Supercritical water co-liquefaction of LLDPE and PP into oil: properties and synergy

Abstract

The supercritical water liquefaction of PE/PP mixtures yields around 86.84–90.70% oil without catalyst or H2.

Thermodynamic feasibility of shipboard conversion of marine plastics to blue diesel for self-powered ocean cleanup

“…SI.2 provides a comparison of HTL and pyrolysis for the mixed PE/PP stream. Interestingly, thermodynamic performance profiles of HTL and pyrolysis are very similar to one another, indicating that the differences in drying, heating, and oil yields obtainable by the two processes nearly offset one another (13,23). Therefore, from a strictly thermodynamic standpoint, either pyrolysis or HTL could be a viable shipboard technology option.…”

“…Accordingly, simulations were performed for two individual pure plastics commonly found in the ocean ( 2 ), polypropylene (PP) and polyethylene (PE), as well as a “mixed feed” based on the typical composition of marine plastics (2:1 PE:PP) ( 2 ). The operating temperature, overall conversion, and product yield for each plastic feed were taken from previous work ( 11 – 13 ) and are listed in SI Appendix , Tables SI.2 and SI.3 ( SI Appendix , section SI.1.2 ). Notably, performance for the PP/PE mixed feed was especially promising, as HTL of this feed resulted in 85% oil yield at a modest temperature (400 °C) and with no solid byproduct.…”

“…Interestingly, performance profiles for the PP and the PE/PP feeds exhibit similar characteristics to one another, a promising finding given that the PE/PP mixture is most representative of the composition of plastic present in the Great Pacific Garbage Patch (GPGP) ( 1 ). Based on previous modeling of the depolymerization of mixtures, the likely explanation for the favorable performance observed for PE/PP is an autocatalytic effect arising from radicals formed by PP pyrolysis ( 13 ).…”

“…The shredded plastic is then combined with desalinated water to 10 wt % to 30 wt % solids, preheated in the heat exchanger, pumped to pressure, and heated to reaction temperature. The stream exiting the reactor is cooled to form organic and water-rich products ( 11 – 13 ) which are separated in a gravity separator. Residual organics in the aqueous phase are removed in a hydrogen peroxide/ultraviolet (UV) oxidation system prior to recycling.…”

“…A viable technology for converting plastics into a usable fuel is hydrothermal liquefaction (HTL), which utilizes high temperature (300 °C to 550 °C) and high pressure (250 bar to 300 bar) to transform plastics into monomers and other small molecules suitable as fuels ( 11 – 13 ). Oil yields from HTL are typically >90% even in the absence of catalysts and, unlike pyrolysis, yields of solid byproducts—which would need to be stored or burned in a special combustor—are less than 5% ( 11 – 13 ), thus conferring certain comparative advantages to HTL. Ideally, a vessel equipped with an HTL-based plastic conversion system could fuel itself, creating its fuel from recovered materials.…”