US2763600A - Upgrading of heavy hydrocarbonaceous residues - Google Patents

Description

ffl 18, 1956 C, E ADAMS ET AL `2,763,600

UPGRADING OF HEAVY HYDROCARBONACEOUS RESIDUES Filed May 19, 1951 United States Patent UPGRADING F HEAVY HYDRGCARBNACEOUS RESIDUES Clark E. Adams and Charles N. Kimber-lin, Jr., Baton Rouge, La., assignors to Esso Research and Engineering Company, a corporation of Delaware Application May 19, 1951, Serial No. 227,236

4 Claims. (Cl. 196-52) The present invention relates to a process of treating hydrocarbons. More particularly, the invention pertains to a method of producing from relatively heavy or high boiling hydrocarbonaceous residues of the type of topped or reduced crude, pitch, asphalt or similar heavy residues increased quantities of motor fuel range fractions of improved quality as well as higher boiling distillate fractions suitable for further cracking. Briefly, the invention provides for coking heavy residues of the type specified in contact with a dense, turbulent, fluidized mass of subdivided inert solids to produce volatile coking products and coke and then subjecting the total volatile coking products immediately and without condensation to catalytic cracking for a relatively short time in the presence of large proportions of finely divided catalyst suspended in the vapors to be cracked.

It has been known for a long time that motor fuels and higher boiling distillate oils may be produced by coking crude residua, that is by subjecting the residues to cracking at severe conditions including relatively high temperatures and long holding times. The use of cracking catalysts in this reaction has likewise been proposed. However, serious difficulties have been encountered in this type of operation chieliy as the result of the high ash content of the feed and the high rate of coke formation. Aside from the fact that the heavy coke deposits in the coking vessels and transfer lines require frequent cleaning periods and plant shut-downs, catalyst contamination and deactivation by Icoke and diflicultly removable ash constituents of the feed is so rapid that crude residua have been considered highly undesirable as feed stocks for conventional catalytic cracking processes.

Some of these difficulties may be avoided in accordance with prior suggestions by coking residues in a dense, turbulent bed of hot subdivided catalytically inert solids, such as coke, pumice, kieselguhr, spent clay, sand, or the like, fluidized by upwardly llowing gases or vapors. These solids serve primarily as a carrier for the coke formed and as a scouring agent preventing coke deposition on equipment walls. Also gasoline yields are somewhat higher as a result of the high surface area of the solids. The coke deposited on the solids may be burnt off in a separate fluid-type heater vessel from which hot solids may be returned to supply heat required for coking. It is a matter of record that fluid operation affords greatest advantages with respect to heat transfer and economy,

temperature control, ease and continuity of operation, etc.

While procedures of this type avoid catalyst contamination and heat supply by circulating catalyst, they are essentially thermal rather than catalytic in character and, therefore, result in the production of motor fuels of relatively low octane rating. The addition of a cracking catalyst in itself to the inert material is no complete solution of the problem because there still remains the diliiculty of catalyst contamination and deactivation by ash constituents of the feed, which cannot readily be removed by simple oxidative regeneration. In addition,

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large amounts of inert solids must be circulated together with the catalyst between reactor and regenerator.

It has also been suggested to pass the entire volatile effluent of a fluid-type inert solids coking zone without substantial heat loss or condensation to a separate iiuidtype dense phase catalytic cracking reactor. This method affords important advantages with respect to heat econonly, quality and yield of valuable products as well as continuity of operation. However, the arrangement of a second fluid-type dense phase reactor considerably adds to investment and maintenance cost. The connecting line between the two reactors which is maintained at coking temperatures is substantially free of subdivided solids, thus permitting coke deposition on the walls and plugging of the line. In addition, dense phase fluid operation does not readily lend itself to short time low severity cracking which is conducive to higher yields of better quality gasoline when applied to the volatile coking products of dense phase inert solids fluid-type coking of residual oils. The present invention eliminates these drawbacks.

lt is, therefore, the principal object of the invention to provide improved means for producing motor fuels by coking heavy residua in contact with lluidized inert solids followed by catalytic cracking of the total volatile coking product on subdivided suspended catalysts. Other objects and advantages will appear from the description of the invention given below wherein reference will be made to the accompanying drawing, the single ligure of which is a semi-diagrammatical illustration of a system suitable to carry out a preferred embodiment of the invention.

