Chemical Engineering Journal (v.158, #2)
Ethylene removal using biotrickling filters: Part I. Experimental description
by Sang-Hun Lee; Congna Li; Albert J. Heber; Cheng Zheng (pp. 79-88).
The control of liquid flow is one of the most significant factors that affect operation of biotrickling filters. This study evaluated removal of ethylene (C2H4) using biotrickling filters at various liquid recirculation flow rates. Perlite and glass beads were utilized as media in eight and two reactors, respectively. Trickle liquid recirculation flow rates ranging from 2.7 to 26Lh−1 (velocity of 0.4–3.7mh−1) were used. Two perlite reactors were operated with the liquid being recirculated intermittently for 10min every hour at a recirculation flow velocity of 13Lh−1 (velocity of 1.9mh−1). Inlet gas contained about 30mgm−3 of C2H4 and 0–40mgm−3 of ammonia (NH3).The results showed that C2H4 removal efficiencies increased as time elapsed, but the increasing rate of C2H4 removal was different based on the reactor types. One of the two perlite biotrickling filters with low liquid recirculation flow exibited a high C2H4 removal up to 90%, but other biotrickling filters reached only about 40–70% of C2H4 removal efficiency, due to either a relatively high mass transfer limitation or poor distribution of nutrients. This study denotes that a trickle liquid flow over 0.8mh−1 (5.4Lh−1) had a significant detrimental effect on ethylene removal due to high mass transfer limitation that suppresses microbial growth for ethylene degradation. Therefore, the perlite biotrickling filters with flow rates as low as 0.4mh−1 (2.7Lh−1) can gave the best performance in high ethylene removal.
Keywords: Biofiltration; Biotrickling filter; Ethylene; Perlite; Liquid recirculation
Ethylene removal using biotrickling filters: part II. Parameter estimation and mathematical simulation
by Sang-hun Lee; Albert. J. Heber (pp. 89-99).
Mathematical models of biofiltration often encounter uncertain parameters characterizing mass transfer, microbial degradation, biofilm growth, and biofilm detachment. The genetic algorithm, which is one of the most reliable methods for optimization although it has rarely been addressed in biofiltration models up to now, was utilized to estimate the unknown parameters using given experimental data. This study combined genetic algorithm and biofiltration equations to obtain simulated ethylene (C2H4) removal efficiencies with estimated parameters. Sensitivity analysis of each parameter was assessed to observe the significance of each parameter.As a result, the simulation well characterized C2H4 removal efficiencies for most of the reactors. The large difference in removal efficiencies among reactors could be mostly explained using the mass transfer parameters. Perlite biotrickling filters with low continuous liquid flow tended to increase C2H4 removal efficiencies, due to a large active surface area of biofilm facilitating C2H4 transfer from the gas to the biofilm phase. Conversely, most of the other reactors underwent relatively low C2H4 removal because of high liquid flow that generated a severe mass transfer limitation. The low C2H4 removal in the biofilters with discontinuous liquid recirculation flow, in spite of the lowest liquid flow rate was, probably caused by a low active microbial growth condition.
Keywords: Biofiltration; Biotrickling filter; Ethylene (C; 2; H; 4; ); Genetic algorithm; Parameter estimation
A new electron exchange material Ti(IV) iodovanadate: Synthesis, characterization and analytical applications
by Syed Asfaq Nabi; Mu. Naushad (pp. 100-107).
A new inorganic cation exchange material Ti(IV) iodovanadate has been synthesized under a variety of conditions. The experimental parameters such as mixing volume ratio, order of mixing and pH established for the synthesis of the material. The most stable sample has been prepared by adding aqueous mixture of 0.1M potassium iodate and 0.1M sodium vanadate into 0.1M solution (CCl4 medium) of titanium chloride at pH 1. The material is characterized using various analytical techniques like XRD, FTIR, TGA–DTA and SEM. A tentative structural formula has been proposed on the basis of chemical composition, pH titration, FTIR and thermogravimetric analysis. The ion exchange capacity and distribution coefficients of various metal ions have been determined to understand the cation exchange behavior of the material. On the basis of distribution studies, the material was found to be selective for Pb2+ ion. Its selectivity has been examined by achieving some important and analytically difficult binary separations, viz. Cr3+–Pb2+, Fe3+–Pb2+, Zn2+–Pb2+, Cd2+–Pb2+, etc. The material has bee also used as an electron exchange material. The oxidation of Fe(II) to Fe(III) has been achieved by batch-equilibrium technique successfully. The decomposition of hydrogen peroxide by the material has also been studied. The practical utility of Ti(IV) iodovanadate has been demonstrated by separating metal ions quantitatively from a synthetic mixture using the packed column of Ti(IV) iodovanadate.
Keywords: Synthesis; Inorganic cation exchange material; Electron exchange material; Ti(IV) iodovanadate; Metal ion separation; H; 2; O; 2; decomposition
Removal of Cr(III, VI) by quaternary ammonium and quaternary phosphonium ionic liquids functionalized silica materials
by Yinghui Liu; Lin Guo; Lili Zhu; Xiaoqi Sun; Ji Chen (pp. 108-114).
