US2738307A - Hydrocracking of heavy oils - Google Patents

Description

Filed April 9. 1951 March 13, 1956 LA VERN H. BECKBERGER HYDROCRACKING OF' HEAVY OILS MM M Jfzc@ ATTORNEYS United i States Patent O HYDROCRACKING F HEAVY OILS La VernI-I. Beckherger, Markham, Ill., assigner to Sirlclair Relining Company, New York, N. Y., a corporation of Maine Application April 9, 1951, Serial No. 220,091

6 Claims. (05196-49) My invention relates to a combination fluid coking and cracking process for converting heavy oils into good yields of light, low-boiling hydrocarbons. According to my process, a heavy oil, e g. a reduced crude, is charged into a body of coke particle continuously maintained in iiuidizedcondition in a coking reaction. The larger coke particles which form are selectively removed and contacted with steam in a separate zone for generation of a water gas mixture, which is returned to the coking reaction as the fiuidizing medium. The overhead from the coking reaction is admixed with activated coke particles withdrawn from the water gas generator to form a uid suspension and the mixture is cracked to gasoline-range products.

In the co-pending application of Kenneth M. Watson, Serial No. 121,575, tiled October l5, 1949, now U. S. Patent 2,707,702, a coking process is disclosed which has the important advantage of being continuously operable without wall and reactor coking and resultant shutdown. Essentially, the process involves maintaining a bed of relatively adsorbent coke particles as seed particles in a fluidized state in the reaction zone and charging a hydrocarbon oil therein. The large particles built up by coke laydown are selectively and continuously removed from the reaction zone. Selective removal of these large coke particles is accomplished by a size classifying or elutriating system opening directly into the uidized bed of coke particles. The coke formed in the process is selectively deposited on the relatively adsorbent seed particles and the coke product is selectively withdrawn in the form of the larger particles by means of the internal elutriator which retains the smaller particles in the bed of seed coke and allows the larger particles to fall into a transportation and storage system from which they are removed as net coke make. As the uidizing medium, steam, flue gases having a low oxygen content or an inert gas such as nitrogen or a naphtha or light refractory gas oil are disclosed. The lighter components ofthe charge oil, together with the lighter decomposition products and the fluidizing and elutriating media, are taken oft overhead.

Heavy oils of the nature of residual stocks, e. g. reduced crudes, make poor charging stocks for catalytic cracking processes. Such oils ordinarily contain compounds which may either temporarily or permanently poison the catalyst, e. g., metallic salts, nitrogen-base compounds, sulfur and sulfur-containing compounds. Residual oils also contain asphaltenes and fused-ring aromatics which tend toward excessive coke make. Accordingly, in conventional practice it is practically necessary to remove such coke-forming constituents prior to cracking with a catalyst by such expedients as fractionation, deasphalting, visbreaking, pitching `or coking.

Thus residual stocks are only susceptible `to catalytic cracking when specially pretreated. The fact that clean gas oils are requisite forV catalytic` cracking processing usually means considerable extra handling is involved and that operational continuity is poor and this accounts in part for the relatively higher economic cost of such operations.

I have devised a combination tluid-type process for converting such heavy oils into good yields of gasolinerange boiling hydrocarbons by a continuous process wherein the coking operation described above is carried out in conjunction with a cracking step. According to my invention, a heavy oil is charged into a body of coke particles maintained in fluidized condition in a coking reaction vessel. The large coke particles which form are selectively removed and are contacted with steam in a separate Zone in huid-type admixture for the generation of a water gas mixture which is returned to the Coking reaction as the fluidizing medium. The lighter components of the heavy oil charged to the coking vessel are taking o overhead and are admixed with activated coke particles from the water gas generator in amount suflicient to provide a uid suspension. The uidized admixture of oil and coke particles are cracked in a reaction zone at a temperature in the range approximating 900 to 1100 F. for a period of time sufficient to effect reaction into good yields of gasoline range boiling hydrocarbons. The gasoline and other valuable light products are then separated from the eil-'tuent products of reaction.

l have also found that the overall yield of light, gasoline-range hydrocarbon products can be further improved by addition of promoting compounds to the coking and cracking steps. Accordingly, I add the carbonate of a metal selected from the left hand side of groups l and ll of the periodic vtable to accelerate the water gas reaction or I add an inorganic acid to promote the cracking reaction, or both reactions are so promoted. As exemplary of such water gas promoters, there are sodium carbonate, potassium carbonate and barium carbonate. Suitable cracking promoters include hydrochloric acid, boric acid, phosphoric acid, sulfuric acid, hydrouoric acid, hydroiiuosilicic acid, molybdic acid, vanadic acid, chloroplatinic acid and chromic acid. The promoters are added in small amounts, in quantities up to about 5 per cent by Weight on the reaction mixture.

