Search

The cubic hydrate simulator (CHS) is used to study the methane hydrate production behaviors in porous media by the thermal stimulation with a five-spot well system. The hot water injection rates range from 10.0 to 40.0 ml/min. The thermal stimulation process is analyzed, and the conclusions are that the hydrate decomposition boundary moves from the central point to the surroundings gradually and finally covers almost the entire hydrate field in the CHS during the thermal stimulation process. The heat conduction plays a more significant role than the convection for the heat diffusion in the thermal stimulation process. The increasing injection rate of the hot water enhances the rate of hydrate decomposition, shortens the production time, and decreases the water production volumes, while it has little influence on the final gas production volumes. Furthermore, the change of the hot water injection rate (R-inj)has little influence on the final gas recovery, however, the higher R-inj leads to the higher average production rate and the lower energy efficiency. (C) 2013 Elsevier Ltd. All rights reserved.

The hydrate-based CO 2 (carbon dioxide) separation and capture from CO 2 /H 2 (hydrogen) gas mixtures with the different CO 2 concentrations is investigated in 0.29 mol% TBAB (tetra-n-butyl ammonium bromide) solution. Raman spectroscopic analysis is employed to determine the compositions of the mixed hydrates containing CO 2 , H 2 , TBAB and H 2 O (water). The phase equilibrium conditions shift to extreme conditions as decreasing CO 2 from 40.0% to 10.0% in the gas mixtures. At the temperature of 274.15 K and under driving force of 3.0 MPa, the hydrate formation induction time increases while the CO 2 recovery (or separation fraction) decreases with the decrease of CO 2 . Raman peaks for CO 2 gas shift to higher frequency side of 6–10 cm −1 as the CO 2 concentration turns from 40.0% to the range of 10.0–18.0%. Meanwhile, no Raman spectral signal is detected for H–H stretching vibration in the mixed hydrates.

Effects of diluents on premixed laminar dimethyl ether (DME)/air flames were studied experimentally and numerically. The results show that measurements and predictions in laminar burning velocities are in reasonably good agreement. Laminar flame speeds of DME mixtures decrease with the increase of dilution ratio. For a specific diluent ratio, suppression effect of diluent decreases in the order of carbon dioxide, nitrogen and argon. Influences of argon and nitrogen are mainly due to the increase of specific heat of the non-fuel gases in the mixture, and that of carbon dioxide is resulted from the combination effect of dilution and direct reaction. CO2 participating reaction, CO+OHCO2+H, competes for H radical in the chain branching reaction H+O2 O+OH. This competition decreases concentration of the radicals like H, O and OH, leading to a significant reduction in laminar burning velocity.

Tungsten carbide/titanium oxide (WC/titanium dioxide (TiO2)) particles are prepared by microwave-assisted heating in conjunction with ionic liquid and the subsequent reduction–carbonization. The platinum particles are loaded on the WC/TiO2 to prepare Pt-WC/TiO2. The electrocatalytic performances of the Pt-WC/TiO2 toward methanol oxidation are evaluated by cyclic voltammetry, chronoamperometry, and the CO stripping tests. It is found that electrocatalytic activity of Pt-WC/TiO2 is enhanced by adding ionic liquid (IL) during sample preparation. The results indicate that better performance toward methanol oxidation and higher tolerance to CO are achieved with an optimal addition of 1.5 ml 1-methyl-imidazoliumtetr-afluoroborate for preparing Pt-WC/TiO2. To investigate the function of IL, the phase structure and morphology of samples at different stages during preparation are examined by X-ray diffraction and transmission electron microscopy. Ionic liquid is found to act as not only a good solvent offering the excellent microwave absorption, but also a structure-directing agent to control the morphology and structure of sample, which affect the activity of the final catalysts.

Methane (CH4) hydrate dissociation and the mechanism by depressurisation are investigated by molecular dynamics (MD) simulation. The hydrate decomposition processes are studied by the vacuum removal method' and the normal method. It is found that the hydrate decomposition is promoted by depressurisation. The quasi-liquid layer is formed in the hydrate surface layer. The driving force of dissociation is found to be controlled by the concentration gradient between the H2O molecules of the hydrate surface layer and the H2O molecules of the hydrate inner layer. The clathrates collapse gradually, and the hydrate decomposes layer by layer. Relative to our previous MD simulation results, this study shows that the rate of the hydrate dissociation by depressurisation is slower than that by the thermal stimulation and the inhibitor injection. This study illustrated that MD simulation can play a significant role in investigating the hydrate decomposition mechanisms.

A self-assembly process prepared needle-like crystals at room temperature. Calcination and temperature-programmed carburization processes facilitated an evolution of the as-prepared crystals into hollow, needle-like mesoporous tungsten carbide (WC). This synthesized, large-sized (approximately 3 mm) WC exhibited a highly specific surface area (9.74 m2/g). Moreover, the mesopores were centered at 20.2 nm for its advanced formation, and these could further enlarge to 34.2 nm via direct carburization. The successful synthesis of the materials is associated with the formation of a pre-assembled precursor with increased volatilized components and needle-like structure. Various pore evolutions during the synthesizing processes were discussed to explain the formation of mesostructures. The H2 adsorption/desorption highly improves with the introduction of the mesoporous structure. The synthesized, needle-like WCs with mesoporous structure may be potential candidates for catalytic and adsorptive applications.

A complete set of scaling criteria for gas hydrate reservoir of five-spot well system case is derived from the 3D governing equations, involving the mass balance equation, the energy balance equation, the kinetic model, the endothermic model and the phase equilibrium model. In the scaling criteria, the key parameters of the experiment are the water/gas production rates, the water injection rate, and the production time. By using the scaling criteria, the experimental results can be enlarged to a field scale. Therefore, the experimental results and the scaling criteria could be used to evaluate the hydrate dissociation strategies and the gas production potential of the hydrate reservoir.

