Liquid-solid mass transfer in a rotating packed bed reactor with structured foam packing

A rotating packed bed (RPB) reactor has substantially potential for the process intensification of heterogeneous catalytic reactions. However, the scarce knowledge of the liquid-solid mass transfer in the RPB reactor is a barrier for its design and scale-up. In this work, the liquid-solid mass transfer in a RPB reactor installed with structured foam packing was experimentally studied using copper dissolution by potassium dichromate. Effects of rotational speed, liquid and gas volumetric flow rate on the liquid-solid mass transfer coefficient (k_LS) have been investigated. The correlation for predicting k_LS was proposed, and the deviation between the experimental and predicted values was within ±12%. The liquid-solid volumetric mass transfer coefficient (k_LSa_LS) ranged from 0.04-0.14 1^-1, which was approximately 5 times larger than that in the packed bed reactor. This work lays the foundation for modeling of the RPB reactor packed with structured foam packing for heterogeneous catalytic reaction.     

Mass transfer performance of a rotating packed bed equipped with blade packings in removing methanol and 1-butanol from gaseous streams

The removal of methanol and 1-butanol from gaseous streams by absorption with water was investigated in the RPB equipped with blade packings. The overall volumetric gas-phase mass transfer coefficient (K_Ga) for methanol and 1-butanol absorption was observed to increase with the rotational speed, the gas flow rate, and the liquid flow rate. Also, the local volumetric gas-phase mass transfer coefficient (k_Ga) was estimated, and then the portion of the total resistance to mass transfer in gas phase was determined. The result indicated that more than 90% of the total resistance to mass transfer in methanol and 1-butanol absorption was found to be due to the gas phase. Comparison with the conventional packed tower demonstrated that mass transfer efficiency in the RPB equipped with blade packing was higher than that in the conventional packed tower. Consequently, the RPB equipped with blade packings would be an excellent absorber for the removal of alkanols from the exhausted gases.     

Modeling and experimental studies on absorption of CO2 by Benfield solution in rotating packed bed

This work presents the modeling and experimental investigation on absorption of CO₂ by Benfield solution in rotating packed bed (RPB). A model was established to illustrate the mechanism of gas–liquid mass transfer with reactions in RPB at higher gravity level. Experiments were carried out at various rotating speeds, liquid flow rates, gas flow rates and temperatures in RPB, with Benfield solution as the absorbent. The validity of this model was demonstrated by the fact that most of the predicted y_o (mole fraction of CO₂ in outlet gas) agreed well with the experimental data with a deviation within 10%. The presented profile of K_Ga (gas-phase volumetric mass transfer coefficient) along the radial direction of the packing could reasonably explain the end effect in RPB. As a result, this model is reliable in describing the removal of CO₂ by Benfield solution in RPB at higher gravity level.     

Mass transfer studies on split-packing and single-block packing rotating packed beds

In this work, SO₂ absorption in aqueous NaOH (gas side mass transfer resistance controlled system) and O₂ desorption from the water (liquid side mass transfer resistance controlled system) are experimentally evaluated for enhancement in the controlling side volumetric mass transfer coefficient using the novel split-packing and conventional single-block rotating packed bed (RPB) designs. In the split-packing RPB design, mass transfer characteristics for co-rotation and counter-rotation of adjacent rings are studied. For the SO₂ absorption system, results show a significant reduction in the controlling mass transfer resistance for split-packing over single-block packing for large RPBs. However, the mass transfer coefficients for co- and counter-rotation are comparable. For the O₂ desorption system, at low rotation rates, the split-packing design gives higher mass transfer rates compared to the single-block packing. This difference disappears as the rotation rate is increased. Possible reasons for the experimental observations are speculated. The results suggest the split packing design to be more suitable for gas side mass transfer resistance controlled systems.     

Mass transfer characteristics in a rotating packed bed with split packing

The rotating packed bed (RPB) with split packing is a novel gas–liquid contactor, which intensifies the mass transfer processes controlled by gas-side resistance. To assess its efficacy, the mass transfer characteristics with adjacent rings in counter-rotation and co-rotation modes in a split packing RPB were studied experimentally. The physical absorption system NH3–H2O was used for characterizing the gas volumetric mass transfer coeffi-cient (kyae) and the effective interfacial area (ae) was determined by chemical absorption in the CO2–NaOH sys-tem. The variation in kyae and ae with the operating conditions is also investigated. The experimental results indicated that kyae and ae for counter-rotation of the adjacent packing rings in the split packing RPB were higher than those for co-rotation, and both counter-rotation and co-rotation of the split packing RPB were superior over conventional RPBs under the similar operating conditions.     

