US2443607A - Heptane isomerization - Google Patents

Description

June 22, 1948. B. L. EVERING- v 2,443,607

f HEPTANE ISOMERIZATION Filed March 31, 1943 v v 2 Sheets-Sheet l June 22, i948. B. L. EVERING I 2,443,607

HEPTANE ISOMERIZATION Patented .inne 22, 1943 UNITED HEPTANE ISOMERIZATION Bernard L. Evering, Chicago, Ill., assignor to Standard Oil Company, Chicago, Ill., a corporation of Indiana Application March 31, 1943, Serial No. 481,331

1 Claim.

This invention relates to a light naphtha isomerization system and it pertains more particularly to an improved method and means for producing dimethyl pentanes and trimethylbutane (triptane) from a C7 hydrocarbon fraction which is substantially free from olens.

The practical isomerization of parafnic hydrocarbons by Friedel-Crafts catalysts, exemplified by metal halide hydrocarbon complexes promoted by hydrogen halide activators, becomes increasingly diilicult with hydrocarbon chains of increasing length. Butanes are readily isomerizable in the absence of hydrogen and cracking inhibitors. Pentanes are readily isomerizable in the presence of small amounts of cracking inhibitors and in the absence of hydrogen. Hexanes are isomerizable under suitable hydrogen pressures, preferably in the presence of cracking inhibitors such as critically small amounts of aromatics or naphthenes. Heptanes are more diicultly isomerizable and in the case of normal heptane even the use of cracking inhibitors and substantial hydrogen pressures fails to completely overcome the tendency toward cracking with resultant production of lower boiling products, rapid decrease in isomerization rate and relativelyshort catalyst life. I have discovered, however, that by eliminating normal heptane from a C7 hydrocarbon fraction which isr substantially free from olens and which contains optimum amounts of aromatics or naphthenes the remainder of the Cv fraction may be readily isomerized at a temperature within the approximate range of 100-300 F., preferably 150-180 F., under a hydrogen pressure Within the range of 300-3000 pounds per square inch, for example about 1000 pounds per square inch.

An object of my invention is to convert parafnic hydrocarbons of relatively low octane number, particularly Ci hydrocarbons, into a valuable high octane number motor fuel component suitable for aviation gasolines. A further object is to provide a method and means for obtaining maximum yields of dimethyl pentanes and triptane from a C7 parainic hydrocarbon iraction at minimum expense. A further object is to provide an improved method and means for increasing effective catalyst life and catalyst activity vin a C7 isomerization system and to pro- 2 duce a maximum amount of dimethyl pentanes and triptane with the minimum amount of catalyst. Other objects Will be apparent as the detailed description of my invention proceeds.

It `has been known for years that heptanes could be isomerized by means of Friedel-Crafts catalysts and the most successful results to date have been obtained by laluminum halide-hydro carbon complexes promoted by hydrogen halide activators with lsubstantial hydrogen pressures under approximately the same conditions that hexanes are isomerized. The isomerization of hep-tanes, however, has been heretofore commercially unattractive because of the catalyst degradation which always occurred in the presence thereof and in hexane isomerization plants great pains have been taken to eliminate substantially all of the heptanes from the charging stock. In hexane isomerization, normal hexane is a desirable component of the charging stock along With methyl pentanes for the production of dimethyl butanes. I have discovered, however, that in the case of heptanes, normal heptane is unexpectedly and unexplainably detrimental when present in the charging stock in relatively large concentrations. By substantially eliminating normal heptane from the charging stock to a heptane isomerization system or by recycling a sufficiently large amount of methyl hexanes (which have been freedfrom normal heptane) so that the normal heptane concentration in the charging stock is below 10% and preferably below about 5%. I can convert Cv hydrocarbons almost quantitativelyv into dimethyl pentanes and triptane which have a CFR-R. octane number of about and which are characterized by a remarkably favorable rich mixture performance in aviation engines. The isomerization with an aluminum chloride-hydrocarbon complex may be elected in simple ltower reactors using about 2 to 20%, for example, about 6% by weight oi hydrogen chloride based on charge, employing hydrogen at the rate of about 10K) to 300 cubic feet per barrel of stock charged, for example about 200 cubic feet per barrel, employing a reaction temperature Within the range of to 300 F., preferably within the range of 150 to 180 employing a conversion pressure Within the approximate range of 300 to 3000 pounds per square inch, preferably about 1000 pounds to 150'0 pounds per square inch and employing a space velocity within the approximate range of .3 to 3 volumes of liquid charging stock per hour per volume of complex in the reactors and a feed rate within the range of about 45 to 450 gallons of liquid feed per hour per square foot of cross sectional area of reactor. The charging stock should preferably contain a small amount of aromatics or naphthenes or both; aromatics should preferably be within the approximate range of .3 to 3 and naphthenes in the approximate range of 2 to 20%. When a mixture of naphthenes and aromatics is present in the charging stock the amounts of each component may be correspondingly reduced.

