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. Nitrogencontaining 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−π 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 nitrogencarrying 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 algaebased 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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This study incorporates computational and laboratory experiments to determine specific interaction mechanisms between conjugated structures (interrupted and continuous conjugates) and selected polyaromatics hydrocarbons (PAH) stacks such as those found in oxidized asphaltene molecules. The theoretical results obtained by quantum-mechanical calculations and molecular dynamics simulations show that both continuous and interrupted conjugates are effective to weaken the π-intersheet forces and decrease the size of PAH nanoaggregates, with interrupted conjugates being more efficient than continuous conjugates to exfoliate PAH stacks. Owing to their limited partial entrance into the PAH stacks, interrupted conjugates are not trapped inside the PAH interlayer, and can easily detach from the stacks. This allows an interrupted conjugate not to be consumed in interaction with one PAH stack, making the interrupted conjugate available to affect many other stacks in the matrix. The higher exfoliation capacity of the interrupted aromatic conjugates is also evidenced in the results of our experiments based on UV−vis and rheometry analyses. This is reflected in a higher reduction in the polydispersity index and a higher increase in both the crossover frequency and crossover modulus of aged bitumen (containing stacks of large PAH referred to as asphaltene nanoaggregates) when it is doped with an interrupted conjugate (fluoranthene) compared to when it is doped with a continuous conjugate (pyrene). The study results contribute to the body of knowledge by providing an in-depth understanding of how variation in the π-electron distribution of conjugated structures affects their efficacy to exfoliated self-assembled stacked structures of polyaromatic hydrocarbons such as asphaltenes.

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