US2813918A

US2813918A - Solvent extraction with the operation of the uppermost portion of the extractor as a vapor liquid fractionation zone

Info

Publication number: US2813918A
Application number: US359828A
Authority: US
Inventors: Robert A Findlay
Original assignee: Phillips Petroleum Co
Current assignee: Phillips Petroleum Co
Priority date: 1953-06-05
Filing date: 1953-06-05
Publication date: 1957-11-19
Anticipated expiration: 1974-11-19

Description

1957 R. A. FINDLAY 2,813,918

SOLVENT EXTRACTION WITH THE OPERATION OF THE. UPPERMOST PORTION OF THE EXTRACTOR AS A VAPOR LIQUID FRACTIONATION ZONE Filed June 5, 1953 2 Sheets-Sheet l 26 F'RACTIONATIO SECTION LIQUID-LIQUID EXTRACTION FEED 2 l4 FLASH p SECTION 2 47 SOLVENT EXTRACT RECOVERY MAKE-UP SOLVENT INVENTOR.

R.A. FINDLAY ATTORNEYS 2,813,918 THE OPERATION OF THE UPPERMOST QUID FRACTIONATION ZONE 2 Sheets-Sheet 2 Filed June 5, 1953 m 4 Y A 8/ A W. [I m R M E 9 I MN N 1 a E w T N n m E :41|iill1j W T 223 .00 UZEI ZO PU K.H V I A 7% M E E T A N B G m m X U l MT Y L 7 E M B n s 7 R 7 X 2 w P 7 u a R 9 I 3 I n J u m 1 2 [I uJ l a 8 H V B- Iv. Q v 2 F M \f K JW ON DN mm mm G ATW T NN mum 1 mo my? WX mm mm 5 W[ h. r

hired States Patent @tfice Z,8l3,9l8 Patented Nov. 19, l957 SULVENT EXTRACTIUN WITH THE OPERATEON 0F THE UPPERMQST PORTION OF THE EX- TRACTOR AS A VAPOR LIQUID FRAC'HQNA- THEN ZONE Robert A. Findlay, Eartlesville, Okla, assignor to Phillips Petroleum Company, a corporation of Delaware Application June 5, 1953, Serial No. 359,828 7 Claims. (Cl. 260-674) This invention relates to a process for the separation of a mixture of hydrocarbons into its component parts. In a further aspect this invention relates to the solvent extraction of a hydrocarbon stream to obtain a paraflin fraction and an aromatic fraction. In a further aspect this invention relates to liquid phase, selective solvent treatment of hydrocarbon streams. In a further aspect this invention relates to apparatus for the solvent extraction of the mixture of hydrocarbons.

Each of the following objects is obtained by at least one of the aspects of this invention.

An object of this invention is to provide a method for the separation of hydrocarbon streams. A further object of this invention is to provide a new method for the treatment of a hydrocarbon stream with a selective solvent. A further object of this invention is to provide a process for liquid-liquid extraction of aromatic hydrocarbons from a hydrocarbon stream containing aromatic and paralfinic hydrocarbons. A further object of this invention is to provide apparatus for carrying out the process of this invention.

Other objects and advantages will be apparent to one skilled in the art upon reading this specification and the drawings, which are a part thereof, and which comprise:

Figure l, which shows a semi-diagrammatic view of a preferred form of this invention, and,

Figure 2, which shows a modification of the invention.

In prior work with selective solvents it has been found that some of the solvents with highest selectivity have low solubility, this solubility being so low at times at the boiling point of the hydrocarbon being treated that they are only partially miscible. It has been suggested that extractive distillation be used with such solvents but in such case it is necessary to have two liquid phases and one gas phase on each tray. Because of interfacial effects this tends to result in emulsions and foaming which give low tray capacity. Furthermore, there is an increased possibility of channeling of either liquid phase resulting in poor contacting of one with the other or with the gas. High pressures have been used to make the hydrocarbon and the solvent miscible, but this decreases the selectivity and increases decomposition and corrosion problems.

