US2427954A - Copolymerization of butenes and propene - Google Patents

Description

Sept. 23, 1947. F. E. FREY coPoLYMERIzATIoN oF BUTENES AND PROPENE Filed Nov. 21, 1959 2 Sheets-Sheet 1 Sept. 23, 1947. F. E. FRI-:Y

COPOLYMERIZATION OF BUTENES AND PROPENE Filed Nov. 21, 1959 2 Sheets-Sheet 2 INVENTOR FREDERICK E. FREY BY um .www

AT I'ORNEYS vPatented Sept. 23, 1947 2.421.954 I coroLYMaarzA'rroN or' sumas AND PBPENE Frederick E. Frey, Bartlesville, Okla., assigner to Phillips Petroleum Company, a corporation oi" Delaware Application November 2l, 1939, Serial No. 305,549'- 6 Claims. (Cl. Zeil-683.15)

This invention relates to the manufacture of volatile hydrocarbon oils, and in particular to the manufacture oi.' hydrocarbons whose molecules are highly branched in structure and peculiarly suitable for motor fuel in internal combustion engineswhere aliphatic characteristics and high antiknock value are important. It relates more specifically to the production of valuable motor fuel from isobutane, or from a mixture of hydrocarbons containing isobutane as the essential constituent, and represents a continuation of the work disclosed in Patent No. 2,116,723, entitled "Process for manufacturing hydrocarbon oils, of which I am a coinventor.

Itis an object of this invention to produce normally liquid hydrocarbons from hydrocarbons having low molecular weights.

It is also an object of this invention to Droduce hydrocarbons in the motor fuel boiling range which have good antidetonating characteristics.

It is a further object of this invention to produce a paramnic motor fuel having good antidetonating characteristics from normally gaseous paraffin hydrocarbons.

An object of this invention is to produce highly branched, aliphatic hydrocarbons boiling in the motor fuel range from a mixture containing propene and at least one butene.

Further objects and advantages will become apparent as the following disclosure and discussion proceed.

It has been shown that, when used as fuel for internal-combustion engines, especially thpse of the spark-ignition type. various hydrocarbons have quite widelyl different combustion and deto nation characteristics. Thus, in general. olefin hydrocarbons are less likely to produce or cause detonation when used as a fuel than are the corresponding paraiiln hydrocarobns. Even among one given class of hydrocarbons. such as the Paramus for example, the various individual hydrocarbons dier widely among themselves as to their combustion characteristics. This is exemplifled by the detonation characteristics of normal heptane and of isooctane (2,2,4-trimethylpentane), the well known standards used for evaluating detonation; the first causing detonation to a considerable extent and having, by definition, a rating of zero octane number, and the latter causing little if any detonation, even in engines having quite high compression ratios, and having by definition a rating of 100 octane numbers. Even hydrocarbons belonging to the same class and having the same molecular 2 weights have widely `different detonation characteristics: as exemplied by various heptanes.

There isconsiderable advantage to be gained from using fuels wtih good antidetonating qualities, inasmuch as only fuels which can be so classified can be used in engines with high compression ratios. It is well known that it is possible to obtain a high thermal efficiency in such an engine, and it has been found that the potentia1`power to be obtained using an engine operating. in each case, at the highest permissible compression ratio, may be per cent greater with a given hydrocarbon with high antidetohating qualities as a fuel than when using an isomeric` hydrocarbon Iwith lower antide'tonating qualities. As an example, the maximum possible compression ratio of an engine using normal heptane as a fuel is about 3:1, while with its isomer. 2.2.3-trimethy1 butano, the maximum ratio is about 13:1. An engine with the latter compression ratio would actually not operate lf normal heptane were the fuel.

I have discovered that a valuable motor fuel, consisting essentially of highly branched aliphatic hydrocarbons, and having very good antidetonating characteristics..may be prepared from isobutane, or normal butane, or from mixtures of butanes and especially' those rich is isobutane in a new and novel processto lbe hereinafter set forth. This is accomplished by a novel combination of the dehydrogenation' of the hydroi or certain portions or fractions of them, can be used directlyy as motor fuel, and generally as premium motor fuel, especially when blended with straight run or natural gasolines, or the like.

tion step, which may be either thermal or catalytic or a combination thereof, produces considerable'amounts of free hydrogen, and generally an amount sumcient to hydrogenate all the unsaturated hydrocarbons in the motor fuel boiling range produced in the catalytic polymerization step. When my process is operated to produce saturated hydrocarbons in the motor fuel boiling range, it is possible to operate it so that the dehydrogenation step is combined with the hydrogenation step and produces the free hydrogen which is consumed in thisv step.

I may also operate my process on a charge stock containingpropene and butenes from an outside sourcesuch as cracking-still gases, vapor recovery gases from a reflnery wherein cracking and/or reforming operations are carried out, and the like. With such a charge stock, wherein the propene to butenes ratio, on a molecular basis, is preferably greater than 0.,5:1, the hydrocarbon mixture is passed to the polymerization step, with or without additional separation, but with the addition of re'cycle propene, the polymerization of the olens is carried out as has been discussed, butane is separated from the eiiluent of thepolymerization and is dehydro- Agenated, hydrogen-containing gases are separated and a. mixture containing catalytically polymerizable oleilns, such as propene and butenes, is passed to the catalytic-polymerization step.

In'the catalytic polymerization of propene and butenes, it is desired that optimum` amounts of hydrocarbons in the-motor fuel boiling` range be formed, the optimum amounts being determined with a consideration for antidetonating qualities and boiling range as wellas for per cent of yield based on the charge stoclr.y In many instances .there will be formed, by the polymerization, hydrocarbon polymers which have boiling points or ranges too high to be included as a part of the motor fuel product, depending somewhat on the specifications to Vwhich the motor fuel is made as well as upon the operating conditions of the poly-- mei-ization" step. l It is also a part of my invention to subject hydrocarbon polymers so produced and boiling above the desired motor fuel range to a depolymerization to produce hydrocarbons hav'- sides methane in an amount substantially equivaient to the propene, and unreacted isobutene. The eiliuent of this dehydrogenation is passed to separatingmeans, and a hydrocarbon fraction is readily separated which consists essentially of propene, isobutene, and isobutene, and this mixture is sent to the catalytic polymerization step. In such a case, I prefer to operate under conditions such that propene is only slowly polymerized with itself, whereby I have found that copolymerization between propene and isobutene takes place forming highly branched heptenes and decenes and the like, along with isohexenes and isooctenes. This is especially 'true of these polymerization conditions are established along with a relatively high ratio of propene to butene.

I establish and maintain such a ratio in the following manner. Whenrthe operation of such a process is started, the ratio oi propene to isobutene will be low, and I have found that appreciable amounts of the propene will pass through the polymerization step unreacted. I now separate this unreacted propene from the eilluent of the polymerization and return it -to the inlet. Thus, in the succeeding period o! operation, the ratio of propene to isobutene will be somewhat higher, and a little more of the propene will enter into the reaction. I `continue this procedure, until the ratio of propene to isobutene is sumclent to insure that the amount of propene 'which enters into the polymerization reaction is substantially the same as the amount of propene charged to this step, exclusive of the recycled propene, but at the same time, with an appreciable amount of unreactedpropene in the eilluent of this step, which is recycled to the charge to the polymerization. In operating such a process I prefer that substantially all the butenes charged to the polymerization step shall enter into polymerization reactions, so that although the eiiluent of the polymerization step will contain appreciable quantites of unreacted propene, it will contain little if any unreacted isobutene or other butenes Thus my process is most satisfactorily operated when thepolymerization *conditions of temperature and pressure are such that propene is only slowly polymerized with ltseli', and the reaction time is such that the eiiluent contains very little unreacted butenes.

