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The Li2CO3--Na2CO3--K2CO3 carbonate system exhibits superior sulfur interception capacity and thermodynamic stability in the molten salt oxidation (MSO) of cation exchange resins (CERs) with high sulfur content. However, the spent salt from the MSO process cannot be reused to reduce the operating cost and further improve the reduction ratio. Therefore, the optimal oxygen equivalent for treatment is obtained by thermodynamic equilibrium analysis of the MSO process of CERs as 1.08 multiples of the theoretical oxygen demand and the corresponding approximate chemical formula in this work. The results of the equilibrium analysis are used as the basis to propose a replenishment cycle for the MSO process (MSO-RC), which replenishes the consumed carbonate to restore the SO2 adsorption capacity and treatment capacity of the spent salt. During the experiments, the oxidation efficiencies of MSO-RC are higher than 99%, and the volume reduction ratio is improved by 12% compared with the traditional MSO. In addition, the MSO-RC maintains sulfur interception rates above 80% across multiple cycles and preserves over 94.7% Li2CO3 by adding cost-effective Na2CO3 and K2CO3 into the molten salt system. The MSO-RC process significantly improves the efficiency of process operation with lower operational costs. [ABSTRACT FROM AUTHOR]

Cationic exchange resins are used in nuclear power circuits to remove the nuclide ions to maintain the safe and efficient operation of nuclear power plants. Meanwhile, the production of spent resins is expanding significantly due to the rapid technological advancements in the nuclear industry, causing the study of resin treatment to be of great significance. This study reveals the catalytic behavior of Mn from cation exchange resins during molten salt oxidation. Mn has many isotopic ions and a catalytic effect on the treatment process. Kinetic analysis reveals that the introduction of Mn decreases the activation energy of the styrene–divinylbenzene skeleton from 48.164 kJ mol−1 to 41.696 kJ mol−1 and decreases the degradation temperature of the resin by 78 °C. Compared to the original resin, the destruction and removal efficiency of Mn-doped cation exchange resin increased from 75.07% to 85.28% during molten salt oxidation at 650 °C. According to the scanning electron microscope analysis and characterization studies, Mn promotes a 55.71% reduction in the average particle diameter of resin structural fragments. Fourier-transform infrared spectroscopy analysis of the resin residues demonstrates that Mn doping influences the catalytic decomposition of –SO2– and S–O within sulfonic acid groups. This catalytic effect induces destabilization and subsequent ring-opening of the benzene ring. These results imply that Mn doping can facilitate molten carbonate oxidation destruction of cation exchange resins. The X-ray diffraction analysis of waste salt reveals that with increasing oxidation time, the transformation of Mn proceeds as (Mn2O6)6− → (MnO3)2− → (MnO2)− at 750 °C. [ABSTRACT FROM AUTHOR]

Heteroatom doped metal-free catalysts are one of the most promising replacements for platinum for the alkaline oxygen reduction reaction (ORR). Due to the lack of metal atoms, they are extremely stable and environmentally friendly. However, production of carbon nanomaterials can have a very high CO2 footprint. In this study, we present ORR catalysts made directly from CO2via molten salt CO2 electrolysis. The deposited carbon powder is doped with nitrogen using pyrolysis in the presence of dicyandiamide. The effect of molten carbonate electrolyte composition towards the final ORR activity in 0.1 M KOH is studied. A thorough physico-chemical study of the starting carbons and N-doped catalysts is presented with SEM and TEM imaging, BET analysis, Raman and X-ray photoelectron spectroscopy as well as the rotating disk electrode method. The onset potential and half-wave potential of the better catalyst were −50 and −175 mV vs. SCE in 0.1 M KOH, respectively. [ABSTRACT FROM AUTHOR]

High-temperature molten salts are an excellent electrolyte to bring about redox reactions at a rapid rate without using rationally designed nano-structured catalysts. However, the large-scale electrolyzer is constrained by the use of expensive and resource-deficient lithium salts. Using Earth-abundant CaCO3 releases the pressure of using strategic lithium resources, but the low solubility of CaO in molten carbonates disables the capability of capturing CO2. In addition, the separation of carbon from water-insoluble CaO and CaCO3 consumes a large amount of acids. To tackle these challenges, we report a CaCO3-containing molten carbonate electrolyzer to prevent the use of lithium salts, and a molten CaCl2 dissolver to separate carbon from CaO that is soluble in molten CaCl2 and can capture CO2 by carbonization. More importantly, we develop a salt-soluble-to-water-insoluble approach for producing ultrafine CaCO3 using molten salt as a soft template. Overall, this study opens a pathway to use cheap and Earth-abundant molten CaCO3 as a mediator to convert CO2 to oxygen at a cost-effective inert anode, with value-added carbon at the cathode, and ultrafine CaCO3 through a salt-to-solution process. [ABSTRACT FROM AUTHOR]

Electrolysis of molten carbonates provides an effective means to achieve the direct conversion of the greenhouse gas carbon dioxide to readily available carbonaceous fuel or chemicals. In this study, CO2 was electrolyzed in a Li–Na–K ternary carbonates mixture using galvanized Fe as the cathode and nickel as the anode. In particular, the effect of BaCO3 on the generation of carbon was studied. The results demonstrate that BaCO3 addition facilitates the deposition of compact carbon materials. Moreover, decreasing the temperature and increasing the current density lead to the formation of loosened carbon products. Though Li–Na–K–Ba electrolysis exhibits a higher cell voltage than that using Li–Na–K carbonates, BaCO3 addition can significantly ease anode corrosion and the corresponding corrosion inhibiting action is discussed. In summary, a facile CO2 absorption and a mitigatory nickel anode corrosion were observed when BaCO3 was dissolved in Li–Na–K carbonates and further investigation is expected. [ABSTRACT FROM AUTHOR]

The direct synthesis of diethyl carbonate (DEC) from ethanol and carbon dioxide over Ce0.8Zr0.2O2 catalysts was investigated in continuous mode at atmospheric pressure. Three main parameters, namely molar ratio of ethanol/CO2, flux and temperature, have significant influence on the formed DEC amount and were studied systematically. With 32 mmolDEC L−1cat h−1 achieved at ambient pressure, an ethanol/CO2 molar ratio of 3 and a temperature of 100 °C the continuous approach offers a higher productivity compared to batch reactions, normally performed in autoclaves under much higher pressure. Moreover, in order to shift the equilibrium to promote the formation of DEC, four inorganic porous membranes, (i) MFI zeolite, Si/Al ratio ∼57; (ii) MFI zeolite, Si/Al ratio ∼270; (iii) LTA (NaA) zeolite; and (iv) a microporous carbon membrane, have been applied for product removal in a catalytic membrane reactor. A relationship between the amount of removed water achieved by the membranes and the enhancement of formed DEC amount was found. The productivity can be increased to 47 mmolDEC L−1cat h−1 using an MFI-57 membrane. [ABSTRACT FROM AUTHOR]