US2902430A - Removal of metal contaminants from catalytic cracking feed stocks with sulfuric acid - Google Patents

Description

p 1, 1959 c. N. KlMBERLlN, JR, ETAL 2,902,430

REMOVAL OF METAL CONTAMINANTS FROM CATALYTIC CRACKING FEED STOCKS WITH SULFURIC ACID Filed Feb. 21, 1955 5 e e moaocnnsous l0 msnumon svsm 0ATALYTIO cnAcxmc SYSTEM 4 emu: 0|L-| I61 IIAPTHA cnuoe OIL near us 0|L1 fi g 1 \w nnvv cAs OIL f a new Q 1 L -mxmc zouz ESIDUAL on w.) 85mm M M ACID sumcz CHARLES n. xmamun JR. WILLIAM J. umox lNVENTORS BY ATTORNEY United States atent O REMOVAL OF METAL CONTAMINANTS FROM CATALYTIC CRACKING FEED STOCKS WITH SULFURIC ACID Charles Newton Kimberlin, Jr., and William Judson Mattox, Baton Rouge, La., assignors to Esso Research and Engineering Company, a corporation of Delaware Application February 21, 1955, Serial No. 489,572

'5 Claims. (Cl. 208-90) This invention concerns a novel process for upgrading petroleum fractions to be subjected to catalytic cracking. The invention particularly concerns a technique utilizing sulfuric acid in order to remove metal contaminants and refiractory aromatic hydrocarbons from petroleum stock to be subjected to catalytic cracking. The process is economic and attractive for selectively achieving these objections in a manner substantially improving the quality of cracking stocks.

One of the principal refining operations in commercial use at this time concerns the catalytic cracking of gas oil fractions of a petroleum oil. Until relatively recently, the gas oil distillate fraction employed as a catalytic cracking feed stock was a fraction boiling in the relatively low boiling range of about 500 to 800 F. However, in order to secure greater yields of cracked products and to reduce the portion of the petroleum oil constituting the residual portion higher boiling than gas oil, there has been a great deal of incentive for extending catalytic cracking to higher boiling feed stocks. Toward this end, the end point of the gas oil fraction subjected to catalytic cracking has risen to greater than 900 F. Diificulties have been encountered in attempting to crack gas oils of this character including a substantial portion boiling above about 900 F. It has heretofore been appreciated that one of the difliculties involved in cracking such feed stocks is the presence of metal contaminants in the feed stocks. These metal contaminants include nickel, vanadium and iron compounds which are particularly deleterious. High boiling fractions for catalytic cracking have also been produced by deasphalting, and deasphalted oils thus produced are also very high in such metal contaminants.

The metal compounds are inherently and unavoidably carried over into the high boiling gas oils when including products boiling above about 900 B, because of entrainment and volatility of metal compounds in high temperature fractionation and because of the solubility of metal compounds in deasphalted oil produced from deasphalting higher boiling fractions. Heavy gas oils derived from typical crude oils will contain about to 20 pounds of metal contaminants per 1000 barrels. When segregating heavier boiling gas oils or when deriving such oils from particular crude oils, contaminant concentrations as high as 50 pounds per 1000 barrels may be encountered. The presence of these metal contaminants in the catalytic cracking zone causes poisoning of the catalyst, adversely affecting the conversions obtained, product distribution, and catalyst life. In addition to these problems, it is well known that the cracking characteristics of a petroleum fraction depend to a large extent on the presence of high molecular weight condensed ring aromatic hydrocarbons. Such aromatic hydrocarbons occur to some extent in virgin gas oils separated from petroleum crude oil. More sen'ously, however, the process of catalytic cracking results in the formation of substantial portions of such refractory aromatic mate- 2,902,430 Patented Sept. 1, 1959 rials. As a result, difiiculty is encountered in attempting to recycle catalytically cracked oils for further cracking.

The present invention is uniquely adapted to solve the problems referred to, that is, to eliminate the presence of metal contaminants and to remove refractory aromatic hydrocarbons. This is achieved in accordance with the invention by treating the catalytic cracking stocks under critical conditions with sulfuric acid. The invention is based on the discoveery that sulfuric acid has the property of selectively reacting with metal contaminants and refractory aromatic hydrocarbons so as to form sludge constituents which can be separated. Treated oils of improved cracking characteristics can be obtained in yields above ranging upwardly to or more and containing tolerable limits of metal contaminants.

The principles of the present invention are diagrammatically illustrated in the accompanying drawing which shows a preferred embodiment of the invention.

