O2 Mass Transfer Research Articles

An advanced electro-Fenton degradation system with triboelectric nanogenerator as electric supply and biomass-derived carbon materials as cathode catalyst

On the basis of the advantages of electro-Fenton (EF) and the flexible design of triboelectric nanogenerator (TENG) and biomass carbon materials, a self-powered EF system is conceived, which is self-driven by a flexible multilayered TENG (FM-TENG) using carbon materials derived from long bean as the cathode catalyst for oxygen reduction. The synthesized carbon material is promising electrocatalyst due to its macro-/meso-porous structure, large surface area (2270m2g−1), high nitrogen content and superhydrophilicity, which can facilitate dissolved O2 mass transfer and promote the oxygen reduction. The instantaneous short-circuit current, transferred charge and open-circuit voltage of FM-TENG could reach 650μA, 1.7μC and 750V, respectively, corresponding to an instantaneous power density of 2.6Wm−2 (500kΩ). Driven by FM-TENG, 4-dimethylaminoazobenzene can be decomposed to CO2 and inorganic ions by hydroxyl radical (•OH) generated via EF process. Cyclic voltammogram, gas chromatograph-mass spectrometer, UV–vis spectra and the H2O2 measurement together disclose such degradation mechanism in single-compartment cell (S-cell) and double-compartment cell (D-cell). Here, S-cell is preferable owing to the high efficiency, simple setup and low voltage. This provides a proof-of-concept of an innovative EF process using biomass-derived carbon materials as oxygen reduction electrocatalyst and FM-TENG as the electric supply to power the degradation of organic pollutants.

Micro-Membrane Electrode Assembly Design to Precisely Measure the in Situ Activity of Oxygen Reduction Reaction Electrocatalysts for PEMFC.

An in situ micro-MEA technique, which could precisely measure the performance of ORR electrocatalyst using Nafion as electrolyte, was designed and compared with regular thin-film rotating-disk electrode (TFRDE) (0.1 M HClO4) and normal in situ membrane electrode assembly (MEA) tests. Compared to the traditional TFRDE method, the micro-MEA technique makes the acquisition of catalysts' behavior at low potential values easily achieved without being limited by the solubility of O2 in water. At the same time, it successfully mimics the structure of regular MEAs and obtains similar results to a regular MEA, thus providing a new technique to simply measure the electrode activity without being bothered by complicated fabrication of regular MEA. In order to further understand the importance of in situ measurement, Fe-N-C as a typical oxygen reduction reaction (ORR) free-Pt catalyst was evaluated by TFRDE and micro-MEA. The results show that the half wave potential of Fe-N-C only shifted negatively by -135 mV in comparison with state-of-the-art Pt/C catalysts from TFRDE tests. However, the active site density, mass transfer of O2, and the proton transfer conductivity are found to strongly influence the catalyst activity in the micro-MEA, thereby resulting in a much lower limiting current density than Pt/C (8.7 times lower). Hence, it is suggested that the micro-MEA is better in evaluating the in situ ORR performance, where the catalysts are characterized more thoroughly in terms of intrinsic activity, active site density, proton transfer, and mass transfer properties.

Gas mass transfer with microbial CO2 fixation and poly(3-hydroxybutyrate) synthesis in a packed bed bioreactor

Gas mass transfer is the rate-limiting step in CO2 fixation by a hydrogen-oxidizing bacterium Cupriavidus necator under chemolithoautotrophic conditions. The mass transfer rates (i.e. the gas uptake rates) were measured in a packed bed bioreactor under the conditions of microbial growth on CO2. The kLa values of O2 and H2 were determined under either O2 or H2 limitation, respectively, and the ratio was proportional to a square root ratio of the molecular diffusivities in water, indicating that a surface renew model is suitable for the gas mass transfer in the packed bed. At a low gassing rate, the O2 mass transfer coefficient was to different extent affected by packing materials, bed geometry, liquid velocity, and liquid distribution. The liquid distributor and/or bed void space exhibited a high effect on the mass transfer coefficient. With microbial growth, the gas fermentation was becoming limited either by dissolved O2 or H2, depending on gas composition, but neither O2 nor H2 limitation could trigger the formation of a substantial amount of poly(3-hydroxybutyrate) (PHB) under nutrient-rich conditions. Instead, when a nitrogen nutrient control strategy was applied, PHB synthesis was significantly improved and the PHB content reached up to 67wt% of cell mass.

