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

Abstract

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 nucleation 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.

Ultrarapid Formation and Direct Observation of Methane Hydrate in the Presence of l-Tryptophan

“…In the kinetic reactor, a hydrate film was clearly observed in the pure water system, as shown in Figure (A7)­(image on theright). The formation of the hydrate films was also found in our previous work. , For the 1.0 wt % SDS solution, the hydrate started to nucleate at several points of the surface of the solution simultaneously. Then, a hydrate film also formed.…”

“…However, when the concentration of l -Trp was 0.01 wt %, it had no promotion effects, as shown in Figure d. The formed hydrate film provides a mass-transfer barrier for the water molecules and the gas molecules to meet, and the amount of the formed hydrate was little . The l -Trp molecules could also change the property of the inner wall of the container and promote the upward climbing of the water molecules along it, as shown in Figure e.…”

“…The formation of the hydrate films was also found in our previous work. 37,38 For the 1.0 wt % SDS solution, the hydrate started to nucleate at several points of the surface of the solution simultaneously. Then, a hydrate film also formed.…”

“…The formed hydrate film provides a mass-transfer barrier for the water molecules and the gas molecules to meet, and the amount of the formed hydrate was little. 37 The L-Trp molecules could also change the property of the inner wall of the container and promote the upward climbing of the water molecules along it, as shown in Figure 13e. Due to the adsorption of L-Trp molecules onto the surface of the hydrate crystals, they interfered with the normal growth of the hydrate crystals and resulted in the loose and porous structure.…”

Formation Characteristics of Carbon Dioxide Hydrate in a High-pressure Flow Loop

“…The impact of PVP and L-tyrosine on the mixed gas hydrate's induction time was researched by Talaghat et al 33 The findings showed that L-tyrosine was more effective in inhibiting enzyme activity than PVP, and PVP performed better when L-tyrosine was added in modest amounts. The inhibitory impact of carboxymethylcellulose (CMC) on CO 2 hydrate was investigated by Shen et al 34 They believed that the inhibition mechanism of the CMC is mainly by mass transfer. CMC can slow down hydrate formation and reduce hydrate production, but there was no inhibitory effect when the concentration is less than 0.1 wt %.…”