南海神狐海域及祁连山冻土区天然气水合物的拉曼光谱特征

采用显微激光拉曼光谱对我国在南海神狐海域及祁连山冻土区首次钻获的天然气水合物实物样品进行了详细的研究, 探讨了其笼型结构特征及其气体组成. 结果表明, 南海神狐海域天然气水合物样品是典型的I型结构(sI)水合物, 气体组分主要是甲烷, 占99%以上; 水合物大笼的甲烷占有率大于99%, 小笼为86%, 水合指数为5.99. 祁连山冻土区天然气水合物气体组分相对复杂, 主要成分除甲烷外(70%左右), 还有相当数量的乙烷、丙烷及丁烷等烃类气体, 从拉曼谱图上可初步判断其为II型结构(sII)水合物; 水合物的小、大笼的甲烷占有率的比值(θ_S/θ_L)为26.38, 远远大于南海神弧海域水合物的0.87, 这主要是由于祁连山水合物气体组分中的大分子(乙烷、丙烷及丁烷等)优先占据水合物的大笼, 大大减少了大笼中甲烷分子的数量.     

含低剂量抑制剂体系气体水合物生成动力学

水合物管道堵塞是油气工业安全生产的重要问题之一, 目前低剂量抑制剂以其经济性、环境友好性等优点, 逐步取代传统抑制剂. 文中在8.5 MPa、4 ℃条件下, 1.072 L反应釜内, 采用甲烷、乙烷和丙烷混和气, 研究了含低剂量抑制剂聚乙烯吡咯烷酮(PVP)和GHI1的水合物生成体系反应过程, 计算分析了压缩因子和自由气量随反应时间的变化, 对比了在相同反应程度下添加PVP和GHI1后水合物含气量的区别, 探讨了GHI1组合抑制剂的抑制机理. 实验结果表明PVP和GHI1能抑制水合物生长, 不能有效抑制水合物成核; 添加PVP的体系, 在实验气体组成下, 甲烷乙烷进入水合物小晶穴, 并且甲烷优先进入小晶穴; GHI1对丙烷乙烷的抑制能力强于甲烷; 对比GHI1和PVP的反应过程, 认为协同剂二乙二醇丁醚的羟基和醚类结构加强反应体系中的氢键, 和PVP结合使用, 通过氢键和空阻达到抑制效果.     

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。     

微波场中乙烷及丙烷气体水合物的分解特性

研究了2.45GHz微波场中I型乙烷水合物及II型丙烷水合物的热激分解过程,基于晶体表面两步分解机制的动力学模型,结合传热传质分析了其分解特性.结果表明:水合物在微波场中的加热分解是一个与实际微波电磁场相互耦合的过程,微波体积加热的特点强化了水合物颗粒表层的传热传质过程,时间累积的热效应增大了水合物晶体破解速率;在120至540W入射功率下,乙烷、丙烷水合物气化速率分别达到0.109-0.400mol·min-·1L-1及0.090-0.222mol·min-1·L-1.在一定范围内增大微波功率可显著提高水合物分解速率,其中乙烷水合物一直处于功率主控区,丙烷水合物更早进入功率和分解动力机制共同控制区.     

气体分子对甲烷水合物稳定性的影响

通过B3LYP方法, 在6-31G(d,p)水平下, 分别优化了结构I型甲烷水合物十二面体和十四面体晶穴结构. 结果表明, CH4分子使晶穴的相互作用能降低, 增强了晶穴的稳定性. 计算了晶穴中甲烷分子C—H键的对称伸缩振动频率, 计算结果与实验值相符合. 研究发现CH4分子影响晶穴中氧原子的电荷分布, 从而增强了氢键的稳定性. 通过分子动力学方法研究水合物晶胞中气体分子的占有率对水合物稳定性的影响, 进一步说明气体分子对水合物晶穴稳定性的重要作用.     

