This invention relates generally to emulsion-based methods and apparatus for producing microparticles, for example microcapsules and microbeads. More specifically, it relates to such methods and apparatus for the continuous production of microparticles containing biological or chemical agents.

Microparticle technology is used in many different applications including, for example, encapsulation of volatile flavourings in foods and beverages (e.g.

peppermint oil in chewing gum); encapsulation of nutrients in foods and beverages (e.g. vitamin C in energy drinks) and active agents in cosmetic products to protect them from premature breakdown (e.g. by oxidation); encapsulation of active ingredients in foods (e.g. raising agents in frozen bread dough); encapsulation of pharmaceuticals to modify their release rate; transformation of solvent soluble agricultural chemicals into an aqueous dispersion; and in the production of active composite materials such as self-healing coatings or anti-fouling paints.

Microparticles include microbeads and microcapsules. Microcapsules generally comprise a core of a composition which is distinct from the surrounding shell or coating. Microbeads may take various forms and may, in some cases, be substantially homogeneous in composition. More typically, however, these may be inhomogeneous containing many small droplets in a carirer matrix.

Known techniques for the production of microparticles containing biological or chemical agents include emulsion-based manufacturing methods. These involve the formation of an emulsion from first and second liquid phases which are immiscible with one another. After an emulsion is formed, a chemical reaction or physical process is used to convert the dispersed phase into microcapsules or to produce hardened microbeads.

Traditionally, microparticles are produced as a batch process. Batch processing has many disadvantages, in particular the lack of flexibility in production batch size (usually determined by the reactor size and associated economics) and also the fact that process monitoring and quality control have to be performed on a whole batch, often leading to yield management issues if measurements are outside of specifications at later processing stages. Any batch-to-batch variation is not acceptable for many microparticle products where a final product with consistent properties (e.g. microparticle size and size distribution) is required. Continuous manufacturing processes on the other hand allow ultimate flexibility on batch production size and also enable far more agile yield management if continuous, in-line process measurements are employed.

A further disadvantage of many batch production methods is that the main process control variable is time. For example, when using a high shear mixing device to create an emulsion in a vessel containing oil and water, the characteristic length scale of the emulsion will not only be influenced by the speed of the mixing device but will be primarily controlled by the time for which the mixing is performed. This means that feedback cannot be employed in process control since once the process has gone too far, time cannot be reversed.

In contrast to batch production, continuous processes are far more suitable for control via feedback mechanisms as control variables can be varied in order to maintain measurements between upper and lower control limits. Continuous production methods for the manufacture of microparticles have been demonstrated. A number of methods have been developed using microfluidic techniques. Many of these techniques produce highly controlled microparticles in a serial process (i.e. one at a time) which may be acceptable for biological applications where a small number of very uniform particles (e.g. capsules) are required, but is unsuitable for low-cost, high volume production.

Production methods for microcapsules generally involve a two stage process. In a first stage droplets of a carrier liquid are formed defining the size of the capsules. This usually involves an emulsion process in which droplets of a first liquid (i.e. a discontinuous phase) are created within a continuous phase of a second liquid which is immiscible with the first, for example droplets of oil in water. In a second stage, a chemical reaction is performed to form a protective shell around the droplets and thus produce the microcapsules. In some production methods, both of these stages are performed as a batch process, for example oil and water are added to a reaction vessel where high shear mixing is used to form a dispersion of the whole batch. Once a fine enough dispersion has been formed a chemical or physical change is induced which results in the formation of a protective shell around the dispersed droplets. A physical process may, for example, involve a temperature reduction to solidify a material. A chemical reaction may involve a change in pH or the introduction of one or more reactive species which leads to a polymerisation reaction at the surface of the dispersed droplets. In other processes the first stage may be carried out semi-continuously. For example, droplets of oil may be sprayed into a water bath or created through centrifugal force by spinning a perforated drum of hot gelatin solution within a cooled oil bath so that droplets which are spun out through the perforations then cool and form gelatin shells within the oil. This process requires harvesting and measurement of the resulting microcapsules as a batch.

A similar emulsion-based process may be employed in the production of microbeads. In a first stage, an emulsion may be formed from any organic and aqueous liquids which are immiscible with one another and a polymer material which is capable of forming the matrix of the microbeads. After formation of the emulsion, the dispersed liquid (e.g. a volatile organic solvent) may be removed from the emulsion (e.g. by solvent evaporation or extraction) in order to produce the microbeads.

Continuous production of an emulsion with dimensional control has been achieved using a micro jet reactor. This is described, for example, in WO 00/61275 and in US 2016/051956. These earlier applications describe a three input device in which two reacting liquids impinge directly on each other and are expelled from the reaction device with a perpendicular gas flow. This device permits a continuous process which can be used to emulsify immiscible liquids and also perform precipitation reactions and other similar particle forming processes, but the necessity to introduce a gas flow makes controllable chemical reaction difficult. This system also has the disadvantage of requiring very high operating pressures, e.g. above 50 bar and preferably above 500 bar, more preferably between 1000 bar and 4000 bar.

Another known continuous production process involves the use of static mixers to form emulsions and channel mixers to perform reactions (Theron et al.,

"Transposition from a batch to a continuous process for microencapsulation by interfacial polycondensation" Chemical Engineering and Processing, vol. 54, pages 42-54, 2012). However, a significant disadvantage of this method is that the energy absorption in the process is directly proportional to the number of elements in the static mixer - this makes it preferable to circulate the emulsion through the mixer several times rather than add more elements to the system. This results in the process running more efficiently in a 'semi-batch' mode.

A need thus exists for alternative methods and apparatus for the production of microparticles, more specifically for such methods and apparatus which enable their continuous production.

In accordance with a first aspect, the present invention provides a method of producing microparticles (e.g. microcapsules), wherein the method comprises the step of forming an emulsion from at least two immiscible liquids under cyclonic flow conditions.

It has been appreciated by the Applicant that by using the method in accordance with the present invention in which a cyclone is formed from a mixture of at least two immiscible liquids it may be possible to produce an emulsion comprising a substantially uniform dispersion of a first liquid within a continuous phase of a second liquid. The emulsion is effectively formed as the liquids repeatedly cross each other's paths under cyclonic flow, with one liquid (the continuous phase) dividing the other liquid (the discontinuous phase) into droplets. The discontinuous phase droplet size is repeatedly reduced until a final, desired droplet size is achieved.

The Applicant has recognised that the production of an emulsion with a

substantially uniform dispersion may lead to the production of microparticles with a relatively uniform size distribution. This may be advantageous depending on the specific application of the microparticles. The method of the invention thus comprises the production of an emulsion from at least two immiscible liquids under cyclonic flow conditions where such an emulsion is capable of producing

microparticles (e.g. microcapsules or microbeads). Effective formation and confinement of a cyclone may be achieved by supplying (e.g. by injecting) the at least two immiscible liquids into a cyclone chamber.

Therefore, in one set of embodiments the step of forming an emulsion comprises introducing the at least two immiscible liquids into a cyclone chamber. By forming a cyclone in this manner the Applicant has discovered that it is possible to exploit the controllable shear forces and cyclonic flow to produce an emulsion with a relatively uniform size distribution. The production of an emulsion and the size distribution of droplets may be dependent on the flow rate of the liquids into the cyclone chamber and there may be a minimum flow rate below which emulsification does not occur. Therefore it may be necessary to ensure that the liquids enter the cyclone chamber with a sufficiently high flow rate and/or pressure which may readily be determined by those skilled in the art.

The Applicant has recognised that producing an emulsion with a uniform size distribution is key to producing microparticles with a uniform size distribution, and therefore this step of creating an emulsion by mixing the two immiscible liquids in a cyclone chamber is key to the production of the microparticles.

