Higher Mass Transfer Coefficient Research Articles

CO2 Capture by Alkaline Solution for Carbonate Production: A Comparison between a Packed Column and a Membrane Contactor

A comparison between a traditional packed column and a novel membrane contactor used for CO2 absorption with carbonate production is addressed in this paper. Membrane technology is generally characterized by a lower energy consumption, it offers an independent control of gas and liquid streams, a known interfacial area and avoids solvent dragging. Those advantages make it a potential substitute of conventional absorption towers. The effect of the concentration and the flow rates of both the flue gas (10–15% of CO2) and the alkaline sorbent (NaOH, NaOH/Na2CO3) on the variation of the species present in the system, the mass transfer coefficient, and the CO2 removal efficiency was evaluated. Under the studied operation conditions, the membrane contactor showed very competitive results with the conventional absorption column, even though the highest mass transfer coefficient was found in the latter technology. In addition, the membrane contactor offers an intensification factor higher than five due to its compactness and modular character.

Ethylene/ethane separation and mass transfer characteristics through absorption by AgNO3 solutions in microchannels

Chemical absorption using silver ion is a potential way for ethylene recovery, which can be significantly enhanced by the use of microreactors. This work presents an experimental study on the characteristics of absorption of ethylene into aqueous AgNO3 solutions. The effects of several parameters including channel length, channel diameter, flow rates, temperature and AgNO3 concentration are investigated in terms of absorption fraction, molar absorptivity and mass transfer coefficients. It is demonstrated that very high liquid side mass transfer coefficients in the range of 3–85 s−1 can be obtained in microchannels, indicating significant process intensification. Based on the results, an empirical correlation was proposed for the prediction of mass transfer coefficients.

Adsorption with catalytic oxidation in a recirculating bed reactor for contaminated groundwater

A novel nanoremediation concept, which is based on in situ trapping of organic contaminants by adsorption and catalytic oxidation in combination with oxidants such as hydrogen peroxide is presented. In earlier works we explored the porous structure of a modified natural clinoptilolite loaded with iron as a supported catalyst (NZ -A-Fe). The supported catalyst prevents iron release during all the process. This paper presents novel results for BTX (Benzene, Toluene and Xylene) removal from aqueous solution considering that adsorption and oxidation processes are taking place simultaneously. The experiment was achieved by fluxing an aqueous solution of BTX 3.3 mM and hydrogen peroxide, at neutral pH, using the same reservoir. After 870 min, C/C0 reaches near 10% for each pollutant. The system removed 65 mg BTX in the present conditions (13 mg/g NZ-A-Fe). The results indicate that the recirculation bed reactor is an excellent system to remove by adsorption and oxidation processes BTX from water due to high mass transfer coefficients and other advantages when compare to batch reactor experiments.

Intensified extraction of uranium(VI) in impinging-jets contactors

The mass transfer performance of confined impinging-jets (CIJs) contactors was investigated for metal separations. In particular, the extraction of uranium(VI) from aqueous nitric acid solutions (3 M) into 30% v/v TBP/Exxsol D80, relevant to spent nuclear fuel reprocessing, was studied for different cell geometries, i.e. main chamber size (D = 2 and 3.2 mm) and jet diameter (dj = 0.25 and 0.5 mm), and different operating conditions, i.e. residence time (τ = 1–9 s), total jet velocity (utot = 2.6–8.6 m/s), and reactor length (L = 7–85 cm). For all conditions investigated, the aqueous phase was the dispersed one. Drop sizes were also measured with high-speed imaging. It was found that the extraction efficiency increased by increasing residence time for a constant total jet velocity regardless of the chamber size. At a constant residence time, higher extraction efficiency was achieved at high total jet velocities, which are associated with larger interfacial areas (smaller drops). The extraction efficiency reached 70% in most of the cases investigated in less than 2 s. In addition, high overall volumetric mass transfer coefficients (up to 1 s−1) were obtained at short residence times. Using regression analysis, a correlation for the overall volumetric mass transfer coefficient was developed from the experimental data with an average deviation of 9%.

