Absorption Of Pure Carbon Dioxide Research Articles

Kinetics of the Absorption of Pure CO2 by Mixtures of Diisopropanolamine and Triethanolamine in Aqueous Solution

ABSTRACTThis study analyzes the absorption of pure carbon dioxide in aqueous solutions of mixtures of di‐isopropanolamine (DIPA) and triethanolamine (TEA). A stirred tank batch reactor was used with a known flat interface area. The variables considered were temperature within the range 288–313 K and concentration in the interval 5–20% (in weight), being DIPA/TEA relations 75/25, 50/50, and 25/75. The temperature control for the DIPA/TEA 75/25, 50/50, 25/75 systems in the absorption experiments, at all the concentrations and temperatures assayed, showed no differences between that of the liquid phase with respect to the operation, implying that the processes occurred under isothermal conditions. The results show that for the DIPA/TEA 75/25 CO2 was absorbed in a moderately fast reaction regime, following a second‐order reaction for the total alkanolamine and a first‐order reaction for the CO2, whereas for the DIPA/TEA 50/50 and 25/75 systems the process followed first‐order kinetics with respect to CO2 and the mixture of alkanolamines, in a moderately fast reaction regime.

Kinetic Study of the Absorption of Carbon Dioxide by Aqueous Triethanolamine Solutions

Abstract In this work, the absorption of pure carbon dioxide by aqueous triethanolamine solutions (TEA) was studied in terms of the kinetic process. The process was made in a stirred tank reactor with a flat and known interfacial area, the operating variables being temperature (288 to 313 K) and concentration in the range 0.1-2.0 M. From the results, it was deduced that the absorption of pure carbon dioxide by aqueous triethanolamine takes place under isothermal conditions in which there is an instantaneous reaction regime at low concentrations, while at higher concentrations it takes place in a moderately fast reaction regime, following a first-order kinetic with respect to alkanolamine. In these conditions of concentrations and temperatures essayed, an expression for the constant kinetic was deduced.

Absorption of CO<sub>2</sub> into Alkane/Water Emulsions in a Stirred Tank

Absorption of pure carbon dioxide into aqueous emulsions of three different n-alkanes (n-heptane, n-dodecane and n-hexadecane) has been studied at 0 to 100% oil volume fraction in a stirred tank at a high stirring speed (1000 min−1). Phase inversion (o/w to w/o) occurs for n-dodecane and n-hexadecane at 60–65% oil volume fraction; for n-heptane, there is no clear inversion point. The volumetric mass transfer coefficient kLa was evaluated from the pressure decrease during saturation under isochoric and isothermal (298.2 K) conditions. The o/w emulsions of both n-dodecane and n-hexadecane show the same trends: kLa first increases to a maximum at 2% oil fraction, then decreases towards the phase inversion region. The maximum might indicate an additional transport mechanism; the decrease at higher oil fractions is expected based on the increase in emulsion viscosity. Differently, the o/w emulsions of n-heptane always show higher kLa values compared to pure water. The increase in kLa (by +280% at 25% n-heptane) might be explained by a bubble covering mechanism enabled by the high spreading coefficient. In w/o emulsions of n-hexadecane, from 100% oil to the phase inversion region, kLa monotonously decreases with increasing fraction of the dispersed water phase as expected due to the viscosity effect. Surprisingly, for both n-heptane and n-dodecane, kLa does not decrease, but rather increases substantially. At the phase inversion region, the relative kLa increase compared to pure oil is by +107% for n-dodecane, and even +143% for n-heptane.

Absorption of carbon dioxide into laminar falling films of aqueous kaolin slurries containing sodium hydroxide

AbstractTo confirm the theory for gas absorption accompanied by an instantaneous irreversible reaction in laminar falling films of power‐law liquids which was presented in a previous paper, experiments were carried out on the absorption of pure carbon dioxide into aqueous kaolin slurries containing sodium hydroxide by using a long wetted‐wall column. The experimental data were in fairly good agreement with the theoretical predictions, the average deviation being 3.0%. The discussion on the effect of the power‐law index of the liquid upon the reaction factor suggested an approximate method of estimating the reaction factors for power‐law liquids.

Gas absorption in laminar falling films of pseudoplastic liquids

AbstractGas absorption into laminar falling films of power‐law liquids was studied theoretically and experimentally. The convective‐diffusion equation was solved by the method of separation of variables and the analytical solution for the average Sherwood number was obtained as a function of the Graetz number and the power‐law index of the liquid. Experiments were carried out on the absorption of pure carbon dioxide, hydrogen and helium into aqueous kaolin slurries by using a long wetted‐wall column and the average absorption rates were measured as a function of the mass flow rate of the liquid. The experimental results were in good agreement with the theoretical predictions.

