Showing papers in "Industrial & Engineering Chemistry Research in 2004"
TL;DR: A review of the various types of catalysts that have been used in several research works to reduce the tars in the producer gas derived from the biomass gasification process is presented in this paper.
Abstract: A project is carried out to develop a process for tar elimination downstream of a gasifier making use of cheap and active materials as catalysts. In the first stage of the project, screening of catalysts was carried out in a fixed-bed tubular reactor. The results of the fixed-bed experiments will be used in the design of the process. This paper presents a review of the various types of catalysts that have been used in several research works to reduce the tars in the producer gas derived from the biomass gasification process. The catalysts are divided into two classes according to their production method: minerals and synthetic catalysts. A summary of the review and recommendations for good catalyst candidates and future work are also provided.
731 citations
TL;DR: In this article, the authors focused on the treatment of hazardous wastewater (bearing heavy metals and organic compounds) by photocatalysis and the effects of various parameters such as pH, light intensity, dissolved oxygen, etc.
Abstract: Photocatalysis has been a widely studied technology since the 1970s. Many investigations have been carried out with the aim of understanding the fundamental processes and enhancing photocatalytic efficiencies especially for water, air, and soil pollution control. In this comprehensive paper, studies focused on the treatment of hazardous wastewater (bearing heavy metals and organic compounds) by photocatalysis and the effects of various parameters such as pH, light intensity, dissolved oxygen, etc., are reviewed. In addition, the design features and efficiencies of various photoreactors used for this process are discussed. Some studies on the economic analysis of photocatalytic systems are also included. It can be concluded that the photocatalysis process is suitable for the treatment of drinking water and industrial wastewater. Also, harvesting the energy of the sun for photoreactions would make it a cleaner and more cost-effective treatment method.
677 citations
TL;DR: In this paper, two types of ionic liquids, 1-alkyl-3methylimidazolium [AMIM] tetrafluoroborate and hexafluorophosphate and trimethylamine hydrochloride (AlCl3−TMAC), were demonstrated to be potentially applicable for sulfur removal from transportation fuels.
Abstract: Two types of ionic liquids, 1-alkyl-3-methylimidazolium [AMIM] tetrafluoroborate and hexafluorophosphate and trimethylamine hydrochloride (AlCl3−TMAC), were demonstrated to be potentially applicable for sulfur removal from transportation fuels. EMIMBF4 (E = ethyl), BMIMPF6 (B = butyl), BMIMBF4, and heavier AMIMPF6 showed high selectivity, particularly toward aromatic sulfur and nitrogen compounds, for extractive desulfurization and denitrogenation. The used ionic liquids were readily regenerated either by distillation or by water displacement of absorbed molecules. The absorbed aromatic S-containing compounds were quantitatively recovered. Organic compounds with higher aromatic π-electron density were favorably absorbed. Alkyl substitution on the aromatic rings was found to significantly reduce the absorption capacity, as a result of a steric effect. The cation and anion structure and size in the ionic liquids are important parameters affecting the absorption capacity for aromatic compounds. At low concen...
439 citations
TL;DR: In this article, the effects of temperature and space time on the transformation over a HZSM-5 zeolite catalyst of several model components of the liquid product obtained by the flash pyrolysis of vegetable biomass (1-propanol, 2-polyphenol, phenol, and 2-methoxyphenol) have been studied.
Abstract: The effects of temperature and space time on the transformation over a HZSM-5 zeolite catalyst of several model components of the liquid product obtained by the flash pyrolysis of vegetable biomass (1-propanol, 2-propanol, 1-butanol, 2-butanol, phenol, and 2-methoxyphenol) have been studied. The transformation of alcohols follows a route similar to that of methanol and ethanol toward the formation of hydrocarbon constituents of the lumps of gasoline and light olefins. Phenol and 2-methoxyphenol have a low reactivities to hydrocarbons, and the deposition of coke of thermal origin caused by the condensation of 2-methoxyphenol is noticeable. The generation of catalytic coke and the deactivation by this cause attenuate as the space time and water content in the feed are increased. To avoid the irreversible deactivation of the HZSM-5 zeolite, operations must be carried out at a temperature below 400 °C. Above this temperature, the increase in product aromaticity is also significant.
