Carbonaceous mesophase is a liquid crystalline material that can form as petroleum is pyrolyzed into coke. The material is thought to be made up of discotic mesogens in the form of planar, polyaromatic molecules. Researchers have previously developed thermodynamic models to predict mesophase formation in different feeds based on molecular weight, independent of the chemical structures found in any given sample of material. Using Fourier transform ion cyclotron resonance mass spectroscopy (FT-ICR MS), we were able to observe how the elemental compositions of hydrocarbon molecules evolved with thermal treatment. Using this information, we devised a new approach for modeling petroleum-based liquid crystal phase behavior using both molecular weight and elemental compositions to describe the material's composition. This approach permits molecules of large molecular weight to not automatically be considered mesogens and for nonideal solution behavior and mesophase content to be parametrized independently. Through comparing different methods, we also demonstrated the important role nonideal solution effects have on the calculated phase behavior as well as the impact of pseudocomponent number on the size of the mesophase coexistence region. Further theoretical and experimental work is needed to develop more general, predictive models.

Differential scanning calorimetry (DSC) was used to study the fast aging behavior of two petroleum pitch materials despite being only three to five years old. We observe that these highly aromatic pitches with broad distributions of both molecular weight and aromaticity exhibit large enthalpic relaxation endotherms in initial DSC heating scans, and 20-32 °C reductions in the fictive temperature and 0.35-0.87 of θK, which are indicative of aged glasses similar to ultrastable glasses and 20 MA aged amber. Quantifying the degree of thermodynamic stability relative to the Kauzmann temperature vs. the aging time demonstrates that these materials age just as quickly as low fragility metallic glasses. Additionally, we observe that pitches age faster than polymers reported in the literature when compared using down-jump experiments. We hypothesize that the fraction of higher aromaticity of pitch molecules plays a crucial role in faster dynamics. The unique aging behavior and the ability to produce pitches in bulk quantities using pilot-scale equipment, while being possible to tailor their molecular composition, make them a useful material for studying complex aging dynamics in the deep glassy state.

Journal Article Understanding Nucleation of Mesophase Pitch Tactoids using 4D-STEM Get access Robert Colby, Robert Colby Research, ExxonMobil Technology and Engineering Company, Annandale, NJ Search for other works by this author on: Oxford Academic Google Scholar Kazem Edmond, Kazem Edmond Research, ExxonMobil Technology and Engineering Company, Annandale, NJ Search for other works by this author on: Oxford Academic Google Scholar Daniella Mendez, Daniella Mendez Research, ExxonMobil Technology and Engineering Company, Annandale, NJ Search for other works by this author on: Oxford Academic Google Scholar Stuart Smith Stuart Smith Research, ExxonMobil Technology and Engineering Company, Annandale, NJ Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 29, Issue Supplement_1, 1 August 2023, Pages 274–275, https://doi.org/10.1093/micmic/ozad067.125 Published: 22 July 2023

Laser desorption ionization (LDI) mass spectrometry has been widely applied for the analysis of pitch-related materials. LDI is particularly useful when samples have very low solubility. However, LDI conditions, such as laser power output, can have significant impact on the resulting mass spectra. In this work, we examined the LDI of coronene and two petroleum pitch samples, a M-50 isotropic pitch and a thermally treated M-50 pitch that contained a mesophase. LDI at varying laser power is coupled to ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) to determine the impact of laser power on the elemental compositions of the pitch samples. Coronene is shown to form large polycyclic aromatic hydrocarbon (PAH) oligomers at high laser powers. Variations in laser power clearly affect mass distributions and compound-type distributions of the pitch samples. The impact of laser power is more significant and visible for the thermally treated pitch sample, where increased laser power generated high levels of fully dealkylated (or denuded) polycyclic aromatic hydrocarbons (dPAHs) and fullerenes. The presence of two types of PAH ions containing even and odd numbers of hydrogen atoms were observed. Even-hydrogen-number PAHs are molecular ions produced by direct laser ionization. The origins of odd-hydrogen-number PAHs are more complicated. They can result from dealkylation of larger PAHs, protonation of the parent molecule, and/or ionization of neutral PAH radicals. The latter can be a significant contributor to the odd-hydrogen-number PAHs. For analytical applications, a balance in laser power is needed to vaporize the non-volatile pitch molecules while also minimizing potential secondary thermal reactions during the LDI process. When laser power is controlled at a similar level, LDI-MS provides useful information to understand pitch compositional change from thermal treatment.

A rapid and quantitative image analysis method has been developed for analyzing reflected cross-polarized light micrographs of coke samples, enabling the determination of the coke's morphology. The method uses k-means clustering to segment the image into four discrete domain types and quantifies their sizes and anisotropy. From this analysis, an optical texture index (OTI) is computed following a procedure similar to the manual approaches used in the past to rank needle coke samples. Significant improvements in sample statistics and data throughput are possible compared to past methods because of the automated approach. The computed OTI can be further used to calculate a shot index (SI) using two reference cokes and the sample of interest. The reference cokes are produced from known sponge-forming and shot-forming vacuum residues. The shot index evaluates the tendency of a feed and process condition to form shot coke. We demonstrate the utility of this technique by systematically altering these variables and quantifying their impacts on the resulting shot index; examples included: (i) feed properties, (ii) thermal severity, (iii) chemical conversion of vacuum residues with elemental sulfur (percent levels) before coking, and (iv) blends of asphaltenes from the sponge-forming reference vacuum residue. These results demonstrate that this quantitative image characterization technique is useful for evaluating feeds, additives, process conditions, and blends for more indepth understanding of commercial delayed coking processes.

