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• Two steps of CH 4 hydrate formation in the presence of CP were observed. • Gas uptake as high as 131.80 mmol/molH 2 O was obtained in this work. • The stability of methane hydrates was characterized in this work. • A new strategy for methane hydrate storage and transportation was proposed. The work systematically investigates the kinetic of methane(CH 4) hydrate formation in the presence of cyclopentane（CP）by measuring induction time, hydrate formation rate, and gas uptake. The results showed that there are two steps for CH 4 hydrate formation in the presence of CP: Step 1, pure CP hydrate formation. Step 2, gas enters the empty cages of pure CP hydrates to form CP/CH 4 mixed hydrates. Besides, the rapid hydrate formation rate and high CH 4 uptake are observed from hydrate formation in this work. At the optimum conditions of 288.15 K and CP mole fractions of 5.6 mol%, the gas uptake and the time required for completion of hydrate formation are 131.80 mmol/mol H 2 O and 138 min, respectively. Relative to the highest reported gas uptake obtained in the presence of thermodynamic promoter (72.0 mmol/mol H 2 O), the value increased by 83%. More strikingly, the work shows that high gas uptake hydrates formed at relatively low temperatures can be stored and transported at relatively high temperatures, as high as 298.15 K, without significantly reducing the gas uptake, thereby providing one of the cost-effective methods for hydrate storage and transportation, that is forming hydrates at relatively low temperatures and storing and transporting hydrates at relatively high temperatures. Further, we proposed a schematic of the process chain of SNG(storing natural gas via solid hydrate) technology in vehicular and detailed discuss the current status of SNG technology development. It can be concluded that using the strategy that storage and transportation hydrates at a low-pressure condition instead of at ambient pressure (1.0 atm) may be a more realistic choice to industrialize SNG technology. [ABSTRACT FROM AUTHOR]

• Morphology and rheological behavior of CO 2 hydrate slurry in flow-loop are studied. • Tween-80′s effect in flow assurance depends greatly on shear-thinning behavior and bubble. • Defoamer(BK601) has negative effects in preventing hydrates aggregation. • The mechanism of Tween-80 in preventing hydrates aggregation is summarized. In this work, the flow of carbon dioxide (CO 2) hydrate slurry is systematically investigated by analyzing its rheological behavior, apparent viscosity, and crystal shape. The results show that blocking is easy to occur in the pure water system, while no blockage is observed from the system containing Tween-80. Besides, we confirm that the hydrate slurry formed in the pure water system is a dilatant fluid with shear-thickening behavior. However, that obtained from the system containing Tween-80 are pseudoplastic fluids with shear-thinning behavior. The time development of hydrate slurry flow in the system with or without Tween-80 showed that the shear-thinning behavior is a key factor in preventing the hydrate slurry from blockage. In addition, in the presence of Tween-80, hydrates will form on the surface of the bubble. These hydrates are easily dispersed on top of the liquid phase and will not adhere to the top wall of the pipeline. However, in pure water, a dense adhesive layer is observed on the top of the pipeline, which will reduce the flow area in the pipeline, increasing the flow resistance. Overall, the main role of Tween-80 in preventing hydrates from aggregation includes two aspects, (1) changing the type of fluid from dilatant to pseudoplastic; (2) providing bubbles for hydrate formation. The addition of defoamer(BK601) will reduce the Tween-80′s effects in preventing hydrates by reducing shear-thinning behavior and the amount of bubbles. [ABSTRACT FROM AUTHOR]

• Synergistic effect of corn cob and THF on CH 4 hydrate formation is studied. • The CH 4 uptake as high as 98.09 mmol/mol H 2 O is obtained from this work. • Two stages of CH 4 hydrate formation are observed in the system. • Both 512 and 51264 cages of sII are ocScupied by CH 4 molecules. A porous medium with a high specific surface area can be used to promote hydrate formation. In this work, the kinetics of methane (CH 4) hydrate formation in the presence of corn cobs and Tetrahydrofuran was systematically studied by determining the hydrate formation process, induction time, gas uptake, and hydrate formation rate. The results showed that hydrates form immediately as the CH 4 loading and the multi-stage of hydrate formation is observed. Relative to THF solutions, the addition of corn cobs has a positive effect on CH 4 uptake at THF concentrations <= 3.0 mol%. The optimum conditions of CH 4 hydrate formation in this work is corn cobs + THF (3.0 mol%) solution. In these conditions, the highest final gas uptake, approximately 98.40 ± 6.26 mmol/molH 2 O, and the shortest time required to achieve 90% of this gas uptake, approximately 3.12 h, is achieved. Besides, though the conditions adopted in this work are above the phase equilibrium of sI CH 4 hydrate formation, only sII hydrates are observed in this work. Meanwhile, except at the stoichiometric THF concentration of 5.6 mol%, it was confirmed that CH 4 molecules are not only trapped in the 512 cages of sII but also encaged in the 51264 cages of sII. [ABSTRACT FROM AUTHOR]

