US2382724A - Catalytic cracking process - Google Patents

Description

1945' c. H. KOLLENBERG 2,382,724

CATALYTIC CRACKING PROCESS Filed June 5, 1943 Heuiing Oil rociions Gas Oil Porcffinic Oil ATTORNEY.

Patented Aug. 14, 1945 CATALYTIC cmcxmo raocass Conrad H. Kollenberg, Goose Creek, Tex assignor to StandardOil Development Companya corporation of Delaware Application June 5, 1943, 'Serial No. 489,734 I 2 Claims. on. 196-52) The present invention relates to a method for cracking hydrocarbon oils in the presence of a powdered solid catalyst. More particularly, it is concerned with the reduction and/or the prevention of coke deposits on the powdered solid during the cracking of the hydrocarbons.

One of the more important features of catalytic cracking processes employing the fluid or powdered catalyst technique, in which the finely divided catalyst moves along with the oil flowing through the reaction system and after reaction is oil side-stream.fraction and a highly paraflinic oil issubstltuted therefor.

More specifically, the invention comprises adding' to the bottom of the primary fractionating completed is separated and regenerated in a zone 7 outside of the reaction system, is the regeneration of the spent catalyst. Deposition of coke and tarry material on the finely divided powder increases the amount of burning necessary in the regeneration system and consequently reduces the throughput of a given unit when the amount and degree of regeneration of catalyst becomes greater than the facilities can care for.

It is usual practice in most catalytic cracking operations employing the powdered catalyst technique to withdraw from the primary fractionating zone a-slurry of oil and catalyst for recycling to the reaction system. A small amount of powdered catalyst is always carried over into the primary fractionating zone with the vapors leaving the cyclone, operating immediately ahead of the primary fractionating zone. amount of catalyst is concentrated in the heavier fractions of the oil in the fractionating zone,

by washing in the bottom section thereof and is carried out with the heavy oil fraction which remains from the distillation. This heavy oil, being subjected to repeated recycling and conversion, is highly aromatic in nature and has been found to contribute largely to the formation of carbonaceous deposits on the catalyst particles in the reaction zone. Efforts have been made in the past to reduce the amount of coke formed on the catalyst by filtering out the residual oil remaining in the catalyst. As will be recognized by those skilled in the art, this expedient requires special equipment which is expensive and sometimes unavailable.

It has now been discovered that the catalytic cracking operation may be improved so'that the amount of coke deposited on the catalyst in the reactor system is reduced to a minimum by sub- This small.

stituting for the aromatic oil withdrawn from the bottom of the fractionation zone a highly paraffinic oil having a boiling range above the boiling range of the feed oil to the cracking system. This expedient obviates the formation of coking particles on the finely divided powder used as a catalyst; In the practice of this invention the aromatic oil which has been found to be the main source of trouble is distilled out in the primary fractionating system and is withdrawn as a heavy zone of a powdered catalyst cracking operation a petrolatum fraction obtained from a crude petroleum which is highly parafilnic in nature. One specific feature of the present invention is to introduce the paraihnic oil into the bottom of the fractionating tower continuously with substantially all of the products of cracking being continuously distilled out, so that the amount of aromatic constituents recycled to the reaction system is maintained at a minimum.

The amount of petrolatum added to the bottom of the primary iractionating zone will vary depending on the capacity of the particular unit. Generally for a catalytic cracking unit charging between 10,000 and 15,000 barrels per day of feed oiL-about 300 to 1,000 barrels per day of the paraffinic petrolatum should be added. A like amount of aromatic slurry oil should be discarded. Depending again on the size of the unit, the amount of powdered catalyst carried over from the cyclone immediately ahead of the primary fractionating zone will vary directly with the unit capacity;

about 2 to 5 tons per day will carry over from the cyclone and be recycled from the bottom of the primary fractionaing zone in a unit of the size mentioned above.

The paraflinic petrolatum oils employed are characterized by having a boiling range higher than that of the feed to the cracking system. The characteristics of an oil giving good results is compared with the aromatic slurry oil in the following table: I Table I Aromatic Petroiatum slurry on Gravity, API. 28.8 14.2 Distillation at 10 mm. pressure:

IBP F 355 243 344 391 1 Cracked.

The conditions employed in the reaction system of the process of the present invention will vary depending on the charge stocks employed but generally will-range from about 850 to 1000 F.

with pressures of about 10 to 20 lbs/sq. in. The temperature in the bottom of the prmary fractionating zone will range in the neighborhood oi in the tower. As mentioned before, this desirable boiling rang is embodied in petrolatum fractions from parafiinic crudes.

The present invention will be better understood by reference to the drawing in which the single figure isa front elevation in diagrammatic form of the portion of a catalytic cracking process with which the present invention is concerned. It is to be understood that the cracking unit will embody other necessary equipment.