Micromixing efficiency of rotating packed bed with premixed liquid distributor

Rotating packed bed (RPB), in which high gravity is simulated by a centrifugal force, plays an important role in process intensification of fluid mixing and mass transfer. However, uneven initial liquid distribution in RPB leads to poor micromixing efficiency in local areas of the packing. Therefore, a premixed liquid distributor is proposed in this work to improve the liquid distribution in RPB. Micromixing efficiency of RPB with the premixed liquid distributor was studied by adopting the iodide–iodate reaction as working system and show better micromixing efficiency compared to that of RPB with non-premixed liquid distributor. Also, the effects of operating conditions (e.g. rotational speed, acid concentration, volumetric flow rate) and geometries using the premixed liquid distributor on micromixing efficiency (characterized by segregation index X_S) were investigated. The results show that segregation index X_S decreases with the increase of rotational speed, and the decrease of acid concentration and volumetric flow rate.     

Oxygen mass transfer coefficient in bubble column slurry reactor with ultrafine suspended particles and neural network prediction

The gas–liquid volumetric mass transfer coefficient was determined by the dynamic oxygen absorption technique using a polarographic dissolved oxygen probe and the gas–liquid interfacial area was measured using dual‐tip conductivity probes in a bubble column slurry reactor at ambient temperature and normal pressure. The solid particles used were ultrafine hollow glass microspheres with a mean diameter of 8.624 µm. The effects of various axial locations (height–diameter ratio = 1–12), superficial gas velocity (u_G = 0.011–0.085 m/s) and solid concentration (ε_S = 0–30 wt.%) on the gas–liquid volumetric mass transfer coefficient k_La_L and liquid‐side mass transfer coefficient k_L were discussed in detail in the range of operating variables investigated. Empirical correlations by dimensional analysis were obtained and feed‐forward back propagation neural network models were employed to predict the gas–liquid volumetric mass transfer coefficient and liquid‐side mass transfer coefficient for an air–water–hollow glass microspheres system in a commercial‐scale bubble column slurry reactor. © 2012 Canadian Society for Chemical Engineering     

旋转填充床反应器流体流动可视化研究进展

旋转填充床反应器是一种典型过程强化装置,对化工过程中的传质与混合过程具有较好的强化作用。流体流动作为旋转填充床反应器中最为基础的性质,对研究、优化旋转填充床反应器的结构和性能至关重要。光学成像技术与数值模拟作为研究旋转填充床反应器中流体力学性质的重要手段在近年来得到了飞速发展。对近三十年来,旋转填充床反应器可视化研究进行了综述,从早期光学成像开始,在此基础上引入早期计算流体力学模拟,直至现在高速数码摄像可视化和基于真实结构的模拟。对旋转填充床的可视化观测从填料表面逐渐向填料内部发展,对其数值模拟从初步的数学模型发展到包含详细填料几何结构、详细流体特性的流动模拟。现有研究已对填料区、空腔区中的流体流动有了较为详细的描述。     

Intensification of G/L absorption in microstructured falling film. Application to the treatment of chlorinated VOC’s – part I: Comparison between structured and microstructured packings in absorption devices

The absorption of tetrachloroethylene – the VOC – in di-ethyl-hexyl-adipate – the solvent – was carried out as an example of gaseous waste treatment. Two gas–liquid contactors were used: a column provided with as structured Sulzer EX^® packing and a microstructured falling-film absorber provided with thin vertical channels, manufactured by the Institut für Mikrotechnik Mainz (IMM). The overall transfer coefficient of VOC, K_Ga, was calculated from the absorption efficiency of the various runs carried out, allowing comparison of the two gas–liquid contactors. Due to the high solubility of the considered VOC, mass transfer was shown to be mainly controlled by gas-side transfer rates. Transfer coefficient K_Ga of the two absorbers were found to be comparable, but with gas and liquid velocity in the microstructured absorber from one to two orders of magnitude below those in the column, expressing the high transfer performance offered by the microsystem. Moreover, the thickness of the liquid film in the channels was below 100 μm, much lower than that in a structured packing near 500 μm. This shows that lower liquid flow rates can be used for efficient absorption in the microsystem. It is shown that contrary to conventional structured packing, the designed contact specific area in the microabsorber strictly corresponds to the interfacial G/L surface. This enables more compact and to miniaturize G/L contactors to be designed.     

