US2188051A - Extraction process - Google Patents

Description

Jan. 23, 1940. v. LANTz 2,188,051

EXTRACTION PROCESS Original Filed Nov. 1, 1957 2 Sheets-Sheet l Compssor'.

Stripper F/aah Poi Hash Jan. 23, 1940. v. LANTz EXTRACTION PRocEss original Filed Nov. 1, 1937 Condenser 2 Sheets-Sheet 2 Reserva/r Compressor i D/uen o 58 ln/zllal 5l O/l l e Mlker 44 L/qhP/fzase a4"t 35 We@ HenvyP/vose/ 1Lo2 ws/ 63 Phase 65 l Separator M/xer 64 Condenser 56 rCompressor 66 Compressor 6a o 7 Flash Pot Str/pper i F/ash Pol' Stripper 5 i i Flash Pot stripper F/ah Pol /n ven tor Patented Jan. 23, 1940 UNITED STATES PATENT oFFlcE EXTRACTIGN PROCESS Application November l, 1937, Serial No. 172,207 Renewed December 4, 1939 Claims.

This invention relates to the extraction of various oils, such as mineral, vegetable, marine, animal, or ethereal oils, and particularly the higher molecular oils, to separate them into frac- 5 tions having diierent properties.

It is known to extract such oils with liquid carben dioxide at ordinary temperatures. Such a process is, for example, disclosed in the United States patent to Auerbach, No. 1,805,751. In such a process the ratio of quantities of the dissolved and undissolved fractions is limited by the solubility of the oil in the carbon dioxide, and ls diicult to regulate except by varying the quantity of the carbon dioxide employed it being necessary to use a proportionately larger quantity of carbon dioxide to dissolve more oil. An increase in the temperature causes oils to be even less soluble in carbon dioxide, while the use of lower temperatures is not feasible because of the solidication of the oils. The use of larger quantities of carbon dioxide is, moreover, not practical because exceedingly large amounts of the solvent are required to effect the dissolution of an appreciable amount of oil therein, in view of the relatively low solubility of oil in carbon dioxide.

It is an object of the present invention to provide a process for the extraction of oils with a solvent containing a liqueed gas of the type of carbon dioxide, in which it is possible to vary the relative sizes of the extraction products without using prohibitively large quantities of the solvent. It is a further object of this invention to provide a process of the type described in which it is` possible to produce a plurality of different fractions from the same initial stock in a simple manner. Other objects will be apparent from the following specification.

According to the present invention it was found quite unexpectedly that when a mixture of a liquid low molecular aliphatic hydrocarbon, which may be either normally gaseous or normally liquid, and liquid carbon dioxide is employed as a solvent for extracting higher molecular oils, the sizes of the phases produced may be nicely regulated by varying the ratio of the hydrocarbon and the carbon dioxide in the solvent, and that it is not necessary to employ proportionately larger amounts of carbon dioxide to increase the proportion of the oil which is dissolved in the solvent mixture. In fact, the results obtained in the process according to the present invention are so far contrary to those obtainable in the Auerbach process thatan increase in the quantity of the carbon dioxide acu tually reduces the amount Yof oil dissolved, when the ratio of the low molecular hydrocarbon to the oil being treated is maintained constant.

While it has heretofore been proposed to employ liquid parainic hydrocarbons in connection with other liquid selective solvents such processes did not permit the regulation of the sizes and qualities of the products produced over a wide range with the facility .and in the manner of the present process, since in such processes, with a given amount of hydrocarbon diluent, the addition of larger quantities of the selective solvent, in general, eiiects an increase in the amount of oil dissolved, and the use of larger quantities of the paraiiinic hydrocarbon diluent in such cases reduces the amount of oil dissolved in the solvent. This is contrary to the present process in which an increase in the amount of carbon dioxide lowers the quantity of oil dissolved and the parainic hydrocarbon diluent promotes the solubility of the oil.

