US2276089A - Recovery of solvents from oils - Google Patents

Description

March 1o, 1942.

E. G. RAGA-rz RECOVERY OF SOLVENTS FRONTOILSVIV Filed .J une 26, 1957 ZowPresS. Eyczpaz'aior fHz'gZL Press. E'Ylaporaiar Se @Tutor/l l p .all

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Patented Mar. 10, 1942 UNITI-:D rsrl-Ires PATENT OFFICE I 2,276,089 RECOVERY OF SOLVENTS FROM OILS Edward G. Ragatz, San Marino, Calif., assignor to Union Oil Company of California, Los Angeles, Calif., a corporation of California Application June 26, 1937, Serial No. 150,658

`(Cl. 2oz- 61) 5 Claims.

The present invention relates to methods of and apparatus for evaporating, and more particularly pertains to systems employed for recovering solvents from products produced by extraction processes. Specically, the invention covers the regulation and control of the multiple evaporating systems employed for the recovery of solvents which have been or are being used for extraction purposes, as for example, in the solvent extraction of petroleum oils to produce fractions which are respectively more and less parafnic in nature than the oils treated.

It is an object of this invention to provide a process and system for the recovery of the solvents from oils`with maximum eiciency and with minimum loss of solvent. Another object is to provide a system of` this type which will produce a high degree of'control, particularly as to the temperature and pressure conditions, thus providing for a high degree of economy in the utilization of heat and in the recovery of the solvents.` Still further objects of the invention will be apparent from the following description.

The solvent treatment of various types of oils is now quite well known in the art. these processes remove the oils, whether animal, vegetable dr mineral, from the solids in which they are found. In other cases and this is particularly true in the case of a mineral oil, a solvent treatment is employed to reject such substances as asphalt and/ or wax originally present in the oil and detrimental to its use, particularly when the mineral oil is of the lubricating oil type. As previously stated, a further example of solvent extraction process is one in which a mineral oil fraction is separated into two or more components on the basis of the selective solvent power of the solvent. Processes of this type have been used for the treatment of motor fuel stocks, kerosene stocks and particularly lubricating oil stocks, in the latter case the solvent extraction producing components which are respectively more and less parailinic in nature than the original lubricating oil treated. When a lubricating oil stock is treated with solvents such 'as liquefied normally gaseous hydrocarbons, phenol, cresylic acid, n itrobenzene, etc., whether alone or in combination with other solvents such as benzol, under temperature and pressure conditions such as to form atleast two liquid phases, as a general rule one of these phases usually termed the extract phase contains a greater amount of the solvent employed land the relatively more soluble portion of the oil, while the Some of prises aA lesser amount of the solvent together with the less soluble portion of the oil. When the solvent is removed from the extract and raflinate phases the oil constituents contained therein are respectively known as extract .and raffinate.

Although the process and system presented hereinbelow will be described in commotion with the recovery of the solvent from either the extract or ranate phases of the above type of solvent extraction, it is to be understood that the invention is equally lapplicable to solvent recovery from any type of process in which a solvent has been used for the separation or extraction of any type of materials regardless of their source. The details of the invention will become apparent from the description presented hereinbelow, particular reference being made to the drawing, which represents diagrammatically two embodiments of the process and in which:

Fig. 1 shows a conventional two-stage evaporating system employed for the recovery of solvent vapors from the extract phase produced during the solvent extraction of a lubricating oil stock, said system embodying the features of the present invention, and

Fig. 2 is a similar embodiment of the invention as applied to a single-stage evaporating system of the above type.

Referring now to the drawing and more particularly to Figure 1, the extract phase comprising a mixture of oil and solvent is introduced into the solvent recovery system through line I0 from a source not shown in the drawing. For the purpose of heat economy,\ this stock is ad'- vantageously compressed, as for example tov a pressure of approximately 200-215 lbs. per square inch. Before entering the rst evaporator the stock first passes through a preheater II andk then, after passing through line I2, is further heated in I3 which is a heater 'employing steam for the indirect heating of the stock passing therethrough. After leaving preheater I3 the stock passes through line I4 and enters the rst or high pressure evaporator I6, in which a portion ofthe solvents are evaporated from the mixture. In the specic example in which the solvent-oil mixture was compressed to approximately v200-215 lbs., the evaporator or separator I6 is maintained at approximatelythat pressure. The oil and the solvent still remaining liquid at the temperature and pressure conditions maintained in separator I6 leave said evaporator through line Il and are conveyed to the other phase known as the ramnate phase comsecond or low pressure evaporator I8' in which heat exchanger I I.

