US2316965A - Method of removing weakly acidic bodies from hydrocarbon fluids - Google Patents

Description

Patented Apr. 20, 1943 METHOD OF REMOVING WEAKLY ACIDIlC BODIES FROM HYDROGARBON FLUIDS Timothy L. McNamara, Arlington Heights, and

Lawrence M. Henderson, Winnetka, 111., assignors to The Pure Oil Company, Chicago, 111., a corporation of Ohio No Drawing. Application December 28, 1940,

Serial No. 372,204

6 Claims. (01. 196-30) This invention relates to a method and reagent for removing weakly acidic substances from water immiscible liquids and more particularly to method and reagent for removal of mercaptans and other acidic organic sulfur compounds from hydrocarbon oils.

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

It is known that the eflicacy of alkaline-reacting solutions in removing mercaptans from hydrocarbon liquids can be materially improved by adding to 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 solutizers, has proved beneficial but the amount of mercaptans removed with these reagents is not as great as is frequently desired.

It has been found that excellent results may be obtained by the use of aqueous alkali solutions containing a cheap, readily available material obtained in the course of ordinary refining operations. Such a material is acid oil which has been treated in a particular manner as hereinafter set forth, to greatly improve its properties as a solutizer. The term acid oil or acid oils as herein used refers to the oily liquid containing naphthenic and/or other acids and/or phenolic compounds, including thiophenols which is separable from alkaline wash liquors, which have been employed in the washing of petroleum oils such as petroleum distillates, particularly cracked distillates, upon acidification, the acid oils separating at the top as an oily layer. .Acidification may be effected by addition of mineral acids, acid salts, carbon dioxide or other means known to be suitable for efiecting this result. Separation of the acid oils from the aqueous layer may be facilitated by dissolving the oils in a suitable solvent such as petroleum naphtha, prior to efiecting separation.

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

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

It has been discovered that if acid oils, preferably after elimination of aliphatic mercaptans, recovered from spent alkali wash liquors which have been employed in the washing of petroleum oils are washed with substantial quantities of water subsequent to separation of the acid oils from the spent alkaline solutions, the acid oils thus obtained are excellent materials for enhancing the ability of aqueous alkali treating reagents to extract weakly acidic organic compounds, for example, mercaptans, from water immiscible liquids such as hydrocarbon oils. Furthermore, such Washed acid oils are greatly superior to the unwashed oils for this purpose. The beneficial effects of the acid oils prepared in accordance with this invention may be secured by simply dissolving the washed acid oils in the aqueous alkali solution which it is desired to use as a treating ieagent. Acid oils suitable for use in accordance with the invention are prepared by washing ordinary acid oils with substantial quantities of water, or dilute aqueous solutions the pH of which is preferably not substantially below 3 and not substantially in excess of 9. It is meant to include dilute aqueous solutions containing neutral, acid or basic materials as well as ordinary or pure water, the principal consideration being that the solutions be dilute solutions and that the pH values fall within the aforementioned range. Aqueous solutions having a pH above 9 can beused but in this case the quantity of solution must be regulated so that the resulting aqueous phase is between approximately pH 3 and 9.

As an illustration of my invention, acid oil which was obtained from spent aqueous alkali solution which had been used to Wash mixed straight run and cracked gasoline obtained from East Texas, Van Zandt, and Schuler crudes and from which the readily hydrolyzable compounds,

principally mercaptans, had been removed by steaming, was dissolved in an equivalent volume of hexane and washed with suitable proportions of aqueous washing solutions the pH value of which was varied by addition of appropriate quantities ofacids oralkalies. After the Washing operation, the acid oil solution was heated to evaporate hexane and a treating reagent prepared which contained the following materials in the indicated proportions by weight: 25% washed acid oil, 25% free sodium hydroxide and 50% water. Ten volumes of such treating reagent were used to treat 100 volumes of mercaptan containing gasoline. The results of the washin operations are shown in Table I:

