Calculation Of Mass Transfer Coefficients Research Articles

Simulation of MEG Packed Distillation Column Using an Equilibrium Stage Model–Case Study on Operating Parameters of Farsa Petrochemical Company–Assaluyeh–Iran

Abstract Two types of equilibrium and non–equilibrium stage models are generally used to simulate the mass transfer of packed distillation column. Using non–equilibrium model requires the calculation of mass transfer coefficients, thus, usually equilibrium–based methods are preferred to be used for simulations of distillation columns. In this paper, packed column distillation of production of Mono Ethylene Glycol in FARSA SHIMI Company (Assaluyeh –Iran)’s Ethylene Glycol portion has been simulated through using the equilibrium model and solving the related equations. The simulation has been carried out in the MATLAB environment. The column also has been simulated in the Aspen Hysys and Aspen Plus ver.2006.5 environments. Then, the output has been compared with software results, designing and operating data of the underlying columns which demonstrate good consistency with the model. Having the model validated, the effect of some operating parameters has been analyzed through the model.

Screening Zeolites for Gas Separation Applications Involving Methane, Nitrogen, and Carbon Dioxide

An experimental evaluation of the kinetics and equilibrium capacities of pure fluids as a fast and effective means to screen an adsorbent's gas separation potential is described. Equilibrium adsorption capacities for pure N2, CH4, and CO2 have been determined using a Micromeritics ASAP2020 sorption analyzer, for three commercially available zeolites: natural chabazite, H+ mordenite, and Linde 4A molecular sieve over the temperature range from (248 to 302) K and pressure range from (0.001 to 120) kPa. Toth models were regressed to the equilibrium data for each gas and used to generate inferred equilibrium selectivity maps over a wider range of temperature and pressure for the purpose of targeting any future mixture measurements. For each gas, the rate of adsorption at 100 kPa was measured as a function of temperature and used with a linear driving force model to calculate mass transfer coefficients. In most cases the ratio of the mass transfer coefficients for each pair of gases was close to unity and did ...

Removal of aluminum from metallurgical grade silicon using electron beam melting

Small amounts of metallurgical grade silicon were melted in an electron beam furnace in different experimental conditions in order to investigate the aluminum (Al) evaporation behavior during the electron beam melting (EBM) process. Impurity was significantly decreased in the early periods of melting at 9, 15, and 21 kW. These changes slowed down with the extension of the melting time. Moreover, the removal reaction of Al by evaporation from molten silicon during the EBM process occurred in accordance with the first order kinetics. The calculated mass transfer coefficients of Al at 1941, 1964, and 2051 K increased with the increase of melting temperature. The removal rate of Al was controlled by the transportation of Al from the bulk of silicon metal to the molten/vacuum interface within the range of the experimental temperature.

Determination of the interfacial area and mass transfer coefficients in the Taylor gas–liquid flow in a microchannel

The interfacial area in the Taylor (slug) gas–liquid flow in a microchannel was measured by the Danckwerts' (chemical) method, using CO 2 absorption from the CO 2/N 2 mixture into KHCO 3/K 2CO 3 buffer solutions, containing NaOCl as a catalyst. The rate of absorption was determined and the Danckwerts' plots were constructed. Reasonable agreement with the geometrical area measured photographically was obtained. This fact allowed to determine for the first time the mass transfer coefficients separately for liquid film and liquid caps. A correlation for the calculation of mass transfer coefficients has been proposed.

Remobilization of Polychlorinated Biphenyl from Baltic Sea Sediment: Comparing the Roles of Bioturbation and Physical Resuspension

