US3305479A - Copper chloride sweetening process - Google Patents

Description

Feb. 21, 1967 J. F. GRUTSCH ETAL 3,305,479

COPPER CHLOHIDE SWEETENING PROCESS Filed Oct. 16, 1964 United States Patent iice 3305 479 CUPPER CHLGRHD SWEETENHNG PROCESS .lames Francis Grutsch and Edward Arthur McGee,

Hammond, and Russell Clayton Mallatt, Crown Point,-

This invention relates to the treatment of petroleum distillates. More specifically, the invention pertains to the improvement of color and colorhold properties of treated distillates which are heated during the process of treating.

`Our invention is an improvement in a process for liquid phase treating of hydrocarbon distillate, such as for example, gasoline, kerosene, heater oil, `diesel oil, furnace oil, etc., in which process said `distillate is heated, for example, to 80-300" F., which comprises dissolving oxygen, as substantially pure oxygen, air, or other oxygen-containing gas, in said distillate for va time lbefore said heating sufficient to impart improved color and color stability to the product of said treating. Examples of treating processes in which our invention is advantageously employed are copper chloride sweetening, aqueous alkali metal hydroxide treating, etc. The time that the distillate contains dissolved oxygen before the heating is preferably at least about five minutes, with times of 2 hours to five days or longer having proven satisfactory.

Our invention is applicable to lprocesses which already employ air or oxygen, but in a different manner. We have discovered that a process for swe-etening hydrocarbon distillate by contacting the distillate with CuCl2 and oxygen is surprisingly improved 'by contacting the distillate with oxygen or air at least about five minutes before contacting `the oxygen-containing distillate with CuCl2. We prefer to provide at least above five minutes contact time between addition of at least about 0.001 s.c.f./bbl./mer captan number of oxygen, either as substantially pure oxygen, air or other oxygen-containing gas, and the contacting of oxygen-containing distillate with CuCl2. `By our invention, we provide an improved method of sweetening and imparting improved color and colorhold (color stability) properties to hydrocarbon distillate in treating of the distillate by dissolving oxygen therein and contacting the resulting oxygen-containing distillate with CuClz which comprises dissolving in the distillate to be treated at least about 0.001 s.c.f. of oxygen per barrel of distillate per mercaptan number of the distillate at least about five minutes 'before the dissolved-oxygen-containing distillate is contacted with the CuCl2 for sweetening. If desired, the entire amount of oxygen required by the copper chloride sweetening process (plus the desired excess) may be dissolved in the distillate at least about ve minutes before the distillate is contacted with the CuCl2. Our preferred method of providing oxygen is to dissolve air in the distillate to be sweetened.

A preferred embodiment of our invention is the improvement in a process for copper chloride sweetening of hydrocarbon distillate lby the steps of mixing aqueous caustic with said distillate, separating said caustic from said distillate, passing the separated distillate through a salt bed to remove water therefrom, dissolving oxygen in 3,305,479 Patented Feb. 21, 1967 the distillate, contacting the oxygen-containing distillate with CuCl2, recovering treated distillate from the contacting, and water-washing said treated distillate, which comprises dissolving oxygen-containing gas in said distillate prior to the mixing of aqueous caustic with the distillate whereby oxygen is present in the distillate to be sweetened at least about ve minutes prior to the contacting of the oxygen-containing distillate with CuClg.

The copper chloride sweetening process is well known in the art. It has the advantage over doctor sweetening of requiring no sulfur. The copper chloride catalyst may be employed as a fixed-bed, as a slurry, or as a solution. Corrosion problems have limited the use of the solution technique.

In simplified form, copper chloride sweetening reactions are:

Over-all, the reactions are:

4RSH-l-O2 2RSSR+2H2O An excess of oxygen 1.5 to 3 times the theoretical) is used to obviate incomplete regeneration, which would have an adverse effect on the gum content and the inhibitor response of the product.

A small amount of water is formed in the sweetening reaction. In the fixed-'bed and slurry processes, the water must be removed as it forms; otherwise it will ac-cumulate in the catalyst and interfere with the operation. One method of removal is to heat the feed to a temperature high enough that the water of reaction dissolves in the product stream. Reaction temperature is raised approximately 1 F. for each unit increment of mercaptan number of the feedstock. Mercaptan number is expressed as milligrams of mercaptan sulfur per one hundred milliliters of sample.

In copper chloride sweetening employing as catalyst a clay-CuCl2 slurry, the feed is pre-washed with caustic to remove hydrogen sulfide. It is then coalesced to remove traces of caustic, warmed, and charged to a slurry reactor. After caustic washing, coalescing, and warming, the fe-ed is mixed with air or oxygen and then with a slurry of copper chloride (one part) and clay (4-10 parts). The mixture is sent to a reactor-separator, from which catalyst is recycled to the feed. Treated product may be water-washed before it is withdrawn from the system. In a fixed-bed plant, air is mixed with the feed, and the mixture is passed downow over a lbed of catalyst.

