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.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part application of U.S. Pat. No. 9,862,894, formerly co-pending application Ser. No. 15/212,180, filed Jul. 15, 2016, and issued on Jan. 9, 2018, which is a continuation application of U.S. Pat. No. 9,394,495, formerly co-pending patent application Ser. No. 14/488,926, filed on Sep. 17, 2014, and issued on Jul. 19, 2016, which claims the benefit of Provisional Application No. 61/879,409, filed Sep. 18, 2013; and this application claims the benefit of U.S. Provisional Application Nos. 62/514,639 and 62/519,149, filed Jun. 2, 2017, and Jun. 13, 2017, respectively; and U.S. Pat. No. 9,862,894 claims the benefit of U.S. Provisional Application No. 62/349,441, filed Jun. 13, 2016, all of which applications and patents are hereby incorporated herein by reference, in their entirety.

TECHNICAL FIELD

The present disclosure relates to further processing of hydroprocessed base oils through subsequent solvent treatment to create improved properties, and more particularly improved low temperature properties, viscosity index, oxidation stability, and volatility properties.

BACKGROUND

Finished lubricants include two general components, lubricating base stocks and additives. Base stocks are made by producers, which may be refiners which make base stocks from crude oil, or re-refiners which make base stocks from used lubricating oils. Lubricating base stock is the major constituent in these finished lubricants and contributes significantly to the properties of the finished lubricant. In general, a few lubricating base stocks are used to manufacture a wide variety of finished lubricants by varying the mixtures of individual lubricating base stocks and individual additives. While finished lubricants may be used, for example, in automobiles, diesel engines, axles, transmissions, and a wide variety of industrial applications, motor oil in crankcases of cars and trucks is the largest volume single market for finished lubricants.

A base oil is created by blending two or more base stocks together and it is thus generally base oils (e.g. the blended base stocks) which are used to make the finished lubricants. Base oils typically comprise over 70% of the finished lubricant and additives make up the balance. Additives are blended with the selected base oil blend to provide a finished lubricant composition as intended to improve (or “correct”) select properties of the finished lubricants. Typical additives include, for example, pour point depressants, anti-wear additives, extreme pressure (EP) agents, detergents, dispersants, antioxidants, viscosity index improvers, viscosity modifiers, friction modifiers, de-emulsifiers, antifoaming agents, corrosion inhibitors, rust inhibitors, seal swell agents, emulsifiers, wetting agents, lubricity improvers, metal deactivators, gelling agents, tackiness agents, bactericides, fungicides, fluid-loss additives, colorants, and the like.

In making finished lubricants, motor oil manufacturers blend base oils and additives to formulate products that meet the finished lubricant specification. Manufacturers seek to minimize use of expensive additive (“correction”) fluids that are otherwise required to compensate for any shortfall in the base oil. Viscosity Index (VI) is a measure of the degree to which the viscosity of a base oil changes over changes in temperature. Less change is better, and less change correlates to a higher VI number. Viscosity Index Improvers (referred to as VI Improvers) are widely used in making motor oils, serving to maintain a higher thickness of the oil at higher temperatures than would otherwise be the case. However, VI improvers are not only expensive but they increase lubricant viscosity, thus making it more difficult to achieve low cold cranking viscosities. It is thus advantageous to use base oils of higher VIs (before adding VI Improvers), since this both minimizes additive cost and reduces the amount of correction fluid needed to achieve the cold cranking specification, which requires thinner base oils in the 0 W and 5 W motor oil grades. Base oils able to be blended into finished lubricants that achieve the 0 W and 5 W motor oil grade requirements generally require a viscosity level of no greater than 120 SUS (at 100° F.) or alternatively measured 4.5 centistokes (at 100° C.). At such low viscosity levels the volatility specification of 15% or 13% typically can only be achieved in Group III base oils. Thus, motor oil manufacturers seek base oils with higher VIs and excellent low temperature properties, and additionally low volatility.

