US2031205A - Process for solvent extraction of oils - Google Patents

Description

l Patented Feb. 18, 1936 .UNITED 'STATES-f' PATENT oFFi-CE 2,031,205 raocsss ron soLX-sligr Ex'rnAcrroN or Ulric B. Bray, Palos Verdes Estates, Calif., as-

signor to Union Oil Company of California, Los Angeles, Calif., a corporation of California Application April 3, 1934, Serial No. 718,815 l Y 8 Claims. (Cl. 196-13) This invention relates to the extraction of oils by employing a selective solvent. Although applicable to the treatment of other oils, it refers the desirable paraflnic hydrocarbons.

the Sel When I use the term paraiiinic hydrocarbons I mean those highly saturated compounds which are present in petroleum and which are characterized by a low temperature viscosity susceptibility, i. e. theyA exhibit a minimum change of viscosity for a given change in temperature. They also are characterized by relative 'stability to air and sunlight, exhibiting little tendency -toward discoloration or sludge formation. This definition is not meant to include those compounds' which are usually solid or semi-solid at ordinary temperatures and which are known as wax or petrolatum'k but, of course,*it is obvious t my invention is meant to also include tive extraction of waxy oils. As a matter of convenience hereafter, I will refer to the undesirable, components, such as olefnic, naphthenic and/or aromatic hydrocarbons, as the- "non-paramnic" components of petroleum.

These fractions are characterized by a relatively high temperature viscosity susceptibility and are relatively unstable to air and sunlight,v exl hibiting discoloration and sludge formation.

A further indication of the purity of a lubricating oil is its viscosity gravity constant. This constant represents the parailinicity or naphthenicity of an oil. A high value represents a high degree of naphtheniclty while low values inl dicate relatively greater paraillnicityl 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. 'I'he viscosity gravity con-- stants referred to in this application have been determined bythe method employed by Hill and Coates as set forth in the Journal of AIndrustrial and Engineering Chemistry, vol. 20, page 641 of 1928. The. parainic hydrocarbons to which I refer hereinafter are characterized by relatively low viscosity gravity constant, while the nonparailinic" constituents of petroleum are char-` acterized by relatively high viscosity gravity conbenzene, and furfural are highly selective as solvents for the non-parafnie hydrocarbons. When these solvents are commingled with petroleum m or petroleum fractions under the proper conditions of temperature, the undesirable non-l-paranic 'hydrocarbons pass into solution to a greater or less extent but a substantial proportion of the desirable paraiiinic hydrocarbons remains ly,

undissolved. The solution of undesirable hydrocarbons and solvent settles to the bottom of the container'and forms an extract phase when relatively heavy solvents are employed. The relatively light paraiilnlc hydrocarbons rise to the 20 top of the vessel and form a raiiinate phase. These'phases are then readily separable by ordinary decantation means. 'I'he rafnate phase is usually found'to contain a small quantity of the selective solvent and the extract phase ordinarily 25 contains a relatively large quantityof the solvent. 'I'hese fractions may be puriiied by distillation whereby the solvent is distilled away from the hydrocarbon oils.

Inthe usual solvent extraction of mineral oil' 30 with selective solvents, such as those above mentioned, the separation is not complete. Particularly,` all of the paraiiinie hydrocarbons, i. e. the more valuable lubricants, arenot obtained in the raiilnate phase but instead some of the high grade 35 parainic oil fractions are found in the extract phase. Due to the similarity of the various hydrocarbon components of mineral oil fractions,

such as lubricating oils, the solubility of the un- In other words, in a phase separation of extract and ramnate fractions from mineral oil by employing a selective solvent, an equilibrium of parailinic components and nonparaiiinic coniponents is established between the phases. -Consequently, some of the desirable paraiiinic fractions are found in the extract instead ln the raiiinate. f

The solubility of oils of relatively high paraillnicity in the extract phase can be reduced by the addition of an anti-solvent thereto. n antisolvent may be deiined as a material which tends to prevent the solution of those hydrocarbon fractions which, except for the presence of the anti-solvent. would be dissolved in the extract phase upon extraction of the oil with a selective solvent. The addition of an anti-solvent to the extract phase causes a phase separation between an intermediate'rafilnate and the remaining extract phase. This intermediate ramnate comprises oil of -quality superior to the oil remaining dissolved in the extract phase and it is an object' of this invention to return the intermediate rathnate thus rejected to the selective solvent extraction in order that the high quality parafiinic fractions normally lost in the extract phase will be recovered in the final rafhnate.

