US2081524A - Process for solvent extraction of - Google Patents

Description

Patented May 25, 1937 UNITED STATES PATENT OFFICE PROCESS FOR SOLVENT EXTRACTION OF PETROLEUM FRACTIONS .No Drawing. Application October 27, 1934, Serial No. 750,382

Claims.

The present invention relates to the extraction of petroleum fractions by the use of selected solvents. Although useful in the treatment of oils such as animal and vegetable oils, it refers 5 more particularly to the production of high grade lubricating oils by the so-called selective solvent extraction process, as well as to the separation of petroleum fractions, such as nitrogen base into their components.

It is well known that petroleum fractions used for the production of lubricating oils contain parafiinic hydrocarbons as well as hydrocarbons of the olefinic, naphthenic, and/or aromatic types. It is also known that high grade lubricating oils must be substantially free from the above mentioned olefinic, naphthenic and/or aromatic compounds, thus substantially consisting of parafiinic hydrocarbons. This is due to the fact that paraffinic oils of a given viscosity have a lower specific gravity, a higher flash test, a

small change of viscosity per unit change in temperature, and a higher hydrogen to carbon ratio in comparison with non-parafi'inic oils of the same viscosity. Also parafiinic oils are more stable and therefore more desirable as lubricants especially when used at relatively high temperatures or when the operating temperatures vary within the relatively wide range.

The term parafiinic hydrocarbons or parafiinic oils" refers to those high saturated compounds which are present in petroleum, and in fractions thereof, and which compounds are characterized by a low temperature-viscosity susceptibility, i. e. compounds which exhibit a minimum change in viscosity for a given change in temperature. These paraffinic hydrocarbons are also characterized by a relatively high stability to air and sunlight, exhibiting little te'ndency toward discoloration or sludge formation. The non-paraffinic components of petroleum are the fractions having a relatively higher temperature-viscosity susceptibility, and a relative instability to the action of air and sunlight.

One of the main indications of the grade of a given lubricating oil is its viscosity gravity constant. The viscosity gravity constants referred to in the present invention have been determined by the method employed by Haughton and Robb, as set forth in the J ournalof Industrial Engineering Chemistry, Analytical Edition, vol. 3, (1931) at page 144. The viscosity gravity constant (usuallyindicated as V. G. C.) represents the paraflinicity or non-paraflinicity of an oil, a high V. G. C. value indicating that the oil predominates in non-paraflinic components, while a low V. G. C.

value indicates relatively greater parafllniclty.

It may therefore be stated that the paraflinic hydrocarbons referred to herein have a relatively low V. G. C., while the non-paraflinic" constituents of petroleum'are characterized by relatively 5 high V. G. C.

It has been previously found that the described parafiinic hydrocarbons may be separated from the non-parafiinic components of the petroleum fractions by the use of solvents which dissolve the above mentioned non-parafilnic hydrocarbons I but exhibit only a very limited solvent power upon the desirable paramnic hydrocarbons. A number of such solvents having the above described selective solvent characteristics have been found. For example, it has been previously shown that such materials as chloraniline, chlorophenol, cresol, dichlorethyl ether, liquid sulphur dioxide, alone or commingled with benzene, or mixtures thereof, have highly selective solvent powers for the non-paraflinic hydrocarbons. Thus, when these solvents are commingled with a petroleum or a fraction thereof, under proper conditions or temperatures, the undesirable nonparaffinic hydrocarbons pass into solution in said solvents to a greater or lesser extent, leaving a substantial proportion of the desirable parafiinic hydrocarbons undissolved. When relatively heavy solvents are employed for the above described solvent extraction, the solution of the undesirable hydrocarbons in the solvent settles to the bottom of the container forming an extract phase, while the relatively light paraflinic hydrocarbons rise to the top of the vessel and constitute a raflinate phase. These phases may then be readily separated as by ordinary decantation.

It is also known that nitrogen bases, which constitute one of the components or fractions of a petroleum oil, consist of a mixture of bases, some of which are highly aromatic in character while others are in a reduced state. This second group of nitrogen bases may be classified and termed as the naphthenic or non-aromatic nitrogen bases. One of the primary uses of these nitrogen bases is the use thereof as an intermediate in the manufacture of dye substances and of other synthetic materials. However, in order to utilize these nitrogen bases most efiiciently as such intermediates, it is highly desirable to have the crude material, consisting of the nitrogen bases of the aromatic and non-aromatic type, be segregated and separated into fractions according to the chemical nature of the bases. In other words the nitrogen bases may be best utilized when they are first separated into two groups, one containing the highly aromatic nitrogen bases, while the other includes the naphthenic or non-aromatic bases. It has been discovered that this separation of nitrogen bases may also be produced by the use of selective solvents, which preferentially dissolve most of the bases of one of said groups, leaving the other group substantially undissolved.

