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The chemical building blocks that comprise petroleum asphaltene molecules were determined by thermal cracking of samples under conditions that minimized alterations to aromatic and cycloalkyl groups. Favorable hydrogenation conditions that used tetralin as a hydrogen-donor solvent and an iron-based catalyst allowed asphaltenes derived from different crude oils to yield approximately 50–60 wt % distillates (

Thin film pyrolysis was used to thermally crack asphaltene molecules into their constituent building blocks at 500 °C. By using a thin film of liquid of ca. 20 μm, the cracked products were rapidly released into a much colder sweep gas stream to quench the reactions and minimize further decomposition. The liquid products were condensed and collected, with over 91% material balance on the recovery of gas, liquid, and coke product. Simulated distillation of the condensed liquid products showed a wide range of compounds with boiling points up to more than 700 °C produced in various stages of the reaction. Less than 1% of the original mass of the asphaltenes was released in the form of light gases such as methane and ethane. The liquid components boiling below 538 °C comprised 15–20% of the initial asphaltenes, and contained a wide range of chemical structures including paraffins, olefins, naphthenes, aromatics, thiophenes and sulfides, and nitrogen-containing compounds, identified by gas chromatography–field...

Solid bitumen can arise from several reservoir processes acting on migrated petroleum. Insoluble solid organic residues can form by oxidative processes associated with thermochemical sulfate reduction (TSR) as well as by thermal chemical alteration (TCA) of petroleum. TCA may follow non-thermal processes, such as biodegradation and asphaltene precipitation, that produce viscous fluids enriched in polar compounds that are then altered into solid bitumens. It is difficult to distinguish solid bitumen formed by TCA from TSR since both processes occur under relatively high temperatures. The focus of the present work is to characterize solid bitumen samples associated with TSR- or TCA-processes using a combination of solid-state X-ray Photoelectron Spectroscopy (XPS), Sulfur X-ray Absorption Near Edge Structure Spectroscopy (S-XANES), and 13C NMR. Naturally occurring solid bitumens from three locations, Nisku Formation, Brazeau River area (TSR-related); La Barge Field, Madison Formation (TSR-related); and, the Alaskan North Slope, Brooks Range (TCA-related), are compared to solid bitumens generated in laboratory simulations of TSR and TCA. The chemical nature of solid bitumens with respect to organic nitrogen and sulfur can be understood in terms of (1) the nature of hydrocarbon precursor molecules, (2) the mode of sulfur incorporation, and (3) their concentration during thermal stress. TSR-solid bitumen is highly aromatic, sulfur-rich, and nitrogen-poor. These heteroatom distributions are attributed to the ability of TSR to incorporate copious amounts of inorganic sulfur (S/C atomic ratio >0.035) into aromatic structures and to initial low levels of nitrogen in the unaltered petroleum. In contrast, TCA-solid bitumen is derived from polar materials that are initially rich in sulfur and nitrogen. Aromaticity and nitrogen increase as thermal stress cleaves aliphatic moieties and condensation reactions take place. TCA-bitumens from the Brooks Range have

We have developed a method for calculating from first principles the amounts and composition of products resulting from the thermal decomposition of a solid complex carbonaceous material. Advanced solid state analysis provides chemical and property measurements for kerogen that are used to construct a representative model of its chemical structure (CS). These chemical structural models are then coupled with a chemical yields (CY) model that is based primarily on free radical reaction mechanisms. The combined model, CS–CYM offers the ability to predict the thermal conversion of kerogen under a wide range of heating rates and temperature. Results from laboratory heating experiments are compared with those calculated with CS–CYM and show excellent agreement with a variety of bulk physical and chemical properties, open and closed system pyrolysis yields and product compositions, and open system kinetics. The reliability of CS–CYM in predicting the thermal reactions that occur under laboratory conditions indicates that we have captured a significant portion of the thermal reaction mechanisms and pathways that occur in nature. Hence, we believe that CS–CYM approach provides a better prediction of the thermal chemistry that occurs under geologic conditions than extrapolation of experimental results conducted at much higher temperature and faster heating rates where reactions, product distributions and modes of expulsion may differ significantly from basinal processes.

