US3839489A - Isomerization with asf5 and/or sbf5 and with trifluoromethanesulfonic acid or hf and high h2 partial pressure - Google Patents

Abstract

1. AN IMPROVED ALKANE ISOMERIZATION PROCESS WHICH COMPRISES ISOMEERIZING NORMAL PARAFFINS HAVING FROM 4 TO 8, INCLUSIVE CARBON ATOMS TO SKELETAL ISOMERS CONTAINING THE SAME NUMBER OF CARBON ATOMS BY CONTACTING THE PARAFFINS UNDER ISOMERIZATION CONDITIONS WITH A LIQUID PHASE CATALYST SELECTED FROM THE GROUP CONSISTING OF ARSENIC PENTAFLUORIDE, ANTIMONY PENTAFLUORIDE, AND MIXTURES THEREOF WITH EITHER TRIFLUOROMETHANESULFONIC ACID OR HDROGEN IN THE PRESENCE OF SUFFICIENT HYDROGEN TO PROVIDE A HYDROGEN PARTIAL PRESSURE OF 900-4000 P.S.I.G. DURING SAID ISOMERIZATION TO SUPPRESS CRACKING OF PARAFFINIC REACTANTS TO LESS DESIRABLE CRACKED PRODUCTS AND INCREASE SELECTIVELY TO DRSIRED ISOMERIC PRODUCTS.

Description

United States Patent 'ice 3,839,489 ISOMERIZATION WITH AsF AND/0R SbF AND WITH TRIFLUOROMETHANESULFONIC ACID 0R HF AND HIGH H PARTIAL PRESSURE John E. Mahan and John R. Norell, Bartlesville, Okla., assignors to Phillips Petroleum Company No Drawing. Filed Feb. 28, 1972, Ser. No. 230,076 Int. Cl. C07e 5/28, 5/30 US. Cl. 260-683.68 6 Claims ABSTRACT OF THE DISCLOSURE Paraffinic hydrocarbon feedstocks are contacted with liquid phase superacid systems in the presence of high partial pressures of hydrogen to minimize cracking of reactant paraffinic hydrocarbons to less desirable products and increase the selectivity of the conversion of parafiinic hydrocarbons to skeletal isomers containing the same number of carbon atoms. In one specific embodiment, normal heptane-containing hydrocarbon feedstocks are contacted with a liquid phase catalyst system comprising at least one Group Vb fluoride selected from arsenic pentafluoride, antimony pentafluoride, and mixtures thereof and at least one of trifluoromethanesulfonic acid and HP in the presence of sufficient hydrogen to provide a hydorgen partial pressure of at least about 900 p.s.i.g. to yield with good selectivity C isomers of heptane.

This invention relates to hydrocarbon conversion. In accordance with another aspect, normal paraflins are isomerized with high selectivity to skeletal isomers containing the same number of carbon atoms by contacting with a liquid phase catalyst system comprising a Group Vb fluoride and an acid at high hydrogen partial pressures of at least about 900 p.s.i.g. to suppress cracking and increase selectivity. In accordance with a further aspect, this invention relates to an improved process for the skeletal isomerization of normal paraffins in the presence of a liquid phase catalyst system comprising a Group Vb fluoride and at least one of trifluoromethanesulfonic acid and HP at hydrogen partial pressures of at least about 900 p.s.i.g. to suppress cracking and increase selectivity to skeletal isomers containing the same number of carbon atoms. In accordance with a further aspect, this invention relates to the isomerization of normal heptane with high selectivity to C isomers by contacting with a liquid phase superacid system in the presence of sufficient hydrogen to provide a hydrogen partial pressure in the range 1000-2000 p.s.i.g.

It is well known that the more highly branched isomers of the paraffinic hydrocarbons occurring in petroleum gasoline fractions are more valuable than the corresponding slightly branched or straight chain hydrocarbons because of their higher octane ratings. The demand for motor fuels of greater octane number has increased markedly as the automotive industry has provided gasoline engines with increasingly higher compression ratios to attain greater efiiciency. One of the economically important ways in which the increased demands for high octane fuels can be met is through the isomerization of the light naphtha components of such fuels.

