A high pressure semicontinuous batch electrolyzer is used to convert CO₂ to formic acid/formate on a tin-based cathode using bipolar membranes (BPMs) and cation exchange membranes (CEMs). The effects of CO₂ pressure up to 50 bar, electrolyte concentration, flow rate, cell potential, and the two types of membranes on the current density (CD) and Faraday efficiency (FE) for formic acid/formate are investigated. Increasing the CO₂ pressure yields a high FE up to 90% at a cell potential of 3.5 V and a CD of ∼30 mA/cm². The FE decreases significantly at higher cell potentials and current densities, and lower pressures. Up to 2 wt % formate was produced at a cell potential of 4 V, a CD of ∼100 mA/cm², and a FE of 65%. The advantages and disadvantages of using BPMs and CEMs in electrochemical cells for CO₂ conversion to formic acid/formate are discussed.

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 < pK_a) 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 pK_a 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.

The capture of CO₂ from power plant flue gases provides an opportunity to mitigate emissions that are harmful to the global climate. While the process of CO₂ capture using an aqueous amine solution is well-known from experience in other technical sectors (e.g., acid gas removal in the gas processing industry), its operation combined with a power plant still needs investigation because in this case, the interaction with power plants that are increasingly operated dynamically poses control challenges. This article presents the dynamic modeling of CO₂ capture plants followed by a detailed validation using transient measurements recorded from the pilot plant operated at the Maasvlakte power station in the Netherlands. The model predictions are in good agreement with the experimental data related to the transient changes of the main process variables such as flow rate, CO₂ concentrations, temperatures, and solvent loading. The validated model was used to study the effects of fast power plant transients on the capture plant operation. A relevant result of this work is that an integrated CO₂ capture plant might enable more dynamic operation of retrofitted fossil fuel power plants because the large amount of steam needed by the capture process can be diverted rapidly to and from the power plant.

A clear understanding of the dynamic behavior of the whole chain of conventional power generation to CO₂ storage is necessary. The rapidly increasing share of renewable energy makes the energy delivered to the grid more fluctuating leading to an impact on the CCS chain as well. A 250 MW scale carbon capture plant with CO₂ compression has been modelled with Dymola (dynamic) and with Aspen Plus (steady-state). It is evident that large perturbations in flue gas flow rate will make it difficult to control the water balance. Moreover, parallel compression trains may be necessary to prevent compressors to run in spill back mode.

Currently the low carbon prices, low Spreads and regulatory uncertainties hampers the business cases for coal-fired power plants with post-combustion capture (PCC) in Europe. Improvement of the business case of coal-fired power plants with post combustion capture requires a different approach in terms of operational dispatch and in terms of investment planning. Both items have been assessed using a comprehensive power plant valuation model developed by TNO. To change the typical base-load production profile of a coal-fired power plant into a more flexible production profile, a Flexible Operating Mechanisms (FOMs) has been developed for PCC. Based on the results of the techno-economic modeling, FOMs improve the business case. Next to this, FOMs present coal fuelled power plants with additional flexibility. This added flexibility could allow coal plants to provide auxiliary services to the grid and remain competitive in relation to cleaner gas-fired plants. The increase of operational flexibility with FOMs created a significant improvement of the NPV value and, therefore, it is justified to look in much more detail how the operational flexibility of a coal-fired power plant with Carbon Capture can be improved. Running a power plant with a 100% capture unit at base load will require significant amount financial support to close the gap. Starting with a smaller capture unit reduce the financial risk and could improve the business case of the coal-fired power plant without PCC from a marginal cost point of view. The main reason for this is the increase of flexibility, by switching on/off the capture unit. Next to this, the decision to invest is always affected by the opportunity costs of making a commitment now, and thereby, giving up the option of waiting for improved market condition. Increasing the size of the capture plant in stages enables the investor to manage those opportunity cost much better.