METHOD FOR PREPARING MICROCAPSULES BY DOUBLE EMULSION

Abstract

The present invention relates to a method for preparing solid microcapsules, comprising the steps of: a) adding under agitation a composition C1 comprising at least one active material to a cross-linkable liquid composition C2, wherein the active material is an additive to be used in the oil industry, composition C1 and composition C2 being immiscible with each other, so that a first emulsion is obtained, said first emulsion comprising droplets of composition C1 dispersed in composition C2, b) adding under agitation the first emulsion obtained in step a) to a liquid composition C3, composition C3 and composition C2 being immiscible with each other, so that a second emulsion is obtained, said second emulsion comprising droplets dispersed in composition C3, c) loading the second emulsion obtained in step b) in a mixer which applies a homogeneous controlled shear rate to said second emulsion, said shear rate being from 1 000 s.sup.1 to 100 000 s.sup.1, so that a third emulsion is obtained, said third emulsion comprising droplets dispersed in composition C3, and d) cross-linking the droplets obtained in step c), so that solid microcapsules dispersed in composition C3 are obtained.

Claims

1. Method for preparing solid microcapsules (20), comprising the steps of: a) adding under agitation a composition C1 comprising at least one active material to a cross-linkable liquid composition C2, wherein the active material is an additive to be used in the oil industry, composition C1 and composition C2 being immiscible with each other, so that a first emulsion is obtained, said first emulsion comprising droplets (1) of composition C1 dispersed in composition C2, b) adding under agitation the first emulsion obtained in step a) to a liquid composition C3, composition C3 and composition C2 being immiscible with each other, so that a second emulsion is obtained, said second emulsion comprising droplets (5) dispersed in composition C3, c) loading the second emulsion obtained in step b) in a mixer which applies a homogeneous controlled shear rate to said second emulsion, said shear rate being from 1 000 s.sup.1 to 100 000 s.sup.1, so that a third emulsion is obtained, said third emulsion comprising droplets (10) dispersed in composition C3, and d) cross-linking the droplets (10) obtained in step c), so that solid microcapsules (20) dispersed in composition C3 are obtained.

2. Method according to claim 1, wherein the active material is solubilized into composition C1.

3. Method according to claim 1, wherein the active material is dispersed in the form of solid particles into composition C1.

4. Method according to claim 1, wherein the active material is an additive to be included in lubricants, lubricating base oils, fuels, bitumens, or in the drilling fluids, sludges or muds, or an additive to be used in oil exploration/production.

5. Method according to claim 1, wherein composition C2 comprises at least one monomer or polymer, at least one cross-linker and at least one initiator of polymerization.

6. Method according to claim 1, wherein the viscosity of composition C2 at 25 C. is from 500 mPa.Math.s to 100 000 mPa.Math.s.

7. Method according to claim 1, wherein the viscosity of composition C2 is higher than the viscosity of composition C1.

8. Method according to claim 1, wherein during step a), the volume of composition C1 to the volume of composition C2 ratio is from 1:10 to 10:1.

9. Method according to claim 1, wherein the viscosity of composition C3 at 25 C. is higher than the viscosity at 25 C. of the first emulsion obtained in step a).

10. Method according to claim 1, wherein during step b), the volume of the first emulsion to the volume of composition C3 ratio is from 1:10 to 10:1.

11. Method according to claim 1, wherein the mixer used in step c) is a Couette-geometry mixer, comprising two concentric cylinders, an outer cylinder of inner radius R.sub.o and an inner cylinder of outer radius R.sub.i, the outer cylinder being fixed and the inner cylinder being rotating with an angular velocity .

12. Method according to claim 11, wherein the angular velocity w of the rotating inner cylinder is over than or equals to 30 rad.Math.s.sup.1.

13. Method according to any one of claim 11 or 12, wherein the gap d=R.sub.o R.sub.i between the two concentric cylinders is from 50 m to 1 000 m.

14. Method according to claim 1, wherein during step d), the cross-linking is carried out by submitting the double droplets (10) obtained in step c) to a source of light, able to initiate the cross-linking of composition C2.

15. Series of solid microcapsules (20), said microcapsules (20) being obtainable by the method of claim 1, each microcapsule (20) comprising: a core comprising a composition comprising at least one active material as defined in claim 1, and a solid cross-linked shell surrounding said core, wherein the standard deviation of microcapsule diameter distribution is below 25% or below 1 m.

16. Series of solid microcapsules (20) according to claim 15, wherein the average diameter of the solid microcapsules (20) is less than or equal to 10 m.

17. Series of solid microcapsules (20) according to claim 15, wherein each solid microcapsule (20) is surfactant-free.

18. Series of solid microcapsules (20) according to claim 15, wherein each solid microcapsule (20) is water-free.

19. Composition comprising a series of solid microcapsules (20) according to claim 15, and a lubricating base oil.

20. Method for releasing an active material, comprising a step of applying a mechanical shear stress to a composition comprising a series of solid microcapsules (20) according to claim 15.

