Sulphonation of Eastern Black Spruce Chips, Part II

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Abstract
Eastern black spruce, Picea mariana, chips have been treated to high yields, at temperatures from 120° to 150°C, with sodium bisulphite solutions of pH 4 and total SO2 concentrations from 0.23 to 1.92 mol L−1. The rate of sulphonation depends on the concentration of sites available for sulphonation and total SO2 concentration to the power of 0.4; it increases by approximately 70 percent for each 10°C temperature rise. It is postulated that sulphonation at pH 4 occurs by two mechanisms, one which is dependent on total SO2 concentration and involves a quinonemethide intermediate and one which is independent of total SO2 concentration and involves a carbonium ion intermediate. The rates of yield loss and lignin loss are dependent only on temperature and approximately double for each 10°C temperature increase. High total SO2 concentrations are necessary for efficient production of high strength ultra-high yield pulps from black spruce chips when treated with sodium bisulphite solutions.