With these limitations and novel features, this part of my invention readily distinguishes over conventional polymerization steps wherein the oleflns charged are incompletely polymerized, and

the unreacted portion is recycled to the process along with fresh charge stock. In such procy stantially the same identity as the original olens ing lower boiling points, some of which will be in t the motor fuel boiling range, and to incorporate 'these latter hydrocarbons as a part of the total product. Concomitantly there will also be produced gaseous olen hydrocarbons, which can-be incorporated iivith the charge stock to the poly` merization step,

In one -modification of operating my process, n

I prefer to use a charge stock consisting essentially of isobutane.

in a very satisfactory and economical manner, producing a maximum of olellns which can be With this modiilcation, I can employ thermal dehydrogenation as the nrst step I catalytically polymerized with little if any olef I iinio material-such as ethylene. These oleiins consist primarily of propene and isobutene with only minor amounts of other hydrocarbons, lle-Q charged t'o the process, and theserecycled oleiins are accompanied-by excessive amounts of inert material such as paraflln hydrocarbons, or elabo- .rate oleiln-paraftln separation steps must be incorporated in the process to get away from this objectionable material. In contrast, in the proc- 'ess of. my invention only a particular oleiin, propene, is recycled to the polymerization step. and `the butenes are substantially 4completely converted. Any small amounts of unreacted butenes are not recycled directly to the polymerization step,'b`ui. pass with butane to the dehydrogenation step.f The-propene may readily be separated lin a relatively pure state by fractlonal'distillal tion, both from the polymer product and from lunreacted butane, which in its .turn is readily separated from-other hydrocarbons and can be acumen recycled in a relatively pure state to theldehydrogenation step.

My invention will now be described in connection with Figures l and 2, which together form aA 'butane, enters the system through conduit i0,

and is compressed to a suitable pressure by pump il. In many cases where isobutane comes directly from a fractional distillation, or other separation step, it may be under a pressure sufficiently high so that the pump il will not be necessary, and it may. of course, be omitted in such cases. Since a high superatmospheric pressure tends to affect the subsequent dehydrogenation adversely, the pressure should generally be only suilicient to overcome the pressure drop through the apparatus up to the compressor ti, and to provide a slight superatmospheric pressure at the inlet to this compressor. Such a pressure will not need to be in excess of 200 lbs/sq. in., and will generally be considerably less than that.

The isobutane, at a desired pressure, then passes through conduit l2, conduit i3 supplied with valve It, to the transfer line heat exchanger It, where it passes in indirect, counter-current heat exchange relationship with the emuent of the dehydrogenation to be described. From the heat exchanger it the stream passes through conduit I6 supplied with valve il to conduit is, and on to the dehydrogenation step. With this arrangement, valve 2i in by-pass 22 is closed, but if desired all or any part of the stream may be diverted from the heat exchanger i through this by-pass byproper control of the valves it, Il,

and 2l. From conduit i8 the stream passes through coils 2t located in the furnace 2d. When the process is so operated that thermal dehydrogenation of the hydrocarbon stream is accomplished, these coils will be of such dimensions that the hydrocarbon stream is heated rapidly to a dehydrogenat-ion temperature of the order of 1000 to 1250 F. and held within this temperature range for a period such that from about l0 to 40 mol per cent of the emuent material consists of normally gaseous olefin hydrocarbons. With such a procedure, the emuent of the coils .til passes through conduit 25, controlled by valve 2t, heat exchanger id, conduit '21, cooler 2t and conduit s0 to the scrubber 3|.

When it is desired to carry out a catalytic dehydrogenation, this may be done by opening valve 32 in conduit 33 and valve tt in conduit tu, thus connecting the catalyst chambers it into the system, and closing valve 26. In the modification illustrated, the catalyst chambers t@ comprise relatively small tubes illled with a suitable dehydrogenation catalyst, and so located that large amounts of hot combustion gases pass over them. With this modiilcation of operation, the relative volume of the coils '28 are such that the hydrocarbon stream is rapidly heated to 'a desirable reaction temperature, such as between about 850 to 1150" F., and passes directly into contact with the dehydrogenation catalyst. As reaction prograsses, heat is absorbed, and this is made up by heat transfer from the combustion gases surrounding the catalyst tubes 3B. Although only one source of heat in the furnace 24 is shown, it will be understood that additional burners solely for supplying heat to the catalyst tubes, or

other means for supplying heat to the catalyst and'reactants at the desired temperature level. may be used. The dehydrogenation eiiiue'nt passes from the catalyst chambers 3B through conduit t! controlled by valve u, and through conduit 2B to heat exchanger I! and thence through the remainder of the apparatus as has been and will be described. f desired, preliminary thermal dehydrogenation may be obtained in coils 23, followed immediately by a catalytic dehydrogenation in the chambers 38. y

In the scrubber 3i any carbon and/or tar is separated from the stream and removed through conduit Il controlled by valve 30. This removal may be aided by the use of a heavy absorption oil or other means if desired, as will be evident to those skilled in the art, details pertinent to such a modification not being shown. 'I'he rest of the emuent stream, freed of such impurities, passes from scrubber 3| through conduit dil to compressor tl, wherein it is compressed to a pressure of the order of lb./sq. in. The compressed stream ses through conduit t2 to cooler and condenser t8 and through conduit td to separator tt.

Under the pressure developed by compressor iii and at the temperature affected by cooler and condenser tu, most of the hydrocarbons having four and more carbon atoms per molecule, along with an appreciable proportion of propene and lighter hydrocarbons, will be condensed, and will be present in separator t5 in the liquid phase. This liquid hydrocarbon mixture which contains hydrocarbons to be polymerized, passes from the separator t6 through conduit te, controlled by valve tl, to the polymerization-feed stripper or separator E0. The unliqueed material passes from scrubber tu through conduit ts controlled by valve tu.

The polymerization-feed stripper operates under a pressure slightly less than that existing in the separator tu. such as a pressure of about' 125 ib./sq. in., so that an intermediate pump is not necessary. The stripper or separator tu comprises essentially a fractionating column, heated at the bottom by conventional heating means, such as a steam coil ti. The top of the stripper is cooled by the expansion and vaporization of a liquid propene recycle stream, to be hereinafter descrid. A liquid hydrocarbon mixture comprising essentially propene, along with s'ome propane formed and accumulated in the system, passes from the propene accumulator B2, which is equipped with a vent pipe B3 controlled by a valve tt, passes through conduit 55 to pump tu, and then through conduit tl controlled by valve bt. As one method of operating, this propene stream may be introduced directly into the top of the separator 50 through an expander and spray nozzle t0.

At this point, a considerable amount ofthe stream is vaporized, producing a' large refrigeration eect, the vapors passing up from the body of the separator are cooled by direct heat exchange in an eillcient manner, and heavier constituents of these vapors are condensed to liquid. Uncondensed vapors, which comprise light hydrocarbons, a small amount of hydrogen which was dissolved in the stream passing through conduit t3, vaporized propene and propane, and only small amounts of butenes and butanes, passes from the stripper 50 through conduit BI controlled by valve 82, and is mixed with the vapors passing from separator 4B through conduit 48. Not all of the propane is'vaporized, but remains as a liquid and passes down the stripper along .brought to a polymerization temperature.

, 7 V with the liquid butenes andbutanes so that the liquid at the bottom of the stripper contains, besides butenes and heavier hydrocarbons, appreciable amounts-oi' the three-carbon hydrocarbons introduced through conduit 4I along with recycled threeggarbon hydrocarbons. In this man-- ner, after the process 'is in steady operation, it is possible that the relative amount of propene in the feed stock to the polymerization, to be described, will be appreciably higher than the relative amount of propone in thedehydrogenation eluent.

