US2642466A - Production of olefinic hydrocarbons - Google Patents

Description

June 16, 1953 P.. 1GARNER Erm.

PRODUCTION OF OLEFINIC HYDROCARBONS Filed June 9, 1950 l gl R E A G 5M E E wem J .E Vm m PY Mmmm mi w T T N Wh m w Patented June 16, 1953 PRODUCTION OF OLEFINIC HYDROCARBONS Philip James Garner, Booten, `Wirral, 'and Sidneyl .Edgar Miles, Mold, England, assignors to Shell Development Company, San Francisco, l(laliik, a

corporation of Delaware Application June 9, 1950, Serial No. 167,052 In Great Britain July 28, 1949 Il Claims.` (Cl. 2GB- 683) This invention relates to a process for the production of olefinic hydrocarbons, and more particularly to a process .for the thermal kcracking of high molecular weight parafnic hydrocarbons, such as paraffin wax, to yield mixtures of olenic hydrocarbons including various longchain olenes, as for instance thosecontaining fifteen or more carbon atoms per molecule.

Ihe thermal cracking of paraiiinic hydrocarbon waxes and waxy .materials has been known yand practiced for some time, in accordance with the teachings of the Van Peski U. S. Patent No. 2,172,228. The range of unsaturated aliphatic hydrocarbons produced .thereby individually yor in admixture nds application in the synthesis of a variety of useful commercial products, Waxes of various types have been the subject of such cracking conversions, the paraffin wax-containing materials being particularly valuable as cracking stock. Such materials may, for instance, include waxy material recoverable from a rmineral oil distillate or residue by chilling and pressing or by known solvent extraction processes, such as solvent dewaxing of parafnic waxy mineral oils and fractions thereof. As cracking stock, purified products are not essential, Aand Avaluable hydrocarbons can for instance be obtained from a slack wax derived by solvent extraction of ,a waxy mineral lubricating coil.

In the treatment of a parafn wax-containing mineral, as for instance slack wax, to vobtain olenic hydrocarbons having at least ve carbon 'atoms in the molecule, vapor phase cracking is effective, and to this end vthe material is subjected to preliminary vaporization in a flash evaporator unit at a suitable temperature which generally is just below 500 C. Thereafter cracking is effected in the vapor phase at between l500" C. and 600 C. under moderately elevated pressures up to about 60 pounds per square inch to yield the desired olenic materials.

It is frequently found, however, that only a fraction of the initial material undergoes evaporation in the flash evaporator unit, and is much as 20 to 50% of the material may remain as a residue, herein referred to as evaporator residue. From the standpoint of the efiicency of the cracking operation such an evaporator residue is a marked disadvantage, and the more so because such evaporator residue is not itself a product of much commercial value. Accordingly any steps which minimize the amount of evaporator residue and increase the volume of hydrocarbons passing to the cracking furnaces,

therebycenha-ncing v:the yield `of cien-nic hydro-carbons, constitute la most Vdesirable technical advance in this ,particularfield It is, therefore, :a pri-ncipalobject of the pres- -ent invention to improve the overall eiciencyof thermal cracking operations -for the conversion of higher molecular weight hydrocarbons to 'oleiin-ic material. -A more specific yobject is to l:provide a process .adapted to eiect a more complete conversion of waxy hydrocarbons and waxyhydrocarbon .fractions to olenic hydrocarbons suitable for the synthesis of valuable commercial products. Astill more specific object -is to .provide an improved process for the more complete conversion of l-waxy hydrocarbon materials to 7oleflnic .hydrocarbons which are largely -of ari-alphaolenc character.

The foregoing Aand -other 'objects and the .Inanner of .their accomplishment will be more'f-ully understood from the following description ofthe invention, lwhich will be made with reference to the accompanying drawing, constituting a part of the specification, which drawing comprises a single figure representing schematically the method and apparatus for carrying out the thermal cracking of waxy hydrocarbon materials in accordance with 'the invention.

