Adsorption of Carbon Dioxide to Polysaccharides in the Supercritical Region

The adsorption isotherms for C0₂ to several polysaccharides were measured in a pressure range between 0 and 29.4 MPa by the gravimetric method. The adsorption of C0₂ to two kinds of starches (potato and corn) and to dextrin increased linearly with increasing pressure to reach a maximum, and then decreased sharply to constant level at higher pressure. These adsorption characteristics are similar to those of proteins reported previously. On the other hand, the adsorption of C0₂ to cellulose showed a high level at the beginning of the increase in pressure, without any significant change in the sub-critical pressure region, and then fell to the minimum before reaching a constant level at higher pressures. These adsorption characteristics of cellulose could be related to its micropore structure. The pressure at which the maximum adsorption occurred (P_max) was located on the P-T line of the C0₂ phase diagram where (dpfdP)_T was a maximum, this result being different from the Menon correlation of P_max = P_c(T/T_c)² proposed for adsorption to macroporous adsorbents.