Methanolysis

Reaction Mechanism

The reaction takes place in a closed reactor where the textile waste is exposed to superheated methanol. This solvent dissolves the polyester and hydrolyzes the ester linkages, converting the polymer into dimethyl terephthalate and ethylene glycol. These monomers are soluble in the hot solvent, which allows them to be separated from insoluble contaminants such as cotton, elastane, or metal zippers.

The reaction requires high temperatures and pressures to achieve complete depolymerization, making it highly effective at handling mixed textile inputs that are unsuitable for mechanical recycling.

Monomer Recovery

Once the reaction is complete, the mixture is cooled to crystallize the dimethyl terephthalate, which is then separated by filtration. Ethylene glycol is recovered from the remaining liquid through distillation. These purified monomers are then fed back into the polymer synthesis line to produce new polyester fibers of identical quality to virgin resin.

This closed-loop recycling pathway prevents downcycling and reduces the demand for petrochemical feedstocks.

Process Limitation

The process requires a high capital investment for specialized high-pressure equipment and consumes a significant amount of energy. The use of volatile organic solvents also necessitates robust safety systems to prevent leaks and explosions. It is less economical for clean, unblended polyester waste where mechanical recycling is more cost-effective.

The method is primarily used for complex, dyed textile waste.