US2215915A - Selective solvent extraction of petroleum - Google Patents

Description

SOPL-24, 1940. 1 Q COPE ET AL 2,215,915

SELECTIVE SOLVENT EXVTRACTION OF PETROLEUM Filed Aug. 17, 1937 2 Sheets-Sheet l JOHN Q. COPE W/LL/AM H CLAUSSEN Sept. 24, 1940. J, Q COPE Er AL 2,215,915

SELECTIVE SOLVENT EXTRACTION OF PETROLEUM Filed Aug. 17, 193'? 2 Sheetsfsheet .2

Invenfors y JOHN Q. COPE W/L /AM H. CLAUSSEN y Allomey Patented Sept. 24,

I UNITED STATE-s fPilTN'ry f-joFFlcE- f SELECTIVEy SOLVENT EXTRACTION F PETROLEUM John Q. Cope and William H. Claussen, Berkeley, Calif., assignors to Standard Oil Company of California, San Francisca-Calif., a corporation of Delaware Application August 17, 1937, Serial N0. 159,522

Claims.A

This invention relates to a process of rening 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 enect a more efllcient 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 diierent 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 ve, six and seven carbon atoms in the naphthene ring. Because of close similarity in properties it has been very din'icult 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 rening 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 raffinate relatively more paraiflnic 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 oi selective solvent refining 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 aromatics and/or naphthenes on the one hand and parains 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 retainin the extract. t Accordingly, ithas heretofore been regarded as necessary to adopt a temperature intermediate the above mentioned high and low extremes such that a given solvent will ryield 'aj satisfactory quantity' of ranlnate and yet also give a reasonably efficient separation or refinement of the petroleumoils. .l y. 4Wefhave discovered that by increasing Ithe temperatureof extraction to the boiling point ofthe hydrocarbons beingv extracted, a remarkable and unpredictable reversal lin the effectiveness and se- 'process of reiining petroleum with a selective lectivity of the 4solvent extraction process is produced.

Accordingly, an object of the present invention is to provide a simple, effective and improved solvent.

Another object is to provide a process of reflning petroleum with a selective solvent by counter currently 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 boiling 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 paralnic compounds,

Another object is to provide a process of selective solvent extraction capable of effecting substantially quantitative separation of aromatic and/or naphthenic hydrocarbons from a normally liquid fraction of natural petroleum contain,- ing parafnic 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. 1 is a diagrammatic flow sheet illustrating a multi-stage vapor phase selective solvent extraction process embodying the principles of this invention.'

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

Briefly, the process of this inventioninvolves counter currently contacting normally liquid petroleum hydrocarbons with a higher boiling selective `solvent maintained in liquid phase and' at atemperature above the boiling point of the hydrocarbonsl ybeing treated. By "this vprocess, aromatic hydrocarbons, or' when desired naphthenichydrocarbons, or both, are' selectively extracted from the mixed vapor phase petroleum hydrocarbons-.- l Y j f v l In the process as illustrated by the ow sheet of Fig. 1, the petroleum stock to be treated is passed from storage through pipe I, heat exchangers 2 and 3, and conduit 4 to the vaporizer 5. The petroleum is converted from liquid to vapor phase in the vaporizer 5 and then passes through line 6 and valve I2 to extracting column 1.

To insure intimate contacting in the extraction column between the vapor phase petroleum and the liquid phase selective solvent, various means may be adopted. A tower` lled with suitable packing of refractory earthenware, glass, etc., comprises one eiective form of apparatus for this purpose. A tower constructed in the same manner as an ordinary fractionating column of a bubble capv type is also an eilcient means of insuring eiective contact between the vapor phase petroleum and the liquid phase extracting solvent. In Fig. l, three extraction co1- umns are shown but it is apparent that the number may be increased or decreased as conditions such as efliciency of the extraction, the Volume of materials to be treated, etc., require.

After extraction in tower 1 the raflinate vapors pass from the top of the tower through line 8 to the bottom of extraction tower 9. The rainate` from extraction tower 9 likewise passes through line I0 to tower II where the raffinate hydrocarbons, still is vapor phase, are again extracted by the selective solvent. The nal vapor phase railinate flows from the top of extraction tower II through conduit I4 and control valve I5 to heat exchanger 2 where partial condensation occurs. Provision is made for returning a portion or all of the partial condensate from heat exchanger 2 through valve controlled line I6 to either extraction tower 9 or II or both by means of independent return pipes controlled by valves I1 and I8 therein. The remaining raffinate is cooled in condenser I9, condensed to liquid phase and passed to storage. Valve controlled conduit I 6A provides means for supplying additional condensate for reflux when the desired reflux ratio is higher than that obtainable by using the partial condensate alone.

