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ChemEngineering, Volume 3, Issue 1 (March 2019)

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Cover Story (view full-size image) Layered double hydroxides display good adsorption and ion exchange properties for the removal of a [...] Read more.
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Open AccessArticle
Improved Kinetics and Water Recovery with Propane as Co-Guest Gas on the Hydrate-Based Desalination (HyDesal) Process
ChemEngineering 2019, 3(1), 31; https://doi.org/10.3390/chemengineering3010031
Received: 9 December 2018 / Revised: 23 February 2019 / Accepted: 6 March 2019 / Published: 12 March 2019
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Abstract
Water is a key resource for sustainable development and plays a crucial role in human development. Desalination is one of the most promising technologies to mitigate the emerging water crisis. Thermal desalination and reverse osmosis are two of the most widely employed desalination [...] Read more.
Water is a key resource for sustainable development and plays a crucial role in human development. Desalination is one of the most promising technologies to mitigate the emerging water crisis. Thermal desalination and reverse osmosis are two of the most widely employed desalination technologies in the world. However, these technologies are energy intensive. Clathrate-hydrate-based desalination (HyDesal) is a potential energy-efficient desalination technology to strengthen the energy–water nexus. In our previous study, we proposed a ColdEn-HyDesal process utilizing waste Liquefied Natural Gas (LNG) cold energy based on a fixed-bed reactor configuration. In this study, we evaluated the effect of 10% propane in three different gas mixtures, namely, nitrogen (G1), argon (G2), and carbon dioxide (G3), as hydrate formers for the HyDesal process. The achieved water recovery was very low (~2%) in the presence of NaCl in the solution for gas mixtures G1 and G2. However, high water recovery and faster kinetics were achieved with the G3 mixture. To improve the water recovery and kinetics of hydrate formation for the G2 gas mixture, the effect of sodium dodecyl sulfate (SDS) was evaluated. The addition of SDS did improve the kinetics and water recovery significantly. Full article
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Open AccessArticle
Layered Double Hydroxides for the Catalytic Isomerization of Linoleic Acid to Conjugated Linoleic Acids (CLAs)
ChemEngineering 2019, 3(1), 30; https://doi.org/10.3390/chemengineering3010030
Received: 20 January 2019 / Revised: 5 March 2019 / Accepted: 6 March 2019 / Published: 10 March 2019
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Abstract
Several hydrotalcite-type compounds with different divalent (Mg2+, Ni2+, Cu2+, Zn2+) and trivalent (Al3+, Cr3+) cations and different ratio compositions were tested for the isomerization of linoleic acid in order to study [...] Read more.
Several hydrotalcite-type compounds with different divalent (Mg2+, Ni2+, Cu2+, Zn2+) and trivalent (Al3+, Cr3+) cations and different ratio compositions were tested for the isomerization of linoleic acid in order to study their role on the obtention of specific conjugated linoleic acids (CLAs) with anticarcinogenic and nutritional properties. This is a complex reaction due to the high number of possible isomers of linoleic acid together with the significant competition of the isomerization reaction with other secondary undesired reactions. All catalysts showed very high conversions of linoleic acid, but condensation products were mainly obtained, especially for the hydrotalcite-type compounds with higher Mg/Al ratios due to their higher Brønsted basicity and for the catalysts with higher Ni2+ content or with the presence of Cu2+, Zn2+ in the layers because of the influence of the higher acidity of these cations on the Brønsted basicity of the hydroxides. The best results were achieved for the catalysts with Mg/Al ratio around 2.5–3, resulting in 29–38% of selectivity to the identified CLAs. Full article
(This article belongs to the Special Issue Advanced Applications of Layered Double Hydroxides)
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Open AccessArticle
Synthesis of Chalcone Using LDH/Graphene Nanocatalysts of Different Compositions
ChemEngineering 2019, 3(1), 29; https://doi.org/10.3390/chemengineering3010029
Received: 19 January 2019 / Revised: 27 February 2019 / Accepted: 6 March 2019 / Published: 9 March 2019
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Abstract
Layered double hydroxides (LDH) or their derived mixed oxides present marked acid-base properties useful in catalysis, but they are generally agglomerated, inducing weak accessibility to the active sites. In the search for improving dispersion and accessibility of the active sites and for controlling [...] Read more.
Layered double hydroxides (LDH) or their derived mixed oxides present marked acid-base properties useful in catalysis, but they are generally agglomerated, inducing weak accessibility to the active sites. In the search for improving dispersion and accessibility of the active sites and for controlling the hydrophilic/hydrophobic balance in the catalysts, nanocomposite materials appear among the most attractive. In this study, a series of nanocomposites composed of LDH and reduced graphene oxide (rGO), were successfully obtained by direct coprecipitation and investigated as base catalysts for the Claisen–Schmidt condensation reaction between acetophenone and benzaldehyde. After activation, the LDH-rGO nanocomposites exhibited improved catalytic properties compared to bare LDH. Moreover, they reveal great versatility to tune the selectivity through their composition and the nature or the absence of solvent. This is due to the enhanced basicity of the nanocomposites as the LDH content increases which is assigned to the higher dispersion of the nanoplatelets in comparison to bulk LDH. Lewis-type basic sites of higher strength and accessibility are thus created. The nature of the solvent mainly acts through its acidity able to poison the basic sites of the nanocatalysts. Full article
(This article belongs to the Special Issue Advanced Applications of Layered Double Hydroxides)
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Open AccessArticle
Sol-Gel Processes in Micro-Environments of Black Shale: Learning from the Industrial Production of Nanometer-Sized TiO2 Polymorphs
ChemEngineering 2019, 3(1), 28; https://doi.org/10.3390/chemengineering3010028
Received: 15 February 2019 / Revised: 1 March 2019 / Accepted: 4 March 2019 / Published: 8 March 2019
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Abstract
Micro-environments in black shale are reactors for geochemical reactions that differ from the bulk scale. They occur in small isolated pores of several 10 s to 100 s of nanometers without or with limited ionic exchange by diffusion to the surrounding matrix. The [...] Read more.
