US2442440A - Manufacture of gasoline - Google Patents

Description

.June 1948. L. P. scovlLLE MANUFACTURE OF GASOLINE Filed Jan. l5, 1943 2 YSheets-Sheet l NNZJFDmMD P. SCOVILLE VENTOR 'illy WO- NGC 596mm holt Iii' INVENTOR 2 Sheets-Sheet 2 Ll wo a L. P. SCOVILLE MANUFACTURE OF GASOLINE `lume l, 1948.

Filed Jan. 15, 1943 LOREN P. SCOVILLE mwN. 24101@ wn.

WENT- mgm now A Patented June 1 1948 MANUFACTURE OF GASOLINE Loren P. Scoville, Yonkers, N. Y., assgnor to The Texas Company, New York, N. Y., a corporation of Delaware Application January 15, 1943, Serial No. 472,439

1 Claim. 1 This invention relates to the manufacture of gasoline, such as aviation gasoline and motor fuel, from normally gaseous and liquid hydrocarfbons. More particularly, the invention relates to the stabilization and fractionation of refinery hydrocarbon fractions, such as cracked naphtha and natural gasoline, and the catalytic conversion of e'iuent low-boiling or normally gaseous hydrocarbons to gasoline hydrocarbons of high anti-knock value.

One of the principal objects of the invention is to provide an improved process of stabilizing and fractionating petroleum products or fractions, such as cracked naphtha, and of converting low-boiling or normally gaseous eilluents of such stabilization and fractionation to gasoline hydrocarbons of high anti-knock value, to thereby increase the yields of aviation gasoline and motor fuel produced from available renery fractions, eliminate or minimize corrosion, and secure other advantages.

Another object of the invention is to provide a novel method oi" stabilizing and fractionating hydrocarbon mixtures to obtain a better separation of desired fractions, while at the same time providing a higher stabilization pressure and a greater overhead condensate recovery with available cooling water or other medium for the same reboiler temperature.

Still another object of the invention is to provide an improved method of stabilizing and fractionating hydrocarbon mixtures containing both parai'n'ns and olens of the same number of carbon atoms per molecule, whereby a portion of a Y normal paraiiin may be retained in the stabilized bottoms for volatility While electing a greater recovery of the olens of the same carbon atom content in the overhead.

Another object of the invention is t provide an improved method of stabilizing raw cracked naphtha and polymerizing overhead low-boiling or normally gaseous unsaturated hydrocarbons to polymer gasoline, wherein a portion of a W-boiling normal paraiiin is retained in the stabilized cracked naphtha for volatility, while at the same time a greater proportion of the oleiins of the same carbon atom content as the low-boiling normal paraffin are removed in the overhead. to thereby increase the yield of polymer gasoline,

Still another object of the invention is to provide an improved method of stabilizing raw cracked naphtha and natural gasoline, and alkylating overhead low-boiling or normally gaseous isoparains with olens to produce aviation gasoline, wherein a greater recovery of lowboiling olens and isoparalns is eiected from the raw cracked naphtha and the natural gasoline to thereby materially increase the yield of aviation gasoline, While low-boiling normal paraln components are retained in the stabilized naphtha or gasoline for volatility. t

A further object of the invention is to provide apparatus for carrying out the method of this invention, Iwhich apparatus is simple in construction, is readily available and easily controlled, and economical in operation and maintenance.

Other objects and advantages of the invention will be apparent from the following description when taken in conjunction with the accompanying drawing and appended claim.

In the drawing which illustrates preferred embodiments of the invention: v

Fig. 1 is a diagrammatic illustration of apparatus for carrying out the method of this 1nvention as applied to the stabilization of raw cracked naphtha and the polymerization of eiliuent gases therefrom; and Y i Fig. 2 is a diagrammatic illustration of apparatus for carrying out the method of this .1nvention as applied to a modication involving the stabilization and fractionation of raw cracked naphtha and natural gasoline, and the alkylation of eilluent low-boiling or normally gaseous isoparaffins and olens therefrom.