It has now been found `that an lincreased yield of olenic lhydrocarbon-s is obtained bythe thermal phase cracking of waxy hydrocarbon Inaterials in accordance with prior practice, when the evaporator residue, 'resulting from the usual evaporation of the waxy stock immediately preceding the Vthermal lvapor phase cracking, is subjected in the liquid phase to a temperature between about 390 C. fand 450 C. for a period of time varying from about four hours to one quarter of an .hour--which thermal'treatment is hereinafter generally referred to as soaking or thermal soaking of the product-thus so modifying the nature of the residue that on further flash evaporation thereof Afurther amounts of material are vaporized and .may be 'effectively subjected to vapor phase thermal cracking to produce olenic hydrocarbons, and the residue finally remaining is substantially reduced, say to an amount which is between one-twentieth and one-tenth of the amount of the original feedstock.

Since the essentialfeature of the present invention is the thermal soaking of that waxy material which is not normally volatile when flashed in the evaporator up to 500 C., such thermal soaking may be applied either to the initial wax feedstock, to a combination of fresh feedstock and recycle feedstock (that is to say, volatile uncracked or partially cracked hydrocarbon material which has been condensed in a fractionator and separated from the desired cracked olenic hydrocarbons), or to the evaporator residue. However, since. the evaporator residue is of smaller bulk than the other materials, it is preferred to subject only this material to the said soaking treatment since smaller capacity equipment is thus needed. Furthermore, it has been found that products yielding a higher proportion of valuable olenic hydrocarbons on cracking are obtained by soaking the evaporator residue without vadmixture of fresh wax feed or fresh wax terial, ata temperature in the region of 500 C.

to 600 C. includes the step of subjecting at least that part of the feedstock which is not initially vaporizable when ashed 'with or without steam `at temperatures just below 500 C. to a thermal soaking, namely a heat treatment at between 390 C. and 450 C. for a period of'4 hours to 1A; of an hour.

In accordance with a preferred embodiment, the invention comprises in a vapor phase thermal cracking of a hydrocarbon slack wax at a temperature intermediate of 500 C.Y and 600 C., the step of subjecting at least that part of the feedstock which cannot be'readily initially vaporized in a flash evaporator at 480 C. to 500 C., to a thermal Soaking, namelyla heat treatment at a temperature of from'about 400 C. to 440 C., and preferably between 405 C. and 425 C., for a period of time of from about 2 hours to l hour, the longer period of soaking being applied at the lower temperature. g Y v In the preferred method of practicing the present invention the' vapor phase cracking of the'hydrocarbons is effected in the presence of superheated stem which vmay be, and preferably is, v-

present in the flash evaporator and the flash evaporator residue is subjected without admixture with initial feedstockmaterial or recycle feedstock to the foregoing specified thermal soaking treatment after which it is subjected to vaporizing treatment in the flash evaporator with further amounts of fresh feedstock and/or recycle feedstock.

'The invention will now be further illustrated by reference to the accompanying diagrammatic drawing which shows a plant for `cracking slack wax'in accordance with theA novel process. The plant represented' in the drawing comprises a furnace 'I I with a preheating coil I2 and a cracking coil I4, a soaking tank I 5, lashevaporator I6 rand a fractionatorV I'I.

Fresh feed of slack wax comprising Colon (Venezuela) 'residual slack wax at a temperature of about 100or C. is introduced through the pipe I9 at the bottom of the fractionator I1 wherein it mixes with hot recycle feedstock, and the mixture at 340 C. to 360 C. into which steam may be injected ows through pipe 20 to the preheating coil I2 in the furnace II, where its temperature is raised to about 480 C; to 500 C. Then'ce it is passed' vby a'pipe ZI to the flash evaporator I6 whereit mixes with preheated steam initially 'at a temperature of about 440 C. and a pressureof 60 to `90 pounds per square inch (gauge) illimduced into evaporator IB through the pipe 22. The mixture of the resulting vaporized hydrocarbons and steam then passes through the pipe 24 to the vapor phase cracking coil It in the furnace I I where the temperature is about 540 C. to 560 C. and where cracking takes place in about 15 to 25 seconds. The mixture from the cracking coil I4 passes Via the pipe 24 to a fractionator I1 and receives an admixture of quenching Water from the pipe 25 to assist condensation. A mixture of oleinic hydrocarbons is withdrawn from the top of the fractionator I1 and condensed hydrocarbons (re-cycle feedstock) are recycled with fresh feed admitted via pipe I9. The plant pressure is maintained at from about l0 to about 25 pounds per square inch gauge.