An important feature of my invention is the avoidance of large amounts of normal heptane in the charging stock introduced into the conversion system. Normal heptanes may be uti-l lized if they are admixed with enough methyl hexanes so that the total amount of normal hep-` tanes in the charging stock is less than about 10% or preferably less than about By effecting only a small amount of isomerization in each pass and recycling a large amount of methyl hexanes I can utilize at least a substantial portion of the x normal heptane content of a charging stock without exceeding the stated maximum normal heptane concentration in the Yconversion zone itself. The recycle stream in the preferred example of my invention is three tenths to ve times the volume of the charging stock stream which is introduced from an external source. For converting pure normal heptane into dimethyl pentanes and triptane it may, however, be necessary to recycle five to twenty ve volumes or even more of methyl hexanes for each volume of normal heptane introduced from an outside source.

The invention will be more clearly understood from the following detailed-description read in conjunction with the accompanying drawings which form a part of this specification and in which Figure 1 is a schematic flowsheetdiagrammatically illustrating a system for isomerizing light naphtha components with maximum lefflciency for the production of aviation gasoline, this gure bringing out the relationship between a heptane isomerization step with other isomerizing and refining steps, and

Figure 2 is a schematic flow diagramof a heptane isomerization system per se.

The charging stock for the manufacture of aviation gasoline may be a virgin light naphtha or any other hydrocarbon mixture of similar constitution and boiling range providing that the mixture is substantially free fromolens and free from excessive amounts of aromatics and naphthenes. It is desirable, however, that the charge contain about .3 to 3% of aromatics or about 2 to 20% of naphthenes or a correspondingly diminishing amount of each if both are present, the higher concentrations being mostdesirable in the upper temperature range and the lowerconcentrations in the lower'temperature range. Usually a crude Virgin light naphtha will contain suiicient aromatics or naphthenes for C7 isomerization and the important consideration is theremovaly of effective amounts of such aromatics or naphthenes from material which is recycled to the heptane isomerization unit.

Referring to Figure 1, a crude light naphtha boiling up to about 20D-to 250 F. may be charged through line H to a fractionation system schematically illustrated as tower I2. In practice a series of towers will be employed instead of a single column. Propane and lighter hydrocarbons and gases may be taken overhead through line i3. Isobut-ane may be withdrawn through line iiiand introduced together with olens from line i5 to alkylation system i5 to form an alkylate introm duced by line il to storage tank i8. Normal butane m-ay be withdrawn through line l@ to isomerizer system 20 and the product stream from the isomerizer may be returned to the fractiona tion system through line 2 i. Isopentane may be withdrawn through line 22 to storage tank 23. Normal pentane may be Withdrawn through line 24 to pentane isomerizer 25 together with about .5 to 2% of aromatics from line 2t. The isomerization products are returned by line 2l to fractionation system l2.

