天然气水合物的导热系数

分析介绍了关于水合物导热系数类玻璃体变化规律的三种模型及其相关测试手段、样品制备方法和测试结果。针对物性和测试手段的特点，笔者指出在制备测试样品的时候就要注意其生成品质。最后对比了国外相关实验结果和本实验室对制冷剂水合物的测量结果。     

硝酸钕和钐的水合物在水中溶解热的测定

本文用补偿式数字量热计测定了六水、四水硝酸钕和六水、五水硝酸钐298.15K时在水中的溶解热,求得了它们的标准生成热、相应的标准脱水焓和晶格能。     

13C固体核磁共振测定气体水合物结构实验研究

采用高功率1H去偶结合魔角旋转13C固体核磁共振技术,在低温常压条件下对合成的乙烷和丙烷气体水合物进行了测试,获得了两种纯气体水合物的13C核磁共振谱图,初步建立了固体核磁共振波谱法测定天然气水合物的实验方法.实验表明:乙烷水合物的13C核磁共振谱图中仅有一条谱线(δ7.7),结构类型为sI,且乙烷分子仅填充在大笼中(...     

丙烷气体水合物合成实验的设计与研究

针对高中化学和大学化学中有关气体水合物的内容,设计了丙烷气体水合物的教学实验。该实验采用简单的方法合成丙烷水合物,操作简单、安全,实验重复性高,可以调动学生的学习兴趣。通过实验,便于学生了解丙烷水合物的物理化学性质、水合物相图的构成及作用。     

天然气水合物抑制剂用高分子研究进展

海底天然气开采过程中,甲烷和水可以形成天然气水合物,阻塞油气管道。本文先简要介绍高分子化合物用于水合物抑制剂的发展过程,从抗冻抑制剂的结构与性能关系,探讨了高分子型的低剂量天然气水合物抑制剂的特性、作用机理和主要影响因素。近年来的研究发现在寒冷地区海洋鱼类和昆虫体内存在一些抗冻蛋白,不仅能够降低水的冰点,而且能抑制天然气水合物的形成,是绿色环保的天然抑制剂,模拟这些具有抗冻性能的蛋白质结构的高分子化合物为今后水合物抑制剂研究提供一个新的发展方向。本文还提出了今后值得开展研究和应用的若干问题。     

一个考虑沉积物孔径分布特征的水合物相平衡模型

天然气水合物的相平衡条件一直是水合物相关研究的重点和难点. 本文探讨了沉积物孔隙大小及其分布特征对水合物相平衡条件的影响机理, 提出了有效孔隙半径的概念, 并利用沉积物孔隙大小分布特征, 假设孔径分布呈正态分布, 建立了水合物饱和度和有效孔隙半径之间的定量关系; 与传统的van der Waals-Platteeuw相平衡模型相结合, 提出了一个考虑沉积物孔隙大小及其分布特征的相平衡模型. 相对于传统模型, 本模型所表达的相平衡条件不再是二维平面的p-T曲线, 而是温度、压力以及水合物饱和度之间的三维定量关系. 这一特征使得所建模型既能较为真实地反映水合物形成与分解机理, 又能有效地考虑孔隙大小分布对水合物相平衡条件的影响. 通过与实验数据对比, 证明了所建模型的预测结果优于其他模型. 本模型在温度和压力条件确定的情况下还可以预测沉积物中水合物的饱和度, 因此, 可用于地层中水合物储量计算.     

环丙沙星水合物与无水合物晶型的相互转变(英文)

化合物的水合状态有赖于结晶溶媒中水的活度(aH2O).通过制备不同体积比水-有机溶媒的潜溶剂来控制aH2O,用粉末X射线衍射(PXRD)、热重分析(TGA)和差示扫描热量(DSC)等方法表征在具有不同aH2O的水-甲醇中平衡一段时间后的过剩环丙沙星固体的结晶状态.同时采用高效液相色谱测定环丙沙星水合物、无水合物以及它们的混合物在具有不同aH2O的水-甲醇混合溶液中的溶解度.结果表明溶解度变化规律与在相应aH2O的水-甲醇中多余固体的晶型变化规律基本一致.利用实验所得数据构建了环丙沙星无水合物/水合物相稳定性与aH2O的关系图.将该图像与放置于室温以及一定相对湿度条件下时间长达十二周的样品的PXRD数据对比,表明本实验所用的研究方法能够快速、精确地预测无水合物与水合物之间的相互转变过程以及水-有机溶媒的aH2O对它们的相对稳定性的影响.     

