US2794770A - Stabilization of cracked distillate fuel oils - Google Patents

Description

June 4, 1957 W..'H. ALDERSON ETAL 2,794,770

STABILIZATION OF CRACKED DISTILLATE FUEL OILS Filed May 18. 1953 2 Shee'ts-Sheet l CAUSTIC ALCOHOL ATTORNEYS" June 4, 1957 w. H. ALDERSON EIAL I 2,

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HI'LLLIIS k N g Q w 2% "a 1 w -O U? I: J? m im a. m 0 2 3 g 0,.2 0 .1 i :Zu g- -u '2 (In my 2:15 rig A I INVENTORS Q o W/LL/AM H. ALDERSON J, g HOWARD AL EN 3 Q I 4 BY WVBLS ATTORNEYS United States STABILIZATION OF CRACKED DISTILLATE UEL OILS Application May 18, 1953, Serial No. 355,804

4 Claims. c1. 196-41) This invention relates to a process for treating cracked petroleum hydrocarbons and, more particularly, to a process for stabilizing cracked distillate fuel oils useful as fuels for industrial and household furnaces or burners, as fuels for diesel engines, and the like.

Thermally or catalytically cracked petroleum hydrocarbons boiling within about the range of 300 to 750 F., generally known as cracked distillate fuel oils, such as cracked gas oil, and which find utility as furnace oils, diesel fuels, and the like, suffer from the disadvantage of instability. During storage, such oils develop objectionable color characteristics and gum-like oil-insoluble materials or sludges which upon use of the oils cause plugging and clogging of filters, screens, and burner tips, thus detracting from their usefulness and impairing their marketability. Also, in refinery practice it is advantageous to form blends of cracked fractions with straightrun stocks for the uses above enumerated. For example, products from catalytic cracking plants include a partly or completely converted stock in the gas oil boiling range, called catalytic cycle oil. An advantageous disposition of this cycle oil is its use as furnace oil blended with straight-run oils, for example, straight-run gas oil. Inclusion of the cycle oil in the furnace oil, however, so impairs the stability of the blend that it is often necessary to divert it to black fuel oil of lower value. Generally, blends of straight-run and cracked distillate fuel oils are not compatible; that is, the blend is less stable than would be expected from the stability of the components before blending. Such blends, because of their incompatibility, have not enjoyed wide acceptance.

We have now found that we can overcome the problem of instability attendant cracked petroleum distillate fuel oils by a process which, broadly, comprises subjecting the cracked distillate, for example, cracked gas oil, to the action of a treating agent mixture comprising alcohol and an alkali metal hydroxide as indispensable components, and also, preferably a third component, water, to give reaction products therewith, followed by the removal of said reaction products, as filtration, water-washing and the like. We have found, moreover, as hereinbelow to be more fully shown, that the limits of amount, expressed as weight percent, of each component present in the alcoholic caustic treating agent are critical.

More specifically, the invention contemplates a process involving the intimate admixture of unstable hydrocarbon fuel oil, and a treating agent comprising a mixture of caustic, such as sodium or potassium hydroxide, and a low molecular weight alcohol, such as methyl, ethyl, normal and isopropyl alcohols, and ethylene glycol, as solvent or carrier for the caustic. Since the alcoholic caustic treating agent in addition preferably contains Water, the caustic may be added in the form of a solution, solutions 'varying in strength from about 30 B. to about 50 B. being satisfactory. As hereinabove indicated, the limits of amounts of each component present in the treating agent have been found to be critical, and as shown in atent I ice Figure 1, are defined by the area plotted in the triangular diagram.

In carrying out the alcoholic caustic treating step with a suitable treating agent, it is preferred to operate at a somewhat elevated temperature, e. g., F., in order to accelerate chemical reaction of the agent with the materials in the oil causing the instability, although temperatures just above the freezing point of the treating agent, and temperatures just below the boiling point of the alcohol are not precluded from the broader aspects of the invention.

The amount of treating agent employed can vary widely, and is suitably expressed in terms of caustic content of the treating agent. Thus, amounts of 0.0005 to 0.0500, preferably 0.0010 to 0.0100, pound equivalents of alkali metal hydroxide per 100 pounds of oil represent satisfactory operating ranges.

