Method and apparatus for producing core-shell calcium hydroxide-calcium carbonate particles
A method for preparing calcium carbonate (CaCO 3 ) coated calcium hydroxide (Ca(OH) 2 ) particles. The method includes introducing liquid carbon dioxide into a reaction vessel, introducing calcium hydroxide particles into the reaction vessel, and effectively mixing the calcium hydroxide particles into the liquid carbon dioxide. The method further includes inducing a phase change in the liquid carbon dioxide so as to coat the calcium hydroxide in dry ice. In a different embodiment, liquid carbon dioxide may be introduced into a throttle valve inducing a phase change into a mixture of a gaseous carbon dioxide and a solid dry ice, and calcium hydroxide particles can be introduced into an exit stream with said mixture, inducing heterogeneous nucleation of the dry ice. In addition, both embodiments include sublimating the dry ice after a predetermined residence time to control the thickness of the calcium carbonate coating on the calcium hydroxide particles.
1. A method of preparing calcium carbonate (CaCO 3 )-coated calcium hydroxide (Ca(OH) 2 ) particles comprising:
introducing liquid carbon dioxide into a reaction vessel without inducing a phase change in the liquid carbon dioxide;
feeding calcium hydroxide particles into an auxiliary chamber;
flushing the calcium hydroxide particles in the auxiliary chamber with the liquid carbon dioxide to form a mixture;
introducing the mixture into the reaction vessel to be further mixed with the already present liquid carbon dioxide;
inducing a phase change in the liquid carbon dioxide so as to coat the calcium hydroxide particles in dry ice; and
sublimating the dry ice after a predetermined residence time to control the thickness of the calcium carbonate coating on the calcium hydroxide particles.
2. The method of claim 1 , wherein the liquid carbon dioxide introduced into the reaction vessel is at a pressure of 8 MPa and a temperature of −25° C.
3. The method of claim 1 , wherein the liquid carbon dioxide is introduced into the reaction vessel at a pressure range of 0.518 MPa to 16 MPa and a temperature range of −56.56° C. to 30.98° C.
4. The method of claim 1 , wherein the reaction vessel is a high-pressure reactor, the high-pressure reactor further comprising a stirrer for mixing.
5. The method of claim 1 , wherein the reaction vessel is an inline mixer.
6. The method of claim 1 , wherein inducing the phase change in the liquid carbon dioxide is performed using a throttle valve to flash the liquid carbon dioxide into dry ice.
7. The method of claim 6 wherein the throttle valve flashes at an exit pressure of 0.1 MPa.
8. The method of claim 6 , wherein the throttle valve flashes at an exit pressure range of 0.01 MPa to 0.518 MPa and a temperature lower than −56.56° C.
9. The method of claim 1 , wherein controlling the thickness of the calcium carbonate coating on the calcium hydroxide particles occurs over the predetermined residence time in a separator vessel at a pressure of less than or equal to 0.518 MPa.
10. The method of claim 1 , further comprising:
collecting gaseous carbon dioxide from the sublimation of the dry ice; and
inducing a phase change in the gaseous carbon dioxide to provide liquid carbon dioxide to be introduced into the reaction vessel.