US2081497A - Extraction process - Google Patents

Description

Patented May 25, 1937 STTES A iT FFHQE EXTRACTICN PROCESS Application January 14, 1935, Serial No. 1,597

12 Claims.

This invention relates to the separation of a mixture of liquids intoits components by means of selective solvents and is a continuation in part of my application Serial Number 639,342, filed October 24, 1932. It is applicable to the separation of any liquid mixtures the components of which show a differential solubility in the selective solvent employed. While applicable for example to the separation of fatty acids from fatty oils or to the separation of saturated fatty oils from unsaturated ones, it finds a ready and universal application in the production of high grade lubricating oils from petroleum fractions and will be described in connection with such a process although it may be equally well used in other processes such as those mentioned above.

It has been found that desirable parafiinic hydrocarbons can be separated from the undesirable olefinic, naphthenic, and/or aromatic compounds, by the use of solvents which selectively dissolve undesirable hydrocarbons but which exhibit very limited solvent power upon the desirable parafiinic hydrocarbons. The term parafiinic hydrocarbons signifies those highly saturated compounds which are present in petroleum and. which are characterized by a low temperature viscosity susceptibility, i. e. they exhibit a minimum change in viscosity for a given change of temperature. They are also characterized by relative stability to air and sunlight and exhibit little tendency towards discoloration or sludge formation. This definition as applied to lubricating oils is not meant to include those compounds which are usually solid or semi-solid at ordinary temperatures and which are known as wax or petrolatum; but, of course it is obvious that my present invention is meant also to include the selective solvent extraction of wax-bearing oils. Thus, it may be used for separating by differences in solubility, when the components are in liquid form, oils from waxes or low melting point waxes from high melting point waxes. As a matter of convenience, hereinafter, I will refer to the undesirable components such as oleiinic, naphthenic,

and/or aromatic hydrocarbons as the non-paraflinic components of petroleum. These latter fractions are characterized by a relatively high temperature viscosity susceptibility and are relatively unstable to air, and sunlight, exhibiting discoloration and sludge formation.

A further indication of the purity of a lubricating oil is its viscosity gravity constant. This constant represents the paraifinicity or naphthenicity of an oil; a high value representing a high d gree of naphthenicity while the lower values indicate greater parafiinicity. Lubricating oils ob tained from natural crudes range from 0.903 viscosity gravity constant for an extreme Gulf Coast type, to 0.807 for an extreme Pennsylvania type, or even beyond. The viscosity gravity constants herein referred to have been determined by the method employed by Hill and Coats as described in the Journal of Industrial and Engineering Chemistry, Volume 20, page 641 (1928). The paraffinic hydrocarbons or fractions to which I refer hereinafter are characterized by a relatively low viscosity gravity constant while the nonparaffinic constituents of petroleum are characterized by relatively high viscosity gravity constants.

A large number of selective solvents for extraction have been found; for example, it has been shown that such materials as aniline, chloraniline, nitrobenzene, dichlorethyl ether, phenol, chlorphenol, cresol, cresylic acid, sulphur dioxide, sulphur dioxide and benzene, furfural, and many others are highly selective solvents for the nonparafiinic hydrocarbons. When these solvents are commingled with petroleum or petroleum fractions under the proper conditions of temperature, the undesirable non-paraffinic hydrocarbons pass into solution to a greater or less extent but a substantial proportion of the desirable paraflihic hydrocarbons remains undissolved. The solution of undesirable hydrocarbons and solvent settles to the bottom of the vessel in which the extraction is carried out and forms an extract phase when relatively heavy solvents are employed. The paraifinic hydrocarbons which are lighter than the solution of the undesirable hydrocarbons in the heavy solvent rise to the top of the Vessel and form a rafiinate phase. These phases are readily separable by ordinary decantation or by centrifuging. On examination of the phases it is found that the rafiinate phase usually contains a small quantity of selective solvent and the extract phase ordinarily contains a relatively large quantity thereof. These fractions may be purifled by any suitable means such as distillation for the purpose of removing the solvent. If desired, the rafiinate may be subjected to chemical treatment or to treatment with an adsorbent agent or to both treatments.

By the term rafiinate I mean that portion of the oil which contains a preponderant amount of the desirable fractions (low viscosity gravity constant fractions) while the term extract is meant to designate that fraction of the oil containing a preponderant amount of undesirable components and which is to be removed in the obtainment of the finished product.