A fraction boiling between about and about F. and consisting chiefly of dimethyl butanes is withdrawn through line 2B to storage tank 29. A fraction boiling predominantly within the range of about 135 F. to about 165 F. is withdrawn by line 30 to hexane isomerization system 3 i into which hydrogen is introduced through line 32. This stream will usually contain the desired amount of naphthenes or aromatics for inhibiting cracking. The product stream from the hexane isomerizer may be returned to the fractionation system through line 33.

A fraction boiling within the approximate range of about to 185 F. may be withdrawn through line 313 to dimethyl pentane storage tanl; 35; this line may be unnecessary, however, when a separate fractionation system is employed in the heptane isomerization step per se. A fraction boiling within the approximate range of about F. to about 205 F. is introduced by line 30 Ato heptane isomerization system 3l into which hydrogenv is introduced through line 30. If die methyl pentanes and triptane are not previously removed from the charging stock, then the boiling range of the fraction removed through line 35 may be about 165 to 205 F. Hydrocarbons boiling above 205 F. are withdrawn from the base of the fractionation system through line 39k to hydroformer $0. Here again, however, the lheptane isomerization system itself may be employed to segregate the hydroformer charge in which case the end point of the fraction withdrawn through line 36 may be 215 F. or higher, i. e., at least high enough to include substantially all of the normal heptane. When normal heptane isY thus included inthe charge to line 36 there must, however, be sufcient recycle of methyl hexanes so that the normal heptane content of the charging stock which is actually introduced into the conversion Zone will not exceed 10% and will preferably be below 5%.

The products from the heptane isomerization system are introduced through line M to the Ce tower 42, the overhead from which it is returned by line i3 to fractionation system i2'. The bottoms fromtower ft2 are introducedby line fil to dimethyl pentane tower f5-the overhead stream from which it is introduced by line i5 to dimethyl pentane storage tank 35, The overhead stream from line 45 should boil within the approximate range of about 165 F. tov about 185 and should consist essentially of dimethyl pentanes andtriptane along with cyclohexane and benzene. This particular fraction boiling between 165 and 185 F. has been foundsto have a remarkably high octane number and what is still more important is that it has the property of unusually high richmixture performance which makes it a valuable component for aviation gasoline.

The bottoms from line it are introduced into line il to fractionating column ll. Methyl hexanes together with dimethyl cyclopentanes, ethyl pentane, etc., i. e., the fraction boiling from about 185 to about 205 F., is removed as an overhead stream through line 59, condensed and recycled to line Sii for further isomerization in heptane isomerizer 3l. It should be particularly pointed out that this recycle stream is substantially free from normal heptane as well as from naphthenes boiling above about 205 F.

The bottoms from ractionator column i3 are Withdrawn through line 50 for introduction into hydroformer all. This hydroiormer or dehydroaromatization unit is preferably of the type employing a Vlth group metal oxide on active alumina and it is operated under such conditions as to convert the charging stock to aromatics with a net production of hydrogen. Such units are well known in the art and no detailed description thereof is therefore necessary. Hydrogen from the hydroformer may supply lines 32 and 38 and any excess may be withdrawn through line 5l. Aromatics may be separated and separately stored, e. g., in benzol tank 52, toluene tank etc., and any unconverted or separated parafflnic hydrocarbons may be recycled by line Eil to fractionation system l2. It may be desirable to remove residual olens from this predominantly 'paraflinic fraction before recycling by line 5d to fractionation system l2. This may be accomplished by subjecting the fraction to a sulfuric acid treating step or to a spent aluminum chloride catalyst complex treating step. As an alternate method the olefins in this fraction may be conserved by hydrogenation or alkylation with isoparaflin.

