Supercritical fluid extraction for purification of waxes derived from polyethylene and polypropylene plastics

Abstract Polyethylene (PE) and polypropylene (PP) feedstock contain various additives, such as fillers and colorants, which either degrade or carry through the depolymerization process; thereby causing intense dark colors and a pungent petroleum odor. The combination of color and odor imposes several challenges, limiting the potential markets of the wax products. This study put emphasis on the development of an innovative and environmentally sustainable process based on supercritical fluid extraction (SCFE) to remove organic and inorganic contaminants that cause color and odor in waxes derived from recycled polymers. In terms of organic impurity removal, for PE 81% and for PP 97% removal efficiency was achieved. The color of PE and PP in terms of lightness under CIELAB (lightness, green-red, blue-yellow) color space was improved by 13 and 40 units, respectively. The purified waxes could be utilized in a variety of market segments, including color masterbatch, roofing shingles, rubber, and coatings. Compared with traditional purification technologies based on solvent extraction and absorbent filters, SCFE process offers exceptional advantages, including fast reaction rates, little liquid waste, ease of separation of solutes, and fewer separation stages. This novel process enables producing high-value water white waxes from reclaimed polymeric feedstock with a focus on clean technologies and enhanced resource efficiency.