Film Mass Transfer Coefficient Research Articles

Modelling, simulation and factorial design as tools for the in silico process optimisation of fructooligosaccharide production by immobilised fructosyltransferase in a basket reactor

Modelling, simulation and optimisation of the production of fructooligosaccharides (FOS) by fructosyltransferase immobilised on inorganic niobium support and applied in a basket reactor (BR) were used for in silico optimisation of the process. Simulink and MATLAB 6.0 were used as computational tools. The kinetic process data were obtained experimentally using purified fructosyltransferase produced by Rhodotula sp. Optimisation experiments were carried out using simulation, according to the factorial design methodology, using a two central composite rotatable design. In the first design, the variables with the highest influence were determined; in the second design, the conditions to produce FOS were optimised. The optimum conditions were 14 Ui/ml for the activity of enzyme, immobilised in a niobium ore, and a stirring speed of 45 rpm. Under these conditions, FOS yield was 50.6% after 24 h of synthesis, at 50°C and pH 4.5. The results demonstrated the good efficiency of the BR, as well as showing that the film mass transfer coefficient around the biocatalyst has a significant influence during the reaction and production of FOS.

CO2 Mass Transfer and Solubility in Aqueous Primary and Secondary Amine

Abstract Three amines were tested as solvents for CO 2 capture: monoisopropanolamine (MIPA) and 3 amino 1 propanol (MPA), which are primary amines, and diethanolamine (DEA), which is a secondary amine. The three amines were tested at 7 molal in water, which corresponds to 30 wt % monoethanolamine (MEA). The CO 2 absorption rate and solubility in the solvents was measured using a bench scale wetted wall column (WWC) at 20–100 °C and over the range of CO 2 loading expected for coal flue gas. The experimental data are analyzed to suggest performance in a real process. The performance of the three new amines are compared against literature results for 7 m MEA and other solvents with amines of related structures, such as 10 m Diglycolamine (DGA) ® and 4.8 m 2-amino-2-methyl-1-propanol (AMP). The mass transfer performance and the CO 2 carrying ability of the amine are related to the structural hindrance and the pKa. The CO 2 absorption rate of 7 m MIPA and 7 m DEA are competitive with 7 m MEA. For 7 m MPA, the measured liquid film mass transfer coefficient is about 20% lower than 7 m MEA. The CO 2 solubility data are used to generate a semi-empirical model for each of the new solvents. The results for CO 2 solubility at 40 °C suggest that MIPA and MPA have similar CO 2 capacity to MEA, whereas DEA has double the CO 2 capacity of the three primary amines. Based on the comparison of data collected in this work and literature results, it is generalized for unhindered amines that the overall CO 2 mass transfer performance of the solvent is inversely related to the pKa of the amine. Also, the CO 2 capacity of the amine increases with the relative hindrance of the nitrogen group in the amine molecule.

Numerical Analysis for CO<sub>2</sub> Absorption and Regeneration Behavior in Porous Solid Sorbent by Modified Unreacted-Core Model

Lithium ortho-silicate (Li4SiO4) is a suitable solid sorbent for capturing CO2 from solid oxide fuel cells. CO2 absorption reactors packed with porous-solid spherical pellets of Li4SiO4 show unsteady temperature distribution and capture ratio behavior owing to the unsteady CO2 absorption rate and highly exothermic process. The CO2 absorption rate of this sorbent reportedly depends on temperature, CO2 concentration, and CO2 accumulation, expressed as the weight change of the sorbent. Nevertheless, discussions of detailed mechanisms of CO2 absorption by this sorbent are rare. In this study, the modified unreacted core model is proposed to explain the mechanism of CO2 absorption of a porous-solid spherical pellet, and numerical analysis was conducted to simulate the unsteady behavior of the sorbent. Important properties such as the reaction rate constant, the gas film mass transfer coefficient, and the coefficient for effective diffusion through the product layers were empirically derived using thermogravimetry and a diluted packed-bed reactor. Numerical analysis by applying these parameters to the modified unreacted core model adequately explained the complicated CO2 absorption and regeneration behaviors.

