Values Of Effective Interfacial Area Research Articles

Hydrodynamics and mass transfer characteristics of packed bubble columns

The mass transfer and hydrodynamic characteristics of packed bubble columns using 0.038 m stainless steel Pall rings, 0.038 m ceramic Intallox saddles, 0.038 m polypropylene Intallox saddles and 0.050 m carbon steel Pall rings were determined in a 0.385 m i.d. column where the gas was dispersed into quiescent liquid. The values of effective interfacial area and liquid-side mass transfer coefficient were determined by using chemical methods. The values of gas holdup, mixing time, effective interfacial area and liquid-side mass transfer coefficient were correlated with the superficial gas velocity and dispersed height to diameter ratio for each of the packings studied.

Mass transfer and hydrodynamic characteristics of tower packings larger than 0.025 m nominal size

Mass transfer and hydrodynamic characteristics of 0.038 m stainless steel Pall rings, 0.038 m polypropylene Pall rings, 0.038 m polypropylene Intalox saddles, 0.05 m carbon steel Pall rings and 0.05 m polypropylene Pall rings were determined in a column of 0.385 m internal diameter. The values of effective interfacial area and liquid-side mass transfer coefficient were obtained by chemical methods. The data on the dynamic liquid hold-up were obtained for an air-water system. The metal Pall rings showed superior performance over the polypropylene Pall rings of corresponding size. The values of the dynamic hold-up, a′ and k La′ were correlated with the superficial liquid velocity for each packing studied.

Mass transfer characteristics of low H/D bubble columns

AbstractThe mass transfer characteristics of 0.2, 0.6 and 1.0 m diameter bubble columns having a low height to diameter ratio (0.6 < H/D < 4) and operated at low superficial gas velocities (0.01 < VG < 0.08 m/s) were investigated. Different types of spargers were used to study their effect on the column performance.The values of effective interfacial area, a, and volumetric mass transfer coefficient, kLa, were measured by using chemical methods. The values of a and kLa were found to vary from 40 to 420 m2/m3 of clear liquid volume and from 0.01 to 0.16 s−1, respectively, in the range of VG, and VL covered in this investigation. The value of the liquid‐side mass transfer coefficient, kL, was found to vary from 3 × 10−4 to 7 × 104 m/s. The effect of the physical properties of the system on the values of a was also investigated. The height to diameter ratio and the column diameter did not have significant effect on the values of gas holdup, a and kLa. It was found that the sparger design is not of critical importance, provided multipoint/multiorifice gas spargers are used.The comparative performance of bubble columns having low H/D with horizontal sparged contactors and tall bubble columns has been considered.

Hydrodynamics and mass transfer characteristics of co‐current downflow packed tube columns

AbstractHydrodynamics and effective interfacial area in a 25 mm i.d. packed tube column were studied over a wide range of operating conditions for demister pad packings (DPP). Flow maps have been prepared. Values of effective interfacial area as high as 1880 m−1 in the spray flow regime were obtained. Data on pressure drop and effective interfacial area have been correlated for different flow regimes. Values of liquid side volumetric mass transfer coefficient, kL a, were measured by absorption and desorption of oxygen in different packed tube columns containing Pall rings (standard and low height to dia. ratio), multifilament wire gauge packings (MFWGP) and DPP. kL a was found to vary from 0.017 to 0.34 s−1 for DPP.Values of wall side solid‐liquid mass transfer coefficient, kSL, were obtained in a 25 mm i.d. copper tube column packed with MFWGP by the dissolution of copper in acidic dichromate solutions. Values of wall side heat transfer coefficient could be obtained by analogy.

Fast liquid-liquid reactions: role of emulsifiers

The effect of emulsifiers such as sodium dioctyl sulfosuccinate, sorbitan monooleate, etc., on the rate of alkaline hydrolysis of higher formate esters was studied. The extraction of these formate esters is accompanied by a fast pseudo-first-order reaction in the diffusion film. Values of effective interfacial area were measured in a mechanically agitated contactor; the specific rate of extraction was measured in a stirred cell of known interfacial area. The effects of speed of agitation and the emulsifier concentration on the effective interfacial area were studied. Emulsifiers can increase the effective interfacial area markedly; the highest increase was by a factor of 14.

