多元气-液-固复杂体系相平衡

石油流体中含有气相、液相及可能遇到的固相包括水合物、石蜡和沥青质等,涉及多元气-液-固复杂体系的相平衡问题.为防止这些沉积物堵塞造成安全隐患,需要确定水合物、石蜡、沥青质沉积起始条件以及沉积量.本文针对化学热力学理论在含水合物、石蜡和沥青质的多元-多相平衡研究中的应用进行了综述.水合物相平衡模型较为成熟,主要有两类,其一为基于等温吸附理论的van der Waals-Platteeuw型热力学模型;其二为基于双过程水合物生成机理的Chen-Guo水合物热力学模型.石蜡沉积一般采用活度系数法、状态方程法及多固相模型描述.沥青质絮凝、沉积则可采用溶解度参数模型、状态方程法、胶体模型和标度理论模型进行计算.同时对多元气-液-固复杂体系的相平衡研究发展方向进行了展望.     

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.     

石英砂中甲烷水合物稳定条件研究

采用不同粒径(160～200目、200～300目、300～400目、400～600目)细颗粒石英砂模拟自然界中沉积物实验合成甲烷水合物, 采用多步升温分解法测定了甲烷水合物的稳定温度-压力(p～T)条件. 结果发现细颗粒石英砂对甲烷水合物的稳定条件有明显影响, 温度最大下降1.5 K. 其中160～200目的石英砂是实验测试条件下石英砂对甲烷水合物稳定条件有无影响的分界目数. 每一种石英砂在不同的温度压力下甲烷水合物p-T数据点较为离散, 并且不同石英砂中p-T数据曲线出现交叉, 这与文献中采用规则的硅胶、玻璃球等测得的结果有所不同. 文献中测定的甲烷水合物p-T数据点温度相对于纯水中甲烷水合物p-T数据点温度向左偏移量相同.     

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。     

基于PC-SAFT方程研究多孔介质中水合物相平衡的预测模型

对多孔介质中水合物的形成条件预测模型进行了研究.利用微扰链-统计缔合流体理论状态方程(PC-SAFT)结合van der Waals-Platteuw模型和毛细管Kelvin模型,建立了用于多孔介质水合物体系的相平衡预测模型.在此模型基础上,针对甲烷水合物和CO2水合物对界面张力作了进一步的研究.根据多孔介质水合物相平...     

利用统计缔合流体理论状态方程预测混合气体水合物的平衡形成条件

利用统计缔合流体理论(SAFT)状态方程结合van der Waals-Platteeuw统计力学模型用于预测含有甲烷、乙烷、丙烷、乙烯、丙烯、H₂S, CO₂, N₂和H₂二元气体水合物的平衡形成条件. 对于气相和液相, 应用SAFT方程来描述. 在气相和液相相平衡的模拟过程中, SAFT方程考虑了硬球斥力、成链力、色散力以及缔合相互作用. 对于水合物相, 采用van der Waals-Platteuw模型来计算. 该方法的预测结果与实验数据吻合.     

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．     

水合物反应液中水活度系数模型研究进展

水合物反应液中水活度系数的计算对水合物相平衡特性的研究及水合物技术的应用具有重要意义。 通过调研大量的国内外资料,概括了Margules、Wilson、NRTL、UNIQUAC及UNIFAC活度系数方程及其关联式等模型及其应用,结果表明,Margules模型常用于二元体系活度系数的计算,但对高温高压体系条件下的溶液适用性较差;Wilson模型参数回归误差稍大且不适于溶质与离子不能完全互溶体系;UNIQUAC模型在含水或咪唑类离子反应液体系中误差较大;多元离子体系相平衡的研究中常选择NRTL模型;UNIFAC模型拟合效果较好,可实现较高浓度体系活度系数的精确计算,应用较广泛。 水活度关联方程参数拟合效果好,且准确度高,但在高温高压水合物反应液体系中的计算仍是一个技术难点,是今后的研究方向。     

甲烷水合物导热机理的分子动力学模拟

甲烷水合物导热系数是甲烷水合物勘探、开采、储运以及其他应用过程中一个十分重要的物理参数.我们采用平衡分子动力学（EMD）方法Green-Kubo理论计算温度203.15～263.15K、压力范围3～100MPa、晶穴占有率为0～1的sI甲烷水合物的导热系数,采用的水分子模型包括TIP4P、TIP4P-Ew、TIP4P-FQ、TIP4P/2005、TIP4P/Ice.研究了主客体分子、外界温压条件等对甲烷水合物导热性能的影响.研究结果显示甲烷水合物的低导热性能由主体分子构建的sI笼型结构决定,而客体分子进入笼型结构后,使得笼型结构导热性能增强,同时进入笼型结构的客体分子越多,甲烷水合物导热性能越强.研究结果还显示在高温区域（T〉TDebye/3）内不同温度作用下,所有sI水合物具有相似的导热规律.压力对导热系数有一定影响,尤其是在较高压力条件下,压力越高,导热系数越大.而在不同温度和不同压力作用过程中,密度的改变对导热系数的增大或减小几乎没有影响.     

