US3268616A - Process for producing 2-methyl-2-pentene - Google Patents

Process for producing 2-methyl-2-pentene Download PDF

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US3268616A
US3268616A US269062A US26906263A US3268616A US 3268616 A US3268616 A US 3268616A US 269062 A US269062 A US 269062A US 26906263 A US26906263 A US 26906263A US 3268616 A US3268616 A US 3268616A
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pentene
methyl
acid
isomerization
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William R Edwards
Robert D Wesselhoft
Bert B Williams
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Exxon Mobil Corp
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Humble Oil and Refining Co
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    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C11/00—Aliphatic unsaturated hydrocarbons
    • C07C11/02—Alkenes
    • C07C11/107—Alkenes with six carbon atoms
    • C07C11/113—Methylpentenes
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C5/00—Preparation of hydrocarbons from hydrocarbons containing the same number of carbon atoms
    • C07C5/22—Preparation of hydrocarbons from hydrocarbons containing the same number of carbon atoms by isomerisation
    • C07C5/23—Rearrangement of carbon-to-carbon unsaturated bonds
    • C07C5/25—Migration of carbon-to-carbon double bonds
    • C07C5/2506—Catalytic processes
    • C07C5/2525—Catalytic processes with inorganic acids; with salts or anhydrides of acids
    • C07C5/2531—Acids of sulfur; Salts thereof; Sulfur oxides

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  • PENTENE 2 ETHYL -1- BUTENE AND HEAVIER N-PARAFFINS,ISOPARAFFINS, 2,3 DIMETHVL'I'BUTENE 2 METHYL PENTENE AND LIGHTER AND OTHER OLEFINS 202 ISOMERIZATION DISTILLATION ZONE DISTILLATION TOWER 210 214 TOWER -;'1:5 It: SETTLER 2 26 CAT NAPHTHA 1 1 2
  • United States Patent 1 means PROCESS FOR PRODUCING Z-METHYL-Z- PENTENE William R. Edwards and Robert D. Wesselhoft, Baytown, Tex., and Bert E. Williams, Princeton, N.J., assignors to Humble Oil 3: Refining Company Filed Mar. 29, 1963, Ser. No. 269,062 11 Claims. (C1. 260-6832.)
  • the source streams for production of 2-met-hyl-2- pentene in accordance with the present invention are refinery streams containing the isomeric C olefins such as Z-methyl l-pe-ntene, 2-rnethyl-2-pentene, cisand trans-B-methyl-Z-pentene, cisand trans-3-hexene, etc.
  • Suitable source streams are catalytic naphthas produced by catalytic cracking of gas oils, thermal naphthas produced by thermal cracking of gas oils, acid catalyzed dimerization products such as the propylene dimers produced by phosphoric acid dimerization, etc.
  • the preferred source is catalytic naphtha because it is available in large quantities.
  • the process comprises distilling a catalytic naphtha to obtain a heart out boiling below about 146 F. and suitably within the range of 133 F. to 146 F., contacting the heart cut in an isomerization zone with 60 to 75 weight percent sulfuric acid to isomerize the 2- rnethyl-l-pentene in the heart cut into 2-methy1-2-pen tene, and fractionating the isomerized product to obtain Z-methyl-Z-pentene as a product free from cisor trans- 3-methyl-2-pentene, trans-24hexene, and cisand trans- 3-hexene.
  • 2-methyl-2-pentene is valuable as a feedstock for the production of 4-methyl-1-pentene or neoheptanoic acids.
  • Z-methyl-Z-pentene B.P. 153.1" C.
  • These isomers boil very close to 2-methyl-2-pentene: the cisisomer boils at 153.7 C. (within 1 F. of Z-methyI-Z-pentene), while the transisomer boils at 158.8 C. (within 7 F. of the Z-methyI-Z-pentene).
  • the cis-3-methyl-2-pentene occurs in catalytic naphtha in about the same amount as does Z-methyl-Z-pentene.
  • Z-met-hyIZ-pentene it is virtually impossible to obtain Z-met-hyIZ-pentene as a product free from cis-3-methyl-2-pentene by simple fractionation.
  • the trans-Z-hexene and trans-3-hexene isomers of 2-methyl-2-pentene also boil within 1 F. of the 2- methyl-Z-pentene and occur in relatively substantial amounts in catalytic naphtha. These compounds also would contaminate the Z-methyl-Z-pentene obtained by simple fractionation of catalytic naphtha.
  • this problem is solved by sacrificing all of the 2-methyl-2-pentene which is normally present in catalytic naphtha to obtain a heart out from which 2-methyl-2-pentene may be obtained.
  • the heart cut is chosen to contain Z-methyl-lpentene and is subjected to controlled isomerization to yield Z-methyl-Z-pentene. Unconverted Z-methyl-l-pentene may be separated from the Z-methyl-Zpentene product by distillation.
  • the isomerization step must be rigorously controlled Patented August 23, 1966 in order to avoid the formation of equilibrium amounts of the various isomers of Z-methyI-Z-pentene. That is, the isomerization must be selective in converting 2-methyl-l-pentene into Z-methyl-Z pentene without isomerizing the 2-rnethyld-pentene feed or Z-methyI-Z-pentene product into S-methyl-l-pentene, cisand trans-3-methyl- Z-pentene, 2-ethyl-1abutene, cisand trans-4-methyl-2- pentene, and 4-methyl-1-pentene.
  • the nonselective isomerization might result only in a loss of product selectivity; however, since the cis-3- methyI-Zpe-ntene which is formed could not be removed, 2-methyl-2-pentene of the required high purity could not be recovered.
  • the present invention utilizes critical temperatures and acid concentrations to avoid the methyl shift which gives rise to the above listed isomers.
  • the present invention comprises a first distillation step yielding a 133 F. to 146 F. heart out feedstock for selective isomerization.
  • 'llhe heavier materials including the cis-3-rnethyl-2-pentene and Z-methyI-Z-pentene which naturally occur in the catalytic naphtha are discarded.
  • those compounds which would isomerize in the latter step to form cis-3-methyl-2-pentene (such as Z-ethyl-Lbutene) are also removed from the feedstock to the isomerization step. Therefore, 2-ethyll-butene and higher boiling compounds are removed from the isomerization feedstock so that the heart out feedstock to the isomerization zone has an upper boiling range limit of about 146 F.
