US 3306849 A
Description (OCR text may contain errors)
Feb. 28, 1967 l P. P. BOZEMAN, JR.. ET AL 3,305,849
HYDROCARBON SOLVENT REFINING PROCESS Filed Aug. 2v. 1964 2 shams-snee*b 1 Feb. 28, 1967 P. P. BOZEMAN, JR., ET AL HYDROARBON SOLVENT REFINING PROCESS Filed Aug. 27. 1964 2 Sheets-Sheet 2 .Wma
United States Patent O ,306,849 HYDROCARBON SOLVENT REFINING PROCESS Paul P. Bozeman, Jr., Groves, and Robert A. Woodle, Nederland, Tex., assignors to Texaco Inc., New York, NX., a corporation of Delaware Filed Aug. 27, 1964, Ser. No. 392,416 6 Claims. (Cl. 208-314) This invention relates to a hydrocarbon treating process employing liquid-liquid solvent extraction. More particularly, it relates to an improved method of recovering the solvent in the solvent refining of a petroleum fraction, for example, a gas oil or a lubricating oil stock.
In accordance with the process of this invention, a hydrocarbon oil is contacted with a solvent in a first solvent extraction zone forming raffinate and extract-mix phases. The extract-mix phase is cooled effecting separation of a hydrocarbon phase from a remaining extractmix phase of reduced hydrocarbon content. The remaining extract-mix phase is contacted with a low boiling hydrocarbon solvent in a second extraction zone effecting re-extraction of the hydrocarbons from the selective solvent. Raffinate from the second extraction zone comprising selective solvent is returned to the primary extraction zone and the new extract-mix phase comprising hydrocar-bon oil extract and low boiling hydrocarbon solvent is subjected to distillation separating said ilow boiling hydrocarbon solvent which is returned to the second extraction step. Extract oil is withdrawn as distillation bottoms.
Solvent extraction is widely used in the petroleum industry to effect fractionation of hydrocarbon oil. Substances of low hydrogen to carbon ratio, for example, aromatic hydrocarbon and polar substances such as sulfur compounds are relatively soluble in solvents such as furfural, other aldehydes such as benzaldehyde, phenol, nitrobenzenes, ketones, etc. Although other solvents may be employed in the process of this invention, we prefer to employ furfural which is low in cost, readily available, and possesses superior solvent characteristics. When a hydrocarbon oil containing mixtures of hydrocarbons of high and low hydrogen to carbon ratio and polar substances is contacted with such a solvent, the hydrocarbons of low hydrogen to car-bon ratio and polar substances are extracted from a raffinate comprising the more parafiinic hydrocarbons of high hydrogen to carbon ratio. The raffinate phase comprises oil with a relatively small amount of dissolved solvent and the extract-mix phase contains the bulk of the solvent and a relatively small amount of dissolved oil and polar compounds. The extract-mix and rafiinate phases are then fractionated to separate solvent for recycle to the extraction ysystem from the refined oil product and extract. Since the raffinate phase comprises oil with a relatively small amount of dissolved solvent, this solvent may be advantageously separated by distillation with steam or by washing with water. In the case of furfural, the furfural is separated as a steam-furfural azeotrope Iwhich has a boiling point of 208 F. at 760 mm. When furfural is recovered by washing the rafiinate with water, the furfural is recovered from the water washings by distillation, again as the azeotrope boiling at 208 F.
The extract-mix phase contains the bulk of the solvent with only a relatively small amount of dissolved hydrocarbon. Heretofore, the solvent has usually been separated by distillation wherein most of the solvent is separated by distillation in the absence of steam at its boiling point which when the solvent is furfural, is 323 F. at 760 mm. Separation in the absence of steam is desirable since otherwise an inordinately large amount of azeotrope is produced which must be redistiilled for separation of dry solvent. In steam stripping, there is a tendency to 3,306,849 Patented Feb. 28, 1967 Mice entrain low boiling constituents of the hydrocarbon feed in the relatively large amount of solvent-water azeotrope distilled overhead which results in oil dilution of the solvent. When distilling furfural from extract-mix from the extraction yof high boiling oils, for example, vacuum residue, the high distillation temperatures encountered foster polymerization and decomposition of the furfural. Although the amount of polymerization and decomposition occurring may be small, the products of polymerization and decomposition are solid coke-like materials. These polymerization and decomposition products tend to foul heat exchange surfaces thereby reducing the efiiciency of heat transfer and reducing the throughput which may be obtained in the furfural recovery equipment.
