Reversible microcapsule filter cake
The invention teaches a method of efficiently dewatering a microcapsule slurry to form a water re-suspendable filter cake of microcapsules. The process comprises providing an aqueous slurry of microcapsules dispersed in an aqueous solution; adding an agglomeration agent and dispersing the agglomeration agent into the aqueous slurry; adjusting the pH to a pH level sufficient to agglomerate the dispersed microcapsules; and filtering the aqueous slurry of microcapsules by gravity, vacuum or pressure filtration to thereby form a filter cake of dewatered microcapsules. The agglomeration agent is sodium polyphosphate, sodium tetrapolyphosphate, sodium hexametaphosphate, and/or sodium tripolyphosphate; or with anionic microcapsules or coatings even alkaline earth metal salts such as magnesium chloride, calcium chloride or barium chloride, or even aluminum salt such as aluminum chloride.
1. A method of dewatering a microcapsule slurry to form a water re-suspendable filter cake of microcapsules comprising:
providing an aqueous slurry of microcapsules dispersed in an aqueous solution, wherein the microcapsules are cationic microcapsules having an acrylate wall;
adding an agglomeration agent selected from an alkali metal polyphosphate or an alkaline earth metal polyphosphate and dispersing the agglomeration agent into the aqueous slurry of microcapsules;
adjusting the pH of the aqueous slurry of microcapsules to at least a pH of 5 to agglomerate the microcapsules;
centrifuging or filtering the aqueous slurry of microcapsules by gravity, vacuum, or pressure filtration to form a filter cake of dewatered microcapsules.
2. The method according to claim 1 wherein the pH is adjusted using a caustic material selected from sodium hydroxide, potassium hydroxide, ammonium hydroxide, a hydride of an alkali or alkaline earth metal, an alkoxide, or a metal amide.
3. The method according to claim 1 , wherein the agglomeration agent is sodium polyphosphate.
4. The method according to claim 1 wherein the agglomeration agent is selected from the group consisting of sodium tetraphosphate, sodium hexametaphosphate and sodium tripolyphosphate.
5. The method according to claim 1 wherein the microcapsules have a volume-average microcapsule size of 15 microns or less.
6. The method according to claim 1 wherein the microcapsules of the aqueous slurry of microcapsules are coated with cationic polymer selected from the group consisting of polyvinyl amine, polyvinyl formamide, polyallyl amine and copolymers of any of the foregoing.
7. A method of dewatering a microcapsule slurry to form a water-resuspendable filter cake of microcapsules comprising:
providing an aqueous slurry of microcapsules dispersed in an aqueous solution wherein the microcapsules are cationic microcapsules having an acrylate wall, adding an agglomeration agent selected from an alkali metal polyphosphate or an alkaline earth metal polyphosphate to the aqueous slurry of microcapsules and
dispersing the agglomeration agent into the aqueous slurry of microcapsules; adjusting the pH of the aqueous slurry of microcapsules from pH 4 to 10 to agglomerate the microcapsules; and centrifuging or filtering the aqueous slurry of microcapsules by gravity, vacuum, or pressure filtration to form a filter cake of dewatered microcapsules.
8. The method according to claim 7 wherein the pH is adjusted using a caustic material selected from sodium hydroxide, potassium hydroxide, ammonium hydroxide, a hydride of an alkali or alkaline earth metal, an alkoxide or a metal amide.
9. The method according to claim 7 wherein the microcapsules have a volume-average microcapsule size of 15 microns or less.
10. The method according to claim 7 wherein the microcapsules of the aqueous slurry of microcapsules are coated with cationic polymer selected from the group consisting of polyvinyl amine, polyvinyl formamide, poly allyl amine and copolymers of any of the foregoing.