Method of separating, from a liquid mixture, a liquid in dispersed phase from a liquid in continuous phase

From a liquid mixture containing a liquid in a continuous phase and a liquid in the form of drops in a phase dispersed therein, the liquid in the dispersed phase is separated from the liquid in the continuous phase by passing the liquid mixture through a liquid-permeable layer (11, 12), arranged in chamber (10), with through-holes of which at least the majority has a cross section area which is greater than the cross section area of at least the main part of the drops in the dispersed phase, the liquid mixture being sheared, by means of a rotor (23) arranged in the chamber on the inlet side of the liquid-permeable layer, over the layer while maintaining a film (24) of liquid, movable along the layer, from the dispersed phase on the layer and while maintaining a higher pressure on the inlet side of the layer than on its outlet side. Drops of dispersed liquid then coalesce in the film and in the through-holes of the layer and can thus be separated from the liquid in the continuous phase.

The present invention relates to a method of separating, from a liquid 
mixture containing a liquid in a continuous phase and a liquid in the form 
of drops of a phase dispersed therein, the liquid in the dispersed phase 
from the liquid in the continuous phase. 
The invention is related to the separation of different kinds of liquids 
which are dispersed in another liquid, such as mineral oil or a vegetable 
oil dispersed in water, water dispersed in oil, an organic solvent, for 
example xylene, dispersed in water, an organic fuel, for example paraffin 
dispersed in water, and so on. Separation processes of this kind are used, 
inter alia, in the treatment of oil-containing water from oil refineries 
or oil platforms, in solvent recovery, and in connection with extraction 
processes. 
The equipment that is used to separate liquids which are insoluble in one 
another from one another may, inter alia, consist of sand beds, filter 
beds, and coalescence filters in the form of thick, compressed filter 
mats. These beds have a poor cleaning effect, especially as regards 
dispersed small drops. The filter mats are rapidly clogged by solid 
particles and waxes. Common to these separation devices is that the 
regeneration thereof is complicated. 
The present invention relates to a particularly efficient method of 
separating a liquid in dispersed phase and a liquid in continuous phase in 
a liquid mixture thereof. The method according to the invention enables 
the use of equipment which is particularly easy to regenerate. 
According to the invention, the liquid mixture is passed through a 
liquid-permeable layer, arranged in a chamber, with through-holes of which 
at least the majority has a cross section area which is larger than the 
cross section area of at least the main part of the drops of the liquid in 
the dispersed phase, the liquid mixture being sheared, by means of a rotor 
arranged in the chamber on the inlet side of the liquid-permeable layer, 
over the layer and while maintaining a higher pressure on the inlet side 
of the layer than on the outlet side thereof, drops of the liquid in the 
dispersed phase coalescing in the film, and while passing through the 
through-holes in the layer. After passage of the liquid-permeable layer, 
the coalesced liquid is separated from the liquid in the continuous phase. 
The liquids are suitably discharged from the chamber through separate 
outlets. 
The rotation of the rotor gives rise to the formation of a thin film of 
liquid from the dispersed phase along the layer. This film covers 
substantially the surface of the entire layer and is moved along the layer 
as a result of the rotation of the rotor. When parts of the layer arrive 
above the orifice of the through-holes in the layer, they are pressed 
through the holes because of the pressure difference on the two sides of 
the layer. Coalescence occurs partly by drops of dispersed liquid being 
"rubbed" against the liquid film in connection with the shearing of the 
liquid mixture, partly by increased contact between drops and film upon 
passage thereof through the holes. Because the liquid film temporarily and 
partially covers the orifices of the holes, the cross section area of the 
holes will be smaller than the nominal area, which increases the 
probability of small oil drops coalescing in the layer. If no rotor is 
used, the liquid mixture passes unchanged through the liquid-permeable 
layer. 
