多孔甲烷水合物样品导热系数的测定和模拟

天然气水合物是由水分子和气体分子在一定温压条件下形成的一种类冰状笼形化合物．天然气水合物主要存在于海底和大陆的永久冻土区和青藏高原等多年冻土区,是一种潜在的替代能源．在考虑对天然气水合物资源进行开采和考察地球温压变化对含水合物层的影响时,有必要掌握水合物的热物性和含水合物层的有效导热系数,但目前报道的水合物导热系数数据不一、差异很大．水合物是一种非化学计量的化合物,因此很难获得一个不含自由气、自由水的零孔隙率完美样品．利用多孔介质的理论模型对多孔水合物的导热系数进行预测是获得水合物本征导热系数的有效途径之一．我们在一个自行设计的实验台上使用HotDisk系统独特的单面测试技术,并利用瞬态平面热源法测定了含甲烷气的多孔甲烷水合物的有效导热系数,获得该样品的导热系数和温度以及所加压力的关系．为了研究含甲烷气的多孔甲烷水合物的有效导热系数与孔隙率的关系,我们利用自相似的Sierpinski地毯分形模型,先假设多孔介质体系由多孔介质和流体两部分组成,而多孔介质颗粒则由随机分布不相接触的颗粒和带有接触热阻的自相似分布颗粒组成,再通过一维热流假设和采用等价电阻网络（即通过电一热阻模拟分析得到系统的热导率）分别模拟了干砂（含空气）和多孔甲烷水合物样品（含自由甲烷气）导热系数与样品孔隙度的关系,推测了无孔隙水合物样品的导热系数．实验和模拟结果均显示样品的有效导热系数随着孔隙度的增大而降低,样品的有效导热系数在30％的孔隙度时降低了25％．通过分析实验结果和模拟结果发现,无孔隙甲烷水合物样品的导热系数约为0．7Wm^-1K^-1．     

海洋沉积物孔隙水总碱度的现场分析方法

海洋沉积物孔隙水总碱度及其分布对海洋天然气水合物的调查研究具有重要意义.孔隙水总碱度异常对于判断天然气水合物的存在具有重要的指示作用.建立了利用微量水样品测试总碱度的方法,将2.00 mL孔隙水样品加入10.00 mL已知总碱度的海水样品中,使用盐酸标准溶液滴定、pH计监控法测定混合溶液的总碱度,然后计算出加入孔隙水样品的总碱度.方法所需样品量少,测定结果的相对标准偏差小于2％(n=12),方法简便可行,可用于船上海洋沉积物孔隙水总碱度的现场测定.     

GC–IRMS测定白色块状天然气水合物气体中的碳氢同位素

研究了GC–IRMS联用技术测定烃类气体碳氢稳定同位素的方法。利用气相色谱仪将烃类气体各组分分开,通过高温燃烧/裂解转化为CO2和H2,然后导入MAT–253稳定同位素质谱仪进行测试。用该方法测试的标准甲烷气体碳、氢同位素值和其标定值一致,测定结果的相对标准偏差分别为0.222‰和0.950‰。用该法测定了广东沿海珠江口盆地东部海域首次钻获的高纯度天然气水合物样品所释放的烃类气体碳氢稳定同位素值,其中δ13C为–69.78‰(VPDB),δD为–184.4‰(VSMOW)。GC–IRMS法精确度高,可用范围广,适用于海洋天然气水合物样品所释放烃类气体碳氢同位素的测定。     

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(...     

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.     

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.     

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。     

天然气水合物分解热的确定

利用可视化高压流体测试系统研究了6个体系（甲烷、合成天然气、甲烷－环己烷、甲烷－环戊烷、甲烷－甲基环己烷（MCH）、合成天然气－甲基环己烷）水合物的形成条件，根据水合物相平衡数据应用Clausius-Clapeyron方程计算了Ⅰ型、Ⅱ型和H型水合物的分解热，结果表明水合物分解热与填充水合物晶格的气体分子直径有关。     

测定气体水合物相平衡数据的高压 PVT装置

建立了一套用于研究气体水合物的高压流体PVT（压力－体积－温度）测试系统。分别利用低压和高压传感器在温度268－283．2K时,压力6－40．2kPa和4600－7200kPa范围内采用恒温试压法分别对1,1－dichloro-1-fluoroethane(1,1二氯－1－氟乙烷）和甲烷气体水合物相平衡点进行了测试;并将所得两组数据与文献值相比较。该装置温度、压力范围较宽,可用于气体水合物相平衡实验。     

