Recycling waste polymers as a source of carbon in steelmaking: Fundamental high temperature investigations on structure evolution and carbon dissolution into molten iron

Abstract

This research is focused on establishing the feasibility of utilizing waste polymeric materials as an alternative source of carbon in steelmaking for carburizing purpose. Three polymeric materials, namely waste CDs, Bakelite and waste Carbon fiber reinforced polymers (CFRP) were investigated. Their structural evolution obtained at different pyrolysis temperatures showed that chars from waste CDs and Bakelite showed more ordered carbon structure with increasing pyrolysis temperature. The high temperature pyrolysis of CFRP did not have much effect on structural parameters but solid, highly pure and non porous structure of carbon fibers (~ 98% C) were reclaimed. Pyrolysis of polycarbonate based waste CDs produced ~19 wt% char residue (~89 % C), Bakelite produced ~41 wt% char residue (~ 73 wt% C), waste CFRP produced ~ 60 wt% char residue (~98 wt% C) at 1550 °C. Investigations on carbon dissolution into molten iron were carried out at 1550 ̊C as a function of time. For waste CDs and waste CFRP, the carbon pick up by molten iron was found to be very rapid and reached 4.12 %C and 5.20 %C within 2 minutes respectively. For Bakelite char the carbon pickup by molten iron was found to be very slow and reached ~ 0.26 % within 2 minutes. Overall carbon dissolution rate constant (K) for waste CD char, CFRP char and Bakelite were found to be 19.2 x 10 -3 s-1, 22.2 x 10 -3 s-1, 0.41 x 10-3 s-1 respectively. High carbon pickup by using waste CDs and waste CFRP was found to be in a range similar to that observed for synthetic graphite and was much higher than coke and coal chars. Bakelite results were found to be in a range similar to traditional carbonaceous materials such as metallurgical coke and coals. The recycling of waste plastics for steelmaking application can therefore help reduce or even eliminate to a great extent several problems associated with waste plastic recycling and their disposal along with a reduction in the usage of traditional carbonaceous materials.