KR840000578B1 - A process for solvent refining a lubricating oil - Google Patents

Abstract

A lubricating oil feedstock is solvent-refined by placing it in contact with N-methyl-2-pyrrolidone (I), which selectively extracts aromatics. This produces an extract phase rich in aromatics contg. a major amt. of (I) and a non-aromatic raffinate phase contg. a minor amt. of (I). The improvement is that residual solvent (remaining after solvent removal by flash vaporization, distn. and/or rectification) is removed from the two phases by stripping with an inert gas, such as N2. The resulting mixt. of inert gas and solvent vapor is then cooled to condense the solvent, and the inert gas and the solvent is recycled.

Description

Solvent Purification Method of Lubricant

The accompanying drawings are distribution diagrams showing the solvent purification process.

The present invention relates to an improved process for solvent extraction of petroleum powder containing aromatic and non-aromatic components.

In particular, the process relates to an improved process for recovering solvents from hydrocarbon extracts in solvent extraction systems.

In the present invention, energy can be significantly reduced in the solvent extraction process as compared with the process necessary for introducing the conventional solvent recovery operation. The process of the present invention is effective in recovering the solvent from the extraction phase in several separation stages consisting of at least three pressure stages.

It is well known to separate aromatic and unsaturated components from more saturated hydrocarbon components in hydrocarbon oil raw materials by various methods including solvent extraction of aromatic and unsaturated hydrocarbons. The most economical process is extraction with furfural, N-methyl-2-pyrrolidone and phenol. The removal of aromatics and other undesirable components from lubricating oil-based feedstocks enhances the viscosity index, color, oxidation stability, thermal stability, and inhibition of the base oil and final lubricating oil product. Numerous solvents are known which are not compatible with at least one of the mixed oils and cannot be partially mixed with the oils under the conditions of temperature and pressure used in the solvents which purify the raw materials forming two liquid phases in the extraction zone. have. The two liquid phases generally consist of an extract phase containing most of the solvent together with the aromatic component dissolved in the raw material and a raffinate phase containing non-aromatic components in the raw material together with a small amount of solvent. Solvents known to be useful in the process of solvent extraction of petroleum based lubricant raw materials include furfural, N-methyl-2-prolidone, phenol and other well known organic and inorganic solvents.

As a good solvent for extracting aromatic hydrocarbons from mixtures of aromatic and non-aromatic hydrocarbons, N-phenmethyl-2-pyrrolidone has recently been used instead of furfural and phenol. It is well recognized by refining technicians that N-methyl-2-pyrrolidine is advantageous as a lubricant extractant for removing undesired aromatic and polar components from lubricant based raw materials, and some of the technicians Other solvents, such as phenol or furfural, have been used in the past or present to purify lubricating oil-based feedstocks.

N-methyl-2-pyrrolidone is the best solvent because of its chemical safety, low toxicity and the ability to produce high quality refined oil. Solvent extraction processes that describe typical conventional solvent recovery operations are described in US Pat. Nos. 3,329,606; 2,461,066; 3,470,089; And 4,013,549.

The process of the present invention is particularly applicable to phenol, furfural and N-phenmethyl-2-pyrrolidone purification plants using inert gas or steam to strip existing solvents. From single or multistage solvent recovery systems and products, the present invention is particularly suitable for converting simultaneous furfural and phenolic processing equipment to N-methyl-2-pyrrolidone solvent systems, which saves the energy required for solvent purification processes.

In recovering a hydrocarbon extractant (i.e., N-methyl-2-pyrrolidone) from an oil-solvent mixture (i.e., an extraction phase and a raffinate phase), stripping with an inert gas rather than water vapor is a solvent compared to conventional steam stripping. Purification can be simplified and the energy required for the process can be saved. The solvent is separated from the oil-solvent mixture by a combination of distillation and stripping. Steam stripping is commonly used in solvent purification processes. Inert gas stripping is described in US Pat. No. 2,923,680; 4,013,549 and 4,057,491.

