US2721831A - Stabilization of catalytically cracked gasoline - Google Patents

Description

Oct. 25, 1955 A, JENNINGS ET AL 2,721,831

STABILIZATION OF CATALYTICALLY CRACKED GASOLINE Filed June 29, 1951 T HI acn'nes R. Stridqlond' Patented Oct. 25, 1955 STABILIZATION OF CATALYTICALLY CRACKED GASOLINE Louis A. Jennings, Mountainside, and Barney R. Strickland, Westiield, N. J., assignors to Esso Research and Engineering Company, a corporation of Delaware Application June 29, 1951, Serial No. 234,334

2 Claims. (Cl. 196-29) This invention concerns a novel process for the sweetening and stabilization of a catalytically cracked gasoline. In accordance with this invention an oxygen-free cupric chloride reagent is employed to treat catalytically cracked gasoline in the absence of oxygen in a manner operative to selectively oxidize mercaptans present in the gasoline to the form of stable odor-free disulfide compounds.

For some time it has been appreciated that raw catalytically cracked gasolines possess unique properties distinguishing these gasolines from virgin naphthas or from thermally cracked gasolines as regards the oxidation characteristics. Thus, catalytically cracked gasolines unlike virgin 01' thermally cracked gasolines are peculiarly sensitive to oxidation. A raw catalytically cracked gasoline on mere exposure to air during normal storage, for example, will rapidly undergo changes result ing in the severe degradation of the gasoline as exemplified by gum formation. This phenomenon is disclosedin U. S. Patent No. 2,525,152 of Strickland and Lewis, patented October 10, 1950. It is there shown that a catalytically cracked gasoline, particularly as derived from a high sulfur content cracking stock, is uniquely characterized by the inclusion of relatively large amounts of arematic mercaptans together with olefins and diolefins. Again, it is pointed out in the patent referred to that the aromatic mercaptans apparently act as a catalyst to cause the oxidation of olefins and diolefins when oxygen is present, forming peroxides which have the effect of destroying the aromatic mercaptans andproducing excessive gum. Oxygen sensitive gasolines of this type are-obtained on the catalytic cracking of gas oils or other feed stock having a sulfur content. of more than about 0.8 Weight percent of sulfur. In some manner stocks of this nature when subjected to catalytic cracking form substantial quantities of aromatic mercaptans. As pointed out, thermally cracked gasolines or virgin gasolines are not of this nature and do not contain any substantial quantities of aromatic mercaptans.

This invention is therefore of specific application to the treatment of catalytically cracked gasolines containing aromatic mercaptans, olefins and diolefins. More specifically, the gasolines to be treated by the process herein disclosed are those gasolines derived from the catalytic cracking of a petroleum fraction boiling inthe range of about 400 F. to 1000 F. or somewhat higher, when such fractions contain more than about 0.8% sulfur. For example, when a West Texas gas oil, having a boiling range of about 400 F. to 700 F. and having a sulfur content of about 1.5%, is catalytically cracked to a 50 to 60% yield of 400 F. end point gasoline, the gasoline will have about a 30 copper number; that is, 30 milligrams of mercaptan sulfur per 100 milliliters of gasoline. This figure corresponds to approximately 0.035% sulfur as aromatic mercaptans. Or again, when a mixed gas oil of about 0.8% sulfur is catalytically cracked to a 50% yield of 400 F. end point gasoline, the amount of aromatic mercaptan sulfur in the gasoline is about 0.017 gram per milliliters of gasoline.

The aromatic mercaptans which may be present are thiophenols, thiocresols, or thioxylenols. These may all be considered as being mono or di-alkyl substitutedthiophenols in which the alkyl group contains one to three carbon atoms. which may be present are thiophenol, methyl thiophenol, dimethyl thiophenol, ethyl thiophenol, diethyl thiophenol, propyl thiophenol, and dipropyl thiophenol.