In accordance with the present invention, heavy hydrocarbonaceous residues of the type specified above are contacted at coking conditions in a dense phase fluid-type reactor with a dense, turbulent, uidized mass of catalytically substantially inert solids to convert the feed into lower boiling volatile products and coke depositing on the inert solids and to remove contaminating ash constituents of the feed. The total volatile eliiuent of this coking stage is mixed immediately and without any prior condensation with finely divided cracking catalyst in relatively high proportions and the mixture formed is passed at cracking conditions in the form of a dense suspension and at a relatively high velocity through a narrowly confined extended path for a time sulicient to produce optimum yields of high quality motor fuels. The process is preferably so operated that the cracking catalyst is added to the volatile eiuent of the coking stage immediately after the removal therefrom of solids fines entrained from the fluid coking Zone, so that the time interval for which the vapors are subjected to coking temperatures in the absence of suspended solids 'is reduced to a minimum or practically eliminated. The best place for introducing at least a part of the catalyst is the point at which the vapors enter -thevapor withdrawal line of the coking reactor.

While some of the inert solids previously suggested for the iluid coking of residues, such as sand, pumice, spent clays, silica gel, etc., may be used in the coking bed, coke affords greatest advantages in the process of the invention because product coke deposited on this material forms a valuable oy-product which may be recovered as a high B. t. u. fuel, as a raw material for activated carbon, for the production of'carbon electrodes, etc. Conventional cracking catalysts including activated clays, activated alumina, synthetic composites of silica gel with alumina, magnesia, and/ or boria, etc. may be used in the catalytic cracking zone.

Fluidization conditions in the coking zone may be maintained within conventional ranges. The particle size of the inert solids depends, of course, to a certain extent on their density. Assuming a density of the order of that of coke, the particle size may be about lll-200 microns, preferably 50p-15() microns. Linear superficial lluidizing velocities of the iiuidizing medium may vary from 0.35 ft. per second, preferably from about 0.5-1.5 ft. per second, to establish an apparent density of the iiuidized bed of about 20-50 lbs. per cu. ft. and a definite upper interface Within the coking zone. The cracking catalysts, most of which have ydensities similar to that of coke, may be used in substantially the same size ranges and should be added to the vaporous coking zone eifluent in amounts of about 30G-5000 lbs. per barrel of residuum feed. The mixture of vapors and catalyst may be passed through the transfer line cracking zone at a vapor velocity of about 5-25 ft. per second, preferably about lil-20 ft. per second to establish apparent densities of the turbulent suspension of about l-ZO lbs. per cu. ft., depending partly on the slope of the cracking path which may vary from substantially horizontal to substantially vertical with upward iiow of the reactants. The steeper the slope of the path the more pronounced is the tendency of the solids to lag behind the gases by the phenomenon known as hindered settling and the 'denser is the suspension and the greater the tendency of solids back-mixing against the flow of the reactants. However, normally no definite interface develops at these conditions. Horizontal to slightly inclined cracking paths conducive to apparent densities of about 5-15 lbs. per cu. ft. and to limited hindered settling and catalyst back-mixing are preferred for the purposes of the invention.

Reaction conditions may include coking temperatures of about 850-1l00 F. and catalytic cracking temperatures of about 800-1000 F. Pressures ranging from atmospheric to about 100 p. s. i. g. may be employed throughout. The solids hold-up in the coking zone may be chosen to permit vapor residence times of about -60 seconds. Substantially shorter vapor residence times of about 2-10 seconds, preferably about 4 8 seconds, are maintained in the catalytic cracking zone.

Heat required by the endothermic coking and catalytic cracking reactions may be supplied by indirect heating or by the circulation of reheated process solids in any manner known in the art. However, in accordance with the preferred method of heat supply the heat generated by a combustion-type of catalyst regeneration is used to maintain the desired temperatures in the coking and catalytic cracking zones. It has been found that the coke deposited on the catalyst in the course of the catalytic cracking reaction carried out in accordance with the invention is sufficient for this purpose. Briefly, this may be accomplished by separating used catalyst from the cracked vapors, burning coke olf the catalyst in a dense vphase fluidtype regeneration zone and circulating coker solids from the coker through a heat exchange coil immersed in the regenerator bed and back to the coker, while returning hot regenerated catalyst to the catalytic cracking zone.

Having set forth .its objects and general nature, the invention will be best understood from the following .description of the embodiment rillustrated by the drawing.

