Role of the interlayer space of montmorillonite in hydrocarbon generation: An experimental study based on high temperature–pressure pyrolysis

The interlayer clay–organic complex is an important clay–organic association in sedimentary environments. However, the effects of organic matter storage in the interlayer space of clay minerals on the thermal degradation of organics and the generation of hydrocarbons have not been investigated. In this study, montmorillonite (Mt) and 12-amoniolauric acid (ALA) were used to prepare an interlayer Mt–ALA complex and a Mt–ALA complex in which Mt and ALA were simply mixed. Pyrolysis experiments on the ALA and Mt–ALA complexes were conducted in a confined gold capsule system at a fixed temperature and pressure of 350 °C and 36 MPa, respectively. X-ray diffraction, elemental analysis and Fourier transform infrared spectroscopy were used to characterize the Mt–ALA complexes, and automatically controlled gas chromatography along with a pyrolysis furnace was used to detect the volatile components released during pyrolysis. In the absence of Mt, the pyrolysis of ALA yielded only a small amount of C_1–5 hydrocarbons and CO₂. The amounts of C_1–5 hydrocarbons released from the pyrolysis of the interlayer Mt–ALA complex and the mixed Mt–ALA complex are approximately 43 and 5 times greater than the amounts released from ALA alone, respectively. The Brønsted acid sites in the interlayer space of Mt, which arise from the interlayer dissociated water, significantly promote the cracking of hydrocarbons through a carbocation mechanism, the isomerization of normal hydrocarbons and alkene–alkane conversion through hydrogenation, resulting in high i-alkane/n-alkane and alkene/alkane ratios in the pyrolysis products. The Lewis acid sites of Mt are primarily involved in the decarboxylation of ALA during pyrolysis and are responsible for CO₂ generation.     

Organic geochemistry of the British Kimmeridge clay: 2. Acyclic isoprenoid alkanes in Kimmeridge shale oils

The C15---C20 isoprenoid alkane composition of Kimmeridge Clay shale oils produced by Fischer assay has been examined, and compared with the isoprenoid composition of corresponding bitumens. C16 and C18 isoprenoid alkanes are generally dominant in shale oils, while pristane (C19) and phytane (C20) dominate in bitumens. A significant proportion of the phytane in many shale oils is derived from simple evaporation of free (bitumen) phytane, while free pristane contributes less to shale oil composition. Some shale oil phytane and a large proportion of pristane is kerogen-derived. Certain shale oils contain lower concentrations of isoprenoid alkanes than corresponding bitumens, suggesting that some free alkane is thermally degraded during pyrolysis. Results thus indicate three sources for shale oil isoprenoid alkanes: thermal evaporation of free alkanes (particularly for phytane), kerogen decomposition, and possibly the cracking of higher homologues for C15---C19 alkanes. Kerogen-derived isoprenoids are suggested to arise by thermal desorption of adsorbed free alkane (particularly for phytane) and from C---O and C---C bonded species (excluding phytane) via postulated clay catalysed hydrogenation of initially formed alkenes. Comparison of shale oil and bitumen pristane/phytane ratios allows groups of oil shales to be defined, dependent on source composition, organic carbon content and maturity. Shale oil pristane/phytane ratios can also help to determine depositional environments and source composition, although maturity, shale mineralogy and competing alkene-forming pyrolytic reactions may also affect the ratios.     

Hydrothermal alteration of sedimentary organic matter in the presence and absence of hydrogen to tar then oil

Hydrothermal alteration (hydrous pyrolysis) experiments, in the absence and presence of H₂ (reductive), were conducted on organic matter from marine and lacustrine sediments. The experiments were carried out at discrete temperatures from 150 °C to 350 °C to assess the yields and compositions of the bitumen (tar) formed and subsequently at higher temperatures the oil generated. The yield of bitumen was observed to increase with increasing temperatures. Under hydrous pyrolysis conditions with hydrogen, the yield increases by an order of magnitude and immature lacustrine organic matter shows the highest yield. Bitumen, the extractable organic matter at temperatures below 250-300 °C, contains mainly polar compounds, an unresolved complex mixture (UCM) of branched and cyclic compounds, with low amounts of saturated hydrocarbons. The polar compounds include n-alkanoic acids, n-alkanedioic acids, n-alkanols, isoprenoid ketones and methyl alkanoates. At temperatures above 300 °C, the bitumens transform into petroleum products with saturated hydrocarbons (n-alkanes and biomarkers) and UCM as the major components (>95% of total yield). The degree of maturation of the generated oil increases with increasing temperature under both pyrolysis conditions to full maturity at >350 °C. Although, the bitumen yield is much higher under conditions with added hydrogen, the maturity of the generated oil is lower than with just hydrous pyrolysis.     

