US2341917A - Method of removing mercaptans from hydrocarbon liquids - Google Patents

Description

Patented Feb. 15, 1944 METHOD or REMOVING MERCAPT'ANS FROM HYDROCARBON- memos Lawrence M. Henderson, Winnetka, and George W. Ayers, Jr., Chicago, 111., assignors to The Pure Oil Company, Chicago, 111., a corporation of Ohio No Drawing. Application September 5, 1941,

Serial No. 409,652

21 Claims.

This invention relates to a method. of removing acidic bodies from otherwise neutral Water immiscible fluids. More particularly, this invention is directed to the problem of removing mercaptans from hydrocarbon oils.

This application isa continuation in part of application, Serial No. 388,982, filed April 17,

1941, in the names of Lawrence M. Henderson and George W. Ayers, Jr.

Hydrocarbon oils,rparticularly light distillates resulting fromv cracking higher boilingfractions frequently contain mercaptansand other acidic sulfur compounds which requireremoval inorder to: render the..oi1 fsweetf, and non-corrosive.

It has been common practice in the petroleum refining art to remove part of the sulfur compounds by washing withcaustic alkali and then tosweeten with doctor solution, The disadvantage in- ;volved in this type of treatment is that a considerable portion of the sulfur remains in the oil washing for removal of mercaptans and other sulfur compounds has been efiected by adding to the caustic solution materials such-as sodium or potassium isobutyrate, commonly known as solutizers or solubility promoters, i. e., substances which enable the alkali solution to extract larger amounts of acidic substances such as mercaptans from fluids in which they are contained. r

We have discovered that the results obtained by washing with caustic alkali solutioneither alone or containing known solubility promoters canbe considerably improved upon by adding to caustic alkali solution poly-hydroxy-diphenyls which are of themselves good solubility promoters and which have thefurther ability to act as solventizers for solubility promoters whose solubility in alkali solutions is low. By the term solventizer is meant a substance which will enable larger quantities of the solubility promoter to dissolve in the caustic solution.

It has been found that soaps of alicyclic carboxylic acids such as naphthenic acids are good solubility promoters. However, caustic alkali solutions of fairly high concentration will dissolve only relatively small quantities of naphthenic or-other alicyclic carboxylic acids and the soaps forth, is 3,4-dihydroxydiphenyl' thereof, and in the quantities that the soap or acid is dissolved in the caustic alkali it has no material effectinsofar as enhancing the ability of the caustic solution to remove acidic substances such as mercaptans and .thiophenols from hydrocarbon oils. However,- if a-material is added having the ability to increase the'solubility of the soap or acid in the caustic alkali and a sufficient amount of soap or acid is added to the caustic solution; the ability of the caustic to remove mercaptans and other sulfur compounds isgreatly enhanced. On the other hand, caustic-alkali-solutions of low concentrations will dissolve relatively large amounts of naphthenic orother acids and their soaps, but in'low' concentrations the causticalkali solution per se or with addition oftheacid or soap is relatively ineffective in removing mercaptans from the oil. If an attempt is made to increase the concentration of the caustic to, a point where it is fairly effective in removing mercap tans, the naphthenic acid or other acid soap precipitates out of solution.

Although we havefound' that the poly-hydroxy-diphenylsin general are useful as solubility promoters'and' as solventizers, the dihydroxydiphenyls, and particularly those in .7 which the hydroxy groups are in ortho position to each other are particularly effective. As an example of a compound within the class we have set 'In orderto realize to an appreciable ententj the benefits of the invention, the solution should eessof the amount requiredto stoichiometrically react with the solventizers and solubilitypromoters present. Thus, irrespective of whether the solutizers or solubility promoters are added to alkali solutions in acidic form or .as the alkali metal reaction products thereof, theiinished treating solutions are considered tobej-alkali metal hydroxide solutions containing thetalkali imetal reaction products of the. materials; employed as solventizersand solubility promoters.

'When used, as solventizer, the amount ofthe "polyhydroXy-diphenyl may vary with theiparticul ar solutizer used since some solubility promot ers '-require less solventizer to eifect' solution thereof than do others. We have found that lamOl ts as low as 2%, and amountsxup to 40%,