In the usual solvent extraction of mineral oil with selective solvents, such as those above mentioned, the separation between the desirable parafiinic'fractions and the undesirable nonparafiinic fractions is not complete. Particularly, all of the paraiiinic hydrocarbons, i. e. the more valuable lubricating fractions are not obtained exclusively in the raffinate phase but some of these high grade parafinic fractions are found in the extract phase. In other words, the extract phase possesses certain desirable paralfinic hydrocarbons which by their inherent properties belong in the rarlinate phase. In terms of the viscosity gravity constant, I find that in the ordinary solvent extraction processes the difference in viscosity gravity constant between the oil in the extract phase and the oil in the rafiinate phase is insufiicient due to the fact that the viscosity gravity constant of the extract oil is decreased on account of the presence of admixed parafiinic hydrocarbons. Due to the similarity of the various hydrocarbon components of mineral oil fractions, such as lubricating oils, the solubility of undesirable non-paraffinic fractions and the desirable parafiinic fractions in the selective solvent usually differs only in degree and there is, therefore, a tendency for desirable high grade parafiinic oils to be carried away with the extract, resulting in a loss in the yield of paraffinic fractions obtained. In other words, in a phase separation of rafiinate fractions from mineral oil by employing aselective solvent, an equilibrium of paraflinic components and non-paraf finic components is established between the phases and unless means are taken to disturb this equilibrium the above mentioned loss of desirable fractions is bound to occur.

A desirable condition in solvent extraction is one in which a reasonably small proportion of oil is dissolved per unit volume of extract. Obviously the high viscosity gravity constant fractions are very soluble in the solvent employed while a decreasing solubility is exhibited as the paraffinicity increases. When operating on an ascending temperature scale advantage is taken of the difference in solubility of the non-paraffinic fractions in the solvent. In this manner an optimum oil concentration is obtainable in each stage.

It is, therefore, an object of my invention to recover the maximum amount of desirable components in a solvent extraction process.

It is another object of my invention to recover in a solvent extraction process the maximum yield of desirable components from a mixture while rejecting certain fractions containing substantially only the undesirable components and none of the desirable components whose recovery is sought.

In a more limited sense, it is an object of my invention to treat petroleum fractions with selective solvents in such a manner that the extract phase to be discarded is substantially devoid of parafiinic fractions of a viscosity gravity constant usually associated with high grade lubricating fractions and is therefore, of a high viscosity gravity constant while the raflinate phase so produced is to contain substantially only low viscosity gravity constant fractions. In other words:

It is an object of my invention to obtain in a selective solvent extraction of petroleum fractions, the maximum difference in parafiinicity (judged for example by the viscosity gravity constant) between the rafiinate and extract oil resulting from such an extraction.

Solvent extraction processes which employ a series of extraction stages operating countercurrently, and on an ascending temperature scale, that is, the temperature of the last stage from which the raffinate phase leaves is considerably higher than the temperature of the first stage from which the extract phase leaves, are undoubtedly an improvement over the previous countercurrent extraction processes, at constant temperature, but they nevertheless possess certain inherent disadvantages. In their practical operation considerable difiiculty is encountered in maintaining the equipment under control at all times because of the tendency for surging of the raifinate phase to occur. This surging results from minor variations in temperature due to practical difliculties in temperature control since in processes of this nature variations of a few degrees materially affect the solubility of the oil in the selective solvent. This may result in excess accumulation of rafiinate in certain stages or insufiicient amounts thereof in others which will tend to upset the operating conditions of the column.

As a means for overcoming such difiiculties and for obtaining the benefits of operating on an ascending temperature scale to an enhanced degree, and to produce the maximum yield of low viscosity gravity constant material I intend to use the hereinafter described process and apparatus.

Briefly described, my invention consists of a selective solvent extraction process operating in a plurality of main stages in which each main stage consists of a mixing stage, a primary settling or treating stage which constitute what I prefer to call an. extraction stage, and a secondary settling or rejection stage. The purpose of the mixing stage is to insure thorough intermixing of the oil and solvent and may be substituted by other means to establish equilibrium between phases. For instance I may use orifice mixers or heat to complete miscibility and cooling, as hereinafter explained. The rafiinate from each extraction stage is introduced into a subsequent mixing stage. The extract from each extraction stage is passed into a secondary settling or rejection stage operating at a reduced temperature wherein certain desirable fractions present in the extract from the extraction stage are rejected in a separate rafiinate phase, simultaneously producing an extract in this rejection stage of poorer quality than the extract entering from the treating stage. This extract phase produced in equilibrium with the rejected rafiinate is transferred as produced into the mixing stage of a next lower or previous main stage wherein its function is that of a selective solvent. By rejecting part of the oil from the extract phase in multiple rejection, the remaining extract which is used as solvent in a lower or previous extraction stage has added solvent power due to the deficiency of oil in the extract phase. The extract discharged from the last rejection stage (operating at the lowest temperature) is practically devoid of desirable paraffinic, low viscosity gravity constant fractions and may be discarded, or if desired, this extract may be cooled to a temperature below that of the rejection stage from which it was derived for the purpose of rejecting a second grade oil of low paraifinicity.