It will be noted 'from the above description that the lighter or heavier components formed in any of the isomeriaation or treating systems are automatically fractionated to provide charging stocks for other systems, all of the propane and lighter gases being withdrawn through line I3 and all of the heavier products being withdrawn as polymer through 55 to the hydroformer. The dimethyl pentanes and triptane from tank 35 may be blended with the desired amo-unts of neohexanes from tank 29, isopentane from tank 23', alkylate from tank i8 and benzol irom tank 52 for making an vaviation gasoline of any desired volatility, octane number and rich mixture performance. The benzol from tank 52 may be alkylated lfor making isopropyl benzol, or other alkyl .benzols which may be desirable for use in aviation fuels. As indicated in Figure 1, the various isomerization products, etc. may be blended to form aviation motor fuel which may be withdrawn from the system through line 56 or each fraction may be separately withdrawn for other specic purposes.

Figure 1 graphically illustrates the fact thlat the diiilculty of isomerization increases with the length of the hydrocarbon chain to be isomerized it being understood, of course, that a Friedel- Crafts catalyst, preferably `an aluminum halidehydrocarbon complex, is employed for eiecting the isomerization in each od these steps. Butane may be isomerized without addition of cracking inhibitors or hydrogen. 1entane does not re- `o uire hydrogen but does require a cracking inhibitor which in this case is a small amount of aromatics supplied f Fro-m benzol tank 52 via-line 26'. Hexan-e requires hydrogen for prolonging' catalyst life and catalystactivity and if the charging stock to this system is deficient of aromatics or naphthenes such 'components should likewise be added to the charge. Normal hexane in large amounts is desinable in the charging stock to the hexane isomerization system.

Coming to heptane, however, I have discovered that the amount of normal heptane in the charging stock entering the isomerization system must be maintained withinl the critically small limits or entirely eliminated if catalyst life and catalyst activity are to be such as to make the process commercially feasible. The conversion conditions for heptane isomerization are somewhat milder than in the case of hexane isomerization, more hydrogen is required with higher operating pressures and cracking inhibitors should be employed. By eliminating normal heptane froml the recycle stream and employing relatively large amounts of recyclestream as compared with incoming rfresh feed I can effectively keep the normal heptane concentration in isomerizer 3l below 10% or even below 5% and by this means I can. obtain almost 'quantitative conversion orf heptanes to dimethyl pentanes and triptane.

It may be desirable to include in the feed to the heptane isomerization step sufficient parailinic hydrocarbons of lower molecular weight than helptanes to further decrease the degeneration of the heptanes to these lighter products. 'Ihis may be accomplished by closing valves (not shown) in the Ct, C5, C6 and the M55-185 F. fraction draw-oir lines from fractionator l2. (See Figure 1.) The total drawoi which is thereby made lby line Sli is sent to heptane isomerizer 3l and the product is sent to the heptane fractionation system from which the C4, C5 and Ca is withdrawn as an overhead stream which is fractionated in a separate fractionating system (not shown) to supply separate C4, Ct and Ce isomerization feed streams described above.

The heptane isomerization system itself is illustrated in more detail in Figure 2. The charging stock stream from line 36 is introduced at the upper part of hydro-gen chloride absorber 51 which may be operated at a pressure of about 300 pounds per square inch and a temperature ouf about F. Gases containing hydrogen chloride may be introduced at the base od the absorber through line 58 and make-up hydrogen,v chloride may be introduced through line 59. Un-- absorbed gases are discharged from the top o` the absorber through line 60. The charging stock: which may con-tain about 6% of dissolved hydro-- gen chloride is then pumped by pump Si througlr heater t2 to a low point in tower t3 which is about; one-half to two-thirds full of an aluminum'chloride-hydrocarbon complex. riihis complex may be made by the action of aluminum chloride on the charging stock itself in the presence of hydrogen chloride or it may be made from other hydrocarbons but it should not be made from olefms or aromatics, the best results being obtainable by complexes made from paraflins, particularly isoparains. Such complexes are already well known to those skilled in the art and Will require no further detailed description.

