USRE23779E - Selective solvent extraction of - Google Patents

Description

Feb. 9, 1954 J, Q COPE ET AL Re. 23,779

SELECTIVE SOLVENT EXTRACTION 0F PETROLEUM Original Filed Aug 1'7, 1957 2 Sheets-Sheet 1 Feb. 9, 1954 J. Q. COPE ET AL Re 23,779

SELECTIYE SOLVENT EXTRACTION OF' PETROLEUM Original Filed Aug. 17, 1937 2 Sheets-Sheet 2 N N` EM wf m ,mcy ww l@ W IY /nmU Wm. my,

@mir- Reuma Feb. 9, 1954 SELECTIVE SOLVENT EXTRACTION OF PETROLEUM John Q. Cope, El Cerrito, and William H. Claussen, Berkeley, Calif., assignors, by mesne assignments, to California Research Corporation, San Francisco, Calif., a corporation of Delaware Original No. 2,343,611, dated March 7, 1944, Serial No. 357,892, September 23, 1940, which is a division of Serial No. 159,522, August 17, 1937. Ap-

plication for reissue April 9, 1953, Serial No.

Claims.

Matter enclosed in heavy brackets appears in the original patent but forms no part ol' this reissue speciieatlon; matter printed in italics indicates the additions made by reissue.

This invention relates to a process of refining petroleum with a selective solvent. More particularly, it involves a process of treating normally liquid petroleum hydrocarbons in vapor phase with a liquid phase selective solvent to effect a more eiilcient separation of the hydrocarbon components into fractions of different chemical types.

As is well known, normally liquid petroleum contains a complex mixture of hydrocarbons of different types. For example, certain natural petroleums are known to contain a minor percentage of aromatic hydrocarbons and a major proportion of parailins and/or naphthenes having five, six and seven carbon atoms in the naphthene ring. Because of close similarity in properties it .has been very diilicult to separate these hydrocarbons according to their chemical types. Liquid phase extraction of petroleum oils with selective solvents at temperatures substantially below the point at which the solvent is completely miscible with the oils, constitutes one known method of refining petroleum and separating aromatic' and/or naphthenic hydrocarbons from the remaining oil. Although such a process produces an extract containing relatively more aromatic and/or naphthenic hydrocarbons and a rainate relatively more parafinic in nature, the separation is only qualitative and yields fractions containing substantial quantities of hydrocarbons which it was desired to eliminate.

It is a well accepted general rule in the art of selective solvent rening that an increase in the temperature of extraction, although it increases the yield of extract obtained, decreases the selectivity of a given solvent and yields an extract in which the separation between aromatlcs and/ or naphthenes on the one hand and parafilns on the other hand is less sharp than obtained at lower temperatures. That is, as temperature of extraction is increased, the yield of raffinate is lowered and the extract contains more and more of the hydrocarbons which it is desired to keep in the raffinate. When the temperature of extraction is lowered, the yield of rainate increases but it contains an increased amount of the type of hydrocarbons (e. g. aromatic and/or naphthenic) which it is desired to retain in the extract. Accordingly, it has heretofore been regarded as necessary to adopt a temperature intermediate the above mentioned high and low extremes such that a given solvent will yield a satisfactory quantity of raiilnate and yet also give a reasonably efficient separation or refinement oi' the petroleumoils.

tion is to provide a. simple, effective and improved process of refining petroleum with a selective solvent.

Another object s to provide a process of reflning petroleum with a. selective solvent by countercurrently contacting a normally liquid petroleum fraction with a liquid phase selective solvent having a preferential solvent action for one class of carbon compounds such as aromatics, at a temperature no lower than the initial bolling point of said petroleum fraction under the conditions of extraction and preferably no lower than the dew point of the petroleum fraction.

A further object is to provide a single multistage extraction process for continuously separating :petroleum into a plurality of separate portions comprising a fraction highly aromatic in character, a fraction containing a high content of the sulfur bodies present in the petroleum, a fraction highly naphthenic in character and a fraction consisting of highly paraiiinic compounds.

Another object is to provide a process of selective solvent extraction capable of eiiecting substantially quantitative separation of aromatic and/or naphthenic hydrocarbons from a normally liquid fraction of natural petroleum containing paraflinic compounds having boiling points as much as 20 to 60 F. higher than the `lowest boiling aromatic compound present.

An additional object of the invention is to provide a process capable of eiecting quantitative separation of aromatics from a fraction of natural petroleum containing a minor proportion of hydrocarbons of the aromatic type.