气体水合物膜生长动力学研究进展

由于大多数水合物客体不溶于水,水相与客体相界面首先形成一层气体水合物膜,气体水合物膜生长是水合物生长的主要形式,研究水合物膜生长规律对于理解水合物生长动力学及进一步开发促进和抑制水合物生长的应用技术具有重要意义.本文综述了近年来气体水合物膜生长形态、横向生长和增厚生长的理论和实验研究进展.首先介绍了不同客体-水体系(包括气/液界面、液/液界面和气-液-液体系)形成的水合物膜生长形态随实验条件的变化规律,然后分别从横向生长和增厚生长两方面总结了水合物膜生长的实验和模型方面的研究工作,阐述了常见的膜生长速率和膜厚度的测量方法,分析了水合物膜生长的传热和传质机理.同时展望了未来水合物膜生长研究的发展方向.     

气体水合物垂直换热管外融冰快速成核与静态渗透生长

通过HCFC141b气体水合物在一根垂直换热管外的生成过程可视化实验研究, 发现了融冰快速成核以及水沿垂直换热管自发渗透入客体相中连续生长气体水合物的现象, 并分别利用周公度和Sloan的假说以及表面自由能理论对这两种现象进行了机理性解释, 进而研究出一种新型的气体水合物生成方法——气体水合物换热管外融冰渗透生长方法. 由于不需要机械扰动, 利用该方法生成的气体水合物非常密实, 含水率低, 克服了机械扰动系统中能耗高且生成的水合物含水率高的缺点, 将促进气体水合物储气或蓄冷等应用技术的发展.     

FID/TCD并联气相色谱法测定天然气水合物的气体组成

建立了一种氢火焰离子化检测器（FID）与热导检测器（TCD）并联检测的气相色谱分析技术。该方法一次进样,即可实现天然气水合物中C1~C6、CO2、H2S、O2+N2 16种气体成分的同时测定。实验优化了色谱柱、升温程序、柱流速、进样口温度、检测器温度、TCD参考气和尾吹气流速等仪器分析参数。在优化条件下,16种气体分子在实验浓度范围内线性关系良好,r2为0.999 03~0.999 98,方法检出限为0.000 3~0.046 mol/mol,相对标准偏差（n=6）为1.6%~5.0%。对祁连山冻土区、南海神狐海域、人工合成水合物样品的分析表明,该方法简便实用、灵敏可靠,可满足天然气水合物气体组成的分析要求。     

氮气笼型水合物的激光拉曼光谱

在253K和16MPa的压力下,于实验室内合成了氮气水合物,用显微共焦拉曼光谱对其N-N和O-H键伸缩振动的光谱特征进行了研究．结果表明,氮气水合物中的N-N和O—H键的拉曼峰分别为2322．4和3092．1cm^-1,与天然的空气水合物中的数据十分接近．另外,还测定了液氮和溶解于水中的氮分子中N—N键的拉曼峰值,分别为2326．6和2325．0cm^-1．氮气笼型水合物分解的拉曼谱图表明,氮分子同时进入水合物的大笼和小笼中,但由于氮分子在大、小笼中的环境氛围十分接近,其拉曼位移相差不大,故拉曼谱图只能显示N—N键伸缩振动一个峰．     

