US2859176A - Sweetening of sour hydrocarbons - Google Patents

Description

United StatesPatent SWEETENING F soon HYDROCARBONS Garbis H. Meguerian, Park Forest, 111., and William P. Fair-child, Munster, Ind., assignors to Standard Oil Company, Chicago, 111., a corporation of Indiana No Drawing. Application June 27, 1955 Serial No. 518,358

7 Claims. (Cl. 208-234) This invention relates to the sweetening and sulfur content reduction of mercaptan-containing petroleum naphthas.

Sulfur content of motor gasoline has become of concern in recent years since high sulfur crudes are often used. One of the most common methods of reducing the sulfur content of materials boiling inthe gasoline range is to remove the mercaptans therefrom by extraction with an aqueous caustic solution. It is necessary to produce a sweet product, i. e., one which is essentially free of mercaptans. The well-known extraction processes are not able to completely remove the mercaptans and the effluent naphtha from the extraction process must be sweetened by other techniques, such a'sdoctor treating or copper chloride sweetening. It is obvious that the necessity for sweetening in a second procedure has an economic disability on the extraction processes. a

Furthermore, certain sour naphthas contain mercaptans which are very difiicultly extractable by the presently known processes. Thus virgin naphthas are very difficultly sweetenable by extraction by processes such as aqueous causticor caustic-methanol extraction. The naphtha obtained in the thermal coking of residual oils and heavy gas oils is extremely refractory and is not considered as sweetenable by extraction even utilizing causticmethanol solution. a

An object of the invention is an extraction process for the sweetening of sour petroleum naphthas. Another object is a process wherein refractory naphthas may be sweetened by extraction alone. Still another object is a combination process wherein sour virgin naphthas and sour-coke still naphthas may be sweetened by extraction, and the extracting solution regenerated and reused. Other objects will become apparent in the course of the detailed description.

The sour petroleum naphthas which are charged to the process of the invention are any mercaptan-containing virgin naphthas or coke still naphthas. In general, the

naphthas boil in the range between about 100 F. and

430 F.'at atmospheric pressure. thas maybe derived from the so-ca'lled delayed coking process, the fluid coking. process, the contact coking process or batch still coking operations. Y

The mercaptan extraction step is carried out by contacting the sour naphtha with an aqueous solution in an amount at least sufficient to extract. all the mercaptans and to produce a sweet effluent naphtha. The amount used will vary with the effectiveness of contacting and the type of apparatus used. In general, between about 10 volume percent and about 200 volume percent of aqueous solution is used, based on sour naphtha charge.

The contacting of the naphtha is carried out in the absence of added free oxygen to avoid oxidation of mercaptans, as an important object is to reduce the sulfur perature. between about 60 F. and about 150 F. It is,

preferred to' operate at the lowest temperature that con- The coke still naph-.

tacting time permits. In general, the lower the temperature of operation, the longer the contacting time needed to obtain sweetening of the sour naphtha. It is preferred to operate at a temperature between about F. and F.

The aqueous solution utilized in the process of this invention consists essentially of water, an alkylphenol mer captan solubility promoter, a water-soluble alkylenepolyamine mercaptan solubility promoter, free alkali-metal hydroxide, a copper-polyamine complex mercaptan oxidation catalyst and water. At least about 5 weight percent of free alkali-metal hydroxide, such as sodium hydroxide or potassium hydroxide is. present in the aqueous solution. More thanthis amount may be presentup to the saturation amount. It is preferred to operate with a-free alkali-metal hydroxide concentrationof between about 10 and 20 weight percent. In addition to the free alkali-metal hydroxide, the solution will contain alkalimetal hydroxide combined with alkylphenol mercaptan solubility promoter. Increasing the free alkali-metal hydroxide concentration up to about 12 weight percent has a favorable effect on the rate of mercaptan oxidation.

