Note: Descriptions are shown in the official language in which they were submitted.
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DISPE~SIO~ OF I~ISCIB'~ P~SES
This invention relates to an apparatus and method for producing dispersions of
two or more im~iscible phases, for example in the manufacture of emulsions and
encapsulated products wherein the properties of the dispersed phase droplets
must be carefully controlled.
The production of oil-in-water and ~ater-in-oil emulsions and other ~ultiphase
mixtures is of significant economic importance worldwide but the method of
manufacture can be problematical, especially in scale-up from laboratory to
pilot and production levels. ~or example, emulsions are often made in batches
and variations between batches occur since the process may be irreproducible
during large-scale manufacture.
For example, most existing methods of emulsion manufacture rely on the
establishment of turbulent flow in a fluid-mixing regime consisting of two
immiscible liquids contained within a single manufacturing vessel. Due to
turbulent eddies produced by vigorous stirring, one phase is broken up into
droplets (the discontinuous phase) which becomes suspended in the other
(continuous) phase. The size and size-distribution of these droplets is of
critical importance, since it det~ ~nes the stability of the emulsion against
coalescence and its suitability for intended use. ~or a given pair of phases
processed by this existing method, the droplet size is det~, 'ned primarily by
the size of the turbulent eddies and the time exposure to those eddies. There
have been proposed in the literature (Walstra, Encvclopaedia of Emulsion
Technology, Vol. l, 1983, Belcher (Ed), Dekker, New York)) relationships which
correlate the droplet size with the energy input (through agitation) per unit
volume. The value of the energy input depends upon the surface tensions of the
li~uids, their density and the power input for an agitator of given geometry.
The energy input might typically vary from 104 watts per cubic meter (for a
paddle stirrer) to lOl2 watts per cubic meter (for a high-pressure
homogeniser).
The long-standing problem is that such processes are inefficient because
neither can the turbulence be controlled or generated consistently throughout
the volume of liquid in large manufacturing vessels, nor can the behaviour of
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any pair of immiscible phases be predicted on a la-ge scale based on
experiments in a labo-ator~:. The consequence is that ene.gy s used
inefficiently and, more importantly, it is not possible to control the droplet
size or the size distribution with any confidence.
Alternative methods have been proposed based, for example, on droplet
formation using electrostatic or ultrasonic nozzles; nevertheless the
resulting product quality, cost and scalability of these methods are
unattractive.
Various methods have recently been proposed wherein a membrane is used to
facilitate the mixing of two phases. In Japanese Patent Application No.
2-214537 (published 27th August 1990) there is proposed a method of preparing
emulsions wherein the aqueous phase is passed under pressure through the pores
of a membrane into an oil phase conta;n;ne a surfactant, the membrane being
subjected to ultrasonic radiation during the process. Nakashima et al., Key
Engineering Materials, 1991, Vol. 61-62, pp S13-516, describe a method of
preparing emulsions wherein the oil phase is passed through a ~rane into an
aqueous phase containing a surfactant, a condition being that the oil phase
must not wet the membrane. ~urther work by Nakashima et al. is described in
various patent specifications, namely EP 546,174 Al, US 4,657,875 and US
5,326,484. In these, the membrane is made of glass and its pores are of
uniform size.
In more specialised technology, EP Specification No. 452,140 Al describes a
method for the manufacture of emulsions by passing one phase into another
through a membrane, particularly in the field of making foodstuff spreads. W0
Specification No. 87/04924 is addressed to the manufacture of liposomes and
involves the use of a commercially-available asymmetric ceramic filter.
According to the present invention there is provided a method for preparing a
mixture of the emulsion type wherein a discontinuous phase is introduced into
a Circulating continuous phase by passage through a membrane which is
characterised by at least one of the following features:-
(a) it consists of a ceramic or sintered metal material;
(b) it is formed in a plurality of segments which may be identical or
different from each other;
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(c) at ieast one segment is tubular in shape and divergent in diameter along
the length of the tube.
