US2297773A - Hydrocarbon conversion - Google Patents

Description

Oct. 6, 1942. E. R. KANHOFER HYDR6CARB0N CONVERSION Filed July 31 muwzun 200 ELMER R. KANHOFER ATTORNEY Patented Oct. 6, 1942 3 1 HYDROCARBON CONVERSION Elmer R. Kanhofer, Chicago, 111., Universal Oil Products Company,

assignor to Chicago, 111.,

a corporation of Delaware Application July 31, 1939, Serial No. 287,485 2 Claims. (01. 196-49) This invention relates to a process which involves a series of concomitant steps wherein hydrocarbon oils are converted into substantial yields of high octane rating gasoline having a relatively low olefin content and improved properties with respect susceptibility to antiknocking agents and, in addition, improved storage stability and low sulfur content.

The invention involves principally high temperature catalytic" cracking of a hydrocarbon oil, separation of the conversion products from the high temperature reaction into a gasoline boilingrange traction and recycle, return of the recycle to the high temperature catalytic cracking step, low temperature catalytic cracking of a mixture of the gasoline boiling range hydrocarbons from the high temperature cracking treatment and a saturated oil, introduced from an outside source, fractionation of the low temperature conversion products to separate the gasoline, boiling range hydrocarbons from the higher boiling hydrocarbons, recovery of the former, and the return of the latter to the high temperature catalytic cracking treatment.

The term high temperature catalytic cracking treatment as used throughout the specification and claims refers to the treatment of a hydrocarbon oil boiling above the range of gasoline in the presence of a cracking catalyst at a temperature in the range of from 800 to 1200 F. and at a pressure ranging, for example, from substantially atmospheric to 200 pounds or more per square inch whereby to eifect substantial conversion into gasoline boiling range hydrocarbons and/or to the treatment of gasoline boiling range hydrocarbons whereby to improve the prises passing a hydrocarbon oil in the heated vaporous state in contact with a catalyst mass in a high temperature cracking zone whereby to effect substantial conversion of said oil to gasoproperties of the same by changing the structure of the molecules without materially altering its boiling range; whereas low temperature catalytic cracking treatment refers to the treatment of a mixture of hydrocarbon oil containing the cracked gasoline from the high temperature cracking treatment and an added hydrocarbon oil preferably saturated such as, for example, straight-run oils containing paraflins and naphthenes, in the presence of a cracking catalyst at a temperature in the range of 500 to 800 F., but preferably from 700 to 800 F and at a pressure ranging, for example, from substantially atmospheric to 200 pounds or more per square inch whereby to increase the degree of saturation of the olefinic hydrocarbons subjected to treatment line, cooling the conversion products, separating a non-vaporous liquid residue from the vaporous conversion products, recovering the former, iractionating said vaporous conversion products to separate fractionated vapors boiling in the range of gasoline from the higher boiling vaporous conversion products, condensing the latter in the fractionating zone as reflux condensate and returning it to the high temperature catalytic cracking zone, comingling said fractionated vapors with a saturated oil and passing the mixture in the heated state in contact with a catalyst mass in a low temperature cracking zone whereby to saturate a substantial portion of the olefinic hydrocarbons contained in the mixture, iractionating the conversion products from the low temperature cracking zone to separate fractionated vapors boiling in the range of gasoline from the higher boiling hydrocarbons, recovering the former, condensing the latter in the fractionating zone as reflux condensate and returning it to the high temperature catalytic cracking zone.

In an ordinary catalytic cracking process which employs relatively high temperatures and relatively short contact times, gasoline is produced which contains high percentages of olefinic hydrocarbons which, although increasing the octane rating of the same, are responsible for the poorer susceptibility of the gasoline to added antiknocking agents, such as tetraethyl lead and, in addition, are at least partly responsible for the poorer storage stability because of gum formation. It has been found that if the gasoline produced in a high temperature cracking treatment is commingled with a saturated straight-run hydrocarbon oil and the mixture. subjected to contact with a catalyst mass having essentially the same and at the same time effect some cracking of the heavier hydrocarbons.

