Polymorph control of calcium carbonate by reactive crystallization using microbubble technique

In this study, we used the minute gas–liquid interfaces around CO₂/NH₃ microbubbles as new reaction fields where the crystal nucleation progresses and developed a crystallization technique to control the polymorphism of calcium carbonate (CaCO₃). In the regions around the gas–liquid interfaces of CO₂/NH₃ microbubbles, Ca²⁺ and CO₃²⁻ ion concentrations can be adjusted because of the characteristic of the electric charge on the bubble surface and the decrease in CO₂ concentration based on unit bubble caused by minimization of bubble size, and because of the pH difference between local pH at the gas–liquid interface and overall pH in the bulk liquid caused by mixing of NH₃ with CO₂; hence, the polymorph change of CaCO₃ is expected to occur. CaCO₃ was crystallized at 298 K by a semi-batch type reaction in which CO₂/NH₃/N₂ bubbles were continuously supplied to an aqueous Ca(NO₃)₂ solution using a self-supporting bubble generator. The solution pH during crystallization was maintained at a constant level of 6.9–12.0 by adding HNO₃ and NH₄OH solution. The average bubble size (d_bbl) was varied in the range of 40–1000 μm by controlling the N₂ flow rate, and the molar ratio of CO₂/NH₃ (αCO₂/NH₃${\alpha }_{\text{C}{\text{O}}_2\text{/N}{\text{H}}_3}$) was set at a specified value of 0.20–1.00 at a constant CO₂ flow rate. The following results were obtained by varying solution pH, d_bbl, and αCO₂/NH₃${\alpha }_{\text{C}{\text{O}}_2\text{/N}{\text{H}}_3}$: at a constant d_bbl of 40 μm and αCO₂/NH₃${\alpha }_{\text{C}{\text{O}}_2\text{/N}{\text{H}}_3}$ of 0.20, vaterite and calcite were major products at a solution pH lower than 9.0 and at a solution pH greater than 11.0, respectively, while aragonite was crystallized predominantly in the solution pH range of 9.7–10.5; at a constant solution pH of 9.7 the crystallization of aragonite was accelerated remarkably with a decrease in αCO₂/NH₃${\alpha }_{\text{C}{\text{O}}_2\text{/N}{\text{H}}_3}$ and d_bbl.     

Design of an airlift loop bioreactor and pilot scales studies with fluidic oscillator induced microbubbles for growth of a microalgae Dunaliella salina

This study was conducted to test the feasibility of growing microalgae on steel plant exhaust gas, generated from the combustion of offgases from steel processing, which has a high CO₂ content. Two field trials of batch algal biomass growth, mediated by microbubble transfer processes in an airlift loop bioreactor showed only steady growth of biomass with 100% survival rate. The gas analysis of CO₂ uptake in the 2200 L bioreactor showed a specific uptake rate of 0.1 g/L/h, an average 14% of the CO₂ available in the exhaust gas with a 23% composition of CO₂. This uptake led to a steady production of chlorophyll and total lipid constituency in the bioreactor, and an accelerating exponential growth rate of biomass, with a top doubling time of 1.8 days. The gas analysis also showed anti-correlation of CO₂ uptake and O₂ production, which along with the apparent stripping of the O₂ to the equilibrium level by the microbubbles, strongly suggests that the bioreactor is not mass transfer limited, nor O₂ inhibited. Removing O₂ inhibition results in high growth rates and high density of biomass.     

Removal of residual pesticide, fenitrothion, in vegetables by using ozone microbubbles generated by different methods

The effects of ozone microbubbles (OMB) generated by different methods on removal of residual fenitrothion (FT) in three kinds of vegetables were examined. FT-infiltrated lettuce, cherry tomatoes and strawberries were immersed in solutions containing OMB generated by using a microbubble generator of a decompression-type or a gas-water circulating-type combined with an ozone generator at an initial OMB concentration of 2.0 ppm for 0, 5 or 10 min. Residual FT in each vegetable was removed more efficiently by the OMB treatments with the decompression type than with the gas-water circulation type, showing that the pesticide-removing effect of OMB varies with the method of OMB generation.     

