US2341878A - Process for removing acids from hydrocarbons - Google Patents

Description

Patented Feb. 15, 1944 UNITED STATES PATENT OFFICE PROCESS FOR REMOVING ACIDS FROM HYDROCARBONS Alan C. Nixon, San Francisco, and David Louis Yabrofl, Berkeley, calin assignors to Shell Dee velopment Company, San Francisco, Calif; a

corporation!!! Delaware Nop'mwing; Application May 17,1941, Serial No. 394,,0 04 i 11 Claims.

This invention deals with an improvement in processes for extracting weak acids from hydrocarbons. More particularly, it is concerned with a method for improving the rate of separation of alkaline extracting solutions from hydrocarbon oils or of facilitating steam stripping the resulting spent alkaline solution, if thelattcr is desired, or both.

It is known that hydrocarbon oils frequently contain weak acids such as those having 'disso-.

ciation constants below about 10- g., I IgS, mercaptans, alkyl phenols, etc., which acids for various reasons must be removed. A numbe of processes have been developed for extracting them, all of which have in common the step of treating the hydrocarbon oil containing the acid with an alkaline solution, andthereafter separating the resulting alkaline solution containing For reasons of econsalts of the absorbed acid. omy, the resulting spent alkaline solution is usually regenerated, steam stripping in general being the preferred method of regeneration, The regenerated solution is then reused for the ex traction of further quantities of acids from hydrocarbons containin them.

Particular processes for the extraction of weak acids normally associated with petroleum oils are,

' the sour gasoline' substantially completely, natfor example, processes involving the extraction of H28 from gaseous or liquid hydrocarbons with aqueous solutions of tripotassium phosphate,.sodium phenolate, sodium borate, sodium or potassium carbonate, organic bases such as ethanolamine, diamino propane],- piperidine, etc or involving the extraction of alkyl phenols from hydrocarbon distillates with strong solutions of alkali metal hydroxides, preferably having concentrations ofabout 25%-50%; or involving the extraction of mercaptans with so-called solutizer solutions, 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 solutlzers are, for example, 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 glycerines in which the total number of carbon atoms in the alkyl radicals is from 1 to 4; mono methyl glyceryl 'ether; diamino, dihydroxy or amino hydroxy 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 to 5 carbon atoms, or, in the case of potassium ural 81113 inhibitors, i." e., alkyl phenols normally contained in the gasolines, a're'only partially ex tr acted, an alkyl phenol equilibrium being established between the gasoline andthe extracting solution. Therefore, it is veryoften advan tageous to employ for the'ext'raction a solutizer solution to which one ha'sadded purposely acertain amount of alkyl phenolates. However, phenolates may'also be preserit in solutizer solutions without having been added thereto on" purpose. Many gasoline's, 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 a'steam regeneration stage and back to the extraction stage, even bare traces of alkyl phenols contained in the gasoline will eventually build up in the solutizer solution until the concentration of the alkyl phenolate in the solutizer solution is in equilibrium with the concentration of the alkyl phenols in the incoming 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 of anywhere between about 3%-20% alkyl phenolates in the solutizer solution, even though the original treating .solution may have been free from phenolates.

Unfortunately, aqueous solutions containing a substantial amounts of alkyl phenolates are. known to have a tendency toward forming emul-' sions which separate but slowly, and it has been found in the past that in order to avoid emulsion troubles, the concentration of the alkyl phenolates must be kept below certain limits, otherwise more or less permanent emulsions may'form (U. S. Patent 2,202,039).

from hydrocarbon tions which are used for extracting weak acids oils 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 His are troubled" primarily with foaming, whereas the processes dealing with the extraction of mercapa need be added to improvethe rate of settling or tans and phenols, etc., frequently are subject not only to foaming, if steam regeneration is involved, but also to difficulties involving everyidegreeof reduced rate of separation to formation of stubborn emulsions which are even by centrifuging. I