Kinetics of absorption of carbon dioxide into aqueous sodium sulfite solutions

AbstractThe rates of absorption of pure carbon dioxide into aqueous sodium sulfite solutions containing or not containing sodium sulfate were measured at 15, 25, 35 and 45°C and at atmospheric pressure using a liquid‐jet column, a wetted‐wall column, and a quiescent‐liquid absorber. The experimental results were analyzed by the chemical absorption theory based on the penetration model. The second‐order forward rate constants for the reaction between carbon dioxide and sulfite ion in aqueous solutions were calculated and correlated as a function of temperature and ionic strength of the solution. The chemical equilibrium constants for the reaction were also determined from the measurements of the total solubility of carbon dioxide in aqueous sodium sulfite solutions.

Gas absorption at a liquid surface agitated by vortex rings

AbstractUnderwater vortex rings have been formed at orifices of between 25.4 and 63.5 mm diameter and projected upwards at the surface of the water. The conditions of ring formation at which significant surface deformation occurs have been correlated. The absorption of pure carbon dioxide by the water surface with impinging vortex rings has been measured and related to the following variables: time of fluid impulse through the orifice, orifice diameter, volume of displaced liquid, and depth of submergence. A simplified mass transfer model based on the penetration theory approximately correlates the data.

ABSORPTION OF CARBON DIOXIDE INTO AQUEOUS DIETHANOLAMINE SOLUTIONS

The rates of absorption of pure carbon dioxide into aqueous diethanolamine solutions were measured at 25°C in a liquid-jet column and a wetted-wall column. Experimental results were analyzed with the chemical absorption theory based on the penetration model. Physical solubility of carbon dioxide in aqueous diethanolamine solutions was determined from the absorption rates measured in a near pseudo first-order reaction regime and was found to show a salting-out effect. The measured absorption rates were in good agreement with the theoretical predictions for gas absorption with an irreversible third-order reaction.

Absorption of carbon dioxide into aqueous monoethanolamine solutions

AbstractThe rates of absorption of pure carbon dioxide into aqueous monoethanolamine solutions with a surface active agent were measured at 15°, 25°, 35°, and 45°C in a liquid jet column and a wetted wall column. Experimental results were analyzed with the chemical absorption theory based on the penetration model. Physical solubility of carbon dioxide in aqueous monoethanolamine solutions was determined from the absorption rates measured in a near pseudo first‐order reaction regime and was shown to be considerably larger than the physical solubility in water. The measured absorption rates were in good agreement with the theoretical predictions for gas absorption with an irreversible second‐order reaction, when the variation of the physical solubility of carbon dioxide due to the change in the composition of the solution during the absorption process was taken into account.

Absorption of carbon dioxide into aqueous sodium hydroxide and sodium carbonate-bicarbonate solutions

The rates of absorption of pure carbon dioxide into aqueous sodium hydroxide and sodium carbonate-bicarbonate solutions have been measured using a liquid-jet column, a wetted-wall column and a quiescent-liquid absorber. The experimental results are analysed on the basis of the penetration theory for gas absorption accompanied by a two-step chemical reaction, which was presented by the authors in a previous paper. The data are in good agreement with the theoretical predictions.

MASS TRANSFER IN A MULTISTAGE VIBRATING DISK COLUMN WITH COCURRENT GAS-LIQUID FLOW

Mass transfer characteristics of a cocurrent multistage vibrating disk column are studied by the absorption of pure carbon dioxide into water. Axial mixing in the liquid phase is taken into account by using a back-flow model. Disk vibration definitely enhances the mass transfer rate at low gas velocity and high liquid velocity. On the other hand, at high gas velocity and low liquid velocity, disk vibration does not noticeably improve the mass transfer characteristics, and even worsens them in some cases. The increase in absorption rate by disk vibration can be well estimated by information on the gas holdup characteristics, the mass transfer characteristics without vibration, the gas bubble size data and the axial mixing characteristics in the liquid phase.

