KR850001273B1 - Recovery of solvent in hydrocarbon processing systems - Google Patents

Abstract

Solvent refining of lubricating oil feeds is effected by (a) extracting aromatics from the feed using N-methyl-2-pyrrolidone (NMP) under pressure; (b) removing solvent from the extract in a series of vaporization zones, each operating at a higher pressure than the preceding zone, in which the first zone is operated at a pressure below that in the extraction zone, the last zone is supplied with heat from an external source and each preceding zone is supplied with heat by heat exchange with vapor from the next succeeding zone; (c) vaporizing the extract/solvent mixt. from the last zone in a vacuum flash zone; (d) heating the extract, solvent mixt. from the vacuum flash zone in admixture with an added inert gas; and (e) vacuum- stripping the mixt. with an inert gas.

Description

Lubricating Oil Solvent Purification

1 is a simplified diagram of a first embodiment of the method of the present invention.

2 is a simplified copper diagram of a second embodiment of the method of the present invention.

* Explanation of symbols for main parts of the drawings

5 absorption tower 15 absorption tower

25: extraction tower 35: low pressure flash tower

45: drying tower 48: central flash tower

55: high pressure flash tower 65: vacuum flash tower

71: stripping tower 86: vacuum flash tower

96: stripping tower

The present invention relates to an advanced process for recovering the solvent used to process petroleum fractions containing components having different physical and chemical properties. More particularly, the present invention relates to a method for recovering a solvent from a hydrocarbon extract in a lubricating oil solvent purification process using N-methylpyrrolidone as a solvent.

It is well known that aromatic and unsaturated components in hydrocarbon oil feedstocks can be separated from more saturated hydrocarbon components by various methods, including solvent extraction of aromatic and unsaturated hydrocarbons. The solvent has affinity with at least one component of the hydrocarbon larvae feedstock and is preferably partially incompatible with the filler material under the temperature and pressure conditions applied in the solvent extraction step. There are two liquid phases in the extraction zone, and the two liquid phases generally contain the extract phase containing most of the solvent together with the aromatic components dissolved in the filler material, and the extract residue containing a small amount of the solvent and the non-aromatic components in the filler material. It is composed of phases. Among the solvents known to be useful in the solvent extraction process of petroleum based lubricating oils are furfural, N-methyl-2-pyrrolidone, phenol and various other known organic and inorganic solvents. The removal of aromatics and other undesirable components from the lubricating organic raw materials improves the viscosity index color, oxidation stability and thermal stability, and the inhibition of base oils and lubricating oil products produced from hydrocarbon feedstocks.

Most recently, N-methyl-2-pyrrolidone has been replaced by furfural and phenol as the preferred solvent for extracting aromatic hydrocarbons from mixtures of aromatic and non-aromatic hydrocarbons. The advantages of N-methyl-2-pyrrolidone as a solvent are described, for example, in US Pat. No. 4,057,491. N-methyl-2-pyrrolidone is more effective at solvent extraction of aromatics from relatively low temperatures and low solvent to oil lubricating oil fillers than most other known solvents.

N-methyl-2-pyrrolidone is generally the most preferred solvent due to its chemical stability, low toxicity and its ability to produce refined oils of improved quality. Several conventional methods are described in US Pat. Nos. 3,461,066 and 3,470,089, using N-methyl-2-pyrrolidone as a solvent and describing conventional solvent recovery operations.

The process of the present invention is useful for improving N-methyl-2-pyrrolidone purification equipment using single or multistage solvent recovery systems and for vapor or inert gas stripping of solvent from the product. The process of the present invention is also particularly suitable for converting furfural and phenol processing plants to N-methyl-2-pyrrolidone solvent systems while reducing energy requirements in solvent purification processes.

Solvent purification in recovering N-methyl-2-pyrrolidone from oil-solvent mixtures such as extract phase and extract residue, for example, in a solvent purification system that separates the solvent from the oil-solvent mixture by using distillation and stripping together. Stripping with inert gas rather than stripping with steam can reduce in-process energy requirements as compared to conventional steam stripping. Inert gas stripping is described, for example, in US Pat. No. 2,923,680; 4,013,549; 4,057,491.

