US3107213A - Caustic treating process - Google Patents

Description

Oct. 15, 1963 Filed Feb. 12, 1959 2 Sheets-Sheet 1 l5 TREATED] ALKALINE- S3Efi$zfi I 25 24 awe I VENT EXTRACTIQN 2o DISULFIDES TOWER I OXIDATION .U UNIT 1 HYDROCARBON II ALKALINE 5, L l2 RECOVERY 22 TOWER WASH oIL 24 REGENERATED SPENT ALKALINE SOLUTION ALKALINEPHENOLIC SOLUTION FIGURE-l Charles 0. Cole Jackson Eng Georges G. Lukk Inventors Charles B. Rupur Norman L. ShIpley By Rims. QMJMLL Agenr Oct'. 15, 1963 c. o. COLE ETAL 3,107,213

CAUSTIC TREATING PROCESS Filed Feb. 12, 1959 2 Sheets-Sheet 2 ousnvo NI s'llo GIOV maoaad "loA Inventors Agent VHlHdVN GBLVHHL Charles 0. Cole Jackson Eng Georges G. Lukk Charles B. Rupur Norman L. ShIpIey NI SNVldVOHHW HO S'IONEIHdOIHJ.SOI'ION3Hd :IO NOLLOHOHH .LNBOHBd United States Patent 3,107,213 CAUSTIC TREATING PROCESS Charles 0. Cole, Jackson Eng, Charles B. Rupar, and Norman L. Shipley, Sarnia, Ontario, Canada, and Georges G. Lukk, Westfield, N.J., assignors to Esso Research and Engineering Company, a corporation of Delaware Filed Feb. 12, 1959, Ser. No. 792,895 3 Claims. (Cl. 208-230) The present invention deals with the caustic treating of petroleum fractions. More particularly, it concerns a method for removal of mercaptans and thiophenols in a manner making maximum use of caustic while reducing problems of waste caustic disposal.

The treatment of various hydrocarbon streams with alkaline solutions so as to reduce their mercaptan and thiophenol contents is well known in the art. Mercaptans are undesired due to their noxious smell. Sulfur'containing compounds are in general undesirable since the presence of sulfur adversely affects stability and combustion characteristics of fuels. In addition to removing mercaptans and thiophenols, the alkali extraction will also remove phenolic compounds such as phenol, the cresols, and higher phenolics, normally present in the petroleum fraction to be treated. In treating a typical cracked naphtha, for example, these phenolics will comprise up to 1 wt. percent of the hydrocarbon oil While the total quantity of mercaptans and thiophenols may be about 0.1 wt. percent or less. In the conventional method of caustic washing such a naphtha fraction, up to 90 wt. percent or more (based on phenolics present in the 'naphtha) will be extracted along with mercaptans and thiophenols.

The extraction of phenolics presents several significant problems. It has been ditlicult'to dispose of the spent caustic containing phenols which continuously pass into the. alkali solution during extraction. Lange amounts of a high phenolic content, caustic stream cannot be tolerated in rivers, streams, etc., due to their harmful effect on aquatic life. Thus, heretofore it was required to treat such caustic in order that their phenolic content be considerably reduced. Additionally, the extraction of phenols is not of particular value and the alkali consumed thereby is essentially wasted with regard to its availability for the removal of mercaptans and thiophenols.

In accordance with the present invention, means are taught whereby optimum use is made of available alkali, and minimum difiioulties in disposal of alkaline solution are incurred. More particularly, a sufficient quantity of phenolics is added to the alkaline solution to be used for extraction of hydrocarbon oil so that the concentration of phenolics in solution is in equilibrium with the phenolic compounds present in the hydrocarbon oil to be treated. The free alkali content of the alkaline solution is maintained at a very low value, i.e. less than 2 Wt. percent. When the alkaline solution containing an equilibrium concentration of phenolics is contacted with the hydrocarbon oil, thiophenols and mercaptans are extracted Whereas the solution does not extract phenolics from the oil. Since thiophenols and mercaptans are more acid than phenolics, the equilibrium relationships are such that the available small quantity of free alkali will essentially only be utilized for removal of undesired sulfur-containing compounds as opposed to the extraction of phenolics.

