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Gas hydrates are nonstoichiometric nano-structured crystalline compounds which are stabilized by gas molecules incorporated in the cages made of hydrogen bonding of water molecules at suitable thermodynamic conditions. The gas hydrate as a technology has been successful for several potential applications in various engineering fields, such as, gas separation, carbon dioxide sequestration, gas storage and transportation, desalination of salt water and wastewater treatment. Recently, metal-based nanofluids are considered as interesting kinetic promoter candidates for accelerating formation of gas hydrates. Although organic-based kinetic promoters are widely studied for the rapid formation of gas hydrates, research of a new material system is still a challenge. In this study, Silver (Ag) nanofluids as kinetic promoter of sulfur hexafluoride (SF6) hydrate were prepared by electrical explosion of pure metal wire in deionized water. The kinetics of SF6 gas hydrates were evaluated with different concentration of Ag nanofluids at condition of 276 K and 0.7 MPa, respectively. The Ag nanofluids, as kinetic nano-prompter, showed excellent effect on the formation of SF6 hydrates.

The PMMA (poly methyl methacrylate)/clay nanocomposite powders were synthesized by In-Situ suspension polymerizations using microwave heating. The PMMA/clay nanocomposites were also sampled using injection moulding to make specimens for material characterization. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) indicated the formation of a highly intercalated clay layer in the nanocomposites. It was found that the microstructure of PMMA/clay nanocomposites was strongly dependent of content of clay. Thermo gravimetric analysis (TGA) indicated an improvement in the thermal stability of nanocomposites compared to that of the pure PMMA. Differential scanning calorimetry (DSC) showed that the nanocomposites had a higher glass transition (Tg) temperature than the PMMA. Fourier-transform infrared (FT-IR) spectroscopy indicated an interaction between the carbonyl group of PMMA and hydroxyl group of the clay. Therefore, a possible reason in enhanced material properties of nanocomposites is that the chemical interaction and nanostructure of PMMA polymer and intercalated inorganic silicate layer has increased the thermal stability of the PMMA/clay nanocomposites.

Natural gas hydrate plugging is one of the costly and challenging problems for the oil and gas industry, especially for subsea fields. One way to prevent gas hydrate formation at low cost is the use of low-dosage hydrate inhibitors (LDHI). Poly(N-isopropylmethacrylamide) (PNIPAM) with amide group have previously been shown to be an outstanding low-dosage hydrate inhibitor (LDHI). PNIPAMs are usually polymerized via radical polymerization, which can allow control over the molecular weight. We have synthesized PNIPAMs using control radical polymerization giving a fairly high degree of polymerization control. Additionally various Kinetic Hydrate Inhibitors (KHIs) were tested as CH4 hydrate inhibitors with polymeric hydrate inhibitor, PNIPAM. Furthermore, to check the synergetic effects of tetra butyl phosphonium bromide (TBPB), PNIPAM and their mixture TBPB-PNIPAM were tested as KHIs for methane gas hydrate formation. In this paper we present results on the performance of various polymeric inhibitors in KHI tests on methane gas in stirred autoclaves and on structure I hydrate formation. When PNIPAM alone was used as a single KHI, PNIPAM exhibited worst performance among the KHIs tested in this study. However the mixing of TBPB with PNIPAM further extended the induction time and reduced the CH4 hydrate growth rate. TBPB was an excellent synergist in blends with PNIPAM for kinetic hydrate inhibition of structure I forming CH4 hydrate. In summary, the mixture TBPB-PNIPAM was proven that great synergist for prevent the CH4 hydrate and good potential in achieving the industrial application of Oil & Gas production technology and therefore was a significantly meaningful discovery in the field of energy production.

Fluorinated gases (F-gases), such as 1,1,1,2-tetrafluoroethane (HFC-134a) and sulfur hexafluoride (SF6), are used widely in a variety of industrial processes but they are some of the most potent gr...

Poly(N-vinylcaprolactam) (PVCap) has previously been shown to be an outstanding low-dosage hydrate inhibitor (LDHI). The inhibition performance of LDHI is known to be influenced by molecular weight (Mw) and molecular weight distribution. In this study, PVCaps were synthesized by two different methods. The first method, reversible addition–fragmentation chain transfer (RAFT) polymerization, was used to prepare PVCap with a narrow molecular weight distribution (about Mw/Mn 1.5). In a semi-batch stirrer reactor, hydrate inhibition performance of PVCap was evaluated. It was found that the inhibition performance was increased when the PVCap molecular weight decreased. PVCap with the narrower molecular weight distribution also showed the better inhibition performance.

