Carbon dioxide transfer coefficient

Coppock and Meiklejohn (C9) determined liquid mass-transfer coefficients for the absorption of oxygen in water. The value of k, was observed to vary markedly with variations of bubble velocity, from 0.028 to 0.055 cm/sec for a velocity range from 22 to 28 cm/sec. These results appear to be in general agreement with the results obtained by Datta et al. (D2) and by Guyer and Pfister (G9) for the absorption of carbon dioxide by water. 

Gal-Or and Hoelscher (G5) have recently developed a fast and simple transient-response method for the measurement of concentration and volumetric mass-transfer coefficients in gas-liquid dispersions. The method involves the use of a transient response to a step change in the composition of the feed gas. The resulting change in the composition of the liquid phase of the dispersion is measured by means of a Clark electrode, which permits the rapid and accurate analysis of oxygen or carbon dioxide concentrations in a gas, in blood, or in any liquid mixture. 

A supercritical fluid exhibits physical-chemical properties intermediate between those of liquids and gases. Mass transfer is rapid with supercritical fluids. Their dynamic viscosities are nearer to those in normal gaseous states. In the vicinity of the critical point the diffusion coefficient is more than 10 times that of a liquid. Carbon dioxide can be compressed readily to form a liquid. Under typical borehole conditions, carbon dioxide is a supercritical fluid. 

A comprehensive review of work on the absorption of carbon dioxide by alkaline solutions has been carried out by Danckwerts and Siiarma(43) who applied results of research to the design of industrial scale equipment. Subsequently, Sahay and Sharma(44) showed that the mass transfer coefficient may be correlated with the gas and liquid rates and the gas and liquid compositions by ... 

Thus, when deahng with gas transfer in aerobic fermentors, it is important to consider only the resistance at the gas-liquid interface, usually at the surface of gas bubbles. As the solubihty of oxygen in water is relatively low (cf. Section 6.2 and Table 6.1), we can neglect the gas-phase resistance when dealing with oxygen absorption into the aqueous media, and consider only the liquid film mass transfer coefficient Aj and the volumetric coefficient k a, which are practically equal to and K a, respectively. Although carbon dioxide is considerably more soluble in water than oxygen, we can also consider that the liquid film resistance will control the rate of carbon dioxide desorption from the aqueous media. 

The diffusion coefficient as defined by Fick s law, Eqn. (3.4-3), is a molecular parameter and is usually reported as an infinite-dilution, binary-diffusion coefficient. In mass-transfer work, it appears in the Schmidt- and in the Sherwood numbers. These two quantities, Sc and Sh, are strongly affected by pressure and whether the conditions are near the critical state of the solvent or not. As we saw before, the Schmidt and Prandtl numbers theoretically take large values as the critical point of the solvent is approached. Mass-transfer in high-pressure operations is done by extraction or leaching with a dense gas, neat or modified with an entrainer. In dense-gas extraction, the fluid of choice is carbon dioxide, hence many diffusional data relate to carbon dioxide at conditions above its critical point (73.8 bar, 31°C) In general, the order of magnitude of the diffusivity depends on the type of solvent in which diffusion occurs. Middleman [18] reports some of the following data for diffusion. 

Knaff and Schlunder [9] studied the evaporation of naphthalene and caffeine from a cylindrical surface (a sintered metallic rod impregnated with the solute) to high-pressure carbon dioxide flowing over an annular space around the rod. They studied the diffusion flux within the bar and in the boundary layer. The mass-transfer coefficient owing to forced convection from cylinder to the gas flowing in the annular duct was correlated, using the standard correlation due to Stephan [7]. For caffeine, it does not require a free-convection correction, as the Reynolds dependence is that expected by a transfer by forced convection. This is... 

In the cases above, a two-parameter model well represents the data. A model with more parameters would be more flexible, but by using a partition constant, K, or a desorption rate constant ka and k, , for the mass-transfer coefficients, the data are well described (see Figs. 3.4-15 and 3.4-13). While K would be a value experimentally determined, kp can be estimated from eqn. (3.4-97) with the external mass-transfer coefficient, km, estimated from the correlation of Stiiber et al. [25] or from that of Tan et al. [27], and the effective diffusivity from the Wakao Smith model [36], Typical values of kp obtained by fitting the data of Tan and Liou are shown in Fig. 3.4-16. As expected, they are below the usual mass-transfer correlations, because internal resistance diminishes the global mass transfer coefficient. These data correspond to the regeneration of spent activated carbon loaded with ethyl acetate, using high-pressure carbon dioxide, published by Tan and Liou [45]. 

