Thermodynamic Inhibition Effect Research Articles

Experimental measurement and model prediction on methane hydrate equilibrium conditions in the presence of organic carboxylic sodium salts

Gas hydrate inhibitors are employed to mitigate gas hydrate formation in pipelines. The effects of thermodynamics inhibition were evaluated by measuring the vapor - liquid aqueous solution - solid hydrate (VLH) equilibrium conditions on methane (CH4) hydrate in the presence of three organic carboxylic sodium salts (sodium formate, sodium acetate, sodium propionate) in this study. The experiments were carried out in the temperature range of 273.65 K to 281.65 K. Compared with deionized water, in the electrolyte solutions of sodium formate, sodium acetate and sodium propionate with mole fraction of 0.010 and 0.020, the VLH equilibrium pressure change (ΔP) increased by 12.93, 27.68 %; 18.78, 38.15 %; 23.51, 49.41 %, respectively. Both of the three organic carboxylic sodium salts have obvious thermodynamic inhibition effect on CH4 hydrate. The strength of hydrate inhibition is related to the carbon chain length of organic carboxylate. The dissociation enthalpy (ΔHdiss) of CH4 hydrate in three organic carboxylic sodium salts solutions remains quite uniform with deionized water, which indicates that three organic carboxylic sodium salts have not been involved in the formation of hydrate nucleus. The Chen-Guo hydrate model and N-NRTL-NRF activity model were employed to predict the VLH equilibrium conditions in electrolyte solutions. In the three organic carboxylic sodium salts solutions, the average absolute relative deviations (AARD) of the VLH equilibrium condition data between the predicted and the experimental were 0.81, 2.17, and 3.02 %, respectively. In the sodium chloride (NaCl) and potassium chloride (KCl) solutions, the AARD between the predicted and literature were 1.44, 1.69 %, respectively. The model has good universality and accuracy. Both sodium acetate and sodium propionate are food grade preservatives. Consequently, these are beneficial for the development of environmental-friendly hydrate inhibitors.

Thermodynamic analysis for hydrogen production from the reaction of subcritical and supercritical gasification of the C. Vulgaris microalgae

New technologies are essential for the efficient generation of biofuels. This work focuses on finding the best thermodynamic conditions, inhibition effects, and system conformations for the conversion of the microalgae Chlorella Vulgaris into hydrogen (H2). The conversion reaction was conducted in subcritical and supercritical water and modeling was developed as optimization problems in GAMS software. Chemical and phase equilibrium calculations were performed using Gibbs global energy minimization and entropy maximization methodologies. Thermal effects, microalgae feed composition, CH4 inhibition, and recycling of part of the produced H2 were evaluated. In supercritical gasification, a system with a temperature around 900 K, a microalgae composition between 10 and 15% (wt./wt.), and a high H/C ratio offers optimized conditions for H2 production. The inhibitory effect of CH4 is positive, increasing the mass composition of H2 by about 49% under the aforementioned conditions of temperature and composition. At lower temperatures, the inhibitory effect is more pronounced. The recycling of H2 for feed favored an increase in its mass fraction of 12.5%, in addition to increasing the endothermicity of the system without greater energy expenditure. Subcritical gasification reactions remain a challenge. A more in-depth study of the reactional paths is necessary to make its implementation feasible.

Study on the hydrate inhibition effect of nano-silica in drilling fluids

Preventing hydrate crystallization in drilling fluid is the key to ensure the safety of deep water drilling. In this work, hydrate inhibition effect of nano-silica in deep water drilling fluids was measured and compared with the typical hydrate inhibitors containing KCl-PVP and EG-PVP. The three phase equilibrium and the formation kinetics of CH4 hydrate in the drilling fluids were measured. The micro-morphological features of the formed hydrates were observed by SEM. Results showed that EG-PVP drilling fluid was found to have the best thermodynamic inhibition effect on CH4 hydrate where the deviation of the equilibrium pressure in EG-PVP drilling fluid and pure water was initially 2 MPa as the temperature was below 5 °C and increased up to about 5 MPa when the temperature was 10 °C. Nano-silica had almost no thermodynamic inhibition performance on CH4 hydrate. Kinetic measurements revealed that EG-PVP and KCl-PVP drilling fluids prolonged the hydrate nucleation to more than 48 h, but failed to remain the hydrate inhibition effect after aging tests. Nano-silica was unable to prolong the nucleation time, but was effective in reducing the initial hydrate growth rate and less affected by aging tests. SEM images revealed that nano-silica prevented phase separation in hydrate growth and induced the CH4 hydrate to form a spongy-like structure which was fragile in agitated drilling fluid. Therefore, nano-silica could be viewed as a potential synergist of hydrate inhibitors.

