US3258421A - Desulfurization of hydrocarbon oils - Google Patents

Description

June 28, 1966 J. F. GRUTSCH DESULFURIZATION OF HYDROCARBON OILS Filed NOV. 13, 1964 m 1 MG QE INVENTOR. James E Grufsc/r A TTOR/VEY United States Patent 3,258,421 DESULFUREZATION 0F HYDROCARBON OILS James Francis Grutsch, Hammond, Ind., assignor to Standard Oil Company, Chicago, Ill., a corporation of Indiana Filed Nov. 13, 1964, Ser. No. 410,914 13 Claims. (Cl. 208-206) This invention relates to the refining of hydrocarbon oil, and more particularly to the removal of mercaptan compounds from hydrocarbon oil fractions.

Sulfur is undesirable in gasolineand distillate fuels.

Mercaptans are especially undesirable because they have objectionable odors, even in very low concentrations. Aqueous caustic washing will remove some lower-boiling mercaptans, but the higher-boiling mercaptans are not removed because of their lower solubility in the caustic phase. Consequently, mercaptans are often converted into disulfides, which are practically odorless, by one of a number of sweetening processes. These processes, however, generally do not reduce sulfur content, and sometimes increase it. By definition, a stock is sweet if it passes the doctor test. The sensitivity of the test varies with the mercaptan compound present and is at best sensitive to about four parts of mercaptan sulfur per million parts (4 ppm). Another way of expressing rnercaptan sulfur content in hydrocarbon oils is by mercaptan number which is expressed as milligrams of mercaptans sulfur per 100 milliliters of sample. Because sulfur compounds lower the octane number of leaded gasolines, and because the products from combustion of sulfur-containing oils such as gasoline, kerosene, heater oil, fuel oil, jet fuel, diesel oil, etc, are highly corrosive to fines, stacks, and exhaust systems, sulfur compounds must be removed to produce high quality products. There are several commercially available treating processes which will reduce the sulfur content of hydrocarbon oils, however, the treated products are frequently objectionable because they are colored. The development of color in treated hydrocarbon oils is undesirable because it interferes with tinting by the addition or dyes, and because the presence of color in normally colorless products indicates to the customer existence of contamination, even though the concentration of contaminants may be within acceptable limits. Hyrodesulfurization processes remove sulfur and produce good color, but they require a hydrogen feed stream and operate at high pressure, therefore they are expensive.

The reaction of acrylonitrile and related compounds with mercaptans present in hydrocarbon oil is described as a method for mercaptan removal from the oil in a paper entitled, Determination of Disulfides in the Presence of Thiols, published in the bound volume, General Papers Presented Before the Division of Petroleum Chemistry of the American Chemical Society, September 14-19, 1952, Atlantic City, NJ, at pages 1l3118. S'weetening of hydrocarbon mineral oils by reacting acrylonitrile or related compounds with mercaptans in the oils is also described in United States Patents 2,758,- 058, issued August 7, 1956, and 2,893,952, issued July 7, 1959. In attempting to use these processes for sweetening hydrocarbon oils it was found that the products, while sweet, were unacceptable from the standpoint of color and color-stability, the treated oil becoming too dark for the color to be measured by the Saybolt color test after standing only a few hours in the presence of air, such as occurs in storage tanks.

In accordance with the present invention, a hydrocarbon oil treating process is provided which produces a highly satisfactory reduction in objectionable mercaptan sulfur content and imparts color stability. The treatment according to the present invention is capable of proice viding a greater reduction in objectionable sulfur content than prior art low-pressure treatments, e.g., with aqueous caustic or by doctor treating, while at the same time providing a substantially colorless treated product which does not become highly colored upon standing in the presence of oxygen.