A series of silica-based organic–inorganic hybrid materials were prepared by the sol–gel process for Cr(III) and Cr(VI) adsorption. These silica materials generally had high surface areas, good physical–chemical stability and high thermal stability. Trialkylmethylammonium bis 2,4,4-trimethylpentylphosphinate ([A336][C272]) and trihexyl(tetradecyl)phosphonium bis 2,4,4-trimethylpentylphosphinate (Cyphos IL 104) were explored as porogens to prepare porous silica and as extractants to extract chromium ions. Cyphos IL 104 and [A336][C272] functionalized silica sorbents (SG-2, SG-5) can be effectively used for the removal of Cr(III) and Cr(VI) from aqueous solutions by adjusting pH values, whereas trialkylmethylammonium chloride (Aliquat 336) and bis(2,4,4-trimethylpentyl)phosphinic acid (Cyanex 272) functionalized silica sorbents (SG-3, SG-4) can only be used for the removal of the single chromium species, Cr(VI) or Cr(III). The maximum adsorption amounts of Cr(III) and Cr(VI) were 2.14 and 19.31mgg−1 for SG-2 and 2.32 and 15.29mgg−1 for SG-5. Langmuir and Freundlich isotherm models were used to evaluate the adsorption of Cr(III) and Cr(VI) on sol–gel sorbents. The adsorption kinetics of Cr(III) and Cr(VI) on SG-2 and SG-5 could be well described by pseudo-second-order kinetic model. In terms of Cr(III) and Cr(VI) uptake capacities and kinetics, SG-2 and SG-5 appeared to be more suitable for Cr(III) and Cr(VI) removal than SG-3 and SG-4.
Keywords: Adsorption; Ionic liquid; Sol–gel; Cyphos IL 104; Aliquat 336; Cyanex 272
Selective adsorption of phenanthrene in nonionic–anionic surfactant mixtures using activated carbon
by Chi Kyu Ahn; Seung Han Woo; Jong Moon Park (pp. 115-119).
Surfactant enhanced soil washing is an efficient remediation process for sites contaminated with hazardous hydrophobic organic compound (HOC). To reduce the cost of the process, the used surfactant should be recovered. This paper presents investigation of selective adsorption of HOC in nonionic–anionic surfactant mixtures by activated carbon as a means of recovering surfactants, using phenanthrene (PHE) as an HOC, Triton X-100 (TX100) as a nonionic surfactant, and sodium dodecyl sulfate (SDS) as an anionic surfactant. The sorbed amount of TX100 on activated carbon decreased from 0.433 to 0.227mmol/g as SDS dose increased. However the sorbed amount of PHE increased from 0.125 to 0.178mmol/g as SDS dose increased because molar solubilization ratio of the surfactant mixtures decreased. As a result, selectivity for PHE sorption that represents the ratio of PHE partitioning to surfactant partitioning increased with increase in the proportion of SDS in the surfactant mixture. Selectivity for PHE to surfactant was much higher than 1 over a wide range of surfactant composition. The highest selectivity, 95.97±49.94 at 5.61×10−2mmol-PHE/L, was obtained in the solution containing only SDS. These results suggest that addition of anionic surfactant may improve surfactant recovery when selective adsorption for surfactant recovery is included in soil remediation by surfactant enhanced soil washing.
Keywords: Nonionic–anionic surfactant mixture; Activated carbon; HOC; Selective adsorption; Soil washing
Photodegradation of 4-chlorophenol using XeBr, KrCl and Cl2 barrier-discharge excilamps: A comparative study
by M. Gomez; M.D. Murcia; N. Christofi; E. Gomez; J.L. Gomez (pp. 120-128).
A study on 4-chlorophenol (4CP) photodegradation has been carried out using UV radiation delivered from three different excimer lamps: XeBr, KrCl and Cl2, with maximum emission wavelengths of 283, 222 and 259nm, respectively. The influence of initial 4-chlorophenol concentration on the photodegradation process was examined with pollutant concentrations ranging from 50 to 500mgL−1, and degradation progress was followed by determining the residual 4-chlorophenol, as well as that of the main photoproducts, hydroquinone (HQ) and benzoquinone (BQ). All excilamps were able to degrade 4CP. XeBr and the KrCl excilamps achieved almost total 4-chlorophenol degradation, with the removal efficiency of the Cl2 excilamp being considerably lower. The KrCl excilamp, in spite of requiring longer exposure times compared with the XeBr, needed a much lower UV dose and, consequently, a lower energy consumption for degradation and, as a result, has been considered the most effective and efficient in 4CP removal. Additionally, and by defining the limit of 4-chlorophenol degradation, a modified pseudo-first order kinetic model was used to fit the kinetics of the 4-chlorophenol degradation process where good agreement between experimental data and those predicted by the model was found. Shielding effects are considered to have an influence on 4-chlorophenol degradation as there is a decrease in the pseudo-first order rate constant with increasing 4-chlorophenol concentrations for the three excilamps. In addition, there is a noticeable decrease in the maximum removal of 4-chlorophenol for the Cl2 excilamp due to the same effect.
Keywords: Wastewater treatment; 4-Chlorophenol; XeBr excilamp; KrCl excilamp; Cl; 2; excilamp; Photodegradation; UV dose
Development of mesoporous structure and high adsorption capacity of biomass-based activated carbon by phosphoric acid and zinc chloride activation
by Tzong-Horng Liou (pp. 129-142).
This paper reports the preparation of activated carbon from two different types of agricultural biomass materials, sugar cane bagasse and sunflower seed hull, by phosphoric acid and zinc chloride activation. The experiments in this study vary the pre- and post-treatment procedures, the impregnation ratio of the activating agent, and the carbonization temperature. In recent years, the high surface area and high mesopore proportion of carbon have attracted a lot of attention for potential applications in the green resources such as hydrogen energy storage and carbon dioxide capture. However, the traditional methods for fabricating activated carbon produce a mainly microporous structure. The experimental results show that the activated carbon produced by base-leaching has a mostly mesoporous structure, which effectively enhances its adsorption capacity. The carbon materials obtained from zinc chloride activation of both sugar cane bagasse and sunflower seed hull have mesopore volumes as high as 1.07 and 0.95cm3/g, and mesopore contents of 81.2 and 74.0%, respectively. The surface area and pore volume of carbon produced using zinc chloride activation were higher than that produced using phosphoric acid activation. The total activation process of bagasse and hull occurs in three reaction stages. This study also presents a corresponding pyrolysis mechanism that agrees well with the experimental results. The proposed method of preparing mesoporous activated carbon is not complicated, and is suitable to bulk production.
