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SCHKenFez http://blogs.law.harvard.edu/tech/rssAdsorption of Ethanol on Activated Carbon
http://fez.schk.sk/view/changeme:5230
Adsorption and desorption equilibria of ethanol were measured on two types of activated carbon: Supersorbon HS4 and Dezorex DB1 at temperatures −10ºC, 0ºC, 10ºC, and 20ºC. Experiments were performed within the range of relative pressures from 0 to 1. The analysis of equilibrium data con rmed adsorbed molecules interactions at lower temperatures and higher adsorbate concentrations. Relatively low values of adsorption heats suggest physical adsorption on homogeneous adsorption surfaces. From the modi ed Dubinin—Astakhov equation was found out the volume of micropores, in which the physical adsorption occurred; for activated carbon Supersorbon HS4 it was 350 cm3 kg−1 and for Dezorex DB1 340 cm3 kg−1. At higher relative pressures, capillary condensation occurred. During adsorption and desorption of ethanol on activated carbon a not signi cant hysteresis was manifested. The starting point of this hysteresis, at which capillary condensation of ethanol started, was estimated: AGr = 4.6 kJ mol−1, which corresponds to the values p/Ps from 0.12 to 0.15 at −10ºC to 20ºC for both activated carbons Supersorbon HS4 and Dezorex DB1.2010-01-07 09:40:54
Besedová, E.
og Bobok, D.
Diusion of Ethanol Vapours in Activated Carbon Particles
http://fez.schk.sk/view/changeme:5234
In adsorbers with a bed height equal to the diameter of activated carbon particles the course of stepwise adsorption of ethanol from a stream of air and the course of stepwise desorption of ethanol by a stream of air with a lower content of ethanol compared with adsorption or by a stream of pure air were examined. The stepwise measurements were performed at a concentration of ethanol in air ranging from 0 to 0.35 mol m−3, which corresponds to the concentration of ethanol on activated carbon from 0 to 4180 mol m−3. From experimentally measured data effective diffusion coefficients De were calculated for each adsorption and desorption step. The calculated values of De are ranging from 1.182x10−10 to 6.308x10−10 m2 s−1. These values are dependent on the adsorbate concentration. From experimental data also values of De were calculated for each time of the stepwise adsorption and desorption. These values were used for the determination of the dependence of De on the adsorbate concentration: De = −4.7424x10−21q3 + 5.6130x10−17q2 − 5.9684x10−14q + 1.7647x10−10 By comparison of the obtained values of the e ective di usion coecient with values calculated by models it follows that during the transport of ethanol in particles of activated carbon Supersorbon HS4 both Knudsen di usion and surface di usion are decisive.2010-01-07 09:48:00
Bobok, D.
og Besedová, E.
Error in the Estimation of Effective Diffusion Coefficients from Sorption Measurements
http://fez.schk.sk/view/changeme:5040
A gravimetric sorption method was employed for the estimation of effective diffusion coefficients of water in silica gel particles. Air with a certain concentration of water passed through an adsorber with a fixed bed of silica gel particles with a height equal to the diameter of a single particle. The adsorber was weighed at chosen time intervals. This method is based on the assumption of zero mass transfer resistance in the fluid phase surrounding the adsorbent particles. From the two- lm theory it follows that for the measurement conditions employed here, the maximum resistance in the fluid phase is 12.5 %. Hence, the resistance in the solid phase is loaded by a maximal error of 12.5 %. The total error of the estimated values of the effective diffusion coefficients is not greater than 40 %. The values of the effective diffusion coefficients obtained by the measurements of the stepwise adsorption and the values of the effective diffusivity obtained by the measurements of the stepwise desorption are within the range 0.90 x 10−10—2.1 x 10−10 m2 s−1. Data obtained in this way are in agreement with data published in the literature. Comparison of the estimated values of the effective diffusion coefficients with those calculated under the assumption that the water transport in silica gel particles takes place solely by molecular diffusion or by Knudsen diffusion demonstrates that the latter does not occur under the conditions investigated.2009-12-21 10:29:19
Bobok, D.
og Besedová, E.
Mechanism of Ethanol Vapours Diffusion in Particles of Activated Carbons
http://fez.schk.sk/view/changeme:5069
A gravimetric sorption method was employed for the estimation of effective diffusion coefficients of ethanol vapours in particles of activated carbons Supersorbon HS-4, Dezorex FB-4, Silcarbon SIL-15 Extra. The course of the stepwise adsorption of ethanol from a stream of air and the course of the stepwise desorption of ethanol by a stream of air with lower content of ethanol compared with that used for adsorption, or by a stream of pure air were examined. From measured data the effective diffusion coefficient De was calculated for each adsorption and desorption step. The calculated values of De were ranging from 4.06x10−11 to 1.42x10−9m2s−1 and the dependences of De on adsorbate concentration were found for all activated carbons. The transport of ethanol vapours in pores of activated carbons proceeds via combination of Knudsen diffusion and surface diffusion.2009-12-21 11:31:55
Bobok, D.
og Besedová, E.
Modelling of Gas Phase Adsorption on Activated Carbon. I. Experiment and Equilibrium Model
http://fez.schk.sk/view/changeme:5190
The course of breakthrough curve of acetone and cumene vapours mixture from a stream of nitrogen on a fixed bed of activated carbon Dezorex DB1 was measured at ambient temperature. During the process a competitive adsorption occurs, whereby acetone as the less adsorbing component was displaced by cumene. Mathematical models describing the course of equilibrium adsorption for isothermal and nonisothermal conditions were developed and used. The modified Langmuir isotherm for a two-component mixture was applied to describe the adsorption equilibrium. Experimental breakthrough curve was compared to the curves computed by equilibrium isothermal and nonisothermal models. The breakthrough point of acetone on a fixed bed of activated carbon of a length 12 cm occurred after 55 min of contact time. According to the equilibrium nonisothermal model and isothermal model the breakthrough time of about 80 min and 95 min was calculated, respectively. The model breakthrough curves are much steeper. It can be expected that after involving the resistance against mass transfer into the model the shape of the model breakthrough curves will not be so steep.2010-01-04 13:54:41
Besedova, E.
og Bobok, D.
og Bafrncova, S.
og Steltenpohl, P.