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Alkaline Hydroxide Depolymerization Technology for Efficient PET Recycling and Byproduct Management - | Virginia Tech Intellectual Properties (VTIP)

Alkaline Hydroxide Depolymerization Technology for Efficient PET Recycling and Byproduct Management

THE CHALLENGE:

Poly(ethylene terephthalate) (PET) is extensively used in packaging, textiles, and various consumer goods. The recycling of PET reduces the consumption of materials to produce the virgin PET and processes recycling PET have the potential to provide economic value. Supply chains and the economic incentive to collect and recycle waste PET reduces the consumption of fossil fuel derived feedstock and reduces the rate of mismanaged PET waste contributing to the growing global plastic waste problem. Chemical recycling methods, such as hydrolysis producing TPA from PET, aid this effort, by breaking down PET into its original monomers that can be conveniently purified, enabling the production of high-quality recycled materials from low-purity PET waste, drastically expands the scope of recoverable PET waste.

Current PET chemical recycling technologies face challenges that hinder their effectiveness and efficiency. Traditional hydrolysis processes often suffer from low efficiency in separating and recovering key components such as ethylene glycol (EG) and terephthalic acid (TPA), resulting in significant material losses and increased operational costs. Most hydrolysis units use alkaline hydroxides and managing the salt byproduct is energy-intensive and generates environmental waste, increasing the overall ecological footprint. High energy consumption and water usage in these processes further limit their viability, while impurity handling remains a persistent issue, affecting the quality of the reclaimed monomers. These limitations highlight the need for more efficient, energy-saving, and environmentally friendly recycling methods to overcome the shortcomings of existing PET depolymerization techniques.

OUR SOLUTION:

A novel system for depolymerizing poly(ethylene terephthalate) (PET) employs a concentrated alkaline hydroxide solution, optionally enhanced with ethylene glycol (EG), at temperatures ranging from 120 to 240°C. The process efficiently breaks down PET into disodium terephthalate and EG through a reaction carried out under elevated pressures. Following the reaction, the mixture undergoes neutralization, cooling, and separation to isolate solid disodium terephthalate from liquid EG and impurities. The EG is purified using advanced distillation methods, while the terephthalic acid (TPA) is recovered through crystallization. Additionally, the system incorporates a heat-integrated multi-effect evaporation process to concentrate salt byproducts, significantly reducing energy consumption and enabling the regeneration of acids and bases for reuse.

This technology distinguishes itself through its comprehensive and energy-efficient approach to PET recycling. By integrating innovative separation techniques such as dividing-wall columns and multi-effect evaporation, it maximizes the recovery of valuable products while minimizing waste and energy usage. The early separation of EG and effective impurity management streamline the process, reducing water vaporization and simplifying downstream purification steps. Furthermore, the flexible distillation configurations and the ability to regenerate acids and bases through electrolysis enhance the system's sustainability and economic viability. These differentiating features collectively address key challenges in chemical recycling, offering a more sustainable and efficient solution for PET depolymerization.

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