the pressure is considerably lower than that maintained in the 'rst separator. This is realized by the maintenance of a reducing valve I9 in line I1,-the opening of said valve being regulated and/or actuated by the liquid level in the high pressure evaporator I5. The oil-solvent mixture being conveyed through line I1 to the low pressureevaporator I8 passes successively through a heat exchanger 2l' and then through a steam heater 22. The solvent vapors separated in the high pressure evaporator I6 leave the latter through line 25, are conveyed flrst through heater 2I to preheat the solvent-oil mixture being conveyed to the low pressure evaporator, then through line-25 through the heat exchanger II on line I8, and are then withdrawn through line 21. The condensed and uncondensed solvent mixture, passing through line 21, is then conveyed into separator 28 wherein the vapors are separated from the Yliquefied solvent, the former,leaving through line 38 while the latter is withdrawn through line 3I.

By' virtue of the pressure v"and temperature conditions maintained in I8, the oil-solvent mixtureintroduced thereinto separates into its constituent components, the oil leaving said' separal,

tor through line 33 controlled by oat valve 34, while the deoiled solvent vapors leave the separator through line.35. These vapors as well as the vapors passing through line 38 are then liquefied in a condenser 38, and may .then be used again for solvent extraction purposes. For this purpose they may be employed alone or mixed with the liquid solvents coming through line 3l.

The system illustrated and described hereinabove, however, is extremely unstable as to temperature, pressure, and ratios of vapors to condensate.` In fact this system is impractical in view of its relatively high utilization of heat. Thus, anyvariation in the amount of heat conveyed in steam heater I3 to the stock being transmitted to the high pressure separator, causes the evaporation of a relatively increased amount of solvent vapors, which leave said separator through line and arel conveyed through line 26 to the This further heats the extract phase or stock being conveyed through the system, thus tending to further raise its temperature. Simultaneously, or immediately thereafter, the increase in pressure in the high pressure evaporator" IB tends to create a back pressure on line I4, thus reducing the quantity of feed stock entering said separator.

results in a decrease in the quantity of solvent vapors evaporated in the separator and conveyed through lines 25 and 28 to the heat exchanger I I. This causes a substantial Ireduction in the heat imparted to the incoming feed stock, thereby substantially lowering the temperature of said stock when it enters separator I6. It is thus seen that the operating conditions of the system are such that they tend to oscillate constantly from one extreme to the other. It is therefore a further object of the present invention to avoid the above described defects and to provide a systemgwhereby said operating conditions may be adequately `and perfectly controlled, thereby stabilizing theV conditions and avoiding excessive heat utilization and/or incomplete solvent recovery.

To avoid the above defects and disadvantages, applicant has discovered that it is necessary to provide the above or similar systems with a cer- Obviously, Asuch a decrease in the rate of throughput in turn tain combination of controls. Thus, it has been found that a substantially complete control may be established by providing vapor line 38 with a back-pressure regulator (indicated by numeral 39), and by regulating the introduction of heat to steam heater I3 sothat the quantity of vapors passing vfrom separator 28 through said backpressure regulator 39 on line 38 is at a minimum, or at least within a certain minimum range. Such a regulation, which obviously may be realized either automatically or manually, will produce an optimum heat efllciency, and will, tog'ether with other controls to be described hereinbelow, result in the establishment and maintenance of constant and stable conditions in the solvent recovery system.

Referring again to Figure 1 and for the purpose of accomplishing the above results, steam line 48, employed for the introduction of steam to heater I3, is provided with a valve 4I, which, as previously stated, may be of the manually actuable type, but which, in the preferred embodiment is automatic and, as shown, responsive to the rate'of flow of vapors through line 38 upstream of back-pressure valve 39. For this purpose, line v38, upstream of valve 39, is provided with an orice meter 38, and valve 4I is connectedA by means of a pipe 42 with said meter 38 so that valve 4I is thus actuable responsive to the volume of the vapors passing through line 38. Obviously, valve 4I can thus be set so that the introduction of steam through line 48 into heater I3 will be such that the vapors passing through line 38 are held to a minimum, and so that any variation in the quantity of these vapors will correspondingly vary the rate of said steam introduction. It is obvious that regulation of heat supply to the system so that the quantity of vapors passing through line 38 are maintained at a minimum, is only for the purpose o f realizing optimum heat efficiency. Therefore, if conditions in ythe-system are such that it is more economical to use a greater quantity of heat, such a condition may result in a greater ow of vapors through line 38. Whatever this may be, the provision of valve 4I on steam line 48 and the regulation of said valve in response to uctuations in rate of flow through line 38 upstream of backpressure valve 39, will result in the maintenance of stable conditions in the system by regulating the temp'erature and pressure conditions so that the above described flow of vapors through line 38 is maintained at the given constant. In` view of the fact that there is a certain lag in the system, it is preferred to regulate valve 4I fin response .to the flow through meter 38, the arrangement or setting being such that the rate of flow through line 38 may vary within a certain predetermined range before valve 4I on steam line 48 is actuated.` Obviously, however, in some instances the regulation of valve 4I i may be made to be responsive to pressure changes in line 38.

