Critical Growth Rate of Hydrate Crystal Growth Inhibitors in the Low Growth Rate Region

• Published in: Crystal growth & design Vol. 21; no. 9; pp. 4979 - 4985
• Main Authors: Muraoka, Michihiro, Kelland, Malcolm A, Yamamoto, Yoshitaka, Suzuki, Kiyofumi
• Format: Journal Article
• Language: English
• Published: American Chemical Society 01.09.2021
• ISSN: 1528-7483; 1528-7505
• DOI: 10.1021/acs.cgd.1c00421

We tested poly­(N-vinylpyrrolidone) (PVP) K-12, K-15, K-30, K-90, poly­(N-vinylcaprolactam) (PVCap), tetrapentylammonium bromide (TPeAB), tetrabutylammonium bromide (TBPB), polyacryloylpyrrolidine (PAP), poly­(N-isopropylmethacrylamide) (PNIPMAM), and hyperbranched polyesteramide (PEA) as hydrate crystal growth inhibitors (HCGIs). We used a tetrahydrofuran (THF) sII hydrate system using a unidirectional growth apparatus. The HCGI concentration c = 0.5 wt % and the growth rate V ranged from 0.005 to 10 μm s–1. The growth rates of TPeAB, PVP K-12, K-15, TBPB, and PEA were found to be critical in the region of a low growth rate with the degree of supercooling ΔT approaching 0. However, PVP K-30, K-90, PAP, PNIPMAM, and PVCap remained effective at V = 0.005 μm s–1. These results enhance the persuasiveness for the model that the HCGI effect is explained by the residence time on the crystal surface of HCGI, τ, and time interval t* required to increase the interface curvature. In addition, we determined the threshold growth rate of THF hydrate for examining HCGI performance on sII gas hydrate. Thus, when 0.005 ≤ critical growth rate V* < 0.01 μm s–1, the HCGIs are moderate inhibitors on sII gas hydrate. When V* < 0.005 μm s–1, the HCGIs are strong inhibitors on sII gas hydrate.