In the extraction step, the operating conditions are chosen such that primary extraction residues with a dewaxing viscosity index of about 75-100 are preferred. The solvent extraction temperature is suitably 43-100 ° C., preferably 54-95 ° C. and the solvent capacity is suitably 50-500 volume percent, preferably 100-300 volume percent based on the hydrocarbon feedstock. The extraction pressure at the extraction residue and solvent interface is preferably 1.4-2 bar. Water or wet solvent may be injected into the base of the extractor to control solvent power and selectivity. Dewax to the pour point where the first extraction residue is desired to produce a finished lubricant base material. If desired, the refined or de-leaded oil can be subject to finishing treatments such as mild hydrogenation, etc., to improve color and stability.

Extraction tower operation involves the backflow of two immiscible liquid phases. The mechanical viability of the process thus depends on the density difference between the multisolvent or extract phase and the multioil phase or extract residue. If the solvent capacity range is within 100-500 volume percent, that is, within 100-500 volume percent of solvent for each 100 volume percent of lubricating oil feedstock, the density difference increases with increasing solvent volume. Very low solvent capacities, such as less than 100 percent, result in very low density differences that severely limit the discharge of feed to the solvent extraction tower.

N-methyl-2-pyrrolidone is such a solvent effective for aromatics when the solvent capacity required to achieve the desired extraction residue quality for some hydrocarbon fillers is extremely low. When operating an extraction tower with anhydrous N-methyl-2-pyrrolidone at the minimum dosage, ie about 100 percent and at a temperature of about 60 ° C., the quality of the purified oil is higher than desired and in some cases the yield of the purified oil is Lower than desired.

The method of the present invention operates the extraction step with an anhydrous solvent capacity that is effective to rapidly separate the two liquid phases in the extraction column and discharges the extract phase and the point where the water or wet solvent is introduced near the discharge point of the extract phase, that is, the hydrocarbon feedstock into the separation system. This problem is solved by introducing into the extraction column between the points and refluxing the extraction column to obtain the product of the desired quality of the extraction residue with high refined oil yield.

Until now, it has been proposed to add water to N-methyl-2-pyrrolidone in the extraction column or to mix it with the reflux solvent in order to reduce the solubility of the aromatic hydrocarbon in the solvent. The present invention provides an improved method of using N-methyl-2-pyrrolidone as a solvent to separate solvents from extracts and extract residues, remove oil contamination in solvents, and control the water content of solvents in solvent purification systems. To provide. In one preferred embodiment of the present invention, the present invention provides a process for obtaining purified oil of high quality at a given solvent capacity by using anhydrous solvent as the primary solvent in an extraction column and using water or a wet solvent at reflux. Solvent recovery can be simplified as a result of reduced energy requirements in the process.

In summary, the present invention provides an advanced method for recovering solvent from an extract obtained on a solvent-based lubricating oil basestock, in which removal of the solvent from the extract is first performed by evaporating the solvent partially in the low pressure solvent evaporation zone and then gradually higher. This is achieved by further evaporation of the solvent from the extract in various zones under pressure and heat is supplied externally only to the final high-pressure evaporation zone, where heat in each previous evaporation zone is subjected to heat exchange with steam from each subsequent evaporation zone. And a portion of the vapor from the final high pressure evaporation zone is mixed with the steam from the medium pressure evaporation zone and supplied to the low pressure solvent evaporation zone as a heat source. In a preferred embodiment the solvent is further evaporated in the sub-atmospheric flash zone and then recovered from the extract by evaporation in a high-pressure evaporation zone at a temperature of at least 5 ° C. higher than the high pressure zone temperature.

In another embodiment, the solvent remaining in the oil in the extract from the high-pressure evaporation zone is at least 5 ° C. higher than the high-pressure flash evaporation zone in the presence of an inert gas after flash evaporating the solvent from the extract fraction in the flash zone below atmospheric pressure. The solvent is further recovered from the extract by further evaporating the solvent from the extract and then stripping the extract with an inert gas under low excess atmospheric pressure. The method of the present invention will be more readily understood by the accompanying drawings and detailed description of the two embodiments.

1 is a simplified copper diagram of a first embodiment of the method of the present invention.

2 is a simplified isometric view of the second embodiment.