According to a further feature of the invention there is provided an apparatus
so designed as to enable the method of the invention to be carried out, said
apparatus comprising a membrane as defined above together with means for
providing a circulating continuous phase, means for providing a discontinuous
phase and a source of pressure to force the discontinuous phase through the
membrane.
The factors which determine the size of the droplets in the discontinuous
phase, and the size-distribution of said droplets, are:-
(i) the shape, surface chemistry and pore size and size distribution of the
membrane;
(ii) the rate of flow of the continuous phase across the membrane;
(iii) the pressure under which the discontinuous phase is forced through the
membrane;
(iv) the individual temperatures of the two phases; and
(v) the interfacial tensions, densities and viscosities of the phases.
The membrane itself is preferably formed from a ceramic material, and more
particularly it is preferably substantially tubular in
shape with the pores passing radially through the material of the tube. The
size and size-distribution of the pores of the membrane will be determined by
the type of emulsion desired. ~or example, if oil phase droplets of diameter
1 ym are desired, a pore size of the order of 0.35 ym will be required. The
surface chemistry of the membrane may be adapted to provide varying degrees of
wettability.
When the membrane is formed of sintered metal it will preferably have a rolled
surface finish.
The method and apparatus of the invention may be adapted to produce either a
single-phase emulsion or an emulsion containing a plurality of discontinuous
phases, and it may work in either a batch-process or a continuous production
mode.
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When a batch-process is desired, the membrane may be formed in ~he shape of a
diver~ing tube. The continuous aqueous phase is circulated and recirculated
through the inside of the tube and the discontinuous oil phase is forced
through the tubular membrane wall into the continuous phase. The tube is made
divergent in o-der to maintain constant shear force along the length of the
mem~rane surface, as the total vol~me and viscosit-- of the emulsion increase
as more oil phase is added to the aqueous phase during passage along the tube.
This divergence is however not abso~utely essential to the operation of the
invention. The pore structure of the membrane may be varied, both in terms of
individual pore area and number of pores per unit area of the membrane, to
ensure that there is uniformity of droplet size along the length of the tube.
The circulation of aqueous phase is stopped when the volume of oil phase in
the emulsion has reached the desired level.
When a continuous process is desired, the continuous phase is recirculated via
a storage vessel from which the desired emulsion is bled off when the volume
of oil phase has reached the desired level.
The membrane may consist of a single tubular structure as described above, or
it may consist of a plurality of such tubular structures arranged serially, to
form a segmented tubular structure. The individual segments of the tubular
membrane may be adapted to permit a plurality of different droplet sizes or
size distributions of the same oil phase, or to provide a plurality of
different oil phases, with droplet sizes or size distributions which may be
the same or different. The surface chemistry and geometry of the membrane
itself, and the pressure under which the oil phase is forced through the
membrane, can be varied as desired for each of the individual segments.
It is also important that the temperatures of the different oil phases, and
indeed that of the continuous phase, may be individually adjusted to optimise
the operation of the invention.
According to a further feature of the invention there is provided a method of
p-reparing a mixture of the emulsion type wherein the discontinuous phase
consists of an encapsulated substance, which comprises the use of a segmented
membrane of the type described above wherein a first seg - t distributes a
discontinuous phase into a continuous phase, and a further segment distributes
a further discontinuous phase which coats the first discontinuous phase.
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The initial emulsion s prepared as generally desc-ibed above. The
encapsulation process may then be carried out, for example, by passing the
initial emulsion through a conical tube into a narrower-bore membrane tube
incorporating a flo~-splitter along its axis to reduce the effective flow area
between the splitter and the membrane surface. The further oil phase
introduced into the narrower-bore membrane tube, b~ means generally desribed
above, then forms a coating on the droplets of the initial oil phase. It must
be understood that the surface properties of the further membrane are
important in controllin~ the oleophilicity of the further oil phase and thus
improving the coating of the initial oil phase.
According to a further feature of the invention there is provided a method of
controlling the start-up of an emulsification process as described above,
which comprises the use of on-line measurements of the size and
size-distribution of the initially-formed discontinuous phase droplets as a
feed-back signal to control the cross-flow velocity of the continuous phase
and thereby ensure that the desired size and size-distribution of the final
discontinuous phase droplets are obtained.
