Method for determining the kinetics of cracking and coking of shale oil vapours in fluidized beds

The secondary cracking and coking of oil vapours produced from oil shale retorting have been previously shown to depend upon the nature and temperature of the substrate over which these reactions occur. To realistically examine the kinetics of these reactions during fluidized bed retorting, an apparatus has been developed which permits shale oil vapours generated in one fluidized bed to pass over selected substrates in a second fluidized bed. Substrates can be fed as a batch or continuously. In the batch mode, the substrate is heated to reaction temperature and is then exposed to shale oil vapours for a chosen period of time. Carbon deposition onto the solid is monitored in real-time by combusting the pyrolysis products and measuring the oxides of combustion with an on-line mass spectrometer. The extent of carbon uptake is also determined by elemental analysis of the substrate following reaction. These two methods of analysis were shown to correspond well under all the conditions investigated. In the continuous mode, substantial amounts of product oil can be collected so the effects of cracking may be evaluated. The rates of carbon deposition onto processed shales and pure minerals have been measured.     

Removal of hydrogen sulphide by combusted Rundle oil shale: sulphidation of iron oxides

Oil shale from the Rundle deposit of Queensland, Australia, after retorting and combustion in air, contains haematite and magnetite. Studies of the reactions of hydrogen sulphide with this combusted shale, and with the individual iron oxides, showed the sulphidation kinetics to be first order with respect to hydrogen sulphide, with activation energies of 35 ± 1, 59 ± 3 and 66 ± 2 kJ mol⁻¹ respectively for haematite, magnetite and combusted shale. Under dry conditions the shale trapped 36 mg of hydrogen sulphide per gram of combusted shale. With steam present, the iron oxides did not trap hydrogen sulphide and the combusted shale was also ineffective because, apart from negligible sulphidation of its iron oxide minerals, another sulphur-trapping mineral, calcium oxide, had effectively been removed by silication during combustion. The potential to control hydrogen sulphide (produced during steam retorting of shale) by recycled combusted Rundle shale is therefore poor, but a characteristic of this shale during pyrolysis is that most hydrogen sulphide is released above 500 °C, so that by minimizing retort temperatures, consistent with appropriate oil recovery, substantial control of hydrogen sulphide should be possible.     

Pyrolysis of oil shale in supercritical toluene: Reaction mechanism and role of hydrogen

Oil shale from the Stuart A deposit in Queensland, Australia has been pyrolysed in supercritical toluene in the presence and absence of gas-phase molecular hydrogen. Data have been collected in a 300-cm³ stirred tank autoclave, at a nominal residence time of 1 h, temperatures of 698 and 733 K, and 14.43 MPa total pressure (at temperature). Results for conversion of organic carbon to oil have been computed based on a carbon balance on the reaction system. The data have shown toluene to be an excellent dense-gas medium for production of shale oil from oil shale. Carbon conversions and oil yields of 86% and 95%, respectively, were achieved in the presence of gas-phase molecular hydrogen. Carbon conversions were severely depressed in the absence of hydrogen, clearly indicating the need for hydrogen activity in order to obtain high oil yields. An overall oil yield of 160% of Fischer Assay was achieved at a relatively low hydrogen consumption and moderate operating conditions.     

Hydroprocessing of stuart a (Australian) oil shale

Research on production of shale oil by direct hydrogenation of oil shale has been conducted in batch stirred autoclave reactors. The objective of the work has been to elucidate the effect of operating variables on conversion of organic carbon, and the resulting product yield structure (oil/gas). Yields of oil and gas (hydrocarbon and carbon oxide) have been quantified for hydroprocessing under a wide range of operating conditions using both hydrogen donor and pyrolysis oil (non-donor) solvents. The effects of temperature, reaction time, pressure, hydrogen partial pressure, and solvent characteristics on yield structure are described.     

Pyrolysis kinetics for Green River oil shale from the saline zone

The nature of the organic and mineral reactions during the pyrolysis of Saline-zone Colorado oil shale containing large amounts of nahcolite and dawsonite has been determined. Results reported include a material-balanced Fischer assay and measurements of gas evolution rate of CH₄, C₂H_x, H₂, CO and CO₂, Stoichiometry and kinetics of the organic pyrolysis reactions are similar to oil shale from the Mahogany zone. X-ray diffraction and thermogravimetric analysis results are used to help determine the characteristics of the mineral reactions. Kinetic expressions are reported for dawsonite decomposition, and it is demonstrated that the temperature of dolomite decomposition is substantially lower than for Mahogany-zone shale because of the presence of the sodium minerals.     

