GB2220151A

GB2220151A - Countercurrent extraction

Info

Publication number: GB2220151A
Application number: GB8908657A
Authority: GB
Inventors: Pal Meszaros; Kalman Rajnai; Arpadne Erdelyi; Istvan Somogyi; Laszlo Szommer; Peter Arva; Aba Boros; Bela Csukas; Miklos Delzsenyi; Karoly Moser; Jozsef Vass
Original assignee: Nitrokaelepek
Current assignee: Nitrokaelepek
Priority date: 1988-04-18
Filing date: 1989-04-17
Publication date: 1990-01-04
Also published as: HU203843B; GB8908657D0; DE3912613A1

Description

1 A 1 PROCESS AND APPARATUS MR THE MMISTAGE, CYCLICALLY CONTINUOUS, RRENT

CONTACTING OF A LIQUID PHASE AND A SOLID PHASE HAVING A DIPPERENT DENSITY AND/OR A ILIQUID PHASE IMMISCI1M WITH THE FIRST MENTIONED-LIQUID PHASE.

The invention concerns a process and apparatus for the multistage, cyclically continuous, countercurrent contacting of a liquid phase and a solid phase having a different density and/or a liquid phase immiscible with the first mentioned liuqid phase.

The countercurrent contacting of a liquid phase with a solid phase of different density therefrom and/or with a liquid phase which does not mix therewith is a practical task of great significance for the carrying out of which several processes are known (Ahell, King: New Developments in Liquid-Liquid Extractors, AIChE Symp. Ser. 80, 238, 1984).

The processes used belong to three basic groups:

- operating units based on simultaneous mixing and separation, - processes in which the mixing and the separation are carried out in discrete apparatuses, and - the intermittently or cyclically operating mixing-separating methods.

The processes belonging to the first group are characterised in that the mixing and the separation take place at the same spatial location and at the same time. To this group belong, for instance, the rotating disc extractors where non-mixing phases fed in spontaneous countercurrent are mixed together in superposed spaces by mechanical mixing elements (e.g. Kosters, W.C.G.; Rotating-Disk Contactor, Lo, T.C., Baird, M.H.I. and Hanson, C. eds.: Handbook of Solvent Extraction, Wiley- Interscience, New York, 1983). These methods are primarily suitable for contacting two liquids and are less reliable in the presence of solid materials.

The operating units belonging to the second group are characterised in that the mixing and the separation are carried out in two discrete apparatuses, e.g. mixing in a vessel which is mechanically agitated, and separation in a settling centrifuge, 2'1 220151 1 1 2 or in the case of a solid-liquid system, in a filtering centrifuge. These processes may be operated equally in intermittent or continuous modes of operation. Pneumatic mixing in place of mechanical mixing is also possible. The investment costs involved in performing the mixing and separation in separate functional units is further increased particularly by the more costly construction of the separating unit.

To the third group belong the cyclically operating mixingseparating processes, e.g. mixer settler processes. In these processes mixing and phase-separation take place in the same volume or space of the operative units but one after the other in time. A disadvantage of the mixing-separating processes is that in the presence of a solid phase the forwarding of material is difficult.

Our aim with the invention is the improvement of known processes and the creation of a process and apparatus which make it possible to form the operating units assuring multistage countercurrent contacting from simple elements and which, moreover, may be utilised equally well for any desired phase system such as two immiscible liquids, sedimenting solid material, floating solid material as well as the simultaneous presence of a gas phase in the above-mentioned cases.

The invention is based on the recognition that with the aid of modern computing and control technology the operating units made from simple elements such as pipes, pipe bodies, spaces with agitators, pumps, air-lifts etc. can be organised into an operative whole.

