Chemical Recycling Of Polycarbonate Research Articles

Depolymerization of Waste Polycarbonates to Value-Added Products.

Additive free aminolysis method developed for the depolymerization/upcycling of polycarbonates. We report here chemical recycling of polycarbonate under ambient conditions to get its monomer bisphenol A, monoaminocarbamate and biscarbamates in 1 : 2 : 1 ratio respectively. By employing the secondary amine as the aminating reagent, facilitates the depolymerization to work under additive/catalyst free conditions. The developed method deals with depolymerization of waste polycarbonates and works even with late-stage amine derivatives such as amoxapine and desloratadine which are drugs molecules known to treat neurotic disorders and allergies respectively. The reaction can be scaled up and works with similar efficacy which depicts the efficiency of the depolymerization of wasteend-of-life polycarbonate plastic waste. The biscarbamate and bisphenol-A was further subjected for the post functionalization to obtain amides and phenol in good yields.

The catalytic activity of metal–organic frameworks (MOFs) and post-synthetic modified MOF towards depolymerisation of polycarbonate

Chemical recycling of polycarbonate (PC) recovers valuable chemicals like monomers but often requires catalysts for mild reaction conditions and high conversion rates. This study explores the use of metal–organic frameworks (MOFs) as catalysts for PC methanolysis. We investigated the catalytic activity of amine-containing MOFs, specifically ZIF-8, MAF-6, and UiO-66-NH2, which have basic active sites favouring PC depolymerisation. MOFs were characterised using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and Brunauer–Emmett–Teller (BET) analysis. We examined the effects of temperature, catalyst content, and time on PC recycling efficiency and also conducted post-synthetic modification (PSM) of MOF-5 to assess its catalytic performance in PC depolymerisation. Methanolysis yielded bisphenol A (BPA) and dimethyl carbonate (DMC), with conversion rates confirmed by nuclear magnetic resonance (NMR). MOF catalysts significantly enhanced conversion rates compared to reactions without catalysts, with ZIF-8 and MAF-6 achieving nearly 100% PC conversion. PSM of MOF-5 with ethylenediamine (ED) led to increased PC conversion. Additionally, the MOF-based catalysts were recovered and reused for up to three cycles.

Chemical recycling of polycarbonate and polyester without solvent and catalyst: mechanochemical methanolysis

Mechanochemical methanolysis of polyester and polycarbonate eliminated catalyst and solvent.

Environmentally benign chemical recycling of polycarbonate wastes: comparison of micro- and nano-TiO2 solid support efficiencies

Abstract Polycarbonate (PC) wastes, including optical discs (CDs) and digital optical discs (DVDs), were chemically recycled into valuable materials such as 4,4′-(propane-2,2-diyl)diphenol (BPA) and etherified derivatives of BPA using sodium hydroxide (NaOH) as the alkali metal catalyst and nanostructured titanium dioxide (nano-TiO2) and microstructured titanium dioxide (micro-TiO2) as the solid supports in the binary green system consisting of water and 2,2′-oxydi(ethan-1-ol) (DEG) under conventional heating method, and data were compared. In this study, the effects of various parameters, such as solvent composition, concentration of NaOH, and solid support, were studied on the reaction progress. In these reactions, the importance of water as the green solvent was investigated in achieving pure BPA as the valuable material. When used with 20% aqueous DEG (pbw), a pure BPA can be obtained at 70% yield in the presence of nano-TiO2 and micro-TiO2 as the solid supports. According to the results, the use of nano-TiO2 in comparison with micro-TiO2 accelerates the chemical recycling of PC wastes. The nano-TiO2 catalyst recovery shows that the recovered solid support is applicable for four cycles. The obtained products were characterized using spectroscopic methods, namely, 1H NMR, 13C NMR, and Fourier transform infrared spectroscopy as well as gas chromatography-mass spectrometry.

