US2395627A - Preparation of soluble oil - Google Patents

Description

Fb 25 594 H. L. JOHNSON ETAL. 29595927 PREPARATION 0F SOLUBLE OIL Filed May e, 194s Arrow/V- Patented Feb. 26, 1946 yUNITED STATES PATENT GFF-ICE 2,395,627 PREPARATION F SOLUBLE OIL Herbert L. Johnson,4 Norwood, and John Harold Perrine, Prospect Park, Pa., assignors to Sun Oil Company, Philadelphia, Pa., a corporation of New J erse'y Application May 6, 1943, Serial No. 485,844

9 Claims.

, This invention relates to soluble oils and to.

The so-called soluble oils, which .comprise homogeneous mixtures of oil and emulsifying agent, constitute a well recognized and distinctA type of product. They are distinguished from oils such aS used for engine lubrication particu- Y larly in that they have capacity for dilution with Water to form oil-in-water emulsions whereas engine lubricants do not possess this characteristic. The soluble oils are used widely in the arts as cutting oils, spray oils, rust-proofing oils or the like. In such applications the oil is employed in aqueous dilution in the form of an oil-in-'water emulsion. Probably the widest' application for soluble oils is as cutting oils in metal working operations, such as cutting," grinding, boring, grooving, cold-drawing and the like, in which the oil-v Water dispersion serves the two-fold purpose of a lubricant and a coolant for the metal being fabricated. Among the essential requirements of high-grade cutting oils may be mentioned thel ability of the undiluted oil to remain homogeneous under storage conditions, the ability to form exmany useful applications in the arts, either asI fractions of relatively pure chemical type or as mixtures of various types having characteristics desirable for specific purposes, provided the proper segregation of components into fractions could be effected. However, due to the complexity of the oxidized material, not only has resolution of the mixture into fractions of relatively will. result in failure of the process.

carbons. 'cially successful process no doubt has been due pure chemical type so far proved to be impossible, at least on a commercial scale, but also the segregation of fractions having properties suitable for various specific uses heretofore has been exceedingly difficult to accomplish and in most cases impractical as a commercial operation.

It also is known to prepare soluble oils from certain naturally occurring petroleum acids,

commonly called naphthenic acids. U. S. Patent No. 2,056,913, issued to Terrell et al., describes a method of recovering such acids and preparing soluble oils therefrom. However, as far as applicants are aware, no process of commercial value has been known heretofore for preparing high-grade soluble oils from synthetic acids derived by partial oxidation of petroleum hydro- Previous failure to provide a commertothe complexity of the oxidized mixture, i. e. the presence of diilicultly separable types of compounds having characteristics detrimental to soluble oils along with the desiredcomponents.

The present invention provides a commercially feasible process of oxidizing petroleum hydrocarbons and separating from the oxidation product an acidic fraction in which detrimental constituents, are substantially absent and which therefore may be'used to prepare soluble oil of highest quality. The process comprises a series ofinterrelated stepseach of which functions as a part ofa unitary procedure and contributes to the success of the process as a whole.

More specifically, the present invention provides a method of producing soluble oil, which includes the following procedural steps in the order named:

With the exception of step 3, all steps are so' vital to the successful production of high quality soluble oil that the elimination of any one step Also substantial variations in operating conditions as set forth hereinafter likewise may cause failure. Although step 3 may be omitted without affecting the quality of the final product, its inclusion is highly desirable for economic commercial operation, as hereinafter morefully explained.

Fractional acidication of the deoiled sa- For a general understanding of the process to which this invention is directed, reference should be had to the accompanying drawing which diagrammatically illustrates the procedural steps. The process preferably is carried out in a batchwise manner and will be described as such herein, although, as will be obvious ,to those skilled in the art, it may be conducted also as a continuous process.

The first step in the process comprises subjecting a charge stock to liquid phase partial ox-. idation in the absence of a special catalyst. Preferably fresh charge stock, comprising a mineral oil meeting certain specications as hereinafter set forth, is blended with unsaponifiable material'separated from a previous batch o f oxidized oil, hereinafter referred to as recycle stock. and the blend is oxidized at a temperature of 13o-150 C., preferably 140 C.. by blowing therethrough and intimately contacting therewith a free-oxygen containing gas, preferabLv air, under a superatmospheric pressure, preferably 50-100 pounds per square inch gauge. A stream of vent gases, containing the lowest boiling oxidation products, is withdrawn from the oxidation zone continuously throughout the oxidation period and` may be passed to a. condenser or other suitable equip ment for recovery of the contained oxidation products. The oxidation preferably is continued until the batch has a saponiication value of 110-120 nig. KOH/gram, the corresponding acid number being about 50-55, at which point the maximum yield of desirable reaction products is reached. The resulting mixture, comprising oxidation products of numerous chemical types and unoxidized oil, is treated with a strong aqueous solution of an alkali metal hydroxide, preferably. caustic soda, in the theoretical amount required for complete saponification. A Mixing is eiected at sufficiently high temperature, preferably 80-90 C., and for sufficient length of time to saponify all the esters and other diflicultly saponiiiable constituents, completeV saponication being very important for obtaining a product suitable for producing high-grade soluble oils. After complete saponification thesoap-oil mixture is-diluted with a relatively large proportion of water, preferably three volumes of water being added for each volume of the oily mixture of products from the oxidation step, and the resulting mixture is allowed to settle, preferably at a temperature of SLP-90 C., until a clean separation of aqueous and oil phases is obtained. Soaps of relatively low molecular weight acids act here as de-emulsifying agents and play a major role in effecting a sharp separation of the two phases. The oil phase, comprising unoxidized oil and unsaponiiiable water-insoluble oxidation products such as alcohols, aldehydes and ketones, separately is withdrawn `and returned as recycle stock to the oxidation step, where it is blended with fresh charge stock and further subjected to oxidation. lis later shown, this recycle stock has a catalytic effect in the oxidation step and serves to promote the desired oxidation reaction.