The task set for the invention may be solved by means of a process wherein the two phases are introduced in opposition to each other at the two ends of a cascade consisting of a plurality of serially connected stages. In the mixing-separating space of the individual stages the phases are mixed at least once per cycle, are spontaneously separated by gravity, the separated phases are at least partially transferred between the neighbouring stages in countercurrent and are discharged at the two ends of the cascade. The lighter phase is fed from the z f 3 outside into the uppermost stage of the cascade the stages of which are arranged in an inclined row and, after separating the phases, starting from the lowermost stage and advancing stepwise to the uppermost stage, in the a predetermined quantity of heavier phase is introduced in the individual stages from a discrete space portion of the given stage into the lower portion of the mixing-separating space, whereby an appropriate quantity of the lighter phase is expelled from the mixing-separating space and is fed gravitationally to the mixing-separating space of the lower stage or, respectively, in the lowermost stage the lighter phase is led out. The heaviest phase is fed into the first stage and between two neighbouring stages is stepped from the lower to the higher one and is discharged from the uppermost stage.

Advantageously, the lighter phase is expelled from the individual stages by increasing the pressure of a closed gas space disposed above the heavier phase in a separate space connected to the mixing-separating space in the manner of communicating vessels, then by removing the overpressure the equilibrium of the communicating vessel is restored. The creation and removal of the overpressure may take place e.g. by means of valves or other shut-off fittings in such a manner that the gas space is connected alternatingly with a manostat (pressure source) of higher pressure and then one of lower pressure. The operation of the fittings may take place by means of any suitable timer, but preferably by means of a control unit having a programmable microprocessor.

In another advantageous mode of realising the process the lighter phase is displaced from the individual stages by introducing, preferably by gravity, a heavier phase into the mixing-separating space from the separate space portion. In this case, advantageously, the expulsion of the lighter phase as well as the transfer of the heavier phase are performed in each individual stage, starting from the lowermost one.

According to the process the lighter phase is passed to the mixing-separating space and/or separate space portion of the adjacent higher stage. In some cases a portion of the heavier 1 1 4 phase led out from the mixing-separating space of the individual stages is recycled to the separate space portion of the stage. The feeding of the heavier phase may take place by any suitable feeder, expediently by a pump or by pneumatic means. 5 It is expedient according to the process to perform level sensing in the mixing-separating space and in the separate space portion and to regulate the quantities fed on the basis of this. In using the process either the heavier or the lighter phase may be a solid material which in the course of separation settles out from the liquid or floats to the upper part of the liquid space. The liquid phase may also contain gas bubbles. The individual components of the phases may during the process interreact physically and/or chemically with each other.

The apparatus according to the invention has serially connected stages provided with couplings suitable for tho feeding in and the discharging of the phases and for transferring the phases, and the stages are provided with mixing-separating spaces equipped with agitators. The individual stages also contain a separate space portion connected by way of ducting with the lower portion of the mixing-separating space, and are also provided with fittings, expediently valves or pumps, for regulating the flow of the heavier phase through the ducting. The stages are arranged in an inclined row and the upper part of the mixingseparating space of each stage is provided with couplings serving for the feeding and discharging of the lighter phase as well as for the transfer from the top downwardly by gravitation of the lighter phase. The bottom of the mixing-separating space is connected by way of a pump or an air-lift to the mixingseparating space and/or the separate space portion of the adjacent higher stage.

In an advantageous preferred embodiment of the apparatus the separate portion is closed at the top, is disposed next to the mixing-separating space and is connected thereto in the manner of communicating vessels, and is equipped with gas inlet and gas outlet fittings, expediently valves.

In another advantageous preferred embodiment, the separate 1 space portion is open and is disposed above the mixing-separating space and is connected therewith by way of a duct provided with a shut-off device, e.g. a valve.

In yet another preferred embodiment the bottom of the mixing-separating space is connected to the separate space portion of the same stage as well as that of the adjacent higher stage by way of a pump and shut-off fittings, expediently valves.

In the apparatus the shut-off devices, expediently valves, are expediently connected with a micro-processor controlled timer.

A pump may be mounted in the duct connecting the separate space portion with the mixing-separating space. A mixer as well as level sensors may also be disposed in the separate space portion.