437 citations
TL;DR: In this article, the catalytic transformation over a HZSM-5 zeolite of key components of the liquid product obtained by the flash pyrolysis of biomass, namely, acetaldehyde, ketones (acetone and butanone), and acetic acid, has been studied, and great differences in reactivity and degradation to coke have been found.
Abstract: The catalytic transformation over a HZSM-5 zeolite of key components of the liquid product obtained by the flash pyrolysis of biomass, namely, acetaldehyde, ketones (acetone and butanone), and acetic acid, has been studied, and great differences in reactivity and degradation to coke have been found. Acetaldehyde has a low reactivity to hydrocarbons, with a noticeable deactivation caused by coke deposition, which can be attributed to its capacity for oligomerization with the trimer trimethyltrioxane obtained as an intermediate product. The transformation of ketones [less reactive than the alcohols studied in part I of this work (see the preceding paper in this issue)] and of acetic acid (which gives rise to acetone as the primary product) mainly occurs through decarboxylation and, to a lesser degree, dehydration. Above 400 °C, this transformation gives olefins and aromatics according to a reaction scheme similar to that better known for the reaction of alcohols. The generation of coke (attenuated by the pr...
403 citations
TL;DR: In this article, the removal of rhodamine B, fast green, and methylene blue from wastewater using red mud, an aluminum industry waste, was reported to achieve 95−97% removals in column experiments at a flow rate of 0.5 mL/min.
Abstract: Successful removal of rhodamine B, fast green, and methylene blue from wastewater was achieved using red mud, an aluminum industry waste. The percentage removals of rhodamine B, fast green, and methylene blue on this adsorbent were 92.5, 94.0, and 75.0, respectively. Studies were conducted to delineate the effects of initial absorbate concentration, pH, adsorbent dose, contact time, temperature, and adsorbent particle size. Up to 95−97% removals of rhodamine B, fast green, and methylene blue were achieved in column experiments at a flow rate of 0.5 mL/min. The adsorption was found to be exothermic in nature. The developed system is very useful, rapid, and reproducible for the removal of the three dyes.
394 citations
TL;DR: In this paper, the authors used regular solution theory to predict the solubility of room-temperature ionic liquids in RTILs at low pressure and temperature changes in CO2 and C2H4 measurements.
Abstract: The ability to predict the solubility of gases in room-temperature ionic liquids, RTILs, would be very useful in determining the most efficient RTIL to use in an industrial process. This work uses data from CO2 and C2H4 solubility measurements to show that regular solution theory can be used to model gas solubilities in RTILs at low pressures. This work further discusses how changes in pressure and temperature affect the solubility of gases in RTILs.
330 citations
TL;DR: In this paper, a common mass balance for all of these processes is used to define a parameter that highlights the minimum sorbent performance required to keep sorbent makeup costs at an acceptable level.
Abstract: Power plants are prime candidates to apply CO2 capture for final storage as a mitigation option for climate change. Many CO2 capture concepts make use of a sorption−desorption cycle to separate CO2 from flue gas or O2 from air. These include commercial absorption processes, as well as processes using new sorbent formulations, adsorption, and high-temperature chemical looping cycles for CO2 and O2. All of these new processes must confront the large scale of carbon flows typical in a power plant. In this work, a common mass balance for all of these processes is used to define a parameter that highlights the minimum sorbent performance required to keep sorbent makeup costs at an acceptable level. A well-established reference system for which reliable commercial data exist (absorption with monoethanolamine, MEA) is used as a technoeconomic baseline to show that some of the sorbents being proposed in the open literature might need to be tested under laboratory conditions for tens of thousands of sorption−desor...
320 citations
TL;DR: In this article, the thermal and catalytic decomposition of urea over a fixed-bed flow reactor system has been examined for the selective catalytic reduction (SCR) of NOx from mobile sources.