Referring to FIG. 1, the petroleum based lubricating oil feedstock is fed into line 1 into the solvent purification process and divided into two streams. Part of the feedstock goes through line 2, heaters 3 and 4 to the top of absorption tower 5 where the lubricating oil feedstock is inert stripping gas such as nitrogen containing solvent vapor entering the bottom of absorption tower 5 via line 6 and It is in intimate countercurrent contact. Absorption tower 5 consists of a countercurrent vapor-liquid contacting tower in which the liquid flowing below the tower is in intimate contact with the gas and vapor flowing up through the tower. Devices such as, for example, bubble cap trays, perforated pipes, and filling materials for intimate contact between vapor and liquid are to be installed in the tower. Preferred embodiments of the invention are described as special embodiments. In this embodiment the lubricating oil feedstock from line 2 is heated to a temperature of 66 ° C. in heater 3 and absorption tower 5 is operated at 1.7 bar. Solvent vapor in absorber 5 is absorbed by the recovered solvent back into the process together with the lubricating oil feedstock and the feedstock. The stripping medium from which the solvent is removed is discharged through line 7 to the heater 8 for reuse in the process.

The second part of the lubricant feedstock from line 1 goes to the top of absorber 15 via line 12, heater 13 and line 14 where the lubricant feedstock is a mixture of steam and solvent vapor entering the bottom of absorber 15 via line 16. It is in intimate contact with the backflow. Absorber 15 consists of a countercurrent contact tower similar to that of absorber 5 described above and can be operated at a pressure of 1.1 bar and a temperature of 102-104 ° C. in one particular embodiment. The solvent-free vapor therefrom goes to line condenser 18 via line 17 where it condenses and accumulates in the late drum 19 where it is stored until solvent content inspection and discharged to the sewer if low enough.

The lubricating oil feedstock flows from the bottoms of the absorbers 5 and 15 merge together into the bottom of the extraction tower 25 via line 22, heater 23 and line 24 where the lubricating oil feedstock is introduced into the top of the extraction tower via line 26. It is in intimate countercurrent contact with anhydrous N-methyl-2-pyrrolidone solvent. As used herein, "anhydrous" N-methyl-2-pyrrolidone means N-methyl-2-pyrrolidone containing 0.3 weight percent or less of water. As a special embodiment the extraction tower 25 is operated under interfacial pressure of 1.4-2 bar and in this embodiment at 1.4 bar pressure at 46 ° C. extract outlet temperature and 63 ° C. extract residue outlet temperature.

The extract residue mixture, consisting of 85% hydrocarbon oil and solvent mixture, is discharged from extraction tower 25 via line 28 and subjected to extraction residue recovery from the solvent. The extraction residue after solvent separation becomes a solvent refined lubricating oil base material which is a preferred product of the process. Recovery of the solvent from the extract residues will be described later. Most of the solvent is contained in the extraction mixture discharged from the bottom of the extraction column 25. In this example, the extract mixture, consisting of about 85% of the solvent, exits from tower 25 and passes through heat exchangers 32, 33, 34, which serves to preheat the mixture via line 31 to the low pressure flash tower 35 where water and Some of the solvent is evaporated. Flashtop 35 is equipped with a vapor-liquid contacting device, such as a cascade tray, at the top to allow countercurrent contact between the reflux liquid flowing down the tower and the solvent vapor flowing over the tower. A portion of the extraction mixture from the base of the tower 35 is cooled by a device not indicated and reintroduced to the top of the tower 35 via reflux in a known manner via line 37. The flashtop 35 can be operated under a pressure of 1.15-1.4 bar and in this particular embodiment the flashtop pressure is 1.15 bar and the temperature is about 202 ° C.

Solvent vapors separated from the flashy 35 to extraction mixture contain water vapor. Solvent vapor mixed with water vapor is sent to heat exchanger 33 via line 39 where most of the solvent vapor and a small amount of water vapor is condensed and the extract mixture from line 31 is preheated. Condensate and non-condensing steam are sent to accumulator 42 via line 41 and part of the feed is sent to drying tower 45 as described below.

Most of the extract mixture from which part of the solvent was removed by evaporation in flashtop 35 is sent through heat exchangers 46 and 47 to a medium pressure flashtop 48 similar to the low pressure flashtop 35. The medium pressure flashtop 48 is suitable for operation under a pressure of 1.7-1.97 bar and the pressure of the medium pressure flashtop in this particular embodiment is 1.72 bar and the temperature is 232 ° C. Very few of the extract solvent mixtures from the base of flashtop 35 are indicated, but are introduced to the top of flashtop 48 by reflux according to known methods.

