Approach to a pulse photoelectrocatalytic process for the degradation of organic pollutants

Ag–TiO₂ composite film was supported on indium–tin oxide glass (ITO) by a dip‐coating and subsequent photodeposition procedure. The composite film was employed as the photoanode for photoelectrocatalytic (PEC) degradation of Acid Orange II. The degradation efficiency for the PEC process on the Ag–TiO₂/ITO electrode with a 0.8 V anodic bias is significantly higher than that for a photocatalytic process on Ag–TiO₂/ITO film or for a PEC process on a neat TiO₂/ITO photoanode. A new PEC technology with a pulse anodic bias was also proposed in order to solve the problem of the loss of deposited Ag from the Ag–TiO₂/ITO. It was found that the PEC process with a 4.2 V pulse anodic bias could much more efficiently degrade Acid Orange II than that with a constant anodic bias of 0.8 V or 4.2 V. Moreover, when the duration of the open and close circuit time was identical, the treatment efficiency was observed to be optimal. Copyright © 2003 Society of Chemical Industry     

Radiation model of a TiO2‐coated,quartz wool,packed‐bed photocatalytic reactor

The radiation field of a packed‐bed photocatalytic reactor filled with quartz wool coated with titanium dioxide was modeled using the Monte Carlo technique and the following information: the radiation flux emitted by the lamps, the diameter size distribution of the quartz fiber cloth, the mass of quartz fibers and of TiO₂ that was immobilized on the fiber surface as well as the refractive index, and the spectral absorption coefficient of the materials of the system. Modeling predictions were validated with radiometer measurements of the transmitted radiation through the reactor, the root mean square error being <9.7%. Finally, by means of a parametric study, the validated model was used to analyze the effect of the design variables, such as the radii of the quartz fibers, thickness of the TiO₂ coatings, and amount of TiO₂‐coated quartz wool, on the distribution and nonuniformity of the radiative energy distribution inside the reactor. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

Temperature response to reactant concentration perturbations in a packed‐bed reactor

Unsteady‐state operations are known to enhance the performance of some packed‐bed reactor systems. However, negative effects of this type of operation should not be neglected. Temperature excursions developed during transients may accelerate some deactivation mechanisms, reducing catalyst lifetime and selectivity. Temperature response to perturbations in reactant concentration was studied for CO oxidation over Pt/Al₂O₃ in a packed‐bed reactor. Experiments were conducted in the CO concentration range for which multiple steady states are observed. Temperature and concentration profiles in the packed‐bed reactor at steady state were found to depend on the dynamic history of the reactor prior to the steady‐state condition.     

Simultaneous phenol removal and biological reduction of hexavalent chromium in a packed‐bed reactor

BACKGROUND: Phenol and hexavalent chromium are considered industrial pollutants that pose severe threats to human health and the environment. The two pollutants can be found together in aquatic environments originating from mixed discharges of many industrial processes, or from a single industry discharge. The main objective of this work was to study the feasibility of using phenol as an electron donor for Cr(VI) reduction, thus achieving the simultaneous biological removal/reduction of the two pollutants in a packed‐bed reactor. RESULTS: A pilot‐scale packed‐bed reactor was used to estimate phenol removal with simultaneous Cr(VI) reduction through biological mechanisms, using a new mixed bacterial culture originated from Cr(VI)‐reducing and phenol‐degrading bacteria, operated in draw–fill mode with recirculation. Experiments were performed for feed Cr(VI) concentration of about 5.5 mg L^?1, while phenol concentration ranged from 350 to 1500 mg L^?1. The maximum reduction/removal rates achieved were 0.062 g Cr(VI) L^?1 d^?1 and 3.574 g phenol L^?1 d^?1, for a phenol concentration of 500 mg L^?1. CONCLUSION: Phenol removal with simultaneous biological Cr(VI) reduction is feasible in a packed‐bed attached growth bioreactor. Phenol was found to inhibit Cr(VI) reduction, while phenol removal was rather unaffected by Cr(VI) concentration increase. However, the recorded removal rates of phenol and Cr(VI) were found to be much lower than those obtained from previous research, where the two pollutants were examined separately. Copyright © 2008 Society of Chemical Industry     

石墨负载TiO2薄膜电极光电催化降解甲基橙研究

采用溶胶-凝胶法制备石墨负载TiO2薄膜电极，以125W高压汞灯为光源，以负载TiO2薄膜的石墨片为工作电极，铂电极为对电极，饱和甘汞电极为参比电极，建立三电极的光电催化体系，以甲基橙为降解对象．考察了初始浓度、涂敷层数、外加电压、通入空气对甲基橙降解速率的影响。研究表明，石墨是光催化剂良好的载体．外加电压可以促进光催化降解的效率，外加电压2V、涂敷3层、通入空气时对目标物质的降解效果最好。     

