Directed precipitation of anhydrous magnesite for improved performance of mineral carbonation of CO2

The final publication is available at Elsevier via http://dx.doi.org/10.1016/j.jece.2017.06.048 © 2017. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/This paper studies the indirect aqueous carbon sequestration via Mg(OH)2 using directed precipitation technique. This technique produces anhydrous MgCO3 (magnesite), the most desirable carbonated phase for sequestration. The formation of magnesite is significantly affected by its kinetics of precipitation in an aqueous carbonation medium. This study considers directed precipitation strategy to control precipitation of anhydrous magnesite through enhancement of the heterogeneous precipitation. Heterogeneous precipitation is implemented using seeding material that could improve the conversion efficiency of the directed carbonation of Mg(OH)2. A ternary phase diagram is achieved which represents the relative concentration of possible precipitated phases: brucite (Mg(OH)2), magnesite and hydromagnesit (Mg5(CO3)4(OH)2·4H2O). The results reveal the fundamental role of heterogeneous precipitation on the magnesite concentration and conversion percentage of Mg(OH)2 wet carbonation process. Two seeding materials, hydrophobic activated carbon and hydrophilic alumina, were tested and the influence of the surface chemistry of varying seeding sites (hydrophobic vs. hydrophilic seeds) was elaborated. At the carbonation temperature of 100°C and 150°C, a heterogeneous precipitation using hydrophilic alumina results in lower concentrations of anhydrous magnesite in precipitated compounds, even as compared to the seedless solution, owing to the hydrophilic properties of alumina. In contrast, use of activated carbon as heterogeneous nucleation sites in an aqueous medium results in a magnesite concentration of around 60% and the corresponding carbonation conversion of about 72% under the controlled condition of 200°C and 30bar CO2 pressure.Network of Centres of Excellence - Carbon Management Canada (CMC)Natural Sciences and Engineering Research Council of Canada (NSERC)Waterloo Institute for Nanotechnology (WIN

Highly pressurized partially miscible liquid-liquid flow in a micro-T-junction. I. Experimental observations

© 2017 American Physical Society, https://doi.org/10.1103/PhysRevE.95.043110This is the first part of a two-part study on a partially miscible liquid-liquid flow (liquid carbon dioxide and deionized water) which is highly pressurized and confined in a microfluidic T-junction. Our main focuses are to understand the flow regimes as a result of varying flow conditions and investigate the characteristics of drop flow distinct from coflow, with a capillary number, Ca-c, that is calculated based on the continuous liquid, ranging from 10(-3) to 10(-2) (10(-4) for coflow). Here in part I, we present our experimental observation of drop formation cycle by tracking drop length, spacing, frequency, and after-generation speed using high-speed video and image analysis. The drop flow is chronologically composed of a stagnating and filling stage, an elongating and squeezing stage, and a truncating stage. The common "necking" time during the elongating and squeezing stage (with Ca-c similar to 10(-3)) for the truncation of the dispersed liquid stream is extended, and the truncation point is subsequently shifted downstream from the T-junction corner. This temporal postponement effect modifies the scaling function reported in the literature for droplet formation with two immiscible fluids. Our experimental measurements also demonstrate the drop speed immediately following their generations can be approximated by the mean velocity from averaging the total flow rate over the channel cross section. Further justifications of the quantitative analysis by considering the mass transfer at the interface of the two partially miscible fluids are provided in part II.University of TorontoUniversity of Waterlo

Highly pressurized partially miscible liquid-liquid flow in a micro-T-junction. II. Theoretical justifications and modeling

© 2017 American Physical Society, https://doi.org/10.1103/PhysRevE.95.043111This is the second part of a two-part study on a partially miscible liquid-liquid flow ( carbon dioxide and deionized water) that is highly pressurized and confined in a microfluidic T-junction. In the first part of this study, we reported experimental observations of the development of flow regimes under various flow conditions and the quantitative characteristics of the drop flow including the drop length, after-generation drop speed, and periodic spacing development between an emerging drop and the newly produced one. Here in part II we provide theoretical justifications to our quantitative studies on the drop flow by considering ( 1) CO2 hydration at the interface with water, ( 2) the diffusion-controlled dissolution of CO2 molecules in water, and ( 3) the diffusion distance of the dissolved CO2 molecules. Our analyses show that ( 1) the CO2 hydration at the interface is overall negligible, ( 2) a saturation scenario of the dissolved CO2 molecules in the vicinity of the interface will not be reached within the contact time between the two fluids, and ( 3) molecular diffusion does play a role in transferring the dissolved molecules, but the diffusion distance is very limited compared with the channel geometry. In addition, mathematical models for the drop length and the drop spacing are developed based on the observations in part I, and their predictions are compared to our experimental results.China Scholarship Council: 20120491016