Carbon nanotube band electrodes for electrochemical sensors

Utilization of carbon nanotubes (CNTs) in fabrication of electrodes for electrochemical detection often faces a conflicting goal: achieving both high response current and high mass transfer coefficient. Typically, electrodes made in a form of CNT ensembles offer high response current as a result of the large number of CNTs. However, these electrodes have substantially low mass transfer coefficients due to overlapping of diffusion fields between neighboring CNTs. To resolve this conflict, we design band electrodes made of vertically-aligned CNT (CNBEs), which are macro-sized in length and submicro-sized in width. We show that the distinct dimensions of the CNBEs allow both high response currents and mass transfer coefficients. We also demonstrate that CNBEs offer excellent detection performances including wide linear range, high sensitivity, and low limit of detection in channel flow voltammetry.

Designing a CO2 supply strategy for microalgal biodiesel production under diurnal light in a cylindrical-membrane photobioreactor

A cylindrical membrane photobioreactor with high CO2 mass transfer coefficient was designed and installed under customized unidirectional lighting. Combinatorial effect of light and CO2 on the growth of Chlorella sp. FC2 IITG was studied and an optimal CO2 supply without pH control strategy was developed under diurnal light similar to sunlight (17-2000-17 µE m−2 s−1). Unprecedentedly, broad range of saturated light levels (700–1500 µE m−2 s−1), reversible photoinhibition, no pH control requirement and dark-phase growth were noticed altogether in the strain. Under diurnal light, final biomass titer of 5.79 g L−1 and overall biomass productivity of 1.29 g L−1 day−1 were observed. The results were similar to optimal light (1130 µE m−2 s−1) and CO2 (2%) conditions. Subsequently, a highest FAME productivity of 265 mg L−1 day−1 was observed in last two days of lipid induction phase.

Mass transfer characteristics of the liquid film flow in a rotating packed bed for CO2 capture: A micro-scale CFD analysis

Rotating packed beds (RPBs) are promising to be employed for CO2 capture from the flue gas due to their high mass transfer efficiency. Therefore, good predictions of the mass transfer characteristics for RPBs are crucial for their design. In this paper, a method based on CFD simulation is proposed to investigate the liquid film flows and mass transfer characteristics within RPBs. Local mass transfer coefficients along the radial direction of an RPB have been obtained. The results obtained show that high surface roughness and high rotational speed enhance the CO2 absorption into the liquid film, thus generating a high mass transfer coefficient, and the larger the RPB radial position, the higher the mass transfer coefficient.

Modeling of downdraft gasification process: Studies on particle geometries in thermally thick regime

In this study, a downdraft gasifier model is coupled with a single-particle model to analyze the effects of particle geometries such as slab, cylindrical, and spherical on different parameters. Simulations were performed using particles in a thermally thick regime with larger particle sizes of 0.003–0.05 m, which are generally used in commercial gasifiers. This combination of the downdraft gasifier model and single particle model was implemented using Comsol Multiphysics software program. The results obtained are in good agreement with those of obtained in previous studies. The low thermal conductivity of biomass (kB), small particle size (dp), high gas temperature (Tg), higher molar fraction of oxygen in primary air (XO2), and high mass-transfer coefficient (km) favor the formation of carbon monoxide (CO), hydrogen (H2), high tar conversion, and higher lower heating value. To maximize the CO composition and tar conversion, the initial gas temperature (Tg) is more crucial. The least sensitive parameter is the thermal conductivity of biomass (kB) in relation to product composition of CO, carbon dioxide (CO2), H2, and methane (CH4). The sensitivity for all the parameters is found to be the highest for the spherical geometry and is least for the slab geometry.