Carbon nanothreads, which are unique one-dimensional sp3-rich polymers, combine high tensile strength with flexibility owing to subnanometer widths and diamond-like cores. These extended carbon solids are constructed through pressure-induced polymerization of sp2 molecules such as benzene. Whereas a few examples of carbon nanothreads have been reported, the need for high onset pressures ( ≥ 17 GPa) to synthesize them precludes scalability and limits scope. Herein, we report the scalable synthesis of carbon nanothreads based on molecular furan, which can be achieved through ambient temperature pressure-induced polymerization with an onset reaction pressure of only 10 GPa due to its lessened aromaticity relative to other molecular precursors. When slowly compressed to 15 GPa and gradually decompressed to 1.5 GPa, a sharp six-fold diffraction pattern is observed in situ, indicating a well‐ordered crystalline material formed from liquid furan. Single-crystal X-ray diffraction of the reaction product exhibits three distinct d-spacings from 4.75 to 4.9 Å, whose size, angular spacing, and degree of anisotropy are consistent with our atomistic simulations for crystals of furan nanothreads. Further evidence for polymerization was obtained by powder XRD and Raman/IR spectroscopy. Comparison of the IR spectra with computed vibrational modes provides identification of spectral features characteristic of specific nanothreads, namely syn, anti, and syn/anti configurations. Furan therefore presents a strategic entry toward scalable carbon nanothreads.

Petroleum pitch M-50 (or A-240) has been well-known in making valuable carbon materials through thermal treatments. How these molecules react to produce carbon materials and the mechanisms of thermal polymerization and molecular weight growth under thermal conditions are of great significance and yet still unclear. Structures produced by thermal reactions of M-50 pitch were characterized with non-contact atomic force microscopy and compared to the structures in M-50 pitch previously characterized (Chen, P.; Metz, J. N.; Mennito, A. S.; Merchant, S.; Smith, S. E.; Siskin, M.; Rucker, S. P.; Dankworth, D. C.; Kushnerick, J. D.; Yao, N.; Zhang, Y. Petroleum pitch: Exploring a 50-year structure puzzle with real-space molecular imaging. Carbon 2020, 161, 456-465, DOI: 10.1016/j.carbon.2020.01.062). Reaction products were generated from M-50 pitch by two different approaches: an ex situ approach via thermal treatment at 400 degrees C under N-2 and an in situ approach via reaction directly on a Cu(111) surface. Polycyclic aromatic hydrocarbons (PAHs) from the ex situ reaction are larger than those in the starting M-50 pitch and with fewer methyl groups. Both types of five membered rings, conjugated and non-conjugated, are observed. Very large PAHs are formed under the in situ surface conditions as a result of reactions catalyzed by the Cu surface, with five-membered rings preserved as planar moieties in the product. The data suggest that methyl groups play important roles in initiating the polymerization and molecular weight growth of M-50 pitch molecules, but the reactivities of five-membered rings remain unclear.

Pitch-based carbon fibers are of considerable interest as high-performance materials. There are reports over the last several decades detailing (i) methods of improving pitch-based carbon fiber performance, and (ii) reducing the cost of production via novel processing techniques. However, there remain considerable challenges in producing high-performance pitch-based carbon fibers consistently on an industrial scale. This is arguably due to the difficulty of scaling the melt-spinning process to compensate for variability in pitch feedstock quality and a lack of understanding of processing-structure-performance relationships. This work focuses on the early stages of heat treatment (pyrolysis) of isotropic pitch and its effect on the chemical, thermal, and rheological properties of the pitch, which help determine its processability. More specifically, we quantify significant changes in chemical structure, Mw, Tg, Ts, and shear and extensional rheology as a function of pyrolysis time at 400 °C. The extensional rheology, in particular, shows that the 'stretchability' of the pitch samples strongly depends on pyrolysis severity, and is important for characterizing 'drawability'. Using a novel analysis of the uniaxial stretching kinematics, we show an isothermal 'drawability window' that allows for the largest axial and radial Hencky strains at constant rate. We hypothesize that this extensional drawability window could facilitate the successful processing of pitch into high quality fiber, minimizing the trial-and-error approach currently used in the field.

Elemental sulfur is used to cross-link heavy coker gas oil (HKGO) with only 0.44 wt% olefinic hydrogen content in the absence of solvent; subsequent pyrolysis yields sulfur-doped porous carbon with Brunauer–Emmett–Tell (BET) surface area (s.a.) around 1714–1785 m2 g−1.

Petroleum pitch has played a significant role in carbon science as a key abundant resource for polycyclic aromatic hydrocarbons in making various higher value carbon materials. Despite many detailed studies using advanced characterization techniques over 50 years, the exact nature of the molecular structures of petroleum M-50 pitch and their mesophase products remains unclear, due to the molecular diversity and the low solubility of this material. In this study, we applied real-space single molecule imaging non-contact atomic force microscopy to obtain exact structures of individual molecules, and compared the results from other characterization techniques to validate some of the previously hypothesized average structures. We identified a diverse slate of largely catacondensed polycyclic aromatic hydrocarbons with short alkyl chains, such as methyl and methylene groups. Furthermore, both single core and multi-core structures have been observed, in contrast to previous assertions that only one type would be present. The presence of these structures enables a mechanistic rationalization for their formation and allows potential mechanisms for the thermal conversion of pitch into larger bonding networks to be postulated.