Reaction kinetics between CO2 and oil-shale residual carbon. 1. Effect of heating rate on reactivity

The reaction kinetics between CO₂ and residual carbon from Colorado oil shale (Mahogany Zone) have been investigated using both isothermal and nonisothermal methods. It was found that oil-shale residual carbon is approximately an order of magnitude more reactive than subbituminous-coal char although the surface areas are similar. The reactivity of the residual carbon was found to vary by a factor of two for samples prepared by retorting the shale at heating rates between 0.033 and 12 °C/ min. Since the surface area of the residual carbon is approximately independent of the amount of oil coking, the heating-rate effect cannot be explained by pore filling. Surface areas of the residual organic carbon in shale were estimated by comparing the surface area of retorted shale (about 3% carbon) with that of retorted shale which had been decharred by oxidation at 400 °C. Surface areas of 250–400 m²/g and 100–200 m²/g were obtained using CO₂ and N₂ respectively as the adsorbed gases. Mercury porosimetry results are also presented.     

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.     

Laboratory and modelling investigation of a Colorado oil-shale block heated to 900 °C

A cylinder of oil-shale, 17.2 by 17.0 cm diameter, was heated in a retort from 23 to 900 °C at a rate of 18 °C h^?1. Total mass loss, oil yield and evolution of individual products are monitored. A one-dimensional model is developed to simulate the heating of the cylinder of oil-shale and the chemistry occurring as the oil-shale is pyrolysed. This model, containing the heat-transport equation and laboratory kinetic data, of ten occurring chemical reactions provides a good estimation of the experimental results. Only the extent of evolution of CO differed significantly from the experiment. The model is used to investigate thermal gradients in large cylinders heated at 1 and 3 °C min^?1 and to determine extents of heat transfer into the walls of an in-situ retort.     

DTA derived kinetics of Jordan oil shale

The thermal behaviour of Jordan oil shale has been studied in a DTA apparatus in an He atmosphere. The thermal curves for both untreated and decarbonated shale exhibited two distinct endothermic peaks related to the softening and evolution of organic matter. The first peak relates to molecular rearrangement of the kerogen where nonisothermal kinetics found that the activation energy (E_a) in the range 13.4–25.1 kJ mol^?1 for both untreated and decarbonated samples. For the second peak, E_a was obtained from first order kinetics and varied from 54.9 kJ mol^?1 for decarbonated shale to 79.6 kJ mol^?1 for untreated samples. The effect of particle size on the DT curves was studied and showed a drift from zero base line. Spent shale for reference material improved the profile of DTA curves and minimized drift as compared to use of α-alumina.     

Influence of heating rate on the pyrolysis of oil shale

The decomposition of oil shale from the Kvarntorp deposit in Sweden has been investigated using isothermal and non-isothermal methods. It was found that the heating rate during the initial non-isothermal period in the isothermal experiments had a considerable effect on the rate of devolatilization. At heating rates in the order of 10⁵°C/s the total weight loss exceeded the weight loss predicted from the volatile matter according to a proximate analysis.The effect of particle and sample size on the rate of decomposition (weight loss) was studied and found to have a significant influence at heating rates of the order of 10⁵°C/s while no effect was detected at heating rates around 200 °C/s (isothermal) or below 50°C/min (non-isothermal). The decomposition at low heating rates was completed at temperatures below 600°C and about 50 percent of the devolatilization could be described by first order kinetics with an apparent activation energy of 130 KJ/mole.At heating rates of 200°C/s (isothermal) the decomposition could also be described by simple first order kinetics but with an activation energy of 67 KJ/mole, thus indicating a different rate-determining mechanism.     

Kinetics of oil generation from oil shale from Liaoning province of China

The intrinsic kinetics of oil generation from 0.124 dm³ kg^?1 Chinese oil shale were determined by a non-isothermal method. Overall first-order kinetics satisfactorily represented the mechanism of kerogen decomposition. The kinetic parameters were determined as 142.8 kJ mol^?1 and 7.495 × 10⁶ s^?1 for activation energy and pre-exponential factor, respectively.     

