US2560374A

US2560374A - Treatment of sour petroleum distillates

Info

Publication number: US2560374A
Application number: US77443A
Authority: US
Inventors: Albert J Shmidl
Original assignee: Standard Oil Development Co
Current assignee: Standard Oil Development Co
Priority date: 1949-02-19
Filing date: 1949-02-19
Publication date: 1951-07-10
Anticipated expiration: 1968-07-10

Description

Patented July 10, 1951 TREATMENT OF SOUR PETROLEUM DISTILLATES Albert J. Shmidl, Houston, Tex., assignor, by

mesne assignments, to Standard Oil Development Company, Elizabeth, N. J., a corporation of Delaware No Drawing. Application February 19, 1949, Serial No. 77,443

9 Claims. 1

The present invention is directed to a method for treating sour petroleum distillates. More particularly, the invention is directed to the sweetening of sour petroleum distillates in the 2 small amounts of catalytic reagents are employed. In the foregoing description of the prior art, it will be seen that the prior art workers added compounds such as phenols and certain amines presence of an alkali metal hydroxide and a mild b to the alkaline solutions which were employed to oxidizing agent. treat sour petroleum distillates. I have now Prior to the present invention, it has been found that, in distinction to the prior art workknown to treat sour petroleum distillates with ers, improved results may be obtained by adding aqueous alkaline solutions, such as solutions of catalytic amounts of an alcoholic amine to the alkali metal hydroxide, to remove hydrogen sulsour petroleum distillate. Therefore, in accordfide and other acidic bodies, following which the ance with the present invention the foregoing sour distillates were treated with sodium plumbite objects may be achieved'by adding to sour petrosolution to convert deleterious sulfur compounds leum distillates small amounts of alkanol amines to compounds which are largely innocuous. This and then contacting the sour distillates containand other prior art processes relied on the addi-' ing the alkanol amine with a very small catalytic 'tion of sulfur to cause the conversion of the quantity of asolutionof an alkali metal hydroxide sulfur compounds from mercaptans to disulfides. while maintaining in contact therewith a mild Other processes convert the undesirable comoxidizing agent. pounds by means of lead sulfide'which is then Accordingly, it may be seen that the present separated from the gasoline. Frequently, the invention may be described briefly as involving separation of lead sulfide from the gasoline was treating a sour petroleum distillate boiling in the not complete, and consequently, some was carried range from about 50 to 750 F. by contacting the over into storage, which was disadvantageous. distillate with a solution of an alkali metal hy- Furthermore, the addition of sulfur to gasoline droxide while maintaining in the sour distillate frequently impaired the octane number level of a catalytic amount of an alkanol amine and the gasoline since it is well known that sulfur and adding to the contacted mixture a mild oxidizing its compounds affect gasoline detrimentally. agent suflicient to sweeten said distillate, follow- Efforts have been made in the prior art to ing which the alkali metal hydroxide is separated remedy this situation, and the workers in the from the contacted distillate. field have turned to adding certain compounds, The alkanol amines employed in the practice 'such as phenols and amines, to alkaline solutions, of the present invention include the ethanol such as sodium hydroxide, to cause conversion amines such as mono-, di, and triethanol amine, through an oxidation mechanism of the delethe mono-, di-, and tripropanol and butanol terious compounds in the sour naphtha. Freamines and the higher members of the same quently such expedients are unsatisfactory in not homologous series. The compounds used in the completely sweetening the product, and an afterpresent invention have the general structural treatment, by one of the well known procedures, formula NH3-r(CyH2yQH) a: where N is the amine becomes necessary. nitrogen, as is an integer from 1 to 3,, and y is an From the foregoing discussion of the prior art, integer from 1 to 18, inclusive. it will be seen that the petroleum refining indus- 40 These compounds may be employed in try has been faced with a problem of converting amounts, based on the naphtha, varying from deleterious sulfur compounds present in petro- 0.001 to 1.0 per cent by volume, with a preferred leum distillates to those which do not detrimenrange from about 0.01 to 0.15 per cent by volume. tally affect the quality of the product. It is to be emphasized that the specified amount It is, therefore, the main object of the present of the alkanol amines should be added to the invention to provide a treating process in which naphtha and not to the alkaline solution. These improved results are obtained in converting obcompounds are employed generally in a small jectionable sulfur compoundsto harmless bodies. amount effective to sweeten the naphtha in ac- Another object of the present invention is to cordance with the present invention and may provide an improved sweetening process in which exert a catalytic action on the sweetening operaan active material is added to the petroleum distion. 7 r tillate being sweetened to catalyze the conversion The alkaline solution employed in the present of deterious sulfur compounds. invention should be a solution of an alkali metal Another object of the present invention is to hydroxide. Preferably the solution should be provide an improved sweetening process in which an aqueous solution having a Baum gravity 3 in the range from about 30 to 50 B. but solutions of lower strengths may be used under some conditions. For example, a 40 B. aqueous solution of sodium hydroxide gives satisfactory results.