of thepo'lyhydroxy-diph'enyls may he used. 'It

is preferred thatin no case'shoulditheamount tachecl to carbon in the ring or phenyls should be to be particularly effective as solubility prmot-- ers are the naphthenic acids and their metal salts, although it is to polyhydroxy-diphenyls are also useful as-solventizers in connection with other types of solube understood that the bility promoters such as the low boiling fatty acids, 1. e., fatty acids having less than '1 carbon atoms in the molecule, and their alkali metal salts. By the term naphthenic acids it is intended to include all alicyclic acids which occur' naturally in crude petroleum and which are predominantly cyclic in structure such as carboxylic acidsof cyclopentane and cyclohexane ring structure. These acids, generally speaking, fall within the empircal formulae CnHzn 1COOH, CnH21i-3CO0H and CnHZn-oCOOH and contain a cyclo-paraffinic ring having a carboxyl group atto an aliphatic chain which is in turn attached to carbon in the ring, The acids may be monoor poly-cyclic, usually the former. An increase in the length of the aliphatic chain or in the number of aliphatic group substituents increases the tendency of the acids to behave as aliphatic acids. Since soaps of aliphatic acids, even those of as low molecular weight as heptylic acid, are too insoluble in sodium hydroxide solution to possess substantial merit-as mercaptan solubility promoters, it is not desirable to have too many aliphatic carbon atoms per molecule present because of the concomitant low solubility. It is accordingly preferred to use those naphthenic acids which have at least "a definite minimum solubility in aqueous alkali solution. Acids which have this alkali solubility are those acids which dissolve substantially completely to the extent of 18.7 pounds in a solution of 6.3 pounds of commercial 5 cresol, 18.3 pounds of sodium hydroxide and 56.7 pounds of water at temperatures of about 70 F. It is apparent that in applying this solubility test to compositions containing-mixtures of naphthenic acids of varying molecular weight-and structure, that some of the acidsmay dissolve and others remain undissolved. If the dissolved acids are soluble to the aforementioned extent, they are alkali soluble within the meaning of this invention. Naphthenic acids containing over about 8 or 9 carbon atoms per molecule, such as those containing between about 11 and 16 carbon atoms, are particularly effective. The naphthenic acids are especially useful if it is desirableto use sodium hydroxide solution which ordinarily is the cheapest of the available strong basessince the naphthenic acids have been found to have considerably greater'solubility in sodium hydroxide solutions than aliphatic acids of a corresponding number of carbon atoms.

When using the polyhydroxydiphenyls. alone as solubility promoters in connection with alkali metal hydroxide solutions, the polyhydroxydipresent in solution in amounts not less than by weight of the solution and may be used in amounts up to substantially the maximum solubility, although it is preferable not to use more than 90% of the maximum amount which is soluble in the solution. The free alkalimetal hydroxide content of the solution should not be below 5% and may range up to ter56.7 grams.

30%. Larger amounts of free alkali are undesirable for the reason that the solution becomes too VlSCOlls and causes emulsion difficulties when mixed with the liquid to be treated.

As an example illustrating the invention a solution was prepared containing. naphthe nic ac1ds18.7 grams, 3,4-dihydroxydiphenyl-63 grams, sodium hydroxide18.3 grams and we- 7 V This solution was mixed with 'gasolme, prepared by high pressure thermal cracking of petroleum oil, in the ratio of 7 parts by volume of treating solution to parts by volume of gasoline. The mixture was shaken for fifteen minutes in an atmosphere of nitrogen n order to exclude air. The mercaptan-sulfur 1n the gasoline was reduced from 0.0302% by weight to 0.0063%,- thus effecting a removal of 79% of the mercaptans. The same gasoline treated with a 15% by weight sodium hydroxide solution reduced the mercaptan-sulfur to only 0.0170%, thus effecting a removal of only 44% of the mercaptans.

In the foregoing examplethe naphthenic'acids had the following characteristics:

0.0130, thus effecting a removal of 57% ofv the mercaptan-sulfur as compared to a removal of only 44% of the mercaptan-sulfur by a straight 15% sodium hydroxide solution.

It will be apparent that in preparing treatin reagents in accordance with the invention, the solventizer may be added to alkali metal hydroxide solutions in the form of alkali metal comof illustration and are not intended to limit'the invention to the specific quantities given or the particular compounds named. Mixtures of the. various solventizers may be used as well as mixtures of different soaps; It is important, however, that sufficient quantities" of-free alkali,

solventizer and soap be present to obtain the full benefits of the invention.

Although we have found that solutions containing from of free caustic alkali up to the maximum amount soluble in the solution may be used, it is preferred to use solutions which contain not over 20% of free sodium hydroxide and not over 30% of free potassium hydroxide, since it is not possible to keep in solution desirable amounts of solubility promoters when the free alkali concentrations are too high. The free alkali content will, therefore, be governed largely by the concentration of solubility promoter which is found to be the most effective and by the viscosity of the solution. Very effective results have been obtained with solutions containing from 8% of 20% of free sodium hydroxide and 10% to 30% of free potassium hydroxide. When using polyhydroxy-diphenyl as solubility promoters alone, amounts between 10% and 30% give good results and when using as a solventizer, amounts ranging from 5 to by weight have been found to be sufficient. The invention also contemplates the use of alcoholic alkali as well as aqueous alkali solutions. Potassium hydroxide solutions are in general more effective in extracting mercaptans than are sodium hydroxide solutions containing equal amounts of the hydroxide.

