Phase behavior of clathrate hydrates: a model for single and multiple gas component hydrates

Presented here is a model that accurately predicts equilibrium pressures as a function of temperature of hydrates with CH₄, C₂H₆, C₃H₈, N₂, H₂, and CO₂ and their mixtures as guests. The model parameters fit to a subset of the equilibrium pressure data for single guest hydrates allow the prediction of phase behavior in mixed guest hydrates. For single guest hydrates, our model improves upon the van der Waals and Platteeuw (vdWP) model with a percent absolute average deviation (%AAD) from all equilibrium pressure data of 5.7% compared to 15.1% for the vdWP model. Predictions of equilibrium pressures for all available mixed guest hydrates result in a 11.6%AAD with our fugacity-based model compared to 18.6% for the vdWP model. Also, our model leads to a prediction of the structure change of the methane-ethane hydrate within 5% of its known equilibrium composition in the vapor phase without any adjustment of its parameters. We have also found that at temperatures above , double occupancy of nitrogen in the large cavity of structure II hydrate is important for the prediction of accurate equilibrium pressures.     

Historical perspectives on gas hydrates and citation impact analysis

Gas hydrates, or clathrate hydrates, is a multidisciplinary field of research involving potential applications to the oil and gas industry, energy security, and innovative technological applications with literature referenced back to 1810. The field of gas hydrates or clathrate hydrates has progressed over the past several decades from academic curiosity-driven research to industrially relevant research related to flow assurance and methane hydrates in nature as an energy resource. In the recent few decades, several innovative and sustainable applications have emerged with gas hydrate or clathrate hydrate as a technology enabler. In this work, I present a bibliometric analysis of the field of gas hydrates or clathrate hydrates for the period from 1901 to 2020 from the Web of Science core collection database of Clarivate Analytics. In total, 12 152 journal publications (review and original research articles) were analyzed from Web of Science core collection database spanning 121 years (1901–2020). Top countries, top cited review articles, and original research articles along with top source titles (journals) are identified and highlighted. In addition, the field classifications and citation rate trends have been analyzed and presented. Network visualization maps are presented for countries, sources, and organizations by analysing citations in VOSviewer. Co-occurrence analysis is performed to identify the top keywords and their links through network visualization based on VOSviewer.     

天然气水合物资源勘探开发技术研究进展

天然气水合物储量巨大,是人类理想的潜在的替代能源。对世界天然气水合物资源基本特征和分布情况进行了介绍,对国内外天然气水合物勘探开发技术以及环境效应进行了阐述。     

Phase behavior of gas hydrates in nanoporous materials: Review

A precise understanding of phase behavior for a variety of both artificial and natural processes is essential to achieving scientific and technological goals. There has been growing research interest in gas hydrates confined in nanoporous media aiming to simulate and analyze the unique behavior of natural gas hydrates in sediments. Moreover, the appearance of peculiar properties due to the confinement effect stimulates research on gas hydrate technology for gas separation, such as CO₂ capture from versatile pre/post combustion emissions. In spite of their importance, reliable phase equilibrium data on gas hydrates confined at a nanoscale are scattered throughout the literature, while those in bulk state are abundant. Accordingly, we surveyed the previous studies on the phase behavior of gas hydrates in various nanoporous materials to include and provide valuable information and knowledge for start-up researchers in various gas hydrate fields.     

硫酸铬钾结晶水合物用作气相色谱固定相的研究

硫酸铬钾结晶水合物用作气相色谱固定相的特性进行了研究 ,结果表明 ,其色谱性能良好 ,可作固定相使用。     

四丁基溴化铵-二氧化碳-水体系半笼水合物相平衡数据的测定

水合物相平衡数据是利用水合物捕集二氧化碳的基础数据,利用定容逐步加热的方法测量了四丁基溴化铵-二氧化碳-水三元体系水合物的相平衡数据,实验测量的压力和温度分别为1.0-4.3 MPa,282.75-292.15 K,四丁基溴化铵水溶液的质量分数为5％ -30％.实验结果表明:在一定的温度条件下,与纯水中二氧化碳水合物形...     