It is noted that the aqueous soap layer result- I material has been found to be not only beneficial but even necessary for compounding soluble oil of the highest quality from the product resulting from the subsequent purification steps.

The next step in the process comprises subjecting the -aqueous soap layer to partial or fractional acidication, preferably at a temperature of 80-90 C. Prior to carrying out this operation, it is desirable, although not requisite, that a light lubricating oil of the type to be,used in the nal step of compounding the soluble oil, for instance a distillate oil having a viscosity of 100 seconds S. U. at 100 F., be added to facilitate separation of layers in both the present step and the subsequent water washing step. The added oil promotes the separation mainly by lowering the specific gravity of the resulting synthetic acid layer, which otherwise would have a gravity of approximately 0.98, if preferred starting material had been used, or in other words not considerably less than that of the aqueous phase. A suitable amount of such oil to add is that equal in volume to the fresh charge stock which has been subjected to oxidation. After such addition, the mixture is subjected to fractional acidification by treating with a strong mineral. acid, preferably sulfuric acid, in amount suiiicient to acidify only a fraction of the soaps. The correct proportion of mineral acid to use depends somewhat on the particular conditions obtaining in the oxidation step and the degree of oxidation effected, especially on the proportion of Oxy-acids formed. For the preferred conditions, the correct proportion is that equivalent to ,about per cent of the alkali employed in the saponication, or in other words an amount of mineral acid equivalent to only about 50 per cent of the carboxyl groups. It has been discovered that such partial or fractional acidication selectively converts to acids the soaps of the weaker acids, i. e. of those having the lower dissociation constants, while leaving soaps of stronger acids unaffected. It also has been discovered that these stronger acids, comprising the lower molecular weight acids and oxyacids, are highly detrimental and therefore must be substantially absent from the puried product s from which soluble oil of the present invention is compounded. After partial acidification, the mixture is allowed to settle, preferably at -90 C., until a clean separation is obtained. As in the preceding deoiling step, soaps of the low molecular weight acids serve as de-emulsifying agents. The resulting lower layer, comprising an aqueous solution or dispersion of soaps of the stronger acids (low molecular weight acids and Oxy-acids) and, in addition, any Water-soluble unsaponifiable products of the oxidation such as low molecular weight alcohols, aldehydes or ketones not removed in the vent gases from the oxidation step, is drawn off and either discarded or separately processed for recovery of contained oxidation products.

The upper layer comprises a mixture of the weaker carboxylic acids and oil and, in addition, contains some soaps as well as some water-soluble free acids as contaminants. These soaps and water-soluble acids, although present in relatively small amounts, would be highly detrimental if allowed to remain in the mixture and so must be removed before compounding of the soluble oil. This is accomplished by agitating the layer,

'preferably still at 80-90 C., with an equal'volume of water, allowing the resulting mixture to stratify and withdrawing the aqueous layer with the said contaminants dissolved therein. The removed aqueous layer may be added to the soap layer obtained after the fractional acidification step and separately processed therewith or may be discarded. The washed oily layer may contain some water insuspension which may be removed by blowing with air.

'I'he refined synthetic acid product 'resulting from the above outlined 4procedure is a particu larly suitable stock for compounding soluble cil of excellent quality according to the formula and procedure hereinafter disclosed and described. It also may be used for preparing products of various other types such as greases, metallic derivatives for color lakes, siccatives or organic salt catalysts.

The starting material of the process outlined above consists of a petroleum fraction of lubricating oil consistency, containing a suiiicient proportion of naphthenic constituents so that an average of at least one naphthene ring per molecule obtains. The `naphthenic constituents are desirable in order that the acidic product obtained by oxidation and subsequent purification will resemble natural naphthenic acids rather than fatty acids, since naphthenic acids `have characteristics making them more suitable than fatty acids for the production of soluble oils of -the type herein concerned. More particularly,

soluble oils prepared from naphthenic acids should be slightly alkaline for-best results whereas those prepared from fatty acids should be acidic (i. e. containing free fatty acids). Since the desired product of the present invention is the alkaline type soluble oil, it accordingly is desirable that the synthetically produced acidic material resembles natural naphthenic acids in this respect. The desirability of having -suflcient naphthenic components in the starting material does not necessitate the use of petroleum fractions derived only from the so-called naphthenic base crudesjalthough these are preferable,lfor in many cases fractions derived from either mixed base or paraiin base crudes contain sufficient naphthenic components to be useful.

