Over-all Mass Transfer Coefficients Research Articles

Method for measuring bubble size under low-light conditions for mass transfer enhancement in industrial-scale systems

Shadowgraphy-based image processing studied in the literature on multiphase processes has led to meaningful advances in mass transfer enhancement via interfacial area enlargement. However, the industrial applications of shadowgraphy have been limited due to the requirement of an additional light source at specific locations. To overcome this limitation, in this study, a new bubble size measurement technique in low-light conditions is proposed. The technique uses reflected LED image on the bubble surface to estimate the bubble size in low-light conditions and includes a newly derived measurement correlation model, which was validated with lab-scale experimental data. Furthermore, the proposed model was applied to industrial-scale bubble systems for hydrogen fluoride (HF) removal. Using the bubble properties identified through analysis, the overall mass transfer coefficient (OMTC) was determined as an indicator of HF mass transfer enhancement. The optimal conditions for HF mass transfer were determined by identifying the system with the highest OMTC. By manipulating the pressure difference and flow rate, OMTC was increased by ∼78% of the base case.

Epoxide-based PDMS TFC membrane fabricated via the T-FLO technique for the phenol separation

Poly(dimethylsiloxane) (PDMS), as the valuable candidate for the phenol separation material, is modified easily owing to its various silane coupling agents and precursors. However, the reported overall mass transfer coefficient (OMTC) of PDMS is not high enough. The silane coupling agents for PDMS TFC fabrication are limited to amine-based ones. Hence, the applications of polysiloxane membranes are hindered severely. Therefore, in this work, dense PDMS films containing epoxide-based, amine-based, and epoxide-amine mixed silane coupling agents were prepared to explore their phenol mass transfer performance. And then, the effect of the precursor molecular length and the mass ratio of the precursor to the silane coupling agents were examined. Besides, the feasibility of preparing the optimized epoxide-based poly(dimethylsiloxane) (EPDMS) membranes by the thin-film liftoff (T-FLO) technique was observed. The phenol OMTC of epoxide-based PDMS TFC (TFC-E) membranes was studied for the first time. The TFC-E performed a remarkable phenol OMTC of 39.6 × 10−7 m s−1 and good long-term stability, which endowed the promising potential applications.

Thermodynamic parameters of Am(III), Cm(III) and Eu(III) extraction by CyMe4-BTPhen in cyclohexanone from HNO3 solutions

The thermodynamic parameters of the extraction system consisting of CyMe4-BTPhen dissolved in cyclohexanone and Am(III), Cm(III) and Eu(III) in HNO3 in the aqueous phase have been determined. Kinetic extraction experiments were carried out under various temperatures (15–45 °C) and the corresponding over-all mass transfer coefficients were used for the calculation of apparent activation energy and frequency factor values. The values of reaction enthalpy and entropy were also calculated using the distribution coefficients resulting from the experiments mentioned above. Based on the calculated data, the rate-controlling processes and the exothermic character of the studied extractions were determined.

Mass Transfer Process in Nonporous Tubular Membrane for Extraction of Phenol with Caustic Stripping Solution

Mass extraction process of phenol from aqueous solution to a caustic solution through nonporous silicone rubber membrane was investigated. The effects of liquid flow status, pH of stripping solution, initial phenol concentration, transmembrane pressure, and system temperature on mass transfer coefficient were discussed. Based upon the resistance-in-series model, the overall mass transfer coefficient (OMTC) across membrane was calculated. The experiment results showed OMTCs presented logarithmic relation to the Reynolds number, while the changes of flow status had little effect on OMTCs at the higher Reynolds numbers (Ret>86.5 and Res>2000), which indicated that mass transfer of phenol was dominated by membrane resistance for nonporous membrane system (3.72×10-7m•s-1). The presence of transmembrane pressure went against permeability of phenol. Moreover, OMTC was linearly proportional to the initial phenol concentration in the range of 5,000-7,500 mg•l-1, and reached a plateau value at higher phenol initial concentration. OMTC was directly proportionate to the temperature in this process. Mass transfer of phenol through nonporous membrane was scarcely affected by pH value of the stripping solution.