In conventional renery practice, it 1s customary to stabilize raw cracked naphtha as obtained .from the cracking of petroleum hydrocarbons to remove normal butane and lighter, the eilluent gases then being treated and converted in part to gasoline hydrocarbons of hlgh antlknock value by various processes including polymerization and alkylation. The resulting conversion products are stabilized and fractionated to recover an aviation gasoline, and a portion of the normal butane may be blended back with the stabilized cracked naphtha for volatility. As applied to polymerization, it is customary to stabilize the raw cracked naphtha to remove overhead C4 and lighter. The overhead gases may then be fractionated to separate a selected C4 fraction, and the resulting C4 fraction is then polymerized to polymer gasoline, stabilized and hydrogenated to provide a saturated isoparafnic aviation gasoline, On the other hand, the overhead gases may be condensed, and the condensate comprising mainly C3C4 hydrocarbons polymerized and stabilized to form a high octane motor gasoline. In an effort to secure maximum yields of this gasoline, the raw cracked naphtha may be deeply stabilized to remove substantially all of the normal butane and lighter, so that practically all of the C4 olens' are obtainedin' the'overhead. In thisv operation, difficulties may be-encountered in condensing the desired amount of overhead gases with the use of available cooling water without refrigeration due to the lower stabilizer pressure required for a given available reboiler temperature; and the increasedyield of polymerizable olens in the stabilizer4 overheadmaybe counterbalanced by the oleiins remaining uncondensed and passing to the reiinery gaslines, rather than being passed in the condensate to the polymerization unit. On th'e other hand, if lthe stabilizer pressure is maintained constant, this deep .stabilization of the v:cracked naphtha re- ',quires a'higher reboiler temperatura-which may be .above Vthat normally obtainable -with the 1available renery high pressure `Asteam supply. .-fAlso,-the deep-stabilization lowers the front end .volatility of the stabilized cracked naphtha-so :that it will not meet specificationsfor motorfuel, and necessitates the'blending back of normalrbu- .tane with-the stabilized cracked naphtha to meet -front end volatility specifications.

Consequently, in many refineries; a'compromise is eiected on the basis oi" the available Vhigh pressure steam supply and the'. availablez cooling Awa- 'ter temperaturebetween-thedeep stabilization of theraw cracked .naphtha describedV aboveandl an operation in which a substantial proportion of the C4 vhydrocarbons Vare left .in vthe stabilized cracked naphtha forvolatility. Whilethis .latter operation retainsnormal butaneinthe stabilized `cracked naphtha, itis also -accompaniedzby a' substantial loss of the C4 olefins, particularlyzbutyl- `ene-2, in the stabilizer .'bottoms. Tlf'hisfresults in a loss of desirable oleiins in the :polymer charge, with-a resultant decrease in yield of aviation or motor gasoline 'from .that theoretically possible from the available refinery stocks.

In order to operate ata suicientlyhigh stabilizer pressure to condense the major portion of the desirable constituents of .the overhead'from theraw cracked naphtha stabilizer, it has 'been previously proopsed to inject water into the reboiler of the stabilizer, However, this method isnecessarily limitedto anincrease in stabilizer pressure of approximately fiftypounds per square inch for a given reboiler temperature and', in addition, may ,result in increased corrosion.

.In .accordance with the present invention, `an improved method of operation .is provided for `stabilizing ther-aw cracked naphtha directlyto desired volatility andR. V. P., while at the same .time -the portion -of C4 retained in the stabilizer lhottonls-consists largely-of Anormal butane, and -a materially .increased .proportion of C4 olens for the .particular relatively flow reboiler temperature Vused is secured inthe roverhead; Moreover, .this method at the same time enables .the stabilizer `operating pressure `to .be increasedsubstantially more than the above-noted'fifty pounds der v1a given reboiler temperature without the use of water injection, whereby an increased recovery of the valuable unsaturated hydrocarbons is obtained in the overhead condensate by the use of available cooling water, or the same recovery canA drocarbon 'fraction may be introduced at any .point within the tower below the point of entry of the-normarreiiuX-condensate, but preferably is added below :the vpoint of entry of raw cracked naphtha charge, Very good results have been secured'byintroducing this saturated C4 recycle streaminto the stabilizer reboiler.

