3V Tech chlor-alkali unit is studied and designed to treat the brine coming from the purification section of the Demeto plant. The Demeto plant requires caustic soda and hydrochloric acid to perform the reaction, namely the depolymerisation of PET or other plastic material, and the purification of ethylene glycol and terephthalic acid up to the purity specification required by plastic producers. The side stream of the process consists in a brine solution. By means of electric energy, this brine is electrolysed by the chlor-alkali unit to produce caustic soda, hydrogen and chloride, which will be subsequently reacted in a burner to produce hydrochloric acid. In this way, caustic soda and hydrochloric acid can be recycled back in the previous sections, closing the loop of chemical demand of the plant and promoting the circularity of the whole project.
The pilot unit is designed to deal with the peculiar brine coming from the purification section, whose set of pollutants is completely different from a typical brine obtained with commercial salt, due to the reactive process it comes from and the feedstock the plant is fed with. For this reason, the brine is treated through a final purification by means of chelating resins to reach the strict purity specification required by the electrolyser. The aim of the experimentation is to analyse the final performance of the electrolyser and tuning the operating parameters and resins treatment to maximise it.
A global view of the pilot plant can be seen in the following picture, where the electrolyser can be spotted in the cell room.
The plant is designed to be automatically operated, but in the pilot tests the supervision of the operators is irreplaceable to monitor the process and identify any possible problem.
A dedicated effort has been carried out to design a pilot scale electrolyser able to be as flexible as possible and to be easily dismounted in order to analyse the effect of the process on the electrodes and the membranes.
All the information gained with the experimentation will be transferred to the industrial scale plant design, with the goal of producing hydrochloric acid and caustic soda minimising the electrical consumption and the purge of the plant.