It is an objective of the process of this invention to provide a means of separating solvent from the extractmix of a solvent refining process without high temperature distillation. Another objective is to produce an extract fraction of intermediate quality. Another advantage of the process of this invention is that in solvent refining with furfural, furfural distillation is eliminated in favor of light oil distillation with savings in heat due to dstillation of less material with lower heat of vaporization. A further objective is that furfural polymerization and decomposition and attendant fouling of towers and exchangers are reduced.
In accordance with this invention, extract-mix from the solvent extraction of a hydrocarbon oil at a temperature within the range of about 140 to 240 F. is cooled to approximately 100 F. effecting separation of about 30 to 50 percent of the extract 'oil contained in the extractmix as an intermediate oil phase. This intermediate oil .phase is separated and remaining extract-mix comprising to 96 volume percent solvent and 4 to 10 percent extract oil is contacted with a light hydrocarbon solvent. Suitable light hydrocarbon solvents include liquidified petroleum gases including propane which has a boiling point of 44 F. and other liquid petroleum fractions boiling up to about 500 F. The light hydrocarbon solvent is desirably parafiinic in nature, that is, comprised principally of aliphatic hydrocarbons. The endpoint of the hydrocarbon solvent should be at least below the initial boiling point of the charge oil to the furfural treating process to facilitate separation of the light hydrocarbon solvent from the extract product by distillation. The light hydrocarbon solvent is applied to the extract-mix at a solvent dosage of about l to 2 volumes -of light hydrocarbon per volume of extract-mix. An extraction temperature of about 100 F. is employed. Under these conditions the hydrocarbon content of the extract-mix is transferred from the extract-mix to the light hydrocarbon solvent forming a raffinate comprising furfural essentially free of extract oil. Desirably, the furfural raffinate is heated and passed to a stripping zone wherein any dissolved water or light hydrocarbon is removed and the stripped furfural is recycled for reuse in the primary solvent extraction. The light hydrocarbonextract oil mixture leaving the solvent regeneration extractor is distilled to recover the extract oil and separate the light hydrocarbon solvent for reuse.
In accordance with this invention, the solvent an extract oil are separated from the extract-mix in two stages, the first stage of separation being effected by cooling and the second stage being effected by re-extraction of remaining extract-mix with a light parafiinic solvent. In the first step, the extract-mix is cooled from the primary solvent extraction outlet temperature within the range of about to 240 F. to a temperature Within the range of about 90 to 120 F. and preferably about 100 F. In this cooling step, approximately 30 to 50 percent of the oil contained in the extract-mix separates as a hydrocarbon phase. This hydrocarbon phase is separated and may be utilized as an intermediate oil. In addition, the cooling step cooperates with the succeeding re-extraction step -by enabling the light hydrocarbon solvent to displace a `greater amount of extract hydrocarbon from the extract-mix or to effect a given extraction with a lesser amount of light parainic solvent than would be required at the temperature of the primary extract-mix outlet. Cooling may be effected by indirect heat exchange with cold water or by adding cold light parafiin hydrocarbon solvent. Cooling water may be provided by conventional cooling towers or may be chilled by refrigeration tor autorefrigeration. Cooling by the addition of light paraffin hydrocarbon is advantageous in dealing with extract containing wax or other materials of high pour point.
The accompanying drawings diagramm-atically illustrate the process of this invention. Although the drawings illustrate :arrangements of apparatus in which the process of this invention may be practiced, it is not intended to limit the invention to the particular materials or apparatus described.
FIGURE l illustrates the process of this invention with the separation of an intermediate oil.
FIGURE 2 illustrates an embodiment of the process of this invention wherein a plant designed for separation of furfural from the extract-mix by distillation is modified to employ the cooling and re-extraction process of this invention.