A cyclone chamber for use in the production of a cyclone from the at least two immiscible liquids may comprise: at least one inlet, a closed base and an outlet connected to the cyclone chamber.

In a set of embodiments, the emulsion is produced from at least two immiscible liquids under reverse cyclonic flow conditions. In one set of embodiments the step of forming a cyclone may thus comprise forming a reverse flow cyclone from said liquids. In such embodiments the cyclone chamber comprises a closed base and comprises a cross section which decreases in a direction away from an outlet connected to the cyclone chamber. The method may comprise passing of the at least two immiscible liquids into said cyclone chamber via at least one liquid inlet and thereby forming a reverse flow cyclone from said liquids in which the liquids travel in a first direction away from the inlet to the closed base and thereafter reverse direction and travel towards the outlet so as to form an emulsion in the cyclone chamber. The cyclone chamber for use in forming a reverse flow cyclone may take any shape with a decreasing cross section, but in a set of embodiments it comprises a frusto- conical portion. The Applicant has found that at least in preferred embodiments this can allow a higher quality emulsion to be achieved with a narrower distribution of droplet sizes for the same or lower pressure. Without being bound by any particular theory and emphasising that this is not intended to be limiting it is believed that the use of a reverse flow cyclone causes shear in the liquids, breaking up the laminar flow of at least one of the liquids into droplets. Using a cyclone means that it is possible to exploit the controllable shear forces and cyclonic flow to produce a substantially uniform dispersion.

If the proportions of the immiscible liquids are not equal then the tendency will be for the minor liquid phase to form dispersed droplets within a continuum of the greater liquid phase within the cyclone. The characteristic size of such droplets will be influenced by, amongst other things, the shear rate within the cyclone - i.e. by the rate of flow of the liquids around the walls of the cyclone chamber. This rate of shear can be controlled by the dimensions of the cyclone chamber - for a given volume flow rate of liquid into a cyclone chamber, a chamber of smaller diameter will induce higher shear rate than a chamber of larger diameter. The shear forces within the cyclone may also, more usefully, be controlled by the volume flow rate of liquids into the chamber. In particular, the droplet size of the minor (i.e. dispersed or discontinuous) phase may be usefully controlled by the volume flow rate of the major (i.e. continuous) phase into the cyclone chamber. Therefore in one set of embodiments, the flow rates of the two immiscible liquids may be altered to adjust the properties of the emulsion and, in turn, the resulting microparticles.

In order to produce the microparticles it will generally be necessary for a chemical reaction or a physical change to occur within the emulsion, for example to produce a capsule shell or coating (and thus a microcapsule), or to produce a hardened polymeric matrix (i.e. a microbead).

The microcapsules will typically comprise a solid or semi-solid shell around the droplets of the first immiscible liquid such that the droplets cannot coalesce back to form a continuous bulk of the liquid. In its simplest form, the production of microcapsules involves mixing at least two immiscible liquids to form an emulsion and then encapsulating one of the liquid phases to create the microcapsules.

Therefore, in one set of embodiments, the method further comprises the step of microencapsulation of at least one of the immiscible phases. As will be discussed, this step may be performed at various different stages during the production process.

As discussed, microbeads are typically substantially homogeneous in composition. These may, for example, be produced by hardening of the dispersed phase. The production of microbeads may thus involve mixing at least two immiscible liquids to form an emulsion and then solidifying or hardening the dispersed liquid phase to create the microbeads. Therefore, in one set of embodiments, the method further comprises the step of solidifying the dispersed phase. As with microencapsulation, this step may similarly be performed at various different stages during the production process.

The process of the invention may be considered to effectively first produce a controlled dispersion, i.e. an emulsion, of a first immiscible liquid within a second immiscible liquid and then the step of forming microparticles. Dependent on the method used to form the microparticles, the first and/or second immiscible liquids may comprise one or more additional reagents capable of forming a shell or protective matrix. One or both liquids may further comprise at least one biological or chemical agent either dissolved or dispersed therein.

In one set of further embodiments in which the at least two immiscible liquids are introduced into a cyclone chamber, the further step of microparticle formation (e.g. microencapsulation) is performed in said cyclone chamber. In these embodiments, the emulsification and encapsulation / solidification are performed simultaneously within the cyclone chamber. In this case, the composition of the two immiscible phases is selected such that upon contact the shell forming or solidification reaction begins. This is made possible if the flow rate of the continuous phase is sufficiently higher than that of the droplet forming phase such that droplets of the minor phase are formed as that phase enters the cyclone chamber. The Applicant has appreciated that such a method is particularly advantageous as it allows for the production of microparticles using a single cyclone chamber. This therefore means that a relatively small amount of equipment is required to produce the microparticles. This may make the process significantly cheaper and open up the process of microparticle production to a larger market. For example, the process could be performed at the point of use (i.e. in-situ), for example onboard a piece of agricultural equipment wherein a microencapsulation process may be used to encapsulate one or more agrochemicals. In addition, using less equipment is further advantageous as it reduces the amount of equipment which has to be cleaned and/or maintained.

However, the Applicant has also recognised that producing micro particles using a single cyclone chamber is not the only method of producing these and in an alternative set of embodiments in which the at least two immiscible liquids are introduced into a cyclone chamber, the step of microparticle formation (e.g.

microencapsulation) is performed in a second reaction chamber in which the emulsion is subjected to chemical and/or physical conditions which are capable of producing microparticles. For example, the emulsion may be contacted with a suitable shell forming or solidification promoting reagent in the second reaction chamber. This second reaction chamber may require two or more inlets - one for supply of the emulsion and one or more additional inlets which may be used for the supply of one or more other liquids which carry reactive species or other

chemistries suitable for microparticle production. The second reaction chamber also requires one or more outlets arranged such that the liquids mix and the shell forming or solidification reaction proceeds to a sufficient extent during the journey of the liquids between the inlets and the outlet. Such a set of embodiments may be advantageous as it may allow more control over the production of the

microparticles. It may also allow for the continuous production of the microparticles.

The second reaction chamber may take any suitable form so long as it allows the reaction to proceed to a sufficient extent. The second chamber may be one of many different chambers, for example it may be a second cyclone chamber (e.g. a reverse flow cyclone chamber). This has the advantage that it may be employed to provide more shear to the emulsion and reduce the droplet size further during the shell forming or solidification reaction. Also, use of a reverse flow cyclone chamber ensures efficient mixing of any additional reactive species throughout the emulsion (e.g. throughout the miscible phase of the emulsion). In certain embodiments, however, this need not be a cyclone chamber, for example this may be a simple mixing chamber. Mixing in this chamber may be performed under turbulent flow conditions, for example using a turbulent mixing device such as a static or dynamic mixer. As an alternative to the second reaction chamber, in-line mixing of the emulsion and any reactant required to effect microparticle formation may be carried out. For example, the emulsion and any reactant may be introduced into the same pipeline via a Y-junction or T-junction. If additional mixing is desired, in-line mixing may be carried out in an in-line dynamic mixer, an in-line static mixer or a coil mixer in which the emulsion is subjected to chemical and/or physical conditions capable of producing microparticles.

In a further set of embodiments the two immiscible liquids which form an emulsion in the cyclone chamber may pass directly into a container (e.g. a holding tank) which contains a further liquid or into which a further liquid is supplied in order to effect microparticle formation, e.g. microencapsulation. Mixing need not necessarily be carried out in this container. Thus, it may be the case that in this container a further liquid is one capable of promoting encapsulation or solidification. In one set of embodiments, this further liquid may be miscible with the continuous phase of the emulsion and contains reactive species or provides appropriate conditions (e.g. pH, temperature, etc.) which promote the encapsulation or solidification reaction. This type of embodiment may render the process only semi- continuous as although the emulsion is produced and may be controlled as a continuous process, the encapsulation or solidification may be performed batch- wise and the microcapsules must be harvested as a batch at the end of the process.

