Reactive absorption of CO 2 in NaOH: Detailed study of enhancement factor models

Carbonate Hydrogenated to Formate in the Aqueous Phase over Nickel/TiO2 Catalysts

Carbonate hydrogenation to formate is a promising route to convert captured carbon dioxide into valuable chemicals, thus reducing carbon emissions and creating a revenue return. Developing inexpensive catalysts with high activity, selectivity, and stability remains challenging. We report a supported non-noble metal catalyst, Ni/TiO2 , with great selectivity over 96 % and excellent stability in catalyzing the conversion of carbonate into formate in aqueous solution. Ni0 and Ni2+ species are both observed in Ni/TiO2 catalysts, and the synergistic effect of these two Ni components leads to high activity and high selectivity of carbonate hydrogenation to formate.

A PBM-CFD Model with Optimized PBM-Customized Drag Equations for Chemisorption of CO2 in a Bubble Column

In this work, a computational fluid dynamics (CFD) approach based on two-fluid model (TFM) is introduced to describe the reversible two-step reactions found in the chemisorption process of ${\text{C}}{{\text{O}}_2}$ by an aqueous ${\text{NaOH}}$ solution in a lab-scale bubble column reactor. The population balance model (PBM) is applied to track the bubble size distribution with considering the coalescence and breakage terms, which then leads to a CFD-PBM model for describing the chemisorption of CO2 in an aqueous ${\text{NaOH}}$ solution. Drag force is considered for the interfacial momentum transfer and a modified PBM-customized drag model with the correction factor is subsequently adopted, in which the contribution of different bubble size groups in each computational cell is computed. The tested boundary conditions include superficial gas velocities, gas-inlet sparger and the reactor dimension. Detailed and comprehensive investigations are done in the evolution of gas holdup, pH value, concentration distribution and bubble diameter distribution which are essential in optimizing the reactor performance in terms of yield and selectivity. Importantly, the current CFD-PBM model is able to predict the entire reaction process.

Experimental Analysis of a Bubble Wake Influenced by a Vortex Street

Bubble column reactors are ubiquitous in engineering processes. They are used in waste water treatment, as well as in the chemical, pharmaceutical, biological and food industry. Mass transfer and mixing, as well as biochemical or chemical reactions in such reactors are determined by the hydrodynamics of the bubbly flow. The hydrodynamics of bubbly flows is dominated by bubble wake interactions. Despite the fact that bubble wakes have been investigated intensively in the past, there is still a lack of knowledge about how mass transfer from bubbles is influenced by bubble wake interactions in detail. The scientific scope of this work is to answer the question how bubble wakes are influenced by external flow structures like a vortex street behind a cylinder. For this purpose, the flow field in the vicinity of a single bubble is investigated systematically with high spatial and temporal resolution. High-speed Particle Image Velocimetry (PIV) measurements are conducted monitoring the flow structure in the equatorial plane of the single bubble. It is shown that the root mean square (RMS) velocity profiles downstream the bubble are influenced significantly by the interaction of vortices. In the presence of a vortex street, the deceleration of the fluid behind the bubble is compensated earlier than in the absence of a vortex street. This happens due to momentum transfer by cross-mixing. Both effects indicate that the interaction of vortices enhances the cross-mixing close to the bubble. Time series of instantaneous velocity fields show the formation of an inner shear layer and coupled vortices. In conclusion, this study shows in detail how the bubble wake is influenced by a vortex street and gives deep insights into possible effects on mixing and mass transfer in bubbly flows.