US2364582A - Process for removing acids from hydrocarbons - Google Patents

Description

Patented Dec. 5, 1944 PROCESS FOR REMOVING ACIDS FROM HYDROCARBONS Orris L. Davis and Alan C. Nixon,'0akland, Calif,, assignors to ShelLDevelopmentCompany, San .Francisco, Calif., a. corporation of Delaware No Drawing. Application July'l7,i19"42, Serial-No. 451,376

16 Claims.

This invention deals with an improvement in processes for extracting weak'acids from hydrocarbons. Moreparticularly, it is concerned with a method for improving the rate of separationof alkaline extracting solutions from gasolines or for fac'ilitating steam stripping the resulting spent alkalinesolution, ifthe-latt'eris desired, or both.

It is known that gasolines frequently contain weak-acids such as those having dissociation constants below about e. g. HzS, mercaptans, alkyl phenols, etc.,'which acidsmustgbe removed for various reasons. A number of processes have been developed for extracting these acids. All of these (processes have in common the step of treatingthe hydrocarbon oil containing theacid with an alkaline solution, and thereafter separating the hydrocarbon oil'from'the resulting alkaline solution containing salts of the absorbed acid. For reasonsof economy, the resulting spent alkaline solution is usually regenerated, steam stripping in "general being'the preferred method of regeneration. The regenerated solution is then used for the extraction of further quantities of :acids from hydrocarbons containing them.

*Examples of particular processes for the extraction of weak acids normally associatedwith petroleum oils are: processes involving the extraction 'of H28 from gaseous 'or liquid hydrocarbonsbyuse of aqueous .solutions of tripotassium phosphate, sodium phenolate, sodium borate, sodium or potassium carbonate, organic bases such as ethanolamine, diamino ,propanol, piperidine, etc. processes involving the extraction of a1- kyl phenols from hydrocarbon distillates with solutions of alkali metal hydroxides, preferably having concentrations of about 25-50%; and processes involving the extraction of mercaptans with so-called solutizer solutions by the solutizer process, etc.

In 'the solutizer process, a sour gasoline distillate containing mercaptans is extracted with an aqueous caustic alkali solution containing one or several solutizers or solubility promoters for mercaptans. Suitable solutizers are, for example, alcohols such as methanol, ethanol, propanol, etc. aliphatic alkanolamines and amino alkyl amines in which "the alkyl radicals contain 2 or 3 carbon atoms; diamino alcohols, glycols and amino glycols of 3 to 5 carbon atoms; alkyl glycerinesin which the total number of "carbon atoms in the alkyl radicals is from :1 to 4; monomethyl glyceryl ether; diamino, dihydroxy or 'aminohydroxy alkyl ethers or thioethers in which the alkyl radicals have from "2 to 3 carbon atoms;

alkali metal salts of fatty acids having from '3 to5 carbonatoms;-or, inthe case of potassium salts, having from l 1106 carbon atoms; amino or hydroxy fatty acids having-from2 to 7 carbon atoms, *phenyl acetic acid, hydroxy or amino phenyl aoetic'acid, alkyl phenols,etc.

It is known that among the many solutizers whichare'employed topromote solubility of mercaptans in'strong'ly alkaline aqueous solutions, the alkali metal 'alkyl phenolates aid in the production of sweet gasolines, of reasonable oxidation stabilities. This phenomenon, which has been described in the Yabrofi-White Patent 2,-223379835 due to the'fact that while mercaptans are extracted fromthe sourgasoline substantially completely, natural gum inhibitors, i. 'e. alkyl phenols normally contained in the gasolines, are only partially extracted, an alkyl phenol equilibrium being established between the gasoline and the extracting solution. Therefore, it is very often-advantageousto employ for the extraction a solutizer solution to which a certain amount of alkyl "phenolates is added. Many gasolines, and more particularly almost all cracked gasolines, contain "alkyl phenols, at least a portion of which will accumulate in the solutizer solution. Inasmuch as the solutizer solution is continuously circulated'from an extracting stage to asteam regeneration stage and back to the extraction stagegeven traces of alkylphenols contained inthe gasoline will eventually build up in thesolutizer solution until the concentration of thealkyl \phenolate in the solutizer solution is inequilibrium with the'concentration of the alkylphenolsin theincoming gasoline. It has been found that in spite of thorough caustic alkali pretreatment, the incoming gasoline may contain enough alkyl phenols to establish over 'an extended period of operation an equilibrium 'concentration-ofanywhere between about 3 and 20% alkyl phenolates in the solutizer solution, even though the original treating solution may have been free from phenolates.

