JPS585957B2 - Solvent purification method for lubricating oil - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved method for solvent extraction of petroleum fractions containing aromatic and non-aromatic components.

More particularly, the present invention relates to an improved recovery method for recovering solvent from hydrocarbon extracts in a solvent extraction system.

The method of the present invention significantly reduces the energy requirements of solvent extraction methods compared to methods using conventional solvent recovery operations.

According to the invention, recovery of the solvent from the extraction phase takes place in a plurality of separation stages, including at least three pressure stages.

It is well known that the aromatic and unsaturated components of petroleum feedstocks can be separated from the more saturated hydrocarbon components by a variety of methods including solvent extraction of aromatic and unsaturated hydrocarbons.

In particular, extraction with furfural, N-methyl-2-pyrrolidone and phenol is widely used commercially.

When aromatic components and other undesirable components are removed from lubricating oil raw materials, the viscosity, color, and
Oxidative stability, thermal stability and inhibition response are improved.

having an affinity for at least one component of the blended oil feedstock and being partially insoluble with the oil feedstock under the temperature and pressure conditions used in the solvent refining of the feedstock, creating two liquid phases in the extraction zone; Many solvents are known to form.

These two liquid phases essentially consist of an extraction phase containing a predominant amount of solvent along with the dissolved aromatic components of the feedstock, and a ruffinate phase containing the non-aromatic components of the feedstock along with a minor amount of solvent. There is.

Solvents known to be useful in solvent extraction processes of lubricating oil base oils include furfural, N-methyl-2-pyrrolidone, and a variety of other well-known organic and inorganic solvents.

Recently, N-methyl-2-pyrrolidone has surpassed furfural and phenol in importance as the preferred solvent for the extraction of aromatic hydrocarbons from mixtures of aromatic and non-aromatic hydrocarbons. It's arrived.

The advantages of N-methyl-2-pyrrolidone as a lubricating oil extraction solvent to remove undesirable aromatic and polar components from base oils are similar to those using other solvents in base oil refining, such as phenol or furfural. It is now well recognized by businesses.

N-Methyl-2-pyrrolidone is generally the most preferred solvent because of its chemical stability, low toxicity, and ability to produce high quality refined oils.

Typical prior art solvent extraction methods demonstrating commonly used solvent recovery operations are U.S. Pat. No. 3,329,606;
No. 6, No. 3470089 and No. 4013549.

The process of the present invention utilizes one or more stages of solvent recovery and steam or inert gas stripping of the solvent from the product to remove existing phenol, furfural and N-methyl-2-
It can be particularly adapted to pyrrolidone purification equipment.

The present invention provides equipment for the furfural and phenol process to N-
It is particularly suitable for conversion to methyl-2-pyrrolidone solvent systems, thereby significantly reducing the energy requirements of solvent purification processes.

When a hydrocarbon extraction solvent, such as N-methyl-2-pyrrolidone, is separated and recovered from an oil-solvent mixture, that is, an extraction phase and a ruffinate phase, by a combination of distillation and stripping, stripping with an inert gas instead of water vapor is advantageous compared to the conventional method. Compared to steam stripping, solvent purification is simplified and energy requirements are reduced.

Steam stripping is common in solvent refining processes, and stripping with inert gas is used, for example, in U.S. Pat.
No. 57491.

In conventional lubricating oil refining methods, the solvent extraction step is performed under conditions that recover approximately 30-90% by volume of the lubricating oil raw material as roughinate or refined oil and approximately 10-70% by volume of the raw material as aromatic extracts. done below.

The lubricating oil raw material is mixed with solvents such as furfural or N-methyl-2-pyrrolidone at a temperature at least 5°C, preferably at least 50°C below the temperature at which the lubricating oil raw material is completely miscible in these solvents. be brought into contact.

Particularly preferred solvents are furfural and N-methyl-2-pyrrolidone, which effectively solvent extract aromatics from lubricating oil feedstocks at lower temperatures and solvent-to-oil ratios than most other known solvents. .

In the extraction step, operating conditions are selected to produce a primary raffinate with a dewaxed viscosity index of about 75-100, preferably about 85-96.

