US 2795532 A
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United States Patent REFINING HEAVY MINERAL OIL FRACTIONS WITH AN ANHYDRGUS MIXTURE OF 'SODHUM HYDRQXIDE AND POTASSIUM HYDRQXIDE Earl M. Honeycutt, Claymont, Del., assignor to Sun Oil Company, Philadelphia, Pa., a corporation of New Jersey No Drawing. Application October 4, 1954, Serial No. 460,269
3 Claims. (Cl. 196-36) This invention relates to refining of heavy mineral oil fractions by contact thereof in vapor phase with liquid alkaline treating agents.
It is known in the art to remove naphthenic acids from mineral lubricating oils by contacting vapors of the oil with molten sodium hydroxide or with aqueous sodium hydroxide solution. in such treatment, the naphthenic acids contained in the vapors react with sodium hydroxide to form sodium naphthenates in the liquid phase present in the treating zone.
One manner of operation involves circulating liquid alkaline material comprising sodium hydroxide, sodium naphthenates, and mineral lubricating oil through a caustic treating section comprising several trays of a fractionating tower. A portion of the alkaline material withdrawn from the bottom of the caustic treating section is recycled to the top of the section.
A serious problem encountered is the formation of carbonaceous deposits on the surfaces of the equipment, and the plugging of conduits, downcomers, etc. by carbonaceous solids. These objectionable carbonaceous deposits are believed to be formed by thermal decomposition of sodium naphthenates, mineral oil, etc. in the caustic treating section. It is further believed that these carbonaceous materials include sodium carbonate which acts as a binder for the other carbonaceous materials. Such sodium carbonate may have been formed, for example, by decomposition of sodium naphthenate to liberate carbon dioxide and reaction of the latter with sodium hydroxide to form the carbonate, or by oxidation of hydrocarbons to form carbon dioxide and reaction of the-latter with sodium hydroxide, or by other mechanism.
The present invention provides a novel manner of reducing the fouling and plugging of apparatus by carbonaceous materials. According to the present invention, a mineral oil fraction is contacted in vapor phase with a mixture of sodium hydroxide and potassium hydroxide, which mixture contains about to 95 moles of sodium hydroxide per 90 to 5 moles of potassium hydroxide. It is believed that the mechanism of the improvement obtained according to the invention involves the inhibition of the action of sodium carbonate, or of potassium carbonate, as a binder for other carbonaceous materials, or the removal of carbonates from already-formed deposits or agglomerates of carbonaceous materials, thus breaking up the deposits or agglomerates.
The following example illustrates the invention:
Reduced naphthenic crude petroleum was preheated to about 650 F. and introduced into a vacuum flash zone in a lower portion of a distillation tower. The flashed vapors were introduced into a treating section wherein they were countercurrently contacted with descending liquid alkaline material which had, on the lowermost tray of the treating section, the following approximate composition:
Weight percent Liquid m'l 85-88 Alkali metal naphthenates 1 Alkali metal hydroxides 1-2 Liquid alkaline material was removed from the lowermost tray of the treating section, and a portion of the removed liquid alkaline material was recycled to an upper portion of the treating section. The remainder of the alkaline material was introduced into an extraction z'one employing aqueous isopropanol as solvent for alkali metal naphthenates and petroleum naphtha as solvent for oil. Liquid oil recovered from the alkaline material in the extraction operation was recycled to an upper portion of the treating section.
Fresh alkali metal hydroxide wasintroduced into an upper portion of the treating section at a rate sufficient to maintain the above concentration of alkali metal naph thenates and excess alkali metal hydroxides in the liquid alkaline material on the lowermost tray of the treating section. The liquid temperature on the lowermost tray of the treating section was about 630 F.
The uncondens'ed vapors passed from the top of the treating section into the fractionating section and upwardly therethrough. Normal reflux was maintained from the fractionating section to the treating section by means of a liquid downcomer from the lowermost tray of'tlie fractionating section of the top tray of the treating section.