Characteristics of integrated micro packed bed reactor-heat exchanger configurations in the direct synthesis of dimethyl ether

The performance of three integrated micro packed bed reactor-heat exchangers (IMPBRHEs) for direct DME synthesis over physical mixtures of CuO–ZnO–Al₂O₃ and γ-Al₂O₃ catalysts was experimentally investigated. Systematic variations in reactor and slit dimensions and configuration were analyzed in terms of thermal behaviour, mass transfer, pressure drop and residence time distribution (RTD). The pressure drop was always small (<0.12 bar) relative to the total pressure (50 bar), and linear dependence with GHSV confirms the predicted laminar flow for Re = 0.1–2. A narrow RTD was estimated by the dispersion analysis. Careful temperature measurements confirmed that the reaction temperature is mainly controlled by the oil heat exchange to give a practically uniform temperature profile for set inlet oil temperatures of 220–320 °C. The micro packed beds were found free of the internal as well as external mass transfer limitations, as showed by no significant change in the CO conversion and DME yield for different catalyst particle sizes, no effect of varying the linear gas velocity, and no effect of manipulating reactant diffusion coefficient. Packed bed microstructured reactors hence provide an isobaric and isothermal environment free from transport limitations for the direct DME synthesis, in the kinetic regime as well as at equilibrium conversion.     

Efficient capture of carbon dioxide with novel mass‐transfer intensification device using ionic liquids

A novel mass‐transfer intensified approach for CO₂ capture with ionic liquids (ILs) using rotating packed bed (RPB) reactor was presented. This new approach combined the advantages of RPB as a high mass‐transfer intensification device for viscous system and IL as a novel, environmentally benign CO₂ capture media with high thermal stability and extremely low volatility. Amino‐functionalized IL (2‐hydroxyethyl)‐trimethyl‐ammonium (S)?2‐pyrrolidinecarboxylic acid salt ([Choline][Pro]) was synthesized to perform experimental examination of CO₂ capture by chemical absorption. In RPB, it took only 0.2 s to reach 0.2 mol CO₂/mol IL at 293 K, indicating that RPB was kinetically favorable to absorption of CO₂ in IL because of its efficient mass‐transfer intensification. The effects of operation parameters on CO₂ removal efficiency and IL absorbent capacity were studied. In addition, a model based on penetration theory was proposed to explore the mechanism of gas–liquid mass transfer of ILs system in RPB. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2957–2965, 2013     

Evaluation of a rotating packed bed equipped with blade packings for methanol and 1-butanol removal

Absorption removal of methanol and 1-butanol from gaseous streams with water was investigated in the RPB equipped with blade packings. The removal efficiency (E) of methanol and 1-butanol was found to increase with the RPB speed and the liquid flow rate but decrease with the gas flow rate. Also, the overall volumetric gas-side mass transfer coefficient (K_Ga) for methanol and 1-butanol absorption was observed to increase with the RPB speed, the gas flow rate, and the liquid flow rate. According to the obtained dependence of K_Ga on the gas and liquid flow rates, the mass transfer in methanol and 1-butanol absorption was observed to be controlled primarily by the gas-side mass transfer. Furthermore, the height of a transfer unit (HTU) for methanol and 1-butanol absorption decreased with the RPB speed and the liquid flow rate but increased with the gas flow rate. The obtained results demonstrated that mass transfer efficiency of the RPB equipped with blade packing was comparable to that of a hollow fiber absorber. Consequently, the RPB equipped with blade packings has a great potential in the removal of alkanols from the exhausted gases.     

