US1982513A

US1982513A - Process for continuous refining of mineral oils with liquid so2 and the like

Info

Publication number: US1982513A
Application number: US668112A
Authority: US
Inventors: Grote Wolfgang; Obergfell Paul
Original assignee: Edeleanu GmbH
Current assignee: Edeleanu GmbH
Priority date: 1932-05-04
Filing date: 1933-04-26
Publication date: 1934-11-27
Anticipated expiration: 1951-11-27

Description

Nov. 27, 1934. w. GROTE ET AL PROCESS FOR CONTINUOUS REFINING 0F MINERAL OILS WITH LIQUID S02 AND THE LIKE 2 Sheds-Sheet .1

N \swmg m Zinventora 1 a. 3- m mNN I m n I I Filed ApIiI 26, 1933 QNN any Graft I I alt/l 012a their (Ittornegs Nov. 27, 1934.

W. GROTE ET AL PROCESS FOR CONTINUOUS REFINING OF MINERAL OILS WITH LIQUID S03 AND THE LIKE Filed April 26, I933 2 Sheets-Sheet 2 1" vattornega "'7 \70 Zinnentors Wolfgang 6514122 I lkuul absraflzll UNITED ,STA

Patented Nov. 27, 1934 PROCESS FOR CONTINUOUS REFINING OF I MINERAL OILS WITH LIQUID S02 AND THE LIKE Wolfgang Grote, Berlin-Wilmersdorf, Germany,

and Paul Obergfell, New York, N. Y., assignors to Edeleanu Gesellschaft m. b. H., a corporation of Germany Application April 26, 1933, Serial No. 668,112 In Germany May 4,, 1932 '16 Claims. (CL 196-37) rss PATENT OFFICE This invention relates to an improved method for the treatment of liquid hydrocarbons, particularly mineral oils, with liquid-SO: and like solvents used over and over, that is, maintained in 5 a closed cycle.

" leum fractions continuously introduced and saturated constituents. Upon allowing equilibtreated with varying amounts of solvent.

The invention has special reference to the well known Edeleanu process" of treating petroleum fractions. Briefly, this process consists in mixing the oil or fraction with liquid-50:, the latter being a solvent for unsaturated, aromatic, sulfur containing, and carbon-residue producing constituents, and, being relatively insoluble in the tract layer. The upper layer consists of the refined oil (raiflnate) containing a small amount of dissolved liquid-S02, and will be referred to hereafter as the rafllnate-solution". The lower layer consists of the bulk of the liquid- SO: containing the extracted compounds (which have value as by-products), and will be referred to hereafter as the extract-solution. The two layers are mechanically separated and freed of liquid-S02, resulting in the finished railina and finished extract.

In actual practice, a continuous,"closed treatment' cycle is used and the liquid-SO: recovered and reused. The untreated oil is continuously introduced and treated with the liquid-S01 in a counter-current tower, the raflinate-solution being continuously withdrawn from the upper part of the tower and the extract-solution from the lower part. The respective solutions are freed from the contained liquid-SO: by being passed through a series of evaporators, the first stage in each case being under pressure and the last stage under vacuum, whereby the liquid-SO: is driven off as a vapor. The liquid-S02 vapor is collected, condensed, and reused.

The patent to Cattaneo, Edeleanu, et al, No. 1,840,765, issued January 12, 1932, maybe referred to for further details of the Edeleanu 0on tinuous treatment" process as' heretofore practised in the United States and many foreign countries. I

In some cases a continuous multiple-batch method of treatment is used wherein the untreated oil is not treated in a counter-current tower but in a series of mixing tanks and settling tanks, as illustrated in the patent to Edeleanu et al, No. 1,666,560, issued April 17, 1928. In this case, the raflinate-solution and extract-solution are likewise free of liquid-SO: in a series of evaporators and the recovered liquid-SO: reused. In either method of treatment, the extraction or treatment apparatus is referred to as the mixer.

With respect to the extractionor treatment part of the systems heretofore used, it has been necessary to provide a collecting tank for the rafflnate-solution leaving the mixer and a corresponding collecting tank for the extract-solution, in order that a steady flow of the solutions to the evaporation (liqui 80: recovery) part of would be the case when a fluctuation occurred in the flow of untreated oil or liquid-S02 admitted to the mixer. Furthermore, it has been necessary to provide a great number of sight-glasses in the mixer in order to control that the upper level (top of raflinate-solution) would not fallrbe low the upper outlet, as this would cause the raftinate-solution pump to lose suction and interrupt the flow of solution to the evaporator; and so that the lower level (top of extract-solution and bottom of rafllnate-solution) would be maintained at a mid-point to prevent extract-solution from being drawn, off by the rafiinate-solution pump or raiflnate-solution being drawn off by the extractsolution pump.

