US2616833A

US2616833A - Treatment of hydrocarbon distillates

Info

Publication number: US2616833A
Application number: US213348A
Authority: US
Inventors: Joseph A Chenicek; Kenneth M Brown
Original assignee: Universal Oil Products Co
Current assignee: Universal Oil Products Co
Priority date: 1951-03-01
Filing date: 1951-03-01
Publication date: 1952-11-04
Anticipated expiration: 1969-11-04

Description

Nov. 4, 1952 J. A. CH ENICEK ET AL TREATMENT OF HYDROCARBON DISTILLATES FiledMa'rch l, 1951 lull mummDmum orrwqzu INVENTORSZ mm NM. m M CM. R 0 A T T T, W A m WE U f Patented Nov. 4, 1952 TREATMENT OF HYDROCARBON DISTILLATES Joseph A. Chenicek, Bensenville, and Kenneth M. Brown, Hinsdale, Ill., assignors to Universal Oil Chicago, 111., a corporation Products Company, of Delaware Application March 1, 1951, Serial No. 213,348

9 Claims.

This invention relates to the treatment of a sour hydrocarbon distillate and more particularly to a novel combination process to produce a substantially sweet hydrocarbon distillate, which is substantially free from gum forming components, by a series of mutually related and interdependent steps.

One method of treating hydrocarbon distillates containing mercaptans isto subject the distillate to treatment with caustic solutions in order to remove a substantial proportion of the mercaptans therefrom. When treating a cracked gasoline, the final sweetening maybe effected by adding a phenylene diamine compound to the gasoline and allowing the gasoline to remain in storage until it becomes sweet. Because the phenylene diamine compound also serves as an oxidation inhibitor, this method of treating is referred to as inhibitor sweetening. However, it has been found that, with some gasolines, this method of treating results in the desired sweetening but also results in an excessive increase in the gum content of the gasoline. The present invention is directed to a novel method of retaining the benefits of the inhibitor sweetening and at the same time reducing gum formation.

In one embodiment the present invention relates to a combination process for producing a substantially sweet hydrocarbon distillate of reduced gum formation which comprises treating a sour hydrocarbon distillate with an alkali metal hydroxide to remove a substantial proportion of the mercaptans contained therein, regenerating the used alkali metal hydroxide, commingling a phenylene diamine compound with thetreated hydrocarbon distillate and allowing the resultant mixture to remain in storage in the presence of air until the distillate is substantially sweet, and scrubbing the substantially sweetdistillate with the regenerated alkali metal hydroxide.

In a specific embodiment the present invention relates to a combination process for producing a substantially sweet gasoline of reduced gum formation which comprises treating a sour cracked gasoline with a caustic solution previously used in the process in the manner to be hereinafter set forth, regenerating the used caustic solution, commingling from about 0.001% to about 0.1% by weight of N,N-di-secondary-bu tyl-p-phenylene diamine with the treated gasoline, subsequently treating the last mentioned gasoline with the regenerated caustic solution, and utilizing the caustic solution 'from the last mentioned treating as said first mentioned caustic solution.

The novel combination process of the present invention is explained further in the accompanying diagrammatic flow drawing which illustrates one specific embodiment thereof.

The novel combination process is particularly applicable to the treatment of sour cracked gasolines, although it is understood that it may be employed, with suitable modifications, for the treatmentof other cracked products including cracked kerosene, cracked light gas oil, etc'., as well as for the treatment of substantially saturated hydrocarbon distillates including straight run gasoline, natural gasoline, kerosene, gas oil,

etc V In the interest of simplicity the following description will be directed to the treatment of a sour cracked gasoline also containing hydrogen sulfide. This is the normal gasoline production recovered from a cracking operation. Referring to the drawing, the gasoline is introduced through line i to 'prewash zone 2. wherein it is contacted with caustic introduced through line 3. Any suitable system may be employed to remove the hydrogen sulfide from the cracked gasoline and this may comprise either a batch or continuous type of operation. The caustic utilized in this step of the process generally is of low gravity of below about 20 Baum and/or has been used previously in other processes. The used caustic from this step contains sodium sulfides which are difiicult to regenerate and, in most cases, it has been found to be more economical to discard rather than to undergo the time and expense of regenerating the same. The used caustic may be removed from zone 2 through line 4 and may be discarded or further handled as desired.

