Poisoning Effects of Water and Dyes on the [Bmim][BF4] Catalysis of Poly(Ethylene Terephthalate) (PET) Depolymerization under Supercritical Ethanol

Abstract

Supercritical ethanolysis (scEtOH) is a method that allows the production of monomers, e.g., diethyl terephthalate (DET), from Polyethylene terephthalate PET chemical recycling. The use of the ionic liquids (ILs) such as 1-n-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF4]) as a catalyst has advantages in such processes by enhancing the yield at reduced times, as shown in previous work from our lab. However, the effects of water and dyes (from the coloured PET-bottles) regarding those advantages have not been investigated. Here, a study of the effects of water and dyes on IL-catalysis is provided. Results showed that the yield related to DET formation was 98% when anhydrous ethanol was employed, but decreased to 30% (or less) when water was present in the reaction even in low amounts. Furthermore, the DET-formation yield also decreased to 66% or to 21% if 2-aminoanthraquinone or zinc phthalocyanine were present, respectively, even in anhydrous conditions. Poisoning effect on the IL-catalysis was observed in both cases. Thus, these data are relevant for expanding the study of ILs as catalysts in this and other reaction systems.

Solubilization and Upgrading of High Polyethylene Terephthalate Loadings in a Low‐Costing Bifunctional Ionic Liquid

“…[20] As ar esult,t he performance of some ILs in polymer treatment can be influenced or inhibited by the moisture content. [21] For instance, using 1-butyl-3-methylimidazoliumt etrafluoroborate ([C 4 C 1 Im][BF 4 ]) as the solvent, the yield of diethyl terephthalate (DET) decreased from 98 to 30 %( or less) if water was presenti nt he reaction mixture even in low amounts( e.g.,1wt %H 2 Oi ne thanol). [21b] In the presentw ork, Figure 1d epictst hat the solubilizationo fP ET in [Ch] 3 4 ], we employed fluorescencem icroscopy,F ourier-transform infrared (FTIR) spectroscopy,n uclear magnetic resonance (NMR) spectroscopy, and gel-permeation chromatography (GPC).…”

Directing Depolymerization of PET with Subcritical and Supercritical Ethanol to Different Monomers through Changes in Operation Conditions

“…Pressure decrease from 40 to 20 bar at 225 °C was detrimental since an almost complete degradation was only achieved after 180 min of reaction, which implied 90 additional minutes to complete the degradation regarding the 40 bar/225 °C treatment. This delay may be resolved by the use of suitable catalysts. − Accelerating subcritical ethanolysis kinetics by catalysis would be another strategy to explore an efficient upscaling of this technique, but the comprehensive use of catalysts entails checking several aspects (efficiency, selectivity, reuse) that are out of the scope of this work. Decreasing the reaction temperature even further below the critical point, 20 bar/200 °C, yielded remarkable efficiency losses: 66.9% PET was degraded after 90 min and further degradation was not observed for longer treatments.…”

“…De Castro et al first explored depolymerization of PET in supercritical ethanol at 255 °C, initial pressure of 115 or 165 bar, and reaction times between 5.0 and 6.5 h. 11,12 They found that PET was completely depolymerized and the main products obtained were diethyl terephthalate (DET), EG, and BHET. Later efforts by the same research group have been focused on the search for catalysts such as ionic liquids 13,14 or metal oxides 15 that lead to faster degradation kinetics under the same temperature and pressure conditions. The current work aims at expanding the available knowledge about this safe and efficient depolymerization process of PET by broadening the assayed ranges of temperature, pressure, reaction time, and weight ratio of PET to ethanol (% wt) in the absence of any catalyst.…”

“…De Castro et al first explored depolymerization of PET in supercritical ethanol at 255 °C, initial pressure of 115 or 165 bar, and reaction times between 5.0 and 6.5 h. , They found that PET was completely depolymerized and the main products obtained were diethyl terephthalate (DET), EG, and BHET. Later efforts by the same research group have been focused on the search for catalysts such as ionic liquids , or metal oxides that lead to faster degradation kinetics under the same temperature and pressure conditions.…”

Insights into the depolymerization of polyethylene terephthalate in methanol

“…Due to the high density and high kinetic energy of supercritical condition above the critical one, the reaction rate under supercritical condition is higher than that under critical one. However, the experimental conditions (such as the reaction temperature 255°C and pressure 11.65 MPa) are always stringent 22 and difficult to be industrially applied. Therefore, an environmentally friendly depolymerization method with simple and moderate reaction conditions is more desirable.…”