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The work described in this thesis was aimed at obtaining a better understanding of the neutral sulphite semichemical pulping process employed by Mondi Kraft's Piet Retief mill, and to investigate ways to improve this process. The unique feature of the process in this mill is that hardwood and softwood species are pulped simultaneously in a continuous digester. The pulping trials described were carried out in a laboratory batch digester which was build as a part of this project. Pulps were evaluated for yield, Hypo number as an indication of the residual lignin content and strength properties. The first part of the experimental work focused on the effect that different pulping variables have on the process and the resulting pulp. Variables investigated were the chemical charge, pulping temperature, chip composition and anthraquinone dosage. The second part of the work was to investigate ways in which the process can be improved. In particular it was investigated whether it would be advantageous to pulp hardwood and softwood separately and mix the two pulps together after pulping. The effect of changing to an alkaline sulphite process was also briefly investigated. It was found that the current process is optimized as far as the chemical charge and pulping temperature is concerned. Increasing the softwood percentage used to 50 % (from current value of 41 %) increases the tear strength, whilst decreasing it to 30 % increases the tensile strength of the resulting pulp. It was also determined that increasing the AQ dosage from 0.1 % to 0.5 % might bring savings in chemical costs. It is suggested that this is investigated in a mill trial. It was further found that pulping the two species separately improves the tear strength of the pulp by about 20 % compared with that which was pulped simultaneously. The results indicate that no benefits concerning the chemical costs, pulping temperature, pulp yield, burst strength or tensile strength are to be gained from separate pulping. Preliminary results indicated that significant strength increases and possible chemical cost savings are to be gained by changing from a neutral sulphite to an alkaline sulphite process. Further work to determine the reproducibility of these results, as well as the effect of different chemical charge and ratios is suggested. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2000.

SAPPI SAICCOR is a pulp and paper mill situated in Umkomaas, 50 kms south of the port of Durban in South Africa. It was the first company to produce high grade dissolving pulp from the Eucalyptus tree and is currently the world's largest manufacturer of chemical cellulose. SAICCOR is one of the few pulp and paper mills that produces its dissolving pulp by the acid sulphite process using both calcium and magnesium as bases in the form of calcium bisulphite and magnesium bisulphite. Four streams of effluent are produced during their process, namely, the calcium spent liquor, the magnesium pulp condensate and two streams from the bleaching stages. An acid hydrolysis of the effluent streams yielded a range of organic compounds such as lignans and lignin - type precursors as well as a triterpenoid. Column chromatography and thin layer chromatography, using various ratios of hexane, dichloromethane, ethyl acetate and methanol, were carried out in isolating and purifying the compounds. The structures of these compounds were determined using NMR spectroscopic and mass spectrometric techniques. / Thesis (M.Sc.)-University of Natal, Durban, 2003.

SAPPI SAJCCOR, whose factory is situated south of Durban, South Africa, is one of the few paper and pulp mills that uses the acid sulphite process with calcium and magnesium bases to produce a high-grade cellulose pulp. Four streams of effluent, namely, the calcium - spent liquor stream, the magnesium condensate stream and two streams from the bleaching effluent are produced during this sulphite pulping process and they contain a variety of organic compounds extracted from the wood. Characterisation of the effluent was based on isolation using column chromatography and identification using NMR techniques. A range of constituents, such as lignans and lignin - type precursors, a trilerpenoid and fatty acids were isolated and identified. X-ray diffraction was used to identify an inorganic residue obtained from the calcium - spent liquor stream and gas chromatography/mass spectrometry was used to identify a wax residue. which builds up in the process. In addition to this, the carbohydrate content of the four streams of effluent was detennined using UV/visiblc spectroscopy. / Thesis (M.Sc.)-University of Natal, Durban, 2001.