含临界区流体混合物的统计缔合理论研究

含临界区流体混合物汽液平衡等热力学性质的研究是化工热力学的一个难题。本文用改进的统计缔合流体理论方程(SAFT-CP)^[1,2]结合范德华单流体混合规则(vdWl)计算了含临界点的二元混合物的汽液平衡。与原始的SAFT方程^[3/4]相比，SAFT-CP方程以非球形的硬体项作为参考流体，代替原来的硬球项，考虑了分子成链对色散作用的影响，对于极性流体，考虑了分子的偶极-偶极相互作用而忽略了缔合作用。本文计算的二元体系包括非极性-非极性体系：二氧化碳-丙烷、二氧化碳-丁烷和二氧化碳-戊烷，以及非极性～极性体系：硫化氢-戊烷、甲烷-丙酮和二氧化碳-甲醇。含临界点在内的计算结果与文献实验值符合很好，表明该方程适用于二元混合物含临界区的相平衡计算，具有广阔的应用前景。     

分子模拟方法预测流体热力学性质

流体的热力学性质数据对化工过程设计具有重要意义,除实验测定外,也可采用分子模拟方法计算。为了考查分子模拟方法预测流体热力学性质的准确性和可靠性,本文以环氧乙烷为例,基于所开发的分子力学力场,综合采用分子动力学和蒙特卡罗等多种分子模拟方法,预测了环氧乙烷在较大温度范围内的气液相平衡、第二维里系数、热容、粘度系数等多种热力学性质。结果表明,采用分子模拟方法所预测的热力学性质与实验值吻合良好,所计算的环氧乙烷的液体密度、气相第二维里系数、热容和粘度系数的平均偏差分别在1%、5%、5%和10%以内。由此可见,分子模拟方法可以成为获取流体热力学性质的另1种可靠手段。     

丙烷超临界状态下乙烯淤浆聚合体系组分的物性计算

以生产HDPE过程中丙烷溶剂处于超临界状态下乙烯淤浆聚合过程为研究对象,应用POLYMER PLUS为计算平台,建立含聚乙烯的复杂体系的热力学物性参数的计算方法。通过研究,可见PC-SAFT方程可以准确地计算所研究聚合物系统各组分的热力学物性;处于超临界状态的丙烷的热力学参数可以通过饱和蒸汽压、液相密度以及超临界密度数据拟合得到,且计算丙烷的饱和液相密度和超临界密度的偏差在1.9%以内;聚乙烯的热力学方程参数以及聚乙烯与丙烷的交互参数可以通过聚合物和丙烷在液态和超临界状态时的液相密度拟合得到,计算的聚乙烯和丙烷的混合密度偏差在0.78%以内;应用PC-SAFT方程计算操作条件范围内的聚乙烯热能和聚合热的偏差也在3%以内。     

用NPT系综模拟计算方阱位能流体

本文介绍了 NPT 系综原理及其计算机实施步骤;应用作者编制的计算机程序模拟计算了方阱流体的性质,表明该程序能够正确地描述方阱流体的行为。当采用其它势能函数时,也可以模拟计算其它模型流体的性质。     

烯烃类分子的分子力学力场及热力学性质预测

高质量的分子力学力场是准确预测分子各种性质的前提。本文借助第一性原理计算开发了新的适用于烯烃类分子的全原子力场,将所得力场计算和预测不同的热力学性质、传递性质以及气液相平衡性质。该力场不但可以准确预测分子的气相性质,且可得到和实验值吻合较好的液相热力学性质。与已有力场相比,在应用范围和精度都有明显的改进。借助分子动力学和蒙特卡洛模拟,计算密度和实验值偏差±0.01g/ml左右,蒸发焓为±0.3 kcal/mol左右,热容为±1.0 cal/mo1·K左右,热胀系数为±10~(-4)K~(-1)左右,以及粘度为±0.02 centipoise左右。     

人工神经网络技术在超临界流体密度预测中的应用

超临界流体的性质常与其密度相关。因此,如何精确计算超临界流体在不同操作条件下的密度值,对于超临界流体过程的研究和设计均十分重要。本文尝试采用人工神经网络技术来预测计算超临界流体的密度。网络结构为3层BP网,经优化中间隐藏层单元数为6。通过训练和学习,在压力6MPa-8MPa、温度300K-320K范围内,神经网络预测的密度值,其相对误差<0.35％。比P-B状态方程计算的结果精确。     

通过改进物性参数估计提高1,10-癸二酰在超临界CO_2流体中溶解度的计算精度

关于1,10-癸二酰在超临界CO_2流体中溶解度计算精度的改进,是在利用Aspen Plus对其物性参数进行模拟的基础上,采用PR方程对其溶解度数据进行关联和计算。溶解度的计算值与实验值符合很好,最大相对偏差为2.53%,最大计算方差为8.83×10~(-5)。该方法为改进固体在超临界流体中溶解度数据计算关联精度提供了一种新的途径。     

