US2317055A - Method for removing organic acidic substances from hydrocarbon fluids - Google Patents

Description

Patented Apr. 20, 1943 i METHOD REMOVING ORGANIC ACIDIC gsggncns FROM HYDRO CARBON Lawrence M. Henderson, Winnetka, George W.

Ayers, In, Chicago, and Donald 0. Bond, Northbrook, 111., assignors to The Pure Oil Company, Chicago. 111., a corporation of Ohio No Drawing. Application December 30, 1949,

Serial No. 372.354

15 Claims. (Cl. 198-30) This invention relates to a method and reagent for removing weakly acidic substances from members of the fatty acid series, for example,

sodium or potassium i'sobutyrate.

It has been found that the ability of alkali solutions to remove acidic bodies from waterimmlscible liquids can be enhanced by adding thereto suitable quantities of rosin or colophony. The solubility of rosin or alkali metal rosin salt,

the caustic solution to remove mildly fur compounds is greatly enhanced.

It is, of course, possible to use caustic alkali solutions of low concentration since these solutions will dissolve larger mounts of rosin, but in low concentration, caustic alkali solution per se or saturated with rosin is relatively ineffective in removing mercaptans from petroleum acidic sul ,mils. If an attempt is made to increase the conwhich is the form in which rosin exists in aqueous alkali solutions, in aqueous alkali solutions is relatively low and it is necessary in order to secure satisfactory results to use a solventizer therefor, i. e., a substance which will enable larger quantities of the rosin to dissolve in the alkali solution. By rosin" or colophony" it is intended to include the various grades of natural wood and gum rosin regardless of the exact origin or method of production which may be employed. Such rosin ordinarily contains pr e-. dominant proportions, usually about 80 to 90% by weight of abietic acid, its anhydride and/or isomers or derivatives of abietic acid.

Aqueous alkali solutions of fairly high concentration of alkali will dissolve only relatively small quantities of rosin or the alkali metal salt thereof and in the quantities that the rosin is dissolved in the aqueous alkali, it has no material efiect in so far as enhancing the ability of the alkali solution to remove acidic substances such as mercaptans from hydrocarbon oils. However, if a material is added having the ability to increase the solubility of the rosin in caustic alkali and a sufllcient amount of rosin is added to the caustic solution, the ability of centration of the alkali to a point where it is effective in removing mercaptans, the rosin salt precipitates from the solution. It is therefore essential that a solventizer for the rosin be employed.

Although a number of different weakly acidic hydroxy aromatic compounds, such as phenols and alkyl phenols, for example, phenol, xylenols, 0-, m-. D-, cresol and alpha naphthol can be used as solventizers for the rosin, it has been found that those phenolic compounds having more than six carbon atoms per molecule and thiophenols such as thiophenol, m-thiocresol and o-thiocresol which per se have the ability to enhance the mercaptan extracting power of aqueous alkali solutions give excellent results. The solventizer must be soluble in the resulting solution toan appreciable extent, preferably at least 5% by weight of the solution.

A large number of tests were carried out using ordinary commercial wood rosin of grade. Thisrosin had an acid number of 161 as determined by titration in hot alcohol solution with standard potassium hydroxide solution using phenolphthalein as an indicator. Numerous mixtures were prepared containing various proportions of water, sodium hydroxide, rosin and cresol. The cresol used was a commercial grade of 5 degree meta-para cresol obtained from the Barrett Company. The components of each of the various mixtures were mixed, heated on a waterbath for 30 minutes with occasional shaking and were then allowed to stand for at least six hours at room temperature, after which the presence 01 absence of undissolved material was noted. Those mixtures in which the components were completely dissolved were used in treating separate samples of the same cracked gasoline. In'ali cases the amount of treating solution used was 7% by volume of the gasoline sample treated. The treating solution and gasoline were contacted by shaking vigorously for 5 minutes in a closed container in an atmosphere or nitrogen, the treated gasoline separated and mercaptan sulfur analyses made. From the results of these analyses the percentage of mercaptan sulfur removed from the gasoline by each solution was calculated. The results of these tests are shown in the following table.

solubility drops to 0.37 and 0.19% by weight respectively, and the resulting solutions are no better for mercaptan removal than straight sodium hydroxide solutions of equivalent free alkali content. With a 2.5% solution 01' sodium hydroxide, 5% of rosin is not soluble even with as much as of cresol solventizer present to promote solubility of the rosin. However, when Team:

Treatment of Toledo 0. H. P. gasoline with NaOH-cresol-rosin solutions Per cent removal oi meroaptan sulfur Per cent free NaOH Per mint ms 5% cresol 10% cresol 16% cresol 20% cresol cresol cresol us a tlen mocnpoonoa cup-o Insol.-undissolved material present.

"-apparently soluble when made but precipitated when contacted with gasoline.

+-saturated solution, with respect to rosin. Percent mercaptan suiiur in untreated gasolme0.0206. In the foregoing table the sodium hydroxide, rosin and cresol content of various aqueous alkali metal hydroxide treating reagents are shown in per cent by weight together with the extraction efllciency of the reagents of the indicated compositions. No effort was made to treat samples of gasoline with those reagents in which insoluble material was noted since the insoluble material might dissolve in gasoline with detrimental efiect. In this table as well as throughout the specification and claims the alkali concentration referred to as "free alkali is the alkali concentration as determined by titration of the alkali reagent solutions with standard acid to a phenolphthalein end point. By means of this titration, alkali which is in combination .with weakly acidic solventizers such as cresol is titrated as free alkali, whereas alkali which in combination with rosin is not neutralized and is not included in this estimation of free alkali content.

