US2229209A - Hydrocarbon oil treatment - Google Patents

Description

Patented Jan. 21, 1941 UNITED STATES PATENT OFFICE HYDROCARBON OIL TREATMENT Application August 19, 1938, Serial No. 225,673

8 Claims.

The present invention relates to the separation of hydrocarbon oils of relatively short boiling range and containing parafiinic and naphthenic constituents into fractions respectively richer in such constituents by shortpath distillation at very low pressures. By short path distillation is meant the vaporization of oil molecules from a film of liquid oil at pressures of less than substantially 100 microns and the condensation of the vapors by contact with a condensing surface in close proximity to the vaporizing surface, the distance between the vaporizing and condensing surfaces being relatively short and preferably of the order of the mean free path of the vaporized oil molecules.

A principal object of this invention is the separation of a hydrocarbon oil of relatively short boiling range and containing paraffinic and naphthenic constituents into a plurality of fractions at least one of which is more parafiinic than the original oil and at least one of which is more naphthenic than said oil. The more parafiinic fraction or fractions may comprise one or more distillates or the distillation residue, 1 while the more naphthenic fraction or fractions invariably comprise one or more distillates first vaporized from the oil.

Briefly, my process comprises producing by distillation, for example, by means of a conventional pipe still and fractionatirg column, a viscous oil fraction having a relatively short boiling range, i. e., of less than substantially 300 F. (assay distillation over point to 90% point at m. m.) and then redistilling said oil fraction at a pressure of less than substantially 100 microns to separate such oil into fractions respectively more paraifinic and more naphthenic than said oil.

It is recognized in the art that mineral oils, 401 such as petroleum, comprise essentially a mixture of hydrocarbons of various groups or homologous series of compounds, such for example,

as parafiins of the general formula CnH2n+2, olefines of the general formula CnHZn, hydroaromatics and polymethylenes of the same empirical formula, and various other series of compounds of chain and/or ring structures in which the hydrogen to carbon ratio is less than in the foregoing series. A large number of individual compounds of each series and of differing boiling points are present in petroleum,

The various types'of crude petroleum, which are generally classified into three groups, namely, parafiinic base, naphthem'c or asphaltic base, and mixed base, contain the various series of hydrocarbons mentioned heretofore in different proportions. For example, in the paraffinic base crude oils, such as those obtained from the oil fields of Pennsylvania, there is a relatively high proportion of hydrocarbons having a chain structure and a high hydrogen to carbon ratio, whereas in the naphthenic or asphaltic base crude oils, there is a relatively large proportion of hydrocarbons having ring structures and a low hydrogen to carbon ratio. Mixed base crude oils, such as are obtained from the Mid-Continent oil fields, contain hydrocarbons in proportions intermediate between these two extremes.

The paraffin base oils and their distillates are said to be more paraffinic than the mixed base oils and their distillates and these in turn are more parafilnic than the naphthene base oils and their distillates. Conversely the naphthene base oils are more naphthenic than the mixed base oils and these in turn more naphthenic than the parafiin base oils. The usual criteria of the degree of paraffinicity or naphthenicity of an oil are the viscosity-gravity constant and the viscosity index. The viscositygravity constantis a constant relating viscosity and specific gravity and is described in an article entitled The viscosity-gravity constant of petroleum lubricating oils by J. B. Hill and H. B. Coates which will be found in vol. 20, page 641 et seq., of Industrial and Engineering Chemistry. Viscous .oils resulting from the conventional distillation of Pennsylvania type crudes have viscosity-gravity constants ranging from about .805 to about .828 and in most instances are below .820. Those resulting from the distillation of Mid-Continent crudes have viscosity-gravity constants ranging from about .835 to about .855, Whereas those from naphthenic crudes are generally higher than .860. The viscosity index is a coefficient based on the change of viscosity with temperature and is described by Dean and Davis in vol. 36, page 618 of Chemical and Metallurgical Engineering. The more parafiinic oils are characterized by low viscosity-gravity constants and high viscosity indices, whereas the.

more naphthenic oils are characterized by higher viscosity-gravity constants and lower viscosity indices.

