Selective oxidation of quinoline in an emulsified system using carbon nanotubes derived from LDPE as catalysts: pH effect
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abstract
Nitrogenated compounds are naturally found in petroleum-based products. Upon their
combustion, hazardous gases (NOx) are generated, leading to environmental and health
issues. To overcome the downsides related to nitrogen oxides,1 catalytic oxidative
denitrogenation (ODN) with H2O2 is currently seen as a suitable alternative to traditional
hydrodenitrogenation. In this work, the catalysts for ODN consisted of carbon nanotubes
synthesized from low-density polyethylene as a carbon source by chemical vapor deposition
(850 °C, 1 h). A simulated fuel was prepared by dissolving quinoline (QN) in 2,2,4-
trimethylpentane ([N]0 = 50 ppm, [QN]0 = 460 ppm). ODN was carried out in an emulsified
system (80:20 2,2,4-trimethylpentane:water, Vtotal = 20 mL) at 50 °C, 4 h, Ccatalyst = 2.5 g L-
1 and VH2O2, 30 wt.% = 0.9 mL (5.5× the stoichiometric ratio for QN mineralization). The
emulsion was formed by sonication for 15 min. The obtained results are summarized in Fig.
1. ODN carried out at the initial pH (pH0) 3.5 resulted in 74% of QN removal from the oil
phase, which is far higher when compared to only 15% removal occurring by mass
transference (test conducted with an aqueous phase free of H2O2 and catalyst). At pH0 = 6.5,
QN removal from the oil phase decreased drastically to 33%, indicating that a lower pH
favor QN removal.
This work was financially supported by project “PLASTIC_TO_FUEL&MAT – Upcycling Waste
Plastics into Fuel and Carbon Nanomaterials” (PTDC/EQU-EQU/31439/2017), by Base-UIDB/50020/2020 and
Programmatic-UIDP/50020/2020 funding of LSRE-LCM - funded by national funds through FCT/MCTES (PIDDAC), and
CIMO (UIDB/00690/2020) through FEDER under Program PT2020. Fernanda F. Roman acknowledges the Foundation
for Science and Technology (FCT) and the European Social Fund (FSE) for the individual research grant with reference
SFRH/BD/143224/2019
