US2913396A - Contact carrier for hydrocarbon conversion - Google Patents

Description

United States Pat;

CONTACT CARRIER FOR HYDROCARBON CONVERSION No Drawing. Application October 28, 1953 Serial No. 388,903

9 Claims. (Cl. 208-107) This invention relates to a solid contact material or carrier for effecting conversion of hydrocarbon oils into more valuable products and to a process of hydrocarbon conversion employing the contact material. More particularly, the invention is concerned with a carrier and process of the character indicated which are effective in converting heavy hydrocarbons like topped crudes to gasoline and other valuable liquid hydrocarbons in high yields and with minimum formation of coke.

In modern petroleum refining practice, it is highly advantageous to convert as much as possible of the higher boiling portions of a petroleum oil to materials boiling in the gasoline range. At the present time, this is accomplished by several processes known broadly as catalytic cracking, wherein higher boiling hydrocarbons are converted to gasoline in contact with a particulate solid. In modern catalytic cracking processes this particulate solid acts catalytically in the cracking zone to increase the rate of desired reactions and serves as a carrier on which carbonaceous residues are deposited and continuously transported to a regeneration zone wherein they are removed by burning. After regeneration the hot particulate solid is returned to the cracking zone and provides the heat required for the cracking reactions. It has been found that the limiting factor in the capacity of such cracking processes is the regeneration step, i.e., the capacity of the regenerator to burn olf the carbonaceous residues on the carrier. Thus, catalytic cracking processes have been employed on distillate charge stocks from which only small yields of carbonaceous residues are obtained. Although it is desirable to convert the residuum fraction of the crude to lighter products, this fraction has not been employed as charge stock for known catalytic cracking processes, primarily because of the high yields of carbonaceous residues obtained from such heavy stocks in these processes. For example, pilot plant tests indicate that the processing of a 25% by volume residuum from Kuwait crude by conventional catalytic cracking techniques will yield about 30% of carbonaceous residue based on the charge weight, causing rapid deactivation of the catalyst and placing such an excessive load on the regeneration system that operation cannot be carried out economically.

It has been thought that the only way to avoid these difficulties was to prevent the asphaltenes and other undesired components of the heavy oil from entering the cracker, e.g., by giving the oil a pretreatment. Thus, socalled delayed coking has been used as a method of preliminarily treating a heavy feed stock for subsequent conventional catalytic cracking. However, the delayed coker is expensive with respect to capital and operating costs, the yield of valuable hydrocarbons is low, and a large proportion of the charge is converted solely to low value coke.

Propane deasphalting has likewise been used for the preliminary treatment of heavy oils to provide feed stocks suitable for conventional catalytic cracking operations. This processing scheme offers little advantage over the delayed coker.

As a result of the lack of commercially satisfactory means for handling heavy stocks, it has been customary practice to market many heavy, sour crudes or petroleum residua as Bunker C fuel oil or as asphalt, where possible. Since, however, these hydrocarbon oils generally have a relatively high sulfur content, the Bunker C fuel market is limited and the asphalt market is small in relation to the large amounts of such stocks available. As a result, many wells which would produce large quantities of heavy, sour crudes are shut-in.

Since heavy crudes are forming an ever greater proportion of the total crudes available for gasoline production, the satisfactory processing of such crudes, and particularly the processing of such crudes to produce high octane gasoline, without the concurrent formation of large quantities of undesired by-products, are technical and economic problems of increasing importance.

It is an object of the present invention to provide a contact material or carrier for use in the conversion of hydrocarbons which is eifective to convert heavy hydrocarbons directly into valuable liquid hydrocarbonswithout preliminary treatment of the charge stock.

It is a further object to provide a process of hydrocarbon conversion which utilizes the improved carrier to produce high quality liquid products from heavy oils with minimum coke formation and commercially attractive feed rates.

