Design and optimization of a reverse electrodialysis stack for energy generation through salinity gradients

A model for design of Reverse Electrodialysis stacks for energy generation is presented and solved. A new optimization function is proposed for RED, which accounts for river water consume, net power density and thermodynamic efficiency of the process. The parameters of residence time and thickness of the compartments are successfully optimized using the new proposed function. Results suggest small residence time, compartments thickness, and transversal area and Long/Width ratio for maximum energy generation.Se presenta y resuelve un modelo para diseño de pilas de Electrodiálisis inversa. Se propuso una nueva función de optimización para RED, que tienen en cuenta el consumo de agua de río, la densidad de potencia neta y la eficiencia termodinámica del proceso. Los parámetros de tiempos de residencia y espesor de compartimientos fueron optimizados correctamente usando la nueva función propuesta. Los resultados sugieren pequeños tiempos de residencia, compartimientos de espesores delgados, poca área transversal y relaciones bajas de Longitud/ Ancho del compartimiento para máxima generación de energía

Energy generation from salinity gradients through reverse electrodialysis and capacitive reverse electrodialysis

El presente trabajo constituye el primer esfuerzo en Colombia y América Latina para desarrollar la tecnología de electrodiálisis inversa para obtención de energía a partir de gradiente salino. En esta tesis se utiliza un modelo en estado estacionario previamente descrito en la literatura y se desarrolla un modelo dinámico para describir el comportamiento de las tecnologías electrodiálisis inversa (RED) y electrodiálisis inversa capacitiva (CRED). Los modelos son validados experimentalmente. Se realiza la construcción y puesta en marcha de un generador de energía funcional para RED y CRED, se estudia el efecto de espaciadores conductores con geometrías alternativas sugeridas en la literatura. Además se estudia el potencial de generación de energía en Colombia mediante la prueba de la pila construida, utilizando agua recogida en campañas de campo proveniente del río Magdalena y del mar Caribe. La máxima densidad de potencia obtenida experimentalmente fue de 0.14 W/m2 para una pila de RED con 10 celdas con soluciones artificiales, mientras que la máxima potencia obtenida para CRED fue de 0.035 W/m2 para un stack con 3 celdas y espaciadores utilizando agua del río Magdalena y del mar Caribe. Finalmente se estudia experimentalmente el efecto que tiene en la concentración en equilibrio de membranas de intercambio iónico selectivas, el uso de soluciones de NaCl en presencia de iones bivalentes. Se estudia el efecto de los iones más abundantes en el agua de mar, tales como Mg+2, Ca+2 y SO4 -2 . Se observa un comportamiento de decrecimiento exponencial en la absorción de iones monovalentes en presencia de iones bivalentes, es decir, a bajas concentraciones de iones bivalentes (concentraciones similares al agua de mar), la capacidad de absorción de iones monovalentes de la membrana disminuye considerablementeAbstract: The present thesis work constitutes the first effort in Colombia and America Latina for developing Reverse Electrodialysis (RED) technology for energy recovery from salinity gradients. This thesis develops a dynamic model for RED and CRED and it also uses a stationary state model presented in literature to describe energy generation through salinity gradients. The model is experimentally validated. A lab scale energy generator for RED and CRED is designed, constructed and operationalized. The effect of conductive spacers with an alternative geometry suggested in literature is studied. Besides, the potential of energy generation in Colombia is studiedby testing the stack with waters from the Magdalena River a nd the Caribbean Sea. Maximum power density obtained experimentally was 0.14 W/m2 for a 10 cell RED stack using artificial solutions, while maximum power obtained for CRED was 0.03 W/m2 for a stack of 3 cells with spacers and river and sea water. Finally the effect that bivalent ion solutions have over equilibrium concentration in ion Exchange membranes (IEM) is experimentally tested. The ions studied are the most abundant in sea water: Mg+2, Ca+2 and SO4 -2 . An exponential decrease is observed in the absorption capacity of the membranes for monovalent ions, i.e. at low concentrations of bivalent ions (similar to the ones found in seawater), the absorption capacity of ionovalent ions decreases substantially.Maestrí

Design and optimization of a reverse electrodialysis stack for energy generation through salinity gradients