The present invention provides a method of sweetening a mercaptan-containing hydrocarbon oil which comprises reatcing mercaptans in said oil under substantially anhydrous conditions in the presence of solid caustic and in the substantial absence of oxygen with a nitrile compound having the general formula:

where R, R, and R" are each selected from the group consisting of hydrogen, methyl, and ethyl radicals. Where a substantially colorless product having good color stability is desired, it is essential that oxygen be excluded from the oil to be treated and, following contacting of the oil will solid caustic in the presence of the above defined compound, the treated oil is thoroughly water- Washed prior to permitting the treated oil to contact oxygen 'or air. The presence of any liquid water in the oil feed is highly undesirable, because water is attracted to the surface of the solid caustic forming undesirable aqueous caustic which fouls the surface of the solid caustic particles and also causes polymerization of the treating chemical, e.g., acrylonitrile, being employed. Preferably, the feed oil is substantially anhydrous.

A convenient method of obtaining a dry, oxygen-free feed stream is to withdrawn the feed oil as a bottoms or side stream from a distillation column. The oil is then fed directly to' the treating process without intermediate storage, where it would be subject to contamination by water and/ or oxygen. If storage is necessary, gas blanketing can be used to exclude moisture and air. Thus, another embodiment of the present invention is a process for sweetening and imparting color stability to a mercaptan-containing hydrocarbon oil which comprises contacting the oil with solid caustic in the substantial absence of oxygen and in the presence 'of a compound having the general formula: I

where R, R, and R" are each selected from the group consisting of hydrogen, methyl, and ethyl radicals, recovering treated oil from said caustic and washing said treated oil with water to produce a sweetened, colorstable oil. A preferred treating compound is acrylonitrile. Preferably sodium hydroxide or potassium hydroxide is used as the solid caustic with which the oil containing the treating agent is contacted, however, other solid bases may be employed. Sodium hydroxide is generally preferred because of its low cost.

Many different oils having a variety of end uses can be terated to advantage with the process of the present invention. Typical hydrocarbon oils which are advantageously treated according to this process are gasoline blending stocks, finished gasoline, kerosene, jet fuel, heater oil, furnace oil, diesel oil, etc. The process is adaptable for operation over a Wide range of temperature. Operating temperature is generally in the range of 50 to 250 F., preferably in the range of about to 200 F. Liquid phase contacting is employed, therefore the use of elevated pressure may be necessary in order to maintain the liquid phase when light materials are treated at the higher temperatures.

The water washing step is also carried out in the liquid phase. Any suitable method for contacting thoroughly the Water and oil may be employed. One method,

3 which has been found to be satisfactory, is to inject water into the suction of a centrifugal pump which discharges into a settling drum wherein the water is allowed to separate from the oil. In some cases, particularly water-wash step with or without any previous separation.

EXAMPLE 1 A chemical sweetening pilot plant with a flow scheme w treating heavier oils Such as diesel oil and e similar to that illustrated in the figure was operated for Water does not f' ,settle from the 011 m sweetening of various feed streams. A summary of the the settlmg f leavmg the 011 Wlth haze An g experimental results from a number of tests is shown in statlc Preclpltator, as thqse used for SeParatmg Table I. Flake sodium hydroxide was used as the solid drocarbon'water emulslons dunng water'washmg Crud? caustic in each of the tests. The product from each test 1 can b advantageously d m la e of or ln as sweet by the doctor test and the product was sparktion to a settling drum to separate the o1l-water mixture ling clear and Water White s y The results resulting from i116 Water Washlng f W111 P a of these tests show that the process of the present inven- Cl ar and brlght, hale-free treated When m; tion is effective for removing mercaptan sulfur from merdistillate fuels, it is desirable that a stringent water wash r captan-containing hydrocarbon il and al o at the ame be used in order to remove essentially completely sotime producing a colorless product.

Table I Test Feed Acrylonitrile Contact Time Contacting Product No. Feed Type Mercaptan used, percent with Temp., F. Mercaptan No. of Theory Caustic, min. No.

