US2316759A - Method for removing weakly acidic sulphur compounds from hydrocarbon liquids - Google Patents

Description

Patented Apr. 20, 1943 METHOD FOR REMOVING WEAKLY ACIDIC SULPHUR Coll/[POUNDS FROM HYDRO- CARBON LIQUIDS Donald 0. Bond, Northbrook, Ill., assignor to The Pure Oil Company, Chicago, 111., a corporation of Ohio No Drawing. Application July 2, 1941, Serial No. 400,801

14 Claims.

This invention relates to a method and reagent for removing weakly acidic substances from water immiscible liquid and more particularly to method and reagent for removal of mercaptans and other acidic organic sulphur compounds from hydrocarbon oils.

It is common practice in the petroleum refining industry to treat petroleum distillate, particularly cracked distillate, with alkali solutions in order to remove acidic organic sulphur compounds such as mercaptans.

It isknown that the efiicacy of alkaline reacting solutions in removing mercaptans from hydrocarbon liquids can be materially improved by incorporating in such solutions various compounds such as alkali salts of the more volatile members of the fatty acid series, for example; sodium or potassium isobutyrate. The use of such salts, commonly known as solubility promoters or solutizers, has proved beneficial but the amount of mercaptans removed with these reagents is not as great as is frequently desired.

It is an object of this invention to provide an improved method of removing organic acidic compounds, particularly sulphur compounds from Water-immiscible liquids such as hydrocarbon oils.

It is another object of this invention to provide a composition of matter which is highly useful for enhancing the ability of aqueous alkali solutions to remove organic acidic compounds, especially sulphur compounds from water-immiscible liquids such as hydrocarbon oils.

It has now been found that acidic compounds such as mercaptans may be removed from pctroleum oils with a high degree of efficiency by the use of aqueous alkali solutions in which are incorporated alkali soluble oxidation products resulting from the oxidation of petroleum hydrocarbons. These products function as solubility promoters for increasing the solubility of the mercaptans in the aqueous alkali solutions. acidic oxidation products of petroleum hydrocarbons may be formed by either the vapor or liquid phase, preferably the latter, oxidation of normally liquid petroleum hydrocarbons. This oxidation may be carried out with air or oxygen or other oxidizing agents, with or Without catalysts, at any desired superatmcspheric pressure but is ordinarily conducted at pressures of the order of 15 to atmospheres and at temperatures ordinarily not in excess of about 160 (3., although higher temperatures may be employed.

The products produced by oxidation of petroleum oils ordinarily vary considerably in compo- The.

sition, although it is generally believed that a major portion of the oxidation products are acidic in character, probably of the nature of fatty acids. Crude oxidation mixtures, resulting from the liquid phase oxidation of parafiin wax, have been known to contain higher fatty acids and their anhydrides, oxy-acids, alcohols, ketones, alcohol-ketones, lactones and unsaturated acids.

The petroleum oil acidic oxidation products may be obtained, for example, by blowing air through kerosene or melted paraffin wax in the presence of suitable catalysts such as potassium permanganate and other manganates and permanganates of the alkali metals or ammonium. One method of preparing such acidic material is to melt crude scale wax derived from petroleum and mix therewith an aqueous solution containing a small amount of potassium permanganate and soda ash. This mixture is heated to a temperature of about 110 C. and air forced through the mixture for a period of about 18 hours. This reduces the unsaponifiable content of the mixture to about The oxidized acidic materials are obtained by neutralizing the oxidation mixture with aqueous alkali at a temperature of about 170 0., and a pressure of about P. S. I. The resulting water solution of the alkali reaction products is separated from the Water insoluble material and the aqueous solution extracted with naphtha to more completely remove unsaponified material. The aqueous solution is acidified with dilute sulphuric acid and the acidic oxidation products set free. These are dried and may be fractionated by distillation under vacuum. A distillation may, if desired, be carried out on the crude oxidation mixture prior to saponification. The acidic products derived by oxidation of petroleum hydrocarbons differ as to odor and appearance from similar pure straight chain fatty acids of approximately the same molecular weight. They also differ in that they do not readily solidify at low temperatures. Analysis of the crude mixtures obtained as a result of the oxidation process is particularly difiicult because of the lack of stability of some of the Oxidation products which products break down upon distillation, thus producing new materials not originally present in the crude oxidation mixture.

The acidic oxidation mixture, whatever its exact composition may be, is soluble in aqueous alkali solutions and materially enhances the ability of such solutions for removing mercaptans from petroleum oils. While oxidation mixtures from any of the less volatile petroleum hydrocarbons are useful in accordance with this invention, it is preferred to use those oxidation products obtained by the oxidation of relatively high molecular weight petroleum hydrocarbons, such as those hydrocarbons of about to 30 carbon atoms.

