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Ambarticus myanmaricus gen. et sp. nov. is described from mid-Cretaceous amber of Myanmar based on examination of a single female specimen, and represents the unique taxon inclusion of fossils of the family Dytiscidae (Coleoptera: Adephaga) from Oriental Region. A new tribe, Ambraticini trib. nov. is established. The new taxon is assigned to subfamily Dytiscinae. This description represents one of a limited number of diving beetle taxa described from fossiliferous amber and is currently the oldest known fossil assigned to Dytiscinae. Key morphological characters of the new taxon are illustrated, and compared with tribes of Dytiscinae.

The decomposition behaviors of methane hydrate below the ice melting point in porous media with different particle size and different pore size were studied. The silica gels with the particle size of 105–150 μm, 150–200 μm and 300–450 μm, and the mean pore diameters of 12.95 nm, 17.96 nm and 33.20 nm were used in the experiments. Methane recovery and temperature change curves were determined for each experiment. The hydrate decomposition process in the experiments can be divided into the depressurization period and the isobaric period. The temperature in the system decreases quickly in the depressurization process with the hydrate decomposition and reaches the lowest point in the isobaric period. The hydrate decomposition in porous media below ice-melting point is very fast and no self-perseveration effect is observed. The hydrate decomposition is influenced both by the driving force and the initial hydrate saturation. In the experiments with the high hydrate saturation, the hydrate decomposition will stop when the pressure reaches the equilibrium dissociation pressure. The stable pressure in the experiment with high hydrate saturation exceeds the equilibrium dissociation pressure of bulk hydrate and increases with the decrease of the pore size.

Natural gas hydrate (NGH) is considered as an alternative energy resource in the future as it is proven to contain about 2 times carbon resources of those contained in the fossil energy on Earth. Gas hydrate technology is a new technology which can be extensively used in methane production from NGH, gas separation and purification, gas transportation, sea–water desalination, pipeline safety and phase change energy storage, etc. Since the 1980s, the gas hydrate technology has become a research hotspot worldwide because of its relatively economic and environmental friendly characteristics. China is a big energy consuming country with coal as a dominant energy. With the development of the society, energy shortage and environmental pollution are becoming great obstacles to the progress of the country. Therefore, in order to ensure the sustainable development of the society, it is of great significance to develop and utilize NGH and vigorously develop the gas hydrate technology. In this paper, the research advances in hydrate-based processes in China are comprehensively reviewed from different aspects, mainly including gas separation and purification, hydrate formation inhibition, sea–water desalination and methane exploitation from NGH by CH4–CO2 replacement. We are trying to show the relevant research in China, and at the same time, summarize the characteristics of the research and put forward the corresponding problems in a technical way.

Clathrate hydrate is a kind of environment-friendly material for storing hydrogen under a certain condition of temperature and pressure. In this work, tetrahydrofuran aqueous solution with concentration of 3.0 mol% was adopted to investigate hydrogen storage process. Moreover, thermal property of hydrate was measured by high pressure differential scanning calorimeter, and mechanism of hydrate-based hydrogen storage was studied by in-situ Raman. Especially, gas uptake, morphology and structures change of compounds from gas/liquid interface towards hydrate layer were monitored in the process of hydrate formation. Thermal experiments illustrate that thermal data for tetrahydrofuran-hydrogen binary hydrate under extra high pressures could be effectively obtained by high pressure differential scanning calorimeter, moreover, memory effect shows no influence on thermal state of hydrate but weakly affects water aggregation. Kinetics and microscopic experiments illustrate that a special pressure drop and some tetrahydrofuran hydrates with unstable structure can be found under conditions of 273.15 K and 14.53 MPa. The pressure drop involves into hydrogen molecules tunneling movement among hydrate cavities. Moreover, hydrogen molecules show a positive effect on binary hydrate stability. Further, the density of 1.875 g/Lwater shows that hydrogen storage process via clathrate hydrate is an excellent method to store hydrogen.

Herein, a new superfine nano Pd/Ni-Mo2C (2–6 nm) catalyst is developed via a facile, alkali-induced self-assembly strategy. The catalyst exhibits excellent performance towards ethanol electro-catalytic oxidation in alkaline system, with an activity of 2832.2 mA/mgPd and a residual current density of 447.8 mA/mgPd, which is 2.6 and 4.7 times enhancements compared with the commercial 10% Pt/C catalyst (1107.6 mA/mgPd and 96.1 mA/mgPd).

The methane hydrate formation and the methane hydrate dissociation behaviors in montmorillonite are experimentally studied. Through the analyses of the microstructure characteristic, the study obtains the porous characteristic of montmorillonite. It is indicated that methane hydrate in montmorillonite forms the structure I (sI) crystal. Meanwhile, molecular dynamics simulation is carried out to study the processes of the methane hydrate formation and the methane hydrate dissociation in montmorillonite. The microstructure and microscopic properties are analyzed. The methane hydrate formation and methane hydrate dissociation mechanisms in the montmorillonite nanopore and on the montmorillonite surface are expounded. Combining the experimental and simulating analyses, the results indicate the methane hydrate formation and methane hydrate dissociation processes have little influence upon the crystal structure of porous media from either micro- or macro-analysis. It is beneficial to the fundamental researches on the exploitation and security control technologies of natural gas hydrate in deep-sea sediments.

