Polyester Glycolysis: Chemical Textile-to-Textile Recycling

Reaction Conditions

Temperature 200°C

Catalyst loading (Zn-acetate) 0.50 wt%

Ethylene glycol : PET ratio 4.0 : 1

Reactor Control

Live Readouts

Ester-bond conversion p

0.0%

Number-avg M_n

18,500 g/mol

BHET monomer yield

0.0%

Intact PET chain Free BHET monomer

How it works

Chemical (feedstock) recycling breaks polyester back into monomer instead of just re-melting shredded fiber. In glycolysis, excess ethylene glycol (EG) attacks the ester bonds of PET chains, catalyzed by a metal salt, converting long chains into bis(2-hydroxyethyl) terephthalate (BHET) — a virgin-quality monomer that can be re-polymerized into new fiber with none of the strength loss that mechanical (shred-and-respin) recycling causes each cycle.

–[OC-C6H4-CO-O-CH2CH2-O]n– + n HOCH2CH2OH
        (PET chain)              (ethylene glycol)
   →  n HOCH2CH2-OOC-C6H4-COO-CH2CH2OH
              (BHET monomer)

dp/dt = k·(1 − p)                 first-order in remaining ester bonds
k = A·exp(−Ea/RT)·f(cat)·g(EG:PET)   Arrhenius + reagent terms
Xn = 1 / (1 − p)                   Carothers degree-of-polymerization
Mn = Xn · M0,  M0 ≈ 192 g/mol       PET repeat-unit molar mass

Temperature — sets the Arrhenius term exp(−Ea/RT); every +10°C roughly doubles the rate constant k.
Catalyst loading — zinc-acetate (or similar) coordinates the carbonyl and lowers the effective activation barrier; more catalyst speeds bond cleavage.
EG : PET ratio — excess glycol drives the equilibrium toward full monomerization (Le Chatelier); low ratios stall conversion before completion.
The reactor view shows each PET chain as 10 linked units; as ester bonds cleave they detach into free, faster-drifting BHET monomer (gold) suspended in the glycol.

Real-world relevance: BHET-route glycolysis is the basis of several commercial textile-to-textile polyester recycling processes — it recovers monomer purity independent of how many times the fiber has already been mechanically recycled, at the cost of running a hot, catalyzed chemical reactor instead of a shredder.

Reaction time: 0.0 min k = 0.000 min⁻¹

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