I have invented a method which eliminates these difficulties and offers a simplified means of extracting aromatics from a hydrocarbon stream using a high boiling viscous solvent. This method comprises operating the column at such temperature and pressure conditions as to be at or near the boiling point of the raflinate portion of the feed. The lower and major portion of the column is operated as a liquid-liquid contacting zone with the solvent phase being continuous. The ramnate layer, containing hydrocarbon with solvent dissolved therein, appears on the top of the continuous solvent phase layer. A liquid stream of this raffinate layer is withdrawn from the column, passed through a reboiler, and reintroduced into the upper portion of the fractionator. Sufficient heat is introduced in this reboiler to vaporize at least the major portion of the hydrocarbon without vaporizing the selective solvent. Thus, the upper portion of the column operates as a vapor-contactor with a continuous vapor phase. Solvent free raffinate is removed from the top of the column and the solvent, having been thrown out or" solution as the hydrocarbon is evaporated, settles directly into the solvent layer.

For a more complete understanding of the invention, attention is directed to Figure l which shows, in diagrammatic form, preferred apparatus for the practice of this invention.

In Figure l the fractionatcr Ill is provided with impervious barrier 11, forming upper section 12 and lower section B. Feed conduit 24, after passing through heat exchanger 16 extends into the central portion of section 12 of the fractionator, this fractionator being provided with suitable trays 17. These trays can comprise bubble caps, perforated plates, Koch Kaskade trays and the like. Solvent line 28 extends into the upper portion of section 12 from solvent recovery zone 19 as will be more fully described hereafter. Extending from the upper portion of fractionator 10 is raflinate removal conduit 21, this conduit being provided with a pressure valve 22 and heat exchanger 23, which functions as a condenser to supply reflux to line 24 and liquid product to line 26. Positioned in proximity to fractionator 10 is reboiler 27, which can be of standard construction, such as, for example, a thermosiphon reboiler. Above solvent inlet conduit 18 there is provided an interface level controller 28, and at a level above controller 23 there is provided liquid level controller 29. Extending from the upper portion of fractionator ll), between the control conduits of liquid level controller 29, there is provided conduit 31 extending to one end of reboiler 2'7. From the other end of reboiler 27, conduit 32 extends to chamber 10 at a level above removal conduit 31. Valve 33 in conduit 31 is controlled by liquid level controller 29.

Extending around partition 11 is conduit 34, this conduit being provided with valve 36 and heater 37. Extending from the upper portion of section 13, there is provided conduit 38, having condenser 39 therein, to reflux accumulator 41, the level in this accumulator being controlled by liquid level controller 42, which, in turn, controls the amount of heat supplied to heat exchanger 37 by means of valve 43 in the heat exchange material supply conduit 44. Level controller 42 functions by opening valve 43 when the level in accumulator 41 drops. Opening valve 43 results in greater. vaporization of the material supplied by conduit 34 and a resulting increase in material in accumulator 4-1. From reflux accumulator 41 extends conduit 46, this conduit being provided with pump 47 and extending into the lower end portion of section 12 of fractionator Ill. From the lower end portion of section 13, there is provided conduit 49 which extends to solvent recovery zone 19. Various means of solvent recovery and separation of the extract phase therefrom are well known in the art and, in the interests of simplicity, are not shown in Figure 1. This solvent can be recovered by means of a fractionating column, a water wash, or other suitable means. An extract layer removal conduit is shown as conduit 51 and conduit 18, previously described extends back to the column, this conduit having a pump 52 therein. Make-up solvent conduit 55 is connected to conduit 18. Bypass conduit 53 extends around heat exchanger 16 for optional use. Conduit 18 is also provided with heat exchanger 54.

Figure 2 illustrates an alternative method of separating the extract from the solvent, and the apparatus varies in the treatment of the solvent layer. In the upper portion of the drawing the apparatus is the same as shown in Fig. 1 and the same reference numerals are used where applicable. in the lower portion of the column, section 13 is provided with removal conduit 38, this conduit being provided with condenser 39. A separating tank 71 is connected to condenser 39 by means of conduit 72. Extending from the upper portion of separating tank 71 there is provided reflux return conduit 73, this conduit having pump 74 therein. Positioned in proximity to separating tank 71 is fractionating column 74. From the lower end portion of separating tank 71 there is provided conduit 76 extending into fractionating column 74. Bypass conduit 77 connects conduit 38 and fractionating column 74. Extending from the upper portion of fractionator column 74 is conduit 78, this having condenser 79 located therein, and provided with branch conduit 81 for reflux return to fractionating column 74. Extending from the lower end portion of fractionator is conduit 82 and extending from the lower end portion of fractionating column 74 is conduit 83. Makeup solvent line 84 is provided, this conduit communicating with conduit 18, which, in turn, provides solvent return from

columns

10 and 74 through connecting

conduits

82 and 83.