Energy shortage and carbon emission reduction are the two big problems in the development of human society. The technologies involving CH4-CO2 binary hydrate is considered to be promising for CH4 recovery and carbon emission reduction. The DSC, Raman, FTIR, Cryo-SEM and PXRD are employed to investigate the thermal process, the micro structure and compositions of the CH4-CO2 hydrate formation and decomposition. The investigations reveal that there are not one kind of hydrate but rather multi-kinds of hydrates coexistence during the hydrate formation. The mechanism of gas hydrate formation could be considered as, under a certain condition, the component with lower enthalpy prior to entrap the cavities to stabilize the hydrate cages in the process of constructing hydrate cages by water molecules, and once the relevant cages are stabilized, the hydrates thereby exist. To fully disperse the oil additive (e.g. CP) into water can effectively improve the gas consumption and enhance CO2 separation efficiency in the process of CH4-CO2 binary hydrate formation. The methods presented here can also be employed for other fields such as hydrate-based sea-water desalination, CO2 separation and H2 purification from IGCC syngas, gas transportation, and other fields.

Hydrate-based carbon dioxide (CO2) capture and hydrogen (H2) purification is a promising technology in clean energy fields. In this work, in order to reveal the effect and mechanism of tetrahydrofuran (THF) on the hydrate-based CO2 separation from Integrated Gasification Combined Cycle (IGCC) syngas, the CO2/H2/THF hydrates formation processes were studied with and without memory effect. According to the pressure drop curves, there appear two pressure plateaus in the CO2/H2/THF hydrate formation processes. Furthermore, with the usage frequency of the THF solution increasing, the plateau effects are more ambiguous and difficult to be observed. It is interesting that the Raman spectra for CO2 and H2 molecules also reveal slim Raman shifts between the two different hydrate plateaus. According to the powder X-ray diffraction (PXRD) patterns, indeed, the detail Miller indices indicates that CO2/H2/THF hydrate mainly forms THF•16.8 H2O structure in the first plateau, while mainly forms THF•17 H2O structure in the second plateau. The reason for this phenomenon is mainly the influence of CO2, its large molecular size and the localized tension it causes in the water network of the small cages which can enhance the storage capability for the large cages of THF hydrate. The experimental results illustrate that the highest Split fraction (S.Fr) is 69.02% obtained at 6 MPa/284.85 K (memory effect), and this work highlights that the memory solution are more suitable for industrial application.

In this work, the effect of fulvic acid (FA) concentration and memory effect on methane hydrate formation and dissociation in mixed sand-clay porous media were studied at 15 MPa and 8.0 oC. The mixed sand-clay porous media were prepared based on the marine sediments composition of the South China Sea. The results demonstrated that the hydrate formation in porous media includes rapid formation stage and slow formation stage, and there is no obvious difference in fresh and memory solution systems. The low mass concentration of FA (2.0 wt.% FA) has a slightly acceleration effect for the hydrate formation and the hydrate formation time is shorter than that in pure water system. The high mass concentration of FA evidently inhibit the hydrate formation, especially for the 10.0 wt.% FA, the amounts of hydrate formation is significantly less than that in pure water system. The FA solutions can significantly accelerate the hydrate dissociation, and the gas released rate from hydrate increases with the increase of FA concentration. In addition, the gas recovery rate can be improved effectively by high concentrated FA.

In this work, the temperature characteristics of hydrate slurry related to transition heat in the cyclopentane (CP)/methane (CH 4 ) hydrate formation process were investigated. A crystallizer with a special heat-insulating layer of aerogel and vacuum insulating layer was designed to hold the transition heat, and the hydrate slurry and the residual water could be heated. Temperatures were measured in the process of the hydrate formation under the conditions of 4 ℃and 8.5 MPa. The highest temperature of hydrate slurry (T h ) and the maximum temperature difference (∆T max ) between T h and the initial temperature were adopted to evaluate the influence of different conditions on the temperature characteristics during the hydrate formation. The experimental results indicated that the hydrate formation interface and thermal interface obviously moving from the initial gas/CP interface towards CP/water interface. The hydrate slurry could be heated up to 23.47 ℃ and the ∆T max of 19.47 ℃ could be obtained, and such high heat could be effectively collected and used elsewhere.

Simultaneously capture of CO2 and H2S is vital for obtaining clean fuels from fossil fuels. This work proposes the hydrate formation process for simultaneously capture of CO2 and H2S from simulated syngas with new synergic additives. The synergic additives comprises acidic gas solvent (tetramethylene sulfone (TMS)) and traditional hydrate promoter (tetra-n-butyl ammonium bromide (TBAB)). The effect of the synergic additives was evaluated based on kinetic curves, separation efficiency and gas selectivity. The results show that, with the help of the synergic additives, both CO2 or H2S could be simultaneously captured from the simulated syngas by the hydrate formation process. Furthermore, the synergic additives could not remarkably accelerate the formation rate and improve the gas storage capacity for the simulated syngas hydrate, but also enhance the selectivity of CO2 or H2S in the hydrate process.

