Mixing immiscible liquids

0001The present invention relates to methods or processes of mixing substantially immiscible liquids.

0002The invention is concerned with methods of mixing immiscible liquids in order to produce, for example, detergent compositions. It is commonly desired to provide detergent compositions which comprise at least two immiscible liquids, for example a surfactant composition and a benefit agent dispersed therein. Examples of such detergent compositions are set out in WO 96/02224 and WO 96/02225 as well as WO 96/02229, all of which are incorporated herein by reference.

0003It is frequently desired to control the average droplet size of the dispersed phase in such mixtures of immiscible liquids. For example, in WO 96/02224 and WO 96/02225, it is desired that the benefit agent has a weight average droplet size in the range 50-500 microns.

0004Methods and apparatus for mixing substantially immiscible liquids are well known in the art. For example, high shear mixers such as turbine mixers, cavity transfer mixers or static mixers can be used. EP-A-0761724 describes a method for the continuous preparation of organopolysiloxane emulsions which comprises two steps. In the first step, polysiloxane gum, water and emulsifying agent are fed into a mixer having a first stage comprising a turbine-type rotor, a relaxation stage and a final stage comprising a turbine-type rotor. In common with many prior art processes for the production of emulsions, the final stage appears to have the function of reducing the average particle size (i.e., producing a finer emulsion) of the product leaving the first stage. More shear is accordingly applied in the final stage than in the first stage.

0005In the second step, the emulsion of the first step and diluting water are fed into a mixer of generally the same design as that used in the first step. In common with many prior art processes, the product of the first step is mixed with another component before entering the second step.

0006However, in addition to controlling the average droplet size, it may also be desirable to control the distribution of droplet sizes. In particular, it may be particularly desirable to have a narrow droplet size distribution, in which a relatively large percentage of the droplets are within a given range of the average droplet size.

0007An article by Harold P. Grace entitled "Dispersion phenomena in high viscosity immiscible fluid systems and application of static mixers as dispersion devices in such systems" (Chemical Engineering Communications, Vol. 14, pp 225-277) contains descriptions of experiments in which a mixture of immiscible fluids is passed through two or more static mixers in series, preferably separated by a relaxation zone. In the experiments described on page 256-258, the second mixer applies the same or a higher shear to the mixture than the first mixer, and a narrower drop size distribution is obtained than passing the mixture through a single static mixer.

0008The present inventors have discovered that, where a first liquid (the "dispersed phase") is dispersed in a second liquid (the "continuous phase") with which it is substantially immiscible, by subjecting it to a first mixing step, the quantity of droplets of size outside a certain range from the average droplet size can be reduced by subjecting the mixture to at least one further mixing step in which the dispersion is subjected to less shear than in the first mixing step. This applies particularly to the case where substantially no further components are added before the second mixing step.

0009Accordingly, in a first aspect, the present invention provides a method or process of dispersing a first liquid in a second liquid with which it is substantially immiscible, comprising the steps of subjecting the first and second liquids to a first mixing step to produce a first dispersion of the first liquid in the second liquid, and subjecting the first dispersion, without addition of substantial quantities of further components, to a second mixing step, to produce a second dispersion of the first liquid in the second liquid, wherein the first dispersion is subjected to same or lower shear, preferably lower, in the second mixing step than is applied to the first dispersion in the first mixing step.

0010In a second aspect, the present invention provides a method of treating a dispersion of a first liquid in a second liquid with which it is substantially immiscible, to reduce the quantity of droplets of size outside a given range from the average droplet size, comprising subjecting the dispersion to a mixing step of the same shear or lower as the mixing step in which the dispersion was produced.

0011In the second aspect of the invention, the second mixing step is used to reduce the quantity of droplets of size outside a given range from the average droplet size.