The rejected railinate from the rejection stage is returned to the original mixing stage of the same main stage where it is commingled with the oil and solvent entering this stage. If desired, I may pass the rejected raffinate to a subsequent mixing stage. The rejected rai-linate by passing upwards in the system prevents the accumulation of good oil in the lower or cooler sections of the system which accumulation would reduce the concentration of poor oil of high naphthenicity (high viscosity gravity constant) by dilution and hence interfere with the extraction of such poor oil. Good oil (of low viscosity gravity constant) is prevented from being carried down the system by the extract phase by means of the rejection stage which returns the good oil at each stage permitting the poor oil to go down.

In the preferred method of operation, the mixing and primary settling stages of each main stage will be operated at the same temperature, but these temperatures will be successively higher as the rafiinate oil approaches its final treating stage to be removed as a finished product.

The rejection stages or secondary settling stages will ordinarily also operate on an ascending temperature scale but in each case the temperature of the rejection stage should be sufficiently below the temperature of the corresponding primary settling stageso that substantial rejection will take place on cooling of the extract phase which separates in the primary settling stage and which is subsequently introduced into the corresponding rejection stage. While this temperature differential is of course dependent upon the type of solvent, the nature of material to be treated and the desired quality of the finished product, I have found a temperature differential of from 15 to F. very suitable, although I expressly wish to point out that any temperature which is capable of bringing about a re jection of a desirable fraction from an extract phase may be employed.

My invention may be better understood from the annexed drawing which more or less diagrammatically illustrates the apparatus, and process of my invention.

Fig. 1 is a flow diagram illustrating a preferred arrangement of the apparatus which may be used to carry out my process.

2 is a more simplified flow diagram in which the mixing stages illustrated in Fig. 1 have been omitted. The various pumps, heaters and valves illustrated in Fig. l have also been omitted in the drawing. Its primary intention is to illustrate the flow of the various materials in connection with the example hereinafter set forth.

Referring to Fig. 1 in this drawing an apparatus and process employing three main stages of extraction are illustrated although of course any number of such stages may be employed to obtain the desired results.

A, A and A represent three mixing stages; B, B and B" represent three primary settling or treating stages. and C. C C" represent three secondary settling or rejection stages. Each rejection stage is provided with a suitable cooler, stage C with cooler 33, stage C with cooler 40 and stage C with cooler 39. The numerals 24, i i and 55 represent devices which may be used to regulate the temperature of the material flowing from the mixing to the primary settling stage, operating as heaters or as coolers as desired. Mixing stages A, A and A" are preferably in- Sula-ted to avoid loss in. temperature and if desired, may be provided with suitable agitation means not illustrated in the drawing. The mixture of liquids entering these stages may be heated to the temperature required therein by means of heaters 80, 90 and H10 respectively.

In the operation of my process, the oil or any petroleum fraction, is introduced into the system by means of pump [3 and line l2 provided with valve H. The oil feed is commingled with a raffinate rejected from rejection stage C and which leaves this stage via line l8 provided with pump i1 and valve [6. The oil feed is also commingled with an extract which is produced in the subsequent rejection stage C which extract flowing through line 2| containing valve l9 and pump 20, acts as a solvent for the oil to be treated introduced through line [4. Lines 2|, l8 and I2 unite to form line [4 provided with valve l5 which introduces the mixture of oils and solvent into mixing stage A. The mixture of oil and solvent after intermixing in A, exits from this mixing stage through line 22 provided with valve 23 and passes into treating stage B. The temperature of the mixture in line 22 may be adjusted by means of temperature regulator 24 which, as previously stated, may operate either as a cooler or as a heater.