Potassium catalysed gasification of Kentucky oil shale char

The steam gasification of a Kentucky oil shale char has been studied in a semi-batch fixed bed reactor. The effects of temperature (973–1173 K), catalyst loading (0–15% K₂CO₃) and pressure (up to 0.65 MPa) on the gasification rates and make-gas composition have been determined. Although gasification rates were increased by a factor of about three in the presence of 10% K₂CO₃, they were still significantly lower than those previously measured with western shale chars. The reason for this could be attributed to the relatively high hydrogen concentrations produced in the fixed-bed configuration since severe hydrogen inhibition has been previously reported for a similar shale char. There was no significant effect of the potassium catalysis on either the make-gas composition or the quantities of sulphur released during gasification. The only significant influence of pressure was to increase the methane make and this was independent of the catalyst loading.     

油页岩热解特性及其甲烷释放规律研究

为研究油页岩热解特性及热解过程中甲烷的释放规律,采用热重-傅里叶变换红外光谱（TG-FTIR）对龙口（LK）、内蒙（NM）、汪清（WQ）三个地区的典型油页岩进行热解实验,并结合固相红外（FTIR）对油页岩的官能团结构进行分析。研究结果表明,油页岩热解过程可分为四个阶段,热解反应及挥发分释放主要发生在第二阶段（400～600℃）。甲烷的析出与油页岩结构中的脂肪烃（光谱范围3000～2800 cm^-1）密切相关,脂肪烃含量越多,热解过程中释放的甲烷越多。通过对甲烷析出曲线分峰拟合及结合动力学分析,得出甲烷的生成是由一个脱吸附过程和四个化学反应共同作用的结果。     

Chemical transformations during pyrolysis of Rundle oil shale

Rundle shale (Queensland, Australia) was pyrolysed at 12.5 K min⁻¹ to 350–500 °C for 10–240 min. The structures of the liquid products and pyrolysis residues were investigated by a number of n.m.r. spectroscopic techniques including cross-polarization and dipolar dephasing. N.m.r. provided a simple method for detecting nitrile carbon and measuring terminal and internal olefinic hydrogen in shale oil. It was found that the ratio of terminal olefinic hydrogen to internal olefinic hydrogen in shale oil increases by a factor of three over the range 350–500 °C. Moreover, the results suggest that aromatic rings in Rundle shale residues are not highly substituted and hence that aromatic ring condensation reactions are not important during pyrolysis. From elemental, yield and n.m.r. data, the conversion of aliphatic carbon to aromatic carbon during pyrolysis was found to be as high as 25% at 500 °C.     

程序升温下页岩油泥热解机理

采用热重分析仪,进行了桦甸和汪清页岩油泥在不同升温速率（5 ℃/min,10 ℃/min,20 ℃/min,40 ℃/min）下热失重实验,并通过瓦斯气析出情况研究页岩油泥热解机理。结果表明,页岩油泥热解分为3个阶段：第一阶段（20～180 ℃）为水分和轻质组分析出;第二阶段（180～360 ℃）重质组分稳定析出,是动力学研究的重点;第三阶段（360～600 ℃）为半焦炭化及矿物质失重过程。研究发现,催化剂K2CO3能有效降低油泥热解温度及其残渣率,而Al2O3对油泥热解催化不明显甚至起抑制作用。在页岩油泥热解过程中,生成的有机大分子侧链发生C—C键断链,生成小分子的烷烃和不饱和烃,在低压高温条件下,其断链位置倾向于碳链端部,使得小分子烃含量较多。     

Study of pyrolysis kinetics of oil shale

The pyrolysis experiments on oil shale samples from Fushun, Maoming, Huangxian, China, and Colorado, USA, were carried out with the aid of thermogravimetric analyzer (TGA) at a constant heating rate of 5 °C/min. A kinetic model was developed which assumes several parallel first-order reactions with changed activation energies and frequency factors to describe the oil shale pyrolysis. The kinetic parameters of oil shale pyrolysis were determined on the basis of TGA data. The relationship between the kinetic parameters was further investigated and the correlation equations of x_∞-E and ln A-E were obtained. These equations show that the final fractional conversion of each parallel reaction, x_∞(j), can be expressed as an exponential function of the corresponding activation energy. The plot of ln A-E for different reactions becomes a straight line. These relationship equations can provide important information to understand the pyrolysis mechanism and to investigate the chemical structure of oil shale kerogen.     