Still another object of the invention is to provide a process of hydrocarbon conversion which in a single step produces high yields of valuable liquid products from heavy oils which cannot be processed by conventional catalytic cracking methods without a preliminary treatment.

The invention is based on the discovery that the particulate contact material or carrier employed for cracking heavy oils must possess certain internal structural characteristics which may be defined in terms of values determined by two relatively simple tests. If the structural characteristics of the particulate contact material are maintained within the limits prescribed hereinbelow, cracking of a heavy stock may be eflected with a high feed capacity and with minimum formation of carbonaceous residue. However, if the prescribed limits are exceeded, either the feed capacity of a given reaction system will be markedly reduced or a high yield of carbonaceous residue will be obtained. More specifically, there is provided, in accordance with the invention, a carrier which has a BET value below 50 square meters per gram, as defined by Brunauer, Emmett and Teller (J. Am. Chem. Soc. 60, 309 (1938)), together with a toluene absorption index in excess of 7, as measured by the hereindescribed method. The toluene absorption value is preferably at least 10 and is as high as possible, but with commonly available materials it generally will not exceed about 25. The carrier thus provided has an extensive surface for sorption which makes possible largefeed rates of hydrocarbon oils without impairing the fluidizing characteristics of the carrier, but the surface is of such a character that the sorbed oil is readily removed from the carrier by cracking and stripping so that little carbonaceous residue is obtained from slow polymerization reactions of the type which occur when such oil is tenaciously retained by the carrier.

While this invention is not bound to any particular theory concerning the structure of the contact material, it seems reasonable to believe that each particle of the contact material contains many relatively large pores or' fissures in which oil may be retained without the exteriorsurface of the particle becoming ostensibly wet and without. the particle agglomeration which results when fluidized particles'become superficially wet. Moreover, these pores or fissures are sufficiently large that the oil or products therefrom can be readily removed from the particle, minimizing coke formation by the aforementioned mechanism. Thus, the BET value, conventionally expressed as the surface area of a unit Weight of solids, provides a measure of the number of ultramicroscopic pores or fissures. The toluene absorption value provides a measure of the capacity of a solid to sorb liquid Without Wetting the particle surface sufiiciently to impair fluidization. With a carrier having a BET value and a toluene absorption index within the herein prescribed limits, high feed capacity operation with heavy oils is 7 possible.

The BET value is determined by a conventional test which has been widely employed since it was initially described (Brunauen Emmett and Teller, J. Am. Chem. Soc. 60, 309 (1938)). The results of this test are conventionally expressed in terms of the square meters of surface area on one gram of solid under given test conditions. The method used to carry out this test is described, for example, in Physical Methods of Organic Chemistry, second ed., Interscience Publishers, Inc., 1949, vol. I, chap. 10, p. 468 et seq., and The Adsorption of Gases and Vapors, Stephen Brunauer, Princeton University Press, 1943, vol. I, chap. III, p. 29 et seq. As will be evident from the examples which follow, the carriers of this invention have BET values which are markedly lower than those of carriers conventionally employed in catalytic cracking processes.

The procedure for the determination of the toluene absorption index is as follows: A sample of the particulate carrier is placed in a vertical glass column, then wetted down with toluene, after which air is blown up through the sample in the column until a fluidized bed is obtained. At this time, a sample of the solid is removed from the column and its toluene content determined. The glass column employed has a total height of 100 cm. and is composed of 3 sections, the lowest being 3.5 mm. I.D., 2.5 cm. in height, the middle section 22 mm. I.D., 80 cm. in height, and the top section being 34 mm. ID, and 17.5 cm. in height. The carrier to be tested is initially dried and then charged to the column, filling it statically to approximately the midpoint of the middle (22 mm. ID.) section. Toluene is then poured into the column in sufiicient quantity to wet thoroughly the solid therein. A gas, conveniently air, is fed at room temperature (65-75 F.) to the bottom of the column at a rate corresponding to a superficial velocity of one foot per second in the middle section. During this time the sample is periodically stirred with a long twisted rod to move material which may stick to the walls of the column. Air flow is continued until the solid in the column begins to move freely and expands to the top of the middle (22 mm. ID.) section. At this time, a sample of the solid is immediately removed from the column, weighed, and placed in an oven at a temperature of about 110 C. After two hours at this temperature, the solid is cooled and reweighed. The dilference in these weights represents the weight of toluene sorbed on the sample when a true fluidized condition of the carrier was achieved. To obtain the toluene absorption index, this quantity is converted to the basis of 100 grams of sample, and thus represents the weight percent of toluene sorbed on the dry sample when the fluidized condition was obtained.

