US2046951A - Processes of treating petroleum oils - Google Patents

Description

Patented July 7, 1936 UNITED STATES PATENT OFFICE 2,046,951 PROCESSES OE TlgllillgllNG PETROLEUM I No Drawing. Application March 14, 1933,

Serial No. 660,768 r 20 Claims. (Cl. 196-13) This invention relates to processes of treating petroleum oils; and it comprises a method of improving petroleum products, and particularly lubricating oils or lubricating stocks, wherein the oil or stock is extracted with certain alkyl esters of hydroxy acids, such as lactic acid and glycollic acid,.and having convenient boiling points around or above 300 F; the oil or stock and the extract being afterward gravitationally separated and solvent ester removed from each; all as more fully hereinafter set forth and as claimed.

Petroleum oils and products are ordinarily mixtures of hydrocarbon components differing in solubility in, or miscibility with, various'solvents; and particularly with solvents containing oxygen as a part of the molecule. Such solvents are rarely indefinitely miscible with petroleum hydr carbons. In a general way, the miscibility or solubility of highly unsaturated, of highly naphthenic and of aromatic constituents of petroleum is greater than that of constituents having more of a parafiin nature; a fact utilized in the well known process of purifying oils with liquid S02.

This differential solvent power has been utilized in different ways and for different purposes in the art; notably in the S02 process mentioned; in separating more oily from less oily components of slack wax; in separating unsaturated and aromatic constituents from burning oils and in extracting the more naphthenic components of lubricating oils. Sometimes, the oil, etc. is simply thinned with the solvent; sometimes, itis washed with successive small portions of solvent and sometimes, a mixture of oil and solvent is heated to a temperature at which miscibility results; the resultant solution beingthen cooled to cause a separation. In any way of operating, there result two layers of liquid containing the two components. These layers are physically separated, that is, are drawn off separately, and are each treated torecover the solvents; usually, by fractional distillation. Solvent occurs in bothlayers.

The present invention provides solvent liquids which are useful for somewhat similar purposes, and these liquids exhibit wide diiferences in their miscibility with various different chemical constituents of petroleum oil; small difierences in chemical composition of these constituents being accompanied by wide differences in miscibility These liquids also have a convenient variation of miscibility with temperature, and allow the pro-' duction of hot homogeneous mixtures which separate on cooling. Their specific gravity is higher than that of petroleum oils and this quality permits formation and separation of under layers containing a considerable amount of dissolved oil; They are,'further,- of a convenient boiling point, ranging between 300 and 400 F., thereby rendering their removal from an oil mixture easy and are but little affected by water or steam. Since the solvent is usually removed from the separated oil fractions by volatilization (distillation) this stability is advantageous. Withinthe boiling range mentioned (300-400 F.) removal of solvent from the extracted oil can be eiiected, even at atmospheric pressure, withoutcracking or injuring the lubricating oil.

These liquids are the various alkyl esters of certain hydroxy acids; organic acids which, like lactic and glycollicacids, have an alcohol group in the molecule. They contain oxygen inseveral forms, as carbonyl and as hydroxyl, as well as the esterifying' oxygen atom. Their convenient properties as differential solvents are possibly due to this molecular structure. Among the esters which have been used and have been found particularly suitable are the organic alkyl esters of hydroxy compounds of the lower membered fatty acids. Examples of these esters are isopropyl lactate, ethyl lactate and other lactic acid esters of hydroxy compounds which function as alcohols. Isopropyl glycollate is another useful ester. Ethyl lactate boils at 310 F., n-propyl lactate at 370, isopropyl lactate at 330 and normal butyl lactate at 371. None of these esters is corrosive, poisonous, irritating or readily inflamma ble. Triethyl citrate has shown itself of value.

All these esters exhibit a wide differential'in miscibility with constituents of petroleum oil and all have a convenient boiling point, so that they may be. readily removed after use. While they may be used in the other operations stated ante, they will be described here more particularly in their use in improving lubricating oils and lubricating oil stocks.

Minerallubricating oils are characterized by an undesirably great variation of viscosity with temperature. This is particularly true of mineral lubricating oils produced from crude oils of naphthenicerigin and such oils are far from ideal for use where extremes of temperature, are encountered. For example, atypical naphthenic lubricating oil having suitable viscosity for use in automobile engines at operating temperature is muchtoo stifi for use at the starting temperatures frequently encountered in winter time. Such an oil, on extraction with isopropyl lactate, gives a lubricating oil with much better temperatureviscosity relationships.