It has also been found that the mercaptanextracting efficiency of aqueous alkali solutions U containing the aforesaid acidic petroleum oxidation products may be further enhanced by inand the mercaptan-extracting efliciency thereby greatly improved by the use of a solventizer in conjunction with the oxidation products.

Although it is trueth'a't the solubility'in aqueous alkali solution of the oxidation products may be increased by decreasing the concentration of alkali in the solution, it is also true that the solutions containing low concentrations of alkali 'are materially less effective for removing mercaptans from petroleum oils. By employing a solventizer' for the oxidation products, larger. quantities thereof may be dissolved in strong alkali solutions and themercaptan-removing efficiency of the solutions'thereby greatly improved. Various compounds have been found to be useful as solventizers for the oxidation products. These compounds also have merit per so as solubility promoters; Included among such come pounds are glycols such as ethylene glycol, phen'ols including phenol, 0-, mand p-ethyl phenol, normally liquid xylenols and mixtures thereof, cresols, 2,3,5-trimethylphenol, butyl-pyrogallol, 3A dihydroxydiphenyl, .p-chlor-m-cresol, alphanaphthol, thiophenols such as thiophenol, oand iii-thiocreol, c'hlorphenols 'such as o-' and pchlorphenol and 2,4,5-trichlorphenol. Alkyl phenols such as the various cresols and mixtures of cresolshave been found to be particularly effective solventizers.

' In a specific example, a commercialmixture o f petroleum oxidation products known as Alox 800" was employed as a solubilitypromoter in aqueous sodium hydroxide solutions. This material was manufactured byv catalytic air-oxidation of 45 B. gravity Pennsylvania petroleum distillate. The Alox 800, according to a booklet publishedby the vendors of thismaterial; The Alox Chemical Corporation, has the following properties:

Paornnrrns or ALox 800 iB. gravity at 158 F 16-142 Specific gravity at'158'F 0.9725.0.9593. Viscosity (saybolt) 45-60 sec. at 100 F. Cold test (A. S. T. M.) 80 F. Flash (C. O. C.) 200-220 F. Fire (0.0. C.) 220-250 F. Acid number 250-350. Saponification number 350-450. Iodine number 20 maximum. Molecular weight 174 (average).

The foregoing material is presumably composed largely of fatty acids of various molecular weights.

a In order to determine the proportion of mate rials present in' the Alox .800 within specific boiling ranges and the relative; effectiveness of fractions of different boiling range as solubility promoters, a sample of 2000 cc. was charged to a vacuum still equipped with an efiicient fractionating column and the material distilled up to an overhead temperature of approximately 400 F. Data on this fractionation, together with data showing the eflicacy of the various fractions as solubility promoters in sodium hydroxide solutions, are shown in Table I.

Table I Overhead RSH-S 1 Cut No. Co. in out Press. temp removed M'm. F. Per cent 50 25 120 56 50 25 210 56 100 25 100 25 100 25 100 25 100 25 100 25 100 15 100 15 100 17 100 15 100 15 80 17 1 RSH sulphur in untreated gasoline-0.025.

Cut No. 1, shown in Table I, consisted of about 7 10% of an oily layer and about 90% of another layer having an odor resembling that of acetic acid. The ability of the various cuts to enhance the ability of sodium hydroxide solutions for removing mercaptans from gasoline was determined by preparing aqueous treating solutions employing the various cuts of Alox 800 as solubility promoters. Solutions containing 20% by weight of sodium hydroxide and 10% by Weight of the various distillation cuts were prepared and the solutions employed in an amount of 7% by volume for treatingseparate samples of the same cracked gasoline by agitating the treating solutions for five minutes with the gasoline under an atmosphere of nitrogen. The gasoline used was a sample of untreatedcracked gasoline obtained from a commercial combination high pressure cracking unit. It will be seen that cuts 4 to 10, inclusive, were appreciably better solu bility promoters as indicated by the higher vproportion of mercaptans removed from the gasoline, than were cuts 1 to 3, although in all cases the treating.solutionscontaining the fractions of the oxidation products were superior to straight sodium hydroxide solution containing the same total amount'of sodium hydroxide. It will be further noted that cuts 11 to 13, inclusive,-were not evaluated as solubility promoters. This was due to the fact that treating solutions containing these materials in the same concentrations as extraction efficiency of 20% sodium hydroxide solution from 54% to 68%, which is a substantial increase in the meroaptan-removingefliciency of the aqueous sodium hydroxide solution. Particularly effective results were .obtained with fractions 6 to 10. In view of the boiling range of these fractions, the fractions contain no substantial amounts of acyclic acids containing less than 9 carbon atoms per molecule.