Abstract: The thermal and catalytic decomposition of urea over a fixed-bed flow reactor system has been examined for the selective catalytic reduction (SCR) of NOx from mobile sources. The conversion of urea into NH3 and HNCO, the two major products from the thermal decomposition of urea, increased with the reaction temperature and the reactor space time. Urea was completely decomposed into NH3 and HNCO at 350 °C when the residence time was longer than 0.1 s. As the reaction temperature increased to 400 °C or higher, complete decomposition of urea was possible at a much shorter residence time of the feed gas stream. The simultaneous thermal and catalytic decomposition of urea was also examined in a dual-reactor system in which the first reactor was for thermal decomposition and the second was for catalytic decomposition, specifically over copper exchanged ZSM5 catalyst. The role of the catalyst in the decomposition of urea into NH3 and HNCO was negligible; urea decomposition occurs mainly by the thermal reaction. H...
313 citations
TL;DR: In this article, the influence of experimental conditions on the chemistry of biomass degradation in supercritical water, the effect of heating rate and of different catalysts on the product distribution during hydropyrolysis of glucose is investigated.
Abstract: To understand the influence of experimental conditions on the chemistry of biomass degradation in supercritical water, the effect of heating rate and of different catalysts (1 wt % of Raney nickel and 0.5 wt % K2CO3) on the product distribution during hydropyrolysis of glucose is investigated. Glucose in aqueous solution (5 wt %) is selected as a model compound for cellulosic biomass. The heating rates are 1 or 3 K/min up to 500 °C, and then, the reactor is kept at this temperature for 1 h. Despite the long reaction time of 1 h at 500 °C, the presence of catalysts has an significant influence on intermediates of glucose gasification such as phenols or furfurals. The influence of catalyst and the heating rate on these intermediates and the product yields points to the assumption that the chemical processes during heating have a drastic effect on the results of the gasification process at 500 °C.
313 citations
TL;DR: In this article, the decomposition behavior of five selected amino acids in high-temperature and high-pressure water was studied using a continuous-flow tubular reactor, and the effect of temperature on reaction products, pathway, and rate was determined as a function of reaction time.
Abstract: Decomposition behavior of five selected amino acids in high-temperature and high-pressure water was studied using a continuous-flow tubular reactor. The reaction was carried out in the temperature range of 200−340 °C at a pressure of 20 MPa. Alanine and its derivatives leucine, phenylalanine, serine, and aspartic acid were used as model amino acids. The effect of temperature on reaction products, pathway, and rate was determined as a function of reaction time. Alanine decomposed into lactic acid and pyruvic acid, then finally mineralized to carbon dioxide with an activation energy of 154 [kJ/mol] at 20 MPa. The degradation rate decreased in the following order: aspartic acid, serine, phenylalanine, leucine, and alanine. The general reaction network of amino acids under hydrothermal conditions takes two main paths: deamination to produce ammonia and organic acids, and decarboxylation to produce carbonic acid and amines. Deamination was the predominant reaction in the decomposition of aspartic acid, an ac...
TL;DR: In this article, the authors explored the arguments for using solubility parameters and the regular solution theory for modeling gas solubilities in five different room-temperature ionic liquids (RTILs) at low partial pressures and low mole fractions.
Abstract: This paper explores the arguments for using solubility parameters and the regular solution theory for modeling gas solubilities in five different room-temperature ionic liquids (RTILs) at low partial pressures (<1 atm) and low mole fractions (<0.1). The experimentally measured and reported carbon dioxide (CO2) solubilities at low mole fractions (<0.05) suggest positive deviations from Raoult's law for CO2/RTIL solutions. These CO2 solubility deviations from Raoult's law indicate that CO2/RTIL complexations are not the sole controlling factor in relative CO2 solubilities. The RTILs' energies of vaporization and molar volumes appear to be factors in determining relative CO2 solubilities between RTILs. The energies of vaporization for the RTILs were empirically estimated from their melting points.