Keywords: Activated carbon; Mesoporous structure; Sugar cane bagasse; Sunflower seed hull; Chemical activation
Direct UV photolysis of propranolol and metronidazole in aqueous solution
by Renato F. Dantas; Otidene Rossiter; Allan Kardec Ribeiro Teixeira; Anderson S.M. Simões; Valdinete Lins da Silva (pp. 143-147).
The aim of this work was to study the direct photolysis of two pharmaceuticals: propranolol (PRO) and metronidazole (MET) promoted by ultra violet radiation (UV). For this purpose, 50 and 100mgL−1 aqueous solutions of PRO and MET were irradiated by two different UV sources: a UV-254 germicidal lamp (UV-C) and a UV-365 black light lamp (UV-A). After 8h of irradiation, direct UV photolysis promoted substantial pharmaceuticals removal, especially with the use of UV-C radiation (near 50%). However, on average only 12% of the organic matter content was photodegraded. The photo-transformation of both compounds promoted the formation of more biodegradable byproducts. Nevertheless, PRO direct UV-C photolysis produced byproducts with less toxic character while MET irradiation promoted a slight increase of toxicity. Direct photolysis of PRO using solar radiation was proved to be as effective as those runs carried out with the UV-C device. Kinetic constants based on time and UV-C fluency were in a magnitude order of 10−2h−1 and 10−5cm2mJ−1, respectively.
Keywords: Pharmaceuticals; UV; Direct photolysis; Toxicity; Kinetics; Biodegradability
Catalytic oxidation of Methyl Orange by an amorphous FeOOH catalyst developed from a high iron-containing fly ash
by Yi Li; Fu-Shen Zhang (pp. 148-153).
Heterogeneous photo-Fenton process using an amorphous FeOOH as catalyst was studied to degrade Methyl Orange (MO) dye in aqueous solution. The amorphous FeOOH was prepared by dissolution and precipitation using a high iron-containing fly ash as raw material. The ash not only provided iron source but also acted as a supporter of amorphous FeOOH. Coating the fly ash particles with the amorphous FeOOH significantly enhanced the removal of MO, and 2.5g of catalyst was sufficient to degrade 50mg MO from 1l of aqueous solution at pH 7.0 after 80min. Oxidant concentration, solution pH, UV/dark/sunlight and recycling of the catalyst were investigated in order to evaluate the photo-Fenton effects. Moreover, variations of particle size before and after preparation, separation of solid–liquid and stability of the amorphous FeOOH in the catalyst were studied. It was testified that the amorphous FeOOH on the surface of fly ash was stable and the Fenton catalyst was easily separated from the aqueous system.
Keywords: Photo-Fenton; Fly ash; UV/H; 2; O; 2; Mesoporous structure; Amorphous FeOOH
Degradation of chlorinated hydrocarbons by UV/H2O2: The application of experimental design and kinetic modeling approach
by Petra Kralik; Hrvoje Kusic; Natalija Koprivanac; Ana Loncaric Bozic (pp. 154-166).
The aim of the study was to develop a detail mathematical model describing the degradation of chlorinated hydrocarbon pollutants in water by UV/H2O2 process. As a model representative of chlorinated hydrocarbons para-chlorophenol ( p-CP) was chosen. A degradation mechanism of parent pollutant to its aromatic and aliphatic by-products, as well as the mineralization of simulated wastewater, was included in the model. The optimal values of operating parameters of UV/H2O2 process influencing the treatment efficiency were established by the means of the two-factor three-level Box–Behnken experimental design combining with response surface modeling (RSM) and quadratic programming. The results of such experimental design using different statistical tools showed that pH 6.8 and pollutant/oxidant ratio 1:199 maximize the performance of oxidative treatment system. The model was tested to evaluate accuracy in predicting system behavior at different process conditions and pollutant concentrations. Rather high accuracy of developed model was demonstrated at all tested conditions. Good accordance of the data predicted by model and the empirically obtained data was confirmed by calculated standard deviation (SD) for each experimentally monitored parameter. Hence, the developed mathematical model describing the kinetic of p-CP degradation by UV/H2O2 can be characterized as interpretable, transparent and accurate, and therefore can be used as a tool for maximizing efficiency of wastewater treatment process.
Keywords: Chlorinated hydrocarbons; p; -Chlorophenol; UV/H; 2; O; 2; Experimental design; Kinetic modeling
Cr-doped titanite pigment based on industrial rejects
by W. Hajjaji; C. Zanelli; M.P. Seabra; M. Dondi; J.A. Labrincha (pp. 167-172).
This work reports the development of inorganic pigments based on chromium doped titanite (CaTiSiO5). For economical and environmental reasons, wastes were used as raw materials but similar formulations from pure reagents were also prepared to assess the effect of impurities contained in wastes. Pigments were characterised by XRD, SEM+EDS microprobe analysis, and UV–vis–NIR spectroscopy. The colouring mechanism (the pigment is reddish brown) seems to result from the combined contribution of octahedral Cr(III) and tetrahedral Cr(IV) species replacing Ti4+ and Si4+, respectively. In both pure reagents and waste-based pigments, colorimetric parameters were evaluated and their colouring performance was tested in transparent and opaque ceramic glazes. Intense and stable brown hues were developed with optimized formulations, i.e. containing 0.044Cr at 1300°C.
Keywords: Chromium doping; Titanite; Ceramic pigment; Marble sawing sludge; Galvanizing waste; Foundry sand
Batch adsorption of 4-nitrophenol by acid activated jute stick char: Equilibrium, kinetic and thermodynamic studies
by M. Ahmaruzzaman; S. Laxmi Gayatri (pp. 173-180).