The hydrocarbon fraction of virgin olive oil and changes resulting from refining

In numerous Spanish virgin olive oils, 6,10-dimethyl-1-undecene, various sesquiterpenes, the series ofn-alkanes from C14 to C35, n-8-heptadecene and squalene are the only less volatile components detected by gas chromatography in the hydrocarbon fraction. In oils from olives of the Arbequine variety, a series ofn-9-alkenes has also been found. In refined oils, notable features are the absence of the most volatile compounds and the appearance of other hydrocarbons produced during the refining process. Among these,n-alkanes, alkadienes (mainlyn-hexacosadiene), stigmasta-3,5-diene, isomerization products of squalene, isoprenoidal polyolefins coming from hydroxy derivatives of squalene and steroidal hydrocarbons derived from 24-methylene cycloartanol were identified. Physical refining produces larger amounts of degradation products and greater losses ofn-alkanes than chemical processing. Squalene is the major hydrocarbon component in all oils, both virgin and refined. The ranges of concentration for the different hydrocarbons found in Spanish virgin olive oils are presented.     

Organic geochemistry of the British Kimmeridge Clay: 3. The occurrence and distribution of acyclic isoprenoid C19 alkenes in Kimmeridge Clay shale oils

The occurrence and distribution of acyclic isoprenoid C19 alkenes (pristenes) in Kimmeridge Clay shale oils has been examined. Pristenes comprise ≈ 9 to 15% of isolated alkene fractions, and ≈ 8% of total shale oil non-aromatic hydrocarbons. They are generally much more abundant than pristane, possibly because only limited hydrogenation of isoprenoid alkenes occurs during pyrolysis. Two pristene isomers are identified (mass spectrometry, retention indices, g.c. co-injection), with prist-2-ene the more abundant in several Kimmeridge shale oils. Prist-2-ene/prist-1-ene ratios show some correlation with sediment oil yield and clay mineral content. Clay-rich low oil yield sediments often give prist-2-ene dominated shale oils, whereas high oil yield sediments show prist-1-ene dominance. Results suggest the conversion of prist-1-ene to prist-2-ene during pyrolysis by a time dependent, thermodynamically favourable double bond rearrangement. Two mechanisms are suggested for the generation of prist-1-ene, the primary pyrolysis product, from C20 units CC bonded to Kimmeridge oil shale kerogen: lt]o li](i) a thermolytic, radical induced tertiary hydrogen abstraction followed by homolytic β CC bond cleavage, or li](ii) in the presence of clay minerals, a clay catalysed carbonium ion route involving Lewis acid tertiary hydrogen abstraction and heterolytic β CC bond fission. Prist-1-ene double bond rearrangement is suggested to occur by a clay-catalysed ionic pathway involving proton-donor site double bond protonation followed by collapse of the resultant tertiary carbonium ion by Lewis base deprotonation. While rearrangement is likely to be retarded in analytical flash pyrolysis, Fischer pyrolysis conditions (and laboratory thermal maturation) allow more time for secondary rearrangement. Where the rate of rearrangement is enhanced by increased clay catalyst concentration, e.g. clay rich Kimmeridge shales, prist-2-ene becomes increasingly prominent in the resultant pyrolysates.     

Lixiviation of argillaceous rocks: Impact of oxidation degree states on organic compound mobilization

This work aims to study the influence of oxidation degree state which reached by organic matter included in argillaceous rocks on lixiviation and mobilization of compounds. Experimental lixiviation was carried out on two argillaceous rocks sampled in the surface deposit of the Andra laboratory (Bure, France). Molecular and spectroscopic characterizations of the organic matter extracts reveal two different oxidation levels reached by these samples: (i) a well preserved and (ii) an oxidized samples. Dissolved organic matter content and molecular investigation of sediment bitumen show that hydrophobic molecules (hydrocarbons) remain stable during lixiviation whereas specific polar compounds (alkanoic acids) are progressively removed by water. Moreover, occurrence of secondary alkanols with a molecular distribution similar to initial n-alkanes suggests that even in the well preserved sample, oxidation already occurs and that secondary alkanols can be used as specific markers for low intensity oxidation.     

