Thermal Alteration Products Research Articles

Chemical composition and speciation of particulate organic matter from modern residential small-scale wood combustion appliances

Combustion technologies of small-scale wood combustion appliances are continuously developed decrease emissions of various pollutants and increase energy conversion. One strategy to reduce emissions is the implementation of air staging technology in secondary air supply, which became an established technique for modern wood combustion appliances. On that account, emissions from a modern masonry heater fuelled with three types of common logwood (beech, birch and spruce) and a modern pellet boiler fuelled with commercial softwood pellets were investigated, which refer to representative combustion appliances in northern Europe In particular, emphasis was put on the organic constituents of PM2.5, including polycyclic aromatic hydrocarbons (PAHs), oxygenated PAHs (OPAHs) and phenolic species, by targeted and non-targeted mass spectrometric analysis techniques. Compared to conventional wood stoves and pellet boilers, organic emissions from the modern appliances were reduced by at least one order of magnitude, but to a different extent for single species. Hence, characteristic ratios of emission constituents and emission profiles for wood combustion identification and speciation do not hold for this type of advanced combustion technology. Additionally, an overall substantial reduction of typical wood combustion markers, such as phenolic species and anhydrous sugars, were observed. Finally, it was found that slow ignition of log woods changes the distribution of characteristic resin acids and phytosterols as well as their thermal alteration products, which are used as markers for specific wood types. Our results should be considered for wood combustion identification in positive matrix factorisation or chemical mass balance in northern Europe.

Maghemite soil nodules reveal the impact of fire on mineralogical and geochemical differentiation at the Earth’s surface

Fires occur frequently over large parts of the Earth’s surface. They potentially exert a significant influence on the mineralogical and geochemical characteristics of an environment that is otherwise considered to be dominated by low temperature processes. We test this hypothesis by comparing the mineralogy and geochemistry of (i) magnetic, iron-rich soil nodules, (ii) non-magnetic iron soil nodules and (iii) a published dataset of surficial sediments from eastern Australia.Maghemite-rich nodules are present in soils from around the world. It has been argued that they are thermal alteration products of non-magnetic precursors, but this remains controversial. We use detailed petrographic and mineralogical analyses to demonstrate that maghemite occurs as part of a high temperature mineral assemblage including hematite and χ-alumina, within a magnetic nodule microfabric indicative of fire-induced dehydroxylation and sintering of non-magnetic precursors at temperatures of up to 600°C. The genetic link between magnetic and non-magnetic nodules means that their comparison offers insights into the geochemical impact of fire.Our results show that magnetic nodules are depleted in Si, Y, Zr and HREE but enriched in Fe and Cr relative to non-magnetic nodules that occur in close spatial proximity. Magnetic nodules also show variable but distinctly low Y/Ho (21.4±0.4) and Zr/Hf (29.3±0.8) as well as anomalously low La relative to the other LREE. In situ laser ablation analyses show that this is largely due to the presence of χ-alumina that is depleted in HREEs and has extremely low Y/Ho (mainly <20), as well as the low Zr/Hf of χ-alumina and the maghemite-hematite matrix, with no involvement from zircon. We propose a multi-stage process of formation where fire transforms non-magnetic nodule precursors into proto-magnetic nodules. This is associated with thermal transformation of clays as well as Fe and Al oxyhydroxides, followed by isochemical segregation into a sintered core with low Si, Y/Ho, Zr/Hf and La/Gd and a reciprocal cortex. Preferential loss of the weathering-sensitive cortex, which is rarely preserved on the magnetic nodules, then results in geochemical differentiation of magnetic nodules relative to their non-magnetic precursors.We propose that the elevated Zr/Hf and Y/Ho ratios previously reported for Australian fluvial sediments reflect, at least in part, the long history of palaeo-fires in the catchments of these rivers, with preferential removal, transport and sedimentation of the readily weathered, high Y/Ho and Zr/Hf cortex material that is a product of thermal alteration of Fe nodules. In addition, since magnetic Fe nodules are demonstrably related to fire, they may represent a promising, directly dateable record of severe fires, which can complement the sedimentary charcoal record.

