Properties of Hydroprocessed Base Oils

Abstract

Solvent extraction is applied to a hydrotreated base oil to create at least one higher quality product stream and at least one lower quality product stream, wherein the at least one higher quality product stream includes an improvement over the hydrotreated base oil in at least one of viscosity index, low temperature properties, volatility, and oxidation stability relative to that of the feedstock.

Claims

1. A method comprising the step of applying to a hydrotreated base oil a solvent treatment comprising at least one solvent to produce at least one first base oil, and one or more additional base oils, wherein the at least one first base oil has a higher paraffinic content than occurred in the hydrotreated base oil.

2. The method of claim 1 wherein the hydrotreated base oil feedstock is derived from one of a crude oil feedstock and a used lubricating oil feedstock.

3. The method of claim 1 wherein the hydrotreated base oil has been hydrotreated under a pressure of at least 600 psig.

4. The method of claim 1, further comprising a step of utilizing in the solvent treatment at least one of a preferentially selective paraffinic solvent, and at least one of a preferentially selective solvent for at least one of aromatic, polar, and naphthenic constituents.

5. A method for controlling at least one of volatility and viscosity of a base oil product by applying to a hydrotreated base oil feedstock a solvent treatment in which a first base oil is created that has a VI that is greater than that of the hydrotreated base oil feedstock and a further fractionation step comprising no less than two of: a. removal of solvent from the raffinate from which the first base oil was made, b. volatility of the first base oil that is at least one of (1) less than or equal to 15% or (2) less than or equal to 13%, in each case as measured by ASTM D-5800, and c. viscosity of the first base oil that is less than that of the hydrotreated base oil feedstock.

6. The method of claim 5 wherein the hydrotreated base oil feedstock is derived from one of a crude oil feedstock and a used lubricating oil feedstock.

7. The method of claim 5 wherein the hydrotreated base oil contains at least 90% saturates.

8. The method of claim 5 wherein the hydrotreated base oil contains less than 300 PPM of sulfur.

9. The method of claim 5 wherein the hydrotreated base oil has been hydrotreated under a pressure of at least 600 psig.

10. A method comprising a step of applying to a hydrotreated base oil feedstock a solvent treatment in which a first base oil is created that has an improved result, whenever tested either as a base oil or as a component of a finished lubricant, in at least one of the following ASTM tests relative to that of the hydrotreated base oil feedstock. a. Wear and Oil Thickening (D-7320), b. Wear, Sludge, and Varnish Test (D-6593), c. High Temperature Deposits, TEOST MHT (D-7097), d. High Temperature Deposits TEOST 33C (D-6335), e. Aged Oil Low Temperature Viscosity, ROBO Test (D-7528) f. Aged Oil Temperature Low Temperature Viscosity (D-7320). g. Determination of Oxidation Stability of Straight Mineral Oils (IP-306), h. Test of Susceptibility of Ageing According to Baader (DIN 51554), i. Oxidation Characteristics of Inhibited Mineral Oils (D-943), j. Determination of the Sludging and Corrosion Tendencies of Inhibited Mineral Oils (D-4310), k. Oxidation Stability of Steam Turbine Oils by Rotating Pressure Vessel Oxidation Test (RPVOT), (D-2272), l. Determination of oxidation stability and insolubles formation of uninhibited turbine oils at 120 C. without the inclusion of water (Dry TOST Method) (D-7873), m. Determination of Oxidation Stability of Inhibited Mineral Turbine Oils (IP-280), n. 3462 Panel Coker Test (FTM 791A), o. Standard Test Method for Corrosiveness and Oxidation Stability of Hydraulic Oils, Aircraft Turbine Engine Lubricants and Other Highly Refined Oils (D-4636), p. Pneurop Oxidation (DIN 51352), q. Standard Test Method for Thermal Stability of Hydraulic Oils (D-2070), r. Hydrolytic Stability of Hydraulic Fluids (Beverage Bottle Method) (D-2619), or s. Oxidation Characteristics of Extreme Pressure Lubricating Oils (D-2893)

11. The method of claim 10 wherein the hydrotreated base oil feedstock is derived from one of a crude oil feedstock and a used lubricating oil feedstock.

