US2945076A - Process for producing olefins - Google Patents

Description

July 12, 1960 w. A. PARDEE 2,945,076

PRocE-ss FOR PRoDucING oLEFINs Filed April l5; 1957 Pnocnss non PnonUcrNc oit-arms William A. Pardee, Fox Chapel, Pa., assigner to Gulf Research & Development Company, Pittsburgh, Pa., a corporation of Delaware Filed Apr. 15, 1957, ser. No. 652,946

s claims. (ol. 26o-m3) This application relates to a process -for producing olens and more particularly to a process for produclng normal alpha-olens by cracking paranic stocks.

Olens, particularly normal alpha-olefins, are often extremely desirable for use in many chemical reactions. For example, `a convenient land extensive use for olelins resides in the Oxo process wherein they are reacted withv hydrogen and carbon 'monoxideV in the presence of a catalyst, generally cobalt carbonyl, at high pressures and moderate temperatures to produce a product predominating in aldehydes having one more carbon atom than said olens. The aldehydes produced are often, in turn, hydrogenated to the corresponding alcohols. Since primary straight chain aldehydes and, particularly, the corresponding alcohols are extremely valuable commercially, it is apparent that normal alpha-olelins would be considered attractive as charge stock in the Oxo process.

In accordance with the present invention, paralnic hydrocarbons such as petroleum waxes, are subjected to well-defined cracking and recovery operations wherein a large conversion of said hydrocarbons to a product predominating in normal alpha-olens is obtained. At the same time, secondary reactions likely to result in the production of undesirable diolefns `and isomerization, polymerization, decomposition, etc., products are inhibited.

As an illustration of but one embodiment of my invention, -a :Elow diagram of the present process is shown in Figures 1, 2 and 3 of the drawings, which drawings Iare hereby incorporated in and made part of the present application.

A parainic charge stock is introduced into the system by line 2, preferably in the molten state at a temperature of about 200 to about 300 F. Prior to its introduction into the cracking zone, the charge can be joined by a recycle stream, described and dened hereinafter, in line .4. In order to vaporze the combined charge in line 6, Water is introduced in the system by line 8 and convertedv to steam in heater 9 by any convenient means, for example by gas burners, not shown, to a temperature of about 900 to about 1200 F. The temperature of the Vsteam should be high enough to vaporize kthe combined charge from line 6 but low enough to prevent appreciable cracking thereof before its entry into the cracking zone. The pressure of the charge in line 6 and of the steam produced in line 3, though not critical, should be suiicient to overcome pressure drop through the system. I have found that a pressure between about 15 to about 40 pounds per square inch gauge is sucient for such purpose. In order to obtain efficient and optimum vaporization of the charge stock and to control the contact time of the charge stock in the cracking chamber, the ratio of 'steam to charge stock is extremely important. In general at least about 2 percent byweight, and preferably -about 3 to about 40 percent by weight, of steam, based upon the total charge stock, is suicient to vaporize the charge stock satisfactorily and maintain the desired contact time. As charge stock any paraiinic hydrocarbon v asume Patented July 12, 1960 such as wax, natural as well as synthetic, is suitable, although a petroleum wax is preferred. It is `further preferable that the wax be substantially free of oil. While waxy materials containing up to about 41 percent by weight of oil have been used successfully, a preferred charge would contain less than about 16 percent by weight of oil. Best results are obtained using petroleum paraflfins having a melting point of about 130 to about 140 F. and an oil content of less than about one percent by Weight.

The molten charge stock and steam are combined in linelt) and passed through cracking chamber 12 wherein the vaporized charge stock is cracked and a hydrocarbon mixture predominating in C2 to C20 oleiins, in the present example, is obtained. In order to obtain satisfactory cracking in chamber 12, careful control of the reaction conditions therein is required. The temperature must be at least about 1000 F. in order to crack the charge stock at a reasonable rate, but should be maintained below about l250 F. in order to inhibit secondary reactions and prevent excessive coking in chamber 12. Preferably a temperature of about 1000 to about 1175 F. and a pressure of 4about one to about three atmospheres is extremely satisfactory. The residence time is similarly extremely important in order to obtain satisfactory cracking and inhibit secondary reactions. In general a residence time, dependent, of course, upon the remaining variables, is about 0.2 to about 6.0 seconds, particularly about 0.5 to about 3.0 seconds.