Referring to FIGURE l, oil feed, for example, a lubricating oil stock, in line 1 is passed to treating tower 2 wherein the oil feed is countercurrently contacted with solvent introduced through line 3 forming extract-mix and raffinate phases. Raffinate phase is withdrawn through line 4 and passed to refined oil stripping tower 5. In refined oil stripping tower 5, solvent is separated by distillation through line 6 for recovery and reuse and refined oil free of solvent is discharged through line 7 for blending or further refining.
Extract-mix from tower 2 is withdrawn through line 10, cooled in cooler 11 and passed through line 12 to phase separator 13. Cooling of the extract-mix causes a hydrocarbon phase to separate from the extract-mix. This hydrocarbon phase is withdrawn from the top of phase separator 13 through line 15 and is passed to intermediate oil stripping tower 16. In tower 16 the hydrocarbon phase is stripped separating the dissolved solvent through line 17 for reuse in the extraction process. The stripped intermediate oil is withdrawn through line 18 for further refining or blending.
Extract-mix phase from separator 13 is withdrawn through line 20 and passed to solvent recovery tower 21. In solvent recovery tower 21, the extract-mix phase is countercurrently contacted with light paraftinic hydrocarbon introduced into tower 21 through line 22. Solvent substantially free of extract oil is withdrawn from the bottom of solvent recovery tower 21 through line 3 for return to treating tower 2. Light hydrocarbon and dissolved extract voil are withdrawn from the top of solvent recovery tower 21 through line 25 and passed to extract stripping tower 26. In extract stripping tower 26, the light hydrocarbon is separated las distillate and returned to solvent recovery tower 21 through line 22. Stripped extract is discharged through line 27 for further refining or use.
With reference to FIGURE 2, oil feed in line 35 is passed to treating tower 36 and countercurrently contacted with furfural solvent introduced into tower 36 through line 37. Rafiinate comprising refined oil :and containing a small amount of dissolved furfural is withdrawn through line 39 and passed to solvent recovery facilities not shown. The extract-mix, at an outlet temperature within the range of about 140 to 240 F., is
withdrawn from tower 36 through line 40. Extract-mix in line 40 is passed through cooler 45 where the temperature Iis reduced to about 90 to 120 F. Cooled extractmix is passed through line 46 to phase separator 47. In phase separator 47, the lighter hydrocarbon phase separates and is withdrawn through line 50u The remaining extract-mix containing a reduced yamount of dissolved hydrocarbon is withdrawn through `line 51 to solvent regeneration tower 52 wherein it is countercurrently contacted with light hydrocarbon introduced through line S3. In tower 52, the extract hydrocarbon is re-extracted from the furfural and the latter is withdrawn as rafiinate through line 54. Light hydrocarbons and re-extracted hydrocarbons are withdrawn through line 55, and passed through heat exchanger 56, line 57, heat exchanger 58 and line 59 to atmospheric flash tower 60.
In flash tower 60, the light hydrocarbon is separated as distillate at about atmospheric pressure and is withdrawn through line 65. The light hydrocarbon distillate is condensed in exchanger 56 and passed through line 66 to line 53 for reuse in solvent regeneration tower 52. Bottoms from flash tower 60 -comprising extract hydrocarbons and some light hydrocarbon are withdrawn through line 67 and heated in heater 68. The resulting heated light hydrocarbon-extract mixture is passed through line 69 to pressure flash tower 70 maintained at a pressure of about 30 p.s.i.g. In pressure fiash tower 70, the remaining light hydrocarbon is flashed and withdrawn as distillate through line 71. The distillate is cooled in heat exchanger 58 and passed through line 72 and combined with the light hydrocarbon distillate in line 53. The flashed extract hydrocarbon from the bottom of tower 70 is withdrawn through line 75, combined with the hydrocarbon phase in line 50, and the mixture is passed to vacuum steam stripper 76.
