ENCAPSULATION OF HYDROPHILIC ADDITIVES

Abstract

The instant invention relates to a process for the encapsulation of a non-amine hydrophilic compound C, comprising the steps of: (E1) providing a reverse emulsion containing: an oil phase (O), comprising a curable mixture of isocyanate and polyalkyldiene hydroxylated or polyol dispersed in said oil phase, drops of an aqueous phase W.sup.1, containing: said non-amine hydrophilic compound C; and at least 5% by weight of a compound C carrying more than 2 amine groups; (E2) pouring the reverse emulsion of step (E1) in a second water phase W.sup.2 to make a multiple emulsion water/oil/water; and, then, (E3) curing into polyurethane all or part of the curable mixture contained in the oil phase.

Claims

1. A process for the encapsulation of a non-amine hydrophilic compound C, the process comprising the steps of: (E1) providing a reverse emulsion containing: an oil phase (O), comprising a curable mixture of isocyanate; and polyalkyldiene hydroxylated or polyol dispersed in said oil phase, drops of a water solution or dispersion (aqueous phase W.sup.1), containing: said non-amine hydrophilic compound; and at least 5% by weight, based on the total weight of the phase W.sup.1, of a compound C′ carrying more than 2 amine groups; (E2) pouring the reverse emulsion of step (E1) in a second water phase W.sup.2 to make a multiple emulsion water/oil/water, containing, as the internal water phase, drops including the non-amine hydrophilic compound C; and, then, (E3) curing into polyurethane all or part of the curable mixture contained in the oil phase, whereby a formulation is obtained, containing, dispersed in the phase W.sup.2 particles of polyurethane encapsulating an aqueous internal phase including the non-amine hydrophilic compound C.

2. The process of claim 1, wherein the oil phase (O) has a viscosity lower than the viscosity of phase (W.sup.1) in the conditions of steps (E1) and (E2).

3. The process of claim 1, wherein the water phase (W.sup.1) includes fatty acid esters.

4. The process of claim 1, wherein the water phase (W.sup.2) contains a mineral salt.

5. The process of claim 1, wherein the water phase (W.sup.2) contains a protective colloid and rheological agent.

6. The process of claim 1, wherein the compound C′ includes at least one polyethyleneimine.

7. The process of claim 1, wherein the compound C is a boric acid or another crosslinker of the guar.

8. The process of claim 1, wherein compound C is a dispersing agent or a clay inhibitor.

9. A formulation obtained according to the process of claim 1, comprising drops of a water phase including non-amine hydrophilic compound encapsulated in particles of polyurethane, said particles being dispersed in a water phase.

10. A method for allowing a targeted release of a compound C just at the drill bit by drilling with the formulation of claim 9.

11. The process of claim 1, wherein the non-amine hydrophilic compound C, does not contain any amine group.

12. The process of claim 3, wherein the fatty acid esters are esters of rapeseed oil.

13. The process of claim 4, wherein the mineral salt is NaCl.

14. The process of claim 5, wherein the protective colloid and rheological agent is xanthan gum.

15. A method for allowing a targeted release of a compound C, wherein capsules comprising the formulation of claim 9 are sheared entering the fractures and as fractures are closing at the end of a fracturing operation.

Description

Example 1

Encapsulation of Boric Acid According to the Invention

Preparation of a Reverse Emulsion

[0076] An aqueous medium w1 containing 10% by weight of boric acid was prepared by dissolving 38.5 mg of boric acid in 270 g of an aqueous solution of Polyethyleneimine (PEI at 50% by weight in water: Lupasol P from BASF) in 75 g of water.

[0077] The aqueous medium was dispersed within an oil phase as follows:

[0078] A mixture m1 was prepared, containing 500 g of a hydroxylated (OH functionalized) butadiene of molecular weight 2000 g/mol and an average 2.6 hydroxyl function per chain. and t500 g of a rapeseed oil methyl ester with an acid index below 0.2 mg KOH/g. 75.17 g of the aqueous medium w1 were mixed with 71.75 g of the mixture m1 to form an emulsion, and then 9.56 g of isophorone di-isocyanate trimer supplied diluted with 30% wt butyl acetate (Tolonate IDT 70B from Perstorp). was added to the formed emulsion. The particle size of the emulsion is set by acting on the agitation speed. The mixing time after the addition of isocyanate is set to 5 mn.

Preparation of a Multiple Emulsion

[0079] An aqueous phase w2 was prepared by mixing 111 g of NaCl and 5.05 g of xanthan gum (Rhodopol 23P available from the firm Solvay) in 883.3 g of water. The reverse emulsion, as freshly obtained according to the previous step, was poured slowly into 330.3 g of this phase w2 under agitation (3 blades paddle) and then dispersed under vigorous stirring. conditions to achieve a multiple emulsion.

Formation of the Polyurethane Shells

[0080] The obtained multiple emulsion was allowed to cure at room temperature (20° C.).

Example 2

Formation of a Borate Gel from the Formulation of Example 1

[0081] 5 g of the formulation prepared in example 1, containing boric acid encapsulated in polyurethane shells, was mixed with 200 g of an aqueous solution comprising 0.5% by weight of a guar (Jaguar 322 available from the firm Solvay) and 2% of KCl.

[0082] A solution of very low viscosity, easily pumpable, is obtained (270 mPa.Math.s at 1 s.sup.−1) and the solution remains of low viscosity at low and moderate shear.

[0083] When applying a high shear using a Silverson 4LRT rotor stator blender equipped with a 2 mm square hole high shear screen workhead at 7000 rpm, a gelation is triggered (due to the liberation of the boric acid), and a high viscosity is obtained (5550 mPa.Math.s at 1 s.sup.−1).