Clathrate Formation Research Articles

STUDY THE EFFAECT OF TWEEN 80 ON CLTHRATE HYDRATE FORMATION BEHAVIOR FOR R-134A

Clathrate hydrates are complex molecules formed by the contact between water and gas at high pressure and low temperatures. One of the important aims of gas hydrate technology is to enhance the formation of hydrate and reduction the induction time for clathrate formation. Effect of the different promoters (nonionic surfactant Tween80) on R-134a gas hydrate formation has been investigated in the isochoric system experiment. It is noted that the surfactants have a significant effect of increasing the speed of nucleation as well as improving the growth of hydrate. In the experiment, the effect of Tween80 surfactant was studied to determine its effect on the composition and cooling capacity of 134 hydrates. From kinetic models, many objective functions such as the amount of gas consumed (Δn), the growth rate (r (t)), the apparent rate constant (Kapp) and conversion of the water to hydrate were obtined. The improvement of hydrate growth is marked by the addition of surfactants, which in turn increase the solubility of hydrate gas and reduce the contact angle. In addition, surfactants positively the contact with the gas through the increase of the gas diffusion in the water and this increases the rate of formation of hydrate. Best value achieved at a surfactant concentration of 100 ppm with maximum gas consumed amount (0.16 mol) and less indction time 32 min.

Factors Promoting the Formation of Clathrate-Like Ordering of Water in Biomolecular Structure at Ambient Temperature and Pressure.

Clathrate hydrate forms when a hydrophobic molecule is entrapped inside a water cage or cavity. Although biomolecular structures also have hydrophobic patches, clathrate-like water is found in only a limited number of biomolecules. Also, while clathrate hydrates form at low temperature and moderately higher pressure, clathrate-like water is observed in biomolecular structure at ambient temperature and pressure. These indicate presence of other factors along with hydrophobic environment behind the formation of clathrate-like water in biomolecules. In the current study, we presented a systematic approach to explore the factors behind the formation of clathrate-like water in biomolecules by means of molecular dynamics simulation of a model protein, maxi, which is a naturally occurring nanopore and has clathrate-like water inside the pore. Removal of either confinement or hydrophobic environment results in the disappearance of clathrate-like water ordering, indicating a coupled role of these two factors. Apart from these two factors, clathrate-like water ordering also requires anchoring groups that can stabilize the clathrate-like water through hydrogen bonding. Our results uncover crucial factors for the stabilization of clathrate-like ordering in biomolecular structure which can be used for the development of new biomolecular structure promoting clathrate formation.

Storage of Methane Gas in the Form of Clathrates in the Presence of Natural Bioadditives.

Methane (CH4) and carbon dioxide (CO2), the important greenhouse gases, are capable of forming clathrate hydrates under some suitable thermodynamic conditions. The gas storage capacity of these materials is high, and therefore they are often useful in gas storage applications. Certain expensive and toxic chemicals are employed to accelerate/decelerate the process. In this study, we report rapid (∼30–50 min) and effective (∼80%) methane hydrate conversion in the presence of three naturally occurring additives such as dry powders from Nelumbo nucifera (Indian lotus), Piper betle (betel), and Azadirachta indica (neem), at lower concentrations (0.5 wt %). Obtained results were carefully compared with the well-known kinetic promoter (sodium dodecyl sulfate). All the biomaterials are equally good kinetic promoters for methane hydrates, although the required subcooling is significantly large. However, no hydrate formation is observed with CO2 gas.