The invention is more particularly illustrated in Fig. 1, which showsthe raw cracked-naphtha -asbbtained from a renery cracking operation being charged. by pump l0 throughfline ll finto -an intermediatevpoint of stabilizer I2. Thelatter maybe a conventional fractionating tower of themultple bubble plate type, andxisequipped with a line i3 for withdrawingliquid. from a pool within the base oi thetower and passing the same through a reboiler i4 heatedbyhigh pressure steam supplied to heating con-i5,.theheatedhydrocarbon being returned to the .base f ythe tower by line I6. .A bottoms .of stabilized cracked naphtha is withdrawn .fromthebase of thetower by line ifi. Overhead.gases-composedrof-Cnand lighter pass by. line I8 Vto water-cooledfccndenser i9 and thenceby rundownline .20 tdaccumulator 2l. Uncondensedgas, mainly `C2 and lighter,-is bled off Afrom .accumulator :2l byV overheadY line '22 .to Vsuitable gas-.collecting lmeans not shown.

Liquid condensate, .consisting largely ofCs-C, fis withdrawn from the accumulatorthrough line 23and forced by ipump 24 lthrough'line 25. .The latter communicates `with-branched lines so that aportion ofthe/condensatemay be returnedby line 21 to the upper-portionvof tower :I2 to serve as reflux therein, while another portion passes vby line 28..to.a polymerization unitindicated generally at 29,

Any conventional catalytic or thermal polymerization vunit for converting thelolefinic 'constituents of the-charge to polymerinay be employed. Since the polymerization unit 'per se forms no part of the present invention, further illustration thereof is deemedunnecessary. By way vof example, the unit 29 may bea conventionalphosphoric acid unit provided with a-heater in which the charge is .raised to a temperature of about 3504500" F. andthen passed through a catalytic tower or converter containingkieselguhr on which is rabsorbed the'phosphoric: acid catalyst. The operation thus far described is .a so-calied non-selective polymerization in which both C: and C4 olens are polymerized in the presence of each other. However, it is'to be understood that the overhead condensate Lfrom the stabilizer l2 could be further fractionated .to separate mainlya'C4 fraction, whereby cross-polymerization of .fnormalan'd isobutylenes :occurs in the unitiZS. 'In any Vevent,litiis' toibel understood that the C4 oleins of the charge are largely consumed in the polymerization step to form higher boiling normally liquid polymers.

The resulting polymerization products are passed by line 3D to a depropanizer 3| where Cs and lighter are removed overhead by line 32 and the depropanized polymer gasoline is withdrawn as bottoms by line 33. The overhead gas passes to condenser 34 and thence by rundown line 35 to an accumulator 36 from which condensate is withdrawn by line 3l and returned by pump 38 through line 39 to an upper portion of tower 3| to serve as redux therein. It is also to be understood that the depropaniz'er 3| may be equipped with a suitable heating coil or reboiler in the conventional manner.

