Solubility of ethylene in 2,2,4-trimethylpentane and 1-octene mixture

With a static type equilibrium cell and the pressure decaying method, the solubility of ethylene in a mixture of 2,2,4-trimethylpentane and 1-octene was measured in the temperature range of 323.15-423.15 K, pressure range of 5-25 bar, and 1-octene concentration from 0 to 85 wt%. The experimental results show that the solubility of ethylene in a 2,2,4-trimethylpentane and 1-octane mixture increases with system pressure but decreases with system temperature.The experimental solubility data were also expressed in the vapor-liquid equilibrium relationship and correlated by the bubble pressure calculation using the Peng-Robinson equation of state (PR EOS) incorporated with the van der Waals one-fluid and the Zhong-Masuoka mixing rules. Among the deviations between the experimental and correlated results, the largest value of average absolute relative deviation is 1.73% for pressure at 423.15 K and that of average absolute deviation is 0.0024 mol fraction for vapor composition at 373.15 K by the Zhong-Masuoka mixing rule.     

Calculation of mixture equilibrium binary interaction parameters using closed cup flash point measurements

Proper design and operation of separation processes are highly dependent on phase equilibrium calculations. The common method to treat polar/nonpolar systems, and also mixtures of normal compounds where the sizes are significantly different is to use binary interaction parameters. This paper presents a method to calculate mixture binary interaction parameters using closed cup flash point measurements. The measured and literature closed cup flash points of different binary mixtures (ethanol + n-octane, 1-propanol + n-octane, 1-propanol + n-decane, n-octane + n-decane, 1-propanol + water, 1-butanol + n-octane, 2-butanol + n-octane, and water + propionic acid) are used to calculate binary interaction parameters. These binary interaction parameters together with common activity models are then used to calculate vapor–liquid equilibrium compositions of different binary mixtures considered in this study. The validity of the proposed method was successfully approved by comparing the calculated equilibrium compositions with experimental data.     

SOLUBILITY OF ANTHRACENE IN BINARY ALKANE + 2-PROPOXYETHANOL SOLVENT MIXTURES

Experimental solubilities are reported for anthracene dissolved in six binary mixtures containing 2-propoxyethanol with n-hexane, n-heptane, n-octane, cyclohexane, methylcyclohex-ane, 2,2,4-trimethylpentane and tert-butylcyclohexane at 298.15 K. Results of these measurements are used to test a mathematical representation based upon the combined Nearly Ideal Binary Solvent (NIBS)/Redlich-Kister model. For the seven systems studied, the model was found to provide an accurate mathematical representation of the experimental results, with an overall average absolute deviation between measured and calculated values being on the order of 0.5 per cent or less.     

SOLUBILITY OF ANTHRACENE IN BINARY ALKANE + 2-METHOXYETHYL ETHER SOLVENT MIXTURES

Experimental solubilities are reported for anthracene dissolved in six binary mixtures containing 2-methoxyethyl ether with n-hexane, n-heptane, n-octane, cyclohexane, methyl-cyclohexane and 2,2,4-trimethylpentane at 298.15 K. Results of these measurements are used to test a mathematical representation based upon the combined Nearly Ideal Binary Solvent (NIBS)/Redlich-Kister model. For the six systems studied, the model was found to provide an accurate mathematical representation of the experimental results, with an overall average absolute deviation between measured and calculated values being on the order of 0.4 per cent or less.     

基于多种状态方程模型的冷凝法油气回收对比

冷凝法回收油气过程的模拟计算采用何种状态方程尚无定论,建立油气混合物相平衡模型和组分热物理参数模型,进行油气回收过程模拟的对比。相平衡模型主要由状态方程、物质的量平衡方程、热力学平衡条件方程和模型迭代步骤组成,状态方程包括SRK方程、PR方程、TJS方程和理想气体方程。模拟结果表明：状态方程选用SRK、PR和TJS方程,经实验数据验证,满足精度要求;将油气视为理想气体时,计算结果与实际气体状态方程的模拟结果相差较大,冷凝温度越高,偏差越大,油气混合物在冷凝过程中不能视为理想气体;SRK、PR、TJS和Aspen Plus的模拟结果比较一致,相平衡计算应优先选用SRK或TJS方程。     

Solubility of carbon dioxide in pentaerythritol ester oils. New data and modeling using the PC-SAFT model

