Integrated and improved process for the production of acrylic fibers

An integrated process for the production of acrylic fibers comprising the following steps:

• i) polymerizing comonomers in aqueous suspension in the presence of a quantity of solvent ranging from 3 to 25% by weight, with respect to the total weight of the aqueous suspension, wherein the solvent is the same solvent used in the following steps ii)-vi) and wherein the water that constitutes the aqueous suspension comprises recycled water coming from a last washing step of the spinning step, in an amount ranging from 10 to 40% by weight, with respect to the total weight of the water of the aqueous suspension, said polymerization being catalyzed by a redox ammonium persulfate/ammonium bisulphite pair in the presence of catalytic quantities of iron sulfate, with the subsequent removal of the unreacted monomers, first filtration of the aqueous suspension and washing of the same, obtaining a first filtration cake comprising polymer and water with traces of solvent in a ratio ranging from 40/60 to 60/40 by weight;
• ii) dispersing said first filtration cake obtained in step i) in a solvent/water mixture or in a pure solvent in a weight ratio ranging from 2 to 10 times the weight of the cake and for a time ranging from 5 to 15 minutes, under stirring, to provide a polymeric dispersion;
• iii) separating the solid/liquid phases of said polymeric dispersion by filtration or centrifugation, obtaining a second cake comprising polymer and solvent/water mixture, in a ratio between solvent and water ranging from 60/40 to 85/15 by weight;
• iv) redispersing the second cake obtained in step iii) in the same solvent or water/solvent mixture of step ii) in a weight ratio ranging from 2 to 10 times the weight of the polymer in the cake, at room temperature or at a temperature lower than room temperature for a time ranging from 5 to 20 minutes, obtaining a homogeneous dispersion or slurry wherein the weight ratio between solvent/polymer ranges from 90/10 to 70/30;
• v) heating the homogeneous dispersion or slurry obtained in step iv) until the complete dissolution of the polymer and obtaining a homogeneous spinning solution;
• vi) feeding the homogeneous spinning solution obtained at the end of step v) to a spinning step.