Combined Comprehensive Two-Dimensional Gas Chromatography Analysis of Polyaromatic Hydrocarbons/Polyaromatic Sulfur-Containing Hydrocarbons (PAH/PASH) in Complex Matrices

A new gas chromatographic method has been developed that is able to quantify polycyclic aromatic hydrocarbons (PAH) and polycyclic aromatic sulfur-containing hydrocarbons (PASH) up to four rings. The method combines the power of both flame ionization detection (FID) and sulfur chemiluminescence detection (SCD) in series on a single comprehensive two-dimensional gas chromatography (GC × GC) system and provides mass fractions of compounds separated by carbon number <i>n</i> (C_<i>n</i>H_<i>x</i>S_<i>y</i>) and class. In addition to PAH and PASH separation, the method is extended toward nonaromatic and monoaromatic (sulfur-containing) compounds (paraffins, naphthenes, monoaromatics, thiols, sulfides, disulfides, and thiophenes). The 95% confidence interval is doubled when a single injection technique is used instead of a more-accurate double injection technique. A flexible correction procedure that combines the advantages of the two-dimensional separation of GC × GC and its ability to easily define overlapping groups between the FID and the SCD chromatograms is applied. The method is validated using theoretical reference mixtures and is applied on three commercial gas oils with sulfur content from 0.16 wt % up to 1.34 wt %. The repeatability is good, with an average of 3.4%, which is in the same range as the much more expensive Fourier transform ion cyclotron resonance–mass spectroscopy (FTICR-MS) technique

Coking Resistance of Specialized Coil Materials during Steam Cracking of Sulfur-Free Naphtha

The reactor material strongly affects coke formation during steam cracking of hydrocarbons. Therefore, in the past decade several specialized reactor materials have been developed that have proven to be efficient in reducing coke formation for ethane steam cracking. However, their beneficial anticoking properties are questioned when heavier feedstocks such as naphtha are cracked. Therefore, the effect of the composition of the reactor material has been investigated for ethane and naphtha cracking in an electrobalance setup under industrially relevant conditions. A significant reduction of coke formation is obtained for specialized alloys compared to typical Fe–Cr–Ni heat resistant steels when a sulfur-free naphtha is cracked. A thin layer of alumina on the surface along with manganese chromite provides the highest resistance to coking, as was demonstrated by the SEM and EDX analyses. The decrease in coking rate translates in a run length increase of 50% for a typical naphtha furnace equipped with reactors made out of an Al-enhanced alloy instead of typically applied heat resistant steel

Influence of the Reactor Material Composition on Coke Formation during Ethane Steam Cracking

An experimental study of the coking tendency of nine different materials was carried out in a quartz electrobalance setup with a jet stirred reactor (JSR) under industrially relevant ethane steam cracking conditions: <i>T</i>_material = 1159 K, <i>P</i>_tot = 0.1 MPa, χ_ethane = 73%, dilution δ = 0.33 kg_H2O/kg_HC. A strong influence of the composition of the materials on the coking rate as a function of time on-stream was observed. The initial coking rate varied from 5 × 10^–4 g·m^–2·s^–1 to 27 × 10^–4 g·m^–2·s^–1, while the asymptotic coking rate changed in the range of 2 × 10^–4 g·m^–2·s^–1 to 6 × 10^–4 g·m^–2·s^–1. SEM and EDX analyses of coked and uncoked coupons revealed that the composition of the oxide layer in contact with the cracked gas, formed after the initial preoxidation or decoking, has an important influence on the amount of coke deposited. Materials that formed a thin Al₂O₃ layer on the coupon surface showed a higher coking resistance. A uniform surface composition and a high resistance to spalling and fractures are other important characteristics of good materials

Coking Tendency of 25Cr-35Ni Alloys: Influence of Temperature, Sulfur Addition, and Cyclic Aging

25Cr-35Ni base alloys are the most frequently used materials for steam cracking reactors. The influence of cyclic aging, reactor temperature, and adding sulfur containing compounds before or during cracking on the rate of coke deposition on a classical 25Cr-35Ni alloy is evaluated using a jet stirred reactor equipped with an electrobalance. As expected, the initial and asymptotic coking rate increased with increasing reactor temperature. Scanning electron microscopy coupled with energy dispersive X-ray (SEM-EDX) analysis indicated that more Ni and Fe is present on the surface at higher cracking temperatures. Presulfidation led to increased coke deposition and decreased CO yields compared to the reference. When a sulfur containing compound was added continuously, coke deposition increased significantly but carbon oxide formation was suppressed. A pronounced amount of coke was measured in the reactor, followed by suppressed generated amounts of carbon oxides downstream. When combined with the continuous addition of sulfur containing compounds, presulfidation has little effect. Depending on the conditions, the effect of aging of the material is different: during the reference run and when only presulfidation was applied, coking rates increased as the material aged. When sulfur containing compounds were added continuously, with our without presulfidation, coking rates decreased as the material aged. This can be related with increased amounts of MnCr₂O₄ and Cr₂O₃ observed by SEM and EDX analysis

