Evaluation and Valorization of Pyrolytic Char from Commingled Waste Plastics

Abstract

Graphitic materials can be synthesized using a plethora of transformation processes. This work utilized waste plastic slow pyrolysis as a pathway to synthesize graphitic materials. The raw materials for the pyrolysis process were collected from a dump site in Auchi environment, Edo State, Nigeria which included grocery bags, disposable cups, plates, drinking water bottles, etc. These plastics were identified as PP, PET, and HDPE, after which they were cleaned and sorted and their sizes, reduced. Two runs were carried out with comingled plastics while three other runs were conducted with HDPE, PP, and PET waste plastics singly. A locally fabricated laboratory-scale pyrolyzer was used to convert the plastic waste into char. The reaction was carried out at 300 oC, and varied reaction times between 60 and 120 mins. The five Samples retrieved at the end of the slow pyrolysis were evaluated based on their elemental composition (XRF) and Physico-chemical properties like porosity, percentage moisture, and ash content. The XRF analyzer showed that the char included SiO2 (> 16%), Al2O3 (6%), CaO (>19%), and some amount lost during ignition (LOI > 31%). PP was found to have the highest porosity (45.93%) while HDPE at 60 minutes of slow pyrolysis had the highest amount of moisture (0.84%) and ash content (36.78%). PP alone produced the highest quantity of solid dry-textured char (67.51%) followed by HDPE (54.67) while PET was majorly waxy with the least trace of char (12.54%). These results showed that the product formed could be considered a graphitic material, for use as a solid fuel, good adsorbent, and possible catalyst.