In the previous lubricating oil refining process, the solvent extraction step is carried out under conditions effective to recover about 30-90% by volume of the raw material of the lubricating oil with the extract residue or refined oil and to extract about 10-70% by volume of the raw material as the anti-fog extract. . The lubricating oil is contacted with a solvent such as furfural or N-methyl-2-pyrrolidine at a temperature of at least 5 ° C. (at least 50 ° C. is preferred) and below the temperature at which the lubricating oil in the solvent can be thoroughly mixed.

Particularly preferred solvents are furfural and N-methyl-2-pyrrolidone, both of which are effective at solvent extraction of aromatic components from the lubricating oil raw material in relatively low temperatures and in a small amount of solvents relative to oil rather than the best known solvents.

In the extraction step, operating conditions are selected to primarily produce a raffinate having a viscosity index of about 75-100 (preferably about 85-96) removed. When using furfural as a solvent, the solvent range is in the range of about 100-600% and the extraction temperature is in the range of about 46-110 ° C. (preferably about 60-95 ° C.) to obtain the desired IV product. When using N-femethyl-2-pyrrolidone as the solvent, the solvent extraction temperature is in the range of 43-100 ° C (preferably 54-95 ° C) and the amount of solvent is 50-500% (100-300). % Is preferred).

Water or wet solvent is mixed with the solvent introduced or recycled to the bottom of the extractor to control solubility and selectivity.

The wax is removed from the primary raffinate to the pour point to produce a fully processed, lubricant-based feedstock. If necessary, the refined or dewaxed oil can be finally treated to enhance color and stability (eg mild hydrogenation).

The present invention is an improved method of stripping a solvent from extracts and raffinate products, removing oil impurities in the solvent and controlling the water content of the solvent in a solvent purification system. The process of the present invention simplifies solvent recovery and purification compared to conventional processes and significantly reduces the energy required for the solvent purification process.

The process of the present invention will be described in detail with reference to the accompanying drawings. The accompanying drawings are flow diagrams illustrating a solvent purification process using a solvent recovery operation improved according to the process of the present invention.

Feed lubricating oil, which may contain foreign matter, is introduced into the apparatus via line 5 and heated to 65-120 ° C. in heater 6. The preheated feedstock is introduced via line 7 to the top of the absorber-stripper column 8 and properly maintained at a pressure in the range of 100-515 kpa (0-60 psig), where the feedstock is introduced to the bottom of stripping column 8 via line 9. Dehydrated by an inert stripping gas.

Appropriate devices (eg perforated bubble caps or cascade trays) are attached to column 8 for tight countercurrent contact between the feed lubricating oil and the stripping gas. Inert gas containing water vapor exits the top of column 8 via line 10. As a result, the dehydrated raw material is discharged from the bottom of column 8 and introduced by pump 11 into the bottom of the extraction tower through heaters 12 and 13 where the raw material is brought into contact with the solvent introduced into the top of extraction tower 14 via line 17. . The wet solvent from the solvent purifier 30 is introduced into the column bottom of the extraction column 14 via line 99.

The raffate mixture, consisting of 85% hydrocarbon oil mixed with solvent, exits extraction tower 14 via line 19 to recover raffinate from solvent. After separation of the solvent, raffinate is a preferred product based on solvent purified lubricating oil.

Most of the solvent is present in the extract mixture recovered from the bottom of extraction column 14. The extraction mixture containing about 85% solvent is then recovered from tower 14 via line 18. The extract mixture is first processed to recover the solvent from the extract and then to recover the extract as a commodity. Most extraction mixtures, typically containing about 85% of solvent, are introduced into the low pressure flash tower 22 through heat exchangers 20 and 21 which preheat the extraction mixture. Flash top 22 has a pressure of 170-205 kpa (10-15 sig). The extract mixture from column 14 is refluxed to the top of column 22 via lines 31 and 32. The solvent separated from the extract in flash tower 22 is discharged to heat exchanger 20 via line 24. After the solvent vapor has been condensed and again cooled in chiller 26, the solvent is introduced via line 27 into the solvent purification and storage tank 30 for reuse.

