Clathrate Hydrate Crystal Growth Research Articles

Attempt to Clarify the Synergistic Effect Mechanism of Clathrate Hydrate Crystal Growth Inhibitors

Attempt to Clarify the Synergistic Effect Mechanism of Clathrate Hydrate Crystal Growth Inhibitors

Crystal Growth of Clathrate Hydrate Formed with Carbon Dioxide and Deuterium Oxide: Implications for Hydrate-based Tritium Separation

Crystal Growth of Clathrate Hydrate Formed with Carbon Dioxide and Deuterium Oxide: Implications for Hydrate-based Tritium Separation

Crystal growth of clathrate hydrate formed with H2\u2009+\u2009CO2 mixed gas and tetrahydropyran

Hydrate-based gas separation technology is applicable to the CO2 capture and storage from synthesis gas mixture generated through gasification of fuel sources including biomass. This paper reports visual observations of crystal growth dynamics and crystal morphology of hydrate formed in the H2 + CO2 + tetrahydropyran (THP) + water system with a target for developing the hydrate-based CO2 separation process design. Experiments were conducted at a temperature range of 279.5–284.9 K under the pressure of 4.9–5.3 MPa. To simulate the synthesis gas, gas composition in the gas phase was maintained around H2:CO2 = 0.6:0.4 in mole fraction. Hydrate crystals were formed and extended along the THP/water interface. After the complete coverage of the interface to shape a polycrystalline shell, hydrate crystals continued to grow further into the bulk of liquid water. The individual crystals were identified as hexagonal, tetragonal and other polygonal-shaped formations. The crystal growth rate and the crystal size varied depending on thermodynamic conditions. Implications from the obtained results for the arrangement of operating conditions at the hydrate formation-, transportation-, and dissociation processes are discussed.

Clathrate Hydrate Inhibition by Polyisocyanate with Diethylammonium Group.

Polymers containing amide groups have been used as kinetic hydrate inhibitors (KHIs). The amide group has good performance for hydrate nucleus adsorption, resulting in inhibition of hydrate growth. Polyisocyanates composed of an amide backbone can be KHI candidates; however, the use of polyisocyanates as KHIs has not yet been reported. Herein, we prepared water-soluble poly[3-[[2-(diethylamino)ethyl]thio]-1-propyl isocyanate-ran-hexyl isocyanate] (P(DETPIC-ran-HIC)) to investigate the ability of polyisocyanates to inhibit hydrate formation. In the tetrahydrofuran (THF) clathrate hydrate crystal growth inhibition tests, P(DETPIC-ran-HIC) showed better performance than the polyamide, poly(N-vinylpyrrolidone) (PVP).

Crystal Growth of Clathrate Hydrate with Ozone: Implication for Ozone Preservation

Preservation using hydrates as a storage medium is the only technology that enables long-term and high-concentration O3 preservation. This study reports the visual observations of the crystal growt...

Effects of Water Soluble Guest on Clathrate Hydrate Crystal Growth

Effects of Water Soluble Guest on Clathrate Hydrate Crystal Growth

Crystal Growth of Clathrate Hydrate with Methane plus Partially Water Soluble Large-Molecule Guest Compound

This paper reports the visual observations of the formation and growth of clathrate hydrate formed with methane plus a partially water soluble guest, tetrahydropyran (THP). THP is known to form a s...

Surfactant Effects on Crystal Growth Dynamics and Crystal Morphology of Methane Hydrate Formed at Gas/Liquid Interface

This paper presents visual observations aiming to clarify the underlying physics of surfactant effects on clathrate hydrate crystal growth at the interface between methane gas and water with surfactant. Sodium dodecyl sulfate (SDS), which is commonly used in industrial processes, was used in this study. Various SDS mass fractions from 0 to wSDS = 100 ppm with a step of size 10 ppm were examined, where wSDS represents the mass fraction of SDS aqueous solution. The crystal growth behavior and the crystal morphology of the methane hydrate at the interface varied depending on surfactant concentration and ΔTsub. In systems with wSDS ≤ 20 ppm, the nucleation occurred on the droplet surface (gas/liquid interface), then grew laterally, and finally covered the whole droplet surface. On the contrary, at wSDS ≥ 30 ppm, the droplet shape was not maintained and enhanced hydrate crystal growth was observed compared to those systems with wSDS ≤ 20 ppm. Individual hydrate crystals at wSDS = 20 ppm were observed to be sma...

