Biomass gasification in fluidized beds is a process of important commercial value. The simulation of these fluidized bed units strongly depends on establishing bubble dynamics in dense phase sand ...fluidized beds. In these studies, the selected biomass pellet dimensions were 2.7 cm in length and 0.8 cm in diameter. To develop bubble dynamics studies in the present research, a combination of CREC-Optiprobes and a video micro-camera were employed. This was done to record bubble velocity and bubble dimensions in a 200–900 μm particle sand fluidized bed. The effects of biomass pellet concentration on the bubble rise velocity and bubble size and shape were evaluated at conditions close to minimum fluidization. On this basis, a theoretical bubble dynamic model was established. This phenomenologically based model included an adjustable bubble wake parameter, with model predictions providing the bubble chord, bubble frontal ratio, and bubble rising velocity.
This study reports the kinetics of the photocatalytic degradation of phenol using four different TiO2 catalysts. It is shown that phenol yields hydroquinone, catechol, benzoquinone and acetic and ...formic acids as main intermediate species. A phenomenological unified kinetic model (UKM) based in a “series–parallel” reaction network is proposed. The UKM follows a Langmuir–Hinshelwood kinetics with this being applicable to the various TiO2 photocatalysts studied. The UKM requires a number of significant assumptions in order to be used effectively avoiding overparametization. This approach also requires that the adsorption constants be obtained independently. As a result, the UKM is adapted for each specific TiO2 photocatalyst to describe the experimental photoconversion data. It is concluded that this approach provides good and objective parameter estimates with low to moderate cross-correlation among kinetic parameters and acceptable 95% CIs.
► A unified series–parallel reaction network describes phenol photoconversion on TiO2. ► This approach can be used in the kinetic modeling of different TiO2 photocatalysts. ► Adsorption constants are determined under dark conditions. ► Kinetic parameters are defined with low cross-correlation and reduced spans.
The radiation field in an annular photocatalytic reactor is simulated using a Monte Carlo method (MC) for two TiO2 suspensions in water. Simulations are performed by using both the spectral ...distribution and the wavelength-averaged scattering and absorption coefficients. The Henyey−Greenstein phase function is adopted to represent forward, isotropic, and backward scattering modes. It is assumed that the UV lamp reflects the backscattered photons by the slurred medium. Photoabsorption rates using MC simulations and spectral distribution of the optical coefficients agree closely with experimental observations from a macroscopic balance. It is found that the scattering mode of the probability density function is not a critical factor for a consistent representation of the radiation field. MC simulation for the optimal catalyst concentration reveals that the maximum LVREA is reached at a concentration of 0.14 g L−1 for TiO2 Degussa P25. From this concentration, the apparent optical thickness is determined to be 2.8476 which is in agreement with the optimal one previously reported. This concentration is comparable to that determined experimentally for phenol photocatalytic degradation.
A lack of fresh water is one of the most significant problems currently affecting humanity. Water scarcity also affects industries, with the mining industry being one of the most affected. One ...possible solution to water scarcity is the recirculation of water. Water in mining is usually treated with physicochemical methods, but in metallurgical processes, reagents are added, accumulate until reaching the point of saturation, and are often not successfully removed. In this sense, electrocoagulation has shown great efficiency in the treatment of organic contaminants, heavy metals, and metallic ions, and was applied in this study to eliminate ions and undesirable organic compounds present in mining–metallurgical process water. Furthermore, this process has shown great efficacy in relation to toxic metals like arsenic because their presence reduces the efficiency of other processes such as flotation. In this study, two types of electrodes were used: stainless steel and aluminum. The best results were achieved with stainless steel electrodes, which were able to eliminate 90% of copper ions in water. The turbidity of the water during the process was measured to determine the amount of solid present in the water, and a reduction of around 95% was observed when using aluminum electrodes. The sedimentation of clots occurred in two stages: Firstly, the coagulant was formed to trap organic matter as its size increased, until a particle size that was sufficient for settling was achieved. A zero-order kinetic model was fit for this stage of the process. Secondly, the formed clots continued to settle, and a second-order kinetic model was fit for this stage. Flotation tests were carried out on the process and electrotreated water to evaluate the recovery of Zn, Pb, Ag, and Au. An increase of 1.5% was found for gold, and an increase of 2% was found for silver, while a significant improvement was identified for zinc, augmenting recuperation by 30% when electrotreated water was used. For lead, no considerable change in recovery was observed in either form of water. The formed clots were analyzed using Scanning Electronic Microscopy, and we found that metal ions were trapped in the clots. This study demonstrates the potential of electrocoagulation for clarifying mine water, which is ordinarily very difficult to clarify.
The photocatalytic degradation of phenol and other phenolic compounds can follow different pathways depending on the reaction conditions. It is found that the photocatalytic oxidation of phenol is ...faster in acidic pHs with an optimum pH value of 3.2. On the basis of experimental data, it is concluded that the photocatalytic oxidation of phenol, ortho-dihydroxybenzene (o-DHB), para-dihydroxybenzene (p-DHB), and 1,4-benzoquinone (1,4-BQ) can all be described with a series − parallel reaction scheme. The present study reports a detailed reaction network incorporating possible reaction steps based on data obtained for the oxidation of phenol and its three aromatic intermediates. Four carboxylic acids (fumaric acid, maleic acid, oxalic acid, and formic acid) are detected as intermediates in the photocatalytic oxidation of phenol, o-DHB, p-DHB, and 1,4-BQ, suggesting that, in the oxidation of any phenolic compounds, these acids are part of the oxidation breakdown of more complex molecules. Additionally, two kinetic models are proposed with different degrees of complexity. A first model (KM#1) contains enhancements to that proposed by Salaices et al. (Chem. Eng. Sci. 2004, 59, 3) and helps predict the formation and disappearance of aromatic compounds only. In a second kinetic model (KM#2), a lumped acid concentration and CO2 formation are incorporated to account for the formation and disappearance of carboxylic acids as well as for the overall rate of mineralization. Both models provide a very good fit of the experimental data and work for a wide range of phenol concentrations (20−50 ppm C in phenol). Parameters estimates with statistical indicators for both models are also reported in this study.