Most of the extract mixture from which some solvent is removed is recovered from the lower end of column 22 by pump 36 and introduced into high pressure flash tower 39 through heaters 37 and 38. The high pressure flash tower 39 operates at a pressure in the range of 375-415 kpa (40-45 psig). A small amount of the extraction mixture from the bottom of extraction tower 14 is refluxed through lines 31 and 33 to the top of the high pressure separator 39. The solvent mixture from the low pressure flash tower 22 is fed to tower 39 and refluxed to tower 22 via lines 40, 31, 32 and 33.

Solvent vapor from the top of the high pressure flash tower 39 through line 41 is introduced into the heat exchanger heat exchanger directly from the bottom of the extraction tower 14, where the solvent vapor is condensed and preheated the extraction mixture before being introduced into the low pressure flash tower 22. The recovered solvent is introduced via line 42 into the solvent storage reagent and storage tank 30 for reuse in the process.

The hydrocarbon oil extract recovered from the bottom of autoclave 39 through line 44 contains some solvent (eg, 5-15 vol% solvent) and 95-85 vol% hydrocarbon. This extraction mixture enters vacuum flash tower 46 via line 44 to recover more solvent from the extract. The vacuum flash tower 46 typically consists of a countercurrent vapor-liquid contact tray, cascade or pore tray type construction. Some extraction mixture from extraction tower 14 or low pressure flash tower 22 is refluxed through lines 36 and 47 to the top of vacuum flash tower 46. The vacuum flash tower operates in the pressure range of 10-100 kpa.

In vacuum flash tower 46, separation of the extract from the solvent proceeds again. Solvent vapor is recovered from the top of the flash tower 46 through line 48 to condenser 49 and solvent accumulator 50. Non-condensable gas recovered from accumulator 50 through line 51 to a suitable vacuum source may be discarded or recycled through line 86.

The extract-rich fraction is withdrawn from the abutment of flashtop 46 via line 54 and introduced to the top of stripper 55. The stripper 55 is a countercurrent vacuum-liquid contact column provided with a gigpotlay in which the liquid extract flowing downward through the column is contacted with an inert stripping gas introduced into the lower end of the stripper 55 via line 56. Some extraction mixture from the bottom of extraction tower 14 is fed to the top of stripper 55 via lines 36 and 57. Some of the extraction mixture from the bottom of the low pressure flash tower 22 is refluxed through lines 40 to towers 22, 39, 46 and 55.

Extraction oil, containing about 50 ppm of solvent and consisting of 80% unsaturated hydrocarbons and about 20% saturated hydrocarbons, is recovered from the bottom of stripper 55 by pump 58 and passes through heat exchanger 59. The silver is cooled by direct heat exchange with the raffinate mixture from the top of the extractor 14 and exited from the apparatus via line 60 as product.

Inert stripping gas and stripped solvent vapor are introduced via line 62 to condenser 63 where solvent vapor is condensed from the top of stripper 55. Solvent condensate is collected at condensation accumulator 64. Inert gas separated from the condensate is discharged to line 65 for recycling as described below.

The raffinate mixture exiting the tower from extraction tower 14 via line 19 is heated in heat exchanger 59 by direct heat exchange with the extract stripped from extract stripper 55 and then into vacuum flash tower 70 where the solvent is separated from the raffinate mixture. Pass through heat exchanger 67 and heater 68 before introduction. A small amount of raffinate mixture from line 19 is returned to the top of vacuum flash tower 70 through line 71 bypassing heat exchangers 59 and 67 and heater 68. Another portion of the raffinate mixture from line 19 is returned to the top of stripper 75 via line 72 bypassing heat exchangers 59 and 62 and heater 63.

Solvent vapor separated from the raffinate mixture in flashtop 70 is recovered to line 48 from the tower and introduced into condenser 49 where solvent vapor is condensed with solvent vapor from flashtop 46. The condensation solvent is collected in the condensate accumulator 50 and the non-condensing gas is recovered via line 51 as described above.

