Kinetics of formation of carbon dioxide clathrate hydrates

The new experimental apparatus capable of observing the clathrate hydrate formation kinetics was developed in this study. Experimental data on the kinetics of carbon dioxide hydrate formation were carefully measured. The experiments were carried out in a semi-batch stirred tank reactor with stirring rate of 500 rpm at three different temperatures between 275.2 and 279.2 K and at pressures ranging from 2.0 to 3.5 MPa. The kinetic model was adopted to predict the growth of hydrates with only one adjustable parameter which represented the rate constant for the hydrate particle growth. The model was based on the crystallization theory coupled with the two-film theory for gas absorption into the liquid phase. The model predictions matched the experimental data very well with the largest deviation of 7.18%, which is within experimental error range. This study is the first for the kinetic data of carbon dioxide hydrate formation and important in developing carbon dioxide fixation process using clathrate hydrate phenomenon.     

Determination of the activation energy and intrinsic rate constant of methane gas hydrate decomposition

Experimental data on the kinetics of methane gas hydrate decomposition are reported. The isothermal/isobaric semi‐batch stirred‐tank reactor, used by Kim et al. (1987), was modified to include an on‐line particle size analyzer. The experiments were conducted at temperatures ranging from 274.65 K to 281.15 K and at pressures between 3.1 and 6.1 MPa. The model of Clarke and Bishnoi (1999, 2000) was used to determine the intrinsic rate constant. It was found that the activation energy for methane hydrate decomposition is 81 kJ/mol and the intrinsic rate constant of decomposition is 3.6 × 10⁴ mol/m² Pa.s.     

甲烷水合物在纯水中的生成动力学

The kinetic behavior of methane hydrate formation in pure water was investigated.12 sets of experimental data on methane hydrate formation were determined at temperatures ranging from 273.65 to 276.15K and pressures ranging from 4.47 to 8.47MPa.The duration of three stages in methane hydrate formation,known as the dissolution,nucleation and growth periods,that are lacking in open literature,was obtained.The effect of pressure and temperature on the kinetics of methane hydrate formation was also studied.     

Kinetics of methane hydrate formation in aqueous electrolyte solutions

Experimental data on the kinetics of methane hydrate formation in aqueous electrolyte solutions are reported. The experiments were carried out in a semi-batch stirred tank reactor in three NaCl and two KCl solutions as well as in a solution containing a mixture of NaCl and KCl at three different nominal temperatures from 270 to 274 K and at pressures ranging from 3.78 to 7.08 MPa. The kinetic model developed by Englezos et al. (1987a) was adapted to predict the growth of hydrates. The model is based on the crystallisation theory coupled with the two-film theory for gas absorption in the liquid phase. The kinetic rate constant which appears in the model was that obtained earlier for methane hydrate formation in pure water. The effect of the electrolytes was taken into account through the computation of the three-phase equilibrium conditions and the corresponding fugacities. Overall, the model predictions match the experimental data very well with the largest prediction error being less than 10%.     

Kinetics of methane hydrate decomposition

The kinetics of methane hydrate decomposition was studied using a semibatch stirred-tank reactor. The decomposition was accomplished by reducing the pressure on a hydrate slurry in water to a value below the three-phase equilibrium pressure at the reactor temperature. The data were obtained at temperatures from 274 to 283 K and pressures from 0.17 to 6.97 MPa. The stirring rates were high enough to eliminate mass-transfer effects. Analysis of the data indicated that the decomposition rate was proportional to the particle surface area and to the difference in the fugacity of methane at the equilibrium pressure and the decomposition pressure. The proportionality constant showed an Arrhenius temperature dependence. An estimate of the hydrate particle diameters in the experiments permitted the development of an intrinsic model for the kinetics of hydrate decomposition.     

