Effects of magnetic field on CO2 hydrate phase equilibrium

The conditions and influencing factors of hydrate formation is significant for hydrate technology. Combining with the existing literatures and the experimental data of this work, the phase equilibrium of CO₂ hydrate in (NaCl/CaCl₂/MgCl₂) ionic solutions, pure water-sediment system and (NaCl/CaCl₂/MgCl₂) ionic solution-sediment systems under the static magnetic field (0.39 T) was studied. Moreover, the effect mechanism of magnetic field on hydrate phase equilibrium in different systems was analyzed in terms of intermolecular interaction. Under the same pressure, the magnetic field increased the phase equilibrium temperature of CO₂ hydrate by 2.0–2.8 K in the three ionic solutions, which improved the hydrate formation conditions. This is mainly due to that the magnetic effect increases water activity and weakens the ionic hydration shells, thus promotes hydrate formation. In addition, compared with the ionic solution systems without magnetic field, the magnetic field increased the hydrate phase equilibrium temperature by 0.1–2.5 K in the ionic solution-sediment systems. However, the degree of temperature increase is less than that in the magnetic field-ionic solution systems, which is because the magnetic field enhances the binding between ions and the sediment particle in sediment-bearing systems. Compared with the magnetic field-ionic solution systems, the water activity in the magnetic field-ionic solution-sediment systems is lower, which makes hydrate formation more difficult. Moreover, with the movement of cations and anions in magnetic field, the crystals may be formed due to ion collisions, enhance the capillary action in ionic solution-sediment systems, and then hinder the hydrate formation. Therefore, the sediments can weaken the magnetic field promotion to hydrate formation.