Acid value reduction of waste edible oil via two-step catalysis for effective asphalt rejuvenation

This study addresses the poor rejuvenation efficiency of waste edible oil (WEO) with high acid value (AV) by developing a two-step catalytic modification method. The process involves acid-catalyzed esterification followed by base-catalyzed transesterification. The chemical characteristics of WEO before and after modification were systematically characterized using gel permeation chromatography, gas chromatography-mass spectrometry, Fourier-transform infrared spectroscopy, and nuclear magnetic resonance. The rejuvenation potential of modified WEO was then evaluated through comprehensive performance tests, including penetration, softening point, temperature sweep, frequency sweep, and bending beam rheometer measurements. Finally, comparative spectroscopic analysis of different binders was performed to elucidate the rejuvenation mechanism. The results showed that the optimum conditions were a methanol-to-WEO ratio of 8:1, and a concentrated sulfuric acid dosage of 0.75 wt%, at 52 °C for 1.5 h; followed by a methanol-to-oil ratio of 9:1, 1 wt% potassium hydroxide, at 55 °C for 1 h. The process reduced AV from 2.06 to 0.16 mg KOH/g, achieving >91.77 % fatty acid methyl ester conversion. Comprehensive characterization confirmed the chemical transformation. The modified WEO effectively restored the rheological properties and chemical structure of aged asphalt compared to WEO. The rejuvenation mechanism was identified as primarily physical blending. Overall, this method provides an effective solution for recycling high-AV WEO in asphalt pavement rehabilitation.