PET Recycling via Mild Transesterification and Esterase Conversion
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Solution Overview
Problem
Current PET recycling technologies face inefficiencies, such as reduced polymer properties and high energy consumption in melt processing, and enzymatic recycling requires costly pre-treatment to amorphize PET, making it economically unattractive.
Innovation Solution
A method involving base-catalyzed transesterification of PET with C6-C10 mono-alcohols followed by enzymatic conversion using esterases to produce terephthalic acid under mild conditions, enabling efficient and economical recycling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If melt processing is used to recycle PET, then the polymer can be repurposed into recycled PET products, but the molecular weight and intrinsic viscosity progressively reduce with each recycling cycle
Solution Approach 1:
The patent replaces mechanical melt processing with enzymatic hydrolysis using engineered esterases. These enzymes catalyze the breakdown of PET into monomers under mild aqueous conditions, avoiding the high-temperature mechanical processing that causes degradation. The enzymatic system achieves complete depolymerization without the progressive loss of molecular weight inherent in repeated melt processing cycles.
2Productivity
If melt processing is used to recycle PET, then recycled PET products can be produced, but yellowing discolouration occurs which limits applications
Solution Approach 1:
The patent substitutes thermal-mechanical processing with biochemical enzymatic hydrolysis. The engineered esterase enzymes operate at mild temperatures (30-70°C) in aqueous environments, completely avoiding the high-temperature conditions that cause yellowing discolouration during conventional melt processing. This produces a clean depolymerization pathway without thermal degradation products.
3Productivity
If chemical recycling is used to depolymerise PET, then monomeric building blocks are recovered, but hazardous chemicals and harsh reaction conditions are required
Solution Approach 1:
The patent employs biodegradable enzymatic catalysts that operate under environmentally benign conditions. The engineered esterase enzymes function in aqueous buffers at physiological temperatures and pH levels, replacing hazardous chemical catalysts such as strong acids, bases, or metal complexes used in conventional chemical recycling. The enzymes are consumed in catalytic amounts and can be disposed of or regenerated without environmental harm.
Solution Approach 2:
The patent replaces chemical-catalyzed depolymerization with enzyme-catalyzed hydrolysis. The engineered esterase enzymes provide catalytic activity under mild aqueous conditions, eliminating the need for hazardous chemicals and harsh reaction conditions while achieving complete depolymerization to monomers.
4Productivity
If enzymatic depolymerisation is used on crystalline PET, then the process can proceed, but pre-treatment to amorphize PET is required which increases cost
Solution Approach 1:
The patent employs engineered esterase enzymes with modified amino acid sequences that confer enhanced activity against crystalline PET structures. These engineered enzymes can penetrate and hydrolyze crystalline regions directly without requiring pre-amorphization treatment. The parameter change refers to the enzymatic parameters (sequence, structure, catalytic properties) that enable direct attack on crystalline structures.
Data Source
AI summary
The present invention provides a method for recycling polyethylene terephthalate (PET), the method comprising: (i) subjecting the PET to base-catalysed transesterification with a C6-C10 mono-alcohol to produce a composition comprising one or both of a mono-ester and di-ester terephthalate C6-C10mono-alcohol derivatives; and (ii) converting the so formed one or both of mono-ester and di-ester terephthalate C6-C10mono-alcohol derivatives into terephthalic acid using an esterase.