1 Kerosene 3.2 150 4.3 100 2.3 2 do 3.2 150 4.3 150 1.5 3.2 150 4. 3 185 1.2 3.2 100 4.3 150 1.7 6.7 150 4.3 115 2.6 6.7 150 4.3 180 1 6. 7 263 12. 7 140 1. 0 s. 4 185 28.0 175 07 s 30. 7 150 20. 0 150 0. 4

dium naphthenates formed during the contacting with EXAMPLEZ the solid caustic. This is important from the standpoint of color and color stability, since sodium naphthenates, and/or perhaps other materials present in the contacted oil tend to form color upon contact with oxygen or air. These are removed by water washing.

Turning now to the figure, which is a schematic fiow diagram of a preferred embodiment of the invention, hydrocarbon oil feed, from which liquid water has been removed, is passed from source 10 via line 11, to feed pump 12. Treating chemical, e.g., acrylonitrile, is passed from source 13 via line 14 into feed line 11 and thence to the feed pump 12. The feed containing the treating chemical is discharged from the feed pump 12 into feed preheater 16 via line 17. In feed preheater 16 the feed-chemical mixture is heated to the desired contact temperature, usually within the range of 50 to 250 F. The heated oil-chemical mixture is passed via line 18 into a bed of solid caustic contained within vessel 19. Any solid alkali metal hydroxide may be used as the solid caustic contact material, however, flake sodium hydroxide is usually preferred. The contact time of the feed-chemical mixture with the solid caustic is normally within the range of about 1 to 100 minutes, preferably about 2 to 20 minutes. Effluent from the solid caustic vessel 19 is passed via line 21 to centrifugal booster pump 22. Water from line 23 is introduced into line 21 at junction 24 and passed into the centrifugal booster pump 22 along with the effluent from solid caustic vessel 19. The water is thoroughly mixed with the oil in the centrifuagl pump 22 and discharge line 26 through which the oil-water mixture is discharged from the pump into water settler 27. In the water settler 27, water separates from the treated oil and is withdrawn from the settler 27 via line 28 and discharged to the sewer. Separated oil is withdrawn from the water settler 27 and passed via line 29 to product cooler 31. Color-stable sweet product is then passed to storage via product line 32.

In another embodiment of my treating process, the oilchemical mixture is contacted under treating conditions with the solid caustic in the form of a slurry of finely divided caustic particles. The solid caustic particles are recovered from the treated oil after the desired contact time with the oil-chemical mixture, or removed in the The sweetening pilot plant was operated without chemical addition to determine the elfect of merely passing No. 1 fuel oil feed over solid caustic and then water washing it. After about 12 hours operation under conditions of 11.7 minutes contact time with the solid caustic and a temperature of 158 F. the feed and product each had a mercaptan number of 9.0, showing that mere caustic contact followed by water washing eflected no mercaptan removal. Acrylonitrile addition was then started at a rate of 150% of the theoretical amount necessary to react with all the mercaptans present in the feed, other processing conditions remaining unchanged. The mercaptan number of the product was determined one hour after acrylonitrile addition was started and found to be down to 0.32.

EXAMPLE 3 To show the excellent colorhold property of oil treated in accordance with the present invention a sample of heater oil treated with acrylonitrile as the treating chemical and having a color of 30+ Saybolt, was put into a clear glass bottle and stoppered with a cork. An air space was left above the oil. The sample was then placed in a north window and thus exposed to natural day-light for a period of several weeks. The color of the treated oil remained crystal-clear and water-white with no signs of darkening. Oil treated by conventional finishing processes turns dark-colored when exposed to day-light in this manner. This shows the remarkable color stability imparted to the oil by the treating process of the present invention.

EXAMPLE 4 To illustrate that undesirable product, from the standpoint of color, is produced when aqueous caustic is used, in place of the solid caustic employed in the present invention, and contact with oxygen is not avoided, milliliters of mercaptan-containing heater oil is placed in a separatory funnel and 200 percent of the stoichimetric amount of acrylonitrile required to react with the mercaptans present in the oil is added. Next, 20 ml. of aqueous 20% sodium hydroxide solution is added and the funnel stoppered and shaken to thoroughly contact the aqueous and oil phases. The aqueous phase is then allowed to settle and is drawn oif from below the oil phase. The oil is then water washed by adding 100 ml. of distilled water to the funnel, mixing the water and oil by shaking, allowing the water to settle and then withdrawing it. The resulting oil, while sweet to the doctor test, is too dark colored after standing for only about 3 hours for the color to be measured by the Saybolt test.