The raffinate containing some solvent is introduced via line 74 from the bottom of the vacuum flashtop 70 to the top of the stripping column 75, where the residual solvent is stripped with an inert gas into which the residual solvent is introduced via line 76 to the bottom of the stripper 75. By removing from the raffinate. The raffinate liberated from the solvent was recovered as a product from the bottom of stripper 75 by pump 77 and passed indirectly heat exchanged with raffinate mixture from line 19 in heat exchanger 67 to obtain line 78 as refined lubricant, the main product of the process. Is discharged through.

Condensate from accumulator drums 50 and 64 enters solvent purification and storage 30 by pumps 79 and 80, respectively. Re-use in processes such as distillation, azeotropic separation, absorption, gas stripping, etc. and several steps are used in solvent purification to remove water and remove polymers, oils, etc. if excess water is present. Excess water from any foreign material can be removed via solvent 81 from solvent purification and storage 30. If necessary, the solvent is recycled through line 83 to line 17 by pump 82.

After separating the condensation solvent in the condensate separator 64, the inert gas from strippers 55 and 75 may contain solvent vapor. Inert gas from separator 64 is again compressed by compressor 85 and passed through line 86 to absorber-stripper 8 which acts as an absorber for the solvent vapors remaining in the inert gas fluid.

Depending on the pressure in tower 8, the inert gas fluid leaving compressor 85 at a pressure of 170-410 kpa (10-45 psig) or higher will increase in temperature due to the heat of compression in the compressor. This gas fluid can be heated or cooled as needed to maintain the desired temperature in the absorber-stripper tower 8 at 65-150 ° C.

In absorber-stripper 8, the solvent vapor is absorbed from the inert gas and the water entering the device together with the lubricating oil supply fluid is evaporated into the inert gas. Inert gas containing water vapor exits absorber-stripper column 8 through line 10 and is cooled in condenser 88 to a temperature sufficient to condense water vapor from the inert gas fluid. Condensate separated from the inert gas is collected in condensate separator 89 and condensate containing water from condenser 89 flows out through line 90. Inert gas, from which water and solvent vapors have been removed, is introduced via strip 91 and heater 92 through strips 56 and 76 into strippers 55 and 75, respectively.

Stripping gases contain, but are not limited to, significant amounts of inert gases such as nitrogen, methane, carbon dioxide, and the like. Nitrogen is a good inert gas for use in this process.

Two important advantages have been obtained by contacting the fresh lubricating oil feedstock with the previously used inhomogeneous stripping gas in the process of stripping the solvent from the extract and the parinate product. The solvent is recovered from the stripping gas and water is simultaneously removed from the raw materials.

In the solvent for refining the lubricating oil raw material, light oil tends to accumulate in the solvent. Since light oil accumulates in the solvent in the conventional solvent purification process, a distillation step is required separately during the solvent purification process to remove the accumulated oil. Such diesels usually occur with solvents and stripping media from extraction and raffinate flash towers and strippers.

Some of the extract mixtures from extraction tower 14 or flash tower 22 in the process of the present invention are used to reflux to flash towers 22 and 39 in a solvent recovery process. In the preferred embodiment illustrated, the extraction mixture from extraction tower 14 or low pressure flashtop column 22 is also used to reflux to an extract recovery column, ie flashtop 46 and stripper 55. In this implementation, the reflux to vacuum flash tower 70 and stripper 75 in the raffinate recovery process contains some of the raffinate mixtures exiting from solvent extraction column 14.

The first extraction mixture from column 14, or extract mixture from column 22, in which a significant amount of solvent has been separated, can be used by refluxing into flash towers 22 and 39 to prevent diesel oil from flowing out of the column with the separated solvent.

Similarly, the relatively low volatility of the extract and raffinate fraction in other towers prevents the contamination of lower hydrocarbons in the solvent vapor. At the same time, raffinate and extract reflux fluid are good absorbents for any lower hydrocarbon vapors that tend to flow out of various solvent separation towers. Pretreatment of fresh lubricating oil raw material with recycle inert gas and refluxing the extracts and raffinates in several towers simultaneously can reduce or significantly reduce the amount of purification solvent required for the process.