The liquid-permeable layer with through-holes may consist of one single 
element in the form of a woven or felted product having through-holes, for 
example a net or a mat built up of fibres of a polymer material such as 
polypropylene, polyethyleneglycol terephthalate, polyamide, polysulphon, 
or polyurethane, or fibres of a metallic material such as stainless steel. 
The layer may, inter alia, also have the form of a sintered porous 
(through-pores) or perforated homogeneous plate of metal such as stainless 
steel or of a ceramic material such as aluminum oxide. The through-holes 
in such a layer suitably have a cross section area of 
0.01.multidot.10.sup.-3 -10.multidot.10.sup.-3 mm.sup.2. 
The liquid-permeable layer may also consist of an element of the described 
kind as supporting element and a layer of a small-sized particulate 
material, dynamically applied on the above-mentioned element, for example 
consisting of silicon dioxide, diatomaceous earth, zirconium dioxide, 
aluminium oxide, titanium dioxide, glass, or a polymer material. In a 
layer composed in this manner the through-holes have the same cross 
section area as when using a layer consisting of one single element, i.e. 
suitably a cross section are of 0.01.multidot.10.sup.-3 
-10.multidot.10.sup.-3 mm.sup.2. To achieve such a cross section area of 
the composite layer, the through-holes in the supporting element suitably 
have a cross section area of 1.multidot.10.sup.-3 -300.multidot.10.sup.-3 
mm.sup.2 and the particulate material suitably a mean particle size of 
5-300 .mu.m. The particulate material is suitably applied on the 
supporting element from a suspension supplied to the chamber of the 
separation device while maintaining a pressure difference between the two 
sides of the supporting element. In certain cases it may be suitable to 
construct the liquid-permeable layer of a supporting element and several 
particulate layers arranged one above the other, a particulate layer 
located nearer to the supporting element then having a greater particle 
size than a particulate layer located further from the supporting element. 
A composite liquid-permeable layer constructed in the above-mentioned 
manner has through-holes with the same cross section as stated above for a 
layer consisting of one single element. 
The choice of size for the holes in the liquid-permeable layer is dependent 
on the size of the drops of the dispersed liquid. If the drops are small, 
the cross section area of the holes is in the lower part of the stated 
interval, and if the drops are large they are in the upper part of the 
interval. 
In carrying out the method according to the invention, the flux which is 
maintained through the liquid-permeable layer is dependent on the liquid 
treated, but generally the flux is in the interval 1-50 m.sup.3 /m.sup.2 
h. The liquids on the outlet side of the liquid-permeable layer are 
suitably directed to move along the layer. The velocity of flow is then 
preferably maintained at at most 2 m/sec. 
The rotor is suitably provided with an axis of rotation perpendicular to 
the liquid-permeable layer and is formed with parts, for example wings, 
which are movable along the surface of the layer and brings about the 
shearing of the liquid mixture over the layer. The rotor is preferably 
also utilized for regeneration of the layer, coatings and possibly parts 
of the liquid-permeable layer then being removed and these parts replaced 
by new material. In order to bring the parts which are active during the 
regeneration, such as scrapers on the rotor, into mechanical contact with 
the liquid-permeable layer, the rotor can be made displaceable relative to 
the layer in the direction of the axis of rotation. Alternatively, the 
rotor can be provided with movable scrapers adapted to be brought into 
mechanical contact with the liquid-permeable layer when the rotor rotates 
in one direction of rotation, whereas when the rotor rotates in the 
opposite direction of rotation they are blocked from contact with the 
layer. 
According to one embodiment, the method according to the invention is used 
to carry out extractions, whereby the liquid in the dispersed phase 
consists of an extraction agent for extraction of one or more substances 
from the liquid in the continuous phase. The liquid in the dispersed phase 
with substances taken up from the liquid in the continuous phase is then 
separated, after passage of the liquid-permeable layer, in coalesced state 
from the liquid in the continuous phase.