Thermodynamic evaluation of inhibitors for methane-hydrate formation

The present paper presents an experimental study on the thermodynamic effect of three amines including (3-Aminopropyl)triethoxysilane (APTES), (3-Aminopropyl)triethoxysilane (APTMS), and Triethylenetetramine (TETA) on methane hydrates. Hydrate-Liquid-Vapour Equilibrium (HLwVE) data for methane hydrate were evaluated in the presence of 7 wt% and 20 wt% APTES, APTMS, and TETA, and with pressure ranging from 2.0 to 9.0 MPa. The thermodynamic effect of these amines on methane-hydrate formation has been investigated via measuring the methane-hydrate dissociation temperature, in applying an isochoric pressure-search method. The results reveal that APTES, APTMS, and TETA effectively shift the hydrate equilibrium curve to higher-pressure and lower-temperature regions for the methane + amine + water system. All of these three show thermodynamic-inhibition effects similar to the lower-concentration case (7 wt%), but with increasing concentration to 20 wt% for the thermodynamic-inhibition effect in the order APTES > APTMS > TETA. The average hydrate-suppression temperature (ΔT), as a ‘signature’ of thermodynamic-inhibition effect on methane hydrates measured for 7 wt% APTES, APTMS and TETA was 1.5, 1.5, and 1.3 K, respectively. ΔT increased with increasing amine concentration; these values were 5, 4.3, and 3.2 for 20 wt% APTES, APTMS, and TETA, respectively. Hydrate-onset time was further delayed due to the synergistic inhibition effect of inhibitors. The results show that these amines have a kinetic effect on gas-hydrate formation, such as for methane-hydrate formation in presence of APTMS: here, the hydrate formed after several cycles with the help of the memory effect. Moreover, the inhibition impact of these amines was compared with conventional hydrate thermodynamics, and found to be in the range of some and similar to ethylene glycol at 5 wt%. Furthermore, the addition of 5 wt% APTMS to sea salt not only enhances the thermodynamic inhibition effect, but also inhibits kinetically the formation of methane hydrate. For modelling of methane-hydrate dissociation conditions, the solid-solution theory of van der Waals and Platteeuw was applied for the hydrate phase along with the Peng–Robinson equation of state for the gas phase. Taken together, this study elucidates a novel class of thermodynamic hydrate inhibitors, which can control methane-hydrate formation efficiently.

Mechanisms of synergistic inhibition of hydrophilic amino acids with kinetic inhibitors on hydrate formation

The effects of hydrophilic amino acids on hydrate formation are a global hot spot of research, and yet the mechanisms behind such effects need to be further investigated. The mechanism of synergism between hydrophilic amino acids and hydrate kinetic inhibitors has not been clarified. Given the aforementioned, this research analyzes the effects of L-arginine, glycine, and their combination with PVP K90 and VC-713 on the formation of tetrahydrofuran (THF) hydrates, and manages to systematically reveal the relevant mechanisms by integrating various experimental methods. It is shown that L-arginine and glycine can disturb water molecules and reduce their activity, and thus they present both kinetic and thermodynamic inhibition effects. The combinations of 0.5 wt%–5.0 wt% L-arginine and glycine with 0.5 wt%–1.0 wt% kinetic inhibitors are found with synergistic inhibition effects on hydrate formation, and the combination of 4.0 wt% glycine with 1.0 wt% VC-713 is associated with the best synergistic inhibition performance.