A further object of the invention is to provide` improved selective` solvents for extraction of petroleum.

In the drawings,

Fig. l is a diagrammatic flow sheet illustrating a multi-stage vapor phase selective solvent extraction' process embodying the principles of thi invention.

Fig. 2 is a vdiagrammatic illustration of a lprocess utilizing a single stage vapor phase contacting tower for carrying out the selective solvent extraction process of this invention.

Briefly, the process of this invention involves tracting solvent.

3 countercurrently contacting normally liquid pe- -troleum hydrocarbons with a higher boiling selective solvent maintained in liquid phase and at a temperature above the boiling point of the hydrocarbons being treated. By this process aromatic''hydrocarbons, orwhen desired naphthenic hydrocarbons, or both, are selectively extracted from the mixed vapor phase petroleum hydrocarbons.

In the process as illustrated bythe flow sheet of Fig. 1, the petroleum stock to be treated is passed from storage through pipe I, heat exchangers 2 and 9, and conduit I to the vaporizer 5. The petroleum is converted from liquid to vapor phase in the vaporizer 5 and then passes through line 9 and valve I2 to extracting column 1.

To insure intimate contacting in the extracotion column between the vapor phase petroleum and the liquid phase selective solvent, various means may be adopted. A tower iilled with suitable packing of refractory earthenware. glass, etc.. comprises one eiective form o! apparatus for this purpose. A tower constructed in the same manner as an ordinary iractionating column of a bubble cap type is also an eflicient means of insuring effective contact between the vapor phase petroleum and the liquid phase ex- In Fig. l, three extraction columns are shown4 but it is apparent that the number may be increased or decreased as conditions such as eiliciency of the extraction, the volume of materials to be treated, etc., require.

- After extraction in tower 1 the raillnate vapors pass from the top of the tower through line 8 to the bottom oi extraction tower 9. 'I'he rafnate from extraction tower 9 likewise passes through line Ill to tower II where the raiiinate hydrocarbons, still in vapor phase. are again extracted by the selective solvent. The iinal vapor phase rafnate flows from the top oi' extraction tower I I through conduit Il and control valve I9 to heat exchanger 2 where partial condensation occurs. Provision is made i'or returning a portion or all of the partial condensate from heat exchanger 2 through valve controlled line I9 to either extraction tower 9 or II or both by means of independent return pipes controlled by valves I1 and I9 therein. The remaining ramnate is cooled in condenser I9, condensed to liquid phase and passed to storage. Valve controlled conduit ISA provides means for supplying additional condensate for reflux when the 'desired reilux ratio is higher than that obtainable by using the partial condensate alone.

The selective solvent which has been referred to in the previous paragraphs. flows through .extraction columns 1, 9 and II counter-currently to the vapor phase petroleum being extracted. Fresh solvent is admitted to the top oi' towerv Il through inlet line 20 controlled by valve 29A. The solvent flows down through the column and extracts those hydrocarbons for which it has a selective action from the upwardly flowing vapor phase petroleum. The solvent with the selectively dissolved petroleum vapors is continu-- ously removed from the bottom of the column through line 2| to vaporizer 22. To obtain more emcient extraction it is desirable to heat the solvent in a vaporizer such as 22 in order to vaporizo a substantial proportion of the dissolved hydrocarbons and recirculate these vapors to the extraction column. This procedure tends to eliminate hydrocarbons of the raiiinate type which have condensed or which have been dissolved in the solvent. Also. the recirculation of these vapors provides a method of adding heat totower Il.

The solvent, aiter being heated in vaporizer 22, ows through line 29 into the top of extraction tower 9. The solvent then countercurrently extracts petroleum vapors intower 9 and flows through line 25, heater 26 and line 21 to the top of tower 1 in the same manner ss in the previously described extraction step. From the bottom of extraction tower 1 the 'solvent to gether with the dissolved hydrocarbons is removed through line Il to vaporizer 92 where a smal1 portion ofthe dissolved hydrocarbons is vaporized and returned to the extraction tower s `1 through line 99. The selective solvent and extract then ow from the vaporizer 92 through valve 24 and line 95 to fractionating still 9|. Thef extracted hydrocarbonsare separated from the selective solvent by distillation and are removed from the top of the fractionating column through line 31. passed through heat exchanger 3 and condenser 99 to storage.