12. The method of claim 10 wherein the hydrotreated base oil contains at least 90% saturates.

13. The method of claim 10 wherein the first base oil has a viscosity index of at least 120.

14. The method of claim 10 wherein the hydrotreated base oil has been hydrotreated under a pressure of at least 600 psig.

15. A method comprising the step of applying to a hydrotreated base oil a solvent treatment comprising at least one solvent to create at least one product stream with an improvement in at least two of: a. viscosity index, b. volatility, and c. at least one of cold crank viscosity, Brookfield viscosity, pour point, and cloud point, relative to that of the feedstock.

16. The method of claim 15 wherein the hydrotreated base oil feedstock is derived from one of a crude oil feedstock and a used lubricating oil feedstock.

17. The method of claim 15 wherein the hydrotreated base oil contains at least 90% saturates.

18. The method of claim 15 wherein the hydrotreated base oil contains less than 300 PPM of sulfur.

19. The method of claim 15 wherein the first base oil has a viscosity index of at least 120.

20. The method of claim 15 wherein the hydrotreated base oil has been hydrotreated under a pressure of at least 600 psig.

21. The method of claim 15 wherein the hydrotreated base oil is hydrotreated at a pressure less than 1500 psig and a temperature less than 650 F.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

[0034] FIG. 1 is a block diagram illustrating three different general pathways and seven different general routes for creating base lube oils from crude oils according to the prior art.

[0035] FIG. 2 is a block diagram illustrating three different general pathways and nine different general routes for creating base lube oils from used lubricating oils according to the prior art.

[0036] FIG. 3 is a block diagram illustrating three different general pathways and seven different general routes for creating base lube oils from crude oils where the instant invention is noted as being implemented as the last step in the processing scheme.

[0037] FIG. 4 is a block diagram illustrating three different general pathways and nine different general routes for creating base lube oils from used lubricating oils where at least one embodiment of the present invention is noted as being implemented as the last step in the processing scheme and only in the instance where the base oil has first received hydrotreatment.

[0038] FIG. 5 is a block diagram showing a preferred mode for implementing the solvent extraction step on a hydroprocessed base oil processed through a solvent extraction column and with raffinate and extract streams shown having removal and recovery of solvent as well as generation of the higher quality and lower quality product streams.

[0039] FIG. 6 presents a chart and table showing analytical results for the higher and lower product quality streams were created when the process of at least one embodiment of the present invention was applied to a virgin hydroprocessed base oil (Purity 1003 from Holly-Frontier/PetroCanada).

[0040] FIG. 7 presents a chart and table showing analytical results for the higher and lower product quality streams were created when the process of at least one embodiment of the present invention was applied to a virgin hydroprocessed base oil (HCC 150 from Heritage Crystal Clean).

[0041] FIG. 8 is a block diagram showing how the raffinate (or extract) is passed to a first solvent recovery column with residual passed to a second solvent recovery column, which second solvent recovery column preferably also includes volatility and viscosity control functions.

DETAILED DESCRIPTION OF THE INVENTION

[0042] The following description is presented to enable any person skilled in the art to make and use the invention, and is provided in the context of a particular application and its requirements. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present invention. Thus, the present invention is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein.

[0043] Additionally, as used herein, the term substantially is to be construed as a term of approximation. Further, the term hydroprocessing is used herein to refer to hydrocracking, hydrotreatment, hydrofinishing, catalytic de-waxing, and iso-dewaxing as well as any associated technologies which apply hydrogen and catalysts under conditions of temperature, pressure, and residence times to achieve improvement in the feedstock. While streams and products created by other hydroprocessing technologies may also provide suitable feedstocks for the present disclosure, and the invention is thus not limited to processing only hydrotreated base oils, a preferred hydroprocessing technology for creating feedstock for at least one embodiment of the present invention is hydrotreatment (also referred to as hydrotreating).

