Comparison of heavy metal ions removal from industrial lean amine solvent using ion exchange resins and sand coated with chitosan

Abstract

The accumulation of heavy metal ions in natural gas sweetening unit causes problems such as corrosion, foaming and fouling of the equipment. Heavy metal ions being chelated to lean amine solvent cannot be removed from the solvent by simple heating in the regenerator, hence requiring new approaches for heavy metal ions removal from aqueous solution of lean amine (methyldiethanolamine) solvent is mandatory. In this study, three different grades of commercial ion exchange resins (A–C) including chitosan coated Resin C and sand coated with chitosan (SCC) were tested to remove major heavy metal ions from raw industrial lean amine (MDEA) solution employing the principles of adsorption. Finally, Resin C and SCC were used for elaborate batch and continuous adsorption studies. SEM and FTIR analysis mapped the surface morphology changes and coating of chitosan before adsorption process over the adsorbent. The equilibrium batch sorption studies for heavy metal ions removal were fitted into Langmuir, Freundlich, Temkin and Dubinin–Radushkevich (D–R) isotherms The Langmuir model predicted maximum uptake capacity for chitosan coated resin C and SSC (in brackets) 38.022 (14.184) μg/g for chromium, 59.88 (75.7575) μg/g of iron and 22.47 (185.185) μg/g of lead having total maximum metal removal of 6.858 (5.0226) μequivalence/g. The sorption kinetics obeys pseudo-first-order having rate constant 0.0111 min−1 (0.0095 min−1) for chromium ions. The negative values of Gibb's free energy explains spontaneity of the reaction with endothermic heat of adsorption for the removal of heavy metal ions using resin C and SCC. The breakthrough curves for removal of metal ions in column bed with 2.54 cm column diameter and flow rate of 4.5 ml/min was achieved within 8 h. The parameters k and τ for chitosan coated resin C and SCC were determined to be 0.014 (0.015) min−1 and 551.25 (525.7867) min.