DE1054626B - Process for stabilizing hydrocarbon oils - Google Patents

Description

The invention relates to a method of stabilizing hydrocarbon oils, in particular of lubricating oils, against oxidation, discoloration and sludge formation during storage at temperatures below 100 ° C.

It has been proposed to treat lubricating oils and greases with trisodium phosphate protect against oxidation at high temperatures. It was further suggested that hydrocarbon oils, which are subject to oxidative deterioration, with various inorganic ones Salts such as sodium and potassium triphosphate, diphosphates and the corresponding silicates treat.

The invention differs from these proposals in that it is based on the knowledge that the oxidation of hydrocarbon oils below 100 ° C can be inhibited by bringing the oils into contact with a mixture of oil-insoluble substances which, in dilute aqueous solution, has a buffer system a p _H in the range of 9.5 to 10.5 results. At high temperatures, some of these inherently effective systems are much less useful. As a result, certain of these substances are suitable, which at high temperatures, eg. B. at about 149 ° C, have a stabilizing effect, also for stabilization at low temperatures, z. B. at about 66 ° C, but the reverse is not always true. In fact, the stabilization of various mineral oils, e.g. B. heating oils, lubricating oils and greases, with long storage times and temperatures between about -18 and + 66 ° C, usually even up to 100 ° C, a completely different problem than the stabilization of lubricating oils at higher operating temperatures. Salts or systems which are quite brittle for one purpose are often completely useless for the other purpose, although certain other systems are sometimes usable for both purposes.

The choice of salt mixtures or salt-acid mixtures that would form the buffer solution in dilute solution, can be fairly easily determined by the _pH value is determined the system in dilute aqueous solution.

The inventive method for stabilization of hydrocarbon oils against oxidation at temperatures below 100 ° C is characterized by bringing the oil with a mixture of oil-insoluble substances in contact, which in dilute aqueous solution, a buffer system with a p _H in the range of 9.5 to 10.5 forms. As a mixture of oil-insoluble substances in the context of the invention, the following are preferably considered:
1. an oil-insoluble metal salt of a polybasic

Method of stabilization
of hydrocarbon oils

Applicant:

Esso Research and Engineering Company, Elizabeth, N.J. (V. St. A.)

Representative: E. Maemecke, Berlin-Lichterfelde West,
and Dr. W. Kühl, Hamburg 36, Esplanade 36 a,
Patent attorneys

Claimed priority:
V. St. v. America September 30, 1952

Acid together with the corresponding acidic salt,

2. an oil-insoluble amine together with a salt thereof,

3. an oil-insoluble weak acid together with a metal salt thereof.

A weak acid is to be understood as meaning an acid whose ionization constant is just as large or is smaller than that of acetic acid.

The first group of the substance mixtures listed above preferably includes an alkali salt of a polybasic acid together with the corresponding acidic salt. It is expedient to choose sodium as the alkali metal and phosphoric acid, carbonic acid or boric acid as the polybasic acid. If the salt of an amine is used, a hydrochloric or sulfonic acid salt thereof is preferably used. The combinations that are particularly suitable as buffer systems include sodium and potassium phosphate, for example Na ₃ PO ₄ or K ₃ PO ₄ , which can be mixed with the corresponding acidic salt, ie Na ₂ HPO ₄ or K ₂ HPO _1. Sodium and potassium carbonate can also be used very well in a mixture with the corresponding acidic salts for the purpose according to the invention, but are unsuitable for stabilization at high temperatures. Amines such as methylamine, butylamine and methylthionyl-n-butylamine are also mixed with

809 789/460

their salts are quite useful. Are there already small amounts of an acid that is stronger than that polybasic acid of the salt to be added, so you can also use a salt of this polybasic acid for add yourself alone, with the added salt together with the acidic salt that forms in the process the period of time during which stabilization is required to exert the desired protective effect. Usually the concentration of the mixture should be such that the necessary hydrogen ion concentration arises in the water phase contained in the oil. With enough close contact and in In the absence of a water layer, the concentration of the mixture can be up to 0.001% of the total weight of the oil product to be protected. If, however, between the bulk of the oil and only limited contact is given to the salts, the salt concentration, calculated as % By weight of the oil, can be increased up to 0.5% and even preferably up to 1%. One can work with larger quantities, but these are usually not required. The salts are preferably finely divided and so arranged for contact with the oil that the Brownian motion and other molecular movements and / or convection currents within the oil this in sufficient Bring contact with the protective mixture. Such a system can be made by a permeable or fibrous material, such as paper sheets or fabric, such as canvas, with the aqueous solutions of the selected salt mixture or hydrochloric acid mixture soak.

