Patent Application
20050237854
The present invention relates to a method for continuously and dynamically mixing at least two fluids. This method is particularly suitable for rapid and/or complex kinetic chemical reactions such as anionic polymerizations.
The invention also relates to a micromixer which is able to implement this method.
Currently, one of the most commonly used techniques for mixing two or more liquids consists of using a closed, semi-closed or open vessel, equipped with a mechanical stirrer of propeller, turbine or similar type, and injecting one or more of the reagents into the vessel.
The mixing can be carried out due to the energy dissipated by the mechanical stirring. Unfortunately, in certain cases, these devices do not allow micromixing times to be achieved which are sufficiently short for rapid and complex reactions to be implemented, and above all, they are unsuitable in the case of polymerization reactions where the viscosity increases rapidly over time.
The static mixers, placed in line in a conduit or at the inlet of a reactor, allow a good mixing of the liquids. Nevertheless, they are, most of the time, used as premixers before entering into a reactor or when the constraints of time or viscosity are not redhibitory. These devices are good for homogenizing solutions, but are not really suitable for certain polymerization reactions, in particular rapid reactions, because the risks of blocking up are significant. This is the case, in particular, for polymerizations with high levels of solid.
The tangential jet mixers (which can be used in particular for anionic polymerizations as described in EP-A-0749987) or RIM (“Reaction Injection Molding”) mixing heads are confined jet mixers, i.e. with jets in contact with the wall of the mixer. They are very efficient, but cause blockages when high polymer contents are involved, or require the injection of products by pumps which are resistant to high pressures (several hundreds of bars). Moreover the RIM mixing heads require discontinuous operation.
The mixer by impact of free jets (i.e. without the jets being in contact with the walls of the mixer) is known and has been described for creating emulsions or in liquid-liquid extraction methods, for example by Abraham TAMIR, “Impinging-Stream Reactors. Fundamentals and Applications”, Chap. 12: Liquid-Liquid Methods, Elsevier (1994).
Devices with free jet impact have also been described for precipitation or polymerization. They are constituted by two jets orientated according to a given angle and the impact of which causes a rapid micromixing; cf. Amarjit J., Mahajan and Donald J. Kirwan “Micromixing Effects in a Two Impinging-Jets Precipitator, Aiche Journal, Vol. 42, no. 7, pages 1801-1814 (July 1996); Tadashi Yamaguchi, Masayuki Nozawa, Narito Ishiga and Akihiko Egastira “A Novel Polymerisation Method by Means of Impinging Jets”, Die Angewandte Makromolekulare Chemie 85 (1980) 197-199 (no. 1311). The drawback of these systems is that they only allow the mixing of two fluids and that the jets are all of the same diameter and, consequently, if the mixture is to be effective, the respective flow rates in each jet must be the same. In the case of a polymerization reaction, the monomer arriving in a first jet and the initiator solution in a second jet with the same flow rate as the first, it is thus seen that the quantity of solvent in the system is necessarily relatively large, which means that recycling operations, which are generally costly, have to be envisaged downstream of the polymerization method.
Then a method was developed which is described in the French patent application published under the no. 2 770 151 for continuously mixing by free jet impact at least 2 fluids and recovering the mixture in the form of a resulting jet, so as to overcome the limitations which have just been described.
However, the drawback of this system is that it requires a very precise adjustment of the injection device in order that the jets of fluids correctly come into contact at a given point.
In the international patent application published under the no. WO 97/10273 a device is described for dispersing isocyanate-terminated polyurethane prepolymers comprising a dynamic mixer allowing an average residence time of 10 to 120 seconds to be achieved. However, this type of mixer is not suitable for the more rapid reactions whose average residence time in the mixer must be much shorter, in order to allow a mixing of the reagents in a sufficiently short time compared to the reaction half-life. As when the reaction and mixing rates are of the same order of magnitude, strong competition arises between these two methods. Thus, as this international application shows, a slow reaction does not require a very rapid mixing method, while the development of a rapid reaction is greatly disturbed by a slow mixing.
The object of the European patent application published under the no. EP 824 106 is a method for the preparation of cellulose particles which have cationic and/or anionic groups, in which a dynamic mixer is used comprising a stator and a rotor equipped with blades of cylindrical shape. The drawback of such a mixer is that the aggregates of matter are subjected to multiple velocity gradients which stretch and contract them in a random way, causing very significant concentration gradients.
The present invention thus aims to propose a method and a mixer for dynamically and continuously mixing at least two fluids.
It advantageously applies to the mixing of reactive fluids and in particular, to the anionic polymerization of at least one (meth)acrylic monomer.