An alternative modification, not shown, by

' which this propene stream may be recycled and also used as a refrigerant, makes use of indirect heat exchange for cooling vapors from the top part of the polymerization-feed stripper. In this modification, the vapors from the top of the column are passed through a condenser and cooler in indirect .heat exchange relationship with the expanding and vaporizing propene stream.' The cooled, and partially condensed eiiiuent ispassed to a separator. From this separator a portion of the liquid is passed tothe top of the stripper as a liquid reflux, while the vapors from the separator` follow the same course as shown for the vaporspassing from` stripper 50 through conduit Il. The expanded and vaporized propene stream,

' now at a relatively low pressure, may be reintroduced to the system as recycle by passing it to the inlet oi' the scrubber 3|. This specific modification is disclosed and claimed in the application of Hays and Maher, Serial No. 336,250, flied May 20, 1940. This is now Patent 2,351,123, issued June 13, 1944. Other modifications by which such a. recycle propene stream may be used will `'now be and to pass another portion through valve II in conduit I6 to pumpll. From pump ll the lmixture passes through c'onduit l2 and valve Il to heat-exchanger means Il, wherein the temperature is suitably adjusted, as will loe/discussed. From heat exchanger Il the mixture passes through conduit l5 and valve 88 to manifold 80. It may at times be desirable for all or a portion of the hydrocarbon mixture not to pass through heat exchanger al, and this may be by-passed4 I one or more points to the reaction mixture in console source of hydrocarbons charged to my process.

The feed or charge stock for the polymerization step, which consists essentially of hydrocarbons having three and four carbon atoms per molecule comprising both olens and paramns, and which -is in the liquid phase, passes from stripper through conduit il. In one modification thisV stream passes-through conduit 07 and valve il to pump 10, valve in conduit Sbeing closed. A portion of the propone stream coming from accumulator 52 through conduit 51 may be introduced at this point,v being diverted from conduit $7 through conduit 1i controlled by valve 12. The liquid hydrocarbon mixture is compressed by pump 10 to-a pressure suitable for subsequent catalytic polymerization of the oleflns present therein, and the mi ure passes through conduit Il to heater 'Il rein the hydrocarbons are The mixture then 4passes through conduit 15 to the I polymerization chamber 11. The eiiluent of chamber 1l passes through conduit 'Il and valve 10 to a separating means such as the debutanizer Il.

. An alternative, and not completely equivalent but often more preferable method of operating the polymerization -step is to pass only a portion of tact with the polymerization catalyst, as bypasslng the mixture through one-or more of the conduits 9|, s2, n and s4 controlled by valves as, n,

.portion of the unheated material passing through conduit 81 may be added to the manifold 9| at some point further along its length such as between conduitst! and 93, orthe material may be separately mixed or blended by means of another manifold, not shown, with each of the individual streams flowing through these individual conduits, thus facilitating control'of the temperatures of these streams. In place of using one long catalyst chamber, and adding these streams at various points throughout the length of this chamber, a number of smaller chambers may be used in series with the addition of a portion of the charge before each of the smaller chambers.

The introduction of a portion of the reactants at a plurality of points to the reaction mixture as it passes through a reaction zone. or at a plurality of points throughout the length of a reaction zone, has a number of advantages. The olens to lbe polymerized are roughly divisible into two classes, a highly reactive class which includes isobutene, and a less reactive class which includes propeneA and any normal butenes and the like. I have found that when the reaction con- ,ditions are such thatthe less reactive oleflns, considered byv themselves, are only slightly or slowly polymerized, a considerable extent of copolymerization takes pla'ce when more reactive oleilns are also present in the mixture, with the formation of copolymers, or hybrid polymers. This copolymerization is especially favored if .the relative amount of the more reactive .olenns, such as isobutene, islow, as has been. previously discussed herein. 'I'he polymerization reaction is quite exothermic. so that thel temperature of the reacting mixture, and the reactivity of the oleflns to be polymerized, rises as -the 4stream passes through the reaction zone. The arrangement of' apparatus just described permits additional hydrocarbon material to be added to the reaction mixture, and at a temperature lower. than that existing in the mixture at the point of the addition, so that the resultant mixture will be at a desirable reaction temperature. Such `a procedure is described more fully in my copending application SerialNo. 294,377, filed September li,

1939, now Patent 2,377,411, issued June 5,1943.

With any manner of adding initial reactants to the polymerization chamber. a further` modification of operationmay be practiced by passing a portion of the eiliuent of the polymerization directly back to the inletof the polymerization chamber. i, In the apparatus shown, this can be Lt-annees..." I

- The heavier means or pump il! to conduit ll. This modihcation is also more fully discussed in my;

oopending vapplication Serial Nassim?. In the -separating means. or debutanizer,

ediuent o! the polymerization isseparated into' two'iractions. one consisting essentially of hydrocai-bons having iour and fewer carbon atoms per molecule, and the other fraotionconsisting vesse'ntially of hydrocarbons having more than iour carbon atoms per moiecule. vThis separationis eilected and aided by bubble trays, or the like, not shown. heating means for the kettle reprethe top represented by cooling coil |04. `.The lighter fraction passes from the top ot the debutaniaer 00 in a 'vapor state through conduit |00 controlled by a lvalve |00. cooler |01, and conduit |00 to the separating means.` or depropanizer, III, the streambeing compressed to a suitable pressure by a pump |00. located' in conduit |00 This hydrocarbon mixture will consist essentially of unrescted butanes. principally isobutane, possibly along with small amounts of butenes, and oi a considerable proportion oi propene along with some propane. In separating means ||0 a separation is made between the butanes and the lighterhydrocarbons. This is aided by bubble trays. not shown. heating means and cooling means ior the top represented by -coolingcoil H0. The butano fraction, comprising essentially isobutane, passes from the separating means l l0 through conduit ||0, controlled by a valve H0, and is passed to conduit |2 where it is mixed with fresh isobutane being charged to the dehydrogenation. A fraction containing propene and the like leaves the'separating means ||0 as a vapor through conduit H0. controlled by a valve H0. and passes through cooler and condenslng means and conduit |'i0 to the accumulator 02. Light or otherwise undesirable hydrocarbons may. from time to time be vented from the accumulator 02 through vent 03 controlled by a valve 00.

The hydrocarbon. fraction containing oleiln polymers passes from separating means 00 through conduit and may be discharged from the system as desired, by opening valve |2 i. However, it will generally be treated further in the apparatus shown, by passing it from conduit |20 through conduit |22 controlled by a valve |20 to separating means |20, valve |2| being closed. In separating means |20. which may consist of a f conventional fractionating column, a vseparation is made between lighter fractions oi' the polymer in the motor fuel boiling range, and heavier, higher boiling, hydrocarbons. This separation is aided by bubble trays. not shown, heating means for the kettlerepresented by heating coil |20, and cooling means for the top represented by cooling coil |21. The separation may also be aided by a reduced pressure on the hydrocarbons as may be effected by low pressure distillation or by steam sented by heating coil |00. and' cooling means for Y ofthe motor fuel boilingvr-ange., depending somewhat on the end-point oi the vtraction-taken overhead through conduit "Land polymers boiling. labove the rnotovr-iuel range. .passfi'rom separating means |00 through conduit |00, controlled by a valve |00, to an accumulator ill. and may bewithdrawn )therefrom asy desired through conduit |00 controlled. by a valve Mi. .These heavier pcly-` i mers may be depolymerised bypassing them .at an elevated temperature and a relatively low pressure over a suitableoatalyst which in certain cases,` may be substantially the same as the-polymerization catalystused to polymerise the gaseousolenns. This depolymerization operation may be carried out by passing the lheavy polymer [from accumulator |01 through conduit |00. con-v duit illicontrolled by a valve |40. valve ill being closed, to a pump I and thence through conduit |00 tohe'ater |40, whereinthey are heated .to a temperature ci the order oi about 500 to 900A F.. and then through conduit |01 .to the chamber |00. A suitabledepolymerization catalyst. not

shown. is used in this chamber, and efiects a depolymerization of the heavy polymer. forming hydrocarbons `in. the motor fuel boiling range along with lighter olefin hydrocarbons with little formation'oi extremely heavy hydrocarbons or l'for the kettle represented by heating coil Hi,

of very light, saturated hydrocarbons such as methane and ethane. The efduent of .this depolymerization is d from the chamber |00 through conduit |00 controlled by a valve I0| to a separating means |02. Since the depolymerization operates under a low pressure, the pressure for separation may preferably be higher. The pressure on the material passing through conduit |00 may be readily raised by obvious means. not shown in detail. Separating means |02 may comprise a fractionator such as is known in the art., and if the sensible heat of the hydrocarbon stream passing through conduit |00 is not sumcient to heat the kettle product, additional heat may be added by suitable means such as the heating coil |00. Cooling at the top may be eected by an arrangement represented by cooling coil |00. A hydrocarbon fraction comprising hydrocarbons in the motor fuel boiling range passes from separating means |00 through a conduit |00 controlled by a valve |00, and through valve |01 to conduit 10 and are introduced into separating means 00.

