US2494335A - Method for producing high purity normal heptane - Google Patents

Description

Patented Jan. 10, 195O METHOD FOR PRODUCING HIGH PURITY NORMAL HEPTAN E Keith J. F. Dutson,

of Delaware Baytown, Tex., assignor, by mesne assignments, to Standard ment Company, Elizabeth, N. J.,

Oil Developa corporation Application September 29, 1947, Serial No. 776,688

The present invention relates to an improved method for producing normal heptane. More particularly, it is concerned with a method of hydroforming petroleum hydrocarbons to obtain high yields of substantially pure normal heptane.

In the process of the present application, either straight-run gasolines or catalytically or thermally cracked gasolines or any other hydrocarbon mixture containing normal heptane may be employed as the feed stock. It is well known that normal heptane is present in different amounts in gasolines from different sources. In general, nor-- mal heptane is present in higher concentrations in some straight-run gasolines than in catalytically or thermally cracked gasolines. However, in many catalytically or thermally cracked gasolines, normal heptane is present in substantial amounts, the amount which is present depending on the nature of the feed stock cracked, and the cracking conditions maintained. Usually, however, normal heptane will be present in larger quantities in straight-run distillates and in the process hereinafter described I prefer to utilize as a feed stock a straight-run gasoline rich in normal heptane although any petroleum hydrocarbon fraction containing normal heptane may be utilized.

As is well known, in addition to containing normal heptane as well as other paraflinic hydrocarbons, gasolines also contain various quantities of olefins, naphthenes and aromatics in addition to small amounts of contaminating compounds containing sulfur, nitrogen, oxygen, etc. For example, a gasoline containing normal heptane will normally also contain methylcyclohexane. Such gasolines often contain olefinic hydrocarbons boiling at the same temperature as normal heptane. Of course, the relative amounts of each of these several types of hydrocarbons present in a gasoline will depend on a number of factors including the source of the crude from which it is derived and the prior treatment to which it has been subjected.

One of the chief difficulties in the manufacture of normal heptane from tion of normal heptane from other hydrocarbons that are mixed therewith. One of the methods most commonly used for the separation of hydrocarbons is fractional distillation. This method of separation depends for its effectiveness upon the difference in boiling points of the hydrocarbons to be separated. When the boiling points of two or more hydrocarbons are substantially identical, separation by fractionation is impractical if not impossible. In preparing-nonnal hepgasoline is the separaand a reforming 7 Claims. (Cl. 260-676) Boiling I Hydrocarbon Ptnt,

n-Heptane Heptene-L Heptcne-2 Heptene-3 Methylcyclohexane It will be seen from the above tabulation that if normal heptane is to be secured in a relatively pure form, methods of separation other than fractional distillation or in addition thereto must be employed.

With the development of high octane motor fuels, normal heptane has become an important and costly material which is used in relatively large quantities as a standard for evaluating the octane rating of motor fuels. Normal heptane is used as the low octane number standard while iso-octane is used as the high octane number standard in this evaluation, and in order to be of value for this purpose both constituents must be available in relatively pure form. Iso-octane is now available in commercial quantities-but normal heptane is still difiicult to secure in ade quate quantities. By the practice of my inven tion, large quantities of normal heptane can be made available at relatively low cost.

In the process of my invention 'for preparing relatively pure normal heptane from gasoline fractions, I utilize several steps. Basically I em ploy the hydroforming reaction as it is conven' tionally carried out. As is well known in the art, the hydroforming process is characterized by chemical reactions which take place'when'hydroe carbon oils, particularly hydrocarbons boiling in the gasoline range, are reacted at a temperature in excess of 500 F. in the presence of hydrogen catalyst; These reactions in volve a net effect of removing hydrogen from the hydrocarbon molecules. Although some olefins are formed in the process the chemical reactions involved are complex and are generally considered to consist mainly-of dehydrogenation and cycliza tion although other side reactions may and do occur. The-.catalystsutilized in: the hydroform' ing reaction may be selected from a wide variety of materials. Especially satisfactory catalysts for this reaction comprise major portions of aluminum oxide and minor portions of oxides or sulfides of metals of the IV and, V, VI and VIII groups of" the :pe'riodicrsystem. The oxidesr-and sulfides of vanadium-molybdenum, chromium,

tungsten and nickel are particularly efiective. The aluminum oxide incorporated in the catalyst may be used in its various formssuchas activated alumina, bauxite, aluminum hydroxide, alumina gels and peptized alumina gels. As examples of the type of catalyst found suitablein-the hydroforming reactions which may bementioned-are alumina or peptized alumina gels containing from conduct the hydroformingreaction ata temperag turerange of about 900 to 950Fpand atpressures oiabout I80 to250 pounds per square inch gauge.

