On the Manufacture of Pulp by Ammonium Sulphite Process (No. 4)

Abstract

The cooking of beech by ammonium bisulphite (NH4HSO3) is investigated, and at the same time the cooking is compared with those by Na base bisulphite and neutral ammonium sulphite. The results are as follows : 1) The number of pulps obtained by the following conditions : liquor ratio 1 : 6, cooking temperature 130-150°C, SO2 concentration of cooking liquor 2.5-8.5%, pH of cooking liquor 2.8, time at cooking temperature 4 hours, yield 40-76% against bone dry chip and on the whole dark in colour and rich of specks. Such undesirable defects, which are more conspicuous than those of the corresponding yield pulp by neutral ammonium sulphite, are not reduced at all by elongating the penetrating time of liquor from 2 to 4 hours, and somewhat lightened by changing the base from NH3 to Na. Japanese report, Fig. 1) 2) The cooking velocity by Na base is found to be correspondent to that of 2-4°C lower cooking temperature by NH3 base. (J. r. Fig. 1, 2, 3) 3) The pulp produced by this process shows about 5-6% lower pentosan content in comparison with the same yield pulp by neutral ammonium sulphite process. (J. r. Fig. 5) 4) The holocellulose content of the pulp by this process is somewhat lower, and the lignin content and the Roe number are both higher in comparison with those of the pulp by neutral ammonium sulphite. (J. r. Fig. 3, 7, 8) 5) The pH of the waste liquor by this process is almost like as that in the case of Abies Sachaliensis, but some amount of pH drop observed in lower SO2 concentration range at 150°C cooking. (J. r. Fig. 4) 6) It seems that the content of lignin containing some amount of sulphur in case of sulphite pulp is not correctly measured by 72% H2SO4 method, and the Roe number of the pulp must give more rational estimating standard for lignin content in this case. (J. r. Fig. 7, 8, 9) 7) The mechanical strengths of the pulp by this process are somewhat inferior to those by neutralammonium sulphite and Na base bisulphite cooking. (J. r. 10) By these reasons, it is concluded that the chemical and semichemical pulps of beech by ammonium bisulphite process are not desirable for paper making purpose.