Mass transfer process of hydrogen via ceramic proton conductor membrane of electrochemical hydrogen pump

Abstract The blanket tritium recovery system using the electrochemical hydrogen pump with proton conductor membrane has been proposed. The feature of the electrochemical hydrogen pump is that the driving force of hydrogen transportation is a potential difference. Therefore, it might be effective to apply the hydrogen pump to the blanket sweep gas (the low hydrogen and water vapor pressure). Perovskite-type ceramic such as SrCe 0.95 Yb 0.05 O 3− α , is one of the candidate proton conductor for hydrogen pump and its ionic hydrogen transportation properties have been investigated. In this work, the basic mass transfer equation for hydrogen, in which the apparent proton conductivity is used as the over-all mass transfer coefficient, is proposed. And then, the apparent proton conductivities were estimated from experimental data using these equations, and mass transfer of hydrogen via proton conductor membrane was discussed by using the apparent conductivity.

Treatment of highly-concentrated phenol wastewater with an extractive membrane reactor using silicone rubber

Application of membrane extraction process to the removal of phenol from its aqueous solution was investigated. The ability of poly (dimethylsiloxane), i.e. PDMS and poly (methyl vinyl) siloxane (PVMS) in the membrane extraction of water–phenol mixtures was compared. It was found that PDMS was more suitable for the operation under strong base condition. PDMS and sodium hydroxide solution were applied in the process. The effects of feed flow rate, phenol concentration, temperature and pH in the stripping solution and ionic strength on the process were studied. The effects of liquid flow status and system temperature on the membrane surface on the overall mass transfer coefficient (OMTC) and the permeability for phenol through the membrane were also discussed. The experimental results showed that the phenol removal efficiency was over 95% under the conditions of a flow rate 2.0 l·d –1, phenol >5000 mg·l –1, at 323.2 K and pH 13.0. OMTCs increased with increasing salt concentration. The order of OMTC was 10 –7 m·s –1, and the experimental data was agreement with the Arrhenius relationship for the temperature dependence of the permeability of phenol through the polymer.

Insights into the Transport of Toluene and Phenol Through Organic Solvent Nanofiltration Membranes

Overall mass transfer coefficients (OMTCs) during membrane solvent extraction (MSE) for a microfiltration membrane Accurel, an organic solvent nanofiltration (OSN) membrane MPF 50, and silicone rubber were investigated with a hydrophilic solute (phenol) and a hydrophobic solute (toluene) in a membrane solvent extractor. Decanol was used to extract phenol or toluene from water. In MSE of phenol from water, MPF 50 has an OMTC intermediate between Accurel and silicone rubber, and has a much higher breakthrough pressure than Accurel. For MPF 50, it was observed that the solute–membrane interaction makes a major contribution to the mass transport of hydrophobic compounds, such as toluene, through the membrane. This suggests that solution-diffusion type models may be more appropriate than pore-flow models for describing transport of solvents through these kinds of membranes.

Recovery of Aniline from Aqueous Solution Using the Membrane Aromatic Recovery System (MARS)

This paper describes a new process for the recovery of aromatic, cyclic, and aliphatic amines from aqueous streams, the membrane aromatic recovery system (MARS). The process comprises a stripping vessel, where the amines are extracted through nonporous membranes and concentrated into an HCl solution as hydrochloride salts, and a two-phase separator in which the solution from the stripping vessel is separated into an aniline-rich phase and an aqueous phase by adjusting the pH to caustic conditions with NaOH. In this study, aniline was recovered from a synthetic wastewater using silicone rubber tubing as the membrane. The stripping-solution temperature was 50 °C, and the HCl concentration was 10.45 wt %. After recovery, an organic-rich product phase containing 96.5 wt % aniline and 3.5 wt % water was obtained. The overall mass-transfer coefficients (OMTCs) for a range of amines were also investigated to demonstrate the wide potential application of MARS technology.

Braided silicone rubber membranes for organic extraction from aqueous solutions: II. Application to contained liquid membranes

Aqueous–aqueous extraction experiments were performed in a double tube mass exchanger (DTMEx) in order to investigate mass transfer characteristics of steel-braided non-porous membranes in a contained liquid membrane (CLM) module. Toluene was the permeating molecule, polydimethylsiloxane (PDMS) and ethylene propylene diene monomer (EPDM), were used as non-porous membrane materials, and silicone oil and polypropylene glycol (PPG) as liquid membranes. The liquid membrane contribution to the overall mass transfer resistance was assessed for different module configurations (e.g. varying membrane separation distance) and operating modes (e.g. stationary and mobile liquid membrane). The liquid membrane was found to be the dominant resistance when the module was operated with a stationary liquid membrane, a large separation distance between the braided membranes, and non-porous membranes with high affinity for the permeating molecules. When the liquid membrane was circulated through the module this resistance became negligible compared to the cumulative resistances in the aqueous hydrodynamic boundary layers (HBLs) and membrane at the feed and extractive side, resulting in overall mass transfer coefficients (OMTCs) up to 2.7×10 −5 m s −1. CLMs with braided membranes and mobile liquid membrane may therefore be advantageously used for aqueous–aqueous separation of hydrophobic molecules in modules operating with high liquid velocity in the membrane tubes.

