Rotor-stator Reactor Research Articles

Selective Absorption of HCl from a Gas Mixture with CO2 by Alkali Solution in a Rotor–Stator Reactor

Selective Absorption of HCl from a Gas Mixture with CO₂ by Alkali Solution in a Rotor–Stator Reactor

Integrated high-gravity process for HCl removal and CO2 capture using carbide slag slurry in a rotor-stator reactor: Experimental and modeling studies

The treatment of flue gas containing HCl and CO2 has garnered significant attention. This study proposes an integrated high-gravity process based on a rotor-stator reactor (RSR) for HCl removal and CO2 capture through mineralization using carbide slag slurry (CSS), an industrial waste. Experimental and modeling studies were conducted to investigate the absorption performance and mass-transfer mechanism. Considering the properties of CSS, Ca(OH)2 slurry was used to simulate CSS for HCl and CO2 absorption in the RSR. The influences of solid content, rotational speed, gas flow rate, and liquid flow rate were investigated, resulting in HCl and CO2 absorption efficiencies of 87.3%–98.9% and 33.8%–65.7%, respectively. Two mechanistic mass-transfer models were established based on surface renewal theory and penetration theory, respectively, to depict the process. The predicted values aligned well with the experimental results, with deviations generally less than 25%. The study further explored the absorption of HCl and CO2 using an actual CSS operated in recycle in the RSR and investigated the characteristics of the solids in fresh and carbonated CSS using XRD, TGA, and SEM. The results indicated that the actual CSS had excellent absorption performance, generally consistent with Ca(OH)2 slurry, and that Ca(OH)2 in CSS was almost completely converted to CaCO3 (calcite).

Study on HCl removal by glycerol in a rotor-stator reactor and desorption of HCl

The emission of hydrogen chloride (HCl) flue gas poses threats to environment and human health, and the removal of HCl from flue gas has attracted much attention. In this work, HCl removal from a simulated flue gas by glycerol was conducted by employing the rotor-stator reactor (RSR) as an absorber. The effects of rotational speed, glycerol flow rate, gas flow rate and glycerol temperature on the removal percentage of HCl, overall gas-phase volumetric mass transfer coefficient and height of mass transfer unit were investigated. With the increase of HCl concentration in the inlet gas from 700 mg/m3 to 2400 mg/m3, the removal percentage remained about 94.5%. Then the mechanism of the HCl absorption by glycerol was investigated, and it was revealed that this process was dominated by physical absorption. Experiments on HCl desorption from glycerol were carried out at different temperatures, and it was found that there was almost no HCl left after glycerol was desorbed at 170 °C for 40 min. After five cycles, the absorption capacity of glycerol for HCl was almost constant. These results indicate that glycerol is a good absorbent for HCl removal from flue gas and the recovery of HCl dry gas.

Study on CO2 absorption by novel choline chloride-diethylenetriamine-water deep eutectic solvents in a rotor-stator reactor

Excessive CO2 emissions from flue gas lead to the greenhouse effect and catastrophic climate change and have become a global concern. To address this problem, novel choline chloride-diethylenetriamine-water (ChCl-DETA-H2O) deep eutectic solvents (DESs) with high CO2 absorption capacity was synthesized in this study. It was found that the DES with a composition of 1ChCl-5DETA-2H2O had the highest CO2 absorption capacity, which was up to 0.250 gCO2/gDES. The as-synthesized DESs were adopted for CO2 absorption in a rotor-stator reactor (RSR), and the effects of ChCl-DETA-H2O molar ratio, high gravity factor, liquid flow rate, gas flow rate, temperature, and inlet CO2 concentration on the CO2 absorption efficiency, overall gas-phase volumetric mass-transfer coefficient (KGa) and height of a transfer unit in the RSR were investigated. Analyses on the mechanism of CO2 absorption in the DES suggest that carbamate formed after CO2 absorption by 1ChCl-5DETA-2H2O. A comparison with the traditional packed columns indicates that the KGa in the 1ChCl-5DETA-2H2O/RSR process was about one order of magnitude larger than that in the DETA/packed column process. Also, the 1ChCl-5DETA-2H2O/RSR process achieved a higher CO2 absorption efficiency and KGa than the DETA/rotating packed bed process. This work demonstrates that the RSR enhanced the absorption of CO2 by the DES and the combination of RSR and DES can provide an efficient process for CO2 capture.

