The use of solvent extractions and solubility theory to discern hydrocarbon associations in coal, with application to the coal-supercritical CO 2 system

Jonathan J. Kolak; Robert A. Burruss

doi:10.1016/j.orggeochem.2014.05.002

Home/Archive/USGS

USGS · 70112470

The use of solvent extractions and solubility theory to discern hydrocarbon associations in coal, with application to the coal-supercritical CO 2 system

Jonathan J. Kolak·Robert A. Burruss

View original source ↗Export metadata ↓

Abstract

Samples of three high volatile bituminous coals were subjected to parallel sets of extractions involving solvents dichloromethane (DCM), carbon disulfide (CS 2 ), and supercritical carbon dioxide (CO 2 ) (40 °C, 100 bar) to study processes affecting coal–solvent interactions. Recoveries of perdeuterated surrogate compounds, n-hexadecane-d34 and four polycyclic aromatic hydrocarbons (PAHs), added as a spike prior to extraction, provided further insight into these processes. Soxhlet-DCM and Soxhlet-CS 2 extractions yielded similar amounts of extractable organic matter (EOM) and distributions of individual hydrocarbons. Supercritical CO 2 extractions (40 °C, 100 bar) yielded approximately an order of magnitude less EOM. Hydrocarbon distributions in supercritical CO 2 extracts generally mimicked distributions from the other solvent extracts, albeit at lower concentrations. This disparity increased with increasing molecular weight of target hydrocarbons. Five- and six-ring ring PAHs generally were not detected and no asphaltenes were recovered in supercritical CO 2 extractions conducted at 40 °C and 100 bar. Supercritical CO 2 extraction at elevated temperature (115 °C) enhanced recovery of four-ring and five-ring PAHs, dibenzothiophene (DBT), and perdeuterated PAH surrogate compounds. These results are only partially explained through comparison with previous measurements of hydrocarbon solubility in supercritical CO 2 . Similarly, an evaluation of extraction results in conjunction with solubility theory (Hildebrand and Hansen solubility parameters) does not fully account for the hydrocarbon distributions observed among the solvent extracts. Coal composition (maceral content) did not appear to affect surrogate recovery during CS 2 and DCM extractions but might affect supercritical CO 2 extractions, which revealed substantive uptake (partitioning) of PAH surrogates into the coal samples. This uptake was greatest in the sample (IN-1) with the highest vitrinite content. These findings indicate that hydrocarbon solubility does not exert a strong influence on hydrocarbon behavior in the systems studied. Other factors such as coal composition and maceral content, surface processes (physisorption), or other molecular interactions appear to affect the partitioning of hydrocarbons within the coal–supercritical CO 2 system. Resolving the extent to which these factors might affect hydrocarbon behavior under different geological settings is important to efforts seeking to model petroleum generation, fractionation and expulsion from coal beds and to delineate potential hydrocarbon fate and transport in geologic CO 2 sequestration settings.

Explore related subjects

Organic Geochemistry Article

Keep this discovery

Explore connections, maps & timelines

BibTeX RIS

Jonathan J. Kolak, Robert A. Burruss. 2014. The use of solvent extractions and solubility theory to discern hydrocarbon associations in coal, with application to the coal-supercritical CO 2 system. https://doi.org/10.1016/j.orggeochem.2014.05.002

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related USGS reports

USGS2026

Evidence for a biological origin of uranium-rich carbon masses within the Ediacaran Salt Range Formation of Pakistan

Thucholites are unique organic structures found in igneous and sedimentary rocks composed of a U-C-rich interior enclosed by an organic outer shell. Their formation and occurrence have perplexed scientists for over 100 years. Typically, thucholites are sparse in sedimentary rocks but where found in abundance, they may be the result of rapid paleoecological disruptions, e.g., volcanic ashfall. Here, we evaluated thucholites from the Ediacaran Salt Range Formation of the Indus Basin in Pakistan using field emission scanning electron microscopy (FESEM) and nanoscale secondary ion mass spectroscopy (NanoSIMS) to propose a two-stage mechanism for thucholite development. NanoSIMS results suggest organic matter in thucholite cores formed by biological fractionation (represented by the presence of lighter 13 C/ 12 C and 34 S/ 32 S) while the outer organic mantle formed via radiolysis-induced polymerization. FESEM elemental analysis confirms compositional differences between the two thucholite components (core and mantle), further implying their contrasting origins. Dimensional comparison of thucholite cores and their U-bearing mineral morphologies to ancient and modern U-biomineralized microbes suggests that the thucholite cores formed from metal-biological interactions. The presence of volcanogenic biotite, alkali feldspar, and clay spherules (interpreted as devitrified volcanic glass) with thucholite suggests that the thucholite cores in the Salt Range Formation are biological responses to rapid paleoenvironmental change from volcanic eruption which preserved the fossilized morphologies of Proterozoic microorganisms.

