US2234549A - Process for production of lubricating oil - Google Patents

Description

March 11, 1941. BRAY 2,234,549

PROCESS FOR PRODUCTION OF LUBRICATING OIL v Filed July 17, 1935 130 140 TEMPERATURE OF MISCIBJLJTY' or EQUAL VOLUMES 01L 4? SOLVENT INVENTOR. Ulric B B ray Isl/w MM ATTORNEY.

Patented Mar. 11, 1941 UNITED STATES 2,234,549 PRocEss FOR PRODUCTION or LUBRIcAnnc. on.

.Ulric B. Bray, Palos Verdes Estates calm, as-

signor to Union Oil Company of California,

Los Angeles, Calif., a corporation of California Application July 1'7, 1933, Serial No. 680,719

12 Claims.

This invention relates to a process for the treatment of petroleum. More specifically it relates to the treatment of petroleum with selective solvents.

In the production of lubricating oil for internal 5 combustion motors it is highly desirable to obtain a product which exhibits a low temperature viscosity susceptibility, a low Conradson carbon value, a high stability towards sunlight and a low oxidation value. Crude lubricating oil fractions produced either as distillates or as residues are usually composed of mixtures or parafiinic, naphthenic, aromatic and olefinic hydrocarbons. The olefinic hydrocarbons are highly unsaturated and their presence in the finished lubricating oil is undesirable because of their unstable characteristics. The compounds are unstable and usually darken whenexposed to sunlight. Furthermore, they have a tendency towards polymerization with the result, after .a 20 considerable period, that these compounds are converted into resinous substances which increase the sludge value of the oil.

The aromatic and naphthenic hydrocarbons present in crude lubricating oil fractions are un- 25 desirable because of their high temperature viscosity susceptibility. These compounds exhibit too great a change in viscosity for a given change in temperature. The paraffi'nic hydrocarbons present in crude lubricating oil fractions are the 30 most desirable materials to be employed as lubricants. These compounds are highly saturated hence, from a chemical standpoint, theyv are rather inactive and do not exhibit atendency towards the formation of undesirable resinous 35 or sludge forming constituents. Furthermore,

these compounds exhibit a low temperature .vis-

cosity susceptibility. In other words, they eX hibit a minimum change in viscosity for given change in temperature. Furthermore, these highly saturated hydrocarbons are stable to sunlight, exhibiting low oxidation value and do not have a tendency towards the formation of sludge forming constituents. When I use the term paraffinic hydrocarbons I mean'thosecompounds which arepresent in petroleum, having the aforementioned characteristics and which are liquid at ordinary temperatures. This group of hydrocarbons does not include those compounds present which are usually solid or semi-solid at ordinary temperature and which are known as wax or parafiins.

In the production of lubricating oil from crude petroleum residues or distillates, it'is conventional in the art to separate'thedesirable parafiinic hydrocarbons from the undesirable olefinic, naphthenic' and/or aromatic compounds by the use of solvents which selectively dissolve the undesirable hydrocarbons present in the petroleum fraction but which exhibit only a very limitedsolvent poWer', on the desirable paraffinic hydrocarbons ,As a matter of convenience hereafter, I will referto the desirable lubricating oil constituents of petroleum as the paraflinic hydrocarbons and to. the undesirable constituents, such as 10 olefinic, naphthenicAand/or aromatic hydrocarbons as the non-paraifinic constituents 01' petroleum.

A number of selective solventshave been found desirable to separate .the parafiinic from the 15 non-paraflinic hydrocarbons, for example-it has been shown that suchmaterials as sulphur dioxide, beta-beta dichlorethyl ether, chloraniline, nitrobenzol, aniline and furfural are highly selective as the solvents for the no-n-parafiinic hydrocarbons. The foregoing selective solvents are relatively heavy as'compared to petroleum. When these relatively heavy solvents are commingled with petroleum or petroleumfractions under the proper conditions of temperature, the undesirable non-parafiinic hydrocarbons present pass into solution but'the desirable paraffinic hydrocarbons remain undissolved. If the commingled mass is allowed to remain in a quiescent state the solution of-undesirable hydrocarbons dissolved in the selective solvent settles to the bottom of the container and forms what is known :as an extract phase. The relatively light parafiinic hydrocarbons rise to the top of the vessel and form a rafiinate phase. These phases are then readily separable by ordinary decantation means. The raflinate phase is usually found to contain a small quantity of the selective solvent'and the extract phase ordinarily contains a relatively large quantity of the sol- 40 vent. These fractions may be purifiedbysubjecting them to distillation whereby the solvent is distilled away from the hydrocarbon oils.