The alkali metal hydroxide may be lithium, sodium, or potassium hydroxide, but sodium hydroxide will be preferred on account of its availability.

The temperature at which the treating operation is conducted will usually be atmospheric temperature and may range from about 60 F. up to about 120 F., although higher temperatures up to 200 F. may be used. A preferred temperture range will be from about 70 to about 95 F. Satisfactory results have been obtained at atmospheric temperatures encountered in the Texas Gulf Coast area.

The present invention will be further illustrated by the following specific example:

EXAMPLE I A portion of a hydrogen sulfide free refined kerosene, which was a solvent raffinate having a copper number of 50 and a Saybolt color of 20, was divided into two parts. To one part was added 0.05% by volume of triethanol amine and the -stock was then contacted with 5% by volume of 40 B. sodium hydroxide solution in the presence of three times the theoretical amount of oxygen required to sweeten, employing two minutes agitation in an agitator equipped with paddles operating at 1200 revolutions per minute. The second portion was contacted with 5% by volume, based on the kerosene, of B. sodium hydroxide solution to which had been added 0.05% by volume, based on the kerosene, of triethanol amine. The kerosene was then contacted with the sodium hydroxide solution of triethanol amine in the presence of three times the theorectical amount of oxygen for two minutes under violent agitation in an agitator equipped with paddles, operating at 1200 revolutions per minute. The sodium hydroxide solution was separated from each of the two treated portions of the kerosene and the copper number and color of the treated kerosenes determined. The data in the first column of Table I represent the treatment in accordance with the present invention whereas the data in column 2 represent'prior art techniques where the catalyst is added to the sodium hydroxide rather than to the kerosene.

Saybolt Color The data in Table I indicate the markedly superior result obtained by treatment of the kerosene in accordance with the present invention, in which the triethanol amine was added prior to contact with sodium hydroxide in the presence of oxygen over that obtained when treating in accordance with the prior art methods in which the kerosene was contacted with a sodium hydroxide solution of triethanol amine. The copper number of the naphtha treated according to my invention was reduced to 32 after contact with sodium .hydroxide, and droppedto after 1 hour, to 23 after .3 hours, and to 8 after 24 hours, whereas that of the kerosene treated conventionally was substantially unchanged. Of great significance is the color of the kerosene to which triethanol amine had been added and which was treated in accordance with the present invention. It will 'be noted that the color after 24 hours was 20, the same as the kerosene initially, whereas the color of the kerosene when treated in accordance with conventional techniques had dropped to 12. The color of the kerosene treated in accordance with the present invention was even better than that of kerosene treated only with 40 B. sodium hydroxide, since the latter dropped to 18 after standing in storage for 24 hours.

In the foregoing example, the improvement obtained in the present invention has been illustrated by the copper number test. This is a well known analytical procedure employed in the petroleum industry. A description of the method of test may be found in U. 0. P. Laboratory Test Methods for Petroleum and Its Products, third edition, page 1-1-61, Universal Oil Products Company, Chicago, 1947. This test is a measure of the mercaptan sulfur content of the oil being tested.

(In the practice of the present invention, it is to be understood that the sour petroleum distillates employed as feed stocks are free from, or deficient in catalytic, oxidation promoting *compounds and will not sweeten in contact with a mild oxidizing agent and alkali metal hydroxide. The great majority of petroleum distillates to be sweetened in general refinery practice will be found to fall in this category.

Although ll'lOt illustrated by the example, one of the particular advantages of the present nvention resides in the catalytic effect of the alkali metal hydroxidesolution. The alkali metal hydroxide appears to function as a true catalyst since the .small amount used may be recycled to treat large quantities of sour petroleum distillate. A small amount of the alkali metal hydroxide solution may be entrained in the treated naphtha, and, therefore, it may be necessary to replace the entrained amount with fresh solution. In short, it is contemplated in the practice of the present invention that the alkali metal hydroxide solution will be reused over and over again, since it is notnecessary to regenerate this solution.

The invention has been described and illustrated by employment of a mild oxidizing agent such as oxygen. It is contemplated that mixtures of oxygen with other gases, such as air, may be employed. It is also contemplated that other mild oxidizing agents such as peroxides, permanganates, and the like may be used. For example, a hydrogen peroxide solution may be employed as the mild oxidizing agent.

In practicing the present invention, it is to be understood that the petroleum distillate maybe subjected to a preliminary treatment for removal of hydrogen sulfide if the distillatecontains hydrogen sulfide. Such preliminary treatment may include washing with a dilute alkali metal hydroxide solution or blowing with a free-oxygen containing gas such as air. If hydrogen sulfide and/or other acidic compounds'are present and are not removed, the alkali metal hydroxide solution employed as the catalyst may very quickly become'seriously depleted in activity.

