Recovery of methane from coal-bed methane gas mixture via hydrate-based methane separation method by adding anionic surfactants

To screen a preferable kinetics promoter, the effects of sodium dodecyl sulfate (SDS) and sodium dodecyl benzene sulfonate (SDBS) within tetrahydrofuran (THF) solution on recovering methane (CH₄) from simulated coal-bed methane (CBM) were investigated at 279.15 K and 1.50–4.50 MPa. The results show the addition of surfactants can remarkably enhance the hydrate formation rate. However, gas uptake, CH₄ split fraction and split factor in THF-SDS solution are superior to those in THF-SDBS solution. Therefore, THF-SDS solution is an ?appropriately integrated additive for recovering CH₄ from coal-bed methane gas mixture.     

纳米Fe3O4固载聚苯乙烯球对甲烷水合物生成与分解的影响

为了提高甲烷水合物合成反应中的传热效率,选取纳米Fe3O4作为导热材料,将不同量的纳米Fe3O4固载在聚苯乙烯球(PSNS)上,通过乳液聚合法制备了20%Fe3O4/PSNS和40%Fe3O4/PSNS两种新型聚苯乙烯球,并研究了PSNS,20%Fe3O4/PSNS,40%Fe3O4/PSNS三种聚苯乙烯溶液和十二烷基硫酸钠(SDS)对甲烷水合物生成与分解的影响。实验结果表明:三种聚苯乙烯溶液生成的水合物储气倍数和分解后甲烷回收率均高于SDS的100V/V,72.50%;对比三种聚苯乙烯溶液的促进效果发现,Fe3O4的存在明显缩短了水合物反应平衡时间,随着Fe3O4含量的增加,反应平衡时间由18 h缩短到9 h;Fe3O4提高了甲烷回收率,以20%Fe3O4/PSNS和40%Fe3O4/PSNS为促进剂时,水合物分解后甲烷回收率分别为92.15%,89.80%,都高于PSNS的85.00%。     

Hydrogen production from methane hydrate with sequestering of carbon dioxide

Methane hydrate exists in large amounts in certain locations, in sea sediments and the geological structures below them and below artic regions permafrost, at low temperature and high pressure. It has recently been shown that there are suitable methods for producing methane, perhaps on a floating platform. There it could be reformed in an endothermic process to produce hydrogen and carbon dioxide. Some of the methane could be used to provide heat energy for a power plant on the platform to provide all needed power and support for the reforming process. After separation, hydrogen is the valuable and transportable product. All carbon dioxide produced on the platform could be separated from other gases and then sequestered, in one of several possible forms. In this way, hydrogen could be made available without the release of carbon dioxide to the atmosphere and the hydrogen could be an enabling step toward a world hydrogen economy, free of particles and carbon dioxide pollution.     

含甲烷水合物多孔介质渗透性的实验研究

为研究多孔介质中甲烷水合物对其渗透性的影响,开发了一套适合在该条件下测量渗透性的实验装置。研究了多孔介质孔隙度与渗透率的关系;用BZ-01、BZ-02玻璃砂模拟多孔介质进行了渗透率测量实验,测试了不同甲烷水合物饱和度下多孔介质渗透率的变化情况。结果表明,多孔介质中甲烷水合物的存在会导致其渗透率急剧下降,饱和度-渗透率曲线呈指数分布。根据实验数据拟合出了渗透率随饱和度变化的经验公式,并将实验数据与渗透率模型进行了比较,发现在实验条件下生成的甲烷水合物符合平行毛细管模型,水合物占据毛细管中心,多孔介质中的流动形成环状流。     

Hydrogen production by radio frequency plasma stimulation in methane hydrate at atmospheric pressure

Methane hydrate, formed by injecting methane into 100 g of shaved ice at a pressure of 7 MPa and reactor temperature of 0 °C, was decomposed by applying 27.12 MHz radio frequency plasma in order to produce hydrogen. The process involved the stimulation of plasma in the methane hydrate with a variable input power at atmospheric pressure. It was observed that production of CH₄ is optimal at a slow rate of CH₄ release from the methane hydrate, as analyzed by in light of the steam methane reforming (SMR) and the methane cracking reaction (MCR) processes in accordance with the content of gas production. In comparison with the steam methane reforming (SMR), it was found that methane-cracking reaction (MCR) was dominant in conversion of CH₄ into hydrogen. An H₂ content of 55% in gas production was obtained from conversion of 40% of CH₄ at an input power of 150 W. The results clearly show that hydrogen can be directly produced from methane hydrate by the in-liquid plasma method.     