In situ 3‐D mapping of pore structures and hollow grains of interplanetary dust particles with phase contrast X‐ray nanotomography

AbstractUnlocking the 3‐D structure and properties of intact chondritic porous interplanetary dust particles (IDPs) in nanoscale detail is challenging, which is also complicated by atmospheric entry heating, but is important for advancing our understanding of the formation and origins of IDPs and planetary bodies as well as dust and ice agglomeration in the outer protoplanetary disk. Here, we show that indigenous pores, pristine grains, and thermal alteration products throughout intact particles can be noninvasively visualized and distinguished morphologically and microstructurally in 3‐D detail down to ~10 nm by exploiting phase contrast X‐ray nanotomography. We have uncovered the surprisingly intricate, submicron, and nanoscale pore structures of a ~10‐μm‐long porous IDP, consisting of two types of voids that are interconnected in 3‐D space. One is morphologically primitive and mostly submicron‐sized intergranular voids that are ubiquitous; the other is morphologically advanced and well‐defined intragranular nanoholes that run through the approximate centers of ~0.3 μm or lower submicron hollow grains. The distinct hollow grains exhibit complex 3‐D morphologies but in 2‐D projections resemble typical organic hollow globules observed by transmission electron microscopy. The particle, with its outer region characterized by rough vesicular structures due to thermal alteration, has turned out to be an inherently fragile and intricately submicron‐ and nanoporous aggregate of the sub‐μm grains or grain clumps that are delicately bound together frequently with little grain‐to‐grain contact in 3‐D space.

Application of lipid biomarker analysis to evaluate the function of ‘slab-lined pits’ in Arctic Norway

Gas chromatography–mass spectrometry (GC–MS) and bulk carbon isotope determinations have been performed on samples (‘cemented organic residues’, charcoal, sediment and fire-cracked rock) excavated from 12 slab-lined pits from various locations in Arctic Norway to test the premise that these archaeological features were used for the extraction of oil from the blubber of marine mammals, such as seal, whale and walrus. A wide range of lipid compound classes were detected especially in the cemented organic residues and in the charcoal samples. The presence of long-chain unsaturated and isoprenoid fatty acids together with oxidation and thermal alteration products of unsaturated acids such as dicarboxylic acids, dihydroxyfatty acids and ω-(o-alkylphenyl)alkanoic acids suggests that these features were used for marine oil extraction at elevated temperatures. Notably the location of the hydroxyl groups in the dihydroxyfatty acids provides a record of the positional isomer of the precursor fatty acid and allows confirmation that 11-docosenoic (cetoleic) acid, the most abundant C 22:1 isomer in marine oil, was a major component of the original lipid. Further information was provided by the presence of long-chain fatty acyl moieties in surviving triacylglycerols and the presence of cholesterol. A fungal metabolite, mycose (trehalose), was found in all samples apart from a fire-cracked rock and points to microbiological activity in the pits. Bulk isotope analysis conducted on the ‘cemented organic residues’ is consistent with modern reference samples of blubber and oil from seal and whale. These data provide clear analytical evidence of the function of slab-lined pits in the archaeological record and suggest widespread exploitation of marine mammals for producing oil for heating, lighting and myriad other uses in the past.

Understanding the Application of Raman Spectroscopy to the Detection of Traces of Life

