Adsorptive Properties of Biobased Adsorbents
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Adsorptive Properties of Biobased Adsorbents LESZEK CZEPIRSKI∗ AND EWA KOMOROWSKA-CZEPIRSKA AGH–University of Science and Technology, Faculty of Fuels and Energy, 30-059 Cracow, Poland [email protected]
´ JOANNA SZYMONSKA Department of Chemistry, Agriculture University, 30-059 Cracow, Poland
Abstract. Water and methanol vapor adsorption isotherms for native and modified potato starch were investigated. For obtaining the best fit for the experimental data several models based on the BET approach was evaluated. The hypothesis that water is adsorbed on the starch granules at the primary and secondary adsorption sites as well as a concept considering the adsorbent fractality were also tested. It was found, that the equilibrium adsorption points in the examined range of relative humidity (0.03–0.90) were most accurately predicted by using a three-parameter model, proposed by Kats and Kutarov (1998). For methanol a good representation of experimental data was obtained using model proposed by Talu and Meunier (1996). Keywords: bio-based adsorbents, water and alcohols adsorption, BET model, fractal dimension
1.
Introduction
Parameters of isothermal equilibrium sorption process for food products are very important both from scientific and practical point of view. Carbohydrate biopolymers (like starch, cellulose, hemicellulose) easily and selectively adsorb water vapor from air, alcohols or organic vapors (Beery and Ladisch, 2001; Ladisch, 1997; Anderson et al., 1996). These biobased adsorbents containing different classes of chemical compounds are chemically heterogeneous. Moreover, they are also physically heterogeneous because of both crystallite and amorphous phases present in their molecules. In practice, the equilibrium data are necessary for calculating the parameters of processes like drying and packaging, which depend mainly on the product water activity. In many cases, the obtained isotherm can represent, with reasonable accuracy, the sorption data for the whole range of water activities. The aim of this study was to determine the water, methanol and ethanol sorption isotherms and to evalu∗ To
whom correspondence should be addressed.
ate the utility of various adsorption models for describing its sorption on potato starch granules. 2.
Material and Methods
The sample of native potato starch and samples modified by deep freezing/thawing process were used in this work (Szymonska et al., 2000; Krok et al., 2000). Water and alcohols vapour adsorption isotherms were measured volumetrically at 298 K using a device for simultaneous determination of isotherms and kinetic of adsorption (Ciembroniewicz and Komorowska-Czepirska, 1985). Before the experiment samples were outgassed at 343 K to residual pressure about 10−4 mmHg. 3.
Results and Discussion
The representative examples of water and alcohols sorption isotherm for potato starch granules are given in Fig. 1. Water isotherm belongs to the II type (according to the IUPAC classification) and describes the
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Figure 1.
Czepirski, Komorowska-Czepirska and S
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