The fresh alkali metal "hydroxide charged to the caustic treating section was a mixture of sodium hydroxide and potassium hydroxide containing 5 to 20 mole percent potassium hydroxide for a two-month period of continuous operation. During part of this time, the sodium hydroxide and potassium hydroxide molar concentrations were 95 percent and 5 percent respectively, during another part 90 percent and 10 percent respectively, and during another part percent and 20 percent, respectively. All of these concentrations were found to be satisfactory.
The pressure drop undergone by rising vapors in passing through the caustic treating section remained at a level between about 15 mm. Hg and 25 mm. Hg during the two-month period. The pressure drop is a measure of the extent of formation of carbonaceous deposits in the treating section, since the greater the extent of deposit formation, the greater the obstruction of vapor flow, and the greater the pressure drop. The l5-25 mm. Hg pressure drop obtained in this example represents a satisfactory operating range.
It is believed that the beneficial results obtained according to the invention probably result from the greater ability of alkaline treating agents containing sodium hydroxide-potassium hydroxide mixtures to dissolve and hold in solution alkali metal carbonates which are formed by decomposition of carbonaceous materials in the treating section. This greater ability results in a reduction in the amount of solid carbonates available to form objectionable deposits.
It appears further that potassium carbonate has greater solubility than sodium carbonate in alkaline treating agents containing sodium hydroxide-potassium hydroxide mixtures. At any rate, it has been found that when insoluble materials do form in operation according to the invention, they contain a greater ratio of sodium to potassium than that contained in the sodium hydroxide-potassium hydroxide mixture, thus indicating that potassium carbonate is held in solution in the treating agent more strongly than sodium carbonate.
The process of the present invention is preferably carried out using a liquid alkaline refining agent containing about 60-95% oil, and preferably at least about oil, since it has been found that such operation together with the use of a mixture of sodium and potassium hydroxides results in a process wherein deposit formation 3 and the resulting disadvantageous etfects are particularly greatly reduced.
The invention is applicable generally to petroleum fractions having A. P. I. gravity within the approximate range from 10 to 40. Usually, the process is applied to the refining of vapors from which lubricating oils are subsequently condensed. However, gas oil vapors can also be refined according to the invention.
The mixture of sodium and potassium hydroxides which is used according to the invention is preferably used as the sole alkaline material charged to the caustic treating, though other alkaline materials, e. g. lime, can also be employed in minor amounts.
In the preceding example beneficial results were obtained from the use of a caustic mixture containing 5 to 20 parts of KOH per 100 parts of NaOH-KOH mixture. Even more beneficial results can be obtained with greater proportions of KOH, e. g. 30 to 70 parts per 100, since the eutectic mixture, which occurs at about 50 mole percent KOH, has optimum ability to hold alkali metal carbonates in solution. Also, greater proportions of KOH have the advantage of favoring the formation of KzCOs, which is more soluble in the treating agent than NazCOs. However, the present greater cost of KOH may render it more advisable to use relatively small proportions of KOH, and satisfactory results can be obtained with the small proportions.
In the preceding disclosures of relative amounts of sodium hydroxide and potassium hydroxide, the figures given are based on total alkali metal hydroxide, though other constituents are present in the liquid alkaline treating agent.
The invention claimed is:
1. Process for refining mineral oil which comprises: contacting naphthenic-acid containing vapors of a mineral oil fraction having A. P. I. gravity within the approximate range from 10 to with a liquid treating agent consisting essentially of a molten anhydrous mixture of sodium hydroxide and potassium hydroxide, said mixture containing about 10 to 95 moles of sodium hydroxide per to 5 moles of potassium hydroxide, thereby to inhibit coating and plugging of the apparatus employed with carbonaceous materials formed during the contacting.
2. Process according to claim 1 wherein said liquid treating agent contains 60 to oil.
3. Process according to claim 1 wherein said fraction has average molecular weight at least as high as that of gas oil.
' References Cited in the file of this patent UNITED STATES PATENTS 1,784,262 Wheeler et al Dec. 9, 1930 2,227,811 Moser Jan. 7, 1941 2,481,300 Engel Sept. 6, 1949