While my invention has been described with reference to specific examples and particular embodiments thereof, it is to be understood that modifications and variations evi-dent to persons skilled in the art from the above description are deemed to be within the spirit and scope of my invention.

I claim:

1. A method of sweetening a rnercaptan-containing hydrocarbon oil which comprises reacting mercaptans in said oil under substantially anhydrous conditions in the presence of solid caustic and in the substantial absence of oxygen with a nitrile compound having the general formula:

RO=O-CEN where R, R, and R" are each selected from the group consisting of hydrogen, methyl, and ethyl radicals.

2. A process for sweetening and imparting color stability to a mercaptan-containing hydrocarbon oil which comprises contacting said oil with solid caustic in the substantial absence of oxygen and in the presence of a compound having the general formula:

RC=COEN I'k! I l/I where R, R, and R" are each selected from the group consisting of hydrogen, methyl, and ethyl radicals, and washing said contacted oil with water to produce a sweetened, color stable oil.

3. A method of converting mercaptans in mercaptancontaining hydrocarbon oil to organic sulfides which method comprises removing liquid Water from said oil, admixing with said oil at least about one mol of acrylonitrile for each mol of mercaptan contained in said oil, contacting said mixture with solid caustic, thoroughly mix-ing water with said oil following said contacting, separating said oil from admixture with said water and recovering as product a color stable oil of reduced mercaptan c-ontent.

4. The method of claim 3 wherein said solid caustic is sodium hydroxide.

5. The method of claim 3 wherein said solid caustic is potassium hydroxide.

6. A process for converting mercaptans in a mercaptan-containing hydrocarbon oil feed and imparting color stability to said oil feed which process comprises removing oxygen and liquid water from said feed, contacting the resulting dry and oxygen free oil with solid caustic in the presence of at least about one mole of acrylonitrile per mol of mercaptan in said feed, water washing said contacted oil, and separating from said water washing treated oil havin-g reduced mercaptan content and improved color stability.

7. The process of claim 6 wherein said oil feed is gasoline.

8. The process of claim 6 wherein said oil feed is jet fuel.

9. The process of claim 6 wherein said oil is heater oil.

10. The process of claim 6 wherein said oil feed is diesel oil.

11. The process of claim 6 wherein oxygen and water are removed from said feed oil by distillation.

12. The process of claim 6 wherein said contacting with solid caustic is carried out at a temperature within the range of about to 250 F.

13. The process of claim 6 wherein said oil is dehazed following said water washing by passing said water washed oil through an electrostatic precipitator.

References Cited by the Examiner UNITED STATES PATENTS 1,791,521 2/1931 Bjerregaard 208-232 2,034,837 3/1936 Schulze et al. 208-189 2,381,293 8/ 1945 La Lande 208-230 2,471,108 5/1949 Hill 208-230 2,604,437 7/1952 Conner et al. 208-230 2,725,339 11/1955 Browning et al. 208-230 2,758,058 8/1956 Schneider et al. 208-207 2,893,952 7/1959 Chenicek 208-206 3,128,155 4/ 1964 Mattox 20 8-234 vDELBERT E. GANTZ, Primary Examiner.

PAUL M. C OUG I-ILAN, Examiner.

R. H. SHUBERT, Assistant Examiner.

Claims (1)

1. A METHOD OF SWEETENING A MERCAPTAN-CONTAINING HYDROCARBON OIL WHICH COMPRISES REACTING MERCAPTANS IN SAID OIL UNDER SUBANTIALLY ANHYDROUS CONDITIONS IN THE PRESENCE OF SOLID CAUSTIC AND IN THE SUBSTANTIAL ABSENCE OF OXYGEN WITH A NITRILE COMPOUND HAVING THE GENERAL FORMULA:

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