TL;DR: In this paper, an adsorption and photocatalytic reduction of Cr(VI) to Cr(III) inaqueous solutions by UV/TiO2 photocatalysis has been investigated.
Abstract: Semiconductor photocatalytic reduction is a relatively new technique for the removal of dissolved toxic metal ions from wastewater. In this paper, adsorption and photocatalytic reduction of Cr(VI) to Cr(III) inaqueous solutions by UV/TiO2 photocatalysis has been investigated. It has been observed that the pH of the solution plays an important role in this reaction. An acidic medium is favorable for Cr(VI) photocatalytic reduction, where 94% of Cr(VI) was photoreduced within 1 h at pH 3 when 2 g/L of TiO2 was used as the slurry. An adsorption study shows that the photocatalytic reduction mainly occurs on the surface of TiO2. The presence of Fe(III) improved the photocatalytic reduction of Cr(VI) because it was observed that an additional reaction between Fe(II) and Cr(VI) takes place in the UV/TiO2 reduction process. A new combination of photocatalytic reduction and metal ion coprecipitation using Fe(OH)3 for complete removal of aqueous Cr [Cr(VI) as well as Cr(III)] was designed, which reduced the chromiu...
TL;DR: In this paper, the performance of carbon dioxide (CO2) absorption into aqueous solutions of single and blended alkanolamines was evaluated experimentally in a bench-scale absorber packed with high-efficiency packings.
Abstract: The performance of carbon dioxide (CO2) absorption into aqueous solutions of single and blended alkanolamines was evaluated experimentally in a bench-scale absorber packed with high-efficiency packings. The absorption experiments were conducted under atmospheric pressure, using a feed gas mixture containing 10% CO2 and 90% nitrogen. Monoethanolamine (MEA), diethanolamine (DEA), diisopropanolamine (DIPA), methyldiethanolamine (MDEA), 2-amino-2-methyl-1-propanol (AMP), and their mixtures including MEA−MDEA, DEA−MDEA, MEA−AMP, and DEA−AMP were tested in this work. The absorption performance was presented in terms of the CO2 removal efficiency, absorber height requirement, effective interfacial area for mass transfer, and overall mass-transfer coefficient (KGae). Comparison of the absorption performance between the tested alkanolamines was made over ranges of operating conditions to establish the correlation between single- and blended-alkanolamine systems.
TL;DR: In this article, a nickel-enriched catalytic bed material was tested for tar reduction in a 100 kWth dual fluidized bed biomass steam gasifier, and the results obtained at the pilot scale represent an important intermediate step in preparing the technical breakthrough of dual-fluidized bed steam gasification.
Abstract: A nickel-enriched catalytic bed material was tested for tar reduction in a 100 kWth dual fluidized bed biomass steam gasifier. Gas composition and tar content were measured after the reactor and compared with data from gasification tests without a catalytic bed material. H2, CO, CO2, and CH4 contents in the product gas, as well as tar conversion rates, are reported for different amounts of catalytic active bed material and different operating conditions. Water conversions, gas yields, and lower heating values were calculated. The catalyst showed no noticeable deactivation in two tests of 30 and 45 h. These results obtained at the pilot scale represent an important intermediate step in preparing the technical breakthrough of dual fluidized bed biomass steam gasification.
TL;DR: In this paper, the authors examined the rate of oxidative degradation of MEA under conditions typical of a CO2 capture process and found that degradation rates are controlled by the physical absorption of O2 and NH3 evolution rates ranged from 0.2 to 8.0 mM/h.
Abstract: This study examines the rate of oxidative degradation of MEA under conditions typical of a CO2 capture process. Experiments examined the effects of amine concentration, CO2 loading, O2 concentration, and agitation rate at 55 °C. Degradation rates were quantified by measuring the rate of NH3 evolution from the amine solutions using FT-IR analysis. Results show that degradation rates are controlled by the rate of physical absorption of O2 and NH3 evolution rates ranged from 0.2 to 8.0 mM/h. Previous studies were re-examined and compared to the current study and appear to have been performed under conditions that were mass transfer limited. This would indicate the previous literature values for degradation kinetics were actually O2 absorption rates. An estimate of the degradation rate for a CO2 absorber was made assuming the degradation was controlled by the rate of O2 absorption and was shown to be equal to or less than values reported in the literature.