When furfural is used as a solvent, the temperature is about 46-110°C (115-230°F) to obtain the desired product.
), preferably about 60-95C (140-205°F)
Extraction temperatures in the range of 100% to 600% are used.

If N-methyl-2-pyrrolidone is used as the solvent, the solvent extraction temperature is 43-100C (110-210F), preferably 54-95C (130-205F) and 50-500%, preferably 100C. A solvent blending ratio of ~300% is suitable.

To control solvency and selectivity, water or a wet solvent may be added to the bottom of the extractor or mixed with the recycled solvent.

To obtain the finished base oil, primary Rough Ine-1 is dewaxed to the desired pour point.

If desired, the refined or dewaxed oil can be subjected to finishing treatments to improve color and stability, such as gradual hydrogenation.

The present invention improves the extraction of solvent from the extraction phase and the roughinate phase, the removal of solvent oil contamination, and the control of the water content of the solvent in the solvent purification system, and also reduces solvent recovery and purification operations compared to conventional methods. simplicity and significant savings in energy requirements in solvent purification processes.

Next, the embodiment shown in the drawings will be described in detail.

The lubricating oil feedstock, which may contain water from the outside, enters the apparatus via line 5 and is maintained at a temperature of 65-120C (approximately 150-250F).
is heated in the heater 6 to a temperature of .

The preheated feedstock passes through line 7, suitably 100
The absorption gas maintained at a pressure of ~415 kpa (0~4.2 kg/cr2, gauge pressure) is introduced into the upper part of the stripping tower 8 and enters the lower part of the tower 8 via piping 9. is forced out of the feedstock.

Column 8 is equipped with suitable devices, such as perforated bubble caps or cascade trays, to ensure intimate countercurrent contact between the lubricating oil feed and the stripping gas.

The inert gas containing water vapor is discharged from the upper end of the column 8 via a pipe 10.

The water-free feedstock produced is drawn from the lower part of column 8 and transferred by pump 11 via heater 12 and line 13 to the lower part of extraction column 14, where it is transferred via line 17 to the upper part of column 14. It is in intimate countercurrent contact with the incoming solvent.

Wet solvent from the solvent purification storage device 30 enters the garden section of the extraction column 14 via line 99.

The roughinate mixture, typically 85% petroleum mixed with solvent, exits the extraction column 14 via line 19 and is processed to recover the raffinate from the solvent.

The roughinate after solvent separation is the main ingredient of solvent refined lubricating oil, ie the desired process product.

The predominant portion of the solvent is present in the extraction mixture removed from the bottom of the extraction column 14.

The extraction mixture, which in this example consists of about 85% solvent, is
8 and then taken out from the column 14.

The extraction mixture is first processed to remove the solvent from the extract and then processed to recover the extract as a commercially available process product.

The predominant portion of the extraction mixture, typically containing about 85% solvent, is passed through heat exchangers 20, 21 to preheat the extraction mixture and directed to a low pressure flash evaporation column 22.

The column 22 typically has a pressure of 170 to 205 kPa (0.7 to 1
．． 05 kg/fl2, gauge pressure).

The extraction mixture from column 14 is led via lines 31, 32 to the top of column 22 as reflux.

The solvent separated from the extract in column 22 is discharged via line 24 to heat exchanger 20 where the solvent vapor is condensed and further cooled in cooler 26 before the solvent is transferred to line 27.
After that, it is transferred to the solvent purification and storage device 30 for reuse in the process.

The predominant portion of the extraction mixture after the solvent has been removed is removed from the bottom of column 22 by pump 36 and transferred via heater 37 and line 38 to high pressure flash distillation column 39 .

Column 39 suitably has a pressure of 375-415 kpa (2.8-31
．． It is operated at a pressure of 5 kg/ii2, gauge pressure).

A recessive portion of the extraction mixture from the bottom of column 14 is connected to line 31
, 33 to the upper part of column 39 as reflux to column 39.

Alternatively, the solvent mixture from column 22 is routed to line 40.
, 31, 32, 33 as reflux and may be fed to the columns 22, 39.