Modelling the effect of liquid motion on bubble nucleation during beer dispense

Beer dispense involves ejecting supersaturated beer under gas pressure, from a nozzle into a receiving vessel. Bubble nucleation therefore occurs in a flowing liquid. This situation is encountered in other processes, but is not accounted for in current nucleation models. An experimental system was developed to measure bubble production rates and sizes in laboratory scale beer dispense. Experimental results indicate that bubble nucleation is affected by both liquid flow rate and dissolved gas composition. Pre-existing gas nuclei models have been adapted using bubble and droplet detachment models to include the effect of liquid motion and gas composition. The adapted nucleation models were compared to the experimental results. Predicted bubble detachment radii and overall nucleation rates were affected by liquid flow rate, direction of liquid flow, dissolved gas composition, the contact radius and the level of contact angle hysteresis. Accurate predictions were achieved for different surface orientations and liquid flow directions. Accurate predictions occurred at hysteresis levels of 3.5°, 7.5° and 20° for liquid flow rates of 0.6, 2.2 and , respectively. It is clear that the predicted overall nucleation rate however, also depended on the number of nucleation sites and how many of these were active; although values for these parameters were not experimentally determined in this case. Further understanding of the exact number and size of nucleation sites available and the contact angle for the particular combination of liquid and solid used is required to improve the fit of the model to the experimental data.     

Effects of ozone microbubble treatment on removal of residual pesticides and quality of persimmon leaves

This study investigated the effects of ozone microbubble (OMCB) treatment on the removal of residual fenitrothion (FT) and benomyl pesticides from red and green persimmon leaves, and also the treatment effect on the leaf colours, physical properties and flavour. The continuous bubbling OMCB treatment was more effective than the non-bubbling OMCB treatments at reducing the FT and benomyl agricultural pesticide residues from both the red and green persimmon leaves. Moreover, the bubbling OMCB treatment had no effect on the colour and pulling strength of the leaves. These results indicate that the treatment by bubbling OMCB is an extremely effective method for removing the residues of FT and benomyl in persimmon leaves and has relatively little effect on leaf quality characteristics.     

Encapsulation of perfluorocarbon gases into lipid-based carrier by PGSS

For the first time, gas-filled microparticles were successfully prepared using a supercritical fluid based technology. Low molecular weight perfluorcarbon (PFC) gases, C₃F₈ or C₄F₈, have been encapsulated into Gelucire^® 50/13 (lipid-based carrier: polyethylene glycol glycerides), using PGSS^® (Particles from Gas Saturated Solution) technique. Particles were produced from the fast expansion of the melted lipid carrier saturated with a mixture of (CO₂ + PFC). The presence of the gas into the produced microparticles was verified by Nuclear Magnetic Resonance (NMR) analysis of fluorine atom. The effect of carrier to PFC mass ratio and PFC structure on the entrapment efficiency of the PFC gas into the particles was evaluated at fixed at 8.5 MPa and 353 K. These parameters were fixed in a preliminary study according to the morphology, size and flowability of the particles. The stability of encapsulated C₄F₈ in microparticles showed to be higher than C₃F₈; it was determined to be 2 h, at room conditions at the optimized carrier: PFC mass ratio of 30:1.     

Wavelet autocorrelation identification of the turbulent flow multi-scales for drag reduction process in microbubbly flows

Measurement of turbulent flow was performed in a fully developed channel flow for both single-phase and microbubble injection conditions. A drag reduction was achieved by microbubble injection in the boundary layer. Further understanding of this phenomenon has a significant impact on energy saving. In this experiment, the Reynolds number was 5128 based on the half height of the channel. The particle image velocimetry (PIV) technique was used to obtain two-dimensional full-field velocity components in the streamwise direction near-wall normal plane. Wavelet autocorrelations were applied to the streamwise fluctuating velocity fields. By applying wavelet analysis, many of the shortcomings of Fourier analysis were overcome. The comparison of the wavelet analysis results between single-phase flow and microbubble flow indicated that the microbubbles drag reduction is a multi-scale mode, in which the small-scale fluctuations are suppressed.     

