US3657109A

US3657109A - Motor fuel production

Info

Publication number: US3657109A
Application number: US864807A
Authority: US
Inventors: Bruce O Beyaert
Original assignee: Chevron Research and Technology Co
Current assignee: Chevron USA Inc
Priority date: 1969-10-08
Filing date: 1969-10-08
Publication date: 1972-04-18
Anticipated expiration: 1989-04-18

Abstract

A combination process for obtaining motor fuel from a mixture of hydrocarbons comprising isobutane and normal butane involving alkylation and paraffin disproportionation and preferably also light hydrocarbon dehydrogenation.

Description

[151 3,657,l09 51 Apr. 18, W72

United States Patent Beyaert 4 6 W 60 m6 6 2 m m u N "1 u m m m w m a m mm mm "V e" U nu U h X m t 0 e O FDGHB 680099 46666 99999 lllll 77 55 1 32018 00 446 42558 H mm m 5 C 9 mm m m Im EC R h use I ua r, E c W 0 Umh.m FBCC 0e m m M m Mn UH Primary Examiner-Herbert Levine Attorney-A. L. Snow, F. E. Johnston, C. J. Tonkin and T. G. De Jonghe [57] ABSTRACT A combination process for obtaining motor fuel from a mixture of hydrocarbons comprising isobutane and normal butane involving alkylation and paraffin disproportionation and preferably also light hydrocarbon dehydrogenation.

OLEFIN ZONE ALKYLATION ZONE DEHYDRQGENATION m u .w. F g .m w r D 1 m m C 7 N 3 3 8 6 0 6 2 SW m N" m m A m S Em m A 6 v m S E T. 7 m9 H 5 8 9 2 3 3 MOTOR FUEL PRODUCTION BACKGROUND OF THE INVENTION 1. Field of the lnvention The present invention relates to the production of valuable hydrocarbons such as high-octane fuels by a combination process. More particularly, the present invention relates to the production of motor fuels by a combination process involving alkylation and paraffin disproportionation, and preferably also .paraffin dehydrogenation.

. The basic elements of most alkylation units are the same. The heart of an alkylation process is the reactor, in which the fresh feed of olefin and isoparaffin (usually isobutane) together with recycle isoparaffin is contacted in the presence of an acid catalyst to form alkylate. Facilities are provided to settle the catalyst from the product alkylate and to recycle the catalyst, to remove traces of acid catalyst from the product alkylate and to fractionate recycled isobutane from the product.

To prevent propane from building up in the recycle isobutane, a small depropanizer is usually provided to remove propane from a slipstream. Also, a debutanizer is usually provided to separate normal butane from the product alkylate.

Although disproportionation of hydrocarbons is not normally used to produce motor fuels, disproportionation is an important reaction in the motor fuel production process of the present invention.

The term disporportionation is used in the present specification to mean the conversion of a hydrocarbon of a given molecular weight to new hydrocarbons of both higher and lower molecular weight. For example, butane may be dis proportionated according to the reaction:

It is known that paraffins can be disproportionated. For example, U.S. Pat. No. 3,445,541 discloses a high-temperature process which may be applied to the disproportionation of either paraffins or olefins having from three to six carbon atoms per molecule. According to the process of U.S. Pat. No. 3,445,541, the hydrocarbon feed is contacted with a combined dehydrogenanon-disproportionation catalyst at conditions of temperature and pressure to promote appreciable amounts of both dehydrogenation and disproportionation. According to the disclosure of U.S. Pat. No. 3,445,541, a temperature between 800 and l,200 F. can be used for the disproportionation-dehydrogenation reaction. The lowest temperature used for processing a paraffin in accordance with any of the examples of U.S. Pat. No. 3,445,541 is 980 F., and, typically, the temperatures used for paraffin disproportation according to U.S. Pat. No. 3,445,541 are between 1,040 and l,125 F.