The evaporator residue which accumulates in the base of the evaporator I6, is passed via a pipe 26 through Ya coil 21 in the furnace I I to the soaking tank I5. The volume of this tank I5 and the conditions in coil 21 are so related to the throughput rate of the plant that the required soaking conditions are established in this tank, for ex ample 2 hours residence at 410 C. The soaked residue leaves the tank vI 5 through the pipe 2t and joins the stream of material in the coil I2.

A pipe 30 leading from the base of the soaking tank I5Vis used to bleed off continuously a quantity of evaporator residue equivalent to from about 5% to about 10% of the fresh feed. The exact quantity thus bled off is adjusted to be the minimum consistent With the prevention of coking and may generally be regarded as Waste; in some cases, however, it is convenient to subject it to a soaking treatment in a location other than that of the continuous process described above. Bled-off residue soaked in this way is preferably accumulated in a storage vessel until a convenient quantity has been obtained for soaking treat ment; this soaking is thus carried out as a discontinuous or lbatch treatment.

Valved" lines 3| and' 32, provided with valves Atil and 35, respectively,'and valves 36, 3'? and 39,

in lines '26, 20 and I9, respectively, make it possible to pass either fresh feed from the line I0 or a recycle feed from the line 20, or mixtures of these two, as well as evaporator residue, to the soaking tank I5, by'means of valve manipula tions which are evident from the drawing.

vSince the placement of required pumps, temperature recorders and controls, other valves, level controls and the like will be evident to one skilled in the art, various auxiliary equipment has been omitted from the drawing. V V l It will be readily understood that the process described above may be modified by allowing the evaporator residue to accumulate either in the evaporator or in a suitable storage vessel and then to carry out the soaking as a separate operation distinct from the'main cycle of operations, for example in a separate apparatus.

The advantage derivedfrom the thermal soaking step of the present invention is illustrated by the comparative results obtained in the vapor phase thermal crackingof vaporizable material obtainable from soaked and unsoaked evaporator residues produced in a plant cracking operation using a waxy feed stock comprising a Colon short residue slack wax. From the pertinent data, whichiare given in Table I, it can be seen that the soaking of the evaporator residue reduced substantially the final residue which had to be discarded as Waste,

TABLEI Eiect ,of thermal soaking on caporizatton of evaporator .residue Run N'O 1 `2 3 '4 Feed Colon Eyaporator Residue Unsoaked -ISoalnei'l Evaporator level cm 8 '25 '25 "B Vaporizer temperature C.. 490 476 488 482 Evaporator bottom temp.v1 C. 424 '425 425 'i123 Unit pressure p. si. g-- 20 20 2U Steam/hydrocarbonratio w../w l.0:0.20 1:0.21 1:0.23 1;0.722 Residue as'percent on feed 75 57 36 45 1 Temperature of liquid-in evaporator. Y

The conditions of soaking the evaporator resi- 1 Mol. wt. calculated from refractive index and melting point.

The soaked residue had the appearance of heavy fuel oil, but it still had a denite set period. An increase of 30% in the residence time produced a material which was still liquid at room temperature.