Each of the esters mentioned is completely miscible while hot with an equal volume of lubricating oil; the temperature required for complete miscibility being highest for ethyl lactate and lowest for butyl lactate. Each one of them can be used for making a mixture with lubricating oil at a high temperature which will separate into two layers at a lower temperature; and the heavier (underlying) layer will contain, predominately, the more naphthenic constituents of the lubricating oil, while the upper and lighter layer is a lubricating oil containing some solvent andv proportionately freed of the undesirable naphthenic constituents. The miscibility temperature and the separationtemperature with each ester differ for different oil stocks and lubricating oils, being higher in general for mid-continent stocks than for coastal stocks. The particular ester most suitable varies to some extent with the stock; but for general purposes, isopropyl lactate is regarded as particularly advantageous.

Instead of heating to the miscibility temperature and then cooling to the separation temperature, it is possible to directly wash the oil with the solvent at temperatures within the separation range. Successive small portions of solvent may be used; and occasionally with greater advantage countercurrent washing in appropriate apparatus is possible, because of the differences in specific gravity between solvent and oil. However, the described operation of producing a homogeneous, or substantially homogeneous, solution of oil and ester at elevated temperatures, followed by cooling and consequent separation is generally the more advantageous. Simpler apparatus suffices for this operation and less labor is required.

The typical mode of operation when using the heating and cooling operation is as follows. .A lubricating oil or lubricating stock, as the case may be, is mixed with about its own volume of the solvent and the mixture is heated, while being stirred, until a homogeneous, or substantially homogeneous, liquid is produced. Ordinarily, heating is to a temperature a few degrees above that required for miscibility, as this quickens the operation. The mixture is then allowed to cool while being gently stirred. Cooling is continued down to a point below that at which separation of the two phases begins to take place. This is generally 30 to 50 Fahrenheit below the miscibility temperature. Stirring is then discontinued. Separation occurs, and two layers result; the upper containing a. purified oil and some solvent, and the lower comprising solvent and the extracted components of the oil undergoing treatment. The lower layer will contain the bulk of the solve'nt. The two layers are mechanically separated in any of the ordinary ways, as by drawing off the lower layer, and the liquid of each layer is then treated to recover the solventthis being ordinarily done by distillation.

The solvent may be removed from the extracted fractions by ordinary fire distillation, or

by filming the oil and solvent mixture to form an extended surface, and evaporating under reduced pressure.' Distillation in a fractionating column with the aid of a partial vacuum (approximately 30 to 50 mm.) is advantageous, as good separation is readily obtained. If batch distillation be effected at atmospheric pressure, in finishing the distillation the undistilled "oil may rise to excessively high temperatures before the last of the solvent is removed. 'Hence, reduced pressure is advantageous. Steam distillation can be used, but is not particularly desirable.

Alternatively, the bulk of the solvent or its last aceaoci traces can be extracted from the oil by water. The water extract, on distillation, gives an azeotropic mixture distilling over before the solvent itself distils, which, in the case of isopropyl lactate, represents approximately two parts of water and one part of lactate, and has a vapor temperature on distillation of 207.5 F. The solvent may be washed out of the treated oil by use of a condensate of this 2:1 mixture. The wash liquid on distillation will yield again the azeotropic mixture, leaving dry esters behind. Because of its low boiling point, any residual washing liquid left in the oil is readily removed by common means.

When solvent is removed from the oil by distillation in presence of steam there is apt to be some hydrolysis of the ester, and some of the esters are more easily hydrolyzed than others. They are all, however, resistant to the action of water and steam and this resistant property, coupled by the fact that they are more or less miscible with water, is advantageous in the present invention. Inhibitors, such as lecithin, may be used to restrain hydrolysis.

In all cases of treating naphthenic lubricating oils or lubricating 011 stocks, the treated oil has a better temperature viscosity curve, This, is an advantage of the group of solvents used in the present invention.

The present invention is an additional step in the processes of making commercial lubricating oil; and it is to be understood that usual refining processes may be applied to the oil before and after the operation of the present invention.

