This study evaluates the kinetic hydrate inhibition (KHI) performance of four quaternary ammonium hydroxides (QAH) on mixed CH4 + CO2 hydrate systems. The studied QAHs are; tetraethylammonium hydroxide (TEAOH), tetrabutylammonium hydroxide (TBAOH), tetramethylammonium hydroxide (TMAOH), and tetrapropylammonium hydroxide (TPrAOH). The test was performed in a high-pressure hydrate reactor at temperatures of 274.0 K and 277.0 K, and a concentration of 1 wt.% using the isochoric cooling method. The kinetics results suggest that all the QAHs potentially delayed mixed CH4 + CO2 hydrates formation due to their steric hindrance abilities. The presence of QAHs reduced hydrate formation risk than the conventional hydrate inhibitor, PVP, at higher subcooling conditions. The findings indicate that increasing QAHs alkyl chain lengths increase their kinetic hydrate inhibition efficacies due to better surface adsorption abilities. QAHs with longer chain lengths have lesser amounts of solute particles to prevent hydrate formation. The outcomes of this study contribute significantly to current efforts to control gas hydrate formation in offshore petroleum pipelines.

---

The relative inhibition performance technique proposed by Koh et al. [67] was used to effectively compared the hydrate inhibition impact of the QAHs. The method wasused to account for the kinetic system-dependency effect of the tested inhibitors. Therelative inhibition performance (RIPinduction time) factor was estimated using Equation (2).RIPinduction time values 0 correspond to a superior hydrate inhibitory performance:

RIPinduction =induction timeinhibitor-induction timewater/induction timewater (n) where n is the number of QAHs tested in this work.

---

QAHs as Kinetic Hydrate Inhibitors:Identifying effective kinetic hydrate inhibitors is crucial, especially in applications like offshore petroleum pipelines, where preventing gas hydrate formation is essential for operational efficiency and safety.

Isochoric Cooling Method:The choice of experimental method is critical for accurately studying hydrate formation kinetics. Isochoric cooling involves keeping the volume constant during cooling, providing insights into the inhibitory effects of the QAHs under specific conditions.

Temperature and Concentration Conditions: Studying the KHI performance under different temperatures and concentrations allows for a comprehensive understanding of the inhibitors' effectiveness across a range of conditions, reflecting real-world scenarios.

Contribution to Gas Hydrate Control in Offshore Petroleum Pipelines:Effective KHI performance can contribute to improving the reliability and safety of offshore petroleum pipelines by preventing hydrate-related issues.

---

Market Demand for Gas Hydrate Inhibitors:A need for inhibitors to prevent the formation of gas hydrates in CH4 + CO2 mixed systems, especially in offshore transmission pipelines.

Efficiency of QAHs:The QAHs studied are reported to inhibit the formation of mixed gas hydrates effectively, with a focus on increasing the hydrate formation induction time and decreasing the initial rates of hydrate formation.

Variability in Inhibition Efficiency: The efficiency of inhibition depends on the percentage proportions of CH4 and CO2 in the mixed gas systems, as well as the type of gas system involved.

Mechanisms of Inhibition: Mechanisms for kinetic hydrate inhibition, including disrupting the activity of water and gas dissolution via adsorption and lowering the subcooling temperature.

---