Joback method

The Joback method, often named Joback–Reid method, predicts eleven important and commonly used pure component thermodynamic properties from molecular structure only. It is named after Kevin G. Joback in 1984 and developed it further with Robert C. Reid. The Joback method is an extension of the Lydersen method and uses very similar groups, formulas, and parameters for the three properties the Lydersen already supported (critical temperature, critical pressure, critical volume). Joback and Reid extended the range of supported properties, created new parameters and modified slightly the formulas of the old Lydersen method.

The Joback method, often named Joback–Reid method, predicts eleven important and commonly used pure component thermodynamic properties from molecular structure only. It is named after Kevin G. Joback in 1984 and developed it further with Robert C. Reid. The Joback method is an extension of the Lydersen method and uses very similar groups, formulas, and parameters for the three properties the Lydersen already supported (critical temperature, critical pressure, critical volume). Joback and Reid extended the range of supported properties, created new parameters and modified slightly the formulas of the old Lydersen method.

Model strengths and weaknesses

Strengths

The popularity and success of the Joback method mainly originates from the single group list for all properties. This allows one to get all eleven supported properties from a single analysis of the molecular structure. The Joback method additionally uses a very simple and easy to assign group scheme, which makes the method usable for people with only basic chemical knowledge.

Weaknesses

Newer developments of estimation methods have shown that the quality of the Joback method is limited. The original authors already stated themselves in the original article abstract: "High accuracy is not claimed, but the proposed methods are often as or more accurate than techniques in common use today." The list of groups does not cover many common molecules sufficiently. Especially aromatic compounds are not differentiated from normal ring-containing components. This is a severe problem because aromatic and aliphatic components differ strongly. The data base Joback and Reid used for obtaining the group parameters was rather small and covered only a limited number of different molecules. The best coverage has been achieved for normal boiling points (438 components), and the worst for heats of fusion (155 components). Current developments that can use data banks, like the Dortmund Data Bank or the DIPPR data base, have a much broader coverage. The formula used for the prediction of the normal boiling point shows another problem. Joback assumed a constant contribution of added groups in homologous series like the alkanes. This doesn't describe the real behavior of the normal boiling points correctly. Instead of the constant contribution, a decrease of the contribution with increasing number of groups must be applied. The chosen formula of the Joback method leads to high deviations for large and small molecules and an acceptable good estimation only for mid-sized components.

Normal boiling point

T_\text{b}[\text{K}] = 198.2 + \sum T_{\text{b},i}.

Melting point

T_\text{m}[\text{K}] = 122.5 + \sum T_{\text{m},i}.

Critical temperature

T_\text{c}[\text{K}] = T_\text{b} \left[0.584 + 0.965 \sum T_{\text{c},i} - \left(\sum T_{\text{c},i}\right)^2 \right]^{-1}. This critical-temperature equation needs a normal boiling point T b . If an experimental value is available, it is recommended to use this boiling point. It is, on the other hand, also possible to input the normal boiling point estimated by the Joback method. This will lead to a higher error.

Critical pressure

P_\text{c}[\text{bar}] = \left [0.113 + 0.0032 \, N_\text{a} - \sum P_{\text{c},i}\right ]^{-2}, where N a is the number of atoms in the molecular structure (including hydrogens).

Critical volume

V_\text{c}[\text{cm}^3/\text{mol}] = 17.5 + \sum V_{\text{c},i}.

Heat of formation (ideal gas, 298 K)

H_\text{formation}[\text{kJ}/\text{mol}] = 68.29 + \sum H_{\text{form},i}.

Gibbs energy of formation (ideal gas, 298 K)

G_\text{formation}[\text{kJ}/\text{mol}] = 53.88 + \sum G_{\text{form},i}.

Heat capacity (ideal gas)

C_P[\text{J}/(\text{mol}\cdot\text{K})] = \sum a_i - 37.93 + \left[ \sum b_i + 0.210 \right] T + \left[ \sum c_i - 3.91 \cdot 10^{-4} \right] T^2 + \left[\sum d_i + 2.06 \cdot 10^{-7}\right] T^3. The Joback method uses a four-parameter polynomial to describe the temperature dependency of the ideal-gas heat capacity. These parameters are valid from 273 K to about 1000 K. This can be extended to 1500K with some degree of uncertainty.

Heat of vaporization at normal boiling point

\Delta H_\text{vap}[\text{kJ}/\text{mol}] = 15.30 + \sum H_{\text{vap},i}.

Heat of fusion

\Delta H_\text{fus}[\text{kJ}/\text{mol}] = -0.88 + \sum H_{\text{fus},i}.

Liquid dynamic viscosity

\eta_\text{L}[\text{Pa}\cdot\text{s}] = M_\text{w} exp{ \left[\left(\sum \eta_a - 597.82\right) / T + \sum \eta_b - 11.202\right] }, where M w is the molecular weight. The method uses a two-parameter equation to describe the temperature dependency of the dynamic viscosity. The authors state that the parameters are valid from the melting temperature up to 0.7 of the critical temperature (T r   3 ) and one ketone group (C=O). Since the methyl group is present twice, its contributions have to be added twice. Online molecular drawing and property estimation tool with the Joback method Online property estimation with the Joback method

Text derived from https://en.wikipedia.org/w/index.php?oldid=1309334695 under CC BY-SA 4.0; modifications have been made.