常见客体分子对笼型水合物晶格常数的影响

Natural gas hydrates are considered as ideal alternative energy resources for the future, and the relevant basic and applied research has become more attractive in recent years. The influence of guest molecules on the hydrate crystal lattice parameters is of great significances to the understanding of hydrate structural characteristics, hydrate formation/decomposition mechanisms, and phase stability behaviors. In this study, we test a series of artificial hydrate samples containing different guest molecules (e.g. methane, ethane, propane, iso-butane, carbon dioxide, tetrahydrofuran, methane + 2, 2-dimethylbutane, and methane + methyl cyclohexane) by a low-temperature powder X-ray diffraction (PXRD). Results show that PXRD effectively elucidates structural characteristics of the natural gas hydrate samples, including crystal lattice parameters and structure types. The relationships between guest molecule sizes and crystal lattice parameters reveal that different guest molecules have different controlling behaviors on the hydrate types and crystal lattice constants. First, a positive correlation between the lattice constants and the van der Waals diameters of homologous hydrocarbon gases was observed in the single-guest-component hydrates. Small hydrocarbon homologous gases, such as methane and ethane, tended to form sI hydrates, whereas relatively larger molecules, such as propane and iso-butane, generated sⅡ hydrates. The hydrate crystal lattice constants increased with increasing guest molecule size. The types of hydrates composed of oxygen-containing guest molecules (such as CO₂ and THF) were also controlled by the van der Waals diameters. However, no positive correlation between the lattice constants and the van der Waals diameters of guest molecules in hydrocarbon hydrates was observed for CO₂ hydrate and THF hydrate, probably due to the special interactions between the guest oxygen atoms and hydrate "cages". Furthermore, the influences of the macromolecules and auxiliary small molecules on the lengths of the different crystal axes of the sH hydrates showed inverse trends. Compared to the methane + 2, 2-dimethylbutane hydrate sample, the length of the a-axis direction of the methane + methyl cyclohexane hydrate sample was slightly smaller, whereas the length of the c-axis direction was slightly longer. The crystal a-axis length of the sH hydrate sample formed with nitrogen molecules was slightly longer, whereas the c-axis was shorter than that of the methane + 2, 2-dimethylbutane hydrate sample at the same temperature.     

Kinetic studies of gas hydrate formation with low-dosage hydrate inhibitors

Pipeline blockage by gas hydrates is a serious problem in the petroleum industry. Low-dosage inhibitors have been developed for its cost-effective and environmentally acceptable characteristics. In a 1.072-L reactor with methane, ethane and propane gas mixture under the pressure of about 8.5 MPa at 4 °C, hydrate formation was investigated with low-dosage hydrate inhibitors PVP and GHI1, the change of the compressibility factor and gas composition in the gas phase was analyzed, the gas contents in hydrates were compared with PVP and GHI1 added, and the inhibition mechanism of GHI1 was discussed. The results show that PVP and GHI1 could effectively inhibit the growth of gas hydrates but not nucleation. Under the experimental condition with PVP added, methane and ethane occupied the small cavities of the hydrate crystal unit and the ability of ethane entering into hydrate cavities was weaker than that of methane. GHI1 could effectively inhibit molecules which could more readily form hydrates. The ether and hydroxy group of diethylene glycol monobutyl ether have the responsibility for stronger inhibition ability of GHI1 than PVP.     

A novel correlation for estimation of hydrate forming condition of natural gases

An inherent problem with natural gas production or transmission is the formation of gas hydrates, which can lead to safety hazards to production/ transportation systems and to substantial economic risks. Therefore, an understanding of conditions where hydrates form is necessary to overcome hydrate related issues. Over the years, several models requiring more complicated and longer computations have been proposed for the prediction of hydrate formation conditions of natural gases. For these reasons, it is essential to develop a reliable and simple-to-use method for oil and gas practitioners. The purpose of this study is to formulate a novel empirical correlation for rapid estimation of hydrate formation condition of sweet natural gases. The developed correlation holds for wide range of temperatures (265–298 K), pressures (1200 to 40000 kPa) and molecular weights (16−29). New proposed correlation shows consistently accurate results across proposed pressure, temperature and molecular weight ranges. This consistency could not be matched by any of the widely accepted existing correlations within the investigated range. For all conditions, new correlation showed average absolute deviation to be less than 0.2% and provided much better results than the widely accepted existing correlations.     