Micro-environments in black shale are reactors for geochemical reactions that differ from the bulk scale. They occur in small isolated pores of several 10 s to 100 s of nanometers without or with limited ionic exchange by diffusion to the surrounding matrix. The example of the formation of titania polymorphs brookite (and anatase) in black shale demonstrates that pH < 4 of the pore waters or lower must prevail to enable dissolution of Ti-bearing precursors followed by the precipitation of these metastable solids. Comparably low pH is applied during the industrial production of nanometer-sized brookite or anatase by sol-gel methods. The process parameters during industrial production such as low pH, negative Eh, or low ionic strength (to promote agglomeration) allow a comparison with parameters during geochemical processes leading to titania formation in black shale. Sol-gel processes are suggested herein as key geochemical processes in micro-environments of black shale in order to understand the formation of single brookite crystals or agglomerates on a nanometer scale. Full article
(This article belongs to the Special Issue TiO2 Nanoparticles: Synthesis and Applications)
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Open AccessArticle
Evaluation of Biogas Biodesulfurization Using Different Packing Materials
ChemEngineering 2019, 3(1), 27; https://doi.org/10.3390/chemengineering3010027
Received: 18 December 2018 / Revised: 26 February 2019 / Accepted: 28 February 2019 / Published: 8 March 2019
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Abstract
The packing material selection for a bioreactor is an important factor to consider, since the characteristics of this material can directly affect the performance of the bioprocess, as well as the investment costs. Different types of low cost packing materials were studied in [...] Read more.
The packing material selection for a bioreactor is an important factor to consider, since the characteristics of this material can directly affect the performance of the bioprocess, as well as the investment costs. Different types of low cost packing materials were studied in columns to reduce the initial and operational costs of biogas biodesulfurization. The most prominent (PVC pieces from construction pipes) was applied in a bench-scale biotrickling filter to remove the H2S of the biogas from a real sewage treatment plant in Brazil, responsible for 90 thousand inhabitants. At the optimal experimental condition, the reactor presented a Removal Efficiency (RE) of up to 95.72% and Elimination Capacity (EC) of 98 gS·m−3·h−1, similar to open pore polyurethane foam, the traditional material widely used for H2S removal. These results demonstrated the high potential of application of this packing material in a full scale considering the robustness of the system filled with this support, even when submitted to high sulfide concentration, fluctuations in H2S content in biogas, and temperature variations. Full article
(This article belongs to the Special Issue Advances in Biogas Desulfurization)
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Open AccessArticle
CNT and H2 Production During CH4 Decomposition over Ni/CeZrO2. I. A Mechanistic Study
ChemEngineering 2019, 3(1), 26; https://doi.org/10.3390/chemengineering3010026
Received: 17 January 2019 / Revised: 27 February 2019 / Accepted: 28 February 2019 / Published: 7 March 2019
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Abstract
This work presents a new insight into the potential of a Ni/CeZrO2 catalyst in two separate processes: (i) Chemical Vapor Deposition (CVD) using methane as a feedstock to obtain carbon nanotubes (CNTs) and H2, and (ii) catalyst regeneration with H [...] Read more.
This work presents a new insight into the potential of a Ni/CeZrO2 catalyst in two separate processes: (i) Chemical Vapor Deposition (CVD) using methane as a feedstock to obtain carbon nanotubes (CNTs) and H2, and (ii) catalyst regeneration with H2O that yields H2. The direct reaction of methane with H2O (steam methane reforming (SMR)) leads to H2 and CO (and CO2), whereas carbon deposition—regardless of its type—is an unwanted reaction. The concept presented in this work assumes dividing that process into two reactors, which allows one to obtain two valuable products, i.e., CNTs and H2. The literature data on CNT production via CVD ignores the issue of H2 formation. Moreover, there is no data concerning CNT production in fluidized bed reactors over ceria-zirconia supported metal catalysts. The results presented in this work show that CNTs can be formed on Ni/CeZrO2 during CH4 decomposition, and that the catalyst can be easily regenerated with H2O, which is accompanied by a high production of H2. The ability of Ni/CeZrO2 to be regenerated is its main advantage over the Ni-MgO catalyst that is popular for CNT production. This paper also shows that the Ni/CeZrO2 catalyst has the potential to be used for CNT and H2 production in a larger scale process, e.g., in a fluidized bed reactor. Full article
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Open AccessArticle
CNT and H2 Production during CH4 Decomposition over Ni/CeZrO2. II. Catalyst Performance and Its Regeneration in a Fluidized Bed
ChemEngineering 2019, 3(1), 25; https://doi.org/10.3390/chemengineering3010025
Received: 18 January 2019 / Revised: 6 February 2019 / Accepted: 14 February 2019 / Published: 5 March 2019
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Abstract
In this work, a ceria-zirconia supported nickel catalyst (Ni/CeZrO2) was for the first time used in a fluidized bed reactor in order to obtain carbon nanotubes (CNTs) and H2 in the reaction of the decomposition of CH4. The [...] Read more.
In this work, a ceria-zirconia supported nickel catalyst (Ni/CeZrO2) was for the first time used in a fluidized bed reactor in order to obtain carbon nanotubes (CNTs) and H2 in the reaction of the decomposition of CH4. The same catalyst was afterward regenerated with H2O, which was accompanied with the production of H2. The impact of catalyst granulation, temperature, and gas hourly space velocity (GHSV) on the amount and type of carbon deposits was determined using thermogravimetric analysis (TGA) and scanning and transmission electron microscopy (SEM and TEM). The presence of randomly oriented and curved CNTs with an outer diameter of up to 64 nm was proved. The Ni/CeZrO2 particles were loosely covered with CNTs, freely dispersed over CNTs, and strongly attached to the external CNT walls. TEM proved the presence of a Ni/CeZrO2@CNT hybrid material that can be further used as catalyst, e.g., in WGS or DRM reactions. The impact of GHSV on hydrogen production during catalyst regeneration was determined. The catalyst was subjected to cyclic tests of CH4 decomposition and regeneration. According to the obtained results, Ni/CeZrO2 can be used in CH4 conversion to CNTs and H2 (instead of CH4 combustion), e.g., in the vicinity of installations that require methane utilization. Full article
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Open AccessArticle
Activated Carbon, Carbon Nanofibers and Carbon-Covered Alumina as Support for W2C in Stearic Acid Hydrodeoxygenation
ChemEngineering 2019, 3(1), 24; https://doi.org/10.3390/chemengineering3010024
Received: 20 December 2018 / Revised: 2 February 2019 / Accepted: 28 February 2019 / Published: 5 March 2019
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Abstract
Carbon materials play a crucial role in sorbents and heterogeneous catalysis and are widely used as catalyst support for several reactions. This paper reports on an investigation of tungsten carbide (W2C) catalyst on three types of carbon support, namely activated carbon [...] Read more.