Structure‐H gas hydrates in petroleum reservoir fluids

An integrated experimental/modelling investigation was conducted on the potential of newly discovered strueture‐H (sH) hydrates formation in petroleum reservoir fluids. A thermodynamic model was validated against a series of experimental data on a natural gas with various quantities of methylcyclohexane (MCH). Three mixtures were tested where structure‐II (sII), sII/sH and sH were the stable structures. The validated thermodynamic model was employed to predict the stable hydrate structure for a large number of real reservoir fluids, (i.e., black oils, volatile oils and gas condensates). The results showed that sII is the stable hydrate structure for all systems investigated in this work. However, sH might co‐exist with sII in some reservoir fluids where transportation of hydrates as slurry is being considered.     

Impact of the fluid flow conditions on the formation rate of carbon dioxide hydrates in a semi‐batch stirred tank reactor

CO₂ hydrate formation experiments are performed in a 20 L semi‐batch stirred tank reactor using three different impellers (a down‐pumping pitched blade turbine, a Maxblend?, and a Dispersimax?) at various rotational speeds to examine the impact of the flow conditions on the CO₂ hydrate formation rate. An original mathematical model of the CO₂ hydrate formation process that assigns a resistance to each of its constitutive steps is established. For each experimental condition, the formation rate is measured and the rate‐limiting step is determined on the basis of the respective values of the resistances. The efficiencies of the three considered impellers are compared and, for each impeller, the influence of the rotational speed on the rate‐limiting step is discussed. For instance, it is shown that a formation rate limitation due to heat transfer can occur at the relatively small scale used to perform our experiments. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4387–4401, 2015     

Conversion of calcium aluminate cement hydrates at 60°C with and without water

There have been different hypotheses about the transformation mechanisms of calcium aluminate cement hydrates and this work aims to clarify the long‐running debate about the conversion approaches. In this work, CAH₁₀ and C₂AH₈ were produced from the pastes of calcium aluminate cement (CAC) cured for 24 hours at 10 and 20°C separately. And the cured pastes were continually cured at 60°C for 3 days with water and without water, respectively. The hydration of the pastes was halted by freeze‐drying, and the phases and microstructure of hydrates were investigated by XRD and SEM, respectively. The results indicate that CAH₁₀ and C₂AH₈ converted into C₃AH₆ and AH₃ in water presence at 60°C, but did not transform into C₃AH₆ and AH₃ without water. It is confirmed that the conversion of CAH₁₀ and C₂AH₈ to C₃AH₆ and AH₃ happens through preceding solution of CAH₁₀ and C₂AH₈ and subsequent precipitation of C₃AH₆ and AH₃.     

Piezo-elasticity and stability limits of monocrystal methane gas hydrates: Atomistic-continuum characterization

Gas hydrates are guest-host crystalline materials formed by water cages and guest gases such as methane and carbon dioxide under simultaneously relative high-pressure and low-temperature conditions. With this unique guest-host structural feature, gas hydrates can be used for gas storage and carbon dioxide (CO₂) sequestration, creating challenges such as flow assurance and geological stability. Some of these challenges are related to material instabilities caused by changing external conditions. Thus, this paper aims to determine the theoretical pressure stability limits of monocrystal defect-free sI methane gas hydrates at 0 K using accurate density functional theory to simulate the hydrate's thermodynamic and elastic responses under varying pressures. The pressure stability limits are determined by Born stability criteria and piezo sensitivity factors. The important brittle-to-ductile transitions of gas hydrates are established. Also, polycrystalline mechanical properties, including the Poisson ratio and Young modulus, are calculated from the second-order elastic constants obtained from the monocrystal sI methane hydrates, which provide the upper bounds. Taken together, the piezo-sensitivity of a complete set of elastic properties of sI methane gas hydrates and material stability limits determined by atomistic calculations provide new data and fundamental understanding for technological applications.     