甲烷水合物在纯水中的生成动力学

引言一些低分子量气体,如石油和天然气中C_1～C_4轻烃、氮气、硫化氢、二氧化碳和惰性气体等,在一定压力和温度的条件下可与水形成一类笼形结构的冰状晶体,即所谓的气体水合物．气体水合物是一类较为特殊的包络化合物：主体水分子通过氢键相互结合形成一种内含空隙的笼形框架,客体分子则被笼罩于这些空隙中．主、客体分子之间的作用力为vanderWaals力．水合物晶体最为常见的两种结构分别称为结构I（体心立方构型）和结构Ⅱ（金刚石构型）．甲烷和水形成结构I水合物．文献阐述了开展水合物生成动力学研究的重要意义．但由于水合物生成…     

全可视化反应釜内二氧化碳水合物的生成分解特征

二氧化碳水合物封存技术已成为目前碳封存研究的热点。该技术中对于二氧化碳水合物的生成分解特征及其影响因素的研究是当前的重点和难点。本文设计了高压全透明双反应釜实验平台,以高纯度二氧化碳和去离子水作为研究对象,在17℃、7MPa的初始温压条件下,进行了二氧化碳水合物的初次和二次生成分解实验,并设置对照组对搅拌的影响进行了研究,而后与甲烷在相同条件下的实验进行对比。实验结果表明,搅拌会促进二氧化碳水合物的生成,在400r/min的转速条件下,缩短诱导时间可达40%,增大压降速率可达15%,形成更多且更致密厚实的水合物,并延缓了分解;多次生成可以减少水合物的诱导时间,但对于水合物生成的总量几乎没有影响。与甲烷水合物相比,二氧化碳水合物生成的量大且更难以分解,实验结果有利于二氧化碳的海洋水合物封存技术的开发应用。     

A water droplet size distribution dependent modeling of hydrate formation in water/oil emulsion

Experimental data on chord length distributions and growth rate during methane hydrate formation in water‐in‐oil emulsions were obtained in a high pressure stirring reactor using focused beam reflectance measurement and particle video microscope. The experiments were carried out at 274.2 K for 10–30% water cuts and agitation rates ranging from 200 to 500 rpm initially at 7.72 MPa. Rapid growth was accompanied by gradually decrease in rate. Free water was observed to become depleted during rapid growth while some water remained encapsulated inside hydrate layers constituting a mass transfer barrier. The apparent kinetic constants of methane hydrate formation and free‐water fractions were determined using a newly developed kinetic model independent of the dissolution rate at the gas–oil interface. It was illustrated that continued growth depends on distribution and transfer of water in oil‐dominated systems. This perception accords with observations of hydrate film growth on suspended water droplet in oil and clarifies transfer limits in kinetics. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1010–1023, 2017     

Kinetics of gas hydrate formation from mixtures of methane and ethane

Experimental data on the kinetics of formation of gas hydrates from three mixtures of gaseous methane and ethane are reported. the experiments were conducted in a semi-batch stirred tank reactor at temperatures from 273 to 284 K and of pressures from 0.68 to 5.60 MPa. An intrinsic kinetic model for the growth of the gas hydrate is proposed. It is extension of the model for pure component hydrate formation. The model is based on the crystallization theory coupled with the two-film theory for the gas absorption into the liquid phase. the model does not contain any adjustable parameters. The kinetic rate constants which appear in the model are those obtained previously from pure component formation data. The results indicate that the formation rate is proportional to a lienar combination of the differences in the fugacities of the dissolved gases and their three-phase equilibrium fugacities at the experimental temperature. The effect of the mixture composition is taken into account indirectly through the computation of the three-phase equilibrium conditions and of the fugacities. the total gas consumption rate is proportional to the second moment of the particle size distribution.     

A kinetic study of methane hydrate formation

The kinetics of methane hydrate formation, after commencement of nucleation, were studied using a semibatch stirred tank reactor. The temperatures studied in the experiments were from 274 to 284 K over a pressure range of 3–10 MPa. The results of the experiments revealed that the formation kinetics were dependent on the interfacial area, pressure, temperature and degree of supercooling. The history of water sample affected the induction delay times for nuclei formation, but it had no observable effects on the overall kinetics of hydrate formation after the nucleation had commenced. A consistent semi-empirical model was formulated to correlate the experimental kinetic data.     

甲烷水合物分解动力学

根据两种测量水合物分解动力学的方法———恒定分解压力法及压力变化法 ,采用气体水合物静力学实验装置测定了甲烷水合物的分解动力学数据 .由建立的分解动力学模型计算了甲烷水合物的分解速率 ,较好地拟合了所测得的实验数据 .实验数据验证了分解速率和水合物平衡压力下的逸度与实验压力下的逸度之差有关 ,计算的分解活化能为 73.3kJ·mol^-1(甲烷 ) .     