As stated, catalytically cracked gasolines of the character indicated are peculiarly sensitive to oxidation causing excessive gum formation. This sensitivity is so marked that such stocks cannot be successfully processed even under a nitrogen blanket unless the nitrogen employed is of extremely high purity containing less. than about 0.01% of oxygen. Thus, for example, in the conduct of the process disclosed and claimed in U. S. Patent No. 2,525,152 which is adapted to successfully extract aromatic mercaptans, it has been found that the process will be advantageously effected in the presence of nitrogen containing oxygen in proportions as small as 0.002%. Consequently, as brought out in the cited patent, in order to successfully treat catalytically cracked gasolines so as to remove aromatic mercaptans by means of caustic extraction, oxygen must be rigorously excluded during processing.

It has now been discovered. however that under the conditions herein disclosed, catalytically cracked gasoline of the extraordinary oxygen susceptibility indicated can be satisfactorily processed by an oxidation treatment so as to permit the conversion. of the aromatic mercaptans present to harmless disulfide compounds. The possibility of successfully selectively oxidizing the aromatic mercaptans in this manner without causing degradation of the gasoline quality is particularly striking in view of the disclosures of PatentNo. 2,525,152.

The manner in which this selective oxidation is achieved is to employ a cupric chloride treating reagent whichmust be completely free of oxygen and must be employed. in the complete absence of oxygen. Under these conditions it is possible to cause the selective conversion of aromatic mercaptans present in a catalytically cracked gasoline to disulfide compounds. The gasoline may therefore be successfully sweetened and stabilized by this cupric chloride treatment. The cupric chloride reagent to be employed may comprise either a solid. cupric chloride reagentor a solution of cupric chloride. For example, solid cupric chloride may be supported on a suitable carrier such as clay, bauxite, pumice or diatomaceous earth, preferably in weight percentages of about 10 to 15% of cupric chloride based on carrier. Again a solution of cupric chloride in water may be employed. In this case a solution is employed having about 10 to 15 weight percent ofcupric chloride dissolved therein. In either case cupric chloride per se or a mixture of copper sulfate and am monium chloride or sodium chloride may be used. Contact With solid reagent may be accomplished eitherin a fixed bed or as a slurry. When using a fixed bed the gasoline is passed through the bed at a rate of about one volume per volume of treating agent per hour. In the slurry process One volume of reagent is mixed with 4 to 5 volumes of gasoline to be treated. In these processes the water content of the solid reagent is controlled to about 5 to 25% and usually about 10% to 20% by weight. This is accomplished by drying or water addition to the feed and control of the gasoline temperature in contact Specifically, the aromatic mercaptans.

with the solid in order to regulate the solubility of water in the effluent treated gasoline.

The treatment with the cupric chloride solution reagent is conducted by maintaining the catalytically cracked gasoline in liquid phase and intimately contacting the cracked gasoline with the cupric chloride reagent at temperatures of about 70 to 130 F. The proportion of solution to use is a function of the mercaptan content of the feed but normally would be in the range of to 50% by volume based on feed. If desired, the operation can be conducted at pressures other than atmospheric, although the pressure employed does not appear to be critical. It is extremely important that the process be conducted so as to completely exclude the presence of oxygen during treatment with the cupric chloride reagent. Thus, it is necessary that the cupric chloride reagent be completely freed of oxygen prior to use and that provisions be made to exclude oxygen during treatment with the cupric chloride. This can be achieved on a commercial scale by employing sealed apparatus, preferably operated somewhat above atmospheric pressure so as to prevent possibility for leakage of air into the system. Alternatively, if desired, the gasoline may be blanketed during processing with an inert gas containing substantially no oxygen. Thus, for example, nitrogen having a purity of about 99% and containing no more than about 0.01% of oxygen may be employed to protect the catalytically cracked gasoline during processing. Thus, for example, the cupric chloride treating reagent cannot be regenerated in the conventional manner by blowing air into the treating zone in which the cupric chloride is employed to treat the catalytically cracked gasoline.

The necessity for conducting the process of this invention so as to completely exclude oxygen necessitates adoption of an unique regenerating procedure for regenerating spent cupric chloride treating reagent. Several alternative regeneration processes may be employed.

