|Publication number||US2146147 A|
|Publication date||Feb 7, 1939|
|Filing date||Jun 28, 1934|
|Priority date||Jun 28, 1934|
|Publication number||US 2146147 A, US 2146147A, US-A-2146147, US2146147 A, US2146147A|
|Inventors||Forrest Henry O, Keith Jr Percy C|
|Original Assignee||Standard Oil Co|
|Export Citation||BiBTeX, EndNote, RefMan|
|Referenced by (4), Classifications (7)|
|External Links: USPTO, USPTO Assignment, Espacenet|
30 HEN Q: 3 3 5 fie B 3 33 Fast 0 4 Sheets-Sheet l INVENTORS: my C. KeL't/Z my 0. F0 mC/j ATTORNEY Filed June 28, 1934 P. C. KEITH, JR El AL PROPANE SOLVENT TREATING PROCESS A 60 Lzfig of Oil, in Solvent Tende ncyz fo r'q 'ec 11 from pro c ans M "of Oil in Propane p 1801!]. JOOL/Z J SOZabILZ Feb. 7, 1939.
Feb. 7, 1939. P. c. KEITH. JR.,-ET AL 2,146,147
PROPANE SOLVENT TREATING PROCESS Filed June 28, 1934 4 Sheets-Sheet 2 noL 15.54191. zileman HiLZs Beszldaum @180 No propane I60 u sad '3 ropane used in, 8 first extraction 8100 Vllbcositg Gravity Conszfcznt (8J0?) fig/.3
NO p p With/propane? used 0.880 0890 0,900 l/c'scos L'zig Gravity (610%) INVENTORS: I Percy G KeL 292, Jr.
mg ATTORNEY 7 Feb. 7, 1939.
P. C. KEITH. JR., Er AL PROPANE SOLVENT TREATING PROCESS 4 Sheets-Sheet 3 Filed June 28, 1934- Percgg/Igeoh in [BY 1 INVENTORS:
7 ATTORNEY W M x $61 NNO Q M Qwwm wudmx fioumm m. .u. nHunHUNnun. .n 4 NM 0% m Wm Q m gQQk C m W md 9 fimwfiwwfi fit.-- L" Feb. 7, 1939. P, c. KEITH. JR;, ET AL PROPANE SOLVENT TREATING PROCESS Filed June 28, 1934 4 Sheets-Sheet 4 Patented Feb. 7 1939 UNITED STATES PROPANE-SOLVENT TREATING PROCESS Peapack, and Henry 0. J., assignors to Standard Percy 0. Keith, Jr.,
- Oil Company, Chicago, 111., a corporation of Indiana Application June 28, 1934, Serial No. 732,919
13 Claims. (01.196-13) This invention relates to improved methods and means for fractionating hydrocarbon oils by' means of solvents, and it pertains more particularly to the fractionation of lubricating oil stocks into paraflinic oils of high viscosity index and low grade naphthenic oils.
An object of our invention is to use a selective naphthenic solvent and a light hydrocarbon solvent such as propane in the most effective manner to-obtain maximum yields of paraffinic oils of all viscosities. We have discovered that when selective naphthenic solvents are employed without the use of propane and the like, a largeamount of low viscosity paraflinic oils is lost in the extract or low grade oils. It' is also known that oils may be fractionated by means of propane and the like, in which case the rejected portion consists chiefly of high viscosity oils. In order to obtain the maximum yield of both low and high viscosity parafllnic oils from any given stock,
it would seem that both a selective naphthenic solvent and a light hydrocarbon solvent or the like should be used, so that one might modify and 4 supplement the other. We have found, however; that the light hydrocarbon exerts an important eilect upon the miscibility temperature, and that in most cases it is impractical to carry out the object of our invention is to provide a multi-step process wherein one step is primarily designed The invention will be more clearly understood from the following detailed description of preferred embodiments and particularly by reference to the accompanying drawings which form a part of the specification and in which:
Figure 1 is a graph showing the characteristics of selective naphthenic solvents;
Figure 2 is a graph, showing the corresponding characteristics of propane and the like;
Figure 3 is a graph showing the effect of 'solvent extraction, with and without propane, on the viscosity of the raflm'ate;
ure 4iisa similar graph showing the effect of solvents with and without propane on A. P. I. gravities .of raili'nates;
Figure 5 is a flow diagram of our process wherein high viscosity parafllnic oils are extracted in the absence of appreciable amounts ofpropane entire extraction process in the presence of both naphthenic solvent and light hydrocarbon. The
and low viscosity paraflinic oils are recovered in another step; and
Figure 6 is another modification wherein the low viscosity paraiiinic oils are extracted in the first step in the presence of propane and the high viscosity paraflinic oils are subsequently recovered either by removing propane therefrom or by changing the solvent ratio or recycling final extract or asphaltic material.