Efficient promotion of methane hydrate formation and elimination of foam generation using fluorinated surfactants

Methane hydrate preparation is an effective method to store and transport methane. In promoters to facilitate methane hydrate formation, homogeneous surfactant solutions, sodium dodecyl sulfate (SDS) in particular, are more favorable than heterogeneous particles, thanks to their faster reaction rate, more storage capacity, and higher stability. Foaming, however, could not be avoided during hydrate dissociation with the presence of SDS. This paper investigated the ability of five fluorinated surfactants: potassium perfluorobutane sulfonate (PBS), potassium perfluorohexyl sulfonate (PHS), potassium perfluorooctane sulfonate (POS), ammonium perfluorooctane sulfonate (AOS), and tetraethylammonium perfluorooctyl sulfonate (TOS) to promote methane hydrate formation. It was found that both PBS and PHS achieve a storage capacity of 150 (V/V, the volume of methane that can be stored by one volume of water) within 30 min, more than that of SDS. Cationic ions and the carbon chain length were then discussed on their effects during the formation. It was concluded that PBS, PHS, and POS produced no foam during hydrate dissociation, making them promising promoters in large-scale application.     

Latest progress in numerical simulations on multiphase flow and thermodynamics in production of natural gas from gas hydrate reservoir

Natural gas hydrates are promising potential alternative energy resources. Some studies on the multiphase flow and thermodynamics have been conducted to investigate the feasibility of gas production from hydrate dissociation. The methods for natural gas production are analyzed and several models describing the dissociation process are listed and compared. Two prevailing models, one for depressurization and the other for thermal stimulation, are discussed in detail. A comprehensive numerical method considering the multiphase flow and thermodynamics of gas production from various hydratebearing reservoirs is required to better understand the dissociation process of natural gas hydrate, which would be of great benefit to its future exploration and exploitation.     

甲烷水合物及其沉积层导热特性的研究现状

总结了近年来国内外甲烷水合物及其沉积层导热特性的研究现状,从实验测试和模拟研究两方面分析了甲烷水合物及其沉积层的导热影响因素、相关规律和导热机理。研究结果表明：纯质水合物的导热性能与外界温度、压力、客体分子数量、多孔介质、笼形结构等因素有关,其值大小主要由主体水分子形成的笼形结构决定;而水合物沉积层导热系数的大小主要依赖于实验样品的组成成分、初始水饱和度、各组分分布,与温度、压力以及垂直有效应力关系不大。最后,指出了现存研究方法中一些值得改进的地方,并对今后的研究工作进行了展望。     

Evaluation of the economic impact of hydrogen production by methane decomposition with steam reforming of methane process

There has been considerable interest in the development of more efficient processes to generate hydrogen. Currently, steam methane reforming (SMR) is the most widely applied route for producing hydrogen from natural gas. Researchers worldwide have been working to invent more efficient routes to produce hydrogen. One of the routes is thermocatalytic decomposition of methane (TCDM) - a process that decomposes methane thermally to produce hydrogen from natural gas. TCDM has not yet been commercialized. However, the aim of this work was to conduct an economic and environmental analysis to determine whether the TCDM process is competitive with the more popular SMR process. The results indicate that the TCDM process has a lower carbon footprint. Further research on TCDM catalysts could make this process economically competitive with steam methane reforming.     

Enhancement of methane hydrate formation using a mixture of tetrahydrofuran and oxidized multi‐wall carbon nanotubes

Methane hydrate is a kind of gas hydrate formed by physical binding between water molecules and methane gas, which is captured in the cavities of water molecules under a specific temperature and pressure. Pure methane hydrate of 1 m³ can be decomposed into methane gas of 172 m³ and water of 0.8 m³ at standard conditions. Methane hydrate has many practical applications such as separation processes, natural gas storage transportation, and carbon dioxide sequestration. For the industrial utilization of this substance, it is essential to find a rapid method of manufacturing it. This work studies the formation of methane hydrates by using tetrahydrofuran (THF) and oxidized carbon nanotubes (OMWCNTs) by testing different fluid mixtures of THF and carbon nanotubes. The results show that when the mixed fluid contained THF, the OMWCNTs showed the gas consumption 5.2 times that of distilled water at 3.4 K subcooling. Also, THF's effects as a thermodynamic phase equilibrium promoter were preserved when it was used with OMWCNTs. Therefore, it can be expected that when OMWCNTs are used with an aqueous mixture of THF, both the favorable phase equilibrium of THF and the high gas consumption of the carbon nanotubes can be obtained. Copyright © 2013 John Wiley & Sons, Ltd.     