In a preferred embodiment, spent alkaline solution, i.e. solution rich in extracted mercaptans and thiophenols, is

3 1 ,2 13 Patented Oct. 15, 1963 "ice regenerated by oxidizing the mercaptans and thiophenols to disulfides, separating out the disulfide, and recycling alkaline solution containing equilibrium quantities of phenolics to the hydrocarbon extraction zone.

The present invention is generally applicable to the alkaline treatment of oils containing mercaptans and phenolics. Among fractions suitable for treatment are catalytically cracked naphtha, heavy virgin naphtha, kerosene, and the various middle distillates.

The benefits of the present process are as follows:

(l) Maximum use of alkali to remove undesirable compounds such as mercaptans and thiophenols.

(2) Increased product yields since phenolics remain in the hydrocarbon oil treated.

(3) Spent caustic disposal problems are markedly reduced since the quantity of phenolic-containing, spent alkaline solution ultimately to be withdrawn from the system is considerably less than in conventional processes.

(4) Data has shown that the presence of phenolics in gasoline, etc. are not detrimental. In fact, certain phenolics are natural inhibitors. Thus, the oil treated in the present process would normally require less antioxidant inhibitor addition since natural inhibitors have not been removed.

It is to be clearly noted that the present invention is clearly distinguishable from the conventional use of solutizers, as for example shown in U.S. Patent 2,351,- 467. Although it has previously been suggested to add limited quantities of various materials to alkaline washes, e.g. amines, phenols, etc., the preservation of an equilibrium concentration of phenolics in said alkaline solution so as to prevent substantially any extraction of phenolics from the hydrocarbon to be treated was not heretofore contemplated. In the prior art systems, the phenolic concentration in said wash solution was substantially below equilibrium requirements and/ or the relatively large quantity of free alkali employed resulted in substantial phenol extraction from the hydrocarbon oil treated. The greater the amount of free alkali, the greater will be the degree of phenolics extraction from the hydrocarbon oil.

By way of nomenclature, the term alkaline solution denotes the basic (as opposed to acidic) solution formed by dissolving alkali-metal compounds in water. Though hydroxides of sodium and potassium are preferred, various salts such as carbonates may also be employed. The term free alkali is used to denote the quantity of unreacted alkali present in solution, i.e. the quality of alkali available for interaction with mercaptans, thiophenols and phenolics.

The various aspects and modifications of the present invention will be made more clearly apparent by reference to the following description, examples and accompanying drawings.

FIGURE 1 depicts a preferred mode of operation whereby extracted mercaptans are removed while regenerating alkaline solution for further extraction.

FIGURE 2 illustrates experimental results derived from the study of alkaline extraction of a hydrocarbon oil containing mercaptans, thiophenols and phenolics.

Turning to FIGURE 1, the system shown therein basically comprises extraction tower 10, oxidation or regeneration vessel l1, and akaline recovery tower 12.

It is desired to extract a light, catalytically cracked naphtha, boiling in the range of to 330 F. The hydrocarbon contains about 0.02 wt. percent thiophenols, 0.2 wt. percent phenolics and has a mercaptan content of 0.01 wt. percent. It is desired to reduce the thiophe- 1101 and mercaptan contents to less than about 0.002 wt. percent and 0.002 wt. percent respectively.

in the caustic is sufficiently great so as to be in equilibriurn' with the phenolics, such as phenol and cresols, present in the hydrocarbon oil to be treated. Normally about volumes of hydrocarbons are treated per volume of caustic introduced by line 14, but each volume of fresh causticpheno-lics solution can be used to treat up to 1000 volumes of oil before regeneration in unit 11, as will be later described. 'I'he alkaline solution of line 14 can be derived in large part from recycle caustic withdrawn by lines 16 and :17.

Tower 10 can be any conventional extraction apparatus. It preferably is a multi-contactingstaged unit, the staging and nature of the caustic solution introduced thereto being such thatthe treated oil removed through line contains at most the concentration of mercaptans and thiophenols indicated previously. The Washed oil will contain substantially the same quantity of phenolics, is. 0.2 wt. percent, as the initial oil feed.