According to laboratory research, we have found that C, paraffins can be disproportionated to form propane and C paraffins at temperatures below 950 F., and that the paraffin disproportionation catalysts are more stable at these lower temperatures and that the paraffin disproportionation process shows a higher selectivity for, and ultimate yield of, C paraffins at temperatures below950 F and preferably below 800 F.

SUMMARY OF THE INVENTION According to the present invention a combination process involving alkylation and paraffin disproportionation is provided for producing motor fuel from a mixture of hydrocarbons comprising isobutane and normal butane, which process comprises:

a. Feeding the mixture of hydrocarbons and a heavier hydrocarbon fraction to a fractionation zone and therein b. F ractionating the feed to the fractionation zone to obtain at least an isobutane-rich stream, a normal butane-rich stream and said motor fuel,

c. Reacting at least a portion of the isobutane-rich stream with an olefin in an alkylation zone to form raw alkylate,

d. Disproportionating at least a portion of the normal butane-rich stream in a disproportionation zone to form raw disproportionate, and

e. Feeding the raw alkylate and the raw disproportionate to the fractionation zone as the aforesaid heavier hydrocarbon fraction.

In the process of the present invention it is particularly preferred to generate the olefin feed for the alkylation zone by dehydrogenation of at least a portion of the propane which is generated by the disproportionation of the normal butane feed to the disproportionation zone. Preferably the propane is converted to the olefin feed for the alkylation zone by catalytic dehydrogenation or by thermal cracking. Because propane is essentially always generated in the disproportionation of normal butane, it is very advantageous to use the disproportionation-generated propane in the overall process to produce motor fuel. Ordinarily, the propane might be burned as a fuel gas, but in accordance with a preferred embodiment of the present invention the propane is converted to an olefin such as ethylene or propylene, and this olefin is used as at least part of an olefmic feed for reaction with the isoparaffin in the alkylatron zone.

The alkylation step of the combination process of the present invention can employ a number of known alkylation processes, including HF and H SO alkylation. The alkylation step is operated at conditions of temperature and pressure known according to the prior art.

Similarly, in those preferred embodiments of the present invention wherein propane is converted to an olefin feed for the alkylation zone, the conversion is carried out as, for example, by catalytic dehydrogenation or by thermal cracking in accordance with operating conditions known according to the prior art.

However, in the present process combination invention it is preferred to carry out the disproportionation of the normal butane feed at relatively low temperatures compared to temperatures previously indicated to be desirable for paraffin disproportionation using a dehydrogenation-disproportionation type catalyst. It is preferred to carry out the normal butane disproportionation at temperatures below 950 F., and still more preferably, below 800 F. Temperatures in excess of 800 F., and particularly in excess of 950 F., result in the production of appreciable amounts of olefins in the disproportionation zone, and in most instances it is not desired to produce a motor fuel which has a particularly high olefin content. Catalysts such as disclosed in the two patent applications by T. R. Hughes entitled Saturated Hydrocarbon Averaging, Ser. No. 864,870, and Saturated Hydrocarbon Conversion, Ser. No. 864,871, both filed Oct. 8, 1969 and now abandoned, are well suited for disproportionation at temperatures below 950 F. and particularly below 800 F. The above mentioned patent applications are incorporated by reference in their entirety into the present patent application.

A particularly preferred hydrocarbon feed source for the process of the present invention is a natural gas plant, or a gas recovery plant, C hydrocarbon fraction. The notation C -lindicates propane and heavier hydrocarbons. The C fraction may contain a substantial amount of hydrocarbons which are in the C,+ boiling range. Normally, the feed consists mostly of propane, C and C hydrocarbons, with the C; hydrocarbon content being being relatively low (l-lO volume percent C s) compared to the propane and C s. Propane is normally present to the extent of about 5 to 60 volume percent in the net feed.

in accordance with the preferred embodiment of the present invention wherein propane is dehydrogenated to form at least a part of the olefinic feed for the alkylation zone, a portion of the propane feed to the dehydrogenation step is usually obtained from the fractionation zone by the fractionation of propane from the net feed. Thus, propane in the net feed usually augments the propane fractionated from the raw disproportionate fed to the fractionation zone. The olefins which are formed in the dehydrogenation zone can be used as chemical feedstocks, for example to a polyethylene or polypropylene chemical plant, in addition to their preferred use in the alkylation step of the present invention.