Although the 'hydroforming reaction is essentially a dehydrogenation reaction in which hydrogen is produced, it is well known that the presenceof excesshydrogen resultsin higher yields ofdesired products and, consequently, in practicing my invention, I introduce hydrogeninto the hydroforming zone.

I-Ieptenes are also sometimes present in the gasolines utilized-as feed-stocks. Further, small quantities of heptenesrmay be'produced during the :hydroiorming :reaction. 35inch .olefins will, therefore, rappearinz-the distillate fraction :recovered 'from the .hydroiorming operation and cannot be readily separated from normalrheptane *hy fractional distillation. Consequentlm-I remove such olefins iirom this fraction by acid :treating with sulfuric acid in amanner wellknown to the art. rInthis step, the distillate fraction may ;be agitated with concentrated sulfuric acid at attem- :peratureibetween about 140;F. and 210 F. :after which the .mixture .is allowed :to separate into an acidtlayer anda hydrooarbonilayer. Thishy- 'd-rocarbon layer contains :iewdf any, 'olefins xb'oilingat or.nea-rtheboilingpoint of norma12hep- .tane-andconsequently a normaliheptane fraction substantially .free :of .h-epten-es may be distilled therefrom.

.As previously pointed \out, both normal heptane and methylcycl'ohexane are present initypical feedsitoahydroforming unit. Under:the conditions Fmamtained in the hydroforming unit in my process, methylcyclohexane .is converted "to toluene while normal =heptane .is affected relaitivelyilittle during the reaction. .Since the boiling point of :toluene is "110;8' 16., :any toluene formed -the process may be easily separated from-the normal heptaneLby-iractional distillai "tion. :Ininy invention, I utilize -.the marked ditierence:inboiling-points of normal heptanean'd toluene .as .one .of the factors in producing the relatively apure normal heptane.

.Qne specific embodimentof the presentilnvenitioncomprises -a process whereby a hydrocarbon mixture containing normal heptane is subjected to. :the :hydroforming reaction "and the products dromethe ireactor are :separatedby fractionation into three :iractions, :namely, airaction boiling converting the remaining l.

below 200 F., a fraction boiling between about 200 and 215 F., and a fraction boiling above about 215 F. The fraction boiling between 200 and 215 F. contains normal heptane,methylcyclohexane, the heptenes and small amounts of other hydrocarbons. In order .to prepare a relatively pure normal heptane, this fraction is subjected to a second hydroforming step for the purpose of methylcyclohexane contained in .this. fraction to toluene. In this ssteplthe hydroforming conditions employed are such as will convert all or substantially all of the-"methylcyclohexane present to toluene and thismaybeaccomplished without materially aifecting the normal 'heptane present. The products from this second hydroforming step are again fractionated into three fractions, namely,

materials boiling below about 205 a fraction boiling between about 205 and 215 F. and a fraction boiling above about 215 F. The fraction boiling between about 205 F. and 215 now containsonly normal heptane and olefins boiling in this range. Thisiraction is subjected to acid treatment under'such conditions as to leave'the normal heptanerelatively unaffected while at the same'time polymerizing and otherwise converting the olefins present to compounds having boiling points materially removed from the boiling point of normalheptane. "The acid treated productis againfractionatcd and separated into three fractions, namely, :a Traction boiling below about 203 F., a fraction boiling between about 208- F. and =about 2ll 'F.,zand':aTraction boiling above about 2 11 F. 'Thefraction boiling between about 208: and 211""1. constitutes the finished product and consists of normal'heptane of purity or better. "Normalheptane of very high purities, for example, 99% or better, may be obtained in my process by closely controlled fractionation and-by proper'controlof hydroforming conditions. Instocks containing a very'high percentage of methylcyclohexane it may be'necessary to introduce-an additional hydroforming and fraction-ationstep "just prior to the acid treating step. It is understood that it is meant to include such additional hydroformlng and fractionation steps in this process where the nature of particular feed stocks requires that such additional steps be employed. However, it is normally unnecessary in thepra'cticepf'my invention to employ such additional steps "since, except in unusual cases, substantially all of the methylcyclohexane present in the fraction boiling between 200 and 215' F.=from the hydroiorming unit may be converted to toluene with one hydroiormin stage.

