Process intensification in gas-liquid mass transfer by nanofluids: Mechanism and current status

Alkaline absorbents for SO2 and SO3 removal: A comprehensive review

Injection of an alkaline absorbent into the flue gas can significantly reduce SO2 and SO3 emissions. The article presents alkaline absorbents employed in industrial processes to remove SO2 and SO3 from flue gases, detailing their characteristics and applications across various process conditions. It summarizes the mechanisms and influencing factors behind SO2 and SO3 removal, outlines the impact of multi-component gases, particularly SO2, on SO3 removal in actual flue gases, and elucidates this competitive phenomenon from a theoretical standpoint. The article compares the application scenarios and efficiencies of alkaline absorbents across different processes, identifies the optimal combinations of various absorbents and processes, and proposes a synergistic approach for the removal of SO2 and SO3. The findings demonstrate that by injecting calcium- or sodium-based absorbents into dry processes, SO2 and SO3 can be removed efficiently and cost-effectively, with process optimization and absorbent modifications further enhancing the SOx removal efficiency. In the future, by blending two or more absorbents and applying them to dry processes, a synergistic removal of SO2 and SO3 can be achieved.

Investigation into the Enhancement of Gas-Liquid Mass Transfer of Absorption of H2S by MDEA with Carbon Quantum Dots

Although the addition of fine particles can enhance mass transfer, the stability of suspension is still a challenge. Responding to this, this study introduced carbon quantum dots (CQDs) with good hydrophilicity into a desulfurizer. N-doped carbon quantum dots (N-CQDs) were prepared by the hydrothermal method and characterized by TEM, FT-IR, and XPS. The stability and rheological properties of MDEA-based CQD solutions with different concentrations were studied. CQD solutions with low concentrations showed good stability, and the viscosity of CQD solutions was positively correlated with concentration and inversely correlated with temperature. The desulfurization experiment showed that the desulfurization effect and mass transfer enhancement of MDEA-based CQD solutions were coinfluenced by the viscosity and concentration of the solution; 0.01 vol % CQD solution had the best desulfurization effect, and the mass transfer coefficient was 0.66 mol/(m3h kPa), which increased by 26.61% compared to the base solution.

Efficient utilization of free radicals in advanced oxidation processes under high-gravity environment for disposing pollutants in effluents and gases: A critical review

Advanced oxidation processes (AOPs) using strongly oxidizing radicals are promising for wastewater treatment and gas purification. Nevertheless, the short half-life of radicals and the limited mass transfer in traditional reactors cause under-utilization of radicals and low pollutant removal efficiency. High-gravity technology (HiGee)-enhanced AOPs (HiGee-AOPs) have been demonstrated a promising way to enhance radical utilization in a rotating packed bed reactor (RPB). Here, we review the potential mechanisms of intensified radical utilization in HiGee-AOPs, structures and performance of RPB, and applications of HiGee in AOPs. The intensification mechanisms are described from three aspects: enhanced generation of radicals by efficient mass transfer, in-situ radical utilization under frequent liquid film renewal, and selective effect on radical utilization due to micromixing in RPB. Based on these mechanisms, we propose a novel High-gravity flow reaction with the essence of efficiency, in-situ, and selectivity in order to better explain the strengthening mechanisms in HiGee-AOPs. HiGee-AOPs possess great potential for treating effluent and gaseous pollutants due to characteristics of High-gravity flow reaction. We discuss the pros and cons of different RPBs and their applications to specific HiGee-AOPs. HiGee improve the following AOPs: (1) facilitate interfacial mass transfer in homogeneous AOPs, (2) enhance mass transfer to expose more catalytically active sites and mass-produce nanocatalysts for heterogeneous AOPs, (3) inhibit bubble accumulation on the electrode surface of electrochemical AOPs, (4) increase the mass transfer between liquid and catalysts in UV-assisted AOPs, (5) improve the micromixing efficiency of ultrasound-based AOPs. Strategies outlined in this paper should inspire further development of HiGee-AOPs.

Oxygen mass transfer enhancement by activated carbon particles in xylose fermentation media

In this work, the effect of activated carbon particles on the production of xylonic acid from xylose by Gluconobacter oxydans in a stirred tank bioreactor was investigated. The enhancement of the oxygen transfer coefficient by activated carbon particles was experimentally evaluated under different solids volume fractions, agitation and aeration rates conditions. The experimental conditions optimized by response surface methodology (agitation speed 800 rpm, aeration rate 7 L min^-1, and activated carbon 0.002%) showed a maximum oxygen transfer coefficient of 520.7 h^-1, 40.4% higher than the control runs without activated carbon particles. Under the maximum oxygen transfer coefficient condition, the xylonic acid titer reached 108.2 g/L with a volumetric productivity of 13.53 g L^-1 h^-1 and a specific productivity of 6.52 g/g_x/h. In conclusion, the addition of activated carbon particles effectively enhanced the oxygen mass transfer rate. These results demonstrate that activated carbon particles enhanced cultivation for xylonic acid production an inexpensive and attractive alternative.

Experimental Investigation on Solar–Thermal Conversion and Migration Characteristics of Nanofluids

Solar–thermal conversion and migration characteristics of nanofluids have attracted intensive attention recently. Due to the strong absorption of solar energy, solar collectors with nanofluids have wide applications in many areas including desalination and power generation. Researchers have mainly focused on the macroscopic performance of nanofluids in solar collectors, but the nanoparticles’ migration characteristics with vapor during phase transformation have not been further investigated. Therefore, an experimental investigation on solar–thermal conversion characteristics of nanofluids and migration characteristics with vapor during phase transformation was conducted in this work, in order to verify the enhancement effect of nanoparticles on solar energy absorption and explore the nanoparticles’ migration behavior with vapor. It was found that part of Ag nanoparticles migrate out of the nanofluids with generated vapor by boiling nanofluids, and most of the nanoparticles remained in the nanofluids. In addition, more Ag nanoparticles migrated with vapor with the increased heating power. The concentration of migrated nanofluids was 20.58 ppm with a power of 16.2 W and 31.39 ppm with a power of 20 W. The investigation pointed out the potential danger of nanofluids in the process of utility and provided a reference for the standardized application of nanofluids.