Membrane aromatic recovery system (MARS) — a new membrane process for the recovery of phenols from wastewaters

This paper describes a new process for recovery of aromatic acids and bases, the membrane aromatic recovery system (MARS). The process comprises a stripping vessel, where phenols are extracted through nonporous membranes and concentrated into a NaOH solution as phenolate, and a two-phase separator in which the solution collected from the stripping vessel is separated into a phenolic phase and an aqueous phase by adjusting pH to acidic conditions with the addition of HCl. Silicone rubber tubing was used as a membrane in this study. The temperature in the stripping vessel and NaOH concentration in the solution fed into the stripping vessel are two important operating parameters. In this study the temperature was 50°C and NaOH concentration 12.5 wt.%. At steady-state, the total phenol concentration in the stripping solution can be orders of magnitude higher than in the wastewater, ensuring a high phenol recovery efficiency. The work found phenol recovery efficiencies of over 94%, with a recovered organic-rich phase comprising 86.5 wt.% phenol, and the balance water. The overall mass transfer coefficients (OMTCs) for other phenols were investigated to demonstrate the wide potential applications of MARS technology. Insights into OMTCs and permeabilities of phenols include the effect of Reynolds number in the tube side on OMTC, and the effect of temperature on the permeabilities of phenolic compounds in the membrane. The membrane resistance dominates the OMTCs of phenols in this study. The van’t Hoff–Arrhenius relationship for the temperature dependence of the permeability of the penetrant through the polymer gave excellent agreement with our experimental data.

Mass transfer coefficients in mixer-settler extraction column.

The volumetric over-all mass transfer coefficient K c a and the volumetric dispersed phase mass transfer coefficient k d a in a mixer-settler extraction column were measured. In the measurement of K c a, iodine was extracted from I 2 -KI aqueous solution into heptane, while iodine was back-extracted from a heptane solution of iodine into sodium thiosulfate aqueous solution to obtain k d a. By using specific interfacial area determined from the estimated Sauter mean diameter of the dispersed drops and the estimated holdup of the dispersed phase, the mass transfer coefficients for the dispersed and the continuous phases were determined from the volumetric coefficients K c a and k d a. The coefficient k d for the dispersed phase coincided with the theoretical value based on diffusion within a rigid sphere using the residence time distribution of dispersed drops. On the other hand, the coefficient k c for the continuous phase agreed well with the correlation of mass transfer around a rigid sphere by assuming that the relative velocity of the dispersed drop to the continuous phase was given by the terminal settling velocity of a rigid sphere having the same diameter and density as the drop.

Two-phase nitration of toluene. Part II

The rate of the two-phase nitration of toluene has been determined in a stirred batch reactor over the range 62–78% sulphuric acid using an initial nitric acid concentration of 0.56 mol l −1 and a molar ratio of nitric acid to toluene of 1.06:1. At the lower concentrations of sulphuric acid the transition from kinetic to mass transfer control is observed, and at the higher concentrations, the transition from slow to fast reaction. In the slow reaction diffusional regime at 25°C and 2500 rev/min, the product of the interfacial area per unit volume of the acid phase, a′, and the over-all mass transfer coefficient k has the value 0.069 sec −1. It is found that a′k increases slowly but steadily with temperature and varies approximately as the square of the stirring speed.

Correspondence. Effect of Gas Rate on Over-all Mass Transfer Coefficients and the Perfect Mixing Theory

ADVERTISEMENT RETURN TO ISSUEPREVArticleCorrespondence. Effect of Gas Rate on Over-all Mass Transfer Coefficients and the Perfect Mixing TheoryR. G. RobinsonCite this: Ind. Eng. Chem. Process Des. Dev. 1964, 3, 2, 191–192Publication Date (Print):April 1, 1964Publication History Published online1 May 2002Published inissue 1 April 1964https://doi.org/10.1021/i260010a017RIGHTS & PERMISSIONSArticle Views24Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (222 KB) Get e-Alerts