It may be generally stated that the isoparaflinic and branched chain parafiinc hydrocarbons are of greater commercial value to the petroleum industry than the corresponding straight chain hydrocarbons. Thus, for example, 2,2-dimethylbutane has a higher octane rating than the isomeric normal hexane. Isobutane is more valuable than normal butane since the former can be used as a basis for the preparation of 8-carbon atom, branched chain hydrocarbons by alkylation with butylene.

3,839,489 Patented Oct. 1, 1974 The isomerization of normal paraflin hydrocarbons into the corresponding branched chain homologs is well known. For efiecting the isomerization, it is customary to employ certain metal halides, particularly aluminum chloride or aluminum bromide, in conjunction with certain promoters such as hydrogen chloride, hydrogen bromide, or boron fluoride. Recently, strong acid systems such as solutions of fluorosulfonic acid and antimony pentafluoride have also been disclosed as useful isomerization catalysts. An important problem arising with the use of these highly active catalysts is that they promote side reactions such as cracking and disproportionation. These side reactions are particularly evident at high conversion conditions and lead to the formation of substantial amounts of undesirable light and/ or heavy side products.

Accordingly, an object of this invention is to provide an improved hydrocarbon conversion process.

Another object of this invention is to provide an isomerization process whereby high selectivity to skeletal parafiinic isomers is achieved.

A further object of this invention is to provide an isomerization process whereby cracking to undesirable products is minimized.

A further object of this invention is to provide an improved isomerization process for the conversion of paraffinic hydrocarbon to skeletal isomers with high selectivity.

Another object of this invention is to provide an improved isomerization process for the conversion of normal heptane with high selectivity to skeletal isomers.

Other objects and aspects as Well as the several advantages of the invention will be apparent to those skilled in the art upon further consideration of the specification and the appended claims.

In accordance with the invention, it has been found that parafiinic hydrocarbons can be isomerized to skeletal isomers with high selectivity with minimum cracking by conducting the isomerization with liquid phase superacid catalyst systems in the presence of high hydrogen partial pressures above about 900 p.s.i.g.

Further in accordance with the invention, it has been found that normal parafiins can be isomerized with high selectivity to branched isomers containing the same number of carbon atoms by contacting paraflinic hydrocarboncontaining feedstocks with a liquid phase catalyst comprising at least one Group Vb fluoride selected from arsenic pentafiuoride, antimony pentafluoride, and mixtures thereof and at least one of trifluoromethanesulfonic acid and hydrogen fluoride under hydrogen partial pressures ranging from 900 to 4000 p.s.i.g. to suppress cracking of paraflinic reactants to less desirable cracked products and increase selectivity to desired isomeric products.

In accordance with one specific embodiment, normal heptane isomerizes with high selectivity to branched C isomers by contacting with a liquid phase catalyst comprising either antimony pentafluoride or arsenic pentafluoride and HF or trifiuoromethanesulfonic acid at hydrogen partial pressures in the range l0002000 p.s.i.g.

In accordance with another embodiment, Z-methylhexane is isomerized to C isomers with good selectivity by contacting with a liquid phase catalyst system comprising antimony pentafluoride and hydrogen fluoride at hydrogen partial pressures in the range 1000-2000 p.s.i.g.

Suitable parafiinic hydrocarbon-containing feedstocks for the purposes of the present invention will contain normal paraflinic hydrocarbons having from 4 to 8, inclusive, carbon atoms in the molecule and can be exemplified by normal butane, normal pentane, normal hexane, normal heptane, normal octane, and the like. While the feed can substantially comprise a purified normal paraffinic hydrocarbon stream, it is also contemplated that mixtures of various paraffic hydrocarbons can be employed.

One component of the liquid phase catalyst system of the present invention comprises a fluoride of a Group Vb element. Specific examples of these fluorides include antimony pentafluoride and arsenic pentafluoride, as well as mixture thereof.

