US2386135A - Production of dienes - Google Patents

Description

R. p; MORRIS ETAL 2,386,135

PRODUCTION OF DIENES Oct. 2, 1945.

Filed June 15, 1942 PenTad/ne Hydro catbon lnvnfors. R err c. Morris.

Roberf J by their flflomey! Patented Oct. 2, 1945 Calif., assignors to Shell Development. Company, San Francisco, Calif., a corporation of Delaware Application June 15, 1942, Serial No. 447,139

3 Claims. (Cl. 260-680) This invention relates to the art of cracking hydrocarbons and more especially to the manufacture of diolefines and other valuable products by vapor phase cracking of especially selected and prepared feeds.

Diolefines, and especially butadiene and isoprene are useful as starting materials in the manufacture of 'elastomers; that is, polymeric materials which have elastic properties similar to rubber, and find successful applications in differentarts. Eiastomers maybe produced either by polymerizing a dioleflne alone or by copolymerizing dienes and other unsaturates.

The behavior of different dienes is often similar but, as could be expected, marked differences in conditions required for polymerization or copolymerization, or in properties of the resulting products, may be caused by variations of molecular weight and structure.

Each diene has its own characteristics which make it superior for certain uses and inferior for others. Thus,- for example, rubber-like products formed by copolymerizing styrene with butadiene are harder than those obtained by copolymerizing it with isoprene and. thus less adapted to some purposes.

It is well known to prepare dienes bydehydrogenation of corresponding olefines, by dehalogenation or dehydrohalogenation of corresponding halogen derivatives, dehydration of corresponding alcohols, etc. These methods, however, besides having certain other disadvantages, as for may greatly change the yields of, and conversion per pass to, these dienes but fails to alter appreciably their relative proportion in the cracked products.

It is an object of this invention to provide a Y process for the manufacture of valuable hydrocarbons, especially dienes and particularly pentadienes, by treating and cracking a selected hydrocarbon stock which is readily available.

Another object is to provide a practical method for varying the composition of dienes produced from a hydrocarbon feed by cracking and particularly for varying the relative proportion of butaand pentadienes.

Another object is to produce hydrocarbon fractions rich in diand mono-oleflnes and aromatics from which these valuable hydrocarbons can be separated in a simple manner. Still further objects include simplified procedures, decreased cost in the manufacture of dienes, and other improve-' ments f oimd hereinafter.

This invention is based on the discovery that the nature of the cracked products obtained by cracking normal hydrocarbons and particularly example the cost involved in preparing the startparticularly of butadiene. The proportion of the diene in the cracked products is, however, small, and it is associated with major amounts of saturated and ethylenic hydrocarbons having nearly equal vapor pressures. Thus, their recovery is dimcult and their yields are small.

Certain selected hydrocarbon feeds yield, upon cracking under particular conditions, relatively large proportions of dienes and relatively dienerich fractions from which these hydrocarbons may be recovered more economically. Here again, however, only one diene or several dienes only in one given proportion may be obtained from one feed.

Thus by cracking normally liquid normal monooleflnes in the vapor phase at temperatures above 600 C., gases may be obtained which contain substantial amounts ofbutadiene, and selected narrow boiling fractions of such gases may comprise, almost 50% of this gas. Pentadiene is simultaneously produced in smaller amounts.

Varying the conventional cracking conditions such as temperature, pressure, residence time, etc.,

normal m'onp-olefines may be radically changed if the feed is subjected to an isomerization prior to cracking. Thus, while dienes obtained from unisomeriz'ed wax olefines comprise mainly butadiene, those obtained therefrom after isomerization predominate in pentadienes.

According to one aspect of this invention, normally liquid normal mono-olefines are subjected toisomerization and thereafter cracked in the vapor phase at a temperature above about 600 C. to yield pentadiene.

According to another aspect of this invention, a varying proportion of the feed is subjected to isomerization, or a constant proportion is isomerized to a varying degree prior to cracking and the nature of diolefines in th cracked products is thereby regulated.