0012The invention will now be further described by way of example only with reference to the accompanying drawings, in which: <ul id="ul0001" list-style="dash"><li>Figure 1 shows a schematic illustration of apparatus for use with the method of the first or second aspect of the invention;</li><li>Figure 2 shows a suitable means of introducing a flow of first liquid into a flow of second liquid;</li><li>Figure 3 shows a schematic illustration of apparatus according to the third aspect of the invention where the liquid may be recycled; and</li><li>Figures 4, 5 and 6 are graphs of droplet size distribution obtained with the apparatus of Figures 1 and 3.</li></ul>

0013The present invention is suitable for dispersing any liquid in another liquid with which it is immiscible. The present invention is particularly suitable for mixing a liquid surfactant composition selected from anionic, nonionic, zwitterionic and cationic surfactant agents or solutions thereof, and a substantially immiscible benefit agent, for example as set out in WO 96/02224. The present invention is particularly suitable for mixing silicone oils, gums and modifications thereof such as linear and cyclic polydimethylsiloxanes, amino, alkyl, alkyl aryl and aryl silicone oils with surfactant compositions.

0014Other examples of benefit agents are set out in WO 96/02224.

0015The relative quantities of first and second liquids is not critical. Preferably, there is a greater quantity by volume of second liquid than first liquid, preferably at least twice the quantity.

0016The first and second liquids may be of any desired viscosities. The present invention is, however, particularly suitable for mixing liquids with viscosities in the range 0.001 to 100 Pas at a shear rate of 100 s^-1.

0017The first liquid may be partially soluble in the second liquid, as long as at least part of the first liquid forms a separate phase.

0018The process of the present invention may be used to produce surfactant compositions as set out in fore example WO 96/02224, WO 96/02225 and WO 96/02229. The surfactant composition produced may comprise for example a washing composition, shampoo or body washing composition.

0019The present invention may also be used in the production of food stuffs, or personal products such as cosmetics.

0020The first and second dispersions are preferably of the type which can be described as an emulsion with the first liquid as the dispersed phase and the second liquid as the continuous phase.

0021The first step is preferably carried out in a relatively high shear mixer such as a cavity transfer mixer, extruder mixer, mixer with stirring element(s), colloid mill, ball mill, turbine-type mixer, or an intensive mixer. More preferably, however, the first step is carried out in a static mixer.

0022The present invention is particularly concerned with dispersing immiscible liquids using static mixers. Static mixers are will known in the art. They comprise means for mixing media, in which there are substantially no moving parts. Instead, the internal configuration of the static mixer is such that when a fluid medium is passed through it, turbulence and/or shear is generated, whereby mixing or dispersion can occur.

0023Any suitable kind of static mixer may be used for the first mixing step. In a0 static mixer, mixing action is achieved by the continuous splitting, extension and transposition of flow components.

0024The internal configuration of the static mixer may be defined by vanes, baffles, flow splitters and flow dividers, tubes, helixes or any other suitable device. Suitable static mixers are produced, for example by Kenics (trademark) and Sulzer (trademark).

0025It is important to note that it is not the absolute speed of the first or second mixer which are critical to the invention, but the relative shear imparted by the second mixer relative to the first, e.g., the second must be same or lower, preferably lower.

0026The first and second liquid may be fed to the static mixer in any suitable manner. For example, there may be a simple junction pipe before the static mixer. Alternatively, a stream of the first component may be injected into a stream of the second component through a tube which is arranged at a small angle or substantially parallel to the flow direction. This minimizes mixing before the static mixer, and allows improved control of particle size distribution. The first component is preferably injected flowing in the same direction as the second component, but it may be injected flowing in the reverse direction.

0027Preferably, a relaxation step or low shear step is provided between the first and second mixing steps. In the low shear step, the first dispersion of the first liquid in the second liquid is subjected to equal, preferably less, shear than in the first static mixing step or the second mixing step. The low shear step may comprise feeding the first dispersion into a container. However, the low shear step may simply comprise a pipe length. The first dispersion flowing through the pipe will be subject to a certain amount of pipe shear at the edges, but this may be minimized by having a low flow velocity and most of the dispersion flowing through the pipe will be distant from areas of shear. Preferably, the pipe length shall be at least 1, preferably at least 3, more preferably 10 diameters in length. In general there is no criticality to the pipe length. In the low shear step, the shearing to which the dispersion is subjected is "relaxed".

0028The mixer of the second mixing step may comprise a duct having a screen, baffle or nozzle, or a second, lower shear static mixer.

