Phase Equilibrium of Methane Hydrate in the Presence of Aqueous Solutions of Quaternary Ammonium Salts

Abstract

Families of various quaternary ammonium salts (QAS) have been of great interest to gas hydrate based investigations. In this work, an attempt has been made to understand the effect of QAS of the bromide family with increasing alkyl chain length, such as tetra-methyl, tetra-ethyl, and tetra-butyl ammonium bromide (TMAB, TEAB, and TBAB) at two different concentrations (0.05 and 0.1 mass fraction) in an aqueous solution on the hydrate–liquid–vapor (H-L-V) phase equilibrium of the methane hydrate system. Various experiments were performed to capture phase equilibrium data in the equilibrium pressure range of 7.6–4.2 MPa and temperature range of 282.4–276.8 K. It has been observed that the addition of TMAB and TEAB shifts the phase equilibrium curve of methane hydrate to higher pressure and lower temperature conditions. TMAB and TEAB have shown thermodynamic inhibition unlike TBAB which has shown a promotion effect. The Clausius–Clapeyron equation is used to calculate the enthalpy of dissociation of methane hydrate in various QAS aqueous solutions to examine the effect of QAS on methane hydrate structural information. The electrical conductivity measurements were also made to correlate the hydrate inhibition effectiveness of QAS on methane hydrate system. In addition, a phase equilibrium model has been extended to predict the phase behavior of methane hydrate + (TMAB, TEAB, or TBAB) aqueous solutions for a total 91 experimental phase equilibrium data points obtained from this work and the literature. The absolute average relative deviation in equilibrium pressure (AARD/P (%)) observed from the proposed model with the experimental equilibrium pressure data produced in this work and from several sources in the literature have been observed to lie within ±3.2%, indicating the robustness of the model.

Review on Application of Quaternary Ammonium Salts for Gas Hydrate Inhibition

“…It is observed that the addition of TMAB and TEAB shifts the phase equilibrium curve of CH 4 gas hydrate to lower temperature and higher pressure regions, whereas the addition of TBAB demonstrates characteristic of hydrate formation effect. Electrical conductivity experiments results indicate that the shorter alkyl chain length of the ammonium ILs yield to higher electrical conductivity, and the sequence of electrical conductivity is TMAB > TEAB > TBAB [56]. The electrical conductivity is also found to be directly proportional to the concentration.…”

“…In evaluating the performance of QAS for gas hydrate inhibition, several methods has been applied, such as the T-cycle method and using highpressure micro differential scanning calorimetry equipment. The Isochoric constant cooling method or T-cycle method is one of the most used method, carried out by [37,[56][57][58][59][60][61][62] with different type of gases to study on the kinetic inhibition of the selected compounds. In this method, 100 mL of liquid sample is poured into the cell which is then vacuumed thoroughly to remove excess air that may still exist in the cell [20,63].…”

“…The electrical conductivity is also found to be directly proportional to the concentration. In general, ILs with higher electrical conductivity show higher thermodynamic hydrate inhibition effects [43,56].…”

“…Recently, Ref. [56] have studied on the effects of tetrabutyl ammonium bromide (TBAB), tetraethyl ammonium bromide (TEAB), and tetramethyl ammonium bromide (TMAB), [56] on inhibiting CH 4 gas hydrate formation by isochoric pressure search method. The experiment was conducted at temperature range of 282.4-276.8 K and pressure range of 4.2-7.6 MPa by varying concentrations, i.e., 0.05 and 0.10 mass fraction.…”

Looking Beyond Energy Efficiency: An Applied Review of Water Desalination Technologies and an Introduction to Capillary-Driven Desalination

“…This minimum energy depends only on the concentration of solutes regardless of any specific technology, mechanism, or number of stages [98,99]. Simple thermodynamic calculations reveal that the MTES is ideally 0.79 kWh/m 3 for full and 1.09 kWh/m 3 for 50% recovery of freshwater from typical seawater [100][101][102][103][104][105]. Using the second law efficiency, this value jumps to 1.9 kWh/m 3 [51].…”