Nanoporous materials can significantly promote the formation process of gas hydrate by reducing the barrier of physical chemistry. In this work, the CO2/H2/H2O hydrates formation with tetra-n-butyl ammonium bromide (TBAB) and nano Al2O3 or carbon nano tube (CNT) were studied and compared in term of kinetic curves. It was found that both TBAB-Al2O3 and TBAB-CNT could promote the CO2/H2/H2O hydrate formation process. Furthermore, compared with TBAB-Al2O3, TBAB-CNT has the better promotion effect on the CO2/H2/H2O hydrate formation process. It is interesting that the CO2/H2/H2O hydrate formation process with TBAB-Al2O3 represents reformation phenomenon. It possibly forms sI CO2/H2/H2O hydrate firstly and finally forms semiclathrate CO2/H2/H2O hydrate.

A novel hydrate drilling simulator was built to investigate the drilling process in the hydrate-bearing sediments. The simulator consists of a high pressure vessel, a drilling system, a drilling fluid injection system and a drilling fluid treatment system. The simulator can be used to simulate the drilling process in the hydrate reservoir. The drilling process in TBAB-hydrate-bearing sediments was experimentally studied and visually observed with different temperature of the drilling fluid. The TBAB-hydrate-bearing sediments were prepared by mixing the TBAB solution and quartz sands under the temperature of 4 ℃ in the high pressure vessel. The drilling simulation was carried out by keeping the environment temperature constant at 4 ℃. It was found that the temperature of the drilling fluid significantly affects the stability of the drill hole. The drill hole collapses obviously at the temperature of 8 ℃ of the drilling fluid.

Hydrate-based gas separation or storage has been proposed and developed as one of the most promising technologies due to the high efficiency and low cost, but promoters are crucial for the hydrate formation process. In this work, the CO2/H2/H2O hydrate formation processes with tetra-n-butyl ammonium bromide (TBAB), tetrahydrofuran (THF) and cyclopentane (CP) with or without memory effect were compared in terms of both kinetic curves and Raman spectrum, respectively. All the hydrates were formed with similar concentration at the same temperature and pressure with and without memory effect. It was found that, among the three additives with fresh water, THF has the best promotion effect on the hydrate formation rate while TBAB has the best promotion effect on the hydrate formation amount. Among the three additives with memory water, TBAB has the best promotion effect on both the hydrate formation rate and hydrate formation amount. Furthermore, the Raman spectrum reveals that the CO2 molecules are enclathrated in the S-cages of structure-II hydrate for the CO2/H2/H2O hydrate formed with THF or CP.

Significant challenges still remain in the development of suitable materials for storing hydrogen for practical applications. Clathrate hydrates, as a special inclusion compounds, could be tailored by changing the storage pressure and temperature to adapt ambient conditions. In this work, the hydrates were adopted to encage hydrogen in tetrahydrofuran (THF) aqueous solution with concentration of 3.0 mol%. The formation and dissociation behaviors were investigated by a high pressure micro-differential scanning calorimeter at the operating pressure of 18 MPa, 25 MPa and 34 MPa. Experimental results show that the memory water only affects the hydrate formation behavior instead of the hydrate dissociation behavior. The dissociation temperature of the THF-H2 hydrate increases with the increase of the operating pressure, and its dissociation equilibrium data can be obtained. The dissociation temperatures of the THF-H2 hydrate are 9.26 ℃, 10.94 ℃ and 12.67 ℃ at the operating pressure of 18 MPa, 25 MPa and 34 MPa, respectively. It is fundamental for performing the kinetics and microscopic experiments.

Visual evidences to understand the interactions between hydrate decomposition and heat/mass transfer are currently lacking. This study proceeds from the hydrate morphology to visualize the interactions between depressurization-induced hydrate decomposition and heat/mass transfer from different scales. Reactor-scale hydrate distribution evolution shows that the dominant influencing factor of hydrate decomposition transforms from heat transfer to mass transfer. More importantly, pore-scale visual evidences suggest that the mass transfer of gas shows significant effects on hydrate morphology evolution. Specifically, the limited gas diffusion in liquid phase could lead to the hydrate morphology evolution from patchy pore-filling to “grain-bridging” during hydrate decomposition. The combination of grain-bridging hydrate together with the water layer that wraps the hydrate is termed as “hydrate bridge” in this work. It is also worth noting that the grain-bridging hydrate could accelerate fluid flow in pores according to our seepage simulation results. These findings provide visual evidences for variations in physical properties of hydrate-bearing sediments during hydrate decomposition. Since physical properties of hydrate-bearing sediments play important roles in hydrate decomposition, the hydrate morphology evolution characteristics analyzed here are valuable for hydrate exploitation in field tests.

New energy development and carbon emission reduction are two important issues of sustainable development for human beings. Hydrate-based methane - carbon dioxide (CH4-CO2) replacement is the promising technology for it can realize CH4 production from natural gas hydrate (NGH) and CO2 capture and sequestration (CCS) in the strata simultaneously and stably. This work reported the micro mechanism and the influence of the hydrate-based CH4-CO2 replacement by differential scanning calorimetry (DSC) measurements and in situ Raman spectroscopy measurements. It was found the replacement is affected by the potential energy of destruction ( E ped ) and the binding energy ( E b ). The replacement happens only when the E ped is larger than the E b . The concentration of CO2 around the hydrate is the controlling influence on the replacement. The higher the concentration of CO2, the greater the E ped , and the higher CH4 production efficiency.

