Abstract: An apparatus for coagulating particles of dissolved solids from an aqueous solution is provided. The apparatus includes an upright stirring vessel and a rotatable stirrer. The stirrer includes a substantially vertical shaft having a plurality of flat, radially extending blades secured symmetrically around the shaft such that the flat surfaces of each blade are substantially parallel to the plane of rotation of the blades. A plurality of knives extends upwardly and downwardly from each blade, each knife being a flat piece fixed to the top or underside surface of the blade so as to be approximately perpendicular to the longitudinal direction of the blade to which it is fixed and the flat surfaces of each knife being substantially tangential to the cylindrical plane of rotation of the knife. In a further embodiment of the apparatus, obstructing plates are secured to the inner wall of the vessel so as to obstruct the swirling motion in the solution provided by the stirrer.

Abstract: This invention relates to a process for separating polyvinyl alcohol from a solution. To an aqueous solution of polyvinyl alcohol, a coagulating agent is added. The coagulating agent consists essentially of a salting agent and a salt of boric acid. The salting agent is a member which is selected from the group consisting of an inorganic acid salt of a metal of the first or second groups of the periodic table, an inorganic ammonium salt and an inorganic aluminum salt. Following addition of the coagulating agent, the resulting mixture is agitated in order to coagulate the polyvinyl alcohol. The coagulated polyvinyl alcohol is then separated from the mixture.