HCl removal and recovery using choline chloride-glycerol deep eutectic solvent in rotor–stator reactor: Molecular mechanism, experimental and modeling studies

Efficient removal and recovery of HCl from off-gas are significant for environmental protection and resource utilization. In this work, the absorption process of HCl using choline chloride-glycerol (ChCl-Gly) was studied in three aspects: molecular mechanism, experimental and modeling studies. Firstly, the molecular mechanism of HCl absorption into ChCl-Gly was studied by the σ-profiles, binding models and intermolecular interaction, and it was revealed that the H atom of HCl binds with O and Cl of ChCl-Gly to form hydrogen bonds. Secondly, in view of the absorption characteristics, the process intensification of HCl absorption into ChCl-Gly was proposed by using a rotor–stator reactor (RSR). The influences of the high gravity factor, gas flowrate, ratio of gas flowrate to liquid flowrate and HCl concentration in gas inlet on the removal efficiency of HCl and overall gas-phase volumetric mass-transfer coefficient (KGa) in the removal of HCl by ChCl-Gly in the RSR were explored, and it was found that a larger high-gravity factor led to a better mass transfer effect and higher HCl removal efficiency. In addition, a mass transfer model was built to describe the process of HCl absorption into ChCl-Gly in the RSR, and the model predictions agreed well with the experimental data, and the deviations between experimental and predicted KGa were generally less than ±25 %. Finally, the prospects for industrial applications of HCl removal and recovery using deep eutectic solvents in RSR were discussed.

Study on the Effective Mass Transfer Area and the Local Gas-Side Mass Transfer Coefficient in a Rotor–Stator Reactor

Study on the Effective Mass Transfer Area and the Local Gas-Side Mass Transfer Coefficient in a Rotor–Stator Reactor

Intensification of HCl removal from flue gas using a rotor-stator reactor

The emission of HCl in flue gas causes serious environmental problems and its removal methods have attracted wide attention. This work investigated the intensification of HCl removal from flue gas in a rotor–stator reactor. The effects of high gravity factor, gas flow rate, water flow rate, temperature and inlet concentration of HCl on the removal efficiency of HCl, overall volumetric gas-phase mass-transfer coefficient (KGa) and height of a transfer unit in the removal of HCl by water in the rotor–stator reactor were investigated. Comparisons with conventional column indicated that the rotor–stator reactor had better mass-transfer performance and may have economic advantages in HCl removal. Comparison experiments showed that KGa and height of a transfer unit in the rotor–stator reactor were 10.9–45.2% higher and 41.5–55.7% lower, respectively, than those in a rotating packed bed, indicating that rotor–stator reactor has a superior capability for the removal of HCl in flue gas and other processes controlled by gas-side mass transfer. An artificial neural network model was established to predict the KGa of HCl removal from flue gas by water in the rotor–stator reactor. This work demonstrates that rotor–stator reactor is an effective process intensification technology for the removal of HCl from flue gas.

Removal of Dissolved Oxygen from Water by Nitrogen Stripping Coupled with Vacuum Degassing in a Rotor–Stator Reactor

Oxygen is a harmful substance in many processes because it can bring out corrosion and oxidation of food. This study aimed to enhance the removal of dissolved oxygen (DO) from water by employing a novel rotor–stator reactor (RSR). The effectiveness of the nitrogen stripping coupled with vacuum degassing technique for the removal of DO from water in the RSR was investigated. The deoxygenation efficiency (η) and the mass transfer coefficient (KLa) were determined under various operating conditions for the rotational speed, liquid volumetric flow rate, gas volumetric flow rate, and vacuum degree. The nitrogen stripping coupled with vacuum degassing technique achieved values for η and KLa of 97.34% and 0.0882 s−1, respectively, which are much higher than those achieved with the vacuum degassing technique alone (η = 89.95% and KLa = 0.0585 s−1). A correlation to predict the KLa was established and the predicted KLa values were in agreement with the experimental values, with deviations generally within 20%. The results indicate that RSR is a promising deaerator thanks to its intensification of gas–liquid contact.