Alkaline solution containing extracted mercaptans and thiophenols is withdrawn by line 16. About 90% of the extract can be recycled by line 17 for further contact with the oil to be washed. Continuously, or periodically if so desired, mercaptans and thiophenols must be removed from the caustic treat solution in order to 'allow for further extraction of sulfur-containing compounds. This is preferably done by means of oxidation unit 11, although in the broadest aspects of the present invention, any regeneration process efifecting such a result is applicable.

The spent caustic is thus sent to unit 11 wherein air or other oxygen-containing gas introduced through line 19 serves to convert the metallic salts of the extracted mereaptans and thiophenols to their disulfide forms, thus freeing sodium hydroxide for further extraction, i.e. for further interaction with the sulfur compounds present in the hydrocarbon oil. Air regeneration of caustic, per se, is Well known in the art. Very briefly described, unit 11 operates at a temperature of 50 to 200 F. e.g. 100 F., approximately 5 to 10rnoles of oxygen being employed for each mole of mercaptans and thiophenols. Though not shown, for the sake of simplicity a number of contacting passes between the caustic and the air are generally employed. Gases are vented through line 20.

Though mercaptides are converted by oxidation, there is no substantial eifect on the concentration of phenols (and carboxylic acids) present in the alkaline solution. Thus thealkaline solution withdrawn by line 21 will comprise substantially the same concentration of phenolics as the solution in line 18, as well as containing disulfides. It has a free caustic content of about 0.01 to 1 wt. percent. Since it is desired to have, a low concentration of free caustic in the extraction tower, a relatively simple regeneration step is readily employe Disulfides are removed from the alkaline solution in tower 12. A wash oil substantially free of thiophenols and mercaptans is introduced into tower '12 by inlet 22, thereafter countercurrently contacting the regenerated alkali solution and extracting disulfides therefrom. The wash oil is normally a virgin or cracked naphtha fraction and is preferably a stock which is to be hydrofined subsequently. Tower '12 operates at ambient temperature, about 0.1 to 10 volumes of wash oil being employed per volume of regenerated alkaline solution. The spent wash oil containing disulfides is Withdrawn by line 23 and may be sent to hydrofining, where the disulfides are split into hydrocarbons and hydrogen sulfide.

. The regenerated alkaline solution is thereafter recycled to extraction tower 10 by line 24.

Though not normally necessary or desired (from the 4 standpoint of easily maintaining phenolics equilibrium), a very small quantity of fresh alkali may be added to the system, thus supplementing the regeneration step. Since ultimately the concentration of carboxylic acids will tend to limit the life of the alkaline solution, the fresh caustic addition preferably will operate in conjunction with the purging of spent, high acid oil content solution, periodically done through line 25. Such a high acid all solution, which represents the alkaline solution to be disposed of, is readily saleable for the recovery of the acid oils While dilute solutions of acid oils are not. Thus, none or very little solution ultimately need be discharged into streams or the like.

Various modifications may be made to the system described above. Generally, when starting up the process, an equilibrium concentration of phenolics in the caustic will be secured by washing a minor portion of the overall oil feed with caustic until the phenolics build up to an equilibrium value. The resulting alkaline is then used for the practice of the present invention. Of course, extraneous phenolics may be added to the caustic if desired. Though it is theoretically desired to prevent any extraction of phenolics from the oil during the alkaline wash, it is realized that practical inefiiciencies may result in some change of phenolics concentration. The term substantially constant as applied to phenolics concentration denotes this small degree of inherent departure from desired results.

Table 1 presents a compilation of data applicable to the system heretofore described.

TABLE 1 Preferred range Broad range 5 to 1,000.--. 5 to 20. 50 to 200... to 120.

0.01 to 2.0--- 0.02 to 1.0.

0.25 170 10-.-. 5 to 10. 50 to 80 to 120.

Various experiments illustrating the practicality of the present invention will now be described. With specific reference to FIGURE 2, an experiment was conducted with respect to illustrating that there exists a range of conditions within which an alkaline solution will effectively remove thiophenols and mercaptans from a hydrocarbon without extracting phenolic materials there from.

A catalytically cracked naphtha containing 0.134 wt. percent phenolics, 0.011 wt. percent thiophenols and having a mercaptan no. of 5.4 (equivalent to a 0.007 wt. percent mercaptan sulfur'concentratiou) was treated with an 18 B. solution of caustic. The caustic had previously been used in plant operation to contact about 1000 volumes of naphtha before being employed in the present experiment. Thus, it contained 31 vol. percent acid oils and had approximately 2% free caustic soda.