The solvent is continuously recirculated fromv still 39 through line 29 to the extracting system as previously described. New orv additional solvent can be supplied to the system as needed through valve controlled line 99 from the solvent lstorage tanks. It is to be noted at this point that the solvent entering theextraction system from the still 99 is heated to a temperature above the boiling point of both the extract and rafiinate. The temperature oi' vthe solvent in the extraction towers must of course be maintained below that at which a major proportion ci' the extract would be vaporized from or remain un- This temperature is. howeverrabove the normal dew point of the extract as well as of the rai'- nate hydrocarbons at the the system.

An auxiliary line 29 leading from vaporiz'er 5 and a control valve In are provided so that the petroleum vapors may be introduced into extraction tower 9 rather than into extraction tower 1. When the vapors are so introduced. control valve lil will be open and valve I2 in vapor line I will be closed. It is also apparent thatA the incoming hydrocarbon vapors may be introduced in both towers 1 and 9 by opening both valves 49 and I2.

Under various conditions it is desirable to remove side streams or cuts from the extracts of the different stages or extraction. Accordingly, valve controlled conduits 4I and I2 have been provided for this purpose and permit the removal ot extract cuts from extractors 9 and II respectively.l The portions 'of extract removed through these conduits will be separately distilled in a fractionating still similar to 36 shown in Figure 1 to separate the extracted compounds from the solvent. These additional stills have been omitted from the tlow sheet for the sake of simplicity.

By controlling the conditions of extraction in the various stages it is possible to obtain an expressures existing in tract from treater 14 which is substantially free asma essary to maintain the temperature in treater 1 above the boiling point of the sulfur bodies, naphthenic compounds and paraillnic compounds in the petroleum, but within the range at which aromatic compounds are preferentially extracted by the selective solvent. In a similar manner the temperature in extractor 9 will be above the boiling point of the naphthenes and parailns, but within the range at which sulfur compounds are preferentially dissolved by the selective solvent. In treater Il the temperature will be sufficiently high to cause vaporizatio'n of the paraiiinic compounds and yet within the range at which naphthenes will be extracted by the selective solvent. Obviously, the speciilc temperatures, pressures and solvent-to-oil ratio necessary to produce these results will vary with the selective solvent being used and with the petroleum stock being treated. With a given solvent and a given stock the proper conditions can be readily determined by experiment.

In view of the above discussion it is apparent that by the process represented in the flow sheet of Fig. 1 a. petroleum fraction can be continuously separated into four separate fractions of distinctl'y diiferent chemical constitution by passing the petroleum fraction through a series of three or more extraction zones, passing a liquid phase selective solvent through each of said extraction zones, intimately contacting the petroleum and the selective solvent in said extracting zones, maintaining said selective solvent in each of the zones at a temperature no lower than the boiling point of the petroleum fraction under the conditions of extraction in that zone, maintaining the temperature of the solvent above the boiling point of the non-aromatic compounds in the rst zone of extraction but below the point at which all aromatic compounds would be vaporized from the solvent, maintaining the temperature of the solvent in the second extracting zone above the boiling point oi the paraillnic and naphthenic compounds but below the point at which all sulfur bodies would be vaporized from the selective solvent and maintaining the temperature of the solvent in a third extraction zone above the boiling point of the paraiiinic compounds, but within the range at which substantially all the cyclic non-benezenoid compounds are selectively dissolved. The parailinic compounds will then be removed in vapor phase from the third extraction zone and aromatics, sulfur bodies and naphthene compounds in the extracts from extraction zones 1, 2 and 3, respectively.

An added refinement which may be utilized in the process illustrated by Fig. '1 comprises operating extraction towers 1. 9 and Il at successively decreasedv temperatures and pressures. In this species o f operation extractor 1 will be maintained at substantially atmospheric pressures, for example, extractor 9 at an intermediate reduced pressure and extractor Il at the lowest pressure and highest vacuum. Vacuum can be produced by the use of condenser i9 and pump 45 or by other suitable and well-known arrangements of apparatus. Throttle valves 42 and M in vapor lines l and Il respectively are utilized to effect a pressure differential between extractors 9 and Il. Pumps 'It and 41 in lines 21 and 23 serve to feed the solvent from the zones o1' lower pressure to the zones ot successively higher pressures. Pump I8 is provided in the reux line to extractor 9 to feed the reflux from line I6 to extraciir 9. This pump is necessary when' as in the case of the present species of operation extractor 9 is operated at higher pressures than extractor II. 4

By utilizing successively higher vacuum, that is successively reduced vapor pressures in the successive stages of extraction, improved separation of aromatics from parafns and greater eiiiciency of operation may be obtained.