The depropanized polymer gasoline passes by line 33 into a debutanizer 49 also equipped with a conventional heating coil or reboiler at the base of the tower (not shown), and from which a saturated C4 stream consisting essentially of normal butane and isobutane is removed as overhead by line 4| and a stabilized polymer gasoline is withdrawn as bottoms by line 42 for passage to motor gasoline storage or to a hydrogenator (not shown) in the case of selective polymerization in the production of aviation gasoline as is well understood. The saturated C4 gases pass by line 4| to condenser 43 and run down line 44 to an accumulator 45. The saturated C4 condensate is withdrawn from accumulator 45 by line 46 and forced by pump 41 in part through line 49 to the top of tower 40 to serve as redux therein, and in part by line 49 to the reboiler I4 of cracked naphtha, stabilizer |2 The amount of saturated C4 which is recycled through line 49 to stabilizer l2 can be varied within substantial limits. For example, a relatively small amount of recycle on the basis of the raw cracked naphtha charged will give improved operation, and this can be varied up to the recycle of substantially all of the saturated C4 condensate not required as reflux in debutanizer 49. Thus, a recycle rate of as little as one part by volume f saturated C4 to a hundred parts by volume of raw cracked naphtha charged and up to equal parts by volume or more may be employed. In the latter case, it is obvious that additional saturated C4 from an external source would be required in initiating operation and until there had been substantial buildup of the saturated C4 in the system. Generally, about one part of saturated C4 to twenty parts by volume of raw cracked naphtha charged up to one part of recycle to ten parts of naphtha charged are preferred to maintain the proper balance in the system. It will be understood that this will very for diierent reboiler temperatures and diilerent temperatures of available cooling water and can readily be determined in actual operation by those skilled in this art for the particular conditions encoun- '60 tered to provide the most efficient operating conditions. In operation, the amount of recycle may be controlled by any conventional rate of dow controller in accordance with the rate of feed of the raw cracked naphtha to stabilizer l2. This is illustrated diagrammatically by ratio flow controller 50 between line and line 49 with air connection regulating a valve 52 in recycle line 49. It is to be understood that the hydrocarbon recycle can also be combined with direct water injection into the stabilizer tower, if desired. to obtain the cumulative effect on increase in tower pressure for a given reboiler temperature of both the hydrocarbon injection and the water injection.

'Ihe following results were obtained in comparative runs in commercial operation on a combined `raw cracked naphtha stabilization operation and a polymerization of the stabilizer overhead condensate by a conventional phosphoric acid polymerization process.. In one run, the raw cracked naphtha stabilizer was operated in conventional manner without hydrocarbon recycle and injection into the reboiler of the stabilizer. In another run, a saturated C4 fraction obtained in the stabilization of the polymerization products as in Fig. 1 above was recycled at the rate of 14.6 B. P. H. into the reboiler of the raw cracked naphtha stabilizer to which the raw cracked naphtha was fed at the same rate as in the previous run, namely, at about 208 B. P, H. The following were the conditions and results of the run: v

without b u- Btlmifw tme injection tane injected into reboiler into reboler Rates in barrels per hour:

Charge to raw cracked napththa. 208 208 Butane injection into reboiler 0 14. 6 Charge to polymerization uni 45. 55 60. 98 Redux to stabilizer tower 124. 45 131. 02 4Redux ratio 2. 3:1 2. 0:1 Stabilizer bottoms R. V. P. in lbs. 10. 1 10.5 Redux material-Dist. IBP F -44 5 Redux material-Dist. 98% od at.. +30 +34 Pressure, lbs. per sq. in. gauge:

Stabilizer tower top 215 212 Redux accumulator drum 211 208 High pressure steam for reboiler 174 172 Temperature, F.:

Stabilizer tower top 136 146 Raw naphtha to tower 208 208 Reboiler vapor 345 342 Redux accumulator drum.- 88 88 Water supply to condenser 8l 82 Water discharged from condenser. 94

Charge plus butano recycle combined Liquid Vol. Per B. P. H.

cent Liquid,

Vol. Per B. P. H.

cent

Analysis Chg. to Stabilizer:

Methane 0.42 0. 87 0. 39 0.87 Ethylene 0. 73 l. 52 0.68 1.52 Ethane. 3. 79 7.88 3. 54 7. 88 Propylene- 3. 77 7.84 3. 52 7. 84 Propane 6. 26 13. 02 5. 85 13.02 Isobutane 2. 30 4. 78 3. 04 6. 76 Isobutylene+ butylene-l. 3. 53 7. 34 3. 63 8. 09 Normal butan 6. 51 13. 54 10.00 22. 25 Butylene-2 3. 71 7. 72 4. 57 l0. 18 PentoneS-l- 68. 98 143. 49 64. 78 144. 19 Analysis butane recycle:

Isobutane 13. 58 1. 98 Isobutylene-lbutylene-l 5. 15 0. 75 Normal butano 59. 64 8. 7l 16. 84 2. 46 4179 Y 0.70

