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

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 8.8 mL batch reactor fabricated from Hastelloy C-276 with respective design temperature and pressure of 500 °C and 50 MPa. The ability of SCW to remove nickel from Ni-EP was studied at temperatures of 450-490°C and water partial pressures (WPPs) of 25-45 MPa. Conversion of Ni-EP was found to slightly increase at WPP of 25-35 MPa; beyond this, the effect was found to be large, increased exponentially up to the WPP of 45 MPa. The overall Ni-EP conversion was 95.02% at the temperature of 490 °C, WPP of 25 MPa and reaction time of 180 min. 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 10.03 kcal/mol and a pre-exponential factor 2.17 × 10 ³ s ^{- 1}. Experimental results revealed that Ni-EP undergoes a series of reactions, ending in demetallation and ring fragmentation.