Referring to Figure 1 of the drawings, an initial oil from tank I is fed via pump 2 to mixer 3, wherein it is mixed with a liquid parainic hydrocarbon diluent, such as propane, butane, or isopentane, and with liquid carbon dioxide, fed from tanks 4 and 5 via valves 6 and 1, the ratio of the diluent to the carbon dioxide being proportioned to dissolve the desired quantity of oil. The resulting mixture is fed to a phase separator, such as a centrifuge or settling chamber, indicated at 8, in which it is separated into a light liquid phase, withdrawn at 9, containing the greater part -of the carbon dioxide and the diluent, and a heavier liquid phase, withdrawn at I0. The phases may be withdrawn continuously or intermittently. The latter fed to a ilash pot II for the separation of the carbon dioxide, which is returned to the tank 5 via compressor I2 and condenser I3, the residual portion of the heavy phase being treated in the stripper I4 for the removal of the hydrocarbon diluent and any remaining carbon dioxide. The diluent is returned to the tank 4 via compressor I5 and condenser I 6, and the undissolved oil passes to a receiving tank Il. The lighter phase withdrawn at 9 may be similarly treated for the recovery of the solvent mixture.

It is a feature of the present process that a relatively large proportion of the initial oil can be separated in the lighter phase without the use of large amounts of solvent. It is, therefore, possible to recover a relatively large amount of oil, such as, for example, from 40 to 90% in the lighter phase, and then to fractionate this dissolved oil further. In this operation, the dissolved oil is treated with a second solvent mixture containing the same or different components as the rst solvent mixture, used in the iirst extraction step, but/having a lower solvent power for the oil. When the components of the second sol# vent mixture are the same, the ratio of diluent to the carbon dioxide is preferably lower although it is also possible to cause phase 'separation by lowering thesolvent power by increasing the temperature, or by removing a portion of the solvent mixturefrom the lighter phase. vAccording tothe preferred-embodiments the separation ofthe light liquid phase into new phases is effected either. by adding more liquid carbon dioxide to the light phase,or by adding lboth diluent and carbon dioxidefbut lmore of the latter, or by lowering the concentration in the phase of the diluent.

. As illustratediin Figure 1, the lighter phase maybe brought toa higher pressure by a pump, and :commingled with an added quantity of liquidcarbondioide,y fed via the valve I8, mixed i in the mixer I9,V and separated into new lighter and heavier -liquid phases inthe separator'20. A s explained above, an added quantity of dilu- Vent;may also befintroduced via valve 2|, whereby "the dilution ratio is increased and a sharper frac- 'tionatiori-is often eiected. The light and heavy phases nare withdrawn via valved lines 22 and 23, fand 'freedfrom the solventin ilash pots 24 and S25 and strippers 26 'and 21, as explained for the frst heavy' phase, `the oil fractions being stored .iin tanks 28'jvand 29..

- fIt shouldv be. .noted that the successive operationsdescrbed can all` be carried out in a Vsingle tank provided withja.` stirring device and with `means' forintermittently 'or` continuously drawoi the` lheavy "phase and supplying carbon `dioi'xiieoi-afmixture of rcarbon dioxide and: a

`'dilufent-.

According to a modification of the process i1- lustrated in Figure 2, the 'initial oil from the tank 30 is fed through pump 3|\ commingled with a diluent and carbon dioxide supplied from the tanks 32 and 33 at rates regulated by valves 34 and 35; after intimate mixing in the mixer 36, the resulting light and heavy liquid phases are separated-,in the separator 31, as described for Figure `1. The further treatment of the light phase according to Figure 2follows the third of the above-mentioned preferred modes, that is, the light phase is fed to a ash pot 38 or other distilling apparatus via a throttling valve 39 for the separationof all or a portion of the diluent.`

The carbon dioxide will in most cases also be it is, however, `often more economical to compress 4it inl the compressor V4|), cool it in the condenser 4|, and introduce it lahead of the mixer' 36 via reservoir 42 and valve' 43. It is then only necessary to vfeed sufficient materials through the valves 34 and 35 to make up the deiiclency of the solvent mixture which is not recovered from the light'phase in the flash pot and which is dissolved in the heavy phase.