1 Unwashed acid oil.

It will be noted from the results in the foregoing table that the amount of mercaptan sulfur removed from the untreated gasoline was substantially greater when treating reagents were employed containing the washed acid oil as com pared to the amount removed when using equivalent quantities of unwashed acid oil, provided that the acid oil was washed with aqueous solutions which had pH values ranging from 3.2 to 9.0. When the pH value of the washing solution was 2.5 or 1.0, the washed acid oils were either not improved or were worse than the unwashed acid oils. 7 v

It will be noted from Table I that there is a considerable difference in the efficacy of the reagent used in sample I as compared with sample 5. Different untreated-gasolines were employed on these examples and it is well known that mercaptans are much more readily extracted from some gasolines than from others. It is apparent from the data in Table I that although improved results are obtained when the pH of the washing solution is between about 3 and 9, the best results are obtained as the pH value is increased to 9 and it is preferred to use washing solutions having a pH value between approximately 7 and 9. r

In another example a reagent was prepared containing the following materials in the indicated proportions by weight: 32.2% washed acid oil, 20.6% free sodium hydroxide and 47.2% water. The washed acid oil was prepared by dissolving the unwashed acid oil in an equivalent volume of hexane, washing with 96 volumes of water the pH of which was 7.0 and subsequently removing the hexane by evaporation. Upon contacting an untreated gasoline wtih 10% by volume of the aforementioned reagent, the mercaptan sulfur content of a gasoline was reduced from 0.02459}, by weight to 0.0007%. The treated distillate was sweet to the doctor test. The application of the same amount of alkali reagent, which differed from the foregoing reagent only in that it contained unwashed instead of washed acid oil, to the same untreated gasoline, reduced the mercaptan sulfur content from 0,0245% to 0.0027%. This treated samplewas sour to the doctor test. .This clearly shows the superiority of the reagent containing the washed acid oil.

The amount of water washing solution applied equavilent volue of hexane and washed in the same manner as the samples shown in Table I is shown in Table II.

Table II Mercaptan sulfur in olumes of gasoline Mercaptan Treat N 0 wash Water sulfur per volume of acid oil remove Untreated Treated Percent Percent Percent None 0. 048 0.0110 77. l 5 0. 048 0.0096 80.0 10 O. 048 0. 0079 83. a 30 0. 048 0. 0074 84. 6 60 0. 048 0.0066 80. 2 07 048 (l. 0053 89. 0 265 0. 048 0. 0044 90.8 1 30 0. 048 0.0088 81. 0

1 Not in hexane solution.

In each treat in Table II, the weight composition of the treating reagents used were the same as those employed in the treats shown in Table I. From the results in Table II it will be seen that improved effectiveness of the acid oils was obtained by increasing the amount of substan tially neutral Water used to wash the acid oils to as high as 265 volumes per volume of acid oil. There is no definite upper limit to the amountof water to be used, but from a practical standpoint and a consideration of mechanical losses usually involved in water washing, operations, it appears undesirable to use water substantially'in excess of 200 volumes per volumeof acid oil. In general, smaller ratios of wash water to acid oil are required to effect a giVen improvement in the washed acid oil as the pH of the wash water is increased to approximately 9. Most effective results with Wash water of approximately 7 pH were'obta'ined when over 60 volumes of water were used, although substantial improvement was effected with as little as 5 volumes of water. With washing solutions of higher alkalinity, smaller volumes will be found effective. 7

It will be noted that in all of the examples set forth in Table II with the exception of samples, the acidloil was Washed in hexane solution. As shown by the results in sample 8, it is not necessary that the acid oils be in hexane solutionQalthough ithas been found that improved acid oils are obtained, more rapid settling effected and mechanical losses reduced when the acid oils are Washedin. a substantially non-viscous water immiscible solvent. 5 v. f

