Effect of impeller on sinking and floating behavior of suspending particle materials in stirred tank: A computational fluid dynamics and factorial design study

The present study focuses upon the effect of the impeller on sinking and floating behavior of suspending particles in stirred tank reactor, employing computational fluid dynamics (CFD) simulation where factorial design is used to investigate the main and interaction effects of design parameters on the particle distribution performance of four typical impeller designs. Factorial design results show the effect of diameter and width of the impeller and off-bottom clearance on sinking particles is different from that of floating particles and regression equations for sinking particles and floating particles are achieved separately. Meanwhile, optimal equations which quantitatively reveal the effect of impeller factors on suspension quality and energy input is established for impeller improvement. Besides the development of computational models, the combination of CFD simulation with factorial design method provides a useful approach to gain insight into the suspension behavior of sinking and floating particles, also it guides to optimize the impeller design.     

Photocatalytic degradation of azo dyes by organic-capped anatase TiO2 nanocrystals immobilized onto substrates

The UV-induced photocatalytic degradation of two azo dyes, Methyl Red and Methyl Orange, has been carried out in aqueous media in the presence of oleic acid (OLEA)- and tri-n-octylphosphine oxide (TOPO)-capped anatase TiO₂ nanocrystal powders (mean particle size: 6 nm) deposited onto a quartz substrate. The progress of photodegradation was followed by combining UV–vis absorption measurements with HPLC–MS analysis. The abatement efficiency for the two organic compounds was compared with that obtained with commercial TiO₂ P25 Degussa by evaluating a few significant variables, such as the dye chemical structure, pH of the solution, and catalyst surface status. Identification of several by-products by HPLC–MS analysis has allowed to propose a reasonable degradation pathway for both target molecules. Significantly, although all titania catalysts were effective in removing both parent dyes and their related derivatives, the degradation rate by the OLEA-capped TiO₂ nanocrystals was double as that obtained with both its TOPO-capped analogous and TiO₂ P25 Degussa. It is suggested that efficient catalysis strictly depends on microscopic mechanisms that occur at the catalyst surface, basically involving specific dye adsorption and local density of terminal OH moieties.     

Soybean oil-based thermoset reinforced with rosin-based monomer

A full bio-based cured resin was synthesized by copolymerization of acrylated-epoxidized soybean oil (AESO) and 2-acrylamidoethyl dehydroabietic acid (DHA-HEMAA). The rigid rosin-based monomer 2-acrylamidoethyl dehydroabietic acid was first prepared from dehydroabietic acid and N-hydroxyethylacrylamide, which was characterized by nuclear magnetic resonance and Fourier transform infrared (FTIR) spectrometry techniques. The cured resin was then synthesized and characterized by FTIR spectroscopy, differential scanning calorimetry, dynamic thermomechanical analysis, and thermogravimetric analysis, as well as using a Kruss tensiometer and a universal testing machine. The results indicated that the resin cured with rosin-based monomer exhibited excellent thermomechanical properties. The crosslink density and thermal stability of cured samples containing DHA-HEMAA at molar ratio between 10 and 30% were higher than those of AESO/DHA-HEMAA0 sample. With increasing DHA-HEMAA content, the glass transition temperature (T_g), elongation-at-break, and tensile strength of samples increased, in the stated order, from 16 to 38 °C, from 24 to 45.8%, and from 1.7 to 6.5 MPa. Due to DHA-HEMAA with a hydrophenanthrene structure, the θ values increased with the increase of DHA-HEMAA molar ratios. The full bio-based rosin thermosetting resins may have great potentials in practical application fields, such as coating, adhesive, and packaging materials.     

Improved Compaction in Multilayer Capacitor Fabrication

The most common defects found in multi-layer ceramic capacitors are derived from residual porosity formed when solvents and binders are released from a ceramic green body. Without a well-controlled compaction technique, defects between sheets in the stacked body are often present, leading to lamination problems. This paper suggests alternative approaches, using compaction applied before and/or after the process of binder burnout with the intention of reducing the number of stacking-generated defects and the volume of voids formed after binder burn-out. Barium titanate tapes and stacked multilayer electroded discs have been investigated and characterised by microstructural examination and density measurement. The resulting properties are described, and the behaviour of the multi-layers discussed in terms of the microstructure and processing procedures. It is shown that the porosity content of sintered samples compacted at 300 MPa is approximately half that of samples compacted at 30 MPa when both are sintered at 1300°C for 2 h. A further improvement of densification can be achieved by a postcompaction treatment after binder burn out.     

Isolation and identification of procyanidins in apple pomace

The chemical nature of the procyanidin components in apple pomace was investigated as part of a programme seeking alternative uses of the large quantity of pomace that is being generated from the apple juice industry. The homogeneous nature of the procyanidin fractions was demonstrated by the isolation and identification of a range of epicatechin oligomers, namely epicatechin-(4β-6) epicatechin, epicatechin (4β-8) epicatechin, epicatechin (4β-8) epicatechin (4β-8) epicatechin and epicatechin (4β-8) epicatechin (4β-8) epicatechin (4β-8)-epicatechin. The procyanidin polymers were also isolated and purified by a Sephadex LH20 column and shown to consist exclusively of epicatechin units. The chemical structures of these procyanidins were established by ¹³C-NMR spectroscopy, by acid-catalysed degradation reaction with phloroglucinol and by electrospray mass spectrometry.     

