Thermal Pyrolysis of Polystyrene Aided by a Nitroxide End-Functionality. Experiments and Modeling

Abstract

The thermal pyrolysis of polystyrene (PS) is gaining importance as the social pressure for achieving a circular economy is growing; moreover, the recovery of styrene monomer in such a process is especially relevant. In this study, a simple thermal pyrolysis process in the temperature range of 390–450 °C is developed. A working hypothesis is that by using a nitroxide-end functionalized PS (PS-T or dormant polymer), the initiation process for the production of monomer (unzipping) during the PS pyrolysis could be enhanced due to the tendency of the PS-T to activate at the nitroxide end. Two types of PS were used in this work, the first one was synthesized by free-radical polymerization (FRP-dead polymer) and the second by nitroxide-mediated polymerization (NMP) using three levels of nitroxide to initiator ratio: 1.3, 1.1, and 0.9. Analysis of the recovered products of the pyrolysis by gas-mass spectroscopy shows that the yield of styrene increases from ∼33% in the case of dead polymer to ∼38.5% for PS-T. A kinetic and mathematical model for the pyrolysis of dead and dormant polymer is proposed and solved by the method of moments. After a parameter sensitivity study and data fitting, the model is capable of explaining the main experimental trends observed.

Use of waste plastics for the preparation of adhesives for wood bonding

“…Šernek, M., Turičnik, V., Repič, R., & Šega, B.: Use of waste plastics for the preparation of adhesives for wood bonding Leta 2017 je bila letna proizvodnja plastike na globalni ravni 230 milijonov ton, v letu 2020 pa naj bi se povečala na kar 400 milijonov ton (Tawfik et al, 2017). Glede na naraščajoči družbeni pritisk na skrb za okolje in sedanje trende v smeri krožnega gospodarstva, bi bila najboljša možnost ravnanja s plastičnimi odpadki njihova predelava v določene kemijske spojine (monomere) z zahtevano čistostjo in kakovostjo, ki bi se ponovno uporabila kot surovina pri isti polimerizaciji ali v drugih postopkih (Ordaz-Quintero et al, 2020).…”

Thermal Pyrolysis of Polystyrene Aided by a Nitroxide End-Functionality Improved Process and Modeling of the Full Molecular Weight Distribution

“…One hypothesis that has already been proved right by our previous studies [ 1 ] is that the introduction of a nitroxide moiety at the end of the polystyrene chains increases the probability of initiating depolymerization reactions on these labile structures when subjected to a heat treatment, more specifically at the oxygen-carbon bond between the nitroxide and the polymeric chain-end at temperatures that are slightly higher than the ceiling temperature to promote the depropagation reaction, maximizing the production of styrene monomer. This occurs in addition to the initial rupture at other parts of the structure that also leads to depropagation in these conditions.…”

“…Amongst the variety of potential solutions for waste management that include recycling, landfill disposal and combustion, pyrolysis is the one technique that allows the recovery of high-value products usually in the form of complex mixtures. This alternative has acquired significant industrial and academic interest in recent years as a possible and promising disposal option; it does not require dumping waste in landfills, toxic gas production is minimized, and valuable products are recovered, including fuels and monomers that can be later used in other processes or in the synthesis of new polymers [ 1 , 2 , 3 ].…”

“…In this work, we report a significantly improved process for the thermal pyrolysis of PS based on a process previously published by our group [ 1 ]. In the present process, the yields of styrene monomer recovered increase from about 28–38% to about 58–75%.…”

“…In the present process, the yields of styrene monomer recovered increase from about 28–38% to about 58–75%. Moreover, a more detailed and enhanced mathematical model for the description of the process is described and discussed, based on a previous model developed in our group [ 1 ]. In the new model, assumptions used in our previous model are removed and are proved to generate serious deviations from what the new assumption-free model predicts.…”