In one specific embodiment theinvention comcharacteristics as that employed in the high temperature cracking treatment at a temperature in the range of 500 to 800 F. for a relatively longer period of time than that employed inthe preceding cracking treatment, a gasoline product is obtained composed primarily oi! paraflinic and aromatic hydrocarbons, which has a relatively high octane rating, and a good susceptibility of antiknocking agents whereby it is possible with the addition of relatively small amounts of tetraethyl lead to obtain a gasoline suitable for aviation purposes.

It is believed that in the low temperature cataa low potential gum content, a

lytic cracking treatment, as described above, that a portion of the hydrogen from the saturated hydrocarbons and particularly the naphthenlc hydrocarbons is transferred to the oleflnic hydrocarbons formed in the high temperature cracking treatment, whereby the oleflnic hydrocarbons become saturated to form paramnic hydrocarbons and the naphthenic hydrocarbons are converted to aromatic hydrocarbons. Various other reactions, such as, for example, dehydrogenation and cyclization of an aliphatic hydrocarbon to form an aromatic hydrocarbon with the formation of 2 or 3 molecules of hydrogen which attach to the unreacted oleflnic hydrocarbons, may also take place. A further discussion in connection with what may possibly take place is unnecessary, since the invention does not concern itself with the chemistry of the various reactions, but it is concerned primarily with the process in which the cracking reaction may be conducted.

The accompanying diagrammatic drawing shows'in conventional side elevation one specific form of the apparatus in which the object of the invention may be accomplished. It is to be understood that the invention is not limited to processing in the specific form of apparatus hereing disclosed and that various modifications'of the process and apparatus herein described may be made without departing from the broad scope of the invention.

Referring now to the drawing, the charging stock, comprising either a relatively wide boiling range hydrocarbon oil which may be substantially completely vaporized or any fraction thereof, is introduced through line I and valve 2 to pump 3, which discharges through line 4 and valve 5, after which the charging stock is commingled with cycle stock, formed as hereinafter described, and mixture introduced to heating coil 6. The 'oil in passing through heating coil 6 is substantially completely vaporized therein and raised to the desired temperature, which may range, for example, from 800 t 1200 R, without substantial pyrolytic cracking thereof by means of heat supplied from furnace l. The heated hydrocarbon vapors leaving heating coil 6, at a pressure ranging, for example, from substantially atmospheric to 200 pounds or more per square inch, are directed through line 8 and valve 9 into reactor i0 wherein the vapors are subjected to contact with a cracking catalyst disposed therein while maintaining the hydrocarbon vapors at substantiallythe same temperature as that employed on the outlet of the heatin coil whereby to effect substantial conversion of the gasoline boiling range hydrocarbons.

The preferred cracking catalysts for use in the present process consist in general of a precipitated alumina hydrogel and/or zirconia hydrogel composited with silica hydrogel, the gel composite being washed, dried, formed into particles and calcined to produce a catalytic mass. It is not intended, however, that the process should be limited to these particular catalysts, for other catalysts, such as, for example, the hydrosilicates of alumina, acid treated clays, and the like, may be used within the broad scope of the invention.

In the following specification and claims ihe terms silica, alumina, silica-zirconia, and silicaalumina-zirconia masses are used "in the broad sense to designate the synthetic composites referred to above. The preferred catalysts may be prepared by precipitating silica from a solution as a hydrogel within or upon which the alumina and/or zirconia are deposited also by to produce a rather crumbly and granular maprecipitation as hydrogels. The silica hydrogel may conveniently be prepared by acidifying an aqueous solution of sodium silicate by the addition of a required amount of hydrochloric acid. After precipitating, the silica gel is preferably washed until substantially free from alkali metal salts. The washed silica hydrogel. is then suspended in a solution of alumina and/or zirconium salts and an alkaline precipitant, such as ammonium hydroxide, ammonium carbonate or ammonium sulfide added to the solution to precipitate aluminum and/or zirconium hydrogels. The final precipitate, comprising essentially hydrated silica and hydrated alumina and/or zirconia, is washed to substantially completely remove water soluble materials and dried at about 300 F.

terial which may be ground and pelleted or sized to produce particles of catalyst after which the catalyst particles are calcined at a temperature in the approximate range of 1000 to 1500 F. 'Various other procedures, such as, for example, co-precipitation of the hydrated gels may be employed, when desired, to produce the preferred catalyst.

