Refining mineral oils

Feb. 17, 1942

2,273,104

<img file="US2273104A_D0001.tif" />

W. O. HEILMAN

REFINING MINERAL OILS Filed Feb, 24, 1941

AL.KAL( 5O4U77OA/

<img file="US2273104A_D0002.tif" />

SPgHT

<img file="US2273104A_D0003.tif" />

Patented Feb. 17, 1942

2,273,104

UNITED STATES PATENT OFFICE

2,273,104

REFINING MINERAL OILS

William O. Heilman, Cranford, N. 3., assignor to Standard Oil Development Company, a corporation of Delaware

Application February 24, 1941, Serial No, 380,272

Claims.

The present invention is concerned with the refining of mineral oils. This invention is more particularly concerned with the removal of mercaptan compounds from petroleum oils, particularly from petroleum oils boiling in the heavy naphtha heating oil and gas oil boiling ranges. In accordance with the present process, objectionable mercaptan compounds are removed from oils of this character by a process in which the feed oil is segregated into a relatively high and into a relatively low boiling range fraction. The relatively low boiling range fraction is contacted with an alkali metal hydroxide solution under conditions to secure substantial complete removal of the mercaptan compounds therefrom. This is secured by utilizing a relatively large amount of alkali metal hydroxide solution as compared to the volume of relatively low boiling feed oil being treated. The partially spent alkali metal hydroxide solution is then utilized for the removal of the mercaptan compounds from the relatively high boiling range fraction.

It is known in the art to refine petroleum oils by various operations in order to produce products of a satisfactory quality. For example, it is known in the art to remove objectionable mercaptan compounds by various operations. One operation comprises treating the mercaptancontaining feed oil with a so-called “doctor solution” which comprises a sodium hydroxide solution of lead oxide under conditions to convert the mercaptan compounds to disulfide compounds. This operation does not reduce the total sulfur content of the oil but merely converts the sulfur compounds into relatively innocuous materials. In an operation of this character, the process usually comprises treating the lead mercaptide bearing oil with free sulfur in a manner to precipitate lead sulfide and to form the corresponding alkyl disulfides. The disadvantage of an operation of this character is that considerable care must be exercised with respect to the addition of the free sulfur. If insufficient sulfur is added all the mercaptides are not removed from the oil, which results in a product of inferior quality. On the other hand, if an excess of sulfur be added, this excess sulfur remains dissolved in the treated oil which increases its corrosiveness and in many instances necessitates rerunning of the oil. Thus, various suggestions have been made that objectionable compounds, such as mercaptans, be removed from the oil in a manner to completely free or at least considerably lower the total, sulfur content of the treated oil. For example, it has been suggested (Cl. 196—32) that the oils be treated with an alkali metal hydroxide solution such as with a sodium hydroxide solution. However, in order to remove the mercaptan compounds satisfactorily, particularly the relatively high boiling mercaptan compounds, it is necessary to use a relatively large quantity of the reagent based upon the volume of oil treated. This is particularly the case when treating relatively high boiling oils as, for example, those oils boiling in the heavy naphtha, heating oil, and gas. oil ranges, as for example, those oils which boil in the general range from 250° F. to about 750° F.

I have, however, now discovered a process by which a relatively low total quantity of alkali metal hydroxide solution may be used as compared to the total volume of feed oil being desulfurized. In accordance with my invention, the feed oil is segregated into a relatively low boiling fraction and into a relatively high boiling fraction. The relatively low boiling fraction is contacted with the total volume of alkali metal hydroxde solution whereby the ratio of alkali metal hydroxide solution to the quantity of oil being treated is relatively high, since only a relatively small amount, that is the low boiling fraction, is contacted. Under these conditions, when utilizing a relatively large amount of alkali metal hydroxide solution to feed oil, substantial complete removal of the mercaptan compounds is obtained. The partially spent alkali metal hydroxide solution containing the lower boiling mercaptans present as mercaptides, and likewise containing constituents which function to enhance the affinity of the partially spent alkali metal hydroxide solution for the relatively higher boiling mercaptans present in the higher boiling segregated fraction, is utilized in contacting the segregated relatively higher boiling feed fraction in a secondary treating zone. Under these conditions substantial complete removal of the mercaptan compounds is secured from both the relatively high and the relatively low boiling seggregated fraction of the feed oil.

My process may be readily understood by reference to the attached drawing illustrating an embodiment of the same. For purposes of description, it is assumed that the feed oil comprises a heating oil fraction boiling in the general range from about 250° F. to 600° F. The feed oil is introduced into a distillation zone i by means of line 2 in which it is segregated into a relatively low boiling fraction which is removed by means of line 3 and a relatively high boiling fraction which is removed by means of line 4.

