Thermodynamics Review and Theory Boxi Chen Khang Tran Roger Chiquito Perez Sandra Nouketcha Shanshan Jin Olufunke Lawal

Outline What is thermodynamics The laws of thermodynamics Chemical-reaction equilibria ( gibbs- free energy Thermodynamics models (Aspen) Conclusion Questions

Introduction

What is Thermodynamics? (19th century) Power developed from heat Why is it important? Analysis and prediction of physical systems Relationship to engineering and industry Design systems Unit operations - gas absorption, heat transfer Unit processes - oxidation, catalysis Thermodynamics is the generation of power into work. It studies the effect of work, heat, and energy on a system. It deals with the transfer of energy from one place to another and one form to another. Why is it important? It allows us to study systems that will be untraceable and to also make predictions based on given conditions. This is because thermodynamics does not depend on any model of the structure of matter. It governs chemical reactions and processes that convert energy in the form of heat to other forms of energy. Engineering...to design systems...Chemical engineering; unit processes and operations...energy requirements for an operation, extent of a process occuring, energy changes.

1. Laws of Thermodynamics

Zeroth Law of Thermodynamics If two bodies are each in thermal equilibrium with some third body they are also in equilibrium with each other.

First Law of Thermodynamics Energy is conservation, which means energy can be neither created nor destroyed, but it can be transferred or changed from one form to another.

First Law of Thermodynamics The first law applies to the system and its surroundings. The energy change of the closed system equals the net energy that is transferred to heat and work. For any thermodynamic process, in general one needs to account for changes occurring both within a system as well as its surroundings. Since the two together forms the “universe” in thermodynamic terms. This law says that there are two kinds of processes, heat and work, that can lead to a change in the internal energy of a system. Since both heat and work can be measured and quantified, this is the same as saying that any change in the energy of a system must result in a corresponding change in the energy of the surroundings outside the system. In other words, energy cannot be created or destroyed. If heat flows into a system or the surroundings do work on it, the internal energy increases and the sign of q and w are positive. Conversely, heat flow out of the system or work done by the system (on the surroundings) will be at the expense of the internal energy, and q and w will therefore be negative. The wider application of the first law involves formulating the energy balance differently in order to accommodate the fact that most thermodynamic systems, i.e., equipments, in continuous process plants are essentially open systems: they allow mass transfer across their boundaries (i.e., through inlet and outlet). Examples include pumps, compressors, reactors, distillation columns, heat exchangers etc. Since such open systems admit both material and energy transfer across their boundaries the thermodynamic analysis necessarily involves both mass and energy balances to be carried out together.

Second Law of Thermodynamics Entropy is how organized or disorganized energy is in a system of atoms or molecules. The state of entropy of the entire universe, as an isolated system, will always increase over time. The second law also states that the changes in the entropy in the universe can never be negative. The change of entropy suggests that time itself is asymmetric with respect to order of an isolated system, meaning: a system will become more disordered, as time increases.

Third Law of Thermodynamics The entropy of a system approaches a constant value (0) as the temperature approaches absolute zero (–273.15°C) . The third law of thermodynamics states that the entropy of a system approaches a constant value as the temperature approaches absolute zero. The entropy of a system at absolute zero is typically zero, and in all cases is determined only by the number of different ground states it has. Specifically, the entropy of a pure crystalline substance (perfect order) at absolute zero temperature is zero. This statement holds true if the perfect crystal has only one state with minimum energy. The third law essentially tells us that it is impossible, by any procedure, to reach the absolute zero of temperature in a finite number of steps. Most of the direct use of the third law of thermodynamics occurs in very low temperature applications, to predict the response of various materials to temperature changes. Another useful application of the third law is the computation of absolute entropies of pure substances at temperatures other than 0 K from their heat capacities and heats of transition.

1. Gibbs free energy

Gibbs Free Energy ΔG=ΔH-TΔS Effect of temperature on Gibbs free energy Gibbs free energy is a measure of chemical energy It combines enthalpy and entropy into a single value It predicts reaction spontaneity (ΔG<0) Chemical system tend naturally towards state minimum gibbs free energy ΔH ΔS ΔG Spontaneity - + Always Spontaneous at high temperatures Spontaneous at low temperature Never -measure driving force or reactivity of the reaction -enthalpy{total kinetic and potential energy of a system at constant P} represents the heat content (kj/mol) - entropy the degree or disorder (kj/mol.K) -Spontaneous-->reaction proceed to the right andis product favored. If dG=0 → rxn is in equilibrium

Application of Gibbs free energy process simulation of distillation processes: Estimation of activity coefficients useful for models such as the NRTL (Non-Random Two-Liquid), UNIQUAC (UNIversal QUAsiChemical) and the Wilson model separation processes: Absorption (where it is related with Henry’s law) Chemical engineering kinetics and reactor designs synthesis of nanomaterials The Gibbs free energy is also central to crystallization processes 2. It is useful in process simulation of distillation processes. Typically the estimation of activity coefficients useful for models such as the NRTL (Non-random two-liquid), UNIQUAC (UNIversal QUAsiChemical) and the Wilson model.Absorption (where it is related with Henry’s law) and adsorption separation processes.

1. Thermodynamic Models / EOS

Equations of State (EOS) EOS are convenient tools to use to relate two or more functions of state Many EOS are fitted empirical functions Fitting parameters are typically functions of critical temperature and pressure, which generalizes EOS to all species that have available critical point data

Common EOS Models Ideal Gas Law Van der Waals EOS (Modified Ideal Gas Law) Peng-Robinson Redlich-Kwong, Suave Redlich Kwong NRTL UNIFAC, UNIQUAC

Why is this important? Thermodynamic quantities may be hard to calculate otherwise Does not involve differential equations Many simulation software (including Aspen) utilizes these EOS to speed up calculations When using a simulation software, it is important to choose the appropriate model

1. Applications/ Models Selection

Industrial Requirements Simplicity over complexity Fewer models (single?) which can do more Wide range of properties and conditions Both thermodynamic (equilibrium and other) and transport properties needed

Model Selection Different industries use different models based on experience Oil and gas processing → PR, SRK High non-ideality → Specialized models Amine sweetening unit in gas processing

Model Selection (Water, alcohol, acids) Non-idealities expected Non-condensable components: Co2, N2, O2 http://www.just.edu.jo/~yahussain/files/Thermodynamic%20Models.pdf

1. Conclusion

Application of Thermodynamic Theory Thermodynamic theories and principles are used to model chemical reactions and molecular interactions Models allow for quantitative understanding of abstract concepts The appropriate model takes into account the relevant parameters in a given system In industry the simplest models are the most successful Few applicable models

Sources Hussain, Y. Thermodynamic models and physical properties. Kontogeorgis, G. Thermodynamic models for process and product design. Center for Energy Resources Engineering.