US2591946A - Sweetening high-boiling petroleum distillates - Google Patents

Description

April 8, 1952 J. H. KRAusE ErAL SWEETENING HIGH-BOILING PETROLEUM DISTILLATES Filed Jan. 31, 1950 5 Sheets-Sheet l Alle April 8, 1952 Filed Jan. 3l, 1950 REGENERA T50 v55 7, KOH No cop/DER 1N sYsrEM J. H. KRAUsE Erm. 2,591,946

SWEETENING HIGH-BOILING PETROLEUM DISTILLATES y 3 Sheets-Sheet 2 w/rH 0.17:. COPPER +6 4 COLOR SAYBOLT UNIVERSAL Ln 'I No .-1.0 'oN Nwdvousw INVENTORS.'

Jack i1.y Krause Theodore B. Tom

4T 7 ORNE Y April s, 1952 J. H. KRAUSE ETAL SWEETENING HIGH-BOILING PETROLEUM DISTILLATES Filed Jan. 31, 1950 O O O O O Q m qm N 3 Sheets-Sheet 3 IOO 3o 4o so AERATloN TIME (MINUTES) J'NVENToRs: Jack A. Krause Theodore 7" om T'ORIVEY Patented pr. 8, 1952 SWEETENING HIGH-BOILING PETROLEUM DISTILLATES f Jack H. Krause and Theodore B. Tom, Hammond,

Ind., assignors to Standard Oil Company, Chicago, Ill., a corporation of Indiana Application January 31,1950, Serial No. 141,391

Claims.

This invention relates to the refining of hydro carbon distillates and more particularly to the refining of heavy naphthas, kerosene, heater oil and furnace oils derived from straight-run crude distillation or from cracking processes, either thermal or catalytic. Still more particularly the invention relates to a method of treating such stocks with concentrated caustic alkali solutions to remove mercaptans therefrom while avoiding undesirable color degradation or formation of oilsoluble color bodies.

It has heretofore been the practice to treat sour mercaptan-containing hydrocarbon distillates with alkaline solutions of various sorts to remove the mercaptans. Where low molecular weight mercaptans are involved as in the case of low-boiling distillates such as light naphthas, removal of mercaptans can be effected by simply washing with caustic alkali, e. g. caustic soda or caustic potash. For this purpose it is usually the practice to employ a caustic soda solution of about 10 to 20 per cent concentration. The caustic` solution can be regenerated by steaming or air blowing to distil'off the mercaptans or convert them to insoluble disulfides which can be separated from the caustic solution..

In the case of higher boiling stocks, particularly kerosene and heater oils, the removal of the mercaptans is much more diiiicult because vof their increased oil solubility or higher oil- Water partition coefficient due to their higher molecular weight. Numerous methods have been proposed and practiced for removing heavy mercaptans of the type found in these higher boiling distillates. Alkaline solutions containing organic solvents or so-called solutizers have been employed. Caustic-methanol solutions have a similar action. Chemical reagents which oxidize the mercaptans to disuldes in the presence of the oil have also been extensively employed. Among these are the familiar alkaline sodium plumbite or doctor solution, alkaline hypochlorite solutions, etc. Some attempts have been made to remove mercaptans from petroleum distillates by treating with anhydrous caustic in the form of a dry powder or in solution or suspension in anf organic solvent such as methanol. When operating in this way, however, serious color formation has resulted especially where the treatment was conducted at elevated temperature, for example 150 F. and upwards. It has been found that to prevent color formation under these conditions it has been necessary to carefully exclude oxygen or air. v

We have now discovered that mercaptans can be removed from sour hydrocarbon sdistillates, even of the heater oil distillate boiling range, without serious color formation by treating with a controlled amount of air or oxygen in the presence of an aqueous potassium hydroxide of about 50 to 60 per cent by weight at a temperature of about to 125 F. (but high enough to prevent solidication of caustic), -at atmospheric or superatmospheric pressure and in the presence of a particular type of copper catalyst. Under these conditions we have discovered that the mercaptans are converted to odorless disulfides without the formation of objectionable color bodies. The oil refined in this manner has also been found to be satisfactory from the standpoint of its burning characteristics when employed in sleeve-type burners. The amount of oxygen employed either as air or commercial oxygen is preferably about one and one-half to two and one-half times that theoretically required for converting the mercaptans present to disuldes.

