The present invention relates to a method of extracting a lubricating oil feedstock to yield a primary extract useful as a high BMCI extract and a primary raffinate. The primary raffinate is further subjected to a multi stage extraction in the presence of a solvent to produce a secondary raffinate useful as a high viscosity index lubricating oil. In particular, the present invention relates to a process for obtaining high BMCI extracts and high viscosity index raffinate by refining a lubricating oil feedstock. More particularly, the present invention relates to a process for solvent refining of a hydrocarbon based lubricating oil stock containing aromatics and non aromatics with extraction solvent to separate a high BMCI extract in a first stage and a high viscosity index raffinate in a second stage.
It is well known in the art to refine lubricating oils or upgrade lubricating oil stocks. It is especially known in the art to refine lubricating oils to produce oils of high viscosity index in good yields. While various procedural steps are known in the refinement and/or upgrading of lubricating oils, the essential steps vary depending upon the quality of the oil required. The quality of lubricating oil is normally measured in terms of some of its basic characteristics such as pour point, viscosity index, colour and oxidation stability to name a few. The requirements for various lubricating applications varies considerably and depending upon the ultimate use intended, a proper balance between the aforementioned characteristics become essential.
It is well known that lubricating oils intended for various basic purposes require amongst other properties, a high viscosity
index. It has been customary in the past to increase the viscosity index of lubricating oils by adding thereto a certain class of compounds known as viscosity index improvers. While, this satisfied the demand for lubricating oils with high viscosity index to a certain extent, increased demands for wide temperature range transmission fluids arid functional fluids, which would normally require a very high amount of viscosity index improvers have created a need for alternative methods for preparing such lubricating oils at the same time minimising the quantity of viscosity index improvers employed.
The prior art is replete with various processes for the refining of lubricating oil feedstocks. Conventionally, solvent extraction methods were applied to increase the viscosity index of the lube oil stock obtained either by vacuum distillation or by deasphalting a vacuum residuum. The raw lube distillate and deasphalted oil normally contain polyaromatic hydrocarbon which are required to be removed to obtain high viscosity index lube oil base stock. In the typical solvent extraction process the oil undergoing treatment is subjected to liquid-liquid contact with a selective solvent which preferentially resolves the more aromatic constituents. During the treatment, two liquid phases are formed - a raffinate phase consisting of substantially solvent refined oil with reduced amount of aromatic hydrocarbons and an extract phase containing a majority of the solvent along with a high content of aromatic hydrocarbons. Some of the common solvents which have been suitable include furfural, phenol, N-methyl-2-pyrrolidone, liquefied sulfur oxide, to exemplify a few.
In this connection, US Patent No. 3, 472, 757 of October 14, 1969 describes a solvent refining process employing N-methyl-2 pyrrolidone to separate low viscosity index low oxidation and thermal stability constituents from the feedstock.
US Patent No. 3, 661, 772 of May 9, 1972 discloses an improved process for the manufacture of lubricating oil product of improved viscosity index by refining the feedstock for removal of constituents of low viscosity index by solvent extraction with an aqueous solvent phase. This patent is based on the discovery that adding 2 to 15% by weight of water to the solvent results in production of lube oil with improved viscosity index.
US Patent No. 3, 702, 817 of November 14, 1972 describes a modification wherein the lubricating oil feedstock is solvent refined to produce a raffinate phase and an extract phase. The extract is catalytically hydrorefined and thereafter, combined with the raffinate or recycled to solvent refining step to improve the overall raffinate yield.
In US Patent No. 3, 476, 635 dated July 17, 1973, the process envisages solvent extraction of lubricating oil fraction from paraffin based crude to form lube oil stock of intermediate viscosity index. The said stock is thereafter subjected to dewaxing, followed by solvent fractionating to produce lubricating oil stocks of high viscosity index and low viscosity index respectively.
Finally, US Patents Nos. 5, 039, 399 of August 13, 1991 and 5, 041, 206 of August 20, 1991 teach extraction of lubricating oil stock with N-methyl-2-pyrrolidone to yield a primary raffinate useful as a high viscosity index lubricating base oil and a primary
extract. The primary extract is then mixed with an antisolvent and chilled to yield a secondary raffinate. The former teaches a further solvent extraction step to yield medium to high viscosity index lubricating oils.
Many of the aforesaid process employ counter current extractions in which the lighter lubricating oil phase is introduced into the center or bottom section of the counter current extraction tower. The oil phase is allowed to flow upwardly so that it comes into contact with a downwardly flowing stream of solvents. Primary raffinate, is recovered from the top of the extraction tower. Even multistage solvent extraction processes are envisaged wherein either the raffinate or the extract phase or both are subjected to repeated extractions to enhance a desired property.