  • the initial distillation step it is also desirable to remove the 2,3-dirnethyl-1-butene and lighter compounds.
  • these compounds will not appreciably isomerize to form deleterious materials, they do constitute an ad ditional load on the system and are suitably removed before the isomerization step by establishing a lower limit of about 133 F. on the heart out.
  • these compounds may be passed through the system and separated in a final distillation step wherein the substantially pure Z-methyI-Z-pentene is recovered.
  • the preferred distillation step comprises the separation of a heart cut which excludes 2,3- dimethyl-l-butene and lighter compounds and 2-ethyl-1- butene and heavier compounds.
  • the preparation of the preferred feedstock is illustrated in Table I, below, wherein the composition of the catalytic naphtha raw charge is compared with the heart cut feedstock to the isomerization zone.
  • the heart out which is obtained from the first distillation step may be isomerized in one of two ways. Firstly, it may be isomerized by extraction and regeneration followed by distillation, or it may be passed through an isomerization zone without net extraction, and then distilled. Generally, under either alternative, the isomerization will be accomplished by contact with sulfuric acid having a concentration of 60% to 75% by weight and at a temperature above 20 F. Where no net extraction is to be accomplished, the upper temperature limit may be as high as 80 F.; where extraction and regeneration are used, the upper temperature limit is 60 F.
  • the acid-to-hydrocarbon ratio where no net extraction is used may range from 0.1:1 to 10:1; where extraction-regeneration is used, the range may be from 0.05:1 to 10:1. In both cases the time may range suitably from minutes to 3 hours.
  • Z-methyI-Z-pentene may be recovered which is substantially free of cis-3-methyl-2- pentene.
  • FIG. 1 which represents schematically a first embodiment wherein concurrent extraction and isomerization of the heart out is utilized
  • FIG. 2 wherein isomerization without extraction is utilized.
  • one mode of the present invention is seen to comprise introducing a C through 430 F. catalytic naphtha by way of line 101 for distillation in tower 102.
  • the tower 102 is shown schematically as separating from the desire-d heart cut 2,3- dimethyl-l-butene and lighter, which is removed overhead by way of line 104, and 2-ethyl-1-butene and heavier compounds, which are removed by way of bottoms line 106.
  • the heart out is removed from tower 102 by way of line 108 and passed into an extraction zone 110 wherein it is contacted with from 0.1 to volumes of 62 to 75 Weight percent sulfuric acid per volume of heart cut stream.
  • the sulfuric acid and heart out stream are intimately contacted in the liquid phase by means of agitator 111, at a temperature within the range from F. to 60 F., and for a time period within the range from 5 minutes to 3 hours. Above 60 F. the extraction efficiency becomes too low for efiicient operation, the isomerization selectivity fails, and polymerization losses increase. Below 20 F. the acid becomes too viscous for facile handling.
  • the contact time depends upon the temperature, acid strength, mixing efliciency, acid-to-hydrocarbon ratio, desired recovery, etc.
  • the operating pressure has little effect and may vary from snbatmospheric through superatmospheric pressure.
  • the tertiary olefin (2-methyl-1- pentene) is selectively extracted and passes into the acid phase; the remaining hydrocarbons are substantially unaffected and pass out of the extraction zone as a raffinate comprising c-4-methyl-2-pentene, 2,3-dimethylbutane, t- 4-methyl-2 pentene, Z-methylpentane, 3-methylpentane, and l-hexene.
  • the 2-methyl-1- pentene is isomerized to yield Z-methyl-l-pentene and 2-methyl-2-pentene in the approximate ratio of 1:5. No cisor trans-3-methyl-2-pentene is formed during the controlled extraction-isomerization step.
  • the resulting admixture of fat acid and undissolved hydrocarbon ralfinate is removed from the zone by way of line 112 and passed into a settler 114.
  • the undissolved hydrocarbon rafiinate is removed by way of line 116 while the fat acid is passed by way of line 118 through a heater 120 which raises the temperature of the fat acid very quickly to a temperature which causes the fat acid to release the tertiary olefins (predominantly 2-methyl-2-pentene with some unreacted 2-methyl-1- penetene) and form an admixture of a lean acid phase and a tertiary olefin (Z-methyI-Z-pentene-rich) phase.
  • Other acid-olefin regeneration techniques may be used, but indirect heating at a fast rate is preferred.
  • the fat acid is heated in exchanger 1 20 at a minimum rate of 400 F. per minute to a final temperature of at least 150 F. (preferably about 220 F.) in order to obtain the release of substantial amounts of the 2-methyl-1- pentene and Z-methyl-Z-pentene without substantial losses to polymer.
  • the lean acid phase which remains is substantially free of combined tertiary olefins, thus an admixture of lean acid and released tertiary olefins is formed in the heater 120.
  • the admixture of lean acid and tertiary olefin hydrocarbon phase is passed by way of line 122 into a second settler 124, from whence the lean acid is recycled by way of line 126 into the contacting zone 110.
  • the tertiary hydrocarbon phase is removed from the separator 124 by Way of line 128, either as a liquid or as a vapor.
  • the hydrocarbon phase removed by way of line 128 comprises an admixture of about 16% 2-rnethyl-1-pentene and 84% Z-methyl-Z-pentene, with no cisor trans-3-methyl-2-pentene present.
  • the stream 128 may be passed into a second distillation tower 1 30, from whence the 2-me-thyl-2-pentene is recovered by way of bottoms line 132.
  • the 2-1nethyl-1-pentene is passed overhead as a substantially pure product by way of line 134 and may be recycled to the extraction-isomerization zone 110 by means not shown.
  • the catalytic naphtha C through 430 cut is shown as being charged into tower 20 2' by way of line 20 4.
  • the 2,3- dimethyl-labutene and lighter compounds are withdrawn by Way of line 206, and the 2-ethyl-1-butene and heavier compounds (including 2 methyl-2-pentene) are removed by way of line 208.
  • a heart out which is identical to that obtained in the process of FIG. 1, is removed by way of line 209 and passed into an isomerization zone 210.
  • the isomerization zone 210 is similar to the extraction zone of FIG. 1, except that there, is no net extraction accomplished in the contact zone.