甲烷水合物在静态体系中生成反应的促进

静态体系生成甲烷水合物是个缓慢的、不完全的过程。即使使用表面活性剂也不能实现反应物的100％转化。本文讨论了在静态反应停止后,使用系统温度振荡的方法来促进水合反应的继续进行,直至完全转化。在系统温度从-10～4℃之间周期振荡时,原本停滞的水合反应在水的相变温度附近又开始发生反应,由于水合物合成时铠甲效应的存在,水在样品中的过冷度达到10℃左右。文中对样品的热物性测试表明,在经过几个温度变化周期后,反应非常完全,反应器中样品是100％的甲烷水合物。     

聚乙烯唑啉作用下甲烷水合物分解的分子动力学模拟

利用分子动力学模拟系统研究了不同质量浓度下(1.25%、2.50%、6.06%)聚乙烯唑啉(PEtO)对甲烷水合物的分解作用. 模拟体系为甲烷水合物2′2′2的超胞和聚合物对接体系. 模拟发现水分子间氢键构架的水合物笼型结构在PEtO的作用下出现扭曲, 最终导致水合物笼型结构完全坍塌. 通过氧原子径向分布函数、均方位移以及扩散系数比较不同浓度PEtO的作用, 证实在一定浓度范围内, PEtO的浓度越高, 其水合物分解作用越强. 此外, PEtO 具有一定的可生物降解性. PEtO 对水合物的作用为: PEtO 吸附在水合物表面, 其中的酰胺基(N―C＝O)与成笼的水分子形成氢键, 破坏邻近的笼形结构, 令水合物分解; PEtO不断分解表面的水合物, 直到水合物笼完全分解.     

Study of CCl3F hydrate formation and dissociation in W/O emulsion by differential scanning calorimetry and X-ray diffraction

Differential scanning calorimetry (DSC) and time-resolved synchrotron X-ray diffraction as a function of temperature (XRDT) were combined in a novel way in order to study conditions of formation and the amount of gas clathrate formed in dispersed systems. The formation and dissociation of trichlorofluoromethane hydrate CCl₃F·(H₂O)₁₇ in a water-in-oil emulsion were followed by using these combined techniques. An emulsion containing 3 wt.% NaCl was submitted to a cooling and heating cycle between 20 and −50 °C. During cooling, a single exothermic peak at −43 °C, found in DCS thermograms was assigned to the freezing of under-cooled water droplets; however, no noticeable signal related to hydrate crystallisation was detected. Conversely, during subsequent heating, the progressive melting of ice was followed by an endothermic signal indicative of hydrate decomposition. From X-ray diffraction performed on an emulsion sample, it was possible to identify the exact condition of CCl₃F·(H₂O)₁₇ formation. XRDT diffraction patterns clearly demonstrated that only ice crystallised in the aqueous droplets during cooling and that the hydrate only formed during heating simultaneously with melting of ice. From the solid–liquid phase diagrams of systems H₂ONaCl and CCl₃FH₂ONaCl and from the DSC and XRDT experiments, the composition of the droplets was deduced. The upper limit of the amount of hydrate that could form in the system was calculated.     

氯盐溶液中甲烷水合物高压分解条件及影响因素

向水合物储层注入盐类溶液是水合物常规开采技术之一,所以必须掌握储层压力条件下盐类溶液中水合物分解条件及其影响因素.本文研究了NaCl、MgCl2、CaCl2氯盐溶液中甲烷水合物分解条件,结果表明NaCl(2.0、1.0、0.5 mol·L-1)、MgCl2 (1.0、0.5 mol·L-1)和CaCl2 (1.0、0.5 mol·L-1)溶液中甲烷水合物的分解温度比纯水中分别降低了(4.8、2.4、1.0 K (NaCl))、(5.3、1.5 K (MgCl2))和(4.3、1.8 K (CaCl2)).以van der Waals 和Platteeuw 热力学模型为基础,结合电解质溶液中水的活度方程(Pitzer-Mayorga 方程),给出了氯盐溶液中水合物分解条件热力学模型,进而比较了模型计算值与实验值,结果显示两者非常吻合.分析表明,氯盐溶液中离子静电作用产生的水分子溶剂化效应和盐析效应降低了水的活度而导致水合物分解温度降低.     