Further tests were carried out in an effort to determine the most efiective concentrations of acidic petroleum oil oxidation products in aqueous alkali metal hydroxide solution in order to secure the highest efliciency in extracting mercaptans from petroleum oils. At the same time tests were made on solutions employing a solventizer for the petroleum oxidation products in order to determine the further increase in extraction efficiency which could be obtained by further increasing the concentration of the petroleum oil oxidation products. The same commercial petroleum oi1 oxidation product, namely, Alox 800 was used in this work as was employed in securing the data shown in Table I. The acid number of the Alox 800 was 282. Commercial cresol was used as the solventizer. The mercaptan extracting efficiency of aqueous sodium hydroxide solutions, similar solutions containing Alox 800, and similar solutions containing both Alox 800 and cresol are shown in Table II.

Table II RSH RSH NaOH NaOH Alox800 splphm sulphur total free 113-784 cresol m retreated mov a gasoline Percent Percent Percent Percent Percent Percent 5.0 5.0 0 0 0.0281 52 15.0 15.0 0 0 0.0281 54 15.0 13.0 10 0 0.0281 67 15.0 11.0 20 0 0. 0284 64 15.0 9.0 30 0 0.0284 69 15.0 7. 0 40 0 0. 0284 73 15.0 5. 0 5O 0 0.0284 68 20.0 20.0 0 0 0.025 54 20. 0 18. 0 l0 0 0. 0284 70 20. 0 l6. 0 20 0 0. 0284 71. 20.0 14.0 30 0 20. 0 13. 3 10 0. 0284 79 20. 0 12. 3 10 0.0284 76 20.0 11.3 i0 20. 0 7.6 25 20 0. 0284 81 20. 0 16.3 0 l0 0. 0284 64 20.8 11. 3 16. 7 16. 7 0. 0281 83 1 Insoluble material present.

1 Slight precipitate.

In preparing the treating reagents shown in Table II, aqueous solutions were prepared containing the amounts of sodium hydroxide, Alox 800 and cresol indicated in the various samples in the table. These treating reagents Were contacted with agitation with untreated cracked gasoline obtained from a commercial combination, high-pressure cracking unit in an amount of 7% by volume for a period of five minutes under an atmosphere of nitrogen. The difference between the mercaptan content of the original gasoline and the treated gasoline was calculated to a basis of percentage of mercaptan removal and was taken as a criterion of the effectiveness of the treating reagents for removing mercaptans from gasoline.

The data in Table II clearly show that Alox 800 may be dissolved in aqueous sodium hydroxide solution in amounts up to 50% by weight and that these solutions are materially better than similar solutions of sodium hydroxide which contain the same amount of free sodium hydroxide but which do not contain any mercaptan solubility promoter. While as much as 50% of Alox 800 is soluble in sodium hydroxide solution, it should be noted that this amount was soluble in a solution which contained only 5% by weight of free sodium hydroxide. By free sodium hydroxide is meant that sodium hydroxide present in these solutions over and above the amount of sodium hydroxide required for combination with the solubility promoter and solventizer present in the solution. When a solution (18) containing 24% of free sodium hydroxide was used, 5% of Alox 800 was not soluble.

The data in Table II further show that when a solventizer, such as commercial cresol, is used in conjunction with the Alox 800 the solubility of the latter in strong aqueous sodium hydroxide solutions is materially increased and that such solutions are superior in mercaptan-extracting eihciency to those solutions of lower concentration of Alox 800. Note, for instance, the extraction efilciency obtained in examples 15, 17 and 22. Each of these treating reagents removed over of the mercaptan sulphur from the gasoline in a single extraction in accordance with the aforedescribed method. In some cases, as noted in examples 11, 14, 18, 19, 20, 21, 23, 24, 25 and 26, a homogeneous solution was not formed and in these cases the mercaptan-extracting efficiency was not determined since the solutions were considered to be unsatisfactory as treating reagents. The solution shown in example 22 also contained insoluble material but the amount Was so small as to not interfere with the use of the solution for treating gasoline. The insoluble material in all of the solutions could, of course, have been removed and the remaining homogeneous solution employed as a treating reagent.

In another example a similar commercial mixture of petroleum oxidation products known as Alox 400 was employed as a solubility promoter in aqueous sodium hydroxide solutions. This material was prepared in substantially the same manner as the Alox 800 but was prepared from 36-40 B, gravity petroleum distillate. According to the manufacturers, this material has the.

following representative properties:

B. gravity at 158 F 11-9".

Specific gravity at 158 F 1007-09930 Viscosity (Saybolt) at 210 F 91-101. Cold test (A. S. T. M.) 20-25 F. Flash (C. O. C.) 250-270 F. Fire (C. O. C.) 280-300 F. Acid number -130. Saponification number -210. Iodine number 20 maximum Ash 0.5-1.0,

.mercaptan sulphur content on a separate sample of the same gasoline to 0.0121%.

