Catalytic Transformation of PET and CO₂ into High‐Value Chemicals

Abstract

Polyethylene terephthalate (PET) and CO2, two chemical wastes that urgently need to be transformed in the environment, are converted simultaneously in a one‐pot catalytic process through the synergistic coupling of three reactions: CO2 hydrogenation, PET methanolysis and dimethyl terephthalate (DMT) hydrogenation. More interestingly, the chemical equilibria of both reactions were shifted forward due to a revealed dual‐promotion effect, leading to significantly enhanced PET depolymerization. The overall methanol yield from CO2 hydrogenation exceeded the original thermodynamic equilibrium limit since the methanol was in situ consumed in the PET methanolysis. The degradation of PET by a stoichiometric ratio of methanol was significantly enhanced because the primary product, DMT was hydrogenated to dimethyl cyclohexanedicarboxylate (DMCD) or p‐xylene (PX). This synergistic catalytic process provides an effective way to simultaneously recycle two wastes, polyesters and CO2, for producing high‐value chemicals.

Depolymerization within a Circular Plastics System

“…Li et al demonstrated a transformation that utilized PET, CO 2 , and H 2 to produce a dicarboxylated cyclohexane derivative (Figure 6). 157 Tanaka et al instead captured EG with dimethyl carbonate, which led to good yields of DMT (72−91%) and ethylene carbonate (69−86%) at 65 °C. 158 Mild methanolysis conditions have been reported with respectable yields of DMT (71−86%) attainable at 70 °C using MeOK, K 2 CO 3 , or TBD as catalyst.…”

“…Li et al demonstrated a transformation that utilized PET, CO 2 , and H 2 to produce a dicarboxylated cyclohexane derivative (Figure ). Tanaka et al. instead captured EG with dimethyl carbonate, which led to good yields of DMT (72–91%) and ethylene carbonate (69–86%) at 65 °C .…”

“…(b) Conversion plots that demonstrate the driving impact that PET consumption has on methanol yield and CO 2 consumption. (a) Adapted and (b) reproduced with permission from ref . Copyright 2021 John Wiley & Sons.…”

Artificial photosynthesis bringing new vigor into plastic wastes

“…As an example of the selective conversion of PLA into alanine, 75 commercial PLA was directly utilized as a feedstock for alanine generation with the aid of ammonium hydroxide that served as the agent for both depolymerization and nitrogen source for PLA upgrading. In another case, the conversion of primary PET into value‐added chemicals (e.g., dimethyl cyclohexanedicarboxylates [DMCD]) was developed 135 . During this process, the PET depolymerization was investigated in the presence of methanol, and the obtained product (i.e., dimethyl terephthalate) could be utilized as feedstock for hydrogenation, generating high‐value chemicals (i.e., DMCD).…”

“…In another case, the conversion of primary PET into value-added chemicals (e.g., dimethyl cyclohexanedicarboxylates [DMCD]) was developed. 135 During this process, the PET depolymerization was investigated in the presence of methanol, and the obtained product (i.e., dimethyl terephthalate) could be utilized as feedstock for hydrogenation, generating high-value chemicals (i.e., DMCD). The forementioned studies have paved a new avenue for plastic upgrading, in which plastic wastes could be converted into valuable substances.…”