. In the art of distillation of viscous mineral oils as heretofore practiced, the oils were separated into fractions of progressively decreasing volatility, and increasing viscosity and specific gravity. The oil fractions so separated did not differ as between themselves with respect to the types of hydrocarbons present, the parafiin base crudes yielding a series of parafiinic fractions of different viscosities and the naphthenic base crudes yielding a corresponding series of naphthenic fractions of different viscosities. In other words, distillation at atmospheric pressure or at commercially available pressures of the order of 5-10 mm. produced fractions of different molecular weights, boiling ranges, viscosities, and gravities, but such fractions exhibited no substantial change in ratio of the various types of hydrocarbons Comprising said fractions, i. e., the ratio of paraffins to naphthenes did not vary to substantial extent as between the fractions.

I have found, however, that by means of short-path distillation conducted at pressures of less than substantially 100 microns, and preferably at pressures of less than 50 microns, I am able to separate a hydrocarbon oil having a relatively short boiling range and containing paraffinic and naphthenic constituents into fractions respectively richer in parafiinic and naphthenic constituents. The hydrocarbon oils to be distilled in accordance with my invention are characterized in having a boiling or distillation range of less than substantially 300 F. at 10 m. m. pressure, and preferably of the order of 200 F. or less. While pressures of from about 50 to about 100 microns will permit a satisfactory distillation separation of many hydrocarbon oils, I prefer to employ pressures of less than 50 microps, for example, of the order of 1 to 20 microns, particularly in the distillation of the very high boiling oils.

It is well-known that viscous hydrocarbon oils, such as those within the lubricating oil range, comprise a complex mixture of hydrocarbons including hydrocarbons of the paraffinic type and hydrocarbons of the naphthenic type, many of which have substantially the same boiling point at atmospheric pressure. Separation of such hydrocarbon oils into fractions differing in chemical composition, i. e., fractions more paraifinic and more naphthenic than the initial oil, cannot be effected by conventional distillation at atmospheric pressure or at reduced pressures of the order of 5-10 m. m. which are now commercially available, since the values of the temperature coeflicient of the vapor pressure of the paraffinic and naphthenic constituents are not significantly different at atmospheric pressure or reduced pressures of the order of 5-10 m. m. Heretofore the only practical method of separating oils into parafiinic and naphthenic oil fractions has been selective solvent extraction with solvents having preferential solvent power for naphthenic oil constituents.

However, I have found that even complex, viscous hydrocarbon oils, and particularly those having a relatively short boiling range, may be separated into fractions respectively more parafiinic and more naphthenic by distillation at pressures such that the values of the temperature coefficient of the vapor pressure of the paraffinic and naphthenic hydrocarbons are substantially different. By reason of this change in the relative partial pressures of the paraffinic and naphthenic constituents at very low pressures, i e., less than about 100 microns, I am able to effectively separate a relatively closeboiling oil into fractions of different chemical types, e. g., fractions respectively richer in parafiinic and naphthenic constituents. By operating at pressures of less than substantially 100 microns, and preferably at pressures of less than 50 microns, the partial pressure of the naphthenic constituents is much greater than that of the paraflinic constituents and separation by distillation may be effected, although the partial pressures of both may be substantially the same at atmospheric pressure.

Short-path or high vacuum distillation apparatus suitable for carrying out my distillation separation of a viscous mineral oil into at least one fraction more paraifinic than the initial oil and at least one fraction more naphthenic than said initial oil is shown in the accompanying drawing.

Referring to the drawing, hydrocarbon oil having a relatively short boiling range, 1. e., less than substantially 300 F., is introduced through valve-controlled line I into a conventional electrically-heated degassing unit 2 wherein the oil is heated to a temperature, for example, 175 F. to 300 F. under a pressure of the order of 2 m. m. to 15 m. m. in order to remove the major portion of the dissolved gases and moisture contained in the oil. The partially degassed and dehydrated oil is then passed from the first degassing unit by means of line 3 into a second unit 4 operating within substantially the same temperature range as unit I but at a reduced pressure of, for example, 50 to 150 microns. In the unit 4 traces of dissolved gas, as Well as a small amount, i. e., usually less than 1%, of the lowest boiling components of the charge oil is removed. The degassed oil is then introduced by means of line 5 into an electrically heated heating unit 6 operating at substantially the same reduced pressure and at the same or slightly higher temperature than that employed in the degassing unit 4. The heating unit 6 is utilized primarily for maintaining the oil at the desired temperature prior to its introduction into the short-path distillation apparatus. Reduced pressure is maintained in the degassing units 2 and 4, and the heating unit 6, by means of valve-controlled lines I, 8 and 9, respectively, which are connected to a conventional evacuating system (not shown).

