Insights into the depolymerization of polyethylene terephthalate in methanol

Abstract

With concern to sustainable development, it is necessary to establish a recycling process of polyethylene terephthalate (PET). Methanolysis of PET is promising for chemical recovery of PET and the products are mainly dimethyl terephthalate (DMT) and ethylene glycol (EG), but the conditions of state‐of‐art depolymerization are severe. Here, we synthesized ionic liquid [HO3S‐(CH2)3‐NEt3]Cl‐[ZnCl2]0.67 with Brönsted–Lewis di‐acid and used it to efficiently catalyze the methanolysis of PET (mmethanol:mPET about 4) at milder temperature of 195°C with yield of DMT about 78.4%. Reaction kinetics was studied and the result indicated the depolymerization of PET was a first‐order kinetic reaction with the apparent activation energy of DMT formation about 17.63 kJ mol−1. Random sampling experiment was also conducted and the results showd that DMT was the product of deep depolymerization of PET and two methanol molecules were needed to form DMT and EG in the depolymerization process. This study provides an efficient method to the recycling use of PET and wais significant to waste recovery and green environment.

Development of Eco-Friendly and Sustainable PET Glycolysis Using Sodium Alkoxides as Catalysts

“…These signals are attributed to the BHET monomer, confirming that the main product of PET glycolysis with both catalysts (EtONa and MeONa), with both substrates (white and colored PET), and after multiple recycling runs is the monomer BHET. Furthermore, 13 C NMR of EG after recycling run R2 was also performed and is given in Figure 6S showing that NMR spectra after initial and recycling run R2 are similar, thereby conforming the filtrate after multiple glycolysis runs still constitute EG. The 13 C NMR results are also validated by HPLC and the chromatogram shown in Figure 7S indicates that the BHET monomer is the main product of PET glycolysis.…”

“…Furthermore, GR1 results show that both filtrates from colored PET waste were successfully recycled to get PET conversion up to 95%. The BHET crystals obtained under various conditions were subjected to 13 C NMR and signals at δ = 61, 67, 130, 134, and 166 ppm can be seen in Figure 5S. These signals are attributed to the BHET monomer, confirming that the main product of PET glycolysis with both catalysts (EtONa and MeONa), with both substrates (white and colored PET), and after multiple recycling runs is the monomer BHET.…”

“…Chemical recycling is a potential approach to managing PET waste, wherein post-consumer polymers are broken down into monomers or other useful products. Reported methods of the chemical recycling of PET waste usually involve aminolysis, ammonolysis, hydrolysis, , glycolysis, and methanolysis. , The glycolysis method has attracted significant attention for PET waste management due to mild reaction conditions, the use of low-volatility solvents, and the possibility of continuous operation . Many companies have commercialized this process .…”

“…Thus, the potential of BHET precipitation without the need for water, subsequent reuse of EG, and catalyst tolerance in mixed PET waste provide valuable insights in developing more sustainable approaches for PET glycolysis to meet the future demands of waste recycling.The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acssuschemeng.3c01872. Substrate preparation for glycolysis; different susbtrates used in the present study; PXRD measurements of BHET obtained under various operating conditions; DSC scan of produced BHET;13 C NMR spectrum of produced BHET under various glycolysis conditions;13 C NMR spectrum of filterate containing EG after initial and recycling run 2; HPLC chromatogram of BHET obtained with white PET waste after multiple glycolysis runs; HPLC chromatogram of BHET obtained with green PET waste with EtONa (G1a) and MeONa (G2a); predicted vs experimental run; desirability function of optimum solution 1; desirability of optimum solution 2; optimum conversion for desirability entry 1; optimum conversion for desirability entry 2; ICP measurements; parameters in HPLC analysis; experimental layout and output responses based on the Box−Behnken design; fit summary of the tested models for PET conversion X; ANOVA for response surface quadratic model for PET conversion X; and list of possible solutions after DoE optimization (PDF)…”

Ionic Liquid‐Assisted Depolymerization of Condensation Polymers: A Review

“…Additionally, they concluded that the ILs could be reused at least six to eight times without compromising the conversion rate [93] . Imidazolium‐based ILs have received the most extensive research of all the ILs for PET depolymerization as shown in Table 2 [94–121] . It is generally true that ILs containing metal ions are usually more catalytically efficient than their metal‐free counterparts; however, the existence of metal ions significantly reduces the purity of depolymerized products to a great extent.…”