Heavier hydrocarbons in the boiling range o! those return all 0r. a considerable amount of this fracdistillation, either oi which may be effected with |20,` controlled by valve |20, through cooler and condenser |00 and conduit lli to the accumulator |02, from which it may be removed, as desired, through conduit |00 controlled by a valve |00.

tion to the depolymerization, and this may be accomplished by opening valve |00 in conduit |0| and passing the stream to conduit |42, completely or` partially closing valve |00. than this recycle stream may be discharged from the process through conduit |02 controlled by valve |03, or if desiredall or any part oi. this material may be recycled to the depolymerization step through conduit |04 controlled by a valve |00, passing to conduit |0| and ilnally to conduit |02, with proper control oi' valve |03. A hydrocarbon fraction too light to be included in motor fuel, may be discharged from the process through conduit |00 controlled by a valve |01. These hydrocarbons are generally suitable for polymerizahydrocarbontraction whign'w.

Material heavier' polymerization-feed stripper 58 through conduit 85. In some cases, the life oi the depolymerization catalyst may be increased byeliminating from the. charge stock the heaviest part oi' the heavier polymers produced in the polymerization step. This may beaccomplished by conventional iractionating means, not shown, which can be inserted in the first part of conduitl I, as will beunderstood by those skilled in the art. g

The ,hydrocarbons in the :motor fuel `hamm;

rangeproduced by my polynterizationprocess arel quite valuable as motor fuel, inasmuch as the` individual hydrocarbons are highly branched -in structure.

This, land their oleiinic properties, make the blending octane numbers of these hydrocarbons 'quite high. However, for some uses. such as ior aviation motor fuel, it is much better to have a paramnic motor fuel with a high octane number'than to-have a motor fuel which contains substantial amounts of oleiin hydrocarbons. Since the oleiin products of my process are highly branched, when they are sublected to nondestructive hydrogenation there results a paraihnic product having a high octane number, generally having a'rating as determined by the ASTM method D347-34T of about 8 5 to 90 or better, and with a very good response to the addition of small amounts of tetraethyl lead or other detonation inhibitor. Inasmuch as considerable amounts of hydrogen are produced in the dehydrogenation of the gaseous paraiiin charged to the process even when thermal dehydrogenation is used, a hydrogenation step can also be incorporated and cooperatively combined with my polymerization process.

The material passing in the gas phase from separator 45 through conduit 48 controlled by valve 48 contains hydrogen produced in the dehydrogenation step, along with some methane and other hydrocarbons, some of which will be oletlns having three and four carbon atoms per molecule, and which are desired as charge stock l moved from separator |84 through conduit |88` controlled by a valve |88 and passes to conduit 44 to be introduced to the separator 45.- Constituents in the vapor phase pass from separator |84 through conduit |81 controlled by a valve |88 to a compressor |88, wherein they are compressed to a still higher pressure, and passed through conduit |88, cooler and condenser |8| and conduit |82 to separator |88; Again higher boiling constituents are liqueiled, and this liquid fraction is i passedfrom separator |88 through conduit |84 controlled by a valve |85 to the conduit v|88. and

lis reintroduced into separator |84. Thematerial winch remains in the gaseous phase, and which now comprises an appreciable concentration oi hydrogen and methane with only small amounts ofheavier hydrocarbons, but which however, still contain some propene and butenes, passes from separator is: through conduit m controlled by a valve |81 to the bottom of the absorber 288.

f In theabsorber 288 the material which has passed trom the separatorV |88 in the gaseous state, which is now at an elevated pressure oi the order of about 750 |b./sq. in., is contacted with lean absorption oil introduced at the top of the. absorber through conduit 2|8. oil is introduced in such amounts that essentially allthe hydrocarbons having three and more carbon atoms per molecule which are present in the material passing through conduit |88, along with much oi' the lighter hydrocarbons, are absorbed,

' and the residue gas containing principally hydrogen and methane passes from the absorber 288 through conduit 28|. The rich absorption oil passes from the absorber 288 through conduit 282 controlled by a valve 288, to heater 284 and thence through conduit 285 to the top of the stripper 288. which it enters at a low pressure of the order oi about 25 to 50 lb./sq. in. or less, and at a temperature of about 200 F. A portion oi the residue gas from conduit 28| is passed through conduit 281 controlled by a valve 288 to the bottom oi the stripper 288, and passes upward through .the stripper counter current to the descending oil. The rich absorption oil entering through conduit 285 has essentialhr allA the light hydrocarbons removed from it, and the resultant gaseous mixture passes from the top oi the stripper through conduit 288, controlled by a valve 2|8, to conduit |18 and on to conduit 88, whereby valuable propene and butenes removed by the absorption oil in the absorber 288 are returned to the system. The resultant lean absorption oil leaves the stripper through conduit 2li, controlled by a valve 2|2,

through cooler 2 |8 and conduit 2 |4 to an accumulator 2|8. From the accumulator the absorption oil is removed through conduit2i8, controlled by a valve 2|1 and is pumped by pump 2|8 through conduit 2i8 and valve 228 to the top of absorber 288.

The gas passing through conduit 28| has a high content of free hydrogen, and may be partially or completely used in the hydrogenation to be described by passing the amount desired from conduit 28| to conduit 28|| through fby-pass 284 controlled by a valve 285. Howeven'the material other than free hydrogen, is substantially only hydrocarbon material, and this may be removed or greatly decreased in amount, by a,conventlonal oil absorption system, it such is desired.

A portion of the lean absorption oil is passed from conduit 2|8 through conduit 22| controlled by a valve 222 to the -top of an absorber 228. Part or all of the gas remaining in conduit 28| is passed through valve 225 to the bottom of the absorber 228 Any undesired portion of this gas may, be removed from the system through conduit 228 controlled by a valve 221, and at times a part may be directly passed through conduit 284 and valve 285. In the absorber 228 most of the hydrocarbon material is removed from the gas, leaving substantially pure hydrogen. This hydrogen passes from the absorber 228 through conduit 288 controlled by a valve 28|, and may be passed to the hydrogenation step to be described, or may be removed from the system for other uses as may be desired through conduit 282 controlled by a valve 288. The rich absorption oil leaves the bottom of this second absorber through conduit 288 controlled by a valve 281, and is passed to the top of the stripper 288, wherein light hydrocarbons it has absorbed in absorber 228 are removed and pass-'from the system, together with any stripping gas used, through conduit 248 controlled by a valve 24|.

This absorption e 13" As stripping gas some of the excess hydrogen and gases from the separator passing through conduit 215 may be used, or gases from any other source. not shown, may be used. The lean oil passes from the stripper 288 through conduit 242, controlled by a valve 248, to conduit 2li and accumulator 2|5.