Experimental study of methane and carbon dioxide solubility in 1,4 butylene glycol at pressures up to 11 MPa and temperatures ranging from 303 to 423 K

This work reports solubility data of methane and carbon dioxide in 1,4 butylene glycol and the Henry's law constant of each solute in the studied solvent at saturation pressure. The measurements were performed at 303, 323, 373, 398 and 423.15 K and pressures up to 3.8 MPa for mixtures containing carbon dioxide and pressures up to 10.9 MPa for mixtures containing methane. The experiments were performed in an autoclave type phase equilibrium apparatus using a technique based on the total pressure method (synthetic method). All investigated systems show an increase of gas solubility with the increase of pressure. A decrease of carbon dioxide solubility with the increase of temperature and an increase of methane solubility with the increase of temperature were observed. From the variation of solubility with temperature, the partial molar enthalpy and entropy change of each mixture were calculated.     

Kinetic and Phase Behaviors of Catalytic Cracking Dry Gas Hydrate in Water-in-Oil Emulsion

The systematic experimental studies were performed on the hydrate formation kinetics and gas-hydrate equilibrium for a simulated catalytic cracking gas in the water-in-oil emulsion. The effect of temperature, pressure and initial gas-liquid ratio on the hydrate formation was studied, respectively. The data were obtained at pressures ranging from 3.5 to 5 MPa and temperatures from 274.15 to 277.15 K. The results showed that hydrogen and methane can be separated from the C₂₊ fraction by forming hydrate at around 273.15 K which is much higher temperature than that of the cryogenic separation method, and the hydrate formation rate can be enhanced in the water-in-oil emulsion compared to pure water. The experiments provided the basic data for designing the industrial process, and setting the suitable operational conditions. The measured data of gas-hydrate equilibria were compared with the predictions by using the Chen-Guo hydrate thermodynamic model.     

Molecular dynamics study on growth of carbon dioxide and methane hydrate from a seed crystal

In the current work, molecular dynamics simulation is employed to understand the intrinsic growth of carbon dioxide and methane hydrate starting from a seed crystal of methane and carbon dioxide respectively. This comparison was carried out because it has relevance to the recovery of methane gas from natural gas hydrate reservoirs by simultaneously sequestering a greenhouse gas like CO₂. The seed crystal of carbon dioxide and methane hydrate was allowed to grow from a super-saturated mixture of carbon dioxide or methane molecules in water respectively. Two different concentrations (1:6 and 1:8.5) of CO₂/CH₄ molecules per water molecule were chosen based on gas–water composition in hydrate phase. The molecular level growth as a function of time was investigated by all atomistic molecular dynamics simulation under suitable temperature and pressure range which was well above the hydrate stability zone to ensure significantly faster growth kinetics. The concentration of CO₂ molecules in water played a significant role in growth kinetics, and it was observed that maximizing the CO₂ concentration in the aqueous phase may not result in faster growth of CO₂ hydrate. On the contrary, methane hydrate growth was independent of methane molecule concentration in the aqueous phase. We have validated our results by performing experimental work on carbon dioxide hydrate where it was seen that under conditions appropriate for liquid CO₂, the growth for carbon dioxide hydrate was very slow in the beginning.     

Kinetics of ethane hydrate formation

The kinetics of ethane hydrate formation after commencement of nucleation were studied at temperatures from 274 to 282 K over a pressure range of 0.6–2.6 MPa. Gaseous ethane was reacted with liquid water in a semi-batch stirred tank reactor. The results of the experiments revealed that the reaction rates were governed by the same kinetic parameters as those found for the methane hydrate formation, i.e. interfacial area, pressure, temperature and degree of supercooling. A semi-empirical model was used to correlate the experimental data.     

Kinetics of formation of methane and ethane gas hydrates

An intrinsic kinetic model with only one adjustable parameter is proposed for the formation of methane and ethane gas hydrates. Experimental formation data were obtained in a semi-batch stirred tank reactor. The experiments were conducted at four temperatures from 274 to 282 K and at pressures ranging from 0.636 to 8.903 MPa. The kinetic model is based on the crystallization theory, while the two-film theory model is adopted for the interfacial mass transfer. Experiments were performed at various stirring rates to define the kinetic regime. The study reveals that the formation rate is proportional to the difference in the fugacity of the dissolved gas and the three-phase equilibrium fugacity at the experimental temperature. This difference defines the driving force which incorporates the pressure effects. The gas consumption rate is also proportional to the second moment of the particle size distribution. The rate constants indicate a very weak temperature dependence.     