Solvent vapor leaving the top of the medium pressure flash tower 48 is sent to the heat exchanger-condenser 34 via line 49 where it is indirect heat exchanged with the extract mixture from the base of the extraction tower 25 to condense a portion of the solvent vapor and the extract mixture to low pressure. Preheated prior to introduction into flashtop 35. The condensate from the heat exchanger-condenser 34 is sent through line 50 as solvent-free for reuse. Non-condensing solvent and water vapor from the heat exchanger 34 are sent via line 51 to drying tower 45 as part of the feed to the drying tower.

Some of the solvent was further removed due to evaporation in the flashtop 48 and the extract mixture was discharged from the bottom of the flashtop 48 and passed through heat exchanger 52 line 53 to the heater 54 where the mixture was heated to a temperature of 288-310 ° C. It is sent to a high pressure flash tower 55 to remove most of the remaining solvent from the extract mixture. The high pressure flashtop 55 is suitably operated under a pressure of 2.9-3.14 bar and the pressure in this particular embodiment is 2.9 bar. Some of the extract solvent mixture from the base of the flashtop 35 is not shown but is introduced to the top of the high pressure flashtop 55 in a known manner as reflux. Most of the solvent vapor leaving the top of the high pressure flash tower 55 is sent to the heat exchanger 47 via line 56 where it is indirect heat exchanged with the extract mixture from the low pressure flash tower 35 to condense the solvent vapor and the extract mixture is subjected to the medium pressure flash tower 48. Heat is supplied prior to introduction into the furnace. Solvent vapor is condensed in thermal bridge 47 and the condensate is sent to solvent condenser 47B via line 47A and then to anhydrous solvent reservoir 92 via line 106 and then anhydrous solvents are fed to extraction tower 25.

A portion of the solvent vapor from the high pressure flash tower 55 according to the invention is sent via line 57 and 49 to the heat exchanger 34 via line 49 in a mixture with the solvent vapor from the medium pressure flash tower 48 to extract from the extraction column 25. The heat is supplied to the mixture while maintaining the desired temperature on the low pressure flash tower 35. For this purpose it is suitable for 2-10% of the solvent vapor from the high pressure flash tower 55 to be sent to lines 57, 49 and heat exchanger 34. The hydrocarbon oil extract from the bottom of the high pressure flash tower 55 via expansion valve 58 and line 59 still contains some solvent, for example 20% solvent and 80% hydrocarbon extract. The extract mixture is reheated in a heater 60 to a higher temperature than the high pressure flash tower 55 and sent to the vacuum flash tower 65 to recover more solvent from the extract. The vacuum flashtop can be operated at a temperature of 293-315 ° C. under pressure ranging from 0.25-0.55 bar and the pressure in this particular embodiment is 0.45 bar and the temperature is 293 ° C. Some of the extract solvent mixture from the bottom of the flashtop 35 is not shown but is fed to the top of the vacuum flashtop 65 as reflux by known methods.

The separation of another extract from the solvent takes place in vacuum flash tower 65. Solvent vapor is withdrawn from the top of flashtop 65 and sent to condenser 67 and solvent accumulator 68 via line 66. The non-condensing gas is discharged from accumulator 68 and sent to a suitable vacuum source, although not indicated through line 69, and can be discharged from this unit. The extract-rich fraction is discharged from the base of the flashtop 65 and introduced through line 70 to the top of the extract stripping tower 71. The extract stripping tower 71 is a typical counter-current vapor-liquid contact tower in which a liquid extract flowing down through the tower and an inert stripping gas introduced from the bottom of the tower 71 through line 72 are contacted with a bubble cap tray. A portion of the extract mixture from the bottom of stripping tower 71 is cooled and returned to the top of the tower as reflux via line 73.

Extraction oil containing less than about 50 ppm of solvent and composed of 80% by weight of unsaturated hydrocarbon and about 20% by weight of saturated hydrocarbon is discharged from the lower end of stripping tower 71, cooled through heat exchanger 74, Is the product of and is discharged from this system. An inert stripping gas, such as nitrogen and stripping solvent vapor, is withdrawn from the top of the stripping tower 71 and sent to line condenser 77 where the solvent condenses.

Solvent condensate is collected in condensate accumulator 78 and recycled to extraction tower 25 via line 79 to anhydrous reservoir 92. The inert gas separated from the condensate solvent in separator 78 is recycled by compressor 80 and sent to line 6 and absorber 5 to recover the trace amount of solvent contained in the recycle stripping gas. In this example the extract stripping tower 71 is operated at pressures slightly above atmospheric pressure such as 1.1-1.3 bar and 299 ° C. Condenser 77 cools the stripping gas and solvent to 60 ° C. to allow most of the solvent to condense from nitrogen or other stripping gas prior to recycling to absorber 5. Absorber 5 recovers almost all of the residual solvent from the recycled nitrogen stream.