Thus, the subject of the invention is a method comprising the following steps:
A subject of the invention is also a micromixer comprising:
Such a micromixer has the double advantage of not inducing a large pressure loss and being able to be easily adjusted so as to adapt to changes in the operating conditions such as the flow rates and viscosities. In fact it only requires changing the speed of rotation of the rotor, the shape of the blades or counter-blades, or their number.
Moreover, the effectiveness of the mixing does not diminish along the longitudinal axis of the rotor as is the case in a standard mixer in the shape of a tube.
Moreover, the micromixer according to the invention is very effective even when the viscosities are high.
According to another aspect of the invention, a polymerization method is proposed, in which the method of dynamically and continuously mixing and the micromixer according to the invention are used.
This method comprises the following steps:
Other characteristics and advantages of the invention will now be described in detail in the following description which refers to the figures, in which:
Mixing Method According to the Invention
The method for dynamically and continuously mixing according to the invention has been described in a general way above.
It can be implemented for mixing more than two fluids. However, for the sake of simplicity, it will now be described for an implementation with two fluids.
According to the invention, the rotor can be driven in rotation at a speed which can reach up to 30,000 r.p.m.
Preferably, a speed of rotation of the rotor greater than 5,000 r.p.m is chosen, in order to obtain a homogeneous mixing and less than 20,000 r.p.m, so as to limit overheating phenomena.
The introduction of the first and second fluids preferably occurs in at least two places which are diametrically opposed with respect to the axis of the rotor of the micromixer.
The method according to the invention is generally used with a fluid temperature comprised between −100° C. and 300° C. It is preferably used with temperatures comprised between −80° C. and 110° C.
It can be implemented with fluid pressures comprised between 0.1 and 100 bars absolute. Preferably, it is used with pressures comprised between 1 and 50 bars absolute.
The fluids can be introduced into the mixer at a flow rate between 1 g/h and 10,000 kg/h. Preferably, the flow rate of the fluids is comprised between 1 kg/h and 5,000 kg/h.
The ratio of the mass flow rates of the fluids can be very variable. It is generally comprised between 0.01 and 100, preferably between 0.1 and 10.
The method according to the invention can allow mixing of fluids whose viscosity is comprised between 1 mpa.s and 103 Pa.s. Preferably, this viscosity is comprised between 10 mPa.s and 10 Pa.s.
The method according to the invention is used with residence times for the fluids in the micromixer generally greater than 1 ms. Preferably, the operating conditions are adjusted so that the residence time is comprised between 5 ms and 10 s.
Polymerization Method According to the Invention
The mixing method which has just been described is particularly suitable for the micromixing of reactive fluids. It preferably applies to reactive liquids.
It can thus advantageously be implemented for the production of an intimate mixture of liquids which is to produce chemical reactions with rapid and/or complex kinetics, such as anionic polymerizations, or polymerizations with high levels of solid.
Thus, the mixing method according to the invention can constitute a part of a more global polymerization method.
This polymerization method according to the invention in particular applies to the mixture of reactive fluids intended for anionic polymerization, at least one of which comprises at least one (meth)acrylic monomer.
As (meth)acrylic monomer, there can thus be mentioned in particular acrylic anhydride, methacrylic anhydride, methyl, ethyl, propyl, n- and tert-butyl acrylates, ethylhexyl, nonyl, 2-dimethyl amino ethyl and methyl, ethyl, propyl and n- and tert-butyl methacrylates, ethylhexyl, nonyl and 2-dimethyl amino ethyl.
The actual polymerization can occur outside the micromixer according to the invention, or it can begin inside the micromixer and continue outside this micromixer, for example in an appropriate reactor.
The method according to the invention can be used in any polymerization installation. In particular the one illustrated by
The method according to the invention can in particular be used for the preparation of polymers according to the methods described in European patent applications published under the numbers EP 749 987, EP 722 958 and EP 524 054.
Micromixer According to the Invention
The micromixer according to the invention is able to implement the method which has just been described.
This micromixer has been described in a general way above.
For more details about its structure reference can be made to FIGS. 1 to 6 which give an illustration of the structure of this micromixer.
In
These blades 3 are distributed in groups 3a, 3b, 3c, 3d, 3e, 3f and 3g, the blades of each group are arranged around the shaft 2, in the same plane perpendicular to the longitudinal axis of the shaft 2, and the groups of blades being spaced out from each other along the longitudinal axis of the shaft 2. This can be seen clearly in
In
The blades are approximately identical to each other and are in the form of a cutting edge. One of their longitudinal sides forms a tangent at the circumference of the shaft 2. The free end of each blade 3 can be tapered.
A 60 degree rotation of the shaft allows one blade to occupy the place that one of its two neighbours occupied before this rotation.