Investigating carbonaceous microstructures and material in Earth's oldest sedimentary rocks is an essential part of tracing the origins of life on our planet; furthermore, it is important for developing techniques to search for traces of life on other planets, for example, Mars. NASA and ESA are considering the adoption of miniaturized Raman spectrometers for inclusion in suites of analytical instrumentation to be placed on robotic landers on Mars in the near future to search for fossil or extant biomolecules. Recently, Raman spectroscopy has been used to infer a biological origin of putative carbonaceous microfossils in Early Archean rocks. However, it has been demonstrated that the spectral signature obtained from kerogen (of known biological origin) is similar to spectra obtained from many poorly ordered carbonaceous materials that arise through abiotic processes. Yet there is still confusion in the literature as to whether the Raman spectroscopy of carbonaceous materials can indeed delineate a signature of ancient life. Despite the similar nature in spectra, rigorous structural interrogation between the thermal alteration products of biological and nonbiological organic materials has not been undertaken. Therefore, we propose a new way forward by investigating the second derivative, deconvolution, and chemometrics of the carbon first-order spectra to build a database of structural parameters that may yield distinguishable characteristics between biogenic and abiogenic carbonaceous material. To place Raman spectroscopy as a technique to delineate a biological origin for samples in context, we will discuss what is currently accepted as a spectral signature for life; review Raman spectroscopy of carbonaceous material; and provide a historical overview of Raman spectroscopy applied to Archean carbonaceous materials, interpretations of the origin of the ancient carbonaceous material, and a future way forward for Raman spectroscopy.

Characterization and quantification of biomarkers from biomass burning at a recent wildfire site in Northern Alberta, Canada

The composition of organic matter (OM) in pine vegetation and soil samples from a pine forest which was charred by a wildfire was analyzed using solid-state nuclear magnetic resonance ( 13C NMR) and gas chromatography–mass spectrometry (GC–MS) of solvent extracts to study the effects of thermal alteration on soil organic matter (SOM). The NMR data revealed the presence of unaltered biomolecules (cellulose, proteins) and low contents of aromatic C (15%) in the charred pine wood and cones while the charred soil samples exhibited higher contents of aromatic C (39–56%). The solvent extraction of charred and uncharred plant and soil samples yielded diterpenoids, triterpenoids, steroids, a series of aliphatic lipids, phenols and carbohydrates indicating the predominant input of higher plant OM and minor contributions from microorganisms and/or fauna. The lower yield of solvent extractable aliphatic lipids in the charred samples versus the uncharred samples suggests that these compounds are thermally degraded during a wildfire. Molecular markers for the burning of cellulose (levoglucosan, mannosan, galactosan) were detected in all charred samples. The comparison of charred and uncharred samples allowed the identification of unaltered pine derived biomolecules and their thermal alteration products in the charred samples. Terpenoid and steroid biomolecules were in part altered during incomplete combustion to aromatic, unsaturated and polar derivatives (“pyromolecules”) that still retained the characteristic skeleton of their precursors. Since some of the polar degradation products found in the charred soils can be generated either from thermal or microbial degradation, the aromatic and unsaturated hydrocarbon products are preferred as molecular markers for SOM burning. Ratios of biological precursors to aromatic (diterpenoids) or unsaturated products (steroids) indicate that the cyclic lipids in the pine wood and the soil surface horizon were highly altered. In conclusion, the solvent extractable lipids and carbohydrates in charred SOM are valuable, source-specific molecular markers for the burning of plant biomass and for tracing the biogeochemistry of charred residues in soils.

Sources of Fine Organic Aerosol. 9. Pine, Oak, and Synthetic Log Combustion in Residential Fireplaces

Combustion of wood in residential fireplaces contributes approximately 14% on an annual average of the total primary fine particle organic carbon (OC) emissions to the Los Angeles urban atmosphere and up to 30% of the fine particulate OC emissions on winter days. This paper presents comprehensive organic compound source profiles for smoke from burning pine, oak, and synthetic logs in residential fireplaces. Mass emission rates are determined for approximately 200 organic compounds including suites of the n-alkanes, n-alkenes, cyclohexylalkanes, n-alkanals, n-alkanoic acids, alkenoic acids, dicarboxylic acids, resin acids, hydroxylated/methyoxylated phenols, lignans, substituted benzenes/benzaldehydes, phytosterols, polycyclic aromatic hydrocarbons (PAHs), and oxy-PAHs. Wood smoke constituents reflect to a great extent the underlying composition of the wood burned: pine and oak logs produce smoke that is enriched in lignin decomposition products, pine smoke is enriched in resin acids and their thermal alteration products, while smoke from the synthetic log burned here bears the major signature of the petroleum products combined with traces of the sawdust components from which it is made. Resin acids are discussed as potential wood smoke tracers in the environment, and it is shown that the time series of resin acids concentrations in the Los Angeles atmosphere follows the extreme seasonal variation in wood use reported in previous emissions inventories for the Los Angeles urban area.