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

The nature of the substances responsible for 'thezdifliculties is notdefinitely established. It maybe that a substance is involved which is relatedtoj gums' that form. in gasolines; oris related to resinous fmaterials formed as by'interaction ,ofsome .ofthe components of the hydrocarbons (possibly impurities), with the alkaline treating solutionor .a component-thereof. For example, it isquite possible that in thecase of solutizer treatm nt withl' solutions j containing phenolates, aphenol type. resin is formed, for instance, by interaction-with mercaptans, aldehydes or other impurities. Such apossibiiity is 'not excluded in view'of thefact that solutizer solutions containing phenolates have in the past given the greatest; difficulties. provide;means' for improving the rate of separation of aqueous alkaline. treating solutions from hydrocarbons which are being treated. Another purpose is simultaneously or independently to reduce the foaming tendency of the treating solutlonswhencregenerating by steam stripping such spentsolutlonscontaining absorbed weak acids. Still another. purpose'of this'invention is to provide' means for preventing the formation of emulsions caused by the .jpresence of accumulated emulsifiersin solutizer solutions, particularly in those containing alkyl phenolates; and it is yet anotherpurpose .to provide a remedy for breaking emulsionsformed by hydrocarbon distillates in solutizer solutions. We have discovered that the addition of small amounts of a waterrsoluble, surface active alkali metal salt of anbrganic sulfonic or sulfate ester acid which is free from carboxyl radicals, preferably contains at least carbon atoms and has a molecular weight below about 1000, to an aqueous alkaline extracting solution results not only in reduced foaming and improved rate of separation, but also in aneffective and rapid break of emulsions which may form between hydrocarbon oils 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, e. g., in amounts of a few tenths of a 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.

The types of organic sulfonic and sulfate ester acids which produce surface active salts, as well as theirmethods of manufacture, are generally well known.

The amounts of the surface active salts which difllcult to separate.

.,- Accordingly, it is a purpose o f this invention to breaking solutizer emulsion or both are usually quite small and normally-vary from about .00l% to 1% by weight of the solutizer solution. Different types of alkaline solutions are capable of dissolving different amounts of the active salts. In general, the presence of alkyl phenolates in the aqueous solution greatly enhances the solvent .power for the salts. Preferably the amount added should not exceed its solubility limit in the aqueous solution. I

In order to be more or less permanently useful in a regenerative process wherein the spent ex- .tracting solution is continuously regenerated and recirculated for further extracting hydrocarbon oils containing weak acids, it is desirable that the active salts have a number of properties as follows:

In the first place, an all around suitable salt must not only accelerate the rate of separation of the solutizer solution from the treated hydrocarbon oil or break emulsions .between the two or both, but at the same time it must reduce foaming of solutizer solution upon regenerating it by steam stripping. We have found that a great number of surface active compounds, such as soaps of fatty or sulfated or sulfonated fatty acids cause violent foaming of the solutizer solution in which they are dissolved. I

In the second place, it is desirable that the beneficial effect of the salt shall not be restricted to and be dependent on a specific range of concentration substantialy narrower than the limits indicated above-that is to say, there should not be a sudden reversal of the beneficial effect, i. e., an increase in the emulsification or foaming tendencies or both, of the extracting solution upon addition of a slight excess of the salt over the optimum quantity. On the contrary, the beneficial effects should extend over substantially the entire range of concentration indicated, and I changes in the effects due to deviations from the optimum concentration should be only matters of Many surface active salts, particularly the ordinary soaps such as sodium stearate, sodium oleate, etc., while efiecting de-emulslflcation in certain specific amounts, when present in slightly larger amounts increase, rather than decrease, the emulslon'tendencies of the extracting solution. For example, sodium stearate in a concentration of .06% effectively broke a semi-stable solutizer emulsion, while in .08% concentration a stable emulsion remained. 1

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 acti e compounds may act as emulsifiers, rather than as settling accelerators or emulsion breakers or both. For this reason, it is important that the concentration of the active compounds in the aqueous alkaline solution be limited to within the approximate useful limits indicated. 1

For the same reason, it is essential that the hydrocarbon distillate which is being treated be substantially free from sulfate ester acids or sulfonic acids. Such acid sulfuric" acid derivatives may be the result of a sulfuric acid treatment,

and, if present in the distillate, should be removed prior to subjecting the distillate to our treating process, as by a pre-scrubbing with dilute aqueous caustic alkali.

Another necessary property of the salt is that it be soluble or colloidally dispersable in effective amounts in the aqueous extracting solutionfor example, when applied to the solutizer process, be soluble in an aqueous solution containing caustic alkali in a normality of at least about 2, and in addition containing substantial amounts, e. g.. normally 15% or more, of the solutizer or solutizers, such as alkali metal phenolatesand other solutizers described above.