.which normally 'solid paraffin wax or highly paraf finic distillates predominating in crystallizableparamnsare cracked in the vapor phase at temperatlireg below 600 0. Especially large yields of such paraffin are obtained by subjecting these hydrocarbons in the presenceof steam to temperatures of 540 C. to 570 C. and pressures below products. If the maximum 75 p. s. i. for a time period from 3 to 6 seconds,

and quenching the cracked products. Distillates obtained therefrom boiling under 300 C; predominate in normal monoolefines and are very suitable for use as cracking stocks of this invention, particularly the distillates boiling .from about 60 C. to 210 C.

Other sources of normal olefines include, for example, the dehydration of normal alcohols obtained by reduction of naturally occurring normal fatty acids, dehydrohalogenation of mono halogenated normal paraflins, etc. These methods arehowever, in general less practical than in the art and include, for example, activated alumina, e. g., bauxite which has been dehydrated; alumina which has been heated to about 400 C. to 700 C. and washed with acid; ion exchange agents such as hydrated aluminum silicates; particularly zeolites and permutites such as are morefully described in U. S. Patent .No.

2,175,252 to Han Hoog; manyso-called cracking catalysts comprising oxides such as silica, alumina, magnesia, zirconia, thoria, many polymerization catalysts such as so-ca'lled solid phosphoric acid catalystsf etc. Suitable commercial catalysts include, for example, Porocel, Doucil, Nalco No. 300 catalyst, etc.

The conditions of isomerization-that is, temperature, pressure and contact time, vary greatly with the nature of the catalyst used. Temperaturesin the range of 250 C. to 500 C. are often suitable. Low temperatures in general cause the isomerization to proceed slowly, while high temcreasing the contact time, or by a combination of peratures tend to cause dehydrogenation orcracking or polymerization or several of these undesirable side reactions. Suitable pressures are in general of the order of atmospheric or moderately above, for example, '7 to 100 p. s'. i. absolute. Low pressures necessitate larger volumes ,yof catalyst and apparatus for a given contact" time, high pressures favor undesirable polymerization Contact time depends greatly on temperature and the nature of the catalyst, and may vary -i'rom less than a second to several minutes, shorter contact times resulting in less complete ison'ierization while longer contact times favor undesirable side reactions. Under conditions of pressure and temperature favorable to the isomerization of normal olefines, there is no appreciable isomerization of aliphatic and alicyclic hydrocarbons. The extent of isomerization produced will depend on the desired composition of the cracked possible yield of pentadienes is desired, isomerization will be conducted until equilibrium is substantially reached. If it is desired to increase the yield of pentadienes without reaching its maximum, the isomerization will be conducted .so as to isom'erize the straight chain olefines only partially.

A change in the degree of isomerization may be caused by changing the catalyst or by by-passing amounts of iron.

rapid coke formation such as copper oelrtaining these methods.

The degree of isomerization of a normal olefinic feed may be determined by any of the standard methods, for example, by the change produced in its octane rating since it is well known that the branching of carbon chains increases the octane number of hydrocarbons.

Another indication of the extent of isomerization is obtained by the relative proportion of C4 and C5 hydrocarbons in the cracked products. Isomerization decreases this proportion, i. e. isom- -erized olefines yield on cracking a relatively larger amount of C5 hydrocarbons in the C1-C5 cut.

Thus the degree of isomerization may be measured, regulated, and controlled by the relative ratio of butadiene and pentadiene, or of Ce and C5 hydrocarbons produced by cracking, or by the octane number of the isomerized olefines, or by other suitable indices.

The first two methods or any other based upon the properties of the cracked products are pro!- erable as they allow compensation for irregulanb ties of the feed by varying the degree of isomerization so as to maintain a steady production.

The vapor phase cracking step of this process is conducted so as to gasify 15% to of the feed per pass. We define as gasified that part of the cracked products which consists of molecules having less than six carbon atoms. The

cracking temperature, 1. e., the maximum temperature to which the cracking stock is heated, 18,

pressures of about atmospheric or below, and

preferably not substantially above to .p. s..i. Thus, pressures above atmospheric sufficient to overcome the resistance of conduits, condensers, and other equipment which follow the cracking zone may be maintained therein. If desired, the cracking may be conducted in the presence of steam, nitrogen and other substan tially inert gases and the concentration of such gases may vary from traces up to 95 mol per cent of the mixture.

