Development of heterogeneous catalyst by ionically bonding macrocyclic Zr–Zr complex to montmorillonite clay for depolymerization of polypropylene

The homonuclear macrocyclic Zr–Zr complex was synthesized by reacting 2,6-diformyl-4-methylphenol with 1,2-phenylenediamine and zirconium oxychloride. The heterogeneous complex catalyst was prepared by ionically bonding it on zirconium pillared montmorillonite. The heterogeneous complex catalyst was shown to be stable at the depolymerizing temperature of polypropylene and the reaction product was a waxy solid alone without forming liquid and gaseous material. The FTIR analysis of this solid was shown to have exactly the same IR of the polypropylene indicating that the depolymerization occurs predominately by first formation of polymer radicals by random scission of the polypropylene chain. The chain radical, thus generated, combines with the catalyst to give a radical cation complex and the movement of this along its chain by bond shift reaction produces low molecular waxy product. Experiments have shown that the molecular weight of this waxy product depends upon the reaction temperature as well as the residence time and all its physical properties (melting point and solubility) can be matched with those of the paraffin wax.

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