Impinging Stream-rotating Packed Bed Research Articles

Preparation of Ultrafine Nitroguanidine by One-Step Crystallization in an Impinging Stream-Rotating Packed Bed

To solve the problems of the traditional production process of ultrafine nitroguanidine (NQ), such as a long process and easy pollution caused by recrystallization, the ultrafine NQ (2–6 μm) was prepared by the one-step crystallization in an impinging stream-rotating packed bed (IS-RPB). The influence of operation parameters on the size of the NQ crystal was discussed through various particle size characterization methods. Results show that the size of ultrafine NQ prepared in the IS-RPB was 2.0–3.0 μm, which was smaller than that of market products and conformed to the military standard. Simultaneously, the crystal morphology tended to reduce the length, meeting the target requirement of “shorter and thicker” high-end products. The role of high dispersion and strong mixing in the IS-RPB was the key to continuous and one-step nucleation and crystallization of NQ. One-step crystallization in the IS-RPB is a push flow operation process, where abundant accumulation of the raw material will be avoided effectively, and the safety of energetic material processing will be enhanced greatly. Ultrafine NQ can be prepared without recrystallization, which greatly reduces the energy consumption and the pollution of organic impurities to the product and the environment, providing a new way for the continuous production of ultrafine NQ.

Facile synthesis of CoFe2O4-graphene oxide nanocomposite by high-gravity reactor for removal of Pb(II)

Heavy metals pose a serious threat to human health due to high toxicity and non-biodegradability, and the selection of adsorbent is crucial for the adsorption separation technology. In this paper, based on the problem of non-uniform micromixing in traditional stirred tank reactor (STIR) in the preparation of adsorbent, an impinging stream-rotating packed bed (IS-RPB) using the high gravity technology is proposed to quickly prepare CoFe2O4-graphene oxide nanocomposite (CoFe2O4-GO-RPB) in less than 1 min. Compared with STIR, IS-RPB has the advantages of good micromixing effect, short characteristic mixing time and easy formation of uniform supersaturated environment. The reactivity of CoFe2O4-GO-RPB was evaluated through the adsorption performance towards Pb(II), and the adsorption capacity was 459.8 mg·g−1 at the initial concentration of Pb(II) of 1000 mg·mL−1 and pH of 6. The adsorption behavior of CoFe2O4-GO over Pb(II) was preferably described by Langmuir isotherm model and Elovich model, and the analysis of XPS and FT-IR confirmed that Pb(II) was adsorbed by the action of electrostatic adsorption, ion exchange and complexation. Herein, a facile way of rapid preparation of CoFe2O4-GO with excellent reactivity is provided, and the preparation method of high-gravity co-precipitation will enrich the application of CoFe2O4-GO for hazardous heavy metal remediation from wastewater.

Preparation of L-cysteine modified MnFe2O4 nanoparticles based on high-gravity technology and application for the removal of lead

MnFe2O4 nanoparticles, usually applied as a magnetic adsorbent for removing heavy metals in wastewater, have attracted widespread attention for the characteristics of excellent magnetic properties and chemical stability. This study firstly used high-gravity technology coupled with surface modification by L-cysteine to prepare novel L-cysteine modified MnFe2O4 nanocomposite (MnFe2O4-Cys) with small size (< 10 nm), narrow size distribution range and good dispersion in water, and serves as the efficient adsorbent for Pb(II) removal from water. The different preparation conditions were optimized and the obtained products were charactered through a series of characterization methods. As compared to a traditional stirred reactor, the MnFe2O4-Cys prepared via high-gravity technology using impinging stream-rotating packed bed (IS-RPB) reactor (MnFe2O4-Cys-R) has higher crystallinity and saturation magnetization (57.16 emu·g-1). As seen from TEM images and DLS results, the MnFe2O4-Cys-R exhibits a small average size of 7.25 nm and good dispersion in water. Besides, the BET specific surface area of MnFe2O4-Cys-R (169.63 m2·g-1) is 31.2% higher than that of unmodified MnFe2O4 (129.26 m2·g-1) prepared by IS-RPB reactor (MnFe2O4-R). The adsorption behavior of Pb(II) on MnFe2O4-Cys-R is best described by pseudo-second-order kinetic and Temkin isotherm models, respectively, whereas Elovich kinetic and Freundlich isotherm models are best for describing the adsorption of Pb(II) on MnFe2O4-R. The realized experimental maximum adsorption capacity of MnFe2O4-Cys-R is 137.45 mg·g-1, which is 1.98 times that of MnFe2O4-R (69.50 mg·g-1). This study provides a new route for production of small uniform MnFe2O4 nanoparticles with excellent magnetic and adsorption performance for wastewater treatment.