Mass transfer in packed columns: Co-current (downflow) operation: 1 in. And 1.5 in. Metal pall rings and ceramic intalox saddles: Multifilament gauze packings in 20 cm and 38 cm i.d. columns

The theory of gas absorption accompanied by fast pseudo- mth order reaction was used to obtain values of effective interfacial area, a, in 20 and 38 cm i.d. packed columns which were operated co-currently (downflow). Values of a were obtained for 1 in. and 1.5 in. metal Pall rings; 1 in. stainless steel Pall rings, having length (height) to diameter ratio of 1.0, 0.75, and 0.5; 1 in and 1.5 in. ceramic Italox saddles; and stainless steel multifilament wire gauze type packing over a wide range of gas and liquid superficial velocities. The gas superficial velocity was varied from 30 to 255 cm/sec in the 20 cm i.d. column and 14 to 73 cm/sec in the 38 cm i.d. column. The liquid superficial velocity was varied from 0.2 to 3 cm/sec in the 20 cm i.d. column and 0.2 to 1 cm/sec in the 38 cm i.d. column. Different flow regimes, namely, trickle flow (film flow), pulse flow and transition from pulse to disperse flow, were covered. The values of a were found to be in the range of 0.6 to 2 cm 2/cm 3 for the trickle flow (film flow) regime, and 2.4–5 cm 2/cm 3 for the pulse flow regime. In the case of multifilament wire gauze packing (MFWGP) remarkably high values of a up to 16 cm 2/cm 3 were obtained in the pulse to disperse flow regime.

Mass transfer and hydrodynamic characteristics of gas inducing type of agitated contactors

AbstractPower consumption, rate of gas induction (Q), fractional gas hold‐up and mass transfer characteristics of 0.41, 0.57 and 1.0 m i.d. gas inducing type of agitated contactors were studied. The power consumption was measured by a torque table. The values of effective interfacial area (a), and liquid side mass transfer coefficient (kLa) were obtained by using chemical methods. Two types of impellers (pipe and flattened cylindrical) were employed. The impeller speed was varied from 3 to 11.7 r/s.The effects of impeller diameter, baffle position, orifice area on the impeller, number of impeller blades, position of impeller from the bottom and liquid submergence on the values of Q and a were investigated. Further, the effect of liquid viscosity and surface tension on the values of Q was studied.A satisfactory agreement was found between the observed and the predicted value of the minimum impeller speed at which gas induction occurs. The performance of the gas inducing type of agitated contactor has been compared with the conventional mechanically agitated contactor.

Mass transfer characteristics of horizontal agitated contactors

AbstractThe values of effective interfacial area, a, and liquid side mass transfer coefficient, kLa, were obtained in 0.385, 0.57 and 1.0 m i.d. horizontal agitated contactors by using chemical methods. Propeller type of impellers were employed for agitation. Two modes of operation were studied: (i) surface aeration and (ii) sparging of gas. The impeller speed was varied from 50 to 700 rev/min, and the nozzle gas velocity was varied from 40 to 160 m/s. The effects of impeller spacing, liquid submergence and nozzle gas velocity on the values of a and kLa were investigated. A scale‐up criterion is discussed.

Mass transfer characteristics of horizontal agitated contactors

AbstractThe values of effective interfacial area, a, and liquid side mass transfer coefficient, kLa, were obtained in 0.385, 0.57 and 1.0 m i.d. horizontal agitated contactors by using chemical methods. Propeller type of impellers were employed for agitation. Two modes of operation were studied: (i) surface aeration and (ii) sparging of gas. The impeller speed was varied from 50 to 700 rev/min, and the nozzle gas velocity was varied from 40 to 160 m/s. The effects of impeller spacing, liquid submergence and nozzle gas velocity on the values of a and kLa were investigated. A scale‐up criterion is discussed.