Referring now in detail to the drawing, the system illustrated therein essentially comprises a dense phase fluid-type coker l1, .a catalytic transfer line type reactor 23 and a dense phase fluid-type catalyst regenerator 37. The functions and coaction of these elements will be forthwith described using the conversion of virgin crude distillation bottoms into motor fuels as an example. It should be understood, however, that the systems may be employed for the conversion of .other coke-forming feed stocks `into the same or different products in a substantially analogous manner.

ln operation,`reduced crude, such as a 2.53.5% bottoms fraction from the vacuum distillation of a South Louisiana crude or a similar heavy residue, is supplied substantially in the liqud Vstate at a temperature of about 30D-500 F. to line 1 and further preheated to about 500700 F. in heat exchanger 3 as will appear more clearly hereinafter. The preheated feed discharges through line 5 and a spray nozzle 7 into a lower portion of coker 11 at a point above a suitable gas distributing means such as a perforated plate or grid 13. Coker 11 contains a dense, turbulent, iiuidized mass M11 of inert solids, having an upper interface L11 and maintained at about 850-l050 F. The oil feed rate to coker 11 may be about 0.5 barrel to about 25 barrels per hour per ton of solids hold-up in coking zone 11 at oil vapor residence times of about l0 to 60 seconds in mass M11. The feed rate depends upon the temperature; at SSW-959 F.y the feed rate may be 0.5-4 bbl./hr./ton, at 950%1050" F. the rate may be about 2.5-10 bbl./hr./ton, above l050 F. the rate may be about 5-25 bbl./hr./ ton. A iiuidizing gas such as steam, hydrocarbon gases or vapors is supplied through line 1S and grid i3 to establish a linear superficial gas velocity of about 0.3-3 ft./sec. and an apparent density of about 2li-50 lbs/cu. ft. in mass M11. Any of the inert solids mentioned above may be used in coker 1l. However, coke having a particle size of about 50-150 microns is preferred. The temperature in coker 11 is maintained at about 850-105G F. as will appear hereinafter. Atmospheric or a slightly elevated pressure is generally most desirable. At these conditions, the oil feed may be converted to yield about 88-90 wt. percent of volatile products and about 10-12 wt. percent of coke which is deposited on the coke in mass M11, when feeding, for example, a South Louisiana vacuum residuum having an API gravity of about 12 and a Conradson carbon of about 17%. Simultaneously, the ash contaminants are removed from the feed and largely retained by mass M11. To prevent an excessive accumulation of coke particles which have by coke Ideposition grown to a nonflui'dizable size and to recover product coke, a standpipe 16 is provided through which coke may be Withdrawn from mass M11 as required. A portion of the coke Withdrawn may be recovered through line 18. The remainder may be ground in grinder 29 to a fluidizable size and returned via lines 22 and 15 to mass M11. Volatile products containing entrained coke fines pass overhead from level L11 into suitable gas-solids separation means such as cyclone separator 17 provided with solids return pipe 19.

The vaporous products substantially free of entrained coke leave separator i7 taough line 2.1 which leads directly into transfer line reactor 23. ln order to reduce the time for which the hot coking products are free of suspended solids to the practical minimum closely approaching zero, at least a portion of the cracking catalyst required for the catalytic cracking reaction is introduced through line 25 into line 2l close `to its intake end adjacent to separator 17. Any remainder of the required catalyst supply may be fed through line 2:7 to reactor 23. .Lines 2S and 27 receive regenerated catalyst admixed with carrier gas from line Z9 at a temperature of about 80.0- 1050" F. as will appear more clearly hereinafter. The total catalyst feed rate to reactor .23 should be about 3D0-5,000 lbs. per barrel of residuum. The mixture of catalyst and reactants vmay enter reactor 2.3 at a tempera- `ture of Vabout Gl000 F. Due to the endothermic heat of cracking the temperature will decrease as the mixture of voil and catalyst pass through the Vtransfer line. The amount of this drop in temperature will depend upon the conversion in the transfer line and upon the catalyst lto oil ratio, and may be as much as 50 F.

