US2322482A

US2322482A - Production of motor fuels by alkylation

Info

Publication number: US2322482A
Application number: US248422A
Authority: US
Inventors: Eldon E Stahly; Erwin M Hattox
Original assignee: Standard Oil Development Co
Current assignee: Standard Oil Development Co
Priority date: 1938-12-30
Filing date: 1938-12-30
Publication date: 1943-06-22
Anticipated expiration: 1960-06-22

Description

- June 22,1943. E, E. sTAHLY ETAL PRODUCTION OF MOTOR FUELS BY ALKYLATION Filed Dec. 30, 1938.

n A JAP l: n :I Il

NWINOO mw O Patented June 22, 1943 PRODUCTION F`MOTOR FLS BY ALKYLATION i l f" Eldon E. Stahlyand Erwin M. Hattox, Baton:

,i i Rouge, La., assignors to Standard Oil Develop- `ment Company, a corporation of Delaware "ApplicationI December 30, 1938, Serial No. 248,422

Claims.

The present invention` relates to the process of reacting olens with other hydrocarbons, and pertains, more particularly, to the production of saturated hydrocarbons boiling within the motor fuel boilingy range by vthe'allrylatic'n of normally gaseous straight or branched chainvm'ono-oleflns. c

More particularly,V the present invention is directed to a method for controlling thetype of product by such a reaction.`

:It is.,kn`own'that saturated' hydrocarbons containing tertiary carbonatoms, hereinaaifte'r referred to as tertiary hydrocarbons, will react with oleflns in the presence lof concentrated mineral acids to produce a wide rangel of products. Thereactions involved are `ert'remely complicated .and are little understood. i It is known'that the nature-of y'the reaction product will vary with the reaction conditions and with the type of mixture employed as' starting materials. For any given `mixture of starting materials and for a given set of operating conditions, however, the nature of thehproducts produced bythe procedure heretofore followed is beyond the control of the operator.

According to the present invention, the nature' of the productor such a reaction iscontrolled to avconsiderabledegree byadding to the feed stock one or more hydrocarbons normally contained 'in the product under the conditionsfemployed, the formation of which it isV desired to suppress. `It has nowbeen established that the formation of one of the normal components of the product can be substantially completely prevented by addition-to the feedstock of that component, or fraction of components the forma-- tion of which it is desired to Suppress if these components are added in at least an amount in which they would be normally produced.

The processor the present invention is parv fuels b-y several methods such-as the destructive hydrogenation of selected distillates or crudes, the extraction with sulfur dioxide of certaindistillates or crudes, and the'catalyticcracking under selected conditions of such extract. The fuels produced by the first method 1 are rather high priced due to the limited quantityof suitable raw material. Thefuels produced .by the latter two methods' have so low an initial octane number and so low a lead susceptibilitythat the amount of lead required to convert them into 100 octane fuels makes their cost well nigh prohibitive.. In contrast thereto.` 'it has been` found that the` present' process` readily lends itselfv to the production of highly satisfactoryA safety fuels.

In the production ofy safetyfuels by the present v,

alkylation process, it is possible to convert substantially all of the new feed into Cm and higher n f fractions by recycle of'Ca to C9 fractions.. It is readily.- apparent toone skilled in the. art, how ever, that the invention is notv conned to theAA addition or suppression of the C5 tovCs fractions alone, but itis readily understood that any de-A sired light. fraction may. be returned and recycled to the reaction zone. I f an extremely high boiling fuel is desired, itis contemplated to return to the original alkylation zone fractions boiling below the C12 fraction, or, for exv in ample below the C10 fractionl depending upon. the degree of safety required in the fuel. Usually a fuel having a Tag closed cup flash :in rexcess of 100 F. isentirely suitable for safety fuel. Likewise, it has been foundentirely feasible, for the purposes of the present invention, to retain as a bottoms, in the final fractionating tower hydrocarbons having aboiling point above the C14-C16 fractions. 4These heavy fractions may be returned to the alkylation reactor. Whilethe final products produced by the process of 'the present invention do not, in most-cases, attain an octanenumber of 100, nevertheless they form an extremely desirablefbase stock for the preparation of safety fuels. Usually @they have an octane. number clear of somewhere in the neighborhoodv of to 94. It is, therefore, a relatively simple matter to raise that octane number by the use of lead tetraethyl, for example, .to the re! quired aviation standard.

