The impact of metal nanoparticles (NPs) on biological systems, especially plants, is still not well understood. The aim of this research was to determine the effects of zinc oxide (ZnO) NPs in velvet mesquite (Prosopis juliflora-velutina). Mesquite seedlings were grown for 15 days in hydroponics with ZnO NPs (10 nm) at concentrations varying from 500 to 4000 mg L(-1). Zinc concentrations in roots, stems and leaves were determined by inductively coupled plasma optical emission spectroscopy (ICP-OES). Plant stress was examined by the specific activity of catalase (CAT) and ascorbate peroxidase (APOX); while the biotransformation of ZnO NPs and Zn distribution in tissues was determined by X-ray absorption spectroscopy (XAS) and micro X-ray fluorescence (μXRF), respectively. ICP-OES results showed that Zn concentrations in tissues (2102 ± 87, 1135 ± 56, and 628 ± 130 mg kg(-1) d wt in roots, stems, and leaves, respectively) were found at 2000 mg ZnO NPs L(-1). Stress tests showed that ZnO NPs increased CAT in roots, stems, and leaves, while APOX increased only in stems and leaves. XANES spectra demonstrated that ZnO NPs were not present in mesquite tissues, while Zn was found as Zn(II), resembling the spectra of Zn(NO(3))(2). The μXRF analysis confirmed the presence of Zn in the vascular system of roots and leaves in ZnO NP treated plants.
Nanosilver is one of the first nanomaterials to be closely monitored by regulatory agencies worldwide motivating research to better understand the relationship between Ag characteristics and antibacterial activity. Nanosilver immobilized on nanostructured silica facilitates such investigations as the SiO2 support hinders the growth of nanosilver during its synthesis and, most importantly, its flocculation in bacterial suspensions. Here, such composite Ag/silica nanoparticles were made by flame spray pyrolysis of appropriate solutions of Ag-acetate or Ag-nitrate and hexamethyldisiloxane or tetraethylorthosilicate in ethanol, propanol, diethylene glucolmonobutyl ether, acetonitrile or ethylhexanoic acid. The effect of solution composition on nanosilver characteristics and antibacterial activity against the Gram negative Escherichia coli was investigated by monitoring their recombinantly synthesized green fluorescent protein. Suspensions with identical Ag mass concentration exhibited drastically different antibacterial activity pointing out that the nanosilver surface area concentration rather than its mass or molar or number concentration determine best its antibacterial activity. Nanosilver made from Ag-acetate showed a unimodal size distribution, while that made from inexpensive Ag-nitrate exhibited a bimodal one. Regardless of precursor composition or nanosilver size distribution, the antibacterial activity of nanosilver was correlated best with its surface area concentration in solution.
The description and operation of a novel cyclic electrowinning/precipitation (CEP) system for the simultaneous removal of mixtures of heavy metals from aqueous solutions are presented. CEP combines the advantages of electrowinning in a spouted particulate electrode (SPE) with that of chemical precipitation and redissolution, to remove heavy metals at low concentrations as solid metal deposits on particulate cathode particles without exporting toxic metal precipitate sludges from the process. The overall result is very large volume reduction of the heavy metal contaminants as a solid metal deposit on particles that can either be safely discarded as such, or further processed to recover particular metals. The performance of this system is demonstrated with data on the removal of mixtures of copper, nickel, and cadmium from aqueous solutions.
Removal of selenate from solution is investigated in batch electrochemical systems using reactive iron anodes and copper plate cathode in a bicarbonate medium. Iron anodes produce ferrous hydroxide, which is a major factor in the removal of selenate from solution. Iron anodes also generate a significant decrease in the oxidation-reduction potential (ORP) of the solution because it prevents generation of oxygen gas at the anode by electrolysis. The removal rates varied from 45.1 to 97.4%, depending on current density and selenate concentration. The transformation of selenate by the process is modeled based on a heterogeneous reaction coupled with electrochemical generation of ferrous and hydroxide. The rates are optimized at lower initial concentrations, higher electrical currents, and the presence of anions. Presence of dissolved oxygen does not cause any significant effects the removal of selenate.
The description and operation of a novel, hybrid spouted vessel/fixed bed filter system for the removal of arsenic from water are presented. The system utilizes zero-valent iron (ZVI) particles circulating in a spouted vessel that continuously generates active colloidal iron corrosion products via the "self-polishing" action between ZVI source particles rolling in the moving bed that forms on the conical bottom of the spouted vessel. This action also serves as a "surface renewal" mechanism for the particles that provides for maximum utilization of the ZVI material. (Results of batch experiments conducted to examine this mechanism are also presented.) The colloidal material produced in this fashion is continuously captured and concentrated in a fixed bed filter located within the spouted vessel reservoir wherein arsenic complexation occurs. It is demonstrated that this system is very effective for arsenic removal in the microgram per liter arsenic concentration (i.e., drinking water treatment) range, reducing 100 μg/L of arsenic to below detectable levels (≪10 μg/L) in less than an hour.A mechanistic analysis of arsenic behavior in the system is presented, identifying the principal components of the population of active colloidal material for arsenic removal that explains the experimental observations and working principles of the system. It is concluded that the apparent kinetic behavior of arsenic in systems where colloidal (i.e., micro/nano) iron corrosion products are dominant can be complex and may not be explained by simple first or zeroth order kinetics.
Of the many types of biomolecules used for molecular imprinting applications, proteins are some of the most useful, yet challenging, templates to work with. One method, termed the 'epitope approach', involves imprinting a short peptide fragment of the protein into the polymer to promote specific adsorption of the entire protein, similar to the way an antigen binds to an antibody via the epitope. Whole lysozyme or the 16 residue lysozyme C peptide was imprinted into porous silica scaffolds using sol-gel processing. After removing template, scaffolds were exposed to lysozyme and/or RNase A, which was used as a competitor molecule of comparable size. When comparing protein- to peptide-imprinted scaffolds, similar amounts of lysozyme and RNase were bound from single protein solutions. However, while whole lysozyme-imprinted scaffolds showed about 4:1 preferential binding of lysozyme to RNase, peptide-imprinted scaffolds failed to show statistical significance, even though a slight preferential binding trend was present. These initial studies suggest there is potential for using peptide-imprinting to create specific protein-binding sites on porous inorganic surfaces, although further development of the materials is needed.
