DE1804060A1 - Process for increasing the throughput in liquid-liquid extraction - Google Patents

Description

METALLGESELLSCHAFT Frankfurt / Main, October 15, 1968

Aktiengesellschaft DrWer / EV

Patent Department 18 04 060

f Prov. No. 5588 )

Process for increasing the throughput in liquid-liquid extraction

In the liquid-liquid extraction with mixer and separator is the dispersion produced in the mixer is separated again in the separator. In a system that consists of several extraction stages connected in series exists, the throughput is determined by the separation speed of the dispersion in the separators. Low cutting speed requires large separators and thus a lot of solvent for filling the extractor.

The present invention is directed to increasing the speed of separation the dispersion in the separators of a liquid-liquid extraction by the action of an electric field.

The separation of dispersions of two liquid phases is known to be used in the electric field in crude oil desalination and the refining of oils with aqueous acids or alkalis. The one to be separated Phase mixture contains the water or the aqueous solution as a dispersed phase. It should not contain more than 10 to 15% of the organic, make an oily continuity phase. Otherwise, at the applied high voltage of over 1000 volts, even with a turbulent flow in the separator bridges of the highly conductive aqueous phase between the Form electrodes in which currents flow with currents far above

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20 Amp. / M electrode area can occur. The current flow between the electrodes immersed in the dispersion is normally around 2 to 20 / mA per m of electrode area.

There are also methods of extracting liquid mixtures of more organic Substances with selective polar solvents known, in which both the phase mixture and the phase separation under the action of electrical Fields can be made. In this context, polar solvents are to be understood as meaning liquids whose dielectric constant is at least is twice that of the liquid to be extracted.

From the French patent 1490 034 a method for increasing the throughput in the liquid-liquid extraction of mixtures of organic compounds with organic solvents known to the mixer / separator principle. The phase separation in the separators is carried out in an electric field of 1-60 volts / cm, preferably 10-30 volts / cm made by applying a Direct or alternating current voltage of 10 to 500 volts, preferably 110 to 220 volts, is generated at electrodes in the separator. In the separator several horizontal electrodes, some of which can be earthed, are arranged one above the other. One electrode can be sufficient if the separator housing is grounded as a counter electrode. The voltage on the electrodes is periodic for short, approximately equal time intervals of 0.1 see. until 2 see. alternately on and off. The one to be dismantled Phase mixture should consist of 20 to 70% by volume, expediently about 50% by volume, of polar phase and is made up before entering the separator mixed so intensely that the polar phase is dispersed in the non-polar phase. The appropriate ratio of the two phases for this can be adjusted if necessary, that a part of the

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the non-polar phase removed from the separator in the circuit in the is returned to the mixer upstream of the separator.

It has now been shown that in cases where the polar phase is a has a relatively high conductivity or the phase mixture has a high proportion contains a strongly polar phase, a phase inversion easily occurs, after which the weakly polar phase as a dispersion phase in the strongly polar continuity phase is present. In the case of phase mixtures in which the more polar component forms the continuity phase, an intervening occurs the live electrode and earth have a high current flow, which causes a further emulsification of the phases in one another, i.e. counteracts the phase separation. Even if with a weak electric Field of only 1 volt / cm is worked, an inversion cannot be safely avoided. In the known method, the Formation of the inversion can be avoided that the voltage applied to the electrodes in short approximately equal time intervals is switched on and off alternately. However, as has been shown in many cases, this measure can only cause inversion to occur delay but not prevent.

It has now been found that for the separation of a phase mixture It is not the strength of the electric field that is decisive, but that it primarily depends on the amount of the phase mixture communicated electrical energy arrives, which is measured as watt, the product of voltage and current, V.A. The one to be communicated to the phase mixture electrical energy should be 0.5 to 500 per m of separator area V.A., in particular 1 -100 V.A. The value that is favorable for the respective phase mixture can easily be found in a simple preliminary test determine. The level of voltage depends on the conductivity of the to be separated phase mixture and the distance between live Electrode and the grounded counter electrode. With large lead

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ability of the phase mixture, the voltage must be lower than with low conductivity.

It was also found that even before the formation of an inversion Disturbances in the separation occur if too much energy is used. The performance of the separator is then lower, so that the throughput of the separator has to be reduced in order to achieve a clean phase separation and a breakthrough to prevent foreign phase in the processes of the pure phases. If, on the other hand, the amount of energy is reduced, the throughput can be increased again.

If these relationships are observed, it is no longer necessary to use the . To pulse current flow, i.e. to switch it on and off for a short time.

The favorable amount of energy is only slightly dependent on the electrode size, as long as the area of the electrodes is 25% - 95% of the cross section of the separator. It is advisable not to make the electrodes too small to be selected, otherwise the energy distribution over the cross section of the separator will be uneven. Large electrodes favor the formation of inversions, if the energy rises above the optimal value, while electrodes of medium size are still normal even with a slight overload work. An electrode area that is 35% - 60% of the cross section of the separator is advantageous amounts to. The electrodes are expediently horizontal and thus parallel to the phase boundary surfaces that are being formed built-in and can consist of perforated sheets, frames covered with wire mesh or the like. There can be several electrodes on top of each other one or more of which can be earthed. However, a single electrode, which is the grounded separator housing, is also sufficient serves as a counter electrode, but a grounded electrode can also be used.

