US2476729A - Catalytic oil cracking with air - Google Patents

Description

y 1949. c. J. HELMERS 2,476,729

CATALYTIC OIL CRACKING WITH AIR Filed Jan. 14, 1947 GASES WELSAS HOLVNOILDVHJ PEBBLES I RECYCLE AIR PSI

PREHEATER INVENTOR. .C. J. HELMERS ATTORNEYS STEAM OIL CHARGE Patented July 19, 1949 UNITED STATES PATENT OFFICE 2,476,729 I L t t 7 CATALYTIC OIL CRACKING WITH AIR Carl J. Hehners, Bartlesville, Okla., assignor to Phillips Petroleum Company, a corporation of I 7 Delaware Application January 14, 194 7,Seria l No. 722,063

' 1 Claim. 1

The present invention relates to the catalytic conversion of hydrocarbon oils. More particularly, it relates to a novel process for cracking or otherwise converting relatively heavy hydrocarbon oils in a manner which will simplify preheating of the oil and permit maintenance of more uniform cracking temperatures within the catalyst bed. v

In the catalytic cracking of hydrocarbon oils, such oils are ordinarily vaporized and preheated to conversion temperatures in a preheating furnace which is usually of a tubular type. Where the feed comprisesheavy hydrocarbon oils, due to the high temperatures required to vaporize the highest boiling components of the feed, excessive thermal cracking, accompanied by the formation of coke in the furnace tubes is sustained in the preheater. This thermal cracking and coke formation represent an economic loss, and in addition require frequent cessation of operations for the purpose of cleaning or burning out the furnace tubes to remove coke deposits and avoid restriction of flow and impairment of heat transfer efiiciency in the preheater. Addition of steam is sometimes employed in the preheating furnace to assist in vaporization of the feed but this expedient increases the vapor volume going through the coils, and thereby increases pressure drop and the average coil pressure. This increase in pressure also tends to repress the vaporization of the high-boiling constituents.

In accordance with the present invention, the foregoing difliculties are overcome by preheating the feed to a temperature such that at least a portion of the highest boiling constituents is not vaporized, and introducing the incompletely vaporized material into the cracking zone along with a desired proportion of oxygen-containing gas. In this manner controlled oxidation of a portion of the hydrocarbon feed will occur within the reactor with a resultant increase in the temperature to a point sufficient to effect vaporization of the unvaporized components. It has further been found that in a mixture of heavy hydrocarbons and air oxidation does not effectively take place until a surface is supplied on which the oxidation reaction can proceed. For this reason the oxidation will occur Within the catalyst bed, and thus vaporization of the oil will also occur within the bed accompanied by cracking and carbon deposition on the catalyst. It has further been found that in introducing the oxygen and hydrocarbon at the inlet to the bed in the manner described herein, localized combustion at the inlet will not occur as might be expected, but that there 55 is an even distribution of the temperature rise due to combustion, throughout the catalyst bed. Whil the catalyst itself will serve as a'satisfactory sur face for the combustion, it has been found prefer able to interpose a layer of relatively inert refractory material between the catalyst and the inlet and permit the partial combustion to take place on the surface supplied thereby. In this manner the vaporization of the feed may be completed on the inert surface and less difiiculty is encountered with pressure drop caused by in-j creased carbon deposit on the catalyst, while at the same time the catalyst activity is maintained at a higher level. V

It is therefore, an object of the present invention to provide a process for the catalytic cracking of hydrocarbons wherein complete vaporization of the feed is effected without causing excessive cracking and carbon deposition in the vaporizing or preheating means. It is a further object of the present invention to provide a process for the catalytic cracking of hydrocarbons wherein at I least a portion of the endothermic heat loss is supplied by partial combustion of the feed in such a manner that the heat thus supplied is uniformly distributed throughout the catalyst bed.

In one specific embodiment of my invention, the charge oil is heated in a minimum time in the preheater under conditions such that only about to per cent of the oil is vaporized at the preheater coil outlet. One of the points in a preheater Where coking is most troublesome is that point where the last small portion of the oil is vaporized. In this method of operation, this point is not encountered in the tubes of the preheater. If air is mixed with the heated oil at some point between the preheater outlet and the reactor, the additional heat necessary for the cracking will be supplied by oxidation at the catalyst surface, i. e; at precisely the point Where it is needed. It is advantageous to provide an inert surface, such as magnesite pebbles or the like, where oxidation can take place to supply the heat necessary to complete the vaporization, particularly when a relatively heavy oil is being charged and the amount of liquid hydrocarbon entering the reactor is 20 per cent or higher. By completing this vaporization on the inert surface, less diificulty is encountered with pressure drop caused by carbon deposits and the catalyst activity is maintained at a higher level. However, it is also an advantage of this process that the oxidation takes place throughout the contact mass and is not a localized reaction at the first surface contacted. The invention may be described with reference to the attached drawing which illustrates a reactor and flow sheet for practicing the invention. The heavy hydrocarbon to be cracked which may be gas oil, or a similar high boiling oil is charged to preheater 4, via lines I and 3, with or without added steam from line 2. This charge is heated to a suitable temperature, say in the range of 850 to 1050 F. in coil 5 with a pressure in the range of zero to-ZOO p. s; i. At the preheater coil outlet the incompletely vaporazied material is removed through line 6 and air from line I is introduced therein a suitable amount, for example in the. range of to 600 cubic feet per barrel'of charge.