Reactor Ill is preferably of the type which employs a plurality of relatively small diameter reactor tubes containing the desired catalyst, the tubes being confined within an enclosed zone to which heat from an external source may be supplied for the purpose of maintaining the reactants at the desired temperature during the conversion reaction. In addition, since relatively short periods of operation are employed in catalytic cracking because of the rather rapid deposition of carbon upon the surfaceand within the pores of the catalyst particles which necessitates frequent reactivation, it is preferred that a plurality of reactors be employed, although only one is shown in the drawing, in order that one or more may be segregated .and the catalysts disposed therein subjected to reactivation while conversion of the hydrocarbon vapors is being accomplished in the other or others. Suitable means, not shown, may be employed for reactivating the catalyst disposed within the various reactors during the period those particular reactors are segregated from the balance for the purpose of reactivation.

Although the reactor described above constitutes the preferred type of reactor, it is not intended that the invention should be limited in this respect, for various other types of reactors, known to those in the art, may be substituted therefore without departing from the broad scope of the invention.

The conversion products leaving reactor l0 are directed through line i l and valve 12, cooled to a temperature below that at which thermal cracking is effected, commingled with a suitable cooling oil, introduced as hereinafter described, and the mixture supplied to the separating zone I4 of fractionator and separator l3 wherein the nonvaporous liquid conversion products are separated from the vaporous conversion products and the former withdrawn by way of line l5 and valve l6, cooled and recovered as a product. of the process.

.The vaporous conversion products are directed through separating tray l'l into fractionating zone 18, which forms the upper portion of fractionator and separator l3, wherein they are fractionated to separate fractionated vapors boiling in the range of gasoline from the higher boiling conversion products, the latter being condensed as reflux condensate in zone l8. Reflux condensate collected on separating tray I1 is directed therefrom through line i8 and valve 28 to pump 2|. Pump 2| discharges through line 22 and a portion or all of said reflux condensate may be directed through line 23 and valve 24 to cooling and storage. Preferably, however, it is directed through valve 25 in line 22 into line 4 wherein it commingles with the charge and is subjected to substantial further cracking in commingled state therewith. When desired, a portion of the reflux condensate in line 22 may be directed through line 26 and valve 21 into line II for use as cooling oil to the conversion products therein. Other hydrocarbon oils may also be employed for cooling the conversion products in line H, the purposes of which and the methods of introduction being described more in detafl later.

. Fractionated vapors separated in zone l8 are withdrawn from the upper portion thereof through line 28 and, when desired, a portion directed through valve 29 to vapor pump 38, discharges through line 3| and valve 32 into line 49,

for treatment as hereinafter described, and the remaining portions of the vapors in line 28, sumcle'nt for use as a refluxing medium in zone l8, directed through line 33 and valve 84 to cooler and condenser 35 wherein the normally liquid hydrocarbons are condensed. The condensed normally liquid hydrocarbons, together with the undissolved and uncondensed gases in condenser 35 are directed through line 36 and valve '31 to receiver 38 wherein the undissolved and uncondensed normally gaseous hydrocarbons, including hydrogen, are separated from the distillate, the former being withdrawn from receiver 38 by way of line 39 and valve 40. When only a portion of the fractionated vapors is subjected to cooling and condensation in condenser 35, all of the distillate collected in the lower portion of receiver 38 would be returned to the upper portion of zone l8 by wayof line 4|, valve 42, pump 43, line 44, and valve 45. However, when all of the fractionated vapors are subjected to cooling and condensation in condenser 38, only a portion of the distillate collected in receiver 38 would be returned as a refluxing and cooling medium in zone I8. The remaining portion of the distillate is directed through line 45 and valve 41 to pump 48, which discharges through line 49 and valve 50, and the distillate in line 49 or the vapors, introduced as previously described, commingled with a suitable saturated hydrocarbon oil, introduced as hereinafter described, and the mixture introduced to heating coil The saturated hydrocarbon oil oommingled with the distillate or vapors in line 49 may comprise, for example, any one of the following: gasoline, naphtha, kerosene, or gas-oil, or any mixture thereof and is supplied for the purpose of donating hydrogen to the oleflnic hydrocarbons contained in the fractionated vapors.