Finished lubricants must meet the specifications for their intended application as defined typically by the concerned governing organization, although increasingly many equipment manufacturers are creating their own specifications. Motor oil specifications in the United States are set by the International Lubricant Standardization and Approval Committee (ILSAC), a tri-partite group of original equipment manufacturers or OEMs (car and truck manufacturers), additive companies, and base oil producers. ILSAC will periodically issue revised standards for motor oils which are termed GF (for Gasoline Fuel) and are followed by a number, that number currently being 5, and the current GF-5 standards became effective on Oct. 1, 2011.

Among other requirements, GF-5 stipulates that motor oils must meet the specifications defined in SAE J300 (established by the Society of Automotive Engineers) for 0 W, 5 W, 10 W, and higher multi-grade oils, which include tests for cold cranking viscosity at very low temperatures. The “W” in the grade designations stands for Winter and it defines the cold temperature requirements of the motor oil grade. Low temperature performance is critical for engine oils because of cold temperature conditions that engines are exposed to prior to start-up in various cold climates. A lube oil base stock that provides improved low temperature performance could allow inclusion of lower quality, less expensive co-base stocks or a reduction in the amount of viscosity modifier or pour point depressant in the engine oil formulation.

A key measure of low temperature performance is measured by the low-temperature cranking viscosity (cold crank viscosity) as is defined in test method D-5293 (“D” in the test method identifier denotes its approval as an ASTM test method). This test method is abbreviated as CCS (for Cold Crank Simulator) and it is conducted at different temperatures for each grade of lube oil. Column 2 in Table 1 in SAE J300 (copied below) shows the Low-Temperature Cranking Viscosity (measured in mPa-s) requirements for grades of motor oil, the most restrictive of which are found on the first two rows, 0 W and 5 W. The third column shows the Low Temperature Pumping Viscosity (often referred to as the mini-rotary viscometer test, or MRV test, and measured as per D-4684).

TABLE 1
SAE viscosity grades for engine oils(1)(2)
Caution: kinematic viscosity ranges for SAE 8 to SAE 20 viscosity grades partially overlap. How to assign a single
viscosity grade to an engine oil satisfying the kinematic viscosity specifications of more than one grade is covered in
Section 6 of this document.
	Low-Temperature	Low-Temperature (° C.)	Low-Shear-Rate	Low-Shear-Rate
	(° C.)	Pumping	Kinematic	Kinematic	High-Shear-Rate
SAE	Cranking	Viscosity(4) mPa · s	Viscosity(5) (mm2/s)	Viscosity(6) (mm2/s)	Viscosity(6) (mPa · s)
Viscosity	Viscosity(3), mPa · s	Max with	at 100° C.	at 100° C.	at 150° C.
Grade	Max	No Yield Stress(4)	Min	Max	Min
0 W	6200 at −35	60 000 at −40	3.8	—	—
5 W	6600 at −30	60 000 at −35	3.8	—	—
10 W	7000 at −25	60 000 at −30	4.1	—	—
15 W	7000 at −20	60 000 at −25	5.6	—	—
20 W	9500 at −15	60 000 at −20	5.6	—	—
25 W	13 000 at −10	60 000 at −15	9.3	—
8	—	—	4.0	<6.1	1.7
12	—	—	5.0	<7.1	2.0
16	—	—	6.1	<8.2	2.3
20	—	—	8.9	<9.3	2.8
30	—	—	9.3	<12.5	2.9
40	—	—	12.5	<16.3	3.5 (0 W-40, 5 W-40, and
					10 W-40 grades)
40	—	—	12.5	<16.3	3.7 (15 W-40, 20 W-40,
					25 W-40, 40 grades)
50	—	—	16.3	<21.9	3.7
60	—	—	21.9	<28.1	3.7
(1)Notes - 1 mPa · s = 1 cP; 1 mm2/s = 1 cSt
(2)All values, with the exception of the low-temperature cranking viscosity, are critical specifications as defined by ASTM D3244 (see text, Section7.)
(3)ASTM D5293: Cranking viscosity - The non-critical specification protocol in ASTM D3244 shall be applied with a P value of 0.95.
(4)ASTM D4684: Note that the presence of any yield stress detectable by this method constitutes a failure regardless of viscosity.
(5)ASTM D445
(6)ASTM D4683, ASTM D4741, ASTM D5481, or CEC L-36-90.