The gasoline now substantially free from hydrogen sulfide is withdrawn from zone 2 through line 5 and is directed to caustic scrubber 6. In the particular case here illustrated, the gasoline in zone 6 is passed in countercurrent fiow with casutic solution previously used in the manner to be hereinafter set forth in detail. The caustic solution is introduced into zone 6 by way of line 1. Zone 6 may contain any suitable contacting means including bubble trays, baflle plates, side to side pans, etc. or it may be packed with suitable packing material, such as carbon Raschig rings, etc.

" The caustic scrubbing in zone 6 may be effected at any suitable temperature which generally will be about atmospheric. However, the temperature may range from about'50 toabout 200 F. When desired, a solutizer also may be included in the caustic in order to improve the efliciency of the mercaptan extraction. Suitable solutizers include alcohols and particularly methyl alcohol, ethyl alcohol, propyl alcohol, etc. isobutyrates such as potassium isobutyrate, sodium isobutyrate, etc., alkali metal salts such as sodium phenolates, cresylates, xylenolates, similar potassium salts, etc. It is understood that in place of caustic solution, other suitable alkali metal hydroxide solutions may be employed, including potassium hydroxide, etc.

In zone 6 a major proportion of the mercaptans contained in the gasoline will be removed through the formation of sodium mercaptides. The caustic solution containing sodium mercaptides is withdrawn from zone 6 through line 8 and is subjected to regeneration in regenerator 9.

The caustic solution for use in accordance with the present invention must be of a gravity of at least Baum and preferably is of from about to about 48 or more Baum gravity. This is an essential feature of the present invention because, for the reasons to be hereinafter set forth, it is necessary that a strong caustic solution be used in the subsequent treating step of the process in order to remove the hydroperoxides which are responsible for the formation of gum in gasoline.

The used caustic solution introduced into regenerator 9 is treated therein in any suitable manner in order to regenerate the caustic solution and to remove the mercaptans therefrom. In one method steam is introduced through line It and the steam serves to hydrolyze the mercaptides and to strip out the mercaptans, which are removed from zone 9 through line II. In another method the regeneration may be effected by indirect heating, in which case a heating coil or other suitable means is disposed in the lower portion of the regenerator and a suitable heating medium is .passed therethrough. In any event, a regenerated caustic solution of at least 30 Baum gravity is withdrawn from the lower portion of regenerator 9 through line I2 for further use in the process in the manner to be hereinafter set forth in detail.

The treated gasoline from caustic scrubber 6 will now be substantially reduced in mercaptans and is withdrawn from zone 6 through line I3. Because the inhibitor sweeting reaction comprises the oxidation of mercaptans to disulfides, it is necessary that air be present in the sweetening step of the process. Generally sufficient air will be entrained 0r dissolved in the gasoline to efiect the desired oxidation and it will be unnecessary to introduce air from. an extraneous source. However, when sufficient air is not contained in the gasoline, air from an extraneous source may be introduced through line I4 to commingle with the gasoline in line I3.

In the case here illustrated, a phenylene diamine compound is introduced through line I5 and is commingled with the gasoline in line I3, and the resultant mixture is directed into inhibitor sweetening zone I6. It generally is preferable to pass. the mixture. in. line I3 through a suitable mixing device, such as a duriron mixer, an orifice mixer, etc., illustrated at IT, in order to obtain intimate mixing of the gasoline and phenylene diamine compound. It is understood that the, phenylene diamine compound and/or air may be introduced directly to inhibitor sweetening zone I6, in which case zone I6 preferably includes suitable mixing means, such as mixing paddles, illustrated at I8. In anothermethod, the. desired mixing may be obtained by suitable circulation of the mixture in zone I5. In still another method the air may be introduced to zone I6 in such a manner that it will serve to efiect intimate mixing of the components therein.

Any suitable phenylene diamine compound may be employed in accordance with the present invention and preferably comprises N,Ndi-secondary butyl p phenylene diamine which is presently commercially marketed as UOP Inhibitor No. 5. Other phenylene diamine compounds include N,N'-di-alkyl-p-phenylene diamines in which the alkyl groups contain from one to about 12 carbon atoms per molecule, including such compounds as N,N'-di-isopropyl-pphenylene diamine, N,N'-di-secondary-amyl-pphenylene diamine, N,N'-di-secondary-hexyl-pphenylene diamine, N-isopropyl-N-secondarybutyl-p-phenylene diamine, Nisopropyl-N-secondary-amyl-p-phenylene diamine, etc. The phenylene diamine compound is utilized in a concentration of less than about 1% by weight and preferably of from about 0.000.l% to about 0.1%.