One of the important advantages of the present invention is that the fractionation zone provides fractionation for several processing steps in the overall process combination. In the preferred embodiment just referred to, the fractionation zone provides separation of propane from the net feed to the invented process as well as providing for separation of propane generated in the disproportionation step and propane which is generated due to side reactions in the alkylation step.

The fractionation zone, in accordance with the process of the present invention, also serves to fractionate isobutane from other constituents (C and possibly C in the net fed to the process, as well as fractionating isobutane from the raw alkylate from the alkylation step, and, if necessary, fractionating isobutane from the raw disproportionate formed in the disproportionation step of the present invention.

Therefore, the fractionation zone in the process of the present invention serves as a common fractionation zone for a number of integrated processing steps. The economic attractiveness of the process of the present invention is increased because of the fact that common fractionation facilities may be used for several of the processing steps of the present invention.

Preferably the fractionation zone consists essentially of a deisobutanizer" distillation column with associated equipment (reboiler, overhead system, etc.) and a debutanizer column with associated equipment. The feed to the deisobutanizer preferably includes the net feed and the raw alkylate and the raw disproportionate. The bottoms from the deisobutanizer are preferably fed to the debutanizer for fractionation into a normal butane-rich stream and the product motor fuel. The normal butane-rich stream from the debutanizer is fed to the disproportionation step of the present invention. An isobutane-rich stream is removed from the upper part of the deisobutanizer and fed to the alkylation step of the present invention. A propane-rich stream is preferably withdrawn as an overhead vapor from the deisobutanizer. Thus the deisobutanizer could be referred to as a depropanizer, but because isobutane is a major stream withdrawn from the upper part of the column, the column is referred to as a deisobutanizer. In certain instances, depending on overall material balance, it is economically preferable to use a depropanizer column to remove propane from the combined net feed, raw alkylate and raw disproportionate prior to feeding these combined streams to the deisobutanizer. Therefore, it is to be understood that the deisobutanizer zone can include a depropanizer distillation column located ahead of a deisobutanizer distillation column.

Thus, according to a preferred embodiment of the present invention, a motor fuel is produced from a mixture of hydrocarbons comprising at least isobutane and normal butane using a common deisobutanizer fractionation zone and a debutanizer fractionation zone in accordance with the following steps:

a. Feeding the mixture of hydrocarbons to a deisobutanizer zone together with a heavier hydrocarbon fraction,

Fractionating isobutane from the feed to the deisobutanizer zone to obtain an isobutane-rich stream and a deisobutanizer heavy stream,

c. Feeding the isobutane-rich stream with an olefin to an alkylation zone wherein they are reacted together to form a raw alkylate,

d. Feeding the deisobutanizer heavy stream to a debutanizer zone and therein e. Fractionating normal butane from the feed to the debutanizer zone to obtain a normal butane-rich stream and said motor fuel,

f. Feeding the normal butane-rich stream to a disproportionation zone wherein the normal butane is disproportionated to form raw disproportionate, and

g. Feeding the raw alkylate and the raw disproportionate to the deisobutanizer zone as the aforesaid heavier hydrocarbon fraction.