It has been found that the expensive collecting tanks and the operators supervising them may be dispensed with and a more effective automatic control secured. This is accomplished, in the case where a counter-current tower is used as the mixer, by passing a portion of the raiiinate-solution drawn from the tower back into the upper part of the tower, the amount thus returned being regulated by a float controlled valve responsive to fluctuations in the upper level; and by also passing a portion of the extract-solutiom back into the lower part of the tower, the amount so returnedbeingregulated by a float controlled valve responsive to-fluctuations in the lower level. This recirculation is effected by the respective ramnate-solution and extract-solution pumps, which must of course have a suflicient capacity to take care of both the direct flow to the evaporators and the recirculating flow.

When a series of mixing and settling tanks are used in place of a counter-current tower, the desired result is secured by equipping the first and last settling tanks with level controls, operated in the same way as those of the countercurrent tower. In some cases it may be desirable to equip'all of the settling tanks with 'level conrols.

In both instances, the improved result may be broadly characterized as following from automatic maintenance of the levels in the mixer (treating and separating apparatus).

With respect to the evaporation (liquid-S02 recovery) part of the system, it has heretofore been necessary to provide very voluminous evaporator drums in which the fluctuations in the flow of the solutions were equalized before entering the more sensitive vacuum evaporators where" such fluctuations would otherwise cause an undesirable increase in thefinal SO: content of the finished reaflinate and extract.

The low pressure and vacuum evapor'ators have a limited operating capacity, as it is necessary to provide gas pumps for drawing off the expelled S02 vapors and compressing them up to a pressure such that condensation can be effected with cooling water, and these gas pumps necessarily have a limited suction capacity. In case that the premise stages of the evaporation systems were not carefully supervised and the supply of heat to these evaporators was not constantly accom- .modated to the fluctuations in the flow of the sosufllcient S02 necessary for the production of apure raflinate and extract.

It has.been found possible bya particular come bination of pressure and temperature controls on -the pressure evaporators (which do not require gas pumps) and of level controls regulating the liquid levels in the evaporators and the flow of solution therebetween, to permit of small capacity evaporators and the securing of the desired SO2- free raflinate and extract despite fluctuations in the incoming raffinate' and extract solutions, whether due to changes in the oil being treated, changes in the amount of liquid-S02 used for treatment, or other changes.

The result of these improvements in both the extraction and evaporation parts of the system is that the cost of the plant, the operating expenses, and number of operators are all materially reduced and a more uniform and satisfactory continuous operation under varying conditions is effected, whereby a more uniform refined product will be produced. Various specific advantages will be evident to those skilled in the art from the following detailed description.

shown one embodiment of my invention for purposes of illustration,

Fig. 1 is a'fiow sheet of a complete extraction and liquid-S02 recovery system for the continuous refining of mineral oils' with liquidSOz;

Fig. 2 is a vertical central section, partly diagrammatic, of a portion of the mixer and the level control for the raffinate-solution in the mixer, indicated diagrammatically in Fig. 1; and

Fig. 3 is a vertical central section, partly diagrammatic, of a fluid level control for'the evaporators, indicated diagrammatically in Fig. 1.

Referring to Fig. 1, the untreated petroleum being greater than that of the oil, the two will pass in counter-current relation to each other within the mixer, the oil rising and the liquid- S02 sinking. As the oil rises, the constituents that it is desired. to remove will be extracted by the liquid-S02 and the resulting raflinate-solution, containing usually about 10-20% by weight of liquid-S02 dissolved therein, will'collect in the upper part of the mixer, The liquid-S02 and constituents dissolved therein (which are, in gen eral, the unsaturated, aromatic compounds comprised in the oil) 1. e., the resulting extractsolution containing usually 80-90% of liquid-S02,

collects in the bottom part of the mixer 12.

Due to the double phase effect, previously described, the result will be an upper layer ofraffinate-solution resting on a lower layer of extract-solution. Two levels will exist, the upper level being the top of the rafllnate-solution layer; and the lower level being the top of the extractsolution layer, this being also the, plane of demarcation between the two layers.

The rafiinate-solution is withdrawn from the mixer 12, at a point above the liquid-S0: inlet, through line 16 by liquid transfer pump 1'! and into line 18, controlled by valve 19.

