Copyright (c) 2009 Berkeley Electronic Press All rights reserved. http://www.bepress.com/ijcre Recent documents in International Journal of Chemical Reactor Engineering en-us Fri, 06 Nov 2009 23:22:13 PST 3600 http://www.bepress.com/ijcre/vol7/A54 http://www.bepress.com/ijcre/vol7/A54 Thu, 05 Nov 2009 09:51:05 PST A series of high surface area (~700 m2/g) nanostructured coupled semiconductor photocatalysts (NCSP) based on transition metals (M = Cr, V) doped titania-silica aerogel of various molar ratios of Ti:Si (1:25, 1:33 and 1:50) were synthesized via direct synthesis and wet impregnation methods. All samples reveal well-dispersed TiO2 with three different types of Ti coordination namely isolated Ti, non-isolated Ti and octahedrally coordinated Ti species. Cr and V (5 wt%)-titania silica aerogel under visible light irradiation reduced the bandgap energy of T25 to 2.9 eV. The photocatalytic activity of NCSP is 3 fold more active than photocatalyst supported on amorphous silica. Cr (5 wt%)-titania silica aerogel photocatalyst gives the highest conversion of styrene under both UV and visible light irradiation (55% and 47% respectively). Halimaton Hamdan catalysis http://www.bepress.com/ijcre/vol7/A53 http://www.bepress.com/ijcre/vol7/A53 Wed, 04 Nov 2009 14:42:58 PST The production of Substitute Natural Gas from biomass (Bio-SNG) is an attractive option to reduce CO2 emissions and replace declining fossil natural gas reserves. The Energy research Center of the Netherlands (ECN) is working on the development of a technology to convert a wide range of biomass into Bio-SNG. The ECN Bio-SNG technology is based on indirect gasification of biomass. The MILENA indirect gasifier is developed to produce a gas, which can be upgraded into SNG with a high efficiency. Because of the indirect heating of the gasification process, no air separation is required. Char and tar are removed from the producer gas and are used as fuel to produce the required heat for the gasification process. The OLGA tar removal technology is used to remove tar and dust from the gas. After gas cleaning, the gas is catalytically converted into a mixture of CH4, CO2 and H2O. After compression and removal of CO2 and H2O, the remaining methane can be used as Bio-SNG. ECN produced the first Bio-SNG in 2004, using a conventional fluidized bed gasifier. The lab-scale MILENA gasifier was built in 2004. The installation is capable of producing approximately 8 Nm3/h methane-rich medium calorific gas with high efficiency. The lab-scale installation has been in operation for more than 1000 hours now and is working fine. Several biomass fuels were tested. Woody biomass appears to be the most suited fuel. The lab-scale gasifier is coupled to lab-scale gas cleaning installations (including OLGA) and a methanation unit. The integrated system was tested during several duration tests. The 30 kWth lab-scale gasifier was scaled up to 800 kWth biomass input. ECN has recently finished the construction of this pilot-scale gasifier, which has been taken into operation in the summer of 2008. First results, using wood as a fuel, show that the gas composition is similar to gas from the lab-scale installation. The pilot scale gasifier will be coupled to the existing pilot scale OLGA gas cleaning unit in 2009. Tests with the pilot-scale MILENA and OLGA will form the basis of a 10 MW MILENA - OLGA - gas engine demonstration plant. This demonstration will be taken into operation in 2012 and will be followed by a large SNG demonstration. 10 MW biomass input is seen as an attractive commercial scale for combined heat and power production from biomass. The scale foreseen for a commercial single-train Bio-SNG production facility is between 50 and 500 MWth. The expected net overall efficiency from wood to Bio-SNG is 70%. Christiaan M. van der Meijden new chemical reactor concepts http://www.bepress.com/ijcre/vol7/A52 http://www.bepress.com/ijcre/vol7/A52 Wed, 04 Nov 2009 14:42:55 PST In this work, modeling of a catalyst pellet (uniform, non-uniform) for Fischer-Tropsch Synthesis (FTS) is studied. Under FTS conditions the pores of catalyst pellet are filled with heavy hydrocarbons leading to transport restrictions through the pellet. On the other hand, the active materials used as catalysts are often expensive metals dispersed on large-surface area supports. In order to