Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The present invention relates to an apparatus for enriching
chemicals in water by means of continuous liquid-liquid extraction
in an extraction vessel with mechanical stirring.
~he increasing concentration of chemicals menacing the
environment in our waterways necessitates substantially continuous
supervision of the content of certain chemicals such as oil and
chlorinated hydrocarbon, particularly polychlorinated biphenyls
(PCB). The presence of such chemicals in lakes and rivers causes
undesirable biological results, and careful supervision of their
content is therefore necessary. Since these chemicals occur in
very small quantities, it has so far been difficult to develop a
sufficiently reliable and robust apparatus suitable for operation
at a sampling point in waterways or at sea.
The extraction devices known so far are only intended for
use in laboratories. Manual extraction processes are extremely
laborious and are not suitable for large quantities of water.
Attempts have also been made to separate these chemicals by filter-
ing them t-hrough carbon filters, which enable a high degree o~
absorption, but have the drawback that the filtrate is altered
after a short time so that it is no longer identical to the
chemicals originally caught. Furthermore, it has proved difficult
to extract the chemicals from the carbon filter. It is also known
to use porous polyurethane foam as filtér, which has been found
to be better than the carbon filter, but both these filters become
clogged by particles in the water. This means, for instance, that
it is difficult to check the water flow.
The object of the present invention is to provide an apparat-
us which will eliminate the drawbacks mentioned above and which,
due to its robust construct;on, can be used for field work and,
due to its simple construction, can be looked after by an unquali-
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field operator. It should also be possible to use the apparatus immersed
below the surface of the water for separation in situ.
According to the present invention there is provided apparatus for
extracting dissolved substances from water by means of a solvent, which
comprises an extraction vessel; a stationary container, having side walls
and a bottom but open at the top, arranged in the lower part of the extrac-
tion vessel there being an annular gap between the side walls of the con-
tainer and said vessel; said container having therein a stirrer, and acting
as a mixing container; an inlet conduit for supplying solvent to the vessel;
an inlet conduit for supplying water to the container, where water is mixed
with solvent in the extraction vessel; an outlet conduit for removing water
from the bottom of the annular gap between the extraction vessel and the
container; and means in said annular gap to reduce the turbulence caused by
the stirring in the mixture of water and solvent moving down in said annular
gap, so that the solvent rises to the upper part of the extraction vessel
and only water is removed through the outlet conduit, said means for reduc-
ing the turbulence in the annular gap comprising a partition provided with
openings, which partition divides said gap into an upper section and a
lower section.
In the accompanying drawings which illustrate two embodiments of
the present invention:
Figure 1 shows a section through an extraction apparatus according
to a first embodiment of the invention.
FiguTe 2 is a section along the line II-II in Figure 1.
Figure 3 is a section along the line III-III in Figure 1.
~ Figure 4 shows a second embodiment of the invention with the
addition of a means for continuously examining the extract.
The extraction apparatus according to Figures 1-3 comprises an
extraction vessel 1 consisting of a glass cylinder 2 having a lid 3 at the
top and a bottom 4. Inside the extiaction vessel is a container 5, provided
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with a peripheral flange 6 sealing against the inner wall of the glass cy-
linder. The extraction vessel 1 is divided by the container 5 and flange
6 into an upper depositing zone A, a lower mixing zone B, an annular first
separating chamber C and a second separating chamber D located below the
first. The chambers C and D communicate with each other through openings
8 in the flange 6. The first separating chamber C has a cross-section which
becomes wider towards the peripheral flange 6. The chamber C communicates
with the zone A through an annular gap 7. The material used for the lid 3,
bottom 4 and container 5 is a plastic such as polytetrafluorethylene which
is resistant to the chemicals occurring.
The container 5 contains a rod-shaped stirring member 10 being
placed freely at the bottom of the container 5. The stirring member 10 can
be rotated by means of a magnetic stirrer 9, operated by a switch 38.
The lid 3 of the glass cylinder is provided with an inlet channel
11 for supplying the water to be extracted and a channel 12 which can be
used for adding the solvent. The bottom plate 4 of the glass cylinder is
provided with outlet openings 13 communicating through an annular groove
14 with an outlet channel 15.
The upper portion of the outer wall of the container 5 is provided
with protruding portions 16, looking like saw-tooths in cross-section, thus
giving the separating chamber C alternating wider and narrower sections, in
order to reduce the liquid turbulence in this chamber C.
The apparatus according to Figures 1-3 functions in the following
manner:
The extraction ~ssel 1 is filled to about one third of its volume
with a solvent which will not mix with water, for example cyclohexane. The
inlet channel 11 is connected to one end of a tube 17, the other end of
which is placed in the water to be examined. A pump 19 is connected to the
outlet channel 15 which, through a tube 18, draws the water through the
apparatus. The reference character 37 in Figure 1 indicates the interface
between
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the body 36 of water and the body 35 of solvent before the stirrer
9 has been started.
Upon starting the magnetic stirrer 9 the stirring member 10
produces vigorous stirring in the vessel 5 and the adjacent zone A
thus mixing the solvent with the water entering the apparatus to
form a water-solvent emulsion. Chemicals in the water which can
be extracted by the solvent are thus dissolved out of the water.
The stirrer 10 produces an eddy current which extends into the
depositing ~one with gradually decreasing effect. Since the mix-
ing ~one B is narrower, i.e. has a smaller cross-sectional area
than the depositin~; zone, a less turbulent region is obtained
just opposite the gap 7, where separation of the two liquid
phases is initiated. Due to the suction force of the pump 19 the
water-solvent emulsion flows into the first separation chamber C
where the turbulence of the liquid is further reduced and continu-
ed separation of the lighter solvent from the extracted water
takes place. Because of the difference in density, the lighter
solvent will rise to the depositin~ zone A where the two liquids
wiil separate into layers. From the first separation chamber C
the water, together with a small quantity of solvent,will reach
the second separating chamber D where the flow of water is sub-
stantially laminar and any remaining d~oplets of solvent will
flow upwardly through the holes 8. The extracted water, which
does not contain any solvent droplets, leaves the apparatus
through the outlet channel 15.
It will be understood t~lat the entire quantity of solvent
remains in the apparatus during the whole extraction process.
When the desired quantity of water has passed through the apparat-
us the extraction operation ;s discontinued, the solvent is remov-
l30 ed from the apparatus, and ;ts content of' substance extracted
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from the water is analyzed. This analysis of course depends on
the nature of` the substance. The analysis does not form part of
this invention, and will not be described here.
For an apparatus having the dimensions shol~m in Fig. 1 a
flow rate of 1-10 litres of water per hour has been found suit-
able, the quantity of solvent (cyclohexane) being 250 ml. The
apparatus according to the invention has enable~ a concentration
of poly-chlorinated biphenyl as low as 0.2 ng per litre of water
to be analyzed.
In Fig. 4 the same reference characters as in Figs. 1-3
have been used for equivalent parts. The apparatus according to
Fig. ~ contains an external circulation conduit 24 containing
means 25 for the continuous photometric analysis of the solvent.
The solvent is circulated by means of a pump 46. A collar-~haped
partition 27 is provided in the upper portion of the zone A to
separate the two ends of the conduit 24 and to reduce the turbul-
ence in the zone A. A propeller ~3, driven by a motor 44, in the
zone B mixes the two liquids to produce the water-solvent emulsior .
The separating chambers C and D are separated by a wall 45 con-
taining the openings 8. The apparatus makes it possible to as-
certain continuously, in the course of the extraction process,
the amount of substance having been tr,ansferred from the water
to the solvent.