Description

EXAMPLES

Example 1Preparation of Solid Capsules

[0303] Dispersions of solid capsules were prepared according to the following procedure, which corresponds to the method of the invention. [0304] a first emulsion was produced through the drop-wise addition and mixing of Composition C1 to Composition C2 at a predetermined volume fraction, Composition C1 and/or Composition C2 were optionally previously heated in order to be melted, [0305] a second emulsion was then produced by adding and mixing the first emulsion to Composition C3 at a predetermined volume fraction, [0306] the polydisperse double emulsion thus obtained was then added to a Couette mixer as represented in FIG. 2, and sheared at an injection speed of 8 mL/min, and [0307] the monodisperse double emulsion thus obtained was finally UV polymerized to provide a dispersion of solid capsules.

[0308] The percentages below are given in weight.

Encapsulation of Borates

Dispersion 1

[0309] Composition C1: OLOA 9750borate additive (Oronite) (100%)

Composition C2: CN 991 (Sartomer, Arkema) (84.6%)

[0310] HDDAhexanediol diacrylate (Sigma Aldrich) (9.4%) [0311] 2,2,2-Trifluoroethyl acrylate (Sigma Aldrich) (5%) [0312] Darocure 1173 (Ciba) (1%)

Composition C3: PAO 100 (Exxon Mobil) (100%)

[0313] First emulsion: C1 (50%) in C2 (50%)
Second emulsion: first emulsion (13.32%) in C3 (86.68%)
Shear rate: 6 248 s.sup.1
UV exposure: 3 minutes

[0314] Dispersion 1 contained monodisperse solid capsules encapsulating borates, having a shell thickness of 0.40 m (as measured by Transmission Electron Microscopy).

Dispersion 2

[0315] Composition C1: OLOA 9750borate additive (Oronite) (100%)

Composition C2: CN 991 (Sartomer, Arkema) (84.6%)

[0316] HDDAhexanediol diacrylate (Sigma Aldrich) (9.4%) [0317] 2,2,2-Trifluoroethyl acrylate (Sigma Aldrich) (5%) [0318] Darocure 1173 (Ciba) (1%)

Composition C3: PAO 100 (Exxon Mobil) (100%)

[0319] First emulsion: C1 (80%) in C2 (20%)
Second emulsion: first emulsion (8.32%) in C3 (91.68%)
Shear rate: 6 248 s.sup.1
UV exposure: 3 minutes

[0320] Dispersion 2 contained monodisperse solid capsules encapsulating borates, having a shell thickness of 0.30 m (as measured by Transmission Electron Microscopy).

Dispersion 3

[0321] Composition C1: OLOA 9750borate additive (Oronite) (100%)

Composition C2: CN 991 (Sartomer, Arkema) (89%)

[0322] HDDAhexanediol diacrylate (Sigma Aldrich) (10%) [0323] Darocure 1173 (Ciba) (1%)

Composition C3: PAO 100 (Exxon Mobil) (100%)

[0324] First emulsion: C1 (33.33%) in C2 (66.67%)
Second emulsion: first emulsion (20%) in C3 (80%)
Shear rate: 2 083 s.sup.1
UV exposure: 3 minutes

[0325] Dispersion 3 contained solid capsules having a diameter of 2.3 m, a core diameter of 1.0 m, a shell thickness of 0.65 m, and a borate content of 6.67% by weight.

Dispersion 4

[0326] Composition C1: OLOA 9750borate additive (Oronite) (100%)

Composition C2: CN 991 (Sartomer, Arkema) (89%)

[0327] HDDAhexanediol diacrylate (Sigma Aldrich) (10%) [0328] Darocure 1173 (Ciba) (1%)

Composition C3: PAO 100 (Exxon Mobil) (100%)

[0329] First emulsion: C1 (50%) in C2 (50%)
Second emulsion: first emulsion (13.32%) in C3 (86.68%)
Shear rate: 2 083 s.sup.1
UV exposure: 3 minutes

[0330] Dispersion 4 contained solid capsules having a diameter of 2.0 m, a core diameter of 1.0 m, a shell thickness of 0.5 m, and a borate content of 6.67% by weight.