The upper level of the raflinate-solution in the mixer 12 is maintained at the desired point above the outlet by forcing a portion of the rafiinatesolution in line 18 back into the upper-part of mixer 12, this-being accomplished by pump 17 and line 20 which branches off from line 18 in advance of valve 19. The amount of rafilnatesolution thus circulated back is regulated by float rafllnate-solution to maintain the level at the predetermined point.

An illustrative form of valve 21 is shown in de-. tail in Fig. 2. Referring to Fig. 2, the outlet 22 in the upper part of mixer 12 conducts the raffinate-solution into line 16. The raflinate-solution circulated back flows through line 20 to valve 21, which has a regulating chamber 23 communicating with line 20 and with line 24, the latter conducting the recirculated ramnate-solution into the upper part of the mixer at a point below outlet 22.

Valve 21 has a float chamber 25 above the regulating chamber. The float chamber communicates with mixer 12 by meansvof two pipes: pipe 26 which enters the mixer at a point just above the desired rafllnate-solution (upper) level, and pipe 27 which enters just below this level.

Within .chamber 25 is a float 28 which is attached by dependent vertical rod 29 to the valve mechanism in chamber 23. The two chambers are separated by wall 30, the latter having a sleeve 31 through which passes rod 29.

With this arrangement it is evident thatvthe raflinate-solution from the mixer-can flow freely into chamber 25 and that'the liquid level in this chamber will at all times be the same as that in the mixer. Float 28 and rod 29 will therefore chamber 23. The upper conical extension narrows upwardly and the lower conical extension widens downwardly. Attached to rod 29 are two valve disks, 33 and34, contained respectively within the upper and lower conical extensions of chamber 32.

It will be seen that an upward movement of rod 29 (and valve disks 33 and 34) will cause an increased resistance to the flow of raflinate-solution from line 20 to pipe 24 and the mixer, and visa versa, with the result that the rate of flow of rafiinate-solution back into the mixer will increase when the upper level drops and will decrease when the upper level rises.

Thus valve 21, by automatically increasing or decreasing the amount of raflinate-solution forced back into the mixer through line 20 by pump 17, causes the upper level in the mixer to be maintained at a predeterminedpoint above the rafiinate-solution outlet.

Referring again to Fig. 1, the extract-solution is drawn from the bottom of mixer 12 into line 35, by liquid transfer pump 36, and is forced into line 37, controlled by valve 38. A portion of the extract-solution is continuously recirculated back into the lower part of the mixer, passing through line 39 which branches off from line 37 at a point in advance of valve 38. Pump 36 serves to force the recirculated solution through line 39 and the,

rate of flow is automatically regulated by float controlled valve 40, which is responsive to changes in the lower level (top of extract-solution) in the mixer. Valve 40 is similar to valve 21 already described and shown in Fig. 2, and the arrangement results in the lower level in the mixer being automatically maintained at a predetermined point between the bottom outlet and the top outlet.

The foregoing description relates to the extraction part of the system. The following description relates to the evaporation part of the system, wherein the railinate-solution and extractsolutionare freed of liquid-S0: and the latter recovered.

The extract-solution is carried by line '37 through heat-exchanger 50, where it is heated by the finished extract leaving the system, and then passes through heating device 51 and into "highpressure evaporator 52 which in the illustrative apparatus consists of a vertical drum.

This high-pressure evaporator is provided in the extract evaporation system only for the purpose of recovering by multiple effect a part of the heat necessary for the evaporation of the large amount of SO: in the extract solution. This multiple effect is achieved in such a way that $02 vapors expelled from the extract-solution at high pressure are used as heating medium in the next following pressure stage.

High-pressure evaporator-52 is operated at a pressure of about 11-13 atm. abs. (150-480 pounds gauge). centration of the extract-solution, leaving the evaporator drum can be maintained substantially constant (this being an important part of the invention) by adjusting the temperature of the incoming extract-solution so as to maintain a substantially constant pressure in the evaporator drum. The temperature control of the extract- It has been found that the con-- solution entering high-pressure evaporator 52 is effected by regulatingthe amount of heat added to the solution in heating device 51 by means responsive to changes in pressure in evaporator 52 The heating is effected by steam which enters by line53 and flows partly through line 54 (controlled by valve 55) and partly through by-pass line 56 (controlled by valve 57) to line 58, and

thence through heating device-5l, from'which it leaves by line 59. Valve 55 is automatically controlled by pressure responsive device 60 which responds to changes in the vapor pressure in evaprelative changes in pressurethan relative changes in temperature. I

The liquid level in high-pressure evaporator 52 'is maintained constant by float controlled valve 61 which regulates the flow of extract-solution leaving the evaporator by line 62, this valve also serving to reduce the pressure in line 62 tothat of the next and lower pressure evaporator.