The invention is described below merely by way of example with the aid of the accompanying drawings wherein Figure 1 is a preferred embodiment in side view of one stage of apparatus according to the invention; Figure 2 is the stage according to Figure 1 in front elevation; Figure 3 shows the stage according to Figure 1 in plan view; is a diagram of a six-stage apparatus; shows a detail in plan view of the apparatus according to Figure 4; is a diagrammatic illustration of one embodiment of connecting the air-lifts; is a plan view of a portion of Figure 6; is a diagrammatic view of another embodiment of connecting the air-lifts; is a plan view of a portion of Figure 8; is a diagrammatic illustration of the periodic operation of the apparatus and is a diagrammatic illustration of another embodiment of apparatus according to the invention.

Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 6 Figures 1 to 3 show one stage of a preferred embodiment of apparatus according to the invention respectively in side, front and plan view. The stage consists of a cylindrical mixingseparating space 2 and a separate space portion 3 connected with the bottom of the mixing-separating space 2 in the manner of communicating vessels by way of a duct 4. Couplings 5 for the transfer of the lighter phase are connected at an inclination of approximately 700 to the upper portion of the mixing-separating space 2. In order to mix the phases disposed in the mixing- separating space 2 an air-lift 18 is connected from the outside to the body of the apparatus into which an air stream may be introduced via valve 25. The level 26 indicates the nominal charging level of the apparatus. Above the level 26 of the separate space portion 3 there is a closed gas space the top of which is connected via valves 12a and 12b to manostats at different pressures. To discharge the heavier phase, the duct 4 connected to the bottom of the mixing-separating space 2 is provided with a coupling 7 to which an air-lift 22 is connected.

In operation of the apparatus, the phases contained in the 20 mixingseparating space 2 up to the level 26 are mixed by way of the air-lift 18 operated by the air introduced via the valve 25. After cessation of the mixing the phases spontaneously separate and the lighter phase becomes the uppermost layer. Thereafter air is introduced via valve 12a into the separate space portion 3 and the pressure within the closed space is increased. The equilibrium of the communicating vessel is thereby broken, the level rises in the mixing- separating space 2 and the lighter phase layered at the top is discharged by spontaneous gravitational flow through the lower coupling 5. The feeding-in of the lighter phase through the upper coupling 5 now takes place from the neighbouring and similarly constructed higher stage. The heavier phase forming the lower layer is discharged by the air stream introduced via the coupling 7 into the air-lift 22. The he avier phase may be charged either into the mixingseparating space 2 or into the separate space portion 3.

Figure 4 illustrates in diagrammatic front elevation a six- 1 7 stage apparatus consisting of stages I-VI connected in a downwardly inclined series. The lighter phase passes into stage I from the feeder 17 and passes between the individual stages by gravity via the couplings 5 and finally reaches a vibrating screen 28. The heavier phase is passed by a pump 29 into stage VI,, is transferred between the stages by way of the air-lift 22 (Figure 2) and is discharged from stage I via the coupling 7.

Figure 5 is a plan view of -the apparatus according to Figure 4. Two airlifts belong to each of the stages I-W of which air- lift 18 performs the external circulation/mixing of the phases in the mixing cycle while the air-lift 22 feeds the heavier phase to the adjacent higher stage.

Two variants of connecting the air-lifts are shown in Figures 6-9. In the variant according to Figures 6 and 7 the heavier phase is fed f rom the bottom of the stage with the aid of air-lift 22 to the mixing-separating space 2 of the adjacent higher stage. In the variant according to Figures 8 and 9 the heavier phase is recycled from the bottom of the stage to the separate space portion 3 of the adjacent higher stage 3.

Naturally in both embodiments the air-lifts 18 serving for agitation recirculate the material into the mixing-separating space 2 of their own stage.

