Pulping of Beech Wood Using Different Acid and Alkaline Pulping Processes - A Comparison

Beech wood is the most important hardwood for pulping in Middle Europe. Beech chips from a German mill were pulped employing different pulping processes. Acid sulphite pulping (pH 1.7) produces low pulp yield and low pulp strength. This pulp however is easily bleachable. Magnefite pulping (pH 4.0) improves pulp strength and stopping cooking at higher Kappa number enhances yield and pulps strength even more. These pulps had the highest yield of all used processes and bleaching to 88% ISO could be performed in two peroxide stages. The Kraft process provided good pulp yield and strength. This pulp could be bleached to 88% ISO in a TCF-sequence. The best overall results could be achieved with the ASA process. This pulp has high yield, excellent strength properties and a good bleachability.