Numerical studies of hydrate dissociation and gas production behavior in porous media during depressurization process

In this study,a numerical model is developed to investigate the hydrate dissociation and gas production in porous media by depressurization.A series of simulation runs are conducted to study the impacts of permeability characteristics,including permeability reduction exponent,absolute permeability,hydrate accumulation habits and hydrate saturation,sand average grain size and irreducible water saturation.The effects of the distribution of hydrate in porous media are examined by adapting conceptual models of hydrate accumulation habits into simulations to govern the evolution of permeability with hydrate decomposition,which is also compared with the conventional reservoir permeability model,i.e.Corey model.The simulations show that the hydrate dissociation rate increases with the decrease of permeability reduction exponent,hydrate saturation and the sand average grain size.Compared with the conceptual models of hydrate accumulation habits,our simulations indicate that Corey model overpredicts the gas production and the performance of hydrate coating models is superior to that of hydrate filling models in gas production,which behavior does follow by the order of capillary coating>pore coating>pore filling>capillary filling.From the analysis of t1/2,some interesting results are suggested as follows:(1) there is a "switch" value(the"switch"absolute permeability) for laboratory-scale hydrate dissociation in porous media,the absolute permeability has almost no influence on the gas production behavior when the permeability exceeds the "switch" value.In this study,the "switch" value of absolute permeability can be estimated to be between 10 and 50 md.(2) An optimum value of initial effective water saturation Sw,e exists where hydrate dissociation rate reaches the maximum and the optimum value largely coincides with the value of irreducible water saturation S wr,e.For the case of Sw,Swr,e,there are different control mechanisms dominating the process of hydrate dissociation and gas production.     

H and H NMR studies of cyclohexane nanocrystals in controlled pore glasses

The formation and behaviour of cyclohexane and cyclohexane-d₁₂ nanocrystals in mesoporous solids of well-defined dimensional constraints are studied by ¹H and ²H NMR. The NMR line widths, spin–spin relaxation times (T₂), spin–lattice relaxation times (T₁) and diffusivities (D) were measured as a function of temperature, and the results are discussed with reference to the values obtained for the bulk materials. The confined solids exhibit substantial changes in the phase behaviour and molecular dynamics. Thus, the line-shape measurements reveal a two-phase system consisting of a highly mobile component at the surface of the pore and a plastically crystalline phase in the centre of the pore. The liquid-like surface layer in the mesopores is observable well below the reduced transition temperature of the confined cyclohexane. However, the T₂ and diffusion measurements show that the mobile phase also embraces a minor component attributed to non-frozen liquid in pockets or offshoots.     

Dissociation behavior of “dry water” C_3H_8 hydrate below ice point:Effect of phase state of unreacted residual water on a mechanism of gas hydrates dissociation

The results on a dissociation behavior of propane hydrates prepared from "dry water" and contained unreacted residual water in the form of ice inclusions or supercooled liquid water(water solution of gas) were presented for temperatures below 273 K.The temperature ramping or pressure release method was used for the dissociation of propane hydrate samples.It was found that the mechanism of gas hydrate dissociation at temperatures below 273 K depended on the phase state of unreacted water in the hydrate sample.Gas hydrates dissociated into ice and gas if the ice inclusions were in the hydrate sample.The samples of propane hydrates with inclusions of unreacted supercooled water only(without ice inclusions) dissociated into supercooled water and gas below the pressure of the supercooled water-hydrate-gas metastable equilibrium.     

多孔介质中甲烷水合物的分解特性

利用定容降压方法测定了在不同多孔介质中甲烷水合物的分解实验数据, 所使用的多孔介质平均孔径分别为9.03, 12.95, 17.96和33.20 nm, 其中孔径为12.95 nm的多孔介质采用了3个粒径范围, 分别为0.105～0.150, 0.150～0.200和0.300～0.450 mm; 其它孔径的多孔介质的粒径范围为0.105～0.150 mm. 在封闭的条件下测定了不同温度与不同初始生成压力下甲烷水合物的分解实验数据(实验温度范围为269.15～278.15 K, 初始生成压力范围为4.1～11.0 MPa), 结果表明, 水合物的分解速度随着初始生成压力的增加和水浴温度的降低而升高, 也随孔径的增加而升高, 但随多孔介质粒径的增大而降低. 在孔径较大和分解温度较低时, 多孔介质中水合物分解引起的温度降低会使水结冰, 从而减缓水合物的分解速度.     