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。     

基于量子化学计算方法的天然气水合物稳定性研究进展

天然气水合物以资源丰富、优质、洁净等特点,被视为21世纪新能源。天然气水合物稳定性的研究对天然气水合物资源勘探开发具有重要意义。本文简述了微观、介观、宏观、矿藏四个尺度天然气水合物稳定性的研究,重点从微观量子尺度介绍了量子化学计算方法对水合物晶体结构及其稳定性以及水合物宏观物理特性微观表征的计算研究。应用量子化学计算方法可以对天然气水合物的晶体结构、电子轨道分布、振动光谱、成键特性及主客体相互作用进行计算研究,其结果能够为天然气水合物在油气储运、水合物成藏、开采及其综合利用等方面的研究提供理论支持。目前,量子化学计算方法的优化与分子动力学模拟、分子力学模拟等方法的结合将有助于水合物形成和分解微观机理研究的发展,提升计算精度和扩大研究体系,为矿场尺度的天然气水合物资源开采利用提供理论支持。     

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.     

Use of Electrical Resistance to Detect the Formation and Decomposition of Methane Hydrate

The changes of electrical resistance(R)were studied experimentally in the process of CH_4 hydrate formation and decomposition,using temperature and pressure as the auxiliary detecting methods simultaneously.The experiment results show that R increases with hydrate formation and decreases with hydrate decompositon.R is more sensitive to hydrate formation and decompositon than temperature or pressure,which indicates that the detection of R will be an effective means for detecting natural gas hydrate(NGH)quantitatively.     

Experimental and theoretical investigation of simple gas hydrate formation with or without presence of kinetic inhibitors in a flow mini-loop apparatus

Gas hydrates are ice-like crystalline compounds, which form through a combination of water and suitably sized guest molecules under low temperature and elevated pressure conditions. These solid compounds give rise to problems in the natural gas oil industry because they can plug pipelines and process equipment. Low dosage hydrate inhibitors are a recently developed hydrate control technology, which can be more cost-effective than traditional practices such as methanol and glycols. The kinetics of hydrate growth has been modeled by numerous authors who have measured the gas consumption rate during hydrate formation in batch agitator reactors.     

Kinetic hydrate inhibitor performance of new copolymer poly(N-vinyl-2-pyrrolidone-co-2-vinyl pyridine)s with TBAB

In oil and gas field, the application of kinetic hydrate inhibitors (KHIs) independently has remained problematic in high subcooling and high water-cut situation. One feasible method to resolve this problem is the combined use of KHIs and some synergists, which would enhance KHIs’ inhibitory effect on both hydrate nucleation and hydrate crystal growth. In this study, a novel kind of KHI copolymer poly(N-vinyl-2-pyrrolidone-co-2-vinyl pyridine)s (HGs) is used in conjunction with TBAB to show its high performance on hydrate inhibition. The performance of HGs with different monomer ratios in structure II tetrahydrofuran (THF) hydrate is investigated using kinetic hydrate inhibitor evaluation apparatus by step-cooling method and isothermal cooling method. With the combined gas hydrate inhibitor at the concentration of 1.0 wt%, the induction time of 19 wt% THF solution could be prolonged to 8.5 h at a high subcooling of 6℃. Finally, the mechanism of HGs inhibiting the formation of gas hydrate is proposed.     

钻井液添加剂对形成天然气水合物的影响

针对深水钻井中水基钻井液易形成天然气水合物从而导致钻井作业无法正常进行的问题,利用自行设计研制的气体水合物反应装置,模拟深水钻井温度压力条件,对水基钻井液添加剂进行了天然气水合物形成的实验研究。分析了各实验体系形成水合物的过冷度。以过冷度为评价指标,评价了各种钻井液添加剂在深水钻井水合物形成过程中的作用。结果表明,在钻井液使用的加量范围内,阳离子聚丙烯酰胺CPAM、两性离子聚合物FA367等对天然气水合物的形成有抑制作用,且随着加量的增加抑制作用增强;磺甲基丹宁SMT、木质素磺酸盐FCLS对天然气水合物的形成有微弱的促进作用,但影响不大。聚合物添加剂的离子类型对天然气水合物的形成影响不大。     

