Experimental and DFT Approach on the Determination of Natural Gas Hydrate Equilibrium with the Use of Excess N2 and Choline Chloride Ionic Liquid as an Inhibitor
Abstract:This work presents the characterization of hydrate-forming conditions of a Qatari natural gas-type mixture, QNG-S1, obtained using two different experimental methods, namely, a benchtop reactor and a gas hydrate autoclave. The obtained experimental results were found to be in agreement with each other. Another mixture in which the QNG-S1 sample was diluted with nitrogen (N 2 ) in a 1:1 ratio was also characterized for hydrate dissociation conditions using a rocking cell apparatus only. The thermodynamic hydrat… Show more
“…Table 3 , shows the CH 4 HLVE data points obtained using the rocking cell assembly for three experimental trials. The experimental results were found to be in good agreement with the literature data and the standard error in the repeated experiments was about 0.05 K. More experimental procedures and equipment details have been reported in our previous works 13 , 35 , 51 – 55 . Figure 1 ( A ) Rocking Cell (RC-5) assembly used for the experiment, ( B ) stainless steel balls for agitation, and ( C ) stainless steel cell with screw cap.…”
Qatar has the third-largest natural gas reserves in the world and is the second largest Liquefied natural gas (LNG) exporter in the world. These reserves are mainly located in its offshore North Field where the gas is extracted, transported to the onshore units, and is converted to LNG for international export. The formation of natural gas hydrates in the offshore subsea lines can cause unwanted blockages and hinder the smooth supply of gas supply from offshore to onshore units. In the present work, the formation and dissociation of methane gas hydrates have been studied in the ultra pure water system (UPW), artificial seawater (ASW), and Qatar seawater (QSW) at different conditions (4–10 MPa) using standard rocking cell rig. The naturally occurring seawater was collected from Ras Laffan seacoast located in Doha, Qatar. The seawater sample was examined for elemental analysis (SO4, Cl, Na, Ca, Mg, K, and Fe) using inductively coupled plasma atomic emission spectroscopy (ICP-AES) technique and its other properties like density, electrical conductivity, and pH were also measured. The experimental results show that the CH4 pure water HLVE curve is suppressed by about 3 K in Qatar seawater and 2 K in artificial seawater. The hydrate inhibition strength of the Ionic liquids (ILs) salts 3-Ethyl-1-methyl-1H-imidazol-3-ium methane-sulfonate [C7H14N2O3S] and 3-Ethyl-1-methyl-1H-imidazol-3-ium dicyanoazanide [C8H11N5] was evaluated in both the ultra pure water and Qatar seawater systems. Their performance was compared with methanol and other ILs salts reported in the literature. The selected ILs exhibited poor hydrate inhibition effect in the ultra pure water systems, but they show a noticeable thermodynamic and kinetic hydrate inhibition effect in the Qatar seawater system. The computational 3D molecular models of ILs and methanol were generated to cognize the plausible hydrate inhibition mechanism in the presence of these inhibitors.
“…Table 3 , shows the CH 4 HLVE data points obtained using the rocking cell assembly for three experimental trials. The experimental results were found to be in good agreement with the literature data and the standard error in the repeated experiments was about 0.05 K. More experimental procedures and equipment details have been reported in our previous works 13 , 35 , 51 – 55 . Figure 1 ( A ) Rocking Cell (RC-5) assembly used for the experiment, ( B ) stainless steel balls for agitation, and ( C ) stainless steel cell with screw cap.…”
Qatar has the third-largest natural gas reserves in the world and is the second largest Liquefied natural gas (LNG) exporter in the world. These reserves are mainly located in its offshore North Field where the gas is extracted, transported to the onshore units, and is converted to LNG for international export. The formation of natural gas hydrates in the offshore subsea lines can cause unwanted blockages and hinder the smooth supply of gas supply from offshore to onshore units. In the present work, the formation and dissociation of methane gas hydrates have been studied in the ultra pure water system (UPW), artificial seawater (ASW), and Qatar seawater (QSW) at different conditions (4–10 MPa) using standard rocking cell rig. The naturally occurring seawater was collected from Ras Laffan seacoast located in Doha, Qatar. The seawater sample was examined for elemental analysis (SO4, Cl, Na, Ca, Mg, K, and Fe) using inductively coupled plasma atomic emission spectroscopy (ICP-AES) technique and its other properties like density, electrical conductivity, and pH were also measured. The experimental results show that the CH4 pure water HLVE curve is suppressed by about 3 K in Qatar seawater and 2 K in artificial seawater. The hydrate inhibition strength of the Ionic liquids (ILs) salts 3-Ethyl-1-methyl-1H-imidazol-3-ium methane-sulfonate [C7H14N2O3S] and 3-Ethyl-1-methyl-1H-imidazol-3-ium dicyanoazanide [C8H11N5] was evaluated in both the ultra pure water and Qatar seawater systems. Their performance was compared with methanol and other ILs salts reported in the literature. The selected ILs exhibited poor hydrate inhibition effect in the ultra pure water systems, but they show a noticeable thermodynamic and kinetic hydrate inhibition effect in the Qatar seawater system. The computational 3D molecular models of ILs and methanol were generated to cognize the plausible hydrate inhibition mechanism in the presence of these inhibitors.