The release of a [¹⁴C]-labeled tri-chloro-biphenyl compound ([¹⁴C]PCB 32) from sediment to water was quantified weekly in a 30 d microcosm experiment with re-circulating water. Two modes of bioturbation-driven PCB release: 1) bioturbation by the amphipod Monoporeia affinis (a particle bio-diffuser) and 2) bioturbation by the polychaete Marenzelleria sp. (a bio-irrigator) were compared to the PCB release caused by physical sediment resuspension generated by a motor-driven paddle, used twice a week. Bioturbation by the amphipod M. affinis caused a significantly higher remobilization of both particle-associated (PCBpart) and dissolved PCB (PCBdiss) than the other treatments. Bioturbation by Marenzelleria sp. and physical resuspension caused a similar release of PCBdiss despite a significantly higher amount of total suspended solids in the water column after physical resuspension. In all treatments, the release of PCBdiss was more than one order of magnitude higher than of PCBpart, indicating a significant potential exposure route to pelagic organisms, such as fish, of the most bioavailable PCB form. Calculated mass transfer coefficients (0.3-1.3 cm/d) correspond to previously reported values for tri-chlorinated PCBs. Results from this experiment indicate that biological reworking of sediments can be just as, or even more, important than physical resuspension for the remobilization of sediment-bound contaminants.

SMB chromatography design using profile advancement factors, miniplant data, and rate‐based process simulation

AbstractThis article describes a systematic miniplant‐based approach to rapid development of simulated moving bed (SMB) chromatography applications. The methodology involves analysis of single‐column pulse tests to screen adsorbents and operating conditions and to determine initial values of profile advancement factors used to specify flow rates for an initial SMB miniplant experiment. A lumped‐parameter linear driving force rate‐based model is developed by fitting process data from a single miniplant run. The data are fit in a two‐step procedure involving initial determination of effective adsorption isotherm constants as best‐fit parameters with subsequent adjustment of calculated mass transfer coefficients to refine the data fit. The resulting simulation is used to guide further miniplant work and minimize experimental effort. The methodology is illustrated with miniplant data for a binary protein separation showing excellent agreement between model results and process data generated over a wide range of operating conditions. © 2009 American Institute of Chemical Engineers AIChE J, 2009

Dissolution mechanism of polymers in high pressure–high temperature n‐alkanes—Application to blends separation

AbstractThe use of a high temperature–high pressure near critical solvent is an interesting alternative to dissolve high‐molecular‐weight polyolefins with alkanes. This characteristic allows their separation from the blends with other polymers. In the present work, the polymer dissolution of commercial polypropylene (PP) and polystyrene (PS) in n‐alkanes at high pressure and high temperature is analyzed. The comprehension of the different polymer dissolution behaviors and solvent affinities clarifies the understanding of the mechanism of PP/PS physical blend separation under these conditions. The PP dissolution in n‐pentane and n‐heptane was interpreted in terms of chain disentanglement and solvent diffusion. A mathematical model is proposed to predict the experimental results and to calculate mass transfer coefficients in order to quantify the PS barrier effects. It is possible to assess the effect of the temperature on the pure PP solubilization using these coefficients. In blends separation, it was demonstrated that the PS, insoluble at the same conditions, hinders the PP diffusion. As the PS blend content increases, the separation efficiency decreases. Particularly, mass transfer coefficient increases with PP content while PS is the matrix (PS barrier decreases). Afterwards, PP has no ulterior barriers and mass coefficient remains constant. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers

Effect of surface roughness on the kinetics of mass transfer during gas carburizing *

Abstract Despite its worldwide application, gas carburizing faces certain challenges in control and variability. No current carburization model accounts for the effect of surface roughness and is able to predict observed case depth variations. An investigation of the effect of surface roughness on gas carburizing performance, with the aim of developing a functional relationship between surface roughness and the mass transfer coefficient, is reported. A further objective was to model surface roughness effects on the carbon concentration profile and corresponding case depth variations. A scanning laser microscope was used to measure 3D roughness parameters and surface area of AISI 8620 steel samples subject to various surface preparation operations. Carburizing response was analyzed in terms of weight gain, microhardness and carbon concentration profiles. The weight gain and surface carbon concentration were used to calculate the mass transfer coefficient. The carburizing kinetics was found to be directly proportional to the surface roughness and was a function of surface area available for carbon transfer. The calculated mass transfer coefficients and mass transfer coefficients from the literature were used as input to the carburization model. Experimentally determined concentration profiles validated the model prediction. It is included that the model can be used to estimate initial surface conditions to improve carburizing performance and for effective process control. ▪

Barrier Effect to Water Vapour of Early European Painting Materials on Wood Panels