We assembled a set of models that allows investigation of local variables that are difficult to measure, validation of mechanistic physical models, and comparison of different numerical solutions. Population balances (PB) for bubbles were combined with local flow modelling in order to investigate G–L mass transfer in an air–water system. Performance of three different impeller geometries was investigated: Rushton (RT), Phasejet (PJ) and Combijet (CJ). Simulations were compared against experimental mixing intensity, gas hold-up, vessel-averaged volumetric mass transfer rates (kLa), and local bubble size distributions (BSDs).The simulations qualitatively predict kLa's with different impellers at the fully dispersed flow region and gave new insight on how kLa is formed and distributed in the stirred vessels. The used bubble breakage and coalescence models are able to describe both air–water and viscous non-Newtonian G–L mass transfer. Difference between experimental mass transfer rates of the three impellers was within experimental error, even trough the flow patterns, gas distribution, and local BSDs differ considerably. The population balance for bubbles was modelled in two different ways, with multiple size groups (MUSIGs) and with the bubble number density (BND) approach. MUSIG calculations took over twice as much computational time than BND, but there was little difference in the results. The Rushton turbine kLa was described with best accuracy, which is not surprising since most phenomenological models are fitted based on RT experiments. We suggest that these models should be validated over a wider range of vessel geometries and operating conditions.
1,2-Dichloroethane (EDC) is known to be hazardous to the environment and public health. In this study, application of radio frequency (rf) plasma as an alternative technology for the decomposition of EDC was demonstrated. The species detected in the effluent gas stream included CO2, CO, HCl, CCl4, C2HCl3, C2H3Cl, C2Cl4, CHCl3, C2HCl5, COCl2, C2H2, C2H4, C2H6, and HCOOH. The decomposition fraction of EDC [ηC2H4Cl2, (Cin−Cout)/Cin×100 (%)] was dependent on input power. When input power was 80 W, stable products such as CO, CO2, and HCl were dominant and other product species were inhibited. Equivalence ratio [ϕ=(C2H4Cl2/O2)actual×(O2/C2H4Cl2)stoichiometric] was the other important operational parameter in a plasma system. When the chlorocarbon/oxygen flow was fuel rich, more soot formation was found in the plasma reactor. When it was fuel lean, CO2 and CO dominated over other product species. Within the mixture of EDC and dichloromethane (DCM), the competition of DCM with EDC could affect the decomposition fraction of EDC.
New types of polymer condensation adducts were synthesized through the reaction of 3-amino-1,2,4-triazole-5-thiol (AZ) with glutaraldehyde in the absence and in the presence of thiourea at different molar ratios. The adsorption behavior of the chelating polymers towards Ag(I) from aqueous solutions was studied. Better adsorption behavior was achieved for Ag(I) by thiourea polymeric adducts. The chelating matrix obtained from a molar ratio of 2:1:3 of AZ, thiourea and glutaraldehyde, respectively, showed uptake capacity of 3.6 mmol/g. These polymers were evaluated for their recovery of Ag(I) from aqueous solutions using batch methods. The obtained polymers achieved promising results in the selective separation of Ag(I) from other metal ions. Both kinetics and thermodynamic parameters of the adsorption process were obtained. The data indicated that the adsorption process is an endothermic reaction and kinetically proceeds according to pseudo-first-order model. These parameters indicated that the polymers can be applied in the recovery of Ag(I).
The Ir/SiO2 and K ion-promoted Ir/SiO2 catalysts were fully characterized and catalytically studied using the ring-opening reaction of 1,3-dimethylcyclohexane (1,3-DMCH) as a probe reaction. This reaction could take place during the catalytic process underwent either by gasoline or by diesel fuel for enhancing of octane numbers or cetane numbers (CNs), respectively. The Ir catalysts were characterized by chemisorption of CO and H2, temperature-programmed techniques, X-ray photoelectron spectroscopy (XPS), extended X-ray absorption fine structure spectroscopy (EXAFS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. The addition of potassium ions to Ir/SiO2 catalyst produce severe superficial changes that are reflected in its ability for catalyzing the ring-opening reaction of 1,3-dimethylcyclohexane and the selectivity to primary product from substituted to unsubstituted C–C cleavages. Ir dispersions slightly increased with rising K surface density up to 3.1 atoms nm−2, but strongly decreased at higher K loadings due to the non-uniform decorative effect of potassium over Ir particles.This contribution also reveals that the opening of CC bonds at substituted or unsubstituted positions can be tuned varying the promoter loading. That is, the dicarbene reaction path typically occurs on Ir/SiO2 catalyst, facilitating the formation of branched products through the opening of CC bonds at unsubstituted positions. On the other hand, the metallocyclobutane intermediates become operative over K ion-promoted Ir/SiO2 catalysts. This involves a metal atom and three C atoms to form cyclic intermediate specie that undergoes the opening of CC bonds at substituted positions and facilitates the formation of unbranched products, which are more desirable in the production of diesel fuel.
Supercritical fluid extraction is a clean environmental chemical engineering process that has been given an interest to many researchers worldwide. The assessment of the feasibility of the extraction process utilizing a near critical solvent would be speeded up if it is possible to predict solubility data. Solubility data were measured for carbon dioxide with a mole ratio 1.35 of octane to ethanol using a phase equilibrium loading re-circulating high-pressure type apparatus at pressures up to 100 bar and at temperature 75 °C. The experimental data were then compared with calculated theoretical data which is calculated form the regular solution equations. A thermodynamic procedure is employed to each phase by applying activity coefficient expressions related to interaction parameters which are dependent on the pressure.
A transient heat transfer model is developed for analyzing the thermal performance of a thermochemical reactor for the solar-driven dissociation of ZnO in the 1600–2136 K range. The reactor consists of a rotating cavity-receiver lined with ZnO particles that are directly exposed to concentrated solar radiation. The model couples radiation, convection, and conduction heat transfer to the reaction kinetics for a shrinking domain and simulates a transient ablation regime with semi-batch feed cycles of ZnO particles. Validation is accomplished in terms of the numerically calculated and experimentally measured temperature profiles and reaction extents for a 10 kW reactor prototype tested in a high-flux solar simulator and subjected to peak solar concentration ratios exceeding 5000 suns. Scaling-up the reactor technology to 1 MW solar thermal power input has the potential of reaching a solar-to-chemical energy conversion efficiency of 56%.
Experiment design—response surface methodology (RSM) is used to model and to optimize the activation of methane (C1) using ethane (C2) as co-reactant into higher hydrocarbons, over Zn-containing zeolite catalyst. The application of this methodology allows a better understanding of the influence of the different factors: time on stream (TOS), space velocity of C2 (GHSV-C2), molar fraction of C1/(C1 + C2) (XC1) and reaction temperature, on the C1 conversion, reducing the operation costs, achieving efficiency and effectiveness of this process. Box–Behnken design was development with different levels of the factors, determining its influence on the C1 conversion in order to obtain responses surfaces. In this way, we found the best combination in the reaction parameters that allowed us to optimize the process. The results indicated that the reaction time, the XC1 and the interactions of the TOS–temperature factors, have the main influence on C1 conversion, in agreement with the experimental results reported previously.