Synthesis of MnO2/PPy nanocomposites by novel emulsifying device and its electrochemical performances

The manganese dioxide/polypyrrole (MnO2/PPy) nanocomposites were synthesized by miniemulsion polymerization (W/O), which prepared by impinging stream-rotating packed bed (IS-RPB), a novel emulsifying equipment. The obtained MnO2/PPy nanocomposites were characterized by HRTEM, DLS, and BET. The effects of high gravity factor, impact velocity, p-toluenesulfonic acid, potassium permanganate, and reaction time on the specific capacitance of MnO2/PPy nanocomposites were studied. Moreover, we investigated herein its electrochemical performances under suitable operating conditions by cyclic voltammetry, galvanostatic charge–discharge, electrochemical impedance spectroscopy, and cycling life. The results revealed that the obtained MnO2/PPy nanocomposites were flower-like spherical with a high specific surface area of 177.1 m2/g. Besides, the specific capacitance of MnO2/PPy nanocomposites was 231.9 F/g at 0.5 A/g. The electrochemical performances of MnO2/PPy nanocomposites were superior to that prepared MnO2. It is certain that IS-RPB could be used as an effective emulsifying device due to the process intensification and has great potential in industrial applications.

Liquid nitrogen freezing method for exploring the mixing characteristics of liquid/liquid heterogeneous in outer packing cavity of Impinging Stream-Rotating Packed Bed

Impinging Stream-Rotating Packed Bed (IS-RPB) is a reactor developed to strengthen the mass and heat transfer in liquid-liquid mixing processes. The impingement, packing and packing edge cavity zones are crucial features in which mass transfer is highly relevant. In a heterogeneous system composed of an oleic and an aqueous phase, understanding the droplet diameter distribution in the packing edge cavity of an IS-RPB is a key to modeling and evaluating its mass transfer performance. However, such pattern is still unclear. In this work, the flow pattern of the oleic and aqueous phases, including the transitions of fluid ligament flow and droplet flow, and the oil droplet in mixing of oleic and aqueous phases in the packing cavity were studied under different experimental conditions by using a liquid nitrogen freezing method and studied by Optical microscopy. The results showed that droplet determined by this method has good reproducibility with a deviation within 8.4 %, and with a detection limit below 1 μm.

High-gravity continuous preparation of chitosan-stabilized nanoscale zero-valent iron towards Cr(VI) removal

Nanoscale zero-valent iron (nZVI) is easy to agglomerate and be oxidized by surrounding media, and even can't be prepared continuously, which have seriously restricted its application in environmental restoration. Herein, we report a facile technique for the continuous preparation of nZVI with excellent dispersion and stability on a large scale using impinging stream-rotating packed bed (IS-RPB) as the reactor and chitosan as the stabilizer. The effects of high-gravity factor, liquid flow and the additive amount of chitosan on the removal capacity of the chitosan-stabilized nZVI (CS-nZVI) were investigated. It was discovered that the removal capacity toward Cr(VI) was firstly increased and then reduced with each operating parameter increasing. The reactivity of CS-nZVI prepared via different reactors (traditional stirred tank reactor (STR) and IS-RPB) was studied through the removal of Cr(VI). With enhancement mass transfer and rapid micromixing capacities of IS-RPB reactor, CS-nZVI prepared in IS-RPB (CS-nZVI-R) had higher reaction rate constant (0.0836 min−1) and adsorption capacity (101.837 mg g−1) than that prepared in STR. CS-nZVI-R was shown higher stability and reusability, and it could be reused more than four times. Furthermore, this as-prepared CS-nZVI-R can be used for the selective removal of Cr(VI) in the presence of NO3–. In short, it provides an effective route for the controllable continuous preparation of high reactive nZVI, which would expand the application of nZVI in the field of heavy metal pollution remediation.

