Metal-Oxide-Doped Silica Nanoparticles for the Catalytic Glycolysis of Polyethylene Terephthalate

Abstract

Polyethylene terephthalate (PET) was depolymerized to monomer bis(2-hydroxyethyl) terephthalate (BHET) using excess ethylene glycol (EG) in the presence of metal oxides that were impregnated on different forms of silica support [silica nanoparticles (SNPs) or silica microparticles (SMPs)] as glycolysis catalysts. The reactions were carried out at 300 degrees C and 1.1 MPa at an EG-to-PET molar ratio of 11:1 and a catalyst-to-PET-weight ratio of 1.0% for 40-80 min. Among the four prepared catalysts (Mn3O4/SNPs, ZnO/SNPs, Mn3O4/SMPs, and ZnO/SMPs), the Mn3O4/SNPs nanocomposite had the highest monomer yield (> 90%). This high yield may be explained by the high surface area, amorphous and porous structure, and existence of numerous active sites on the nanocomposite catalyst. The BHET yield increased with time and reached the highest level where equilibrium was established between BHET and its dimer. The catalysts were characterized by their SEM, TEM, and BET surface areas, and via XRD, whereas the monomer BHET was characterized by HPLC and FT-IR. The glycolysis with the Mn3O4/SNPs nanocomposite as the glycolysis catalyst produced a maximum BHET in a short reaction time.

Recovery of Terephthalic Acid by employing magnetic nanoparticles as a solid support

“…All the mentioned catalysts such as alkalies, metal acetate, zeolites, ionic liquids and etc, in the PET glycolysis reactions required long reaction times and contributed low BHET and TPA yields. In order to resolve these drawbacks and improve reaction conditions Imran et al [14,15] used thermally stable and highly selective silica nanoparticle-supported metal (Mn, Zn, Ce) oxides as the catalysts for PET depolymerization. After that, Park et al [16] outstretch graphene oxide and manganese oxide as the catalysts for PET glycolysis.…”

Poly (ethylene terephthalate) recycling for high value added textiles

“…The glycolysis rate and BHET monomer yield are dependent on various reaction parameters such as temperature, PET/ethylene glycol ratio, and type and amount of catalysts. A number of studies are summarized in Table 3, detailing the optimum glycolysis conditions and reaction parameters obtained (Dulio et al 1995;Pingale et al 2010;Xi et al 2005;Troev et al 2003;Shukla and Kulkarni 2002;Shukla et al 2008;Imran et al 2011;Wang et al 2009;Yue et al 2011). …”

Titanate Nanotubes Modified With Zinc and Its Application in Post‐Consumer PET Depolymerization

“…Without the use of catalysts, the reaction is extremely slow, taking up to 9 h to reach conversions above 50% . Several catalysts are mentioned in literature, such as manganese, cobalt and zinc oxides, ionic liquids and silicon‐doped metal nanoparticles, but the most commonly used is zinc acetate, which presents good results of PET conversion and BHET yield . However, these examples may require high energy or high cost for the production of the catalysts.…”