Sulfide emissions in sewer networks: focus on liquid to gas mass transfer coefficient.

H2S emission dynamics in sewers are conditioned by the mass transfer coefficient at the interface. This work aims at measuring the variation of the mass transfer coefficient with the hydraulic characteristics, with the objective of estimating H2S emission in gravity pipes, and collecting data to establish models independent of the system geometry. The ratio between the H2S and O2 mass transfer coefficient was assessed in an 8 L mixed reactor under different experimental conditions. Then, oxygen mass transfer measurements were performed in a 10 m long gravity pipe. The following ranges of experimental conditions were investigated: velocity flow [0-0.61 m.s-1], Reynolds number [0-23,333]. The hydrodynamic parameters at the liquid/gas interface were calculated by computational fluid dynamics (CFD). In the laboratory-scale reactor, the O2 mass transfer coefficient was found to depend on the stirring rate (rph) as follows: KL,O2 = 0.016 + 0.025 N3.85. A KL,H2S/KL,O2 ratio of 0.64 ± 0.24 was found, in accordance with previously published data. CFD results helped in refining this correlation: the mass transfer coefficient depends on the local interface velocity ui (m.h-1): KL,O2 = 0.016 + 1.02 × 10-5 ui3.85 In the gravity pipe device, KL,O2 also exponentially increased with the mean flow velocity. These trends were found to be consistent with the increasing level of turbulence.

Effect of solids on O2 mass transfer in an oscillatory flow reactor provided with smooth periodic constrictions

In the present work, it is studied for the first time the use of an oscillatory flow reactor provided with smooth period constrictions (OFR-SPC) in gas-liquid mass transfer process when a solid phase is present. The superficial gas velocities (uG), solids loading (calcium alginate beads: 0–15% (v/v)) and the oscillatory conditions (frequency and amplitude) effects on volumetric liquid side mass transfer coefficient (kLa) are experimentally evaluated. The liquid-side mass transfer coefficient, kL, and the specific interfacial area, a, are studied individually. The results show that kLa increases with both superficial gas velocity and oscillatory conditions, in two and three-phase systems, the oscillatory conditions being the ones with the highest impact on the gas-liquid mass transfer process. The presence of solids seems to have a negligible influence on kLa in all experimental conditions for the range of solids loading studied. This behavior was not observed in other reactors where a negative solids (calcium alginate beads) influence on the mass transfer process was verified. Globally, the results show the importance of hydrodynamic phenomena on the mass transfer process in two and three-phase systems, indicating OFR-SPC as a good alternative to the conventional reactors, especially when a third phase is present.

Freestanding doubly open-ended TiO2 nanotubes for efficient photocatalytic degradation of volatile organic compounds

We synthesized freestanding doubly open-ended TiO2 nanotubes (DNT) film and compared their photocatalytic activity and durability during the repeated degradation cycles of volatile organic compounds (VOCs) with those of TiO2 nanotubes (TNT) film. DNT exhibited higher activity and durability for the photocatalytic degradation of gaseous acetaldehyde and toluene than TNT. The doubly open-ended structure of DNT allows O2 molecules to be easily supplied to the active sites, which increases not only the intrinsic photocatalytic activity but also the resistance to catalyst deactivation. The freestanding DNT film was additionally loaded with TiO2 nanoparticles (NP@DNT) in the inner wall to further increase the activity for VOC degradation. The photocatalytic activity of NP@DNT was higher than bare DNT and bare TNT by 1.3 and 1.8 times, respectively. Unlike the case of DNT, the TiO2 nanoparticles loaded TNT (NP@TNT) exhibited a lower activity than bare TNT, probably because the TiO2 nanoparticles blocked the TNT channels with hindering the mass transfer of O2 and VOC molecules. DNT with doubly open-ended structure serves as a versatile platform of fabricating nanostructured photocatalysts with maintaining the open channel structure that facilitates the mass transfer of O2 and VOC molecules.