Treatment of Acid Red 73 wastewater by the O3/RSR-BCR process

Rotor-stator reactor (RSR) was employed in tandem with bubble column reactor (BCR) to enhance Acid Red 73 (AR73) degradation by ozonation in a simulated dyeing wastewater in this work. It was found that AR73 and COD degradation efficiencies of more than 97 % and 30 % respectively were achieved in the O3/RSR-BCR process. Due to the excellent mass transfer effect of RSR, AR73 degradation efficiency in the O3/RSR-BCR process was significantly higher than that in the O3/BCR process, exhibiting the effect of lowered ozone consumption as well as reduced BCR volume as a result of shorter liquid residence time. The advantages of the O3/RSR-BCR process for AR73 wastewater treatment were attributed to the high O3 absorption efficiency in RSR and relatively long reaction time of O3 with pollutants in BCR. The results demonstrated that the O3/RSR-BCR process can be an efficient decolorization technique in dyeing wastewater treatment.

Continuous acid-catalyzed esterification using a 3D printed rotor–stator hydrodynamic cavitation reactor reduces free fatty acid content in mixed crude palm oil

Free fatty acid (FFA) content in FFA-rich mixed crude palm oil (MCPO) was reduced through a continuous esterification process. The reaction conditions were optimized, the yield purified esterified oil was determined, and the average total electricity consumption of the entire process was evaluated. The key component of this study was the cost-effective, 3D-printed rotor that was installed in a continuous rotor–stator hydrodynamic reactor. The surface of the rotor was designed with spherical holes where the center-to-center distance between them was fixed. Response surface methodology (RSM) using central composite design (CCD) was employed to analyze the design of experiments (DOE) and optimize FFA-content reduction. The optimized conditions were 17.7 vol% methanol, 2.9 vol% sulfuric acid, a 3000 rpm rotor speed, and surface holes measuring 4 mm in diameter and 6 mm in depth. The experimental results showed that the FFA content in MCPO was reduced from 11.456 to 1.028 wt% upon esterification under these optimal conditions. The maximum yield of esterified oil from the phase separation step was 96.07 vol%, and that of the purified esterified oil was 91.27 vol%. The average total energy consumed by this hydrodynamic cavitation reactor to produce this esterified oil was 0.0264 kW h/L. This 3D printed rotor–stator reactor is a promising, novel reactor technology for producing biodiesel from FFA-rich oils.

Experimental investigation of effective gas-liquid specific interfacial area in a rotor-stator reactor

This work aimed to experimentally determine the effective gas-liquid specific interfacial area (ae) in a countercurrent flow rotor-stator reactor (RSR) by chemical absorption of CO2 into NaOH solution. The effects of different operating parameters such as rotation speed, liquid volumetric flow rate and gas volumetric flow rate on ae were investigated. Results indicate that higher rotation speed, gas and liquid volumetric flow rates favor larger ae. A correlation to predict ae of gas-liquid phases in RSR is also established, and the predicted values are in agreement with the experimental data with deviations within 5 %.

Degradation of indigo carmine by coupling Fe(II)-activated sodium persulfate and ozone in a rotor-stator reactor

Rotor-stator reactor (RSR), a novel high-gravity device, was employed in the O3/persulfate (PS)/Fe2+ process to enhance the degradation of indigo carmine (IC) in simulated wastewater. It was found that IC degradation efficiency increased with the increase of Fe2+ concentration, RSR rotation speed, O3 concentration and gas-liquid ratio, but decreased with the increase of IC concentration and temperature. When the rotation speed of RSR increased from zero to 1200 rpm, IC degradation efficiency increased from 25.6% to 64.2%. Because of the synergetic effects of the oxidative species (O3, OH, SO4− etc.), IC degradation efficiency in the O3/PS/Fe2+ process was significantly higher than that in the O3 or PS/Fe2+ process. The high IC degradation efficiency can also be attributed to the good micromixing effect of the RSR. When the O3/PS/Fe2+ process in the RSR was adopted before the sequencing batch reactor activated sludge process, both IC and COD degradation efficiencies increased significantly as a result of the improved biodegradability of the IC wastewater. Furthermore, a possible degradation mechanism of IC in the O3/PS/Fe2+ process was proposed.

