Patent ID: 8273134

Claim:
A method for spinning and washing aramid fiber and for recovering sulfuric acid comprising: a) spinning an aramid polymer from an aramid polymer and sulfuric acid spin dope by expelling the spin dope through a spinneret to obtain an expelled spin dope, coagulating the expelled spin dope with water or diluted sulfuric acid by transporting the expelled spin dope through a coagulation bath containing water or diluted sulfuric acid to obtain a coagulated yarn in a coagulation bath having an inlet for water or diluted sulfuric acid and an outlet for sulfuric acid enriched water; b) washing the coagulated yarn with water to obtain a washed yarn and a washing water containing sulfuric acid; c) recycling the sulfuric acid enriched water to a sulfuric acid recovery unit; d) increasing the sulfuric acid content of the recycled sulfuric acid enriched water by evaporation to obtain evaporated sulfuric acid consisting of 20 to 98% sulfuric acid and water; e) mixing the 20 to 98% sulfuric acid obtained in step d) with oleum to obtain 98-105% sulfuric acid; and f) recycling the 98-105% sulfuric acid to a spinning unit for inclusion as at least a portion of the sulfuric acid spin dope.