Calculation of Thermodynamic Properties in Pure Organic Compounds
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Section I: Basic and Applied Research
Calculation of Thermodynamic Properties in Pure Organic Compounds Y.C. Li, C.P. Wang, and X.J. Liu
(Submitted August 8, 2008; in revised form September 12, 2008) The reduced Gibbs free energies of 30 types of pure organic compounds were calculated by using the Sanchez and Lacombe model (SL model). The calculated results for each pure organic compound are presented as both polynomial expressions and graphs. This database of pure organic compounds will provide basic information in thermodynamic assessments of binary, ternary and higher-order organic systems or organic-inorganic systems.
Keywords
organics, SL model, thermodynamic properties
2. Sanchez-Lacombe Model The SL model[3] was proposed by Sanchez and Lacombe based on an Ising fluid theory. Some details of this model are presented as follows. Gibbs free energy (G) can be expressed as:
1. Introduction
G ¼ E þ PV kT ln X; Organic compounds are widely used in chemical industry, biotechnology, and medical applications.[1] For example, tri- and tetra-ethylene glycols were mainly used as drying agents for natural gas, as humectants, as solvents, and in the manufacture of vinyl plasticizers.[1,2] Phase diagram and thermodynamic database are effective tools for developing new materials, and are widely applied in inorganic systems. Now, more and more attention has been paid to that of organic systems. Recently, some thermodynamic theories and models in the organic and polymer systems have been proposed, such as the Sanchez-Lacombe (SL) model,[3] the Flory-Huggins model,[4] the Universal quasi-chemical activity coefficient (UNIQUAC) model,[5,6] etc. The Flory-Huggins model is most widely used because of its simplification; however, it is not available for vapor phase. The universal quasi-chemical activity coefficient (UNIQUAC) model is more accurate, but it is also more complex. The Sanchez-Lacombe model can be used to calculate the vapor phase because the holes of the fluid are considered, and it is not as complex as the UNQUAC model. The main purpose of our work is to establish a more integrated and valid database of organic system. Therefore, in the present paper the SanchezLacombe model is used for calculating the reduced Gibbs free energies of both liquid and vapor phases of pure organic compounds.
Y.C. Li, C.P. Wang, and X.J. Liu, Department of Materials Science and Engineering, College of Materials, and Research Center of Materials Design and Applications, Xiamen University, Xiamen 361005, P.R. China. Contact e-mail: [email protected].
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ðEq 1Þ
where E is the configurational (potential) energy, V is the volume of a system, X is the number of configurations, T is the absolute temperature, and P the pressure. In order to determine X, a simple case of dimers and holes on a rectangular lattice is considered.[7] A schematic diagram of organic molecules (r = 3) is shown in Fig. 1. Guggenheim[8,9] proposed an approximate method to calculate the value of X for a multicomponent mixture of r-mers on a lattice: N d Nr ! Nq ! Z=2
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