US2189850A - Process for refining petroleum distillates - Google Patents

Description

Patented Feb. 13, 1940 DIST Thomas C. Whitner, Jr.,

Elizabeth, N. J., assignor to Standard Oil Development Company, a corporation of Delaware No Drawing. Application March 6, i937,

Serial N0.-129,353

11 Claims.

This invention relates to the refining of petroleum distillates and particularly to sour dis-- tillates, i. e., those distillates which contain dissolved mercaptans. It also involves the sweeten ing of such dlstillates by the removal of mer captans in the form of complex salts of heavy metals.

Mercaptans, which are organic sulphur-containing compounds characterized by possessing one or more --SH groups per molecule, are especially objectionable in petroleum distlllates because of their highly disagreeable odors and theircorrosive action on metals. Metal containers, for example, may be unduly corroded when 5 such distillates are stored in them for considerable periods of time. Likewise, sour distillates when employed as fuels, e. g., gasoline, for internal combustion engines, may effect corrosion of the fuel tank, feed lines, or engine parts with which the come in contact. Furthermore, in addition to their objectionable odor (even when present in small proportions) mercaptans are catalysts for gum formation, particularly in cracked gasolines. When the latter are emdeposited on various parts of the engine, for illustration, on the intake manifold or intake valves of the engine. In the case of intake valves delayed seating may result,'thus giving rise to imperfect operation of the engine.

One method for the elimination of ercaptans (i. e., the sweetening of sour distilla es) comprises agitating the sour distillate with sodium plumbite (doctor) solution thus forming lead mercaptides which are for themost part soluble in the oil. The addition of elemental sulphur to the distillate then results in the lead mercaptides being converted into lead sulphide, which is insoluble in the distillate, and organic disulphide which remain dissolved in the oil. The lead sulphide can be removed by decanta- I tion or filtration of the distillate or by any other convenient means. The presence of the latter type organic sulphur-containing compounds (disulphldes), because of their much less disagreeable odor and decreased corrosive action, is not as objectionable as that of mercaptans.

When an aqueous ammoniacal solution of a copper salt is used in the above described sweet-- ening operation instead of sodium plumbite, the

products are insoluble copper sulphide and solu- J ble organic disluphides.

Still another procedure whereby mercaptans may be converted to disulphides consists in'heat- 5 ing the sour distillate with an aqueous hydroployed as fuels for automobiles the gum may be chloric acid solution of cupric chloride. In this instance the cupric chloride is reduced to cuprous chloride and themercaptans are oxidized to disulphides. Hydrogen chloride, which is formed also during the operation, is dissolved in the J water present.

From the foregoing, it will be noted that the usual refining procedures for the elimination of mercaptans in sour petroleum di'stillates, i. e., sweetening of petroleum distillates, consists in converting mercaptans to the corresponding disulphides which remain dissolved in the oil. I have found that sweetening of sour petroleum distillates may be accomplished by converting mercaptans to the corresponding oil-soluble copper mercaptides and extracting these from the distillate, presumably in the form of complex ammonio copper derivatives. By the term petroleum is meant not only straight-run distillates, obtained by distillation of crude petroleum,

butalso cracked distillates, shale oil distillates,

and the like.

I employ an alkyl derivative of ammonia as an extracting agent which is insoluble or only slightly soluble in petroleum hydrocarbons, examples of such alkyl amino compounds being ethanolamine and ethylene diamine. Preferably also these amino compounds are anhydrous or substantially so. If aqueous solutions of such are employed, water should be present in minor proportions as its presence reduces the solubility of copper mercaptides in the alkyl amino derivatives and consequently greatly decreases their efficiency as extracting media.

One procedure whereby I may sweeten sour petroleum distillates is as follows: The distillate is agitated first with an aqueous ammoniacal solution of cupric sulphate. This solution may be prepared by dissolving cupric sulphate in water,

adding aqueous ammonia to precipitate cupric hydroxide and continuing the addition of am moniauntil the precipitate is redissolved. Or the cupric hydroxide may be precipitated from the aqueous solution by other alkali, e.'g., sodium hy-,-

droxide, and then redissolved bylmeans of aque-,

- copper may be used in place of the sulphate.

