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.     

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.     

Thermogravimetry and decomposition kinetics of British Kimmeridge Clay oil shale

The characteristics of volatile matter evolution and the kinetics of thermal decomposition of British Kimmeridge Clay oil shale have been examined by thermogravimetry. TG has provided an alternative to the Fischer assay for shale grade estimation. The following relation has been derived relating TG % volatiles yield to the shale gravimetric oil yield: oil yield (g kg^?1) = (TG volatiles, % × 5.82) ? 28.1 ± 14.5 g kg^?1. A relationship has also been established for volumetric oil yield estimation: oil yield (cm³ kg^?1) = (TG volatiles, % × 4.97) – 5.43. TG is considered to give a satisfactory estimation of shale oil yield except in certain circumstances. It is found to be less reliable for low yield shales producing <≈40 cm³ kg^?1 of oil (≈10 gal ton^?1) where oil content of the TG volatiles is low: volumetric yield estimation accuracy is affected by variations in shale oil specific gravity. First order rate constants, k = 4.82 × 10^?5s^?1 (346.3 cm³ kg^?1shale) and k = 6.78 × 10^?5s^?1 (44.6cm³ kg^?1shale) have been obtained for the devolatilization of two Kimmeridge oil shales at 280 °C using isothermal TG. Using published pre-exponential frequency factors, an activation energy of ≈57.9 kJ mol^?1 is calculated for the decomposition. Preliminary kinetic studies using temperature programmed TG suggest at least a two stage process in the thermal decomposition, with two maxima in the volatiles evolution rate at ≈450 and 325 °C being obtained for some samples. Use of published pre-exponential frequency factors gives activation energies of ≈212 and 43 kJ mol^?1 for these two stages in the decomposition.     

Characteristics of jet fuels produced from hydrogenated shale oils

Shale oils from the United States (Geokinetics, Occidental, Paraho and Tosco II) were hydrotreated, fractionated into jet fuel cuts (boiling range 121–300°C), then characterized to evaluate their suitability as jet fuels. Nitrogen content was considerably higher, though the amount of hydrogen was relatively lower, than in typical petroleum jet fuels. Sulfur content was significantly below the acceptable limit. Trace metal contents in shale oil jet fuels were below the maximum levels for those in petroleum jet fuels. Vanadium, copper, lead and alkali metals were not present. Physical properties, except freezing points, were comparable to those of standard jet fuels.     

Thermal degradation of shale oils: 1. Kinetics of vapour phase oil degradation

As vertical modified in-situ retorts (VMIS) have been scaled up and tested, the overall oil yield has declined and is generally lower than that observed in an above-ground process. This reduced oil yield could adversely affect the economics of VMIS retorting. Diminished yields are attributed to a combination of factors associated with scale-up such as in complete rubblization, wide particle size distributions (large blocks of shale), and poor flow distributions. Additionally, oil losses can occur by comparatively long exposure of the oil vapours to high temperatures, by exposure to successive condensation and revaporization of the oil as it travels down the retort, and finally by long time thermal exposure of the condensed oil retained in the bottom portion of large VMIS retorts. To study such vapour phase degradation of shale oil using oil produced from Occidental Petroleum's No. 6 VMIS retort, a tubular continuous flow reactor, with an on-line gas chromatograph for gas composition monitoring was used to study thermal degradation of shale oil under retorting conditions. Oil and a combination of gases including steam were metered into the preheater and then the vapours passed into a quartz tubular reactor where the temperature and residence time of the gaseous mixture were controlled. Complete mass balances were performed giving the weight fraction of oil converted to noncondensable hydrocarbon gases and coke. This experimental design is novel because high temperature thermal degradation of shale oil was studied for the first time under steady state flow conditions with carefully controlled residence time and temperature. A range of temperatures (425–625 °C) and residence times (2–10 s) were used in a series of factorial-designed experiments (3²) to accurately determine the effects of these variables. Results of the study showed that the addition of steam to the carrier gas did not reduce oil degradation losses but did react with the coke thereby changing the product gas composition and quantity. A first-order oil degradation rate expression was used to model the rate of oil loss. The calculated activation energy was 17.3 kcal mol^?1. Chemical analyses of the product liquids and gases confirmed previously reported findings that the oil loss indices (alkene/alkane, ethylene/ethane, naphthalene/(C₁₁ + C₁₂), and gas/coke) increase with increasing oil degradation.     