Experimental Investigation of the Effect of Nanofluid on Thermal Energy Storage System Using Clathrate

Climatic change illustrates the need to new policy of load management. In this research, a special design of thermal energy storage (TES) system, with an appropriate storage medium that is suitable for residential and commercial buildings has been constructed and commissioned. Direct contact heat transfer is a significant factor to enhance the performance of TES. Numerous experimental runs were conducted to investigate the clathrate formation and the characteristics of the proposed TES cooling system; in addition, the effect of using nanofluid particles Al2O3 on the formation of clathrate under different operating parameters was evaluated. The experiments were conducted with a fixed amount of water 15 kg, mass of refrigerant to form clathrate of 6.5 kg, nanofluid particles concentration ranged from 0.5% to 2% and the mass flux of refrigerant varied from 150 to 300 kg/m2 s. The results indicate that there is a significant effect of using nanoparticles concentration on the charging time of the clathrate formation. The percentage of reduction in charging time of about 22% was achieved for high nanoparticles concentration. In addition, an enhancement in charging time by increasing the refrigerant flow rate reaches 38% when the mass flux varied from 200 to 400 kg/m2 s. New correlation describing the behavior of the temperatures with the charging time at different nanoparticles concentrations is presented.

Methane hydrates: Nucleation in microporous materials

Clathrates are well-known compounds whose low thermal stability makes them extremely rare and appreciated. Although their formation mechanism is still surrounded by many uncertainties, these ice-like structures have the potential to be an alternative for transport and storage of different gases, especially methane. For the formation of methane clathrates extreme pressure conditions and a narrow temperature window are needed. Microporous materials have been proposed to provide nucleation sites that, theoretically, promote clathrate formation at milder conditions. While activated carbons and Metal-Organic Frameworks (MOFs) have already been studied, very little is known about the role of zeolites in this field. In this work, we study the formation of methane clathrates in the presence of RHO zeolite. Experimental results based on adsorption and operando synchrotron X-Ray diffraction demonstrate the formation of clathrates at the surface of the zeolite crystals and reveal mechanistic aspects of this formation at mild conditions.

X-ray powder diffraction study of the stability of clathrate hydrates in the presence of salts with relevance to the Martian cryosphere

Water on the present day Martian surface is thought to exist in two thermally distinct sub-surface reservoirs: as ice in the cryosphere and as groundwater located deeper in the crust. These sub-surface environments are thought to contain saline, rather than pure, water and laboratory studies on whether or not clathrate hydrates can form in such environments are lacking. We fill this gap by performing synchrotron radiation X-ray powder diffraction to investigate the formation and evolution of clathrate hydrates in weak chloride solutions at CO2 pressures, and over temperature ranges, that are similar to those found in the Martian regolith. We have found that clathrate hydrates can form under conditions relevant to the Martian cryosphere, despite the presence of chloride salts. We find that the dissociation temperatures for CO2 clathrate hydrates formed in saline solutions are depressed by 10–20 K relative to those formed in pure water, depending on the nature of the salt and the CO2 pressure. We suggest that the inhibiting effect that salts such as MgCl2, CaCl2 and NaCl have on clathrate hydrate formation could also be related to the salts’ effect on the formation of the low temperature phase of ice. However, despite the inhibiting effect of the salts, we conclude that the presence of clathrate hydrates should still be possible under conditions likely to exist within the Martian cryosphere.

Enclathration of Ethane, Propane, and Propylene into Urea Clathrates and Roles of Methanol on Urea Clathrate Formation.

As a guest molecule of urea clathrate, a long-chain normal alkane and its derivative with low substituents in methanol solutions have been reported. To investigate the role of methanol in the urea clathrate formation, in the present study, we used propane (C3H8), propylene (C3H6), ethane (C2H6), and methane (CH4) as guest molecules. Raman spectra and powder X-ray diffraction profiles revealed that, regardless of the existence of methanol, the C3H8, C3H6, and C2H6 molecules are enclathrated into urea clathrates with a hexagonal structure, whereas there is no urea clathrate formation enclathrating CH4. The pressurization of the urea clathrates including C2H6 and C3H8 reveals that no pressure-induced structural phase transition occurs at pressures up to 200 MPa. In spite of the guest molecule much shorter than the lattice constant of the c-axis of the hexagonal channel structure, the urea clathrates have a fairly rigid structure against the compression. Methanol as an auxiliary solution is not always necessary for the urea clathrate formation. Methanol plays a role in decreasing the activation energy of the urea clathrate formation, although it makes urea clathrate thermodynamically unstable due to the high solubility of urea in methanol.