This test is based on the similarity in the physical properties of toluene at room temperature and those of heavy aromatic residuum fractions at cracking temperatures. Thus, the test provides an approximate measure of the quantity of aromatic liquid hydrocarbons which may be retained on the carrier at actual cracking conditions without impairment of the fiuidizing characteristics of the carrier.

The carrier with the desired combination of BET value and toluene absorption index is preferably of a particle size which is readily fluidized. As is well known, the optimum particle size range varies widely with the specific density and particle shape of the carrier and with the density and viscosity of the gaseous medium employed for fluidization. However, suitable carriers are predominantly finer than 20 mesh and preferably are at least 50% by weight finer than mesh.

An illustrative example of a contact material which meets the specified combination of BET value and toluene absorption index is provided by trihydric bauxite which is ground and then subjected to a temperature of 1800 to 2000" F. for 4 to 100 hours. The solid thus obtained has a BET value of 30 to 40 square meters per gram and a toluene absorption index of about 18 to 19.

Similarly, trihydric bauxite may be heated to 1000 F. for 8 to 24 hours, after which it may be impregnated with a solution of a relatively inexpensive inorganic salt such as sodium chloride, sodium fluoride or calcium chloride. Bauxite treated in this manner to contain of the order of 2% by weight of sodium chloride has a BET value of 20 square meters per gram and a toluene absorption index of 14.

Although activated clays and analogous cracking catalysts usually have BET values exceeding 200 square meters per gram, such solids can be converted into materials suitable for use in accordance with the invention by treatment with steam at temperatures above 1400 F. After such treatment, a sample prepared from Attapulgite was found to have a BET value of 45 square meters per gram and a toluene absorption index of 19.7. Other known methods of decreasing the BET values of cracking catalysts to below about 50 square meters per gram may be used.

Petroleum coke, as usually prepared, has a satisfactory BET value but a low toluene absorption index. The toluene absorption index may be increased to prepare a carrier in accordance with the invention by treatment with steam at temperatures in the range of about 1600 to 2200 F. A typical coke prepared by this procedure possessed a BET value of 22 square meters per gram and a toluene absorption index of 13.5.

In using a carrier of this invention, very significant results are obtained with heavy hydrocarbon oils having API gravities less than about 25 and Ramsbottom carbon values exceeding about 3. The heavy hydrocarbon oils may be heavy whole crudes, coal tar and shale oil as well as petroleum residua of topping operations.

Conversion of the hydrocarbon oil in the presence of the carrier is efiected at a temperature in the range of about 800 to 1050" F. and preferably in the range of about 875 to 1025 F. The pressure in the system, including the conversion zone and the regeneration zone, is advantageously maintained in the range of 15 to 800 pounds per square inch gage (p.s.i.g.). Preferably, the pressure is maintained above about p.s.i.g. and more particularly in the range of 250 to 650 p.s.i.g. The oil partial pressure, calculated on the basis of the unconverted feed, is generally in the range of about 5 to 100 p.s.i., preferably in the range of 10 to 75 p.s.i.