N.m.r. study of US Eastern and Western shale oils produced by pyrolysis and hydropyrolysis

Shale oils produced from US Eastern and Western oil shales by pyrolysis and hydropyrolysis processes have been investigated by both ¹H and ¹³C high-resolution n.m.r. techniques. Eastern shale oils produced by hydropyrolysis, and subsequently hydrotreated, were also included. From the n.m.r. data of the shale oils, the average molecular structure parameters were calculated. These parameters quantitatively represent the differences observed in the n.m.r. spectra of the various shale oils because of changes in the chemical composition. Mol percentages of aromatics, olefins, and alkanes were also determined for the shale oils, and show that the composition of the shale oil is dependent upon the geographic origin of the oil shale, the pyrolysis method, and the hydrogenation process. In addition to the study of shale oils, solid-state ¹³C n.m.r. spectra of Eastern and Western oil shales before and after pyrolysis and hydropyrolysis were obtained. The spectral data show that the carbon aromaticities for the Eastern oil shales and shale oils are higher than for the Western oil shale and shale oils. The data also show that hydropyrolysis relative to pyrolysis reduces the amount of residual organic carbon remaining on the spent shales. Carbon aromaticity data for both oil shale and shale oil suggest that the organic moieties present in kerogen may be retained in the shale oils to a greater extent after hydropyrolysis than after pyrolysis.     

Comparative studies on the yield and quality of oils extracted from Moroccan oil shale

In the present work, the effect of solvent on the sub and supercritical extraction of the organic matter from Tarfaya's oil shales was studied. The experimental results revealed that the extraction yield obtained by the phenol is very high compared to that obtained by the toluene or without solvent. In addition, the solvent had a significant effect on the yield and the composition of the obtained oil. The analyses carried out on the recovered oils allowed us to establish that the phenol is a very efficient solvent for oil shale extraction, giving a better quality of the oils extracted containing a large proportion of maltenes and aromatics compounds and fewer amounts of sulphur and paraffin compounds.     

煤系共伴生油页岩热解残渣利用技术

油页岩残渣是油页岩热解过程中排放的固体废物,约占油页岩的80%~90%。中国油页岩残渣利用率较低,残渣堆积量日益增多,后续问题十分突出。煤系油页岩残渣的资源化利用成为油页岩热解提油产业发展的瓶颈。介绍了油页岩热解加工利用现状及其残渣在废水处理和废气吸附方面的应用,分析了当前页岩热解残渣利用过程中存在利用方式单一的问题,并结合油页岩热解残渣结构和组成的特殊性,提出了油页岩残渣用作环保材料如吸附剂的发展方向。     

Acoustic wave propagation in oil shale: 1. Experiments

This study examines the propagation characteristics of compressional (P) and shear (S) acoustic waves through cored and broken Green River oil shale specimens. Both compressional and shear wave velocities (V_p and V_s) are sensitive to shale organic content, showing a monotonic decrease with increasing organic content in the range 30–200 L/t. Trends in the dependence of V_p and V_s on temperature are explained by thermal alterations in the shale matrix which include release of free and bound water molecules, pyrolysis of organic matter and re-cementation of the shale matrix by the products of pyrolysis. The temperature dependence of V_p and V_s is less pronounced when the acoustic energy propagates in a plane parallel to the shale bedding planes. Channelling of acoustic energy via mineral-rich layers has been invoked to explain the anisotropy. The degree of anisotropy is also dependent on shale organic content; the differences becoming less pronounced at high levels of organic content. Data on V_p and V_s for burnt and retorted shales show minimal temperature dependence, although these values are sensitive to the initial organic content of the material. Finally, measurements on broken pieces of shale reveal the expected increase in V_p and V_s with increasing compaction pressure. The decrease in V_pand V_s with decreasing particle size down to 0.6?0.3 mm is rather anomalous and can be explained only by the presence of a large number of narrow voids in the material.     

Steam cracking of coal-derived oils and model compounds: 1. Cracking of tetralin and t-decalin

Cracking of tetralin and t-decalin has been investigated in the temperature range between 700 and 850 °C and with residence times between 0.08 and 0.4 s. Most of the tetralin is dehydrogenated to yield 1,2-dihydronaphthalene and naphthalene. Other main products are indene and styrene, whereas t-decalin is predominantly cracked into ethylene and BTX aromatics. The kinetics of decalin decomposition can be described by a first-order irreversible reaction, whereas the behaviour of tetralin has to be expressed in terms of a reversible reaction. The overall activation energies are determined.     