The on-line measurements may be obtained by the use of laser 5C~nning
microscopy, conductivity mea~u~ ts and/or other suitable measu~ t
methods. These measurements may separately be used to provide quality
assurance of the desired product.
The invention is further illustrated but not limited by way of example with
reference to the following drawings:-
In the first embodiment, exemplified in ~igures l to 8,
FiRure 1 shows a schematic diagram of a single module cross-flow membrane unit
which comprises:-
(a) a vessel (2) containing the aqueous phase which is adapted to provide for
the recirculation of that phase;
(b) a vessel (llj containing the oil phase;
(c) a membrane cross-flow unit (10) through which the oil phase may be passed
into the aqueous phase; and
(d) a final product vessel t18).
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--6--
Both vessels (2) and (11) are provided with heatin~ means (1) and (12)
respectively and vessel (18) is provided with cooling means (19). ~essel (11)
is further provided with filling means (8) and a source of pressure (9). The
various pumps, guages and valves which interconnect the vessels will
hereinafter be described under the description of the procedure for operation.
The membrane unit (10) is shown in more detail in Fi~ure l(a). The cylindrical
membrane itself (25) is supported by a (usually stainless steel) body (22) and
a further (usually stainless steel) concentric body (26), separated fro~ (22)
by seals (23) and adjustable by cl2mp means (29), provides a chamber (24)
for the oil phase. Entry means are also provided for a gaseous purge (21), for
the oil phase (27) and for the aqueous phase (28).
In operation, vessel (2) is filled to the appropriate level with the aqueous
phase through valve (4), valve (17) and sampling valve (15) being closed.
Vessel (11) is filled to the appropriate level with the oil phase, suitably
emulsified, through funnel and valve (8), purging and pressure valve (9) being
open and valve (13) closed. The contents of both vessels are heated to the
applop~iate temperature by means of the heating tapes (1) and (12). The
aqueous phase is then caused to flow through the apparatus by operation of
pump (16) and regulation by valve (4) as shown by flowmeter (3) and pressure
guages (5) and (14).
The oil phase in vessel (11) is brought to the appropriate pressure by means
of pressure valve (9), initially air being purged from the chamber (24) by
having valves (6) and (13) open, valve (8) closed and relief valve (7) set to
safety level. When all air is purged, valves (6) and (13) are closed and the
oil pressure is brought to and maintained at the appropriate level by means of
valve (9). The emulsification process is begun by opening valve (13), the oil
phase being forced under pressure through entry (27) and through the membrane
(25) into the aqueous phase running through the membrane unit (10).
The process is continued until the volume of oil in the emulsion reaches the
desired level. This can be dete ;ned by noting the volume of oil phase
remaining in vessel (11) and by samples of the emulsion removed through
sampling valve (15). Small variation in the rate of flow of the aqueous phase
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can be controlled b~ ~alve (4). The process is termjn~ted by closing valve
(13) and switching off pressure valve (9). The finished product is transferred
to vessel (18) by closing valve (4) and opening valve (17), and may then be
cooled to the appropriate temperature by use of jacket (19) and removed from
the system through valve (20).
Fi~ure 2 shows a sequence of photographs, ta~en with a high-speed
video-camera, of the detachment of an oil droplet from a pore of a membrane.
The data shown are for a coarse pore of 98 ~m diameter and a pressure drop of
2 psi. The double-hatched picture represents the final detchment of the
droplet from the pore; it can be seen that increasing the cross-flow velocity
of the aqueous phase from 0.19 m/s to 0.40 m/s decreases the droplet formation
time from 2380 milliseconds to 420 milliseconds.
Fi~ure 3 shows an electron-micrograph of a ceramic membrane surface with a
wide range of pore sizes.
FiRure 4 shows in graphical form the relationship between pore size
distribution, cross-flow velocity of the aqueous phase and predicted oil
droplet size distribution. The droplet size distribution can be controlled by
varying the pore size distribution 8S well as by varying the cross-flow
velocity.
