Method for destabilizing a Pickering emulsion

Abstract

The present invention relates to a Pickering destabilisation method. The present invention also relates to a method for phase separation, and specifically to a method for separating hydrocarbons for hydrocarbon extraction, as well as to a method for manufacturing porous substrates and to a method for manufacturing finished products.

Claims

1. A process of destabilizing a Pickering emulsion comprising: (i) preparation of a Pickering emulsion comprising: a continuous phase in which nanoparticles are suspended, and a non-continuous phase, which is an immiscible liquid dispersed in said continuous phase in the form of droplets, (ii) injection into the continuous phase of a solvent which is miscible with said continuous phase, so as to trigger coalescence between the continuous and non-continuous phases, the non-continuous phase/nanoparticles ratio by weight being between 4 and 20,000, and (iii) separation, by pumping, either of the continuous phase or of the noncontinuous phase, wherein the solvent is (a) water when the continuous phase is an alcohol of formula ROH, in which R is a C.sub.1 to C.sub.8 hydrocarbon chain, or (b) an alcohol of formula ROH, in which R is a C.sub.1 to C.sub.8 hydrocarbon chain when the continuous phase is water.

2. The process as claimed in claim 1, in which the non-continuous phase/nanoparticles ratio by weight is between 100 and 10,000.

3. The process as claimed in claim 1, in which the continuous phase is chosen From water or an alcohol of formula ROH where R is a C.sub.1 to C.sub.8 hydrocarbon chain.

4. The process as claimed in claim 1, in which the non-continuous phase is a mineral oil, a fluorinated oil, a fatty acid or a (meth)acrylate oligomer.

5. The process as claimed in claim 1, in which the non-continuous phase is a mineral oil comprising a mixture of hydrocarbons.

6. The process as claimed in claim 1, in which the non-continuous phase is a (meth)acrylate oligomer selected from the group consisting of tripropylene glycol diacrylate (TPGDA), ethylene glycol dimethacrylate, polyethylene glycol diacrylate (PEGDA), pentaerythritol triacrylate, trimethylolpropane triacrylate (TM PTA) and 1,6-hexanediol diacrylate.

7. The process as claimed in claim 1, in which the amount of the solvent injected during stage (ii) represents between 10% and 70% by volume, with respect to the total volume of the continuous phase.

8. The process as claimed in claim 1, in which the nanoparticles are selected from the group consisting of silica, gold, iron oxide, cerium oxide, titanium dioxide or clay nanoparticles and quantum dots.

9. The process as claimed in claim 1, in which the nanoparticles have a diameter of between 10 and 50 nm.

10. The process as claimed in claim 1, in which the concentration of nanoparticles is between 0.1 and 20 g.Math.l.sup.l with respect to the continuous phase.

11. The process as claimed in claim 1, in which the nanoparticles are silica nano-particles modified at the surface by etherification of the silanol groups by an alcohol or by grafting an organosilane at their surface.

12. The process as claimed in claim 11, in which the organosilane is an organoalkoxysilane.

13. The process as claimed in claim 11, in which the continuous phase is water and the degree of covering of the silica nanoparticles by the organosilane is between 5% and 40%.

14. The process as claimed in claim 11, in which the continuous phase is an alcohol of formula ROH, where R is a C.sub.1 to C.sub.8 hydrocarbon chain, and the degree of covering of the silica nanoparticles by the organosilane is between 40% and 85%.

15. The process as claimed in claim 1, in which the solvent is injected into the continuous phase at a flow rate of between 10.sup.5 and 10.sup.2 m.sup.3/h during stage (ii).

16. A process of manufacturing porous substrates, comprising stages (i), (ii), and (iii) as defined according to claim 1, followed by a stage of drying of the coalesced phase obtained on conclusion of stage (iii).

17. A process of manufacturing finished materials, characterized in that it comprises stages (i), (ii), and (iii) as defined according to claim 1, followed by a stage of polymerization under UV irradiation, and in that the non-continuous phase is a (meth)acrylate oligomer.