Another prerequisite .of the starting material is that it should not contain more than a certain maximum concentration of aromatic components. It has been found that aromatics greatly increase the resistance of the oil to oxidation, apparently having an inhibiting effect on the oxidation of the other ltypes of components present. When suiiiciently severe oxidizing conditions are employed to' force oxidation 'of highly aromatic oils, there is a tendency toward the formation of sludge rather than the desired oil-soluble acidic reaction products. The maximum concentration of aromatics, above which the desired oxidation cannot be effected, depends on two factors. First, the maximum allowableconcentration is related to the molecular weight of the starting material; the lower the molecular weight the Ygreater being the allowable concentration. Section rates:

Proportion of aromatic rings 270 S. U.` viscosity stock without recycle 270` S. U. viscosity stock with recycle l Not over 7% Kerosene with recycle Not over 16% Not over 4% The synthetic acids resulting from the oxidabase crudes, a viscosity range of 150-350 seconds S. U. at 100 F. corresponds to a molecular weight range suitable for the preparation of soluble oils according to the invention, although the preferred viscosity of the starting material isy about 270. Low molecular weight fractions, such as kerosene, give reaction products of too low molecular weight to` be suitable in the present applical tion.

Most petroleum fractions of suitable molecular weight range, .which have been obtained from crude petroleum by the usual distillation procedure without further treatment, contain too high an aromatic content to be useful per se as charge stock for the process and therefore require pretreatment to reduce the concentration of aromatics therein. Any suitable pretreatment whereby the concentration of aromatics is reduced sufficiently may be used; for instance, solvent extraction or treatment with concentrated or fuming sulfuric acid may be employed. The latter method, which has been used widely in the arts for the production of so-called white oils, is a convenient means of preparing suitable charge stock. For instance, a 270 viscosity oil Aromatic rings Naphthenic rings Parailinic chains Itis noted that for any given oil the refractive index of the oil affords a convenient means of determining when the aromatic content is sufciently low, and is used in preference to the somewhat 'diicultWatermann analysis method as a means of routine control of the pretreating step. Thus for an oil such as the above, a refractive index below '1.4890 indicates that the oil may be oxidized withoutthe addition of recycle stock, an index of 1.4890-1.4920 lindicates that the oil will oxidize satisfactorily if mixed with recycle 5 stock, and an index above 1.4920 indicates that the oil will not oxidize properly even if recycling is employed.

In the oxidation step the main factors affecting therate of oxidation, besides the aromatic content of the charge and the effect of recycling as indicatedabove, are pressure and temperature. The air rate appears to have little eifect provided the exit or vent gas contains a substantial percentage of free oxygen. In order to ensure a practicaloxidation rate, the pressure should be maintained above atmospheric pressure. generally above 25 pounds per square inch gauge, but not in excess o! about 175, and preferably should be 50-100. At the preferred temperature a pressure below about 25 gives a rate of oxidation which is too slow to be practical. As the pressure is increased, the reaction rate also increases kuntil a pressure of about 100 pounds per square inch is reached; whereupon further increases cause the rate to diminish, until at a pressure exceeding about 175 the rate again has become undesirably slow. It has been discovered that this decrease in rate at pressures above about 100 pounds per square inch is due to retention of low boiling oxidation products in the reaction mixture and that such products retard or inhibit the oxidation reaction. At lower pressures these low boiling products. on forming, rapidly are removed in the vent gas and so do not affect the reaction rate appreciebly.v

The temperature at which the oxidation suitably may be carried out is coniined to a relatively narrow range. With a charge stock such as the one described above, a temperature of approximately 140 C. gives the best results although any 'temperature within the range of about 130-150 C. may be used. Below this range, for example at 120 C., the rate of oxidation is exceedingly slow; on the other hand at temperatures above about 150 C., say at about 155 C. and higher, there is formed4 an undesirable oilinsoluble sludgelike .product having no utility in the present application. The optimum temperature and the limits of temperature for practical commercial operation may vary somewhat, depending on the composition and molecular weight of the charge stock, and therefore a definite optimum temperature or the limits of temperature suitable for all charge stocks cannot be speciiied. In all cases, however, the temperature should be suiliciently high to give a commercially practical rate of oxidation but not so high as to cause the formation of sludge-like products. It appears that temperatures lower than about 120 C. or higher than approximately 165 C. are seldom if ever suitable.. n

It obviously is desirable that the oxidation be .carried to ,such a degree as to eiect maximum yield of the desired product, and it has been found that this maximum is obtained when the oxidized oil reaches a saponication value of about 110-120 at which point the corresponding acid value is about Sil-55. Itlis permissible to stop thereaction at any point short of this degree of oxidation provided the product obtained from the subsequent purifying procedure has. a, saponiiication value suiliciently high to produce soluble oil according to the formula hereinafter disclosed; for

instance, the reaction might be stopped when the.