This work describes the sorption of 134Cs, 60Co and 152+154Eu by crystals of unmodified and phosphoric acid modified silico-antimonates (SiSb). Equilibrium and selectivity sequence for co-exiting metal ions under strongly acidic conditions of HClO4, H2SO4, HNO3 and HCl were investigated. The results showed that the silico-antimonate either in the high Sb5+ content or in the phosphated form possesses acidic characters and shows cation-exchange properties more efficient in acidic media. Kinetic studies indicated that pseudo-second-order model gave better fitting parameters comparing to that of pseudo-first-order one. The thermodynamic parameters of the sorption processes revealed spontaneous and endothermic nature. High negativity of ΔG° values for the modified SiSb confirms the positive role of phosphoric acid impregnation in the sorption process. The break-through capacities of the studied ions were further calculated from a column investigation.
The adsorption capacity on and the desorption from pure activated carbons, silica and NaX zeolite, of hexamethylcyclotrisiloxane (HMCTS or D3, a common siloxane impurity in biogases) has been evaluated in laboratory experiments using synthetic biogas. The adsorption mode of this molecule has also been investigated by FT-IR spectroscopy. HMCTS adsorbs on silica by hydrogen bonding on the surface hydroxyl groups. However, its desorption up to 200 °C by purging with nitrogen as well as by vacuum treatment, is incomplete, leaving surface hydroxyl groups partially affected. Limited desorption is observed also from activated carbons at temperatures between 20 and 200 °C. On zeolite NaX molecular adsorption as well as reactive adsorption occurs, partial desorption being obtained by purging with nitrogen already at room temperature. In the three adsorbents, polymerization of HMCTS to silicone is found during adsorption in dynamic conditions. This is supposed to be the common cause of the only partial regenerability of all these solids after HMCTS adsorption.
The commercially available 13X (NaX) zeolite in the form of extrudates were impregnated with 15% AlCl3 and characterized by qualitative methods. Experimental runs for the kinetic study were carried at three different temperatures (400, 425, and 450°C) with a constant benzene to ethanol molar ratio of 3:1 and varying the space velocity under isothermal conditions in the reactor. Experiments were carried out to choose the zone in which the mass transfer resistances were negligible. Different models based on Langmuir–Hinshelwood–Hougen–Watson reaction mechanisms were proposed and a mathematical fit for the best model was found. The activation energy and frequency factor were evaluated by using Arrhenius relationship. The model parameters were estimated by non-linear regression analysis.
Inverse gas chromatography has been used to evaluate the adsorption parameters (ΔH, ΔS and ΔG) of some probes, each representing a class of organics (n-hexane, cyclohexane and benzene) on 4A and 13X zeolites. The adsorption parameters of the probes on 4A were determined in the finite concentration region, and those on 13X were determined in the infinite dilution region. The interactions between the probes and the surface were discussed in the light of determined thermodynamic parameters of adsorption. It was found that the adsorption isotherms for 4A conform with the Langmuir equation and benzene exhibits more negative ΔH than for n-hexane and cyclohexane on both 4A and 13X. Also, interactions of the benzene and n-hexane with 13X were found to be stronger than that on 4A.
Selective adsorption of propylene from mixtures with propane over a lithium-exchanged zeolite 13X has been studied.Adsorption equilibrium of pure gases has been evaluated at three different temperatures by volumetric and gravimetric methods. Propylene is adsorbed preferentially over propane, particularly at low pressures. Adsorption equilibrium can be well described with the multi-site Langmuir and the Virial models. At 1 bar and 323 K, the amount adsorbed of propylene is 2.5 mol/kg while the loading of propane is 2.0 mol/kg.The dynamic behavior of the sample has also been evaluated on the bench scale in a fixed-bed for binary breakthrough performance. Macropore adsorption controls the diffusion process within the extrudates of the zeolite. The mathematical model could satisfactorily predict the behavior of the bed. The data obtained in this work allows to model any adsorption-based process for propane/propylene separation, like vacuum pressure swing adsorption and simulated moving bed.
Reactive Red 194 (RR194), Reactive Yellow 145 (RY145) azo dyes and synthetic textile dye-bath effluent were treated with O3 and H2O2/UV-C processes. The operating parameters such as dye concentration, hydrogen peroxide concentration and pH values were evaluated to find the optimum conditions for the H2O2/UV-C processes. It was observed that while H2O2/UV-C process was more pH dependent in decolorization and dearomatization reactions, ozonation was less selective and more effective in both decolorization and dearomatization reactions. Results indicated that the decolorization and dearomatization rate of each dye are well defined by pseudo-first order reaction kinetics. In general, decolorization reactions were faster than dearomatization reactions in both systems, though ozonation had faster reaction rates in both decolorization and dearomatization compared to the corresponding reaction rates taking place during the application of the H2O2/UV-C process. According to decolorization efficiency it can be inferred that effect of OH radical scavengers (e.g. CO32−, Cl−) present in the synthetic dye-bath as well as radical formation promoter (e.g. OH−) was probably hidden due to complexity of the synthetic dye-bath matrix.
In this study, the efficiency of the integrated process was investigated in which the pre-ozonation step was followed by activated sludge process (ASP) in treating the aqueous Acid Red-151 (AR 151) solutions. The percent dye removal in the integrated process was found to be 47% for a pre-ozonation time of 30 min, instead of 25% in the singly ASP without pre-ozonation. The treatment efficiency of this process could be higher if the pre-ozonation time of 120 min yielding maximum enhancement of biodegradability at a peak value of BOD5/COD ratio were used before the biological treatment process.
The catalytic ozonation of RR198 solution in the presence of MgO nanocrystal catalysts was investigated in a laboratory scale batch reactor. The effects of solution pH (2–12), reaction time, MgO dosage (1–6 g/L), and initial dye concentration (100–500 mg/L) on color and COD removal were evaluated, and the findings were compared to those of ozonation without a catalyst. The results indicate that adding MgO nanocrystals into the ozonation reactor greatly accelerated the rate of RR198 degradation, thereby reducing the reaction time and improving the reduction of color and COD compared to conventional ozonation. The optimum pH and catalyst dosage values were determined to be 8 and 5 g/L, respectively. The complete removal of color was observed in COP at this optimum condition for an RR 198 concentration of 200 mg/L at a reaction time as short as 9 min, while the time required to attain the same performance at single ozonation was 30 min. Furthermore, the COP could markedly increase the ratio of BOD5 to COD from below 0.1 in raw solution to 0.63 to 0.38 for dye solutions of 100 and 500 mg/L, respectively; thus, RR 198 was converted to biodegradable compounds. Therefore, the COP on MgO nanocrystals is considered as an effective and feasible process for pre-treating the azo dye-laden solutions, making possible a post-treatment of the effluent in a biological system.
