Recovering CH4 from natural gas hydrate with CO2 in porous media below the freezing point

The recovery of methane from gas hydrate layers that have been detected in permafrost regions is a promising perspective in the future. In order to study the replacement characteristics of CO₂–CH₄ hydrate in permafrost environments, simulation experiment was carried out in this work. The results indicated that the replacement rate and efficiency increased with the increasing of injection pressure of CO₂ gas. And the replacement rate and efficiency reached up to 0.403?mmol/h and 13.20% during the experiment. Furthermore, the results also showed that the replacement rate of CO₂–CH₄ hydrate was slower below the freezing point.     

Molecular insights into structural properties around the threshold of gas hydrate formation

Molecular modeling is used to obtain the formation mechanism and stability of structure I methane hydrate. A simple approach is presented to reveal the formation of the characteristic cage of structure I hydrate by water molecules around the methane guest molecules after 1 ns via reducing the temperature from 400 to 275 K under canonical ensemble condition. Then, the stability of methane clathrate hydrate structure is studied during the simulation time of 200 ps. To evaluate the structure of methane hydrate, the radial distribution functions of host–host, host–guest, and guest–guest molecules are obtained. The results prove the methane hydrate formation and its stability.     

Thermodynamic optimization for crystallization process of gas hydrate

In this paper, thermodynamic optimization is applied to analyze the crystallization process of the gas hydrate related to the gas hydrate cool storage system. Thermodynamic optimization model of the gas hydrate crystallization process is established. By taking the entropy generation minimization as the optimization objective, both the optimal control strategy and the optimal cooling rate of the gas hydrate crystallization process are determined. The minimum entropy generation corresponding to the optimal cooling rate decreases by 7.8% compared with normal situation. The results presented in this paper can provide important guidelines for optimal design and operation of the gas hydrate crystallization process. Copyright © 2010 John Wiley & Sons, Ltd.     

Effect of the foam of sodium dodecyl sulfate on the methane hydrate formation induction time

The aim of this paper is to study the effect of sodium dodecyl sulfate (SDS) foam on methane formation nuclei process. The experimental data were compared with SDS solution in the absence of foam. Repeat experiments proved that the nucleation rate in the presence of SDS foam was 1.15 × 10^?1 min^?1, which was notably faster than 1.18 × 10^?2 min^?1 in the absence SDS foam. It indicated that the SDS foam can significantly accelerate nuclei process, which thus made the nuclei process instantaneous. The foam surface area, the interior gas pressure of the bubble and foam film were investigated to find out the reasons behind promoting nuclei process by SDS foam. The larger interface area of gas liquid provides more nucleation sites, whereas the effect of interior gas pressure on the nuclei process is not significant due to the negligible pressure variation. The result can be used to prevent the pipeline plugging during the gas well production or the gas transmission.     

一个深海能源土的温度-水压-力学二维微观胶结模型

天然气水合物以胶结形式赋存时,对深海能源土的强度和变形特性影响显著,且其影响程度与所处温度、水压与力学环境密切相关。旨在建立可考虑温（温度）-压（水压）-力（力-位移与胶结破坏准则）耦合影响的深海能源土微观胶结模型。首先,依据能源土中水合物胶结可发生于两种接触形式（直接接触与有间距）的土颗粒间,提出适用于两种胶结模式的力-位移准则和胶结破坏准则。其次,提出温压距离参数L（表示在无量纲化处理后的温度-水压坐标平面,土体所处温度与水压点到水合物相平衡线的最小距离）,并依据文献资料分析,建立水合物胶结强度、刚度与参数L间的关系。最后,建立由水合物饱和度确定的粒间水合物胶结尺寸计算方法,并据此进一步建立了胶结强度与刚度同水合物饱和度间的关系。该模型可以方便地植入离散元程序,从而用于深海能源土的宏微观力学分析。     