Both CO 2 and SF 6 are potent greenhouse gases responsible for global warming and associated environmental issues. Hydrate-based separation and capture of these gases from gas mixtures produced by industry have been proposed, and improving the commercial viability of these processes is crucial. Here, we report the phase equilibria and characterization of binary hydrates containing CO 2 and SF 6 . The introduction of SF 6 considerably lowered the formation pressure of CO 2 hydrates by readily occupying the structure II hydrate cages and hence altering the crystal structure. Hydrate phases with different crystalline structures were found to coexist as a result of competition in occupying different hydrate cages. The structural instability caused by the coexistence of structure I and II hydrates was observed, and this feature would be important to understand the mixed gas hydrate systems. The ability of SF 6 to significantly reduce the formation pressure of hydrates suggests that it has a potential to serve as a hydrate promoter. This feature of SF 6 combined with its non-toxic and non-flammable properties would be efficient for practical applications such as CO 2 sequestration using hydrates.

In order to evaluate hydrate-based desalination (HBD), experiments with seawater samples were carried out at various conditions (i.e. hydraulic pressure, washing step, and hydrate-forming gas). Before and after the hydrate process, cations (Na+, K+, Mg2 +, Ca2 +, and B3 +) and anions (Cl− and SO42 −) were analyzed by inductively coupled plasma atomic emission spectroscopy (ICP-AES) and ion chromatography (IC). In a single stage of CO2 hydrate process without any pretreatment, 71%–94% of each cation was removed in the following order: K+ > Na+ ≈ Mg2 + ≈ Ca2 + > B3 + and 73%–83% of each anion was removed. When the brines on the surface of hydrate pellets were removed, the ion removal efficiency increased above 4%. It was also found that the desalting efficiency depended on the hydrate-forming gas (CO2 > CH4) and the hydraulic pressure (6–10 MPa) to produce hydrate pellets. In this study, the removal efficiency of cations and anions in a real seawater sample using HBD processes were reported for the first time.

The characteristics of methane–propane hydrate crystal growth on the surface of gas bubble in pure water were investigated using optical microscope and compared with those in aqueous solutions of sodium dodecyl sulfate (SDS) or poly-N-vinylcaprolactam (PVCap). Most of morphology works in literature mainly focused on the hydrate crystal growth at the gas/water interface or surface of water droplets. However, this study monitors crystal growth at the bubble surface. In the case of pure water, smooth hydrate film was formed initially and the film surface on the bubble became rough as experiment proceeded. It was also observed that the hydrate crystals developed as the dendritic shape from the surface of hydrate film. In the presence of SDS, drastic changes in morphology were observed in that smoke-like crystals appeared from the top of the bubble. Besides, the gas bubble was not fully covered by hydrate film when the SDS concentration increased. In the PVCap solution, seed-like or small spot of hydrate crystals occurred sparsely on the bubble surface and spread out the whole surface as experiment progressed. The experimental results showed that the presence of SDS or PVCap affect morphological characteristics of methane–propane hydrate crystal on the surface of gas bubble.

Spherical biphasic calcium phosphate (BCP) micro-granules consisting of hydroxyapatite (HAp) and tricalcium phosphate (TCP) were prepared using a rotary spray drying and sintering process. A significant phase transformation of TCP in BCP granules occurred according to the relative content of HAp and TCP in the BCP granules depending on the sintering temperature. The crystal growth of HAp in BCP was suppressed by a phase transformation of TCP with a change in the electron density distribution in a crystal unit cell. In addition, these progressive changes in the hydroxyl and phosphate group of BCP granules might be due to the phase transformation of TCP. Consequently, such structural changes in the BCP granules led to an unexpected change in granule size and micro-cracks on their surface at high temperatures.

Spherical tricalcium phosphate (TCP) micro-granules were prepared using a jet wheel impact atomization and calcination process. Spherical TCP granules were obtained which can exhibit phase transformation between the alpha and beta polymorphs as a function of the heating temperature. The progressive changes in the phosphate group of TCP granules were attributed to the phase transformation. Consequently, such structural changes in the TCP micro-granules can be used to control the dissolution and degradation of TCP through the controlled density and microporosity of the micro-granules.