Oxygen-prebleached kraft pulp (OKP) was bleached with H2O2 activated with a copper complex coordinated with 2,2′-dipyridylamine (dpa) or 4-aminopyridine (4-ap) under alkaline conditions. Bleaching of OKP by H2O2 activated with the Cu(II)–dpa complex decreased the kappa number (k) and viscosity (v) of the pulp by 26 and 0.7%, respectively. In contrast pulp bleaching without the coordinator resulted in a decrease in k and v values of 25 and 7.8%, respectively. Thus, selectivity for delignification, expressed by k/v, was increased 12-fold by the coordination with dpa. ESR demonstrated that the coordination with dpa suppressed the production of OH by 57%. These results support the involvement of a hydroperoxo complex of Cu(II) formed by the reaction of −OOH with [Cu(II)(dpa)(H2O)3]2+. When the OKP was bleached with H2O2 activated with a Cu(II)–4-ap complex, selectivity (k/v) in pulp bleaching increased by 2.6-fold and production of OH decreased by 47%. We conclude that Cu(II)–dpa is a catalyst potentially applicable to totally chlorine free (TCF) bleaching sequences due to its high selectivity for delignification.
The continuous-flow adsorption of 2,4-dichlorophenol (2,4-DCP) from aqueous solution by immobilized Phanerochaete chrysosporium biomass in a fixed-bed column was studied. The effects of flow rate, influent concentration of 2,4-DCP and bed depth on breakthrough curves and biosorption capacity were investigated. The experimental results showed that the breakthrough time decreased with increasing flow rate, increasing influent concentration and decreasing bed depth. The data also indicated that the equilibrium uptake of 2,4-DCP increased with decreasing flow rate and increasing influent concentration of 2,4-DCP. Two models were employed to predict the breakthrough curves and to determine the characteristic parameters of the column useful for column design. The Thomas model was able to predict the breakthrough curve in the range of relative concentration (Ce/Ci) higher than 0.3, whereas the validity of the Bohart-Admas model was limited to the initial part of breakthrough curve at all flow rates and influent concentrations of 2,4-DCP studied. The feasibility of reusing the immobilized fungal beads through five adsorption/desorption cycles in fixed-bed column was investigated.
The adsorptive removal of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) by bituminous shale (BS) has been studied by means of batch technique. Kinetic data well fit to McKay equation at the lowest initial concentration of 6 × 10−5 M, which assumes a two-resistance diffusion model. The effective film-diffusion coefficients, which correspond to initial fast stage of the adsorption, are in the magnitude ∼10−11 m2/s whereas particle-diffusion coefficients corresponding to the latter slow stage are ∼10−14 m2/s in the studied concentration range of (0.6–4.0) × 10−4 M. Both film- and particle-diffusion coefficients decrease as the initial concentration increases while the effective diffusion coefficient of 7.73 × 10−13 m2/s calculated from Paterson's equation based on a one-resistance diffusion model changes neither initial concentration nor temperature. Average activation energies calculated by applying Arrhenius equation to film-diffusion coefficients are found to be positive whereas they change around zero for particle-diffusion process. Thermodynamic parameters estimated according to Eyring equation based on the transition state theory indicate the existence of both energy and entropy barrier in the system.Experimental equilibrium data points are found in accordance with the curves calculated according to Freundlich, Dubinin–Radushkevich (D–R) and Langmuir isotherm equations. Adsorption capacities of the BS for 2,4-D calculated from isotherm parameters increase with increasing temperature and decreasing pH.
The present work investigates the mechanism of the photocatalytic and adsorptive treatment of an aqueous DNP (2,4-dinitrophenol) solution in an annular-flow reactor installed with a TiO2/AC-PET film (a polyethylene terephthalate film adhesively fixing activated carbon particles covered with a thin and porous film of titanium dioxide). Unfortunately, the experimental result indicates that it is impossible to correctly measure the time courses of product ion concentrations because they are adsorbed onto or desorbed from AC particles. Therefore, a computer simulation methodology using mathematical models is introduced in order to elucidate the treatment mechanism. Treatments of aqueous DNP solutions using the TiO2-PET film reveal that the diffusion of DNP from a bulk solution to a TiO2 film is based on the gradient of DNP concentration, generated by a rapid adsorption of DNP onto AC and photocatalytic reaction, in the very neighborhood of TiO2 film, and this diffusion increases the DNP concentration at the surface of TiO2 film, thereby enhancing the rate of photocatalytic decomposition. Moreover, it is found that the TiO2/AC-PET film can lower the burden of the adsorption of DNP onto AC compared with the AC-PET film because a part of DNP molecules are photocatalytically decomposed and the percentage of this decomposition is increased at a lower linear velocity. In conclusion, the mathematical model taking into consideration a film-diffusional effect can successfully explain the complicated mechanism of the treatment of an aqueous DNP solution using the TiO2/AC-PET film.
This paper reports the photooxidation of 2,4-dichlorophenoxyacetic acid (2,4-D) in aqueous solution employing hydrogen peroxide and ultraviolet radiation. A kinetic model to represent the degradation of 2,4-D and that of equally toxic intermediate products, such as 2,4-dichlorophenol (DCP) and chlorohydroquinone (CHQ), is presented. The model includes the parallel, direct photolysis of 2,4-D and the most important reaction intermediates. The experimental work was performed in a batch, well-stirred tank reactor irradiated from its bottom using a low power, germicidal, tubular lamp placed at the focal axis of a cylindrical reflector of parabolic cross-section. Herbicide degradation initial rates twenty times faster than those obtained employing UV radiation alone were found. In order to reach more useful conclusions about the ability of the process to reduce the contamination to innocuous final products, simultaneous measurements of the total organic carbon (TOC) were performed. By application of the kinetic model to the whole set of concentration versus time experimental data, the values of the kinetic parameters were obtained. The model permits a good representation of the reaction evolution in a rather wide range of 2,4-D and H2O2 initial concentrations.