Noble Gas Abundance Ratios Indicate the Agglomeration of 67P/Churyumov–Gerasimenko from Warmed-up Ice

Abstract The origin of cometary volatiles remains a major open question in planetary science. Comets may have either agglomerated from crystalline ices condensed in the protosolar nebula (PSN) or from amorphous ice originating from the molecular cloud and interstellar medium. Here, based on the recent argon, krypton, and xenon measurements performed by the ROSINA mass spectrometer on board the European Space Agency’s Rosetta spacecraft in the coma of 67P/Churyumov–Gerasimenko, we show that these noble gas relative abundances can be explained if the comet’s building blocks formed from a mixture of gas and H2O grains resulting from the annealing of pristine amorphous ice (i.e., originating from the presolar cloud) in the PSN. In this scenario, the different volatiles released during the amorphous-to-crystalline ice phase transition would have been subsequently trapped at lower temperatures in stoichiometric hydrate or clathrate hydrate forms by the crystalline water ice generated by the transition. Once crystalline water was completely consumed by clathration in the ∼25–80 K temperature range, the volatile species remaining in the gas phase would have formed pure condensates at lower temperatures. The formation of clathrates hydrates and pure condensates to explain the noble gas relative abundances is consistent with a proposed interstellar origin of molecular oxygen detected in 67P/Churyumov–Gerasimenko, and with the measured molecular nitrogen depletion in comets.

Stability of Hydrogen Hydrates from Second-Order Møller-Plesset Perturbation Theory.

The formation of gas hydrates and clathrates critically depends on the interaction between the host water network and the guest gas species. Density functional calculations can struggle to quantitatively capture these dispersion-type interactions. Here, we report wave function-based calculations on hydrogen hydrates that combine periodic Hartree-Fock with a localized treatment of electronic correlation. We show that local second-order Møller-Plesset perturbation theory (LMP2) reproduces the stability of the different filled-ice-like hydrates in excellent agreement with experimental data. In contrast to various dispersion-corrected density functional theory implementations, LMP2 correctly identifies the pressures needed to stabilize the C0, C1, and C2 hydrates and does not find a spurious region of stability for an ice-Ih-based dihydrate. Our results suggest that LMP2 or similar approaches can provide quantitative insights into the mechanisms of formation and eventual decomposition of molecular host-guest compounds.

Guest Occupation Effects on the Transition of Crystalline Syndiotactic Polystyrene: Selection Criteria for Fundamental Structures γ ‐I and γ ‐II

AbstractMolecular dynamics simulations are performed on clathrate forms of crystalline syndiotactic polystyrene containing toluene, chloroform, and carbon dioxide, to investigate the effects of guests on thermally induced structural transitions. Two crystalline forms, γ ‐I and γ ‐II, are produced. γ ‐I is obtained from crystals with lower guest occupation ratios, while γ ‐II is obtained from crystals with higher ratios. The b‐length of the crystal unit cell of the γ ‐II form is twice of that of the γ ‐I form; the other lattice parameters are almost identical. Based on a hypothesis that the experimentally observed γ form is a mixture of the γ ‐I and γ ‐II forms, X‐ray diffraction patterns for film samples with uniplanar orientations are reasonably interpreted. The thermodynamically stable form is γ ‐I, although the γ ‐II form is preferentially produced in the presence of guest molecules.

A Grand Canonical Monte Carlo Study of the N2, CO, and Mixed N2–CO Clathrate Hydrates

In this paper we report the use of Grand Canonical Monte Carlo (GCMC) simulations to characterize the competitive trapping of CO and N2 molecules into clathrates, for various gas compositions in the temperature range from 50 to 150 K. The simulations evidence a preferential trapping of CO with respect to N2. This leads to the formation of clathrates that are preferentially filled with CO at equilibrium, irrespective of the composition of the gas phase, the fugacity, and the temperature. Moreover, the results of the simulations show that the small cages of the clathrate structure are always filled first, independent of either the guest structure or the temperature. This issue has been associated with the rather significant differences in the calculated heats of encapsulation (∼2–3 kJ/mol) between the smallest and the largest cages. In addition, calculations with the simplified ideal adsorbed solution theory (IAST) are developed to allow a comparison with the results arising from the GCMC simulations. Inter...