Briefs - " Correspondence, Effect of Gas Rate on Over-All Mass Transfer Coefficients and the Perfect Mixing Theory"

Briefs - " Correspondence, Effect of Gas Rate on Over-All Mass Transfer Coefficients and the Perfect Mixing Theory"

The effect of concentration driving force on liquid-liquid mass transfer

The enhancement of the rate of mass transfer due to concentration driving force-induced interfacial turbulence has been investigated in several typical liquid-liquid systems. The three solvent pairs studied were: isobutanol-water, 85 volume % tributyl phosphate (TBP) in n-hexane-water, and 85 volume % tributyl phosphate in carbon tetrachloride-water. Nitric acid was the solute in all three systems. The experiments were conducted in an unbaffled stirred-vessel extractor operated as a steady state continuous flow device. The stirring speed was 72 rev/min for all experiments. For all the systems transfer from the organic to the aqueous phase was unstable. The over-all mass transfer coefficient increased sharply by factors of 1·5–4 as the driving force was increased. Transfer from aqueous to organic was stable, except for the TBP-n-hexane system where the mass transfer coefficient increased at high driving forces. The transfer coefficient was found to depend only on the concentration driving force, except for the TBP-hexane system where it appeared to be a function of concentration level as well as driving force. The results were consistent with the qualitative features of Marangoni instability, although several aspects of the data could not be explained on this basis.

The correlation of individual film coefficients of mass transfer in a stirred cell

To assist in the interpretation of over-all mass transfer coefficients in liquid-liquid extraction in stirred cell experiments the following improved correlation has been derived on the basis of the data of Lewis: ▪ This relation has been confirmed by new experimental data obtained using a cell of slightly modified construction. Systems studied were: 1. The benzene-water- isopropyl alcohol system. 2. The benzene-water-amyl alcohol system. 3. The ethyl acetate-water system. 4. Systems (1) and (2) in the presence of polyethylene oxide in the aqueous phase to increase the viscosity. During the development of the correlation it is shown that the individual film coefficients, k 1, are not entirely independent of the diffusion coefficients, D 1, of the respective phases, so that the transfer is not completely controlled by eddy diffusivity. It was found that k 1 is proportional to D 1 with an exponent of 1 6 , which is less than the exponent of 1 2 required if the transfer takes place only by unsteady-state diffusion into stagnant surface elements, but which is nearer the exponent of zero required if the transfer takes place by a turbulent mixing process.

Mass Transfer between Drops of Organic Solvents and Water

In the previous paper3), it was reported that the rate of mass transfer between drops of organic solvents and water was reduced by the addition of some substances. In the present work, a study on the rate of extraction from drops of organic solvents to drops in pure systems has been made paying special attention to these poisonous substances. For butylacetate, -IPE-and MIBK-water systems which are not liable to be contaminated easily, results agreed approximately with the published data (Table 2), but the observed Kd values were much larger than the published data for the benzene-water system (Table1). This discrepancy between the author's and the published data cannot be accounted for by any experimental errors. It seems likely that it is due to difference in purity of the benzenes, solutes and waters used and to the resultant contamination by trace quantities of poisonous substances.The observed Kd values were largest at the beginning of free rise, and they decreased when the height of rise increased due to the transfer of acetic acid or propionic acid whose distribution favors water.The observed Kd values for 24 systems (3 solutes and 8 solvents) were compared with the predicted Kd volues which were calculated by Eq. (3) for kd and ke (Fig. 8). The over-all mass transfer coefficients for non-contaminated systems can be approximately predicted by Eq. (3), but further studies with due attention to poisovous substances will have to be carried out to obtain more accurate correlations.

Operational Mechanism of Pulsed Flow in a Packed Extration Column

Performance data are given for a packed extraction-pulse column on the systems of ethylether-uranyl nitrate-water and benzene-acetic acid-water. Considering the relationship between the capacity factor and holdup of the column, the results obtained are summarized as follows:1) Proportion of the free holdup to the total holdup is represented by the following equation, Apparent contact area is calculated from the above Xf value and dispersed drop size. The contact area increases with the increase in intensity of pulsed condition, until it attains a saturated value. The saturated point is in the vicinity of amXf=25-30 [m/hr].2) The effect of pulsation on the over-all mass transfer coefficient is much smaller than that on the cotact area.3) The effect of column height on the over-all capacity factor depends mainly on the abnormally large valae of the over-all mass transfer coefficient of the fresh surface at the bottom of the column.