Dispersion 5

[0331] Composition C1: OLOA 9750borate additive (Oronite) (100%)

Composition C2: CN 991 (Sartomer, Arkema) (84.6%)

[0332] HDDAhexanediol diacrylate (Sigma Aldrich) (9.4%) [0333] 2,2,2-Trifluoroethyl acrylate (Sigma Aldrich) (5%) [0334] Darocure 1173 (Ciba) (1%)

Composition C3: PAO 100 (Exxon Mobil) (100%)

[0335] First emulsion: 01 (33.33%) in C2 (66.67%)
Second emulsion: first emulsion (20%) in C3 (80%)
Shear rate: 6 248 s.sup.1
UV exposure: 3 minutes

[0336] Dispersion 5 contained solid capsules having a diameter of 2.3 m, a core diameter of 1.0 m, a shell thickness of 0.50 m, and a borate content of 6.67% by weight.

Dispersion 6

[0337] Composition C1: OLOA 9750borate additive (Oronite) (100%)

Composition C2: CN 991 (Sartomer, Arkema) (80.1%)

[0338] HDDAhexanediol diacrylate (Sigma Aldrich) (8.9%) [0339] 2,2,2-Trifluoroethyl acrylate (Sigma Aldrich) (10%) [0340] Darocure 1173 (Ciba) (1%)

Composition C3: PAO 100 (Exxon Mobil) (100%)

[0341] First emulsion: C1 (33.33%) in C2 (66.67%)
Second emulsion: first emulsion (20%) in C3 (80%)
Shear rate: 6 248 s.sup.1
UV exposure: 3 minutes

[0342] Dispersion 6 contained solid capsules having a diameter of 2.3 m, a core diameter of 1.0 m, a shell thickness of 0.50 m, and a borate content of 6.67% by weight.

Encapsulation of Fatty Amines

Dispersion 7

[0343] Composition C1: Comperlan LDfatty amines (BASF) (100%)

Composition C2: CN 991 (Sartomer, Arkema) (94%)

[0344] HDDAhexanediol diacrylate (Sigma Aldrich) (5%) [0345] Darocure 1173 (Ciba) (1%)

Composition C3: PAO 100 (Exxon Mobil) (100%)

[0346] First emulsion: C1 (20%) in C2 (80%)
Second emulsion: first emulsion (25%) in C3 (75%)
Shear rate: 9 373 s.sup.1
UV exposure: 10 minutes

Example 2Resistance to Hydrolysis

[0347] In presence of water, borates nanoparticles have the tendency to hydrolyze and to form crystals.

[0348] In order to demonstrate the resistance to hydrolysis of the encapsulated borates, water (1% by weight) was added to Dispersion 1 and Dispersion 2.

[0349] A control sample was also prepared by adding water (1% by weight) to a dispersion comprising 4% of non-encapsulated borates (corresponding to OLOA9750 (Oronite)) into PAO 100 (Exxon Mobil).

[0350] The mixtures were let to rest for 10 days. The bottom of the decanted dispersions were washed with heptane and filtered on a 0.22 m filter. Said filter was then put on a MEB+EDX system to detect the presence of potassium borate crystals.

[0351] On the filter corresponding to Dispersion 1, a large population of solid capsules was observed together with only few crystals of potassium borate.

[0352] On the filter corresponding to Dispersion 2, solid capsules were also observed. Only traces of potassium borate crystals were observed.

[0353] On the filter corresponding to the control sample, a high content of potassium borate crystals was observed.

Example 3Extreme Pressure Properties

[0354] Dispersions 3, 4, 5 and 6 were tested for their extreme pressure properties on a four-ball wear test machine according to D55136 Standard.

[0355] The dispersions were diluted to reach 4% OLOA 9750 and Zn DTP, calcium sulfonate and sulfurized olefin were added with the following amounts (the percentage are weight percentages based on the total weight of the composition): [0356] PAO 100 (Exxon Mobil): 54.58%, [0357] base oil of group III (SK): 36.40%, [0358] ZnDTP (Lubrizol): 0.26%, [0359] Calcium sulfonate (Chevron Oronite): 1.72%, and [0360] sulfurized olefin (Arkema): 3.04%.

TABLE-US-00002 Last Load Wear Scar before Seizure (kg) diameter (mm) Control (free borates) 120 0.53 Dispersion 3 130 0.53 Dispersion 4 130 0.52 Dispersion 5 140 0.57 Dispersion 6 120 0.54

TABLE-US-00003 First Load of Wear Scar systematic seizure (kg) diameter (mm) Control (free borates) 160 1.04 Dispersion 3 150 0.6 Dispersion 4 140 0.74 Dispersion 5 160 0.78 Dispersion 6 160 0.73

[0361] Dispersions 3 and 4, comprising solid capsules encapsulating borates without fluorinated treatment, showed good results which are equivalent to those obtained with a dispersion of free borates (control).

[0362] Dispersions 5 and 6, comprising solid capsules encapsulating borates with fluorinated treatment, showed good results which are equivalent to those obtained with a dispersion of free borates (control).

[0363] The dispersions obtained according to the method of the invention thus provided good extreme pressure properties, with or without fluorinated treatment.

