US2447051A - Process for removing acidic sulfur compounds from hydrocarbon distillates - Google Patents

Description

Patented Aug. 17, 1948 UNITED STATES PATENT OFFICE PROCESS FOR REMOVING ACIDIC SULFUR COMPOUNDS FROM HYDROCARBON DIS- TILLATES Donald 0. Bond, Northbrook, and Nelson B.

Russell, Winnetka, 11]., assignors to The Pure Oil Company, Chicago, 111., a. corporation of This invention relates to a method for removing acidic sulfur compounds from water-immiscible fluids and is more particularly concerned with regeneration of alkaline reagents which have been employed to remove mercaptans from petroleum oils.

It is now common practice to extract mercaptans and other acidic sulfur compounds from hydrocarbon fluids, particularly gasoline and similar light oil distillates, by treatment of the distillate with aqueous alkali solution containing solubility promoters. One process for extracting mercaptans from petroleum distillates is the Mercapsol process in which an aqueous sodium hydroxide solution, containing alkali metal naphthenates together with cresols as solubility promoters, is used. The Mercapsol process and the reagent used therein are disclosed in Patent No. 2,297,621. Other solubility promoters which are in commercial use are the alkali metal salts of low boiling fatty acids, particularly isobutyric acid.

Aqueous alkali solutions of the type just described, after they have :been used to extract mercaptans from petroleum distillates, are ordinarily regenerated for re-use by steam stripping at temperatures of the order of ZOO-300 F. Steam stripping hydrolyzes the mercaptides, thereby releasing mercaptans which pass overhead with the steam. While this method of regeneration has proved satisfactory, the cost of the steam required for the stripping operation is relatively high.

It is an object of this invention to provide a process for removing acidic sulfur compound from hydrocarbon fluids.

It is another object of this invention to provide an improved method of regenerating alkali solutions which have been used for removing acidic sulfur compounds from hydrocarbon fluids.

It is still a further object of the invention to provide a method for regenerating used alkali solutions by means of oxygen or oxygen-containing gas.

Still another object of the invention is to provide a catalyst capable of accelerating regeneration of used alkali solutions by means of air blowing.

Other objects and advantages will be apparent from the following description of the invention.

It has now been found that regeneration of alkaline solutions which have been used for removing acidic sulfur compounds from water-immiscible fluids such as petroleum oils may be greatl accelerated by contacting the solutions with free oxygen-bearing gas, such as air, in the presence of a small amount of 3,4 dihydroxy diphenyl and/or 2,5 dihydroxy diphenyl or mixtures of the two.

In accordance with the invention the hydrocarbon fluids from which it is desired to extract merca-ptans or other acidic sulfur compounds are contacted with aqueous alkali solution such as aqueous sodium or potassium hydroxide containing from about 5 to 30% by weight of free alkali metal hydroxide, with or without solubility promoters, in a ratio of approximately 5 to 50% by volume of alkali solution per volum of liquid undergoing treatment. The used alkali solution is then contacted with air preferably countercurrently in a packed tower in the presence of 3,4 and/or 2,5 dihydroxy diphenyl in an amount of from approximately .05 to 3 percent by weight of the alkali solution. The used alkali is contacted with a sufficient amount of air and for a suflicient length of time to reduce the mercaptan content to a point suitable for re-use of the solution in further extraction of mercap'tans and/or other acidic sulfur compounds. The regeneration is preferably not carried to completion since the catalyst may be destroyed if all the mercaptan or other acidic sulfur vcompound is removed from the alkali solution undergoing regeneration thereby necessitating the replacement of the catalyst for the succeeding regeneration step. Ordinarily we do not reduce the mercaptan sulfur content of the used alkali during regeneration below 0.2 to 0.6% by weight.

The air regeneration may be conducted at ordinary atmospheric temperatures. Temperatures between and F. are satisfactory. Lower or higher temperatures may be used. However, lower temperatures require longer periods for regeneration whereas higher temperatures are not desirable because of the possibility of forming undesirable oxidation by-products.

