For three groups of systemshomogeneous, liquid–liquid, and solid–liquidabsorption heats of carbon dioxide capture by amine solutions were determined with continuous calorimetry. In the case of a phase-separation solvent, the heat of phase separation is added to conventional absorption heat, and the loading range of heat of phase separation is important in process design. With the merits of continuous measurement, the phase-change loading points were obtained in liquid–liquid and solid–liquid phase-separation systems as the heat release of carbon dioxide products to achieve a more stable state. The loading points where a leap in absorption heat appears coincide with those where the turbidity in solvents changes, which was confirmed by ocular inspection in both systems. In liquid–liquid systems, the presence of water in 2-(ethylamino)ethanol:diethylene glycol diethyl ether:water contributes to the decrease in absorption heat. Even though the formation of bicarbonate is minor even in solvent with water, the increase in its formation contributes to this decrease in absorption heat because of its lower formation heat as compared to that of carbamate. In solid–liquid systems, a significant increase in absorption heat is attributed to the crystallization energy of carbonate salt emitted on the breakdown of the supersaturation.
The physical or mechanical effects induced by ultrasound were investigated through the viscosity change in degradation of polymers. The viscosity change was observed with polyethylene oxide in both aqueous and benzene solution; while polystyrene in only benzene solution. The frequency of ultrasound in these experiments varies from 20 kHz to 1 MHz, under a constant dissipated power. The viscosity ratio and the apparent degradation rate were obtained as a function of the irradiation frequency. From the analysis of these experiments, the mechanical effects are found to slow down above 100 kHz when the frequency increases. In case of the analysis of solution viscosity, since this method yields the same apparent results in both aqueous and benzene solutions, our study propose an alternative simple, cost effective method to quantify the mechanical effects in sonochemistry.
Developing energy-saving absorbents for carbon dioxide (CO 2 ) is essential for improving carbon capture and storage (CCS) technologies. Recently, we have designed phase separation solvents, which can significantly reduce the regeneration energy for CO 2 capture and separation down to 1.6 GJ/ton-CO 2 et al. Int. J. Greenhouse Gas Control2018, 75, 1−7]. For further developing better solvents, this paper studied a theoretical approach with conductor-like screening model for real solvents (COSMO-RS) to screen the amine/ether/water systems to identify phase separation solvents upon CO 2 absorption. In this work, liquid−liquid equilibria of 21 amine/ether/water systems were determined both before and after CO 2 absorption. Experimentally, it has already been demonstrated that the phase behavior of these systems is classified into three categories: phase separation type, miscible type, and immiscible type. This study demonstrates that the octanol/water partition coefficient is empirically able to search for a combination of amine and ether compounds, in which the system exhibits the phase separation behavior by absorbing CO 2 . The COSMO-RS calculations successfully reproduced experimental phase behavior with a rate of agreement of more than 80% by accounting the following two factors: (i) ion pairing for the description of the association/dissociation state for ionic species and (ii) relevant low-lying conformations of ether and amine, which are rationalized by experiments such as conductivity and excess enthalpy measurements. Moreover, we also validated the ability of the COSMO-RS calculation to qualitatively describe the compositions of 2-(ethylamino)ethanol, diethylene glycol diethyl ether, and water in CO 2 -rich and CO 2 -lean phases at varying CO 2 loading conditions.
We examined the influence of liquid height on mechanical and chemical effects in 20 kHz sonication with a new Langevin-type transducer. Mechanical effects were evaluated from the degradation of polyethylene oxide in aqueous solution and chemical effects were measured with potassium iodide solution. Standing waves or reactive zones were observed using sonochemical luminescence and aluminum foil erosion. The observed wavelength was reduced by coupled vibration, compared with the wavelength calculated by dividing velocity by irradiation frequency. As liquid height increased, mechanical effects were suppressed. In the case of chemical effects, the stable sonochemical efficiency gained at a height of over 120 mm, and the sonochemical efficiency were also markedly higher than those of a conventional horn-type one.
Electrochemical reduction of CO 2 comprising the CO 2 reduction reactuib (CO 2 RR) and oxygen evolution reaction (OER) is one of the most promising technologies for electrification of the chemical process industry. Here, the performance of a electrocatalyst with a three-dimensional structure of InZnCu on Cu foam (CF) is presented. This electrocatalyst was fabricated by electrodeposition of In and Zn over Cu and exhibited a superior reduction of CO 2 to CO at a Faradaic efficiency of 93.7% at −0.7 V and an excellently long duration of 100 h. Due to the synergy of the thin In layer, the Zn nanosheets provided a high surface-active area and strong mechanical robustness during the reaction. Additionally, a two-electrode system was constructed based on the CF-modified surface, which provided valuable guidelines on the overall CO 2 RR−OER system for further evolution. Furthermore, due to the facile synthesis, the bimetal-layer double hydroxide (LDH) exhibited high conductivity and high OER performance. Hence, the two-electrode system assembled excellent electrocatalysts for the CO 2 RR−OER (InZnCu/CF||Cu(OH) 2 NWs@NiCo-LDH/CF) with high conversions of CO 2 to CO of 67% and 88% at 2 and 50 mA cm −2 , respectively. Notably, the CO 2 RR−OER system exhibited excellent stability in a 40 h CO 2 conversion with a constant current density of 2 mA cm −2 at an ultralow voltage of 1.59 V. Moreover, the calculation of the energy input converting CO per ton of CO 2 resulted in a low energy input range for further development in scalability. This overall CO 2 RR−OER proposes development in electrochemical CO 2 reduction for industrial applications.
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