The purely exemplary cycles of the periodic operation of the apparatus may be surveyed with the aid of the diagram shown in Figure 10. The individual cycles are as follows:

(a) W By opening the valve 25 all the external agitating air-lifts 18 of every stage are actuated and the phases are mixed'for a predetermined period. The heavier phase introduced into the mixing-separating space 2 during the mixing cycle breaks up from the top downwardly the light phase floating to the top of the solution. The air-lift 18 recirculates the suspension by increasing the flow velocity.

(b) Separation By shutting the valves 25 the mixing is stopped and there is a waiting time of prescribed length. During this period 8 spontaneous separation of the phases takes place.

(c) Stepping or (advancing) the lighter phase.

Starting from the lowermost stage and advancing in the reverse direction the valve 12a of each stage is sequentially opened and the level of liquid of the separate space portion 3 is pressed from the basic level L to the preset level G. This has the effect of raising the level in the mixing-separating space 2 and the corresponding volume of lighter phase flows to the adjacent lower stage. On attaining the level G the valve 12a is closed and the valve 12 b is opened. Thereby the overpressure in the gas space 11 is destroyed and the equilibrium of the communicating vessel is restored. In order to ensure that all the prescribed volume of the lighter phase is transferred the compression may be performed sequentially several times. By starting the "stepping" at the lowermost stage VI and advancing upwardly, the "stepping" is performed at every stage and finally at stage I lighter phase is fed in from the outside (Figure 4). In those stages where the light phase has already been fed in, the air-lift 18 performing the circulating mixing is immediately actuated. (d) Mixing This is performed for a prescribed period as in (a). (e) Separation This is performed for a prescribed period as in (b).

(f) OStepping" the heavy phase First from the uppermost stage I (Figure 4) heavy phase is discharged by means of the air-lift 22 until a preset level has been reached. Thereafter from stage II such an amount of heavy phase is fed via the associated air-lift 22 to the stage I as is required to restore the base level L, and then the heavy phase is "stepped backwards" serially. Finally the lowermost stage VI is also filled up by way of the pump 29. Thereafter the operation of the apparatus continues with cycle (a) as above.

The apparatus is operated by a microcomputer utilising a control algorithm. In addition to what has been described above the control system provides an alarm signal, i.e. stops on 9 reaching the lower limiting level A or the upper limiting level F.

Another preferred embodiment of the apparatus according to the invention is illustrated in Figure 11. In this embodiment the apparatus is constructed wholly from conventional mechanically mixed elements and in place of air-lift conveyors conveying is effected by pumping.

The apparatus consists of four mixing-separating spaces 2 disposed at a slope of 300 and provided with mechanical agitators 20, together with four stages I-IV disposed above them and consisting of separate space portions 14 provided with agitators. The separate space portions 14 are connected with the bottom portions of the mixing- separating spaces 2 by way of ducts 15 provided with valves 13. The lighter phase passes from stage'to stage via couplings 5. The heavier phase is passed into the separate space portion 14 of stage 1V by a pump 29. The heavier phase is transferred from the bottom of the mixing-separating spaces 2 by way of pumps 21 and valves 30 to the separate space portions 14 of the adjacent higher stage and f rom stage I to the ambient atmosphere as well as into the separate space portion 14 of their own.stage by way of valves 31.

The operation of the cascade is controlled on the basis of the liquid level 16 prevailing in the separate space portion 14. The cycles of operation are as follows:

(a) Miximg This is performed by the mechanical agitators 20 for the prescribed period.

(b) Separation By switching off the agitators of the mixing-separating spaces 2 the system is rested for a prescribed period. (c) R!jroin - From the separate space portion 14 of stage IV a volume of heavy phase is passed via valve 13 and duct 15 into the mixing- separating space 2 which corresponds to the amunt of light phase to be fed out (level control).

By means of the pump 29 a predetermined, level controlled amount of heavy phase is passed into the separate portion 14.

While the valve 30 directed towards stage III is closed heavy phase is f ed via pump 21 and open valve 31 belonging to stage IV into the separate space portion 14 of stage IV and its level 16 is restored thereby.

Thereafter the valve 30 is opened and the valve 31 is closed and the separate space portion 14 of stage III is f illed up to the desired level.