State of the art and kinetics of refrigerant hydrate formation

This study aims to introduce suitable hydrate forming-refrigerants well-suited for air-conditioning systems through a kinetic study. The formation of clathrate hydrates is a time-consuming process. Hence, in an air-conditioning system, which uses refrigerant hydrate as a media for storage of cold energy, the knowledge of the hydrate formation rate, is crucial. In this experimental study, the rate of hydrate formation of four refrigerant blends, including R404A, R406A, R408A and R427A have been investigated. The induction time for hydrate formation, apparent rate constant of the hydrate reaction, water to hydrate conversion during hydrate growth, storage capacity, and the rate of hydrate formation of these refrigerants at various pressures and temperatures have been obtained using a kinetic model. The effect of sodium dodecyl sulfate (SDS) on the hydrate nucleation rate was also investigated. This study also aims to prepare a review on gas hydrates applications and characteristics in the power generation systems and cold storage applications including air conditioning systems. The advantages and disadvantages of this compound over traditional storage media and phase change materials (PCMs) including water, ice, salt hydrates, eutectic salts, paraffin waxes and fatty acids, slurries and phase changed emulsions have been reviewed.

Influence of amino acid additives on solution behaviour of L-alanine

<p>The solubility experiment of L-alanine solution was performed in a 250ml jacketed glass crystallizer without and with amino acid additives at temperature from 15<sup>o</sup>C to 75<sup>o</sup>C by means of gravimetric method. On the whole, L-leucine additive significantly altered the solubility of L-alanine and Glycine additive caused an erratic pattern on the solubility data of L-alanine. The hydrophobic methyl side chain of L-leucine additives is believed to contribute to the formation of water clathrate in the solution which affected the interaction of L-alanine molecules in water solvent and thus modified the solubility of L-alanine. Finally, thermodynamic data analysis of L-alanine solution was extensively assessed. The negative deviation of L-alanine from the ideal solution is as a result of high solute-solvent interaction, which is due to the hydrophobicity and clathrate phenomenon of the water molecules in the solution.</p><p>Chemical Engineering Research Bulletin 20(2018) 23-29</p>

Inhibition of structure II hydrates formation by salt-tolerant N-vinyl lactam-based terpolymers

This work presents experimental results on the inhibition performance of low-dosage hydrate inhibitors (LDHIs). The studied LDHIs, namely terpolymers of N-vinylcaprolactam and alkylimidazolium bromide or benzyl ammonium chloride and hydroxyethyl methacrylate or acrylamide derivatives, were synthesized at the Mexican Petroleum Institute with the objective of producing high performance inhibitors with higher cloud points than that exhibited by the poly(N-vinylcaprolactam) homopolymer. Three experimental methods were used to evaluate the hydrate inhibition performance of the synthesized terpolymers: 1) the capacity to inhibit the formation of tetrahydrofuran (THF) hydrates (atmospheric pressure and −0.5 °C); 2) the capacity to inhibit the formation of natural gas hydrates under high pressure and low temperature conditions (∼6 MPa, ∼1 °C, a subcooling of 16 °C for the studied natural gas sample); and 3) the determination of the cloud point temperature of the terpolymers in aqueous systems with varying salinity (atmospheric pressure and temperatures ranging from 2 °C to 81 °C). The inhibition performance and the high solubility (in highly saline aqueous systems) of the synthesized terpolymers indicate that these compounds could be considered promising kinetic hydrate inhibitors or gas-well anti-agglomerants to prevent or delay the formation or agglomeration of clathrate hydrates during the production and transport of hydrocarbons.