While many of the aforesaid prior art processes do teach procedures for obtaining good yield of high viscosity index lube oil, there is no suggestion or teaching in respect of recovery of high BMCI extract. The high BMCI (Bureau of Mines Correlations Index) extracts find particular application in rubber process oils, as carbon-black feed stocks and manufacture of other speciality carbon materials such as electrode pitches and metallurgical grade petroleum coke.
Accordingly, it is an object of the present invention to provide a process for the refining of lube oil feedstock to produce a primary extract useful as a high BMCI extract.
It is a further object of the present invention to provide a process for refining lubricating oil feedstock to obtain a primary raffinate which is subjected to multi stage extractions to yield high
viscosity index lubricating oil.
It is yet a further object of the present invention to obtain high BMCI extracts in a single step without compromising on the yield of high viscosity index raffinate.
The above and other objects of the present invention are achieved by subjecting a lubricating oil feedstock to a solvent extraction, preferably N-methyl-2 pyrrolidone or furfural to yield a primary extract and a primary raffinate. The primary extract is recovered for use as high BMCI extract. The primary raffinate is repeatedly contacted with the solvent in a multi stage extraction column to yield a secondary raffinate which is useful as a high viscosity index lubricating oil.
Accordingly, the present invention provides a process for refining a hydrocarbon based lubricating oil stock containing aromatics and non aromatics components which comprises subjecting said feed stock to a single stage extraction in the presence of a solvent of the kind such as herein described to produce a high BMCI primary extract and a primary raffinate, subjecting said primary raffinate to a multi stage extraction in the presence of said solvent to produce a secondary raffinate of high viscosity index and a secondary extract of intermediate BMCI.
Any conventional solvent may be used for solvent extraction. Typical solvents would include for furfural, N-methyl-2-pyrrolidone, (NMP) phenol, dichloroethyl ether and liquid sulfur dioxide. The most preferred solvents are N-methyl-2-pyrrolidone and furfural. N-methyl-2-pyrrolidone is particularly preferred because of its chemical stability and ability to produce lighter
coloured refined oils. In addition, it can be used at lower temperature and lower dosage than the other solvents. Excellent results are obtained if the solvent employed is aqueous N-methyl-2-pyrrolidone with water content ranging from 0.3 to 15 weight percent.
It is preferred that the single stage extraction is carried out at a temperature above the pour point of the feedstock but below the miscibility temperature with the solvent particularly at least 40° F below the miscibility temperature. While the temperature range will vary depending upon the initial feedstock and choice of the solvent, determining the temperature range will pose no difficulty to a person skilled in the art. Secondly, the temperature will vary between 100°F to 250°F. During multi stage extraction, it is preferred that the solvent to oil dosage is maintained in the range of 100 to 500 weight percent.
The feedstock suitable for used in the process of the present invention would include hydrocarbons or mixture of hydrocarbons selected from paraffinic or naphthenic crudes, such as deasphalted residual oils, heavy vacuum gas oils, shale and tar sand oil derivatives, coke distillates, and heaviest fractions of catalytic craking cycle oils.
There is no requirement that the solvent employed in the single stage and multistage extraction steps be the same. Different solvents or a combination of conventional solvents may be used. For the sake of economics and ease of performance of the process, it will be preferable to employ the same solvent for both the extraction steps.
The apparatus used for carrying out the process is not critical. Conventional single stage and multistage extraction columns may be used. The extraction column should be capable of conducting counter current solvent extractions and be operable between a temperature range of 100° to 250°F which would represent a temperature range of at least 40°F less than the solvent oil miscibility temperature and the pour point temperature of the feedstock.
Solvent refined oils particularly paraffinic oil generally contain substantial amount of wax which causes the oil to have a high pour test and high cloud point. It is therefore, within the scope of the invention to envisage, if desired, removal of waxy materials which may be effected by any conventional method such as methylethylketone-toluene solvent de-waxing method. In such de-waxing method, the wax bearing oil is diluted with the aforesaid solvent. The diluted oil mixture is thereafter chilled to a temperature at which the wax is precipitated as solid crystals. Wax is separated by filtration and the oil is separated from the solvent by distillation.
The present invention will now be described with reference to the accompanying drawings in which the single figure is a simple flow diagram of the lube oil extraction process for use in the present invention.
The solvent suggested for this process is NMP or furfural which has a preferential affinity for aromatic compounds as compared to paraffinic compounds. The deaerated feed (raw lube distillate/DAO) is routed to a single stage extraction zone where it
comes in intimate contact with solvent admixed suitably with water. The solvent dosage in single stage extraction zone can be in the range of 30 vol% to 100 vol% relative to the lubricating oil feedstock. The water content can vary in the range of 0 vol% to 15 vol% relative to the solvent. The extraction temperature is kept above the pour point of the feedstock but below the miscibility temperature of the solvent. As a result of the intimate contact, the heavy aromatic constituents of the feed are dissolved in the solvent. The stream is passed through a decanter where two phases simultaneously form. The upper phase is a primary raffinate phase which is lean in polyaromatics and the lower phase is a primary extract phase rich in aromatics and comprises a major portion of the solvent. The primary extract phase after solvent recovery (not shown in the drawing) having high BMCI components can be sent to tankage for use as a feedstock for carbon black rubber process oils or for mixture of other speciality carbon materials such as electrode pitches and metturgical grade petroleum coke.
