Sequential Extraction of Coal Tar Pitch and Structural Characterization of Enriched Large Polycyclic Aromatic Hydrocarbons

Abstract

Four fractions separated sequentially from a coal tar pitch by two different methods are examined by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI TOF-MS) and 50/24 matrix analysis, to evaluate both separation effectiveness and characteristics of large polycyclic aromatic hydrocarbons (PAHs) in variable fractions. Both Soxhlet extraction and anti-solvent precipitation can sequentially produce four fractions that have narrower molecular mass distribution with specific structural features of PAHs. The results show that the overall molecular mass (MM) and ring size of large PAHs abundant in the fractions gradually shift to higher values as solvent strength increases, with some overlap between two adjacent fractions. A broad range of peaks in MS spectra has been resolved as 4-to about 25-ring PAHs by 50/24 matrix analysis, with some detailed molecular structure elucidated. For example, the PAHs in the light HS fraction include 4 to 11-ring aromatics with more ortho-condensed structure. On the other hand, heavier fractions contain more aromatic rings fused by bay-condensations that result in quaternary aromatic carbons. Besides structural insights, SEM morphologically reveals differences in the extraction effectiveness between Soxhlet and antisolvent, due to mass transfer and diffusion limitations in bituminous material.

Analyzing solid fossil-fuel pitches by a combination of Soxhlet extraction and Fourier transform ion cyclotron resonance mass spectrometry

“…While almost threequarters of the PP is soluble in toluene, the toluene-soluble fraction only accounts for 46% of the CTP. This is in line with previous reports [12,31,33] that petroleum pitch mainly consists of large polycyclic aromatic hydrocarbons with long aliphatic side chains. These compounds are much more soluble in organic solvents than molecules from their coal tar pitch counterpart, in which the condensed aromatics with short alkyl side chains are more abundant.…”

“…While this finding is in line with previous time-of-flight MS measurements [12], the mass resolution of the TOF MS was insufficient to distinguish the mass splitting of CH4/O (36.4 mDa), N/CH2 (12.6 mDa), and H4S/C3 (3.4 mDa). Thus, during these earlier measurements [12,31,33], only the dominant hydrocarbon components were considered while the heteroatom-containing molecules were S1.…”

“…Due to its unparalleled mass resolving power and accuracy, Fourier transform ion cyclotron resonance mass spectrometry (FT ICR MS) is employed in this study to examine the individual components, especially the heteroatom-containing compounds, of these complex pitch samples. Moreover, the soluble and insoluble components of solid pitches in typical organic solvents, such as dichloromethane, toluene, quinolone, N-methylpyrrolidine and pyridine, have significant impact on the mesophase formation and graphitization [31,33,34]. Nevertheless, the structural and compositional differences of the soluble and insoluble parts of solid pitches have not been well investigated.…”

Correlation of Mesophase Properties with Molecular Structures of Pitches from Different Sources

“…The numberaverage molecular weight (M N ), the weight-average molecular weight (M W ), and the molecular weight distribution index (MWD) of three pitches were calculated, respectively, according to the following formulas. 30…”

Laser Desorption Ionization of Large Condensed Polycyclic Aromatic Hydrocarbons in Petroleum Pitch and Thermally Treated Products

“…It was observed that large non-volatile biomolecules can be ionized intact when mixed with metal powder and/or the proper organic matrix. , The applications of MALDI and LDI to analyze petroleum-related products have been recently summarized in a review . MALDI, using a range of matrices and sample preparation methodologies, has been combined with time-of-flight (TOF) and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) for the analysis of various types of pitches derived from coal tar, lignin, and processed petroleum bottoms. − Because aromatic molecules can effectively absorb laser energy and serve as a matrix, direct LDI is also commonly used for analysis of PAHs in heavy petroleum, − pitch, , and soot formed in flame/combustion. ,, In comparison to MALDI, LDI is simpler in operation and frequently used to assess compositional changes of pitch during thermal treatment, where samples are fairly refractory with low solubility. However, it has been noted that LDI experimental variables, such as laser power, can have significant impacts on the resulting mass spectra of the samples and, consequently, affect the interpretation of mass spectrometric data.…”