The acid oil test (neutralizing of caustic'with'sulfuric acid) was a direct measure of the'phenolic content since the naphtha did not contain carboxylic acids.

The naphtha and caustic solution were then contacted The degree of mercaptan and thiophenol reduction, as

well as the degree of phenols extraction and buildup of acid oil concentration, is depicted in FIGURE 2.

With the initial treats, the caustic reduced the micphenol content of the naphtha by 100 percent and the mercaptan content by 80, while extracting 40% of the phenolics in the naphtha. With additional treats, the thiophenols and mercaptans were preferentially extracted. The degree of extraction of phenols continuously decreased (with a consequent buildup of acid oils in the caustic), until when each volume of initial caustic had treated 200 volumes of naphtha, equilibrium was reached between the phenolics in the caustic and in the naphtha, and thus no further phenolics were extracted. However, it is seen that during the interval of 200 to 250 volumes of naphtha/volume of caustic, the percentage of thiophenol and mercaptan reduction remained fairly constant. Ultimately, the caustic became saturated with these materials and their degree of removal decreased with continued use of the caustic.

It is therefore evident that there exists an interval (indicated as the cross-hatched area of FIGURE 2) wherein caustic did not extract phenolics from the oil but yet satisfactorily removes thiophenols and mercaptans. Thus by operating in this interval, maximum utilization of free caustic is possible. In the present example, about 0.4 wt. percent free caustic was present during this range. By controlling the addition of regenerated caustic, these treating conditions, i.e. 40 volume percent phenolics in caustic and about 0.4 wt. percent free caustic, may be maintained and caustic will be expended for extraction of mercaptans and thiophenols only.

It is to be noted that the use of a conventional phenol solutizer would result in conditions corresponding to those of less than 200 volumes of naphtha per volume of caustic as shown in FIGURE 2.

Table 2 illustrates the oxidative regeneration of a caustic solution employed to treat a light catalytic naphtha feed oil.

TABLE 2 Air Regeneration of Spent Caustic From Treating of Light Cat. Naphthzz Mercaptan Number Reduction Conditions:

Charge 1500 ml. Air rate 0.15 s.c.f.m. Temperature 150 F. Agitation Mechanical agitation and air blowing. Sampling Hourly check onmercaptan no.

Regeneration Data:

1 Caustic sample was acidified in presence of n-heptane of zero mercuptan no. Aliquot of n-heptane was titrated potentiometrically for mercaptan content. Bracketed figures were obtained by direct poteutiornetric titration of Caustic.

As seen above, the mercaptan no. of the caustic was markedly decreased, thus freeing caustic which had been chemically held by the mercaptides. The free caustic content was increased approximately 2.6 fold. The acid oil content of the caustic was not materially affected by the oxidative regeneration step. Although it was reduced from about 37 to 32 vol. percent, the relatively small quantity of regenerated caustic per volume of recycled caustic employed in the extraction zone ensures.

that substantial phenolic equilibrium is maintained.

Having described the present invention, that which is sought to be protected is set forth in the following claims.

What is claimed is:

1. In the process of removing mercaptans and thicphenols from a hydrocarbon oil additionally containing phenolic compounds, wherein said hydrocarbons are washed with an alkaline solution, the improved method of conserving alkali which comprises utilizing an alkaline solution containing less than 1.0 wt. percent free alkali, maintaining a sufiicient concentration of phenolics in said alkaline solution so as to be in equilibrium with the phenolic compounds in said hydrocarbon oil, said alkaline solution extracting said mercaptans and thiophenols while preserving the amount of phenolic compounds in said hydrocarbon oil at substantially the same amount contained therein prior to washing with said alkaline solution, and directly recycling at least a portion of said alkaline extracting solution for further contact with said hydrocarbon oil.

2. The improved method of claim 1 wherein said hydrocarbon oil is a catalytically cracked naphtha, and said alkaline solution is regenerated by an oxidation reaction.

3. The improved method of claim 1 wherein said alkaline solution is contacted at total of 5 to 1000 volumes of oil per volume of solution prior to being subjected to regeneration.