Modeling and Experimental Studies of Adsorptive Dewatering of Selected Aliphatic Alcohols in Temperature Swing Adsorption System

Based on experimental work, closely coupled with mathematical modeling, an analysis was performed of the adsorptive drying of selected water-aliphatic alcohol solutions. The experimental work involved ethanol, n-propanol, and n-butanol dehydration using two adsorbents, 3A and 4A zeolite molecular sieves. The isothermal model developed in this paper incorporates an overall linear mass driving force, including liquid film mass transfer and intraparticle diffusion coefficients, a variable axial diffusivity, and experimentally determined Langmuir-Freundlich isotherms. Breakthrough curves generated by the model were compared with those obtained experimentally, giving a fairly good fit. The model simulations enabled determination of the water content profiles in adsorbent beds.

Mathematical modeling and mass transfer considerations in supercritical fluid extraction of Posidonia oceanica residues

Posidonia oceanica residues were extracted with supercritical CO2 in order to isolate phenolic compounds. The process was optimized by developing a mathematical model based on mass transfer mechanism consisting of adsorption of supercritical fluid on the solid particles, desorption of solute and convective transfer of solute phase along the column. Henry relation between solute concentrations on the surface of the solid (Cs) and in the solid (q) was approximated in order to describe the adsorption/desorption equilibrium. The model parameters such as solid-liquid film mass transfer coefficient (kf), molecular diffusivity coefficient (DAB) and axial dispersion (Dax) were estimated using empirical methods. The linear driving force model was applied to improve the yield of total phenolic acid recovery. The optimum parameters were elicited as 25MPa, 323.15K and a co-solvent mass ratio of 20% yielding 34.97μg per gram of dry feed and the model satisfactorily described the extraction yield which can be used for scale-up purposes.

Effect of CO2 stripping on pH in open‐recirculating cooling water systems

A simplified mathematical model has been developed to evaluate the effect of CO2 stripping on pH of recirculating cooling water in power plant cooling systems. Experimental data from three pilot‐scale cooling towers using treated municipal wastewater as makeup water were used to determine the CO2 mass transfer coefficients in the gas phase kg and aqueous phase kw. The optimum values of the gas film mass transfer coefficient and water film mass transfer coefficient were determined by regression to be kg = 8.4 × 10−6 m/s and kw=8.4 × 10−8m/s, respectively. The results also indicate that the model is capable of predicting the pH of the cooling loop as a function of makeup water alkalinity and cooling loop alkalinity (in case of salt formation) as well as the operating parameters of the cooling system. © 2013 American Institute of Chemical Engineers Environ Prog, 33: 275–282, 2014

Least squares estimation of kinetic parameters in batch adsorption of phenol with confidence interval analysis

Adsorption kinetics of phenol on granular coconut shell activated carbon and granular coal based activated carbon was investigated by the model of homogeneous surface diffusion plus external film mass transfer with the stirred batch adsorber. The model was solved numerically by finite element and the parameter estimation was performed with the nonlinear least squares method. Through the confidence interval analysis and evaluation of the error sum of squares, higher precision of the parameter estimates can be obtained by combining more decay curves; the decay curves with the different initial solution concentrations and adsorbent dosages can be well represented with identical film mass transfer coefficient and surface diffusivity, and the effect of surface adsorption coverage on the surface diffusivity is negligible in the adsorption systems. The values of the film mass transfer coefficient and surface diffusivity are in the order of magnitude 10−5 and 10−12, respectively.

