US2255417A - Process for refining hydrocarbons - Google Patents

Description

' troleum distillates. I

sweetening of sour distillates, that is, the re- Patentecl SepL 9, 1941 PROCE SS FOR REFININ G HY DBO CARBONS Carleton Ellis, Montclair, Thomas C. Whitner, Elizabeth, and Wilbur V. Keegan, West New 'York, N. 1., assignors to Standard Oil Development Company, a corporation of Delaware No Drawing.

I 8 Claims.

This invention relates to the refining of pe- It pertains especially to the moval or elimination of mercaptans from various petroleum fractions. volves' decreasing the sulphur content of petroleum distillates simultaneously with the sweetening operation.

Petroleum fractions, particularly those resulting from the distillation'of high-sulphur crude oils, ,contain dissolved sulphur compounds in greater or lesser proportions. These compounds include not only the simpler forms such as hydrogen sulphide and even elemental sulphur, but also more complex varieties such as mercaptans, dialkyl disulphides, thioethers, and the like. Hydrogen sulphide and certain low-boiling mercaptans, such as ethyl mercaptan, may beextracted from the distillate at hand with an aqueous solution of sodium hydroxide, potassium hydroxide, sodium carbonate, or other alkaline substances. At the same time elemental sulphur, at least in part, is removed also from the petroleum hydrocarbons undergoing treatment. Such an operation, however, does not always completely eliminate mercaptans, particularly those of relatively high boiling points, and as a consequence the liquid hydrocarbons may possess an extremely disagreeable and obnoxious odor. v

In instances when the distillate contains an unusually large proportion of sulphur compounds (equivalent, for example, to 0.3 or 0.5 per cent of sulphur, or even higher), after the alkali extraction, treatment with sulphuric acid may be employed to effect additional removal of sulphur compounds. Afterwards the distillate is washedsuccessively with dilute aqueous alkali and with water, and then distilled. Even after these operations a sour (or mercaptan-containing) fraction is often secured.

' Many procedures have been developed for the removal or elimination of mercaptans. These include subjecting the sour distillate to the action of aqueous sodium. plumbite (or the socalled doctor solution) or an ammoniacal solution of a copper -salt, whereby the mercaptans are converted. into oil-soluble lead or copper mercaptides, respectively. Addition of elemental sulphur to a distillate containing such This invention also in- Application December 3, 1938, Serial No. 243,766

hydrogen chloride or alkali chlorides) whereby the cupric-salt is reduced to the cuprous state, and mercaptans are oxidized to dialkyl disulphides. Other agents which may be used to efiect transformation of mercaptans to dialkyl disulphides are oxygen, ozone, potassium dichromate or permanganate, hydrogen peroxide, and the like.

- This invention comprises a method of sweetening sour petroleum distillates by treatment'of such distillates, after conversion of mercaptans to metallic mercaptides, with salts of halogenated carboxylic acids. It also involves an appreciable reduction in the sulphur content of distillates possessing a relatively large proportion of mercaptans. It also includes the use of such salts either in the solid state or when dissolved either in water or in a non-aqueous medium.

One method of effecting sweetening, according i to this invention, consists in subjecting the sour distillate to the action of an aqueous sodium plumbite or an ammonical aqueous solution of a. copper salt whereby the mercaptans (dissolved in the distillate) are converted into lead or copper mercaptides, respectively. The leaded or coppered petroleum fraction is treated afterwards with aqueous solution of an alkali, or other water-soluble salt of a halogenated earboxylic acid. Preferably the latter operation is carried out at atmospheric temperature and-without the application of heat. It is observed that inmany instances such an operation yields distillates which are sweet (1. e.,, mercaptan-free) and contain no dissolved metallic compounds.

