Showing papers on "Mass transfer coefficient published in 2022"

Intensified biogas upgrading via various wastewater using microchannel

Abstract: In this article, several ideas have been proposed for CO2 separation and biogas upgrading using industrial wastewater. Synthetic gas (60% CH4, 40% CO2) has been upgrading in atmospheric pressure in a T-shaped microchannel using municipal, meat processing, water distillation, dairy, caustic, and fish pond wastewater. The municipal, fish pond, and meat processing wastewater contain ammonia, while dairy, and water distillation wastewater contains Ca2+, and Mg2+. Also, the caustic refinery wastewater contains NaOH, with higher alkalinity for CO2 separation. The effect of temperature, gas, and liquid flow rate were investigated. RSM analysis provided a function of three dependent variables of quadratic model for prediction of responses (CO2 removal efficiency and total mass transfer in gas phase) by each absorbent, and all models were meaningful. In addition, given that all R2 values were greater than 0.94, it was indicated that experimental values for removal of CO2 and mass transfer coefficient are favorably consistent with the values of the model. Maximum CO2 absorption was obtained at 30°C, liquid flow rate of 150 mL/hr, and biogas flow rate of 50 mL/min. According to the results obtained for mass transfer coefficient, these coefficients are at least 5 to 22 times greater than mass transfer coefficient in chemical absorption in normal absorption towers, such as packed towers.

Removal of manganese (II) from aqueous solution by ionic liquid impregnated polymeric sorbent and electrodeionization (EDI) techniques

Abstract: Manganese is an element that is essential for the proper functioning of humans and animals, as it is needed for the functioning of many cellular enzymes. However, overexposure to this metal can be toxic to many organ systems and at various stages of life. In this work, ionic liquid impregnated polymeric sorbent (ILIS) and electrodeionization (EDI) processes were used to remove manganese (Mn2+) from aqueous solutions. The removal of Mn2+ by ILIS is pH dependent and maximum removal is achieved at pH 9. The sorption of Mn2+ on ILIS reached equilibrium in 20 min. For Mn2+ removal by EDI, the applied potential, feed flow rate and H2SO4 concentration in the electrode compartment were optimized. When the applied potential and feed flow rate were increased, the Mn2+ concentration in the feed solution decreased. Varying the H2SO4 concentration in the electrode compartment did not result in differences in the removal rate. The largest calculated flux for Mn2+ is 6.92 × 10−5 mol/m2s, and the mass transfer coefficient is 8.16 × 10−4 m/s. In the last phase of the experiment, ILIS-EDI hybrid techniques were used for the removal of Mn2+. In this case, more than 99.9% was removed from the solution.

Nanoporous polypropylene membrane contactors for CO2 and H2S capture using alkali absorbents

Abstract: The paper reports a comprehensive review of the performance of nanoporous gas-liquid polypropylene membrane contactor with NaOH absorbents for removal of H2S and CO2 components from the gas streams. The experiments at different operation conditions, including variation of acid gas content in a feed stream, alkali concentration in absorbent, gas and liquid absorbent volume flow rates, absolute and gas-liquid differential pressures are discussed as a function of the absorbent saturation levels. In-liquid diffusion of components and gas/membrane contact times were determined as main governing factors limiting contactor efficiency. Mass transfer rates of acid gas removal on the membrane contactor over 3 × 10−3 mol/(m2 × s) for CO2 and 7.5 × 10−3 mol/(m2 × s) for H2S were attained. Ultimate processed gas quality with H2S content below 5 ppm and CO2 content below 0.01% was achieved at the contactor performance over 7 m3/(m2 × h) and initial acidic gas content of 2%, while achieving a membrane packing density in the contactor over 3000 m2/m3. The paper also provides an experimentally-proven theoretical model for calculating removal efficiency and residual acid gas partial pressures depending on the membrane parameters and operation conditions. It is shown, the mass transfer coefficient and removal efficiency differ significantly for H2S and CO2 due to the difference in dissolution mechanism involving kinetically limited deprotonation reaction of solvated water in case of CO2(aq) while engaging direct deprotonation of H2S. This allows to attain residual partial pressure of H2S in retentate stream equal to the equilibrium pressure above the absorbent solution, while CO2 residual pressure exceeds an equilibrium value few orders of magnitude. The effect has been successfully utilized for the selective removal of H2S from both CO2 and H2S-containing mixtures with H2S/CO2 selectivity exceeding 1500.

