Integrating superstructure-based design of molecules,processes, and flowsheets

The key to many chemical and energy conversion processes is the choice of the right molecule, for example, used as working fluid. However, the choice of the molecule is inherently coupled to the choice of the right process flowsheet. In this work, we integrate superstructure-based flowsheet design into the design of processes and molecules. The thermodynamic properties of the molecule are modeled by the PC-SAFT equation of state. Computer-aided molecular design enables considering the molecular structure as degree of freedom in the process optimization. To consider the process flowsheet as additional degree of freedom, a superstructure of the process is used. The method results in the optimal molecule, process, and flowsheet. We demonstrate the method for the design of an organic Rankine cycle considering flowsheet options for regeneration, reheating, and turbine bleeding. The presented method provides a user-friendly tool to solve the integrated design problem of processes, molecules, and process flowsheets.     

Supercritical phase behavior for biotransformation processing

In recent works, supercritical carbon dioxide turned out to offer innovative and highly effective alternatives for the workup of biphasic whole-cell biotransformation reaction mixtures. Further optimization of the downstream processing, e.g. by supercritical extraction of the product, requires a reliable simulation of the phase behavior in those systems. In this work, binary and ternary systems containing carbon dioxide and organic components from the biotransformation reaction mixture, such as styrene (substrate), (S)-styrene oxide (product), 2-phenylethanol (byproduct), octane (inducer), and bis-2(ethylhexyl)phthalate (solvent) were measured and modeled for temperatures ranging from 308.15 to 350.15 K and pressures ranging from 5 to 70 MPa using the PC-SAFT equation of state. The obtained results offer the possibility to precisely predict the phase behavior in this system, thus enabling the modeling of e.g. supercritical-fluid extraction steps.     

PGSS-drying: Mechanisms and modeling

Micronization of polyethylene glycol from aqueous solutions has been successfully performed with particles from gas-saturated solutions (PGSS)-drying process, producing spherical PEG particles with average particle size of 10 μm and residual water content below 1 wt%. Based on experimental results, an analysis of the fundamentals of the process has been developed, discussing mass and energy balances, phase equilibrium conditions, mass transfer rates and atomization mechanisms. Some discrepancies between experimentally observed moisture concentration in powder and calculations based on the mass balance and the phase equilibrium have been observed, which have been attributed to the kinetic evolution of pressure and temperature along the expansion path. The static mixer used to saturate the solution with CO₂ has been analyzed with phase equilibrium and mass transfer calculations, concluding that a significant fraction of water is extracted to the gas phase already in the static mixer, and high CO₂ concentrations are achieved in the liquid due to the high solubility of CO₂ in PEG. All experimental trends of variation of particle size with process parameters can be explained considering a flash-boiling atomization mechanism dependant on the concentration of CO₂ in the solution after the static mixer.     

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。     

Aromatic volatile organic compounds absorption with phenyl-based deep eutectic solvents: A molecular thermodynamics and dynamics study

The suitability of phenyl-based deep eutectic solvents (DESs) as absorbents for toluene absorption was investigated by means of thermodynamic modeling and molecular dynamics (MD). The thermodynamic models perturbed-chain statistical associating fluid theory (PC-SAFT) and conductor-like screening model for real solvents (COSMO-RS) were used to predict the vapor–liquid equilibrium of DES–toluene systems. PC-SAFT yielded quantitative results even without using any binary fitting parameters. Among the five DESs studied in this work, [TEBAC][PhOH] consisting of triethyl benzyl ammonium chloride (TEBAC) and phenol (PhOH), was considered as the most suitable absorbent. Systems with [TEBAC][PhOH] had lowest equilibrium pressures of the considered DES–toluene mixtures, the best thermodynamic characteristics (i.e., Henry's law constant, excess enthalpy, Gibbs free energy of solvation of toluene), and the highest self-diffusion coefficient of toluene. The molecular-level mechanism was explored by MD simulations, indicating that [TEBAC][PhOH] has the strongest interaction of DES–toluene compared to the other DESs under study. This work provides guidance to rationally design novel DESs for efficient aromatic volatile organic compounds absorption.     

Experimental and modeling asphaltene precipitation in presence of DBSA using PC-SAFT EOS

Asphaltene precipitation and subsequent deposition in production tubing and topside facilities present significant cost penalties to crude oil production. Therefore, it is highly desirable to predict their phase behavior and the efficiency of dispersants in preventing or delaying deposition. Very few studies have been carried out on the molecular interactions between asphaltenes and different dispersants. As a result, the mechanisms by which dispersants stabilize asphaltenes are still open to discussion. The authors introduced a new method to characterize asphaltenes in perturbed chain statistical association fluid theory equation of state (EOS; perturbed-chain statistical association fluid theory EOS [PC-SAFT-EOS]) and correctly model the effect of dodecyl benzene sulfonic acid (DBSA) dispersant on the thermodynamic behavior of asphaltenes. Using the filtration method the effect of the ionic dispersant (DBSA) on asphaltene precipitation for different concentrations of n-heptane was measured experimentally, then modeled through PC-SAFT EOS. In the approach only the hard-chain and the dispersion terms are taken into consideration, and PC-SAFT parameters were calculated based on Gonzales et al. (2007 Gonzalez, D. L., Hirasaki, G. J., Creek, J., and Chapman, W. G. (2007). Modeling of asphaltene precipitation due to changes in composition using the perturbed chain statistical associating fluid theory equation of state. Energy Fuels 21:1231–1242.[Crossref], [Web of Science ®] , [Google Scholar]) based on molecular weight (Mw) and aromaticity factor (γ). Additionally, the model could correctly predict the amount of asphaltene precipitation upon addition of DBSA dispersant.     

PC-SAFT理论对CO2-甲醇体系相平衡的研究

本文结合统计缔合流体理论（PC-SAFT）,把纯流体关联而得的分子参数作为输入,对某一确定温度范围内二氧化碳-甲醇二元体系相平衡进行研究,并且分析温度、压力和两相密度对界面性质的影响,并对PC-SAFT方程计算结果与实验数据进行了比较与分析。     

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。     

Mathematical modelling of the solubility of supercritical CO2 in poly(l-lactide) and poly(d,l-lactide-co-glycolide)

Two mathematical models, Sanchez–Lacombe equation of state and the Perturbed-Chain Statistical Associating Fluid Theory were applied for modelling the phase equilibrium for the poly(l-lactide)–CO₂ and poly(d,l-lactide-co-glycolide)–CO₂ systems. Aspen Polymer Plus software was used. The results were compared with previously obtained experimental values for solubility. The solubility of scCO₂ in the two biodegradable polymers was calculated for three different temperatures (308, 313 and 323 K) in the pressure range (10–30 MPa). The characteristic parameters for the components and the binary interaction parameters for the models were optimized in order to obtain the best fit between the estimated and the experimental gas solubility data. The results suggest that both SL EOS and PC-SAFT are reliable models in describing the phase equilibrium of the PLLA–CO₂ and PLGA–CO₂ systems at the proposed working conditions.