The catalyst composition of the present invention also comprises trifluoromethanesulfonic acid and/or As indicated above, the formation of undesirable side products can be suppressed and the selectivity to desired skeletal iosmers can be increased by carrying out the isomerization in the presenece of at least 900 p.s.i.g. of hydrogen pressure. The hydrogen pressure can vary from 900 to 4000 p.s.i.g., but with pressures generally in excess of 2000 p.s.i.g. hydrocarbon conversion decreases. Accordingly, it is preferred to carry out the isomerization reaction at hydrogen partial pressures in the range 1000- 2000 p.s.i.g.

The reaction conditions for isomerization of the feed can be in the range of to 100 (3., usually 15 to 65 C., and pressure suflicient to maintain the hydrocarbon reactants and catalysts as liquids in the reaction zone and the temperatures and pressures should be chosen accordingly. The time of contact is subject to wide variation, the length of residence time dependent in part upon the temperature and catalyst concentration employed. In general, contact times ranging from about minutes to 48 hours, preferably minutes to about 2 hours, are employed.

The mole ratio of paraflinic hydrocarbon to Group Vb fluoride forming the catalyst of the invention will generally be in the range 50:1 to 02:1, preferably 1:1 to :1. The mole ratio of trifluoromethanesulfonic acid or HF to Group Vb fluoride catalyst components will generally be in the range 100:1 to 02:1, preferably 1:1 to 20:1.

The process of the invention is conducted as a batch 4 SPECIFIC EXAMPLES In the practice of this invention, the process is carried out in a 30 ml. Hastelloy B autoclave. Antimony pentafluoride and arsenic pentafluoride which are very hygroscopic and fume profusely in air were weighed and transferred under a nitrogen atmosphere. The antimony pentafluoride or arsenic pentafluoride and liquid hydrogen fluoride or trifluoromethanesulfonic acid were then mixed and transferred to the reactor at ice bath temperature. Normal heptane was added and the reactor was pressured with the desired amount of hydrogen. The reactor was heated by means of a water bath to the desired temperature for the specified period of time.

Workup involved cooling the Hastelloy B autoclave in Dry Ice-acetone, venting the hydrogen, and then rapidly pouring the cold mixture into a Teflon separatory funnel. The upper hydrocarbon layer was drained into a cold (Dry Ice-acetone temperature) Fischer-Porter aerosol compatibility bottle containing about 5 grams of potassium carbonate. The bottle was quickly capped with a head equipped with a pressure gage and a silicone septum for withdrawing glc samples. Results were reported as selectivities based on the glc (gas-liquid chromatography) analyses.

EXAMPLE I A liquid catalyst system comprising antimony pentafluoride and HF was used to eflect the isomerization of normal heptane in accordance with the procedure set forth above at varying hydrogen partial pressures. The isomerization was effected at a temperature of 25 C. for a period of three hours. Approximately 0.5 mole nheptane, ml. HF, and 0.5 mole SbF were used in each run. The results of the normal heptane isomerization are given below in Table I.

TABLE I Isomerization of normal heptane with liquid Sbfi/HF at 25 C.

11-01 percent conver- 112, Total sion p.s.1.g: 03 04's 05's 05's 0 's Heavies cracking 96. 0 0 3. 0 30. 0 24. 0 21. 0 9. 0 13. 0 99. 0 400 4. 3 35. 8 25. 6 21. 6 10. 3 2. 4 g 99. 4 700 19. 2 49. 3 6. 8 6. 4 18. 2 0. 1 81. 8 98. 6 1, 000 25. 5 43. 7 0. 5 0. 6 29. 7 Trace 70. 3 96. 0 500 15. 0 34. 0 Trace Trace 50. 0 0. 0 49. 0 96. 0 1, 600 20. 0 28. 0 1. 0 1. 0 50. 0 0. 0 50 O 53. 0 2, 000 9. 2 14. 3 1. 0 1. 1 74. 4 0. 0 25: 6 15. 2 2, 700 9. 3 14. 3 3. 1 1. 2 71. 7 O. 4 28. 3 9. 3 4, 900 9. 2 13. 7 5. 9 1. 9 69. 4 0. 0 30. 7

