US2947684A - Controlling the surface area of siliceous cracking catalysts - Google Patents

Description

hydrocarbons. cracking of hydrocarbons in the presence of catalyst of 2,947,684 Patented Aug. 2., 1960 CUNTRQLLING THEE Um ACE AREA OF SILICEOlJ-S CRACKFNG CATALYSTS Paul H. Eohnson and Charles R. Eherline, Bartlesviile,

Okla, assignors to Phillips Petroleum Company, a corporation of Delaware No Drawing. Filed Jan. 2, 1958, Ser. No. 766,566

8 Ciaims. (Cl. 263-418) This invention relates to the catalytic conversion of In one aspect it relates to the catalytic reduced surface area. In another aspect it relates to catalytic cracking of hydrocarbons containing heavy metals, such as nickel and vanadium, in the presence of a cracking catalyst of reduced surface area.

Catalyst surface area as used herein, is determined by the nitrogen adsorption method as set forth in the article by Brunauer, Emmet and Teller, Journal of the American Chemical Society, volume 57, page 1754 (1935). i

In conventional petroleum refining the crude petroleum is first distilled to produce various distillate fractions and a residuum boiling above 700 F. Motor fuels are normally produced from the distillate fractions by suitable refining processes including thermal or catalytic cracking, reforming, isomerization, alkylation, etc., While the residuum is worked up to yield marketable high molecular weight products such as lubricating oils, waxes, asphalt, road oils, fuel oils and the like. More recently, however, the demand for motor fuels has increased so greatly that it has become desirable to use the residuum as an additional source of raw materials for motor fuels.

It has been known for a long time that motor fuels may be produced by thermal cracking of crude residuum. The use of cracking catalysts in this reaction has also been proposed, however, serious difliculties have been encountered in the catalytic cracking of residuum, chiefly as a result of metal contamination from the hydrocarbon feed. Heavy metals such as nickel, vanadium, chromium and iron in the feed stocks, accumulate on the cracking catalyst where they catalyze reactions which adversely affect product distribution.

The catalysts used in conventional catalytic cracking operations usually have an average surface area in the range of 250 to 350 square meters per gram prior to use.

During use in a cracking process, the average surface area is gradually reduced, and catalyst having a surface area of 140 to 180 square meters per gram is maintained in the unit by adding new catalyst at the proper rate and removing used catalyst at an equal rate. Concomitantly with the reduction in surface area, the catalyst frequently becomes contaminated with metals entering the process in the feed. With feed stocks containing much above about 10 ppm. metals, particularly above 50 ppm, normal catalyst addition rates are insufiicient to maintain metals contamination of the catalyst at a low level with the result that gas and coke production is increased to uneconomically high levels and the gasoline yield is thereby reduced. Further, with such feeds it is uneconomical to maintain the metals contamination at a reasonably low value by increasing the new catalyst addition rate.

It is an object of this invention to provide an improved process for the catalytic conversion of hydrocarbons.

Another object of this invention is to provide an imsired cracking in the reaction vessel.

' ceous material.

nesia, silica-alumina-thoria, etc.

proved process for the catalytic cracking of hydrocarbons, such as crude residuum.

Still another object of this invention is to provide a process for improving selectivity in the catalytic cracking of hydrocarbons.

Yet another object of this invention is to provide improved selectivity in the catalytic cracking of crude residuums containing heavy metals.

These and other objects of the invention will become more readily apparent from the following detailed description and discussion.

In the ,broad aspect of the invention a zone of fluidized cracking catalyst is maintained under suitable conditions to effect conversion of a hydrocarbon feed, a hydrocarbon oil containing heavy metals is introduced to said zone, catalyst contaminated with heavy metals is with drawn from said zone, uncontaminated catalyst having a surface area of between about 25 and about square meters per gram is added to said zone in an amount sufficient to balance the rate of catalyst Withdrawal and the catalyst flow rates are controlled to provide in said zone catalyst having an average surface area of between about, 25 and aboutSO square meters per gram.

In one aspect of the invention the uncontaminated catalyst added to the zone of fluidized cracking catalyst has a surface area betweenabout 40 and about 60 square meters per gram.