Aqueous solutions containing substantial amounts of alkyl phenolates are not advantageous becausethey have a tendency to form emulsions which separate slowly. It hasbeen found in the past that in order to avoid emulsion troubles the concentration of the alkyl phenolates must be'kept below certainlimits, otherwise more or less permanent emulsions may form (U. S. Patent 2,202,039)

It has further been found that alkaline solutions which are used for extracting weak acids from hydrocarbon oils of the gasoline range as described above and which are thereafter regenerated by steam stripping, may gradually accumulate substances which act as emulsifiers and foam inducers. In general, processes dealing with the removal of H25 are troubled primarily with foaming, whereas the processes dealing with the extraction of mercaptans, phenols, etc., frequently are subject not only to foaming, but also to the formation of stubborn emulsions which reduce the rate of separation.

As a result, maximum throughput through an extraction unit of a given size may be greatly reduced, or else the use of large settlers or of centrifuges may be required. Likewise, the capacity of steam strippers may be greatly curtailed.

The nature of the substances responsible for foaming and emulsion difficulties is not definitely salts preferred are those which are free from carboxyl radicals, contain at least carbon atoms per molecule, and have a molecular weight below about 1000. Such salts have been found particularly effective in the breaking of emulsions which may form between gasolines and the treatprealkali in a normality of at least about 2 and, in

addition, containing substantial amounts (e. g. normally %"or more) of the solutizer or solutizers suchias alkali metal phenolates and other 1 solutizers described above.

established. It may be that a substance is inb volved which is related to the gums that form in .gasolines due to oxidation or it maybe due to resinous. materials formed as by interaction of some of the components of the gasolines (possibly impurities) with the alkaline treating solution or acomponent thereof. For example, it is quite possible that in .the case of solutizer treatment with solutions containing phenolates, a phenol type resin is formed, for instance by interaction with mercaptans, aldehydes or other impurities. Such a possibility is supported by the fact that solutizer solutions containing phenolates have in the past given the greatest difficulties.

Accordingly it is a purpose of this invention to provide means for improving the rate of separation of aqueous alkaline treating solutions from gasolines which are being treated. Another purpose is to reduce the foaming which occurs during regeneration of the treating, solutions by steam stripping. invention is to provide means for preventing the formation of emulsions caused by the presence of accumulated emulsifiers in solutizer solutions, particularly in those containing alkyl phenolates; and it is yet another purpose to break emulsions formed by gasolines in solutizer solutions.

This invention comprises maintaining in an aqueous alkaline treating solution small amounts of two substances:' (1) a water-soluble surface active alkali metal salt of an organic sulfonic or sulfate ester acid; and (2) a mineral oil, which combination is added to reduce emulsification and foaming between gasolines and the solution. The term surface active as herein used refers to the ability of the salt to reduce materially the surface tension of pure water when added thereto in small amounts, that is, in amounts of a few tenths of one percent. The term water-soluble is not limited to substances which form true solutions but includes substances which spontaneously form colloidal solutions or dispersions as well. I

In order thatv these two substances which are added to the aqueous alkaline treating solution may be more or less permanently useful in a regenerative process wherein said solution is continuously regenerated andfrecirculated for further extracting gasolines' containing weak acids, it is desirable that these substances have a number of definite properties. The required properties of the surface active salts (1) will be discussed first. I

The types of organic sulfonic and sulfate ester. acids which produce these surface active salts,

as wellas their methods of manufacture, aregen- Still another purpose of this.

Further, the active salts should not be extracted from the solutizer solution when the latter is in contact with the gasolines. The presence of alkali metalsalts of sulfonic or sulfate acids in gasolineadversely affects many of its properties, e. g. its stability, A. S. T. M. gum, copper dish gum, color, etc. Therefore it is desirable that the salts be substantially insoluble in hydrocarbon oils, after being wetted by water, although they may be and often are soluble or colloidally dispersable in hydrocarbons when wetted by the latter.