The article describes the performance of acid activated jute stick char (AAJSC) for the adsorption of 4-nitrophenol (4-NP) from aqueous solution in batch mode. Jute stick, a bulk volume agricultural waste, was utilized for adsorption. The char of jute stick prepared at 773K was activated with phosphoric acid and adsorption experiments were carried out at 298, 308 and 318K. Equilibrium adsorption data were analyzed using two-parameter models—Langmuir, Freundlich, Temkin, Dubunin-Radushkevich and three-parameter-Redlich-Peterson model. The goodness of the fit was measured using linear regression coefficient ( R2) value and five different error functions. The adsorption data was found to be well described by Langmuir model. The equilibrium time for adsorption was achieved within 4h. Studies showed that adsorption decreases with the increasing temperature. pH studies were also performed to obtain the equilibrium pH for adsorption. The pseudo-first-order, pseudo-second-order and Elovich kinetic models were applied to test the kinetic data, and were found to closely follow the pseudo-second-order kinetic model. The thermodynamic constants of the adsorption process; Δ G°, Δ H° and Δ S° were evaluated as −18.79kJ/mol at 25°C, 3917.4J/mol, 76.21J/molK−1 respectively. These showed that the adsorption process was endothermic and spontaneous.
Keywords: Adsorption; Acid activated jute stick char (AAJSC); Isotherm; 4-Nitrophenol (4-NP); Langmuir; Freundlich; Temkin; Dubunin-Radushkevich; Redlich-Peterson; Error analysis
Linuron decomposition in aqueous semiconductor suspension under visible light irradiation with and without H2O2
by Y.F. Rao; W. Chu (pp. 181-187).
The degradation of LNR in TiO2 suspension with and without H2O2 was investigated under the irradiation of visible light at 419nm. The removal of LNR in TiO2-P25 suspension can be increased from 10% to nearly 100% by simply adding H2O2 to the process after 3h of reaction. Various types of TiO2 including anatase, rutile and TiO2-P25 exhibited different photocatalytic activities on LNR decay, while their performances were strongly dependent on the presence and/or absence of H2O2. The performance of using other metal oxides (semiconductors) as alternatives for TiO2 was also studied. Among three selected semiconductor oxides, ZnO was found to be most effective for the reaction without H2O2, while significant rate enhancement was observed for TiO2-P25 and WO3 as H2O2 was used.The H2O2-assisted TiO2 photocatalysis using visible light could be optimized by adjusting TiO2 dosage, initial concentration of H2O2 and the initial pH of the system. The LNR decay rate, generally, increased with the increase of TiO2 dosage, but too high the TiO2 was not cost-effective due to the light attenuation. The initial H2O2 concentration did not show a significant influence on the reaction rate because the amount of the available electrons on the TiO2 surface is likely the rate-limiting factor rather than the concentration of H2O2. A neutral initial pH level was found to be favorable for the H2O2-assisted photocatalysis under visible light, which made the proposed process more attractive for real application.
Keywords: Photocatalysis; Semiconductor; Hydrogen peroxide; Linuron; Hydroxyl radicals
Moringa oleifera—A solid phase extractant for the removal of copper, nickel and zinc from aqueous solutions
by M. Helen Kalavathy; Lima Rose Miranda (pp. 188-199).
Moringa oleifera (MO) wood, a solid waste was used for the preparation of activated carbon (ACMO) for the removal of copper, nickel and zinc from synthetic wastewater. Effects of various operating variables namely solution pH, contact time, carbon dose, adsorbate concentration and temperature on the removal of metal ions have been studied. Thermodynamic parameters such as free energy change, enthalpy change and entropy change were calculated. The optimum pH for the adsorption for all the above mentioned metals was found to be 6. The adsorption process was found to be endothermic for Cu and exothermic for Ni and Zn. The Langmuir, Freundlich, Temkin and Dubinin Radushkevich isotherm models were used to analyze the equilibrium data at different temperatures. The data were also fitted to kinetic models such as pseudo-first-order and pseudo-second-order model. Kinetic studies showed that the adsorption followed a pseudo-second-order model. The intra-particle diffusion rate constants and effective diffusion coefficient for different temperatures were evaluated and discussed. Adsorption occurs both by film diffusion and particle diffusion mechanism. The ACMO could be regenerated using 0.1M H2SO4, with up to 98% recovery for all the three metals.
Keywords: Moringa oleifera; SEM; FT IR; Heavy metals; Adsorption isotherms; Adsorption mechanism; Desorption
Biosorption of selenium from aqueous solution by green algae ( Cladophora hutchinsiae) biomass: Equilibrium, thermodynamic and kinetic studies
by Mustafa Tuzen; Ahmet Sarı (pp. 200-206).
The equilibrium, thermodynamics and kinetics of selenium(IV) biosorption from aqueous solution by dead green algae ( Cladophora hutchinsiae) biomass was investigated. Optimum biosorption conditions were determined with respect to pH, biomass concentration, contact time, and temperature. The equilibrium data were analyzed using the Langmuir, Freundlich and Dubinin–Radushkevich (D–R) isotherm models. The maximum biosorption capacity of C. hutchinsiae biomass for Se(IV) was found to be 74.9mg/g at pH 5, biomass concentration 8g/L, contact time 60min, and temperature 20°C. The biosorption percentage decreased from 96% to 60% as temperature was increased from 20 to 50°C during the equilibrium time.From D–R model, the calculated mean biosorption energy (10.9kJ/mol) indicated that the biosorption of Se(IV) onto C. hutchinsiae biomass was taken place by chemical ion-exchange.The highest recovery (95%) was achieved using 0.5M HCI. The high stability of C. hutchinsiae permitted a slightly decrease about 20% in recovery of Se(IV) ions after ten times of adsorption-elution process. The calculated thermodynamic parameters, Δ G° (between −18.39 and −16.08kJ/mol at 20–50°C) and Δ H° (−45.96kJ/mol) showed that the biosorption of Se(IV) onto C. hutchinsiae biomass was feasible, spontaneous and exothermic, respectively. The experimental data was also fitted to the Lagergren's first-order and pseudo second-order kinetic models. The results revealed that the pseudo second-order reaction model provided the best description these data with coefficients of determination in range of 0.992–0.999. The biosorption rate constant was calculated as 24.9×10−2g/(mgmin).