. Per cent Free sodium hydroxide to 20 Petroleum oil oxidation product 5 to 25 Solventizer 5 to 20 Although the preferred concentrations of alkali metal hydroxide, petroleum oil oxidation products and solventizer have been set forth, it is to be understood that in no case is more petroleum oxidation product or solventizer to be used than will form a homogeneous solution. In general, it is preferred to use the petroleum oil oxidation products and sclventizer in amounts not in excess of about 90% of the maximum solubility of these materials in aqueous alkali metal hydroxide solution.

While in the specific examples shown, sodium hydroxide was employed as the alkali, the invention also contemplates the use of other alkali metal hydroxides such as potassium hydroxide. It will be apparent that in preparing treating reagents in accordance with the invention, the sol-r ubility promoter and solventizer may be added to the aqueousalkali metal hydroxide solutions in the form of alkali metal compounds or the alkali metal compounds may be formed in situ by the addition of the acidic materials to mixtures containing appropriate amounts of alkali metal hydroxide.

Treating solutions prepared in accordance with 7 this invention can be regeneratedin the same manner as aqueous alkali metal hydroxide solutions, namely, by boiling or by steam stripping and reused, either with or without adjusting the alkali concentration of the solution andwith or. without further addition of petroleumioil oxidation product and/ or solventizer therefor. While in general the data indicate that higher concentrations of free sodium hydroxide, petrol eum oil oxidation product and solventizer produce reagents having the highest extraction eiiiciencies, it is not always preferable to use the highest possible concentrations of these materials inasmuch as such solutions are frequently rather viscous and thus give rise to troublesome emulsions, thereby making it diflicult to completely and efficiently separate the treating reagent from the liquid treated.

The specific examples given areonly by way of illustration and are not intended to limit'the invention to the specific quantities disclosed or the particular petroleum oxidation product 01' solventizer named. V V

What is claimed is: a

1. In a method for removing acidic substances from otherwise neutral water-immiscible organic V fluids, the step which comprises contacting :said fluids with aqueous alkali solution containing not less than 5% by weight of free alkali metal hydroxide and at least 5% by weight of acidic petroleum oxidation products obtained by the oxidation of petroleum hydrocarbons containing from about 10 to 30 carbon atoms in the molecule.

2. The step in accordance'with claim 1 in which the acidic substances are mercaptans, the organic fluids are hydrocarbon liquids and the aqueous of solventizer for the acidic petroleum oxidation.

terials in approximately the indicated proportions by Weight:

Per cent Free sodium hydroxide 18 Alox 400 20 5. The step in accordance with claim 3 in which the aqueous solution also contains a substantial amount of a solventizer for the acidic petroleum oxidation products.

6. The step in accordance with claim 3 in which the; aqueous solution also contains a substantial amount of alkyl phenol as solventizer for the acidic petroleum oxidation products.

7. The step in accordance with claim 3 in which the alkali metal hydroxide is sodium hydroxide, the amount of free sodium hydroxide is approxirnately 7% and the amount of acidic petroleum oxidation products is approximately 40%.

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

step which comprises contacting said liquids withv aqueous solution containing not substantially less: than 5% free alkali metal hydroxida'not substantially less than 5% acidic petroleum oxidation products obtained by the oxidation of relatively high molecular weight hydrocarbons and not substantiallyless than 5% solventizer for the oxidation products.

9. The step in accordance with claim. 8 in which the solventizer is alkyl phenol.

alkali solution also contains a substantial amount 10. The step in accordance with claim 8"in which the solventizer is cresol.

11. In a method for removing Weakly acidic sulfur compounds from hydrocarbon liquids, the step which comprises contacting said liquids with aqueous solution containing not substantially less than 5 free sodium hydroxide, not substantially less than 5% acidic petroleum oxidation products obtained by the oxidation of relatively high molecular weight hydrocarbons and not substantially less than 5 alkyl phenol.

12. The step in accordance with claim 11 in which the petroleum oxidation products are Alox 800 and the alkyl phenol is cresol.

f 13. In amethod for removing weakly acidic sulfur compounds from hydrocarbon liquids, the stepwhich comprises contacting said liquids with aqueous solution containing notsubstantiallyless than.5% Iffree alkalimetal hydroxide, not substantially less'than 10%. acidic petroleum oxida- Per cent