Effect of Hydrogen Bonding Energy and Freezing Point Depression of Quaternary Ammonium Salts on the Thermodynamic Gas Hydrate Inhibition

The effects of the hydrogen bonding energy interaction and freezing point depression on five quaternary ammonium salts (QAS) of gas hydrate systems are discussed in this study. Tetramethylammonium bromide, tetraethylammonium bromide, tetramethylammonium acetate, tetraethylammonium acetate tetrahydrate, and tetramethylammonium iodide were among the QAS studied. Methane (CH4) and carbon dioxide (CO2), frequently encountered in flow assurance pipelines, are included in the considered hydrate system. The experimental temperature range is 274-285 K, with 3.40-8.30 and 2.0-4.0 as the corresponding pipeline pressures for CH4 and CO2. For different mass concentrations (1, 5, and 10 wt.), the thermodynamic influence, i.e., average suppression temperature (�T), of the studied system was reported, and its relationship with the hydrogen bonding energy (EHB) interaction and freezing point temperature (Tf) of QAS was investigated. The structural impact of QAS (in the form of alkyl chain variation) and anions on thermodynamic hydrate inhibition (THI) behavior via hydrogen bonding energy interactions and freezing point is also covered in the research. According to the findings, the increase in the alkyl chain length of QAS reduced the decrease in EHB bonding ability. On the other hand, the presence of an anion had a significant impact on QAS. The EHB and QAS freezing Tf are concentration-dependent phenomena; higher QAS concentration in the system resulted in lower Tf temperatures and higher EHB energies, which influenced hydrate mitigation positively. The work is novel as it establishes the relationship between EHB and average suppression temperature and also between depression in freezing point with average suppression temperature. Since QAS are considered among potential THI inhibitors, further development is required for a generalized correlation based on the EHB interaction and Tf © 2023 American Chemical Society.