Predicting the Autoaccelerating Hydrogen Peroxide Decomposition Rate after Mixing with Sodium Hydroxide

Due to the large amount of inherent chemical energy,
implementation
of hydrogen peroxide pulp bleaching requires a high level of safety
design and process review. Even with safety controls, in-place accidents
have occurred at kraft pulp bleaching facilities. Using a combination
of experiments and chemical engineering analysis, we present a validated
model of hydrogen peroxide decomposition under alkaline conditions
that are typically found in kraft pulp bleaching processes. Using
the model, we then calculated several characteristic parameters required
to determine the criticality class and control system safety integrity
level (SIL) for an industrial-scale bleaching process. When designed
for 10 wt % hydrogen peroxide, pulp bleaching systems are inherently
safe as long as it is used in a process with adequately sized pressure
relief. Process designs using greater than 10 wt % hydrogen peroxide
require controls with SIL 4, which is the highest level of control.
This level is required for processes that present the most risk and
have the most severe consequences. Regardless of the hydrogen peroxide
concentration, processes without adequately sized pressure relief
should never be considered safe. Finally, both the experimental and
model results show the dramatic acceleration of hydrogen peroxide
decomposition by iron. Because membrane-grade sodium hydroxide often
has an order of magnitude lower concentration of iron than diaphragm-grade
sodium hydroxide, choosing membrane-grade results in reduction in
potential hazard.