用分子模拟法预测环氧乙烷液体的热力学性质

国际工业流体模拟大赛(IFPSC)是一项致力于用分子模拟解决实用问题的国际大赛。第四届工业流体大赛的题目是用一个力场、几种模拟方法预测环氧乙烷液体的多种热力学和动力学性质。采用TEAM环氧乙烷力场参加了那次竞赛并取得了优秀的成绩。尽管TEAM全原子力场能确算大部分竞赛的要求,但是明显高估了热传导系数。作者等研究了计算热传导系数的方法,最终在计算中考虑量子效应而解决了问题。为了进一步考察全原子力场在计算热力学性质上的准确性,作者等在相当大的温差范围内计算。结果证实,TEAM环氧乙烷力场是目前计算热力学性质方面有突出表现的全原子力场。     

二氧化碳-醋酸乙烯体系相平衡的GEMC模拟

采用吉布斯系综蒙特卡罗方法 (GEMC)来研究二氧化碳-醋酸乙烯二元组分的汽-液相平衡性质。以Tra PPE-UA力场为原始模型,采用量子化学方法构建出适用于醋酸乙烯分子的特定力场。选择适合与Tra PPE-UA力场结合使用的Tra PPE-EH力场建立二氧化碳模型,采用NPT-GEMC方法计算二氧化碳-醋酸乙烯二组分体系的汽-液相平衡性质,所得模拟结果与实验值吻合较好。在313.15 K时,二氧化碳在醋酸乙烯中摩尔分数的模拟值与实验值的相对误差范围是3.8%~7.6%;在333.15 K时,相对误差范围是3.7%~11.3%;随着压力增加误差逐渐增大,接近混合物临界区域时误差最大。模拟结果表明构建的醋酸乙烯力场具有较高的模拟精度,可用于预测醋酸乙烯体系的汽-液相平衡性质。     

基于CPA状态方程计算水蒸汽的热力学物性

水和水蒸气的热力学性质是工程中重要的基础数据,获得可靠的计算途径对于工程设计具有重要的意义。本文利用CPA方程研究了水和水蒸气热力学性质的计算,建立了基于CPA方程的热力学性质计算模型,主要研究了水的饱和状态、水和水蒸气的PVT性质以及焓值计算。通过考察研究发现,在(0～22)bar范围内,CPA方程计算的水的热力学性质与其实验数据具有良好的一致性,所计算的数据与实验数据的平均相对偏差小于1%,最大偏差不超过5%,满足工程计算的精度需要,证实了CPA方程适用于工程中水和水蒸气的热力学性质计算。     

Equation of state of solid,liquid and gaseous tantalum from first principles

We present ab initio calculations of the phase diagram and the equation of state of Ta in a wide range of volumes and temperatures, with volumes from 9 to 180 Å³/atom, temperature as high as 20 000 K, and pressure up to 7 Mbars. The calculations are based on first principles, in combination with techniques of molecular dynamics, thermodynamic integration, and statistical modeling. Multiple phases are studied, including the solid, fluid, and gas single phases, as well as two-phase coexistences. We calculate the critical point by direct molecular dynamics sampling, and extend the equation of state to very low density through virial series fitting. The accuracy of the equation of state is assessed by comparing both the predicted melting curve and the critical point with previous experimental and theoretical investigations.     

渣油制氨气化—变换系统流程模拟

本文对UBE型渣油制氨的气化—变换系统进行稳态模拟。用马丁-候状态方程作为热力学模型来计算真实气体的热力学性质,并在此基础上引入平衡温距的概念来描述高温高压下的气化反应。根据Prausnitz提出的方法建立了8.7MPa压力下的汽液平衡模型,用校正的动力学方程来计算变换反应速度,采用序贯模块法进行了流程模拟。以设计工况为基准的实例分析表明模拟结果与实际数据符合良好。对各关键单元进行的模拟操作分析,为该系统的优化计算和改进现行操作工况提供了较好的依据。     

Comparison between the artificial neural network system and SAFT equation in obtaining vapor pressure and liquid density of pure alcohols

Vapor pressure and liquid density of 20 pure alcohols were correlated using an artificial neural network (ANN) system and statistical associating fluid theory (SAFT) equation of state. The SAFT equation has five adjustable parameters as temperature-independent segment diameter, square-well energy, number of segment per chain, association energy and association volume. These parameters can be obtained by a non-linear regression method using the experimental vapor pressure and liquid density data. In continue, the vapor pressure and liquid densities of pure alcohols were estimated by using an artificial neural network (ANN) system. In the neural network system, it is assumed that thermodynamic properties of pure alcohols depend on temperature, critical properties and acentric factor. The best network topology was obtained as (4-10-2). The weights connection and biases were obtained using batch back propagation (BBP) method for 611 experimental data points. The average absolute deviation percent (ADD%) for vapor pressure of pure alcohols for ANN system and SAFT equation of state are 3.593% and 3.378%, respectively. Also, the average absolute deviation percent (ADD%) for liquid density of pure alcohols for ANN system and SAFT equation of state are 0.792% and 1.367%, respectively. The results emphasized that the artificial neural network can more accurately predict thermophysical properties of pure alcohols than the SAFT equation of state.     