The intermittent depressurization may sustain hydrate production. But its production features and influencing factors in the real setting have not been clear. Thus, the intermittent depressurization with the participation of the water layers was performed in the laboratory samples. The hydrate production features were studied from pressure changes, temperature changes, gas and water production, multi-phase flow, and residual hydrates. On the other hand, the influencing factors were analyzed from the back pressure, the recovered pressure, and the retarded temperature recovery. The results showed that gas and water production was increased by 44.05 % and 97.14 %, respectively. The abnormal depressurization, the fresh hydrate formation, and the retarded temperature recovery were observed. Moreover, hydrate dissociation and gas flow were weakened by the thickened water films around hydrate grains and the quick depressurization along with the preferential flow channels. Hence, residual hydrates accounting for 49.15 % were still found after the intermittent depressurization. Besides, the back pressure of 2.6 MPa increased gas production by 22.915 L; the recovered pressure of 3.92 MPa reduced water production by 47.85 %; the wait for temperature recovery increased hydrate dissociation rate of 15.29 %. This work may benefit the achievement of the sustainable hydrate production in actual hydrate reservoirs.

Memory effect of gas hydrate is a double-edged sword in hydrate-based application and natural gas hydrates exploitation. In this work, in order to acquire a comprehensive understanding of memory effect, we conduct a series of experiments on hydrate reformation and dissociation under different grain filling patterns and thermal history conditions. Experimental results reveal that the memory effect can not only shorten the induction time of hydrate nucleation but also significantly reduce the hydrate formation rate by enhancing the homogeneous distribution of gas hydrate in pores. The homogeneous hydrate distribution under memory effect has been further investigated and evaluated by the hydrate heterogeneity degree and dead-end porosity for the first time. More importantly, the decrease in heterogeneity degree and dead-end porosity driven by memory effect shows significant effects on hydrate dissociation behaviors. On the one hand, the improved homogeneous distribution of gas hydrate under memory effect impairs the heat transfer from the environment to hydrate-bearing sediments, thereby reducing the hydrate dissociation rate. On the other hand, the decreased dead-end porosity can lead to the expansion of fluid flow channels in hydrate-bearing sediments, thus increasing the hydrate dissociation rate. These findings are significant for efficient and secure gas production in field tests since the violent gas/water flow in reservoirs would lead to the rapid hydrate reformation during gas production from hydrate-bearing reservoirs.

A novel colorimetric immunoassay strategy is developed based on metal ion chelation-induced color generation and alkaline phosphatase(ALP)-catalyzed signal amplification. The intense purple-colored Cu(I)-bicinchoninic acid (BCA) complex is utilized as a promising chromogenic reporter for the visual ALP-linked immunoassay. In the presence of target, ALP is introduced to catalyze the cascade conversion of L-ascorbic acid 2-phosphate (AAO) to L-ascorbic acid (AA), which results in Cu2+ reduction to Cu+ and subsequently in situ formation of purple-colored Cu(I)-BCA complex. The complex is water-soluble and exhibits a strong absorbance at 562 nm due to the ligand-to-metal charge-transfer (LMCT). The absorbance value is in turn proportional to the level of target analyte. Based on this concept, an ALP-linked colorimetric immunoassay is established with Cu(II)-BCA mixture as a color developing reagent for rabbit IgG detection, achieving a linear range from 0.1 ng mL−1 to 25 ng mL−1 and a LOD of 0.05 ng mL−1. Its potentiality for practical application is also investigated by detection of a cancer biomarker, prostate specific antigen (PSA), in spiked human serum. A linear range from 0.5 ng mL−1 to 25 ng mL−1 and a LOD at 0.38 ng mL−1 are achieved, which is much lower than the cut-off value of PSA in human blood. The proposed method holds many advantages including low cost, good color stability, reliability and excellent compatibility with the existing ELISA platform, providing a promising colorimetric immunoassay platform for bio-chemical analysis in a variety of fields.

In order to study the mechanism of methane hydrate formation in porous media, the formation experiments of methane hydrate in porous media at the constant pressure were performed in the temperature range of 274.15–276.15 K and the pressure range of 5–8 MPa. The silica gels with the average pore diameters of 129.5, 179.6, and 332 A were used as the porous media for the experiments. The experimental results indicate that the final gas consumption increases with the increase of the formation pressure and the decrease of the formation temperature. Based on the shrinking core model, the reaction-controlled kinetic model and the diffusion-controlled kinetic model for hydrate formation in silica gels were built, respectively. The reaction-controlled kinetic model well fits the kinetic data in 129.5 A and 179.6 A silica gels, and the diffusion-controlled model well fits the kinetic data in 332 A silica gels with a relatively high regression coefficient (R2 > 0.99). The formation rate of the methane hydrate is controlled by the gas diffusion process in 129.5 A and 179.6 A silica gels, and is controlled by the reaction process in 332 A silica gels.