  • the isomerization is accomplished by passing the hydrocarbon stream 209 in contact with a 62 to weight percent sulfuric acid at a temperature within the range of 20 F. to F. and for a time of 5 minutes to 3 hours, depending upon the temperature, acid strength, and acidto-hydrocarbon ratio. At higher temperatures, polymerization losses increase and the isomerization selectivity fails.
  • the acid-to-hydrocanbon ratio may range from 0.05 to 10 volumes of acid per volume of hydrocarbon feed.
  • the control of the acid strength is related .to the temperature of isomerization as well as to its efliciency as an isomerization catalyst.
  • the temperature should be maintained within the range of 20 F. to 80 F. Below 20 F., the acid becomes too viscous for facile handling, whereas, at above 80 F., the competing isomerization reaction and polymerization begin to have deleterious effects.
  • the lower temperatures will be used with the higher acid concentrations, and vice versa, in order to optimize the process and avoid the above-mentioned deleterious effects.
  • the effluent from the isomerization zone 210 is removed by way of line 212 and passed into a settler 214, from which is removed a fat acid recycle.
  • the fat acid recycle stream 216 remains saturated with the tertiary olefin so that there is no net extraction of the tertiary olefins in passage through the isomerization zone, and regeneration of the fat acid is not required.
  • the recycle stream is forced by way of pump 218 and line 220 back into the isomerization zone 210 for further contact with fresh hydrocarbon.
  • the hydrocarbon stream (containing 2-methyl-1-pentene, 2-methyl-2-pentene, and the other heart out hydrocarbons) is separated from the fat acid and removed from settler 214 by way of line 224 and is passed into a distillation zone 226, from whence the 2-methyl-2-pentene is removed by way of line 228 as a substantially pure product, whereas the normal and isoparafiins, and olefins including 2-methyl-l-pentene are removed by way of line 230. No cis-3-methyl-2-pentene is formed in the isomerization reaction and, therefore, the 2-methyl-2-pentene is uncontaminated with that compound.
  • the 2'methyl-2-pentene may be withdrawn as a side stream instead of a bottoms stream as schematically shown, with the small amounts of polymer formed in the process being removed from the column bottoms.
  • the final product before fractionation in the process of FIG. 1 comprises only Z-methyl-l-pentene and 2-methyl-2-pentene, which may be used as a chemical feedstock without further separation.
  • the product obtained in the process of FIG. 2 must In order more fully to establish the present invention, the following examples are submitted.
  • Example 1 In order to show the deleterious effects of operations at higher acid strengths, a run was made utilizing 80 Weight percent sulfuric acid in the process of FIG. 2, wherein isomerization and distillation were used.
  • a mixture of 2-methyl-1-pentene and 50% C parafiins was contacted with 80% by weight sulfuric acid at a temperature of 80 F. for a period of 1 hour.
  • the ratio of acid to hydrocarbon was about 1:3.
  • the efliuent from the contacting zone was separated and analyzed to determine the extent and direction of the isomerization reaction. It was found that all of the Z-met'hyl-l-pentene had disappeared, but the product contained only C paraffins and polymer. All of the 2-methyl-1-pentene was lost to polymer. No 2-methyl-2-pentene was recovered.
  • Example 2 The procedure of Example 1 was followed while using 80% H SO but at a lower temperature, 32 F.
  • Example 3 The procedure of Example 1 was followed in isomerizing a 50-50 mixture of Z-methylpentane and 2-methyl-lpentane with H at 32 F. at a contact time of one hour.
  • the product comprised 45% Z-methyl-Z-pentene, 5% Z-methyl-l-pentene, and 50% Z-methylpentane (calculated on a polymer-free basis). About 0.5% polymer was produced.
  • Example 4 The procedure of Example 1 was followed in isomerizing a 50-50 mixture of Z-methylpentane and Z-methyl-lpentene with 69% H SO at 32 F., 80 F., and F., with samples taken at half-hour intervals to determine the course of the reaction at 32 F. and 80 F. The results are shown below, with product analyses on a polymer-free basis.
  • the acid strength must be maintained within the range of 62 to 75 weight percent and the temperature within the range of 20 F. to 80 F.
  • Example 5 In order to establish the necessity of excluding the 2-ethyl-1-butene and heavier, which necessitates discarding the Z-methyl-Z-pentene present in the catalytic naphtha, a run was made by obtaining a heater cut catalytic naphtha stream boiling within the range from 140 F. to 155 F. and including cis-4-methyl-2-pentene and heavier materials down to and including 2-methyl-2- pentene.
  • the heart cut catalytic naphtha contained 6.5% 2- methyl-l-pentene, 8.5% Z-ethyl-l-butene, 12% 2-methyl-' 2-pentene, and 12% cis-3-methyl-2-pentene. This stream was contacted with 70% by weight sulfuric acid for one hour at 40 F., with an acid-to-oil ratio of 1:3.
  • Example 6 An admixture of 50% 2-methyl-l-pentene and 50% C paraffins was submitted to a series of runs wherein the hydrocarbon admixture was contacted with 70 weight percent sulfuric acid for a period of about one hour at various temperatures. The results are tabulated below.
  • a method of producing high purity 2-methyl-2- pentene from a catalytic naphtha which comprises fractionating said catalytic naphtha to obtain an isomerization feedstock boiling within the range of about 133 F. to about 146 F., and containing Z-rnethyll-pentene, contacting said isomerization feedstock with 60% to 75% sulfuric acid at a temperature within the range of 20 F. to 60 F. for a time within the range from 5 minutes to 3 hours whereby at least a portion of said 2-methyl-1-pentene is selectively isomerized to 2-methyl-2-pentene to produce an isomerized stream, and
  • a method in accordance with claim 1 wherein said Z-methyl-Z-pentene is recovered by separating said acid from said isomerized stream, and distilling said isomerized stream to obtain 2-methyl-2-pentene as a substantially pure product.
  • a method of producing high purity 2-methyl-2- pentene from a hydrocarbon stream containing isomeric C olefins which comprises fractionating said hydrocarbon streams to obtain an isomerization feedstock boiling within the range of about 133 F. to about 146 F., and containing 2- rnethyl-l-pentene, contacting said isomerization feedstock with 60% to 75 sulfuric acid at a temperature within the range of 20 F. to 60 F. for a time within the range from 5 minutes to 3 hours,
  • a method in accordance with claim 6 wherein said Z-methyl-l-pentene is isomerized by extraction into said sulfuric acid to form a fat acid extract, and said Z-methyl-2-pentene recovered by regenerating said acid extract to form an acid phase and a 2-methyl-2-pentene-rich phase, and distilling said 2-rnethyl-2-pentene phase to recover said 2-methyl-2-pentene.
