Batch sedimentation is considered in the case where there is no flocculation and no aggregation. In contrast to the Kynch theory and its extensions, the present treatment uses a similarity solution instead of the method of characteristics. The results are compared with previous theoretical findings. Instead of using quartic and cubic solids flux curves as in the literature, application is made to the most widely used two-parameter Richardson and Zaki solids-flux function.
Immobilized metal ion affinity gel is a regenerable carrier used in separation technique on the basis of a reversible interaction between the gel and a specific transition metal ion as a ligand. An experimental investigation concerning the development of an immobilized metal ion affinity gel and the adsorption and desorption properties of metal ions was carried out by using a Chelating Sepharose Fast Flow gel and divalent transition metal ions of Co2+ and Ni2+. In order to characterize and predict metal ion adsorption and desorption completely, one seeks the information about the adsorption isotherms and the necessary physical parameters for adsorption and desorption along with their mechanisms. In this experimental investigation it is considered that the two –CH2COOH groups in the gel combine with metal ions stoichiometrically and the adsorption and desorption mechanisms of the metal ions onto and from the gel are theoretically analyzed on the basis of adsorption and desorption equilibriums and the dissociation equilibrium. Consequently, the model equations, which allow quantitative consideration of the adsorption and desorption mechanisms, can be derived as a function of the concentration of hydrogen ions at the outer aqueous phase. The values of adsorption effectiveness factor were calculated as 0.87 for Co2+ and 0.90 for Ni2+. Finally, the gel adsorption isotherm and the adsorption, desorption equilibriums of metal ions can be explained fairly well by these models.
To investigate the influence of ‘single-file’ diffusion on nonequilibrium transport phenomena inside zeolite nanopores, we calculated permeate velocities of guest species in AFI-type AlPO4-5 and MFI-type silicalite membranes, using a grand canonical ensemble molecular dynamics (GCMD) simulation. We chose as examples He/CH4 and CH4/SF6 mixtures through AlPO4-5, and CH4/CF4 mixtures through silicalite. In AlPO4-5 systems, He permeates much faster than CH4 in an He/CH4 mixture, whereas CH4 moves at nearly the same speed as SF6 in the CH4/SF6 mixture. In CH4/CF4 mixtures in silicalite, the permeate velocity of each component becomes close to each other, compared with that of pure gas. These results suggest that ‘single-file’ permeation occurs where one guest species cannot overtake the other inside nanopores under a concentration gradient, especially if at least one component has a molecular diameter similar to the host pore size. Moreover, the calculated separation factor for CH4/CF4 mixtures through silicalite showed a strong correlation with the permeate velocities of the guest species, suggesting the influence of ‘single-file’ permeation on the absolute values of the separation factor. Particularly, it is concluded that the decrease in CH4 permeate velocities directly leads to the decrease in the separation factors, compared with ideal separation factors. Finally, using these data from GCMD simulations and other molecular simulation techniques, we propose a methodology to predict transport diffusivities in binary mixtures. In this paper, the transport diffusivities of CH4/CF4 mixtures in silicalite were calculated based on Maxwell–Stefan (MS) theory. Further efforts to achieve the systematic estimation of these transport diffusivities will lead to the prediction of multicomponent separation factors using only single-component data.
Packed bed reactors using metal hydride are attracting a lot of attention as potential future hydrogen storage systems, actuators, etc. However, their low effective thermal conductivities lead to low performance. In this study, carbon fiber brush with high thermal conductivity was installed in a reactor to improve the effective thermal conductivity. We found that the carbon fiber brush at 1.0 vol% reduced the reaction time by 30%. A two-dimensional mathematical model describing the heat and mass transfer was developed to predict the thermal performance. Expansion of particles due to absorption is also considered in this model. The model was compared with the experimental results, and it predicted the time variations of the averaged reacted fraction and local reactor temperature very well. The model suggests that heat transfer rather than mass transfer controls the overall reaction.