β-Cyclodextrin/attapulgite (β-CD/ATP) composites were prepared for the adsorption of 2,4-didichlorophenol (2,4-DCP) and 2,6-didichlorophenol (2,6-DCP) from aqueous solution. β-CD/ATP composites mainly possessed mesopores, high surface area and big pore volume which were benefit for the adsorption capacity. The batch mode adsorption experiments with respect to pH, temperature, initial concentration, contact time and binary dichlorophenol solution were investigated. Equilibrium data, at various temperatures, were described by the Langmuir, Freundlich and Dubinin–Radushkevich isotherm models. The Langmuir isotherm model was fitted to the experimental data significantly better than the other models. The kinetic data were well fitted to the intraparticle diffusion equation, which indicated that three steps belonged to the pseudo-second-order adsorption process. Intraparticle diffusion increased with the increase of adsorbate concentrations while film and pore diffusion decreased. The initial adsorption factor, Ri, showed that initial adsorption for 2,4-DCP was intermediate while was strong for 2,6-DCP. The thermodynamics parameters (positive values of ΔH° and ΔS°, negative values of ΔG°) indicated that binding systems between β-CD/ATP composites and adsorbates (2,4-DCP and 2,6-DCP) were endothermic, entropy gained and spontaneous in nature.
Anatase titanium dioxide (TiO2) in particle sizes of roughly 0.5–20 μm was prepared from amorphous TiO2 in an aqueous H2O2 solution by heating at 90 °C for 9 h and directly deposited on a PET film. On the other hand, granular activated carbon (AC) particles in sizes of 1–2 mm in diameter were adhesively deposited on a PET film, and their surfaces were also coated with TiO2. The resulting three preparations (TiO2-, AC-, and TiO2/AC-PET films) were set up in an annular-flow reactor to treat aqueous solutions of 2,4-dinitrophenol (DNP) in a batch-recirculation mode. The rate of DNP adsorption onto the TiO2/AC-PET film without UV irradiation was almost the same as that onto the AC-PET film, indicating that the attraction of DNP to AC was not lowered in the presence of TiO2 film. Observation of SEM photographs suggests that this result is attributed to the porous structure of the thin TiO2 film covering AC particles. The rate of DNP removal by the TiO2-AC PET film under UV irradiation was 2.9 times higher than that by the TiO2-PET film under UV irradiation, and was 1.1 times higher than the rate of DNP adsorption onto the AC-PET film. The rate of DNP removal by the AC-PET film decreased by 40% after six runs, while that by the TiO2/AC-PET film decreased by 22%. Durable experiments using the TiO2/AC-PET and AC-PET films clarified that the lifetime of the TiO2/AC-PET film is at least two times longer than that of the AC-PET film. This result suggests that DNP molecules are photocatalytically decomposed when passing through the porous TiO2-PET film, which lessens a burden of DNP adsorption on AC. Moreover, the DNP treatments in the batch-recirculation flow system suggested that the TiO2/AC-PET film saturated with DNP can be successfully regenerated at 60 °C.
The present study deals with the adsorption potential of thermally activated carbon developed from maize cob for the removal of 2,4-dichlorophenol (2,4-DCP) from aqueous solutions. Studies were conducted to delineate the effects of contact time, 2,4-DCP initial concentration, pH and temperature. The kinetics of 4-DCP adsorption from a solution onto an adsorbent was explored experimentally. Non-linear form of pseudo-second-order model showed a better fit with good correlation co-efficient. Bangham's and intra-particle diffusion model were also used. Non-linear form of Langmuir isotherm model was applied and the data correlate well and the maximum adsorption capacity was found to be 17.94 mg/g for the particle size of 250–500 μm. Acidic pH was favorable for the adsorption of 2,4-DCP. Studies on pH effect and desorption showed that chemisorption mechanism was involved in the adsorption process. Thermodynamic study showed that adsorption of 2,4-DCP on maize cob carbon is more favored. The change in entropy (ΔS°) and heat of adsorption (ΔH°) of maize cob carbon were estimated as 26.91 J/(K mol) and 6.78 kJ/mol, respectively.
The adsorption characteristics of 2,4,6-trichlorophenol (TCP) on coconut husk-based activated carbon prepared under optimized conditions were evaluated. Batch adsorption studies were conducted to study the effects of various parameters such as initial concentration, agitation time and solution pH on TCP adsorption. Adsorption capacity was found to increase with increase in initial concentration and agitation time, while acidic pH was more favourable for the adsorption of TCP. Equilibrium data were analyzed by the Langmuir, Freundlich, Temkin and Redlich–Peterson models by using non-linear regression technique. The equilibrium data were best represented by the Langmuir isotherm, yielding maximum monolayer adsorption capacity of 716.10 mg/g at 30 °C. The adsorption kinetics was found to follow the pseudo-second-order kinetic model. The mechanism of the adsorption process was determined from the intraparticle diffusion model. Boyd plot revealed that the adsorption of TCP on the activated carbon was mainly governed by particle diffusion. Coconut husk-based activated carbon was shown to be an efficient adsorbent for removal of TCP from aqueous solutions.
Herein, TNT oxidation by Fenton-like systems in the presence of naturally occurring iron-bearing minerals was investigated in aqueous suspension at neutral pH. TNT degradation pseudo-first-order rate constant's (ksurf) values were found to be: 3.75 × 10−4 L m−2 min−1 > 2.55 × 10−4 L m−2 min−1 > 1 × 10−4 L m−2 min−1 > 1 × 10−6 L m−2 min−1 for pyrite, green rust, magnetite and goethite, respectively. Degradation efficiency was correlated with the increasing Fe(II) content in the mineral structure. Similar behavior was observed in more complex systems, including iron-coated quartz and iron-doped clays. Particularly, magnetite, Fe3O4 (mixed ferrous–ferric oxides), was efficient to promote Fenton-like reactions at pH 7 and its catalytic activity was preserved when incorporated into mineral assemblages with silica quartz or clay. For magnetite-bearing mineral systems, the addition of a non-toxic iron chelatant, carboxy-methyl-cyclodextrin (CMCD), improved TNT mineralization by a factor of 3. This increase in oxidation yield could in part be explained by the increased iron dissolution rate prompting higher Fenton's reaction efficiency. Consequently, CMCD might be used as an alternative to toxic iron chelating agents such as EDTA and NTA in in situ chemical oxidation (ISCO) processes for contaminated soil remediation.
The degradation of 2,4,6-trinitrotoluene (TNT) in wastewater using nanoscale zero-valent iron (nZVI) was investigated. The results showed that >99% TNT was degraded when the initial TNT concentration was 80 mg L−1 after degradation for 3 h by 5 g L−1 of nZVI at pH 4, 40 °C using a rotary oscillation incubator operating at 200 rpm. The Langmuir–Hinshelwood kinetics model fit the kinetics of TNT degradation by nZVI well. Fourier transform infrared (FT-IR) and ultraviolet–visible spectrophotometry showed that TNT was adsorbed on the surface of nZVI, and this reduced TNT in aqueous solution. X-ray diffraction (XRD) demonstrated that the surface of nZVI changed during the degradation of TNT.