As just indicated, sweetening operations according to this invention are efiected preferably at atmospheric temperature. 'This condition is important, since it is well known that on being subjected to the application of substantial external heating, lead as well as other metallic mercaptides are decomposed into the correspondmetallic mercaptides effects precipitation of the mg metallic sulphide and thioether. In the case of petroleum distillates containing dissolved metallic mercaptides, heating would result, of course, in the distillate becoming sweet (or mercaptanfree) and a portion of the sulphur being removed as load sulphide. In'this invention it is proposed to secure sweetening and also reduction in sulphur content by treatment of distillates containing dissolved metallic mercaptides with salts of halogenated carboxylic acids unaccompanied 'by thermal decomposition of such metallic mercaptides to metallic sulphides and thioethers.

The above described procedure has been found .be overcome by the following procedure.

to work well in the case of halogenated carboxylic acids of relatively low molecular weights, as,

for example, chloroor bromoacetic acid. When halogenated acids are employed which have a relatively large number of carbon atoms in the molecule, say, 10, 12, 14 or more, their watersoluble salts are soaps and considerable difilculty, due to foaming or emulsifying of the oil and water layers, may be experienced. However, it was observed that such difficulties could The requisite quantity of soap of the halogenated 'carboxylic acid is. dissolved in a small proportion of a solvent (e. g., ethyl or isopro- -py1 alcohol) which exhibits an appreciable solubility in the hydrocarbon liquid undergoing treatment. This solution then is added to the distillate containing dissolved metallic mercaptides. Such an operation results in the formation of a finely-divided, slowly-settling suspension of soap in the distillate. Although clear, homogeneous solutions of alkali soaps in hydrocarbons may be secured by employing a sufficiently large proportion of liquid which is a solvent for both soap and hydrocarbon, nevertheless in the preferred methodof treating, this condition is avoided since it involves separation afterwards of relatively large quantities of solvent from the sweetened distillate. It is preferable also that the alcohol, or other solvent, be sufficiently anhydrous to permit its complete miscibility with the petroleum distillate and to avoid formation of two liquid layers.

After interaction is complete between the alkali soap of the halogenated carboxylic acid and the metallic mercaptides, all insoluble or precipitated material may be removed by filtration, decantation or other convenient means. The filtrate then is washed with water to eliminate dissolved alcohol and very finely suspended alkali soap. This latter operation should be done with minimum agitation or stirring, otherwise troublesome emulsions may be encountered. One method. of water washing comprises spraying water into a body of distillate and allowing the droplets to travel slowly downwards through the oily liquid, and eventually to coalesce and to form a liquid aqueous layer; The latter may be withdrawn as necessary.

As previously mentioned, either aqueous solution of alkali or other water-soluble salts of halogenated carboxylic acids-as well as suspensions' (or solutions) in substantially non-aqueous media are suitable as sweeting agents. However, it has been noted also that such alkali salts as well as corresponding heavy metal salts are equally applicable as sweeting agents when employed in the solid state. In some instances the distillate containing dissolved metallic mercaptides may be; agitated vigorously with a finely ground portion of the salt until interaction between the latterand the metallic mercaptides is complete. In other cases probably a more convenient method comprises filtration of the distillate (containing, for example, dissolved lead or copper mercaptides) through one or more beds of the salt. oftentimes, when the latter operation is employed, it is advisable to admix the salt with an inert materialsuch as sand, since in this manner flow of the liquid through the solid mass can be expedited.

portion of the latter appeared to depend upon the quantity of mercaptans present originally in the sour distillate and upon the molecular weight of the halogenated carboxylic acid. As a general rule the larger the proportion of mercaptans in the sour distillate and the larger the molecular weight of the halogenated carboxylic acid employed, then the greater was the quantity of soluble metallic compounds in the sweetened petroleum fraction. These metallic compounds failed to respond to tests for metallic mercaptides and in some instances appeared to exhibit soap-like characteristics or to yield corresponding alkali derivatives which possessed emulsifying properties. For purpose f differentiation these metallic compounds are designated hereinafter as metallic or heavy metal soaps.

