二元交互参数化PC-SAFT在超临界乙烯配位聚合体系相平衡计算中的应用

超临界烯烃配位聚合技术是近年来国际聚烯烃工业领域中的重要进展之一,超临界体系相平衡计算则是该聚合工艺设计与优化操作的基础。本文以链扰动统计缔合流体理论(PC-SAFT)状态方程描述工业级超临界乙烯配位聚合体系的相平衡,得到了适用于该复杂体系的PC-SAFT二元交互参数。与公开报道的实验数据比较表明,获得的二元交互参数可准确描述该超临界体系在较宽温度、压力范围的相平衡。基于上述二元交互参数,针对2个不同双峰聚乙烯产品牌号,计算了工业装置内多组分的相平衡状态,结果表明,反应器内的[H2]/[C2H4]摩尔比、淤浆密度的计算值与工业数据吻合较好,验证了二元交互参数的适用性。研究结果为进一步的工艺流程模拟与优化奠定了基础。     

RG-CPA方程计算超临界CO2-醇体系汽液相平衡

综合考虑缔合作用和密度涨落的影响,将经重整化群修正的CPA方程（RG-CPA方程）扩展到二元体系汽液相平衡的计算。通过一个温度下的汽液相平衡数据回归得到二元交互作用参数,预测其他温度下的相平衡。采用这种方法计算了超临界CO₂与醇二元体系的汽液相平衡性质和临界曲线。结果表明,RG-CPA方程预测超临界CO₂与醇二元体系的气液相组成和密度具有较高的精度,液相组分平均绝对偏差为0.032,气相组分平均绝对偏差为0.019。与原始CPA方程相比,RG-CPA方程能更好地预测气液临界曲线。     

PC-SAFT在烯烃共聚物体系物性计算中的应用进展

综述了PC-SAFT状态方程在计算共聚物性质以及共聚物-溶剂相平衡方面的研究进展,介绍了用PC-SAFT状态方程计算的几种共聚物体系的相平衡以及计算值与实验值的比较情况。结果表明PC-SAFT状态方程可以很好地描述二元共聚物-溶剂体系的相平衡。此外,对于由极性和非极性重复单元构成的共聚物,需要用相互作用参数来校正不同类型重复单元之间的相互作用力。     

乙烯淤浆聚合物体系的相平衡计算

乙烯淤浆聚合反应体系的流程模拟与优化过程中气液相平衡的准确计算影响到聚乙烯生成量和聚乙烯分子量的模拟. 通过再参数化含链扰动统计缔合流体理论(Perturbed-Chain Statistical Associating Fluid Theory, PC-SAFT)状态方程,建立了乙烯淤浆聚合体系物性的计算方法. 以文献数据为基准,利用Polymers Plus软件平台,分别得到了乙烯、氢气、己烷、聚乙烯、氮气纯组分的PC-SAFT方程的模型参数,并在准确确定纯组分模型参数的基础上,得到了乙烯-己烷、氢气-己烷、氮气-己烷、以及聚乙烯-乙烯、聚乙烯-己烷组分二元交互系数. 计算结果表明,采用再参数化PC-SAFT状态方程可以准确计算乙烯淤浆聚合反应体系的纯组分物质性质和两组分之间的相平衡. 同时对工业过程中5个不同牌号聚乙烯的反应器内气液平衡状态进行了模拟计算,氢气与乙烯在气相的摩尔比与工业分析值能很好地吻合,最大误差为7.5%.     