Treating solutions in accordance with this invention can be regenerated in the same manner as caustic alkali solutions, namely, by boiling or by steam stripping, and reused either with or without adjusting the alkali concentration of the solution, and with or without further addition of solutizers and/or solventizers.

We claim:

1. The method of removing acidic bodies from otherwise neutral Water immiscible organic fluids which comprises contacting said fluids with a solution containing at least 5% by weight of free alkali metal hydroxide and a substantial amount of the reaction product of alkali metal hydroxide and a polyhydroxydiphenyl.

2. Method in accordance with claim 1 in which the polyhydroxydiphenyl is a dihydroxydiphenyl.

3. Method in accordance with claim 1 in which the polyhydroxydiphenyl is a dihydroxydiphenyl in which the hydroxy groups are in ortho position to each other.

4. Method in accordance with claim 1 in which the polyhydroxydiphenyl is 3,4-hydroxydiphenyl.

5. Method of removing mercaptans from hydrocarbon liquids which comprises contacting said liquids with a solution containing at least 5% by weight of free alkali metal hydroxide and a substantial amount of the reaction product of alkali metal hydroxide and a polyhydroxydiphenyl.

6. Method in accordance with claim 5 in which the polyhydroxydiphenyl is a dihydroxydiphenyl.

'7. Method in accordance with claim 5 in which the polyhydroxydiphenyl is a dihydroxydiphenyl with the hydroxy groups in ortho position to each other.

8. Method in accordance with claim 5 in which the polyhydroxydiphenyl is lift-dihydroxydiphenyl.

9. Method of removing mercaptans from hydrocarbon liquids which comprises contacting said liquids with a solution containing not less than 5% of free alkali metal hydroxide and not less than 5% of a polyhydroxydiphenyl in the form of its alkali metal reaction product.

10. Method in accordance with claim 9 in which the polyhydroxydiphenyl is a dihydroxydiphenyl.

11. Method in accordance with claim 9 in which the poly-hydroxydiphenyl is a dihydroxydiphenyl with the hydroxy groups in ortho position to each other.

12. Method in accordance with claim 9 in which the polyhydroxydiphenyl is 3,4-dihydroxydiphenyl.

13. Method in accordance with claim 5 in which the solution in addition contains a solubility promoter selected from the group consisting of the alkali metal salts of alicyclic carboxylic acids and low boiling fatty acids and the polyhydroxydiphenyl-alkali metal hydroxide reaction product is present in sufiicient amount to keep the solubility promoter in solution.

14. Method in accordance with claim 5 in which the solution in addition contains not less than 10% by weight, calculated as acid, of a solubility promoter selected from the group consisting of the alkali metal salts of alicyclic carboxylic acids and low boiling fatty acids and the polyhydroxydiphenyl-alkali metal hydroxide reaction product is present in sufiicient amount to keep the solubility promoter in solution.

15. Method of removing mercaptans from hydrocarbon liquids which comprises contacting said liquids with a solution containing not less than 5% of free alkali metal hydroxide, not less than 10% by weight, calculated as acid, of a solubility promoter selected from the group of alkali metal salts of alicyclic and low boiling fatty acids. and not less than 2% by weight but sufiicient polyhydroxydiphenyl in the form of its alkali metal reaction product to keep the solubility promoter in solution.

16. Method in accordance with claim 15 in which the polyhydroxydiphenyl is a dihydroxydiphenyl.

17. Method in accordance with claim 15 in which the polyhydroxydiphenyl is a dihydroxydiphenyl with the hydroxy groups in ortho position to each other.

18. Method in accordance with claim 15 in which the poly-hydroxydiphenyl is 3,4-dihydroxydiphenyl.

19. The method in accordance with claim 1 in which the solution contains alkali metal naphthenates in sufiicient amount to enhance the ability of the solution to remove acidic bodies from the hydrocarbon liquid and the alkali metalpolyhydroxydiphenyl reaction is present in amounts sufficient to keep the naphthenates in solution.

20. The method in accordance with claim 5 in which the solution contains alkali metal naphthenates in sufiicient amount to enhance the ability of the solution to remove acidic bodies from the hydrocarbon liquid and the alkali metalpolyhydroxydiphenyl reaction product is present in amounts sufiicient to keep the naphthenates in solution.

21. The method in accordance with claim 9 in which the solution contains alkali metal naphthenates in sufficient amount to enhance the ability of the solution to remove acidic bodies from the hydrocarbon liquid and. the alkali metalpolyhydroxydiphenyl reaction product is present in amounts sufiicient to keep the naphthenates in solution.

LAWRENCE M. HENDERSON. GEORGE W. AYERS, JR.