External Diffusion Resistance Research Articles

Alumina microspheres for the adsorption of fatty alcohols containing oxygenates in Fischer-Tropsch synthetic oils

The efficient and economical removal of oxygenated compounds from Fischer-Tropsch synthetic oil is vital to the promotion of high-quality chemical development in the coal chemical industry. In this study, alumina microspheres with high specific surface area, high pore capacity, and small particle size were prepared. The adsorption thermodynamics, adsorption kinetics, and column adsorption experiments were systematically conducted on various fatty alcohols bearing different carbon numbers, in mixtures of α-olefins and alkanes with different carbon numbers. The competitive adsorption behavior between weakly polar, oxide-containing methyl acetate and 12-alcohols on an alumina surface was investigated to better reduce the actual system. The Freundlich model exhibited a better fit than the Langmuir model. The adsorption kinetics and proposed first-order kinetic equations fitted better to the Crank model. Comparing the adsorption effect of commercial alumina and the alumina microspheres prepared in this study, it was observed that a smaller particle size and larger pore volume reduced the internal and external diffusion resistance of adsorption, and a larger specific surface area provided more adsorption sites for the adsorption of the oxide-containing compounds. The competitive adsorption behavior of fatty alcohols and methyl acetate on the surface of γ-alumina was explored using a combination of density functional theory (DFT) calculations and experimental techniques. The results of this study can prove to be extremely useful for the efficient removal of oxide-containing compounds from Fischer-Tropsch synthetic oils.

Polyethyleneimine/polydopamine-functionalized self-floating microspheres for caramel adsorption: Interactions and phenomenological mass transfer kinetics

A polyethyleneimine/polydopamine-functionalized self-floating microsphere (EHGM/PDA/PEI) bears an etched hollow glass microsphere as a support, polydopamine as an interfacial cross-linking “glue”, and polyethyleneimine as a functional monomer was fabricated and used as a decolorization sorbent for sugarcane juice. The advantages of EHGM/PDA/PEI for sugarcane juice decolorization were attributed to its richness of target polyethyleneimine monomers, well-connected and abundant three-dimensional network-like aperture structure, and nontoxicity. Moreover, EHGM/PDA/PEI has excellent self-floating performance to allow separation from the adsorption system after decolorization and may have a faster separation speed and lower energy consumption than conventional solid–liquid separation methods. Synthetic caramels were used as model colorants of sugarcane juice to assess EHGM/PDA/PEI performance. The adsorption capacity of EHGM/PDA/PEI for caramels was 18.36 mg/g with a removal efficiency of 91.80% in the adsorption equilibrium state. The interaction mechanisms revealed that the caramel adsorption on EHGM/PDA/PEI was mostly mediated by protonated amine groups, followed by electron sharing. Two layers of caramels adhered onto EHGM/PDA/PEI were mainly mediated by electrovalent bonds between carboxylate and protonated amine. On average, one caramel molecule can be shared by 3–4 protonated amine groups of EHGM/PDA/PEI, which suggests a parallel sorption orientation. Four phenomenological mass transfer models [external diffusion resistance (EXTDR), internal diffusion resistance (INTDR), EXTDR–INTDR mixed, and adsorption onto active sites (AOAS)] proposed new and unique insights into the dynamic properties of the adsorption process.

Insights into mass transfer mechanism and micro-interaction of melanoidin adsorption on polyethyleneimine-functionalised pomelo-peel-derived aerogel

Melanoidins are recalcitrant colouring and polluting polymers present in the effluent streams of molasses-based distilleries. Adsorption is the most prospective technology with ease of operation and high efficiency. Herein, the removal of melanoidins from spent wash was investigated by synthesising a polyethyleneimine (PEI) functionalised pomelo-peel (PP) derived aerogel (PEI-PPA). The PEI-PPA is distinguished by the porous network structure and abundant accessible functional groups (mainly protonated primary amine) that are conducive to the elimination of colouring contaminants (melanoidins). The incorporation of PEI into supporting matrices (i.e., PP–derived aerogel) effectively improved the melanoidin adsorption capacity (from a previous-best research of 230 mg/g to the current 615.70 mg/g), while the melanoidin removal rate reached 92.36 %. The independent gradient model and Hirshfeld surface analysis were used to investigated the possible electroweak interaction relationship between PEI-PPA and melanoidin. By analysing the number of melanoidin molecules bonded to each active site using a novel double-layer adsorption model, a mixed inclination (parallel and non-parallel orientation) of melanoidin onto the PEI-PPA surface was found. For the two mass transfer models fitted results, the adsorption onto the active sites (AOAS) model better described the behaviour of melanoidin adsorption by PEI-PPA than the external diffusion resistance–internal diffusion resistance (EDR–IDR) mixed model under the same conditions, revealing the AOAS was rate-controlling during the mass transfer process. AOAS both contained chemisorption and physisorption. The calculated rates of chemisorption were far higher than those of physisorption before equilibration, indicating chemisorption was main the rate-determining step. Altogether, this work proposed an effective conversion for PP into bio-adsorbent and provided a detailed analysis of mass transfer mechanism.