saponlfication value is even as low as about 30.

of pentane,'the following approximate percenty ages of pentane-insoluble products were obtained: y

Saponliicaton Percent value oi recutaneaction mixture, oluble mg. KOH/g. products Although these values for pentane-insoluble products probably-include small percentages of low molecular `weight acids such as acetic acid,

propionic acid, etc., which arepresent in minorproportions and would be insoluble in pentane, nevertheless they may be takenas approximate indicationsof the Oxy-acid concentration. These This is undesirable, however. for economic commex-cial operation. likewise the oxidation may be continued for a substantial extent past the point of maximum yield, and by appropriately adjusting conditions in the subsequent purification steps a purified product suitable for compounding soluble oil may be obtained in relatively low yield.

` The decrease in yield on continuing the oxidation past a saponiflcation value of 110-120 is due to the increased formation of Oxy-acids which have been found to be highly detrimental in soluble oil manufactured in accordance with this invention. These Oxy-acids are soluble in the reaction mixture and so remain dissolved therein during the oxidation, but are insoluble in light petroleum hypentane-insoluble oxy-acids are viscous, oily products having a clear, deep red color, and should not be confused with the oil-insoluble sludge-like products caused by too high oxidation temperature as referred to above. The tabulated data indicate that no more than about l0 per cent .Oxy-acids are present at the degree of oxidation corresponding to maximum yield (110-120 saponication value) but that further oxidation causes rapid increase in the proportion of these undesirable reaction products. Such larger proportions, although being undesirable, are permissible to an extent provided conditions in the subsequent fractional acidification step are so adjusted as to avoid acidification of the oxyacid soaps and thus allow these components to be substantially removed from the desirable oxi- -dation products. When the oxidation is carried to a degree considerably beyond that contemplated by the present invention, a, point eventually is reached at which incipient separation of highly oxygenated acidic products from the reaction mixture will occur. These highly oxygenated, reaction mixtureinsoluble products are not the same type products as the Oxy-acids referred to above but represent a higher degree of oxidation. The point oi incipient separation, which will not be reached at a saponication value even as high as 180, corresponds to a much more severe oxidation than is embraced by the present invention.

All of the steps in the process following the 1 oxidation step may be carried out at a temperaafter saponication, somewhat lower temperatures may be employed in the purification steps if desired, although this usually tends to lengthen the time required for mixing and settling operations.

In the saponification step following oxidation it is requisite for successful production of high vquality soluble oil that complete saponification be effected. Since ester-like oxidation products are the last to saponify, incomplete saponiflcation will result in substantial amounts of esters remaining in the saponified mixture; and although a major proportion will be removed in the deoiling step as recycle stock, the n'al product will contain an appreciable concentration of esters. It has been found that these esters are highly deleterious to the soluble oil, in that they undergo delayed hydrolysis on prolonged standing of the soluble oil, that is, they slowly hydrolize to the corresponding acids and alcohols, and in so doing eventually cause the soluble oil to change from slightly alkaline to acidic with a resultant considerable depreciation in the emulsion stability characteristics. If, through incomplete saponicaton here, esters are permitted to be present in the product from the' purication steps but this ester-containing product is completely saponified in the step which just pre'- cedes the final compounding step thereby destroying all esters, nevertheless the desired soluble oil quality will not be attained due to the presence in the soluble oil of an appreciable at 80-90 C. until complete saponication is obtained. An excess lof alkali may be added but this is not necessary and merely results in an increased consumption of both alkali and the mineral acid required in the fractionalacidiilcay tionstep. It is desirable for the mixture during agitation to have a water content of about -20 per cent; this ensures fluidity, and facilitates intimate mixing. If air blowing is used as a means of agitation, water may be added from time to time to compensate for that lost through evaporation.

'I'he saponied mixture contains a large proportion of unsaponiable material comprising unoxidized oil. alcohols, aldehydes, ketones and .the like. It obviously is rdesirable that this unsaponiable material be separately recovered in order to provide recycle stock which. asv has been explained, has a beneficial effect-in the oxidation step, as well as to decrease the consumption of fresh charge stock per unit volume of soluble oil produced, since the fresh charge stock due to the intensive pretreatment usually required represents a considerable fraction of the lc ost .of the process and any saving in this starting material consequently is of considerable advantage. 4In order to separate a substantial proportion oi' the unsaponiable material it has been found necessary to dilute the saponified mixture with water, otherwise substantially no separation is obtained. The following tabulation serves to show the effect of degree of dilution on the proportion of unsaponilable material recovered after settling the diluted mixture for one-half hour at r It is noted that no appreciable increase in recoving soap layer contains unsaponiable material in amount equivalent to about 10 per cent of the charge to the oxidation step. It has been found that this unsaponiable material later is bene-4 cial in that it improves compatibility between the synthetic acids and hydrocarbon oil, im-V proves compatibility between soaps of the acids and such oil, and 4improves emulsibility of the soluble oil-product. If this 10 per cent unsaponifiable lmaterial is removed from the soap layer, `for instance by extraction witha low boiling naphtha, before further processing, the nal solubleoil product will lhave definitely poorer emulsion stability characteristics than otherwise.

