Process for Treating and Regenerating Used Oil Products

This invention related to the field of oil products, particularly mineral oils. It relates especially to a process for treating used oils to recover a usable oil from such residues.

Used oil products, generally considered as bothersome wastes, represent considerable tonnage in various fields of use such as, for example: oils obtained from draining engines and transmissions of various vehicles, oils obtained from mechanical machines or electric devices, various industrial oils, liquid or semifluid wastes of fatty bodies, etc.

At present, most of these oil wastes are either burned or subjected to various regeneration treatments. For example, according to a known process, the dirty oil is dehydrated by heating it at a temperature of about 150.degree.-160 .degree. C., then subjecting it to treatment with concentrated sulfuric acid. After filtering and heating the dirty oil at about 300.degree. C., two products are obtained. One is regenerated oil of the VEDOL or other type and the other is a blackish muddy residue called "acid mud", the volume of which represents at least 30% of the recovered product after sulfuric acid treatment.

These prior art processes of regenerating dirty oils require the use of several treatment phases and the use of costly and/or dangerous products, such as for example, sulfuric acid in the technique mentioned above.

One of the objects of the invention is to propose a process for making possible the separation of dirt from used oil without resorting to successive complex treatments conducted at high temperatures and which require specially suited equipment.

Another object is to obtain the most complete quantitative separation of impurities possible from a used oil, while recovering a reusable oil containing the usual additives of a new base oil and exhibiting characteristic properties fairly equivalent to the latter.

According to the essential characteristics of the new process of the invention, the dirty oil is agitated, in the presence of a quaternary ammonium salt or mixture of salts, and then is subjected to a decanting operation, the supernatant fraction then being recovered as a regenerated, directly reusable oil.

It has been found in a surprising way, that starting with a black oil, for example, an oil drained from a vehicle, an oil product is recovered still containing additives usually incorporated in a base lubricating oil. Examples of such additives are agents improving the index of viscosity and flow at low temperatures, extreme pressure additives, etc.

Although various quaternary ammonium compounds, preferably containing a fatty chain, could be used in the process (see, for example, C. A. Lawrence, Quaternary Ammonium Germicides, Academia Press, New York, 1950), it is especially advantageous to use quaternary amonium amine or hydroxide halide salts, such as arylammonium halides of the alkyl-dimethylbenzlammonium chloride type or corresponding homologs thereof.

It has been found that the best results are obtained when the decanting adjuvant contains, in its chemical composition, at least one aryl ring substituted by at least one fatty alkyl radical containing 8 to 18 and preferably 12 to 18 carbon atoms. Thus, anionic or non-ionic dispersing or emulsfying agents characterized by this definition are suitable for use within the scope of the invention. However, cationic compounds such as ammonium salts have the advantage of high effectiveness and are reasonably priced.

The amounts of ammonium salt used are obviously a function of and dependent on the type of oil product and dirt or pollutants it contains. In general, 0.1 to 3 parts of NH.sub.4 + salt (calculated dry) for 100 parts of used oil are used. In practice, the salt is used in the form of a concentrated aqueous solution, for example 70 to 80%, which is diluted, for example, 5 to 15 times with water. When the dilution is considerable, the aqueous phase, corresponding to the amount of dilution water used, is recovered and separated as a lower decanting layer.

The agitation operation is performed for several minutes using any known means (a mechanical or electromagnetic agitator) either at normal ambient temperature or slightly higher by heating to temperatures of 30.degree. to 50.degree. C. making it possible to obtain complete decanting results in several minutes or several hours rather than in several days.

It has been further found that the rate of separation of dirt and the quality of the oil recovered are often improved when the pH of the operational medium is either close to neutral or somewhat acidic. Dirty lubricating oils, as for example, oils from draining engines, are often slightly acidic.

The quaternary ammonium solution has a slightly basic pH For this reason, it is often desirable to acidify this solution, for example, by adding a weak acid, such as citric acid or the like, so that the treatment medium finally has a slightly acidic pH. However, in other cases and depending on the particular oils treated, decanting is performed most efficiently at neutral or slightly basic pH. Finally, in still other cases, the decanting time can be reduced by introducing, in the agitated used oil, extemporaneously prepared mixtures of an aqueous solution, which is acidified with a NH.sub.4 + salt, and an aqueous solution of the same NH.sub.4 + salt made basic, for example, by the addition of a small amount of sodium carbonate or the equivalent.