The blades 3 of a group of blades 3a are preferably aligned respectively with the blades of another group of blades 3b along the longitudinal axis of the rotor, so that in a top view and looking in the direction of the longitudinal axis of the rotor 1 (
The rotor 1 is intended to cooperate with a stator 4 which is seen firstly in
As is seen in
Preferably, the inlet 6 is diametrically opposed with respect to the inlet 5.
According to one embodiment of the invention, the stator 4 comprises disks 8 which are seen out of the stator in
When the stator 4 is mounted, as is seen in
The specific shape of the disks 8 can be seen in
The recess 9 has the shape of a circular hole, one part of which is occupied by extensions 10 of the disk 8. These extensions 10 project with respect to the wall 11 of the disk 8 delimiting the recess 9.
These extensions 10 of the disks 8 have approximately the same shape and the same dimensions as the blades 3 of the rotor 1. That is why in the remainder of the present description they are called counter-blades 10.
Each disk 8 thus comprises its group of six counter-blades 10 arranged in a regular manner on the circumference of the wall 11. Each counter-blade is inclined at 60 degrees with respect to its two nearest neighbours.
As for the blades 3 of the rotor 1, a 60 degree rotation of a disk 8 allows a counter-blade 10 to occupy the place that one of its two neighbours occupied before this rotation.
The counter-blades 10 of a group of counter-blades 10 are also preferably aligned respectively with the counter-blades of another group of counter-blades 10 along the longitudinal axis of the stator, so that in a top view and looking in the direction of the longitudinal axis of the stator 4 (
With reference to
The disks 8 are in contact with each other, stacked inside the stator 4, so that each group of blades 3 (with the exception of the first and the last) is inserted between two groups of counter-blades 10.
Thus, when the shaft 2 of the rotor 1 turns, each group of blades 3 can turn freely, i.e. without being impeded by the adjacent groups of counter-blades 10. The blades 3 and the counter-blades 10 are preferably inclined in opposite directions so that, during rotation of the rotor, they come close to each other like the blades of shears, and thus cause shearing of the fluids.
Moreover, looking from the inlet 5 of the micromixer towards its outlet 7, it is noted that a space 13 is provided, in longitudinal direction, between each group of blades 3 and the group of counter-blades 10 which precedes it (except in the case of the first group of blades situated close to the inlet of the stator) and another space 14 is also provided between each group of blades 3 and the group of counter-blades 10 which follows it (except in the case of the last group of blades situated close to the outlet of the stator).
Moreover, as is seen in
The spaces 15 have a minimum size in the case of
The spaces 15 have a maximum size when, looking in the direction of the axis of the shaft 2, the blades 3 are superposed on the counter-blades 10 and hide them.
As can be deduced from
Generally, the stator 4 also comprises a fluid distributor 17 approximately in the form of a washer and situated at the level of the feed of the stator 4 and upstream of the disks 8, if referring to the general direction of circulation of the fluids.
One end of the distributor 17 is in annular contact with the first disk 8.
The distributor 17 comprises at least one opening for the first fluid and at least one other opening for the second fluid, these openings being cut in the washer radially and communicating respectively with the entries 5 and 6 of the stator 4.
Thus, the fluids entering through the entries 5 and 6 are taken through the openings of the distributor 17 close to the shaft 2 of the rotor 1.
Generally, the central hole 18 of the distributor 17 has a diameter approximately the same as that of the circular hole of a disk 18 delimited by the wall 11 of this disk. It follows that when the rotor 1 is mounted in the stator 4, a first group of blades 3 of the rotor 1 can optionally be inserted inside the central hole 18 and turn freely therein.
At its lower end, i.e. the one opposite the one which is in contact with a disk 18, the distributor 17 optionally has a bore 19 intended to receive a ring seal 20 which is also in contact with the shaft 2 of the rotor 1.
The stator 4 is generally-fixed onto a support 21 in a standard way using a bolt (not represented).
Operation of the Micromixer
The rotor 1 is generally driven in rotation in a standard way by means for driving in rotation such as an electric motor (not represented). However, a motor capable of maintaining a constant speed of rotation, independent of the resisting torque to which it can be subjected, (e.g. milling machine motor), is preferably chosen.
The direction of rotation of the rotor is that of the inclination of the blades 3.
As is seen by observing
The openings of the distributor 17 take the fluids towards the centre, into the central hole 18. The fluids are then confined between the shaft 2 and the walls of the central hole 18 and are in contact with a first group of blades 3.
Under the effect of the pressure of the fluids and of the rotation of the shaft 2, the first blades, in cooperation with the first counter-blades, shear the fluids which progress through the spaces 14, then 15 and 13.
The fluids then rapidly encounter other blades 3 and counter-blades 10 until outlet 7 of the mixer where they are intimately mixed.
The intimate mixture of the fluids can then be used in numerous applications.
For example, it can be introduced into a tubular reactor or similar, and chemical reactions can occur, as described previously.