. Furthermore, the salts should be reasonably air through the packing glands, and this air is then dissolved in the on being pumped.v

.In'scme few instances, it may become desirable to remove the surface active salt from the extracting solution, in which case it should have a property which makes possible such separation. In"most instances the removal can be accomplished relatively easily by adding small amounts of lime water or other hydroxide or water-soluble saltof a pclyvalent metal to the extracting solution, polyvalent metal salts and particularly the calcium salts of most organic sulfonates and sulfates of this invention being insoluble in the solutizer'or similar extracting solutions and being precipitated as a curd which can be settled or filtered out.

Of the two classes of surface active compounds suitable for the purpose of this invention, i. e. the alkali metal salts of sulfonic acids and sulfate ester acids, the former are preferred as being in general more resistant to hydrolysis. Resistance to hydrolysis in the presence of free caustic alkali and under the conditions .of' steam regeneration is an important property when it is desired that the efiect of the surface active salts be more or less permanent.

Suitable sulfonates and sulfates may, if desired, contain non-functional radicals such as halogen, hydroxyl, ether, amino, imino, hydrosulfide, sulfide, carboxyl ester, etc., radicals.

Specific sulfonates which we have found to be manufacture of medicinal oils by acid treatment;

the products of. treating: kerosene or lube oil, ex-- tracts with concentrated sulfuric acid; various aliphatic or alicyclic sulfonic acids such as fatty sulfonic acids, fatty aromatic sulfonic acids, naphthene sulfonic acids; sulfonic acids of various aromaticthydrocarbons, such as various alkylated benzenes, diphenyls, xylenes, diphenyl methanes, naphthalenes, anthracenes, phenanthrenes, tetralines, alkyl phenols such as those contained in cracked petroleum distillates, alkylated chlornaphthalenes, naphthylamines, diphenyl oxides, chlorinated diphenyl oxides, sul-, fides or amines; alkylated pyridines, quinolines, isoquinolines, pyrrols, pyrrolidines, piperidine, thiophenes, thiophanes, etc. or various sulfonic acids of carboxylic acid esters or amides, such as the ester sulfo-carboxylic acids or sulfonato amides having the general formulae:

RSO2,M

ORSO3M o=o-R' respectively, wherein the R radicals are organic radicals, such as aliphatic or cyclic hydrocarbon radicals, M is an alkali metal and n. is an in- 1 tegar normally not greater than 2.

.'While the carboxylic acid esters and amides listed above are very effective herein, many of them have the disadvantage of being susceptible to hydrolysis during steam regeneration of the solutizer solution forming free carboxylic acids upon decomposition, .the salts of which are likely to cause foaming. a

The alkali metal salts of sulfonic acids possessing at least one alkyl radical are in general far more effective than the salts of corresponding sulfonic acids not possessing them. For example, the alkali metal salts of naphthalene or anthracene sulfonic acids are only mildly beneficial, whereas the corresponding salts of, for example, monoor dibutyl naphthalene sulfonic acids or of retene sulfonic acid are highly effective.

The sulfonates may be prepared in various ways. Aromatic sulfonates are most readily obtained by simply treating aromatic compounds with concentrated or fuming'sulfuric acid. Aliphatic sulfonates may be obtained under some conditions by treating olefines or diolefines with concentrated sulfuric acid, or by treating organic acid sulfates with sodium sulfite so as to eliminate sodium sulfate, or by oxidation of mercaptans with nitric acid, etc. Satisfactory sulfonates may also be obtained by treating a lubricating oil with concentrated or fuming sulfuric acid.

Sulfate ester acids of which the alkali salts are suitable herein are, for example: the fatty sulfates, such as mono lauryl, cetyl,'steary1, etc., sulfateacids; mono esters of sulfuric acid obtained by treating with concentrated to moderately concentrated sulfuric acid various olefines or alcohols such as the long chain olefines obtained in the vapor phase cracking of wax at about 1020-1040 F., polymers obtained in the polymerization of normally gaseous olefines with inorganic polyoxy acids or Friedel-Crafts catalysts, fatty, or naphthenic alcohols obtained in the catalytic reduction of fatty or naphthenic acids, alcohols obtained by condensation of ketones or aseaasa aldehydes followed by, ahydrogenatiom oralkyl 75 ters of degree.

aromatic mono esters of sulfuric acid, etc. A convenient source for many of the active sulfate ester acids is the sludges obtained in the acid treatment of cracked distillates, or the spent acids obtained in the polymerization of olefines,

or in the alkylation of isoparaffins with olefines with sulfuric acid.