Enhanced generation of H2O2 and radicals on Co9S8/partly-graphitized carbon cathode for degradation of bio-refractory organic wastewater

In electrochemical advanced oxidation processes (EAOPs), the hydrogen peroxide (H2O2) could be in-situ generated from the two-electron (2e−) oxygen reduction reaction (ORR), which was then converted to OH radicals in the role of cathode catalyst. To improve the efficiency of H2O2 generation, cobalt sulfide/partly-graphitized carbon (Co9S8/PGC) composites as EAOPs cathodes were synthesized via a simple simultaneous carbonization method. The structural and electrochemical properties of Co9S8/PGC were investigated. Results demonstrated that Co9S8 with coexistence of Co2+/Co3+ was tightly embedded into the PGC skeleton. Abundant oxygen-containing groups on the PGC surface could improve the wettability and hydrophilicity of the Co9S8/PGC (800°C), contributing to the formation of more catalytic active sites in the porous structure. Synergistic effect between Co9S8 and PGC could improve the electron transfer efficiency and O2 mass transfer by increasing the contact interface area between electrode and electrolyte, inducing the high selectivity for 2e−ORR. The mixed-valence nature of Co9S8 (Co2+/Co3+) exhibited high catalytic activity for promoting the OH generation from H2O2. Degradation rates of phenol and TOC removal rate of ceftazidime reached approximately 89.1 and 84.3% at 120 and 480min, respectively, indicating that Co9S8/PGC cathode had promise for further application.

Bacterial-cellulose-derived carbon nanofiber-supported CoFe2O4 as efficient electrocatalyst for oxygen reduction and evolution reactions

Exploration of cost-effective electrocatalysts with high catalytic activity toward the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) remains a key challenge in the development of metal-air batteries. In this study, bacterial-cellulose-derived carbon nanofiber-supported CoFe2O4 (CFO/CNF) has been prepared via a facile and green method. The three dimensional (3D) interconnected CNF network support with high surface area not only provides high electronic conductivity but also promotes the mass transfer of O2 and electrolyte during the ORR and OER. Furthermore, the strong coupling between CFO and CNF allows for fast charge transfer, facilitating the electrocataltyic processes. These lead to the high electrocatalytic activity of as-prepared CFO/CNF nanocomposite toward both the ORR and OER, outperforming CFO and CNF, respectively. Meanwhile, the stability of CFO/CNF nanocomposite toward the ORR and OER is much higher than that of benchmark Pt/C (20 wt.%) and RuO2/C (20 wt.%), respectively.

Mechanism of the CuII-catalyzed benzylic oxygenation of (aryl)(heteroaryl)methanes with oxygen.

A mechanistic study of the copper-catalyzed oxidation of the methylene group of aryl(di)azinylmethanes was performed. Initial reaction rates were measured making use of in situ IR reaction monitoring and a kinetic analysis of the reaction was executed. The reaction proved to be first order in oxygen concentration. For substrate and acid concentration, saturation kinetics due to O2 mass transfer limitation were observed. The occurrence of mass transfer limitation was further confirmed by examining the effect of the stirring rate on the initial reaction rate. Interestingly, the effect of the concentration of the catalyst on the rate shows that higher loadings result in a maximal initial rate, followed initially by a steady decrease and subsequently a rate plateau when the concentration is increased further. Mass transfer limitation and increased concentration of dinuclear catalytically active species rationalizes this hitherto unprecedented rate behavior. Continuous-wave and pulsed electron paramagnetic resonance methods were used to characterize the catalytic species present in the solution during the reaction and confirmed the presence of both mono- and dinuclear copper species. Analysis of a diverse substrate scope points towards imine-enamine tautomerization as a crucial process in the oxidation reaction. DFT calculations of these equilibrium constants (pKeq) provided us with a qualitative tool to predict whether or not a substrate is viable for oxidation under the reaction conditions developed.

