Performance of elemental mercury removal by activated char prepared from high-chlorine Turpan-Hami coal

This paper provides a new thought that a cost-effective chlorine-rich carbon-based sorbent could be prepared by directly pyrolyzing high chlorine coal in order to capture the elemental mercury, simultaneously realizing valueadded utilization of the remained char instead of combustion during low rank coal pyrolysis poly-generation. In this work, the concentration and forms of chlorine in one kind of Turpan-Hami coal were determined quantitatively according to the proposed procedures. Then the release behavior of chlorine and the transformation of chlorine from inorganic state to organic were investigated during coal pyrolysis from 400 to 1000 degrees C. Moreover, the Hg0 removal performance was examined in a lab-scale fixed bed reactor by the char before and after CO2 activation. The results indicate that over 90 % of chlorine in raw coal is inorganic in the forms of ionic Cl and crystal NaCl, and ionic Cl can be transformed to inorganic NaCl and organic C-Cl species during coal pyrolysis, thus providing chlorine active adsorption sites for Hg0 chemisorption based on the results of temperature programmed desorption and adsorption kinetic analysis. Furthermore, CO2 activation can improve the char porosity and specific surface area, thus promoting the external mass transfer of Hg0 by increasing the opportunity of chlorine active sites being exposed to vapor Hg0. 100 % of Hg0 removal efficiency is achieved in the first hour and equilibrium adsorption amount is 400 ug/g for the activated char obtained by pyrolyzing coal at 600 degrees C combining with CO2 activation at 900 degrees C, indicating the good Hg0 removal performance of the as-obtained chlorinated activated char.

Automated summary

This paper proposes a new method of preparing a cost-effective chlorine-rich carbon-based sorbent by directly pyrolyzing high chlorine coal to capture elemental mercury and utilize remaining char. The study shows that the transformation of chlorine forms during coal pyrolysis can provide active adsorption sites for Hg0 chemisorption, and CO2 activation can enhance the adsorption performance of char.