This invention is applicable in general to the catalytic cracking of hydrocarbon oils, and in particular petroleum fractions, such as gas oils, fuel oils, distillates, crude residuum s, etc. Catalytic cracking of hydrocarbons is carried out conventionally in a vessel containing a dense phase bed of fluidized catalyst superposed by a dilute phase. Hydrocarbon feed material and catalyst are introduced to the dense phase bed, the feed and/or catalyst being at a sufiicient temperature .topromote the de The reaction prod ucts in gaseous form are withdrawn overhead. from. the reaction zone through a suitable type of catalyst recovery apparatus which returns recovered catalyst to the dense phase bed. As the. reaction proceeds the catalyst becomes deactivated due to contamination with carbona- In order to provide a substantially constant level of activity in the reaction zone, catalyst is continuously withdrawn from the reactor dense phase bed and introduced to a regeneration vessel wherein there is also maintained a dense phase bed of fluidized catalyst superposed by a dilute phase. Oxygen or an oxygen con- .taining gas is introduced to the regeneration zone whereupon combustion of the carbonaceous deposit on the catalyst takes place and the catalyst is increased inactivity. The combustion gases arewithdrawn overhead from the regeneration zone through a suitable catalyst recovery system and regenerated catalyst is returned to the reaction zone.

The catalyst employed in the catalytic cracking process may be prepared by the acid activation of various. clays, such asfullers earth and bentonitic clays such 3911153 3? morillonite clay. The catalyst can also be a synthetic catalyst derived from silica gel or other forms of. silicic acid, for example of the silica alumina or silica magnesia type with suitable additions of other active constituents such as zirconia, thoria, or the like. Examples of typical synthetic catalysts include such materials as silicaalumina, silica-boria, silica-alumina-boria, silica-thoria, silica-zirconie, silica-alumina-zirconia, silica-magnesia, alumina boria, silica-alumina -beryllia, silica-bori-mag- For the purpose of providing effective fiuidization, it is desirable that the catalyst contain particles having a range of size varying from 1 to about 200 microns.

' about 300 parts per million.

The hydrocarbon feed to the catalytic reaction is usually a hydrocarbon oil such as a gas oil either light or heavy, a naphtha, a crude oil, a reduced crude oil, a crude residuum, or other suitable hydrocarbon material. The reaction is usually carried out ir r a temperature range of between 600 and about 1000 F., the particular temperature employed depending on the catalyst used and the feed material. The relative quantities of catalyst and feed material are controlled to provide a superficial velocity in the catalytic reaction zone of between 0.5 and about feet per second, more preferably between about 1.5 and about 3 feet per second. The reaction conditions are further defined by the catalyst-to-oil ratio' which usually varies between about 4 to 1 and about to 1 pounds per pound and the weight space velocity which is usually between about 3 and about pounds of feed per hour per pound of catalyst present in the reactor.

The dense and dilute phases in the reactor are characterized by the great difference in their effective density.

For example the dense phase contains between about '5 and about 35 pounds of solids per cubic foot whereas the dilute phase contains from as low as 0.001 to about 0.02 pound of catalyst per cubic foot.

The regeneration of contaminated cracking catalyst is carried out as previously stated in a system similar to that employed in the cracking reaction. Usually the regeneration temperature is between about 700 and about 1150 F. with a temperature of between about 1,000 and 1,100 F., being preferred. The concentration of solids in the dense and dilute phases and the velocities required to maintain fiuidization are the same'in regeneration as in the cracking operation. The amount of oxygen required for regeneration depends principally on the degree of contamination of the catalyst entering the regenerator and the level of contamination to which the catalyst is reduced during this operation. Usually the quantity of oxygen entering the regenerator is controlled to provide a ratio of between about 30 and about 40 standard cubic feet of oxygen per 100 pounds of catalyst (1.0 percent coke burn off).

The pressure in both operations, cracking and regeneration, varies between about 5 and about 100 pounds or higher, the particular pressure employed in each stage being dependent to a great extent on the physical location of the vessels with respect to each other. Thus if the regenerator is at a physically higher level than the reactor, the pressure of the regenerator can be carried at a lower level than the reaction pressure and the differential overcome by the static head of fluidized catalyst flowing from the regenerator to the reactor. v

