Fluid Phase Equilibria
Volume 546,
15 October 2021
, 113121
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Abstract
Saline water and organic inhibitors have considerable effects on preventing the formation of clathrate hydrates in gas and oil industries. The purpose of this study was to demonstrate a model that is capable of estimating the effects of NaCl, KCl, CaCl2 and methanol aqueous solutions on the equilibrium dissociation conditions of pure and gas mixture hydrates in wide ranges of pressure and temperature. The e-NRTL activity coefficient model is employed to describe the non-ideally of the liquid/aqueous phase. The solid solution theory of van der Waals and Platteeuw is applied to characterize the hydrate phase. The gas phase is described by the Peng-Robinson (PR) equation of state. No adjusting or fitting parameter is used. A comprehensive evaluation of the estimated values and literature data reveals the great accuracy of this model. To give a definite opinion, the obtained results of the proposed model were compared to experimental data and the results of four other thermodynamic models where the e-NRTL based model exhibits the least average absolute deviation (AAD). The average AAD of the e-NRTL based model results over 828 experimental data points was determined to be 0.59 K, which demonstrates an excellent agreement between the experimental data and the predicted/estimated values.
Introduction
Clathrate hydrates, or gas hydrates, possess solid crystalline structures, which are created in the presence of water molecules (called host molecules) and gas and/or some volatile liquid molecules (called guest molecules or hydrate former) under low temperatures and high pressures [1]. Formation of different hydrate structures (typically sI, sII and sH) depends upon the guest molecular size [1]. Clathrate hydrates can cause blockage of petroleum drilling equipment, and production and transportation facilities [1]. To prevent the risk of gas hydrate obstruction in natural gas flow-lines and equipment, two routine functional techniques can be implemented i.e., preheating the gas pipeline and altering free water by injecting thermodynamic and kinetic hydrate inhibitors [1]. Thermodynamic hydrate inhibitors (THIs) such as some mineral salts, alcohols, glycols and some groups of ionic liquids can be utilized for shifting hydrate phase equilibrium curve to lower temperatures at the pressure of system by diminishing the water chemical potential and consequently the water activity / fugacity [1]. THIs detach the free water by creating hydrogen bonding between inhibitor(s) with the water molecules [2]. Saline water accompanying produced gas and oil is often saturated with the ions like Na+, K+, Mg2+, Ca2+, Cl−, Br−, etc. Saline water can naturally inhibit the hydrate formation for the reason that the ions make strong electrostatic forces with water molecules [1]. Various studies have been presented with different models to determine the equilibrium dissociation conditions of gas hydrates in the presence of pure water and different inhibitors [1].
The first study on the properties of clathrate hydrates was undertaken by Barrer and Stuart [3] using statistical thermodynamics. A similar method to the study of hydrate crystalline structure using a statistical thermodynamic approach was developed by van der Waals and Platteeuw [4]. Parrish and Prausnitz [5] and later Holder etal. [6] developed generalized approaches based on the van der Waals and Platteeuw [4] (vdWP) theory to characterize the clathrate hydrate in equilibrium with pure water. To improve the accuracy of the Holder's model [6] to pressures over 105 kPa, Javanmardi etal. [7] introduced a relation for the molar volume of CH4 hydrate as a function of pressure and temperature and subsequently extended their relation to CO2, C2H6, N2 and Xe hydrates.
Bhawangirkar etal. [8] presented a model to predict the L-H-V (liquid water-hydrate-vapor) and I-H-V (ice-hydrate-vapor) phase equilibria of methane, ethane, propane, CO2 and N2+water system. To model the gas/vapor phase fugacity, Peng-Robinson-Stryjek-Vera (PRSV) [9], Patel-Teja (PT) [10,11] and Soave-Redlich-Kwong (SRK) [12] equations of state were employed. Their model is appropriate for sI hydrates. Nasrifar and Moshfeghian [13,14] developed a combining rule to predict the dissociation conditions of pure and mixtures of gas hydrates in aqueous solutions containing dissolved gases and thermodynamic inhibitors such as methanol, glycerol, monoethylene glycol (MEG), triethylene glycol (TEG), mineral salts and their mixtures. The model was found accurate especially for CO2 hydrate.
