Supercritical Water Oxidation of Acrylic Acid Production Wastewater in Transpiring Wall Reactor

Abstract

Destruction of acrylic acid production wastewater was investigated under SCWO conditions in a transpiring wall reactor with H₂O₂ as the oxidant. Experiments were performed at various temperature ( T = 623–723 K), pressure (P = 18–32 MPa), residence time (τ = 10–40 s), and dosage of H₂O₂ (η = 0–2.0) to investigate their effect on the destruction efficiency. The destruction efficiency of wastewater was monitored by analyzing COD on the liquid effluent samples. Experimental results indicated that oxidant dosage, reaction temperature, pressure, and residence time had a significant effect on the COD removal. Destruction efficiency increased with the T, P, τ, and η. Greater than 99% of destruction efficiency was achieved at T = 723 K, P = 28 MPa, τ = 34.3 s, and η = 1.2. The optimum operation conditions were T = 693–723 K, P = 24–28 MPa, η = 1.2–1.6. Salt precipitation was observed at the reactor entrance cross and inner ceramic tube. SEM photos of the ceramic tube indicated that the ceramic tube was corroded and plugged. Because of the existence of induction time, the first-order rate law was modified with residence time subtracting induction time. Global power-law rate expression was regressed from experimental data, with the reaction order of feed wastewater (based on COD), oxidant and water was assumed to be first, zero, and zero, respectively. The resulting pre-exponential factor A was 4.97 s⁻¹, the activation energy Ea was 20.64 kJ/mol⁻¹, and the induction time τ_ind was about 8 s.