Of course it may be the case that there are further chambers and/or containers employed in the production of the microparticles. Thus, the process may in fact involve a plurality (e.g. a large number) of cyclone chambers or other types of mixing chambers and holding tanks, as required.

As will be understood, the process of the invention may involve the use of any number of liquids provided that the product from their combination is at least two liquids which are immiscible with one another and thus capable of forming an emulsion under cyclonic flow conditions (e.g. reverse flow cyclonic conditions). Other reagents which may be present in one or more of the liquids include agents capable of stabilizing the emulsion (e.g. emulsifiers) and, optionally, agents capable of promoting microparticle formation (e.g. encapsulation or solidification). One or more biological or chemical agents may also be present, either dissolved or dispersed in at least one of the liquids used to form the emulsion.

It may be desirable that the microcapsules formed in the process have a shell that has a sufficient robustness or are sufficiently solidified so as to prevent the droplets from re-coalescing after exiting the cyclone chamber or, where employed, the second reaction chamber. Provided that this condition is met, the microcapsules or microbeads will remain in contact with the reactive species after leaving the reaction chamber and will continue to react until they are either separated from the liquid or the reaction reaches an end point - either by deliberate intervention (e.g. introduction of a reaction terminating species) or by natural course (e.g.

consumption of one or more of the reactants or other natural means such as the reaction becoming limited by diffusion of the reactive species through the formed shell). If required, after leaving the cyclone chamber (or the second chamber, where this is employed) additional reagents may be introduced to further react or harden the shells.

As is described above, it may be possible to achieve a continuous production of the microparticles. This may mean that it would be possible to produce microparticles on demand and in exact quantities. Such a continuous process may also be advantageous as it may be possible to monitor and dynamically change the production process in order to modify the properties of the microparticles which are produced. Monitoring of the microparticles may include monitoring various properties of the particles. In certain applications it may be desirable to have a specific size distribution. For example, a pharmaceutical inhaler may require all particles to be less than about 10 microns in diameter so that they can be inhaled deep into the lungs. Conversely, a similar device for the delivery of flavour capsules may require that these are all greater than about 50 microns so that they are not inhaled beyond the back of the mouth. Therefore, in one set of embodiments, the method of producing microparticles further comprises the step of determining the size distribution of the resulting microparticles. Many methods exist for the measurement of such critical dimensions - e.g. light scattering and diffraction methods, optical microscopy, high speed photography, image analysis, turbidity measurements as well as inference methods such as viscosity measurements. It may be useful simply to know the size distribution of the microparticles which are produced and they can then be used accordingly. However, it may sometimes be desirable to dynamically change the size distribution during the microparticle production process. For example, this may be desirable to maintain the size distribution close to a target size distribution or it may be simply because a different size distribution to that which is already being produced is required. Therefore in a further set of embodiments, the method of producing microparticles further comprises the step adjusting at least one method or apparatus parameter to alter the size distribution of said microparticles. Adjusting the size of the microparticles may be achieved in a variety of different ways including but not limited to: changing the flow rate of one or both of the at least two immiscible liquids, changing the temperature, changing the pH, changing the size of the cyclone chamber, or changing the ratio of the at least two immiscible liquids. It will be appreciated that one or more of these parameters may be changed to alter the dimensions of the microparticles as desired. Therefore, by constructing a suitable control system which employs feedback from a measurement to control system parameters, a highly controllable continuous method for microparticle production may be achieved. Controlling the flow rate of the liquids may be achieved, for example, by changing the pump speed of the pump(s) supplying the at least two immiscible liquids to the cyclone chamber.

The ability to adjust the size of the microparticles in this way is particularly advantageous when the method is employed to continuously produce

microparticles as the size of the microparticles can be monitored and production can be adjusted or stopped accordingly. This dynamic control over the size of the microparticles is particularly advantageous, especially when contrasted with prior art techniques, for example that described in US 4,228,216, wherein, for example, once a process for the production of a batch of microparticles has commenced, it is not possible to dynamically control their size. In such instances, if, at the end of production, the size of the microparticles is not appropriate, then the entire product may not be usable.

The Applicant has recognised that in order to further improve the quality of the emulsion produced it may be desirable to introduce a gas into the cyclone chamber. Therefore, in another set of embodiments the method comprises the step of forming a cyclone (e.g. a reverse flow cyclone) from at least two immiscible liquids in the presence of a gas. For example, the method may comprise the further step of introducing a gas into the cyclone chamber. By introducing a gas, i.e. a fluid of low viscosity, into the cyclone chamber there is increased shear on the liquid mixture, causing increased break up of the flow. This is because there are shear forces between the liquids and gas, as well as due to the counter-rotating parts of the cyclone. This may lead to an emulsion with further improved properties, for example a more uniform particle size distribution.

In a set of embodiments, the step of forming a cyclone involves introducing the at least two immiscible liquids into the cyclone chamber separately. The cyclone chamber may therefore comprise at least two liquid inlets. In a set of embodiments, the cyclone chamber for use in the production of the emulsion thus comprises a plurality of liquid inlets. These inlets may be connected to a plurality of liquid sources. In this case they can therefore be used to mix a plurality of liquids at the point of use. As discussed herein, this is advantageous as it has been found to give very efficient mixing and avoids the need to store the mixed liquids which may not be stable for prolonged periods of time.

Any of the liquid inlets to the cyclone chamber may also serve as gas inlets in those embodiments in which a gas supply is provided to the chamber. Alternatively, the apparatus may also have one or more additional gas inlets. These could be connected to the same gas source or a plurality of different gas sources.

In an alternative set of embodiments, the step of forming a cyclone comprises introducing the at least two immscible liquids into the chamber together. In such a set of embodiments the cyclone chamber may comprise a single liquid inlet. The source of the at least two immiscible liquids may be removably attached to the cyclone chamber. This may, for example, allow different immiscible liquid sources to be connected to the cyclone chamber to ultimately produce different

microparticles as desired. Alternatively, the source of the at least two immiscible liquids may be an integral part of the cyclone chamber and its associated apparatus.

The at least two immiscible liquids may be supplied to the cyclone chamber by any suitable means, for example these may be introduced through pipes or tubes and may be pumped, forced by a gas or other pressure source. In such a set of embodiments where control over the flow rate is desired the method of producing microcapsules may comprise adjusting the flow rate of the pump. Alternatively the liquids may be pressurised by other means, e.g. by a pressurised source of gas, an electric fan or expansion of volatile organic compounds (VOCs). In such a set of embodiments, the flow rate may for example be adjusted by adjusting the pressure of the gas.

The liquids for use in production of the emulsion may be supplied to the cyclone chamber at ambient temperature or at any temperature required from just above freezing to just below boiling for the particular liquid. The temperature may also be selected according to the stability of any biological or chemical agent contained therein. Temperature ranges will be dependent on the phase changes of the liquids used and may be selected accordingly. In some cases, for example, it may be desirable to cool the emulsion to prevent the liquid phases from becoming fully miscible with one another. Alternatively, it may be desirable to operate at higher temperatures in order to maintain one of the liquid components as a liquid, for example to prevent this from solidifying (e.g. paraffin wax is solid at ambient temperatures but may be molten at 60°C or higher). Pressure may similarly be adjusted as required and the method may be carried out at any pressure compatible with the apparatus used. Suitable operating pressures may be in the range of about 0.5 barg to 9 barg, for example.