In this communication, a novel platanus hispanica-like, highly integrated hierarchical electrocatalyst, with Co–carbon nanotubes anchored through porous Co embedded carbon sphere frameworks (Co–CNTFs), was fabricated using a chemical vapor deposition (CVD) method. More importantly, the prepared Co–CNTFs demonstrate even better activity than commercial Pt electrocatalysts in an alkaline medium. This presented CVD approach provides an effective way to grow metal–CNTs in situ through various metal-complex-derived functional nanomaterials and can be expanded to metallic oxide, metallic sulfide, and metallic phosphide, among others, to introduce carbon nanotube frameworks with a multitude of potential applications.

The behavior of hydrate formation in porous sediment has been widely studied because of its importance in the investigation of reservoirs and in the drilling of natural gas hydrate. However, it is difficult to understand the hydrate nucleation and growth mechanism on the surface and in the nanopores of porous media by experimental and numerical simulation methods. In this work, molecular dynamics simulations of the nucleation and growth of CH4 hydrate in the presence of the surface and nanopores of clay are carried out. The molecular configurations and microstructure properties are analyzed for systems containing one H2O hydrate layer (System A), three H2O hydrate layers (System B), and six H2O hydrate layers (System C) in both clay and the bulk solution. It is found that hydrate formation is more complex in porous media than in the pure bulk solution and that there is cooperativity between hydrate growth and molecular diffusion in clay nanopores. The hydroxylated edge sites of the clay surface could serve as a source of CH4 molecules to facilitate hydrate nucleation. The diffusion velocity of molecules is influenced by the growth of the hydrate that forms a block in the throats of the clay nanopore. Comparing hydrate growth in different clay pore sizes reveals that the pore size plays an important role in hydrate growth and molecular diffusion in clay. This simulation study provides the microscopic mechanism of hydrate nucleation and growth in porous media, which can be favorable for the investigation of the formation of natural gas hydrate in sediments.

A novel three-dimensional 117.8-L pressure vessel, which is called a Pilot-Scale Hydrate Simulator (PHS), is developed to investigate the gas production performance from hydrate-bearing porous media using the huff and puff method through both experimental and numerical simulations. The methane gas and deionized water are injected into the pressure vessel to synthesize methane hydrate. The grain sizes of the quartz sand in the vessel are between 300 and 450 μm. The huff and puff stages, including the injection, the soaking, and the production, are employed for hydrate dissociation. A single vertical well at the axis of the PHS is used as the injection and production well. The whole experiment consists of 15 huff and puff cycles. The numerical simulation results agree well with the experiment. Both the experimental and numerical simulation results indicate that the injected water is mainly restricted around the well during the injection stage. The system pressure fluctuates regularly in each cycle, and the ...

Pt-Sn/WC(O)/C catalysts with different Pt/Sn molar ratio have been prepared by microwave-assisted reduction method. In the synthesis, PtSn alloy was supported on WC(O)/C which was synthesized by the temperature-programmed carburization after the pretreatment of AMT precursor. XRD result shows that Pt particles are reduced successfully. Compared to the reflections of Sn-free sample, the diffraction peaks of PtSn alloy catalysts shift to lower angle slightly. The electrocatalytic activities towards ethanol oxidation reaction were investigated using cyclic voltammetry and chronoamperometry techniques in acid media. The sample of Pt3Sn2/WC(O)/C presents the highest peak current density (332.2 mA/mg-Pt) and stability.

This work presents the thermodynamic study of separating CH4 and CO2 from the simulated landfill gas (LFG) [CO2 (0.45) + CH4 (0.55)] based on hydrate crystallization in the presence of tetra-n-butyl ammonium bromide (TBAB), tetrahydrofuran (THF), dimethyl sulfoxide (DMSO), and their mixtures. The mole fractions of TBAB, THF, and DMSO aqueous solutions were fixed at 0.0234, 0.0556, and 0.0165, respectively. The equilibrium hydrate formation conditions were measured by T-cycle method in the temperature range of (274.15 to 294.95) K and the pressure ranges up to 6.72 MPa. The gas phase in the crystallizer at the equilibrium points was also sampled and analyzed. For the additives with the fixed concentrations studied in this work, it was found that both TBAB and THF can remarkably reduce the equilibrium hydrate formation pressure of LFG mixture gas, but the effect of THF is better than that of TBAB in the high temperature region, while DMSO have no obvious pressure drop effect on the equilibrium hydrate forma...

In this work, the effects of stirring and bubbling methods on hydrate-based carbon dioxide (CO2) separation from integrated gasification combined cycle (IGCC) synthesis gas are compared. Then, an integrated process of bubbling in conjunction with temperature fluctuation is proposed and adopted in the experiments, which are conducted in bench and scaled- up equipment. The experimental results show that the bubbling method has a similar positive effect on the CO2 separation as the stirring method. The optimal volume ratio of tetra-n-butylammonium bromide (TBAB) solution to the reactor shifts to 0.75 after the volume of the reactor is enlarged 100-fold, and at that ratio, the total 15.3 mol of gas is consumed and the mole concentration of CO2 in the gas phase reduces from 40.0 to 13.2%. The results indicate that the integrated process and scaled-up equipment are feasible for hydrate-based CO2 separation.

The equilibrium hydrate formation conditions for CO 2 /H 2 gas mixtures with different CO 2 concentrations in 0.29 mol% TBAB aqueous solution are firstly measured. The results illustrate that the equilibrium hydrate formation pressure increases remarkably with the decrease of CO 2 concentration in the gas mixture. Based on the phase equilibrium data, a three stages hydrate CO 2 separation from integrated gasification combined cycle (IGCC) synthesis gas is investigated. Because the separation efficiency is quite low for the third hydrate separation, a hybrid CO 2 separation process of two hydrate stages in conjunction with one chemical absorption process (absorption with MEA) is proposed and studied. The experimental results show H 2 concentration in the final residual gas released from the three stages hydrate CO 2 separation process was approximately 95.0 mol% while that released from the hybrid CO 2 separation process was approximately 99.4 mol%. Thus, the hybrid process is possible to be a promising technology for the industrial application in the future.