In the fractional acidification' step it is of prime importance that the proper proportion of mineral acid be added. If too vsmall a proportion is used, a low yield of desirable product will result; on the. other hand, if too large a proporition is used, the resulting product will containl acids having relatively strong acidic properties,

which is highly undesirable since the 'soaps of such acids tend to be oil-insoluble and cause gelation as well as poor emulsibility of the final soluble oil. The correct proportion of mineral acid to use depends mainly on the amount of-oxyacids formed during oxidation, and also may depend to an extent on the particular pressure employed in the oxidation step, since the retention of the verylow boiling acidic products is 4related to this factor. When the oxidation is effected under the preferred pressure and is carried to a degree corresponding to a saponification value 'of 110-120, a .proportion of mineral acid equivalent to about per cent of the carboxyl groups should be used. Also, since there is little difference in the percentage of Oxy-acids formed for lowerdeg'rees of oxidation, about the same -proportion of mineral acid is required when the oxidation is stopped at saponiication values below 11G-120. However, for higher saponification values, correspondingly smaller proportions of mineral acid are required due to increased percentages of Oxy-acids.

It has been found that complete'removal of the undesirable components does not result when the fractionally acidied mixture is allowed to separate into aqueousand oily layers and the aqueous layer is withdrawn. Instead the oily layer conof relatively strong acids, which must be removed a vin order to yield a product suitable for making high quality soluble oil. Substantially complete `1 removal of these undesirable constituents is ei'- fected in the water washing stepas described above. Although there is a tendency toward emulsion formation in this step since only a small -tion step has been used and that lubricating oil has been added in amount equal to the desirablek synthetic acids. The difference between saponiiication and acid values indicates the presence of some diicultly neutralizable constituents, believed to be lactones, the soaps of which readily are formed in the subsequent saponifying step. It should be understood that these lactones. al-

though they represent a higher degree of oxidation than simple carboxylic acids, are not the same as the Oxy-acids referred to above, but, in contradistinction to said oxy-acids, are substantially pentane-soluble and form soaps which appear to have a beneiicial rather than detrimental A effect on the quality of the nished soluble oil.

The last step in the process before finally com pounding the soluble oil comprises saponication of the refined stock resulting from the above described purication procedure. This is accomplished by mixing the rei-ined stock with a strong aqueous solution of an alkali metal hydroxide, preferably with 50 B. caustic soda, at 8090 C. and for suicient time to effect substantiallycomplete saponliication. A small excess of alkali is used so that the finally compounded soluble oil will be slightly alkaline, preferably so that it will have a free alkalinity equivalent to G01-0.10% NaOH. It has been found to be of prime importance that this saponication be carried vout before 'the refined` stock is blended with other ingradients of the soluble oil; for otherwise, the compounded soluble oil on standing may exhibit gelation. No reason is apparent as to why the specific order of saponication followed by blending is of such importance; nevertheless, it has been found effective as a means of avoiding this undesirable gelation tendency.

The final step of compounding the soluble oil comprises blending the saponied stock, suitably at 80-90 C., with lubricating oil and vari- (2) Sulfonate concentration as indicated bythe organic S03 content.

(3) Mutual solvent content. (4) Water content. It has been found that the best grade soluble oil should conform tothe following specifications: Y

Equivalent carboxyl saponiiication value l18-20 Organic S03 content 0.45%*minimuin Mutual solvent vcontent 0.5% minimum Water content 2.5-2.75%

, asados? oil should be slightly alkaline, for instance containing G01-0.10% free NaOH.

When the soap content is equivalent to a carboxyl saponication value of less than about 18. emulsibility` usually is not up to the desired standard for highest grade soluble oils; on the other hand, when it exceeds the concentration indicatedv by a carboxyl saponification value of about 20,

there is an increasing tendency for the undiluted soluble oil blend to exhibit heterogeneity or incompatibility oi the soaps and hydrocarbon oil. A soap concentration within the range equivalent to lll-204 carboxyl saponification value therefore is preferred, although some variation of these limits is permissible when high quality is not re-l quired.

Sulfonates are added to the soluble oil for the purpose of imparting rust-inhibiting characteristics thereto. It has been found that when the soluble oil is used as cutting oil in metal working operations the presence of sulfonates in concentrations speciiled herein prevents rusting of the, metal under service conditions. Sulfonates derived from petroleum lubricating oil fractions by treatment with strong sulfuric acid followed by neutralization with an alkali metal hydroxide as practiced in white oil manufacture have particula;` utility for the purpose. The'percentaee of or.t ganic S03 alfords a convenient means of indicating the proper sulfonate concentration. In order to attain the desired rust-preventive characteristcs the sulfonate content should be equivalent to not less thanabout 0.45% organic S03, for instance between 0.45% and 0.60%, when sodium sulfonates resulting from 'white oil manufacture are used. Larger proportions of sulfonates may be employed, although this usually effects little if any further improvement in quality of the soluble oil; however, since sodium sulfonates themselves are good emulsifying agents, the use of such I larger proportions will permit lower concentrations of the synthetic acid soaps than specified above without loss of quality.

