US2121323A - Solvent refining process - Google Patents

Description

Patented June 2l', 1938 UNITED STATES PATENT oFFicEff ard H. Gross, Beacon, N. Y.,

assignors to The Texas Company, NewYork, N. Y., a corporation of Delaware Application February 6, 1935, Serial No. 5,214

` 8 Claims. (Cl. 196-13) phases, the above mentioned `retained bodies are This invention relates to 'the treatment of hydrocarbon oil, and particularly to a method of. treating hydrocarbon'oil, such as mineral oil, with 'a selective solvent. l

The invention broadly contemplates a process for solvent reiining mineral oil for `the production of lubricating oil of high viscosity index, low pour test. and other desired properties and characteristics.

The invention. comprises extractively treating mineral lubricating oil stock with a selective solvent, such as furfural, for example, wherein the oil is separated into an extract phase containing low viscosity index constituents of the oil together with some constituents of intermediate viscosity index, and a rafnate phase comprising high viscosity index constituents of the oil and retaining some of the extract phase. The two resulting phases are separated, cooled, and centrifuged or settled, to separate all or a portion of the retained matter. The retainedl matter thus separated from each phase is advantageously returned all or in part to the zone of extraction wherein it is brought into contact with fresh oil undergoing treatment. y

In the case of a w -bearing oil, the raiiinate phase, after removal of the retained material, is

dewaxed for the production of low pour testV lubricating oil.

The process of this invention ist-particularly Well adapted to the solvent refining of mineral lubricating oil stock with a solvent ofthe character of furfural, and wherein lthe extractive treatment with the selective solvent is effected at temperatures of around 200 F., or in the range from about 150 to 250 that the railinate phaseresulting from extraction at such temperatures may retain an appreciable amount of extract phase material. Similarly, the extract phase may contain a substantial quantity of relatively parafdnic oil of intermediate viscosity temperature characteristics. At the higher temperatures prevailing, during -such extractions, the rafllnate a substantial amount of.` the solvent. This retained solvent contains dissolved thereinja certain amount ol .extract phase oil. Also, at such temperatures, the extract phase may comprise substantial amounts of oil of intermediate vis cosity index due to the increased solvent power of the solvent at elevated temperatures. It has been found that by separately removing the extract and rafhnate phases from the extracy and subjecting each phase to cooling, centrifuging or settling the cooled tion zone, and either F. It has been found oil tends to retaine largely, if not completely, separated therefrom. In the ease of the raflinat'e phase, it is advantageous to subject it to centrifuging to remove the retained extract phase material, while in the case of the extract phase, it is usually sufficient to cool and subject it to settling or standing only, in order to separate the retained oil of intermediate character.

so returned. On the other hand, the oil of intermediate character separated from 'the extract phase alone may be returned to the extraction zone. The latter oil may thus be referred to as a cycle oil. It isthought that substantial benet results by returning .this cycle oil to the extraction zone where its presence tends to favorably iniiuence the subsequent separation of fresh oil into phases respectively rich in parainic and nonparainic constituents of the oil.

In the case of` certain oils being. treated as, for example, heavy residual fractions derived from mixed base crudes, it has been found that improved results Vare realized by centriiuging the raflinate phase resulting from extractionl with furfural at high temperatures. These ,oils contain certain constituents of an asphaltic nature which to some extent remain in the raffinate phase. It has'been found that this asphaltic material can be readily removed by centrifuging the raffinate phase, even without prior cooling. The material removed by the centrifuge is of a gelatinous nature and itsv removal results in a ramnate oil of improved qualities as regards decreased carbon residue, resistance' to oxidation, stability of color, etc. as a consequence, subsequent acid treatment of the rafiinate oil, which would otherwise be necessar'y, may be avoided.

In order to more clearly describe the invention, reference will vnow be made to th'accompanying drawing illustrating a flow diagram adapted to carry out the process of our invention.

