Thermodynamic modeling of aqueous ionic liquid solutions and prediction of methane hydrate dissociation conditions in the presence of ionic liquid (2023)

Gas hydrates are solid solutions which cause flow assurance problems and risks to line integrity in the petroleum industry. Thermodynamic inhibitors are usually injected during production to avoid hydrate formation. In recent years, many authors have reported Ionic Liquids (ILs) as inhibitors. However, there are not many studies on thermodynamic modeling in the literature involving ILs as hydrate inhibitors, especially when it comes to the applicability of the Cubic Plus Association (CPA) and Soave-Redlich Kwong (SRK) Equation of State. In light of this, the aim of this work was to evaluate methane hydrate equilibrium in the presence of ILs as inhibitors using van der Waals-Platteeuw solid solution theory along with these Equations of State to describe liquid and gas phases. The commercial software Multiflash and its interface with excel were employed to calculate hydrate equilibrium pressures. Data from the literature on 12 imidazolium-based ILs were taken into account by varying carbon chain length and anion basicity. Both Equations of State resulted in accurate equilibrium predictions with similar deviations between calculated and experimental data (overall ARD 4.64% for CPA, and 4.49% for SRK) considering p and T conditions in the range of 2.5–35Mpa and 272–295K respectively. 2B association was considered for ILs, while 4C association was used for water. In general, longer cation carbon chain lengths and higher anion basicity resulted in lower accuracy.

Mixing ionic liquid (IL) and water can influence the thermodynamic characteristics such as water activity. Hence, some ILs can be utilized as inhibitors for hydrate systems. This work was intended to determine the three-phase equilibria of methane hydrate in aqueous solutions of 32 ILs using the least squares support vector machine (LSSVM), adaptive neuro-fuzzy inference system (ANFIS), and classification and regression tree (CART). The modeling studies on clathrate hydrates in aqueous solutions of ILs are also reviewed. The used databank contains anion groups such as sulphate, dicyanamide, tetrafluoroborate, and halides. The dissociation temperature of methane hydrate in aqueous solutions of ILs is modelled considering the ILs' critical pressure and critical temperature, the pressure of hydrate system, and the concentration of IL in aqueous phase as the independent parameters. All the developed models are found to well represent/predict the methane hydrate dissociation temperatures in aqueous solutions of ILs. The calculated values of average absolute relative deviation for the presented LSSVM, ANFIS, and CART models are equal to 0.08, 0.31, and 0.10, respectively. Hence, the results reveal that the introduced CART and ANFIS models cannot compete with the developed LSSVM approach in representing the dissociation temperatures of the methane + hydrate + IL + water systems studied in this research work. Using the proposed LSSVM model, all the investigated database equilibrium temperatures are within the absolute deviation percent of 0.0-1.0% except the data that show an absolute deviation percent of 1.35%. The findings of this study can help researchers and engineers to better understand the effects of ILs on methane hydrate stability conditions toward effective hydrate management.

One of the major problems in flow assurance, especially in the case of deep subsea pipelines, is the accumulation of gas hydrates that leads to significant issues such as pipe plugging and cracking. Utilization of thermodynamic inhibitors is an effective method to prevent hydrate formation in pipelines. Recently, ionic liquids (ILs) have been recognized as new hydrate inhibitors due to their strong electrostatic charges, which form hydrogen bonds with water molecules. In this work, the capability of the PC-SAFT/UNIQUAC model combined with the van der Waals-Platteeuw theory is assessed for estimation of the methane hydrate dissociation temperatures in the presence of various IL solutions. Five pure-component parameters of PC-SAFT EOS for ILs are fitted by using experimental data of liquid density. Furthermore, vapour-liquid and hydrate equilibria experimental data are employed to adjust the binary interaction parameters of the PC-SAFT EOS ($k_{\mathit{ij}}$) and the UNIQUAC model ($u_{\mathit{ij}}$), respectively. Methane hydrate dissociation temperatures are successfully forecasted by using the proposed model for ten (10) IL systems with different concentrations in which the overall average absolute deviation for temperature (AADT %) of the model is lower than 1.5%. The results clearly demonstrate that the developed thermodynamic model is capable of precisely obtaining the methane hydrate dissociation temperatures in the presence of IL solutions, though, for [EMIM][Cl] solutions with a concentration of more than 30wt%, the model overestimates the methane hydrate conditions. The proposed thermodynamic modeling strategy can assist to screen suitable IL solutions with an optimal composition for hydrate formation inhibition in terms of technical, economic, and environmental prospectives.