2. 26 1. 03 1. 50 0. 91 4. 48 2.04 2.24 1. 36 9.54 4. 34 13. 90 8. 48 11.30 5.15 13. 32 8.12 34 15. 19 28. 92 17. 63 Isobutane. 6. 35 2. 89 6. 78 4. 13 lsobutylene+ butylene-l 8. 7l 3. 97 9. 66 5. 89 Normal butane 15.91 7. 25 15.79 9.63 Butyle11e2 6. 71 3. 05 6. 49 3. 96 PentaDes-l- 1. 40 0. 64 1. 40 0.85 Analysis stabilized bottoms:

Isobutane-l-normal b t 6. 73 6. 96 11.04 5. 78 2. 68 4. 25 PentaneS-i 142.85 90. 36 143. 34

area/14o without bu- Bwltlifw tim-1e necio tane injected into reboiler ma remuer Total Q4 in stabilizer charge B. P. H.. 33. 38 47. 28 'TotalV saturated butane in stabilizer charge B A. 18. 32 29.01

A esin stabi lzer charge B. P. H 15.06 18. 27 Saturated butanes in feed to polymerization unit B, l. E: l0. 14 13. 76 Unsaturated butylenes in feed to polymerization unit l.- l H".- 7- 02 9- S5 Saturated-butanes to stabilizer bottoms n.1?. `6.73 11.04 Unsaturated but es to stabilizer bottoms B. P. H 5. 78 4. 25 'Percentage of available saturated butanes to- Feed to polymerization unit 55. 35 47. 43 Stabilizerbottdp1s 36. 74 38. 06 Percentage of available unsaturated butyienes to? Feed to polymerization unit 46.61 53. 91 Stabilizer bottoms 38. 38 23. 26 Overhead gas from stabilizer accumulator drum B. P. H 7.14 2A 09 Eroznthe above, it will be noted that with substantially the same high pressure steam supply to the stabilizer reboiler and substantially the same reboiler Vapor temperature, and with approximately the same cooling water temperature for the stabilizer overhead condenser, very material advantages were secured with the butane recycle and injection into the reboiler of the stabilizer. Thus, the percentage of available butyleues left in the stabilizer bottoms dropped from approximately 38% to 23%, while the percentage of available butanes left in the bottom-s was increased from approximately 37% to 38%, and the Reid vapor pressure of the stabilized bottoms was maintained or even slightly increased from 10.1 to 10.5 pounds, Moreover, the percentage of available butylenes in the feed to the polymerization unit was increased from approximately 46.5% to 54% while the percentage of available saturated butanes decreased from approximately 55.5% to 47.5%. At the same time, there was a substantially increased condensation of the stabilizer overhead and consequently an increase in the charge to the polymerization unit, 'as is shown by the drop in the overhead gas from the accumulator drum trom 7.14 to 2.99 barrels per hou'r.

It is thus seen that, by the method of the present invention, the raw cracked naphtha was stabilized to desired Volatility and Reid vapor pressure while at the same time a substantially improved separation between saturated butanes and unsaturated butylenes was secured so that a greater proportion of the saturated butanes remained in the stabilized cracked naphtha while a greater proportion of the unsaturated butylenes was removed overhead, condensed and thus recovered for the polymerization feed. These beneficial results were secured solely by recycling the available butane fraction from the polymer debutanizer to the stabilizer reboiler, and without otherwise altering the conditions of operation including high pressure steam supply to the reboiler or temperature of cooling water to the stabilizer overhead condenser.

While the invention has been described above in connection with a polymerization unit, it is to be understood that the invention is also applicable to other conversion processes for converting low-boiling or normally gaseous hydrocarbons to high octane gasoline hydrocarbons suitable for aviation fuel. Likewise, while the invention has been described in connection with 'the stabilization of raw cracked naphtha to obtain a separation between saturated butanes and unsaturated butylenes, it is to `be understood that the invention is also applicable to eiecting a desired separation between pentanes and @mylenes, hexanes and hexylenes, etc.

