Utilization of Asphaltenes as Inexpensive and Abundant Precursors of Novel Carbon-Based Nanomaterials
Vargas, Francisco M.
Doctor of Philosophy
Asphaltene deposition causes many difficulties and imposes challenging flow assurance problems for the oil industry throughout the globe. Asphaltenes are the heaviest and most polarizable fraction of crude oil. They have a high tendency to destabilize and deposit in the wellbore, oil reservoir formations, transportation pipelines, surface facilities, and heat exchangers. The significant difficulties associated with asphaltene deposition can cost oil companies millions of dollars each year. This problem will almost certainly become worse as the oil industry is moving towards production from deep-water reservoirs and implementation of the enhanced oil recovery by miscible gas injections. Despite the tremendous efforts and studies undertaken over the past decades, a full understanding of asphaltene behavior and its inherent physical and chemical characteristics has not been achieved. More importantly, the successful utilization of this problematic but high potential material has not been extensively explored. In this dissertation, a series of comprehensive experimental methods were presented to better understand and predict the occurrence and the scale of asphaltene deposition. As a part of these methods, a novel NIR spectroscopy technique was developed to accurately monitor the kinetics of asphaltene precipitation and aggregation in crude oil systems. The effects of different variables, such as temperature, the driving force towards precipitation, and the addition of commercial chemical dispersant were evaluated. Unlike currently available techniques, this new method is fast and simple: it requires less than 2 ml of sample for each measurement, with the capability of performing experiments at high temperatures. The amount of precipitated asphaltene can be easily estimated by using a newly developed method called “Absorbance Ratio”, in which the light transmittance values from the spectroscopy experiments are readily translated into precipitated asphaltene amounts. These simple and quick lab-scale experiments facilitate establishing modeling tools to scale the asphaltene precipitation and aggregation parameters to real-field, high-pressure, and high-temperature conditions. Furthermore, the potential production of carbon-based nanoparticles from asphaltenes was investigated in this work. To achieve this goal, first, a physical spray drying method was developed, in which fully dissolved asphaltene solutions were sprayed on a hot surface in order to evaporate the solvent quickly. Once the solvent evaporated, individual asphaltene nanoparticles with a high association tendency could be separated and deposited on the substrate. Scanning electron microscopy (SEM) results showed that asphaltene nanospheres as small as 20 nm in diameter were generated. The impact of different variables, such as temperature, type of the hot surface, and the asphaltene solution concentration on the size and morphology of the particles, were also discussed. Additionally, a new method of chemical oxidation by a concentrated nitric acid, followed by heat treatment was applied to asphaltenes. This oxidation reaction resulted in water-soluble and photoluminescent carbon-based nanoparticles. In this new method, the nitric acid used for oxidation could be recycled and reused as well. Moreover, the utilization of asphaltenes in two different areas of electrocatalysis and energy storage was pursued. To achieve these ideas, asphaltene samples were converted into nitrogen-doped graphene-like nanosheets (N-GNS) and highly porous activated carbons. These novel nanomaterials with exceptional properties, such as high surface area, good conductivity, high porosity, and ion mobility, were tested as catalysts for hydrogen evolution reactions and as electrodes for supercapacitors. The N-GNS sample, due to its high electrochemical active surface area (ECSA), presence of a mixture of porous structures, uniform layers, and effective doping of nitrogen atoms within the carbon matrix, was considered as an excellent candidate for the hydrogen evolution reaction (HER). The results illustrated a significant catalytic performance from the N-GNS sample when used as a catalyst in hydrogen evolution reactions. In addition, a novel method was developed to chemically transform asphaltenes into highly porous activated carbon with an interconnected honeycomb-like structure. The obtained activated carbon illustrated an impressive, ultra-high surface area of 3868 m2/g. The results of the study indicate that this new technique not only allowed a greater yield of asphaltene-derived activated porous carbon output as compared to the conventional activation method, but also created a mixture of microporous and mesoporous networks, which demonstrated favorable properties for supercapacitor applications. Finally, the hydrophobicity of asphaltenes was utilized in modifying commercially available melamine sponges to transform them into hydrophobic and oleophilic absorbent materials. The asphaltene-coated sponges showed excellent selectivity towards organic solvents and repelled water as soon as they came into contact with the liquids. In addition, the robust and flexible physical structure of sponges would enable them to be used multiple times. Overall, it was shown that the asphaltene-coated sponges, due to their impressive selectivity, high absorption capacity and good recyclability, could be promising candidates for large scale removal of oil spills and other organic liquids from water. Ultimately, the findings presented in this dissertation suggest that what is currently considered an undesirable fraction of crude oil, which has a tendency to deposit in wellbores, pipelines, and downstream facilities, can be repurposed into a desirable material with remarkable properties for nanoparticles fabrication, electrocatalysis, energy storage, oil spill removal, and other applications.