Fi~ure 5 shows in graphical form the effect of increasing the cross-flow
velocity of the aqueous phase on:-
(a) droplet size;
(b) number of oil droplets produced per pore per unit time;
(c) escape velocity of oil droplets from the pore (measured using a high-speed
video-camera); and
(d) Reynolds Number based on the tube diameter of the membrane module.
All data were obtained using a coarse pore size of 98 ~m diameter and a
pFessure drop of 2 psi. It can be seen that increasing cross-flow velocity
reduces the size of the oil droplets but increases the production rate
thereof.
. .
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Fi~ure 6 shows in isometric diagrammatical form the relationship between oil
droplet size and:-
(a) cross-flo~ ~elocity of the aqueous phase; and
(b) pressure drop across the membrane.
Fi~ure 7 shows in graphical form an example of the evolution of droplets per
area (m2) of membrane. This example is from a batch production process using a
coarse membrane with narrow pore size distribution.
Fi~ure 8 shows a schematic diagram of a segmented membrane tube (corresponding
to item 10 in Figure 1) which allows for either two sizes of droplets of the
same oil phase (in which case the same type of oil phase will be contained in
chambers 1 and 2 and the membranes 3 and 4 will differ from each other) or for
two different oil phases (in which case two different oil phases will be
contained in chambers 1 and 2 and the membranes 3 and 4 may be the same or
different). This system may be extended by the use of additional membrane
segments to cater for more than two different oil phases and/or oil droplet
sizes.
In a second embodiment, exemplified in Figures 11 to 16,
Fi~ure 11 shows a schematic diagram of a single module cross-flow membrane
unit, similar to that shown in Figure 1, which is adapted to provide
continuous emulsion production at room temperature. It comprises a continuous
(aqueous) phase tank equipped with a stirrer, a discontinuous toil) phase
tank, a washing tank, a continuous phase circulation pump, a pressure guage
and a membrane module, all labelled, and valves numberet 1 to 6 the functions
of which are described below.
FiFure ll(a) shows the membrane module in diagramatic form; it is similar to
that described in Figure l(a) and is appropriately labelled. The ceramic
element is 600 mm. in length and has a 5 mm. internal diameter. The inner
surface may be coated so as to produce a mean pore size in the range of 0.1
upwards~ and typicallY O.2~m.
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In ope ation, the two phase tanks are filled ~ith appropriate fluids, the
memb.ane ,s satura-ed ~ith aqueous phase and ~lth all ~alves closed ~he pump
and stirrer (the latter slo~ly enough to prevent vortex motion) are switched
on. By adjustment of the pump the flow rate of the a~ueous phase through the
membrane is reduced to that desired. Valves 3 and 6 are then opened and air
allowed into the system to produce the desired pressure of the oil phase. The
emulsification process is then started by opening valve 2.
The droplet-size dis.ribution in the aqueous phase tank was monitored until
the desired emulsion had been formed, at which time the process was stopped by
closing all valves, releasing the air pressure and stopping the pump and
stirrer. The finished product was released from the aqueous phase tank and the
system washed out before the next operation.
In a third embodiment, exemplifiet in Figures 21 to 27,
FiRure 21 shows a schematic diagram of a single ~odule cross-flow membrane
unit which comprises:-
(a) a vessel (2) cont~;n;ng the aqueous phase which is adapted to provide for
the recirculation of that phase;
(b) a vessel (43) containing the oil phase;
(c) a membrane cross-flow unit (14) through which the oil phase may be passet
into the aqueous phase; and
(d) a final protuct vessel (31).
Both vessels (2) and (43) are provided with heating means (4) and (32)
respectively and vessel (31) is providet with cooling means (25). Vessel (43)
has a removable lid ant-is further provided with a source of pressure (39).
The various pumps, guages and valves which interconnect the vessels will
hereinafter be describet under the description of the procedure for operation.
The membrane unit (14) is shown in more detail in FiRure 21(a). The
cylindrical membrane itself (46) is supported by a (usually stainless steel)
boty (52) and a further (usually stainless steel) concentric body (45),
separated from (52) by seals (49) and adjustable by clamps (44,48), provides a
chamber (50) for the oil phase. Entry means are also provided for a gaseous
purge (51), for the oil phase (47) and for the aqueous phase (53).