  • a method of producing high-purity 2-methyl-2- pentene from a catalytic naphtha which comprises fractionating said catalytic naphtha to obtain an isomerization feedstock boiling within the range of about 133 F. to about 146 F. and containing 2- methyl-l-pentene, contacting said isomerization feedstock with 60% to 70% sulfuric acid at an acid-to-hydrocarbon ratio within the range of 0.05:1 to about 10:1 by volume, at a temperature within the range of 20 F.

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Description

g- 23, 1965 w. R. EDWARDS ETAL 3,268,616
PROCESS FOR PRODUCING 2-METHYL2PENTENE Filed March 29, 1963 2' 3 DIMETHYL'I' BUTENE AND LIGHTER Z-METHYL-l-PENTENE RAFFINATE '04 34 :28 DISTILLATION EXTRACTION DISTILLATION TOWER ZONE Ho SEPARATOR\ TOWER I02 II 11 CAT- NAPHTHA Eg ii I22 /|30 iOl SETTLER J -J us \J 25 I26 LEAN ACID RECYCLE T Y 2.
PENTENE 2 ETHYL -1- BUTENE AND HEAVIER N-PARAFFINS,ISOPARAFFINS, 2,3 DIMETHVL'I'BUTENE 2 METHYL PENTENE AND LIGHTER AND OTHER OLEFINS 202 ISOMERIZATION DISTILLATION ZONE DISTILLATION TOWER 210 214 TOWER -;'1:5 It: SETTLER 2 26 CAT NAPHTHA 1 1 2|8 FAT ACID RECYCLE 228 Z-METHYLZ'PENTENE 2- ETHYL-l- BUTENE AND HEAVIER PEG. 2.
INVENTORS. WlLLIAM R.EDWARDS,
ROBERT D.WESSEl -HOFT, BY BERT B- WILLIAMS,
United States Patent 1 means PROCESS FOR PRODUCING Z-METHYL-Z- PENTENE William R. Edwards and Robert D. Wesselhoft, Baytown, Tex., and Bert E. Williams, Princeton, N.J., assignors to Humble Oil 3: Refining Company Filed Mar. 29, 1963, Ser. No. 269,062 11 Claims. (C1. 260-6832.)
The present application is related to our copending application Serial No, 217,890 (filed August 20, 1962), now US. Patent No. 3,173,968, and to the copending Edwards and Wesselhoft application Serial No. 115,400 (filed June 7, 1961), now US. Patent No. 3,150,201.
The present invention relates to the production of 2- methyl-Z-pentene from hydrocarbon streams such as depentanized catalytic naphthas; e.g., catalytic naphthas boiling within the range of C to 430 F. More partioularly, the present invention is directed to the production of Z-methyI-Z-pentene, either as a pure product or in admixture with Q-methyl-l-pentene, but uncontaminated with or free from cisor trans-3=methyl-2-pentene.
The source streams for production of 2-met-hyl-2- pentene in accordance with the present invention are refinery streams containing the isomeric C olefins such as Z-methyl l-pe-ntene, 2-rnethyl-2-pentene, cisand trans-B-methyl-Z-pentene, cisand trans-3-hexene, etc. Suitable source streams are catalytic naphthas produced by catalytic cracking of gas oils, thermal naphthas produced by thermal cracking of gas oils, acid catalyzed dimerization products such as the propylene dimers produced by phosphoric acid dimerization, etc. The preferred source is catalytic naphtha because it is available in large quantities.
Briefly, the process comprises distilling a catalytic naphtha to obtain a heart out boiling below about 146 F. and suitably within the range of 133 F. to 146 F., contacting the heart cut in an isomerization zone with 60 to 75 weight percent sulfuric acid to isomerize the 2- rnethyl-l-pentene in the heart cut into 2-methy1-2-pen tene, and fractionating the isomerized product to obtain Z-methyl-Z-pentene as a product free from cisor trans- 3-methyl-2-pentene, trans-24hexene, and cisand trans- 3-hexene.
2-methyl-2-pentene is valuable as a feedstock for the production of 4-methyl-1-pentene or neoheptanoic acids. However, in using the Z-methyl-Z-pentene (B.P. 153.1" C.) as a feedstock in the production or" chemical prod ucts, it is important that the cisand transisomers of 3 methyl-2-pentene be excluded. These isomers boil very close to 2-methyl-2-pentene: the cisisomer boils at 153.7 C. (within 1 F. of Z-methyI-Z-pentene), while the transisomer boils at 158.8 C. (within 7 F. of the Z-methyI-Z-pentene). The cis-3-methyl-2-pentene occurs in catalytic naphtha in about the same amount as does Z-methyl-Z-pentene. Thus, it is virtually impossible to obtain Z-met-hyIZ-pentene as a product free from cis-3-methyl-2-pentene by simple fractionation. Additionally, the trans-Z-hexene and trans-3-hexene isomers of 2-methyl-2-pentene also boil within 1 F. of the 2- methyl-Z-pentene and occur in relatively substantial amounts in catalytic naphtha. These compounds also would contaminate the Z-methyl-Z-pentene obtained by simple fractionation of catalytic naphtha.
. By the practice of the present invention, this problem is solved by sacrificing all of the 2-methyl-2-pentene which is normally present in catalytic naphtha to obtain a heart out from which 2-methyl-2-pentene may be obtained. The heart cut is chosen to contain Z-methyl-lpentene and is subjected to controlled isomerization to yield Z-methyl-Z-pentene. Unconverted Z-methyl-l-pentene may be separated from the Z-methyl-Zpentene product by distillation.