Effect of toluene proportion on the yield and composition of oils obtained by supercritical extraction of Moroccan oil shale

Supercritical extraction of Tarfaya's oil shale by toluene revealed that the solvent proportion has a significant effect on the yield and the composition of the obtained oils. The analyses carried out on the recovered oils allowed to establish the optimal operating conditions giving the highest oil yields. In addition, it was observed that these oils contain a large proportion of aromatics compounds.     

Steam cracking of coal-derived oils and model compounds: 2. Cracking of hydrogenated coal-derived oils

Coal-derived oils of different degrees of hydrogenation and of different boiling ranges as well as a petrol-based gas oil (for comparison) have been thermally cracked at 830 °C with a residence time of 0.14s. Hydrogenated coal-derived middle oil yields less light olefins than gas oil (32 versus 40 wt%) but substantially more BTX aromatics (21 versus 7 wt%). The amount of olefins (42 wt%) from hydrogenated coal-derived light oil is higher and that of BTX aromatics (16 wt%) is slightly less than obtained from middle oil. Perhydrogenated coal-derived middle oil (> 99% saturated compounds) has been cracked within a wide temperature- and residence time range to verify the applicability of two crack severity functions designed to represent the product distribution. The latter are compared with that of t-decalin and naphtha.     

SO2 emissions from the oxidation of retorted oil shale

Sulphur dioxide emissions from the oxidation of retorted Colorado oil shale at temperatures > 530 °C are <0.2% of the sulphur present. Sulphur is retained in the oxidized shale by displacement reactions with carbonates to form sulphates. Thermal decomposition of carbonates is not necessary.     

Hydrotreatment of pyrolysis oils from biomass: reactivity of the various categories of oxygenated compounds and preliminary techno-economical study

This paper describes essential aspects of the hydrotreatment of pyrolytic oils in the light of results obtained until now at the Université Catholique de Louvain. Stability of pyrolysis oils necessitates a two-step processing. A low temperature hydrotreatment enables stabilization through reactions like olefin, carbonyl and carboxylic groups reduction. Further hydrotreatment aims at hydrodeoxygenation of phenols and hydrocracking of larger molecules. Results about catalysts, reaction conditions and parameters enabling or influencing the control of the reaction are summarized. Based on these laboratory data, a preliminary techno-economical evaluation is made. 50 wt.-% yields in hydrocarbons for deep hydrorefining of pyrolysis oils can be expected. Nevertheless, a moderate hydroconversion with partial elimination of oxygen would be, economically, more advantageous.     

Formation mechanism of solid product produced from co-pyrolysis of Pingdingshan lean coal with organic matter in Huadian oil shale

A mixture of Pingdingshan lean coal and acid-treated Huadian oil shale was co-pyrolyzed in a drop-tube fixed-bed reactor in the temperature range of 300℃–450℃.To reveal the formation mechanism of the solid co-pyrolysis product,changes in some physicochemical properties were investigated,using analysis by X-ray diffraction,X-ray photoelectron spectroscopy,scanning electron microscopy,pore analysis,thermogravimetry,and electron spin resonance.X-ray diffraction showed that the lattice plane spacing for the co-pyrolyzed mixture decreased from 0.357 nm to 0.346 nm and the average stacking height increased from 1.509 nm to 1.980 nm in the temperature range of 300°C–450°C,suggesting that pyrolysis treatment increased its degree of metamorphism.The amount of oxygen-containing functional groups and pore volume decreased with increasing temperature.Thermogravimetry and electron spin resonance results showed that synergistic effects occurred during the co-pyrolysis process.A formation mechanism for the solid product was proposed.Hydrogen-rich radicals generated from the pyrolysis of the oil shale were trapped by hydrogen-poor macromolecular radicals of the intermediate metaplast produced from coal pyrolysis,thereby increasing the yield of solid product.     

Co-current combustion of oil shale - Part 1: Characterization of the solid and gaseous products

Co-current combustion front propagation in a bed of crushed oil shale (OS) leads to the production of liquid oil, of a flue gas and of a solid residue. The objective of this paper was to provide a detailed chemical characterization of Timahdit oil shale and of its smoldering combustion products. The amount of fixed carbon (FC) formed during devolatilization is measured at 4.7% of the initial mass of oil shale whatever the heating rate in the range 50-900 K min⁻¹. The combustion of oil shale was operated using a mix of 75/25 wt. of OS/sand with an air supply of 1460 l min⁻¹ m⁻². In these conditions, not all the FC is oxidized at the passage of the front, but 88% only, with a partitioning of 56.5% into CO and the rest into CO₂. A calorific gas with a lower calorific value of 54 kJ mol⁻¹ is produced. Approximately 52% of the organic matter from OS is recovered as liquid oil. The front decarbonates 83% of carbonates.     

