A novel resource conversion strategy of waste plastic express packaging bags using supercritical water-ammonia process: Optimization by response surface methodology

With the rapid development of e-commerce and express delivery industries, a large number of waste plastic express packaging bags (WPEPBs) are generated and urgent to be safely disposed. In this work, a novel resource conversion strategy was developed to produce high value-added chemicals from WPEPBs by supercritical water ammonia (SWA) process without any catalyst. WPEPBs could be converted into two parts by the SWA process: oil and solid residue. More than 80 % of the oil was identified as long-chain alkanes and alkenes due to the decomposition of polyethylene (PE) contained in WPEPBs. The presence of NH3 in SWA was beneficial to improve the production of long-chain alkenes. The plasticizers in WPEPBs including bisphenol A (BPA) and phthalate ester (DEHP) could be efficiently converted into aniline (≈15%) and 2-ethylhexanol (≈4 %) due to the high reactivity of NH3 in the SWA process. Compared with the degradation of WPEPBs in supercritical water, the SWA process could reduce side effects and improve the purity of target products. High-purity CaCO3 powder could be further recovered from the solid residue. The optimal parameters of the SWA process for the conversion of WPEPBs by Response Surface Methodology (RSM) were 440.5 ℃, 90 min, and CNH3 of 4.8 wt%. The conversion ratio of WPEPBs (CWPEPBs) and CaCO3 recovery ratio (RCaCO3) were 99.10 % and 98.85 %, respectively. In contrast to traditional methods for recycling of plastic waste such as mechanical recycling and incineration, the SWA process is believed to be a clean and high-efficiency resource conversion strategy for WPEPBs.