Theinvention may be illustrated by one speciflc embodiment of the reaction in which an isoparaln, such as isobutane, is caused to reactV with olens, such as C4.o1ens and particularly isobutylene. The ultimate objective of the invention is the production of hydrocarbons boiling in the range of about 300'to about 500 F. and having the required flash point. Normally, however, the products of this reaction boil over the whole gasoline rangeand include hydrocarbons ranging from lsopentane through C12 and heavier hydrocarbons. In accordance with the present invention,alkylate d hydrocarbons produced in the `reaction and boiling above about 500 F. may

be separated from the nal productand recycled to the original reaction zone. By employing this procedure, the percentage of these higher hydrocarbons ultimately produced is reduced considerably more than would normally be the case, but

there is a resulting increase' in the fraction boiling below these heavier recycled fractions. However, the production of the lighter ends. such as those hydrocarbons boiling below 300 F., may also be suppressed by separating from the final product these lighter fractions and returning them in substantial amounts to the original reaction zone. The return of both the heavier and the lighter undesired fractions of the nal product to 'the reaction zone results in a material increase in the amount of the desired fractions, that is. those fractions, say from Cru to C14 or even as high as C16.

It may be desirable, at times, to produce a motor fuel having a slightly lower flash point, in

which case only Cs to C7 fractions, and possibly a Ca fraction as wellY are recycled to the original reaction zone. If a final product is desired having an end point of about 275-300 F., then it is desirable torecycle'to the original reaction zone hydrocarbon fractions from the product composed of C9 and higher hydrocarbons. For such a fuel, a suitable procedure is to add to the initial material being alkylated both Cm and heavier hydrocarbons and C to C1 fractions so as to force the reaction to as great an extent as possible toward the production of Ca hydrocarbons. Such a procedure normally produces high octane number gasoline which would be considerably lighter in character than the average safety fuel.

Another specific embodiment of this reaction is found in reacting an isoparailin, such as isobutane, with oleflns, such as C4 oleflns, and particularly isobutylene. The principal objective of this reaction is the production of Cs hydrocarbons of the branch type. Normally, however, the products of this reaction boil over the whole gasoline range and include hydrocarbons ranging from isopentane through Cia hydrocarbons, or higher. If, in accordance with the present invention, C9 and higher hydrocarbons of the type ordinarily produced by this reaction are added to the feed stock, the percentage of Cs and higher hydrocarbons in the product is much lower than would normally be the case, with a resulting increase in the Cs fractions. By the same token, the production of C5 and C1 hydrocarbons can be suppressed by addition of these hydrocarbons. 'I'he preferred procedure, according to the present invention, is to add to the initial material both C9 and heavier, and C5 to C1 fractions so as to force the reaction to as great an extent as possible, toward the production of Cs hydrocar- ,former case the nature of the product is influenced only by change in the ratio of tertiary hydrocarbons to olefin in the fresh feed. lin the latter case the recycle stock contains all of the products normally produced and naturally results in the formation of more of the same products. In other words, it is to be understood that according to the present invention, the material recycled, in addition to unconverted fresh feed, is a portion "of the normal nal product the formation of which it is desired to suppress.

'I'he present invention is applicable to all reactions between olefins and other hydrocarbons regardless of the catalyst or activating agent which may be employed, or the presence or absence of such an agent. It has been found that the desired eect of the selective recycle operation is realized in the reaction between olefins and tertiary hydrocarbons whether the catalyst is concentrated sulfuric acid, vconcentrated sul'- furic acid plus an oxide of a fifth group element, such as phosphorus pentoxide, a metal halide, such as boron vchloride oraluminum chloride, or aluminum chloride alone or in conjunction with an alkyl halide; acidtreated clays, phosphoric acid, etc. 'Ihe desired effect is realized in reactions such as that between lisobutane and ethylene, whether the olefin is employed in its monomeric or polymeric form.

