Patent GB-776066-A (GB)
Title: Improvements in the manufacture of very high molecular weight organic substances
Inventor: JOHNSTON DAVID ROBERT
IPC: C08B17/02
Filed: 1954-03-11
Abstract: <PICT:0776066/IV(a)/1> <PICT:0776066/IV(a)/2> Organic substances of very high molecular weight, such as cellulose derivatives and vinyl polymers, are precipitated from their solutions or latices by forming streams of the solution or latex and of a precipitant in contact with one another, and causing the streams to intermix intimately and completely, and so as to form a suspension or slurry of precipitate in a liquid medium comprising the precipitant, while they are still travelling freely.  A "precipitant" is defined as a liquid non-solvent for the organic substance which is miscible with the solvent in which the organic substance is dissolved.  Preferably the stream of solution, or each stream of solution if there is more than one, is bounded on both sides by precipitant.  The streams of solution and precipitant may be caused to intermix while out of contact with any solid surface, for instance by extruding the solution and precitant under pressure into a precipitating vessel large enough to allow the streams to intermix completely before they strike a wall of the vessel, or the streams may intermix in a closed conduit, or less desirably an open channel, with the wall of which at least one of them is in contact.  The streams may initially travel in any direction, which may remain the same or may change. The slurry of precipitate in the mixture of solvent and precipitant may be mixed with a further quantity of precipitant. 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.  Cellulose acetate may be precipitated from solutions obtained in its manufacture.  The cellulose acetate solution may be extruded either at room temperature or at a higher temperature, which may be below or above the boiling point of the solvent.  For example, solutions of cellulose acetate in acetic acid which have been ripened at about 50-80 DEG  C. may be extruded at about the ripening temperature.  The precipitant may be at about the same temperature as the cellulose acetate solution, or at a higher or lower temperature.  The precipitant, or both the precipitant and the solution, may be heated to a temperature such that part or all of the solvent is vaporized as the streams of solution and precipitant are mixed, particularly when a low boiling solvent such as methylene chloride is used.  In the example, a solution of acetone-soluble cellulose acetate in about three times its weight of 75 per cent aqueous acetic acid at 65-70 DEG  C., obtained in the manufacture of the acetate, is extruded through the middle annular orifice of a triple annular nozzle 11 (Fig. 1) extending into a precipitating vessel 10 or a similar type of nozzle 60 (Fig. 3) extending into a closed conduit 65 of circular cross-section.  At the same time aqueous acetic acid of 7.4-14 per cent concentration and at 70 DEG  C. is extruded at a considerably higher linear speed through the innermost and outermost annular orifices of the nozzle.  When the precipitating vessel 10 is employed, further aqueous acetic acid at the same temperature and of the same concentration is introduced through the liquid inlet 12 (Fig. 1) near the nozzle.  The slurry formed by the mixing of the streams of cellulose acetate solution and dilute acetic acid is run off from the precipitating vessel through the outlet 13 or from the discharge end of the conduit 65, and the precipitate and the liquid are separated by decantation. The height and length of the vessel 10 shown in Fig. 1 are such as to allow the streams of solution and precipitant leaving the nozzle 11 to complete their trajectory without impinging on any wall of the vessel.  The vessel 10 may be circular in cross section, but is preferably considerably higher than it is wide, having, for example, an elliptical or rectangular cross-section. The nozzle 11 is provided with feed pipes 14, 15 (fed from a common feed line 17) for precipitant and a feed pipe 16 for the solution.  The streams of precipitant and solution start to intermix as soon as they have left the nozzle 11, and the composite stream which they form follows a roughly parabolic path, rising near to the top of the vessel 10 and falling to the bottom at a point short of the outlet 13.  The triple annular nozzle 60 shown in Fig. 3 is provided with feed pipes 61, 62 (fed from a common feed line 64) for the precipitant and a feed pipe 63 for the solution.  The nozzle 60 opens into one end of a conduit 65 having a bore (except in the immediate vicinity of the nozzle) about equal to the outside diameter of the outermost annular orifice of the nozzle.  At its input end 66 the conduit 65 expands and fits round the nozzle 60, forming with it a liquid-tight joint.  