- An amount of heavy phase corresponding to the amount of light phase to be transferred is passed from the separate space portion 14 of stage III into the mixing separating space 2.

- By means of pump 21 of stage III (valve 30 closed, valve 31 open) a preset, level-controlled aiount of heavy phase is fed into the separate space portion 14 of stage III, then by opening the valve 30 and closing the valve 31 the separate space portion 14 of stage II is filled to the desired level.

- The stepping is continued from stages II and then I in accordance with the above.

- Finally, from stage I heavy phase is discharge via valve 30.

In what follows, an example of the utilisation of the invention is described.

Emaple, A four-stage apparatus constructed similarly to that shown in Figure 4 and made up of the stages illustrated in Figures 1 to 3 consisted of mixing and separating spaces 2 having a diameter of 500 mm, separate space portions 3 having a diameter 300 mm and an overall height of 2000 mm. 100 1/h sulphonated cation exchange resin were fed into stage I of the apparatus in 65 kg/h volume% sulphuric acid solution. 167 kg/h 48-50 volume% sulphuric acid solution were introduced into stage IV. In all the stages the resin f loated on the top of the solution. At a mass flow of 82 kg/h, 80 volume% sulphuric acid was discharged j 11 from stage I, while from stage IV 100 1/h ion-exchange resin and 150 kg/h 50 volume% sulphuric acid solution were discharged. The operating cycles of the apparatus were as follows: (a) mixing: 4 minutes; (b) phase separation: 4 minutes; (c) resin feeding:

from stage IV to a vibrating screen, from stage III to stage IV, from stage II to stage III, from stage I to stage II, and from a feeder to stage I; (d) mixing: 4 minutes; (e) phase separation: 4 minutes; (f) feeding the solution:

from stage I to discharge, f rom stage II to stage I, f rom stage III to stage II, and into stage IV by a pump.

The feeding of the resin takes place on the basis of the level measured in the separate space portion by means of air fed into the separate space portion. Airlifts were used for feeding the solution and for agitating the mixing-separating spaces.

In the annexed claims reference numbers have been used purely by way of example in order to facilitate comprehension, but it is hereby declared that absolutely no limitation of scope whatsoever is intended thereby.

z 12

Claims

CLAIM

1. A process for the multistage, cyclically continuous, countercurrent contacting of a liquid phase with a solid phase of differing density and/or with a non-immiscible liquid phase, wherein the two phases are introduced in opposition with each other at the two ends of a cascade consisting of several serially connected stages, the phases are mixed together at least once per cycle in the mixing-separating spaces of the individual stages, are spontaneously separated by a gravitational method, the separated phases are at least partially transferred in countercurrent flow between the adjacent stages and are discharged at the two ends of the cascade, characterised in that the lighter phase is fed from the outside into the uppermost stage of the cascade, the stages being arranged in a sloping row, and starting from- the lowermost stage and stepping stage by stage to the uppermost stage, a predetermined amount of heavier phase is introduced, after the separation of the phases, into the lower portion of the mixing- separating space from a separate space portion of the stage, whereby to expel the lighter phase from the mixing- separating space, the lighter phase is then passed gravitationally into the mixing-separating space of the adjacent lower stage and, respectively, discharged from the lowermost stage while the heavier phase is fed into the lowermost stage and is raised between adjacent stages from a lower to a higher stage and is discharged from the uppermost stage.

2. A process according to claim 1 characterised in that the lighter phase is displaced from the individual stages by increasing the pressure in a closed gas space above the heavier phase in a separate space portion communicating with the mixingseparating space in the manner of communicating vessels and then by removing the overprpssure, the equilibrium of the communicating vessel is restored.

3. A process according to claim 2 characterised in that the expulsion and transfer of the lighter phase is performed serially and sequentially in all the stages, and then starting 13 from the uppermost stage, the transfer of the heavier phase is performed also serially and sequentially.