Simulated degradation of glyceryl ethers by hydrous and flash pyrolysis

Hydrous and flash pyrolysis were carried out on phytanyl ethers isolated from a methanogen ( Methanosarcina barkeri), a haloalkaphile ( Haloalkaphile sp.) and a thermoacidophile ( Sulfolobus sulfotaricus). No thermal alteration products of the intact ether lipids were observed below 150°C. From 150–300°C, slight pyrolysis of the intact glyceryl ethers was observed, although recovery of the parent compounds averaged >95%. As pyrolysis temperature increased, the alcohol and aldehyde were the first products formed following direct cleavage of the ether bond. At 600°C, the corresponding alkene also became a dominant flash pyrolysis product. With increases in pyrolysis temperature to 900°C, increasing amounts of volatile alkenes were produced. Based on the observed fragmentation patterns, we suggest that phytanol is first cleaved from the intact glyceryl ethers, followed by degradation of the phytanol to the corresponding alkanes or shorter chain components. In addition, as shown by other investigators, the alteration products may also be directly incorporated into higher molecular weight fractions.

Thermal Stability of Hydrocarbons: Laboratory Criteria and Field Examples

Though hydrocarbons are widely viewed as being thermally unstable in nature, cracking to gas in reservoirs, there has been very little work to address the chemical feasibility of the concept. The present effort provides a test of this view by developing from laboratory experiments criteria for recognizing thermally altered hydrocarbons and then applying the criteria to two condensates that are believed to have been exposed to temperatures of 175−200 °C for 30 million years. The observation that the two samples exhibit none of the characteristics expected for thermal alteration products suggests that hydrocarbons are far more stable in nature than is generally recognized. The stability of hydrocarbons in nature means that an alternative mechanism must be devised to explain the presence of gas in deep reservoirs. A new mechanism is proposed which is expected to yield the appropriate isotopic and molecular distribution of products, operates in the source rock, uses established chemical pathways, and does not require any exotic catalysts.

Composition of higher molecular weight organic matter in smoke aerosol from biomass combustion in Amazonia

Smoke particulate matter was sampled by high volume filtration from a controlled burn of forest litter in the northern forest reserve of INPA about 70 km north of Manaus, Amazonas. The extract of the filter was separated after methylation into hydrocarbon, ketone, carboxylic acid ester and polar fractions and then analyzed by gas chromatography and gas chromatography-mass spectrometry. The total lipid extract yield was ∼13 mg/m 3 of smoke. The major organic components of the smoke particles were straight-chain aliphatic and triterpenoid compounds from vegetation wax, biopolymers, and gum/resin. Polynuclear aromatic hydrocarbons (PAH) from the combustion process were found at high levels and aromatized derivatives from natural product precursors were also important components. Petroleum hydrocarbons representing urban and vehicular emissions were not detectable. The n-alkanes ranged from C 19 to C 35, with a carbon number maximum (C max) at C 29/C 31 and an odd-to-even carbon predominance > C 25 (CPI 20–35 = 3.6). Terminal olefins ( n-alk-1-enes) were also present and ranged from C 17 to C 35, with a C max at C 22 and an even-to-odd carboon predominance (CPI 17–35 = 0.8). The n-alkanes are derived mainly from vegetation wax and the alk-1-enes with other oxygenated compounds (e.g., ketones, acids, triterpenoids) are thermal alteration products from gum/resin and biopolymers. These alteration products coupled with the PAH are the tracers for biomass combustion.