In the above table, motor oils that achieve below 6,200 mPa-s at −35 degrees centigrade (C) will meet the cold cranking requirement for 0 W, whereas motor oils that are above 6,200 mPa-s but less than 6,600 mPa-s will meet the cold cranking requirement for 5 W motor oils. Thinner oils (that is, lower in viscosity) are needed to achieve improved (lower) cold cranking viscosities. As is shown in the third column of Table 1 above, the low temperature pumping viscosity MRV test is applied at temperatures ranging from −15 C down to −40 C and in this test any show of stress will constitute a failure.

The core challenge in meeting these low temperature tests is that even as thinner oils tend to have improved low temperature properties, thinner oils are also typically more volatile, and volatility is restricted in GF-5 to 15% or below as measured by D-5800 (also referred to as NOACK). In the case of DEXOS™, which is General Motors' specification, the motor oil must not exceed a NOACK volatility of 13%. Most particularly, in the lightest motor oil grades (0 W and 5 W), it is difficult if not impossible to economically achieve both a low cold crank viscosity and comply with the 15% (or 13% in a DEXOS™ specification) volatility specification without using base stocks having higher VIs. Thus lower CCS values and lower volatility fight each other but are addressable in the lightest viscosity motor oil grades by use of base oils with higher VIs. Higher viscosity grades (that is thicker oils) have less difficulty achieving both their cold cranking levels and the volatility specification since heavier base oils are inherently far less volatile than lighter base oils and the cold cranking viscosity level is higher (e.g. less stringent).

In addition to cold cranking viscosity, finished lubricant manufacturers also evaluate other important low temperature characteristics such as pour point (preferably measured as per D-97) and cloud point (preferably measured as per D-2500). An additional low temperature test method is the Brookfield Viscometer Test which measures low temperature viscosity (preferably measured as per D-2983, or “Brookfield Viscosity”) and is applied to qualify Automatic Transmission Fluids (ATF's) and hydraulic fluids. Cold cranking viscosity, Brookfield Viscometer Test, MRV test, pour point, and cloud point are referred to herein as comprising “low temperature properties”. In each of these instances, a lower number denotes a higher performance level. As examples, a cold cranking viscosity of 3,500 is better than 4,000, a pour point of −15° C. is better than −10° C., and a cloud point of −5° C. is better than 0° C.

Finished lubricant standards are becoming increasingly challenging to meet in response to continually evolving and increasingly demanding market applications. Whereas historically higher lubricant standards in the earlier years were achieved through better additives, in the 1990s and thereafter higher base oil quality has increasingly been required to meet the higher finished lubricant standards. Most notably, increasingly stringent finished lubricant standards in motor oils now increasingly require base oils with excellent low temperature properties (including lower viscosity thus achieving better fuel economy), lower volatility (thus achieving lower emissions) and higher oxidation stability (thus lasting longer in use).

Oxidation stability is a further important property of base oils (and in the finished lubricants) as a major goal is to maximize 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. Therefore oil stability and durability (as indicated by oxidation stability) is of particular importance in evaluation of base oils and in the finished lubricants made from base oils. Oxidation stability, and its associated elements of sludge, deposit and viscosity control, apply in making passenger car motor oil (PCMO), Heavy Duty Engine Oils (HDEOs), and many industrial lubricants.

Oxidation stability is defined and measured in numerous tests based on the specific market application of the lubricant. Such tests define standards in base oils or finished lubricants and may be established by equipment manufacturers or by third party organizations. In the GF-5 requirements created by ILSAC which took effect in October 2011 and are applied to PCMOs, no less than 6 (of about 21) tests are directed towards measuring different aspects of oil stability. These tests include: 1. Wear and Oil Thickening (D-7320), 2. Wear, Sludge, and Varnish Test (D-6593), 3. High Temperature Deposits, TEOST MHT (D-7097), 4. High Temperature Deposits TEOST 33C (D-6335), and 5. Aged Oil Low Temperature Viscosity, ROBO Test (D-7528) or 6. Aged Oil Temperature Low Temperature Viscosity (D-7320).