For the purposes of the present example, reactor 2.3 yis shown as a substantially horizontal pipe having a length/ diameter ratio of at least about 12/1 which should be designed for a velocity of about itl-20 ft./sec. and a vapor residence time of about 4-8 seconds at the feed rates involved. At the conditions specified, the sus-pension in reactor 23 will have a density of about 2-15 lbs/cu. ft., no appreciable solids `settling or backmixing taking place. Reactor 239 discharges into a suitable gas-solids separator such as cyclone 311 from which a mixture of cracked products and carrier gas, substantially free of catalyst, may be withdrawn through jline to be passed to conventional product recovery equipment (not shown).

In the course of the catalytic cracking reaction, coke is deposited on the catalyst requiring its regeneration. For this purpose, catalyst separated in cyclone 31 is dropped through dip-pipe 35 into catalyst regenerator 37 which is supplied with air through line 39 and grid 41, sufiicient in amounts to restore catalyst activity by coke combustion. The linear superfici-al velocity of the gases in regenerator 37 is maintained at about 0.3-1.5 ft./sec. conductive to the formation of a dense, turbulent fluidized catalyst mass M37 having a definite interface L37 and an apparent density of about 20-50 lbs/cu. ft. and exhibiting excellent heat transfer characteristics. Flue gases are Withdrawn overhead from level L37 through cyclone separator 43 to be vented through line 45. Separated catalyst fines may be returned via dip-pipe 47 to mass M31 or discarded through line 49.

Combustion of the amount of coke which must be removed for catalyst regeneration generates so much heat that excessive temperatures detrimental for the cat-alyst will be reached unless a portion of this heat is dissipated. Cooling of mass M37 is therefore required. In accordance with the invention advantage is taken of this requirement to supply the heat needed in coker 11. For this purpose, a heat exchange coil or bank of heat exchange pipes 51 i-s immersed in mass M37, both the intake and discharge ends of which are arranged in mass M11 of coker 11. An impelling gasiform diluent such as steam is injected via taps t into lines 53 and 55 connecting coil 51 with mass M11. The direction of diluent injection as indicated by the inclination of taps t is such that coke from mass M11 circulates through line 53 to coil 5'1 and through line 55 back to mass M11. ICoke circulation may be readily so controlled in this manner that, at a practical surface area of coil 51, the catalyst in mass M37 may be maintained at desirable temperatures of about 10001l50 F. and mass M11 at the coking temperatures specified above. Suitable circulation rates may be about 1-3 tons of coke per barrel of residuum feed assuming an immersed surface area of coil S1 of about 0.5-2 sq. ft. per barrel of daily feed rate.

Regenerated catalyst 4is withdrawn substantially at the temperature of mass M37 through line 57 and may be further cooled to `about 800-1050 F. in heat exchange with the feed residuum in heat exchanger 3 as described above. rPhe cataly-st in line 57 may be stripped and aerated by means of steam or other inert gas injected through lines 59. Make-up catalyst may be added through line 61 as required. Line 57 discharges into line 29 which is supplied via line 63 with a suitable carrier diluent such yas steam or hydrocarbon gas in amounts and at a velocity adequate to convey the catalyst to lines 25 and/or 27 as described above.

The system illustrated in the drawing permits of various modifications. For example, lthe oil feed may be injected together with the tiuidizing medium through line 15 and grid 13, rather than through nozzle 7. Other modifications within the spirit of the invention will appear to those skilled in the art.

It will be appreciated that the yields will vary somewhat with the severity of the operations in both the thermal and catalytic zones and also with the rate of catalyst replacement. When operating as described with a sufficiently high catalyst replacement rate to maintain the catalyst in a high state of activity and selectivity, the following may be given as illustrative of the yields to be expected from a South Louisiana vacuum residuum of gravity of about 12 API and Conradson carbon of about 17%:

(1) 4-12 wt. per cen-t (based on residuum) of catalytic coke. All of this coke must be burned for catalyst regeneration.

(2) 8-22 wt. per cent gas including 4-12 wt. per cent of propylene that can be polymerized to `further increase gasoline yield.

(3) 3652 vol. per cent `of gasoline boiling up to 430 F. and having an octane number of -96 by the research method.

(4) 8-18 vol. per cent heating oil 'boiling within the range of 430650 F.

(5) 15-25 vol. per cent of bottoms eut boiling above about 650 P. This material may be recycled.

The above description and exemplary operations have served to illustrate specific embodiments of the invention ybut are not intended to be limiting in scope.