or a continuous operation. The apparatus employed can be of a conventional nature and can comprise a single reactor equipped with sufficient stirring devices. Good agitation is important because the less dense paraflinic hydrocarbon layer is not miscible with the denser liquid acid phase. Unreacted reactants, catalyst and other products of the reaction can be separated from the desired product and from one another such as by distillation and returned in whole or in part to the isomerization zone. The resultant product can be further processed as by alkylation and the like or be employed directly as a high octane gasoline blending agent. The reaction zone is preferably constructed of materials which are resistant to corrosion by the catalyst. For example, the reactor can be a Monel lined reactor. It is preferred that the reaction be carried out under anhydrous conditions in an inert atmosphere. Trifluoromethanesulfonic acid fumes copiously upon exposure to air and the Group Vb halides are also bydrolyzed on exposure to atmospheric moisture.

Referring to the above table, it will be observed that conversion drops ofl rapidly above 2000 p.s.i.g. hydrogen whereas the selectivity to isomerized C s remains high. It is to be further noted from the above table that Runs 5 and 6, which were carried out at 1500 and 1600 p.s.i.g. hydrogen, result in 96 percent n-C, conversion with a selectivity of 50 percent to C and the formation of no heavies. It will also be observed from the above table that although heptane conversion was high for Runs 1 and 2, the total cracking was also above percent. It will be observed from the above table that 400 p.s.i.g. hydrogen did not reduce the selectivity to cracking as compared to 0 p.s.i.g. hydrogen. Runs carried out at 1500-16000 p.s.i.g. hydrogen reduces selectivity to cracking to about 50 percent. Little or no acid soluble oils were formed and selectivity to heavies in Runs 3 through 9 was less than 0.5 percent.

6 The extent of n-heptane isomerization is shown by the the same number of carbon atoms by contacting the relative weight percentages of the C isomers in Table paraflins under isomerization conditions with a liquid II below. phase catalyst selected from the group consisting of arsenic DMP TMB DMP 2-MH *The following abbreviations are used in Table II: 2,2-DMP for 2,2-dimethylpentane; 2,4-DMP for 2,4-dimethylpentane; 2,2,3-TMB for 2,2,3-tn'methylbutane; 3,3-DMP for 3,3- dimethylpentane; 2,3-DMP for 2,3-dimethylpentane; 2-MH for J-methylhexane; 3-MH for 3-methylhexane; 3EP for 3-ethylpentane; 02-01 for normal heptane.

EXAMPLE II pentafluoride, antimony pentafluoride, and mixtures thereof with either trifiuoromethanesulfonic acid or hy- Normal heptane was isomerized to its branched isomers drogen in the presence of sufficient hydrogen to provide by contacting with a mixture of antimony pentafluoride ahydrogen partial pressure of 9004000 p.s.i.g. during said and trifiuoromethanesulfonic acid (Run 10) and arsenic isomerization to suppress cracking of paratfinic reactants pentafluoride and HF (Run 11) at approximately C. to less desirable cracked products and increase selectively for three hours in the presence of high hydrogen partial to desired isomeric products.

pressures. In Run 10, 0.055 mole of antimony pentafluo- 2. A process according to claim 1 wherein the paraffinic ride, 0.5 mole n-heptane and 50 ml. (84 g., 0.56 mole) of 25 hydrocarbon comprises normal heptane and the hydrogen trifiuoromethanesulfonic acid were used. In Run 11, 0.053 partial pressure is in the range 10004000 p.s.i.g. mole of arsenic pentafluoride, 0.5 mole of n-heptane and 3. A process according to claim 1 wherein the isom- 50 ml. of HF were used. Results of the isomerization of erization is conducted at a temperature in the range 0- normal heptane are given below in Table III. 100 C., with a paraffinic hydrocarbon to Group Vb TABLE III 70-01 per- Percent seleetivities 'lemp., Time, H2, cent con- Run Catalyst 0. hours p.s.i.g. version 03 04's 05's CnS 01's Heavies 10 sbF /omso fl 3.0 1,500 96.8 14.9 20.0 0.5 0.8 56,6