Preparation of TiO2 and Fe-TiO2 with an Impinging Stream-Rotating Packed Bed by the Precipitation Method for the Photodegradation of Gaseous Toluene.

Nano-TiO2 has always been one of the most important topics in the research of photocatalysts due to its special activity and stability. However, it has always been difficult to obtain nano-TiO2 with high dispersion, a small particle size and high photocatalytic activity. In this paper, nano-TiO2 powder was prepared by combining the high-gravity technique and direct precipitation method in an impinging stream-rotating packed bed (IS-RPB) reactor followed by Fe3+ in-situ doping. TiOSO4 and NH3·H2O solutions were cut into very small liquid microelements by high-speed rotating packing, and the mass transfer and microscopic mixing of the nucleation and growth processes of nano-TiO2 were strengthened in IS-RPB, which was beneficial to the continuous production of high quality nano-TiO2. Pure TiO2 and iron-doped nano-TiO2 (Fe-TiO2) were obtained in IS-RPB and were investigated by means of X-ray diffraction (XRD), Raman, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS) and Brunauer–Emmett–Teller (BET) analysis, which found that pure TiO2 had a particle size of about 12.5 nm, good dispersibility and a complete anatase crystal at the rotating speed of packing of 800 rpm and calcination temperature of 500 °C. The addition of Fe3+ did not change the crystalline structure of TiO2. Iron was highly dispersed in TiO2 without the detection of aggregates and was found to exist in a positive trivalent form by XPS. With the increase of iron doping, the photoresponse range of TiO2 to visible light was broadened from 3.06 eV to 2.26 eV. The degradation efficiency of gaseous toluene by Fe-TiO2 under ultraviolet light was higher than that of pure TiO2 and commercial P25 due to Fe3+ effectively suppressing the recombination of TiO2 electrons and holes; the highest efficiency produced by 1.0% Fe-TiO2 was 95.7%.

Nanoscale zero-valent iron modified with carboxymethyl cellulose in an impinging stream-rotating packed bed for the removal of lead(II)

A novel impinging stream-rotating packed bed (IS-RPB) was proposed to continuous, macro and industrialized prepare nanoscale zero-valent iron (nZVI) with simultaneously modified with carboxymethyl cellulose (CMC) for the removal of Pb2+. The obtained CMC-nZVI particles were characterized by transmission electron microscopy (TEM), dynamic light scattering (DLS), X-ray powder diffraction (XRD), thermogravimetric analysis (TGA) and Fourier transform infrared (FTIR) spectroscopy. The components on the surface of CMC-nZVI after react with Pb2+ were also analyzed by X-ray photoelectron spectroscopy (XPS). The IS-RPB makes it possible for the continuous, macro and industrialized preparing of CMC-nZVI particles, and CMC can significantly improve the dispersion and reduce aggregation of nZVI particles. The effects of solution pH, initial Pb2+ concentration and reaction time on the removal efficiency of Pb2+ by nZVI and CMC-nZVI particles were also investigated. The results show that CMC-nZVI particles outperform nZVI particles in removing Pb2+, and the removal efficacy reaches a maximum of 838.84 mg·g−1 for nZVI particles and 1237.32 mg·g−1 for CMC-nZVI particles at pH = 6.0. The adsorption of Pb2+ by nZVI and CMC-nZVI particles can be described by the Langmuir isotherm adsorption model with a R2 of 0.999, and the calculated maximum adsorption capacity is 900.90 and 1376.07 mg·g−1 for nZVI and CMC-nZVI particles. The adsorption of Pb2+ follows the pseudo second-order kinetics with a linear correlation coefficient R2 of 0.999. In addition, the effect of co-existing cations such as Na+, Cu2+, Ni2+ and Cd2+ on Pb2+ removal efficiency was also investigated. The results showed that Na+ had no effect on Pb2+ removal efficiency and Cu2+ and Ni2+ had inhibited Pb2+ removal efficiency. Cd2+ had an inhibitory effect on Pb2+ removal efficiency when the concentration was 50 mg·L−1 and 100 mg·L−1, Cd2+ enhanced Pb2+ removal efficiency while the concentration of Cd2+ was 200 mg·L−1.