What is claimed is:

1. The process of coking and cracking heavy residual hydrocarbon oils which comprises passing said oils through a relatively dense fluidized bed of catalytically inert preheated solids, thereby forming coke and hydro carbon vapors, passing the vapors out of said zone into immediate contact with finely divided preheated cracking catalyst having a temperature of at least 800 F. and not greater than 1050 F. to form a relatively disperse suspension of said catalyst in said vapors so as to keep said vapors substantially continuously in contact either with said inert solids or said catalyst to pre-vent degradation thereof and formation of coke deposits, passing said suspension along a narrow restricted path of substantial length at a linear velocity sutiicient to maintain said disperse suspension and for a time, 2 to 10 seconds, sufcient to accomplish substantial cracking of said vapors, separating the catalyst from the suspension and passing it through a uidized regeneration zone with an oxidizing gas to reheat and regenerate the catalyst, and transferring heat from the regenerator by both returning regenerated catalyst to the zone of said suspension and by indirectly reheating the inert solids in the coking zone by circulating solids in indirect heat exchange between the coking zone and the regeneration zone.

2. Process according to claim 1 wherein the inert solids in the coking zone are predominantly coke particles obtained by the coking operation.

3. The process of converting heavy residual oil to lower boiling products which comprises contacting said oil with a uidized mass of hot particulate solids which are catalytically inert, at a temperature within the range of about 850 to 1100 F. and for a time to substantially crack said oil to vapors, passing said vapors with entrained fine particles of said solids through a solids separation zone to substantially remove said solids, and immediately adding other solid particles at a temperature of at least 800 F. and not greater than 1050 F., said particles being added directly to the outlet from the sepa ration zone to join with the vapor stream leaving said separation zone said solid being added in sufficient proportions substantially to prevent condensation of said vapors and formation of carbonaceous deposits in the outlet from said separation zone.

4. Process according to claim 3 wherein said added solid particles comprise cracking catalyst particles.

References Cited inthe file of this patent UNITED STATES PATENTS 2,348,009 Johnson et al. May 2, 1944 2,378,531 Becker June 19, 1945 2,382,755 Tyson Aug. 14, 1945 2,388,055 Hemminger Oct. 30, 1945 2,396,109 Martin Mar. 5, 1946 2,445,328 Keith July 20, 1948 2,471,104 Gohr May 28, 1949 2,675,294 Keith Apr. 13, 1954

Claims (1)

1. THE PROCESS OF COKING AND CRACKING HEAVY RESIDUAL HYDROCARBON OILS WHICH COMPRISES PASSING SAID OILS THROUGH A RELATIVELY DENSE FLUIDIZED BED OF CATALYTICALLY INERT PREHEATED SOLIDS, THEREBY FORMING COKE AND HYDROCARBON VAPORS, PASSING THE VAPORS OUT OF SAID ZONE INTO IMMEDIATE CONTACT WITH FINELY DIVIDED PREHEATED CRACKING CATALYST HAVING A TEMPERATURE OF AT LEAST 800* F. AND NOT GREATER THAN 1050* F. TO FORM A RELATIVELY DISPERSE SUSPENSION OF SAID CATALYST IN SAID VAPORS SO AS TO KEEP SAID VAPORS SUBSTANTIALLY CONTINUOUSLY IN CONTACT EITHER WITH SAID INERT SOLIDS OR SAID CATALYST TO PREVENT DEGRADATION THEREOF AND FORMATION OF COKE DEPOSITS, PASSING SAID SUSPENSION ALONG A NARROW RESTRICTED PATH OF SUBSTANTIAL LENGTH AT A LINEAR VELOCITY SUFFICIENT TO MAINTAIN SAID DISPERSE SUSPENSION AND FOR A TIME, 2 TO 10 SECONDS, SUFFICIENT TO ACCOMPLISH SUBSTANTIAL CRACKING OF SAID VAPORS, SEPARATING THE CATALYST FROM THE SUSPENSION AND PASSING IT THROUGH A FLUIDIZED REGENERATION ZONE WITH AN OXIDIZING GAS TO REHEAT AND REGENERATE THE CATALYST, AND TRANSFERRING HEAT FROM THE REGENERATOR BY BOTH RETURNING REGENERATED CATALYST TO THE ZONE OF SAID SUSPENSION AND BY INDIRECTLY REHEATING THE INERT SOLIDS IN THE COKING ZONE BY CIRCULATING SOLIDS IN INDIRECT HEAT EXCHANGE BETWEEN THE COKING ZONE AND THE REGENERATION ZONE.

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