Treatment of sour distillates with the ammoniacal cupric sulphate solution converts the mercaptans to copper mercaptides, the presence of thexlatter being indicated by the distillate becoming yellow in color. This is particularly noticeable with light colored oils. Also, the depth of color is greater as the proportion of mercaptans originally present in the oil is increased. The petroleum oil is then agitated with the alkyl' amino derivative, for example, ethanolamine, extraction of they copper mercaptides being indicated by the disappearance of the yellow color of the oil layer (in the case of light colored dis tillates) and the change in color from light straw-yellow,'or almost white, to a deep blue of the amino layer.. The development of this blue color which is characteristic of ammonio copper/compounds, e. g., (NHanCu may be attributed in this instance to the formation of a similar alkyl amino complex, i. e.,

and separation of the mixture into oil and amino layers, the latter can be withdrawn, additional copper salt dissolved in it (if necessary), and the amino solution again used for the conversion of mercaptans in other portions of sour distillates to copper mercaptides. Extraction of copper mercaptides with alkyl amino derivatives may then be effected as described above.

Another variation comprises treating a sour petroleum fraction, e. g., gasoline or kerosene,

with a solution of the copper salt in either 'aqueous ammonia or the alkyl amino derivative and after separation of the solution subjecting the petroleum hydrocarbons (containing dissolved copper mercaptides) to distillation under subatmospheric pressure. In this manner a portion of the petroleum'fraction can be taken overhead and a sweet distillate obtained. The liquid residue in the still is then cooled and the dissolved copper mercaptides extracted as described above. In such an operation care must be exercised to maintain the temperature of the liquid in the still below that at which decomposition of copper mercaptides occur. If desired' distillation may be effected in the presence of an inert gas, e. g., steam.

Sour petroleum distillates generally, if not always, contain a greater or lesser proportion of dissolved hydrogen sulphide. As this compound (hydrogen sulphide) reacts readily with the aqueous ammoniacal solution of cupric sulphate, or other copper salts, to form insoluble copper sulphide it should be removed prior to the sweetening operation. This removal can be accomplished by washing the distillate with a dilute aqueous solution of alkali, e. g., sodium carbonate or hydroxide.

The quantity of amino compounds required for extraction of the copper mercaptides depends to a; large extent upon the proportion of mercaptans originally present in the sour oil. With some oils the volume of alkyl amino derivative need be only 10 per cent that of the volume of oil being extracted. In other instances 25 per cent by volume is suflicient. On the other hand,

some oils may contain iinitially such a high procoming deep yellow in color.

portion of mercaptan that two ormore extractions with the alkyl amino compound may be necessary before. complete removal of the coparation of a portion of dissolved oil and/ or other dissolved water-insoluble material. After removal of the latter, the diluted extracting agent may be subjected to fractional distillation.

Instead of recovering the extracting agent by distillation, as previously mentioned, recovery may be accomplished by heating the spent agent to a temperature sufiicient to effect decomposition of the dissolved copper compounds, probably to copper sulphide and thioethers. The insoluble copper compounds thus formed are removed "by filtration. If present in sufficient quantity, the thioethers or other liquids (resulting from the decomposition of copper mercaptides) insolublein extracting agent may form a separate layer and be removed, for example, by decantation. Often the temperature required for decomposition of the copper mercaptides is much lower than that necessary to effect separation of the extracting agent and dissolved copper compounds by distillation. Any decomposition of the extracting agent, due to heating to a high temperature, and subsequent loss in efficiency may thereby be lessened considerably.

The following examples will illustrate my invention. In each instance the distillate, prior to treatment, was washed with dilute alkali to effect removal of dissolved hydrogen sulphide.

Example 1.Sour gasoline was agitated with aqueous ammoniacal cupric sulphate solution until the mercaptans were converted to copper mercaptides. This operation resulted in the gasoline, which was originally almost colorless, be-

The mixture was allowed to settle whereby separation into two layers occurred. The oil layer was withdrawn and agitated with 10 per cent by volume of ethanolamine. After standing for some time the mixture formed two layers, an almost colorless gasoline layer, and a deep blue amine layer. The gasoline and amine layers were then separated. The gasoline layer gave no test for mercaptans when treated with sodium plumbite (doctor) solution.

Example 2.-A portion of the gasoline from Example 1 after agitation with aqueous ammoni acal cupric sulphate solution was treated with hydrogen sulphide, and the precipitated copper was treated with hydrogen sulphide and the precipitated copper sulphide filtered, washed, dried and weighed. In this instance 100 cc. of gasoline yielded 2 mg of copper sulphide.

extraction step was about 25 per cent of that of the gasoline. After separation of the deep M blue colored amine layer, the gasoline gave no test for copper (on treatmentwlth hydrogen sulphide) or for mercaptans (with doctor solution).