In this work, the solubility of carbon dioxide, CO₂, in pentaerythritol tetraheptanoate (PEC7) and in pentaerythritol tetranonanoate (PEC9) has been performed from 283 to 348 K and pressures up to 7.5 MPa in an isochoric high-pressure gas solubility apparatus. The solubility values are very similar in terms of mole fractions of CO₂ in both pentaerythritol esters. The experimental gas solubility data, together with those available in the literature for other CO₂ + pentaerythritol tetraester systems, were satisfactorily correlated with the PC-SAFT equation of state. The average absolute deviations of the gas solubility correlations were less than 3.9% for all the systems. In addition, PC-SAFT model was applied in a semi-predictive manner: the pure component's molecular parameters and the binary interaction parameter optimized from solubility data were used to calculate the types of the phase diagram as well as the densities and excess molar volumes in broad temperature and pressure ranges. The results obtained show the robustness of the model and these parameters to calculate properties not included in the fitting procedure.     

用SRK方程与PR方程求算双组分混合气体热力学性质

流体热力学性质的计算是化工热力学中的一类重要计算,立方型方程经常用于这类计算中。SRK方程与PR方程是在RK方程基础上发展而来的,具有比RK方程更好的计算精度。但现有教材中没有给出PR方程和SRK方程的剩余焓、剩余熵的计算公式,缺失了流体热力学性质计算的系统性。本文通过立方型状态方程的一般形式推导出PR方程和SRK方程的剩余焓、剩余熵的计算公式,利用Excel电子表格计算双组分混合气体的热力学性质。计算过程简捷明了,利于学生更好地理解混合物热力学性质的计算过程。     

Experimental study and PC-SAFT simulations of sorption equilibria in polystyrene

The knowledge of sorption equilibria of blowing agents in polystyrene (PS) is necessary for the optimization of PS foam production. The sorption equilibria were studied experimentally using a gravimetric apparatus and simulated by the perturbed-chain statistical associating fluid theory (PC-SAFT) equation of state. As chlorinated and fluorinated hydrocarbons are being phased out, alternative blowing agents are important. We place emphasis on n-pentane, as sorption data for the PS+n-pentane system are scarce in the literature. The measured n-pentane and iso-pentane sorption isotherms were used to evaluate the PC-SAFT binary interaction parameters. The sorption of CO₂, N₂ and He in PS was also studied. Cosorption of pentanes in PS was predicted and comparison of the results with our experimental data proved good performance of the PC-SAFT model. The industrially interesting sorption enhancement and inhibition effects were studied using both experimental and simulated ternary data.     

状态方程在气固相平衡计算中的应用

状态方程法是研究气固平衡的一种常用方法,但是目前仅有SRK和PR方程运用于元素硫沉积机理的研究。采用RK、SRK、PR、PT和LHSS状态方程对含硫天然气气固相平衡进行了计算,并且比较了不同状态方程对计算结果的影响。通过算例分析可知,对含硫天然气气固相平衡进行计算时每种状态方程都会存在误差,而误差主要来源于实验过程中的误差、状态方程参数设置的误差、数值计算方法的误差等。计算结果表明,采用RK和SRK方程计算误差较大,PR和PT方程两者计算误差差别不大,LHSS方程更适合描述含硫天然气的气固相平衡。     

PR方程与SRK方程在计算水露点中的比较与应用

水露点是天然气管道输送安全的一个重要指标。介绍了PR方程与SRK方程,利用两个方程的不同混合法则及相平衡计算,通过编写程序,计算出在相同条件下,不同方程之间计算出的水露点的差异,得出利用PR方程计算出的水露点较SRK方程计算的结果偏低。     

Influence of solvent type on dibenzothiophene adsorption onto activated carbon fiber and granular coconut-shell activated carbon

The adsorption behavior of dibenzothiophene (DBT) on an activated carbon fiber (ACF) and a granular coconut-shell activated carbon (GCSAC) in the solvents n-hexane, n-decane, toluene, and mixture of n-decane and toluene was investigated. The DBT adsorption onto both samples was more active in n-hexane than in n-decane. The lowest DBT adsorption was observed in toluene. Regardless of the type of activated carbons and solvents, all the isotherms fit the Freundlich equation better than the Langmuir equation. At low equilibrium concentrations of <2 mass ppm-S, GCSAC displayed greater capacity for DBT adsorption than did ACF in all the tested solvents. The adsorption kinetics of ACF and GCSAC in all the tested solvents were governed by a pseudo-second-order model.     