The selective solvent which has been referred to in the previous paragraphs, ows through extraction columns 1, 9 and II counter currently to the vapor phase petroleum being extracted. Fresh solvent is admitted to the top of tower II through inlet line 20 controlled by valve 20A. The solvent ows down through the column and extracts those hydrocarbons for which it has a selective action from the upwardly owing vapor phase petroleum. The solvent with the selectively dissolved petroleum vapors is continuously removed from the bottom of the column through line 2I to vaporizer 22. To obtain more efcient extraction it is desirable to heat the solvent in a vaporizer such as 22 in order to vaporize a substantial proportion of the dissolved hydrocarbons and re-circulate these vapors to the extraction column. This procedure tends to eliminate hydrocarbons of the rainate type which have condensed or which have been dissolved in the solvent. Also, the re-circulation f these vapors provides a method of adding heat to tower II.

The solvent, after being heated in vaporizer 22, flows through line 23 into the top of extraction tower 9. The solvent then counter current- 1y extracts petroleum vapors in tower 9 and ows through line 25, heater -26 and line 21 to the top of tower 1 in the same manner as in the previously described extraction step. AFrom the bot- )4. toni of extraction tower 1 the solvent together with the dissolved -hydrocarbons is removed through line 3l to vaporlzer 32 where a small portion of. the dissolved hydrocarbons is vaporized and returned to the extraction tower 1 through line 33. The selective solvent and extract then flow from the vaporizer 32 through valve 34 and line 35 to fractionating still 36. The extracted hydrocarbons are 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 38 to storage.

The solvent is continuously re-circulated from still 36 through line 20 to-thc extracting system 'as previouslyl described. New or additional solvent can be supplied to the system as needed through valve controlled line 39 from the solvent storage tanks. It is to be noted at this point that the solvent entering the extraction system from the still 36 is heated to a temperature above the boiling point of both the extract and rainate. The temperature of the solvent in the extraction towers must of course be maintained below that at which a major proportion of the extract would be vaporized from or remain undissolved in the solvent while being extracted. This teml perature is, however, above the normal dew point of the extract as well as of the rainate hydrocarbons at the pressures existing in the system.

An auxiliary line 28 leading from vaporizer 5 and a control valve 40 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 40 will be open and valve I2 in vapor line 6 Will be closed. It is also apparent that the incoming hydrocarbon vapors may be introduced in both towers 1 and 9 by opening, both valves 40 and I2.

Under various conditions it is desirable to remove side streams or cuts from the extracts of the diierent stages of extraction. Accordingly, valve controlled conduits 4I and 42 have been provided for this purpose and permit the removal of extract cuts from extractors 9 and II respectively. 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 ow sheet tor the sake of simplicity.

By controlling the conditions of extraction in the various stages it is possible to obtain an extract from treater 1 which is substantially free from sulfur compounds and which is predominantly or entirely aromatic in chemical constitution. Likewise, by proper control an extract cut from treater 9 which contains a high proportion of sulfur bodies present in the petroleum and an extract cut from treater II which is predominantly naphthenic in character may be obtained. In order to obtain these results it is of course necessary to maintain the temperature in treater 1 above the boiling point of the sulfur bodies, naphthenic compounds and paramnic 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 paraillns, but within the range at which sulfur compounds are preferentially dissolved by the selective solvent. In treater Il the temperature will be suiliciently Vses lline 54, vaporizer 55, and line 56 to a single exhigh to cause vaporization of the lparafilnic com;v pounds 'andyet within" the ran'geatfwhich naph- 4thenespwll be extracted 'by the vselective solvent.'

Obviously, the speciflcftemperatures, pressures and solvent-to-oilratio y necessary'` to produce these Vresults will vary with' the selectivesolvent being used and withv the petroleum stool: being treated; With avv given solvent and a-given stock thev proper conditions can be-readily determined lYe'xperiment. f I

In view of the abovediscussion it is apparent thatv by the process represented inthe iow sheet of Fig. 1 a petroleum fraction can be continuously separated into .four separate fractions of distinctly diierent chemical constitution vby 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 of ther paraflinic and naphthenic compounds but below the point at which all sulfur bodies would be vaporized from the selective l 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-benzenoid compounds are selectively dissolved. The parafnic 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 I, 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 decreased temperatures and pressures. In this species of operation extractor 1 will be maintained at substantially atmospheric pressures, for example, extractor 9 at an intermediate reduced pressure and extractor Il at thev 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 43 and 44 in vapor lines 8 and I0 respectively are utilized to effect a pressure differential between extractors 9 and Il. Pumps 46 and 41 in lines 21 and 23 serve to feed the solvent from the zones of lower pressure to the zones of successively higher pressures. Pump 48 is provided in the reux line to extractor 9 to feed the reflux fromline I6 to extractor 9. This pump is necessary when as in the case of the present species of operation extractor 9 is operated atv higher pressures than extractor Il.