Carbon materials play a crucial role in sorbents and heterogeneous catalysis and are widely used as catalyst support for several reactions. This paper reports on an investigation of tungsten carbide (W2C) catalyst on three types of carbon support, namely activated carbon (AC), carbon nanofibers (CNF) and carbon-covered alumina (CCA). We evaluated their activity and selectivity in stearic acid hydrodeoxygenation at 350 °C and 30 bar H2. Although all three W2C catalysts displayed similar intrinsic catalytic activities, the support did influence product distribution. At low conversions (<5%), W2C/AC yielded the highest amount of oxygenates relative to W2C/CNF and W2C/CCA. This suggests that the conversion of oxygenates into hydrocarbons is more difficult over W2C/AC than over W2C/CNF and W2C/CCA, which we relate to the lower acidity and smaller pore size of W2C/AC. The support also had an influence on the C18-unsaturated/C18-saturated ratio. At conversions below 30%, W2C/CNF presented the highest C18-unsaturated/C18-saturated ratio in product distribution, which we attribute to the higher mesopore volume of CNF. However, at higher conversions (>50%), W2C/CCA presented the highest C18-unsaturated/C18-saturated ratio in product distribution, which appears to be linked to W2C/CCA having the highest ratio of acid/metallic sites. Full article
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Open AccessArticle
Illustrative Case Study on the Performance and Optimization of Proton Exchange Membrane Fuel Cell
ChemEngineering 2019, 3(1), 23; https://doi.org/10.3390/chemengineering3010023
Received: 31 October 2018 / Revised: 9 February 2019 / Accepted: 27 February 2019 / Published: 2 March 2019
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Abstract
Modeling is a powerful tool for the design and development of proton exchange membrane fuel cells (PEMFCs). This study presents a one-dimensional, two-phase mathematical model of PEMFC to investigate the two-phase transport process, gas species transport flow and water crossover fluxes. The model [...] Read more.
Modeling is a powerful tool for the design and development of proton exchange membrane fuel cells (PEMFCs). This study presents a one-dimensional, two-phase mathematical model of PEMFC to investigate the two-phase transport process, gas species transport flow and water crossover fluxes. The model reduces the computational time for PEMFC design with guaranteed accuracy. Analysis results show that the concentration and activation overpotentials of the cell decrease with the increase of operation pressure, which result in enhanced cell performance. Proper oxygen stoichiometry ratio in the cathode decreases the cell activation overpotential and is favorable for performance improvement. The cell ohmic resistance correspondingly increases with the increase of catalyst layer thickness, which leads to a deteriorated cell performance. The improvement on cell performance could be facilitated by decreasing the membrane thickness. Predicted results show that the present model is a useful tool for the design optimization of practical PEMFCs. Full article
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Open AccessArticle
Reactivity and Heavy Metal Removal Capacity of Calcium Alginate Beads Loaded with Ca–Al Layered Double Hydroxides
ChemEngineering 2019, 3(1), 22; https://doi.org/10.3390/chemengineering3010022
Received: 13 January 2019 / Revised: 21 February 2019 / Accepted: 27 February 2019 / Published: 1 March 2019
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Abstract
Layered double hydroxides (LDHs) present multiple applications due to their versatility and reactivity. Thus, Ca–Al LDHs with Friedel’s salt structure (HC) have been proposed as heavy metal scavengers due to their buffering capacity at basic pHs. Nevertheless, the control of the reactivity of [...] Read more.
Layered double hydroxides (LDHs) present multiple applications due to their versatility and reactivity. Thus, Ca–Al LDHs with Friedel’s salt structure (HC) have been proposed as heavy metal scavengers due to their buffering capacity at basic pHs. Nevertheless, the control of the reactivity of LDHs such as HC is necessary to optimize their applications. Here, the reactivity of an HC prepared by a coprecipitation method was modified by its inclusion in calcium alginate (CaAlg) beads prepared by ionic gelation. The obtained beads (CaAlg/HC) showed good dispersion of the HC particles in the alginate matrix and were used to test the acid base reactivity and heavy metal uptake capacity compared with pure CaAlg beads and HC powder separately. The pH buffering capacity of CaAlg beads was enriched by the inclusion of HC that, in turn, was modulated in its reactivity. Thus, the HC dissolution times changed from mere seconds for the powder to tens of minutes when enclosed in the beads in a kinetic profile determined by the diffusive step. On the other hand, Cu2+ uptake capacity of CaAlg/HC beads combined the Cu(OH)2 precipitation capacity of HC with the complexation capacity of alginate, reaching good affinity and capacity for the obtained beads. Nevertheless, the precipitation of the hydroxide was produced outside the bead, which would induce the addition of an additional separation step to produce an acceptable Cu2+ elimination. Full article
(This article belongs to the Special Issue Advanced Applications of Layered Double Hydroxides)
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Open AccessBrief Report
Effect of Water Saturation on H2 and CO Solubility in Hydrocarbons
ChemEngineering 2019, 3(1), 21; https://doi.org/10.3390/chemengineering3010021
Received: 31 August 2018 / Revised: 24 January 2019 / Accepted: 28 January 2019 / Published: 22 February 2019
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Abstract
The effect of water on the solubility of syngas in hydrocarbons has typically been ignored when developing models for Fischer-Tropsch slurry bubble column reactors (SBCR), despite water being a major by-product. Therefore, a generalized correlation was developed to predict water solubility in hydrocarbons [...] Read more.
