Patent GB-776535-A (GB)
Title: Improvements in the manufacture of organic substances of very high molecular weight
Inventor: JOHNSTON DAVID ROBERT
IPC: C08B17/02
Filed: 1954-03-02
Abstract: <PICT:0776535/IV(a)/1> Organic substances of very high molecular weight, such as cellulose derivatives and vinyl polymers, are precipitated from their solutions or latices by causing unsupported streams of the solution or latex and of a precipitant to impinge simultaneously on the same area or on immediately adjacent areas of the surface of a body of the precipitant.  A "precipitant" is defined as a liquid nonsolvent for the organic substance which is miscible with the solvent in which the substance is dissolved, and a "body of precipitant" is defined as a mass of precipitant which is capable of absorbing at least the greater part of the momentum of the unsupported streams.  The unsupported streams of solution and precipitant are preferably substantially parallel and in contact, and the stream or streams of solution are preferably surrounded by a stream or streams of precipitant.  While the unsupported streams of solution and precipitant may remain distinct until they reach the surface of the body of precipitant, a certain amount of mixing may take place in advance of this surface, the degree of mixing being increased, if desired, by causing the stream or streams of precipitant to travel more rapidly than the stream of solution or by promoting turbulent flow in one or more of the streams or by causing the streams to converge slightly.  The precipitant in the unsupported stream or streams and that in the body of precipitant should preferably either be identical or, if they are mixtures, should at least contain the same chemical components, so as to facilitate recovery.  The amount of precipitant in the unsupported stream or streams should preferably in itself be sufficient to precipitate the whole of the organic substance from the stream of solution.  The substance precipitated may be a cellulose ester or ether, a polyvinyl compound such as polyvinyl chloride, alcohol or acetate, or a copolymer derived from two or more vinyl or vinylidene compounds, e.g. a copolymer of vinylidene chloride and acrylonitrile.  The solution may be extruded to form the unsupported stream or streams either at room temperature or at a higher temperature, which may be above or below the boiling point of the solvent.  The precipitant may be at the same temperature as the solvent or at a lower or higher temperature.  The solution or precipitant or both may be heated to a temperature such that part or all of the solvent is vaporized as or after the streams of solution and precipitant impinge on the body of precipitant.  As shown in Fig. 1, the solution of the organic substance to be precipitated is fed through feed pipe 19 to the middle annular orifice of a triple annular nozzle 16 (such as is described in Specification 750,008) while the precipitant is fed from the common feed line 20 and feed pipes 17, 18 to the innermost and outermost annular orifices of the nozzle 16, which extends vertically through the top of the vertical cylindrical precipitating vessel 10 about half way between the axis and the wall of the vessel.  The streams of solution and precipitant impinge on the surface of the body of precipitant in the vessel 10 and are rapidly mixed with each other and with the precipitant already in the vessel.  The slurry of precipitate so produced leaves the vessel 10 through the overflow discharge duct 12 leading to a separating vessel or a shaking screen (not shown). The mixing of the solution and precipitant in the vessel 10 is aided by the propeller-type stirrer 14 mounted on the driven vertical shaft 15, and the slurry may be diluted with further precipitant introduced through the additional feed pipe 11.  The vessel 10 is provided with a temperature control jacket 13 and a drain 12A.  The triple annular nozzle 16 is described and shown in greater detail and two other types of nozzles are also described and illustrated, all three being identical with those described and shown in Specification 750,008.  In the example, a solution of acetone-soluble cellulose acetate in about three times its weight of 75 per cent aqueous acetic acid, obtained in the manufacture of the acetate, is extruded at 65-70 DEG  C. through the middle annular orifice of the triple annular orifice 16 into 14 per cent aqueous acetic acid at about 70 DEG  C. occupying the precipitating vessel 10 up to the level of the overflow duct 12, while at the same time 7.4 to 14 per cent aqueous acetic acid at 70 DEG  C. is extruded through the inner and outer annular orifices of the nozzle. Simultaneously further 14 per cent aqueous acetic acid at about 70 DEG  C. is fed into the vessel 10 through the inlet pipe 11, and the diluted slurry of cellulose acetate in aqueous acetic acid is discharged through the overflow duct 12.ALSO:<PICT:0776535/III/1> Organic substances of very high molecular weight, such as cellulose derivatives, are precipitated from their solutions or latices by causing unsupported streams of the solution or latex and of a precipitant to impinge simultaneously on the same area or on immediately adjacent areas of the surface of a body of the precipitant.  