Solid CO2 hydrates for sustainable environment: Application in carbon capture and desalination

Abstract

The world population has reached 7.9 billion and is growing, which creates the necessity to manage the water-energy nexus. India’s energy sector predominantly depends on coal-fired power, which generates ∼ 70% of electricity while utilizing ∼ 30 billion cubic meters of water (bcm) and is responsible for global warming (the increasing CO2 level) and the water crisis. In this direction, gas hydrate-based carbon capture and seawater desalination are potential technologies for clean water production while utilizing flue gas coming from coal-fired power plants. Gas or clathrate hydrates are ice-like crystalline materials that form at a suitable temperature and pressure conditions. Hydrates form a cage-like structure of water molecules while encapsulating the CO2 molecules and rejecting the salts. One mole of hydrate utilizes 85% water and 15% CO2, which is one of the motivations to develop hydrate-based desalination technology. However, sluggish kinetics of hydrate formation and low temperature or high-pressure conditions is the major bottleneck to deploying a hydrate-based approach. Therefore, in the current work, cyclopentane (CP, 6 mol%) is used as a thermodynamic promoter which shifts the hydrate forming temperature (equilibrium conditions) from 277 to 291 K at ∼ 2.0 MPa pressure compared to non-CP system. Moreover, in context to enhance the rate of hydrate formation, the performance of hydrophobic amino acid (l-leucine) is evaluated for the formation kinetics of binary CP-CO2 hydrates in saline (3.5 wt% NaCl in water) and non-saline media. The experimental results indicate that salinity suppresses the water to hydrate conversion by 50% (first 60 min data). The addition of 1000 ppm l-leucine helps to enhance the initial hydrate formation rate resulting in a higher percent of hydrate conversion in lesser process time. However, kinetic inhibition effect was observed at high content of l-leucine (5000 ppm). Our findings offer new insights into integrated hydrate-based carbon capture and seawater desalination approach.