Zeolitic MCM-22 and activated carbon have been used as adsorbents for removal of heavy metals (Cu2+ and Pb2+) and humic acid from aqueous solution. The adsorption behaviour has been investigated in single- and binary-adsorbate systems and the effect of humic acid on metal adsorption was obtained. It is found that the MCM-22 and activated carbon are effective in metal ion and humic acid adsorption. In single component system, the MCM-22 presents the adsorption capacities of Cu2+, Pb2+, and humic acid at 33, 94, and 78 mg/g, respectively, while the activated carbon exhibits the adsorption capacities of Cu2+, Pb2+, and humic acid at 12, 61, and 74 mg/g, respectively, lower than those on the MCM-22. Solution pH will significantly influence the adsorption. Cu2+ and Pb2+ adsorption will increase with increasing pH while humic acid shows a decreasing trend as pH is increased. In binary-adsorbate system, metal–humic acid interaction will affect the adsorption of metal and humic acid on the MCM-22 and activated carbon. On the MCM-22, Cu2+, Pb2+ will present competitive adsorption with humic acid. On the activated carbon, Pb2+ and humic acid also exhibit competitive adsorption, while Cu2+ and humic acid will have a complexation effect, resulting in an increase of Cu2+ adsorption on the activated.
Kinetic experiments on the hydrogenation of toluene were performed on 0.5 wt.% Pt/ZSM-22 at temperatures in the range 423–498 K, H2 inlet partial pressures of 100–300 kPa and toluene inlet partial pressures of 10–60 kPa. Construction of a kinetic model was based on a critical evaluation of available literature data on the hydrogenation of aromatic components together with physicochemical studies on the interaction of aromatic components and related hydrogenated products with metal surfaces as well as on quantumchemical calculations. This lead to a general kinetic model, analogous to the Horiuti Polanyi mechanism for ethylene hydrogenation, with the first four H atom addition steps not in quasi-equilibrium. Chemisorption of H2 and toluene was assumed to occur on identical sites. No dehydrogenated surface species was taken into account. The preexponential factors were calculated using transition state theory. A model with equal surface reaction rate coefficients for the H addition steps was selected as the best model. The estimated toluene and H2 chemisorption enthalpies amounted to −70 and −42 kJ mol−1. An activation energy in the range of 40–50 kJ mol−1 was found. Under typical reaction conditions, 60% of the surface is covered by toluene and 20% by H atoms. The remaining 20% are free. Negligible amounts of partially hydrogenated species were found to be present on the catalyst surface.
Two different commercial (tubular NaA zeolite and flat polymeric (PERVAP® 2201)) membranes were used in a vapor permeation process to remove water from the reaction atmosphere during the synthesis of isopropyl propionate. The reaction was carried out in a batch reactor using 3 wt.% (relative to propionic acid) of para toluene sulfonic acid as the catalyst. Effects of membrane type and initial alcohol/acid molar ratio on the performance of the combined process were investigated. Experiments were carried out with three different levels of alcohol/acid molar ratio. It was found that the coupled process was generally capable of enhancing the conversion of reversible esterification reaction. However, complete acid conversion was achieved in a shorter period of time with zeolite membrane than with polymeric membrane. In addition, initial molar ratio of the reactants had a strong effect on both acid conversion and on water flux through the membranes.
The decolorization of azo dye by titanium dioxide (TiO2) with 360 nm ultraviolet (UV) light was studied in a batch reactor. Response surface methodology was applied to optimize four independent parameters, viz. UV light intensity, the concentration of TiO2, initial pH, and stirring speed, in the photocatalytic degradation process of the dye Reactive Red 239. To obtain the mutual interaction between these four parameters and to optimize these parameters during the process, a 24 full-factorial central composite design (CCD) and response surface methodology were employed. The results of our experiments indicate that the concentration of TiO2 exhibits a significant positive effect on the efficiency of decolorization, whereas initial pH shows a significant negative effect. The optimized condition of the photocatalytic degradation of Reactive Red 239 is as follows: UV light intensity, 16.08 W/m2; TiO2 concentration, 3.06 g/l; initial pH, 2.64; stirring speed, 880 rpm. Under this condition, the maximal decolorization efficiency of 99.82% was achieved.
Diclofenac has been irradiated under UV-C light at 254 nm. The effect of some operating variables has been investigated. The kinetics of the process has been analysed by means of the corresponding quantum yield. The presence of free radical promoters has also been considered.Diclofenac initial concentration plays an important role in its conversion profile. First order kinetics is ruled out under the applied experimental conditions. The process efficiency is significantly enhanced if oxygen is bubbled instead of air. Diclofenac quantum yield values in the range ≈0.1–0.3 mol Einstein−1 were obtained depending on the operating conditions used (air or oxygen) and the kinetic methodology followed. The mineralization level achieved also increased from 30 to 80% when oxygen was sparged instead of air. The presence of free radicals promoters did not improve the diclofenac removal efficiency.
The UV/H2O2 process has often been proposed as an effective treatment technology for remediation of colored wastewaters. However, it has frequently been noted that it is not as economically efficient as other treatment technologies. To limit this drawback as much as possible, an effort to optimize the treatment technology from both the economical and operating points of view is needed.This paper presents a study on determination of cost optimal operating conditions for decoloration and mineralization of C. I. Reactive Blue 268 by the UV/H2O2 process. Dye concentration, hydrogen peroxide concentration, pH, treatment time, and temperature were considered to be influential operating parameters. Cost of electricity, cost of hydrogen peroxide, and cost of water needed to adjust the dye concentration were considered to be relevant operating costs.The presented approach is based on response surface methodology in conjunction with mathematical programming. The results obtained clearly indicate that, in order to assure effective and economically efficient operation, the UV/H2O2 process should be simultaneously optimized from the perspective of both operational and economic efficiency.
In the field of gas–solid fluidization, bubbles, and all features regarding them, have a very great importance, as they significantly affect the process performance. Numerous experimental studies on bubbles, and their formation, evolution, and properties, have been performed in the past. These investigations appear particularly difficult, due to the nature of these systems, since the gas phase is distributed in both the bubble and the emulsion phase. Several experimental approaches have been developed to tackle this study. Among these, the Digital Image Analysis Technique purposely developed in Part I of the present work, based on the use of a video camera for monitoring the phenomenon coupled with image analysis has been found viable and effective.Moreover, the bubbles behaviour and characteristics have been described by means of a variety of mathematical models. In recent years, in particular, computational fluid dynamics (CFD) tools have been found to be very effective in providing a powerful framework through which these models can be implemented and numerically solved.This paper combines both experimental and computational studies, presenting the comparison, performed by DIAT, between experimental data and relevant CFD simulations. In particular, simulations have been performed by means of the ANSYS-CFX code. The comparison comprises the following quantities: bed expansion, bubble hold-up, size evolution, distribution, density, aspect ratio, and bubble velocimetry data.