The conventional method of separating the undesirable non-parafiinic hydrocarbons from a I hydrocarbon mixture consists in treating this mixture with a selective solvent. under the proper conditions of temperature by the addition of sufficient solvent to the oil to remove the major portion of these undesirable hydrocarbons. Where one portion of the selective. solvent is insufficient to remove the major portion of the undesirable hydrocarbons present the method of treatment may be modified and the oil may be successively treated severaltimes by the addition.

of fresh solvent to the partially treated oil until a highly refined oil is obtained which is relatively free from the undesirable hydrocarbons. For example, an oil may be treated with liquid sulphur dioxide at a temperature of about 10 F. and the rafiinate so obtained may be successively treated with sulphur dioxide at the same temperature until the major portion of non-paraffinic hydrocarbons has been extracted from the oil.

I have found in the treatment of hydrocarbon mixtures with selective solvents that the major portion of the non-paraffinic material is easily removable but that if the major portion of these constituents has been separated from the oil under treatment that the separation of the remaining portion becomes very difficult. These non-paraflinic constituents of the petroleum function as blending agents for the selective solvent and facilitate the ease by which the nonparaifinic constituents can be removed. After the major portion of these undesirable constituents has been separated from the oil the solvent power of the remaining oil for pure selective solvents is reduced to so low a value that it is difficult to remove any further substantial quantity of these undesirable fractions. from the oils. I have found it desirable to add to the selective solvents certain agents which increase its miscibility characteristics: with the oil. For ex mple, such materials as carbon bisulphide, carbon tetrachloride, tetrachlorethane, xylol, toluol, benzol or ethers, increase the solvent power of the selective solvents and hence facilitate the miscibility of the oil with the solvents. For the sake of. convenience, I will hereafter refer to the foregoing materials as modifiers, and when I speak of a selective solvent containing a modifying agent I mean one of the foregoing materials which increases the ease of miscibility of the selective solvents with the oil.

It is. therefore, an object of my invention to extract oil with selective solvents containing a modifying agent,

These modifying agents may be added to the solvent and the modified solvent may then be employed to separate the oil into its paraffinic and non-paraflinic constituents or, if desired, the modifying agent may be added directly to the oil and the oil containingthe modifying agent may then be treated with. a. selective solvent.

This modified solvent for the extraction of non-paraffinic constituents from petroleum may be employed. in any conventional extracting system. For example, modified solvent may be employed in an extraction column in which the oil undergoing extraction. is flowed countercurrently to the stream of solvent. Furthermore, I may employ this modified solvent in a stage extraction. system wherein the: raflinate passing to each successive stage is contacted countercurrently or concurrently with a fresh portion of the modified solvent.

Where stage extraction is employed itis usual- 1y necessary to separate each successive stage at the same temperature.. However, in some cases I find it desirablev to operate each succes- It is, therefore, another object of my invention to extract hydrocarbon mixtures into their parafiinic and non-paraffinic fractions by the use of a modified solvent employed at one temperature and then to re-extract the rafiinate so produced with this modified solvent at a higher temperature.

As a specific example of the method of carrying out my invention, a sample of Kettleman Hills long residuum having a gravity of 19 A. P. I. at 60" F., Saybolt Universal viscosity at 210 F. of 102 seconds and a viscosity gravity constant of 0.876 was extracted with a mixture of aniline and 20% benzol in the following manner:

(1) Four extractions with a mixture of 80% aniline and 20% benzol at 80 F., followed by Two extractions with a mixture of 80% aniline and 20% benzol at F., followed by Two extractions with a mixture of 8 aniline and 20% benzol at F., followed by (4) Two extractions with a mixture of 80% aniline, and 20% benzol at F.