Fabrication of effective electrocatalysts combining two pure phases including carbide and phosphide with a certain proportion by the clean and simple strategies still remain a challenge. Here we synthesized tungsten carbide/tungsten phosphide-coated N-doped carbon (W 2 C/WP@NC) by one-step pyrolysis process without participation of PH 3 . In this synthesis process phosphotungstic acid, a heteropolyacid provided P and W atoms while 2,6-diaminopyridine, a heterocyclic compound with strong alkalinity acted as C and N source. 2,6-diaminopyridine was carefully chosen because it made a contribution to the complete decomposition of phosphotungstic acid where WO 4 2− and PO 4 3− groups were formed which both were essential to formation of WP phases. An overpotential of 83 mV which was required to achieve a current density of 10 mA cm −2 in 0.5 M H 2 SO 4 exhibited the high electrocatalytic activity of W 2 C/WP@NC catalyst in hydrogen evolution reaction (HER). The weight ratio of W 2 C to WP was calculated by Rietveld refinement and near edge X-ray absorption fine structure (XANES). W L 3 -edge XANES spectra of different samples confirmed that little amount of WP could tune the electron state on W species. The enhanced HER performance was attributed to the favorable electron distribution on W species in W 2 C/WP@NC which approached to the balance between H-atom adsorption and desorption.

A porous g-C3N4/TiO2 with hierarchical heterostructure has been successfully fabricated through a in situ assembling of small needle-like TiO2 on the surface of ultrathin g-C3N4 sheets. The ultrathin g-C3N4 sheets with carbon vacancies and rich hydroxyl groups were found to facilitate the nucleation and in situ growth of TiO2 and also to modulate the surface chemical activity of the g-C3N4/TiO2 hierarchical heterostructure. The as-designed photocatalytic heterojunction degraded Acid Orange with 82% efficiency after 10 min under simulated solar light, and possessed excellent cycle stability. Relative physical characterizations and photochemical experiments reveal that engineering the interface/surface of g-C3N4 plays a vital role in effectively constructing heterostructures of g-C3N4/TiO2, thus realizing efficient photoinduced electron-hole separation during photocatalytic process.

The research on the micro-mechanism and efficiency of CH4-CO2 replacement from natural gas hydrates are investigated in this work by a series of experiments with pure CO2, CO2/N2, CO2/H2 and CO2/He gas mixtures under 4.5 MPa and 274.0 K. In situ Raman and FTIR are employed to determine the micro structures and components of the hydrates. The results indicate the small gas molecules help to increase the rate of CH4-CO2 replacement, and adding H2 or N2 into the system has great effect on enhancing the CH4 exploitation efficiency as H2 or N2 molecules can weaken the van der Waals forces between CH4 molecule and hydrate crystal cave and further lead to the deformation of the hydrate cavities in the process. The Raman spectra illustrate no hydrate structure change exists in the replacement process, and the FTIR spectra illustrate the replacement can happen in both large and small cavities. The mechanism of CH4-CO2 replacement in the hydrate can be descripted as the introduction of CO2 breaks the balance of two phases of CH4 and CH4 hydrate, resulting in the deformation or dissociation of the CH4 hydrate, and finally forming CO2 hydrates with free water by the hydrate structure reconstitution.

Hydrate carbon dioxide (CO2) separation is a promising method for reducing carbon emission. In this work, water-solubility of tetrahydrofuran (THF) was added into water to generate the single gas/liquid interface. In order to understand hydrate nucleation and crystallization well, CO2 concentration in the residual gaseous phase was measured, morphology of the hydrate formation was filmed, and structure changes of compounds around the gas/liquid interface was monitored by in situ Raman spectrometer. Two groups of experiments were carried out at 274.15 K and 4.0 MPa in the systems with and without gas supply. The experimental results illustrate that hydrate formation is completed in 5 h according to CO2 concentration, gas consumption and morphology, however, the compound transition and hydrate crystallization are still in process from the microstructure point of view. For the system with gas supply, the hydrates initially occur in the gas/liquid interface due to stable gas flux in the boundray layer, where Raman spectra change regularly at the beginning. Such stable gas flux has a positive impact on changing water aggregation. This change of water aggregation benefits for the original structures in the process of hydrate nucleation. With the hydrate formation, the hydrate nucleation interface is moving from the gas/liquid interface towards the THF solution. Otherwise, for the system without gas supply, no obvious hydrate was observed in the gas/liquid interface, and Raman spectra around the interface change with the saltation from gaseous phase towards the THF solution. For the two systems, THF hydrates form prior to the multi-hydrates and keep forming, and both intensity of Raman peaks around the interfaces is the weakest.

Due to the huge reserves, natural gas hydrate is considered as a potential energy resource in future. Therefore, developing methods of gas recovery from hydrate reservoirs for commercial production are attracting extensive attention. In this work, hydrate dissociation and gas recovery from the gas-saturated and water-saturated hydrate accumulations are investigated in a pilot-scale hydrate simulator. Depressurization, thermal stimulation, and depressurization assisted thermal stimulation method are adopted in this work. Furthermore, the mechanisms of fluid flow and the heat transfer during hydrate dissociation in different hydrate accumulations are elucidated by large-scale experimental results. The experimental results indicate that the fluid flow mechanisms and the heat transfer characteristics during the gas recovery from hydrate reservoirs are greatly influenced by the initial water saturation. The Optimum gas production method is also different for different hydrate accumulations. The depressurization is optimized method for hydrate dissociation in the gas-saturated reservoir considered from the aspect of gas-water ratio. Thermal stimulation results in the lowest gas-water ratio and the lowest hydrate dissociation ratio, and is not effective for both the gas-saturated and water-saturated hydrate reservoir. The depressurization assisted thermal stimulation is the optimum method for the hydrate dissociation in the water-saturated sample.