TL;DR: In this paper, the kinetics of reduction with CH4, H2, and CO and oxidation with O2 of a Cu-based oxygen carrier prepared by impregnation on alumina to be used in a chemical-looping combustion (CLC) system have been determined in a thermogravimetric analyzer.
Abstract: The kinetics of reduction with CH4, H2, and CO and oxidation with O2 of a Cu-based oxygen carrier prepared by impregnation on alumina to be used in a chemical-looping combustion (CLC) system have been determined in a thermogravimetric analyzer. The oxygen carrier exhibited high reactivity in both reduction and oxidation with times for complete conversion lower than 40 s at 1073 K and 5−70 vol % of the fuel gas and 5−21 vol % of O2. The analysis of the sample carried out by scanning electron microscopy using energy-dispersive X-ray and chemisorption showed that the CuO was well dispersed in the porous surface of the alumina matrix and a uniform thin layer on the porous surface was considered. The shrinking-core model for platelike geometry of the reacting surface was used for the kinetic determination, in which the chemical reaction controlled the global reaction rate. No effect of the gas products (H2O and CO2) on the reaction rate was detected. The reaction order depended on the fuel gas, and values of 0...
TL;DR: In this article, a suitable extractant−diluent system for lactic acid extraction on the basis of distribution coefficient, toxicity, and feasibility for backextraction is suggested.
Abstract: Growing demand for biodegradable polymer substitutes for both conventional plastic materials and new materials of specific uses such as controlled drug delivery or artificial prostheses draws attention to the need for improvement of conventional processes for lactic acid production. Reactive extraction with a specified extractant giving a higher distribution coefficient has been proposed as a promising technique for the recovery of lactic acid. A critical analysis of the available literature data has been made, and some general conclusions have been drawn. A suitable extractant−diluent system for lactic acid extraction on the basis of distribution coefficient, toxicity, and feasibility for backextraction is suggested. Also, methods for backextraction and recovery are suggested.
TL;DR: In this article, steam hydration of CaO was used to increase both pore area and pore volume to improve long-term conversion to CaCO3 over multiple cycles, resulting in directly measured conversions as high as 52% and estimated conversions up to 59% after up to 20 cycles.
Abstract: Cyclic carbonation and calcination reactions were investigated for capturing CO2 from combustion and gasification processes. Sorbent particles in the size range 600−1400 μm were subjected to multiple capture cycles at atmospheric pressure to obtain a surface mapping of conversion based on calcination and carbonation temperatures. Steam hydration of CaO was utilized to increase both pore area and pore volume to improve long-term conversion to CaCO3 over multiple cycles. The steam hydration improved the long-term performance of the sorbent, resulting in directly measured conversions as high as 52% and estimated conversions as high as 59% after up to 20 cycles. It is estimated that the increase in conversion has improved the economics of the proposed process to the point where commercialization is attractive. It has been shown that when carbonating in the temperature range from 700 to 740 °C, calcination temperatures from 700 to 900 °C can be used without seriously reducing the conversion of CaO for CO2 capt...
TL;DR: In this paper, a drag model based on the energy minimization multiscale (EMMS) approach was proposed to simulate the gas-solid flow in a circulating fluidized-bed riser.
Abstract: To consider the critical effect of mesoscale structure on the drag coefficient, this paper presents a drag model based on the energy-minimization multiscale (EMMS) approach. The proposed structure parameters are obtained from the EMMS model, and then the average drag coefficient can be calculated from the structure parameters and further incorporated into the two-fluid model to simulate the gas-solid flow in a circulating fluidized-bed riser. Simulation results indicate that the simulated flow structures are different for the EMMS-based drag model and the hybrid model using the Wen and Yu correlation and the Ergun equation. The former shows its improvement in predicting the solids entrainment rate, the mesoscale heterogeneous structure involving clusters or strands, and the radial and axial voidage distributions. The simulation results support the idea that the average drag coefficient is an important factor for the two-fluid model and suggest that the EMMS approach could be used as a kind of multiscale closure law for drag coefficient.