The effects of pyrolysis conditions on Israeli oil shale properties

This paper reports on a study which was undetaken to identify the influence of pyrolysis parameters on the qaulity and quantity of oil from the EF'E oil shale deposit in Israel. Pyrolysis experiments were performed in three reactors which allowed variations in heating rate, bed geometry, pressure, temperature, and residence time of the pyrolysis products. These parameters were varied in a series of pyrolysis tests to identify the controlling mechanisms. The pyrolysis results indicate that high oil yields can be achieved with proper process conditions. Secondary reactions of the oil (cracking and coking) are both minimized when temperature and residence time for oil in the reaction zone are kept to a minimum. When the oil remains in the hot zone, such as in the Fischer Assay, cracking lowers the oil yield and increases light hydrocarbon gases. In addition secondary reactions increase the aromaticity, decrease the nitrogen and increase the sulphur content of the oil. All evidence suggests that the Israeli shale oil is more prone to cracking than a Colorado Green River shale oil on which similar tests were performed. The average molecular weight of the Israeli oil is lower, the rate of evolution is higher and the Fischer Assay oil yield is lower.     

A kinetic and mechanistic comparison for Jordan oil shale pyrolysis and dissolution

Jordan shale pyrolysis at temperatures ranging from 280 to 518°C has been compared with thermal dissolution at temperatures from 230 to 315°C. The samples undergoing reactions were also compared when decarbonated (HCl treated shale), to verify the catalytic effects of the inorganic mineral matter.Pyrolysis reactions were studied by isothermal weight loss and non-isothermal decomposition experiments. The shale underwent softening and molecular rearrangement with a small but detectable weight change, from gaseous desorption up to 300°C. Then the kerogen began to fragment, yielding high molecular weight hydrocarbons which were evolved as volatile matter up to a temperature of about 500°C. The kinetics of both processes followed a first-order relation with time and gave an activation energy of 38.5 kJ/ mole which is well in the range of a diffusion controlled reaction. The yields were up to 23% by weight of untreated shale and 42% of decarbonated shale.For dissolution conversions of up to 90 percent by weight of shale organic matter was attainable at temperatures in the range of 315°C. The Arrhenius plot was resolved into two straight lines; one corresponding to diffusion control (E_a = 42.6 kJ/mole) and the second beginning at T = 275° with E_a = 85.6 kJ relating to cracking and hydrogenolysis of aromatic clusters. For decarbonated (carbonate-free) shale, the kinetics were first-order throughout, with E_a = 37.6 kJ/mole.The extent of kerogen sulfur removal reactions with tetralin was checked by analyzing for sulfur content in oil extract and residue. The sulfur concentrations of the gases were obtained by difference. The C/H ratios of extract and pyrolysis oil were determined to verify solvent effects.A mechanism is suggested which relates the kinetics to the transformation of kerogen to oil, gas and coke.     

Gas evolution during oil shale pyrolysis. 2. Kinetic and stoichiometric analysis

Nonisothermal rate measurements for the evolution of H₂, CH₄, C₂ hydrocarbons and C₃ hydrocarbons during the pyrolysis of Colorado oil shale have been analysed using the recent kinetic theory of Antony and Howard AIChE J. 1976, 22, 625. This analysis yields a simple set of rate expressions, which can be used for modelling kerogen pyrolysis under typical retort heating conditions. A stoichiometric representation of kerogen pyrolysis is also developed. These results are then used to derive a simple mechanistic picture of oil shale pyrolysis between 25 and 900 °C.     

Fluidized bed steam retorting of Kentucky oil shale

A three-inch (7.6-cm) diameter fluidized bed reactor has been used at the Kentucky Center for Energy Research Laboratory (KCERL), operated by the Institute for Mining and Minerals Research (IMMR), to investigate the fluidized bed retorting characteristics of Kentucky oil shales. Because steam has been indicated to be a reactive pyrolysis gas for both Eastern and Western U.S. oil shales by many, a main objective of the fluidized bed investigation was to determine the effects of steam as a fluidizing medium. This was accomplished by comparing the yields and compositions of the products from steam and N₂ retorting under otherwise equivalent fluidized bed conditions. Oil yields obtained from steam fluidization were approximately 2% greater than oil yields obtained from N₂ retorting. Steam retorting released significantly more pyritic sulfur from the shale, providing evidence that reduced hydrogen scavenging from the kerogen for H₂S production was a possible mechanism for the increased oil production. Steam fluidization resulted in increased oil collection efficiency, and represented the most significant difference between the steam and nitrogen systems. Liquid product quality was similar for both steam and N₂ fluidization and the oils were more aromatic, more viscous, higher in density, higher in nitrogen content, and lower in volatility than Fischer Assay oil derived from the same shale.     