The isomerization step must be rigorously controlled Patented August 23, 1966 in order to avoid the formation of equilibrium amounts of the various isomers of Z-methyI-Z-pentene. That is, the isomerization must be selective in converting 2-methyl-l-pentene into Z-methyl-Z pentene without isomerizing the 2-rnethyld-pentene feed or Z-methyI-Z-pentene product into S-methyl-l-pentene, cisand trans-3-methyl- Z-pentene, 2-ethyl-1abutene, cisand trans-4-methyl-2- pentene, and 4-methyl-1-pentene. Under other circumstances, the nonselective isomerization might result only in a loss of product selectivity; however, since the cis-3- methyI-Zpe-ntene which is formed could not be removed, 2-methyl-2-pentene of the required high purity could not be recovered. As hereinafter set forth, the present invention utilizes critical temperatures and acid concentrations to avoid the methyl shift which gives rise to the above listed isomers.
The present invention comprises a first distillation step yielding a 133 F. to 146 F. heart out feedstock for selective isomerization. 'llhe heavier materials, including the cis-3-rnethyl-2-pentene and Z-methyI-Z-pentene which naturally occur in the catalytic naphtha are discarded. Further, those compounds which would isomerize in the latter step to form cis-3-methyl-2-pentene (such as Z-ethyl-Lbutene) are also removed from the feedstock to the isomerization step. Therefore, 2-ethyll-butene and higher boiling compounds are removed from the isomerization feedstock so that the heart out feedstock to the isomerization zone has an upper boiling range limit of about 146 F.
In the initial distillation step, it is also desirable to remove the 2,3-dirnethyl-1-butene and lighter compounds. Although these compounds will not appreciably isomerize to form deleterious materials, they do constitute an ad ditional load on the system and are suitably removed before the isomerization step by establishing a lower limit of about 133 F. on the heart out. Alternatively, these compounds may be passed through the system and separated in a final distillation step wherein the substantially pure Z-methyI-Z-pentene is recovered.
Thus, it is seen that the preferred distillation step comprises the separation of a heart cut which excludes 2,3- dimethyl-l-butene and lighter compounds and 2-ethyl-1- butene and heavier compounds.
The preparation of the preferred feedstock is illustrated in Table I, below, wherein the composition of the catalytic naphtha raw charge is compared with the heart cut feedstock to the isomerization zone.
TABLE I Cut. Heart Out Compound F. B.P. Naphtha, Isomeriza- M01 percent tion Feed M01 percent 3,3-dimethy1-1-butene 106. 2 0. 05 Cyclopentene. 111. 6 0. O5 Cye1opentane 120. 7 0. 50 2,2-(limethylbutan 121.5 0.04 4 methyl-1-pentene 129. 0 0. 34 3-rnethyl-l-peutene 129. 5 0. 42 2,3-dimethy1-1-butene 132. 2 0. 94 o4-methyl-2pentene 133. 3 0. 33 2,3-dimethylbutane 136. 4 0. 27 t-4-methyl-2-pentene 137. 4 0. 81 2-methylpentane 140. 5 3. 0O 2-rnethy1-1-penten 141. 3 2. 33 3-rnethylpentane. 146. 0 1. 72 l-hexene 146. 3 0. 27 2-ethyl-1-butene 148. 4 0. 79 3-methy1eyclopentene 149. 0 1. 35 4 methy1eyclopentene 149. 0 1. 35 c-3-hexene 151. 6 0. 33 t-B-hexeue 1. 152. 7 0. 43 2-mcthy1-2-pentene 1 153. 1 2. 62 c-3-methyl-2-pentene 153. 7 2. 67 t-2-hexene- 154. 2 0. 81 n-Hexane 155. 7 1. 39 e2-hexene 156. 0 0. 76 t-3-methy1-2-pente1 158. 8 1. 78 Methyleyelopentane. 161. 3 2. 1G 2,3-d1methyl-2-butene 163. 8 0. 71 l-methylcyclopeutene 168. 4 2. 22
The horizontal lines in Table I represent the cut points and the heart cut is included therebetween. Note that Z-rnethyl-Z-pentcne lies below the second line, and is not included in the isomerization feed. This loss of product is necessary if the desired high purity in the final product 2-methyl-2-pentene is to be realized.
The heart out which is obtained from the first distillation step may be isomerized in one of two ways. Firstly, it may be isomerized by extraction and regeneration followed by distillation, or it may be passed through an isomerization zone without net extraction, and then distilled. Generally, under either alternative, the isomerization will be accomplished by contact with sulfuric acid having a concentration of 60% to 75% by weight and at a temperature above 20 F. Where no net extraction is to be accomplished, the upper temperature limit may be as high as 80 F.; where extraction and regeneration are used, the upper temperature limit is 60 F. The acid-to-hydrocarbon ratio where no net extraction is used may range from 0.1:1 to 10:1; where extraction-regeneration is used, the range may be from 0.05:1 to 10:1. In both cases the time may range suitably from minutes to 3 hours.
By each of these alternatives, Z-methyI-Z-pentene may be recovered which is substantially free of cis-3-methyl-2- pentene.
The present invention will be more clearly understood by advertence to the drawing wherein is shown:
FIG. 1 which represents schematically a first embodiment wherein concurrent extraction and isomerization of the heart out is utilized; and
FIG. 2 wherein isomerization without extraction is utilized.
Referring now to FIG. 1, one mode of the present invention is seen to comprise introducing a C through 430 F. catalytic naphtha by way of line 101 for distillation in tower 102. The tower 102 is shown schematically as separating from the desire-d heart cut 2,3- dimethyl-l-butene and lighter, which is removed overhead by way of line 104, and 2-ethyl-1-butene and heavier compounds, which are removed by way of bottoms line 106. The heart out is removed from tower 102 by way of line 108 and passed into an extraction zone 110 wherein it is contacted with from 0.1 to volumes of 62 to 75 Weight percent sulfuric acid per volume of heart cut stream. The sulfuric acid and heart out stream are intimately contacted in the liquid phase by means of agitator 111, at a temperature within the range from F. to 60 F., and for a time period within the range from 5 minutes to 3 hours. Above 60 F. the extraction efficiency becomes too low for efiicient operation, the isomerization selectivity fails, and polymerization losses increase. Below 20 F. the acid becomes too viscous for facile handling. The contact time depends upon the temperature, acid strength, mixing efliciency, acid-to-hydrocarbon ratio, desired recovery, etc. The operating pressure has little effect and may vary from snbatmospheric through superatmospheric pressure.
