Synergistic enhancement of CO₂ hydrate synthesis via magnetic stirring coupled with gas bubbling

CO₂ hydrate is an ice-like crystalline compound with attractive high heat of fusion with 500 kJ/kg under low-temperature conditions, therefore receiving attention in long-time, long-distance and high-efficient cold transportation scenarios. However, due to the high equilibrium pressure, slow synthesis kinetics and low conversion rate of CO₂ hydrate, its application is limited, leading to the necessity of a synthesis enhancement method for CO₂ hydrate. In this paper, an enhanced synthesis method of the combination of magnetic stirring and bubbling is proposed. To investigate the improvement of the proposed enhanced synthesis method by quantitate analysis, a modified equation of state is proposed to accurately calculate the amount of the formed CO₂ hydrate under the high-pressure and low-temperature range in the experiment. Based on the modified equation of state, the effects of magnetic stirring speed, the application of bubbling and the effect of bubbling rate on the morphology, induction time, synthesis rate, and the synthetic amount of CO₂ hydrate are examined. It is found that the synergistic effect of magnetic stirring and bubbling significantly improves CO₂ hydrate synthesis beneath the liquid–gas interface, yielding 7.13 times and 4.64 times improvements compared with the magnetic stirring cases under 200 rpm and 400 rpm magnetic stirring speeds, respectively. Besides, the CO₂ hydrate synthetic amount exhibits an optimum at around 250 mL/min bubbling rate (0.2964 mol, 20.46 % conversion) under 200 rpm magnetic stirring. The experimental results show the effectiveness of the proposed enhanced synthesis method on CO₂ hydrate, contributing to the development of cold thermal energy storage technology by using CO₂ hydrate.