18. A process of destabilizing a Pickering emulsion comprising: (i) preparation of a Pickering emulsion comprising: a continuous phase in which nanoparticles are suspended, and a noncontinuous phase, which is an immiscible liquid dispersed in said continuous phase in the form of droplets, (ii) injection into the continuous phase of a solvent which is miscible with said continuous phase, so as to trigger a coalescence between the continuous and noncontinuous phases, the noncontinuous phase/nanoparticles ratio by weight being between 4 and 20,000, wherein the nanoparticles are silica nano-particles modified at the surface by grafting an organoalkoxysilane at their surface; and the solvent is (a) water when the continuous phase is an alcohol of formula R OH, in which R is a C1 to C8 hydrocarbon chain, or (b) an alcohol of formula R OH, in which R is a C1 to C8 hydrocarbon chain when the continuous phase is water.

19. A process of destabilizing a Pickering emulsion comprising: (i) preparation of a Pickering emulsion comprising: a continuous phase in which nanoparticles are suspended, and a noncontinuous phase, which is an immiscible liquid dispersed in said continuous phase in the form of droplets, (ii) injection into the continuous phase of a solvent which is miscible with said continuous phase, so as to trigger a coalescence between the continuous and noncontinuous phases, the noncontinuous phase/nanoparticles ratio by weight being between 4 and 20,000, wherein the solvent is (a) water when the continuous phase is an alcohol of formula R OH, in which R is a C1 to C8 hydrocarbon chain, or (b) an alcohol of formula R OH, in which R is a C1 to C8 hydrocarbon chain when the continuous phase is water; and the solvent is injected into the continuous phase at a flow rate of between 10.sup.5 and 10.sup.2 m.sup.3/h during stage (ii).

Description

(1) In addition to the arrangements which precede, the invention also comprises other arrangements which will emerge from the remaining description which follows, which relates to examples demonstrating the advantageous properties of the process of the invention and also to the appended figures, in which:

(2) FIG. 1 illustrates the process of the invention, the coalescence being triggered by addition of a miscible liquid to the continuous phase,

(3) FIG. 2 illustrates the destabilization of an oil-in-ethanol emulsion by addition of a small amount of water to the continuous phase,

(4) FIG. 3 represents a microfluidic chip: A) Top view, and B) Cross sectional view (along the dotted lines of the top view),

(5) FIG. 4 represents the state of dispersion of nanoparticles by measurement of their hydrodynamic diameter by dynamic light scattering,

(6) FIG. 5 indicates the percentages by volume of miscible liquid to be added to a continuous ethanol phase, in which a fluorinated oil stabilized by silica nanoparticles is dispersed, in order to trigger the coalescence (expressed as percentage of residual silanol functional groups, 100% corresponding to the most hydrophilic nanoparticles).

EXPERIMENTAL PART

Example 1

Process for the Destabilization of a Pickering Emulsion According to the Invention

Synthesis of Silica Nanoparticles:

(7) The silica nanoparticles used for the stabilization of the emulsion are synthesized in a 20 ml jacketed beaker provided with a magnetic stirrer and thermostatically controlled using circulation of water regulated at a temperature of 60 C. 20 ml of an aqueous arginine solution having a concentration of 610.sup.3 mol.Math.l.sup.1 are subsequently added. After stirring for 15 minutes, 537 mmol of tetraethoxysilane are introduced into the beaker. Stirring is subsequently maintained at a speed of 500 revolutions per minute for a period of time of 48 hours.

(8) The SiO.sub.2 nanoparticles obtained have the following characteristics: a diameter of between 10 and 20 nm, a very low polydispersity; the size distribution is Gaussian with a standard deviation s=0.8 nm, a density of 2.2 g.Math.cm.sup.3.

(9) The surface of the nanoparticles is covered with silanol SiOH groups, which confers a highly hydrophilic nature on them. In order for the nanoparticles to be able to be adsorbed at the interface of the dispersed and continuous phases, it is necessary to render them partially hydrophobic. This modification is described in the procedure below.