The carrier of this invention may be utilized in any apparatus designed for the conversion of hydrocarbons in the presence of a fluidized mass of particulate contact material. A particularly suitable form of apparatus is disclosed in the copending application of I A. Finneran, Jr. and F. B. Grosselfinger, Serial No. 299,114, filed July 16, 1952, now Patent No. 2,861,943, issued November 25, 1958. In this apparatus, the oil is injected into a fluidized mass of carrier in a cracking zone in the presence of the gaseous products resulting from the regeneration of the carrier. The carrier in the cracking zone accumulates a deposit of carbonaceous residue and is continuously transferred to the regeneration zone for the removal of the carbon by reaction with oxygen and steam. With regeneration temperature of at least 1600 F., substantial amounts of hydrogen are formed in this regeneration process and this hydrogen in the regeneration produot gases is beneficial to the conversion of the hydrocarbons in the cracking zone. The hydrogen partial pressure in the cracking zone is advantageously in the range of about 35 to 200 p.s.i., preferably 75 to 150 p.s.i.

The following specific examples are further illustrative of the invention without, however, being intended as limitative thereof:

EXAMPLE 1 In order to determine the effect of the BET value of the carrier on the coke yield from a heavy liquid hydrocarbon stock, various carriers were tested under identical cracking conditions. Since it was known that some of these carriers would agglomerate and would prevent operation over the desired test interval, a special test unit was used in which the carrier was continuously stirred at the desired cracking conditions. Thus, when agglomeration did occur, the stirrer eifectively prevented the development of large pressure drops and the discontinuance of the test.

The charge stock employed for this work was a 14 API East Texas residuum. This stock gave a Ramsbottorn carbon value of 10.7 as determined by the standard API procedure. The conversion pressure was maintained at 150 p.s.i.g., the temperature at 950 F., the oil feed rate at 1 volume of liquid per hour per volume of carrier, and the hydrogen rate at cubic feet (standard conditions) per pound of oil fed, providing a hydrogen partial pressure of about 140 p.s.i. Various carriers, as shown in Table I, were tested over a two-hour interval without regeneration of the carrier. The coke yield, expressed as weight percent of the charge fed, is given in the third column of Table I for all of the carriers tested. The first two columns provide the toluene absorption index and BET value for the various carriers.

Table I Toluene Coke Absorp- BET Yield, Carrier tion Value, Weight Index M /gm. Percent of Charge 2 4. 5 12. 5 3 6 l2. 5 Petroleum coke... 3 26 13.0 Cyclocel (equilibrated at 1,800 F. and

containing 30% by weight of coke) 4 30 13.0 Cyclocel (equilibrated at 1,800 F.) 16 40 13. 0 Cyclocel (unequilibrated) 19 265 18.0 Silica-alumina cracking catalyst 22 450 22.0 Activated carbon 21 950 32.0

As illustrated in Table I, relatively low coke yields (not above about 13.0 wt. percent) are obtained by employing carriers which possess BET values between 4.5 and 40 m. gm. However, employing unequilibrated Cyclocel, fresh silica-alumina cracking catalyst or activated carbon, which possess BET values of 265 m. gm. and higher, the coke yield increases rapidly and consequently there is a large loss in the yield of the more valuable liquid products.

EXAMPLE 2 Four of the carriers of Table I were then tested in a continuous fluidizing unit, operating in accordance with the preferred embodiment of this invention. These carriers were:

(1) Magnetite, giving a toluene absorption index of 3 and a BET value of 6 m. gm.

(2) Petroleum coke derived from a commercial source, having a toluene absorption index of 3 and a BET value of 26 m. gm.

(3) Cyclocel, a commercially available activated bauxite, which was initially equilibrated by calcining at 1800 F. for four days and on which 30% by weight of coke was initially deposited. This carbon-containing d equilibrated Cyclocel gave a toluene absorption index of 4 and a BET value of 30 m. gm. (4) Cyclocel equilibrated as in (3) above but initially containing no coke. This carrier had a toluene absorption index of 16 and a BET value of 40 m. /gm.

