天然气水合物的形成机理及防治措施

天然气水合物是在天然气开采加工和运输过程中,在一定温度和压力下,天然气与液态水形成的冰雪状结晶体。在天然气开采加工和运输过程中,会堵塞井筒管线阀门和设备,从而影响天然气的开采、集输和设备的正常运转。本文通过分析天然气水合物的形成条件,得出了几条具有实际意义的水合物防治措施,对天然气的安全生产具有一定的现实意义。     

察尔汗盐湖盐田卤水管理的数学方法探讨

以盐田系统蒸发、结晶相平衡为依据,用数学方法对盐田各阶段的进出卤水量进行计算,以寻求盐田管理的简单、实用化模型。     

天然气水合物的形成与防治

天然气水合物是天然气与水在一定的压力和温度下形成的结晶笼状固态化合物。水合物可能导致管道、仪表和分离设备的堵塞,对长距离的输送是有害的。概述了天然气水合物的形成条件以及目前水合物的物理和化学防治方法,指出了实验新型脱水工艺,开展动态模拟实验,以及筛选动力学混合型抑制剂是今后水合物防治的发展方向。     

Macroscopic investigation of hydrate film growth at the hydrocarbon/water interface

Clathrate hydrate film growth has been investigated at the hydrocarbon/water interface for cyclopentane and methane hydrate, using video microscopy combined with gas consumption measurements. Hydrate formation was characterized by the film thickness, propagation rate across the hydrocarbon/water interface, and gas consumption. The film formation processes of cyclopentane and methane hydrate were measured over the temperature range of 260-273 K and pressure range of atmospheric to 8.3 MPa. Hydrate formation was initiated by the propagation of a thin, porous film across the hydrocarbon/water interface. This thickening rate was strongly dependent on the hydrate former solubility in the aqueous phase, in the absence and presence of hydrate. The methane hydrate film thickness began at about and grew to a final thickness (20-) which increased with subcooling. The cyclopentane hydrate film thickness began at about and grew to a final thickness (15-) which again increased with subcooling. The hydrate film grew into the water phase. Gas consumption indicated that the aqueous phase supplied hydrate former during the initial hydrate growth, and the free gas supplied the hydrate former for film thickening.     

超声波作用于天然气水合物形成分解研究进展

简述了超声空化的基本理论;介绍了国内外超声波影响天然气水合物形成分解的研究进展、超声波对水成核结冰影响的研究情况;最后进行了简要总结并提出几点建议,指出开展相应研究的必要性。     

Clathrate hydrate formation using liquid jets impinging on each other: An observational study using paired water jets or water and methylcyclohexane jets

This paper reports the experimental attempt at visually observing and characterizing the formation and/or growth of clathrate-hydrate crystals accompanying the impingement of two cylindrical jets of either the same liquid, water, or two mutually immiscible liquids, water and methylcyclohexane (MCH), in a difluoromethane (HFC-32) gas phase held at a constant pressure. We observed that the hydrate crystals intermittently emerged on the liquid sheet radially expanding from the point of the jet collision, flowed to the periphery of the sheet, and then engulfed in the droplets when they were disintegrated from the periphery of the sheet. The observations of the droplets falling in the gas phase indicated that even some of the droplets initially containing no hydrate started to be covered by hydrate films presumably as the result of delayed hydrate nucleation on the individual droplets. The measurements of the gas consumption rate due to hydrate formation showed that the ratio of the water-to-hydrate conversion and the efficiency of using the cool energy supplied by the liquid jets for hydrate formation tended to increase as the liquid flow rate per jet increased and thereby intensified the liquid atomization, indicating an increasing proportion of hydrate formation on the droplets with an increase in the liquid flow rate.     

Crystallization of Cephradine Polymorphs and Hydrates from Mixed Solvents of Methanol and Water

Cephradine monohydrate (CPH) crystallizes with a needle‐like shape which leads to severe agglomeration and slow filtration. Effects of different operating conditions on the particle size and shape as well as the filterability of the crystal products are described. The solubility and stability of one anhydrate of cephradine (CPA1) and CPH as a function of temperature and water activity was investigated in different methanol and water mixtures. A solvent‐mediated transformation from CPH to CPA1 was observed at water mole fractions below 0.2–0.35 depending on the temperature. The crystallization behavior of CPH was studied by linear cooling and antisolvent crystallization. Lowering the cooling rate and addition of seeds led to an increase in particle size and improvement of filterability.     

