Exploiting Synergistic Effects of Intermolecular Interactions To Synthesize Hybrid Rejuvenators To Revitalize Aged Asphalt
F Pahlavan and A Samieadel and SG Deng and E Fini, ACS SUSTAINABLE CHEMISTRY & ENGINEERING, 7, 15514-15525 (2019).
This paper examines the merits of using a hybrid bio-oil derived from algae and swine manure to rejuvenate aged bitumen by restoring the bitumen properties which are degraded during oxidative aging. Nitrogen- containing compounds have been found to be effective for decreasing the size of molecular agglomerates which are intensified during aging provided they adequately penetrate into the oxidized asphaltene agglomerations. The enhancement effect is mainly attributed to their electronic structures, including the polar head and hydrocarbon tail which can interact with asphaltene with CH-pi interactions. In this study, we hypothesize that combining bio-oils extracted from high- protein algae and swine manure can help balance the heteromolecule content, which in turn leads to synthesizing an effective hybrid biorejuvenator to revitalize aged bitumen. Computational analysis was used to determine the specific rejuvenation mechanisms between the hybrid biorejuvenator and an oxidized asphaltene dimer found in the aged bitumen. Our analysis via density functional theory showed that the biorejuvenation process involves a two-step mechanism: First, the biorejuvenators interact with polar sites of the asphaltene nanoaggregates in aged bitumen to increase intersheet spacing referred to as the lock-and-key mechanism. Second, the biorejuvenators intercalate into the intersheet spacing within the stacks of asphaltene to induce deagglomeration. Accordingly, the hybrid biorejuvenator was designed to have molecules targeting either of the two mechanisms. Therefore, blending molecules of the algae-based bio-oil, which are mainly effective in the first step with those of swine-manure-based bio- oil, which are effective in the second step led to a biorejuvenator with significantly higher efficiency than either of them individually. This was attributed to heteroaromatic motifs and nitrogen carrying compounds with a hydrocarbon tail, which contribute to opening (lock-and-key) and intercalation mechanisms, respectively. The enhanced efficiency of the hybrid biorejuvenator was further verified via a series of laboratory experiments as well as molecular dynamics simulations; it was found that the hybrid biorejuvenator is more effective to increase crossover modulus and decrease size of asphaltene nanoaggregates of aged bitumen than the swine-manure-based bio-oil and the algae based bio-oil alone. Regardless of the bitumen origin, the hybrid biorejuvenator was able to promote deagglomeration of oxidized asphaltene and revitalize aged bitumen.
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