The conditions of operation of the 'reaction to which the present invention is applicable are well known and need not be dealt with in great detail here. In general, it may be stated that when sulfuric acid is employed as a catalyst it should be of a strength of at least and preferably between about and 100%. The operating temperature can vary over a fairly wide range beginning at about 20 F. and extending to about F. With other catalysts this temperature may be as high as 500 lF. Temperatures lower than 20 F. can be used with sulfuric acid but slightly higher temperatures are preferred. The operation may be conducted on a batch basis or on a continuous basis. In the former type of operation, in the case of the rey action between isobutane and isobutylene, the use of molecular proportions of the former to the latter as high as 4:1 have been suggested. In the continuous operation of this process, it has been found that this ratio of 4:1 may be used in the fresh feed stock but that the ratio of isobutane: olelln in the reaction mass at the point of introduction of the feed stock should be at least 30:1. Likewise, it has been established that certain recycle ratios should be observed for the procurement of the best results, and more especially that certain minimum ratios of acid to oleflns at thepoint of introduction into the reaction mass of the latter should be maintained.

Furthermore, it is contemplated to carry out the process either under atmospheric or superatmospherlc pressure. In carrying out thereaction at superatmospheric pressures, pressures may range from a few pounds over atmospheric up to and including 3000 1bs./sq. in., but it is generally preferable to operate between about 40 and about 200 lbs/sq. in., gauge. The desire to adequately mix the reactants plus the obvious advantages of operating a continuous process make it attractiveto use pressure sufficient to maintain the reactants in the liquid phase. In the case of batch operation, vigorous mechanical stirring is adequate to insure excellent yields of the nal product. However, in a continuous system, the maintenance of the reactants in the liquid phase is quite desirable, since the reactants may then be readily dispersed into the reactor by means of dispersion plates, jets of restricted internal diameter, porous thimbles, turbo-mixers, centrifugal mixing pumps, etc.

Iacetate A predetermined minimum amount oflow boiling reaction products and, if desired,A a predetermined amount of high boiling reaction products are maintained within the reaction zone.

The amount o1' these added reactionproducts and paranins reacted. Such variations will also be affected by the various operating conditions, such as pressure, temperature, throughput, nature of the catalyst, etc., each o'f which should, of necessity, be interdependently correlated with the others for best operating conditions so that as a practical matter it is not possible to accurately state the specific quantities of any given light and/or heavy condensed product which should be present in order to meet all conditions of operation.

It .has been found, however, that in a continuous process, the continuous recycle of undesired reaction products to the alkylation chamber eventually builds up the equilibrium concentration of the undesired reaction products so that as a practical matter, the determination of the exact amount of recycle feed to the reaction chamber is of little moment. If desired, it is possible to determine this concentration of undesired 'products to be present by laboratory tests, either by a determination of the percentage of the reactor charge composed of products found in previous reactions (in cases where the reaction and recycle has been running sufliciently long` to have determined that no greater quantity of undesired products are being discharged from the reactor than are being introduced into the same) or by progressively increasing the quantity of lighter reaction products charged to the reactor until a point is rea'ched'at which smaller quantities of lighter reaction products are being evolved from the reactor than are being introduced into it.

`Having thus described the general nature and the objects of the invention, a more detailed description of the invention will be made'by reference to the accompanying drawing which is a diagrammatic representation of one form of apparatus suitable for carrying out the process and securing the resultscontemplat'ed by the invention.

For illustrative purposes only, there is shown in the accompanying drawing a diagrammatic illustration representing a process adapted to alkylate paraillnic `gases in the liquid phase `by means of olens in the liquid phase in the presence of a liquid catalyst such as an inorganic l.

mineral acid. Itis to be understood,l however, that theprocess may be readily adapted to use a solid alkylatlon catalyst in )place of thevliquid catalysts and that the process, in its broader aspects, is not restricted to any particular method of alkylation or alkylation catalyst, but contemplates a processapplicable to any catalytic alkylation process.` The specificv embodiment of the inventiondescribd Abelow in connection with the description of the drawing is intended to be purely illustrative of theprinciples of the invention and in no sense is it toy be considered as limiting of the invention involved, I

A suitable mono-olefin-parailin mixture is compressed and fed into line 2 through open valves 3 and 4 `so`that the liquid feed stock is dispersed into the alkylation reactor 5 by any `suitable vdispersion -device 6 such as a porous thimble, a jet, perforated disc,'turbo mixer or the like, where the dispersed feed is contacted with a liquid cata- Iif) lyst, for example, concentrated sulfuric acid, which has been introduced through valve 24 into pipe 23 and into reactor 5 through valve 39. The liquid acid catalyst may be also compressed and introduced through line 59 through valve 60 into feed line 2 where it undergoes a partial mixing withthe feed stock prior to the passage through the dispersion device 6 into reactor 5.