The separation device according to FIG. 1 comprises a chamber 10 of 
cylindrical shape and two circular liquid-permeable layers 11 and 12 
arranged at the end surfaces of the chamber 10. The edges of the layers 
11, 12 are sealingly attached to the walls of the chamber 10 by seals (not 
shown). Each liquid-permeable layer 11, 12 comprises a supporting element 
11a and 12a, respectively, of a fine-meshed fabric having a central round 
recess 11a.sub.1 and 12a.sub.1, respectively, and of layers 11b and 12b, 
respectively, of small-sized particle material of the kind illustrated in 
FIG. 2. At one point on the envelope surface, the chamber 10 is provided 
with an inlet 13 for the liquid mixture that is to be treated in the 
separation device, and at a diametrically opposite point on the envelope 
surface, the chamber 10 is provided with a sealable outlet 14 for 
discharge of the liquid during regeneration. The outlet 14 can also be 
used to allow part of the liquid mixture to pass past the layers 11 and 12 
while separation is in progress. The inlet 13 and the outlet 14 are 
arranged in the side walls 15 and 16 of the chamber 10. The liquid mixture 
that passes through the layers 11 and 12 passes out into spaces 17a and 
17b between the layers 11 and 12, respectively, and the end walls 18 and 
19, respectively, of the chamber 10. By means of a connection, not shown 
(at a plane different from that shown in FIG. 1), the upper part of the 
space 17a is arranged to communicate with the upper part of the space 17b, 
and in similar manner the lower part of the space 17a is arranged to 
communicate with the lower part of the space 17b. The space 17b (and hence 
the space 17a) is provided with an outlet 21 for the lighter liquid in the 
liquid mixture and with an outlet 22 for the heavier liquid. 
Alternatively, the space 17a may have outlets of its own corresponding to 
the outlets 21 and 22 of the space 17b. The layers 11 and 12 are supported 
by loose supporting net 40 and 41, respectively, with corrugated 
supporting plates 42 and 43, respectively, against the ends walls 18 and 
19. 
As shown in FIG. 3, the chamber 10 comprises a rotor 23, in the exemplified 
case comprising an axis of rotation 23a, the centre line of which 
coincides with the symmetry axis of the cylindrical chamber 10, and two 
wings or blades 23b. The rotor shaft is journalled in the walls of the 
chamber 10 by means of sealing bearings (not shown). 
When the separation device is in operation, the liquid mixture that is to 
be subjected to separation is less via the inlet 13 continuously into the 
chamber 10 of the separation device whereas the outlet 14 is normally 
closed. The liquid mixture may consist of water containing oil droplets, 
such as oil-containing water from oil refineries or oil platforms or waste 
water from cutting processes. When the rotor 23 rotates, a film 24 (FIG. 
2) of oil is formed on the layers 11 and 12. Oil drops in the liquid 
mixture outside these layers 11, 12 coalesce in the film 24, which is 
moved by the shearing forces exerted on it during the rotation. When the 
liquid mixture is pressed through the layers 11 and 12 because of the 
pressure difference on both sides of these layers, the oil film 24 
successively accompanies the liquid mixture through the layers 11, 12. On 
passing through the through-holes of the layers 11, 12, additional 
coalescing is achieved. When, after having passed through the layers 11, 
12, the liquids reach the spaces 17a and 17b, the lighter phase, in this 
case oil, can be discharged with the outlet 21 in the upper part of the 
spaces 17a and 17b, and the heavier phase, in this case water, can be 
discharged via the outlet 22 in the lower part of the spaces 17a and 17b. 
The pressure difference that is maintained during the process described 
may, for example, amount to 0.03-1 MPa. 
In the exemplified case the supporting element 11a and 12a, respectively, 
in the liquid-permeable layers 11 and 12, respectively, consists of a 
fabric of polypropylene with a mesh width of 50 .mu.m. The meshes are 
designated 11a.sub.2 in FIG. 2. The fabric has a thickness of 300 .mu.m. 