CO2 reduction with Zn particles in a packed‐bed reactor

A two‐step solar thermochemical cycle for splitting CO₂ with Zn/ZnO redox reactions is considered, consisting of: (1) the endothermic dissociation of ZnO with concentrated solar radiation as the heat source and (2) the non‐solar, exothermic, reduction of CO₂ to CO by oxidizing Zn to ZnO; the latter is recycled to the first step. The second step of the cycle is investigated using a packed‐bed reactor where micron‐sized Zn particles were immobilized in mixtures with submicron‐sized ZnO particles. Experimental runs were performed for Zn mass fractions in the range 67–100 wt % and CO₂ concentration in the range 25–100%, yielding Zn‐to‐ZnO conversions up to 71% because of sintering prevention, as corroborated by SEM analysis. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

纳米TiO2光电催化降解工业废水技术研究进展

纳米TiO2光电催化技术,能有效减少太阳能光催化降解工业废水反应中光生电子与光生空穴的复合,提高量子利用率,从而大幅度提高光催化效率。简要介绍了纳米TiO2光电催化技术机理和应用该技术处理工业废水的技术特点;综述了二维纳米TiO2光电催化体系、三维纳米TiO2光电催化体系、分隔式纳米TiO2光电催化体系,以及矿物担载纳米TiO2光电催化体系等在国内外的研究进展;展望了纳米TiO2光电催化技术降解工业废水的应用前景。     

光催化降解活性染料K-GL的动力学及其盐效应

以分散态纳米TiO2为光催化剂,在鼓泡流化床光催化反应器中对活性翠兰K-GL染料溶液进行光催化降解实验研究。通过改变光催化剂投入量、染料溶液的初始浓度和Na2SO4与NaCl的掺加,探讨了影响光催化降解K-GL的因素,运用Langrmuir-Hinshelwood动力学方程对染料降解动力学规律进行了研究。结果表明,TiO2光催化降解活性翠兰K-GL的反应遵循准一级反应动力学方程,且表观反应速率表常数随活性翠兰溶液初始浓度的升高而降低;反应的催化剂最佳投入量为0.122g/L;光催化体系中的Na2SO4对于染料K-GL的降解表现出明显的促进作用,在较低浓度下,Na2SO4的最佳添加量为0.104mol/g,且随着其浓度的升高,表观反应速率常数随之增大;而掺加不同浓度的NaCl对光催化降解K-GL有抑止作用。     

Application of chitosan‐entrapped β‐galactosidase in a packed‐bed reactor system

The model enzyme β‐galactosidase was entrapped in chitosan gel beads and tested for hydrolytic activity and its potential for application in a packed‐bed reactor. The chitosan beads had an enzyme entrapment efficiency of 59% and retained 56% of the enzyme activity of the free enzyme. The Michaelis constant (K_m) was 0.0086 and 0.011 μmol/mL for the free and immobilized enzymes, respectively. The maximum velocity of the reaction (V_max) was 285.7 and 55.25 μmol mL^?1 min^?1 for the free and immobilized enzymes, respectively. In pH stability tests, the immobilized enzyme exhibited a greater range of pH stability and shifted to include a more acidic pH optimum, compared to that of the free enzyme. A 2.54 × 16.51‐cm tubular reactor was constructed to hold 300 mL of chitosan‐immobilized enzyme. A full‐factorial test design was implemented to test the effect of substrate flow (20 and 100 mL/min), concentration (0.0015 and 0.003M), and repeated use of the test bed on efficiency of the system. Parameters were analyzed using repeated‐measures analysis of variance. Flow (p < 0.05) and concentration (p < 0.05) significantly affected substrate conversion, as did the interaction progressing from Run 1 to Run 2 on a bed (p < 0.05). Reactor stability tests indicated that the packed‐bed reactor continued to convert substrate for more than 12 h with a minimal reduction in conversion efficiency. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1294–1299, 2004     

Photocatalytic degradation of gaseous trichloroethene using immobilized ZnO/SnO2 coupled oxide in a flow‐through photocatalytic reactor

The photocatalytic degradation of gaseous trichloroethene (TCE) was investigated on immobilized ZnO/SnO₂ coupled oxide in a flow‐through photocatalytic reactor. It was found that gaseous photocatalysis is an efficient method for volatile organic compounds' abatement and air purification. Degradation of ～100% was found for TCE at the concentrations examined, up to 400 ppmv, in a flow‐through dry synthetic gas stream. In our tested conditions, the flow rate had little influence on the photocatalytic degradation efficiencies of TCE, while the relative humidity had a significant influence on the photocatalytic degradation of TCE. The photocatalytic degradation efficiencies of TCE increased slowly below 20% relative humidity and then decreased as the relative humidity increased further. The deactivation of used immobilized photocatalyst was not observed within the 200 h testing period in the present experiment, although the surface of the photocatalyst changed greatly during the use of the photocatalyst. Copyright © 2004 Society of Chemical Industry     

