Induction of styrene backbone cracking by functional group removal in cation exchange resins during thermal decomposition: Kinetic analysis and structural evolution

Abstract

Cation exchange resin (CER) is widely used in chemical production and nuclear power station. However, the thermal degradation and utilization of spent CERs present challenges. For safe and efficient thermal degradation treatment, kinetic analysis using non-isothermal thermogravimetry (TG) was conducted to investigate the oxidation process of CERs under air atmosphere. The study determined that the Avrami-Erofeev (m = 4, f(α) = 4(1-α)[-ln(1-α)]3/4) and Power law model (n = 1/3, f(α) = 3α2/3) were the most appropriate reactions models for the temperature ranges of 300–397.5 °C and 397.5–467.5 °C, respectively. Moreover, the destruction of the sulfonic functional group (-SO3H) and skeleton at different temperature stages were analyzed by FT-IR. The carbon and sulfur elements transformation in gas products and residues were analyzed by combining on-line mass spectrometry and infrared carbon-sulfur analysis. The results reveal that the degradation process of CERs can be divided into four stages: dehydration, functional group degradation, skeleton degradation, and residual carbon oxidation. Functional groups are used as active sites to form reaction cores. Then the skeleton is decomposed by the power law model, which provides a new research idea for the thermal decomposition of polymers. In addition, the study offers insights into advancing polymer heat treatment technologies and for safety evaluation.