The role of ash layer in syngas combustion in underground coal gasification

Underground coal gasification (UCG) proceeds generally in the presence of an ash layer on the coal (or char) surface. The ash layer would not only increase the mass transfer resistance to gases as reported in the literature but also lead to reactions of O2 with syngas (CO and H2) generated from the ash–char interface. This paper studies the effects of ash layer in a specially designed one-dimension gasification assembly using a bituminous coal char by analyzing the ash and the gases components. The ash content of the char is 26.3wt.% and the deformation temperature (DT) is 1460°C. It is found that at 1300°C the ash layer does not reduce the O2 mass transfer until it is thicker than 1.3mm. The ash layer, however, allows O2 to react with CO generated from the ash–char interface to form CO2, which raises the local temperature in the ash layer leading to local ash melting and transfers the char reaction from partial oxidation by O2 in the absence of an ash layer to the Boudouard reaction, i.e. between char and CO2.

Mechanistic model coupling gas exchange dynamics and Listeria monocytogenes growth in modified atmosphere packaging of non respiring food

A mechanistic model coupling O2 and CO2 mass transfer (namely diffusion and solubilisation in the food itself and permeation through the packaging material) to microbial growth models was developed aiming at predicting the shelf life of modified atmosphere packaging (MAP) systems. It was experimentally validated on a non-respiring food by investigating concomitantly the O2/CO2 partial pressure in packaging headspace and the growth of Listeria monocytogenes (average microbial count) within the food sample. A sensitivity analysis has revealed that the reliability of the prediction by this “super-parametrized” model (no less than 47 parameters were required for running one simulation) was strongly dependent on the accuracy of the microbial input parameters. Once validated, this model was used to decipher the role of O2/CO2 mass transfer on microbial growth and as a MAP design tool: an example of MAP dimensioning was provided in this paper as a proof of concept.

Kinetic Study of La0.75Sr0.25Cr0.5Mn0.5O3-Δ Nanoelectrodes for Symmetrical-SOFC

One of the main technological challenges of the solid oxide fuel cells (SOFC) is to reduce its operating temperature. Nanostructured materials open this possibility since the microstructure plays a fundamental role on the electrocatalytic activity of the electrodes. In this context, the understanding of the limiting mechanism steps for both O2 reduction and H2 oxidation reactions is a main objective in order to improve the design of the nanostructured electrodes. La0.75Sr0.25Cr0.5Mn0.5O3- δ (LSCM) perovskite has demonstrated a promising combination of properties for its employ as electrode (anode and cathode, simultaneously) in symmetrical-SOFC, among which it can mention: phase and dimensional stability, high electrochemical activity in both reducing and oxidizing atmospheres, and chemical compatibility with various solid electrolytes. In recent works, we present the synthesis by combustion of pure-phase LSCM nanocrystallites [1], and the bottom-up building process of nanostructured LSCM electrodes employing La0.8Sr0.2Ga0.8Mg0.2O3-δ(LSGM) as electrolyte [2]. In particular, the influence of the electrode crystallite size on the electrochemistry behavior as both anode and cathode was studied by electrochemical impedance spectroscopy (EIS). In this work, we present an electrode kinetics study of the nanostructured LSCM material by employing EIS measurements in different oxidizing and reducing atmospheres. Figures (a) and (b) present the EIS spectra of LSCM/LSGM/LSCM cell varying the oxygen and hydrogen partial pressures, i.e. pO2 and pH2 respectively. As it can be observed, when both pO2 and pH2 increase the electrode polarization resistance decrease, which indicates that the LSCM nanocrystallites are electrocatalytically active both for the oxygen reduction as well as hydrogen oxidation. Figures (c) and (d) show the evolution of the polarization resistance with the pO2 and pH2 obtained by fitting of the EIS spectra by using Electrical Equivalent Circuits. In both cases, two EIS arcs at high and low frequency (HF and LF, respectively) can be resolved showing complex mechanisms. In the H2 oxidation, the HF contribution with n ≈ 0 is independent of H2 concentration, probably due to a charge transfer process, while the LF contribution with n ≈ 0.5 could involve atomic species, e.g. H2-dissociative adsorption or H-surface diffusion [3]. On the other hand, in the O2 reduction, the HF contribution with n ≈ 0.25 is typically assigned to O-surface transport process whereas the LF arc with n ≈ 1 is generally attributed to O2 mass transfer in the gas phase [4].