超重力旋转床中水脱氧过程的模型化研究

超重力旋转床是一种高效的强化传质和混合的新型设备。今提出了超重力旋转床中的水脱氧过程的传质模型,分别采用欧拉方法和拉格朗日方法对超重力旋转床中的气相和液滴的运动行为进行了数值模拟;在此基础上计算了液滴的传质系数,计算结果和实验结果符合较好,平均误差为7．9％。当超重力旋转床中液体存在的主体形式更接近于液滴时,模型计算结果误差减小。进一步讨论分析了液体和气体流量、转速以及填料内径的变化对于超重力旋转床体积传质系数的影响,分析表明旋转填料对液体剧烈地剪切破碎分散作用是强化传质过程的主要原因。     

A unified approach to the hydraulics and mass transfer in randomly packed towers

New robust correlations and mechanistic model of macroscopic fluid dynamic and gas–liquid mass transfer characteristics for randomly packed towers were developed based on first principles, neural network computing and dimensional analysis (artificial neural network and dimensional analysis, ANN–DA). These tools concerned the loading and flooding capacities, the total liquid hold-up, the irrigated pressure drop, the local volumetric liquid-side, k_La, and gas-side, k_Ga, mass transfer coefficients, the overall volumetric, K_La and K_Ga, mass transfer coefficients, and the packing fractional wetted area. Validation of these tools was performed by interrogating a broad experimental database including over 10,750 measurements published in the literature over the past seven decades. The fully-predictive mechanistic model proved powerful in forecasting the tower hydraulics below the loading point without requiring any adjustable parameter. On the other hand, the ANN–DA correlations proved highly powerful in correlating the tower fluid dynamics and gas–liquid mass transfer regardless of the operating flow regime. These approaches were also benchmarked with respect to the comprehensive Billet and Schultes (Trans. Industr. Chem. Eng. 77 (1999) 498) phenomenological approach and the classical Onda et al. (J. Chem. Eng. Japan 1 (1968) 56) mass transfer correlations.     

Distillation studies in rotating packed bed with split packing

Rotating packed bed (RPB) with split packing has been developed recently to overcome the limitation of negligible tangential slip velocity between vapor and packing obtained with single rotating packing element of conventional RPB design. This work evaluates the performance of this contactor for separation of binary mixture methanol–ethanol by distillation. Experiments were carried out at total reflux condition. The height equivalent of a theoretical plate (HETP) of 2.9 cm was obtained at F-factor = 0.6 (m/s) (kg/m³)^0.5 and rotor speed of 1100 rpm. Comparison with distillation studies reported for this system in the literature indicated that the mass transfer performance of this rotor design was superior to that of conventional RPB. Analysis of the experimental data also suggested that the rotor speed influenced the overall volumetric mass transfer coefficient to a greater degree in this design.     

Gas‐Liquid Mass Transfer in Fibrous Bed Reactor with Counter‐Current Liquid Recycle

In this work, the gas‐liquid mass transfer in a lab‐scale fibrous bed reactor with liquid recycle was studied. The volumetric gas‐liquid mass transfer coefficient, k_La, is determined over a range of the superficial liquid velocity (0.0042–0.0126 m.s^–1), gas velocity (0.006–0.021 m.s^–1), surface tension (35–72 mN/m), and viscosity (1–6 mPa.s). Increasing fluid velocities and viscosity, and decreasing interfacial tension, the volumetric oxygen transfer coefficient increased. In contrast to the case of co‐current flow, the effect of gas superficial velocity was found to be more significant than the liquid superficial velocity. This behavior is explained by variation of the coalescing gas fraction and the reduction in bubble size. A correlation for k_La is proposed. The predicted values deviate within ± 15 % from the experimental values, thus, implying that the equation can be used to predict gas‐liquid mass transfer rates in fibrous bed recycle bioreactors.     

Removal of ozone from air by absorption in a rotating packed bed

This work investigated the feasibility of ozone (O₃) absorption by H₂O₂ solution in a rotating packed bed (RPB). The overall volumetric gas-phase mass transfer coefficients (K_Ga) were determined as functions of pH of H₂O₂ solution, O₃ concentration, H₂O₂ concentration, RPB speed, gas flow rate, liquid flow rate, and RPB type. The K_Ga values were highly dependent on the pH of H₂O₂ solution. Also, the K_Ga values increased with O₃ concentration and H₂O₂ concentration. As expected, the RPB speed positively affected the K_Ga values for all RPBs. Furthermore, the obtained results indicated that the K_Ga values increased as the inner radius of the bed was increased and the outer radius of the bed was decreased. Moreover, the K_Ga values increased with an increasing liquid flow rate and an increasing gas flow rate for all RPBs. The dependences of K_Ga on the gas flow rate and the liquid flow rate indicated that the resistance to mass transfer in the gas-phase for O₃ absorption was higher than that in the liquid phase in the RPB.     