So when shipping mineral oils, such. B. in tankers or tankers, maintain a buffer system by placing one or more sheets of paper, tissue or the like in the oil Products that are impregnated with the mixture or this in some other way in their Contain fibers. This simple tool removes the discoloration, which is usually the oxidation and accompanied by sludge formation in oils during storage or transport, extremely strong degraded.

It is already known to add a mixture of naphthalene, anthracene or phenanthrene with caustic soda, caustic potash or quicklime and trisodium phosphate and optionally borax to heating oils in order to keep the sludge already contained in the oil in suspension and to prevent it from separating in the burner system. Apart from the fact that polynuclear aromatic hydrocarbons, such as naphthalene, anthracene or phenanthrene, are an essential component of these additional mixtures and the mixtures have a strongly alkaline reaction due to their composition, they also cannot exert the color-stabilizing effect of the mixtures according to the invention, since this effect is based on the fact that the additive mixture is chosen such that it forms in dilute aqueous solution, a Puffersvstem of a p _H of 9.5 to 10.5.

Furthermore, there is a method for cleaning used lubricating oils from incomplete combustion formed coal particles known, which consists in the fact that the used oil with an aqueous Solution of trisodium phosphate stirred vigorously, the mixture heated, then the aqueous phase can settle at the bottom, with the coal particles contained in the oil as an intermediate layer between the aqueous phase and the oil phase settle, and finally the clear oil is drawn off. This too

Process cannot stabilize the color of hydrocarbon oils and does not cooperate a buffer mixture.

In order to demonstrate the effectiveness of the invention, the samples described below were prepared and alternately heated and cooled. The samples were first heated to a certain temperature, usually 66 ° C, for 100 hours and then cooled. Then they were examined and heated again for 100 hours. In this way, the samples were exposed to a temperature of 66 ° C. for 500 hours over the course of 28 days. An acid-refined distillate from coastal crude oil served as the hydrocarbon sample. This oil (A) had a viscosity of 13 cSt at 98.9 ° C. 300 g of this oil were ^{poured into a 600 cm 3} beaker made of Pyrex glass, whereupon a steel plate cleaned with a sandblasting fan was three quarters of its length into the oil immersed. Traces of sulfuric acid and petroleum sulfonic acids as well as the following salts were added to the various samples:

No. 12: I weight percent Na ₃ PO ₄ , based on the oil,

a) moistened in a paper sack,

b) dry in a paper sack,

c) mechanically dispersed in the oil.

No. 2: I weight percent Na ₂ CO ₃ in a paper sack.

# 3: I weight percent NaOH in a paper sack.

No. 4: 1 weight percent amine resin according to U.S. Patents 2,334,594 and
2,340 036.

No. 5: blank sample,

a) heated like samples 1 to 4,

b) kept at 25.0 ° C for the duration of the experiment.

40 There was no stirring during the test and the samples were exposed to the atmosphere. It was found that an effective way to bring the salt into contact with the oil was to immerse the salt in the oil in a porous fabric or paper sack. Apparently it is not necessary to distribute the solid salt finely in the oil, since effective contact is already established through the impregnated fabric. The effect depends on the concentration of the salt in the total water or acid contained in the oil and therefore only secondarily on the surface of the solid salt.

Na ₂ CO ₃ and Na ₃ PO ₄ behaved the same, while NaOH gave a much worse result ~ and attacked the steel plate. The success of the Na ₂ CO ₃ - and Na ₃ PO ₄ system is attributed to the fact that both compounds in the preferred range of p _H 9.5 to 10.5 to form with the added acid buffer systems. Sodium hydroxide makes the medium to be strongly alkaline by approaches p _H fourteenth An examination of the oils after the end of the experiment showed that no sodium phosphate or carbonate had dissolved in the oil. The wetting of the sodium phosphate did not appear to be necessary if the hydrated salt was used or if the oil was not heated above the boiling point of the water. Apparently, however, a trace of water must be present in order to activate the buffer system. The progress of oxidation was considered a function

