Experimental studies on 3A and 4A zeolite molecular sieves regeneration in TSA process: Aliphatic alcohols dewatering-water desorption

The objective of this work are in-depth experimental studies of the thermal regeneration of the zeolite molecular sieves 3A and 4A used to dewatering of aliphatic alcohols: ethanol, n-propanol and n-butanol. The experimental results of water desorption during regeneration stage of temperature swing adsorption (TSA) process, following the dewatering stage of alcohols on adsorbent fixed bed contained in column are presented. Multitemperature Langmuir-Freundlich and dual-site Langmuir-Langmuir equilibrium models were used to correlate experimental equilibrium data of water adsorption from gas phase on 3A zeolite at temperatures 100-250 °C. The thermal stability, water adsorption capacity, adsorption selectivity and thermal desorption efficiency of zeolites were studied using DTA-TGA, XRD, IR and UV-Vis-NIR methods. DTA-TGA investigations, carried out in the range of temperature 20-1000 °C revealed that water removing from 3A zeolite molecular sieve takes place up to 400 °C and from 4A up to 500 °C. However, in temperatures higher than 240 °C (3A zeolite) and 230 °C (4A zeolite) decrease of the water desorption rate was observed. Investigated zeolites reveal structural stability up to at least 500 °C, and heating above this temperature lead to an irreversible collapse of structure and a loss of adsorptive capacity. The influence of the inlet purge air temperature (200-250 °C), and air mass flux density (0.170-0.306 kg/m2s) on the zeolite dynamic water adsorption capacity, desorption and cooling steps duration, were studied. The lowest purge air and energy consumption were measured for regeneration temperature of 250 °C. Dynamic adsorption equals to 65% of the equilibrium adsorption capacity.