Following the mixing of alcoholic caustic treating agent and oil, the whole is allowed to settle whereby an oil phase separates from the alcoholic caustic phase. The oil phase is then isolated, and, in a preferred embodiment of the invention, is Washed thoroughly with water, preferably hot, e. g., F., in order to remove entrained alcoholic caustic and undesirable water-soluble reaction products from the oil. An oil phase is then separated from an aqueous phase, and the water entrained in the oil phase is removed, as by air brightening.

The process of the invention can be carried out batchwise, continuously or semi-continuously.

It has been ascertained that the precipitates and gums which a cracked distillate fuel oil, such as cracked gas oil, deposits on aging have their source in the polar fraction of the oil, and are formed by oxidation of the latter. Thus, stocks from which the polar fraction has been removed, as by adsorption, are stable with respect to color and gum formation. The polar fraction amounts to between about 0.5% and 3% of the whole cracked stock. Chromatographic and chemical analyses of this polar fraction show that it contains material of varying polarity of acidic, basic, phenolic and neutral nature, while the gum-forming ability of the most polar fractions is greatest, all fractions contain unstable constituents. These polar fractions are converted to gums on contact with air, and gum formation is accelerated at elevated temperatures.

In View of the foregoing explanation of the nature of the deposits, gums and sludges formed in the oil during storage, the function of the alcoholic caustic treating agent is to segregate the undesirable polar compounds by chemical reaction, the reaction products being then removed by washing. Moreover, in order to effect such chemical reactions satisfactorily, it has been found that caustic and alcohol must both be present in the treating agent, since it has been ascertained that no chemical reaction occurs when washing the unstable oil with either dilute aqueous alcohol or aqueous caustic alone and the undesirable compounds are not removed, as a result of which the oil remains unstable.

Further features and advantages of the invention will be apparent from the following description of the invention given in connection with the appended Figures 1 and 2, wherein Figure l is a triangular graph defining the area from which a suitable make-up of the treating agent can be determined; and Figure 2 illustrates a suitable arrangement of apparatus for the carrying out of one embodiment of the invention by a two-stage step counterflow action in both the treating of the oil with the reagent, and the later washing of the treated oil.

Referring to Figure 1, the apieces A, B and C represent respectively the components alkali metal hydroxide, water, and alcohol. Within the triangle points 1, 2, 3

p and 4 define an area from which amounts, by weight percent, of components to vproduce an operative treating agent can be determined. It .will be seen by reference to the various numerals in the graph that the amount of caustic .in the treating agent must be present. at least to the extent of 2% (point 4) and not more than-58% (point 2'). Similarly, the alcohol. may :range .in amount from as little as 6% '(line 12) to 98% (point 4.), while the water can range from to 7.4%, although 30 to 60% water is preferred.

Referring now to Figure 2, treating of the oil with the reagent is effected by a two-stagestep counterflow action, according to which fresh reagent contacts previously treated oil and fresh oil is contacted with previously used reagent. In effecting such treatment, caustic material, such as a 45 B. sodium hydroxide solution stored in vessel 1 is transferred by means of pump 2 through line be tested .isfirst screened .througha. 100 mesh. sieveinto an unstoppered quart bottle to give contact with air, the bottle then being placed in an oven and heated for four weeks at a temperature of 140 F., in order to accelerate aging. After aging the sample is withdrawn from the oven and allowed to cool.

A Gooch crucible .is prepared by placing apiece of filter paper at the bottomof atarred crucible, and a filter mat is formed by pouring. a slurry of asbestos thereover. The crucible is then dried in an oven at 190 F. for one'to one and one-half hoursand stored in a constant humidity vessel for at least three hours before weighing. The