Claims (14)

the darkening of the oil measured, expressed in values of the Robinson scale. The results for the various samples are shown graphically in FIG. FIG. 2 gives the values obtained on treatment of a phenol-extracted mid-continent distillate, Oil B, with 1 percent by weight of trisodium phosphate. After a slight initial darkening, the color of the oil remained constant for 300 hours. 3 and 4 show the results for two acid-refined coastal distillates of a viscosity of about 8.8 and 15.6 cSt, respectively, at 98.9 ° C. These oils are designated as C-55 Oil and C-70 Oil. In both cases, however, no stabilization of the color value is obtained. The trisodium phosphate only appeared to cause a decrease in the rate of darkening in this case. This can possibly be attributed to the different origins and the different treatment of the Colombian oils and the Mid-Continent products. It is possible that higher concentrations of trisodium phosphate are required when using coastal products in order to achieve the same stabilization as with the mid-continent oils. Another possible explanation for these results could be that trisodium phosphate inhibits an acid-catalyzed oxidation process without affecting other reactions. The sulfur-containing constituents of an oil, for example, are known to darken when heated, without absorbing oxygen or undergoing an acid-catalyzed oxidation process. In order to further demonstrate the dependence of the color stabilizing effect on a controlled pH system, a mixture of sodium carbonate and sodium borate acting as a buffer was used to treat a sample of acid-refined coastal distillate (oil A-70). By changing the proportions of the individual components, the pH was changed in the range from 9.2 to 11. As in the previous experiments, these salt mixtures were also dissolved in distilled water and pieces of tissue or tissue paper were impregnated with them, but in contrast to the experiments described above, the fabrics were dried after the impregnation. The concentration was 1.0 percent by weight of the oil sample. The results of these experiments are summarized in FIG. Those systems which contain trisodium phosphate and the buffer corresponding to pH 10 show almost the same color stabilization. The sample which contains the buffer of pH 9.2 shows no color-stabilizing effect, but only a delay in darkening, while the buffer of pH 11 has an effect between those of pH 9.2 and pH 10. Fig. 6 shows the relationship between color stability and Ph for Oil A-70. Thereafter, a maximum of color stability is achieved at a very specific pH value in the vicinity of 10. It appears that systems which form buffered aqueous solutions from pH 9.5 to 10.5 are best at preventing the oxidation of the common hydrocarbon oils and therefore stabilizing them. These systems can be introduced into the hydrocarbon solution in the form of cartridges or porous bags, or they can be adsorbed on canvas. They do not require intimate mixing with the oil, although they can also be finely divided or suspended in this, if necessary. They do not contaminate the oil and do not attack the metal containers in which the oils are stored. They also have the further advantage of being relatively cheap. Patent claims: 1. A method of stabilizing hydrocarbon oils against oxidation at temperatures below 100 ° C by the addition of oil-insoluble salts, characterized by bringing the oil in question with a mixture oil-insoluble buffer substances in contact, which, in dilute aqueous solution, a p _H in the range of 9 5 to 10.5 results. 2. The method according to claim 1, characterized in that there is an oil-insoluble as buffer substances Metal salt of a polybasic acid and the corresponding acidic salt are used. 3. The method according to claim 1, characterized in that one is used as buffer substances oil-insoluble amine and a salt thereof are used. 4. The method according to claim 1, characterized in that there is one as buffer substances oil-insoluble weak acid and a metal salt thereof are used. 5. The method according to claim 2, characterized in that alkali salts are used. 6. The method according to claim 2, characterized in that sodium salts are used. 7. The method according to claim 2, 5 and 6, characterized in that salts of phosphoric acid, Carbonic acid or boric acid used. 8. The method according to claim 2, characterized in that a mixture is approximately the same Amounts of trisodium phosphate and disodium phosphate or of tripotassium phosphate and dipotassium phosphate used. 9. The method according to claim 2, characterized in that there is a mixture of sodium carbonate and sodium bicarbonate or of potassium carbonate and potassium bicarbonate are used. 10. The method according to claim 3, characterized in that the amine is methylamine, n-butylamine or methylthionyl-n-butylamine is used. 11. The method according to claim 3 and 10, characterized in that one is used as the amine salt those of hydrochloric acid or a sulfonic acid are used. 12. The method according to claim 1 to 11, characterized in that the mixture of buffer substances applies in an amount of 0.001 to 1 percent by weight of the oil. 13. The method according to claim 1 to 12, characterized in that the buffer mixture on a porous support, preferably on cloth or paper. 14. The method according to claim 1 to 12, characterized in that the buffer mixture in a porous container in which the oil hangs. Considered publications:
U.S. Patent Nos. 2,137,727, 1,302,094. Legacy Patents Considered:
German Patent No. 961 478. For this purpose 2 sheets of drawings © 809 789/460 3.59