Heat of sorption: A comparison between isotherm models and calorimeter measurements of wood pulp

Abstract

The paper introduces a method to validate heat of sorption measurements from isotherms by comparing them to direct measurements using reaction calorimetry. We have evaluated some frequently used single temperature isotherm models (BET, GAB) as well as two multi temperature isotherm equations (Anderson, Heikkilä). It turned out that the isotherm models with better isotherm curve fitting characteristics did not deliver the best results for the heat of sorption.Multi temperature isotherm models like for example the Heikkilä equation are able to deliver good results in terms of modelling the isotherm data and determining the heat of sorption. Single temperature models are fitting the isotherm data better than the multitemperature models, but failed to deliver correct values for the heat of sorption .We specifically investigated the heat of sorption at very low moisture content, which is most relevant for paper drying. The resulting heat of sorption curves were analyzed with respect to their saturation behavior which is expected to occur below BET monolayer Downloaded by [FU Berlin] at 13:45 07 July 2015 2 moisture. The heat of sorption from Heikkilä's model was the only one to show the expected saturation at very low moisture content.

Review on Self-Heating of Biomass Materials: Understanding and Description

“…The DHS can be determined directly by calorimetric measurement with various techniques, among which the one often used is to measure the heat of wetting and then calculate the DHS as the derivative with regard to the moisture content. − The DHS can also be determined indirectly by the isosteric method. It is based on the Clausius–Clapeyron equation to derive the DHS from the measured moisture sorption isotherms, the relationships of equilibrium moisture content via relative humidity for a material at two or more temperatures. ,, The calculated is also called net isosteric heat of sorption.…”

Influence of relative humidity on the strength of hardwood and softwood pulp fibres and fibre to fibre joints

“…Nevertheless, same as in the case of individual fibres, it is quite possible that different results would be obtained if the joints had been conditioned in a unrestrained state. It must be mentioned that differences in the cooking-, bleaching-or drying process have a large impact on the water sorption of pulp fibers at different levels of relative humidity (Leuk et al 2016). It can be expected that this will also affect the strength of the fibres and fibre-fibre joints.…”

Changes in the hygroscopic behavior of cellulose due to variations in relative humidity

“…This, hornification, in turn reduces the reactivity of pulp (Khanjani et al 2017;Nelson and Oliver 1971;Grethlein 1985) especially with repeated drying cycles (Leuk et al 2015) due to irreversible microfibril aggregation or 'stiffening of the lignocellulose matrix' (Hult et al 2001;Newman 2004;Suchy et al 2010a and2010b).…”