Needless to say, the active salts should not be extracted from the solutizer solution when the latter is in contact with the hydrocarbon oils. The presence of alkali metal salts of sulfonic or sulfate acids in gasoline adversely 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. 1 I

Furthermore, the salts should be reasonably stable toward the action of small amounts of oxygen in the presence of strong caustic and at the elevated temperatures of steaming which are necessary in the regeneration step. Most hydrocarbon oils contain small but definite amounts of dissolved oxygen which may have entered during storage or during pumping of the oil. Pumps, particularly those of the' rotary type, unless specially protected, usually suckin some air through the packing glands, and this air is then dissolved in the oil being pumped.

In some 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 salt of a polyvalent metal to the extracting solution, polyvalent metal salts and particularly the calcuim 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 our purpose, 1. e., the alkali metal salts of sulfonic acids and sulfate ester acids, the

' former are preferred as being in general more resistant tohydrolysis. 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 effect of the surface active salts be more or less permanent. Moreover, the sulfonates are in general superior to the sulfates with respect to suppressing foaming during steaming, the sulfates as a general rule causing little change in this phenomenon, whereas sulfonates reduce the foaming markedly and in many instances completely eliminate it.

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 suitable for our purpose are, for example, watersoluble alkali metal salts of petroleum sulfonic acids such as the salts of green acids" produced inthe manufacture of medicinal oils by acid I treatment; or of the products of treatingxkerosene or lube oil extracts with strong sulfuric acid, etc.; or of various aliphatic or alicyclic sulfonic acids such as fatty sulfonic racids, fatty aromatic sulfonic acids, naphthene sulfonic acidsror of sulfonic acids of various aromatic hydrocarbons (particularly those which, contain one or more alkyl radicals and which may contain non-functional substituents), such as various alkylated benzenes, diphenyls, xylenes, diphenyl methanes, naphthalenes, anthracenes,. phenanthrenes, tetralines; alkyl phenols-such as those. contained in cracked petroleum distillates; aliqlate'd' chlornaphthalenes, nabhthylamineajdiphenyl oxides, chlorinated diphenyl oxides, dlphenylfsulfides, diphenyl amines, phenylnaphthylamines, dinaphthyl ovides, sulfides or amines; alkylated pyridines, quinolines, isoquinolines. pyrrols, pyrrolidines, piperidine, thiophenes,'. thiophanes, etc.; or of various sulfonic acids of. carboxylic acid esters or amides, such as for example, of the ester sulfo-carboxylic acids oti ulfonatonmides havingthe generalformulae:

respectively, wherein the R radicals are organic radicals, such as aliphatic or cyclic hydrocarbon and amides alkyl radical are in general far more effective than the salts of corresponding sulfonic acids not possessing them. vFor example, the alkali metal salts of naphthalene or anthracene sulfonic acids are only mildly beneficial for our purpose, whereas the corresponding salts of, for example,'mono or dibutyl naphthalene sulfonic acids orcf retene sulfonic'acid are highly effective. i

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 dioleflnes with strong 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.

Sulfate ester acids, me alkali salts 6: which are suitable for our purpose are, for example,

the fatty sulfates, such as mono lauryl, cetyl, stearyl, etc., sulfate acids; or mono esters of sulfuric acid obtained by treating with strong to'moderately strong sulfuric acid various ole- 4 asanavs agent is first dissolved or dispersed in the hydrocarbon, a portion only will be retained by the aqueous solution upon contact under ordinary extraction conditions, the remainder remaining in the hydrocarbon phase. on the other hand, if the'agent is first dissolved or thoroughly dispersed in the aqueous solution, it is not usually extracted by the hydrocarbons to any noticeable extent under normal extracting conditions.

Our preferred method of introducing the surface active agents comprises first producing a slurry in water of the free sulfate or sulfonic acid or of an alkali metal salt thereof. This than a day being required to obtain complete separation. The addition-of requisite amounts of a surface active salt of this invention materially reduces the settling time, often causing a complete separation in a few minutes.

In the table below, effects of a number of representative surface active salts covered by this invention are shown. To evaluate their performance, samples of a solutizer solution having the following composition:

KOH 6- normal Potassium isobutyrate 1.5 normal Potassium phenolate 1.0 normal were subjected to an emulsion test in which they were agitated with a cracked gasoline under standardized conditions, and the resulting emulsion was then allowed to settle. The time required for substantially complete separation was noted, and whether or not at the end of the settling time a rag was left at the interface.