Reaction temperatures are normally between and F. At lower temperatures, the reactions are slow; at higher temperatures there are undesirable side reactions.

Because copper catalyzes the deterioration of the treated product, even minute amounts must be removed or deactivated. Water washing does not remove all the copper, and sodium sulfide or zinc sulde washes are sometimes used, particularly with cracked stocks. Chelating agents are :always added to the final product to sequester residual copper and deactivate it. These agents are widely known as metal deactivators. Copper chloride processes may be used to sweeten a variety of hydrocarbon distillates, e.g.,

gasoline, kerosene, jet fuel, fuel oil, diesel fuel, heating oil, etc.

It has `been found that certain hydrocarbon distillates degrade markedly in colorhold stability during sweetening and upset the copper chloride process such that it is two or three days before satisfactory product can again be made. Although it is not known with certainty, and We do not intend to be held to any particular theory, it is believed that the color formers are aromatic mercaptans. Certain aromatic mercaptans are easily oxidizable to sulfnic and/or sulfonic acids. These acids may react with olens to give polymerization and/or condensation products which are colored. Brown flocculent solids a-re also sometimes produced.

By the color of hydrocarbon distillates we mean the color rating as determined by the conventional tests, i.e. ASTM D156 if in the Saybolt color range or ASTM D-1500 if in the ASTM color range. A good-colored distillate would be one lighter than about Saybolt. By good colorhold properties, and by color-stability, we mean the property of hydrocarbon distillate to maintain a good color rating (i.e. no darker than about +10 Saybolt) upon standing in storage.

The colorhold properties of distillates are determined experimentally by heating a 100-milliliter sample for 60 minutes in an oil bath maintained at 290 F. The sample is then allowed to cool and the color, which we term aged color, is determined by the conventional tests. A distillate having good colorhold properties is one which has an aged color no darker than about +10 Saybolt.

Referring now to the figure, which is a preferred embodiment of our improved process, sour hydrocarbon distillate charge from source 10 is passed through line 11 by a pump, not shown, into mixer 12. A slip-stream of the charge material from line 11 is passed via line 13 through eductor 14 and returned via line 15 to the charge stream passing through line 11. Air is passed through line 16 into eductor 14 where it is mixed with and dissolves in the slipstream of charge material. Caustic, preferably aqueous sodium hydroxide, is passed via line 17 into the charge stream now containing air and flowing through line 11 into mixer 12. In mixer 12 the caustic is thoroughly mixed with the hydrocarbon distillate charge and passed via line 18 into caustic settler 19. Settled caustic is withdrawn from the caustic settler via line 21 and recirculated to line 17. Spent caustic is withdrawn from line 21 via line 22. Caustic-washed distillate, still containing dissolved oxygen, is passed from the settler 19 via line 23 into salt drum 24. The salt drum 24 contains granulated salt, preferably sodium chloride, which coalesces and removes traces of entrained caustic and/or water. Brine is withdrawn from the bottom of the salt drum via line 26 and discarded. The feed is generally preheated before caustic washing by a preheater, not shown. The pre- Wash removes any H28 from the charge which would poison the copper chloride catalyst. The caustic is completely separated from the oil in the settler before salt tower clarification. The holdup volume in the piping, settler and the salt drum is usually sufficient to provide at least about five minutes contact time of the oxygen with the oil. If these vessels do not provide sufficient holdup time, additional volume is provided.

