Ammonia capture by adsorption on doped and undoped activated carbon: Isotherm and breakthrough curve measurements

Abstract

Doped and undoped activated carbons were characterized by scanning electron microscopy, energy dispersive spectrometry, helium pycnometry, mercury intrusion porosimetry, and adsorption isotherms of nitrogen and carbon dioxide. The adsorption isotherms of ammonia were measured at 278, 293, 303, and 318 K and pressures up to 105 kPa using a manometric system on both activated carbons. These measurements showed that the doped activated carbon had the highest ammonia adsorption capacity, especially at low ammonia partial pressures. The Toth isotherm model was used to correlate the adsorption isotherms and estimate the isosteric heats of adsorption at 278 K and at zero fractional loading that were 25.6 and 41.9 kJ.mol−1 for undoped and doped activated carbon, respectively. Ammonia breakthrough curves were measured with both activated carbons in a pilot column. The behavior of doped and undoped activated carbon during adsorption/desorption cycles shows that despite the possibility of regeneration and enhancement of undoped activated carbon, the doped activated carbon provides better single use performance. A study of the operating parameters of doped activated carbon was conducted to evaluate the effects of ammonia concentration, gas flow rate, operating temperature, and relative humidity. The occurrence of two independent ammonia adsorption mechanisms (chemical and physical) on the doped activated was demonstrated.