High-pressure electrochemical reduction of CO2 to formic acid/formate: effect of pH on the downstream separation process and economics

We use a high-pressure semicontinuous batch electrochemical reactor with a tin-based cathode to demonstrate that it is possible to efficiently convert CO2 to formic acid (FA) in low-pH (i.e., pH < pKa) electrolyte solutions. The effects of CO2 pressure (up to 50 bar), bipolar membranes, and electrolyte (K2SO4) concentration on the current density (CD) and the Faraday efficiency (FE) of formic acid were investigated. The highest FE (∼80%) of FA was achieved at a pressure of around 50 bar at a cell potential of 3.5 V and a CD of ∼30 mA/cm2. To suppress the hydrogen evolution reaction (HER), the electrochemical reduction of CO2 in aqueous media is typically performed at alkaline conditions. The consequence of this is that products like formic acid, which has a pKa of 3.75, will almost completely dissociate into the formate form. The pH of the electrolyte solution has a strong influence not only on the electrochemical reduction process of CO2 but also on the downstream separation of (dilute) acid products like formic acid. The selection of separation processes depends on the dissociation state of the acids. A review of separation technologies for formic acid/formate removal from aqueous dilute streams is provided. By applying common separation heuristics, we have selected liquid–liquid extraction and electrodialysis for formic acid and formate separation, respectively. An economic evaluation of both separation processes shows that the formic acid route is more attractive than the formate one. These results urge for a better design of (1) CO2 electrocatalysts that can operate at low pH without affecting the selectivity of the desired products and (2) technologies for efficient separation of dilute products from (photo)electrochemical reactors

Coastal zone problems and environmental strategies to be implemented at Edremit Bay, Turkey

WOS: 000231093100003PubMed ID: 15983860This case study examines the coastal zone problems focusing on the existing conflicts between tourism and commercial activities on the coasts of Edremit Bay, Turkey, and attempts to suggest solutions to these problems. Edremit Bay is a characteristic example of such a conflict in collective use of natural resources. The study area, with its 100-km-long sandy beach, naturally attracts different coastal user groups with different beneficial expectations: in terms of rest and recreation for one group and commercial gain offered in a variety of ways for another group, Significant coastal zone problems exist in the study area. Deterioration of shoreline due to tourism activities and illegal constructions, damage to the coastal ecosystem due to domestic/industrial wastewater discharges and some agricultural activities, and disordered urbanization are only a few of the many problems. The data presented here were partly derived from field study and partly collected from local state or private organizations. In this study, it is emphasized that there is a need for viable economic and environmental strategies to be designated in Edremit Bay, Turkey, in order to provide sustainable resource use. For this purpose, an integrated project together with a relevant planning chart including subprojects is also suggested, The success of a local environmental protection management project depends on active participation of all stakeholders including governmental organizations and nongovernmental organizations

Analysis and comparison of the forces by the nonlinear long waves on the piled system at Derince Port Turkey

The pile system of the ship berthing structure at Derince Port was damaged by the August 17, 1999 Izmit earthquake. The reasons might the earthquake shaking and the effect tsunami waves in Izmit Bay, Turkey. Tsunami, is a special type of the wave and can be generated by the sea bottom deformation related to generally the earthquake or the earthquake triggered mass failure mechanisms. These kind of waves in shallow regions are assumed to resemble the solitary, cnoidal or N-waves. Theoretical approaches for the solution of run-up problems of tsunamis showed that the shape of the wave Is important (Tedepalli and Synolakis, 1994, Synolakis, 2001). The similar comparison may be made for the forces on the structure. The computation of the forces and displacements on the piled structures according to the attack of long waves can help to discuss the damage occurred at the piled system at Derince Port In this study by using the observed tsunami wave characteristics in Izmit bay, different type of long wave theories are applied to compute the forces and displacements on the damaged piled system at Derince Port. The reasons of the damage of the piled system are discussed by comparing the computed forces and displacements

Determination of mangrove forest performance in reducing tsunami run-up using physical models