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10-- - -
In operation, vessel (') is filled to the appropriate level with the aqueous
phase through valve (20). ~essel (43) is filled to the appropriate level with
the oil phase, suitably emulsified, through a removable lid. The contents of
both vessels are heated to the appropriate temperature by means of the heating
tapes (4) and (32). The aqueous phase is then caused to flow through the
apparatus by operation of pump (19) and regulation by valve (~), as shown by
flowmeter (3) and pressure guages (12) and (1/).
The oil phase in vessel (43) is brought to the appropriate pressure by means
of pressure valve (39) and air regulator (38), initially air being purged from
the chamber (50) by having valves (47) and (51) open and relief valve (35) set
to safety level. When all air is purged, valves (4/) and (51) are closed and
the oil pressure is brought to and maintained at the appropriate level by
means of valve (39) and regulator ~38). The emulsification process is begun by
opening valves (40, 41), the oil phase being forced under pressure through
entry (47) and through the membrane (46) into the aqueous phase running
through the membrane unit (14).
The process is continued until the volume of oil in the emulsion reaches the
desired level. This can be dete 'ned by noting the volume of oil phase
,~ -in;ng in vessel (43) and by samples of the e~ulsion removed through
sampling valve (13). Small variation in the rate of flow of the aqueous phase
can be controlled by valve (7) or lobe pump (19). The process is terminated by
closing valves (40,41) and switching off pressure valve (39), thus releasing
the pressure drop. The finished product is transferred to vessel (31) by
switching valve (22), and may be cooled to the appropriate temperature by use
of jacket (25j and removed from the system through valve ~30).
~i~ure 22 shows an accurate representation of the droplets growing at a pore,
derived from observations made with a high-speed camera, at given times. The
results shown are for a single coarse pore of 98 microns diameter and a
pressure drop of 2 psi. It can be seen that increasing the cross-flow velocity
of the aqueous phase from 0.19 m/s to 0.40 m/s decreases the droplet formation
time from 2380 milliseconds to 420 milliseconds.
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Fi~ure 23 shows:-
(a) an electron micrograph of a ceramic membrane surface;
(b) image analysis which reveals the apparent surface pores; ant
(c) a cross-section through the membrane showing an example of the finer
coating layer overlving a coarser substrate.
Fi~ure 24 shows in graphical form the effect of increasing the cross-flow
velocity of the aqueous phase on:-
(a) droplet size;
(b) number of oil droplets produced per pore per unit time;
(c) escape velocity of oil droplets from the pore (measured using a high-speed
video-camera); and
(d) Reynolds Number based on the tube diameter of the ~rane module.
A11 data were obtained using a coarse pore size of 98 ~m diameter and a
pressure drop of 2 psi. It can be seen that increasing cross-flow velocity
reduces the size of the oil droplets but increases the number thereof.
Fi~ure 6 shows in isometric diagrammatical form the relationship between oil
droplet size, cross-flow velocity of the aqueous phase and pressure drop
across the membrane.
PiRure 26 shows a s~hematic diagram of a segmented m~ ~ane tube
(corresponding to item 14 in Figure 1) which allows for either two sizes of
droplets of the same oil phase (in which case the same type of oil phase will
be contained in chambers 1 and 2 and the membranes 3 and 4 will differ from
each other) or for two different oil phases (in which case two different oil
phases will be contained in ch- hers 1 and 2 and the membranes 3 and 4 may be
the same or different). This system may ~e extended by the use of additional
membrane segments to cater for more than two different oil phases and/or oil
droplet sizes.
Fi~ure ~7 shows the droplet size distribution manufactured using a dualmembrane assembly (as described in Figure 26) having mean pore diameters of
0.5 microns and 4.0 microns, and operated at 40 psi and 10 psi repectively.
RE~TI Fl ED St~ (RULE 91 )
IS~IFP
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In the Examples set out below, all Z compositions are weightlweight.