Gas evolution during oil shale pyrolysis. 1. Nonisothermal rate measurements

The rate of evolution of CH₄, CO, CO₂, H₂, C₂ hydrocarbons, and C₃ hydrocarbons during pyrolysis of Colorado oil shale between 25 and 900 °C is reported. All experiments were performed nonisothermally using linear heating rates varying from 0.5 to 4.0 °C min^?1. Hydrogen is the major noncondensable gas produced by kerogen pyrolysis. The amount of H₂ released is influenced, via the shift and Boudouard reactions, by the CO₂ evolved from mineral carbonates. Lesser amounts of C₁, C₂, and C₃ hydrocarbons are produced. On the basis of heat content, however, the combined C₁ to C₃ hydrocarbons contribute twice as much as H₂ to the heating value of the pyrolysis gas. The evolution of H₂ and CH₄ involves processes that are interpreted as a ‘primary’ pyrolysis of the kerogen to generate oil, and a higher temperature ‘secondary’ pyrolysis of the carbonaceous residue. The CO formed is a product of the Boudouard reaction; nearly complete conversion of the carbon residue to CO via this reaction is observed.     

Evaluation of several methods of extraction of oil from a Jordanian oil shale

A Jordanian oil shale from the El Lajjun deposit has been reacted with N₂, H₂ and CO in the presence and absence of water in the temperature range 300–425 °C. The effect of adding Fe, Cu, Ni, Sn and NaAlO₂ as potential catalysts to some of these reactions has been studied but none led to improved oil yields. Most of the organic material in the oil shale was converted to asphaltene at 355 °C, but the oil yield was low at this temperature. At 425 °C nearly all the organic product was in the form of oil.     

Kinetics of Colorado oil shale pyrolysis in a fluidized-bed reactor

Previous hydrocarbon evolution data were reanalysed to determine improved rate expressions for oil generation from Colorado oil shale under rapid pyrolysis conditions. Contributions from low-molecular-weight gases were subtracted from flame-ionization detector data to obtain the rate of oil generation alone. Equally good fits to the data were obtained using two parallel first-order reactions or a single reaction with an effective reaction order of 1.51. The latter expression was easier to incorporate into global process models. The rate expressions were independent of shale source (Anvil Points or Tract C-a) and particle size (0.5–2.4 mm). The kinetic data were consistent with the previous conclusion that the small incremental oil yield possible for fluidized-bed pyrolysis requires a longer residence time than that estimated by kinetic expressions derived from slow-heating data.     

油页岩半焦热解特性

利用热重分析仪对油页岩半焦热解特性进行了研究.综合考虑制取半焦所获得的页岩油品质、半焦成分、发热量和循环流化床设计,认为干馏温度介于500～600℃为宜;干馏度对半焦热解初析温度和低温段热解过程有影响,但对高温段热解影响不明显,高温干馏所制取的半焦其热解过程包含于低温所制取的半焦热解过程中;随升温速率的提高,相同温度下的半焦热解度降低,当升温速率超过40℃•min^-1后,升温速率对半焦热解过程影响不大;最后采用Coasts法计算了油页岩半焦热解动力学参数,计算结果可供数值仿真和工程设计参考.     

油页岩颗粒的热解模型

以实验为依据,分析了油页岩的热解机理及特性,并充分考虑了油页岩中挥发分在整个热解过程的作用,在此基础上建立了与油页岩固有热解特性相适应的热解模型。在能量方程中考虑了油页岩挥发分的热解反应吸热量及其挥发分的释放对油页岩固体颗粒质量的影响,并根据油页岩的热解特性,采用分阶段模型来描述油页岩的热解过程,以减小一步本征动力学方程带来的较大误差,还对模型进行了实验验证。     

页岩灰和FCC催化剂调控油页岩热解产物二次反应特性

采用两段反应器对油页岩热解初级挥发分进行二次催化反应特性研究,考察了第2段反应器内不同的催化载体、反应气氛与停留时间对油气收率及品质的影响。结果表明,在考察的停留时间范围内页岩灰具有相对适中的催化活性来调控热解挥发分产物的二次反应,水蒸气气氛能够进一步提高热解油收率约5%,并能够在一定程度上抑制裂解气体中C₂~C₃组分的生成。页岩灰作为催化载体能够转化热解油中VGO（馏程>350℃）等重质组分,随停留时间增加油品馏程向轻组分转移。油品组分GC-MS结果表明,较短停留时间内（<3 s）,水蒸气添加能够有效抑制热解油中脂肪烃类的过度裂解,与氮气相比提高汽柴油馏分含量20%以上。过长的停留时间（3~5 s）会造成VGO等馏分缩聚生成焦炭,从而大幅降低热解油收率。