One of the main disadvantagesin using any of the above described solvents for the separation of petroleum fractions into their components (both petroleum oils into their parafiinic and non-paraflinic constituents. and nitrogen bases into their aromatic and non-aromatic components) resides in the fact that the high solvent power of these solvents necessitates very low operating temperatures to produce the necessary phase separation. Thus, when a solvent characterized by high solvent power is employed under normal operating temperatures and pressures, it dissolves, when treating lubricating oil stock, not only the non-parailinic constituents but also some or even all of the parafiinic fractions. Similarly a solvent having a high solvent power at normal operating temperatures will dissolve all of the nitrogen bases. The temperature at which such a condition occurs, i. e. when the solvent dissolves all of the components of a petroleum fraction, is termed herein as the miscibility temperature.

Solvents which have a miscibility temperature close to or lower than the temperature at which extraction operations are to be carried out are termed "solvents of a high solvent power". O bviously such miscibility temperature varies with the type of petroleum fraction treated and character of selective solvents employed. Thus, the miscibility temperature of a mixture containing two volumes of dichlorethylether to one volume of mixed nitrogen bases was found to be below 0 F., while the miscibility temperature of equal volumes of dewaxed S. A. E. 20 distillate of Santa Fe Springs crude oil and of orthochloroaniline is 54 F. In view of these low miscibility temperatures of solvents having a high solvent power, a proper phase separation of petroleum fractions treated with these solvents cannot be obtained at normal temperatures. It is therefore necessary to operate at lower temperatures and in most cases to employ artificial cooling to bring the temperature below atmospheric. Obviously, such lowering of operating temperatures is cumbersome and uneconomical.

It is therefore an object of the present invention to provide a process whereby petroleum oils and petroleum fractions may be rapidly and economically separated into their components. It is a further object of the present invention whereby the separation of the mixed petroleum fractions may be carried out without the necessity of lowering the temperature of the mixture being treated. It is a still further object of the present invention to provide a process whereby the separation of mixed petroleum fractions into their constituent components may be carried out rapidly, efllciently and economically at substantially normal temperatures.

It has now been discovered that the low miscibility point of solvents having a high solvent power may be raised by the use of a modifying agent or agents soluble in the solvent but having a low solvent power for the oil to be treated. Such a raising of the miscibility temperature of the active solvent permits extraction of petroleum fractions at high temperatures as compared to the temperatures necessary for proper phase separation when the same petroleum fractions are treated with the solvent alone. This modifying agent may be denominated an "anti-solvent, and may be defined as a material which tends to prevent the solution in the solvent of those hydrocarbon fractions which, except for the presonce of the anti-solvent, would be dissolved in the extract phase during the extraction of the petroleum fraction with a selective solvent having a high solvent power. In view of the above stated low solvent power of the anti-solvent for the petroleum fractions treated, their miscibility temperatures are quite high. Therefore the ad dition of such anti-solvents to the active solvent raises the miscibility temperature of the mixture, thus permitting the obtaining of phase separation at higher temperatures. Aside from this rise in the miscibility temperature, the addition of the modifying agent to the selective solvent may be stated to have the effect of decreasing the solvent power thereof towards a part of the constituents of the petroleum fraction being treated. This is due to the fact that the extremely low miscibility of the modifying agent or anti-solvent with the oil being treated in effect decreases the solvent power of the selective solvent.

It has been further discovered that organic amides such as acetamide, diacetamide, triacetamide, propionamide, benzamide, carbamide, acetanilide, acet-B-naphthalide, acet-O-toluidide, or the like, may be used as the anti-solvents employed to modify the action of the selective solvents. Therefore amides of fatty acids, of dibasic acids and of aromatic acids may be employed as such modifying agents or anti-solvents. In view of the extremely low miscibility temperature of the anti-solvent, the quantity of such anti-solvent necessary to raise the miscibility temperature of the solvent employed is comparatively small. Thus a few percent of such anti-solvent, when added to a mixture of a petroleum fraction and of a solvent having a high solvent power, are sufficient to permit proper phase separation at normal temperatures.

The invention may therefore be broadly stated as residing in a process of separation of petroleum oils and/or petroleum fractions into their constituent components by means of selective solvents having a high solvent power, wherein a modifying agent is added to and commingled with the mixture for the purpose of aiding phase separation. The invention further resides in the addition of small quantities of modifying agents for the purpose of elevating the possible temperature range I of solvent extraction operations due to the elevation of the temperature of miscibility of the mixture. The invention still further resides in the use as such anti-solvents or solvent modifiers of organic amides, and more particularly of the amides of fatty acids, of dibasic acids, and/or of aromatic acids.