as little-as one volume percent or less of alkylphenol may be present in the solution or as much as the saturation amount may be present. It is preferred to operate with an alkylphenol concentration between about 10 and 20 volume percent in the aqueous solution. The alkylphenols may be pure compounds, such as cresol, xylenol,

- ethylphenol, nonylphenol, etc., or they may be mixtures of alkylphenols.- Particularly suitable mixtures are those derived from phenolic compound-containing petroleum hydrocarbons such as cracked naphthas, coke still naphthas, cycle stocks, and some distillate fuels, such as West Texas heater oil. The alkylphenols derived by caustic treating from naphthas are commonly spoken of as petroleum cresols. Those obtained by caustic treating of cycle stocks or heater oils and which boil at about the boiling point of xylenol, about 400? F. and higher, are commonly known as petroleum xylenols. Other sources of alkylphenols are wood tars. It is preferred to utilize petroleum cresols or xylenols.

The aqueous solution also contains another mercaptan solubility promoter, alkylene polyamine, where each alkylene group contains from 2 to 4 carbon atoms. Even very small amounts of promoter polyamine in the aqueous solution increases the solubility of mercaptans in the.

solution. For example, as little as one volume percent orless. Amounts of promoter polyamine up. to the saturation concentration of the solution may be utilized. The usage of promoter polyamine is limited to that giving the desired extraction as the presence of large amounts of promoter polyamine in the aqueous solution may result in uneconomi losses of the promoter polyamine to the sweet oil. The loss of material to the sweet oil may be reduced to a very low amount by using about 10 volume percent or less of the promoter polyamine.

The promoter polyamine is a water-soluble alkylene o polyamine wherein the alkylene group contains from 2 to 4 carbon atoms. The solubility of the polyamines difiers.

However, any polyamine which is sufiiciently soluble to Patented Nov. 4,

produce a concentration of at least the preferred amount is suitable for use in the process. Examples of polyamines which may be used as mercaptan solubility proferred source of promoter alkylene. polyamine.

There is also present in the. aqueous solution a mercaptan oxidation catalyst which is the complex formed. by the reaction of a water-soluble. copper salt and a hereinafter defined. alkylene polyamine. The complex is probably a. chelate.

The. copper salts utilized may be. organic or inorganic. salts which are appreciably soluble in water. Examples; of water-soluble copper salts which are suitable for use in the formation'of the catalyst of the invention are cupric acetate, cupric bromate, cupric bromide, cupric chlorate, cupric chloride, cupric fluoride, cupric fluosilicate, cupric. formate, cupric lactate, cupric nitrate, cupric sulfate, cupric methanesulfonate, cupric ethanesulfonate, cupric benzenesulfonate, and cupric toluenesulfonate. These salts may beused either in the anhydrous form or. in the hydrated form. The widely available and relatively inexpensive cupric, sulfate, sold. as blue. vitriol, i. e.,

' CuSO .5H O', is. apreferred water-soluble copper salt.

The other component of the catalyst is an alkylene polyamine. The alkylene group may be either ethylene or propylene. The catalyst alkylene polyamines may contain oneor more alkylene groups. It is preferred to utilize those alkylene. polyamines whichare very water soluble and simultaneously of relatively low oil. solubility. Examples ofv the alkylene. polyamines which may be utilized in preparing the catalyst are ethylene diamine, diethylene triamine, triethylene tetramine, tetraethylene. pentamine, propylene diamine, dipropylene triamine, triT propylene tetramine, and tetrapropylene pentamine.

These promoter polyaminesmay be; mi

These alkylene polyamines may be utilized in GP. grade,. 7

the technical grade, or the commercial purities.. The

commercially available grade of diethylene triamine isa preferred source of alkylene polyamine for use in the' preparation of the oxidation catalyst.