' crucible is then Weighed and the weight noted (a), the

of caustic metering pump 5 through line 6 and introduced into mixing zone 7, wherein it is intimatelyadmixed with fuel oil and alcohol, such as methanol, the alcohol being taken from vessel 8, transferred through line 9 into metering case 10 by means of alcohol metering pump 11 and line 12 into line 6. The fuel oil is taken from storage tank 17, transferred by meansof pump 19 through line 21 and heat exchanger 22, then through mixer 23, introduced into settling zone 24 for preliminary treatment with recycled reagent from settler 29, after which it is removed through line 26 and introduced into line 6 for passage into mixing zone 7. Spent reagent is withdrawn from settler 24 through line 27. The mixture of caustic alcohol and oil is passed from mixing zone 7 through line 28v and is introduced into settler 29. In settler29 an oil phase separates from analcohol-caustic sludge phase. The sludge phase is withdrawn from settler 29 through line 31 and by means of constant volume pump 37 passed into line 21, wherein it contacts fresh incoming oil. After separation of an oil phase from the alcoholic caustic phase in settler 29, the oil phase is sub jected to a two-stage step counterflow washing action, according to which fresh water contacts previously washed oil, and unwashed oil is contacted with previously used water. Thus, the oil phase is withdrawn from settler 29 through line 41 and in mixing zone 44-mixed with water taken from water settler-coalescer 59, and passed through line 60 by means of pump 61. The mixture of Water and oil is then passed through line 46 and heat exchanger 48 and introduced into water settler 49, wherein there is preferably maintained an elevated temperature, e. g., about 180 F. In water settler 49, the mixture separates into an oil phase and an aqueous phase. The-aqueous phase is eliminated from the system through line 51. 'The oil phase is withdrawn through line 52 and mixed-with additional water introduced through line 53 into mixing zone 55, following which the mixture is introduced through line 57 into water settler-coalescer 59. Water settler-coalescer 59 is preferably packed with suitable material, such as rock packing, to increase surface area. In water settler-coalescer 59 an oil phase separates from an aqueous phase, the aqueous phase being removed therefrom throughline 60 by means of pump 61 and-used for mixing with oil from settler 29as previouslyshown. The oil phase is withdrawn from water settler-coalescer 59 through line 63 and introducedinto drying zone 65, which is suitably packed, such as with ceramic Raschig ring-s, and the water removed from the oil 'by means of heated air introduced through line 66. Following drying the finished oil is removed from air brightener 65 through line 67 and pump 68, and waterand air through line '69.

A convenient method of determining the stability of a cracked distillate fuel oil, and the one used in obtaining the data hereinbelow appearing, is the s o-called Filter Residue test, according to which test the amount of insoluble solids finer than 100 mesh present in distillate fuel oils, in parts per million, -by weight, is determined. The test is carried out as follows: A sample of the oil to weight of the dried mat also being noted '(b).

A weighed 500 ml. portion (a) of the cooled sample is transferred to a separatory funnel. The separatory funnel is mounted over. the Gooch crucible so that the stem of the funnel extends well into the crucible. The sample .is then I filte're'd by suction,- and the filteredoil retained undiluted foriuse in calculating the Adsorption Factor.

The empty sample bottle is then washed thoroughly withfiltered petroleum ether, and the washings passed through the separatory funnel and filter. Two additional 250 ml. portions of filtered petroleum ether are added to the separatory funnel and .filtration is carried out at a reduced suction rate sothat the petroleum ether filters slowly. The walls .of the crucible, inside and outside,

and the tip of the separatoryfunnel are washed "with filtered petroleum ether,"after which the crucible is sucked dry, placed in an .oven at about F. .for one to one and one-half hours and then placed in a constant humidity vessellfor atlleast three hours. The Weight of the crucible is then determined (d).

The retained oil from the first filtration -.is passed through a-second Gooch crucible prepared like the hint mentioned one, the crucible having been tarred (2), so that the actual weightiof the filtersmat is .known (f). The crucible is washed with petroleumether and dried as in the first-described filtration operation. The dried crucible is weighed and the weight noted .(g). These weights are used in calculating the Adsorption Factor.

'The material adhering to-the walls of the sample bottle is dissolved with a hot mixture of 8 volumes of benzene plus 2 volumes of ethyl alcohol. The solvent-gum mixture is then evaporated to drynessin'a small tarredheaker, and then weighed .(h). l

Filter residue, in parts per million'of fuel oil, by weight,

is calculated by means'of the following equations W=p p m Filter residue wherein A satisfactory cracked distillate should have a filter residue not exceeding about 25 parts of unfilterable matter by weight per million parts fuel by weight.