Stereospecific analysis of triacylglycerols from vegetable oils by two procedures—II: Normal and high-oleic sunflower oils

Triacylglycerol stereospecific analysis of normal (NOS) and high-oleic sunflower (HOS) oils was carried out by two procedures to study the influence of variety and growing conditions. Four cultural varieties, two NOS and two HOS, were grown in seven different places of Italy. Three of the four varieties were grown both in dry conditions and with irrigation. Concerning the triacylglycerol fatty acid compositions, the results showed no significant differences between irrigated and nonirrigated samples (P>0.05), between the two NOS, and between the two HOS varieties. Between NOS and HOS varieties, only stearic acid showed no significant differences (P>0.05). The fatty acid compositions of the sn-2 position of NOS and HOS samples showed different percentage abundances (P<0.01), especially for oleic and linoleic acids. Fatty acid distributions in the sn-1 and sn-3 positions indicated a certain asymmetry. The relationships between the percentage intrapositional content of each acid (one sn-position at a time) and its percentage content in the original triacylglycerol matrix were studied. A general regression model was used to verify if the content of each acid at the three stereospecific positions changed at the same rate as the content in the intact triacylglycerols. The interpositional compositions of all varieties of NOS and HOS oils showed analogous trends for each acid.     

Modeling calcium dissolution from oil shale ash: Part 1. Ca dissolution during ash washing in a batch reactor

Batch dissolution experiments were carried out to investigate Ca leachability from oil shale ashes formed in boilers operating with different combustion technologies. The main characteristics of Ca dissolution equilibrium and dynamics, including Ca internal mass transfer through effective diffusion coefficients inside the ash particle were evaluated. Based on the collected data, models allowing simulation of the Ca dissolution process from oil shale ashes during ash washing in a batch reactor were developed. The models are a set of differential equations that describe the changes in Ca content in the solid and liquid phase of the ash-water suspension.     

Physical behaviour of oil shale at various temperatures and compressive loads: 1. Free thermal expansion

The effects of grade and specimen orientation on the free thermal expansion of oil shale were investigated. The expansion was found to increase with the grade of the specimen and to be dependent on orientation. The change in heating rate from 1.0 K min⁻¹ to 3.5 K min⁻¹ had little effect on the expansion of oil shale. It was found that many of the oil shale specimens would settle under their own weight once kerogen left the oil shale. The thermal expansion coefficients in the temperature range 373–473 K were determined to be little affected by increases in grade. A polynomial correlation of expansion versus grade and temperature in the temperature range 298–698 K is presented. The behaviour at temperature up to 1000–4000 K was also investigated.     

Transformer oils prepared from the vacuum distillates of Egyptian crude paraffinic petroleum

Vacuum gas oil and spindle oil obtained from the vacuum distillation of paraffinic crude oil from the Western Desert region of Egypt were utilized for transformer oils production. The vacuum gas oil, spindle oil and blends therefrom containing different percentages of these oils and were subjected to aromatic extraction, dewaxing catalytic hydrogenation processes. The aromatic extraction process used N-methyl-2-pyrrolidone as solvent, for a feed ratio of 0.7:1 (wt/wt) at an extraction temperature of 55 °C, while in the dewaxing process the wax is removed by chilling the raffinate at − 42 °C using MEK-toluene (60:40,vol/vol). The hydrofinishing process was achieved in a pilot plant using NiO–MoO₃/Al₂O₃ catalyst. These refining processes improved the viscosity indices and the pour points of the resulting oils and removed most of the polar impurities. It was found that, the transformer oil formulated from 7:3 b.w. vacuum gas oil:spindle oil respectively meets the IEC 60296-2003 standard specifications requirements. Its sulfur content is very low and non-corrosive. The gassing tendency is also low due to its low aromatic content. Further, the electrical properties which are significant for transformer oils fulfill the standard specifications as a result of the low water content and polar contaminants. Moreover, addition of 2,4-dimethyl-6-tertiary butyl phenol increases the oxidation stability of the produced oil, by acting as a free radical inhibitor.