The'catalyst is prepared by reacting, in an aqueous. medium, the water-soluble copper salt and the alkylene polyamine. Sufficient alkylene polyamine is added to the aqueous medium to complex all. of the copper salt. The;

particular amount of alkylene polyamine added is de-- pendent upon the particular alkylene polyamine being used. It appears that when. utilizing ethylene diamine or propylene diamine that the complex is tetrahedral and contains two moles. of. the, diamine and one gram atom of copper ion. More simply, the complex can be prepared by slowly adding the polyamine to a concentrated solution of copper salt in water. until a. blue precipitate appears. The presence of excess amine in the aqueous medium containing the complex salts out the complex in the form of. a blue solid. The aqueous. medium cone. taining dissolved complex is. a blue color. essentially free of excesspolyamine is obtained by decanting the aqueous medium from the. precipitated bluesolid" Or a and drying the solid at moderate temperature. solution of complex in water of known concentration can be prepared by adding polyamine to an aqueous solution of copper salt until the first appearance of precipitate; the precipitate can be redissolved by the additionof water'to the preparation'vessel. In any event, the pres.- ence of excess polyamine has no deleterious eifect on the catalytic activity of the copper-polyamine complex.

The aqueous solution contains at least a catalytically efiective amount of the copper-polyamine complex catalyst. In general, the aqueous solution will contain be- A complex.

4 tweenabout 0.02 and 1 weightpercent; calculated as copper, of the catalyst. More usually the catalyst content will be between about 0.1 and 0.3 weight percent as copper. The larger amounts of catalyst have a favorable effect on the rate of mercaptan oxidation.

The sour naphtha and the aqueous solution are intimately contacted for a time. sufiicient to extract essentially all the mercaptans from the naphtha. For maximum sulfur reduction in the. sweetening operation, it is preferred that the efliuent naphtha be sweet. However, since some sweetening'takes place in storage, it may be desirable to produce an eflluent naphtha which is still slightly sour, i. e., has a mercaptan number of l or 2. The aqueous solution which now contains dissolved mercaptans in the form of mercaptides is separated from the sweet naphtha usually by gravity settling" and decantation.

The mercaptide-containing solution is regenerated for reuse in the process by contacting the fat solution with free oxygen. The free oxygenmaybe obtained from air,

commercialcylinder oxygen,. or an. oxygen-producing;-

chemical, such as hydrogen peroxide. Suflicient free oxygen is passed intothe fat solution to convert essentially all of the mercaptans to the corresponding disulfides... .Usuallymore tha-n;thev stoichiometricamount is used. In

general, the free. oxygen usageisbetween about 15.0 and 300%. of the. theoretical.

The regeneration step is carried out at. a temperature-- between about 40 F. and about 200 F. Preferably the regeneration step is carried out at the lowest temperature" that thecontacting time permits. However,'the lower the; temperature of operation, the. longer. the. contacting;time;- needed; to obtain complete oxidationof the mercaptan. It.is preferred to operate the regeneration step at. aboutthe temperature of the mercaptanextraction zone. The:

copper-polyamine eatalystis notsusceptibleto. oxidation.

and therefore the regeneration. stepv may be carried. out. until all, of the: mercaptans, havebeen converted to. disuli fides. This is in markeddistinctionfrorn the extraction processes wherein polyhydroxy benzene-type materials. are used. as the mercaptan oxidation catalyst; in. these:- processes, a substantial amount. of mercaptan must. re-- main unconverted in order to reduce the oxidation ofithe polyhydroxy benzene; catalyst...

The disulfides produced from the mercaptans arerof' limited solubility in the aqueous solution and a considerable amount of these may be separated. from the regen erated aqueous solution by gravity settling and decantat- However, the remainingdisulfides would be dis" solved from the solution by the naphtha. undergoing extraction and would increase the. sulfur content of the In order to maximize the reduction in sulfur contentof: the sour naphtha, it' is necessary to remove tion.

naphtha.

from the regenerated solution the dissolved disulfides;

The. disulfides are readily removed'from the regenerated. solution by washing with a liquid hydrocarbon, preferably" a liquid hydrocarbon higher boiling than naphtha. For

A parexample, gas oils and cycle stocks are suitable; ticularly suitable wash hydrocarbon is'a lower boiling gas oil derived from catalytic cracking operation commonly known as lightcatalytically cracked gas oil.