The effect of water on the solubility of syngas in hydrocarbons has typically been ignored when developing models for Fischer-Tropsch slurry bubble column reactors (SBCR), despite water being a major by-product. Therefore, a generalized correlation was developed to predict water solubility in hydrocarbons at high temperatures, and was used to calculate the effect of water saturation on H2 and CO solubility in hydrocarbons using the Span Wagner equation of state. The presence of water was shown to have a much more significant effect on H2 solubility in hydrocarbons, compared to CO. Full article
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Open AccessArticle
Layered Double Hydroxide Sorbents for Removal of Selenium from Power Plant Wastewaters
ChemEngineering 2019, 3(1), 20; https://doi.org/10.3390/chemengineering3010020
Received: 28 December 2018 / Revised: 30 January 2019 / Accepted: 20 February 2019 / Published: 22 February 2019
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Abstract
Selenium is an essential trace element but is increasingly becoming a contaminant of concern in the electric power industry due to the challenges of removing solubilized selenate anions, particularly in the presence of sulfate. In this work, we evaluate granulated layered double hydroxide [...] Read more.
Selenium is an essential trace element but is increasingly becoming a contaminant of concern in the electric power industry due to the challenges of removing solubilized selenate anions, particularly in the presence of sulfate. In this work, we evaluate granulated layered double hydroxide (LDH) materials as sorbents for selenium removal from wastewaters obtained from a natural gas power plant with the aim to elucidate the effect of competing ions on the sorption capacities for selenium removal. We first present jar test data, followed by small-scale column testing in 0.43 inch (1.1 cm) and 2 inch (5.08 cm) diameter testbed columns for the treatment of as-obtained cooling tower blowdown waters and plant wastewaters. Finally, we present field results from a pilot-scale study evaluating the LDH media for treatment of cooling tower blowdown water. We find that despite the high levels of total dissolved solids and competing sulfate ions, the selenium oxoanions and other regulated metals such as chromium and arsenic are successfully removed using LDH media without needing any pre-treatment or pH adjustment of the wastewater. Full article
(This article belongs to the Special Issue Advanced Applications of Layered Double Hydroxides)
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Open AccessArticle
Quality Characteristics of Biodiesel Produced from Used Cooking Oil in Southern Europe
ChemEngineering 2019, 3(1), 19; https://doi.org/10.3390/chemengineering3010019
Received: 27 December 2018 / Revised: 12 February 2019 / Accepted: 13 February 2019 / Published: 16 February 2019
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Abstract
The potential of households’ used cooking oil (UCO) recycling for biodiesel production is massive. This study aims to promote the shift from UCO inappropriate disposal to sustainable recycling. UCO is classified as municipal waste under the code 20 01 25 (edible oils and [...] Read more.
The potential of households’ used cooking oil (UCO) recycling for biodiesel production is massive. This study aims to promote the shift from UCO inappropriate disposal to sustainable recycling. UCO is classified as municipal waste under the code 20 01 25 (edible oils and fats), according to the European Waste Catalogue. Inappropriate UCO disposal increases the operating cost of wastewater treatment, the risk of groundwater contamination, as well as the greenhouse gas emissions that are associated with its biodegradation. Recycling UCO-to-biodiesel offers a sustainable solution in the exploitation of a problematic waste and its transformation into an energy resource, thus contributing to the reduction of environmental pollution and fossil fuel dependence. This paper includes critical recommendations in order to overcome bottlenecks to successfully promote the UCO-to-biodiesel chain. Quality control of the biodiesel—produced exclusively from UCO—was performed according to the European Standard EN 14214 and the results are presented in the paper. The analysis studies the outcomes from four Southern European countries (Spain, Portugal, Italy, and Greece), which hold the top four places in annual per capita olive oil consumption in the European Union (EU). Full article
(This article belongs to the Special Issue Advances in Bio-Fuels Production)
Open AccessArticle
A Comparative Study of Ultrasound Biodiesel Production Using Different Homogeneous Catalysts
ChemEngineering 2019, 3(1), 18; https://doi.org/10.3390/chemengineering3010018
Received: 30 December 2018 / Revised: 24 January 2019 / Accepted: 1 February 2019 / Published: 11 February 2019
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Abstract
Biodiesel (BD) is a liquid fuel that consists of mono alkyl esters of long chain fatty acids derived from vegetable oil or fat. Recently, biodiesel has received additional attention and intense research has been performed in this field due to its favorable atmospheric [...] Read more.
Biodiesel (BD) is a liquid fuel that consists of mono alkyl esters of long chain fatty acids derived from vegetable oil or fat. Recently, biodiesel has received additional attention and intense research has been performed in this field due to its favorable atmospheric CO2 balance compared with conventional fossil fuels (net energy balance of 3.0–4.0 MJ/MJ). In this work, a comparison of transesterification of Canola oil with methanol under ultrasound and under mechanical stirring is reported. The general aspects of the ultrasound transesterification process and a comparative study of different types of homogeneous catalysts (NaOH, KOH, CH3ONa, tetramethyl ammonium hydroxide and four guanidines) are described. Special attention is given to ultrasound transesterification reaction using guanidines as catalysts. Full article
(This article belongs to the Special Issue Advances in Bio-Fuels Production)
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Open AccessArticle
Extraction Centrifuges—Intensified Equipment Facilitating Modular and Flexible Plant Concepts
ChemEngineering 2019, 3(1), 17; https://doi.org/10.3390/chemengineering3010017
Received: 13 December 2018 / Revised: 21 January 2019 / Accepted: 30 January 2019 / Published: 11 February 2019
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Abstract
In recent years, modularization of chemical production plants has become a widely discussed trend to overcome some of key issues the chemical industry struggles with. High volatility in raw material and customer markets, shorter product life cycles, cost pressure and increasing competition are [...] Read more.