CO2 absorption into K2CO3/KHCO3 solution enhanced by organic phase in a rotor–stator reactor

ABSTRACTThis work studied the gas–liquid–liquid (G–L–L) reaction system of CO2 absorption into K2CO3/KHCO3 buffer solution enhanced by organic phase in a rotor–stator reactor (RSR). The effects of volume fraction of organic phase, type of organic phase, rotational speed of RSR, gas and liquid volumetric flow rate, and temperature on CO2 absorption percentage were investigated. Results indicate that the addition of the organic phase with a volume fraction of 1.3–1.6% had significant promoting effect on CO2 absorption. CO2 absorption percentage increased with increase in the rotational speed of the RSR but decreased with rise in liquid temperature and gas–liquid ratio. This work demonstrates that RSR can significantly enhance liquid–liquid mixing and gas–liquid mass transfer processes in the G–L–L system.

Visual study on the characteristics of liquid and droplet in a novel rotor-stator reactor

Abstract Rotor–stator reactor (RSR), an efficient mass transfer enhancer, has been applied in many fields. However, the hydrodynamic characteristics of liquid flow in RSR are still a mystery despite they are fundamental for the mass transfer performance and processing capacity. In view of the above, this paper studies the liquid–liquid flow and liquid holdup in RSR under various conditions with a high-speed camera. The paper firstly demonstrates two flow patterns and liquid holdup patterns that we obtained from our experiment and then presents in succession a flow pattern and a liquid holdup criterion for the transition of film flow to filament flow and complete filling to incomplete filling. It is found that experimental parameters, including rotor–stator distance, rotational speed and volume flow rate exert great influence on the average droplet diameter and size distribution. Besides, by comparison and contrast, we also find that the experimental values match well with our previous predicted calculations of the average diameter, and the relation between the average diameter and the mean energy dissipation rate.

Study on the Synthesis of 2,3,5-Trimethyl-1,4-Benzoquinone by an RSR+STR Tandem Process

This study presents a novel RSR+STR tandem process for the catalytic oxidation of 2,3,6-trimethylphenol (TMP) to synthesize 2,3,5-trimethyl-1,4-benzoquinone (TMQ) in a gas–liquid–liquid three-phase reaction system by combining a rotor-stator reactor (RSR) with a conventional stirred tank reactor (STR). The effects of various operating conditions including rotation speed of the RSR, gas volumetric flow rate, liquid volumetric flow rate, water volume fraction in the liquid phase and reaction temperature on the TMP conversion and TMQ yield were investigated. The TMP conversion and TMQ yield in the RSR+STR tandem process reached 86.9% and 20.0%, respectively, which were much higher than those in the STR process under the same conditions where the conversion and yield were only 46.8% and 6.8% respectively. It is suggested that the improvement of TMQ synthesis in the RSR+STR tandem process is ascribed to the intensification of liquid–liquid mixing, gas–liquid transfer and oxidation reaction in the RSR.

Synthesis of Ni-CeO2 nanocatalyst by the microemulsion-gas method in a rotor-stator reactor

Ni-CeO2 nanocatalyst was synthesized by the reaction of cerium nitrate and nickel nitrate microemulsion with ammonia gas in a rotor-stator reactor (RSR) in this work. The effect of the RSR rotation speed, ammonia gas flow rate and calcination temperature on the properties of the Ni-CeO2 nanocatalyst was investigated, and the catalytic activity of the as-prepared nanocatalyst in the reaction of CO2 reforming of methane was studied. Experimental results indicated that the catalytic activity of the Ni-CeO2 nanocatalyst prepared in the RSR increased with an increasing rotation speed and ammonia gas flow rate, but increased first and decreased then with the increase of the calcination temperature. Due to the excellent micromixing and mass transfer effects of the RSR, the Ni-CeO2 nanocatalyst prepared in the RSR had a smaller size, narrower size distribution and higher catalytic activity compared to that prepared in a stirred tank reactor (STR). Methane and CO2 conversions and CO selectivity in the reforming reaction with the Ni-CeO2 nanocatalyst prepared in the RSR were 15%–25% higher than those with the Ni-CeO2 nanocatalyst prepared in the STR.

