STUDIES ON THE MEASUREMENT OF HEAT OF ADSORPTION OF MINERAL ACIDS ON POLYAMIDE BY FLOW METHOD

Abstract

The heat of adsorption of mineral acids on polyamide powders A_??_D (sample A_??_D have different amount of amino end group) were measured with application of the thermal detection type automatic recording liquid chromatography as a flow type micro calorimeter. The heat of adsorption was obtained by total variation of temperature (peak area) which corresponded to overall calorific values in the thermal detection column with calori-corrector unit and adsorption amounts. Observed values of heat of adsorption are influenced considerably by experimental temperature, concentration of acid, state of the amorphous region of polyamide. Observed values were corrected by the ratio of adsorption amounts on equilibrium (48 hr) and contact time on flow method (ca. 30min). Corrected values (-ΔHc°) are plotted with θ (=[H]f/[S]f) and these at saturated adsorption (-ΔH°c•θ=1)are obtained by extrapolation to θ=1. Good agreement is observed among the values of -ΔH°c•θ=1 for different samples A_??_D. As the temperature increases (30°_??_50°C), -ΔH°c•θ=1 values of HCl, HBr and HI increase. Proposed value of -ΔH°c•θ=1 of acids are 8.2 kcal/mol (HCl, 30°C), 8.9 kcal/mol (HCl, 40°C), 10.4 kcal/mol (HCl, 50°C), 11.3 kcal/mol (HBr, 40°C) and 13.5 kcal/mol (HI, 40°C). It is assumed that these differences by acids used depend on differences of the heat of adsorption of anion (Cl-, Br- and I-)to protonated amino end group (-NH3+) on polyamide.