Javanmardi etal. [15] presented a new approach based on Aasberg-Petersen [16] model to calculate the inhibition effects of aqueous solutions of mineral salt, alcohol and their mixtures on gas hydrate formation. Mohammadi and Tohidi [17] developed a correlation which is influenced by water freezing point suppression concept for variety of organic inhibitors and salts. Dufal etal. [18] used the Statistical Associating Fluid Theory with Variable Range (SAFT-VR) equation of state (EOS) [19] along with the classical vdWP theory [4] to consider methanol, ethanol, MEG, TEG, polyethylene glycol (PEG) and NaCl aqueous solutions influences on the clathrate hydrate inhibition. Sharifi etal. [20] considered the dissociation conditions of different clathrate hydrates in the presence of NaCl, KCl, CaCl2, MEG and methanol aqueous solutions using the extended UNIQUAC [21] and vdWP [4] models. Hu etal. [22] presented the Hu-Lee-Sum (HLS) correlation for calculating the gas hydrate dissociation temperatures of both sI and sII in aqueous solutions of mixed salt and organic inhibitor such as NaCl, KCl, CaCl2, MgCl2, NH4Cl, NaBr, KBr, CaBr2, methanol, ethanol, glycerol, MEG, diethylene glycol (DEG) and TEG.
Pourranjbar etal. [23] reported some experimental data for dissociation conditions of methane hydrate in aqueous solutions of TBAB promoter. They also applied the vdWP [4] and e-NRTL [24] models to investigate the effects of NaCl and MgCl2 inhibitors on CH4+TBAB+water system. Tse and Bishnoi [25] examined Zuo and Guo [26], Aasberg-Petersen and e-NRTL [24] models to determine CO2 hydrate dissociation conditions in the presence of NaCl, KCl, and CaCl2 aqueous solutions. It was remarked that the model of Zuo and Guo performs better in aqueous solutions of a single salt.
Kwaterski and Herri [27] calculated the osmotic coefficient and mean molal ion activity coefficient for a binary and a ternary salt aqueous solution with the e-NRTL [24] model. They also considered the NaCl, KCl and CaCl2 aqueous solutions inhibition effects on the CH4 and CO2 clathrate hydrates formation by implementation of the vdWP theory [4] and e-NRTL model [24]. Avula etal. [28] developed a model for estimating methane hydrate stability conditions in the attendance of 21 ionic liquids (ILs) aqueous solutions, which were selected from various ionic and anion groups. The results were also compared to NRTL [29] and Pitzer-Mayorga [30] models predictions. Later, Avula etal. [31] employed an improved model to consider the effects of aqueous solutions of common mineral salts including NaCl, KCl and CaCl2, six ILs (selected from imidazolium cationic group and different anion group) and their mixtures on the stability conditions of CO2 hydrate. Gupta etal. [32] investigated the thermodynamic inhibition effects of some aromatic and aliphatic ILs on formation of methane hydrate. They revealed that the aromatic ILs are superior to aliphatic ILs in preventing methane hydrate formation.
This study takes into consideration the capabilities of different models in determining the equilibrium dissociation conditions of gas hydrates that coexist with aqueous solutions of methanol and prevalent salts like NaCl, KCl and CaCl2. In this regard, three predictive hydrate models were applied including Javanmardi etal. [15], Nasrifar and Moshfeghian [13] and Mohammadi and Tohidi [17]. Additionally, Holder's model [6] with the ex-UNIFAC [33] and the e-NRTL [34] activity coefficient models were implemented.
As mentioned earlier, the investigation of e-NRTL model [24] in the field of gas hydrates is promising but limited. That is why the main focus of this study was on the e-NRTL model [24]. The intended model is capable of taking into account simultaneously the non-electrostatic forces and the electrostatic forces caused by molecular species and salts species, respectively. The model considers the binary interaction parameters independent of temperature and salt-salt interaction parameters equal to zero. The model would benefit from these simplifying assumptions.