.35

2.273.104

The relatively low boiling fraction is contacted in an initial treating zone 4 with an alkali metal hydroxide solution which for the purpose of description is taken to be a sodium hydroxide solution. The sodium hydroxide solution is with- 5 drawn from sodium hydroxide storage 6 and introduced into contacting zone 4 by means of line 5. Operating temperature and pressure conditions and the quantity of sodium solution used are adapted to secure substantially complete 10 removal of the mercaptan compounds from the segregated relatively low boiling fraction of the feed oil. The treated segregated oil fraction, free of mercaptan compounds, is withdrawn from contacting zone 4 by means of line 7 while 15 the spent sodium hydroxide solution is withdrawn by means of line 8 and passed into secondary contacting zone 9. In secondary contacting zone 9 the spent sodium hydroxide solution contacts the relatively high boiling segre- ₂o gated fraction of the feed oil under conditions to remove the relatively high boiling mercaptan compounds from this segregated fraction of the feed oil. The relatively high boiling segregated fraction of the feed oil free of mercaptan com- ₉pounds is withdrawn from contacting zone 9 by means of line iO and preferably combined with the segregated low boiling fraction of the feed oil removed from zone 4. The total feed oil is withdrawn from the system by means of line I i, ₃θ and further refined or handled in any manner desirable. The spent sodium hydroxide solution is withdrawn from contacting zone 9 by means of line 12 and passed to regeneration zone 13 in which the sulfur compounds are removed ₃therefrom preferably by steam to convert the same to mercaptans which are removed overhead by means of line 14. Sludge and soap constituents are removed as a bottoms by means of line 15 while the regenerated sodium hydroxide ₄₀solution is removed by means of line IG and recycled to zone 4. Under certain conditions, it may be desirable to remove the mercaptide compounds from the partially spent sodium hydroxide solution removed by means of zone 4 before introducing the same into zone 9. If this ^Jadaptation of the invention be employed, the partially spent sodium hydroxide solution is introduced into zone 17 by means of line 18 in which the mercaptides are converted to mer- .θ captans and removed overhead by means of line 19. The partially spent solution free of mercaptans is withdrawn from zone 17 by means of line 20 and passed to contacting zone 9 as described. ₅₅

The process of the present invention may be widely varied. It is to be understood that zones I, 4, 9, 17 and 13 may comprise any suitable number and arrangement of units. The process essentially comprises utilizing a relatively large ₆₀volume of alkali metal hydroxide solution on a segregated relatively low boiling fraction of a feed oil, removing the partially spent alkali metal treating reagent and utilizing the same for treating the relatively high boiling segregated frac- ₆₅tion of the feed oil from which the mercaptans are more difficultly removable. By segregating the feed oil as described, the quantity of the treating reagent is at least doubled providing the feed oil be segregated into approximately equiva- 70 lent volumes. Thus the effectiveness of the reagent in removing the mercaptans from the relatively low boiling segregated fraction is increased approximately 100%. I have found that the partially spent reagent after removal from the 75 relatively low boiling fraction is more effective in the removal of the more difficultly removable mercaptans from the high boiling fraction than fresh reagent. Although I do not wish to be limited by any theory or mechanisms or with respect to the reactions involved, it appears that the alkali metal hydroxide solution absorbs constituents from the relatively low boiling segregated fraction of the feed oil which materially enhances its affinity, although partially spent, for the more difficultly removable mercaptans.

The invention may be adapted for the treatment of any relatively high boiling petroleum feed oil. It is, however, particularly suitable for use in treating petroleum oils boiling in the heavy naphtha, heating oil, and gas oil boiling ranges, as for example, for the treatment of petroleum oils boiling in the range from about 250° F. to about 700° F. It is particularly effective in the treatment of heating oils such as those boiling in the range from about 250° F. to 600° F. In general, it is preferred to segregate a feed oil into two fractions in which the final boiling point of the low boiling fraction and the initial boiling point of the high boiling fraction approximate the mid-boiling point of the feed oil. Thus, for example, when treating petroleum oils boiling in the range from about 250° F. to 600° F., it is preferred that the final boiling point of the relatively low boiling fraction be in the range from about 425° F. to 450° F., and the initial boiling point of the high boiling fraction be in the range from about 400° F. to 425° F. A particular adaptation of the present invention is in the treatment of a petroleum oil fraction boiling in the range from about 400° F. to 650° F. Under these conditions, the final boiling point of the relatively low boiling fraction is about 525° F. to 550° F„ whereas the initial boiling point of the relatively high boiling fraction is in the range from about 500° F. to 525° F.

Although any alkali solution may be used, I particularly prefer to employ alkali metal hydroxide solutions, especially a sodium hydroxide solution. When utilizing a sodium hydroxide solution, I prefer to use a solution of from about 15 to 25% sodium hydroxide solution and to use from about 0.2 to 0.4 volume of sodium hydroxide solution per volume of oil.

The manner in which the feed oil is segregated may be varied widely. In general, the relatively low boiling fraction should not comprise over 50% of the total volume of oil and should preferably comprise less than this amount. A very desirable operation is to segregate a relatively low boiling fraction comprising from about 10% to 30%, preferably about 20%, of the oil as the low boiling fraction.