Isothermal and nonisothermal crystallization kinetics of nylon-11

Analysis of the isothermal, and nonisothermal crystallization kinetics of Nylon-11 is carried out using differential scanning calorimetry. The Avrami equation and that modified by Jeziorny can describe the primary stage of isothermal and nonisothermal crystallization of Nylon-11. In the isothermal crystallization process, the mechanism of spherulitic nucleation and growth are discussed; the lateral and folding surface free energies determined from the Lauritzen–Hoffman equation are ς = 10.68 erg/cm² and ς_e = 110.62 erg/cm²; and the work of chain folding q = 7.61 Kcal/mol. In the nonisothermal crystallization process, Ozawa analysis failed to describe the crystallization behavior of Nylon-11. Combining the Avrami and Ozawa equations, we obtain a new and convenient method to analyze the nonisothermal crystallization kinetics of Nylon-11; in the meantime, the activation energies are determined to be −394.56 and 328.37 KJ/mol in isothermal and nonisothermal crystallization process from the Arrhonius form and the Kissinger method. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 2371–2380, 1998     

Kinetics of thermodegradation of palm kernel oil derived medium‐chain‐length polyhydroxyalkanoates

Oligomeric hydroxyalkanoic acids have potential industrial, medical, and pharmaceutical applications and they can be produced from the degradation of high molecular weight polyhydroxyalkanoates by a number of different ways. Thermal decomposition takes place in the absence of organic solvent and other chemicals and this justified the method of producing low molecular weight PHA as green chemistry. The kinetics for thermal degradation of medium‐chain‐length polyhydroxyalkanoates (mcl‐PHA) prepared from saponified palm kernel oil (SPKO) was studied by thermogravimetric analysis (TGA) technique. Employing the nonisothermal Kissinger's method, the degradation activation energy, E_d, and pre‐exponential factor, A, were 129 kJ mol^?1 and 1.15 × 10¹⁰ s^?1, respectively. Specific degradation rate constant, k was found to increase at higher heating rate. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Precipitation of asphaltenes from solvent-diluted heavy oil and thermodynamic properties of solvent-diluted heavy oil solutions

Ratios of n-heptane (hep) to toluene (tol) affect the solubility of the asphaltenes in heavy oil extraction processes. Consequently phase changes and time after mixing n-heptane and heavy oil in toluene are important for understanding produced emulsions. The kinetics of phase change when n-heptane is added to toluene-diluted heavy oils, and the thermodynamic properties of partially deasphalted heavy oils were studied. The methods used were monitoring precipitation in time using light microscopy, quantitative asphaltenes analysis by near infrared spectroscopy, refractive index and densities measurements, and calculated solubility parameters of mixtures. At critical mass ratios of hep/tol from 1.37 to 2.0 in diluted heavy oil the precipitated asphaltene particles were observed under the microscope after lag times from 2 h to instantly. Lag times were longer at low initial oil concentration. The floc growth time decreased as heavy oil concentration in toluene increased. The growth patterns in time appeared as dots to beads (strings) to clusters (fractal-like flocs). Final wt% precipitated asphaltenes vs. mass fraction (hep+tol)/heavy oil followed sigmoidal relationships. Curves showing wt% soluble asphaltenes vs. mass fraction hep/tol after 24 h initially followed the same shape as time zero curves and diverged at the onset ratios of hep/tol. Slope for precipitated asphaltenes vs. solubility parameters curve showed a break at 16.4 MPa^1/2. Linear correlations were established for concentrations of soluble asphaltenes in residual oils and density, for refractive index and density and for refractive index and solubility parameter. The latter correlation was in accordance with Lorenz-Lorentz theory. These equations provided a means by which oil density, refractive index and solubility parameter can be predicted when these measurements are difficult to measure practically.     

Effect of nano-nucleating agent addition on the isothermal and nonisothermal crystallization kinetics of isotactic polypropylene

Using differential scanning calorimetry (DSC) technique, a comparative study has been made of the isothermal and nonisothermal crystallization kinetics of nonnucleated isotactic polypropylene (iPP) and of nucleated iPP with 0.5 wt% of single-walled carbon nanotubes (SWCNTs) as a nucleating agent. The Avrami exponents (n) of iPP and nucleated iPP are close to 3.0 for isothermal crystallization. These results indicate that the addition of nucleating agents did not change the crystallization growth patterns of the neat polymer and that crystal growth was heterogeneous three-dimensional spherulitic. The results show that the addition of SWCNTs can shorten the crystallization half-time (t _1/2) and increase the crystallization rate of iPP. In the nonisothermal crystallization process, the Ozawa model failed to describe the crystallization behavior of nucleated iPP. The Cazé–Chuah model successfully described the nonisothermal crystallization process of iPP and its nanocomposite. A kinetic treatment based on the Ziabicki theory is presented to describe the kinetic crystallizability, in order to characterize the nonisothermal crystallization kinetics of iPP and nucleated iPP. Polarized light microscopy (PLM) experiments reveal that SWCNTs served as nucleating sites, resulting in a decrease of the spherulite size.     

