Removal of metal contaminants from lean MDEA solvent using clay and polymer composite

Nowadays chemical absorption using alkanolamine solutions, such as N-methyldiethanolamine (MDEA), is the most feasible method for the removal of H2S and CO2 in gas sweetening unit. However, the accumulation of heavy metals in the sweetening unit can lead to several problems such as foaming and fouling. In addition, iron being chelated to lean alkanolamine cannot be removed easily in the regenerator and causes errosion over long time. In this research work, sepiolite clay was studied as a low cost adsorbent for iron removal from MDEA. Different treatment for sepiolite clay has been investigated. The modified material was characterized by IR spectroscopy, XRD, SEM and BET. It was found that treatment with HNO3 was the best in improving the adsorption capacity of sepiolite. To determine the adsorption uptake of iron for raw and nitric acid treated sepiolite, kinetic, thermodynamic and adsorption isotherm studies were done using lean MDEA. The experimental data were analyzed using the Langmuir and Freundlich adsorption models. The Langmuir isotherm fitted well the raw sepiolite while Freundlich isotherm fitted better the acid treated samples. According to Langmuir model, the maximum adsorption uptake for raw and treated sepiolite are 0.53 and 3.3 mg/g, respectively. It was found that adsorption of iron on sepiolite before and after treatment is endothermic and spontaneous. Pseudo-second order model best represent the kinetics adsorption of iron. Desorption experiment showed that treated sepiolite can be regenerated using 0.1 M HNO3 for three consecutive cycles without obvious loss of its iron removal efficiency. The adsorption characteristics of treated sepiolite make it a promising adsorbent for iron removal. Additionally, a series of composite based on acrylamide and nitric acid treated sepiolite was prepared. The polymer samples with different sepiolite amounts were characterized by means of IR and SEM analysis. The composite exhibited less sorption capacity than sepiolite alone.