Synthesis, characterization and performance of adsorbents for mercury vapor removal

Abstract

Mercury pollution is a growing concern due to its toxicity, volatility, and bioaccumulation in the environment. The main and most problematic source of mercury emission comes from the coal-fired power plants and gas processing activities. Hence, mercury needs to be removed and adsorption has been proven to be an excellent method due to easiness of operation and efficiency. In this study, coconut husk such as coconut pith and fiber were used as alternative low-cost adsorbents in exchange to the existing conventional elemental mercury (Hgo) adsorbents. The potential use of coconut based-adsorbents for elemental mercury removal from gas streams has not yet been fully explored due to lack of research in this regard. This research focused on synthesis and modifications of coconut husk such as surface, carbonization and sulfurization treatments in order to enhance elemental mercury adsorption performance. The adsorbents were characterized using proximate analysis, scanning electron microscope (SEM), Fourier transform infrared (FTIR) spectroscopy, nitrogen adsorption/desorption (NAD), carbon-hydrogennitrogen- sulfur (CHNS) analysis and X-ray photoelectron spectroscopy (XPS) measurement. The Hgo adsorption experiments were conducted using a conventional flow type packed-bed reactor system with nitrogen as carrier gas. The results show that the chemical, physical, morphological and spectral properties of the adsorbents were greatly influenced by the modification methods used. Adsorbents obtained through carbonization and sulfurization treatments produced the best Hgo adsorption capacity. The experimental data exhibited that the increase of thermal carbonization up to 900 oC, resulted in high adsorption capacity of 6067.49 µg/g. The sulfurization at lower temperature (i.e. CPS300) resulted in the highest adsorption capacity (26077.69 µg/g). Enhancement in Hgo adsorption capacity might due to the higher sulfur compounds on the surface which acts as active site towards elemental mercury. The adsorption data revealed that the adsorbent with larger equilibrium adsorption capacity possessed poor adsorption reaction kinetics and diffusion process. This study also revealed that the char adsorbent could sustain Hgo adsorption capacity over multiple regeneration cycles. However, sulfurized-char is non-regenerative adsorbent, which can be utilized for longer adsorption process. Finally, the present findings indicate that the coconut husk can be potential low-cost elemental mercury adsorbents by applying appropriate modifications such as carbonization and sulfurization treatments. In addition, the utilization of coconut husks can reduce waste disposal problems and thus improving environmental quality and sustainability.