I have found that when oil is countercurrently extracted with a selective solvent and the extract phe therefrom is commingled with an antisolv ent toreject an intermediate rainate, this intermediate ralnate is characterized by a viscosity gravity constant intermediate that of the raffinate and extract respectively produced by the extraction. It is an object of my invention to aid the rectication of the oil during extraction and to promote the recovery of paraiilnic fractions in the raffinate by introducing this rejected raffinate of intermediate quality into the extraction system, preferably into that zone wherein the oil being extracted has substantially similar viscosity gravity constant. The equilibrium of phase distribution in the various zones of the countercurrent extraction is thus undisturbed by the introduction of the intermediate rejected raiiinate.l

The anti-solvent which I may employ to reject the intermediate ramnate from the extractphase is preferably one which is only partially soluble in the rejected ramnate and is adapted to form a two-phase system with the rejected raflinate and is soluble in the remaining extract phase. Therefore, it is a further object of my invention to extract an oil with a selective solvent to produce ramnate and extract phases and to reject an intermediate raffinate from said extract phase by commingling the latter with an anti-solvent only partially soluble in the rejected raiilnate and soluble in the remaining `extract phase. The rejected intermediate raflinate is -thus relatively free from selective solvent and from anti-solvent and may be directly introduced into that zone of the extraction wherein the oil being extracted has substantially the same viscosity gravity constant as the rejected raffinate being introduced ithout upsetting the equilibrium of the extrac- As an anti-solvent having these characteristics, I may employ liquid ammonia, or even water maybe used as an anti-solvent when the water forms a solution with the selective solvent with whichit is employed. Under certain con ditions, the anti-solvent may be a substance which is a selective solvent when employed alone.

For instance, there may be miied with the extract phase to fimction as an anti-solvent a selective solvent having less solvent power for the 'higher grade material present therein than'the solvent power of the selective solvent originally used to produce the extract. As an example, oil

may be treated with chloraniline or a mixture of liquid sulphur dioxide and benzene to obtain an extract phase. These solvents are characterized by high solvent power for higher grade material. To the extract phase thus produced there may be added liquid sulphur dioxide or other solvent having relatively 'less solvent power for the higher grade material. For this reason and under these conditions, certain selective solvents may be employed as anti-solvents and by their presence in the extract phase the higher grade fractions therein are rejected to form an intermediate raffinate.

Insome cases, the addition of an anti-solvent to the extract phase renders temperature reduction unnecessary to separate relatively lhigh quality oil fractions therefrom. In other cases, refrigeration of the extract phase will be necessary but will be less than when no anti-solvent is present. In a solvent extraction process of this character, the expense of refrigeration is a substantial item in the cost of operation. My process lowers this cost.

I have found that when temperature reduction is necessary for rejection and when the anti-solvent employed is a liquid, normally gaseous susbtance such as sulphur dioxide or the like, the rejection of desirable oils from the ex' tract phase by the presence of said anti-solvent is aided when the pressure is suillciently reduced ln the rejection stage to cause evaporation of a portion of the anti-solvent, thereby reducing the temperature of the mixture f the extract phase and anti-solvent remaining liquid. In this case the liquid, normally gaseous anti-solvent also operates as an internal refrigerant. After evaporation for internal refrigeration, sufficient amounts of the liquid normally gaseous antisolvent should remain in the liquid phase with the 4extract phase to function as an anti-solvent.

After separation of final raflinateA and nal extract according to my invention, it is, of course, obviousv that these phases may be separated from any solvent and/or anti-solvent associated -therewith by distillation or other appropriate means.

'I'he figure is a schematic arrangement of one form o f apparatus which may be employed to carry out my process.

Referring to the figure, oilenters the system via line Il controlled by valve Ii by action of pump l2 and passes into extractor i5 through line I4. It is countercurrently extracted with selective solvent introduced through line I6 controlled by valve I1 by action of pump Il. Rafnate phase from extractorv i5 is removed via line I8 controlled by valve 2li. Extract is removed from extractor I5 by action of pump 2l in line 22 controlled by valve 23.