~xample 1
An aqueous phase was prepared by adding so-bitol mono-oleate ~"Span" 80)
(2.5%) to a stirred solution of polyoxyeth~lenesorbitan mono-oleate ("Tween"
20) (2.5%) and (sodium "Nipastat") (0.3%) in water (64.7%) and the mixture was
loaded into the aqueous phase tank of an apparatus as described in Figure 11.
Mineral oil (30.0~) was loaded into the oil phase tank and the emulsification
process was carried out for 4.5 hours with an initial crossflow velocity of
5.09 m/sec., to produce a 30% oil-in-water emulsion. The pore size
distribution and droplet size distribution are sho~n in ~i~ure 1~; the mean
droplet size was 2.03 ~m. and the mean pore size was 0.41 ~m., giving a ratio
of 4.g5. In general terms the droplet size distribution may be described in
terms of a distribution coefficient E which is defined by the equation:-
E = (D90 - DlO)lD5o
wherein D90, D50 and D10 are the particle sizes obtained when the cumulative
frequencies of the emulsion product when measured on a Malvern Instruments
Mastersizer are 90%, 50% and 10% respectively. For a perfect monodisperse
system E iS zero. In the present Example the emulsions produced give an E
value of not more than 0.6, and at best not more than 0.3. The distri~ution of
pore sizes in the membrane can be defined by the same E being not more than
0.6 and that no single pore has a size greater the 150% of the mean pore size.
The droplet size and size distribution remained unchanged for several weeks,
although there was some early phase separation. ~i~ure 12(a) shows a
photomicrograph of the product (magnification x 400); the striations in,the
image are caused by marks on the camera lens.
Example 2
An aqueous phase consisting of a solution of triethanolamine (3.0%) and sodium
'-'Nipastat" (0.3%) in water (66.7%) was loaded into the aqueous phase tank of
an apparatUs as described in Figure 11. A solution of isostearic acid (3.0%)
in mineral oil (27.0%) was loaded into the oil phase tank and the
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emulsification process was carried out for 6 hours with four different
crossflow velocities- Fi~ure 13(a) shows the pore size distribution (identical
with that shown in Figure 12) and FiRure 13(b) shows the droplet size
distribution for each of the four velocities. The crossflow velocities are
given as a ran~e, because as the concentration of oil in the emulsion
increases, it becomes more viscous (as indicated b~ the reduction in Reynolds
number, which is a function of velocity times density divided by viscosity).
In practice, the velocity falls by about 10% by the end of the process. The
blip on the graph of droplet size distribution at the highest crossflow
velocity arises from the inability of the measUriDg equipment to deal with
very small droplet sizes.
Fi~ure 14 shows the relationship between initial crossflow velocity and mean
droplet size. There is an almost linear decrease of mean droplet size with
increasing velocity.
Fi~ure 15 shows the relationships between the time progression of the process
and:-
(a) concentration of oil in the emulsion (30% by the end of the process);
(b) mean droplet size;
(c) crossflow velocity through the membrane; and
(d) viscosity of the emulsion.
The oil concentration (a) and the viscosity (d) both as expected increase with
time and the crossflow velocity (c) falls as explained above. The ~ean droplet
size (b) in practice decreases slightly with time.
Fi~ure 16 shows a photomicrograph of the product of Example 2 when the highest
exemplified crossflow velocity (5.09 m/sec) is used; the droplets are smaller
than those obtained from Example 1 as shown in Figure 12(a).
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Ex~mple 3
This example describes by way of illustration the manufacture of a
cosmetic-t~pe em~lsion at room temperature, and the effect of the cross-flow
velocity on the droplets so produced.
An aqueous phase consisting of a solution of triethanolamine (3.0%) and sodium
'Nipastat' (0.3%; a preservative) in water (66.7~) was loaded into the aqueous
phase tank (Figure 21, item 2) and a solution of isostearic acit (3.0%) in
mineral oil (27.0Z) was loaded into the oil phase tank (Figure 21, item 43).
