Differences in the behaviour of US bituminous and subbituminous coals during short contact time liquefaction

The short contact time (SCT) liquefaction of Belle Ayr subbituminous coal has been compared with that of Illinois No. 6 and Pittsburgh seam bituminous coals. Each bituminous coal was highly solubilized (90 wt%, daf coal) in 3–4 min at 450 °C and 13–16 MPa hydrogen pressure. More than 80 wt% of each coal was converted to solvent-refined coal (SRC, pyridine-soluble residuum), with only small quantities of distillate oil and C₁–C₄ gas being formed. A longer reaction (up to 30 min) gave only a small increase in total conversion, but gas and distillate yields increased significantly. Iron sulphides did not appear to catalyse coal solubilization. By contrast, only 65 wt% of the Belle Ayr coal dissolved rapidly in SCT liquefaction and pyrite addition catalysed the conversion of the remaining insoluble organic matter (IOM). With an equivalent amount of pyrite present the Belle Ayr coal also gave more C₁–C₄ gas and substantially more distillate in SCT liquefaction than the bituminous coals. These differences in product distributions obtained from bituminous and subbituminous coals in SCT liquefaction can be rationalized on the basis of differences in the structures of the starting coals. However, the origin of high IOM yields with the Belle Ayr coal remains unclear.     

Short contact-time liquefaction of subbituminous coal: Directions for improving coal conversion

This study was undertaken to find ways to solubilize subbituminous coal in high yield at short contact times. Short contact-time hydroliquefaction runs were carried out in a continuous unit using Belle Ayr subbituminous coal with a solvent rich in hydrogen-donor molecules derived from the Lummus ITSL process, and also with solvents lower in donor concentration derived from the SRC processes. Catalysis by pyrite, molybdenum and supported cobalt-molybdenum was also studied. It was found that pyrite and other hydrogenation catalysts enhanced solubilization and also increased production of distillate oil. Solvent quality seemed to have no effect on the solubilization of Belle Ayr coal. The availability of H₂S also appeared to have no effect. Provided that pyrite was present, reaction could be carried out at severities high enough to give insoluble organic matter yields equivalent to those obtained with bituminous coals (5–10 wt% daf coal). At equivalent levels of solubilization, however, hydrocarbon gas and distillate yields were invariably higher for the subbituminous coal. Implications for two-stage processing of Belle Ayr coal are discussed.     

Evaluation of kinetic parameters of coal ignition

A method is presented of evaluating the kinetic parameters for the ignition reaction of coal based on the Semenov's thermal ignition theory adopted to coal particle ignition. The evaluated apparent activation energy, E, for bituminous coal, anthracite and bituminous coal char are in the range 46–103 kJ mol^?1. A verification was made by comparing the measured induction periods for the coal particles with those calculated numerically. The oxidation rate is controlled by diffusion into pores.     

Study of the kinetics of sewage sludge pyrolysis using DSC and TGA

Thermogravimetry and differential scanning calorimetry were used to examine, in nitrogen, four sewage sludges at modest heating rates. A mechanism consisting of two independent reactions was derived for an undigested sludge. The parameters are: n₁ = 10, E₁ = 130 kJ mol^?1, A₁ = 1 × 10¹⁸s^?1, n₂ = 15, E₂ = 250 kJ mol^?1, A₂ = 1 × 10²⁵s^?1, with initial weight fractions of W₁ = 0.20, W₂ = 0.43, the remainder being non-reactive ash. Analysis was performed by comparing Friedman multiple-heating-rate analyses of experimental and model curves in an iterative manner. DSC experiments provide an understanding of the pyrolytic reaction mechanism and heat transfer in the thermogravimetric analyser. DSC analysis of sewage sludge was sensitive to decomposition reactions of small quantities of organic salts in the sludge. Sewage sludge could be a profitable pyrolysis feedstock if mixed with municipal solid waste.     