Thus my invention offers several important advantages.

4Superiicially, heavy oils, e. g. straight-run residual stocks,

which are generally unsuited in such condition for catalytic cracking are eiectively converted to good yields of gasoline-range products. And since the coking operation is continuous the entire process may be operated without interruption or intermittent shutdown. Because the iuidizing gas, i. e. the water gas, contains a high concentration of hydrogen, the coke forming constituents in the charge oil are in part hydrogenated to lighter products in the coking vessel. Since the hydrogen is present in the coking reaction overhead with the eitluent oil products, additional hydrogenation and suppression of coke formation occurs further along in the cracking reaction.

The present invention also has the important additional advantage in that the process produces its own catalyst because the coke particles prepared are used for the cracking step. By regulation of the coking reaction through the elutriator the size of such catalyst particles may be accurately controlled. By contacting steam with the coke particles for generation of the water gas mixture, the coke is simultaneously activated and'hence when withdrawn for fluid admixture with the oil to be cracked, it is specially suited for cracking to good yields of high quality gasoline products. Thus instead of producing mere low cost coke, the coke is instead utilized in large proportions as a valuable, highly active catalyst. In addition, when the water gas mixture is injected into the coking reactor, it also takes along coke nes. These lines then act as seed coke for the coking reaction and hence my process also produces its own seed coke.

The process is capable of supplying its own heat requirements. The coke produced in excess of water gas generation requirements may be oxidized to provide such heat requirements. A heat balance is also achieved in the system between the water gas and the coking reactions. Since the hot water gas mixture is taken olf at highly elevated temperatures and is passed to the coking reaction at a somewhat lower temperature, regulation of the oxygen to steam ratio in the water gas generator will serve to etliciently control the temperature therein.

The process according to my invention will be more clearly understood by reference to Figure 1 of the accompanying drawings, which represents a somewhat schematic flow plan of my process.

The essential elements in the system are the uid coking zone, represented by iluid coker 1.5, the water gas generation zone, illustrated by fluid water gas generator 25, and fluid cracking zone, reactor 26. The water gas generator employed is adapted to handling of the coke particles while in iluid suspension and the reactor is a conventional fluid-type reactor.

As illustrated in the drawing, a residual stock, e. g. a reduced crude, is charged to the process by line 11. The feed is preheated to a temperature of about 750 F. in fired heater 1.2 and is introduced by line 13 and spray 14 into the coke bed of the fluid coker 15. To commence the operation the coke bed is charged with seed coke, for instance that obtained from a prior run. The size range of the seed coke for startup should be relatively narrow for ease in iluidization, between about 100 to 200 mesh particles (Tyler). 'In steady state operation, however, the size of the coke particles in the fluid coker will reach an equilibrium distribution determined by the overall process conditions. Fluidizing water gas at about 1200" F. from hot water gas manifold 30 is introduced to the bottom of reactor 15 by line 17. Dispersion gas is taken from the same manifold by line 18.

Coke draw-olf is effected through elutriator 19 which opens directly into the coke bed through the grid plate 20. Elutriating Water gas is provided by manifold 30 and is introduced near the bottom of elutriator 19 by line 21. The coke make is taken off by Y-connection 22 where it may be passed to storage receiver 23 by line 24 or to the water gas generator 25 by line 25a. The coke removed from the process may be used as a source of heat, that is, as fuel in the heater. The lighter components of the reaction mixture pass overhead by line 27 which contains cyclone separator 2S to remove some of the coke particles therefrom.

