THE EFFECT OF LIQUOR CONCENTRATION ON THE RATE OF DELIGNIFICATION IN NEUTRAL SULFITE AND NEUTRAL SULFITE-ANTHRAQUINONE PULPING

A study was conducted to investigate the effect of liquor concentratio n on the rate of delignification in neutral sulphite and neutral sulph ite-anthraquinone pulping of black spruce wafers. The rates of deligni fication were determined at 175 degrees C over the concentration range of 54-82 g sodium sulphite per litre with an alkali ratio of 0.85 (ex pressed as sodium oxide) and with a liquor-to-wood ratio of 12.5/1. Ne utral sulphite-anthraquinone pulping experiments were conducted by add ing 0.5% anthraquinone (AQ) on o.d. wood to the liquor The initial pH was approximately II for all cooks. Cooking times were varied in order to reach pulp yields in the range of 50 to 80%. The effect of liquor concentration on the delignification rate expressions for both neutral sulphite and neutral sulphite-anthraquinone pulping was developed. It was observed that the reaction rate orders with respect to sodium sul phite charge were 0.28 and 0 for the delignification rate of neutral s ulphite and neutral sulphite-anthraquinone pulping, respectively. The experiments extended to lower liquor-to-wood ratios (5/1) for NS-AS pu lping. A negligible effect of liquor concentration on NS-AQ pulping wa s observed.