As mentioned previously many of the residual and heavier oils contain substantial quantities of heavy metals, such as nickel and vanadium, which accumulate on the cracking catalyst. These metals are not removed by regeneration of the catalyst andtend to increase at a continuing rate unless controlled in some manner. The

conventional method for limiting the amount of metals which become associated with the catalyst is to add uncontaminated catalysts to the reaction system, and at the same time withdraw an equal amount of contaminated catalyst. Catalyst addition and withdrawal can be either continuousor intermittent. By properly controlling the catalyst addition and withdrawal ratesit is possible to closely control the metal contamination of the catalyst. In the conventional commercial cracking operation it is usually desirable to carry out the cracking process with a catalyst containing on the'avera'ge not more than about 500 parts per; million of nickel oxide and vanadiumpentoxide and. preferably not more than The operating conditions necessary to provide this level of catalystcontamination vary depending on the concentration-of metals in the hydrocarbon feed, the hydrocarbon feed rate, the particular catalyst employed, the amountof catalystinthe system, etc. In the usual commercial operation thecat- In carrying out the invention in one embodiment therei of a residual fraction of a crude oil, comprising about 10 percent by volume of the total crude, is contacted with a cracking catalyst, such as a synthetic silica-alumina catalyst, under suitable conditions to provide conversion of the hydrocarbon oil. As the catalytic reaction proceeds, metals present in the feed material are deposited on the catalyst and accumulate thereon. Uncontaminated catalyst is added to the reaction system, and an equal quantity of contaminated catalyst is withdrawn, the rates of catalyst addition and withdrawal being controlled to provide catalyst in the reaction system having an average surface area of between about 25 and about 50 square meters per gram. A catalyst having an area in this range is provided by adding to the reaction zone an uncontaminated catalyst having a surface area of between about 25 and about square meters per gram and more preferably between about 40 and about 60 square meters per gram. As compared to this operation, in conventional catalytic cracking, as previously pointed out, the catalyst in the reaction zone has a surface area of between about and about 180 square meters per gram and the fresh makeup catalyst introduced to the cracking zone has a surface area of between about 250 and 350 square meters per gram.

Makeup catalysts having the desired area for use in the invention, namely 25 to 90 square meters/ gram, can be provided from conventional catalysts of high surface area by contacting the conventional catalysts with superheated steam over a period of time. In carrying out this operation the temperature is preferably maintained in the range of 1100 F. to 1400" F., with the time of contact varying from about 10 to about 20 hours, and employing steam having a pressure of between about 30 and about pounds. The particular temperature, time and steam pressure required are dependent on the specific catalyst which is being treated and on the final surface area desired. As an example, it is possible to convert a catalyst having a surface area of about 275 square meters per gram to a catalyst having a surface area of about 90 square meters per gram by contacting said catalyst with 150 pounds steam at a temperature of about 1100 F. for about 16 hours.

Although it is contemplated introducing uncontaminated catalyst to the reaction system to control catalyst surface area, it is also within the scope of the invention to utilize as makeup partially contaminated catalyst.- Also, as desired, the catalyst makeup can comprise fresh catalyst or used catalyst, or a mixture thereof. The only limitation is that the catalyst have a suitable initial surface area to provide the desired average surface area in the reaction zone.

The following data are presented in illustration of a preferred embodiment of the invention:

Example An equilibrium natural clay (montmorillonite) catalyst from a commercial unit was employed to carry out catalytic cracking tests in a fluidized bed.

The operating conditions employed in the cracking tests were as follows:

Temperature, F 900 Pressure, lb./sq. inch gage 10 Space rate, lb. oil/lb. catalyst/hr. 1.24.5 Steam diluent, lb. barrel, feed 40-50 In the tests, all conditions were held constant except space rate, which was varied to obtain 50% conversion.

In run A a portion of a plant equilibrium catalyst having a surface area of square meters per gram was used to crack a Borger 7.6 percent residuum. The same catalyst was then used to crack the residuum having an extremely high metals content until the metals content of the catalyst reached 4000 parts per million. The catalyst of increased metals content was then tested (run B) using the Borger 7.6 percent residuum.

In run C a second portion of the plant equilibrium catalyst having a surface area of 160 square meters per gram was used to crack a Borger 10.1 percent residuum. The same catalyst was then used to crack a residuum having an extremely high metals content until the metals content of the catalyst reached 4,000 parts per million. During this operation catalyst was periodically withdrawn and replaced by new catalyst having a surface area of 250-300 square meters per gram in order to maintain the surface area of the catalyst in the unit at 160 square meters per gram. When the metals content of the catalyst reached 4000 parts per million the catalyst was tested with Berger 10.1 percent residum (run D).

The results of runs A, B, C and D are presented in the table below.

RunB

13. 7.6% Borger Residuum 1 Percent of converted material. 1 Volume percent of crude oilremaining after distillation of lower boiling components.