Bubble characteristics are very important in the design of fluidized beds because they govern hydrodynamics and efficiency of the operation for which the bed is used. In this work, a digital image analysis technique has been developed to study the fluidization dynamics of a lab-scale two-dimensional bubbling bed. Digital image analysis may supply a great quantity of information; it is non-intrusive, capable of securing several properties simultaneously and cost effective. The image analysis method here developed allows for the simultaneous measurements of various significant bubble properties, i.e. bubble size and bubble velocity distributions, bed height and bubble-phase hold-up, by means of a purposely in-house developed software. Present results were compared with relevant literature correlations and resulted in sound agreement, thus confirming the large potential of the technique here developed.
The biosorption of Acid Red 337 and Acid Blue 324 from aqueous solution on Enteromorpha prolifera was investigated in a batch system. Optimum initial pH and temperature values for AB 324 and AR 337 dyes were found as 3.0 and 2.0, 25 and 30 °C, respectively and the optimum dye uptake amounts per unit mass were obtained at 0.5 g/l biosorbent concentration for both dyes. The Langmuir, Freundlich and Redlich–Peterson adsorption models were applied to experimental equilibrium data and the isotherm constants were calculated using Polymath 4.1 software. The monolayer covarage capacities of E. prolifera for AB 324 and AR 337 were obtained as 160.6 and 210.9 mg/g, respectively. It was observed that the biosorption data fitted well to Redlich–Peterson model than the other models. The external diffusion and intraparticle diffusion models were also applied to biosorption data of AR 337 and AB 324 and it was found that both the surface adsorption as well as intraparticle diffusion contribute to the actual adsorption process. The constants obtained from the pseudo-second order kinetic model at different temperatures were evaluated and the activation energies for the biosorption of AB 324 and AR 337 were found to be −31.5 and −19.87 kJ/mol, respectively. Thermodynamic parameters such as enthalpy, entropy and Gibb's free energy changes were also calculated and it was concluded that the biosorption of these acidic dyes on E. prolifera was exothermic in nature.
Photocatalytic membrane reactors (PMRs) seem to be a very promising method of solving problems concerning separation of photocatalyst as well as products and by-products of photodegradation from the reaction mixture. In the presented studies an anatase-phase TiO2 was applied for degradation of Acid Yellow 36 (AY36) in the PMR coupling photocatalysis and direct contact membrane distillation (DCMD). The effect of different process parameters such as dye concentration, reaction temperature and photocatalyst loading on the effectiveness of degradation of AY36 was investigated. Moreover, in order to compare the effectiveness of AY36 photodegradation during photocatalysis alone and the hybrid process, additional experiments without application of MD were conducted. The addition of TiO2 to a feed did not affect the permeate flux, regardless of the process conditions applied. The flux remained constant and equal to the maximum permeate flux during about 400 h of experiments. The highest decolorization of AY36 solution during hybrid process was observed at the highest photocatalyst loading applied (0.5 g TiO2/dm3). The increase of the reaction temperature from 313 to 333 K resulted in an increase of the photodegradation rate of AY36. After 5 h of the hybrid process the effectiveness of dye degradation calculated on a basis of AY36 mass in a feed solution amounted to 31, 36 and 42% for the reaction temperatures of 313–333 K. Similar results were obtained when photocatalysis was conducted in the MD installation but with disconnected MD module. It was found that an improvement of AY36 photodegradation could be achieved by a decrease of initial dye concentration. Comparing the results obtained in a conventional slurry photoreactor and in the PMR and taking into account both, the rate of azo dye degradation and the quality of the product, it could be concluded that more beneficial configuration seems to be the PMR.
The kinetic behavior of heterogeneous esterification of acetic acid with methanol over an acidic cation-exchange resin, Amberlyst 36, was investigated by using a packed-bed reactor. The kinetic experiments were conducted at temperatures from 313.15 K to 328.15 K and the molar ratios of methanol to acetic acid in the feed stream from 1 to 5. The reaction rate was found to increase with increasing temperature, but the equilibrium conversions of acetic acid changed slightly over the entire range of reaction temperatures. It is suggested that the heat effect of this reaction is negligible over the experimental conditions. It was also found that the equilibrium conversion of acetic acid increases with the molar ratios of feed increasing from 1 to 5. The relative adsorption strength between any two reacting species was determined from the results of binary adsorption experiments. The magnitude of adsorption strengths follows the order of water > methanol > acetic acid > methyl acetate. The kinetic data were correlated with the ideal-quasi-homogeneous (IQH), the nonideal-quasi-homogeneous (NIQH), the Eley–Rideal (ER), and the Langmuir–Hinshelwood–Hougen–Waston (LHHW) models, respectively, to determine the kinetic parameters. Among these investigated models, the ER and the LHHW are equally well and obviously better than IQH model.Highlights► Kinetic behavior of acetic acid with methanol over Amberlyst 36 has been studied. ► Adsorption strengths: water > methanol > acetic acid > methyl acetate. ► The ER and the LHHW models correlated satisfactorily the kinetic data.
The aim of this work was to apply an experimental response surface methodology (RSM) to optimization of the Acid Yellow 36 (Ay 36) decolorization procedure the electro-Fenton process (EFP) using boron-doped diamond (BDD) electrodes. RSM was used for the evaluation of different operation parameters, process modelling, optimization study, and model prediction analysis. Optimization of the electro-Fenton process for decolorization of 60 mg L−1 of synthetic azo dye solution was analyzed using a central composite design (CCD) in RSM. The response variable for the experimental design was a percentage of the color removal. The three considered factors, at two different levels, were current density (j = 8 and 23 mA/cm2), catalytic Fe2+ concentrations (0.1 and 0.3 mmol L−1), and electrolysis time (10 and 50 min). According to RSM, the optimum operation conditions were Fe2+ = 0.24 mmol L−1, j = 23 mA/cm2, and t = 48 min. The maximal decolorization efficiency of 98% was achieved under these conditions.