In previous studies [23,25,27], the single solvent salt version of e-NRTL model [24] and vdWP theory [4] were used to only calculate the equilibrium dissociation conditions of CH4 and CO2 simple hydrates in the presence of NaCl, KCl and CaCl2 aqueous solutions. However, in this study, the e-NRTL model [34] was used for mixed organic inhibitor-salt aqueous systems, which was generalized by Chen and Song [34] where vdWP model [4] is utilized to determine the dissociation temperatures of CH4, C2H6, C3H8 and CO2 clathrate hydrates as well as binary, ternary and quaternary clathrate hydrates mixtures in aqueous solutions of methanol and the aforesaid salts. Finally, the output results of each model are compared and the most successful model for calculating clathrate hydrate dissociation conditions in the presence of thermodynamic inhibitors aqueous solutions is demonstrated.
Section snippets
Liquid-gas-hydrate phase equilibrium
At equilibrium conditions, chemical potential of water in liquid/aqueous and hydrate phases must be equal (neglecting water content of gas/vapor phase) [5]:where μwL and μwH are the chemical potentials of water in liquid/aqueous phase and hydrate phase, respectively. Assuming a hypothetical empty hydrate lattice represented by β phase, multiplying Eq.(1) by -1 and adding the chemical potential of β phase (μwβ) to both sides of Eq.(1) leads to [5]:where ∆μwL=μwβ-μwL and ∆μwH=μwβ-μ
Results and Discussion
In this study, the dissociation conditions of methane, ethane, propane, CO2 hydrates and their binary, ternary and quaternary gaseous mixtures in aqueous solutions of methanol and salt were determined using Holder's approach [6], the vdWP solid solution theory [4] and the e-NRTL activity coefficient model [34]. In addition, the hydrate dissociation conditions of the same systems were also determined by ex-UNIFAC [33], Nasrifar and Moshfeghian [13], Javanmardi etal. [15] and Mohammadi and
Conclusions
The e-NRTL [34] , ex-UNIFAC [33] activity coefficient based models and three other hydrate models [13], [15], [17] were applied to determine the gas hydrate dissociation temperatures in aqueous solutions of methanol and salt. The results reveal that e-NRTL [34] based model, which was developed by Chen and Song [34], best describes the LHV phase equilibria in mixed salt and methanol aqueous solutions. The systems comprised of pure CH4, C2H6, C3H8, C4H10, CO2 and gaseous mixtures of CO2+C1, C1
CRediT authorship contribution statement
Foroozan Keshavarzi: Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Software, Validation, Writing – original draft. Jafar Javanmardi: Conceptualization, Funding acquisition, Investigation, Methodology, Project administration, Resources, Supervision, Writing – review & editing. Khashayar Nasrifar: Conceptualization, Investigation, Methodology, Validation, Visualization, Writing – review & editing. Amir H. Mohammadi: Conceptualization, Project administration,
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
The authors are thankful to the Shiraz University of Technology for supporting this work.
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Citation Excerpt :
The comparisons demonstrate that not only the coulombic forces, but also the short-range interactions contribute greatly to the accurate predictions of hydrate phase equilibrium in saline solution. Calculated with the van der Waals-Platteeuw type models in work by Sharifi et al. [55] and Keshavarzi et al. [56], as well as this work, the average absolute deviation for hydrate equilibrium temperatures of synthetic natural gas (SNG), are depicted in Fig. 4. The average absolute deviations in pressure for (SNG + water + salt) system of NaCl, KCl, and CaCl2 are 5.344 %, 7.777 %, and 3.050 %, respectively.
The phase equilibrium of gas hydrate is fundamental for flow assurance, energy exploitation, and hydrate concerning technique. In this study, the electrolyte NRTL equation coupled with the two-step hydrate model of Chen and Guo was successfully applied to predict the phase equilibrium of gas hydrate in the presence of single and binary mixed electrolytes. The predicted results were in good agreement with the available experimental data over a wide range of electrolyte concentrations when taking into account the contributions of long-range and short-range interactions in saline solution. Validated with 943 hydrate experimental data of pure gas and gas mixture formed in single and mixed electrolytes, the average absolute deviations in pressure are 5.42% and 4.71%, respectively. More importantly, it is further investigated that the proposed model shows a better performance for the high-concentration saline solution with concentration up to the near-saturation, with an average deviation of 0.59K for methane hydrate. Therefore, the proposed model in this work is significant for comprehending gas hydrate phase behavior in saline solution, and provides better guidance for hydrate exploitation and industrial applications.
