Simple but tricky: Investigations of terephthalic acid purity obtained from mixed PET waste

Cosimbescu, Lelia; Merkel, Daniel R.; Darsell, Jens T.; Petrossian, Gayaneh

doi:10.1021/acs.iecr.1c02604

Simple but tricky: Investigations of terephthalic acid purity obtained from mixed PET waste

Journal Article · 08 September 2021 · Industrial and Engineering Chemistry Research

DOI:https://doi.org/10.1021/acs.iecr.1c02604· OSTI ID:1827277

Cosimbescu, Lelia ^[1]; Merkel, Daniel R. ^[1]; Darsell, Jens T. ^[1]; Petrossian, Gayaneh ^[1]

BATTELLE (PACIFIC NW LAB)

In this study, we report for the first time, the basic depolymerization of mixed waste-polyethylene terephthalate (PET) by hydrolysis and subsequent terephthalic acid monomer recovery at high purity using benign reaction conditions. Several conditions were tested for depolymerization such as PET chips size, concentration of aqueous sodium hydroxide (20 or 30%), organic co-solvent (ethylene glycol or ethanol), temperature at which the reaction was run and duration of the heating. More importantly, several batches of PET were utilized as starting materials including a commercial PET, chopped PET obtained from clean bottles whose caps and labels were removed and the purity of the product from each condition was evaluated via nuclear magnetic resonance (1HNMR and 13CNMR), differential scanning calorimetry (DSC) and powder Xray diffraction (XRD). Unsurprisingly, the conversion of PET is dependent on the particle size varying from 100% conversion for fine powder to 73% conversion for (300 µm, mesh 6 – 20 or mesh 14-20). Ethanol appears to be more efficient as a co-solvent than ethylene glycol, with higher PET depolymerization conversions (94% versus 75-80%), shorter reaction times (2h versus 6h) and lower temperatures (80 °C versus 110 °C). The terephthalic acid (TPA) recovered appeared to have only subtle differences among the batches, most notably a pink color when the reaction was run in ethanol/base. The DSC of the compounds produced in ethylene glycol water appear to display a melting point (280-288 °C) while the samples prepared in ethanol as well as a commercial sample did not. Overall, the purity of the various TPA batches is comparable, and similar to commercial TPA, demonstrating the utility of the method to depolymerize realistic waste streams. The method is simple, demonstrated on multigram scale (15-30g) and allows for the complete removal of waste other than PET unaffected by alkaline conditions.

Research Organization:: Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)

Sponsoring Organization:: USDOE

DOE Contract Number:: AC05-76RL01830

OSTI ID:: 1827277

Report Number(s):: PNNL-SA-162009

Journal Information:: Industrial and Engineering Chemistry Research, Vol. 60, Issue 35

Country of Publication:: United States

Language:: English

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Simple but tricky: Investigations of terephthalic acid purity obtained from mixed PET waste

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Simple but tricky: Investigations of terephthalic acid purity obtained from mixed PET waste

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