This paper reports results of experimental measurements of diffusive water vapour flux through spruce wood specimens coated with 16 combinations of paint layers replicated according to materials and techniques used in the period from the late Middle Ages to the Renaissance period. Layers represented two base preparations (ground), four polychrome paint layers and presence or absence of varnish. The flux of water vapour was measured from sorption tests in unsteady-state conditions. The internal resistance to the transport of water in wood and the external resistance due to the coating layers was calculated with a numerical method. The results show that all painting layers reduce the flux and that there are significant differences among paint layer combinations. The calculated mass transfer coefficient is an important physical characteristic of the material and it allows improved models for the understanding and prediction of the influence of coatings and painting layers on the hygroscopic and deformative behaviour of wooden objects subjected to changes in environmental climatic conditions.

Removal process of CO2 using MDEA aqueous solutions in a bubble column reactor

Abstract Present work analyses the behaviour and mass transfer of N-methyldiethanolamine (MDEA) in the removal process of carbon dioxide using a bubble column reactor (BCR) as gas–liquid contactor. The use of this type of equipment requires the interfacial area determination for the following mass transfer coefficient calculation based on absorption kinetics. In this work, a photographic method based on the bubble diameter determination, has been employed. The effect of contactor, operation conditions, liquid-phase nature and chemical reaction upon the mass transfer coefficient and interfacial areas have been analysed.

Separation of As(III) and As(V) by hollow fiber supported liquid membrane based on the mass transfer theory

Separation of As(III) and As(V) ions from sulphate media by hollow fiber supported liquid membrane has been examined. Cyanex 923 was diluted in toluene and used as an extractant. Water was used as a stripping solution. The extractability of As(V) was higher than As(III). When the concentration of sulphuric acid in feed solution and Cyanex 923 in liquid membrane increased, more arsenic ions were extracted into liquid membrane and recovered into the stripping solution. The mathematical model was focused on the extraction side of the liquid membrane system. The mass transfer coefficients of the aqueous phase (k i ) and organic phase (k m ) are 7.15×10−3 and 3.45×10−2 cm/s for As(III), and 1.07×10−2 and 1.79×10−2 cm/s for As(V). Therefore, the rate-controlling step for As(III) and As(V) in liquid membrane process is the mass transfer in the aqueous film between the feed solution and liquid membrane. The calculated mass transfer coefficients agree with the experimental results.

Effect of surface roughness on kinetics of mass transfer during gas carburising

Despite its worldwide application, gas carburising faces certain challenges in control and variability. No current carburisation model accounts for the effect of surface roughness and is able to predict observed case depth variations. An investigation of the effect of surface roughness on gas carburising performance, with the aim of developing a functional relationship between surface roughness and the mass transfer coefficient, is reported. A further objective was to model surface roughness effects on the carbon concentration profile and corresponding case depth variations. A scanning laser microscope was used to measure 3D roughness parameters and surface area of AISI8620 steel samples subject to various surface preparation operations. Carburising response was analysed in terms of weight gain, microhardness and carbon concentration profiles. The weight gain and surface carbon concentration were used to calculate the mass transfer coefficient. The carburising kinetics was found to be directly proportional to the surface roughness and was a function of surface area available for carbon transfer. The calculated mass transfer coefficients and mass transfer coefficients from the literature were used as input to the carburisation model. Experimentally determined concentration profiles validated the model prediction. It is concluded that the model can be used to estimate initial surface conditions to improve carburising performance and for effective process control.

Calculation of Gas Carburizing Kinetics from Carbon Concentration Profiles based on Direct Flux Integration

Initiated by the need of industry for gas carburizing process control and optimization, this paper focuses on understanding the effect of the time, temperature and carbon potential on the mass transfer coefficient and carbon diffusivity in Austenite. A method for direct flux integration has previously been proposed to calculate these kinetic parameters from the experimental carbon concentration profiles. AISI 8620 steel discs were gas carburized at different levels of atmosphere carburizing potential for selected austenizing temperatures. Analyses of the carburized parts included experimental measurement of weight gain, surface carbon concentration and carbon concentration profiles. The time-dependent weight gain and surface carbon content measurements allowed calculation of the time average mass transfer coefficient, while carbon concentration profiles were used to calculate the concentration dependent carbon diffusivity for selected process parameters. Excellent agreement was found between the calculated mass transfer coefficient and carbon diffusivity values and those reported in the literature. The calculated values served as input in the previously developed carburizing model validating the predicted results by comparison with the experimental concentration profiles.