Processing conditions in the uid coker may be varied somewhat according to the nature of the feed stock. Thus a unit embodying my invention ordinarily charges a heavy oil such as a reduced crude. a cracking still tar or an asphalt and is run for a maximum yield of clean distillate. Under these conditions l. have found that a coke bed temperature of about 800 to 1200" F. is satisfactory. About 900 to 1000 F. is particularly desirable. To prevent heater and line coking, the heavy oil charge is heated to about 700 to 800 F. in the presence of water gas in a conventional external furnace or heater coil and is sprayed into the reactor bed. The hot water gas, in addition to preheating the oil, minimizes excessive coke formation because of the hydrogen present.

The coke reactor pressure is advantageously kept relatively low, ranging from about atmospheric to about 75 p. s. i. The density of the luidized coke bed varies from about 25 to about 50 pounds per cubic foot but is generally of the order of about to 40 pounds per cubic foot. Fluidizing water gas flow lower than about 1 foot per second is suilicient for 100 to 200 mesh coke particles. Higher superficial velocities are limited by excessive carry-over.

The lighter components pass overhead by line 27 and are carried to reactor 26. The coke formed in the reaction required for heat and water gas is transported by steam from line 29 to water gas generator 25. The steam is preheated in admixture with oxygen, to about 350 F.

The mixture of steam, oxygen and coke is reacted in the generator and the water gas resulting is carried by manifold line 30. Cyclone separator 31 separates out a large portion of the coke fines prior to passage to the manifold lines 30 and 45.

Reaction conditions in the water gas generator may be varied somewhat and depend largely upon the available oxygen. A temperature between about 1200 to 1600 F. is generally employed, advantageously about 1400 F. The fines that carry over to the coking reactor serves as a continuous source of seed particles for the coking reaction. The hot elfuent water gas mixture given off at about 1400o F. provides practically all of the heat for the coking reaction and the actual rate of flow in the lines in and out of the generator are suitably regulated for such a heat balance. To minimize inert gas handling through the processing stages and to provide a maximum hydrogen partial pressure throughout, I utilize high purity oxygen in the generator. Generally, oxygen purity at least as high as per cent is necessary to minimize such inert gas formation. per cent plus pure oxygen may be needed in some instances to accomplish this. In addition, heat balance is maintained on the fluid coke and water gas generator by regulating the ratio of oxygen to steam in the generator.

The water gas formation is accelerated by the introduction into generator 25 of a small amount of sodium carbonate. The sodium carbonate is added from line fr?. as a finely divided solid in admixture with steam. The metal carbonate promoters are usually added in iinely-divided form by direct injection into the generator bed by means of the steam line, or addition may be made through the cyclone. The hot coke particles in the generator 25 are removed through standpipe 33 and injected into the oil line 27 from the coker overhead.

The activated coke particles are then mixed with the distillate stream to form a suspension of the uid type, and the mixture is cracked. The coke particles are added in considerable excess over the distillate portion, that is, in excess of a coke-oil ratio of 1:1 to as high as 30:1 Generally, ratios of about 5:1 to 15:1 are particularly satisfactory. The size of the coke particles used in the fluid suspension are regulated back at the coker by appropriate adjustment of the elutriating means. Usually, the particle size measure is varied between about 50 to mesh ("l`y1er); satisfactory results are provided when the size varies between about 5 and 50 per cent on a 100- mesh screen. The density of the reactor bed will vary between about 25 to 35 pounds per cubic foot and about 28 to 30 pounds per cubic foot is usually provided. The reaction is carried out at moderate temperatures in the range approximating 900 to l000 F., advantageously at about 950 F. The reaction pressures may be varied bctween about atmospheric to 50 p. s. i. g. Advantageously, the reaction is carried out at about 950 F. for a pressure between about l0 to 30 p. s. i. g.

A small amount of hydrochloric acid gas is added by line 3d to promote the cracking reaction. The acid promotors are usually added as a gas to the coke as it is taken from the generator or to the coke-oil stream just prior to entrance into the cracking zone.

