Abstract
Hydrate-based CO2 capture from large emission sources is considered a promising process for greenhouse gas mitigation. The addition of nanoparticles may promote or inhibit the formation of hydrates. In this work, CO2 hydrate formation experiments were performed in a dual-cell high-pressure reactor. Non-modified, hydrophilic modified and hydrophobic modified aluminum oxide (Al2O3) nanoparticles at different concentrations were added to assess their promoting or inhibitory effects on CO2 hydrate formation. The equilibrium temperature and pressure, induction time, and total gas consumption during CO2 hydrate formation were measured. The results show that the presence of Al2O3 nanoparticles exerts little effect on the phase equilibrium of CO2 hydrates. Under the experimental conditions, the addition of all Al2O3 nanoparticles imposes an inhibitory effect on the final gas consumption except for the 0.01 wt% addition of hydrophilic modified Al2O3 nanoparticles. The induction time required for the nucleation of CO2 hydrates mainly ranges from 70 to 90 min in the presence of Al2O3 nanoparticles. Compared to the absence of nanoparticles, the addition of non-modified and hydrophilic modified Al2O3 nanoparticle reduces the induction time. However, the hydrophobic modified Al2O3 nanoparticles extend the induction time.
Highlights
Gas hydrates or clathrate hydrates, are non-stoichiometric compounds composed of water and gas molecules under specified pressures and low temperatures
The peaks observed at 2850 and 2918 cm−1 are caused by the symmetric and asymmetric stretching, respectively, of the ethyl group (–CH2 −), and the absorption peak at 2971 cm−1 is caused by the methyl group (–CH3 ) [35]. The embedding of such groups can be considered the successful modification of Al2 O3 nanoparticles
All the experimental results reveal an inhibitory effect on the final gas consumption except for the 0.01 wt% addition of hydrophilic modified Al2 O3 nanoparticles
Summary
Gas hydrates or clathrate hydrates, are non-stoichiometric compounds composed of water and gas molecules under specified pressures and low temperatures (generally above the freezing point of water). One volume unit of CO2 hydrates ideally contains. 175 standard volume units of CO2 gas and generates pure water upon disassociation [4]. In recent years, researchers have studied CO2 hydrates as a means of gas separation and seawater desalination [5]. CO2 is a primary greenhouse gas generated by large fossil fuel end users, such as coal burning power plants, steel works, and chemical plants. Traditional CO2 capture methods mainly include the chemical absorption method, adsorption method, and membrane separation method [9,10], but they experience the problems of a high energy consumption and small adsorption amount. The hydrate-based CO2 capture process has Energies 2020, 13, 5380; doi:10.3390/en13205380 www.mdpi.com/journal/energies
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