The hydrate-based carbon dioxide (CO2) capture from the integrated gasification combined cycle (IGCC) synthesis gas using the bubble method is investigated with a set of visual equipment in this work. The gas bubble is created with a bubble plate on the bottom of the equipment. By the visual equipment, the hydrate formation and the hydrate shape are visually captured. With the move of the gas bubble from the bottom to the top of the reactor, gas hydrate forms firstly from the gas–liquid boundary around the bubble, then the hydrate gradually grows up and piles up in the bottom side of the bubble to form a hydrate particle. The gas hydrate shape is affected by the gas flow rate. The hydrate is acicular crystal at the low gas flow rate while the hydrate is fine sand-like crystal at the high gas flow rate. The bubble size and the gas flow rate have an obvious impact on the hydrate-based CO2 separation process. The experimental results show the gas bubble of 50 μm and the gas flow rate of 6.75 mL/min/L are ideal for CO2 capture from IGCC synthesis gas under the condition of 3.0 MPa and 274.15 K.

The gas production behavior from methane hydrate in the sediment by depressurization was investigated in a novel pilot-scale hydrate simulator (PHS), a three-dimensional pressure vessel of 117.8 L. Experimental results are compared with those in a cubic hydrate simulator (CHS) with the effective volume of 5.8 L to reveal the dependence of the production behavior on the size of the hydrate reservoir. Results show that the gas production processes in the two simulators consist of three periods: the free gas production, mixed gas (free gas and gas dissociated from the hydrate) production and gas production from hydrate dissociation. The first and second periods are mainly controlled by the pressure reduction rate. The heat conduction from the ambient is main driving force to dissociate the hydrate in the third period. The cumulative gas production in the third period with the PHS and CHS is much higher than those in the first and second periods. However, the gas production rate in the period is low. The duration for gas production with the PHS is approximately 20 times as many as that with the CHS. Water production behavior with the PHS is different with that with the CHS during the gas production. The system temperature change tendency with the PHS is the same with that with the CHS during the gas production. The unique difference is that there is also a temperature rise period with the CHS.

The effects of the flow rates of cyclopentane (CP) and methane gas, operating pressure, and experimental temperature on the formation of cyclopentane-methane hydrate were investigated using a novel bubble column reactor. The results indicated that, with either an increase of the operating pressure or a decrease of the experimental temperature, the induction time decreased whereas the cumulative gas consumption and gas conversion ratio increased. In addition, with an increase of the flow rate of methane gas, the induction time decreased, whereas the cumulative gas consumption increased. The gas conversion ratio increased first from 61.5% to 93.1% when the flow rate of methane gas increased from 159 to 234 mL/min and then decreased from 93.1% to 83.2% when the flow rate of methane gas continuously increased from 234 mL/min to 308.9 mL/min. This decrease was attributed to an increase of the discharge rate of methane from the reactor. It was noted the average methane consumption rate could be effectively enha...

Pilot-Scale Hydrate Simulator (PHS), a novel three-dimensional 117.8-L pressure vessel was developed to investigate the gas production from methane hydrate in porous media using the huff and puff method. In situ methane hydrate was synthesized in the pressure vessel with methane gas and deionized water in quartz sand with grain sizes between 300 and 450 μm. In the PHS, a 9-spot distribution of vertical wells, a single horizontal well and 49-spot distributions of the thermometers and resistance ports are respectively placed in three horizontal layers, which equally divide the vessel into four parts. During the experiment, the huff and puff stages, including the injection, the soaking and the production, are carried out for hydrate dissociation. A vertical well at the axis of the PHS was used as the injection and production well. The initial hydrate saturation before dissociation is 33.66% in volume, and the percentage of the hydrate dissociated could be approximately 94% after 15 huff and puff cycles. The experimental results indicate that with the constant hot water injection rate, the range of the thermal diffusion is restricted around the well, and depressurization rather than thermal stimulation is dominant for gas production. The decline of the cumulative gas produced during each cycle and the diminishing uptrend of the percentage of the hydrate dissociated indicate that the hydrate dissociation rate decreases over time. The gas production efficiency is improved by prolonging the hot water injection time, while this enhancement is limited by the stronger pressurization effect.

To determine the appropriate operating conditions for separating methane (CH4) from drainage coal-bed methane (CBM) mixed with air, a hydrate-based methane separation method is proposed. The amount of gas uptake, CH4 concentration in decomposed gas phase, CH4 split fraction, and CH4 separation factor are investigated at the initial operating pressure range of 1.50–4.50 MPa and 279.15 K in the presence of sodium dodecyl sulfate (SDS) with the concentration range of 0–1000 ppm in 1.0 mol % tetrahydrofuran (THF) aqueous solution. The results indicate that the 1.0 mol % THF aqueous solution with the addition of 300 ppm SDS at 2.50 MPa and 279.15 K is the optimal condition for recovering CH4 from the drainage CBM via hydrate formation. Under the condition, the final amount of the gas uptake, the CH4 concentration in decomposed gas phase, the CH4 split fraction, and the CH4 separation factor after a one-stage hydrate-based separation are up to 0.1364 mol, 69.93 mol %, 86.44%, and 10.77, respectively. The result...

Tungsten carbide (WC) with controlled pore size distribution was synthesized using a novel “precursor reassembly” method. The precursor crystal was assembled by mixing ammonium metatungstate (AMT) and ammonium carbonate (AC) in distilled water, followed by hydrothermal treatment. The mesostructure, crystal phase, and amount of deposited graphitic carbon can be conveniently tuned by controlling carburizing atmosphere (CO or a CO/H 2 mixture). Moreover, the influence of precursor preparation (AMT/AC mass ratio and hydrothermal temperature) on the materials was also investigated. The resultant materials with low carbon content were mesoporous WCs, which showed high specific surface areas (11.3–20.4 m 2 g −1 ) and adjustable pore-size distributions (average pore size: 15.3–22.3 nm). A mechanism for the formation of WC with a controllable porous framework is proposed. Finally, cyclic voltammetry was used to investigate the inference of different mesoporous structure.