Experimental and modelling study of ammonium based ionic liquids in the absence and presence of methanol for CO2 hydrates

The thermodynamic hydrate inhibition behavior of two ammonium based ionic liquids (AIL), namely tetra methyl ammonium tetrafluoroborate (TMABF4) and tetraethyl ammonium tetrafluoroborate (TEABF4) and their mixtures with methanol for CO2 hydrates is significant to study. The Hydrate Liquid Vapor Equilibrium (HLVE) values for CO2 hydrates are determined using the T-cycle method in the pressure range of 2.0 to 3.4 MPa at 5 and 10 wt% solution concentrations. For the studied systems, the inhibition effect including average suppression temperature (Ŧ) and dissociation enthalpies (Hdiss), are determined. TMABF4 in pure as well as in mixture with methanol showed higher thermodynamic hydrate inhibition effect in comparison with TEABF4. The average suppression temperature values for TMABF4 and TMABF4 + methanol are 0.90 K and 3.81 K respectively at 10 wt% concentration. In addition, Dickens and Quinby Hunt model is utilized for the prediction of CO2 hydrate liquid vapor equilibrium. The modelling results match well with the experimental data. The employment of these chemicals in the thermodynamic inhibition of CO2 hydrates systems may lead to their usage in the field of flow assurance as they exhibited hydrate inhibition effect.

Experiment and model investigation of D-sorbitol as a thermodynamic hydrate inhibitor for methane and carbon dioxide hydrates

Pipe plugging and cracking caused by gas hydrate blockage is the major problem in oil/gas flow assurance, especially in deep subsea pipelines. Thermodynamic inhibitors(THIs) are one of the effective methods to inhibit the formation of gas hydrate. This work evaluates the thermodynamic inhibition effect of D-sorbitol, a polyhydroxy compound, for both methane (CH4) and carbon dioxide (CO2) hydrates. The gas-liquid-hydrate equilibrium (GLHE) conditions for CH4 and CO2 were measured by the isothermal pressure search method in the presence of aqueous D-sorbitol solutions (1.00, 2.00, 3.00 mol%). The equilibrium pressure change (ΔP) and hydrate dissociation enthalpies (ΔHdiss) were used to reflect the thermodynamic effects of D-sorbitol on CH4 and CO2 hydrates. The ΔP data show that D-sorbitol has an obvious inhibition impact on CH4 and CO2 hydrates formation. Compared with deionized water system, CH4 hydrate GLHE pressure increased by 11.6, 25.0, 41.4%, while CO2 hydrate GLHE pressure increased by 10.1, 18.6, 32.7% in 1.00, 2.00, 3.00 mol% D-sorbitol solutions, respectively. The ΔHdiss data demonstrate that D-sorbitol does not participate in the formation of the hydrate crystal structure. Chen-Guo hydrate thermodynamic model and Wilson activity model were applied to predict the GLHE conditions of both CH4 and CO2 hydrates in the presence of D-sorbitol. The calculated results can well match the experimental values. The average relative deviations (ARD) between calculated and experimental data for CH4 and CO2 hydrate are less than 2.39% and 3.76%, respectively. D-sorbitol is a non-toxic and environment-friendly compound. The results in this work indicate that D-sorbitol can be applied to flow assurance strategies for hydrate blockage prevention.

Experimental and modeling studies on enhancing the thermodynamic hydrate inhibition performance of monoethylene glycol via synergistic green material

This paper presents an experimental and modeling studies on the thermodynamic inhibition effects of the mixture of monoethlyene glycol (MEG) and glycine (Gly) on the carbon dioxide hydrate phase boundary condition. The monoethlyene glycol and glycine (1:1) mixture inhibition effects were investigated at concentrations of 5, 10, and 15 wt.% and pressure ranges from 2.0–4.0 MPa. The effects of the proposed mixture on the carbon dioxide hydrate phase boundary were evaluated by measuring the dissociation temperature of carbon dioxide hydrate using a T-cycle method. The synergistic effect was evaluated based on comparison with pure MEG and Gly data. The results show that 15 wt.% of MEG and Gly mixture displays the highest inhibition effect compared to the 5 and 10 wt.% mixtures, respectively. However, the synergistic effect is higher at 10 wt.%. Dickens' model was also adopted to predict the phase equilibrium data of CO2 hydrates in the presence of the mixture. The modified model successfully predicted the data within a maximum error of ± 0.52 K.