The mixture of cracked products and steam removed from cracking chamber 12 is passed to flash tower 14 by line I3. Before this mixture is passed into flash tower I4, it is quickly cooled from cracking temperature to a temperature of about 600 to about 800 F., preferably to a temperature of about 675 to about 725 F. to forestall further-cracking and/or secondary reactions. This time interval is extremely important and must be less than about 2 to about 3 seconds, preferably between about 0.02 to about 0.10 second. The cooling is effected by a recycle stream from line 16, the composition of which will be defined hereinafter. The purpose of iash tower 14, which is operated at a pressure of about 10 to about 30 pounds per square inch gauge and a temperature of about 600 to about 700 F., is to effect a separation of the steam and lighter products from the heavier liquid products produced in the cracking operation. Moreover suicient recycle of heavier product is thus provided to cool the cracked product before its entry into flash tower 14. A mere separation of steam, as condensed water, from the total cracked products would be exceedingly di'icult because of a tendency to form an emulsion therewith.

Under the pressure and temperature conditions existing in flash tower 14, set `forth above, the products removed from the top of the tower through line 18 co1nprise C12 to C20 and lighter hydrocarbons, preferably C16 to C18 and lighter hydrocarbons, and water as steam. The `products `are then passed through cooler 20 wherein the steam is condensed .to water. The .temperature in cooler20 is not critical as long as it is suciently low to condensethe steam ther-ein but not so low as to effect precipitation or crystallization of waxy materials which may be present in the stream due to incomplete separation in ash tower 14. In .gener-al a temperature of about to about 125 F., preferably'about 100 F., is satisfactory. In addition to water, some of `the heavier cracked products .are also condensed in cooler 20. The cooled product is removed lfrom cooler 20 by line 22 and passed .to separator 24 which is operated at a temperature of .about to about 125 F. and a pressure of about 8 to about 12 pounds per square inch gauge. The water is removed from the base of separator 24 by line 26, whileCg lto C6 and lighter cracked products,

3 preferably C5 and lighter, are removed overhead by line 28.. The remainder of the cracked products are removed from the side of separator 214 by line 30.

From the base of ash Ytower 14, through line 32, is removed the remainder of the product which may not have been removed overhead by line 18', that is about YC12 to `about C20 and heavier, preferably about C10 to about C12 and heavier hydrocarbons. Since it is necessary to cool the cracked products entering flash tower 14, as previously pointed out,V and since it is extremely desirable to eect such cooling without resorting to the addition to the system of extraneous material which would subsequently have to be removed from the product, if not from the system, often at .great trouble and expense, -a portion of the product in line 32 is recycled` by line '34, and passed through cooler 35 wherein therproduct is cooled toa temperature of about 300 to about 500 preferably C11 to `C10 and lighter hydrocarbons while the fraction removed from the base of fractionator 64 by line 4 comprises C12 `to C20 and heavier hydrocarbons, preferably C11 to C10` and heavier hydrocarbons. rlhe bottom fraction is preferably recycled and joins the fresh charge i-n line 2 as previously described. This recycle comprises about 100 to .about'300 percent by weight, based on the fresh charge in line 2. In the event, however, operation isV such, dor example, that line 18 contains all or substantially all of the C .and lighter hydrocarbons in Ithe cracked product and C1, and heavier hydrocarbons are to be used as recycle of line 4, the overhead fromvtar stripper 46 need not be sent to frac- Y `tionator 64 but can be passed directly to line 4 for F. The cooled product is then introduced into line 13 by line 16. The amount of recycle depends on many variables, for example, its temperature, the temperature of the cracked product in line 13, the temperature desired in ilash tower 14, etc. In general, atleast about 100, and preferably about 150 to about 300 percent, by Weight of recycle, based on the cracked product in line 13, is suicient to effect the desired cooling.