The amounts of surface active salts which must. be added to increase the rate of separation of the I emulsion are generally quite small and vary from tion greatly enhances the solvent power for the salts. Preferably the amount added should not exceed its solubility limit in aqueous solution. However, within reasonable limits, the amount of salt necessary is directly proportional to the amount of emulsifiers present in the solution.

It is desirable that the beneficial effect of the salt shall not be restricted to and be dependent on a specific range of concentration substantially narrower than the limits indicated abovethat is to say, there should not be a sudden reversal of the beneficial effect, i. e. an increase in the emulsification tendencies of the extracting solution upon addition of a slight excess of the salt over the optimum quantity. On the contrary,

the beneficial elfects should extend over substantially the entire range of concentration indicated, and changes in the eifects due to deviations from the optimum concentration should be only mat- Many surface active salts, particularly, the ordinary soaps such as sodium stearate, sodium oleate, etc., while efiecting deemulsification in certain specific amounts, when present in slightly larger amounts increase rather than decrease the emulsion tendencies of the extracting solution. For example, sodium stearate in a concentration of .06% effectively broke a semi-stable solutizer emulsion, while in a .08% concentration a stable emulsion remained.

It is, however, understood that the beneficial effects of the surface active salts of this invention do not extend to all concentrations thereof. When present in excessive amounts, e, g. in amounts substantially above about 1%, even the best of the active compounds may act as emu1- sifiers, rather than as settling accelerators or emulsion breakers or both. For this reason it is important that the concentration of the demulsifyingagents in the aqueous alkaline solution be limited to within the approximate useful limits indicated.

For the same reason it is essential that the.

' kali.

The properties of the second of these additive substancesthe mineral oils (2)-will now be discussed in detail.

It has been found that in the absence of surface active salts of sulfonic and sulfate ester acids, heavy aromatic oils, e. g. those having high boiling ranges, are the best defoaming agents. However, they are not satisfactory in systems involving the treatment of hydrocarbon oils of the gasoline range, because if even very small In general, the

amounts of such oils are extracted by the gasoline they will detrimentally increase the gum content of the gasoline. This detrimental effect is also characteristic of other heavy oils, including heavy parafiinic oils, although only the arcmatic oils have any appreciable defoaming'properties. by themselves. The lighter the oil added the more easily it is lost by extraction and/or stripped out during steam regeneration. Relatively light aromatic oils in the gas oil range which do not give detrimental gum in gasoline due to the small amounts extracted by the gasoline are not so effective as defoaming agents as are the heavier aromatic oils. Although such light aromatic oils alone are better defoamers than the'light parafiinic oils the former have the disadvantage of frequently causing fluorescence.

Paraffinic oils by themselves are ineffective as defoamersand often act as pro-foamers; however, in combination with the surface active salts of the type previously described they have the unexpected property of very greatly improving the defoaming properties of these salts. This property is also true for light aromatic oils but not to such a noticeable extent. matic oils should not be used if fluorescence in the treated gasoline is undesirable.

Therefore, it is important to obtain an oil which is light enough not to cause undesirable gum content in the gasoline, but yet heavy enough not to be too easily lost in the stripper. Suitable light oils should be free from asphalts, resin, and gum-forming impurities, and must possess boiling ranges between about 400 and about 900 R, preferably between about 500 and about 750 F. Their viscosities may range between about 30 and 200 Saybolt Universal seconds at 100 R, preferred viscosities being between about 40' and '70 seconds at 100 F. Because of general undesirability of fluorescence it is preferred to employ paraffin oils having aniline points above about 122 F., and a specific dispersion below about 150 as determined by a method disclosed in an. article by Von Fuchs and Andersen in Industrial and Engineering Chemistry, vol. 29, No. 3, March 1937, .pp. 319-325.

There are still other properties which these oils must possess: they must be readily dispersible ineffective amounts in the aqueous treating or extracting solution, so that the maximum effect may be obtained, and they should be reasonably stable toward the action of small amounts of oxygen, in the presence of strong caustic at the elevated temperatures employed in the regeneration step.

