US2120209A - Method for solvent extraction of oil - Google Patents

Description

June 7, 1938. u. B. BRAY METHOD FOR SOLVENT EXTRAQTION OF OIL Filed March 21, 1934 I INVENTOR. ZIZrzc5.Bray BY I Mr ATTORNEY.

Patented June 7, 1938 UNITED STATES METHOD FOR SOLVENT EXTRACTION OF OIL Ulric B. Bray, Palos Verdes Estates, Calif., as-

signor to Union Oil Company of California,

Los Angeles, Calif., a

Application March 21,

6 Claims.

This invention relates to a process for the treatment of petroleum with selective solvents. Although it may be employed for use with other petroleum fractions, it is especially applicable to the treatment of lubricating oil.

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

The aromatic and naphthenic hydrocarbons present in crude lubricating oil fractions are undesirable because these compounds exhibit too great a change in viscosity for a given change in temperature. The. paralfinic hydrocarbons present in crude lubricating oil fractions are the most desirable materials to be employed as lubricants. These compounds are highly saturated hence, from a chemical standpoint, they are rather inactive and do not exhibit a tendency towards the formation of undesirable resinous or sludge-forming constituents. Furthermore, these compounds exhibit a low temperature viscosity susceptibility. In other words, they exhibit a minimum change in viscosity for a given change in temperature. Furthermore, these highly saturated hydrocarbons are relatively stable to sunlight, exhibiting little tendency toward discoloration or sludge formation. When I use the term paraffinic hydrocarbons I mean those compounds which are present in petroleum having the aforementioned characteristics and which are liquid at ordinary temperatures. This group of hydrocarbons does not include those compounds present which are usually solid or semisolid at ordinary temperature and which are known as wax or petrolatum.

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 highvalue represents a Furthermore, they have a high corporation of California 1934, Serial No. 716,581

high degree of naphthenicity while low values indicate relatively greater paraflinicity. Lubricating oils 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 constant referred to in this application has been,

determined by the method employed by Hill and Coates as set forth in the Journal of Industrial and Engineering Chemistry, vol. 20, page 641 of 1928.

As a matter of convenience hereafter I will refer to those constituents of petroleum characterized by relatively low viscosity gravity constant as the parafiinic hydrocarbons, and to those constituents of petroleum characterized by relatively high viscosity gravity constant, as the non-paraffinic constituents of petroleum.

In the production of lubricating oil from crude petroleum residues or distillates, it is becoming conventional in the art to separate the desirable parafiinic hydrocarbons from the undesirable olefinic, naphthenic and/or aromatic compounds by the use of solvents which selectively dissolve the undesirable hydrocarbons present in the petroleum fraction but which exhibit only a very limited solvent power on the desirable paraflinic hydrocarbons.

A number of selective solvents have been found desirable to separate the paraflinic from the nonparafiinic hydrocarbons, for example, it has been shown that such materials as sulphur dioxide, beta beta dichlorethyl ether, chloraniline, nitrobenzene, aniline and furfural are highly selective as the solvents for the non-paraifinic hydrocarbons. The foregoing selective solvents are relatively heavy as compared to petroleum. When these relatively heavy solvents are commingled with petroleum or petroleum fractions under the proper conditions of temperature, the undesirable non-paraffinc hydrocarbons present pass into solution to a greater or less extent but the desirable paraifinic hydrocarbons remain largely undissolved. If the commingled mass is allowed to remain in a quiescent state the solution of undesirable hydrocarbons and solvent settles to the bottom of the container and forms what is known as an extract phase. The relatively light parafi'inic hydrocarbons rise to the top of the vessel and form a raflinate phase. These phases are then readily separable by ordinary decantation means. The rafiinate phase is usually found to contain a small quantity of the selective solvent and the extract phase ordinarily contains a relatively large quantity of the solvent. These fractions may be purified by subjecting them to distillation whereby the solvent is distilled away from the hydrocarbon oils.

Due to the general similarity of the various hydrocarbon components of mineral oil fractions such as lubricating oils, solubilities of the undesirable, non-parafllnic fractions and the desirable paraffinic fractions in a selective solvent usually differ only in degree, and there is, therefore, a tendency for desirable, high grade paraffinic oil 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 extract and rafrlnate fractions from mineral oil employing a selective solvent, an equilibrium of paraifinic components as well as non-paraflinic components is established between the phases. Consequently, some of the desirable paraiiinic fraction is found in the extract instead of in the rafi'inate.