[0044] Preferred process conditions for hydrotreating as contemplated in the present disclosure are preferably in the general ranges of 450 F. to 700 F., and 600 psig to 1,500 psig. These process conditions preferably result in a loss of less than 10% of the lube fraction, and more preferably result in a loss of less than 5% of the lube fraction, and most preferably result in a loss of less than 2% of the lube fraction, with the lube fraction being defined as a range in which the majority of the liquid to be hydrotreated has boiling points from 550 F. to 1050 F. (these are atmospheric equivalent temperatures as this distillation will occur under vacuum to avoid cracking). Hydrotreatment achieves improvement in color, reduction in hetero-atoms (sulfur, nitrogen, and oxygen), and conversion of unsaturated components (such as aromatics) to saturates (such as naphthenes). Many of the conversions from aromatics to saturates create naphthenic components, and hydrotreatment also may result in naphthene ring opening and isomerization, thus converting some naphthenes to paraffins, and some paraffins to iso-paraffins.

[0045] For purposes of applying specific solvents and process conditions, a preferable solvent is n-methyl-2-pyrollidone (nMP) although other solvents may be utilized. Solvent to oil ratio ranges preferably include 0.3 to 10.0, more preferably include 0.5 to 5.0, and most preferably include 1.0 to 2.0, temperature ranges preferably include 25 C. to the lesser of the boiling point of the solvent (under the pressure conditions being applied), more preferably include 50 C. to 150 C. (or the lesser of the boiling point of the solvent under the applicable pressure conditions), and most preferably include 60 C. to 90 C. (or the lesser of the boiling point of the solvent under the applicable pressure conditions). Pressure conditions can range from vacuum (for example as may be applied in the case of extractive distillation) to ambient and beyond up to any pressure as may be applied to maintain intimate mixing of the solvent and the feedstock in a phase as best promotes the desired results of the applied process. The number of theoretical stages of the extraction column preferably falls in the range of 1 to 10, more preferably in the range of 2 to 8, and most preferably in the range of 5 to 7.

[0046] In the present disclosure, solvent treatment is defined as applying one or more solvents which will: (a) preferentially remove naphthenic, aromatic, polar, and/or waxy compounds from a hydrotreated base oil (as in the case of a solvent applied in solvent extraction) or (b) alternatively remove paraffinic compounds from a hydrotreated base oil (as in the case of a solvent removing paraffinic compounds as applied in solvent de-asphalting), or (c) use a combination of both (a) and (b) approaches. The combination of the two approaches described in (c) may be any sequence of first (a) then (b), or first (b) then (a), or both (a) and (b) may be applied together simultaneously. In the case of (a) and (b) being applied simultaneously, then solvent treatment will preferably include two solvents, namely a preferentially selective naphthenic/aromatic/polar/waxy solvent and a preferentially selective paraffinic solvent.

[0047] In the varied configurations noted above, the solvent or solvents are preferably applied at different entry points to a contactor, extractor, centrifuge, extraction column (including a Scheibel Column), distillation column, or other device, which preferably promotes separation of material by molecular weight and gravitational or centrifugal force. Where a column is utilized then the preferred mode is to operate the solvent and oil countercurrently. Under the operating conditions of the process, wherever two solvents (referred to herein as dual solvents) are employed such dual solvents will preferentially not be miscible with each other but will instead preferentially have increased affinity for enhancing or detracting components which each is either removing or acting as a replacement for, such as for example paraffinic components in the case of one solvent, and aromatic/polar/naphthenic/waxy components in the case of the other solvent. In the case of dual solvents, temperature can have a particularly significant impact wherein two solvents which are substantially immiscible at one temperature are substantially miscible at another temperature. Whether practicing a single solvent or dual solvents, in the present disclosure all solvents are preferably recovered from the product streams and re-used in the process. As used herein, the terms constituents, compounds, and components are used interchangeably.

