US2086168A - Process for the solvent extraction of petroleum oils - Google Patents

Description

Jul 6, 1937. 4 'D. R. MERRILL 2,086,168

PROCESS FOR THE SOLVENT EXTRACTION OF PETROLEUM OILS Filed Noy'. 27f19ss 20 Q Z5 1! 2 p10 #1 A 21 v I 61v 3 23 65 INV-ENTO R., Dal 1a R Merrill BY I g 6 ATTORNEY. 1

Patented July 6, '1937 rnocnss' ron 'rnn SOLVENT EXTRACTION or PETROLEUM OILS David R. Merrill, Long Beach, Calif., assignor to Union Oil Company of California, Los Angeles, Calif., a corporation of California Application November 27, 1933, Serial No. 699,904

6 Claims.

This invention relates to the treatment of oils,

such as mineral lubricating oils, by extraction with selective solvents.

It has been found that desirable paraflinic hydrocarbons can be separated from the undesirable olefinic, naphthenic and/or aromatic compounds by the use of solvents which selectively dissolve the undesirable hydrocarbons but which exhibit only a very limited solvent power upon 10 the desirable paraflinic hydrocarbons.

When I use the term paraifinic hydrocarbons I mean those highly saturated compounds which are present in petroleum characterized by a low temperature viscosity susceptibility, i. e., they exhibit a minimum change in viscosity for a given change in temperature, and characterized by relative stability to air or sunlight, exhibiting little tendency toward discoloration or sludge formation. This definition is not meant to include those compounds whichare usually solid or semisolid at ordinary temperatures and which are known as wax or petrolatum. As a matter of convenience hereafter, I will refer to the undesirable components, such as olefinic, naphthenic and/or aromatic hydrocarbons as the non-paraflinic components. of petroleum. These fractions are characterized by'a relatively high temperature viscosity susceptibility and are relatively unstable to air or sunlight, exhibiting 3o discoloration and sludge formation.

A further indication of the purity of a lubricating oil is its viscosity gravity constant. This constant is an index of the paraflinicity or naphthenicity of an oil. A high value represents 5 a high degree of naphthenicity while low values indicate relatively greater paraflinicity. Lubricating oils from natural 'crudes range from about 0.903 viscosity gravity constant for an extreme Gulf Coast type to 0.807 for an extreme Pennsyl- 40 vania type, orevenbeyond. 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 45 641, of 1928.

A number of selective solvents for extraction have been found; for example, it has been shown that such materials as liquid sulphur dioxide, beta beta dichlorethyl ether, chloraniline, nitro-ben- 50 zone, aniline and'furfural are highly selective as 'solverits for the non-paraffinic hydrocarbons. These solvents may be used alone or modified by the presence of such agents as carbon bi-.

sulphide, xylene, benzene, toluene, carbon tet- 55 rachloride, ethers, tetrachlor-ethane. or the like.

When these relatively heavy solvents are commingled with petroleum or petroleum fractions under the proper conditions of temperature, the undesirable non-parafiinic hydrocarbons pass into solution to a greater or less extent but the desirable paraffinic hydrocarbons remain largely undissolved. 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 paraffinic hydro- 10 carbons rise to the top of the vessel and form a raflinate phase. These phases are then readily I separable by ordinary decantation means. The raflinate phase is usually foun'd 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 distillation whereby the solvent is distilled away from the hydrocarbon oils.

In selectively extracting certain oils containing substantial proportions of highly aromatic or non-paraffinic fractions characterized by high viscosity gravity constant, for instance, a residual oil such as a Kettleman Hills long residuum which was deasphaltized and dewaxed by liquidpropane, difiiculty has been encountered in obtaining the desired separation of the rafiinate and extract phases, especially with selective solvents, such as dichlorethyl ether or sulphur dioxide which are not good solvents for asphalt. Under the conditions necessary to produce a high grade raiiinate characterized by low viscosity gravity constant, the rafiinates in the various states tend to form with the extract phases a finely divided dispersion which does not break readily. The rafiinate phase is slow to coalesce and consequently the extract phase entrains part of the raflinate as it is removed from the system. Although I do not desire to be limited by this theory, I. believe that the asphaltic components and perhaps other similar materials present in the oil are colloidally active in emulsifying the extract and railinate phases whereby phase separation is hindered. Phase separation of such oil is especially difiicult when the selective solvent'employed has low solvent power for asphalt.

- It is also diflicult to obtain the desired separation of oil in a rejection stage in which an extract phase from an extraction stage is cooled to produce a rejected raffinate. In many cases, particularly at low temperature, the rate of separation of this rejected oil is very slow, due apparently to ,either a supersaturation of the raflinate components in the extract phase and/or. to a separation of these components'in extremely fine dispersed form characterized by a slow rate of coalescence of the droplets. In consequence, the

formation of large droplets which would rise to form a continuous upper raffinate phase is hindered.