In industrial applications, such as in the manufacturing of Hydraulic Fluids, Turbine Oils, Compressor Oils, and Industrial Gear Oils, oxidation stability is also measured in many other tests including; Determination of Oxidation Stability of Straight Mineral Oils (IP-306), Test of Susceptibility of Ageing According to Baader (DIN 51554), Oxidation Characteristics of Inhibited Mineral Oils (D-943), Determination of the Sludging and Corrosion Tendencies of Inhibited Mineral Oils (D-4310), Oxidation Stability of Steam Turbine Oils by Rotating Pressure Vessel Oxidation Test (RPVOT), (D-2272), Determination of oxidation stability and insolubles formation of uninhibited turbine oils at 120° C. without the inclusion of water (Dry TOST Method) (D-7873), Determination of Oxidation Stability of Inhibited Mineral Turbine Oils (IP-280), 3462 Panel Coker Test (FTM 791A), Standard Test Method for Corrosiveness and Oxidation Stability of Hydraulic Oils, Aircraft Turbine Engine Lubricants and Other Highly Refined Oils (D-4636), Pneurop Oxidation (DIN 51352), Standard Test Method for Thermal Stability of Hydraulic Oils (D-2070), Hydrolytic Stability of Hydraulic Fluids (Beverage Bottle Method) (D-2619), and Oxidation Characteristics of Extreme Pressure Lubricating Oils (D-2893), among others. The ability to meet the standards of these oxidation tests often requires using higher quality base oils.

The American Petroleum Institute (API) has classified base oil by quality into groups, with mineral oils constituting Groups I, II and III, and other non-mineral derived oils constituting Groups IV and V (Group VI is a European classification). In API's classification system, higher quality is designated by a higher number. Thus Group III is higher quality than Group II and Group II is higher quality than Group I. In general, Group II lube base stocks have much poorer CCS-volatility relationships relative to Group III and Group IV base stocks.

TABLE 2
API Base Oil Group Classifications
	Viscosity
Group	Index	Saturates and Sulfur	Other
I	80-120	<90% and/or >=0.03%
II	80-120	>=90% and <0.03%
III	≥120	>=90% and <0.03%
IV			PAO Poly Alpha Olefin
V			Poly Esters (others)
VI		Europe Only (ATIEL)	PIO (Poly Internal Olefins)

The API Base Oil Group classification system defines base oil quality by three criteria: 1) sulfur content (preferably low to reduce harmful emissions), 2) saturates (to improve oxidation stability, reduce sludge and deposit formation, and achieve better VIs and lower volatilities), and 3) viscosity index (VI) (the higher, the better). As noted above, VI measures the rate of change in viscosity in response to change in temperature. VI is a calculated number relative to reference base oils based on the measurement of viscosity at two temperatures, 40° C. and 100° C. A higher VI indicates less viscosity change in response to temperature change, and thus higher quality base oil. Saturates in general (which include both paraffinic and naphthenic compounds, which are also referred to as cyclo-paraffinic compounds) are well known to have a smaller change in viscosity in response to temperature compared with aromatics and polar compounds, and thus have higher VIs. It is thus well known that a higher level of saturates in base oil increases quality as the more saturated base oils achieve higher VIs, although there are distinctions even with the saturates category as noted next.

Within the saturates category of compounds, paraffinic compounds are known to have higher VIs than naphthenic components. While paraffinic components are known to have a higher VI than naphthenic compounds, naphthenic compounds are known to have better low temperature properties than paraffinic oils. Whereas VI is calculated based on viscosity measurements at 40° C. and 100° C., in contrast (and as noted in Table 1 above) calculation of cold cranking viscosity is measured at −35° C., −30° C., and −25° C., for the grades of 0 W, 5 W and 10 W, respectively. The CCS temperatures of −35° C., −30° C., and −25° C. are each far below the 40 C (lowest) temperature used for determining VI. It is thus evident that, while both VI and cold crank measure viscosities of oil, the temperature ranges covered by these two test methods are vastly different, spanning a huge range from 100° C. on down to −35° C. This is a difference of 135° C. (243° F.). The combination of the two specifications, VI and cold crank, highlights a fundamental challenge for motor oils; they are required to operate across a very broad temperature range, in both very high temperature and very low temperature environments. This is appropriate since engine oils, once manufactured, may be sold and used anywhere in any season, but they must always protect the engine in all operating environments.