Over most of its length the conduit 65 is horizontal, but near its output end 67 turns vertically downwards. In the conduit 65 the streams of precipitant and solution are intimately mixed and the slurry of precipitated cellulose acetate thus formed leaves the conduit through the vertical outlet 67.  The triple annular nozzles 11 and 60, and two other types of nozzles which are also described and shown in additional drawings, are identical with those shown and described in Specification 750,008.ALSO:Organic substances of very high molecular weight, such as cellulose derivatives, are precipitated from their solutions or latices by forming streams of the solution or latex and of a precipitant in contact with one another, and causing the streams to intermix intimately and completely, and so as to form a suspension or slurry of precipitate in a liquid medium comprising the precipitant, while they are still travelling <PICT:0776066/III/1> <PICT:0776066/III/2> freely.  A "precipitant" is defined as a liquid non-solvent for the organic substance with is miscible with the solvent in which the organic substance is dissolved.  Preferably the stream of solution, or each stream of solution if there is more than one, is bounded on both sides by precipitant.  The streams of solution and precipitant may be caused to intermix while out of contact with any solid surface, for instance by extruding the solution and precipitant under pressure into a precipitating vessel large enough to allow the streams to intermix completely before they strike a wall of the vessel, or the streams may intermix in a closed conduit, or less desirably an open channel, with the wall of which at least one of them is in contact.  The streams may initially travel in any direction, which may remain the same or may change.  The slurry of precipitate in the mixture of solvent and precipitant may be mixed with a further quantity of precipitant.  The substance precipitated may be 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.  Cellulose acetate solution may be extruded either at room temperature or at a higher temperature, which may be below or above the boiling point of the solvent.  For example, solutions of cellulose acetate in acetic acid which have been ripened at about 50-80 DEG C. may be extruded at about the ripening temperature.  The precipitant may be at about the same temperature as the cellulose actate solution, or at a higher or lower temperature.  The precipitant, or both the precipitant and the solution, may be heated to a temperature such that part or all of the solvent is vaporized as the streams of solution and precipitant are mixed, particularly when a low boiling solvent such as methylene chloride is used.  In the example, a solution of acetone-soluble cellulose acetate in about three times its weight of 75 per cent aqueous acetic acid at 65-70 DEG C., obtained in the manufacture of the acetate, is extruded through the middle annular orifice of a triple annular nozzle 11 (Fig. 1) extending into a precipitating vessel 10 or a similar type of nozzle 60 (Fig. 3) extending into a closed conduit 65 of circular cross-section.  At the same time aqueous acetic acid of 7.4-14 per cent concentration and at 70 DEG C. is extruded at a considerably higher linear speed through the innermost and outermost annular orifices of the nozzle.  When the precipitating vessel 10 is employed, further aqueous acetic acid at the same temperature and of the same concentration is introduced through the liquid inlet 12 (Fig. 1) near the nozzle.  The slurry formed by the mixing of the streams of cellulose acetate solution and dilute acetic acid is run-off from the precipitating vessel through the outlet 13 or from the discharge end of the conduit 65, and the precipitate and the liquid are separated by decantation.  The height and length of the vessel 10 shown in Fig. 1 are such as to allow the streams of solution and precipitant leaving the nozzle 11 to complete their trajectory without impinging on any wall of the vessel.  The vessel 10 may be circular in cross section, but is preferably considerably higher than it is wide, having, for example, an elliptical or rectangular cross-section.  The nozzle 11 is provided with feed pipes 14, 15 (fed from a common feed line 17) for precipitant and a feed pipe 16 for the solution.  The streams of precipitant and solution start to intermix as soon as they have left the nozzle 11, and the composite stream which they form follows a roughly parabolic path, rising near to the top of the vessel 10 and falling to the bottom at a point short of the outlet 13.  The triple annular nozzle 60 shown in Fig. 3 is provided with feed pipes 61, 62 (fed from a common feed line 64) for the precipitant and a feed pipe 63 for the solution.  The nozzle 60 opens into one end of a conduit 65 having a bore (except in the immedia