HIGH EFFICIENCY VESSELS FOR BLEACHING LIGNOCELLULOSIC, CELLULOSIC AND SYNTHETIC POLYMERIC FIBROUS MATERIALS

摘要

A process is disclosed which leads to a substantial improvement in the efficiency of bleaching lignocellulosic and like materials with hydrogen peroxide. This has been achieved by reducing the rate and extent of nonproductive decomposition of peroxide. The bleaching of lignocellulosic materials at increased temperatures and pressures accelerates the rate of pulp bleaching and the rate of peroxide decomposition. Conventional bleaching technology limits these non-productive reactions by including silicates or chelating agents in the bleaching solution. Here it is shown that a substantial part of the peroxide decomposition that occurs upon exposure to process equipment is decreased substantially by using an appropriate metallurgy. A bleaching vessel having at least a contact surface, i.e., a surface in contact with the processed pulp, constructed from zirconium, niobium, hafnium, tantalum or alloys thereof is described which limits peroxide decomposition. The use of zirconium, niobium, hafnium, tatalum or alloy thereof eliminates the requirement for silicate and other sequestering agents in the bleaching solution. This novel bleaching technology is used to improve the efficiency of alkaline peroxide with both conventional as well as with new high temperature lignocellulosic bleaching processes or processes which generate peroxide species under alkaline conditions.