Hydrodynamic shrinkage of liquid CO2 Taylor drops in a straight microchannel

This is an author-created, un-copyedited version of an article accepted for publication in Journal of Physics: Condensed Matter. The publisher is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at https://doi.org/10.1088/1361-648X/aaa81cHydrodynamic shrinkage of liquid CO2 drops in water under a Taylor flow regime is studied using a straight microchannel (length/width similar to 100). A general form of a mathematical model of the solvent-side mass transfer coefficient (k(s)) is developed first. Based on formulations of the surface area (A) and the volume (V) of a general Taylor drop in a rectangular microchannel, a specific form of k(s) is derived. Drop length and speed are experimentally measured at three specified positions of the straight channel, namely, immediately after drop generation (position 1), the midpoint of the channel (position 2) and the end of the channel (position 3). The reductions of drop length (L-x, x = 1, 2, 3) from position 1 to 2 and down to 3 are used to quantify the drop shrinkage. Using the specific model, k(s) is calculated mainly based on Lx and drop flowing time (t). Results show that smaller CO2 drops produced by lower flow rate ratios (Q(LCO2)/Q(H2O)) are generally characterized by higher (nearly three times) ks and Sherwood numbers than those produced by higher Q(LCO2)/Q(H2O), which is essentially attributed to the larger effective portion of the smaller drop contributing in the mass transfer under same levels of the flowing time and the surface-to-volume ratio (similar to 10(4) m(-1)) of all drops. Based on calculated pressure drops of the segmented flow in microchannel, the Peng-Robinson equation of state and initial pressures of drops at the T-junction in experiments, overall pressure drop (Delta P-t) in the straight channel as well as the resulted drop volume change are quantified. Delta P-t from position 1-3 is by average 3.175 kPa with a similar to 1.6% standard error, which only leads to relative drop volume changes of 0.3 parts per thousand to 0.52 parts per thousand

Complexity of globally coupled chaotic electrochemical oscillators

Interactions among small sets of two to eight nickel electrodes undergoing chaotic electrodissolution in sulfuric acid were studied. A single oscillator under these conditions exhibits low-dimensional chaotic behavior. Global coupling among the electrodes was added with the use of external resistors in a manner such that the strength of the coupling could be varied while the other parameters of the system remained constant. Such global coupling is of course equivalent to an appropriate local coupling for the two-electrode system and even for a three-electrode system if arranged in a ring. We investigate the changes in complexities of both the individual oscillators and of the total current as functions of coupling strength and of array size. The dynamics of the individual oscillators are almost identical to those of the single oscillator at added coupling strengths of zero (where the oscillators are almost independent) and at maximum coupling strength (where they are synchronized). There are two trends (with exceptions) with changing coupling strength

Dissimilar joining of carbon/carbon composites to Ti6Al4V using reactive resistance spot welding

The final publication is available at Elsevier via https://dx.doi.org/10.1016/j.jallcom.2018.09.018 © 2019. This manuscript version is made available under the CC-BY-NC-ND 4.0 license https://creativecommons.org/licenses/by-nc-nd/4.0/A 2D C/C composite with a high porosity (low strength) and a 3D C/C composite with a low porosity (high strength) were investigated for dissimilar joining to Ti6Al4V via reactive spot welding. It was determined that infiltration of melted metal into the composite and formation of a continuous thin TiC layer at the interface of the joints were the dominant joining mechanisms. The 2D C/C composite with a flat surface was successfully joined to Ti6Al4V due to the infiltration of the melted Ti6Al4V into its porous content. On the other hand, it was necessary to drill rectangular grooves onto the surface of the 3D C/C composite to facilitate the infiltration of the melted Ti into the composite, which produced high-strength joints. Surface patterning was determined to be necessary to join the components with mismatching coefficients of thermal expansion. The strength of the 2D C/C composite and Ti6Al4V joints was found to be 7 MPa, while the maximum strength of the groove-patterned 3D C/C composite and Ti6Al4V joints reached 46 MPa.Natural Sciences and Engineering Research Council of Canad

On nonequilibrium shrinkage of supercritical CO2 droplets in a water-carrier microflow

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. The following article appeared in Applied Physics Letters, 113(3), 033703 and may be found at https://doi.org/10.1063/1.5039507.We report an experimental study on the hydrodynamic shrinkage of supercritical carbon dioxide (scCO(2)) microdroplets during a nonequilibrium process. After scCO(2 )microdroplets are generated by water shearing upon a scCO(2) flow in a micro T-junction, they are further visualized and characterized at the midpoint and the ending point of a straight rectangular microchannel (width x depth x length: 150 mu m x 100 mu m x 1.5 mm). The measured decreases in droplet size by 8%-36% indicate and simply quantify the droplet shrinkage which results from the interphase mass transfer between the droplet and the neighboring water. Using a mathematical model, the shrinkage of scCO(2) droplets is characterized by solvent-side mass transfer coefficients (k(s): 1.5 x 10(-4)-7.5 x 10(-4) m/s) and the Sherwood number (Sh: 7-37). In general, k(s) here is two orders of magnitude larger than that of hydrostatic liquid CO2 droplets in water. The magnitude of Sh numbers highlights the stronger effect of local convections than that of diffusion in the interphase mass transfer. Our results, as reported here, have essential implications for scCO(2)-based chemical extractions and carbon storage in deep geoformations. Published by AIP Publishing.Carbon Management Canada: C39