Oxidation reaction kinetics of Athabasca bitumen

The oxidation reaction kinetics of bitumen from Athabasca oil sands have been investigated in a flow-through fixed bed reactor using gas mixtures of various compositions. The system was modelled as an isothermal integral plug-flow reactor. The oxidation of bitumen was found to be first order with respect to oxygen concentration. Two models were examined to describe the kinetics of bitumen oxidation. In the first, the Athabasca bitumen is considered to be a single reactant and the oxidation reaction a single irreversible reaction. The activation energy for the overall reaction was found to be 80 kJ mol^?1. This model is limited to calculating the overall conversion of oxygen. Because the fraction of oxygen reacting to form carbon monoxide and carbon dioxide increases with temperature, a more sophisticated model was proposed to take this into account. The second model assumes that the bitumen is a single reactant and that the oxidation of bitumen may be described by two simultaneous, parallel reactions, one producing oxygenated hydrocarbons and water, the other producing CO and CO₂. The activation energy for the first reaction was found to be 67 kJ mol^?1, and for the second, 145 kJ mol^?1. This more sophisticated model explains the result that at higher temperatures more oxygen is consumed in the oxidation of carbon, because this reaction has a higher activation energy than the reaction leading to the production of oxygenated hydrocarbons and water. This model can also predict the composition of the product gases at various reaction conditions.     

Liquefaction of partially dried and oxidized coals: 3. Liquefaction results

Samples of partially dried and oxidized Belle Ayr subbituminous coal were liquefied in a recycle donor solvent (SRC-ll heavy distillate) to observe the effect of coal pretreatment on conversion. Because subbituminous coals have moisture contents typically > 25%, it would appear useful to dry these coals prior to liquefaction; however, the drying of Belle Ayr coal, either in nitrogen or oxygen-containing gases, resulted in a significant decrease in yields of liquefied coal products. The liquefaction residues recovered from these runs were examined by optical microscopy and were found to contain high levels of coke. This coke appeared to have formed by polymerization of coal-derived liquid products.     

Calorimetric study of quinoline interaction with o-phenylphenol and coal-derived asphaltenes

A calorimetric method is presented for the simultaneous evaluation of equilibrium constant, K, and molar enthalpy, ΔH^o, for 1:1 adduct formation of quinoline (Qu) with coal-derived asphaltenes in solvent benzene. Asphaltene (A), together with its acid/neutral (AA), and base (BA) fractions used in this study were isolated from a centrifuged liquid product (CLP) sample prepared from Kentucky hvAb coal at 27.6 MPa hydrogen pressure and 723 K, with reactor charged with glass pellets. The computed K values for the interaction of Qu and A, AA, and BA are, within experimental error, the same, 18–19 dm³ mol^?1; whereas there is large variation in the ΔH^o values (Qu-A, ?16.92 ± 0.21 kJ mol^?1; Qu-AA, ?14.74 ± 0.04 kJ mol^?1; Qu-BA, ?11.76 ± 0.04 kJ mol^?1). For Qu-A and Qu-AA systems, hydrogen-bonding occurs between the aromatic phenols (present in A and AA) and quinoline, which is a strong hydrogen-bond acceptor, in addition to other molecular interactions. The hydrogen-bonding interaction in the Qu-BA system is lacking because both Qu and BA are hydrogen-bond acceptors. Since asphaltenes are really mixtures, we have taken a pure compound, o-phenyl-phenol (OPP), and obtained thermodynamic parameters for its interaction with quinoline (Qu). OPP was chosen to represent the aromatic phenols found in coal liquefaction products. Results obtained are: K (dm³ mol^?1): 10.4 (in CS₂), 6.2 (in CCl₄); ΔH^o (kJ mol^?1): ?31.40 (inCS₂) ?27.80 (inCCl₄). The solvent effect is apparent. By using o-phenylanisole as a model non-hydrogen-bonding donor (Dietz Blaha, Li J. Chem. Thermodynamics, 1977, 9, 783), the relative contribution of H-bond to π-interactions in the total enthalpy change for the OPP—Qu system is estimated to be 3:1.     