Application of a novel respirometric methodology to characterize mass transfer and activity of H2S-oxidizing biofilms in biotrickling filter beds

The elimination capacity of gaseous H2S biofiltration can be limited either by mass transfer or bioreaction in the biofilm. Assessment of the biological activity of immobilized cells (biofilm) usually implies morphological and physiological changes during the adaptation of cells to respirometric devices operated as suspended cultures. In this study, respirometry of heterogeneous media is advised as a valuable technique for characterizing mass transport and biological activity of H2S-oxidizing biofilms attached on two packing materials from operative biotrickling filters. Controlled flows of liquid and H2S-containing air were recirculated through a closed heterogeneous respirometer allowing a more realistic estimation of the biofilm activity by the experimental evaluation of the oxygen uptake rate (OUR). Specific maximum OUR of 23.0 and 38.5mmol O2 (g biomass min)−1 were obtained for Pall rings and polyurethane foam, respectively. A mathematical model for the determination of kinetic-related parameters such as the maximum H2S elimination capacity and morphological properties of biofilm (i.e., thickness and fraction of wetted area of packing bed) was developed and calibrated. With the set of parameters obtained, the external oxygen mass transport to the wetted biofilm was found to limit the global H2S biofiltration capacity, whereas the non-wetted biofilm was the dominant route for the gaseous O2 and H2S mass transfer to the biofilm. Oxygen diffusion rate was the limiting step in the case of very active biofilms.

Study of the Oxygen Reduction Reaction on the Coupled Galvanic Carbon Steel - Stainless Steel

The main objective of this work is to study the electrochemical behavior of galvanic coupling between carbon steel, CS, and stainless steel, SS, in an alkaline environment simulating the conditions prevailing in a repaired structure in which stainless steel rebar’s will be an option. Previously research conducted in different parts of the world on this subject reach agreement with the fact that AISI 304 SS and 316 SS embedded in concrete offers high corrosion resistance in aggressive environments but only for the case of new structures, and no further explanation has been given on the behavior of SS when in contact with CS. Galvanic coupling between these two metals should increase the corrosion process of the more anodic, CS in this case, but this phenomenon does not occur in practice.Galvanic coupling was investigated by means of the electrochemical coulostatic technique. Tests performed allow determining the Tafel slopes of anodic and cathodic processes. The Tafel slope values obtained show that the process is being controlled by the reduction of oxygen, O2 in the environment where the samples were placed. On the basis of these kinetic parameters, a mechanism for the corrosion process is proposed in which the rate determining step would be O2 mass transfer process. The diffusion of O2 would take place through a formed oxide film, passivating in nature. Due to the formation of this oxide film, the cathodic oxygen reduction reaction, ORR, on stainless steel surface would be very slow. The high polarization of ORR rate would be the factor controlling the whole process, then minimizing the risk of damage by galvanic corrosion, demonstrating the feasibility of using stainless steel in the repairing of concrete structures.

Sustainable autotrophic production of polyhydroxybutyrate (PHB) from CO2 using a two-stage cultivation system

