US2547181A

US2547181A - Distillate sweetening process

Info

Publication number: US2547181A
Application number: US70584A
Authority: US
Inventors: Theodore B Tom; Jack H Krause
Original assignee: Standard Oil Co
Current assignee: Standard Oil Co
Priority date: 1949-01-12
Filing date: 1949-01-12
Publication date: 1951-04-03
Anticipated expiration: 1968-04-03

Description

Patented Apr. 3, 1951 J U TE sT rEs PATENT OFFICE I v i Q Q I I DISTILLATE raocss I Ind., assignors to Standard Oil Company, Ohicago, 111., a corporation of Indiana No Drawing. Application January 12, 1949, Serial No. 70,584

In the manufacture of heater oils from high sulfur crudes, it has been found that, whereas the sour heater oil distillate gives satisfactory performance in burning tests, the same oil gives objec'tionable deposits in certain sleeve-type burn- Claims. (01.196-32) 2 or preferably oxygen into the oil as it leaves the last stage of the caustic-methanol extraction and then allow the oil which is saturated with oxygen to stand for a short time before finally Washing with water to remove the last traces of caustic and dissolved methanol.

The reaction is quite rapid and'usually requires onlyabout one-half hour at room temperature, e. g. 60 to 80 F. In winter when the oil is cold, it is desirable to warm it to a temperature within the range of about60 to 100 F. in order to hasten 1 the reaction of the oxygen and mercaptans re ers after it has been subjected to sweetening with the usual reagents such as doctor solution, cope perchloride, etc. However, if the oil .is extracted with'a caustic-methanol solution which chemicall'y removes the ill-smelling mercaptans instead of simply converting them to disulfide s, then the oil .will give satisfactory performance in burner operation.

The removal of mercaptans bythe use of caustic-methanol suffers the disadvantage,however, in that it is extremely difiicult to lower the mercaptan number of the oil to a point where it will pass the usual doctor test for a'sweet oil. In other words, the caustic-methanol solution is not generally capable of making the oil salable and it is common practice to follow caustic-methanol treatment with doctor sweetening or copper sweetening. The caustic-methanol treatment applied in stages readily reduces the mercaptan number to about '5 or but it is substantially impossible to reduce the mercaptan numberbelow 1 which is ordinarily accepted as the upper limit for a sweet oil. The mercaptan number, sometimes called the copper number, is the milligrams of mercaptan sulfur per 100 milliliters of oil, generally determined by titration with a standardized copper salt solution.

An object of our invention is to eliminate the z extra treatment of caustic-methanol extracted oils with doctor solution, copper chloride, sodium hypochlorite, or other usual sweetening reagent. Another object of our invention is to produce oils which will satisfactorily meet the doctor. test when treated by the caustic-methanol process. Still another object of our invention is to facilitate washing of oil treated with caustic-methanol solutions.

We have discovered that the caustic-methanol treated oil can be satisfactorily sweetened by contacting it with oxygen or air after the separation of the caustic-methanol solution and before washing with water or neutralization of the caustic. For our purpose it is sufiicient to inject air maining in the oil after caustic-methanol extraction. The time required for the reaction is usually only about twenty minutes to threehours andtherefore, in a continuous operation, it is not necessary to maintain a large volume of the oil-in contact with oxygen. Accordingly, only a small aging tank may be required for the oxygen treat ment, after which the oilmay be washed with water to recover dissolved methanol and then-sent immediately to storage or to the market. The oxygen or air treatment also aids in washing the oil bright, the strong caustic-methanol solution having a tendency to leave a colloidal dispersion in the. oil which is difiicult to wash out with water.

. Where the extraction of mercaptans by the caustic-methanol is especially efficient and the mercaptan number of the extracted oil is low, e. g. 2 to 5, the oil can often be sweetened by the oxygen treatment by simply injecting oxygen into the line leading from the caustic-methanol extractor to the final water-washing step of the process. Rapid solution of oxygen in the oil can be obtained by injecting oxygen into the stream of oil just before entering a centrifugal pump where excellent mixing and diffusion of the oxygen into the oil is obtained. If the oxygen is injected under pressure, e. g. 10 to p. s. i., the rate of solution-is increased, thereby still further reducing the time required for the sweetening effect. The amount of oxygen required is quite small and varies with the residual mercaptans in the extracted oil. Thus, with an oil having a mercaptan number of about 5, it is desirable to inject from about 5 pounds to about 20 pounds of oxygen per thousand barrels.