Phase separation takes place in treating stage B, the raffinate from this stage passing via line 26, valve 25 and pump 21 to the subsequent mixing stage A while the extract phase leaves the treating stage or primary settling stage B via line 29 and valve 28 and passes through cooler 30 placed in line 29 whence it passes into the secondary settling or rejection stage C in which a raffinate is rejected due to the decrease in temperature which raffinate passes via line 18, valve I6 and pump I! into the original mixing stage A as previously described. The rafiinate from stage B is commingled with a railinate rejected from rejection stage C of the subsequent main stage, which raflinate is introduced into mixing stage A via line 42, valve 43 and pump 44. This rejected raffinate from stage C together with the raflinate obtained from the previous primary settling stage (stage B) flowing in line 26, through valve 25 and pump 27, are commingled with the extract from rejection stage C, which extract is discharged from rejection stage C" by means of line 45, valve 64 and pump H. Lines 26, 42 and 45 as well as the materials flowing therein join to form line 45 which is provided with valve 47 and heater 90 and which discharges into the mixing stage A. The mixture of oil and solvent leaves mixing stage A via line 49 and valve 48 and passes into primary settling stage B. The temperature of the materials flowing in this line may be regulated by means of temperature regulating device 4|. The raflinate separating in primary settling stage B passes via line 52, valve 513 and pump 5| into mixing stage A" together with a rafiinate rejected from rejection stage C" via line 53, valve and pump 56, and the selective solvent introduced into the system via line 5?, pump 58 and valve 59. The extract separated in primary settling stage B leaves this stage via line i5 and valve 10 and passes through cooler ill positioned in line 15 whence it passes into rejection stage C the raflmate of which passes into mixing stage A together with the other materials as previously described, while the extract from this stage passes into the previous mixing h 63 to storage not indicated in the drawing. The extract leaves primary treating stage B" via line 65, valve 66 andpump 61 and passes through cooler 19 placed in line 65 into rejection stage C". The rejected rafiinate from stage C" is commingled with the selective solvent and the rat"- finate from the previous primary settling stage (B') and the mixture is introduced into mixing stage A" via line 69 and valve 89 through heater I00.

As an illustration of the temperatures which I may employ in my process when operating on lubricating oils of medium S. A. E. grades and using sulphur dioxide/benzol as a solvent, I have found thatby operating stages A, A and A", as Well as stages B, B and B, at 85 F., 100 F., and 110 F., very desirable results may be obtained. These temperatures are, however, merely representative of a typical operation using a specific solvent and will vary widely with different solvents and' stocks to be treated. The selection of the temperatures will depend upon such cons'iderations'as the temperature of miscibility of the particular oil and the particular solvent.

The temperatures prevailing in the respective mixing stages a'ndprimary settling stages are preferably identical but in case any temperature adjustment is desired, I may do so by means of temperature regulating devices 24, ll and 5 3 as previously described. The temperatures in rejection stages C, C and C" respectively, may be typically illustrated in comparison with the above given temperatures for 'the treating and mixing as F., 80? F., and 90 F., thus establishing a difierence in temperature between the primary settling stages and the rejection stages of approximateiy 30 F. Larger or smaller temperature differences may be successfully used in my process, as may be seen from the example hereinafter set forth.

The final extract which separates in rejection stage C may if desired be passed through line 3|, valve 32 into cooler 33 where it is cooled to a suitable low temperature, and from which it passes through line 3 1 and valve 35 into separator P from which a rejected rafiinate of low paraffinicity may be removed via line 39 and valve 3 8 and passed to storage not shown. The extract which'may be removed from the bottom of separator P via line 31 and valve 36 is practically devoid of fractions useful as lubricating oils and maybe discarded or used for any suitable purpose.

As may be readily seen from the drawing, the

rafiinate from each primary settling stage B and B is moved upwardly in the system and pass-es to a subsequent mixing stage where it is treated with successively purer solvent until it is treated in the final mixing stage (A") with pure solvent. The rafiinate from B is removed to storage as a low V. G. C. oil and may be given a customary finishing treatment. The extract from each primary settling stage is separated into a rejected raffinate and an extract of lower parafiinicity than the extract from the primary settling stage. The rejected raflinate is returned to the mixing stage of the same main stage for further treatment. In this manner a greater spread in parafiinicity between the raiiinate leaving the primary settling stage and the extract leaving the secondary settling or rejection stage is'obtained than in the usual single stage of countercurrent extraction.

The extract, removed from each rejection stage, passes downwardly in the system and acts as solvent in the next lower mixing stage, the oil fractions dissolved in this extract becoming more and more naphthenic in character in each stage as the extract passes toward its exit from the system.