In-depth understanding of the CH4 hydrate formation and decomposition processes is essential for energy recovery as well as related transportation/storage technologies. Raman spectroscopy is well suited for hydrate studies of aqueous-hydrate conditions, because it is not susceptible to interference from aqueous environments. In order to obtain more specific and ongoing information on the CH4 hydrate formation and dissociation, two different in-situ Raman spectroscopies with specially designed fiber-optic probes were used in a semi-batch stirred reactor (total volume 365 mL). With these arrangements, it was possible to obtain macroscopic (gas uptake, releasing, CH4 solubility) and microscopic (structural, cage occupancy, water structure) data simultaneously during CH4 hydrate formation and decomposition. Based on in-situ Raman observations, we are able to determine the time-dependent encapsulation of CH4 in large and small cage through hydrate formation and decomposition. In all experiments, the Raman intensity of the OH-stretching band (3000–3800 cm−1) was significantly reduced or increased at the point where hydrates were formed or dissociated, which is expected to provide valuable information for further hydrogen-bond research including hydrate study. In addition, in-situ Raman spectroscopy was used to determine the concentration of dissolved CH4 under hydrate formation/decomposition conditions and the results were in good agreement with experimental data in the literature.

Many researches have been carried out to reduce and/or to capture the major global warming gases. Especially, the hydrate formation mechanisms were intensively investigated for carbon dioxide sequestration and storage process applications. In this study, the characteristics of film-type crystal growth mechanism of carbon dioxide hydrate were comprehensively examined. Carbon dioxide hydrate crystal was formed in semi-batch type stir reactor at various pressure conditions while the temperature was fixed to be constant to reduce and minimize the guest gas solubility effects. A supply gas composition was 99.999 % of Carbon dioxide, the observation data was collected by optical microscope adopted CCD camera (Nikon DS-5M/Fi1/2M-U2). This study revealed that the guest gas pressure changes significantly altered the crystal growth mechanism and film growth rate of carbon dioxide hydrate crystal. The critical pressure of the carbon dioxide hydrate of crystal growth mechanism change was found to be 2.0 MPa. The capillary force and gas concentration gradient also significantly changed the film-type crystal growth mechanism of carbon dioxide hydrate crystal.

Natural gas hydrates are solid hydrogen-bonded water crystals containing small molecular gases. The amount of natural gas stored as hydrates in permafrost and ocean sediments is twice that of all other fossil fuels combined. However, hydrate blockages also hinder oil/gas pipeline transportation, and, despite their huge potential as energy sources, our insufficient understanding of hydrates has limited their extraction. Here, we report how the presence of amino acids in water induces changes in its structure and thus interrupts the formation of methane and natural gas hydrates. The perturbation of the structure of water by amino acids and the resulting selective inhibition of hydrate cage formation were observed directly. A strong correlation was found between the inhibition efficiencies of amino acids and their physicochemical properties, which demonstrates the importance of their direct interactions with water and the resulting dissolution environment. The inhibition of methane and natural gas hydrate formation by amino acids has the potential to be highly beneficial in practical applications such as hydrate exploitation, oil/gas transportation, and flow assurance. Further, the interactions between amino acids and water are essential to the equilibria and dynamics of many physical, chemical, biological, and environmental processes.

Gas hydrates are solid crystal structures formed by enclathration of gaseous guest species into 3-dimensional lattice structure of hydrogen-bonded water molecules. These compounds can be potentially used as an energy storage/transportation medium because they can hold a large amount of gas in a small volume of the solid phase. In addition, huge amount of natural gas, buried in seabeds or permafrost region in the form of the solid hydrate, is regarded as a future energy source. In this study, synthesized natural gas, whose composition is 90.0 mol% of methane, 7.0 mol% of ethane, and 3.0 mol% of propane, was used to identify formation behaviors of natural gas hydrates for the purpose of applying the gas hydrate to a storage/transportation medium of natural gas. According to the experimental results obtained by means of the solid-state NMR and high-resolution powder XRD methods, it is found that formed natural gas hydrates have crystal structure of the structure-II hydrate, and that methane occupies both small and large cages, while the others only occupy large ones. In addition, both the NMR spectroscopy and the gas chromatograph showed that there exists preferential occupation among the natural gas components during the hydrate formation. Compositional changes after the hydrate formation revealed that the preferential occupation is in order of propane, ethane, and methane (propane is the most preferential guest species when forming natural gas hydrates).