K—Mg—Al—Si—O—F玻璃析晶机制的研究

研究了Ｋ－Ｍｇ－Ａｌ－Ｓｉ－Ｏ－Ｆ系玻璃中组分Ｆ的引入方式对玻璃析昌机制的影响。以ＭｇＦ２方式引入Ｆ的玻璃发生分相,随后整体析出ＭｇＦ２,云母晶体以先析ＭｇＦ２作为异相质点成核长大,形成可发削的氟金云母微晶玻璃;而以ＫＦ方式引入Ｆ的玻璃在热处理过程中并不发生分相,结果保在其表面形成粗大枝晶状硅镁石。玻璃中Ｆ的引入方式不同导致了基础玻璃结构上的差异,从而导致了截然不同的两种析晶机制－－体积析晶和表面     

德国用环戊烷代替氟里昂（CFC）作为硬质PU泡沫发泡剂的新技术

本文介绍了环戊烷的运输，多元醇／环戊烷混合装置及混合料储存的技术并详细叙述使用环戊烷作为发泡剂的安全方法。     

Influence of Emulsifiers on the Formation and Crystallization of Solid Lipid Nanoparticles

The production of solid lipid nanoparticles by means of hot homogenization uses two different techniques: emulsification (liquid state) and crystallization (solid state). Both these processes depend on many parameters, such as composition, energy input, or geometry of the emulsification device. In former investigations known from the literature, the influence of the emulsifier concentration and the potential of controlling the polymorphic forms of the solidified particles were not investigated in detail. Here, these two factors were analyzed on the example of palm oil particles stabilized with emulsifiers suitable for foods. The influence of the emulsifier concentration on the resulting droplet and particle sizes is very high, up to a certain level. However, beside this influence, the polymorphic form of the solidified particles can be controlled by the right choice of emulsifier type and concentration.     

水合物研究与应用现状

从热力学和动力学的角度对水合物生成的实验和理论研究成果进行了系统评述。着重介绍了水合物作为潜在能源以及在近临界和超临界萃取、生物酶活性控制和提取、海水脱盐淡化、气体混合物分离等领域中的应用状况。     

Crystallization Rates for Amorphous Sucrose and Lactose Powders from Spray Drying: A Comparison

Sorption tests have been used to assess the effects of temperature, relative humidity, and molecular structure on the crystallization process within spray-dried lactose and sucrose at both room temperature and 40°C. Increasing the temperature by 10°C more than doubled the crystallization rate, up to three times for the case of lactose. Below a threshold value of the relative humidity, little to no crystallization was found, with this threshold being 51% for sucrose, at room temperature, which was lowered to 32% at 40°C. These results are consistent with the picture of the process as an activated rate one. Lactose and sucrose, which have the same molecular weight of 342 g/mol but different molecular structures and thus glass transition temperatures, showed similar overall crystallization rates for the same material temperatures, in contrast with the overall predictions of the Williams-Landel-Ferry (WLF) equation. The WLF equation suggests that the crystallization rate is a function of the difference between the material and the glass transition temperatures, but it is still possible that this equation may predict the effect of changing material temperature and relative humidity for a particular material.     

The role of diffusional resistance on crystal growth: Interpretation of dissolution and growth rate data

Experimental results on crystal growth and dissolutions kinetics were taken from literature to test two theoretical models describing the crystal growth from solutions. One of the models, designated by two-step model (TSM), is being used for many years to describe the relation between crystal growth rates with supersaturation, temperature and hydrodynamic conditions. The other model was presented in a previous work and will be called concurrent-step model (CSM). The chosen literature data allowed calculating the mass transfer coefficients during crystal growth, for different hydrodynamic conditions. The obtained results are interpreted taking into consideration well-established mass transfer theories. According to the TSM, the measured crystal growth kinetics can only be explained by means of an unrealistic variation of the mass transfer coefficient with the relative crystal-solution velocity. Conversely, mass transfer coefficients obtained by the CSM were confirmed by appropriate semi-theoretical correlations, both in their order of magnitude and in their behaviour. In addition, crystal growth and dissolution experiments of sucrose were carried out at in a batch crystallizer for different agitation speeds. The resulting kinetics are used to test the CSM in a system that is significantly different from the inorganic salts used in the analysed literature works. As predicted by this model, the existence of an adsorbed layer in the crystal surrounding is likely to have affected the solute molecular diffusivity in the medium. Based on this premise, the results obtained with sucrose are well described by the CSM.     