Modeling of CO2 Absorption Kinetics in Aqueous 2-Methylpiperazine

CO2 absorption into 8 molal (m) 2-methylpiperazine (2MPZ) is modeled in Aspen Plus using a previously developed rigorous thermodynamic model. With the regression of three reaction rate constants for carbamate and bicarbonate and one parameter for diffusion activation energy, the kinetic model represents CO2 flux measured in a wetted-wall column at 40–100 °C with 0.1–0.4 mol CO2/mol alkalinity with a relative deviation from −20% to 20%. The kinetic reaction rate is interpreted with activity-based termolecular kinetics and the rate constants are correlated with the Bro̷nsted theory. The liquid film mass transfer coefficient (kg′) is well represented by the model at medium to rich CO2 loading. The power to which kg′ is dependent on the rate constant of 2MPZ carbamate formation (k2MPZ–2MPZ) decreases from ∼0.5 at very lean loading to nearly 0 at rich loading, whereas it is increasingly dependent upon the diffusion coefficient of the reactants and products and the physical liquid film mass transfer coefficient (kl0) as loading and temperature increases. In the liquid film, 2MPZ and 2MPZCOO– are the major reactants and protonated 2MPZ carbamate and bicarbonate are the major products. The pseudo-first-order region for 2MPZ narrows and shifts to higher value of kl0 as temperature increases. Under typical industrial conditions, the gas film resistance contributes less than 25% of the total resistance.

Determination of Mass Transfer Coefficients for A Mixture of Compost, Sugarcane Bagasse, and Granulated Activated Carbon as Packing Medium in Biofilter

ABSTRACT A laboratory-scale biofilter unit packed with a mixture of compost, sugarcane bagasse, and granulated activated carbon (GAC) in the ratio of 55:30:15 by weight was used for a biofiltration study of air stream containing benzene, toluene, ethylbenzene, and o-xylene (BTEX). The effect of superficial velocity on mass transfer coefficient for the packing was studied by maintaining gas flow rates of 3, 4, 5, 6, and 8 L min−1 for inlet concentrations of 0.1, 0.4, and 0.8 g m−3 for each of benzene, toluene, ethylbenzene, and o-xylene. The maximum elimination capacity was found to be 20.92, 22.72, 20.73, and 18.94 g m−3 h−1 for BTEX, respectively, for stated flow rates. Removal efficiency of BTEX decreased from 99% to 71% for increasing inlet concentration from 0.1 to 0.8 g m−3. Gas film mass transfer coefficient predicted by modified Onda's equation was within ±10% of the experimental values.

Characterization of Novel Structured Packings for CO2 Capture

Structured packing is widely being considered for post-combustion CO2 capture because of its high mass transfer per unit of pressure drop. The hydraulic and mass transfer performances of structured packings with different corrugation angles were measured. The effective mass transfer area was measured by absorption of CO2 with 0.1 gmol/L NaOH. The liquid film mass transfer coefficient was measured by desorption of toluene into air. The gas film mass transfer coefficient was measured by absorption of SO2 from air into 0.1 gmol/L NaOH. The effective area and the liquid film mass transfer coefficient are dependent on liquid velocity while the gas film mass transfer coefficient is a function of gas velocity. Increasing the corrugation angle from 45° to 60° (Mellapak 250Y to Mellapak 250X) resulted in (1) a 54% decrease in pressure drop, (2) a 6% decrease in effective area, (3) a 17% decrease in kG, and (4) a 18% decrease in kL. Increasing the corrugation angle from 45° to 70°, a larger difference was found in pressure drop, kG and kL. However, the impact of corrugation angle on effective area is not significant. In conclusion, increasing the corrugation angle will have a benefit on pressure drop with a negative impact on mass transfer properties. Future work will be focused on economic analysis between operation costs (related to pressure drop) and capital costs (related to mass transfer properties) to determine the optimum corrugation angle for a particular separation task.