Study on the activity coefficients and solubilities of amino acids in aqueous solutions with perturbed-chain statistical associating fluid theory

Perturbed-chain statistical associating fluid theory (PC-SAFT) was applied for modeling the thermodynamic properties of aqueous amino acid solutions. To account for the association phenomena of amino acids occurring in the aqueous solution, the zwitterionic forms of amino acids are assumed to be associating species with proton donor and acceptor sites. Also, in order to reduce the number of adjustable parameters of PC-SAFT equation of state (EoS) for amino acids from five to three, it is assumed that segment numbers of amino acids are linearly related with the molecular weight of amino acids, and the association volume parameters of amino acids can be set to a fixed value. Thus, 3-parameters of PC-SAFT EoS for amino acids were estimated by simultaneously fitting the activity coefficients of amino acid and densities data in the aqueous amino acid solutions. The PC-SAFT EoS with estimated 3-parameters of amino acid is found to well describe activity coefficients of amino acid and densities of the aqueous amino acid solutions. Also, this equation was used for predicting solubilities of amino acids as well as the water activities and osmotic coefficients in the aqueous amino acid solutions. The predicted values of these properties are in good agreement with the experimental data.     

Validity of the swelling method for the determination of the interaction parameter

By selecting solvents with a very weakly concentration-dependent interaction parameter χ with poly(dimethylsiloxane) (PDMS) and using experimental values of the elastic modulus of dry, end-linked PDMS networks, the Flory-Rehner theory and the phantom network assumption we obtained good agreement between the values of χ from equilibrium swelling and those obtained from intrinsic viscosity measurements on solutions of linear chains. The solvents used were 2,3-dimethylpentane and 2,2,4-trimethylpentane at 25°C.     

Performance of five equations of state for the prediction of vle and densities of natural gas mixtures in the dense phase region

This paper examines the degree of uncertainty of five Equations of State (EOS) for the prediction of densities in the dense phase region which is beyond the ranges of pressure and temperature originally specified for these equations. Predicted densities were compared with measured values for different hydrocarbon mixtures including a rich mixture. The results show that the GERG equation of state, originally specified for the range of P -8 C, outperforms all other equations in the region up to P=30 MPa and T > -8 C. In this range, its mean deviation from measured values of densities was found to be less than -0.015% and standard deviation ( ) also less than 0.015%. The AGA-8 equation, which identified several regions of pressures and temperatures with different uncertainties, also performed quite well with a mean deviation of -0.2% and less than 0.4% in the region up to P=30 MPa. The other equations showed relatively high deviation: ～2.7% for BWRS,-5.1% for PR and 2.5% for RKS. Unlike GERG and AGA-8, however, these three equations can also be used to predict the vapour-liquid-equilibrium (VLE). VLE predictions were compared with measured values for eight binary mixtures of methane (C1) and ethane (C2). It is recommended to use PR for VLE prediction, as quite good agreement between measured data and prediction by PR was demonstrated.     

Modeling the phase equilibria of asymmetric hydrocarbon mixtures using molecular simulation and equations of state

Monte Carlo simulation (MC) is combined with equations of state (EoS) to develop a methodology for the calculation of the vapor–liquid equilibrium (VLE) of multicomponent hydrocarbon mixtures with high asymmetry. MC simulations are used for the calculation of the VLE of binary methane mixtures with long n-alkanes, for a wide range of temperatures and pressures, to obtain sufficient VLE data for the consistent fitting of binary interaction parameters (BIPs) for the EoS. The Soave-Redlich-Kwong (SRK), Peng-Robinson (PR), and Perturbed Chain - Statistical Associating Fluid Theory (PC-SAFT) EoS are considered. The ability of each EoS to correlate the VLE data is assessed and the selected ones are used to predict the VLE of multicomponent gas condensate mixtures. MC simulations proved to be very accurate in predicting the VLE in all conditions and mixtures considered. The BIPs regressed from the simulation dataset lead to equally accurate modeling results for multicomponent mixtures, compared to those regressed from experimental data. © 2018 American Institute of Chemical Engineers AIChE J, 65: 792–803, 2019     