The air-hydrocarbon mixture flows into, reactor 9 wherein it contacts a layenof. inert, heat-resistlyst suitable for the purpose. The inert material may be magnesite pebbles or any like refractory material with a relatively-low adsorptive power.- This material may also be in. the form of granules of. any desired configuration instead of pebbles. Partial combustion of the hydrocarbon charge ocours; on the surface of theinert material with a resulting increase in temperature of the feed to a desired level. The liquid remaining in the charged mixtureis thereby vaporized in this zone by heat liberated in theactionof the oxygen with the hydrocarbon or with previously deposited carbon whichmay be present on the-material. The thus heated-vapors thenpass-on through catalyst bed ll under cracking conditions. The efiluent vapors are removed by line l2 and introduced into afractionator l3 from which gasoline is separated throughline l4, light gasesthrough linel5. and heavy andunconverted material through line- I 6 for. recycle-to the preheater or removal from the system.

The inert material is.preferablydisposed in a layeradjacent to the catalyst. bed; and in the case of a vertical bed will beat the top or bottom depending on the position of theinlet. The inert material may also be disposed in a separate bed or chamber in direct communication with the catalyst chamber if desired, but optimum results are achieved where a single continuous bed is formed.-

This process permits inclusion of much higherboiling'material than the usual in the charge to the catalytic unit since excessive preheater coi ing isavoided in vaporizing the liquid hydrocarbon charge.- The efficiencyof utilization of the added oxygen in the process is as high as 90 to 95 per cent.

Examples In. threecomparative runs. aheavygas oil was cracked-by passing it downward through a vertical catalyst chamber containing calcined bauxite. This gas-oil'had an API gravity at 60 F; of 31.0 and hadthe followingzAsTM'distillation characteristics:

oil space velocity through: the chamber wasv 1;? liquid; volumes per; volume of: catalyst; perhour.

50 responding volume of ceramic pebbles.

The charge was diluted with 60 pounds of steam per barrel of oil. The pressure was 85 p. s. i. In the first run no air was added to the charge. In the second run, 2500 cubic feet of air per hour was 5 charged at the inlet of the catalyst chamber.

The following data were obtained:

Table I 10 Run l 2 3 Air Injected, cu. it. per hr None 2, 500 None Reactor Temperatures, E.:

Inl L 935 936 953 8% in. below inlet (top of bed) 934 953 M8 11% in. below inlet 928 949 948 17% in. below inlet. 910 936 923 23% in. below inlet. 917 942 930 28% in. below inlet. 898 922 908 36% in. below inlct 890 917 901 44% in. below inlet- 885 909 895 49 in. below inlet 883 908 893 54% in. below inlet (bottom of be 881 900 895 Outlet 827 848 832 Average bed temperature". 903 926 915 Conversion, vol. per cent of charge l9. 1 32. (l 21. 2

In comparing. runs. land 2, the inlet temperature was the same, but. in thefirst section of. the.

bed in run 2, a temperatureincrease was effected product composition-from all three runs. was about thesame.

Run 3 was carried outat. ahigher initial temperature-in the absence of air, and demonstrates the effect of addingair at the inletas-in run:2 in

raising the temperature in. the variouspor-tions of the bed and in raising the average temperature of the bed. The conversion. in run 2 was 32.0. as against 21.2 in run 3.

In another series of runs a topped crude-gas 0 oil blend having an API gravity of 29.2. was

cracked. Four runs-weremade at a feed rate of 8-barrels of oil and about 15 pounds of steam per barrel of oil per hour. The process period for each run was 3 hours. Runs 4-and5 were madewitln out injecting air, and runs 6 and 7 were made while injecting about 100.cubicfeet of air penbarrel of feed. Before runsGand-F, the chamber. was opened and 9 inches of catalyst: were removed from the top of the bed and replaced with-a cor The chamber contained 3211 pounds of catalyst inithe runs without pebbles and 2954 pounds in those with 9 inches of pebbles.

The results of these. runs are summarized in l Top of catalyst bed9 inches of pebbles above catalyst.

The results in Table II demonstrate the-temperature effect resulting-from combustioninithe pebble-layer, with increased temperature-andwaporization of: feed. The; temperature: rise due to combustion in the pebble layer is evenly distributed in the catalyst bed, with resulting increase in percentage of conversion.

I claim:

A process for the catalytic conversion of a hydrocarbon oil containing as a minor portion constituents capable of forming coke upon complete vaporization thereof which comprises preheating said oil to a. temperature such that substantially all of the non-coke forming but substantially none of the coke forming constituents of said oil are vaporized, admixing all of said preheated oil with an oxygen-containing gas, contacting all of the resultant mixture with a bed of inert, noncatalytic, granular heat resistant material and efiecting therein combustion of said hydrocarbon oil to elevate the temperature to a point sufficient to eflect complete vaporization of said hydrocarbon including said coke-forming constituents, and then contacting the completely vaporized mixture with a contiguous bed of cracking catalyst under cracking conditions to crack said hydrocarbons.

CARL J. HELMERS.

REFERENCES CITED The following referenlces are of record in the

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