The solvent vapor leaving the top of the high pressure flash distillation column 39 via line 41 passes through the heat exchanger 21 by indirect heat exchange with the extraction mixture from the bottom of the extraction column 14, condensing the solvent vapor and passing into the flash evaporation column 22. Preheat the extraction mixture before entering.

The recovered solvent is transferred via piping 42 to the solvent purification storage device 30 for reuse in the process.

The petroleum extract removed from the bottom of the flash evaporation column 39 via line 44 still contains small amounts of solvent, for example 5-15% by volume, and 95-85% by volume of hydrocarbons.

This extraction mixture is fed via line 44 to a vacuum flash evaporation column 46 for further recovery of solvent from the extract.

The column 46 is typically equipped with countercurrent gas-liquid contact trays, suitably of the cascade or bubble tray type.

A portion of the extraction mixture from column 14 or column 22 is fed as reflux to the top of column 46 via lines 36, 47.

Column 46 may be operated at a pressure of 10-100 kPa.

The extract is further separated from the solvent in column 46.

Solvent vapor flows from the top of the column 46 through a pipe 48 to a condenser 49.
and taken out to the solvent accumulator 50.

Uncondensed gas removed from accumulator 50 via line 51 to a suitable vacuum source, not shown, is either disposed of or recycled via line 86.

The extract-rich fraction is taken out from the bottom of the column 46 via a pipe 54 and led to the top of a stripping column 55.

Stripping column 55 is typically a countercurrent liquid-vapor contact column with bubble trays, and the liquid extract flowing down the column is passed through an inert strip that is led to the bottom of stripping column 55 via piping 56. Contacted with ripping gas.

A portion of the extraction mixture from the lower part of the extraction column 14 is transferred to a pipe 36,
51 and is fed as reflux to the upper part of column 55.

Alternatively, a portion of the extraction mixture from the bottom of column 22 may be fed to columns 22, 39, 46, 55 via line 40 as reflux.

Extracted oil containing less than about 50 ppm of solvent and typically consisting of 80% unsaturated hydrocarbons and about 20% saturated hydrocarbons is removed from the bottom of column 55 by pump 58, passed through heat exchanger 59, and then transferred to the column. It is cooled by indirect heat exchange with the roughinate mixture from the top of 14 and exits the apparatus via line 60 as a process product.

The inert stripping gas and the solvent vapor expelled by the stripping are discharged from the upper part of the column 55 through a pipe 62 to a condenser 63, where the solvent vapor is condensed.

Solvent condensate is collected in condensate accumulator 64.

The inert gas separated from the condensate is discharged to line 65 and recycled to the process as described below.

The roughinate mixture taken out from the upper part of the column 14 via the pipe 19 is heated in the heat exchanger 59 by indirect heat exchange with the extract discharged from the column 55, and then transferred to the heat exchanger 6.
7 and heater 68, it enters a vacuum evaporation column 70 where the solvent is separated from the roughinate mixture.

The recessive portion of the roughinate mixture from line 19 bypasses heat exchangers 59, 61 and heater 68 and is conducted via line 71 to the top of column 70 as reflux.

Another portion of the roughinate mixture from line 19 is transferred to line 7.
2 and is led to the upper part of column 75 as reflux.

The solvent vapor separated from the ruffinate mixture in column 70 is removed from the top of column 70 into line 48 and transferred along with the solvent vapor from column 46 to condenser 49 where the solvent vapor is condensed.

The condensed solvent is collected in the accumulator 50, and the uncondensed gas is taken out via the pipe 51 as described above.

Roughinate, still containing some solvent, is removed from the bottom of column 70 via line 74 to the top of column 75, and residual solvent is removed from the raffinate via stripping with inert gas, which enters the bottom of column 75 via line 76. is removed.

Roughinate from which the solvent has been substantially removed is removed as a process product from the bottom of column 75 by pump 77, and is indirectly heat exchanged with the raffinate mixture from line 19 in heat exchanger 67, which is the main product of the process. The purified lubricant is discharged through a pipe 78.

Condensate from accumulators 50, 64 is transferred to purification storage device 30 by pumps 79, 80, respectively.

