Ammonium Base Alkaline Sulfite Chemical Pulping of Beech Wood

Abstract

This paper describes the results of alkaline pulping of beech wood, which has been cooked by ammonium sulfite and ammonium hydroxide solutions. In series of cooking, liquor concentration, maximum temperature and cooking duration at maximum temperature were varied. Evaluation of pulpings were investigated by analysises of the residual lignin and pentosans in resultant pulps, bleaching and paper strength tests.Summary of results are shown as follows ;1) It was found that the best conditions for cooking were as follows : Liquor composition : Ammonium sulfite 18%, Ammonium hydroxide 30%Liquor to wood ratio 4.5 : 1Maximum temperature 180°CTime at maximum temperature 2hr.2) Total pulp yield ranged from 55.8% to 64.6%. It was decreased with increasing sulfite-ion concentration. The pulp yield was increased rapidly in proportion to ammonium-ion concentration in the range of lower concentrations, but this relation was reversed over some ion concentration. This changing point was moved to the higher ammonium-ion concentration with increasing sulfite-ion concentration.3) Residual lignin in pulps stood in the range of 0.89-6.90% (based on oven dry wood). The rate of delignification was proportion to [NH4] [SO3] 3.016. The ability of delignification with sulfite-ion was about three cubed times as much as that of ammonium-ion.4) The degradation of pentosans by cooking were controlled with increasing the concentration of ammonium-ion, but were activated with increasing the concentration of sulfite-ion.5) Whiteness of bleached pulps were slightly lower than that of the ordinary bleached chemical pulps. In the case of well cooked pulps, decreasing of pentosans by bleaching was a little. The maximum decrement of pentosans was not exceeded about 4%. Yields of bleached pulps stood in the range of 53-56% (based on oven dry wood).6) The strength properties of unbleached pulps were lower than those of the ordinary sulfate pulps, but those were improved by bleaching treatment. The strength properties of bleached pulps were similar to those of the ordinary bleached sulfate pulps. The pulps cooked by 18% ammonium sulfite and 40% ammonium hydroxide solution showed best strength properties.