Inhibitor sweetening in zone I6 generally will be effected within a comparatively short time which, preferably should not be more than about 24 hours. The. inhibitor sweetening generally is effected at substantially atmospheric temperatures which usually range from about 50 to about F. However, when desired, the inhibitor sweetening may be efiected at a higher temperature which may range up to F. or more; and this may be accomplished by introducing the gasoline through line I3 at the desired temperature and/or by heating zone I 6 in any suitable manner, such as by the use of suitable heatin coils disposed therein in order to heat and/or maintain the components therein at the desired temperature.

After the desired time in storage the gasoline, which now is substantially sweet, is withdrawn from zone I6 through line I9 and is introduced to caustic scrubbing zone 20. Zone 20 may contain suitable contacting means as hereinbefore described in connection with zone 6, and the caustic scrubbing therein may be effected at substantially the same temperature as heretofore described for zone 6. In the case here illustrated, the substantially sweet gasoline is passed in countercurrent contact in zone 20 with the regenerated caustic solution introduced thereto through line I2. As hereinbefore set forth, it is an essential feature of the present invention that the caustic solution used in zone 20 be of at least 30 Baum gravity and preferably in from about 40 to 48 or more Baum gravity.

The reason why it is essential to use a strong caustic solution in zone 20 is believed to be as follows, although it is understood that we are not limited to this specific explanation. Cracked gasolines contain dimcultly removable mercaptans, such as tertiary alkyl mercaptans. These mercaptans are not removed by caustic scrubbing in zone 6 and will remain in the gasoline supplied to inhibitor sweetening zone I6. During the inhibitor sweetening reaction, the tertiary alkyl mercaptans, for example, react to form free radicals which in turn react with olefins and oxygen to form hydroperoxide free radicals. The hydroperoxide free radicals can react with mercaptans with the formation of disulfides or they can. be instrumental in catalyzing oxidation reactions. leading to gum formation. Since the mercaptans which react most readily with the hydroperoxide free radical are those which are most easily removed from the gasoline by caustic scrubbing in zone 8, these mercaptans are not available for reaction with-the hydropenoxide free radical and, therefore, the reaction-results in the formation of hydroperoxides which lead to gum formation in the gasoline if they are not-removed. In accordance with the present invention, the hydroperoxides are removed from the gasoline in caustic scrubbing zone l and this requires a strong caustic solution as hereinbefore set forth.

The caustic solution containing the hydro peroxides is withdrawn from zone 20 through line 2| and is directed by way of line I, to'be utilized in caustic scrubber 6 to treat the gasoline containing mercaptans. In zone 6 the-hydroperoxides react with the mercaptans to form disulfides. As hereinbefore set forth, the formation of disulfides will occur in zone 6 because the readily re-' actable mercaptans are present in this .zone but will not occur in zone 20 because these readily reactable mercaptans are not present in zone 20.

In another embodiment of the invention the caustic solution withdrawn from zone '20 may be directed through line 2| to caustic regenerator 9. In caustic regenerator 9 the hydroperoxide sodium salts are decomposed to sodium hydroxide and to oxygen-containing hydrocarbons presumably alcohols, and the latter are stripped from the caustic in regenerator 9 and arewithdrawn with the mercaptans through line I I.

The treated gasoline from zone 20 is withdrawn therefrom through line 22 and, as hereinbefore set forth, the gasoline is substantially sweetand is reduced in gum forming components.

In the interest of simplicity, valves, pumps and similar appurtenances have been omitted from the drawing but it is understood that they will be used as required. It is also understood that, when solutizers or other materials are to be utilized in the process, they may be introduced in any suitable manner and also that the required fractionation or other separating means will be included.