Each of the above extractions was made with 100 volume percent of solvent based on the original charge of Kettleman Hills long residuum residue stock.

The viscosity gravity constant of the raffinate produced after the four extractions at 80 F. was found'to be 0.839.

The viscosity gravity constant of the rafrinate after the extraction at 100 F. was found to be 0.820.

The viscosity gravity constant of the rafiinate after the final extraction of 110 F. was found to be 0.812.

As a further example of the method of carrying out my process a Santa Fe Springs, propane extracted, dewaxed lubricating oil stock having a gravity of 19.8 A. P. I. at 60 F., a Saybolt Universal viscosity at 210 F. of 90 seconds and a viscosity gravity constant of 0.870 was extracted with a mixture of 65% aniline and 35% benzol in the following manner:

( One extraction at 75 F., followed by Two extractions of the rafiinate produced in (1) at 110 F.

Each of the foregoing extractions was made with 100. volume percent of solvent based on the original charge. of Santa Fe Springs, extracted, dewaxed lubricating oil stock.

The rafiinate produced after the final extraction at 110 F. had a viscosity gravity constant of 0.827.

The viscosity gravity constant referred to in this application has been determined by the method employed by Hill and Coates set forth in the Journal of Industrial and Engineering Chemistry, vol. 20, page 641 of 1928.

This constant represents the parafiinioity or naphthenicity of an. oil. A high value represents a high degree of naphthenicity while low values indicate relatively greater parafiinicity.

Lubricating oils, from natural, crudes range from 0.903 for an extreme Gulf Coast type to 0.807 for an extreme Pennsylvania type, or even beyond.

I have also found that the stock, being treated is more efficiently separated into its paraflinic and non-parafiinic constituents providing it does a not extend over too wide a range in molecular weight. Selective solvents. do not efficiently separate hydrocarbon mixtures into their parafiinic or non-parafiinic components if they contain compounds having a wide variation in molecular weight. Low molecular weight para-ffinio mate- 2,234,549 rialsappear to have the same miscibility rep:

erties as high molecular weight non-parafiinic materials. Hence, if-a' wide fraction, i. e., a fraction having hydrocarbons present which show wide variation in molecular weight or boiling point. is extracted with a selective solvent, 2. raflinate is produced which contains'the relatively low molecular weight paraffinic constituents contaminated more or less with relatively high molecular weight non-parafiinic constituents because of thefaot that the high molecular weight non-paraflinic constituents are insoluble to about the same extent as the paralfinic constituents, that these high molecular weight bodies do not dissolve in the solvent and are recovered along with the. highly paraffinic -material in the raffinate where they exist as contaminants. In some instances I find that the high molecular weight, non-parafilnic material is more'insoluble than the highly paraffinic fractions present m a given stock. If this stock is refined with a selective solvent the highly paraffinic, low molecular weight constituents are dissolved by the selective solvent and are recovered along with the undesirable non-paraffinic fractions and the high molecular weight non-paraffinic fractions present in the stock being more insoluble than the low molecular weight, highly paraflinic material are not dissolved in the selective solvent and recovered as a rafiinate fraction. It is, therefore, obvious that the most efficient extraction of a hydrocarbon mixture can be obtained only when the stock to be extracted is a narrow cut, that is, contains hydrocarbons having a relatively narrow molecular weight range. When I extract stocks having a narrow molecular weight range 1 am able to efficiently separate the parafiinic and non-paraffinic con-,

stituents. By extracting petroleum fractions having a narrow molecular weight range with a selective solvent, such as sulphur dioxide, betabeta dichlorethyl ether, chloraniline, nitrobenzol,

aniline or furfural, I am able to efficiently separate the desirable parafiinic hydrocarbons from the undesirable non-parafiinic hydrocarbons. Furthermore, I find that modified solvents are aids in separating these narrow fractions into their respective components. For example, when I mix the foregoing group of solvents with modifying agents, such as benzol, carbon disulphide, carbon tetrachloride, tetrachlorethane, xylol or toluol, I find that I am able to obtain a sharper separation of parafiinic from the non-parafiinic hydrocarbons.

