Methods For Producing Superabsorbent Polymers For Use In Agricultural Applications

Abstract

Methods and systems for producing superabsorbent polymer particles for use in agricultural applications are disclosed. A monomer is graft polymerized onto a starch to form a starch graft copolymer. The moisture content of the starch graft copolymer is reduced through the use of an extruder.

1 . 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.   
   
   
       2 . The system of  claim 1 , wherein 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 to about 40% by weight or less, in one or more passes through the heated extruder 
   
   
       3 . The system of  claim 2 , wherein the heated extruder further comprises at least one vent, such that a vacuum source is coupled to the at least one vent. 
   
   
       4 . The system of  claim 1 , wherein the extrusion screw comprises a double-screw system, wherein flights of each screw intermesh as they rotate. 
   
   
       5 . The system of  claim 1 , 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. 
   
   
       6 . The system of  claim 1 , 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. 
   
   
       7 . The system of  claim 1 , 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. 
   
   
       8 . The system of  claim 1 , 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.   
   
   
       9 . The system of  claim 1 , 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.   
   
   
       10 . The system of  claim 9 , 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.   
   
   
       11 . The system of  claim 10 , 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.   
   
   
       12 . 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; and 
 an extrusion screw passing through a length of 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 of between about 20 rpm to about 150 rpm, and the heated extruder produces a heat at a temperature of between 50° C. and 160° C., 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.   
   
   
       13 . The system of  claim 12 , wherein the extrusion screw is configured to operate at a pressure of between 25 psi and 40 psi. 
   
   
       14 . The system of  claim 12 , wherein the polymerization dough pumped into the inlet has a viscosity of between 2.5 million centipoise and 0.5 million centipoise. 
   
   
       15 . The system of  claim 12 , wherein the heated extruder further comprises:
 an outlet comprising a die plate, the die plate configured to pass the polymerization dough after the dough passes through the heated extruder.   
   
   
       16 . The system of  claim 15 , 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.   
   
   
       17 . The system of  claim 16 , 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.