水对采空区遗煤吸附电厂烟气影响的理论计算

为研究电厂烟气注入采空区时,煤中含水率和烟气中水分对于封存温室气体CO_2和抑制煤自燃的影响,建立干煤和湿煤结构模型,采用巨正则系综蒙特卡洛方法,计算了不同水分含量的烟气组分CO_2/O_2/N2/H_2O在干煤以及不同含水率的湿煤中的吸附行为。结果表明,烟气中CO_2竞争性最强吸附量最大,O_2的物理吸附量极小,烟气中H_2O含量不影响CO_2、N2和O_2的吸附量,可不进行干燥处理直接将电厂烟气注入采空区。随着煤中含水率增加,水分占据孔隙空间,范德华作用减弱,H_2O-H_2O之间的氢键作用增强且提供了额外吸附位。H_2O的等量吸附热升高,吸附位移向吸附作用更强的低相互作用能区域,吸附大量水形成水团簇,与CO_2竞争吸附位,并且占据吸附空间抑制CO_2、O_2、N2的吸附,使其吸附量降低50%以上,因此,注入烟气时应充分考虑采空区煤体的含水率问题。     

NMR/MRI study of clathrate hydrate mechanisms

Clathrate hydrates are of great importance in many aspects. However, hydrate formation and dissociation mechanisms, essential to all hydrate applications, are still not well understood due to the limitations of experimental techniques capable of providing dynamic and structural information on a molecular level. NMR has been shown to be a powerful tool to noninvasively measure molecular level dynamic information. In this work, we measured nuclear magnetic resonance (NMR) spin lattice relaxation times (T1's) of tetrahydrofuran (THF) in liquid deuterium oxide (D2O) during THF hydrate formation and dissociation. At the same time, we also used magnetic resonance imaging (MRI) to monitor hydrate formation and dissociation patterns. The results showed that solid hydrate significantly influences coexisting fluid structure. Molecular evidence of residual structure was identified. Hydrate formation and dissociation mechanisms were proposed based on the NMR/MRI observations.     

Detecting gas hydrate behavior in crude oil using NMR

Because of the associated experimental difficulties, natural gas hydrate behavior in black oil is poorly understood despite its grave importance in deep-water flow assurance. Since the hydrate cannot be visually observed in black oil, traditional methods often rely on gas pressure changes to monitor hydrate formation and dissociation. Because gases have to diffuse through the liquid phase for hydrate behavior to create pressure responses, the complication of gas mass transfer is involved and hydrate behavior is only indirectly observed. This pressure monitoring technique encounters difficulties when the oil phase is too viscous, the amount of water is too small, or the gas phase is absent. In this work we employ proton nuclear magnetic resonance (NMR) spectroscopy to observe directly the liquid-to-solid conversion of the water component in black oil emulsions. The technique relies on two facts. The first, well-known, is that water becomes essentially invisible to liquid state NMR as it becomes immobile, as in hydrate or ice formation. The second, our recent finding, is that in high magnetic fields of sufficient homogeneity, it is possible to distinguish water from black oil spectrally by their chemical shifts. By following changes in the area of the water peak, the process of hydrate conversion can be measured, and, at lower temperatures, the formation of ice. Taking only seconds to accomplish, this measurement is nearly direct in contrast to conventional techniques that measure the pressure changes of the whole system and assume these changes represent formation or dissociation of hydrates - rather than simply changes in solubility. This new technique clearly can provide accurate hydrate thermodynamic data in black oils. Because the technique measures the total mobile water with rapidity, extensions should prove valuable in studying the dynamics of phase transitions in emulsions.     

P-T stability conditions of methane hydrate in sediment from South China Sea

For reasonable assessment and safe exploitation of marine gas hydrate resource, it is important to determine the stability conditions of gas hydrates in marine sediment. In this paper, the seafloor water sample and sediment sample (saturated with pore water) from Shenhu Area of South China Sea were used to synthesize methane hydrates, and the stability conditions of methane hydrates were investigated by multi-step heating dissociation method. Preliminary experimental results show that the dissociation temperature of methane hydrate both in seafloor water and marine sediment, under any given pressure, is depressed by approximately -1.4 K relative to the pure water system. This phenomenon indicates that hydrate stability in marine sediment is mainly affected by pore water ions.