US2646389A - Sweetening hydrocarbon distillates - Google Patents

Description

IJuly 2l, 1953 G. H. wElsEMANN SWEETENING HYDROCARBON DISTILLATES 3 Sheets-Sheet l Filed March., 8, 1950 m S Q E EE@ G. H. WEISEMANN SWEETENING HYDROCARBON DISTILLATES July 2l, 1953 5 Sheets-Sheet 2 Filed Maron 8, 1950 1ro .-10 'oN Nvldvoasw n Y MM M T ,R

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July 21, 1953 G. H. wl-:lsEMANN I 2,646,389

3o 4o AERATloN TIME (MINUTES) O D C O O o s Ln d' m N 'HO :l0 'ON NVidVDHSW JN V EN TOR. Ger H. Weisem ann BO/MQ/wg ATTORNEY Patented .lu-ly 2l, 1.953

e SWEETENTNGl HYDROCARBON Dls'rlLLA'rEs.

Gert H. Weisemann, Hobart, Ind., assignor to UNITED STATES. PATENT OFFICE Standard Oil Company, Chicago, Ill., a corporation of Indiana Applicati'n March s, 1950, serial No. 148,303

9 claims. (ci. 1%;29) l l This invention relates'to the rening of hydrocarbon distillates, such as h eavy naphtha, kerosene, heater oil and furnace oil, which areV derived from the distillation of crude oil vor from cracking processes, either thermal or catalytic. More particularly the invention relates to a method of treating such stocks with concentrated y potassium hydroxide solutions in the presence of a copper catalyst to remove mercaptans there'- from.

'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 rthe practice to employ a caustic soda 'solution of about 10 to 20 percent concentration. lThe 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 boilingA stocks, particularly kerosene and heater oils, thev removal of mumV of vcolor degradation; Another object is vto speed up mercaptan removal by the use of-a copper catalyst in conjunction with air and caustic. Still another object isv to removeV mercaptans from sour hydrocarbon distillates by the use of air and regenerated caustic in the presence of a copper catalyst. A particular object is to reduce `the mercaptansin sour hydrocarbon distillates Whichboil'above the gasoline range with a' minimum of color degradation or formation of oil-soluble color bodies. l

It has been discovered that mercaptans can be removed from sour hydrocarbon distillates, even of the heater oil distillate boiling range, i. e. 35o-650 F., without serious color formation by treating with a controlled amount of air or oxygen in the presence of an aqueous potassium hydroxide solution having aconcentration in the range of about 50 to 60,per cent by weight at a the mercaptans is'much more dicult because' f of their increased oil solubility or'higherv oilwater partition coeflicient due to their higher molecular Weight.' Numerous methods have been proposed and-practiced for' removing heavy mercaptans of the type found in these higher 4boiling distillates. Alkaline solutions containing organic solvents or so-called solutizers have been employed. Caustic-methanol solutions' have a similar action. Chemical reagents which oxidize Y the mercaptansv to disulfldes in the presence of Vthe oil have also been extensively. employed. v'Among these are the familiar alkaline sodium plumbite or doctor solution, alkaline hypochlorite l solutions, etc. Some attempts have been made to remove mercaptans vfrom petroleum distillates by treating with anhydrous caustic in the form of a dry powder or in solution or suspension in an organic solvent such as methanol. When operating yin this way, however, serious color formation has resulted especially Where the treatment was conducted at elevated temperatures', 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.

An object of this invention is to remove mercaptans from sour hydrocarbonoils with a minitemperature'of about 80 to 125 F. (but high enough to prevent solidiflcation of caustic), at

atmospheric or superatmospheric pressure and in the presence of a particular type of copper catalyst. Under these conditions the mercaptans are converted to disulldes without the formation of objectionable color bodies. The oil t rened in this manner has` also been found tovbe satisfactory from the standpoint of its burning characteristics when employed in sleeve-type burners. I The amount of oxygen employed either as air Or'commercial oxygen is preferably about be used, e. g. up to 0.5 per cent by weight basedl on-KOH, but usually it is not necessary to exceed 0.1 per cent. It is preferred to add the copper in the formV of an aqueous solution ofy a copper salt such as copper chloride, sulfate, nitrate or acetate. The copper salt solution may be added directlyv to the potassium hydroxideV 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 then passed to another mixer into which air or oxygen is introduced. If desired, however, air may be introduced into th'eoil and KOH before adding the copper catalyst, the air, oil,.KOI-l and catalyst being all maintained in intimate contact until mercaptans are substantially eliminated.