Liquefaction of partially dried and oxidized coals: 2. Coal characteristics

Samples of Belle Ayr (WY) subbituminous and Powhatan No. 5 mine (Pittsburgh Seam) bituminous coals were dried with gases including nitrogen, air and nitrogen/air mixture at temperatures essentially from ambient to 200 °C as part of a study to measure liquefaction behaviour. While the oxygen uptake of the subbituminous coal was up to 3 wt% and that of the bituminous coal was up to 8 wt%, the physical and chemical characteristics of both coals appeared to undergo only minor changes during treatment. However, CPAA oxygen analysis showed an apparent reaction of water with the coal, and FT—i.r. spectral results showed the formation of carbonyls and carboxylic acids with an indication of the formation of ethers.     

Kinetics of redox reactions of ilmenite for chemical-looping combustion

The objective of this study was to establish the kinetic of both reduction and oxidation reactions taking place in the chemical-looping combustion (CLC) process using ilmenite as an oxygen carrier. Because of the benefits of using of pre-oxidized ilmenite and the activation of the ilmenite during the redox cycles, the reactivity of both the pre-oxidized and activated ilmenite was analyzed. The experimental tests were carried out in a thermogravimetric analyzer (TGA), using H₂, CO or CH₄ as reducing gases, and O₂ for the oxidation step. Thus, the reactivity with the main reacting gases was analyzed when natural gas, syngas or coal are used as fuels in a CLC system. The changing grain size model (CGSM) was used to predict the evolution with time of the solid conversion and to determine the kinetic parameters. In most cases, the reaction was controlled by chemical reaction in the grain boundary. In addition, to predict the behaviour of the oxidation during the first redox cycle of pre-oxidized ilmenite, a mixed resistance between chemical reaction and diffusion in the solid product was needed. The kinetic parameters of both reduction and oxidation reactions of the pre-oxidized and activated ilmenite were established. The reaction order for the main part of the reduction reactions of pre-oxidized and activated ilmenite with H₂, CO, CH₄ and O₂ was n=1, being different (n=0.8) for the reaction of activated ilmenite with CO. Activation energies from 109 to 165 kJ mol⁻¹ for pre-oxidized ilmenite and from 65 to 135 kJ mol⁻¹ for activated ilmenite were found for the different reactions with H₂, CO and CH₄. For the oxidation reaction activation energies found were lower, 11 kJ mol⁻¹ for pre-oxidized and 25 kJ mol⁻¹ for activated ilmenite.Finally, simplified models of the fuel and air reactors were used to do an assessment of the use of ilmenite as an oxygen carrier in a CLC system. The reactor models use the reaction model in the particle and the kinetic parameters obtained in this work. Taking into account for its oxygen transport capacity, the moderated solids inventory and the low cost of the material, ilmenite presents a competitive performance against synthetic oxygen carriers when coal or syngas are used as fuel.     

Thermogravimetry-combustion characteristics of high-carbon fluidized-bed cyclone ashes

Thermogravimetry combustion characteristics are obtained for three samples of high-carbon cyclone ash, the samples received from an R & D fluidized bed combustion unit utilizing Ohio No. 6 bituminous coal with limestone. Non-isothermal TG combustion in air (at a programmed heating rate of 2 °C min^?1) for a cyclone ash (25.0 wt% carbon) indicates two chemically different combustibles, ≈82 wt% of higher reactivity with maximum weight-loss rate at 490 °C and 18 wt% correspondingly of lower reactivity at 645 °C. Isothermal TG combustion of the same ash at 700 °C and at 850 °C also indicates the presence of the two types of combustibles and gives an E_a of about 150 kJ mol^?1 for combustion of the lower reactivity type. Additionally, each of two other samples of cyclone ash (20.1 and 6.9 wt% carbon) contains two types of combustibles as evidenced by TG combustions. Non-isothermal TG combustion of feed coal, a single maximum weight loss at 440 °C, shows the coal has greater reactivity than each of the three ashes. A combustion chemistry explanation for two types of combustibles is suggested by the postulated reactivity order for the organic matter or maceral groups of coal, i.e., vitrinite ? exinite ? inertinite.     