First, it is possible to treat spent cupric chloride reagent by employing insufficient oxygen or air to completely regenerate the reagent after removal from the gasoline treating zone. Oxygen is supplied during this separate regeneration step so that the regenerated copper chloride solution will retain at least a small percentage of cuprous ions. In the practice of this regeneration process about 90 to 98% or preferably about 95% of the theoretical oxygen requirements to accomplish complete regeneration is to be employed.

As an alternative regeneration procedure, an excess of oxygen may be used to completely regenerate the copper chloride treating reagent. Thereafter oxygen-free nitrogen of the character heretofore described or other oxygen-free inert gas may be blown through the regenerated copper chloride reagent so as to completely eliminate all excess air or oxygen. Purging with such inert gas may be successfully carried out by employing about 50 to 150 cu. ft. of gas per thousand lbs. of copper chloride reagent.

Finally, the copper chloride reagent can be successfully regenerated by employing the theoretical oxygen requirements or an excess thereof, provided the regenerated reagent be blended back with a controlled amount of spent reagent. Thus, for example, in the case in which a copper chloride solution is regenerated with an excess of about 10% oxygen, the regenerated solution may be safely conditioned for reuse by blending with about 2 to 10 wt. per cent of spent copper chloride reagent based on the weight of the copper chloride contained in the reagent.

In order to fully disclose the nature of this invention, a typical embodiment of the invention will be described with reference to the accompanying drawing, diagrammatically illustrating a sweetening process for catalytically cracked gasoline.

Referring to this drawing, the numeral 1 designates a catalytic cracking zone. Catalytic cracking zone 1 may comprise any desired arrangement for securing the catalytic cracking of a suitable cracking feed stock. For example, zone ll may consist of what is known as a fluidized catalytic cracking apparatus in which critical amounts of vaporized oil feed are passed through particles of the cracking catalyst, so as to maintain the catalyst as a liquid-like body characterized by the hydraulic properties of a liquid. The feed material supplied to cracking zone 1 may comprise a gas oil boiling above the gasoline boiling range, for example, in the range of about 400 to lO00 F. This gas oil is introduced to zone 1 through line 2 and the cracked products are removed from zone 1 through line 3.

The cracked products are passed through a cooling zone 4 and thence to a distillation zone 5 operated to permit removal of an overhead product through line 6, having an end point of about 400 F. Higher boiling constituents may be removed as a bottoms product through line 20 and if desired, fractionated side stream products can be obtained from zone 5. The overhead stream is passed through a cooling zone 21 and is then introduced to a second distillation zone 7. Here, uncondensed gases, including hydrogen sulfide, for example, are removed overhead through line 8 while a bottoms product is removed through line 9 constituting the cracked gasoline boiling in the range of about to 400 F.

In accordance with this invention the catalytically cracked gasoline of line 9 is introduced to a mixing zone 11 in which the gasoline is contacted with a copper chloride reagent. The copper chloride reagent may be introduced to zone 11 through line 10. After suitable treatment of the gasoline with the copper chloride reagent in zone 11 the mixture of gasoline and spent copper chloride reagent will be removed through line 12 and introduced to separation zone 13. Here gasoline is removed as the final finished product through line 14 while the separated copper chloride reagent is removed through line 15 for passage to regeneration zone 16. The gasoline product of line 14 may be finished as desired although it is particularly contemplated that a small proportion of a copper deactivator be mixed in the gasoline to overcome the effects of traces of copper that may be picked up during sweetening. For example, a suitable copper deactivator comprises N,N'- disalicyal-1,2-diaminopropane which is employed in proportions of about 5 pounds per 1000 barrels. As an additional step after copper sweetening and prior to addition of metal deactivator the gasoline may be treated with an aqueous solution of sodium sulfide or a solid reagent consisting of zinc sulfide on an inert carrier such as pumice. The spent copper chloride reagent is regenerated in zone 16 as for example, by contact with air introduced to zone 16 through line 25. After suitable regeneration, the copper chloride reagent may then be recycled to zone 11 for further treatment of cracked gasoline.

