Pore structure development of in-situ pyrolyzed coals for pollution prevention in iron foundries

A protocol was devised for preparing pyrolyzed coals that could be made in-situ at foundries to capture volatile organic compound (VOC) emission. This pyrolysis created extensive micropore volume in lignite over a broad range of temperature and time; and could use waste heat from cupola exhaust gases by a heat-exchange tube. For foundry application, moderate porous carbon with relatively uniform pores over wide ranges of temperature and time would be more practical than highly porous activated carbon (AC) that requires narrowly-controlled operations. This pyrolysis protocol was developed in a thermogravimetric analyzer (TGA) and in a small tube furnace, while using lignite, bituminous coal, and anthracite. The lignite yielded the most pore volume; and this was relatively uniform (0.1–0.13 mL/g of pores) while temperatures were 600–900 °C, and times were 0–60 min. Smaller grain sizes yielded improved porosity; and this corresponded to more release of phenols and naphthalenes from smaller grains, as discerned by TGA–mass spectroscopy (MS). TGA–MS also revealed that improved pore development between 600–800 °C corresponded to the release of CO2 and H2O; and concurrently higher slurry pH linked to less oxygenated functionality. Adsorption of benzene was compared between the in-situ porous carbon and a commercial AC.