Example 4.--'Ihe mercaptans in sour gasoline were converted to the copper mercaptides by aqueous ammoniacal cupric sulphate, as de-' scribed in Example 1. The gasoline was. then agitated twice with small portions of ethanolamine. At the end of the second operation the gasoline gave a negative test for mercaptans (with sodium plumbite solution) but a slight test for copper (with hydrogen sulphide). A third extraction with ethanolamine removed the last traces of copper from the gasoline.

Example 5.sour Diesel fuel, prepared by the distillation of Colombian crude oil, was treated asdescribed ln Example 1 with ammoniacal cupric sulphate solution and ethanolamine.

The resulting all gave a negative test for mercaptans (with doctor solution) and only a slight test for copper (with hydrogen sulphide).

Example 6'.-'Finely ground cupric sulphate was thoroughly mixed with ethanolamlne until a saturated solution of the salt in the amine was obtained. Undissolved material was. removed by filtration. The deep blue colored amine solution of the copper salt was agitated with sour gasoline to convert the mercaptans to copper mercaptides. 'Ihe gasoline containing dissolved copper. mercaptides was .then extracted with ethanolamlne captides.

Example 7.The ethanolamine solution of copper sulphate, from Example 6, after agitation with sour gasoline was withdrawn, again saturated with cuprlc sulphate, as described in Example 6, and again employed to convert mercaptans in sour gasoline to copper mercaptides.

Example 8.-Ethanolamine after being employed as an extracting agent for copper mercaptides, as described in Example 1, was subjected to distillation at atmospheric pressure to separate it from dissolved copper compounds.

The distillate was pale yeldow in color.

Example 9.-'-Sour gasoline was treated with aqueous ammoniacal cupric' sulphate, as described in Example 1 and then extracted three tlm with ethanolamine which proportion of amine employed fpr each extraction was 1 0 per cent by volume. After treat-' ment, the gasoline gave a negative test for mercaptans and only a very slight test .for copperi Example 10.--A sample of ethanolamlne which was dark blue in color, and which had been em- At the end oi; this period the liquid was filtered through, paper to remove suspended material.

.The filtrate so-obtained was-a transparent liquid having a very light blue' color. This filtrate was t8 ehect removal oi'copper merg was recoveredby distillation as described in Example 8. The

. v 3 used to extract copper mercaptides from gasoline. as described in Example 1.

Example 11.Two hundred volumes of sour gasoline were treated with aqueous ammoniacal cupric sulphate solution as described in Example 1. The coppered distillate (i; e., distillate containing dissolved copper mercaptides) was then distilled. In this latter operation, the pressure was maintained at to mm. of mercury and the temperature of the liquid in thestill was not allowed to exceed 60 C. Seventy volumes, or 35 per cent, were taken overhead. The distillate so obtained gave no test for mercaptans or copper.

The residual liquid in the still, or still bot-,

toms, was then cooled and extracted with 5 per cent by volume of ethanolamine to remove dissolved copper mercaptides The resulting prodnot also gave negative tests for the presence of mercaptans or copper 'mercaptides.

head'distillate to give a sweetened gasoline.

Example 12.One hundred and fifty volumes of sour kerosene, after treatment with aqueous ammoniacal cupric sulphate, were distilled. In this instance the pressure was maintained at 40 to 315 mm. of mercury and the temperature of the liquid in the still was not allowed to exceed 100 C. Twenty-two and one-half volumes, or

'15 per cent, were ,taken overhead. The still bottoms, after cooling, were extracted with 5 per cent by volume! of ethanolamine to remove copper mercaptides. Both the overhead product and the still bottoms (after extraction) gave negative tests for mercaptans and copper mer-.

captides. The two fractions were blended to give a sweetened kerosene.

Example 13.- -One hundred and thirty volumes of sour kerosene were treated with aqueous ammoniacal cuprlc sulphate .solution, to convert the mercaptans into oil-soluble copper mercaptides. The coppered kerosene was then subjected to steam distillation, the pressure being maintained at to mm. of mercury and the temperature of the liquid in still at 55 to 60 C. Twenty-six volumes, or 20 per cent, were taken overhead. The still bottoms, after cooling to These-- sweetened bottoms were blended with the overatmospheric temperature, were extracted with ethanolamine; Both the overhead distillate and the extracted bottoms failed to react with the doctor solution or give a test for copper with hydrogen sulphide. 'These two fractions were blended to v ive a sweetened kerosene.