The extract residue mixture discharged via line 28 from the top of the extraction tower 25 usually consists of 15 vol% solvent and 85 vol% hydrocarbons. In this particular embodiment, the extraction column is operated at 100% by volume, that is, anhydrous solvent capacity of 1 solvent per oil filler capacity. In a particular embodiment, the extract residue mixture exits the extraction tower at a temperature of 63 ° C. Extraction residue mixture from line 28 is collected in tank 82 and heated in heat exchanger 83 and ignition heater 85 and then introduced into vacuum flashtop 86 where solvent is separated from the extraction residue mixture. In one preferred embodiment the extraction tail vacuum vacuum tower 86 is operated at a pressure of 0.7 bar and a temperature of 298 ° C. Reflux from a suitable source such as anhydrous N-methyl-2-pyrrolidone is supplied as reflux via line 87 to the top of the vacuum flash tower 86.

Extraction residue Vacuum flashtop 86 separates most of the solvent from the extraction residue. Solvent vapor is withdrawn from the top of flashtop 86 via line 88 and sent to heat accumulator 83 and condenser 89 to solvent accumulator 90. Condensate solvents from accumulators 90 and 68 are sent via tank 79 through tank 92 where anhydrous solvent is withdrawn to extraction tower 25 via line 26. The non-condensable gas is discharged from the solvent accumulator 90 via line 93 to a suitable vacuum source for disposal or further treatment for the purpose of recovering solvent vapor therefrom.

The extract residue, which still contains some solvent, is discharged from the bottom of the vacuum flash tower 86 through line 95 and sent to the top of the stripping tower 96 where the residual solvent is removed from the extract residue by stripping by an inert phase. do. Inert gas from absorber 5 is introduced into bottom of stripping tower 96 via lines 7 and 97. Some of the extraction residue from the extraction residue condenser 98 is not shown but is reintroduced to the top of the extraction residue stripping tower 96 by reflux in a known manner. In a preferred embodiment, the extraction residue stripping tower 96 is operated at a pressure of slightly higher than atmospheric pressure, for example at 1.1-1.3 bar and a temperature of 288 ° C. The nitrogenous solvent from stripper 96 is combined with the nitrogenous solvent from stripper 71 and cooled in condenser 77 to condense the solvent from the stripping gas recycled to absorber 3.

The solvent, almost free of solvent, is extracted from the bottom of stripper 96 and cooled through heat exchanger 98 and then discharged as main product of the process via line 100 as refined lubricating oil.

The solvent purification system of the process consists of a drying tower 45 where the steam from the low pressure flash tower 35 and the medium pressure flash tower 48 or steam mixed with the solvent vapor are processed to be recovered as an anhydrous solvent for reuse in the extraction column 25. . Solvents containing water vapor or steam go from the low pressure flash tower 35 to heat exchanger 33 via line 39 where the steam is cooled and partially condensed by heat exchange with the extraction mixture leaving the base of extraction tower 25 via line 31. . The resulting vapor-liquid mixture consisting of wet solvent, solvent vapor and water vapor is passed to line accumulator drum 42 via line 41 where the wet solvent (liquid) is separated from the solvent vapor and vapor. From the accumulator drum 42 the wet solvent is introduced into the drying tower 45 via line 101 and the solvent vapor containing vapor is introduced into the drying tower 45 via line 102 where the anhydrous solvent is separated from the vapor and solvent vapor. Solvent vapors from steam separator 48 containing water vapor are sent via line 49 to heat exchanger-condenser 34 where they are cooled and partially condensed by indirect heat exchange with the extract mixture from line 31. In the heat exchanger-condenser 34 the extract mixture is preheated prior to introduction into the low pressure flash tower 35 and some of the solvent vapor from line 49 is condensed. The condensed solvent has little water vapor and is discharged from the heat exchanger-condenser 34 and sent via lines 50, 49B through line 106 to the anhydrous solvent accumulator 92. Non-condensing steam from heat exchanger-condenser 34 is sent to drying tower 45 via line 51 where solvent is recovered.