A pure spinel-type phase was attained by solid state reactions at room temperature, with no intermediate compounds. Its formation and the structural evolutions have been characterized by thermogravimetry-differential scanning calorimetry (TG/DSC) tests, X-ray diffraction (XRD) and scanning electron microscopy (SEM). Related electrical analyses were also performed. The results showed that the powders and ceramics prepared by the solid state reactions at room temperature exhibit a good electrical property because of narrow grain size distribution, controlled morphology, and high purity. Most importantly, this new approach greatly simplifies the preparation processes.

The synergic effect of Cyclopentane (CP) and Tetra-n-butyl Ammonium Bromide (TBAB) on the hydrate-based carbon dioxide (CO2) separation from IGCC (Integrated Gasification Combined Cycle) syngas is investigated by measuring the gas uptake and the power X-ray diffraction (PXRD) patterns in this work. The CP with CP/TBAB solution ratio of 5 vol% added into the 0.29 mol% TBAB solution can remarkably increase the gas uptake at 4.0 MPa and 274.65 K. The PXRD patterns of the semi-clathrate (sc) hydrate and structure II (sII) hydrate are obtained for the CP/TBAB/gas/H2O system. The synergic effect of the CP and the TBAB includes two aspects: On one hand, the CP molecules housed in the hollow centers of the large cavities together with TBAB cations (TBA þ ) make the sc hydrate more stable. On the other hand, the TBA þ displaced out of the large cavities by the CP molecules make the ionization reaction of TBAB in the solution going toward the reverse direction. Thus, the more TBAB molecules exist in the solution and form the more sc hydrate, resulting in the considerable increase of the gas uptake.

A new method of temperature fluctuation is proposed to promote the process of hydrate-based CO2 separation from fuel gas in this work according to the dual nature of CO2 solubility in hydrate forming and non-hydrate forming regions [1]. The temperature fluctuation operated in the process of hydrate formation improves the formation of gas hydrate observably. The amount of the gas consumed with temperature fluctuation is approximately 35% more than that without temperature fluctuation. It is found that only the temperature fluctuation operated in the period of forming hydrate leads to a good effect on CO2 separation. Meanwhile, with the proceeding of hydrate formation, the effect of temperature fluctuation on the gas hydrate gradually reduces, and little effect is left in the completion term. The CO2 separation efficiencies in the separation processes with the effective temperature fluctuations are improved remarkably.

The gas production behavior from methane hydrate in a porous sediment by depressurization was investigated in a three-dimensional (3D) cubic hydrate simulator (CHS) at 281.15 K, hydrate saturation of 33.1%, and a production pressure range of 4.5–5.6 MPa. The results show that the gas production process consists of three periods: free gas production, mixed gas (free gas and gas dissociated from the hydrate) production, and gas production from the hydrate dissociation. The temperature in the near-well region in the 3D hydrate reservoir changes during gas production in five stages. In the first period, the free gas in the system is released and the temperature change is not significant. In the second period, the temperature increases because of the reformation of the hydrate. In the third period, the temperature at each measuring point decreases quickly to the lowest value because of the considerable dissociation of the hydrate. The fourth period is the thermostatic hydrate dissociation period. During this p...

Ultrafine mesoporous tungsten carbide (WC) was prepared from as-synthesized mesoporous WC using high-energy ball milling treatment. X-ray diffraction (XRD), scanning electron microscopy (SEM), and nitrogen adsorption-desorption techniques were used to characterize the samples. Brunauer-Emmett-Teller (BET) surface areas of WC samples increased with the increasing ball milling time and kept constant at 10–11 m2·g−1 for over 9 h. The electrocatalytic properties of methanol electro-oxidation at WC powder microelectrodes were investigated by cyclic voltammetry, chronoamperometry, and quasi-steady-state polarization techniques. The results reveal that ball-milled WC exhibits higher activity for methanol electro-oxidation than as-synthesized mesoporous WC. The suitability of ball-milled WC for methanol electro-oxidation is better than platinum (Pt) micro-disk, although the current peak is not as high as the Pt micro-disk. Moreover, increasing the methanol concentration and reaction temperature promotes methanol electro-oxidation on ultrafine mesoporous WC.

Trapping CO 2 in hydrates is a promising approach to reduce the greenhouse gas emissions. This work presents the efficient separation process of CO 2 from the simulated fuel gas (39.2 mol % CO 2 /H 2 binary mixture) based on the hydrate crystallization in the presence of tetra-n-butylammonium bromide (TBAB). The experiments were carried out in the TBAB concentration range of 0.14―1.00 mol %, the temperature range of 275.15―285.15 K, the driving force range of 1.00―4.50 MPa, the gas/liquid phase ratio range of 0.86―6.47, and the hydrate growth time from 15 to 120 min. The results indicate that the increase of the TBAB concentration or the driving force can enhance the separation efficiency, except when the TBAB concentration is above 0.29 mol % or the driving force is above 2.50 MPa. The lower gas/liquid phase volume ratio and the hydrate growth time can also promote gas consumption. However, H 2 more competitively encages into the hydrate phase with time. In addition, the temperature change has little effect on the CO 2 separation efficiency with the fixed driving force. It is worth noting that the one-stage hydrate formation/ decomposition process for the fuel gas in the presence of 0.29 mol % TBAB at 278.15 K and 2.50 MPa driving force could obtain a 96.85 CO 2 -rich gas and a 81.57 mol % H 2 -rich gas. The split fraction (SFr) and separation factor (SF) of CO 2 are 67.16% and 136.08, respectively. On the basis of the data of the separation efficiency, a hybrid conceptual process for precombustion capture based on only one hydrate formation/decomposition stage coupled with membrane separation is presented.