It will be noted that in the operation as shown in the drawing, in no case is the rejected rafl'inate produced in a rejection stage brought into countercurrent relationship with the extract phase entering such rejection stage. However, as an alternative method of operation, one or more countercurrent stages of treatment may be introduced between a treating stage and the corresponding rejection stage.

Although such countercurrent treating stages may be introduced into any or all of the sets of treating and rejection stages, the preferred point for introduction of such countercurrent treating stages is between the treating stage at which the feed is introduced and the rejection stage operating on the extract phase from this treating stage. In normal practice such intermediate countercurrent treating stage or stages will be operated at temperatures intermediate between those of the main treating stage. and the rejection stage. Such use of auxiliary treating stages in which the rejected raflinate is brought into contact with the extract phase entering the rejection stage will serve to improve the degree of fractionation obtainable in the solvent extraction process and thus give increased yields of products of the desired quality.

The advantages of my process using a multiplicity of rejection stages preferably on an ascending temperature scale may be briefly stated as follows: By my multiple rejection scheme, operating on an ascending temperature scale, it is possible by regulating the temperature and type of solvent to maintain in each extraction stage an equilibrium between extract and rafiinate in which the extract phase contains an optimum or predetermined oil concentration. In case of an excessive extraction of desirable oil fractions in any one extraction stage this defect is immediately cured by the rejection stage associated with the extraction stage, which extraction stage, operating at a lower temperature will tend to reject the desirable fractions improperly removed in the extraction stage.

The oil rejected from the rejection stage is not contacted alone with fresh extract butcis returned out of countercurrent relationship with the extract oil to the extraction stage where it is originated and where it is admixed with the rafiinate feed entering this stage. Therefore, there is no accumulation of good oil in the cooler stages of my process which good oil would tend to interfere with the extraction of the poor oil present in such stages.

- Due to the combined advantages of operating on an ascending temperature scale and the introduction of a rejection unit into each stage, it is possible to obtain a higher degree of separation between the desirable and undesirable components of an oil with any selective solvent than was possible heretofore. By my method of operation, a solvent which is ineiiioient in the usual countercurrent extraction processes is rendered eflicient and commercially usable. In other words, my process of selective solvent extraction is comparable with the action of a ratchet, allowing only one material (for instance the ramnate oil) to move in one given direction without allowing any portions thereof to flow back into the direction from which they came.

While only three main stages have been illustrated in Fig. 1, it is pointed out that any number of such stages may be used. Systems of the type illustrated in Fig. 1 may successfully operate on any number of stages. For instance, I have found that by employing six stages very successful results may be obtained. This statement is merely for illustration as systems containing a greater or lesser number than six main stages may be successfully employed. The number of stages will in general be dependent upon the stock to be treated, the quality of the desired product, the solvent used and other operating conditions including temperature.

Instead of using a series of mixing stages (A, A and A), for the purpose of effecting a thorough intermixing between the oil and solvent, I may use instead a series of individual heating units in which the oil and solvent in each main stage are heated to complete miscibility and then pass the solution of oil and solvent through a cooler operating at a temperature adapted to bring about phase separation in the particular oil solvent mixture in any particular stage. The phases so produced are then introduced into a series of primary settling stages operating at ascending temperatures and which correspond to the previously mentioned primary settling stages (B, B, B). The remaining steps are identical to those described in connection with the operation using a mixing stage in each main stage.

The following is given as an example illustrating my process. The temperature, rate and amount of solvent and other descriptive matter set forth therein are given by way of illustration and are not intended as limitations upon my invention.

Referring to Fig. 2, B1, B2, B3, B4, B5 and Be represent six extraction stages; C1, C2, C3, C4, C5 and Cs represent six rejection stages operating at temperatures below those prevailing in the corresponding extraction stages. Both the extraction stages and the rejection stages operate on an ascending temperature scale as may be seen from the table in this example. The extract from each extraction stage B is shown in the drawing as leaving the bottom of this stage and is passed into the corresponding rejection stage operating at a lower temperature than the extraction stage (for instance the extract from extraction stage B3 is passed into rejection stage C3). The rafi'inate from each extraction stage is passed to the subsequent extraction stage operating at a higher temperature. Thus the rafiinate leaving extraction stage B2 at the upper section is passed to extraction stage B3. The raifinate from each rejection stage is introduced into the same extraction stage from which it was derived; for instance, the railinate from rejection stage C3 is passed into extraction stage B3. The extract produced in each rejection stage is passed to the previous extraction stage where it acts as a selective solvent. As may be seen from Fig. 2, the extract produced in rejection stage C4 is passed to extraction stage B3 where it is commingled with the rafiinate from extraction stage B2 and the rejected rafiinate from rejection stage C3 and wherein it acts as the selective solvent.