AlF_3－YF_3－BaF_2－CaF_2－MgF_2－SrF_2系统玻璃形

ＡｌＦ＿３－ＹＦ＿３－ＢａＦ＿２－ＣａＦ＿２－ＭｇＦ＿２－ＳｒＦ＿２系统玻璃形成和析晶性能董大奎，马福定，黄德新（上海建材学院２００４３４）ＦｏｒｍａｔｉｏｎａｎｄＣｒｙｓｔａｌｌｉｚａｔｉｏｎＢｅｈａｖｉｏｒｏｆＡｌＦ＿３－ＹＦ＿３－ＢａＦ＿２－Ｃ...     

Solubility and Aging of Calcium Silicate Hydrates in Alkaline Solutions at 25°C

Calcium silicate hydrate (C-S-H) gels are the principal bonding material in portland cement. Their solubility properties have been described, enabling pH and solubilities to be predicted. However, the gels also interact with other components of cements, notably alkalis. C-S-H has been prepared from lime and silicic acid in solutions of sodium hydroxide or potassium hydroxide and by the hydration of tricalcium silicate (C₃S) in sodium hydroxide solutions. Analyses of aqueous phases in equilibrium with 85 gels show that the aqueous calcium and silicon concentrations fit smooth curves over the range of increasing sodium concentrations. Where anomalous data occur, they correspond to solids with low lime contents: such gels are tentatively assumed to fall into a region where the presence of another gel phase influences the aqueous composition. Dimensional changes have been observed in the hydration products of C₃S as a function of alkali content and these may be relevant to the alkali-silica reaction. The significance of this and other data is discussed with reference to real cement systems.     

Microscopic observations of clathrate-hydrate films formed at liquid/liquid interfaces. II. Film thickness in steady-water flow

A series of experiments were carried out to measure, with the aid of direct observations through a high-resolution optical microscope, the local thickness of a ring-shaped hydrate film formed over the surface of each discoid drop of HCFC-141b (CH₃CCl₂F) held stationary in a narrow liquid-water channel confined by two transparent, parallel plates, while the experimental system was controlled at a temperature below the hydrate/liquid-water/liquid-HCFC-141b equilibrium temperature, T_tri, at atmospheric pressure. It was revealed that the thickness may be significantly different from place to place over the same hydrate film and that the thickness at each location decreases with an increase in the water flow rate and with a temperature rise. To clarify the dependency of the local film thickness thus measured on the convective mass transfer of the hydrate-guest substance from the film surface to the water flow, we performed numerical simulations of the convective mass transfer and also chromatographic measurements of the solubility of HCFC-141b in liquid water so that we could predict the local mass transfer coefficient and the mass flux of the hydrate guest, HCFC-141b, at any location along the hydrate-film/liquid-water interface. Plotting the film-thickness data obtained at each temperature level against relevant predictions of the mass transfer coefficient or the mass flux, we found the film thickness to be nearly inversely proportional to the mass transfer coefficient or the mass flux. This finding supports the idea that the film thickness is determined by the balance between the rate of hydrate-crystal dissociation induced by the aforementioned convective mass transfer and the rate of hydrate-crystal formation depending on the liquid-water permeation into the hydrate film.     

熔融结晶洗涤分离塔传递行为的数学模型及实验

通过对熔融结晶洗涤分离塔的传递行为进行分析,建立了简化的数学模型,得到了晶层内的压力分布、温度分布和杂质浓度分布表达式。并将理论模型的计算结果和实验结果进行比较,二者吻合较好。     

笼形水合物及水合物技术现状及展望

简要介绍了笼形水合物概念及水合物研究史。阐述了水合物的3种晶体结构以及客体分子对晶体结构的影响，讨论了密度、热导率等物性，评述了水合物生成条件和生成机理方面的研究成果。着重介绍了水合物技术在水溶液浓缩和海水淡化、气体混合物分离、气体储运、近临界和超临界萃取、生物蛋白酶提取等主要领域中的应用状况。