Dichloromethane solvation pre-treatment coupled with NaCl-mediated “zero acid mist” hydrolysis for harmless treatment of waste chloroaluminate ionic liquid

In the C₄ alkylation process, waste chloroaluminate ionic liquid (CIL) catalysts pose significant environmental risks due to their strong acidity, toxicity, and extreme reactivity. Upon contact with water, these waste CILs undergo violent, self-accelerating hydrolysis reactions that release large amounts of heat and hydrochloric acid mist, leading to severe secondary pollution. To address this issue, this study proposes a novel “zero acid mist” hydrolysis treatment strategy that ensures the safe and environmentally friendly disposal of waste CILs under optimized reaction conditions. The results demonstrate that pretreating the waste CIL with dichloromethane (DCM) at a 1:1 volume ratio, followed by reaction with a 15 wt% NaCl aqueous solution (3:40 mass ratio) at 5 °C for 30 min, effectively suppresses reaction intensity and minimizes acid mist emissions. Enthalpy analysis confirms that these optimized conditions significantly reduce the reaction heat. The subsequent neutralization of the acidic hydrolysate with a 3 wt% NaOH solution (25,57 volume ratio) achieves pH = 7, yielding high recovery rates of 98.96 % for Al 3+ and 95.37 % for Cu 2+ . After calcination, the recovered solids were confirmed to be copper–aluminate spinel (CuAl₂O₄). Cyclic experiments further determined the optimal reuse frequency of the neutralized solution. The mechanistic investigation revealed that the combined DCM solvation and NaCl-mediated common-ion effect underpin the “zero acid mist” phenomenon. This process not only mitigates secondary pollution but also enables efficient metal recovery and solution recycling, establishing a closed-loop treatment system consistent with circular economy principles. The proposed method offers a simple, safe, and sustainable solution for the harmless treatment and resource utilization of waste CILs in the petrochemical industry.