Nanosized TiO2-SiO2 particles were prepared by controlled hydrolysis of titanium tetraisopropoxide (TTIP) and tetraethylorthosilicate (TEOS) in microemulsions stabilized by anionic surfactants. Anionic surfactants ammonium carboxylate perfluoropolyether (PFPE-NH4) and sodium bis (2-ethylhexyl) sulfosuccinate (AOT) were used for formation of stabilized microemulsions in the W/C and W/O systems, respectively. The physical properties of the prepared particles have been investigated by TG-DTA, FT-IR, XRD and HRTEM. It is shown that the XRD pattern of the TiO2-SiO2 particles dried at 105 °C without calcination indicates amorphous. The particles calcined at 500 °C were identified as nanocrystalline anatase regardless of TTIP/TEOS molar ratio. The crystallite size of prepared particles decreased with increasing the silica content. From FT-IR analysis, the band for Ti-O-Si vibration was observed. The micrographs of HRTEM shown that the TiO2-SiO2 nanoparticles have a spherical morphology with a narrow size distribution and then the lattice fringe was 3.5 Å, which corresponds to the lattice spacing of (101) plane in the anatase phase.

In this study, we investigated the effect of tetra-n-butyl ammonium bromide (TBAB) on separation and/or collection of CO2 from CO2/H2 (40:60) gas mixture via hydrate crystallization. The phase equilibrium conditions shifted to milder conditions as increasing the amount of TBAB additive up to 3.0 mol%. The existence of the critical concentration of the additive effects on the phase equilibrium conditions was also observed. The hydrate formation rate in 1.0 mol% TBAB solution showed the highest value while the hydrate formation rate in 3.0 mol% TBAB solution showed the lowest value. Raman analyses revealed that only CO2 gas molecules enclathrated under experimental conditions carried out in this study. The phase equilibrium temperature of CO2–H2 (40:60) mixture gas hydrate systems with TBAB additive located in the range of between 283 and 290 K at the integrated gasification combined cycle (IGCC) process pressure range of 2.5–5.0 MPa. This study provides the potential of hydrate process to separate the CO2 gas from CO2–H2 (40:60) mixture gas in IGCC process without significantly lowering the processing temperature.

This study aims to examine the thermodynamic feasibility of separating sulfur hexafluoride (SF(6)), which is widely used in various industrial fields and is one of the most potent greenhouse gases, from gas mixtures using gas hydrate formation. The key process variables of hydrate phase equilibria, pressure-composition diagram, formation kinetics, and structure identification of the mixed gas hydrates, were closely investigated to verify the overall concept of this hydrate-based SF(6) separation process. The three-phase equilibria of hydrate (H), liquid water (L(W)), and vapor (V) for the binary SF(6) + water mixture and for the ternary N(2) + SF(6) + water mixtures with various SF(6) vapor compositions (10, 30, 50, and 70%) were experimentally measured to determine the stability regions and formation conditions of pure and mixed hydrates. The pressure-composition diagram at two different temperatures of 276.15 and 281.15 K was obtained to investigate the actual SF(6) separation efficiency. The vapor phase composition change was monitored during gas hydrate formation to confirm the formation pattern and time needed to reach a state of equilibrium. Furthermore, the structure of the mixed N(2) + SF(6) hydrate was confirmed to be structure II via Raman spectroscopy. Through close examination of the overall experimental results, it was clearly verified that highly concentrated SF(6) can be separated from gas mixtures at mild temperatures and low pressure conditions.