The use of DTA to study spontanceous ignition of cellulose

The use of differential thermal analysis has enabled spontaneous ignition behaviour of cotton cellulose to be investigate. The temperature. T_i, at which the onset of spontaneous ignition occurs is recorded as a function of the oxygen concentration of the flowing oxygen-nitrogen atmosphere to which the cellulose sample is exposed in the DTA furnace, when heated at a defined heating rate. The dependence of T_i, on heating rate has enabled the activation energy, E_p, of the rate-determining flammable pyrolysis product reaction to the determined using both a previously derived simple kinetic model and the technique of Ozawa. E_p, increases from a lower limiting value of 112 kJ mol^?1 at zero oxygen concentration to an asymptote value of 169 kJ mol^?1 at oxygen volume concentrations above 30%. This effect is described in terms of oxygen catalysis of competing pyrolysis routes. At a given heating rate, increased oxygen concentration reduces T_i. A plot of 1/T_i versus In [O₂] gives two liner regions which intersect at an oxygen concentration of about 20%, suggesting that two combustion mechanisms exist, one above and the other below this value. Below this concentration, which is similar to the conventional limiting oxygen for cellulose, significant char remains, suggesting that ignition of gaseous products only occurs. If the difference in slopes is sttributed to the variations in E_p with oxygen concentration, then a value for the activation energy of gaseous product oxidation, E_ox = 215 kJ mol^?1 is derived.     

Effect of particle size on thermal decomposition and devolatilization kinetics of melon seed shell

Thermogravimetric analysis (TGA) and devolatilization kinetics of melon seed shell (MSS) at different particle sizes (150?µm and 500?µm) and at different heating rates (10, 15, 20, and 25?°C/min) were investigated with the aid of TGA. The results of the TGA analysis show that the TGA curves corresponding to the first and third stages for 150?µm particle sizes exhibited some bumps that developed at the first and third stages of pyrolysis. It was also observed that at constant heating rate, the maximum peak temperature increases as the particle sizes increase from 150 to 500?µm, whereas 500?µm particle sizes exhibited higher peak temperatures compared to 150?µm particle sizes. The resulting TGA data were applied to the Kissinger (K), Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO) methods and kinetic parameters (activation energy, E and frequency factor, A) were determined. The E and A obtained using K method were 74.27?kJ mol^?1 and 3.84?×?10⁵?min^?1 for 150?µm particle size, whereas for 500?µm particle size were 97.12?kJ mol^?1 and 3.74?×?10⁷?min^?1, respectively. However, the average E and A obtained using KAS and FWO methods were 82.35?kJ mol^?1, 1.29?×?10⁷?min^?1, and 88.50?kJ mol^?1, 1.32?×?10⁷?min^?1 for 150?µm particle sizes. While for 500?µm particle sizes, the E and A were 108.46?kJ mol^?1, 3.14?×?10⁹?min^?1, and 113.05?kJ mol^?1, 7.56?×?10⁹?min^?1, respectively. It was observed that E and A calculated from FWO and KAS methods were very close and higher than that obtained by K method. It was observed that the minimum heat required for the cracking of MSS particles into products is reached later at higher peak temperatures since the heat transfer is less effective as they are at lower peak temperatures.     

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.     