In the extraction step, the tertiary olefin (2-methyl-1- pentene) is selectively extracted and passes into the acid phase; the remaining hydrocarbons are substantially unaffected and pass out of the extraction zone as a raffinate comprising c-4-methyl-2-pentene, 2,3-dimethylbutane, t- 4-methyl-2 pentene, Z-methylpentane, 3-methylpentane, and l-hexene. While in the fat acid, the 2-methyl-1- pentene is isomerized to yield Z-methyl-l-pentene and 2-methyl-2-pentene in the approximate ratio of 1:5. No cisor trans-3-methyl-2-pentene is formed during the controlled extraction-isomerization step.
The resulting admixture of fat acid and undissolved hydrocarbon ralfinate is removed from the zone by way of line 112 and passed into a settler 114. The undissolved hydrocarbon rafiinate is removed by way of line 116 while the fat acid is passed by way of line 118 through a heater 120 which raises the temperature of the fat acid very quickly to a temperature which causes the fat acid to release the tertiary olefins (predominantly 2-methyl-2-pentene with some unreacted 2-methyl-1- penetene) and form an admixture of a lean acid phase and a tertiary olefin (Z-methyI-Z-pentene-rich) phase. Other acid-olefin regeneration techniques may be used, but indirect heating at a fast rate is preferred.
The fat acid is heated in exchanger 1 20 at a minimum rate of 400 F. per minute to a final temperature of at least 150 F. (preferably about 220 F.) in order to obtain the release of substantial amounts of the 2-methyl-1- pentene and Z-methyl-Z-pentene without substantial losses to polymer. The lean acid phase which remains is substantially free of combined tertiary olefins, thus an admixture of lean acid and released tertiary olefins is formed in the heater 120.
The admixture of lean acid and tertiary olefin hydrocarbon phase is passed by way of line 122 into a second settler 124, from whence the lean acid is recycled by way of line 126 into the contacting zone 110. The tertiary hydrocarbon phase is removed from the separator 124 by Way of line 128, either as a liquid or as a vapor. The hydrocarbon phase removed by way of line 128 comprises an admixture of about 16% 2-rnethyl-1-pentene and 84% Z-methyl-Z-pentene, with no cisor trans-3-methyl-2-pentene present. If it is desired to recover the 2-methyl-2- pentene as a substantially pure product, the stream 128 may be passed into a second distillation tower 1 30, from whence the 2-me-thyl-2-pentene is recovered by way of bottoms line 132. The 2-1nethyl-1-pentene is passed overhead as a substantially pure product by way of line 134 and may be recycled to the extraction-isomerization zone 110 by means not shown.
Thus, it is seen that a highly efficient process of producing high purity Z-methyl-Z-pentene from catalytic naphthas has been provided wherein the 2-methyl-1-pentene is chosen as the sole source of 2-methyl-2-pentene, even though the catalytic naphtha stream contains more 2-methyl-2-pentene than Z-methyl-l-pentene. This anomaly is necessitated by the demand for high purity, which is unobtainable by simple distillation of the naphtha stream.
Referring now to FIG. 2, wherein is shown a preferred mode of the present invention, the catalytic naphtha C through 430 cut is shown as being charged into tower 20 2' by way of line 20 4. As in the process of FIG. 1, the 2,3- dimethyl-labutene and lighter compounds are withdrawn by Way of line 206, and the 2-ethyl-1-butene and heavier compounds (including 2 methyl-2-pentene) are removed by way of line 208. A heart out, which is identical to that obtained in the process of FIG. 1, is removed by way of line 209 and passed into an isomerization zone 210. The isomerization zone 210 is similar to the extraction zone of FIG. 1, except that there, is no net extraction accomplished in the contact zone.
The isomerization is accomplished by passing the hydrocarbon stream 209 in contact with a 62 to weight percent sulfuric acid at a temperature within the range of 20 F. to F. and for a time of 5 minutes to 3 hours, depending upon the temperature, acid strength, and acidto-hydrocarbon ratio. At higher temperatures, polymerization losses increase and the isomerization selectivity fails. The acid-to-hydrocanbon ratio may range from 0.05 to 10 volumes of acid per volume of hydrocarbon feed.
In the isomerization step it is critical to maintain both the acid strength and the temperature Within definite specified limits. Below 62%, the sulfuric acid becomes quite corrosive and is unsuitable for use in steel equipment. In addition, the efiiciency of the acid begins to drop as the acid strength becomes lower than 64.5%. At the upper level, however, as the acid strength increases above about 75%, the Z-methyl-I-pentene tends toisomerize to produce all isomers including the cis-3-methyl-2-pentene.
Also, at these higher acid concentrations, polymerization of the olefins becomes a real problem and makes the process economically unfeasible.
Therefore, it is seen that the control of the acid strength is related .to the temperature of isomerization as well as to its efliciency as an isomerization catalyst. The temperature should be maintained within the range of 20 F. to 80 F. Below 20 F., the acid becomes too viscous for facile handling, whereas, at above 80 F., the competing isomerization reaction and polymerization begin to have deleterious effects. The lower temperatures will be used with the higher acid concentrations, and vice versa, in order to optimize the process and avoid the above-mentioned deleterious effects.
Returning to FIG. 2, the effluent from the isomerization zone 210 is removed by way of line 212 and passed into a settler 214, from which is removed a fat acid recycle. The fat acid recycle stream 216 remains saturated with the tertiary olefin so that there is no net extraction of the tertiary olefins in passage through the isomerization zone, and regeneration of the fat acid is not required. The recycle stream is forced by way of pump 218 and line 220 back into the isomerization zone 210 for further contact with fresh hydrocarbon.
The hydrocarbon stream (containing 2-methyl-1-pentene, 2-methyl-2-pentene, and the other heart out hydrocarbons) is separated from the fat acid and removed from settler 214 by way of line 224 and is passed into a distillation zone 226, from whence the 2-methyl-2-pentene is removed by way of line 228 as a substantially pure product, whereas the normal and isoparafiins, and olefins including 2-methyl-l-pentene are removed by way of line 230. No cis-3-methyl-2-pentene is formed in the isomerization reaction and, therefore, the 2-methyl-2-pentene is uncontaminated with that compound.
In the final distillation step of the process of FIG. 2, as well as in FIG. 1, the 2'methyl-2-pentene may be withdrawn as a side stream instead of a bottoms stream as schematically shown, with the small amounts of polymer formed in the process being removed from the column bottoms.