Intensified solvent extraction and separation of cobalt from Ni-rich leaching solution in impinging stream-rotating packed bed contactor

ABSTRACT This work describes the separation of Ni and Co from a real feed solution in chloride media with high Ni content. The extractant used was P507 (2-ethylhexyl phosphoric acid-2-ethylhexyl ester) in a laboratory scale Impinging Stream–Rotating Packed Bed (IS-RPB) contactor. Key variables including feed solution pH, extractant concentration, saponification degree, high gravity level and total volumetric flow rate of fluids amongst other variables were examined. A McCabe–Thiele diagram of the extraction stage predicted that at a total volumetric flow rate of 90 L/h, feed solution pH of 5, saponified P507 concentration of 25% and high gravity of 83, almost 99% of cobalt, would be extracted within three stages. With regard to the scrubbing results, the co-extracted nickel was scrubbed efficiently from the loaded organic solution using a mixture of 0.02 M CoCl2 and 0.5 M hydrochloric acid solution, The purified Co solution was achieved after stripping the loaded-organic phase with 1 M HCl. The maximum value of the overall volumetric mass transfer coefficient for the IS-RPB extractor was found to be 0.16 s−1 which was superior to that of conventional extractors such as mixer-settler and centrifugal extractors, providing strong confidence for its industrial application.

One-step synthesis of hydrophobic magnesium hydroxide nanoparticles and their application in flame-retardant polypropylene composites

Hydrophobic magnesium hydroxide (MH) nanoparticles were prepared by a one-step synthesis method in a high-gravity environment generated by a novel impinging stream–rotating packed bed (IS-RPB) reactor. The reactant solutions were simultaneously and continuously pumped into the IS-RPB reactor, and then Tween 80 was added as a surface modifier. The morphology, structure, and properties of blank and hydrophobic MH were characterized. The effects of MH nanoparticles on the flame retardancy, thermal stability, and mechanical properties of PP/MH composites were also studied. We found that the obtained MH nanoparticles exhibited hexagonal lamella with a mean size of 30 nm, excellent hydrophobic properties (e.g., high water contact angle of 112°), and improved thermal stability of MH. The limiting oxygen index (LOI) further showed that increased MH loading can significantly improve flame-retardant performance, which reached 29.3% for PP/MH composites with 30 wt% hydrophobic samples. The thermal stability and mechanical properties of the PP/MH composites with hydrophobic samples were also much higher than those of PP/MH composites with blank MH. Results showed that the one-step synthesis had high potential application in the large-scale production of hydrophobic MH nanoparticles.