In a specific embodiment of this invention producing a lubricating oil of improved temperatureviscosity characteristics from naphthenic stock, the stock was a naphthenic distillate with a viscosity of 1300 at F. and of '73 at 210 F. The viscosity index was -2 and the specific gravity at 60 F. was 0.9345. One volume of this stock was mixed with 1 volume of isopropyl lactate and heated to F. Complete miscibility occurred at 131 F. The mixture was cooled to 95 F. with stirring and the cooling continued without stirring to 86 F. Separation occurred and the lower layer was drawn off and was found to be composed of 19 per cent oil and 81 per cent solvent. The upper layer was composed of 81 per cent oil and 19 per cent solvent. The solvent was distilled off from both layers under 25 mm. mercury absolute pressure. It distilled oil? at approximately F.

The lubricating oil derived form the upper layer was of improved quality. It was, however, retreated. To this end, it was mixed with an equal volume of the same solvent and heated to 140 F. Miscibility occurred at 135 F. The mixture was cooled to 104 F. with the stirrer going and further cooled without stirring to 95 F. The lower layer had the same composition as the first operation, viz., 19 per cent oil and 81 per cent solvent, while the upper layer, like the upper layer of the preceding treatment, was also 19 per cent solvent and 81 per cent oil. Both layers were treated as before described to remove and recover solvent.

narily, one or two treatments are considered suf- 70 extraction, 12 per cent. The first extraction left 76' aosacsi t2 per cent of the stock in the oil layer and. the other two extractions reduced this, respectively, to 68 per cent and 56 per cent. It will be noted' that there was. no appreciable change in the solubility in the several extractions. The final product obtained had a viscosity at 100 F. of 1020 and at 210 F. of '71, the viscosity index being '34. The lubricating oil finally obtained was submitted to the usual acid treatment and alkali wash and clay filtering to produce a commercial oil.

In another specific embodiment, treating a paramnic stock and using n-butyl lactate, a midcontinent lubricating stock after being subjected to the usual refining and dewaxing by centrifugal methods was mixed with an equal volume of nbutyl lactate. On'heating, a homogeneous liquid was formed at 100 F., but heating was continued to 113 F. The mixture was cooled with stirring to 68 F. Stirring was then discontinued and cooling continued to 59 F. Separation occurred and the lower layer was drawn off and was found to contain 21 per cent oil and 79 per cent solvent. The upper layer contained 23 per cent solvent. Both layers were distilled to recover solvent. The upper, or oil layer, was freed of solvent. The oil was then diluted with half its volume of light naphtha, was washed twice with a small proportion of water, was freed of naphtha, and then air blown till dry. An 80 per cent yield was obtained.

The viscosity data were as follows:

Viscosity Viscosity Viscosity 100" 210" index Original 870 74 72 Finished 780 72 78 per cent solvent, while the lower layer contained about 82 per cent solvent and 18 per cent naphthenic oil. The lubricating oil showed a viscosity at 100 F. of 1190 and at 210 F. of 72; the viscosity index being 12. The yield of lubricating ofl, calculated back tolubricating stock, was per cent.

In the three foregoing examples, solvent and oil were used in about equal volumes. Sometimes, other ratios are desirable. In a typical operation, 2 volumes of isopropyl lactate were used for 1 volume of the coastal oil used in the first and third previous examples. With these proportions, the temperature of complete miscibility was 135 F. and the temperature was dropped to F., at which temperature there was clear separation into two layers. The upper layer contained 80 per cent of oil, while the lower layer contained about 18 per cent of extract from'theoil. The total yield of lubricating oil was 53.5 per cent of the stock and it had the following characteristics:

Viscosity Viscosi Viscosit 210 ty index y Original. 'Undissolvcd oil. Dissolved oil While the process has been specifically dewlth another portion of the said liquid ester.

scribed in its application to lubricating oil only, it can be used in separating any pair of proximate constituents of an oil having differing solubility.

In a specific embodiment of the present invention using countercurrent contact, a slow cur- 5 rent of isopropyl lactate at a temperature around 95 F. was allowed to pass downward through a packed tower of the type of ascrubbing tower. A slow current of the same coastal oil mentioned ante was sent upward through the tower from a point somewhat above its base, the eflluent oil at the top being removed at a point somewhat above the point of introduction of isopropyl lac tate. The rates of flow were controlled to give a. ratio of solvent to oil of between 1:1 and 2:1. n The so-scrubbedoil was treated to recover the solvent and solvent was also recovered from the charged solution passing out at the base. The results obtained were like those obtained in the detailed examples given ante.