Our invention will be described as applied to the fractionation of a 155 A. P. I. Kettleman Hills residuum, but it should be understood that the invention is equally applicable to any other lubricating oil stock from Pennsylvania, Mid- Continent or coastal crudes. Our invention is applicable to distillate stocks as well as residuums andto stocks which have had preliminary acid, clay, or dewaxing treatments, as well as untreated stocks. In fact, it is applicable to any solvent extraction system for recovering mixtures of high and low viscosity rafiinates.
in our preferred examples we will discuss the use of cresylic acid and phenol as preferred solvents, but it should be understood that our invention is generic in this respect and that we may employ anyselective solvent which is known to the art. Examples of suitablesolvents include, by way oi. example (and without limitation), chlorinated phenols, ortho, meta and para cresols and mixtures thereof, coal tar and wood tar acids usually associated with phenol and/or cresol, piridine, furfural, nitrobenzene, aniline, chloraniline, benzaldehyde, benzonitrile, nitrotoluene, phenyl acetate, beta beta dichlorethyl ether, sulfur dioxide, crotonaldehyde, nitro-phenols,
' ethyl chloracetate, gylcol diacetate, methyl formate, etc., and/or mixtures of one or more of these compounds with a modifying solvent and/or with another of said compounds.
We refer to propane in this specification as an example of our hydrocarbon solvent. The propane serves the important functions of selectively rejecting the more viscous oil fractions, modifying the miscibility temperatures, and effecting phase separation and fractionation. While we describe propane as our preferred embodiment, it should be understood that we may use ethane, butane, isobutane, pentane, andhexane'with perhaps'some propylene, butylene,' etc., or mixtures ofone or more of said hydrocarbons. We prefer to use normally gaseous hydrocarbons, preferably with a vapor pressure of about that of propane. We do not limit ourselves to the use of light hydrocarbons for this purpose and we may employ any light, solvents which are equivalent to u 2 the propane in properties of selectively rejecting high viscosity oil fractions.
Theory or explanation While we do not limit ourselves to our theory,
we will describe it in order to explain the significance of the various steps of the process which will be hereinafter described.
The selectivity of naphthenic solvents employed in lubricating oil manufacture may be generally illustrated as shown in Figure 1, poor solvents being illustrated by the solid lines and good. solvents being illustrated by dotted lines. These lines are typical of the effect of molecular weight and viscosity index (hereinafter called V. I.) on solubility of' oil in any given solvents. A solvent of good selectivity is, therefore, one which tends to dissolve equally all fractions of a given vis cosity index. If We assume extraction to be carried out under conditions represented by the line A-B, we will have everything to the left of A-B as a raffinate and everything to the right of A-B (the shaded area) as an extract. If a perfeet solvent could bev employed, there would be no oil in the extract of higher V. I. than 100 and there would be no oil in the rafilnate of lower V. I than 100.
' The best available solvents tend to dissolve low viscosity paraifinic oils in preference to high viscosity oils of the same parafiinicity. C-D may represent a good solvent employed to give a 100 V. I. oil,--all material to the right of line CD being lower than 100 V. I. and all material to the left being higher than 100 V. I. In this case the fractionation into raffinate and extract will still be along line A-B so that the extract (shaded area) will contain low molecular weight oils of higher V. I.-than 100, as represented by triangle A00. The average V. I. of the rafl'lnate from O to A is higher than 100 because it averages from 100 to about 110. On the other hand, the average V. I. of the rainnate from to B is lower than 100 because this portion of the rainnate contains material as low as'90 V. I. as indicated by triangle ODB. The average V. I. from A to B is 100, but it will be seen that valuable low molecular weight parafilnic oils are lost in this extract.