0029Where static mixers are used for the mixing steps, it is particularly preferred that the first and second static mixers are substantially different. For example, they may be of different diameter. Preferably, the second static mixer is of larger diameter than the first static mixer.

0030According to the present invention, there may be further mixing steps through which the dispersion is passed; preferably each mixing step is separated from the previous mixing step by a relaxation step.

0031Where a plurality of static mixers are used in series, the last static mixer should preferably be that which applies the lowest shear to the liquid dispersion. Preferably, each successive mixer applies less shear than the mixer upstream of it.

0032Instead of passing the mixture through two mixers in series, the inventors have discovered that a similar effect may be obtained if the dispersion is passed at least twice through the same mixer. Thus according to a third aspect of the invention there is provided a method or process of dispersing a first liquid in a second liquid with which it is substantially immiscible, comprising the steps of placing at least one of the first or second liquids in a storage vessel, feeding the liquids to a mixer to provide a first dispersion of the first liquid in the second liquid, the first dispersion being fed from the storage vessel back to the mixer, without addition of substantial quantities of further components to the vessel.

0033This aspect provides a modification of the invention defined above, in that some of the liquid originally in the vessel may still be present when the first dispersion reaches the vessel. Accordingly, the first dispersion is mixed to a certain extent with the addition of the first or second liquid component from the vessel. However, no substantial addition of further components other than the first and second liquids takes place. This is distinct from known processes, where a new component is dosed into the vessel or dispersion after the first dispersion is returned thereto.

0034In this aspect of the invention, the storage vessel may have a volume which is substantially equal to the volume of liquid in the pipes and static mixer, but is preferably at least 5 times the volume of liquid in the pipes and static mixer.

0035A low shear mixing device such as a stirrer may be additionally provided in the storage vessel. The mixing device may be any one of a variety of devices which are well known to those skilled in the art.

0036In this aspect of the present invention, the first dispersion is circulated through the static mixer for a sufficient period of time so that, on average, substantially all of the first liquid and the second liquid pass at least twice through the mixer. Preferably, this is achieved by ensuring that the volume that has passed through the mixer is equal to at least twice, more preferably at least three times the total volume of first and second liquid.

0037In this aspect of the invention, the second liquid may be stored in the storage vessel before mixing with the first liquid.

0038The process of this aspect of the invention may be run continuously, with the dispersion being removed continuously from the storage vessel or from a point down stream of the mixer. The inflow rate of first liquid and second liquid and the removal rate of dispersion thereof may be balanced with the rate of flow of liquid through the static mixer so that, on average, the residence time of liquid in the system is such that it must pass at least twice through the mixer.

0039The second aspect can provide the use of a first and second mixer to provide a dispersion of a first liquid in a second liquid, which dispersion has substantially the same average droplet size but a narrower droplet size distribution than would be obtainable by passing the first and second liquid through the first or second mixer, comprising passing the first and second liquid through the first and second mixer in sequence.

0040In the first, second and any subsequent dispersion, the first liquid will exist as droplets (the dispersed phase) in the second liquid (the continuous phase). The skilled person will be able to select process parameters to ensure that a desired average particle size is obtained. For example, the relative viscosities of the first and second liquid must be taken into account. The flow rate through the mixer, the design of mixer and the length and diameter of the mixer may be altered appropriately. Alterations to these parameters may be made by the skilled person without inventive experimentation in order to obtain the optimum parameters for any given target droplet distribution.

0041The droplet size distribution is typically measured by a Malvern Mastersizer (Mastersizer is a Trademark).

0042The shear rate in the first and second mixing step may be measured or calculated, for example, by one of the following methods: <ul id="ul0002" list-style="none"><li><u>FOR SMX (SULZER) DESIGN:</u> shear rate = (K) times (velocity) [=] 1/sec K = f(diameter);    K(0.62") = 146 1/inch    K(1.02") = 77 1/inch In general, any size diameter may be used although of course, different diameters will have a different K value which can be obtained, for example, from the manufacturer. </li><li><u>FOR KMS (KENICS) DESIGN:</u> shear rate = (3) times (shear in empty pipe) = (3) times (8 times velocity/diameter of pipe) [=] 1/sec.</li></ul>

0043The shear rate will depend upon the mixer design and operating conditions as noted in the equations above. However, as no substantial quantity of additional components are added between the first and second steps, it is relatively simple to compare the shear rate in the two mixing steps.

