New equipment and new technique for measuring activity coefficients and Henrys constants at infinite dilution
Résumé
New equipment is presented along with various experimental procedures and setups to cover a large range of applications. It represents a considerable improvement in terms of speed, accuracy, and simplicity with respect to classical gas stripping methods known as dilutor techniques. Furthermore, range of conditions of its use is larger in terms of: temperatures (from 90 to 600 K), corrosive power, and toxicity of handled compounds. Solutes that could adsorb inside sampling valves or on the walls of transfer lines between sampling valve and GC detector are now studied easily; thanks to new design and procedure. Activity coefficients of one solute into one solvent at five temperatures, several repeatability tests included, are obtained in worst cases in less than 3 h. One accurate activity coefficient measurement (toluene in water) at one temperature can be realized in less than 2 min, after loading of the dilutor cell, instead of more than half an hour for unreliable results with previous equipment. It must be pointed out that the slope determination (slope of the logarithm of the exponential decay of solute composition in vapor phase which is in equilibrium with liquid phase) is the highest source of errors (flow rate, temperature, number of moles of solute are known with high accuracy with respect to slopes); they are now determined within few % instead of up to tens of % in the most difficult cases leading to higher accuracies of measured activity coefficients, Henrys constants at infinite dilutions or solubility data. Successful comparisons with literature data and reproducibility tests are presented herein.