The ability to predict accurately the thermal conversion of complex carbonaceous materials under a wide range of heating rates and temperatures is of value in both petroleum exploration and refining operations. Modeling the thermal cracking of kerogen and coal under basinal heating conditions improves the pre-drill prediction of oil and gas yields and quality, thereby ultimately lowering exploration risk. Modeling the chemical structure and reactivity of asphaltenes from petroleum residues enables prediction of coke formation and properties in refinery processes, thereby lowering operating cost. Previous compositional yield models based on laboratory yield measurements have been developed for specific materials, such as isolated coals and kerogens, but extrapolation to predict oil and gas generation during geologic burial is problematic. Furthermore, models based on a few reference carbonaceous materials may not simulate varying compositions of kerogen and residues seen in nature. We have developed a method to calculate the amounts and composition of products resulting from the thermal decomposition of a solid complex carbonaceous material. This procedure provides a means of using laboratory measurements of complex carbonaceous solids to construct a representative model of its chemical structure (CS) that is then coupled with elementary reaction pathways to predict the chemical yield (CY) upon thermal decomposition. Data from elemental analysis (C, H, N, O, S), solid state 13C NMR, X-ray photoelectron spectroscopy (XPS), sulfur X-ray absorption structure spectroscopy (XANES), and pyrolysis-gas chromatography (GC) are used to constrain the construction of core molecular structures representative of the complex carbonaceous material. These core structures are expanded stochastically to describe large macromolecules (>104 cores with ∼106 atoms) with bulk properties that match the experimental results. Gas, liquid and solid product yields, resulting from thermal decomposition, are calculated by identifying reactive functional groups within the CS stochastic ensemble and imposing a reaction network constrained by fundamental thermodynamics and kinetics. An expulsion model is added to the decomposition model to calculate the chemical products in open and closed systems. Product yields may then be predicted under a wide range of time–temperature conditions used in rapid laboratory pyrolysis experiments, refinery processes, or geologic maturation.

The expulsion of hydrocarbons from kerogen is the initial step in the primary migration process, during which the composition of the expelled petroleum is enriched in saturated and aromatic hydrocarbons while the retained bitumen is enriched in polar compounds. The physical and chemical principles responsible for this chemical fractionation are not well understood, and numerous theories have been proposed to explain the expulsion process. A multicomponent equilibrium likely exists between the kerogen matrix and the expelled fluid during petroleum generation and expulsion. To test whether such equilibrium can explain the nature and extent of chemical fractionation, an extended Flory-Rehner Regular Solution Theory model was developed and applied to a series of kerogens of varying structure, generative potential, and maturity. Thermodynamic parameters for immature Type II and IIIC kerogens (solubility parameter, cross-link density, and native swelling) were derived experimentally and extended to higher maturity. Mixtures of model compounds with well-defined properties were created to reflect the composition of primary generated products of kerogen thermal decomposition. Multicomponent equilibrium then was calculated under closed system conditions. The amount and composition of modeled expelled products are most sensitive to the generative potential and cross-link density of the kerogen. In general, lower source richness and cross-link density is associated with bitumen retention and a relative enrichment of the aliphatic components in the expelled fluid. Higher source richness and cross-link density result in earlier expulsion of fluids that are enriched in polar components. The predicted compositions of expelled fluids correspond well with the compositional range observed for produced petroleum. The predicted bitumen (kerogen-retained, soluble organic matter) compositions are uniformly >50% C 14 + NSOs at all levels of maturity for all modeled kerogens. A chemically driven equilibrium mechanism based on Regular Solution Theory can explain almost completely the nature and extent of chemical fractionation that takes place during expulsion.

The need for detailed molecular information from kinetic models has given rise to the practice of modeling the chemistry at either the molecular or mechanistic level. These models are often used to...

X-ray photoelectron spectroscopy (XPS) was used to identify the forms of nitrogen present in Green River Type I and Bakken Type II kerogen concentrate samples and to follow the changes in nitrogen forms in the tars and chars produced upon pyrolysis. Pyrrolic nitrogen is the most abundant form of nitrogen, followed by pyridinic, amino, and quaternary types. XPS results show that upon devolatilization at 510 °C, the resultant kerogen tar and char contain mostly pyrrolic and pyridinic forms while amino groups are preferentially released into the tar. A portion of the quaternary nitrogen initially present in the Bakken kerogen appears in the 510 °C char and tar. Similar transformations were found for low-rank coal. These transformations occur at lower temperatures at long pyrolysis times for both kerogen and low-rank coal. Severe pyrolysis of the devolatilized kerogen char (T = 630−810 °C) results in the appearance of an asymmetric carbon (1s) line shape indicative of very large polynuclear “graphitic-like” u...

