STUDIES ON THE MANUFACTURE OF DISSOLVING PULP BY THE SIVOLA PROCESS (I)

THE SIVOLA PROCESS GIVES HIGHER YIELD OF PULP (1)

Abstract

Previously the authors have confirmed (unpublished) that if the Sivola process is employed the yield of dissolving pulp is considerably higher than by the ordinary process in comparison of a given alpha-cellulose content of pulp. The Sivola process is characteristic in the following points: (1) Pulp is refined with the alkali in a stage of the second cooking before screenig and chlorination treatments. (2) As refining agent a mixture of sodium carbonate and sodium sulfite is used instead of sodium hydroxide in the ordinary process. (3) Pulp is refined with a alkaline solution containing sulfite spent liquor from a stage of the first cooking.
In the present paper, therefore, in order to see why the Sivola process gives a higher yield of pulp, six kinds of process shown in Fig, 1 are adopted for the preparation of dissolving pulp, and the yields and alpha-cellulose contents of resulting pulps are examined. The results are as follows:
(1) Between the two processes in which the cooked chips with a sulfite liquor are digested with an alkaline liquor before or after screening treatment, the yield of final bleached pulp is higher in the former than in the latter. This is due to the fact that considerable parts of screenings in the cooked chips can be pulped in the former process (Fig. 2).
(2) There is little difference in the yield of final bleached pulp between the two processes in which chlorination treatment is carried out before or after the alkaline cooking (Fig. 2).
(3) Even if the alkaline digestion is inserted at any stage, the alpha-cellulose contents of bleached pulps were unchanged, so far as it is carried out under the same condition (Fig. 3).
(4) From the results of (1), (2) and (3), it may be said that the yield of pulp at equal alpha-cellulose content is higher in the alkaline cooking before screening treatment than after the screening (compare curve (a) with (b) in Fig. 4).
(5) Digestion with a mixture of sodium carbonate and sodium sulfite gave a final bleached pulp, in higher yield than that with sodium hydroxide (compare curve (a) or (b) with (a′) or (b′), respectively, in Fig. 4).
(6) Relation between yields alpha-cellulose contents of bleached pulps are considered to be unchanged by total amout and mole ratio of sodium carbonate and sodium sulfite within the range of the experiment.