Although the synthesis of silver nanoparticles via chemical
precipitation
is the easiest to scale up for industrial production, the use of conventional
stirring methods suffers from large and widely distributed particle
sizes due to poor macro- and micromixing efficiency which is vital
in providing the necessary supersaturated conditions. These problems
can be mitigated using the high-gravitational mixing method which
significantly improves mixing efficiency and greatly reduces reaction
times. In this work, we describe the preparation of silver nanoparticles
from green materials using a high-gravitational rotating packed bed
reactor and present our findings on the significance and effects of
concentration and feed flow rate of reactants and packed bed rotation
speed on the sample particle size and recovery yield. Taguchi statistical
analysis was used to optimize each parameter for small particle size
and high product yield. To determine the particle size and silver
concentration of the synthesized samples, dynamic light scattering
(DLS) and inductively coupled plasma mass spectrometry (ICP) were
used respectively. X-ray diffraction (XRD), UV–vis spectroscopy,
and transmission electron microscopy (TEM) imaging were used for further
characterization of the produced nanoparticles.
Template-free, single crystalline novel hydroxyapatite
(HAp) nanorings
with an inner diameter of 70 nm were grown by a combined high gravity
and hydrothermal approach. Nanodisks were suggested to be formed by
oriented aggregation and Ostwald ripening of mostly calcium pyrophosphate
nanospheres prepared initially by the high gravity method with a stepwise
increase of flow rate of phosphate solution. The prolonged hydrothermal
treatment of nanodisks appeared to induce the nanoring formation via
acid penetration along the dislocations in HAp nanodisks. The presence
of edge dislocations in the central region of nanodisks was confirmed
by high resolution transmission electron microscopy. The mechanical
evaluation of high molecular weight polyethylene (HMWPE) composite
with various shaped HAp nanocrystals and in vitro cellular analysis
of HAp nanocrystals revealed that mechanical and bioactive performances
improved with an increase of the specific surface area of HAp nanocrystals.
The enhanced mechanical performance of HMWPE/HAp nanoring composite
and the excellent cell viability for HAp nanorings are attributed
to the superior interface bonding and cell activity, respectively,
both of which are enhanced by the high specific surface area.
This study used sodium glycinate as an absorbent to absorb CO2 in the bubble column scrubber under constant pH and temperature environments to obtain the operating range, CO2 loading, and mass transfer coefficient. For efficient experimentation, the Taguchi method is used for the experimental design. The process parameters are the pH, gas flow rate (Qg), liquid temperature (T), and absorbent concentration (CL). The effects of the parameters on the absorption efficiency, absorption rate, overall mass transfer coefficient, gas–liquid molar flow rate ratio, CO2 loading, and absorption factor are to be explored. The optimum operating conditions and the order of parameter importance are obtained using the signal/noise (S/N) ratio analysis, and the optimum operating conditions are further verified. The verification of the optimum values was also carried out. The order of parameter importance is pH > CL > Qg > T. Evidence in the 13CNMR (Carbon 13 Nuclear Magnetic Resonance) spectra shows that the pH value has an effect on the solution composition, which affects both the absorption efficiency and mass transfer coefficient. There are 18 experiments for regeneration, where the operating temperature is 100–120 °C. The heat of regeneration was measured according to the thermodynamic data. The CO2 loading, the overall mass transfer, and the heats of regeneration correlation are also discussed in this work. Finally, an operating policy for the CO2 absorption process was confirmed.
A lab-scale bubble-column scrubber is used to capture CO 2 gas and produce ammonia bicarbonate (ABC) using aqueous ammonia as an absorbent under a constant pH and temperature. The CO 2 concentration is adjusted by mixing N 2 and CO 2 in the range of 15-60 vol % at 55 • C. The process variables are the pH of the solution, temperature, gas-flow rate and the concentration of gas. The effects of the process variables on the removal efficiency (E), absorption rate (R A ) and overall mass-transfer coefficient (K G a) were explored. A multiple-tube mass balance model was used to determine R A and K G a, in which R A and K G a were in the range of 2.14 × 10 −4 -1.09 × 10 −3 mol/(s·L) and 0.0136-0.5669 1/s, respectively. Results found that, R A showed an obvious increase with the increase in pH, inlet gas concentration and gas temperature, while K G a decreased with an increase in inlet gas concentration. Using linear regression, an empirical expression for K G a/E was obtained. On the other hand, ammonia bicarbonate crystals could be produced at a pH of 9.5 when the gas concentration was higher than 30% and γ (=F g /F A , the gas-liquid molar flow rate ratio) ≥ 1.5.
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