The technical feasibility of Cupriavidus necator DSM 545 for sustainable autotrophic polyhydroxybutyrate (PHB) production from CO2 using a two-stage cultivation system was evaluated. In this cultivation method, cell mass growth occurred under heterotrophic conditions using two different organic substrates, namely glucose and waste glycerol. In both cases, PHB biosynthesis was triggered by applying nitrogen and oxygen limitation at three different cell mass concentrations under autotrophic conditions using a gas mixture of H2, O2 and CO2. To ensure that the test conditions were relevant for later industrial application, O2 concentration was kept below the safety value during autotrophic PHB production. PHB production from CO2 on waste-glycerol grown cell mass resulted in a PHB concentration of 28g/L, which is the highest reported value in literature for PHB synthesized from CO2 at an O2 concentration below the lower explosion limit of 5vol%. The fermentation performance decreased when nutrient limitation was delayed at higher cell mass concentrations. Furthermore, it was shown that PHB production from CO2 at high cell mass concentration is metabolically feasible, but under the tested conditions the mass transfer of O2 was limiting PHB accumulation. Characterization of the produced polymers showed that the organic carbon source affected the properties of PHB and that the cultivation method developed in this study provided PHB with properties similar to a commercial PHB and PHB typically found in literature. It can be concluded that heterotrophic–autotrophic production of PHB by C. necator is a promising cultivation method to reduce the overall production cost of PHB. In order to compete with the current heterotrophic cultivation system, the oxygen transfer rate must however be enhanced to achieve a higher PHB productivity.

Mass transfer coefficients considering boundary layer reaction in oxy-fuel combustion of coal char

In comparison with conventional air combustion, char particle reacts with higher concentrations of O2 and CO2 in the oxy-fuel combustion. At higher temperatures, strong Stefan flow is formed at the char surface and the CO gas-reaction occurs in the boundary layer, which have significant effects on the char reaction and the mass transfer. But Stefan flow and CO gas-phase reaction are often neglected in the study of conventional coal combustion. In this work, with the consideration of CO oxidation and Stefan flow in the boundary layer of a char particle, modifications to the mass transfer coefficients were presented for the coal oxy-fuel combustion. Better improvement was achieved in predicting the mass transfer coefficient by comparing with the experimental data. Further analyses indicated that the mass transfer coefficient of O2 decreases and that of CO2, increases in the presence of CO gas-phase reaction. Moreover, the closer the CO flame sheet is to the char surface, the smaller the correction factor of O2 mass transfer coefficient and the larger the correction factor of CO2. If only considering the oxidation reaction at the particle’s surface, the minimum correction factor of O2 is 0.5 which is 32.5% lower than that in the absence of CO gas-phase reaction. If only the surface gasification reaction is considered, the correction factor for CO2 will increase rapidly at the flame location of about ten times the particle radius, and reach 1.0 at three times the particle radius which means that it is unnecessary to correct the diffusion coefficient. This is very different from the case neglecting the boundary layer reaction. If the surface oxidation and surface gasification are considered simultaneously, the increase of the number of surface reaction will decrease the mass transfer coefficients for both O2 and CO2, and will have greater influence on CO2 transfer than on O2. These changes of reactive gas mass transfer indicate the significant impacts of CO homogeneous reaction in the oxy-fuel combustion of coal char.

Reconstruction of the oxygen uptake and carbon dioxide evolution rates of microbial cultures at near-neutral pH during highly dynamic conditions

The reconstruction of the dynamically changing rates of O2 uptake and CO2 production during short term bioreactor perturbation experiments, from dissolved oxygen and offgas O2 and CO2 measurements, requires a model describing the mass transfer and dispersion of O2 and CO2 in the system as well as the sensor dynamics. Additionally, if perturbation experiments are carried out at near-neutral pH levels, also the inter conversion of dissolved carbon dioxide and bicarbonate needs to be taken into account. While developing such a model we found that for an accurate description of the systems dynamic response on a time-scale of seconds, it is required to incorporate not only the mass transfer between gas bubbles and broth, but also between headspace and broth. The delay and dispersion in the measurements of the gas analyser, due to the length and complexity of the offgas system, was accounted for by determining the impulse response of the offgas system. This model could be fitted excellently to an identification data set. Finally the model was successfully applied to reconstruct the dynamic rates of O2 uptake and CO2 production of a culture of Penicillium chrysogenum, which was perturbed by a glucose pulse.

