Design of an Extractive Distillation Column for the Environmentally Benign Separation of Zirconium and Hafnium Tetrachloride for Nuclear Power Reactor Applications

Nuclear power with strengthened safety regulations continues to be used as
an important resource in the world for managing atmospheric greenhouse gases and
associated climate change. This study examined the environmentally benign separation
of zirconium tetrachloride (ZrCl4) and hafnium tetrachloride (HfCl4) for nuclear power
reactor applications through extractive distillation using a NaCl-KCl molten salt mixture.
The vapor–liquid equilibrium behavior of ZrCl4 and HfCl4 over the molten salt system was
correlated with Raoult’s law. The molten salt-based extractive distillation column was
designed optimally using a rigorous commercial simulator for the feasible separation of
ZrCl4 and HfCl4. The molten salt-based extractive distillation approach has many potential
advantages for the commercial separation of ZrCl4 and HfCl4 compared to the conventional
distillation because of its milder temperatures and pressure conditions, smaller number of
required separation trays in the column, and lower energy requirement for separation,
while still taking the advantage of environmentally benign feature by distillation.
A heat-pump-assisted configuration was also explored to improve the energy efficiency of
the extractive distillation process. The proposed enhanced configuration reduced the
energy requirement drastically. Extractive distillation can be a promising option competing
with the existing extraction-based separation process for zirconium purification for nuclear
power reactor applications