Estimation of ultra-stability of methane hydrate at 1 atm by thermal conductivity measurement

Thermal conductivity of methane hydrate was measured in hydrate dissociation self-preservation zone by means of the transient plane source (TPS) technique developed by Gustafsson. The sample was formed from 99.9% (volume ratio) methane gas with 280 ppm sodium dodecyl sulfate (SDS) solution under 6.6 MPa and 273.15 K. The methane hydrate sample was taken out of the cell and moved into a low temperature chamber when the conversion ratio of water was more than 90%. In order to measure the thermal conductivity, the sample was compacted into two columnar parts by compact tool at 268.15 K. The measurements are carried out in the temperature ranging from 263.15 K to 271.15 K at atmospheric pressure. Additionally, the relationship between thermal conductivity and time is also investigated at 263.15 K and 268.15 K, respectively. In 24 h, thermal conductivity increases only 5.45% at 268.15 K, but thermal conductivity increases 196.29% at 263.15 K. Methane hydrates exhibit only minimal decomposition at 1 atm and the temperature ranging from 263.15 K to 271.15 K. At 1 atm and 268.15 K, the total gas that evolved after 24 h was amounted to less than 0.71% of the originally stored gas, and this ultra-stability was maintained if the test was lasted for more than two hundreds hours before terminating.     

Liquid chromatographic methods for chloral hydrate determination

Liquid chromatographic methods, based on reversed-phase (RP) and anion-exchange mechanisms, have been developed for chloral hydrate determination. Both methods are preceeded by derivatization of chloral hydrate. For RP separations, different reagents [namely dansylhydrazine and o-(4-nitrobenzyl)hydroxylamine] have been studied, but the best results have been achieved using 1,2-benzenedithiol with UV detection at 220 nm. The anion-exchange method is based on derivatization with NaOH to form sodium formate that is then analyzed by anion-exchange, with suppressed conductivity detection. Derivatization conditions were optimized in order to reach the best yield of reaction. The optimization of the procedure allowed to determine chloral hydrate with detection limits as low as 0.2 μg/l with good linearity and reproducibility. The anion-exchange method was also applied for chloral hydrate determination in a drinking water sample. A preconcentration procedure has also been studied.     

Molecular dynamics simulations of the mechanisms of thermal conduction in methane hydrates

The thermal conductivity of methane hydrate is an important physical parameter affecting the processes of methane hydrate exploration,mining,gas hydrate storage and transportation as well as other applications.Equilibrium molecular dynamics simulations and the Green-Kubo method have been employed for systems from fully occupied to vacant occupied sI methane hydrate in order to estimate their thermal conductivity.The estimations were carried out at temperatures from 203.15 to 263.15 K and at pressures from 3 to 100 MPa.Potential models selected for water were TIP4P,TIP4P-Ew,TIP4P/2005,TIP4P-FQ and TIP4P/Ice.The effects of varying the ratio of the host and guest molecules and the external thermobaric conditions on the thermal conductivity of methane hydrate were studied.The results indicated that the thermal conductivity of methane hydrate is essentially determined by the cage framework which constitutes the hydrate lattice and the cage framework has only slightly higher thermal conductivity in the presence of the guest molecules.Inclusion of more guest molecules in the cage improves the thermal conductivity of methane hydrate.It is also revealed that the thermal conductivity of the sI hydrate shows a similar variation with temperature.Pressure also has an effect on the thermal conductivity,particularly at higher pressures.As the pressure increases,slightly higher thermal conductivities result.Changes in density have little impact on the thermal conductivity of methane hydrate.     

Hydrate film growth at the interface between gaseous CO_2 and sodium chloride solution

Greenhouse gas CO2 has become a serious problem for human beings. The hydrate technology has been considered as a possible approach to sequester CO2. In this work, the lateral growth rates of a CO2 hydrate film in aqueous NaCl solutions of different concentrations were measured by means of suspending a single gas bubble in liquid. The results show that the film growth rates depended on not only the driving force, but also the NaCl concentration, and the film growth rates decreased with the increasing NaCl c...