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The installation height of the electrodes will be chosen so that as possible no live electrode is immersed in the cohesive, more polar liquid during operation. Appropriate the top electrode is placed at a height that is 50% - 90%, preferably 60% - 85% of the height between the bottom of the separator and the outlet of the upper light phase.

If several electrodes, e.g. three, are used, one becomes expedient ground the middle one and apply different voltages to the other two electrodes. The electrode located in the the less polar phase, the higher the voltage, and the lower the voltage in the more polar phase. The mirror rises separating lower phase, which is usually the more polar, up to the lower electrode, this is grounded and the middle one is connected the low voltage switched. Finally, the middle electrode can also be earthed or switched off, so that then only the top electrode is energized.

The electrostatic deposition can be done with alternating or direct current operate. In general, alternating current will be preferred in order to avoid electrolytic corrosion caused by the use of direct current are possible to avoid.

To adjust the favorable amount of energy, the voltage is after Depending on the corresponding current strength, which is between a few milliamps and several amps, varies. Thereby the amperage measured while the voltage is changed by tapping on a transformer or by means of an electronic voltage regulator will. Since the layer heights of the separating phases and / or the Conductivity of the phase mixture during operation of the separator

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can change because, for example, the ratio of strongly polar too little polar liquid shifts due to changes in throughput, it can be advantageous to adjust the voltage in a known manner automatically, with a regulator set to the favorable energy value, the voltage depending on the respective Amperage changed.

With a given voltage, the favorable amount of energy can also go through Interposition of a capacitor or, especially when using direct current, a resistor can also be set. When working with alternating current, the favorable amount of energy can also be set in that the electrodes are connected to an electrical Insulation to be coated. Ceramic compounds or plastic coatings, e.g. made of polytetrafluoroethylene, are suitable for this. The stronger the insulating layer, the lower the amount of energy passed through it. In addition, the voltage can be regulated by a transformer that can be tapped off.

While it was previously difficult to mix liquid phase mixtures with a very strongly polar phase such as water or aqueous solutions of electrolytes, to be separated electrostatically, because in this case very high currents occur that lead to inversion, these can now also be separated if such a low voltage is applied to the electrodes that the favorable amount of energy is not exceeded «,

The illustration and the following serve to explain the invention Examples;

In the picture is a separator with 3 electrodes, the can be box-shaped or cylindrical in shape, in vertical section shown.

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The housing 1 of the separator is a standing cylinder. The inlet 2 for the to be separated are in the middle of its jacket Phase mixture, at the top of the process 3 for the pure light phase and at the bottom of the process 4 for the pure heavy phase arranged as a connecting piece. In front of the outlets of the drains, there is a dividing plate on a chord in the circular separator cross-section 5 installed, which leaves a slot 6, 7 each at the top and bottom for the flow of the two pure phases to the processes. In the separator the horizontal electrodes 8, 9, 10 are arranged and with the connections introduced through insulators 11, 12, 13 in the jacket 1 14, 15, 16 connected. For example, an alternating voltage can be applied to electrodes 8 and 10 while electrode 9 is grounded. In In a practical version of the cylindrical separator, the height is 600 mm, the diameter 2,000 mm, the useful area of the separator 2, 7sqm. The upper edge of the partition 5 is 570 mm above the separator base, the upper slot 6 and the lower slot are each 30 mm wide. The upper electrode 8 is 470 mm, the middle electrode 9 is 310 mm and the lower electrode 10 is 150 mm the case back. From the phase mixture introduced into the separator 17 (hatched in the figure), the heavy phase 18 (hatched in the figure) separates downwards and the lighter phase. Phase 19 (not hatched in the figure) upwards. Through the lower Slot 7 of the partition 5, the heavy phase flows to the outlet nozzle 4, through the upper slot 6 the light phase to the nozzle To study the effect of the electric fields between the electrodes, so much phase mixture is pumped through the separator per unit of time, up to 2 Vd in the running pure phases. % Foreign phase occurs. Then the performance limit of the separator has been reached. The load on the separator becomes heavier as cubic meters of throughput Phase expressed per square meter of usable separator area and hour, the supplied energy as VA / square meter. By changing the voltage on the

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Electrodes depending on the current flow can achieve the optimal energy consumption can be easily determined in each individual case.

example 1

A phase mixture containing N-methylpyrrolidone as the heavy phase with 13% by weight of water and the light phase is fed into the separator Mixture of equal parts toluene and gasoline containing, introduced. The volume ratio of the two phases is 1: 1. At the top Electrode is a voltage of 320 volts corresponding to a field strength of 20 volts / cm, at the lower one a voltage of 100 volts, correspondingly a field strength of 6.2 volts / cm, applied. The middle electrode is grounded. There can be up to 97 in / h phase mixture, so 48.5 m / h heavy phase can be separated. The burden of separating

r, 2

this is therefore 18 m ° / m h of the heavy phase. WITHOUT EFFECT βΐ-η Q

With an electric field, the load capacity is only 7 m / m h difficult phase. The following currents were measured at the voltages mentioned above:

At the upper electrode 28 m Amp. Corresponding to an energy consumption of 9 VA in total cross-section, that is 3.3 VA / m.