In this work, 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM-BF₄) and tetra ethyl-ammonium chloride (TEACl) were investigated to study their effects on thermodynamic stability conditions of methane clathrate hydrate. Different BMIM-BF4 and TEACl aqueous solutions (4.77 wt% (0.57 mol%) TEACl + 4.85 wt% (0.43 mol%) BMIM-BF₄, 9.15 wt% (0.20 mol%) TEACl + 9.38 wt% (0.90 mol%) BMIM-BF₄ and 11.82 wt% (1.63 mol%) TEACl + 11.82 wt% (1.20 mol%) BMIM-BF₄) were used as thermodynamic inhibitors which have not been reported in literature. The experiments were conducted at constant volume from 274.6 K to 283.4 K and 3.18 MPa to 7.93 MPa. Moreover, methane hydrate phase equilibria in the aforementioned ioinic liquids (ILs) aqueous solutions were modeled. For this purpose, the chemical potential of water in hydrate phase is calculated using the van der Waals–Platteeuw (vdWP) theory. The Peng-Robinson (PR) equation of state (EoS) is used for calculation of fugacity in the gas phase. Water activity in the aqueous phase is determined by the NRTL activity coefficient model. Successful comparison of the experimental data with the modeling results confirms the model accuracy. It can also be observed that mixtures of the two aforementioned ionic liquids can inhibit methane hydrate formation more than each of single ILs. Furthermore, the studied ILs inhibit methane hydrate formation more at higher pressures.

Recently ionic liquids (ILs) are introduced as novel dual function gas hydrate inhibitors. However, no desired gas hydrate inhibition has been reported due to poor IL selection and/or tuning method. Trial & error as well as selection based on existing literature are the methods currently employed for selecting and/or tuning ILs. These methods are probabilistic, time consuming, expensive and may not result in selecting high performance ILs for gas hydrate mitigation. In this work, COSMO-RS is considered as a prescreening tool of ILs for gas hydrate mitigation by predicting the hydrogen bonding energies (E_HB) of studied IL inhibitors and comparing the predicted E_HB to the depression temperature (Ŧ) and induction time. Results show that, predicted E_HB and chain length of ILs strongly relate and significantly affect the gas hydrate inhibition depression temperature but correlate moderately (R=0.70) with average induction time in literature. It is deduced from the results that, Ŧ increases with increasing IL E_HB and/or decreases with increasing chain length. However, the cation–anion pairing of ILs also affects IL gas hydrate inhibition performance. Furthermore, a visual and better understanding of IL/water behavior for gas hydrate inhibition in terms of hydrogen bond donor and acceptor interaction analysis is also presented by determining the sigma profile and sigma potential of studied IL cations and anions used for gas hydrate mitigation for easy IL selection.

Three ionic liquids (ILs), 1-ethyl-3-methylimidazolium bromine ([EMIM]Br), 1-butyl-3-methylimidazolium bromine ([BMIM]Br), and 1-hexyl-3-methylimidazolium bromine ([HMIM]Br), were used as the solvent for separation of {tert-butyl alcohol (TBA)+water} azeotrope. Vapor–liquid equilibrium (VLE) data for {TBA+water+IL} ternary systems were measured at 101.3kPa. The results indicate that all the three ILs produce an obvious effect on the VLE behavior of {TBA+water} system and eliminate the azeotropy in the whole concentration range. [EMIM]Br is the best solvent for the separation of {TBA+water} system by extractive distillation among the three ILs. The experimental VLE data for the ternary systems are correlated with the NRTL model equation with good correlations. Explanations are given with activity coefficients of water and TBA, and the experimental VLE-temperature data for {TBA or water+IL} binary systems.