A comparison of triglyceride oil hydrogenation in a downflow bubble column using slurry and fixed bed catalysts

The hydrogenation of the triglyceride oil, soya bean oil, has been studied in the temperature range 130–160 °C and in the pressure range 100–600 kPa using (i) a 5% w/w Pd/C slurry catalyst and (ii) a 3% w/w Pd/Al₂O₃ Raschig ring catalyst in a cocurrent downflow contactor (CDC) reactor. Separate studies of residence time distribution (RTD) were carried out in a modified CDC device in order to determine dispersion numbers and dispersion coefficients. The RTD measurements indicated that the overall flow was a mixture of well‐mixed and plug flow for the unpacked CDC, so that the entry section (0–30 cm from entrance) was perfectly mixed and the remainder of the column (30–130 cm) gave predominantly plug flow behaviour. The introduction of random packing in the form of 13 mm Raschig rings gave rise to increased back mixing in the lower part of the CDC and the overall dispersion number increased due to liquid and gas circulation around the packing elements. Kinetic studies revealed an initial rate reaction order of 1.24–1.26 with respect to hydrogen concentration both in slurry and fixed bed CDC reactors and is interpreted as a combination of a parallel pair of first and second order reactions during the initial stages of reaction. Mass transfer coefficients for gas absorption (k_La) and liquid–solid mass transport (k_s) were determined for both types of reactor. The k_La values lay in the range 1.0–3.33 s⁻¹ and the liquid–solid transport resistances (X_LS) were all <1%, so that the reaction was almost totally surface reaction rate controlled. Apparent energy of activation measurements gave values of E_A = 49 ± 6 kJ mol⁻¹, which is strongly indicative of surface reaction rate control involving the hydrogenation of an olefinic double bond. The selectivity in respect of linolenate (three double bonds) removal and linoleate (two double bonds) retention was high with, for palladium, relatively low trans‐isomer production (<30%). The overall selectivity was slightly, but significantly, better for the fixed bed CDC reactor and this is attributed to the greater degree of plug flow behaviour in the latter, despite the bed causing an increase in dispersion number. However, there is no reaction in the well‐mixed section of the fixed bed CDC reactor as there is in the slurry CDC reactor and this is likely to improve selectivity in a consecutive reaction sequence. © 2000 Society of Chemical Industry     

Research and development of advanced structured packing in a rotating packed bed

As the core component of the rotating packing bed, packing is a place for efficient gas–liquid mixing and mass transfer. In this paper, a 3D structured packing composed of a mesh structure and a support structure was designed. The mesh structure is a ring-shaped mesh surrounded by triangular meshes, which is stable in structure and can achieve a high degree of dispersion and aggregation of the liquid phase. The support structure is composed of ring-shaped structural units arranged at a certain a...     

Ammonia removal by air stripping in a semi-batch jet loop reactor

Ammonia is very toxic chemical and it can be removed by air stripping at high pH. JLRs have found applications in wastewater treatment processes due to their high mass transfer rates. In JLRs, intrinsic high turbulence result in a very large air-liquid surface area for greater mass transfer. Therefore, in this study, ammonia removal by air stripping from synthetically prepared ammonia solution at the high pH in a semi-batch JLR due to its high mass transfer capabilities have been investigated. Investigated parameters in a JLR were initial ammonia concentration (10–500 mg/L), temperature (20–50 °C), air flow rate (5–50 L/min) and liquid circulation rate (35–50 L/min). While it was demonstrated that temperature and air flow rate have a significant effect on the ammonia removal, it was determined that initial ammonia concentration and liquid circulation rate have no significant effect on the ammonia removal. The overall volumetric mass transfer coefficients (K_La) have been calculated from obtained model and it was determined that increasing temperature and air flow rate have a very significant effect on K_La. It was concluded that JLR provides higher mass transfer capabilities than other type of reactors even if less air is given.