Where a petroleum fraction contains hydrocarbons extending over a wide molecular weight range, I findit desirable to subject thefraction' to distillation for the production of narrow cuts.

By ordinary distillation it is possible to separate petroleum mixtures into cuts which have a sumciently narrow molecular weight range that they beable to solvent extract each fraction in the most eflicient manner, the graph shown in the figure has been constructed from a large number of extractions using BB dichlorethyl ether. (Similar graphs are obtainedwith other solvents, such as aniline, sulphur dioxide, benzol.) In this graph, only fairly narrow fractions as regards both. boiling range and composition viscosity gravityconstant are considered, and the temperat'ure of miscibility of equal volumes of solvent and-oil isplottedagainst the flash point of the oil; The flash point is plotted for convenience in place of average boilingpoint 'ormolecular weight,

which is permissible with closely cut, fractionated oils such as thoseunder discussion. The figure shows iso-graphs corresponding to different viscosity gravity constants, or degrees of parafiinicity,

same miscibility temperature, or conjugate solvent property with respect to dichlorethyl ether, as a low molecular weight fraction of 400 F. flash point having a viscosity gravity constant of 0.810 (highly paraffinic). It is obvious that when these two fractions are present in the same mixture they cannot be separated by means of BB dichlorethyl ether, with respect to which they have identical solvent properties; and in attempting to solvent refine a propane deasphaltized and dewaxed long residuum having a wide boiling range,

.a considerable portion of highly paraffinic low viscosity stock is lost to extract along with the high viscosity low grade extract. Similarly the rafiinate obtained is not of uniform quality throughout its boiling range, but is of better quality at the lower boiling range and is of successively poorer quality as we explore the higher boiling fractions of the rafrfinate. In order to overcome the disadvantage of overlapping solvent properties of high molecular weight low grade material on the one hand and low molecular weight high grade materialorr the other hand, I fractionate the oil by distillation before proceeding with the solvent treatment. In this manner I avoid the presence, in the the same stock, of oils of equal solvent property and widely different degrees of parafiinicity. Each fraction of the stock is then given its appropriate treatment to obtain the maximum yield of high-grade raflinate with the least loss of high grade material to extract. It will be readily apparent from the graph that the severity of the treating conditions (as indicated by the temperatures employed with a solvent of constant composition, for example, or by the percentage of modifier used at a constant or increased temperature) should increase as the average molecular weight, (average boiling point or flash point) of the fraction to be treated in creases. I

In order to illustrate the advantage from a practical standpoint of operating as described above, the following experiments are recorded. A

sample of propane deasphaltized, dewaxed Kettleman Hills long residuum was extracted with sulphur dioxide and then with sulphur dioxidebenzene to obtain a high quality raffinate repre-' senting a yield of 18.08% of oil of 0.820 viscosity gravity constant on the basis of the dewaxed long residuum. The same deasphaltized and dewaxed stock was distilled into two overhead fractions and a heavy residuum before solvent treating; the two overhead fractions were treated directly with sulphur dioxide and with sulphur dioxide containing 30% of benzene at 85 and 95- F., respectively, and the heavy residuum was given a light acid treatment (10 1b. 98% sulphuric acid per barrel of oil) in the presence of propane, and then subjected to extraction with sulphur dioxide and sulphur dioxide containing 30% benzene at 115, F. The respective yields on the basis of the dewaxed stock were 12.7% of oil of 0.813 viscosity gravity constant for the light cut, 9.3% of oil of 0.8 15 viscosity gravity constant for the middle cut, and 8.2% of 0.820 viscosity gravity constant for the heavy cut, giving a combined yield of finished oils of 30.2% of oil of 0.816 viscosity gravity constant average on the basis of the dewaxed long residuum. It is obvious that the yield of finished oils has been increased by over 50% by separating the dewaxed stock into fractions of narrower molecular weight range and then extracting each of these fractions separately. After treatment, the fractions may be recombined in any proportions required to meet the market demands for different viscosity grades of oil. The significant data obtained in these experiments are shown in the following tabulation.