The remainder of the heavier product is passed by line 36 through valve v3&8 wherein the pressure is reduced to about 3 to rabout 8 pounds per square inch gauge, preferably to about atmospheric pressure. The product at a reduced pressure and at a somewhat reduced temperature, because of its movement through lines 36 and 40 and its reduction in pressure in passing through valve 38, is heated, if necessary, in heater 42 by any convenient means, to a temperature of about the same order )as that existing in flash tower 14.

The product leaving heater 42 by way of line 44 is passed to tar stripper 46 wherein tar and other. similar .products present in the bottoms product are removed therefrom. This is effected by passing about 40 to about 70 pounds` of steam per barrel of product in line 44, at a temperature of about 600 to about 800 F. into the base of tar stripper 46 by line 48. A Vtemperature of about 600 to about 800 F. and a pressure of about 2 .to .about 6 pounds per square inch gauge is employed therein. As a result thereof, tar :and heavier coke-forming products'are removed `from the base of tar stripper 46 by line 50.

Removed overhead by line 51 are the remainder of the cracked products enter-ing .tar stripper, not removed by line `50, and steam. The mixture in line 51 is then passed through cooler 52, which is operated at a ternperature suiliciently low to condense the steam and some of the cracked products but not so low as to elect precipitation or crystallization of waxy materials which may be present in the stre-am due to incomplete separation in tar stripper e6 or llash tower 14. Generally a .temperature of about 75 .to about 125 F. is suflicient. The cooled product is removed from cooler 52 by line 54 and passed to separator 56 which is operated at a temperature or" about 100 to about 125 F. and a pressure Yof about 0 to about 5 pounds per square inch gauge.

Water which is condensed is removed from the base of separator 56 by line 53 and C0 to about C0 hydrocarbons, .preferably about C1 to about C5 hydrocarbons are removed overhead by line 60. The remainder of the Ycracked product which has been liqueed is removed from theseparator 56 by line 61 and is preferably pressured by pump 62 to a pressure of about 15 to about 25 pounds per square inch gauge. The product in line 61 is thereafter introduced into lfraction'ator 64, which is maintained at a reboiler temperature of about 400 to about n 700 F. anda pressure of about 25toabout 5 pounds per square inch gauge, wherein the product is separated 'into two fractions. The overhead, which is lremoved by line 66, comprises C12 to C20 and lighter hydrocarbons,

recycle.

As shown in Figure 1, the olens produced are recovered and found `in lines 23, 60 and 66. The recovery of the oleiins inthese lines into their individual components, or even combinations or fractions of olens, can be eected in any desiredmanner. For example, in the event the oleiins in lines 28 and 60 comprise C2, C2 and *C1 oleiins, they can be combined, as shown in Figure 2, in line 68, compressed, dried by conventional Ymeans (not shown) and passed to fractionator 70 which can be operated at a pressure of `about 250 to about 400 pounds per square inch gauge and an overhead temperature of about 0 to about 5 F. Methane and `any other lighter constituents which may be present, are removed overhead by line '72, while C2, Cavand C4 hydrocarbons are removed Vfrom the base of fractionator 70 by line 74. From line 74, the C2, C3 and C1 fraction is passed to fractionator 76 which is operated at a' pressure of `about 250 to about 350 pounds per square inch gauge and an overhead temperature of abouti-10 to -about -|-l0 F. Here the C2 fraction is removed overhead by line 78 and the C3 and C4 fraction is removed `from the base by line 80. The C2 stream maybe split into C21-I1 `and C21-I0 by means of a column operating lat about 270`pounds per square inch and an overhead temperature of labout 20 to about 23 F. The C0 and C4 stream may be further separated by similar distillation in a column (not shown) operating at about 250 pounds per square inch tand an overhead temperature of about 110 to about 115 F.

