Parallel-process characterization and apparent kinetic analysis of short-term thermal aging of soybean oil at 150 ℃ under different copper morphologies

Abstract

This study quantifies morphology-dependent short-term thermal aging of soybean oil at 150 ℃ (0–96 h) in four systems (Blank, Cu, CuO, and Cu₂O) by jointly tracking gas-phase cracking signatures and liquid-phase molecular-weight evolution. The experimental campaign evaluated the time-dependent accumulation of typical dissolved gases (H₂, CH₄, C₂H₆, and C₂H₄), with cumulative C₂H₆ selected as the representative cracking descriptor, and characterized liquid-phase structural growth by gel permeation chromatography using the increment of the high-molecular-weight tail area (Da > 2000) relative to 0 h as the polymerization/structural-growth descriptor. For the modeling phase, both descriptors were parameterized using a unified Hyperbolic saturation accumulation model, X(t) = at/(1 + Kt), enabling direct, morphology-to-morphology comparison of the apparent amplitude (a) and time-scale (K) parameters over the finite short-term window. The fitted parameters reveal distinct copper-morphology effects on cracking versus tail-growth behaviors, including systematic differences in cumulative levels and characteristic time scales across Blank/Cu/CuO/Cu₂O. An apparent cracking–polymerization coupling coefficient (η) was further derived to benchmark the relative dominance of gas formation versus tail growth under each morphology. ATR-FTIR and ICP measurements provide supporting evidence for concurrent functional-group evolution and copper migration/dissolution, consistent with copper-mediated modification of the reaction network. Overall, the results establish a compact, descriptor-based apparent kinetic benchmarking scheme that enables consistent comparison of parallel cracking and structural-growth processes in soybean-oil insulating liquids under different copper morphologies.