Poorer solvents, as indicated by. the solid lines, are even worse in their tendency to reject valuable light oils in'the extract. Line EF marks the boundary between oils above and belowlOO V. I. in this case and line AB marks the separation of extract from raifinate. Here it will be seen that the extract (shaded area) will contain light oil of upwards of 120 V. I. (line GI-I crosses AB) and the amount of high V. I. low viscosity oil lost in the extract is represented by triangle ADE.- The remaining low viscosity oil in the raffinate-is enough higher than 100 V. I. to compensate for the high molecular weight low V. I. oil that is in the rafilnate as shown by triangle OBF.
The yield of rafllnate fromthe poor solvent is substantially the same as the yield of raffinate with the good solvent, but the distribution of components is quite different. The poorer solvent gives raflinates containing larger amounts of low V. I. high molecular weight fractions, and the poorer the solvent, the more good oil of low molecular weight is lost in the extract.
To produce the maximum obtainable yield of high V. I. oil, it is necessary to include high V. I. low molecular weight oils, which, as illustrated in Figure 1, are usually lost with the extract.
75 The importance of this phenomenon becomes (iii greater and greater as the length of the out of the oil to be treated increases and it is of major importance in treating long residue. or long distillates.
In Figure 2 we have illustrated the effect of pro- 5 pane tending to reject high molecular weight or high viscosity fractions. At normal temperatures propane precipitates asphalt completely, if no other oil is present, and further separations can be made according to molecular weight by varying conditions of temperature and pressure. Propane tends to protect the light fractions and reject the heavier ones, but only on the basis of molecular weight and not on the basis of viscosity index. Propane is not a preferentially paramnic solvent because it dissolves naphthenic oils as readily as it dissolves parafinic oils.
Figures 1 and 2 are not intended to be quantitative, but are intended to aid in understanding Figures 3 and l and explaining the invention illus- 2Q trated in Figures 5 and 6. A large number of solvent extraction tests carried out with and without propane showed that the yields of a given V. G. C. (viscosity gravity constant) are essentially the same regardless of whether or not propane is used in the extraction. Although the V. G. C.s are substantially the same with and without propane, the actual visoosities and gravities are considerably different in these two cases. In Figure 4 we have shown these differences between experiments with and without propane in comparing viscosities with V. G. C.s. Thus in treating to .83 V. G. C. the viscosity when propane is used is 92 and when propane is not used is 151.
Since the absence of propane gives yields of considerably higher viscosity oils, it would seem that they should likewise have a lower A. P. I. gravity and such is indeed the case, as illustrated in Figure 4. In treating to .83 V. G. C. with pro- 0 pane, the viscosity of the rafiinate is 92 seconds Saybolt at 210 F. and its gravity is 24.8" A. P. I.- When no propane is used, the viscosity of the rafinate is 151 seconds Saybolt at 210 F. and its gravity is 233 A. P. I. g
Since the yields of oils of a given V. G. C. are. the same from both methods of operation and since the ratioof; low viscosity oil to high viscosity. oil is much greater in one case than in the other,
it is necessary to conclude that some low viscosity high V. I. oil was lost when operating without propane and that some high viscosity high V. I. oil was lost when operating with propane. These data confirm the previous conclusion that propane tends to reject the high viscosity paraflinic oils and that single solvents tend to dissolve low viscosity fractions thereon It might at first appear from this discussion that a proper balance between propane and sol---- vent would result in the maximum yield of high V. I. oil. However, it does not seem to be feasible to balance the propane-solvent ratio for proper extraction conditions relative to V. I. and at the same time relative to miscibility and maximum yield. There are rather narrow limits of .operability fixed by miscibility temperatures line H, condenser l8 and Propane absent in first treating step First we will describe the system wherein propane is substantially absent in the first step,- that step from which the first quality raflinate is removed. Such a system is illustrated in Figure 5. The oil stock enters the first treating step III, which may be a multi-stage countercurrent extraction system, through line H either from a storage tank, from a depropanizer, or from some priorrefining step.- Solvent from tank I2 is forced by pump 3 and line l4 into the-opposite end of the first treating step. Raflinate is removedtherefrom through line l5 and introduced into solvent recovery still I6, the solvent being passed through line H and condenser l8 to storage tank l2. First quality high V. I.) parafiin oil is removed from the system through line I9.