Enough of the wash hydrocarbon isutilizedto remove essentially all the disulfide from the regenerated solution.

The: amount utilized will be dependent upon the amount" of disulfide in the regenerated solution'and also upon the type: of theoil as well as the efliciency of the washing Usually between about 25" and '200 volume.

operation. percent, based on regenerated solution of the'wash hydrocarbon oil is utilized.

regenerated solution is recycled to th'e mercaptan extraction step.

An illustrative embodiment of the process of this" invention is set out; A virgin. naphtha boiling over the A rangeof about 200 F. and 405 derived from the distillation of Mid-Continent crude, is contacted with dilute aqueous sodium hydroxide solution to remove hydrogen sulfide and some mercaptan. The mercaptan numberof the etfluent naphtha is about 10. The H S-free virgin naphtha is contacted, in a continuous countercurrent tower, with an aqueous solution. About 2 volumes of virgin naphtha are present per volume of aqueous solution. 1

The aqueous solution consists of sodium hydroxide and water, about 65 volume percent; suflicient sodium hydroxide is present to have about 18 weight percent of free sodium hydroxide in the aqueous solution. Fifteen volume percent of commercial diethylene triamine is used as the promoter polyamine. The remaining 20 volume percent of the aqueous solution consists of petroleum cresols derived by caustic extraction of thermally cracked naphtha. In addition to the water, sodium hydroxide, diethylene triamine, and cresols, the aqueous solution contains a copper-diethylene triamine complex in an amount suflicient to have present in the aqueous solution 0.20 weight percent of copper-polyamine catalyst calculated as copper.

The continuous countercurrent contacting is carried out under conditions to exclude the presence of free oxygen other than that dissolved in the aqueous solution and/ or the sour virgin naphtha. The tower is operated under conditions such that the extraction is carried out at a temperature of 110 F. and for a contacting time of about minutes. Sweet effiuent naphtha is withdrawn from the tower. The efliuent naphtha contains some entrained aqueous solution as well as some dissolved diethylene triamine. The effiuent naphtha is washed with about one volume of water per five volumes of naphtha to remove entrained solution and dissolved polyamine.- When desired, the diethylene triamine may be recovered from the wash water by distillation.

The mercaptan-containing aqueous solution is removed from the tower and is passed into another tower where it is continuously contacted with cylinder oxygen at a temperature of about 110 F. for a time sutficient to convert all of the mercaptan to disulfides. Two-hundred percent of the stoichiometric amount of free oxygen is introduced into the regeneration tower. solution is passed into a third contacting tower where it is intimately contacted with 1 part of light catalytically cracked gas oil per 2 parts of aqueous solution. The gas oil removes from the regenerated solution the disulfides produced, by the oxidation of mercaptans. The disulfidecontaining gas oil is utilized in this instance as refinery fuel. The washing operation is carried out under conditions such that the temperature of the regenerated solution is not reduced markedly below the extraction tower temperature. The regenerated solution passing out of the disulfide removal tower is free of rnercaptan and disulfide and is recycled to the mercaptan extraction tower for reuse.

The results obtainable with the process of the invention are illustrated by the following working examples. These examples are not to be considered as limiting the scope of the invention.

The catalyst solution was prepared by adding one gram of cupric sulfate pentahydrate to 8 ml. of water and 7 ml. of diethylene triamine. The addition of more polyamine caused the precipitation of a blue solid. In all cases, the copper polyamine complex containing aqueous media were deep blue in color. To prepare the catalyst containing aqueous alkaline media, portions of the preformed complex solutions were added to the aqueous alkaline media.