EXAMPLE In order to illustrate more fully the operation of this invention the following example is included, it being understood that this example is included for illustrative purposes and is not to be considered in an unduly limiting is fed to the column through feed line 14, being heated, in heat exchanger 16 to a temperature of approximately 200 to 215 F. Diethylene glycol at approximately the same temperature is fed to the column through conduit 18 using a solvent to hydrocarbon feed ratio of 5 /2 to 1. When the pressure on the column is maintained at about p. s. i. g. the column is under liquid phase operation between level 91 and partition 11. Between partition 11 and level 92 there is a continuous solvent phase with the aromatic fraction of the feed stream dissolved therein. The liquid raflinate layer is maintained between

levels

91 and 92. A portion of this raflinate layer is withdrawn through conduit 31 and introduced into reboiler 27 Where it is heated to a temperature approximately 5 F. above that maintained in the column, this temperature being sufiicient to vaporize the major portion of the paraffins in the raflinate layer. This heated material is reintroduced into the column, the portion above level 91 functioning as a fractionating section wherein the vapor phase is the continuous phase. Solvent in the hydrocarbon layer is thrown out of solution and settles into the solvent layer. Through conduit 21 solvent free raflinate is removed, condensed in condenser 23 and is removed as the rafiinate product through conduit 26. A portion of the raflinate is returned to the column as reflux through conduit 24. The composition of this raffinate is as follows, the percentages being given in weight percent,

Percent Heptanes 30 Hexanes 66 Aromatics (mainly toluene) 4 Through conduit 34 a portion of the solvent having aromatics dissolved therein is withdrawn from the lower end portion of section 12, heated in heat exchanger 37 and, at a temperature in the range of 300 to 320 F., flashed into section 13, this causing a portion of the aromatics to be vaporized since the pressure in this section is maintained at approximately atmospheric pressure. Aromatic reflux is obtained by condensing aromatic vapors withdrawn through conduit 38, these aromatics being stored in reflux accumulator 41. Reflux is returned to section 12 through conduit 46, as required by means of pump 47.

The balance of the solvent containing the extract dissolved therein is conveyed to solvent recovery zone 19 through conduit 49, a product being withdrawn by means of conduit 51 and the solvent being returned to the column through conduit 18 as required by means of pump 52. This solvent is passed through heat exchanger 16 to heat the incoming feed, although a portion may be bypassed through conduit 53. Heat exchanger 54 serves to provide the solvent feed at the correct temperature for introduction into the column. The product removed from the solvent recovery zone as the extract has the following composition, the percentages again being given in weight percent,

Percent Benzene 28 Toluene 72 Paraflins 0.2

A simple automatic control system utilizing liquid level controllers is used so that the separation is substantially automatic. A liquid level controller 28 functions to maintain the interface 92 between the raflinate layer and the layer in which the solvent phase is continuous at a constant level. Valve 36 is controlled by controller 28, this valve controlling the amount of liquid removed from the lower portion of section 12. Level controller 29, which operates valve 33 is set to maintain a raffinate layer at approximately level 91. Level controller 42 on reflux accumulator 41 operates valve 43 which, in turn, varies the amount of heat supplied in heat exchanger 37 and thus the amount of material vaporized in zone 13.

The operation of the apparatus shown in Figure 2 is substantially that of Figure 1, except that a different method of extract-solvent separation is employed, a fractionating column 74 being used in Figure 2. In this modification interface level controller 28 performs the same function as in Figure 1 in permitting a certain amount of liquid to be introduced into zone 13. In this zone heat is supplied to the extract layer and the hydrocarbon is boiled therefrom by means of a stripping action. Hydrocarbon vapors containing some solvent are removed through conduit 38, condensed in cooler 39 and introduced into separating tank 71. From the upper end portion of tank 71 an aromatic reflux stream is returned to zone 12 and the balance is introduced into fractionating column 74. If desired, a portion of the material can be bypassed directly into fractionating column through conduit 77. This column operates as the usual fractionating column, an extract portion being taken off overhead, with a small amount of reflux being returned, and the solvent being removed from the lower portion of the column through conduit 83. This solvent, in connection with that obtained in the stripping section 13 and removed by conduit 82 from this section is returned to the fractionating column to conduit 18. Makeup solvent is supplied through conduit 84.

