THERMODYNAMIC AND KINETIC-PARAMETERS FOR THE SUPERCRITICAL EXTRACTIONOF BIPHENYL FROM A CONTAMINATED SOIL

Carbon dioxide supercritical extraction is applied to a soil artificia lly contaminated with biphenyl. We studied three aspects of the extrac tion process in order to control it. An ''excess function equation of state'' model is used to represent the thermodynamic properties of the binary biphenyl-carbon dioxide mixture. This model allows calculation of solid compound solubility and of liquid-gas equilibrium. The adsor ption of biphenyl in soil in the presence of supercritical carbon diox ide is experimentally studied. In order to demonstrate the influence o f the non-ideal character of the supercritical fluid on the amount ads orbed, we used a Bragg Williams lattice model. The adapted model allow s adsorption calculation for a given set of temperature-pressure-fluid composition data. Both thermodynamic models are necessary to shape th e extraction behaviour. In the soil, the pollutant is distributed betw een a precipitated phase and an adsorbed phase. Thus, the extraction m odel contains a dissolution kinetic term and a desorption kinetic term . Three parameters are unknown: the dissolution rate coefficient, the overall mass transfer coefficient between soil particles and the fluid and the fraction of precipitated biphenyl from the total quantity in soil. These parameters are estimated by fitting the model with experim ental data. Copyright (C) 1996 Elsevier Science Ltd.