[0048] To illustrate one embodiment of how solvent extraction may be implemented according to the present disclosure, in FIG. 5 the hydroprocessed base oil 500 is introduced and charged to solvent extraction column 505 at connection point 504 which preferably occurs in a lower section of solvent extraction column 505. As a preferred mode of the invention a solvent (for example preferably nMP) is recycled back into solvent extraction column 505 at connection point 503, which preferably is positioned in an upper section of solvent extraction column 505. The solvent in this instance is heavier and thus it falls down through Solvent Extraction Column 505 passing counter-currently by Hydroprocessed Base Oil 500 which, being lighter, is rising up Solvent Extraction Column 505. As the solvent passes by and mixes with Hydroprocessed Base Oil 500, the solvent preferentially attracts impurities out of Hydroprocessed Base Oil 500, with such impurities preferentially being aromatics, naphthenic, and/or waxy components. The Hydroprocessed Base Oil 500, after rising to the top of the column, has had its impurities substantially removed and then is called raffinate. In Raffinate 515, the solvent is distilled overhead and recovered and returned via Solvent Recycle 520 for entry into Solvent Extraction Column 505 at connection point 503. Similarly, the solvent, after descending to the bottom of Solvent Extraction Column 505, then has collected all the impurities and is then called extract. In Extract 530, the solvent is distilled overhead and recovered and returned via Solvent Recycle 522 for entry into Solvent Extraction Column 505 at connection point 503. Not shown is a small makeup of solvent over time as solvent is passed out with the products. However, in a properly designed and constructed unit, solvent losses are preferably extremely low (on the order of parts per million). After the solvent is removed from the raffinate, the liquid that remains is passed as stream 540 and becomes a higher product quality base oil 550. Similarly after the solvent is removed from the extract, the liquid that remains is passed as stream 535 and becomes lower product quality base oil 545.

[0049] Not shown in FIG. 5 are elaborate and often proprietary inner column mechanical items which are designed to promote intimate contact between solvent and feedstock to maximize the performance of the extraction process. Also Raffinate 515 and Extract 530 may be one or more distillation columns in series and also are preferably capable of additional functions beyond just solvent recovery as is described in further detail below with respect to FIG. 8.

[0050] Turning to the results achieved by applying principles of the present invention (e.g. solvent treatment applied to processing a hydroprocessed base oil) to processing multiple feedstocks, it was demonstrated quite unexpectedly that a highly favorable improvement of the low temperature properties of the higher quality product was achieved and at yields in excess of 80%. This favorable effect, and these favorable yields, was achieved in both virgin and re-refined base oils. By volume, the higher quality product is the vast majority of the volume of the products generated from each feedstock (about 85% in these experiments). More specifically, cold crank viscosities were reduced on average by about 15% in a re-refined hydrotreated base oil and by about 13% in a virgin hydrotreated base oil across temperature ranges of 25 C. to 35 C. Moreover, the improvement in the low temperature properties was accompanied by a favorable increase in the viscosity index in the ranges of 3 to 4 VI points (higher VI increases were achieved in alternative modes of operating but this data is not reported) and without a materially negative impact on volatility. With respect to the lower quality product (which is about 15% yield of the feedstock), cold crank viscosities were increased, and thus it was degraded versus the feedstock. However, even with higher cold crank viscosities, the lower quality product remained a highly marketable base oil suitable for use in many applications. In addition, surprisingly favorable effects on pour point and cloud point in certain of the higher quality and the lower quality products were generally observed as well. Finally, indicatively oxidation stability in the higher product quality stream is increased by removal of the less stable aromatic and naphthenic compounds as a result of the solvent extraction process which created the higher VI product.

[0051] Although applying solvent extraction using n-methyl-2-pyrollidone to virgin and re-refined hydroprocessed base oils in actual bench and pilot scale processes has demonstrated creation of substantially improved higher quality and lower quality streams, in the lower quality product, a haze or cloudiness was observed. This haze issue was addressed by filtering, in which a vacuum pump was attached to a filtering flask and the lower quality product was pulled (by the vacuum) into a receiving flask through Whatman filter paper inside a Buchner funnel. Following the filtration step, the lower quality product in the receiving flask was clear, without any haze or cloudiness.