Referring to Fig. 3, which shows valve 61 in detail, it will be seen that this valve is somewhat similar to valve 21, shown in Fig. 2 and described in connection therewith, with the difference that the flow through valve 61 is decreased rather than increased by a fall in the liquid level actuating the valve float.

The high-pressure evaporator 52 communicates with float chamber 63 of valve 61 by means of pipe 64 which is positioned just above the liquid level, and pipe 65 which enters the evaporator drum below the liquid level, these two connections causing a liquid level to be maintained in float chamber 63 corresponding to that in the evaporator. Float 66 and vertical rod 6'7 depending therefrom into regulating chamber 68 of the valve rise or fall in direct response to a rise or fall of the liquid level.

Line 62, coming from the bottom of the highpressure evaporator, communicates with regulating chamber 68 of the valve. Within regulating chamber 68 is a valve chamber 69, communicating directly with outlet line '70 of the valve, and having two vertical conical extensions concentrio with rod 67 and communicating with chamber 68. The upper conical extension widens upwards and the lower conical extension narrows downwardly. Attached to rod 67 are two valve disks '11 and '12, contained respectively within the upper end lower conical extensions of chamber 69. It will be seen that an upward movement of rod 67 (and valve disks 71 and 72), corresponding to a rise in the liquid level in evaporator 52, will cause a decreased resistance to the flow of extract-solution from evaporator52, and hence will a constant in high-pressure evaporator 52 is withdrawn from the top of the evaporator by line'73 and passes through heat-exchanger '75 where it is condensed as the result of being cooled by cooler extractsolution from the high-pressure evaporator 52, which is cooled by the vaporization of part of the S02 contained therein caused by the reduction in its pressure'occurring at the control valve 61.

The condensed S02 vapor from heat exchanger '75 flows through line '73 to valve '76, where its pressure is reduced to condenser pressure and thence by line '77, controlled by, valve '78, to liquid-SO: storage tank 13.

The extractesolution is continuously withdrawn from evaporator 52 by line 62, controlled by valve 61, just described, and flows by line '70 through heat exchanger '75, where it becomes heated by condensing of the hot S02 vapor passing through the heat exchanger by line '73.

The extract-solution leaving heat exchanger '75, having now had a large portion of its S02 content removed, is further evaporated at "condenserpressure-this pressure (normally 4-6 atm. abs.) being such that the envolved SOz vapors can be condensed in a water cooled condenser. The condenser-pressure evaporation is eifected in two stages, consisting of vapor chamber '79 and the evaporator 80.

The extract-solution, having been heated in heat exchanger '75, enters the upper part of vapor chamber '79 which is maintained at condenser-pressure by having its upper part connected by line 81 to the upper part of condenserpressure evaporator 80. Additional evaporation of S02 from the extract-solution takes place in chamber '79 since the solution is not only at a higher temperature but at a lower pressure than when it left high-pressure evaporator 52. The evolved S02 va'por passes by line 81 into the upper part of condenser-pressure evaporator while the depleted extract-solution is withdrawn from the bottom of evaporation chamber '79 by line 82, and flows through steam heater 83 and thence into condenser-pressure evaporator 80. Heating is effected by steam entering byline 84, the amount being automatically regulated by valve 85 in a manner similar to the steam regulation of heater 51 already described, and after flowing through heater 83 it leaves by line 86.

Valve 85 is automatically controlled-by a temperature responsive device 8'7 which responds to changes in the temperature of the liquid in condenser-pressure evaporator 80, and thus controls .the heating of the extract-solution entering the evaporator so that the liquid in the "evaporator will be maintained at constant temperature.

It has been found that the liquid-S02 concentration in the extract-solution leaving the condenser-pressure evaporator 80 can lee-maintained constant (which is an important part of our invention) by thus maintaining the temperature of the liquid in the evaporator. It has also been found that a change in concentration is reflected in this case by agreater relative change in temperature than relative change in pressure, and hence that it is advantageous to have the flow of steam in heater 83 controlled by means responsive to temperature changes in the liquid in the evaporator. This means of control is just the opposite to what has been found most desirable with respect to the heating control of the extract-solution entering the high-pressure evaporator. r

In condenser-pressure evaporator 80, a further evaporation .of SO: from the extract-solution occurs due to the heating to which the latter has been subjected since leaving vapor chamber '79. The evolved S0: vapor, together with the SO:

vapor from vapor chamber '79. leaves the top of condenser-pressure evaporator 80 by line 88 and thence passes to line 89, leading to condenser 90, where the S02 vapor is condensed by cooling water.