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

Theilow sheet of Fig. 2 illustrates an alternative simple but very effective method for operating the process of this invention. In thisv arrangement petroleum stock to be treated passes from storage through valve controlled line 50, heat exchanger 5l, line 52, heat exchanger 53,

traction tower 51. vThe 'liquid phase: Aselective solvent together with its dissolved extractL flows from'the bottom of t0'wer,;51' through. line 58y to vaporizer 59; Arportionruonly.A ofthe extract `is flashed through 1ineI60 to I tower.- 51;' '1. Solventv isy continuously removedvfrom vaporizer59 through liney 6I and passed to still62 for removal ofthe .extracted hydrocarbons.v V4The 'extract is'separated from the solvent -in .fractionatingl column 63 land iiows= throughxline 64,-heat exchanger:y 53, line 6v5land condenser 66 tostorage. The selective solvent is continuously `removedirom thev stilland recirculated 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 54, 58, 6I and 61 to produce a liquid seal and prevent the flow of vapors through these conduits.

Rafnate vapors ilow from the top of extraction tower 51 through line 68 to heat exchanger 5| where partial condensation occurs. As much of this partial condensate as is desired may be returned to the extraction tower through vline 10 controlled by valve 1|. The remainder of the raiiinate passes through condenser 69 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 partialcondensate alone.

In a single stage extraction process it is essential that the vapor phase hydrocarbons and liquid phase solvent be intimately contacted. One eilicient means for eiecting this result comprises the' conventional bubblecap fractionating column in which the vapors to be extracted rise upwardly through a series of bubble caps and are ktherebv intimately mixed with the downflowing extracting solvent. Such an extraction tower is the preferred form utilized in the process of both Fiss. 1 and 2. Y

To illustrate the characteristics of the process the following data are given:

A` natural petroleum cut having a boiling range 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 xylenols which had been topped at 450 F., as the selective solvent are given below:

Anline point of stock -feds 44.4 F. Anline point of rafnate-; F. Aniline point of extract 15 F.

In this run 'theA temperatures of feed and selective solvent were 5 to10, and 10 to 20, respectively, above the dew .point ofthe stock. l

A series of tests was run to determine the effect of reux of the raflnateon the aniline point spread and yield of extract. Two series o f data into' vapor.. formlf-vand re-circulated were obtained. one for a solvent thinner ratio of ilve to one, and one for a ratio of oneV to one. The extract yield was held constant to 40% and the other variables, such as temperature, as close to those values given above as possible. The reflux ratio was varied during these tests to determine the effects on the aniline points of the rafnate and extract. It was found that the optimum reux ratio is zero. At that ratio the aniline point .of 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 of the extract.

When the optimum reflux ratio of zero is used, it was found that the optimum ratio of solvent to petroleum was approximately three to one. Increased ratios up to as hig'h as five to one give appreciable benefits in the extraction process. I'he increased efciency of extraction which results from solvent ratios above ilve to one are relatively small.

In an arrangement of apparatus such as shown in Fig. 2 where the still 62 is separated from the extraction column by liquid seals so that extract solvent extraction in the vapor phase.

and railinate hydrocarbons which is permissible if pure aromatics are to be obtained by selective When paramnic and aromatic hydrocarbons are being separated,v those parainic 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. Parafiine hydrocarbons having boiling points 20 to 60 F. above the boiling point of the aromatics being extracted can, on the other hand, be eiectively separated as railinate vapors. Paralne hydrocarbons having boiling points equal to or lower than the aromatics being extracted present no diillculty whatever since they are readilyvseparated in the vapor phase. In other words, when the parainic and naphthenlc 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. 1 illustrates results obtained with diierent solvents in treatments on different types vapors cannot return to the extraction column, of petroleum oils.