We have found that the treating reaction is greatly facilitated by the presence of a small amount of copper, e. g. about .004 to 0.1 per cent by weight based on the potassium hydroxide solution in the form of a catalytically active copper compound or copper complex such as colloidal copper oxide.l This corresponds to about 0.01 to 0.3 per cent of copper chloride, CuCl2.2I-I2O. With some catalysts larger amounts of copper may be used, e. g. up to .5 per cent by weight based on KOH, but usually it is not necessary to exceed .1 per cent. It is preferred to add the copper in the form of an aqueous solution of a copper salt such as 'copper chloride, sulfate. nitrate or acetate. The copper salt solution may be Aadded directly to the potassium hydroxide solution if the latter is hot enough to avoid formation of a black precipitate. When added in this way, for example to boiling potassium hydroxide solution, a blue complex forms which appears to be a colloidal copper compound; in this form and concentration the copper remains in active condition and does not precipitate from the potassium hydroxide treating reagent.

The copper catalyst can also be added to an intimate reaction mixture of KOH solution and oil, the oil in this case forming the continuous phase of an emulsion so that when the copper salt is introduced it is also dispersed and results in'the formation of active catalyst instead of inactive black precipitate. When operating in this way the solution of KOH is mixed with the oil, for' example in a continuous mixer, during or after which a solution of a water-soluble copper salt is introduced. The oil and treating agent is lthen passed to another mixer into which air or oxygen is introduced. If desired, however; air may be introduced into the loil and KOH before adding the copper catalyst, the air, oil, KOH and catalyst being all maintained in intimate contact until mercaptans are substantially eliminated.

The invention ,is illustrated by ,the drawings which form'a part of this specification and which show diagrammatically in Figure 1 an apparatus suitable for carrying out the process. 2 and 3 are graphs of data illustrating the results obtained in the process.

The following data illustrate the effect of concentration of copper catalyst on the rate of mer` Figures captan oxidation reactions and .the color'of'the oil. The oil used in these experiments .was a straight-run west Texas heater oil having a color of about 1'7 Saybolt Universal .and a mercaptan.:

number of 69. The treats were carried vout at about 80 F. with air and 1% by volume of an A fuller understanding of the treating processv` will be obtained from Figure 1 of thedrawingU in which the principal reaction vessel isv indicatedby A and the Vused KOH reconcentrator r by B. Coalescersl vC and D are provided formore complete removal -of Vcaustic 'fromthe oil and E is a settler for'removing wash Water fromthe .treated oil. Referring vto the drawingfthe sour oil'is introduced byline .III and-the temperature is adjusted by heater-II to af-satisa preliminary wash with analkaline^ solution,"

e. g. sodium hydroxide' or carbonate', Vto remove stream of air and oil entering mixer. I3. The

An .aqueous KOHsolution of 55` -per jcent con' centration is introduced by line .IB Aintofthe ;r

resulting mixture iiows by y1ine .I"I to reactor. A

where partial separation of KOH solution takes place.

Oil and unused air pass by line I8 `to air separator I9 from which the air is discharged by .Y It is preferred to maintain the reac.-

line 20.

torrA under pressureffor.y example about-.1100..`

p. s. i. g.. reducing, thegpressure by 'valve2I to about 15 p.- s.A i.` g. to'facilitate separation 4of air .in separator I9. Theuse of pressure. with@ airfincreases the rate. of. oxidation, .andpres-1- sures .in the range of 25 to 200 p. s. i. g.arev satisfactory. Where oxygen-is used, :pressure is not ordinarily required. From I9 theio1l-iiows by line 22 to coalescer C which is packedwith;

a fibrous or nely granular material such as glass wool, rock wool, sand, etc.. providing- -anf' extensive surface for the removal of colloidally suspended KOH solution from the oil. The coalescer maybe a horizontal-drum packed with glass wool, as indicated, connected with settling chamber 23, or it may be a packed vertical drum, preferably arranged for downflow of oil thru the packing withv a separating chamber at the bottom.v By effecting a more rapid and complete removal of KOH, the coalescer serves to arrest' the development of color in the presence of the. KOHisolution.A

From coalescer C the oil iiows by line 24 to a secondA stage coalescer D. The residence time of the. oil in the coalescers is suitably about 5 to 10 minutes. From coalescer D the oil iiows by line 25 to water mixer 25, water being introduced into the oil-stream' by lineI 21. Mixer 26 of the oriflce'type is shown, altho any suitable eicient Ymechanical mixer "may be ,sube stitutedy therefor.l The Vamount of waterintro'- duced may'suitably be-about 5 to 10 percent of the Volume of thel oil. The water-oil mixtureH is conducted by line `28 to water settler E froml which waste waterV is withdrawnl by line '29. Washed oil flows by line 3D to water coalescer 3|, the iinished oil being discharged fromthe systemv by line 32. lescer is discharged 'by line 33. If desired, a preliminaryv water'wash maybe given the oil in advance of contactor4 '26 for the purpose ofA recoveringjKOH entrained in the oil.