All of the aforementioned carriers were initially ground to provide a particle size distribution between 20 mesh and pan, averaging about 140 mesh, with about 10% by weight between 325 mesh and pan.

The fiuidizing apparatus for converting the heavy oil feed stock was similar to that shown in Figure 1 of co pending application Serial No. 299,114, and comprised an upper cracking zone, a lower regeneration zone and an intermediate stripping zone containing a fixed bed of coarse packing bodies. A fluidized mass of the particulate carrier extended from the bottom of the regeneration zone through the packed stripping zone and tenninated in a psuedo-liquid level in the cracking zone. Preheated oil was charged to the cracking zone at a rate of pounds per hour and was there cracked at a temperature of 975 F. in the presence of hydrogen. The carrier, containing carbonaceous material deposited by the hydrocarbons undergoing conversion, was circulated from the cracking zone down through the stripping zone to the regeneration zone where the carbon deposit was gasified at a temperature of 1800 F. by reaction with high-purity oxygen and steam. The gas produced by this regeneration was of high hydrogen content, and this gas flowed upwardly through the stripping and cracking zones to provide stripping gas and the hydrogen for the cracking zone. Regenerated carrier was circulated from the regeneration zone through a lift conduit to the cracking zone. The total gasiform eflluent leaving the pseudo-liquid level of the fluidized carrier mass was passed to conventional recovery equipment for separating the various gaseous and liquid product fractions.

The total pressure in the apparatus was maintained at 400 p.s.i.g. Oxygen was supplied to the regeneration zone at a rate of about 180 standard cubic feet per hour and steam at 720 standard cubic feet per hour. The calculated hydrogen partial pressure in the cracking zone was p.s.i. The carrier circulation rate was about 250 pounds per hour. The heavy oil charge stock employed in these tests was identical with that employed in Example 1.

The apparatus was found to be inoperable when magnetite, petroleum coke or equilibrated Cyclocel initially containing 30% by weight of coke was employed as the carrier. It proved impossible to maintain carrier circulation beyond 12 hours of operation with each of these three carriers. After the apparatus was shut down, examination of its interior revealed that the carrier had become highly agglomerated in the short period of its operation. The formation of coke bridges was extensive throughout the apparatus.

However, operation with the equilibrated Cyclocel which did not initially contain 30% by weight of coke was very successful. The test run with this carrier was maintained for 14 days and then shut down voluntarily. No operating difiiculties were experienced and the circulation rate of the carrier was easily maintained at the desired level. Inspection of the apparatus, after concluding this run, showed that the carrier was still completely fluidizable.

Thus, Example 1 illustrates that low coke yields are obtained when the carrier possesses a BET value below about 50 m. /gm., while Example 2 illustrates that for operability in a fluidized system the carrier must have a toluene absorption index of at least about 7, preferably between 10 and 20.

It will be appreciated that the carrier must be selected to withstand the process conditions, particularly the elevated regeneration temperature, to which it will be exposed. As disclosed in copending application Serial No.

299,114, it is highly desirable to regenerate the carrier of a conversion process in which the feed stock is a heavy oil at temperatures of at least about 1600 F., preferably in the range of 1700 to 2000 F. In short, the particulate carrier must be resistant to physical disintegration or fusion under operating conditions.

What is claimed is:

1. In the process for cracking a heavy hydrocarbon oil having an API gravity of not more than about 25 and a Ramsbottom carbon value of at least about 3 by injecting said oil into a fluidized mass of a particulate contact carrier maintained at a cracking temperature above about 800 F. and at a pressure of 15 to 800 p.s.i.g. such that the partial pressure of oil is 5 to 100 p.s.i., the improvement of simultaneously minimizing coke formation and agglomeration of said particulate contact carrier during the cracking of said oil, which comprises pretreating said particulate contact carrier to modify the structural characteristics thereof and attain a toluene absorption index of at least about 7 and a BET value of not more than about 50 whereby said particulate contact carrier is rendered substantially non-catalytic, and forming and maintaining a fluidized mass of the thus pretreated and non-catalytic particulate contact carrier, into which fluidized mass while at said cracking temperature said oil is injected.