The method of the invention may comprise supply of the at least two immiscible liquids into the cyclone chamber at the same time, but in a set of embodiments one liquid may be introduced before the other, i.e. sequentially. This may allow the first liquid to set up a cyclone (e.g. a reverse flow cyclone) before the other liquid is introduced, which may increase the quality of the emulsion. Alternatively or additionally, the method may comprise the step of terminating the supply of one of the liquids into the cyclone chamber after terminating the supply of the other liquid into the chamber. This may allow the cyclone chamber to be cleaned, removing some or all of the liquid which may remain in the chamber after its supply into the chamber has ceased. Alternatively or in addition, a gas may be passed through the cyclone chamber for the purpose of cleaning. The apparatus of the invention may be arranged to execute such operations in use. Alternatively, the liquids may only be supplied as a user demands, allowing the order in which the liquids enter the chamber and the length of time for which they are present to be tailored by the user, rather than operating in a predetermined manner.

Depending on the properties of the immiscible liquids, the Applicant has recognised that it may be desirable to feed the liquids into the cyclone chamber in a specific manner. Therefore, in a set of embodiments the method further comprises introducing the at least two immiscible liquids into the cyclone chamber through feed-in-tubes. The inlets may comprise feed-in tubes, which connect a liquid source to the cyclone chamber. These feed-in tubes may be cylindrical but in a set of embodiments one or more of the inlet tubes is tapered, reducing in cross-section towards the chamber. This may be beneficial for some liquids. Taking the central axis of the cyclone chamber extending from the base and around which the reverse cyclone circulates in use, the feed-in tubes may approach the chamber at any of a range of angles to the axis and the angle may be different for each but in a set of embodiments the angle between the feed-in tubes and the axis of the chamber is substantially 90°.

In a set of embodiments, the feed-in tubes are substantially tangential to the cyclone chamber, preferably in the same rotational sense. This causes the liquids to enter the chamber in the same direction, enhancing the reverse flow cyclone formed. Enhancing the reverse cyclone may improve the quality of the emulsion produced from the at least two immiscible liquids.

The inlets may be arranged at any angular spacing around the chamber, but in a set of embodiments they are arranged equiangularly. The feed-in tubes may have different lengths, but in a set of embodiments they are all of equal length. This allows for even mixing of the liquids, as they undergo the same conditions as they approach the cyclone chamber. The inlets could be arranged in a number of different planes, but in a set of embodiments they are all in substantially the same plane. This ensures that the liquids all form cyclones of substantially the same size, causing even mixing and similar sized droplets. The outlet could simply comprise an aperture in the top of the cyclone chamber (the top being defined as the wall furthest from the base where the cyclone reverses direction) with no significant axial extent. However in a set of embodiments the outlet is elongate (i.e. has a longitudinal extent greater than its maximum diameter). In a set of embodiments, the outlet is tapered so as to reduce in cross section away from the cyclone chamber. This allows for a smooth transition from the interior of the cyclone chamber to the distal mouth of the outlet which may be beneficial in some circumstances.

In a set of embodiments the outlet extends into the cyclone chamber, proud of the top of the chamber. In a set of such embodiments the outlet extends further along the axis of the chamber towards the base than the location of at least one, preferably all, of the inlets. This can help to prevent liquid from the inlets 'short- circuiting' the chamber by travelling directly out of the outlet without forming a reverse cyclone. This can also be achieved with a wall, baffle or other formation which is separate from the outlet. Thus in general in a set of embodiments the cyclone chamber is arranged such that liquid entering one or more inlets is required to turn by more than 90° to the axis to exit from the outlet.

Additionally or alternatively, the outlet may extend away from the cyclone chamber, for example where this may be used to produce a spray. Features of the outlet can be changed in order to modify the shape of the spray, for example the outlet cross- sectional shape or length.

The cyclone chamber may have an aspect ratio, defined as the ratio between the length of the chamber (from the base to the beginning of the outlet or the widest point of the outlet) divided by the diameter of the chamber at its widest point. In a set of embodiments the aspect ratio is between 1 and 5, e.g. between 1 and 2, e.g. between 1 and 1.5 The absolute dimensions of the cyclone chamber will depend upon the application of the microparticles. However one of the advantages which the invention provides is that an emulsion can be formed using a relatively small cyclone chamber. In a set of exemplary embodiments the cyclone chamber is less than 3 cm in diameter (at its widest point), e.g. less than 1 cm in diameter, e.g. less than 0.6 cm, e.g. less than 0.4 cm. The cyclone chamber may have a length (as defined herein) less than 5 cm, e.g. less than 3 cm, e.g. less than 1 cm.

For microparticle production on an industrial scale, larger cyclone chambers may be used.

The minimum diameter of the outlet (which may be at the furthest point from the interior of the chamber) may be selected according to the flow rate desired in the spray, but is preferably between 0.1 mm and 1 mm, e.g. between 0.2 mm and 0.5 mm. In a set of embodiments, this value is between 2 and 20% of the chamber diameter (at its widest point), further between 5 and 15%.

The feed-in tubes can be varied in size according to the application, with both the diameter and length affecting the quality of the emulsion produced. In a set of embodiments, the feed in tubes are between 0.1 mm and 1 cm in diameter. In a set of embodiments, the feed in tubes have a diameter of between 2 and 20% of the chamber diameter (at its widest point), further between 5 and 15%. In a set of embodiments the feed-in tubes are between 0.5 cm and 5 cm in length.

The ratio between the minimum diameter of the outlet and the diameter of the feed in tubes may vary according to the application and the desired droplet size, but in a set of embodiments the optimal ratio is between 0.5 and 2, e.g. approximately 1.

The ratio of the two liquid pressures and, where a gas is present, the ratio of the liquid and gas pressures may affect the droplet size produced by the cyclone chamber. Suitable pressure ratios can be determined as required. Having a greater gas pressure may, for example, create smaller liquid droplets, creating a finer dispersion.

The methods herein described may be employed batch-wise or continuous. When used in a batch process the size of the batch can be altered by changing various parameters of the process used for production of the microparticles, such as the flow rate of the liquids into the cyclone chamber, and the running time, etc.

In certain embodiments, the methods of the invention provide a continuous process for making an emulsion and/or microparticles.

The methods and systems herein described provide for tight control over the droplet size and droplet size distribution in the emulsions, which in turn provides for control over the resulting particle size and particle size distribution of the microparticles which are produced. Droplet (and thus micro particle) size and size distribution can be manipulated by altering various features of the methods and systems such as, but not limited to, altering the size (length or width) of the cyclone chamber in which the emulsion is produced, rearranging the inlet and outlet positions, alteration of the physical properties of the phases to be mixed, altering the flow of liquids (and, where present, any gas) into the cyclone chamber, adjusting the residence time of the emulsion in the cyclone chamber, etc.

In some embodiments, the methods involve a process of making an emulsion and/or microparticles having a pre-determined size distribution. The microparticles may range in size from submicron to mm dimensions. In certain embodiments, the microparticles may range in size (i.e. diameter) from 1 to 200 microns, e.g. from 10 to 100 microns. The selection of microparticle size will be dependent on their application. For some applications, for example, about 1 to 10 microns may be desirable whereas for others a size in the range of about 100 to 200 microns may be preferred.

The resulting microparticles will generally be produced in the form of a suspension, for example as a suspension of microparticles in the continuous phase used in their preparation. The presence of emulsifying agents may aid in their dispersion.