When the steam/hydrocarbon vapor products of runs l and 4 (Table I) and equivalent steam/hydrocarbon vapor product produced from fresh Colon slack wax feed were thermally cracked separately and under similar conditions to produce olenic hydrocarbons, and the respective cracked products were quenched and fractionated, and the Cla-Cm cracked "distillate fraction was separated therefrom, the results were as given in Table III. Data are 'also included for similar runs using soaked and unsoaked Concepcion evaporator residues.

alpha-olefin content of c. d. fresh Colon wax run The material increase in the C9C1s cracked distillate product from the soaked evaporator residues, While maintaining comparable bromine numbers and alpha-olefin contents as compared with the unsoaked evaporator residues is apparent from the tabulated data in Table III. At the same time the alpha-olefin content is as much s 'about 60% of wmat it is for the fresh waxy According to `a. further modification of fthe process of this invention there is introduced into the `soaking tank selected hydrocarbon fractions with the object of establishing therein equilibrium conditions which tend toproduce larger amounts of products subsequently vaporizable for the desired cracking operation. yThus hydro carbon fractions of gasoline boilingr range may be introduced to increase the yields of waxy products suitable for vapor phase cracking from the material undergoing soaking. `Since this modied technique involves maintaining sufficient pressure in the :soaking tank to keep the more volatile hydrocarbon gasoline boiling range fraction liquid, it is generally more conveniently carried out With batchwise soaking.

The additional cracked unsaturatedv hydrocarbons which can be made available by subjecting the initial :feedstock or evaporator residue to a thermal soaking as specified above Withythe subsequent .application of vapor Iphase cracking conditions to the material so treated constitute a range of `products of very considerable value and interest in a diversity of syntheses of interest both in the chemical and petroleum fields. The nature of these additional unsaturated products may perhaps differ a little from those obtained by the vapor-phase cracking of the untreated initial waxy feedstock but the differences, if any, do not detract from their value as raw materials for various commercial manufactures.

Although the improvement upon which the present invention is predicated may be applied in general to any evaporator'residues resulting from the vaporization of waxy `hydrocarbon materials to produce hydrocarbon vapors suitable for vapor phase thermal cracking to olenic hydrocarbons, the usual distillate waxes are generally substantially completely vaporzable under the indicated evaporator conditions. However, even then the more diicultly vaporizable residual material resulting from the vapor phase cracking of the vaporized distillate Waxes may be advantageously subjected to the soaking treatment in accordance With the invention. The invention is particularly applicable to hydrocarbon stocks containing those higher boiling, higher molecular weight, parafhnic hydrocarbons such as the isoor branched-chain paraffin hydrocarbons which are not suiiiciently branched in character to constitute material suitable for lubricating oil manufacture. Such isomeric paraflin hydrocarbons are characteristic components of petroleum residual slack waxes.

The invention claimed is:

1. In the process for producing olefinic hydrocarbons by vapor phase thermal cracking of waxy hydrocarbons wherein a paraffin Wax-containing material is vaporized substantially at a temperature belo-W about 500 C. and without substantial cracking thereof and thereby is separated from a dilcultly vaporizable fraction `and the vaporized portion is subjected to thermal cracking in the presence of steam at la temperature in the range of from about 500 C. to about 600 C., the improvement which comprises the steps of subjecting at least a substantial portion of the separated diflicultly vaporizable `fraction to a thermal soaking at from about 390 C'. to -about 450 C. for a period of time of from about 1A of an hour to about 4 hours, thereafter subjecting it to the aforesaid vaporizing operation, and subjecting the resulting vapor-.ized portion to theafresaid'-vapor phase thermal cracking operation. f

2. In the processfor producing olefinic hydrocarbons by vapor phase thermal cracking of waxy hydrocarbons wherein a paraffin wax-containing material is vaporized substantially at a temperature below about 500 C. and without substantial cracking thereof and thereby is separated from a diiicultly vaporizable fraction and the vaporized portion is sub-jected to thermal cracking in the presence of steam at a temperature in the range of from about 500 C. to about 600 C., the improvement which comprises the steps of subjecting at least a substantial portion of the separated diflicultly vaporizable fraction to a thermal soaking at from about 400 C. to about 440 C. for a period of time of from about 1 to about 2 hours, after which the soaked material is subjected to the aforesaid vaporizing operation and the resulting vaporized portion is subjected to the aforesaid vapor phase thermal crackingopera tion. 3. A process for producing olenic hydrocarbons from parain Wax-containing material which comprises heating a petroleum residual slack wax to a temperature of from about 480 C. to about 500 C. and separating the heated material at that temperature and without substantial cracking thereof into a Vapor fraction and a dicultly Vaporizable residue fraction, subjecting the separated vapor fraction in the presence of steam to thermal cracking within the range of from about 540 C. to about 560 C'. for a period of time sufficient to effectively convert the vaporous hydrocarbons into olenic hydrocarbons Without substantial formation of coke therefrom, promptly quenching the cracked product vapors and fractionating and condensing the vapors, subjecting the separated diflicultly vaporizable residue'fraction from the initial vaporization to ,a thermal soaking at from about 390 C. to about l450" C. for a period of time of from about 1A; of an hour to about 4 hours, and combining the soaked residue with heated fresh feed material after which it is subjected to the aforesaid vaporizing operation and the resulting vaporizedportion is subjected to the aforesaid Vvapor phase thermal cracking operation to produce an additional quantity of oleflnic hydrocarbons from the initially diflicultly Vaporizable residue fraction.

