| 摘要 |
1,016,505. Polyacrylonitrile spinning. SNIA VISCOSA SOC. NAZIONALE INDUSTRIA APPLICAZIONI VISCOSA S.p.A. Oct. 16, 1963 [Oct. 22, 1962], No. 40875/63. Heading B5B. Organic solvents are recovered from coagulation and stretching baths used in the wet spinning of polyacrylonitrile, and comprising organic solvents and concentrated aqueous solutions of potassium formate or acetate, by extraction, using monomeric acrylonitrile as an extracting agent. Extraction may be effected at room temperature and in one stage, or in two or more successive stages. Desirably the congulating or stretching bath contains 25-45% by weight of water and 5-40% by weight of organic solvent, especially dimethylformamide. In general, the bath is extracted with acrylonitrile and on standing separates into an upper layer containing mainly dimethyl formamide and acrylonitrile, with a small proportion of water, and a lower layer containing an aqueous solution of the potassium salt, a small proportion of dimethyl formamide, and a smaller proportion of acrylonitrile. The proportion of water in the upper layer may be reduced by salting-out with potassium formate or anhydrous potassium acetate, whereupon separation occurs into two layers, an upper layer consisting of mainly of dimethyl formamide and acrylonitrile, with a small proportion of water, and a lower layer consisting of the concentrated aqueous solution of the salt. This lower layer may be added to the first mentioned lower layer and recycled into the spinning process after removal of the acrylonitrile and suitable dilution, while the combined upper layers may be purified by passage through carbon granules or ion-exchange resins, distilled and recycled for polymerization. The method is especially useful where the polyacrylonitrile is obtained by polymerization of monomeric acrylonitrile in dimethyl formamide. |