Depending on their intended use and the nature of any auxiliary chemical reagents (e.g. emulsifiers, pH modifiers, etc.) used in their preparation, the resulting dispersion of micro particles may be used directly, i.e. without further processing. This may be the case, for example, where the continuous phase is aqueous (e.g. water) and the product is to be formulated with other liquid components.

Alternatively, it may be desirable to separate the micro particles from the liquid phase in which these are produced. Therefore, in a set of embodiments, the method further comprises the step of recovering said microparticles. Steps for recovery of the microparticles are well known and may be selected by those skilled in the art taking into account factors such as the methods and reagents used in their production (e.g. the nature of the continuous phase to be separated), and their chemical composition (e.g. the nature of any encapsulated biological or chemical agent). Suitable recovery methods include, but are not limited to, solvent extraction (e.g. when forming hardened microbeads), decantation, filtration, drying (e.g. spray drying), etc. Any method used to recover the microparticles should be selected taking into account the effect this may have on the encapsulated active material. This may be the case, for example, when handling microparticles containing biologically active agents which are susceptible to degradation under certain processing conditions, e.g. at elevated temperatures.

The suspension of microparticles or, where these have been separated, the recovered microparticles may be used in various different applications dependent on the nature of any biological or chemical agent which they may carry. If desired, these may be formulated with other carriers or excipients to produce the final formulation. The choice of any carriers or excipients will be dependent on the end use but may include physiologically tolerable carriers such as sterile water, saline or buffered solutions at physiological pH (e.g. where these are intended for pharmaceutical use). Other additives which may be present include preservatives and/or surfactants to enhance the dispersibility of the microparticles in the final composition.

The Applicant has appreciated that the cyclone chamber used in the preparation of the microparticles could be used to spray directly. In such cases, the microparticles may be produced at the point of use (i.e. in-situ). This may be beneficial for certain applications, for example where the resulting microparticles can suitably be applied by spraying. Non-limiting examples include the spraying of agrochemicals (e.g. pesticides, herbicides, etc.); spraying of bioactive agents in the form of nasal sprays; spraying of paints, pigments or dyes; spraying of cosmetic products where a uniform coverage is desirable (e.g. make-up products, skin creams, etc.); and the spraying of flavours or fragrances, corrosion inhibitors, active adhesives or coatings, disinfectants, etc.

The Applicant has appreciated that a benefit of in-situ production of the

microparticles is the ability to produce these On demand', i.e. as required and according to need. This has a number of important advantages. For example, it minimises any waste of the product. Significantly, however, this aspect of the invention may address the stability problems of combined formulations, e.g.

formulations which contain a combination of active agents which degrade once mixed. In such cases, mixing of the active agents reduces the shelf life of the product or may require that the product is stored under refrigerated conditions which is not only inconvenient but, where this is a pharmaceutical for example, this can also reduce patient compliance. In order to overcome these problems, it may be required that such formulations are presented as separate components which are mixed in a controlled ratio on demand, e.g. immediately prior to, during or following application. Conventionally, these are therefore kept apart during storage and only dispensed and mixed at the point of use. One difficulty with existing products is the variability in the degree of mixing which can affect the efficacy of the product (e.g. where this is a pharmaceutical or cosmetic which contains active components). The method and apparatus herein described provide for On demand' production of microparticles from two or more components which are chemically incompatible with one another (e.g. when in contact for prolonged periods).

In one set of embodiments, the invention thus provides a method of producing emulsions and/or microparticles containing two or more chemically incompatible agents. In such methods, the two or more chemically incompatible agents are stored separately prior to their combination to form an emulsion under cyclonic flow conditions as herein described. For example, these may be stored in separate chambers or in compartments of a dual- or multi-chamber which are connected to the cyclone chamber. Suitable chemistries for the production of emulsions and emulsion-based microparticles (e.g. microbeads or microcapsules) are well known and described in the art and may be selected for use in any of the methods herein described. Generally, emulsion production will involve mixing of at least two immiscible liquids such as oil and water. Where two phases are present this will result in an oil-in- water or water-in-oil emulsion. In some embodiments more than two liquids may be used to produce double emulsions, e.g. oil-in-water-in-oil or water-in-oil-in-water emulsions. In these methods, first and second phases are emulsified to form a water-in-oil or oil-in-water 'internal emulsion'. This internal emulsion is then emulsified again with a third phase to form an oil-in-water or water-in-oil 'external emulsion'. Typically, the emulsions produced in the methods of the invention will be single emulsions. In a particular embodiment the two immisible liquids may comprise an aqueous phase and an organic phase which comprises at least one biological or chemical agent dissolved or dispersed therein and one or more polymers capable of forming a microbead. Contact of the organic phase with the aqueous phase forms an emulsion which comprises droplets of the organic phase dispersed in the aqueous phase. Removal of organic solvent from the emulsion droplets forms hardened microbeads. These may subsequently be recovered from the aqueous phase and, if required, dried. The organic phase may contain one or more solvents in which the polymer is soluble. Examples of such solvents include, but are not limited to, the following: methylene chloride, ethyl acetate, benzyl alcohol, acetone, acetic acid, propylene carbonate, and mixtures thereof.

Microbeads may be made with a variety of polymers including, but not limited to, the following: poly(lactide), poly(glycolide), poly(lactide-co-glycolide), poly(lactic acid), poly(glycolic acid), poly(lactic acid-co-glycolic acid), polycaprolactone, polycarbonates, polyesteramides, polyanhydrides, poly(amino acids), polyesters, polyorthoesters, polyacetyls, polycyanoacrylates, polyetheresters,

poly(dioxanones), poly(alkylene alkylate)s, copolymers of polyethylene glycol and poly(lactide) or poly(lactide-co-glycolide), polyurethanes, and any copolymers or blends of two more such polymers. Biodegradable polymers and/or physiologically tolerable polymers may be chosen, as desired. Suitable chemistries for the production of microcapsules from an emulsion are well known in the art and include both chemical and physical methods which result in the formation of a protective shell around the dispersed droplets. Physical processes may, for example, involve a temperature reduction to solidify a shell forming material. Chemical processes may involve a change in pH as a result of the addition of a suitable pH adjusting agent, or the use of one or more reactive species which lead to a polymerisation reaction at the surface of the dispersed droplets to form the shell.

Polymerisation methods are particularly suitable for the production of protective shell coatings and include, for example, in-situ and interfacial polymerisations. These are well known and described in the art. Such methods involve the use of at least two monomers which are polymerisable to form the polymer shells or coatings.

Interfacial polymerisation involves the reaction of two monomers in two different phases to produce a polymer at the interface between the continuous and discontinuous phases. In one embodiment of the methods herein described a first polymerisable monomer may be provided in one of the at least two immiscible liquids and will form part of the emulsion formed during the first stage of the process. For example, this may be present in the discontinuous phase (e.g. the oil phase). Introduction of a second polymerisable monomer will generally be carried out during the second stage of the process whereby to form the microcapsules. For example, the second monomer may be introduced in a further liquid miscible with the continuous phase (e.g. the aqueous phase). Polymerisation of the first and second monomers at the droplet-continuum interface results in the production of a polymer shell or coating. Examples of such reactions include the reaction between a diamine and diacid chloride to produce a polyamide shell, the reaction between a diisocyanate and a diamine to produce a polyurea shell, and the reaction of diisocyanate with a diol to produce polyurethane.

Other shell forming methods include complex coacervation (phase separation) and solvent evaporation or extraction. Coacervation involves spontaneous liquid-liquid phase separation and can occur when oppositely charged species such as polyelectrolytes (e.g. gelatin and gum arabic) are mixed.