Continuous lipase‐catalyzed synthesis of hexyl laurate in a packed‐bed reactor: optimization of the reaction conditions in a solvent‐free system

BACKGROUND: Hexyl laurate has been applied widely in cosmetic industries and is synthesized by chemical methods with problems of cost, environmental pollution, and by‐products. In this study, Lipozyme^® IM77 (from Rhizomucor miehei) was used to catalyze the direct‐esterification of hexanol and lauric acid in a solvent‐free system by utilizing a continuous packed‐bed reactor, wherein the aforementioned difficulties could be overcome. Response surface methodology (RSM) and three‐level‐three‐factor Box‐Behnken design were employed to evaluate the effects of synthesis parameters, such as reaction temperature (45–65 °C), mixture flow rate (0.25–0.75 mL min^?1) and concentration of lauric acid (100–300 mmol L^?1) on the production rate (µmol min^?1) of hexyl laurate by direct esterification. RESULTS: The production rate was affected significantly by the mixture flow rate and lauric acid concentration. On the basis of ridge‐max analysis, the optimum synthesis conditions for hexyl laurate were as follows: 81.58 ± 1.76 µmol min^?1 at 55 °C, 0.5 mL min^?1 flow rate and 0.3 mol L^?1 lauric acid. CONCLUSION: The lipase‐catalyzed synthesis of hexyl laurate by Lipozyme^® IM‐77 in a continuous packed‐bed bioreactor and solvent‐free system was successfully developed; optimization of the reaction parameters was obtained by Box–Behnken design and RSM. Copyright © 2008 Society of Chemical Industry     

Optimization of inulinase production by solid‐state fermentation in a packed‐bed bioreactor

BACKGROUND: This work is focused on inulinase production by solid‐sate fermentation (SSF) using sugarcane bagasse, corn steep liquor (CSL), pre‐treated cane molasses, and soybean bran as substrates in a 3‐kg (dry basis) packed‐bed bioreactor. SSF was carried out by the yeast Kluyveromyces marxianus NRRL Y‐7571 and response surface methodology was used to optimize the temperature, air flow rate and initial mass of cells. RESULTS: The optimum inulinase activity (436.7 ± 36.3 U g^?1 dry substrate) was obtained at 24 h at an inlet air temperature of 30 °C, air flow rate 2.2 m³ h^?1 and 22 g of cells for fermentation. Inulinase productivity at these conditions was 18.2 U gds^?1 h^?1. Kinetic evaluation at the optimized conditions showed that the maximum inulinase production was verified at 24 h of fermentation. The carbon dioxide and the metabolic heat generation are directly associated with the consumption of total reducing sugars present in the medium. CONCLUSION: The high productivity achieved in this work shows the technical viability of inulinase production by SSF in a packed‐bed bioreactor. Copyright © 2009 Society of Chemical Industry     

Continuous biotransformation of pyrogallol to purpurogallin using cross‐linked enzyme crystals of laccase as catalyst in a packed‐bed reactor

Cross‐linked enzyme crystals (CLEC) of laccase were prepared by crystallizing laccase with 75% (NH₄)₂SO₄ and cross‐linking using 1.5% glutaraldehyde. The cross‐linked enzyme crystals were further coated with 1 mmol L^?1 β‐cyclodextrin by lyophilization. The lyophilized enzyme crystals were used as such for the biotransformation of pyrogallol to purpurogallin in a packed‐bed reactor. The maximum conversion (76.28%) was obtained with 3 mmol L^?1 pyrogallol at a residence time of 7.1 s. The maximum productivity (269.03 g L^?1 h^?1) of purpurogallin was obtained with 5 mmol L^?1 pyrogallol at a residence time of 3.5 s. The productivity was found to be 261.14 g L^?1 h^?1 and 251.1 g L^?1 h^?1 when concentrations of 3 mmol L^?1 and 7 mmol L^?1 respectively were used. The reaction rate of purpurogallin synthesis was maximum (2241.94 mg purpurogallin mg^?1 CLEC h^?1) at a residence time of 3.5 s, when 5 mmol L^?1 pyrogallol was used as the substrate. The catalyst to product ratio calculated for the present biotransformation was 1:2241. The CLEC laccase had very high stability in reuse and even after 650 h of continuous use, the enzyme did not lose its activity. Copyright © 2006 Society of Chemical Industry     