- Reactor 5 is equipped with temperature control coils 'I by means of which it is possible to either heat the reactor, as has been found to be desirable Where certain catalysts are employed, or to cool the reactor by circulating ice water or cooled brine through the coils 1 in cases where itis desirable to maintain a fairly low temperature in the reactor. This latter temperature control has been found to be desirable when using concentrated sulfuric acid as the catalyst.

It has also been found desirable to recycle the olen-parailin-sulfuric acid mixture leaving reactor 5 through line B back to reactor 5. `Fairly long periods of reaction under rather. mild reaction conditions have proved to be more desirable than short reaction periods under more drastic reaction conditions. Accordingly, thepartially reacted mixture above mentionedis passed into line 9 through valve II) (valve I3 being closed) into heat treater 33, which may be either a heating or cooling unit depending upon the type of catalyst used. In the case of a'sulfuric acid catalyst, the effluent from reactor 5 is cooled in unit 33 and lthen passed through valve 38 into line 31. The cooled hydrocarbon-acid partially reacted mixture is then reintroduced into the reactor 5 in one of two methods. This mixture may be reintroduced into the reactorV by closing valve 64, opening valve 63 and allowing the mixture to pass through pipe 62 into -feed pipe 2 thereby permitting the mixture to be redispersed through mixing and dispersion device 6 into reactor 5, or valve 63 may be closed and valves 39 and B4 opened, thereby permitting the mixture to be conducted into the reactor 5 through pipes 23 and 31.

After :the mixture has been subjected to suilicient reaction to form a'recoverable amount of product, valves IIJ and I3 are adjustedso that only part of the reaction mixture is recycled, and pipe Il conducts the remainder of the reaction mixture into cooler I2 and pipe I4 conducts the cooled reaction `mixture into acid separator I5 where the acid settles to the bottom of the separatorfand is drawn oi through valve Il into pipe I6. Valves I9 and 24 may be closed and the separated acidreturned to reactor 5 through line 23 and opened valve 39. The separated acid may also be commingled with the'feed stock and reintroduced into'reactor 5 through the dispersion and mixing device 6 by closing

valves

422, 24, 39, andopening valves I9 and 2|, the acid then flowing from line I6 into lines I8 and 20 into feed line 2. It is also advantageous at times to close valve 2l and openvalves 22 and 58. thereby permitting lthe separated acid to beA fed linto recycle lines 55 and 6I prior to its mixing with tne feed stock and being reintroduced into the reactorV 5. The contents of these recycle lines will be described in detail hereinafter. It is also l possible, by closing valves I9, 24 and 39 and open- 24 or SII. However, it is preferred to draw the spent acid from thersystem through valve 24.

In such a case, valves I1 and 24 are open While valves I9 and 39 remain closed.

The upper hydrocarbon layer in separator I is drawn off through pipe 25 and led through pressure reducing valve 26 and then immediately conducted vinto stabilizer 21 where any normally vgaseous hydrocarbons are flashed. To insure substantially complete removal of these hydrocarbons, stabilizer 21 may be equipped with Iheating coils 28 although this is not always necessary. The normally gaseous and lighter liquid hydrocarbons fiashed from stabilizer 21 are led through valve 30 into pipe 29. These may be either con- 'ducted from the system by closing valve 50 and butanelfeed, a Cs cut might be the only one withdrawn from a trap out tray in fractionator 40, or, .if desired, a Cs-Cs cut and a C10-C12 might both be withdrawn, in which case two trap out trays suitably spaced would be required. The desired .products are withdrawn through a line or lines 42 by opening a valve or valves 43. The fractionator may be provided with a reboiler or heating coil 44 to insure a sharper fractionation. Products lighter than those desired are removed from fractionator 40 through valve 46 and pipe 45 and products heavier than those desired are removed from fractionator 40 through valve 56 and line 55. Both of these undesired fractions may be removed from the system through valve 48 and pipe 41, valve 49 being closed, and through valve 69 and line 68, vvalve 61 being closed, respectively.