Modeling on the Phase Equilibrium of Gas Hydrate in Electrolytes Containing System
2022, SSRN
Research article
Studies on stable phase equilibria of quaternary system LiBr-NaBr-SrBr2-H2O at 308.15 and 323.15 K
Fluid Phase Equilibria, Volume 546, 2021, Article 113093
The stable phase equilibria of LiBr–NaBr–SrBr2–H2O were studied at 323.15 K and 308.15 K by the isothermal solution equilibrium method. The isothermal phase diagram of the quaternary system was drawn by using solubilities of salts and solid phase identification. The X-ray powder diffraction method was used to identify the corresponding equilibrium solid phases of the invariant points in the quaternary system. The quaternary system LiBr–NaBr–SrBr2–H2O at 323.15 K has no double salts or solid solution. There are two invariant points, five univariant curves, and four crystallization fields corresponding to LiBr•H2O, NaBr, SrBr2•2H2O, and SrBr2•6H2O respectively, of which NaBr has the largest crystallization field, indicating that its solubility is the smallest and it is the easiest to be precipitated from the saturated solution. The phase diagram of quaternary system LiBr-NaBr-SrBr2-H2O at 308.15 K has three invariant points, seven univariant curves, and five crystallization fields corresponding to LiBr•2H2O, NaBr, NaBr•2H2O, SrBr2•2H2O, and SrBr2•6H2O, respectively. Among them, the crystallization field of LiBr•2H2O is the smallest, indicating that the solubility of LiBr•2H2O in this system is the largest.
Research article
Modeling of H2S absorption in some ionic liquids with carboxylate anions using modified HKM plus association EoS together with RETM
Fluid Phase Equilibria, Volume 546, 2021, Article 113135
In current work, mHKM-CPA EoS together with the RETM was employed to correlate H2S absorption into five carboxylate ionic liquids, including 1-ethyl-3-methylimidazolium acetate ([emim][Ace]), 1-butyl-3-methylimidazolium acetate ([bmim][Ace]), 1-hexyl-3-methylimidazolium acetate ([hmim][Ace]), 1-ethyl-3-methylimidazolium lactate ([emim][Lac]) and 1-ethyl-3-methylimidazolium propionate ([emim][Pro]). The RETM proposes a chemical reaction between IL and H2S so that the liquid phase concentrations may be obtained by solving the model. Moreover, mHKM-CPA EoS contributes to VLE calculations. In the model, H2S considered as associating component with 4 association sites while the ILs assumed as non-self-associating compounds with one electron donor/acceptor sites.
Fourteen adjustable variables of mHKM-CPA EoS for pure components were calculated using experimental liquid density and vapor pressure data. Afterward, binary systems were correlated by applying RETM. Indeed, two nested loops calculate the liquid phase, total pressure, and vapor phase concentrations, respectively.
The parameters of the pure ILs were calculated with maximum AAD% below 0.3. Moreover, the binary results present 4.41 as the overall AAD% for 317 data points. Furthermore, a comparison between the results of the used model with those of the SRK-CPA was performed to show the capability of the mHKM-CPA EoS. As the outputs show, the model has a good ability to correlate the H2S solubility in the ILs concerning the classic SRK-CPA EoS.
Research article
Pair-correlation functions and freezing transition in a 2D binary mixture of ultrasoft colloidal particles interacting via Hertzian potential
Fluid Phase Equilibria, Volume 546, 2021, Article 113125
Density functional theory (DFT) of freezing and hypernetted chain (HNC) integral equation theory has been used to investigate the nature of pair-correlations and the freezing transitions in a binary mixture of ultrasoft colloidal particles confined to a two-dimensional (2D) plane. The particles of the system interact via Hertzian type model potential with varying softness. The accuracy of the pair-correlations obtained by HNC theory has been tested by performing NVT Monte Carlo (MC) simulation. The partial pair correlation functions of the mixture are found to exhibit non-monotonous behaviour whose nature depends on the softness of the potential and composition. Pair-correlations obtained by solving the HNC integral equation theory have been used in DFT to determine the freezing parameters of fluid-substitutionally disordered triangular solid. The constant pressure phase diagrams in the composition-temperature plane are found to be narrow spindle types.