In recent years, modularization of chemical production plants has become a widely discussed trend to overcome some of key issues the chemical industry struggles with. High volatility in raw material and customer markets, shorter product life cycles, cost pressure and increasing competition are just a few of them. Modularization of chemical production offers the opportunity to deal with these issues. The unit operations, which are capable to be applied in modular plant concepts, are subject of on-going research. On the reaction side, tubular continuous flow reactors are typical assets and methods for design and operation are available on a high technical level. Separation units on the downstream side are not yet developed to technical maturity. This paper focuses on extraction centrifuges, which are promising devices due to their large range of application, small volumes, high separation efficiency and excellent scalability. Industrial examples show the performance of extraction centrifuges in multi-purpose large-scale production facilities and prove that these units are predestined for application in modular plants. Full article
(This article belongs to the Special Issue Progress in Thermal Process Engineering)
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Open AccessReview
Transition Metal–Nitrogen–Carbon (M–N–C) Catalysts for Oxygen Reduction Reaction. Insights on Synthesis and Performance in Polymer Electrolyte Fuel Cells
ChemEngineering 2019, 3(1), 16; https://doi.org/10.3390/chemengineering3010016
Received: 11 December 2018 / Revised: 21 January 2019 / Accepted: 31 January 2019 / Published: 11 February 2019
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Abstract
Platinum group metal (PGM)-free catalysts for oxygen reduction reaction (ORR) have attracted increasing interest as potential candidates to replace Pt, in the view of a future widespread commercialization of polymer electrolyte fuel cell (PEFC) devices, especially for automotive applications. Among different types of [...] Read more.
Platinum group metal (PGM)-free catalysts for oxygen reduction reaction (ORR) have attracted increasing interest as potential candidates to replace Pt, in the view of a future widespread commercialization of polymer electrolyte fuel cell (PEFC) devices, especially for automotive applications. Among different types of PGM-free catalysts, M–N–C materials appear to be the most promising ones in terms of activity. These catalysts can be produced using a wide variety of precursors containing C, N, and one (or more) active transition metal (mostly Fe or Co). The catalysts synthesis methods can be very different, even though they usually involve at least one pyrolysis step. In this review, five different synthesis methods are proposed, and described in detail. Several catalysts, produced approximately in the last decade, were analyzed in terms of performance in rotating disc electrode (RDE), and in H2/O2 or H2/air PEFC. The catalysts are subdivided in five different categories corresponding to the five synthesis methods described, and the RDE and PEFC performance is put in relation with the synthesis method. Full article
(This article belongs to the Special Issue Functional Materials for Renewable Energy Technologies)
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Open AccessArticle
Electrochemical Carbon Dioxide Reduction in Methanol at Cu and Cu2O-Deposited Carbon Black Electrodes
ChemEngineering 2019, 3(1), 15; https://doi.org/10.3390/chemengineering3010015
Received: 7 December 2018 / Revised: 29 January 2019 / Accepted: 1 February 2019 / Published: 8 February 2019
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Abstract
The electrochemical reduction of carbon dioxide in methanol was investigated with Cu and Cu2O-supported carbon black (Vulcan XC-72) nanoparticle electrodes. Herein, Cu or a Cu2O-deposited carbon black catalyst has been synthesized by the reduction method for a Cu ion, [...] Read more.
The electrochemical reduction of carbon dioxide in methanol was investigated with Cu and Cu2O-supported carbon black (Vulcan XC-72) nanoparticle electrodes. Herein, Cu or a Cu2O-deposited carbon black catalyst has been synthesized by the reduction method for a Cu ion, and the drop-casting method was applied for the fabrication of a modified carbon black electrode. A catalyst ink solution was fabricated by dispersing the catalyst particles, and the catalyst ink was added onto the carbon plate. The pH of suspension was effective for controlling the Cu species for the metallic copper and the Cu2O species deposited on the carbon black. Without the deposition of Cu, only CO and methyl formate were produced in the electrochemical CO2 reduction, and the production of hydrocarbons could be scarcely observed. In contrast, hydrocarbons were formed by using Cu or Cu2O-deposited carbon black electrodes. The maximum Faraday efficiency of hydrocarbons was 40.3% (26.9% of methane and 13.4% of ethylene) at −1.9 V on the Cu2O-deposited carbon black catalyst. On the contrary, hydrogen evolution could be depressed to 34.7% under the condition. Full article
(This article belongs to the Special Issue Carbon-Based Materials and Their Electrochemical Applications)
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Open AccessArticle
Application of Mathematical Modelling to Reducing and Minimising Energy Requirement for Oxygen Transfer in Batch Stirred Tank Bioreactors
ChemEngineering 2019, 3(1), 14; https://doi.org/10.3390/chemengineering3010014
Received: 27 September 2018 / Revised: 20 November 2018 / Accepted: 30 January 2019 / Published: 3 February 2019
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Abstract
In this study, microbial kinetic and oxygen transfer modelling coupled with energy analysis was applied to investigate how manipulation and control of agitator power input and air flowrate can reduce and minimise the total energy requirement in a batch aerobic bioprocess subject to [...] Read more.
In this study, microbial kinetic and oxygen transfer modelling coupled with energy analysis was applied to investigate how manipulation and control of agitator power input and air flowrate can reduce and minimise the total energy requirement in a batch aerobic bioprocess subject to constraints. The study showed that major energy savings can be made by appropriate selection of these variables and how they are controlled throughout a bioprocess. In many bioprocesses, the oxygen concentration in the liquid is controlled at a constant value. This may be achieved by maintaining the agitator power at a constant value and varying the air flowrate or vice versa, or by continuously varying both. The modelling showed that the minimum or near-minimum total energy requirement occurred when operating at the onset of impeller flooding throughout the bioprocess by continuously varying both impeller power and air flowrate over the bioprocess time. Operating at the onset of flooding may not be practical to implement in practice. However, the minimum energy can be approached by dividing the bioprocess time into a small number of time segments with appropriately chosen constant agitator powers and varying the air flowrate within each segment. This is much more practical to implement. Full article
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Open AccessArticle
Multisensory Gas Chromatography for Field Analysis of Complex Gaseous Mixtures
ChemEngineering 2019, 3(1), 13; https://doi.org/10.3390/chemengineering3010013
Received: 5 December 2018 / Revised: 25 January 2019 / Accepted: 28 January 2019 / Published: 2 February 2019
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Abstract
A novel approach to analysis of complex gaseous mixtures is presented. The approach is based on the utilization of a compact gas chromatograph in combination with an array of highly integrated and selective metal oxide (MOX) sensors. Thanks to the implementation of a [...] Read more.