Kinetic study of the manganese‐based catalytic hydrogen peroxide oxidation of a persistent azo‐dye

BACKGROUND: The discharge of synthetic dyes by the textile industry into the environment poses concerns due to their persistence and toxicity. New efficient treatment processes are required to effectively degrade these dyes. The aim of this work was to study the degradation of a persistent dye (Drimarene Brilliant Reactive Red K‐4BL, C.I.147) using H₂O₂ oxidation catalysed by an Mn(III)‐saltren catalyst and to develop a kinetic model for this system. RESULTS: Dye oxidation with H₂O₂ was significantly improved by the addition of the catalyst. As the pH was increased from 3 to 10, the oxidation rates increased significantly. The kinetic model developed in this study was found to adequately explain the experimental results. In particular, dye oxidation can be described at high pH by pseudo‐first‐order kinetics. A Michaelis–Menton type equation was developed from the model and was found to adequately describe the effect of H₂O₂ and catalyst concentrations on the apparent pseudo‐first‐order rate constant. Optimum catalyst and H₂O₂ concentrations of 500 mg L^?1 and 6.3 g L^?1, respectively, were found to give maximum reaction rates. CONCLUSION: Catalytic H₂O₂ oxidation was found to be effective for the removal of persistent dye and the results obtained in this work are of significance for design and scale‐up of a treatment process. Copyright © 2009 Society of Chemical Industry     

Production of structured triacylglycerols in an immobilised lipase packed‐bed reactor: batch mode operation

Structured triacylglycerols with caprylic acid at the sn‐1 and sn‐3 positions of the glycerol backbone and eicosapentaenoic acid (EPA) at the position sn‐2 were synthesised by acidolysis of a commercially available EPA‐rich oil (EPAX4510, Pronova Biocare) and caprylic acid catalysed by the 1,3‐specific immobilised lipase Lipozyme IM. The reaction was carried out in an immobilised lipase packed‐bed reactor by recirculating the reaction mixture through the bed. The exchange equilibrium constants between caprylic acid and the native fatty acids of EPAX4510 were determined. The n‐3 polyunsaturated fatty acids (PUFAs), EPA and docosohexaenoic acid (DHA), were the most easily displaced by the caprylic acid. The exchange equilibrium constants were 3.68 and 3.06 for EPA and DHA, respectively. The influence of the flow rate of the reaction mixture through the packed‐bed and the substrate concentration in the reaction rate were studied. For flow rates between 74 and 196 cm³ h^?1 (bed of 6.6 mm internal diameter and 0.46 porosity) and triacylglycerol concentrations between 0.036 and 0.108 M , the data fitted well to an empirical kinetic model which allowed representative values of the apparent kinetic constant to be obtained. Hence, the average reaction rates and kinetic constants of exchange of caprylic acid and native fatty acids of EPAX4510 could be calculated. In the conditions indicated, the parameter (lipase mass × time/triacylglycerol mass, m_Lt/V[TG]₀) constituted the intensive variable of the process for use in predicting the composition of structured triacylglycerols at different reaction times. At equilibrium, the structured triacylglycerol produced had the following composition: caprylic acid 59.5%, EPA 9.6%, DHA 2.2% and oleic acid 11.8%. Copyright © 2004 Society of Chemical Industry     

三相流化床光催化氧化活性红紫X-2R的研究

活性红紫X-2R是一种偶氮型活性染料.本文采用P25型TiO2催化剂,在三相流化床光催化反应器中对活性红紫X-2R染料废水进行光催化降解研究.实验结果表明,催化剂TiO2投加量为1.0g·L-1,溶液pH值为中性时,溶液初始浓度越低,空气流量越大,活性红紫X-2R去除效果越好.     

The degradation of an azo dye in a batch slurry photocatalytic reactor

The photocatalytic degradation of a commercial azo-reactive textile dye, Remazol Red F-3B, has been investigated in a batch slurry reactor using semiconductor catalysts like, ZnO and TiO₂, and two UV sources emitting mainly at 254 and 365 nm. Non-irradiated catalysts and non-catalyzed UV irradiation have negligible effect on the dye degradation. Initial pH, dye concentration, light power and catalyst loading as well as the catalyst type and UV wavelength are considered as process variables. The results showed that decolorization and TOC removal efficiencies of ZnO are higher under 365 nm UV. On the other hand, when two photocatalysts are compared, the decolorization performance of ZnO is higher than TiO₂ under 365 nm UV_, while TiO₂ performs better under 254 nm UV. Furthermore, from the TOC removal point, TiO₂ performs better than ZnO irrespective of the UV wavelength. TiO₂ irradiated under 254 nm UV degrades successfully both benzene and naphthalene derivatives.