US2474411A - Method of reclaiming the hydrocarbon content of used hydrocarbon lubricants - Google Patents

Description

Patented June 28, 1949 METHOD OFRECLAIMINGT'IHE HYDROCAB- BON CONTENT OF-YUSEDQHYDBOCARBON I LUBRICANTS FrederickC. Bersworth, VeronayN. J.-

No Drawing. Application March 17', 1948,"

Serial No. 15,516

7 Claims;

Tliis 'invention' relates tov chemistry and to onelor more metalliesaltsof one-or more fattyacids and during the service userof the said lubricant a plurality of organic and inorganic impurities are introduced into: the =oil and lubricant whichgreatly complicatethe refining of such used-lubricantsior the recovery of the hydrocarbon-content thereof.

I havediscovered that the major portion of suchv metallic soap compounds and inorganic im-' purities present in usedhydrocarbon lubricants may. be effectively removed therefrom by digestingnthe .said lubricant while in its liquid phase withwian'aqueoussolution containing an alkali metal? hydroxide and: ethylene diamine tetraaceticnacid in such relative amounts providing:

notrlessthan two and not over fourmolar weights of the :hydroxide for each molar -Weight of the tetra-acetic acid present in the solution.

The strength or concentration of these constituents in the solution 'may'b'e'widely varied without-departure from-the invention depending in partupon'the amountof metal soaps and inorganicrimpurities :present in thelubricant and in part uponxwhether or not the fatty acid'content' of theilubricant is to be separated initially or ina subsequent operation; In general, however, a 20 'to'40% solution of these constituents has been-:found the most practical concentration. to employ withmost used mineral oil lubricants with the total volumethereof varied-to meet variations in 'impurity content of the lubricant and to accomplish the fatty acid separation initially orsubsequently, as desired.

Gerieral1y,I prefer to digest the liquid phase lubricant witha suitable volume of about a 30%- solution of these-constituents with vigorous agitatior'ito form a thorough mixture or emulsionand fof'an'extended'time' sufiicient" to solubilize the fattyacidfisoap' compounds and associated in: organic'impurities in the aqueous solution, thusremovingthese impurities in one operation. Alternatively, thefatty acids can be selectively reclaimed in the hydrocarbon fractionlfor recovery therefrom in a subsequentoperation.

Tlifiche'mical reaction involved inthe present invention'consists essentiallyof a base exchange reaction between the alkali metal salt of ethylene diamine tetra-acetic acid'present in the alkaline aqueous solution and the metallic soap compounds present in the lubricant, resulting in the formation of poly-metallic salts of the ethylene diamine' tetra-acetic acid with concurrent formation of free' fatty acids or the alkali-metal salts ofsaidfree fatty'acids, dependingupon the amount-of metallic soaps present in the lubricant," the amount'of alkali metal ions present=in the solu-- tion and the amount of basic metal compounds present as inorganic impurities in the lubricant.

Norma1ly,'in an alkaline pH solution-containing alkali metal hydroxide .and ethylene diamine' tetra-acetic acid any free or unneutralized secondary carboxylic groups in the tetra-acetic acid are acidic in reaction towards metallic fatty-acid Y soap" compounds and towards basic metal com pounds such as metal oxides, hydroxides and' carbonatesf-present'in the lubricant forming poly-*- metallid-salts therewith and liberating the free fatty'acidsof the metallic fatty acid-soapcompounds unlessthere are excess'alkali metal ions" present to neutralize said fatty acids.

These poly-metallie salts are highly soluble in" water-and in'their-ionized state are *highly re:- active as base exchange compounds towards neutral metallic Shawnee-11mm metal ion that is a stronger base than-rthe :metal ion neutralizing either of the secondary carboxylic groups of the tetra acid. The'stronger base ion of the neutral salt displaces the weaker'bas'e on the secondary J carboxylic groups of the poly-metallic amino acid salt, in a base exchange reaction, the lesser basic neutral salt resulting, if an inorganic salt, then forming a complex compound with the tetra salt of the amino acids of high solubility but of un certain composition.

Where, however, there are no basic inorganic. compounds present in the lubricant, the unneu tralized carboxylic groups react directly with metallicsoap compounds producing poly-metal salts of the' tetra acid and liberating the free fatty acidsl In 'the practice of the present invention, it is preferable .to substantially completely removefrom thelubricant all basic metal compounds and. to'substantiall'y completely decompose'all metallic soap compounds present in the lubricant thereby converting.thelubricant to-a metal-free hydrocarbon.containingldissolved free fatty acids which are subsequentlyiremoved from the mineral oil lubricant,by saponification and solution in water. As it is difficult .to obtain preciselythis chemicals;- condition, it is preferable to employ a sufficient amount of excess alkali metal hydroxide in the aqueous solution to saponify a small part of the liberated fatty acids, thereby to insure the substantially complete removal of associated inorganic impurities present in the lubricant.