Cardiac rehabilitation after acute myocardial infarction permits recovery of the heart function and enables secondary prevention programs in which changes in lifestyle habits are crucial. Cardiac ...rehabilitation often takes place in hospitals without coordination with primary healthcare and is not focused on individual patient preferences and goals, which is the core of the motivational interview. The objective of this study was to evaluate the efficacy of a cardiac rehabilitation program with a motivational interview in patients discharged from hospital after acute myocardial infarction.
A randomized, non-pharmacological clinical trial in six primary healthcare centers in Barcelona (Spain) will assess whether a tailored cardiac rehabilitation program consisting of four motivational interviews and visits with family physicians, primary healthcare nurses and a cardiologist, coordinated with the reference hospital, results in better cardiac rehabilitation than standard care. A minimum sample of 284 participants requiring cardiac rehabilitation after acute myocardial infarction will be randomized to a cardiac rehabilitation group with a motivational interview program or to standard primary healthcare. The main outcome will be physical function measured by the six-minute walk test, and the secondary outcome will be the effectiveness of secondary prevention: a composite outcome comprising control of blood pressure, cholesterol, diabetes mellitus, smoking and body weight. Results will be evaluated at 1,3 and 6 months.
This is the first clinical trial to study the impact of a new primary healthcare cardiac rehabilitation program with motivational interviews for patients discharged from hospital after myocardial infarction. Changes in lifestyles and habits after myocardial infarction are a core element of secondary prevention and require patient-centered care strategies such as motivational interviews. Therefore, this study could clarify the impact of this approach on health indicators, such as functional capacity.
ClinicalTriasl.gov NCT05285969 registered on March 18, 2022.
Several TiO2 based semiconductors with different Pt loadings are prepared using incipient impregnation, wet impregnation and the sol-gel method. These photocatalysts are evaluated in the ...Photo-CREC-Water II Photoreactor for hydrogen production via water dissociation, using an organic renewable scavenger (ethanol). Results obtained show the influence of the photocatalyst preparation in the production of hydrogen and in the observed quantum yields. Furthermore, it is established that the reaction networks leading to hydrogen production, using various photocatalysts, share common features. This analysis is developed by both identifying and quantifying different chemical species and their changes with irradiation time. Key species in this oxidation–reduction network are hydrogen, hydrogen peroxide, ethanol, methane, ethane, acetaldehyde and carbon dioxide. On this basis, it is shown that under an inert gas atmosphere, ethanol consumption is sub-stoichiometric. This points towards simultaneous ethanol consumption and the formation of the ethanol scavenger.
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•A kinetic model for VOC photodegradation in air using supported TiO2 is developed.•Adsorption and photoreaction are incorporated using a “series-parallel” network.•Independent ...adsorption constants are calculated with equilibrium experiments.•The kinetics is simplified in order to avoid over-parameterization.•The proposed kinetics is in agreement with a photon density distribution on TiO2.
This research reports the kinetic studies for acetone and acetaldehyde photoconversion in the gas phase utilizing a scaled-up Photo-CREC-Air unit with TiO2. The inclusion of intermediate species in the reaction network is required for the kinetic modeling of a wide range of oxygenate pollutant concentrations. The proposed “in parallel-series” reaction network encompasses a Langmuir-Hinshelwood (L-H) kinetics including species adsorption and intrinsic reaction parameters. The estimated kinetic parameters provide a successful prediction of various measurable chemical species. It is shown that the proposed kinetic model can be simplified, under low initial model pollutant concentrations. This is critical to avoid model overparameterization. The proposed kinetic model while being restricted to two model pollutants (acetone and acetaldehyde) and one specific photoreactor (e.g. 55.1L Photo-CREC-Air), provides a framework to establish the photodegradation kinetics of other organic species in air, for larger photoreactor scales.
Photocatalytic efficiency is evaluated using quantum yields (QYs) and the photochemical thermodynamic efficiency factor (PTEF). The PTEF allows establishing reactor efficiency as the ratio of ...utilized enthalpy for the formation of consumed OH• free radicals over the absorbed photon energy. A key consideration for the evaluation of efficiency factors is the establishment of macroscopic energy balances together with an accurate assessment of evolved and absorbed photons. Of considerable help are the experimental devices developed at the Chemical Reactor Engineering Centre (CREC)/University of Western Ontario (UWO) laboratories. Photoconversion kinetics is required for calculation of the OH• consumption rates and establishment of the related kinetic parameters. PTEFs and QYs have been applied by CREC‐UWO researchers for efficiency calculations in photocatalytic reactors for the decontamination of air, water, and hydrogen production.
Photocatalysis opens great opportunities for water and air purification as well as for hydrogen manufacturing. The photocatalytic reactor efficiency using quantum yields and photochemical thermodynamic efficiency factors is reviewed. Efficiencies are established using experimental devices and methodologies developed at the Chemical Reactor Engineering Centre/University of Western Ontario, Canada.
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