Referring to the drawing, the numeral 1 diagrammatically identifies a crude oil distillation system. This system may constitute, for example, a combination of atmospheric and vacuum distillation operations. Crude oil may be brought into distillation system 1 through line 2 wherein it may be separated into a variety of fractions of different boiling range. Thus, light gaseous constituents primarily constituting C C hydrocarbons may be withdrawn as an overhead product through line 3. Light boiling liquid fractions such as naphtha may be withdrawn from side stream withdrawals such as line 4. Distillation is to be conducted so as to permit withdrawal of a side stream fraction through line 5 constituting a light gas oil boiling in the range of about 400 to 900 F. Such a gas oil is well adapted for catalytic cracking and will contain substantially no metal contaminants. A heavy gas oil fraction boiling in the range of about 950 to 1100 F., or higher, up to about 1300 R, will be withdrawn through line 6. This heavy gas oil fraction will contain substantial portions of metal contaminants. The residual oil higher boiling than the gas oil will be removed as a bottoms product through line 7.

In accordance with this invention, the heavy gas oil, line 6, is subjected to sulfuric acid treatment in zone '3. As an example of the specific treatment to be carried out, about 30 pounds of sulfuric acid (having a concentration of about 80 wt. percent) per barrel of oil to be treated will be brought into zone 8 through line 9. About 10% of cycle oil, by weight of heavy gas oil, derived from catalytic cracking system 10, to be described hereinafter, will be mixed with the acid and heavy gas oil. Agitation means are provided in zone 8 together with suitable arrangements to permit heating the mixture of these constituents at a temperature of about 200 F. After thorough mixing of the cycle oil, gas oil and acid under these conditions, the mixture may be brought into a settling zone 11 through line 12. An upper layer of treated oil may be withdrawn from the settling zone through line 13 while a lower layer constituting acid sludge may be withdrawn from the bottom of the settling zone through line 14 for disposal as desired. The stream of line 13 may be stripped of any sulfur dioxide by air blowing or steam stripping. This is not ordinarily an essential step of the process however.

The treated mixture of cycle oil and heavy gas oil of line 13 is preferably mixed with the light gas oil of line 5. This mixture is then brought into the catalytic cracking system 10 through line 15. The cracking carried out in zone 10 may be of any desired type but it is preferred that this cracking should be conducted in accordance with the fluidized solids cracking technique.

The fluidized solids technique for cracking hydrocarbons comprises a reaction zone and a regeneration zone, employed in conjunction with a fractionation zone. The reactor and the catalyst regenerator are or may be arranged at approximately an even level. The operation of the reaction zone and the regeneration zone is preferably as follows:

An overflow is provided in the regeneration zone at the desired catalyst level. The catalyst overflows into a Withdrawal line which preferably has the form of a U-shaped seal leg connecting the regeneration zone with the reaction zone. The feed stream introduced is usually preheated to a temperature in the range from about 500 to 650 F, by heat exchange with regenerator flue gases which are removed overhead from the regeneration zone, or with cracked products. The heated feed stream is then introduced into the reactor. The seal leg is usually sufiiciently below the point of feed oil injection to prevent oil vapors from hacking into the regenerator in case of normal surges. Since there is no restriction in the overflow line from the regenerator, satisfactory catalyst flow will occur as long as the catalyst level in the reactor is slightly below the catalyst level in the regenerator when the vessels are maintained at about the same pressure. Spent catalyst from the reactor flows through a second U-shaped seal leg from the bottom of the reactor into the bottom of the regenerator. The rate of catalyst flow is controlled by injecting some of the air into the catalyst transfer line to the regenerator.

The pressure in the regenerator may be controlled at the desired level by a throttle valve in the overhead line from the regenerator. Thus, the pressure in the regenerator may be controlled at any desired level by a throttle valve which may be operated, if desired, by a differential pressure controller. If the pressure differential between the two vessels is maintained at a minimum, the seal legs will prevent gases from passing from one vessel into the other in the event that the catalyst flow in the legs should cease.

The reactor and the regenerator may be designed for high velocity operation involving linear superficial gas velocities of from about 2.5 to 4 feet per second. However, the superficial velocity of the upflowing gases may vary from about 1 to 5 feet per second and higher. Catalyst losses are minimized and substantially prevented in the reactor by the use of multiple stages of cyclone separators. The regeneration zone is also provided with cyclone separators. These cyclone separators usually include 2 to 3 or more stages.