Liquid-side and Gas-side Mass Transfer Coefficients in Towers Packed with Spheres

In our previous papers, equations for the liquid-side and the gas-side mass transfer coefficients in towers packed with Raschig rings and Berl saddles had been obtained. In this paper, experiments with ceramic spheres were made in order to clarify the influence of the shape of packings.By measuring the wetted surface area (aw) in towers packed with 1/2″-, 1″-spheres, the relation was expressed by Eq.(2).The liquid-side and the gas-side capacity coefficients (kLa, kGa) in towers packed with 1/2″-, 1″-, 4/3″-spheres, respectively, were measured by means of the absorption of pure carbon dioxide and/or ammonia by water, and their correlated equations with liquid and gas flow rates were obtained as shown in Table 2 and Table 3.Assuming that the effective surface area (a) is equal to the wetted surface area (aw) as described in the authors' previous reports, kL and kG were obtained by dividing kLa and kGa by aw respectively.

Effect of Wetting Agent on Liquid Phase Mass Transfer Rates in Packed Columns

An experiments on the absorption of pure carbon dioxide by water containing a wetting agent (Emerl), was conducted in a 7.0cm dia. column packed with 15mm Raschig rings.The results obtained are shown in Fig. 1, as a plot of kLa vs. L on a logarithmic scale. The effect of wetting agent on the absorption rates can be observed in this figure and more clearly in Fig. 2, where kLa at a constant value of L (15, 000kg/m2·hr) is plotted against the concentration of the againt. With the increase in the concentration, kLa decreases until it reaches the minimum at a certain concentration, and then it begins to increase. These results are similar to those obtained by Rennolds7) on the desorption of carbon dioxide, which was carried out using 1/2in. carbon Raschig rings as packings.Variation of kLa with the change in the concentration of the agents may perhaps be due to the fact that the two effects are contradictory to each other. With the increase in the concentration of the agent. liquid phase mass transfer coefficient, kL, decreases, but the effective interfacial area, a, increases, -the former probably because of the incomplete mixing of liquid at the juncture points of packing pieces, 6) and the latter because of the decrease in surface tension.4)Based on this idea, the effect of surface tension on the effective interfacial area has been determined for the case where 15mm Raschig rings are used. which shows good agreement with the results reported in the previous paper.4)

Effective Interfacial Area for Liquid Phase Mass Transfer in Packed Columns

The present work was undertaken for the purpose of obtaining a general correlation for the effective interfacial area in packed columns. Studies were made on the absorption of pure carbon dioxide by various solvents in a 7.0cm or 12.5cm column packed with Raschig rings and Berl saddles. The experimental apparatus employed is shown in Fig. 1, and the characteristics of packings used and the run series studied are listed in Tables 1 and 2, respectively.The values of HL are shown in Figs. 2 to 5, plotted against liquid rates on logarithmic coordinates. The effective interfacial areas for liquid phase mass transfer were determined from HL data by using Eq. (1). based on the assumption that the values of kL in a packed column are approximately equal to those for single piece of packings5), when their Reynolds numbers are the same. The fractional effective areas, aL/at, were plotted against liquid rates on logarithmic coordinates, as shown in Figs. 6, 7, 8, 10 and 11. respectively.The values of aL/at, varied with the liquid rate to the 0.455 power for all packings and systems used.The effects of the physical properties of liquid were nearly the same on the effective area and on the wetted area2); the viscosity of liquid had no significant effect on aL, as shown in Figs. 6 and 7, but the surface tension of liquid showed a considerable effect, varying with each packing as shown in Fig. 12.The present data on the effective area could be correlated by Eqs. (4) and (5) for Raschig rings and Berl saddles, respectively. Figs. 14 and 15 show the comparisons between the values obtained from these equations and the effective areas calculated, by means of Eqs. (1) or (2), from the previous data on liquid phase mass transfer rates in packed columns. Considerably good agreement is observed between the values obtained from the authors' equations and the previous data.