Keywords: C. hutchinsiae; Selenium; Biosorption; Equilibrium; Thermodynamics; Kinetics
In situ characterization of local hydrodynamic parameters in closed-loop aeration tanks
by Yannick Fayolle; Sylvie Gillot; Arnaud Cockx; Laetitia Bensimhon; Michel Roustan; Alain Heduit (pp. 207-212).
The objective of this experimental study was to collect and to interpret data in order to better understand the oxygen mass transfer phenomena occurring in full-scale aeration tanks equipped with fine bubble diffusers and slow speed mixers (inducing horizontal liquid flows). Bubble size, local depth and oxygen mass transfer coefficient were measured in situ for a given air flow rate (1555Nm3h−1) and for two different axial liquid velocities. The increase in the global oxygen transfer coefficient is of 29% when the mean axial liquid velocity varies from 0 to 0.42ms−1. The small influence of the liquid velocity on the local bubble Sauter diameter (about −4%) cannot explain the increase in kL a20. This increase in kL a20 with the axial liquid velocity is mainly due to the attenuation of the vertical liquid circulation induced by the gas injection.
Keywords: Aeration; Bubble size; Gas hold-up; Horizontal flow systems; Wastewater treatment
Adsorption of complex phenolic compounds on active charcoal: Breakthrough curves
by Dominique Richard; Maria de Lourdes Delgado Núñez; Daniel Schweich (pp. 213-219).
The transient adsorption of catechol from aqueous solution (C0=5kg/m3) on activated carbon in an upflow fixed-bed column at 293K was studied. The critical time at which the early breakthrough of the maximum admissible concentration (Ccrit=0.3×10−3kg/m3) occurs is deduced from a Homogeneous Surface Diffusion Model (HSDM) that accounts for adsorption equilibrium and mass-transfer kinetics. The mass-transfer coefficient is measured using a thin bed adsorption method and a correlation is proposed to account for its dependence with the flow rate. The sensitivity of the model for the prediction of the critical time to the different parameters is discussed and it is found to be mostly dependant upon the mass-transfer coefficientKf and the adsorbant mean particle diameterdP. In addition, the critical time has been proved to increase with the adsorption capacityqmax. The existence of an optimal flow of polluted effluent through the column to achieve the removal of the pollutant with the highest efficiency is observed.
Keywords: Activated carbon; Adsorption; Catechol; Breakthrough curve; HSDM
Modeling, simulation and analysis of the liquid-phase catalytic oxidation of toluene
by Wang Hangzhou; Chen Bingzhen; He Xiaorong; Zhao Jinsong; Qiu Tong (pp. 220-224).
The liquid-phase, catalytic oxidation of toluene with air in a continuous stirred tank reactor has become the main technology for producing benzoic acid. Designs are aimed at obtaining high product conversion rates but the reaction is strongly exothermic and therefore it is also important to maintain stable operation to guarantee product quality. However, there is currently no suitable process simulation model available for study. In this paper, a mathematical model of the reaction system is established and validated by comparison to literature data. Steady-state variables were calculated for a series of the operating conditions, using the homotopy continuation method, revealing the existence of multiple steady-state solutions. Two steady-state solutions were found for each operating condition, which had different conversion rates and sensitivities to changes in operating conditions. The operating point having the highest conversion rate was the most sensitive to changes in operating conditions, thus requiring a superior control system. A trade off must be carried out between conversion rate and production stability. Consequently, in practice, a number of factors must be considered simultaneously to select a compromise design.
Keywords: Toluene; Benzoic acid; Catalytic oxidation; Modeling; Operating conditions analysis
CoZnAl catalysts for ethanol steam reforming reaction
by M. Noelia Barroso; Manuel F. Gomez; Luis A. Arrúa; M. Cristina Abello (pp. 225-232).
The ethanol steam reforming was studied at 500 and 600°C on CoZnAl catalysts with different Co loading (9 and 25wt.%) and a Zn:Al atomic ratio nearly constant (Zn:Al ≅0.6). The catalysts were prepared by the citrate sol–gel method and characterized by different techniques such as AA, TG, BET, TPR, XRD, RAMAN and SEM-EDX. They were active in the ethanol steam reforming at atmospheric pressure in the temperature range studied, but with significant differences in their performance. High hydrogen selectivities, better than 80%, were obtained on catalyst with high Co loading (25wt.%). CO, CO2 and minor amount of CH4 were the only carbon products at 600°C.
Keywords: Ethanol steam reforming; Hydrogen production; CoZnAl catalysts
Numbering-up and mass transfer studies of liquid–liquid two-phase microstructured reactors
by M.N. Kashid; A. Gupta; A. Renken; L. Kiwi-Minsker (pp. 233-240).
Microstructured reactors are known to provide high heat and mass transfer rates for liquid–liquid two-phase systems when used as a single channel. For industrial scale production, scale-up of microstructured reactors is essential to achieve throughput in the required range which is done by numbering-up of a single channel. The important issues are uniform flow distribution and identical slug size in all channels. In the present work, a capillary microstructured reactor is numbered up for six capillaries and the mass transfer performance is investigated for various operating conditions. A cationic surfactant was used to study the effect of interfacial tension on the mass transfer performance. If compared to conventional contactors, the mass transfer coefficients were approximately one order of magnitude higher allowing the process intensification. The results obtained demonstrate the benefits of microstructured reactors and confirm that the throughput of conventional reactors can be achieved.
Keywords: Microstructured reactors; Liquid–liquid slug-flow; Numbering-up; Mass transfer; Process intensification
Dynamic modeling and process optimization of an industrial sulfuric acid plant
by Anton A. Kiss; Costin S. Bildea; Johan Grievink (pp. 241-249).
