US2303663A - Motor fuel manufacture - Google Patents

Description

Patented peeovl, 11942 UNITED STATES PATENT. OFFICE;

. Moron FUEL MANUFACTURE Rodney v. shankiana, chicago, n1., signor to Standard Oil Company, Chicago, Ill., a corporation of Indiana TApplication December 30, 1938, SerialNo. 248,626

(cl. 19e-1o) 5 Claims. This invention relates to motor fuel `manufacture and more particularly to processes for the manufacture of motor-fuel constituents having high antiknock properties; Still more specifically it relates to the production of such motor fuel constituents of the branched-chain paramn type from readily availablemixtures of normally gaseous hydrocarbons. Y

In the operation of many reneries large quantities of hydrocarbon gases having three to four considerable proportion of unsaturated constituents are produced.- Plant butane for example is a fraction composed of the butanes and butylenes which is a suitable Istarting material for practicing my invention. Another such material Ais a somewhat wider cut containing propaneand propylene as well as the butanes and butylenes.- However, it is not essential that the feed stocks used in carrying out my invention contain unsaturated hydrocarbons, since in certain forms thereof saturated fractions having three to four carbon atoms per molecule, such as those obtained from natural gas, can be used to advantage.

I have found that such hydrocarbon fractions stituents having four carbon atoms per molecule. A further object is to provide a novel unitary process for the. production of liquid hydrocarbons suitable for use as aviation gasoline constituents from readily available mixtures of normally gaseous hydrocarbons. Further objects and advantages of my invention will be apparent l0 carbon atoms per molecule and containing a three to four carbon atoms per molecule in the presence of an alkylation catalyst, isomerizingv 2'5- vthe normal butane to form isobutane, utilizing can be most efliciently. utilized by converting them to branched-chain parailln hydrocarbons boiling in the motor fuel range by a combination of alkylation, fractionation and isomerization whereby the various constituentsare handled so that the largest yield of branched-,chain paraffin hydrocarbons is obtained therefrom; Whilethe exact nature of the nal product depends to a considerable extent upon the character of the ,H

feed stock, it can be said that in general it consists predominantly .of branched-chain paraflins having seven to' eight carbon atoms per molecule,

and for this reason has a very high antiknockl value and is very stable against the formation of gum and other deterioration products Furthermore my product has a higher heat content per unit ofweight than other types of hydrocarbon fuels and is therefore particularly suited for use as a major constituent of aviation gasoline.` A

It is an object of my invention to provide an eilicient method for the production of valuable motor fuel constituents which are rich s in branched-chain paraflin hydrocarbons from. normally gaseous hydrocarbon Another the isobutane thus formed in the alkylation step,

and passing the o-ga's from the alkylation step into the fractionation step. o If propane is supplied to the fractionation step as well as4 the butanes, a fraction rich in propane can also be object is to provide a process for manufacturing normally liquid hydrocarbon mixtures having good antiknock and stability characteristics from obtained, and this can be dehydrogenated to propylene and the latter utilized as all or a part lof the olen supplied to the alkylation step.

Optionally a portion of the normal butane fraction can Abe similarly dehydrogenated and the resulting butylene utilized for the 'alkylation of isobutane. My invention also Vincludes many other features which will be brought out as the description thereof proceeds.

While my invention has a large number-of applications, several examples will sulce to make it easily understood in its various modifications,v and the flrstof these will bring out my improved method of producing a fraction containing a large proportionof branched-chainhep'- tanes and octanes from a normally gaseousimixgases containing substantial proportions of conil ferring now to the drawing, the normally gaseous feed stock is introduced into the system by means of line l and pump 2, and passes through valve 3 into line 4, in which it is admixed with-a stream of hydrocarbons rich in isobutane from a source which will be described below supplied by pump relatively low-temperature low-pressure reaction in the presence of concentrated sulfuric acid or the like, or by relatively lhigh-temperature highpressure reaction over a solid alkylation catalyst such as sodium or lithium chloro-aluminate on an inert support such as pumice. vIf the latter type of alkylation is used in practicing my invention, pressures of the order of 500-1500 pounds per square inch and temperatures of 1 50500 F. are suitable, but I prefer the former type oi lalkylation and will describe my invention in connection therewith. Briefly, low-temperature lowpressure alkylation of isobutane with olens having three to four carbon atoms per molecule is carried out by intimately contacting them in the y liquid phase with concentrated sulfuric acid hav-l ing an H'aSOr content of S10-100% and preferably 95-98% at a temperature of about 0 F. toV

100 F. and a pressure between atmospheric and about 50 pounds per square inch. The time of contact may range from about 10 minutes to about 180 minutes and is preferably from about 60 minutes to about 90 minutes.