Research article
Sequestration of light hydrocarbons in Ionic Liquids at high-pressures: Consistency and thermodynamic modeling
Fluid Phase Equilibria, Volume 546, 2021, Article 113119
Ionic liquids are applicable in the recovery of valuable products, remotion of polluting agents, and used in many CO2-capture techniques. In this work, high-pressure vapor-liquid equilibria of twenty-one binary mixtures of light hydrocarbons+IL has been modelled with Peng-Robinson/Stryjek-Vera equation of state applying Wong-Sandler mixing rules and van Laar model for the gamma-phi approach and Perturbed Chain-Statistical Associating Fluid Theory equation of state for the phi-phi approach. Critical properties were determined using a group contribution method. Adjustable characteristic pure component parameters were obtained using predicted vapor pressures and saturated liquids densities values. Experimental data, obtained from literature, were subjected to thermodynamic consistency area test. For the thermodynamic modelling, adjustable parameters were fitted between predicted and experimental bubble pressure. Van Laar and interaction parameters were regarded as temperature-dependent. Results obtained for both models, in terms of the main deviations between experimental and calculated pressures, were reasonably satisfactory.
Research article
pvTz properties of 2,3,3,3-tetrafluoroprop-1-ene+1,1-difluoroethane binary system measured in the two-phase and superheated vapor regions
Fluid Phase Equilibria, Volume 546, 2021, Article 113173
In this work, 25 two-phase and 136 vapor-phase pvTz measurements for the binary system containing 2,3,3,3-tetrafluoroprop-1-ene (R1234yf) and 1,1-difluoroethane (R152a) are presented. The reported measurements were carried out using an isochoric apparatus along seven isochores with densities equal to (12.694, 13.812, 13.914, 14.527, 16.273, 16.942, 19.086)kg1m−3 and specific volumes equal to (0.052395, 0.059026, 0.061453, 0.068837, 0.071869, 0.072401, 0.078775)m3kg−1 for temperatures from (263 to 373)K for seven R1234yf mole fractions (0.1342, 0.2508, 0.3975, 0.4501, 0.5784, 0.7850, 0.8981). The vapor-liquid equilibrium properties of the R1234yf+R152a binary system were assessed from the two-phase experimental data by employing the flash method with the Peng-Robinson equation of state and the multi-fluid Helmholtz-energy explicit model available in REFPROP 10.0. The vapor-liquid equilibrium properties derived from the two-phase measurements agreed with the literature experimental properties. The vapor-phase measurements were compared with the properties calculated from the Peng-Robinson equation of state and REFPROP 10.0, obtaining low deviations.
Research article
Thermodynamic modeling of aqueous Ca2+– Na+ – K+ – Cl− quaternary system
Fluid Phase Equilibria, Volume 409, 2016, pp. 193-206
We present a comprehensive thermodynamic model for the aqueous Ca2+ – Na+ – K+ – Cl− quaternary system with electrolyte concentrations up to saturation and temperatures up to 473K. This work is part of a larger effort to develop an engineering thermodynamic model for high salinity produced water in oil and gas production. Built on the thermodynamic framework of symmetric electrolyte Non-Random Two Liquid (eNRTL) theory, the model correlates composition dependency of the solution nonideality with two binary interaction parameters for each of the molecule-electrolyte pairs and the electrolyte-electrolyte pairs present in the system. The model further correlates temperature dependency of the binary parameters through a Gibbs–Helmholtz type equation with three temperature coefficients. We identify the binary parameters and their temperature coefficients for the (Ca2+ Cl−):H2O pair, the (Ca2+ Cl−):(Na+ Cl−) pair and the (Ca2+ Cl−):(K+ Cl−) pair by regressing experimental phase equilibrium, calorimetric and salt solubility data. These binary parameters are then integrated with published binary parameters for other subsystems present in the quaternary system. Together the eNRTL model and the model parameters offer a comprehensive thermodynamic model for the quaternary system; and it shows excellent agreement with literature data for the quaternary system and its subsystems.