The following examples are given in further illustration of the practice and advantages of the invention:

Example 1 (a) Catalytically cracked gas oil having an ASTM D-158 distillation range of 481 F. to 640 F., a sulfur content of 1.15% (ASTM, lamp) and an APIJgra'vity- Example 2 (a) A catalytically cracked gas oil having an ASTM D-158 distillation range of 465 F. to 598 F., a sulfur content of 1.07% (ASTM, lamp), and an API gravity of 23.8 was treated at ambient laboratory temperature for one-half hour with 20% of its volume of isopropyl alcohol containing 0.5 equivalent of potassium hydroxide per liter of alcohol solution, which corresponds to 0.110 pound equivalents of pure potassium hydroxide per hundred pounds of oil. The hydrocarbon phase was separated, water washed and dried. The filter residue test on the treated stock was 5 p. p. m., whereas the original oil had a filter residue of 149 p. p. m.

(b) A portion of the treated stock was then blended with an equal volume of a straight-run gas oil having an ASTM D-158 distillation of 360 F. to 678 F., a sulfur content of 0.46% (ASTM, lamp), an API gravity of 32.1", and a filter residue of 15 p. p. m. The filter residue on the blend was 7 p. p. m.

(c) A second blend of the straight-run stock with an equal volume of the untreated catalytically cracked gas oil had a filter residue of 58 p. p. m.

Example 3 (a) A portion of a cracked gas oil sample with an ASTM D-158 distillation range of 460 F. to 620 F., a sulfur content of 0.54% (ASTM, lamp), an API gravity of 23.1", and a filter residue of 56 p. p. m. was blended with an equal volume of the straight-run gas oil of Example 2. A filter residue test on the blend gave a value of 61 p. p. m., illustrating the incompatibility of cracked and straight-run stocks.

(b) Another portion of the same cracked gas oil was treated at 150 F. with 10% of its volume of a reagent consisting of one volume of methanol in two volumes of 45 B. aqueous sodium hydroxide, the reagent composition thus corresponding to 33 weight percent sodium hydroxide, 21.5 weight percent alcohol, and 45.5 weight percent water, and the indicated volume of reagent used in treating corresponding to 0.111 pound equivalents of alkali metal hydroxide per hundred pounds of gas oil. The filter residue of the oil was reduced to 8 p. p. m.

(c) An experiment similar to (b) was carried out employing only 1% of the reagent, based on volume of the oil, thus corresponding to 0.011 pound equivalents of alkali metal hydroxide and a preferred reagent quantity. In this case, the filter residue test gave a value of 12.

Example 4 1,800 barrels of catalytically cracked gas oil having an ASTM D-158 distillation range of 410 F. to 614 F., a sulfur content of 1.06% (ASTM, lamp), and an API gravity of 24.5 was treated at 120 F. with a caustic methanol reagent in a large tank provided with a pump capable of circulating the contents of the tank at the rate of 1,000 barrels per hour. The reagent used was volume percent, based on the volume of the oil, of a solution consisting of 1 volume of methanol and two volumes of 45 B. aqueous sodium hydroxide, that is the same reagent used in Example 3. The amount of reagent used corresponds to 0.008 pound equivalents of sodium hydroxide per 100 barrels of gas oil. The contents of the tank were circulated for 2 /2 hours and then allowed to settle for five hours at the end of which time about 50% of the treating agent had settled and was thereafter removed. The oil was then washed twice at 150 F. with five volumes of water. After washing, the oil was air brightened by blowing with air at 160 F. for 12 hours.

6 Before treatment, the oil gave a residue test of 150 p. p. m., while after treatment the oil gave a residue test of only 9 p. p. 111.

Example 5 Catalytically cracked gas oil having an ASTM D-l58 distillation range of 420-614 F., a sulfur content of 1.06% (ASTM, lamp), and an API gravity of 24.5 was intimately mixed at 120 F. with a caustic methanol reagent formed with two volumes of 45 B. caustic and one volume of methanol, the amount of reagent employed being equivalent to 0.0014 pound equivalents of base per 100 barrels of oil. Following reaction, the mixture was washed with water to remove the caustic, and the washed product then air brightened. The oil before treatment gave a residue test value of p. p. m. while the finished oil had a residue test value of only 6 p. p. m. A series of runs were made employing portions of the catalytically cracked gas oil of Example 2. These portions of oil were intimately contacted to efiect uniform distribution of the caustic methanol treating agent throughout the oil, following which the oil was washed to rid it of the caustic and then air brightened to dry it. In all instances the reagent was employed in an amount of .5 of the volume of the oil. The nature and composition of the reagent and the residue values of the various runs are hereinbelow tabulated.