Experimental and Kinetic Modeling Study of Cyclohexane Pyrolysis

The pyrolysis of undiluted cyclohexane has been studied in a continuous flow tubular reactor at temperatures from 913 to 1073 K and inlet feed flow rates in the range 288–304 g·h^–1 at 0.17 MPa reactor pressure with average reactor residence time of 0.5 s calculated based on the pressure in the reactor, the temperature profile along the reactor, and the molar flow rate along the reactor estimated by the logarithmic average of the inlet and outlet molar flows. The reactions lead to conversions between 2% and 95%. Forty-nine products were identified and quantified using two-dimensional gas chromatography equipped with thermal conductivity and flame ionization detectors. The products with molecular weights between those of hydrogen and naphthalene constitute more than 99 mass % of the total products. A kinetic mechanism composed exclusively of elementary step reactions with high pressure limit rate coefficients has been generated with the automatic network generation tool “Genesys”. The kinetic parameters for the reactions originate either directly from high level ab initio calculations or from reported group additive values which were derived from ab initio calculations. The Genesys model performs well when compared to five models available in the literature, and its predictions agree well with the experimental data for 15 products without any adjustments of the kinetic parameters. Reaction path analysis shows that cyclohexane consumption is initiated by the unimolecular isomerization to 1-hexene but is overall dominated by hydrogen abstraction reactions by hydrogen atoms and methyl radicals. Dominant pathways to major products predicted with the new model are discussed and compared to other well performing models in the literature

Experimental and Modeling Study on the Thermal Decomposition of Jet Propellant-10

Jet Propellant-10 (JP-10) pyrolysis is performed in a continuous flow tubular reactor near atmospheric pressure in the temperature range of 930–1080 K, a conversion range of 4–94%, and two dilution levels of 7 and 10 mol % JP-10 in nitrogen. Identification and quantification of the pyrolysis products of JP-10 are based on online two-dimensional gas chromatography with a time-of-flight mass spectrometer and a flame ionization detector. JP-10 starts to react at 930 K and is fully converted at 1080 K. Among the more than 70 species up to C₁₄H₁₀ that were identified and quantified, tricyclo­[5.2.1.0^2,6]­dec-4-ene was identified for the first time, indicating the importance of bimolecular H-abstraction reactions in the consumption of JP-10. Critical assessment of the experimental data with the JP-10 combustion model by Magoon et al. [Magoon, G. R.; Aguilera-Iparraguirre, J.; Green, W. H.; Lutz, J. J.; Piecuch, P.; Wong, H. W.; Oluwole, O. O. Detailed chemical kinetic modeling of JP-10 (<i>exo</i>-tetrahydrodicyclopentadiene) high-temperature oxidation: Exploring the role of biradical species in initial decomposition steps. Int. J. Chem. Kinet. 2012, 44 (3), 179−193] showed that the model predictions of JP-10 agree reasonably well. The newly acquired and highly detailed experimental data help in understanding the thermal decomposition chemistry of JP-10 and can be used to validate future kinetic models of JP-10 pyrolysis

Experimental and Modeling Study on the Thermal Decomposition of Jet Propellant-10

Jet Propellant-10 (JP-10) pyrolysis is performed in a continuous flow tubular reactor near atmospheric pressure in the temperature range of 930–1080 K, a conversion range of 4–94%, and two dilution levels of 7 and 10 mol % JP-10 in nitrogen. Identification and quantification of the pyrolysis products of JP-10 are based on online two-dimensional gas chromatography with a time-of-flight mass spectrometer and a flame ionization detector. JP-10 starts to react at 930 K and is fully converted at 1080 K. Among the more than 70 species up to C₁₄H₁₀ that were identified and quantified, tricyclo­[5.2.1.0^2,6]­dec-4-ene was identified for the first time, indicating the importance of bimolecular H-abstraction reactions in the consumption of JP-10. Critical assessment of the experimental data with the JP-10 combustion model by Magoon et al. [Magoon, G. R.; Aguilera-Iparraguirre, J.; Green, W. H.; Lutz, J. J.; Piecuch, P.; Wong, H. W.; Oluwole, O. O. Detailed chemical kinetic modeling of JP-10 (<i>exo</i>-tetrahydrodicyclopentadiene) high-temperature oxidation: Exploring the role of biradical species in initial decomposition steps. Int. J. Chem. Kinet. 2012, 44 (3), 179−193] showed that the model predictions of JP-10 agree reasonably well. The newly acquired and highly detailed experimental data help in understanding the thermal decomposition chemistry of JP-10 and can be used to validate future kinetic models of JP-10 pyrolysis

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

Value Added Hydrocarbons from Distilled Tall Oil via Hydrotreating over a Commercial NiMo Catalyst

The activity of a commercial NiMo hydrotreating catalyst was investigated to convert distilled tall oil (DTO), a byproduct of the pulp and paper industry, into feedstocks for the production of base chemicals with reduced oxygen content. The experiments were conducted in a fixed bed continuous flow reactor covering a wide temperature range (325–450 °C). Hydrotreating of DTO resulted in the formation of a hydrocarbon fraction consisting of up to ∼50 wt % <i>n</i>C₁₇+C₁₈ paraffins. Comprehensive 2D GC and GC–MS analysis shows that the resin acids in DTO are converted at temperatures above 400 °C to cycloalkanes and aromatics. However, at these temperatures the yield of <i>n</i>C₁₇+C₁₈ hydrocarbons irrespective of space time is drastically reduced because of cracking reactions that produce aromatics. The commercial NiMo catalyst was not deactivated during extended on-stream tests of more than 30 h. Modeling the steam cracking of the highly paraffinic liquid obtained during hydrotreatment of DTO at different process conditions indicates high ethylene yields (>32 wt %)

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