Solvent treatment directly of dewaxed long residuum Flash point=460 F. (Cleveland open cup) Solvent Tests on sample RuLuveiy Temp. of volume Sample trea tg ient, Ratio qulphur di 21 2331115 pezcefilt Grla vityt ggggglg \girsgos'gy en soc ...a I v1 "me/benzene stock (.0 F. megs? constant Dewaxed residuum l9. 2

No. 1.. 16 100/00 150 8. 71 4.4 No. 2. 8 100/00 100 3. 94 5. 2 N0. 3 30 100/00 100 2. 48 6. 2 N 0. 4. 30 70/30 5. 60 12. 2 N 0. 28 70/30 80 5. 21 14. 4 No. 6- 31 70/30 80 6.97 17. 7 No. 30 50/50 70 10. 18 19. l N o. 30 50/50 70 8. 51 20. 4 N o 40 50/50 70 6. 97 22. 1 No. 50 50/50 60 6. 48 23. 5 N o. 56 50/50 60 7. 74 24. 7 No. 64 50/50 60 7. 34 25. 5 Raflinat 18. 08 26. 0

Solvent treatment of distilled fractions of dewared long residuum Light cut (35% of long residuum) Flash point=425 F. (Cleveland open cup) Solvent Tests on sample Tcmlp.1 of misei i ity s 1 5"? t R3523? s b It t 100 amp 0 ea men ay 0 v0 ume F. Ratio sulphur di- 33:33:? g fig g gfi fgg Universal percent dioxide benzene Stock R gzlzcgs itly. onstant chlltligg lyl Light dist 21.3 Extract:

N0. 1 100/00 100 16.01 9. 1 N0. 2 85 100/00 100 8. 96 11. 8 N0. 3 85 100/00 100 5. 38 14. 8 N0. 4- 85 100/00 80 3. 23 16. 4 No. 5. 85 100/00 80 2. 58 17. 6 No. 6.- 85 100/00 70 l. 91 18. 5 No. 7. 85 70/30 70 4. 39 23. I No. 8. 85 70/30 70 6. 61 24. 9 No. 9- 85 70/30 70 7. 41 25. 9 No. l0 85 70/30 70 6. 62 26. 6 Raflinate 36. 30 29. 4

Middle cut (30% of long residuum) Flash point=470 F. (Cleveland open cup) Solvent Tests on sample Tcmglof misei i ity s 1 t t t Rieglmgy s b It t 100 amp e tea men ay 0 vo ume F. Ratio sulphur di- $232512 :35; Universal ssfig percent di Ida/benzene stock 60 F. 3 constant g'l Middle cut 19. 7 70 0. 77 Extract:

No. 95 100/00 100 I6. 8. 4 134 962 N0 /00 100 9. 84 Y 10'. 6 N0. 95 100/00 100 5.75 I 12.6 N o. 95 100/00 80 3. 32 15. 0 N0. 5- 95 100/00 80 2. 91 17. 1 N 0. 95 100/00 70 2. 17 18. 3 N n. 95 70/30 70 4.96 21.8 N0. 95 70/30 70 7. 24 23. 5 N0. 05 70/30 70 7.98 24.7 No. 96 70/30 70 7; 80 25. 6 Raifiuate 31. 13 28. 0 I

Acid treated heavy cut 19.25 7 ,long. residuum) Solvent v J Tests on sample Temp, pf U miscibility S 1 i2Terg1p. of; g z S b It witlh 100 amp e rea men V ay vo ume "F. Ratio sulphur diggggg: 353 f??? Universal gs g pgrcenthdlmade/benzene stock a. 60 F. constant c z ifg yl In confirmation of my contention that extraction of a stock of very wide boiling range results in depriving the raflinate of some of its-valuable high grade low viscosity fractions, it will benoted from the above tabulations that when the long residuum is solvent extracted, the extracts ob-' tained in the later stages are actually lower in viscosity than the rafiinate, andotherexperiments have shown that the viscosity'ofthe'long residuum raflinate from treatment withdichlorethyl ether or sulphur dioxide-benzene mixtures goes through a minimum and then rises as the extraction continues depriving it of some of the low viscosity high grade materials. However,-in solvent treating the fractions obtained upon distilling the same stock, this'behavior is not observed. a r