A "precipitant," is defined as a liquid non-solvent for the organic substance which is miscible with the solvent in which the substance is dissolved, and a "body of precipitant" is defined as a mass of precipitant which is capable of absorbing at least the greater part of the momentum of the unsupported streams.  The unsupported streams of solution and precipitant are preferably substantially parallel and in contact, and the stream or streams of solution are preferably surrounded by a stream or streams of precipitant.  While the unsupported streams of solution and precipitant may remain distinct until they reach the surface of the body of precipitant, a certain amount of mixing may take place in advance of this surface, the degree of mixing being increased if desired by causing the stream of streams or precipitant to travel more rapidly than the stream of solution or by promoting turbulent flow in one or more of the streams or by causing the streams to converge slightly.  The precipitant in the unsupported stream or streams and that in the body of precipitant should preferably either be identical, or, if they are mixtures, should at least contain the same chemical components, so at to facilitate recovery.  The amount of precipitant in the unsupported stream or streams should preferably in itself be sufficient to precipitate the whole of the organic substance from the stream of solution.  The substance precipitated may be a cellulose ester or ether, a polyvinyl compound such as polyvinyl chloride, alcohol or acetate, or a copolymer derived from two or more vinyl or vinylidene compounds, e.g. a copolymer of vinylidene chloride and acrylonitrile.  The solution may be extruded to form the unsupported stream or streams either at room temperature or at a higher temperature, which may be above or below the boiling point of the solvent.  The precipitant may be at the same temperature as the solvent or at a lower or higher temperature.  The solution or precipitant or both may be heated to a temperature such that part or all of the solvent is vaporized as or after the streams of solution and precipitant impinge on the body of the precipitant.  As shown in Fig. 1, the solution of the organic substance to be precipitated is fed through feed pipe 19 to the middle annular orifice of a triple annular nozzle 16 (such as is described in Specification 750,008) while the precipitant is fed from the common feed line 20 and feed pipes 17, 18 to the innermost and outermost annular orifices of the nozzle 16, which extends vertically through the top of the vertical cylindrical precipitating vessel 10 about half way between the axis and the wall of the vessel.  The streams of solution and precipitant impinge on the surface of the body of precipitant in the vessel 10 and are rapidly mixed with each other and with the precipitant already in the vessel.  The slurry of precipitant so produced leaves the vessel 10 through the overflow discharge duct 12 leading to a separating vessel or a shaking screen (not shown).  The mixing of the solution and precipitant in the vessel 10 is aided by the propeller-type stirrer 14 mounted on the driven vertical shaft 15, and the slurry may be diluted with further precipitant introduced through the additional feed pipe 11.  The vessel 10 is provided with a temperature control jacket 13 and a drain 12A.  The triple annular nozzle 16 is described and shown in greater detail and two other types of nozzles are also described and illustrated, all three being identical with those described and shown in Specification 750,008.  In the example, a solution of acetone-soluble cellulose acetate in about three times its weight of 75 per cent aqueous acetic acid obtained in the manufacture of the acetate, is extruded at 65-70 DEG C. through the middle annular orifice of the triple annular orifice 16 into 14 per cent aqueous acetic acid at about 70 DEG C. occupying the precipitating vessel 10 up to the level of the overflow duct 12, while at the same time 7.4 to 14 per cent aqueous acetic acid at 70 DEG C. is extruded through the inner and outer annular orifices of the nozzle.  Simultaneously further 14 per cent aqueous acetic acid at about 70 DEG C. is fed into the vessel 10 through the inlet pipe 11, and the diluted slurry of cellulose acetate in aqueous acetic acid is discharged through the overflow duct 12.