MASS CONDUCTIVITY OF FLAT FIBROUS MATERIALS DURING THEIR CONVECTIVE DRYING

The kinetics of drying dense woolen fabric under various temperature conditions was experimentally investigated. The mass-conducting properties of the fabric were determined depending on its moisture content and the temperature of the drying agent. Data on the thermophysical characteristics of drying objects, including mass conductivity coefficients, are necessary for calculating the kinetics of the drying process. Information on mass conductivity coefficients is not available for many materials, including fabrics, since their experimental determination is difficult. Experimental studies of the kinetics of convective drying of dense woolen fabric were carried out on a specially created installation under conditions excluding external diffusion resistance. To calculate the mass conductivity coefficients, a zonal method was used to determine the concentration dependence of the mass conductivity coefficient from the drying kinetics curves obtained at different temperatures. The nonlinear nature of the dependence of the mass conductivity coefficient on the moisture content of the material and the temperature of the drying agent is established. For the convenience of engineering calculations, the obtained data on the mass conductivity coefficients are approximated by formulas expressing their dependence on the moisture content of the material and temperature. The coefficients of mass conductivity calculated by the zonal method using experimental curves of drying kinetics are compared with the coefficients of mass conductivity calculated using the obtained dependence of the coefficients on the moisture content of the material and the temperature of the drying agent. The good quality of the approximation of the experimental curves obtained for the mass conductivity coefficient in this study and the applicability of the latter for calculations are shown. The obtained data on the kinetic coefficients of mass conductivity can be used to calculate the kinetics of the drying process of various dense woolen fabrics.

Effective melanoidin adsorption of polyethyleneimine- functionalised molasses-based porous carbon: Adsorption behaviours and microscopic mechanisms

Sugar industry is an integral part of the food and agriculture sector of the national economy. Cane juice decolourisation is a crucial process in sugar production that directly impacts the final colour value of the sugar. However, the chemicals used in traditional methods may be harmful for food safety. Thus, advanced and effective alternatives methods should be developed to further address the problems on sugar production and quality. In this study, polyethyleneimine-functionalised molasses-based porous carbon (PMPC) was prepared from cane molasses, and was reversely applied to remove melanoidins from cane juice. The melanoidin removal efficiency by PMPC was 91.66% with the adsorption capacity of 550.00 mg/g in the adsorption equilibrium state. From the adsorption thermodynamics analysis, the adsorption process of melanoidins onto PMPC was spontaneous and endothermic. Analysis of the interaction mechanisms demonstrated that the successful adsorption of melanoidins by PMPC was mainly achieved through the electrostatic interations and other weak interactions (hydron-bond interaction), and a melanoidin molecule can be bonded with three to four protonated amine groups of PMPC. In addition, the mass transfer behaviour of the melanoidins adsorbed onto PMPC was determined using the mixed model of external and internal diffusion resistance, and the active-onto-site adsorption model. The results showed the melanoidins adsorbed by PMPC was a multilayer adsorption process dominated by chemisorption. Therefore, PMPC was proved to be an ideal adsorbent for cane juice decolourisation, with the advantages of green, high efficiency, and recyclability.