The current legislation imposes tighter restrictions in order to reduce the impact of chemical process industry on the environment. In this context, this study presents the dynamic model, simulation and optimization results for an industrial sulfuric acid plant. The dynamic model, implemented in PSE gPROMS includes a catalytic reactor (five pass converter), heat exchangers such as economizers and feed-effluent heat exchangers, mixers, splitters and reactive absorption columns. The kinetic parameters were fitted to the real plant data, while the remaining model parameters were estimated using classical correlations. The modeling results agree very well with the real plant data.The model implemented in gPROMS is useful for evaluating the dynamic behavior of the plant and for minimization of the total amount of SOx emissions. The SOx emissions could be significantly reduced by over 40% by optimizing operating parameters such as air feed flow rates or split fractions. However, only minor increases in energy production can be achieved due to the plant already operating near full capacity. The simulations also show that operational problems may occur when the process is disturbed due to production rate changes or catalyst deactivation, the non-linear response of the plant leading to sustained oscillations. Besides controllability, operability and optimization studies the gPROMS plant model is also useful for operator training and various scenario assessments.
Keywords: Sulfuric acid; Adiabatic reactors; Absorption; Optimization; SOx emissions; Energy savings
Continuous production of biodiesel in a packed-bed reactor using shell–core structural Ca(C3H7O3)2/CaCO3 catalyst
by Li-Shan Hsieh; Umesh Kumar; Jeffery C.S. Wu (pp. 250-256).
The continuous production of biodiesel was studied by using a steady-state packed-bed reactor. The shell–core Ca(C3H7O3)2/CaCO3 solid-base catalyst was prepared with a mechanical strong core of CaCO3 for continuous transesterification of soybean oil in a packed-bed reactor. Alcohol–oil ratio, retention time and reaction temperature were evaluated to obtain optimum reaction conditions. The yield of fatty acid methyl esters (FAME, i.e. biodiesel) achieved 95% at the reaction temperature 60°C, alcohol–oil molar ratio of 30:1 and retention time of 168min. The reusability of catalyst was checked up to 5 cycles and found negligible decrease in the catalyst activity. Water in the oil can significantly decrease the yield due to the deactivation of Ca(C3H7O3)2 and hydrolysis of FAME. The transesterification of soybean oil, canola oil and sunflower oil also was compared with model compound, triolein, using powder Ca(C3H7O3)2 in the batch reactor. Although these oils contained different triglyceride mixtures, their FAME yields were comparable. A Langmuir–Hinshelwood rate equation was established for the transesterification of soybean oil with methanol. Regression of experimental data indicated that the transesterification was an endothermic reaction with the enthalpy change of 23,504J/mol and the activation energy was 42,096J/mol.
Keywords: Biodiesel; Soybean oil; Solid-base catalyst; Transesterification; Packed-bed reactor
Studies on segregation of binary mixture of solids in a continuous fast-fluidized bed. Part IV. Total solids holdup, axial solids holdup and axial solids concentration
by K. Ganesh Palappan; P.S.T. Sai (pp. 257-265).
The segregation pattern of a binary mixture of particles is studied in a continuous fast-fluidized bed of 3.65m height and 69mm ID. The influence of operating variables such as gas velocity, solids feed rate and feed composition on total solids holdup and axial solids holdup is studied. Empirical correlations are proposed for the total pressure drop in the fast fluidization regime when density and/or size segregation occur. The influence of the operating variables on the axial concentration of solids in both the dense and dilute phases is analyzed.
Keywords: Fast fluidization; Density segregation; Binary solids; Axial solids holdup; Axial solids concentration; Bed pressure drop
Exact analytical solutions of diffusion reaction in spherical porous catalyst
by Eugen Magyari (pp. 266-270).
A nonlinear model of coupled diffusion and nth-order chemical reaction in a spherical catalyst pellet is revisited in this paper. As we are aware, except for the linear case n=1, no exact solutions of this model have been reported until now. In the present paper several such solutions are given in a closed analytical form. The existence and uniqueness of solutions in the whole range n≥0 of the reaction order and of the Thiele modulus ϕ is discussed in some detail.
Keywords: Catalyst pellet; Spherical geometry; Diffusion; n; th-Order reaction; Exact solutions
Optimal trade-off design of integrated fermentation processes for ethanol production using genetically engineered yeast
by Ming-Liang Chen; Feng-Sheng Wang (pp. 271-280).
In this study, we considered a multi-stage integrated extractive fermentation with cell recycling for ethanol production using the genetically engineered Sacchromyces yeast 1400 (pLNH33), which can utilize glucose and xylose as carbon sources to produce ethanol. Each stage consists of a stirred-tank bioreactor, a cell settler and an extractor. A generalized mathematical model was formulated to express the multi-stage integrated process. The aim of the optimization problem was to obtain the maximum overall productivity and conversions subject to the interval inequality constraints for the residual glucose and xylose concentrations and the total sugar supply. A fuzzy goal attainment method was applied to the multiobjective problem in order to achieve the maximum satisfaction for all design requirements. From the computational results, the integrated extractive fermentation with cell recycling (involving the extraction of ethanol from the extractor in situ to alleviate product inhibition) led to an optimal overall productivity that was 8.0% higher than that obtained by the method of continuous fermentation with cell recycling, and about 13-fold higher than that obtained by the method of continuous fermentation without cell recycling.
Keywords: Recombinant yeast; Renewable fuel; Continuous fermentation; Fuzzy optimization; Sensitivity analysis; Hybrid differential evolution
Numerical prediction of particle dispersions in downer under different gravity environments
by Yang Liu; Guohui Li (pp. 281-289).
Particle dispersion behavior of dense gas–particle flows in a downer affected by gravity environment is numerically simulated using an Euler–Euler two-fluid approach incorporating unified-second-order-moment two-phase turbulent models and kinetic theory of granular flows (USM-θ). Anisotropy of gas–solid two-phase stress and the interaction between two-phase stresses are fully considered by two-phase Reynolds stress model and the transport equation of two-phase stress correlation. The flow behavior of particles in a downer of Wang et al. (1992) experiments is predicted under earth gravity, lunar gravity and microgravity environment. Simulation results of particle concentration and particle velocity are in good agreement with measurement data under earth gravity environment. Comparison earth gravity to lunar and microgravity condition, peak value of particle concentration is shifted to near center region and axial particle fluctuation velocity is larger than that of approximately 3.0 times. Particle temperature, particle heterogeneities dispersion and particle–particle collision are weakened due to decrease gravity. Furthermore, roles of particle and gas kinetic energy in particle–fluid system are alternated. Both particle kinetic energy and gas kinetic energy are greater than ones under earth gravity conditions.
