US2546345A - Dethiolizing hydrocarbons - Google Patents

Description

Patented Mar. 27, 1951 [TED STATES PATENT OFFICE DETHIOLIZING HYDROCARBONS James: L. Meadows and -JohnN. Martin, Port Arthur,TTex., assignors to The Texas Company,

-New York, N. Y., a corporationof Delaware 'NoDrawing. Application-March 4,1950, Serial No. 147,766

6 Claims.

This invention relates to the treatment of -hydrocarb'ons for theremoval of sulfur compounds,

particularly mercaptans.

In recent years-it hasbeen found. necessary to refine increasing amounts ofuhigh sulfur crudes.

As a result ot-the increased mercaptan content :of the distillates it has become highly desirable to remove the mercaptans as: such from the distillates .rather thanbtonsimply convert them to less iodoriferous materials as is done in the case of conventional doctor'sweetening. The: present invention is. concerned with. certain. improvements lll'li effecting the..positive removal of .the

' .mercaptans fromtthe hydrocarbons.

By treating gasoline, :for'examplewith aqueous alkali metal. hydroxides; a .a portion..- of. .the mercaptans; more particularly the lower. molecular weight mercaptans; may be removed but it is not possiblerbyisuch:treatmentto effect. a complete removal ofithechigher mercaptans andproducea doctor-sweet product. .A .substantially amine in the glycol ether solution of alkali metal hydroxide this, impairment in color may be .inhibited and a substantially completeremoval of mercaptans efiected.

- The invention contemplates the. treatment of light hydrocarbon distillates such as gasoline and kerosene with an alkali'metal hydroxide'in an ether of a polyhydric alcohol and an alkanolamine. The major portion of the solvent consists of the glycol ether and a minor portion of the alkanolamine. Preferred glycolyethers are diethylene glycol monomethylethen, commonly known as methylCarbitol, and ethylene glycol monomethyl ether commonlyknown as methyl Cellosolve. Methyl Cellosolve is considered superior to methyl Carbitol with respect to color degradation and reduction of alkalinityin continuous operation but isnot as good-.asvmethyl Carbitol from the standpoint-of mercaptan extraction. The alkanolamine employed as. a-color inhibitor is preferably an alkanolamine which is substantially insoluble. in=naphtha such-as. ethanolamine and .propanolamine. Since the glycol ethers are-soluble tosome extent inxnaphthait-is advantageousstoremploy asv the color inhibitor an alkanolamine which is moreor less insoluble in hydrocarbons so as to-thus-reduce the solubility of the treating solution intthehydrocarfully removed but without substantial impair- .moval of mercaptans is eifected-with practically 'noincrease in color.

bons. :It is. preferable to employ .alkanolamines of low viscosities suchasmonoethanolamine or .monoisopropanolamine rather than diethanol- I amine or triethanolamine.

In the treatment of straight run distillates'or distillates which are substantially free from-phenols, the efiect of the alkanolamine in inhibiting color formationis-verymarked. Thuswfor' example, in a series of treats straight run naphthas having. colors rangingifrom 0.9 to 1.5 on the 18 inch Lovibond cell weretreated with solutions-of ,"potassium hydroxide inmethyl Carbitol-containing'no: alkanolamine. The treatment effected a substantially complete removal of-themercaptans butv the color of the. products ranged from .25 to v45 on the 18inch Lovi'bond cell. In aseries of comparative treats. the solvent containing the .-potassium hydroxide was composed of methyl Carbitol: and 5%monoethanolamine. In the latter treats mercaptans were. againsuccessmentin-color, the color ranging from 0.8:to' 2.0

on the 18 inch Lovibond cell. Thus, intreating straight run products or oils which contain practically no phenols a substantially complete. re-

In the case of cracked distillates or. -stocks Whl0h contain substantial proportions of phenols -it appears that the presence of phenols somewhat complicates the matter of-color impairment. .In a series of batch runs a cracked-gasoline containing phenols was-treated-withsolutions of potassium hydroxide in'meth'yl Carbitol.