Effects of 0.29 mol% tetra-n-butyl ammonium bromide (TBAB) solution in conjunction with cyclopentane (CP) on the hydrate-based pre-combustion CO2 capture are investigated by the measurements of the gas uptakes, CO2 separation efficiencies and induction time of the hydrate formation at the different temperatureepressure conditions. The results show that the volume of the TBAB has an effect on the CO2 separation and the induction time, and the addition of the CP into the TBAB solution remarkably enhances the CO2 separation and shortens the induction time. The system with the CP/TBAB solution volume ratio of 5 vol% and TBAB solution/reactor effective volume ratio of 0.54 is optimum to obtain the largest gas uptake and the highest CO2 separation efficiency at 274.65 K and 4.0 MPa. Compared to the results with tetrahydrofuran (THF) as an additive [1], the gas uptake is enhanced by at least 2 times and the induction time is shortened at least 10 times at the similar temperatureepressure condition. In addition, the CO2 concentration in the decomposed gas from the hydrate slurry phase reaches approximately 93 mol% after the first-stage separation at 274.65 K and 2.5 MPa. The gas uptakes of more than 80 mol% are obtained after 400 s at the temperature range of 274.65e277.65 K and the pressure range of 2.5e4.5 MPa.

The dissociation behaviors of methane hydrate under constant pressure in the marine sediments from the South China Sea were experimental studied. The experiments were carried out in a high-pressure reactor with the effective volume of 416 cm3. The marine sediments with mean pore diameter of 12.178 nm and total pore volume of 4.997×102 mL/g, surface area of 16.412 m2/g were used for the experiments. The mass fraction of water in the marine sediments is 40%. The methane hydrate was formed at the initial pressure of 14.4 MPa and dissociated by depressurization through the gas release from the reactor to the supply vessel with the volume of 1091 cm3. The moles of the gas released were calculated by the pressure change in the supply vessel. The dissociation experiments were carried out at the temperature range of 274.15–281.15 K and the dissociation pressure range of 3.0–5.0 MPa. The experimental results show that the hydrate begins to dissociate during the depressurization period, resulting in the significant decrease of the temperature in the reactor to be below the melting-point due to that the hydrate dissociation is an endothermal process. The lowest temperature during the hydrate dissociation in marine sediments is significantly lower than that in silica sands. The methane hydrate can dissociate when the pressure is higher than the equilibrium dissociation pressure for bulk methane hydrate. The dissociation rate of methane hydrate, the final gas dissociated from the hydrate and the final hydrate dissociation ratio increase with the decrease of dissociation pressure. For the experiments with different experimental temperature, the hydrate dissociation rate increases with the increase of the experimental temperature, and the final gas dissociated from hydrate is affected by the initial hydrate saturation in the marine sediments. The hydrate can dissociate completely when the dissociation pressure is lower than the equilibrium hydrate dissociation pressure corresponding to the experimental temperature for the bulk hydrate.

To determine the suitable operating conditions for the hydrate-based CO(2) separation process from a fuel gas mixture, the hydrate nucleation and growth kinetics of the simulated fuel gas (39.2 mol % CO(2)/H(2) gas mixture) in the presence of tetra-n-butyl ammonium bromide (TBAB) are investigated. The experiments were conducted at the TBAB concentration range of 0.14-1.00 mol %, the temperature range of 275.15-282.45 K, the driving force range of 1.00-4.50 MPa, the gas/liquid phase ratio range of 0.86-6.47, and the hydrate growth time of 15-120 min. It is found that the addition of TBAB not only shortens the induction time and accelerates the hydrate growth rate, but also enhances CO(2) encaged into the hydrate. However, the number of total moles of gas consumed and the number of moles of CO(2) transferred into the hydrate slurry phase decrease with the increase of the TBAB concentration when the TBAB concentration is above 0.29 mol %. The induction time reduces, and the number of moles of gas consumed, the hydrate formation rate, and the number of moles of CO(2) encaged into hydrate phase increase with the increase of the driving force. However, when the driving force is more than 2.5 MPa, H(2) prefers to go into the hydrate phase with the increase of the driving force, as compared to CO(2). In addition, the temperature has little effect on the hydrate formation process.

To determine the appropriate operating conditions for separating carbon dioxide from flue gas via the hydrate formation, the effects of the concentrations of dodecyl trimethyl ammonium chloride (DTAC) in 0.29 mol% Tetra-n-butyl ammonium bromide (TBAB) aqueous solution and the initial pressures on the induction time of the hydrate formation and CO(2) separation efficiency are investigated. The experiments are conducted at the DTAC concentration range of 0-0.056 mol%, initial pressures range of 0.66 MPa-2.66 MPa and temperature range of 274.95 K-277.15 K. The results indicate that the initial pressure of 1.66 MPa in conjunction with the concentration of 0.028 mol% DTAC is most favorable for CO(2) separation. At the condition, the induction time of forming the hydrate can be shortened considerably and CO(2) can be purified from 17.0 mol% to 99.4% with the two-stage hydrate separation process. CO(2) split fractions for Stage 1 and Stage 2 are 0.54 and 0.39, respectively, and the separation factors are 9.60 and 62.25, respectively. Crown Copyright (C) 2010 Published by Elsevier Ltd. All rights reserved.

The spinel Li-Mn-O-F compound cathode materials were synthesized by solid-state reaction from calculated amounts LiOH-H2O, MnO2(EMD) and LiF. The results of the electrochemical test demonstrated that these materials exhibited excellent electrochemical properties. It's initial capacity is - 115 mAh.g1 and reversible efficiency is about 100%. After 60 cycles, its capacity is still around 110 mAh.g1 with nearly 100% reversible efficiency. The spinel Li-Mn-O-F compound possibly has two structure models: interstitial model [Li]-[Mn3+xMn4+2-x]O4Fδ, in which the fluorine is located on the interstice of crystal lattice, and substituted model [Li]-[Mn3+xMn4+2-x]O4-δFδ, which the fluorine atom substituted the oxygen atom. The electrochemical result supports the interstitial model [Li][Mn3+xMn4+2-x]O4Fδ.