Extraction of nitrobenzene from aqueous solution in impinging stream-rotating packed bed

A liquid-liquid extraction of nitrobenzene (NB) in impinging stream-rotating packed bed (IS-RPB) was proposed using cyclohexane as an extractant, presented for its improvement of micromixing and mass transfer performance. The effects of pH, phase ratio (the flow rate of organic phase/aqueous phase) and rotating speed of IS-RPB on removal efficiency and extraction stage efficiency of NB were investigated experimentally in IS-RPB. The experimental result showed that the removal rate of NB reached 94.93%, and extraction stage efficiency was 99.99% in IS-RPB, respectively, under the following experimental conditions including: a pH of 6.4, a temperature of 25 °C, a phase ratio of 1:1, a liquid flow rate of 50 L/h, a rotating speed for IS-RPB of 400 r/min, and an initial impinging velocity of 7.88 m/s. Besides, IS, RPB and IS-RPB were compared based on the removal rate of NB and extraction stage efficiency in the same experimental conditions. Compared with other mixing devices, IS-RPB has better extraction stage efficiency and shorter extraction time than other extraction devices, proving that high gravity technology can be utilized to effectively improve the extraction stage efficiency and has a good application prospect.

Emulsified behaviors for the formation of Methanol-Diesel oil under high gravity environment

Abstract The emulsified behaviors in the process of preparing methanol-diesel emulsified fuel are investigated by the application of an impinging stream-rotating packed bed (IS-RPB). The emulsified processes are composed of the combinations of initial emulsification of impinging stream process, intensified emulsification of IS-RPB and perfect emulsification of back-splashing and atomization to complete the entire emulsified process through the analysis of force posed on all fluid particles in IS-RPB. The existence of the three emulsified processes is proved using the computational fluid dynamics (CFD) simulations. The turbulent kinetic energy and velocity vector of the three emulsified processes using the CFD simulations were analyzed logically, which proved the existence of the three emulsified processes. Based on the analysis and CFD simulations, the properties of stabilization, dispersion, micro-mixing and power consumption performance were compared under the IS-RPB and high speed stirrer, which further prove the practicability and advancement of this technology for methanol-diesel emulsified fuel.

Simultaneous formation of nanoscale zero-valent iron and degradation of nitrobenzene in wastewater in an impinging stream-rotating packed bed reactor

A novel process based on an impinging stream-rotating packed bed (IS-RPB) was proposed for preparing nanoscale zero-valent iron (NZVI) and degrading nitrobenzene (NB) simultaneously. The obtained NZVI particles were characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy experiments (HRTEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The experimental results showed that the NB removal efficiency increased with the augment of liquid flow rate and initial reactant concentrations. The NZVI prepared with Fe2+ as an iron source had high reactive activity and its removal efficiency of NB could be maintained at a high level in acidic or a weakly basic condition (pH<8). Compared with the traditionally mixing method, the IS-RPB could reduce the iron dosing amounts by 49.6% and the prepared NZVI could achieve 100% efficiency of the NB removal. Considering the operational cost and treatment efficiency, the optimal ratio between NaBH4 and iron concentration could be in the range of 2.0–3.0. Through the strong micro-mixing intensification performance of IS-RPB, the reported approach has compensated for the shortcomings of the traditional nanoparticles production such as complicated procedures and the potential oxidation of Fe0. This study encourages further optimization and development of the high gravity system towards industrial production of NZVI and large-scale NB-containing wastewater treatment.

Continuous preparation of nanoscale zero-valent iron using impinging stream-rotating packed bed reactor and their application in reduction of nitrobenzene

Nanoscale zero-valent iron (nZVI) was continuously prepared by high-gravity reaction precipitation through a novel impinging stream-rotating packed bed (IS-RPB). Reactant solutions of FeSO4 and NaBH4 were conducted into the IS-RPB with flow rates of 60 L/h and rotating speed of 1000 r/min for the preparation of nZVI. As-prepared nZVI obtained by IS-RPB were quasi-spherical morphology and almost uniformly distributed with a particle size of 10–20 nm. The reactivity of nZVI was estimated by the degradation of 100 ml nitrobenzene (NB) with initial concentration of 250 mg/L. The optimum dosage of nZVI obtained by IS-RPB was 4.0 g/L as the NB could be completely removed within 10 min, which reduced 20% compared with nZVI obtained by stirred tank reactor (STR). The reduction of NB and production of aniline (AN) followed pseudo-first-order kinetics, and the pseudo-first-order rate constants were 0.0147 and 0.0034 s−1, respectively. Furthermore, the as-prepared nZVI using IS-RPB reactor in this work can be used within a relatively wide range pH of 1–9.