While some loss may occur in a primary extraction of lubricating oil with a selective solvent for the production of a low grade primary extract and a primary rafiinate, the loss of desirable paraffinic fractions in the extract is especially severe when the raflinate produced by the primary extraction is further treated by a selective solvent to produce a high grade raffinate and an intermediate grade extract. In the production of a low grade primary extract and a primary rafiinate in the first extraction, the difference in solubility of the respective oils is usually so great that commercially satisfactory separation is obtainable. In some cases, however, such a process results in a substantial loss of parafiinic components in the low grade extract. The difference in solubility between the intermediate grade extracts and hi h grade railmate produced by a succession of extractions is usually not so great and there is, therefore, more tendency for paraffinic oil to be carried away with the intermediate grade extracts.

It has been proposed to regulate the solvent power of the extracting agent at any stage of the treatment in accordance with the solubility of the material to be extracted and as the refining of the stock by extraction progresses in a stepwise manner, the solvent power of the treating agent may be increased. 7

By substantially increasing the solvent power or ease of miscibility of the treating agent, it is possible to fractionate the raflinate obtained after extraction with the pure solvent into a further extract of lower solubility than the first extract obtained by the use of said pure solvent and a second raffinate of consequently lower solubility than the first raffinate. This may be accomplished by first extracting a hydrocarbon mixture with a pure selective solvent, for instance one of the solvents set forth above, and then to retreating the raffinate so produced with a modified solvent. As modifying agents such materils as carbon bisulphide, xylene, benzene, toluene, carbon tetrachloride, ethers or tetrachlorethane may be employed with the selective solvent.

By these processes the oil feed is divided in one general operation into three or more fractions of different viscosity gravity constants. As previously stated, the successive extractions produce a high grade raffinate and intermediate grade extracts characterized by solubilities which are not very different from each other. Consequently, in ordinary treatment of mineral oil by successive extractions, a substantial portion of the paraffinic fraction is soluble in the extract-solvent mixture rafiinate by rectifying the phases.

and is lost therein, resulting in a corresponding loss in yield of desirable high grade rafiinate.

It has also been proposed to regulate the solvent power of the extracting agent at any stage of the treatment by controlling the temperature at which the extraction takes place. For instance, the temperature at which the primary extraction takes place may be relatively low in order to reduce correspondingly the solvent power of the solvent. The low grade extract thus produced may then contain substantially only the highly aromatic and most soluble fractions of the mineral oil. Subsequent to recovery of the primary raffinate from the low grade extract, the former may again be solvent extracted at a higher temperature than that which prevailed in the primary extraction. The extraction at higher temperature may be accomplished by the same solvent as that used in the primary extraction or a solvent of greater or less solvent power than that employed for the first extraction may be used for the second extraction. These successive extractions likewise produce a high grade rafiinate and intermediate grade extracts having relatively similar solubilities and consequently substantial quantities of desirable paraffinic components are lost in the extract phases. Such loss also occurs when mineral oil is successively extracted with the same solvent at the same temperature.

It is an object of my invention to retain the desirable, high grade parafiinic fractions in the raffinate produced by solvent extraction of mineral oils.

The paraffinic fractions may be retained in the This may be accomplished in a series of successive extractions by interrningling the extract phases with raffinate phases of low content of paraffinic constituents. The equilibrium established in the phase separation of these mixtures is such that the parafiinic content of these extracts tends to be re-distributed into the raffinate phase. When an oil is recovered as a rejected raffinate from the extract phase by cooling, it may be re-introduced into the extraction system for rectification purposes.

I have found that when oil is countercurrently extracted with a selective solvent and the extract phase therefrom is cooled to reject an intermediate rafiinate, this intermediate raffinate is characterized by a viscosity gravity constant intermediate that of the raflinate' and extract respectively produced by the extraction. It is an object of my invention to aid the rectification of the oil dun'ng extraction, and to promote the recovery of paraffinic fractions in the raffinate by introducing this rejected raffinate of intermediate quality into the extraction system preferably into that zone which contains oil of substantially similar characteristics. The equilibrium in the various zones of the countercurrent extraction is thus maintained.

I have also found that when oil is first extracted in a primary extraction zone to produce an ex-' Therefore, it is a further object of my invention to extract an oil with a selective solvent, separate a raifinate insoluble in the solvent from the extract phase, extract the rafiinate with a selective solvent to produce a final raifinate and an intermediate extract phase, remove the selective solvent from the intermediate extract phase and introduce the intermediate extract into the first mentioned extraction.

