Limestone’s performance as a solid adsorbent for HF and HCl generated in refrigerant destruction applications

Abstract

The viability of two solid adsorbents, limestone and cement powder, for use in a flow-through packed-bed column for HCl and HF gas neutralization following refrigerant destruction was studied. Neutralization tests performed at 408 K using 5% HCl in N₂ and 5% HF in N₂, showed that limestone had a significantly higher adsorption capacity for both HF and HCl. ∼49% of fed HCl, and between 7.8%–16.2% of fed HF gases were adsorbed by 7 g of limestone for a gas flow rate of 6.67×10⁻⁶ m³/s (STP) over 30 to 180 minutes. Effective diffusivities (D _e ) of HCl and HF into the limestone particles were 1.5×10⁻⁹ and 2.2×10⁻⁹ m²/s, respectively, indicating that a solid diffusion mechanism dominance would limit the suitability of this method as a solid adsorbent in the tested form. Under these conditions, complete particle conversion times were 227 hours for HCl-limestone and 154 hours for HF-limestone. Considering the long conversion times observed, shorter conversion times would require micron-scale particle sizes, suitable for entrained flow but not for a packed-bed arrangement. A Na₂CO₃/Limestone slurry used to neutralize the reactor effluent proved efficient within this system, and may be a more suitable alternative for acid neutralization involving HF.