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Upgrading Asphaltenes by Oil Droplets Striking a Charged TiO-Immobilized Paper Surface 2
Yin-Hung Lai, Zhenpeng Zhou, Basheer Chanbasha, and Richard N. Zare Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b02338 • Publication Date (Web): 12 Oct 2017 Downloaded from http://pubs.acs.org on October 13, 2017
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Oil microdroplets are sprayed in air at room temperature onto untreated TiO2 nanoparticles coated on filter paper to which we apply an electrical potential to initiate oil degradation. The biphasic (hydrophobic/hydrophilic) reaction occurs at the interface of microdroplets and the charged TiO2 surface on the microsecond time scale. Extracted sample is analyzed using laser desorption laser ionization mass spectrometry. The fragmentation yield is increased by cycling the process. 67x67mm (72 x 72 DPI)
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Upgrading Asphaltenes by Oil Droplets Striking a Charged TiO2-Immobilized Paper Surface Yin-Hung Lai1‡, Zhenpeng Zhou1‡, Chanbasha Basheer1,2, and Richard N. Zare1* 1
Department of Chemistry, Stanford University, Stanford, California 94305, United States
2
Department of Chemistry, King Fahd University of Petroleum and Minerals, Dhahran 31261,
Saudi Arabia
ABSTRACT
The conversion of heavy oil fractions into lighter ones is highly essential for meeting the growing demand for fuels in continuous depletion of oil reserves and for environmental remediation. We demonstrate an oil degradation approach where oil microdroplets are sprayed in air at room temperature onto untreated TiO2 nanoparticles coated on filter paper to which we apply an electrical potential. Two model polycyclic aromatic hydrocarbons as well as a crude oil sample show degradation on the microsecond time scale. Heterogeneous catalysis of a biphasic (organic/ aqueous) reaction occurs at the interface of microdroplets and the charged TiO2 surface. The fragmentation yield is increased by cycling the process. The relative fragmentation yield of a model compound (rubrene) increased from 16.9 % in the first cycle to 32.6 % in the third cycle. This convenient and efficient method suggests possible future industrial applications.
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1. INTRODUCTION The main goal of oil upgrading is to break down heavy fractions of crude oil (asphaltenes) into smaller molecules for the development of alternative fuels and to facilitate oil recovery.1-4 Development of alternative fuels is a promising strategy to overcome continuous depletion of conventional oil reserves and to meet the growing demand for fuels.5-6 Furthermore, oil degradation is also useful for environmental remediation, such as an accidental discharge of oils to water resources, which might pose severe threats to ecological systems.7-8 However, because of rigid structures, high density, and high viscosity, methods used to break down asphaltenes, such as hydro- and thermal cracking4 and supercritical fluid processing,9 are required to act at elevated temperatures and pressures. The development of nanoparticles as catalysts to improve the degradation efficiency of heavy oil has received much interest.1,
4, 10-12
Photocatalytic degradation utilizing titanium dioxide
(TiO2) is one of the most promising methods because of its low cost and environmental friendliness.13 Extensive efforts have been devoted to improving the photocatalytic efficiency of TiO2, such as modifications to reduce the band gap,14-15 increase reactivity,16 and nanofabrication to enlarge the surface-to-volume ratio.17 Degradation of asphaltenes still only takes place in strongly acidic or basic environments in reactors, even with the presence of TiO2 plus intense UV irradation.10, 18 Moreover, photocatalytic degradation normally takes minutes to days.19-22 These factors lead to difficulty in scaling up for industrial use. A low-cost, rapid, and environmentally friendly alternative is urgently needed for oil upgrading. We report a new method to expedite the degradation rate of asphaltenes by spraying oil microdroplets onto the charged surface of a filter paper coated with TiO2 nanoparticles under ambient conditions. In our system, no light is needed; instead, we apply voltage to initiate the
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heterogeneously catalytic degradation process. The timescale of degradation is in microseconds. We utilized a spray source to generate oil microdroplets. This method allows us to conduct degradation reactions on or near the surface of the microdroplets where acceleration of reaction rates has been reported.23-25 Sample extracted from the paper is collected with a glass tube and analyzed using our laboratory-built laser desorption/ laser ionization mass spectrometer (L2MS).26 L2MS, which minimizes the interference from ion-molecule interaction, enables us to probe unknown structures in a complex system. Compared to conventional chromatography, L2MS is capable of resolving individual molecule species for an extended mass range in a single experiment with very little sample handling.27 Two model compounds, rubrene and hematoporphyrin, which are commonly found in asphaltenes, are studied. We propose an electric-field-induced mechanism for oil degradation process on the charged surface of a TiO2immobilized filter paper involving the generation of OH radicals. The fragmentation yield is increased by cycling the process, which means to retreat the oil sample that has contacted the charged TiO2-coated paper. Finally, proof of concept was shown for this method by degrading a crude oil sample without dilution. 2. MATERIALS AND METHODS 2.1. Reagents. Rubrene, hematoporphyrin, and TiO2 (anatase,