The first hypothesis seems unlikely to be true in view of the rather wide variation in the ratio of carbon dioxide s kinetic diameter to the diameter of the intracrystalline pores (about 0.87, 0.77 and 0.39 for 4A, 5A and 13X, respectively (1J2)). The alternative hypothesis, however, (additional dif-fusional modes through the macropore spaces) could be interpreted in terms of transport along the crystal surfaces comprising the "walls" of the macropore spaces. This surface diffusion would act in an additive manner to the effective Maxwell-Knudsen diffusion coefficient, thus reducing the overall resistance to mass transfer within the macropores. 

Carbon dioxide at I5°C moves over a hot plate at 250°C, such that the convection heat transfer coefficient is 30 W/(m2.°C). If the heat transfer is 3 kW, calculate the area of the plate. 

Perez and Sandall (1974) studied the absorption of carbon dioxide in aqueous carbopol solution. The rheological behavior of the solution was described by the power law model with flow behavior indices varying from 0.91 to 0.59. For an agitated vessel with a turbine impeller, the mass-transfer coefficient across the unbroken interface was correlated as... 

Saturated steam at 100 lb/in2 abs is to be used to heat carbon dioxide in a cross-flow heat exchanger consisting of four hundred 1-in-OD brass tubes in a square in-line array. The distance between tube centers is j in, in both the normal- and parallel-flow directions. The carbon dioxide flows across the tube bank, while the steam is condensed on the inside of the tubes. A flow rate of I lb ,/s of CO at 15 lb/in2 abs and 70°F is to be heated to 200°F. Estimate the length of the tubes to accomplish this heating. Assume that the steam-side heat-transfer coefficient is 1000 Btu/h ft2 °F, and neglect the thermal resistance of the tube wall. 

Abstract—Gas-liquid interfacial areas a and volumetric liquid-side mass-transfer coefficients kLa are experimentally determined in a high pressure trickle-bed reactor up to 3.2 MPa. Fast and slow absorption of carbon dioxide in aqueous and organic diethanolamine solutions are employed as model reactions for the evaluation of a and kLa at high pressure, and various liquid viscosities and packing characteristics. A simple model to estimate a and kLa for the low interaction regime in high pressure trickle-bed reactors is proposed. 

While phase equilibria for the a-tocopherol/carbon dioxide system at high pressures have been studied by several authors [1-6], only a few measurements of dynamic viscosity [7], thermal conductivity [7] and mass transfer coefficients [3] were carried out. The present study of the interfacial tension in the a-tocopherol/carbon dioxide system at temperatures between 313 and 402 K and pressures from 10 to 37 MPa aims on the one hand at completing characterisation of this system and on the other at contributing to understanding interfacial phenomena in mass transfer processes. 

The reported study on gas-liquid interphase mass transfer for upward cocurrent gas-liquid flow is fairly extensive. Mashelkar and Sharma19 examined the gas-liquid mass-transfer coefficient (both gas side and liquid side) and effective interfacial area for cocurrent upflow through 6.6-, 10-, and 20-cm columns packed with a variety of packings. The absorption of carbon dioxide in a variety of electrolytic and ronelectrolytic solutions was measured. The results showed that the introduction of gas at high nozzle velocities (>20,000 cm s ) resulted in a substantial increase in the overall mass-transfer coefficient. Packed bubble-columns gave some improvement in the mass-transfer characteristics over those in an unpacked bubble-column, particularly at lower superficial gas velocities. The value of the effective interfacial area decreased very significantly when there was a substantial decrease in the superficial gas velocity as the gas traversed the column. The volumetric gas-liquid mass-transfer coefficient increased with the superficial gas velocity. 

Saada25 measured the gas liquid mass-transfer coefficients for absorption of carbon dioxide into NaOH solutions for cocurrent upflow. Goto et al.8 evaluated the liquid-gas mass-transfer coefficients for the desorption of oxygen from water into nitrogen in a 2.58-cm-i.d. glass tube packed with CuO-ZnO particles... 

FIG. 14-71 Overall mass transfer coefficients for carbon dioxide absorbed from air by IN caustic solution. Packing = 2-inch metal raschig and pall rings. Air rate = 0.61 kg/s m (450 Ib/hrTt ). To convert from Ib/hrfFto kg/s-m, multiply by 0.00136. To convert from Ib-moles/hr fR atm to kg-moles/s-m atm, multiply by 0.0045. [Eckert et al, Chem. Eng. Progr., 54(1), 70 (1958).]... 

The second generation of nonporous membranes was silicon based which displayed increased CO2 permeabilities. In 1965, Bramson et al. commercialized the first nonporous membrane BO [18]. Since the diffusion coefficient of oxygen and carbon dioxide in air is about four orders of magnitude higher than in blood, the gas side mass-transfer resistance was negligible. The major resistance to respiratory gas transfer was due to the membrane and the liquid side concentration boundary layer [19]. Though nonporous membrane BOs reduced blood damage, up to 5.5 m membrane surface area was often required to ensure adequate gas transfer rates. 

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