While I have only shown batch extraction in the examples described, I do not propose to limit myself by this method of operation. Other methods of employing the modified solvents which I have described to separate oil into its paraflinic and non-parafiinic fractions are within the spirit of my invention. For example, .I may countercurrently extract the oil in a continuous countercurrent extraction system. In such a system, the oil to be extracted is introduced into the lower zone of an extraction column. 7, Modified solvent is introduced into the upper zone of this extraction column. The oil and solvent flow in countercurrent relationship vand as the solvent passes downward through theextraction column in countercurrent relationship to the upward flowing stream of oil it dissolves a portion of the non-paraffinic fractions present in the oil. The

solvent and dissolved non-paraffinic fractions are removed as an extract phase from the extraction column. The partially refined oil is recovered as a raffinate from the upper zone 'of the extraction column. This fraction is then fiowed into the lower zone of another extraction column where it is countercurrently extracted with a further portion of fresh solvent containing a modifying agent to remove further quantities of the impiuities present in the oil passing to that column.

7 If necessary the oil may be further refined in the manner just described by passing it to additional towers where it can be countercurrently extracted with additional quantities of a selective arate. the undesirable non-paraninic fractions present in the oil. However, I do not propose to limit myself by employing constant temperatures throughout the extraction system as I may also employ successively higher temperatures in each stage of extraction to aid in the separation of the non-paraflinic constituents from the oil undergoing extraction. Where an increase in temperature is employed in each successive stage the solvent is thereby made more miscible with the oil fractions being extracted in that particular stage. As the miscibility of oil and solvent is determined'to a large extent by the aromatic oil content of the oil undergoing extraction it is desirable to increase the temperature in each successive extraction stage in order to compensate for the removal of those fractions which make the oil and solvent more miscible in those stages. This is accomplished by modifying the solvent or increasingthe temperature at which the extraction is carried out. a

As a further modification of the method of carrying out my continuous countercurrent extraction system I may add the modifying agent and oil to be extracted into the lower zone of an extraction column. In the top of this column I may add a pure selective solvent selected from the group which I have previously described. From the bottom of the extraction column I may withdraw an extract phase comprising the major portion offthe solvent introduced into the top of the column and dissolved non-parafiinic fractions; From the top of the extraction column I may withdraw a rafiinate fraction more or less freed from those non-parafiinic constituents. To this raffinate fraction I may add a further quantity of the modifying agent and then introduce thisyrafilnate fraction containing the modifying agentiintothe lower zone of a second extraction column. Intothe top of. the second extraction column I may add a further quantity of the pure selective solvent and countercurrently extract the oil and modifying agent flowing into the second'column. From the second column I recover an extract phase containing the selective solvent, the modifying agent and a further, quantity .of non-paraffinicjfractions. I also recover from the top of the second column a rafiinate fraction which is more or less freed from the non-paraffinic hydrocarbons. If any. further solvent extraction is required to remove any remaining non-paraflinic hydrocarbons present in this second rafiinate this may be accomplished bypassing this rafiinate to additional extraction towers where the process is again repeated employed in the two previous stages.

Another modification of my process consistsin extracting hydrocarbon mixtures containing parafiim'c and non-parafiinic constituents with a pure selective solvent or with a pure selective solvent containing a modifying agent or first with a pure selective solvent followed by reextraction of the raflinate with a selective solvent containing a modifying agent to produce a final raifinate exhibiting a low temperature viscosity susceptibility and relatively free from non-paraflinic fractions having relatively high temperature viscosity susceptibility coupled with a distillation of the final raflinate to further separate this fraction into an overhead fraction having a low viscosity gravity constant and a still residue having a comparatively high viscosity gravity constant. It appears that the solvent extraction methods are only effective in separating to a greater or less degree the paraffinic and non-paraffinic fractions contained in a constant of 0.812.