Although diethylene glycol has been used in the example, other well-known solvents can be used in the present process. These include ethylene glycol, triethylene glycol, propylene glycol, the monomethylether of diethylene glycol, the ethanolamines, and the like.

As many possible embodiments may be made of this invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawing is to be interpreted as illustrative and not in an unduly limiting sense.

I claim:

1. In the process of separating the components of a hydrocarbon stream by liquid-liquid contacting with a selective solvent which is more dense and higher boiling than said hydrocarbon stream, the improvement which comprises withdrawing a liquid stream of raflinate phase from the contacting zone containing rafiinate and selective solvent, adding sufficient heat to said stream to vaporize at least a portion of said raflinate portion, introducing said stream into the upper portion of the contacting zone at a point above the level of its removal, and removing vaporized raflinate from the upper end portion of said zone while allowing the solvent to settle into the lower portion of said zone.

2. A process of treating a hydrocarbon stream with a selective solvent which is more dense and higher boiling than said hydrocarbon stream, in a fractionator comprising introducing said stream into the central portion of said fractionator, introducing said selective solvent into said fractionator at a point above said feed, maintaining temperature and pressure conditions to provide liquidliquid contacting below the point of inlet of said solvent, withdrawing a liquid stream of raflinate phase containing raflinate and selective solvent from said fractionator at a point above said solvent inlet, adding sufiicient heat to said last-mentioned stream to vaporize at least a portion of the raflinate, reintroducing said last mentioned stream into said fractionator at a point above the level of its removal, removing vaporous raflinate as a product, allowing liquid selective solvent to flow back into the liquid-liquid contacting section of said fractionator, removing said solvent containing the extract, and separating said extract from said solvent.

3. A process for separating a mixture of hydrocarbons into a parafiin fraction and an aromatic fraction by treatment with a selective solvent which is more dense and higher boiling than said hydrocarbons, comprising introducing said mixture into the central portion of a fractionator, introducing said selective solvent into said fractionator at a point above said feed, maintaining temperature and pressure conditions to provide liquid-liquid contacting below the point of inlet of said solvent, withdrawing a liquid stream of raflinate phase from said frac tionator at a point above said solvent inlet, adding suflicient heat to said last mentioned stream to vaporize at least a portion of the paraflin fraction; reintroducing said last mentioned stream into said fractionator at a point above the level of its removal, removing vaporous parafiins as a product, allowing liquid selective solvent to flow back into the liquid-liquid contacting section of said fractionator, removing solvent containing aromatics dissolved therein; and separating aromatics from said solvent.

4. A process for treating a hydrocarbon stream with a selective solvent which is more dense and higher boiling than said hydrocarbon stream which comprises introducing said stream into the central portion of a fractionator, said fractionator having a liquid-liquid extraction zone in the central portion thereof, a fractionation zone in the upper portion thereof, and a flash zone in the lower portion thereof; introducing said selective solvent into the upper portion of said liquid-liquid extraction zone, removing a liquid stream comprising rafiinate hydrocarbon having solvent dissolved therein from a point in said fractionator above the point of solvent inlet; adding suflicient heat to vaporize at least a portion of said raffinate hydrocarbon; introducing said stream into the fractionator at a point above the point of its removal; removing vaporous raflinate from the upper end portion of said fractionation zone; condensing at least a portion of said raflinate; returning at least a portion of said condensed railinate to the upper end portion of said fractionator as reflux removing a liquid stream of solvent having extract dissolved therein from the lower end portion of said liquid-liquid extraction zone; adding suflicient heat to said stream to vaporize at least a portion of the extract; introducing said stream into said flash zone; removing and condensing at least a portion of said extract, introducing at least a portion of said condensed portion of said extract into the lower end portion of said liquidliquid extraction zone as a reflux stream; removing solvent having extract dissolved therein from the lower end portion of said flash zone; recovering extract from said solvent; and returning said solvent to said liquid-liquid extraction zone.