The flow sheet of Fig. 2 illustrates an alternative simple but very effective method for operating the process of this invention. In this arrangement petroleum stock to be treated passes from storage through valve controlled line 50, heat exchanger 5l, line 52, heat exchanger 53, line 5I, vaporizer 55, and line 56 to a single extraction tower 51. The liquid phase selective solvent together with its dissolved extract flows from the bottom of tower 51 through line 58 to vaporizer 59. A portion only of the extract is flashed into vapor form and re-circulated through line 60 to tower 51. Solvent is continuously removed from vaporizer 59 through line 6l and passed to still 62 for removal of the extracted hydrocarbons. The extract is separated from the solvent in fractionating column S3 and flows through line 64, heat exchanger 53, line and condenser 66 to storage. .The selective solvent is continuously removed from the still and re-circulated to extraction tower 51 through valve controlled line 61. The liquid level in the vaporizers 55, 59 and 62 is maintained above the conduit connections 5l, 58, 6i and S1 to produce a liquid seal and prevent the flow of vapors through these conduits.

Rafiinate vapors flow from the top of extraction tower 51 through line 68 to heat exchanger 5I where partial condensation occurs. As much of this partial condensate as is desired may be returned to the extraction tower through line 10 controlled by valve 1I. The remainder of the raiiinate passes through condenser B8 to storage. Valve controlled conduit 12 provides means for supplying additional condensate to the reflux line when the desired reflux ratio is higher than that obtainable with the partial condensate alone.

In a single stage extraction process it is essential that the vaporphase hydrocarbons and liquid phase solvent be intimately contacted. 'One ethcient means for effecting this result comprises the conventional bubble cap fractionating column in which the vapors to be extracted rise upwardly through a series of bubble caps and are thereby intimately mixed with the downilowing extracting solvent. Such an extraction tower is the preferred form utilized in the process of both To illustrate the characteristics of the process the following data are given.

A natural petroleum cut having a boiling range l of 200 to 300 F. was extracted in a single bubble cap tower with an arrangement of apparatus similar to that illustrated diagrammatically in Fig. 2. The data of a typical'run using crude xyienols which had been topped at 450 F., as the selective solvent are given below:

7 Temperature of stock entering column F 245 Reiiux ratio of ratllnate.v ..v .1.9 Extract yield pervcent..l 38 Aniline point o! stock i'ed "F 44.4 Aniline point of raillnate F 85 Anilme point ot extract F 15 In this run the temperatures oi feed and selective solvent were to 10, and 10 to 20, respectively. above the dew point of the stock.

A series of tests was run to determine the eil'ect of reilux of the raihnate on the aniline point spread and yield or extract. Two series of data were obtained, one for a solvent thinner ratio oi iive to one. and one for a ratio oi' one to one. The extract yield was held constant to 40% and the other variables, such as temperature, as close to those values givenvabove as possible. The reflux ratio was varied during these tests to determine the eilects on the aniline points of the remnate and extract. Itwas found that the optimum re flux ratio is zero. At that ratio the aniline point o! the extract is as low as can be obtained with that particular extract yield and solvent stock ratio. The lower the yield, of course, the lower the aniline point oi the extract.

When the optimum reiiux ratio oi zero is used, it was found that the optimum ratio oi' solvent to petroleum was approximately three to one. Increased ratios up to as high as ilve to one give appreciable benets in the extraction process. The increased eiiciency ot extraction which results from solvent ratios above ve to one is relatively small.

In an arrangement of apparatus such as shown ln Fig. 2 where the still 62 is separated from the extraction column by liquid seals'so that extract vapors cannot return to the extraction column, it was Iiound that the optimum raillnate to reilux radio was approximately 2:1.

` lectively the much more volatile constituents would be sedissolved at the high temperatures involved and that the less volatile raillnate hydrocarbons having a boiling point 20 to 80 higher than that of the extract hydrocarbons would be almost quantitatively separated as a vapor phase.

'There is. of course. a practical limit to the range of boiling point spread between the extract and raillnate hydrocarbons which is permissible if pure aromatics are to be obtained by selective solvent extraction in the vapor phase. When paraillnic and aromatic hydrocarbons are being separated, those parailinic hydrocarbons having a boiling point more than 100 F. above the boiling point of the aromatics are dissolved in the solvent and will be removed with the extract in a vapor phase extraction process. Parafne hydrocarbons having boiling points 20 to F. above the boiling point of the aromatica being extracted can, on the other hand, be efi'ectively separated as ralllnate vapors. Parafine hydrocarbons-having boiling points equal to or lower than the armatics being extracted present no difficulty whatever since they are readily separated in the vapor phase. In other words, when the paraillnic and naphthenic compounds present in the petroleum cut have boiling points no more than 60 F. above the lowest boiling aromatic which is extracted, an extract free from these higher boiling compounds can be produced.