At this point the distinction between the two processes should be kept in mind. The final product before fractionation in the process of FIG. 1 comprises only Z-methyl-l-pentene and 2-methyl-2-pentene, which may be used as a chemical feedstock without further separation. However, the product obtained in the process of FIG. 2 must In order more fully to establish the present invention, the following examples are submitted.
Example 1 In order to show the deleterious effects of operations at higher acid strengths, a run was made utilizing 80 Weight percent sulfuric acid in the process of FIG. 2, wherein isomerization and distillation were used.
A mixture of 2-methyl-1-pentene and 50% C parafiins was contacted with 80% by weight sulfuric acid at a temperature of 80 F. for a period of 1 hour. The ratio of acid to hydrocarbon was about 1:3. The efliuent from the contacting zone was separated and analyzed to determine the extent and direction of the isomerization reaction. It was found that all of the Z-met'hyl-l-pentene had disappeared, but the product contained only C paraffins and polymer. All of the 2-methyl-1-pentene was lost to polymer. No 2-methyl-2-pentene was recovered.
Thus, it is seen that even at relatively mild temperatures when using highly concentrated (80%) sulfuric acid, the reaction is not selective to the formation of the 2-methyl-2-pentene. Instead, the olefin in the feedstock is completely degraded to polymer.
Example 2 The procedure of Example 1 was followed while using 80% H SO but at a lower temperature, 32 F.
The same results were obtained. All of the Z-methyll-pentene was lost to polymer.
Example 3 The procedure of Example 1 was followed in isomerizing a 50-50 mixture of Z-methylpentane and 2-methyl-lpentane with H at 32 F. at a contact time of one hour.
The product comprised 45% Z-methyl-Z-pentene, 5% Z-methyl-l-pentene, and 50% Z-methylpentane (calculated on a polymer-free basis). About 0.5% polymer was produced.
Example 4 The procedure of Example 1 was followed in isomerizing a 50-50 mixture of Z-methylpentane and Z-methyl-lpentene with 69% H SO at 32 F., 80 F., and F., with samples taken at half-hour intervals to determine the course of the reaction at 32 F. and 80 F. The results are shown below, with product analyses on a polymer-free basis.
TABLE II 2methylpentane 2-methy1-1pentcnc 2-methyl-2-pentene Polymer Z-methylpentane 2methyl-l-pentene 2-methyl-2-pentene Polymer 2-methylpentane 2-methyl1-pentene 2-mcthyl-2-pentene Polymer be fractionated because the normal and isoparatfins, and other olefins, remain in admixture with the 2-methyl-2- pentene. However, in neither case is any cis-3-methylpentene-Z present in the final product.
Note that the product analyses are on a polymer-free basis, while the amount of polymer formed is given as Weight percent of the olefin charged. The increase in 2- methylpentane above the original 50% level is due to extraction of a portion of the 2-methyl-l-pentene into the acid, which was not regenerated. Under lined-out continuous operations, there would be no net extraction and the 2-methylpentane would constitute only 50% of the product. The ratio of Z-methyl-l-pentene to 2- methyI-Z-pentene would, however, remain about the same as above indicated although the percentage of each would be increased in proportion to the decrease in Z-methylpentane.
The above data show that at 32 F. no polymer was formed, and the isomerization process reached substantial equilibrium at about 1 hr. to 1 /2 hrs. after initiation.
At 80 F., substantial equilibrium is reached in /2 hr. to 1 hr., and polymer losses are minimal. Longer times of contact do not increase the isomerization, but only form polymer.
At 100 F., after only one hour, 40% of the olefin was converted to polymer. This indicates that even When using 69% acid, the higher temperature renders the process economically unattractive due to losses of product to polymer. It is therefore seen that the increase of temperature from 80 F. to 100 F. resulted in a loss of selectivity in the isomerization reaction, with a concomitant increase in polymer losses.
Thus, in order to control the isomerization reaction selectively to produce 2-methyl-2-pentene from 2-methyll-pentene, while avoiding the production of polymer and cis-3-methyl-2-pentene, the acid strength must be maintained within the range of 62 to 75 weight percent and the temperature within the range of 20 F. to 80 F.
Example 5 In order to establish the necessity of excluding the 2-ethyl-1-butene and heavier, which necessitates discarding the Z-methyl-Z-pentene present in the catalytic naphtha, a run was made by obtaining a heater cut catalytic naphtha stream boiling within the range from 140 F. to 155 F. and including cis-4-methyl-2-pentene and heavier materials down to and including 2-methyl-2- pentene.
The heart cut catalytic naphtha contained 6.5% 2- methyl-l-pentene, 8.5% Z-ethyl-l-butene, 12% 2-methyl-' 2-pentene, and 12% cis-3-methyl-2-pentene. This stream was contacted with 70% by weight sulfuric acid for one hour at 40 F., with an acid-to-oil ratio of 1:3.
Upon distillation to obtain a 2-methyl-2-pentene concentrate, it was found to contain 73% 2-methyl-2-pentene and 27% cis-3-methyl-2-pentene. Obviously, this is unacceptable when a product uncontaminated with cis-3- methyI-Z-pentene is required.
Example 6 An admixture of 50% 2-methyl-l-pentene and 50% C paraffins was submitted to a series of runs wherein the hydrocarbon admixture was contacted with 70 weight percent sulfuric acid for a period of about one hour at various temperatures. The results are tabulated below.
From Table III it is seen that at 100 F. two deleterious effects conjoin: (1) the selectivity of the isomerization begins to fail and (2) the polymer make markedly increases. Thus, the higher temperatures are undesirable. In order to avoid these deleterious effects, the contacting temperature is kept below about 80 F.
Having disclosed in detail the-present invention, along with the best mode of practicing it, what is desired to be covered by US. Letters Patent should be limited not by the specific examples given, but rather by the appended claims.
We claim:
1. A method of producing high purity 2-methyl-2- pentene from a catalytic naphtha which comprises fractionating said catalytic naphtha to obtain an isomerization feedstock boiling within the range of about 133 F. to about 146 F., and containing Z-rnethyll-pentene, contacting said isomerization feedstock with 60% to 75% sulfuric acid at a temperature within the range of 20 F. to 60 F. for a time within the range from 5 minutes to 3 hours whereby at least a portion of said 2-methyl-1-pentene is selectively isomerized to 2-methyl-2-pentene to produce an isomerized stream, and
recovering 2-methyl-2-pentene from said isomerized stream as a substantially pure product. 2. A method in accordance with claim 1 wherein the isomerization feedstock and sulfuric acid are contacted at an acid-to-hydrocarbon ratio within the range of 0.05:1 to 10:1 by volume.