The depleted extract-solution leaves the bottom of condenser-pressure evaporator 80 by line 91, the rate of flow being controlled by float controlled valve 92 so as to maintain a'constant liquid level in the evaporator. Valve 92 and themeans of control is identical with valve 61 already described and shown in detail in Fig. 3.

The extract-solution passes through steam heater 93 and into atmospheric-pressure evapneed not be designed to care for possible high over loads, since the extract-solution entering atmospheric-pressure evaporator 95 will have a sub-' stantially constant S02 concentration, and this will prevent large fluctuations in the amount of S02 vapor evolved in the evaporator.

The depleted extract-solution leaves the bottom of atmospheric-pressure evaporator 95 by line 99, the rate of egress being controlled by valve (which may be identical with valves 61 and 92) so as to maintain a constant liquid level in the evaporator. From valve 100 the extract-solution flows with or without further heating to vacuumevaporator 101 in which a high'vacuum is maintained. Due to the latter, a practically complete removal of SO: from the extract-solution may be effected. The S0: vapor evolved-in evaporator 101 is withdrawn from the top through line 102, which communicates with line 103 leading to the low pressure side of gas pump 104 which serves to maintain the high vacuum in the evaporator.

This pump 104 also need not be designed for large over loads, as the amount of SO: vapor evolved in vacuum evaporator 101 will not vary much, due to the substantially. constant SO: concentration of the incoming extract-solution resulting from the control arrangement described.

Furthermore, due to the substantially constant SO: concentration of the incoming extract-solution, there will be no danger that insufficient SO: will be evolved from the solution during its passage through the evaporator to cause the extract leaving the evaporator to have too high an S0: content.

The liquid leaves the bottom of vacuum evapo-- rator 101 through line 105 as finished extract practically freed of liquid-S02. Liquid transfer pump 106 forces the extract into line 110, controlled by valve 10'7, through which it leaves the system, after first passing through heat exchanger 50 in which it is cooled.

The liquid level in vacuum evaporator 101 is maintained constant in the same way as the upper level in the mixer 12 is maintained constant. A portion of the extract is recirculated through line 108, which branches oif from line 110 between the pump and the valve, back to line 105 which leads from the bottom 01' the evaporator to the pump 106. The rate of recirculation is regulated by float controlled valve 109 which is responsive to changes in the liquid level in the evaporator and which has the same construction as valve 21, shown in Fig. 2, already described. Pump 106 runs at a constant rate and hence the effect 01 recirculating a portion of the extract is to raise or lower the liquid level in the evaporator as the rated recirculation is increased or diminished by valve 109. Thus the liquid level is held constant.

Having now described the removal of the liquid-SO: from the extract-solution, the removal of the liquid-SO; from the ramnate-solution leaving mixer 12 will now be described. This removal.

is effected in condenser-pressure evaporator 122, atmospheric-pressure evaporator 128, and vacuum evaporator 132, which correspond respectively to extract-solution evaporators 80, 95'and 101, and which have corresponding automatic control devices, and hence need not be described in detail. The rafllnate-solution from mixer 12' flows through line 18 and passes through heat exchanger 120 where it is heated by the finished raflinate leaving the system. The raflinate-solution then passes through heater 121 and into condenser-pressure evaporator 122. The amount of steam passing through heater 121 is automatically regulated by temperature responsive device 123 (corresponding to temperature responsive device 87 already described) so that the temperature of the liquid in theevaporator 122 will be held constant, andhence the S02 concentration in the raflinate-solution leaving the evaporator will be maintained substantially constant.

The evolved SO: vapor passes into line 124 and.

is conducted to line 88 and thence to the condenser 90.

The depleted ramnate-solution leaves the condenser-pressure evaporator 122 by line 125, the flow being regulated by valve 126 (corresponding to valve 92) so as to maintain a constant liquid level in the evaporator, and passes through heater 127 and into atmospheric-pressure evaporator 128.

Pump 98 serves to withdraw from this evaporator 128 the S02 vapors evolved therein which leave it byline 129. and pass through line 9'7 leading to the low pressure side of the pump.