Table No. l illustrates results obtained with diil'erent solvents in treatments on diierent types of petroleum oils.

Referring to this table, it will be noted that an aromatic product having an aniline point of l All aniline points were determined by the equal volume method or b refractive index. l Apparatus provided with liquid seal between extraction and extract sytripper columns.

-\-75.4 F. was produced from a 200-300 F. cut

It has also been found that with various selective solvents, such as xylenol, the extraction process is selective with respect to raillnate hydrocarbons having a boiling point as much as' 60 above the boiling point of the aromatic hydrocarbons being extracted. In ordinaryselective solvent liquid phase extraction processes.` selectivity decreases with increase in temperatures. At temperatures of 400 to 500 F., such as are involved in the process of this invention, selective solvents have heretofore been regarded as entirely ineffective since they dissolve the rafiinate hydrocarbons practically as readily as 4the extract hydrocarbons obtained at lower temperatures. Also, it is a generally accepted principle that as between two solutes solvent, the higher the boiling point of a given solute the `less is its tendency to vaporize fromv the solution. That is, the lowest boiling dissolved hydrocarbon components should most readily vadissolved in a given from a California crude, the aniline point of the stock being 44.3 under conditions wherein phenol was employed as the selective solvent and the yield of extract held to 18%. Aniline point is a well-known measure of aromatic content, and the low aniline point 75.4" F. is indicative of the purity of the product respecting relative ahsence of non-aromatic materia.

A selective solvent useful for the present process should be highly selective and should have a boiling point well above the end point of the stock to be treated. A boiling point above approximately 300 F. will generally be found desirable for extraction of normally liquid low boiling hydrocarbons. Preferably the solvent should covery by water extraction is possible. Constant boiling mixtures oi' the solvent with water should not be formed or additional complications will result from the use of water in solvent recovery. Various solvents with the above desired properties have been found and are listed in Table No. 2.

In order to test the relative selectivity of solvents a simple comparative test was adopted. 'I'his test consisted of adding a petroleum cut having a boiling point of from 215 to 240 F. to 150 cc. of the solvent. The petroleum was added slowly and with constant stirring so that the solvent could be maintained at 250 F. during the test. A portion of the dissolved petroleum was vaporized from the mixture at this temperature and the first 3 cc. of overhead were taken for an aniline point test. The elevation of this aniline point over that of the original stock is designa-ted selectivity."

Table No. 2 lists the solvents tested in the order of their selectivity as determined by this method. Solvents having a selectivity factor greater than 25 are operative in the vapor phase extraction process of this invention providing they also have a boiling point substantially above the dew point of the hydrocarbon fraction being extracted. Attention is directed to the fact -that .this test merely indicates the relative selectivity of the solvents and that much greater aniline point spreads are obtained by the actual process of lthis invention. For example, xylenol has a, selectivity of 32.1 as determined by the test but gave an aniline point spread of 103 F. between the extract and railinate when used to treat a 200 to 300 F. boiling point petroleum cut (see Table l).

TABLE NO. 2

Belec- Solu- Bolvent V. P F. tivity bility l Tetramine 54. 3 48 Triacetin 47. 7 90 Acetanilide 45. 8 80 Diethanolamine 43. 9 15 Nitrobenzene.- 42. 8 170 Aniline 42. 4 140 Chlorex" 39. 7 136 Diarninopropanol 39. 7 15 Tricresylghosphate. 38. 9 95 Benzalde yde 38. 2 162 Trietbanol am ine 36. 15

Dibutyl phthalate 410 at 20 mm 27. 6 140 l Number olcc. oi 215-240 F. straight run petroleum cut dissolved by 150 cc. of solvent at 250 F. and one atmosphere total absolute pressure.

Tetraethylene glycol and triethylene glycol have selectivity factors of 56.7 and 55 respectively. These solvents also have very high boiling points and are highly efficient selective solvents for vapor phase extraction.

Triethylene glycol is a preferred selective solvent for the present process. It has a very high selectivity, is stable, non-corrosive and has the very high boiling point of 550 F. The high selectivity of this compound is illustrated by a run in which a petroleum stock having a boiling point range of from 200 to 300 F. was treated and an extract produced having an aniline point of 40 F. The spread of aniline point between the railinate and the extract was 143.2 as compared with 103 with' xylenol under the same conditions. Even with a 300 'to.400 F. boiling range petroleum cut which necessitated extraction at much higher temperatures than with the 200 to 300 F. cut, a 24 F, aniline extract was produced and a total spread of aniline point between ramnate and extract of 104.2 obtained.