TL;DR: In this article, the effect of small amounts of water, in regard to inhibiting the adsorption of carbon dioxide (CO2), on several different cationic forms of zeolite X was investigated using the zero length column (ZLC) technique, coupled with temperature-programmed desorption (TPD) measurements.
Abstract: The effect of small amounts of water, in regard to inhibiting the adsorption of carbon dioxide (CO2), on several different cationic forms of zeolite X has been investigated using the zero length column (ZLC) technique, coupled with temperature-programmed desorption (TPD) measurements. This is shown to be a very effective way to study the effect of a strongly adsorbed species (water) on the adsorption of a less-strongly adsorbed species (CO2 or propane (C3H8)). It was observed that, for all systems studied, the Henry constant declines exponentially with the loading of water. As expected, this effect is stronger for CO2 than for C3H8.
TL;DR: In this paper, the pilot-scale pyrolysis of scrap tires in a continuous rotary kiln reactor was investigated at temperatures between 450 and 650 °C, and the char yield remained constant with a mean of 39.2−42.8 wt %.
Abstract: The pilot-scale pyrolysis of scrap tires in a continuous rotary kiln reactor was investigated at temperatures between 450 and 650 °C. As the reactor temperature increased, the char yield remained constant with a mean of 39.8 wt %. The oil yield reached a maximum value of 45.1 wt % at 500 °C. The pyrolytic derived oils can be used as liquid fuels because of their high heating value (40−42 MJ/kg), excellent viscosity (1.6−3.7 cS), and reasonable sulfur content (0.97−1.54 wt %). The true-boiling-point distillation test showed that there was a 39.2−42.3 wt % light naphtha fraction in the pyrolytic oil. The volatile aromatics were quantified in the naphtha fraction using gas chromatography−mass spectrometry. The maximum concentrations of benzene, toluene, xylene, styrene, and limonene in the oil were 2.09 wt %, 7.24 wt %, 2.13 wt %, and 5.44 wt %, respectively. The abundant presence of aromatic groups was also confirmed by functional group Fourier transform infrared analysis. The concentration of polycyclic ar...
TL;DR: In this article, a segment contribution activity coefficient model is proposed for fast, qualitative estimation of the solubilities of organic nonelectrolytes in common solvents, based on the polymer non-random two-liquid model.
Abstract: A segment contribution activity coefficient model, derived from the polymer nonrandom two-liquid model, is proposed for fast, qualitative estimation of the solubilities of organic nonelectrolytes in common solvents. Conceptually, the approach suggests that one account for the liquid nonideality of mixtures of complex pharmaceutical molecules and small solvent molecules in terms of interactions between three pairwise interacting conceptual segments: hydrophobic segment, hydrophilic segment, and polar segment. In practice, these conceptual segments become the molecular descriptors used to represent the molecular surface characteristics of each solute and solvent molecule. The treatment results in component-specific molecular parameters: hydrophobicity X, polarity Y, and hydrophilicity Z. Once the molecular parameters are identified from experimental data for common solvents and solute molecules, the model offers a simple and practical thermodynamic framework to estimate solubilities and to perform other p...
TL;DR: In this article, the authors used ab initio calculations and a continuum model to study the mechanism for formation of carbamate from CO2 and alkanolamines, and concluded that a single-step, third-order reaction is the most likely.
Abstract: Ab initio calculations and a continuum model have been used to study the mechanism for formation of carbamate from CO2 and alkanolamines. The molecules studied are ethanolamine and diethanolamine. A brief review is also made of published experimental observations relevant to the reaction mechanism. The ab inito results suggest that a single-step, third-order reaction is the most likely. It would seem unlikely that a zwitterion intermediate with a significant lifetime is present in the system. A single-step mechanism also seems to be in good agreement with the experimental data.