In the practice of the invention, it will be desirable to use an amount of oxygen in excess of the theoretical required to sweeten the sour petro- :leum distillate. Ordinarily, .an amount of about 5. 300% of the theoretical amount to sweeten may be employed. However, sweetening in accordance with the present invention may be obtained with considerably lesser quantities of oxygen. In fact, sweetening may be obtained in some cases by contact with the oxygen present in the treating vessel. It will be desirable to employ an amount of oxidizing agent at least equivalent to the theoretical amount required to sweeten.

The invention has been described and exemplilied by employment of 0.5 to 5.0% by volume of the catalytic alkali metal hydroxide solution. It is contemplated that as little as 0.1 and as much as by volume, or more, of the alkali metal hydroxide solution, based on the sour naphtha, may be employed. Very good results, however, are obtained with 1% by volume and this amount will be preferred.

The nature and objects of the present invention having been completely described and illustrated, what I wish to claim as new and useful and to secure by Letters Patent is:

1. A method for sweetening a sour petroleum distillate containing mercaptans and having a final boiling point no greater than 750 F. which comprises adding to said distillate a small but effective catalytic amount no greater than 1% by volume of an alkanol amine and, then agitating the distillate containing the alkanol amine with a small amount no more than 5% by volume of a solution of an alkali metal hydroxide while adding a sufficient amount of a mild oxidizing agent to convert the mercaptans to disulfides and to obtain a sweetened distillate.

2. A method in accordance with claim 1 in which the alkanol amine is an ethanol amine.

3. A method in accordance with claim 1 in which the alkanol amine is a propanol amine.

4. A method in accordance with claim 1 in which the alkanol amine is a butanol amine.

5. A method in accordance with claim 1 in which the alkanol amine is employed in an amount in the range from 0.001 to 1.0% by volume of the sour petroleum distillate.

6. A method in accordance with claim 1 in which the mild oxidizing agent is a free-oxygen containing gas.

7. A method for sweetening a sour petroleum distillate containing mercaptans and having a final boiling point no greater than 750 F. which comprises adding to said distillate a small but effective catalytic amount no greater than 1% by volume of triethanol amine and then agitating the distillate containing triethanol amine with no more than 5% by volume of an aqueous solution of an alkali metal hydroxide while adding a sufficient amount of mild oxidizing agent to convert the mercaptans to disulfides and to obtain a sweetened distillate.

8. A method for sweetening a sour petroleum distillate containing mercaptans and having a final boiling point no greater than 750 F. which comprises adding to said distillate an amount of triethanol amine in the range between 0.001%

and 1.0% based on said distillate and then agitating the distillate containing triethanol amine with an effective amount of a sodium hydroxide solution not over 5% by volume based on the sour distillate while adding a sufficient amount of a free oxygen containing gas to convert the mercaptans to disulfides and to obtain a sweetened distillate. I

9. A method for sweetening a sour petroleum distillate containing mercaptans and having a final boiling point no greater than 750 F. which comprises adding to said distillate 0.05% by volume of triethanol amine based on the distillate and then agitating the distillate containing triethanol amine with 5% by volume based on the sour distillate of an aqueous B. sodium hydroxide solution while adding three times the theoretical amount of oxygen required to convert the mercaptans to disulfides and to obtain a sweetened distillate.

ALBERT J. SHMIDL.

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

UNITED STATES PATENTS Number Name a Date 2,152,720 Yabrofi Apr. 4, 1939 2,152,723 Yabrofi Apr. 4, 1939 2,186,398 Yabroff Jan. 9, 1940 2,364,582 Davis et a1. Dec. 5, 1944 2,434,868 Sample et al. Jan. 20, 1948 2,453,067 Happel Nov. 2, 1948

Claims

1. A METHOD FOR SWEETENING A SOUR PETROLEUM DISTIALLATE CONTAINING MERCAPTANS AND HAVING A FINAL BOILING POINT NO GREATER THAN 750* F. WHICH COMPRISES ADDING TO SAID DISTILLATE A SMALL BUT EFFECTIVE CATALYTIC AMOUNT NO GREATER THAN 1% BY VOLUME OF AN ALKANOL AMINE AND, THEN AGITATING THE DISTILLATE CONTAINING THE ALKANOL AMINE WITH A SMALL AMOUNT NO MORE THAN 5% BY VOLUME OF A SOLUTION OF AN ALKALI METAL HYDROXIDE WHILE ADDING A SUFFICIENT AMOUNT OF A MILD OXIDIZING AGENT TO CONVERT THE MERCAPTANS TO DISULFIDES AND TO OBTAIN A SWEETENED DISTILLATE.