A model for design of Reverse Electrodialysis stacks for energy generation is presented and solved. A new optimization function is proposed for RED, which accounts for river water consume, net power density and thermodynamic efficiency of the process. The parameters of residence time and thickness of the compartments are successfully optimized using the new proposed function. Results suggest small residence time, compartments thickness, and transversal area and Long/Width ratio for maximum energy generation.Se presenta y resuelve un modelo para diseño de pilas de Electrodiálisis inversa. Se propuso una nueva función de optimización para RED, que tienen en cuenta el consumo de agua de río, la densidad de potencia neta y la eficiencia termodinámica del proceso. Los parámetros de tiempos de residencia y espesor de compartimientos fueron optimizados correctamente usando la nueva función propuesta. Los resultados sugieren pequeños tiempos de residencia, compartimientos de espesores delgados, poca área transversal y relaciones bajas de Longitud/Ancho del compartimiento para máxima generación de energía

Design and optimization of a reverse electrodialysis stack for energy generation through salinity gradients

A model for design of Reverse Electrodialysis stacks for energy generation is presented and solved. A new optimization function is proposed for RED, which accounts for river water consume, net power density and thermodynamic efficiency of the process. The parameters of residence time and thickness of the compartments are successfully optimized using the new proposed function. Results suggest small residence time, compartments thickness, and transversal area and Long/Width ratio for maximum energy generation

Calcination-free production of calcium hydroxide at sub-boiling temperatures.

Calcium hydroxide (Ca(OH)2), a commodity chemical, finds use in diverse industries ranging from food, to environmental remediation and construction. However, the current thermal process of Ca(OH)2 production via limestone calcination is energy- and CO2-intensive. Herein, we demonstrate a novel aqueous-phase calcination-free process to precipitate Ca(OH)2 from saturated solutions at sub-boiling temperatures in three steps. First, calcium was extracted from an archetypal alkaline industrial waste, a steel slag, to produce an alkaline leachate. Second, the leachate was concentrated using reverse osmosis (RO) processing. This elevated the Ca-abundance in the leachate to a level approaching Ca(OH)2 saturation at ambient temperature. Thereafter, Ca(OH)2 was precipitated from the concentrated leachate by forcing a temperature excursion in excess of 65 °C while exploiting the retrograde solubility of Ca(OH)2. This nature of temperature swing can be forced using low-grade waste heat (≤100 °C) as is often available at power generation, and industrial facilities, or using solar thermal heat. Based on a detailed accounting of the mass and energy balances, this new process offers at least ≈65% lower CO2 emissions than incumbent methods of Ca(OH)2, and potentially, cement production

Optimizing alkaline solvent regeneration through bipolar membrane electrodialysis for carbon capture

This work demonstrates and characterizes the use of a bipolar membrane electrodialysis for pH-driven CO2 capture and solvent regeneration using potassium hydroxide solutions. The impact of potassium concentration, current density and load ratio on the CO2 desorption efficiency was analyzed and substantiated with an equilibrium model. The system was tested with partially saturated solutions that mimic the expected carbon content of alkaline solvents that have been in contact with flue gas (carbon loading of 0.6 and K+ concentration from 0.5 M to 2 M). Among the tested current densities, 1000 A/m2 demonstrated the highest CO2 desorption efficiency but also the highest energy consumption, whereas 250 A/m2 exhibited the lowest energy consumption (8.8 GJ/ton CO2) but lower CO2 desorption. Efficiency losses were associated with H+ transport across the membranes at high load ratios and decrease of the bipolar membranes water dissociation efficiency at low current densities. This work establishes key performance indicators and describes fundamental characteristics of continuous bipolar membrane electrodialysis systems for regeneration of alkaline solvents used in post-combustion CO2 capture

A Rigorous Integrated Approach to Model Electrochemical Regeneration of Alkaline CO₂ Capture Solvents

This work develops a rigorous model for electrochemical regeneration in Aspen Custom Modeler (ACM), designed to seamlessly integrate into ASPEN Plus, allowing to model complete carbon dioxide (CO2) capture – electrochemical regeneration cycles on a single modelling platform. The modelling of CO2 electrochemical cells has gained significant attention in CO2 capture and utilization processes. This emphasizes the importance of modelling in driving the progress of CO2 electrochemical cells which combines absorption by alkaline solvents and electrochemical solvent regeneration. In such process, potassium hydroxide (KOH, or other metal hydroxides) is used as a solvent for CO2 capture. This process involves a series of chemical reactions that result in the formation of potassium carbonate (K2CO3) and potassium bicarbonate (KHCO3). After CO2 is captured through absorption, the K2CO3/KHCO3 solution is directed towards the regeneration cell where an electrochemically driven pH swing takes place facilitating the desorption of CO2. The cell’s primary objective is to lower the pH of the solution by generating protons at the anode, thereby moving its chemical equilibrium towards carbonic acid. Given the limited solubility of CO2 in water, it desorbs once it reaches saturation. The residual solution can be reclaimed in the cathode compartment and recycled. Electrochemistry models are currently unavailable in popular simulation software like ASPEN Plus, thus making the development of integrated process models, in this case for CO2 capture, more challenging. Here, we introduced a rigorous model to be applied in ACM/ASPEN Plus software to simulate the CO2 regeneration process. The model’s validity was assessed against experimental measurements. Following this validation, the model was subsequently employed to design pilot plant campaigns for the Horizon 2020 project ConsenCUS