Distributing grids may be employed in the reaction and regeneration zones. Operating temperatures and pressures may vary appreciably depending upon the feed stocks being processed and upon the products desired. Operating temperatures are, for example, in the range from about 800 to 1000 F., preferably about 850 to 950 F. in the reaction zone. Elevated pressures may be employed, but in general, pressures below 100 pounds per square inch gauge are utilized. Pressures generally in the range from 1 to 30 pounds per square inch gauge are preferred. Catalyst to oil ratios of about 3 to 10, preferably about 6 to 8 by weight, are used.

The catalytic material used in the fluidized catalyst cracking operation are conventional cracking catalysts. These catalysts are oxides of metals of groups II, III, IV and V of the periodic table. A preferred catalyst coinprises silica-alumina wherein the weight percent of the alumina is in the range from about 5 to 20%. Another preferred catalyst comprises silica-magnesia where the weight percent of the magnesia is about 20 to 35%.

The size of the catalyst particles is usually below about 200 microns. Usually at least 50% of the catalyst has a micron size in the range from about 20 to 80. Under these conditions with the superficial velocities as given, a fluidized bed is maintained where, in the lower section of the reactor, a dense catalyst phase exists while in the upper area of the reactor a disperse phase exists.

Included in the catalytic cracking system is a product fractionator adapted to segregate gasoline and heavier boiling fractions of the cracked product. For the purposes of this invention, the portion of the cracked products boiling above the gasoline boiling range, that is, above about 450 F., will be called cycle oil. Such cycle oil and in particular the portion boiling above about 750 F. is rich in high molecular weight condensed ring aromatic hydrocarbons. This cycle oil is the material which is brought into the mixting zone 8 through line 16 as has already been described.

The process illustrated and described accomplishes the sulfuric acid treatment of the mixture of cycle oil and heavy gas oil. The treatment results in substantial elimination of metal contaminants present in the gas oil and substantial elimination of refractory aromatic hydrocarbons present in the cycle oil. In order to show the nature and utility of the invention, exemplary data will be referred to hereinafter.

In a first series of experiments, a heavy virgin gas oil having 5% boiling point of about 775 F. and 50% of which boiled above 950 F., was subjected to treatment with sulfuric acid under a variety of treating conditions. The heavy gas oil had a content of 2.3 p.p.m. of nickel and 0.2 ppm. of vanadium. The experiments were particularly conducted at treating temperatures of 95 F. and 200 F., using various quantities of sulfuric acid of varying concentrations. In the case of the treatments conducted at 95 F., it was found necessary to dilute the gas oil in order to provide a separable sludge and in order to hold wax constituents of the gas oil in solution during treatment. A diluent constituting a light virgin naphtha employed in l to 1 vol. ratio with the heavy gas oil was used in these experiments. Summarized data showing these tests are given in Table I.

Table 1 Acid Oorre- Treated 011 00110., Lbs. lated Oil Test Wt. HgSOg/B Temp., Yield at No. Percent (At 97% F. 0.5 ppm. Recov- Nickel, 804 Cone.) N i ery, Wt. p.p.m.

Percent Feed-.. 2. 3

UNDILUTED GAS OIL DILUTED GAS OIL 97 6 92 86 86 0.51 a; s 9 0.76 93 10 97 i 92 i so 0. 29 5 96 92 0. 87 60 5 97 86 94 1.2

Many factors concerning the conduct of the present invention are brought out by the data presented. For simplicity in analyzing these data, attention will be drawn particularly to the column entitled Correlated Oil Yield. By data of the sort presented in this column, it has been established that greater yields of treated oil of equivalent metals content can be achieved at higher temperatures. For example, at the treating temperature of 95 F. the maximum yield of oil-obtainable for a content of 0.5 p.p.m. nickel was about 93%. However, at the higher treating temperature of 200 F., a comparable oil yield of 96% was obtainable. These data therefore show the real advantage of increased selectivity in treatment obtainable by use of elevated treating temperatures.

Considering the relation between recovery of treated oil and the metal content of the treated oil at a given temperature, the data show that the yield obtainable is sharply dependent on the acid concentration. Thus, for example, at the treating temperature of 200 F. the oil yield dropped off sharply at acid concentrations other than about 80%. These data therefore show that selectivity of acid treatment for metal removal without intolerable loss of oil yield depends critically upon the acid concentration employed.

Comparing the data at the two treating temperatures given, it is also shown that greater acid concentrations are required at lower treating temperatures.

It is also shown that greater acid concentrations are required at lower treating temperatures in order to appreciate maximum oil yield. Thus, the critical acid concentration for use at 200 F. is about 80% while that for 95 F. is about 93%. This factor is particularly significant in considering the nature of the sludge formed with reference to the concentration of the treating acid. Thus, it has been found that the fluidity and separability of acid sludge formed in this process critically relates to the concentration of the acid employed. In particular, the acid sludge formed can be separated and handled much more effectively when employing sulfuric acid of lower concentration.