In order to purify the solvent to be reused in the process, various steps, such as distillation, azeotropic separation, absorption, gas stripping, etc., are carried out, primarily to remove excess water (if any). It can also be used to remove polymers, oils, etc.

Excess water from any external sources is removed from purification storage device 30 via piping 81.

The solvent is recycled to the process via line 17 via line 83 by pump 82 if necessary.

After the solvent condensate has been separated in accumulator 64, the inert gas from columns 55, 75 may still contain some solvent vapor.

The inert gas from the accumulator 64 is transferred to the compressor 85
It is pressurized again at , and is transferred to the absorption stripping tower 8 via a pipe 86 .

Column 8 serves as an absorption device for the solvent vapor remaining in the inert gas stream.

Suitably from 170 to 310 k depending on the pressure inside the column 8
The inert gas stream leaving the compressor 85 at a pressure of Pa (0.7-3.2 kg/cl2, gauge pressure) or higher is hot due to the heat of compression in the compressor 85.

This gas stream can be heated or cooled as necessary to maintain the desired temperature within column 8, suitably at a temperature of about 150 to about 300 degrees Fahrenheit.

In column 8, solvent vapor is absorbed from the inert gas, and the water that enters the apparatus with the lubricating oil feed stream is vaporized and becomes contained in this inert gas.

The inert gas containing water vapor leaves column 8 via line 10 and is cooled in condenser 88 to a temperature sufficient to condense the water vapor from the inert gas stream.

The condensate separated from the inert gas is collected in a separator 89 from which water-containing condensate is discharged via line 90.

The inert gas from which water and solvent vapor have been removed is transferred to the pipes 56 and 76 via the pipe 91 and the heater 92, and is transferred to the columns 55 and 76.
5 respectively.

Stripping gases include, but are not limited to, substantially inert gases such as nitrogen, methane, carbon dioxide, and the like.

A suitable inert gas for use in the process is nitrogen.

By contacting the fresh lube oil feedstock with the inert stripping gas used in the previous process to strip the solvent from the extract and ruffinate,
Two important advantages are obtained.

That is, the solvent is recovered from the stripping gas and
Water is simultaneously removed from the feedstock.

During solvent refining of lubricating oil raw materials, there is a tendency for light oil to accumulate in the solvent.

When light oil is accumulated in the solvent in the conventional solvent refining process, it becomes necessary to separately perform distillation in the solvent refining process to remove the accumulated oil.

This light oil is normally carried off from the extract and raffinate flash evaporation and stripping columns along with the solvent and stripping media.

According to the solvent purification method of the present invention, a portion of the extraction mixture from extraction column 14 or flash evaporation column 22 is used as reflux to columns 22, 39 in the solvent recovery system.

In the illustrated preferred embodiment, the extraction mixture from extraction column 14 or flash evaporation column 22 is also used as reflux to extract recovery columns vacuum evaporation column 46 and stripping column 55.

In this embodiment, the vacuum evaporation tower 7 of the roughinate recovery system
The reflux to stripping column 75 consists of a portion of the raffinate mixture discharged from the top of extraction column 14.

The extraction mixture from column 22 from which the majority of the solvent has been separated or the primary extraction mixture from column 14 is used as reflux to columns 22, 39, so that the gas oil is carried away from these columns together with the separated solvent. This is substantially prevented.

Similarly, in other columns, the extraction and raffinate fractions have relatively low volatility, reducing or preventing carry-off of light hydrocarbons in the solvent vapor.

At the same time, the raffinate and extract reflux are good absorbents for the light petroleum vapors that would tend to be carried away from the respective solvent separation columns.

The combination of pretreatment of fresh lube oil feedstock with recycled inert gas and refluxing the extract and raffinate to their respective columns eliminates or substantially reduces the amount of solvent purification required for the process. .

According to a particular example of the purification method of the present invention, wax distillate (WD-20) containing 45 ppm water is heated to 20,400 k9
(45,000 lbs.) to the absorption stripping column according to the purification process of the present invention and 12.7k97 hours (28 lbs./hr.) transported from the raffinate and extract stripping column of the solvent purification unit as described above. 2 containing N-methyl-2-pyrrolidone vapor of
With recirculating nitrogen gas at a rate of 40 ky/hr (551 lb/hr) at 115°C and 138 kPa (0.14 kPa
g/cvt, absolute pressure).