, While the above methods of adding the copper catalyst work very well when fresh caustic solution is used, the use of regenerated caustic solutions which contain material dissolved out of the sour hydrocarbon results in a very large increase in the amount of copper catalyst needed. The addition of the copper catalyst to the'hot regenerated caustic results in the formation of a heavy precipitate and the blue color of the catalytically active caustic solution does not appear until all the poison has been reacted. These reactive materials are believed to be oxygenated hydrocarbons. The heavy precipitate must be removed or it clogs the lines and the meters used in the process. I have discovered that the addition of the copper catalyst, as a concentrated water solution, directly to the oil, so as to form a very fine dispersion, probably a WatVer-in-oil emulsion, before the caustic solution is added eliminates this problem and also results in better finishedY oil color with less catalyst consumption than is obtainable with fresh caustic-catalyst solution addition.

` The invention is illustrated by the drawings which form a part of this specification and in which:

Figure 1 is a schematic diagram of an apparatus suitable for carrying out the process, and

Figures 2 and 3 are graphs of data illustrating the results obtained in the process. Y

It has been found that the use of a copper catalyst results in a phenomenal increase in the mercaptan oxidation reaction rate with markedly 4 stood but 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 zobtained by treating 500 cc. of a sour West Texas heater' oil with 1% by volume of KOH solution at 120o 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 per cent KOH. The lower curve illustrates the improved-results obtained with the same KOH solution containing 0.1 per cent by weight of CuCl2.2I-l2O. n

In the operation of my 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. 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 -1-16 color and a mercaptan number'of 65. The treating reagent was a 55 per cent aqueous KOH solution containing 0.1 per cent CuCl2.2H-2O, the ratio of solutionV to oil being l per cent by volume. The oil and solution werel vigorously agitated in the presence of air. The following results were obtained:

Color, Saybolt Time,

1 Data interpolated.

improved Saybolt coloi` as is shown by the fol- @1101221520 Mel'itfm Colglay' lowing tabulated data. The aeration times to Minutes Num er Univelrsal reach a mercaptan number of 5 and color of the nished oil were obtained using l volume perV g +13 cent of 55% aqueous KOH, 4.85 cubic feet of air 0-3 10 1910 per hour to 500 cc. ofloil and 0.1% by weight, 60 12 lgon caustic, of CuCl2.2H2O addition. 23 9'9 iz 1o 7.4 12 15 4.5 9 No Catalyst Catalyst Added 5 i3. 1 12 o F Y 0 1 s 10.3 12 -7 10 8.3 12 Minutes Color Minutes Color l5 3.2 9 s 17.3 12 005 1o 13.5 11 Not Attamabia. 14 +10 15 10. s 9 150 -24 9 +10 s 23.7 1o 4 +10 001 10 19.6 9 2 +4 15 13.1 7

It has been found that the use of the copper catalyst tends to prevent color formation, apparently by directing the oxidation reaction toward the conversion of mercaptans to disulfides. The cause of color formation is not fully under- It is to be noted that the maximum oxidation rate occurred with Aa copper concentration of about 0.1 to 0.2 per cent CuCl2.2H2O. It is also to be noted that the oi1 obtained under these conditions showed an improved color.

l input was 51.85 cubicn feet per hour.

It is ldesirable to separate lthe oilfrom the caustic solution after arcontact time vof about 25 to 40 minutes in order to avoid color formation and a contact time greater than one hour has beenfound to decrease the Saybolt color value from 16 to 5 or lower. Usually a Contact time of to 30 minutes is sufficient, depending largely on the temperature. 1

The ratio of caustic solution to oil may be varied over' a range from 0.5 per cent by volume to or 15 per cent by volume, although about 5 per` cent 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. Thev 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: y

Heater oil treated with/55% KOH and air in presence of copper catalyst Color-Saybolt YUniversal Untreated oil.` i y17 Settled to remove spent KOH solution 9 Coalesced ;1 13 Coalesced and washed withwater 16 readily whereas the NaOl-I becomes emulsied or f dissolved in the heavy oil and is difficult to rey move, even in the subsequent water washing operation.

Figure 3 illustrates the superior action of AKOH in comparison with NaOH solutions. The aeration time for reduction in mercaptan numberrls considerably greater for NaOH solution of the same concentration. Thus the aeration time required to reduce the mercaptan number from 80 to.60 was approximately 48 minutes with 25 per cent NaOH and only 24.- minutes with KOH solution of the same concentration.