Example 4Thermogravimetric Analysis

[0364] Dispersion 7 was studied by TGA to evaluate the benefits of the encapsulation.

[0365] The results are given in FIG. 3, which represents the weight loss (%) according to time, at a temperature of 150 C.

[0366] The --- plotline corresponds to empty capsules (control n 1), the . . . plotline corresponds to the capsules of Dispersion 7 (encapsulated Comperlan LD), and the continuous plotline corresponds to a composition comprising free Comperlan LD (control n 2).

[0367] These results showed that encapsulation of Comperlan LD reduces the rate of weight loss compared to the free form, and thus showed that Comperlan D degraded at a reduced rate when encapsulated according to the invention and the capsule shell provided a barrier preventing or reducing the rate of evaporation until shell degradation.

Example 5Comparison of Different MethodsCharacterization of the Monodispersity

[0368] Solid microcapsules were prepared using the following compositions C1, C2, and C3: [0369] Composition C1: ExxonMobil PAO40 (Polyalpha olefin with a viscosity of 892 mPa.Math.s at 25 C.) [0370] Composition C2: [0371] 89% CN981 (Sartomer, Arkema) [0372] 10% Hexanediol diacrylate [0373] 1% Darocure 1173 (photo-initiator) [0374] Composition C3: ExxonMobil PAO100 (Polyalpha olefin with a viscosity of 2989 mPa.Math.s at 25 C.)

[0375] An overhead stirrer (Heidolph RZR 2021) equipped with a three-bladed propeller was used to fabricate the emulsions. Mixing speed was set to 1 000 rpm. All steps were performed at 25 C.

Step a):

[0376] Composition C1 was added dropwise under constant mixing to composition C2 until a ratio C1:C2=1:4 was reached. After this step an emulsion C1-in-C2 was formed.

Step b):

[0377] The C1-in-C2 emulsion obtained after step a) was added dropwise under constant mixing to composition C3 until a ratio C1-in-C2:C3=1:4 was reached. After this step a double emulsion C1-in-C2-in-C3 was formed.

Mixing Step:

[0378] The double emulsion C1-in-C2-in-C3 was then sheared with different kinds of mixer: [0379] an overhead stirrer (Heidolph RZR 2021) equipped with a three-bladed propeller with a mixing speed of 1 000 rpm, [0380] an Ika T25 Ultra-Turrax mixer for 5 minutes at 24 000 rpm, or [0381] a Couette-geometry mixer, with a flowrate of 8 mL/min and rotation speed of 450 rpm, corresponding to a shear rate of 9373 s.sup.1 (homogeneous high-shear mixing, corresponding to the conditions of step c) of the method of the invention).

Step d):

[0382] The emulsions were then submitted to UV irradiation to polymerize the microcapsules for 6 minutes using a Dymax Light Box ECE 2000 having an output light intensity of 0.1 W/cm.sup.2 at 365 nm. The series of solid microcapsules thus obtained were subsequently imaged with an Olympus IX71 microscope equipped with a UPlanSApo 100/1.4 objective and with a JEOL JEM 2010F transmission electron microscope. The resulting images were treated with Image J software to extract the distribution of microcapsule diameters.

[0383] The distribution of the series of microcapsules are represented in FIG. 4 (microcapsule diameter distribution) and FIG. 5 (shell thickness distribution), wherein the --- plotline corresponds to the overhead stirrer, the . . . plotline corresponds to the Ultra-Turrax mixer, and the continuous plotline corresponds to the Couette-geometry mixer.

[0384] The series of solid microcapsules resulting from a mixing step carried out in an overhead stirrer (standard emulsification) has an average diameter is 9.05 m and the standard deviation of the distribution is 8.16 m or 90%. The average shell thickness is 2.32 m and the standard deviation of the distribution is 2.01 m or 87%.

[0385] This result illustrates the fact that standard mixers such yield solid microcapsules having very broad size distributions.

[0386] The series of solid microcapsules resulting from a mixing step carried out in Ika T25 Ultra-Turrax mixer, which provides heterogeneous high-shear mixing, has an average diameter of 5.18 m and a standard deviation of 4.35 m or 84%. The average shell thickness is 1.50 m and the standard deviation of the distribution is 1.38 m or 92%.

[0387] This result illustrates the fact that mixers such as the Ika T25 Ultra-Turrax allow decreasing the average size of the microcapsules, because of the high shear applied to the double emulsion, but still yield very broad size distributions.

[0388] By contrast, the series of solid microcapsules obtained according to the method of the invention, which results from a mixing step carried out in a Couette-geometry mixer, has an average diameter of 0.13 m and a standard deviation of 0.03 m or 23%.

[0389] This result demonstrates the relevance of the Couette-geometry mixer to obtain both small sizes of microcapsules and narrow distributions.