Experimental Data and Modeling the Adsorption-Desorption and Mobility Behavior of Ciprofloxacin in Sandy Silt Soil

The improved understanding of the behavior of antibiotics in soil is of great importance due to their environmental hazard and frequent detection. In this work, the adsorption-desorption and mobility behaviors of ciprofloxacin in sandy silt soil, affecting the fate of ciprofloxacin in the environment, were studied by a series of batch tests and column tests. In batch tests, the effects of contact time, initial ciprofloxacin concentration, sandy silt soil dosage, solution pH, and ionic strength on ciprofloxacin adsorption and desorption in sandy silt soil were considered. Adsorption results were satisfactorily modeled, with good fittings to the pseudo-second-order model (R2 > 0.999) and Langmuir model (R2 > 0.991), with the value for Langmuir’s maximum adsorption capacity (qm) 5.50 mg g−1. Ciprofloxacin adsorption decreased sharply by increasing the pH from 7.0 to 10.0 and the ionic strength from 0.01 to 0.2 mol L−1 CaCl2. Comparatively, ciprofloxacin was more readily desorbed from sandy silt soil at alkaline and high ionic strength conditions. Breakthrough curves of ciprofloxacin obtained from the column experiments were described by the two-site model, Thomas model, and Yan mode. Of these models, the two-site model was the most suitable to describe the mobility of ciprofloxacin. The retardation factor (R) obtained in the two-site model was 345, suggesting strong adsorption affinity with ciprofloxacin on the sandy silt soil surface. The results from the Thomas model suggested the extremely small external and internal diffusion resistances. The Yan model was not suitable. Cation exchange interaction, electrostatic interaction, mechanical resistance, entrapment between porous media, and gravity sedimentation were proposed to be the important adsorption mechanisms.

Roles of Surfactants in Oriented Immobilization of Cellulase on Nanocarriers and Multiphase Hydrolysis System.

Surfactants, especially non-ionic surfactants, play an important role in the preparation of nanocarriers and can also promote the enzymatic hydrolysis of lignocellulose. A broad overview of the current status of surfactants on the immobilization of cellulase is provided in this review. In addition, the restricting factors in cellulase immobilization in the complex multiphase hydrolysis system are discussed, including the carrier structure characteristics, solid-solid contact obstacles, external diffusion resistance, limited recycling frequency, and nonproductive combination of enzyme active centers. Furthermore, promising prospects of cellulase-oriented immobilization are proposed, including the hydrophilic-hydrophobic interaction of surfactants and cellulase in the oil-water reaction system, the reversed micelle system of surfactants, and the possible oriented immobilization mechanism.

Recovery of dysprosium by biosorption onto a biocomposite from sericin and alginate

Dysprosium is a critical rare-earth metal used in high-tech industry. Its recovery from secondary sources is fundamental in the context of circular economy. The use of polymer-based biosorbents is promising for this purpose. In this work, we employ a biocomposite produced from waste protein from silk yarns processing, sodium alginate, and polyvinyl alcohol for dysprosium recovery by batch biosorption in aqueous medium. The pH range between 4.5 and 5.0 for dysprosium biosorption and calcium release by biosorbent beads was defined by chemical equilibrium diagrams. Kinetics assays indicated that the equilibrium times and dysprosium biosorbed amounts at equilibrium were 120 to 390 min and 0.048 to 0.139 mmol/g, respectively. Kinetic data followed the pseudo-first order model and were governed by external diffusion resistance. The kinetics profiles also indicated that the cationic exchange between dysprosium and calcium was stoichiometric. Additionally, calcium nitrate/nitric acid (0.1 mol/L) was selected for the reuse cyclic assays, due to the higher elution efficiency of dysprosium achieved. Beads reusability and dysprosium recovery were performed for up to four reuse cycles and achieved biosorption and desorption efficiencies above 94 and 98%, respectively. The characterizations of beads loaded with Dy(III) indicated that biosorbent maintained its macroporous structure, low porosity and specific surface area, lower thermal resistance, and amorphous structure. Finally, cationic exchange mechanism was confirmed by techniques of energy-dispersive X-ray spectroscopy and Fourier-transform infrared spectroscopy. Therefore, the use of crosslinked sericin/alginate beads is the first step towards achieving a sustainable valorization of sericin and recovery of high added value metals.