In order to improve the catalytic activity of magnesium ortho-vanadate (Mg3V2O8) for the oxidative dehydrogenation of propane, Mg3V2O8 doped with Fe3+ (Fe–Mg3V2O8) was prepared. The improvement of the conversion of propane from 4.8% on Mg3V2O8 to 8.2% on 5% Fe–Mg3V2O8 together with the rather similar selectivity to propylene on un-doped and doped catalysts (62.3 and 61.0%, respectively). To evaluate the redox nature of Fe–Mg3V2O8 during the oxidative dehydrogenation, the catalysts used for the conversion of propane with and without gaseous oxygen were analyzed by XRD, solid state 51V MAS NMR, XAFS, and XPS. After the propane conversion without oxygen, complete conversion of Fe–Mg3V2O8 to Mg2VO4 and MgO together with a small amount of Fe2O3 was observed by XRD, while the reduction of V5+ to V4+ was detected by 51V MAS NMR and V K-edge XAFS from the catalyst. However XPS analysis showed that such a reduction was not observed over the surface of Fe–Mg3V2O8 since oxygen was supplied from bulk to the surface of the catalyst to keep V5+ over the surface. After the treatment of the reduced catalysts with gaseous oxygen, the complete regeneration of Fe–Mg3V2O8 from the reduced phase was confirmed by those analyses.
Calcinations of a tantalum-O–phenylene-O hybrid copolymer under an argon atmosphere have been found to give nano-sized tantalum oxide-carbon clusters composite material. ESR spectral examinations of the composite material suggest that the electron transfer from the tantalum oxide particles to the carbon clusters took place to raise a visible-light responsive function with an oxidation site in the tantalum oxide particle and a reduction site in the carbon cluster.
By utilizing a microreactor, extraction of ethyl ester of docosahexaenoic acid (DHA-Et) and eicosapentaenoic acid (EPA-Et) from an organic solution into an aqueous silver nitrate solution has been investigated. Slug flow preapared by using a T-shape microreactor was used to extract DHA-Et and EPA-Et. Utilizing slug flow created large specific interfacial area between aqueous and organic phases, and ultra fast extraction has been achieved. Extraction of both DHA-Et and EPA-Et took less than 20 s to reach equilibrium. In all of the experiments, the amount of DHA-Et or EPA-Et extracted was the same to that expected from the batch experiment. These facts indicate that the microreactor system can realize an ultra-fast examination system of extraction equilibrium. In addition, by maintaining the temperature quite low, a drastic improvement of extraction ratio is exhibited under a low silver nitrate concentration condition. That is, it can easily cut down silver nitrate by utilizing a microreactor. This is preferable for the practical operation.
In order to enhance the decomposition performance of a small sonoreactor, a metallic reflection plate was placed in a liquid. The material, placement position and diameter of the reflection plate were changed. The reaction field was observed to be produced below the reflection plate, and became stronger with increasing reflectivity of the reflection plate. The placement position and diameter of the reflection plate had the optimal values for the decomposition performance, and the decomposition performance was enhanced by about 20% at the optimum condition.
The effect of liquid height on chemical reactions induced by sonication was investigated under a low frequency of 44.3 kHz using a large-scale parallelepiped sonochemical reactor. The experiments were conducted with the liquid height of 87 to 592 mm, which were equivalent to the sample volumes of about 18–80 dm3. The effect of the liquid height was evaluated by calorimetry and potassium iodide (KI) dosimetry. The results demonstrated that there existed an optimum liquid height to enhance sonochemical reactions in the large-scale sonochemical reactor. As a result, it was found that the sonochemical efficiency of the large-scale sonochemical reactor was much higher than that of the laboratory-scale sonochemical reactor below 0.2 dm3 in the sample volume reported previously.