Chloride assisted leaching of chalcocite by oxygenated sulphuric acid via Cu(II)–OH–Cl

The beneficial effect of the addition of sodium chloride upon the leaching kinetics of complex iron–nickel–copper sulphides at elevated temperatures and oxygen pressures has been widely reported since the late 1970s, but the role of chloride is still being investigated or debated. Previous researchers have considered chloride as: (i) a complexing agent for cuprous ions; (ii) a surfactant that disperses the molten sulphur and thus removes passivation of the mineral surface by elemental sulphur during pressure leaching; and (iii) a reagent which increases the surface area and the porosity of the insoluble product layer on the surface. A proper understanding of the role of chloride based on the leaching of individual sulphides of known composition in the absence of host minerals at low pulp densities would be useful for the development of chloride assisted sulphate leaching processes for complex sulphide ores, concentrates, and mattes. In the present study evidence for the formation of basic salts of Cu(II) and Fe(III) during leaching are presented. The published rate data are analysed for the leaching of copper from mono-sized chalcocite particles in oxygenated sulphuric acid solutions maintained at 85 °C, a temperature lower than the melting point of sulphur. The initial leaching follows a shrinking particle (sphere) model, and the apparent rate constants are first order with respect to the concentration of dissolved oxygen and chloride. The intrinsic rate constant for the surface reaction (0.2 m s −1) is two orders of magnitude larger than the calculated mass transfer coefficient of oxygen (3 × 10 −3 m s −1). The proposed reaction mechanism considers the formation of an interim Cu(II)(OH)Cl 0 species which facilitates the leaching process.

Effect of convection on diffusion of small solutes through tissue

Transport of small solutes (MW< 500 da) through tissue is typically diffusion-dominated. In the special case of intraperitoneal therapy, hypertonic solutions are used to introduce drugs or nutrients into the body. The hyperosmolar solution induces convection from the body into the cavity, opposing solute delivery. Our hypothesis is that this convection will retard small solute transfer into peritoneal tissue, if its magnitude approaches the solute mass transfer coefficient (MTC). To test this, we measured the effect of osmotic volume flux (Fluxosm) on the mannitol MTC using plastic chambers affixed to the abdominal wall peritoneum of 12 SD rats. The chamber fixes the fluid contact area of the peritoneum and permits determination of volume and concentration versus time and the calculation of MTC. 14C-mannitol transport from the chamber to the tissue was measured during two 90 min periods of testing under isotonic or hypertonic (~500 mosm/kg) conditions. If convection from the tissue to the chamber had a significant effect, the magnitude of MTC would decrease. Our results for the isotonic case resulted in a mean ± SE (cm/min × 103) of: Fluxosm, −0.053 ± 0.027 and MTC of 3.09 ± 0.40. The hypertonic case demonstrated a markedly positive Fluxosm into the chamber of 2.33 ± 0.33 (p<0.05 vs isotonic) but no significant change in the MTC (2.80 ± 0.35), disproving our hypothesis. We conclude that this level of convection has insignificant effects on the diffusive transfer of small solutes across the peritoneum into the underlying tissue.

Prediction of mass transfer coefficients in non‐Newtonian fermentation media using first‐principles methods

Bubble flows in non-Newtonian fluids were analyzed using first-principles methods with the aim to compute and predict mass transfer coefficients in such fermentation media. The method we used is a Direct Numerical Simulation (DNS) of the reactive multiphase flow with deformable boundaries and interfaces. With this method, we are able for the first time to calculate mass transfer coefficients in non-Newtonian liquids of different rheologies without any experimental data. In the current article, shear-thinning fluids are considered. However, the results provide the basis for further investigations, such as the study of viscoelastic fluids.

