Compositional Characterization of Pyrolysis Fuel Oil from Naphtha and Vacuum Gas Oil

Steam cracking of crude oil fractions gives rise to substantial amounts of a heavy liquid product referred to as pyrolysis fuel oil (PFO). To evaluate the potential use of PFO for production of value-added chemicals, a better understanding of the composition is needed. Therefore, two PFO’s derived from naphtha (N-PFO) and vacuum gas oil (V-PFO) were characterized using elemental analysis, SARA fractionation, nuclear magnetic resonance (NMR) spectroscopy, and comprehensive two-dimensional gas chromatography (GC × GC) coupled to a flame ionization detector (FID) and time-of-flight mass spectrometer (TOF-MS). Both samples are highly aromatic, with molar hydrogen-to-carbon (H/C) ratios lower than 1 and with significant content of compounds with solubility characteristics typical for asphaltenes and coke (i.e. <i>n</i>-hexane insolubles). The molar H/C ratio of V-PFO is lower than the one measured for N-PFO, as expected from the lower molar H/C ratio of the VGO. On the other hand, the content of <i>n</i>-hexane insolubles is lower in V-PFO compared to the one in N-PFO (i.e., 10.3 ± 0.2 wt % and 19.5 ± 0.5 wt %, respectively). This difference is attributed to the higher reaction temperature applied during naphtha steam cracking, which promotes the formation of poly aromatic cores and at the same time scission of aliphatic chains. The higher concentrations of purely aromatic molecules present in N-PFO is confirmed via NMR and GC × GC–FID/TOF-MS. The dominant chemical family in both samples are diaromatics, with a concentration of 28.6 ± 0.1 wt % and 27.8 ± 0.1 wt % for N-PFO and V-PFO, respectively. Therefore, extraction of valuable chemical industry precursors such as diaromatics and specifically naphthalene is considered as a potential valorization route. On the other hand, hydro-conversion is required to improve the quality of the PFO’s before exploiting them as a commercial fuel

Computational Fluid Dynamics-Assisted Process Intensification Study for Biomass Fast Pyrolysis in a Gas–Solid Vortex Reactor

The process intensification possibilities of a gas–solid vortex reactor have been studied for biomass fast pyrolysis using a combination of experiments (particle image velocimetry) and non-reactive and reactive three-dimensional computational fluid dynamics simulations. High centrifugal forces (greater than 30<i>g</i>) are obtainable, which allows for much higher slip velocities (>5 m s^–1) and more intense heat and mass transfer between phases, which could result in higher selectivities of, for example, bio-oil production. Additionally, the dense yet fluid nature of the bed allows for a relatively small pressure drop across the bed (∼10⁴ Pa). For the reactive simulations, bio-oil yields of up to 70 wt % are achieved, which is higher than reported in conventional fluidized beds across the literature. Convective heat transfer coefficients between gas and solid in the range of 600–700 W m^–2 K^–1 are observed, significantly higher than those obtained in competitive reactor technologies. This is partly explained by reducing undesirable gas–char contact times as a result of preferred segregation of unwanted char particles toward the exhaust. Experimentally, systematic char entrainment under simultaneous biomass–char operation suggested possible process intensification and a so-called “self-cleaning” tendency of vortex reactors

Characterization and Comparison of Fast Pyrolysis Bio-oils from Pinewood, Rapeseed Cake, and Wheat Straw Using ¹³C NMR and Comprehensive GC × GC

Fast pyrolysis bio-oils are feasible energy carriers and a potential source of chemicals. Detailed characterization of bio-oils is essential to further develop its potential use. In this study, quantitative ¹³C nuclear magnetic resonance (¹³C NMR) combined with comprehensive two-dimensional gas chromatography (GC × GC) was used to characterize fast pyrolysis bio-oils originated from pinewood, wheat straw, and rapeseed cake. The combination of both techniques provided new information on the chemical composition of bio-oils for further upgrading. ¹³C NMR analysis indicated that pinewood-based bio-oil contained mostly methoxy/hydroxyl (≈30%) and carbohydrate (≈27%) carbons; wheat straw bio-oil showed to have high amount of alkyl (≈35%) and aromatic (≈30%) carbons, while rapeseed cake-based bio-oil had great portions of alkyl carbons (≈82%). More than 200 compounds were identified and quantified using GC × GC coupled to a flame ionization detector (FID) and a time of flight mass spectrometer (TOF-MS). Nonaromatics were the most abundant and comprised about 50% of the total mass of compounds identified and quantified via GC × GC. In addition, this analytical approach allowed the quantification of high value-added phenolic compounds, as well as of low molecular weight carboxylic acids and aldehydes, which exacerbate the unstable and corrosive character of the bio-oil