Mercury is emitted from coal gasifiers mainly in the form of elemental mercury, mercuric chloride and mercuric sulfide. There is no cost effective method developed to capture mercury at high temperature from the reducing gas environment that is encountered in gasification systems. The value engineering phase of many conceptual engineering studies of gasification processes often recommend development of warm-gas clean-up technologies In this study, a new adsorbent was synthesized and evaluated to capture elemental mercury at syngas conditions.
25 wt% [bmim]Cl+azelaic acid-silica was used to capture elemental mercury in the form of mercury azelate (halatopolymer) in a fixed-bed adsorption process in presence of syngas components. The adsorbent capacity was 6.5 mg/g when the gas contained only Nitrogen, but dropped to 1.0 mg/g in presence of syngas components. The presence of gases that are highly soluble in ionic liquid, such as Hydrogen sulfide and Carbon dioxide, and also reducing gases, such as Hydrogen and Carbon monoxide, had a negative effect on the adsorbent capacity. The presence of oxidizing gases, like moisture and HCl, had a positive effect on the adsorbent capacity.
The adsorbent 25 wt% [bmim]Cl+azelaic acid-silica capacity was influenced by the gas flow rate, adsorbent loading, and silica particle size. The effect of particle size was studied; it was found that the larger particle size adsorbent resulted in lower mercury capture capacity due to enhanced channeling for the larger particle size adsorbent. Also an increase in adsorbent loading beyond 10 mg resulted in decreased adsorbent capacity due to non-uniform loading. Different ionic liquid coating methods were employed to improve the coating uniformity on silica particles.
In this study, a priori assumption of pore blockage was made and the model was further simplified where in it is assumed that the ionic liquid is concentrated at the core of the particle. For the model studied, there was negligible external mass transfer resistance to mass transfer the overall transfer mass transfer coefficient is mainly limited by the mercury diffusion through the ionic liquid. There was good agreement between the experimental and the simulated results using linear isotherms.
|Commitee:||Angelopoulos, Anastasios, Degouvea-Pinto, Neville, Thiel, Stephen|
|School:||University of Cincinnati|
|Department:||Engineering and Applied Science: Chemical Engineering|
|School Location:||United States -- Ohio|
|Source:||MAI 57/06M(E), Masters Abstracts International|
|Keywords:||Adsorbents, Capture, Coal, Elemental mercury capture: syngas: coal gasification: ionic liquid: chelating adsorbents, Gas, Gasification, Mercury, Warm|
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