Other preferred embodiments for the fractionation zone include: (1) just one fractionation column receiving a total feed comprising the net feed, raw disproportionate, and raw alkylate, and separating this total feed into a propane-rich stream, an isobutane-rich stream, a normal butane-rich stream and the product motor fuel, or (2) three fractionation columns, the first fractionation column receiving the total feed as above and splitting the feed into a propane, isobutane-rich stream; and a normal butane, C +-rich stream; the second fractionation column receiving the propane, isobutane-rich stream and splitting it into a propane-rich stream and an isobutane-rich stream for feed to the alkylation step; and the third fractionation column receiving the normal butane, C stream and splitting it into a normal butane-rich feed to the disproportionation step and a product C stream.

As indicated previously, in one preferred embodiment of the present invention, propane is dehydrogenated to form an olefinic feed for the alkylation step of the present invention. In accordance with that concept of the present invention wherein propane is dehydrogenated to form olefinic feed for the alkylation step, a particularly advantageous combination process, which typically would not utilize a common fractionation zone, contains the following steps:

a. Disproportionation of a normal butane-rich stream to obtain propane and C hydrocarbons,

b. Separation of the propane from the C hydrocarbons to obtain a propane-rich stream and a disproportionate C +-rich stream,

c. Dehydrogenation of the propane-rich stream to obtain olefins,

d. Alkylation of an isoparaffin by reacting the isoparaffin with said olefins to thereby form an alkylate.

In accordance with a particularly preferred embodiment of the above steps (a) through (d) combination process, at least a portion of the alkylate is blended with at least a portion of the C disproportionate to form a valuable motor fuel. The octane, for example, of the motor fuel can be regulated by blending more of less alkylate into the C disproportionate. The raw alkylate formed in accordance with the step (d) alkylation is, of course, usually subjected to fractionation to remove at least a large part of the C and lighter hydrocarbons before the alkylate is blended with the C,,+ disproportionate.

In accordance with a particularly preferred embodiment of the present invention, at least a portion of the C disproportionate is isomerized, for example in a conventional pen-hex isomerization unit. The C isomerized product is then preferably blended with the alkylate. When an isomerization step is included, common fractionation facilities are preferably used for the net feed (e.g., a C feed stream from a gas plant) and the alkylation step effluent. The disproportionation step preferably is followed by a separate fractionation step to prepare feed for the isomerization step.

BRIEF DESCRIPTION OF THE DRAWING The drawing is a schematic process flow diagram illustrating a preferred embodiment of the present invention.

DESCRIPTION OF THE DRAWING Referring now in more detail to the drawing, a C stream comprising propane, isobutane, and normal butane is fed via line 1 together with recycle raw alkylate and raw disproportionate in line 2 to fractionation zone 21. Fractionation zone 21 separates the total feed stream into a propane-rich stream withdrawn in line 16, an isobutane-rich stream withdrawn in line 10a, a normal butane-rich stream withdrawn in line 7 and the product motor fuel stream withdrawn in line 20. The term rich is used in the specification to mean a stream containing at least 50 volume percent of the specified component.

It is to be understood that the fractionation zone may be comprised of a number of separate distillation columns and appurtenant equipment. However, in any case there will be at least one distillation column which is common to at least two streams of the process of the present invention.

Particularly preferred combined streams for fractionation in a common distillation column or columns in the fractionation zone of the present invention include: the raw alkylate and the raw disproportionate, the raw alkylate and the net feed, the raw disproportionate and the net feed, or the raw alkylate, the raw disproportionate, and the net feed. The term raw alkylate is used herein to mean alkylation product before final separation of isobutane (including recycle isobutane) from the alkylate; the term raw disproportionate is used to means disproportionation product at least before final separation of iC and normal butane (including recycle butanes) from the disproportionate and usually also before final separation of propane from the disproportionate; and the term net feed refers to the net input to the process of the invention which is a stream containing at least isobutane and normal butane.