The heated charge oil from the heating unit 6 is introduced, by means of valve-controlled line I0, upon the upper closed end of a tubular member II constituting the vaporizer of the distillation apparatus. The tubular member II is heated internally by suitable means, for example, electrically heated resistance wire I2, and such member is provided externally with a spiral member I3 for effecting a uniform distribution of the oil over'the surface of the tubular member II and to increase the surface of such vaporizing member. Since the spiral member I3 is preferably snugly wound about the tubular member II, a portion of the oil introduced at the upper end of member I I flows downwardly along the spiral while the remainder flows downwardly over the surface of the tubular member II between the turns of the spiral member I3. Surrounding the tubular member I I is a jacket I4 provided with a plurality of gutters I5, each connected by means of a valve-controlled line I6 to a receiver I 1. Each of the receivers I1 is provided with a valve-controlled line I8 connected to a suitable evacuating means (not shown), and with a valve-controlled drawoff line I9. Surrounding the jacket I4 is a second jacket 20 through which may be circulated a cooling medium such as air, gas, water or other cooling agent. Jacket I4 is spaced from the tubular vaporizing member II only a relatively short distance, i. e., of the order of 2 inches or less, and constitutes the condensing surface upon which the vaporized oil or distillate is condensed. The jacket I4 is provided at its upper end with a line 2I connected with a freeze-out trap 22, which, in turn, is connected to an evacuating means (not shown) by line 23. The freeze-out trap 22 comprises simply a double- Walled vessel, the inner chamber of which is filled with a refrigerant such as liquefied nitrogen or a mixture of acetone and solidified carbon dioxide, the upper surface of the refrigerant in the chamber being shown by the dotted line. 'Any volatile'materials passingfrom the top of the distillation column through line 21 are'condensed upon the outer surface of the inner chamber and may be withdrawn, when necessary, from the bottom of the trap by means of valve 24. Similarly, if a mercury vapor pump is employed as the evacuating means, such trap functions to condense mercury vapors which may diffuse through line 23 and prevents same from entering the distillation column. During operation of the distillation apparatus, a reduced pressure of less than substantially microns, and preferably less than 50 microns, is maintained within the jacket 14 and the receivers 11.

The oil, in passing downwardly over the heated tubular member H is brought to a vaporizing. temperature, the more volatile components thereof being vaporized in the upper section of the distillation apparatus, and the progressively. less volatile components in the successively lower sections. The vapors, upon condensation upon the walls of jacket I4, form distillate fractions which are collected by the gutters l5 and withdrawn therefrom by means of valve-controlled line I6 into the evacuated receivers l1. While,

in the accompanying drawing, only four sets of gutters and receivers are provided for collecting.

and removing distillate fractions, a greater or lesser number may be employed. Each gutter is connected with two receivers in order that one may be emptied while the other is being filled, thus providing a continuous distillation process. The unvaporized portion of the oil, upon reaching the lower end of the tubular member I I, is withdrawn from the bottom of the jacket 14 by means of valve-controlled lines l6 into receivers I1 evacuated by suitable evacuating means connected to valve-controlled lines 18, and may be removed therefrom, when necessary, through valvecontrolled lines l9.

My invention may be further illustrated by the following examples, which, however, are not to be construed as limiting the scope thereof. A variety of viscous hydrocarbon oils having boiling ranges of less than substantially 300 F. at 10 m. m. pressure were distilled in a short-path distillation apparatus similar to that above described, and the properties of the initial oils and the products of distillation thereof are given in the following tables.

Distillates Stock gfi ggg P roperties Charge Btms.

Cut 1 Cut 2 Cut 3 Cut 4 Cut 5 Vacuum distillate from Pressure 4.1v mi- Vol. percent yield 100.0 18.3 17.8 12.5 8.9 8.0 34. 5 East Texas residuum. crons. PI grav degrees 20. 6 18. 3 19. 9 21. 0 21.7 21. 7 21.6 Boiling range (10 mm.) Max. dist. temp. SU via/ F... seconds 689 403 550 571 590 650 1223 500-700 F. 392 F. SU via/210 F 100 70 83 89 93 100 159 Via-gray. const. 0. 861 0. 885 0. 866 0. 860 0. 854 0. 853 0. 844 Via-index... 31 14 4 25 43 47 71 O. D. color 661 248 314 387 1799 I I Distillates Y i Stock gg gggg Properties Charge Btms.

