Search Results (11)

The conventional synthesis of the Metal–Organic Framework (MOF) MIL-101(Cr)-SO₃H employs hydrofluoric acid as the modulator, posing handling challenges due to its irritating, corrosive, and toxic nature, as well as its reactivity with glass and metals. This study aims to find a new hydrofluoric acid-free synthesis route for MIL-101(Cr)-SO₃H, proposing acetic acid and nitric acid as modulator alternatives. Four MIL-101(Cr)-SO₃H samples were prepared: one without any modulator and the other three using a similar volume of either hydrofluoric acid, acetic acid, or nitric acid as the modulator. The so-obtained mass yield ranked as follows: without any modulator (32.6%) > acetic acid (29.6%) > nitric acid (25.2%) >> hydrofluoric acid (2.2%), whereas the total pore volume and BET surface area followed the order: hydrofluoric acid (0.87 cm³ g⁻¹, 1862 m² g⁻¹) > nitric acid (0.81 cm³ g⁻¹, 1554 m² g⁻¹) > acetic acid (0.72 cm³ g⁻¹, 1374 m² g⁻¹) > without any modulator (0.69 cm³ g⁻¹, 1342 m² g⁻¹). Despite the superior texture parameters obtained using hydrofluoric acid, the low synthesis yield and associated risks make this route non-viable. Acetic or nitric acid-based synthesis offers a promising alternative with a drastically higher yield, safer handling, and reduced environmental impact. In an attempt to improve the textural properties of the hydrofluoric acid-free MOFs, a series of samples were produced with increasing amounts of acetic acid, achieving BET surface areas of up to 1504 m² g⁻¹ and pore volumes of up to 0.81 cm³ g⁻¹. Full article

Traditional methods to develop biomass-based carbon adsorbents generally involve carbonization followed by chemical or physical activation. However, routes involving the hydrothermal treatment of biomass are receiving growing interest. In this work, two different strategies for the synthesis of sustainable CO₂ adsorbents are compared, i.e., in situ ionic activation and hydrothermal treatment followed by activation with CO₂. The latter is a green and simple procedure that does not require the addition of chemicals or acid-washing stages, and which leads to carbon adsorbents with relatively high CO₂ adsorption capacity at low pressures, up to 0.64 mmol g⁻¹ at 15 kPa and 50 °C, conditions relevant for postcombustion CO₂ capture applications. On the other hand, in situ ionic activation can lead to carbon adsorbents with superior CO₂ adsorption capacity in the aforementioned conditions, 0.78 mmol g⁻¹, and with reduced cost and environmental impact compared to conventional chemical activation. Full article

The gasification process involves several reactions that occur simultaneously and are interrelated by several independent variables. Simulation tools can help us to understand the process behaviour and predict the efficiency and final composition of the products. In this work, two thermodynamic equilibrium models developed in Aspen Plus^® software were assessed: a non-stoichiometric model based on the feedstock composition and on the most probable compounds expected from the results of the gasification process using minimisation of Gibbs free energy and a stoichiometric model based on a set of chemical reactions considered as the most relevant to describe the gasification process. Both models were validated with experimental data from a bubbling fluidised bed semi-pilot scale gasifier using pine kernel shells (PKS) as feedstock. The influence of temperature, stoichiometric ratio (SR) and steam to biomass ratio (SBR) were analysed. Overall, predictions of the gas composition and gasification efficiency parameters by the stoichiometric model showed better agreement to the experimental results. Our results point out the significance of an accurate description of the equilibrium composition of producer gas with the stoichiometric model for the gasification of biomass. Full article

The implementation of carbon capture, use, and storage in the cement industry is a necessity, not an option, if the climate targets are to be met. Although no capture technology has reached commercial scale demonstration in the cement sector yet, much progress has been made in the last decade. This work intends to provide a general overview of the CO₂ capture technologies that have been evaluated so far in the cement industry at the pilot scale, and also about the current plans for future commercial demonstration. Full article

The urban sprawl phenomenon has attracted the attention of social researchers since the mid-20th century. It seemed that all relevant aspects had been extensively studied and that it would be difficult to produce new studies with significant contributions. However, in the last decade, we have witnessed a revival of the literature on urban sprawl for three main reasons: (i) the existence of new methodologies to measure the phenomenon based on digital cartography and geo-referenced information, (ii) new hypotheses about the relevance of the formation of metropolitan areas not institutionally integrated into urban sprawl in many places and, mainly, (iii) the role of urban density in the environmental sustainability of cities. The recent literature on this third aspect has grown the most and around which it seems that new and interesting lines of future research will develop. The objective of this work is to present a synthetic review of the most recent literature on urban sprawl as of the end of the second decade of the XXI century. This review can serve to recapitulate the growing consensus that is being formed on the lower environmental sustainability of low-density cities and diffuse limits. Full article