For purposes of simplified illustration, the process of the present invention may be considered in one broad embodiment to consist of just one large fractionation zone with the total feed to the fractionation zone including raw alkylate transferred via

lines

12 and 2, raw disproportionate transferred via lines 9 and 2, and net feed via line 1. This total feed to the large common fractionation zone is then split into the product motor fuel withdrawn via line 20, a normal butanerich stream withdrawn via line 7 and fed to the disproportionation zone, an isobutane-rich stream withdrawn via line 10a and fed to the alkylation zone, and a propane-rich stream withdrawn from the large central fractionation zone via line 16 and burned as fuel, or in a preferred embodiment fed to the dehydrogenation zone for conversion to olefin which is used in the alkylation zone.

The fractionation zone 21, however, can consist of a deisobutanizer zone and a debutanizer zone as is indicated in the drawing. In most instances, the propane stream which is obtained by fractionation in the deisobutanizer zone preferably is further fractionated into a depropanizer to separate isobutane from the propane. The deisobutanizer zone (which is within fractionation zone 21) preferably consists essentially of a deisobutanizer distillation column, although the deisobutanizer zone may be split into two or more columns, particularly in view of the fact that more than two streams are fractionated or separated from one another in the deisobutanizer zone. In certain instances it is preferred to depropanize before the deisobutanizing step.

Referring to the particular schematic embodiment shown in the drawing, a C stream is withdrawn in line 5 from the lower part of the deisobutanizer zone. If the majority of the normal butane is removed from the heavy fraction withdrawn from the bottom of the deisobutanizer zone, then the C fraction from the bottom of the deisobutanizer zone is withdrawn from the process as product motor fuel via

lines

24 and 20. The majority of the normal butane, in accordance with one preferred embodiment of the present invention, is separated from the C fraction by withdrawing the normal butane as a vapor sidestream from the deisobutanizer fractionation column. Withdrawal of normal butane as a vapor sidestream is indicated schematically by line 23. In the typical case, however, normal butane is not withdrawn as a vapor sidestream but is instead contained in the bottom stream withdrawn via line 5 from the deisobutanizer zone.

In this typical case the normal butane and C material withdrawn via line 5 is fed to debutanizer zone 6 for separation of normal butane from C material. The C material is withdrawn from the bottom of debutanizer zone 6 via line 25 and is withdrawn from the process as product motor fuel via line 20. A normal butane-rich stream is withdrawn from the upper part of debutanizer zone 6 via line 22 and is fed to disproportionation zone 8 via line 7. The debutanizer zone preferably consists primarily of a debutanizer fractionation column. The debutanizer fractionation column will, of course, have associated equipment such as a reboiler and an overhead cooling and refluxing system.

The normal butane-rich stream, which is withdrawn from the upper part of the debutanizer zone as schematically indicated by line 22, generally contains considerable amounts of isobutane. The isobutane content can be controlled to less than a few tenths volume percent in the normal butane stream, withdrawn via line 22, depending upon the fractionation obtained prior to the debutanizer zone. However, in the overall process of the present invention usually it is economically preferable in terms of capital investment, operating expense and product value to allow the isobutane content of the normal butane stream withdrawn via line 22 to be in the range of l to 10 volume percent. This has the advantage of resulting in a more branched-chain disproportionate and, therefore, higher octane disproportionate product from disproportionation zone 8. Allowing the isobutane content of stream 22 to be between 1 and 10 volume percent also is advantageous in that the operating expense and capital investment for fractionation is less than if the isobutane is maintained at a very low content in the normal butane stream withdrawn from debutanizer zone 6 via line 22. I

In the alternate schematic embodiment indicated in the drawing wherein normal butane is withdrawn as a vapor stream via line 23 from the deisobutanizer zone, there will usually be between about 1 and 10 volume percent isobutane in the normal butane vapor stream. Also, the normal butane vapor stream will typically contain several volume percent C hydrocarbons. Because the C material may be disproportionated to valuable highermolecular weight hydrocarbons in disproportionation zone 8, in many instances it is very advantageous to omit debutanizer zone 6 to thus realize fractionation operating cost savings as well as investment savings.

