Adsorption of Liquids and Swelling of Wood IV. Temperature Dependence on the Adsorption

Abstract

For the purpose of understanding the swelling phenomenon of wood in liquids, the contributions of enthalpic and entropic terms to the standard free energy change of adsorption have been determined by measuring the temperature dependence of adsorption isotherms. The values of standard enthalpy change of adsorption are smaller for alcohols having both proton-accepting and -donating properties than for acetone having only a proton-accepting property. The results are discussed in terms of the proton-accepting power and the cohesive energy of the respective adsorbate liquids. Methanol showed a larger isosteric heat of adsorption to dried wood than to pre-swollen wood, and the amounts of methanol and acetone adsorbed on dried wood exceeded those on swollen wood within the low activity range. These results indicate the presence of more exothermic sites in dried wood than in pre-swollen wood, and of pre-existing spaces and/or parts loosely hydrogen-bonded between wood constituents in the cell walls of dried wood. KeywordsAdsorption Organic liquids Temperature dependence Standard free energy change Standard enthalpy change Standard entropy change Isosteric heat Brought to you by |

Adsorption of Liquids and Swelling of Wood. Part VI. Saturated Amounts and Some Thermodynamic Values of Adsorption

“…In the present study, the adsorption of several organic liquids that were not examined in the previous paper (Morisato et al 1999b) onto pre-swollen wood samples are measured up to relatively high concentration ranges. The saturated amount of adsorption and the standard free energy changes of adsorption are determined by regression to the adsorption isotherms.…”

“…Using the equilibrium constant obtained by these regressions (Morisato et al 1999b), the standard free energy change of adsorption was calculated. The saturated amount of adsorption (n sa ) and equilibrium constant of adsorption (K) were used as parameters of regression.…”

“…Mantanis et al (1994aMantanis et al ( , 1994bMantanis et al ( , 1995 investigated the rate of wood swelling in water and various kinds of organic liquids, and discussed the results mainly in terms of the activation energy of swelling. Moreover, Morisato et al (1999a) determined the contributions of enthalpic and entropic terms to the standard free energy change of adsorption by measuring the temperature dependence of adsorption isotherms. Moreover, they investigated the relations between swelling rate and extractives, and concluded that a significant increase in the rate of wood swelling took place after removal of extractives.…”

“…Furthermore, in our previous papers (Ishimaru et al 1997a;Ishimaru and Morisato 1997;Morisato et al 1997Morisato et al , 1999a, the saturated amounts of adsorption of alcohols have been assumed to be equal to that of water, because alcohols may be considered to be adsorbed by the OH group similarly to water. In general, saturated amounts of adsorption are calculated based on the hypothesis that the molecule is spherical and that the molecules are closestpacked on the adsorbent.…”

“…Moreover, the standard free energy changes of adsorption have been calculated using the values of the saturated amounts of adsorption obtained in the study (Morisato et al 1999b). Their values were larger than the previous values for all the systems, although the order of the values among the liquids was the same as in the previous study: the values of standard free energy changes of adsorption were smaller for alcohols having both proton-accepting and -donating properties than for acetone having only a proton-accepting property.…”