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Experimental investigation into gas production from methane hydrate in sediments with different contents of illite clay by depressurization
No full textNatural gas hydrates are widely distributed in silty -clayey sediments, that occur largely in a highly dispersed state. However, the characteristics of the gas production behavior from methane hydrate in silty -clayey sediments are not as comprehensively understood than those in sandy sediments. In this study, a series of experiments employing single -stage depressurization method were conducted to dissociate methane hydrates in siltyclayey sediments with mass fractions of illite ranging from 0 to 50 wt%. The depressurization results indicate that for a high illite content (40 wt% and 50 wt%), the dissociation rate of methane hydrate is dramatically reduced by 33 -38% compared to sandy sediments. The lower heat transfer rate in the high-illite-content system caused by the reduced heat conduction of the sediment and more dispersed hydrate distribution results in the lower hydrate dissociation rate. The electrical resistance changes of sediments also indicated that the distribution of hydrate displays a certain degree of heterogeneity, which will cause the resistance changes in sandy sediment more significant than that in silty -clayey sediments. The results are great significant for understanding the gas production behavior of silty -clayey hydrate -bearing sediments and helpful in optimizing methane hydrate exploitation from this specific type of sediment
Liquid-Liquid Equilibrium Behavior of Ternary Systems Comprising Biodiesel plus Glycerol and Triglyceride plus Methanol: Experimental Data and Modeling
No full textHaving a comprehensive knowledge of phase equilibrium is advantageous for industrial simulation and design of chemical processes. For further acquisition of primary data to facilitate the separation and purification of waste oil biodiesel systems, a liquid-liquid equilibrium (LLE) tank is deployed for the ternary system of waste oil biodiesel + methanol + glycerin, thereby enhancing the precision and efficiency of the process. The phase equilibrium system was constructed under the influence of atmospheric pressure at precise temperatures of 303.15 K, 313.15 K, and 323.15 K. The equilibrium components of each substance were analyzed by employing high-temperature gas chromatography, a sophisticated analytical method that enables the identification and quantification of individual components of a sample. Moreover, the ternary liquid-liquid equilibrium data were correlated by implementing the NRTL and UNIQUAC activity coefficient models. Subsequently, the binary interaction parameters of the ternary system were derived by conducting regression analysis. The experimental data demonstrated that the presence of lower methanol content in the system resulted in nearly immiscible biodiesel and glycerol phases, which ultimately facilitated the separation of biodiesel and glycerol. Conversely, with the increase in methanol content, the mutual solubility of biodiesel and glycerol was observed to increase gradually. The results showed that the calculated values of the NRTL and UNIQUAC models aligned well with the experimental values. The root-mean-square deviations of the NRTL and UNIQUAC models at 313.15 K were 2.76% and 3.56%, respectively
Rational design of silica nanoreactor encapsulated Ni for reinforcing coke-resistance in dry reforming of methane
No full textDry reforming of methane (DRM) provides a desired approach to produce valuable syngas in tackling greenhouse gases. Yet it faces a formidable challenge in the design and synthesis of high coke-resistant Ni-based catalysts. Herein, we report a nanoreactor strategy to construct a supported Ni catalyst (Ni@SiO 2 @SiO 2 ) for reinforcing coke-resistance during DRM, by effectively encapsulating small Ni nanoparticles into dendritic fibrous silica (SiO 2 ) nanospheres and coating SiO 2 shell layers. Taking advantage of chemical characteristics of citric acid (CA), CA-chelated Ni impregnation enables the uniform immobilization of Ni species into the radial SiO 2 framework, then following carbonization produces protective carbon layers on the Ni nanoparticle surface during SiO 2 coating, which can be removed via oxidizing calcination. The resultant pomegranate-like nanoreactor catalyst possesses outstanding coke-resistance, without any detectable coke deposition after 200 h of DRM reaction at 700 degrees C, benefiting from effectively restricting metal sintering and fully preventing formation of inert carbon species
Effect of co-pyrolysis of texting and dyeing sludge and modified kaolin on the fate of heavy metals and potential migration mechanisms
