GB649295A - Improvements in and relating to the manufacture of nitrocellulose - Google Patents

Abstract

In the manufacture of nitro-cellulose a part of the residual acid is separated from the pulp resulting from the nitration of cellulose, for example by mechanical means, and the pulp is thereafter drowned in a solution of sulphuric and/or nitric acids, the total acid concentration of which is not less than 25 per cent by weight, provided that in the case of mixed acids the proportion of sulphuric acid to nitric acid is not greater than 2 : 1, the quantity and acid concentration of the immersion solution being such that the total concentration of acids present in the solution after it has been admixed with the pulp does not exceed 60 per cent by weight and is preferably 35-40 per cent by weight. When sulphuric acid is used alone its concentration in the immersion solution prior to the drowning of the pulp is preferably not over 40 per cent by weight. The temperature of the immersion solution may not exceed 20 DEG C. and may be kept below this temperature, e.g. 10-15 DEG C., by passing it over refrigerated brine cooling coils before the immersion operation. After the pulp has been drowned the immersion solution is removed from the pulp and the latter is sprayed with water to remove the remaining acid. The resultant washings may be used for making up further batches of immersion solutions. The separated acid solution may be used again for further immersion operations until the acid concentration reaches the permissible upper limit, at which point the solution wholly or in part may be either diluted and thereafter used in further immersion operations, or may be concentrated. In an example, 50 lbs. of nitrated cotton linters, centrifuged until the pulp retains 30 lbs. of nitric acid and 42 lbs. of sulphuric acid, is drowned in 3000 lbs. of an aqueous solution containing 21.5 per cent of sulphuric acid and 12.3 per cent of nitric acid and the mixture is stirred. The pulp is again centrifuged until it contains 5 lbs. of nitric acid and 5 lbs. of sulphuric acid, sprayed in the centrifuge with 20 lbs. of a 10 per cent solution of nitric acid and discharged from the centrifuge into an excess of water. The quantity of solution separated from the pulp (prior to its being washed) is 3060 lbs. containing 22.3 per cent of sulphuric acid and 12.9 per cent of nitric acid. After the addition of water to restore the original concentration, all but 60 lbs. of the solution is recirculated. It is stated that the process avoids the production of large volumes of very dilute mixed acids and that denitration of the nitrocellulose due to the generation of heat during the removal of the residual acids from the pulp is prevented.