Collision-induced dissociation Fourier Transform ion cyclotron resonance mass spectrometry (CID-FTICR MS) was developed to determine structural building blocks in heavy petroleum systems. Model compounds with both single core and multicore configurations were synthesized to study the fragmentation pattern and response factors in the CID reactions. Dealkylation is found to be the most prevalent reaction pathway in the CID. Single core molecules exhibit primarily molecular weight reduction with no change in the total unsaturation of the molecule (or Z-number as in chemical formula C(c)H(2c+Z)N(n)S(s)O(o)VNi). On the other hand, molecules containing more than one aromatic core will decompose into the constituting single cores and consequently exhibit both molecular weight reduction and change in Z-numbers. Biaryl linkage, C(1) linkage, and aromatic sulfide linkage cannot be broken down by CID with lab collision energy up to 50 eV while C(2)+ alkyl linkages can be easily broken. Naphthenic ring-openings were observed in CID, leading to formation of olefinic structures. Heavy petroleum systems, such as vacuum resid (VR) fractions, were characterized by the CID technology. Both single-core and multicore structures were found in VR. The latter is more prevalent in higher aromatic ring classes.

Laboratory experiments on three different source rock samples indicate that pressure effects on generation kinetics are measurable but minor. Pressure effects are quantified in terms of an activated volume which is analogous to the use of activation energy to quantify temperature effects. Although the three shales had slightly different activated volumes, a value of 27 cm 3 /mol is recommended as typical for the activated volume of the transformation of kerogen to products. With this activated volume, a 1380 bar pressure corresponds to about a 7 °C increase in generation temperature. Since generation commonly occurs at pressures less than 1380 bar, the effects of pressure on generation timing appear minor and well within the range of uncertainty from other causes

The determination of the oil generation kinetics from a given kerogen sample currently involves the assumption that high-temperature short-time laboratory data are equivalent kinetically to the geological conditions of low temperature and long times that existed as oil was generated. This extrapolation from around 400°C down to roughly 100°C covers a range in rate of about 14 orders of magnitude. Clearly, one must be fairly confident that the general chemistry that applies at the laboratory conditions also applies at geological conditions

Insoluble solid bitumens are organic residues that can form by the thermal chemical alteration (TCA) or thermochemical sulfate reduction (TSR) of migrated petroleum. TCA may actually encompass several low temperature processes, such as biodegradation and asphaltene precipitation, followed by thermal alteration. TSR is an abiotic redox reaction where petroleum is oxidized by sulfate. It is difficult to distinguish solid bitumens associated with TCA of petroleum from those associated with TSR when both processes occur at relatively high temperature. The focus of the present work was to characterize solid bitumen samples associated with TCA or TSR using X-ray photoelectron spectroscopy (XPS). XPS is a surface analysis conducted on either isolated or in situ (>25 μm diameter) solid bitumen that can provide the relative abundance and chemical speciation of carbon, organic and inorganic heteroatoms (NSO). In this study, naturally occurring solid bitumens from three locations, Nisku Fm. Brazeau River area (TSR-related), LaBarge Field Madison Fm. (TSR-related), and the Alaskan Brooks range (TCA-related), are compared to organic solids generated during laboratory simulation of the TSR and TCA processes. The abundance and chemical nature of organic nitrogen and sulfur in solid bitumens can be understood in terms of the nature of (1) petroleum precursor molecules, (2) the concentration of nitrogen by way of thermal stress and (3) the mode of sulfur incorporation. TCA solid bitumens originate from polar materials that are initially rich in sulfur and nitrogen. Aromaticity and nitrogen increase as thermal stress cleaves aliphatic moieties and condensation reactions take place. Organic sulfur in TCA organic solids remains fairly constant with increasing maturation (3.5 to not, vert, similar17 sulfur per 100 carbons) into aromatic structures and to the low levels of nitrogen in their hydrocarbon precursors. Hence, XPS results provide organic chemical composition information that helps to distinguish whether solid bitumen, either in situ or removed and concentrated from the rock matrix, was formed via the TCA or TRS process.

The fuel-rich combustion of coals containing calcium in various forms has been studied in a tubular downflow reactor to determine whether or not coal-bound sulfur can be efficiently retained as CaS in the recovered solids. Although physical mixtures of coal and limestone gave only limited sulfur retention, it was discovered that, under certain critical conditions, coals in which calcium had been atomically dispersed by ion exchange could be burned with the bulk of the sulfur remaining in the recovered ash/char mixture. The effect of various experimental parameters upon this new sulfur retention process are reported. Char characterization was done using scanning electron microscopy and x-ray diffraction. Analysis of the data indicated that under the conditions of these experiments, the extent of CaS formation was equilibrium limited when ion exchange Ca was used but less than equilibrium for bulk Ca.

The kinetics of the reaction of limestone/dolomite with H2S have been examined under fuel rich combustion conditions. The experiments were done in a tubular laminar flow reactor with co-current flow of gas and solids. In the temperature region, 1065-1310°C, the results were consistent with the absorption reaction of H2S first order with respect to calcium and half order with respect to H2S. Reactivity of the stones fell off substantially between 1065-1310°C because of severe desurfacing occurring at these temperatures to the limestone and dolomite. A diffusion controlled reaction is believed to be the dominant mechanism.