Shell or coating materials for use in the production of microcapsules are known in the art and may be selected taking into account factors such as desired stability, shell thickness, release profile (e.g. permeability of the coating), biodegradability, biocompatibility, strength, etc. Suitable materials include, for example, polyamides (e.g. nylon), polyurea, polyurethane, hydrocolloids (e.g. gum arabic, gelatin), alginates, urea-formaldehyde resins, melamine-formaldehyde resins, urea- melamine-formaldehyde resins, aminoplasts (e.g. polyamines, polyols), waxes, and polystyrene. Other suitable materials include free radical polymerised materials, e.g. acrylates and methacrylates, which can be thermally, chemically or radiation (e.g. UV) initiated. In order to efficiently produce microcapsules continuously the reaction scheme may need to be carefully chosen. Reactions which are slow and require long periods of heating, cooling or reflux are more suited to batch production methods. On the other hand, rapid reactions and those which can be performed as a second shell forming stage after droplet definition are particularly suitable for continuous processing. These include polymerisation and network forming reactions, for example interfacial polymerisation reactions such as the polyurea reaction described in Yadav, S. K. et al., "Microencapsulation in polyurea shell: Kinetics and film structure" AIChE J., 42: 2616-2626, 1996, the nylon reactions described in Reza Arshady "Preparation of microspheres and microcapsules by interfacial polycondensation techniques" Journal of Microencapsulation, 6: 1 , 13-28, 1989, or the alginate reactions described by Amici et al. in Food Hydrocolloids Volume 22, Issue 1 , January 2008, pages 97-104. Polyurethane reactions are also rapid and may thus be particularly suitable for use in the invention. As will be understood, dependent on the choice of chemistry for production of the emulsion one or more emulsifying agents (e.g. surfactants) may be required to stabililse the emulsion. Emulsifying agents are well known in the art and may be selected from any known non-ionic, cationic and anionic surfactants. Suitable examples include, but are not limited to, the following: polyvinyl alcohol), albumin, lecithin, polysorbates, sorbitan esters and ethoxylated sorbitan esters. A wide range of biological and chemical agents are suitable for use in the production of microparticles as herein described including, but not limited to, the following:

• flavours in foods and beverages, including confectionery (e.g. peppermint oil in chewing gum);

• nutrients (e.g. vitamins and minerals) in foods and beverages;

• cosmetics (e.g. for use in skincare products);

· food additives such as active ingredients in foods (e.g. raising agents in frozen bread dough);

• bioactive agents, e.g. pharmaceuticals;

• agrochemicals, for example pesticides, insecticides, herbicides;

• fragrances

· catalysts, including biocatalysts

• dyes and dye-containing liquids, pigments

• detergents

• textile chemicals

• metals

· paints

• oils

• fuels

Particlar examples of bioactive agents which may be provided in the microparticles include, but are not limited to, any of the following: proteins, nucleic acids, carbohydrates, peptides, small molecule pharmaceutical substances, immunogens, anti-neoplastic agents, hormones, anti-histamines, cardiovascular agents, anti-ulcer agents, bronchodilators, vasodilators, central nervous system agents, anti-infectives (e.g. anti-bacterial, anti-fungal, and anti-viral agents), anti-inflammatory agents, anti-hypertensives, analgesics, anaesthetics, etc.

Examples of pesticides which may be provided in the microparticles include organophosphate insecticides, e.g. ethion. The composition produced by the method of the invention contains a microparticle. In a particular embodiment, a microparticle has a diameter less than about 1 mm, and typically between about 1 and 200 microns. Microparticles include both microbeads and microcapsules, and these may be approximately spherical or have other geometries. In certain embodiments, the microparticle may be a nanoparticle. A nanoparticle may have a diameter in the range of from about 20 nm to about about 2 microns, typically in the range of about 100 nm to about 1 micron. For the production of nanoparticles emulsification to reduce the size of the emulsions to less than about 2 microns, e.g. less than about 1 micron is required.

Microcapsules produced according to the methods herein described may have advantageous properties in view of their size distribution. In some embodiments, the methods of the invention are able to provide microparticles having a narrow, reproducible, particle size distribution. The method is capable of the production of both large and small volumes of microparticles according to need.

Microparticles (e.g. microcapsules or microbeads) obtained or obtainable by any of the methods herein described form a further aspect of the invention. Compositions comprising such microparticles (e.g. microcapsules or microbeads) also form part of the invention.

The invention further extends to apparatus for carrying out the emulsion and/or microparticle production methods herein described. In another aspect the invention thus provides an apparatus for producing an emulsion of at least two immiscible liquids, said apparatus comprising a cyclone chamber connected to an outlet and to liquid sources of at least two immiscible liquids, wherein the cyclone chamber has a cross section which decreases in a direction away from the outlet and a closed base such that in use at least one of the liquids entering the chamber forms a reverse flow cyclone, in which the liquid travels in a first direction away from the inlet to the closed base and thereafter reverses direction and travels towards the outlet. ln the case where microparticle formation occurs within the cyclone chamber, the apparatus may further be connected to a source of a microparticle forming reagent, e.g. a shell forming agent. For the production of micro particles the cyclone chamber may further be connected to a second cyclone chamber or mixing chamber downstream. In another aspect the invention thus provides an apparatus for producing microparticles from at least two immiscible liquids, said apparatus comprising a cyclone chamber connected to an outlet and to sources of at least two immiscible liquids, wherein the cyclone chamber has a cross section which decreases in a direction away from the outlet and a closed base such that in use at least one of the liquids entering the chamber forms a reverse flow cyclone, in which the liquid travels in a first direction away from the inlet to the closed base and thereafter reverses direction and travels towards the outlet, and wherein said cyclone chamber is further connected to a second cyclone chamber or a mixing chamber.

As will be appreciated, the initial step of emulsification as herein described may be advantageous for the production of a uniform emulsion. The first step of producing an emulsion from at least two immiscible liquids as herein described thus forms a further aspect of the invention.

In a broader aspect the invention thus provides a method of producing an emulsion, wherein the method comprises the step of forming an emulsion from at least two immiscible liquids under cyclonic flow conditions (e.g. under reverse cyclonic flow conditions). Any of the features of the methods herein described in respect of the production of an emulsion for use in forming microparticles apply equally to this aspect of the invention. In one embodiment, the method of producing the emulsion is a continuous method. An emulsion obtained or obtainable by any of the methods herein described forms a further aspect of the invention.

A number of embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figs. 1 a and 1 b illustrate a cyclone chamber wherein there are two inlets to the cyclone chamber;

Fig. 2 illustrates the formation of a reverse flow cyclone in a cyclone chamber; Fig. 3 is a flow diagram illustrating emulsification of two liquids using a cyclone chamber;

Fig. 4 is a flow diagram illustrating the production of an emulsion comprising one liquid dispersed in another using a cyclone chamber;

Fig. 5 is a flow diagram illustrating the combination of three miscible liquids with one immiscible liquid in a cyclone chamber to form an emulsion (dispersion);

Fig. 6 is a flow diagram illustrating a feedback and control mechanism to control the properties of an emulsion formed in a cyclone chamber;

Fig. 7 is a flow diagram illustrating the production of microcapsules in a separate mixing chamber;

Fig. 8 is a flow diagram illustrating the production of microcapsules in a separate cyclone chamber;

Fig. 9 is a flow diagram illustrating the formation of an emulsion and production of microcapsules in a single cyclone chamber;

Fig. 10 is a flow diagram illustrating the production of microcapsules using a single cyclone chamber and the introduction of a further fluid which may be a gas or a liquid;

Fig. 1 1 is a schematic of an apparatus arranged to produce microcapsules in accordance with the present invention;

Fig. 12 is a cross section of a reverse cyclone chamber which may be used in accordance with the present invention.

