Removal of the total organic acid anions from an industrial lean diglycolamine solvent using a calcium alginate carbon adsorbent, and molecular modeling studies

Diglycolamine (DGA), one of the alkanolamine solvent used in natural gas sweetening unit, produces total organic acid (TOA) anions as degraded products that has detrimental effects over the operational units. In this study, calcium alginate carbon (CAC) adsorbents were used to remove TOA anions from industrial lean DGA solvent. The adsorbents were characterized by TGA, DSC, Raman, FTIR, and SEM analysis. Effects of different parameters such as the adsorption time, adsorbent dosage, and solution temperature were examined in the batch adsorption experiments. The kinetic data were best fitted to the pseudo-second-order model, highlighting chemisorption as the rate-limiting step. This was also validated using molecular modeling by predicting the intermolecular hydrogen bond formation between the organic acid anions and the calcium alginate molecules. The TOA uptake increased with the increase in the solution temperature from 49.9 mg/g at 25 °C to 72.5 mg/g at 55 °C. The CAC beads were regenerated effectively for six adsorption–desorption cycles in a fixed-bed column. The environmentally friendly CAC adsorbent exhibited significant application potential for the removal of TOA anions from lean DGA solvents.