A minor proportion of a mutual solvent (i. e. a solvent for both oil and water) is added to ensure compatibility of the blended constituents, to reduce viscosity of the blend and to aid emulsibility. Butyl Cellosolve is preferred as the mutual solvent, although various other solvents such as iso` propyl alcohol and other alcohols and alcoholesters may be used. It is desirable to have at least 0.5% mutual solvent in the soluble oil blend but more than 1.0% is seldom if ever required.

The water content of the nal blend should lie within a rather narrow range for best results. preferably within the range of 2.5-2.75%. al-

though a range of 22S-3.0% is permissible. Be-

low 2.25% there is a tendency for gelation to ocour, while above 3.0% there is danger of reaching a Vstate of incompatibility of soaps and oil. Usually the water content is adjusted before addition of the mutual solvent in order to prevent loss of the latter.

While the addition'of minor amounts of sulfonates', a mutual solvent and water are essential to the attainment, in the highest degree. of the qualities desirable in the finished soluble oil, it will be understood that their addition to such oils is known in the art and such addition is not included in the appended claims, which are confined to the process of producing the soluble oil to which said special ingredients are added.

The viscosity of the lubricating oil used in compounding with these other ingredients to produce In addition to these specifications the soluble 75 a finished soluble ci; product is of relatively minor importance. A lightflubricating oil, for instance one` having a. viscosity of 100 seconds S. U. at 100 F., is preferred in order that the viscosity of the product will not be excessive.

Soluble oils prepared in the above described manner are compatible with soluble oils made from natural naphthenic acids and may be blended therewith in any proportion. In some cases this may result in a blend of higher quality in certain respects than either blend alone. Furthermore, refined synthetic acids obtained from the purifying procedure described above may be blended with natural naphthenic acids and the blend then compounded with the other specified ingredients to produce solubleA oil, the only desirable alteration in the soluble oil formula then being a slight reduction in the optimum water content. i

Considerable latitude is permissible in the choice of equipment suitable for practicing the present invention commercially. As previously stated, the process may be operated in a continuous manner, in which case the equipment .would be designed accordingly; however it is preferable to operate batchwise since simple conventional types of commercial equipment then may be employed. Although the process comprises numerous steps, only two major pieces of commercialequipment are needed in order to carry out all of these in batch operation; specically, there is required an autoclave for the oxidation step and one conventional type agitator for all the other steps including the final steps of saponifying the synthetic stock and compoundingthe soluble oil. The autoclave should be constructed of material resistant to the corrosive action of the oxidation products and should be designed so as to withstand the desired pressure. It should be provided with an air inlet line at the bottom and a vent gas line at the top, and with suitable valves for regulating the gas flow and maintaining the desired pressure. It also should be provided with a means for intimately' mixing the air and the charge stock, aparticularly suitable means being a motor driven impeller or turbine-type stirrer. In addition, since the oxidation reaction is highly .exothermic, a cooling coil or other suitable means should be provided for absorbing the heat of reaction and maintaining the temperature. at the desired level. Also some means for heating the charge stock to the desired reaction temperature bottom type agitator, having suilicient heating coils for maintaining the desired temperature and provided with means for effecting agitation such as an air supply line for blowing, is suitable.

The following example will serve to show how the present invention may be carried out in commercial practice: A

Twenty barrels of a 270 S, U. viscosity, white oil, obtained by treatment of a Gulf Coastal distillate fraction with fuming sulfuric acid and composed 'of 1% aromatic rings, 59%' naphthene rings and 40% paraiilnic chains as determined by Watermann analysis, were charged to a barrel autoclave of the indicated design. Twenty-one barrels of the unsaponiable portion of oxidation product derived' from .a previous operation were added to the autoclave and mixed with the fresh charge stock.A 'The mixture was effected by means of an impeller-type mixer. A

pressure oi' 50 pounds per square inch gauge wasl maintained within the autoclave, with airbeing supplied at the rate of about 520 cubic feet per minute (measured at atmospheric pressure) and vent 4gases being withdrawn at the approximate rate of 420 cubic feet per minute. Temperature was maintained at approximately 140 C. throughout the oxidation by means of cooling Water circulated through a coil.A After approximately eight hours the oxidation was discontinued. The oxidized material comprised approxf imately 4 1 barrels having saponiiication and acid values of 114.5 and 54.3, respectively. 'I'his mate rial was pumped from the autoclave into an opentop agitator of approximately 200 barrels capacity and there allowed to cool to C. 4.2 barrels of 50 B. causticsoda solution and approximately the same amount of water were added, and the Amixture was agitated by blowing with air, the