Theextract is removed from the first treating step through line 28 and it may be passed through lines 2| and 2,2 to second treating step 23 of our extraction system. Propane from tank 24 is forced by pump 25 and line 26 into the opposite end of the second treating step, which may likewisebe a multi-stage countercurrent extraction system. Ramnate from the second treating step is withdrawn therefrom through line 21 and introduced into propane still 28. The propane is passed through pipe 29 and condenser 30 to propane storage tank 24. Depropanized oil is withdrawn through lines 3| and 32 tosecond quality lubricating oil storage tank or through lines 3| and 33 to line H or to some other part of the first treating step.
Extract from the second withdrawn through line 34 to depropanizer 35 and thence through line 36 to solvent still 31, the solvent being removed through line 38 to vapor tank I2. The final naphthenic oil is then withdrawn through lines 39 and 48 to a suitable storage system (valve 4| being closed). 1
We may recover the solvent from extract leaving the first treating step before it is introduced into the second treating step. In this case we pass the extract through line 28 directly through line 42 to solvent still 31 and we pass the solventlree extract through lines 39, 43 and 22 to the second treating step 23. The final extract from the second step is then passed through depropanizer 35 and thence through line 46 to storage. being open and the valves in lines 36 treating step may be and 39 being closed.
We have described the operation of the second treating step both in the presence and absence of solvent, but it will benoted that propane is present in both cases. We may, of course, remove a part and retain a part of the solvent in the second step. The important feature of this system is that high molecular weight high V. I. oils are recovered in the first treating step, low
. molecular weight high V. I oils are recovered in the second step and these recovered oils may either be used as a second grade lubricant or they may be recycled to the first step for increasing .the yield therein. By operating our process in two steps, we can maintain both countercurrent extraction systems at optimum temperatures and pressures without having the propane in the second step interfere with the miscibility temperatures in the first step. Theprecise operatingconditions will, of course, depend upon the oil to be treated, on the solvents employed, and on the desired end products. In this particular case we mayemploy about three volumes of phenol to one volume of oil in thefirst step and we may first treating step 45.
extract at about 125 F. In the second step we may operate at about 80 F.,and we may use about three to six volumes of propane per volume of extract from the first treating step. If no solvent is present in the second treating step, it may be necessary to heat the propane extract mixture to temperatures of 140-200 F. in order to effect phase separation and to reject the high molecular weight oils. Thus our second treating step acts as a check valve to prevent the loss of high V. 1., low molecular weight oils with the final extract.
of our invention wherein propane is present in the first treating step and wherein the second treating step is employed as a check valve to prevent the loss of high molecular weight high V. I.
oils with the final extract.
Charging stock in this case will probably come from a propane deasphalting step (not shownor from a propane dewaxing step, so that the oil is already diluted with from about one to five volumes of propane. This diluted propane-oil charging stock is introduced through line 44 to This step may be a multistage countercurrent extraction system with solvent-from storage tank 46 being introduced by pump 41 and pipe 48 at the opposite end of the system. Raflinate is removed from the first treating step through line 49 which leads to propane still 58, the propane being removed through line 5|. Depropanized raifinate is introduced by line 52 to solvent still 53, the solvent being withdrawn through line 54 and condenser 55 to storage tank 46. Thefirst grade high V. 1. oil is with drawn from the system through line 56.
Extract from. the first treating step is withdrawn through line 51 to propane still 58, the propane being withdrawn through line 59 and condenser 60 to propane tank 6|. From this tank the liquefied propane may be forced by pump 62 and line 63 to line 64 leading to a deasphalting system, line 65 leading to a dewaxing system, or line 66 leading to incoming charging stock.
Depropanized or partially depropanized extract from still 58 is withdrawn through line 61 to second treating step 68. Instead of introducing this extract into the second treating step with all of its contained solvent, we. may partially remove the solvent from this extract by passing it through line 69 into solvent still 10, the extract being returned through line 1| to the second treating step and removed solvent being returned through line 12 to solvent storage tank 46. Either naphthenic extract from line 13 or asphaltic material from line 14 or a mixture thereof is introduced through line 15 into the second treating step for recovering high molecular weight high V. I. oils from the extract from the first treating step. The parafiinic oils recovered in this second treating step are withdrawn through line 16 'andare either passed through line 11 to second grade high V. I. oil storage tank or they are returned through line 18 either to the first or one of the succeeding stages of the first treating step. I
Extract is removed from the second treating bit pane-solvent countercurrent extraction system are recovered in the second treating step where in the proportion of solvent, naphthenic: and/or asphaltic materials is maintained high enough to cause the parafinic oils to be thrown out of solution. We may use the second grade lubricating oil as such or we may return it to the first treating step, in which case our yield of high V. 1. oil will be greatly increased because of the fact that neither the high viscosity nor the low viscosity oils are permitted to escape with the final extract. The ratio of solvent to oil in the second treating step of Figure 6 should be about two or three to one and, as hereinabove pointed out, the effect of this ratio can be obtained by recycling solvent-free extract by introducing asphaltic material, or by removing about half of the solvent in preliminary solvent still iii.