The phase equilibrium data of cyclopentane (CP) + methane hydrates in brine water with NaCl mass fractions of w = 0.0.035, 0.070, and 0.100 were measured in the temperature range (284.4 in 301.3) K using a visual high-pressure phase equilibrium apparatus. The dissociation enthalpies of CP + methane hydrates in hot brine water were determined via the Clausius-Clapeyron equation based on these phase equilibrium data. The effect of help gas and salinity on the phase equilibrium of CP hydrate and CP + methane hydrates was studied, respectively. Liquid CP forms hydrates with small-molecule help gas at a temperature region much higher than the quadruple point of pure CP hydrate. Methane partially occupied the small cages of structure II hydrate, which accelerates the nucleation and growth of CP + methane hydrates and increases the stability of the hydrates. The phase equilibrium pressure of CP + methane hydrates increases with the increase in temperature, and it increases linearly with the increase in NaCl concentration in solutions. The higher the temperature, the more remarkable effect the temperature and salinity has on the phase equilibrium pressure. The dissociation enthalpy decreases with the increase in temperature and the NaCl concentration.

The equilibrium hydrate formation conditions for the gas mixture of CO2 and H-2 with tetrabutyl ammonium bromide (TBAB) are measured. The data show that TBAB can reduce the gas hydrate formation pressure as an additive with the mole fraction of (0.14, 0.21, 0.29, 0.50, 1.00, and 2.67) %. The experiments were carried out in the temperature range of (274.05 to 288.55) K and the pressure range of (0.25 to 7.26) MPa. The equilibrium hydrate formation pressure of the CO2 + H-2 + TBAB mixture is remarkably lower than that of the CO2 + H-2 mixture at the same temperature and decreases with the increase in the concentration of TBAB. In addition, to avoid the formation of pure TBAB hydrate, in which there are no CO2 or H-2, for the above gas mixture, the formation conditions of the pure TBAB hydrate with TBAB mole fraction from (0.14 to 2.67) % were also measured.

The acid-base stabilities of Al-13 and Al-30 in polyaluminum coagulants during aging and after dosing into water were studied systematically using batch and flow-through acid-base titration experiments. The acid decomposition rates of both Al-13 and Al-30 increase rapidly with the decrease in solution pH. The acid decompositions of Al-13 and Al-30 with respect to H+ concentration are composed of two parallel first-order and second-order reactions, and the reaction orders are 1.169 and 1.005, respectively. The acid decomposition rates of Al-13 and Al-30 increase slightly when the temperature increases from 20 to ca. 35 A degrees C, but decrease when the temperature increases further. Al-30 is more stable than Al-13 in acidic solution, and the stability difference increases as the pH decreases. Al-30 is more possible to become the dominant species in polyaluminum coagulants than Al-13. The acid catalyzed decomposition and followed by recrystallization to form bayerite is one of the main processes that are responsible for the decrease of Al-13 and Al-30 in polyaluminum coagulants during storage. The deprotonation and polymerization of Al-13 and Al-30 depend on solution pH. The hydrolysis products are positively charged, and consist mainly of repeated Al-13 and Al-30 units rather than amorphous Al(OH)(3) precipitates. Al-30 is less stable than Al-13 upon alkaline hydrolysis. Al-13 is stable at pH < 5.9, while Al-30 lose one proton at the pH 4.6-5.75. Al-13 and Al-30 lose respective 5 and 10 protons and form [Al-13] (n) and [Al-30] (n) clusters within the pH region of 5.9-6.25 and 5.75-6.65, respectively. This indicates that Al-30 is easier to aggregate than Al-13 at the acidic side, but [Al-13] (n) is much easier to convert to Alsol-gel than [Al-30] (n) . Al-30 possesses better characteristics than Al-13 when used as coagulant because the hydrolysis products of Al-30 possess higher charges than that of Al-13, and [Al-30] (n) clusters exist within a wider pH range.

A scheme of de-synchronization via pulse stimulation is numerically investigated in the Hindmarsh Rose globally coupled neural networks. The simulations show that synchronization evolves into de-synchronization in the globally coupled HR neural network when a part (about 10%) of neurons are stimulated with a pulse current signal. The network de-synchronization appears to be sensitive to the stimulation parameters. For the case of the same stimulation intensity, those weakly coupled networks reach de-synchronization more easily than strongly coupled networks. There exists a homologous asymptotic behavior in the region of higher frequency, and exist the optimal stimulation interval and period of continuous stimulation time when other stimulation parameters remain invariable.

The gas production behavior from methane hydrate in porous sediment by injecting the brine with the salinity of 0−24 wt % and the temperature of −1 to 130 °C was investigated in a one-dimensional experimental apparatus. The results show that the gas production process consists of three periods: the free gas production, the hydrate dissociation, and the general gas reservoir production. The hydrate dissociation accompanies the temperature decrease with the injection of the brine (NaCl solution), and the dissociation duration is shortened with the increase of the salinity. With the injection of hot brine, instantaneous hydrate dissociation rate also increases with the increase of the salinity. However, while the NaCl concentration is beyond a certain value, the rate has no longer continued increasing. Thermal efficiency and energy ratio for the hydrate production can be enhanced by injecting hot brine, and the enhanced effectiveness is quite good with the injection of high salinity at lower temperature.

We employ two thermodynamic approaches, based on the equal fugacities and the equal activities, to predict the gas hydrate equilibrium dissociation conditions in the porous media. The predictions are made for the hydrate systems, CH 4 /H 2 O, C 2 H 6 /H 2 O, C 3 H 8 /H 2 O, CO 2 /H 2 O, CH 4 /CO 2 /H 2 O, C 3 H 8 /CH 4 /C 2 H 6 /H 2 O, and CH 4 /CH 3 OH/H 2 O. For the non-hydrate phase, we used the Trebble–Bishnoi equation in the fugacity approach and the Soave–Redlich–Kwong equation in the activity approach. For the hydrate phase, the van der Waals–Platteeuw model incorporated with the capillary model of Llamedo et al. [M. Llamedo, R. Anderson, B. Tohidi, Am. Mineral. 89 (2004) 1264–1270] was used in the two approaches. The predictions are found to be in satisfactory to good agreement with the experimental data. The predictive ability of the fugacity approach is better than that of the activity approach.