As shown in this drawing. the oil to be treated is drawn from a tank I and introduced through aplpe 2 tothe lower portion-"of an extractor l.

. the incoming solvent and oil is such as to maintain-a suitable temperature within the extractor as,for example, within the range from about 150 to about 250 F.

.The extractor 3 is of the tower type adapted to eil'ect countercurrent contact between upwardly moving oil and downwardly moving solvent. In. order to bring about intimate contact between oil and solvent within the extractor, a suitable packing material, such as Raschig rings, may be provided. On the other hand, mechanical agitating or stirring means may be provided for bringing about the desired degree of contact followed by suitable settling and decanting agitators and Asettlers may be arranged so as to eiect countercurrent solvent action in a number of s uccessive stages.

As a result of this contact between oil and solvent, there results a formation of an extract phase containing the dissolved constituents oftheoil, and a raiiinate phase comprising the undissolved paraiilnic constituents of the oil. As previously mentioned,the extract phase retains a portion of oil .of character intermediate as regards viscosity temperature relationship while the rainate phase retains a small quantity of extract phase material.

The extract phase accumulates in the bottom of the extractor, while the ramnate phase accumulatesin the upper portion thereof.

The raillnate phase is removed through a pipe 8 to a cooler 9 wherein it is cooled to a temperature ranging from about thirty to fty degrees below the extraction temperature. The amount: of cooling will depend upon the nature of the oil undergoing treatment. If the oil is substantially wax-free, cooling may be carried to an even lower temperature. On the other hand, in the case of wax-bearing oils, it is desirable to maintain the raffinate phase at a temperature above that at whichit would tend to solidify.

'111e cooled oil is then introduced to a centrifuge or settling chamber Il to eiIe'ct separation of the retained extract phase material and other impurities of an asphaltic nature. In some cases, the ramnate phase oil may be introduced directly to the centrifugeA or settler without previous cooling. The separated material is conducted to a tank II. The centrifuged or settled ramnate phase is then conducted to a tank I2, and from there to a still Il for the removal of any remaining solvent. This solvent removed as a vapor is conducted to a cooler and condenser 20, to which reference is made later.

The solvent-free ramnate oil is then conducted to a tank Il for auch further treatment as may -be desired. In the case of a wax-bearing oil, it

may be delivered to a dewaxlhg plant. yOn the other hand. if it is a wax-free oil, it may, for example, be finished up by clay contact filtration.

The extract phase is removed from the bottom of the extractor I through a coolerv Il wherein it is cooled to a temperature substantially below the 'extraction temperature as, for example.

around thirtyor fty degrees below such temperature. 'The cooled extract phase is then delivered to a settling chamber' I6, wherein the retained oil of intermediate character, insoluble in the solvent at the lower temperature. separates therefrom. j

The separated oil is removed to a tank II. The remaining extract phase is drawn off to a tank I8 and from there to a still I9. The solvent is relmoved from the oil in the still I9 as a vapor.

This vapor is drawn oil, along with solvent vapor from the still Il, to a cooler 20 wherein it is cooled and condensed for re-use. The residual extract oil is drawn off from the stillv I 9 to a tank 2| for such further disposition as may be desired.

The extract phase material separated from the raiilnate phase and accumulating in tank Il, to'

gether with the separated or cycle oil accumulating in the tank I1, is delivered by a pump 22 through a pipe 23 to an intermediate point of the extractor 3, wherein it .mingles with oil undergoing treatment. If desired, this material may be mixed either with the charge or the furfural prior to introduction to the extractor 3.

On the other hand, the separated liquid from tank II may be mixed with fresh furfural entering the extractor 3 or may be introduced thereto at a point where the furfural within the extractor has the same concentration of extract in solution. The cycle oil from tank II may be mixed with the fresh charge to the extractor.

