22 / 2023-07-13 13:35:20

Treatment of organophosphorus esters waste: Efficient degradation with simultaneous phosphorus immobilization

P-containing organic waste,phosphorus immobilization,oxygen carrier,superoxide radical

Phosphorus Material Chemistry and Applied Science > 1) Phosphorus chemistry in material science

Organophosphorus esters (OPEs) are important chemicals functioning as plasticizers, flame retardants, extractants, solvents, additives, etc. The production and use of OPEs products can cause hazardous and refractory organic wastes. If discharged directly without proper treatment, OPEs wastes will inevitably cause secondary pollution to the environment due to the abundant P element in OPEs. Herein, we developed a metal oxide-catalyzed degradation with simultaneous phosphorus immobilization technology to treat typical OPEs waste. Low-cost metal oxides with abundant reserves on earth, such as MnO₂, Fe-Mn-bimetallic oxide, and CeO₂, all could be used as efficient catalysts. Under the investigated reaction conditions (e.g., 180-240 ^oC, 1-5 h, 10-20 g cat. per mL OPEs), in a closed reactor with constant stirring, model OPEs of tributyl phosphate (TBP), tricresyl phosphate (TCP) and tris(2-chloroethyl) phosphate (TCEP) could be efficiently degraded with the P immobilization efficiencies over 90%. P-species released from the reaction process were mainly immobilized as stable inorganic forms of metaphosphate (e.g., Fe(PO₃)₂, Mn(PO₃)₂), phosphate (e.g., Mn₃(PO₄)₂, CePO₄) and pyrophosphate (e.g., Mn₂P₂O₇). Further mechanism studies indicated that surface oxygen vacancy in meal oxides could induce the in-situ superoxide radical (•O₂^-) formation, contributing to OPEs degradation. Meanwhile, metal oxides as oxygen carriers provided sufficient oxygen molecules for flameless combustion, another contribution to OPEs degradation. It was also worth mentioning that gaseous products released from TBP degradation, e.g., non-methane hydrocarbon (NMCH), were lower than the maximum allowable emission concentration limit (120 mg m^-3). Therefore, this study provided a possible alternative for P-containing organic waste treatment with low environmental risk.