Tests were carried out on sweetening of sour distillates using a virgin naphtha boiling over the range of about 100 F. to 325 F. and a coke still heavy naphtha boiling over the range of about 200 F. to 400 F.

The aqueous solution contained 0.15 weight percent The regenerated of the catalyst calculated as copper. The aqueous solue tion contained 20 volume percent of commercial grade diethylene triamine. Eleven percent of free sodium hydroxide was present. About 15 volume percent of petroleum cresols were present.

Test, 1

stream of nitrogen while being stirred. After 5 minutes.

of contacting time at F., the naphtha was found to be sweet to the doctor test.

The sweet naphtha was decanted from the aqueous solution. Air was introduced into the aqueous solution at 75 F. and the air blowing continued until the me1'cap-" tanshad been converted. The disulfides were removed from the regenerated solution by washing with light catalytic gas oil.

Another 300 ml. portion of sour virgin naphtha was introduced into the flask and the washed regenerated aqueous solution was also introduced therein. After 5 minutes of stirring under a nitrogen blanket at 75 F., the second portion of naphtha was sweet to the doctor test.

The aqueous solution was regenerated utilizing the procedure above and utilized to contact a third portion of sour virgin naphtha. Once again, after 5 minutes contacting at 75 F., the sour naphtha was sweet to the doctor test.

This test shows that it is possible by the process of the invention to sweeten a sour virgin naphtha, regenerate the aqueous solution and utilize the regenerated solution to sweeten more sour naphtha. This shows that the aqueous solution may be completely regenerated without loss in extraction efiiciency or loss in catalytic efliciency.

Test 2 In this test, coke still naphtha which had been prewashed with caustic to remove H S was extracted. The coke still naphtha had a mercaptan number of 10.4. It was found that one step of extraction utilizing 50 ml. of aqueous solution per 300 ml. of naphtha did not produce a sweet naphtha. It was necessary to extract batchwise, utilizing three portions of aqueous solution in order to obtain a sweet naphtha. Each step of contacting was carried out at 75 F. for a time of 15 minutes.

The aqueous solution containing mercaptans were regenerated and reused in the sweetening of additional sour coke still naphtha.

Considering the extremely refractory nature of coke still naphtha with respect to the usual extraction processes, it is considered noteworthy that a sweet coke still naphtha was obtained by this process. Operation at higher temperature and a larger amount of aqueous solution permits operation at shorter times and multiple step operation in a continuous tower is readily obtainable.

Thus having described the invention, what is claimed is 1. A sweeteningprocess which comprises contacting (a) a sour petroleum naphtha selected from the class consisting of virgin and coke still naphtha with (b) between about 10 and volume percent, based on said (4) a mercaptan oxidation catalyst consisting of the.

Three-hundred ml. of the.

Fifty ml. of aqueous solution was= 7 copper-polyamine complex formed by the reaction of a water-soluble copper salt and an alkylene polyamine' wherein the alkylene group is selected from the class c011- si sting -of' ethylene' and, propylene, in an amounfbetween" aboutOEOZ and 1 weight percent; calculated as copper, and the remainder essentiallywater, at'a' temperature between about 80 F. and L25"- F. for a time suflicient to extract essentially all of' the mercaptans from said naphtha, separating arr essentially sweet naphtha from mercaptan containing aqueous=solution,- regenerating" said" aqueous solution byconvertingall the mercaptans therein to disulfid'es, utilizing: suflicient free oxygen to carry out said'. conversion at-Va temperature between about 80 and 2. The: process ofclaimz 1" wherein said naphthapis a.

virgin naphtha;

3. Theprocessof claim 1' wherein the, polyamine pro:

mater and thepolyamine' in the camplex,v is diethylenej tri'amin'e; v

' 4. The process 'ofclaim lwherein'the alkylplienolicon:

centraftibn isbetwee'n about 10 and20 volume percent. 'j' I 5i The process of claim I wherein the vfree-liydroiiide concentration is' between, 10"" and'20 weight ercent;

6: The process of Cliiiirtl wherein said copper saltf is I cupric sulfate. 7. The process cupric'chloride'.