4. An improved process for removing mercaptans from a hydrocarbon oil which also contains phenolic materials which comprises: contacting said hydrocarbon oil with an alkaline solution containing a suflicient quantity of phenolics so as to be in equilibrium with the concentration of phenolic materials in said hydrocarbon oil, said alkaline solution further containing less than 1.0 wt. percent free alkali, mercaptans thus being extracted by said alkaline solution while preserving the amount of phenolic materials in said oil at substantially the same amount contained therein prior to contacting with said alkaline solution recycling at least a portion of said alkaline solution for further contact with said hydrocarbon oil; passing alkaline solution containing said extracted mercaptans to an oxidation zone where 7 said mercaptans are converted to disulfides; separating said disulfides from the eilluent of said oxidation zone, and recycling the remaining efiluent comprising alkaline solution containing phenolics for further contact with hydrocarbon oil.

5. The process of claim 4 wherein said hydrocarbon oil is a naphtha fraction and said alkaline solution is a solution of sodium hydroxide.

6. The process of claim 4 wherein air is employed as the oxidizing agent in said oxidation zone.

7. A process for removing mercaptans and thiophenols from a cracked naphtha containing about 0.134 wt. percent phenolics, about 0.011 wt. percent thiophenols and about 0.007 wt. percent mercaptans which comprises contacting a volume of caustic solution containing about 31 vol. percent acid oils and about 2 wt. percent free caustic with about 10 volumes of said naphtha, segregating said caustic solution and said treated naphtha, repeating the contacting and segregating steps with said recovered caustic solution and additional amounts of said untreated naphtha until said caustic solution has contacted about 200 volumes of said naphtha and its free caustic content substantially reduced, and contacting said resulting caustic solution with additional amounts of said untreated naphtha whereby mercaptans and thiophenols are extracted from said untreated naphtha while the amount of phenolics in said naphtha remains substantially the same as contained therein prior to contact with said caustic solution.

8. The process as in claim 7 wherein said volume of caustic solution is regenerated after oontacting about 250 volumes of said naphtha.

References Cited in the file of this patent UNITED STATES PATENTS Yabrofi et a1 Mar. 7, 1939 Yabrolf et a1. May 28, 1940 Yabrofi et a1 Dec. 3, 1940 Caselli et a1. Oct. 7, 1941 Ten Have Sept. 18, 1956 Betts et a1 Nov. 6, 1956 McNeill et a1. Aug. 5, 1958 OTHER REFERENCES 5' Caustic-Methanol Treatment of Naphtha, Library Bulletin of Abstracts; Vol. 16, No. 47, Nov. 19, 1941, pp. 187-8. Universal Oil Products Company, Chicago, Ill.

Happel et al.: Critical Analysis of sweetening 10 Processes and Mercaptan Removal, Petroleum'Refiner, vol. 21, No. 11, November 1942; pp. 102 (406)-109 Urban et a1 Jan. 12, 1960

Claims (1)

1. IN THE PROCESS OF REMOVING MERCAPTANS AND THIOPHENOLS FROM A HYDROCARBON OIL ADDITIONALLY CONTAINING PHENOLIC COMPOUNDS, WHEREIN SAID HYDROCARBONS ARE WASHED WITH AN ALKALINE SOLUTION, THE IMPROVED METHOD OF CONSERVING ALKALI WHICH COMPRISES UTILIZING AN ALKALINE SOLUTION CONTAINING LESS THAN 1.0 WT. PERCENT FREE ALKALI, MAINTAINING A SUFFICIENT CONCENTRATION OF PHENOLICS IN SAID ALKALINE SOLUTION SO AS TO BE IN EQUILIBRIUM WITH THE PHENOLIC COMPOUNDS IN SAID HYDROCARBON OIL, SAID ALKALINE SOLUTION EXTRACTING SAID MERCAPTANS AND THIOPHENOLS WHILE PERSERVING THE AMOUNT OF PHENOLIC COMPOUNDS IN SAID HYDROCARBON OIL AT SUBSTANTIALLY THE SAME AMOUNT CONTAINED THEREIN PRIOR TO WASHING WITH SAID ALKALINE SOLUTION, AND DIRECTLY RECYCLING AT LEAST A PORTION OF SAID ALKALINE EXTRACTING SOLUTION FOR FURTHER CONTACT WITH SAID HYDROCARBON OIL.

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