GB430259A - Improvements in or relating to the manufacture of alpha cellulose - Google Patents

Abstract

<PICT:0430259/IV/1> In the manufacture of alpha-cellulose as a substitute for p cotton pulp for making cellulose esters or for bank note paper &c. from gramineae, e.g. bambooss pulp is boiled for 1 hour at 156 DEG C. and 4,8 atmospheres pressure and for a few hours at 140-143 DEG C. and 3 atmospheres pressure in the same autoclave in a lye containing alkaline hydrate, sodium sulphide, sodium sulphite, e.g. respectively in grams per litre 45, 20, 5 and guaiacol; the pulp being then washed with water emulsified with benzol, then washed two or three times with cold water, discharged into a tank 5 wherein it is mechanically agitated and diluted with water; it is then pumped to a thickener 6, to a conical breaker 7 and to vats 8, 9, 10 wherein it is bleached with sodium hypochlorite, washed, subjected to hydrofluoric acid, again washed passed to a thickener 11 and an autoclave 12 in which it is treated with sodium sulphite at 60 DEG C. and atmosphere pressure and washed in a vat 13 and bleached with hydrogen peroxide or sodium peroxide in a vat 14, passed to a sand-removing device 15 to a centrifugal purifier 16 and to a pulp press 17. The guaiacol is stated quickly to dissolve the coating of lignin gelatinized by the hydrate, allowing new zones of lignin to be attacked by the lye; in this and in the first boiling, air is expelled with the aid of a circulating pump to avoid oxidation. One or more rotary purifiers may be interposed between the tank 5 and the thickener 6, to remove any knots left unground by the mill 1. The vat 9 for the treatment with hydrofluoric acid is lined inside with a plastic material having a rubber basis. The spent lyes and washing waters from the tank 5 are passed to a tank 21, to a multiple-action evaporator 22, to a rotary oven 23 in which they are calcined, to causticizing vessels 25 and to settling tanks 26. The whole process is preferably effected automatically.