In order to demonstrate the efficacy of 3,4 and 2,5 dihydroxy diphenyl, a number of individual compounds and substances were tested in the following manner: 1.86 cubic centimeters of normal butyl mercaptan were dissolved in 50 cubic centimeters of an aqueous sodium hydroxide solution containing 10% by weight of sodium hydroxide in order to give a solution containing 1% by weight of mercaptan sulfur. To the sodium hydroxide solution was added 0.55 gram of the desired catalyst in order to have present 1% by weight of catalyst in the solution. In some cases in order to hasten solution of the catalyst, the solution was agitated with nitrogen which had 3 first been passed through alkaline pyrogallol solution to remove any oxygen. In some cases the entire amount of catalyst did not dissolve in the alkali solution. The solution containing the sodium hydroxide, normal butyl. mercaptan and catalyst was placed in a 100 cc. graduated cylinder filled to the 75 cc. mark with No. 4 glass.

beads. Air was bubbled through the solution for 1 hour at the rate of 0.03'cu'bic foot per'hour' by means of a tube reaching to the bottom of the cylinder. After the solution had been blown for 1 hour with air at room temperature (ap-J proximately 75 F.) it was-extracted witheapproximately 100 cubic centimeters of V. M'. P. 1

naphtha to remove the disulfides that had formed.

The resulting naphtha containing. the disulfides was treated with acidic silver nitrate to remove. any unoxidized mercaptans and the solution was Among the'com:

then analyzed for disulfides. pounds tested were 3,4 dihydroxy diphenyl, 2,5 dihydroxy diphenyl, -4,4 dihydroxydiphenyl, o-hydroxy diphenyl and p-hydroxy diphenyl. The results of these tests are tabulated in the following table. 1

- Table uur oun .on-uy Cataly st Used in Test in Naphtha M emaptan Solution Oxidized 3,4 Diliydroxy Diphenyl 0.125 22. 6 2,5 Dihydroxy diphenyl I 0.125 22.6 None 0.005 0.9 4,4 Dlhydroxy diphenyl 0.005 0. 9 o-Hydroxy diphenyl 0. 004 0.7 p-Hydroxy diphenyl I 0.003 0.5

1 Catalyst did not entirely dissolve.

stored to a condition .suitablcfor reuse. The.

amount of 3,4 and/r. 2,5 dihydroxy diphenyladded to the alkali will depend on the particular catalyst andto some extent upon particular regeneration conditions employed, but is ordinarily from about 0.1 to 2% by weight. The alkali solution may be repeatedly regenerated although it may be necessari to add additional catalyst from 4 time to time to make up for any loss and maintain the desired eificiency.

It is to be understood that the rate of air blowing used in the specific examples herein disclosed is not .to be considered as the most desirable rate for commercial operation. Obviously where large scale equipment is used the rate of airblowing will considerably exceed that used in the'tests;;.The rate of air blowing may vary with- 10 iri'wide limits and will be adjusted in accordance with the size and type of equipment used in the regeneration step to obtain most rapid regeneration with minimum loss of solution by carry-over in the exhaust air.

It is claimed: 1. {Iheprocess of regenerating aqueous alkali solution 'used to extract acidic sulfur compounds from hydrocarbon fluids comprising contacting said solution with free-oxygen containing gas in the presence of a modicum of a hydroxy aromaticcompound selected from .the group consisting of 3,4 dihydroxy diphenyl and 2,5 d-i'hydroxy diphenyl. 4

2. Process in accordance with claim 1 in which the vhydroxy aromatic compound is present in an efi'ective amount between .01 and 2% by weight of the alkali solution.

3. .Process in accordance with claim 1 in which the hydroxy aromatic compound is 3,4 dihydroxy 3 diphenyl.

4. Process in accordance with claim 1 in which the hydroxy aromatic compound is 2,5 dihydroxy diphenyl.

5. The method of regenerating aqueous caustic alkali solution which has been used to extract mercaptan from petroleum distillates, comprising contacting .said solution, containing an amount between about 0.1 and 2% by weight suificient to function as an oxidation accelerator of a hydroxy aromatic compound selected from the group consisting of 3,4 dihydroxy diphenyl and 2,5 dihydroxy diphenyl, with air until a sufficient amount of the sulfur compounds have been converted to disulfides to make the alkali solu- 545 tion efiective for further use in extracting mer- DONALD C. BOND. NELSON B. RUSSELL.