For thepurpose of further control of the conditions in the above-described multi-stage solventuecovery system, it is essential to maintain the fed constant. For' this purpose, une It is provided with a valve 44 adapted to maintain the rate of iiow of solvent-oil through line I8 constant. Furtliestabilization is realized by providing a back-pressure valve 46 'on the vapor line 35 leading from the low pressure separator I8 to condenser 36.

The following`is a specic example of an operation carried out in the above multi-stage recovery system, this example being non-limiting in scope, but merely for purposes of a clearer understanding of the advantages derived from the present invention. Also, although the example is described in connection with the recovery of a sulphur dioxide solvent from the extract phase obtained from the extraction of lubricating oils with said solvent, it is clear that the invention can be used in connection with the removal of any solvent from other materials regardless of the source thereof, and whether it be an extract or, raiilnate phase.

An extract phase, which in the instant case may consist of approximately 16% extract and 84% liquid sulfur dioxide, is continuously fed, at a pressure of 215 .pounds gauge, into the system through line I 0, valve 44 maintaining said rate of input constant. In heat exchanger I I this feed stock is raised to -a tem-perature of about 145 F., while after passage through steam heater I3 it is raised to a temperature of approximately 165 F., at which temperature (and at a :pressure of about 200 pounds gauge) said'extract phase enters the high pressure separator I6. Under the enumerated conditions, slightly over one-half of the sulfur dioxide is evaporated at this stageof operations, these vapors being removed or withdrawn from separator I6 through line 25. The liquid phase is then withdrawn from said separator through line I1, the rate of withdrawal being regulated by valve I9 in response to the .position of float 20 in separator I6. After passing through valve I9, this liquid phase is conveyed, at a pressure of about 80 pounds and a temperature in the neighborhood of 112 F., to heat exchanger 2 I, wherein it is brought in indirect heat exchange with the sulfur dioxide vapors withdrawn froml the above described high pressure separator I6. In this heat exchanger the oil-solvent mixture is raised to a temperature of about 145 F., while the sulfur dioxide vapors are thereby cooled to about 160 F. The oil-solvent mixture is" then conveyed through steam heater 22 wherein it is further heated so that said mixture is at a pres- 'sure of about 72 pounds and a temperature of approximately 300 F. when it enters the low pressure separator I8, and wherein substantially all of the sulfur dioxide isseparated from the extract. The solvent vapors are then withdrawn through line 35. equipped with a back-pressure valve 46 and are conveyed to condenser 36 of any well known type. The extract thus freed from the solvent is continuously withdrawn from the low pressure separator I8 through line 33, the

Vrate of removal being automatically regulated by the float controlled valve 34.

The vapors of sulfur dioxide withdrawn through line 25 from the high pressure separator I6, after passing through heat exchanger 2| as aforesaid,

are then conveyed through line 26 to heat ex-` changer II wherein they preheat the incoming fresh feed stock. Thereafter, these vapors, cooled to about 160 F., are passed through line 21, and enter separator 26 wherein the'condensed p0rtion of the sulfur dioxide separate from the vapors. The condensate is then removed through line 3| controlled by the oat actuated valve 32, while the vapors may be conveyed vto condenser 36 through line 36 equipped with a back-pressure valve 39.

It is easily seen that the above described arrangement permits a thorough control of conditions in the system. Thusly maintaining constant the rate of feed into line I6, and by setting the various valves for Aan optimum operation of the system, it is possible to' obtain optimum and economic heat utilization. Also, any change in the temperature of the sulfur dioxide conveyed to separator 28 (and therefore any change in the quantity `of sulfur dioxide vapors leaving said separator through line 30) will cause an adjustment of the rate of steam injection into heater I3, thereby correcting said condition, and tending to return the pressure-temperature relationships in said system to the predetermined values.

It is also clear that many other arrangements or minor modifications may be made without departing from the scope of the present invention. Thus, if desired, the steam introduced into heater 22 may also be automatically controlled, as for example responsive to the temperature of the oilsolvent mixture leaving said heater. Again, this regulation might also be responsive to the rate of ilow of sulfur dioxide vapors through meter 38 in line 30.