The following examples illustrate the present invention without however limiting its scope.
In these examples, the polymerization installation used is the one represented schematically in
The triblocks (triblock copolymers) ABC 100, ABC 101 and ABC 104 as identified in Examples 1 to 6 are prepared according to the operating method described in the European patent application published under the number EP 524 054 or in the aforementioned application EP 749 987.
The following abbreviations were used:
The average molecular mass in numbers of the PS block was determined by steric exclusion chromatography (SEC) in polystyrene equivalent, after sampling this block during the experiment.
The mass fractions of PS, PB and PMMA were determined by proton NMR.
The products contain a homopolystyrene (PS) fraction and a diblock copolymer fraction poly(styrene-b-butadiene) (SB), these fractions resulting from a non-quantitative blocking efficiency under the synthesis conditions used.
In all cases, the glass transition temperature (Tg) of the PB block is approximately −90° C.
The PMMA blocks are syndiotactic at more than 70% and have a Tg of 135° C.
In Examples no. 1 to 6, the results of SEC are superposed in order for the tests carried out to be better visualized.
The influence of the speed of rotation of the rotor of the micromixer according to the invention on the quality of an synthesized ABC 100 triblock is studied.
For this purpose, at one inlet of the micromixer, a solution of poly(styrene-b-butadiene)-butadienyl lithium and at the diametrically opposed inlet of the micromixer, a solution of methyl methacrylate is introduced.
The flow rates are kept constant, namely, 40 kg/h for Q(SB) and 20 kg/h for Q(M).
After polymerization in the tubular reactor, measurement by SEC is carried out of the intensity of the I(RD) detection as a function of the elution volume Ve.
The results are shown in the form of curves in
No notable difference is observed between the synthesized ABC 100 when passing from V1 to V4.
In all cases, the presence of residual SB in the product obtained is noted.
But the proportion of SB in the synthesized ABC 100 is significantly higher at V0 than for V1, V2, V3, or V4.
This can be explained by the fact that when chemical reactions are in play, it is the bringing into contact of the reagents, the mixing on the molecular level which is important. However, the polmerization kinetics of methacrylates under these conditions is extremely rapid. Moreover, it is known that the efficiency of mixing required for a reactor depends on the relationship between the characteristic time of the reaction considered and the mixing time on the molecular level.
In the case of mixing at V0, the volume energy dissipated in the micromixing zone is smaller, which results in the contact between the reagents being less intimate.
A heterogeneous distribution of the reagents results which causes unwanted reaction terminations.
In other words, the peaks are narrower for V1 to V4, which shows that the dynamic micromixer according to the invention is more effective at a speed greater than V0.
The influence of the speed of rotation of the rotor of the micromixer according to the invention on the quality of a synthesized ABC 101 triblock is studied.
For this purpose, the operation is carried out as in Example 1.
The results are shown in
The same conclusions as in Example 1 are reached, namely:
In this example, in a micromixer according to the invention, the influence of the total flow rate Q (SB)+Q(M), with a constant flow rate ratio Q(SB)/Q(M) and a constant speed of rotation of the rotor, on the quality of a synthesized ABC 100 triblock is studied.
In a first case, the sum of the flow rates Q(SB) and Q(M), respectively, 30 kg/h and 15 kg/h, is equal to 45 kg/h.
In a second case, the sum of the flow rates Q(SB) and Q(M), respectively, 40 kg/h and 20 kg/h, is equal to 60 kg/h.
The results are shown in
It is noted that the increase in the total flow rate leads to better results.
The same study as in Example 3 is undertaken, but synthesizing an ABC 101 triblock instead of the previous ABC 100 triblock.
The results are shown in
It is noted that for this product, ABC 101, the variation in the total flow rate has very little influence on the quality of the synthesized product, from the time when this flow rate has reached a minimum value which is sufficient to allow a characteristic micromixing time which is shorter than the reaction time.
In this example, the results obtained with three types of mixers were compared, namely:
In the three cases, ABC 104 was synthesized with constant flow rates, Q(SB)=30 kg/h and Q(M)=15 kg/h.
The results are shown in
The following is noted:
These results are expressed by different dispersities of population of the different chains, i.e. by different polymolecularity indexes (Ip):
In this example, the operation is carried out as in Example 5, except that higher total flow rates were used, namely, 60 kg/h instead of 45 kg/h.
The results are shown in
The same conclusions are reached as in Example 5.
A significant improvement in the Ip is also noted in the case of the static mixer. Specifically:
Nevertheless, the dynamic mixer according to the invention is clearly performs better than the tangential jet mixer and a fortiori than the static mixer.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0207025 | Jun 2002 | FR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/FR03/01570 | 5/23/2003 | WO | 12/7/2004 |