Referring to the drawing, the figure is a diagrammatic view of one type of apparatus suitable for carrying out my invention.

In the apparatus shown in the figure, oil is introduced into primary extractor I i! by pump II in line I2 controlled by valve I3. Line I2 connects with orifice mixer I4 which in turn communicates with extractor I0 via line I5. Selective solvent is introduced into extractor I0 by pump IS in line H controlled by valve I 8. Extract phase is removed from extractor I0 via line I9 controlled by valve 20. Rafiinate phase from I0 passes by action of pump 2| through line 22 controlled by valve 23.

Extractor I0 is divided into a number of sections 26, 27, and 28 by imperforate plates 20. Each section in turn is divided into a mixing zone 30 and a settling zone 3| by plate 32 provided with port 33. Each mixing zone may be provided with an agitator if necessary, I prefer to introduce the selective solvent into the uppermost section 26. Rafiinate is removed from this section by line 22 as described. Extract phase from section 26 is removed therefrom by pump 35 through line 36 controlled by valve 37 and is intermixed with the raftinate produced in a lower section of the extractor. This mixture passes through line 38, orifice mixer 39 and line 25 into the mixing zone 30 of section 2?. From this mixing zone the mineral oil mixture and solvent passes through port 33 into settling zone 3|. The raffinate from the settling zone of section 2'! is removed therefrom by action of pump 45 and passes via line 46 controlled by valve 4'I into contact with the solvent entering extractor I0 via line II. This mixture passes through orifice mixer 48 and line 49 into section 25.

The extract phase produced in section 2'! is removed by pump 50 through line 5| controlled by valve 52. Line 5| connects with oil feed line I2, and the mixture of extract, solvent and feed passes through orifice mixer I4 and line I5 into section 28 in the manner previously described. The mixture passes through port 33 into settling chamber 3| of section 28 and the rafiinate separated therein is passed by pump 5-3 through line 54 controlled by valve 55. Line 54 joins with line 36 and the commingled material passes through line 38, orifice mixer 39 and line 40 into section 27 in the manner previously described.

Rafiinate from extractor I0 passes through line 22, orifice mixer 56 and line 51 into second extractor 60. Extractor 60 is also divided into a number of sections 6| to 65 by plates 29 and each section is divided into a mixing zone 30 and settling zone 3| by plate 32 provided with port 33. Selective solvent is introduced preferably into the upper section 6| of extractor 60 by action of pump I0 in line II controlled by valve I2. Line 'II connects with orifice mixer I3 which in turn communicates with extractor 60 via line I4. Extract phase from sections 6|, 62, and 63 are removed therefrom by action of pumps I5 through lines I5 controlled by valves TI and passed to the next lower sections respectively via lines I8, orifice mixers I9 and lines 80. Rafiinate phases from sections 63, 64, and 65 are passed by action of pumps 8| through lines 82 controlled by valves 83 into the next upper sections respectively by passage through lines I8, orifice mixers I9 and lines 80. Extract phase from section 64 is removed therefrom by pump 85 through 1ine86, controlled by valve 81. Line 86 connects with line 22 and the mixture is passed into section 65 of extractor 60. Rafiinate phase from section 62 is removed therefrom by action of pump 90 through line 9| controlled by valve 92. Line 9| connects with solvent admission pipe II and the mixture travels through orifice mixer I3 and line I4 into section 6| of extractor 60.

Final raffinate is removed from extractor 60 via line 94 controlled by valve 95. Intermediate extract phase from extractor 60 passes by action of pump I00 through line IIII controlled by valve I02. The intermediate extract phase may then pass through line I03 and valve I04 into cooler I05 and through line I06 into separator I0'I or this equipment may be by-passed by closing valve I04 and opening valve I08. If desired, part of the fiow may be through valve I04 and part through valve I08.

When intermediateextract phase passes through valve I04, its temperature is sufficiently reduced by cooler I05 to cause phase separation in separator I01 into an intermediate rejected raffinate and a further extract. When a liquid, normally gaseous solvent is employed, chilling may be accomplished in I 05 by vaporization of at least part of the solvent with consequent internal refrigeration. This intermediate rejected rafiinate is removed from I0! by pump III] in line III controlled by valve II2. I prefer to return the intermediate raffinate from separator Ill? into that zone of, extractor 60 wherein the oil being extracted has substantially the same viscosity gravity constant as the rejected raffinate being introduced. The viscosity gravity constant of the intermediate rafiinate is usually intermediate that of the final rafiinate issuing from extractor 60 via line 94 and that of the oil entering extractor 60 by line 51. Consequently, the intermediate raiiinate is preferably introduced into extractor 60 at a point intermediate the introduction of the incoming oil and the removal of the final raflinate. Forthis purpose line III is connected with lines H3, H4, and H5 which are respectively controlled by valves I I6, III, and H8 whereby the intermediate rafiinate can be introduced into sections 62, 63 and. 64 as desired. Extract phase passes from separator I0'I by action of pump I20 through line I2I controlled by valve I22. Line I2I connects with line IOI.