The depleted raflinate-solution leaves the bot-' tom of atmospheric-pressure evaporator 128 by line 130, controlled by valve 131 (corresponding to valve 100) so as to automatically maintain the liquid level in the evaporator, and flows directly into vacuum evaporator -132. There the final amount of S02 evaporates 011, due to the high vacuum, and is withdrawn through line 133 and the communicating line 103 leading to the-low pressure side of gas pump 104.

The finished rafllnate is withdrawn from the vacuum evaporator 132 through line 134 by liquid transfer pump 135, and is forced into

line

136, 7 controlled by valve 137, through which, after passing through heat exchanger 120, it leaves the system. I

As with extract vacuum evaporator 101, the liquid level is automatically maintained constant in raillnate vacuum evaporator 132 by recirculating a portion of the raiiinate, the rate of flow being regulated by float controlled valve 138 (corresponding to valve 109).

The S0: vapors from the extract-solution and railinate-solution vacuum evaporators 101, 132) enter pump 104 by line 103 and are pumped up to atmospheric pressure and forced through line 140 into line 97 where they join the S02 vapors from the two atmospheric-pressure evaporators (95, 128). The combined SO: vapors in line 07 are compressed to condenser-pressure and forced by pump 98 into line 89. Here they commingle with the S02 vapors from the two condenser-pressure evaporators (80,122) which enter by line 88 into line 89.

Line 89 leads to condenser 90 to which are conducted the S02 vapors from all of the evaporators,

excepting those from extract high-pressure evaporator 52. Condenser 90 is oi! suitable design and capacity, and condenses these SO: vapors at the pressure corresponding to the temperature of the cooling water. The liquid-SO: so obtained is led from the condenser by line 141 to storage tank 142.

From tank 142 the liquid-S02 flows into line 77 where it joins the liquid-SO: coming byline 73 from extract high-pressure evaporator 52 and having been condensed in heat exchanger 75. The combined liquid-S02 in line '77, which represents all of the liquid-S02 recovered from both the rafflnate and extract solutions, flows into tank 13 through pressure reduction valve 78.

In tank .13 the liquid-S02 is cooled down to the temperature desired for treatment of the mineral oil in mixer 12. Cooling may be efiected by external means or may be accomplished directly by evaporation of a portion of the liquid-S02 in the tank. This latter method is illustrated in Fig. 1. Line 143 leads from the top of tank 13 to line 97 which is connected to the low pressure side of vide the first and final evaporators of the respective raflinate and extract evaporators with automatic valves for controlling the constant level and outflow of the liquid therein. In other cases the above described extract-high pressure evaporator may be dispensed with and the extract solution directly passed into the condenser pressure evaporator. The steam supply to this evaporator would also in this case be regulated by temperature control. I

While the detailed description of the system has been with respect to the treatment of mineral oils and like liquid hydrocarbons with liquid-S02. it will be obvious to those skilled in the art that the invention is applicable to treatment with the recovery of other solvents than liquid-S02; and is applicable to the use and recovery of mixed-solvents containing liquid-soz, such as liquid-SO2- benzol mixtures. obviously not restricted to the particular embodiment thereof herein illustrated and described.

The term volatile solvents" is used in the claims to denote solvents removable by evaporation from the extract andrafflnate of the mineral oil treated, i. e., solvents having boiling points low enough to permit of recovery in evaporation systems of the class herein described. This term is not used restrictively to include use of only one solvent, but applies also to mixtures of solvents containing at least one volatile solvent of the character indicated, as for example,

a mixture. of liquid-SO: and benzol.

of the invention, what is claimed is as follows:

v 1. An improvement in the method of continuously refining mineral oils with volatile solvents such as liquid-S02 and the like, said method including the steps of treating the oil with the solvent, separating out the resulting rafflnate-solution and extract-solution and subjecting the same to evaporation for removal of the solvent for reuse; the raflinate solution being evaporated successively -in zones operated under condenserpressure, atmospheric-pressure and under high vacuum, and the extract-solution being evaporated successively in zones operated under high-pressure, condenser-pressure, a'mosphericpressure and under high vacuum; which. improvement comprises automatically maintaining the liquid levels constant at predetermined points in the treatment and evaporation zones, automatically maintaining a constant predetermined pressure in the extract high-pressure evaporation zone by controlling the heating of the extract-solution entering said zone by and in response to changes of pressure in said zone, and automatically maintaining a constant predetermined temperature in the respective rafilnate and extract condenser-pressure evaporation zones by controlling the heating of the solutions entering said zones by and, in response to changes of temperature in said zones.