The efuent products of reaction are taken off from reactor 26 by line 35' after passing through cyclone separators 36 for the separation of suspended catalyst matter. rEhe vapors are passed to separator 44 by the line 35. ln the separator 134, the components of the efuent are separated. The non-condensible or fixed gases are recovered by line 46, the water (as steam) by line 47, the gasolinerange products by line i8 and diesel fuel or heating oil by line 49. The heavy oil, boiling above about 650 F., and catalyst remaining therein is taken off as a slurry by line 50 and may be recycled as feed material.

l claim:

l. The combination Huid-type process for coking and cracking a heavy oil which comprises introducing the heavy oil into a body of coke particles maintained in uidized condition in a coking zone by injection therein of a water gas mixture, selectively removing large coke particles as formed from the coking zone to the substantial exclusion of smaller particles by size classifying the coke particles by means of an elutriating gas passing into the Vbody of coke particles and contacting a iiuid suspension of said large coke particles with steam in a separate zone to generate a water gas mixture, returning said Water gas mixture to the coking zone as the uidizing medium, taking off the hydrocarbon overhead from the coking zone and admixing same with activated coke particles from the water gas generation zone so as to provide a Huid suspension, cracking said iluid mixture at elevated temperatures in the range approximating 900 to 1100" F. for a time sufficient to produce light gasolinerange boiling hydrocarbons, and separating said gasoline products from the eluent.

2. A process according to claim 1 wherein an inorganic acid is added in amount suicient to promote the cracking reaction.

3. A process according to claim 1 wherein a carbonate of a metal selected from the left hand side of group I and II of the periodic table is added in amount sufficient to promote the water gas reaction.

4. A process according to claim l wherein the oxygen present in the water gas generation zone is of suiciently high purity to substantially minimize inert gas dilution.4

5. A process according to claim 1 wherein the heavy oil and catalyst matter separated from the etlluent products of reaction are recycled to the coking zone.

6. A process according to claim 1 wherein hydrocarbon overhead from the coking zone is admixed with activated coke particles from the water gas generation zone so as to provide a uidized mixture, the uidized mixture is cracked at elevated temperatures in the range approximating 900 to 1100 F. for a time sucient to produce light gasoline-range boiling hydrocarbons and said gasoline products are separated from the effluent.

References Cited in the file of this patent UNITED STATES PATENTS 2,097,989 Schick et al. Nov. 2, 1937 2,407,052 Bailey et al. Sept. 3, 1946 2,416,003 Guyer Feb. 1S, 1947 2,428,715 Marisic Oct. 7, 1947 2,527,575 Roetheli Oct. 31, 1950 2,600,430 Riblett June 17, 1952

Claims (1)

1. THE COMBINATION FLUID-TYPE PROCESS FOR COKING AND CRACKING A HEAVY OIL WHICH COMPRISES INTRODUCING THE HEAVY OIL INTO A BODY OF COKE PARTICLES MAINTAINED IN FLUIDIZED CONDITION IN A COKING ZONE BY INJECTION THEREIN OF A WATER GAS MIXTURE, SELEVTIVELY REMOVING LARGE COKE PARTICLES AS FORMED FROM THE COOKING ZONE TO THE SUBSTANTIAL EXCLUSION OF SMALLER PARTICLES BY SIZE CLASSIFYING THE COKE PARTICLES BY MEANS OF AN ELUTRIATING GAS PASSING INTO THE BODY OF COKE PARTICLES AND CONTACTING A FLUID SUSPENSION OF SAID LARGE COKE PARTICLES WITH STREAM IN A SEPARATE ZONE TO GENERATE A WATER GAS MIXTURE, RETURNING SAID WATER GAS MIXTURE TO THE COKING ZONE AS THE FLUIDIZING MEDIUM, TAKING OFF THE HYDROCARBON OVERHEAD FROM THE COKING ZONE AND ADMIXING SAME WITH ACTIVATED COKE PARTICLES FROM THE WATER GAS GENERATION ZONE SO AS TO PROVIDE A FLUID SUSPENSION, CRACKING SAID FLUID MIXTURE AT ELEVATED TEMEPRATURES IN THE RANGE APPROXIMATING 900* TO 1100* F. FOR A TIME SUFFICIENT TO PRODUCE LIGHT GASOLINERANGE BOILING HYDROCARBONS, AND SEPARATING SAID GASOLINE PRODUCTS FROM THE EFFLUENT.

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