A novel approach to analysis of complex gaseous mixtures is presented. The approach is based on the utilization of a compact gas chromatograph in combination with an array of highly integrated and selective metal oxide (MOX) sensors. Thanks to the implementation of a multisensory detector, the device collects multiple chromatograms in a single run. The sensors in the integrated MEMS platform are very distinct in their catalytic properties. Hence, the time separation by chromatographic column is complemented by catalytic separation by a multisensory detector. Furthermore, the device can perform the analysis in a broad range of concentrations, from ppb to hundreds of ppm. Low ppb and even sub-ppb levels of detection for some analytes were achieved. As a part of this effort, nanocomposite gas sensors were synthesized for selective detection of hydrogen sulfide, mercaptans, alcohols, ketones, and heavy hydrocarbons. Full article
(This article belongs to the Special Issue TiO2 Nanoparticles: Synthesis and Applications)
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Open AccessArticle
Nanocomposites of Barium Titanate Nanoparticles Embedded in Thermosetting Polymer Matrices (Novolac Resin/Unsaturated Polyesters/Epoxy Resin): A Comparative Study
ChemEngineering 2019, 3(1), 12; https://doi.org/10.3390/chemengineering3010012
Received: 23 December 2018 / Revised: 13 January 2019 / Accepted: 28 January 2019 / Published: 1 February 2019
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Abstract
Polymer matrix nanocomposites with embedded ferroelectric barium titanate particles were developed and characterized. The utility of such nanocomposites is the energy storage capability that they exhibit, besides their low weight and cost, in comparison to materials that are customarily used for this purpose. [...] Read more.
Polymer matrix nanocomposites with embedded ferroelectric barium titanate particles were developed and characterized. The utility of such nanocomposites is the energy storage capability that they exhibit, besides their low weight and cost, in comparison to materials that are customarily used for this purpose. The polymers that have been used as matrices in the composites belong to the three most usable thermosetting polymer resins (novolacs, unsaturated polyesters, and epoxy resins), were either laboratory synthesized or commercially supplied. Structure and morphology of the produced composite specimens were studied via Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD), and Fourier Transformation Infrared Spectroscopy (FTIR). Thermal, mechanical and electrical performance was examined via Differential Scanning Calorimetry (DSC), bending and shear strength tests (three-point method), and Broadband Dielectric Spectroscopy (BDS), respectively. Mechanical shear and bending strength values were determined, as well as mechanical failure mode (brittle or elastomer) were estimated. Dielectric measurements disclosed the presence of four relaxation processes (α-mode, β-mode, and γ-mode) and Interfacial Polarization between the system’s constituents. The comparative study ended with the calculation of energy density, so that the energy storing capability could be estimated. Full article
(This article belongs to the Special Issue Preparation of Metal Nanoparticles and Their Application in Catalysis)
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Open AccessEditorial
Acknowledgement to Reviewers of ChemEngineering in 2018
ChemEngineering 2019, 3(1), 11; https://doi.org/10.3390/chemengineering3010011
Published: 19 January 2019
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Abstract
Rigorous peer-review is the corner-stone of high-quality academic publishing [...] Full article
Open AccessArticle
A Multivariate Statistical Analyses of Membrane Performance in the Clarification of Citrus Press Liquor
ChemEngineering 2019, 3(1), 10; https://doi.org/10.3390/chemengineering3010010
Received: 19 October 2018 / Revised: 6 December 2018 / Accepted: 10 January 2019 / Published: 17 January 2019
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Abstract
The orange press liquor is a by-product of the orange juice production containing bioactive compounds recognized for their beneficial implications in human health. The recovery of these compounds offers new opportunities for the formulation of products of interest in food, pharmaceutical and cosmetic [...] Read more.
The orange press liquor is a by-product of the orange juice production containing bioactive compounds recognized for their beneficial implications in human health. The recovery of these compounds offers new opportunities for the formulation of products of interest in food, pharmaceutical and cosmetic industry. The clarification of orange press liquor by microfiltration (MF) and/or ultrafiltration (UF) processes is a valid approach to remove macromolecules, colloidal particles, and suspended solids from sugars and bioactive compounds. In this work the clarification of orange press liquor was studied by using three flat-sheet polymeric membranes: a MF membrane with a pore size of 0.2 μm and two UF membranes with nominal molecular weight cut-off (MWCO) of 150 and 200 kDa, respectively. The membrane performance, in terms of permeate flux and membrane rejection towards hesperidin and sugars, was studied according to a multivariate analyses approach. In particular, characteristics influencing the performance of the investigated membranes, such as molecular weight cut-off (MWCO), contact angle, membrane thickness, pore size distribution, as well as operating conditions, including temperature, and operating time, were analysed through the partial least square regression (PLSR). The multivariate method revealed crucial information on variables which are relevant to maximize the permeate flux and to minimize the rejection of hesperidin and sugars in the clarification of orange press liquor. Full article
(This article belongs to the Special Issue Membrane and Membrane Reactors Operations in Chemical Engineering)
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Open AccessArticle
Solar Energy Assisted Membrane Reactor for Hydrogen Production
ChemEngineering 2019, 3(1), 9; https://doi.org/10.3390/chemengineering3010009
Received: 9 November 2018 / Revised: 10 December 2018 / Accepted: 2 January 2019 / Published: 15 January 2019
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Abstract
Pd-based membrane reactors are strongly recognized as an effective way to boost H2 yield and natural gas (NG) conversion at low temperatures, compared to conventional steam reforming plants for hydrogen production, thereby representing a potential solution to reduce the energy penalty of such [...] Read more.