hydrocarbon mixture. I have discovered that if a hydrocarbon mixture has been resolved into rafiinate and extract fractions by the use of selective solvents or by selective solvents containing modifying agents that I can obtain a further improvement as regards the viscosity gravity constant by subjecting the raffinates obtained by solvent extraction to distillation. The overhead fractions obtained by distilling the raflinate fraction produced from solvent extraction by the use of selective solvents have a lower viscosity gravity constant than the residue left after the distillation. As an example of this method of treating a hydrocarbon mixture, dewaxed Kettleman Hills long residuum, having a gravity of 185 A. P. I. at 60 F., a Saybolt Universal viscosity of 120 seconds at 210 F. and a viscosity gravity constant of 0.873 was treated with pounds of 98% sulphuric acid. The acid treated and dewaxed long residuum was then extracted with 150 volume percent of sulphur dioxide at 80 F. and the raffinate so produced was then re-extracted with 250 volume percent of a mixture of 70% liquid sulphur dioxide and benzol at 80 F. The rafiinate produced by the re-extraction with the sulphur dioxide-benzol mixture had a gravity of 27 A. P. I. at 60 F., a Say-bolt Universal viscosity of 86 seconds at 210 F. and a viscosity gravity constant of 0.814. This material was then subjected to a fire and steam distillation and an overhead fraction was obtained having a gravity of 20.3" A. P. I. at 60 F., a Saybolt Universal viscosity at 210 F. of 53 seconds and a viscosity gravity Bottom residue representing 33.7% of the charge to the still was also obtained. This fraction had a gravity of 244 A. P. I. at 60 F., a Saybolt Universal viscosity at 210 F. of 193 seconds and a viscosity gravity constant of 0.828. From the foregoing data it is apparent that the raflinate produced by extraction with selective solvent is subject to further improvement as regards viscosity gravity characteristics by distillation methods.

It is, therefore, an object of the present invention to extract hydrocarbon mixtures with selective solvents and/or selective solvents containing a modifying agent and to subject the raflinate obtained by the solvent treatment to distillation to produce an overhead fraction having a lower viscosity gravity constant than the oil being distilled and a residual still fraction having a viscosity gravity constant higher than the fraction being distilled.

It is to be understood that the foregoing is merely illustrative of one method of carrying out my invention and that many variations may be made by those skilled at the art within the scope of the invention which I claim.

I claim:

1. A process for the separation of parafiinic and non-paraffinic hydrocarbons from a lubricating oil comprising fractions of substantially equal solvent power but of Widely different degrees of paraflinicity which comprises separating said oil into a plurality of fractions, each fraction being characterized by a narrow molecular weight range, subsequently separately solvent extracting said fractions into a plurality of oil fractions comprising rafiinates insoluble in the solvent and extract phases soluble therein, separating said rafi'inates from said extracts and commingling the raflinates from said extractions.

2. A process according to claim 1 in which the separation of the oil into a plurality of fractions, each fraction being characterized by a narrow molecular weight range, is accomplished by fractional distillation.

3. A process for the separation of paraflinic and non-parafiinic hydrocarbons from a lubricating oil comprising fractions of substantially equal solvent power but of widely different degrees of paraffinicity which comprises fractionally distilling said oil into a plurality of fractions each of which is characterized by a narrow molecular weight range, subsequently separately extracting said fractions with liquid sulphur dioxide into a plurality of oil fractions comprising rafilnates insoluble in the sulphur dioxide and extract phases soluble therein, separating said rafiinates from said extracts and commingling the rafiinates from said extractions.

4. A process for the separation of paraflinic and non-paraflinic hydrocarbons from a lubrieating oil comprising fractions of substantially equal solvent power but of widely different degrees of paraffinicity which comprises fractionally distilling said oil to produce a distillate and an oil residue, subsequently separately solvent extracting said distillate and said oil residue into a plurality of oil fractions comprising raifinates insoluble in the solvent and extract phases soluble therein, separating said extracts from said -raffinates-and commingling the rafiinates from said extraction.

5. A process for the separation of parafiinic and non-paraifinic hydrocarbons from a long residuum comprising fractions of substantially equal solvent power but of Widely different dedrees of parafiinicity which comprises fractionally distilling said long residuum to produce a distillate and a residual oil, subsequently separately extracting said distillate and said residual oil with liquid sulphur dioxide into a plurality of oil fractions comprising rafiinatesinsoluble in said su1-.

phur dioxide and extract phases soluble therein, separating said rafiinates from said extracts and commingling the rafiinates from said extractions.