苯与甲苯及C8芳烃体系固液相平衡计算

针对对二甲苯结晶体系中由苯与甲苯及C₈芳烃组成的二元、三元及多元体系,选取了固液相平衡计算模型—Van′t Hoff方程简式,利用该模型计算二元、三元及多元体系的低共熔点温度及对应的低共熔点组成,并绘制三元体系固液相平衡相图。结果表明：由Van′t Hoff方程简式得到的苯-对二甲苯二元体系固液相平衡计算结果与文献数据吻合较好,表明所选固液相平衡计算模型适合于由苯与甲苯及C₈芳烃组成的体系固液相平衡计算;利用Van′t Hoff方程简式计算得到了由苯与甲苯及C₈芳烃组成的二元、三元、四元、五元和六元体系的低共熔点温度及组成,并预测了苯-甲苯和苯-乙苯二元体系的液相摩尔分数,利用这些数据绘制了对二甲苯-甲苯-苯、对二甲苯-乙苯-苯、苯-乙苯-甲苯3个三元体系的固液相平衡相图,这些数据和相图未见文献报道,可为PX结晶相关的苯与甲苯及C₈芳烃组成的体系固液相平衡研究提供理论指导和依据。     

六氟化铀及氟化物汽液相平衡数据预测及精馏过程模拟

精馏技术提纯六氟化铀是铀转化工艺的重要环节,该精馏工艺的模拟可为工艺设计及操作优化提供关键支撑。然而,由于六氟化铀及氟化物汽液相平衡数据及物性数据的缺乏,六氟化铀提纯精馏工艺的建模和模拟难以开展。为此,利用COSMOtherm和Turbomole软件,预测UF₆与TiF₄二元体系汽液相平衡数据。通过预测已知的WF₆-UF₆二元体系汽液相平衡实验数据以间接验证COSMO-RS模型预测的准确性。利用Aspen Plus软件的物性常数估算系统(property constant estimation system),估算出缺失的无限稀释水溶液Gibbs生成能等物性参数。文献中UF₆饱和蒸气压实验数据与模拟值进行对比,相对误差在1.76%以内。根据文献中的实验数据和预测的汽液相平衡数据,利用Aspen Plus软件回归NRTL模型的二元交互作用参数。针对六氟化铀及氟化物的分离,设计直接分离序列和间接分离序列提纯UF₆的两种方案。设定UF₆产品...     

二氧化碳+重整汽油拟二元体系高压汽液平衡数据的测定及关联

为了满足超临界CO2回收溶剂法提取油砂沥青的提取溶剂重整汽油的工艺需要,采用可变体积高压相平衡装置,在温度为30.3～70.2℃下,测定了4.02～14.01MPa范围内CO2-重整汽油拟二元体系的气液两相的平衡组成、密度以及摩尔体积。通过得到的结果确定了利用超临界二氧化碳来回收重整汽油的操作条件范围。利用基团贡献法估算了重整汽油的特性参数。采用Peng-Robinson方程拟合回归实验数据,得到了CO2-重整汽油体系的交互参数,计算出CO2-重整汽油体系的相平衡数据,结果表明计算值与实验值吻合较好。     

超临界二氧化碳和脂质体系相平衡计算

对超临界CO2和一些脂质体系相平衡计算问题进行了研究.应用Peng-Robinson状态方程及Panagiotopoulos和Reid混合规则,改进能量参数a(T)后,用于计算脂质和超临界CO2组成的二元和三元体系的相平衡,结果与实验数据拟合精度较好.对于一些复杂的混合物如大豆油脱臭馏出物与超临界CO2体系,简化成拟三元、四元等体系进行了计算,计算结果达到一定的精度.     

PC-SAFT理论对CO_2-甲醇体系相平衡的研究

主要结合统计缔合流体理论(PC-SAFT),采用已有的CO2与甲醇纯流体分子参数,同时利用CO2与甲醇纯流体分子参数回归二元交叉作用参数。以CO2、甲醇的纯流体分子参数及回归所得的二元交叉作用参数作为输入,来关联和预测CO2-甲醇二元体系相平衡性质。本文不仅对CO2-甲醇二元体系p-x和p-ρ相图的预测结果与实验数据进行了比较,而且分析了温度、压力和两相密度等因素对CO2-甲醇二元体系界面性质的影响。     