The oil feed is introduced into extraction stage B1, the final raffinate is removed at the top of extraction stage Be, the solvent is introduced in extraction stage B6 operated at the highest extraction temperature, while the final extract is removed from rejection stage C1 operating at the lowest rejection temperature.

The schedule of temperatures of the extraction stages and rejection stages used in the operation about to be described was, as indicated in the following table:

Extractionstages Rejection Degrees Degrees Fahrenheit Fahrenheit B1 50 B2. l00

B3 B4 B5 B5 During part of the operation slightly higher temperatures were used in all stages with the exception of rejection stage C1 as indicated in the schedule of temperatures given herebelow:

Extraction stages Rejection stages Degrees Degrees Fahrenheit Fahrenheit B1 50 The stock used in this example was a dewaxed Santa Fe Springs crude of an S. A. E. 10 grade.

It had the following properties:

The solvent used was liquid sulphur dioxide containing 20% by volume of benzene.

The oil was introduced into treating stage B1 (operating at 85 F.) at the rate of one gallon per hour. It was extracted in the extraction stages (Bi-Ba) with 500 volume per cent of the mixture of sulphur dioxide and benzene described above. The extract from each extraction stage was passed into the corresponding rejection stage operating at a temperature from 15 F. to 40 F. below that of the extraction stage, as may be seen from the table of temperatures. The final ralfinate leaving extraction stage B6 (operating at 140 F.) had a V. G. C. (viscosity gravity constant) of 0.808 as compared with 0.873 for the raw stock introduced into the treating stage B1. It had a Saybolt universal viscosity at 100 F. of 220 seconds with an A. P. I. gravity at 60 F. of 30.5. The yield of finished oil, free from solvent, was 47.6% by volume.

When the same stock was subjected to an ordinary countercurrent extraction process comprising a four stage treatment with liquid S02 followed by an eight stage treatment with 20% benzene in S02, the yield of oil of the same V. G. C. (0.808) was only 39.6. Therefore, according to the method of operation herein described, the improvement in yield of finished material was 8% based on the stock or 20% greater than by the countercurrent extraction process referred to above, which clearly substantiates the advantages of using a multiplicity of rejection stages in connection with a multiplicity of extraction stages, each of them operating on an ascending temperature as described herein.

By my process the yield improvement is shown in actual tests to increase as lower V. G. C. values are reached. Thus, based on an average result obtained in several operations on the same or heavier stocks, the yield improvement at 0.806 to 0.805 V. G. C. often exceeds 11-12% based on the stock, which is a material improvement over the conventional extraction operations.

The extract oil leaving rejection stage C1 (operating at 50 F.) amounted to 52.4% of the original stock, after removal of the solvent. It had a V. G. C. of 0.928, a Saybolt universal viscosity at 210 F. of 48 seconds and an A. P. I. gravity at F. of 15.2.

In one run made according to this example, the extract phase from rejection stage G1 was coo-led in an additional stage (corresponding to rejection stage P of Fig. 1) from the temperature prevailing in this rejection stage (50 F.) to 20 F. About 10% of a second grade oil (based upon the original stock) having a V. G. C. of 0.858 was rejected in its operation.

The benefits obtainable by my invention may be clearly seen from this example. Thus, an oil having an original V. G. C. of 0.873 was resolved into a highly parafiinic oil having a V. G. C. of 0.805 and an extract oil of low parafiinicity having a V. G. C. of 0.928.

As a modification of my process herein described, I may operate all of my extraction stages at the same-temperature and all of my rejection stages at a suitable lower temperature. However, my preferred method of operation is to employ a temperature gradient in both the rejection and the extraction operations.

While the operation herein described has called for the use of a rejection stage in connection with every extraction stage, I may under certain circumstances omit part or all of the rejection stages in the last main stages of the column. That is, I may, if desired, omit the rejection stages in the sectionopposite to that at which the feed is introduced and which if present would operate on an extract of fairly high parafiinicity and at an elevated temperature. For instance, in the above example I might omit rejection stages C3, C4, C5 and C6. In such case the extract phase from extraction stage B3 is passed to extraction stage B4 with a similar procedure taking place with the extract phase from extraction stages B4 and B5 which will pass to the subsequent extraction stages operating at an ascending temperature.