Characterisation and kinetic study of carbon dioxide absorption by an aqueous diamine solution

Aqueous monoamine solvents have been extensively studied for the purpose of CO2 absorption to reduce emissions from sources such as industrial power stations. However, to improve the economic viability of carbon capture technologies, solvents with higher CO2 absorption capacity and faster kinetics are urgently required. Diamines comprising two amino groups have potentially higher CO2 absorption capacity and rates than monoamine solvents, such as monoethanolamine, and could be superior liquid absorbents for CO2 absorption. In this study, we selected six linear diamines with a structure of NH2(CH2)n-R (n=2 or 3; R=NH2, NHCH3 or N(CH3)2) and four monoamines with a structure of NH2(CH2)n-R (R=OH, CH3 or CH(OH)CH3). We then investigated the effect of diamine molecular structure on absorption kinetics and capacity using a bubble column, and confirmed the observed kinetic behaviours of selected diamines at different concentrations using a wetted-wall column and stopped-flow reactor. Under the conditions studied, all selected diamines had an absorption capacity of more than 0.78moles of CO2 per mole of amine, which far outstrips the capacity of monoamines. The hydroxyl group decreased the rate of CO2 absorption, while the methyl group and longer chain lengths increased CO2 absorption rate and capacity; the tertiary amino group exhibited the lowest kinetic performance. N-methylpropane-1,3-diamine (MAPA) had both the fastest absorption rate and the highest mass transfer coefficient. Using Fourier-transform infrared spectroscopy and 13C nuclear magnetic resonance, we elucidated the mechanism involved in the reaction of MAPA with CO2. Our research provides a method for the future selection and design of new diamines for post-combustion CO2 capture.

Comments on the Reliability of Model Simulation of a Rapid Pressure Swing Adsorption Process for High-Purity Product

The uncertainty in the evaluation of the separation performance of a rapid pressure swing adsorption (RPSA) process for production of a high-purity product gas by using a numerical process model can be impractically high as a result of the theoretical or experimental uncertainty in the estimation of the high adsorbate mass transfer coefficient required by such a process. Actual experimental process performance data are required in order to judge the real value of the process.

High frequency ultrasonic-assisted chemical absorption of CO 2 using monoethanolamine (MEA)

The paper aimed to study the chemical absorption of CO2 in monoethanolamine solvent (MEA) using high frequency ultrasonic irradiation of 1.7 MHz. The experiment was conducted at instantaneous regime in order to study the physical enhancement effect of the ultrasound. Hence, a mathematical model is proposed to justify the enhancement effects involved in the absorption process. The parameters of the experiment included ultrasonic power, MEA concentration, temperature, and CO2 partial pressure. Results show that, a significant increase in the chemical absorption rate can be obtained by using ultrasonic power of 18 W, which is up to 60 times faster than the case without ultrasonic irradiation. Besides, the experimental data is in good agreement with the simulated data by obtaining the R2 values ranged from 0.989 to 0.997. Therefore, this study demonstrates a new technology to improve the absorption process. Besides, the enhancement for the chemical absorption using ultrasonic irradiation is believed to be dominated by the fountain formation and also the convective dynamic. In overall, ultrasonic-assisted absorption would be one of the potential alternatives for CO2 capture with its advantages of high mass transfer coefficient and compact design.

Pilot plant fluidized‐bed reactor for degradation of basic blue 3 in heterogeneous fenton process in the presence of natural magnetite