Javanmardi etal. [15]
Nasrifar and Moshfeghian [13]
Mohammadi and Tohidi [17]
© 2021 Elsevier B.V. All rights reserved.
FAQs
What is the formula for clathrate hydrate? ›
The nominal methane clathrate hydrate composition is (CH4)4(H2O)23, or 1 mole of methane for every 5.75 moles of water, corresponding to 13.4% methane by mass, although the actual composition is dependent on how many methane molecules fit into the various cage structures of the water lattice.
What is the role of salinity in clathrate hydrate based processes? ›Clathrate or gas hydrates have gained tremendous interest due to their potential applications in various industries and flow assurance problems in the oil and gas sector. In both directions, salinity plays an essential role in controlling the kinetics/thermodynamics of hydrate formation/dissociation.
What is type 2 clathrate hydrate? ›A type II clathrate hydrate is a water-ice crystal with a structure comprising “large” and “small” polyhedral cavities, with hydrogen-bonded water molecules forming the vertex of each polyhedron.
Where are clathrate hydrates found? ›In particular, methane clathrate hydrates have been found in deep ocean layers, sediments below the Arctic, and permafrost areas where there is a combination of high pressure and low temperature.
What are the conditions for the formation of clathrate hydrate? ›The clathrate “methane-hydrate” is formed when methane dissolves in water, and can be stabilized at high pressure and low temperature, for example at great depth in the ocean. Water forms a zeolite-like cage structure around the yellow and green methane molecules (Kuhs et al. 2000).
How do you determine the chemical formula for a hydrate lab? ›Formula of a Hydrate (Anhydrous Solid⋅xH2O)
In order to determine the formula of the hydrate, [Anhydrous Solid⋅xH2O], the number of moles of water per mole of anhydrous solid (x) will be calculated by dividing the number of moles of water by the number of moles of the anhydrous solid (Equation 5.6).
The salinity of the residual free water in the surroundings of the hydrate formed will increase during hydrate formation. This will lead to a constant reduction in water activity coefficient only affected by dilution due to diffusion and other transport mechanisms.
What is the effect of surfactant crowding on clathrate hydrate growth? ›Surfactant crowding occurs due to rearrangement of surfactants at the guest-water interface during clathrate hydrate growth. The presence of surfactant encouraged radial hydrate growth and formation of hydrate columns.
What are clathrate hydrates with hydrogen bonding guests? ›Abstract. Clathrate hydrates (CHs) are inclusion compounds in which “tetrahedrally” bonded H2O forms a crystalline host lattice composed of a periodic array of cages. The structure is stabilized by guest particles which occupy the cages and interact with cage walls via van der Waals interactions.
How does a clathrate work? ›Clathrates are a class of chemical substance in which a molecule of a certain type is trapped within a cage or lattice formed from molecules of a second type; if the cage is formed from water molecules, the structure is known as a hydrate.
What is the difference between hydrates and clathrates? ›
Hydrates of small gas molecules form only at high pressures when the temperature is higher than the ice point. In contrast, clathrate hydrates of water-soluble molecules form under ambient pressure at temperatures somewhat higher than the ice point, and it is easy to obtain a large single crystal.
Which compound would result in the formation of a clathrate structure? ›The calculation shows O2 is the driving compound for clathrate formation, and pure O2 clathrate is structure II (Sloan & Koh 2007).
What are the uses of clathrate hydrates? ›The potential applications of clathrate hydrate formation are in the following broad categories: recovery of water from electrolyte solutions (desalination); storage of natural gas, hydrogen, and other substances in solid clathrate hydrates; recovery of water from aqueous organic (wastewater treatment and concentration ...
What is an example of a clathrate? ›clathrate A compound in which molecules of one substance, commonly a noble gas, are completely enclosed within the crystal structure of another substance. Typical examples are Kr and Xe encapsulated in zeolite structures, or Ar, Kr, and Xe trapped in water ice.