I 2. The process of claim 1 wherein the contact material is derived from bauxite.

3. The process of claim 1 wherein, the contact material is derived from petroleum coke.

4. The process of claim l wherein the operating pressure is in the range of about 150 to 800 p.s.i.g. and a hydrogen-containing gas is passed through said fluidized mass to provide a hydrogen partial pressure in the range of about 35 to 200 p.s.i.

5. A fluidizable mass of a particulate contact carrier adapted for use in fluidizing processes for cracking heavy hydrocarbon oils at cracking temperatures above about 800 R, which consists essentially of substantially noncatalytic solid particles predominantly finer than 20 mesh, said solid particles having a toluene absorption index of at least about 7 and a 'BET value of not more than about 50.

6. The fluidizable mass of claim 5 wherein the solid particles are derived from bauxite.

7. The fluidizable mass of claim 5 wherein the solid particles are derived from coke.

8. The fluidizable mass of claim 5 wherein the solid particles have a toluene absorption index in the range of 10 to 25.

9. The fluidizable mass of claim 8 wherein the solid particles are bauxite which has been heated to a temperature of at least about 1800" F.

References Cited in the file of this patent UNITED STATES PATENTS 2,100,352 Pier Nov. 30, 1937 2,209,908 Weiss July 30, 1940 2,294,383 Glenbrook Aug. 3, 1940 2,331,292 Archibald et al Oct. 12, 1943 2,362,270 Hemminger Nov. 7, 1944 2,406,112 Schulze Aug. 20, 1946 2,450,753 Guyer Oct. 5, 1948 2,600,430 Riblett June 17, 1952 2,697,681 Murray et al Dec. 21, 1954 2,698,305 Plank et a1 1. Dec. 28, 1954 2,731,395 Iahnig Ian. 17, 1956 2,731,508 Iahnig Ian. 17, 1956 2,738,307 Beckberger Mar. 13, 1956 2,763,601 Martin Sept. 18, 1956 2,763,623 Haensel Sept. 18, 1956 2,791,547 Beiswenger May 7, 1957

Claims (1)

1. IN THE PROCESS FOR CRACKING A HEAVY HYDROCARBON OIL HAVING AN API GRAVITY OF NOT MORE THAN ABOUT 25 AND A RAMSBOTTOM CARBON VALUE OF AT LEAST ABOUT 3 BY INJECTING SAID OIL INTO A FLUIDIZED MASS OF A PARTICULATE CONTACT CARRIER MAINTAINED AT A CRACKING TEMPERATURE ABOVE ABOUT 800* F. AND AT PRESSURE OF 15 TO 800 P.S.I.G. SUCH THAT THE PARTIAL PRESSURE OF OIL IS 5 TO 100 P.S.I., THE IMPROVEMENT OF SIMULTANEOUSLY MINIMIZING COKE FORMATION AND AGGLOMERATION OF SAID PARTICULATE CONTACT CARRIER DURING THE CRACKING OF SAID OIL, WHICH COMRPISES PRETREATING SAID PARTICULATE CONTACT CARRIER TO MODIFY THE STRUCTURAL CHARACTERISTICS THEREOF AND ATTAIN A TOULENE ABSORPTION INDEX OF AT LEAST ABOUT 7 AND BET VALUE OF NOT MORE THAN ABOUT 50 WHEREBY SAID PARTICULATE CONTACT CARRIER IS RENDERED SUBSTANTIALLY NON-CATALYTIC, AND FORMING AND MAINTAINING A FLUIDIZED MASS OF THE THUS PRETREATED AND NON-CATALYTIC PARTICULATE CONTACT CARRIER, INTO WHICH FLUIDIZED MASS WHILE AT SAID CRACKING TEMPERATURE SAID OIL IS INJECTED.