or fractional distillation, and the like, to separate out and collect the desired product The adamantane hydrocarbon or the aminoalkyladamantane can be recovered and recycled back to the reactor for further use.

The following examples illustrate the invention.

Example 1 This example shows how a surface active adamantylalkylamine accelerates intermolecular hydride transfer at a sulfuric acid/hydrocarbon interface and results in the faster isomerization of a branched paraffin (3-methylpentane to 2-methylpentane). Table I lists the surface tension of solutions of different molarity, M of 4-aminobutyl-[1-adamantane] in 95.9 percent H2SO4. Also shown are the isomerization rates of 3-methylpentane obtained under well-stirred conditions using equal volumes of hydrocarbon and acid. For comparison, the isomerization rates with no additive and with dodecylamine (a surfactant which cannot function as a hydride transfer intermediate) are also shown.

Table I Isomerization of 3-methylpentane in Conc. H2SO4, 250C Surface Rate Rel. tension Additive, M constants, hr. rate dynes/cm None 0.021 1.0 59.5 AAB",0.002 0.064 3.0 59.0 AAB,0.005 0.118 5.6 57.7 AAB,0.050 0.16 7.6 50.8 C,2H2sNH2,0.050 0.040 1.9 44.5 ')4-aminobutyl-1 -adamantane=AAB The data indicate a sharp increase in the isomerization rate at the concentration at which AAB begins to depress the surface tension of the acid. The comparison between AAB and C,2H2sNH2 indicates the value of incorporating hydride transfer capability into the surfactant.

Since the isomerization of 3-methylpentane in H2SO4 is believed to involve a slow, ratedetermining hydride transfer, this example indicates that AAB will catalyze this type of process in conc.

H2SO4.

Example 2 This example demonstrates the ability of adamantane to catalyze an isomerization reaction in sulfuric acid. One hundred ml. of conc. H2SO4, (96%) was mixed with one hundred ml. of 3methylpentane in a 500 ml. 2-neck flask at room temperature. The system was stirred vigorously and samples of the hydrocarbon phase were withdrawn periodically and analyzed by gas chromatography for the extent of isomerization. The reaction was then repeated with 0.1 M and 0.3M solutions of adamantane in 3-methylpentane. The relative isomerization rates in the systems were; blank: 0.1 M:0.3M=1 :1.56:2.64. Thus, the net isomerization rate of 3-methylpentane to 2-methylpentane more than doubled with the 0.3M solution, as compared to the control blank.

Example 3 This example shows that hydride transfer is catalyzed by the presence of adamantane in a strong acid containing carbonium ions.

An aluminum bromide solution was prepared by weighing 0.534 grams, 0.002 moles, AlBr3 (purified by sublimation), into an NMR tube. The tube was cooled to -780C and then CD3Br was passed through a bed of CaCI2 (drier), and condensed on the AlBr3 to provide a half milliliter of a 4.0 molar solution. The mixture was warned and shaken quickly to provide the solution for study.

The t-butyl cation-adamantane system was prepared in two ways. One was by adding tbutylbromide and adamantane to the acid mixture just before warming and shaking, and the other was by reversing the procedure and mixing 1-bromoadamantane with isobutane. The additive concentrations were 0.1 M in all cases and provided clear homogeneous solutions.

Nuclear magnetic resonance studies ('H) were done at -400C on a Varian 360-L spectrometer.

Both solutions exhibited substantially identical spectra showing a sharp absorption band with a half width of ca. 4.3Hz for the butyl methyl groups and another sharp absorption band for adamantane's methylene protons. The machine (tertiary or bridgehead), hydrogen atoms, which are the species being transferred as hydrides, are seen as a small broad band.

Solutions of the t-butyl cation with isopentane, norbornane and methylcyclopentane showed a much broader band for the half width of the butyl system, the FWHM being about an order of magnitude greater than before (full width at half maximum height) indicating that much slower intermolecular hydride transfer was occurring in these systems than when adamantane was present.

Since intermolecular hydride transfer is a slow step in isobutane-olefin alkylation, it is reasonably believed that in a paraffin-olefin acid catalyzed alkylation process, such as between isobutane and isobutylene, the presence of adamantane or an adamantyl derivative will substantially increase the reaction rate and improve the process.