The sulfuric acid catalyst is supplied to the lower portion of alkylation chamber 'I by means of pump 8, valve 9 and line I0. Chamber 'I is so arranged that the reacting, constituents and the sulfuric acid are kept in intimate association under the desired conditions during the required reaction time, and is shown as a vertical vessel equipped with stirring mechanism Il, although other types may, of course, be used. Cooling means must also be provided, but these are obvious to those skilled in the art and are omitted from the drawing for the sake of simplicity. The principal products of the reaction are, as stated above, branched-chain heptanes and octanes, but certain heavier branched-chain hy- -drocarbonsand polymers are also formed to some extent. The entire reaction mixture is withdrawn from alkylation chamber 1 by means of line I2 'andintroduced into separator I3 in which the acid is allowed to separate from the liquid hydrocarbons. The separated acid has lost very little of its activity and consequently is recycled supplied by line 2l and withdrawn through line 22 in order to remove traces of acid therefrom.

bottom product withdrawn from fractionating A tower 38 through line 39, the isobutane and pro- The washed product is removed from scrubber 20 through line 23 and forced by pump 24 through heater 25 into fractionating tower 26, which is of the conventionalA vtype and voperated in a welldomin'antly of butanes and lighter gases including unreacted isobutane, a bottom product consisting predominantly of hydrocarbons boiling above about.275 F. and having 9 or more carbon atoms per molecule withdrawn through line 28 and a sidestream containing the products of the'alkylation which is withdrawn through line 29 to treatment or storage. This sidestream fraction ccntains a large proportion of branched-chain paraln hydrocarbons having '7 and 8 carbon'atoms per molecule and is eminently suited for use in airplane fuels.

The bottom product withdrawn from fractionating tower 26 through line 28 is preferably removed from the system through valve 30 and line 3|, but if desired any portion of it can be recycled through valve 32, line 33, pump 5 and tionating tower 38 so constructed and operated.

as to give very close fractionation into four fractions consisting essentially of normal butane, isobutane, propane, and gases lighter than propane. The normal butane fraction is obtained as a line 4 to enrich the isobutane content of the feed stock and adjust the isobutane-olefin ratio mentioned above to the desired value.

The normal butane fraction in line 39 is charged to an isomerization step through valves 45 and 46 and line "by-means of pump 48 and line 49. The isomerization of the normal butane fraction to increase its isobutane content is car- 'ried out in isomerization chamber 50, preferably by treatment with a catalyst of the aluminum chloride type at an elevated temperature, e. g.

from about 250 F. to about 550 F. and more particularly from 350 F. to 475 F., and an elevated pressure, e. g. from about 500 to about 6000 pounds per square inch, in the presence of lan activator for the catalyst and preferably in the presence of propane and free hydrogen.-

The aluminum chloride type catalyst usedin carrying out the isomerization step of my invention can be for example aluminum chloride or aluminum bromide in anhydrous form,and

is preferably introduced into the reactionl zone in the form'of a slurry or solution in alight catalyst.

hydrocarbon oil. practicing my invention relatively small amounts ofcatalyst per unit weight oi' charge, e. g. less than 10%. are required and I prefer to use about 1% to 5% by weight. As

v activator a hydrogen halide or any compound which in the presence oi' the catalyst yields la s,sos,eos

duced into line u and mixed with the feed therein by means of pumps 82 and 83. and lines .84- and hydrogen halide under the reaction conditions can be used, preferablyin an amount sufilcient to supply about 0.03 to 3.0 percent by weight of hydrogen halide .based on the normal butane charged. Hydrogen chloride is the-preferred activator, but hydrogen bromide, carbon tetrachloride or tetrabromide, or the -alkylhalides such as methyl chloride or bromide, ethyl chloride or bromide, etc are also suitable.