This operation, using rejection stages only in the lower main stages, although not giving quite as high a yield of desirable low V. G. C. oils in all instances, is nevertheless entirely feasible and will give an improved yield of highly paraffinic rafiinates as compared with the selective solvent extraction processes so far known.

The temperatures, amounts of solvent, and other phases of the invention disclosed in this application are not to be considered as limitations thereof, since many variations within the scope of this invention and the appended claims may be made by those skilled in the art.

I claim:

1. Process for separating parafiinic and nonparaffinic fractions in an oil containing the same which comprises passing oil in countercurrent relationship with a selective solvent in a plurality of stages arranged in a countercurrent relationship from an initial oil-feed stage to a final solvent feed stage, withdrawing a parafiinic raffinate phase from the solvent feed stage and an extract of low paraffinicity from the oil feed stage and additionally withdrawing intermediate rafiinate phases and extract phases from said stages, passing the intermediate raffinate from one stage to the next succeeding stage, cooling the withdrawn intermediate extract phase to form a rejected raffinate and a remaining extract phase, returning the rejected ramnate for further extraction and passing the remaining extract phase to a preceding stage.

2. Process for separating paraffinic and nonparafiinic fractions in an oil containing the same which comprises passing oil in countercurrent relationship with a selective solvent in a plurality of stages arranged in a countercurrent relationship from an initial oil feed stage to a final solvent feed stage, withdrawing a parafiinic rafiinate phase from the solvent feed stage and an extract of low parafiinicity from the oil feed stage and additionally withdrawing intermediate rafiinate and extract phases from said stages, passing the intermediate raffinate phase from one stage to the next succeeding stage, cooling the withdrawn intermediate extract phase to form a rejected raffinate and a remaining extract phase, passing the rejected raifinate out of countercurrent relationship with the said remaining extract phase to the stage from which the corresponding intermediate extract was removed and passing the remaining extract to the next preceding stage.

3. Process for separating paraffinic andnonparafiinic fractions in an oil containing the same which comprises passing oil in countercurrent relationship with a selective solvent to form an extract phase of low parafiinicity and a highly paraffinic rafiinate phase, withdrawing an oil solvent phase from said countercurrent passage intermediate the points of withdrawal of the said extract and raffinate phases, cooling said withdrawn oil-solvent phase to form. a rejected rafiinate and a remaining extract phase, returning the rejected rafiinate to a point in said countercurrent passage adjacent to the point of withdrawal of said oil solvent phase and returning the remaining extract phase to a point approximating but below the point of withdrawal of said oilsolvent phase.

4. Process for separating paraifinic and nonparaifinic fractions in an oil containing the same which comprises passing oil in countercurrent relationship with a selective solvent in a plurality of stages operating at an ascending temperature and arranged in a countercurrent relationship from an initial oil feed stage operating at the lowest temperature at which oil is extracted with a selective solvent, to a final solvent feed stage operating at the highest temperature at which oil is extracted with a selective solvent, withdrawing a paraffinic rafi'inate phase from the said solvent feed stage and additionally withdrawing intermediate raffinate and extract phases from said stages, passing the intermediate raffinate from one stage to the next succeeding stage operating at a higher temperature, cooling the withdrawn intermediate extract phase to form a rejected raflinate and a remaining extract phase, returning the rejected rafiinate out of countercurrent relationship with said remaining extract phase to the stage from which the corresponding intermediate extract was removed, passing the remaining extract phase to the next preceding stage operating at a lower temperature and recovering an extract of low parafiinicity from the intermediate extract phase of the initial oil feed stage.

5. A process according to claim 4 in which the remaining extract of the oil feed stage is cooled to a temperature sufiiciently low to reject an intermediate grade oil.

6. Process for separating parafi'inic and nonparafiinic fractions in an oil containing the same which comprises passing oil in countercurrent relationship with a selective solvent in a plurality of stages operating at an ascending temperature and arranged in a countercurrent relationship from an initial oil feed stage operating at the lowest temperature at which oil is extracted with a selective solvent, to a final solvent feed stage operating at the highest temperature at which oil is extracted with a selective solvent, withdrawing a paraifinic ratfinate phase from the said solvent feed stage and additionally withdrawing intermediate rafiinate and extract phases from said stages, passing the intermediate raffinate from one stage to the next succeeding stage operating at a higher temperature, cooling the withdrawn intermediate extract phase to form a rejected raffinate and a remaining extract phase, withdrawing the rejected raffinate phase, increasing the temperature of said rejected raffinote phase to approximately that prevailing in the stage from which the corresponding intermediate extract was removed, passing the remaining extract phase to the next preceding stage operating at a lower temperature and recovering an extract of low paraffinicity from the intermediate extract phase of the initial oil feed stage.