In-another embodiment of my invention, relatively pure normal heptane may be produced 'from hydrocarbon feed containing n-heptane by recycling a portion of the material which boils between 200 to 215 F. in the product from the unit used to hydroform the virgin feed back to the virgin 'feed hydroforming unit. The po tion of the fraction boiling between 200 and 215 F. which is-notrecycled is then'aci'd treated to polymerize or otherwise convert the olefins to com pounds-having' boiling'points materially removed irom the boiling point of normal heptane. This 'acid' -treated fraction is then fractionated, three fract ons being-removed, namely, a fraction boil- -ing"below about'208 F., afraction boiling between about '208 andabout'211 F. and a fraction boiling a-boveabout-211 F. The fraction boi ing between about ZO'ii and211'*F. consists of substantially pure normal "heptarre, 'thatds, of 95% -or 3 greaterpurity. "Thepurityof this finished normal heptane is regulated in this embodiment of my invention by proper adjustment of the recycle ratio of the fraction from the hydroforming unit which boils between 200 and 215 F.; the greater the recycle ratio, the greater the purity of the finished normal heptane although it will not usually be necessary to exceed a recycle ratio of :1. This second embodiment of my invention possesses the advantage over the first embodiment discussed above of utilizing only one hydroforming unit although it possesses the disadvantage .over the first embodiment of reducing over-all through-puts through the hydroforming unit.

The practice of the present invention will now be described further in conjunction with the drawing, in which Fig. 1 is in the form of a diagrammatic flow sheet showing one modification of the present inseparated into three fractions, the fraction boiling below about 200 F. being withdrawn through line 5, the fraction boiling between about 200 to 215 F. being withdrawn through line B and the fraction boiling above about 215 F. being withdrawn through line 1. The fraction withdrawn through line 6 contains substantially all of the normal heptane and methylcyclohexane, in addition to some olefins. This fraction may be placed in storage in a conventional storage tank 8 for further finishing if desired. When desired, the material stored in tank 8 is withdrawn through line 9 and discharged into a second hydroformer I!) where these materials are brought in contact with a hydroforming catalyst under hydroforming conditions. The react on product from the second hydroformer is withdrawn through line H and discharged into fractionator l2 where a fraction boiling below about 205 F. is withdrawn through line 13, a fraction boiling between about 205 to 215 F. is withdrawn through line l4 and a fraction boiling above about 215 F. is withdrawn through line IS. The fraction withdrawn through line l4 consists of a major portion of normal heptane, with minor amounts of olefins boiling within this range but contains substantially no methylcyclohexane. The material with drawn through line l5 consists essentially of toluene. The materials in line !4 are discharged to acid treater [6 where they are contacted with sulfuric acid introduced through line H. Spent acid may by withdrawn through line l8 if desired. In acid treater i6 the olefins which were introduced with thenormal heptane through line H are polymerized and otherwise converted to products which have a boiling point materially different from that of normal heptane. Conditions maintained in acid treater I6 are such as to substantially convert the olefins present to higher boiling polymers. The treated mixture is withdrawn from acid treater I6 through line I9 from which it is discharged into fractionator 20 of conventional design where materials boiling below about 208 F. are withdrawn through line 2 l materials boiling from about 208 to about 211 F. are

withdrawn through line 23 and materials boiling above about 211 F. are withdrawn through line 22. The fraction withdrawn through line 23 is the final product and consists of substantially pure normal heptane.