Clathrate Hydrate Crystal Growth in Natural Gas Saturated Water Flow

The growth of clathrate hydrate crystals in a flow of water saturated with simulated natural gas was visually observed. The simulated natural gas was a mixture of methane, ethane, and propane in a molar ratio of 90:7:3 or 98.5:1.4:0.1. The morphology (i.e., the shape and size) of the hydrate crystals that grew in the water flow changed depending on the system subcooling, which denotes the difference between the hydrate-equilibrium and experimental temperatures. At lower subcooling conditions, polygonal flat-plate crystals were observed. When the subcooling temperature was larger than 11.5 K, polygonal crystals were completely replaced by dendritic crystals. Crystals formed in flowing liquid water grew for a longer period of time than those in the quiescent system without any further guest supply. In addition, the coexistence of structure I and II hydrates with the 98.5:1.4:0.1 gas mixture in the continuous supply system was visually confirmed. From these observations, we note that the crystal morphology a...

Catastrophic Crystal Growth of Clathrate Hydrate with a Simulated Natural Gas System during a Pipeline Shut-In Condition

This paper presents a significant finding where capillary-aided catastrophic gas hydrate growth is observed under a shut-in condition (static fluid) for an uninhibited system. With the use of a newly designed apparatus, consisting of six units of identical rocking cell, nucleation and growth are observed. All experiments are conducted under isochoric conditions using 11.0 K subcooling (ΔTsub) as a driving force. A simulated natural gas mixture of 90.0 mol % methane + 10.0% mol % propane is used as a gas phase. The liquid phase used is 3% (Na+, Cl–) brine. The observations of the capillary-aided mass-transport mechanism for a catastrophic gas hydrate growth are presented in this work. Our observations show hydrate crystal formation at a brine wetted area close to the brine/gas interface initiates capillary-aided catastrophic hydrate growth. Moreover, no mass transfer restriction of brine toward catastrophic gas hydrate growth is observed. Furthermore, our results show the denser (less porous appearance) hydrate structures are continuously displaced from the hydrate–water interface (hydrate growth side). This displacement allowed new hydrate crystals to be formed uninterruptedly until the exhaustion of water in the cells. On the basis of macroscopic observations, the capillary-aided mass-transport mechanism for a catastrophic gas hydrate growth is presented.

Crystal Growth of Clathrate Hydrate in a Flowing Liquid Water System with Methane Gas

This paper reports the visual observation of the growth and formation of clathrate hydrate crystals in a stream of flowing liquid water presaturated with methane gas. The experimental apparatus used in this study was devised by inserting a porous pipe inside the reactor, thereby allowing methane hydrate crystals to form and grow in the liquid water stream. The morphology of methane hydrate crystals grown in a liquid water stream varied depending on the system subcooling temperature, ΔTsub. ΔTsub is defined as the difference between the equilibrium temperature of the hydrate, Teq, and the system temperature, Tex. The crystal growth in the bulk of liquid water was observed when ΔTsub > 4.5 K. When 4.5 K < ΔTsub < 9.0 K, polygonal flat plate crystals were observed growing from the porous pipe surface. At 9.0–10.0 K, the crystal morphology enters the transition phase, where the polygonal flat plate crystals started to change into dendritic crystals. When the subcooling temperature, ΔTsub, is greater than 10.0 K, only dendritic crystals were seen to grow into the liquid water. On the basis of these observations, a continuous supply of the guest substance will enhance the growth of methane hydrate as the particle size of the crystals formed in this study was larger than that of the crystals observed in the previous study.