Some specific types. of oils whichmay be used and which have the above required properties are: gas oil, light'lubricating oil, spray oil, and other extracted oils which have been extracted "by such selective solvents as liquid S02, nitrobenzene, nitro-toluene, furfural, acetone, aniline, lpheno-l, cresylic acids, dichlordiethyl ether, SO2- benzene mixtures, other selective solvents, or combinations of solvents above, and anti-solvents such as ethane, propane, butane, petroleum ether, etc., as well as some lower boiling extracts.

The amounts of these oils which must be added to reduce the foaming and improve the rate of separation of the treating solution and the hydrocarbon oil vary from about .001% to about 2% by weight, generally about .1 of the treating solution. Within reasonable limits, the amount of oil necessary is directly proportional tothe amount of foaming agents present in the However, aroit may be necessary from time to time in a con-- tinuous process, 1. e. every10- or 15 cycles of the treating solution, to add small amounts of oil to maintain the concentration in the treating solution within the desired limits to effect efiicient defoaming, because small quantities of the oil are lost due to extraction by the gasoline treated. If desired, this addition may be continuous As indicated before, the surface active sulfates or sulfonates used in the treatment must be wetted by the aqueous solution, rather than by the hydrocarbons. It has been found that if the agent is first dissolved or dispersed in the gasoline, only a portion will be retained by the aqueous solution upon contact under ordinary extraction conditions, the remainder staying in the gasoline phase. On the otherhand, if the agent is first dissolved or thoroughly dispersed in the aqueous solution, it'is not usually extracted by the gasolines to any extent under normal extracting conditions.

generative process such as the solutizer process, 1 it is convenient to addthe active salt and mineral oil, or preferably its slurry in,- water, to the spent extracting solution emanating from the extractor. This solution is then heated and thoroughly agitated in thev steam stripper in the course of the regeneration step, whereby the desired dispersion or dissolution is achieved.

While in the foregoing the invention has been described as applying particularly to regenerative processes such as the sweetening of sour gasolines by the solutizer process, it is also applicable to the extraction of alkyl phenols, etc., from hydrocarbon oils by processes not calling for regeneration such as those described in U. S. Patents 2,134,390 and 2,213,596. In these processes, alkyl phenols are extracted from clistillates containing them with strong caustic soda (25-50% concentration) to result in an extract of high alkyl phenolate content. This extract separates slowly from the distillate, frequently more than a day being required to obtain complete separation. The addition of requisit amounts of a surface active salt of this invention materially reduces the settling time, often causing a complete sepa-- ration in a few minutes. In the table below, effects of a number of representative surface active salts and mineral oils covered by this invention are shown. To evaluate their performance samples of a solutizer solution having the-following composition were subjected to an emulsion and a foaming a molecularweig ht below about 1000, and said test inwhic'h' theyjwere" mixed with a cracked gasoline under conditions similar to those which would be encountered in thesolutizer process. The emulsion test was carried" out by stirring a ml. sample of solutizer solution with 25 ml. of a cracked gasoline for 5 minutes'in a 6" x 1" test tube at a stirrer speed of approximately 2900 R. P. M., and then measuring the time necessary for the solutizer solution to separate 'from the gasoline. The foaming test was carried out by heating a ml; sample of solutizer solution diluted with 5 ml. of water ina 32 x 600 mm. test tube with two carborundum boiling chips (6 mesh) at such arate that boiling starts in 3 minutes :5 seconds. The maximum height reached by the solution and foam after boiling starts in the foam rating. i The results of these tests were as follows: v i I 7 Tube foam rating 5 Sample 1 Surface active alkali setthn metal salt Without With time oil oil 1 None 8. 5 7. 2 Alkylnaphthene sullonate- 8.25 6.625 3 Long-chain alcohol sulfate. 8 6 4 Alkyl aryl sulfonate 8.125 3.875 5 Sulfonated alkyl hvdrou. 7. 25 5.375 6. 625 6. l 7 do 6. 25 4 3 8 Sodium petroleum sulfon' ate -4 5175 3.75 i 3 The total amount of additive surface active salt and/or oil for each test was .1 g./ 100 ml. of solutizer solution. Samples run with both salt and oil additives contained .05 g. /l'00 ml. of each ad'- diti-ve. The oil used in the sample was an East Texas gas oil having a boiling range between 491.9 and 710.6 R, an aniline point of l6'7.9 F., and a specific dispersion of 123. The composition of the oil was 12.3% aromatic carbon (one and two ring), 29.6% naphthene carbon; and 58.1% alkyl carbon.

