Polyester Recycling via Hydrolytic Depolymerization in Green Solvents

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Solution Overview

Problem

Current polyester recycling methods, particularly chemical recycling, face issues with high temperatures using environmentally harmful solvents, leading to racemization and decomposition of monomers, which affects the properties of the new polymer formed.

Innovation Solution

A method involving hydrolytic depolymerization of polyester in a water-alcohol solution at moderate temperatures using 'green' solvents like ethanol, methanol, or 1-propanol, which reduces contaminants and maintains the chemical and physical properties of the new polymer.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If high temperature chemical recycling is used to depolymerize polyester, then the depolymerization efficiency is improved, but racemization and decomposition of monomers occur which adversely affects the chemical and physical properties of the new polymer

Engineering Contradiction:

Improvedepolymerization efficiencyVSAvoidchemical and physical properties of new polymer

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent changes the temperature parameter from high temperature (above melting point) to moderate temperature (below melting point) and changes the solvent parameter from harmful solvents (toluene, dichloromethane, chloroform) to environmentally benign solvents (water, alcohols). This parameter change resolves the contradiction by achieving effective depolymerization at lower temperatures that prevent racemization and decomposition, thus maintaining the chemical and physical properties of the new polymer while still achieving good depolymerization efficiency.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces expensive and harmful solvents (toluene, dichloromethane, chloroform) with cheap and environmentally benign solvents (water, alcohols like ethanol and methanol). This substitution not only reduces environmental harm but also eliminates the need for complex solvent removal and purification steps, thereby preventing monomer decomposition and preserving polymer properties while maintaining productivity.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

2Speed

If high temperature chemical recycling is used to depolymerize polyester, then the depolymerization rate is increased, but environmentally harmful solvents are required which cause contamination and environmental damage

Engineering Contradiction:

Improvedepolymerization rateVSAvoidenvironmental harm from solvents

Core Design Contradiction:

SpeedVSObject-affected harmful factors

Solution Approach 1:

The patent changes the solvent parameter from harmful organic solvents to environmentally benign solvents (water, alcohols) and adjusts the temperature parameter to moderate levels. This resolves the contradiction because the new solvent system achieves effective depolymerization rates at lower temperatures, eliminating environmental harm from solvent use and disposal while maintaining acceptable depolymerization speed.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent converts the traditionally harmful role of high temperature and harmful solvents into a beneficial process by using moderate temperature and environmentally benign solvents. The water and alcohol solvents, which are naturally occurring and environmentally friendly, effectively facilitate depolymerization at lower temperatures, turning what would be a harmful process into an environmentally beneficial recycling method.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Device complexity

If mechanical recycling is used to process polyester, then the process complexity is reduced, but the physical properties of the polymer deteriorate due to mechanical shearing and high processing temperatures

Engineering Contradiction:

Improveprocess complexityVSAvoidphysical properties of polymer

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent replaces the mechanical recycling system (which uses mechanical shearing and high temperature processing) with a chemical recycling system using moderate temperature hydrolysis in water-alcohol solutions. This substitution resolves the contradiction by achieving polymer breakdown and regeneration without the damaging mechanical and thermal stresses that deteriorate physical properties, while the process remains relatively simple and straightforward.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This method effectively recycles polyester into its monomer form using environmentally friendly solvents at lower temperatures, preserving the properties of the original polymer and minimizing environmental impact.

Implementation Method 1

hydrolytically depolymerizing the polyester while the polyester is submerged in the solution

Methodology Applied

Scientific EffectHydrolysis: Hydrolysis

Data Source

PatentUS10259768B2Method of recycling a polyester

Publication Date: 2019.04.16 BOARD OF TRUSTEES OPERATING MICHIGAN STATE UNIV

AI summary

A method of recycling a polyester includes the steps of providing the polyester, preparing a solution containing water and an alcohol, submerging the polyester in the solution, and hydrolytically depolymerizing the polyester while the polyester is submerged in the solution.