These anti-solvents may be used alone or in combination with each other and may be commingled with the selective solvent prior to the extraction of the petroleum fraction-with this mixture. If so desired, the petroleum, or a. fraction thereof, may be extracted with the selective solvent in the presence of little or no anti-solvent,

and after the separation of the raffinate and extract phase produced by this extraction, the antisolvent may be added to the extract phase to cause a further phase separation. The intermediate raflinate thus produced comprises petroleum fractions of a quality superior to those remaining dissolved in the extract phase. Also, this intermediate rafiinate thus rejected by the addition of an anti-solvent to the extract phase obtained from an extraction of an oil with a selective solvent, is characterized by a viscosity gravity constant intermediate between the viscosity gravity constants of the first rafiinate and extract produced by the second phase extraction.

As an example of the operation of the present invention, a mixture of nitrogen bases, as isolated from petroleum fractions, and containing bases which are highly aromatic in character as well as those in a reduced state, to wit: non-aromatic bases, were commingled in a ratio of 1:2 with dichlorethyl ether. This mixture as stated above was found to be completely miscible even at 0 F. To obtain a proper phase separation between the aromatic and non-aromatic nitrogen bases, a solvent containing 32 grams of acetamide per 100 ml. of dichlorethyl ether was substituted for the latter. The miscibility temperature of this mixture, when comminglecl in the proportion of two volumes of this mixture to one volume of nitrogen bases, was found to be 188 F.

It is therefore obvious that phase separation was obtainable at any temperature below the miscibility temperature, the proper operating temperature being determined depending on the purity of the aromatic or non-aromatic nitrogen bases desired. As another example, a mixture containing 16 grams of acetamide per 100 ml. of dichlorethyl ether was commingled with a mixture of nitrogen bases. It was found that the miscibility temperature, when the above described ratios were used, was 148 F. It is therefore obvious that the addition of 10 to 15% of acetamide to a solvent of the dichlorethyl ether type may produce proper phase separation to separate nitrogen bases into aromatic and non-aromatic bases, the operating temperature being governed by the. miscibility temperature between the solvent-anti-solvent mixture and the bases, as well as by the desired purity of the rafimate phase.

The following examples relate to the separation of petroleum oils into their parafiinic and non-paraffinic constituents: An oil having a viscosity gravity constant of 0.855 was commingled with low boiling cresylic acid in the ratio of two volumes of said acid to one volume of the oil. The miscibility temperature of the mixture was found to be 75 F. The temperature of the mixture was then increased to about 103 F., or about 28 F. above the miscibility temperature, and 7.5 grams of acetamide per 100 ml. of solvent were introduced into the mixture. This addition of the acetamide resulted in phase separation, the raffinate phase constituting substantially 20% of the total volume of the mixture. It is thus seen that the presence of the acetamide in effect raises the miscibility temperature of the oil solvent mixture. It is therefore possible to increase the temperature at which the solvent extraction takes place and still obtain a rafiinate characterized by a high viscosity gravity constant and an extract which contains less paraffinic fractions than would be present in said extract were it not for the use of the amide.

In order to further exemplify the application of the present invention to the separation of oils into their parafiinic and non-parafiinic constituents, an oil having a viscosity gravity constant of 0.840 was extracted with dichlorethyl ether, with and without the addition thereto of small quantities of acetamide. It is to be noted that a mixture containing the above oil and dichlorethyl ether in the proportion of 1:1 has a miscibility temperature of about 130 to 134 F. Three series of experiments were made: One in which the solvent was used alone; another in which 3 grams of acetamide per 100 ml. dichlorethyl ether was employed; and the third in which the content of acetamide was raised to 6 grams per 100 ml. of solvent. In each series the oil was commingled with an equal volume of solvent and, after the removal of the extract, an intermediate raifinate was extracted from said extract phase by means of solvent as calculated from the volume of the extract. In each series the first extraction was carried out at a temperature of 117 F., while the second extraction was conducted at 122 F. The final raffinate resulting from the treatment of the above 011 by means of dichlorethyl ether alone constituted 62.3% of the oil treated and had a viscosity gravity constant of 0.831. The final raflinate produced by an extraction with the solvent having 3 grams of anti-solvent per 100 ml. of solvent constituted 74.9% and had the same viscosity gravity constant, to wit: 0.831; while the extraction with the mixture containing the greatest amount of acetamide increased the rafiinate yield to 79% of the original stock, said ramnate having a viscosity gravity constant of 0.831. The viscosity indices of these three raflinates were 80,82 and 83, respectively, thus indicating no impairment in the V. I. but a possible improvement.

The above results indicate clearly the powerful modifying action of acetamide when used in connection with a powerful solvent of the type of dichlorethyl ether. In addition to the improved yield of rafiinate, it has been also found that the time required for the phase separation is considerably decreased when an anti-solvent is employed.