-In the subsequent low-temperature cracking stage a dis'proportionation or hydrogen transfer is effected whereby the olefinic hydrocarbons, subjected to contact with a cracking catalystat a relatively low temperature and a relatively long contact time in the presence of the added saturated hydrocarbon oil, are converted to parafllnic hydrocarbons. The hydrogen necessary for saturating the oleflnic hydrocarbons is'furnished to a great extent by the added saturated hydrocarbon oil and may probably be the result of the reaction which involves dehydrogenation of naphthenic hydrocarbons to aromatics or the one which involves dehydrogenation of an aliphatic hydrocarbon and cyclization of the dehydro- 3 genated product to produce an aromatic. -'l"he reactions referred to above are only suggested as typical reactions and in all probability are the basic ones. However, there is also the possibility that various other reactions take place but since the invention is concerned principally with the process no attempt will be made to enumerate them.

The added saturated hydrocarbon oil may constitute, for example, a straight-run gasoline, naphtha, or kerosene which may be introduced by way of line 52 and valve 53 to pump 84, which discharges through line 58 and valve 56 into line 48. On the other hand, a portion of the charging stock introduced to heating coil 8 may be utilized in this reaction, in which case it would be directed through line 51 and valve 58 into line 49.

The mixture introduced to heating coil 5| is raised to the desired temperature ranging, for example, from 500 to 800 F. by means of heat supplied from furnace 58. The heated hydrocarbon oil is discharged from heating coil 5| under a pressure which may range, for example, from substantially atmospheric to 200 pounds or more per square inch and is directed through line so and valve -6| into reactor 62 wherein it is subjected to contact with a catalyst disposed therein. The catalyst employed in reactor 62 is of essentially the same composition as that described in connection with reactor iii. The difl'erence in the two reactions being the temperature at which the reaction is effected and the contact'times employed, the reaction in reactor It being carried out at a relatively high temperature and short contact time, whereas the reaction in reactor 62 is carried out at a lower temperature and a longer contact time. Reactor 62 and reactor I0 may be of essentially the same design, however, as was previously mentioned, various other types of reactors may be employed to accomplish the desired result.

The conversion products leaving reactor 62 are directed through line 63 and valve 64 into fractionator 85 wherein fractionated vapors boiling in the range of gasoline are separated from the higher boiling hydrocarbons, the latter being condensed as reflux condensate in the fractionating zone. The fractionated vapors are directed from the upper portion of fractionator 65 through line 56 and valve 61 into cooler and condenser 68. Distillate leaving condenser 68, together with undissolved and uncondensed gases, is directed through line 69 and valve 10 into receiver Ii wherein the undissolved and unc0n-= densed gases are separated from the distillate. The gases separated in receiver H are directed from the upper portion thereof through line 12 and valve I8 to storage or disposed of in any suitable manner. A portion of the distillate collected in the lower portion of receiver H is returned to the upper portion of fractionator 65 as a refluxing and cooling medium therein by way of line I4, valve 15, pump 16, line 11, and valve I8. The balance of the distillate collected in receiver H is directed through line 19 and valve 88 to storage or to further treatment a desired.

The reflux condensate from fractionator 65 is directed through line 81 and valve 82 to pump 83. Pump 88 discharges through line 84 Or all or a portion of the reflux condensate may be directed through line 85 and valve 86, cooled and recovered as a product of th process. Preferably, however, it is directed through valve 81 into line and reflux condensate from fractionator and se arator l3 and subjected to conversion, as previously described. When desired, a portion of the reflux condensate in line 84 may be directed through line 88, valve 89, and line 26 for use in cooling the conversion products in line II, as previously described. Other hydrocarbon oils which may be employed for cooling the conversion products in line it may comprise a portion of the charging stock in line t which, in the case here illustrated, may be introduced to line lit by way of line 5i, line 90, and valve ill or, on the other hand, a portion of the hydrocarbon oil introduced to the distillate in line 19 may be used for cooling the conversion products in line iii, in which case it would b directed through line 55, line 92, valve 93, and line at. It may be desirable, for example, especially in the case where fractionated vapors in zone is ar not subjected to cooling and condensation in condenser 35 to introduce the straight-run gasoline or naphtha which is ordinarily added to the distillate in line 69 to the conversion products in line it whereby to decrease the heat requirements in heating coil ti.