Keywords: Unified-second-order-moment model; Gravity; Downer; Dense gas–particle flows; Numerical simulation
Theoretical prediction of cavitational activity distribution in sonochemical reactors
by Vinayak S. Sutkar; Parag R. Gogate; Levente Csoka (pp. 290-295).
Cavitational activity distribution is usually non-uniform in the sonochemical reactor and this hampers the successful design and operation of large scale sonochemical reactors. Theoretical prediction of the cavitational activity can aid in easy optimization of geometry and operating parameters as it replaces use of rigorous and expensive experimental mapping techniques for understanding the cavitational activity distribution. In the present work, an attempt has been made to predict the cavitational activity in terms of pressure field distribution by solving the wave equation in two different geometries of sonochemical reactors. Numerical simulations have been carried out by using Comsol Multiphysics software. The results are also compared with the experimental investigations reported in the earlier literature illustrations. It has been observed that cavitational activity in the case of ultrasonic horn is concentrated only near the transducer surface and is much more non-uniform as compared to the ultrasonic bath reactor with large longitudinally vibrating transducer. Comparison with experimental results has clearly established the correctness of the theoretical simulations in predicting the cavitational activity in the sonochemical reactors and hence its importance in possible scale up and optimization strategies for large scale operation.
Keywords: Ultrasonic horn; Ultrasonic bath; Cavitational activity distribution; Wave equation; Mapping
Mapping of cavitational activity in high frequency sonochemical reactor
by Vinayak S. Sutkar; Parag R. Gogate (pp. 296-304).
In the present work, distribution of cavitational activity in high frequency sonochemical reactor has been quantified with the help of different mapping techniques based on experimental investigations and theoretical analysis. In experimental investigations, amount of iodine liberation at different locations has been quantified whereas quantification of cavitational activity using theoretical analysis is based on the solution of space dependent part of the wave equation with the help of COMSOL Multi-physics software. The effect of frequencies of irradiation with and without presence of electrolyte solution (NaCl) to intensify the cavitational activity has been investigated in order to understand behavior of cavitation phenomena. The analysis presented in the work helps in identifying the regions with maximum cavitational intensity so as to obtain maximum efficacy for the desired physical or chemical transformations.
Keywords: Acoustic cavitation; Cavitational activity; Mapping; Wave equation; Sonochemical reactor
Analysis and optimization of a micromixer with a modified Tesla structure
by Shakhawat Hossain; Mubashshir A. Ansari; Afzal Husain; Kwang-Yong Kim (pp. 305-314).
A flow-analysis method using Navier–Stokes equations has been applied to a parametric study on a micromixer with a modified Tesla structure, and an optimization of this micromixer has been performed with a weighted-average surrogate model based on the PRESS-based-averaging method. The numerical solutions are validated with the available numerical and experimental results. The mixing performance and pressure-drop have been analyzed with two dimensionless parameters, i.e., the ratio of the diffuser gap to the channel width, θ, and the ratio of the curved gap to the channel width, ϕ, for a range of Reynolds numbers from 0.05 to 40. The shape of the microchannel is optimized at the Reynolds number of 40 with two objectives: the mixing index at the exit and the friction factor. The “naïve approach” has been applied to realize a single-objective optimization problem. The optimization results reveal that the mixing and pressure-drop characteristics are very sensitive to the geometric parameters. Sensitivity analysis reveals that in the vicinity of the optimum point, the objective function is more sensitive to ϕ as compared to θ.
Keywords: Modified Tesla structure; Coanda effect; Transverse dispersion; Mixing index; Optimization; Surrogate method
Chitosan based mesoporous Ti–Al binary metal oxide supported beads for defluoridation of water
by Dilip Thakre; Sneha Jagtap; Nikita Sakhare; Nitin Labhsetwar; Siddharth Meshram; Sadhana Rayalu (pp. 315-324).
In the present study, the performance of Ti–Al binary metal oxide supported beads using chitosan template was studied for fluoride removal from drinking water. The adsorbent was synthesized by precipitation method and characterized using FTIR, SEM, XRD and BET. The higher surface area of the synthesized adsorbent 323.83m2/g results in a much higher fluoride removal capacity Qmax=2.22mgg−1 as compared to bare chitosan. Pore size of beads is 42.97Å, suggesting mesoporous nature of adsorbent. Material works very effectively at all pH except at pH greater than 9. The presence of carbonate and bicarbonate ions showed significant decline in the fluoride removal capacity of adsorbent. The experimental data fitted well to Langmuir adsorption model. The kinetic studies indicate that the system follows the pseudo-second-order and intra-particle diffusion model. Thermodynamic study reveals that the fluoride adsorption by Ti–Al binary metal oxide supported beads is an exothermic and spontaneous process. Alum appears to be the promising regeneration media showing 80% regeneration. The applicability of the adsorbent for fluoride removal was tested in field water collected from the Dhar district in Madhaya Pradesh, India.
Keywords: Fluoride removal; Binary oxide; Chitosan; Adsorption isotherm; Thermodynamic parameters
Deposition of SBA-15 layers on Fecralloy monoliths by washcoating
by Hermicenda Pérez; Paloma Navarro; Mario Montes (pp. 325-332).