As was the case in connection with the lighter eilluent from stabilizer 21, these productsmay be recycled to the reactor 5 either in whole or in part. In recycling the lighter fractions from vessels 40. and 21,

valves

32 and 48 are closed and valves v3l), 46, 49,50 and 54 are opened. This allows any unreacted reactants from vessel 21 and -all fractions boiling below the boiling point of the fraction removed fromthe trap out trays of vessel 40 lto be returned through

pipes

29, 45 to compressor 5|, cooling or heating coil 52, the use of a cooling or heating medium being The undesired products of the reaction and the unreacted hydrocarbons which may be removed from the system through pipes 3|, 41 and 69 may be either used for some extraneous purpose or they may be piped directly to another similar unit and used therein. In other words, it is not intended that the scope of the present invention should be restricted to recycling of the undesired products of reaction to the same reactor in which they were formed. It may be found to be advantageous to pipe these products to an analogous or similar unit operated in series or parallel with the above described unit, in which case, the undesired products of oneunit are equally suitable for use in the reactor of a second, third, etc., unit operating upon the same or slightly different feed stock but, at any event, carrying out an a1- kylation 'reaction using substantially the same conditions of operation, catalyst. and substantially the same type of feed stock.

It will, of course, be readily understood .that the heavier products of the reaction are not necessarily completely recycled to the reaction zone, but part of these heavier products may be removed from the system and the remainder recycled to the reaction zone. It is at times'V desirable to maintain the temperature of' the stabilizer sufllciently high to distill DE all lighter fractions of products aswell as unreacted reactants which are not desired in the final product. These products and unreacted reactants together may then be returned to the alkylation zone. In such a case, the fractionating equipment is operated -to secure a separation of the desired fractions, for example, safety fuels, say up to 500 F. end point, and the remainder of the product is taken from the fractionating unit as bottoms and may be returned to the alkylation determined by the optimum temperature requirements for the particular catalyst being used., and

thence into feed pipe 2 bymeans of pipe 53.

The heavier products of the reaction are returned to reactor 5 by opening valves 56, 611., 58

and 4 and closing valves 69, 22 and 60. The

flow is then through pipes 55, 6I and 2. Compressor 51 serves to compress the recycled heavier products to the operating pressures of reactor 5. If desired, valve 58 may be closed and valves 2l and ,22 may be opened so that the recycled products of reaction are contacted with the fresh feed just prior to their introduction into the reactor 5, lines I8 and 29 being used for this purpose. It is therefore possible to mix the acid and then the heavier recycled fractions prior to the introduction of the reaction mixture into the reactor 5.

zone to suppress their further formation.

This specific embodiment of the process has been described as applied to the use of a liquid catalyst. In cases where the catalyst is solid, such as aluminum chloride, sodium aluminum halide complex, zinc chloride, etc., the alkylation reactor 5 may be packed with Silch a catalyst or the catalyst may be supported on a carrier such as pumice, celite, bauxite, acid activated clays, activated carbon, etc., or the catalyst, eitherv supported or unsupported', may be placed on a series of trays mounted within the reactor 5. In place of a' single reaction chamber, two or more chambers, arranged in series or parallel, may be used whereby the catalyst contained in one or more of the chambers may be on stream while theother chambers containing catalysts are undergoing regeneration, thus providing for a continuous process in cases where solid catalysts are used. When solid catalysts are used, the need for separator I5 and its return lines is obviated.

The invention is not limited to the use of reactants from` any particular source. Single parainic and olenic hydrocarbons may be employed. However, it is commercially more feasible .to use mixtures of hydrocarbons containing the requisite parains and olelns. The reacted mixture from catalytic and thermal polymerization units, including the gaseous constituents thereof, maybe directly introduced as reactants into the alkylation reactor 5. Gaseous mixtures evolved from catalytic and thermal cracking units may also be advantageously employed.