Degradation of basic blue 3 (BB3) was studied in a pilot scale fluidized‐bed reactor (FBR) utilizing natural magnetite (NM) nanostructures for heterogeneous Fenton process. The morphology, structure, and specific surface area of NM nanostructure were determined employing scanning electron microscopy, X‐ray diffraction, X‐ray photoelectron spectroscopy (XPS), and Brunauer‐Emmett‐Teller (BET) methods, respectively. High mass transfer coefficients, continuous operating condition and high reaction rates due to suitable and sufficient contact of phases, can be noted as significant advantages of FBR. Influences of factors, which affect performance of fluidized‐bed heterogeneous Fenton process (NM/H2O2), for instances initial concentration of contaminant and H2O2, initial pH of solution and dosage of catalyst were investigated. At the desired operational condition, pH 5, 4 mM of H2O2, and 2.27 g/L of NM after 190 min, the degradation percentage of 84%. Excess amounts of catalyst dosage and hydrogen peroxide tend to scavenge hydroxyl radicals by H2O2 molecules. Whereas low initial concentration of the dye and low initial solution pH, enhanced the BB3 degradation. Reusability of NM through five successive experiments, demonstrated the acceptable proficiency of NM as catalyst for oxidative BB3 degradation. © 2017 American Institute of Chemical Engineers Environ Prog, 36: 1039–1048, 2017

Axial Dispersion and Mass Transfer of a Pulsed Solvent Extraction Column with Novel Ceramic Internals

Two types of novel anticorrosive ceramic internals, the hybrid ceramic internal and ceramic plate, are designed and tested under pilot conditions for future industrial application in lithium extraction from salt lake brine. A standard liquid–liquid system with medium interfacial tension, 30% TBP in Shellsol 2046–water with acetic acid as solute, is used to test axial dispersion and mass-transfer parameters, which are important to determine height of extraction columns, over a range of operating conditions. Results show that the hybrid ceramic internal has 50% lower axial dispersion coefficient and 50% higher mass-transfer coefficient, both contributing to better mass-transfer performance. Under proper operating conditions, the height of the transfer unit of the hybrid ceramic internal can reach as low as approximately 0.2 m, which shows very good efficiency and makes it promising for application in the near future.

Mass Transfer Coefficientin Stirred Tank for p-Cresol Extraction Process from Coal Tar

Indonesia is a country that has a lot of coal resources. The Indonesian coal has a low caloric value. Pyrolysis is one of the process to increase the caloric value. One of the by-product of the pyrolysis process is coal tar. It contains a lot of aliphatic or aromatic compounds such asp-cresol (11% v/v). It is widely used as a disinfectant. Extractionof p-Cresol increases the economic value of waste of coal. The aim of this research isto study about mass tranfer coefficient in the baffled stirred tank for p-Cresolextraction from coal tar. Mass transfer coefficient is useful for design and scale up of industrial equipment. Extraction is conducted inthe baffled stirred tank equipped with a four-bladed axial impeller placed vertically in the vessel. Sample for each time processing (5, 10, 15, 20, 25 and 30minutes) was poured into a separating funnel, settled for an hour and separated into two phases. Then the two phases were weighed. The extract phases and raffinate phases were analyzed by Spectronic UV-Vis. The result showed that mixing speed of p-Cresol extraction increasesthe yield of p-Cresol and the mass transfer coefficient. The highest yield of p-Cresol is 49.32% and the highest mass transfer coefficient is 4.757 x 10-6kg/m2s.

Synergistic effect of microwave irradiation and CaF2 on vanadium leaching

The effect and mechanism of microwave irradiation on vanadium leaching were studied via a comparison between microwave heating and conventional heating. The results show a synergistic effect of microwave irradiation and calcium fluoride (CaF2) on the vanadium leaching efficiency. It is confirmed that the vanadium leaching process can be improved by microwave irradiation when CaF2 is present. The leaching rate of vanadium under microwave irradiation is increased by 8%–15% when 5wt% CaF2 is added; by contrast, in the absence of CaF2, the leaching rate is almost unaffected compared to that by conventional heating. Morphological analysis reveals that the particles are gradually eroded by acid under microwave irradiation, whereas some of the fine particles in samples subjected to conventional heating are tightly covered by a flocculent silicate product. Moreover, a large amount of Al and V and a small amount of Si are dissolved from samples under microwave heating, as revealed by the elemental analysis of leachates. Fourier transform infrared spectroscopic analysis also indicates a higher mass transfer coefficient in the diffusion layer of the raw material by microwave irradiation. When CaF2 is present, the reaction energy barrier is lowered and the leaching process is controlled by the tightly covered product layer, resulting in a prominent effect of microwave irradiation.

