The Achard model

The Achard model combines the UNIFAC group contribution model modified by Larsen et al. [LAR 87], the Pitzer-Debye-Hiickel equation [PIT 73a, PIT 73b] and solvation equations (Figure 2.1). The latter are based on the definition of the number of hydration for each ion, which corresponds to the assumed number of water molecules chemically related to the charged species. It divides the activity coefficient into two terms ... 

The Achard model includes a module for the automatic determination of the present chemical species. As a matter of feet, the decompositions and the solvations that can occur should be taken into account. Figure 2.3 shows two possible situations, one for a sugar and the other for a soda solution. 

In order to operate, the Achard model requires a description of each chemical species present in solution (Figure 2.2). Several cases are possible... 

Due to its structure, the Achard model is a predictive model. Considering a mixed electrolyte solution (e.g. water-NaCl-KCl), it is possible to calculate the activities of all the species and constituents of the media, because the interaction parameters are from binary water-electrolyte systems. However, it is an aqueous solution model where water must always be included in the constituents of the system. 

The Achard model [ACH 92b] facilitates the identification of sugars such as glucose and fructose (Table 3.1). However, it does not allow the a and P forms to be separated. 

In 2003, Gros and Dussap used the initial Achard model to predict the physical-chemical properties of milk from the composition. They could thus find once more the equilibrium pH and the buffering capacity of the milk. 

Delhaye JM, Achard JL (1978) On the use of averaging operators in two phase flow modeling Thermal and Aspects of Nuclear Reactor Safty, 1 Light Water Reactors. ASME Winter Meeting... 

De Schutter, E., Ekeberg, O., Hellgren Kotaleski, J., Achard, P., Lansner, A. BiophysicaUy detailed modelling of microcircuits and beyond. Trends Neurosci. 28, 562-569 (2005) Hirsch, J.A., Martinez, L.M. Laminar processing in the visual cortical column. Curr. Opin. Neurobiol. 16, 377-384 (2006)... 

Cabidoche Y M, Achard R, Cattan P, Clemumt-Dauphin C, MassatF, Sansoulet J, (2009) Long-term pollution by chlordecone of tropical volcanic soils in the French West Indies A simple leaching model accounts for current residue. Environmental Pollution 157 1697 1707... 

In the field of chemical engineering, a very large number of models have been developed for non-ideal solutions. In this chapter, only the model developed by Achard [ACH 92a] will be presented as it provides the basis for the present work. 

---