Salinity and Thermal Effects on CO 2 Hydrate Formation and Distribution Probed by Raman and Optical Microscopy in Micro-capillaries
Year: 2026
Type: article
Abstract: High Resolution Image Download MS PowerPoint Slide Clathrate hydrates of CO 2 were synthesized in NaCl solutions (0–15 wt %) and investigated using micro-Raman spectroscopy and optical microscopy in newly developed high-pressure microcapillaries. This combined approach provides spatially resolved insights into hydrate nucleation, growth, and phase distribution under controlled salinity and thermal conditions, with direct relevance for hydrate-based desalination and CO 2 capture. Spectral markers from the CO 2 Fermi dyad (ν –, ν + ) and O–H stretching region enabled clear discrimination between hydrate-rich domains, hydrate-brine slurries, and residual aqueous phases. In particular, the position and full width at half-maximum of the ν – component were shown to be robust indicators for distinguishing dissolved CO 2, liquid CO 2, enclathrated CO 2, and mixed-phase environments. Regions where hydrates coexist with liquid CO 2 or aqueous solution exhibit intermediate spectral signatures that differ unambiguously from those of the corresponding pure phases. Two thermal sequences were examined following primary hydrate formation below 246 K: (i) heating to (near-) dissociation and (ii) cooling under moderate to strong subcooling. Dissociation temperatures decreased systematically with salinity, from ∼279 K in pure water to ∼273 K at 15 wt % NaCl, consistent with thermodynamic inhibition. Pure water exhibited relatively homogeneous hydrate coverage, whereas saline systems developed pronounced interfacial crystallization and heterogeneous hydrate–brine coexistence. During secondary formation, moderate subcooling (∼4 K) favored hydrate reconversion at the gas–liquid interfaces and on residual seed crystals, while deeper subcooling (≥12 K) increased hydrate coverage but amplified salinity-dependent heterogeneities. The interplay between seed availability, hydrate memory effects, salt-induced inhibition, and gas-bubble dynamics was found to govern nucleation pathways and spatial patterns of growth. These results establish a mechanistic link between microscale hydrate distributions and macroscopic formation kinetics, providing a foundation for optimizing hydrate-based water recovery and carbon management processes.
Source: ACS Omega
Authors: Sadain Zafar, Claire Pirim, Bertrand Chazallon
Language: English
Subfield: Environmental Chemistry
Field: Environmental Science
Domain: Physical Sciences
SDG: Climate action
Open Access status: gold
Estimated APC paid: $1,935
OpenAlex ID: W7130328848