Multi-material layered plastic films are used in the food packaging industry due to their excellent properties; however they cannot be mechanically recycled. In this study, a two-stage hydrothermal liquefaction (HTL) process is proposed and tested for chemical recycling of a two-layer film made of LLDPE-PET. Experimental results showed that after a first subcritical stage at 325 °C, 94% of terephthalic acid (TPA) is recovered from the PET fraction as a solid and 47% of ethylene glycol in the aqueous phase. The unconverted PE was then used as feedstock for a subsequent supercritical HTL stage at 450 °C for 90 min, achieving mass yields of 47% and 29% in a naphtha-gasoline oil and in an alkane-rich gas, respectively. In conclusion, this work proved that a sequential HTL procedure can be used for chemical recycling of multilayer plastics, allowing the recovery of PET monomers to be recycled back to the PET industry and a paraffinic oil and hydrocarbon-rich gas phase that could be used as feedstock for steam cracking to produce virgin materials.

多材质层状塑料薄膜以其优异的性能应用于食品包装行业；然而，它们不能被机械回收。在这项研究中，提出并测试了一种两阶段水热液化 (HTL) 工艺，用于化学回收由 LLDPE-PET 制成的双层薄膜。实验结果表明，在 325 °C 的第一个亚临界阶段后，94% 的对苯二甲酸 (TPA) 作为固体从 PET 馏分中回收，47% 的乙二醇在水相中回收。然后将未转化的 PE 用作后续超临界 HTL 阶段的原料，在 450 °C 下持续 90 分钟，在石脑油汽油和富含烷烃的气体中分别实现 47% 和 29% 的质量产率。总之，这项工作证明顺序 HTL 程序可用于多层塑料的化学回收，