From`reactor A, spent KOH is withdrawnby1 linek 34 to settler 35 Where' potassium cresylates are allowed to collect-'as an'upper layer. The separated KOH is withdrawn by line 36 and pump -3'I and thence iiows by line 38 to reconcentra tor B where it is heated by submerged steam coil 39 to drive oi Waterwhich tends to accumulate in the system, particularly as a byproduct of the sweeteningvreaction. In usual practice, the concentration `may be increased in B from about 51 per cent rto 55 per cent. Water eliminated asvapor is passed by line 40 to condenser 4I and is discharged from the system byline 42. Thereconcentrated KOH flows by line 43 to cooler Mandthence byline 45 to KOH solutionflters 45 which remove potassium carbonate andany other insoluble prodducts which may collect inthereagent. The KOH solution theniiows by line 41 and pump 48 back to mixer I3 byline I3.A Makeup KOH.

is supplied to they system fromtime vto time by line. 49 as needed. Byloperating, concentrator B under. reduced pressure.Y e. g. 5 p. s. i. g., the

temperature can be. held belowabout. 2809 F.' thereby largely avoidingdecomposition.of mer captides to K2S.which is undesirable because it separates andclogs the system. It alsoy rep-- Copper solutionis introduced by line 55 and pump 56. For this purpose'we may use as lO percent solution of copper .chloride or. sulfate. The copper catalyst solution can be introduced at Waste water from the coavarious points in the system but we prefer to add it directly to the hot KOH in concentrator B. Some of the added copper is precipitated from the caustic solution as insoluble copper sulde, CuS. The treated oil contains a trace of copper but not more than 1 part per million. The effect ofthis minute amount of copper on color stability of the oil can be readily offset by addition of a small amount of a metal deactivator, e. g. .001 to .01 percent N,Ndisalicylidinel,2 diaminopropane.

In the operation of our process, it is important to control the temperature within the range of about 80 to 125 F. if a product of satisfactory color is to be obtained. Higher temperatures have been found to increase color formation. We have found that use of the copper catalyst tends to prevent color formation, apparently by directing the oxidation reaction toward the conversion of mercaptans to disuldes. The cause of color formation is not fully understood but it is thought to be due in part to the oxidation of phenolic substances contained in high sulfur oils. This effect is apparent from the data shown graphically in Figure 2 obtained by treating a sour West Texas heater oil with 1% by volume of KOH solution at 120 F. and air at the rate of 4.85

cubic feet per hour. The upper curve shows rapid formation of color, i. e. decrease in Saybolt Universal color values as the mercaptan number of the oil is reduced when treated with air and regenerated 55 percent KOH. The lower curve illustrates the improved results obtained with the same KOH solution containing 0.1 percent by weight of CuCl22H2O.

It is to be noted that the maximum oxidation rate occurred with a copper concentration of about 0.1 to 0.2 percent Cum-22H20. It is also to be noted that the oil obtained under these conditions showed an improved color.

The following data show the effect of temperature on the reaction, particularly with respect to mercaptan number and color. The treats were made by using straight-run west Texas heater oil having a +15 Saybolt coloi` and la mercaptan number of 55. The treating reagent was a 55 percent aqueous KOH solution containing 0.1 percent CuClaZHaO, the ratio of solution to oil being 1 percent by volume. The oil and solution were vigorously agitated in the presence of air. The following results were obtained:

1 Data interpolated.

It is desirable to separate the oil from the caustic solution after a contact time of about 25 to 40 minutes in order to avoid color formation and a contact time greater than one hour has been found to decrease the Saybolt color value from 16 to 5 or lower. Usually a contact time of 5 to 30 minutes is sufficient, depending largely on the temperature.