Extractor I5 is divided into a number of sections 24 to 23 by imperforate plates 29. Each section in turn .is divided into a mixing zone 3l and a settling zone 3l by plate 32 provided with port 33. Each mixing zone may be provided with an agitator, if necessary. Phase separation takes place in each settling zone. I prefer to introduce the selective solvent into the uppermost section 24. Rafnate is removed from this section by line is, while extract phase is removed from Y lthe lowest section 2l as described. Extractphase from section 24 is removed therefrom by pump 3i 'through line 33 controlled by valve 31 and is intermixed with the .rattlnate phase produced in a` lower section of the extractor. 'I'hls mixture passes through line 38 into the mixing zone 3l oi' section 25. From this mixing zone the mineral oil mixture and solvent passes through port 33 into settling zone 3i. The raffinate froln the settling zone of section 23 is removed therefrom byactionofpump 4 0 andpassesvialine" con ,vil

trolled by valve 42'into contact with the solvent entering extractor I5 via line I6.

The extract phases from sections and 28, respectively, are removed by pumps 43 through lines 44 controlled Aby valves 45 for passage through lines 45 and 41, respectively, into sections 26 and21, respectively. Ramnate phases from sections 26, 21 and 28, respectively, are removed therefrom by action of pumps 50 in lines 'of pump 58 through line 54 controlled by valve 55 into section 25^via line I4 in intermixture with oil freshly introducedintoextractor I5.

An anti-solvent passing through line 50 controlled by valve 6I by action of pump 82 is commingled with the extract phase exiting from extractor I5. As previously stated, this extract phase comprises relatively paraillnic hydrocarbons which are desirable in the final ramnate issuing 'via line I9. This mixture of extract phase and antisolvent passes. through line 55 into cooler 54 for the rejection of the intermediatel grade raiiinate from the extract phase. In some cases, cooler 64 may be omitted in which event the intermediate raiilnate will be rejected from the extract phase without temperature reduction. Cooling in 64 may be accomplished by external means, or if the selective solvent and/or the anti-'solvent is 'normally gaseous, cooling may be by the internal refrigeration above described.

The extract phase and anti-solvent then passes through line into separator 86 wherein rejected intermediate railinate is removed. Extract phase passes from separator 55 via line`51 controlled by valve 58.

As previously stated, the rejected intermediate rafnate separated from the extract phase in 55 is characterized by a viscosity gravtiy constant y 'intermediate that oi the final ramnate issuing from extractor I5 via line I5 and that of the extract phase passing from extractor I5 via line 22 and some of the fractions contained therewith are desired in the ilnal ramnate. I prefer toihtroduce the rejected intermediate raffinate into the extraction at apoint'intermediate the points of introduction of selective solvent and l of 011 entering the system. otherwise stated, the

i substantiallythe same viscosity gravity constantrejected intermediate raii'inate may be introduced into the extraction at a` point intermediate the point of introductionof oil entering the system and the point ofremoval of railinate from Vsaid extraction. Preferably, I return thel rejected intermediate raihnate into that portion -of extractor' I5 wherein the oil being extracted has as the rejected ralnate being introduced. In 'order to accomplish-this, the rejected interi mediate railnate passes by action of Vpump 1l through line1l controlled by valve 12. In order f or the rejected intermediate ramnate to enter section 25, it is passed via line 13 and .valve 14 into line 38. In order. to -introduce rejected intermediate ramnate into section 25, it passes via line 'I5 and. valve l5 into line 45. Therejected intermediate ramnate can be .passed into section 211m une 13 and valve 'rrinto une a1.` 'ro pass reiectedinteimediate mmm into aectravel through line 15 andvvalve tion 25 it may 1l into une l.V

In order to exemplify the application of mv invention in the above described apparatus, oil characterized lby viscosity gravity constant of 0.875 may be introduced into extractor I5 via lines I0 and I4. This oil may be selectively extracted with 300 volume percent. phenol introduced via line I5. Final raflinate issuing via line I9 may have a viscosity gravity constant of 0.810. The

extract passing from extractor I5 through line 22 4may be characterized by a viscosity gravity constant of 0.890. To this extract may be added an anti-'solvent such as water to the amount of 20 volume percent. based upon the quantity of oil entering the extractor via line I0. Low grade extract with a viscosity gravity constant of 0.940

issues from separator 56 via line 81. Rejected,

intermediate ralnate with a viscosity gravity constant oi 0.835 is returned to the extractor, in the manner above described, into that zone wherein oil of substantially \the same viscosity 'gravity constant is being for instance, section 26.