When it is desired to saturate the polymers in .the motor fuel boiling range produced in the polymerization step and available in the accumulator |82, this may be done by passing this material through conduit |88 and through conduit 255, controlled by a valve to a pump 252, and then through conduit 258. Hydrogen passing through conduit 280 is compressed by pump or compressor 254 and passes through conduit 255 to be mixed with the material passing through conduit 258, If desired, saturated hydrocarbons may be added as a diluent, these passing from conduit 21| through conduit 255, controlled by a valve 251, to pump 258, and then through conduit 258 to conduit 210. The combined mixture then passes through heater 250 and conduit 25| to the hydrogenation chamber 252. The mixture is heated to a suitable initial reaction temperature in heater 250 and is passed over a body of a hydrogenation catalyst, not shown, in the hydrogenation chamber 252. Hydrogen is added to the unsaturated linkages of the unsaturated hydrocarbons, and the eiliuent, comprising essentially excess hydrogen and paraffin hydrocarbons having the same general boiling range as the unsaturated hydrocarbons charged to the process, passes from the hydrogenation chamber through conduit 258, controlled by a valve 254, to a high pressure separator 255. In this high pressure separator a separation is made between a liquid phase and a gas phase which comprises substantially excess hydrogen plus light gases originally accompanying the hydrogen. This separation is aided by cooling means in the top of the separator, such as the cooling coll 255. This excess hydrogen ls passed from .the top of the separator through conduit 251 and is returned to the hydrogenation through valve 258, compressor 255 and conduit 210 to conduit 255. The material in the liquid state passes from the separator 255 through conduit 21|, controlled by valve 212, to the low pressure separator .213, wherein hydrogen dissolved at the high pressure in the liquid material flowing through conduit 21|, along with any light hydrocarbons, is released and separated. This separation is aided by cooling means in the top of the` separator, such as the cooling coil 214, which condenses hydrocarbons in the motor fuel boiling range which have vaporized. Released hydrogen, along with any light hydrocarbons, passes from the low pressure separator 218 through conduit 215 controlled by a valve 215, and may be passed through valve 215' to the bottom of stripper 288 to be used as a stripping gas, as previously mentioned, and is finally discharged from the system. If desired, al1 or a part of this stream may be returned to the system for recovery of the hydrogen, by passing it through by-pass conduit 211 and valve 218 to conduit |18 and eventually to conduit 80. Any part ot the hydrogen separated in the high pressure separator 255 which is not recirculated may be passed from conduit 251 to conduit 215 through conduit 284 controlled by valve 285.

A hydrocarbon mixture, which comprises cssentially parailin hydrocarbons in the motor fuel range which have highly branched structures, is recovered as a desired product from the low 14 pressure separator through conduit 255, controlled by a valve 28 The dehydrogenation step o! my process may be either thermal or catalytic, or a combination .of both, but in any case it should be at as low a pressure as is practicable. While a subatmospheric pressure may at times be most desirable, it is generally more practical tooperate this step at a slight superatmospheric pressure, which I prefer not to have exceed about 200 lb./sq. in., and which preferably should only be sumciently high to insure adequate ow through the apparatus. With an active dehydrogenation catalyst, the temperature may be as low as 750 F., but Iprefer to .perform catalytic dehydrogenation at between 850 and 1150 F. It the dehydrogenation is to be thermal, somewhat higher temperatures, up to about 1300 F. should be used, with a preferred range for thermal dehydrogenation lying between 1000 and 1250 F. In any case, the reaction time should be such that between about 10 and 40 mol per cent of the eiiluent consists of catalytically polymerizable gaseous oleiins, preferably about 20 mol per cent, and such that lsecondary reactions of the dehydrogenation products do not take place to any appreciable extent. When catalysts are used, I prefer that they should be of the chromium oxide type, as disclosed in U. S. Patents 1,905,383 or 2,098,959, or in the copending application of Matuszak and Morey filed November 9, 193'1, Serial No. 173,708,

vnow Patent 2,294,414, issued September 1, 1942,

or of the bauxite type such as disclosed in Schulze 2,167,602.

As stated more explicitly hereinbefore, the conditions for polymerization should be such that propene is only slowly polymerized with itself, and the eiiluent should contain very little unreacted butenes. Specically, the pressure on this step should be not less than about 200 lb,./sq. in. and preferably is somewhat higher. such as in the range of 600 to 1800 lb./sq. in., and may be as .high as 3000 lb./sq. in. or more. The,` polymerization temperature should generally be in excess of F., and I prefer to operate in the range of to 400 F., although at times, andl especially near the end of a run with a given batch of catalyst, when it hasbecome somewhat deactivated, I may operate my process at polymerization temperatures as high as about 600 F. 'I'he iiow rate will generally be between about 5 and 20 volumes of liquid hydrocarbon charged per hour per volume oi catalyst. that is. the actual volume of the catalyst particles plus the voids inherently present.

The process is not especially dependent on the use of any particular polymerization catalyst, except that the catalyst used preferably should be of a type which has a minimum tendency to promote, under the reaction conditions used, reactions other than the union of olefin hydrocarbons to form oleiin polymers, such as cyclization reactions, dehydrogenation reactions, and the like. I prefer to use a catalyst similar\to the silica-alumina catalyst hereinafter more completely described and discussed but other catalysts may also be used, such as the well known solid phosphoric acid catalysts. catalysts comprising metal phosphates, and the like. It is also not necessary to use a solid catalyst, and catalysts such as liquid sulfuric acid and the like may also be used. Such a liquid catalyst will necessitate certain additional lapparatus which has 'not been shown but which is well known to those` skilled in the art and which can be readily sub.

. tual .practice a number of chambers may be used, in series orin parallel, with other catalyst chambers containing fresh 'or reactivated bodies of catalyst, or bodies of catalyst undergoing reactivation or regeneration so that as the body of catalyst-being used becomes deactivated, the process may be continued with fresh catalyst without more than temporary interruption. This same comment, of course, applies to any dehydrogenation or dehydrogenation catalyst which may be used in the process.

The hydrogenation step should be carried crut catalytically, and any known catalyst which will etiect a non-destructive hydrogenation of unsaturated hydrocarbons may be used. I have been able to obtain very satisfactory hydrogenation of the oleflns produced in my process by passing them, in the presence of hydrogen, over a nickelcopper-alumina catalyst suchas has been dis; closed 4by Thomas G. Strickland in his copending application Serial No. 240,196, filed November 12, 1938, now Patent 2,242,627, issued May 20, 1941. In general,` the hydrogenation temperature will be between about 100 and 650 F., preferably between about 200 and 600F., and is carried out at a superatmospheric pressure which may be as high as 2000 lb./sq. in. or more, but which will generally be between aboutr 200 and 800 lb./sq. in. The hydrogenation may be carried out in a catalyst chamber which consists of a number of small, catalyst-filled tubes which are surrounded by a cooling medium such as is well known in the art. However, I, have been I have found that the silica-alumina catalyst. herein described, is a good depolymerization catalystas well as a polymerizationcatalyst, and I prefer to use it when the depolymerization step is a part of my process. Other catalysts which may also be used include bauxite, various vnatural aluminum silicates, activated alumina, and'the like. The pressure should be as low as possible, and while it may be subatmospheric, it will be preferable to use a slight superatmospheric pressure, such as 30 to 50 pounds/sq. in. gauge, and which should not be in excess of about 100 lb./sq.

- in. The temperature may be between 500 and able to effect the nondestructive hydrogenation of normally liquid unsaturated hydrocarbons by mixing with the unsaturated hydrocarbons from 1 to5 or more volumes of saturated hydrocarbons having the same boiling range, and passing the mixture, with an'excess of free hydrogen, at a hydrogenation temperature, over a body of a solid nickel-containing hydrogenation catalyst, and maintaining a pressure such that the major part of the hydrocarbon material charged to the process is in the liquid phase at the hydrogenation temperature which is maintained at the inlet to the catalytic hydrogenation chamber. As hy.. drogenation proceeds and the heat of reaction is liberated, a part of the hydrocarbon material is vaporized and this heat of reaction is taken up as latent heat of vaporization, without undue temperature rise of the reactants. Such a process is disclosed in detail in my copending application Serial No. 299,219, illed October 12, 1939, now U S. Patent 2,303,118, issued November 24, 1942.