for one-half hour. An upper layer comprising` 21 barrels of oil and water-insoluble unsaponiii-` able oxidation products and a lower layer comprising 151.3' barrels of soap solution were obtained. The upper layer was pumped oil' through a swing line and used as recycle stock in a subsequent oxidation. To the soap layer was added 21 barrels of,a light lubricating oil having a viscosity of 100 seconds S.`U. at 100 F. and 1.08 barrels of sulfuric acid calculated to be sufficient for acidifying 50 per cent of the soaps. The mixture was thoroughly agitated and then permitted to stand for two hours at approximately 80 C., whereby an upper layer comprising 37 barrels of oil-synthetic acids mixture and a lower layer comprising 136 barrels of an aqueous solution of soaps of relatively strong acids and sodium sulfate were obtained. The aqueous layer was drawn off and discarded. The. upper layer was agitated with 37 barrels of water and then allowed to settle for two hours at about 80 C. The

v resulting aqueous layer again was drawn off andl discarded. The upper layer contained a small amount of entrained water which was removedV by air blowing. Thirty-five barrels of refined 'stock having saponiilcatlon and acid values of 49.4 and 30.2', respectively, thereby was obtained.

The refined stock was saponli'led with 1.6 barkali. Saponication was 'accomplished by blowing the mixture of rei-ined stock and alkali at 80 C. for about one-half hour. To the saponined stock 47.2 barrels of light lubricating oil similar to that described above, 5 barrels of crude petroleum sulfonates (mixture oi' lubricating oil and sodium sulfonates) containing 7.4% organic S03, and 1.7 barrels of water were added,'and the resulting mixture was blown with air until substantially homogeneous. 0.5 barrel of butyl Cellosolve then was added and the mixture again blown i'or a short time, whereupon a nnished soluble oil product meeting the following speciilcations was obtained:

Equivalent carboxyl saponication value-- 19 Organic SO; per cent-- 0.46 Butyl Cellosolve do 0.5 Water do 2.6 Free NaOH do ,0.08

kThis product was found to conform to highest standards for cutting oils in laboratory tests and under actual service conditions.

We claim:

l. The process of producing soluble oil from petroleum hydrocarbon starting material having lubricating oil consistency and containing naphthenic constituents in amount providing an average of at least one naphthenic ring per molecule and aromatic constituents in amount insuilicient substantially to inhibit oxidation, which comprises subjecting said starting material to liquid phase partial oxidation by means of a free-oxygen containing gas at a. temperature within the range of 1Z0-165 C. and at a superatmospheric pressure not in excess of 175 pounds per square inch, the conditions of temperature. and pressure being such as to elect a commercially practical rate of oxidation but said temperature being suillciently low to prevent the formation oi sludge-like products, continuing the oxidation until the oxidized mixture contains a substantial proportion of synthetic acids suitable for soluble oil manufacture while avoiding the formation of more highly oxidized acidic products in appreciably detrimental proportion, treating the oxidized mixture with an aqueous solution of alkali metal hydroxide under such conditions as to effect complete saponification and yield an aqueous mixture comprising alkali metal soaps, unsaponiable oxidation products and unoxidized hydrocarbons, fractionally acidifying said aqueous mixture with a mineral acid in amount sufcient to convert to free acids a predominant -proportion of the soaps of relatively weak acids having utility in manufacture: of high quality soluble oil but insufllcient to acidify a substantial proportion of the soaps of relatively strongr acids having characteristics detrimental to high quality soluble oils, separating resulting aqueous and oily phases, washing the oily phase with Water to remove water-soluble contaminants therefrom and thereby yield a refined synthetic acid product the acidic constituents of which include no substantial4 proportion of relatively strong acids, saponifying said product with an alkali metal hydroxide and blending the .saponiiied product with petroleum oil to yield, as the desired iinal product, a blend capable of forming stable oil-in-water emulsions.

2. The process of producing soluble oilfrom petroleum hydrocarbon starting material having lubricating oil consistency and containing naphthenic constituents in amount providing an average of at least one naphthenic ring per molecule and aromatic constituents in amount insufflcient substantially to inhibit oxidation which com- Iprises blending said starting material with the v recycle stock hereinafter specified, subjecting the blend to liquid phase partial oxidation by means of a free-oxygen containing gas at a temperature within the range of l20-.-l65 C. and at a superatmospheric pressure not in excess of 175 pounds per square' inch, the conditions of temperature and pressure being such as to effect a commercially practical rate of oxidation but said temperature being sufliciently low to prevent the formation of sludge-like products. continuing the oxidation until the oxidized mixture contains a substantial proportion of synthetic acids suitable for soluble oil manufacture while avoiding the formation of more highly oxidized acidic products in appreciably detrimental proportion, treating the oxidized mixture with an alkali metal hydroxide under such conditions as to eiect complete saponiication, diluting the saponifled mixture with water, separating from the diluted mixture an oily phase comprising unsaponiable material suitable for use as recycle stock in a subsequent oxidation, fractionally acidifying the remaining aqueous layer with a mineral acidin amount sufficient to convert to free acids a predominant proportion of the soaps of relatively weak acids having utility in manufacture of high quality soluble oil but in suiilcient to acidify a substantial proportion of the soaps of relatively strong acids having characteristics detrimental to high quality soluble oils, separating resultingy aqueous and oily phases, washing the oily phase with water to remove water-soluble contaminants therefrom and thereby yield a rened synthetic acid product the acidic constituents of which include no substantial proportion of relatively strong acids, saponifying said product with an alkali metal hydroxide and blending the saponied product with petroleum oil to yield, as the desired final product, a blend capable of forming stable oil-in-water emulsions.