用激光散射法研究冷冻剂R12水合物的生成动力学

建立了高压混相全透明循环管路装置, 装置中配备有水合物生成器、激光粒度仪和控温系统等, 工作压力可达4 MPa, 用来研究水合物生成动力学行为. 利用激光散射方法, 测定了0.24和0.32 MPa下, 温度为277.1 K 时, 冷冻剂CCl₂F₂, 即R12, 生成水合物的颗粒尺寸和分布, 液体流量范围为300~1400 L/h. 并使用Rosin-Rammler分布分析了所测粒径分布数据. 实验结果表明, 反应初期水相中水合物粒子的直径增加很快, 随着水合物的大量生成, 水相中水合物的浓度不断增加, 水合物颗粒的尺寸逐渐趋于稳定. 在液体流量较大和压力较高的情况下所生成水合物颗粒的浓度较大. 根据物料平衡, 建立了水合物的粒度生长模型, 将水合物生成气消耗量与所生成水合物粒度分布相关联. 基于由粒度生长模型算出的气体消耗量与实测值相近.     

Some comments on the applicability of gas permeation methods to characterize porous membranes based on improved experimental accuracy and data handling

The measurement of the gas permeability coefficient as a function of the mean pressure across a membrane can be used to determine a mean pore radius of the membrane. This method has been applied by several authors to characterize microporous and asymmetric ultrafiltration or hyperfiltration membranes. This paper shows how the data acquisition and handling are improved. Experiments are performed on microporous Millipore membranes with a nominal pore radius of 50 nm and on ultrafiltration merebranes of poly(2,6-dimethyl-1,4-phenyleneoxide) with an expectedly sharp pore-size distribution around 2 nm. For the Millipore membrane an unexpected dependence of the calculated pore radius on the type of gas used in the experiment has been found. Measurements on the ultrafiltration membranes indicate that the viscous flow contribution to the permeability coefficient cannot be determined with sufficient accuracy. It is concluded that application of the gas permeation method has some limitations which were not previously recognized.     

Pore Size Modulation in Flexible Metal-Organic Framework Enabling High Performance Gas Sensing

Pore size plays a critical role in determining the performance of metal-organic frameworks (MOFs) in catalysis, sensing, and gas storage or separation. However, revealing the pore-size/property relationship remains extremely challenging because ideal structure models possessing different pore sizes but having the same components are lacking. In this work, a solvent-coordination directed structure swelling method was developed for modulating the ratio between the large and narrow pore phases of a flexible MOF, MIL-88B . Pore-size-dependent gas sensitivity and selectivity were studied for the first time in the MIL-88B samples. The optimized MIL-88B-20 % sample showed one of the best sensing performances among all the reported MOF-based H₂S-sensing materials. This work not only provides a method to synthesize ideal structure models for revealing the relationship between pore-size and properties, but also may inspire the development of high-performance gas sensing materials.     

Protein adsorption on the mesoporous molecular sieve silicate SBA-15: effects of pH and pore size

A mesoporous molecular sieve silicate, SBA-15, with three pore sizes (38.1 A, 77.3 A, and 240 A) has been synthesized using a non-ionic, tri-block copolymer as a template in a sol-gel method. The effects of synthesis conditions on the pore size and pore-size distribution of this adsorbent have been described. The adsorption of proteins on these crystalline, ordered, materials has been studied. The kinetics of adsorption and equilibrium capacity have been probed with three proteins of different dimensions. The effects of electrostatic interactions and protein size are illustrated. It has been shown that SBA-15 materials can be tailored to show size selectivity for proteins, and very high capacities (450 mg/g) can be obtained. Furthermore, the rates of adsorption are shown to be dependent on the pore size, protein structure and solution pH.     

Formation of the porous structure during the polymerization of meta-divinylbenzene and para-divinylbenzene with toluene and 2-ethylhexanoic acid (2-EHA) as porogens

Macroporous polymers of pure meta-divinylbenzene (meta-DVB) and pure para-divinylbenzene (para-DVB) have been prepared in the presence of toluene and 2-EHA as pore forming agents. The formation of the pore structure has been studied during the polymerization by pore-size distribution measurements, together with determination of the specific surface area from nitrogen sorption isotherms using the BET treatment. In addition, the morphology and texture have been characterized by SEM during the polymerization process. Large differences in the pore-size distribution among all the polymer samples are found. The polymers prepared in toluene as porogen have a pore-size distribution, which mainly consists of small pores, while large pores appear with 2-EHA as porogen. In the presence of 2-EHA, a major change in the pore-size distribution is also observed when the monomer is shifted from para-DVB to meta-DVB, leading to a bimodal distribution. The texture characterization by SEM shows details and discriminates the samples in consistency with what may be expected from pore-size distribution measurements. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3973–3990, 1999     

New equation of adsorption for the calculation of parameters of microporous structure

A new equation describing the equilibrium adsorption of vapors of substances with different physicochemical properties was obtained on the basis of the lognormal distribution of pore volume within the theory of volume filling of micropores. Unlike the existing equations, this equation is more general since it is not related to a specific geometrical model of pores. Adsorption isotherms described by this equation for active carbons with wide pore-size distributions have smaller mean square deviations than those calculated using the Dubinin-Stoeckli equation.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1931–1933, October, 1995.This study was financially supported by the Russian Foundation for Basic Research (Project No. 94-03-09550).     

