Gloria Meyberg Nunes Costa

A Survey of Equations of State for Polymers

The thermodynamics of polymeric systems play an important role in the polymer industry and are often a key factor in polymer production, processing and material development, especially for the design of advanced polymeric materials. Many polymeric products are produced with a solvent or diluent (or a mixture of them) and often with other low molecular weight compounds (plasticizers, among others). A problem which often arises is how to remove the low molecular weight constituent(s) from the final product (polymer). The solution to this problem involves, among other tasks, solving the vapor-liquid equilibrium (VLE) and/or the vapor-liquid-liquid equilibrium (VLLE) problem. Other applications of polymer thermodynamics directly involve the polymerization processes. For example, several processes such as the production of PET (polyethylene terephthalate) are carried out in two-phase (vapor-liquid) reactors. Phase equilibrium compostions of the reacting components will determine their phase concentrations and thus the outcome of the polymerization reaction. Another example is the case of LDPE (Low Density PolyEthylene) made in autoclave reactors where it may be desirable to perform the polymerization reaction nearby but outside the two-liquid phase region, but close to it, which makes accurate liquid-liquid equilibrium (LLE) information at high pressure essential. During PE (polyethylene) or PP (polypropylene) industrial processing, for example, deposition of the polymer on the reactor surface, heat exchangers and flash drums frequently occurs and this can cause clogging in pipelines. Modeling solid-liquid equilibrium (SLE) is a useful basis from which to gain a better understanding of these industrial polymer problems and thus to avoid their occurrence.

Influence of the mixing rule on the liquid-liquid equilibrium calculation

Abstract Liquid-liquid equilibrium data were correlated with three mixing rules that incorporate excess Gibbs energy model into a equation of state: Wong-Sandler, Heidemann-Kokal and MHV2 methods. The Soave equation of state is employed to several binary mixtures, coupled with NRTL, UNIQUAC and UNIFAC models for excess Gibbs free energy. The best results for binary mixtures were obtained with NRTL and Wong-Sandler, then this combination was used to predict the ternary liquid-liquid equilibria.

Solubility of solids in supercritical fluids using equations of state — excess Gibbs free energy models

Abstract Solubilities of several organic solids in four supercritical fluids are calculated with Soave and Peng-Robinson equations of state, incorporating excess Gibbs free energy into the mixing rules, with Heidemann-Kokal, Wong-Sandler and MHV2 procedures. Three excess Gibbs free energy models are used in the mixing rules: NRTL, UNiQUAC and UNIFAC. Furthermore, a comparison between these mixing rules and conventional two-binary-parameter form and modification of the excluded volume parameter in the MHV2 procedure is also presented. The best result were obtained with NRTL model and the Wong-Sandler mixing rule.

Computational Aspects for Optimization of High Pressure Phase Equilibrium for Polymer Industrial Systems

Abstract Many computational problems occur during optimization of high-pressure phase equilibrium of polymer systems due to the existence of critical points and to the possibility of there being more than two equilibrium phases. In this work the main numerical aspects related to high-pressure flash simulation with the Soave-Redlich-Kwong (SRK) and the Sanchez and Lacombe (SL) equations of state are examined. A LDPE (low-density polyethylene) high pressure flash industrial separator is used to case study of 8 resins. The results show that Sanchez-Lacombe equation of state is more appropriate to overcome the numerical difficulties associated with the complexity of polymer systems.

Computation of Crossover Pressure for Synthesis of Supercritical Fluid Separation Systems

Abstract The crossover region is a phenomenological observation which may be used to synthesize supercritical fluid extraction process (SCFEP) and is supported by a number of experimental studies. This phenomenon means that there may be regions of temperature and pressure in the near critical fluid state where the solute solubility decreases with an isobaric increase in temperature. Accurate calculation of solid solubility in supercritical fluid does not imply that crossover pressure calculation has also good accuracy. In this paper, a new method to predict crossover pressure based on cubic equations of state is developed and applied to systems containing supercritical CO2 and bixin. Peng-Robinson-LCVM-UNIFAC equation of state is used in a predictive way and crossover pressure is determined for several conditions. The method described here can in principle be applied to any solid-fluid system used in supercritical fluid extraction process synthesis.