Extract phase from separator I01 if valve I04 is open, or extract phase direct from extractor 60 if valve I08 is open, or a mixture of these, passes through line IOI to heater I23 and thence through line I24 into separator I25. Sufilcient heat is provided in heater I23 to preferably cause substantially complete vaporization of the solvent from the extract phase. The solvent vapors exit via line I26 controlled by valve I2'I. Extract freed of solvent is removed by action of pump I30 through line I20 controlled by valve I29 and passes through cooler I3I before introduction into extractor I0 via lines I32 and 38, orifice mixer 39 and line 40. Because this extract phase comprises oil characterized by viscosity gravity constant intermediate that of the rafiinate issuing through line 22 and that of the oil entering through line I5, I prefer to introduce the same at an intermediate point in extractor I0, preferably into that zone wherein the oil being extracted has substantially the same viscosity gravity constant as the extract being introduced.

In the operation of this apparatus, it is desirable in certain instances to maintain sections 26 to 28 of primary extractor I0 at successively decreasing temperatures, but it is also within the purview of my invention to maintain these sections at the same temperature or even at successively increasing temperatures. Similarly, sections 6| to 05 of secondary extractor may also be at successively increasing or decreasing temperatures, or at the same temperature.

The solvent employed for the second extraction may be the same as that used in the primary extraction. In that case, I usually prefer to use higher temperatures in extractor 60 than in the primary extractor I0, although in some instances the same or a lower temperature than that prevailing in the primary extraction may be used in the second extraction.

In order to exemplify the application of my invention to a solvent extraction process involving a pure solvent for the first extraction, followed by a modified solvent for the second extraction, 300 volume percent. liquid sulphur dioxide, based upon the amount of oil entering via line I2, is introduced through line H, orifice mixer 48 and line 49. This selective solvent passes countercurrently in primary extractor I0 with the incoming oil introduced through line I2, orifice mixer I4 and line I5. This oil may be characterized by a viscosity gravity constant of 0.875. The low grade extract containing the major proportion of non-paraffinic fractions and the major proportion of liquid sulphur dioxide is removed from primary extractor I0 through line I9. This low grade extract may be characterized by a viscosity gravity constant of 0.955. The primary raffinate containing a small proportion of liquid sulphur dioxide constitutes the feed for the second extraction and is characterized by a viscosity gravity constant of 0.838. The solvent employed for the second extraction may be modified by one or more of the aforementioned modifying agents; for instance, this solvent may comprise liquid sulphur dioxide, and 30% benzene, and may be used in the proportion of 300 percent. of solvent based upon the oil introduced into the system through line I2. It is desirable that the high grade raffinate removed via line 94 will contain substantially all of the parafiinic fractions of low viscosity gravity constant, and it is also desirable that the fractions characterized by low viscosity gravity constant present in the intermediate extract removed from the second extraction via line IOI will be substantially recovered by separation from the extract phase. The final raffinate issuing through line 94 may have a viscosity gravity constant of 0.810 while that of the intermediate extract passing through valve I02 may be 0.860.

If desired, valve I04 may be entirely closed, in which event all of the intermediate extract phase passes through line IOI into heater I23 and separator I25, Where the solvent is removed. The extract is then cooled in I3I before introduction into primary extractor I0. This introduction is preferably into that zone of IO where oil of substantially the same viscosity gravity constant is contained. For instance, if the oil passing through line I32 has a viscosity gravity constant of 0.860, I prefer that it be introduced into that portion of extractor I0 wherein the oil being extracted has substantially similar viscosity gravity constant as the extract being introduced in order that the equilibrium of the system may be retained.

If the intermediate extract phase from 60 passes through coil I05 and separator I01, the rejected rafiinate passing through line III may have a Viscosity gravity constant of 0.828, for instance. I prefer that this rejected rafifinate be returned to that portion of the second extractor 60 wherein the oil being extracted has substantially the same viscosity gravity constant as the rejected rafiinate. The extract passing through line IOI, heater I23, line I24, separator I25, line I28, cooler I3! and line I32 to the extractor I0 then may have a viscosity gravity constant of 0.868. I prefer to return this extract to a corresponding portion of extractor I0 in the above described manner.