The residual portion of the lighter phase is withdrawn from the flash pot and mixed in the mixer 44 with a solvent mixture supplied via valves 45 and 46, different from that flashed of! at 38, whence it passed to the phase separator 41. The resulting light and heavy liquid phases are withdrawn i'roxn the separator via valves 48 and 49, and treated in the flash pots 50 and 5| for the recovery of the carbon dioxide, and in the strippers 52 and 63 for the recovery of the diluent and such carbon dioxide as is not separated in the flash pots, the oil fractions being withdrawn at 54 and 55. The carbon dioxide and diluent are returned to the storage tanks via compressors 56 and 51 and condensers 58 and 59.

The heavyphase from theseparator 31 is withdrawn via; afvalve'60, ancl4 may be treated as shown in Figure l. It is, however, possible to extract furtherfquantities of oilirom this phase. For thispurpose,l the heavy phase is commingled with carbon dioxide and a diluent, fed via valves 6|.-and 62,! mixed therewith in the mixer 63, and separatedinto light and heavy phasesin the separator 64'.,- The light and heavy phases, withdrawmvia the valves 65 and 66,- are treated in theila'shf'pots 61and 68 Aand strippers 69 and 10 for the separation of the solventl mixture, and the oiliractions are withdrawn Iromthe process at1land12.A

The process may also be practiced in. a countercurrent manner, as illustrated in vFigure 3. In thisjilgure, represents a countercurrent contact z one, -su'ch as a packed tower, or a con-f tact apparatus provided with mixing and phase separating devices. -fl'he initial oil from the tank |0|;i s -ied viaapuznp |02 to one end of the contactingzoneyand a solvent mixture is fed'to the otherjendfviafline |03.; This` solvent mixture contains vthexfli`q'1i-idpara 'ic -hydrocarbon diluent and the carbo,,r'idiyoxidelv in\th e` ratio=necessary to dissolveth "desired-proportion 'ofthe initial oil, and may be,l btained by' means of interconnected proportionirigfpum .|0`4,` |05,' supplied from tanks its., m14, f f.. l

Inthefco'itact zone flllv-fjthe'solvent and oil flow counter'currently'.; producing" a llight extract phase, withdrawn-i,at*|08jand' a heavier phase containing the' undissolved oil, `withdrawn at |09. The contact zone |00 may, if desired, be provided with temperature regulating means, such as coils ||0, whereby a temperature gradient obtains. The temperature near the point at which the solvent mixture is introduced is preferably lower than that at which the initial oil is introduced.

The withdrawn phases may be further yfractionated, either in the manner described above according to Figures 1 and 2, or in another countercurrent'treatment. If the fractions produced in vthe zone |00 vare to be withdrawn from tthe process,v they are treated in iiash pots r| i and .i I6. The recovered carbon dioxide and diluent-are, respectively, returned to the tanks |01 and |06 via compressors |I1, ||6, and condensers'll9', |20.

I Asthe 'diluent,' anyvsolvent rich in lower aliphatic hydrocarbons may beemployed, such as light gnaphtha, llight gasoline fractions, etc., which may, moreover, contain higher boiling constituents. I preferv to employ a diluent containingat least 75%'of parafdnic hydrocarbons containing less than seven carbon atoms which can be liqueiied. Thus, ethane, propane, butane, isobutane, pentane, iso-pentanes, and hexanes constitute my preferred diluents.V These hydrocarbons may, moreovenbe employed alone, without the presence of higher boiling hydrocarbons or of methane. I prefer, moreover, to employ the branched chain hydrocarbons, particularly isobutane and iso-pentanes, or fractions containing over about '15% oi' the same.

The processv 'may be carried outv at ordinary temperatures, preferably between about 0 C. and the critical temperature of carbon dioxide, although somewhat lower temperatures may also be employed, limited by the solidlilcation of the oils 'I'he ratio of the diluent to the'carbon dioxide. and the ratio ofthe solvent mixture to the oil may be varied within wide limits, and will be apparent from the examples presented below. As was pointed out above, an increase in the ratio of carbon dioxide to diluent decreases the quantity of oil extracted. The use of a larger ratio o! solvent mixture to oil necessitates the use of a higher concentration of carbon dioxide in the solvent. This frequently enhances the selectivity of the solvent mixture, but the use of larger quantitiesof solvent necessitates the use oi larger equipment for handling the materials and for recovering the solvent.

