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 (ΔT), of the studied system was reported, and its relationship with the hydrogen bonding energy (E_HB) interaction and freezing point temperature (T_f) 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 E_HB bonding ability. On the other hand, the presence of an anion had a significant impact on QAS. The E_HB and QAS freezing T_f are concentration-dependent phenomena; higher QAS concentration in the system resulted in lower T_f temperatures and higher E_HB energies, which influenced hydrate mitigation positively. The work is novel as it establishes the relationship between E_HB and average suppression temperature and also between depression in freezing point with average suppression temperature.