Absorption rates and CO2 solubility in new piperazine blends

The absorption rate and CO2 solubility of four new blends using concentrated piperazine (PZ) were measured. The blends are 6 m PZ/2 m hexamethylenediamine (HMDA), 6 m PZ/2 m diaminobutane (DAB), 6 m PZ/2 m bis(aminoethyl)ether (BAE), and 5 m PZ/2 m N-2(aminoethy)lpiperazine (AEP). The liquid film mass transfer coefficient (kg’) of the blends was measured at 20 100°C using a wetted wall column (WWC). PCO2* was measured at 20–100°C using the WWC, and at 100–160°C using a total pressure apparatus. A semi-empirical VLE model was regressed for each blend using measured PCO2*, and the models show good agreement with experimental data. The process performance of the new blends is compared to 5 m PZ/2.3 m AMP, 2 m PZ/4 m AMP, 8 m PZ, and 7 m MEA. The high pKa of primary diamines contributes to high lean and rich loading and low solvent capacity for 6 m PZ/2 m HMDA, 6 m PZ/2 m DAB, 6 m PZ/2 m BAE. The Habs of PZ/AEP and PZ/AMP is competitive with 7 m MEA. PZ/BAE and PZ/HMDA have Habs higher than 8 m PZ but lower than 7 m MEA. The energy performance of the solvent depends on CO2 VLE and thermal stability. 6 m PZ/2 m HMDA, 6 m PZ/2 m AEP, and 5 m PZ/2 m BAE show good energy performance and are competitive with 8 m PZ. At 40°C the absorption rate of 5 m PZ/2 m AEP is about the same as 8 m PZ; 6 m PZ/2 m DAB and 6 m PZ/2 m BAE have 10% lower rates than 8 m PZ.

Adsorption and Desorption Behavior of Lithium Ion in Spherical PVC–MnO2 Ion Sieve

A spherical PVC–MnO2 ion sieve of 2.0–3.5 mm diameter was prepared by the antisolvent method using synthesized Li4Mn5O12 ultrafine powder as the precursor, poly(vinyl chloride) as the binder, and N-methyl-2-pyrrolidone as solvent. Batch experiments of the adsorption capacity (isotherm) and adsorption rate of Li+ on the spherical PVC–MnO2 ion sieve were studied. Spherical PVC–MnO2 had a high adsorption capacity for Li+, and the isotherm data were well fitted by the Langmuir model; the adsorption kinetics were well described by the Lagergren equation. Furthermore, a mathematical model was set up to calculate the film mass transfer coefficient (kf) and pore diffusivity (Dp) of the adsorbent. Continuous flow experiments for study of Li+ adsorption breakthrough and the subsequent desorption (elution) in a PVC–MnO2 packed column were carried out employing six feed solutions of various pH values and concentrations of Li+, Na+, K+, and Mg2+ for simulating brine samples of various salt lakes and/or seawaters. Afte...

Modeling of Adsorptive Drying of N-Propanol

On the basis of experimental work connected with mathematical modeling, a parameter analysis was conducted on the adsorptive drying of water-miscible organic liquids. The experimental work involved dehydration of n-propanol using two desiccants, 3A and 4A zeolite molecular sieves. The equilibrium relationship and fixed bed breakthrough curves were determined experimentally. The parameters required by the model are the equilibrium constants, liquid film mass transfer coefficient, intraparticle diffusion coefficient, and axial diffusivity. A linear driving force (LDF) relation was applied to represent the mass transfer rate in the particle liquid film and inside the adsorbent particle. The fit of the model to experimental breakthrough data was quite good.

Optimization and mathematical modeling of mass transfer between Zostera marina residues and supercritical CO2 modified with ethanol

Abstract Supercritical CO 2 extraction of phenolic compounds from Zostera marina residues was optimized by developing a mathematical model based on mass transfer balances. A linear driving force model was applied considering model parameters such as solute concentration on the surface of the solid ( C s ) and in the supercritical fluid phase ( C f ), film mass transfer coefficient ( k f ) and molecular diffusivity ( D AB ) and axial dispersion ( D ax ) coefficients. Henry's law was used to describe the equilibrium state of solid and fluid phases. The results of the proposed model were compared to that of the experimental data in terms of transport properties and extraction yield at various temperatures (303.15, 323.15, 353.15 K), pressures (15, 25, 35 MPa) and co-solvent mass ratios (0, 10, 20%). The optimum parameters were elicited as 25 MPa, 353.15 K and a co-solvent ratio of 20% yielding 77.22 μg g −1 dry feed. The model satisfactorily described the extraction yield which can be used for scale-up purposes.