Referring to Fig. 2, the invention is shown as applied to the stabilization of raw cracked :Raphtha and natural gasoline and the alkylation of isobutane with C4 and C5 olefins to thereby materially increase the yields of aviation gasoline from available charge stocks. As shown., raw cracked naphtha from a conventional cracking unit is introduced by line 60 to stabilizer il equipped with reboiler 62, and operated to take overhead by line 63 a C5 and lighter fraction-ccntaining a substantial proportion of the Cs olefins. A stabilized cracked naphtha containing a substantial proportion of normal pentane for volatility is withdrawn as bottoms byline 5.4. The overhead fraction is passed through con.- denser 65 to accumulator 66. Condensate .is forced by pump 01 in part through line. 63 to serve as reflux in tower 6|, and in part by line 69 to a depropanizer 10. In the latter, the charge is fractionated to remove overhead through line 1l C3 and lighter, and obtain a bottoms cut consisting essentially of C4 and C5 .which` is passed by pump 12 through line 13 to a conventional alky-lation unit 14.

While any conventional alkylation process `can be employed, the invention is described for purposes of illustration in connection with asulfuric acid alkylation step. In this process, an additional supply of isobutane introduced by the recycle line 15 to be hereinafter further described, or from any other suitable source, is mixed with the olefinic Ci-Cs charge from line 13 in the presence of strong sulfuric acid of about {Z8-100% concentrationat temperatures of about 35-70 F. and under sufcient pressure-to main.- tain the hydrocarbon in liquid phase. Any-con, ventional type of unit, such as the Well known pump and time tank reactor, the jet reactor, or the mixer of the turbo type can be used. The isobutane is maintained in substantial molar excess of the olens; and preferably the operation is of the well known emulsion recycle type in which contact ratios of from 50:1 up to 200:1 or higher are employed. Under these conditions, the isobutane is alkylated by the C4 and Cs ole.- iins to produce good yields of gasoline hydrocarbons or alkylate of high anti-knock value. Itis to be understood that other well known alkyl7 ation catalysts, such as hydrouoric acid, aluminum chloride-hydrocarbon complex, BFs-water complex, and the like can be used; although strong sulfuric acid is preferred for this operaE tion. As the alkylation unit per se forms no part of the present claimed invention, further de, scription thereof is unnecessary. It is understood that in conventional practice, a stream of the reaction products is withdrawn to a suit, able settler where the catalyst is separatedvfrom the hydrocarbons, and the latter are then `neu, tralized before being passed to the stabilizing'and fractionating equipment. These various4 steps and the equipment therefor are well. known. and it is to be understood that the diagrammatic illustration of the alkylation unit represented by the numeral 14 includes the alkylation reactor, settler and neutralizer.

The neutralized hydrocarbon reaction products from the alkylation unit are passed by line 11 to a debutanizer 18 where unreacted -Cl hy,-

drocarbons 'consisting essentially of excess isobutane and normal butane are removed overhead by line 'I9 and a debutanized alkylate is withdrawn as bottoms by line 8U. As the alkylation reaction consumes the olens in the charge, the overhead C4 stream is further fractionated in a butane fractionator 80' where an isobutane out is removed overhead and recycled by line 'l5 to the alkylation unit while a normal butane stream is removed as bottoms by line 8| and passed in whole or part by pump 82 through line 83 to the stabilized cracked naphtha in line 6d to increase the yield and volatility of the motor gasoline.