The methods of the present invention can be usefully employed on finished lubricating oil, as well as on lubricating 011 stocks. 4

While gravitational separation of the two phases of the liquid has been more particularly described, 25 like results can be obtained continuously and more quickly by the use of a centrifuge, the liquid supplied being a mixture of oil and solvent which has been agitated so as to come to solution equilibrium and is at the proper tempera- 30 ture for clear separation.

Removal of residual solvent by the use of water or recycled distillate from the azeotropic distillation is sometimes advantageous as avoiding the heating of the oil incident to recovery by 35 distillation. The water extracts are readily separated by azeotropic distillation into fractions, one of which is prcdominatingly aqueous and the other is predominatinglyester. Either fraction may be recycled in the process. The aqueous fraction is particularly well adapted for washing the oil to get out the. ester solvent.

What we claim is: V

1. The process of separating and recovering proximate constituents of petroleum products which comprises intimately contacting a petroleum product in liquid form 'with a stable liquid alkyl ester of an organic hydroxy acid, said ester having a boiling point not over 400 F., under circumstances permitting development of a twophase liquid and separating the two phases by gravity.

2. The process of claim 1 wherein contact is effected at a temperature high enough to produce homogeneous solution of the two liquids and the temperature is then lowered to develop a twophase liquid.

3. The process of claim 1 wherein contacting is effected between flowing bodies of the two liquids'.

4. The process of claim 1 wherein the petroleum product is a lubricating oil stock containing naphthenic constituents.

5. The process of claim 1 wherein the petroleum product and the ester are contacted in sub-' stantially equal proportions.

6. The process of claim 1 wherein the described operation is repeated, the petroleum product once extracted with liquid ester being again extracted .7. The process of claim 1 wherein the two liquid phases developed are allowed to stratify under ravitation.

8. The process of separating and recovering 75 proximate constituents of petroleum products which comprises intimately contacting such a product with isopropyl lactate, permitting the development of a two-phase liquid and separating the two phases.

9.-The process of separating and recovering proximate constituents oi petroleum products which conprises intimately contacting such a product with isopropyl glycollate, permitting the development of a two-phase liquid and separating the two phases.

10. The process of separating and recovering proximate constituents of petroleum products which comprises intimately contacting such a product with butyl lactate, permitting the development of a two-phase liquid and separating the two phases.

11. The process of separating and recovering proximate constituents of petroleum products which comprises intimately contacting such a product with a liquid ester oi an organic hydroxy acid selected from a group consisting of isopropyl lactate, ethyl lactate, n-propyi lactate, triethyl citrate, isopropyi glycollate and butyl lactate, permitting the development of a two-phase liquid and separating the two phases.

12. The process of separating and recovering proximate constituents of petroleum products which comprises intimately contacting such a product with a stable liquid organic alkyl ester of a hydroxylated low membered fatty acid. said ester having a boiling point not over 400 F., permitting the development of a two-phase liquid and separating the two phases by gravity.

13. The process of claim 12 wherein contact is eiiected at a temperature high enough to produce homogeneous solution of the two liquids and the temperature is lowered to develop a two-phase liquid.

14. The process oi. claim 12 wherein contacting is eflfected between flowing bodies of the two liquids. 5

15. The process 01' claim 12 wherein the petroleum product is a'iubricating oil stock containing naphthenic constituents.

16. The process 0! claim 12 wherein the petroleum product and the allryl ester are contacted in substantially equal proportions.

17. The process of claim 12 wherein the described operation is repeated, the petroleum product once extracted with liquid alkyl ester being again extracted with another portion of the said 15 liquid ester.

18. The process of claim 12 wherein the two liquid phases developed are allowed to stratify under gravitation.

19. The process of separating and recovering proximate constituents of petroleum products which comprises intimately contacting a petroleum product in liquid form with a stable liquid aikyl ester of an o ganic hydroxy acid, said ester having a boiling point not over 400 F., under circumstances permitting development of a two-phase liquid, separating the two phases by gravity, washing the liquid of the lighter phase with a liquid comprising water, distilling the washings under azeotropic conditions to obtain a 3C distillate and a residue as more and less aqueous fractions and recycling one of such fractions.

20. The process of claim 19 wherein the more aqueous fraction is recycled for washing purposes.

ERIC B. HJERPE. WILLIAM A. GRUSE.