In a particular embodiment of the invention, 20,400 kg / hr (45,000 Lb / hr) of wax distillate (WD-20) containing 45 ppm water is fed to the absorber-stripper according to the process of the invention. At this time, the wax distillate is 250 kg of recycle nitrogen gas containing 12.7 kg / hr (28 lb / hr) of N-methyl-2-pyrrolidone vapor from the extraction stripper and raffinate in the solvent purifier as described below. hr (551 lb / hr) and stripped at 115 ° C and 138 kpa (20 psia).

In the absorber-stripper, the solvent contained in the recycled inert gas fluid is recovered from the inert gas. At the same time, the water contained in the lubricating oil raw material is virtually completely evaporated into the nitrogen stripping gas.

The water vapor and nitrogen mixture leaving the absorber-stripper is cooled at 50 ° C. to condense the water vapor. The condensate is separated from the recycle gas fluid, whereupon the dried nitrogen is heated to 290 ° C. and recycled to the stripper; 52.2 kg / hr (115 lb / hr) in heated dry nitrogen is fed to the extraction stripper and 197.7 kg / hr (436 lb / hr) to the raffinate stripper. The raffinate and extraction stripper operate at a bottom pressure of 35 kpa (5 psig) and a top pressure of 20.7 kpa (3 psia). Both strippers are refluxed to N-methyl-2-pyrrolidone at 20 ° C.

The extraction feed fluid enters the extraction stripper at 290 ° C. and the resulting extract flows out at 260 ° C. The fluid fed to the extraction stripper contained 2,2255 kg / hr (4,971 lb / hr) and 435 kg / hr (959 lb / hr) N-methyl-2-pyrrolidone.

154.2 kg / hr (340 Lb / hr) of N-methyl-2-pyrrolidone is fed to the extraction stripper at reflux. The nitrogen stripping gas supplied to the stripper at 290 ° C. and 35 kpasia (5 psia) at a rate of 52.2 kg / hr (115 lb / hr) was 160 with 589.2 kg / hr (1,229 lb / hr) of N-methyl-2-pyrrolidone. Outflow of stripper consultation at < RTI ID = 0.0 > 2 C < / RTI > The columnar from the extraction stripper was raffinate containing 20.7 kpa (3 psia) and 197.8 kg / hr (436 lb / hr) of nitrogen and 836 kg / hr (1,843 lb / hr) of N-methyl-2-pyrrolidone at 155 ° C. It is combined with the pagoda from the stripper.

Nitrogen and N-methyl-2-pyrrolidone vapors from the stripper condense 1,425.2 kg / hr (3,142 lb / hr) of solvent and introduce a condenser that cools to 75 ° C. at 20.7 kpa (3 psia). After removal of the condensation solvent, nitrogen up to 250 kg / hr (551 lb / hr) and containing 12.7 kg / hr (28 lb / hr) of solvent vapor at 75 ° C was introduced into the compressor, where the pressure of the mixture was increased to 120 ° C. At the same time it increases to 17.5 kpa (about 25 psia).

The compression mixture is recycled to the absorber-stripper to recover the solvent vapor prior to reuse in the process.

Claims (1)

Contacting and extracting the lubricating oil raw material with a selective solvent for the aromatic components of the lubricating oil raw material in the raffinate phase containing a small amount of solvent and the extraction region containing a large amount of solvent and forming the extracted phase respectively recovered from the extraction region. Removing some of the solvent from the extraction phase in the solvent separation zone and stripping another portion of the solvent from the extraction phase with an inert stripping gas that forms a mixture of solvent vapor and stripping gas to solvent purify the lubricating oil stock. In; Solvent vapor is absorbed from the stripping gas by the lubricating oil and at least a portion of the foreign water contained in the lubricating oil is evaporated to form a mixture of water vapor and inert gas separated from the lubricating oil in the first contacting zone. A method for purifying a solvent of a lubricating oil, characterized in that the lubricating oil raw material is intimately contacted with a mixture of an inert stripping gas and a solvent vapor.

Images