Kinetic Inhibition of CO2 Hydrate by Carboxymethylcellulose Sodium through Retarded Mass Transfer

The influence of carboxymethylcellulose sodium (CMC-Na) on the formation kinetics of carbon dioxide (CO2) hydrate was investigated by adopting an isothermal and isochoric method. The mass transfer characteristics of CO2 in the solution of CMC-Na were also investigated. Pure water and polyvinylpyrrolidone (PVP) of different molecular weights were used for comparison. Several parameters, such as the concentration of the additives, the stirring condition, and the temperature, were investigated. The experimental results showed that all the additives had almost no inhibition effects on the nudeation of hydrates when the experimental temperature was 273.25 K and the initial pressure was 3.5 MPa. In contrast, PVP could effectively slow the growth rate of CO2 hydrate, while CMC-Na could greatly decrease the ultimate amount of the formed hydrate. The inhibition effects of CMC-Na decreased with the decrease of its concentration and totally lost its inhibition effects at the concentration of 0.1 wt % or lower. Under a stirring condition, carbon dioxide hydrate grew faster than that under a static condition. Temperature had nearly no influence on the mass transfer of CO2 in the solution, and the mass transfer rate of CO2 in the CMC-Na solution was the slowest among all the samples studied. The formation of hydrate mainly took place at the gas/solution interface. Adsorption and interference to crystal growth were supposed to be the mechanism by which PVP molecules inhibited the growth of the hydrate crystal, while mass transfer resistance was supposed to play a key role in the inhibition of CMC-Na. The experimental results could provide some theoretical guidance for the development of a new type of kinetic hydrate inhibitors and the prevention of hydrate.