What is clathrate like water? ›Clathrate hydrate is a crystalline solid of water in which nonpolar molecule, usually gas molecule, is trapped inside the cages of hydrogen-bonded water molecules. Large amounts of natural gases are reserved on the ocean floor in the form of clathrate hydrate.
Under what conditions do hydrates form? ›Gas hydrate forms when methane and water combine at pressure and temperature conditions that are common in the marine sediments of Earth's continental margins and below about 200 m depth in permafrost areas.
What conditions encourage hydrates to form when gas and free water are available? ›As a rough rule of thumb, methane hydrate will form in a natural gas system if free water is available at a temperature as high as 40°F and a pressure as low as 170 psig. Decreasing temperature and increasing pressure are favorable for hydrate formation (Guo et al., 1992).
Under what conditions are methane clathrates stable? ›Methane clathrates are stable at depths greater than about 200 m in permafrost regions and in ocean sediments at water depths greater than about 250 m, provided bottom waters are sufficiently cold. The thickness of the clathrate stability zone depends on surface temperature and geothermal gradient.
How do you determine the hydration and formula of hydrates? ›Divide the mass of the water lost by the mass of hydrate and multiply by 100. The theoretical (actual) percent hydration (percent water) can be calculated from the formula of the hydrate by dividing the mass of water in one mole of the hydrate by the molar mass of the hydrate and multiplying by 100.
How do you identify a hydration reaction? ›For the hydration of alkenes, the general chemical equation of the reaction is the following: RRC=CH2 + H2O → RRC(OH)-CH. A hydroxyl group (OH−) attaches to one carbon of the double bond, and a proton (H+) adds to the other. The reaction is highly exothermic.
How do you analyze hydrates? ›
The moles of water in a hydrate can be determined quantitatively by heating a known mass of the hydrate for a sufficient length of time to establish constant mass, and then determining the mass of the anhydrous material or residue.
What is the hydration process of salts? ›The hydration of a salt is a complex process where mass and heat transfer accompany the exothermic binding of water, with typical volume expansions of 50% due to drastic changes in the crystal structure.
Is salt important in the hydration process? ›While too much sodium in your diet can be unhealthy, skipping salt altogether isn't necessarily the solution. Sodium is a critical electrolyte that, along with potassium and chloride, helps to deliver water to your body's cells. That means a diet that's too low in sodium can actually increase your risk of dehydration.
How does salinity affect the ability of gases to be dissolved in water? ›b) Increasing salinity decreases solubility of gas in water, therefore dissolved O2 concentration decreases.
How do surfactants control the agglomeration of clathrate hydrates? ›This analysis indicates that the surfactants do not necessarily make the coalescence thermodynamically unfavorable: their main role is to slow down the kinetics of this process by decreasing the contact between water and the clathrate and increasing the magnitude of the barrier for water penetration.
What happens when you increase surfactant concentration? ›As the concentration of a surfactant increases, adsorption takes place at the surface until it is fully overlaid, which corresponds to the minimum value of the surface tension (SFT). Micelles form in the volume phase above the transition concentration described as the CMC.
Does surfactant increase or decrease surface area? ›The main purpose of the surfactants is to decrease the surface and interfacial tension and stabilize the interface.
What are methane hydrates also called clathrates )? ›Methane hydrate is a class of clathrate, composed of water and low molecular weight gases, mainly methane, which forms under low temperature, high pressure, and appropriate methane concentrations. From: Geological Controls for Gas Hydrate Formations and Unconventionals, 2016.
What pressure is hydrogen clathrate? ›It can be formed at 250K in a diamond anvil at a pressure of 300MPa (3000 Bars).
Is hydrogen bonding stronger in water or ethanol? ›The intermolecular attractive forces in alcohol are stronger than those in water.
What are the characteristics of clathrate compounds? ›
These compounds have the following characteristics in crystalline structure in addition to having a large void [84]: (1) large unit cell with high symmetry; (2) guest atoms or molecules are physically trapped in the large voids of lattice, and also stabilize the frame structure; and (3) guest atoms or molecular ...
