Effects of residence time on the efficiency of desulfurization and denitrification in the bubbling reactor

Transient simulation of SO2 absorption into water in a bubbling reactor

A bubbling reactor is an important type of gas scrubber to reduce SO2 emissions in maritime shipping. Both experiments and simulations were conducted to study the relationship between the periodic gas bubbling process and SO2 concentration at the outlet of the reactor, and the entrainment of liquid droplets on SO2 absorption. The accuracy of the model was verified by comparing the bubble size, the depth of bubbles injected into the water, and the SO2 concentration obtained in both experiments and simulations. The gas bubbling process is accompanied by bubble formation, rise, and collapse. The gas bubbling period is affected by the disturbance of the liquid level. The period of the SO2 concentration at the outlet of the gas bubbling reactor is smaller than that at the gas jar outlet which acts as the gas buffering region. The amounts of water carried out of the bubbling reactor by the gas bubbling process increase with the gas flow rates. The droplets and liquid film in the gas jar and the connecting tube play an important role in the absorption of SO2. This study encourages more research to reduce the fluctuation of SO2 concentration and consider droplet entrainment in the design of bubbling reactors.

A new phase transfer nanocatalyst NiFe2O4-PEG for removal of dibenzothiophene by an ultrasound assisted oxidative process: kinetics, thermodynamic study and experimental design

In this study, NiFe₂O₄–PEG, an effective nanocatalyst was synthesized via a hydrothermal method using different PEG concentrations and synthesis times. The synthesized nanocatalyst was used in the ultrasound assisted oxidative desulfurization (UAOD) of model fuels (e.g. n-hexane and dibenzothiophene (DBT)) for the first time. The nanocatalyst was then characterized by XRD, FTIR, BET, SEM, VSM and TEM analyses. In addition, central composite design was used to evaluate the effective variables on the UAOD process. The optimal values of effective factors such as catalyst dose, oxidant amount, irradiation time and ultrasonic power to maximize of the percentage of sulfur removal were 0.149 g, 15 mL, 11.96 min, and 70 MHz, respectively. Moreover, the kinetic aspects of the oxidation reaction of DBT in the UAOD process were investigated using a pseudo-first-order model. Furthermore, using the Arrhenius equation, an activation energy of 35.86 kJ mol⁻¹ was obtained. Additionally, thermodynamic analysis showed that the oxidation reaction of DBT was endothermic with a positive Gibbs free of energy, indicating the non-spontaneity of oxidation of DBT in the UAOD process. Moreover, the conversion rate of DBT has increased from 57% at 35 °C to 85% at 65 °C.

In this study, NiFe₂O₄–PEG, an effective nanocatalyst was synthesized via a hydrothermal method using different PEG concentrations and synthesis times.

Innovative Methodology for Sulfur Release from Copper Tailings by the Oxidation Roasting Process

To effectively prevent the accumulation of copper tailings from producing acid mine drainage (AMD) and maximize the comprehensive utilization of copper tailings, the process of oxidation roasting was adopted to release sulfur in the form of SO2 to achieve the purpose of sulfur recovery later. Based on the AMD risk assessment, thermogravimetric (TG) analysis, and differential scanning calorimeter (DSC) analysis, the influences of roasting temperature, residence time, and air flow in the roasting process were investigated. The thermal stability, reaction equilibrium, mineral transformation, and residual S content were characterized by TG-DSC, HSC chemical software 6.0, X-ray diffraction (XRD), and combustion neutralization, respectively. The optimum conditions for sulfur release in the roasting process were shown with a temperature of 1200°C, a residence time of 60 min, and an air flow of 0.8 L/min. Under these conditions, the sulfur release rate was 99.82%, and the residual S content was 0.05%. Subsequently, the process of sulfur release was proposed as four steps: oxidative decomposition of pyrrhotite, formation of ferric sulfate, decomposition of ferric sulfate, and formation of hematite. All of the findings could propose a theoretical and experimental reference for the recovery of the sulfur component from tailings rich in sulfide minerals.