It is noted that in runs A and B, which are exemplary of the invention, an increase in metals content to 4000 p.p.m. resulted in a decrease in gasoline yield of 2.5 percentage units, an increase in carbon of 2.5 percentage units and an increase in hydrogen of 275 cubic feet per barrel. This is to be compared with runs C and D, which are representative of conventional cracking operations; wherein the gasoline yield decreased 5.0 percentage units, the carbon increased 4.5 percentage units and the hydrogen increased 360 cubic feet per barrel.

The preceding discussion and example have been directed to a preferred embodiment of the invention, however, this is not intended in any may to limit the scope of the invention. Thus, in carrying out the invention a variety of feed materials and cracking catalysts can be employed as hereinbefore set forth.

Having thus described the invention by providing a specific example thereof it is to be understood that no undue limitations or restrictions are to be drawn by reason thereof and that many variations and modifications are within the scope of the invention.

We claim:

1. A process for improving cracking selectivity which comprises maintaining a zone of fluidized siliceous cracking catalyst under suitable conditions to effect conversion of a hydrocarbon feed, introducing to said zone a hydrocarbon oil containing above 10 p.p.m. heavy metals, withdrawing metal contaminated catalyst from said zone, introducing uncontaminated catalyst having a surface area of between about 25 and about 90 square meters per gram to said zone in an amount suflicient to balance the withdrawal of contaminated catalyst, controlling the catalyst flow rate to provide an average catalyst surface area in said zone of between about 25 and about 50 square meters per gram and withdrawing a conversion product from said zone.

2. The process of claim 1 in which the hydrocarbon feed is a crude residuum.

3. The process of claim 2 in which the heavy metals comprise metals selected from the group consisting of nickel, vanadium, iron and chromium.

4. A process for improving cracking selectivity which comprises maintaining a fluidized zone of siliceous cracking catalyst under temperature conditions of between about 600 and 1,000 E, introducing to said zone a crude residuum containing about 10 p.p.m. heavy metals at a sufficient rate to provide a catalyst-to-oil ratio of between about 4 to 1 and about 10 to 1 and a weight space velocity of between about 4 to 1 and about 15 to 1, withdrawing metal contaminated catalyst from said zone, introducing uncontaminated catalyst having a surface area of between about 25 and about 90 square meters per gram to said zone in an amount sufiicient to balance the withdrawal of contaminated catalyst, controlling the catalyst flow rate to provide an average catalyst surface area in said zone of between about 25 and about 50 square meters per gram and withdrawing a conversion product from said zone.

5. The process of claim 3 in which the uncontaminated catalyst introduced to said zone has a surface area of between about 40 and about square meters per gram.

6. A process of claim 5 in which the catalyst is a natural clay catalyst.

7. The process of claim 6 in which the crude residuum contains above 5 0 p.p.m. heavy metals.

8. The process of claim 7 in which the catalyst is a montmorillonite clay.

References Cited in the file of this patent UNITED STATES PATENTS Patent No. 2,94%684 August 2 1960 Paul H, Johnson et a1.

It is hereby certified that error a of the above numbered patent requiring 0 'Patent should read as corrected below.

ppears in the printed specification orrection and that the said Letters Column 6 line 25 for "about" read above Signed and sealed this 4th day of April 1961,

(SEAL) Attest: ERNEST W. SWIDER xxxx xm ARTHUR w. CROCKER Attesting Ofilcer Acting Commissioner of Patents

Claims (1)

1. A PROCESS FOR IMPROVING CRACKING SELECTIVELY WHICH COMPRISES MAINTAINING A ZONE OF FLUIDIZED SILICEOUS CRACKING CATALYST UNDER SUITABLE CONDITIONS TO EFFECT CONVERSION OF A HYDROCARBON FEED, INTRODUCING TO SAID ZONE A HYDROCARBON OIL CONTAINING ABOVE 10 P.P.M. HEAVY METALS, WITHDRAWING METAL CONTAMINATED CATAYLST FROM SAID ZONE, INTRODUCING UNCONTAMINATED CATALYST HAVING A SURFACES AREA OF BETWEEN ABOUT 25 AND ABOUT 90 SQUARE METERS PER GRAM TO SAID ZONE IN AMOUNT SUFFICIENT TO BALANCE THE WITHDRAWAL OF CONTAMINATED CATAYLST, CONTROLLING THE CATALYST FLOW RATE TO PROVIDE AN AVERAGE CATALYST SURFACE AREA IN SAID ZONE OF BETWEEN ABOUT 25 AND ABOUT 50 SQUARE METERS PER GRAM AND WITHDRAWING A CONVERSION PRODUCT FROM SAID ZONE.