The normal butane-rich stream, which is withdrawn either as a vapor via line 23 from the deisobutanizer zone or withdrawn via line 22 from the debutanizer zone 6, is fed to disproportionation zone 8 via line 7. Therein the normal butane is disproportionated, preferably at a temperature below 950 F. and still more preferably at a temperature below 800 F., to form raw disproportionate, which is withdrawn via line 9. The raw disproportionate, comprising propane, unconverted butanes, and C hydrocarbons, is transferred via line 2 to deisobutanizer zone 4.

An isobutane-rich stream is withdrawn from deisobutanizer zone 4 via line 10 and from depropanizer column 14 via line 15 or in general from the fractionation zone via line 10a, and fed to alkylation zone 11. In most instances the propane stream withdrawn from the upper part of deisobutanizer zone 4 via line 13 is fractionated to remove isobutane from the propane-rich stream. As is schematically indicated by the drawing, this fractionation is carried out in depropanizer column 14. Isobutane is withdrawn via line 15 from the bottom of the depropanizer column. The isobutane withdrawn via line 15 is combined with the isobutane in line 10 and fed via line 10a to alkylation zone 11 wherein the isobutane is reacted with olefins fed to the alkylation zone via line 18. The raw alkylate which is formed in the alkylation zone with withdrawn from the alkylation zone via line 12 and is transferred together with the raw disproportionate via line 2 to deisobutanizer zone 4, or in general, as is schematically indicated in the drawing, to fractionation zone 21. The raw alkylate stream contains propane, isobutane, and C hydrocarbons. The propane is formed by side reactions in the alkylation reaction, the isobutane is the reactant which is present in large excess for the alkylation reaction (the olefms being very reactive), and the C 30 hydrocarbons are the high-octane motor fuel formed in the alkylation reaction.

The propane-rich stream which is obtained by fractionation of the feed streams to the fractionation zone is fed via line 16 to dehydrogenation zone 17. Dehydrogenation zone 17 can consist of a thermal cracking reactor and associated facilities or a catalytic dehydrogenation reactor and associated facilities. In any case, the propane is dehydrogenated to form propylene and/or ethylene, which is withdrawn from dehydrogenation zone 17 via line 19 and passed at least in part to alkylation zone 11 via line 18. Excess olefins formed in the dehydrogenation zone are withdrawn via line 19a and passed tionation zone as the aforesaid heavier hydrocarbon fracto further processing or used, for example, in chemical manution. facture. 2. process In accordance with claim 1 wherein propane lS generated by the disproportionation of said normal butane- EXAMPLE rich stream and at least a portion of said propane is converted to olefins, which are reacted with isobutane in the alkylation Table l below shows a material balance keyed to the schezone. v

matic process flow diagram. The material balance illustrates 3. A process in accordance with claim 2 wherein the disprothe production of valuable motor fuel from a C feed which portionation is carried out at temperatures below 950 F. is rich in normal butane. The C feed is a typical gas recovery 4. A process in accordance with claim 2 wherein the disproplant C stream. H V W portionation is carried out at temperatures below 800 F. TABLE 1 Stream number Alkylation and Dehydispropor- Fraction- Dispro- Dispro- C; from Alkyladrogenationation ation portionportlon- Alkyla- Alkyla- {ractiontion tion zone Zone ation ation tion tion ation olefin zone Motor Stream descrrptiorn. Ca feed efiiuents feed feed effluent iCi feed etfiuent zone feed efliuent Olefin fuel Component, b.p.d.:

a" t A iC4 6, 100 49, 750 55,850 850 C4. 9, 250 9, 050 18, 300 15, 050 05* 0 12,050 12,150 00 Total 33, 000 77, 500 110, 500 16, 650 17, 150 58, 500 05* octane. F-l

clear 41 7 :Stream IQ and 12a s ho vv t pical Cr and g i eld irom a propane cracking plant. Other by products are not shown for these streams.