At the relatively high temperatures and pressures specified above, namely: 250 F. to 550 F. or preferably 350 F. to 475 F. and 500 to 6000 pounds per square inch, much higher conversions per weight of catalyst are obtained in appreciably reduced reaction times than can be obtained under milder conditions. High tempera'- ture operation in the presence of catalyst and activator alone, however, causes increased degradation of the normal butane tolighter hydrocarbons, principally propane. Under exceptional circumstances a Asmall amount of permanent gases (ethane and lighter) 'are obtained but this is an indication of drastic overtreatment resulting fromtoo high a temperature, too muchcatalyst or too long a time of contact. The formation 88 through valves 88 and 81, respectively. Free hydrogen is supplied to the upperl portion of isomerization chamber 88 through pump 88 and line 88, and is there maintained at the desired reaction pressure, .which is suiiiciently high 'to` causev the hydrogen to dissolve in the agitated lreaction mixture at a Yrate at least as great as it is used up in the reaction. This hydrogen can be obtained from a source outside the lsystem by means of line 10, valve 1|v and line 12, but wheny the dehydrogenation stepof my' process is operated, as will be described below, it is preferably obtained therefrom through line 13, which con-` nects with line 12. Obviously if desired a number of reaction vessels can be used in series or parallel in place of the one shown, or vessels of other types well-known in the art can be substituted therefor.

A portion of the entire reaction mixture is continuously withdrawn from. the upper portion of chamber 80 through line 14 and passes through cooler 18 -into separator 18. The products con-v sist of a catalyst complex which settles out in the` lower portion of separator 18, and an upper layer' consisting of a mixture of isobutane, propane, unreacted normal butane, and some dissolved hydrogen. The catalyst complex is continuously withdrawn from separator 1 8 through line 11 and either recycled to line 84 through valve 18, pump 19 and line 80 or withdrawn from the system through valve 8| and line' 82, or under some conpropane and lighter gases and their presence in the reaction zone is generally undesirable since they act as diluents for the reaction mixture, but minor quantities can, of course, be present.

As hereinabove stated the isomerization reaction is preferably carried out in the presence ,l

of free hydrogen. At the relatively high temperatures at which this reaction is preferably operated, hydrogen greatly retards the` rate of deactivation of the catalyst, thereby allowing especially high yields of isobutane per unit of Referring again to the drawing/the normal butane fraction inline 49 is introduced into the 'lower portion of the isomerization chamber 50,

which is shownA as a Jacketed, pressure vessel equipped with a stirring device 5I so that the reaction materials are 'thoroughly contacted.

The desired reaction temperature is maintained by passing a suitable gaseous or liquid heating agent such as steam through the jacket 82 of isomerization chamber 50 by means of inlet 53 and outlet 54.

Propane in the proper amount is introduced into-line 49 through line 55,l pump 58, line 51 an'd valve 88, and this is preferably a portion of the propane stream 'in-line 4| which is made available by opening valve 59. In some cases, however, it will be necessary or desirable to supply propane from an externall source and this can be done by opening valve 80 in line 8|. Catalyst slurry and activator are likewise introditions a portion'of the complex maybe continuously withdrawn from the system and the re- `mainder recycled. The substantially spent complex can, of course, be regenerated or` the alumi- `num halide recovered therefromy and reintroduced into the system through pump 82.

The upper layer from separator 18 is withdrawn through line 83 and can be passed through valve 84 into line 33 to augment the' isobutanesupply to alkylation chamber 1, since the accompanying normal butane, propane and hydrogen are inert in the alkylation step. It is desirable, however, to avoid such dilution of the reactants in allQlation chamber 1, and theA mixture in line483 is therefore preferably introduced into fractionating tower 38 by means of valve 88, line 86, pump 81, line 88, valve 89 and line 31 for fractionation/ into normal butane, isobutane, propane, and ethane and lighter streams, these streams being utilized as described above. 'I'he hydrogen dissolved in the hydrocarbons in line 83 will eventually appear in .the gases vented through line 43 and can be recovered therefrom and reused in the isomerization step, for example by introduction into line 10. In another method of handling the stream in line 83 the butanes are separated from the propane andlighter gases by fractionation, the propane and lighter fraction recycled to isomerization chamber 88, and the normal butane-isobutane fraction passed through valve 84 and/or valve 88 for purposes described above.