This result is normally obtained by using a sufiicient amount of the alkali metal hydroxidetetra amino acid solution of known alkali metal hydroxide and amino acid content providing a slight excess of free alkali metal hydroxide over that equivalent to 2 molar weights of hydroxide per molar weight of the tetra acid, the slight excess of said hydroxide being available for reaction with the fatty acid content of the lubricant to form fatty acid soap compounds.

Following digestion of the lubricant with the aqueous solution of the present invention, the agitated mixture of hydrocarbon compounds and Water is permitted to settle, the hydrocarbon and water fractions are separated and the said fractions are separately treated as follows:

The hydrocarbon fraction is liquified and is treated with caustic alkali solution to saponify the free fatty acid content thereof and the fatty acid soap solution obtained is separated from the hydrocarbons. The fatty acids may be recovered from this aqueous solution by acidification with mineral acid to a pH of about 4.5 in accordance with known practice. The hydrocarbon fraction may be filtered to clarify and to remove insoluble carbon and other inert impurities dispersed therethrough and the hydrocarbon contents thereof recovered by standard distillation or hydrocarbon cracking processes.

The aqueous solution fraction is preferably concentrated by evaporating off the major portion of the water of solution, acidified first to a pH of 4.5 to precipitate out the fatty acids present, and the ethylene diamine tetra-acetic acid content of the remaining solution is recovered therefrom by acidification with a strong mineral acid to a pH of about 1.2. The acid-soluble metal content of the solution normally may be discarded although in the practice of the invention on any large commercial scale they might represent economically practical recovery values.

As typical examples of the practice of the present invention the following are given:

Example 1 One (1) liter of used automobile oil was put into an apparatus equipped with stirrer and reflux condenser. To this oil was added 100 c. c. of a solution of NaOI-I and ethylene diamine tetra-acetic acid containing between 2 and 3 molar weights of the hydroxide to each molar weight of the acid. The oil-water mixture was heated with vigorous agitation for a period of 2 hours. After allowing the mixture to cool some-what, additional water was added thereto (200 c. c.) and the mixture was again agitated for 15 minutes and again allowed to cool and settle. The top layer contained mineral oil and free fatty acids. The bottom layer contained some fatty acid-Na soap, poly-metallic salts and complex compounds of the di-sodium salt of the tetra acid and suspended carbon particles. The two layers Were separated and the bottom layer was filtered to remove all filterable material including carbon therefrom. The filtrate was then acidified to a. pI-I of 4.5, all-owed to settle and the top layer, consisting of the fatty acids of the fatty acid soap compounds present, were separated from the water fraction. The water fraction is acidified to the isoelectric point of the tetra amino acid, or to a pH of about 1.2. The precipitated tetra amino acid is filtered from the solution and may be re-used in the treatment of additional hydrocarbon lubricants.

The hydrocarbon fraction first separated was treated with caustic alkali to saponify the free fatty acids present therein, and the alkali metal soap compounds formed were dissolved in water and separated from the hydrocarbon compounds and recovered therefrom by acidification to a pH of about 4.5 as above disclosed. The substantially pure hydrocarbon fraction remaining then may be treated as desired for the recovery of the hydrocarbon fractions contained therein, such as by distillation.

Example 2 The same quantity of used automobile oil was treated as above described in Example #1 using a 30% aqueous solution of the di-Na salt of ethylene diamine tetra-acetic acid. In this modification the fatty acids will be found completely isolated in the hydrocarbon layer as the alkali metal ions of th dialkali metal salt are not available for neutralization of these fatty acids. The fatty acids of the hydrocarbon fraction may be saponified by means of NaOI-I or other base and dissolved in water as in Example #1. The tetra amino acid present in the aqueous fraction may be reclaimed by acidification to a precipitating pH of 1.2.

Example 3 Heavy gear grease contaminated after commercial use, was dissolved in light lubricating oil and the mixture treated as per Example #1. All the hydrocarbons present in the grease and lubricating oil and most of the fatty acids segregatedin the lubricating oil fraction and the fatty acid soap and impurities present in the water fraction was treated as above described. The fatty acids were separated from each fraction, as above described, and the substantially pure hydrocarbon compounds and tetra amino acids were recovered as disclosed. The heavy grease component of the hydrocarbon compounds was recovered by fractional distillation.