At the lower electrode 1.4 Amp. Corresponding to an energy consumption

2 would take 140 VA in total cross-section or 52 VA / m.

Example 2

Otherwise the same conditions as in Example 1 were used in the phase mixture the proportion of heavy phase increased to 60%. The following electrical values were measured on the electrodes:

Above 320 volts 95 rn amp. = 11 VA / m ²

Below 100 "16 m" = 600 "

Inversion occurred which soon filled the entire separator.

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The voltage on the lower electrode was then reduced to 20 volts (= 1.3 volts / cm). The separator was now working at a

3 2

load of 22 m / m h again flawlessly, with the amperage on the upper electrode to 0.08 Amp., on the lower electrode

2 ο

to 3.2 A and the energy consumption to 9.5 VA / m or 24 VA / m went back.

Example 3

The composition of the phase mixture was the same as in Example 1. However, the separator only contained the top electrode, which faced the earthed separator housing as a counter electrode.

A current of 0.013 amps was measured at a voltage of 320 volts. The energy consumption was 1.5 VA fm .. The load on the separator was 22 m / mh on the heavy phase, at 60% heavy

In the rer phase the amperage rose to 0.08 Amp. = 10 VA / m, the load had to be reduced to 20 m ^ / m ^ h of heavy phase. By lowering the voltage to 250 volts, the amperage was noticeable

0.06 Amp., So that the energy consumption was 5.5 VA / m. The Ab-

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As a result, the divider load could again be increased to 22 m jmrh. increase.

Example 4

The separator only contained the top electrode, the feedstock had 50% heavy phase. The following results were achieved:

volt Amp, VA / m ² Load m / m h 320 0.028 3.3 16.5 255 0.022 2.1 18th

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By reducing the voltage and the energy consumption, the load on the separator could be increased by 1.5 m ^ / m ^ h. Now a capacitor of 0.3 microfarads was connected between the power source and the electrode. The input voltage of 320 volts in front of the capacitor sank to 185 volts between the capacitor and the electrode to earth. The energy consumption was at a current strength of 0.024
18 m ³ / m ² h.

2
ke of 0.024 Amp. 1.6 VA / m. The separator load was.

This example shows that only the amount of energy required for optimal separation is decisive, regardless of whether the optimal voltage is achieved by a transformer or a capacitor is regulated.

Example ö

In the arrangement according to Example 3 with only one electrode on the separator and a phase mixture of 50% heavy and 50% light phase, the upper electrode was coated with a 2 mm thick layer of polytertrafluoroethylene. At 220 volts alternating voltage and an energy consumption of 30 VA / τα. a separator load of 16 m / mh was reached.

Examples

From an aqueous solution that contained 8% lactic acid, this should extracted with butanol. Without electrostatic separation, the separator could with 60% heavy phase in the phase mixture

ο ο
11 m ^o / mh heavy phase.

With an electrode in the separator and a voltage of 25 volts the throughput rate could be increased to 18 m ^ / m h with an energy consumption of 360 VA / m.

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Claims (9)

PATENT CLAIMS 1. Process for accelerating the separation of the phase mixtures from organic compounds which are immiscible or only slightly miscible with one another or inorganic liquids in liquid-liquid extraction according to the mixer-separator principle by applying a voltage of 10 - 500 volts direct current or Alternating current to horizontal electrodes arranged in a separator, characterized in that the electrodes with an amount of energy of 0.5 - 500 VA / sqm separator surface, preferably 1 - 100 VA / sqm, applied. 2. The method according to claim 1, characterized in that the amount of energy in alternating current by changing the applied Voltage is adjusted by means of a voltage regulator. 3. The method according to claim 1, characterized in that the Amount of energy for a given AC voltage through the interposition of a resistor or a capacitor is set. 4. The method according to claim 1 to 3, characterized in that the amount of energy in alternating current by coating the electrodes is set with electrical insulation. 5. The method according to claim 1, characterized in that the amount of energy for a given DC voltage by a Resistance is adjusted. -12- 009835/1566 6. Process according to Claims 1-5, characterized in that the electrode diameter is 25% - 90%, preferably 35% - 60%, of the cross section of the separator. 7. Process according to Claims 1-6, characterized in that with several electrodes to which different high voltages are applied, is worked, with the separator or a or multiple electrodes are grounded. 8. The method according to claim 1-6, characterized in that only a single current-carrying electrode is used, whereby the separator housing is earthed and / or a special Gegenejdctrode is connected to earth. 9. The method according to claim 1-8, characterized in that the top current-carrying electrode is arranged at a height which is 50% -90%, preferably 60% -85%, of the height at which the light phase drains above the bottom of the separator is located. 009835/1566