As an example of our process, a sour West system.

her was reduced only to 7.5 with this treatment, showing that airblowing the neutralized oil was inefiective in producing a marketable product.

Another oil having a mercaptan number of 63 was extracted with one-fifth volume of a causticmethanol solution giving a mercaptan number of 8.5. After washing with water the oil was blown with air for one-half hour at room temperature and then tested 6 mercaptan number.

When blown with air for one-half hour at room temperature before washing with water, the mercaptan number was reduced from 8.5 to 1.5.

In another operation on caustic-methanol extracted oil, the mercaptan number was reduced to 0.5 by the action of oxygen injected into the oil after the extraction operation and before washing. This oil was sweet to the doctor test,

4 that contains mercaptans which comprises extracting said oil with an aqueous caustic-methanol solution until the major part of the mercaptans are removed from the oil, separating substantially all the mercaptan rich solution from the oil, and contacting the extracted oil which still contains some caustic and methanol with a gas containing free oxygen until the oil is substantially mercaptan-free.

2. The process of claim 1 wherein the substantially mercaptan-free oil is washed with water to recover methanol.

3. The process of claim 1 where in the mercaptan number of the extracted oil is less than i. The processof claim 1 wherein the free oxygen. containing gas is injected into a flowing that is, a sample shaken with a solution of litharge in 10 per cent NaOI-I to which a pinch of sulfur was added, gave no orange-yellow precipitate or rag.

The caustic-methanol solution employed in the extraction operation is usually prepared from a strong solution of NaOH or KOH containing from 40 to 65 per cent caustic in water, the amount of methanol usually being about 10-to a volumes per hundred volumes of the aqueous caustic solution. If desired there may be also incorporated in the solution alkali phenolates,

cresylates, etc. to increase the mercaptan extrac- 12.

desirable to pass the air, after leaving the oil, thru a water scrubber to recover vapors of. methanol which would otherwise be lost from the The methanol dissolves in the water from which it can be recovered by distillation for re-use' in the system, or the water solution of methanol can be used in the regeneration of spent-caustic-methanol solution. Having thus described our invention, what w .claim is:

, .1. The process of sweetening a hydrocarbon oil 0 When air is used to contact the oil, it is often stream of the extracted oil.

5. The process of claim 1 wherein the amount of free oxygen added is between about and 20 pounds per thousand barrels of extracted oil.

6. The process of sweetening a sour. hydrocare bon oil which boils above the gasoline range which comprises extracting said sour oil withv an aqueous caustic-methanol solution until the mercaptan number of the extracted oil is between about 2 and 10, separating substantially all the mercaptan rich aqueous caustic-methanol solution, contacting the extracted oil which still con-.- tains some caustic and methanol for about 20 to 180 minutes with from about to pounds ofiree oxygen per thousand barrels-of extracted oil, and washing the treated oil with water to re: cover methanol therefrom. 7. The process of claim 6 wherein the aqueous caustic-methanol solution has the following composition: from about 10 to volumes of meth: anol per volumes of aqueous solution c011? taining 40-60 weight percent of caustic.

THEODORE B. TOM. JACK H. KRAUSE.

' REFERENCES crrEn Thefollowing references are of record in-the file of this patent:

UNITED STATES PATENTS 2,297,537. Craig et a1. Sept. 29, 1942

Claims

1. THE PROCESS OF SWEETENING A HYDROCARBON OIL THAT CONTAINS MERCAPTANS WHICH COMPRISES EXTRACTING SAID OIL WITH AN AQUEOUS CAUSTIC-METHANOL SOLUTION UNTIL THE MAJOR PART OF THE MERCAPTANS ARE REMOVED FROM THE OIL, SEPARATING SUBSTANTIALLY ALL THE MERCAPTAN RICH SOLUTION FROM THE OIL, AND CONTACTING THE EXTRACTED OIL WHICH STILL CONTAINS SOME CAUSTIC AND METHANOL WITH A GAS CONTAINING FREE OXYGEN UNTIL THE OIL IS SUBSTANTIALLY MERCAPTAN-FREE.