US2428417A - Catalytic alkylation of iso-paraffin with olefins - Google Patents

Description

W'. W. GARY Oct. 7, 1947.

CATALYTIC ALKYLATION OF ISO#PARAFFIN WITH O`LEFINS Filed NOV. 26, 1941.

Nw v MU NJ wR-IGHT w. GARY INVENTOR i BY e? ATTORN EYS Patented Oct. 7, 1%?47 CATALY'IIC ALKYLATION OF ISO-PARAFFIN WITH OLEFIN S l/Vright W. Gary, Los Angeles, Calif., assigner to The M. W. Kellogg Company, Jersey City, N. J., a corporation of Delaware Application November 26, 1941, Serial No. 420,511

7 Claims. (Cl. 26o-683.4)

This invention relates to the alkylation of isobutane with butylene in the presence of a catalyst, and more particularly to the preparation of mixtures of the latter hydrocarbons in their alkylate-forming proportions from certain random mixtures of the various isoand normal C4 parafns and olefins.

As is well known, a high octane aviation fuel blending stock may be obtained by alkylating isobutane with butylene in the presence of catalysts of the sulfuric acid type. In this reaction each mol of iso-butane apparently reacts with one mol of butylene, so that ideally the feed to the process should contain the iso-paraihn and olen in equi-molal proportions. In practice, however, it is customary to obtain feed stocks for alkylation from natural gas and gasoline, refinery residue gases produced in oil cracking operations, and other sources in which not only is there rarely the ideal iso-parafn/olefin ratio, but which almost invariably contain the non-alkylatable hydrocarbon, normal butane.

In many cases, of course, it is possible to combine C4 fractions from diiferent sources and hav-Y ing different iso-paranin/'olen ratios to obtain an approximate balance. In numerous other cases, however, and most frequently when all the materials must be obtained from a single source, gross disparities in the available quantities of isobutane and butylene are met with.

One of the objects of the present invention is to provide a method of preparing a feed stock for alkylation having a balanced iso-butane/butylene ratio from a mixture of C4 hydrocarbons wherein there is a deficiency of butylene.

Another object of the invention is to provide a process whereby an alkylation feed stock may be prepared from normal butano. Other objects and advantages of the invention will appear during the course of the description hereinafter given.

In order to achieve the above and related ends it is contemplated by the invention to convert -normal butane into iso-butane by catalytic isomerization, and then to convert iso-butane into butylene by non-catalytic pyrolysis, or what might be called purely thermal dehydrogenation. I have found that whereas at best a yield of -butylene of only 20 to 25 per cent is obtainable in pyrolyzing normal butane, iso-butano may be thermally dehydrogenate'd to yield as much as 60 per cent of butylene. The combination of an isomerization step with a pyrolysis step thus affords a route whereby butylene deficiencies may be` made up at the expense of the normal b-utane, 55

2 which otherwise could not be used efficiently for the production of alkylate.

In the event that the quantity of butylene obtainable from normal butane in accordance with the invention is still not suiilcient to effect an iso-butane/butylene balance when combined with alkylation reactants already available, I may subject a sufficient quantity of the excess iso-butane to pyrolysis along with the iso-butane obtained from normal butano, and thereby correct even the most disparate iso-butane/butylene ratios. If on the other hand there is more than enough normal butane to produce the butylene required to balance the available quantity of iso-butano, I may withhold from the pyrolysis step a portion of the iso-butane produced by isomerization, the Withheld portion being 0I suillcient sizev to bring into balance the nal overall iso-butane/butylene ratio,

An exemplary embodiment of the invention will now be described in detail and suitable conditions of operation will be given for the several conversion stages involved, the description being with reference to the annexed drawing. The drawing is a schematic flow sheet wherein unitary processing stages are conventionally designated for greater clarity by rectangular blocks bearing identifying legends.

In the drawing, the alkylation step 2 comprises conventional catalytic iso-butane-butylene alkylation in the presence of a catalyst such as 96% sulfuric acid, followed by fractionation of the product into alkylate and unreacted isobutane and normal butane. The presence of unreacted iso-butane in the alkylation product arises from the fact that the alkylation reaction is preferably carried out with about 5 to 8 mols `of iso-butane present per mol of butylene. The

excess iso-butane influences the course of the alkylation reaction Without actually taking part in it, and is Withdrawn unchanged in the product mixture. After being separated from the alkylate and from normal butane this excess iso-butane, or an equivalent amount taken from some other source, must be returned to the alkylation zone to maintain the desired iso-butane/olen ratio therein. 'Ihe latter ratio is not to be confused with the 1:1 ratio in which the two reactants actually combine.