It is apparent from the above description that I have provided an emcient process for converting a mixture of paraffin and olefin hydrocarbons having predominantly three and four carbon atoms per molecule into branched-chain. heptanes and octanes with 'eillciency and economy.A The exact composition of the feed will determine to a considerable extent the rates of flow in the various parts of the system, and the exactnian` ner o1' operation. In any case the'isobutane and.

the olefins having three and four carbon atoms per molecule are substantially completely utilized, while any excess of propane can be removed from the system through valve 90 and line 9| and any excess of normal butane can be similarly removed through valve 92 and line 93.

Under some conditions, and particularly when a feed stock relatively low in olefins is charged by means of line and pump 2 to the alkylation reaction, it is desirable to increase the amount of oieflns available for reaction with isobutane. This can be done by opening valve 94 and allowing at least a portion of the propane fraction in line 4| to flow to a heater 95, in which it is' lI'he dehydrogenated stream is withdrawn' from the bottom of catalyst chamber 96 by means of line 98 and passes through cooler 99, and pump to fractionating tower |0| which is operated under such conditions that hydrogen together with methane, if any is present, is withdrawn from the upper portion thereof through line |02 and theheavier materials which contain predominantly propylene are withdrawn as a liquefled bottom product through line |03. The uncondensed gas can be withdrawn from the system through valve |04 and line |05 or introduced to the isomerization step through valve |06, lines 13 and 12, pump 68 and line 69 so that it may be utilized as hereinabove described. If there is an excess of hydrogen over that required for use in 'the isomerization step, this excess will be withdrawn from the system through line |05, The liquid olefin fraction in line |03 passes through valve |01, lines 44 and 33, pump 5 and `lines 6 and 4 'to alkylation chamber 1 in which,

it is reacted with the isobutane as previously set forth.

It is also possible to cause a portion of the normal butanefraction to be delydrogenated to the normal butylenes by openingv valve |00 in line |09. Obviously by suitable manipulation of valves 94 and |08, any desired quantity of normal butane and/or propane can be dehydrogenated and the corresponding oleflns utilized in the alkylation step.

When the feed stock used is a plant butane fraction consisting predominantly of normal butane, isobutane, and the butylenes, the method of operation is exactly the same as described above, and the product consists predominantly of branched-chain octanes. Obviously, in the system shown propane will be introduced into the system through valve 60 in order to inhibit 'butane decomposition in isomerization chamber 50, and this will eventually nd its way either directlyor through the alkylation step to fractionating tower 38, from which it will be withdrawn as a sidestream through line 4| for further inhibition of butane decomposition. Generally butane fraction in line 39 which is allowed to pass through valve |08 and line |09.

My invention is also adapted to theprocessing of substantially saturated normally gaseous fractions containing isobutane, normal butane and optionally propane. Such fractions are often available from the fractionation of natural gasoline or distillate recovery plant streams or as off-gas from the catalytic polymerization of renery gases or fractions thereof. If the isobutane content is relatively high, it maybe desirable to charge this fraction directly to alkylation chamber 1 by means of line pump 2 and line 4, and in this case the process is operated according to one of the modifications described above, substantiallyall of the olefin supply to alkylation chamber 1 being provided by dehydrogenation of at least a portion of the propane fraction in line 4| and/or the normal butane fractionl in line 39.l

In most cases, however, substantially saturated butane or butane-propane fractions are preferably fed directly into line 31 leading to fractionating tower 38 by means of pump ||0 and-line |i`| through valve ||2, valve 3 of coursel being closed. By using this feed point excessive dilution of the reactants in alkylation chamber 1 is avoided and each ofthe constituent gases is readily available for use in that part of my process in which it is most needed. Any of the modifications of my process including the dehydrogenation step mentioned above can be carried out when the feed stock is charged by means of pump ||0, and ofcourse various combinations of the operating methods herein described can be used without departing from the spirit of my invention. The various steps of my process can of course be carried out en an intermittent or semi-continuous basis, and such operations are yWithin the scope of my invention although I prefer continuous operation.