It has been found that the process described possesses several unique advantages. For example, the process can be relied upon to provide a treated gasoline which will satisfactorily pass the Doctor test for mercaptan content. No further treatment of the cracked gasoline is required in order to secure a Doctor pass product.

A particular advantage of the process of this invention is that sweetening is conducted without causing removal of certain naturally occurring inhibitors present in a catalytically cracked gasoline. It appears, for example, that alkaline reagents such as caustic have the effect of removing these natural phenolic inhibitors. However, the copper chloride reagent does not have this effect, and in fact, the oxidation stability of the gasoline is increased by the copper chloride treatment. This is shown by the data in the following table, indicating the nature of treat applied in the different cases shown, and the induction period of the treated gasoline as obtained by A. S. T. M. test D-525-49.

TABLE I Induction Sample and Treatment Period,

Minutes Catalytically Cracked Naphtha Sample A:

Washed 10% 10 Be. NaOH 55 Washed 10% Copper Chloride Solution 315 Peroolated Through Solid Copper Chloride Reagent... 435 Catalytically Cracked Naphtha Sample B:

Washed 10% 10 Be. NaOH 135 Washed 10% Copper Chloride Solution 380 Poroolated Through Solid Copper Chloride Reagent... 315

As shown in Table I, when a catalytically cracked gasoline is treated with caustic, the treated gasoline has an extremely low induction period. However, if either a solid copper chloride reagent or a solution of copper chloride be employed to treat the gasoline, this effect does not occur and the cracked gasoline is more stable as indicated by the longer induction period reported in Table I.

In order to show the full advantages of the process of this invention, the following data are presented, obtained by treating a catalytically cracked naphtha boiling in the range of about 340 to 430 F. The inspections of this naphtha prior to treatment were as follows.

Naphtha:

Aromatic mercaptan content, mg. S/ 100 ml 19 Conjugated diolefins, wt. 1.5 Monoolefins, wt. Feed:

Sulfur content, wt. 1.5 API gravity 30.0 Mid-boiling point, "F 595 Reactor temperature, F 965 Percent conversion, 430+ 62 This naphtha was treated with a copper chloride reagent consisting of an aqueous solution of copper chloride containing about of cupric chloride. 10 volume percent of this reagent was mixed with the naphtha in liquid phase at a temperature of about 70 F. for about five minutes. Summarized in Table 11 below are results of this treatment showing inspections both before and after the copper chloride treatment.

l Peroxide number after 16 hours storage in contact with 5 volumes of air at room temperature.

Gum tests obtained on a blend of of sample with 75% acid treated gaglglscatalytic naphtha, +5# N,N-di-see-butyl-p-phenylenediamine/5 The data of Table II shows that the naphtha before treatment was extremely unstable, was susceptible to oxidation on exposure to air and had a high gum value as obtained by the ASTM and Copper Dish Gum test. However, after treatment with copper chloride reagent in accordance with this invention, the gasoline was stabilized in all respects.

The extreme importance of treatment prior to exposure of the stock to air is illustrated in the data below. The experiment was conducted on a total catalytic naphtha distillate produced by operation at 960 F. and 61% conversion on West Texas gas oil of 1.6 Wt. sulfur, 21.1 API gravity, and 460 to 1100" F. boiling range (midboiling point 803 F.). In one case the naphtha was sweetened with liquid copper chloride solution (10 vol.

%) before exposure to air. In a second case the same stock was deliberately exposed to air for four days at room temperature and then copper chloride sweetened. This latter procedure might approximate the usual handling method in which no precautions are taken to avoid contact with air.

a Peroxide number after 16 hours storage in contact with 5 volumes of air at room temperature.

b Gum values obtained on stock'containing 2 lbs. N ,N-di-sec-butyl-pphenylenediamine/5000 gals.

The high initial gum figure is believed to be due to the extreme instability of the untreated material, resulting in gum formation during the evaporation of the sample under air blanket in the ASTM gum test procedure.