Experimentally measured methane hydrate phase equilibria and ionic liquids inhibition performance in Qatar\u2019s seawater

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.

Phase Stability Conditions of the Methane + Tetrabutylphosphonium Bromide + Water Semiclathrate Hydrate System in the Presence and Absence of NaCl and/or MgCl2: Experimental Measurements and Thermodynamic Modeling

Gas hydrate, or clathrate hydrate, technology is considered to be one of the promising solutions for natural gas storage and transportation. Tetrabutylphosphonium bromide (TBPB) is capable of sorting out stability issues of hydrate formation effectively. On the other hand, using water from natural resources such as sea, river, or well instead of pure water is essential for hydrate formation in the industrial scale. The current study was organized to investigate the hydrate phase behaviors of CH4 + TBPB formed in saline solutions, which are necessary for potential industrial applications. For this purpose, we first generated hydrate dissociation conditions data of the CH4 + TBPB aqueous solution system over TBPB mass fractions of 0.05 and 0.2. It should be mentioned that there is some discrepancy between hydrate dissociation condition data of the CH4 + TBPB + water system reported in literature, which necessitates generation of accurate and reliable data in this work. Afterward, the effects of the presence of NaCl, MgCl2, and NaCl + MgCl2 in aqueous solutions on the hydrate dissociation conditions of the CH4 + TBPB + water system were studied. All equilibrium points were obtained using a reliable constant-volume pressure-search method in the pressure and temperature ranges of 1–5.5 MPa and 280–292 K, respectively. The experimental results show that the aforementioned salts have dual effects on the hydrate phase stability, depending on TBPB concentration in the aqueous solution. In the case of 0.05 mass fraction of TBPB in the aqueous solution, the presence of NaCl (0.05 mass fraction), MgCl2 (0.05 mass fraction), and NaCl + MgCl2 (0.05 + 0.05 mass fractions) can boost the hydrate stability conditions of the CH4 + TBPB + water system and can act as thermodynamic promoters. However, by increasing the TBPB mass fraction in aqueous solution to 0.20 mass fraction, the aforementioned salts can shift the hydrate stability conditions to high pressures/low temperatures and can act as thermodynamic inhibitors. Furthermore, the experimental results show that the thermodynamic inhibition effects of the mineral salts are higher when the pressure of hydrate formation increases. A thermodynamic model based on the van der Waals–Platteeuw (vdW–P) solid solution theory was also developed for the aforementioned systems. The model employs the Soave–Redlich–Kwong equation of state and the Bromley equations for the gas phase and the aqueous phase, respectively. Results show that the thermodynamic model is capable of predicting the hydrate dissociation conditions with acceptable accuracy.

Organic salts as kinetic and thermodynamic inhibitors for CO2 hydrate precipitation

In this work, we opted for the use of CO2 gas for the respective experiments, due to its greater solubility in water when compared to hydrocarbons, as well as possible applications in pre-salt oil fields (such as the Libra field), where the amount of CO2 varies between 40 and 80%, obstructing the pipelines in the CO2 capture stage. In this context, the objective of this work is to obtain organic salts of different amino acids and alcohols (biodegradable and environmentally friendly compounds) and to test them in a pilot gas hydrate synthesis plant, with the goal of evaluate the inhibition potential of these compounds for CO2 hydrates. The organic compounds were synthesized with good yields and were characterized by NMR (13C and 1H) and elementary analysis. The compounds with greater hydrophilic character showed thermodynamic inhibition effects for the tested condition, while the hydrophobic compounds showed kinetic inhibition effects. The fundamental knowledge and the mechanism on the kinetic and/or thermodynamic inhibition of CO2 hydrates from organic salts obtained in this study are beneficial and extremely important, given the good results presented and the unprecedented application of the tested compounds.