[0052] Filtration processes are readily available at commercial scale so as to achieve a similar result as was achieved with the bench scale filtration apparatus that removed the haze and cloudiness from the lower quality stream. It may be that any favorable impact on the pour point and cloud point in the lower quality product noted above was enhanced by the filtration step which removed the cloudy elements which appeared in the lower quality products after applying the solvent extraction step to the hydrotreated base oils. For example, these cloudy elements could be waxy elements that are then removed with a filtration step. The filter paper was weighed before and after filtration and it showed a minimal increase in weight relative to the amount of the filtered product. So whatever was removed was a very small portion of the lower quality product stream.

[0053] Table 3 shows the analytical results achieved by applying principles of the present invention to two feedstocks, the first a re-refined hydrotreated base oil feedstock available from Heritage Crystal Clean called HCC 150, and the second a virgin hydrotreated base oil feedstock available from PetroCanada (now owned by Holly-Frontier) called Purity 1003. Of notable interest is that even as the VIs of the higher product quality are increased, the cold crank viscosities of the base oils are decreased. Furthermore, in 3 of the 4 instances, there was a material reduction in pour point, which is also favorable. Cloud point also was decreased slightly in 3 of the 4 instances. It was only the higher quality re-refined HCC 150 product which did not exhibit a decrease in cloud point and pour point, although it did show the largest reduction in the cold crank viscosity of about 15% and a material increase of 3 points in VI. Also favorable is a slight reduction in the viscosity of both the higher and lower quality products. Since the processing temperature of each example in Table 3 was at least 225 C. below the temperature in which any cracking might be expected to even start, the slight reduction in viscosity is unexpected.

TABLE-US-00003 TABLE 3 Low Temperature Properties and Viscosity Index Analytical Results Re-refined (HCC 150) Virgin (Purity 1003) Feedstock Product Abs Delta % Delta Feedstock Product Abs Delta % Delta Test ASTM Higher Quality Product Yield = 85% Higher Quality Product Yield = 86% Viscosity @ 40 C. D-445 28.80 27.87 0.93 3.2% 21.60 20.47 1.13 5.2% Viscosity @ 100 C. D-445 5.30 5.24 0.06 1.1% 4.44 4.35 0.09 2.0% Viscosity Index (VI) D-2270 118 121 3 2.5% 117 122 5 4.3% CCS @ 35 C. D-5293 8,302 7,036 1,266 15.2% 3,572 3,115 457 12.8% CCS @ 30 C. D-5293 4,175 3,569 606 14.5% 1,928 1,675 253 13.1% CCS @ 25 C. D-5293 2,253 1,930 323 14.3% 1,114 972 142 12.7% Pour Point D-97 12 12 0 15 21 6 Cloud Point D-2500 5 4 1 8 9 1 Test ASTM Lower Quality Product Yield = 15% Lower Quality Product Yield = 14% Viscosity @ 40 C. D-445 28.80 28.19 0.61 2.1% 21.60 21.18 0.42 1.9% Viscosity @ 100 C. D-445 5.30 5.11 0.19 3.6% 4.44 4.32 0.12 2.7% Viscosity Index (VI) D-2270 118 110 8 6.8% 117 111 6 5.1% CCS @ 35 C. D-5293 8,302 9,959 1,657 20.0% 3,572 3,817 245 6.9% CCS @ 30 C. D-5293 4,175 4,886 711 17.0% 1,928 2,036 108 5.6% CCS @ 25 C. D-5293 2,253 2,576 323 14.3% 1,114 1,164 50 4.5% Pour Point D-97 12 21 9 15 18 3 Cloud Point D-2500 5 7 2 8 12 4

[0054] Of further interest is that as the cold crank viscosity of the higher quality product is decreased, so too is the cold crank viscosity of the lower product quality increased. FIGS. 6 and 7 (and the associated tables therein) show key observations from the above Table 3 both graphically and numerically. In each of these charts, the feedstock is the middle line, the line below is the higher quality base oil, and the line above is the lower quality base oil. For both feedstocks, over each temperature in the range of 35 C., 30 C., and 25 C., the higher quality product achieved materially improved CCS results. Further, in each of the two products as the temperature of the CCS simulator test is reduced, the difference between the cold crank viscosities of the higher quality and lower quality products (as compared to the feedstock) is increased. The results thus clearly demonstrate the positive effect on improving the CCS of the higher product quality stream even as the CCS of the lower product quality stream is degraded.

