Comparative evaluation of different concepts of sulfite pulping technology

The superseding of the sulfite cooking process commenced in earnest in the 1950's with the development and technical establishment of the recovery of chemicals using the krait pulping process. Apart from the very high recovery rate of the pulping chemicals, the fact that rich resin and raw materials of a poorer quality could be used, as well as vastly improved tenacity properties were some of the excellent values of the kraft pulping system compared to the sulfite process. The high degree of brightness of the unbleached pulp and the good bleachability, the most important advantages of the sulfite process. have not yet been able to make up for its disadvantages when compared to the kraft pulping process. in the same way, multi-stage sulfite processes, developed in the 50's and 60's, were unable to turn this trend around. Most developments aimed at extending the range of raw materials which did succeed to a certain extent by increasing the pH value in an initial phase-bisulfite or neutral sulfite. In addition, it was possible to achieve better tenacity values in the case of a two-stage bisulfite-neutral sulfite process as well as a higher wood yield in the combination, neutral sulfite-acid sulfite process. It wasn't until the development of the ASAM process, in the mid 1980's, that we really had a pulping process at our disposal which unites the advantages of the sulfite and the kraft pulping process without simultaneously demonstrating other disadvantages. In the present study the ASAM process was compared with the two conventional pulping processes, the acid magnesium bisulfite and kraft pulping process, using beechwood and producing TCF-bleached paper pulps. The results demonstrate the clear superiority of the ASAM-process compared to the two competitive pulps with regard to the wood yield, tenacity properties and the stability of the degree of brightness.