Thermodynamic inhibition effects of an ionic liquid (choline chloride), a naturally derived substance (urea), and their mixture (deep eutectic solvent) on CH4 hydrates

In this study, the thermodynamic inhibition effects of choline chloride (ChCl, a hydrogen bond acceptor), urea (a hydrogen bond donor), and their mixture (deep eutectic solvent, DES) on CH4 hydrates were investigated with both experimental and computational approaches. The synthesis of DES from the mixture of ChCl and urea was confirmed by measuring its melting temperature through a high-pressure micro-differential scanning calorimeter. Sigma (σ)-profiles of ChCl, urea, and DES obtained by the COSMO-RS software indicated that these substances have great potential to be used as thermodynamic hydrate inhibitors (THIs). The three-phase (gas hydrate (H) – liquid water (Lw) – vapor (V)) equilibria of CH4 hydrates in the presence of ChCl (1.0, 3.0, and 5.0 mol%), urea (1.0, 3.0, and 5.0 mol%), and DES (3.0 mol%) demonstrated that ChCl, urea, and DES contributed to the significant shift of hydrate equilibrium temperature to inhibition regions at a specified pressure and thus can function as effective THIs. Moreover, quantum theory of atoms in molecules (QTAIM) analysis also demonstrated that the strength of hydrogen bonding between inhibitor molecules and hydrate cages (small 512 and large 51262 cages) of CH4 hydrates was in the order of ChCl > DES > urea, which was consistent with experimental results. The experimental and computational results from this study would be helpful for a better understanding of the inhibition mechanism of ChCl, urea, and DES and for their possible application to flow assurance in oil and gas pipelines.

Thermodynamic Inhibition in Chemostat Models : With an Application to Bioreduction of Uranium.

We formulate a mathematical model of bacterial populations in a chemostat setting that also accounts for thermodynamic growth inhibition as a consequence of chemical reactions. Using only elementary mathematical and chemical arguments, we carry this out for two systems: a simple toy model with a single species, a single substrate, and a single reaction product, and a more involved model that describes bioreduction of uranium[VI] into uranium[IV]. We find that in contrast to most traditional chemostat models, as a consequence of thermodynamic inhibition the equilibria concentrations of nutrient substrates might depend on their inflow concentration and not only on reaction parameters and the reactor's dilution rate. Simulation results of the uranium degradation model indicate that thermodynamic growth inhibition quantitatively alters the solution of the model. This suggests that neglecting thermodynamic inhibition effects in systems where they play a role might lead to wrong model predictions and under- or over-estimate the efficacy of the process under investigation.

Doping amino acids with classical gas hydrate inhibitors to facilitate the hydrate inhibition effect at low dosages

AbstractThe formation of gas hydrates in offshore subsea lines is a major flow assurance concern for the oil and gas industry. In this work, the thermodynamic hydrate inhibition (THI) effect of doping amino acids (AA) such as glycine (Gly), l‐alanine (Ala), and histidine (His) with classical gas hydrate inhibitors (CHI) such as methanol (Me), ethylene glycol (EG), and sodium chloride (NaCl) have been examined at diverse operating conditions. The experimental tests were carried out using rocking cell assembly [RC‐5] on pure methane gas at different pressure conditions (40–120 bars) using an equal ratio mixture (1:1) of AA and CHI at a low dosage (2 wt%). The computational three‐dimensional molecular models of AA and CHI were generated to examine electric charge distribution within these molecules and cognize the interaction mechanism between methane hydrates and AA. The experimental results indicate that Me and EG can synergize the THI effect of AA at a low dosage of 1 wt%. The AA doped with Me tend to provide better THI effect compared to AA doped with EG and NaCl. The experimental results also show that the doped AA Ala mixtures provide THI effect similar to pure CHI such as Me, EG, and NaCl at low dosage (2 wt%). © 2020 Society of Chemical Industry and John Wiley & Sons, Ltd.

Hydrate Growth on Methane Gas Bubbles in the Presence of Salt.