Make-up' aluminum chloride may be introduced through line 64 but I would preferably replenish the complex in this tower by introducing complex through Iline (i5 cErom another tower as will be hereinafter described. Spent complex may be -Withdrawn from the base of the tower through.

ling .6i-6- .Hrdrogeu may he introduced. through line .61 at the rate. oi ...hout 20.9. cubic feet. Der barrel. et stoelrcharged! The `charging .Stock is. passed upuardli?. through tower L63 ata Space velocity oialoout to. .3.J ef e one volume oi liquid feed per voluirleot .catalyst iii the tower per hour and .at .a `feed .rate the range Vof about e to 4.5.0 gallons per :hour ner square .foot oi @cross sectionalr areaof reactor, the tower being maintained at a temper ure of about 15.0. to 20,0$7 F., e.- g, .175- F'- and rider a pressure. iwithiri the range oli about 39u toA 30.0.0 pounds per .Square inch. .eg., 10Q() Votlutiis `tier square irich- Title. product .Stream 'leaving tower may. through line ,tu .and cooler et. to teuer lo which .is iileerrise about .oricrhali to'. three.n ttourths full of liquid complex and .inte makeup alurtiiruirrr` chloride may ybe. introdueed through line il. either as a slurry iu oil .or .oomrileir or. as a solution in .a light hydrocarbon o-.r portion of thecharging stock. or in. a. Y other ruitable manner. About .2 to 2. pounds oi .aluminum chloride may beemployed per barrel of stock charged. The. relatively inactive catalyst iii-om the base Aof tower lli ,is preferably returned by pump 12 through iirie ..65 for introduction ih to tower .6.3 although catalyst may he remored trom the base, of tower :10. through .line 1,3- ToWer l. may be operated uruier substantially the. Saure conditions tower 6.3 lout preferably at a. terrioeraturefwliioh `is .at least degrees lower aud which inl this case-may be about 1,59? l5-L The overhead .Stream ,from .tower lo. may he introduced. lov liuev le to .hot settler looeratirie at .substantially coercition. temperature ,and pressure. Settled complex may be returned di rectly by lines lo.. aud ll to tower vlll- The eroduct stream from hot settler 15 passes through line 'i8 to Acooler l5 aud pressure reducing .voire 8.o. to cold. settler o.' which may operate at about atmospheric.'temperature or about loof ;F. arid at a pressure slightly higher that. the pressure maintained on absorber 5]. Settled catalyst material may be withdrawn as. a liquid' Vor .slurry through line 82 and. returned by pump 83 to line il arid tourer. -it- Hrdrogeh, hydrogen chloride and'ligbt gasesV leavethe top of settler ,8l through lirielidL and" are returnedby line 58 toabsorber 57T The liquid product flows over Weir 85. and

1S withdrawn through une as to hydrogen' yenrolt ridestripper 8l which is providedv vv'ith a suitable heater 88 at its base. The stripped hydroglen chlcridefis returned'vianlines BQ'and" 5'? to absorbm.. y, .c

" Thestripped product may be scrubbed with t caustic in neutralizing system 90, washedy with water in Washing system 9| and then introduced by line 4l to hexane tower 42 from the top of which hexanes and lighter materials are withdrawn through line 43. lI he Ci hydrocarbons afrevvthdrawn trom. the base of toyver 4Z through line. ttf arid introduced iht'o. ,dimethyl pehtaue 'to'vver 45, the dimethyl pentane-tr'iptane stream beingvv'ithdravvn overhead ythroughlir'e 476 (-165 to 185 FJ. Methyl hexans, normal heptane and high boiling naphthnes are 'withdrawn from the base of tower 45 through linel4Tand introduced into fractionating column 48.' The methyl hexanes are taken overhead through linefS, condensedfand returned as recycle to line 36.

Any unconverted normal. heptane is Withdrawn from the system through line 5!) together with methyl. cyclohexane and higher boiling naphthenes. As. above pointed out, this particular stoornis a. particularly valuable .charge for. dehy- 8. droarornatization to produce aromatics. any parainic hydrocarbons separated from the aromatic products of dehydroarornatiaation .may be returned for .isomerization after suitable treatment to remove olefms if present in excess.