Air impingement and intermittent drying: Application to apple and to mango

An original drying process combining air impingement and intermittent drying was studied on apple slices and mango cubes. The influence of four operating parameters (air velocity, drying/tempering periods, upper height, and air temperature) on the drying time and on the drying rate was evaluated. Continuous and intermittent drying were compared. The intermittency α = 1/7 (τ_on = 10 seconds and τ_off = 60 seconds) gave the best results. A time savings of 54% for apple and 67% for mango was reached. In continuous drying, a time savings of 4620 seconds was observed by increasing the air velocity from 6 to 40 m s^?1 for apple. Air temperatures of 328 K for apple and of 328 K or 338 K for mango were determined as optimum to prevent case‐hardening. Experimental results were fitted with the analytical solution of Fick's second law and the modified Page equation (average values R² = 0.985 and 0.961, for apple and mango, respectively). For both products, the apparent moisture diffusivity D_app, the drying constant k, the drying coefficient n, and the activation energy E_a, were identified. Activation energies calculated from the analytical solution were 30.3 and 36.8 kJ mol^?1 and were 25.4 and 30.0 kJ mol^?1 using the modified Page equation for apple and mango, respectively. Mango has an increased temperature sensitivity and thus will need less energy for drying than apple.     

Oxidation behaviour of ceramic fibres from the Si–C–N–O system and related sub-systems

The oxidation of Si–C–N–O fibres has been investigated. The oxidation rates and the activation energies for the Si–C–O system are similar to those for crystalline SiC. The oxygen and the free carbon concentrations in the ceramics have a limited influence on the oxidation behaviour. As long as the formed silica scale is protective, oxidation kinetics are essentially controlled by the diffusion of oxygen through SiO₂. The parabolic rates in the Si–C–N–O and Si–N–O systems are lower and their activation energies higher than those for SiC. Their values strongly depend on the ratios of C and N bonds to Si and continuously vary from those for SiC (E_a=110−140kJ mol⁻¹) to Si₃N₄ (E_a=330–490 kJ mol⁻¹). The oxidation mechanism might be related to a complex diffusion/reaction regime via the formation of an intermediate silicon-oxynitride (like for Si₃N₄) or silicon-oxycarbonitride layer. The oxidation behaviour of such complex systems is not significantly influenced by the oxygen nor the free carbon contents. It might be governed by the C/Si and N/Si ratios, limiting the nitrogen concentration gradient of the silicon-oxy(carbo)nitride sub-layer and therefore affecting the diffusion/reaction rates.     

Laboratory-scale coal reactivity testing for entrained gasification

A relatively simple and rapid micro-gasification test has been developed for measuring gasification reactivities of carbonaceous materials under conditions which are more or less representative of an entrained gasification process, such as the Shell coal gasification process. Coal particles of < 100 μm are heated within a few seconds to a predetermined temperature level of 1000–2000 °C, which is subsequently maintained. Gasification is carried out with either CO₂ or H₂O. It is shown that gasification reactivity increases with decreasing coal rank. The CO₂ and H₂O gasification reactions of lignite, bituminous coal and fluid petroleum coke are probably controlled by diffusion at temperatures 1300–1400 °C. Below these temperatures, the CO₂ gasification reaction has an activation energy of about 100 kJ mol^?1 for lignite and 220–230 kJ mol^?1 for bituminous coals and fluid petroleum coke. The activation energies for H₂O gasification are about 100 kJ mol^?1 for lignite, 290–360 kJ mol^?1 for bituminous coals and about 200 kJ mol^?1 for fluid petroleum coke. Relative ranking of feedstocks with the micro-gasification test is in general agreement with 6 t/d plant results.     

Kinetic studies on Victorian brown coal hydroliquefaction

Reaction kinetics of the liquefaction of Victorian brown coal in a process development unit (PDU) having three reactors in series have been studied at temperatures of 430–470°C, and pressures of 15–25 MPa. It is shown that the rate of hydrogen consumption can be expressed as a function of the concentrations of coal and catalyst, hydrogen partial pressure, reaction temperature and residence time, and is controlled by the rates of hydrogenation of polynuclear aromatic components, and the rates of formation and stabilization of radicals. The relative contribution of these reactions, at any temperature, determine the influence of the hydrogen partial pressure on the rate of the hydrogen consumption. The kinetics of the decomposition reactions of brown coal to preasphaltene, asphaltene and to oil also have been studied. The apparent activation energies determined are 25 kJ mol^?1 for the brown coal to preasphaltene, 50 kJ mol^?1 for preasphaltene to asphaltene, 76 kJ mol^?1 for asphaltene to oil, and 184 kJ mole^?1 for oil to gases.     