The modification in Figure 5 gave a second grade oil of relatively low viscosity while the modification of Figure 6 gave a second grade oil of relatively high viscosity. When it is desired to produce first and second grade oils of more nearly the same viscosity, we may return the rafinate oils from the second treating step to the first treating step, as indicated by line d3 of Figure 5 and line it of Figure 6, and we may then subject the combined fractions of high v.1. ramnate to a second solvent extraction system, preferably in the absence of propane and by means of a good solvent. In this case our two-step process prevents any high molecular weight or low molecular weight good oil from being lost with the extract and the extraction of the first raifinate with good solvent gives a second extract which may be used as an intermediate grade lubricating oil.
As hereinabove stated, our invention is applicable for the treatment of all types of oils, including light oils, gas oils, lubricating oils, gear oils, transmission oils, paraffin distillates, heavy hydrocarbon oils and residual oils whether obtained by the distillation, destructive distillation, hydrogenation, destructive hydrogenation or cracking of coals, tars, pitches, lignlte, shales, bitumens, resins, petroleums or other oils or barbonaceous materials. The invention is also applicable to heavy oils prepared by polymerization or condensation of gaseous, liquid or solid hydrocarbons in the presence or absence of catalysts such as sulfuric acid, halides of aluminum, zinc, iron, tin, antimony, or boron, etc. The invention is also applicable to oils prepared by voltolizatlon by means of silent electric discharges and the oils which contain varying amounts of said voltolized oils. The invention is particularly useful for the treatment of long residua or long distillate stocks for the preparation of lubricating oils.
The hydrocarbon oil to be treated may be preliminarily and/or subsequently subjected tovarious refining treatments 'such as dewaxing, acid and clay treating, stabilizing, etc., and these treatments may be accomplished by any well known means.
It should be notedthat our light hydrocarbon solvent is not a preferential parafinic solvent since it dissolves naphthenic oils to essentially the same extent that it dissolves parafiinio oils. This solvent may be considered selective on the basis of molecular weight and noton the basis of paraffinlcity.
As hereinabove desirable to effect. the entire solvent extraction process in the presence of both the preferentially naphthenic solvent and the light hydrocarbon solvent because of stated, we have found it unthe difliculty in obtaining I arca es proper miscibility temperatures, phase separa tions, yields, etc. The simultaneous usethroughout the system of both naphtheric solvents and light hydrocarbon solvents necessitates the use of much larger quantities of both of these solvents g than are required in our process. The use of the light hydrocarbon solvent requires the use oi? much larger amounts ofnaphthenic solvent near the ramnate end of the system and these in-. creased. amounts of naphthenic solvent tend to dissolve larger amounts of good oil at the extract end of the system. By operating our system in two steps we markedly decrease the amount of each solvent required, we obtain even.- greater yields of high viscosity index oils, and we avoid large solvent losses since the solvent losses may be a function of the total amount of solvent which has to be recovered by distillation. Likewise, our invention makes it possible to greatly increase the capacity of treating towers and equipment be- 3 causethey can operate with lesser amounts oi solvent and consequently with greater amounts of oils. It will be seen that our process is capable or great flexibility and that it may be operated at maximum over-all emciency due to the fact that optimum conditions for each solvent may be used in the separate parts of the system.
While we have described our invention in some detail and in connection with a certain theory, it should be understood that we do not limit ourselves to these details or this theory except as de lined by the following claims, thich should be construed as broadly as the prior art will permit.
l. The method of refining lubricating oil stocks to recover both high viscosity and low viscosity paraifinic oils from naphthenic oils, which comprises treating said oil stocks in one system with a preferentially naphthenic solvent in the absence of appreciable amounts of light hydrocarbon solvent, withdrawing raflinate from said system, removing substantially all of said naphthenic solvent from the extract, then treating said extract in another system with a light hydrocarbon solvent at a suii'ilciently high temperature and pressure to remove low viscosity parafilnic oils therefrom, returning said low viscosity parafiinic oils to said first-named system, and with-. drawing the final extract from the second named system.
