Intensification of alkaline electrolysis

abstract no 5

Alkaliflex:publiek eindrapport

In veel rapporten over waterelektrolyse wordt gezegd dat alkalische waterelektrolyse-technologie relatief inflexibel is ten opzichte van alternatieven zoals PEM elektrolyse, maar dit wordt zelden verder toegelicht. In het kader van het Alkaliflex project is de flexibiliteit van alkalische waterelektrolyse dieper onderzocht. Vier flexibiliteitslimiteringen zijn geïdentificeerd: gelijkrichters, gas zuiverheid, warmtemanagement en gas-vloeistofgedrag. Voor de meeste van deze limiteringen zijn oplossingen beschikbaar om de flexibiliteit te verhogen en alkalische technologie is dan ook niet inherent inflexibel. Wel is het zo dat de oplossingen om de flexibiliteitslimiteringen weg te nemen geld kosten en het per project bepaald zal moeten worden of dit aantrekkelijk is.\u3cbr/\u3eVerder is het zeer de vraag of zeer flexibele elektrolyzers wel nodig zijn. De huidige behoefte aan zeer snelle flexibiliteit is namelijk beperkt en zeker op de lange termijn zal de waarde van korte termijn flexibiliteit waarschijnlijk afnemen door een toenemend flexaanbod. Daarentegen zal er door een toenemend aandeel van zonne- en windenergie wel meer behoefte komen aan flexibiliteit op uurbasis, maar hiervoor is zeer snel op- en afschakelen minder belangrijk. De minimale last waarop een elektrolyzer kan opereren blijft waarschijnlijk wel heel belangrijk.\u3cbr/\u3eHet Alkaliflex project laat ook zien dat er kansen zijn voor de ontwikkeling van efficiëntere elektrolyzers op basis van betere elektrodestructuren en dunnere membranen. In het Alkaliflex project is een eerste prototype van een nieuwe laboratorium-elektrolyzer ontwikkeld op basis van 3D-print technieken, die al beter presteert dan een commercieel verkrijgbare laboratoriumelektrolyzer. Voor verdere ontwikkeling is er wel behoefte aan modellen die het complexe gas-vloeistof gedrag in elektrolyzers beter kunnen beschrijven. De huidige modellen hebben nog veel moeite om het gedrag in sterke elektrolieten en bij hoge gasfracties te beschrijven.\u3cbr/\u3

Evidence for heme release in layer-by-layer assemblies of myoglobin and polystyrenesulfonate on pyrolitic graphite

Layer-by-layer assemblies of myoglobin and polystyrenesulfonate (PSS) on pyrolitic graphite have been investigated with the goal of determining the origin of the voltammetric response of these films. From the similar midpoint potential, coverage and electron transfer behavior compared with those of adsorbed free heme, it was concluded that the observed voltammetric peak is due to heme adsorbed at the electrode surface. This suggests that the interactions between the pyrolitic graphite electrode, PSS and myoglobin can result in heme release from the protein followed by heme adsorption on the electrode

Process for the preparation of cyclic organic carbonates

The present invention relates to process for the preparation of a cyclic organic carbonate comprising: reacting carbon monoxide and chlorine to form phosgene; reacting phosgene with a di-or polyhydric alcohol containing a vicinal diol moietyto form a reaction mixture comprising the cyclic organic carbonate and hydrogen chloride, which reaction proceeds via a chloroformate intermediate; and oxidizing the hydrogen chloride to chlorine and water, which chlorine is recycled to the phosgene synthesis reaction

Maxwell-Stefan modeling and experimental study on the ionic resistance of cation-selective membranes in concentrated lye solutions

\u3cp\u3eBoth experimental investigation and mathematical modeling have been combined to clarify the influence of membrane properties, temperature, electrolyte concentration, and current density on membrane resistance of Nafion 117 in concentrated lye solutions. The ionic resistance was measured with and without membrane using four electrodes for 15 wt% and 32 wt% sodium hydroxide, temperatures up to 90 °C, and current densities up to 25 kA/m\u3csup\u3e2\u3c/sup\u3e. The results from the measurement using Direct Current (DC) method as well as Electrochemical Impedance Spectroscopy (EIS) method indicate that membrane resistance is a function of temperature and lye concentration but is independent of current density. A mathematical model based on the Maxwell-Stefan approach has been developed to predict the ionic membrane resistance, and the model has been validated using the measured experimental data. A more suitable semi-empirical correlation for Maxwell-Stefan diffusivities is proposed by replacing the expressions for binary diffusivities based on infinite dilution with the concentration-dependent binary diffusivities. The new proposed correlation performs better in the model validation with the experimental data than the expressions using infinite dilution diffusivities.\u3c/p\u3