(10) Modification of the Surface of the Nanoparticles:

(11) 200 ml of the suspension of nanoparticles prepared above are placed in a flask provided with a magnetic bar. 1 ml of trimethylethoxysilane is subsequently added. The mixture is stirred at 750 revolutions per minute using a magnetic stirrer for a period of time of 8 hours.

(12) The grafted nanoparticles are subsequently washed with water and the dispersion solvent is removed by ultrafiltration under pressure using a 30 kD membrane. Three rinsing operations are subsequently carried out with 50 ml of pure water in order to completely remove the synthesis solvent.

(13) Preparation of the Pickering Emulsion:

(14) Different Pickering emulsions were prepared according to distinct methods of preparation.

(15) In these emulsions: the continuous phase is either water or ethanol comprising silica nanoparticles as prepared above, at a concentration of 0.4 g.Math.l.sup.1, the dispersed phase is a fluorinated oil: perfluorotripropylamine FC-3283 (3M France).
1st Method of Preparation: Use of a Mechanical Stirring Device

(16) The suspension of silica nanoparticles formed above is diluted to a concentration of 0.4 g.Math.l.sup.1.

(17) The two phases to be emulsified are placed in a sample tube and then stirred vigorously according to different methods: by manual stirring for a period of time of 30 seconds, by mechanical stirring using an IKA Ultraturrax T8.01 high-pressure homogenizer at 25 000 revolutions/minute for 10 seconds, by manual stirring for 10 seconds, in order to form a coarse dispersion, followed by ultrasonication of the mixture with a Bioblock Scientific 88169 device for 1 minute.

(18) The noncontinuous phase or continuous phase concentration of the emulsion is 10% and the noncontinuous phase/nanoparticles ratio by weight is 250.

(19) 2nd Method of Preparation: Use of a Microfluidic Device

(20) The suspension of silica nanoparticles formed above is diluted to a concentration of 0.4 g.Math.l.sup.1.

(21) The two phases to be emulsified are injected into a microfluidic chip and then sheared at a junction with a width of 50 m and a height of 10 m. In this embodiment, the local shearing is controlled, which makes possible good reproducibility during the formation of the droplets, the latter consequently being monodispersed.

(22) Several shearing geometries already described in the literature can be used, such as, for example, convergent flows referred to as flow focusing (Anna et al., Appl. Phys. Lett., Vol. 82, No. 3, 20 Jan. 2003), coaxial flows (Umbanhowar et al., Langmuir, Vol. 16, No. 2, 2000), T-junction flows and terrace flows (Kobayashi et al., Colloids and Surfaces A: Physicochem. Eng. Aspects, 296 (2007), 285-289). In this example, a hybrid shear geometry, such as that described by Mallogi et al., (Appl. Phys. Lett., Vol. 82, No. 3, 20 Jan. 2010), was used. Three syringes comprising the two immiscible phases (one syringe containing the dispersed phase and two syringes containing the continuous phase with the modified silica nanoparticles) are placed on three syringe drivers. The fluids are dispensed at set flow rates: Q.sub.dispersed phase=0.3 l/min, Q.sub.continuous phase 1=7 l/min, Q.sub.continuous phase 2=1.5 l/min.

(23) The microfluidic chip is represented in FIG. 3. The phase to be dispersed is sheared at a first convergent flow (width W.sub.1=50 m, height h.sub.1=10 m) by the continuous phase comprising the modified nanoparticles. The droplets formed emerge in a new convergent flow which is wider and higher (width W.sub.2=100 m, height h.sub.2=100 m). The droplets are then entrained by a new inflow of continuous phase comprising the modified nanoparticles over a distance of several tens of centimeters in order for the nanoparticles to be able to be effectively adsorbed on the surface of the droplets, this being the case before the droplets come into contact with one another. The residence time is of the order of 20 seconds, which is sufficient for the amount of nanoparticles adsorbed to prevent the coalescence of the droplets formed. The Pickering emulsion thus formed, the noncontinuous phase/continuous phase concentration of which is 3% and the noncontinuous phase/nanoparticles ratio by weight of which is 75, is collected directly at the outlet of the microfluidic chip and stored for subsequent use.