The latest performance standards established by ILSAC (GF-5) are specified tests which focus on ensuring the finished lubricant (which is the base oil and additives together in combination) will achieve certain explicit measures of fuel efficiency, catalyst compatibility, minimum levels of wear and deposits, and, of notable importance in the lighter lubricant viscosity range, a limitation on volatility. Over the years, the increased GF standards have translated into enormous pressure on both virgin base oil producers and additive manufacturers to improve their products by creating higher quality base oils and higher performance additive packages to create higher quality motor and engine oils. For base oils today, this means increased demand for higher quality Group II base oils and, in many cases, Group III base oils. This ever upward quality trend has continued for many years and virgin base oil producers have been forced to upgrade their facilities to produce higher quality base oils to meet the more stringent emissions and fuel economy standards. Most of the smaller, less efficient refineries producing only Group I virgin base oil could not justify the capital upgrades and either shut down their base oil plants within the refinery, or shut down the entire refinery. Understanding the historical evolution of the technologies for making base oils is helpful to place in context the novelty of the present invention.

To make base oils from crude oil (called virgin base oils), first crude oil is distilled in an atmospheric column and then the bottoms from the atmospheric column pass to a vacuum column, in which a distillate called Vacuum Gas Oil (or VGO) is created. In certain instances the residual from the vacuum column may be processed in a solvent de-asphalting unit to create de-asphalted oil (or DAO). As shown in FIG. 1 (Sourced from Solomon Associates, as reported in Lubes N′ Greases Magazine, March 2016, page 34), the distillate or DAO is then processed by one of three different pathways to make Group I, II or III base oils. The first pathway (box 100 in FIG. 1) starts with solvent extraction and then the raffinate produced from solvent extraction is further processed by solvent de-waxing and hydrofinishing to create Group I base oils (the lowest quality). This was the first technology upgrade and generally began in the 1960s when hydrotreating was first applied to base oils, which was about 30 years after solvent extraction was first introduced in the 1930s. Exxon-Mobil introduced an innovation on the existing Group I base oil process which inserted hydrocracking or hydrotreating capability after solvent extraction and before the wax treatment step and these are the two smaller boxes called Raffinate Hydrocracking or Raffinate Hydrotreating which are then followed by the solvent or catalytic dewaxing steps. Exxon's approach enables Group II and Group III base oils to be created by upgrading the raffinate produced in the initial solvent extraction step (which was applied to the VGO or DAO feedstock).

The next innovations crude oil refiners developed were hydroprocessing technologies such as hydrocracking, hydrotreatment, hydrofinishing, catalytic de-waxing, and iso-dewaxing, and these are shown in dashed boxes 130 and 160 in FIG. 1. As used herein, the term “hydroprocessing” is used 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. Box 130 in FIG. 1 originates with a Fuels Hydrocracker (e.g. targeted for making gasoline, diesel, jet fuel and the like) whereas box 160 originates with a Lube Hydrocracker (e.g. targeted for making lube oils). As shown each of these two pathways will make higher quality Group II and Group III base oils. The advanced hydroprocessing technologies shown in boxes 130 and 160 are now the dominant processes used for making base oils, substantially displacing the traditional solvent extraction-solvent de-waxing-hydrofinishing processing route to base oil production shown in the upper large box. Exxon has continued to produce using its Raffinate Hydroprocessing technologies with some success as well.

While most lube base oil is made from crude oil, it is well known that used lubricating oil is an excellent feedstock for re-refining into base oil (which are then called re-refined base oils). FIG. 2 shows the multiple pathways to creating base oils from used lubricating oils. As the first step re-refining technologies most commonly apply vacuum distillation (200), thermal de-asphalting (230), or solvent de-asphalting (260), which create one or more intermediate liquids, certain of which are then further upgraded to create marketable base oil, most commonly either by clay treatment, solvent extraction, or hydrotreatment. (In the 1960s, acid/clay treating was prevalent but was discontinued due to extensive by-product solids creation that became ground pollutants, creating many super-fund sites that incurred massive clean-up costs.)