Figs. 1 a and 1 b show a device 102, which uses a cyclone chamber 104 to produce an emulsion using a reverse flow cyclone which can then be withdrawn through the exit aperture 106. This embodiment comprises two ports for connecting to fluid sources 108, 1 10, which may be for two immiscible liquids or for a gas and a mixture of immiscible liquids, respectively. Where these are for a gas and a mixture of immiscible liquids, it will be understood that the mixture will comprise at least two immiscible liquids capable of forming an emulsion. These ports 108, 110 lead to fluid inlet arrangements 112, 1 13. The fluid inlet arrangements 112, 113 comprise feed-in tubes 114, 115 which taper from the ports 108, 110 to the cyclone chamber 104. This tapering allows fluid to enter the cyclone chamber 104 with minimal turbulence, and increases the velocity of the fluid. The feed-in tubes 1 12, 113 are tangential to the cyclone chamber 104, as can be seen from Fig. 1 b. This is beneficial to the formation of a reverse flow cyclone, helping to create a better quality emulsion from the immiscible liquids. The cyclone chamber 104 also contains a tapered outlet 116, which allows for the emulsion in the inner cyclone to be selected and withdrawn through (e.g. sprayed out of) the exit aperture 106. The tapered outlet is surrounded by a wall 1 18, which not only causes the tapering, but also prevents liquids from travelling directly from the inlet arrangements 112, 1 13 to the outlet 116 without forming a reverse cyclone.

Operation of the device will now be described with additional reference to Fig. 2. In use, the two liquids or the gas and mixture of liquids (herein referred to generally as "fluids") enter the cyclone chamber 104 tangentially from the inlets 112, and set up reverse cyclonic flow. The fluids follow the wall of the chamber, forming a spiralling path. This path advances along the length of the chamber, with the diameter of the path followed by the fluids decreasing as the chamber 104 tapers. When the fluids reach the base of the chamber 105, the flow is reversed, setting up a smaller vortex 122 which travels through the centre of the chamber 104. This combination of a large outer vortex 120 travelling in one direction and smaller vortex 122 travelling within the outer vortex 120 in the opposite direction is known as a reverse flow cyclone. There is substantial variation in tangential velocity across the cyclone chamber 104, which creates a steep velocity gradient. This causes efficient disruption of the fluids creating an emulsion from the at least two immiscible liquids which comprises droplets with a small variation in size. The shear forces generated act on the fluids both as they travel down towards the base of the chamber 105, and as they travel back towards the tapered outlet 116. This tapered outlet 1 16 is formed from a wall 1 17 which surrounds the exit aperture 106. This wall 117 extends from the exit aperture 106 past the fluid inlets 1 12, 1 13. This prevents the fluids travelling directly from the inlets 112, 113 to the exit aperture 106, and instead forces them to travel towards the base of the chamber 105, causing them to form a reverse flow cyclone as explained above. As this is a relatively long path, the fluids have an increased residence time in the chamber, enhancing mixing and increasing the quality of the emulsion produced. By also including a gas in the cyclone chamber 104, the shear forces acting on the immiscible liquids are increased, as due to the different molecular weights, there are also shear forces between the gas and liquids, as well as between the two vortices 120, 122.

The tapered outlet 1 16 is arranged such that droplets of a certain size pass through it, as shown by arrow 124, and are able to be withdrawn from (e.g. sprayed out of) the exit aperture 106. This is due to the combination of droplet size and pressure of the fluids, as the radius of the inner cyclone is dependent on droplet size, allowing for a particular size to be selected by changing the maximum outlet radius. Due to the presence of the reverse cyclone, there is no need for a sharp reduction in size at the exit aperture 106, as one of the two immiscible liquids has already formed droplets.

Fig. 3 is a flow diagram illustrating the production of an emulsion from two immiscible liquids: Liquid 1 and Liquid 2. The two liquids are introduced into a cyclone chamber to form a cyclone. This causes the two liquids to mix efficiently within the cyclone chamber and form an emulsion.

Fig. 4 is a flow diagram illustrating the production of an emulsion whereby Liquid 2 is dispersed within Liquid 1. It can be seen that the relative ratio of the liquids which enter the cyclone chamber is such that more than 50% of the total volume of the liquid which enters the cyclone chamber is in the form of Liquid 1 (i.e. the major component) and the volume of Liquid 2 which enters the cyclone chamber is less than 50% (the minor component). The result of supplying the relative volumes as described is an emulsion wherein Liquid 2 is dispersed in Liquid 1 , i.e. droplets of Liquid 2 are formed in the continuum of Liquid 1.

Fig. 5 illustrates a further embodiment of the method of the invention wherein more than two liquids are introduced into the cyclone chamber to form an emulsion comprising a dispersion of Liquid 2 in Liquid 1. In this embodiment three miscible liquids: Liquid A, Liquid B and Liquid C are introduced into the cyclone chamber via separate fluid inlets and a further immiscible liquid, Liquid 2, is introduced into the cyclone chamber via a different fluid inlet. The timing of introduction of the different liquids into the cyclone chamber may be varied, for example these may be introduced sequentially or simultaneously. On mixing, Liquids A, B and C effectively form Liquid 1 as seen in the previous embodiment illustrated in Fig. 4. Liquid 1 and Liquid 2 are immiscible with one another. In Fig. 5 Liquids A, B and C are depicted as being fed into the cyclone chamber separately. As will be understood, these need not be the case and in other embodiments Liquids A, B and C may in fact be mixed before entering the cyclone chamber via a single fluid inlet. As will be understood, the choice of three liquids to form Liquid 1 is merely illustrative of one embodiment of the invention; this liquid may be formed from any number of different miscible liquids as desired. As is the case in Fig. 4 the relative volume of Liquid 2 entering the cyclone chamber is less than 50% of the total volume of liquid and therefore the resulting emulsion comprises a dispersion of Liquid 2 in a continuum of Liquid 1. In Fig. 5 Liquid2 is depicted as a single liquid. As would be understood, in other embodiments, this may comprise a mixture of two or more liquids which are miscible with one another to form Liquid 2. Where two or more liquids are used to form Liquid 2 the set-up and arrangement for their introduction into the cyclone chamber may be as discussed above in respect of Liquid 1.

Fig. 6 illustrates a method of measuring and controlling microcapsule size in accordance with an embodiment of the invention. As is described above, it may be desirable to control the size and/or size distribution of the microcapsules during production. This may be achieved by determining the size of the microcapsules once they have formed and/or by determining the size of the droplets which form within the emulsion prior to formation of the microcapsules. Fig. 6 illustrates an embodiment wherein the size of the droplets is determined rather than the size of the microcapsules. This may be advantageous in that it may be possible to react more quickly and modify the various processing parameters to ensure that the desired size distribution of droplets (and thus microcapsules) is produced. In the embodiment shown in Fig. 6 two liquids, Liquid 1 and Liquid 2, are pumped into a cyclone chamber using pumps P1 and P2, respectively. Liquid 1 and Liquid 2 form a cyclone and mix to form an emulsion. The size of the droplets formed of one liquid in the other is then determined. This may be measured directly or may be determined by other means. Once the size distribution of the droplets has been determined this may then be compared to the desired size distribution. In the embodiment shown in Fig. 6 the size of the droplets may be subsequently modified by sending feedback to the pumps P1 , P2 to control the relative flow rates of the two liquids whereby to change the size distribution of the droplets formed in the emulsion. As described above, controlling the flow rates is merely one means by which the properties of the emulsion can be altered and it will be appreciated that the measurement and control system may feedback to other components of the system which are capable of altering the properties of the emulsion. The measurement and control system may be introduced at various different stages of the production.