It is an object of my invention to facilitate the separation of the raifinate and extract phases during solvent extraction whereby loss of raflinate entrained in the extract phase is substantially reduced.

It is a further object of my invention to accelerate phase separation during the solvent extraction of oil containing substances which tend to stabilize the dispersion of the extract and raflinate phases.

It is another object of my invention to facilitate the separation of a rejected insoluble oil from an extract phase produced by a prior extraction.

I have found that these difliculties can be overcome by increasing the proportion of raffinate to extract phase prior to extraction and/or rejection of oil in the presence of a selective solvent. The

increased proportion of raflinate results in the production of a dispersion of raflinate and extract phase during solvent extraction characterized by a large number of droplets of larger size than those produced when only a relatively small proportion of raflinate is present. The proportion of rafiinate to extract phase can be increased in several ways. For instance, to an oil characterized by a relatively small proportion of valuable paraffinic components which are separable from extract phase with difficulty during extraction with a selective solvent, a relatively highly paraffinic oil may be admixed prior to solvent extraction for the purpose of increasing the ratio of raflinate to the extract phase. This highly'paraffinic oil may come from any suitable source. It may be an unextracted oil containing a larger proportion of paraffinic components to nonparaflinic components than the oil which is difficultly separable during solvent extraction.

A suitable source of highly paraflinic oil for intermixture with the less parafiinic oil is a raffinate produced by extraction of mineral oil with a selective solvent. This railinate may be derived from the same or a different source than the oil to be extracted according to the .present invention.

As illustrative of my invention, the" oil characterized by the above mentioned difliculties during extraction may be mixed with a portion of the raflinate phase produced in the same extraction. Also the extract phase characterized by difficulty of separation of oil rejected by cooling the same may be mixed with a portion of the oil rejected therefrom.

By intermingling a portion of the r'aifinate phase with incoming feed, preferably. at a temperature above that of the settling chamber in which phase separation of extract and said raffinate occurs, the droplets which form in the mixture are of larger size and the coalescence of the raifinate is accelerated. Also, the concentration of oil in solution in the extract phase will be increased with the result that on subsequent cooling to the temperature of separation, the quantity of oil separated will be larger and there will be less tendency for a state of supersaturation to exist and a greater tendency for the products to coalesce.

The drawing is a diagrammatic view of a preferred form of apparatus suitable for carrying out my invention.

Referring to the figure, oil to be extracted is introduced into the system through line l0 controlled by -valve II by action of pump l2. In

' mixing chamber I5, with which line H] connects,

the oil is intermixed with solvent introduced via lines l6 and I1, valve I8 and pump 19 and with r-aflinate introduced via lines 31 and I1 recycled from settler 30 to be described. Rejected oil, described below, from rejection settler 45 may also comprise part of the stream of oil passing through lines 31 and I]. In order to secure thorough intermixture of solvent, oil and recycled raflinate, the mixture is passed by action of pump 22 from the feed end of chamber l5 via line 20 controlled by valve 2| into heater 23 wherein its temperature is raised, preferably to a point at which complete miscibility will occur.

The mixture is then recycled via line 24 into the 'finate phase is removedv from the settling chamber via line- 33 controlled by valve 32. Extract phase exits through line 35 controlled by valve 36. In order to increase the proportion of raffinate toincoming oil for the purpose of accelerating phase separation in 30 by increasing the rate of coalescence of the ramnate phase therein, a portion of the raiiinate accumulated in settling chamber 30 is intermixed with incoming fresh oil by passage through line 3'! controlled by valve 38 by action of pump 39. Line 31 connects with feed line l6.

Due to the general similarity of the various hydrocarbon components of mineral oil fractions, such as lubricating oils, solubilities of the undesirable, non-paraffinic fractions and of the desirable paraflinic fractions in' a selective solvent usually differ only in degree and there is, therefore, a tendency for desirable, high grade parafiinic oil to be carried away withthe extract resulting in a loss in the yield of paramnic fractions obtained. In other words, in a phase separation of extract and ra-flinate fractions from mineral oil employing a'selective solvent, an

equilibrium of paraflinic components as well asnou-paraflinic components is established between the phases. Consequently, some of the desirable parafiinic fraction is found in the ex tract instead of in the raflinate.