Referring now to the drawing, numeral 11 represents a pipe line carrying vaporized heated hydrocarbons from a superheater not shown. Regenerated catalyst from a powdered catalyst regenerating system (not illustrated) is introduced intoline II by way of line l2 in which a suspenvention, the oil circulated by way of lines 24 and I 3 to line II was highly aromatic in nature and caused deposition of coke upon the catalyst in the reaction zone. By introducing a high boilin parafllnic oil through line 2! into line 24 and by recycling 0. part of the efiluent from line 24 through line 28 into fractionating tower H, the highly aromatic fractions are caused to be distilled out with the gas oil fraction through line 23.

It will be understood by persons skilled in the art that the oil recycled through line 28 may be introduced at any suitable point in tower ll.

' However, in the modification shown in the drawsion of powder in vaporized oil is maintained.

There is also injected into line I l, by way of line I2, a slurry of oil and catalyst withdrawn from the bottom of fractionating zone ll which will be described in further detail hereinafter.

The combined streams of catalyst and oil are injected into reactor zone I! by way of line H and-are passed therethrough at a rate allowing a sufficient retention time for reaction to be completed.

The stream of powdered catalyst and cracked hydrocarbons leaving reactor l5 by way of line I8 is injected into cyclone separator I! which is connected directly to spent catalyst hopper I! in the manner shown. Cyclone I1 is a means for separating powdered catalyst from the vaporized oils in a manner well known in the art.

The vaporized hydrocarbons leaving cyclon H by way of line l9 are injected thereby into fractionating zone I while spent catalyst is withdrawn from spent catalyst hopper 18 through line 20 for regeneration in a regeneration stage notshown in the drawing.

The vaporized hydrocarbons injected into fractionating zon H by way of line I! contain a small percentage of the powdered catalyst not separated from the hydrocarbons in cyclone H. In usual operations, the powdered catalyst will comprise less than about 0.1% by weight of the vaporized hydrocarbons injected into the fractionating zone ll, it being impractical to obtain absolute separation of the catalyst and vaporized hydrocarbons in cyclone ll.

Fractionating zone ll comprises all the usual equipment required to separate hydrocarbons by distillation and may include one or more distillation towers. Fractionating zone I4 is provided with line 2| for removal of fractions boiling below 400 F., with line 22 for withdrawal of the heating oil fraction boiling between about 400 and 600 E, and with line 23 for withdrawal of the gas oil fraction boiling in the range of about 550 to 850 F. A heavier fraction is discharged from fractionating zone II by way of line 24.

Connected to line 24 is line 25 in direct communication with storage tank 20 which contains.

a petrolatum oil fraction obtained from a crude petroleum of parafllnic nature. Located in line 25 is pump 21 for transferring the parafnnic oil from tank 26 by way of line 25 into line 2|.

Line 2 connects into line It to allow recyclin of the oil fraction withdrawn from the bottom of fractionating zone ll by way of line 24 toline H connecting to reactor zone l5. In this manner the catalyst carried over from cyclone 11 into fractionating zone I4 is returned to the reaction system along with the oil remaining after distillation of the aforementioned fractions.

It was at this point, prior to the practice of the present invention, that the aforementioned dimciflties were encountered in r ycling the slurry oil to reactor zone ll. Prior to the present ining, it is assumed that the vapors entering tower I4 through line l9 are highly superheated. Hence, by cooling the oil recycled through line 20 in cooling means 29 and introducing this cooled oil into tower I at a point above the entrance of line l9, it is possible to remove much of the superheat and provide a stripping action in the bottom of the distillation tower.

Other modifications will occur to those skilled in the art without departing from the spirit of the invention. Thus, when the vapors in line 19 are not highly superheated, the oil withdrawn through line 24 and recycled through line 28 may be passed through a heating means provided 4 in place of cooler 29 and introduced into tower I at a point below the entrance of line is.

It will thus be seen in the foregoing description that the essence of the present invention resides in the continuous discarding of the deleterlous heavy aromatic fractions and the con tinuous injection of an oil which does not crack into cokey material to as great an extent as the aromatic oil for which it was substituted.

The nature and objects of the present invention having thus been described and illustrated, what I desire to claim as new and useful and to secure by Letters Patent is:

1. In a catalytic cracking process in which a finely divided catalyst is carried in suspension in oil vapors through a cracking zone and some of such catalyst is can'ied over by the vaporous products from said cracking zone into a subsequent fractionating zone, the steps of introducing into said fractionating zone a parafiinic oil having a boiling range substantially above that of the highest boiling components of said vaporous products, taking off said latter components at an intermediate point from said fractionating zone, taking off from the bottom of said zone a suspension of catalyst in said parafllnic oil and conducting said suspension to the cracking zone.

2. In a catalytic cracking process in which a finely divided catalyst is carried in suspension in oil vapors through a cracking zone and some of such catalyst is carried over by super-heated vaporous products from said cracking zone into a subsequent fractionating zone, the steps of introducing into said fractionating zone at a point above the point of-introduction of said superheated vapors a paraflinic oil having a boiling range substantially above that of the highest boiling components of said vaporous product, taking of! said latter components at an intermediate point from said fractionating zone above the point of introduction of said paramnic oil, continuously withdrawing a, suspension of catalyst in said paramnic oil from the bottom of said zone, continuously passing a portion of said suspension

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