Robust cleaning mechanism permanently detaches hydrocarbon species from silicate surfaces by amphiphiles

This paper studies the role of 1-methyl-2-pyrrolidone (NMP) additive to enhance the desorption power of toluene to detach the bitumen from siliceous surfaces. The latter desorption is critical for successful recycling of old asphalt roads where aged bitumen is expected to come off the stones and blend with virgin bitumen used in construction of new roads. Toluene, a documented neurotoxin, has been commonly used to separate aged bitumen from siliceous surface; increasing toluene desorption power and dosage efficiency allows reduced application rate leading to significant environmental and economic benefits. Here, we used the laboratory experiments and computational modeling to understand mechanism of desorption afforded by a hybrid solvent made from blends of toluene and NMP. Our results showed the hybrid solvent interacts with both bitumen and siliceous surfaces; this in turn allows the solvent not only dissolve the asphaltene agglomerates in aged bitumen, but also supersede bitumen compounds for adsorption to silica. Our modeling revealed the hybrid solvent creates an amphiphile that is both able to attach to the asphaltene molecules and interact with polar water molecules, thus making a monolithic cluster that is easy to detach from the siliceous surface under hydraulic pressure. This was further evidenced in a high reduction in the shear-thinning rate of bitumen-silica matrix when hybrid solvent was introduced; for instance, in the case of severely aged bitumen bonded to silica, shear-thinning rate reduced by 60% when hybrid solvent was introduced. Study outcomes provide insights into the merits of using hybrid solvent for desorption as well as its working mechanism. Such insights set a path for future efforts in pavement recycling and promote resource conservation and sustainable development.