利用两种模型预测多孔介质中气体水合物平衡分解条件

分别利用两种热力学方法(基于逸度相等的方法与基于活度相等的方法)预测了不同多孔介质中气体水合物的平衡分解条件, 对于非水合物相, 逸度方法采用Trebble-Bishnoi (TB)方程, 而活度方法则使用Soave-Redlich-Kwong (SRK)方程, 对于水合物相, 两种方法都利用了van der Waals-Platteeuw模型结合Llamedo等关于毛细管力作用模型来模拟. 两种方法的预测结果与实验结果吻合, 逸度方法的预测效果要好于活度方法.     

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...     

四元交互体系Li+,Mg2+/Cl-,SO42--H2O25℃相平衡及物化性质研究

本文采用等温溶解平衡法研究了四元交互体系Li⁺,Mg²⁺/CI^-,SO-H₂O 25℃的机关系和平衡液相的物化性质(密度、粘度、电导率、折光率和pH).该体系25℃有七个相区Li₂SO₄·H₂O,MgSO₄·7H₂O,MgSO₄·6H₂O,MgSO₄·5H₂O,MgC1₂·6H₂O,LiCI·MgCl₂·7H₂O,LiCI·H₂O,十一条单变量线,五个共饱点。其中LiCI·H₂O+LiCI·MgCl₂·7H₂O+Li₂SO₄·H₂O为一致零变量点。与文献中的研究结果比较,我们得到两个新相区MgSO₄·6H₂O和MgSO₄·5H₂O.用经验和半经验公式计算了平衡液相的密度、折光率。由实验测定的溶解度数据求得了高锂浓度下的Pitzer参数。对该体系25℃溶解度进行了理论计算复证。     

钛硅分子筛催化环己酮液相氨肟化固定床工艺

采用固定床模式,研究了钛硅分子筛催化环己酮制环己酮肟液相氨肟化反应.结果表明,该工艺模式具有可行性与普适性.优化的反应条件为:温度333K,体系氨浓度>2%,酮/H₂O₂摩尔比=5,H₂O₂空速0.083h^-1.此时环己酮转化率、环己酮肟选择性、H₂O₂转化率及其有效利用率分别达18.7%,99.5%,94.7%和98.7%.进一步研究了H₂O₂在该过程中的反应行为,发现固定床工艺模式能有效提高H₂O₂的有效利用率,其主要原因是该模式有利于羟胺的生成及其进一步与酮反应生成肟.适当的空速与氨和酮的浓度是实现H₂O₂高效利用的关键因素.     

基于 H2/O2 等离子体和钛硅沸石的丙烯气相环氧化方法

 将 H₂/O₂ 非平衡等离子体现场产生的气态 H₂O₂和丙烯与耦合反应器中钛硅沸石 TS-1 直接接触, 实现了丙烯气相环氧化反应. 结果表明, 非平衡等离子体生成气态 H₂O₂ 的速率由介质阻挡放电的输入功率决定, 环氧丙烷的生成速率和选择性取决于钛硅沸石催化剂和反应条件. 在 H₂ 和 O₂ 进料流量分别为 170 和 8 ml/min, 介质阻挡放电输入功率为 3.5 W, 环氧化反应温度为 110 ^oC, 丙烯进料量为 18 ml/min, 催化剂用量为 0.8 g 的条件下, 生成环氧丙烷产率达 246.9 g/(kg•h)、环氧丙烷选择性和 H₂O₂ 有效利用率分别为 95.4% 和 36.1%, 反应 36 h 内未见催化剂失活.     

多孔金属有机骨架材料储氢性能分子模拟

采用优化的DREIDING力场参数, 通过巨正则系综蒙特卡洛(GCMC)模拟方法对H₂在IRMOF-1、IRMOF-61和IRMOF-62共3种金属有机骨架(MOFs)材料中的吸附平衡性能进行了比较研究. 结果表明, 该力场能够在全压力范围内很好地复制H₂在IRMOF-62材料中的等温吸附曲线; 但对低压下H₂在IRMOF-61中的等温吸附曲线预测出现低估. 与IRMOF-1相比, 具有互穿骨架结构的IRMOF-61和IRMOF-62材料在常温下的储氢能力并无明显提高. 进一步比较77 K时100 kPa、3.0 MPa下H₂在上述MOFs材料中达到吸附平衡时的几率密度分布发现, H₂会优先吸附在Zn₄O骨架附近靠近苯环的位置;对具有互穿结构的MOFs材料而言,由于其孔腔尺寸缩小, 使得H₂优先吸附位区域零散化. 适当长度的有机配体形成的互穿骨架结构能增强与H₂分子之间的相互作用, 具备较高的储氢能力; 而有机配体尺寸过长则会增加骨架结构中H₂吸附死角, 对H₂的吸附能力反而出现下降.     