From the foregoing it will be seen that my invention contemplates the substantial removal of mercaptans from sour petroleum distillates. This removal is accomplished by converting the 'mercaptans to their corresponding oil-soluble copper mercaptides and then extracting'these copper compounds as complex amino derivatives. Also my invention eliminates the necessity of using elemental sulphur inothe sweetening operation 'as is required in the ,usual plumbite (doctor) sweetening operation for the precipitation of lead as lead sulphide, or for the precipitation oi} copper as copper sulphide when ammoniacal copper solutions are employed. In both of these latter operations extremely careful regulation of the quantity of elemental sulphur employed is necessary otherwise the sweetened gasoline will be rendered corrosive to metals. Furthermore, the usual sweetening operations involve the conversion of mercaptans to disulphides; the'latter remaining dissolved in the gasoline, or other petroleum distillate. As the Y presence of disulphide is known to reduce the -sensitiveness of gasolines to antiknock agents,

sessing one or more hydroxyl groups in the molecule. The latter type, often called alkylol amines, are exemplified by monoethanolamine (or simply ethanolamine), HOC2H4NH2, and triethanolamine, (HC2H4) 3N. Preferably I employ those alkyl derivatives of ammonia which'react quickly with the oil-soluble mercaptides to form complex amino copper compounds insoluble in the oil but readily soluble in the extracting agent. To illustrate, copper mercaptides dissolved in oil are slowly extracted by agitating the oil with triethanolamine- This is indicated by the slow change in color of the triethanolamine layer from a light yellow to a greenish-blue. To secure substantially complete extraction with this liquid, however, is time-consuming On the other hand, ethanolamine (monoethanolamine) quickly extracts copper mercaptides from oils, as indicated by. the very rapid change in color, of the ethanolamine layer to a deep blue.

My' invention, therefore, involves the sweetening of sour petroleum distillates containing mercaptans by reacting on the mercaptans to form soluble copper mercaptides and the extracting these. copper mercaptides from the oil by means of a selective solvent. It also comprises distilling the coppered distillate (i.e., dis- 'disulphides from feed stock of the sour mercaptan-containing type. I

Irrespective of the particular procedure used, that is whether batch or continuous operation, I am enabled by the hereindescribed process to obtain, as a product from sour gasoline, a motor spirit substantially free from mercaptans and disulphides.

What I claim is: I

l. A process of removing mercaptans-from sour petroleum distillate which comprises constillate containing dissolved copper mercaptides) verting the mercaptans to copper mercaptides 4 which remain dissolved in the distillate, and extracting the copper mercaptides from said distillate with an alliyl amine.

2. A process of removing mercaptans from a sour petroleum distillate, according to claim ,1, Y

in which ethanolamine is the extracting agent.

3. A process of removing mercaptans from sour petroleum distillate, according to claim 1, in which ethylene diainine is the extracting agent.

4. The process of treating a sour petroleum distillate which comprises converting the mercaptans present in said distillate to copper mercaptides, and extracting the copper mercaptides from said distillate with an alkyl amine, whereby a sweetened petroleum distillateis obtained,

5. The process of treating a sour petroleum tans present in said distillate to copper mercap,

tides, extracting the copper mercaptides from said distillate with an alk'ylol substituted ammonia, whereby a sweetened petroleum distillate is obtained, and recovering said extracting agent.

8. Andrnproved process for treating hydrocarbon oils comprising bringing a sour petroleum distillate in contact with an. ammoniacal cupric treating agent, whereby the mercaptans in the distillate are converted to copper mercaptides, then extracting the said mercaptides from the oil with an alkyl amine.

9. An improved process for treating hydrocarbon oils comprising bringing the sour petroleum distillate in contact with an ammoniacal solution of a cupric salt whereby the mercaptan in the oil is converted to copper mercaptide, then extracting the said mercaptide from the oil with an alkyl amine.

10. The sweetening process which comprises reacting on mercaptans of petroleum oils to form soluble copper mercaptides and extracting the mercaptides with an alkylol'amine.

11. The sweetening process which comprises reacting on mercaptans of a sour petroleum distillate to form soluble copper mercaptides, distilling said distillate under sub-atmospheric pressure and at a temperature lower than that at which the copper mercaptides decompose, whereby at least 10% of said distillate is taken overhead, and extracting copper mercaptides from the distillation residue with an alkylol amine. THOMAS C. WHITNER, JR.