Re-refining has now evolved from the 1960s to where use of hydrotreating and to a lesser extent solvent extraction have become preferred processing technologies as the second step following vacuum distillation, thermal deasphalting or solvent de-asphalting. In the vast majority of all re-refining technologies, prior to the hydrotreating step or the solvent extraction step, atmospheric and vacuum distillation is utilized to remove both light ends and asphaltenes. The reason vacuum distillation is preferred is that thermal de-asphalting will create cracking which degrades the quality of the intermediate liquid. Solvent de-asphalting creates DAO, and DAO is a poor feedstock and the process leaves behind much of the valuable base oil fraction, thus creating poor yields. When vacuum distillation is used to create the intermediate liquid in a re-refinery, the distillate (charged to the clay treater, hydrotreater or solvent extraction unit) is called a vacuum gas oil (VGO). Although still produced in far lower quantities than virgin base oils, use of re-refined base oils made by hydrotreating of VGO has dramatically increased in recent years as the quality of the used motor oil pool has increased dramatically with higher lubricant standards, thus resulting in higher quality re-refined base oils. Because of the increased quality of the used lubricating oil feedstock today, it is now possible to use hydrotreating of VGO made from used lubricating oils to make excellent quality Group II+(with a VI of 115 to 119) and even Group III base oils, in part by being selective about sourcing feedstocks.

While hydrotreatment of VGO made from used lubricating oils can achieve high quality base oils, technically it is also possible to use solvent extraction of VGO made from used lubricating oils to even make Group III base oils. However, as the final step in making re-refined base oils solvent extraction suffers from three large challenges. Firstly, the sulfur level of the primary base oil is usually in the range of 200 to 300 ppm or more, which although it falls within the Group II specification, is still high compared with hydrotreated base oils. Secondly, the color of the base oil is often yellow versus the almost clear base oils typically produced by hydrotreating. Thirdly, the extract by-product created from solvent extraction of VGO is not suitable for sale as base oil, and is typically sold as low value fuel oil; thus solvent extraction has lower base oil yield.

In U.S. Pat. No. 3,617,476 issued to Woodle in 1971, a process is disclosed in a sequence involving first applying mild hydrogenation, then followed by solvent refining and dewaxing. The mild hydrogenation conditions includes a pressure not greater than 600 PSIG and the patent notes a highest VI achieved of 111, thus not even achieving Group II+. Such mild process hydrogenation conditions are not capable of achieving the advanced levels of de-aromatization, de-sulfurization, and de-nitrification demanded by today's higher quality finished lubricant specifications, and this is demonstrated partly by the upper VI value of 111 reported in Woodle '476. In U.S. Pat. No. 4,085,036 issued to Murphy in 1978, a process is disclosed applying hydro-desulfurization to a feedstock (a lubricating oil fraction created by distillation of crude oil) containing at least 1.5% sulfur, whereupon the residual portion of the distillation is subjected to a de-asphalting step and the de-asphalted oil therefrom is combined with the distillate and then solvent extracted. The raffinate from the solvent extraction step is then subjected to de-waxing, followed by one or more finishing steps such as hydrofinishing and clay treating. The purpose of Murphy '036 process is to remove sulfur more efficiently but the patent makes no claims to any improvements in either viscosity index or low temperature properties.

An alternative process for creating a lubricating oil from the residual of vacuum distillation of an asphaltic crude oil by means of solvent treatment is offered in U.S. Pat. No. 3,414,506 (issued to Compagne in 1968). A de-asphalted oil is created by applying a methanol/butanol mixture, which is then further processed by applying hydrotreatment to the de-asphalted oil. A de-waxing step is noted as an option in between the de-asphalting step and the hydrotreating step. The process creates a 44% asphaltic stream and other lower valued streams, and achieves a maximum VI of only 95 in the base oil product with base oil yields ranging from just 15.5% to 28.5%. While this process does recover base oil contained in the vacuum residual (which would otherwise be lost most likely as fuel oil), the patent does not address what happens to the majority stream, which is the distillate from vacuum distillation (the VGO).

