Interactions of the Main Components in Paper‐Plastic‐Aluminum Complex Packaging Wastes during the Hydrothermal Liquefaction Process

Degradation of Waste Tetra Pak Packaging with Hydrothermal Treatment in Sub-/Supercritical Water

Tetra pak packaging is one of the most frequently used types of packaging in the food industry. The recycling of the tetra pak packaging waste presents a difficult task because of its multi-layered, multi-component structure. In this study, the degradation of tetra pak packaging in subcritical (SubCW) and supercritical (SCW) water was investigated. The experiments were carried out in one (SCW) or two stages (SubCW and SCW), whereby the influence of the reaction temperature and time on the yield and composition of the products obtained was investigated. The maximum oil phase yield achieved in a one-stage and a two-stage degradation process was 60.7% and 65.5%, respectively. The oil and gas phases were composed of different types of hydrocarbons. Higher temperature and longer time led to higher amounts of saturated aliphatic hydrocarbons in both the oil and gas phases. The aqueous phase contained sugars (glucose, fructose) and sugar derivatives (levulinic acid, glyceraldehyde, furfurals). Based on these results, the degradation pathway of waste tetra pak packaging in SubCW and SCW was proposed. The results of the study show that the degradation of waste tetra pak packaging with SubCW and SCW is a promising recycling process.

Hydrogen Recovery from Waste Aluminum-Plastic Composites Treated with Alkaline Solution

An alternative solution to the problem of aluminum-plastic multilayer waste utilization was suggested. The process can be used for hydrogen generation and layer separation. Three different sorts of aluminum-plastic sandwich materials were treated with an alkali solution. In the temperature range of 50-70 °C, for tablet blisters of polyvinylchloride and aluminum (14.8 wt.%), the latter thoroughly reacted in 15-30 min. For sheets of paper, polyethylene, and aluminum (20 wt.%), full hydrogen 'recovery' from reacted aluminum component took 3-8 min. From the lids of polyethylene terephthalate, aluminum (60 wt.%), and painted polyethylene with perforations, the aluminum was consumed after 45-105 min. The effect of perforations was the reduction of the process duration from nearly 90 min for the lids with no perforations to nearly 45 min for the perforated ones (at 70 °C). Perforations provided better contact between the aluminum foil, isolated between the plastic layers, and the alkali solution. Hydrogen bubbles originating near those perforations provided foil separation from the upper painted plastic layer by creating gas gaps between them. The remaining components of the composite multilayer materials were separated and ready for further recycling.