In steam stripper 76 a small amount of dissolved furfural is removed from the extract oil by stripping with steam introduced through line 77. Vapors of furfural and steam are withdrawn through line 78. The furfural-water vapor mixture in line 78 is passed through line 79, cooler 80 and line 81 to separating drum 82. Separating drum 82 is provided with weirs 83 and 84. Furfural layer containing a small amount of dissolved water and dissolved hydrocarbon -separates in the end compartment of separator 82 behind Weir 83. Furfural layer is withdrawn through line and combined with the furfural in line 54. The water phase and light hydrocarbon phase overfiow weir 83 and separate into a heavier water phase which accumulates between weirs 83 and 84 and light hydrocarbon which overfiows Weir 84 and is collected in the other end compartment. Water phase is withdrawn through line 86 and passed to water stripper 87. In water stripper 87 an azeotrope of furfural and water is separated as distillate through line 88 and water free of furfural is withdrawn through line 89. The vapors in line 88 are condensed in cooler 90 and passed through line 91 to line 81 and to phase separator 82. Light hydrocarbon layer is withdrawn from separator 82 through line 95 and is combined with the hydrocarbon in line 53 for use in solvent recovery tower 52.
The furfural phase in line 85 and line 54 are passed to furfural drying tower 96. In tower 96, an azeotrope of furfural and water is removed as distillate through line 97 and combined with the furfural-water vapors in line 79 for condensation and eventual return to separator 82. Dried furfural is withdrawn from the bottom of fnrfural tower 96 through line 37 for return to treating tower 36.
Example l A lubricating oil stock is furfural refined producing a refined oil of SAE l0 grade. The lubricating oil stock has the following characteristics: gravity, API 28.8; flash, COC, F. 410; viscosity, SUS/100 F. 158; viscosity, SUS/210 F. 43.0; VI 82.0; pour, F. 75; color, Lovibond 1/2 cell 45; refractive index at 70 C., 1.4730.
The lubricating oil stock at a rate of 5,000 barrels per day is contacted with furfural at a dosage of 350 percent, in a rotating disc conta-ctor. Rafnate i-s withdrawn at 230 F. and is stripped producing 3,500 barrels per day of refined oil of the following quality; gravity, API 33.5; flash, COC, F. 410; viscosity, SUS/100 F. 122; viscosity, SUS/210 F. 41.6; VI 112; pour, F. 90; color, Lovibond 6" cell 50; refractive index 1.4540. Extractmix containing 8.2 volume percent extract oil is withdrawn at 185 F. at a rate of 18,382 barrels per day. The extract-mix is cooled to 100 F. separating 469 barrels per day of intermediate oil phase containing 4 percent dissolved furfural. The intermediate oil phase is stripped separating 450 barrels per day of intermediate oil having a gravity of 28.0 API, a COC flash of 400 F.; a viscosity -of 45.0 SUS/210 F.; a VI of 78.0; and a refractive index of 1.4740. Extract-mix phase at 100 F. and containing 5.9 volume percent extract oil is re-extracted at 100 F. by contacting with 22,390 barrels per day of a light paraffinic solvent in a second rotating disc contactor. The light parat-linie solvent comprises 97 volume percent paraffinic hydrocarbons and boils within the range of 211 to 348 F. by ASTM distillation. Ra'inate comprising furfural containing 8.2 volume percent hydrocarbon is stripped separating a small amount of dissolved light hydrocarbon and water and is recycled to the primary lubricating oil contacting step. Extract-mix from the re-extraction step comprising 90 volume percent light parainic solvent and 4.5 vol-ume percent extract oil is separated and redistilled producing 1050 barrels per day of extract oil and 21,000 barrels per day of light parafiinic solvent. The extract oil has a gravity of 15.2 API; a COC fiash of 400 F. and a refractive index of 1.5362.
Example Il A feature of this invention is that the secondary or reextraction step is effected at a lower temperature than the primary extraction. This lower temperature of reextraction results in greatly increased re-extraction efficiency. The effect of temperature on the amount of oil displaced by re-extraction of an extract-mix from the solvent extraction of a cracked light cycle gas oil with a light paraffinic solvent is shown in Table I:
The effect of temperature on the amount of oil displaced from an extract-mix containing 33 volume percent extract oil is shown in Table II:
TABLE 1I Furfural Light Parafin Extract-Mix Extract Oil Dosage, Vol. Rex-extraction Light Parafrn Yield, Wt.
Percent Dosage, Vol. Contacting Percent Percent Temp., F.