Methane bubble dispersions in a water column can be observed in both vertical subsea piping as well as subsea gas seepages. Hydrate growth has been shown to occur at the gas-water interface under flowing conditions, yet the majority of the current literature is limited to quiescent systems. Gas hydrate risks in subsea piping have been shown to increase in late life production wells with increased water content and with gas-in-water bubble dispersions. The dissolution of subsea methane seepages into seawater, or methane release into the atmosphere, can be affected by hydrate film growth on rising bubbles. A high-pressure water tunnel (HPWT), was used to generate a turbulent, continuous water flow system representative of a vertical jumper line to study the relationship between bulk methane hydrate growth and bubble size during a production-well restart. The HPWT comprises a flow loop of 19.1 mm inner diameter and 4.9 m length, with a vertical section containing an optical window to enable visualization of the bubble and hydrate flow dynamics via a high-speed, high-resolution video camera. Additional online monitoring includes the differential pressure drop, viscosity, temperature, flow rates, and gas consumption. Experimental conditions were maintained at 275 K and 6.2 MPa during hydrate formation and 298 K and 1.4 MPa during hydrate dissociation. Hydrate growth using freshwater and saltwater (3.5 wt % NaCl) was measured at four flow velocities (0.8, 1.2, 1.6, and 1.9 m s-1). The addition of salt is shown in this work to alter the surface properties of bubbles, which introduces changes to bubble dynamics of dispersion and coalescence. Hydrate volume fractions and growth rates in the presence of salt were on average ∼32% lower compared to that in freshwater. This was observed and validated to be due to bubble size and dynamic factors and not due to the 1.5 K thermodynamic inhibition effect of salt. Throughout hydrate growth, methane bubbles in pure freshwater maintained larger diameters (2.4-4.2 mm), whereas the presence of salt promoted fine gas bubble dispersions (0.1-0.7 mm), increasing gas-water interfacial area. While gas bubble coalescence was observed in all freshwater experiments, the addition of salt limited coalescence between gas bubbles and reduced bubble size. Consequently, earlier formation of solid hydrate shells in saltwater produced early mass-transfer barriers reducing hydrate growth rates. While primarily directed toward flow assurance, the observed relationship between hydrates, bubble size, and saltwater also applies to broader research fields in subsea gas seepages and naturally occurring hydrates.

Formulation and characterization of water-based drilling fluids for gas hydrate reservoirs with efficient inhibition properties

Natural gas hydrates are presently considered as a potential source of future energy as it is widely distributed along the continental margins and in the permafrost areas. However, the drilling operation through such hydrate-bearing formation is quite risky because of unconsolidated formation, fragile nature of formation and uncontrolled dissociation of hydrate during drilling. In this study, an attempt was made to overcome the issues by a specially designed nanoparticle-enhanced water-based drilling fluid for its potential application in hydrate reservoirs. The rheological properties of different water-based drilling fluids, formulated by bentonite, carboxymethyl cellulose (CMC), SiO2 nanoparticle, barite and salts were studied both at high pressure and low temperature condition. Results show that the rheological properties, such as plastic viscosity, apparent viscosity, gel strength, yield point are highly promising. It has been found that silica nanoparticles and CMC reduce the fluid loss properties but CMC has a greater effect on fluid loss than silica nanoparticles. Zeta potential value of the formulated drilling fluids indicates their higher stability and strong function of the used nanoparticle. Inhibition effect of drilling fluid on hydrate formation was evaluated by using the drilling fluid with an optimized formulation in an autoclave hydrate cell at high pressure and low temperature. The experimental results reveal that the designed drilling fluid shows excellent inhibition effects on hydrate formation. This happens because of excellent thermodynamic and kinetic inhibition effects of CMC, salts and SiO2 nanoparticles.

Experimental and modelling study on the effect of maltose as a green additive on methane hydrate

The thermodynamic effect and kinetic process of maltose on methane hydrate formation were studied in this work. The gas-liquid-hydrate equilibrium (GLHE) conditions were measured using the isothermal pressure search method in deionized water and maltose aqueous solutions, respectively. The experimental results show that maltose has obvious thermodynamic inhibition effect on methane hydrate formation. The dissociation enthalpies (ΔHdiss) of methane hydrate in different solutions remain quite uniform, which indicates that maltose has not been involved in the formation of hydrate nucleus. The kinetic process of maltose on methane hydrate is evaluated by methane consumption, gas storage capacity (GSC) at 5.00 MPa and 276.15 K. The gas-hydrate steady-state time is longer due to the lower driving force of high concentration maltose aqueous solution at same temperature and pressure. Compared with deionized water, the GSC is lower in a high concentration of maltose aqueous solution. The Chen-Guo hydrate thermodynamic model and Wilson activity coefficient model are applied to calculate the GLHE conditions of methane hydrate in the presence of maltose. The calculation results are well correlated with the experimental values. Maltose is a renewable and edible biological product. Consequently, it is beneficial for the development of green biologically-based additive of hydrate.