The heating of the hydrocarbons to the crack-- ing temperature may be achieved by contact with a heated surface, for example in an externally heated coil, or in a preheated brick checker work, or by admixture of hot, substantially inert gases, or by a combination of these methods. The rate of heating should be as high as to avoid undesirable side reactions at the intermediate temperatures. In order to avoid destruction of dienes formed in the cracking, the cracked product should be quenched rapidly from the cracking temperature down to safe temperatures, mi erably below about 400 C.

In orderto prevent excessive coke formation in the cracking zone, it is often preferred that this zone be constructed of non-ferrous metals or alloys containing less than predominating Materials which do not cause alloys, e. g., aluminumor phosphor-bronze, or refractory ceramics, are thus preferred in the constructionof surfaces which are exposed to hydrocarbons at cracking temperatures.

Cracking according to this invention is preferably purely thermal, i. e. non-catalytic, and is conducted in the absence of catalyst, be it added catalysts such as gaseous haicgenated compoimds, solid catalytic metals or oxides, or

, cracking temperature is raised. The real velocity .of the gaseous hydrocarbons in the cracking zone is very dlfllcult to' determine accurately, because the volume the cracking stock changes rapidly under the cracking conditions. Therefore, in defining this invention, we prefer to utilize the concept of liquid space velocity which is the liquid volume of the feed delivered to the cracking zone per volume of said zone per hour. The crackin zone is defined as the space occupied by gas in which the temperature is within C. of the maximum cracking temperature. Liquid space velocity can be accurately measured, and, for a given pressure. temperature, and dilution, determines the real space velocity of the vapors.

The cracked products thus obtained comprise dienes as well as many other gaseous and liquid hydrocarbons. These products may be withdrawn, treated, separated and used as may be desired but it is advantageous to prepare and utilize certain portions thereof as follows.

The cracked products are subjected to fractional distillation to produce a light gaseous fraction substantially free of C4 and heavier; a Cr-Cs fraction rich in and containing substantiallyall the butaand penta-dienes; a cracked naphtha or a middle oil fraction or both; and

tars.

The first and last of these fractions, 1. e. dienefree gases and tars, are preferably withdrawn.

The CeCs fraction is treated to separate there-.

from the dienes by conventional methods.

The cracked naphtha has a compositionvarying with the intensity of the cracking, i. e., it

may substantially retain the composition of the cracking feed, or it may have become more or less aromatic. 1

If the cracking is relatively superficial, i. e., the

'g'asiflcation per pass is of the order of for example, 15% to 40% and preferably 20% to the ungasified portion oi the cracking stock 50%, but this is ingeneral less desirable as'it produces aromatics insmall. though appreciable amounts whichare sumciently large to be objectionable in cracking, yet not large enough to make their recovery desirable.

The naphtha fraction may also contain p013- oleflnes having six and morecarbon' atoms. These hydrocarbons maybe desirable in themselves; on

the other hand, they may interfere, for example,

in the cracking because of their tendency 0. polymerize, or inthe recovery of aromatics with the aid of selective solvents because oi their solubility therein which comes close to that or aromatics. It is thus often desirable to separate and eliminate them. a

Our process is illustrated in the accompanying drawing which represents a simplified flow diagram of an embodiment of this invention.

For simplicity, the drawing does not show pumps, tanks, heat exchangers, valves, by-passes,

vents, reboilers, condensers, coolers; and other auxiliaries, the proper placement of which will be at once evident to those skilled in the art.

A paraffinic hydrocarbon mixture is introduced from storage, not shown, into zone I wherein a distillate oil rich in normal mono-oleflnes is prepared and withdrawn through line 2. The preparation of these mono-oleflnes in zone i may be conducted substantially as described in the above-mentioned Van Peski U. S. Patent No. 2,172,228. Oils rich in, e. g., comprising 5.0%.or more of, normal mono-oleiines may also be pro-v duced in any other suitable manner and be admitted from a source not shown through line 3. which jolnsline 21' The mixed fluids are led through line 2 into isomerization zone 4 wherein they are treated under iscmerizing conditions in the presence oi a' suitable catalyst. This isomerization may be conducted substantially as described in the above.- mentioned Han Hoog,-U. 8. Patent No. 2,217,252.

