Calorimetric assessment of adsorbents bonded to metal surfaces: Application to type A silica gel bonded to aluminium

Abstract

Abstract A recent publication concerned the use of a thermoelectric module to control temperature in an inert sample and to meter heat flow to the sample. This technique has been adapted for an active sample containing a layer of Type A beaded silica gel particles, bonded to aluminium at which point the sample temperature was measured. The adsorption of water vapour was considered, as might occur in adsorption chillers. During experiments, nominal sample temperatures were maintained to within 0.2 K and accuracy of heat flow measurement generally to within 11% not withstanding a correction for heat losses. The rejected heat of adsorption was fitted to an exponential recovery with r 2 > 99% yielding the adsorption capacity and kinetic rate constant for each experiment. For the silica gel selected (Type A) and in the loading range 3%–30%, previous data published by a different research team were reproduced to within 10% (3 mm diameter particles) and 20% (1 mm diameter particles). Kinetic rate constants were far bigger than would be inferred from Knudsen diffusion alone. The constants fell onto straight lines on Arrhenius plots; the inferred activation energies were far less than two independent measurements for RD type silica gels, but in line with one theoretical expectation. Kinetic rate constants did not vary in inverse proportion to the square of particle diameter; the same discrepancy is partly evident in other publications.