Colony-Specific Cuticular Hydrocarbon Profile in Formica argentea Ants

The cuticular hydrocarbons of the ant Formica argentea were identified by gas chromatography/mass spectrometry. Behavioral bioassays tested the role of each class of cuticular hydrocarbon in nestmate recognition, and statistical analyses looked for potential colony-specific signatures. The cuticular hydrocarbons of F. argentea consist of n-alkanes, alkenes, and methyl-branched alkanes. Behavioral bioassays demonstrated that changes in the alkene and methyl-branched alkane signature of F. argentea increased aggression, but changes in alkanes did not. Statistical analyses demonstrated that F. argentea workers present a colony-specific hydrocarbon profile based on their methyl-branched C₂₉ alkane signature. Using this signature alone, it is possible to group worker ants statistically by nest, suggesting that methyl-branched C₂₉ alkanes may be important in nestmate recognition for this species. These results support the idea that variation in positional isomers of cuticular hydrocarbons of the same carbon chain length may provide enough information for nestmate recognition. Although the addition of alkenes increased aggression in F. argentea, alkenes did not provide a colony-specific signature. This study reinforces the idea that investigators studying nestmate recognition should not examine cuticular hydrocarbon profiles as a whole but rather, should look for colony-specific signatures embedded in parts of the profile.     

Low temperature air oxidation of n-alkanes in the presence of Na-smectite

This paper is the continuation of a study concerning the catalytic effects of clay on organic matter and especially n-alkanes during oxidation carried out at low temperature. The influences of clay minerals were investigated to understand their role better during natural oxidation of organic matter.n-Alkanes oxidation experiments in presence of Na-smectite were carried out at 100 °C during 512 h and reveal an important production of oxygen-bearing molecules to the detriment of initial n-alkanes. Thus, Na-smectite allows to initiate the auto-oxidation of n-alkanes due to its chemical (charged sheets) and/or physical (high specific area) properties. The evolution of oxygen-bearing molecules distribution enables to distinguish two competitive chemical pathways. On one hand, alcohols and ketones are produced with an aliphatic chain length similar to the starting n-alkanes. On the other hand, aliphatic chain cleavages occur and principally produce 1-alcohols, 2-ketones, carboxylic acids and 3-substitued γ-lactones. These oxygen-bearing compounds are more and more preponderant and evidence the fact that cleavage mechanisms become progressively dominant.     

Chemical structure of the high-molecular-weight hydrogenation products of coal from the Zashulanskoe field

The results of experimental studies on the determination of the chemical structure of asphaltenes and preasphaltenes in the liquid products of the hydrogenation of coal from the Zashulanskoe field in the Chita oblast. It was found that, in the preasphaltenes, the value of f _a and the concentrations of oxygen groups (OH, COOH, and C=O) were greater and the concentrations of CH₂ and CH₃ groups were smaller that those in the asphaltenes. The highest concentration of CH₂ groups was found in substances soluble in n-hexane (oils). It is likely that the change in the character of high-molecular-weight hydrogenation products formed from the structural fragments of the organic matter of coal (OMC) largely depended on reaction conditions, namely, the rate of heating and the isothermal exposure time.     