In the absorption stripping column, the solvent contained in the recycled inert gas stream was recovered from the inert gas.

At the same time, the water contained in the lubricating oil feedstock was completely vaporized and contained in the nitrogen stripping gas.

The mixture of nitrogen and water vapor leaving the absorption first pumping tower was cooled to 50°C to condense the water vapor.

Condensed water was separated from the recycle gas stream and the resulting dry nitrogen was heated to 290°C and recycled to the stripping column.

52.2 kg/hr (115 lb/hr) of heated dry nitrogen was fed to the extract stripping column,
．． 7 kg/hr (436 lb/hr) was fed to the roughinate stripping tower.

The raffinate and extract stripping column has a bottom pressure of 3.5 kPa (approximately 0.35 kg/ffl, absolute pressure) and a top pressure of 20.7 kPa (approximately 0.21 kg/cmi, absolute pressure).
absolute pressure).

Both stopping towers were refluxed with 20C of N-methyl-2-pyrrolidone.

The temperature at which the extract feed stream enters the extract stripping column is 2
90°C, the temperature at which the product extract leaves the stripping column is 2
The temperature was 60°C.

Extractate content of the feed stream to the extract stripping column 22
The N-methyl-2-pyrrolidone content was 435 kg/hour (959 pounds/hour).

154.2 kV/hour (340 pounds/hour) of N-methyl-2-pyrrolidone was fed as reflux to the extract stripping column.

52 at 290℃, 35kPa (0.14kg/cm2)
．． Nitrogen stripping gas fed to the stripping column at a rate of 2k9/hr (115 lb/hr) was
160°C, 20.7 kpa with 9.2 kg/hr (1299 bonds/hr) of N-methyl-2-pyrrolidone
(0.21 kg/ant) was discharged from the top of the stripping column.

The top stream of the extract stripping column was
．． 21kg/cm2).

155C, N-methyl-2-pyrrolidone 836 kg/
time (1843 lb/hr) and nitrogen 197.8 kg
Roughinate stripping column overhead stream consisting of 436 lb/hr (436 lb/hr).

Nitrogen and N-methyl- from these stripping columns
2-pyrrolidone vapor is supplied to the condenser and the pressure is 20.7kPa.
(0.21 kg/Cm2), cooled to 75°C, and
25.2 kg/hour (3142 lb/hour) was condensed.

12.7 kg of solvent vapor at 75°C after removal of solvent condensate
The pressure of the mixture was increased to 175 kPa (approximately 1.85 kg/hr) by supplying nitrogen containing 28 lb/hr (28 lb/hr) to the compressor.
/cm2), and the temperature was accordingly raised to 120C.

The compressed mixture was recycled to an absorption stripping column to recover solvent vapors before reuse in the process.

[Brief explanation of drawings]

The figure is a flow sheet showing the solvent purification method according to the present invention. 8...Absorption-stripping tower. 14...Extraction tower. 22...Flash evaporation tower. 55, 75... stripping tower. 46, 70...vacuum distillation column. 49, 51, 88...
Condenser.

Claims (1)