2. The method of refining a lubricating oil stock which comprises extracting a propane solution of said lubricating oil stool; with a selective naphthenlc solvent, removing propane from both the extract and rafiilnate'pheses thus produced, extracting the depropanized extract with a selective naphthenic solvent in the absence of appreciable amounts of propane to recover high viscosity paramnic oils therefrom, and returning. said high viscosity paramnic oils to the step of solvent extraction with the propane-naphthenic solvent.
3. The method of refining a lubricating oil stock with selective solvents which comprises extracting said oil with a preferentially naphthenic solvent in the absence of substantial amounts of propane whereby low viscosity parafllnic oils are left in the extract, removing substantially all of the solvent from the extract, treating the solventfree extract with propane to reclaim low molecular weight high viscosity index oils from high molecular weight low viscosity index oils, and returning said low molecular weight oils to said. first extraction system whereby maximum yields of high viscosity index oilsai'e' obtained and no appreciable amounts of high or low viscosity parafiinic oils remain in the final extract.
4. The combination of claim 3 wherein the propane treatment is at temperatures of 200 F.
5. The method of claim 1 wherein the naph 7. The process of claim 1 wherein the light.
hydrocarbon solvent is propane.
8. The process of claim 1 wherein the naphthenic solvent is a phenolic compound and the light hydrocarbon solvent is propane.
9. The process of claim 1 wherein the naphthenic solvent is nitrobenzene and the light hydrocarbon solvent is propane.-
10. The method of refining a-lubricating oil stock which comprises extracting a propane solution of said lubricating oil stock with a selective naphthenic solvent, removing propane from both the extract and raflinate phases thus produced, and extracting the depropanized extract with a selective naphthenic solvent in the absence of appreciable amounts of propane to recover high viscosity paraflinic oils from the final extract.
11. The method of refining a lubricating oil stock which comprises extracting said oil stock with a preferentially naphthenic solvent in the absence of light hydrocarbon diluents whereby a high quality, high viscosity parafiinic oil is produced, removing at least a portion of the solvent from the extract, and countercurrently extracting the extract with a liquefied normally gaseous hydrocarbon to produce a second grade parafiinic oil of relatively lowviscosity and a final extract which is substantially free from paraifinic components.
12. The method of refining a lubricating oil stock which comprises extracting said oil stock with a mixture of a selective naphthenic solvent and propane to recover the low viscosity paramnic components, removing propane from the extract and subsequently extracting it with at least two or three volumes of a naphthenic solvent in the absence of propane to recover high viscosity parafiinic oils from the final extract, blending said, high viscosity paraffinic components with said low viscosity parafiinic components and finally extracting said mixture of parafiinic oils with a selective solvent to separate a first grade parafiinic oil from an inferior grade paraflinic oil.
13. The method of refining a lubricating oil stock which comprises countercurrently extracting said stock with a mixture of a naphthenic solvent and a saturated liquefied normally gaseous hydrocarbon, removing said normally gaseous hydrocarbon from the extract produced by said countercurrent extraction and countercurrently extracting said remaining extract with a naphthenic solvent for recovering high viscosity paraflinic oils which were discarded from the first countercurrent extraction system by the liquefied normally gaseous hydrocarbons.
PERCY C. KEITH, JR. HENRY O. FORREST.
|Citing Patent||Filing date||Publication date||Applicant||Title|
|US2728708 *||May 17, 1954||Dec 27, 1955||Exxon Research Engineering Co||Solvent recovery|
|US2758141 *||Nov 19, 1951||Aug 7, 1956||Phillips Petroleum Co||Separation of aromatics by so2 extraction|
|US2935469 *||Dec 22, 1952||May 3, 1960||Vose Richard S||Solvent refining process|
|US4592832 *||Sep 6, 1984||Jun 3, 1986||Exxon Research And Engineering Co.||Process for increasing Bright Stock raffinate oil production|
|U.S. Classification||208/314, 208/323, 208/328|
|International Classification||C10G21/14, C10G21/00|