HBS pulping (4) - ECF bleaching of HBS pulp and thermo-stabilization of HBS solvents

Abstract

Todomatsu (Abies sachalinensis Mast.) chips as softwood gave T-pulp with a Klason lignin (KL) content of 5.6% and a viscosity degree of 21.5 cP at a yield of 50.3% by HBS pulping with a mixture of 70% aqueous R-1, 3- and 1, 4-butanediol (as RHBS shown in Fig. 1) at 210°C for 3 h. Birch (Betula platpylla var. japonica Hara) chips were cooked with 80% RHBS at 180°C for 3 h to give B-pulp with a KL content of 5.0% and a viscosity degree of 43.4 cP at a yield of 54.3%. Chinese reed gave R-pulp with KL and ash contents of 2.5 and 6.3% in a yield of 48.7%, when cooked with 80% RHBS at 200°C for 2 h. B- and R-pulps were fully bleached by ECF sequence with OD, and T-pulp with ODEPP. Bleached B- and T-pulps had TI of 12.4 and 17.6 mN · m2/g, indicating that TI of HBS pulp was remarkably improved by ECF bleaching. Seventy and 80% aqueous HBS such as 1, 3- and 1, 4-butanediol, propylene glycol and 1, 5-pentanediol were quantitatively recovered on heating at 190°C for 2 h, so they can be reused repeatedly as pulping solvents without distillation for purification and also with a little loss.