The purpose of this study was to identify and characterize compounds that are refractory to the hydrodenitrogenation process.

Ion mobility coupled with mass spectrometry was proven to be an efficient way to characterize complex mixtures such as petroleum samples. However, the identification of isomeric species is difficult owing to the molecular complexity of petroleum and no availability of standard molecules. This paper proposes a new simple indicator to estimate the isomeric content of highly complex mixtures. This indicator is based on the full width at half maximum (FWHM) of the extracted ion mobility peak measured in millisecond or square angstrom that is corrected for instrumental factors such as ion diffusion. This value can be easily obtained without precisely identifying the number of isomeric species under the ion mobility peaks. Considering the Boduszynski model, the ion mobility profile for a particular elemental composition is expected to be a continuum of various isomeric species. The drift time-dependent fragmentation profile was studied and confirmed this hypothesis, a continuous evolution of the fragmentation profile showing that the larger alkyl chain species were detected at higher drift time values. This new indicator was proven to be a fast and efficient method to compare vacuum gas oils for which no difference was found using other analytical techniques. Graphical Abstract ᅟ.

Plastic wastes cause well-known harmful effects for the environment and contribute to the depletion of landfill sites. Pyrolysis oil produced from plastic waste materials is considered as an important source to produce monomers, fuel, and chemicals that both circumvent some of the environmental concerns associated with nonrenewable fossil resources and alleviate waste disposal concerns. In order to improve conversion and valorization processes, an advanced molecular description is essential. Such as petroleum crude oils, plastic pyrolysis oils are complex mixtures composed of thousands of chemical species covering a wide range of masses and polarities. Molecular characterizations require the use of high-resolution instruments such as Fourier transform ion cyclotron resonance mass spectrometers. In this study, we report the characterization of plastic pyrolysis oil by the main atmospheric pressure ionization: electrospray ionization (ESI) in positive and negative modes (±), atmospheric pressure photoionization (APPI) in positive mode (+), and atmospheric pressure chemical ionization (APCI) in positive mode (+). A large predominance of hydrocarbon compounds was observed in APPI (+) and APCI (+). Moreover, the use of both sources highlighted different types of molecules such as paraffins, diolefins, and more particularly triolefins, which have not yet been reported. Basic and neutral nitrogen-containing species (N1 and N2 classes) were highlighted by ESI (+) and ESI (−), respectively. Oxygen-containing species O1–O4 were identified principally by ESI (−) but also in APPI (+) and APCI (+) and attributed as carboxylic acid and alcohol functional species. The same functionality of oxygen is founded in N x O y compounds observed in ESI (+) and ESI (−).

This study aims to identify and characterize compounds refractory to hydrodenitrogenation (HDN). The efficiency of a vacuum hydrocracking unit in removing nitrogen-containing compounds to produce a low-nitrogen-content effluent is examined. Molecular, structural, and compositional knowledge is a requisite for the optimization development of the hydrotreatment step processing unit because changes in the chemical composition of petroleum have a direct impact on physical properties and, thus, overall vacuum gas oil (VGO) upgrading processes. Two samples, a VGO and a effluent obtained after the HDN process containing 10 wppm of N, were analyzed by negative-mode electrospray ionization ultra-high-resolution tandem mass spectrometry (ESI–FT-ICR) and ion mobility spectrometry–mass spectrometry (IMS–MS). FT-ICR mass spectrometry provides ultrahigh mass resolving power to separate and characterize compounds in the highly complex petroleum samples. The fragments generated by MS/MS of selected N1 refractory compounds were used for structural elucidation. Species with a double bond equivalent of 10 and 13, which proved to be highly refractory, were analyzed in more detail. On the other hand, the TWIMS–TOF MS measurements enabled the entire ion mobility analysis of refractory species to hydrotreatment processes. The MS/MS spectra revealed a specific pattern allowing for the identification of the molecular nucleus. Furthermore, it allowed for the understanding of the fragmentation pathways: loss of alkyl chains in the first step and opening and rearrangement of the nuclei after that. Ion mobility separation, in combination with MS/MS, allowed for the identification of the different conformations and the revealment of the typical fragments of these molecular nuclei. In particular, the ion mobility peak width indicates isomeric diversity and collision cross section (CCS) determination and provides structural information. The IMS analysis of the identified refractory precursor shows the evolution of its compounds at different processing stages and indicates that some families and structural conformations of N1 species are more resistant to hydrotreatment. Isomers presenting low CCS values in negative mode are more resistant to HDN processes. The combination of TWIMS–TOF MS and ultra-high-resolution mass spectrometry opens exciting and promising prospects for structural determination of complex mixtures, in particular, problematic compounds in petroleum refining processes.