Experimental measurement and thermodynamic modeling of cyclopentane hydrates with NaCl,KCl, CaCl2, or NaCl‐KCl present

Consistent phase equilibrium data for cyclopentane hydrates in presence of salts are vitally important to many industries, with particular interest to the field of hydrate‐based water separation via cyclopentane hydrate crystallization such as desalination. However, there are very little experimental equilibrium data, and no thermodynamic prediction tools. Hence, we set up a method to generate a great deal of much needed equilibrium data for cyclopentane hydrates in diverse saline solutions with a wide range of salt concentrations. Our method does furnish verified, reliable and accurate equilibrium data. Plus, three thermodynamic approaches are developed to predict equilibrium, and provide tools for simulations, by considering the kind of salt and concentrations. All three models are in very good accordance with experimental data. One method, using a new correlation between occupancy factor and water activity, might be the best way to obtain consistent, quick, and accurate dissociation temperatures of cyclopentane hydrate in brine. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2207–2218, 2018     

Phase equilibria of methane/TBAC mixed hydrates in the presence of produced water

Produced water (PW) is a by-product and one of the major pollutants from the oil and gas industry. PW contains various pollutants and must be treated as per environmental regulations before its disposal or reuse. Thus, it presents a substantial economic and ecological problem in the oil and gas industry. Currently, there is ongoing research on various methods to treat PW efficiently. Hydrate-based water desalination is one of the promising technologies. There is a continuing effort to identify a suitable hydrate former that can enhance the commercial feasibility of the process. This study investigates tetra-n-butyl ammonium chloride (TBAC) + methane as a potential clathrate former. The hydrate equilibrium temperatures of the mixed hydrates (TBAC + methane) are significantly higher at a given pressure than methane hydrates, suggesting the suitability of mixed hydrates for process development. There was a significant increase in the phase equilibrium temperature at 5 wt.% TBAC in the presence of PW compared to deionized water (DI), but the effect faded away as TBAC concentration increased in the solution. This can be attributed to a higher amount of chloride ions as the TBAC concentration is increased. These results elucidate the necessity to optimize the TBAC concentrations to develop an efficient hydrate desalination process for higher saline concentrations.     

Driving force in first-order phase transitions and its application to gas hydrate nucleation from a single phase

Classical nucleation theories of general application are taken as starting point to analyze the driving force for multicomponent gas hydrate nucleation from a single homogeneous phase. It is shown that the ratio between the specific surface energy and the critical radius of nucleation has a single value irrespective of the analyzed driving force expression. From this result, two driving force expressions for multicomponent gas hydrate nucleation are derived in the context of the so-called generalized nucleation theory, and it is demonstrated that the driving force for gas hydrates can be estimated using the same information given for the determination of the incipient formation points of the dispersed phase from a saturated phase. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

多孔介质中天然气水合物相平衡条件研究进展

天然气水合物主要赋存于各种沉积物孔隙之中,只有6%左右以块状纯水合物的形式存在。现在对于天然气水合物相平衡条件的研究主要集中在对多孔介质各因素的考察。就目前研究成果来看,理论预测自然条件中水合物稳定条件的准确性仍然较差,其主要原因：水合物稳定存在的天然条件影响因素远比实验室中（大多预测模型基于实验室建立）的影响因素复杂得多;实际中的介质微孔孔径并不恒定,呈分布状态,且分布比较复杂;自然条件下的多孔介质的成分、结构都非常复杂。     

天然石英砂中CO_2水合物的分解动力学

The decomposition kinetics for formation of CO2 hydrates in 90 cm3 wet natural silica sands were studied systematically using the depressurization method at the temperatures ranging from 273.2 to 277.2 K and the pressures from 0.5 to 1.0 MPa. The effects of temperature, pressure, particle diameter, porosity, and salinity of formation water on the decomposition kinetics were investigated. The results show that the dissociation percentage increases as temperature increases or as the initial decomposition pressure decreases. An increase in porosity or a decrease in particle diameter of silica sands accelerates the decomposition. Increasing the salinity of the formation water gives rise to a faster decomposition. However, a combination of the present results with the observa-tions in literature reveals that the effect of the coexisting ionic solute depends on its chemical structure.     

