Process intensification: water electrolysis in a centrifugal acceleration field

Intensification of hydrogen production by carrying out water electrolysis in a centrifugal acceleration field has been demonstrated. A prototype single cell rotary water electrolyser was constructed, and a number of design challenges with regard to the practical application were addressed. The rotary electrolyser was tested over a range of current density, centrifugal acceleration, electrolyte concentration, temperature, and electrode geometry. The test results showed that at normal cell operating conditions (7.7M KOH solution, 348K) much of the cell voltage benefits were achieved at an acceleration of about 16g (g=9.81ms-2), equivalent to a rotational speed of 500rpm (revolution per minute) for the rotary cell. The rotary electrolyser cell voltage was about 0.25-0.5V, less than the equivalent static cell under similar operating conditions, depending on the current density. The cell voltages achieved, without an effective electrode catalytic coating, were comparable with typical industrial values of fully developed pressurised cells. At a higher acceleration of 41g, the rotary cell's current density can be up to 13.5kAm-2 without causing gas bubble blinding of the membranes and electrodes. When comparing with typical current densities (about 5kAm-2) found in commercial systems, this study demonstrated the potential of intensification

Potentials of pervaporation to assist VOCs' recovery by liquid absorption

International audienceGas treatment by liquid absorption is a well-known process to remove volatile organic compounds (VOCs) from industrial waste gases. Usually the liquid is an organic solvent of high boiling point; however, after VOCs' absorption it must be regenerated for the possible reuse and this step is classically achieved by heating the liquid. The paper presents the work directed to investigate an alternative regeneration step based on a liquid–vapour membrane separation, i.e. pervaporation. Because most of the energy required in pervaporation processes is consumed to remove the minor component from the initial mixture by selective permeation through the membrane, one can expect a significant energy cut in the operational costs linked to the regeneration of the liquid if the pervaporation step can substitute the heating one. The results reported here show that the technological possibility to use pervaporation is first governed by the stability of the membrane in the absorption liquid. The viability of the overall process is actually controlled by the mutual affinity between the VOCs, the solvent phase and the polymeric material. As a matter of fact, whereas VOCs have to exhibit strong affinities to both the solvent and the membrane material, the polymer has to be well resistant and even repellent to the solvent to avoid the possible sorption in the membrane that would drastically depress the pervaporation efficiency. In other words the membrane transport properties must be specific for the VOCs. This goal was reached following several experimental approaches, going from membrane modifications to the selection of suitable heavy protic solvents. Hence it has been shown for the case of dichloromethane (DCM) that low molecular weights polyalcohols (e.g. glycols) appeared to be suitable media to allow in particular the specific transport of DCM. On the other hand, polydimethylsiloxane (PDMS) based membranes were selected for their stability in these polyglycols and for their marked affinity for DCM. The simulation of the hybrid gas treatment process at pilot-scale was also achieved by a simple model relying on experimental data for both vapour liquid equilibria and permeation flux. A simple comparison of the energy needed to regenerate the heavy solvent by each possible step has also been made

Interest of Poly[bis(trifluoroethoxy)phosphazene] Membranes for Ammonia Recovery–Potential Application in Haber Process

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