Air pollution poses a serious threat to public health, especially in developing countries, and how to reduce it has gained great attention over the past decades. In this work, a hierarchical-structured composite, ultrafine TiO 2 encapsulated in a nitrogen-doped porous carbon framework, was fabricated and used as a photocatalyst to degrade ammonia gas. In addition, a gas sensor test system lined with a photocatalytic apparatus was proposed to estimate the degradation of ammonia gas, which allowed for facile in situ analysis and assessment of the photodegradation process of the toxic gas. Due to the large surface area, abundant pore structure, good gas adsorption property, extended light harvesting capacity and charge transfer capability of the nitrogen-doped porous carbon, the as-prepared ultrafine TiO 2 encapsulated in the nitrogen-doped porous carbon framework displayed excellent photocatalytic activity and degraded ammonia gas with 100% efficiency after only 5 min of light irradiation.

CO2 hydrates can be used for long term storage of CO2 in the deep ocean. Clay minerals are the most important components of the marine sediments. In this study, the formation behaviors of carbon dioxide hydrate in kaoline clay and bentonite clay with partially water saturated were studied in a closed system. The mass ratio of water to Kaoline and Bentonite clays is 20%. The experiments were carried out at the temperature of 279.15 K and the initial formation pressure range of 4.8-3.4 MPa. The liquefaction of the carbon dioxide was observed in the cooling process by setting the temperature of the water bath to the valued experimental temperature. The temperature in the crystallizer begins to rise quickly when the hydrate starts to form and then decreases gradually after reaching the highest value. For the experiments in kaoline clay, the temperature decreases gradually along with the equilibrium hydrate formation temperature, and the hydrate formation rate is controlled by the heat transfer process. The final conversion of the water to hydrate increases with the increase of the initial formation pressure and restrained by the equilibrium hydrate formation pressure. For the experiments in bentonite clay, the temperature during the hydrate formation is much higher than the equilibrium temperature for CO2 hydrate formation. The final pressure is much higher than the equilibrium pressure of CO2 hydrate, and increases with the increase of the initial formation pressure, indicating that the equilibrium pressure CO2 hydrate in bentonite clay is higher than the bulk CO2 hydrate.

The CO2 and SO2 capture from the simulated flue gas simultaneously by gas hydrate process were experimentally studied using tetra-n-butyl ammonium bromide (TBAB) as the hydrate formation promoter in this work. The effects of initial pressure, SO2 enrichment, the ratio of gas and liquid and TBAB concentration on CO2 and SO2 capture have also been studied. The results indicate that about 95% of SO2 in flue gas can be removed by gas hydrate capture process, but the vast majority of SO2 are captured by dissolution, and gas hydrate formation has very little effect on SO2 removal. SO2 enrichment in solution increases SO2 concentration in residual gas. The intial pressure, TBAB concentration and the ratio of gas and liquid volume has very small effect on SO2 capture, but have some effects on CO2 capture. Both the dissolution and hydrate formation have a role on CO2 capture. The CO2 concentration in residual gas reduces to about 8 mol% after the hydrate capture, and the S.Fr.CO2 reaches above 60%, and the S.F.CO2 reaches around 8.

The widespread need for carbon dioxide (CO2) and hydrogen sulfide (H2S) removal from potential gaseous fuel processes associated with upgrading of natural gas, biogas and landfill gas has led to a continuing interest in developing acid gas capture technologies. This work experimentally investigated the hydrate-based acidic gases (CO2 and H2S) capture for clean methane (CH4) fuel from biogas or natural gas with new synergic additives, which comprised physical gas solvent (TMS) and traditional hydrate promoter (TBAB). The results show that, with the synergic additives, the equilibrium hydrate formation pressures were moderated by about 90% relative to pure water, the selectivity of CO2 over CH4 and the selectivity of H2S over CH4 could achieve 18.56 and 11.38, respectively. Compared with TBAB, the synergic additives could improve the hydrate formation rate and the gas storage capacity by 149% and 84%, respectively. Furthermore, the promotion effect could be enhanced when with the help of H2S. It has been shown that CO2 and H2S could be synchronously captured through the hydrate formation process. It will be of importance to the fundamental study of enhancing gas hydrate formation process, and of practical significance for the hydrate-based application industry.

In order to study the formation behavior and controlling factor of methane hydrate in porous media, the formation experiments of methane hydrate in porous media at the constant pressure were carried out in the temperature range of 274.15 - 276.15 K and the pressure range of 6 - 8 MPa. The silica gels with the mean pore diameter of 12.95 nm, 17.96 nm and 33.20 nm were used as the porous media for the experiments. The experimental results indicated that the hydrate formation rate and the final gas consumption in porous media increases with the increase of the formation pressure, the decrease of the formation temperature. Based on the shrinking core model, the kinetic models for hydrate formation in silica gels under the reaction control and gas diffusion control were built, respectively. The methane hydrate formation is controlled by the gas diffusion process in silica gels with the mean pore diameter of 12.95 nm and 17.96 nm, and is controlled by the reaction process in silica gels with the mean pore diameter of 33.20 nm.