The degree of isomerizationmay be controlled 4 by regulating the temperature of Jacket 5. This is still predominantly composed of mono-oleilnes.

It is advantageously recracked and treated like the original cracking stock, for example by recirculation as part of said stock.

If the cracking is deep, 1. e., the gasiflcation is of the order of 65%, for example 50% to 85%, and preferably to 70%, the naphtha fraction of the cracked products may contain substantial amounts of aromatic hydrocarbons which apparently are formed by secondary reactions such as polymerization or condensation of the primary products. In this case, it is advantageous to separate valuable aromatic hydrocarbons such as benzene, toluene, styrene, etc., from the naphtha fraction and, if desired, to further crack the re- 'maining mono-oleflnes. This latter procedure;

1. e., the deep cracking, is often preferable because the cracking yields in the gaseous products per temperature may. for example, be regulated by suitable means not shown, so as to produce a most convenient or desirable proportion of butadiene and penta'dienes. Lowering the temperature of zone 4 reduces the extent of isomerization and increases the yield and proportion of butadiene, while increasing this temperature increases the isomerization, thereby raising the yield and proportion of pentadienes.

v The isomerized or partially isomerized oleflnes are obtained through line 6.

scribed may be preferably admitted through line B and commingled therewith; g

r The mixed fluids, preferably in vapor form, are led through line 6 into cracking coil I in turnace 9 in which the desired conditions of tem perature, pressure, and residence time are maintained, for example at 700 0., atmospheric presa source not shown, and are separated from tars overhead through vapor line l5.

products are withdrawn from the system throush and other relativelyheavy materials in iractional distillation column IS. The lighter products, including gases and naphtha, are taken The heavier line I1.

.The. products in line I! pass into stabilizer ll.

I Suitable recycle stock obtained in the process as hereinafter dewherein an overhead fraction consisting essentially of C5 and lighter components is separated from a heavier naphtha fraction; the latter, substantially free of C5 and lighter components, is

- taken through-line 2| and may go through line 23 to storage not shown, or preferably may serve as recycle stock which is returned through lines 25, 8 and 6 to the cracking coil 1. If the-cracking shod: is composed of hydrocarbons substantially heavier than Cs, it is advantageous to also eliminate from the recycle stock those compoor by polymerization with or without suitable catalysts such as poly-oxy acids, e. g., H2804, HsPOi, etc., or Friedel-Crafts catalysts, or by the Dials-Alder reaction involving the use of maleic anhydride-type reagents, etc.

The overhead C5 and lighter fraction from stabilizer i9 is taken through conduit 29 to a fractionating system wherein it is subjected repeatedly to fractional distillation. In column 3| a bot-- tom fraction is produced comprising predominantly hydrocarbons having five carbon atoms, which is taken through line 83, and a lighter fraction substantially free from C5 components. The latter is taken overhead through line to ira'ctlonator 31, where a bottom fraction comprising predominantly hydrocarbons having four carbon atoms is produced and withdrawn through line 33. Remaining gases substantially freefrom C4 and heavier components are withdrawn overhead throimh line 4!.

Thus, separate C3 and C4 fractions are takenthrough lines 4| and 33, respectively.

The C4 fraction which contains butadiene is led through line 39 to column 43, wherein it is sublccted to extractive distillation with a suitable solvent having a relatively high boiling range and greater solvent power for butadiene than for butylenes and butanes. This liquid is supplied to the top of extractor 43 through line '45 and is contacted with the ascending Ci vapors so as to produce a fat solvent chargedwith substam I tially pure butadiene. This fat solvent is eliminated from the bottom of the column 43 through line 41. This fat liquid is separated by fractional distillation in fractionator 49 into the lean solvent and butadiene. The hutadiene so produced is withdrawn through overhead line "5 I while the lean solvent. is drawn off at the bottom through line and is returned to extractor 43. The butylenes and bulanes separated from the butadiene in column 43 are withdrawn through line 53. The large proportion of olefines in this fraction makes it valuable for the manufacture of polymer or alkylate gasoline.

