Reaction Mechanism Study On The Refractory Wastewater Treatment For Energy Gas Production Via Catalytic Supercritical Water Gasification

In recent years,severe environmental pollution and energy shortage problems have emerged with the accelerated process of industrialization and urbanization,which produced massive refractory organic wastewater that are harmful to the public health and environment.The catalytic supercritical water gasification（SCWG）technique used for wastewater treatment could not only degrade organic pollutants but also manipulate product distribution.Reaction mechanism is crucial to the process optimization,however,it is hard to obtain the reaction pathways via the experimental method.In this work,Reax FF reactive molecular dynamics simulations were used to investigate the treatment of refractory wastewater through catalytic SCWG technique,dibutyl phthalate（DBP）and naphthalene（NAP）were selected as model compounds with Ni and iron oxide chosen as catalyst,respectively.Ni catalyst could facilitate the bond cleavage while the roles of SCW were to promote cracking and serve as H sources.For the evolution of dissociated side chains,the cooperative effects enhanced the cracking of long-chain fragments and generation of saturated products.For the aromatic ring-opening stage,a Ni-catalyzed process involved successive bond scission and migration of carbon chains into catalyst bulk was dominant.The synergistic effects were also supposed to improve H₂ yield.Furthermore,the Ni catalyst was deactivated during gasification process,which was caused by carbon deposition and surface oxidation.H₂ reduction could remove the surface oxygen atoms from the Ni catalyst to regenerate the deactivated catalyst.Synergistic effects between iron oxide catalyst and SCW promoted the degradation of NAP and the production of H₂ and CO.SCW served not only as H source but also as O source,while the roles of iron oxide were to provide lattice oxygen,catalyze SCW to produce active species,and weaken C-C bonds.Increasing the use of H₂O raised H₂and CO yields along with the lattice oxygen supplement,high hydrogen recovery was achieved at high NAP concentration.SCW media inhibited the iron loss,while calcination in O₂ environment could regenerate the catalyst by cleaning up carbon deposition and replenishing lattice oxygen.