Oxidation Coefficient Research Articles

Application, performance and mechanism of high-entropy catalysts for degradation of heterocyclic compounds

High-entropy catalysts have attracted great interest due to their unique microstructures, excellent thermal stability and catalytic activity for various reactions. In this study, three high-entropy catalysts were prepared by doping CeO2 with transition metal oxides that have full redox cycle capability. Their performance for the ultra-fast catalytic oxidation degradation of heterocyclic compounds was investigated. Compared with the reaction without catalysts, the high-entropy catalysts could significantly shorten the residence time and improve the reaction efficiency, indicating that they could promote the oxidation reaction. Under the conditions of reaction temperature (T) = 390 °C and oxidation coefficient (OC) = 2.90, the chemical oxygen demand (COD) removal rate of the high-entropy oxide catalyst (AlTiCeFeCu)Ox@TA reached 94.52 % after 8 min of reaction. Moreover, characterization analysis revealed that the high-entropy catalysts prepared by doping appropriate transition metal oxides exhibited excellent catalytic activity and stability, providing new insights for the research of efficient catalysts in the ultra-fast oxidation system.

Gasification of landfill leachate in supercritical water: Effects on hydrogen yield and tar formation

Landfill leachate was gasified in supercritical water (SCW) in a batch reactor made of 316 SS. The effects of temperature, pressure, reaction time and oxidation coefficient (OC) on the pollutant removal efficiencies and gasification characteristics were investigated. To observe the formation of tar and char visually, a capillary quartz reactor was also used. Results indicated that CO2, H2 and CH4 were the most abundant gaseous products. Temperature has an appreciable effect on the gasification process. Increasing temperature enhanced the H2 yield (GYH2) and TOC removal efficiency (TRE) significantly. Although the influence of reaction time on the fractions of gaseous products was negligible at time above 300 s, the yields of H2, CH4, and CO2 increased with reaction time whereas the CO, C2H4 and C2H6 yields decreased. Tar and char formation was evident on the interior surface of capillary quartz reactor. Adding a little oxidant could increase H2 and CH4 yields and decrease tar and char formation. GYH2 reached up to the maximum of 231.3 mmol L−1 leachate at 500 °C, 25 MPa, 600 s and 0.2 OC, which was 2.4 times of that without oxidant.

Treatment of penicillin with supercritical water oxidation: Experimental study of combined ReaxFF molecular dynamics

Supercritical water oxidation (SCWO) of penicillin (PCN) was investigated under different operating conditions. The chemical oxygen demand (COD) removal rate could reach 99.4% at 400 °C, 24 MPa, 1min and oxidation coefficient (OC) of 2. Experimental results showed that COD removal had no significant dependence on temperature and pressure variations. By contrast, COD removal could be significantly promoted with OC increasing from 0 to 2.0, but the effect was negligible as the OC further increased; similarly, longer residence time than a definite value seemed to contribute little to COD removal. Initial and deeper degradation pathways of penicillin were proposed based on the reactive force field (ReaxFF) molecular dynamics (MD) simulations. By tracing the evolution of intermediates, the migration routes of S and N during the SCWO process were obtained with H2S and NO2 produced as the corresponding products. Simulation results showed that SCW and oxidant not only accelerated the degradation by producing highly reactive radicals or molecules, but also participated in reactions by serving as H and O sources. Moreover, catalysis of water clusters in C-heteroatom bond cleavage was also observed.

Effect of Oxidation Coefficient on Products of Sewage Sludge Treatment in Supercritical Water

Abstract Supercritical water treatment is a promising technology for sewage sludge disposal. The influences of oxidation coefficient (OC) as well as temperature on products of sewage sludge treatment in supercritical water were studied systematically. The results show that CO2 yield obviously increased with raising OC or temperature. Oxidant helped to convert N-containing compounds into N2. A small amount of oxidant increased H2 yield but excess oxidant decreased it. OC had significant effect on the COD (chemical oxygen demand) and NH3-N (ammonia nitrogen) concentration of liquid products. Most of organic compounds disappeared at OC=1.0 as temperature changed from 450 to 500, and diethyl phthalate was main stubborn substance in the liquid phase. The contents of some elements (such as Si, Al and Ca) in solid residue was almost double compared with those in dry basis SS.

Supercritical water oxidation of a pesticide wastewater

In this research, we studied supercritical water oxidation (SCWO) of a pesticide wastewater under a wide range of operation conditions in two reaction plants. The results show that reaction temperature, oxidant coefficient (OC), and residence time (t) can improve the wastewater XCOD (removal efficiency of chemical oxygen demand). The residence time and OC have important influences on XCOD at higher reaction temperatures (>500°C). It is significant to increase the preheating rate for the XCOD improvement of the pesticide wastewater in SCWO. XCOD and XTN (removal efficiency of total nitrogen) are 99.42% and 86.70% at 600°C, 25MPa, OC=3.0 and t=2.0min, respectively. More than 92wt% total organic carbon (TOC) and 86.70wt% total nitrogen in the wastewater are converted into CO2 and N2 under the above conditions, respectively. Inconel 625 can be used as the reactor material in the wastewater SCWO plant, and its corrosion rate is approximately 0.6mm/year at 600°C, 25MPa and OC=3.0 conditions. We also primarily design a 100t/d SCWO plant for the tested pesticide wastewater treatment on the basis of accomplished investigations. SCWO together with traditional wastewater treatment methods is proposed to harmlessly dispose the complicated wastewater. This information is valuable for guiding the large-scale SCWO plant design for pesticide wastewater treatment.

Plasma PAF-acetylhydrolase activity, inflammatory markers and susceptibility of LDL to in vitro oxidation in patients with type 1 diabetes mellitus

Aims We evaluated if type 1 diabetic patients have altered levels of low-grade inflammatory markers including platelet-activating factor acetylhydrolase (PAF-AH) activity, high-sensitivity C-reactive protein (hs-CRP), white blood cells count (WBC), erythrocyte sedimentation rate (ESR) and LDL-cholesterol oxidation coefficient (OxC), and whether their levels are related to clinical complications and the metabolic profile. Methods We studied cross-sectionally 118 outpatients with type 1 diabetes both with ( n = 38) and without ( n = 80) clinical chronic complications, and 110 controls subjects. Results Diabetic patients had higher levels of PAF-AH activity ( p = 0.02), hs-CRP ( p = 0.001), WBC ( p = 0.004) and ESR ( p = 0.0001) than controls. Patients with type 1 diabetes had earlier OxC than the non-diabetic subjects at 1 and 3 h ( p = 0.01) after the addition of CuSO 4. No difference was noted between patients with and without chronic complications. In the patients, correlations were found between PAF-AH activity and OxC at 1 and 3 h. Conclusions It was concluded that the susceptibility of LDL to in vitro oxidation and low-grade inflammation are increased in patients with type 1 diabetes and related to each other. The presence of these markers is probably independent of the presence of chronic clinical complications and reveals the development of early pro-inflammatory state.