6. A process for the separation of parafiinic and non-paraffinic hydrocarbons. from a long residuum comprising fractions of substantially equal solvent power but of widely different degreesof paraffinicity which comprises fractionally distilling said long residuum to produce a distillate and a residual oil, acid treating said residual oil,.,removing the acid and reaction products from said residual oil, separately solvent extracting said distillate, and said acid treated residual oil each into a plurality of oil-fractions compris- .ingraflinates insoluble in said solvent and ex.

tract phases soluble therein, separating said raffinates from said extracts and commingling the rafiinates from said extractions.

7. In the process of refining a mineral lubricating oil the steps of fractionating the oil by distillation into fractions having narrower boiling ranges, extracting all or part of these fractions with a preferential solvent thereby producing a series of narrow boiling rafiinates and extracts, and combining all or part of the raffinates to a composite raflinate which constitutes a larger part of the original fraction than is obtained by extraction of the original oil in one treatment to a similar product.

8. A process for improving the yield of a desired refined product from a mineral lubricating oil fraction of a relatively wide boiling range approximately equal to the boiling range of the desired product comprising the steps of fractionating the oil by distillation into fractions having narrower boiling ranges, extracting these fractions with a preferential solvent thereby producing a series of narrow boiling rafiinates and extracts, and combining the raffinates to a composite rafiinate which constitutes a larger part of the original fraction than is obtained by extraction of the original oil in one treatment to a similar product.

9. In the process of refining a mineral lubricating oil fraction the steps of fractionating the oil to separate it into a plurality of cuts of narrow boiling ranges, extracting some of these cuts with a preferential solvent, thereby producing a series of narrow boiling rafiinates and extracts, and combining some of the rafiinates to a composite raiiinate which constitutes a larger part of the original oil fraction than is obtained by extraction of a composite of the cuts forming sources of the combined rafiinates in one treatment to a similar product.

10. In the process of separating an initial mixture of components belonging to different chemical groups, each chemical group containing components of different molecular sizes, said chemical groups being characterized by different solubilities in a preferential solvent, into two portions, one of which is a concentrate of. components of the group preferentially soluble in the said solvent, and the other is a concentrate of components of the other group, the steps of fractionating the mixture to separate it into a plurality of cuts of narrower boiling ranges, extracting some of these .cuts with a preferential solvent for one of said chemical groups to produce a series of narrow boiling rafiinates and extracts, and blending at least two corresponding extraction products to produce a composite product which constitutes a greater part of the initial mixture than is obtainedby the extraction of a composite of the cuts forming the sources of the blended extraction products in one treatment to a similar product.

11. In the process of separting an initial mixture of components belonging to difierent chemical groups, each chemical group containing components of different molecular sizes, said chemical groups being characterized by different solubilities in a preferential solvent, into two portions, one of which is a concentrate of components of the group preferentially soluble in the said solvent, and the other is a concentrate of components of the other group, the steps of fractionating the mixture by distillation to separate it into, a plurality of cuts of narrower boiling ranges, extracting some of these cuts with a-prcferential solvent for one of said chemical groups to produce a series of narrow boiling rafi'inates and extracts, and blending at least two rafilnates to produce a composite rafiinate which constitutes a greater part of the initial mixture than is obtained by the extraction of a composite of the cuts forming the sources of the blended extraction products in one treatment to a similar prodnot.

12. In the process of separating an initial mixture of components belonging to different chemical groups, each chemical group containing components of different molecular sizes, said chemical groups being characterized by dilferent solubilities in a preferential solvent, into two portions, one of which is a concentrate of components of the group preferentially soluble in the said solvent, and the other is a concentrate of components of the other group, the steps of fractionating the mixture to separate it into a plurality of cuts of narrower boiling ranges, extracting a pair of the adjacent cuts with a preferential solvent for one of said chemical groups to produce a series of narrow boiling raffinates and extracts, and blending a pair of corresponding extraction products derived from adjacent cuts to a composite product which constitutes a larger part of the initial mixture than is obtained by extraction of a composite of said adjacent cuts forming sources of the blended extraction products in one treatment to a similar product.

ULRIC B. BRAY.

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