As described therefore the process of. this invention concerns a method for stabilizing a catalytically cracked gasoline by treatment with an oxygen-free copper chloride reagent in a manner to exclude the presence of oxygen during treatment. This treatment is effective to sweeten the gasoline, to stabilize the gasoline against subsequent exposure to air and to provide a gasoline of low gum content. As brought out, a particular advantage of this process is the manner in which sweetening is achieved without removal or degradation of inhibitors which normally occur in the catalytically cracked gasoline.

What is claimed is:

1. In the process of producing a stable cracked gasoline which consists of the following steps: catalytically cracking a gas oil feed stock boiling above about 400 F., and containing more than about 0.8% sulfur, fractionating the products of the said cracking step and separating a distillate fraction boiling in the gasoline boiling range substantially free of hydrogen sulfide but containing substantial quantities of mercaptans, said mercaptans consisting principally of aromatic mercaptans resulting from the cracking step to the substantial exclusion of aliphatic mercaptans, and said distillate stock containing both olefins and diolefins, thereafter contacting said distillate stock with a treating agent consisting of a solution of cupric chloride which is free of oxygen, thereafter separating the treated distillate stock from the spent cupric chloride reagent, and thereafter regenerating the spent cupric chloride reagent in a separate zone under conditions in which from about to 98% of the theoretical oxygen requirement to completely regenerate the reagent is employed, and thereafter recycling at least a portion of said reagent to contact said distillate fraction.

2. Process as defined by claim 1 wherein about of the theoretical oxygen is employed.

References Cited in the file of this patent UNITED STATES PATENTS 1,386,768 Day Aug. 9, 1921 1,608,339 Ridge et a1. Nov. 23, 1926 1,687,992 Phillips et al. Oct. 16, 1928 1,810,369 Peterkin June 16, 1931 1,815,563 Henderson et al. July 21, 1931 1,940,861 Henderson Dec. 26, 1933 1,948,565 Day Feb. 27, 1934 1,963,556 Morrell June 19, 1934 1,964,219 Schulze June 26, 1934 2,253,011 Benedict Aug. 19, 1941 2,270,248 Benedict et al. Jan. 20, 1942. 2,293,395 Lovell et al Aug. 18, 1942

Claims (1)

1. IN THE PROCESS OF PRODUCING A STABLE CRACKED GASOLINE WHICH CONSISTS OF THE FOLLOWING STEPS: CATALYTICALLY CRACKING A GAS OIL FEED STOCK BOILING ABOVE ABOUT 400* F., AND CONTAINING MORE THAN ABOUT 0.8% SULFUR, FRACTIONATING THE PRODUCTS OF THE SAID CRACKING STEP AND SEPARATING A DISTILLATE FRACTION BOILING IN THE GASOLINE BOILING RANGE SUBSTANTIALLY FREE OF HYDROGEN SULFIDE BUT CONTAINING SUBSTANTIAL QUANTITIES OF MERCAPTANS, SAID MERCAPTANS CONSISTING PRINCIPALLY OF AROMATIC MERCAPTANS RESULTING FROM THE CRACKING STEP TO THE SUBSTANTIAL EXCLUSION OF ALIPHATIC MERCAPTANS, AND SAID DISTILLATE STOCK CONTAINING BOTH OLEFINS AND DIOLEFINS, THEREAFTER CONTACTING SAID DISTILLATE STOCK WITH A TREATING AGENT CONSISTING OF A SOLUTION OF CUPRIC CHLORIDE WHICH IS FREE OF OXYGEN, THEREAFTER SEPARATING THE TREATED DISTILLATE STOCK FROM THE SPENT CUPRIC CHLORIDE REAGENT, AND THEREAFTER REGENERATING THE SPENT CUPRIC CHLORIDE REAGENT IN A SEPARATE ZONE UNDER CONDITIONS IN WHICH FROM ABOUT 90% TO 98% OF THE THEORETICAL OXYGEN REQUIREMENT TO COMPLETELY REGENERATE THE REAGENT IS EMPLOYED, AND THEREAFTER RECYCLING AT LEAST A PORTION OF SAID REAGENT TO CONTACT SAID DISTILLATE FRACTION.

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