Synthesis and characterization of coaxial SnO2–SiO x core–shell nanorods

Free-standing coaxial SnO2–SiO x core–shell nanorods were synthesized in a kinetically controlled manner by the chemical vapor transport method. The free-standing SnO2–SiO x core–shell nanorods appear with uniform morphology exhibiting smooth surface, diameters of 100–200 nm, and length of 1 μm. The low oxygen partial pressure and high reaction temperature are advantageous to form the (101) surface, which decreases the (101) crystal surface energy. The [101] growth direction in our process also satisfies the lowest energy principle in thermodynamics due to change of (101) surface energy. A heterogeneous nucleation site was provided by the SiO x dismutation reaction, and the formation of core–shell (SnO2–SiO x ) structure should result from the phase separation energy. The free-standing coaxial SnO2–SiO x heterostructured nanorods grow by modification of the mass transfer coefficient. As-grown depositions show shrimp-like, flower-like, and worm-like morphologies under a higher mass transfer coefficient. Formation of the free-standing core–shell structure depends on the vertical growth mechanism.

Modeling Thin-Layer Drying of Turnip Slices Under Semi-Industrial Continuous Band Dryer

This study aims at investigating the thin-layer drying behavior of turnip slices in a multistage semi-industrial continuous band dryer. Turnip slices with the thickness of 4 mm were used for the drying experiments. The experiments were conducted at three air temperatures of 45, 60, and 75C, three air velocities of 1, 1.5, and 2 m/s, and three belt linear speeds of 2.5, 6.5, and 10.5 mm/s with three replications for each treatment. To estimate the drying kinetic of turnip slices, six mathematical models were used to fit the experimental data of thin layer drying. Consequently, the Midilli et al. model was selected as the best mathematical model to describe the drying kinetics of the turnip slices. The effective moisture diffusivity varied from 8.37 × 10−10 to 4.82 × 10−9 m2/s. The energy of activation varied from 12.80 to 26.31 kJ/mol using Arrhenius type equation. After well training of the ANN models, proved that the ANN model was relatively better than the empirical models. The best neural network for the prediction of moisture ratio (MR) and drying rate was feed forward back-propagation with 4-10-10-2 structure, training algorithm of Bayesian regulation and threshold functions of tansig-purelin-logsig. The best R2 value for predication of MR and drying rate were 0.9990 and 0.9619, respectively. Practical Applications Turnip is one of the oldest cultivated vegetables that have been used for human expenditures since prehistoric times. Drying process has been used for decades in food processing industries for efficient long-term preservation of final products. It has the potential to deliver safe food products through enzyme inactivation and microbe destruction. Advantages of semi-industrial continuous band drying are including short processing time, high mass transfer coefficients, low energy consumption, and high quality. To model experimental drying data, many correlations that are available in literature may be used. However, artificial neural network (ANN) methodology has become increasingly popular recently because of its capability of giving more general and precise results as also presented in this study.

Chemisorption of sulfur (IV) oxide using the horizontal apparatus with bucket-like dispersers

