Brazilian Journal of Chemical Engineering最新文献

This research involved the implementation of steam-assisted dry reforming (SDR) on methane utilizing a CoMo/Al₂O₃ nanoflake catalyst under microwave irradiation. The CoMo/Al₂O₃ nanoflakes demonstrated superior catalytic activity for reforming reactions, attributed to their enhanced surface exposure to incident microwaves and heightened microwave absorption capability. Fischer–Tropsch (F–T) synthesis was employed for the production of liquid fuels, with the predicted syngas ratio (H₂/CO) easily adjustable by varying the steam-to-carbon ratio (S/C) supplied to the reactor. Achieving an H₂/CO ratio greater than one was feasible with an intake S/C ratio below 0.1 and 200 W of microwave power. In comparison to carbon-based catalysts, the CoMo nanoflakes exhibited significantly higher catalytic stability after 16 h of time-on-stream (TOS) during the SDR process under microwave irradiation. The utilization of microwaves in this process opens novel routes for methane reforming to fuel, offering distinct advantages.

Abstract

Anaerobic co-digestion of organic wastes and plant biomass generates an environmentally friendly energy source. Anaerobic co-digestion of cow dung (CD), goat manure (GM), and cactus cladodes (CC) was investigated under mesophilic laboratory conditions. A 14-day-long daily biogas production potential and methane content were evaluated for the three substrates co-digested at different mix ratios. Physicochemical properties showed significant differences between the raw and digested substrates. Biogas production started after the first day of anaerobic digestion for all substrates, with the peak observed near day fourteen. The anaerobic co-digestion of 66.7% GM and 33.3% CC substrate mixture produced the highest biogas yield. The cumulative biogas production study also revealed that the same substrate combination achieved better biogas yield. The anaerobic digestion of CD, GM, and CC showed a significant increase in biogas yield followed by a reduction in volatile and total solid contents. The 100% CC, 33.3% CC + 66.7% CD, 33.3% CC + 66.7% GM, and 33.33% CC + 33.33% CD + 33.33% GM anaerobic digestions achieved biogas with methane content (%) of 56.02, 72.6, 56.65, and 67.95, respectively. The 33.33% CC + 33.33% CD + 33.33% GM anaerobic co-digestion achieved the highest methane content compared to other substrates. The CC + CD + GM and CC + GM mixtures had a C/N ratio ranging from 20 to 30, contributing to better biogas yield with more methane content than substrates deviating from such a ratio. For all substrates, the methane content of the biogas ranged from 50 to 72.6%. The study also revealed that the co-digestion of CC with GM resulted in a better cummulative biogas yield and cumulative methane content.

Biotechnology has increasing relevance worldwide in the mining sector, either as a response to the recovery of metals (gold, silver, copper, zinc, nickel, among others) as well as an alternative in the bioremediation of contaminated soil and water, frequent problems directly linked to mining activities. Hence, acidophilic microorganisms are of special scientific and industrial interest for the sustainable use of mineral resources. Nowadays, a wide variety of acidophilic chemolithotrophic microorganisms (MOs) are recognized, Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans, Acidithiobacillus caldus, and Leptospirillum ferrooxidans, among others; those MOs grow in culture medium at pH ≤ 3 and obtain cellular energy from the oxidation of inorganic compounds, such as sulfur and iron. These microorganisms have different abilities to act on the mineral, converting insoluble metal sulfides into soluble metal sulfates of those species that are of interest, or that prevent optimal recovery of a specific mineral. Such microorganisms have been applied in biomining operations and are internationally known for the recovery of valuable metals from low-grade ores and refractory ores. Likewise, these acidophilic MOs can bioremediate soils contaminated with metals, extract metals from sludge generated as a byproduct in wastewater treatment, detoxify hazardous waste and recover metals from electronic waste; so the main interest of biomining processes lies in the economic impact that has benefited the world, since it is known that 5% of the gold and 20% of the copper that has been extracted worldwide are using this type of bacteria in bioleaching processes. The objective of this review is to expand the knowledge of the characteristics and applications of the main acidophilic microorganisms used in the solubilization/extraction of minerals, whether for the recovery of metals, bioremediation, or reduction of metals in different systems.