VAnother liquid phase liydrogenation process for the non-destructive hydrogenation of unsaturated hydrocarbons in the motor fuel boiling range, which may be incorporated with my process, and in which liquid butane or the like is used as a material which vaporizes from the reacting mixture and absorbs heat of reaction, is disclosed in the copending application of Harold J. Hepp and Jean P. Jones, Serial No. 327,518, illed April 2, 1940, now Patent 2,332,572, issued October 26, 1943. Still another process is disclosed in my copending application Serial No. 240,195, filed November 12, 1938, now U. S. Patent 2,303,075, issued November 24, 1942.

While the depolymerization step may be carried out in the absence of a catalyst, I .prefer that it should be a catalytic depolymerization.

900 F., and will generally be in the upper part of the range such as between 700 and 850 F. The heating of the charge stock to the reaction temperature should be as rapid as possible, especially when the temperature at the inlet to the reaction chamber is in the upper part of the range given, so that uncatalyzed decomposition of the hydrocarbons will be at a minimum. 'Ihe reaction is quite endothermic, but although it may lbe desirable to operate so 'that the catalyst mass is in heat-exchange relationship with a heat-supplying medium, I have found that satisfactory results may be obtained by using a single body of catalyst and heating the charge stock to within the upper part of the range given. The reaction time will be roughly in an inverse relationship with the temperature, and at higher temperatures a reaction time somewhat shorter than that which will produce maximum depolymerization is preferred, in order not to decrease the activity of the catalyst too rapidly. I have obtained satisfactory results with a llow rate of the total charge, that is fresh charge plus recycled material, between 0.5 and 5 liquid volumes per volume of catalyst per hour.

As an example of the operation of one modiflcation of my process, a hydrocarbon mixture comprising essentially pure isobutane, as represented by the analysis given in column 1 of Table I, was mixed with Aabout 2.5 times as much recycled iscbutane, and was passed through the thermal dehydrogenation coil 23, vlay-passing the catalyst chambers 3B. A dehydrogenation temperature between 1150 and 1220 F. was maintained, a gauge pressure of about 25 1b./sq. in. being maintained at lthe exit of this dehydrogenation section. The eiiluent, which had the composition shown in column 3, was passed to separator, 45 and separated into liquid and vaporous portions, the liquid portion having the composition shown in column l. This mixture was passed to the polymerization-feed stripper 50, which was suitably heated at the bottom and was cooled at the top by the direct introduction of recycle liquidpropene from accumulator 52, which was partially vaporized at 60, and which had the composition shown in column 7.

A hydrocarbon mixture comprising propene and butenes, containing recycled propene from the unvaporized .portion of the material introduced at 60 and a portion of the vaporized propene which had been recovered in separator I5, and having the composition shown in column 5, was passed to the polymerization catalyst.

An olefin polymerization catalyst comprising alumina associated with silica, and which will be spoken of as a silica-alumina catalyst" was prepared by first forming a silica gel from a liquid sodium silicate of 41 B. gravity containing 8.9 per cent NaaO, 28.5 per cent S102, and 62.6 per cent H2O, and from commercial sulfuric acid of 66. B. gravity. The sodium silicate solution, or "water-glass was diluted by adding 1.5 volumes 17 of water and the acid was diluted with 'l volumes of'watex'.` Equal volumes of these two resulting asolutions were mixed by rapidly flowing the sov dlum silicte'solutlon into the acid solution withv thorough stirring. The mixture was then allowed to stand overnight, andy had set and stifiened to a iirm gel about 12 hours after mixing the solutions. 'This gel was broken up' by forcing it through a coarse screen of about one inch mesh, was washed for 16 hours, and was then partially dried in hotl air to a degree suncientto shrink the gel only to a point where it attained sunlcient rigidity to ring slightly when tumbled. It was again washed and then treated with boiling water containing in solution about 5.5 per cent of aluminum sulfate, the treatment continuing for about 2 hours. The gel was washed, partially dried and again treated with an aluminum sulfate solution. After this treatment, the treated gel was washed with water until the eiiluent Wash water was substantially free of sulfate, but care was taken to insure that the wash water was not alkaline. After this treatment the activated gel was thoroughly dried, and was then classified as to size. In this manner of preparation, a limi ited amount of alumina was thoroughly and intimately incorporated with silica, forming a silica-alumina catalyst which is quite eilicient in promoting the polymerization of normally gase- 'ous olen hydrocarbons to polymers in the motor-fuel boiling range.

The catalyst was classified as to size'in three different batches; (1) larger than 12 mesh, (2)

between 12 and 20 mesh, and (3) between 20 and 35 mesh, and was then placed in the chamber with the finest catalyst on the bottom, the intermediate in the middle, and the coarsest catalyst on top. It has been found that this procedure results in a decrease in the pressure drop which would occur if unclassified catalysts were used, and also results in a condition of greatest pressure drop near the bottom of the catalyst bed, which lessens the tendency of the mass of catalyst to become packed. Such an operation is disclosed by Karl H. Hachmuth in U. S. Patent 2,283,499, issued May 19, 1942.

After the catalyst chamber was filled, a stream of propane was passed through the chamber at about 250 F. which further dried the catalyst and displaced all the air. At the beginning'of a period of use of a fresh batch of catalyst, the hydrocarbon stream from the bottom of the polymerization-feed stripper 50 was heated to a, temperature of about 220 F., under a pressure of about 1500 lbs/sq. in. and passed over the silicaalumina catalyst at a rate of about volumes per hour per volume of catalyst, which was found to insure a minimum of unreacted butenes in the eiliuent. As the catalyst decreased' in activity,

the temperature of the hydrocarbon stream charged to this step of the process was raised,

providing thereby a constant amount of polymerization. This was continued until a finalv temperature of about 600 F, was reached, at which time the catalyst was judged to be inactive, and

the process was continued at a lower temperature using a fresh batch of catalyst. The eiliuent of the polymerization catalyst had the composition' shown in column 6. This eiliuent was passed to separating means, and there was separated a propene-recycle fraction, an isobutane fraction, and

a fractlon'comprising normally liquid-hydrocarbons in the motor fuel boiling range. When the polymerization temperature was in the range of about 570 F., the polymer and motor fuel frac- `tions had the compositions shown in Table II. It

will be seen that although this was not a partieularly favorable temperature, nevertheless a substantial portion oi' the polymer had been formed by the copolymerization of propene and lsobutene. The fraction in the motor fuel boiling range was passed over a nickel-containing hydrogenation catalyst at a pressure of about 700 1b./sq.l in., and a temperature of about 300 F.. in the presence of free hydrogen-containing gases produced by the dehydrogenation step and passing from absorber 223` through conduit 230, the composition being about as shown in column 8 of Table I. The hydrogenated motor fuel produced from polymer formed at about 300 F. had the characteristics shown in the last part of Table II. In addition to having a high'octane number, it was quite responsive to the addition of small amounts of tetraethyl-lead.

Tasas I Compositions in dehydrogenatimi--polymerizationJ process [Stream (mol per oent)] Feed to Component Fresh Recycle Dehydro- Pol mer- Feed Isoenation izaon,

butane Eiuent Feed Stripper Tsar.: I (Continued) Compositions in dehydrobenaton-polymeriza tion process [Stream (mol per eeuw] Component Pclymer- Pol mer- Hydrogen ization, izaion, rprl Hfrr Feed Eiliuentl y geatign 68.3 30.0 a .s SI5 56.3 0- 7 1. 2

l Liquid volume per cent.