The following examples are introduced to illustrate further the novelty and utility of the present invention but not with the intention of unduly limiting the same. 7

Example I A cracked gasoline containing hydrogen sulfide and mercaptans may be treated with a caustic solution of Baum gravity in a batch type operation to remove hydrogen sulfide. The gasoline free from hydrogen sulfide is then subjected to treatment with a caustic solution of 48Baum gravity to remove a substantial proportionof the mercaptans. The used caustic is regenerated by steam stripping. The caustic scrubbed gasoline is then commingled with 0.005% by weight of N,N' di secondary-butyl-p-phenylenefidiamine and,'after passing through a duriron mixer, is sent to a storage tank and allowed to; remain therein for 24 hours. The gasoline from the storage tank is then scrubbed with the regenerated caustic solution of 48 Baum gravity, and the sed caustic therefrom employed for-{treating the gasoline in the caustic scrubbing treatment. The caustic scrubbing and inhibitor sweetening operation are all efiected at substantially atmospheric temperature. The gasoline withdrawn from the last caustic scrubbing will be .substantially sweet and of reduced gum contentl For example, the gasoline when) caustic scrubbed and inhibitor sweetened without the I final caustic treatment of the present combination process may have a copper dish gum content of above 150 mg. after 2 days in storage. 0n theother hand, when treated by the combination process of the present invention, the gasoline may have a copper dish gum content of less than about Example II Cracked gasoline may be treated in substan tially the same manner as described in Example I but using 0.02% by weight of N,N-di-isopropyl-,

p-phenylene diamine as the inhibitor and sweetening agent.

Example III Cracked light gas oil may be treated in substantially the same manner as described in Example I but using 0.01 by weight of N,N-di-secondary-butyl-p-phenylene diamine and effecting the inhibitor sweetening at a temperature of F; V n y Example IV A straight run gasoline containing mercaptans is treated in substantially the same manner as described in Example I but in this case the in: hibitor sweetening reaction is effected at atem perature of F.-

We claim as our invention:

1. A combination process for producing a substantially sweet hydrocarbon distillate of reducedgum formation which comprises treating a sour hydrocarbon distillate with an alkali metal hydroxide to remove a substantial proportion of the mercaptans contained therein, regenerating the used alkali metal hydroxide, commingling a phenylene diamine compound with the treated hydrocarbon distillate, and subsequently treating the hydrocarbon distillate with the regenerated alkali metal hydroxide.

2. A combination process for producing a substantially sweet hydrocarbon distillate of reduced gum formation which comprises treating asour hydrocarbon distillate with an alkali metal hydroxide solution previously used in the process in the manner to be hereinafter set forth, regencrating the used alkali metal hydroxide solution, commingling a phenylene diamine compound with the treated hydrocarbon distillate and allowing the resultant mixture to. remain in storage in the presence of air until the distillate is substantially sweet, subsequently treating the substantially sweet-distillate with the regenerated alkali metal hydroxide solution, and utilizing the alkali metal hydroxide solution from the last mentioned treating step as said first mentioned alkali metal hy-. droxide solution. Y

3. A combination process for producing a sub stantially sweet hydrocarbon distillate of reduced gum formation which comprises treating a hydrocarbon distillate containing hydrogen sulfide and mercaptans with caustic solution of below about 20 Baum gravity-to remove hydrogen sulfide, separating a hydrocarbon distillate free of hydrogen sulfide and treating the same with caustic solution of at least 30 Baum gravity to remove a substantial proportion of the mercaptans from said distillate,lregenerating the used caustic solution to ,recoveii a regenerated caustic solution of at least 30 .Baum gravity, commingling N,N'-di-secondary butyl-p-phenylene diamine in an amount of not more than about 1% by weight with said treated hydrocarbon distillate and allowing the resultant mixture to remain in storage in the presence otiair until the distillate is substantially sweet, subsequently treating the substantially sweet distillate with the regenerated caustic solution of at least 30 Baum gravity,

and utilizing the caustic solution from thelast mentioned treating as said first mentioned caustic solution of at least 30 Baum gravity;

4. A combination process for producing a substantially sweet gasoline of reduced gum formation which comprises treating a sour gasoline with an alkali metal hydroxide solution previously used in the process in the manner to be hereinafter set forth, regenerating the used alkali metal hydroxide solution, commingling a phenylene diamine compound in an amount of not greater than about 1% by weight with said, gasoline, subsequently treating the last mentioned gasoline with the reregenerated caustic solution, and utilizing the caustic solution from the last mentioned treat ing as said first mentioned caustic solution.