Graphical abstract

The role of acidophilic bacteria in several industrial sectors. Created with BioRender.com.

Abstract

Gluconic acid is a chemical raw material widely used in the food and chemical industries that can be produced by oxidizing glucose and available sugar-rich substrates such as biomass. The abundance of glucose and fructose in industrial waste from lignocellulose and inverted sugar makes them a promising sustainable feedstock. In this work, the catalytic conversion of a glucose and fructose mixture into gluconic acid in an alkaline medium using Pd (4%)—Pt (1%)—Bi (5%)/C catalysts under flowing air was studied. Previously, the traditional chemical conversion of glucose into gluconic acid produced large amounts of by-products. In this work, we combined glucose and fructose to investigate the latter's influence on conversion. The selectivity to gluconic acid was significantly improved by fructose, indicating a new approach for using biomass and by-products such as glucose and fructose syrup. The first step was to conduct a series of experiments at different temperatures and pH levels. The second step was to experiment with adding fructose under optimal conditions. The gluconic acid was about 90%. The yield was approximately 79% at 55 °C and pH 9.5 using the same method with only glucose. Combining experimental data, we propose a kinetic model with a TOF (turnover frequency) between 1.0 and 5.5.

Abstract

This study compared the performance of microbial fuel cells (MFCs) using parchment paper as a separator to a CMI7000 proton exchange membrane. The MFCs were operated in two chambers with whey solution as the substrate. Parameters such as COD removal, internal resistance, power density, current density, and Coulombic efficiency ratio (CE) were evaluated. The CMI7000 membrane exhibited the highest COD removal at 92%, while the parchment paper achieved removal percentages ranging from 72 to 91%. The internal resistance was lower for the parchment paper separator for the first run, the internal resistances were 68 Ώ and 84 Ώ for parchment paper and CMI7000, respectively. The maximum energy densities were 219 mW/m² (5.74 mA/m²) and 421 mW/m² (8.24 mA/m²) for parchment paper and CMI7000 membrane, respectively. The CE values for parchment paper were 36.32% and 33.5%, while for the CMI7000 membrane, they were 42.73% and 32.0%, for the two runs. Overall, the study demonstrated that the parchment paper separator performed reasonably well in terms of COD removal, internal resistance, energy density, and Coulombic efficiency ratio compared to the CMI7000 membrane in microbial fuel cells.

Abstract

Over the past few decades, environmental contamination from the wastewater industry has gravely threatened the environment and public health. According to reports, thousands of different dyes and pigments are used in a range of industries around the world each year, producing more than 7 × 10⁵ tonnes of synthetic dyes. Environmental contamination can be prevented by using semiconductor metal sulfide nanostructures (MSNSs) with doping and heterojunction as photocatalysts for the long-term, economical removal of hazardous organic dyes. The current review focuses on the degradability of hazardous dyes in the environment by metal sulfide nanoparticles such as ZnS, CdS, CuS, Ag₂S, CoS, and FeS.

Vanadium pentoxide (V₂O₅) thin films were grown on porous silicon (PS) layer by electron beam evaporation technique under an oxygen partial pressure. The morphology of the porous surface before and after V₂O₅ deposition for different evaporation times was observed by the Scanning Electron Microscope (SEM). The predicts changes of the chemical composition and bonds at the porous surface have been studied by FTIR and Raman spectroscopies. Photoluminescence (PL) spectroscopy was carried out to study the effect of vanadium pentoxide thickness on the optical properties of V₂O₅/PS nanocomposites. The PL spectrum of PS show a red-shift of 90 nm following the deposition of vanadium pentoxide while a quenching of the PL intensity was observed. Referring to FTIR and Raman results, the origin of this shift can be attributed to the formation of oxidized vanadium elements at PS surface as well as the creation of localized states by V₂O₅ molecules inside the band gap of PS. The wavelength dependence of optical transmittance, reflectance and absorption coefficients were investigated. An increase in the optical band gap from 1.95 to 2.18 eV was obtained due to Moss-Burstein effect as well as the presence of vacancy defects in V₂O₅ film.