The C5 fraction, rich in pentadiene, is given a treatment similar to that of the C4 fraction. Line 83 leads it to column 55, wherein it is extracted in the vapor phase by a lean solvent supplied through line 51. The resulting fat solvent is drawn off through line 52, and the residual pentones and amylenes are withdrawn through line 8|. The fat solvent is fractionallv distilled in fractionator l3 to isolate pentadienes which are withdrawn through line 68, while the lean solvent is recirculated through line 51.

Suitable solvents tor the vapor phase extraction of dienes include, forexample, alcohols such :as butyl alcohols, amyl alcohols, cyclohemnol, etc; aldehydes such as furfural. or. benzaldehyda eta; ketones such as acetone, methyl ethyl ketone, methyl propyl ketone, acetophenone. cyclohexanone; others such asdi-isopropyl ether, dichlorethyl ether, dioxane; organic nitrogen bases such methods-such as fractional and as aniiinetoluidine, phenyl hydrazine, ethylene diamine. ethanol diamine; phenols such as phenol, cresol, xylenols; esters such as ethylene chlorhydrin, dimethyl phthalate, diethyl. tartrnte, ethylene dichloride, lactic acid nitrile, acetonitrlle, di-isopropyl or ally] sulfate, ethyl borate or ethyl orthosllicate; other organic derivatives or mineral acids such as nitrobenzene, nitromethane, nitroethane, and many other polar oompouniis.

The recovered pentadienes usually comprise a mixture of isoprene (2-methyl butadiene), piper.- ylene (n-pentadiene) and cyclopentadiene. This mixture may be either withdrawn through line 51 or, if desired, maybe further fractionated to separate the several Cs dienes from one another by leading it through line 69 to zone ii, wherethe cyclopentadieneis dimerized by subjecting the -mixture to moderate heat in the liquid phase The resulting product is fractlon'ally distilled-the dimer forming the distillation residue which is taken through line I3 tobe withdrawn through line 15, or to be regenerated by exposure to high temperature and vacuum in a depolymerizlng zone 79, to which line Tl leads. The vapors of the acyclic pentadienes are removed from the dimerization zone H through line a I, and may be further separated in iractionator :83 to produce isoprene which is taken overhead through line 85 and piperylene, which is obtained at the bottom, through line 81. v The process as illustrated in the'drawine can also be carried'out in a difl'erent manner if desired. The cracking in coil I may be intensified, for example, by reducing the space velocity to about 40 under the same conditions of Pressure and temperature, so as to obtain a 'gasificatlon of about 65%. The naphtha fraction produced under these circumstances and taken through line 2| from fractionator 19 contains aromatic hydrocarbons.

These valuable hydrocarbons may be and the recycle stock recovered by convenient extractive distillittlGIL or liquid-liquid extraction, or both. Fbr example, the liquid withdrawn through line 21 is led through line either to be discardedor further-treated as will be described.

, The or and Crfractions thus separatedarenich in benzene and toluene, respectively. The Ca fraction is conducted through line '93 to column in: wherein it is it extractive distillation with a lean selecti ,e'solventtor aromatics introduced flinoughp f5. fat solvent rich in benzene leaves through 1mm the residual Co hydrocarbons arewlthdrawn overhead through line 139,01; may be returned -to the cracking coil 1 ,lines 25,-! and c. The

83 and preferably through zone s eared fat solvent is fractionally distilled in fractionator Ill so that the lean solvent is recovered asthe bottom fraction andreturned through line lot-to extractor ll,-and the benzene is obtained over-;

head through line ill.

The gaseous C1 fraction is conducted through line "to column I I twherein it is extracted with a lean solvent forl aromatics introduced through line H1." The fat solvent rich in toluene leaves through line H0, and the residual C1 hydrocarbon's are withdrawn overhead through line HI and may be returned to the cracking coil 1 through lines' 2! and 0. The fat solvent is fractionate'd in'fractionator I23, so that the lean solvent is recovered as the bottom fraction and is through line II! to extractor H5. 'The toluene is obtained overhead through line I25.