Numerical Study on Single Flowing Liquid and Supercritical CO2 Drop in Microchannel: Thin Film, Flow Fields, and Interfacial Profile

Taylor segments, as a common feature in two- or multi-phase microflows, are a strong flow pattern candidate for applications when enhanced heat or mass transfer is particularly considered. A thin film that separates these segments from touching the solid channel and the flow fields near and inside the segment are two key factors that influence (either restricting or improving) the performance of heat and mass transfer. In this numerical study, a computational fluid dynamics (CFD) method and dense carbon dioxide (CO2) and water are applied and used as a fluid pair, respectively. One single flowing liquid or supercritical CO2 drop enclosed by water is traced in fixed frames of a long straight microchannel. The thin film, flow fields near and within single CO2 drop, and interfacial distributions of CO2 subjected to diffusion and local convections are focused on and discussed. The computed thin film is generally characterized by a thickness of 1.3~2.2% of the channel width (150 µm). Flow vortexes are formed within the hydrodynamic capsular drop. The interfacial distribution profile of CO2 drop is controlled by local convections near the interface and the interphase diffusion, the extent of which is subject to the drop size and drop speed as well

Photocatalytic performances of ZnO nanoparticle film and vertically aligned nanorods in chamber-based microfluidic reactors: Reaction kinetics and flow effects

The final publication is available at Elsevier via https://doi.org/10.1016/j.apcatb.2017.03.020 © 2017. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/The nanoparticle seed layer (a film) and vertically aligned nanorods of zinc oxide (ZnO) with different lengths were fabricated within a novel chamber-based microfluidic (microchamber) reactor with a varying height of 0.127-5 mm and characterized with their microstructures, photocatalytic performances as well as qualitative reaction kinetics. The ZnO seed layer was produced by a sol-gel procedure and the nanorods were hydrothermally grown on seed layer coated glass substrates. These ZnO samples were integrated into the microchamber reactor through a seven-layer sandwiched configuration. The aqueous methyl orange (MO) solution was chosen as a model polluted water. By comparing the ultraviolet-visible (UV-vis) absorbance of the original MO solution and the post-treatment sample, the reaction constants were calculated, representing the efficiencies of the reactors. The ZnO samples, usually possessing a large amount of defects, with a higher crystal quality showed an enhanced activity. The reaction constant was featured of a plateau with accelerating flow rates, exhibited an exponentially decreasing function of the chamber height, and declined with increasing the initial concentration of the MO solution. The efficiency of the microchamber reactor was found to be one to two orders of magnitude higher than that of a batch reactor. The rate determining step was suggested to be the mass transport related adsorption of MO on ZnO. The measured reaction properties and the reactor design should be of considerable significance to the scaling-up and optimization of microchamber catalytic reactors dedicated to water purification and other applications. (C) 2017 Elsevier B.V. All rights reserved

Polyamide 6.6 separates oil/water due to its dual underwater oleophobicity/underoil hydrophobicity: Role of 2D and 3D porous structures

The final publication is available at Elsevier via https://dx.doi.org/10.1016/j.apsusc.2018.10.041 © 2019. This manuscript version is made available under the CC-BY-NC-ND 4.0 license https://creativecommons.org/licenses/by-nc-nd/4.0/Porous polyamide functionalized by plasma or various coatings has been investigated for oil/water separation. In literature, polyamide has rarely been studied for oil removal, and this work investigated the performance of bare polyamide 6.6 (nylon 6.6) in terms of the oil/water separation efficiency and the intrusion pressure, inspiring cost-effective solutions for large-scale oil removal in the industry. Both polyamide meshes possessing two-dimensional (2D) one-layer pores and nonwoven fabrics with three-dimensional (3D) irregular pores were found to be able to separate oil/water with a high efficiency above 98.5%. This finding was attributed to the dual underwater oleophobicity and underoil hydrophobicity of these polyamide samples. The roles of 2D and 3D structures in oil/water separation were illustrated, to provide a new insight into filter designing. Due to its greater intrusion pressure, the 3D netting structure was suggested as being more beneficial for oil/water separation than the 2D structure.Natural Sciences and Engineering Research Council of Canad