Mechanocatalytic Oxidative Cracking of Poly(ethylene) Via a Heterogeneous Fenton Process

Abstract

In this work, mechanocatalytic oxidative cracking is used to overcome the chemical inertness of poly(ethylene) (PE) and the difficulties associated with processing this solid feedstock. An Fe 2 O 3 -based Fenton system is applied to introduce oxygen-based functional groups to the PE backbone with hydrogen peroxide as the oxidant. Once an oxygen-based functional group is introduced, the polymer chain can be cleaved to achieve cracking effectivity, with only CO, CO 2 , O 2 , and H 2 O as byproducts. The resulting fragments can be used as intermediates to produce fuels and sustainable chemicals.

Kinetic Phenomena in Mechanochemical Depolymerization of Poly(styrene)

“…Thus, by adding a chemical catalyst powder to the reactor, styrene production may be enhanced during milling due to the increased surface interactions between PS and the catalyst particles. Several candidate materials were milled with PS90 to gauge their catalytic ability, including the three main metal components of 316-grade stainless steel: Fe, Cr, and Ni metals, as well as several inorganic materials that have appeared in the mechanochemistry or depolymerization literature in other contexts: piezoelectric barium titanate BaTiO 3 , solid acid boric acid (BA), and iron­(III) oxide Fe 2 O 3 . Holding other parameters constant, monomer yields for PS90 milled with these additives are shown in Figure a.…”

“…Although it is demonstrably feasible to break polyolefin bonds by ball milling, to the best of our knowledge, only in 2021, ball milling was used intentionally to depolymerize a polyolefin, when Balema et al detected styrene in low yield by milling PS. Ball-mill depolymerization of the structurally related poly­(α-methylstyrene) (PMS) as well as oxidative cracking of poly­(ethylene) inside a ball mill have also been reported.…”

Modeling Mechanochemical Depolymerization of PET in Ball-Mill Reactors Using DEM Simulations

“…One promising alternative is the depolymerization of polymers in the solid state via mechanically-induced reactions. − Mechanochemical reactions are typically performed in ball mills, in which contacts and collisions between grinding surfaces (balls and reactor wall) supply the energy required to chemically transform the (usually particulate) solid reactants caught between these surfaces. ,− Mechanochemistry has been successfully demonstrated on a laboratory scale for the production of lignocellulosic biomass, , cellulose, − ammonia − and lignin. − Particularly for poly(ethylene terephthalate) (PET), Štrukil and Tricker et al recently demonstrated its complete depolymerization to monomers inside ball mills. Moreover, mechanochemical routes have recently been explored for the depolymerization of various polymers such as polystyrene (PS), , polyethylene (PE), and poly(α-methylstyrene) (PMS) and in the dechlorination of polyvinyl chloride (PVC). , In addition to the ability to efficiently process solid reactants, ball milling is a highly scalable industrial process being utilized in a wide variety of grinding applications, from minerals and cement, to chemicals and pharmaceuticals. − Despite these advantages, mechanochemical reactions are often seen and modeled as “black-boxes”, which hinders the fundamental understanding of mechanically induced reactions . In attempts to model mechanochemical reactions, semiempirical models have been proposed across various branches of mechanochemistry. ,,,, However, these models are often limited by extrapolation issues, which restrict their utility in exploring conditions such as reactor geometry or grinding media material that would lead to optimal performance.…”