Many modifications of my invention'and of the apparatus shown herein for practicing it will be apparent to those skilled in the art,who

will beable to supply numerous details not illustrated in the drawing, such as heat exchangers, provisions for fractionating tower control, surge drums, etc. I do not, therefore, desire to be 1 limited to the specific embodiments herein despeaking, valve 94 will be kept closed under these conditions and any olefin deficiency made up by the dehydrogenation of a portion of the normal scribed, but only by the scope of the following claims.

I claim:

l. The method of producing valuable motor fuel constituents from a substantially saturated normally gaseous hydrocarbon mixture containing considerable proportions of normal butane and isobutane which comprises fractionating said mixture in a fractionating zone to form a fraction rich in normal butane and a fraction rich in isobutane, dehydrogenating a portion of said fraction rich in normal butane to form butylenes and hydrogen, introducing said butylenes and said fraction rich is isobutane into in alkylation zone containing a catalyst and maintained under conditions suitable for the reaction of butylenes and isobutane to form branched-chain octanes, removing the products from said alkylation zone, separating a normally liquid fraction containing said octanes and a normally gaseous fraction from said products, introducing said normally gaseous fraction into said fractionating zone, isomerizing the remaining portion of said fraction rich in normal butane in thepresence of a catalyst of the aluminum chloride type and an activator for said catalyst at an elevated temperature to t asoaces y produce a further quantity of isobutane, and uulizing said further quantity of isobutane in said 'alkylation zone.

2. The method of producing valuable motor fuel constituents from a substantially saturated normally gaseous hydrocarbon mixture containing considerable proportions of propane, isobutaneand normal butane which comprises tracp moving the products vfrom said alkylation zone.

separating a normally-liquid fraction containing said heptanes and a normally gaseous traction from said products, introducing said normally gaseous' fraction into said fractionating zone,'.

isomerizing at least a portion of said fraction rich in normal butane in the presence of a catalyst in an isomerization zone to produce a further quantity of isobutane and utilizing. saidgfurther Vquantityof isobutane in said alkylation zone.

`il. The method oi claim 2 wherein said further quantity of isobutane together with unchanged normal butane isvintroduced 1into said fractionf ating rbne.

4. The method 'of claim 2 -wherein aportion.

of said fraction rich in propane is supplied to s'aid isomerization zone. l A

5. The method of producing valuable motor l fuel constituents which comprises fractionating a substantially saturated normally gaseous hydrocarbon mixture containing considerable proportions of propane, normal butane'and isobutane in a traotionating zone to form at least three fractions rich in propane, normal butane and isobutane respectively, introducing said fraction rich in isobutane into an alkylation zone for reaction with at least one olefin having three to iour carbon' atoms per molecule in the presence of sulfuric acid havinga concentration of about 90% to 100% at a temperature of about 0 1i'.v to about 100 F.. the molecular` ratio of isobutane to' olefin in said alkylation zone being maintained at avslue not 1ess than about 2 to 1, passing at least a portion o! said fraction rich in propane over a dehydrogenation catalyst at a temperature ranging from about 900 F. to

about l200 F. to produce propylene and hydrocatalyst at al temperature inthe range from about 250 F. to about 550 F. and a pressure of about 500 toabout 6000 pounds per Square inch, removing-the isomerized products from said isomerization zone, introducing at least the major portion of the isobutane contained in, said isomerized products into ,said alkylation'zone, removing the products from said alkylation zone, separating a normally gaseous fraction and` a normally liquid -fraction containing branched- Y chain paraffin hydrocarbons having -7 to 8 car- 35 bon atoms per molecule from said last-mentioned products, introducing said normally gaseous fraction into said fractionation zone, and withdraw` ing said normally liquid traction from the system.

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