Example 4 The lubricant reclamation process may be carried out as described in either of the above examples in the presence of excess caustic alkali such as NaOH or KO-H, sufficient in amount to saponify the fatty acids as they become available for saponification by metallic ion base exchange with the alkali metal salt of ethylene diamine tetra-acetic acid, if desired. In this method the amount of amino acid employed may be reduced in amount to that required to react with the metal ions present in the lubricant to form poly-metallic salts therewith. Alternatively, the hydrocarbon lubricant may be washed with the di-Na tetra-acetic acid salt only and in amount only slightly in excess of that necessary to take up the metallic ions present in which case all fatty acids will be found in the hydrocarbon fraction from which the fatty acids may be removedby saponification with NaOI-I or KOH and solution in water followed by subsequent acidification and reclamation of the metal free fatty acids from the aqueous soap solution,

Where the hydrocarbon lubricant contains an alkali metal-fatty acid soap compound, the treatment of the same in accordance with the present invention normally results in the concentration of these soap compounds in the aqueous fraction as such soaps are generally soluble in water. Where the hydrocarbon lubricant contains metallic fatty acid soaps other than alkali metal soaps, treatment of the lubricant in accordance with the present invention normally results in the concentration of the fatty acid content thereof in the hydrocarbon fraction except where the amount of alkali metal ions present in the solution is in excess of that equivalent to two molar weights of alkali metal hydroxide to each molar weight of ethylene diamine tetra-acetic acid, in which case fatty acids in an amount equivalent to this excess free alkali will be saponified and the soap compounds formed will concentrate in the water fraction.

It is believed apparent that the invention as described hereinabove may be widely modified without essential departure therefrom and all such modifications and departures thereof are contemplated as may fall within the scope of the following claims.

What I claim is:

1. The method of treating used hydrocarbon lubricants and greases to recover the hydrocarbon compounds therein which comprise agitating the said hydrocarbons while in liquid phase for an extended time interval with an aqueous solution containing ethylene diamine tetra-acetic acid and an alkali metal hydroxide in such relative amounts providing not less than two and not over four molar weights of the alkali metal base for each molar weight of the acid and then separating the hydrocarbons from the aqueous solution.

2. The method of claim 1, wherein the said aqueous solution contains a concenration of about 30% of an alkali metal salt of ethylene diamine tetra-acetic acid containing at least two oarboxylic groups neutralized by an alkali metal and wherein the relative volumes of the oil and aqueous solution is at least sufficient to provide an excess of the said amino acid salt over the impurities present in the said oil.

3. The method of claim 1, wherein the said aqueous solution contains alkali metal base and amino acid in the relative proportions providing the di-alkali metal salt of said amino acid and wherein the oil fraction after being separated from the aqueous solution is treated with a caustic alkali solution to saponify the fatty acids present therein, and wherein such fatty acids are recovered from the aqueous solution obtained by acidification of the said aqueous solution to a pH of about 4.5.

4. The method of claim 1, wherein the said aqueous solution contains alkali metal base and amino acid in the relative proportions providing the trito tetra-alkali metal salt of the amino acid and wherein the said solution contains a sufficient amount of this said salt to provide sufficient alkali metal ions in excess of two molar weights per molar weight of the amino acid to react with the fatty acid soap content of the said oil to solubilize the same as alkali metal soap compounds in the aqueous solution.

5. The method of treating used mineral oil lubricants to recover the hydrocarbon compound content thereof which comprises digesting the lubricant in its liquid phase with an aqueous solution containing a di-alkali metal salt of ethylene diamine tetra-acetic acid, the amount of said salt being in excess of that theoretically required to solubilize substantially all basic inorganic compounds present in the lubricant and to acidify substantially all metallic soap compounds present in the lubricant, separating the hydrocarbon compounds remaining from the aqueous solution, treating the hydrocarbon compounds with a strong caustic alkali solution to saponify the fatty acid content thereof, dissolving the fatty acid soap compounds in water and separating the solution from the hydrocarbon compounds remaining and subjecting the hydrocarbon compounds to distillation to segregate the same from the non-vaporizable residues present therein.

6. The method of claim 5, wherein the ethylene diamine tetra-acetic acid content of the first aqueous solution is recovered by acidification of the solution to a pH of about 1.2 with a strong mineral acid.

'7. The method of claim 5, wherein the fatty acid soap compounds separated from the hydrocarbon compounds as an aqueous soap solution are recovered therefrom by acidification to a pH of about 4.5.

FREDERICK C. BERSWORTH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,030,480 Strezynski Feb. 11, 1936 2,343,435 Wells et a1 Mar. 7, 1944 2,412,945 Bersworth Dec. 24, 1946