Abstract:
Natural biopolymers are gaining increasing attention due to their extraordinary affinity towards adsorption of heavy metal ions. In this research, biopolymers such as chitosan and alginate were used to remove contaminants from lean alkanolamine (methyldiethnolamine; MDEA) solvent. The sweetening of natural gas is mostly done by absorption using single or mixed alkanolamine solutions. Alkanolamine solvent quality deteriorates abruptly while absorbing H2S/CO2 from natural gas and causes foaming in natural gas sweetening unit. Different types of organic as well as inorganic species are present as contaminant in lean MDEA solvent. Heat stable salts such as acetate and propionate are present in high amount in lean MDEA solutions and detected using Ion chromatograph and UV-VIS spectrophotometer. Substantial amount of elements (chromium, iron etc.) were detected using Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) analysis. Chitosan coated sand (CCS) and calcium alginate (Ca-Alg) beads were prepared and used in batch adsorption studies to monitor the removal of these contaminants in MDEA solvents. FTIR studies and SEM analysis were done to observe the underlying principle of bio-adsorbent preparation. It was observed that both CCS and Ca-Alg removed heavy metal ions like chromium (40% and 61%) and iron (21% and 62%) significantly. Ca-Alg could also remove organic acid anions (36%) appreciably. The maximum uptake capacity for chitosan coated sand was found to be 59.88 μgm/gm for iron and 38.022 μgm/gm for chromium.