Evolution of Oxidative Values during Kinetic Studies on Olive Oil Oxidation in the Rancimat Test

A comparative study was carried out in order to evaluate the kinetics of the formation of a number of primary and secondary oxidation products during oxidation of olive oil in the Rancimat test at 100–130 °C. There were good correlations between the Rancimat index (OSI) and stability indices (IP) measured in the Rancimat test with no significant differences in kinetic parameters calculated from them. Mean values of the temperature coefficient, Q₁₀ number, activation energy (E_a), frequency factor (A), and free energy of activation (ΔG⁺⁺) for olive oil oxidation were calculated to be ?3.44 × 10^?2°C^?1, 2.21, 98.91 kJ/mol, 12.17 × 10¹² h^?1, and 128.25 kJ/mol, respectively. Each unit change in E_a was accompanied by an average 1.43 × 10¹² change in A, indicating a higher contribution for factor A than for E_a to the olive oil stability. The E_a and A correlated well with the values of enthalpy and entropy, respectively. The values of OSI or IP could be described well by the ΔG⁺⁺ values. Kinetic data indicated that olive oil stability is more affected by the indigenous antioxidants than by the fatty acid composition.     

Supercritical water oxidation of coal: Investigation of operating parameters' effects, reaction kinetics and mechanism

Supercritical water oxidation (SCWO) of coal was conducted in a continuous tubular reactor under various reaction conditions. Our experimental results show that the removal rate of chemical oxygen demand (COD) had no significant dependence on the temperature variations. Effect of residence time was less significant as exceeded fixed values. Free radical mechanism of SCWO reaction may be a possible explanation for the relative low conversion rate of coal at the range of tested oxygen excess. Compared with other parameters, effect of pressure was less significant. A global power-law rate expression was regressed from experimental data. The reaction orders for coal slurry and oxidant were 1.79 and 0.28 respectively. The reaction activation energy E_a was determined to be 112.3 kJ mol⁻¹, and the pre-exponential factor k₀ was 412 (mol/L)^−1.07 s⁻¹. The deviation between the model and experimental data was within ± 9%. Free radical mechanism, oxidation and hydrolysis mechanisms and phenolic hydroxyl oxidation mechanism were considered to be the possible mechanisms for the SCWO process of coal.     

福建无烟煤CO2气化过程纸浆黑液和钙混合物的催化活性

CO2 gasification of Fuijian high-metamorphous anthracite with black liquor （BL） and/or mixture of BL and calcium stuff （BL＋Ca） as catalyst was studied by using a thermogravimetry under 750-950℃ at ambient pressure. When the coal was impregnated with an appropriate quantity of Ca and BL mixture, the catalytic activity of CO2 gasification was enhanced obviously. With a loading of 8%Na-BL＋2%Ca, the carbon conversion of three coal samples tested reaches up to 92.9%-99.3% at 950℃ within 30min. The continuous formation of alkali surface compounds such as （[-COM], [-CO2M]） and the presence of exchanged Ca, such as calcium phenolate and calcium carboxylates （COO）2Ca, contribute to the increase in catalytic efficiency, and using BL＋Ca is more efficient than that adding BL only, The homogeneous model and shrinking-core model were applied to correlate the data of conversion with time and to estimate the reaction rate constants under different temperature. The corresponding reaction activation energy （Ea） and pre-exponential factor of three anthracites were estimated. It is found that Ea is in the range from 73.6 to 121.4kJ·mol^-1 in the case of BL＋Ca, and 74.3 to 104.2kJ·mol^-1 when only BL was used as the catalyst, both of which are much less than that from 143.5 to 181.4kJ·mol^-1 if no catalyst used. It is clearly demonstrated that both of BL＋Ca mixture and BL could be the source of cheap and effective catalyst for coal gasification.