Nanoporous polypropylene membrane contactors for CO2 and H2S capture using alkali absorbents

Abstract: The paper reports a comprehensive review of the performance of nanoporous gas-liquid polypropylene membrane contactor with NaOH absorbents for removal of H2S and CO2 components from the gas streams. The experiments at different operation conditions, including variation of acid gas content in a feed stream, alkali concentration in absorbent, gas and liquid absorbent volume flow rates, absolute and gas-liquid differential pressures are discussed as a function of the absorbent saturation levels. In-liquid diffusion of components and gas/membrane contact times were determined as main governing factors limiting contactor efficiency. Mass transfer rates of acid gas removal on the membrane contactor over 3 × 10−3 mol/(m2 × s) for CO2 and 7.5 × 10−3 mol/(m2 × s) for H2S were attained. Ultimate processed gas quality with H2S content below 5 ppm and CO2 content below 0.01% was achieved at the contactor performance over 7 m3/(m2 × h) and initial acidic gas content of 2%, while achieving a membrane packing density in the contactor over 3000 m2/m3. The paper also provides an experimentally-proven theoretical model for calculating removal efficiency and residual acid gas partial pressures depending on the membrane parameters and operation conditions. It is shown, the mass transfer coefficient and removal efficiency differ significantly for H2S and CO2 due to the difference in dissolution mechanism involving kinetically limited deprotonation reaction of solvated water in case of CO2(aq) while engaging direct deprotonation of H2S. This allows to attain residual partial pressure of H2S in retentate stream equal to the equilibrium pressure above the absorbent solution, while CO2 residual pressure exceeds an equilibrium value few orders of magnitude. The effect has been successfully utilized for the selective removal of H2S from both CO2 and H2S-containing mixtures with H2S/CO2 selectivity exceeding 1500.

Recent Advancements on Hydrodynamics and Mass Transfer Characteristics for CO2 Absorption in Microreactors

Abstract: Process intensification for CO2 absorption using microreactors has received growing interest from both academia and industry because of their great ability to overcome the mass transfer resistance across the phases boundaries, giving rise to significant improvement in process efficiency. Mass transfer is strongly linked with two-phase flow patterns of CO2-absorbent in microreactors and, subsequently, overall volumetric mass transfer coefficient (ka) intensification relies on hydrodynamics, microreactor structures and applied absorbents. Reviewed literature on this subject indicated that the Taylor flow pattern, spiral and meandering microreactor structures, and primary and secondary amines absorbents were preferred to use for the CO2 absorption in microreactors. Moreover, ka models developed through offline and online characterizations were presented to analyze the contribution of liquid film and bubble caps in mass transfer. Economic analysis was executed to assess the operating feasibility of microreactors at industrial scale throughputs of feed gas and absorbent. The results indicated that the capital expenses of microreactors were significantly higher than those of conventional absorbers because of their extensive number of units and complex design of flow distribution network requirements with high throughputs. However, microreactors exhibited lower operating expenditures than conventional absorbers because of their excellent transport characteristics. Finally, the persisting challenges and remarking conclusions are presented relating to the implementation of microreactors for CO2 absorption.

Mass transfer kinetics during the extraction of m-cresol from model coal tar using betaine/glycerol deep eutectic solvents

Abstract: Betaine/glycerol, a common deep eutectic solvent (DES), is an effective extractant used for separating phenolic compounds from model coal tar. Its mass transfer kinetics during extraction is the basis of industrial applications. The physical properties of the model oil and the DES were measured in this study. Then, the modified Lewis cell was used to determine the mass transfer coefficients and extraction rates of the mass transfer kinetics. The effects of the process parameters, including temperature, stirring rate, specific interfacial area, and water quantity of the DES on the kinetics were investigated. In addition, the mechanism of mass transfer kinetics was studied using simulation and experimental studies. The results demonstrate that the physical properties of DES vary greatly with temperature and water quantity, while the physical characteristics of model oil show less variations. The mass transfer coefficient increases and the extraction rate accelerates with increased stirring rate, temperature, and water quantity in the DES. The DES phase functions as the mass transfer resistance area during extraction. An increase in the specific interfacial area did not result in an obvious variation in the mass transfer coefficient, although the extraction rate increased. Finally, results of the simulation and experimental studies showed that the mass transfer kinetics of extraction are controlled by diffusion. Phenolic compounds diffuse from the oil phase into the DES phase and react with DES by forming hydrogen bonds, resulting in the separation of phenolic compounds.

Performance analysis on open thermochemical sorption heat storage from a real mass transfer perspective

Abstract: Internal mass transfer coefficient is considered as a key parameter for open thermochemical sorption heat storage which usually has a large margin between theoretical and actual value. This paper aims to analyze the role of mass transfer on system performance prediction. Al2O3 and LiCl composite sorbents are prepared and adsorption behavior is tested through a thermal gravimetric analyzer and a small-scale air duct experiment. An equation of kinetic coefficient is fitted to describe adsorption process more accurate than empirical equation. For simulation, a one-dimensional model is established based on dimensionless number of heat and mass transfer, and similarity theory is built to predict output parameters. Results indicate that the sorbent with 16.44 % salt content reaches 0.39 g·g−1 maximum water uptake on the condition of 20 °C, 80 % relative humidity. It is indicated that the system using composite sorbents has a heat storage density of 345.58 kWh·m−3. Parameters that influence system output power and duration are also investigated. By adjusting air flow rate and sorption length of sorption reactor, the system can achieve temperature rise of 30 °C at the exit and a steady output of 6 h. One striking fact is that mass transfer coefficient can be used to well predict the performance of real open adsorption thermal energy storage system which is also conducive to system design and optimization.