Comparison between different presentations of pore size distribution in porous materials

The different presentations of the pore size distribution derived from the gas adsorption method and the mercury porosimetry are connected with some problems. This concerns especially the use of the logarithmically differential pore volume distribution. The incorrect application of this distribution to bimodal pore systems involves the danger of an apparent overemphasizing of larger pores. This effect may also occur using the incremental pore size distribution in case the experimental point spacing considerably increases towards the larger pore radii. The pore volume density distribution defined as the linear derivative of the cumulative pore volume curve with respect to the pore radius has been found the most convenient form among the various kinds of pore volume distribution presentations. It has been shown that the direct comparison between this distribution and the logarithmically differential pore volume distribution is not allowed. Nevertheless, there is a clear connection between these definitions for the pore size distribution so that they are completely equivalent.     

Comparison of oligonucleotide migration in a bicontinuous cubic phase of monoolein and water and in a fibrous agarose hydrogel

Porous hydrogels such as agarose are commonly used to analyze DNA and water-soluble proteins by electrophoresis. More recently lyotropic liquid crystals, such as the diamond cubic phase formed by the lipid monoolein and water, has become a new type of well-defined porous structure of interest for both hydrophilic and amphiphilic analytes. Here we compare these two types of matrixes by investigating the nature of retardation they confer to an oligonucleotide that migrates in their respective aqueous phases. The retardation for a 25-mer oligonucleotide was found to be about 35-fold stronger in the cubic phase than in an agarose hydrogel modified to have the same average pore size. According to modelling, the strong retardation is primarily due to the fact that hydrodynamic interaction with the continuous monoolein membrane is a stronger source of friction than the steric interactions (collisions) with discrete gel fibres. A secondary effect is that the regular liquid crystal has a narrower pore-size distribution than the random network of the agarose gel. In agreement with experiments, these two effects together predict that the retardation in the cubic phase is a 30-fold stronger than in an agarose gel with the same average pore radius.     

Effect of the porosity of PS–DVB-copolymers on ion chromatographic behavior in inverse size-exclusion and ion chromatography

Small and highly pressure-stable PS-DVB copolymers of different porosity had been prepared by a two-step swelling procedure which enabled variation of diluent composition, an important characteristic affecting the porosity. The polymers were characterized by inverse size-exclusion chromatography and scanning electron microscopy. Subsequent chloromethylation and amination resulted in anion exchangers suitable for ion chromatography.The pore volume and the pore-size distribution is substantially affected by the fraction of the solvens component in the diluent. It was apparent from scanning electron microscopy that surface structure and the size of the polymer particles was not affected by diluent composition. The functionalization process led to a decrease in pore volume. The pore-size distribution remained unchanged during functionalization, which can be explained in terms of partial closing of all pore sizes. The chromatographic efficiency of the functionalized polymers in ion chromatography was highly dependent on diluent composition and the extent of functionalization was determined by the total pore volume.The composition of the diluent is an excellent tool for optimization of polymers used for the synthesis of surface-functionalized anion exchangers.     

Comparison between different presentations of pore size distribution in porous materials

The different presentations of the pore size distribution derived from the gas adsorption method and the mercury porosimetry are connected with some problems. This concerns especially the use of the logarithmically differential pore volume distribution. The incorrect application of this distribution to bimodal pore systems involves the danger of an apparent overemphasizing of larger pores. This effect may also occur using the incremental pore size distribution in case the experimental point spacing considerably increases towards the larger pore radii. The pore volume density distribution defined as the linear derivative of the cumulative pore volume curve with respect to the pore radius has been found the most convenient form among the various kinds of pore volume distribution presentations. It has been shown that the direct comparison between this distribution and the logarithmically differential pore volume distribution is not allowed. Nevertheless, there is a clear connection between these definitions for the pore size distribution so that they are completely equivalent. Received: 15 May 1998 / Revised: 8 October 1998 / Accepted: 10 October 1998     

Gel permeation chromatography: Effect of pore-size distribution

The pore-size distributions of various grades of porous glass were determined by gas desorption and mercury porosimeter measurements. This allowed the calculation of elution volumes as a function of pore diameters. The coil sizes of polystyrenes in toluene were obtained for a series of molecular weights from hydrodynamic theory and matched with pore diameters. In this manner, expected calibration curves for gel permeation chromatography could be calculated. Good agreement was found with experimental data.