• Morphologies of hydrate formation in the CH 4 + THF + CP system are characterized. • The mechanism of hydrate layer rupture is determined in this study. • The kinetics of hydrate formation in the CH 4 + THF + CP system are studied. • Three stages of hydrate formation are obtained from the CH 4 + THF + CP system. The morphologies of methane (CH 4) hydrate formation in the system containing different mole ratios of tetrahydrofuran (THF) and cyclopentane (CP) at two different temperatures are systematically studied in this work. The results showed that for all cases conducted at 274.2 K, a hydrate film quickly covers the entire interface between the oil (CP) and the THF solution phase after gas loading, and then a hydrate layer forms, thereby significantly decreasing the following gas-liquids mass transfer efficiency. Raman spectrum shows this hydrate layer is caused mainly by pure THF hydrate. Interestingly, as the temperature increase to 278.2 K, the hydrate layer breaks. This is because, after hydrate layer formation, hydrate still grows at the contact interface of the metal, gas, and liquid phase, and then moves upward. In this process, liquids are gradually transported to the reaction front to form hydrate by capillary force and the hydrate layer's downward curvature gradually increases as the consumption of liquid until rupture. Besides, typical reaction kinetics shows that there are three stages of hydrate formation in the THF + CP + CH 4 system at 278.2 K. (1) hydrate layer formation (pure THF hydrate formation); (2) CP-CH 4 hydrate formation; (3) large amount of THF-CH 4 hydrate formation (after hydrate layer rupture). Further, this work also confirmed that after the hydrate layer rupture, the CH 4 occupancy in 512 cages of sII at the same temperature and promoter's mole fractions is independent of the type of promoters (CP, THF, and CP + THF) used in the system. [ABSTRACT FROM AUTHOR]

• We constructed a 3D temperature field model. • We conducted a comparative analysis of the relationship between an oxidation zone and a cavity. • We analyzed the changes in the intensities of chemical reactions in a gasifier using stoichiometric conservation. • We investigated the effects of shifting the gasifier injection position on the temperature field and gas composition. In this paper, the effects of changing the injection position of a gasification agent on temperature fields and gas compositions are investigated through an experimental model of the underground gasification of coaxial coal. A 3D model of the temperature field is constructed based on the experimental temperature parameters using kriging interpolation; the 900 °C isothermal surface is used as the reference plane to define the oxidation zone, and its plane and volume expansion rate are analyzed. The underground coal gasification experiment is divided into five stages according to the injection location. The average expansion rates of the oxidation zone in each stage are 2.04 cm/h, 1.93 cm/h, 3.44 cm/h, 3.68 cm/h, and 3 cm/h along the X-direction and 0.69 cm/h, 0.09 cm/h, 0.56 cm/h, 1.69 cm/h, and 1.01 cm/h along the Z-direction; the expansion rate along the X-direction is greater than that along the Z-direction. The expansion volumes of the oxidation zone after the five stages increase from 0.0097 m3 to 0.0168 m3, 0.0321 m3, 0.0521 m3 and 0.0657 m3. An analysis of the expanded volume of the oxidation zone compared with the volume of the cavity shows that both features are similar in shape and that the final volume of the cavity is smaller than the final expanded volume of the oxidation zone; the volume of the cavity is approximately 77.3 % of the expanded volume of the oxidation zone. The formation of a cavity requires the temperature to reach the conditions for the oxidation reaction of the coal and the rupture and flaking of the ash layer that accumulates after the reaction by the actions of certain stresses, such as thermal. The composition of the product gas and the strength of the chemical reactions involved are evaluated based on stoichiometric conservation. A short period after a shift in the injection position of the gasifier greatly impacts the chemical equilibrium of the UCG process with a large change in the strength of the chemical reaction, followed by a relatively small change when the gasification process stabilizes. [ABSTRACT FROM AUTHOR]