气体水合物分解热的研究进展

气体水合物作为新一代蓄冷介质,在空调蓄冷领域有良好的应用前景.其分解热是重要的热物性之一,对蓄冷系统的设计至关重要.介绍了国内外气体水合物分解热的研究进展,列出了气体水合物分解热的测量、计算方法以及影响气体水合物分解热的主要因素和影响机理,并指出气体摩尔分数和添加剂摩尔分数均会影响水合物的分解热,且气体分子直径是影响水合物分解热的主要因素.研究为水合物的开采利用、稳定性研究以及蓄冷系统的设计提供了理论基础.     

Catalytic decomposition of methane in the presence of in situ obtained ethylene as a method of hydrogen production

It is predicted that the catalytic decomposition of methane (CDM) can be a promising pro-ecological method of hydrogen production. The main drawback of this process is fast deactivation of the catalyst by the carbonaceous deposit formed on its surface. This problem can be effectively solved e.g. by methane decomposition in the presence of ethylene. However, as ethylene is expensive, an attempt was made to synthesise it in situ, in the process of oxidative coupling of methane (OCM), which was subsequently combined with the CDM process in one reactor. As OCM catalysts the sodium–calcium or lithium–magnesium oxide systems were tested, while the CDM catalyst was activated carbon. The optimum conditions of ethylene production were established and applied to conduct the combined OCM–CDM process. The combined process was found to produce hydrogen in higher yields than when only the activated carbon catalyst was used. This observation was explained by formation of catalytically active carbonaceous deposit appearing as a result of decomposition of ethylene.     

天然气水合物降压开采储层稳定性模型分析

储层稳定性是天然气水合物开采所面临的关键问题。本文基于多孔介质流体动力学和弹性力学,建立了天然气水合物降压开采储层稳定性数学模型,包括储层沉降和井壁稳定性分析两个方面,并以墨西哥湾某处水合物藏的基本参数为例,进行了水合物降压开采储层稳定性的模拟计算。结果表明,在水合物降压开采的过程中,孔隙流体压力降低导致了储层的沉降,最大的沉降发生在井壁附近,水合物分解会加剧储层的沉降;降低井孔压力会造成井壁破坏的潜在危险,在井壁附近,周向和垂向应力达到最大处容易发生失稳破坏,地层的水平应力差会增加井壁的不稳定性。     

Hydrogen production by propylene-assisted decomposition of methane over activated carbon catalysts

Catalytic decomposition of methane (CDM) permits obtaining hydrogen in high yields and – what is essential – it does not lead to release of CO₂. Unfortunately, most of the catalysts used in this process undergo fast deactivation. Their possible regeneration, consisting in the removal of pore blocking carbonaceous deposit of low catalytic activity, leads to generation of undesirable carbon dioxide. An alternative solution for maintaining high catalyst activity in the CDM reaction can be generation of the catalytically active carbonaceous deposit on its surface. Such a deposit can be obtained by decomposition of different organic substances. This paper reports on methane decomposition carried out in the presence of propylene (used in the concentration of 10 or 20%). The reaction was performed at three temperatures of 750 °C, 850 °C or 950 °C. Three types of activated carbon were tested as catalysts: the first one was obtained by activation of pine wood biomass with Na₂CO₃, whereas the second and third ones were commercial carbons (WG-12 and Norit RX3 Extra). According to the results, the addition of propylene to the CDM system effectively reduces deactivation of the activated carbon catalysts and permits fast stabilisation of their catalytic activity at a high level.     