Figure 3 also shows the effect of concentration on rate of mercaptan oxidation and it will be noted that there is atendency-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 Ythe mercaptan number'of yabout 22, whereas 50 per cent KOH permitted the mercaptan number rto bev reduced to about 7. These data were obtained with 500 cc. samples of a West Texas heater oil havinga' mercaptan number of 80, contacted with -airjand 1 per centbyvolume of the caustic solution containing 0.1 per cent CuCl2.2H2O. The temperature of contacting was 85 F. and the rate of air The odor of the oil treated by my KOH-air oxidation process has been found to be satisfactory for marketing requirements if the oxidation per sulfate) based on; oil treated, mercaptan numbers have been reduced to about 1 or prac` tically VZero and treated products or .good odor have been obtained with a Saybolt color of 15 to 17 and with good color stability and excellent burning qualities.

While the above data were taken from bench scale work using fresh caustic with the copper catalyst added to the caustic solution, pilot plant work using regenerated caustic shows the superiority of adding the copper catalyst directly to the sour oil before the introduction of the caustic solution. The following data were obtained on a West Texas heater .oil of about mercaptan number and about |16 Saybolt color. In all cases the treating reagent was a 55% aqueous KOH solution, about 5 parts of this solution was used per 100 parts ofthe sour oil; and all runs were made at about F.

C ase 011 aus 10 f Product Product Coppidded. Mercaptan Color AS Cop, No. saybolt ousolsmo. per.

o. 5 0.13 o. 3 +4 o. 5 0.13 3. 5 +8 0- 2 0.05 2. 2 +15 0.2 o. o5 o. tv +9 0- l 0. 03 0. 5 +9 0.1 o. o3 o. 3 +8 0. 05 0. 01 0, 5v +12 These data show that muchless copper catalyst is needed when the catalyst is added to the oil to get a finished oil that is nearly sweet and at the same time is of better color by 4 or 5 .points on the Best results are obtained when the catalyst I solution is injected into sour oil in such a manner 4that the solution is dispersed throughout the oil in very ne droplets. Preferably the dispersion should be so ne that a water-in-oil emulsion is formed. `The'dispersed copper compound apparently reacts with the KOH solution to form a catalytically active copper compound which is nely dispersed throughout the oil; this dispersion may be an explanation of the fact that less catalyst is needed when the copper solution is added to the oil than when it is added to fresh KOH solution.

A fuller understanding of the treating process will be obtained from-Figure l wherein the principal reaction vessel is indicated by A and the used is carried to a point where the mercaptan number is below about 5. (The mercaptanv number is the number of milligrams Aof mercaptan sulfur per cc. of oil, usually determined by titration with a standardized copper solution.) By employing about 5 volume per cent of caustic solution (55%y concentration and containing about .02 weight per cent of copper in the form of Iactive colloidal copper complex but introduced as aqueous 'cop- .KOH` reconcentrator by B. Coalescers C and D are providedrfor complete removal of caustic from the oil and E is a settler for removing wash water from the treated oil. Referring to Figure 1, the sour oil, which may be given a preliminary wash with an alkaline solution, such as sodium hydroxkthrough meter l the sour oil passes through line 8 to mixer 9l which is indicated to be of the orifice type. Air is-'introduced' by line y"land `owsr through meter I l to line 8 and thence to mixer 9. The copperv catalyst, preferably CuSO4.5H2O or CuCl2.2H2O, in an amount of about 0.1 .Weight per cent on the caustic solution, is introduced in the form of a concentrated water solution, such as 10%, by line I2 and pump I3 into line 8 where 'the solution is finely dispersed throughout the sour oil. An aqueous KOH solution of about 55 concentration is introduced by line l'into line 8 and thence to mixer 9. The KOH solution, the lair and the sour oil-copper catalyst emulsion are thoroughly mixed in mixer 9, a suitable residence time being about 35 seconds.

The resulting mixture ows by line Il to reactor A Where partial separation of KOH solution takes place. Oil and unused air pass by line I3 to air separator I9 from which the air is discharged by line 2). It is preferred to maintain the reactor A under pressure, for example about 100 p. s. i. g., reducing the pressure by valve 2| to about p. s. i. g. to facilitate separation of air in Aseparator i9. The use of pressure With air increases the rate of oxidation, and pressures in the range of to 200 p. s. i. g. are satisfactory.