Clarified oil from the salt drum is passed via line 27 by Way of a booster pump, not shown, through a reactor feed preheater 28 where the temperature of the stock is increased enough to absorb the water produced in the sweetening reaction and maintain a constant moisture content in the catalyst slurry. Too much water causes conglomeration and catalyst eductor plugging; too little water increases catalyst losses and decreases product stability. Normally, an increase of 1 F. for each mercaptan number of the feed will maintain the desired moisture content of about water. With a low mercaptan number charge stock, the reactor preheater may not be required, and water may be added by continuous steam injection to maintain a minimum slurry moisture content. Preheated oil is passed via line 29 into catalyst slurry eductor 31. A slip-stream of this oil, prior to the catalyst eductor 31, is passed via line 32 through air eductor 33 and returned to line 29 via :line 36. Air is introduced into the air eductor 33 via line 34. If desired, all of the required oxygen may be introduced prior to the caustic washing section, vial line 16, and eductor 14, thus eliminating the need for a second injection system such as air eductor 33. The oil flows from line 29 through eductor 31 at the bottom o-f reactor 37. The copper chloride-clay slurry is pulled into the oil stream from the cone of the reactor via line 39 and into the throat of the eductor 31. Make-up CuClz-clay slurry is also fed into the eductor 31 via line 30. The sweetening reaction takes place immediately as the oil containing the catalyst slurry and oxygen passes from eductor 31 through line 38 into the reactor. The reactor 37 provides time for the catalyst and oil to separate. The catalyst is recirculated via line 39 to eductor 31. The oil passes overhead from the reactor 37 via line 41 into water mixer 42 where the oil is thoroughly mixed with water from line 43. The water-oil mixture is passed from the mixer 42 via line 44 into water settler 46. Mixers 12 and 42 may be any conventional type of mixer which will provide good contact between the aqueous phase and the oil. Almost all of the catalyst slurry carried out of the reactor 37 is removed by the water Wash. Any copper that remains in the oil after the water wash is neutralized by the addition of metal deactivator to the product. Metal deactivator inhibits the catalytic effect of trace quantities of soluble copper on gum formation. Settled water is withdrawn from the settler 46 via line 48. Color-stable sweet product hydrocarbon distillate is withdrawn from the settler via line 47.

The beneficial effect of our unexpected discovery that the addition of air (or oxygen) to the oil feed to a treating or finishing process at least about tive minutes before the oil is heated in the process markedly improves color and colorhold properties of the oil is illustrated by the following examples.

EXAMPLE I To demonstrate the effectiveness of our invention, samples of hydrocarbon distillate, in each case No. 1 fuel oil stock, were divided into two parts and one part heated to a temperature of 290 F. in an oil bath and held at that temperature for one hour, then cooled to room temperature, about 75 F., and the color (ASTM D-l56 or ASTM D-1500 as appropriate) determined. The other part of each sample was first shaken in a bottle containing an air space in order to dissolve oxygen in the distillate. Each shaken sample containing dissolved oxygen was then allowed to stand in the stoppered bottle at a temperature of about 75 F. for a period of time and then was heated to 290 F. in an oil bath and held at that temperature for one hour. At the end of the one hour at 290 F. each sample was then cooled to about 75 F. and the color determined as above. Each oxygen treated portion was much lighter in color than the untreated portion. The results of these experiments are shown in Table I.

TABLE I Sample Color Without Time of O2 Color with Oxygen Treat 1 Treat, days Oxygen Treat 1 l All colors are Saybolt colors (ASTM D456) except those marked with an2 aterisk which are ASTM colors (ASTM D-1500).

ours.

EXAMPLE n Commercial sweetening plant tests were conducted on a plant similar to that illustrated in the figure to demonstrate the benefits of dissolving oxygen in the sour hydrocarbon distillate feed at a point providing preoxidation time prior to contacting the feed with CuCl2 for sweetening. Typical operating conditions of this plant during the tests are shown in Table II.

TABLE II [Treating plant operating conditions] Hydrocarbon distillate feed, heater oil No. 1

Feed temperature, F 90-100 Reactor preheat temperature rise, F./RSH

Number 1 1 Reactor temperature, "F 100-110 Reactor pressure, p.s.i.g 40-60 Catalyst eductor pressure differential, p.s.i 4070 Catalyst moisture content, wt. percent 15-20 Catalyst circulation rate, vol. percent based on oil -20 CuClZ-to-clay ratio 1/ 10 Catalyst charge per reactor, CuClZ, lbs 60 Catalyst charge per reactor, clay, lbs 500 Catalyst addition per reactor, CuCl2, lbs/l2 hours 5 Catalyst addition per reactor, clay, lbs./ 12

hours 50 Water wash, vol. percent based on oil 20-30 Chemical consumption, lbs./ 1,000 bbls. of feed except as noted):

Copper chloride 1.5-3.0 Clay -30 Air (total), std, cu. ft./bbl./RSH Number (150/ of theoretical) 0.08 Caustic 5 Metal deactivator 2 Salt, before reactors 15 1 Degrees Fahrenheit per mercaptan number.

Without introduction of air prior to the caustic washing section of the plant, and with all of the air being injected after the reactor feed preheater and just prior to the reactors, there were frequent periods when color unstable product was produced. Typical results during these periods of off-specification production are shown in tests l through 5 of Table III. In each of tests 15, the aged color of the product was darker than +10 Saybolt +10).

Tests 6 through 10, also shown in Table III, show that light colored, color-stable product results when a portion (in this case one-half) of the air is injected into the fuel oil feed stream prior to the caustic wash section of the plant as illustrated by eductor 14 in the tigure. These experimental tests extended over a several-month period during which time no product having an aged color darker than +10 Saybolt was made.