Cut 1 Cut 2 Cut 3 Cut 4 Cut 5 Distillate from mixture Pressure 2.9 mi- Vol. percent yield 100. 0 30. 9 23.8 13. 7 8. 7 6. 7 16. l of East Texas and Vencrons. PI grav degrees 20. 7 18; 4 20. 1 21. 6 22.8 23. 6 23. 2 ezuela crudes. SU via/130 F "seconds" 365 278 377 383 378 386 573 Boiling range (10 mm.) Max. dist. temp.

445615 F. 326 F. SU via/210 F do 69 59 69 72 79 95 Vis.-grav. const 0. 868 0. 892 0. 874 0. 861 0. 851 0. 842 0. 842 Vis.-index 8 -23 -6 20 38 66 58 O. D. color 372 29 42 56 70 84 2640 Distillates Stock gi gggg Properties Charge Btms.

Cut 1 Cut 2 Cut 3 Cut 4 Cut 5 Nitrobenzene rafi'inate oil Pressure 3.0 mi-' V01. percent yield 100.0 27. 6 22. 5 13.8 9. 6 7. 2 20. 2 from East Texas-Vencrons. API grav -.degrees. 28.0 26.8 27.6 29. 8 29. 2 29. 4 29. 3 ezuela distillate. Su vis./130 F- -seconds. 199 156 191 194 206 220 305 Boiling range (10 mm.) Max. dist. temp. SU via/210 F" do 59 51 56 58 60 61 72 470662 F. 327 F. Vis.-grav. eonst. 0. 818 0.822 0.822 0.805 0.808 0. 806 0.803 Via-index 87 55 65 86 88 85 88 D n Distillates 7 Stock. fi gg g Properties Charge 7 Btms.

Cut 1 Cut 2 Cut 3 Cut 4 Cut 5 Nitrobenzene extract oil Pressure 2.3 mi- Vol. percent yield 100.0 30.6 22.0 13.9 8.3 7.7 17.1 from East Texas-Vencrons. API gravity degrees 14. 9 l3. 6 14.3 14.9 15.4 15.9 15. 3 ezuela distillate. SU vis/210 F seconds 93 67 86 99 106 112 188 Boiling range (10 mm.) Max. dist. temp. Via-gray. const 0.911 0. 930 0. 918 0.910 0. 904 0.898 0. 895

Distillates Stock 333 3 528? Properties Charge Btrns.

Cut 1 Cut 2 Cut 3 Cut 4 Cut 5 White oil from Russian Pressure 2.6 mi- Vol. percent yield 100.0 42.4 24.5 8.5 4.6 3.3 16.3 crude. crons. API gray degrees. 27.9 28.0 26. 2 27.4 28.7 29. 1 .29. 3 Boiling range (10 mm.) Max. dist. temp. SU via/100 F. seconds.. 350 192 576 610 590 615 886 4 0 F. 325 F. SU via/210 F do 53 45 59 63 64 66 S2 ViS.-grav. const 0. 822 0. 835 0.830 0.820 0. 810 0. 806 0. 800 Via-index 78 69 53' 67 78 82 95 It will be seen, from the above examples, that in accordance with my invention I am able to separate hydrocarbon oils having a relatively short boiling range into fractions relatively more paraffinic and more naphthenic, respectively, than the initial oil. In the above examples the 1st or the 1st and 2nd distillate fractions are more naphthenic than the initial oil, whereas'the succeeding fractions and residue or bottoms are more parafiinic than the initial oil. This is clearly evident from a comparison of the viscositygravity constants of the initial oil and the various distillate fractions and residue, the 1st and 2nd distillate fractions having a higher viscositygravity constant than the initial oil, and the succeeding fractions and residue having lower'viscosity-gravity constants than said initial oil. While, in the above examples, five distillate fractions and a residue were obtained, the distillation may be carried out in such a manner as to yield a greater or lesser number of fractions, and the fractions may be blended with one another as desired. Or the initial oil may be separated by short-path distillation into only one distillate fraction more naphthenic than the initial oil and a residue which is more parafiinic than said initial oil. While I prefer to effect short-path distillation in a continuous distillation system, I may also carry out such distillation in a batch system of suitable design. Furthermore, the initial oil or the distillate fractions or the residue may be subjected to any desired refinery treatment such as solvent extraction, dewaxing, fullers earth or other adsorbent treatment, acid treatment or other chemical treatment.