The drying tower 45 consists of a fractional distillation tube equipped with a suitable device, such as a porous tube or a bubble cap tray, to ensure intimate countercurrent contact between the steam flowing up through the column and the liquid flowing down. The drying tower 45 is equipped with a reboiler 103 at the bottom of a fractional distillation tube for evaporating all of the water and a part of the solvent introduced into the drying tower as various feed streams. Anhydrous N-methyl-2-pyrrolidone is discharged from the bottom of the drying tower 45 via line 104 and cooled in heat exchanger 105 and sent to anhydrous solvent accumulator 92 via line 106 to be used as an anhydrous solvent in extraction tower 25. In this particular embodiment, the drying tower 45 is operated under a pressure of 1.08 bar and a base temperature of 216 ° C., namely a reboiler temperature and a top temperature of 104-132 ° C.

The steam discharged from the top of the drying tower 45 and a portion of the accompanying solvent vapor are cooled to condenser 109 via line 108 and cooled and condensed. Condensate containing a small amount of solvent accumulates in the water drum 110, from which part of the water is returned to the top of the drying tower 45 as reflux via line 111 and some is introduced as solvent control or reflux to the extraction tower 25 via line 27. do. The remaining portion of the upper steam from drying tower 45 consisting of steam containing a small amount of N-methyl-2-pyrrolidone is sent via line 16 to absorption tower 15 where there is a close counter flow with part of the feed from line 14 Contact occurs to recover the solvent from the vapor.

In solvent refining systems as described herein, water is inevitably introduced into the refining system together with the lubricating oil feedstock and therefore an apparatus must be installed to remove irrelevant water from the system even in an anhydrous solvent extraction system. Another source of moisture in systems as described herein is due to leakage in heat exchangers or heaters that use water or steam as the heat exchange medium. In this method excess water is sent in vapor form via line 16 to absorption tower 15 to remove traces of solvent, which is then condensed in condenser 18 and the wastewater is collected in drum 19.

A second embodiment will be described with reference to FIG. Similar parts in FIGS. 1 and 2 are denoted by the same numerals and the following description describes only the differences between the two systems for treating hydrocarbon oil extracts from the base of a high pressure flash tower 55.

The hydrocarbon oil extract discharged from the bottom of the high pressure flash tower 55 via expansion valve 58 and line 59 still contains a weak solvent and consists, for example, 20% solvent and 80% hydrocarbon extract. This extract mixture is introduced into vacuum flash tower 160 to further recover the solvent from the extract. The vacuum flashtop can be operated at a pressure of 0.25-0.55 bar and at a temperature of 235-260 ° C. in this particular embodiment the pressure is 0.45 bar and the temperature is 243 ° C. A small amount of the extract solvent mixture from the flashtop 35 base is not shown but is introduced at the top of the vacuum flashtop 160 as reflux.

Another separation of the extract from the solvent takes place in vacuum flash tower 160. Solvent vapor is discharged through line 66 from the top of vacuum flash tower 160 and condensed 67 to solvent accumulator 68. Non-condensable gas is withdrawn from accumulator 68 via line 69 to a suitable vacuum source and may be withdrawn from the system.

The hydrocarbon oil extract discharged from the bottom of the vacuum flash tower 160 still contains some solvent and consists of, for example, 7% by volume of solvent and 93% by volume of hydrocarbon extract. The extract mixture is reheated in the presence of an inert gas at a temperature of at least 5 ° C., such as 293-315 ° C., at least 5 ° C. above the temperature of the high pressure flash tower 55 in the heater 165 and introduced into the top of the extraction stripping tower 71.

According to a preferred embodiment of the present invention an inert gas, such as for example nitrogen, is introduced into the heater coil of the heater 165 via compressors 6 and 64 from compressor 80 to increase solvent evaporation in the heater 165. 5-125 mole%, preferably 33 mole%, of the amount of inert stripping gas introduced into the extract stripping tower 71 is introduced into the extract stream in the heater 165. In this embodiment, the liquid hydrocarbon extract components discharged from the heater 165 are under a pressure of 1.2 bar and a temperature of 299 ° C., and the equilibrium solvent remaining in the discharged liquid is usually 1.8% by volume. The vapor-liquid mixture exiting the heater 165 is introduced to the top of the extract stripping tower 71.

The method of the present invention provides an energy efficient solvent recovery system while extracting a lubricating oil filler using anhydrous N-methyl-2-pyrrolidone as a solvent and simultaneously controlling the selectivity of the solvent using water reflux. This is obvious for those skilled in the art.