The removal of these heavy metal soaps may be accomplished by any one of several methods. For example, if the sweetened distillate containing these compounds'is stored for several days, it is found that a precipitate slowly forms, and when removed (e. g., by filtration), a hydrocarbon liquid free of metallic soaps is secured.

.Precipitation may be accelerated by exposure of the distillate to light. In other instances washing the metallic soap-containing distillate with an equeous solution of a salt which will react with the soap to form an insoluble heavy-metal compound has proven effective. Hence, if lead soaps are present, the distillate may be treated with an aqueous solution f sodium sulphate, thus giving rise to the formation of lead sulphate (insoluble) and sodium soaps (soluble in water). Preferably, however, aqueous solutions of "alkalineearth salts of an inorganic nature (e. g., calcium chloride or magnesium sulphate) are employed, since these give rise to the formation of heavy metal salts and alkaline-earth soaps, both of which are substantially insoluble in water and in I the distillate.

ahalog enated carboxylic acid, then any copper soaps remaining dissolved in the distillate can be removed by treatment with aqueous ammonia.

In place of aqueous ammonia however, liquid ammonia may be employed. In other instances derivatives of ammonia, such as the ethanolamines or methylamine, either in aqueous solution or in an anhydrous (or substantially so) condition may be equally eflicacious.

The following examples will illustrate this invention. In each instance the distillate before An unexpected observation was that in some instances the sweetened distillate obtained by treatment was washed 'with a dilute aqueous solution of alkali to remove any dissolved hydrogen sulphide. The following tests were applied to the distillate after it had been subjected to a particular sweetening treatment: (1) To a sample of the hydrocarbon liquid are added a few milligrams of elemental sulphur. The development of a precipitate was taken to indicate-the presence of metallic mercaptides. (2) If no metallic mercaptides were found, a few cubic centimeters of aqueous sodium plumbite were added to the same sample and the mixture shaken vigorously for a few seconds. In this instance if no precipitate was formed, it was concluded that mercaptans were not present. (3') If the two preceding tests were negative (1. e., no evidence 'chloroacetate and sand.

2,255,417 obtained for 'the presence of either dissolved metallic mercaptides or free mercaptans), then another, portion of the treated distillate was subjected to the action of hydrogen sulphide. If a precipitate was secured; this was taken as evidence for the presence of dissolved metallic soaps.

Example 1 A sour petroleum distillate (boiling from 204 to 300 C.) was treated with suflicient aqueous sodium plumbite solution to convert the mercaptans into lead mercaptides. Forty volumes of the distillate containing dissolved lead mercaptides were agitated for 6 hours at 25 to 28 C. with 25 volumes of an aqueous solution (1 molar concentration) of sodium bromoacetate.

At the end of this period the hydrocarbon layer was separated from the aqueous solution. The distillate then gave negative tests for the presence of mercaptans, lead mercaptides and lead soaps.

Example 2 Seventy volumes of the distillate employed in Example 1, after treatment with sodium plumbite, were vigorously agitated with 45 volumes' of aqueous sodium chloroacetate molar concentration) fOr 7.5 hours. Afterwards the mixture was allowed to stand overnight and the hydrocarbon layer then withdrawn. The distillate in this instance also gave negative tests for mercaptans, lead mercaptides and lead soaps.

Example 3 One hundred parts of a sour kerosene fraction,

obtained on the cracking of a West Texas gas oil, after treatment with aqueous sodium plumbite solution, were agitated for 15 hours with 25 parts of solid lead chloroacetate. The treated kerosene fraction gave negative tests for mer-.

captans, lead mercaptides and lead soaps.

Example 4 Thesour kerosene distillate in Example 3 'contained 0.710 per cent of sulphur. After being sweetened with the aid of lead'chloroacetate its sulphur content was 0.664 per cent.

Example 5 A sour gasoline fraction of a cracked distillate was leaded (i. e., treated with aqueous sodium plumbite to change the mercaptans into oil-soluble lead mercaptides) and afterwards filtered slowly through six short columns connected in series and filled with a mixture of solid lead In this instance the ratio by. weight of lead salts to sand was 1:2.