Similarly, the hydrocarbon fraction .in line 66 can be separated into its individual components by any conventional means. Thus as shown in Figure 3, assuming the hydrocarbon fraction in line 66 contains C15 and lighter hydrocarbons, it is sent to fractionator 82 which is operated at a pressure of about 30 to about 100 pounds per square inch and an overhead vapor temperature of about 122 to about 212 F. C5 and lighter hydrocarbons are removed overhead by Vline 84 Aand C0 to C1,-J hydrocarbons are removed from the base by line 86. This latter fraction is passed tofractionator 88, operated at a pressure of about l5 to about 30 pounds per square inch `and `arroverhead vapor temperature of about '150 to about 190 F., where C0 fraction is removed Y lightest individual fraction Vis removed overhead and the yremainder is removed from the base Iand passed to the next ksucceeding column, until the fraction containing ,C15` and higher hydrocarbons is passed by line 94 to fractionator 56, operated at a pressure of about 5 to about 50 millimeters mercury absolute andan overhead vapor temperature of about V240" to about 350 F., wherein the C15 fraction is removed overhead in line 98 and the C10" and heavier fraction is removed from the Vbasethereof byline toline 4 of Figure l.

While it has been shown `above that the hydrocarbon fraction can be separated into its individual components,

this has been done merely for illustrative purposes, and

it is Within the scope of the present invention to separate the hydrocarbon fraction prepared in the cracking zone into fractions containing various numbers of individual components. Thus a C11 to C14 fraction can be removed and used as such in alkylation or sulfonation reactions. Since there is a spectrum of hydrocarbons obtained in the cracking operation in accordance with this process and C2, C6 and C10 hydrocarbons predominate, fractionationV can be effected to remove these as individual components therefrom and not the others. Y

The process of the present invention can be illustrated byY the following example. In -a processing period 2366 pounds of Gulf Process Wax A, a typical regular grade parain wax for this process having the following inspection:

Gravity, API 34.3 Viscosity, SUV, sec- 52.1 210 F. i Flash, P-M, F 435 vPour point, F 115 ASTM D 97-47 `Oil content, percent by wt 22.4

ASTM D 721-53T Carbon residue, Conradson, percent 0.12

ASTM D 189-52 Aniline point, F 251 ASTM D6 l 1-2--5 3T was introduced in line 2 at a temperature of 300 F. and mixed with 4435 pounds of recycle in line 4. The mixture was Iadmixed with834 pounds of steam at a temperature of 1000 F. and a pressure of 28 pounds per square inch gauge from line 8 and the resulting mixture was introduced in cracking chamber 12 which was maintained lat ya temperature of 1040 F. and a pressure of pounds per square inch gauge. The mixture was permitted to remain in the cracking coilS seconds and then removed and cooled to a temperature of 675 F. in 0.10 second by admixing therewith 20,240 pounds of recycle from line 16. The cooled mixture was then passed to ash tower 14, maintained lat -a temperature of 610 F. and a pressure of 15 pounds per square inch gauge, where 32,270 cubic feet of gaseous material comprising 17,970 cubic feet of steam andA 14,300 cubic feet of C12 and lighter hydrocarbons were removed overhead by line 18. This mixture was passed through cooler 20, where the temperature was reduced to 100 F., and then to separator 24. Water was removed from the base of 'separator 24 by line 26, 6970 cubic feet of C5 and lighter hydrocarbons were removed by line 28 and 1030 pounds of C11 to C12 liquid hydrocarbons were removed by line 30.