11 AsF /HF 23-25 3.0 1,500 05.0 23.9 45.0 0.6 0.8 29.4 0.0

It will be observed from the above runs that good fluoride mole ratio of 50:1 to 02:1 and a trifluoroselectivity to C s was observed with no formation of methanesulfonic acid or HF to Group Vb fluoride mole heavies. ratio in the range 100:1 to 0.2: 1.

EXAMPLE III 40 4. A process according to claim 1 wherein said In another run Z-methylhexane was isomerized to its Paramnic hydfocarbon corhprifes z'methylhexane, the branched isomers by contacting with a liquid catalyst hydfogen P Pmssure 15 1n the range 1000-2000 mixture of antimony pentafluoride and hydrogen fluoride P- and the hquid Phase catalyst comprises antimony under high hydrogen partial pressure. In the run, 0.052 Pelltflfiuofide and mole of antimony pentafiuoride, 0.5 mole of Z-methyl- 5- A process according to claim 2 wherein the liquid hexane and ml. of HF were used. Results of the isomphase catalyst is antimony pentafluoride with either hyerization are given below in Table IV. drogen fluoride or trifluoromethanesulfonic acid.

TABLE IV Reaction of 2-methylhexane with SbFs/HF Seleetivities 2-MH Percent H2, 2,2- 2,4- 2,2,3- 3,3- 2,3 3- Conversion p.s.i.g 0 04's O5s Cus n-O DMP DMP TMB DMP DM MH EP Heavies *For abbreviations usedin this table see footnote at bottom of Table II.

As demonstrated by the above example, branched 6. A process according to claim 2 wherein the liquid isomers of n-heptane such as 2-methylhexane or 3-methylphase catalyst comprises arsenic pentafiuoride and hexane can be used alone or in admixture with normal heptane in the present process. I References Clted In the above examples it will be noted that the extent UNITED STATES PATENTS of cracklng 1s shown by the sum of 3,755,493 8/1973 Norell 260683.68

3,766,286 10/ 1973 Olah 260-683.68

(C +C +C s+C +Heavie5) 2,452,812 11/1948 Wachter 3,678,120 7/1972 Bloch 260683.47

W 1 3,594,445 7/1971 Parker 260683.68 e C m- 3,709,817 l/1973 Suggitt et a1 260683.68

1. An improved alkane isomerization process which 3,674,681 4/1972 comprises isomerizing normal parafiins having from 4 to 7 8, inclusive, carbon atoms to skeletal isomers containing Lyon 260-68368 0 GEORGE J. CRASANAKIS, Assistant Examiner

Claims (1)

1. AN IMPROVED ALKANE ISOMERIZATION PROCESS WHICH COMPRISES ISOMEERIZING NORMAL PARAFFINS HAVING FROM 4 TO 8, INCLUSIVE CARBON ATOMS TO SKELETAL ISOMERS CONTAINING THE SAME NUMBER OF CARBON ATOMS BY CONTACTING THE PARAFFINS UNDER ISOMERIZATION CONDITIONS WITH A LIQUID PHASE CATALYST SELECTED FROM THE GROUP CONSISTING OF ARSENIC PENTAFLUORIDE, ANTIMONY PENTAFLUORIDE, AND MIXTURES THEREOF WITH EITHER TRIFLUOROMETHANESULFONIC ACID OR HDROGEN IN THE PRESENCE OF SUFFICIENT HYDROGEN TO PROVIDE A HYDROGEN PARTIAL PRESSURE OF 900-4000 P.S.I.G. DURING SAID ISOMERIZATION TO SUPPRESS CRACKING OF PARAFFINIC REACTANTS TO LESS DESIRABLE CRACKED PRODUCTS AND INCREASE SELECTIVELY TO DRSIRED ISOMERIC PRODUCTS.