Regeneration of alkali treating reagents prepared in accordance with this invention may be readily effected by steaming. or boiling after such reagents have been used in the treatment "of the water-immiscible liquids to remove-readily hydrolyzable organic acidic compounds such as mercaptans. Where the. hydrocarbon or other water-immiscible liquid contains hydrogen sulfide it should be pre-treated with chemicals such as lime, potassium phosphate, sodium carbonate, alkylolamines or sodium hydroxide since hydrogen sulfide interferes with the regeneration of the treating agent. After removal from the crackeddistillateor other liquid to be treated,

' of nonhydrolyzable acidic compounds or comproducts with the alkaline treating reagent, such as hydrogen sulfide, the weakly acidic compounds which form hydrolyzable reaction products with the alkaline treating reagent are then extracted by simply contacting. in continuous counter current or batch operation in the absence of air or other oxidizing medium, the liquid to be treated with the treating reagent and then separating the treated water-immiscible liquid layer and alkaline reagent layer containing the acidic reaction products. The'treating reagent containing the reaction products is then steamed to decompose the hydrolyzable products and the products of the decomposition are removed as vapor. Acid oils suitable for use in the invention may be obtained from used alkali solutions, especially sodium or potassium hydroxide which have been used for washing straight run and cracked distillates containing acidic bodies other than or in addition to aliphatic mercaptans, by appropriate treatment thereof to remove aliphatic mercaptans, such as steaming, followed by acidification with flue gases or other acidic materials as hereinbefore described.

Alkaline treating reagents useful in this invention comprise solutions preferably aqueous solutions although alcohol solutions of alkali metal hydroxide containing dissolved washed acid oils may be used. The reagents may contain in addition, other materials known to enhance the extraction of Weakly acidic organic compounds from water-immiscible liquids. The concentrations of aqueous alkali solutions which may be used are subject to wide variation, the only requisites being that the acid oil be soluble therein and that the resultant solution have the abilit to extract weakly acidic compounds from waterimmiscible liquids. Concentrations of about to 40% by weight of free alkali metal hydroxide may be employed although best results have been obtained when the concentration is above In referring to the concentration of alkali in the treating reagents throughout this specification and in the appended claims it is intended that free alkali, shall refer to that alkali over and above the amount required to neutralize the acid oil present in the reagents. The alkali content of the reagent as thus defined may be readily determined by titration with inorganic acid to a phenolphthalein end point. The amount of acid oil incorporated in such aqueous alkali metal hydroxide solutions may also vary between wide limits up to the limit of solubility of the particular acid oil employed. Best results are obtained when the concentration is at least 15% by weight and not in excess of that amount which is soluble in the particular alkaline solution.

It will be apparent that the washed acid oils may be added to the alkaline solutions as such or as the alkali compounds thereof since they react with alkali solution to form alkali compounds.

What is claimed is:

1. The method of removing weakly acidic bodies from hydrocarbon fluids which comprises contacting said fluids with aqueous alkali metal hydroxide solution containing reaction products of alkali metal hydroxide and acid oil which has been washed with at least 5 times its volume of water, in an amount sufficient to enhance the ability of the solution to remove acidic bodies from said fluid.

2. The method in accordance with claim 1 in which the solution contains in excess of 10% by weight of free alkali and at least 1 5% by weight of acid oil.

3. The method in accordance with claim 1 in which the acid oil is washed with from 5 to 200 volumes of water.

4. The method in accordance with claim 1 in which the acid oil is washed with from 5 to 200 volumes of water in the presence of a waterimmiscible diluent.

5. The method of removing mercaptans from hydrocarbon distillates which comprises contacting said distillates with aqueous alkali metal hydroxide solution containing from 5 to 40% by weight of free alkali and at least 15% of acid oil which has been washed with from 5 to 200 volumes of water.

6. Method in accordance with claim 5 in which the acid oil is washed with over vol umes of water.

TIMOTHY L. McNAMARA. LAWRENCE M. HENDERSON.