Quaternary ammonium salts as thermodynamic hydrate inhibitors in the presence and absence of monoethylene glycol for methane hydrates

The thermodynamic hydrate inhibition (THI) effect induced by three different quaternary ammonium salts (QASs) namely tetraethylammonium iodide (TEAI), tetramethylammonium bromide (TMAB) and tetraethylammoniun (TEAB) on the formation of methane gas hydrates has been investigated. The THI impact is also determined in the presence of monethylene glycol (MEG) for TMAB and TEAB. The inhibition capacity is examined by finding the average suppression temperature. Experiments are performed in the pressure range of 3.45–8.3 MPa at the concentration values of 1, 5 and 10 wt%. Hydrate liquid vapor equilibrium (HLVE) points are calculated by using isochoric thermodynamic cycle (T-cycle) method. COSMO-RS study is also performed to understand the THI behavior of the compounds by analyzing sigma profile. Along with it hydrate dissociation enthalpies (ΔHdiss) are considered. The results revealed that inhibition effect increased with increase in concentration. TMAB showed better impact on hydrate suppression as compared to TEAB and TEAI in pure as well as in mixture with MEG. Moreover, in thermodynamic modeling section, Dickens and Quinby-Hunt model is employed to predict HLVE data. The equilibrium temperatures predicted by model are compared with the experimental results and found to be in good agreement. Hence these compounds can be employed in THI applications and flow assurance schemes.

Raman Spectroscopic Study of the Effect of Aqueous Salt Solutions on the Inhibition of Carbon Dioxide Gas Hydrates.

We present an experimental Raman study on the thermodynamic inhibition effect of different salts (NaCl, KCl, MgCl2, and CaCl2 from 2.5 to 11 wt %) on the formation of carbon dioxide gas hydrates. We performed the experiments in a high-pressure vessel with two phases: a water-rich phase and a CO2-rich phase. We investigated the changes the inhibitors induce in the water-rich phase before the onset of hydrate formation. This includes a study of the change in molar reaction enthalpy between strongly and weakly hydrogen-bonded water and the decrease in solubility of carbon dioxide in water. Additionally, the growth mechanisms of carbon dioxide hydrates were investigated by determining the amount of solid hydrates formed and the reaction constant. The results show that the molar reaction enthalpy, the solubility of CO2, and the amount of solid hydrates formed can be correlated with the effective mole fraction, whereas the reaction constant is not affected by the addition of salts. The decrease of the molar reaction enthalpy can be directly correlated with the equilibrium temperature of the gas hydrates.

Combined Inhibition Effect of 1-Ethyl-3-methy-limidazolium Chloride + Glycine on Methane Hydrate

Ionic liquids and amino acids are recently introduced as novel gas hydrate inhibitors. However, they show less inhibition impact as compared to commercial gas hydrate inhibitors. Therefore, testing the combined effort of some of the best performed ionic liquids and amino acids in open literature would be necessary to understand and probably increase their inhibition performance. In this study, the synergic thermodynamic inhibition effect of 1-Ethyl-3-methy-limidazolium chloride (EMIM-Cl) + glycine on methane hydrate is reported. A sapphire hydrate cell and the T-cycle method was used within the pressures and temperatures ranges of 3 - 11 MPa and 274 – 286 K, respectively. Surprisingly the inhibition preformation of the mixed 1-Ethyl-3-methy-limidazolium chloride + glycine at 10 wt.% was found to be slightly less than pure 1-Ethyl- 3-methy-limidazolium chloride and glycine at same concentration, the results were all found to generally be in the same range with their pure systems (pure 1-Ethyl-3-methy-limidazolium chloride and glycine at 10wt%) . This behaviour is probably due to the colligative properties of 1- Ethyl-3-methy-limidazolium chloride and glycine, thus, causing a relatively equal inhibition impact.