Gas absorption rates in a stirred cell with plane interface in the presence of fine particles

Abstract

The rates of absorption of carbon dioxide into water and into 0.5 mol/L equimolar carbonate buffer solutions (containing varying amounts of arsenite) were measured in a stirred cell with plane interface in the presence of fine solids (activated carbon, kieselguhr and alumina). Experiments show that the absorption rate increases significantly when the activated carbon loading increases up to about 0.2 g/L and thereafter remains constant. No significant effects were observed for other solids. The results could be explained in terms of a "shuttle" mechanism where particles adsorb gas near the interface which is then followed by desorption (or reactions) in the bulk. At very high loadings (above 10 vol. %), the absorption rate decreased for all particles and this could be explained by the blockage of the interface and/or by the sharp increase in the suspension viscosity. ~~Les vitesses d'absorption du bioxyde de carbone dans I'eau et dans des solutions tampon de carbonate Cquimolaires de 0,5 mol/L (contenant difftrentes quantitts d'arsenite) ont CtC mesurtes dans une cellule agitCe avec une interface plane en prCsence de particules solides fines (carbone activC, kieselguhr et alumine). Les exptriences montrent que la vitesse d'absorption augmente de maniere significative lorsque le chargement en carbone activt augmente jusquh environ 0,2 glL, mais reste stable par la suite. Aucun effet significatif n'a CtC relevt pour les autres solides. Les resultats peuvent &re expliquts sous I'angle d'un mtcanisme de "navette" par lequel les particules adsorbent le gaz pres de l'i?terface, suivi d'une desorption (ou rkactions) dans le chargement.A des charges tres ClevCes (au-dessus de 10% en volume), la vitesse d'absorption diminue pour toutes les particules, ce qui peut s'expliquer par le blocage de I'interface ou I'augmentation tres nette de la viscosite des suspensions.

Effect of fine activated carbon particles on the rate of CO2 absorption

“…There it is assumed that the activated carbon or kieselguhr does not affect the reaction rate between C02 and the buffer solution, as discussed by Quicker (1983) and Quicker et al (1986a). Thus k , remains unaffected by solids addition but it can be varied by changing the arsenite concentration.…”

“…The reaction rate constant k , was calculated from the measured NaAsO, concentration and from the estimated ionization to AsO,-. Details of these calculations can be found elsewhere (Quicker et al, 1986a). When the Danckwerts model is used, the gas absorption rate per unit gas-liquid interfacial area, R , is given as:…”

Reactive NO absorption in aqueous FeII(EDTA) solutions in the presence of denitrifying micro-organisms

“…This suggests that the insoluble particles and microorganisms are primary responsible for the decrease in the NO absorption rates and that the composition/properties of the liquid phase is of less importance. Negative effects on mass transfer rates by inert particles have been reported in the literature [11][12][13][14]. A possible explanation is the adherence of the particles to the gas-liquid interface, which lowers the effective gas-liquid interfacial area available for gas absorption (vide infra).…”

“…These may affect the mass transfer of gasphase component to the liquid phase in various ways. Reductions in mass transfer rates have been reported due to a reduction of the gas-liquid interfacial area, a result of the presence of the suspended solids which (partially) adhere to the gas-liquid interface [12,13]. However, enhancement of mass transfer rates is also possible.…”

Fundamental Mechanism of Combined Sorption of Highly and Weakly Soluble Volatile Organic Compounds into Aqueous Slurries of Activated Carbon

“…Numerous studies relative to the effect of adsorbent particles in three phase absorption (Kars et al, 1979;Alper et al, 1980Alper et al, , 1981Alper et al, , 1986Quicker et al, 1989;Tinge andDrinkenburg, 1992, 1995;Kim and Pingel, 1989) showed that the addition of fine activated carbon particles enhance substantially the liquid side mass transfer coefficient k L whereas larger size particles have no significant or much less effect.…”