Alkali Depolymerization of Poly(ethylene terephthalate) in a Quasi‐solid‐solid Kneading Reaction

Abstract

The alkaline depolymerization reaction of poly(ethylene terephthalate) (PET) under quasi-solvent-free conditions was investigated. This is a new approach for recycling PET waste to its monomer building blocks: terephthalic acid and ethylene glycol. The influence of base particle size, reaction temperature, and rotational speed of the employed laboratory kneader on terephthalic acid yield in the quasisolid-solid reaction was investigated. PET is depolymerized almost quantitatively in a reaction time of 5 min at moderate reaction temperatures, with intense mixing affecting the yield of terephthalic acid. The quality of the terephthalic acid monomer, assessed by color index measurements, indicated that the reaction temperature primarily influences the color index of the monomer. By balancing terephthalic acid yield versus color index, optimum reaction conditions were proposed.

Depolymerization of PET Fibers from Textile Blends and Recovery of Terephthalic Acid

“…As proposed by Biermann et al. [21], EG (15.0 g, 13.51 mL) is filled into the preheated mixing chamber before rapidly adding a mixture of sodium hydroxide peals (6.55 g) and textile sample (15 g) and closing the chamber with the pneumatic piston. Once the reagents are filled into the chamber, the measurement of the torque, rotational speed, and mass temperature are started.…”

“…Finally, Biermann et al. [21] described the alkaline hydrolysis of PET flakes using solid sodium hydroxide at different temperatures, followed by the recovery of TA from the resulting reaction mixture.…”

Monomer Recycling as Complementary Technology in a Circular Economy

“…However, the latter also offers the opportunity to apply established measures to reduce the specific energy consumption by utilizing the released heat of depolymerization reaction for the preheating of the reactants. The exothermic depolymerization reaction of PET with (solid) sodium hydroxide (NaOH) follows this approach 36, 41, 42. Additionally, one needs to consider that a proper comparison of economic and ecological effort for alternative technological pathways, such as mechanical or solvent‐based methods vs. chemical recycling, requires that all alternative technology routes are capable of delivering the same technical functionality or solution.…”

“…However, the latter also offers the opportunity to apply established measures to reduce the specific energy consumption by utilizing the released heat of depolymerization reaction for the preheating of the reactants. The exothermic depolymerization reaction of PET with (solid) sodium hydroxide (NaOH) follows this approach [36,41,42].…”

Mechanism and kinetics of enzymatic degradation of polyester microparticles using a shrinking particle–shrinking core model

“…Shrinking Particle (SPM) and Shrinking Core (SCM) models are widely used to describe transport phenomena in solid-fluid chemical reactions, [19][20][21][22][23][24][25] including polymer degradation. [26][27][28][29][30][31] These models by themselves can describe homogenous acid or base hydrolysis of polyethylene terephthalates, but cannot accurately describe the multi-step heterogenous enzymatic degradation of polymers. We postulated that a combined Shrinking Particle (SPM) -Shrinking Core (SCM) model which accounts for each step involved in polymer degradation would more accurately reflect the enzymatic degradation kinetics of polymer microparticles, compared with previously developed kinetic models.…”