ADSORPTION OF CARBON-DIOXIDE TO POLYSACCHARIDES IN THE SUPERCRITICAL REGION

The adsorption isotherms for CO2 to several polysaccharides were measured in a pressure range between 0 and 29.4 MPa by the gravimetric method. The adsorption of CO2 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 CO2 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 CO2 phase diagram where (partial derivative rho/partial derivative P)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.