U.S. Pat. No. 3,691,067 issued to Ashton in 1972 describes applying hydrotreatment to create a series of narrow cut fractions (e.g. liquids having a relatively small boiling range of about 200 to 250° F.) tracking the effect of hydrotreatment on improving the VI of each fraction. While Ashton '067 does not apply solvent extraction to a hydrotreated base oil, a composite product created after hydrotreating and de-waxing exhibits a VI of 93, which is substantially greater than the feedstock VI of 64, and also exhibits a fairly low pour point of −10° F. After hydrotreating but before de-waxing the pour point of the composite product was 110° F. and the VI was 113. Thus the de-waxing step has the beneficial effect of drastically lowering the pour point of the product by about 120° F. Ashton '067 also notes how hydrotreating and dewaxing the distillate increases VI substantially over that of the feedstock with the heavier fractions increasing their VI dramatically higher than the lighter fractions (68 to 83 versus 90 to 95). It is also noted (in Table VII of Ashton) that solvent refining of the charge (which is a heavy raw wax distillate, 80% of which falls in the boiling range of 880° F. to 975° F.) will improve the VI from 64 to a range of 92 to 98 across the fractions. One detriment to the hydrotreating in Ashton '067 is using a temperature of 775° F. with a liquid hourly space velocity (LHSV) as low as 0.24, which in the example creates a yield of only 78.5%, the balance of which is presumably much lighter and less valuable hydrocarbons which are outside the lube fraction boiling range. While claim 1 of Ashton states the process conditions of the process will produce substantially no cracking, the presented process conditions of Ashton would result in substantial cracking as occurred in the cited example, and as may be intimated will occur where the process specifically notes maintaining temperature and space velocity at levels designed to achieve a minimum yield of only 60% (column 3, row 4).

In view of the foregoing, it may be appreciated that there is a growing need for base oils with excellent low temperature properties, in addition to higher viscosity indexes and increased oxidation stability, and which also does not result in a materially degraded level of volatility.

SUMMARY

According to the present disclosure, it has been found that application of solvent treatment to a hydrotreated base oil feedstock yields base oils with excellent low temperature properties, higher viscosity indexes, improved oxidation stability and without any material degradation in volatility. In at least one embodiment of the invention, solvent treatment is applied to a hydroprocessed base oil stream to create at least one higher product quality stream exhibiting improved low temperature properties. Solvent treatment is preferably applied to separate the hydroprocessed base oil stream into two different streams with virtually zero loss of yield in the total (volume or mass) of the two product streams in the aggregate as compared with the volume or mass of the hydrotreated base oil feed stream (on a solvent free basis).

For ease in presentation (and without limitation), this specification describes two different products created by solvent treatment which are referred to as higher quality product or lower quality product (or stream). A preferable solvent demonstrated to achieve the noted improvements is n-methyl-2-pyrollidone and the preferred process uses ranges for solvent to oil ratio, temperature, pressure and number of stages as disclosed herein. Additionally a preferred mode of implementing the invention is to combine the solvent recovery distillation function with a volatility and viscosity control capability thereby extending the functionality of the distillation equipment providing the solvent recovery capability. The invention is applicable to hydroprocessed base oils that have been made from crude oils (aka virgin base oils) and from used lubricating oils (aka re-refined base oils).

Block diagrams in which one process of the present invention is applied to hydroprocessed base oils made from crude oil and used lubricating oils are shown in FIGS. 3 and 4, respectively. In each instance as the final step, solvent treatment is applied to a base oil that was prior created by hydroprocessing, most commonly through hydrotreating, but which also may be produced by hydrocracking or hydrofinishing (as well as other hydrogen based technologies). As noted above, and as will be explained in further detail below, solvent treatment is preferably followed by a fractionation step applied for controlling volatility and enabling creation of products of specific viscosities, with such fractionation step preferably being integrated into the solvent recovery step.

The foregoing has outlined broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

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:

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.

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.

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.

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.

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.

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).

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).

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

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.

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).

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.

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.

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.

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.

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.

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.

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.

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.

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.

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 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

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.

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.

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 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.

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 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%

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.

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.

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.

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).

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.

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.

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.

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.

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.

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.

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.