Surfactant Effects on the Crystal Growth of Clathrate Hydrate at the Interface of Water and Hydrophobic-Guest Liquid

Visual observations of the effect of surfactants on clathrate hydrate crystal growth at the interface of water and cyclopentane has been studied. Surfactants used in the present study are sorbitan monooleate (Span 80), naphthenic acid, and polypropylene glycol. The surfactants were each used at a mass fraction of 0.001% and 0.01%. All the surfactants were soluble in cyclopentane. The crystalline morphology and crystal growth behavior of the hydrate at the interface were found to be substantially affected by the addition of all surfactants. The size of the individual hydrate crystals in the surfactant system was larger than those in the pure cyclopentane system. The observations showed a distinct variation in the behavior of cyclopentane hydrate crystal growth depending on the chemical species of the surfactants, their concentration, and ΔTsub, which is defined as the difference between the equilibrium temperature and the experimental temperature. For the system with surfactants, the growing hydrate crysta...

G121 クラスレート水和物の結晶成長に及ぼす界面活性剤の影響(OS-14:凝固・融解伝熱および結晶成長の新展開(2))

This study is aimed at clarifying the underlying physics of the surfactant effects on clathrate hydrate crystal growth at the SDS aqueous solution/methane (liquid/gas) interface by method of the visual observations. SDS and methane were used as the surfactant and guest substance, respectively. The crystal morphology was clarified according to the ΔT_<sub>, as index of the driving force for the crystal growth. ΔT_<sub> is defined as difference between the system temperature and the hydrate equilibrium temperature. The crystal growth behavior of SDS aqueous solution/methane system was changed because hydrate crystals were detached from the interface.

Crystal growth of clathrate hydrate in liquid water in contact with methane + ethane + propane gas mixture

BACKGROUND Understanding the formation/dissociation characteristics of clathrate hydrates is required for the developments of hydrate-based novel energy technologies such as the transportation and storage of natural gas. Crystal morphology is one of the most important factors for the development of hydrate production facilities. RESULTS Crystal growth of clathrate hydrate in liquid water presaturated with a methane + ethane + propane gas mixture was visually observed and analyzed. The molar ratio composition of the methane + ethane + propane gas mixture was 98.5:1.4:0.1. The composition is that of the gas phase at the steady state achieved during continuous natural gas hydrate production from the feed gas of molar ratio 90:7:3. First of all a hydrate film formed between the mixed gas and liquid water, and then hydrate crystals grew into the liquid water phase from the hydrate film. The morphology of hydrate crystals grown in liquid water varied distinctly depending on the system subcooling (ΔTsub). CONCLUSION Hydrate crystals with polygonal morphology were observed at ∼6 K <ΔTsub < ∼12 K. At ΔTsub > ∼12 K, polygonal crystals were replaced by dendritic crystals, whereas crystal growth was not observed at ΔTsub < ∼6 K. © 2013 Society of Chemical Industry

Tetrahydrofuran hydrate crystal growth inhibition by bis-and tris-amine oxides

Amine oxides are an alternative, non-ionic class of gas hydrate anti-agglomerant (AA) surfactants that are potentially more environmentally-friendly than cationic surfactant AAs. These classes of AAs work by interacting with hydrate crystal surfaces. Recently, we reported on the clathrate hydrate crystal growth inhibition of monoamine oxides using Structure II (SII) tetrahydrofuran (THF) hydrate (Kelland et al., 2012). It was determined that the best hydrate crystal growth inhibition was provided by amine oxides with n-butyl, n-pentyl or iso-pentyl groups, with tributylamine oxide being the best homofunctional trialkylamine oxide investigated. However, replacement of one butyl group with a larger group, forming the tail of an AA surfactant, lowered the inhibition significantly which could have consequences for the use of mono-amine oxides as AAs.We have now investigated bis-amine oxides and discovered that they can give even greater THF hydrate crystal growth inhibition than mono-amine oxides, particularly when the amine oxides have the correct size alkyl groups and are an optimum distance apart. The optimum alkyl group was found to be n-butyl and the optimum distance for bis-amine oxides is with a chain of 5–6 sp3 carbon atoms separating the nitrogen atoms. Alternatively, a heteroatom can be placed in this spacer chain, for example a third nitrogen atom, such as for alkylated derivatives of diethylenetriamine. These results mean that the use of bis-amine oxide surfactants could potentially lead to improved AA performance compared to mono-amine surfactants because of their greater adsorption onto hydrate surfaces. They may also act as improved synergists for polymeric kinetic inhibitors of natural gas hydrates.