As' another example of the operation of my invention, oil characterized by a viscosity gravity constant of 0.840 may-be introduced into extractor I5 for selective extraction with 200 volume percent. of a mixture comprising volume percent. liquid sulphur dioxide and 60 volume percent. benzene. The railinate passing through linel I9 is characterized by a viscosity gravity constant of 0.806 and the extract phase with a viscosity gravity 4constant of 0.860 passing through line 22 is intermingled with 300 volume percent. liquid sulphur dioxide to reject 'an intermediate raillnate characterized by a viscosity gravity constant ofv grade extract phase passing through line 51 may be vemployed as a selective solvent in another solventextraction and the raillnate produced therein may be used as the incoming oil passing to extractor I5 via lines I5 and I4. As a further modification, the cil introduced into my extraetion system may be primarily deasphaltized by commingling with an asphalt precipitant such as liquid .,ethane, propane, butane or the like, and afterV removal of the asphalt, the oil and asphalt precipitant may-pass into extractor I5 via lines n and u for the above describes ointment therein. i

As another modiilcation, if the rejected intermediate raillnate is associated in solutionV with anti-solvent and/or above described asphalt precipitant, this mixture may be heated to vaporize the anti-solvent and/or asphalt precipitant before the rejected lintermediate ralnate, is returned to the extraction into that -zone wherein oil of substantially the'same viscosity gravity constant is being extracted. In this case after removal of these materials, it is preferred to cool the heated rejected intermediate ramnate to the temperature prevailing in the extractor before its introduction therein. 'I'he equilibrium of phase distribution In the extraction isthen maintained. If desired, orifice mixers may be placedin lines I5, 85, 45, 41 and I4 in-order to secure thorough inter-mixture of the various materials passing into therespective sections of the extractor. Also,

sections in which case the oil and solvent can freely flow up and down the column.

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

1. A process for the separation of oil into paraiilnic and non-parai'iinic fractions which comprises, commingling said oil with a selective solvent and thereby forming a raffinate phasev containing paramnic oil fractions and an extract phase containing selective solvent and dissolved oil fractions, separating said phases, commingling said extract phase with an anti-solvent, said anti-solvent being more soluble in the extract phase than in the bramnate phase and adapted to cause separation of the extract phase into two layers, one layer containing oil fractions relatively more paraillnic in character than the other of said layers; separating said layers and returning the more paraiiinic oil layer to the extraction system, ata point between the points oi' introduction of the oil and selective solvent into said system.

2. A method as claimed in claim 1 in which. the selective solvent is sulphur dioxide mixedv cause separation of the extract phase into two layers, one layer containing oil fractions relatively more paraflinic in character than the other of said layers, separating said layers and returning the more paramnic oil layer to that aone of4 the extraction system wherein the oil being extractecl has substantially the same viscositygravity constant as the oil returned to said extraction system. A

4. A process for the separation of oil into paraiilnic and non-paraiiinic fractions which comprises countercurrently extracting said oil with a selective solvent and thereby forming a raf'- flnate phase containing parailinic oil fractions and an extract phase containing selective solvent and dissolved fractions, separating said phases, commingling said extract phase with an antisolvent, said anti-solvent being more soluble in the extract phase than in the raiflnate phase and adapted to cause separation of the extract phase into two layers, one layer containing oil fractions relatively more paraflinic in character than the other of said layers, separating said layers and returning the more paraillnic oil layer to the countercurrent extraction system at a point intermediate the points of introduction of the oil and selective solvent into said system.

5. A process according to claim 4 in which .the point of return to the extraction system of the oil layer recovered from the extract phase is that point at which the viscosity gravity constant of the oil undergoing extraction is substantially the same as the viscosity gravity constant of the oil layer recovered from the extract phase.

6. A process according to claim 1 in which the extract phase containing the anti-solvent is cooled prior to separation of the extract phase into layers.

more paraillnic oil layer recovered from the ex-V tract phase is freed from its selective solvent content and anti-solvent content prior to itsv return to the extraction system.

ULRIC B. BRAY.

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