Other samples of the same solution were sub- Jected to a distillation test in which their rela-' tive foaming tendencies were observed. Results were as follows: I

Table Settling Additi d 32%? r in on compoun on, Grow oam g 100 time in Bag minutes N Positive Moderate. Sodium sulfate of higher secondary aloohol.......'.'. 1% 2 ..do

Sodium lauryl sulfate 67 375 5% Sodium sulfonate ethyl methyl oleoamide 67 54 Sodium sulionate cth l oleoamids 67 5 Do. Sodium troleum s ionate 67 3 Ve much improved. Sodium ydrocarbon sulfonate. 67 5 Blig tly improved. Sodium alkyl aryl suliouate 67 4 Much improved. Dloctyl ester of sodium lulio succlnate 67 3 Mildly improved. Bodiun:l sulionate of complex stearyl alkyl corn- 67 4 Do.

poun s.

Sodium salt of green acids loo 4 the extractor. This solution is then heated and thoroughly agitated in the steam stripper in the course of the regeneration step, whereby the desired dispersion or dissolution is achieved.

While in the foregoing we have described our invention particularly as applied to regenerative processes such as the sweetening of sour hydrocarbon distillates by the solutizer process, it is understood that 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 distillate containing them with strong caustic soda (25%-50% concentration) to result in an extract of high alkylphenolate content. This extract separates but slowly from the distillate, frequently more We claim as our invention:

1. In the process of extracting weak acids normally associated with hydrocarbons from hydrocarbons containing them and being substatitially free from acid sulfuric acid derivatives, with an aqueous alkaline solution, a method of preventing emulsification and foaming comprising treating said hydrocarbons with said aqueous solution containing dissolved a small amount not in excess of 1% by weight of a substantially oilinsoluble, surface active alkali metal salt of an acid selected from the group consisting of organic sulfonic acids and sulfate ester acids, which are free from carboxyl radicals.

2. The process of claim 1 wherein said acids have at least 10 carbon atoms and a molecular weight below about 1000. V

3. In the process of sweetening sour gasoline distillate containing mercaptans and being substantially free from acid sulfuric acid derivatives by extractingit with an aqueous caustic alkali solution containing a solubility promoter for mercaptans, a method of preventing e'muisincation and foaming comprising treating said gasoline with said aqueous solution containing a small amount not in excess of 1% by weight of a substantially oil-insoluble surface active alkali metal salt of an acid selectedfrom the group consistin: of orssnio sulionic acids and sulfate esters. which are free from carboxyl radicals.

4. The process of claim 3 wherein said weak organic acids have dissociation constants below about 10-.

5. In the process of extracting weak acids normally associated with hydrocarbons from hydrocarbons containing them and being substantially free from acid sulfuric acid derivatives, with an aqueous alkaline solution, a method of preventing emulsification and foaming comprising treating said hydrocarbon with said aqueous solution containing dissolved a small amount not in ex cess of 1% by weight of a substantially oil-insoluble, surface active alkali metal salt of a sulfonlc acid having at least one alkyl radical and being free from carboxyl radicals and radicals susceptible to hydrolysis upon steaming-in the presence of caustic alkali.

8. The process of claim 5 wherein said sulfonic acid is a petroleum sulfonic acid.

7. The process of claim 5 wherein said sulfonic acid is a green acid obtained in the treatment of petroleum oils with strong sulfuric acid.

8. The process of claim 5 wherein said sulionic acid is an alkylated aromatic sulfonic acid.

9. The process of claim 5 wherein said sulfonic lution consistins essentially of an aqueous solution of an alkali metal hydroxide havins a normaiity of at least 2 and containing dissolved a substantial amount of a solubility promoter for mercaptans and in addition from about .00l% to 1% by weight of a substantially oil-insoluble, surface active alkali metal salt of an acid selected from the group consisting of organic sulfonlc acids and sulfate ester acids which are free from carboxyl radicals.

11. In the sweetening of sour hydrocarbon oils by treatment thereof with aqueous alkaline solution capable of removing mercaptans from the oil, the method of preventing emulsiilcation of the alkaline solution and oil which comprises effecting said treatment in the presence of a relatively small amount of a substantially oil-insoluble compound selected from the group consisting of sulfonates and sulfate esters having at least 10 carbon atoms and a molecular weight below about 1000.

' ALAN C. NIXON.

DAVID LOUIS YABROFF.