It will be seen from the results in the table that a sodium hydroxide solution containing 5.26% by weight of rosin and having 9.1 pH and containing no free alkali" in accordance with the aforementioned definition has a poor mercaptan extracting power as measured by the proportion of mercaptans extracted from the gasoline and is but little better than the straight dilute alkali solution of equivalent pH.

When the concentration of sodium hydroxide is increased to 5.6% or 10.9% in order to improve the mercaptan extracting power, the rosin sodium hydroxide solutions of 5.6% and 10.9% are used and substantial amounts of rosin dissolved with the aid of cresol, improved extraction efficiency is obtained. While in the case of the solution containing 10.9% sodium hydroxide and 15% rosin it was possible to use a considerable excess of cresol over and above the amount required to dissolve the rosin, the results with the solutions containing 30 and 40% of cresol were not as good as those containing 15 or 20% of cresol. This is believed to be due to the fact that in the case of the solutions containing the higher proportions of cresol, the cresol was present in an amount either equal to or greater than that stoichiometrically equivalent to the free alkali in the solution. This causes a reduction in the pH value of the solution anda resultant loss of extraction eillciency in spite of the higher proportion of cresol dissolved. The stoichiometric equivalent of the free alkali content is based on the following equation:

where R i aryl.

That the cresol alone could not be responsible for the high mercaptan extracting eillciency obtained is clearly brought out by the results obtained when using an aqueous solution containing 15% free alkali and 20% or 40% of cresol. The solution containing 40% of cresol is much less eilective than aqueous alkali solutions of the same sodium hydroxide content and containing no cresol.

In general, the most effective solutions have been found to have compositions within the following limits of concentration: sodium hydroxide 5.6 to 20% by weight; rosin to 20% by weight; cresol to 40% by weight; and preferably in which the free alkali content is not substantially less than the 'stoichiometric equivalent of the solventizer. Particularly good results are obtained when the free alkali content is appreciably in excess of the stoichiometric equivalent of the solventize. It is apparent, of course, that in any case it is not desirable to use more rosin or solventizer than will form a homogeneous solution. A further characteristic which must be taken into consideration is the viscosity of the solution, since this has a direct bearing on the ease with which such solutions separate from the immiscible liquids which are treated. For this reason, solutions of very high concentration of dissolved materials are frequently less desirable.

It will be apparent that in preparing treating reagents in accordance with this invention, the rosin and solventizers may be added as such or as the alkali compounds thereof since both the rosin and solventizer form alkali compounds when dissolved in aqueous alkali solutions.

The specific examples given are only by way of illustration and are not intended to limit the invention to the specific quantities or to the particular compounds named. Mixtures of various solventizers may be used as well as individual compounds. While sodium hydroxide was used in all the examples shown, reagents employing potassium hydroxide are even more effective in mercaptan-extracting efliciency, although the cost of the reagent when using potassium hydroxide is not as low as when using sodium hydroxide. It is also to be noted that other sources of rosin in addition to wood may be employed, as well as materials closely related to rosin such as, for example, tall oil.

Treating solutions in accordance with this in vention are applicable to neutral or basic waterimmiscible fluids and may be regenerated in the same manner as aqueous alkali solutions, namely, by boiling or steam stripping and reusing the regenerated solution either with or without adjusting the alkali concentration and with or without further additions of rosin and/or solventizers.

What is claimed is:

1. In a method for removing organic acidic substances from hydrocarbon fluids, the step which comprises contacting said fluids with aqueous solution containing free alkali in an amount effective to remove acidic substances from said fluids, rosin in the form of its reaction product with alkali metal hydroxide and in sufflcient amount to enhance the ability of the solution to extract said acidic substances from said 'fiuids, and a solventizer for the rosin reaction product.

2. In a method for removing weakly acidic sulfur compounds from hydrocarbon liquids, the

step which comprises contacting said liquids with free alkali being present in an amount not less than the stoichiometric equivalent of the solventizer.

3. The step in accordance with claim 2 where the free alkali is present in an amount in excess of the stoichiometric equivalent of the solventizer.

4. The step in accordance with claim 2 where the solventizer is a phenolate.

5. 'In a method for removing weakly acidic organic sulfur compounds from hydrocarbon liquids, the step which comprises contacting said liquids with aqueous alkali metal hydroxide solution containing free alkali in an amount effective to remove sulfur compounds from said liquids, not less than approximately 5 per cent by weight of rosin in the form of its reaction product with alkali metal hydroxide, and a solventizer for said rosin reaction product comprising alkali metal phenolates, the free alkali content of said solution being not less than the stoichiometric equivalent of the phenols in said phenolates.

6. The step in accordance with claim 5 in which the solventizer is the reaction product of alkali metal hydroxide and an alkyl phenol.

7. The step in accordance with claim 5 where the solventizer is alkali metal cresolate.

8. The step in accordance with claim 5 where the free alkali content is in excess of stoichiometric equivalent of the phenols in the phenolates and is not substantially in excess of 20 per cent by weight.

9. The step in accordance with claim 5 where the concentration of phenolates calculated as phenols is approximately l0 to 40 per cent by weight.

10. The step in accordance with claim 5 where the amount of rosin is not substantially in excess of 20 per cent by weight.

11'. In a method for removing mercaptans from hydrocarbon liquids, the step which comprises contacting said liquids with aqueous metal hydroxide solution containing free alkali in an amount effective to remove-mercaptans from said liquids not less than approximately 5 per cent by weight of rosin in the form of its reaction product with alkali metal hydroxide, and sufficient alkali metal phenolate to maintain the rosin reaction product in solution, the free alkali content of the soultion being in excess of the stoichiometric equivalent of the phenols in the alkali metal phenolates.

12. The step in accordance with claim 11 where the free alkali content is between approximately 5.6 per cent and 20 per cent by weight.