The debutanized alkylate withdrawn by line St is passed by pump 85 through a line 85 to a depentanizer 81 where C5 is removed by the overheadline and depentanized alkylate is removed as bottoms by line 89. It is to be understood that the above-described order of towers can be changed. For example, the raw alkylate can first be depentanized, and the resulting C5 and lighter oftgases fractionated in a series of towers to obtain the various fractions described, including an isobutane cut, a normal butane out, an isopentane cut and a normal pentane cut. The C5 overhead fraction consisting essentially of isopentane and normal pentane is mixed with a stream of debutanized natural gasoline introduced by line 90, and the mixture passed into a. de-isopentanizer 9|. The latter is operated to remove isopentane overhead by line S2, and the de-isopentanized natural gasoline containingthe normal pentane from the alkylate is removed as bottoms by line 93. The latter is passed by pump 9d to a depentam'zer 95 where normal pentane is removed overhead by line 96 and the depentanized natural gasoline discharged as bottoms by line 91. It is to be understood that the fractionating towers 10, 18, 80', 8'lrand 9| are equipped with the usual reboilers or other heating means for the base of the towers, and with suitable condensers and accumulators for the overhead and pumps for supplying condensate as reux to the tops of the towers as well as forcing the remaining portion of the condensate to the next tower or unit in series, which elements are not shown for simplicity in illustration.

The overhead normal pentane fraction passes by line 9E to condenser 99 and thence by rundown line to accumulator |0| from which condensate is withdrawn through line |02 by pump I 03 and forced in part through reux line |04 to the top of tower 95, and in part by recycle line I 05 to the reboiler B2 of the cracked naphtha stabilizer 6 I. In this manner, a saturated C5 stream consisting largely of normal pentane is provided for injection into stabilizer 6| to thereby obtain a. more complete separation of C5 olens in the overhead, while retaining a desired proportion of normal pentane in the stabilized cracked naphtha bottoms. While the above described introduction of debutanized natural gasoline into the fractionating system is advantageous for the production of more isopentane, itis to be understood that this is not essential in accomplishing the broader objects of the present invention. For example, the Cs cut from the stabilization of the alkylate may be directly fractionated into isopentane and normal pentane fractions, Without addition of any natural gasoline cut.

The depentanized alkylate removed from tower 81 by line 89 is forced by pump |01 through line |08 to the alkylate fractionator where a desired aviation gasoline fraction boiling up to about S50-375 F. is removed overhead by line Il and .gasoline from line Y l0 alkylate bottoms are discharged by line and forced bypump ||2 through line H3 to storage or for further treatment. Preferably, theA alkylate bottoms are passed by line ||3 to suitable blending tanks (not shown) where they are mixed with the stabilized cracked naphtha from line 64 to increase the yield ofv motor gasoline. The overhead aviation fraction is condensed in condenser ||5 and passed through rundown line ||6 to accumulator l from which the aviation gasoline is discharged by line |`|8 -to storage or for further treatment. The overhead isopentane fraction from line 92 is passed to suitable condenser and accumulator equipment (not shown) and the condensate' blended with the aviation |'|8 to thereby increase the yield and adjust the volatility of the -aviation gasoline. Itis to be understood that the depentanized natural gasoline from line 91 may, if desired, be passed to a further fractionating tower (not shown) serving as a de-isohexanizer from which an overhead isohexane cut may be obtained for blending with the aviation gasoline from line ll 8 to further increase the yield thereof. The resulting natural gasoline bottoms from this further fractionating operation may then be passed to reforming or other treatment, or may be blended directly with the stabilized cracked naphtha from line 6d for motor gasoline.

It is to be understood that the debutanized natural gasoline introduced by line 9D has been previously stabilized to separate C4s and lighter, and the oigases from this stabilization fractionated to separate an is introduced by line |2l into theisobutane feed for the alkylation unit 74 to thereby serve as an external source of supply of additional isobutane. A normal butane also recovered from, the natural gasoline in this latter operation may be added to the normal butane stream passed by line 83 to the stabilized cracked naphtha in line 64. These elements are not illustrated in the drawing for the sake of simplicity in illustration.

While the invention has been described above combination with a suitable polymerization alkylation unit, from which the desired recycle stream is obtained for injection into the cracked naphtha stabilizer, it is to be understood that the. invention is not limited to these particular catalytic conversion units. Thus, it is obvious that the stabilization method described herein can be applied in conjunction with other catalytic or thermal conversion units, such as isomerization, cyclization and aromatization, and various `combinations of these with polymerization and alkylation. Likewise, the invention is not limited to the stabilization of cracked naphtha and natural or straightrun gasoline fractions, since the particular stabilization and fractionation method is more broadly applicable to the distillation of olen and parain containing hydrocarbon mixtures generally.