Inactivation kinetics of polyphenol oxidase using a two-stage method with low pressurized carbon dioxide microbubbles

Inactivation kinetics of polyphenol oxidase (PPO) by a two-stage method which was additionally pressurized at ambient temperature after carbon dioxide microbubbles (MB-CO₂) was mixed with a solution at low temperature and pressure (two-stage MB-CO₂) was analyzed. The PPO inactivation efficiency of the two-stage MB-CO₂ treatment was higher than that of heat treatment. A decrease in the decimal reduction time (D value) and activation energy during PPO inactivation using the two-stage MB-CO₂ treatment was observed as the temperature of the heating coil and the pressure in the mixing vessel increased. The temperature rise required for a 90% reduction in the D value was increased. Furthermore, the pressure rise required for a 90% reduction in the D value and activation volume increased with the temperature of the heating coil. These results showed that PPO inactivation using the two-stage MB-CO₂ treatment could be achieved with less energy than heat treatment.     

Separation of amine-insoluble species by flotation with nano and microbubbles

Amines (alkylamines–ether amines) are employed on a large scale to separate iron ores by reverse flotation of the gangue particles (mostly quartz and silicates). Quartz gangue particles coated with amine collector are dumped in tailings dams as concentrated pulps. Then, the fraction of the amines that detach from the surfaces and the portion that is soluble in water, contaminate surface and ground-water supplies. This work presents a novel flotation technique to remove decyl-trimethyl-ether-amine (collector employed in Brazilian iron mines) from water. This amine forms precipitates at pH > 10.5 which are removed by flotation with microbubbles (MBs: 30–100 μm) and nanobubbles (NBs: 150–800 nm). Bubbles were generated simultaneously by depressurization of air-saturated water (P_sat of 66.1 psi during 25 min) forced through a flow constrictor (needle valve). The flotation by these bubbles is known as DAF-dissolved air flotation, one of the most efficient separation technologies in water and wastewater treatment. Herein, best results (80% amine removal) were obtained only after selective separation of the MBs from the NBs exploring the fact that while the NBs remain dispersed in water, the MBs rise leaving the system. The MBs, because of their buoyancy, rise too rapidly and do not collide and adhere appropriately at the amine colloids/water interface, even causing some precipitates breakage. It was found that the “isolated” NBs attach onto the amine precipitates; aggregate (flocculate) them and entrain inside the flocs before rising by flotation. Because of the low residual amine concentration in water (6 mg L⁻¹), it is believed that this flotation technique have potential in this particular treatment of residual amine-bearing effluents.     

Vascular and perfusion imaging using encapsulated laser-polarized helium

In this work, the use of hyperpolarized (HP)³He for in vivo intravascular imaging on animal is reported. To overcome the problem of the low solubility of helium in blood, we propose an approach based on helium encapsulation in lipid-based carrier agents. The mean diameter of the³He microbubbles. measured equal to 3.0 ±0.2 μm, makes it possible to conduct in vivo studies. In vitro spectroscopy yielded a longitudinal relaxation time T₁ equal to 90 s and an apparent transverse relaxation timeT ₂ ^* of 4.5 ms. Angiographie imaging (venous and cardiac cavity visualization), as well as lung perfusion imaging, were demonstrated in rats using intravenous injections of microbubble suspensions. Suitable signal and spatial resolution were achieved. The potential of this technique for lung perfusion assessment was assessed using an experimental animal embolism model. Lung perfusion defects and recovery towards a normal perfusion state were visualized. This study was completed with the demonstration of a new ventilation-perfusion lung exploration method based entirely on HP³He.