Phycobiliproteins (PBPs) are light collecting pigments of cyanobacteria that attract growing interest for several industrial applications. Each step of the extraction process is crucial for yield, concentration and quality of obtained pigments. In the current work, we present an optimization scheme of major limiting steps for PBPs extraction from Arthrospira platensis biomass. As first step, the effects of pretreatment, extraction time, and separation conditions on the recovery of PBPs were compared. Subsequently, the influence of pH and concentration of the extraction buffer as well as the addition of preservatives (Polyethylene glycol (PEG), Magnesium chloride (MgCl₂), and Calcium chloride (CaCl₂)) was studied. In addition, the effect of the biomass type (dried vs wet) and its concentration in the extraction buffer was also investigated. Optimal extraction required the use of dry biomass at relatively low ratio (1:50, solvent:biomass), without previous treatment. The use of concentrated phosphate buffer (100 mM) at a neutral pH gave the highest PBPs recovery and concentration after 6 h of extraction followed with a separation at 6000 rpm during 15 min. Calcium chloride used at 1.5% improved by 30% both PBPs recovery and concentration in the crude extract. The optimized protocol allowed the recovery of 464.5 mg/g PBPs from spirulina biomass with concentration of 15.9 mg/ml. The crude PBPs obtained with this extraction method reduced the stable radical DPPH with a percentage scavenging activity of 86.45 ± 1.2%. This protocol could reduce both PBPs time and cost extraction and is easily scalable for industrial application.

The worldwide crisis of the fossil fuels and the current environmental issues have led for the search of new alternative for the energy industrial sector. In this scenario, the production of second-generation ethanol, from the exploitation of lignocellulosic biomasses fractions, has presented itself as a prominent alternative. Thus, the present work aimed to develop a combined process for the sugarcane bagasse (SCB) fractionation using a deep eutectic solvent (DES), a new class of ecofriendly solvents, and diluted acid hydrolysis. The DES delignification process was able to reduce the SCB lignin content in about 48% and, at the optimum hydrolysis conditions (1.1% v v⁻¹ of sulfuric acid and 59 min of hydrolysis time), the delignified material was converted into a solid fraction rich in cellulose (51.11 ± 0.95%, increment of 41.46%) and into a liquor product rich in xylose (18.26 ± 3.14 g L⁻¹). The data statistical analysis proved that the combined strategy was superior to the single and direct acid hydrolyzation of SCB. The structural changes of the material after all investigated pretreatments were confirmed by FTIR and DRX techniques, what reinforce the relevance of the results here reported.

The markers commonly used to detect fraud and adulteration in fuels are conventional organic molecules. Recent developments in nanotechnology have gained an important role in this field. The novelty of this work is the application of multicolor semiconductor fluorescent nanocrystals, CdSe quantum dots (QDs), as gasoline nanomarkers. QDs with fluorescence emissions ranging from green to red were evaluated as gasoline nanomarkers. They retained their colloidal and fluorescence stability after more than 5 years, as verified by visualization under UV light and by absorption and fluorescence spectra. Additionally, they were clearly detected in gasoline concentrations of around 40 ppm. Advantages of this class of nanomarkers over traditional organic molecules markers are: the simpler production process, the high photostability and the ease and sensitivity of detection based on fluorescence emission in multicolored wavelengths. Thus, the application is potentially useful for different gasoline matrices. For instance, CdSe quantum dots could be used to differentiate regular gasoline from gasoline with additives, or differentiate gasolines produced in different sources and thus subjected to different commercial taxation. Therefore, this study presents nanomaterials such as CdSe QDs and their optical properties, used as gasoline nanomarkers, as a technological innovation in the field of Chemical Engineering.

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