The isomerization step 6 is likewise a conventional operation comprising the contacting of normal butane with a suitable catalyst such as aluminum chloride. I prefer to employ with the latter catalyst an isomerization temperature between about F. and 250 F. and a pressure Y narily from about 40 to about 75 per cent of normal butane, 'depending upon the time of Contact with the catalyst. In View of the practical absence of side-reactions, however, it becomes possible to obtain an ultimate yield of iso-butane of Y substantially 100 per cent by returning unreactcd normal butane for further contacting wi'tl'rtlfieV catalyst. As will be hereinafter explained, com'- plete conversion of normal butane to iso-butane is accomplished in accordance with the invention." i

For purposes of illustration, however, it will be assumed that the partially vconverted mixture obtained from the isomerization step 6 contains 40 per cent iso-butane and 60 per cent normal butane.

The pyrolysis step 9 is accomplished by heating iso-butane, suitably in a pipe coil or conventional tubular furnace, to approximately 1000 F. to 1100" F., and maintaining it at the elevated tenihr perature for a brief period.

The yield of butylene which Will be obtained by this pyrolysis is chiefly determined by the operating pressure and by the length of time that the reactant material is maintainedat the conversion temperature. The highest ultimate yields, ranging up to 60 per cent or better, are obtained at atmospheric pressure and with a relatively short conversion time. In order to rec'iluce` the requisite furnace tube volume,- however, it will usually be more economical to employ a pres- 'sure of 100 to 200 pounds per square inch. The pyrolysis reaction is like the isomerization reaction in that complete conversion is not effected in a single pass through the conversion zone. It is unlike the isomerization reaction in that side-reactions result in the formation of appreciable quantities of C3 and lighter hydrocarbons. The pyrolysis step 9 shown in the drawing includ'es removal of the light by-products from the product butylene and unconverted iso`butane, but not the separation of the latter two confstituents. The highest ultimate yields of butylene are obtained in a short time, high recycle ratio Operation wherein the yield per pass is relatively low; 20 per cent per pass is a suitable figure and will be assumed herein for illustrative purposes. l

An ultimate yield of butylene of approximately 50 per cent is readily obtainable in the pyrolysis step and will be assumed for the purpose of the present example. The return of unconverted isobutane 'to the pyrolysis step is indirect and will be understood from the description hereinafter givenl Y I't will be assumed further for illustrative pur poses in the example hereinafter described that a mixture of C4 hydrocarbons, such as might be separated from the byeproduct gas produced in cracking petroleum oils, is available as the net alkylation feed stock and that therelative proportions of the C4 hydrocarbons are as follows: Normal butane, 5-0 mols; iso-butane, v3U mols; and butylene, mols; total, 100 mols.

In the drawing, the above described or mixture is supplied to alkylation process 2 as indicated by line i; there is simultaneously supplied to the process 50 mols of iso-butane and "75 mols of vnormalV butane through line '8,' and 20 .mols of f butylene and 60 mols of iso-butane through line i2. Also,`100 mols of iso-butane are supplied through line Il. The gross feed therefore consists of iso-butane, 240 mols; butylene, 40 mols; and normal butane, 125 mols; total, 405 mols.

In the alkylation reactor, the 40 mols of butylene react with 40 mols of iso-butane to form alkylate, leaving200 mols of iso-butane and 125 mols of normal butane unreacted. The alkylate is separated by fractionation and disposed of as desired, as indicated by line 3.

The 12.5 mols of normal butane are likewise separated and transferred via line l to the isom- Verization step, wherein 50 mols (40 per cent) thereof are converted into iso-butane. VThe isomerization product, consisting of this 50 mols of iso-butane plus the remaining mols of normal butane, is returned via line 8 to the alkylation reactor to make up a portion of the gross feed thereto.

The 200 mols of iso-butane in the alkylation Vproduct is separated by fractionation andafter withdrawal as indicated by line 5 is subdivided into two portions. The first, consisting of mols, is returned immediately to 'the alkylati'on process via line il to maintain the desiredisobutane/butylene ratio of 6:1 (240 mols iso-butane/40 mols butylene) in the alkylation Vrzone.

The second portion of 100 mols is transferred as indicated by line i0 to the pyrolysis step wherea in, in one pass, yields of 20 mols of butylene and 20 mols of light gaseous by-products are obrt'ai'ned by the conversion of 40 mols vof the iso-r butane, 60 mols remaining unaffected. After separation and disposal of the by-p'roducts through line l, the mixture of 60 mols ofV isoa butane and v20 mols of butylener isreturned as indicated by line l2 to the alkylation step. 4

It will be seen that the quantities of materials charged to the individual steps and to the combined system are in balance with the intermediate and nal products. It will also be seen that in this embodiment of the invention, the recycling of unconverted normal butane and iso-butane to 'the isomeriz'ation and pyrolysis steps, respectively, is by way of the alkylation step, wherein removal of the respective 'conversion products'is effected through the agency of the alkylation reaction. Although I prefer to accomplish recycling in this way, it will be understood by those skilled in the art that, if desired, pure iso-butane and butylene could be returned to the alk'ylation step through lines 8, and I2 respectively, instead of partially converted mixtures, by vaugmenting the isomerization and pyrolysis rsteps each with rits own individual fractionation system, whereby unconverted material could be separated for immediate recycling. In the latter event the'quantity of iso-butane recycled through lines 5 and rIl for the benefit of the alkylation reaction would need to be increased, because of the absence of any iso-butane recycle in the butylene returne'c'll 75 mols of iso-butane in the net feed, and a portion of the iso-butane in the net feed would have had to be sent to the pyrolysis step. If on the other hand there had been more than the assumed amount of butylene in the feed stock, a smaller proportion of the total available isobutane would have been pyrolyzed.