Uncatalysed CO2 gasification has been interpreted using the following oxygen exchange mechanism: where Cf is an available active site and C(O) is an occupied site. Reaction (2) is the step which removes carbon (as CO) out of the carbon matrix. In the present work, TGA data for catalytic systems e.g. Ca-impregnated amorphous carbon and K2CO3 mixtures with amorphous carbon, have also been found to support such an oxygen exchange mechanism. The rate constants for the decomposition of the surface intermediate have been shown to have similar activation energies for uncatalysed, K-catalysed, and Ca-catalysed amorphous carbon systems. The activation energy is 58 ± 3 kcal mol−1. In this mechanism the catalyst affects the active site density of the material (i.e., the number of Cf) but does not strongly interact with the desorption process, k2.

We have studied the reactive adsorption of O2 on the edge surface of graphite. At 300°C the efficiency of oxygen uptake showed a strong coverage-dependent reactive adsorption coefficient. In general, the efficiencies were low (< 10−9) over the majority of the coverage range. In contrast, the uptake of oxygen from O2 and H2O on sputter-damaged graphite was far more rapid. Sputter-damaged carbon surfaces exhibit greatly enhanced reactivity and are poor models of edge carbon activity. Thermal stability studies on the resultant oxidized edge graphite surfaces provide information about the energetics of product formation in gasification reactions. CO was the dominant product. A fraction of the oxygen on the surface is very tightly bound with energies greater than 85 kcal/mole. The energy decreases to 70 kcal/mole over a wide coverage range. At the highest attainable coverages representing a small fractional population, the energy decreases further down to 58 kcal/mole. Our results show that increasing the amount of oxygen surface coverage decreases the energy barrier for gaseous CO formation but increases the barrier for O2 dissociation.

A transient kinetic technique was used to measure the intrinsic rate constant k2 of the reaction C(O) → CO + Cf, where Cf is an available site and C(O) is an occupied site. It was found that k2 = 1011.6 ± 2.3 exp[ −(225 000 ± 39000)/RT]min−1. Two systems were studied, one using an uncatalysed carbon, the other a Ca-catalysed carbon. The gasification rates for these two systems differed by a factor of 100, yet they yielded the same k2. This strongly supports the contention that Ca catalyses the system by increasing the number of active sites.

We have separated and studied with surface spectroscopies the dissociative adsorption step from the CO formation step in the O2 and CO2 gasification of glassy carbon. The reactive adsorption probabilities decreased with increased coverage. Differences between O2 and CO2 were apparent at high oxygen coverages where the dissociative adsorption probability at 300°C for CO2 drops below 10−14, which is orders of magnitude less than that of O2. Estimates for the activation energy for dissociative adsorption at high coverage are 32 kcal/mol for O2 and 50–60 kcal/mol for CO2. We have examined the thermal stabilities of the resultant oxidized surfaces that yield desorption energies and provide quantitative information about the product formation step in gasification reactions. A substantial fraction of the oxygen on the carbon surface is very stable with CO formation energies of >80 kcal/mol. The energies decrease as a function of increasing oxygen coverage and at high coverages decrease below 70 kcal/mol. The energetics of CO formation from lattice carbon limit the rate of gasification by CO2. The increased gasification activity for O2 is associated with a more facile gaseous dissociation step causing higher oxygen coverages, which in turn generates lower energy CO formation sites.

We have quantified the oxidation kinetics of Illinois No. 6 bituminous coal between 295 and 398 K. X-ray photoelectron spectroscopy (XPS) was used to determine the changes in the amount of surface organic oxygen and provide an oxygen functional group distribution. GC analysis of the gas-phase products and weight changes from TGA experiments were used to place the XPS results in the context of bulk oxidation

Publisher Summary This chapter discusses the modes of occurrence of inorganic elements in coal, both as mineral phases and as organically bonded elements. The effects that highly dispersed elements may have on coal processing are also reviewed in the chapter. Mineral matter plays a variety of important roles in all coal utilization processes. Inorganically bound elements in present-day coals are the result of at least five mechanisms operating at or from the time of initial peat deposition: (1) incorporation of elements from the original plant material; (2) precipitation of elements from aqueous solution; (3) accumulation of airborne detritus; (4) accumulation of waterborne detritus; and (5) epigenetic mineralization, that is, minerals that have formed in cleats and fractures of the coal deposit. Accumulation of detrital mineral particles and the chemical precipitation of dissolved species from aqueous solution are the major processes by which inorganic elements are introduced into the peat deposit from external sources.