Removed from the base of flash tower 14 were 25,152 pounds of C12 and heavier hydrocarbons. 20,240 pounds of this mixture were passed through cooler 35, cooled therein to a temperature of 490 F. and passed by line 16 to line 13 to cool the product therein to 675 F. The remainder of the product in line 32 was passed through valve 38 where the pressure was reduced to 5 pounds per square inch gauge and thereafter to heater 42 wherein the temperature thereof was raised to 600 F. From heater 42, heated mixture was led to tar stripper 46. 810 pounds of steam at 700 F. wereled into the stripper, wherein the temperature was 650 F. and the pressure 4 pounds per square inch gauge. 870 pounds of tar and similar products were removed from the base of tar stripper 46 by line l50 and 8660 cubic feet of cracked products were removed overhead by line 51. After cooling in cooler 52 to a temperature of 100 F., the cracked products were passed to separator 516 wherein the water which was condensed at the lower temperature was removed by line 58. There was a negligible amount of hydrocarbon gas to be removed overhead in line 60 so that the total hydrocarbon stream comprising 4042 pounds of C12 and heavier materials was removed by line 61. The cracked f 6 products in lines 28, 60 and 61 were thereafter Vseparated into -the individual components in the manner previously described. The results obtained are tabulated below'in Table I Alpha-Glenn Yield, Alpha-Olen Concen- Percent by Weight tration, Percent by of Feed Weight of Oletlns in Carbon Fraction Regular Premium Regular Premium Feed Feed Feed Feed The high yields of total a-oletins from both the fregularf and the premium feed stocks and the high concentrations of the a-olen components in the variouscarbon fractions are illustrative of the effects of rapid heat- Y up time, rapidl quench rate and short residence time in the cracking zone. 4

Obviously many modilications and variations of the invention, as hereinabove set forth, can be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

I claim: e Y

' 1. A method yfor producing normal alpha-ole'ns `which comprises vaporizing a waxy charge by admixing therewith at least about 2 percent by weight of steam at a temperature of about 900 to about 1200 F., heating the resulting mixture at a temperature of about 1000 to about 1250 F. and a pressure of about one to about three atmospheres for about 0.2 to about 6.0 seconds, whereby the wax charge is cracked and a mixture predominating in normal alpha-oleiins is produced, cooling said latter mixture to -a temperature of about 600 to about 800 F. in less than about 3 seconds, passing said cooled mixture into a ash tower, separating and removing a light hydrocarbon fraction from said ash tower,'removing the remainder of said cooled mixture from said tower, cooling and recycling a portion of the said remainder to constitute the sole means whereby the cracked products are cooled prior to their entry into said ash tower, and thereafter separating the cracked product into selected olefinic fractions.

2. A method for producing normal alpha-olefins which comprises vaporizing a waxy charge by admixing therewith at least about 2 percent by weight of steam at a temperature of about 900 to about 1200 F., heating the resulting mixture at a temperature of `about 1000 to about 1250 F. and a pressure of -about one to about three atmospheres for about y0.2 to about 6.0 seconds whereby the wax charge is cracked and a mixture predominating in normal alpha-olens is produced, cooling said latter mixture to a temperature of about 600 to about 800 F. in less than about 3 seconds, passing;

said cooled :mixture into a ash tower, .separating and removing C12 to C20 and lighter hydrocarbons from said ash tower, removing the remainder of said cooled mixture from said tower, cooling a `portion of said remainder to a temperature of about 300 to about 500" F. and recycling said portion of said remainder to constitute the sole means whereby the cracked products are cooled prior to their entry into said ash tower, and thereafter separating the cracked product into selected olenic fractions. I

3. A method for producing normal alpha-oleiins which comprises vaporizing a waxy charge by admixing therewith at least about 2 percent by weight of steam at a temperature of about 900 to about l200 F., heating the resulting mixture at a temperature of about 1000 to about 1250" F. and a pressure of about one to about three atmospheres for about 0.2 to about 6.0 seconds, whereby the wax charge isV cracked and a mixture predominating in normal valpha-ole'iins is produced, cooling said latter mixture to -a temperature of about 600 to about 800 F. in less than about 3 seconds, passing said cooled mixture into a flash tower, :separating and removing a mixture of C12 to C20 andl lighter hydrocarbons and steam from said ash tower, cooling said latter mixture to condense said steam, removiugrwater condensate from said latter mixture, removing-the remainder of said cooled mixture from said tower, cooling a portion of said remainder to a'temperature of about 300 to `about 500 F., admixing with the cracked products said portion of said cooled remainder to consti- `tute the sole means by which the cracked products are cooled prior to their entry into said ilash tower, and thereafter separating the cracked product into selected olelinic fractions.

