A method for predicting the isosteric heat of gas adsorption on solid materials is developed which requires the measurement of a single isotherm - where previous methods, such as the Clausius-Clapeyron approach, require either multiple isotherms or complex calorimetric measurement. The Tóth potential function, stemming from the Polanyi potential function, is evaluated using the Langmuir and Tóth isotherm equations to generate new equations for the isosteric heat. These new isosteric heat equations share common parameters with the isotherm equations and are determined from isotherm fitting. This method is demonstrated in the literature for gas adsorption onto solid adsorbates including zeolites of various surface charge character and non-porous rutile phase titanium dioxide. Predictions are made using the new isosteric heat equations and then compared to calorimetric data.

We have developed two predictive methods for the heats of adsorption that stem from isotherm models and benchmarked them against the Clausius−Clapeyron equation. These are the Toth potential function model and the modified Clapeyron equation. Three adsorbate/adsorbent working pairs are used as examples: n-butane/BAX 1500 activated carbon, isobutane/BAX 1500 activated carbon, and ammonia/Fuji Davison type RD silica gel, all of which are examples of gas physisorption on adsorbents with both micro-and mesopores. Isotherms and corresponding integral heats of adsorption were measured in the range 298−348 K. For n-butane and isobutane, the pressures were up to 235 kPa, and for ammonia, the pressures were up to 835 kPa. Our two predictive methods consistently offer significant improvements over the Clausius−Clapeyron equation. Between the two predictive methods, the Toth model is more robust across all three working pairs studied with predictions generally falling within 10−15% of the values of the measured heats. ■ INTRODUCTIONMost gas adsorption data in the literature are presented as experimentally obtained isotherm measurements without measured heats of adsorption. This is presumably because adsorption experiments that incorporate calorimetry are more expensive and more complicated to both set up and operate than experiments based upon volumetric or gravimetric measurements alone. 1,2 However knowledge of the heat of adsorption can lend insight into surface phenomena. 3 Additionally thermal management is an integral part of the design and operation of systems which make use of adsorption phenomena such as adsorption chillers, 4,5 adsorbed gas storage tanks, 6 and adsorption separation units, 7 all of which require knowledge of the heat of adsorption.Conventionally experimentalists circumvent the dearth of calorimetric data by invoking the Clausius−Clapeyron equation, either through measuring many closely spaced isotherms and applying the equation directly to the data (to wit, the isostere method) 8,9 or by fitting the isotherm data with an isotherm model and then applying the Clausius−Clapeyron equation to the model. 10,11 The isostere method can lead to ambiguous results 1,2,12 particularly if the number of isotherms obtained is low, if the isotherms are widely spaced, or where the uncertainty in the isotherm measurement is high. Moreover even at moderate pressure (p < 1 MPa) the ideal gas assumption inherent in Clausius−Clapeyron can lead to large errors in predicting the heat of adsorption. 13 Theoretical models (e.g., refs 14−17) have been developed for this problem by using numerous isotherm models consistent with statistical mechanics and specific to various different adsorbate/adsorbent modes of interaction. However it remains a challenge to know which model to apply to get a correct prediction of the surface interactions and heat of adsorption without significant prior knowledge of the behavior of the adsorbate/adsorbent system. Savara et al. 18 developed a rigorous method for selecting between a number of 2...

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-Geothermal heat is a sustainable form of alternative energy, commonly associated with the production of electricity along tectonic plate boundaries and in volcanically active zones. Outside of these special regions however it is rare to find a geothermal gradient high enough to achieve pay back on projects for generating electricity. On the other hand regions containing sedimentary aquifers are far more common and these aquifers frequently have a sufficiently high temperature gradient to make direct use of the thermal energy attractive. Meanwhile highly permeable aquifers occurring at shallow depths are possible sources for cooling water or can be both heat sources and sinks when used in combination with heat pumps. We provide a case study for the use of thermally driven absorption chillers on the University of Western Australia campus in Perth and discuss two ongoing projects: one for the heating and cooling of the offices of the Australian Resources Research Council using a reversible heat pump and the other the climate control of the planned Australian International Gravitational Observatory.