ChemEngineering — Open Access Journal

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

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

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

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

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

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

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

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

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

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

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

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

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

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, P_ret = 10 bar and H₂O/CH₄ = 2.25, requiring 1 kg of catalyst load and a membrane area of 1.76 m². Full article

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

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

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

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