understand the catalyst behavior aiming to improve its performance parameters such as effectiveness factor and yield modeling of a catalyst pellet with various types of non-uniform activity distributions are examined. The models were solved by OCFE method at non-isothermal conditions. Moreover, a parametric sensitivity analysis has been carried out to compare the effects of various non-uniform activity distributions, the pellet size, the feed composition and the temperature on the performance of the catalyst. Hadis Zarrin Modeling Catalyst http://www.bepress.com/ijcre/vol7/A51 http://www.bepress.com/ijcre/vol7/A51 Wed, 04 Nov 2009 14:42:49 PST The need for green renewable sources is adamant because of the adverse effects of the increasing use of fossil fuels on our society. Biomass has been considered as a very attractive candidate for green energy carriers, chemicals and materials. The development of cheap and efficient fractionation technology to separate biomass into its main constituents is highly desirable. It enables treatment of each constituent separately, using dedicated conversion technologies to get specific target chemicals. The synergistic combination of aquathermolysis (hot pressurised water treatment) and pyrolysis (thermal degradation in the absence of oxygen) is a promising thermolysis option, integrating fractionation of biomass with production of valuable chemicals. Batch aquathermolysis in an autoclave and subsequent pyrolysis using bubbling fluidised bed reactor technology with beech, poplar, spruce and straw indicate the potential of this hybrid concept to valorise lignocellulosic biomass. Hemicellulose-derived furfural was obtained in yields that ranged from 2 wt% for spruce to 8 wt% for straw. Hydroxymethylfurfural from hemicellulose was obtained in yields from 0.3 wt% for poplar to 3 wt% for spruce. Pyrolysis of the aquathermolised biomass types resulted in 8 wt% (straw) to 11 wt% (spruce) of cellulose-derived levoglucosan. Next to the furfurals and levoglucosan, appreciable amounts of acetic acid were obtained as well from the aquathermolysis step, ranging from 1 wt% for spruce to 5 wt% for straw. To elucidate relations between the chemical changes occurring in the biomass during the integrated process and type and amount of the chemical products formed, a 13C-solid state NMR study has been conducted. Main conclusions are that aquathermolysis results in hemicellulose degradation to lower molecular weight components. Lignin ether bonds are broken, but apart from that, lignin is hardly affected by the aquathermolysis. Cellulose is also retained, although it seems to become more crystalline, probably due to a higher ordering of amorphous cellulose when the samples are cooled down after aquathermolysis. These NMR results are in agreement with thermogravimetric analyses results. Paul J. de Wild Biorefineries Thermochemical Processing of Biomass http://www.bepress.com/ijcre/vol7/A50 http://www.bepress.com/ijcre/vol7/A50 Wed, 04 Nov 2009 14:42:44 PST The efficiency of liquid/liquid dispersion is an important sake in numerous sectors, such as the chemical, food, cosmetic and environmental industries. In the present study, dispersion is achieved in an open-loop reactor consisting of simple curved pipes, either helically coiled or chaotically twisted. In both configurations, we investigate the drop breakup process of two immiscible fluids (W/O) and especially investigate the effect of the continuous phase viscosity, which is varied by the addition of different fractions of butanol in the native sunflower oil. The global Reynolds numbers vary between 40 and 240, so that the flow remains laminar while the Dean roll-cells in the bends develop significantly. Different fractions of butanol are added to the oil in each case to examine the influence of the continuous phase viscosity on the drop size distribution of the dispersed phase (water). When the butanol fraction is decreased, the dispersion process is intensified and smaller drops are created. The Sauter mean diameters obtained in the chaotic twisted pipe are compared with those in a helically coiled pipe flow. The results show that chaotic advection intensifies the droplet breakup until there is a 25% reduction in droplet size. Charbel Habchi Chemical reactors multifunctional heat exchanger-reactors http://www.bepress.com/ijcre/vol7/S2 