Where oxygen is used, vsuperatmospheric pressure is not ordinarily required. From separator 9 the oil flows by line 22 to coalescer C which is packed with a fibrous or nely granular material such as glass Wool, rock Wool, sand, etc., providing an extensive surface for the removal of colloidally suspended KOH solution from the oil. The coalescer may be a horizontal drum packed with glas-s Wool, as indicated, connected with settling chamber 23, or it may be a packed-vertical drum, preferably arranged for downflow of oil through the packing With a separating chamber at the bottom. By eiecting a more rapid and complete removalof KOH, the coalescer serves to arrest the development of color in the presence of the KOH solution.

From coalescer C the oil flows by line 24 to a second'stage coalescer D. The residence time of the oil in the coalescers is suitably about 5 to l0 minutes. From coalescer D the oil iiows by line 25 to Water mixer 26, Water being introduced into the oil stream by line 2l. Mixer 25 of the orifice type is shown, although any suitable eicient mechanical mixer may be substituted therefor. The amount of Water introduced may suitably be 'about 5 to l0 per cent of the volume of the oil.

The water-oil mixture is conducted by line 20 to Water settler E from which waste Water is withdrawn by lineY 29. Washed oil ioWs by line to water coalescer 3l, the nished oil being discharged from the system by line 32. Waste Waiter from the coalescer is discharged by line 33.

From reactor A, spent KOH is withdrawn by line 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 31 and thence flows by line 38 to reconcentrator B Where it is heated by submerged steam coil 3Q to drive off Water which tends to accumulate in the system, particularly as a by-product of the sweetening reaction. Water eliminated as vapor is passed by line Il!) to condenser 4! and is discharged from the system by line 6.2. The reconcentrated KOH -ows by line 43 to cooler 44 and thence by line d5 to KOH solution nlters 46 which remove potassium carbonate and any other insoluble products which may collect in the reagent.

. The KOH solution then flows by line 41 and pump d8 back to mixer S by line i6. Makeup KOH is `supplied tothe .system from time to time by line 49 as needed. If desired, concentrator B may be 8. operated under reduced pressure, e. g. 5 p. s. i. a. and consequently the temperature can be held below about 280 F. thereby largely avoiding decomposition of mercaptides to KzS which is undesirable because Yit separates and clogs the system. Such decomposition also represents a loss of KOH.

From the coalescers C and D, separated KOH solution is conducted by line 50 to separator 35. The cresylate layer from separator 35 is conducted by line 5l to lseparator 52 which may be a storage tank providing an extended time for settling out aqueous caustic. It has been found that the small amount of caustic insoluble copper compounds formed by reaction between the copper catalyst and reactive hydrocarbons is preferentially soluble in the cresylates and passes out of the system with the cresylate layer from separator 35; this fact eliminates the need for special measures to prevent clogging of lines and meters. The recovered KOH is conducted periodically by line 53 to the KOH line 36. If desired separator 52 can be provided with suitable means for heating the cresylates and thereby facilitating the separationof the KOH. The settled potassium cresylates are discharged from the system by line 54.

The finished oil contains a trace of copper .but not more thanY about Vl part per million. The effect of this minute amount of copper on the color stability of the oil can be readily offset by the addition of a small amount of metal deactivator, e. g. 0.001 to `0.01% of N,N-disalicylidine-1,2-diaminopropane.

While a particular system for using the invention has been described in considerable detail, many modications and alternative procedures and conditions will be apparent from the above description to those skilled in the art. The

' amounts of catalyst specified in the accompanying claims refer to copper in the form of an active compound or complex believed to be colloidal 0X- ide; such catalyst is preferably prepared as herein `described using, for example, copper sulfate which has been found to Vgive outstandingly good results.

l claim:

l. The process of removing mercaptans from sour hydrocarbon distillate which is higher boiling than gasoline Without formation of excessive color therein, which comprises dispersing a copper catalyst in the distillate, intimately contacting said catalyst-containing distillate with about l to 15 per cent by volume of an aqueous solution of KOH having a concentration of about 50 to S0 per cent, said copper catalyst, which ranges from about 0.004 to 0.1 per cent by Weight of copper based on the caustic solution, forming a catalytically active copper compound when contacted With the caustic solution, introducing a gas containing an amount of free oxygen about stoichiometrically equivalent to the amount of mercaptans present in said distillate into the mixture of catalyst-containing distillate and KOH, `maintaining the temperature of contacting at about to 125 F. until a substantial reduction in mercaptan content has been obtained and separating spent KOH solution and associated reaction products from the treated oil.