3. A method in accordance with claim 1 wherein said Z-methyl-Z-pentene is recovered by separating said acid from said isomerized stream, and distilling said isomerized stream to obtain 2-methyl-2-pentene as a substantially pure product.
4. A method in accordance with claim 1 wherein said Z-methyl-l-pentene is isomerized by extraction into said sulfuric acid to form a fat acid extract, and said Z-methyl- 2-pentene recovered by regenerating said acid extract to form an acid phase and a 2-methyl-2-pentene-rich phase, and distilling said Z-methyl-Z-pentene-rich phase to recover said 2-methyl-2-pentene.
5. A method in accordance with claim 4 wherein said extract is regenerated by heating said extract to a temperature of at least 150 F. at a rate of at least 400 F. per minute.
6. A method of producing high purity 2-methyl-2- pentene from a hydrocarbon stream containing isomeric C olefins which comprises fractionating said hydrocarbon streams to obtain an isomerization feedstock boiling within the range of about 133 F. to about 146 F., and containing 2- rnethyl-l-pentene, contacting said isomerization feedstock with 60% to 75 sulfuric acid at a temperature within the range of 20 F. to 60 F. for a time within the range from 5 minutes to 3 hours,
whereby at least a portion of said 2-methyl-1-pentene is selectively isomerized to Z-methyl-Z-pentene to produce an isomerized stream, and
recovering 2-methyl-2-pentene from said isomerized stream as a substantially pure product.
7. A method in accordance with claim 6 wherein the isomerization feedstock and sulfuric acid are contacted at an acid-to-hydrocarbon ratio within the range of 0.05:1 to 10:1 by volume.
8. A method in accordance with claim 6 wherein said 2-methyl-2-pentene is recovered by separating said acid from said isomerized stream, and distilling said isomerized stream to obtain 2-methyl-2-pentene as a substantially pure product.
9. A method in accordance with claim 6 wherein said Z-methyl-l-pentene is isomerized by extraction into said sulfuric acid to form a fat acid extract, and said Z-methyl-2-pentene recovered by regenerating said acid extract to form an acid phase and a 2-methyl-2-pentene-rich phase, and distilling said 2-rnethyl-2-pentene phase to recover said 2-methyl-2-pentene.
10. A method in accordance with claim 9 wherein said extract is regenerated by heating said extract to a 9 temperature of at least 150 F. at a rate of at least 400 F. per minute.
11. A method of producing high-purity 2-methyl-2- pentene from a catalytic naphtha which comprises fractionating said catalytic naphtha to obtain an isomerization feedstock boiling within the range of about 133 F. to about 146 F. and containing 2- methyl-l-pentene, contacting said isomerization feedstock with 60% to 70% sulfuric acid at an acid-to-hydrocarbon ratio within the range of 0.05:1 to about 10:1 by volume, at a temperature within the range of 20 F. to 60 F., and for a time period within the range from 5 minutes to 3 hours, whereby at least a portion of said Z-methyI-I-pentene is selectively isomerized to 2-methyl-2-pentene, and whereby a fat acid extract containing said Z-methyl- Z-pentene is formed, separating said fat acid extract from said catalytic naphtha,
heating said fat acid extract to a temperature of at least 150 F. at a rate of at least 400 F. per minute to form an acid phase and a 2-methy1-2-pentenerich phase,
separating said acid phase and said Z-methyI-Z-pentenerich phase,
and distilling said 2-methy1-2-pentene-rich phase to recover said 2-met-hy1-2-pentene.
References Cited by the Examiner UNITED STATES PATENTS 2,463,873 3/ 1949 Heinrich 260683.2 3,150,201 8/1964 Edwards et a1. 260677 3,173,968 3/1965 Edwards et a1 260-6832 FOREIGN PATENTS 832,475 8/ 1960 Great Britain.
DELBERT E. GANTZ, Primary Examiner. R. H. SHUBERT, Assistant Examiner.

Claims (1)

1. A METHOD OF PRODUCING HIGH PURITY 2-METHYL-2PENTENE FROM A CATALYTIC NAPHTHA WHSICH COMPRISES FRACTIONATING SAID CATALYTIC NAPHTHA WHICH COMPRISES ERIZATION FEEDSTOCK BOILING WITHIN THE RANGE OF ABOUT 133*F. TO ABOUT 146*F., AND CONTAINING 2-METHYL1-PENTENE. CONTACTING SAID ISOMERIZATION FEEDSTOCK WITH 60% TO 75% SULFURIC ACID AT A TEMPERATURE WITHIN THE RANGE OF 20*F. TO 60*F. FOR A TIME WITHIN THE RANGE FROM 5 MINUTES TO 3 HOURS WHEREBY AT LEAST A PORTION OF SAID 2-METHYL-2-PENTENE TO IS SELECTIVELY ISOMERIZED TO 2-METHYL-2-PENTENE TO PRODUCE AN ISOMERIZED STREAM, AND RECOVERING 2-METHYL-2-PENTENE FROM SAID ISOMERIZED STREAM AS A SUBSTANTIALLY PURE PRODUCT.
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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2463873A (en) * 1947-10-03 1949-03-08 Standard Oil Dev Co Separation of pentene-1 from its mixtures with other c5 olefins
GB832475A (en) * 1958-05-02 1960-04-13 Goodyear Tire & Rubber Preparation of isoprene
US3150201A (en) * 1961-06-07 1964-09-22 Exxon Research Engineering Co Extraction process
US3173968A (en) * 1962-08-20 1965-03-16 Exxon Research Engineering Co Process for separating olefins

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2463873A (en) * 1947-10-03 1949-03-08 Standard Oil Dev Co Separation of pentene-1 from its mixtures with other c5 olefins
GB832475A (en) * 1958-05-02 1960-04-13 Goodyear Tire & Rubber Preparation of isoprene
US3150201A (en) * 1961-06-07 1964-09-22 Exxon Research Engineering Co Extraction process
US3173968A (en) * 1962-08-20 1965-03-16 Exxon Research Engineering Co Process for separating olefins

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