Chemical recycling of polycarbonate in dilute aqueous ammonia solution under hydrothermal conditions

Polycarbonate (PC) pellets were subjected to dilute aqueous ammonia solution under hydrothermal conditions in a semi-batch reactor at temperatures ranging from 433 to 463 K and at a pressure of 10 MPa. The PC pellets were almost completely converted to bisphenol A (BPA). During an initial certain period, referred to as an induction time, neither BPA nor total organic carbon in solution were detected, and the BPA yield increased with time. The monomer yield was well represented by a surface reaction model, two-thirds-order reaction with respect to the mass of unreacted PC. The overall rate constant of the reaction in 0.6 mol/kg aqueous ammonia solution at 433 K was about 15 times greater than that in 0.6 mol/kg NaOH solution. The rate constant at 433 K was proportional to the ammonia or NaOH concentration. There was a correlation between the induction time and temperature, as well as the ammonia or NaOH concentration. By carrying out the reaction in aqueous mixtures of (NH4)2SO4 and NaOH at various concentrations of NaOH, ammonia was confirmed not to function as an alkaline reagent, but as a nucleophile reagent.

Chemical recycling of polycarbonate in high pressure high temperature steam at 573 K

Polycarbonate (PC) could be completely decomposed into its monomer, bisphenol A (BPA) with high pressure (not atmospheric pressure) high temperature steam (573 K) in 5 min reaction time. The maximum yield of BPA was about 80 mol% based on the starting PC. PC decomposition at 573 K in liquid water phase near the saturated pressure for the comparison. For 30 min in reaction in liquid water at 573 K residual PC still remained and the BPA yield was about 50% as maximum.

Supercritical carbon dioxide assisted extraction from the polycarbonate depolymerization mixture

Chemical recycling of polycarbonate by depolymerization with phenol produces a mixture of phenol, diphenyl carbonate (DPC) and bisphenol A (BPA). We simulate a semibatch extraction process to separate these components. A supercritical carbon dioxide stream flows into an autoclave containing the depolymerization products. The liquid–vapor two-phase system is considered to be in equilibrium during the isobaric isothermal process as the vapor phase is withdrawn sufficiently slowly, maintaining the autoclave temperature and pressure. The VLE behavior is described by the Peng–Robinson equation of state (PR-EOS), using the interaction parameters of the involved six binary systems as determined in our previous work. PR-EOS is coupled with the molar balance equations to calculate the phase fractions and compositions in the investigated systems. The predictions of the simulations are compared with the experimental measurements during extractions from binary systems phenol–CO 2 and DPC–CO 2, ternary systems phenol–DPC–CO 2 and phenol–BPA–CO 2, and quaternary system phenol–DPC–BPA–CO 2. We find a reasonable agreement between our predictions and experimental results.

Chemical recycling of polycarbonate in a semi-continuous lab-plant. A green route with methanol and methanol–water mixtures

Alkali-catalysed depolymerization of polycarbonate (PC) wastes by alcoholysis in supercritical or near critical conditions has been studied in order to recover the essential monomer bisphenol A (BPA) and dimethyl carbonate (DMC) as a valuable by-product. This work aims to study the continuous process and possible scale-up for decomposition of both commercial PC and PC plastic wastes using methanol as solvent/reagent and NaOH as alkali catalyst. Total depolymerization of PC has been achieved working at a temperature range of 75–180 °C and pressures from 2 to 25 MPa. The influence of operation conditions on product yield, selectivity and reaction rate has been studied, including temperature, pressure, methanol/cosolvent ratio and catalyst concentration. BPA yields of 80–90% (kg product/kg PC) were achieved with a further crystallization and separation of the final product, resulting in BPA pure crystals (99.9%). DMC yield reached 35% (kg DMC/kg PC) and was proved to be strongly dependent on pressure and methanol/H2O ratio. Non desired by-product yield was negligible when pure methanol was used as solvent and selectivity decreased with increasing methanol/H2O ratio.