The effect of thermal treatment on the formation and transformation of Al-13 and Al-30 species in highly concentrated hydrolytic polymeric At solutions (HPA) (0.2-1.0 mol L-1) were studied quantitatively using high-field Al-27 nuclear magnetic resonance (NMR) and time-developed Al-Ferron complex colorimetry. The results indicate that the metastable Al-13 species in HPA tends to polymerize and transform into Al-30 and other high polymers upon thermal treatment. The polymerization and transformation are speed up by heating at high temperature. Al-13 content in HPA decreases upon thermal treatment, and Al-30 content increases. Al-13 does not convert to Al-30 quantitatively due to its aggregation and acidic dissociation reactions. Al-13 species is a dominant nanosized Al species in freshly prepared HPA solutions, and its content reaches above 80.0% in HPA with Al-T = 0.2 mol L-1 and optimal hydrolysis ratios (B) (ca. 2.3-2.4). But the content of Al-30 becomes higher than that of Al-13 when the HPA solution is heated at 95 degrees C for more than 12 h. Al-30 becomes the dominant nanosized At species in HPA, and its content reaches 76.8% in sample with Al-T = 0.2 mol L-1 and B = 2.4. Although Al-30 is more stable than Al-13, it is also a metastable species during the process of At hydrolysis, polymerization and precipitation. The decomposition and polymerization of Al-30 are also speed up by increase the heating temperature. The optimal preparation temperature of Al-30 is ca. 95 degrees C. At species in HPA solutions transform into more stable and inert species through inter-species polymerization and intra-species structure rearrangement upon thermal treatment. So Al-b Contents decrease, and Al. contents increase. Al-30 cannot react with Ferron within 120 min, and it is classified as Al-c species in Al-Ferron analysis. The effect of thermal treatment on Al speciation in HPA solutions with different total At concentration and B value were also investigated. (c) 2006 Elsevier B.V. All rights reserved.

Background Cervical cancer remains a major health problem, especially in developing countries. Colposcopic examination is used to detect high-grade lesions in patients with a history of abnormal pap smears. New technologies are needed to improve the sensitivity and specificity of this technique. We propose to test the potential of fluorescence confocal microscopy to identify high-grade lesions. Methods We examined the quantification of ex vivo confocal fluorescence microscopy to differentiate among normal cervical tissue, low-grade Cervical Intraepithelial Neoplasia (CIN), and high-grade CIN. We sought to (1) quantify nuclear morphology and tissue architecture features by analyzing images of cervical biopsies; and (2) determine the accuracy of high-grade CIN detection via confocal microscopy relative to the accuracy of detection by colposcopic impression. Forty-six biopsies obtained from colposcopically normal and abnormal cervical sites were evaluated. Confocal images were acquired at different depths from the epithelial surface and histological images were analyzed using in-house software. Results The features calculated from the confocal images compared well with those features obtained from the histological images and histopathological reviews of the specimens (obtained by a gynecologic pathologist). The correlations between two of these features (the nuclear-cytoplasmic ratio and the average of three nearest Delaunay-neighbors distance) and the grade of dysplasia were higher than that of colposcopic impression. The sensitivity of detecting high-grade dysplasia by analysing images collected at the surface of the epithelium, and at 15 and 30 μm below the epithelial surface were respectively 100, 100, and 92 %. Conclusions Quantitative analysis of confocal fluorescence images showed its capacity for discriminating high-grade CIN lesions vs. low-grade CIN lesions and normal tissues, at different depth of imaging. This approach could be used to help clinicians identify high-grade CIN in clinical settings.

Surface enhanced Raman scattering (SERS) substrate based on fabricated Ag@Au core-shell dendrite was achieved. Ag dendrites were grown on Si wafer by the hydrothermal corrosion method and Au nanofilm on the surface of Ag dendritic nanostructure was then fabricated by chemical reduction. With the help of sodium borohydride in water, Au surface absorbates such as thiophene, adenine, rhodamine, small anions (Br– and I–) and a polymer (PVP, poly(N-vinylpyrrolidone)) can be completely and rapidly removed. After four repeatable experiments, the substrate SERS function did not decrease at all, indicating that the Ag@Au dendrite should be of great significance to SERS application because it can save much resource. Six-month-duration stability tests showed that the Ag@Au core-shell dendrite substrate is much more stable than the Ag dendrite substrates. We have also experimented on fast detection of Cd2+ at 10−8 M concentration by decorating single-stranded DNA containing adenine and guanine bases on the surface of this Ag@Au dendrite. Finite-difference time-domain simulations were carried out to investigate the influence of Au nanolayer on Ag dendrites, which showed that the local electric fields and enhancement factor are hardly affected when a 4 nm Au nanolayer is coated on Ag dendrite surface.

Background Endothelial dysfunction plays an important role in the pathophysiology of coronary artery disease (CAD). Previous studies suggested that human endothelial cell-specific molecule-1 (endocan) may be a novel endothelial dysfunction marker. This study aims to investigate the relationship between serum endocan level and the presence and severity of CAD in patients with hypertension. Methods A total of 190 eligible hypertension patients were enrolled in this study. Serum endocan level was measured by enzyme-linked immunosorbent assay. The presence and severity of CAD were evaluated by coronary angiography. Results Hypertensive patients with CAD had significantly higher serum endocan level than those without CAD (1.63 ± 0.51 ng/mL vs 1.31 ± 0.65 ng/mL, P < 0.05). Multivariate logistic regression revealed that serum endocan level was independently associated with the presence of CAD (odds ratio, 2.662; 95% confidence interval, 1.560–4.544; P < 0.001). Spearman rank correlation analysis demonstrated that serum endocan level was associated with SYNergy between PCI with TAXUS and Cardiac Surgery score (r = 0.349, P = 0.001). Conclusions Serum endocan level is independently correlated with the presence and severity of CAD in hypertension patients, and those with high endocan level may have an increased risk of developing atherosclerosis.