BACE2 suppression in mice aggravates the adverse metabolic consequences of an obesogenic diet

Objective: Pancreatic β-cell dysfunction is a central feature in the pathogenesis of type 2 diabetes (T2D). Accumulating evidence indicates that β-site APP-cleaving enzyme 2 (BACE2) inhibition exerts a beneficial effect on β-cells in different models of T2D. Thus, targeting BACE2 may represent a potential therapeutic strategy for the treatment of this disease. Here, we aimed to investigate the effects of BACE2 suppression on glucose homeostasis in a model of diet-induced obesity. Methods: BACE2 knock-out (BKO) and wild-type (WT) mice were fed with a high-fat diet (HFD) for 2 or 16 weeks. Body weight, food intake, respiratory exchange ratio, locomotor activity, and energy expenditure were determined. Glucose homeostasis was evaluated by glucose and insulin tolerance tests. β-cell proliferation was assessed by Ki67-positive nuclei, and β-cell function was determined by measuring glucose-stimulated insulin secretion. Leptin sensitivity was evaluated by quantifying food intake and body weight after an intraperitoneal leptin injection. Neuropeptide gene expression and insulin signaling in the mediobasal hypothalamus were determined by qPCR and Akt phosphorylation, respectively. Results: After 16 weeks of HFD feeding, BKO mice exhibited an exacerbated body weight gain and hyperphagia, in comparison to WT littermates. Glucose tolerance was similar in both groups, whereas HFD-induced hyperinsulinemia, insulin resistance, and β-cell expansion were more pronounced in BKO mice. In turn, leptin-induced food intake inhibition and hypothalamic insulin signaling were impaired in BKO mice, regardless of the diet, in accordance with deregulation of the expression of hypothalamic neuropeptide genes. Importantly, BKO mice already showed increased β-cell proliferation and glucose-stimulated insulin secretion with respect to WT littermates after two weeks of HFD feeding, before the onset of obesity. Conclusions: Collectively, these results reveal that BACE2 suppression in an obesogenic setting leads to exacerbated body weight gain, hyperinsulinemia, and insulin resistance. Thus, we conclude that inhibition of BACE2 may aggravate the adverse metabolic effects associated with obesity

Cardiac myosin activation with omecamtiv mecarbil in systolic heart failure

BACKGROUND The selective cardiac myosin activator omecamtiv mecarbil has been shown to improve cardiac function in patients with heart failure with a reduced ejection fraction. Its effect on cardiovascular outcomes is unknown. METHODS We randomly assigned 8256 patients (inpatients and outpatients) with symptomatic chronic heart failure and an ejection fraction of 35% or less to receive omecamtiv mecarbil (using pharmacokinetic-guided doses of 25 mg, 37.5 mg, or 50 mg twice daily) or placebo, in addition to standard heart-failure therapy. The primary outcome was a composite of a first heart-failure event (hospitalization or urgent visit for heart failure) or death from cardiovascular causes. RESULTS During a median of 21.8 months, a primary-outcome event occurred in 1523 of 4120 patients (37.0%) in the omecamtiv mecarbil group and in 1607 of 4112 patients (39.1%) in the placebo group (hazard ratio, 0.92; 95% confidence interval [CI], 0.86 to 0.99; P = 0.03). A total of 808 patients (19.6%) and 798 patients (19.4%), respectively, died from cardiovascular causes (hazard ratio, 1.01; 95% CI, 0.92 to 1.11). There was no significant difference between groups in the change from baseline on the Kansas City Cardiomyopathy Questionnaire total symptom score. At week 24, the change from baseline for the median N-terminal pro-B-type natriuretic peptide level was 10% lower in the omecamtiv mecarbil group than in the placebo group; the median cardiac troponin I level was 4 ng per liter higher. The frequency of cardiac ischemic and ventricular arrhythmia events was similar in the two groups. CONCLUSIONS Among patients with heart failure and a reduced ejection, those who received omecamtiv mecarbil had a lower incidence of a composite of a heart-failure event or death from cardiovascular causes than those who received placebo. (Funded by Amgen and others; GALACTIC-HF ClinicalTrials.gov number, NCT02929329; EudraCT number, 2016 -002299-28.)