甲醇-甲醛-聚甲氧基二甲醚三元体系汽液平衡

聚甲氧基二甲醚(PODE_n)是一种含氧量较高的化合物,近年来更是发展为一种优质的柴油添加剂。在101.3 kPa恒定压力下,使用改进的汽液平衡双循环Rose釜测定了甲醇-甲醛-PODE₂三元体系汽液平衡数据。运用最大似然原理,在Aspen Plus软件中,分别采用NRTL、Wilson以及UNIQUAC三种活度系数模型对测定的三元汽液平衡数据进行回归,分别得到三个模型所对应的二元交互参数以及模拟计算值。通过对比模拟值与实验值,得到温度和气相组成的平均绝对偏差,分别小于1.10 K、0.0250和0.0240。三个模型的关联结果均适用于此体系,得到的二元交互参数能够应用于甲醇-甲醛-PODE₂三元体系的精馏设计,为相关物系的工业分离优化奠定了数据基础。     

Modelling of polymerization kinetics and molar mass development in the nitroxide-mediated polymerization (NMP) of styrene in supercritical carbon dioxide using the PC-SAFT equation of state

A mathematical model for polymerization kinetics and molar mass development in the nitroxide-mediated polymerization (NMP) of vinyl monomers in supercritical carbon dioxide (scCO₂) has been developed. The method of moments is used for molar mass development. The perturbed-chain statistical associating fluid theory (PC-SAFT) equation of state is used to estimate the number of stable phases present at equilibrium in the reaction mixture, critical number average chain length at which polymer particles are formed, and monomer concentration in each phase. Pure and binary PC-SAFT interaction parameters are estimated from liquid–liquid equilibrium (LLE) and liquid–vapour equilibrium (LVE) experimental data at 60 to 129°C. The effect of pressure on monomer conversion and molar mass development in the polymerization of styrene (Sty) using benzoyl peroxide (BPO) and 2,2,6,6-Tetramethylpiperidinyl-1-oxyl (TEMPO) at 120°C and 300–500 bar is studied. It was observed that increasing pressure increases polymerization rate without significantly affecting molar mass development.     

Calculation of complex phase equilibria in the critical region of fluid mixture based on multi-fluid lattice equation of state

Quantitative correlation of critical loci and multiphase behaviors has received considerable attention because the increased industrial importance of processes operating within the high-pressure region such as supercritical fluid extraction. However, in the critical region, classical thermodynamic models such as equations of state (EOS) frequently fail to correlate phase equilibrium properties. Recently, the present authors proposed a new lattice-hole EOS based on the multi-fluid approximation of the nonrandom lattice theory. The model requires only two molecular parameters reflecting size and interaction energy for a pure fluid and one additional interaction parameters for a binary mixture. In this work, the reliable applicability of the EOS was demonstrated to various phase equilibria of complex mixtures in the critical region. Demonstration of the EOS was made to calculate multiphase behaviors such as solid-liquidvapor (SLV) equilibria and critical loci of binary complex mixtures at high pressure. For P-T, P-x, and T-ρ phase diagrams tested, the model agrees well with experimental data. This paper was presented at the 8th APCChE (Asia Pacific Conferation of Chemical Engineering) Congress held at Seoul between August 16 and 19, 1999.     

Measurements and correlation of hydrogen-bonding vapor sorption equilibrium data of binary polymer solutions

Vapor sorption equilibrium data of ten binary polymer/solvent systems were measured using sorption equilibrium cell equipped with a vacuum electromicrobalance. Tested solvents were water, methanol, ethanol and npropanol and polymer solutes were poly(ethylene glycol), poly(propylene glycol), poly(tetramethylene glycol) and poly(ethylene oxide). The measured sorption obtained in the present work, were compared with existing literature data and the degree of reliability of the measured data was discussed. Vapor sorption equilibrium data obtained in the present study were correlated by UNIQUAC model and the multi-fluid non-random lattice fluid hydrogen bonding equation of state (MF-NLF-HB EOS) recently proposed by the present authors.     