In exploration of low-cost electrocatalysts for direct methanol fuel cells (DMFCs), Pt modified tungsten carbide (WC) materials are found to be great potential candidates for decreasing Pt usage whilst exhibiting satisfactory reactivity. In this work, the mechanisms, onset potentials and activity for electrooxidation of methanol were studied on a series of Pt-modified WC catalysts where the bare W-terminated WC(0001) substrate was employed. In the surface energy calculations of a series of Pt-modified WC models, we found that the feasible structures are mono- and bi-layer Pt-modified WCs. The tri-layer Pt-modified WC model is not thermodynamically stable where the top layer Pt atoms tend to accumulate and form particles or clusters rather than being dispersed as a layer. We further calculated the mechanisms of methanol oxidation on the feasible models via methanol dehydrogenation to CO involving C-H and O-H bonds dissociating subsequently, and further CO oxidation with the C-O bond association. The onset potentials for the oxidation reactions over the Pt-modified WC catalysts were determined thermodynamically by water dissociation to surface OH* species. The activities of these Pt-modified WC catalysts were estimated from the calculated kinetic data. It has been found that the bi-layer Pt-modified WC catalysts may provide a good reactivity and an onset oxidation potential comparable to pure Pt and serve as promising electrocatalysts for DMFCs with a significant decrease in Pt usage.

A novel solution to the singly quantized vortex is presented for big Bose–Einstein condensates in axis-symmetric harmonic traps, which is valid in the regime of strong coupling parameters. This solution manifests the vortex as a topological soliton and describes correctly its global structure for the whole region of large condensates including the vortex-core, except for the thin boundary region. An improved expression for thermodynamical critical rotation frequency for vortex formation is derived based on our solution, conforming to the known frequency formula given by Lundh et al. in the Thomas–Fermi limit.

Influence of total aluminum concentration (CAlT) on the generation and transformation of nanosized Al13 and Al30 in hydrolytic polyaluminum aqueous solutions was investigated using high field 27Al NMR and time-developed Al-Ferron complex colorimetry. When prepared at the optimal basicity (B) of Al13 generation and 80°C, the Al13 species in polyaluminum solution tends to further polymerize and convert to Al30 and higher polymers when CAlT>0.2 mol · L−1, but Al13 does not convert to Al30 quantificationally, as the formation of Alu from Al13 and Al30 is accelerated in the same way. The conversion rate of Al13 is accelerated by the increase in CAlT. When CAlT>0.75 mol·L−1, Al13 content decreases rapidly, and Al30 content increases continuously and becomes the dominant nanometer polynuclear aluminum species. Alm is one of prerequisites of Al13 conversion to Al30. When CAlT increases and B reduces, the polymerization rate between Al13 and Al13 increases, and at the same time, the dissociation reaction rate of Al13 and Al30 by H+ also increases. The latter becomes the dominant reaction in polyaluminum solution with low B value, so Al30 decreases with the increasing CAlT. The hydrolytic polyaluminum solution with Al13 content beyond 80% can only be prepared under the condition of CAlT

Lower hybrid current drive (LHCD) plasmas in the presence of DC electric filed have been investigated based on Karney–Fisch theory in the HT-7 tokamak. The relatively small scatter in the experimental data with various values of waveguide phasing and lower hybrid power, when plotted in the Karney–Fisch diagram, confirms that a reasonable theoretical interpretation is possible for the HT-7 data. The full non-inductively current drive efficiencies are obtained by fitting the experimental data to the theoretical curve. The efficiency strongly depends on the lower hybrid wave phase velocity.

The deviation effect of spinor mode from the single-mode for a spin-1 Bose gas of trapped atoms is studied beyond the mean field theory. Based on the effective Hamiltonian with nondegenerated level of the collective spin states, the splitting level of the system energy due to the deviation effect has been calculated. For the large condensates of 87 Rb and 23 Na with atom number N>105, the splitting fraction of the energy, arising from the magnetization exhibited by the trapped Bose gas, is found to have a typical order of (10-4~10-8), decreasing as N-2 for 87 Rb and increasing as -N-2 for 23 Na , respectively.

The kinetics of methane hydrate formation in marine sediments with different water saturations are important to assess the feasibility of the hydrate production and understand the process of the secondary hydrate formation in the gas production from hydrate reservoir. In this paper, the behaviors of methane hydrate formation in marine sediments from the South China Sea at different water saturation levels were experimentally studied in isobaric conditions. The marine sediments used in the experiments have the mean pore diameter of 12.178 nm, total pore volume of 4.997 × 10−2 mL/g and surface area of 16.412 m2/g. The volume fraction of water in the marine sediments ranges from 30% to 50%. The hydrate formation rate and the final water conversion increase with the decrease of the formation temperature at the water saturation of 40%. At the same experimental conditions, the hydrate formation rate decreases with the increase of the water saturation from 40% to 50% due to the reduction of the gas diffusion speed. At the water saturation of 30%, the hydrate formation rate is lower than that at the water saturation of 40% due to the effect of the equilibrium hydrate formation pressure, which increases with the decrease of the water saturation. The final water conversion is shown to increase with the increase of the water saturation, even the formation process at higher water did not end. The experiments at low water saturation show a better repeatability than that at high water saturation.

The purpose of this study was to compare patient populations, safety, feasibility, complications, and total costs of the transcatheter and transthoracic device closure treatments for secundum atrial septal defect. From January 2014 to December 2014, we enrolled 155 patients with secundum atrial septal defects in our hospital. The patients were divided into 2 groups: the 70 patients in group A underwent transcatheter device closure, and the 85 patients in group B underwent transthoracic intraoperative device closure with a right lateral mini-thoracotomy. In group A, the total occlusion rate was 94.3% immediately after the operation, 100% at 3 months, and 100% at 12 months of follow-up; the group A results were not statistically different from the group B results (94.1%, 98.8%, 98.8%, respectively). There was a statistically significant difference in the minor complication rate (P