For these reasons, the'extract phase issuing from extraction chamber 30 via line 35 may contain a substantial proportion of valuable paraffinic fractions. The extract phase from' settler 30 passing through line 35 is introduced into the feed end of mixing'chamber 40 via line 34. Similar to mixing chamber 15, chamber 40 is also provided with division plate 26 and port 25 to separate the feed zone from the return zone. The extract phase is mixed in 40 with rejected oil, to be described, and the mixture passes from chamber 40 via line 4| through cooler 42 and line 43 into rejection chamber 45. The temperature of the mixture is sufliciently reduced in cooler 42 to cause separation of an insoluble rejected oil in chamber 45, A sufficient portion of said rejected oil may be recirculated into adaoeaica mixture with fresh quantities of the extract phase from extraction chamber 30 containing further quantities of reject oil to facilitate phase separation and coalescence of this insoluble oil in settling chamber 45. This recirculated rejected oil passes into mixing chamber 40 by action of pump 48 via line 46 controlled by valve 41. In order to secure thoroughintermixture of extract phase and recirculated rejected oil prior to entrance into chamber 45, these materials may be passed from the feed end of mixing chamber 40 via line 5!! controlled by valve 5| by action of pump 52, through heater 53 and into the return end of section 40 via line 54. By recirculating through line 50, heater 53 and line 54 at a rate exceeding the rate of feed of all the streams entering the feed end of said mixing chamber, there will be no flow of unmixed material from the feed end into the return end of the mixing chamber.

Extract phase is removed from rejection settler 45 via line 55 controlled by valve 56. The unrecirculated rejected oil produced therein can be removed from the system as an intermediate raiiinate or it may be returned through line 51 controlled by valve 58 by pump 59 into intermixture with that portion ofthe rafiinate from extraction stage 30 which is recirculated into contact with fresh oil introduced into the system in the above described manner.

In operation of this apparatus, a suitable proportion of recirculated rafiinate from extraction stage 30 to solvent and oil entering the system may be one volume of recirculated raflinate to two volumes of the mixture of solvent and fresh oil. In this case the volume of the final raiiinate will be about one-third that of the oil fed into the system. This proportion, however, is not critical and may be varied from a small proportion of recirculated oil which may be suiiicient in certain instances up to a sumciently larger proportion of recirculated oil and is limited only by the increased cost of pumping, heating and cooling the larger volumes of 011. Similarly, a suitable proportion of rejected oil for recirculation from rejection stage 45 into contact with extract phase in mixer 40 is one volume of recirculated rejected oil to two volumes of extract phase. Preferably the draw-oil lines for raflinate and rejectedoil to be recirculated are at lower points in the settling chambers 30 and 45 than the draw-ofi' lines 33 and 5? in order to allow additional settling with consequent reduction in entrainment of extract phases in the withdrawn oils. In starting operations, there is, of course, initially no raflinate in the rejection stage and diificulty may be encountered in obtaining a raffinate to be recirculated therein as the tendency for coalescence without suflicient recirculation is low. For this reason, connection 60 controlled by valve M has beengprovided to introduce oil feed directly into the rejection stage in order to build up a raflinate in this stage so that recirculation of rafiinate may be initiated therein. Many variations and modifications of the above described invention will be obvious to a man skilled in the art. For instance, additional stages of extraction may be. provided; mixing I claim:

1. A process for the separation of paraflinic and non-paraflinic fractions from mineral oil containing the samewhich comprises extracting said oil with a selective solvent to produce a raflinate insoluble in said solvent and an extract phase, separating said raflinate from said extract and non-parafiinic fractions from mineral oil containing the same which comprises extracting said oil with a selective solvent to produce a raflinate insoluble therein and an extract phase in an extraction stage, cooling said extract phase to produce an insoluble rejected oil and interminglingfurther quantities of oil entering the said extraction stage with said rejected oil and with a portion of the raflinate from said extraction stage prior to extraction therein.

3. A process for the separation of a hydro carbon oil mixture into fractions relatively more paraflinic and fractions relatively less paraflinic in character than the original hydrocarbon oil mixture which comprises admixing said hydrocarbon mixture with oil which is relatively more paraflinic in character than said hydrocarbon oil mixture and further characterized by containing a substantial proportion of oil fractions having the same boiling range as the oil fractions contained in the hydrocarbon oil mixture and thereby increasing the' ratio of parafiinic fractions to non-paraflinic fractions in said mixture, commingling the hydrocarbon oil mixture which has been admixed with! said relatively more parafilnic oil with a selective solvent and thereby forming an extract phase and a raflinate phase and separating said phases.

4. A process as claimed'in claim 3 in which the oil admixed with the hydrocarbon mixture is an oil which has previously been extracted with a selective solvent.

5. A process for the separation of a hydrocarbon mixture into fractions relatively more paraffinic in character and fractions relatively less paraffinic in character than the original oil which comprises admixing said hydrocarbon.

- portion of oil fractions having the same boiling point range as the oil fractionscontalned in the hydrocarbon mixture, heating said mixture of oil and selective solvent-to a temperature sufficiently high to cause substantial complete miscibility between theoil and the solvent, passing the solution of oil and solvent through a cooler and cooling the solution sumciently to cause phase separation between the relatively more paraflinic oil fractions and the relatively less paraflinic oil fractions dissolved in the selective solvent and separating the relatively more parafllnic oil fractions from the relatively less p'aramnic oil fractions dissolved in the selective solvent.

6. A process according to claim 5 in which the oil admixed with the hydrocarbon mixture is an oil which has previously been extracted with a selective solvent.

DAVID R. MERRILL.

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