[Display omitted] • Secondary hydrate formation (SHF) are studied both experimentally and numerically. • A new kinetic model integrates hydrate pore-scale morphology and the SHF characteristics. • Heterogeneous manner of hydrate formation are quantified in Cubic Hydrate Simulator. • The SHF significantly exacerbates the hydrate formation heterogeneity. The challenge of secondary hydrate formation (SHF) is frequently encountered in hydrate formation and dissociation experiments. However, there is currently a lack of modeling theory of SHF kinetics in the field and laboratory tests. In this work, the hydrate formation experiments concerning the SHF are carried out in a cubic hydrate simulator (CHS), where the pressure profiles and temperature spatial distributions are measured. A new kinetic model of hydrate formation integrating hydrate pore-scale morphology and SHF characteristics is developed. The newly developed model with unified kinetic parameters is employed in the Tough + hydrate (T + H) simulator to duplicate the experiment processes numerically, which achieves excellent agreement with the experimental data. The results show that the evolutions of the spatial distributions of the temperature and hydrate saturation behave in heterogeneous manners in the hydrate formation processes. This also reveals that the SHF can significantly exacerbate the hydrate heterogeneity in the CHS. Two additional experiments and comparisons with currently available models have validated the feasibility and accuracy of the new model. This work provides a reliable and adaptable model for describing the entire lifecycle of the hydrate formation kinetics in the porous media. [ABSTRACT FROM AUTHOR]

[Display omitted] • Typical flue gas components all play inhibitory roles for Cd species adsorption. • HCl, CO 2 , and H 2 O have mild inhibitory effects on Cd species removal. • O 2 , NO, and SO 2 strongly exclude the adsorption of Cd species. • The adsorption selectivity of Cd species decreases with the increased temperature. Removal of cadmium (Cd) pollutants from waste incineration (MSW) flue gas by modified activated carbon (AC) is of great potential, yet the influence of flue gas composition on their interaction mechanism is still unclear. Thus, density functional theory and thermodynamic analyses were combined to explore the effects of typical flue gas compositions (O 2 , HCl, NO, SO 2 , CO 2 , and H 2 O) on Cd species capture over the Fe/AC and Mn/AC surfaces. All flue gas compositions inhibit the adsorption of Cd species, wherein their inhibitory effects are mainly divided into two categories, i.e., one with moderate inhibition (HCl, CO 2 , and H 2 O), and the other with significant inhibition (O 2 , NO, and SO 2). For the first category, HCl forms new active sites after adsorption on the surface, while CO 2 and H 2 O have weak competitiveness with Cd species, resulting in mild inhibitory effects. Nevertheless, O atoms of O 2 /SO 2 and N atoms of NO are highly effortless to bond with Fe/Mn atoms, and strongly exclude the Cd adsorption on the active sites, greatly weakening their binding strength. According to thermodynamic analysis, the fixation of Cd species by Fe/AC and Mn/AC spontaneously proceeds with the interference of flue gas components, while the selectivity to Cd species decreases with the increased temperature. In summary, it is instrumental to adjust the operating parameters and AC injection location to attenuate the negative effects of O 2 , SO 2 , NO, and high temperature on Cd capture by Fe/AC and Mn/AC. [ABSTRACT FROM AUTHOR]

• Promoter-CH 4 hydrate formation in a high-pressure microcalorimeter is studied. • The CH 4 hydrate formation thermodynamic behavior depends greatly on the promoter. • The hydrate structure has little effect on its formation thermodynamic behavior. To understand the thermodynamic characteristics of CH 4 hydrate formation in a high-pressure microcalorimeter under different reaction kinetics, five typical systems including CH 4 -H 2 O, CH 4 -Tetrahydrofuran (THF)–H 2 O, CH 4 -Cyclopentane (CP)–H 2 O, CH 4 -Methyl cyclohexane (MCH)–H 2 O, and CH 4 - tert -Butyl methyl ether (TBME)–H 2 O are adopted to conduct experiments in this work. The results show that their hydrate formation thermodynamic characteristics depend greatly on the promoter. For the CH 4 -H 2 O system, a hydrate crystals film will form quickly at the beginning of the reaction, hindering the mass transfer between gas and liquid, thereby presenting an extremely slow hydrate formation kinetics. After adding the water-soluble promoter that cannot form an oil phase, like THF, a rapid hydrate formation process is observed from the cooling stage. However, if the promoter can form an oil phase (CP, MCH, and TBME), regardless of whether the promoter is soluble in water, only a slow hydrate formation kinetics can be observed. This is because the oil phase can separate the water and gas phase, reducing their mass transfer efficiency, thereby restricting the hydrate growth. Interestingly, a rapid hydrate formation process can be obtained during their heating stage. These indicate that high driving force cannot always lead to a rapid hydrate formation kinetics. It is worth mentioning that a similar hydrate formation and dissociation behavior in high-pressure microcalorimeter is observed for water-insoluble promoters (CP, MCH), indicating the hydrate structure will not significantly affect their thermodynamic behavior except for the intensity of the peaks. [ABSTRACT FROM AUTHOR]