Bipolar membrane electrodialysis for the alkalinization of ethanolamine salts

Bipolar membrane electrodialysis for the production of organic bases, in contrast to organic acids, has received little attention in the scientific literature. In the present work we have investigated and compared different membrane configurations for the alkalinization of monoethanolamine salts into the organic base monoethanolamine. A current utilization of only 36% has been obtained for a two compartment configuration with bipolar and anion-exchange membranes. Proton tunneling through the anion-exchange membrane has been identified as the main reason for this relatively low current utilization. Minimizing proton tunneling by employing proton blocking anion-exchange membranes and using a three compartment configuration, the current utilization could be increased to 80%. This bipolar membrane configuration acts as a concentration step as well. A MEA concentration of 32 wt% in the base compartment could be achieved. A disadvantage of the three compartment configuration is the relatively high unit cell potential drop of 3.1 V at a current density of 1000 A m−2 using a compartment thickness of 0.75 mm

Electrodialysis for the concentration of ethanolamine salts

Monoethanolamine (MEA) is currently produced from oil-based chemicals in an energy intensive process. Fermentative MEA production from renewable sources is considered to be a more sustainable process option. In such a process MEA is likely to be produced in a relatively low concentration in protonated form. Monopolar membrane electrodialysis can be applied to obtain a concentrated MEA solution of 10–18 wt% MEA from this dilute stream. The outlet concentration strongly depends on the applied current density. At low current densities (100 A m−2) the concentration is relatively low (10 wt% MEA) due to diffusive water transport. At higher current densities (1000 A m−2) the concentration is higher (18 wt% MEA). Other variables such as inlet concentration and temperature have little influence on the outlet concentration. Current utilization is around 80% and seems independent of current density, diluate conductivity and temperature. On the other hand, cell potential strongly depends on these variables and especially on diluate conductivity. For typical electrodialysis conditions the power consumption is 0.35 kWh/kg MEA

Electron transfer and ligand binding to cytochrome c' immobilized on self-assembled monolayers

We have successfully immobilized Allochromatium vinosum cytochrome c' on carboxylic acid-terminated thiol monolayers on gold and have investigated its electron-transfer and ligand binding properties. Immobilization could only be achieved for pH's ranging from 3.5 to 5.5, reflecting the fact that the protein is only sufficiently pos. charged below pH 5.5 (pI = 4.9). Upon immobilization, the protein retains a near-native conformation, as is suggested by the obsd. potential of 85 mV vs SHE for the heme FeIII/FeII transition, which is close to the value of 60 mV reported in soln. The electron-transfer rate to the immobilized protein depends on the length of the thiol spacer, displaying distance-dependent electron tunneling for long thiols and distance-independent protein reorganization for short thiols. The unique CO-induced dimer-to-monomer transition obsd. for cytochrome c' in soln. also seems to occur for immobilized cytochrome c'. Upon satn. with CO, a new anodic peak corresponding to the oxidn. of an FeII-CO adduct is obsd. CO binding is accompanied by a significant decrease in protein coverage, which could be due to weaker electrostatic interactions between the self-assembled monolayer and cytochrome c' in its monomeric form as compared to those in its dimeric form. The obsd. CO binding rate of 24 M-1 s-1 is slightly slower than the binding rate in soln. (48 M-1 s-1), which could be due to electrostatic protein-electrode interactions or could be the result of protein crowding on the surface. This study shows that the use of carboxyl acid-terminated thiol monolayers as a protein friendly method to immobilize redox proteins on gold electrodes is not restricted to cytochrome c, but can also be used for other proteins such as cytochrome c'

Continuous process for the preparation of methanol by hydrogenation of carbon dioxide

The present invention pertains to a continuous process for the preparation of methanol by hydrogenation of carbon dioxide in the presence of a solid catalyst comprising the steps of (i) feeding a feed comprising carbon dioxide; and at least part of a first recycle gas stream comprising carbon dioxide and hydrogen,to a reactor, to obtain a gaseous feed with a hydrogen:carbon dioxide molar ratio of between 2-18 : 1; (ii) contacting said gaseous feed with a catalyst at a temperature of between200 and 300°C and a pressure of between 40 and 200 bar, thereby forming an outlet stream comprising methanol, water, carbon monoxide, carbon dioxide, and hydrogen; (iii) cooling the outlet stream; (iv) subjecting said outlet stream to a separation step, while optionally at least part of a second recycle gas stream is added to said outlet stream comprising methanol prior to and/or during said separation step, in which separation step methanol and water are separated from non-condensable components, thereby forming a methanol-comprising product stream and a first recycle gas stream; (v) stripping the methanol-comprising product stream using a hydrogen stream, thereby forming a purified methanol product stream and a second recycle gas stream; and (vi)feeding at least part of the first recycle gas stream to step (i) and at least part of the second recycle gas stream to steps (i) and/or (iv)