Acid base catalyzed transesterification kinetics of waste cooking oil

The present study reports the results of kinetics study of acid base catalyzed two step transesterification process of waste cooking oil, carried out at pre-determined optimum temperature of 65 °C and 50 °C for esterification and transesterification process respectively under the optimum condition of methanol to oil ratio of 3:7 (v/v), catalyst concentration 1%(w/w) for H₂SO₄ and NaOH and 400 rpm of stirring. The optimum temperature was determined based on the yield of ME at different temperature. Simply, the optimum concentration of H₂SO₄ and NaOH was determined with respect to ME Yield. The results indicated that both esterification and transesterification reaction are of first order rate reaction with reaction rate constant of 0.0031 min^− 1 and 0.0078 min^− 1 respectively showing that the former is a slower process than the later. The maximum yield of 21.50% of ME during esterification and 90.6% from transesterification of pretreated WCO has been obtained. This is the first study of its kind which deals with simplified kinetics of two step acid-base catalyzed transesterification process carried under the above optimum conditions and took about 6 h for complete conversion of TG to ME with least amount of activation energy. Also various parameters related to experiments are optimized with respect to ME yield.     

Lumped-parameter model for the retorting of a large block of oil shale with an internal temperature gradient

A lumped-parameter model which combines the internal and external heat transfer resistances was proposed for the retorting of a large block of oil shale. In this model the temperature of oil-shale block is obtained by solving the ordinary differential equation of energy balance using an overall heat transfer coefficient U, where U is equal to h/(1 + Bi/5). The results of this model were compared with those of the uniform-temperature model which uses the external heat transfer coefficient h, instead of U, in the energy balance equation and of the rigorous model which calculates the block temperature profile more rigorously by a partial differential equation. The comparison showed that the lumped-parameter model is much better than the uniform-temperature model and is a useful alternative to the rigorous model for modelling the retorting of a large block of oil shale with an internal temperature gradient.     

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.     

Kinetic parameter estimation and simulation of trickle-bed reactor for hydrodesulfurization of crude oil

Hydrodesulfurization (HDS) of crude oil has not been reported widely in the literature and it is one of the most challenging tasks in the petroleum refining industry. In order to obtain useful models for HDS process that can be confidently applied to reactor design, operation and control, the accurate estimation of kinetic parameters of the relevant reaction scheme are required. In this work, an optimization technique is used in order to obtain the best values of kinetic parameters in trickle-bed reactor (TBR) process used for hydrodesulfurization (HDS) of crude oil based on pilot plant experiment. The optimization technique is based on minimization of the sum of the square errors (SSE) between the experimental and predicted concentrations of sulfur compound in the products using two approaches (linear (LN) and non-linear (NLN) regressions).A set of experiments were carried out in a continuous flow isothermal trickle-bed reactor using crude oil as a feedstock and the commercial cobalt–molybdenum on alumina (Co–Mo/γ-Al₂O₃) as a catalyst. The reactor temperature was varied from 335 to 400 °C, the hydrogen pressure from 4 to 10 MPa and the liquid hourly space velocity (LHSV) from 0.5 to 1.5 h⁻¹, keeping constant hydrogen to oil ratio (H₂/oil) at 250 L/L.A steady-state heterogeneous model is developed based on two-film theory, which includes mass transfer phenomena in addition to many correlations for estimating physiochemical properties of the compounds. The hydrodesulfurization reaction is described by Langmuir–Hinshelwood kinetics. gPROMS software is employed for modelling, parameter estimation and simulation of hydrodesulfurization of crude oil in this work. The model simulations results were found to agree well with the experiments carried out in a wide range of the studied operating conditions. Following the parameter estimation, the model is used to predict the concentration profiles of hydrogen, hydrogen sulfide and sulfur along the catalyst bed length in gas, liquid and solid phase, which provides further insight of the process.     

Intrinsic kinetics of low-temperature oxidation of oil shale kerogen

The kinetics of oxidation of kerogen in the Colorado oil shale were measured using a thermogravimetric analysis technique in a continuously increasing temperature mode. The rate data were analysed based on the assumption that, at the relatively low temperatures at which the kinetics were measured, the oxidation reaction takes place on the surface of solid kerogen and that the decomposition of kerogen is not significant. The oxidation rate was determined to be of first order with respect to oxygen partial pressure. The activation energy of reaction was 11.0 ± 2.3 kJ mol⁻¹, and the pre-exponential factor was (6.8 ± 2.5) × 10⁻⁶ m(kPa · s)⁻¹.     