4. A process for producing alpha-olenic hydrocarbons from a mixture consisting essentially Aof high molecular weight paraiiinic hydrocarbons,

including normal paraffin wax hydrocarbons and branched-chain parafn hydrocarbons, which process comprises heating said mixture to a temperature of from about 480 C. to about 500 C. and separating the heated material at thattern- Iperature into a vapor fraction and a dicultly vaporizable residue fraction, the residue fraction comprising a substantial proportion of high molecular weight branched-chain paraihn hydrocarbons, subjecting the separated vapor fraction inthe presence of steam to thermal cracking within the range of from about 540 C. to'about 560 C. to effectively convert the vaporous hydrocarbons into alpha-olenic hydrocarbons, prompty quenching the cracked product vapors and fractionating and condensing the vapors, subjecting the separated diilcultly vaporizable residue fraction from the initial vaporization to a thermal soaking at from about 390 C. to about 450 C. for a period of time of from about 1A; of an hour to about 4 hours, and combining the soaked residue with fresh feed mixture after which it is subjected to the aforesaid vaporizing operation and the resulting vaporized portion is subjected to the aforesaid vapor phase cracking operation to produce an additional quantity of oleflnic hydrocarbons from the initial diflicultly vaporizable residue fraction.

PHILIP JAMES GfARNER..

SIDNEY EDGAR MILES.

References Cited in the file of this patentl UNITED STATES PATENTS Number Name Date 2,008,550 Halloran et al July 16, 1935 2,172,228 Van Peski Sept. 5, 1939 2,374,338 Dunham Apr. 24, 1945 2,532,615 Ewell Dec. 5, 1950

Claims (1)

1. IN THE PROCESS FOR PRODUCING OLEFINIC HYDROCARBONS BY VAPOR PHASE THERMAL CRACKING OF WAXY HYDROCARBONS WHEREIN A PARAFFIN WAX-CONTAINING MATERIAL IS VAPORIZED SUBSTANTIALLY AT A TEMPERATURE BELOW 500* C. AND WITHOUT SUBSTANTIAL CRACKING THEREOF AND THEREBY IS SEPARATED FROM A DIFFICULTY VAPORIZABLE FRACTION AND THE VAPORIZED PORTION IS SUBJECTED TO THERMAL CRACKING IN THE PRESENCE OF STEAM AT A TEMPERATURE IN THE RANGE OF FROM ABOUT 500* C. O ABOUT 600* C., THE IMPROVEMENT WHICH COMPRISES THE STEPS OF SUBJECTING AT LEAST A SUBSTANTIAL PORTION OF THE SEPARATED DIFFICULTY VAPORIZABLE FRACTION TO A THERMAL SOAKING AT FROM ABOUT 390* C. TO ABOUT 450 C. FOR A PERIOD OF TIME OF FROM ABOUT 1/4 OF AN HOUR TO ABOUT 4 HOURS, THEREAFTER SUBJECTING IT TO THE AFORESAID VAPORIZING OPERATION, AND SUBJECTING THE RESULTING VAPORIZED PORTION TO THE AFORESAID VAPOR PHASE THERMAL CRACKING OPERATION.

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