TL;DR: In this article, the authors take a critical view of the deformation of the packing beds in the process of process intensification for gas−liquid mass transfer, and present a critical analysis of their deformation.
Abstract: Rotating packed beds have received considerable attention as a means of process intensification for gas−liquid mass transfer over the past 2 decades. In this work, we take a critical view of the de...
TL;DR: In this article, the authors present a multivariate statistical process monitoring (MSPM) technique based on the assumption that the process has one nominal operating region, which is not the case in many of the existing MSPM techniques.
Abstract: Because many of the current multivariate statistical process monitoring (MSPM) techniques are based on the assumption that the process has one nominal operating region, the application of these MSP...
TL;DR: In this article, a boron-doped diamond thin-film electrode was used for the electrochemical oxidation of aqueous wastes containing 4-nitrophenol (4-NP).
Abstract: The electrochemical oxidation of aqueous wastes containing 4-nitrophenol (4-NP) using a boron-doped diamond thin-film electrode has been studied. Within the parameter ranges used (150−4000 mg of 4-...
TL;DR: In this article, the adsorption performance of pure siliceous BEA zeolite (Si/Al = ∞) was investigated for removing phenol from an aqueous solution (concentration range from 0.1 to 1.6 g·L-1).
Abstract: Adsorption has been investigated to remove phenol from an aqueous solution (concentration range from 0.1 to 1.6 g·L-1). Zeolites were used as adsorbents, and adsorption properties were compared to those of an activated carbon. To adsorb phenol selectively from water, adsorbents must be hydrophobic, i.e., zeolites owning a high Si/Al ratio. Thus, purely siliceous BEA zeolite (Si/Al = ∞) was used with success; the adsorption capacity was slightly higher at low phenol concentration (≤1.6 g·L-1) than the one of activated carbon (surface area close to 1150 m2·g-1). Furthermore, siliceous BEA zeolite appears as an efficient adsorbent able to be easily regenerated while keeping these initial properties.
TL;DR: In this article, a comparison of the results in terms of flow pattern and mixing/segregation kinetics of binary mixtures of particles is performed with different model formulations and different equations for quantifying the particle−fluid interaction.
Abstract: Discrete particle simulation has been recognized as a useful numerical technique for elucidating the fundamentals of granular matter. For gas−solid two-phase flow in fluidization, such simulations are achieved by combining the discrete flow of the particle phase with the continuum flow of the gas phase. However, differences exist in the actual implementation of this idea in the literature. This paper attempts to rationalize this matter by discussing important aspects including the governing equations in relation to the so-called models A and B, which use different treatments of pressure drop in the well-established two-fluid model, different coupling schemes between the gas and solid phases, and different equations for quantifying the particle−fluid interaction. For the purpose of quantitative analysis, gas fluidization of binary mixtures of particles is simulated with different model formulations, and a comparison of the results in terms of flow pattern and mixing/segregation kinetics shows a significant...
TL;DR: In this paper, the metal oxide Fe2O3 on MgAl2O4 support was examined, and particles of diameter 125−180 μm were prepared by freeze-granulation.
Abstract: Chemical-looping combustion (CLC) is a combustion technology with inherent separation of the greenhouse gas CO2. The technique involves the use of a metal oxide as an oxygen-carrier, which transfers oxygen from the combustion air to the fuel. The metal oxide Fe2O3 on MgAl2O4 support was examined, and particles of diameter 125−180 μm were prepared by freeze-granulation. The reactivity was evaluated in a fluidized-bed reactor, where the atmosphere was periodically changed. Reduction was performed in 50% CH4 and 50% H2O, while the oxidation was performed in 5% O2. The sintering temperature and the ratio of metal oxide/inert were varied in order to find the optimal particle properties. The particles were characterized with respect to crushing strength, surface structure, and chemical composition, and 60% Fe2O3 on 40% MgAl2O4 sintered at 1100 °C was found to be the most suitable oxygen carrier. The particle had a high reactivity and showed no tendency to agglomerate or break apart during the cyclic tests. The ...