In another aspect of my invention, the distillate or residue produced by my short-path distillation of a relatively close-cut hydrocarbon oil may be redistilled at low pressure to effect a further separation of parafilnic and naphthenic oil components. For example, a crude petroleum oil may be distilled at atmospheric or reduced pressure to yield an oil fraction having a boiling range of less than substantially 300 R; such fraction may then be subjected to short-path distillation at a pressure of, for example, microns, to produce one or more distillate fractions and a residue; and finally one or more of the fractions or residue so produced may be redistilled at a pressure of, for example, 5 microns, whereby a further separation of components of the fraction or residue may be obtained.

Or, alternatively, one or more fractions or the residue from the first mentioned short-path distillation operation may be redistilled at a higher pressure, for example, of from about 1 to 10 mm. or higher. In the latter case the first distillates produced at pressures of the order of l to 10 mm. will be more parafiinic than the oil charged, and will tend to become less paraffmic asthe distillation progresses, the final distillation residue being, in general, more naphthenic than the oil charged.

What I claim is:

1. The method of separating hydrocarbon oil containing paraffinic and naphthenic constituents into a plurality of fractions of progressively increasing paraffinicity, which comprises producing by distillation a viscous hydrocarbon oil having a boiling range of less than substantially 300 F. at 10 :m. m. pressure, heating said oil at a pressure not substantially in excess of 100 microns to vaporize therefrom oil constituents of progressively increasing par'aifinicity, and condensing the vaporized constituents to produce liquid oil fractions of progressively increasing paraffinicity.

2. The method of separating hydrocarbon oil containing paraffinic and naphthenic constituents into a plurality of fractions of progressively increasing paraflinicity, which comprises producing by distillation a viscous hydrocarbon oil having a boiling range of less than substantially 300 F. at 10 m. in. pressure, heating said oil at a pressure not substantially in excess of 100 microns to VaporiZe therefrom oil constituents of progressively increasing parafiinicity, and condensing such constituents substantially immediately upon vaporization to produce liquid oil fractions of progressively increasing parafinicity.

3. The method of claim 2, wherein the pressure during vaporization of the oil is not substantially in excess of 50 microns.

4. The method of separating hydrocarbon oil having a boiling range of less than substantially 300 F. at 10 In. m. pressure and containing paraflinic and naphthenic constituents into distillate fractions at least one of which is more paraflinic and at least one of which is more naphthenic than said hydrocarbon oil, which comprises heating said oil at a pressure not substantially in excess of 100 microns to vaporize therefrom paraffinic and naphthenic oil constituents, and condensing the vaporized constituents into fractions respectively more parafiinic and more naphthenic than said hydrocarbon oil.

5. The method of separating hydrocarbon oil having a boiling range of less than substantially 300 F. at 10 m. m. pressure and containing paraifinic and naphthenic constituents into a distillate fraction more naphthenic than said hydrocarbon oil and-a residue more parafiinic than said hydrocarbon oil, which comprises vaporizing from said oil, at a pressure not substantially in excess of 100 microns, the more naphthenic components thereof, and condensing said components out of contact with the unvaporized, more paraffinic residual oil.

6. The method of separating viscous hydrocarbon oil having a boiling range of less than substantially 300 F. at 10 m. m. pressure and containing parafiinic and naphthenic constituents into a distillate fraction more naphthenic than said hydrocarbon oil and a residue more paraffinic than said hydrocarbon oil, which comprises heating said 011 at a pressure not substantially in excess of 100 microns whereby the boiling points of the naphthenic constituents are decreased to a substantially greater extent than those of said parafiinic constituents, vaporizing substantially greater quantities of naphthenic constituents than of parafiinic constituents, condensing the vapors substantially immediately upon vaporization and collecting the condensate to produce at least one fraction more naphthenic than the initial hydrocarbon oil and a residue more paraflinic than said initial hydrocarbon oil.

7. The method of separating hydrocarbon oil containing paraflinic and naphthenic constituents into fractions respectively richer in paraflfinic and naphthenic constituents which comprises producing by distillation a viscous hydrocarbon oil having a boiling range of less than substantially 300 F. at 10 m. in. pressure and distilling from said oil the more naphthenic constituents thereof at a pressure not substantially in excess of 100 microns.

8. In the method of separating hydrocarbon oil containing paraffinic and naphthenic constituents into fractions respectively richer in parafllnic and naphthenic constituents, the step which com prises subjecting a viscous oil having a boiling range of less than substantially 300 F. at 10 m. m. pressure and containing paraflinic and naphthenlc constituents to distillation at a pressure not substantially in excess of 100 microns.

WILLARD F. HOUGHTON.

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