4. A process according to claim 1 characterised in that the lighter phase is expelled from the individual stages by introducing the heavier phase expediently gravitationally, from the separate space portion into the mixing-separating space.

5. A process according to claim 4 characterised in that starting from the lowermost stage the expulsion of the lighter phase and the transfer of the heavier phase is performed in each stage.

6. A process according to any of claims 1 to 5 characterised in that the heavier phase is fed into the mixingseparating space and/or the separate space portion of the adjacent higher stage.

7. A process according to any of claims 1 to 6 characterised in that a portion of the heavier phase transferred from the mixing-separating space of the individual stages is recycled to the separate space portion of the stage.

8. A process according to any of claims 1 to 7 characterised in that the heavier phase is transferred by pumping or by pneumatic means.

9. A process according to any of claims 1 to 8 characterised in that level sensing is performed in the mixingseparating space and/or the separate space portion and the fed quantities that are fed in are controlled on that basis.

10. Apparatus for the multistage cylically continuous countercurrent contacting of a liquid phase with a solid phase of differing density and/or a non-immiscible liquid phase, primarily for carrying out the process according to any of claims 1 to 9, which apparatus has serially connected stages provided with couplings for feeding and discharging the phases and for their transfer, the stages each containing a mixing-separating space provided with an agitator, characterised in that the individual stages (I-VI) are provided with a separate space portion (3, 14) connected by way of a duct (4, 15) with a bottom portion of the mixing- separating space 2 as well as with fittings, expediently 1 14 valves (12a, 12b, 13) or pumps, for controlling the flow of the heavier phase through the duct (4, 15), furthermore the stages U-VI) are all disposed in a sloping row and the upper part of the mixing-separating space (2) of each stage U-VI) is provided with couplings (5) serving for the feeding in and discharging of the lighter phase or for assuring the gravitational transfer from the top downwardly of the lighter phase, and furthermore the bottom of the mixing- separating space (2) is connected via a pump (21) or an air-lift (22) with the mixing-separating space (2) and/or the separate space portion (3, 14) of the adjacent higher stage.

11. Apparatus according to claim 10 characterised in that the separate space portion (3) is closed at the top, is disposed next to the mixingseparating space (2) and is connected thereto in the manner of communicating vessels, and is provided with gas inlet and outlet fittings, expediently valves (12a, 12b).

12. Apparatus according to claim 10 characterised in that the separate space portion (14) is open and is disposed above the mixing-separating space (2) and is connected therewith by way of a duct (15) provided with a shut-off device, expediently a valve (13).

13. Apparatus according to claim 12 characterised in that the bottom of the mixing-separating space (2) is connected via a pump (21) and shut-off fittings, expediently valves (30, 31), to the separate space portion (14) of the same stage and of the adjacent higher stage.

14. Apparatus according to any of claims 10 to 13 characterised in that the shut-off fittings, expediently valves (12a, 12b, 13, 30, 31), are connected to a microprocessor controlled-timer.

15. Apparatus according to claim 10 characterised in that a pump is mounted in the pipe (15) connecting the separate space portion (14) with the mixing-separating space (2).

16. Apparatus according to claim 10 characterised in that an agitator is provided in a separate space portion (14).

17. Apparatus according to any of claims 10 to 16 characterised in that level sensors are disposed in the separate space portions (3, 14).

18. Apparatus according to any of claims 10 to 17 characterised in that the shut-of f devices, expediently valves (12a, 12b, 13, 30, 31), the airlifts (18, 22), the agitators (20), the pumps (21, 29) and the level sensors are all connected to a microcomputer.

19. A process according to claim 1 substantially as herein described with reference to and as shown in the accompanying drawings and/or the Example.

20. Apparatus according to claim 10 substantially as herein described with reference to and as shown in the accompanying drawings and/or the Example.

Published 1989 atThePatentOffice, State HouBe,66/71 High Holborn. LondonWC1R4TP. Further copies maybe obtained from The PatentOffice. Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD. Printed by Multiplex techniques ltd, St Mary Cray, Kent, Con. 1187