In a six hour test at 550 F., the maximum decomposition of the triethylene glycol was a change of 0.1% determined from boiling point curves taken before and after the test. Other tests failed to show any decomposition of the triethylene glycol. The maximum corrosion observed on iron or steel was 0.008 inch per year at 550 F.

In a long run using the type of apparatus illustrated by Fig. 2, it was found that a small amount of triethylene glycol distilled over with the extract and rafnate fractions. 'I'he amount of triethylene glycol dissolved in the extract portion of the hydrocarbons was of the order of 0.15% by volume. This small amount of triethylene glycol is easily and completely removed by water washing and the solvent can then be recovered by the evaporation of the water therefrom.

A more advantageous method for recovering the solvent from the wash water is to feed the water containing the solvent into the still and fractionating column along with the extract layer. This method has the advantage that it breaks up the constant boiling mixtures of solvents and high boiling extracts which may tend to form. The water and hydrocarbon extract come over as overhead and are readily separated. In those cases where there has been incomplete removal of water from the selective solvent, lthe effect is merely to render the solvent more selective in the extraction step of the process. 'I'hat is, the aniline point of the extract is lower and the yield of aromatic hydrocarbons decreased.

As stated above, simple water washing completely removes even very minute amounts of -triethylene glycol which may be dissolved in the petroleum. For example, it has been found that when a 300 to 400 F. cut of petroleum is contacted with a water solution containing 20% by weight of triethylene glycol, no detectable amount of triethylene glycol can be found in the petroleum layer. These data indicate that triethylene glycol has a very high partition coefficient between petroleum and water so that this solvent readily diffuses almost quantitatively from oil to water.

Tetramine constitutes anl additional example of a selective solvent which is very eiicient in the process oi' this invention. 'I'his compound is one of a generic group which may be represented by the general formula The first formula is an open chain compound exemplified by diethylene triamine (NHz.C2H4.NH.CaH4.NHz)

triethylene tetramine rNHrczHtNHczHlNaclHtNHn l l and tetraethylene pentamine (NH2.C2H.NH.C2H4.NH,CzH4.NH.CzHs.NHz) Examples oi the second generic formula, which are ring compounds, are diethylene diamine and tricthylene triamine N11 Can \C:HA

It will be noted that these compounds are characterized in that they contain more carbon than nitrogen atoms in their molecules and can be formed by the interaction of ethylene dichloride with ammonia followed byvliberation of free amine by treatment with caustic. 'I'hese compounds which have a boiling point above 300 F. are in general eminently suited i'or use as selective solvents in the process of this invention.

Although a number of specific examples of suitable selective solvents have been given and although triethylene glycol is at present the prei'erred solvent for the process of this invention, it should be apparent to those skilled in the art that the broader aspects oi the invention include the use of a multitude of other selective solvents. High boiling hydroxy ethers, illustrated by diethylene glycol, triethylene glycol andv tetraethylene glycol, comprise .one chemical type oi' selective solvent most suitable for the process` herein disclosed. High boiling hydroxy esters, illustrated by diacetin, dibutyl tartrate, and butyl lactate, are also suitable. Carbitol acetate and butyl "Carbitol" illustrate operative compounds containing hydroxy, ether and ester groups.

Experiments indicate that polar compounds selected from the group consisting of hydroxy benzenes, amines, amides, chlorinated hydrocarbons. esters of polycarboxylic acids, and phosphoric acid esters of hydroxy benzenes are Vin general operative in the process of this. invention. As previously pointed out the solvent selected from this group should have a boiling point sulciently high so that it can be readily maintained in liquid phase under the conditions of extraction. In general, a boiling point above approximately 300 F. is desirable. 4

This application is a division oi' our copending application Serial No. 159,522, led August 17, 1937, and issued as Patent No. 2,215,915, dated Sept. 24, 1940.

While the character of this invention has been described in detail and numerous illustrative examples given, this has been done by way of illustration only and with the intention that no limitation should be imposed upon the invention thereby. It will be apparent to those skilled in the art that numerous modications and variations may be effected in the practice oi this invention which is of the scope of the claims appended hereto.

