Dynamic Peroxide Bleaching in a Benchtop Flow-Through Reactor vs. Pilot Scale Flow-Through Bleaching Tower, 2002 Fall Technical Conference

In addition to the traditional laboratory studies of hydrogen peroxide bleaching in the application of TCF or ECF sequences (1), a pilot-scale bleach tower was built and evaluated in a hydrogen peroxide bleaching application. The performance of this tower was compared to the performance of a laboratoryscale flow through (semibatch) reactor through comparison of tracer break-through curves and bleaching data.

A benchtop flow-through reactor was constructed to study dynamic peroxide bleaching and to examine the reaction front through displacement bleaching. Two feed tanks with H2O2 and NaOH solutions respectively, were pumped through the furnace and mixed in a tee. The mixed solution was fed into the top of reaction tube packed with pulp. The breakthrough curves of peroxide and hydroxide were determined. Experiments in the semibatch bleaching reactor was to observe the rate of peroxide bleaching in a displacement apparatus. Tracer tests were run to determine the hydraulic behavior of the flowthrough reactor. The hydroxide breakthrough curve was much faster than the peroxide breakthrough curve. Brightening was very rapid due to the constant concentration of hydrogen peroxide fed to the reactor. In addition, this study was to simulate the results from the larger packed bed bleaching tower to determine what effects poor hydraulics in the big tower had no bleaching performance. In the pilot-scale bleaching tower, the large size, low flow rates, and nonuniformities of the packed bed led to poorer results with both tracer study and the bleaching runs. The larger pilot scale tower was an eight inch ID with a length of 10 feet in the reaction zone. The bed height was varied inside this zone from 2 to 6 feet for experiments. The tower was run in the downward flow direction to allow for easy variance of the pulp bed height.