.The first portion of filtrate was sour but lead free. After a short time, however, the efllux liquid became lead-free and sweet. Before the filtering operation was stopped suillcient gasoline had been conducted through the apparatus to give a yield of 210 partsot sweetened product to 36 parts of lead chloroacetate. At the time filtration was discontinued the capacity of the lead chloroacetate to sweeten sour distillates apparently had not been exhausted.

Example 6 The sour gasoline fraction used in Example 5 contained 0.290 per cent sulphur. As a result of the sweetening operation the sulphur content decreased to 0.255.

' fraction was sweetened, i. e., gave no tests for hours.

Example 7 About 1 part by-weight of solid sodium monochloroacetate was added to parts by weight of coppered gasoline (i. e., sourgasoline previously treated with an aqueous ammoniacal solution of a cupric salt to change mercaptans into oil-soluble copper mercaptides). The mixture was allowed to stand for three hours with occasional shaking. At the end of this time 0.8 part more of the monochloroacetate was added, and the mixture vigorously agitated. At the end of five hours the gasoline gave negative tests for mercaptans andcopper mercaptides, but a positive test for copper soaps. The latter were extracted from the gasoline with concentrated aqueous ammonia.

' Example 8 One part of B-bromohydrocinnamic acid was dissolved in about 15 parts of alcohol and to Example 9 The potassium salt of o-chlorobenzoic acid was prepared by dissolving the acid in a smallquantity of alcohol and neutralizing the solution with alcoholic potassium hydroxide. The salt which precipitated during this operation was,

Ireed of adhering liquid by filtration and-then dried. About 1 part by weight of the potassium salt .was added to coppered gasoline and the mixture vigorously agitated until the petroleum mercaptans or for metallic mercaptides.

Indications were secured that a small proportion of copper soaps were dissolved in the sweetened gasoline. These soaps could be removed by extraction with aqueous ammonia.

Example 10 To an alcoholic solution containing 2 parts (by weight) of dibromoleic acid was added suificient alcoholic potassium hydroxide to effect neutralization of the acid. This solution of potassium dibromoleate' was added to 100 parts of leaded gasoline and the mixture allowed to stand for Y several hours, during which time some material slowly precipitated. When a small sample of the gasoline failed to give positive tests for mercaptans or for lead mercaptides, the precipitated material was separated from the main body of liquid hydrocarbons by filtration. The filtrate did contain dissolved lead soaps as indicated by test with hydrogen sulphide.

"Example 11 Sweetened gasoline, as prepared in Example 10, which contained dissolved lead soaps and probably also some alkali soaps of dibromoleic acid'was washed with several portions of a 5 per cent aqueous solution of calcium chloride. After separation from the aqueous layer and precipitated material, the hydrocarbon material then failed to respond to tests for the presence of dissolved soaps.

I a non-aqueous liquid.

Example 12 Sweetened gasoline, obtained by the procedure described in Example 10, was placed in a' tall upright cylindrical container, having the upper Example 13 A sample of sour gasoline was treated with aqueous sodium plumbite and the resulting hydrocarbon liquid containing dissolved lead mercapitides was sweetened, as described in Example 10, and afterwards washed with water as indicated inExample 12. The product was free of mercaptans and of lead mercaptides, but contained some dissolved lead soaps. On exposure of the sweetened distillate to sunlight some insoluble material .slowly precipitated. When the latter was removed by filtration, a sweetened gasoline which gave no tests for lead soaps was secured.

Example 14 Coppered sour gasoline was sweetened by agitation with solid sodium dichloroacetate. The product was free of mercaptans and copper mercaptides but did contain dissolved copper On exposure of a sample of this sweetened gasoline to sunlight, it slowly assumed a green color and then a precipitate formed (accompanied by disappearance of the green color). Afterwards the insoluble material was removed by filtration. The gasoline was then found to be free of copper soaps. I

Elimination of copper soaps could be effected also by storing the sweetened sample in the absence of light, though in this instance the time required was considerably longer.