The influence of salinity, carbon and nitrogen sources of growth media on the production of microbial docosahexaenoic acid (DHA) by Schizochytrium sp. was investigated. The obtained results indicated that the strain Schizochytrium sp. showed a wide tolerance to salinity, that is, the optimum salinity was between 50 and 200% in respect to the salt concentration of seawater. Glucose and fructose were the most suitable carbon sources for cell growth as well as DHA accumulation. The mixed-organic nitrogen source led to more DHA yield than the single nitrogen source. Box–Behnken design and surface response methodology were employed to formulate the optimal medium. The optimized medium contained 126.20 g·L–1 glucose, 10.06 g·L–1 yeast extract, 2.06 g·L–1 corn steep liquor and 5.00 g·L–1 soy peptone in seawater at half salt concentration. The maximum biomass, total fatty acid and DHA yield reached 42.9, 34.1 and 13.8 g·L–1 on the optimized culture medium after 5 d of cultivation, respectively. Thus Schizochytrium sp. was proved to be a promising resource for microbial DHA production owing to its high level of productivity after medium optimization.
We successfully developed a new type of micromixer for instant mixing and rapid heating under high pressure and high temperature. The mixer has several distinguished features: the mixing within ten milliseconds, good insulation of heat, and high throughput. We confirmed these features by the examination of mixing experiments. Finally, we tried to produce bohmite nanoparticles by the super critical water reaction at 400°C in 30 MPa, and the fine particles the average diameter of which is ca. 20 nm were obtained. It is expected that the developed micromixer will be applied widely to various reactions that require severe reaction conditions.
The performance of passive direct methanol fuel cells employing porous plates in the anode backing was investigated under closed circuit conditions to clarify the mechanism of methanol diffusion through the porous plate under closed circuit conditions. Three kinds of porous plates were tested to clarify the effect of porosity and water absorptivity on the steady current density using various methanol concentrations. Under the limiting current conditions, where the steady current density was proportional to the methanol concentration, a porous plate with lower porosity lowered the stable current density at a certain methanol concentration. However, the maximum steady current density was hardly changed as compared to that for the case without a porous plate. The effective diffusion coefficient of methanol through the porous plate showed direct proportion to the porosity of the porous plate, suggesting that the entire pores in the plate were filled with CO2 gas produced at the anode surface, through which the methanol diffused as a vapor from the reservoir to the anode.
P(AM-ADE), a novel cationic polyelectrolyte, was N-(2-(acryloyloxy)ethyl)-N′-dodecyl-N,N,N′,N′-tetramethyl ethane-1,2-diaminium dibromide (ADE) copolymerized with acrylamide (AM) in inverse emulsion. The performances of activated sludge conditioned with this polyelectrolyte were investigated and evaluated with capillary suction time (CST), settling rate and water content in sludge cake after filtration. The floc morphological parameters (floc size and fractal dimension) and physical properties (sludge viscosity and zeta potential) were also measured. Compared with common conditioners TC-302 and TC-304, the synthesized polyelectrolyte has the properties of lower molecular weight, higher concentrated charge density and hydrophobically associative interaction due to the special structure of functional cationic monomers. The experimental results indicated that sludge conditioned with P(AM-ADE) could retain less water content in filtrated cake and form relatively more compact flocs. Furthermore, a multilayer adsorption and lower molecular weight resulted in less chance of overdosing. However, more dosage was required to obtain the satisfactory flocculation effect when the P(AM-ADE) was used as sludge conditioner.
The understanding of biological systems has been developed to the point that they can be manufactured. The application of core skills of chemical engineering is being increasingly recognized as of valuable in further advancement of biological systems. To sustain the leading role in the industry, chemical engineers must be familiar with the methods available to create, analyze and manipulate biological molecules and systems, so that the engineering tool kit keeps as complete and up-to-date as possible. Chemical engineers also must be familiar with the biological term, and be comfortable in operating in the biology culture, so that they can effectively translate breakthroughs in fundamental biological research to engineering applications in society. Attempt has been made to put some light on the potential of linkage of biological sciences and chemical engineering and challenges and opportunities for chemical engineers in biological sciences in Pakistan. In order to cope with technological developments and globalization it is suggested to bring innovations into the existing curriculum of chemical engineering programs to develop the human resource in chemical and molecular engineering capable of both biological discovery and product development.