Referring to Fig. 2, a virgin naphtha or other normal heptane-containing hydrocarbon feed is introduced through line 25 into hydroiormer 26 where the introduced feed is contacted with a hydroforming catalyst in the hydroforming unit 26 under hydroforming conditions. The reaction products from the hydrof-orming unit 26 are withdrawn through line 21 and discharged into fractionator 28 of conventional design in which the mixture is separated into a fraction boiling below about 205 F. which is withdrawn through line 29, a fraction boiling above about 215 which is withdrawn through line 30 and a fraction boiling between about 205 F. and 215 F. which is withdrawn through line 3|. The fraction withdrawn through line 3! consists essentially of normal heptane, plus some olefins and other hydrocarbons boiling between 205 and 215 F. A portion of the fraction passing throughline 3! is withdrawn from line 3| through line 32 and valve 33 and discharged into line 34. The amount of material withdrawn from line 3| into line 32, valve 33 and line 34 is controlled by the manipulation of valve 33 and the amount so withdrawn is determined by the purity of normal heptane desired in the finished product. The material in line 34 is admixed with the feed stock entering the hydroformer 26 through line 25. The portion of the fraction in line 3| which is not recycled through line 32, valve 33 and line 34 flows through line 35 and is discharged into acid treater 36. The fraction discharge into acid treater 36 con-- sists essentially ofnormal heptane plus some olefins and other hydrocarbons but contains relatively little methylcyclohexane. Fresh acid may be introduced into the acid treater by means of line 31 and spent acid may be removed from acid treater 36 by means of line 38. In acid treater 36 the olefins introduced through line 35 are converted to polymers and other products by properly controlling the conditions of theacid treatment in a manner well known to the art. The hydrocarbon products leaving acid treater 36 by means of line 39 now consist essentially of normal heptane plus olefin polymers. The materials in line 39 are discharged into fractionator 40 of conventional design from which a fraction boiling below about 208 F. is withdrawn through line 4 l a fraction boiling above about 211 F. is with drawn through line 42, and a fraction boiling between about 208 and 211 F. is withdrawn through line 43. The material withdrawn through line 4'3 is the finished normal heptane and is substantially a pure product.

Itwill be seen from the examples given herein that relatively pure normal heptane cannot be produced from petroleum distillates by means of ordinary distillation, whereas, according to my process, normal heptane of high purity can readily be obtained.

I claim as my invention:

1. A process for preparing substantially pure normal heptane from a naphtha containing normal heptane in admixture with hydrocarbons having similar boiling points including methylcyclohexane which includes the steps of contacting the said naphtha in the presence of hydrogen with a catalyst capable of dehydrogenating methylcyclohexane at a temperature in the range between 900 and 950 F. and at a pressure in asthe range betweendBO and-L250 pounds per square inch under conditions favorable to the dehydrogenation of methylcyclohexane and removing a product from the reaction zone, contacting at least a portion of said product in :thepresence of hydrogen with a catalyst capable of dehydrogenating methylcyclohexaneat a temperature in the range between 900 and 950 F. and at a pressure in the range between 180 and 250 pounds per square inch under conditions favorable to treated product to recover a hydrocarbon frac- "tion'cboiling between about 208F. and 211 F. consisting of substantiallypure normal heptane.

2. Aprocess :forpreparing substantially pure normal 'heptane :from a naphtha containing normal heptane in admixture with hydrocarbons having similar boiling points including methylcyclohexane which includes the steps of contacting said naphtha in the presence of hydro- -gen-in a first stage with-a catalyst effective in dehydrogenating-napthenes at a temperature in the range between 900 and 950 F. and at a pres- ;sure in the rangebetween 180 and 250 pounds per square inch under conditions favorable to the dehydrogenation of .naphthenes to form a product, distilling'the product from said first stage to separate a fraction boiling between about 200 and 215 F., contacting said separated fraction in the presence of hydrogenin a second stage with -a catalyst efiective in dehydrogenating naphthenes under substantially the same conditions prevailing-in said first stage to form a second product, distillingthe product from said second stage to separate-a fraction boiling betweenabout: 205 F. and 215 F., acid treating the said "fraction boiling between about 205 and 215 F. with sulfuric'acid and redistilling the acid treated fraction to recover a fraction boiling between about208 and. 211 F. consisting of substantially 'pure normal 'heptane.