Activated (AC-PW) and non-activated (C-PW) carbonaceous materials were prepared from the Brazilian pine-fruit-shell (Araucaria angustifolia) and tested as adsorbents for the removal of Procion Red MX 3B dye (PR-3B) from aqueous effluents. The activation process lead to increase in the specific surface area, average porous volume, and average porous diameter of the adsorbent AC-PW when compared to C-PW. The effects of shaking time, adsorbent dosage and pH on adsorption capacity were studied. PR-3B uptake was favorable at pHs ranging from 2.0 to 3.0 for C-PW and 2.0 to 7.0 for AC-PW. The contact time required to obtain the equilibrium using C-PW and AC-PW as adsorbents was 6 and 4 h at 298 K, respectively. The values of the function error (Ferror) of fractionary-order kinetic model was at least 15 times lower than the values obtained with pseudo-first-order, pseudo-second order and Elovich kinetic models, indicating that this kinetic model was better fitted to the experimental results. For equilibrium data the Ferror values of the Sips isotherm model were at least 4.0 lower than the values of Langmuir, Freundlich, and Redlich-Peterson isotherm models using C-PW and AC-PW as adsorbents. The enthalpy and entropy of adsorption of PR-3B were obtained from adsorption experiments ranging from 298 to 323 K. Simulated dyehouse effluents were used to check the applicability of the proposed carbons for effluent treatment.
The transport of dissolved pollutants and nutrients in soils depends on the spatial and temporal distribution of soil water. The water flow is strongly affected by the presence of air and the heterogeneity of the soil structure. To investigate the influence of structures and air on the soil water dynamics, the distribution of water in a sand column was tomographed using thermal neutrons. The experiment was conducted using a column filled with 5 × 5 × 6 sand cubes of 1 cm size. Each sand cube was filled with coarse or fine sand material. The volume fraction of the cubes filled with coarse sand was 33%. The cubes were arranged randomly. In the sample realization, a continuous path between top and bottom of the column within the coarse material existed. The continuity of this sand structure is expected to affect the water dynamics. At the beginning of the experiment, the pore space in the column was filled with water. Then, the column was drained by the application of a continuously changing suction force at the bottom of the column. After an equilibration period, the suction was released and water flowed back in the column. The water content in the sand cubes was mapped in intervals of one and a half minutes. A total tomography of the column was carried out in 53 s using an optimized flat panel. To increase the sensitivity of the thermal neutron tomography measurements, a mixture of normal water and heavy water was used. The drainage of the coarse sand was much faster than for the fine sand because the capillary forces are smaller and the hydraulic conductivity is high.
This paper presents a visualization of a 3D gas density distribution, which arose from a safety analysis of a high-temperature gas cooler reactor. The density distribution is reconstructed from holographic interferograms using the techniques of computed tomography. In the reconstruction process, a new reduced bandlimit technique is used in the filtered-backprojection algorithm to deal with the truncated projection data with noise. The results reconstructed from 12 view directions are verified qualitatively by an oxygen molarity detector. It shows that the filtered-backprojection algorithm, integrated with the reduced bandlimit technique, can reconstruct the 3D density distribution from the truncated and noisy projections, and that holographic interferometry is a non-disturbing and powerful tool in flow-visualization for 3D gas flows.
E-waste is one of the rapidly growing environmental problems of the world. However, the utilization of e-waste to produce economically viable materials such as mesoporous silica molecular sieves has not been well studied to date. Electronic packaging resins have been used widely in semiconductor industry. This study uses resin waste from this packaging process as source of Si and cationic surfactant as a template for the synthesis of highly ordered mesoporous silica with large surface area. This investigation reports the effects of various conditions on the self-assembly process of silica including the duration and temperature of the hydrothermal treatment, the molar ratio of water to surfactant, gelation pH, and calcination temperature. Experimental results confirm that MCM-41 with a well-ordered mesostructure is synthesized in strongly basic conditions. These materials had pore structures ranging from 3 to 10 nm. The produced silica is free of sodium impurities and the purity is as high as 99.8 wt%. SEM reveals that the proposed process can be controlled to produce silica particles with various morphologies under acidic or basic media. TEM images clearly illustrate the hexagonal array of uniform meso-channels in the silica materials. The proposed method for synthesizing mesoporous MCM-41 using resin waste provides a viable alternative for recycling and utilizing silicon-containing industrial waste.Highlights► Electronic packaging resin waste is used as Si precursor. ► Cationic surfactant is a template for the self-assembly process of silica. ► Silica materials have pore structures ranging from 3 to 10 nm. ► MCM-41 shows well-ordered hexagonal mesostructure in strongly basic conditions. ► Recycling and utilizing silicon-containing industrial waste.
In the present study, two mesoporous aluminosilicate Al-MCM-41 materials (Si/Al = 30 or 50) were tested as catalysts for the in situ upgrading of biomass pyrolysis vapours in comparison to a siliceous MCM-41 sample and to non-catalytic biomass pyrolysis. The product yields and the quality of the produced bio-oil were significantly affected by the use of all MCM-41 catalytic materials. This behavior was mainly attributed to the combination of the large surface area and tubular mesopores (pore diameter ∼2–3 nm) of MCM-41 materials, with their mild acidity that leads to the desired environment for controlled conversion of the high molecular weight lignocellulosic molecules. The major improvement in the quality of bio-oil with the use of Al-MCM-41 catalytic materials was the increase of phenols concentration (useful chemicals) and the reduction of corrosive acids (undesirable in fuel bio-oils). Higher Si/Al ratios (i.e. lower Al content and lower number of acid sites) of the Al-MCM-41 samples enhanced the production of the organic phase of the bio-oil, while lower Si/Al ratios favoured the conversion of the hydrocarbons of the organic phase towards gases and coke. Moderate steaming of the Al-MCM-41 samples (at 550 and 750 °C, 20% steam partial pressure) decreased their surface area and number of acid sites by 40–60% depending on the Si/Al ratio of the samples and the steaming temperature. However, the steamed samples were still active in the in situ upgrading of biomass pyrolysis vapours, resulting in different product yields and bio-oil composition compared to the parent calcined samples, mainly after higher-temperature steaming.
Large particle MCM-41 was synthesized using preshaped silica gel as the silica source. The physical properties of MCM-41 samples were characterized by X-ray diffraction (XRD), nitrogen physisorption, and field emission scanning electron microscopy (FESEM). The sample showed highly ordered mesoporous structure and spherical morphology with particle sizes of 20–45 μm by pseudomorphic synthesis. The fluidization study showed that the MCM-41 with large particle size, for the first time, can be well fluidized because of the transformation from Geldart C to Geldart A classification. Furthermore, Co–Mo catalyst using large particle MCM-41 as support was successfully applied for the synthesis of single-walled carbon nanotubes (SWCNTs) in a fluidized-bed reactor. The product was monitored by thermogravimetric analysis (TGA), transmission electron microscopy (TEM), Raman and Fluorescence spectroscopy, which suggested the resulted semiconducting SWCNTs possess the narrow (n, m) distribution.