水合/水解对Cd(Ⅱ)活性影响的密度泛函研究

用密度泛函(DFT)B3LYP方法对Cd(Ⅱ)水合与水解产物的几何结构、电子结构、稳定性随水合/水解过程的变化以及水合/水解反应自由能进行了理论研究。结果表明,水合产物的稳定性均优于水解产物,水合反应钝化Cd(Ⅱ),而水解反应活化Cd(Ⅱ);水合物种Cd(Ⅱ)活性顺序为：Cd(H₂O)₆²⁺2O)₅²⁺2O)₄²⁺。水解物种Cd(Ⅱ)活性顺序为：Cd(OH)(H₂O)₅⁺<cis-Cd(OH)₂(H₂O)₄2(H₂O)₄3(H₂O)₂^-4^2-。     

溶液中肼还原钴离子制备纳米金属钴的反应动力学

通过加入NaBH₄作为诱导剂, 可在室温下引发肼与Co^2＋在水-乙醇体系中的还原反应, 制得高纯度纳米金属钴粉. 机理研究表明, 该反应分二段进行: 第一段主要发生Co^2＋被N₂H₄还原的反应(2Co^2＋＋N₂H₄＋4OH^－＝2Co¯＋N₂­＋4H₂O), 第二段主要为金属Co催化的肼分解反应(N₂H₄＝N₂­＋2H₂­)和歧化反应(3N₂H₄＝N₂­＋4NH₃­). Co^2＋被N₂H₄还原是典型的自催化过程, 因此, 加入少量NaBH₄即可在288 K下启动反应. 通过测量气体产物的生成速率, 获得了Co^2＋还原的反应动力学方程, 发现Co^2＋, N₂H₄和产物Co的反应级数分别为1, 0和1, 反应活化能约为89 kJ/mol. 调节Co^2＋的浓度, 纳米金属钴的表面积可从11增加到25 m²/g.     

通过铜(II)、铁(III)和铁(II)与2,2'-联咪唑协同作用构筑的超分子及其结构的研究

在水和乙醇溶剂中, 通过Cu(II), Fe(III)和Fe(II)与2,2-联咪唑协同作用, 构筑了四种新的超分子配合物[Cu(H₂biim)(gly)(H₂O)]Cl•H₂O (1), [Cu(H₂biim)(C₃H₂O₄)(H₂O)]•1.5H₂O (2), [Fe₂(μ-O)(H₂biim)₄(H₂O)₂](NO₃)₄•C₂H₅OH (3)和[Fe(H₂biim)₃]SO₄ (4) (H₂biim＝2,2-联咪唑; gly^－＝甘氨酸根; C₃H₂O＝丙二酸根). 并通过元素分析, 红外光谱和X射线单晶衍射对其组成、结构和谱学性质进行研究. H₂biim配体, 丙二酸根和甘氨酸根三种配体都采用了双齿螯合方式与金属离子配位. 配合物1～4中, 通过H₂biim配体的N—H键与阴离子、水分子和溶剂分子形成多种氢键, 如R(7), R(9)和R(4)等, 以及H₂biim配体之间的π-π堆积, 阳离子不对称单元构筑了多维结构的超分子配合物.     

水滑石层间碘酸根离子的还原性机理研究

通过X射线衍射（XRD）和傅里叶变换红外（FTIR）光谱仪表征发现,经水合肼（N₂H₄·H₂O）和亚硫酸钠（Na₂SO₃）两种还原剂处理碘酸根插层水滑石的产物分别为碘离子插层的水滑石（ZnAl-ILDHs）和硫酸根离子插层水滑石（ZnAl-SO₄LDHs）。进一步研究表明,N₂H₄·H₂O和水滑石的反应为D₇模型的核外层扩散反应,N₂H₄·H₂O在水滑石微球界面和IO₃^-发生反应。而Na₂SO₃则先进入了水滑石层间,然后与层间的IO₃^-反应,其模型符合D₁₁动力学模型。     