Coastal ecosystems such as mangroves fringing tropical coastlines have been recognized as natural protectors of the coastal areas against destructive attack of a tsunami. In this paper, the authors aim to investigate the interaction of a tsunami wave on a typical mangrove forest and to determine its performance in reducing the run-up. A laboratory experiment using a hydraulic ?ume with a mangrove forest model was carried out in which tests were conducted by varying the vegetation widths of 0, 1, 2 and 3 m and average densities of 8, 6 and 4 trees per 100 cm2 using a scale ratio of 1:100. Two conditions of water levels were considered in the experiments at several tsunami wave heights between 2.4 and 14 cm. The dam break method used in the experiments produced two types of waves. At low water condition, a bore was developed and subsequently, a solitary wave was produced during high water. The results of the experiments showed that in general, vegetation widths and densities demonstrate a dampening effect on tsunami run-up. A larger vegetation width was found to be more effective in dissipating the wave energy. The ?rst 1 m width of mangrove forest could reduce 23–32 % during high water and 31–36 % during low water. Increasing the mangrove forest width to 2 and 3 m could further increase the average percentage of run-up reduction by 39–50 % during high water and 34–41 % during low water condition. It was also observed that densities of the mangrove forest do not in?uence the run-up reduction as signi?cantly as the forest widths. For mangrove forest densities to be signi?cantly enough to reduce more tsunami run-up, an additional density of 4 trees/100 m2 needs to be provided. The experiments also showed that mangrove roots are more effective in reducing the run-up compared to the trunks and canopies. The experiments managed to compare and present the usefulness of mangrove forests in dissipating wave energy and results produced are bene?cial for initiating design guidelines in determining setback limits or buffer zones for development projects in mangrove areas

Numerical and Experimental Analysis of Rapid Delta Formation, Turkish coast

The morphology of river mouths can be completely changed by dramatic flow changes caused by climate changes in catchment basins. Agricultural activities that overexploit water produce changes in sediment discharge that are reflected in sedimentation rates in dams. The basic aim of this study is to assess the causes and effects of rapid delta. formation in Gomec (an important tourism centre on the Aegean Sea coast of Turkey), as a result of river catchment changes between 1998 and 2001. The rapidly developing delta covers an area of approximately 2 km length and 100 m width and was studied using numerical simulation and field studies. Bathymetric measurement, flow velocity and oceanographic parameters were measured. Bottom sediment samples were taken from the river and adjacent sea and sources were determined by mineral analysis. River flows and wave properties (determined from hindcast wind data) were used in the numerical model studies. The development of the delta was predicted for different scenarios. It is concluded that unless remedial action is taken, the delta will continue to develop rapidly and will produce both morphological and ecological impacts

Non-invasive current collectors for improved current-density distribution during CO₂ electrolysis on super-hydrophobic electrodes

Electrochemical reduction of CO2 presents an attractive way to store renewable energy in chemical bonds in a potentially carbon-neutral way. However, the available electrolyzers suffer from intrinsic problems, like flooding and salt accumulation, that must be overcome to industrialize the technology. To mitigate flooding and salt precipitation issues, researchers have used super-hydrophobic electrodes based on either expanded polytetrafluoroethylene (ePTFE) gas-diffusion layers (GDL’s), or carbon-based GDL’s with added PTFE. While the PTFE backbone is highly resistant to flooding, the non-conductive nature of PTFE means that without additional current collection the catalyst layer itself is responsible for electron-dispersion, which penalizes system efficiency and stability. In this work, we present operando results that illustrate that the current distribution and electrical potential distribution is far from a uniform distribution in thin catalyst layers (~50 nm) deposited onto ePTFE GDL’s. We then compare the effects of thicker catalyst layers (~500 nm) and a newly developed non-invasive current collector (NICC). The NICC can maintain more uniform current distributions with 10-fold thinner catalyst layers while improving stability towards ethylene (≥ 30%) by approximately two-fold.ChemE/Materials for Energy Conversion and Storag