What is the stability of clathrate compound? ›The clathrate is found to be thermodynamically stable at 25 bar and 150 K. Clathrate hydrates are a class of inclusion compounds in which guests (noble gases or small organic molecules) occupy, fully or partially, cages in the host framework made up of H-bonded water molecules (1).
Which interaction is responsible for formation of clathrates? ›Dipole-induced dipole interaction.
What are the three types of hydrates? ›A hydrate is any compound that has absorbed water molecules from its environment and included them in its structure. There are three types of hydrates: inorganic, organic, and gas (or clathrate) hydrates.
What are the three types of hydrate formation? ›2)interstitial water. 3)hydrogen-bonded water.
What is the melting point of clathrate hydrate? ›The clathrate hydrate melts reversibly at 277 K and C(p) increases by 770 J/mol K on melting.
Do clathrates increase entropy? ›Formation of Hydrophobic Interactions
Tearing down a portion of the clathrate cage will cause the entropy to increase ( ΔS is positive), since forming it decreases the entropy.
Clathrate hydrates are crystals in which water molecules form hydrogen-bonded cages that enclose small nonpolar molecules, such as methane. In the laboratory, clathrates are customarily synthesized from ice and gas guest under conditions for which homogeneous nucleation of hydrates is not possible.
Why are the properties of hydrates important? ›The hydration process has enormous significance for chemical reactions. This is primarily because in many reactions water is present to on extent or another, as water is the main and most popular solvent among all substances.
What are the different types of clathrate compounds? ›Accordingly, clathrates are broadly classified as given below. High temperature and high pressure clathrates, e.g., fullerenes. Low temperature and high pressure clathrates, e.g., gas hy- drates. Normal temperature and pressure clathrates, e.g., clathrin.
Why are gas hydrates important? ›
Gas hydrates are important for three reasons: They may contain a major energy resource. It may be a significant hazard because it alters sea floor sediment stability, influencing collapse and landsliding.
Where is clathrate found? ›Since 1970 Clathrates have been found in many area's along the ocean floor and as of very recently in the fresh water rift lake, Lake Baikal in Russia. The unusualness about this formation is that it is very near the surface at around 150m.
What is the clathrate hydrate of chlorine? ›Chlorine Clathrate Hydrate
Chemical formula: Cl13.3O46H92.
Most common clathrate crystal structures can be composed of cavities such as dodecahedral, tetrakaidecahedral, and hexakaidecahedral cavities. Most clathrate hydrates are 85 mole % water. Clathrate hydrates are derived from organic hydrogen-bonded frameworks.
What is the difference between hydrate and clathrate? ›Hydrates of small gas molecules form only at high pressures when the temperature is higher than the ice point. In contrast, clathrate hydrates of water-soluble molecules form under ambient pressure at temperatures somewhat higher than the ice point, and it is easy to obtain a large single crystal.
What is the general formula of gas hydrates? ›The general formula for a methane hydrate is CH4·nH2O where “n” describes a variable number of water molecules within the lattice structure.
What is the stability of the clathrate? ›It is the only hydrate known to have a stability limit at low temperatures of approximately −150 °C12, 30,31,32. This is because the vapor pressure of dry ice is lower than the dissociation pressure of the CO2 hydrate12.
Which of the following interaction is responsible for clathrate compound? ›Note: Dipole induced dipole interaction is responsible for the formation of clathrate compounds of noble gases with beta quinol.
What are clathrate compounds and how are they formed? ›Clathrate compounds 1) are those in which two or more components are associated without ordinary chemical union but through complete enclosure of one set of molecules in a suitable structure formed by another.
Can hydrates form without water? ›Hydrates can form in a pipeline with no free water if the conditions are suitable and other encouraging factors are present, however, the metastable hydrate nuclei may never achieve the critical radius for further growth and may shrink if equilibrium conditions change.
What is one disadvantage of using gas hydrates? ›
Thus, with increasing depth, the presence of gas hydrate can be a disadvantage in that a given volume of gas hydrate will contain less gas than could be present if the gas were in a free state.
Why is the study of gas hydrates important? ›Gas hydrates are important for three reasons: They may contain a major energy resource. It may be a significant hazard because it alters sea floor sediment stability, influencing collapse and landsliding.