We claim:

l. A process of separating components .oi' a complex mixture containing aromatic and non-aromatic carbon compounds having overlapping boiling ranges which comprises passing said mixture through an extraction zone, passing a liquid phase selective solvent through said extraction zone, in-

timately contacting said mixture with said liquid phase selective solvent, maintaining said selective solvent in said zone at a temperature no lower than the boiling point oi' said mixture, separating a vapor phase non-aromatic raiilnate from said liquid phase solvent, removing the liquid phase solvent containing dissolved aromatic hydrocarbons from said extraction zone, passing said solvent together with its dissolved compounds to a separate stripping zone, maintaining a seal' between said solvent extraction and stripping zones to prevent undesired return of vaporized compounds. and altering the conditions in said extraction zone by returning to said zone controlled amounts o! vapor phase` hydrocarbons stripped from said solvent phase in said stripping zone, said controlled amounts consisting of only the more readily vaporized portion of the hydrocarbons dissolved in said selective solvent.

2. 'Aprocess of separating components of al complex mixture containing aromatic and nonaromatic carbon compounds having overlapping boiling ranges which comprises passing said mixture through an extraction zone, passing a liquid phase selective solvent through said extraction zone, intimately contacting said mixture with said liquid phase selective solvent, maintaining said selective solvent in said'zone at a temperature no lower than the -boiling point of said mixture, separating a vapor phase non-aromatic raillnate from said liquid phase solvent. partially condensing said vapor phase railinate, returning said partial condensate to said extraction zone, removing the liquid phase solvent containing dissolved aromatic hydrocarbons i'rom said extraction zone, passing said solvent together. with its dissolved compounds to a separate stripping zone, maintaining a seal between said,solvent extraction and stripping zones to prevent undesired return of vaporized compounds, and altering the conditions in said extraction zone by returning to said zone controlled amounts of vapor phase hydrocarbons stripped from said solvent phase in said stripping zone, said controlled amounts consisting of only the more readily vaporized portion of the hydrocarbons dissolved in said selective solvent.

3. A process oi separating components of a complex mixture containing aromatic and nonaromatic carbon compounds having overlapping boiling ranges which comprises passing said mixture through an extraction zone, passing a liquid phase selective solvent through said extraction zone countercurrently to said mixture and in an lamount of from approximately three parts'solpassing said solvent together with its dissolved compounds to a separate stripping zone, maintaining a seal between said solvent extraction and stripping zones to prevent undesired return of vaporized compounds, and altering the conditions in said extraction zone by returning to said zone controlled amounts of vapor phase hydrocarbons stripped from said solvent phase in said stripping zone, said controlled amounts consisting of only the more readily vaporized Vportion of the hydrocarbons dissolved in said selective solvent.

'into four fractions oi distinclly diilerent chemicalcgnstitution which comprises passing said petroleum fraction through a series of at least three extraction zones, passing a liquid phase selective solvent through each of said extraction zones, intimately contacting the petroleum and the selective solvent in said zones, maintaining said selective solvent in each of the zones at a temperature no lower than the boiling point of the petroleum fraction under the conditions oi extraction in that zone, maintaining the temperature of the solvent above the boiling point of the non-aromatic compounds in the ilrst zone or extraction but below the point at vwhich all aromatic compounds would be vaporized from the solvent, maintaining \the temperature oi the solvent in the second extraction zone above the boiling point of parafllnic and naphthenic compounds but below the point at which all sulfur bodies would be vaporized from\the selective solvent, maintaining the temperature of the solvent in the third extraction zone above the boiling point of paraiiinic compounds but within the range at which substantially all the cyclic non-benzenoid compounds are selectively dissolved, removing paramnic compounds in vapor phase from said third extraction zone, removing cyclic non-benzenoid compounds in the extract phase of said third'zone, removing sulfur bodies in the extract phase from said second zone, and removing aromatic compounds in the extract phase of said first zone.

5. A process of separating components of a complex mixture containing aromatic and nonaromatic carbon compounds having overlapping boiling ranges which comprises passing a liquid phase selective solvent in one direction through a series of extraction zones, introducing said complex mixture into an intermediate one of said zones, intimately contacting said mixture and selective solvent in said zone, maintaining the selective solvent at a temperature no lower than the boiling point oi said mixture in said zone, separating a vapor phase rafilnate from said liquid phase selective solvent, passing said vapor phase raillnate countercurrently to said selective solvent in the remaining extraction zones on one side of the aforesaid intermediate zone, removing the liquid phase solvent containing dissolved aromatic compounds from said intermediate extraction zone, passing said solvent through the remaining extraction zones on the other side of said intermediate zone, introducing an additional portion of said complex mixture into the aforesaid remaining extraction zones, and countercurrently contacting said liquid phase solvent with said additional portion of 'the mixture.

