Patent GB-346824-A (GB)
Title: Precipitation of cellulose esters
IPC: C08B3/28
Filed: 1930-01-16
Abstract: <PICT:0346824/IV/1> <PICT:0346824/IV/2> To recover cellulose acetate and other organic esters of cellulose form their acidylation solutions in a form in which they can be readily washed, dissolved, &c., and in which a minimum quantity of precipitating liquid is used, one or more streams of the solution is mingled with one or more streams of the precipitating liquid under such conditions that a constituent of the solution is released with disruptive effect.  This latter substance is conveniently liquid sulphur dioxide which may further serve as a solvent in the preparation of the solution.  The heat necessary to effect vaporization may be brought in by the use of hot precipitating liquid, but preferably by the simultaneous introduction of steam or hot vapour, the jets of steam &c. being introduced after the encounter between the jets of solution and precipitant.  When using steam or other precipitant vapour it is possible to dispense with the use of liquid precipitant; wet steam &c. is similarly effective by itself.  Suitable precipitating liquids are water, carbon tetrachloride, benzene and toluene.  It is an advantage to add to the solution of cellulose acetate &c. before precipitation, water or other precipitant in quantity approaching that necessary to produce a gelling of the solution. The commingling of the several streams of liquid and vapour conveniently takes place in a nozzle enclosing a chamber at atmospheric or lower pressure.  As shown, the nozzle comprises a member 26, Fig. 2, provided with a recess into which jets of cellulose acetate solution are delivered through a number of orifices 27; into these jets are projected in succession water jets from inwardly-directed fine orifices 29 and steam jets from a second set of orifices 33.  These jets are conveniently formed by radial grooves on the upper and lower faces of a member 36 adapted to fit into the recess surrounding the main jets 27, the mouth of the recess being finally closed by a widely-flared member 35.  A suitable apparatus comprises an acetylation vessel 3, Fig. 1, a separate hydration and mixing vessel 18, and a precipitation chamber 10 in the upper part of which the nozzle described above, is located; the vessel 18 may be omitted, in which case the acetylation vessel 3 is used for the hydration.  The material to be acetylated, either cellulose such as linters or a degraded cellulose such as hydrocellulose, is treated in the vessel 3 with a mixture of acetic anhydride or chloride, liquid sulphur dioxide alone or mixed with acetic acid, and sulphuric acid as catalyst. After completion of the acetylation process, the product being according to the conditions soluble in either chloroform or alcohol chloroform, hydration is carried out either in the vessel 3 or after the mixture has been discharged into the lower vessel 18; it is convenient to add the water, alcohol, &c., to the mixture in the vessel 3 shortly before its discharge into the vessel 18.  In the latter vessel, digestion preferably with the aid of mild stirring by means of stirrers 21, is allowed to take place until a product of the desired solubility is obtained, the p  digestion being carried out at 65-70 DEG  C., but preferably at 45 DEG  C., and in the presence of an excess of water amounting to 3-5 per cent of the reaction mixture. A quantity of water &c. almost sufficient to produce coagulation is then added, together with sufficient sodium acetate or other reagent to bind the sulphuric acid.  The mixture is then discharged as above described through the precipitation nozzle in the chamber 10, the cellulose acetate in loose fibrous form collecting on the perforated screen 14 forming the upper part of the hinged lower section 13 of the chamber.  Specifications 306,531, [Class 2 (ii), Cellulose &c.], and 346,430 are referred to.