Manufacture of polymer coated proppants
Solid proppants are coated in a process that includes the steps of: (a) coating free-flowing proppant solids with a first component of either a polyol or an isocyanate in mixer; (b) adding a second component of either an isocyanate or a polyol that is different from the first component at a controlled rate or volume sufficient to form a polyurethane coating on the proppant solids; and (c) adding water at a rate and volume sufficient to retain the free-flowing characteristics of the proppant solids.
1. A method for the production of proppant that is coated with a polymeric coating, the method comprising:
(a) coating free-flowing proppant solids in a mixer with a first component comprising a polyol;
(b) adding to the mixer a second component comprising an isocyanate that has at least 2 reactive isocyanate groups and which is added at a controlled rate and volume sufficient to form a polymeric coating on said proppant solids; and
(c) adding water to the mixer at about the time the isocyanate has begun to be added to the mixer at a rate and volume sufficient to retain the free-flowing characteristics of said proppant solids and addition of the water to the mixer does not conclude until all isocyanate has been added.
2. The method according to claim 1 , wherein said proppant solid is selected from the group consisting of ceramic particles, composite particles, and sand.
3. A method according to claim 1 , wherein the method further comprises adding a coupling agent and a catalyst to the mixer.
4. A method according to claim 1 , wherein the water is added to said mixer when said isocyanate begins to be added to the mixer.
5. A method according to claim 1 , wherein the polyol of said first component is a natural oil polyol, an aliphatic polyol, an aromatic polyol, or mixtures thereof.
6. A method according to claim 5 , wherein said polyol of said first component comprises a natural oil polyol.
7. A method according to claim 6 , wherein said natural oil polyol is castor oil.
8. A method according to claim 1 , wherein said coating step a) is carried out at a temperature within the range from about 10 ° C. to about 250 ° C.
9. A method according to claim 1 , wherein said proppant solid is preheated to a temperature within the range of 50° to 250 ° C. before contact with said first component.
10. A method according to claim 1 , further comprising curing the coated proppant under conditions sufficient to produce a coated proppant that exhibits a loss of coating of less than 15 wt % when tested according to ISO 13503- 5:2006(E).
11. A method according to claim 10 , wherein said coating exhibits a loss of less than 5 wt %.
12. The method of claim 3 , wherein the catalyst is a reactive amine catalyst.
13. The method of claim 3 , wherein the coupling agent is a silane.
14. The method of claim 1 , wherein the water is added to the mixer within about 5 to 15 seconds of when the isocyanate is added to the mixer.
15. The method of claim 1 , wherein the water is completely added to the mixer from about 30 to 60 seconds.
16. The method of claim 1 , wherein the water comprises a biocide.