Geochemical characterization of solid residues, bitumen and expelled oil based on steam pyrolysis experiments from Irati oil shale, Brazil: A preliminary study

Steam pyrolysis experiments were performed on immature samples from the Irati oil shale, Paraná Basin, Brazil, using a maximum temperature of 350 °C with up to 98 h exposure time at that temperature. The objectives were to study geochemical and petrographical changes in the source material during stepwise increase in maturity, in steam conditions, comparing the properties of expelled oil with the bitumen retained in the solid residue after experimentation.Petrographical and geochemical parameters such as vitrinite reflectance and T_max, indicated an increase in maturity related to the exposure time of the organic matter to the maximum temperature. However, biomarker ratios such as 22S/(22S + 22R) C₃₁ and C₃₂ homohopanes, 20S/(20S + 20R) and αββ/(αββ + ααα) C₂₉ sterane, which are considered to be indicators of organic matter maturity levels, did not reach their equilibrium values. Some biomarkers frequently used as indicators of specific sources and/or paleoenvironments of deposition such as hopane/sterane ratio, and the concentrations of C₂₇ and C₂₉ steranes showed significant variations related to the stage of maturity. Based on the evaluation of Rock-Eval parameters, the transformation ratios in steam pyrolysis conditions reached levels higher than 80% in samples having 9 and more hours of exposure time to maximum temperature. Bitumen was found to be enriched in components of heavier molecular weight (resins and asphaltenes), whereas the expelled oils contained higher quantities of aliphatic and aromatic components. At relatively low maturity levels the n-alkane distribution of expelled oils indicate a somewhat higher maturity level when compared to the n-alkane distribution of the bitumen retained in the source rock, whereas at higher maturity levels the n-alkane distribution for the expelled oil and for the bitumen is very similar.     

Characterization of molecular markers in smoke from residential coal combustion in China

The organic constituents and distributions of molecular markers emitted from a residential coal-stove burning honeycomb coal briquettes were determined in this study. The major organic components emitted directly in smoke particles were polycyclic aromatic hydrocarbons (PAHs), with abundant hydroxy-polycyclic aromatic hydrocarbons (OH-PAHs), i.e., thermally altered derivative compounds from coal combustion, UCM (unresolved complex mixture of branched and cyclic compounds), n-alkanes and n-alkanoic acids. Other compounds present as minor components included n-alkenes, phenols, alkylbenzenes and n-alkanols. The distributions of the organic compounds in the coal smoke samples were highly variable and dependent on combustion temperature, flame aeration, fire duration, and coal rank. Coal smoke emissions may be identified by some indicators including: (1) presence of hydroxy-PAHs, (2) the decrease in carbon preference index (CPI) of n-alkanoic acids with increasing rank, (3) the decrease of the ratios of 17α(H),21β(H)-29-norhopane to 22R-17α(H),21β(H)-homohopane and 17α(H),21β(H)-29-norhopane to 17α(H),21β(H)-hopane with increasing rank, (4) the increases in the homohopane index [22S/(22S + 22R)] and the 17α(H),21β(H)-hopane to 17β(H), 21α(H)-hopane ratio with increasing rank, and (5) the increase of benzo[e]pyrene/(benzo[e]pyrene + benzo[a]pyrene) with increasing rank. In addition, the diagnostic ratios among PAHs and between PAHs and the corresponding hydroxy-PAHs, such as benz[a]anthracene/(benz[a]anthracene + chrysene), indeno[1,2,3-cd]pyrene/(indeno[1,2,3-cd]pyrene + benzo[ghi]perylene), pyrene/OH-pyrene, and chrysene/OH-chrysene can be used to distinguish bituminous from anthracite coal smoke emissions.     

Rise velocities and gas-liquid mass transfer of bubbles in organic solutions

Bubble size, shape, rise velocity and liquid side mass transfer coefficient have been experimentally determined for bubbles rising in organic systems, consisting of single or mutually soluble components, namely: alkanes (n-dodecane, n-hexadecane), alcohols (ethanol, 1-butanol, 1-octanol) and mixtures thereof. For pure solvents (alkanes and alcohols alike), it was found that the bubbles are non-spherical, and that both the rise velocity and the mass transfer coefficient are close to those expected for bubbles with a mobile surface.For alkane-alcohol solutions, on the other hand, the bubbles become almost spherical, and their rise velocity and mass transfer coefficient decrease, taking values intermediate between those of rigid bubbles and bubbles with a mobile surface. Trace concentrations of either alkane in alcohol or alcohol in alkane are enough for this effect to be observed. The bubbles, however, never become completely rigid in the whole range of concentrations between pure alkane and pure alcohol.Use of Higbie's equation with experimental value of slip velocity to calculate the mass transfer coefficient, k_L, (system n-dodecane/1-octanol) yields somewhat high predictions of k_L, but follows the trend of experimental k_L with concentration for most of the concentration range. However, for very small concentrations of either component, Higbie's equation gives completely wrong results, both in magnitude and in trend. The reason for this behaviour is unknown.     