Magnetic properties, self-reversal remanence and thermal alteration products of smythite

This study is a follow up of the investigation of some magnetic properties and metastability of greigite in samples obtained from Miocene claystones in the Krusne hory (Erzgebirge) Piedmont basins (Bohemia). Three different methods of upgrading the smythite were applied; the magnetic properties of the concentrates are compared. The thermal conversion of smythite sets in at 200°C while greigite converts at 250°C. The first intermediate products to be formed are iron sulphides, marcasite clearly dominating over pyrite and pyrrhotite. Apart from a Fe3+ sulphate with a composition of Fe2(SO4)3, oxidation of these sulphides gives rise to α-Fe2O3. The result of the subsequent decomposition of the mentioned sulphate is the formation of η-Fe2O3, which retains the sulphate structure. The final product of the thermal decomposition at 800°C is α-Fe2O3. In the smythite concentrate the conversion to Fe3+ sulphate and η-Fe2O3 is about twice as intensive as in greigite. No direct conversion to γ-Fe2O3 was found. During the thermal process self-reversals of remanence were observed, in various samples as many as four reversals in the temperature interval from 340 to 590°C. The occurrences of self-reversals of remanence were only observed at high degrees of thermal demagnetization, of the order of 10−2 down to 10−3 in the temperature interval of sulphide origin (below 400°C), and of the order of 10−4 down to 10−6 in the temperature interval of Fe-oxides origin (above 400°C).

Novel tricyclic alkanes in crude oils from Xinjiang Province, China

Several oils from the Zhun-Ge-Er and Tarim Basins in Xinjiang Province, China, were characterised by GC-MS, and two novel series of tricyclic alkanes were observed. On the basis of mass spectral interpretation and comparison with the thermal alteration products of cholesterol, it is proposed that these compounds are structurally similar to steranes, but differ in that ring A is open, due to cleavage of either the 1–10 or 4–5 bond. The distribution of these tricyclic alkanes closely parallels that of the unaltered steranes, suggesting that they are originally derived from the steranes, or original sterols, via a thermal degradation mechanism. The tricyclic alkanes appear to be resistant to biodegradation and hence when all of the regular steranes have been removed by biodegradation, it is still possible to use these tricyclic alkanes for oil/oil or oil/source rock correlations.

SEDIMENTARY ORGANIC MATTER, ORGANIC METAMORPHISM, AND OIL AND GAS OCCURRENCE

ABSTRACT Sedimentary organic-matter constituents, including thermal-alteration products, are useful in the evaluation of petroleum potential in western Canada. It is an accepted hypothesis that organic matter in sediments is the source or the complement, or both, of the hydrocarbons in sedimentary reservoirs. Through visual observation and comparison of the organic matter, the hydrocarbon potential of a sedimentary body and the types of hydrocarbon likely to be found are evaluated. Hydrogen-rich material that has been modified under subaqueous low-oxygen sapropelic conditions lends itself to the formation of liquid and wet (C2 plus) gaseous hydrocarbons through compaction and temperature elevation. This material can be recognized by the presence of amorphous translucent debris. Deposits containing only structured plant cuticles or opaque fusainized (high-carbon) material produce mainly dry gas; those containing a mixture of the amorphous sapropelic debris and recognizable plant debris generally have wet hydrocarbon potential. Organic metamorphism induced by heat (maximum paleotemperature) and pressure modifies the organic matter locked in the sedimentary matrix as well as the mobile products, leading to paraffinic oils and condensates, then to dry gas and pyrobitumens, and finally to graphitization under severe conditions. For mapping, a thermal index of five progressive degrees of thermal alteration is distinguished. Where the two highest degrees prevail, prospects for wet gas and liquid hydrocarbons are negligible unless there has been post-thermal migration from outside the thermally affected area. The highest degree reduces prospects even for dry gas, and the Devonian dry-gas area of northern British Columbia is interpreted on this basis. Many areas with large dry gas reserves have been exposed to low-grade thermal metamorphism. Bitterli (1963a, 1963b) Philippi (1957, 1965) and Gutjahr (1966) have reported on organic-matter studies carried out for Shell Petroleum Corporation; Correia (1967) and others have reported on work in France and the Sahara; and Vassoevich et al. (1967) have summarized certain studies carried out in the U.S.S.R. This paper summarizes some of the work carried out by Imperial Oil Limited.