It is an essential requirement in the practice l of the specific embodiment of the present invention described with reference to the drawing that preferably boiling below the boiling point of the desired final product fraction, and that the feed stock contain at least one mono-olefin. Partially dehydrogenated eld butanes, refinery Cs-Cs and C4 cuts, paraiiinic 4mixtures containing isoparaflins and which have been enriched with mono-olefins from extraneous sources, etc., are suitable. The invention contemplates the reactions of isobutane,l pentanes, etc., with ethylene, propylene, normal or isobutylenes, normal and branched chain amylenes, their dimers, trimers, tetramers, etc., their codimers, otrimers, cotetramers, etc., their crossand inter-polymers, etc. Itis desirable to have in the vfresh feed between about 2 and about 12 mols of isoparamn present Iper mol of mono-olefin. Likewise, from 4 to 24 mols of isobutane should be contacted with each mol of diisobutylene, etc.

'Ihe invention is not limited to any particular catalyst. Any suitable catalyst known to promote alkylation may be employed. Halides of metals, such as iron, nickel, aluminum, zinc, etc., either alone or admixed with smallv amounts of a halide, such as hydrogen halide or its equivalent,

are known to be excellent alkylation catalysts.

Boron fluoride, sodium aluminum complex halides, concentrated inorganic mineral acids, such as sulfuric acid or oxides of elements of the v5th group of the periodic system when used in conjunction With concentrated sulfuric acid are also It has also quite desirable alkylation catalysts. been found advantageous to luse acid treated clays, such as Marsil clay, montmorillonite, bentonite, Floridin, Super Filtrol, etc., not only as suitable carriers for other catalysts but also as Example y1 A feed stock composed of 11.3% of isobutylene, .8% of normal butylene, 69.8% of isobutane and 12.1% of a C5-C7 fraction obtained from a similar experiment'conducted in the absence of said fraction fromthe feed was subjected with stirring in an autoclave at -55 lbs/sq. in. gauge pressure and at a temperature of 70 F. for 21/2 hours to reaction in the presence of 98% sulfuric acid in an amount equal to 93 grams of catalyst per 100 grams of feed. Analysis of the total product indicated a 99% reduction of the olen content of the feed.- The debutanized product which was obtained in a yield of about 148% based upon the olen content of the feed, was fully saturated since it exhibited no bromine number. The newly formed product comprised 13.4% of Cs-Cfl fraction, 36.1% of Ca fraction and 50.5% of C9 and heavier fraction. i

Example 2 A feed stock comprising 7.8% of isobutylene, 4% of normal butylene, 31.6% of isobutane, 41.5% of a C9 and heavier fraction obtained from a previous alkylation reaction and 18.7% of a Cs-Cv fraction obtained from a previous alkylation reaction Was reacted for 21/2 hours at 30 lbs/sq. in. gauge pressure and at a temperature of between about l and about 70 F. in the presence of 75 grams of 93% sulfuric acid per 100 grams of feed. The total product hada bromine number of less than 1, indicating a 97.7% reduction of the olefin content of the feed stock. The composition of the debutanized product was 24.9% of Crt-Cv,

A The high yield of 195% indicates that it is an` 19.6% of Ca and 55.5%. of Co and heavier. An analysis of the newly formed product in this re. action revealed no further formation of Ca-Cv fraction, 91% of Ca fraction and 9% of C and heavier fraction. Thisnewly formed product was obtained. in a 195% yield based upon the total butylene content ofthe feed stock.

In Example 1, the addition of C5Cv to the feed (equivalent to 12.1% of the total feed) resulted in the formation of no new Cs-Cv hydrocarbons. In fact, less Cs-C'z cut was found in the product than was present in the feed which indicates that some of those components were alkylated to produce heavier parailins. The results of Example 2 demonstrate the effect of recycling bqth heavy and light ends. Less Ca-C':

`was found in the product than was added to the feed and only a small increase in C9 and heavier fractions was noted. Approximately 91% of the newly formed product boiled in the Cs range.

extremely efficient reactionv and that this reaction is unquestionably made more efficient by the recycling of heavy and light ends.

