Evaluation of the performance of kinetic inhibitors for clathrate hydrate using unidirectional growth apparatus

Abstract

We study the formation of tetrahydrofuran (THF) clathrate hydrate from polyvinylpyrrolidone (PVP) aqueous solution as a function of growth rate V and adsorbed PVP concentration c using the unidirectional growth technique. This study aims to propose a simple method for evaluating the performance of kinetic hydrate inhibitors (KHIs) for the clathrate hydrate–aqueous solution system. The degree of super cooling ΔT calculated from the growth-induced interface shift under steady-state conditions was used for evaluating the KHIs performance. ΔT at c = 0 wt%, denoted ΔT₀, gradually increased with increasing V. This result suggests that the growth of THF hydrate in solution is limited by the inherent kinetics of the process on the crystal surface. Thus, when evaluating KHIs for an inhibiting effect, the effect of increasing ΔT₀ must be offset by using the formula ΔT − ΔT₀. The dependence of ΔT − ΔT₀ on c at lower growth rates is qualitatively consistent with the theory of Raymond and Devries. However, the trend in the results at a higher growth rate does not agree with the theory. This discrepancy suggests that the crystal grain boundaries trap PVP and complicate the apparent distribution coefficient in the higher growth rate region. Using this method, a single experimental run can be completed within 3.5 h of the compulsory nucleation by setting V = 5 μm s⁻¹. We believe this method is useful for screening various KHIs and clarifying the inhibition mechanism of KHIs.