Comparative studies of oil compositions produced from sawdust,rice husk,lignin and cellulose by hydrothermal treatment

The objective of this study is to investigate the distribution of products, i.e. liquid, gas and solid from wood (sawdust) and non-wood biomass (rice husk), and major biomass components, i.e. lignin, cellulose produced by hydrothermal treatment (280 °C for 15 min) and analysis of liquid hydrocarbons (oils) for the differences in the hydrocarbon composition with respect to feed material. Cellulose showed the highest conversion among the four samples investigated in the present study. Sawdust and rice husk has almost similar conversions. Liquid products were recovered with various solvents (ether, acetone, and ethyl acetate) and analyzed by GC–MS. The oil (ether extract) from the hydrothermal treatment of cellulose consisted of furan derivatives whereas lignin-derived oil contained phenolic compounds. The compositions of oils (ether extract) from sawdust and rice husk contained both phenolic compounds and furans, however phenolic compounds were dominant. Rice husk derived oil consists of more benzenediols than sawdust derived oil. The volatility distribution of oxygenated hydrocarbons were carried out by C-NP gram and it showed that the majority of oxygenated hydrocarbons from sawdust, rice husk and lignin were distributed at n-C₁₁, whereas they were distributed at n-C₈ and n-C₁₀ in cellulose-derived oil. The gaseous products were carbon dioxide, carbon monoxide, methane in sawdust, rice husk, lignin and cellulose. In addition to this, ethylene, ethane and propane were observed for sawdust, rice husk and lignin. The major gas product was carbon dioxide for all samples.     

Improved empirical correlation for petroleum fraction composition quantitative prediction

The prediction of the composition of petroleum fractions and pure hydrocarbon mixtures is a sensitive operation. Up till now, the already developed correlations in the literature are based on experimental data of crude oils. In this work, a new method is proposed for correlations elaboration based on the use of pure hydrocarbons specific data. This technique enables the characterization of the composition (wt%), in paraffins, naphthenes and aromatics, of pure hydrocarbon mixtures and petroleum fractions issued from different crude oils, according to their physical properties that are easily accessible such as normal boiling point (T_b), density (d), refractive index (n) and carbon to hydrogen weight ratio (CH).     

Microbial alteration of organic matter of humic coal during biological desulphurisation

The biodegrading influence of biological desulphurisation on bituminous coal and its density fractions was investigated using gas chromatography-mass spectrometry for organic matter alteration and atomic absorption for the assessment of changes in several trace element concentrations. Changes in extract group composition were assessed by comparing the contents of aliphatic, aromatic and polar compounds separated by preparative thin layer chromatography. Aliphatic compounds show extensive alteration due to biodegradation, mainly removal of n-alkanes and lighter acyclic isoprenoids from extracts. The sterane distribution was strongly affected while hopane/moretane distributions show minor changes. Aromatic hydrocarbons were less influenced but some changes were found. It can be assumed that the degree of biodegradation of density fractions increases with increasing concentration of mineral matter since density fractions with lower mineral concentration show smaller changes as a result of biodegradation than those with higher content of minerals. Reduction of concentrations of the following trace elements occurred: beryllium, chromium, zinc, gallium, cadmium, cobalt, lithium, manganese, copper, molybdenum, nickel, lead, and vanadium. The content decrease of an element is not influenced by its geochemical properties. An equally important factor seems to be bonding to organic and inorganic coal substances.     

Constitution of tars from the flash pyrolysis of Australian coals: 1. Separation

Separation of the maltene fraction of Millmerran flash-pyrolysis coal tar by ion-exchange and adsorption chromatography produced coal-tar resins, aromatic hydrocarbons (AH) and an alkane/alkene fraction. The coal-tar resins comprise acid, base, neutral and polyfunctional fractions. Derivatives of benzene and naphthalene are the main volatile constituents of the AH fraction, while the alkane/alkene fraction consists mainly of straight-chain hydrocarbons from C₁₀ to C₃₄ and small amounts of isoprenoid hydrocarbons, steranes and triterpanes. Fuller's Earth, used in the separation of the maltenes, suffers from the disadvantage of irreversibly adsorbing organic material.     