[0055] Volatility is a measure of the extent of an oil to vaporize in use, with a common test method used to measure volatility being the NOACK ASTM test D-5800. The NOACK test measures the amount of oil that has vaporized when a sample is heated to 250 C. under a 20 mm vacuum, following a 1 hour period in which air is blown across the sample at a fixed rate. In this apparatus, the higher volatility (light ends) are removed from the starting sample and the difference in weight between the starting and ending samples is the measure of volatility.

[0056] Since the products of implementing one embodiment of the present invention are both created from the same feedstock at relatively low temperatures (compared with the cracking ranges of the feedstock), no material is being created (by means of cracking) or removed (in the form of non-condensable gases). Given this, arithmetically the amount of volatility gained by one product should be exactly offset by a commensurate loss in volatility in the other product (after adjusting for yield differences). A hypothetical scenario that presents this arithmetically is shown in Table 4. In Table 4, a 2.5% increase in volatility in Product A (which is 40% of the output) is offset by a 1.7% reduction in Product B (which is 60% of the output). The increase in the volatility of Product A is thus exactly offset by the decrease in the volatility of Product B (after yield adjustment) so that the final weighted volatility of the two products exactly equals the volatility of the feedstock.

TABLE-US-00004 TABLE 4 Arithmetic Calculation of Noack in 2 Products created from a Hypothetical Feedstock Total Light Ends Noack Feedstock to Solvent Extraction Step* 100 15 15.0% Product A 40 7 17.5% Product B 60 8 13.3% Back Blended Result 100 15 15.0% Mass Balance Crosscheck (must be 0 0 0 equal to 0) *Feedstock separated into Product A and B where 100% of the feedstock becomes either Product A or B. Assumes nothing is added to the process during the separation.

[0057] While the above analysis is supported by sound logic, in actual practice the results of volatility testing on the products created by the two feedstocks showed a slight increase in the volatility in all products created from each feedstock, an outcome which is theoretically not possible. This is shown in Table 5 below.

TABLE-US-00005 TABLE 5 Volatility Results (Test Method, NOACK, D-5800) Products Noack delta in Higher Quality Lower Quality Higher Lower Re-refined HCC 150 12.3% 12.8% 15.7% 0.5% 3.4% Virgin Purity 1003 14.7% 15.4% 17.4% 0.7% 2.7%

[0058] How this could happen is not understood. A possible minor contributor might be trace amounts of solvent still remaining in the products after the solvent was removed from the products via distillation. However, testing for solvent in products found at most about 1,900 ppm (0.19%) in some products (and usually it was much less). This means that the vast majority of the volatility increase must be due to some other reason and follow-up on the matter was justified.

[0059] Analytical testing of these products was done at the Southwest Research Institute (SwRI), a world class testing facility in San Antonio, Tex. Testing at SwRI is applied scrupulously using the latest equipment (including regular testing against known standards) and lab technicians are very experienced and diligent. SwRI confirmed that the approach outlined in Table 4 above is theoretically sound, but that Noack's limits of testing accuracy for repeatability is about 0.86% and for reproducibility is about 1.56% (in each case applied to the 12.3% Noack of the HCC 150 feedstock). So a possible contributor to the discrepancy could be the inherent limits in the accuracy of the test method. An alternative measure of volatility was offered which will be investigated in the future.