甲烷催化制氢气的研究进展

阐述了甲烷催化制氢技术研究取得的主要进展，对各种制氢工艺方法、催化剂的种类和性能、反应器的类型、催化剂积炭等方面进行了详细的论述。     

Investigations on the formation kinetics of semiclathrate hydrate of methane in an aqueous solution of tetra-n-butyl ammonium bromide and sodium dodecyl sulfate in porous media

Natural gas hydrate is considered to be an attractive sustainable energy resource for the world. Hydrate as a technology can be of immense importance for various industrial processes, such as multicomponent natural gas separation, gas storage and transportation, and carbon dioxide capture from flue gases and sequestration. A variety of hydrate additives, which includes promoters (thermodynamics and kinetics) and porous media, are being researched to improve the hydrate formation kinetics. However, studies involving the combinations of these are rare in the open literature. In this work, the formation kinetics of methane hydrate/semiclathrate hydrate using tetra-n-butyl ammonium bromide (TBAB) and sodium dodecyl sulfate (SDS) aqueous solutions at various concentrations in a porous medium containing silica sand at initial hydrate formation pressures (7.5 and 5.5 MPa) and temperatures (273.65 and 276.15 K) have been investigated. All the experiments were conducted using 75% water saturation. Various kinetics parameters, such as gas uptake, gas-to-hydrate conversion, and induction time, have been reported. It was found that the combination of TBAB+ SDS showed favorable hydrate formation kinetics in porous media than the TBAB system. This work provides information for further studies involving semiclathrate hydrate applications for various industrial processes.     

An experimental investigation into the effects of zeolites on the formation of methane hydrates

Methane hydrate is an ice‐like nonstoichiometric compound that forms when methane reacts with water at high pressures and low temperatures. It has a lot of practical applications such as separation processes, natural gas storage transportation, and carbon dioxide sequestration. Especially, the industrial use of hydrates requires large amounts of gas to be formed quickly into hydrates. Porous media significantly influence the rate of hydrate formation by reducing the chemical barrier, where zeolites are microporous minerals. This paper deals with natural and synthetic (5A and 13A) zeolites for hydrate formation and gas storage capacity. The results show that methane hydrates are formed much faster in the three zeolite solutions tested compared with their formation in distilled water at low subcooling temperatures (<7 K). It was also observed that the gas consumption was the greatest in the 0.01 wt.% zeolite 13X solution of distilled water. Its gas consumption was 5.1 times that of distilled water at 0.5 K subcooling. Zeolite 13X demonstrated its effectiveness in enhancing and expediting methane hydrate formation. Copyright © 2014 John Wiley & Sons, Ltd.     

海洋渗漏型天然气水合物气力提升特性模型分析

运用多相流体动力学理论，建立了气力提升开采海洋渗漏型天然气水舍物系统工艺参数的数学分析模型。结合实际水舍物藏开采条件，分析了气力提升系统主要工艺参数之间的关系及对提升动态特性的影响规律。在此基础上，对气力提升方法的能量效率进行了计算评估。计算结果表明，该种开采方法的能量效率远高于传统的注热开采方法。     

Production behavior of methane hydrate in porous media using huff and puff method in a novel three-dimensional simulator

The gas production behavior of methane hydrate in porous media using the huff and puff method was investigated in the Cubic Hydrate Simulator (CHS), a novel developed three-dimensional 5.8-L cubic pressure vessel. Three horizontal layers equally divide the CHS into four regions. A 9-spot distribution of the vertical wells, a single horizontal well and a 25-spot distribution of the thermometers are arranged on each layer, respectively. The vertical wells at the axis of the CHS were used as the injection and production wells. The huff and puff method includes the injection, soaking and production stages. The amount of water injected and produced, the gas production rate, the percentage of the hydrate dissociation and the gas-to-water ratio were evaluated. Under the thermodynamic conditions in this work, the gas production from the sediment in this work using the huff and puff method is economically profitable from the relative criterion point of view. The sensitivity analysis demonstrates the dependence of the gas production on the initial hydrate saturation, and the temperature and the injection rate of the injected hot water.     

Development of a reaction mechanism for predicting hydrogen production from homogeneous decomposition of methane

In this paper, a reaction mechanism is developed to model the kinetics of hydrogen production from decomposition of methane. The pyrolysis of hydrocarbons from several combustion mechanisms is compared with experiment to obtain the elementary reactions of this mechanism. Some modifications are then made to reduce the large errors observed at a high residence time. Sensitivity analysis is performed to find the reactions with the highest effect on hydrogen production and their rate constants are changed by using other mechanisms to obtain the lowest error in hydrogen production compared to experimental data. This study shows that modifying the rate constants of the reactions of dissociation of methane to hydrogen and methyl radicals, and the formation of benzene from propargyl radicals have the highest effect on improving the results. The new mechanism reduces the error introduced from existing models for predicting the amount of hydrogen production up to 15%, depending on residence time and temperature levels.