References=ited it! the file of this patent UNLTED: STATES! PATENTS 2,'4L3 ,94S" Bola.- Jan. 7,' 2,432;301 Fettenly- Dec. 9, 1947' 2,651,595 Moulthrops.. Sept; 8; 3 2-,659;691 Gisl'onetxxal Nov. 17-, 1953 2 ,663,674 Krauseisetiala Dec. 22; 19 5 3 2344,8521? Urban; May 8-, 1956: 2 792334:-

of claim 1,.wherein said copper saltl i's Megueriamc. May 14,. 1.951

Claims (1)

1. A SWEETENING PROCESS WHICH COMPRISES CONTACTING (A) A SOUR PETROLEUM NAPTHA SELECTED FROM THE CLASS CONSISTING OF VIRGIN AND COKE STILL NAPHTHA WITH (B) BETWEEN ABOUT 10 AND 100 VOLUME PERCENT, BASED ON SAID NAPHTHA, OF AN AQUEOUS SOLUTION CONSISTING OF (1) FREE ALKALI METAL HYDROXIDE IN A CONCENTRATION BETWEEN ABOUT 5% AND SATURATION, (2) ALKYLPHENOL MERCAPTAN SOLUBILITY PROMOTOR IN A CONCENTRATION OF BETWEEN ABOUT 1 VOLUME PERCENT AND SATURATION, (3) WATER-SOLUBLE ALKYLENE POLYAMINE MERCAPTAN SOLUBILITY PROMOTER IN AN AMOUNT BETWEEN ABOUT 1 VOLUME PERCENT AND SATURATION, EACH ALKYLENE GROUP CONTAINING FROM 2 TO 4 CARBON ATOMS, (4) A MERCAPTAN OXIDATION CATALYST CONSISTING OF THE COPPER-POLYAMINE COMPLEX FORMED BY THE REACTION OF A WATER-SOLUBLE COPPER SALT AND AN ALKYLENE POLYAMINE WHEREIN THE ALKYLENE GROUP SELECTED FROM THE CLASS CONSISTING OF ETHYLENE AND PROPYLENE, IN AN AMOUNT BETWEEN ABOUT 0.02 AND 1 WEIGHT PERCENT, CALCULATED AS COPPER, AND (5) THE REMAINDER ESSENTIALLY WATER, AT A TEMPERATURE BETWEEN ABOUT 80*F. AND 125*F. FOR A TIME SUFFICIENT TO EXTRACT ESSENTIALLY ALL OF THE MERCAPTANS FROM SAID NAPHTHA, SEPARATING AN ESSENTIALLY SWEET NAPHTHA FROM MERCAPTAN-CONTAINING AQUEOUS SOLUTION, REGENERATING SAID AQUEOUS SOLUTION BY CONVERTING ALL THE MERCAPTANS THEREIN TO DISULFIDES, UTILIZING SUFFICIENT FREE OXYGEN TO CARRY OUT SAID CONVERSION AT A TEMPERATURE BETWEEN ABOUT 80* AND 125*F. FOR A TIME SUFFICIENT TO CONVERT ALL THE MERCAPTANS, REMOVING DISULFIDES FROM SAID DISULFIDE-CONTAINING SOLUTION BY WASHING WITH A LIQUID HYDROCARBON OIL IN AN AMOUNT BETWEEN ABOUT 25 AND 100 VOLUME PERCENT BASED ON SAID DISULFIDE-CONTAINING SOLUTION, SEPARATING ESSENTIALLY DISULFIDE-FREE AQUEOUS SOLUTION FROM DISULFIDE-CONTAINING OIL AND RECYCLING SAID SOLUTION TO SAID MERCAPTAN EXTRACTION STEP.