Leonidas Constantinou

Estimation of the acentric factor and the liquid molar volume at 298 K using a new group contribution method

Abstract The method of Constantinou and Gani [Constantinou, L. and Gani, R., 1994. A new group contribution method for the estimation of properties of pure compounds. AIChE J., 40(10): 1697–1710] is extended to the estimation of the acentric factor and the liquid molar volume at 298 K. Thus, it now allows reliable prediction of all the common corresponding-state physical properties. In addition to the accurate estimation of liquid molar volumes at 298 K for low-molecular-weight compounds, the technique can be used for amorphous polymers.

Computer aided product design: problem formulations, methodology and applications

Abstract A general methodology for Computer Aided Product Design (CAPD) with specified property constraints which is capable of solving a large range of problems is presented. The methodology employs the group contribution approach, generates acyclic, cyclic and aromatic compounds of various degrees of complexity (including isomers) and size (including polymers) and provides accurate and consistent estimation of properties. The application range of the methodology has been enlarged and the validity of the predictions improved through the incorporation of a new group contribution based method for estimation of properties. Also, with new problem formulations, it is possible to consider the formation of azeotropes and the miscibility of mixtures for the substitution of compounds, the design of polymers and the design of solvents for extraction operations involving vapor-liquid equilibria (VLE), liquid-liquid equilbria (LLE), solid-liquid equilibria (SLE) and gas solubility. Finally, a computer program based on the extended methodology has been developed and the results from five case studies highlighting various features of the methodology are presented.

Molecular structure based estimation of properties for process design

Abstract This paper presents an analysis of molecular structure based methods for estimation of properties from a process/product design point of view. Properties are classified as primary (dependent only on the molecular structure) and secondary (dependent on the molecular structure and other variables/properties). Estimation methods are classified as “reference” (accurate but computationally expensive) and “approximate” (limited application range but computationally simple). Relationships between molecular structures, properties and design have been identified and how they can be exploited in process/product design are highlighted. Finally, a discussion on how the methods for estimation of properties can be coupled to current and future integrated approaches to process/product design, is presented.

Towards the development of a second-order approximation in activity coefficient models based on group contributions

Abstract A simple modification of group contribution based models for estimation of liquid phase activity coefficients is proposed. The main feature of this modification is that contribution estimated from the present first-order groups in many instances are found insufficient since the first-order groups do not provide all the important molecular structural information. Therefore, addition of second-order terms, which provide the needed extra molecular structural information, is proposed. The scope of the new approach is demonstrated through the well-known UNIFAC model in terms of improved correlation/prediction capabilities, distinction between isomers and ability to overcome proximity effects.

Prediction of volumetric behavior and glass transition temperature of polymers : a group contribution approach

Abstract A simple method is presented for the prediction of PVT behavior and glass transition temperature of polymers over an extended range of external temperatures and pressures from the knowledge of only the molecular structure of their repeating units. Scaling constants of the Lattice Fluid (LF) equation-of-state model of polymers are extracted using experimental PVT data. First-order and second-order groups specific to polymers are identified in their repeating units. These groups can capture even fine structural differences, thus, enabling more precise predictions. A list of these groups is presented along with their contribution to the above scaling constants and the flex energy of the Gibbs–DiMarzio theory for glass transition. Once these parameters are known, the estimation of density and glass transition temperatures of pure polymers is straightforward using the LF theory. The predicted values are in satisfactory agreement with the available experimental ones.