Hydrate dissociation conditions for gas mixtures containing carbon dioxide,hydrogen, hydrogen sulfide,nitrogen, and hydrocarbons using SAFT

A new method, a molecular thermodynamic model based on statistical mechanics, is employed to predict the hydrate dissociation conditions for binary gas mixtures with carbon dioxide, hydrogen, hydrogen sulfide, nitrogen, and hydrocarbons in the presence of aqueous solutions. The statistical associating fluid theory (SAFT) equation of state is employed to characterize the vapor and liquid phases and the statistical model of van der Waals and Platteeuw for the hydrate phase. The predictions of the proposed model were found to be in satisfactory to excellent agreement with the experimental data.     

Experimental and thermodynamic modelling of systems containing water and ethylene glycol: Application to flow assurance and gas processing

Accurate knowledge of hydrate phase equilibrium in the presence of inhibitors is crucial to avoid gas hydrate formation problems and to design/optimize production, transportation and processing facilities. In this communication, we report new experimental dissociation data for various systems consisting of methane/water/ethylene glycol and natural gas/water/ethylene glycol. A statistical thermodynamic approach, with the Cubic-Plus-Association equation of state, is employed to model the phase equilibria. The hydrate-forming conditions are modelled by the solid solution theory of van der Waals and Platteeuw. The thermodynamic model was used to predict the hydrate dissociation conditions of methane and natural gases in the presence of distilled water or ethylene glycol aqueous solutions. Predictions of the developed model are validated against independent experimental data and the data generated in this work. A good agreement between predictions and experimental data is observed, supporting the reliability of the developed model.     

Clathrate hydrate dissociation conditions of refrigerants R404A,R406A,R408A and R427A: Experimental measurements and thermodynamic modeling

Clathrate hydrate dissociation conditions were measured for four “alternative” refrigerants, viz. R404A, R406A, R408A and R427A. The experimental measurements were performed within the pressure range of (0.079 to 9.995) MPa and temperatures ranging from (272.7 to 288.7) K. An isochoric pressure-search method was used to perform the measurements. A thermodynamic model based on the van der Waals–Platteeuw (vdW–P) model was applied for the prediction of the dissociation conditions which were compared to the experimental measurements. The fluid phase was modeled using the MHV2 G^E-EoS mixing rule along with the UNIFAC (original) activity model. The van der Waals–Platteeuw (vdW–P) model was used for the modeling of the hydrate phase. There was reasonable agreement between the experimental and predicted values.     

Gas hydrates in low water content gases: Experimental measurements and modelling using the CPA equation of state

In this communication, new experimental data are reported for the water content of methane and two synthetic gas mixtures in equilibrium with hydrates at pressures range from 5 to 40 MPa and temperature down to 251.65 K. The measurements have been made on equilibrated samples taken from a high-pressure variable volume hydrate cell using a new analyser based upon tuneable diode laser absorption spectroscopy (TDLAS) technology. A statistical thermodynamic approach, with the Cubic-Plus-Association equation of state, is employed to model the phase equilibria. The hydrate-forming conditions are modelled by the solid solution theory of van der Waals and Platteeuw. The thermodynamic model was used to predict the water content of methane and synthetic gases in equilibrium with gas hydrates.     

A model for prediction of gas hydrate formation conditions in aqueous solutions containing electrolytes and/or alcohol

In this contribution, a generalized method for predicting gas hydrate formation conditions in the presence of aqueous solutions, HL₁V calculations, is developed. Each phase is characterized separately. In this respect, the equation of Nasrifar et al. for calculating the activity of water in the presence of electrolytes and an alcohol is extended to water in various mixtures of electrolytes, alcohol and dissolved gas. An equation for calculating the activity of water in the presence of mixtures of electrolytes is also developed. These equations are then used to characterize the aqueous phase in HL₁V calculations. The modified Patel–Teja equation of state is used to characterize the vapour phase and the statistical model of van der Waals and Platteeuw for the hydrate phase. The proposed model is then compared with experimental results and other available models. No adjustable or curve-fitting parameters are used. The agreement with experimental results is very good. The comparison with other models also indicates that the proposed model predicts incipient hydrate formation conditions as good as the other models and in most cases even better.     