Effect of Packed Height on Liquid Phase H.T.U. for Packed Columns

Since the publication of Sherwood and Holloway's paper, 5) it has been believed that the height of a packed column has no effect on the values of HL or kLa and the variation of these values with the packed height, observed in the experimental column, results from the end effects caused by the gas-liquid contact above and below the packing. On the other hand, van Krevelen and others7) state that kL is proportional to the -1/3 power of the packed height and a recent study by Fujita and others1) shows that kLa varies with the packed height to the -0.19 power.This work has been undertaken for the purpose of making sure whether packed height has any effects on the values of HL. Experiments on the absorption of pure carbon dioxide by water were performed in two columns, 6.6 and 12.5cm in inside diameters, respectively, packed with 15mm Raschig rings, with the packed height varying from 0.05 to 1.50m.Observed values of N.T.U. are shown in Figs. 2 and 3, plotted on logarith mic scales against the liquid mass flow rate, with the packed height as a parameter. To obtain the true values of N.T.U. from these data, it is necessary to make correction so as to eliminate the end effects, for which a new method is proposed and employed. In Figs. 5 and 8, the N.T.U. values corrected by the above method are plotted on logarithmic coordinates against water rate. Fig. 5 obtained with the 6.6cm column shows the presence of three regions, A, B and C, so classified according to the values of liquid rate and packed height. The N.T.U. values in regions A, B and C are proportional to the 1.0, 0.92 and 0.56 power of the packed height, respectively, as shown in Fig. 6. The values of HL in region A, therefore, are independent of the packed height, but the HL values in regions B and C vary at the rate of the 0.08 and 0.44 power of the height, respectively, as seen in Fig. 7 and Eqs. 3 to 5. The N.T.U. values with the 12.5cm column, shown in Fig. 8 are proportional to the 1.0 power of the packed height.The HL values, therefore, are independent of the height of the packing, as shown in Fig. 9, and can be represented by the same equation obtained for region A with the 6.6cm column. The variation of HL values in regions B and C with that of the packed height may be due to the non-uniformity of liquid distribution in the column.

Mass Transfer into Liquid Film Flowing over Spheres

This work was undertaken to clarify the mechanism of mass transfer into a liquid film flowing over the surface of a sphere and to see whether liquid is mixed completely or not at the points of juncture between the spheres connected in a vertical row. Experiments were performed on the absorption of pure carbon dioxide by water with and without a wetting agent, in columns containing 1, 3 and 5 spheres, respectively.Experimental data for single sphere are shown in Figs. 3 and 4, and those for multiple sphere in Fig. 6, as the plot of the HL values against the Reynolds number on logarithmic coordinates. Results with single sphere were in good agreement with the theoretical equation based on the assumptions of unsteady-state diffusion and parabolic velocity distribution in the liquid film, as shown in Fig. 5. The addition of a wetting agent caused no change in the absorption rate in the case of single sphere, and the HL values for both the runs with and without agent were the same.Fig. 7 shows the correlation among the results obtained with multiple sphere, when pure water was used as a solvent. Good agreement was obtained between the data and the theoretical equation, derived from the assumption that the mixing of the liquid was complete at the points of juncture between the spheres. Fig. 8 shows a similar plot of the data obtained by Yoshida and Koyanagi.7)When a wetting agent was added to water, the values of HL were higher than those for pure water and increased with the number of spheres, as shown in Fig. 9. The data obtained by authors and those by Lynn, Straatemeier and Kramers5) were in fairly good agreement with the theoretical equation based on the assumption that there was no mixing of the liquid as it flew from one sphere to the next.

Mass transfer in the falling liquid film

Absorption of pure carbon dioxide (97-99%) by the city water was carried out in the wetted-wall column, which was constructed of standard 1/2″ iron pipe. The liquid film height per transfer unit, HL, based on the log. mean driving force was calculated from the data obtained over the range from 100 to 2, 000 of (Re)L. (Re)G was kept constant at about 700 for the majority of runs, since it was found by the preliminary runs that it had not any effect on the rate of absorption.The length of tube was varied from 508 to 1856mm. The discrepancy between the experiments and the theories by Hatta and Pigford was clearly recognized as already pointed out by Sherwood and Pigford in their book. While Emmert and Pigford tried to verify the theory by the interesting experiments using wetting agent, we attempted to explain the discrepancy by other theoretical relations derived here which were based on some added assumptions. These relations are not satisfactory, but they show somewhat better agreement than the previous theoretical lines.We recommend the experimental equations presented here for practical purposes, until a more perfect theory with due regard to the effect of turbulence is established in future.

The absorption of carbon dioxide by liquid drops

AbstractThe process of absorption of pure carbon dioxide by individual drops of water has been studied. It has been shown that, contrary to the assumption of previous workers, the rate of gas absorption of a drop during the period of formation may be very high, especially when the time of formation is short. This is due to the turbulence produced within the drop by the injection of the supply jet, which reduces the resistance to diffusion at the surface of the drop. The absorption coefficient of drops during formation has been shown to be inversely proportional to a function of the time of formation, and directly proportional to the ‘degree of turbulence,’ a concept which can be expressed in terms of orifice dimensions. The influence of the ‘degree of turbulence’ on the magnitude of the overall absorption coeficients used in chemical engineering computations is discussed.