Battery requirements for electrical vehicles are continuously becoming more demanding in terms of energy density and reliability. Nowadays, batteries for drones must be able to supply 100 A for 15 min, not to mention the specifications required for batteries in electrical vehicles. These specifications result in more stringent specifications for battery chargers. They are required to be more efficient, flexible, and, as with any another power equipment, to have reduced size and weight. Since the parallel resonant converter can operate as a current source and as a voltage source, this paper presents a battery charger power stage for lithium ion polymer batteries, based on the above topology, operating in zero voltage switching mode, and implementing frequency and duty cycle control. Full article

The selective separation of CO₂ from gas mixtures representative of flue gas generated in waste incineration systems is studied on two activated carbons obtained from pine sawdust and compared to a commercial activated carbon. Dynamic adsorption experiments were conducted in a fixed-bed adsorption column using a binary mixture (N₂/CO₂) with a composition representative of incineration streams at temperatures from 30 to 70 °C. The adsorption behavior of humid mixtures (N₂/CO₂/H₂O) was also evaluated in order to assess the influence of water vapor in CO₂ adsorption at different relative humidity in the feed gas: 22% and 60%. Moreover, CO₂ adsorption was studied in less favorable conditions, i.e., departing from a bed initially saturated with H₂O. In addition, the effect of CO₂ on H₂O adsorption was examined. Experimental results showed that the CO₂ adsorption capacity can be reduced significantly by the adsorption of H₂O (up to 60% at high relative humidity conditions). On the other hand, the breakthrough tests over the adsorbent initially saturated with water vapor indicated that H₂O is little affected by CO₂ adsorption. The experimental results pointed out the biomass based carbons as best candidates for CO₂ separation under incineration flue gas conditions. Full article

Investigation into clean energies has been focused on finding an alternative to fossil fuels in order to reduce global warming while at the same time satisfying the world’s energy needs. Biomass gasification is seen as a promising thermochemical conversion technology as it allows useful gaseous products to be obtained from low-energy-density solid fuels. Air–steam mixtures are the most commonly used gasification agents. The gasification performances of several biomass samples and their mixtures were compared. One softwood (pine) and one hardwood (chestnut), their torrefied counterparts, and other Spanish-based biomass wastes such as almond shell, olive stone, grape and olive pomaces or cocoa shell were tested, and their behaviors at several different stoichiometric ratios (SR) and steam/air ratios (S/A) were compared. The optimum SR was found to be in the 0.2–0.3 range for S/A = 75/25. At these conditions a syngas stream with 35% of H₂ + CO and a gas yield of 2 L gas/g fuel were obtained, which represents a cold-gas efficiency of almost 50%. The torrefaction process does not significantly affect the quality of the product syngas. Some of the obtained chars were analyzed to assess their use as precursors for catalysts, combustion fuel or for agricultural purposes such as soil amendment. Full article

The effect of post-treatment upon the H₂O adsorption performance of biomass-based carbons was studied under post-combustion CO₂ capture conditions. Oxygen surface functionalities were partially replaced through heat treatment, acid washing, and wet impregnation with amines. The surface chemistry of the final carbon is strongly affected by the type of post-treatment: acid treatment introduces a greater amount of oxygen whereas it is substantially reduced after thermal treatment. The porous texture of the carbons is also influenced by post-treatment: the wider pore volume is somewhat reduced, while narrow microporosity remains unaltered only after acid treatment. Despite heat treatment leading to a reduction in the number of oxygen surface groups, water vapor adsorption was enhanced in the higher pressure range. On the other hand acid treatment and wet impregnation with amines reduce the total water vapor uptake thus being more suitable for post-combustion CO₂ capture applications. Full article

The challenge of developing effective separation and purification technologies that leave much smaller energy footprints is greater for carbon dioxide (CO₂) than for other gases. In addition to its involvement in climate change, CO₂ is present as an impurity in biogas and bio-hydrogen (biological production by dark fermentation), in post-combustion processes (flue gas, CO₂-N₂) and many other gas streams. Selected phenol-formaldehyde resin-based activated carbons prepared in our laboratory have been evaluated under static conditions (adsorption isotherms) as potential adsorbents for CO₂ separation at sub-atmospheric pressures, i.e., in post-combustion processes or from biogas and bio-hydrogen streams. CO₂, H₂, N₂, and CH₄ adsorption isotherms at 25 °C and up to 100 kPa were obtained using a volumetric equipment and were correlated by applying the Sips model. Adsorption equilibrium was then predicted for multicomponent gas mixtures by extending the multicomponent Sips model and the Ideal Adsorbed Solution Theory (IAST) in conjunction with the Sips model. The CO₂ uptakes of the resin-derived carbons from CO₂-CH₄, CO₂-H₂, and CO₂-N₂ at atmospheric pressure were greater than those of the reference commercial carbon (Calgon BPL). The performance of the resin-derived carbons in terms of equilibrium of adsorption seems therefore relevant to CO₂ separation in post-combustion (flue gas, CO₂-N₂) and in hydrogen fermentation (CO₂-H₂, CO₂-CH₄). Full article