Surfactant Effects on Hydrate Crystallization at the Water–Oil Interface: Hollow-Conical Crystals

Clathrate hydrates are icelike crystalline compounds with small guest molecules trapped inside the cages of hydrogen bonded water molecules. Clathrate hydrate crystal growth is studied for the specific case of the guest molecule cyclopentane. Cyclopentane hydrate formation is visualized at a millimeter-scale water drop. Crystal formation takes place at the water–organic interface and has been shown in prior work to occur in a three-step sequence of nucleation, lateral surface growth, and radial growth. This study describes cyclopentane hydrate crystal characteristics during the lateral surface growth and demonstrates the effect of the oil-soluble surfactant sorbitan monooleate (Span 80) on the hydrate crystal growth. A faceted polycrystalline hydrate shell is formed around the water drop in the absence of surfactant. A unique hollow-conical crystal is observed at Span 80 concentrations greater than 0.01% by volume in cyclopentane; the critical micelle concentration is 0.03% Span 80. The conical crystals h...

Crystal Growth of Clathrate Hydrate at the Interface between Seawater and Hydrophobic-Guest Liquid: Effect of Elevated Salt Concentration

This paper reports the visual observations of the clathrate hydrate crystal growth and morphology at the interface of aqueous NaCl solutions and a guest-substance liquid. The hydrate crystal growth was visually characterized in the systems of a wide range of NaCl concentrations from 0.035 to 0.264 in mass fraction. The mass fraction 0.035 was corresponding to that of ordinary seawater, and the salt concentration tested was extended up to the saturation level, i.e., 0.264. Cyclopentane was used as the guest substance. Formation and growth of hydrate crystals at the cyclopentane-NaCl solution interface were observed. We visually analyzed the individual hydrate crystals and classified the morphology of the crystals according to ΔTsub at atmospheric pressure. It was found that the size of the individual hydrate crystals decreased with increasing ΔTsub. The results showed that the morphology of the individual hydrate crystals in any NaCl concentration is roughly similar at a given ΔTsub. We also measured the l...

Crystal Growth of Clathrate Hydrate in Liquid Water Saturated with a Simulated Natural Gas

This paper reports the visual observation of the formation and growth of clathrate hydrate crystals in liquid water presaturated with a simulated natural gas (methane + ethane + propane mixture). The compositions of the methane + ethane + propane gas mixtures are (i) 90:7:3, (ii) 94.1:5.8:0.1, and (iii) 99.47:0.51:0.02 in molar ratio. A hydrate film first formed to intervene between the mixed gas and liquid water, and then hydrate crystals grew in the liquid water phase. The morphology of hydrate crystals grown in liquid water distinctly varied depending on the system subcooling ΔTsub. When ΔTsub is smaller than ∼7 K, hydrate crystal growth in liquid water was not observed. At ∼7 K ∼12 K, polygonal crystals were replaced by dendritic crystals. These changes in morphology were observed with all three gas mixtures. It was found that the morphology in the system with mixed gas of the molar ratio 99.47:0.51:0.02 was differen...

メタン+エタン+プロパン混合ガス飽和水溶液中におけるクラスレート水和物の結晶成長

メタン+エタン+プロパン混合ガス飽和水溶液中におけるクラスレート水和物の結晶成長

A112 液・液界面におけるクラスレート水和物の結晶成長に及ぼす界面活性剤の影響(OS-1:環境・再生可能エネルギ(1))

A112 液・液界面におけるクラスレート水和物の結晶成長に及ぼす界面活性剤の影響(OS-1:環境・再生可能エネルギ(1))