2. The process of sweetening a sour hydrocarbon distillate which is Ahigher boiling than gasoline Without formation of excessive color therein which comprises dispersing a copper compound in the distillate which Will range from about 0.004 to 0.1 per cent by Weight of copper on the caustic solution hereinafter described in the form of a catalytically active copper compound, intimately contacting said catalyst-containing distillate with about 5 to 10 per cent-by volume of an aqueous solution of KOH having a concentration of about 50 to 60 per cent, introducing into the reaction mixture air containing an amount of oxygen stoichiometrically equivalent to about one and one-half to two and one-half times the amc-unt of mercaptans present in said distillate,l

comprises dispersing a concentrated aqueous solui tion of copper sulfate, which solution contains between about 0.01 and 0.05 weight percent of copper based on aqueous KOH solution used in the process'in the distillate, intimately contacting said copper sulfate-containing distillate with about per cent by volume of a concentrated potassium hydroxide solution of about 50 to 60 perV cent concentration, said copper compound forming with the potassium hydroxide solution a copper catalyst which is active as an oxidation catalyst, and with added free oxygen in an amount stoichiometrically equivalent to about one and one-half 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 125 F. under a pressure in the range of atmospheric to 200 pounds per square inch for between about 5 and 30 minutes, then Aseparating spent potassium hydroxide solution with reaction products contained therein from the treated oil, separating potassium cresylates from the withdrawn solution, then subjecting the solution todistillation at low pressure and at a temperature not exceeding about 300 F. for re-` moving water therefrom, and returning the concentrated caustic solution for contacting withV additional amounts of said distillate.

5. The process of claim 1 wherein said distillate is a sour virgin heater oil distillate.

6. The process of claim 1 wherein said copper catalyst is selected from the group consisting of copper chloride, copper sulfate, copper nitrate and copper acetate.

7. The process of claim 2 wherein said` copper compound isselected from the group consisting of copper chloride, copper sulfate, copper nitrate y and copper acetate.

8. The process of claim 4 wherein said copper compound is selected from the group consisting of copper chloride, coppersulfate, copper nitrate and copper acetate.

9. The process of claim 4 wherein said potassium hydroxide solution is a substantially saturated aqueous potassium hydroxide solution.

' GERT H. WEISEMANN.

References' Cited in the le of this patent UNITED STATES PATENTS Number Name Date 723,368 Colin Mar. 24, 1903 1,627,055 Morrell et al May 3, 1927 1,749,240 Black Mar. 4, 1930 1,789,335 Fischeret al. Jan. 20, 1931 2,457,635 Bond Dec. 28, 1948

Claims (1)

1. THE PROCESS OF REMOVING MERCAPTANS FROM SOUR HYDROCARBON DISTILLATE WHICH IS HIGHER BOILING THAN GASOLINE WITHOUT FORMATION OF EXCESSIVE COLOR THEREIN, WHICH COMPRISES DISPERSING A COPPER CATALYST IN THE DISTILLATE, INTIMATELY CONTACTING SAID CATALYST-CONTAINING DISTILLATE WITH ABOUT 1 TO 15 PER CENT BY VOLUME OF AN AQUEOUS SOLUTION OF KOH HAVING A CONCENTRATION OF ABOUT 50 TO 60 PER CENT, SAID COPPER CATALYST, WHICH RANGES FROM ABOUT 0.004 TO 0.1 PER CENT BY WEIGHT OF COPPER BASED ON THE CAUSTIC SOLUTION, FORMING A CATALYTICLLY ACTIVE COPPER COMPOUND WHEN CONTACTED WITH THE CAUSTIC SOLUTION, INTRODUCING A GAS CONTAINING AN AMOUNT OF FREE OXYEN ABOUT STOICHIOMETRICALLY EQUIVALENT TO THE AMOUNT OF MERCAPTANS PRESENT IN SAID DISTILLATE INTO THE MIXTURE OF CATALYST-CONTAINING DISTILLATE AND KOH, MAINTAINING THE TEMPERATURE OF CONTACTING AT ABOUT 80 TO 125* F. UNTIL A SUBSTANTIAL REDUCTION IN MERCAPTAN CONTENT HAS BEEN OBTAINED AND SEPARATING SPENT KOH SOLUTION AND ASSOCIATED REACTION PRODUCTS FROM THE TREATED OIL.

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