AMMONIA SORPTION ON COMPOSITES "CaCl2 IN INORGANIC HOST MATRIX": ISOSTERIC CHART AND FREEZLING COP

New composite sorbents of ammonia “CaCl2/γ-Al2O3” and “CaCl2/vermiculite” were synthesised and studied. The isosteres of ammonia sorption on these composites were measured at T = 20-90C and P = 0.08-9 bar. It was found that the modification of host matrices by the salt dramatically increases the ammonia uptake due to the formation of CaCl2×nNH3 complexes. The isobaric enthalpy and entropy of ammonia sorption were calculated over the uptake range 2.5-22.5 wt. % and 21.5-68.5 wt.% for alumina and vermiculite based composite, respectively. For the confined salt both these values were significantly lower respect to those for the bulk one. The transitions between complexes CaCl2×nNH3 confined to alumina pores were shifted to higher ammonia pressure in comparison with those in bulk. For a single-effect non-regenerative freezing cycle, the values of COP = 0.40 – 0.48 were calculated at the evaporator temperature –18C, condenser temperature 35 – 40C and desorption temperature 117 – 120C. High COP in combination with rapid sorption makes these sorbents promising for application in freezing units driven by relatively low temperature heat.