The Experimental Study of the Kinetics of the Cyclic Adsorption Process of Air Enrichment with Oxygen

For mass transfer cyclic processes in the “adsorptive - porous adsorbent” system when air is enriched with oxygen by the method of short-cycle heatless adsorption, a new method has been implemented for determining the coefficients of mass transfer and mass conductivity of processes in systems with a solid phase from kinetic curves. It has been experimentally proved that during the adsorption separation of atmospheric air, the rate of cyclic “adsorption - desorption” processes can be limited by both internal and external diffusion resistance. The mass conductivity coefficients are determined depending on the mass content of the distributed adsorptive (O2, N2) by a method that does not require the implementation of the intradiffusion kinetic regime. The analysis of the kinetics of the process of air enrichment with oxygen is carried out; the coefficients of mass transfer and mass conductivity, which can be used in kinetic calculations and numerical study of the properties and modes of the cyclic adsorption process of atmospheric air separation and oxygen concentration, are determined.

Modeling carbohydrates oxidation by oxygen catalyzed by bienzyme glucose dehydrogenase/laccase system immobilized into microreactor with carbon nanotubes

This paper presents a mathematical model of a batch stirred tank reactor based on an array of identical spherical porous microbioreactors loaded with non specific glucose dehydrogenase and oxygen reducing enzyme, i.e. laccase. The model was validated by experimental data. The microreactors (MR) are mathematically modeled by a two-compartment model, based on reaction–diffusion equations containing nonlinear terms related to the Michaelis–Menten kinetics of two enzymatic reactions with addition of the mass transport. The dynamics of oxygen concentration change is analysed numerically using the finite difference technique. The transient effectiveness factor and the process duration are investigated at different initial concentration of carbohydate (lactose) as well as at internal and external diffusion resistances. The simulation results show a non-monotonic effect of the initial concentration of lactose and nonlinear effects of the internal and external diffusion limitations on the transient effectiveness.

Multiscale model for steam enhancement effect on the carbonation of CaO particle

A multiscale model including scales at the surface, grain, and particle was developed to understand the steam enhancement mechanism on the carbonation of CaO particle. The interaction of H2O with CaO occurring at the surface scale exhibited an enhancement effect on the product layer diffusion at the grain scale, while the grain growth due to the product layer diffusion at the grain scale exhibited an important effect on the pore structure and intraparticle gas diffusion at the particle scale. The developed multiscale model was validated with the experimental data, and the effect of steam addition on carbonation performance was discussed. The effect of steam on CaO carbonation at higher temperatures (600 ~ 700 °C) was much less significant than that at lower temperatures (400 ~ 500 °C), due to the pore plugging phenomenon. In addition, the controlling step of the carbonation in the presence of steam was analyzed. Calculated results show that the external gas diffusion resistance is small enough during the reaction process. The controlling step of the carbonation at 400 °C is the chemical reaction step, while the controlling step of the carbonation at 700 °C is the intraparticle gas diffusion step.

Kinetics of aluminum extraction from aluminum ash by leaching with sulfuric acid

To explore the high value of aluminum ash development and utilization, factors (granularity of aluminum ash, leaching temperature, leaching time, sulfuric acid concentration, and liquid solid ratio) affecting the leaching rate of aluminum were evaluated. The kinetics of the leaching process was also investigated. The results indicate that the leaching rate of aluminum in aluminum ash can reach 88.9% under the following conditions: leaching temperature, 100 °C; leaching time, 120 min; sulfuric acid concentration, 2.5 mol/L; and liquid–solid ratio (mass ratio), 1.3:1. Studies on the leaching dynamics of aluminum in aluminum ash showed that leaching was divided into two stages. At the initial stage (i.e. at the leaching rate x ≤ 0.3), the external diffusion resistance and the diffusion resistance of the solid product layer are negligible, and leaching is controlled by chemical reaction at the interface. The apparent activation energy was 5733.25 J/mol. At the leaching rate x = 0.3–0.9, the leaching rate was controlled by the non-steady diffusion of the liquid film in the porous solid by the fluid reactant H2SO4. The apparent activation energy was 25390.87 J/mol.