As stated above, Fig. 2 represents a diagrammatic view showing the incorporation of the present invention into the operation of a single stage evaporating system. Referring to this drawing, the feed stock is introduced into. the system through line 50 and, afterpassing through a constant feed valve 5I, is conveyed through heat exchanger 52. The stock then'passes through line 54 and steam heater 55, and is then introduced through line 56 into evaporator 51. The vaporized solvent leaves evaporator 51 through line 60, while the thus liberated oil is withdrawn through line 6I, the rate of discharge being regulated by the oat control valve 62. As in the case of the two-stage evaporating system described hereinabove, the vapors withdrawn through line 60 are first conveyed through heat exchanger 52 to preheat the incoming feed. The solvent is then conveyed through line 64 into separator 6,5 wherein the condensed portion of the solvent separates from the vapors, this condensate being removed through line 66 provided with a iloat control valve 61. The vapors are withdrawn from separator through line 69 .provided with an orifice meter 10 and a back pressure valve 1I. These vapors are then conveyed through line 13 to a condenser 1I. As in the case of the system shown in Fig. I, steam heater 55 is provided with a. steam input line 11 equipped witha valve 16 which may be automatically regulated by means of line 19 so that said rate of steam input into heater 55 will :be responsive to the rate of flow of vapors through meter 10. The provision of the various control valves and back pressure valves in this system,

as well as the regulation of the steam input into heater 55 in response to or in accordance with changes in the rate of flow of solvent vapors through line 69, permit an accurate control of the pressure-temperature conditions in the system, thus stabilizingoperations and accomplishing the objects enumerated above.

Although the present invention has been described in connection with certain specic em- .bodiments thereof, it is to be understood that there is no intention to be limited thereby, since many modifications and variations may be made without departing from the scope of the invention, which is'considered to be limited only tby the appended claims.

I claim:

1. A process for the recovery of solvent and oil from a solution of said oil in said solvent.

whereby a portion of the solvent is evaporated,

.separately removing the evaporated solventl and the liquid fraction still containing a portion of the solvent, further heating the liquid fraction,

conveying said heated fraction into a second evaporator maintained at a relatively lower pressure thereby causing the separation of the remaining solvent in the form of vapors, separately withdrawing said second vapors and the oil from said evaporator, conveying the vaporized solvent from the iirst mentioned evaporator in heat exchange relationship with the feed conveyed respectively to the low pressure and high pressure `evaporators thereby preheating said feeds and causing a partial condensation of the vaporized solvent, separating the uncondensed solvent from the condensate, and regulating the additional heating of the oil-solvent solution entering the first mentioned evaporator by the variations in the rate of condensation of said first mentioned evaporated solvent.

2. In a process accordingl to claim 1 wherein the rate of heating of the incoming oil-solvent solution is controlled to maintain the volume of uncondensed solvent leaving the heat exchange source at a predetermined minimum.

3. In a process according toclaim 1 wherein the rate of introduction of the oil-solvent solution into the solvent recovery system is maintained constant, and wherein the solvent vapors leaving the high pressure evaporator, after passa solution containing a substantial proportion of` said solvent and a mineral oil of a higher boiling range than the solvent, which comprises continuously introducing the solution into a vaporizing zone, continuously and separately withdrawing the evaporated solvent from said vaporizing zone, passing the vaporized fraction in heat exchange relationship with the incoming solution whereby said solution is partially heated While the solvent vapors are thereby partially condensed, separating the condensed solvent from the uncondensed solvent vapors, continuously and separately removing said uncondensed vapors, further heating the incoming partially preheated oil-solvent solution, and regulating said further heating by the rate of withdrawal of the last mentioned uncondensed solvent vapors.

5. A process for the recovery of solvent an oil from a solution of said oil in said solvent, which comprises conveying the solution through two successive vaporizing zones, maintaining a higher pressure in the`iirst vaporizing zone than in the second vaporizing zone, eifecting in the first zone a partial vaporization of the solvent contained in the solution, separately removing the vapors and the unvaporized solution from said first vaporizing zone, conveying said unvaporized solution through the second vaporizing zone maintained at a relatively vlower pressure thereby causing the separation of the remaining solvent in the form of vapors, separately withdrawing said vapors and oil from said second vaporizing zone, conveying the vaporized solvent from the first vaporizing zone inheat exchange relationship with the feed conveyed to the low pressure and high pressure evaporating zones rel spectively thereby preheating said feeds and causing the partial condensation of the vaporized solvent, separating the uncondensed solvent from the condensate thus formed, separately and continuously withdrawing said uncondensed solvent vapors, further heating the oil-solvent solution entering the rst vaporizing zone, and regulating said further heating in response to the variations in the rate of production of the uncondensed solvent vapors.A

- EDWARD G. RAGATZ.

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