Preparation and Crystal Transformation Process of Magnesium Carbonate Hydrate Using MgSO4 as Raw Material

以 MgSO4为原料,通过向 MgSO4溶液中滴加（NH4）2CO3得到碳酸镁水合物。借助 X 射线衍射、扫描电子显微镜、差热分析及 Raman 光谱分析了转变过程中晶体组成和形态变化。研究发现,在 25～45 ℃制备的产物均为单斜晶系、空间群为 P21/n（14）的 MgCO3 3H2O 晶体;在 50～60 ℃结晶产物存在由针状的 MgCO3 3H2O 晶体向单斜晶系、空间群为 P21/c（14）的片状 4MgCO3 Mg（OH）2 4H2O 晶体的转变。从 pH 值变化和生长基元的形成对碳酸镁水合物晶体转变过程进行了分析。     

Universal correlation for gas hydrates suppression temperature of inhibited systems: I. Single salts

Reliable prediction of hydrate suppression temperature in presence of inhibitors, such as salts, over a wide range of pressures (up to 200 MPa) is critically important, especially in the area of deepwater oil and gas production. However, the existing models and correlations that account for salts have severe limitations and deficiencies in estimating the hydrate suppression temperature. Herein, we propose a new correlation, to be called Hu‐Lee‐Sum correlation, that significantly improves the predictions of the hydrate suppression temperature by considering the salt species and concentrations, system temperature and pressure, and hydrate structure. This article represents part I of this work and it will detail the development of the correlation and demonstrate the generality and universality of the correlation to predict the hydrate suppression temperature for any single salt system. Specifically, we show accurate predictions for the hydrate suppression temperature for a number of chloride and bromide salt brine systems. © 2017 American Institute of Chemical Engineers AIChE J, 2017     

Phase equilibrium and crystallization behavior of mixed lipid systems

As complex lipid systems, the phase and crystallization behavior of mixtures of a high-melting milk fat fraction with a low-melting milk fat fraction or canola oil was studied. A turbidity technique was developed to estimate solubility and metastability conditions of these lipid mixtures. Both solubility and metastability of the high-melting milk fat fraction in liquid lipids increased exponentially with temperature. At a given equilibration temperature, liquid phases and solid fractions with nearly identical melting profiles and TAG compositions were obtained regardless of the original concentration of the lipid mixture. The maximum melting temperature (MMT), as measured by DSC, of the liquid phase increased dramatically in the equilibrium temperature range of 27.5–35.0°C but did not change at temperatures below and above this range (down to 25.0°C and up to 40°C in this study). The content of long-chain TAG (C₄₆−C₅₂) increased and short-chain TAG (C₃₆−C₄₀) decreased in the liquid phases as the equilibrium temperature increased. A plot of the TAG group ratio (i.e, long-short-chain TAG) vs. equilibrium temperature was generated to illustrate the phase behavior of the complex lipid system and to represent a solubility curve, from which the supersaturation level for crystallization kinetics was determined. Higher supersaturation and lower temperature resulted in higher nucleation and crystallization rates. Compared to the system with a low-melting milk fat fraction, mixtures of the high-melting milk fat fraction with canola oil had higher nucleation and crystallization rates due to the lower solubility found for this system.     

Simulation and economic evaluation of natural gas hydrates [NGH] as an alternative to liquefied natural gas [LNG]

Despite the fact that relatively little is known about the ultimate resource potential of natural gas hydrates, it is certain that gas hydrates are a vast storehouse of natural gas and significant technical challenges need to be met before this enormous resource can be considered an economically producible reserve. In this theoretical study, a simulation scheme was suggested to produce NGH in an industrial scale using pure water as a carrier and seawater as a cooling source. Parametric study was carried out and rigorous design calculations for different operating parameters were investigated. Further more and economical evaluation was done taken data of locally produced LNG as a comparison. Production rates, storage and transportation from production region to consumer's ends were investigated. Results obtained suggested that NGH with little consideration can be a good alternative for fuel gas carrier.