TABLE II L Characteristics of products Total Motor Component Polymer Fuel Hydroaenated motor fuel Gravity '.A. P. I. at 60 F 65.9 Refractive index at 75 F-' 1 4025 Reid vapor pressure L 3.1 Octane number (AC-294) 89.0

As an example of the operation of the depolymerization step of my process, the total heavv polymer boiling above 333 F.. produced in a process as Just described and consisting of about per cent of the total polymer, was depolymerlzed over a 'granular silica-alumina catalyst prepared as hereinbei'ore described. The charge stock, with between 1 and 5 times an equivalent amount` of recycled heavy material, was passed at a gauge pressure of about 5 pounds per sq. in. over a silicaalumina catalyst at a temperature between 570 and 850 F.. and at a rate of about 1 liquid volume of ri'resh charge per volume of catalyst per hour. The yield was as given in Table In. The heaviest part of the heavy residue in the ei'iiuent was discarded, and the remainder of the heavy residue was recycled to the depolymerization. The gas consisted essentially of isobutene which could be sent back to the polymerization step, and the gasoline so produced, after hydrogenation, had an octane number of 80.8 (ASTM D 357-34T).

Numerous materials comprising compounds of aluminum and silicon, or mixtures of compounds of these elements such as mixtures of their oxides, with or without small amounts of other materials which may act as promoting agents. have `been proposed for use as catalysts in various processes for treating hydrocarbons. Among these com,

pounds are various natural and artificial aluminum silicates, some of which have been proposed 'for use in the polymerization of gaseous oleiins.

Synthetic aluminum silicates may be prepared by the interaction of aluminum chloride, or other aluminum salt, with sodium silicate, or water glass. While some of these synthetic aluminum silicates have good activity as polymerization catalysts, their physical form is poor, the silicate being aline powder dimcult to retainL against a fluid ilow, and many of them must be-briquetted or extruded into pellets before being usecL However, synthetic catalysts of the gel type, or dried-gel type, such as the silica-alumina cata` lyst specically described herein, `have excellent physical properties, being somewhat similar to ordinary sand in gross physical appearance, and their activity in the polymerization of olens is generally much better than that oi either natural or synthetic aluminum silicates. Although a silica-alumina catalyst may be made by other modifications than that specically given herein, the manner of preparation will generally comprise essentially the preparation of a highly hydrous gel, or standing jelly, oi' silica, such as is `well known in the ,art. washing this gel with water to remove a substantial amount of water soluble material, with or without partial drying but 20 without drying to a water content oi' less than vabout 40 orl 45% of water, and treating this gel with an aqueous solution known as an activating solution, containing an aluminum salt. such as aluminum chloride. sulfate or nitrate. In thistreatment it appears that the aluminum is Drei'- erentially adsorbed on. or otherwise associated with the silica. and during the treatment the aluminum content of the activating solution decreases markedly while the pH also decreases. Small amounts of other salts may be included in this activating solution, such as water-soluble salts of zinc. cadmium, beryllium, and the like, in which case the iinal silica-alumina catalyst will also contain small amounts oi these other metals, and it is assumed that these modiiications comprise the oxides of these `other metals, -in the same manner as the aluminum is assumed'to be present as alumina. Although it is not known for sure in just what manner the activation of the silica gel with the aluminum salt solution takes place. the catalyst appears to contain aluminum oxide. or alumina. associated with the silica, and for this reason it is referred to as a silica-alumina catalyst. Alter the activation treatment, the material is washed and dried, and may finally be dehydrated at an elevated temperature. A modification includes drying the treated material only partially, and then subjecting it again to the action of an activating solution, following this by further washing with water, and drying.

A silica-alumina catalyst prepared in this manner from a rm, hydrous silica gel. is substantially a dried gel, and has been found to be superior, both from a physical standpoint as well as from a standpoint of catalytic activity, to a material comprising silica and alumina prepared from a silica which is more or less oi' a loosely aggregated or chalky precipitate. This silicaalumina catalyst. while it may be nely ground and briquetted, or made into various large particles by extrusion, is quite readily used, and may be handled as particles of an ordinary and desired size, without such preparation merely by breaking up the larger particles of dried gel, and screening or sieving to a desired size.

During use, the silica-alumina catalyst gradually loses activity, but this may be restored in any one of a number of ways. The deactivation is accompanied by a deposition of carbonaceous material and this may be removed by burning it on in an atmosphere containing free oxygen.

. Preferably, this type of regeneration, or revivication, is carried out with a very low initial concentration or partial pressure of free oxygen, such as 0.1 atmosphere of pressure, and also with only small amounts of water vapor. As the revivication progresses, the oxygen partial pressure is increased, but it has been found to be preferable to maintain the partial pressure of the water vapor at a continuously low value.

teral with a strong caustic solution such as sodlum or potassium hydroxide, whereby a sodium silicate is formed which -may be used in the production of fresh catalyst.

While my invention has been more particularly described in connection with the dehydrogenation of isobutane, and with the subsequent treatment 21 oi the catalytically polymerizable oleilns thereby produced. it is to be understood that I do not necessarily wish to be so limited in every instance. r

Also I do not'wish to be limited at all times to the thermal dehydrogenation herein specifically described, for as discussed. I may also use any one of numerous various known dehydrogenation catalysts. Also I may use a combination of thermal and catalytic dehydrogenation, which is especially emcient-when vthe charge stock to the dehydrogenation step contains about 35 percent or more normal butane. Also, if a charge stock is available which contains appreciable amounts of both propene and butenes. it may be charged directly Vto the polymerization step, such as through the conduit 58 to the polymerization feed stripper 50. or more directly to conduit 8l through means not shown. In this latter case, the butanes present in such a charge stock could be sent t the dehydrogenatlon'step. the desirable portion o'f the eiliuent beingflnally separated in the polymerization feed stripper, as discussed. In any case, recycled propene can be added to the stream charged to the polymerization catalyst through conduit 1I.

Even when absolutely pure isobutane is charged to the dehydrogenation step, appreciable amounts of propane will be formed with the propene, probably in a manner which includes concomitant hydrogenation .of the propene produced. In the system as shown, excessive build-up of propane has been successfully controlled by occasionally venting gases through conduit 53. However, ii the amount of propane becomes excessive, or if too much propene is lost in this manner, or if considerable amounts of propane are introduced to the system along with unsaturated charge stock charged directly to the polymerization step, the separating means shown may be supplemented by the inclusion of a step for separating propene from propane and reintroducing' propene into the system as recycle stock. This separation may be carried out by any known means such as selective solvent action. or the like, and can be readily incorporated in the process by any one skilled in the art. These and other obvious modifications can be made in the process by those skilled in the art without changing the nature of my invention.