Mass transfer in venturi scrubbers

AbstractThe theory of gas absorption with chemical reaction was used to obtain values of effective interfacial area, a, liquid‐side mass‐transfer coefficient, kLa, and gas‐side mass transfer coefficient, kGa, in a venturi scrubber for the Wet‐Approach mode of operation. Some data were also obtained for the Pease‐Anthony mode of operation in order to make a rational comparison between the two modes of operation. The hydrodynamic characteristics of the venturi scrubber were studied for the two modes of operation over a wide range of gas and liquid flow rates. Further, the effect of the viscosity of the liquid and the surface tension on effective interfacial area was investigated.

Desorption of isoamylene from loaded acid liquors

The desorption of 2-methyl-2-butene (isoamylene) from loaded sulphuric acid solutions, having an acid strength of about 60 per cent (w/w) and loading upto 0·45 g mole of isoamylene per g mole of H 2SO 4, was found to be preceded by a fast reaction, which occurred in the film adjacent to the interface. The specific rates of desorption of isoamylene into inert hydrocarbons— n-heptane and toluene and an inert gas—nitrogen, were found to be proportional to the isoamylene concentration j, expressed as g mole of isoamylene per g mole of H 2SO 4, and agreed among themselves at the same value of j. The technique of desorption preceded by a fast reaction was employed for the measurement of effective interfacial area in liquid—liquid and gas—liquid agitated contactors. The absorption of isobutylene into fresh and loaded solutions of sulphuric acid was also used for the measurement of effective interfacial area in gas—liquid agitated contactors for comparative purposes. The values of effective interfacial area for the gas—liquid system obtained by the desorption technique were found to be comparable with those obtained from the absorption of isobutylene in fresh and loaded solutions of sulphuric acid, under otherwise comparable conditions.

Mass transfer in packed liquid—liquid extraction columns

The mass transfer characteristics of 3·5, 7·3, 10·16 and 15·6 cm i.d. packed liquid—liquid extraction columns were studied with a variety of packings such as, 3 8 , 1 2 and 1 in. ceramic Raschig rings, 5 8 in. stainless steel Raschig rings, 1 2 and 1 in. ceramic Intalox saddles, 5 8 and 1 in. stainless steel Pall rings, and 1 in. polypropylene Intalox saddles and Pall rings. Some data were also obtained for the co-current mode of operation (up-flow) for packed columns, and without packings. In addition the mass transfer charactersitics of a packed extraction column with film flow were studied. The theory of extraction accompanied by a fast pseudo-first order reaction was employed to measure the values of effective interfacial area. The values of overall (continuous and/or dispersed phase) mass transfer coefficient were measured by the Colburn—Welsh technique. A fairly wide range of physical properties of the two phases was covered. The values of overall (continuous phase) mass transfer coefficient and effective interfacial area for new packings such as Pall rings and Intalox saddles, under otherwise similar conditions, are only about 10 and 35 per cent higher, respectively, than those provided by the conventional packings of the same nominal size. However, the flooding velocities for the newer packings are as much as 80 per cent higher than those for the conventional packings of the same nominal size.

Mass transfer in packed columns: co-current operation

The theory of gas absorption accompanied by fast pseudo- m th order reaction was used to obtain values of effective interfacial area in 10,15 and 20 cm i.d. packed columns which were operated co-currently. A variety of ceramic, metal and plastic packings were used. The range of superficial gas and liquid velocities was 50–300 cm/sec, and 0·1–3·5 cm/sec, respectively. Values of gas side mass transfer coefficients for some of the packings were also obtained. In addition some data were obtained for the counter-current mode of operation.

Effective interfacial area in irrigated packed columns

A generalized correlation is proposed for the values of effective interfacial area duing Vaporization, Absorption with and without Chemical Reaction and the values of wetted surface area in terms of dimensionless numbers. The values of effective interfacial area are analysed based on the concept of static and dynamic area, which appears to represent the mechanism of mass trasfer for the above cases. A generalized correlation in terms of Hatta'a group or the reaction factor is also proposed. The results are limited to packed columns with liquid as the dispersed and gas as the continuous phase operated counter-currently below the loading point.