The upper phase containing little solvent and raffinate with low poly aromatic constituents is then sent to a secondary extraction zone where it comes into counter current contact with a selective solvent. The low viscosity index (VI) components are dissolved in the solvent to form a secondary extract phase which is drawn from the tower bottom. The refined oil containing little solvent is withdrawn from the top of the tower as secondary raffinate. The secondary raffinate is sent to raffinate recovery system comprising flash columns and stripper. The recovered
raffinate is sent to tankage for use as high VI lube oil base stock for further processing. The secondary extract phase after solvent recovery involving multiple stages of flashes and stripper is sent to tankage for use consistent with its aromaticity.
In accordance with this invention it has been discovered that a petroleum based lubricating oil stock can be economically processed to yield high BMCI extract alongwith high viscosity index lubricating base oils. The improved process also allows reduction in solvent dosage in multistage extraction column thereby reducing the capital cost for given service. The process also allows flexibility with regard to extract quality to meet the specific requirements.
The present invention will now be described with reference to the following non-limitative example. It will be well understood by a person skilled in the art that various modifications may be carried out in the process without departing from the spirit of the present invention.
EXAMPLE
An interneutral grade distillate derived from Arab Mix crude was extracted with N-methyl-2-pyrrolidone (NMP) in a conventional multistage extraction column to produce high VI lubricating oil base stock- The simulated process conditions are shown below
. Feedstock API 19.2
NMP Solvent Dosage (1.5% water), wt% 193.0
Extraction Temperature, C
Top 70.0
Bottom 60.0
Raffinate Yield, wt% 52.5
Dewaxed oil
VI 98
Pour, C -9
Extract Yield, wt% 47.5
BMCI 90
The extract is having lower BMCI which restrict its use as rubber extender oil or as a carbon black feedstock. To produce simultaneously a part of extract with BMCI as 95 or more with improved process, the simulated process conditions are shown below
SINGLE STAGE EXTRACTION ZONE Case 1 case 2
Solvent Dosage, wt% 54.8 55.28
water content in solvent, wt% 1.5 2.1
Temperature, C 55.0 55.0
Primary Extract
Yield, Wt% 5.1 2.9
BMCI 95 100
Primary raffinate
Yield, Wt% 94.9 97.1
MULTISTAGE EXTRACTION ZONE
Solvent Dosage, wt% 160.0 140.0
Water Content in solvent, wt% 1.5 1.5
Temperature, C
Top 70.0 70.0
Bottom 60.0 60.0
Secondary Extract
Yield, Wt% 42.3 45.5
Secondary Raffinate
Yield, Wt% 52.6 51.6
Dewaxed Oil
VI 98 98
Pour, C -9 -9

WE CLAIM:-
1. A process for refining a hydrocarbon based lubricating oil stock containing aromatics and non aromatics components which comprises subjecting said feed stock to a single stage extraction in the presence of a solvent of the kind such as herein described to produce a high BMCI primary extract and a primary raffinate, subjecting said primary raffinate to a multi stage extraction in the presence of said solvent to produce a secondary raffinate of high viscosity index and a secondary extract of intermediate BMCI.
2. A process as claimed in claim 1 wherein said solvent|selected from one or more of furfural, N-methyl-2-pyrrolidone, phenol, dichloroethyl ether and liquid sulfur dioxide.
3. A process as claimed in claim 1 or claim 2 wherein the
extraction is carried out at a temperature above the pour point of
the feedstock but below the miscibility temperature with the
solvent.
4. A process as claimed in claim 3 wherein said temperature is
in the range of 100°F to 250°F.
5. A process as claimed in any preceding claim wherein said
feedstock is selected from hydrocarbons or mixture of
hydrocarbons selected from paraffinic or nahthenic crudes, such
as deasphalted residual oils, heavy vacuum gas oils, shale and tar
sand oil derivatives, coke distillates, and heaviest fractions of
catalytic cracking cycle oils.
6. A process as claimed in any preceding claim wherein amount
of solvent present in a single extraction step is in the range of 30
vol % to 100 vol % relative to the lubricating oil feedstock.
7. A process as claimed in claim 6 wherein the solvent
comprises up to 15% by volume of a water.
8. A process for refining a hydrocarbon based lubricating oil
stock containing aromatics and non aromatics components
substantially as herein described with reference to and as
illustrated in the accompanying drawing.