Enhanced proton conductivities of chitosan-based membranes by inorganic solid superacid SO42−–TiO2 coated carbon nanotubes

To increase proton conductivity of chitosan (CS) based polymer electrolyte membranes, a novel nanofiller-solid superacide SO₄^2--TiO₂ (STi) coated carbon nanotubes (STi@CNTs) are introduced into CS matrix to fabricate membranes for polymer electrolyte membrane fuel cells (PEMFCs). Owing to the STi coating, the dispersion ability of CNTs and interfacial bonding are obviously improved, hence, CNTs can more fully play their reinforcing role, which makes the CS/STi@CNTs composite membranes exhibit better mechanical properties than that of pure CS membrane. More importantly, STi possesses excellent proton transport ability and may create facile proton transport channels in the membranes with the help of high aspect ratio of CNTs. Particularly, the CS/STi@CNTs-1 membrane (1 wt% STi@CNTs loading) obtains the highest proton conductivity of 4.2 × 10⁻² S cm^–1 at 80 °C, enhancing by 80% when compared with that of pure CS membrane. In addition, the STi@CNTs also confer the composite membranes low methanol crossover and outstanding cell performance. The maximum power density of the CS/STi@CNTs-1 membrane is 60.7 mW cm⁻² (5 M methanol concentration, 70 °C), while pure CS membrane produces the peak power density of only 39.8 mW cm⁻².     

Role of the activation process on catalytic properties of iron supported catalyst in Fischer-Tropsch synthesis

Monometallic Fe and bimetallic Ru–Fe supported catalysts were prepared by impregnation method and tested in Fischer-Tropsch synthesis (F-T). Their physicochemical properties were characterized by BET, SEM-EDS, FTIR, XRD, H₂-TPR, TPD-NH₃ techniques. The catalytic activity tests showed that the activation process has a huge impact on the reactivity properties in the studied process. The most active system in F-T reaction was 40%Fe/Al₂O₃–Cr₂O₃ catalyst which exhibited CO conversion equal 89.9% and the selectivity towards liquid product of 66.6%. The liquid products obtained in F-T process on 40%Fe/Al₂O₃–Cr₂O₃ consisted mainly of linear (76.8%), branched (17.7%) and unsaturated (5.5%) hydrocarbons. The chain growth probability in F-T process was estimated using an Anderson-Schulz–Flory distribution of obtained liquid product for all tested catalysts. The calculated α value for the most active catalyst was 0.76. The activity results indicate that iron carbides formed during activation process affects on the catalytic activity and selectivity of the iron catalyst during F-T synthesis. The activity measurements showed that the activity of the iron supported catalysts depends strongly on the catalyst phase composition and their acidic properties. XRD results confirmed that the most active catalyst in the investigated process exhibited the highest concentration of iron carbides phases on its surface.     

Microwave-assisted metal-catalyzed pyrolysis of low-rank coal: Promising option towards obtaining high-quality products

Microwave-assisted catalytic pyrolysis is considered to be a promising technology for coal-staged conversion due to its high efficiency and selectivity. This work was undertaken to investigate the pyrolysis behavior and products quality of microwave-assisted pyrolysis of low rank coal catalyzed by metallic catalysts (K, Ca and Fe) with both dielectric response and catalytic effect via a microwave tube furnace. The mechanism of metallic catalysts on catalytic cracking tar under microwave radiation was also investigated. The dielectric properties and physicochemical structure of coal chars were characterized by a vector network analyzer, XRD, FT-IR, SEM, EDS, and Raman. The chemical structure characteristics of generated tars were determined by FT-IR and GC-MS. Results manifested that microwave interacted preferentially with metal catalysts by polarization and conductivity loss could efficiently induce the occurrence of catalytic pyrolysis reactions to generate high yield syngas (CO + H₂). Specifically, the dielectric loss factor of resultant chars was considerably improved with the introduction of metallic catalysts especial for Ca and Fe. Furthermore, it is found that metal catalysts dramatically enriched the amorphous carbon structure in produced chars whereas in favour of suppressing the trend of carbon graphitization. Additionally, the transformation of larger polycyclic aromatic compounds into lighter tar species was catalytically accelerated, resulting in the large proportion of single-ring aromatics in tar under the synergistic effect between microwave and metal catalysts.     

Co-fermentation of carbohydrates and proteins for biohydrogen production: Statistical optimization using Response Surface Methodology

In this study, the co-fermentation of carbohydrates and proteins at different ratios (C1–C5) was explored. The rates of particulate carbohydrates degradation in the co-substrate mixtures, not only increased with starch concentrations, but negatively impacted the degradation rates of the particulate proteins. Particulate proteins also negatively impacted particulate carbohydrate degradation rates, albeit to a lesser extent. Generally, there was a synergistic impact on hydrogen production and the optimum ratio that required no pH control occurred at C4 (80% carbohydrates + 20% proteins) with a hydrogen yield of 350 mL H₂/gCOD_added which was 38% higher than the expected, and the fermentation followed the acetate-ethanol pathway. Response Surface Methodology (RSM) was used to optimize the responses to the co-fermentation process at C4. By fitting 20 experimental data points, the responses adequately fitted second-order polynomial models. At the optimized VFA and ammonia concentrations of 580 mg/L and 40 mg/L, respectively, the biohydrogen production process would be feasible without pH control at a carbohydrate-to-protein COD ratio of 4:1.