Summarizing, this invention comprises sweetening a sour petroleum distillate, in which the mercaptans are present as metallic mercaptides, by treatment with a salt of a halogenated carboxylic acid. The salt may be employed in the solid state or in solution either in water or in Treatment is effected preferably at atmospheric temperature and substantially without the application of heat, thus avoiding any thermal decomposition of the metallic mercaptides. This invention also involves a reduction in sulphur content of the distillate simultaneously with the sweetening operation.

, In those instances in which sweetening of the tution derivatives of ammonia, such as ethanolamines, methylamine, ethylene diamine and the like. Still another operation fo the elimination of metallic soapsfrom distillates sweetened according to this invention is subjection of the mercaptanand mercaDtide-free hydrocarbon liquid to the action of sunlight.

1.'The process of refining a-petroleum distillate containing copper mercaptides which comprises treating said distillate in liquid phase with a saltof a halogenated mono-carboxylic acid to convert said merca'ptidesinto copper soaps, and treating said distillate with an alka line compound selected from the group consisttides in liquid phase with a salt of a halogenated mono-carboxylic acid, reacting said salt with the mercaptides to form oil-insoluble derivatives, and removing said derivatives from the oil.

8. In a process of refining liquid hydrocarbons wherein mercaptans have been converted into mercaptides of a heavy metal, the steps comprising treating the hydrocarbons containing the mercaptides of a heavy metal in liquid phase with a salt of a halogenated mono-carboxylic 'acid to yield decomposition derivatives of said 35 mercaptides and of said salt at a temperature sufiiciently low to avoid substantial thermal decomposition of the mercaptides, and removing said derivatives from the liquid hydrocarbons until the liquid hydrocarbons :are substantially free of the mercaptides.

4. A process as described in claim 3, wherein the heavy metal of said mercaptides is selected from .the class consisting of copper and. lead.

5. In a process for sweetening a petroleum distillate containing mercaptans and reducing the sulfur content of the distillate, the steps comprising converting a substantial proportion of the mercaptans into mercaptides of a heavy 'metal which remain dispersed in the distillate,

adding to the distillate a salt of a halogenated mono-carboxylic acid, reacting said salt with said mercaptides dispersed in the distillate while maintaining the distillate in liquid phase and at a temperature sufficiently low to prevent substantial thermal decomposition of the mercaptides, then removing metal derivatives formed by said reaction from the liquid distillate.

6. The process for sweetening a sour petroleum distillate containing mercaptans, which comprises converting the mercaptans into heavy metal mercaptides which remain in the distillate, adding to the distillate containing said mercaptides, a salt of a halogenated mono-carboxylic acid in alcoholic solution, reacting said salt with said mercaptides in the distillate while maintaining the distillate in liquid phase at a temperature sumciently low to prevent substantial thermal decomposition of the mercaptides, separating from the liquid distillate insoluble and precipitated compounds formed by the reaction, and extracting alcohol and salt from the distillate with water. V

7. A process for'reducing the sulfur content of a petroleum distillate containing mercaptans,

which comprises converting said mercaptans into.

copper mercaptides, treating the distillate con-' lead mercaptides, treating the distillate containing the lead mercaptides in liquid phase with a salt of a halogenated mono-carboxylic acid at a temperature suiiiciently low to prevent thermal decomposition of the mercaptides to convert the mercaptides and salt into insoluble soaps and insoluble lead salts, and removing said insoluble soaps and'salts from the distillate.

8. A process for reducing the sulfur content of a petroleum distillate containing mercaptans,

which comprises converting said mercaptans into taining said mercaptides in liquid phase with a salt of a halogenated mono-carboxylic acid at a temperature sufiiciently low to prevent substan-