Caustic Causticzlb. Residue, Methanol Caustic Equivalents p. p. Run By Gravity, per lbs. Final Volume B. Oil Oil Obviously, many modifications and advantages of the invention may be made without departing from the spirit and scope thereof, and therefore only such limitations are to be imposed as are indicated in the appended claims.

We claim:

1. A method of preparing a fuel oil blend boiling within about the range of 300 F. to 750 F., having a filter residue value not exceeding 25 p. p. m. and containing cracked petroleum hydrocarbons boiling within said range as one component, which comprises treating noncompatible cracked petroleum hydrocarbons boiling within about the range of 300 F. to 750 F., and having a filter residue value exceeding 25 p. p. m. with a mixture of a low-boiling alcohol, an alkali metal hydroxide and 30 to 60 percent, by weight of water, the composition of said mixture, moreover, falling within the area defined by the points 1, 2, 3 and 4 of attached Figure 1, and said mixture being used in an amount of about 0.0010 to 0.0100 pound equivalents of alkali metal hydroxide per 100 pounds of oil, to react with the impurities in the oil distillate to give reaction products removable by washing with water, washing the oil distillate to remove said reaction product, drying the washed oil distillate and blending the dried oil distillate with other hydrocarbons boiling within the range of about 300 F. to 750 F. to produce a compatible blend having a filter residue not exceeding 25 p. p. m.

2. Process substantially as described in claim 1, wherein the alcohol is methanol and the alkali metal hydroxide is sodium hydroxide.

3. A process of stabilizing a cracked petroleum distillate boiling within about the range of 300 to 750 F. and containing polar constituents imparting instability to said distillate comprising the steps of admixing said distillate with a treating agent containing alcohol, water and an alkali metal hydroxide in proportions falling within the area defined by the points 1, 2, 3 and 4 of attached Figure 1, said treating agent'being employed in the'proportion of 'about'0.0010 to 0.0100 pound equivalents of alkali metal hydroxide ,per 100 pounds of distillate, said treating agent reacting With-said polar constituents in the References Cited in thefile of this patent UNITED STATES PATENTS Borgstrom Jan. '5, 1932 McCullough Feb. 2, 1943 ,Birkhimer Mar-.28, 1944 Henderson et a1. Sept. 9, 1947 Voorhees Jan. 16, 1951 Tom Apr. 3, 1951 Brooks June 12, 1951

Claims (1)

1. A METHOD OF PREPARATING A FUEL OIL BLEND BOILING WITHIN ABOUT THE RANGE OF 600*F. TO 750*F., HAVING A FILTER RESIDUE VALUE NOT EXCEEDING 25 P.P.M. AND CONTAINING CRACKED PETROLEUM HYDROCARBONS BOILING WITHIN SAID RANGE AS ONE COMPONENT, WHICH COMPRISES TREATING NONCOMPATIBLE CRACKED PETROLEUM HYDROCARBONS BOILING WITHIN ABOUT THE RANGE OF 300*F. TO 750*F., AND HAVING A FILTER RESIDUE VALUE EXCEEDING 25 P.P.M. WITH A MIXTURE OF A LOW-BOILING ALCOHOL, IN ALKALI METAL HYDROXIDE AND 30 TO 60 PERCENT, BY WEIGHT OF WATER, THE COMPOSTION OF SAID MIXTURE, MOREOVER, FALLING WITHIN THE AREA DEFINED BY THE POINTS, 1,2,3 AND 4 OF ATTACHED FIGURE 1, AND SAID MIXTURE BEING USED IN AN AMOUNT OF ABOUT 0.0010 TO 0.0100 POUND EQUIVALENTS OF ALKALI METAL HYDROXIDE PER 100 POUNDS OF OIL, TO REACT WITH THE IMPURITIES IN THE OIL DISTILLATE TO GIVE REACTION PRODUCTS REMOVABLE BY WASHING WITH WATER, WASHING THE OIL DISTILLATE TO REMOVE SAID REACTION PRODUCT, DRYING THE WASHED OUL DISTILLATE AND BLENDING THE DRIED OIL DISTILLATE WITH OHTER HYDROCARBONS BOILING WITH THE RANGE OF ABOUT 300*F. TO 750*F. TO PRODUCE A COMPATIBLE BLEND HAVING A FILTER RESIDUE NOT EXCEEDING 25 P.P.M.

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