After each batch treat the treating solution was regenerated and the operations Were conducted with a number of treating and regenerating cycles. The colorof the naphtha-charge was 15 onthe 18 inch Lovibond cell. When treating with the. hydroxide methyl Carbitol solution ing cycles.

-Inthe case of a-continuous-operation in which the cracked naphtha was continuously charged through the treating unit where it was contacted with solutions of potassium hydroxide in methyl Carbitol and ethanolamine, the used treating solution regenerated by oxidation and the reactivated solution recycled to the treating unit, it was found that smaller proportions of the ethanolamine, such as about 5-10%, were efiective in preventing serious increases in color. There appeared to be some tendency at the beginning of a run for a considerable increase in color after which there would be a substantial drop in color and the run would be continued for a considerable time with practically no color degradation. In all of these runs a substantially complete removal of mercaptans was effected with the production of doctor sweet products.

In order to obtain complete removal of the mercaptans the alkali metal hydroxide such as sodium or potassium hydroxide should be used in strong solution in the glycol ether and alkanolamine, such as normalities of about 2-3 and higher. A normality as low as 0.5, for example, is definitely inferior as regards mercaptan. extraction.

Quantities of dethiolizer solution amounting to some 5 to percent by volume of the hydrocarbon treated are recommended although less amounts can be used. For example, when treating with only 1.25 per cent by volume, complete removal of the mercaptans was not obtained but the product became sweet after standing one day.

The dethiolizer solution may be used in either anhydrous or aqueous condition. However, the presence of water has a beneficial efiect in the glycol ether dethiolizer solution in maintaining extraction efiiciency for increased periods of time. The solution can tolerate about 35% by volume of water without appreciable reduction in extraction efiiciency. In continuous operations with regeneration and recycling of the reactivated dethiolizer and using a dethiolizer solution containing such a quantity of water the period in which the extraction efiiciency is maintained is greatly extended. For example, in one run in which no water was added the production of a completely sweet product ceased at the end of about 100 hours while in a run with water in the fresh dethiolizer solution a sweet product was still being produced at the end of 339 hours when the run was terminated. In another run with fresh dethiolizer solution containing 20% water a doctor sweet product was made through an accumulated time of 760 hours. At the end of 950 hours the mercaptan extraction was reduced to 94.5 per cent but even this naphtha became sweet after standing for one day. In these runs, starting with fresh dethiolizer solution containing 20% water, the recycled solution became diluted with water produced in the regeneration until the water content of the solution actually being used approximated 35%.

In treating cracked stocks or stocks containing material quantities of phenols it is recommended that the stock be pretreated for the removal of phenols prior to the dethiolizing operation. The phenols as well as the lower molecular weight mercaptans can be readily removed by simple caustic treatment. When the dethiolizer solution is applied to the treatment of hydrocarbons containing phenols, alkali in the solution is consumed in reacting with the phenols and furthermore the function of the alkanolamine in inhibitin color is not as satisfactory as when no phenols are present. Thus by the caustic pretreat to remove the phenols the dethiolizer solution is conserved for the more difiicult work of completely removing the mercaptans including the more difiicultly removable higher mercaptans while at the same time the alkanolamine is more effective in inhibiting color degradation.

In practicing the invention in continuous operation the naphtha or kerosene or other stock to be dethiolized is charged to the mercaptan extraction zone, which may include a countercurrent contacting tower or one or more stages comprising mixing and settling units, where the hydrocarbon is contacted with the alkali metal hydroxide solution in the glycol ether and alkanolamine and the used solution is withdrawn and regenerated as by oxidation. The hydrocarbon is washed with water to remove the solvent and any contained alkali, the solvent is recovered by distillation and the regenerated alkali and recovered solvent are recycled to the extraction zone. Makeup hydroxide and solvent are added as needed. The product is doctor sweet and of reduced total sulfur content so that it requires no further treatment for the removal of sulfur compounds.