Although various specific embodiments of the invention 5. A combination process for obtaining motor fuel from a have been described and shown, it is to be understood they are mixture of hydrocarbons comprising isobutane and normal meant to be illustrative only and not limiting. Certain features butane WhlCl'l comprises:

may be changed without departing from the spirit or essence a. feeding the mixture of hydrocarbons to a deisobutanizer of the invention. It is apparent that the present invention has zone together with a heavier hydrocarbon fraction, broad application to the production of motor fuel in a o b. fractionating an isobutane-rich stream from the feed to bination process involving alkylation and parafiin dispropor- 40 t d is tltarl il r Zone t Obtain an isobutane-rich tionation. Accordingly, the invention is not to be construed as Stream and a delsobutaflilef heavy Stream, limited to the specific embodiments illustrated, but only as c. feeding the isobutane-rich stream with an olefin to an aldefined in the appended claims. kylation zone wherein they are reacted together to form a What is claimed is: raw alkylate, 1. A combination process f r b i i motor f l from a d. feeding the deisobutamzer heavy stream to a debutanizer mixture of hydrocarbons comprising isobutane and normal Zone, butane which comprises: e. fractionating a normal butane-rich stream from the feed a. feeding the mixture of hydrocarbons to a fractionation t0 the debutanizer Zone to Obtain a normal ch zone together with a heavier hydrocarbon fraction and Stream and Said motor fuel, therein f. feeding the normal butane-rich stream to a disproporb. fractionating the feed to the fractionation zone to obtain hohahoh Zone Whereih the normal butane 1S p p at least an isobutane-rich stream, a normal butane-rich liohaled to form raw disproportionate. and stream and said motor fuel, g. feeding the raw alkylate and the raw disproportionate to c. reacting at least a portion of the isobutane-rich stream the deisohulanillel Zone as the aforesaid heavier with an olefin in an alkylation zone to form raw alkylate, hydrocarben frflctlond. disproportionating at least a portion of the normal bu- P 9 aficordahce Whh Claim 5 Whereih the p tane-rich stream in a disproportionation zone to form raw Pomohahoh 15 Famed out at temperatures below disproportionate, and 7. A process In accordance with claim 5 wherein the disproe. feeding at least a portion of the raw alkylate to the frac- Portiohahoh Carried out at tempel'hlures below

Claims

2. Aprocess in accordance with claim 1 wherein propane is generated by the disproportionation of said normal butane-rich stream and at least a portion of said propane is converted to olefins, which are reacted with isobutane in the alkylation zone.
3. A process in accordance with claim 2 wherein the disproportionation is carried out at temperatures below 950* F.
4. A process in accordance with claim 2 wherein the disproportionation is carried out at temperatures below 800* F.
5. A combination process for obtaining motor fuel from a mixture of hydrocarbons comprising isobutane and normal butane which comprises: a. feeding the mixture of hydrocarbons to a deisobutanizer zone together with a heavier hydrocarbon fraction, b. fractionating an isobutane-rich stream from the feed to the deisobutanizer zone to obtain an isobutane-rich stream and a deisobutanizer heavy stream, c. feeding the isobutane-rich stream with an olefin to an alkylation zone wherein they are reacted together to form a raw alkylate, d. feeding the deisobutanizer heavy stream to a debutanizer zone, e. fractionating a normal butane-rich stream from the feed to the debutanizer zone to obtain a normal butane-rich stream and said motor fuel, f. feeding the normal butane-rich stream to a disproportionation zone wherein the normal butane is disproportionated to form raw disproportionate, and g. feeding the raw alkylate and the raw disproportionate to the deisobutanizer zone as the aforesaid heavier hydrocarbon fraction.
6. A process in accordance with claim 5 wherein the disproportionation is carried out at temperatures below 950* F.
7. A process in accordance with claim 5 wherein the disproportionation is carried out at temperatures below 800* F.