Patent ID: 8592516

Claim:
A process for drying water-absorbing polymer particles by polymerizing a monomer solution comprising at least one ethylenically unsaturated acid-functional monomer and at least one crosslinker and comminuting a resulting hydrogel to hydrogel particles, then drying the hydrogel particles, said drying comprising use of a heated gas stream, and (a) effecting the drying in two or more temperature zones for which gas inlet temperatures satisfy the condition T n unequal T n+a and the gas inlet temperature T n+a is at least 150° C., where the indices n and a are each a whole number greater than 0, and/or (b) the gas stream is flowed against the hydrogel particles upwardly in an upstream sector of a belt dryer and downwardly in a downstream sector of a belt dryer, the direction of flow being reversed at a water content of 15% to 45% by weight for the hydrogel particles, and/or (c) a layer of the hydrogel particles is flowed against in a belt dryer upwardly to some extent at least, a gas velocity being 5% to 30% of a gas velocity required to lift the hydrogel off the belt.