The above process can advantageously be used for very diverse categories of used oils, of course not including edible oils to avoid any harmful effects due to ingestion of the treating agents. Of these regenerable oils, there can be cited particularly: the oils from draining engines, transmissions and/or the differential of automobile and trucks; lubricating oils of machine tools and other mechanisms; oils of transformers and other electric and electropneumatic devices; hydraulic oil and liquids including synthetic oils, etc.

According to another very advantageous application, it has also been found that the process of the invention is also well suited for recovery, in usable form, of the major part of acid black muds, heretofore rejected as unusable residues in the known treatment, mentioned above, for the regeneration of dirty lubricating oils. Thus, by agitating such a black liquid, containing pollutant particles in suspension, with a ten-fold diluted aqueous solution of a quaternary ammonium salt, then allowing it to decant, these are recovered by the following layers: a heavy layer composed of the diluting layer and the one contained in the acid mud, a very black intermediate layer containing all of the dirt pollutants and a supernatant layer comprising 80-95% of a yellowish oil which is suitable for reuse as a lubricant, after having undergone a neutralizing treatment intended to decrease the acidity of the oil resulting from the great amount of sulfuric acid, which are used in the preliminary phase of regeneration of the used oil.

The invention will be better understood from the detailed description of the following embodiments given by way of non-limiting examples.

(a) the process of the invention was applied to several blackish extremely dirty oils obtained from draining vehicles in various garages and service stations. The quaternary ammonium salt used was HYAMINE 3500 (trademark, Rohm & Haas; alkyldimethybenzyl ammonium chloride where the alkyl is a mixture of 50% of C.sub.14, 40% of C.sub.12 and 10% of C.sub.16), this salt being designated below as salt A. In practice, aqueous solutions of salts in a concentration of about 10% by weight are used.

There was agitated, at normal temperature for about 2 minutes, 1 liter of drained oil containing 250 ml of solution of salt A (the pH of which was about 8), and then it was allowed to decant. After about 48 hours, the lower black deposit was eliminated (about 2% by volume), and there was recovered as an upper layer (the remaining %) an oil of good consistency.

By performing the same operation while heating at a temperature of about 50.degree. C., the decanting time can be reduced to less than 12 hours.

There were treated, for about 10 minutes, and at a temperature of 40.degree. C., five liters of drained oil containing a mixture of 500 ml of a salt A solution having a pH of about 3, resulting from the addition of citric acid, and 500 ml of salt A solution having a pH of 10 (due to addition of sodium carbonate to salt A solution). After decanting for about six hours, an oil of the same external appearance as test 1 was recovered as the major fraction in the upper layer.

There was subjected to agitation 1 liter of drained blackish oil, having a high rate activity, for about ten minutes at a temperature 40.degree. C., using a mixture of 125 ml of salt A aqueous solution adjusted to pH 4, and 125 ml of salt A aqueous solution adjusted to pH 10 as additives to the dirty oil after about 10 hours of decanting and drawing off, as lower and intermediate phases, layers of water and black residues (about 2.5%), the totality of the upper oil layer was recovered.

(b) To evaluate the characteristics of the recovered oils, according to the above tests, standard analyses of the lubricating products were made and the following results were obtained.

When each and all of these characteristics are compared with those of new oils for lubricating engines, now on the market, it is noted that the oil products recovered after decanting, according to the invention, exhibit approximately the same performances. Additives usually used to dope base oils (paraffins, naphthenes, hydrogenated or synthetic), as, for example, agents improving the viscosity or cold flow point were not deteriorated by use of the process. In practice, the above results correspond to the characteristic of synthesis base oils, containing additives, of a grade SAE D 5 W30 used successfully as engine lubricants.

Of course, the invention is not limited to the above specific examples and operating conditions and extends to all variant embodiments included within the spirit and scope of the following claims which would be obvious to one of ordinary skill in the art.