Hydrate Formation and Dissociation of Liquid CO₂ with Seawater Containing Organic Matters in Sand

The hydrate-based CO2 sequestration (HBCS) is a potential technology that can be applied to large-scale oceanic CO2 sequestration. However, the favorable conditions of liquid CO2 to form hydrate for HBCS are rarely involved. In this work, the effect of organic matters present in the ocean on CO2 hydrate formation under liquid CO2 was investigated. Dodecylbenzenesulfonic acid and threonine were found to promote CO2 hydrate growth in seawater, while only a layer of hydrate film at the interface was formed for other organic matters by visual morphology. An interesting finding that differed from that of the seawater system was that urea and carbohydrates in quartz sand were more conducive to CO2 hydrate formation. The gas storage capacity of CO2 hydrate for urea was increased to 91.2 V/V and the hydrate growth rate reached 1.02 mmol CO2/(mol H2O·min), which significantly exceeded more than 2 times that of other organic matters. The results of visual morphology also indicated that larger chunks of white solid hydrates were observed on the surface of the quartz sand in the presence of urea. In the dissociation process of CO2 hydrate for rhamnose and urea, obvious cracks were not constructed, which is conducive to maintaining the stability of the reservoir. Therefore, the research results of organic matters on CO2 hydrate formation in seawater and quartz sand help find proper sequestration areas for real HBCS technology.