The integrated gasification combined cycle (IGCC) process, possessing high efficiency and environmental advantages, produces H 2 -rich syngas at high pressures. Acid gases carbon dioxide (CO 2 ) and hydrogen sulfide (H 2 S) are important and highly undesirable contaminants for syngas, and hydrate-based removal of these contaminants is environmentally attractive. This work experimental investigated the hydrate-based acidic gases (CO 2 and H 2 S) capture for clean hydrogen (H 2 ) fuel from syngas with new synergic additives, which comprise physical gas solvent (TMS) and traditional hydrate promoter (TBAB). The results show that, with the synergic additives, the equilibrium hydrate formation pressure can be moderated by about 90%, the gas selectivity can be improved by 50%, and the formation rate and gas storage capacity can also be improved. Furthermore, the promotion effect can be enhanced when with the help of H 2 S. It has been testified that CO 2 and H 2 S could be synchronously captured through the hydrate formation process.

Heterogenous distribution of gas hydrate in pores is the common characteristic of hydrate formation at various experimental scales. In this work, in order to fill the gap of defining the hydrate phase heterogeneity degree of hydrate-bearing sediments, we conduct a series of pore-scale experiments and simulations on hydrate formation behaviors and two-phase flow properties in hydrate-bearing samples by micro X-ray CT. The enhanced heterogeneous distribution of gas hydrate in small pores has been observed from experimental results, suggesting that the degree of hydrate heterogeneity in sandy or silty sediments may be underestimated. Therefore, the definition of hydrate heterogeneity degree is firstly proposed to characterize the hydrate phase heterogeneity of hydrate-bearing sediments. Additionally, we further investigate the effects of hydrate heterogeneity on fluid flow properties by introducing three types of hydrate distribution in porous media, which are homogeneous, clogging, and clumpy distribution. The clogging type of hydrate distribution could result in the sharply increased rate of permeability reduction, while the clumpy type of hydrate distribution might result in the declined rate of permeability reduction. Meanwhile, the heterogenous hydrate distribution leads to the rapid decrease in gas relative permeability. These findings are significant for laboratory studies and gas recovery in field tests.

The effect of hydrate distribution on the effective thermal conductivity changes of the actual hydrate-bearing sediments is uncertain. To define this effect, in the hydrate-bearing quartz sands, the effective thermal conductivity was measured by the transient hot-wire method, and hydrate distribution was analyzed by the electrical resistance changes. At first, the effective thermal conductivity changes were investigated from gas saturation, gas pressure, water saturation, water pressure, and temperature. Afterward, in three kinds of hydrate formation processes, compared with hydrate distribution, the changing trends of the effective thermal conductivity at five measuring points were analyzed. The results showed that the effective thermal conductivity was increased with decreasing gas saturation and increasing water saturation or water pressure, and impacted slightly by gas pressure and temperature. Moreover, at five measuring points, the non-uniform hydrate distribution caused different changing trends of the effective thermal conductivity during hydrate formation. In the excess-water setting, an increasing trend was only observed at some local measuring point. The decreasing trends at the most of the measuring points were governed by the reduced water distribution. But in the excess-gas setting, at the most of the measuring points, this increasing trend was observed and controlled by the enlarged hydrate distribution. Besides, for some actual sediments in the excess-water setting, hydrate distribution may be not the key factor of the effective thermal conductivity changes, and further studies were required. This research could offer some valuable reference to the thermal properties in the actual sediments.

Natural gas hydrates have attracted much attention in recent years. It is important to investigate the effects of gas occurrence pattern on hydrate growth habits since distribution and morphology characteristics of gas hydrates have significant effects on physical properties of hydrate-bearing reservoirs. In this work, the differences in distribution and morphology properties of gas hydrates under two gas occurrence patterns have been analyzed via the X-ray computed tomography for the first time. Experimental results reveal direct correlations between the hydrate growth habit and the gas occurrence pattern. In the presence of free gas, grain-attaching hydrates are formed at the arc-shaped contact surface of gas and water, and mass transfer at the gas-water interface is the key controlling factor in hydrate formation process. In the presence of dissolved gas, dispersed and dendritic hydrates are formed in liquid phase as the result of gas solubility change, and gas diffusion is the crucial factor that influences the growth habit and morphology of gas hydrates during hydrate formation from dissolved gas. Besides, the maximum saturation of dendritic hydrates formed from dissolved gas is limited by the gas solubility. These conclusions are valuable in the improvement of prediction accuracy of gas production from hydrate-bearing sediments.

In this work, the hydrate-based methane (CH4) separation from coal mine methane (CMM) gas mixture was carried out by bubbling with a scale-up equipment (SHW-II). The influences of gas/liquid volume ratios (0.25 and 0.60), gas bubble sizes (diameter: 20, 50 and 100 μm) and gas flow rates (7.50, 16.13 and 21.50 mL/min/L) on gas consumption and CH4 recovery were systematically investigated at 277.15 K and 1.50 MPa. The hydrate formation morphology was filmed by a camera and the hydrate structure was determined by powder X-ray diffraction (PXRD). Gas bubbles generated when gas mixture flowed into bulk solution through a bubble plate from the bottom of SHW-II. Initially, the gas hydrates formed at the bubble boundary and grew up as the shell around the bubble with the continuously rising of the gas bubble, and finally accumulated in the interface between the gaseous phase and solution. The experimental results showed that the THF/CH4/N2 hydrate in SHW-II presented structure II (sII). The gas/liquid volume ratio, gas bubble size and gas flow rate had influences on gas consumption and CH4 recovery. The increase of gas/liquid volume ratio resulted in the decrease of gas consumption and CH4 recovery, while the increase of gas flow rate caused the decrease of gas consumption. Both the maximum gas consumption and CH4 recovery were achieved at the gas bubble with diameter of 50 μm. The optimal operating condition for large-scale CH4 separation via clatharate hydrate was comprehensively defined as the gas/liquid volume ratio of 0.25, the gas bubble diameter of 50 μm and the gas flow rate of 16.13 mL/min/L at 277.15 K and 1.50 MPa.