• The amount of the reacted carbon was estimated with the volume of oxygen injected. • The energy recovery rate to evaluate the gasification efficiency was proposed. • A gasification temperature evaluation model was suggested. In this paper, UCG simulation experiments were carried out on selected coal samples to study the effects of the gasification agent ratio on the product gas composition and calorific value under different oxygen concentrations. Moreover, an energy recovery evaluation method based on stoichiometric theory was established based on the carbon (C) balance in the generated gas content, and the energy recovery rate and coal consumption of the underground gasification process were evaluated. Based on the composition of the produced gas and the thermodynamic law of conservation, an evaluation model of the underground coal gasification temperature field was established. The gasification chamber temperature in each stage was evaluated by calculating the reaction heat and sensible heat. The experimental and research results showed that when the volume fraction of oxygen in a gasification agent was in the range 40–70 % and the calorific value of the produced gas increased from 10.48 MJ/m3 to 12.48 MJ/m3. The calorific value of the produced gas increased with an increasing oxygen concentration. Furthermore, the energy recovery rate increased from 69.63 % to 83.88 %, indicating that the gasification efficiency of the UCG experiment can be significantly improved with an increasing oxygen concentration. The error between the theoretical value of the coal consumption and the actual monitoring value was within 10 %, which effectively evaluates the coal consumption in the gasification process. The theoretical calculation temperature was consistent with the experimental monitoring temperature results, and the reaction heat was found to also be linearly correlated with the gasification temperature. Therefore, this method can effectively determine the gasification chamber temperature. These monitoring and evaluation methods are expected to guide the analysis of subsurface field experiments. [ABSTRACT FROM AUTHOR]

The silver-modified NiCo 2 O 4 nanosheets on the monolithic 3-DM nickel foam substrate show high catalytic activities for soot combustion under gravitational contact mode, especially with the aid of NO x. [Display omitted] • The crossed macro-porous of NiCo 2 O 4 nanosheets and three-dimensional porous structure of Ni foam can increase contact efficiency between soot and catalysts. • The metal-support interaction between Ag and NiCo-NS weakens the Co-O bond and increases the amount of active oxygen species. • The active oxygen species produced by Ag has the high oxidation ability in the low temperatures. • The optimal amount of Ag on NiCo 2 O 4 nanosheets is 4.5%, and it shows the higher catalytic performance than that of other noble metal catalysts (Pt/Pd/Au). • The 4.5Ag/NiCo-NS possesses the high catalytic stability. Highly active spinel-derived monolithic catalysts loading Ag (xAg/NiCo-NS) have been successfully designed and synthesized and used to catalytic soot elimination. The crossed macro-porous of NiCo 2 O 4 nanosheets and the three-dimensional porous structure of Ni foam not only provides a convenient gas mass transfer channel, but also provides a large number of contact points between soot and catalyst. After loading Ag on the NiCo-NS, the catalytic performance for soot oxidation is improved remarkably. Among the xAg/NiCo-NS catalysts, the 4.5Ag/NiCo-NS sample has the highest catalytic performance with the lowest T 50 (333 °C), which is 50 °C lower than that of the NiCo-NS catalyst and lower than that of other prove metal catalysts (Pt/Pd/Au) in the atmosphere of 500 ppm NO/10 % O 2 /N 2. The metal-support interaction between Ag and NiCo-NS weakens the Co-O bond, increases the amount of surface oxygen vacancies and improves the intrinsic activity determined by turnover frequency (TOF) of the catalyst. Moreover, Ag can also adsorb and activate gaseous oxygen to produce the low-temperature active oxygen species (O 2 −), which can promote the soot combustion in the low temperatures. Based on the catalytic performance for soot oxidation and activation Energy (Ea), the reaction paths for the catalytic combustion of soot on Ag/NiCo-NS are identified. [ABSTRACT FROM AUTHOR]