0044It is acceptable to add minor quantities of additional components such as dye, perfume, and further diluent.

0045The quantity of additional components added should be at such a level that it does not substantially affect the shear applied to the dispersion in any given mixer.

0046Preferably, the level at which additional component is added is less than 20% by weight, more preferably less than 10% by weight, based upon the quantity of first dispersion.

0047The present invention may be used to mix more than two substantially immiscible liquids if necessary, the components being all added to the first mixing step.

0048The quantity of droplets of size outside a given range from the mean size may be represented by the span, defined as follows:<maths id="math0001" num=""><math display="block"><mrow><mtext>Span = D(50)/[D(90)-D(10)]</mtext></mrow></math><img file="EP0937495A2_D0001.tif" /></maths>

0049The terms in the equation are defined as follows:

0050It is assumed that the droplets have a generally normal particle size dispersion. It is assumed that the droplets are generally circular. By definition, 50% of the distribution has a droplet size which is smaller than the diameter D(50). Similarly, 10% of the droplets in the distribution have a size which is smaller than the diameter D(10) and 90% of the droplets have a size smaller than the diameter D(90).

0051According to the present invention, there is provided a method of decreasing Span as defined above.

0052The present invention will be described by way of example only with reference to the accompanying drawing in which: <ul id="ul0003" list-style="dash"><li>Figure 1 shows a schematic illustration of apparatus for use with the method of the first or second aspect of the invention;</li><li>Figure 2 shows a suitable means of introducing a flow of first liquid into a flow of second liquid;</li><li>Figure 3 shows a schematic illustration of apparatus according to the third aspect of the invention; and</li><li>Figures 4, 5 and 6 are graphs of droplet size distribution obtained with the apparatus of Figures 1 and 3.</li></ul>

0053The apparatus of Figure 1 comprises a first vessel 1 for containing the first liquid and a second vessel 2 for containing the second liquid. The second vessel 2 may have a stirrer 3 for preventing the settling of components in the second liquid. Pumps 4 and 5 deliver the first and second liquids to a junction, which will be described further below in relation to Figure 2. The liquids pass from the junction to a first static mixer, shown schematically at 6. The pump rates are set, centrally or otherwise, so that the desired ratio by volume of first to second liquid is achieved.

0054Downstream of the first static mixer 6 there is a pipe 7 of approximately 2 pipe diameters in length. This zone 7 provides a low shear zone in which the dispersion of first liquid in second liquid is subjected to very low shear. Downstream of the low shear zone 7 there is a second static mixer.

0055It should be understood that a relaxation or low shear zone (i.e., 7) is not required, and that the process may be conducted without such a zone being present. That is, for example, the mixers could be set up back to back, particularly, for example, if the two mixers are of two different designs.

0056A refined dispersion 9 is collected at the end of the apparatus.

0057Figure 2 shows a suitable junction arrangement whereby a flow of first liquid may be introduced into a flow of second liquid before being fed into the first static mixer 6. Flow is in the direction shown by the arrows. In pipe 10 there is a nozzle 12 at the end of a pipe 13 which is arranged generally parallel to the flow direction. First liquid is pumped out of the nozzle 12. Preferably, the flow rate of the first liquid is such that the flow velocity is the same as or greater than the flow velocity of the second liquid to minimize shear before entry into the static mixer.

0058Figure 3 is a schematic illustration of apparatus according to the third aspect of the invention. As above, there is a first vessel 14 for the first liquid and a second vessel 15 for the second liquid. Pumps 16 and 17 deliver first and second liquid to a junction, 18, which may be as set out in Figure 2. The liquids are then supplied to a static mixer 19. Downstream of the static mixer 19 there is a recycle line 20 which delivers first dispersion 21 back into vessel 15. An agitator 22 is provided in the vessel 15. The agitator is designed so that it applies very low shear to the mixture of first dispersion and second liquid in vessel 15. The agitator is provided in order to ensure that there is a statistically high chance of all parts of the liquid volume contained in vessel 15 being delivered by the pump 16 to the static mixer 19. Suitable designs of low shear agitator will be familiar to the person skilled in the art. Delivery means 23 are provided for extracting the liquid dispersion from the vessel 15 or pipe 20 after the dispersion has been passed a sufficient number of times through the static mixer 19.