Fig. 7 illustrates an embodiment of the present invention in which microcapsules are produced. In this embodiment monomer A and monomer B are polymerisable with one another to form a polymer coating which surrounds droplets of Liquid 2. In the method which is shown, two immiscible liquids, Liquid 1 and Liquid 2 are introduced into a cyclone chamber. In this particular embodiment Liquid 2 also comprises monomer A. As in other examples, the relative volumes of these liquids may be such that the volume of Liquid 1 accounts for more than 50% of the total volume of liquid introduced into the cyclone chamber and the volume of Liquid 2 + monomer A accounts for less than 50%. The product of mixing these two liquids in the cyclone chamber is an emulsion in which Liquid 2 + monomer A is dispersed in a continuum of Liquid 1. The output of the cyclone chamber is subsequently fed into a mixing chamber which may, for example, be a static mixing chamber or a dynamic mixing chamber. A further quantity of Liquid 1 comprising monomer B is introduced into this mixing chamber whereby to form microcapsules. As will be understood, the precise timing and location of introduction of monomer A and monomer B may be varied, for example monomer A may be introduced together with Liquid 1 into the cyclone chamber and monomer B may be introduced together with a further quantity of Liquid 1 into the mixing chamber. In other embodiments, monomer A and monomer B may be introduced to the cyclone chamber and mixing chamber separately from either Liquid 1 or Liquid 2. As an alternative to the mixing chamber, a container (e.g. a tank) which contains a liquid comprising monomer B (e.g. Liquid 1 + monomer B) may be used.

Fig. 8 illustrates an alternative embodiment of the present invention for the production of microcapsules wherein the step of forming an emulsion from two immiscible liquids is achieved in a first cyclone chamber, cyclone 1 , and the step of microencapsulation is performed in a separate cyclone chamber, cyclone 2, which is provided downstream of cyclone 1. As shown, the introduction of the various liquids and monomers is the same as in the example of Fig. 7. The difference between the method seen in Fig. 7 and that in Fig. 8 is that the step of

microencapsulation takes place in a second cyclone chamber rather than a standard mixing chamber. Any of the different embodiments described above in respect of Fig. 7 relating to the introduction of liquids and monomers A and B may apply equally to the embodiment shown in Fig. 8.

Fig. 9 illustrates another alternative embodiment of the present invention for the production of microcapsules wherein the formation of an emulsion from two immiscible liquids and the step of microencapsulation is performed within the same cyclone chamber. In this embodiment, Liquid 1 comprising monomer A is introduced into the cyclone chamber in an amount greater than 50% of the total volume of liquid and Liquid 2 comprising monomer B is introduced in an amount less than 50% of the total volume of liquid which is introduced into the chamber. Upon mixing of Liquid 1 and Liquid 2 to form the emulsion, monomer A and monomer B come into contact and polymerise. The resulting microcapsules comprise Liquid 2.

Fig. 10 illustrates a similar embodiment to that seen in Fig. 9 in which the step of mixing at least two immiscible liquids to form an emulsion and the step of microencapsulation is performed in a single cyclone chamber. However, this embodiment differs in that an additional fluid, Fluid 3, is introduced into the cyclone chamber. Fluid 3 may be a gas or a liquid. Liquid 1 comprising monomer A and fluid 3 are introduced to the cyclone chamber and together account for more than 50% of the total volume of the liquids entering the chamber. Liquid 2 comprising monomer B is introduced into the chamber and accounts for less than 50% of the total volume of the liquids entering the chamber. Liquid 1 and Liquid 2 are immiscible and together form an emulsion. Monomer A and monomer B are polymerisable to form a polymer coating. The resulting microcapsules contain Liquid 2. Where Fluid 3 is a liquid this should be miscible with the continuous phase (i.e. Liquid 1) rather than the dispersed phase (Liquid 2).

Fig. 1 1 illustrates an apparatus which may be used in accordance with the present invention. The apparatus comprises two separate but interconnected cyclone chambers, cyclone 1 and cyclone 2, and three separate sources of solutions, solution A, solution B and solution C which are connected to inlets to the cyclone chambers via pumps, P1 , P2 and P3, respectively. In this embodiment the output of cyclone 1 is connected to an input of cyclone 2. Solution A is provided to cyclone 1 through the use of a pump, P1 , and also solution B is provided to cyclone 1 through the use of a pump, P2. The output of cyclone 1 is fed into cyclone 2, which also has a separate feed of solution C which is provided through the use of a pump, P3. An emulsion is formed in cyclone 1 which is fed into cyclone 2. The output of cyclone 2 is microcapsules. The properties of the microcapsules will vary depending on the choice of the solutions and any reagents selected for use in forming the microcapsule coating.

Fig. 12 illustrates a cross section of a cyclone chamber for use in the invention in which a reverse cyclone may be established when at least two immiscible liquids are introduced. It can be seen that the relative dimensions of the chamber are indicated. These relative dimensions are merely one illustrative example of a type of cyclone chamber which may be used in accordance with the invention. X may be for example: 5 mm, 10 mm, or 20 mm. Of course it may be possible for

considerably larger chambers to be used depending on the particular application. The invention is illustrated further by way of the following non-limiting examples:

Example 1 - Experimental set-up for emulsion and microcapsule production

An experimental setup was constructed to demonstrate microencapsulation using either a one or two chamber process. The system was constructed to allow the independent supply of three separate liquids. Three 24 V gear pumps were used in order to supply the liquids to the mixing chambers (Fluid-O-Tech

FG304XA0PV10000). The speed of each of these pumps could be independently controlled with a separate 0-5V control input.

The system was flexible and allowed the use of a single reverse flow cyclone chamber; two reverse flow cyclone chambers in series; or the use of a reverse flow cyclone chamber in series with a mixing chamber (non-cyclone). Reverse flow cyclone chambers of various sizes were constructed - see Fig. 12 in which X is 5 mm, 10 mm or 20 mm. Example 2 - Encapsulation of liquid paraffin in nylon shells using two cyclone chambers The following solutions were prepared:

A. 16 g/l of sodium carbonate (Sigma Aldrich) in deionised water with 2.4 g/l of Tween 20 and 8 g/l of Span 20 (Sigma Aldrich - Tween and Span are trademarks of Croda International PLC)

B. Liquid paraffin (APC Pure) containing 32 g/l of sebacoyl chloride (Sigma Aldrich)

C. 250 g/l of hexamethylenediamine (HMDA) (Sigma Aldrich) in deionised water with 20 g/l of Tween 20 to aid in dispersion of the resulting

microcapsules

The equipment detailed in Example 1 was arranged such that pumps 1 and 2 were connected directly to the input of cyclone chamber 1 (10 mm diameter). The output from the first cyclone chamber was used as one of the inputs to a second cyclone chamber (20 mm diameter), together with the output from pump 3. The output of the second cyclone chamber was then directed to a collection vessel for later analysis of the product.

Pumps 1 and 3 were set running with flow rates of 7 ml/s of solution A and 23.5 ml/s of solution C, respectively. Once flow has stabilised, pump 2 was switched on with a flow rate of 7 ml/s of solution B. A flow of a white milky suspension was produced from the output of the system. Characterisation of this suspension under a microscope showed that microcapsules have been formed. Characterisation of this suspension in the Malvern Mastersizer shows a mean particle size of 86 microns.

Example 3 - Encapsulation of liquid paraffin in nylon shell using a single cyclone chamber

The process of Example 2 is carried out but instead using a single cyclone chamber.