Pd-based membrane reactors are strongly recognized as an effective way to boost H2 yield and natural gas (NG) conversion at low temperatures, compared to conventional steam reforming plants for hydrogen production, thereby representing a potential solution to reduce the energy penalty of such a process, while keeping the lower CO2 emissions. On the other hand, the exploitation of solar energy coupled with a membrane steam reformer can further reduce the environmental impact of these systems. On this basis, the paper deals with the design activities and experimentation carried out at a pilot level in an integrated prototype where structured catalysts and Pd-based membranes are arranged together and thermally supported by solar-heated molten salts for steam reforming reaction Full article
(This article belongs to the Special Issue Membrane and Membrane Reactors Operations in Chemical Engineering)
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Open AccessReview
Water and Wastewater Treatment Systems by Novel Integrated Membrane Distillation (MD)
ChemEngineering 2019, 3(1), 8; https://doi.org/10.3390/chemengineering3010008
Received: 30 September 2018 / Revised: 16 December 2018 / Accepted: 7 January 2019 / Published: 15 January 2019
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Abstract
The scarcity of freshwater has been recognized as one of the main challenges people must overcome in the 21st century. The adoption of an environmentally friendly, cost-effective, and energy-efficient membrane distillation (MD) process can mitigate the pollution caused by industrial and domestic wastes. [...] Read more.
The scarcity of freshwater has been recognized as one of the main challenges people must overcome in the 21st century. The adoption of an environmentally friendly, cost-effective, and energy-efficient membrane distillation (MD) process can mitigate the pollution caused by industrial and domestic wastes. MD is a thermally driven process based on vapor–liquid equilibrium, in which the separation process takes place throughout a microporous hydrophobic membrane. The present paper offers a comprehensive review of the state-of-the-art MD technology covering the MD applications in wastewater treatment. In addition, the important and sophisticated recent advances in MD technology from the perspectives of membrane characteristics and preparation, membrane configurations, membrane wetting, fouling, and renewable heat sources have been presented and discussed. Full article
(This article belongs to the Special Issue Membrane and Membrane Reactors Operations in Chemical Engineering)
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Open AccessArticle
Synthesis and Characterization of Reduced Graphene Oxide and Their Application in Dye-Sensitized Solar Cells
ChemEngineering 2019, 3(1), 7; https://doi.org/10.3390/chemengineering3010007
Received: 5 October 2018 / Revised: 29 December 2018 / Accepted: 8 January 2019 / Published: 15 January 2019
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Abstract
Reduced graphene oxide has certain unique qualities that make them versatile for a myriad of applications. Unlike graphene oxide, reduced graphene oxide is a conductive material and well suited for use in electrically conductive materials, such as solar cell devices. In this study, [...] Read more.
Reduced graphene oxide has certain unique qualities that make them versatile for a myriad of applications. Unlike graphene oxide, reduced graphene oxide is a conductive material and well suited for use in electrically conductive materials, such as solar cell devices. In this study, we report on the synthesis of graphene oxide as well as the fabrication and characterization of dye-sensitized solar cells with a photoanode which is an amalgam of reduced graphene oxide and titanium dioxide. The synthesized reduced graphene oxide and the corresponding photoanode were fully characterized using Ultraviolet-visible, Fourier transform infrared (FTIR), and Raman Spectrometry. The morphology of the sample was assessed using Atomic Force Microscopy, Field Emission Scanning Electron Microscopy, Transmission Electron Microscopy, and Energy Dispersive X-ray Spectroscopy. The photovoltaic characteristics were determined by photocurrent and photo-voltage measurements of the fabricated solar cells. The electrical impedances of both sets of devices were also evaluated. Overall, the solar to electric power efficiency of the device with reduced graphene oxide was observed to be higher (2.02%) than the device without the reduced graphene oxide (1.61%). Full article
(This article belongs to the Special Issue TiO2 Nanoparticles: Synthesis and Applications)
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Open AccessArticle
Preliminary Equipment Design for On-Board Hydrogen Production by Steam Reforming in Palladium Membrane Reactors
ChemEngineering 2019, 3(1), 6; https://doi.org/10.3390/chemengineering3010006
Received: 31 October 2018 / Revised: 17 December 2018 / Accepted: 7 January 2019 / Published: 15 January 2019
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Abstract
Hydrogen, as an energy carrier, can take the main role in the transition to a new energy model based on renewable sources. However, its application in the transport sector is limited by its difficult storage and the lack of infrastructure for its distribution. [...] Read more.
Hydrogen, as an energy carrier, can take the main role in the transition to a new energy model based on renewable sources. However, its application in the transport sector is limited by its difficult storage and the lack of infrastructure for its distribution. On-board H2 production is proposed as a possible solution to these problems, especially in the case of considering renewable feedstocks such as bio-ethanol or bio-methane. This work addresses a first approach for analyzing the viability of these alternatives by using Pd-membrane reactors in polymer electrolyte membrane fuel cell (PEM-FC) vehicles. It has been demonstrated that the use of Pd-based membrane reactors enhances hydrogen productivity and provides enough pure hydrogen to feed the PEM-FC requirements in one single step. Both alternatives seem to be feasible, although the methane-based on-board hydrogen production offers some additional advantages. For this case, it is possible to generate 1.82 kmol h−1 of pure H2 to feed the PEM-FC while minimizing the CO2 emissions to 71 g CO2/100 km. This value would be under the future emissions limits proposed by the European Union (EU) for year 2020. In this case, the operating conditions of the on-board reformer are T = 650 °C, Pret = 10 bar and H2O/CH4 = 2.25, requiring 1 kg of catalyst load and a membrane area of 1.76 m2. Full article
(This article belongs to the Special Issue Membrane and Membrane Reactors Operations in Chemical Engineering)
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Open AccessArticle
Hydrogen and Oxygen Evolution in a Membrane Photoreactor Using Suspended Nanosized Au/TiO2 and Au/CeO2
ChemEngineering 2019, 3(1), 5; https://doi.org/10.3390/chemengineering3010005
Received: 8 October 2018 / Revised: 29 November 2018 / Accepted: 4 January 2019 / Published: 10 January 2019
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Abstract
Photocatalysis combined with membrane technology could offer an enormous potential for power generation in a renewable and sustainable way. Herein, we describe the one-step hydrogen and oxygen evolution through a photocatalytic membrane reactor. Experimental tests were carried out by means of a two-compartment [...] Read more.
