Nickel removal from nickel etioporphyrin (Ni-EP) using supercritical water in the absence of catalyst

Abstract

The objective of this study aims to create a method to remove nickel in an environmentally benign way from nickel etioporphyrin (Ni-EP) at a high extent and in a short reaction time using supercritical water (SCW). All experiments were carried out in an 8.8mL batch reactor fabricated from Hastelloy C-276 with respective design temperature and pressure of 500°C and 50MPa. The ability of SCW to remove nickel from Ni-EP was studied at temperatures of 450–490°C and water partial pressures (WPPs) of 25–45MPa. Conversion of Ni-EP was found to slightly increase at WPP of 25–35MPa; beyond this, the effect was found to be large, increased exponentially up to the WPP of 45MPa. The overall Ni-EP conversion was 95.02% at the temperature of 490°C, WPP of 25MPa and reaction time of 180min. Under these reaction conditions, approximately 90.64% of the nickel was removed by the action of SCW and the co-solvent toluene. Reaction of Ni-EP in SCW demonstrably followed first order kinetics, with Arrhenius parameters of activity energy 10.03kcal/mol and a pre-exponential factor 2.17×103s−1. Experimental results revealed that Ni-EP undergoes a series of reactions, ending in demetallation and ring fragmentation.