2. An improvement in the method of continuously refining mineral oils with volatile solvents such as liquid-SO: and the like, said method including the steps of treating the oil with the solvent, separating out the resulting rafflnatesolution and extract-solution and subjecting the same to evaporation for removal of the solvent for reuse; the raflinate-solution being evaporated successively in zones operated under condenserpressure, atmospheric-pressure and under high vacuum, and the extract-solution being evaporated successively in zones operated under highpressure, condenser-pressure, atmospheric-pressure and under high vacuum; which improvement comprises automatically maintaining the liquid levels constant at predetermined points in the evaporation zones, automatically maintaining a constant predetermined pressure in the extract high-pressure evaporation zone by controlling the heating of the extract-solution entering said zone by and in response to changes of pressure. therein, and automatically maintaining a constant predetermined temperature in the respective rafiinate and extract condenser-pressure evaporation zones by controlling the heating of the incoming solutions entering said zones by and in response to changes of temperature therein.

ously refining mineral oils with volatile solvents such as liquid-S02 and the like, said methodincluding the steps of treating the oil with the solvent, separating out the resulting raflinatesolution and extract-solution and subjecting the same to evaporation for removal of the solvent for reuse; the rafiinate-solution being evaporated successively in zones operated under condenser-pres sure, atmospheric-pressure and under high vacuum, and the extract-solution being evaporated successively in zones operated underhigh-pressure, condenser-pressure, atmospheric-pressure and under high vacuum; which improvement comprises maintaining the liquid levelsconstant at predetermined points in the respective evaporation zones by controlling the rate of out-flow of liquid therefrom by and in response to changes in said levels in the case of all except the vacuum evaporation zones and in the case of the latter by continuously recirculating thereto a portion of the respective finished rafilnate and extract at a rate controlled by and inresponse to changes in level therein, automatically maintaining a constant predetermined pressure in the extract highpressure evaporation zone by controlling the heating of the extract-solution entering said zone by and in response to changes of pressure therein, and automatically maintaining a constant predetermined temperature in the respective raflinate and extract condenser-pressure evaporation zones by controlling the heating of the solutions entering said zones by and in response to changesof temperature therein.

4. An improvement in the method of continuously refining mineral oils with volatile solvents such as liquid-SO2 and the like, said method including the steps of treating the oil with the solvent, separating out the resulting rafiinatesolution and extract-solution and subjecting the same to evaporation for removal of the solvent for reuse; the rafflnate-solution being evaporated successively in zones operated under condenserpressure, atmospheric-pressure and under high vacuum, and'the extract-solution being evaporated successively in zones operated under highpressure, condenser-pressure, atmospheric-pressure and under high vacuum; which improvement comprises maintaining the liquid levels constant at predeterminedpoints in the various evaporation zones by controlling the rate of out-flow of liquid therefrom by and in response to changes in said levels in the case of all except the vacuum evaporators, and in the case of the vacuum evaporation zones maintaining the liquid levels constant at predetermined points by continuously recirculating thereto a portion of the respective finished rafilnate and extract at a rate controlled by and in response to changes in level therein.

5. An improvement in the method of continu-' ously refining mineral oils with solvents such as liquid-S02 or solvent mixtures containing S03, said method including the steps of treating the oil with the solvent, separating out the resulting raffinate-solution and extract-solution and removing the solvent therefrom by separately passing the respective solutions through successive evaporation zones operated at decreasing pressures, the next to last zone in each case being under atmospheric-pressure and the final zone under vacuum; which improvement comprises automatically maintaining the liquid levels constant at predetermined points in the treatment and evaporation zones, and maintaining a substantially constant predetermined-solvent con- 3. An improvement in the method of continu-- centration in the railinate and extract solutions entering the respective atmospheric-pressure evaporation zones by automatically controlling the heating of the same solutions when entering the preceding evaporation zones so as to maintain a substantially constant solvent concentration therein.

6. An improvement in the method of continuously refining mineral oils with solvents such as liquid-S02 or solvent mixtures containing .802,

said method including the steps of treating the oil with the solvent, separating out the resulting raifinate-solution and extract-solution and removing the solvent therefrom by separately passing the respective solutions through successive evaporation zones operated at decreasing pressures, the next to last evaporation zone in each a substantially entering the preceding evaporation zones so as I to maintain a substantially constant solvent controlling the heating of centration therein.