The ratio of caustic solution to oil may be varied over a range from 1 percent by volume to 10 or 15 percent by volume, altho about 5 percent by volume has been found to give best results in the case of heater oil from west Texas crude. When employing only 1 per cent KOH solution, the problem of separating the spent KOH solution from the oil is more difficult than when larger volumes of solution are used. The effect of coalescing the treated oil is particularly valuable in the case of low KOH-oil ratios as will be observed from the following table:

Heater oil treated with 55% KOH and air in' presence of copper catalyst Color-Saybolt Universal Untreated oil 17 Settled to remove spent KOH solution 9 Coalesced 13 Coalesced and washed with water 16 When recharging a'coalescer with fresh glass wool or other packing material, it has been found that maximum eiiiciency in removal of color is not obtained until after operating for several hours. This initial operating period of low efiiciency can be shortened by pre-wetting the coalescer packing with the strong KOH solution. When two coalescers are employed in series they can be renewed alternately thereby largely mitigating this unfavorable action at starting.

Attempts to use the cheaper caustic soda instead of KOH for sweetening fuel oil distillates were unsuccessful. In comparison with NaOH solution, KOH gave a faster reaction and a sweet product before color formation developed. The KOH solution also separates from the oil more readily whereas the NaOH becomes emulsified or dissolved in the heavy oil and is diicult to remove, even in the subsequent water washing operation.

Figure 3 illustrates the superior action of KOH in comparison with NaOH solutions. Note that the aeration time for reduction in mercaptan number is considerably greater for NaOH solution of the same concentration. Thus the aeration time required to reduce the mercaptan number from to 60 was approximately 48 minutes with 25 percent NaOH and only 24 minutes with KOH solution of the same concentration. l l

Figure 3 also shows the effect of concentration on rate of mercaptan oxidation and it will be noted that there is a tendency for the oxidation to cease entirely or level off at a given mercaptan number depending on the concentration. Thus 40 per cent KOH leveled off at a mercaptan number of about 22, whereas 50 per cent KOH permitted the mercaptan number to be reduced to about 7. These data were obtained with a West Texas heater oil having a mercaptan number of 80, contacted with air and 1 per cent by 1volume of the caustic solution containing 0.1 per cent CuCla2H2O. The temperature of contacting was F. and the rate of air input was 4.85 cubic feet per hour.

The odor of the oil treated by our KOH-air oxidation process has been found to be satisfactory for marketing requirements if the oxidation is carried to a point where the mercaptan number is below 5. (The mercaptan number is the number of milligrams of mercaptan sulfur per ec. of oil, usually determined by titration with a standardized copper solution.) By employing about 5 volume per cent of caustic saluto-17 and with good color stability and excellent lburning qualities'.

While a particular system Afor using the inven-v tion hasbeen descrbedin considerable detail,

many, modifications-and .alternative procedures preferably prepared in the manners herein de scribed using, for example, coppersulfate, lwhich has been found to give oi'ltstandingly` good re'- Y 1. The process of removing mercaptans from a sour hydrocarbon fuel. oil distillate without formation ofv excessive color therein, which com prises intimately contacting said distillate with about 1 to 15 percentby volume of an aqueous solution of KOH having a concentration of about 50to 60 percent, said-solution containing about .D04-to 0.1 per cent by weight of copper in the former-an active copper compound which is active as an oxidation catalyst,v introducing a freeoxygen containing gas-in an amount about l stoichiometrioally equivalent to the amount of mercaptans present in said distillate-into the mixture of distillate and KOH, maintaining the temperature of contacting Aat about 80 to 125 F. and -separatingspent yKOH solution and associated reaction products fromthe treated oil.

2. The process of sweetening a sour hydrocarbon fueloil'distillate Without formation of excessivecolcr therein which comprises intimately contacting said distillate with about 5 to 10 per cent by volume of an aqueous solution or" KOI-I having a concentration of about 5G to 50 per cent and containing about .004 to 0.1 per cent of copper in 'the form of an active copper compound which is Aactive as an oxidation catalyst, introducing-into the reaction-mixture air containing an amount ofoxygen stoichiometrically equivalent to about one and one-half to two and onehal times the amount of mercaptanspresent in said v distillate, maintaining said reaction mix-- ture -highly agitated and at a temperature of about80 to 125 F. until the mercaptan number of said-distillate is reduced below'about 5, thenseparatingV spent KOH solution -and associated reaction products from the treated oil.