In this study, gas hydrate from CO 2 /H 2 gas mixtures with the addition of tetrahydrofuran (THF) was formed in a semi-batch stirred vessel at various pressures and temperatures to investigate the CO 2 separation/recovery properties. This mixture is of interest to CO 2 separation and recovery from Integrated Gasification Combine Cycle (IGCC) power plants. During hydrate formation the gas uptake was determined and composition changes in the gas phase were obtained by gas chromatography. The impact of THF on hydrate formation from the CO 2 /H 2 was observed. The addition of THF significantly reduced the equilibrium formation conditions. 1.0 mol% THF was found to be the optimum concentration for CO 2 capture based on kinetic experiments. The present study illustrates the concept and provides thermodynamic and kinetic data for the separation/recovery of CO 2 (pre-combustion capture) from a fuel gas (CO 2 /H 2 ) mixture.

gas has been widely used in many industrial fields as insulating, cleaning and covering gases due to its outstanding arc-extinguishing and insulating properties. However, global warming potential of gas is 23,900 times more than that of and it remains in the air during 3,200 years. For these reason, technological and economical effects could be expected for the separation of from gas mixtures by hydrate forming process. In this study, we carried out morphological studies for the hydrate crystal to understand its formation and growth mechanisms. hydrate film was initially formed at the interfacial boundary between gas and liquid regions, and then subsequent dendrite crystals growth was observed. The dendrite crystals grew to the direction of gas region probably due to the guest gas concentration gradient. The detailed growth characteristics of hydrate crystals such as nucleation, migration, growth and interference were discussed in this study.

Sulfur hexafluoride (SF6), whether pure or mixed with inexpensive inert gas, has been widely used in a variety of industrial processes, but it is one of the most potent greenhouse gases. For this reason, it is necessary to separate and/or collect it from waste gas streams. In this study, we investigated the pure SF6 and SF6-N2 mixture gas hydrates formation equilibrium aswell asthe gas separation efficiency in the hydrate process. The equilibrium pressure of SF6-N2 mixture gas was higher than that of pure SF6 gas. Phase equilibrium data of SF6-N2 mixture gas was similar to SF6 rather than N2. The kinetics of SF6-N2 mixture gas was controlled by the amount of SF6 at the initial gas composition as well as N2 gas incorporation into the S-cage of structure-II hydrate preformed by the SF6 gas. Raman analysis confirmed the N2 gas incorporation into the S-cage of structure-II hydrate. The compositions in the hydrate phase were found to be 71, 79, 80, and 81% of SF6 when the feed gas compositions were 40, 65, 70, and 73% of SF6, respectively. The present study provides basic information for the separation and purification of SF6 from mixed SF6 gas containing inert gases.

The influence of the kinetic inhibitor poly( N -vinylpyrrolidone) or PVP on hydrate methane/propane hydrate formation was studied in pre-saturated liquid water with and without the presence of heptane under different undercooling conditions. It was found that when the inhibitor concentration was 0.1 wt%, hydrate formation started as a film at the gas/water interface similar to the crystal behavior without inhibitor. When the inhibitor concentration was 0.5 wt% hydrate formation started at the wall above the gas/water interface and the hydrate film at the gas/water interface was observed as well. However, for inhibitor concentration 1.0 wt%, the hydrate started forming from water droplets attached to the wall above the gas/liquid interface and grew catastrophically. When the inhibitor concentration was 0.1 wt% and undercooling was 13.7 or 8.1 K whiskery or fiber-type hydrate crystals, respectively, were seen within the liquid pool. This morphology was not observed in the absence of PVP. When inhibitor concentration was 0.5 or 1.0 wt% or undercooling was 3.2 K, there was no crystal growth within the liquid pool. Floating crystals were also observed, but were needle-type and thus different from the equiaxed floating crystals found in the system without the inhibitor.

This work investigated the kinetic inhibiting effect of a number of cationic starches in hydrate formation experiments with methane and methane/ethane and methane/propane gas mixtures. The starches were found to exhibit a very weak inhibiting effect except for tapioca starch which increased the induction time (delay of onset of crystallization) by an order of magnitude. The addition of polyethylene oxide (PEO) was found to further enhance the performance of tapioca starch as well as some of the other starches. Finally, the presence of tapioca starch and PEO was found to suppress the memory effect. The results were interpreted based on a mechanism proposed by Zeng et al. [2006a. Effect of antifreeze protein on nucleation, growth and memory of gas hydrates. A.I.Ch.E. Journal 52(9), 3304–3309; 2006b. Effect of antifreeze proteins on the nucleation, growth and the memory during tetrahydrofuran clathrate hydrate formation. Journal of the American Chemical Society 128, 2844–2850] whereby the starches interfere with nucleation through interactions with heterogeneous nucleation sites.