The advantages of the invention may well be illustrated by comparing it with the well known tannin solutizer process which has gone into extensive use. In the latter process the alkyl phenols contained in cracked naphtha are utilized as a solutizer for increasing the solubility of the mercaptans in the alkali metal hydroxide and tannin is added to improve the regeneration of the treating solution by oxidation. The process does not produce a sweet product even when three counter-current extraction stages are used and it is necessary to subject the product to a subsequent sweetening operation. In making this particular comparison runs of a months duration were compared. In the operation in accordance with the invention the cracked naphtha was treated with 4.5 normal potassium hydroxide in a solution consisting of by volume methyl Carbitol and 5% by volume monoethanolamine, with regeneration of the dethiolizer solution by oxidation, recovery of solvent and recycling the regenerated hydroxide and recovered solvent. During practically the whole period of the mercaptans was removed from the naphtha. The product was a sweet finished naphtha. In the tannin solutizer process throughout the period only about 70% of the mercaptans was removed and it was necessary to subject the product to a subsequent sweetening operation.

Although the treatment with the alkali metal hydroxide in the glycol ether and alkanolarnine is particularly advantageous for the treatment of gasoline stocks, the process is also adapted for the removal of the higher molecular weight mercaptans contained in kerosene and middle distillate stocks. Thus, for example, a kerosene stock was treated with 10% by volume of 4N potassium hydroxide in 95% methyl Carbitol and 5% ethanolamine to yield a product negative to the doctor test, while the same stock treated with 10% by volume of the solutizer solution containing the alkyl phenols produced a product which gave a positive doctor test.

.Although a preferred embodiment of the invention has been described herein, it will be understood that various changes and modifications may be made therein, while securing to a greater or less extent some or all of the benefits of the invention, without departing from the spirit and scope thereof.

We claim:

1. The process of dethiolizing hydrocarbons that comprises contacting the hydrocarbons with alkali metal hydroxide in a solvent of which the major portion consists of a glycol ether and of which a minor portion consists of an alkanolamine.

2. The process of dethiolizing hydrocarbons that comprises contacting the hydrocarbons with alkali metal hydroxide in a solvent of which the major portion consists of a glycol ether and of which a minor portion consists of ethanolamine.

3. The process of dethiolizing hydrocarbons that comprises contacting the hydrocarbons with alkali metal hydroxide in a solvent of which the major portion consists of methyl Carbitol and of which a minor portion consists of an alkanolamine substantially insoluble in hydrocarbons.

4. The process of dethiolizing hydrocarbons that comprises contacting the hydrocarbons with a dethiolizing solution of aqueous alkali metal hydroxide in a glycol ether and an alkanolamine in which solution the water content does not exceed about 35% by volume.

5. The process of dethiolizing hydrocarbons that comprises contacting the hydrocarbons with 'alkali metal hydroxide in a solvent of which the major portion consists of methyl Ca rbitol and of which a minor portion consists of ethanolamine.

JAMES L. MEADOWS. JOHN N. MARTIN.

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

UNITED STATES PATENTS Number Name Date 2,168,078 Yabroil Aug. 1, 1939 2,212,105 Yabroff Aug. 20, 1940 2,341,878 Nixon et a1. Feb. 15, 1944 2,364,582 Davis et al Dec. 5, 1944 2,425,777 Adams et al Aug. 19, 1947 2,472,473

Fetterly June 7, 1949

Claims (1)

1. THE PROCESS OF DETHIOLIZING HYDROCARBONS THAT COMPRISES CONTACTING THE HYDROCARBONS WITH ALKALI METAL HYDROXIDE IN A SOLVENT OF WHICH THE MAJOR PORTION CONSISTS OF A GLYCOL ETHER AND OF WHICH A MINOR PORTION CONSISTS OF AN ALKANOLAMINE.