By Way of illustration, the application of t-he invention may be described with reference to the treatment of a steam-reducedcylinder stock derived from Pennsylvania crude by countercurrent extraction with furfural at a temperature of around 230 to 250 F., using about five parts of solvent to one part of oil. I The tests on the reduced cylinder stock before treatment will be as follows:

Gravity A. P. I 25.1 Flash "F 560 Fire "F 640 Saybolt universal viscosity- At 130 F 955 At 210 F 162 Pour "F v v 35 Carbon residue, percent 3.0v

When extracted with furfural under the conditions above stated, the oil and solvent will'separate into a raiiinate phase comprising about 15.0% by volume, and an extract phase comprising about 85.0% by volume.

When the above ramnate and extract phases are separated and the solvent removed therefrom by distillation in the presence of steam, the tests on the resulting railinate, oil and extract phase oil will be as follows:

If, instead of stripping outthe solvent from the raiilnate phase, as above mentioned, it is cooled to about 180 1". and centrifuged at' that temperatureaquantityotretainedextractphase material and some solventwill bey separated from the railinate'plnse. The separated extract phase material will amount to about 2.3% by volume of the raflinate phase and will comprise a heavy black material, which after removal of the solvent will have a high carbon residue content of around 2.39%.

Similarly, if the extract phase, upon removal from the extraction zone, is cooled and settled at a temperature of about 150 F., oil otherwise retained in the extract phase at the extraction temperature willv separate from the mixture. This separated oil is of intermediate character and will amount to about 6% of the original extract phase.

The centrifuged ranate phase, as well as the oil separated from the extract phase, retains a small amount of furfural which may be removedv by distillation. However, if theraffinate phase is to be dewaxed,v the retained solvent may remain therein throughout the dewaxing operation. Likewise, where the oil separated from the extract phase is being returnedtothe extraction zone, it will be unnecessary to remove the retained solvent prior to its return. f

The raffinate oil obtained by centrifuging the rafiinate phase and the oil separated by cooling the extract phase will, after stripping out any remaining solvent, have the following tests:

Centri- Oil separated fuga from exrainate tract phase Gravity A. P. i ze. 1 21. o 575 520 045 610 423 21s 169 94 l. 30 1. 52

It will be observed from the foregoing that centrifuging of the raffinate phase resulted in the removal of a substantial amount of heavy material, namely, 2.3% by volume and having a residual carbon content of 2.39%; also,that by cooling and settling the extract phase, a relatively large amount of oil of intermediate character was separated. This `separated material, according to the process of our invention, is returned to the extraction zone, all or in part, and mixed with fresh oil undergoing treatment.

The remaining extract phase may be stored for such further disposition as may be desired. The centrifuged raffinate oil, in the case of a .wax-bearing oil, is then mixed with asuitable dewaxing solvent mixture, such as a mixture of acetone and benzol, for example, and dewaxed in the usual manner.

The process of this invention is not necessarily restricted to extraction with a specific solvent such as furfural, for it is contemplated that other selective solvents having the essential selective action of furfural as between constituents of the oil of differing viscosity indices may be employed. Thus, the process of this invention is particularly applicable where the solvents ,employed are used at temperatures considerably elevated above normal atmospheric temperature. The ramnate and extract phases obtained when extracting with such solvents as nitrobenzene, aniline and crctonaldehyde may be advantageously )zreated in accordance with the process of our invention.

Furthermore,A the process of this invention is not limited to the treatment' of any particular type of hydrocarbon oil or petroleum fraction. It is adapted to the treatment of either distillate or residual fractions of petroleum.v

annees Obviously, many modifications and variations A of theinvention', as hereinbefore set forth, may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

-f We claim: l

l. In the rening, with a selective solvent, of a heavy lubricating oil stock containing residual carbon-forming bodies which form with the solvent a. small amount of material of a gelatinous nature and which is diiiicultly removable from the resulting raffinate, the method comprisingextracting the oil with a solvent comprising furfural at a temperature of around 200 F., forming an extract phase containing low viscosity index constituents of the oil and a rafnate phase containing high viscosity index constituents and a substantial amount ofsaid gelatinous material, removing the raffinate phase, and centrifuging the railinate phase while at an elevated temperature not substantially below the extraction temperature to remove the gelatinous material contained therein.

