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1. WO2007087359 - METHODS FOR PRODUCING SUPERABSORBENT POLYMERS FOR USE IN AGRICULTURAL APPLICATIONS

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[ EN ]

CLAIMS:
1. A method of producing a superabsorbent polymer product for use in agricultural applications, comprising:
graft polymerizing a monomer onto a starch in the presence of an initiator to form a starch graft copolymer, the starch graft copolymer forming a polymerization dough;
feeding the polymerization dough into a heated extruder; and
reducing the moisture content of the polymerization dough by drying the polymerization dough in the heated extruder.
2. The method of claim 1 , wherein reducing the moisture content comprises reducing the moisture content of the polymerization dough to less than 65% by weight by drying the polymerization dough in the heated extruder.
3. The method of claim 1 , wherein reducing the moisture content comprises reducing the moisture content of the polymerization dough to about 40% by weight or less by drying the polymerization dough in the heated extruder.
4. The method of claim 3, wherein reducing the moisture content of the polymerization dough comprises passing the polymerization dough through the heated extruder multiple times until the moisture content is about 40% by weight or less.
5. The method of claim 1 , further comprising:
saponifying the starch graft copolymer before drying the polymerization dough in the heated extruder;
wherein the monomer is at least acrylonitrile.
6. The method of claim 1 , further comprising:
adjusting a pH of the starch graft copolymer to between about 6.0 and about 8.0 before drying the polymerization dough in the heated extruder.
7. The method of claim 6, further comprising:
cross-linking the starch graft copolymer;
wherein the monomer is other than acrylonitrile and the monomer is chosen from: acrylic acid, acrylamide, methacrylamide, 2-acrylamido-2-methyl-propanesulfonic acid, methacrylic acid, vinyl sulfonic acid, ethyl acrylate, potassium acrylate, and derivatives and mixtures thereof.
8. The method of claim 1 , further comprising: supplying an additive to the polymerization dough, wherein the additive is chosen from at least one of the following: fertilizers, herbicides, pesticides, fungicides, and growth regulators.
9. The method of claim 1 , wherein reducing the moisture content comprises heating the polymerization dough in the heated extruder at a temperature between about 500C and about 160°C.
10. The method of claim 1 , wherein reducing the moisture content comprises heating the polymerization dough in the heated extruder at a temperature between about 125X and about 15O0C.
11. The method of claim 1, wherein the heated extruder comprises an extrusion screw, the method further comprising:
operating the extrusion screw at a speed between about 50 rpm and about 80 rpm.
12. The method of claim 1, wherein the heated extruder comprises at least one vent, the method further comprising:
applying a negative pressure to the at least one vent to facilitate the removal of steam from the heated extruder.
13. The method of claim 1, wherein feeding the polymerization dough into a heated extruder comprises applying a pressure to the polymerization dough greater than atmospheric pressure.
14. The method of claim 1 , further comprising:
cooling the polymerization dough, wherein cooling the polymerization dough is at least one of the following: cooling the polymerization dough at an interval within the heated extruder, and cooling the polymerization dough after the dough exits the extruder and before feeding the polymerization dough into the heated extruder a second time.
15. The method of claim 1 , further comprising:
granulating the polymerization dough after the moisture content of the polymerization dough is reduced in the heated extruder.
16. A system for drying a superabsorbent polymer product subsequent to forming a polymerization dough of a starch graft copolymer, the system comprising: a heated extruder, the heated extruder comprising:
an inlet for receiving the polymerization dough;

an extrusion screw passing through a length of the heated extruder; and
an outlet comprising a die plate, the die plate configured to pass the polymerization dough after the dough passes through the heated extruder; and
a pump feeding system configured to pump the polymerization dough into the inlet;
wherein the extrusion screw rotates at a speed and the heated extruder produces a heat, such that the speed of the extrusion screw and the heat produced by the heated extruder are configured to reduce a moisture content of the polymerization dough.
17. The system of claim 16, wherein the speed of the extrusion sprew and the heat produced by the heated extruder are configured to reduce a moisture content of the polymerization dough to about 40% by weight or less, in one or more passes through the heated extruder
18. The system of claim 17, wherein the heated extruder further comprises at least one vent, such that a vacuum source is coupled to the at least one vent.
19. The system of claim 17, wherein the heated extruder is configured to reduce a moisture content of the polymerization dough to about 40% by weight or less, in between one pass and five passes through the heated extruder.
20. The system of claim 17, wherein the heated extruder is configured to reduce a moisture content of the polymerization dough to about 40% by weight or less, in two passes or less through the heated extruder.
21. The system of claim 16, wherein the extrusion screw comprises a double-screw system, wherein flights of each screw intermesh as they rotate.
22. The system of claim 16, wherein the extrusion screw comprises multiple segments, such that at least two portions of a given segment of the extrusion screw have different flight configurations.
23. The system of claim 16, wherein the heated extruder comprises a series of barrels in communication with each other, wherein the series of barrels comprises between 20 and 24 barrels arranged in series.
24. The system of claim 16, wherein the pump feeding system is configured to deliver the polymerization dough to the inlet of the heated extruder under a pressure greater than atmospheric pressure.

25. The system of claim 16, further comprising:
an air-cooled conveyor in communication with the outlet of the heated extruder, and configured to receive and cool the polymerization dough after exiting from the die plate.
26. The system of claim 16, further comprising:
a granulator configured to granulate the polymerization dough, the granulator receiving the polymerization dough subsequent to the dough exiting from the die plate.
27. The system of claim 26, further comprising:
a particle separation system to separate the granulated polymerization dough based on mesh size, the particle separation system receiving the granulated dough subsequent to the dough exiting the granulator.
28. The system of claim 27, further comprising:
a centrifuge for centrifuging the granulated polymerization dough subsequent to the dough exiting the granulator and previous to the particle separation system receiving the granulated dough; and
a dryer for drying the granulated polymerization dough subsequent to the •dough exiting the granulator and previous to the particle separation system receiving the granulated dough.