Claims (19)

In the method for solvent purification of the lubricating oil feedstock, the lubricating oil feedstock is contacted under pressure with N-methyl-2-pyrrolidone as a selective solvent for the aromatic components of the feedstock in the extraction zone under solvent purification conditions, After generating an extract residue and extract consisting of a small amount of solvent and an extract phase consisting of a large amount of solvent, the extract residue is separated from the extract phase, and the solvent is separated from the primary solvent evaporation zone at a pressure lower than the extraction band. Evaporation followed by evaporation in a plurality of zones at increasingly higher pressures to remove solvent from the extract, wherein heat is supplied externally only to the final high-pressure evaporation zone and heat at each of the preceding evaporation zones It is supplied by heat exchange with steam from the evaporation zone, and this heat supply method is the final high pressure evaporation zone. Solvent purification of the lubricating oil feedstock is configured to send a small amount of vapor from right to mix with the steam from the preceding evaporation zone. The method of claim 1, wherein the pressure in the first stage flash evaporation zone is in the range of 1.15-1.4 bar and the pressure in the subsequent flash evaporation zone is in the range of 1.7-2 bar and 2.9-7 bar, respectively. The process of claim 1 or 2, wherein the extract is evaporated in a flash zone at subatmospheric pressure to recover another solvent from the extract, and from the final high pressure zone to remove residual solvent from the extract using an inert stripping gas. Prior to introducing the extract into the flash zone, the extract was heated to a temperature at least 5 ° C. higher than the temperature of the high pressure zone and then discharged from the flash zone under atmospheric pressure and stripped with an inert stripping gas under low excess atmospheric pressure. Removing traces of solvent. 4. The method of claim 3, wherein the pressure in the vacuum flash band is in the range of 0.25-0.55 bar. 5. The method of claim 4 wherein the inert gas stripping zone is under pressure of 1.1-1.3 bar. A method according to any of claims 3 to 5, wherein a small amount of stripping extract is recovered as reflux into the stripping zone. The method of any one of claims 1 to 6, comprising condensing the solvent-rich vapor from the evaporation zone and returning the recovered solvent into the extraction zone. 8. The method of claim 7, wherein a water-containing solvent is removed from said primary flash evaporation zone and sent to a solvent dryer where water is separated from said solvent by distillation. The method of claim 8, wherein a portion of the solvent-rich vapor from the subsequent high pressure evaporation zone is sent to the solvent dryer. 10. The process of claim 9, wherein 2-10 volume% solvent-rich vapor from said higher evaporation zone is sent to said solvent dryer. The N-methyl-2-pyrrolidone supplied as a solvent to the extraction zone in any one of claims 1 to 10 contains little water and is located between the introduction point of the feedstock and the discharge point of the extraction phase. Introducing water into said extraction zone. 12. The method of claim 11, wherein the moisture is supplied by wet N-methyl-2-pyrrolidone supplied into the extraction zone near the outlet point on the extract. 3. The maximum pressure evaporation zone according to claim 1, wherein the extract and the solvent mixture from the high pressure evaporation zone are flash evaporated in the sub-atmospheric flash band and the extract solvent mixture from the sub-atmospheric flash band is mixed with the added inert gas. The mixture was heated to a temperature of at least 5 ° C. higher than the temperature in the heating zone, and the resultant heated mixture consisting of the inert gas, solvent, and extract was introduced into the stripping zone and stripped with the inert stripping gas under low atmospheric pressure to the extract solvent mixture. And further removing the solvent. The method of claim 13, wherein the amount of inert gas supplied into the heating zone is in the range of 5-125 mol% of the amount of inert stripping gas. 15. The method of claim 14, wherein the pressure at the outlet of the heating zone is in the range of 1.11-1.4 bar. 16. The method of claim 15, wherein said inert gas stripping zone is within a pressure range of 1.1-1.3 bar. The method according to any one of claims 14 to 16, wherein the amount of inert gas supplied in the heating zone is 33 mol% of the amount of inert stripping gas. 18. The method of claim 17, wherein the inert gas is introduced into a solvent extract mixture in a heating zone at the midpoint of the inlet and outlet of the solvent and extract. 19. The method of any one of claims 13-18, wherein the pressure in the sub-atmospheric flash band ranges from 0.25-0.55 bar.

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