GB679213A - Improvements in and relating to the production of cellulose acetate threads - Google Patents

Abstract

An aqueous acetic acid solution of cellulose acetate is extruded into an aqueous bath containing both potassium acetate and acetic acid so as to obtain artificial filaments, and the composition of the bath is maintained substantially constant by continuously or intermittently withdrawing part of the coagulant bath liquor, passing the withdrawn liquor to a heater chamber maintained at a temperature above 297 DEG C. (the melting point of potassium acetate) so that the liquor is converted into a liquid phase consisting mainly of molten potassium acetate and a vapour phase consisting of a mixture of acetic acid and water, and returning the potassium acetate thus separated to the bath. The temperature of the high-temperature evaporator should preferably not exceed 350 DEG C. If desired 5-10 per cent of sodium acetate based on the weight of the <PICT:0679213/IV (a)/1> potassium acetate may be present in the spinning bath liquor and in this case the temperature of the high-temperature evaporator may be as low as 277 DEG C. owing to the lower melting point of the mixture of potassium and sodium acetates. Preferably the withdrawn bath liquor is partially evaporated in a low-temperature evaporator at 80-130 DEG C. before it is passed to the high-temperature evaporator. In an example, a ripened cellulose acetate esterification solution containing aqueous acetic acid as the solvent medium is extruded into a solution containing 15 per cent of acetic acid, 40 per cent of potassium acetate, and 45 per cent of water. A portion of the coagulant liquor is withdrawn from bath 1 and passed through a preheater 2. The liquor now at 57 DEG C. is passed through the low-temperature evaporator 3 at 88 DEG C. and under a reduced pressure. The distillate, consisting of acetic acid and water, is passed through a condenser 4 and collected in tank 5. The concentrated liquor from the evaporator 3 is passed into the high-temperature evaporator 6 maintained at 310 DEG C. by a heat transfer fluid. The distillate, consisting of acetic acid and water, is used to heat the evaporator 3 as it passes to storage tank 5. The solution of acetic acid thus collected may be treated for the recovery of glacial acetic acid. The molten material consisting of potassium acetate with a little acetic acid is fed to mixer 7 where it is dissolved in a portion of the spinning bath liquor. The mixture at 107 DEG C. is used to heat the liquor in preheater 2 and it is then fed back to the spinning bath together with an addition of water. Specifications 281,827, [Class 2 (iii)], and 652,844, are referred to.