Combining experiment and density functional theory to study the mechanism of thermochemical sulfate reduction by hydrogen in supercritical water

Sulfur migration mechanism of pig manure in supercritical water: A combined experimental and DFT study

Pig manure (PM) is a high concentration organic waste rich in sulfur, and its biofuel contains various sulfur-containing pollutants, which reduces the safety of the products. Supercritical water (SCW) can dissolve most organic matter, which is a technology worthy of further study. In order to reduce sulfur pollution in the process of PM resource utilization and better control the conversion path of sulfur, it is necessary to explore the migration mechanism of sulfur in the whole PM-SCW gasification process. The experimental results indicated that H2S was the only gaseous product. Only inorganic compounds (S2-, S2O32- and SO42-) were detected in the liquid. Sulfur in the solid mainly included thiol/thioether, thiophene and sulfone. The influence of different reaction conditions (temperature, residence time, PM concentration and catalysts) on sulfur migration was studied in a batch reactor. It was worth noting that the catalysts had a significant effect on H2S absorption. The lowest H2S yield was 3.2 * 10-4 mol/kg and more than 70% of the sulfur was distributed in the liquid under the condition of addition of K2CO3. While, the RTH2110 fixed most of the sulfur of PM (the maximum value reached 50.94%) in the solid. Thus, adding the catalysts flexibly can choose composition of the products. Furthermore, six possible pathways of sulfur migration in the solid were designed and the kinetic parameters were calculated by density functional theory (DFT). The results provided a basis for controlling sulfur in PM. Subsequently, the sulfur migration pathways during PM-SCW gasification process were comprehensively summarized through the combination of experiment and DFT. It provided a method for sulfur treatment in PM, which had guiding significance for the realization of pollution-free treatment of PM.

Mechanistic insights and catalytic enhancement of phenolic wastewater supercritical water gasification: A combined experiment and density functional theory study

Supercritical water gasification technology provides a favorable technology to achieve pollution elimination and resource utilization of phenolic wastewater. In this study, the reaction mechanism of phenolic wastewater supercritical water gasification was investigated using a combination of experimental and computational methods. Five reaction channels were identified to elucidate the underlying pathway of phenol decomposition. Importantly, the rate-determining step was found to be the dearomatization reaction. By integrating computational and experimental analyses, it was found that phenol decomposition via the path with the lowest energy barrier generates cyclopentadiene, featuring a dearomatization barrier of 70.97 kcal/mol. Additionally, supercritical water plays a catalytic role in the dearomatization process by facilitating proton transfer. Based on the obtained reaction pathway, alkali salts (Na2CO3 and K2CO3) are employed as a catalyst to diminish the energy barrier of the rate-determining step to 40.00 kcal/mol and 37.14 kcal/mol. Alkali salts catalysis significantly improved carbon conversion and pollutant removal from phenolic wastewater, increasing CGE from 58.44% to 93.55% and COD removal efficiency from 94.11% to 99.79%. Overall, this study provides a comprehensive understanding of the decomposition mechanism of phenolic wastewater in supercritical water.

Automated Multi-Objective Reaction Optimisation: Which Algorithm Should I Use?

Multi-objective optimisation algorithms (MOOAs) are, of increasing interest for the efficient optimisation of chemical processes. However, an algorithms performance can vary on a case-by-case basis, depending on the complexity of...

Experimental investigation on gasification of cationic ion exchange resin used in nuclear power plants by supercritical water

Spent ion exchange resins produced by nuclear power plants are radioactive organic waste. Until now, there is no satisfactory industrial treatment. Supercritical water gasification (SCWG) of cationic ion exchange resin (CIER) used in nuclear power plants was carried out in a batch reactor in this study. Results showed that the gasification efficiency increased with the growth of temperature (550-750 °C), addition of alkali homogeneous catalyst (K₂CO₃), proper ratio loading of catalyst to CIER (1:1), decrease of feed concentration (2-10 wt%) and extension of residence time (10-60 min). Carbon gasification efficiency was up to 97.98% with K₂CO₃ added and 30 min at 750 °C in the batch reactor. The gaseous products mainly consist of H₂, CO, CO₂ and CH₄. The GC-MS analysis showed that the organic component in liquid products was mainly composed of benzene, monocycle arenes, phenol group and polycyclic aromatic hydrocarbons. Based on the experimental results, the formation and gasification pathways of CIER in SCW were proposed.