烷基苯磺酸盐表面活性剂的结构与气-液界面性质研究

表面活性剂能够有效降低水-空气界面的表面张力.相似但具有不同结构的表面活性剂分子,如苯基与碳链骨架的连接位点不同的烷基苯磺酸盐,其性质有很大差别.本文用分子动力学模拟方法研究了2、4、6位不同结合位点的烷基苯磺酸盐表面活性剂分子的水溶液表面单分子膜.通过计算不同表面浓度下的表面张力和分析表面分子的微观结构,探索表面活性...     

The thermodynamics of several elements at high pressure

We have used the CALPHAD-compatible equation of state (EOS) based on the explicit Gibbs free energy concept for the solid state of ten important elements: V, Nb, Ta, Mo, W (groups VB and VIB), Pd, Pt (group VIIIB) and Cu, Ag and Au (group IB). The new formulation uses SGTE data for ambient pressure and converges to the quasi-harmonic model at the limit of extreme pressure to calculate the Gibbs free energy as a function of pressure and temperature. The model is based on the available pressure-volume-temperature (PVT) data on the elements and can be usefully extrapolated to extreme pressures. When compared to shock wave data, the modeled EOS holds well, but the fit is not totally satisfactory in the ultrahigh-pressure range. A great advantage of this formulation is that it can be used to calculate thermodynamic properties such as the heat capacity and entropy at very high temperatures and pressures.     

Thermodynamic modeling of the Mg–Al–Sb system

Thermodynamic modeling of the Mg–Al–Sb system is carried out for the first time in this work. Among the constituent binaries in this system, only the Al–Sb and Mg–Sb are re-optimized. Liquid phases are described by the Redlich–Kister polynomial model, whereas the high temperature modification of Mg₃Sb₂ compound in the Mg–Sb system is described by the sublattice model. The constructed database is used to calculate and predict thermodynamic properties, binary phase diagrams of Al–Sb and Mg–Sb, and liquidus projections of the ternary Mg–Al–Sb. The calculated phase diagrams and the thermodynamic properties such as enthalpy, entropy, Gibbs free energy of mixing, and activities are found to be in good agreement with the experimental data from the literature. The established Mg–Al–Sb database predicted a closed ternary liquid miscibility gap, six ternary eutectics, two ternary peritectics, four saddle points and a critical point.     

SteamTablesGrid: An ActiveX control for thermodynamic properties of pure water

An ActiveX control, steam tables grid (StmTblGrd) to speed up the calculation of the thermodynamic properties of pure water is developed. First, it creates a grid (matrix) for a specified range of temperature (e.g. 400-600 K with 40 segments) and pressure (e.g. 100,000-20,000,000 Pa with 40 segments). Using the ActiveX component SteamTables, the values of selected properties of water for each element (nodal point) of the 41×41 matrix are calculated. The created grid can be saved in a file for its reuse. A linear interpolation within an individual phase, vapor or liquid is implemented to calculate the properties at a given value of temperature and pressure.A demonstration program to illustrate the functionality of StmTblGrd is written in Visual Basic 6.0. Similarly, a methodology is presented to explain the use of StmTblGrd in MS-Excel 2007. In an Excel worksheet, the enthalpy of 1000 random datasets for temperature and pressure is calculated using StmTblGrd and SteamTables. The uncertainty in the enthalpy calculated with StmTblGrd is within ±0.03%. The calculations were performed on a personal computer that has a “Pentium(R) 4 CPU 3.2 GHz, RAM 1.0 GB” processor and Windows XP. The total execution time for the calculation with StmTblGrd was 0.3 s, while it was 60.0 s for SteamTables. Thus, the ActiveX control approach is reliable, accurate and efficient for the numerical simulation of complex systems that demand the thermodynamic properties of water at several values of temperature and pressure like steam flow in a geothermal pipeline network.     

多溴二苯并噻吩系列化合物的热力学性质及稳定性的密度泛函理论

本文在298.15 K和1.013×10~5Pa时,根据密度泛函理论(DFT),使用Gaussian 03程序,在B3LYP/6-31G(d)水平上计算117个多溴二苯噻吩系列化合物(PBDTs),得各分子的热力学性质。设计等键反应,计算PBDTs系列化合物的标准生成热Δ_fH~(?)和标准生成自由能Δ_fG~(?)。同时用程序Origin7.5将这些热力学参数与溴原子的取代位置及取代数目线性回归,求出相关方程,研究表明:热力学参数、标准生成热、标准生成自由能与溴原子的取代位置及取代数目之间关系极密切。根据标准生成自由能的相对大小,本文从理论上求得该化合物异构体的相对稳定性顺序。本文研究该化合物热力学性质及其稳定性,对于研究其生成、降解以及对环境的潜在威胁具有重要意义。