Molecular motion in α-methylstyrene and styrene-alkane copolymers studied by 13C n.m.r. spectroscopy

The temperature dependence of the ¹³C n.m.r. relaxation times are reported for a series of copolymers formed between methyl styrene or styrene and various α, ω-alkyl dihalides. The polymers studied contained alkyl blocks with n (the number of CH₂ units) varying from 0–10. The relaxation data indicates that the motion of both the styrene and the alkyl blocks change with the value of n. A comparison of the ¹³C relaxation data with that obtained from ultrasonic relaxation measurements supports the hypothesis that in the higher members of each series the alkane chain moves essentially independently of the ‘styrene’ moiety. The variation in the activation energy of the relaxation of the styrene moiety reflects in part a decoupling of the neighbouring phenyl group motion, as a consequence of the introduction of the alkane block.     

High-yield hydrogen production by supercritical water gasification of various feedstocks: Alcohols,glucose, glycerol and long-chain alkanes

Continuous supercritical water gasification (SCWG) of various feedstocks of C1–C16 was conducted to produce hydrogen-rich gas. These feedstocks represent model compounds of biomass such as methanol/ethanol (alcohol-type), glucose and glycerol (byproducts of biodiesel synthesis), and model compounds of petroleum fuels such as iso-octane/n-octane (gasoline), n-decane/n-dodecane (jet fuels) and n-hexadecane (diesel). Almost complete gasification of all the feedstocks was achieved at 25 MPa, 740 °C and 10 wt% with low total organic carbon values of their liquid effluents. The hydrogen gas yields of each feedstock were very similar to the theoretical equilibrium yields estimated by Gibbs free energy minimization. SCWG at different gasification temperatures (650 and 740 °C) and concentrations (10 and 20 wt%) revealed that methanol and ethanol (alcohols), the simple oxygenated hydrocarbons, were easier to be gasified, producing negligible amounts of liquid products, when compared with long-chain hydrocarbons (iso-octane and n-decane) under the identical conditions. When the feedstock concentration was increased from 10 to 20 wt%, the equilibrium hydrogen ratio from iso-octane gasification decreased from 1.02 to 0.79 while that of n-decane increased from 1.12 to 1.50, implying that a branched hydrocarbon may be more resistant to gasification in supercritical water.     

Adsorption from solution of large alkane and related molecules onto graphitized carbon

A reanalysis of experimental adsorption isotherms and enthalpies of adsorption is made for higher n-alkanes (C₁₆–C₃₂) adsorbed from dilute solutions of nonpolar organic solvents onto graphitized carbon. The submonolayer region of the adsorption isotherms suggests an alignment and close packing of the long-chain alkane molecules parallel to the graphite surface, and the results conform to a simple parallel-layer model with a large Flory-Huggins-type interaction parameter χ^a which is attributed to strong lateral adsorbate-adsorbate interactions. This interpretation of the adsorption isotherms is consistent with the calorimetric data, which yield a pronounced increase of the differential molar enthalpy of displacement with the fraction of surface covered by the long-chain alkane. Preliminary results on competitive adsorption of two solutes are presented in the second part of the paper. Different types of adsorption behaviour (mixed monolayer phase and two-dimensional eutectic) are observed depending on whether the individual solutes form close-packed ordered monolayers at the solution/graphite interface.     

Diffusion of hydrocarbon mixtures in MFI zeolite: Influence of intersection blocking

Branched and cyclic hydrocarbons such as iso-butane, 2-methylpentane, 3-methylpentane, 2,2-dimethyl-butane and benzene are preferentially adsorbed at the intersections of the channels of MFI zeolite; they serve as bottlenecks for molecular traffic in mixtures with linear C1–C6 alkanes. Molecular dynamics simulations show that as the loadings of tardier iC4, 2MP, 3MP, 22DMB, and Bz is progressively increased to four molecules per unit cell the diffusivity of the more mobile linear alkane reduces nearly to zero. The reduction in the n-alkane diffusivity is quantitatively similar irrespective of the branched/cyclic hydrocarbon.