Phase Equilibrium of Isotopologue Methane Hydrates Enclathrated CH3D and CD4

Hydrate equilibrium conditions formed from deuterated methane isotopologues (CH3D and CD4) were measured over a temperature range of (273 to 278) K and a pressure range of (2.6 to 4.2) MPa. The phase boundary of CH3D and CD4 hydrates was shifted to higher pressures and lower temperatures than that of the CH4 hydrate. Crystal structure and cage occupancies of gas hydrate crystals formed from CH3D and CD4 were characterized by Raman spectroscopy. The isotope effect of methane hydrates revealed in this study can be used to explain the isotopic fractionation of hydrogen in methane during the formation of clathrate hydrates observed in natural settings, as reported by previous studies.

Kinetics of CO2 Capture by Hydroquinone Clathrates

Organic clathrates formed by combining hydroquinone (HQ) and CO2 could offer very interesting prospects in the near future, particularly in the field of CO2 capture and storage. However, one of the main limitations hindering the large-scale deployment of this type of clathrate-based technology is the slow enclathration kinetics. Our experiments, performed at different pressures (1.5, 3.0, and 4.5 MPa) and temperatures (298, 323, and 348 K), with HQ in different forms (HQ powder, HQ pellets, and HQ–silica composites, each different in nature and in terms of pore size and HQ content) demonstrated that (i) an increase in both pressure and temperature enhances the enclathration rate, (ii) the textural properties of HQ significantly impact kinetics, and composite materials remain the most efficient for improving HQ clathrate formation kinetics.

Spectroscopic Studies on the Formation and Guest Behaviors of Hydroquinone Clathrate with Binary CO and H2 Gas Mixtures

Syngas clathrate compounds were for the first time investigated using hydroquinone (HQ) with binary CO and H2 gas mixtures as syngas replicas. In combination with X-ray diffraction and Raman spectr...

Study on extraction and clathration process of volatile oil in Tianma-Shouwu tablet

Objective To optimize the extraction and β-cyclodextrin clathration process of volatile oil in Tianma-Shouwu tablet. Methods The extraction of volatile oil was optimized through the orthogonal design L9(34) with the volatile oil extraction amount as assessment index. The saturated aqueous solution preparation of clathrate form was used. The volume of β-cyclodextrin and volatile oil, clathration temperature, clathration time was investigated by central composite design-response surface methodology, with the score of volatile oil inclusion ratio and utilization ratio as the index. The results were fitted by second-order polynomial equation, and then the best clathration process was determined. Results The optimization extraction process of volatile oil in Tianma-Shouwu tablet was as follows: to add 8 times water, immerse 30 minutes, steam distill 6 hours; and the best clathration process was as follows: the ratio of β-cyclodextrin and volatile oil was 9.50︰1, clathration temperature 43 ℃, and clathration time 4.2 hours. Conclusions The optimized extraction and clathration process were reasonable, stabled and repeatable. Key words: Volatile oils; Tianma-Shouwu tablet; Orthogonal test; β-cyclodextrin; Central composite design

Reverse micelles enhance the formation of clathrate hydrates of hydrogen

HypothesisClathrate hydrates of hydrogen form at relatively low pressures (e.g., ca. 10 MPa) when a co-former compound is added. In that case, however, the gravimetric amount of stored hydrogen drops to less than 1 wt% from ca. 5.6 wt% without a co-former. Another factor hindering the entrapment of hydrogen into a clathrate matrix appears to be of a kinetic origin, in that the mass transfer of hydrogen into clathrates is limited by the macroscopic scale of the gas–water interfaces involved in their formation. Thus, the enhanced formation of binary (hydrogen + co-former) hydrates would represent a major achievement in the attempt to exploit those materials as a convenient means for storing hydrogen. ExperimentsHere, we present a simple process for the enhanced formation of binary hydrates of hydrogen and several co-formers, which is based on the use of reverse micelles for reducing the size of hydrate-forming gas–water interfaces down to tens of nanometers. This reduction of particle size allowed us to reduce the kinetic hindrance to hydrate formation. FindingsThe present process was able to (i) enhance the kinetics of the formation process; and (ii) assist clathrate formation when using water-insoluble coformers (e.g., cyclopentane, tetrahydrothiophene).

Formation of methane clathrates in carbon nanotubes: a molecular dynamics study

In this study, we investigated the possible formation of methane clathrates in CNTs with different sizes.