The invention can also be employed in a stabilizing operation where the overhead condensate capacity is insuicient for normal operation, to thereby enable the stabilizer to operate at a higher pressure for the same reboiler temperature, with resultant increased condensation of the overhead at the higher pressure with the same condenser cooling surface. Likewise, the invention can be applied to stabilizing operations where diiiiculty is encountered due to the temperature of available cooling Water for the overhead condensate being too high, since the higher stabilizer pressures resulting from the hydrocarisobutane-rich fraction which bon injection permit increased overhead condensation with the 'higher temperature cooling Water. r'

Obviously `many modifications and .variations ofthe invention, as herein'before set forth', may be rmade Without *departing .from the spirit.` and scope thereof; and thereforeionlysuch limitations should be Vmade as are indicated in' the' appended claim.

I claim:

The method in the stabilization of a raw cracked naphtha,and the' manufacture of gasoline, hydrocarbons of high anti-knock value' from the overhead of the stabilizing operation, wherein the C4 hydrocarbons of 4the rawcracked naphtha consist of substantial proportions each of isobutane, normal butane', is'obutylene, butylene-l and butylene-Z'; and the proportion of thebutylene-z in saidi fraction, is. roughly equivalent to the combined; proportion of isobutylene and butylene-1, which "comprises introducing the .raw cracked naphtha intol an intermediate portion of a'stabiiization andrectic'ation zone', heating the-lower portioniof said zone tovaporizeC4` and lighter vconstituents by indirect heat exchange with a heating'medium, subjecting the overhead from 's aidzone to cooling andondensation at the 'pre'ssure'ofV said zone by'indii'ect'v heat exchange with a cooling" medium; returning 'a portion ofthe 'resultingfcondensate as reflui'rlto anlupper portion of sad zone, 'the'operationibeing lsuch that a portion of 'the C4'. together 'with lighterV constituents passes overheadironi. said zone while' `a stabilized Ycracked 'naphtha containing sufiicient C4 'to meet volatility specifications is ldischarged as bottoms, 'subectinganl other portion' Loffsai'd overhead condensate to catalytic' conversion" to largely" convert' butyl'enes thereof 'into 'high `anti-'knock l`lgasoline hydrocarbons While 'ri-buta'ne'M of-"s`a`id`overh'ad condensate remains inert, *separatingiifni tl' 'products' of said'catalytic conversin' said Ag'asolilr'e hydrocarbons, also` separatin'gfl f'o'ii th'ef pluts of said catalytic c'oriv'ersion'a Ci: fraction conssting mainlyof n-butane, and` recycling` 'said C4 45 consisting niainly'l of n-but'ane" to the iract'io'n I K 0i SL21@ etebilizeltoaantl realisatie@ interior zone in,.sufcient 4proportion in relation .to .the Iraw .cracked .naphtha Ifeed. to accormlilish .the following Athree results, .namely iCl) materially increasathepressure in said zone iora.given temperature :in the t lowerporton of said. zone, (2) materially increase ithe lcondensation `ofrroverfi head vapors from saidfzone for.a\.givenitemper ature ofthe cooling. medium supplied ,thereto, and (3) materially increasefthe combined'rproportion ofrisobu-tylene, butylene-l .and butylene- 2 taken overhead forv ak given retention oi G4 including ifi-butane in .the stabilized Acracked naphtha bottoms to meet volatility specifications. LOREN- P. SCOVILLE.

REFERENCES.. crrnn.

The following reerences arcor recom' in the file of this'patent:

Uurrn s'rnfrns ammira Diagrammatic Flow Sheet in the. Renner, Oct. 1942,- vol. 211, between-.pages 140. and: 141.

Burrell, The VRecoveryv of. Gasolinev -from NaturaLGasf? 1925; pagesaandz46.

Applications. ot rEhe'rmal Pol Oil'-` andi Gas Jour.; June.22, 1989, pages-A52', 53', 66 and; 69f72 (pages.531andJlOtpertinent)

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