2. In the refining, with a selective solvent, of a heavy residual lubricating oil stock containing residual carbon-forming bodies which form with the solvent a small amount of material of a gelatinous nature and which is diicultly removable `from the resulting raiinate, the` method comprising extracting the oil with a solvent comprising furfural at a temperature of around 200 F., forming an extract phase containing low viscosity index constituents of the oil and a ramnate phase containing highi viscosity index constituents and a substantial amount of said gelatinous material, removing the raffinate phase, and centrifuging the removed raiinate phase in the presence of all its retained solvent While at an elevated temperature of around 180--200" F. to

l remove the gelatinous material 'contained theretemperature and thereby separating retained heavy extract material, reducing the temperature of the extract phase to separate therefrom oil of intermediate viscosity index, and removing the oil of intermediate character ,so precipitated. l

4. The method of refining mineral lubricating oil comprising extracting the oil with furfural at a temperature in the range 150 to 250 F., forming an extract phase containing low viscosity index constituents of the oil dissolved in the oil comprising extracting the oil with furtural at?l a temperature in the range 150 to 250 F. in an extraction zone, forming an extract phase containing low viscosity index constituents of the oil dissolved in the bulk of the solvent and a railinate phase comprising high viscosity index constituents of the oil mixed with a small amount of heavyA extract, removing the two phases, centrifuging the removed raiiinate phase at a temperature not substantially below the extraction temperature and thereby separating retained heavy extract material, reducing the temperature of the extract phase substantially below said extraction temperature to separate therefrom oil of intermediate viscosity index, removing the oil oi intermediate character so precipitated, and

returning separated oil of intermediate charac' ter to aforesaid extraction zone. y

6. The method of refining mineral lubricating oil comprising extracting the, oil with an extraction solvent, forming an extract phase Vcontaining low viscosity index constituents of the oil dissolved in the bulk of the solvent' andI a ramnate phase comprising high viscosity index constituents oi' the oil mixed with a small amount of retained heavy extract oil dissolved in extraction solvent amounting to about 2% of the raiilnate phase and suspended in said raiinate phase. removing the two phases, and without substantially altering .the solvent composition. eentrifuging the removed raffinate phaseat a temperature substantially the same as the extraction temperature and thereby separating the small amount of retained heavy extract material. without separation of the raiiinate into liquid phases.

7. The .method of reiining mineral lubricating oil comprising extracting the'oil with an extraction solvent, forming an extract'phase containing low viscosity index constituents of the oil dissolved in the bulk of the solvent and a 10 raiilnate phase comprising high viscosity index constituents of the oil mixed with a small amount of retained heavy extract oil dissolved in extraction solvent, removing the two phases, centriiuging the removed raiiinate phaselat atem-` 15 perature of around 180 to 200 F. and thereby separating retained heavy extract material, -reducing the temperature of the extract phase substantially below said extraction temperature to separate therefrom oil of intermediate viscosity index, and removing the oil of intermediate character so precipitated. v

8. 'I'he method of rening mineral lubricating oil by selective solvent extraction comprising extracting the oil with a selective solvent, forming an extract phase containing low viscosity index constituents of the oil dissolved in the bulk of the solvent and a raiiinate phase comprising high viscosity index constituents of the oil and containing a smallv amount of tarry materiall dissolved in solvent amounting to around 2% or more of the' rafnate phase. removing the railinate phase, and centrifuging the removed raiiinate phase in the presence of all its retained solvent and while at an elevated. temperatureof the order of 150 F. and not substantially below the temperature at which the oil was extracted with the selective solvent thereby to remove said small amount of tarry material without separation of the raiiinate into liquid phases. 40

RBERT E. MANLEY. BERNARD Y. MccARTY. HOWARD H. Gaoss.

Images