3. The process of claim 2 wherein said cil'is washed by intimately contacting with water immediately after separation from said KOH solution.l

4. IheA process of'claim 2 wherein'the time oil contactbetween said distillateA and said KGH solution is about 5 to 60 minutes:

5; The process of claim' 2 wherein-the spent KOH solution separated frcm'the treated distillate is regenerated by subjectingto distillation at distillate which 1 is higher boiling than gasoline and'which contains a largeamount of mercaptanY sulfur, ink whichprocessthe hydrocarbon distll;

late is intimatelycontacted with an amount of oxygen stoichiometrically equivalent to about oneand one-half to two and one-half times the`v amount of mercaptans presentin the distillate and in which process thecontacting is effected in the presence of concentrated aqueouspotassium hydroxide of about 50 to 60 per cent concentra y tion atA a temperature in therange of about to Ffand under a pressure in the range of vabout atmospheric to 200 pounds per square inch for a time of contact in the range of about 5 to;

60 minutes, the improvement which comprises efectingsaid contactingalso inthe presence of an active; copper-catalyst which is active as an oxidation promoter -in an amount of .004 to .1 per cent by weightof copper based on potassium hydroxide present in thel contacting step,- said active f copper Vcatalyst-being in the form of a coppen compound and not in the form or metallic copy 7. The 'prccessof claim G wherein the copper compound is a blue colloidal copper oxide.

8. The process of claim 6 whercinthe copper' compound is formed by adding a copper salt tov a. solution of concentrated potassium; hydroxide under conditionsior avoiding the lfcrmationof appreciable, amounts of black precipitate..

9. The method of claim 8 wherein vthe copperA compound isformed by adding copper sulfate to concentrated aqueouspotassium vhydroxide at a temperature sufficiently high to avoid appreci able formation of black precipitate.

10. The process of treating a sourvirgin heater oil distillate containing a large` amount of mercaptan sulfur, which process comprises intimately contacting said distillate with about 5 per cent by volume of a concentrated potassium hydroxide solution of about 50 to 60 per cent concentration in the presence of a catalytic amount of an active copper compound which is active as an oxidation catalyst and with addedV oxygen in an amount stoichiometrically equivaient toabout vone -and one-hall" to two and one-half times ,the amount of mercaptans present in said distillate, continuing said contacting at a temperature in the range of about 80 to 125o F. under a pressure in the range oatmospheric to 200 pounds` per squarev inch for a time suiilcient to obtain a low mercaptan number' of said distillate without materially impairing the color and color stability thereof, then separating spent potassium hydroxide solution with reaction products contained therein from the treated oil, separating potassium cresylates from the withdrawn solution, then subjecting the solution to distillation at low pressure andA at a temperaturenot exceeding about 300 F. for.

removingwater therefrom, cooling the concen-I trated caustic solution and returning ,said cooled solution for contacting with additional amounts I of said distillate.

JACK H. KRAUSE. THEODORE B. TOM.

REFERENCES CITED The following references are of record inthe iile of this patent:

UNITED STATES PATENTS

Claims (1)

1. THE PROCESS OF REMOVING MERCAPTANS FROM A SOUR HYDROCARBON FUEL OIL DISTILLATE WITHOUT FORMATION OF EXCESSIVE COLOR THEREIN, WHICH COMPRISES INTIMATELY CONTACTING SAID DISTILLATE WITH ABOUT 1 TO 15 PERCENT BY VOLUME OF AN AQUEOUS SOLUTION OF KOH HAVING A CONCENTRATION OF ABOUT 50 TO 60 PER CENT, SAID SOLUTION CONTAINING ABOUT .004 TO 0.1 PER CENT BY WEIGHT OF COPPER IN THE FORM OF AN ACTIVE COPPER COMPOUND WHICH IS ACTIVE AS AN OXIDATION CATALYST, INTRODUCING A FREE OXYGEN CONTAINING GAS IN AN AMOUNT ABOUT STOICHIOMETRICALLY EQUIVALENT TO THE AMOUNT OF MERCAPTANS PRESENT IN SAID DISTILLATE INTO THE MIXTURE OF DISTILLATE AND KOH, MAINTAINING THE TEMPERATURE OF CONTACTING AT ABOUT 80 TO 125* F. AND SEPARATING SPENT KOH SOLUTION AND ASSOCIATED REACTION PRODUCTS FROM THE TREATED OIL.

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