My invention is not limited by any of the illustrative examples herein, but only by the following claims.

I claim:

1. The method of preparing a high octane motor fuel from normal butane which comprises catalytically isomerizing normal butane to form iso-butane, pyrolyzing a portion of the thusproduced iso-butane to produce butylene, and catalytically alkylating thus-produced butylene with iso-butane produced in said isomerization step.

2. A method of preparing a high octane motor fuel from a mixture of iso-butane, normal butane and butylene, wherein there is less than an equimolal proportion of butylene relative to the isobutane, which comprises adding butylene to the mixture and then subjecting the mixture to catalytic Ibutylene-iso-butane alkylation, separating normal butane from the alkylation product and converting thus-separated normal butane into iso-butane by catalytic isomerization, pyrolyzing thus-produced iso-butane to produce butylene, adding thus-produced butylene to further quantities of said mixture to be alkylated as aforesaid, and repeating said sequence of steps.

3. A method of preparing a high octane motor fuel from a mixture of isoand normal butane and butylene which comprises introducing said mixture into a catalytic alkylation zone, simultaneously introducing into said zone a second mixture consisting of normal and iso-butane and a third mixture consisting of iso-butane and butylene, catalytically alkylating iso-butane with butylene in said Zone, withdrawing a product mixture of alkylate, iso-butane, and normal butane from said zone and fractionally distilling it to separate isoand normal butane from alkylate land from each other, contacting the thus-separated normal butane with an isomerization catalyst to form a mixture of normal and isobutane, returning said last-mentioned mixture to said alkylation zone as said second mixture aforesaid, subjecting iso-butane separated from said product mixture to pyrolysis to convert it partially into butylene and lighter by-products, separating said by-products from butylene and uncoverted iso-butane, and returning a mixture of said latter two materials to said alkylation zone as said third mixture aforesaid.

4. In a process for alkylating iso-butane wit butylene in an alkylation step in which iso- .butane is maintained in substantial excess over butylene in a liquid acid catalyst alkylation zone and the reaction products are fractionated to separate an iso-butane fraction and a normal butane fraction, the improvement which comprises subjecting at least a portion of said isobutane fraction to thermal dehydrogenation in a pyrolysis step, recycling any remainder of said iso-butane fraction to said alkylation reaction zone, conducting said thermal dehydrogenation treatment under conditions of temperature and reaction time effective to convert a substantial proportion of the iso-butane to butylene while minimizing the formation of other products, re-

cycling to said alkylation step butylene obtained as a product of said thermal dehydrogenation treatment, subjecting at least a portion of said normal butane fraction to catalytic isomerization treatment to effect conversion thereof to isobutane, and recycling the isomerization product to said alkylation step.

5. In a process for alkylating iso-butane with butylene in an alkylation step in which iso-butane is maintained in substantial excess over butylene in a liquid acid catalyst alkylation zone and the reaction products are fractionated to separate an iso-butane fraction and a normal butane fraction, the improvement which comp-rises subjecting at least a portion of said iso-butane fraction to thermal dehydrogenation in a pyrolysis step, recycling any remainder of said iso-butane fraction to said alkylation reaction zone, conducting said thermal dehydrogenation treatment under conditions of temperature and reaction time effective to convert a substantial proportion of the isobutane to butylene while minimizing the formation of other products, recycling to said alkylation step butylene obtained as a product of said thermal dehydrogenation treatment, subjecting at least a portion of said normal butane fraction to catalytic isomerization treatment to effect con version thereof to iso-butane, and recycling to said alkylation step a mixture of normal butane and iso-butane obtained as a product of said isomerization treatment.

6. The method of preparing a high octane motor fuel which comprises catalytically isomerizing normal butane to form iso-butane, pyrolyzing at least a portion of the iso-butane thus obtained to produce butylene, and catalytically reacting butylene thus obtained with isobutane to produce a motor fuel ingredient of high anti-kno ck value.

7. The method of preparing a high octane motor fuel which comprises pyrolyzing iso-butane to produce butylene, catalytically isomerizing normal butane to form iso-butane and catalytically alkylating butylene thus obtained with isobutane produced in said isomerization step.

WRIGHT W. GARY.

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

UNITED STATES PATENTS Number Name Date 2,069,624 Prutton et al Feb. 2, 1937 2,276,171 Ewell Mar. 10, 1942 2,303,663 Shankland Deo. 1, 1942 OTHER REFERENCES The Reactions of Pure Hydrocarbons, by Egloff, Reinhold Pub. Co., New York, N. Y., 1937, pages 147 to 165. (Copy in Division 31.)

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