A Molten-Salt Pyrolysis Synthesis Strategy toward Sulfur-Functionalized Carbon for Elemental Mercury Removal from Coal-Combustion Flue Gas

Abstract

The emission of mercury from coal combustion has caused consequential hazards to the ecosystem. The key challenge to abating the mercury emission is to explore highly efficient adsorbents. Herein, sulfur-functionalized carbon (S-C) was synthesized by using a molten-salt pyrolysis strategy and employed for the removal of elemental mercury from coal-combustion flue gas. An ideal pore structure, which was favorable for the internal diffusion of the Hg0 molecule in carbon, was obtained by using a SiO2 hard template and adjusting the HF etching time. The as-prepared S-C with an HF etching time of 10 h possessed a saturation Hg0 adsorption capacity of 89.90 mg·g−1, far exceeding that of the commercial sulfur-loaded activated carbons (S/C). The S-C can be applied at a wide temperature range of 25–125 °C, far exceeding that of commercial S/C. The influence of flue gas components, such as SO2, NO, and H2O, on the Hg0 adsorption performance of S-C was insignificant, indicating a good applicability in real-world applications. The mechanism of the Hg0 removal by S-C was proposed, i.e., the reduced components, including sulfur thiophene, sulfoxide, and C-S, displayed a high affinity toward Hg0, which could guarantee the stable immobilization of Hg0 as HgS in the adsorbent. Thus, the molten-salt pyrolysis strategy has a broad prospect in the application of one-pot carbonization and functionalization sulfur-containing organic precursors as efficient adsorbents for Hg0.

Determination of Some Heavy Metals in European and Polish Coal Samples

“…In both cases, four out of six tested coal samples from outside the EU significantly exceeded the results obtained for the samples of Polish coal, and the other two showed similar results. Figure 3 shows the results of measurements of heavy metal concentrations in the samples of hard coal sourced in Poland (9 and 10) and from outside the EU (1)(2)(3)(4)(5)(6)(7)(8). The results show that the averaging of concentrations of all elements indicates greater pollution levels of coals imported to the EU from outside the eastern border of Poland, which is important because all these elements are emitted in a gaseous or solid form to the environment.…”

“…According to the data provided by the Polish Geological Institute, as much as 80% of Polish coal resources are in Upper Silesia. All coal combustion products and those related to its extraction are considered polluting, with a distinction being made between volatile and solid by-products including, e.g., mercury in fuels [1]. Metals in coal are among the most dangerous pollutants in the environment due to their persistence, bi-accumulation, and acute toxicity.…”

Elemental Mercury Removal from Coal-Fired Flue Gas on Sulfur-Modified Activated Biomass Coke: Experiment and Simulation

“…Biochar has an ideal large specific surface area, rich pore structure, strong thermal stability, and great potential to replace industrial activated carbon. − Sulfur-containing substances are usually used for the modification of adsorbents because sulfur can provide a pair of lone electrons to form a covalent bond with mercury during the reaction process, and sulfur shows a strong affinity for mercury . Zhao et al used wood chips as biomass raw materials and selected sulfur-containing substances as modifiers.…”