Stable slurries or suspensions were prepared in order to carry out deposition of SBA-15 layers onto Fecralloy monoliths by washcoating. The suspensions presented an important evolution with ageing time under magnetic stirring, that consisted of a change in viscosity. This change was directly related to the abrasive effect of the magnetic stirring, and caused the breakdown of the big aggregates of the parent SBA-15 into rod-shaped units that became more and more irregular, and the slurries to become less viscous compared with the established usual trend. The viscosity was suitable for washcoating after 120h of magnetic stirring. Although a clear macroscopic effect was observed, the mesoporous nature of the solid was preserved. The amount loaded and the adherence of the coatings depended on the formulation of the slurry. The best results were obtained when colloidal silica was used as a binder.
Keywords: SBA-15; Slurry; Viscosity; SBA-15 Washcoating; Metallic monoliths
Easy γ-to-α transformation of zirconium phosphate/polyphenylphosphonate salts: Porosity and hydrogen physisorption
by Ernesto Brunet; Hussein M.H. Alhendawi; Carlos Cerro; María José de la Mata; Olga Juanes; Juan Carlos Rodríguez-Ubis (pp. 333-344).
The preparation of organic–inorganic materials based on the topotactic exchange reactions of the γ phase of zirconium phosphate and polyphenyl bisphosphonates is reported. The treatment of these materials with hypophosphoric, phosphorous and methylphosphonic acids easily led to an isomerization of the γ phases to their α allotropes. These reactions rendered finely engineered supramolecular structures by means of mild, simple processes performed in the solid–liquid interface. This kind of clean γ-to-α transformations described in our work has few precedents in the literature and allows for the effortless preparation of libraries of similar materials in which the testing of a given set of properties versus subtle structural changes may be easily performed. Using this rationale we have produced materials able to store up to 1.7% (w/w) of H2 at 77K and 1atm with such high ultramicroporosity that the DOE-goal H2 densities established for 2010 could be complied at pressures well below 5atm.
Keywords: Zirconium phosphate; Organic–inorganic materials; Layered materials; Pillared structures; Hydrogen physisorption
Photocatalytic study of two-dimensional ZnO nanopellets in the decomposition of methylene blue
by W.S. Chiu; P.S. Khiew; M. Cloke; D. Isa; T.K. Tan; S. Radiman; R. Abd-Shukor; M.A. Abd. Hamid; N.M. Huang; H.N. Lim; C.H. Chia (pp. 345-352).
We report several significant photodecomposition rates of methylene blue (MB) obtained before and after the refluxing process of own-synthesized two-dimensional (2D) zinc oxide (ZnO) nanopellets. Each photodecomposition rate of MB was found highly dependent on the weight of photocatalyst. The existing photodecomposition rate has been successfully improved to a factor of 22.0 times through refluxing process in excessive pyridine where the surface capping ligand (oleic acid) is removed from the 2D ZnO nanopellets. On the other hand, the refluxed photocatalyst (0.04g) in this study was found to exhibit excellent recyclability up to three cycles. Furthermore, X-ray powder diffraction spectrums for the refluxed photocatatalyst, respectively, before and after three cycles of photocatalytic reactions, has generated the same patterns showing that the photocatalyst is stable and feasible to be used as an efficient photocatalyst material. Hence, these 2D ZnO nanopellets would provide a new alternative route as a highly efficient photocatalyst for wastewater treatment.
Keywords: Zinc oxide; Two-dimensional nanopellets; Characterization; Photocatalyst; Methylene blue; Pseudo-first-order
Novel biodegradable chitosan–gelatin/nano-bioactive glass ceramic composite scaffolds for alveolar bone tissue engineering
by Mathew Peter; N.S. Binulal; S.V. Nair; N. Selvamurugan; H. Tamura; R. Jayakumar (pp. 353-361).
Bioactive glass ceramic nanoparticles (nBGC) were synthesized by sol–gel process and characterized using FTIR, TEM and XRD. Composite scaffolds of chitosan (CS)–gelatin (CG) with nBGC were prepared by blending of chitosan and gelatin with nBGC. The prepared CG/nBGC nano-composite scaffolds were characterized using FTIR, SEM and XRD. The effect of nBGC in the scaffold matrix was evaluated in terms of scaffold properties and biocompatibility. Our results showed macroporous internal morphology in the scaffold with pore size ranging from 150 to 300μm. Degradation and swelling behavior of the nano-composite scaffolds were decreased, while protein adsorption was increased with the addition of nBGC. Biomineralization studies showed higher amount of mineral deposits on the nano-composite scaffold, which increases with increasing time of incubation. MTT assay, direct contact test, and cell attachment studies indicated that, the nano-composite scaffolds are better in scaffold properties and it provides a healthier environment for cell attachment and spreading. So, the developed nano-composite scaffolds are a potential candidate for alveolar bone regeneration applications.
Keywords: Chitosan; Gelatin; Bioactive glass ceramic nanoparticles; Nano-composite scaffolds; Alveolar bone tissue engineering
Particle dynamics simulation of nanoparticle formation in a flame reactor using a polydispersed submicron-sized solid precursor
by W. Widiyastuti; Darmawan Hidayat; Agus Purwanto; Ferry Iskandar; Kikuo Okuyama (pp. 362-367).
Formation of nanoparticles from polydispersed, non-spherical submicron-sized particles via a gas-phase route in a flame reactor was investigated using tungsten oxide particles as a model material. Nanoparticles were formed by the evaporation of non-spherical powder, followed by nucleation, coagulation and surface condensation. The effects of both the flame temperature profile and the carrier gas flow rate on particles formation were studied numerically, and the results were validated by experimental data. The simulation was initiated by the use of computational fluid dynamics (CFD) to obtain the temperature distribution in the flame reactor. Then, evaporation of the feed material was modeled, taking into account both the polydispersity and the shape of the non-spherical particles. A nodal method was selected to solve the general dynamics equation (GDE), which included nucleation, coagulation, and surface condensation terms, for the prediction of particle dynamics. Results of the simulation were consistent with the experimental data, indicating that the selected model adequately predicts the final particle size distribution.
Keywords: Tungsten oxide; Evaporation; A gas-phase route; Non-spherical particles