Table 1 Stock Extract Raiii- Extract Raflinate Solvent solvent Natural petroleum stock treated ggf yield, ang?? aniline to srck rgffx o F percent pas F' point, F. ratio ratio 20o-300 F. cut Calif. crude 44. a 4o 44. 4 115. 2 5. e 1 do 44.3 is 75.4 81.8 5.5 1 o 44.3 o 20.4 114.4 5.6 1 30D-400 F. cut Calif. crude. 42. 6 19 '11.6 44 5 l soo-350 F. nut Calif. crude so. 4 2c 15. 2 47. s 5 1 20D-300 F. cut Calif. crude--.. 44. 4 40 -27 76 5 0 20o-300 F. cut Calif. crude 44. 4 39 4o. 4 102. s 5 o. o 20D-300 F. cut Calif. crude 44. 4 89 -30.8 95. 4 5.0 "1.9

'All aniline points were determined by the equal volume method or by refractive index. "Apparatus provided with liquid seal between extraction and extract stripper columns.

it was found that the optimum rafiinate to reflux ratio was approximately 2:1.

It has alsobeen found that with various selective solvents, such as Xylenol, the extraction process is selective with respect to raffinate hydrocarbons having a boiling point as much as 60 F. above the boiling point of the aromatic hydrocarbons being extracted. In ordinary selective solvent liquid phase extraction processes, selectivity decreases with increase in temperature. 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 ralnate lhydrocarbons practically as readily as the extract hydrocarbons obtained at lower temperatures. Also, it is a generally accepted principle that as between two solutes dissolved in a given solvent, the higher the boiling point of a given solute the less is its tendency to vaporize from the solution. That is, the lowest boiling dissolved hydrocarbon components should most readily vaporize from the solvent and the higher boiling hydrocarbons (such as the rainate hydrocarbons boiling 60 above the extract hydrocarbons in the present process) should tend to dissolve and remain in solution. Certainly it is not obvious that the much more volatile constituents would be selectively dissolved at the high temperatures involved and that the less volatile railinate hydrocarbons having a boiling point 20 to 60 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 150 cc. of the solvent.

A selective solvent useful for the present process should be highly selective and should have a boiling point well above the end point oi 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 not form constant boiling mixtures with hydrocarbons, but if such constant boiling point mixtures are formed, the solubility characteristics of the solvent should be such that complete recovery by water extraction is possible. Constant boiling mixtures of 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. This test consisted of adding a petroleum cut having a boiling point of from 215 to 240 F. to 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 rst 3 cc. of overhead were taken for an aniline point test. The elevation of this aniline point over that of the original stock is designated 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 n Table 2 Solvent Scltilzll- Diethanolamine. Nitrobenzene Aniline "Chlorex 410 atmm Dibutyl phthalate Number oi cc. oi' 2l5-240 F. straight run petroleum cut dissolved by 150 cc. oi 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.1was treated and an extract produced having an aniline point of- F. The spread of aniline point between the raffinate and the extract was 143.2 as compared with 103 with Xylenol under the same conditions. Even with a 300 to 400 boiling range petroleum cut, which necessitated vextraction at much higher temperatures than with the 200 to 300 cut, a 24 F. aniline extract was produced and a total spread of aniline point be tween raiinate 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. 'I'he 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 smallamount of triethylene glycol distilled over with the extract and raffinate fractions. The amount of triethylene glycol dissolved in the extract portion of the hydrocarbons was of the order o! 0.15%

by volume. This small, amount of triethylene glycol*-'is easily "and completely' removed j by water washingand the' solvent can then 4be recovered by the evaporation yof `rthe water therefrom.' i

-`A more2 advantageous vmethod for recovering the solvent-'fromf'the wash water is to feed the f water containing th'ef solvent into fhestm Iand Iractionatingjcolumn along with the extractlayer.

This method has the advantage that it breaks upthe constant i' boiling mixtures of solventsV and high `boilingextracts which may tend to form. Thewater and hydrocarbon lextract come over as overhead' and are readily separated. vIn those cases where there has been 'incomplete removal of water from the selective solvent, the eiect is merely to render the solvent more' selective 1n the extractionstep of the process. That is,the ani# lin'e 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 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 coemcient between petroleum and water so that this solvent readily diffuses almost quantitatively from oil to water.

Tetramine constitutes an additional example of a selective solvent which is very efllcient in the process of this invention. .This compound is one of a generic group which may be represented by the general formula The iirstfbrmula is an open chain compound ex'-V empliiled by i lExamples of thesecond generic formulafwhich y .are ring compounds, are

Diethylene diamine and Triethylene triamine It will be noted that these compounds are characterized in that theycontain more carbon than although triethylene glycol is at present the preferred solvent for the process of this invention,

it should be apparent to those skilled in the art that the broader aspects of the invention include aro the use Vof a multitude oi' other selective solvents. High boiling hydroxy ethers, illustrated by diethylene glycol, triethylene glycol and 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,yand phosphoric acid esters of hydroxy benzenes are in general operative in the process of this invention. As previously pointed out the solvent selected from this group should have a boiling point sufiiciently 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.