(24) Triggering of the Coalescence of the Emulsion:

(25) The layer of nanoparticles is destabilized by modification of the hydrophilic/lipophilic balance of the continuous phase: either by addition of water to the ethanol using a micropipette, so as to render the continuous phase more hydrophilic, or by addition of ethanol to the water using a micropipette, in order to render the continuous phase more hydrophobic.

(26) The state of dispersion of the nanoparticles is then modified and results in the formation of aggregates, as is shown in FIG. 4. The nanoparticles initially dispersed in the water aggregate together when ethanol is added (1st graph) and the nanoparticles initially dispersed in the ethanol aggregate together when water is added (2nd graph).

(27) Formation of Nonspherical Droplets:

(28) The percentages by volume of miscible liquid to be added to a continuous phase in order to trigger the coalescence, in the case of emulsions of fluorinated oil dispersed in ethanol, are shown in FIG. 5.

(29) It is observed that the amount of water to be added increases with the hydrophobicity of the particles and then decreases for very hydrophobic particles.

Example 2

Process for the Extraction of Hydrocarbons

(30) 2 ml of an aqueous solution, comprising water H.sub.2O, 10 g.Math.l.sup.1 of sodium chloride NaCl and 4 g.Math.l.sup.1 of silica nanoparticles, and 2 ml of hexadecane are incorporated in an 8 ml sample tube.

(31) The emulsion is formed by mechanical stirring using an IKA Ultraturrax T8.01 high-pressure homogenizer at 25 000 revolutions/minute for a period of time of 2 minutes.

(32) The noncontinuous phase/continuous phase concentration of the emulsion is 50% and the continuous phase/nanoparticles ratio by weight is 450.

(33) The emulsion formed is subsequently stirred with a magnetic stirrer at 250 rpm. Ethanol (immiscible solvent) is subsequently injected into the Pickering emulsion prepared above by dipping a capillary tube in the sample tube and by applying a flow rate of 10.sup.3 m.sup.3/h for a total volume of ethanol equal to 50% of the continuous phase.

(34) The dispersed phase, i.e. the hexadecane, is no longer in the emulsion form: two phases have formed in the sample tube. The hexadecane, which is lighter, is located above the water. The hexadecane is recovered using a pasteur pipette.

Example 3

Process for the Manufacture of a Filter

(35) 2 ml of an aqueous solution, comprising water H.sub.2O, 10 g.Math.l.sup.1 of sodium chloride and 10 g.Math.l.sup.1 of silica nanoparticles, and 2 ml of a polymerizable (meth)acrylate oligomer, 1,6-hexanediol diacrylate, and also 1% by weight of 2-hydroxy-2-methylpropiophenone are incorporated in an 8 ml sample tube. The emulsion is formed by mechanical stirring using an IKA Ultraturrax T8.01 high-pressure homogenizer at 25 000 revolutions/minute for a period of time of 2 minutes.

(36) The noncontinuous phase/continuous phase concentration of the emulsion is 50% and the continuous phase/nanoparticles ratio by weight is 180.

(37) The emulsion formed is subsequently stirred with a magnetic stirrer at 250 rpm. Ethanol (immiscible solvent) is subsequently injected into the Pickering emulsion prepared above by dipping a capillary tube in the sample tube and by applying a flow rate of 10.sup.4 m.sup.3/h for a total volume of solvent equal to 5% of the continuous phase, this being done in order to form nonspherical droplets.

(38) The sample tube is subsequently placed under a Hamamatsu LC8 UV lamp (4500 mW.Math.cm.sup.2, wavelength 300 nm 450 nm) for 1 minute. Particles are thus obtained which are subsequently recovered and then dried in an oven at a temperature of 50 C. for 24 hours. The powder thus dried is subsequently used to prepare a filter.