4. A method for producing normal alpha-olens which comprises vaporizing Va waxy charge by admixing therewith at least about 2 percent by weight of steam at a temperature of about 900 to about 1200o F., heating the resulting mixture at a temperature of about 1000" to about l25`0 F. and a pressure of about one to about three atmospheres for about 0.2 to about 6.0 seconds, whereby the wax charge is cracked and a mixture predominating in normal alpha-olefins is produced, cooling said latter mixture to a temperature of about `600 to about y800 F. in less than about 3V seconds, passing said cooled mixture into a flash tower, separating and removing a mixture of C12 to C10 and lighter hydrocarbons and steam from-said flash tower, cooling said latter mixture to condense said steam, removing vwater condensate `from said latter mixture, removing the remainder of said cooled mixture from said tower, cooling a first portion of said remainder to a temperature of about 300 to about 500 F., admixing with the cracked products said first portion of said cooled remainder to constitute the sole means by which the cracked products are cooled prior to their entry into said ash tower, removing tar from a second portion of saidremainder, and thereafter separating the cracked product into selected olenic fractions. Y

5. A method for producing normal alpha-olens which comprises vaporizing a waxy charge by admixing therewith at least about 2 percent by weightof steam at a temperature'of about 900 to about 1200 F., heating the resulting mixture at a temperature of about 1000 to' about 1250 F. anda pressure of about one to about three atmospheres for about 0.2 to about 6.0 seconds, whereby the wax charge is cracked and a mixture predominating in normal alpha-oleiins is produced, cooling said latter mixture to a 'temperature of about v600 to about 800 F. in less than about 3 seconds, .passing said cooled mixture into a flash tower, separating and removing a mixture of C12 to C20 and lighter hydrocarbons and steam-from said ilash tower, cooling said latter mixture to condense said steam, removing water condensate from said latter mixture, removing the remainder of said cooled mixture from said tower, cooling a rst portion of said remainder to a temperature of about 300 F. to about 500 F., admixing with the cracked products said first portion of'said cooled remainder to constitute the sole means by which the cracked products are cooled prior to their entry into said flash tower, removing tar from a second portion of said remainder by admixing steam therewith, and thereafter separating the cracked product into selected olenic fractions.

References Cited in the iile of this patent UNITED STATES PATENTS 2,172,228 Van Peski Sept. 5, 1939 12,366,521 Guichet Jan. 2, 11945 I2,736,685 Wilson et al Feb. 28, 1956 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No; 2,945,076 July 12g 1960 William A., Pardee. It is hereby certif-ied that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 8, line 2 foriCl2 to C10" read C'l2 to C20 Signed and sealed this 4th day of April 1961.,

(S EAL) Attest; ERNEST W. SWIDER XEXXXXIX ARTHUR w. CROCKER Attesting Oicer Acting Commissioner of Patents

Claims (1)

1. A METHOD FOR PRODUCING NORMAL ALPHA-OLEFINS WHICH COMPRISES VAPORIZING A WAXY CHARGE BY ADMIXING THEREWITH AT LEAST ABOUT 2 PERCENT BY WEIGHT OF STEAM AT A TEMPERATURE OF ABOUT 900* TO ABOUT 1200*F., HEATING THE RESULTING MIXTURE AT A TEMPERATURE OF ABOUT 1000* TO ABOUT 1250*F. AND A PRESSURE OF ABOUT ONE TO ABOUT THREE ATMOSPHERES FOR ABOUT 0.2 TO ABOUT 6.0 SECONDS, WHEREBY THE WAX CHARGE IS CRACKED AND A MIXTURE PREDOMINATING IN NORMAL ALPHA-OLEFINS IS PRODUCED, COOLING SAID LATTER MIXTURE TO A TEMPERATURE OF ABOUT 600* TO ABOUT 800*F. IN LESS THAN ABOUT 3 SECONDS, PASSING SAID COOLED MIXTURE INTO A FLASH TOWER, SEPARATING AND REMOVING A LIGHT HYDROCARBON FRACTION FROM SAID FLASH TOWER, REMOVING THE REMAINDER OF SAID COOLED MIXTURE

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