Absorption in packed bubble columns

The mass transfer characteristics of packed bubble columns were studied by employing various packings of different sizes and shapes in 10–38·5 cm i.d. columns. The theory of absorption accompanied by pseudo- mth order reaction was used to obtain the values of effective interfacial area. The values of liquid side mass transfer coefficient were obtained by using the theory of absorption accompanied by slow chemical reaction. The superficial gas velocity was varied from 5 to 25 cm/sec. The packed bubble columns showed a considerable improvement in the performance over empty bubble columns. A criterion for the scale-up of these columns has been suggested.

Effective interfacial area and liquid and gas side mass transfer coefficients in a packed column

The theory of gas absorption accompanied by fast pseudo- mth order reaction was used to obtain values of effective interfacial area in a packed column, irrigated with aqueous solutions and provided with 1 in. ceramic Raschig rings, 1 in. P.V.C. Raschig rings, 1 in. ceramic Intalox saddles, 1 in. polypropylene Intalox saddles, 1 in. stainless steel Pall rings and 1 in. polypropylene Pall rings. The values of liquid side mass transfer coefficient were obtained by physical absorption of carbon dioxide in water. In addition, the values of gas side mass transfer coefficient for a range of gas and liquid flow rates were obtained.

Effective interfacial area in packed liquid extraction columns

The theory of extraction accompanied by fast-pseudo-first order reaction was used to obtain the values of effective interfacial area in 7·0 and 9·8 cm i.d. packed columns provided with 3 8 in. and 1 2 in. ceramic Raschig rings. The effect of the flow rate of the dispersed phase and the continuous phase and the physical properties of both the phases on the values of effective interfacial area was studied. In some cases it was possible to obtain the values of effective interfacial area and true liquid side (continuous phase) mass transfer coefficient from a Danckwerts' plot. It was possible to use systems with very low solubility, so that hold-up measurements could be made simultaneously. There is a good agreement between the predicted and the experimental values of effective interfacial area.

Effective interfacial area in a packed column

The theory of absorption accompanied by pseudo nth order reaction was used to evaluate values of effective interfacial area, a, as a function of the liquid flow rate in a laboratory packed column. Oxygen was absorbed in aqueous solutions of cuprous chloride and sodium dithionite. Isobutylene was absorbed in an aqueous solution of sulfuric acid. There is a good agreement among the values of a obtained by using different systems. The value of a appears to be a unique function of the liquid flow rate in the range of liquid properties covered in the investigation.

Air-agitated liquid—liquid contactors

The values of effective liquid—liquid interfacial area in air-agitated liquid—liquid extraction columns were obtained by the method of liquid extraction accompanied by fast pseudo first-order reaction. Some values of physical mass transfer coefficients were also obtained. Effect of variables such as air rate, height to diameter ratio, the type of gas distributor, the dispersed phase hold up etc., on effective interfacial area was studied. Columns ranging in diameter from 6·6 to 20 cm dia. were used. At any given superficial velocity of air the values of effective interfacial area were found to be independent of the type of air distributor, the height to diameter ratio and the column diameter. Superficial air velocity could probably be used as a criterion for scale-up.

Effective interfacial area in agitated liquid—liquid contactors

Liquid extraction accompanied by fast pseudo-first-order reaction was used to evaluate the values of the effective interfacial area in agitated liquid—liquid contactors. It was found that alkaline hydrolysis of n-hexyl, 2-ethyl hexyl, n-octyl formates and n-butyl trichloroacetate could be conveniently employed for this purpose. Vessels ranging in capacity from 1 to 500 1. and provided with appropriate size of baffles and turbine, paddle and propeller agitators were used. The variables investigated included the speed of the agitator, ratio of the agitator diameter to the vessel diameter, height of the agitator from the bottom of the vessel, height of liquid, dispersed phase hold-up, etc. It appears that the peripheral speed of the agitator could be used as a criterion for the scale-up. Values of the effective interfacial area were also obtained in a continuously operated reactor and it was found that under the similar operating conditions the values of effective interfacial area in a batch reactor were practically the same as in the continuous reactor. Some data are also reported for the over-all and true continuous phase mass transfer coefficients for physical extraction.