0059Except in the operating and comparative examples, or where otherwise explicitly indicated, all numbers in this description indicating amounts or ratios of materials or conditions of reaction, physical properties of materials and/or use are to be understood as indicated by the word "about".

0060Where used in the specification or claims, the term "comprising" should be understood to include the presence of stated features, integers, steps, components etc., but not to preclude the presence or addition of one or more features, integers, steps components or groups thereof.

0061The present invention will be further described by way of reference only with regard to the following examples. The examples are not intended to be limiting in any way.

Example 1

0062An apparatus according to Figure 1 was set up with the following conditions.

0063The first mixer 6 comprised a static mixer having six Sulzer SMX elements. The mixer 8 comprised a 25.4cm (twelve inch) Kenics (trademark) KMS mixer, which applies lower shear to the dispersion than the mixer 6.

0064A first liquid comprising silicone oil and a second liquid comprising a xanthan gum-based shower gel was passed through the mixers at a rate of 2 kg/min.

Comparative Example A

0065The same liquid was mixed with a single pass through a single mixer comprising six Sulzer SMX elements.

0066The results of Example 1 and Comparative Example A are shown in Figure 4. It can be seen that the method of the invention allows the droplet size distribution to be narrowed without substantially affecting the average droplet size.

Example 2

0067An apparatus according to Figure 1 was set up as follows.

0068The first mixer comprised a relatively high shear mixer comprising 3 sets of 3 Sulzer SMX elements with 2.54 cm (one inch) spacer elements between the sets. The second mixer 8 comprised a 15.2 cm (six inch) Kenics KMS mixer which applies lower shear to the dispersion than the Sulzer SMX elements.

0069The first liquid comprised silicone oil. The second liquid comprised a liquid hydrogel.

Comparative Example B

0070The same liquid was passed through an apparatus similar to Figure 1, but in which the mixers 6 and 8 and the pipe length 7 are replaced with a single mixer comprising 3 sets of 3 Sulzer SMX elements with 2.54 cm (one inch) spacers between the sets.

Comparative Example C

0071The apparatus of Figure 1 was set up with the following modification.

0072The mixer 6 comprised a relatively low shear mixer comprising a 15.2 cm (six inch) Kenics mixer. The mixer 8 was replaced with a mixer comprising 3 sets of 3 Sulzer SMX element mixer with 2.54 cm (one inch) spacers between the sets which applied higher shear than the Kenics mixer.

0073The droplet size distribution of a liquid produced by passing the liquid mixture through the apparatus of Examples 2 and Comparative Examples B and C are shown in Figure 5. It can be seen that the method of the invention yields a narrower droplet size distribution than the single mixer or the lower shear mixer followed by the higher shear mixer.

Example 3

0074An apparatus according to Figure 3 was set up and used as follows.

0075Silicone oil of viscosity 60,000 centistokes (cst) was placed in the vessel 14.