We claim as our invention:

1. In the process of extracting weak acids nor mally associated. with hydrocarbons from gaso lines containing them and being substantially free from acid-sulfuric acid derivatives with an aqueous alkaline solution, the improvement comprising extracting said hydrocarbons with said aqueous solution containing thoroughly disperseda small amount of a mixture of two agents: (1) a water-soluble surface active alkali metal salt of an acid selected from the group consisting of organic sulfonic acids andsulfate ester acids,

whichacids are free from carboxyl radicals and (2) a mineral oil having a boiling range between about 400 and about 900 F.

2. In the regenerative process of extracting weak acids normally associated with hydrocarbons from gasolines' containing them and being substantially free from acid-sulfuric acid derivatives, with an aqueous alkaline solution to produce a treated hydrocarbon distillate and a spent aqueous solution, wherein said spent solution is regenerated by steam stripping, the improvement comprising extracting said hydrocarbons with said aqueous solution containing dissolved not in excess of about 1% by weight of a water-soluble surface active alkali metal salt of an acid selected from the group consisting of organic sulfonic acids and sulfate ester acids, which acids are free from carboxyl radicals and radicals susceptible to hydrolysis upon steaming in the presence of caustic alkali, having at least 10 carbon atoms and aqueous solution containing dispersed a mineral oil in a concentration not in excess of about 2% by weight thereof, said mineral oil having a boiling range between about 400 and about 900 F.

3. The process of claim 2 wherein said mineral oil is continuously added to said spent solution substantially to maintain said concentration. 4. In the process of sweetening sour gasoline distillates containing mercaptans by extracting them with an aqueous alkaline solution containing a solubility promoter for mercaptans, the improvement comprising treating gasoline with said aqueous solution containing an addition thoroughly dispersed a smallamount of a mixture of two agents: (1) a water-soluble surface active alkali metalsalt of an acid selected from the "group consisting of organic sulfonic acids and sulfate ester acids, which acids are fre from carboxyl radicals, and (2') amineral oil having a boiling range between about 400 and about 900 F.

5. In the process of extracting weak acids normally associated with hydrocarbons from gasolines containin them, and being substantially free from acid-sulfuric acid derivatives, with an aqueous alkaline solution, the improvement comprising extracting said hydrocarbons with said aqueous solution containing thoroughly dispersed a small amount of a mixture of two agents: (1) a water-soluble surface active alkali metal salt of an alkyl naphthene sulfonic acid, and (2) a mineral oil having a specific dispersion of below and a boiling range between about 400 and about 900 F.

6. In the process ofextracting weak acids normally associated with hydrocarbons from gasolines containing them and being substantially free from acid-sulfuric acid derivatives, with an aque ou alkaline solution, the improvement c0mprising extracting said hydrocarbons with said aqueous solution containing thoroughly dispersed a small amount of a mixture of two agents: (1) a water-soluble surface active alkali metal salt of an alkylated hydrocarbon sulfonic acid, and v(2) a mineral oil having a boiling range between about 400 and about 900 F.

7. In the process of extracting weak acids normally associated with hydrocarbons from gasolines containing them and being substantially free from acid-sulfuric acid derivatives, with an aqueous alkaline solution, the improvement comprising extracting said hydrocarbons with said aqueous solution containing thoroughly dispersed a small amount of a mixture of two agents: (1) a water-soluble surface active alkali metal salt of an alkylated aromatic sulfonic acid and (2) a mineral oil having a boiling range be tween about 400 and about 900 F. r

8. In the process of extracting weak acids normally associated with hydrocarbons from gasolines containing them and being substantially free from acid-sulfuric acid derivatives, with an aqueous alkaline solution, the improvement comprising extracting said hydrocarbons with said aqueous solution containing thoroughly dispersed a small amount of a mixture of two agents: (1) a water-soluble surface active alkali metal salt of a petroleum sulfonic acid, and (2) a mineral oil having a boiling range between about 400 and about 900 F.

9. In the process of extracting weak acids normally associated with hydrocarbons from gaso lines containing them and being substantially free from acid-sulfuric acid derivatives, with an aqueous alkaline solution, the improvement comprising extracting said hydrocarbons with said aqueous solution containing dissolved from .001% to 1% by weight of a water-soluble surface active alkali metal salt of an acid selected from the group consisting of organic sulfonic acids and sulfate ester acids, which acids are free from carboxyl radicals and radicals susceptible to hydrolysis upon steamin in the presence of caustic alkali having at least carbon atoms and a molecular weight below about 1000, and said aqueous solution containing dispersed from .001 to 2% by weight of a mineral oil having a specific dispersion of below 150, a boiling range between about 400 and about 900 F., and an aniline point above about 122 F.