" Suitable solvents for the recovery of aromatics by extractive distillation are, for example, phenol, cresylic acids, alkyl phenol mixtures, aniline, alkyl aniline's, diphenyl amine, ditolyl amines, carbitols ('diethylene glycol mono-others) such as methyl," eth'yLand propyl carbitols, chlorinate'dfdialkyl ethers such as betabeta-dichlorethyl ether, nitrobcnzenefnitrotoluene, nitroxylenes, naphthols, ali'yl haphthols, benzo Phenone, phenyl tolyl keacids, dichlorethylether, antimony trichloride, SO: benzene mixtures, or combinations of solvents and anti-solvents such as phenol or cresol' .liquid extraction in extractor I20, as described: or,

alternatively, if desired, the liquid-liquid extraction step may be replaced by further fractional and extractive distillation of the several fractions.

The separation of butaand pentadienes may be conducted as described above by extractive distillation or other vapor phase extraction with similar solvents; or by azeotropical distillation in the presence of anhydrous ammonia, methylamine, 00:, lower alcohols, etc,; or by liquidliquid extraction with acetone, furfural, aniline, phenol, etc.; or through formation of complex compounds with copper or silver salts, 80:, .etc.:-

or by polymerization under the influence of heat,

tone, diphenyl ketone, alkyl phthalates such as dlmethyl phthalate, alkyl salicylates such as methyl salicylate,*benzyl alcohol; benz chlorides; i."e., benzyl, benzal, and benzo chlorides, benzonitrlle, 'diphen'yl oxide, ditolyl oxide, hydroxy pyridine, nitropyridine, chlorinated pyridines', quinoline, isoquinoline, chlorinated quinoline, hydroxy quinolines, 5-n'itro quinoline, tetrahydrofurfuryl alcohol, furfural alcohol, furfural, the

mono glycerol others, such as l-methoxy. glycerol,

2-methoxy glycerol, l-ethox glycerol, 2-ethoxy glycerol, l-propoxy glycerol, 2-propoxy 'glyoerol,

- l-isopropoxy glycerol, z-isopropoxy glycerol; the

glycerol diethers such as 1,2-dlmethoxy glycerol, LS-dimethoxy glycerol, l,2-diethoxy glycerol, 1,3- diethcxy g ycerol, 1,2-dipropoxy glycerol, '1,3-di-. propoxy glycerol, 1,2-di-isopropoxy glycerol, and 1,3-di-isopmpoxy glycerol; the mixed diglycerol ether esters such as l-ethoxy, 2-methoxy glycerol, l-methoxy, 3-propoxy glycerol,.and l-ethoxy, 2-

isopropoxy g cerol.

pressure, light, or catalysts such as Na, K, H2804, HaPQa, P205, A1013, etc.; or a combination thereof.

It may sometimes be preferred to separate the dienes or the aromatics, or bothfiwithout prefractionation or following a degree of fractionation less thorough than described. Alternatively, it may also sometimes be desirable to produce a sharper fractionation before further recovery, or to use directly fractions rich in 'dienes or aromatics, or both, produced by very sharp fractionation.

The following examples illustrate this process;

, Example I A normal-olefin distillate was obtained by cracking wax in the'vaporphase at about- 560? 152. Part of this cut was iso'merizedover "Nalco' No, 300 catalyst composed mainly of silicon.

magnesium, aluminum and oxygen at a temperafractionator' 81 obtained through line l0! con-' tains aromatics. The latter are preferably sepstated by liquid-liquid extraction with a liquid having greater solvent power for aromatics than for oleflnic hydrocarbons, for example liquid $02. For this purpose, the hydrocarbon liquid is delivered through line l0! to extractorv I28 wherein it is extracted with liquid SO: entering through conduit Ill. The rafilnate passes through line "I to a stripper I32 wherein it is stripped of dissolved 80: and thence is preferably returned to the cracking coil 1 through lines I34, 8 and 0. The extract containing aromatics .is conveyed from extractor I28 through line I36 into separa, tor Ill wherein a bottom fraction comprising mainly SOs-free aromatics and an overhead fraction of 80: are produced. The aromatics are obtained through conduit I40 while the S0: is taken overhead through line I42 to beliquefled in' cooler I together with the SO: taken from stripper it: through line m. The liduefled so: is then 182113061109! through conduit I28 into extractor Other solvents suitable for the liquid-liquid extraction are, for examplanitrobenzene, methyl acetate, phenyl acetate, methyl or ethyl cellosolve, furfural. acetone, aniline, phenol, cresylic ture of 472 C. to 480 C. and at a liquid space velocity of 5 volumes of olefines per volume of catalyst.