Table II shows a 30.8 percent yield reduction upon reextraction at 134 F. whereas at 100 F. a corresponding yield reduction of 35.0 percent is obtained. Tables I and II show that at lower temperatures, the light paraffin solvent displaces more oil from the extract-mix than at higher temperatures.
1. A method of treating a hydrocarbon oil wherein said oil is contacted with a selective solvent comprising furfural in a first solvent extraction zone under conditions forming a first rainate phase and a first extract-mix phase, which comprises withdrawing said first extract-mix phase at -a temperature within the range of about 140 to 240 F.,
cooling said rst extract-mix phase to a temperature within the range of about 90 to 120 F., separating a second raffinate comprising hydrocarbon oil extract and dissolved solvent and a second extract-mix phase comprising solvent and remaining hydrocarbon extract oil,
contacting said second extract-mix phase with a liquid paraffin hydrocarbon fraction boiling within the range of about -44 to 500 F. and having an end point of least F. below the initial boiling point of said hydrocarbon oil in a second extraction Zone forming a third rafiinate phase comprising said selective solvent and a third extract-mix phase comprising said remaining hydrocarbon oil and said low boiling hydrocarbon,
recycling at least a part of said third raffinate phase to said rst solvent extraction zone as at least a portion of said selective solvent,
separating hydrocarbon extract oil from said secondary raffinate, and
separatin-g remaining hydrocarbon oil extract from said third extract-mix.
2. The process of claim 1 wherein said second extractmix is passed to said second extraction zone at the temperature at which it is formed.
3. In a hydrocarbon oil treating process wherein a hydrocarbon oil feed is contacted with a solvent feed comprising fnrfural in a primary extraction zone separating a raffinate comprising refined oil and dissolved solvent and a first extract-mix comprising solvent and dissolved extract oil, the improvement which comprises withdrawing said rst extract-mix at a temperature within the range of about 140 to 240 F.:
cooling said first extract-mix phase to a temperature within the range of about 90 to 120 F. effecting separation of a hydrocarbon phase comprising within the range of about 30 to 50 percent of the extract oil contained in said extract-mix and dissolved solvent and a remaining extract-mix phase comprising solvent and dissolved remaining extract oil,
stripping dissolved solvent from said hydrocarbon phase separating a first extract product and solvent for recycle to said primary extraction zone as a portion of said solvent feed, c-ontacting said remaining extract-mix phase with a paraliinic hydrocarbon liquid boiling within the range of -44 to 500 F. and who-lly at least 100 F. bel-ow the boiling range of said hydrocarbon oil feed in a secondary extraction zone effecting formation of a second raffinate phase comprising solvent substantially free of said remaining extract oil an-d a second extract-mix phase comprising said paraiinic hydrocarbon liquid and dissolved remaining extract oil,
recycling at least a part of said second raffinate phase to said primary extraction zone as a portion of said solvent feed and distilling said second extract-mix phase separating said parainic hydrocarbon liquid as distillate for recycle t-o said secondary extraction zone and remaining extract oil as a second extract product.
4. The process of claim 3 wherein said hydrocarbon oil feed comprises a lubricating oil.
5. The process of claim 3 wherein said remaining extract-mix phase and said paraffinic hydrocarbon liquid are lcontacted at a temperature within the range of about 90 to F. in said secondary extraction Zone.
'.7 8 6. The process of claim 3 wherein said remaining eX- References Cited bythe Applicant tract-mix is contacted with said parainic hydrocarbon at UNITED STATES PATENTS a paranic hydrocarbon dosage within the range of about 100 to 200 volume percent `of the remaining extract-mix. 1.211323 6/1938 Maey et a1- 5 2,216,932 10/1940 Atkins. References Cited by the Examiner 2,685,556 8/ 1954 HaChrIlllth. UNITED STATES PATENTS 2,727,848 12/1955 Georglan.
2,305,038 12/1942 Schumacher 208-312 DELBERT E. GANTZ, Primary Examiner. 2,928,788 3/1960 Iezl 208-314 3,186,937 6/1965 Anderson et a1 208-314 10 H LEVINE Asssm Examme