7. An improvement in the. method of continuously refining mineral oils with solvents such as liquid-S02 or solvent mixtures containing S02, said method including the steps of treatingthe oil with the solvent, separating out the resulting raflinatesolution and extract-solution and removing the solvent therefrom by separately passing the respective solutions through systems. of successive evaporation zones operated at decreasing pressures, the next to last evaporation zone in each case being under atmospheric; pressure and the final evaporation zone under vacuum; which improvement comprises automatically maintaining the liquid levels constant at predetermined points in the first and final evaporation zones of the respective rafiinate and extract evaporation systems, and maintaining a substantially constant predetermined solvent concentration in the rafilnate and extract solutions entering the respective atmospheric-pres sure evaporation zones by automatically controlling the heating of the same solutions when entering the preceding evaporation zones so as to maintain a substantially constant solvent concentration therein.

8. An improvement in the method of recovering the solvent contained in the extract-solution resulting from the treatment of mineral oils with volatile solvents such as liquid-S0: and the like, saidmethod including the steps'of passing the extract-solution through successive evaporation zones operated at decreasing orders .of pressure and including a high-pressure evaporation zone;

'which improvement comprises maintaining a substantially constant solvent concentration of the extract-solution flowing from the high-pressure evaporation zone by automatically con-- trolling the heating of the extract-solution entering said zone by and in response to changes in the pressure therein so as to maintain said pressure constant.

9. The method according to claim 8 in whichthe liquid level in the high-pressure evaporation zone is maintained at a predetermined point by automatically controlling the out-flow of the extract-solution therefrom by and in response to changes in the liquid level therein. I

10. An improvement in the method of recovering the solvent contained in the extract-solution resulting from the treatment of mineral oils with volatile solvents such as liquid-SO: and the like, said method including the steps of passing the extract-solution through successive evaporation zones operated at decreasing orders of pressure and including a condenser-pressure zone; which improvement comprises maintaining a substantially constant solvent concentration of the extract-solution flowing from the condenserpressure evaporation zone by automatically conthe extract-solution enteringsaidzonehyandinresponsetochangesin said temperature constant.

11. The method according to claim 10 in which the liquid level in the condenser-pressure evaporation zone is maintained at a predetermined point by automatically controlling the outflow of the extract-solution therefrom by and in response to changes in the liquid level therein.

12; An improvement in the method of recovering the solvent contained in the rafllnate-solution resulting from the treatment of mineral oils with volatile solvents such as liquid-SO: and the like, said method including the steps of passing the rafllnate-solution through zones operatedat decreasing orders of pressure and including a condenser-pressureevaporation zone; which improvement comprises maintaining a substantially constant solvent concentration of the railinate-solution flowing from the condenser pressure evaporation zone by automatically controlling the heating of the rafiinatesolution entering said zone by and in response to changes in the liquid temperature therein so as to maintain said temperature constant.

13. The method according to claim 12 in which the liquid level in the condenser-pressure evaporation zone is maintained at a predetermined point by automatically controlling the out flow of the raflinate-solution therefrom by and in response to changes in the liquid level therein.

14. An improvement in the method of recovering the solvent contained in the extract-solution the liquid temperature therein so as to maintain successive evaporation resulting from the treatment of mineral oils with to changes in the vapor pressure in said zone so as to maintain a constant vapor pressure therein and by automatically controlling the heating of the extract-solution entering the condenser pressure zone by and in response to changes in the liquid temperature in said condenser-pressure zone so as to maintain a constant temperature of the extract-solution therein, and maintaining the liquid level'at a predetermined point in said high-pressure zone by automatically controlling the rate of out flow of the extract solution therefrom by and in response to changes in the liquid level therein.

15. In a method of recovering the solvent contained in the extract-solution resulting from the treatment of mineral oils with volatile solvents such as liquid-S0: and the like, which includes passing the extract-solution through a highpressure evaporation zone, the step of automatically controlling the heating of the solution entering said zone by and in response to changes in the pressure therein so as to maintain said pressure constant and thereby maintain a substantially constant solvent concentration in" the solution leaving said zone.

16. In a method of recovering the solvent con-' tained in raiiinate and extract solutions resulting from the treatment of mineral oils with volatile solvents suchas liquid-SO: and the like, which response to changes in the liquid temperature therein so as to maintain said temperature constant and thereby m aintain a substantially constant solvent concentration in the solution leavlng said zone.

WOLFGANG GROTE. PAUL OBERGFELL.