These factors dictate the importance and criticality of employing a treating temperature of not less than about 200 F., using an acid concentration of about 80%. Thus, while acid concentrations of about 60 to 100% could be employed with some profit, the preferred concentration is specifically about 80%. Again, While temperatures of about 50 to 300 F. may be employed, a temperature of about 200 F. is prefer-red. Temperatures above this level tend to give lower oil yields with high acid consumptions due to occurrence of oxidation reactions.

The experiments referred to above were conducted at atmospheric pressure without the necessity for exclusion of air during treatment. It is a particular feature of this invention that these conditions can be employed. In the experiments referred to, and others which have been conducted, it has been found useful to employ treats of about 5 pounds of sulfuric acid per barrel of oil up to about 50 pounds of sulfuric acid per barrel of oil. Use of the greater acid treats is particularly preferred since greater selectivity for removal of metal contaminants is thereby achieved. Balancing this factor with acid requirements establishes the use of about 30 pounds of sulfuric acid per barrel as the preferred amount for use.

While the present invention has been described with particular reference to the treatment of a heavy gas oil fraction, the invention is also of application to residual oil fractions either before or after deasphalting operations. As an example of this, a deasphalted West Texas residuum containing 2.5 ppm. of vanadium was subjected to treatment with 30 pounds per barrel of 80% sulfuric acid at a temperature of 200 F. A treated oil was obtained in yields of 90% having a vanadium content of 0.46. It will be seen, therefore, that this process was operated to eliminate 83% of the vanadium content of this fraction.

Sulfuric acid treatment of residual oil in accordance with this invention is particularly attractive as a feed preparation step for a coking process. Gas oil derived from coking of residual oil is commonly subjected to catalytic cracking. However, when the residual oil employed as feed to a coking process contains high concentrations of metal contaminants, the resulting gas oil is also characterized by high metals content. Therefore, by applying the process of this invention to a residual oil employed as feed for a coking process, gas oils are obtained of reduced metals content and of improved quality for catalytic cracking.

In practicing this embodiment of the invention, the

coking process employed is preferably a fluid coking operation.

The fluid coking unit consists basically of a reaction vessel or coker and a heater or burner vessel. In a typical operation, the heavy oil to be processed is injected into the reaction vessel containing a dense turbulent fluidized bed of hot inert solid particles, preferably coke particles. A transfer line or staged reactors can be employed. Uniform temperature exists in the coking bed. Uniform mixing in the bed results in virtually isothermal conditions and effects instantaneous distribution of the feed stock. In the reaction zone, the feed stock is partially vaporized and partially cracked. Product vapors are removed from the coking vessel and sent to a fractionator for the recovery of gas and light distillates. A gas oil fraction is also segregated for subsequent catalytic cracking. Any heavy bottoms is usually returned to the coking vessel. The coke produced. in the process remains in the bed coated on the solid particles. Stripping steam is injected into a stripping zone to remove oil from the coke particles prior to the passage of the coke to the burner.

The heat for carrying out the endothermic coking reaction is generated in the burner vessel, usually but not necessarily separate from the reactor. A stream of coke is thus transferred from the reactor to the burner vessel, such as a transfer line or fluid bed burner, employing a standpipe and riser system; air being supplied to the riser for conveying the solids to the burner. Sufficient coke or added carbonaceous matter is burned in the burning vessel to bring the solids therein up to a temperature sufficient to maintain the system in heat balance. The burner solids are maintained at a higher temperat-ure than the solids in the reactor. About 5% of coke, based on the feed, is conventionally burned for this purpose. This may amount to approximately 15% to 30% of the coke made in the process. The net coke production, which represents the coke make less the coke burned, is withdrawn.

By treating the coking feed stock by the process of this invention, a heavier boiling gas oil of reduced metals content can be segregated from the coker products for use as catalytic cracking feed stock. It is particularly practical to obtain a coker gas oil having an end point above 950 F., ranging upwardly to about 1100 F., which has a satisfactorily low metals content for catalytic cracking.

It is a particular feature of this invention that a spent alkylation acid may be employed as the treating acid. In experiments which have been conducted, it has been found that alkylation acid obtained from a commercial alkylation unit gives treating results fully equivalent to the use of fresh acid of the same H O content.

In this connection, spent alkylation acid commonly has a concentration of about 97%. This is preferably diluted to about concentration and may then be used in the process of this invention.