In tests 6-10, 0.04 s.c.f. of air/barrel/mercaptan number was injected into the distillate feed prior to the caustic wash section and the remainder of the air (0.04 s.c.f./bbl./RSH No), the amount required to provide a total of 150% of the theoretical amount of oxygen required for the sweetening reactions, was injected at the old injection point just prior to the reactors. The holdup volume of the caustic settler, salt drum, and piping provided 120 minutes contact time from the point of rst injection of air prior to the caustic washing section, illustrated by eductor 14 in the figure, and the contacting of the oxygen-containing distillate with CuCl2 in the catalyst slurry eductor, illustrated by eductor 31 in the ligure.

1 All colors are Saybolt colors except those marked with au asterisk which are ASTM colors.

As shown by comparison of tests 1-5 with tests 6-10, practice of the present invention results in the production of light colored, color-stable sweetened product even when the feed has poor color stability.

The foregoing description and examples are intended to be illustrative only. Many modifications of our invention will be evident from our description thereof to persons skilled in the art, but such modifications and variations conforming to the spirit of the invention are to be considered within the scope of the claims.

We claim:

1. The process for liquid phase copper chloride sweetening of hydrocarbon distillate fuel oil stock in which process said distillate is heated, the improvement which comprises dissolving oxygen in said distillate for a time of at least about two hours before said heating and adding additional oxygen for said sweetening, which time is sufficient to impart improved color and color stability to the product of said sweetening.

2. In a continuous flow process for sweetening hydrocarbon distillate by contacting said distillate with CuCl2 and oxygen, the improvement which comprises contacting said distillate with oxygen at least about two hours before contacting said distillate and additional oxygen with CuClZ.

3. In a continuous flow process for sweetening hydrocarbon distillate by caustic washing said distillate, adding oxygen to said distillate, and contacting said oxygencontaining distillate with CuCl2, the improvement which comprises providing at least about ve minutes contact time between addition of at least about 0.001 s.c.f./bbl./ mercaptan number of oxygen and said contacting of said oxygen-containing distillate with CuCl2 and additional oxygen for sweetening.

4. An improved method of sweetening and imparting improved color and colorhold properties to hydrocarbon distillate in treating said distillate in a continuous flow process by dissolving oxygen in said distillate and contacting the resulting oxygen-containing distillate with CuCl2 which comprises dissolving at least about 0.001 s.c.f. of oxygen per barrel of distillate per mercaptan number in the distillate to be treated, said dissolving being effected at least about live minutes before said dissolved oxygen-containing distillate is contacted with said CuCl2 and additional oxygen for sweetening.

5. The method of claim 4 wherein said oxygen is provided by dissolving air in said distillate.

6. In a continuous flow process for copper chloride sweetening of hydrocarbon distillate by the steps of mixing aqueous caustic with said distillate, separating said caustic from said distillate, passing said separated distillate through a salt bed to remove water therefrom, dissolving oxygen in said distillate, contacting said oxygencontaining distillate with CuClg, recovering treated distillate from said contacting, and water-washing said treated distillate, the improvement which comprises dissolving oxygen-containing-gas in said distillate prior to said mixing of aqueous caustic with said distillate whereby oxygen is present in said distillate at least about ve minutes 7 prior to said contacting of said oxygen-containing distillate with CuC12 and additional oxygen.

7. The process of claim 6 wherein said oxygen is provided by dissolving air in said distillate and said oxygencontaining-gas is air.

8.- The process of claim 6 wherein the amount .of oxygen dissolved in said distillate prior to said mixing with said aqueous caustic is at least about 0.001 s.c.f. of

oxygen per barrel of distillate per mercaptan number of said hydrocarbon distillate.

References Cited by the Examiner UNITED 7/1904 9/1956 l0/l956 l/1965 STATES PATENTS Amend 208-192 McNeill et al. 208-192 Kalinowski et al. 208-195 Bowers 208-207 DELBERT E. GANTZ, Prfmmly Examiner.

m R. H. SHUBERT, Assistant Examiner.

Claims (1)

1. THE PROCESS FOR LIQUID PHASE COPPER CHLORIDE SWEETENING OF HYDROCARBON DISTILLATE FUEL OIL STOCK IN WHICH PROCESS SAID DISTILLATE IS HEATED, THE IMPROVEMENT WHICH COMPRISES DISSOLVING OXYGEN IN SAID DISTILLATE FOR A TIME OF AT LEAST ABOUT TWO HOURS BEFORE SAID HEATING AND ADDING ADDITONAL OXYGEN FOR SAID SWEETENING, WHICH TIME IS SUFFICIENT TO IMPART IMPROVED COLOR AND COLOR STABILITY TO THE PRODUCT OF SAID SWEETENING.

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