Chemical Engineering Science, Volume 102, 2013, pp. 283-288

We highlight the need for a comprehensive, multi-disciplinary approach for the development of cost-effective water remediation methods. Combining “chimie douce” and green chemical principles seems essential for making these technologies economically viable and socially relevant (especially in the developing world). A comprehensive approach to water remediation will take into account issues such as nanotoxicity, chemical yield, cost, and ease of deployment in reactors. By considering technological challenges that lie ahead, we will attempt to identify directions that are likely to make photocatalytic water remediation a more global technology than it currently is.

Chemical Engineering Science, Volume 102, 2013, pp. 432-441

Successful computational fluid dynamics simulations of poly-disperse flows must include modeling of particulate processes, i.e., nucleation, growth, agglomeration, and breakage. A computationally attractive way of computing the temporal and spatial changes in the particulate phase property distribution function is utilizing the population balance equation (PBE). Finite size domain complete set of trial functions method of moments (FCMOM) is a novel solution method among the “method of moment” family for population balance equation solution. This work focuses on the numerical analysis of FCMOM and its implementation in ANSYS Fluent CFD code to probe its performance in simulations of complex systems using the multiphase CFD approach. Three cases including linear particle growth, homogenous aggregation process, and inhomogeneous aggregation (coalescence) were considered. The results were validated against analytical solutions where available or verified against those obtained by the quadrature method of moments (QMOM) approach.

Chemical Engineering Science, Volume 102, 2013, pp. 163-175

Simultaneous tribo-charging of the wall and particles during pneumatic transport of powders in dilute phase is modelled. The concepts of “simple-condenser model” and “effective work function” are used to take into account the local charge transfer between the two materials during particle-wall collisions. Exact analytical solutions are provided for the model. It is shown that, the tribo-charging process is mainly governed by the ratio between the charge transfer constants of the wall and particles. The results show that for high tribo-charging conditions of wall with respect to particles, the accumulated charge of the particles tends to an asymptotic limit imposed by the charge saturation of the wall. For low charging walls, the particle charge is no more limited by the charge of the wall and increases continuously. Quantitative analyses show that the predominant regime (i.e. particles or wall limited) could be fairly predicted using a dimensionless group ($3\beta D/2d_p$) based on the volume fraction of the powder, β, the pipe diameter, D, and the particles mean diameter, d_p. Furthermore, a dimensionless criterion is established allowing the prediction of tribo-charging regimes and the trend of space evolution of particles charges. A comparison between the experimental and calculated data was carried out and permitted the validation of the model.

Chemical Engineering Science, Volume 102, 2013, pp. 121-128

A model of two-phase non-Newtonian horizontal annular flows, which predicts film thickness and pressure gradient from flowrates only, is presented. In the model, the gas and non-Newtonian liquid flows are calculated separately based on the independent governing equations. The shear stress balance at the gas–liquid interface is calculated in order to link two phases together. The non-Newtonian fluid is assumed as a power-law shear-thinning liquid. The logarithmic velocity distribution is chosen to calculate the turbulent velocity profile in the gas core. The influences of entrainment and aeration are included in the model. The pressure drop, film thickness, void fraction, the frictional multiplier, and Lockhart–Martinelli parameter are predicted. The analytical model is compared with the published experimental investigations, and the results show that the model can predict the film thickness and pressure gradient simultaneously based on the flowrates of liquid and gas. The frictional multiplier and Lockhart–Martinelli parameter are calculated at the same time, and the predicted values are comparable with the experimental data. The difference between the analytical model and the experiments is lower than 10%.

Chemical Engineering Science, Volume 102, 2013, pp. 300-308

Alkane–Tween85–water-systems have been used as model emulsion systems to demonstrate the feasibility of emulsification in stirred media mills. The influence of fundamental process parameters, i.e. emulsion formulation (oil mass fraction and oil-to-emulsifier mass ratio), stress conditions (grinding bead size and stirrer tip speed), process time and especially temperature on the emulsion droplet size and size distribution has been studied for this approach. By lowering the process temperature below the solidification temperature of the oil phase, coalescence and ripening can be significantly reduced. Smallest product droplets with x_1,2<10nm thus are obtained even for nominal oil mass fractions up to 20wt% in the hexadecane–Tween85–water system. The feasibility of the process proposed to produce nanoscale emulsions using oil phases loaded with compounds such as pigments and other fillers is demonstrated.

Chemical Engineering Science, Volume 102, 2013, pp. 461-473