Study on the kinetics of hydrate formation in a bubble column

Gas hydrate formation experiments were performed using methane in the presence of tetrahydrofuran (THF) in aqueous solution in a transparent bubble column in which a single pipe or a sintered plate was used to produce bubbles. The mole fraction of THF in aqueous solution was fixed at 6%. The hydrate formation kinetic behaviors on the surface of the rising bubble, the mechanical stability of hydrate shell formed on the surface of the bubble, the interactions among the bubbles with hydrate shell were observed and investigated morphologically. The rise velocities of individual bubbles with hydrate shells of different thickness and the consumption rates of methane gas were measured. A kinetic model was developed to correlate the experimentally measured gas consumption rate data. It was found that the hydrate formation rate on the surface of the moving bubble was high, but the formed hydrate shell was not very easy to be broken up. The bubbles with hydrate shells tended to agglomerate rather than merge into bigger bubble. This kind of characteristic of hydrate shell hindered the further formation of hydrate and led to the lower consumption rate of methane. The consumption rate of methane was found to increase with the decrease of temperature or increase of pressure. The increase of gas flux led to a linear increase in consumption rate of methane. It was demonstrated that the developed kinetic model could be used to correlate the consumption rate satisfyingly.     

甲烷水合物在纯水和抑制剂体系中的生成动力学

Kinetic data of methane hydrate formation in the presence of pure water,brines with single salt and mixed salts,and aqueous solutions of ethylene glycol(EG) and salt EG were measured.A new kinetic model of hydrate formation for the methane water systems was developed based on a four-step formation mechanism and reaction kinetic approach.The proposed kinetic model predicts the kinetic behavior of methane hydrate formation in pure water with good accuracy.The feasibility of extending the kenetic model of salt(s) and EG containing systems was explored.     

Investigation of carbon dioxide photoreduction process in a laboratory-scale photoreactor by computational fluid dynamic and reaction kinetic modeling

The production of solar fuels via the photoreduction of carbon dioxide to methane by titanium oxide is a promising process to control greenhouse gas emissions and provide alternative renewable fuels. Although several reaction mechanisms have been proposed, the detailed steps are still ambiguous, and the limiting factors are not well defined. To improve our understanding of the mechanisms of carbon dioxide photoreduction, a multiphysics model was developed using COMSOL. The novelty of this work is the computational fluid dynamic model combined with the novel carbon dioxide photoreduction intrinsic reaction kinetic model, which was built based on three-steps, namely gas adsorption, surface reactions and desorption, while the ultraviolet light intensity distribution was simulated by the Gaussian distribution model and Beer-Lambert model. The carbon dioxide photoreduction process conducted in a laboratory-scale reactor under different carbon dioxide and water moisture partial pressures was then modeled based on the intrinsic kinetic model. It was found that the simulation results for methane, carbon monoxide and hydrogen yield match the experiments in the concentration range of 10⁻⁴ mol·m^–3 at the low carbon dioxide and water moisture partial pressure. Finally, the factors of adsorption site concentration, adsorption equilibrium constant, ultraviolet light intensity and temperature were evaluated.     

Kinetics of structure II gas hydrate formation for propane and ethane using an in-situ particle size analyzer and a Raman spectrometer

The kinetics of structure II gas hydrates, formed from pure propane and a mixture of propane and ethane, were investigated and intrinsic rate constants were regressed from the experimental data. The experiments were conducted in a semi-batch stirred tank reactor equipped with an in-situ particle size analyzer and connected to an external Raman spectrometer. Experiments were conducted with pure propane at temperatures ranging from 274 to 276 K and pressures ranging from 0.39 to 0.43 MPa. The intrinsic rate constant for ethane in structure II was subsequently regressed from experimental data on the formation of hydrates formed from an equimolar mixture of propane and ethane at 274 K and 0.35 MPa. Raman spectroscopy was used to verify that ethane was present only in the large sII cavity.