3. A process .for preparing substantially purenormal heptane from a naphtha containing inormal heptane in admixture with hydrocarbons having similar boiling points including methylcylohexane which includes the steps of subjecting the vapors of the said naphtha in a first stage to contact with a catalyst effective in dehydrogenating naphthenes at a temperature in the range between 900 and-950 F. and at apressure in the range between 180 and 250 pounds per square inch. separating from the contacted vapors :pairaction boiling between about 200 and 215 F.,

contacting said fraction in a second stage with -a catalyst effective in dehydrogenating naphthenes at a temperature in the range between -900 and 950 F. and at a pressure in the range between 180 and 250 pounds per square inch .to iiorm a reaction product, separating from the reaction product of said second stage a frac- 'tion boiling between about 205 and 215 F., (3011- normalheptane in admixture with other hydro- ;carbons having similar-boiling points including methylcycloh-exane which includes the steps of contacting said naphtha-lathe presence of hydrogen with a catalyst eifectivein dehydrogenating naphthenes at a temperature inthe rangebetween 900 and-950 F. and ,at a pressure in the range between 180 and --250pounds per square inch, separating a reaction product from said catalyst, distilling the reaction product therefrom to separate airactioniboiling between-about 205 and 215 F., separating said fraction into-a first and second" portion, admixing said'first portion with said feed-naphtha, acid treating the said second portion withwsulfuric acid, distilling the acid treated second portion torecover a -fraction'boiling between'about 208-and 211 F.

.consisting of substantially pure normal heptane.

6. A process for preparing substantially pure normalheptane from a naphtha containing said hydrocarbon in admixture with hydrocarbons having similar'boiling points including :methylcyclohexane which ;-includes the steps-of subjecting 'thevapors of said jnaphtha-to contact with a catalyst effective "in d-ehydrogenating naphthenes ata temperature in'the range between 900 and 950 F. and at a pressure in-the range between-180 and 250 pounds'per square inch, separating fromthe contacted'vapors a fraction boiling betweenabout- 205'and'215 EL, separating said fraction into a first and second portion, admixing said-first'portion with'said reed naphtha-contacting the said second portion with concentratedsulfuric acid and recovering substantially-pure normal heptane from said acid contacted second-portion.

7. A process-in-accordance with claim 5 in which the catalyst employed is aluminum oxide containing 'from- 1 to'20% by weight of molybdenum oxide.

QKE-ITH J. F. DU'ISON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date "2,417,698 McAllister et a1 Mar. 18, 1947 2,425,535 Hibshman *Aug. 12, 1947 FOREIGN PATENTS Number Country Date 544,155 Great'Brita-in -Mar.30, 1942

Claims (1)

1. A PROCESS FOR PREPARING SUBSTANTIALLY PURE NORMAL HEPTANE FROM A NAPHTHA CONTAINING NORMAL HEPTANE IN ADMIXTURE WITH HYDROCARBONS HAVING SIMILAR BOILING POINTS INCLUDING METHYLCYCLOHEXANE WHICH INCLUDES THE STEPS OF CONTACTING THE SAID NAPHTHA IN THE PRESENCE OF HYDROGEN WITH A CATALYST CAPABLE OF DEHYDROGENATING METHYLCYCLOHEXANE AT A TEMPERATURE IN THE RANGE BETWEEN 900* AND 950*F AND AT A PRESSURE IN THE RANGE BETWEEN 180 AND 250 POUNDS PER SQUARE INCH UNDER CONDITIONS FAVORABLE TO THE DEHYDROGENATION OF METHYLCYCLOHEXANE AND REMOVING A PRODUCTION FROM THE REACTION ZONE, CONTACTING AT LEAST A PORTION OF SAID PRODUCT IN THE PRESENCE OF HYDROGEN WITH A CATALYST CAPABLE OF DEHYDROGENATING METHYLCYCLOHEXANE AT A TEMPERATURE IN THE RANGE BETWEEN 900* AND 950*F. AND AT A PRESSURE IN THE RANGE BETWEEN 180 AND 250 POUNDS PER SQUARE INCH UNDER CONDITIONS FAVORABLE TO THE DEHYDROGENATION OF METHYLCYCLOHEXANE AND RECOVERING A PRODUCT FROM SAID LATTER CONTACTING STEP, ACID TREATING THE SAID LAST MENTIONED PRODUCT WITH SULFURIC ACID AND REDISTILLING THE ACID TREATED PRODUCT TO RECOVER A HYDROCARBON FRACTION BOILING BETWEEN ABOUT 208*F. AND 211*F. CONSISTING OF SUBSTANTIALLY PURE NORMAL HEPTANE.

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