Claims: 1. Contacting a lubricating oil feedstock in an extraction zone with a solvent selective for the aromatic components of the feedstock to produce a lubricating oil feedstock containing a ruffinate phase containing a minor amount of the solvent and a predominant amount of the solvent. forming an extraction phase, separating the raffinate phase from the extraction phase, removing the solvent from the raffinate phase and the extraction phase by flash evaporation, distillation, rectification, or a combination thereof, and removing the remaining solvent. , a method of solvent refining a lubricating oil feedstock comprising stripping the extract phase and the ruffinate phase with an inert stripping gas forming a mixture of solvent vapor and stripping gas,
Solvent vapor is extracted from the stripping gas by contacting the stripping gas containing solvent vapor with fresh lubricant feedstock in a countercurrent contact zone prior to introduction of the feedstock into the extraction zone. adsorbed by the feedstock and at least partially vaporizes external water contained in the feedstock to form a mixture of inert gas and water vapor, and directing the mixture to a first condensation zone to remove water vapor from the water vapor. At least a portion of the inert gas is condensed, the inert gas is separated from the water produced by condensation, and the inert gas from which water and solvent are removed is used as the stripping gas to remove the solvent from the ruffinate phase and the extraction phase. A solvent purification method characterized by contacting with. 2. The solvent purification method according to claim 1, wherein the solvent is N-methyl-2-pyrrolidone. 3. The method for refining a solvent according to claim 1, wherein the selective solvent is furafural. 4. The solvent purification method according to claim 1, wherein the selective solvent is phenol. 5. A method of solvent refining a lubricating oil feedstock comprising contacting the lubricating oil feedstock with an aromatic component selective solvent of the feedstock in an extraction zone, wherein the feedstock is heated to a temperature of about 150 to 300°F. (65.56~176.67°G)
temperature and about 0 to 60 psig (0 to about 4.2 kγ/cm
d) in a first contact zone, prior to the solvent extraction operation, in intimate contact with an inert stripping gas to separate the stripping gas from the feedstock and to remove the aroma of the feedstock. by contacting the feedstock in an extraction zone with a solvent that exhibits preferential selectivity for group components;
forming a ruffinate phase containing a minor amount of the solvent and an extraction phase containing a predominant amount of the solvent; removing the raffinate phase and the extraction phase separately from the extraction zone; and removing a portion of the solvent in an extraction solvent separation zone. is removed from said extraction phase;
The inert stripping gas from the first contact zone and the extraction phase are combined in an extraction phase stripping zone for 40 minutes.
0-700°F (2044-371.1C) and O-6
Removing another portion of the solvent from the extraction phase by contacting at a pressure of 0 psia (0-4.2 ky/cm3, absolute pressure) to produce a mixture of stripping gas and solvent vapor; from the extraction phase stripping zone into contact with a fresh lubricating oil feedstock in the first contacting zone to recover solvent from the inert gas and into the feedstock. A solvent purification method characterized by evaporating water contained in. 6. The mixture of stripping gas and solvent vapor is heated at about 15 to 60 psig
, gauge pressure) at a pressure of approximately 100-300°F (
37.78 DEG C. to 148.89 DEG C.) to condense at least a portion of the solvent vapor and to separate the condensed liquid solvent from the inert gas prior to contact with the fresh feedstock. The solvent purification method according to item 5. 7. Where the feedstock contains water and the inert stripping gas separated from the feedstock in the first contact zone contains water vapor, the stripping gas containing water vapor
6. The method of claim 5, further comprising the step of transferring Tuping gas to a condensation zone to condense and separate at least a portion of the water vapor from the inert gas prior to contacting the inert gas with the extraction phase. Solvent purification method. 8. Transferring a dominant portion of the extraction phase from the extraction zone to the extraction solvent separation zone, and transferring a recessive portion of the extraction phase from the extraction zone to the upper part of the extraction solvent separation zone as reflux to the separation zone. Claim 5 further comprising:
Solvent purification method described in section. 9. The method of claim 8, wherein a further recessive portion of the extraction phase from the extraction zone is introduced into the upper part of the extraction phase spooling zone as reflux thereto. 10 by removing a portion of the solvent from the roughinate phase in a roughinate solvent separation zone and then contacting the roughinate phase in a roughinate stripping zone with a portion of the inert gas from the first contact zone. , removing another portion of the solvent from the roughinate phase to form a mixture of inert gas and solvent vapor, and directing the inert gas containing solvent vapor from the roughinate stripping zone to the first contact zone. It further includes a step of transferring.
A method for refining a solvent according to claim 5. 11. The solvent purification method according to claim 10, wherein a recessive portion of the raffinate phase from the extraction zone is supplied to the raffinate solvent separation zone as its reflux. 12. The method of claim 11, wherein another recessive portion of the raffinate phase from the extraction zone is fed as its reflux to the top of the roughinate stripping zone.