As a further example an oil having a viscosity gravity constant of 0.881 and a. viscosity index of 20 was extracted by means of chloraniline containing 20 grams of acetanilide per 100 m1. of solvent, the extraction being conducted at 100 F. with equal volumes of oil to be treated and modified solvent mixture. The miscibility temperature of a mixture consisting of equal volumes of the above oil and of chloraniline alone was found to be 54 F., while the above addition of 20 grams of acetanilide per 100 ml. of solvent increased the said miscibility temperature to 117 F. The raifinate produced by this extraction cone stit-uted 43.7% by volume of the original oil treated, said raflinate having a viscosity gravity constant of 0.853, with a 61 viscosity index. The extract had a V. G. C. of 0.908.

As a still further exemplification of the present invention, and to show the increased selectivity with the use of modifying agents, a dewaxed Santa Fe Springs oil extracted with liquid sulphur dioxide, and having an S. A. E. of 20 and a V. G. C. of 0.833, was intimately commingled with an equal volume of dichlorethyl ether. The miscibility temperature of this mixture was found to be 127 F. At a temperature of 115 F. a phase separation occurred, the extract phase constituting 42.45% of the mixture. After removal of the raflinate phase, 4 grams of acetamide per 100 ml. of extract were added and thoroughly commingled therewith at 115 F. This addition of acetamide produced a second phase separation. The raffinate phase constituted 12.2% of the first extract.

The foregoing exemplary description of my invention is not to be considered as limiting, since many variations may be made within the scope of the following claims by those skilled in the art without departing from the spirit thereof.

I claim:

' 1. In a process for separation of nitrogen bases into groups having highly aromatic and nonaromatic characteristics, the step of selectively extracting said bases with a selective solvent and an acetamide, said extraction being conducted at a temperature above the miscibility temperature of the base-solvent mixture.

2. In a process according to claim 1, wherein the acetamide is used in a proportion of about 10% to 15% of the solvent employed for the extraction.

3. A process for separation of nitrogen bases into their aromatic and non-aromatic constituents, which comprises extracting said bases with a mixture of dichlorethyl ether and acetamide.

4. A process according to claim 3 wherein the extraction is carried out at a temperature above the miscibility temperature .of the ether-base mixture.

5. A process according to claim 3, wherein the acetamide constitutes about 10% to 15% of the volume of dichlorethyl ether used.

6. A process for the separation of petroleum oils into their paraflinic and. non-paraflinic constituents which comprises extracting said. oil with a selective solvent, separating a rafiinate phase substantially insoluble in said solvent from the extract phase, and rejecting an intermediate raflinate from said extract phase by commingling said extract phase with an acetamide.

7. In a process for the separation of petroleum oils into their parafiinic and non-parafiinio constituents, the step of, raising the miscibility temperature of the solvent-oil mixture by the addition thereto of an acetamide, thereby permitting phase separation at higher temperatures.

8. A process for the separation of petroleum oils into their paraffinic and non-paraffinic constituents which comprises extracting said petroleum oils with a selective solvent and a small percentage of acetanilide, said extraction being carried out at normal temperatures and above the miscibility temperature of the oil-solvent mixture.

9. A process according to claim 8 wherein the extraction is carried out by means of chloraniline, the selectivity and miscibility temperature of which is modified by the addition of said acetanilide.

10. Ina process for separation of petroleum oils into their paraflinic and non-paraffinic fractions by extraction with selective solvents having a high selective power, the steps of commingling therewith an amide for the purpose of modifying the miscibility temperature, said amide being selected from the class consisting of acetamide, propionamide, benzamide, acetanilide, acet-B-naphthalide, and acet-O-toluidide.

11. A process for the separation of petroleum fractions into their constituent components by means of a selective solvent, the step of raising the miscibility temperature of the'solvent-petroleum mixture by addition thereto of an organic amide consisting of acetamide thereby permitting phase separation at higher temperatures.

12. A'process according to claim 11 wherein the organic amide is a substituted acetamide.

13. A process according to claim 11 wherein the organic amide is acetanilide.

14. In a process for the separation of petroleum into fractions by means of solvent extrac tion with a selective solvent, the step of raising the miscibility temperature of the solvent-petrolemn mixture by the incorporation therein of a. small quantity of an organic amide selected from the class consisting of acetamide, diacetamide, triacetamide, propionamide, carbamide, benzamide, acetanilide, acet-B-naphthalide and acet- O-toluidide.

15. A process for the separation of mineral oil into fractions which comprises commingling said oil with an organic amide selected from the class consisting of acetamide, diacetamide, triacetamide, propionamide, carbamide, benzamide,

acetanilide, acet-B-naphthalide and acet-O-tolu-' idide and thereby forming a rafiinate phase and an extract phase, said raflinate phase comprising the more paraffinic oil fractions of the oil and said extract phase comprising the bulk of the organic amide and dissolved non-parafiinio fractions of the oil, and separating said phases.

CHARLES DOUGLAS BARNES.