http://www.bepress.com/ijcre/vol7/S2 Wed, 04 Nov 2009 13:18:42 PST Surfactants can increase the low rate of heterogeneous liquid-liquid reactions involving partially miscible substrates through formation of micelles. This is a direct consequence of higher solubilization of substrates by micelles in reaction zones. In this case, rate enhancement of NaOH (base) catalyzed hydrolysis of ethyl acetate was studied. Micelles by cationic surfactant tetradecyl trimethyl ammonium bromide (TTAB) made the rate enhancement. In the presence of NaOH, CMC (critical micellar concentration) of TTAB decreases from its original value and attains the value of 2.97 × 10-4 M. In the absence of TTAB, the second order rate constant increases linearly with temperature. The hydrolysis reaction follows second order kinetics at different temperatures in the presence of different concentrations of TTAB. For a particular temperature, on addition of TTAB beyond CMC, rate constant first increases sharply and then becomes almost constant. At TTAB concentration of 1.485 × 10-3 M, rate constant attains maximum value (2.65 times of rate constant without TTAB) and then it becomes almost constant. The applied model successfully explains change in rate constant due to incorporation of micelles by the addition of TTAB. This model involves certain assumptions like one substrate molecule is solubilized in one micelle; substrate molecule doesn't form a complex with monomer of surfactant; and no competitive inhibition occurs during reaction. Correlations between bulk phase rate constant (k0), micellar phase rate constant (km) and temperature (T) are incorporated into the model for this particular system. Debajyoti Goswami Micellar Catalysis http://www.bepress.com/ijcre/vol7/A49 http://www.bepress.com/ijcre/vol7/A49 Wed, 04 Nov 2009 13:02:23 PST It is well known that the catalytic characteristics of perovskites for various redox reactions depend primarily on the preparation procedure. The conventional method for perovskite preparation, the so-called "ceramic method," involves a calcination step with a temperature of at least 800 oC, resulting in large grain size and low specific surface area (usually several m2/g). Recently, a new method for perovskite preparation designated as reactive grinding has been proposed by our group, generating a large variety of perovskites at room temperature with extraordinarily high specific surface areas on the order of 100 m2/g when grinding additives are used. Additionally, this novel technology is favorable to yield perovskites with an abundant deficiency structure simultaneously with a nanosized crystallite domain. Series of La(Co, Mn)1-x(Cu)xO3 perovskites were prepared by reactive grinding and characterized by XRD, O2-TPD, and H2-TPR showing anion deficiency (O2 vacancy) in lanthanum cobaltites and cation deficiency (O2 excess) in lanthanum manganites. These samples were thereafter used for catalytic purification of NO, CO and soot pollutants coming from an automobile. For NO reduction by CO, a better catalytic performance was found over LaCoO3 compared to LaMnO3. The deNOx activity of LaCoO3 can be considerably improved via 20% Cu substitution, leading to a 97% N2 yield and nearly complete CO conversion at 450 oC. This improvement was ascribed to the ease of generation of anion deficiencies after Cu incorporation, which plays a crucial role in NO adsorption and dissociation. A mechanism was proposed with dissociation of chemisorbed NO upon oxygen vacancies forming N2 and/or N2O, and oxidized perovskite surface, with continuous reduction by CO with the production of CO2. For soot combustion, the better activity was observed again in the case of LaCoO3 with respect to LaMnO3. A mechanism was proposed with an attack of soot by O- species which immigrates from the perovskite surface. Cation deficiency of lanthanum manganites associates with overstoichiometric oxygen from the perovskite lattice, which can be only utilized for an oxidation process but less active compared to molecular oxygen formed upon anion vacancies. In summary, the anion deficiency of perovskite-typed oxides seems to make more contribution for both NO reduction and soot oxidation in comparison with cation deficiency. Runduo Zhang Environmental Catalysis http://www.bepress.com/ijcre/vol7/A48 http://www.bepress.com/ijcre/vol7/A48 Sat, 