0076A substantially homogeneous liquid mixture comprising the following ingredients (all parts are by weight) was manufactured spear and placed in vessel 15. <tables id="tabl0001" num="0001"><table frame="all"><tgroup cols="2" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="78.75mm" /><colspec colnum="2" colname="col2" colwidth="78.75mm" /><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">Hectorite Clay (Laponite XLS Solution)</entry><entry namest="col2" nameend="col2" align="right">1.00</entry></row><row><entry namest="col1" nameend="col1" align="left">Glycerine (Precerine 9083)</entry><entry namest="col2" nameend="col2" align="right">12.0</entry></row><row><entry namest="col1" nameend="col1" align="left">Potassium Hydroxide Solution (48% by wt.)</entry><entry namest="col2" nameend="col2" align="right">3.90</entry></row><row><entry namest="col1" nameend="col1" align="left">Oleic Acid (Priolene 6907)</entry><entry namest="col2" nameend="col2" align="right">3.20</entry></row><row><entry namest="col1" nameend="col1" align="left">Myristic Acid (Prifrac 2940)</entry><entry namest="col2" nameend="col2" align="right">6.40</entry></row><row><entry namest="col1" nameend="col1" align="left">Lauric Acid (Prifrac 2920)</entry><entry namest="col2" nameend="col2" align="right">6.40</entry></row><row><entry namest="col1" nameend="col1" align="left">EDTA Solution</entry><entry namest="col2" nameend="col2" align="right">0.1</entry></row><row><entry namest="col1" nameend="col1" align="left">Cocoamidopropylbetaine (Dehyton k) (30% Solutions)</entry><entry namest="col2" nameend="col2" align="right">5.0</entry></row><row><entry namest="col1" nameend="col1" align="left">Butyl Hydroxy Toluene</entry><entry namest="col2" nameend="col2" align="right">0.05</entry></row><row><entry namest="col1" nameend="col1" align="left">Perfume</entry><entry namest="col2" nameend="col2" align="right">1.80</entry></row><row><entry namest="col1" nameend="col1" align="left">Styrene/Acrylate Copolymer (Lytron 621 B)</entry><entry namest="col2" nameend="col2" align="right">0.40</entry></row><row><entry namest="col1" nameend="col1" align="left">Formaldehyde Formalin</entry><entry namest="col2" nameend="col2" align="right">0.04</entry></row><row><entry namest="col1" nameend="col1" align="left">NaCl (25% Solution) up</entry><entry namest="col2" nameend="col2" align="right">up to 2.00</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">Chlorinated Demineralized Water</entry><entry namest="col2" nameend="col2" align="right">30.15</entry></row></tbody></tgroup></table></tables>

0077The apparatus was run so that pump 17 delivered five parts by weight of silicone oil while pump 16 delivered 95 parts by weight of the above mentioned liquid mixture. The static mixture comprised a three element Sulzer SMX static mixer.

0078The apparatus was run with liquid mixture being recirculated to the vessel. The re-circulation rate was set at 100 kg/hr.

0079The apparatus was run until all the silicone oil had been dosed in. Thereafter, a clock was set to zero and the run continued. The droplet size distribution for the dispersion of first liquid and second liquid was assessed at different times after the clock was started.

0080The number of re-circulations to which each measurement corresponds is not exact, as it cannot be guaranteed that every part of the material in the vessel 15 is re-circulated each time. However, an approximation was reached by multiplying the re-circulation time in minutes by 0.04. Since the mass of liquid in the vessel is 40 kg. and the re-circulation rate is 100 kg./hr., the mean re-circulation time per unit mass is approximately 24 minutes. <tables id="tabl0002" num="0002"><table frame="all"><tgroup cols="2" colsep="1" rowsep="1"><colspec colnum="1" colname="col1" colwidth="78.75mm" /><colspec colnum="2" colname="col2" colwidth="78.75mm" /><thead valign="top"><row><entry namest="col1" nameend="col1" align="center"><b>Time/Minutes</b></entry><entry namest="col2" nameend="col2" align="center"><b>Number of Re-Circulations</b></entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="center">7</entry><entry namest="col2" nameend="col2" align="center">just commenced</entry></row><row><entry namest="col1" nameend="col1" align="center">25</entry><entry namest="col2" nameend="col2" align="center">1</entry></row><row><entry namest="col1" nameend="col1" align="center">55</entry><entry namest="col2" nameend="col2" align="center">2</entry></row><row><entry namest="col1" nameend="col1" align="center">18</entry><entry namest="col2" nameend="col2" align="center">3</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="center">147</entry><entry namest="col2" nameend="col2" align="center">6</entry></row></tbody></tgroup></table></tables>

0081The results are shown in Figure 6.

0082It can be seen from Figure 6 that repeated circulations using the apparatus of Figure 3 result in progressive narrowing of the particle size distribution without substantially altering the average droplet size.