血液透析器の物質移動

Removal rate of renal toxic substances in a dialyzer depends on the mass transfer rate through a dialysis membrane and in the dialysate-side boundary films. To increasing dialysis fluid-side mass transfer rate, the most important factors are jacket structure and hollow fiber shape, so newly developed dialyzers with improved jacket structure and hollow fiber shape that optimize dialysis fluid flow have been made available on the market in recent years.The overall mass transfer resistance is the sum of the resistances due to the membrane itself and the thin boundary film that is formed in the fluids on both sides of the membrane (Series Boundary Film Resistance Model). The boundary film mass transfer coefficient for a fluid flowing within a straight tube has been obtained theoretically. Colburn's equation converted to mass transfer by analogy with the theoretical approximation equation that yields the boundary film coefficient of heat transmission when laminar flow occurs in a straight tube, can be used to calculate the boundary film transfer in laminar mass transfer.In the present study, mass transfer correlation equations between Sherwood number (Sh) containing dialysis fluidside mass transfer film coefficient and Reynolds number (Re) were formed for newly developed dialyzers. The exponents of Re were 0.62 for APS-15S whereas approximately 0.5 for the newly developed dialyzers. The dialysis fluid-side mass transfer film coefficients of the newly developed dialyzers were higher than those of the conventional dialyzer. Based on the mass transfer correlation equations, introduction of short taper, full baffle of dialyzer jacket and further wave-shaped hollow fiber improves the dialysis fluid flow.

Packing Characterization: Mass Transfer Properties

Packing is widely used in post-combustion CO2 capture. This paper is focused on the measurement of three fundamental packing characteristics: effective gas-liquid contact area (ae), gas phase and liquid phase film mass transfer coefficient (kG) and (kL). Results show that contact area initially increases with liquid flow rate before it asymptotes to a value nearly equivalent to the nominal surface area. Initial attempts at constructing new mechanistic models have shown that existing kG and kL models can be improved. Both gas and liquid phase film mass transfer coefficients can be described as a power function of superficial gas or liquid velocity.

Mass Transfer Mechanism of a Water-Sparged Aerocyclone Reactor

Air stripping of ammonia is a widely used process for the pretreatment of wastewater. Scaling and fouling on the packing surface in packed towers and a lower stripping efficiency are the two major problems in this process. New patented equipment that is suitable for the air stripping of wastewater with suspended solids has been developed. Air stripping of ammonia from water with Ca(OH)2, was performed in the newly designed gas-liquid contactor, a water-sparged aerocyclone (WSA). The mechanism of the mass transfer process in the WSA was investigated using a CO2—NaOH rapid pseudo first order reaction system. The results indicated that there is a critical gas phase inlet velocity Ug. When Ug is lower than this value, the increase of the inlet velocity has a double function of both intensifying the liquid side film mass transfer coefficient kL and increasing the specific mass transfer area a; whereas when Ug is larger than this value, the major function of Ug increase is to make the water drops in the WSA broken, increasing the mass transfer area of gas-liquid phases.

Prediction of isoflavone extraction from soybean meal using supercritical carbon dioxide with cosolvents

A mathematical model of a supercritical fluid extraction process was developed and applied to a case study involving the isoflavone extraction from soybean meal using supercritical carbon dioxide with aqueous methanol as a cosolvent. A shrinking core model was applied after considering various mass transfer mechanisms. Model parameters, i.e. solubility (Csat), film mass transfer coefficient (kf), effective diffusivity (De), and axial dispersion coefficient (DL), were evaluated using available correlations. The proposed model satisfactorily described the extraction yield without using any adjustable parameters (AARD=6.54%). The effects of operating parameters, i.e. pressure, temperature, carbon dioxide flow rate, particle size, and cosolvent concentration, on the transport properties and the extraction yield were investigated. Furthermore, a sensitivity analysis of each model parameter was conducted to determine its influence on the prediction of the extracted yield. The model was found to be most sensitive to the film mass transfer coefficient and the solubility.