[0060] Regardless as to the level of accuracy of the NOACK test method, in order to further protect against higher volatility where a product may exceed the 15% (or 13% or any other as specified to the application) level, an additional capability for volatility control as applied in the distillation of the solvent is preferably included, and is now disclosed, as an element of one embodiment of the present invention. This is achieved by designing in further capability into a distillation column which is used in the solvent recovery step after the extraction step is first performed. By doing this, volatility of the higher or lower quality products can be adjusted by removing a small portion of the light base oils and a small portion of the heavier portion of this same light base oil. Furthermore, if products have viscosities that fall outside the range required for a specific market application, then the viscosities can be adjusted by designing the distillation column not only for removal (and recovery) of solvent (and volatility control), but also for fractionation into viscosities as are suited for the specific market application. By doing this, multiple products can be created using a column that would otherwise be used solely for solvent recovery. By incorporating the ability to adjust at least one of volatility and viscosity of the products into a solvent recovery section, capital cost and operating cost savings may be achieved. For example, modifying a traditional design for a column that is used solely for solvent recovery will reduce the capital cost of adding a further column solely for product viscosity or volatility adjustment. Furthermore, using this same column will preferably be implemented to achieve lower operating cost by maintaining some or all of the higher temperatures and reduced pressures as are used for recovery of solvent. Even if a subsequent column is used after a first solvent recovery column, operating cost savings are preferably gained by maintaining some or all of the higher temperatures and reduced pressures as are used in the last distillation column which is recovering the solvent.

[0061] To convey this further element graphically, FIG. 8 illustrates a raffinate (which could separately be an extract stream) stream 800 being charged to a distillation column 810 for purposes of recovery of some of the solvent in stream 840. The material not proceeding overhead 835 (this is the raffinate stream with some of the solvent removed) is then charged to a second distillation column 820 whereupon virtually all remaining solvent is removed and recovered in stream 845. The next heavier fraction depicted in the second distillation column 820 is a Spindle Oil stream 850 as a side draw, as is the next heaver fraction being a Light Base Oil 855. The residual is shown as a Medium or Heavy Base oil stream 860. To achieve volatility control, the column is designed to remove the lighter ends from the Light Base Oil 855 (which then becomes part of the Spindle Oil 850) and to ensure the viscosity target is still met, a portion of the heavier liquid contained in Light Base Oil 855 is instead portioned into Medium or Heavy Base Oil 860 (thus increasing the yield of the Medium or Heavy Base Oil).

[0062] Careful management of the material to be removed from each fraction enables achievement of target viscosities even as the volatility is managed to fall within the required specification. But to place all this in proper context, and as is well known in the industry, in lighter lube oils to achieve both low volatility and low viscosity without exceeding volatility requirements requires a higher VI feed stream, which is thus assumed to preferably be the higher VI raffinate stream used in the above description. Alternatively stated, one cannot simply apply fractional distillation to create a low viscosity, low volatility feedstock without that feedstock being of a sufficiently high product quality from the start. It is thus apparent that, to make lighter viscosity lubricants, at least one process of the present invention must improve the VI of the raffinate to a sufficient degree that the volatility control and viscosity fractionation functions can then be preferentially and beneficially applied; in this way the solvent treatment and fractionation processes of at least one embodiment of the present invention are dependent upon each other.

[0063] The above noted fractionation step can have certain variations, some of which are described next. While the above design presents two columns in series, in some instances it may be preferable to design the process for a single column processing stream 800. In addition, the further volatility control and viscosity fractionation functions (which are in addition to solvent recovery) described above may be included for processing of either or both of the higher and lower product streams should volatility or viscosity control be desired in either of the raffinate or extract streams. Furthermore, in FIG. 8, the products presented are a spindle oil, light base oil, and medium base oil, but the creation of fewer or more products can be designed as alternate configurations to suit specific market requirements. In any event, by implementing the above fractionation step (or using a similar approach), each of solvent recovery, volatility control, and viscosity targeting for specific market applications may all be afforded at reduced capital and operating costs. Proper design of fractional distillation columns is well known and functional design elements needed to achieve not only solvent recovery but also volatility and viscosity control, are achievable as described above if engineered by one of ordinary skill in the art.