It is not necessary to employ the same diluent in all of the stages.' Thus, in successive stages further quantities of diluent of a different molecular weight may be added, together with the carbon dioxide, or the first diluent may be removed, and the different diluent employed in a later stage. In general, it is preferable when employing diiierent di1uents, to use successively lower molecular diluents when treating successive lighter liquid phases. For example, the first light phase in Figure 1 may be produced by employing a mixture of equal parts by weightv oi isopentane and carbon dioxide. Propane and carbon dioxidemay then be introduced to effect a further separation in the separator 20. Similarly, in Figure 2, isopentane or butane may be used in the separation e'ected in the stage 31, and a mixture of carbon dioxide with` ethane or propane may be used in the separatorl. Conversely, it is desirable to treat the heavier phase with the same or with a higher molecular diluent than was employed in producing that phase. I'hus if butane was employed to produce the iirst heavy phase in the separator 31 of Figure 2, a pentane or a hexane may be employed in the separator 6l.

Example I A Coalinga residual had the following properties:

Specific gravity, d; 0. 9784 Refractive index n 1. 5444 Viscosity, seconds Saybolt Universal at Viscosity, seconds Saybolt Universal at 2 l 0 F 247. 5 Viscosity index 3 Several-samples of this oil were each separately dissolved in isopentane, and liquid carbon dioxide was added to the resulting solution in the proportions shown in Table I, all quantities being parts by weight-based on 100 parts by weight oi the original sample. The resulting mixture was agitated for an hour and allowed to stand for two hours, forming two liquid layers, following which these phases were separated and freed from the isopentane and carbon dioxide. During these operations the mixture was held at a pressure of 850 lbs. per sq. in. gauge and the temperature was held at about 2022 C. The heavier phase contained the undissolved oil, together with between 5 and 10% of the solvent mixture; its properties are tabulated in Table I. The lighter phase contained most of the solvent and the dissolved oil; its properties are tabulated in Table II, the run numbers being the same as in Table I:

Table I Amoun Properties of undissolved lohoiit added oil ve Rim N m um spams views www Diluent 00g pum gravity gdt gravity d: 210 F llstllt 190 221 77. 6 I. 0471 20, 785 0. 947 190 253 59.4 1.0299 4,209 0.943 190 53o 32. s 1. 0048 963 0. 930 1m 929 26. 5 0. 9966 037 0.925

Table II Properties ot dissolved oii Viscosity, Run No. speelse Rfg secondsviscosity gravity index Viscosi ity mv ty d: ng' at A: www* It will be noted Athat as progressively larger quantities of liquid carbon dioxide are used'the amount dissolved therein decreases, and that the dissolved oil is progressively more parailinic and less viscous. while the undissolved residual oil becomes less aromatic or naphthenic and less viscous. My process, therefore, effects a separation both on the basis of molecular size and on chemical structure, in that the solvent mixture preferentially dissolves oils by lower viscosity, i. e., oils having smaller molecules, and oils which have lower internal pressures, i. e., oils which are more paraflinic in nature, as indicated by the refractive index, viscosity index, and viscosity gravity constant.

For the purposes of comparison, two samples of the same initial oilwere treated with pure liquid carbon dioxide in the manner described above, with the following results:

It will be noted that pure carbon dioxide dissolved only very small quantities of oil, and that the use of pure carbon dioxide for the fractionation of oils would require excessive quantities of solvent to dissolve an appreciable amount of oil.

Example II A Coalinga residual oil had the properties shown in the last column of Table IV.

Two samples of this oil were separately treated with different solvent mixtures, by'introducing the oil continuously into the uppermost stage of a six-stage countercurrent column equipped with alternate mixing and settling zones, and introducing the solvent mixture consisting of isopentane and carbon dioxide continuously into the lowermost stage the composition and amount of solvent being shown in the table. The temperature was maintained constant at 30 C., and the pressure was sufficient to liquety the solvent. About 90 to 95% of the solvent mixture was present in the lighter phase which contained the dissolved oil. The quantities given are parts by weight based on 100 parts by weight of the original oil, and the quantity for the solvent is the rate of introduction of the solvent, based on the rate of introduction of the oil. The properties oi' the oil obtained from the phases withdrawn at the opposite ends of the column are shown in Table IV.