A simple correlation to predict high pressure solubility of carbon dioxide in 27 commonly used ionic liquids

Engineers often demand the availability of easy correlations without difficult and time-consuming calculations. Up till now, there has been a lack of such correlations for mixtures of CO₂ + ionic liquids. This work proposes a correlation to predict CO₂ solubility in 27 common ionic liquids. The main advantages are its simplicity and minimal input data, namely temperature and pressure. The ionic liquids investigated ranged within a variety of families, having various anions and cations. Compared with the popular engineering models of Peng–Robinson (PR) and Soave–Redlich–Kwong (SRK), the present correlation is much easier to use, yet it is also more accurate (PR, SRK and the proposed model had AARD% values of 43.5%, 44.3% and 4.9%, respectively for a total of 3073 data), even when binary interaction coefficients of PR and SRK are optimized to experimental data (AARD% values of 17.2%, 16.9% and 4.9% for PR, SRK and the proposed model, respectively).     

Isobaric vapor–liquid equilibria for mixtures of tetrahydrofuran, 2-propanol, and 2,2,4-trimethylpentane at 101.3 kPa

Vapor–liquid equilibrium (VLE) at 101.3 kPa have been determined for a ternary system (tetrahydofuran + 2-propanol + 2,2,4-trimethylpentane) and its constituent binary systems (tetrahydrofuran + 2-propanol, tetrahydrofuran + 2,2,4-trimethylpentane, and 2-propanol + 2,2,4-trimethylpentane). The activity coefficients of liquid mixtures were calculated from the modified Raoult's law. Thermodynamic consistency tests were performed for all VLE data. The VLE data of the binary mixtures and ternary mixtures were correlated using the Margules, Wilson, NRTL, and UNIQUAC activity-coefficient models. The models with their best-fitted interaction parameters of the binary systems were used to predict the ternary vapor–liquid equilibrium. All VLE data are also used to calculate the reduced excess molar Gibbs free energy g^E/RT and the deviations in the boiling point ΔT. The calculated quantities of g^E/RT and ΔT were fitted to variable-degree polynomials in terms of liquid composition.     

Hydroisomerization and cracking of n-octane and C8 isomers on Ni-containing zeolites

The hydrocracking and hydroisomerization of n-octane, 2,5-dimethylhexane and 2,2,4-trimethylpentane on Ni-containing ZSM-5, mordenite and beta catalysts was investigated at 20 bar hydrogen pressure and a temperature of 533 K. The activity decreased in the sequence ZSM-5≫BETA≈MOR for the n-octane conversion and increased in this sequence for the conversion of 2,5-dimethylhexane and 2,2,4-trimethylpentane. The selectivity for isomerization of n-octane and 2,5-dimethylhexane was the highest on NiHBETA and the lowest on NiHZSM-5. The trends in the activity and selectivity were explained by the accessibility of the acid sites, estimated by adsorption of probe molecules followed by IR spectroscopy, and by a simulation of the space available in the pores of these zeolites.     

PC-SAFT Equation: A Predictive Tool to Determine Experimental Conditions for Polymer Blend Demixing

Abstract

The perturbed-chain statistical associating fluid theory equation of state (PC-SAFT) was applied to predict the phase behavior of polymer solutions in order to determine the pressure – temperature region for the high molecular weight polymer blend separation by using n-alkanes at high pressure and high temperature. The polymer blends selected were physical blends of polyethylene (PE)/polystyrene (PS), and polypropylene (PP)/PS. The miscibility and immiscibility region of each polymer in different alkanes (n-pentane, n-hexane, and n-heptane) was studied and from this analysis, the experimental conditions of the polymer blend demixing were predetermined. The results obtained were validated with experimental data indicating that the PC-SAFT equation is a good tool to predict experimental conditions for the processing windows of polymer blend separation.     

A MODIFIED PENG-ROBINSON EQUATION OF STATE

A modified form of the Peng-Robinson equation of state is proposed. This equation shows its greatest advantage in the predictions of the volumetric properties in the single-phase region for mixtures, while it performs as good as original Peng-Robinson equation for the predictions of thermodynamic properties of pure components, and vapor-liquid equilibria of mixtures. Also the equation gives apparently more realistic Joule-Thomson inversion curves than both the SRK and PR equations.