5. A combination process for producing a substantially sweet gasoline of reducedgum formation which comprises treating a sour cracked gasoline with a caustic solution previously employed in the process in the manner. to .be hereinafter set forth, separating. causticsolution from.

treated gasoline and regenerating the caustic solution, commingling from about 0.001% to about 0.1% by weight of N,N--di-secondarybutyl-p-phenylene diamine with the treated gas oline, subsequently treating the last mentioned gasoline vwith the regenerated caustic solution, and employing the caustic solution fromthe last mentioned treating as said first mentioned caustic solution. Y

6.. A combination process for producing a substantially sweet gasoline of reduced gum formation which comprises treating a cracked gasoline containing hydrogen sulfide and mercaptans with a caustic solution of less than about Baum gravity to remove the hydrogen sulfide, separating cracked gasoline substantially free of hydrogen sulfide and treating the same with a caustic solution of at least 40 Baum gravity to remove a substantial proportion of the mercaptans from the gasoline, separating gasoline of reduced mercaptan content from the used caustic solution, regenerating the used caustic solution to form a caustic solution of at least 40 Baum gravity, commingling from about. 0.00l to about 0.1% by weight of N,N'-di-secondarybutyl-p-phenylene diamine with the last mentioned gasoline and allowing the resultant mixture to remain in storage in the presence of air until the gasoline is substantiallysweet but contains hydroperoxides, subsequently scrubbing the substantially sweet gasolinewith the regenerated caustic solution of at least 40 Baum gravity to remove hydroperoxides fromth'e gasoline, and

react with the mercaptans contained. in the j l gasoline to. form disulfides, v a

- 7. A combination process for producing a' sub-- stantially sweet gasoline of reduced gum formation which comprises treating a sour gasoline with a caustic solution of at least 40 Baum gravity to remove a substantial proportion of the mercaptans from the gasoline, separating gasoline of reduced mercaptan content from the used caustic solution, regenerating the used caustic solution to form a caustic solution of atleast 40 Baum gravity, commingling a phenylene diamine compound with the last mentioned gasoline and allowing the resultant mixture to remain in storage in the presence of air until the gasoline is substantially sweet but contains hydroperoxides, subsequently scrubbing the substantially sweet gasoline with the regenerated caustic solution of at least 40 Baum gravity to remove hydroperoxides from the gasoline, and supplying the resultant caustic solution containing hydroperoxides to the first-mentioned treating step wherein the hydroperoxides are reacted with mercaptans in said sour gasoline to form disulfides.

8. A process for producing a substantially sweet hydrocarbon distillate of reduced gum formation which comprises treating a sour hydrocarbon distillate with an alkali metal hydroxide solution of suflicient strength to remove a substantial portion of the mercaptans contained therein, regenerating the used alkali metal hydroxide solution, treating the distillate of reduced mercaptan content with a phenylene diamine compound in the presence of air, thereby forming hydroperoxides in the distillate, thereafter contacting the distillate with the regenerated alkali metal hydroxide solution to remove hydroperoxid'es therefrom, and supplying the resultant hydroperoxide-containing solution to the first-mentioned treating step wherein the hydroperoxides are reacted with mercaptans in said sour distillate to form disulfides.

9.'The process of claim 8 further characterized in that said alkali metal hydroxide solution is a caustic solution of at least 30 Baum gravity.

JOSEPH A. CHENICEK. KENNETH M. BROWN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,840,269 Borgstrom Jan. 5, 1932 2,183,968 McCormick et al. Dec. 19, 1939 2,427,212 Henderson et al. Sept. 9, 194'! 1 2,508,817 Devol et al May 23, 1950 2,543,953 Backenstc Mar. 6, 1951 2,552,399 Browder- May 3, 1951

Claims

1. A COMBINATION PROCESS FOR PRODUCING A SUBSTANTIALLY SWEET HYDROCARBON DISTILLATE OF REDUCED GUM FORMATION WHICH COMPRISES TREATING A SOUR HYDROCARBON DISTILLATE WITH AN ALKALI METAL HYDROXIDE TO REMOVE A SUBSTANTIAL PROPORTION OF THE MERCAPTANS CONTAINED THEREIN, REGENERATING THE USED ALKALI METAL HYDROXIDE, COMMINGLING A PHENYLENE DIAMINE COMPOUND WITH THE TREATED HYDROCARBON DISTILLATE, AND SUBSEQUENTLY TREATING