Solvent Extraction of Coal Tar Absorption Oil with Continuous Countercurrent Spray Column

Solvent extraction of absorption oil by aqueous solution of methanol was evaluated using a continuous countercurrent spray column. The structure of the spray column is simple so that the mass transfer phenomenon in the column can be easily examined. The measured liquid-liquid equilibria between the absorption oil and aqueous solution of methanol phases required for calculation of mass transfer coefficients were found to agree with previous values. The operability and separability of extraction using the spray column were then studied. The density of the dispersed raffinate phase was sufficiently larger than that of the continuous extract phase to carry out countercurrent operation without entrainment of dispersed phase droplets into the continuous phase or flooding in the range investigated in this study. Mass transfers of components of interest could be detected in the bench scale spray column with effective height of about 0.5 m. The nitrogen heterocyclic compounds were extracted preferentially to other compounds, such as homocyclic compounds, from the absorption oil, and the separation of these compounds was governed by the liquid-liquid equilibrium. The highest yield and separation selectivity of nitrogen compounds with this column were about 0.4 and 30, respectively. Since the overall mass transfer coefficients increased with the flow rate of the continuous extract phase, some mass transfer resistance occurred in the continuous extract phase.

Experimental investigation of mass transfer performance with some random packings for ammonia rectification in ammonia–water absorption refrigeration systems

In ammonia water absorption refrigeration systems (AARS) a high efficiency purification process to remove the water content from the generated vapour is of great importance. One type of equipment to carry out this process is a packed column. Any type of detailed analysis of a packed column requires the calculation of mass transfer coefficients. Therefore, the correlations to obtain these coefficients become an essential tool for an accurate analysis and design of these devices. An experimental facility has been designed and built to analyze the ammonia–water rectification process in packed columns. In this paper a brief description of the experimental facility is given and the variables required to analyze the column performance are explained. An analytical method to determine mass transfer coefficients from the experimental data is developed. Results of mass transfer coefficients for 15 mm glass Raschig rings, 1 2 ″ ceramic Berl saddles and 1 2 ″ ceramic Novalox saddles random packings are reported. The experimental results are compared with different mass transfer correlations proposed in the literature. In the paper corrected correlations are proposed for the packings considered. These correlations could be used to analyze and design a packed column for AARS.

Analysis and Measurement of Mass Transfer in Airlift Loop Reactors

Inter-phase mass transfer is important to the design and performance of airlift loop reactors for either chemical or biochemical applications, and a good measurement technique is crucial for studying mass transfer in multiphase systems. According to the model of macro-scale mass transfer in airlift loop reactors, it was proved that the airlift loop reactor can be regarded as a continuous stirred tank reactor for measuring mass transfer coefficient. The calculated mass transfer coefficient on such a basis is different from the volumetric mass transfer coefficient in the macro-scale model and the difference is discussed. To describe the time delay of the probe response to the change of oxygen concentration in the liquid phase, a model taking into account the time constant of response is established. Sensitivity analysis shows that this model can be used to measure the volumetric mass transfer coefficient. Applying this model to the measurement of volumetric mass transfer coefficient in the loop reactor, results that coincide with the turbulence theory in the literate were obtained.

Mass transfer characteristics of a novel three-phase airlift contactor with a semipermeable membrane

The effects of hydrocarbon contaminants and solid loading on gas–liquid volumetric mass transfer coefficient, K L a , were studied in a three-phase 25 l concentric cylindrical airlift contactor with a semipermeable membrane. The porous membrane could retain a large volume of immobilized solid particles and enhanced mass transfer and mixing in the airlift contactor. A specific form of the continuity equation was combined with gas holdup values in order to set up an expression for the mass transfer coefficient calculation. Water with different hydrocarbon concentrations of 0–200 mg/l p -xylene and 0–25 mg/l naphthalene were used as liquid media, under varying solid loadings and superficial gas velocities. The results indicated that deviation of mass transfer coefficient could go either way when hydrocarbons were dissolved in water: the most significant reduction in K L a occurred at the concentration of 37 (mg/l) for p -xylene after which K L a recovered and increased slightly. A less severe depression of K L a was observed for naphthalene. Total solid loading in the airlift contactor was limited to the maximum amount of solid entrapped within the porous textile membrane. Higher superficial gas velocity resulted in the increase of the effect of solid loading on K L a .