A perturbation method for the Ornstein-Zernike equation and the generic van der Waals equation of state for a square well potential model

We calculate the generic van der Waals parameters A and B for a square well model by means of a perturbation theory. To calculate the pair distribution function or the cavity function necessary for the calculation of A and B, we have used the Percus-Yevick integral equation, which is put into an equivalent form by means of the Wiener-Hopf method. This latter method produces a pair of integral equations, which are solved by a perturbation method treating the Mayer function or the well width or the functions in the square well region exterior to the hard core as the perturbation. In the end, the Mayer function times the well width is identified as the perturbation parameter in the present method. In this sense, the present perturbation method is distinct from the existing thermodynamic perturbation theory, which expands the Helmholtz free energy in a perturbation series with the inverse temperature treated as an expansion parameter. The generic van der Waals parameters are explicitly calculated in analytic form as functions of reduced temperature and density. The van der Waals parameters are recovered from them in the limits of vanishing density and high temperature. The equation of state thus obtained is tested against Monte Carlo simulation results and found reliable, provided that the temperature is in the supercritical regime. By scaling the packing fraction with a temperature-dependent hard core, it is suggested to construct an equation of state for fluids with a temperature-dependent hard core that mimicks a soft core repulsive force on the basis of the equation of state derived for the square well model.     

Method for predicting the dissociation condition of a simple hydrate phase on an H–Lw–V line in isochoric operation

A method for predicting the location of a dissociation condition on an H–L_w–V line under isochoric operation was presented. To establish the method, the governing equations for the H–L_w–V coexistence under isochoric conditions were derived. Here, a liquid and a vapor phase were expressed by the PR EOS + MHV2 model and a hydrate phase by the van der Waals–Platteeuw model. The molar volume of the vapor phase was calculated from the equation of state, and a simple expression for the molar volume of the hydrate phase was derived. Then, to prove the validity of the proposed method, experimental studies about the dissociation process of the hydrates were performed. The temperature and pressure traces in the hydrate dissociation process, including the location of the dissociation condition, were successfully predicted by the proposed method. In addition, the thermodynamic consistency among the phase models was discussed. It was pointed out that agreement between the calculated and experimental results about the H–L_w–V equilibrium line did not ensure thermodynamic consistency among the phase models.     

Van der Waals interactions: evaluations by use of a statistical mechanical method

In this work the induced van der Waals interaction between a pair of neutral atoms or molecules is considered by use of a statistical mechanical method. With use of the Schro?dinger equation this interaction can be obtained by standard quantum mechanical perturbation theory to second order. However, the latter is restricted to electrostatic interactions between dipole moments. So with radiating dipole-dipole interaction where retardation effects are important for large separations of the particles, other methods are needed, and the resulting induced interaction is the Casimir-Polder interaction usually obtained by field theory. It can also be evaluated, however, by a statistical mechanical method that utilizes the path integral representation. We here show explicitly by use of this method the equivalence of the Casimir-Polder interaction and the van der Waals interaction based upon the Schro?dinger equation. The equivalence is to leading order for short separations where retardation effects can be neglected. In recent works [J. S. H?ye, Physica A 389, 1380 (2010); Phys. Rev. E 81, 061114 (2010)], the Casimir-Polder or Casimir energy was added as a correction to calculations of systems like the electron clouds of molecules. The equivalence to van der Waals interactions indicates that the added Casimir energy will improve the accuracy of calculated molecular energies. Thus, we give numerical estimates of this energy including analysis and estimates for the uniform electron gas.     

On statistical mechanical equations of state for simple fluids : Effective hard spheres and quantum corrections

Nordholm, S., Greberg, H. and Penfold, R., 1991. On statistical mechanical equations of state for simple fluids. Effective hard spheres and quantum corrections. Fluid Phase Equilibria, 90: 307-332.

A comparison is made of the mean field generalised van der Waals theory, based on a variationally determined hard sphere diameter, with the recent equation of state proposed by Song and Mason incorporating a temperature-dependent hard sphere diameter and correlation effects through the second virial coefficient. The simple cell theory ansatz of the former is less accurate but permits a wide range of applications including the estimation of quantum effects on the bulk properties of light fluids at low temperatures. Results for the critical parameters of ³He, ⁴He, H₂, Ne, CH₄ and Ar are examined. The relevance to the corresponding theory of non-uniform fluids is noted.