As an example of the temperature conditions which may exist in the above described process, the oil may be introduced into primary extractor I0 via line I2 at 95 F. for countercurrent extraction with liquid sulphur dioxide introduced at F. The primary rafiinate thus produced may enter section 65 of column 60 at 80 F. The temperature in '60 may be successively increased until the temperature in section 6I is F. In order to produce adequate phase separation of the intermediate extract phase in separator I01, this mixture may be lowered to 20 F. The intermediate extract phase may be heated to 300 F. in I23 to cause substantially complete removal of sulphur dioxide and benzol in separator I25.

My invention is capable of many modifications. For instance, extractors I0 and 60 may be divided into more or fewer sections. Or, in fact, they may be undivided into sections in which case the oil and solvent can freely flow up and down the columns. My invention may be additionally modified by cooling the extract phase passing through line I9 to reject an intermediate rafiinate and by returning this rejected raffinate to that zone in extractor I0 containing oil of substantially the same viscosity gravity constant undissolved in the solvent. Another modification may be to subject the oil flowing through line I32 to extraction with a solvent such as liquid sulphur dioxide in an extractor other than extractor I0.

It is to be understood that the foregoing is merely illustrative of the generic invention, and the examples are not to be taken as limitations thereof, as many modifications of my invention may be made Within the scope of the following claims.

I claim:

1. A process for the separation of parai'finic and non-paraffinic fractions from an oil containing the same which comprises countercurrently extracting said oil with a selective solvent, separating a rafiinate insoluble in said solvent from the extract phase, separating an intermediate raffinate from said extract phase and introducing said intermediate rafiinate into said extraction at that zone wherein oil being extracted has substantially the same viscosity gravity constant as the intermediate raffinate being introduced.

2. A process for the separation vof parafiinic and non-paraflinic fractions from an oil containing the same which comprises countercurrently extracting said oil with a selective solvent, separating a raflinate insoluble in said solvent from the extract phase, cooling said extract phase to separate an intermediate raffinate therefrom and introducing said intermediate rafiinate into said extraction at a point intermediate the points of introduction of selective solvent and oil enter-' ing the system.

3. A process for the separation of paraflinic and non-parafilnic fractions from an oil containing the same which comprises countercurrently extracting said oil with a selective solvent, separating a raifinate insoluble in said solvent from the extract phase, cooling said extract phase to separate an intermediate raflinate therefrom and introducing said intermediate raflinate into said extraction at that zone wherein oil being extracted has substantially the same viscosity gravity constant as said intermediate raflinate being introduced.

4. A process for the separation of paraflinic and non-parafllnic fractions from an oil containing the same which comprises extracting said oil with a selective solvent, separating a rafiinate insoluble in said solvent from the extract phase, extracting said ratfinate with a selective solvent to produce a final rafiinate and an intermediate extract phase, cooling said intermediate extract phase to separate an intermediate rafiinate therefrom, removing the intermediate raffinate from the cooled intermediate extract phase, then removing selective solvent from said intermediate extract phase by distillation, cooling the intermediate extract after said distillation and introducing said cooled intermediate extract into said first mentioned extraction at that zone wherein oil being extracted has substantially the same viscosity gravity constant as said intermediate extract being introduced.

5. A method of contact of oil containing paraffinic and non-parafiinic constituents with a selective solvent in which phase separation occurs to produce a raflinate relatively more paraflinic in character and an extract relatively less paraflinic in character than the original oil which method operates in a countercurrent system of contact between the oil and the selective solvent which comprises countercurrently contacting said oil with a selective solvent and thereby forming a rafiinate phase and an extract phase, separating said phases, cooling said extract phase and recovering an oil fraction therefrom, said oil fraction having a viscosity gravity constant which is higher than the viscosity gravity constant of oil fractions contained in said rafiinate phase and introducing said oil fraction recovered from said extract phase into the extraction system at a point intermediate between the points of introduction in said countercurrent extraction system of the selective solvent and the oil.

6. A method according to claim 5 in which the fraction recovered from the extract phase is introduced into the extraction system at a point in said extraction system wherein the viscosity gravity constant of the oil fractions present at said point issubstantially the same as the viscosity gravity constant of said oil fraction recovered from said extract phase.

ULRIC B. BRAY.

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