6. A process of separating components of a complex mixture containing aromatic and non-aromatic hydrocarbon compounds having overlapping boiling ranges which comprises passing said mixture through an extraction zone, passing a liquid phase selective solvent through said extraction zone, intimately contacting said mixture with said liquid phase selective solvent, maintaining said selective solvent in said zone at a temperature no lower than the boiling point of said mixture, separating a vapor phase non-aromatic rafilnate from said liquid phase solvent, removing the liquid phase solvent containing dissolved aromatic hydrocarbons from said extraction zone, passing said solvent together with its dissolved compounds to a separate vaporizing zone, maintaining a seal between said solvent extraction and vaporizing zones to prevent undesired return of vaporized compounds, vaporizing only a portion of the hydrocarbons dissolved in said solvent in said vaporizing zone, and returning said vaporized hydrocarbons to said solvent extraction zone.

'1. A process of treating a petroleum fraction with a selective solvent which comprises passing a petroleum fraction containing aromatic, cyclic non-benzenoid, and parainic compounds through a series of extraction zones, passing resorcinol through each of said extraction zones at a temperature substantially below its boiling point, in-

' timately contacting the petroleum and the resorcinol in said zones, maintaining the resorcinol at a temperature no lower than the boiling point s oi the petroleum fraction under the conditions of "extraction, maintaining the temperature of said resorcinol above the boiling point oi.' the non-aromatic compounds in the rst zone of extraction and selectively dissolving aromatics in said resorcinol, maintaining the temperature of said resorcinol in a second extracting zone above the boiling point of the parafiinic compounds and 'selectively dissolving cyclic non-benzenoid compounds in the resorcinol, and removing paraiilnlc compounds in vapor phase from the last of said extraction zones.

8. A process of treating a petroleum fraction with a selective solvent which comprises passing a petroleum fraction containing aromatic, cyclic non-benzenoid, and paramnic compounds through a series of extraction zones, passing diacetin through each of said extraction zones at a temperature substantially below its boiling point, in-

' timately contacting the petroleum and the diaromatic compounds in the 'irst zone oi extraction and selectively dissolving aromatics in said diacetin, maintaining the temperature, of said diacetin in a second extracting zone above the boiling point of the parailinic compounds and selectively dissolving cyclic non-benzenoid compounds in the diacetin, and removing parafhnic compounds in vapor phase from the last ofsaid extraction zones.

9. A process o! treating a petroleum fraction with a selective solvent which comprises passing a petroleum fraction containingarornatic, cyclic non-benzenoid, and paramnic compounds through a series of extraction zones. passing anisidine through each o1' said extraction zones at a temperature substantially below its boiling point, intimately contacting the petroleum and the anisidine in said zones, maintaining the anisidine -at a temperature no lower than the boiling point of the petroleum fraction under the conditions of extraction, maintaining the temperature of said anisidine above the boiling point of the non-aromatic compounds in the ilrst zone of extraction and selectively dissolving aromatics in said anisidine, maintaining the temperature of said anisidine in a second extracting zone above the boiling point of the paraflinic compounds and selectively dissolving cyclic non-benzenoid compounds in the anisidine, and removing paralnic compounds in vapor phase from the last of said extraction zones. Y

10. A process of separating aromatic components of a complex mixture containing aromatic and non-aromatic hydrocarbon compounds ncluding parafnic hydrocarbons having overlapping boiling ranges in which the least volatile paramnic hydrocarbon normally boils from approrimately 20 to 60 F. above the normal boil-' ing point of the most volatile aromatic hydrocarbon present in said mixture whereby an extract free from these higher boiling compounds can be 5 produced which comprises passing said mixture through an extraction zone, passing a liquid phase selectivev solvent through said extraction zone, intimately contacting said mixture with said liquid phase selective solvent, maintaining 10 said selective solvent in said zone at a temperature no lower than the boiling point of said mixture. separating a vapor phase non-aromatic rafflnate from said liquid phase solvent, removing the liquid phase solvent containing dissolved 15 aromatic hydrocarbons from said extraction t I6 zone, passing said solvent together with its dissolved compounds to a separate vaporizingzone. maintaining a seal between said solvent extraction and vaporizing zones to prevent undesired return of vaporized compounds, vaporizing only a portion of the hydrocarbons dissolved in said solvent in said vaporizing zone, and returning said vapor-ized hydrocarbons to said solvent extraction zone.

CALIFORNIA RESEARCH CORPORATION,

By L. P. ELLIOTT.

Vice-President.

No references cited.

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