Non-thermal atmospheric plasma synthesis of ammonia in a DBD reactor packed with various catalysts

Plasma synthesis of ammonia (NH3) is a potential and sustainable pathway for nitrogen fixation. In this study, non-thermal plasma (NTP) synthesis of NH3 was conducted in a packed-bed dielectric barrier discharge (DBD) reactor. Different catalysts, including alumina (Al2O3), light magnesium oxide (L-MgO), heavy magnesium oxide (H-MgO), Ru/Al2O3 and Ru/L-MgO, were filled in the reactor and compared for NH3 production. Various characterization techniques were used to determine the specific surface area and pore size, surface morphology, and surface acidity of the catalysts. The effects of reaction conditions on NH3 production were examined. Results showed that the optimal N2/H2 volume ratio was 2:1 since a greater quantity of N2 favored the generation of plasma-excited nitrogen species. The synthesized NH3 can be adsorbed by the acid sites on Al2O3, which reduced the NH3 yield. Higher total gas flow rate improved the NH3 production over various catalysts, mainly due to the reduced external diffusion resistance. More plasma-excited nitrogen and hydrogen species for NH3 synthesis were formed at higher discharge power, yet the increasing rate of NH3 yield became slower when the discharge power was higher than 32 W. Additionally, the NH3 desorption from the catalyst was enhanced at higher temperature, which resulted in higher NH3 yield.

Analysis of the performance of the industrial Co-Mo catalyst for hydrotreatment

The process of hydrotreatment of diesel fuel (fraction 180–320 °C) over fresh and spent (after two-year operation in an industrial reactor) Co-Mo catalyst was studied. It was established that the sulfur contents were rather close to one another in the diesel fuel samples treated using the fresh and spent catalysts, even though the specific surface area was 40 % smaller in the spent catalyst compared to that in the fresh sample. Dependence of effective constant keff of hydrodesulfurization on the temperature of low-temperature hydrotreatment (below 320–330 °C) was characteristic of the kinetic range of heterogeneous catalysis complicated by external diffusion resistance. When the temperature was elevated up to 420 °C, the process of diesel hydrotreatment transferred to the external diffusion region. Activation energies of hydrodesulfurization were comparable over the spent and fresh catalysts (81.1 and 80.5 kJ/mol, respectively). A hypothesis of the specific catalyst deactivation was discussed.

Kinetic study of SO2 adsorption on microfibrous entrapped sorbents for solid oxide fuel cell cathode protection

The kinetics of the non-catalytic gas-solid reaction between MnOx/γ-Al2O3 and SO2 were investigated. A mathematical model based on axial dispersion, external and internal diffusion resistance, as well as a depletion mechanism for the sorbent has been established in this study. It predicted the breakthrough curves of packed bed (PB) and microfibrous entrapped sorbent (MFES) with acceptable deviations. This model consists of two predetermined parameters: the initial sorption rate constant (ko) and the depletion rate constant (kd), which can be determined by fitting the model to experimental data at various temperatures. Due to the uniform flow pattern and minimized bed channeling, MFES outperformed conventional PB consisting of the same sorbent particle size in terms of the reduction in SO2 concentration. The MFES surpassed PB significantly during the in situ regeneration in anode exhaust gas (AEG). Furthermore, MFES maintained its high breakthrough capacity up to five adsorption/regeneration cycles. Therefore, the MFES is a superior approach to remove the potential SO2 from the fuel cell cathode air stream for practical applications.

A kinetic study of the biological catalytic hydration of acrylonitrile to acrylamide

In this study, the kinetic characteristics of the bio-hydration of acrylonitrile by free cell catalysts were studied. Due to the aggregation phenomenon, free cell catalysts showed different characteristic when compared with free enzyme catalysts. The Michaelis constants were obtained through the homogeneous reaction. Both the values of Vm and Km increased with the increase in enzymatic activity, ranging from 100 to 500U/mL, and the variation trend of Km was not consistent with the rule of enzyme-catalyzed reaction. To reduce the external diffusion resistance of acrylonitrile to free cells, a membrane dispersion micro-reactor was used, and the conversion rates of acrylonitrile in the membrane dispersion micro-reactor under all of the experimental conditions reached approximately 90% of the max conversion rates. The reinforcement of the apparent reaction rate by the micro-reactor may have benefitted from the significant increase in the specific surface area of the acrylonitrile droplets and the adsorption of the free cell catalysts on the undissolved droplets.

Kinetic study of the hydration of propylene oxide in the presence of heterogeneous catalyst

The kinetics of the hydration of propylene oxide was studied using a pressurized batch reactor for both uncatalyzed and heterogeneously catalyzed reactions. Lewatit MonoPlus M500/HCO3 - was used as heterogeneous catalyst, which showed better performance than Dowex Marathon A/HCO3 -. The effects of the parameters, namely internal and external diffusion resistances, temperature, catalyst loading and mole ratios of reactants, on the reaction rate were studied. The uncatalyzed and heterogeneously catalyzed reactions were proven to follow a series-parallel irreversible homogeneous mechanism. The temperature dependencies of the rate constants appearing in the rate expressions were determined.