Stable metallic Cu/Zn nanoparticles were prepared in the base oil phase by hydrothermal method. The physical properties, such as crystal structure, crystallite size and crystallinity according to synthesis conditions have been investigated by XRD, FT-IR and TEM. In addition, 4-ball test has been performed in order to investigate the frictional wear properties of prepared nanosized Cu/Zn particles. The peaks of the X-ray diffraction pattern indicate that the particle size was very small and crystallinity of Cu/Zn particles was good. The micrographs of TEM showed that nanosized Cu/Zn particles possessed a spherical morphology with a narrow size distribution. The crystallite size of the Cu/Zn particles synthesized in base oils was 23-30 nm. It was found that the antiwear capacity increases with increasing Cu/Zn concentration. When the concentration of Cu/Zn was 5.0 wt%, the wear scar diameters was 0.38 mm.

Methane-propane clathrate hydrate crystal growth within an enclosure partially filled with liquid water was examined under different undercooling conditions both with and without the presence of n-heptane. Water saturated with guest gas was rapidly undercooled and maintained at constant temperature. The growth of the hydrate phase always started with the formation of a film at the upper surface of the liquid water pool. The visual observations using a microscope revealed detailed features of crystal nucleation, migration, and growth occurring within the water pool. In all experiments, hydrate crystal growth was initiated by the formation of hydrate film at the interface between liquid water and the adjacent gas or n-heptane layer. Hydrate crystals were then observed to grow downward from the film. Undercooling was found to be a key parameter to control the morphology of hydrates growing underneath the hydrate film as it influences the growth rate and configurations of crystals. Moreover, a number of small crystals were seen in the water ascending toward the hydrate film. The evolution of the shape of these crystals was monitored. These crystals were octahedral or triangular or hexagonal platelets. Finally, the role of constitutional undercooling and the memory of the water to the observed crystal growth are discussed.

Gas hydrate formation and decomposition on water droplets using an 89.4% methane—10.6% ethane mixture, and a 90.1% methane—9.9% propane mixture were carried out in a new apparatus suitable for morphology studies. As expected the induction time was found to be much shorter when the water had hydrate memory. All droplets nucleated simultaneously and the droplet size and shape had no noticeable effect on induction time and macroscopic crystal growth morphology for hydrates from the methane–ethane mixture. However, the surface of the hydrate crystals from methane–propane had a “hairy-like” appearance which changed to a smooth surface over time. Moreover, the smaller droplets during hydrate reformation showed an extensive hydrate growth and looked like snow-flakes. Sequential pictures generated by time-lapse videos showed that the time required for hydrate to cover the water droplet surface ranged from 10 to 23 s and was shorter when there was gas-phase agitation (mixing). The growth is postulated to occur in two stages. The first stage lasts about 10–23 s and growth takes place laterally. Growth takes place at the hydrate/gas and the hydrate/water interfaces during the second stage. The implication of the findings for process design of hydrate formation vessels is also discussed.

This study investigates the hydrate inhibition performance of monoethylene glycol (MEG) with poly(vinylcaprolactam) (PVCap) for retarding the hydrate onset as well as preventing the agglomeration of hydrate particles. A high-pressure autoclave was used to determine the hydrate onset time, subcooling temperature, hydrate fraction in the liquid phase, and torque changes during hydrate formation in pure water, 0.2 wt % PVCap solution, and 20 and 30 wt % MEG solutions. In comparison to water with no inhibitors, the addition of PVCap delays the hydrate onset time but cannot reduce the hydrate fraction, leading to a sharp increase in torque. The 20 and 30 wt % MEG solutions also delay the hydrate onset time slightly and reduce the hydrate fraction to 0.15. The addition of 0.2 wt % PVCap to the 20 wt % MEG solution, however, delays the hydrate onset time substantially, and the hydrate fraction was less than 0.19. The torque changes were negligible during the hydrate formation, suggesting the homogeneous dispersion of hydrate particles in the liquid phase. The well-dispersed hydrate particles do not agglomerate or deposit under stirring. Moreover, when 0.2 wt % PVCap was added to the 30 wt % MEG solution, no hydrate formation was observed for at least 24 h. These results suggest that mixing of MEG with a small amount of PVCap in underinhibited conditions will induce the synergistic inhibition of hydrate by delaying the hydrate onset time as well as preventing the agglomeration and deposition of hydrate particles. Decreasing the hydrate fraction in the liquid phase might be the reason for negligible torque changes during the hydrate formation in the 0.2 wt % PVCap and 20 wt % MEG solution. Simple structure II was confirmed by in situ Raman spectroscopy for the synergistic inhibition system, while coexisting structures I and II are observed in 0.2 wt % PVCap solution.