Tuning the Composition of Guest Molecules in Clathrate Hydrates: NMR Identification and Its Significance to Gas Storage

Gas hydrates represent an attractive way of storing large quantities of gas such as methane and carbon dioxide, although to date there has been little effort to optimize the storage capacity and to understand the trade‐offs between storage conditions and storage capacity. In this work, we present estimates for gas storage based on the ideal structures, and show how these must be modified given the little data available on hydrate composition. We then examine the hypothesis based on solid‐solution theory for clathrate hydrates as to how storage capacity may be improved for structure II hydrates, and test the hypothesis for a structure II hydrate of THF and methane, paying special attention to the synthetic approach used. Phase equilibrium data are used to map the region of stability of the double hydrate in P–T space as a function of the concentration of THF. In situ high‐pressure NMR experiments were used to measure the kinetics of reaction between frozen THF solutions and methane gas, and ¹³C MAS NMR experiments were used to measure the distribution of the guests over the cage sites. As known from previous work, at high concentrations of THF, methane only occupies the small cages in structure II hydrate, and in accordance with the hypothesis posed, we confirm that methane can be introduced into the large cage of structure II hydrate by lowering the concentration of THF to below 1.0 mol %. We note that in some preparations the cage occupancies appear to fluctuate with time and are not necessarily homogeneous over the sample. Although the tuning mechanism is generally valid, the composition and homogeneity of the product vary with the details of the synthetic procedure. The best results, those obtained from the gas–liquid reaction, are in good agreement with thermodynamic predictions; those obtained for the gas–solid reaction do not agree nearly as well.     

天然气水合物形成的检测

研制的静态水合物试验装置采用可视观察的方法，可以快速确定天然气水合物的形成条件。动态天然气水合物试验装置在利用直接观测来判断水合物形成点的同时，通过监测装置转轮的扭距、试验介质的温度、压力、流速变化，综合判断天然气水合物的形成，此装置可以很好地模拟现场实际的天然气管输工况，实验结果与理论值及实际值差别较小。     

Structure transition and swapping pattern of clathrate hydrates driven by external guest molecules

We first report here that under strong surrounding gas of external CH4 guest molecules the sII and sH methane hydrates are structurally transformed to the crystalline framework of sI, leading to a favorable change of the lattice dimension of the host-guest networks. The high power decoupling 13C NMR and Raman spectroscopies were used to identify structure transitions of the mixed CH4 + C2H6 hydrates (sII) and hydrocarbons (methylcyclohexane, isopentane) + CH4 hydrates (sH). The present findings might be expected to provide rational evidences regarding the preponderant occurrence of naturally occurring sI methane hydrates in marine sediments. More importantly, we note that the unique and cage-specific swapping pattern of multiguests is expected to provide a new insight for better understanding the inclusion phenomena of clathrate materials.     

Structure and Density Comparison of Noble Gas Hydrates Encapsulating Xenon,Krypton and Argon

Understanding the effect of guest species on the host framework is important for the development of structure-based properties of inclusion compounds. Herein, the crystal structures of the noble gas hydrates encapsulating Xe, Kr, and Ar were studied by powder X-ray diffraction measurements. The crystal structures and hydration numbers of these noble gas hydrates were solved by Rietveld refinements using optimized models with the direct-space technique. It was revealed that host cage size of these hydrates changed depending on the type of guest species even though their unit-cell parameters were the same. Based on the structure models obtained, the densities of Xe, Kr, and Ar gas hydrates were also determined to be 1.837, 1.445 and 1.097 g/cm³ at 93 K, respectively. Our findings, from a crystallographic point of view, may give insight into further understanding the thermodynamic stability and physical properties of gas hydrates encapsulating small guests.     

I型和II型结构气体水合物的记忆效应

利用水合物二次生成实验装置, 采用“定容法”对I型(甲烷、二氧化碳)和II型(丙烷)结构气体水合物的二次生成进行了实验, 研究了不同结构水合物(I型、II型)彼此间的记忆效应, 发现水合物生成过程存在明显的诱导期, I型结构水合物间在二次生成过程中存在着记忆效应. I型与II型结构水合物之间在相互二次生成过程中存在着显著的记忆效应.