An important characteristic of the sulfuric acid treating process described is the ability to remove high molecular weight aromatic hydrocarbons as a sludge along with the metal contaminants. Correlations have been established between the cracking characteristics of oils dependent on their aromatic contact as indicated by the Conradson carbon content of the oil. It has been found that less refractory cracking stocks of better cracking characteristics have lower values of Conradson carbon. As indicative of the improvement in the cracking characteristics obtainable by this process, a feed oil having a Conradson carbon value of 2.3 was subjected to sulfuric acid treatment. This gas oil feed stock was treated with sulfuric acid in an amount of 5 pounds of acid per barrel of oil. It was found that the Conradson carbon inspection of the treated oil Was dropped to 1.5, indicating the superior cracking characteristics of the treated oil.

As indicated, in the preferred conduct of this invention, the heavy gas oil to be treated is mixed with a minor portion of cycle oil from the catalytic cracking operation. It is preferred to employ about 10% by weight of cycle oil in this mixture although amounts ranging up to about 30% may be employed. Inclusion of this cycle oil is particularly desirable in order to permit the upgrading of the cycle oil by elimination of refractory aromatic hydrocarbons in the manner identified above. In addition to this, fluid sludge constituents are formed with the aromatics present in the cycle oil which substantially contribute to the ease with which sludge formed from metal contaminants can be separated. As an example of these factors, a blend of a virgin gas oil with 10% of cycle oil was prepared. The gas oil contained 2.3 p.p.m. of nickel and 0.3 ppm. of vanadium. This blend was agitated with 50 pounds per barrel of 80% sulfuric acid for a period of twenty minutes at 200 F. On permitting this mixture to stand, acid sludge formed during the process separated rapidly and was found to be of an extremely fluid nature. The character of this sludge was remarkably superior to the sludge formed from treatment of the gas oil alone without the inclusion of the cycle oil. The treated oil was substantially free of acid and contained only 0.08 p.p.m. of nickel. Oil recovery was obtained at a yield of 90 wt. percent based on the gas oil plus cycle oil feed or 99 wt. percent based on the gas oil feed. It will be observed that the treatment of the mixture of gas oil and cycleoil together permitted essentially complete recovery of the portion of the oil adaptable for catalytic cracking.

What is claimed is:

1. A process for treating a heavy petroleum oil ineluding constituents boiling above about 900 F. and containing iron, nickel and vanadium contaminants which comprises treating said oil at a temperature in the range between about F. and about 300 F. with from about 5 to about 50 pounds of sulfuric acid per barrel, said acid having a concentration of from about to about 90%; removing acid sludge and recovering treated oil reduced in iron, nickel and vanadium content; and thereafter catalytically cracking said treated oil.

2. A process as defined by claim 1 wherein said oil is treated with said sulfuric acid at a temperature between about 200 and about 300 F.

3. A process as defined by claim 1 wherein said sulfuric acid has a concentration of about 4. A process as defined by claim 1 wherein said oil is treated with sulfuric acid of about 80% concentration at a temperature of about 200 F.

5. A process as defined by claim 1 wherein said oil is diluted with from about 10 to about 30% of catalytic cycle oil prior to treatment with said sulfuric acid.

References Cited in the file of this patent UNITED STATES PATENTS 1,823,614 Lemmon Sept. 15, 1931 2,179,008 Campbell Nov. 7, 1939 2,199,931 Walsko May 7, 1940 2,252,082 Lloyd et al Aug. 12, 1941 2,427,589 Chechot Sept. 16, 1947 2,459,419 Engel et al. Jan. 18, 1949 2,520,407 Hughes Aug. 29, 1950 2,611,735 Coons Sept. 23, 1952 2,682,496 Richardson et a1. June 29, 1954 2,778,777 Powel Jan. 22, 1957

Claims (1)

1. A PROCESS FOR TREATING A HEAVY PETROLEUM OIL INCLUDING CONSTITUENTS BOILING ABOVE ABOUT 900*F. AND CONTAINING IRON, NICKEL AND VANADIUM CONTAMINANTS WHICH COMPRISES TREATING SAID OIL AT A TEMPERATURE IN THE RANGE BETWEEN ABOUT 50*F. AND ABOUT 300*F. WITH FROM ABOUT 5 TO ABOUT 50 POUNDS OF SULFURIC ACID PER BARREL, SAID ACID HAVING A CONCENTRATION OF FROM ABOUT 70 TO ABOUT 90%; REMOVING ACID SLUDGE AND RECOVERING TREATED

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