While I have described in detail a spcciic embodiment of myiinvention it should be understood that my invention is n ot limited thereto. The conversion conditions may vary throughout the ranges earlier set forth in the specification. Any number of towers may be employed in the conversion systeem and in fact the invention is applicable to heptane isomeriaation tvithl other typesof Friedel-Crafts catalysts lstirred raction vesselsyor in reaction vessels co; mailling supported catalystsf With ,other typshoffcatalyst other conversion conditions may be desirable; .for example, with hydrogen fluoride or an aqueous `hydrogen fluoride boron fluoride catalyst higher temperatures may bee'mployed `thanare desirable for the aluminum chloride-hydrocarbon complex.

If desired the neutralization and .Washingv may be limited to the unrecycled'product streams,.i. e., to streams which are not returned to Ian aluminum halide or Friedel-Crafts .conversionfzonle The product fractionator' may likewisesrveas a feed stock fractionator by introducing the hep'- tane charge through line 36a directly intohexane tower 42. In this system as vvell'as in' Figure 1 advantages are obtained by removing desired products from the original feed whereby the con# version zone itself might be operated more effectively. There are many other alternative arlrangements and modifications which will be apparent from the above description to those skilled in the art. 'i

I claim:

The method of producing heptanes having a plurality of branched chains from a hydrocarfbon charging stool: boiling within the light nephtha' boiling. range which charging Stock ,contains more'than 10% Vby volume of normal heptane .and large amounts v of methyl hexanes and cyclic hy,- d'rocarbons, the latter being .of the class .consisting of naphthenes and aromatic hydrocarbons, but which charging stock is substantially free rorh clens and from hydrocarbons higher boiling than normal heptane, which method c omprises diluting. said charging stock with a recycle stream hereinafter dened in s llCh .aHlQlJ-lfls, that thenorrnal heptane content of the. diluted chargingv stool;- is less, than 5% by. volume, contacting said diluted charging stock with an aluminum chloridefhydrocarbon complex iso merzation4 catalyst. promoted by hydrogen chloride in a conversion Zone at ar temperature in the rang? of to 300? F., at a pressure within the, rangev of 300 to 3000. .pounds per, square. inch in the presencecf added. hydrogen, at. a snacevelocity lWithin vthe approximate range ofl .3, to 3 .volumes of liquid charging 'stock' per hour per vollirucl of complex in theconversion .zone and .at a fleedrette within the range of 45 to 450, gallons of. liquid feedfper hour per square foot of cross sectional conversion zone area, removing catalyst and activator from product e'uent leaving .the conversion Zone, then fractionatng said .product emuen't to obtain a fraction of heptanes having ai'plurality of branched chains. and a methyl hexane fraction boiling chiefly. Within the range of F. to 2G5 F, 'and' substantially free from normal heptane and higher boiling hydrocarbons, recycling at least a part of said methyl hexane fraction for. diluting charging stool: as hereinabove set forth and withdrawing fromv thesystem components of the product efuent which are higher boiling than said methyl hexane fraction.

BERNARD L. EVERING.

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

UNITED STATES PATENTS Number Name Date 2,265,870 Schuit Dec. 9, 1941 2,266,012 dOuville et a1 Dec. 16, 1941 2,299,716 van Peski Oct. 20, 1942 2,300,249 Evering et al. Oct. 27, 1942 2,317,142 Goldsby Apr. 20, 1943 2,331,429 Sensel et al. (A) Oct. 12, 1943 2,336,863 Grosse et al. Deo, 14, 1943 OTHER REFERENCES Egloi et al.: Isomerization of Pure Hydrocarbons, pub. by Reinhold Pub. Corp., N. Y. (1942), 28-42. Copy in Div. 31.

Forziati et al.: Proceedings of 24th Annual Meeting A. P. I., 24, III, 34-48 (1943), 196/150.

Schuit et al.: Rec. Trav. Chim., v01. 59, 793-810 (1940).

Images