Salt Range↗

USGS2026

Metalloporphyrins in the Eagle Ford Shale

Using Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS), Zheng et al. (2018, Energy & Fuels 32, 10382) reported abundant iron and vanadyl porphyrins and minor amounts of gallium and nickel porphyrins in asphaltenes extracted from a single lower Eagle Ford Shale sample. This finding is most unusual as iron and gallium porphyrins have been previously found only in coal. In this study, petroporphyrins in samples of the Eagle Ford Shale previously studied by French et al. (2020, Marine Petrol. Geol. 118, 104459), were examined using atmospheric pressure photoionization (APPI) FT-ICR-MS. Vanadyl porphyrins (N4VO) dominated the asphaltenes in thermally immature (VRo < 0.56%) samples decreasing in relative abundance with increasing maturity. Only minor amounts of nickel porphyrins were detected in the immature and early oil samples. The distribution of the vanadyl porphyrins is comparable to those reported for marine oils at varying levels of maturity. Immature samples contained porphyrins that were predominantly deoxophylloerythroetio- (DPEP: DBE = 18) and di- deoxophylloerythroetio (di-DPEP: DBE = 19) porphyrins, while ETIO- (DBE = 17), rhodo- (DBE = 20, 21, and 22) and higher condensed (DBE ≥ 23) porphyrins increased with increasing maturity. The vanadyl porphyrins included species with additional one to three oxygen atoms (N4VOx, x= 1 to 4) and one sulfur atom with one to two oxygen atoms (S1N4VOx, x=1 to 3). The degree of additional oxygen and sulfur atoms is consistent with O/C and Sorg/C of associated kerogen. No iron or gallium porphyrins were detected, showing that they are not a ubiquitous feature of the Eagle Ford. We hypothesize that the previously reported iron and gallium porphyrins (Zheng et al., 2018) were present because the specific sample that was analyzed in detail was from the early onset of the Cenomanian–Turonian oceanic anoxic event (OAE-2) in contrast to the samples investigated in this study that are primarily from the lower part of the Eagle Ford pre-dating OAE-2. Submarine volcanism, associated with eruption of large igneous provinces, occurred pre-OAE-2, injecting iron and other inorganic nutrients, giving rise to algal blooms and the acidification of the seawater. At the onset of OAE-2, boreal water masses flowed into the southern Western Interior Seaway, shifting the water column to more oxygenated conditions. Low pH-high Eh (oxic) conditions enhance the availability of iron and gallium such that these events abruptly changed the seawater chemistry, specifically enriching iron and gallium relative to vanadium and nickel. These pH-Eh conditions are similar to the depositional conditions associated with coals, which are known to contain iron and gallium porphyrins, suggesting similar conditions resulted in iron and gallium metalation of porphyrins in the marine setting of the Western Interior Seaway.

Texas↗

USGS2025

Validation of the U37K' paleotemperature proxy in the South Brazilian Bight from core-top sediments

The paleothermometer based on the alkenone unsaturation index ( U 37 K ′ "> U37K′ ) is often used to reconstruct past sea surface temperatures (SST). In the SW Atlantic Ocean, however, a limited understanding of the seasonal and depth distribution of coccolithophores, which generates the U 37 K ′ "> U37K′ signal preserved in ocean sediments, hinders accurate estimates of past regional SSTs. We analyzed 45 core-top sediment samples from the continental shelf of the South Brazilian Bight (SBB, 23 °S to 28 °S) to assess regional spatial U 37 K ′ "> U37K′ -SST gradients and improve SST estimates. The U 37 K ′ "> U37K′ data were converted to SST using six published paleotemperature equations and compared to modern observational SST data from the World Ocean Atlas (2018) data set. Data indicate that the U 37 K ′ "> U37K′ signal is produced during the austral summer and autumn when regional episodic upwelling events occur over the inner-shelf and the nutricline shoals at the slope. Our analysis of core-top data shows that SST estimates derived from most calibration equations closely align with modern observed temperatures but are skewed toward warmer months associated with upwelling-derived nutrients. Our findings underscore the importance of considering regional and seasonal biases to improve the accuracy of paleotemperature reconstructions. Understanding the factors influencing the SBB U 37 K ′ "> U37K′ signal enables a more meaningful comparison between regional paleoceanographic studies, improving our understanding of past changes in the SW Atlantic Ocean and our ability to predict regional SST response to ongoing and future warming.

South Brazilian Bight↗