What I claim is:

'1. A process for producing normally liquid hydrocarbons of branched structure, which comprises subjecting a hydrocarbon mixture comprised predominantly of butane to dehydrogenation at a lower pressure and a dehydrogenationrg temperature not in excess of 1300 F. to produce butenes and propene, separating from the eiliuent a hydrocarbon fraction comprising hydrocarbons having three and four carbon atoms per molecule, dividing said fraction into at least two portions, adding to one of said portions a recycle hydrocarbon mixture comprising predominantly propene to provide a mixture having a molecular excess of propene over butenes and subjecting the resultant mixture to the action of an olen polymerization catalyst at a polymerization temperature between about '75 and 600 F. to copolymerize and convert the butenes and propene into liquid hydrocarbons, adding other portions of said fraction to the mixture undergoing polymerization at a plurality of points, removing from the ellluent of said polymerization catalyst a fraction comunreacted propene and returning said iractionas said recycle hydrocarbon mixture to be mixed with hydrocarbons initially charged to said p01!- merization catalyst. p

2. A process for producing normaliyliquid .aliphatic hydrocarbons o! branched structure, which comprises subjecting a hydrocarbon mixture comprised predominantly of isobutane to dehydrogenation at a pressure of less than 200 pounds per square inch and a dehydrogenation temperature not greater than about 1300 F. to produce isobutene and propene, ,separating from the effluent a hydrocarbon mixture comprising essentially hydrocarbons having three and four carbon atoms per molecule, dividing said fraction into at least two portions, adding to one of said portions a recycle hydrocarbon mixture comprising propene and subjecting the resultant mixf ture to the action ot an olen polymerization catalyst at a polymerization temperature and pressure to copolymerize isobutene and propene into liquid hydrocarbons, adding other portions oi said fraction at a plurality of points to the hydrocarbon mixture undergoing polymerization, separating a portion of the eiiluent and returning said portion directly to said polymerization catalyst, separating from another portion of said eilluent a fraction comprising liquidhydrocarbons in the motor fuel boiling range so produced and removing said fraction from the eiiluent, and separating also a fraction comprising predominantly unreacted propeneand returning said fraction to the action of said polymerization catalyst.

3. A process for producing normally liquid hydrocarbons in the motor fuel boiling range, which comprises subjecting a normallygaseous hydrocarbon mixture comprising lsobutene to thermal dehydrogenation at a low pressure and a dehydrogenation temperature not greater than 1300 F. to produce isobutene and propene, separating from the'products a hydrocarbon mixture comprising olein hydrocarbons having three and four carbon atoms per molecule. adding to at least a portion of said mixture a recycle hydrocarbon mixture comprising propene, subjecting the resultant mixture to the action of a silica-alumina polymerization catalyst at a polymerization temperature and pressure to copolymerize isobutene and propene forming normally liquid hydrocarbons someof which boil in the motor fuel range and some of which' boil above the motor fuel rangeVpassing at least a portion of the eiiiuent of said polymerization step to separating means, separating from said eiiiuent a. fraction comprising hydrocarbons in the motor fuel boiling range and removing said fraction from the process, separating a fraction comprising propene and reying hydrocarbons in the motor fuel boiling range v and passing said fraction to the irst said separating means, and separating also a fraction comprising olefin hydrocarbons boiling lower than the motor fuel-range and passing the last fraction to said polymerization step.

4. A process for producing normally liquid hyalam bon mixture comprised predominantly of butane to dehydrogenation at a low pressure anda dehydrogenation temperature not in excess of 1300 F. to produce butenes and propene, separating from the eiiluent a hydrocarbon mixture comprising hydrocarbons having three and four carbon atoms per molecule, dividing said fraction into at least two portions, adding to one of said portions a recycle hydrocarbon mixture comprising predominantly propene and subjecting the resultant mixture to the action of an olefin polymerization catalyst at a temperature between about 75 and 600 F. to copolymerize and convert the butenes and propene into liquid hydrocarbons under conditions such that the butenes are substantially completely polymerized, adding other portions of said fraction to the mixture undergoing polymerization at a plurality of points, removing from the eilluent of said polymerization catalyst a fraction comprising normally liquid hydrocarbons so produced and removing said fraction from the process, separating by fractional distillation a fraction comprising predominantly unreacted propene, returning said fraction to be mixed with hydrocarbons initially charged to said polymerization catalyst as said recycle hydrocarbon mixture, separating also by fractional distillation a, predominantly paraillnc fraction comprising essentially four carbon atom hydrocarbons and returning said fraction to be mixed with the hydrocarbons subjecte to dehydrogenation.

5. .A process for producing normally liquid hydrocarbons in the motor fuel boiling range, which comprises subjecting a normally gaseous hydrocarbon mixture comprising isobutane to thermal dehydrogenation at a low pressure and a dehydrogenation temperature not greater than 1300 F. to produce isobutene and propene in a molecular ratio between about 0.5:1 and 2:1, separating from the products a hydrocarbon mixture comprising olefin hydrocarbons having three and four carbon atoms per molecule, adding to at least a portion of said mixture a recycle hydrocarbon mixture comprising a high concentration of propene in an amount such that the molecular ratio of propene to butenes in the total mixture is between about 1:1 and 4:1, subjecting said mixture to a silica-alumina polymerization catalyst, maintaining a pressure on the polymerization step between about 200,and 3000 pounds per square inch, a polymerization temperature between about 75 and 600 F. and such that propene is only slowly polymerized with itself, and a reaction time such that unreacted butenes are substantially absent in the efliuent and normally liquid hydrocarbons some of which boil in the motor fuel range and some of which boil above the motor fuel range are formed, passing at least a portion of the efiluent of said polymerization step to separating means, separating from said eilluent a fraction comprising hydrocarbons in the motor fuel boiling range and removing said fraction from the process, separating a fraction comprising propene in high concentration and returning said fraction to the said polymerization 24 step as said recycle hydrocarbon mixture. separating also a fraction comprising oleiln polymers boiling above the motor fuel range, passing the last said fraction at a low pressure and a reaction temperature over a silica-alumina catalyst to depolymerize said olefin polymers forming lower boiling hydrocarbons, passing the eiiiuent to a ,second separating means. 'separating from said eiiluent a hydrocarbon fraction comprising hydrocarbons in the motor fuel boiling range and passing said fraction to the rst said separating means, and separating also a, fraction comprising olefin hydrocarbons boiling lower than the motor fuel range and passing the last fraction'to said polymerization step.

6. A process for producing normally liquid aliphatic hydrocarbons of branched structure and boiling in the motor fuel range from propene and butenes, which comprises dividing into at least two portions a hydrocarbon mixture comprising propene and butenes in a molecular ratio less than 1: 1, adding to one of said portions arecycle hydrocarbon mixture comprising propene to provide a mixture having a molecular excess of propene over butenes and subjecting the resulting mixture to the action of an olefin polymerization catalyst at a polymerization temperature between about and 600 F. to copolymerlze and convert butenes and propene into liquid hydrocarbons, adding other portions of the first said hydrocarbon mixture at `a plurality of points to the mixture undergoing polymerization, separating from effluents of said polymerization catalyst a hydrocarbon fraction comprising normally liquid hydrocarbons so produced and removing said fraction from the process, separating also from said eilluents a fraction comprising unreacted propene and returning said fraction as said recycle hydrocarbon mixture to be mixed with the hydrocarbons initially charged to said polymerization catalyst.

FREDERICK E. FREY.

REFERENCES CITED The following references are of record in the file of this patenti,

UNITED STATES PATENTS Number Name Date 2,116,723 Frey et al May 10, 1938 2,116,157 Morrell May 3, 1938 2,181,640 Deanesly Nov. 28, 1939 2,178,808 Rosen et al. Nov. f1, 1939 2,065,474 Mueller-Cunradi et al. Dec. 22, 1936 42,168,261 Isham Aug. 1, 1939 2,227,639 Frey et al Jan. 7, 1941y FOREIGN PATENTS Number Country Date 451,788 Great Britain Aug. 12, 1936 OTHER REFERENCES Egloii, Reactions of Pure Hydrocarbons, 1937, pages to 153 and 160 to 163, Reinhold Publishing Co., N. Y.

Certificate of Correction Patent No. 2,427,954. September 23, 1947.

FREDERICK E. FREY It is hereby certified that errors appear inthe printed specification of the above numbered patent requiring correction as follows: Column 1 line 40, for hydrocarobns read hydrocarbons; column 2, line 39, forl rich is read rich in; column 4, line 14, for true of read true if; column 15, line 13, for dehydrogenation read hydrogenation; column 21, line 55, claim 1, for lower read low; column 22, line 37, claim 3, for

isobutene read lisobuta'ne; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 30th day of December, AD. 1947.

THOMAS F. MURPHY,

Assistant Uommz'asioner 0f Patents.

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