Tetrahydrofuran Hydrate Crystal Growth Inhibitor Performance and Mechanism of Quaternary Ammonium and Phosphonium Salts

Abstract

To gain insight into the hydrate crystal growth inhibitor (HCGIs) mechanism, we have studied various quaternary ammonium ionic liquid salts (QAILs) and phosphonium salts for their ability to prevent structure II (sII) hydrate crystal growth. We tested polyvinylpyrrolidone (PVP), polyvinylcaprolactam (PVCap), tetrapropylammonium bromide (TPrAB), tetrabutylammonium bromide (TBAB), tetrapentylammonium bromide (TPeAB), tetrahexylammonium bromide (THexAB), and tetrabutylphosphonium bromide (TBPB) in a tetrahydrofuran (THF) sII hydrate system using a unidirectional growth apparatus to determine the concentration and growth rate dependence. The growth rates of TPrAB, TBAB, and THexAB were found to be critical in the region of low growth rate, with the degree of supercooling ΔT becoming 0 for these additives in the low-growth-rate region. In contrast, PVP, PVCap, TPeAB, and TBPB remained effective at the lowest growth rate of V = 0.04 μm s–1. These trends can be explained by the residence time on the crystal surface of the HCGI, τ, and duration time of crystal growth.

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

“…HCGIs are PVP K-12, K-15, K-30, and K-90. The 0.04 ≤ V <10 μm s –1 range data of PVP-90 are cited from ref . The error bars were calculated from the temperature gradient and the maximum fluctuation of the growth interface shift around the measured point.…”

“…In this study, we employed the same experimental methods reported in a previous paper. , This is our own method for evaluating HCGI inhibition performance. For testing, we used a stoichiometric THF–water (THF–17H 2 O) solution prepared from a dehydrated stabilizer-free THF (99.5 wt % purity, Kanto Chemical Co., Japan) and ultrapure water (18.2 MΩ·cm resistivity).…”

“…Certain quaternary ammonium ionic liquid salts (QAILs) and phosphonium salts can be used for the sII clathrate hydrates as HCGIs. − Typical examples of quaternary ammonium salts are tetrapropylammonium bromide (TPrAB), tetrabutylammonium bromide (TBAB), tetrapentylammonium bromide (TPeAB), and tetrahexylammonium bromide (THexAB). TPrAB, TBAB, TPeAB, and THexAB are weak, moderate, strong, and weak THF hydrate inhibitors, respectively. , Tetrabutylphosphonium bromide (TBPB) is also an HCGI and strong THF hydrate inhibitor. ,− These quaternary ammonium surfactants and TBPB have been shown to be synergist for PVCap on THF and sII gas hydrate. ,− …”

“…The technique evaluates only the growth inhibition effect at any growth rate combined with a stoichiometric THF–water solution. We tested PVP K-90, PVCap, TPrAB, TBAB, TPeAB, THexAB, and TBPB using the same system . The growth rates of TPrAB, TBAB, and THexAB were critical at V = 0.1 μm s –1 , with the degree of supercooling Δ T approaching 0.…”

Adsorption‐Inhibition of Clathrate Hydrates by Self‐Assembled Nanostructures

“…[23] In some cases, video analysis is used to measure the growth rate of the advancing hydrate crystal, and direct observation of clathrate growth was demonstrated. [20,24,33,[25][26][27][28][29][30][31][32] However, these studies were done mainly on polycrystalline samples (with a few exceptions that included millimeter sized crystals [20,28,30] ), making a detailed description of KHI mechanism more difficult to construct. Such a detailed description of ice growth kinetics in the presence of AFPs has unlocked important understanding of AFP-ice interactions.…”