[0064] As noted above, a particularly unexpected outcome of practicing at least one embodiment of the invention was achieving both a large improvement in low temperature properties of the higher quality product relative to that of the feedstock and a simultaneous improvement in the Viscosity Index (VI) in the higher quality product, also relative to that of the feedstock. The result is unexpected because it is known that higher paraffinic content will result in an increased VI and it was further assumed, since the hydrotreated base oils were almost fully saturated, that the VI improvement being achieved could only occur by reducing the proportion of naphthenes in the higher quality product, there presumably being very little (if any) aromatics left in the feedstock to remove. However, it is also known that naphthenes exhibit better low temperature properties than paraffins. Therefore a reduction in naphthenes in the higher quality product would logically be assumed to have resulted in degraded (versus improved) low temperature properties (such as the cold crank simulator results) in the higher quality product. But that did not in fact happen. A posed theory as to how both VI and low temperature properties could simultaneously be improved is that some residual waxy components in the feedstock were removed from the raffinate by the solvent treatment (and then appeared as haze in the extract), thus leaving fewer waxy elements in the higher quality product. But very little waxy material was recovered in the filtration process, indicating that if this is actually the explanation for the improved cold crank viscosity, not much removal is needed to achieve highly beneficial low temperature results. A further item to be reconciled is that waxy compounds are known to increase VI, and so if their removal caused a better result in the cold crank viscosity in the higher quality stream that should also have been accompanied by a worst result in the VI of the higher product quality stream. But that too did not happen. Further investigation into why solvent extraction of hydrotreated base oil created both improved low temperature properties and higher VI in the higher quality products requires compositional analysis of the proportions of paraffins (including n and iso-paraffins), naphthenes (including more particularly proportional content by number of rings), residual wax components, as well as any aromatics (or non-technically described, any quasi-aromatic-naphthenes) that may be drawn into the lower quality product through the solvent treatment step applied according to principles of the present disclosure.

[0065] As discussed in the background of this specification, a major goal of lubricant improvements is to extend and maximize the useful life of the lubricant, thus delaying a need for its replacement in the application. Not only does a longer lubricant life represent cost savings from less frequent changes, but it also indicates a higher average level of performance versus time, thus providing better lubrication even while a lubricant is being degraded during use. To achieve a longer duration of the lubricant, it must have strong oxidation stability and this is measured and is thus an additional important property of base oils. In general, aromatic and naphthenic compounds are less stable and more prone to break down, leading to sludge formation and deposit creation and impaired lubricating capability as the lubricant is degraded from use. Since an effect of solvent treatment is separation of aromatic and naphthenic compounds out of the feedstream to create the higher product quality product, improved oxidation stability of the higher quality product is indicatively achieved by applying principles of the present disclosure. Therefore, in addition to the noted improvements in both the low temperature properties and Viscosity Index of the higher product quality stream, compositional improvement in the higher product quality stream of one embodiment of the present invention forecast improvement in the oxidation stability of the higher product quality stream.

[0066] The present invention is not limited to any particular solvent in the solvent treatment process, or catalyst in the hydroprocessing steps, since feedstocks and process conditions may vary and principles of the present invention may be applied in many varied modes. Solvents are also known for selectively separating aromatics, polars, and other undesirable base lube oil constituents from desirable base lube oil constituents. Preferred solvents typically comprise N-methyl-2-pyrollidone, furfural, phenol, and the like. The optimum solvent may be selected based upon its effectiveness in the process as discussed above, but an alternate approach may be to utilize other solvents known for their preferential selectivity for removing paraffinic components. Such preferred solvents typically comprise propane, acetone, hexane, heptane, isopropyl alcohol, and the like. The optimum solvent may be selected based upon its effectiveness in the solvent treatment process as it may be applied as described according to principles of the present invention or in any alternate embodiment.

[0067] While the present invention has been described by reference to certain of its preferred embodiments, the embodiments presented here are intended to be illustrative rather than limiting in nature and many variations and modifications are possible within the scope of the present invention. Many such variations may be considered obvious and desirable by those skilled in the art based upon a review of the foregoing description of the preferred embodiments that are described in this specification.