31 Oct 2009 11:09:01 PDT Hydrogen sulphide (H2S) is one of the main odor causing, toxic, and corrosive chemicals found in wastewater treatment, pulp and paper and several other industries. One of the main challenges of winter operation of biofilters for H2S removal is to deal with the heat effects of biofiltration process. During winter lower air temperature, snow fall on biofilter vessels and moisture condensation in air ducts decrease percent removal of H2S significantly. In this work, laboratory and field data that are collected during winter operation of biofilters are analyzed and presented. The results demonstrate that temperature within the biofilter should be maintained at a minimum of 15°C to avoid lower percent removal or odor breakthrough resulting from untreated H2S emissions in the air. It was found that heat input to the incoming air by steam addition easily remedy the problem. Zarook M. Shareefdeen biotechnology http://www.bepress.com/ijcre/vol7/R4 http://www.bepress.com/ijcre/vol7/R4 Sat, 31 Oct 2009 11:08:41 PDT There has been tremendous development within mixing operations in industry. Incomplete knowledge of this process caused serious economic losses to process industries. For optimum yields and the economic potential that goes with better understanding of mixing, research in this field continues to grow. The major forms of mixing in industry are either by mechanical or pneumatic agitation. Airlift bioreactors achieve mixing through pneumatic agitation and have gained attention over two decades for their fluid dynamic characteristics and low power consumption. It has been widely applied in bioprocess industries for production of biochemicals, to wastewater treatment in which the performance of this reactor has been overwhelming with respect to its production levels as compared to the conventional mechanical agitation.In this review, mixing through mechanical and pneumatic agitation is compared. An extensive literature is distilled from various investigators on the hydrodynamics and mixing characteristics of airlift bioreactors. This review has emphasis on factors that affect mixing such as the geometrical parameters of the vessel, gas flow rate, properties of the liquid medium, sparger design and measuring techniques employed. In an attempt to understand process related issues, sophisticated advances in the measuring techniques provides more insight into mixing in this reactor. Thus extensive correlations have been proposed by various investigators to predict the hydrodynamic and mixing parameters. Some design modifications proposed by several scholars have also been reviewed. Farouza Gumery Bioreactor deisgn http://www.bepress.com/ijcre/vol7/A47 http://www.bepress.com/ijcre/vol7/A47 Thu, 29 Oct 2009 06:51:14 PDT This article presents ultrasound assisted carbonization method for the synthesis of calcium carbonate nanoparticles (nano calcite). The effect of different surfactants, such as polyacrylic acid, steric acid, sodium tripolyphosphate and myristic acid, on the synthesis of nano CaCO3 was investigated. Concentration of surfactants ranged from 0.2-1.0g/L. X-ray diffraction patterns (XRD) confirmed cubic structure of nano CaCO3 showing characteristic reflection of calcite phase. Transmission electron microscopy (TEM) images showed that the particles are cubical in nature. The use of an ultrasound probe during synthesis leads to narrow distribution of particles. The conductivity and pH value of reaction mixture was measured during the reaction. The time required for the completion of reaction changes with different surfactants was also found. The crystallite size was found to be dependent on surfactant concentration. The minimum time was noted for sodium tripolyphosphate which was 40 min. The crystallite size was found to increase as per the trail sequence of the surfactant, sodium tripolyphosphate, steric acid and polyacrylic acid, myristic acid. The myristic acid shows the biggest crystallite size due to its hydrophobic nature, while sodium tripolyphosphate plays an important role in crystal growth inhibition giving lower crystallite size. Finally, the results presented here demonstrate that nano-calcite crystals can be synthesized, for high potential industrial applications such as filler in the paper and polymer industry. Shirish H. Sonawane Nanotechnology Sonochemistry