The above examples are batch operations. but it is readily understood'that the novel recycle, feature of the present invention is adapted to the process carried out continuously with continuous recycle of heavier and/or lighter products which are undesired or with continuous removal only of the desired products from the 'reaction zone,-allowing the concentration of the heavier and lighter products to build up to an equilibrium within the said alkylation zone.

It will be noted that in the proceduredescribed with reference to the drawing, there is continuous recycle of the reaction mixture containing all components of the product as well as the return to the reaction mixture of selected fractions of the product. Such procedure is desirable in continuous operations where it is desired to maintain a high hydrocarbon content in the reaction mixture. practice of the present invention does not exclude the recycling of a large portion of all components of the reaction product, but is satisfied by such an addition of those selected fractions of the product, the formation of which it is desired to suppress, as will build up in the reaction mixture a higher ratio of undesired product to desired product than would normally obtain vunder the usual conditions of working.

The nature and objects of the present invention having been thus described and illustrated,

.. what is claimed as new and useful and desired to be secured by Letters Patent is:

We claim:

l. In a process which comprises reacting a mono-olefin and a paraflnic hydrocarbon containingv at least one tertiary carbon atom per molecule to produce alkylated hydrocarbons, the

`improvement which comprises introducing into as formed and separated from the desired nal product. l

It will be understood, therefore, that the 3. ln the process of catalytically alkylating isoparaillns with mono-olefins, the improvement which comprises fractionating the resultant reacted mixture to separate from the alkylate produced at least one fraction of a desired boiling range, a lower boiling fraction, and a higher boiling fraction, and returning to an alkylation zone substantially all of said latter fractions in substantially the amount and at substantially the same rate as that at which they are formed in the reaction.

4. A process as in claim 3 wherein the process is conducted continuously.

`5. A process for the production of normally liquid hydrocarbons boiling within the gasoline boiling range which comprises alkylating normally gaseous isoparaflins with monoolefins having a boiling point below that of the desired final product at temperatures between about 10i and about 100 F. in the presence of between about 90% and about 100% sulfuric acid and carrying out the reaction in the presence of a fraction of the final product boiling above the desired ultimate final product and in the presence of another fraction of said iinal product boiling below that of the ultimately desired final product.

6. A process for the production oi' safety fuels which comprises alkylating a .normally gaseous isoparaffin with a normally gaseous mono-olefin in the presence of concentrated sulfuric acid, fractionating the resultant reaction mixture into a fraction' composed predominantly of Cs to C1 hydrocarbons, another fraction composed of' predominantly Ca to C12 hydrocarbons and a third fraction composed predominantly of C13 and heavier hydrocarbons, and recycling the first and third l fractions to the alkylation zone.

predominantly of Cs to C9 hydrocarbons, another fraction composed predominantly of Cio through- Cm hydrocarbons and a third fraction composed predominantly of Cie and heavier hydrocarbons and recycling the first and third fractions to the alkylation zone in substantially the amount and at substantially the same rate as that at which they are formed in the reaction.

8. In a process for the production of saturated liquid hydrocarbons having a boiling range corresponding to that of gasoline wherein isoparafiins are alkylated with mono-olefins by passing a mixture of the reactants together with concentrated mineral acid catalyst into a reaction zoneunder suitable conditions of operation, and the products from said reaction zone are fractionated to separate a desired product of predetermined boiling range and wherein reaction products boiling above and below the desired range are normally formed in the process, the improvement which comprises introducing into the reaction zone a predetermined minimum quantity of said last named higher and lower boiling reaction products sumcient to substantially completely suppress the further formation of said products'during the reaction.

9. A process which comprises alkylating a renery C4 cut containing isobutane and at least one butene in the liquid phase in the presence of 93 to l 98% sulfuric acid, fractionating the resulting alkylate to separate the same into a desired motor fuel boiling range fraction and undesired higher and lower boiling fractions, and returning substantially all of the undesired fractions to the alkylation reactor in substantially the amount and at substantially the same rate as that at which they are formed in the reaction.

10. A process as in claim 9 wherein the process is carried out in a continuous manner and in which the recycle of the'undesired fraction is continuously carried out.

ELDON E. STAHLY. ERWIN M. HATTOX.