Four emulsification processes were then carried out at four different
cross-flow velocities in different batch experiments. The results are shown in
Fi~ure 28. Curve (1) shows the pore size distribution. Curves (2), (3), (4)
and (5) show the droplet size distributions of the product, measured by means
of a Malvern Mastersizer, for each of the cross-flow velocities 1,12, 2.49,
4.34 and 5.09 m/s respectively. Fi~ure 29 shows a typical photomicrograph of a
product manufactured by this process.
Example 4
This example demonstrates how control of droplet size can be achieved by
choice of membrane properties, in particular by choice of pore size.
An aqueous phase was prepared by adding 'Dobanol' (2.96%) and formalin (0.04%)
to a well-stirred solution of sorbitol (36~) in water (36%) and was loaded
into the aqueous phase tank (Figure 21, item 2). Mineral oil (25%) was loaded
into the oil phase tank (Figure 21, item 43) and two emulsification processes
were carried out, one using a ceramic membrane tube (Figure 21[a~, item 46) of
n~- in~l pore size 0.2 micron and the other using a membrane tube of nominal
pore size 0.5 micron. The results are shown in Fi~ure 30 in which curves Pl
and P2 show the pore size distribution, and curves Dl and D2 show the droplet
si~e distribution measured using a Malvern Mastersizer, respectively.
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Example 5
The process described in Example 4 was repeated (using a ceramic membrane tube
of nominal pore size 0.5 micron) except that when the desired oil
concentration was reached (after 100 minutes) more a~ueous phase was
continuously added, and emulsion product was continuously removed, the flow
rates being matched to the oil flux rate so that the emulsion concentration in
the aqueous phase tanX was maintained at that of the final product.
Measu-~ ts of emulsion concentration, production rate and particle size as a
function of time were made using a scanning laser microscope (Type FRBM,
Lasentec Corp.). The results are shown in Fi~ure 31; emulsion concentration in
Ei~ure 31(a), oil flux rate in FiRure 31(b), droplet size number count in
Fi~ure 31(c) and droplet size in Fi~ure 31(d). FiRure 32 shows the pore size
distribution of the membrane (curve 1) and the droplet size distribution
(curve 2). It is clear from these results that the use of on-line
instrumentation with associated computer control enables continuous production
of an emulsion to be achieved.
~xample 6
This example demonstrates the production of a cosmetic emulsion at hightemperature and low shear.
An aqueous phase was prepared by slowly adding 'Carbomer' 934 (0.1%) to well
stirred water (88.25%) maintained at 80~C. and then slowly adding
triethanolamine (1.0~). The solution was loaded into the aqueous phase tank
and maintained at 80~C. by use of the heating tape (Figure 21, item 4). An
oil phase was prepared by heating a mixture of petroleum jelly (6.5%), mineral
oil (2.0%), stearic acid (1.5%), glyceryl monostearate (0.4~) and isopropyl
isostearate (0.25%) to 80~C. and was loaded into the oil phase tank and
maintained at 80~C. by use of the heating tape (Figure 21, item 32). The
emulsification process was carried out at a cross-flow velocity of 0.5 m/s.
CA 022~0366 1998-09-28
W097/36674 PCT/GB97/00910
-16-
FiRure 33(a) shows a cryogenic micrograph of the product obtained by the above
process, whereas Fi~ure 33(b) shows a similar micrograph of an emulsion
prepared by a conventional high shear process. It can be seen that the
lamallae stearate phase appears to beruptured in the conventional high shear
process but is largely intact in the present example, the dispersed oil
droplets being otherwise identical. The product of the present process has
distinctive application properties from the perspective of the user.
Example 7
An aqueous phase in the form of a gel was prepared by adding sodium chloride
(2.0%) to a solution of sodium lauryl ether sulphate (40%), cocoamidopropyl
betaine (10%), cocadiethanolamide (2.0%) and preservative (0.2%) in water
(35.8%) and was loaded into the aqueous phase tanX. Silicone oil was loaded
into the oil phase tank and the emulsification process was carried out using a
stainless steel membrane (Figure 21, item 46; mean pore size 40 microns) until
the concentration of silicone oil in the product was 10%. The droplet size
distribution of the product, which may be used as a shower gel, is shown in
FiRure 34. It can be seen that the droplet size is comparable with the size of
the membrane pore.