Phase stability analysis using the PC-SAFT equation of state and the tunneling global optimization method

Phase stability calculation is a very important topic in phase equilibrium modeling. Usually the phase stability problem is solved by minimization of the tangent plane distance (TPD) function, the sign of the objective function at its global minimum indicating the state of the mixture at given conditions. The TPD function is non-convex and may be highly non-linear, many phase stability problems being really challenging. The tunneling global optimization method had been successfully used for solving a variety of phase equilibrium problems, including stability, with cubic equations of state (EoS). In this work, we test the ability of the tunneling method to solve the phase stability problem for more complex EoS like PC-SAFT. Calculations are performed for several benchmark problems, for mixtures of non-associating molecules, from binaries to multicomponent. In one example, the mixture contains hydrogen sulphide, for which the three parameters required by the PC-SAFT EoS were unavailable in the literature. These parameters, as well as the binary interaction parameter (BIP) between hydrogen sulphide and methane, were calculated based on experimental data.     

超临界CO2二元系统相平衡的数值模拟

应用微扰理论,借助微扰状态方程,对超临界CO2 系统相平衡进行了模拟。编制了求解程序,介绍了状态方程中各参数的确定方法和程序模块的设计思想。针对超临界CO2 /非极性体系、超临界CO2 /极性体系,在不同温度、压力条件下的气液相平衡进行了计算,将计算结果与实验结果进行了比较,结果表明:微扰状态方程适合模拟超高压下的CO2 二元体系的相平衡。     

Calculation of phase equilibrium for water+carbon dioxide system using nonrandom lattice fluid equation of state

For the geological sequestration of carbon dioxide to prevent global warming, the phase equilibrium data for water and carbon dioxide mixture play an important role in process design and operation. In this work, the nonrandom lattice fluid equation of state with hydrogen bonding (NLF-HB EOS) was applied for the prediction of phase equilibrium of mixtures containing water and carbon dioxide. A new set of pure component parameters for carbon dioxide above critical condition was found and optimum binary interaction parameters were reported to correlate mutual solubility of mixtures. The calculated results were compared with the Peng-Robinson Equation of State with the conventional mixing rule (PR-EOS) and the Wong-Sandler mixing rule (PR-WS-EOS). The calculation results show that NLF-HB EOS can correlate mutual solubility of water+carbon dioxide mixtures with reasonable accuracy within a single theoretical framework.     

Unified equation of state based on the lattice fluid theory for phase equilibria of complex mixtures part II. Application to complex mixtures

In part I of the present article [Yoo et al., 1995], new rigorous and simplified lattice-fluid equations of state (EOS) were derived and their characteristic features of the molecular thermodynamic foundation were discussed by applying to pure fluids. In this part II, both EOSs were extended to various phase equilibrium properties of mixtures. Comparison of the models with experimental mixture data ranges from density, to equilibria of vaporliquid, vapor-solid and liquid-liquid phases for nonpolar/nonpolar, nonpolar/polar, polar/polar mixtures. Both models were also applied to supercritical fluid phase equilibria and activities of solvents in polymer solutions. With two temperature dependent parameters for pure compounds and one temperature-independent binary interaction energy parameter for a binary mixtures, results obtained to date illustrated that both EOSs are quantitatively applicable to versatile phase equilibria of mixtures over a wide range of temperatures, pressures and compositions.     

苯乙烯/二氧化碳/聚苯乙烯三元混合物的相平衡预测

A lattice fluid model,Sanchez-Lacombe equation,is used to predict the phase behavior for a styrene/CO2/polystyrene ternary system.The binary parameters involved in the equation were optimized using experimental data.Phase diagrams and the distribution coefficients of styrene between polymer phase and fluid phase are obtained over a wide rang of pressure,temperature and composition.The analysis of ternary phase diagrams indicates that this system at relatively high pressure or low temperature may display two-phase equilibrium,and at low pressures or high temperatures three-phase equilibrium may appear.The distribution coefficients of styrene between the fluid phase and the polymer phase increase asymptotically to unity when the concentration of styrene increases.The results provide thermodynamic knowledge for further exploitation of supercritical carbon dioxide assisted devolatilization and impregnation.