Table IV Run No 7 8 Original oil Amount oi solvent 434 548 Mole percent of carbon dioxide in solvent 68-70 66-68 Amount oi oil dissolved 41. 6 74. 0 100 Properties of dissolved oil:

Specic gravity dg i- 0.9357 0.9553 0.9796\ nen-active index n 1. 520s 1. 5342 1. 55er Viscosity. seconds Saybolt Unlv At 100 F Q 971.7 3085 11,376

At 21%F.. 68.21,? 102 256.? Viscosi dex Color, if S -D 8-D Black Viscosl 0. 877 0. 893 0. 911

The nature of the separation effected is again seen to `be partly onthe basis of molecular size and partlyon the basis of chemical structure, the moreisaturated orl parailinic hydrocarbons of lower molecular sizes` being preferentially dissolved in-the solvent. The yeiect of the compo-V sition is alsozapparent, for while in run'8 only 26%- moreffsolvent -was'- employed than k,in run 7, theeiectof yemploying a solvent containing. carbon. dioxide in lower fconcentrationresulted in the yextriiction of.'l8%-` more oil. l-It should benoted that the solubility of thevoil inthe solvent mixture was about yin. run A7 and 14% in run 8, these values being much v greati'erthan 0.2%, as given in Table While in the foregoing examples various compositions of the solvent mixture containing from vabout 65 to 89 mole percent `of carbon Ydioxide ably lower concentration of carbon dioxide, often l as low as or lower than 25 mole 4,per cent, may 'Y mixture to oil, similarly, may be varied in accordv of oil.

snee with the quantity which im desired to extract. By way of example, it may be stated that lratios of between 1.5 and 6.0 will most usually be employed.

Although I have already disclosed the distillation as a method of separating CO2' from the oil and from the diluent, it is often advantageous to employ a chemical treatment for this purpose. For instance, for removing the last traces of CO: from the treated oil it may be subjected to a treatment with an aqueous solution of a caustic alkali metal or an organic base, like alkylolamines, or of a salt capable of extracting C02. It

is particularly advantageous to employ for this purpose aqueous solutions of reagents which can be readily regenerated by releasing the absorbed CO: upon heating and reused. Examples of the suitable processes are described in the Rosenstein Patent 1,945,163 and patent application Serial No. 25,947, illed June 10, 1935. This process may be substituted for instance, for the distilllng apparatus Il and I4 or 24 and 26 of Figure 1, whereby CO2 and diluent are separated from each other in a continuous manner and returned to their respective receiving tanks.

I claim as my invention:

1. A process for rening oils by extraction with a light hydrocarbon solvent modified with liquid carbon dioxide comprising contacting said oil with a liquid selective solvent consisting substantially of carbon dioxide and light aliphatic hydrocarbons of six or less carbon atoms per molecule, there being no overlapping in boiling range between the lightest fraction of said oil and said light hydrocarbon solvent, maintaining a pressure sufficient to keep the solution of oil and solvent in the liquid phase during the contacting, and producing two liquidA phases, one comprising a solution of a portion of said oil in said selective solvent and the other consisting essentially of an undissolved portion of said oil containing a relatively small portion of said solvent.

2. The process according to claim 1 in which a relatively heavy hydrocarbon fraction is extracted to manufacture lubricating oils.

3. The process according to claim v1 in which the lighter phase ls extracted for a second time with a similar solvent containing different ratios of carbon dioxide and liquid normally gaseous hydrocarbon to cause its separation into second liquid phases and separating said second liquid phases. r

4. 'I'he process according to claim 1 in which the streams of heavy petroleum fraction and solvent are flown countercurrently.

5. The process according to claim 1 in which carbon dioxide and liquid normally gaseous hyy drocarbon are evaporated from the lighter phase and after being liqueiied are returned and brought into contact with an additional quantity VERNON LANTZ.

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