10. In the regenerative process of sweetening a sour gasoline distillate containing mercaptans by extracting it with an aqueous alkaline solution containing alsolubility promoter for meroaptans to produce a treated hydrocarbon distillate and a spent aqueous solution containing absorbed mercaptains wherein said spent solution is regenerated by steam stripping, the improvement comprising dissolving in said aqueous solution a small amount of a water-soluble surface active alkali metal salt of an acid selected from the group consisting of organic sulfonic acids and sulfate ester acids, which acids are free from carboxyl radicals and radicals susceptible to hydrolysis upon steaming in the presence of caustic alkali having at least 10 carbon atoms and a molecular weight below about 1,000, and dispersing in said aqueous solution a small amount of a parafiinic mineral oil having a boiling range between about 500 and about 750 F. and not more than aromatic carbon,

11. A treating solution consisting of an aqueous solution of an alkali metal hydroxidehaving a normality of at least 2 and containing dissolved a substantial amount of solubility promoter for mercaptans, a small amount not in excess of about 1% by weight of a water-soluble surface active alkali metal salt of an acid selected from the group consisting of organic sulfonic acids and sulfate ester acids, which acids are free from carboxyl radicals, and said solution also containing thoroughly dispersed therein not in excess of about 2% by weight of a mineral oil having a boiling range between about 400 and about 900 F.

12. A treating solutionconsisting essentially oi an aqueous solution of an alkali metal hydroxide having a normality of at least-2 and containing dissolved a solubility, promoter for mercaptans, a small amount not in excess of about 1% by weight of a water-soluble surface active alkali metal salt of an acid selected from the group consisting of organic sulfonic acids and sulfate ester acids, which acids are free from carboxyl radiabout 900 F.

cals and radicals susceptible to hydrolysis upon steaming in the presence of caustic alkali having at least 10 carbon atoms and a molecular weight below about 1000, and said solution also containing thoroughly dispersed therein from .001% to 2% by weight of a mineral oil having a boiling range between about 400 and about 900 F. and an aniline point above about 122 F.

13 A treating solution consisting essentially of an aqueous solution of an alkali metal hydroxide having a normality .of at least 2 and containing dissolved a substantial amount of a solubility promoter for mercaptans, and a small amount not in excess of about 1% by weight of a water-soluble surface active alkali metal salt of an alkyl naphthene sulfonic acid and said solution also containing thoroughly dispersed therein from .001% to 2% by weight of a parafiinc mineral oil having a boiling range between about 500 and about 750 R, an aniline point above about 122 F., and not.more than 20% aromatic carbon.

14. A treating solution consisting essentially of an aqueous solution of an alkali metal hydroxide having a normality of at least 2 and containing dissolved a substantial amount of a solubility promoter for mercaptans, and a small amount not in excess of about 1% by Weight of a water-soluble surface active alkali metal salt of an alklated hydrocarbon sulfonic acid, and said solution also containing thoroughly dispersed therein not in excess of about 2% by weight of a mineral oil having a boiling range between about 400 and about 900 F.

15. A treating solution consisting essentially of an aqueous solution of an alkali metal hydroxide having a normality of at least 2 and containing dissolved a substantial amount of a solubility promoter for mercaptans, and a small amount not in excess of about 1% by weight of a water-soluble surface active alkali metal salt of an alkylated aromatic sulfonic acid, and said solution' also containing thoroughly dispersed thercin not in excess of about 2% by Weight of a mineral oil having a boiling range between about 400 and about 900 F.

I 16. A treating solution consisting essentially of an aqueous solution of an alkali metal hydroxide having a normality of at least 2 and containing dissolved a substantial amount of a solubility promoter for mercaptans, and a small amount not in excess of about 1% by weight of a water soluble surface active alkali meta1 salt of a petroleum sulfonic acid, and said solution also con taining thoroughly dispersed therein not in excess of about 2% by weight of a mineral oil having a boiling range between about 400 and ORRIS L. DAVIS. ALAN C. NIXON.