No full textThe existence of heavy metal in texting and dyeing sludge is one of the potential ecological pollutions. In this study, a series of modified kaolin was applied to co -pyrolysis with DS. The biochar characterization and heavy metal analysis reveal the effects of modified additives on the heavy metal behavior and potential mechanisms. Compared to raw texting and dyeing sludge, the total content of Cu, Zn, Cr, Mn, and Ni increased to a maximum value of 170.63, 451.85, 147.86, 731.69, and 57.91 mg/kg in biochar. The proportion of Cu, Zn, Mn, and Ni in stable fractions increased to 99.23 %, 88.71 %, 53.89 %, and 94.04 %, and the potential ecological risk index of biochar experienced a substantial reduction from 154.45 in DS to 11.18 in DAK. Co -pyrolysis and dilution effects synergistically reduced the leaching of heavy metals and promoted their enrichment in biochar. The Al/Si structural phase transition, pore structure, functional groups, and interactions between inorganic mineral components and heavy metals also were affected by acid -base modification. This resulted in the enhancement of heavy metal stabilization fractions and the reduction of environmental risks. This study aims to present an ecofriendly and efficient strategy to further mitigate the environmental risks associated with HMs in hazardous wastes. In addition, it also provides ideas for the application of modified mineral additives in the field of pollutant control
Liquid CO<sub>2</sub>-CH<sub>4</sub> Hydrate Replacement Reaction above 281.15 K: Implication for CH<sub>4</sub> Recovery and CO<sub>2</sub> Sequestration in Marine Environments
No full textTemperature and pressure of natural gas hydrate (NGH) reservoirs influence CH4 recovery and CO2 sequestration through the CO2-CH4 hydrate replacement reaction. The typical temperature and pressure in marine NGH reservoirs are mainly 275.65-294.51 K and 8.41-22.25 MPa, respectively. However, the corresponding CO2-CH4 hydrate replacement reaction under the temperature above 281.15 K has been studied little in previous studies. In this work, six experiments were conducted at 281.15-289.15 K and 15-17 MPa using a self-developed experimental apparatus. These experiments utilized techniques such as general photography, microscopy, temperature and pressure measurements, computational analysis, and gas chromatography to study the dynamic changes in the morphology and distribution of CH4, CO2, and H2O under varying temperatures, pressures, and compositional conditions. The results showed that liquid CO2 replaced CH4 in CH4 hydrates or CH4-CO2 mixed hydrates. This replacement process was featured with multiple mechanisms during the soaking stage and governed by the CH4-CO2 mixed hydrate phase equilibrium, which was controlled by CH4-CO2 mixtures and their compositions. Moreover, the relative increases of the CH4 molar ratio in the CO2-rich fluid phase, the efficiency of CO2 sequestration, and the CO2 sequestration amount in comparison with the CH4 reserves reached 24.97%, 19.53%, and 2.17 times, respectively. CO2 injection pressure and the initial volume fraction of liquid water and the CO2-rich fluid were found to have larger impacts on the CO2-CH4 hydrate replacement reaction above 281.15 K than temperature and the initial volume of CH4 hydrate. Besides, controlling the composition of the CH4-CO2-H2O mixed system and depressurization were proposed to balance CH4 recovery and CO2 sequestration. This work may offer some references for CH4 recovery and CO2 sequestration under real settings
Hydraulic-Thermal-Chemical Coupling Model Considering Hydrate Growth and Aggregation to Study the Hydrate Slurry Multiphase Flow in Oil-Water Systems
No full textA hydrate slurry transport technology based on risk control methods is an important technical means to solve the hydrate blockage of multiphase transport pipelines and to guarantee the safety and efficiency of the exploitation of petroleum resources in deep-water. It is the foundation for the industrial promotion of this technology to adequately understand hydrate slurry flow characteristics, especially the influence of hydrate microbehavior on particle size and its distribution. This research establishes a kinetic model of hydrate aggregation (KMHA) that is developed to reflect the complex physical processes (growth, aggregation, and breakage) of hydrate particles based on the population balance theory by analyzing the microbehavioral mechanism of particles in oil-water-hydrate flow systems. Then, a three-dimensional hydraulic-thermal-chemical coupling model is established by coupling the KMHA with a multiphase flow model to investigate the flow characteristics and heat-transfer characteristics of the oil-water-hydrate slurry. This coupling model is the first to analyze the effect of temperature field on the evolution of hydrate and particle flow characteristics and is able to accurately predict the characteristics of growth, aggregation, and deposition of particles in oil-water-hydrate flow systems. Meanwhile, this model is employed to analyze the hydrate slurry flow in the horizontal pipe
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