Influence of Polyvinylpyrrolidone and Cassava Starch on the Formation Kinetics of CO₂ Hydrate

CO2 hydrate blockages may occur in the application of CO2 capture, utilization, and storage (CCUS). Under specific conditions, CO2 hydrates exhibit great stability and pose significant challenges in prevention and control. Current research primarily focuses on the prevention of natural gas hydrates, while research on the prevention of CO2 hydrates is relatively limited. In this work, the formation kinetics of CO2 hydrates in the presence of two kinetic inhibitors, polyvinylpyrrolidone (PVP) and cassava starch, were investigated. Effects of subcooling, inhibitor concentrations, inhibitor molecular weights, and compositions of the mixture of PVP and starch were considered. The results indicate that at subcooling lower than 6.2 K (2.5 MPa, 272.95 K), 1 wt % PVP-K32 can exhibit good inhibition effect. Cassava starch has a better inhibition effect than PVP, with concentration of 0.2–0.5 wt %, it can effectively inhibit the hydrate formation for more than 6 h at the subcooling of 6.2K (2.5 MPa, 272.95 K). Inhibitor blend (1 wt % PVP-K32 + 1 wt % cassava starch) demonstrates good inhibition performance at the high subcooling of 8.9 K (3.5 MPa, 272.95 K). A significant concentration effect was observed. Under the supercooling of 8.9 K, PVP-K32 can delay the nucleation of hydrates, but its inhibitory effect on the growth process of the hydrates became weak with the increase of concentration. CO2 hydrates exhibited a distinct interface growth phenomenon, forming thin films that act as a barrier to mass transfer. Stable hydrate films along with kinetic inhibitors inhibited the nucleation and growth of hydrates. However, under high turbulence conditions, this inhibitory effect is significantly weakened. In addition, sheet-like or vein-like hydrates morphologies were also observed in the presence of inhibitors. These results can provide support for the development of kinetic inhibitors for CO2 hydrates to address hydrate blockage issues in CO2-related engineering.