An example of one specific operation of the process as it may be accomplished in an apparatus such as illustrated and above described to accomplish the desired results is approximately as follows:

A 303 A. P. I. gravity East Texas gas oil was vaporized and heated to a temperature of approximately 932" 35. without substantial pyrolytic cracking thereof. Heated vapors. under a superatmospheric pressure of approximately 60 pounds per square inch were passed over a silica-alumina-zirconia catalyst at a liquid space velocity of 4 while maintaining the temperature of the vapors at approximately that at which they were discharged from the heater. The conversion products leaving the catalyst zone were cooled to a temperature of approximately 650 F. with reflux condensate formed, as hereinafter described, and the mixture introduced to a separating zone maintained under a superatmospheric pressure of approximately 40 pounds per square inch wherein the non-vaporous liquid residue was separated from the vaporous conversion products. The non-vaporous residue removed from this zone was cooled and recovered as a product of the process. The vaporous conversion products were fractionated to separate fractionated vapors boiling substantially in the range of gasoline from the higher boiling hydrocarbons, the latter being condensed as reflux condensate and returned in part as cooling oil to the conversion products, as aforementioned, th balance being introduced to the heating coil in cummingled state with the charging stock for further conversion.

gravity straight-run naphtha boiling in the range of from 300 to 500 F. in the proportion of and 45% by volume, respectively, and the mixture thereafter heated to a temperature of 750 F. The heated mixture was passed over a silicaalumina-zirconia catalyst at a liquid space velocity of 1 and at a superatmospheric pressure of approximately pounds per square inch while maintaining the temperature substantially constant during the conversion reaction. The conversion products leaving the low temperature cracking zone were subjected to fractionation at a superatmospheric pressure of 40 pounds per square inch to separate fractionated vapors having an end boiling point of 300 F. from the higher boiling conversion products, the latter being condensed as reflux condensate in this zone and returned to the high temperature cracking treatment. The fractionated vapors were subjected to cooling and condensationand the resulting distillate and gas collected and separated.

While employing an operating period of 1 hour before regeneration of the catalyst in the high temperature cracking zone, a yield of approximately 42.5% by volume of 300 end point gasoline having an octane rating of 81.5 and a bromine number of 11- was obtained. The octane rating of this product upon the addition of 6 c. c. of tetraethyl lead was raised to 87. The 300 end point product from the low temperature cracking step, on the other hand, when employing an operating period of /2 hour before regeneration of the catalyst, was equivalent to 62% by volume of the mixture charged to this treatment and had an octane rating of 79 with a bromine number of approximately '7. The octane number of this product upon the addition of 6 cc. of tetraethyl lead was raised to 98.

I claim as my invention:

1. A process for producing motor fuel of high octane rating and relatively low olefin content which comprises subjecting hydrocarbon oil to catalytic cracking at a temperature in the approximate range of 800 to 1200 F. for a contact time such as to form olefinic gasoline, fractionating the resultant products to separate the olefinic gasoline therefrom, commingling a saturated hydrocarbon oil with the separated olefinic gasoline and contacting the mixture with a cracking catalyst at a temperature in the approximate range of 500 to 800 F. for a longer contact time than is employed in the first mentioned catalystic step, the quantity of said saturated oil and said longer contact time being sufficient to saturate at least the major portion of the olefin content of said gasoline, and recovering the gasoline of relatively low olefin content thus produced.

2. The process as defined in claim v1 further characterized in that said saturated oil is a straight run petroleum distillate containing a substantial proportion of gasoline fractions.

ELMER R. KANHOFER.

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