A new apparatus employing a modular, mechanically agitated gas-inducing crystallizer is used to demonstrate the capture of CO2 via hydrate crystallization. The crystallizer enhances the contact of hydrate forming gases with water and thus the rate of hydrate crystallization increases. Flue gas (CO2/N2) and fuel gas (CO2/H2) mixtures were used to represent post- and precombustion capture. A comparison between the rates of hydrate formation in different crystallizers is presented by defining a metric called the normalized rate of hydrate formation. The gas uptake and the separation efficiency for the fuel and flue gas mixtures were found to be greater compared to the results obtained in a smaller scale stirred tank reactor ( Kumar et al., 2009c , Linga et al., 2008 ). The gas uptake and CO2 recovery for flue gas mixture in the presence of THF obtained in this work was higher than that reported in the literature with tetra-n-butyl ammonium bromide and tetra-n-butyl ammonium fluoride ( Fan et al., 2009 , Li et al., 2009 ). Although hydrate crystallization is able to capture CO2, the power required for mechanical agitation was found to be very significant. If the hydrate process is to be used industrially then hydrate crystallization must be carried out without mechanical agitation.

In the present study, we examined the active role of porous silica gels when used as natural gas storage and transportation media. We adopted the dispersed water in silica gel pores to substantially enhance active surface for contacting and encaging gas molecules. We measured the three-phase hydrate (H)-water-rich liquid (L(W))-vapor (V) equilibria of C(2)H(6) and C(3)H(8) hydrates in 6.0, 15.0, 30.0, and 100.0 nm silica gel pores to investigate the effect of geometrical constraints on gas hydrate phase equilibria. At specified temperatures, the hydrate stability region is shifted to a higher pressure region depending on pore size when compared with those of bulk hydrates. Through application of the Gibbs-Thomson relationship to the experimental data, we determined the values for the C(2)H(6) hydrate-water and C(3)H(8) hydrate-water interfacial tensions to be 39 +/- 2 and 45 +/- 1 mJ/m(2), respectively. By using these values, the calculation values were in good agreement with the experimental ones. The overall results given in this study could also be quite useful in various fields, such as exploitation of natural gas hydrate in marine sediments and sequestration of carbon dioxide into the deep ocean.

The emission of carbon dioxide from the burning of fossil fuels has been identified as a major contributor to green house emissions and subsequent global warming and climate changes. For these reasons, it is necessary to separate and recover CO gas. A new process based on gas hydrate crystallization is proposed for the CO separation/recovery of the gas mixture. In this study, gas hydrate from CO /H gas mixtures was formed in a semi-batch stirred vessel at a constant pressure and temperature. This mixture is of interest to CO separation and recovery in Integrated Coal Gasification (IGCC) plants. The impact of tetrahydrofuran (THF) on hydrate formation from the CO /H was observed. The addition of THF not only reduced the equilibrium formation conditions significantly but also helped ease the formation of hydrates. This study illustrates the concept and provides the basic operations of the separation/recovery of CO (pre-combustion capture) from a fuel gas (CO /H ) mixture.

[ ] gas has been widely used as an insulating, cleaning and covering gas due to its outstanding insulating feature and because of its inert properties. However, the global warming potential of gas is extremely high relative to typical global warming gases such as , CFCs, and . For these reasons, it is necessary to separate and collect waste gas. In this study, the effects of a surfactant (Tween) on the formation rate of gas hydrates were investigated. The gas hydrate formation rate increased with the addition of Tween and showed a nearly 6.5 times faster hydrate formation rate with an addition of 0.2 wt.% Tween compared to an addition of pure water. This is believed to be due to the increased solubility of gas with the addition of the surfactant. It was also found that gas hydrate in the surfactant solution showed two-stage hydrate formation rates with a formation rate that increased rapidly in the 2nd stage.