Activation parameters and excitation yields of 1,2-dioxetanes of photogenotoxic interest

The chemiluminescent decomposition of functionalized 1,2-dioxetanes was examined in toluene solution. Activation energies were measured by isothermal and nonisothermal kinetic methods. Quantum efficiencies were determined by Stern-Volmer kinetics, using the fluorescers 9,10-dibromo- and 9,10-diphenylanthracene for the triplet and singlet excitation yields. The derivatives of 3-hydroxymethyl-3,4,4-trimethyl-1,2-dioxetane ( 1a ) have free energies of activation (ΔG^≠) of ca. 25 kcal/mol, but the ΔG^≠ values of the annelated benzofuran-type dioxetanes ( 5 ) are ca. 1 kcal/mol lower. There exists a reasonable correlation between the free energies of activation (ΔG^≠) for the thermal decomposition of the dioxetanes and their triplet excitation flux (E_p^T).     

Investigation of the structure of Estonian oil shale kukersite by conversion in aqueous suspension

Results of oil-shale liquefaction experiments by conversion in aqueous solutions of sodium formate and sodium hydroxide are discussed. The study of the decomposition products shows that not only fatty acids, C₁₄, C₁₆ and C₁₈, but also poly-unsaturated acids, C₂₀, C₂₂ and C₂₄ took part in the formation of kukersite. Additional data are presented to confirm the assumption that polycarbonyl structures are present in kukersite. On thermal decomposition (semi-coking) kukersite yields a considerable amount of 5-alkyl resorcinols. On conversion in aqueous suspension, however, ketones are formed instead of alkyl resorcinols. Kukersite is a rare caustobiolith, distinguished by the presence of significant amounts of unchanged fragments of biological precursor material, mostly decarboxylated alkyl chains of fatty acids.     

Kinetic analysis of high-resolution TGA variable heating rate data

Isothermal and constant heating rate thermogravimetric analysis (TGA) experiments have been performed for examining decomposition of polymers and composites. In practice, low heating rates are necessary to obtain good resolution under nonisothermal conditions thus increasing the time required for experiments. A novel TGA mode, high-resolution TGA (Hi-Res^TM TGA), provides a means to remarkably increase the resolution while often decreasing the time required for experiments. In this variable heating rate mode of Hi-Res^TMTGA, the heating rate is continuously and dynamically varied to maximize resolution. Thus, traditional methods cannot be directly utilized to determine kinetic parameters. Accordingly, in this work, variable heating rate experiments were run on ethylene-vinylacetate (EVA) copolymer, poly(ether ether ketone) (PEEK), and carbon-fiber-reinforced bismaleimide (BMI), whose kinetics have been quantitatively described with traditional isothermal and nonisothermal experiments. Comparison of the different techniques led to the development of a simplified method by which the activation energy, preexponential factor, and reaction order can be extracted from variable heating rate TGA experiments. The technique, based on the principle that maximum weight loss rate is observed at minimum heating rate, gave kinetic results that were in excellent agreement with values that have been determined by traditional isothermal and dynamic experiments. © 1993 John Wiley & Sons, Inc.     

A simple method for determining the spontaneous oil absorption capacity of proteins and the kinetics of oil uptake

A simple method was developed for determining the spontaneous oil uptake and the kinetics of oil uptake by several food protein materials. The amount q of oil taken up by a protein powder during time t was described by the equation q=Qt/(B+t), where Q is the total oil uptake at equilibrium and B is the time required to sorb Q/2. The rate of oil uptake was proportional to the square of the amount of oil that must still be absorbed to reach equilibrium. A specific rate constant for the process was calculated as (BQ)⁻¹ and an initial rate of oil uptake as Q/B.     

Influence of phase evolution and thermal decomposition kinetics on the properties of zircon ceramic

In this study, the relationship between the decomposition process and properties of zircon ceramic was analysed. The decomposition process of zircon was investigated by kinetics model, thermodynamics and experimental phenomena. The Coats-Redfern and Kissinger models were used as basic kinetics models, and thermodynamics, thermogravimetry (TG) and differential scanning calorimetry (DSC) were used to characterize the decomposition process and calculate the kinetics parameters. The microstructure, pores characteristics, densification and physical properties were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Archimedes’ principle. The results showed that the decomposition process of zircon could be divided into two stages, with the first and the second stages controlled by the phase boundary reaction and diffusion control reaction, respectively. The decomposition rate of the first decomposition stage was slow and the mechanism function was g(x) = 1-(1-α)^1/3 while the decomposition rate of the second stage was fast and the mechanism function was g(x)=(1–2/3α)-(1-α)^2/3. The large decomposition amount of zircon increased the amount of liquid phase, which would reduce the densification of zircon.