Influence of pressure and density on adsorption equilibria from near and supercritical solutions - experimental determination and thermodynamic modeling

• Applicant: Privatdozentin Dr. Monika Johannsen
• Subject Area: Chemical and Thermal Process Engineering
• Term: from 2014 to 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 260851204

Adsorption processes using supercritical fluids are gaining increasing importance, with particle diameters reaching into the nanoscale. Exact knowledge of the corresponding adsorption equilibria is of utter importance to design such separation processes efficiently.This proposal applies for a grant to further develop the thermodynamic modeling of density dependent adsorption based on experimental determination of adsorption equilibria of compressible supercritical solutions within a chromatographic column. The physically necessary pressure drop along such a column is a major source of error within the dynamic measurement of adsorption of such fluids. So far, there is a lack of models to describe adsorption in these columns in a theoretically sound manner. In the experimental part of the project the adsorption of binary solutions (CO2 + non-volatile organic solid) is investigated. Adsorptions measurements will be carried out with a large pressure drop in an analytical chromatographic column. By using a second, shorter but otherwise identical column, the adsorption of the supercritical fluid is to be measured within segments in which the density can be assumed constant. Subsequently, different possibilities of thermodynamic modeling will be evaluated and extended if necessary. The goal is to calculate the adsorption in the segments as exactly as possible from the measurements with large pressure drop using the longer column. For modeling, models such as the Peng-Robinson equation of state, SAFT and the Virial equation of state are to be applied. Next to the description of the density dependent adsorption, the number of pure and mixed compound data needed is a criterion for the performance of the model. Based on the adsorption of binary solutions, the experiments and calculations are extended to ternary solutions (CO2 + organic modifier + non-volatile organic solid). Additionally, the adsorption of non-volatile solids dissolved in n-hexane on the same adsorbents is to be measured as reference data. Optionally, the modeling will also be applied to liquid adsorption to test the transferability of interaction parameters between non-volatile solid and adsorbent to the modeling of the supercritical adsorption.

• DFG Programme: Research Grants