5. The process of claim 4 in which the selective solvent is diethylene glycol and the separation is one in which paraflinic hydrocarbons are separated from aromatic hydrocarbons, the paraffins appearing as the raffinate.

6. A process for treating a hydrocarbon stream with a selective solvent which is more dense and higher boiling than said hydrocarbon stream which comprises introducing said stream into the central portion of a fractionator, said fractionator having a liquid-liquid extraction zone in the central portion thereof, a fractionation zone in the upper portion thereof, and a stripping zone in the lower portion thereof; introducing said selective solvent into the upper portion of said liquid-liquid extraction zone, removing a liquid stream comprising rafiinate hydrocarbon having solvent dissolved therein from a point in said fractionator above the point of solvent inlet; adding sufficient heat to vaporize at least a portion of said raffinate hydrocarbon; introducing said stream into the fractionator at a point above the point of its removal; removing vaporous raffinate from the upper end portion of said fractionation zone; condensing at least a portion of said raffinate; returning at least a portion of said condensed raflinate to the upper end portion of said fractionator as reflux, removing a liquid stream of solvent having extract dissolved therein from the lower end portion of said liquidliquid extraction zone and introducing said stream into said stripping zone; vaporizing the extract and a portion of the solvent in said stripping zone by supplying heat thereto; removing vapors from the upper portion of said stripping zone; condensing at least a portion of said vapors to a liquid; passing said liquid to a phase separation zone; passing at least a portion of the extract layer to the lower end portion of said liquid-liquid extraction zone as reflux; passing the balance of said material removed from the upper portion of said stripping zone to a solvent-extract separation zone; recovering an extract from said separation zone; recovering a solvent stream from said stripping zone and said solvent-extract separation zone; and returning said solvent to the upper portion of said liquidliquid extraction zone as the aforementioned solvent feed thereto.

7. Apparatus for the treatment of a hydrocarbon stream with a selective solvent comprising, in combination: a fractionator, said fractionator being provided with an impervious partition extending completely across the lower portion thereof and dividing said fractionator into an upper section and a lower section, a first conduit extending to and communicating with the central portion of the upper section of said fractionator; a second conduit connecting the upper and lower sections of said fractionator; a valve in said second conduit; a heat exchanger in said second conduit; a third conduit communicating with said fractionator at a point above said first conduit; an interface level controller operatively connected to said fractionator at a point above said third conduit, said interface level controller controlling the valve in said second conduit; a liquid level controller operatively connected to said fractionator above said interface level controller; a reboiler positioned in proximity to said fractionator; a heating coil in the lower portion of said reboiler; a fourth conduit extending from said fractionator at said liquid level controller to one end of said reboiler; a valve in said conduit, said valve being connected to said liquid level controller; a fifth conduit extending from the opposite end of said reboiler to said fractionator at a point above said fourth conduit; a sixth conduit extending from the upper end portion of said fractionator; a heat exchanger in said sixth conduit; a seventh conduit extending from the upper portion of the lower section of said fractionator to an accumulator; an eighth conduit extending from said accumulator to the lower portion of said upper section; a

"7 second liquid level controller operatively connected to said accumulator and adapted to actuate a valve controlling the admission of heat to said heat exchanger in said second conduit; and a ninth conduit extending from the lower end portion of the lower section of said fractionator. 5

References Cited in the file of this patent UNITED STATES PATENTS Coahren Aug. 14, 1928 10 Fenske et al Dec. 15, 1936

Claims

1. IN A PROCESS OF SEPARATING THE COMPONENTS OF A HYDROCARBON STREAM BY LIQUID-LIQUID CONTACTING WITH A SELECTIVE SOLVENT WHICH IS MORE DENSE AND HIGHER BOILING THAN SAID HYDROCARBON STREAM, THE IMPROVEMENT WHICH COMPRISES WITHDRAWING A LIQUID STREAM OF RAFFINATE PHASEE FROM THE CONTACTING ZONE CONTAINING RAFFINATE AND SELECTIVE SOLVENT, ADDING SUFFICIENT HEAT TO SAID STREAM TO VA-PORIZE AT LEAST A PORTION OF SAID RAFFINATE PORTION, INTRO-DUCING SAID STREAM INTO THE UPPER PORTION OF THE CON--