The hydrate-based methane (CH 4 ) recovery from coal mine methane (CMM) gas using the bubble method was investigated with a set of scale-up equipment in this work. The gas bubble with different size was created by a bubble plate located on the bottom of the equipment. By the scale-up equipment, the hydrate formation and the hydrate shape were recorded by a video. With the gas bubble rising from the bottom to the top of the reactor, gas hydrate forms firstly at the bubble interface in liquid, then the hydrate gradually grows up and accumulates in the gas/liquid interface. The similar hydrate morphology was observed at the different bubble size and gas flow rate. The gas/liquid ratio, the bubble size and the gas flow rate have an obvious effect on the hydrate-based CH 4 recovery process. The experimental results illustrate that the gas/liquid ratio of 0.25, the gas bubble of 50 μm and the gas flow rate of 16.13 ml/min/L are optimal to recover CH 4 from CMM gas under the conditions of 277.15 K and 1.50 MPa.

The widespread need for the removal of carbon dioxide (CO 2 ) and hydrogen sulfide (H 2 S) from process gas streams associated with hydrogen synthesis plants, upgrading of natural gas, landfill gas recovery, and enhanced oil recovery has led to a continuing interest in developing acid gas separation technologies. This work experimental investigated the hydrate formation processes for capturing acidic gases (CO 2 and H 2 S) from mixture gas (biogas and natural gas) with a new synergic additive, which is composed physical gas solvent (TMS) and traditional hydrate promoter (TBAB). Based on the thermodynamic and kinetic studies, the results show that the hydrate formation process with the synergic additives can capture CO 2 and H 2 S synchronously. The synergic additives not only can considerably moderate the equilibrium hydrate formation conditions, but also make high selectivity of CO 2 and H 2 S over CH 4 during the hydrate formation process, and improve the formation rate and gas storage capacity through their excellent promote effect on the solubility and diffusivity of acidic gases. It will be of practical interest in relation to the fundamental study of enhancing gas hydrate formation and of potential importance for the industry application of gas hydrate.

BaSed on the hot brine in situ seafloor prepared for marine NGHs exploitation, the formation of hydrates and the characteristics of dissolved ions were investigated for the cyclopentane (CP)-methane-NaCl solution (3.5%) system. Both the gas consumption and the solution salinity influenced by two factors - the flow rate of gas (Q(g)) and the mass fraction of CP (M-CP)-were discussed. On one hand, the gas consumption went up at a lower Mcp (3.950 wt%) while dropped down at a higher M-CP (8.340 or 18.775 wt%) with the increase of Q(g). Nevertheless, higher mass fraction of CP behaved more favorable for the gas consumption. On the other hand, there would be a similar trend that the salinity of remaining liquid increased firstly and then decreased with the reaction time at any fixed Q(g) and M-CP, which might be attributed to the adsorption of Na+ and Cl- on the surface of hydrate. Furthermore, PXRD analysis of the hydrate was conducted to confirm this explanation. And it was confirmed that the ion of Na+ or Cl- did not play any role in the construction of hydrate cages. Meanwhile, CP was enclosed in large cavities (51264s) while CH4 was mainly enclosed in the small cavities (512). (C) 2016 Elsevier Ltd. All rights reserved.

The effective thermal conductivity changes in the sediments during depressurization are significant for hydrate exploitation. But these changes cannot be measured directly because of the unavailable stable conditions during depressurization. In this work, in order to form the stable conditions for the measurements, soaking was designed to stabilize temperature and pressure in the sample after depressurization. Afterward, the effective thermal conductivity changes were measured by the transient hot-wire method. To define reasons for these changes, gas-water-hydrate distribution was inferred by the electrical resistance changes. The effective thermal conductivity changes were further analyzed from initial hydrate saturation, back pressure, water-gas production ratio, and gas-water-hydrate distribution, respectively. The results showed that the effective thermal conductivity changes were involved with hydrate dissociation closely. The effective thermal conductivity was increased with increasing initial hydrate saturation and back pressure. Moreover, the effective thermal conductivity was increased by the enlarged water distribution at the early period of hydrate dissociation and decreased by the enlarged gas distribution at the late period of hydrate dissociation. Gas slippage effect and gas-water gravity differentiation played important roles in these gas-water redistribution in the sample. Meanwhile, the sandy grain rearrangement was inferred to improve the contact quality among grains and thus also increased the effective thermal conductivity. Additionally, although there was hydrate dissociation rate of 0.36% during the measurements, the trends of the effective thermal conductivity were not supposed to change. This work may offer some reference to understand the mechanisms of heat transfer in the sediments during depressurization.