Patent GB-777405-A (GB)
Title: Improvements in or relating to preparation of finely-divided cellulose derivatives
IPC: C08B11/20
Filed: 1955-06-30
Abstract: The process of the parent Specification (wherein a film-forming cellulose ether, ester or esterether, alone or associated with plasticisers, is converted into powder form by spraying a lacquer-in-water emulsion containing, in addition to water, a solution of the cellulose derivative in a water-immiscible volatile solvent, into a heated gaseous medium to vaporize liquid from the emulsion) is modified by continuously spraying the emulsion, at a temperature below the boiling-point of the lacquer solvent therein, into an enclosed vessel containing a steam atmosphere, continuously and simultaneously introducing steam into the enclosed vessel at a rate at least sufficient to vaporize substantially all the lacquer solvent from the emulsion being sprayed into the chamber and to precipitate the cellulose derivative, alone or associated with plasticiser, as uniformly small, solid spheroids, preferably not over 5 microns in diameter, in the water of the emulsion droplets, the temperature and pressure in the enclosed vessel and the location of the steam inlet thereto being such as to cause water to collect at the bottom of the vessel, allowing the water droplets containing the precipitated spheroids to form an aqueous suspension of the spheroids in the bottom of the vessel, withdrawing from the vessel vapours consisting essentially of a mixture of solvent vapour and water vapour, and withdrawing the water suspension of cellulose derivative spheroids from the bottom of the vessel.  In the example, a lacquer-in-water emulsion, consisting of a solution of 7.7 parts by weight of cellulose acetate in 54 parts of methylene chloride and 6 of ethyl alcohol dispersed by means of 0.2 part by weight of sodium dioctyl sulphosuccinate in 30 parts of water, is sprayed continuously at room temperature into near the top of a vertical unpacked steam stripping column, into the lower portion of which steam is fed continuously at a rate equivalent to 2.26 parts of steam for each part by weight of total liquid content of the emulsion.  The lacquer solvent is thereby flashevaporated from the emulsion, and the cellulose acetate is precipitated as solid spheroids of diameter 1 to 5 microns which form a suspension in the water derived from the emulsion augmented by that resulting from condensation of the steam. The suspension, containing only 0.1 per cent of methylene chloride and ethyl alcohol respectively, is continuously withdrawn from the bottom of the column by means of a constant level syphon and dewatered by centrifugation, and the wet centrifuge cake is dried on trays in a hot air oven.  Vapours of solvent and steam are continuously withdrawn from the top of the stripping column which is at atmospheric pressure.  The process may be used for the same cellulose derivatives as are referred to in the parent Specification and in addition for nitrocellulose.  The solvents which may be used include chlorinated hydrocarbons such as ethyl, methylene or ethylene chloride, trichlorethylene or carbon tetrachloride; lower aliphatic ethers such as dimethyl, diethyl, methyl ethyl, allyl ethyl, butyl ethyl or di-isopropyl ether; methyl ethyl ketone, benzene, and mixtures of the above solvents with minor proportions of water-soluble solvents such as the lower boiling aliphatic alcohols and esters.