" Both olefinic stocks, 1. e., the unisomerized and the isomerized, were cracked at a temperature of 4 750 C. in a phosphor-bronze tube filled with quartz chips and the cracked products analyzed. The following table shows the results obtained.

Unisomerm Isomorizod Liquid space velocity 128 148 Gasiilcatlon percent. 67 59 Composition of the gas phase:

Hr eight percent. 0.3 0. 2 CH "410.-.- 7. 0 7. 2 C2H| d0- 29.6 8.7 CrHs.-. d0 4.5 3.0 03H. .10.... 22.2 13.3 01H! 1.2 0.6 0 H; butadleno. do.- 0. 6 4. 9 ISO-C4 g 0..- 0. 9 11. 6 llCrHg .0" l1. 6 l4. 2 041110;; 0. 2 3. 2 05H: pentadleno. 0.... 3. 0 8. 7 H10"; 8. 7 22. 8 OlHnm; 00.-.- 0.9 6.1 Total (lienes l3. 5 13. 6 Ratio 0 dieIlBS/Cs dienes 2. 46 0. 56

It will be noted that the isomerization'not only modified the proportion of pentadienes, but also increased the yield of iso-oleflnes and of higher olefines.

While the process of the present invention is hereina-bove described with special reference to normal oleiines for which it is particularly useful and suitable, the principle of isomer-1mg may be applied with proper variations to other cracking feeds such as, for example, waxes and other hydrocarbons which predominate instraight chain molecules 'or naphthenic fractions containing cyclopentane derivatives. In the case of straight chain hydrocarbons isonierization is conducted to produce a branching, while in the case of naphthenes it is conducted to convert fivemembered to six-membered rings, in both cases resulting in an improvement in the dioleflne yield.

We claim as our invention:

1. An improved process for the production of dienes from normal mono olefins containing from 6 to 12 carbon atoms to increase the proportion of C dienes comprising the steps of isomerlzing .said'mono oleflns to produce branched chain olefins, non-catalytically cracking the isomerized product in the vapor phase at a temperature between 650 and 850 C. and at a pressure below about 150 p. s. i. for a time to gasify to 85 per cent thereof to produce dienes, separating C4 and inthepresenceofactivatednluminatoprcducgbranched chain oleflns, non-catalytically-crackm the isomerizcd product in the v por phase at ajtemperature between 650 C. and 856 G. and at a pressure below about 150 p. a. i. for a: time to gasify 15 to 85% thereof to produce dienes, fractionating the cracked products tol form alight fraction of hydrocarbons having-not: more than 6 carbon atoms and a heavier fraction? having the same boiling range as said isomcrioed product, removing Q and Cs dienes from me; light fraction, selectively removing polyoleeflnefrom said heavier fraction, solvent extracting withliquid sulfur dioxide the resulting polyoleiin free heavier fraction, and recycling the resulting aromatic-free and polyolefln-free cracked products to said cracking stepto produce more dienes;

3. An improved process for manufacturing dienes from a hydrocarbon distillate predominate ing-in normal mono-oleflns having 6 to 12 carbon atoms whereby the proportion of pentadienes ob tained is increased, comprising the steps of-isomerizing said distillate to produce branched chain: oleflns, non-catalytically cracking in the vapor phase at a temperature between 650 C. and 850? C. and at a pressure below about 150 p. s. i.- a nor-- mally liquid mixture of said isomerized product and a. recycle oil produced in the process for a I time to gasify 15 to thereof to produce diaries,- separating from the resulting cracked products at least the following fractions: a diene fraction,

- said recycle oil which is substantially free of tarry isomerizing said fraction of normal mono-olefin aromatics and normally gaseous components, and

a tarry fraction.

RUPERT C. MORRiS. ROBERT J.- MOORE}.

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