Assessment of Supercritical CO2 Extraction as a Method for Plastic Waste Decontamination

Abstract

Due to the lack of advanced methods to clean plastic waste from organic contaminants, this study aimed at evaluating supercritical extraction as a decontamination method. Oil-adhesive high-density polyethylene (HD-PE) oil containers were subjected to supercritical extraction using supercritical carbon dioxide. The extraction was conducted at 300 bar, applying various temperatures (i.e., 70, 80 and 90 °C). The study assessed the impact of temperature on the decontamination efficiency. The variation in the samples’ quality was first analyzed using near infrared (NIR) spectroscopy. An analysis of the content of polycyclic aromatic hydrocarbons (PAHs) was followed. Samples treated at 70 and 80 °C showed higher extraction efficiencies, in spite of the lower extraction temperatures. The NIR analysis showed that the plastic specimens did not experience degradation by the supercritical decontamination method. Moreover, the NIR spectra of the extracted oil showed the presence of a wide range of compounds, some of which are hazardous. This has been confirmed by a GC-MS analysis of the extracted oil. Based on the provided assessment, the quality of the decontaminated HD-PE plastic samples—from a contamination point of view—is enhanced in comparison to untreated samples. The level of PAHs contamination decreased to be within the allowed limits defined by the REACH regulation, and also met the specifications of the German Product Safety Committee. This study proved the effectiveness of the supercritical extraction using CO2 in extracting organic contaminants from plastics, while maintaining their quality.

Recycling of polypropylene by supercritical carbon dioxide for extraction of contaminants from beverage cups. A comparison with polyethylene terephthalate and polylactic acid

“…Operational parameters of pressure, temperature, and time were selected according to previous studies reported in the literature. 12,21,22 The following experimental design was considered: (i) effect of matrix and effect of time -PET, PLA, and PP were processed at 80 °C and with varying times of 10, 30, and 60 min; (ii) effect of temperature -PP was processed for 30 min at 60, 70, and 80 °C; (iii) assessment of the reproducibility of the scCO 2 extraction -PP matrix at 80 °C for 30 min was processed in triplicate.…”

“…Supercritical fluids, particularly supercritical CO 2 (scCO 2 ), have been studied for the extraction of plastics with analytical purposes; that is, targeting the analysis of the plastic composition, namely additives and oligomers. [17][18][19][20] As a technology to decontaminate POs for recycling, scCO 2 was applied for PP, 12,21 highdensity polyethylene, 22 linear low-density polyethylene (LLDPE), 12,23 and low-density polyethylene. 24 A theoretical model to analyse extraction yields considering the mechanisms of diffusion through the polymer matrix and the solubility in scCO 2 was developed.…”

The degree and source of plastic recyclates contamination with polycyclic aromatic hydrocarbons

“…To prevent cross-contamination, only glassware was used to conduct the extraction, treatment and analysis of samples. In order to analyse the PAH content in the plastic matrix, samples underwent extraction following the method reported by Alassali et al 26 Randall hot extraction was used as suggested by Geiss et al 20 The PAH content analysis was conducted on the extract aer applying a clean-up and drying steps (as explained below).…”

“…Finally, a solvent recovery step (evaporation step) was applied at 170 C, until the target volume of #20 mL was reached. 26,28 Aer the evaporation step, the reaction vessels were cooled down to room temperature. An internal standard solution was added to the solution to calculate the recovery.…”

“…The analysis of the extract was performed using a gas chromatograph HP 6890 coupled with a single ion monitoring mass selective detector HP 5973 from Agilent Technologies. 26 The used GC-column is HP-5MS, 30 m long, with 0.25 mm internal diameter. Aer the sample injection, the temperature was set at 60 C for 1 min, then it was increased at rate of 20 C min À1 until it reached 160 C. The temperature was further increased, at a rate of 10 C min À1 , to 325 C. A calibration step preceded the analysis.…”