Efficient synthesis of p-phenylenediamine from PET waste via energy-efficient depolymerization and green Hofmann rearrangement

Abstract

The continuous use of post-consumer polyethylene terephthalate (PET) waste remains a major challenge due to its environmental properties and the high energy requirements of traditional recycling methods. In this study, an energy-efficient and environmentally friendly route for the synthesis of p-phenylenediamine (PPD) from secondary PET waste was developed. Terephthalic acid was obtained from PET waste under simple conditions and then terephthalamide was obtained through a catalytic high-pressure ammonolysis process. The main part of the process involved the Hofmann rearrangement reaction, for which an environmentally friendly chlorinating agent was selected based on research.

Various hypochlorite and dichloroisocyanurate salts were analyzed based on their active chlorine equivalents, reaction efficiency, safety, and waste profile. Among the tested reagents, sodium dichloroisocyanurate chlorinated amides to a high degree under alkaline conditions, reduced hazardous waste, and produced harmless by-products. As a result, p-phenylenediamine was obtained in 84% yield. The structure and properties of the synthesized product were confirmed by IR, NMR, TG, and DTA analyses.

This research work demonstrates a green and efficient method for converting PET waste into valuable aromatic diamines. However, it also highlights the importance of choosing an environmentally friendly reagent for the Hofmann rearrangement reaction.

Keywords: Polyethylene terephthalate (PET), ammonilysis, glycerin, sodium urea, dichloroisocyanurate salt, reactor autoclave, amination, terephthalamide.