A solid-state NMR and X-ray powder diffraction investigation of the binding mechanism for self-healing cementitious materials design: The assessment of the reactivity of sodium silicate based systems

The identification of affordable healing agents for cement based materials, able to promote autonomous crack healing, is a challenge to improve the durability of building structures. In this study, a thorough investigation of the reactivity between a hydrated Portland cement and sodium silicate solutions, as healing agents, has been carried out.The goal is to quantitatively assess the chemical reactivity and actual binding capacity of sodium silicate. Mechanical recovery was evaluated by means of a healing agent strength test on hydrated cement treated with sodium silicate. XRPD and Solid-state NMR allowed the definition of reaction times, the involved species, and the nature and stability of the reaction products. Highlights show that sodium silicate reacts not only with Ca(OH)₂ (namely portlandite), but also with calcium aluminate phases (AFt, AFm, TAH) to extract calcium and/or aluminum ions, with the formation of crystalline/semi-crystalline C-S-H/C-A-S-H tobermorite phase.     

Thermodynamic Properties of Ionic Semiclathrate Hydrate Formed with Tetrabutylammonium Propionate

The phase equilibrium temperature and dissociation heat of tetrabutylammonium propionate (TBAPr) hydrate are reported. TBAPr hydrate is a type of ionic semiclathrate hydrates and also could potentially be used as thermal energy storage material. The temperature‐composition phase diagram of the TBAPr hydrate was determined in a defined range of mass fractions. Considering the dissociation heat of differential scanning calorimetry (DSC) measurements, multiple peaks of heat flow were observed in the TBAPr‐water system at the TBAPr mass fraction lower than 0.35, and there was a single peak at the mass fraction higher than 0.37.     

Prediction of carbon dioxide separation from gas mixtures in petroleum industries using the Levenberg–Marquardt algorithm

In this study, two mathematical models for hydrate formation process to separate carbon dioxide by a combination of two different kinds of organic and surfactant promoters are presented. Promoters such as sodium dodecyl sulfate, sodium dodecyl benzene sulfonate, and dodecyl trimethyl ammonium chloride as surfactant promoters; also, tetrahydrofuran, cyclopentane, 1,3-dioxolane, and 2-methyl tetrahydrofuran as organic promoters have been used in recent years. The results showed that a combination of 3000 ppm of surfactant promoters and 4 wt% organic promoters had the highest separation rate of carbon dioxide and; consequently, the investigated models were based on this optimum condition. As a matter of fact, by using these simulations the hydrate formation behavior was predicted with high accuracy; moreover, conducting consuming experiments is not essential anymore. To sum up, in the present research both Vandermonde matrix model and Levenberg-Marquardt algorithm were applied to predict the hydrate formation behavior; in addition, their results were precisely considered and validated with experimental data.     

Induction time,storage capacity,and rate of methane hydrate formation in the presence of SDS and silver nanoparticles

In this communication, the kinetic parameters of methane hydrate formation (induction time, quantity and rate of gas uptake, storage capacity (SC), and apparent rate constant) in the presence of sodium dodecyl sulfate (SDS), synthetized silver nanoparticles (SNPs), and mixture of SDS?+?SNPs have been studied. Experimental measurements were performed at temperature of 273.65?K and initial pressure of 7?MPa in a 460?cm³ stirred batch reactor. Our results show that adding SDS, SNPs and their mixture increases the quantity of gas uptake, water to hydrate conversion, and SC of methane hydrate formation, noticeably. Using 300?ppm SDS increases the SC and the quantity of methane uptake 615, and 770%, respectively, compared with pure water. Investigating the hydrate growth rate at the start of hydrate formation process shows that, using SNPs, SDS, and their mixture increases the initial apparent rate constant of hydrate rate, considerably. Our results show that the system of methane?+?water?+?SDS 500?ppm?+?SNPs 45?µM represents the maximum value of initial apparent rate constant, compared with other tested systems.