CO2Absorption Rate into Concentrated Aqueous Monoethanolamine and Piperazine

The CO2 equilibrium partial pressure and liquid film mass transfer coefficient (kg′) in (7, 9, 11, and 13) m monoethanolamine (MEA) and (2, 5, 8, and 12) m piperazine (PZ) were measured in a wetted wall column. Also examined was 7 m MEA/2 m PZ. Absorption and desorption experiments were performed at (40, 60, 80, and 100) °C over a range of CO2 loading. Amine concentration does not affect the CO2 partial pressure of PZ or MEA solutions as a function of CO2 loading with less than 0.45 mols CO2/mol alkalinity. Changes in amine concentration and temperature often do not affect the measured value of kg′. At higher temperature and CO2 loading in PZ, the diffusion of reactants and products limits CO2 transfer, and kg′ is depressed. PZ (8 m) exhibits a 70 % greater CO2 capacity than 7 m MEA and a 50 % greater CO2 capacity than 11 m MEA. kg′ decreases by a factor of 30 in aqueous MEA with 0.23 to 0.50 CO2 loading. kg′ decreases by a factor of 20 in aqueous PZ with 0.21 to 0.41 CO2 loading. PZ is shown to absorb CO2 2 to 3 times faster than MEA.

Aqueous piperazine derivatives for CO 2 capture: Accurate screening by a wetted wall column

Concentrated aqueous piperazine (PZ) has been identified as a better solvent for CO 2 capture than monoethanolamine (MEA), because it has a greater rate of CO 2 absorption and greater CO 2 capacity. This work evaluates the effect of substitute groups on PZ performance. Many previous screening studies measured absorption/desorption with CO 2/N 2 sparging, which lacks accuracy and cannot be used to estimate actual absorber performance. In this work a wetted wall column was used to accurately measure absorption/desorption rate at typical rich and lean CO 2 loading ( α) and simulate performance of real packing. The method also provides accurate measurement of CO 2 solubility at 40–100 °C. This study provided rate and solubility data at 40–100 °C and practical ranges of CO 2 loading for 8 m 1-methylpiperazine (1-MPZ), 8 m 2-methylpiperazine (2-MPZ), 4 m 2-MPZ/4 m PZ, 7.7 m N-(2-hydroxyethyl)piperazine (HEP), 6 m 1-(2-aminoethyl)piperazine (AEP), 8 m 2-piperidine ethanol (2-PE), and 2 m trans-2,5-dimethylpiperazine (2,5-DMPZ). With the measurements of CO 2 flux ( N C O 2 ) and equilibrium driving force, liquid film mass transfer coefficients ( k g′) are calculated. The rate decreases as of 1-MPZ = PZ > 2-MPZ/PZ > 2-MPZ > HEP > MEA > AEP = 2-PE. This method also allows bracketing and determination of equilibrium CO 2 partial pressure ( P C O 2 * ) at each condition. Semi-empirical solubility models of CO 2 for each amine were regressed from experimental solubility data to find the lean and rich CO 2 loading corresponding to 0.500 kPa and 5 kPa CO 2 partial pressure respectively. Based on the solubility model, the actual operating capacity of the solvents without overstripping decreases in the sequence of 2-PE > 2-MPZ > 2-MPZ/PZ > 1-MPZ > PZ > HEP > AEP > MEA. The enthalpy of CO 2 absorption (Δ H abs) of all the piperazine derivatives is around 70 kJ/mol CO 2.