Deactivation and regeneration of Raney-Ni catalyst during multiphase dehydrogenation of cyclohexane

Hydrogen production via dehydrogenation of cyclohexane is regarded as one of the most promising on-board hydrogen supplier system for hydrogen vehicles. In this study, the deactivation mechanism of Raney-Ni catalyst under “wet-dry” multiphase reaction conditions was studied by means of characterizations. The fresh and deactivated Raney-Ni catalyst was characterized by scanning electron microscope (SEM), thermogravimetry analysis (TGA), X-ray spectroscopy (XRD), Brunauer-Emmett-Teller (BET), mercury porosimetry and granularity analysis. It was found that the deposition of the filamentous carbon, which came from the side reactions of cyclohexane, on the outer layers of Raney-Ni particles was the main reason for the catalyst deactivation. Due to the strong external diffusion resistance during the multiphase reaction process, the carbon was concentrated in the orifices, and the amount of carbon was about 3.25wt.% of the catalyst. The decay of Raney-Ni was a typical orifice coking deactivation. The experimental study also showed that the deactivated Raney-Ni catalyst could be regenerated by coke elimination with water and recovered its activity. In addition, a regeneration mechanism of the deactivated catalyst by coke elimination was proposed.

Methane partial oxidation over a LaCr0.85Ru0.15O3 catalyst: Characterization, activity tests and kinetic modeling

A new LaCr0.85Ru0.15O3 perovskite-type catalyst for CH4 partial oxidation with a high activity and selectivity for syngas with good thermal stability and resistance against coking has been developed. In this paper, the catalyst preparation method, catalyst characterization, results of catalytic tests in a micro-reactor and kinetic modeling are discussed. A partial incorporation of Ru in the perovskite support has been demonstrated which can be responsible for the reported high activity and stability for this catalyst. Reactivity tests have been carried out at both low and high GHSV regimes (≈1–2×107h−1); for the latter case the CH4–O2 partial oxidation reaction system has been studied at incomplete methane (7–18%) and O2 (20–65%) conversion, as rarely reported in the literature. The variation of temperature (650–850°C) and feed gas composition (in terms of CH4, CO, CO2, H2 and H2O inlet partial pressure) allowed to study the reaction system over a wide range of experimental conditions gaining insight in the reaction mechanism. A kinetic model is proposed where CH4 partial oxidation, H2 and CO oxidation and water–gas shift are used to describe the involved lumped reaction network. External diffusion resistances have been found to be negligible whereas internal diffusion resistances have been accounted for by means of a single particle model able to describe the concentration profiles inside the catalyst pellet. Pre-exponential factors and activation energy values for all reactions have been estimated by means of a least square fitting of the experimental data. It is found that CH4 partial oxidation dominates the first region of the catalyst bed while H2 and CO oxidation become important in the remaining part of the bed.

A sophisticated model to predict ash inhibition during combustion of pulverized char particles

Final burnout of char particles from practical fuels such as coal and biomass occurs in the presence of a large ash component. Also, newly utilized coal resources, such as those from India, often contain much larger ash fractions than have traditionally been utilized. In the past, the inhibitory influence of ash on pulverized coal particle combustion has been most frequently modeled using an ash film model, though such films are rarely found when examining partially combusted particles. Conversely, some measurements have suggested that mineral components exposed on the surface of burning pulverized coal (pc) particles may diffuse back into the char matrix, the effect of which can be modeled as an ash dilution effect. To explore the implications of these different ash inhibition models on the temporal evolution of char combustion during burnout, we have developed a new computational model that considers the possibility of an ash film effect, an ash dilution effect, or some arbitrary combination of the two effects acting in tandem, which is the most realistic scenario. This new model predicts that restricted diffusion through the ash film has a significant impact on the char burnout rate throughout its lifetime, whereas char dilution only inhibits combustion significantly when most of the char has been consumed and the combustion mode shifts from predominantly external diffusion control to mixed diffusion control, with sensitivity to both external and internal diffusion resistance. The comparison of the model predictions with experimental results also confirms the previously suggested need to include gasification reaction steps when modeling coal char combustion.