'7. A process according to claim 4 in which the intermediate extract phase is cooled from 15\ F. to 40 F. for the purpose of forming a rejected intermediate grade oil.

8. Process for separating paraffinic and nonparafiinic fractions in an oil containing the same which comprises passing an oil in countercurrent relationship with a selective solvent in a plurality of stages operating at an ascending temperature and arranged in a countercurrent relationship from an initial oil feed stage operating at the lowest temperature at which oil is extracted with said selective solvent to a final solvent feed stage operating at the highest extraction temperature, withdrawing a parafiinic rafiinate from the said solvent feed stage and additionally withdrawing intermediate rafiinate and extract phases from said stages, passing the intermediate raffinate from each stage to the next succeeding stage operating at a higher temperature, cooling the withdrawn intermediate extract phase from part of said stages to form a rejected raffinate phase and a remaining extract phase, returning the rejected raffinate out of countercurrent relationship with said remaining extract phase to the stage from which the corresponding intermediate extract was removed, passing the remaining extract phase to a next preceding stage operating at a lower temperature and recovering an extract of low paraffinicity from the intermediate extract phase of the initial oil feed stage.

9. Process for separating paraffinic and nonparaffinic fractions in an oil containing the same which comprises passing an oil in countercurrent relationship with a selective solvent in a plurality of stages operating at an ascending temperature and arranged in a countercurrent relationship from an initial oil feed stage to a final selective solvent feed stage, withdrawing a paraifinic ralfinate from said solvent feed stage and additionally withdrawing intermediate rafiinate and extract phases from said stages, cooling the Withdrawn intermediate extract phase from part of said stages to form a rejected raifinate phase and passing said rejected raffinate phase in countercurrent relationship with the intermediate extract entering said rejection stage.

10. Process for separating parafiinic and nonparafiinic fractions in an oil containing the same which comprises passing oil in countercurrent relationship with a selective solvent in a plurality of stages operating at an ascending temperature and arranged in a countercurrent relationship from an initial oil feed stage to a final selective solvent feed stage and additionally with drawing intermediate raifinate and extract phases from said stages, cooling the withdrawn intermediate extract phase to form a rejected raffinate and a remaining extract phase, passing the rejected ramnate of the stage at which the oil feed is introduced in countercurrent relationship with the intermediate extract and passing the rejected intermediate raffinate from the remaining stages out of countercurrent relationship with an intermediate extract phase to the stage from which the corresponding intermediate extract was removed.

11. A process for the separation of oil into fractions relatively more parafiinic and relatively less parafiinic than the original stock to be treated which comprises commingling said oil with a selective solvent in a secondary stage of an extraction system and thereby forming a raflinate phase and an extract phase, separating said phases, passing said raffinate to a tertiary extraction stage in said extraction system and commingling said raflinate passing to said tertiary stage with a selective solvent and thereby forming a final rafiinate and an intermediate extract phase and separating said phases, cooling said extract phase recovered from said secondary extraction stage and thereby rejecting an intermediate rafiinate, recovering said rejected raffinate and passing said rejected raflinate to said secondary stage of the extraction system, recovering said extract phase from said secondary extraction system from which the rejected rafiinate has been removed and passing said extract phase from which the rejected rafiinate has been removed to a primary extraction system and extracting oil in said primary stage of said extraction system with said extract phase freed of said rejected raffinate.

12. A process for the separation of oil into fractions relatively more parafiinic and relatively less paraffinic than the original oil comprising introducing the oil to be extracted into a primary extraction zone, introducing selective solvent into said primary extraction zone, removing a rainnate phase from said primary extraction zone, removing an extract phase from said primary extraction zone, cooling said extract phase removed from said primary extraction zone and thereby forming a rejected secondary rafiinate and a final extract phase, recovering the secondary rejected raffinate and returning it to the primary extraction zone, passing said primary raflinate recovered from said primary extraction zone to a secondary extraction zone, introducing selective solvent into said secondary extraction zone, removing a final raflinate from said secondary extrac-- tion zone, removing an extract phase from said secondary extraction zone, cooling said extract phase removed from said secondary extraction zone and thereby forming the tertiary rejected rafinate and a tertiary extract phase, returning the tertiary rejected rafiinate to said secondary extraction zone and. returning said tertiary ex tract phase to said primary extraction zone.

DAVID R. MERRILL.

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