CFD analyses of liquid flow characteristics in a rotor-stator reactor

Rotor-stator reactor (RSR) is a novel device for the intensification of multiphase processes and can greatly boost mass transfer and mixing efficiency. However, due to the unique structure, the flow characteristics in the RSR is unknown and difficult to acquire by experiments. Therefore, this work employed computational fluid dynamics (CFD) technique to reveal liquid flow behaviors in an RSR for the first time. The volume of fluid (VOF) multiphase model, sliding model (SM) and standard k–ε model were used to simulate liquid flow field in a typical two-dimensional computational framework of the RSR. It was found that the droplet size and velocity in the cavity zone of the RSR were in agreement with the published data of the visual experiments. The results show that the liquid was quickly split and synchronized with the motion of the rotor layers when injected into the RSR. Two droplet formation schemes were observed in the RSR: “ligament to droplets disintegration” and “droplets disintegration”. The droplets size distribution could be well described by Rosin–Rammler model. The droplets diameter decreased but the droplet velocity increased with increasing rotational speed, while the droplets diameter increased and the droplet velocity changed little with increasing liquid inlet velocity. With the increase of the number of rotor/stator layers, droplet size decreased and velocity increased. The agreement of the experiment and simulation results indicate that the CFD technique is an effective tool to analyze the hydrodynamic characteristics of RSR.

Mass transfer study of water deoxygenation in a rotor–stator reactor based on principal component regression method

This study investigated mass transfer characteristics in a rotor–stator reactor (RSR) in terms of the overall volumetric mass-transfer coefficient (Kxa) using nitrogen stripping (N2–H2O–O2) and nitrogen stripping coupled with vacuum degassing (vacuum–N2–H2O–O2) processes. Principal component regression (PCR) method was used to establish a mass transfer model, and the number of principal components (PCs) was examined by three different techniques including cumulative percent variance (CPV), average eigenvalue (AE), and cross validation (CV). The prediction performance of the PCR model was compared to that of the multiple linear regression (MLR) model. Results reveal that the number of PCs determined by CV based on the predicted residual error sum of squares can be used to determine the optimal number of PCs to express the relationship between various modeling variables and Kxa. The values of Kxa predicted by the PCR and MLR models in the N2–H2O–O2 system were in agreement with the experimental values with deviations within 15% while those in the vacuum–N2–H2O–O2 system generally agreed with the experimental values with deviations within 15% and 30%, respectively. These results indicate that the PCR method is best suited for mass transfer modeling in an RSR.

Ozonation of o -phenylenediamine in the presence of hydrogen peroxide by high-gravity technology

Abstract The study herein investigated the effectiveness of simultaneous use of ozone and hydrogen peroxide (O3/H2O2 process) to degrade o-phenylenediamine (o-PDA) in a simulated wastewater. A rotor–stator reactor (RSR) was employed to create a high-gravity environment in order to enhance ozone-liquid mass transfer rate and possibly improve the degradation rate of o-PDA. The degradation efficiency of o-PDA (η) as well as the overall gas-phase volumetric mass transfer coefficient (KGa) were determined under different operating conditions of H2O2 concentration, initial o-PDA concentration, temperature of reaction, initial pH and rotation speed of RSR in attempt to establish the optimal conditions. Chemical oxygen demand reduction rate (rCOD) of wastewater treated at a particular set of conditions was also analyzed. Additionally, the intermediate products of degradation were identified using a gas chromatography-mass spectrometer (GC/MS) to further evaluate the extent of o-PDA degradation as well as establish its possible degradation pathway. Results were validated by comparison with those of sole use of ozone (O3 process), and it was noted that η, KGa and rCOD achieved by O3/H2O2 process was 24.4%, 31.6% and 25.2% respectively higher than those of O3 process, indicating that H2O2 can greatly enhance ozonation of o-PDA. This work further demonstrates that an RSR can significantly intensify ozone-liquid mass transfer rate and thus provides a feasible intensification means for the ozonation of o-PDA as well as other recalcitrant organics.

Preparation of Nickel-Cobalt Layered Double Hydroxides for the Battery-like Electrodes in Rotor–Stator Reactor

Nickel-cobalt layered double hydroxides (NiCo LDHs) with different Ni/Co ratios were prepared using rotor-stator reactor technology. The morphology, crystal structure, pore size distribution and electrochemical properties were characterized and the band structure was calculated with LDA+U method in CASTEP code based on density functional theory. The results show that the band gap value of Ni5Co3O16H16 decreases compared to that of Ni8O16H16. The pore size increases and the pore size distribution widens with the increasing cobalt content in the NiCo LDHs. The NiCo LDH with a Ni/Co ratio of 2: 1 has a surface area of 139.9 m(2) g(-1) and a specific capacity of 176.7 mA h g(-1) at a current density of 1 A g(-1) in 6 M KOH. The electrode also exhibits good cycling stability and the capacity retention still remains 98 % after 1000 cycles.