Thermodynamics and Property Models for Chemical Systems

Thermodynamics is the branch of physics that deals with the study of energy transfer and the relationship between heat, work, and temperature. Thermodynamic properties are measurable quantities that characterize the thermodynamic state of a system. They are essential for understanding, analyzing and predicting chemical processes. Thermodynamics properties, such as temperature, pressure, molar volume, enthalpy, entropy, fugacity, compressibility and free energies, provide essential insights into the energy changes and feasibility of chemical reactions. Accurate prediction of these properties empowers chemists and engineers to make informed decisions regarding reaction conditions, process design and optimization, and product selectivity.

On the other hand, thermodynamic property models are a set of mathematical equations developed to describe and predict the behaviour of thermodynamic properties of systems. There are four main groups of thermodynamic models available: the ideal model, the activity coefficients models, the equations of state, and the special methods. The ideal models play a crucial role in understanding and predicting the behaviour of various systems. These models make simplifying assumptions to provide a conceptual framework that allows for easier analysis and calculation of thermodynamic properties. They are characterized by their simplicity and they do not capture all the complexities and real-world behaviour of thermodynamic properties. Real systems often deviate from the ideal behaviour due to factors such as intermolecular forces, phase transitions, non-ideal mixing, and finite heat capacities. The most common of the models is the ideal gas law which relates the pressure, volume, and temperature of an ideal gas. It is expressed as PV = nRT. The ideal gas law provides a simple approximation for gases at low pressures and high temperatures.

The activity coefficients models are especially useful to describe the nonideality behaviours of thermodynamic properties in the liquid phase, while the equations of state are used to calculate the nonideality behaviours in the vapour phase. However, under some conditions, the equations of state can be extrapolated to the liquid phase, and the activity coefficients models to the solid phase. Examples of activity coefficients models are Non-Random Two-Liquid (NRTL), UNIQUAC (UNIversal QUAsiChemical), Margules and Wilson models. While equations of state are Van der Waals, virial equation of state and the Benedict-Webb-Rubin equation. There are also cubic equations of state like Peng-Robinson, Redlich-Kwong and Soave-Redlich-Kwong. The best choice of thermodynamic model depends on the specific system, the level of accuracy required, and the available experimental data.

Among all these models, the best thermodynamic models are characterized by their ability to accurately describe complex systems and thermodynamic properties. These models incorporate realistic assumptions, account for non-ideal behaviour, are parameterized based on extensive experimental data, and ensure thermodynamic consistency. They have a wide range of applicability, from different compositions to phase equilibria and strike a balance between accuracy and computational efficiency. These models undergo validation and comparison, ensuring their reliability and trustworthiness. The level of sophistication required depends on the specific system and desired accuracy, with simpler models sufficing in some cases, while more complex models are needed for capturing intricacies.

Attached herewith is a picture of Dr. Ding-Yu Peng, who, along with Prof. Donald Robinson played a pivotal role in the development of the Peng Robinson Equation of State, which is widely regarded as one of the most commonly used thermodynamic property models in the hydrocarbon processing industries today. It is worth noting that Dr Peng's journey started as a refugee, which adds an intriguing aspect to his remarkable achievements.

Are you currently working on thermodynamic and property models of chemical systems? Let connect. I am currently working on research on the cubic plus association equation of state model for predicting asphaltene precipitation in crude oil during gas injection and I'd love to hear any insightful additions I could grab for the project from experienced people in the field!

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I am Babatunde Rahim Popoola, a chemical process design & integration engineer with a comprehensive understanding of design processes and also manufacturing & construction methods. I run an online platform called Nubyira Process Designer where I assist and tutor students in their research projects and execute plant design projects for clients worldwide.

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