In situ synthesis of hydrophobic magnesium hydroxide nanoparticles in a novel impinging stream-rotating packed bed reactor

Hydrophobic Mg(OH)2 nanoparticles were successfully synthesized via an in situ surface modification method in a novel impinging stream-rotating packed bed (IS-RPB) reactor using oleic acid (C17H33COOH, OA) as a surface modifier, magnesium chloride hexahydrate in the presence of ethanol as a precursor, and sodium hydroxide as a precipitant. The products were characterized by Fourier transform infrared spectroscopy (FTIR), Field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), and thermogravimetry-differential scanning calorimetry (TG-DSC). Compatibility with organic solutions was determined by sedimentation tests. The prepared nanoparticles exhibited regular hexagonal lamella with an average diameter of 30nm when OA is added to the reaction system; this result indicates that OA regulates the morphology of the Mg(OH)2 nanoparticles. XRD revealed that the high-purity Mg(OH)2 product presents a brucite structure, and the I001/I101 of hydrophobic Mg(OH)2 (0.86) was higher than that of the blank Mg(OH)2 (0.63). FTIR analysis showed that OA bonded to the surface of the Mg(OH)2. Compared with the blank Mg(OH)2 product, the product obtained through the proposed method possesses excellent hydrophobic properties, including a high water contact angle of 101.4° and good compatibility with liquid paraffin. TG-DSC analysis indicated that the total percentage of mass loss of hydrophobic Mg(OH)2 (40.88%) was higher than that of the blank Mg(OH)2 product (33.18%). The in situ surface modification method proposed in this work presents potential use in the large-scale production of Mg(OH)2 nanoparticles.

Continuous preparation of Fe3O4 nanoparticles using impinging stream-rotating packed bed reactor and magnetic property thereof

A novel impinging stream-rotating packed bed (IS-RPB) was adopted for preparing Fe3O4 nanoparticles via reactive precipitation using aqueous solutions of FeCl3/FeCl2 and NaOH as raw materials. In order to establish the optimum conditions for the preparation of monodispersed magnetite Fe3O4 particles, experimental conditions such as high gravity factor, liquid flow rate and reactant concentration were investigated in detail. It shows that the size of Fe3O4 nanoparticles became smaller under the higher gravity factor, liquid flow rate and reactant concentration. And the as-prepared Fe3O4 nanoparticles displays superparamagnetic behavior with the saturation magnetizations in the range from 39.0 to 74.0 emu/g. Based on the experimental results, a set of suitable operating parameters (high gravity factor of 65.32, liquid flow rates of 60 L/h and FeCl3·6H2O concentration of 0.321 mol/L) were recommended for the preparation of Fe3O4 nanoparticles. Under this condition, the as-prepared Fe3O4 nanoparticles is monodispersed quasi-spherical nanoparticles with an average diameter of about 8.9 nm and saturation magnetization of 60.5 emu/g, and the production rate reaches 2.23 kg/hour. Through the strong micromixing intensification performance of IS-RPB, this novel approach is suitable for industrial production of magnetic nanoparticles at massive scale.

Preparation of p-Hydroxybenzaldehyde by Hydrolysis of Diazonium Salts Using Rotating Packed Bed

A new type of reactor, featured with impinging stream-rotating packed bed (IS-RPB) and coil pipes, was designed and used to prepare p-hydroxybenzaldehyde (PHB) by hydrolysis from diazonium salts. The influence of operating parameters, such as reaction temperature, reaction time and high gravity factor, on the yield of PHB was investigated. Compared with the traditional kettle-type reactor, the yield of PHB with the new reactor is increased significantly and the reaction time is much shorter. Under the optimum conditions, the yield of PHB is increased from 51% to 84.1%. The reactor offers an opportunity for replacing the traditional batch mode operation with a continuous process.