Rate and Mechanism of Reduction-Dissolution of Chromite in Liquid Slags

AbstractThe dissolution of chromite from the Bushveld Complex of South Africa in liquid slags was studied in the temperature range 1550° to 1665°C under argon gas. The slag compositions were similar to those of ferrochromium production and stainless steel making. Empirical relations between the slag composition and the dissolution of chromite were established through the use of a statistical model. The dissolution process was investigated by using the rotating cylinder technique and measured by the chemical analysis of the samples taken from the melt and the SEM-EDAX analysis of the reacted chromite cylinder samples. The chromite grains were depleted in iron and chromium as the dissolution progressed, leaving behind an alumina and magnesia rich spinel. The experimental data was evaluated by using kinetic models and mass transfer coefficients of chromium, iron and oxygen ions through the phase boundary between the solid chromite cylinder and the liquid slag were determined.The dissolution of chromite in liquid slags increases with increasing stirring rate. SEM-EDAX studies on the reacted chromite cylinders showed that coring took place within the chromite grains subjected to dissolution for sufficient length of time. Chromium and iron concentrations in the chromite were decreasing from the centre towards the surface of the grains while aluminum and magnesium contents were increasing at the edges compared to the centre of the chromite grains. Furthermore, the slag rich in alumina and magnesia diffuses in bulk into the chromite with a net result of increase in the concentration of these elements.The rate of dissolution of chromite in liquid slags was found to be controlled by the mass transfer of oxygen ions (O2−) through the liquid phase boundary between the solid chromite and the liquid slag. The activation energy for the mass transfer of O2− ions was calculated as 30.61 kCal/mol (128.07 kJ/mol).

Thermal detemplation of SBA-15 mesophases. Effect of the activation protocol on the framework contraction

The potential use of the solvothermal extraction (SE) as a preliminary step to calcination for detemplating SBA-15 mesophases is investigated; aiming to reduce the amount of organics to be burnt and thereby the corresponding structural shrinkage. A systematic study was carried out by soxhlet extraction on mesophases hydrothermally aged between 90 and 130°C. The mesophases containing variable amounts of template were then treated by calcination or pyrolysis/calcination. TGA was applied to quantify the template amount after the various treatments. The as obtained materials were characterized by SAXS and Ar ad/desorption for structural and textural information while 1H NMR gave information about the integrity of the as-recycled template.The study shows that solvothermal conditions remove considerably the template, typically from 50 to 10–20wt.%, mainly extracted from the primary mesopores. Possible reuse of the extracted template is questionable as it is poor in polyethyleneoxide compared to the synthesis block-copolymer, Pluronic P123. For all thermal protocols applied (direct calcination, calcination after solvent-extraction or pyrolysis/calcination after solvent extraction), the thermal shrinkage decreases with the aging temperature; that is consistent with the condensation degree of the silica. For each mesophase, it was found that the thermal shrinkage becomes less pronounced when the material is fully templated; thus the template can serve as structural support or can control the mass transfer of O2 and thereby the oxidation rate of the template burning.

Continuous thickening of activated sludge by electro-flotation

The present study was conducted for thickening of activated sludge by continuous electro-flotation (EF) process. The effects of some key factors such as initial pH, current density, operating time, electrode type (stainless steel and graphite) and operation conditions on the sludge thickening by determine of sludge volume reduction (SVR) and sludge solid concentration (SSC) and as well as removal of chemical oxygen demand (COD), total solids (TS), total suspended solids (TSS) and color were investigated. The results showed that the process has a good efficiency. The highest amount of SVR efficiency (89.3%) and SSC (38gL−1) were achieved at current density of 8mAcm−2 in 15min for stainless steel. Moreover, as surface/volume ratio increased, better thickening happened because increases both mass transfer and electro-generation of O2 and H2 at the surface of electrodes in low applied current density. Accordingly, consumed electrical energy was 0.15–1kWhm−3. Although suitable cell design is entirely essential, the use of chemicals and temperature increase are not effective. Consequently, EF is a comparatively appropriate process for thickening; in the water separated from the process, the amounts pertaining to COD, TS, TSS and color were respectively 112, 1601, 140mgL−1 and 5TCU which are useable for subsequent different consumptions.