The particles in the layers 11b and 12b, respectively, consist of 
diatomaceous earth having a particle size of around 20 .mu.m. The 
thickness of the layers 11b and 12b, respectively, is about 400 .mu.m. The 
layers 11b and 12b are applied by sucking up an aqueous suspension of 
diatomaceous earth through the polypropylene fabric. The majority of the 
through-holes in the liquid-permeable, composite layers 11 and 12 has a 
size of about 9 .mu.m and the majority of the oil drops in the liquid 
mixture a size of about 5 .mu.m. 
The rotor 23 can be used to regenerate the layers 11 and 12. In accordance 
with FIGS. 4 and 5, it is preferably provided with scrapers 23d for 
removal of undesirable coatings, formed on the layers 11 and 12, and of 
particle material 11b, if such is used, and need to be replaced. The 
scrapers may be of rubber and have the shape of blades or flaps. they may 
be attached to the rotor via joints 23e in such a way that they fold out 
when the rotor 23 rotates in one direction (during regeneration) but fold 
in when the rotor 23 rotates in the opposite direction (during separation 
of the liquid mixture). During regeneration water or other liquid is 
admitted at either of the inlets and outlets 13 and 14 and discharged 
through the other of the inlets and outlets while at the same time the 
rotor 23 is rotated with folded-out flaps. 
FIGS. 1-5 illustrate a separation device with one chamber only. Normally, 
it is suitable to use a package of several such devices stacked next to 
each other with the inlets 13 connected to a common main conduit, the 
outlets 14 connected to a common main conduit and each of the outlets 21 
and 22 similarly connected to a common main conduit. Such a separation 
device comprising several units stacked one above the other is disclosed 
in Swedish patent application 8704422-8. 
FIG. 6 illustrates the use of the method according to the invention for the 
extraction of toxic substances dissolved in a liquid, for example waste 
water from a process industry, in another liquid (extraction agent) 
insoluble in water having a lower specific weight than water. The 
dissolved substances need to be removed before the waste water is passed 
to a recipient. It may, for example, be a question of a bleaching process 
for paper pulp in which the paper pulp is bleached with chlorine or 
another chlorine-containing bleaching agent, for example a mixture of 
chlorine and chlorine dioxide in an acid solution (pH 1-2). A suitable 
extraction agent in this connection is an organic phosphoric acid ester, 
for example tribytul* phosphate. In accordance with FIG. 6, the 
contaminated water is pumped by a pump 25 in a conduit 26, after the 
supply of extraction agent, from a conduit 27 to a mixer 28 arranged in 
the conduit 26. The liquid mixture of the extraction dispersed in water, 
then obtained, is led to a separation device 29 comprising a plurality of 
separation units of the kind shown in FIGS. 1-5. The water is thus 
separated from the extraction agent in coalesced state and is discharged 
via the conduit 30 which is connected to the outlets 22 on the individual 
separation units in the package to a recipient. In an analogous manner, 
the coalesced extraction agent is discharged via the conduit 31, which is 
connected to the outlets 21 on the individual separation units, to a 
regeneration unit for the extraction agent. The extraction agent is then 
supplied with a cleaning liquid, for example a 5 per cent caustic soda 
solution, via the conduit 32, which is dispersed in the extraction agent 
in a mixer 33. This liquid has the ability to dissolve out the impurities 
in the extraction agent. The liquid mixture obtained in the mixer 33 is 
subjected to a separation in the separation device 34 which is of the same 
kind as, but smaller than, the device 29. The extraction agent thus 
regenerated is discharged via the conduit 27 and is reused. The cleaning 
liquid is discharged via the conduit 35 to be destroyed, for example by 
burning. The devices 29 and 34 are provided with outlets 36 and 37, 
respectively, for discharge of liquid during the regeneration of 
liquid-permeable layers of the types 11 and 12 therein. Each one of these 
conduits is connected to the outlets 14 on the individual separation units 
included. Instead of using tributyl phosphate, other extraction agents can 
be used in the exemplified case such as other organic esters of phosphoric 
acid.