Due to the growing energy consumption and increasing share of fuels with high sulfur content in the global energy balance, there is a need for new, highly efficient methods and apparatus for recycling exhaust SO 2 -containing gases. It is found that SO 2 -low-concentrated gases are advisable to recycle by the liquid-oxidation method using NaOH as an intermediate absorbent and air oxygen as oxidant. Effective head apparatus – horizontal apparatus with bucket-like dispersers (HABD) is proposed for the cleaning process. To confirm the effectiveness of this apparatus in the processes of chemisorption and liquid phase oxidation of SO 2 , a pilot study on enlarged laboratory setup, the head apparatus of which was a scale model of HABD is carried out. The study is conducted in a wide range of concentrations of SO 2 (0,4...34·g/Nm 3 ) and pH of absorbing solutions (pH=3...13) using modern gas-analyzing devices. It is found that the irrigation density of 0.5 m 3 /Nm 3 is technologically feasible. The cleaning process is appropriate to perform under counterflow motion of phases, which will allow combining chemisorption and oxidation in one HABD, provide high degrees of recovery (99.9...100 %) and liquid phase oxidation (80...99 %) of SO 2 . Due to the high velocity of dispersed droplets of ~ 10 m/s and intensive interphase renewal, it is managed to significantly reduce the diffusion resistance in the gas phase and transfer the process to the liquid film and provide high mass transfer coefficients of 0,82·10 -4 …1,80·10 -4 (Pa·s·m 3 ). It is found that at low initial concentrations of SO 2 (0,4...7,74 g/Nm 3 ), the process rate is limited by SO 2 diffusion, and at high (10.54...33.89 g/Nm 3 ) - NaOH diffusion. The process under study is described by the first-order reaction equation and is characterized by high values of the process rate constant – 0.46 s -1 . Pilot studies confirm the high efficiency of HABD in the studied processes, prove the possibility of combining dust collection, chemisorption and oxidation stages in one apparatus.

Hydrodynamics and mass transfer in a tubular reactor containing foam packings for intensification of G-L-S catalytic reactions in co-current up-flow configuration

Stainless steel open-cell solid foams of various linear pore densities (20, 40, 60PPI) are wash-coated with a commercial catalyst and are evaluated as internals for G-L-S reactions in co-current up-flow configuration. Hydrodynamics parameters such as liquid mean residence time, axial dispersion and pressure drop have been determined for an air/water system with superficial velocities between 0.8mm/s and 25mm/s for liquid and between 100 and 900mm/s for gas. A generic piston-dispersion model represents well the liquid hydrodynamics and is used to estimate axial Péclet number and mean residence time for this phase. The Péclet number appears to increase with liquid velocity and foam linear pore density (5<Pe<60 for 20PPI, 10<Pe<140 for 40PPI and 60<Pe<200 for 60PPI). Determined liquid holdups (0.4<ɛL<0.8) are always higher than those encountered in conventional up-flow fixed beds under comparable flow conditions. Liquid superficial velocity and foam linear pore density appear to be the most influent parameters while the gas superficial velocity possesses a less pronounced impact. Pressure drop measurements may indicate the existence of two different flow regimes (bubbly and pulsed regime) and globally the total pressure drop remains low in the experimental domain tested with a maximum value of 0.2bar/m, comparable to literature data. The overall external mass transfer efficiency was determined through the gas/liquid/solid catalytic reaction of α-methylstyrene (AMS) hydrogenation and is compared to theoretical values obtained through correlations for conventional up-flow fixed beds. Very high mass transfer coefficients, in the range of 0.2–0.9s−1 were obtained at low Re numbers, which is one order of magnitude higher than in up-flow fixed beds. A set of correlations is derived for the calculation of the gas/liquid and liquid/solid contributions to external mass transfer and allows explaining the unique bell-shaped Re dependence displayed by the overall mass transfer coefficient.

Gas–Liquid mass transfer in a rotor–stator spinning disc reactor: Experimental study and correlation

The gas–liquid mass transfer of rotor–stator spinning disc reactors is studied for various operating conditions and different reactor geometries with rotor radii between 0.065 and 0.135 m. A new reactor setup with a perforated disc containing 119 narrow channels for direct dispersal of gas into the reactor cavity is examined. High volumetric mass transfer coefficients of up to 12ml3mR−3s−1 can be observed due to the large energy input at high rotational disc speeds of up to 2000rpm. The combination of high turbulence and small gas bubbles as a result of the large shear forces in the cavity is identified to be responsible for the acceleration of the mass transfer at high rotational disc speeds. Correlation with an extended power law model equation allows the first-time quantification of the impact of the main operating parameters such as gas and liquid flow rate and rotational disc speed on the volumetric mass transfer coefficients for different reactor geometries.