Photocatalysis combined with membrane technology could offer an enormous potential for power generation in a renewable and sustainable way. Herein, we describe the one-step hydrogen and oxygen evolution through a photocatalytic membrane reactor. Experimental tests were carried out by means of a two-compartment cell in which a modified Nafion membrane separated the oxygen and hydrogen evolution semi-cells, while iron ions permeating through the membrane acted as a redox mediator. Nanosized Au/TiO2 and Au/CeO2 were employed as suspended photocatalysts for hydrogen and oxygen generation, respectively. The influence of initial Fe3+ ion concentration, ranging from 5 to 20 mM, was investigated, and the best results in terms of hydrogen and oxygen evolution were registered by working with 5 mM Fe3+. The positive effect of gold on the overall water splitting was confirmed by comparing the photocatalytic results obtained with the modified/unmodified titania and ceria. Au-loading played a key role for controlling the photocatalytic activity, and the optimal percentage for hydrogen and oxygen generation was 0.25 wt%. Under irradiation with visible light, hydrogen and oxygen were produced in stoichiometric amounts. The crucial role of the couple Fe3+/Fe2+ and of the membrane on the performance of the overall photocatalytic system was found. Full article
(This article belongs to the Special Issue Membrane and Membrane Reactors Operations in Chemical Engineering)
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Open AccessCommunication
An Efficient Computational Scheme for Two-Phase Steam Condensation in the Presence of CO2 for Wellbore and Long-Distance Flow
ChemEngineering 2019, 3(1), 4; https://doi.org/10.3390/chemengineering3010004
Received: 13 November 2018 / Revised: 8 December 2018 / Accepted: 6 January 2019 / Published: 9 January 2019
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Abstract
Here we present an efficient and robust calculation scheme for two-phase, one-dimensional (1D) steady state steam condensation in the presence of CO2, based on conservation rules and thermodynamic phase relations. The mixing of fluids and phases is assumed to be homogeneous. [...] Read more.
Here we present an efficient and robust calculation scheme for two-phase, one-dimensional (1D) steady state steam condensation in the presence of CO2, based on conservation rules and thermodynamic phase relations. The mixing of fluids and phases is assumed to be homogeneous. Heat transfer is considered between the fluids and the ambient formations. For convenience, state equations are presented in terms of the entropy changes of individual phases, and the simple additive rule for the mixture. To monitor phase changes, the phase rule is checked. This investigation has practical significance for steam injection operation and long-distance pipe flow applications in the geothermal and mid- and up-stream oil and gas industries. Full article
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Open AccessArticle
Photocatalytic and Antimicrobial Properties of Ag2O/TiO2 Heterojunction
ChemEngineering 2019, 3(1), 3; https://doi.org/10.3390/chemengineering3010003
Received: 5 December 2018 / Revised: 28 December 2018 / Accepted: 2 January 2019 / Published: 8 January 2019
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Abstract
Ag2O/TiO2 heterojunctions were prepared by a simple method, i.e., the grinding of argentous oxide with six different titania photocatalysts. The physicochemical properties of the obtained photocatalysts were characterized by diffuse-reflectance spectroscopy (DRS), X-ray powder diffraction (XRD) and scanning transmission electron [...] Read more.
Ag2O/TiO2 heterojunctions were prepared by a simple method, i.e., the grinding of argentous oxide with six different titania photocatalysts. The physicochemical properties of the obtained photocatalysts were characterized by diffuse-reflectance spectroscopy (DRS), X-ray powder diffraction (XRD) and scanning transmission electron microscopy (STEM) with an energy dispersive X-ray spectroscopy (EDS). The photocatalytic activity was investigated for the oxidative decomposition of acetic acid and methanol dehydrogenation under UV/vis irradiation and for the oxidative decomposition of phenol and 2-propanol under vis irradiation. Antimicrobial properties were tested for bacteria (Escherichia coli) and fungi (Candida albicans and Penicillium chrysogenum) under UV and vis irradiation and in the dark. Enhanced activity was observed under UV/vis (with synergism for fine anatase-containing samples) and vis irradiation for almost all samples. This suggests a hindered recombination of charge carriers by p-n heterojunction or Z-scheme mechanisms under UV irradiation and photo-excited electron transfer from Ag2O to TiO2 under vis irradiation. Improved antimicrobial properties were achieved, especially under vis irradiation, probably due to electrostatic attractions between the negative surface of microorganisms and the positively charged Ag2O. Full article
(This article belongs to the Special Issue Heterogeneous Photocatalysis and Photocatalytic Nanomaterials)
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Open AccessReview
Progress in Modeling of Silica-Based Membranes and Membrane Reactors for Hydrogen Production and Purification
ChemEngineering 2019, 3(1), 2; https://doi.org/10.3390/chemengineering3010002
Received: 15 November 2018 / Revised: 3 December 2018 / Accepted: 24 December 2018 / Published: 1 January 2019
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Abstract
Hydrogen is seen as the new energy carrier for sustainable energy systems of the future. Meanwhile, proton exchange membrane fuel cell (PEMFC) stacks are considered the most promising alternative to the internal combustion engines for a number of transportation applications. Nevertheless, PEMFCs need [...] Read more.
Hydrogen is seen as the new energy carrier for sustainable energy systems of the future. Meanwhile, proton exchange membrane fuel cell (PEMFC) stacks are considered the most promising alternative to the internal combustion engines for a number of transportation applications. Nevertheless, PEMFCs need high-grade hydrogen, which is difficultly stored and transported. To solve these issues, generating hydrogen using membrane reactor (MR) systems has gained great attention. In recent years, the role of silica membranes and MRs for hydrogen production and separation attracted particular interest, and a consistent literature is addressed in this field. Although most of the scientific publications focus on silica MRs from an experimental point of view, this review describes the progress done in the last two decades in terms of the theoretical approach to simulate silica MR performances in the field of hydrogen generation. Furthermore, future trends and current challenges about silica membrane and MR applications are also discussed. Full article
(This article belongs to the Special Issue Control and Optimization of Chemical and Biochemical Processes)
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