Example 4 A series of batch alkylation experiments were carried out in which a mixture of 13.6 percent 2 butene and 86.4 percent isobutune was stirred with H2SO4 (conc.) at 1 00C for 15 minutes. After this time the emulsion was allowed to settle and the hydrocarbon phase analyzed by gas chromatography.

In the batch experiments, it is important to note that the acid is not yet in a "steady state" condition and the initial alkylate is distinctly different from that which would be obtained once a lined out condition is reached. The initial alkylate is normally characterized by exhibiting a low "yield", this being herein defined for comparative purposes as the percentage of C5,s in the C4+C8 products divided by the percent of C4-olefin the reactant mixture.

A comparison of alkylation efficiency where additives are present can readily be made (even during the initial alkylation period) by comparing the "yield" in these experiments with an appropriate blank run. This is shown in the following table where 4-(1 '-adamantyl)-butyl-amine and 5-(1 adamantyl)-pentanoic acid are compared with an experiment with no additive.

Table II Conditions: Acid/paraffin, V/V=1/1; 100C, 15 Min.

% 2-butene in isobutane=13.64 Run 1 2 Additive None 4-(1 '-adamantyl)-butylamine Conc., M/1 2x10-3 Product, Wt.%'a' iC4H10 94.42 95.53 nC4H1O 5.49 3.93 2,2,4 TMCs 0.034 0.15 2,5 DMC6 0.004 0.014 2,4 DMC8 0.016 2,2,3 TMC5 0.04 2,3,4TMC5 0.028 0.19 2,3,3TMC5 0.016 0.13 99.99 99.64 Yield 0.59 3.96 Rel. Efficiency; [Y] Additive 1 6.7 [Y] Blank 'a'For comparative purposes this is the distribution of only the C4+C8 components.

The data indicate that the alkylate yield increased 6.7 fold with 4-(1 '-adamantyl)-butylamine.

Claims

1. A process for producing branched paraffinic hydrocarbons wherein a C4-C8 paraffinic compound is contacted at a temperature of about -100 to 1 500C with a strong acid system in a reaction zone characterised by the additional presence in said reaction zone of a reagent which comprises an adamantane hydrocarbon containing at least one unsubstituted bridgehead position or an aminoalkyladamantane containing at least one unsubstituted bridgehead position.

2. A process according to Claim 1 in which said process is an alkylation process, said C4-C6 paraffinic compound is a linear or branched paraffinic compound capable of forming a carbonium ion under strong acid conditions and said process is carried out in the further additional presence of a C2- C5 olefin to produce a C8-C11 branched paraffinic hydrocarbon.

3. A process according to either of Claims 1 and 2 in which said paraffinic compound comprises n-butane, isobutane, n-pentane, iso-pentane, n-hexane, 2-methylpentane, an isomer thereof or a mixture thereof.

4. A process according to Claim 2 and Claim 3 in which said olefin comprises ethylene, propylene, butene-1, cis or trans butene-2, iso-butylene, a pentene, an isomer thereof or a mixture thereof.

5. A process according to Claim 1 in which said process is an isomerization process, said C4-C6 paraffinic compound is a non-cyclic paraffinic hydrocarbon comprising n-butane, n-pentane, n-hexane, 2-methylpentane, 3-methylpentane, isomers thereof or a mixture thereof.

6. A process according to any one of Claims 1-5 in which said acid system contains an acid component selected from AlBr3, Al Cl3, GaCI3, Taxs, SbF5, AsF5, BF3, HF, HCl, HBr, H2SO4, HSO3F, CF3SO3H and mixture thereof.

7. A process according to any one of Claims 1-6 in which said acid system contains a solvent selected from CH3Br, CH2B r2, CH2Cl2, 1 ,2-dichloroethane, I ,2,3-trichlorobenzene, 1 ,2,3,4- tetrachlorobenzene, pentafluorobenzene, HF, H2 SO4, HSO3F, CF3SO3H and mixtures thereof.

8. A process according to any one of Claims 1-7 in which said adamantane hydrocarbon is an unsubstituted adamantane.

9. A process according to any one of Claims 1-7 in which said adamantane hydrocarbon is an unsubstituted adamantane.

10. A process for producing branched paraffinic hydrocarbons substantially as hereinbefore described with particular reference to the Examples.

11. Branched paraffinic hydrocarbons whenever produced by the process according to any one of the preceding claims.