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 'limi'- tation should be imposed upon the invention thereby. It will be apparent to those skilled in the art that numerous modifications and variations may be effected in the practice of our invention which is of the scope of the claims appended hereto.

We claim:

1. A process of treating a petroleum fraction with a selective solvent which comprises passing a petroleum fraction containing aromatic, cyclic non-benzenoid and parafiinic` compounds through a series of extraction zones, passing a high boiling liquid phase selective solvent through ea." of said extraction zones at a temperature substantially below its boiling point, intimately contacting the petroleum and the selective solvent in said zones, maintaining the selective solvent at a temperature no lower than the boiling point of the petroleum fraction under the conditions of extraction, maintaining the temperature of said solvent above the boiling point of the non-aromatic compounds in the first zone of extraction and selectively dissolving aromatios in said solvent, maintaining the temperature of said solvent in a second extracting zone above the boiling point of the paranic compounds and selectively dissolving cyclic non-benzenoid compounds in the solvent, and removing paranic compounds in vapor phase from the last of said extraction zones.

2. A process of treating a petroleum to selectively extract carbocyclic non-paranic hydrocarbons therefrom which comprises passing said petroleum through successive extraction zones, passing a liquid phase selective solvent countercurrently to said petroleum through each of said extraction zones, maintaining the selective solvent in liquid phase and at a temperature above the initial boiling point of the petroleum traction under the conditions of extraction, intimately contacting the petroleum and selective solvent in said zones and maintaining the vapor pressure in at least one of said extraction zones below that of the extraction zone in which the petroleum is rst contacted with the selective solvent.

3. A process of treating petroleum to selectively extract non-paramnic hydrocarbons` therefrom which comprises passing said petroleum through .a series of extraction zones, passing a liquid phase selective solvent *countercurrently through said zone, intimately contacting the petroleum and selective solvent in each oi.' said extraction zones, successively decreasing the vapor pressure in said series of zones from a region of highest pressure at the petroleum inlet zone to a region of lowest pressure at the petroleum outlet zone, and maintaining the temperature of said liquid phase selective solvent in each of said zones above the boiling point of the petroleum at the pressure of extraction in,that zone but substantially below the boiling point of the selective solvent.

4. A process which comprises extracting a petroleum fraction with triethylene glycol, separating an extract phase and a rainate phase, vaporizing dissolved hydrocarbons from said extract phase, and adding water to said extract vaporizer to inhibit formation of constant boiling mixtures of said triethylene glycol and dissolved hydrocarbons in said extract.

5., In a process of treating a. hydrocarbon mixture with a selective solvent to selectively extract carbocyclic non-parafiiuic hydrocarbons therefrom, the steps which comprise passing into an extraction zone a normallyy liquid hydrocarbon fraction containing a mixture of carbocyclic andparalnic hydrocarbons in which the least volatile parainic hydrocarbon normally boils from approximately 20 to 60 F. above the normal boiling point of the most volatile carbocyclic nonparaillnic hydrocarbon in said mixture, passing a liquid phase selective solvent through said extraction zone, intimately contacting said hydrocarbon fraction in vapor phase with said liquid phase selective solvent, separating a vapor phase hydrocarbon raiinate from said liquid phase selective solvent, maintaining said selective solvent at said point of separation above the initial boiling point but no more than approximately 20 F. above the dew point of said hydrocarbon fraction under the conditions of extraction, passing the liquid phase selective solvent containing carbocyclic non-paraftlnic hydrocarbons from sai'd extraction zone to an independent distillation zone, condensing said vapor phase hydrocarbon railinate, and returning to said extraction zone approximately two-thirds oi' said condensed raffinate.

JOHN Q. COPE. WILLIAM H. CLAUSSEN.

Certificate. of Correction Patent No. 2,215,915. September 24, 1940.

' JOHN Q. COPE ET AL. c

It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows: Page 2, first column, line 29, for the word is read in; page 3, second column, line 69, for 15 F. read 15 F. gage 4, line 34, Table 1, fifth column thereof, for *11.6 read |11.6; and that t e said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Oice.

- Signed and sealed this 3rd day of December, A. D. 1940.

[smL] HENRY VAN A RSD'ALE,

Acting Commissioner of Patents.

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