3. The process as defined in claim 2 wherein lubricating oil is added to the aqueous soap layer before subjecting said layer to fractional acidification.

4. A soluble oil capable of forming stable oilin-Water emulsions which comprises a major proportion of lubricating oil, alkali metal soaps of relatively Weak synthetic acids having characteristics suitable for manufacture of high quality soluble oil in concentration equivalent to a carboxyl saponiiication value of 18-20 mgs. KOH per gram, alkali metal sulfonates in concentration atleast suicient to cause said soluble oil to have an organic S03 content of 0.45 per cent, at least 0:5 per cent of an effective mutual solvent, 2.25-3.00 per cent Water and a small percentage of free alkali, said weak synthetic acids having been derived,so as to exclude the presence therein of any substantial proportion of relatively strong synthetic acids detrimental to high quality soluble oil, from the reaction mixture obtained by liquid phase partial oxidation of a petroleum lubricating oil fraction containing a substantial proportion of naphthenic constituents under oxidizing conditions preventing the formation of sludge-like products.

5. The process of producing high quality soluble oil from petroleum lubricating oil containing an average of at least one naphthene ring per -molecule and aromatic constituents in amount insumcient substantially to inhibit oxidation. A

which comprises oxidizing said starting material in liquid phase by means of a free-oxygen containing gasat a temperature within the range of -l65-C. and at a superatmospheric pressure not in excess of 175 pounds per square inch, discontinuing the oxidation when the reaction mixture has a saponiflcation value on the order of 110-120 milligrams KOH per gram, completely saponifying the reaction mixture with an aqueous solution of alkali metal hydroxide thereby to form an aqueous mixture comprising alkali metal soaps, unsaponiable oxidation products and -unoxldized hydrocarbons, fractionally acidialkali metal hydroxide and blending the saponified product with petroleum oil to yield, as the desired nal product, a blend capable of forming stable oil-inwater emulsions.

g 2,895,627 fying said aqueous mixture with -a mineral acid I 6. The process according to claim wherein i the said starting material is a naphthenic base lubricating oil having la S. U. viscosity of about 150-350 seconds at 100 F.

7. Theprocess of producing high quality soluble oil from petroleum lubricating oil containing an average of at least one naphthene ring vper molecule and aromatic constituents in amount insuicient substantially to inhibit oxidation,

which comprises oxidizing said starting material in liquid phase by means of a free-oxygen containing gas at a temperature within the range of 1Z0-165 C. and at a superatmospheric pressure not in excess of 175 pounds per square inch, discontinuing the oxidation when the reaction mixture has a saponiflcation value on the order of 110-120 milligrams KOH per gram, completely saponifying the reaction mixture with an aqueous solution of alkali metal hydroxide, diluting the saponiled mixture with water, separating from the diluted mixture an oily phase comprising unsaponiable material suitable for use as recycle stock in a subsequent oxidation, fractionally acidifying the remaining aqueous layer with a mineral acid in amount required to acidify on theorder of per cent of the alkali metal soaps -thereby liberating relatively weak acids having utility in manufacture of high quality soluble oil, separating resulting aqueous and oily phases, washing the oily phase with Water to remove water-soluble contaminants therefrom and yield a rened synthetic acid product the acidic constituents of which include no substantial proportion of relatively-strong acids detrimental to high quality' soluble oil, saponifying said product with an alkali metal hydroxide and blending the saponied product with petroleum oil to yield, as the desired nal product, a blend capable of forming stable oil-in-water emulsions..

8. The process according to claim 7. wherein the said starting material is a naphthenic base lubricating oil having a S. U. viscosity of 150-350 seconds at F. l v

9. A soluble oil capable of forming stable oilin-water emulsions which comprises a major proportion of lubricating -oil and a minor proportion of alkali metal soaps of relatively weak synthetic acids possessing the characteristics ofthe acid fraction obtained by oxidizing a naphthenic base lubricating oil of about 270 S. U.' viscosity at 100 F. in liquid phase by means ofa free-oxygen containing gas at a temperature within the range of 12o-165 C. and a superatmospheric pressure below 175 pounds per square inch, discontinuing the oxidation when the reaction mixture has a saponification value of -120 milligrains KOH per gram, completely saponifying the reaction mixture with an alkali metal hydroxide, fractionally acidifying about 50 per cent oi' the soaps in the saponied mixture to obtain a relatively' weak acid 'fraction and washing' said fraction with water. t Y HERBERT L. JOHNSON.

JOHN HAROLD PERRINE.

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