“…While there is an overlap between data used in this study and several others published in the field, other equilibrium data sources published in recent years or overlooked in the past have been included. All data sources have been referenced. ,,,,− …”
Section: Methodsmentioning
confidence: 99%
“…All equilibrium data used in this investigation have been obtained from the following sources. All sources of equilibrium data used in the development of models in this research have been referenced. ,,,,− It must be emphasized that not all data from each source is included in the dataset, for instance, several measurements from the popular Deaton and Frost study have been excluded due to a lack of separation of iso butane and n -butane.…”
Due to offshore reservoirs being developed in ever deeper
and colder
waters, gas hydrates are increasingly becoming a significant factor
when considering the profitability of a reservoir due to flow disruptions,
equipment, and safety hazards arising from the hydrate plug formation.
Due to low-dosage hydrate inhibitors such as kinetic inhibitors competing
with traditional thermodynamic inhibitors such as methanol, accurate
information regarding the hydrate equilibrium conditions is required
to determine the optimal hydrate control strategy. Existing thermodynamic
models can prove inflexible regarding parameter adjustment and the
incorporation of new data. Developing a multivariate regression model
capable of generalizing hydrate equilibria over a wide range of conditions,
with results competing with thermodynamic models is worthwhile. A
multilayer perceptron neural network of three hidden layers has undergone
supervised training means of a backpropagation to accurately predict
uninhibited hydrate equilibrium pressure for a range of gas mixtures
with nine input features, excluding hydrogen sulfide and electrolytes,
from a dataset of 1209 equilibrium points, 670 of which are multicomponent
gases, sampled in a rigorous data sampling campaign from existing
experimental studies. Statistical significance of results has been
emphasized, with models validated using 10-fold cross-validation and
holdout validation, facilitating hyperparameter optimization without
overfitting, while stratified holdout ensures testing a wide range
of conditions. The developed model has proven to outperform two popular thermodynamic
models. Various scoring metrics are used, with an average cross-validated R2 of 0.987 ± (0.003). An R2 of 0.993 and mean absolute percentage error of 5.56%
are yielded for holdout validation. Auxiliary models are included
to determine the multicomponent prediction capability and dependency
on individual data sources. Multicomponent data prediction has proven
successful; results prove that the model accurately generalizes hydrate
equilibria and is well suited to predicting unseen data. Positive
results are largely insensitive to exact model parameters, thus indicating
a robust, replicable methodology.
“…The types of IL cations and anions tested for their thermodynamic hydrate inhibition potentials are shown in Figure . A total of about six cationic groups, namely, n -alkyl- n -imidazolium, − n -alkyl-n-ammonium, − choline, n -alkyl- n -pyrrolidinium, n -alkyl- n -piperidinium, and n -alkyl- n -morpholinium have been used for hydrate mitigation testing systems. The n -alkyl- n -imidazolium group is the commonly tested IL family in the literature for hydrate inhibition-related studies.…”
Section: Gas Hydrate Mitigation Using Ionic Liquidsmentioning
confidence: 99%
“…The 41 articles studied about 247 IL systems at varying concentrations (up to 50 wt %) in different gas systems and/or mixed/synergistic studies of ILs, commercial inhibitors (MeOH, EtOH, etc. ), and amino acids (glycine). ,, However, 28 out of the 41 articles were published post the last review on ILs as gas hydrate inhibitors by Tariq et al The 28 articles consist of 163 IL systems with the methane hydrate phase boundary being the most studied. ,,,,,− Followed by CO 2 ,, and mixed CH 4 + CO 2 systems, , other authors have also studied the effect of ILs on natural gas hydrate compositions. , Generally, two main types of methods and apparatuses are used to determine the hydrate phase boundary conditions of ILs. The widely used method is the isochoric pressure search technique ,,,,,− or the T-cycle method; ,,, this method is mostly used in high-pressure autoclave cells, ,,,, rocking cells, ,, and hydreval .…”
Section: Gas Hydrate Mitigation Using Ionic Liquidsmentioning
Ionis liquids (ILs) are promising
novel thermodynamic gas hydrate
inhibitors (THIs) that have gained an ongoing experimental and modeling
research prospect over a decade. In view of this, the path to developing
desirable ionic liquids THIs depends on understanding the state-of-the-art
methods of ILs hydrate inhibition impacts and factors that influence
their performance. This review provides a holistic summary of the
use of ILs as THIs. Almost all the available thermodynamic hydrate
inhibition data of different gas systems in the presence of ILs at
varying concentrations were critically reviewed and analyzed. Also,
all ILs hydrate-related phase behavior modeling studies and their
prediction accuracies are discussed in this work. The hydrate phase
boundary inhibition effects of each IL are provided alongside factors
that affect their inhibition performance. The study showed that IL
cations, anions, and chain length characteristics control their hydrate
inhibition impacts. By far, a narrow hydrate suppression temperature
window below 3 K at 10 wt % IL concentration has been achieved with
accurate predictions using various models. This narrow THI performance
window could be enhanced by exploring novel IL families with low molecular
weights, well-optimized cation–anion interactions, and active
hydrogen bonding interactive functionalities. The findings presented
in this work are relevant for future IL-related breakthrough research
in hydrate inhibition technologies.
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