Potassium hydroxide modified active carbon for adsorptive refrigerators
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Potassium hydroxide modified active carbon for adsorptive refrigerators Bronislaw Buczek · Eliza Wolak
Received: 15 May 2007 / Revised: 6 August 2007 / Accepted: 19 December 2007 / Published online: 9 January 2008 © Springer Science+Business Media, LLC 2008
Abstract Active carbon-methanol pair appears to be suitable for adsorptive cooling systems. The porous structure of commercial active carbon was modified by potassium hydroxide treatment at 750 °C. Such treatment develops the specific surface area of carbon, changes nature of its surface and significantly increases the heat of wetting. The applied way for active carbon modification gives possibility of modeling porous structure, character surface and heat effects of carbonaceous materials for adsorptive refrigerators. Keywords Refrigeration · Active carbon-methanol pair · Heat effects of adsorption Abbreviations CwA specific heat of methanol, J/g °C CwC specific heat of carbon, J/g °C E0 characteristic energy of adsorption, kJ/mol Q heat of wetting, J SBET specific surface, m2 /g Sme mesopores surface area, m2 /g W0 volume of micropores, cm3 /g VA volume of methanol used in the measurement, cm3 Vp volume of pores, cm3 /g dA density of methanol, g/cm3 dHK slit pore width, nm mC mass of carbon, g T increase of temperature, °C B. Buczek () · E. Wolak Faculty of Fuels and Energy, AGH-University of Science and Technology, 30-059 Cracow, Poland e-mail: [email protected] E. Wolak e-mail: [email protected]
1 Introduction Extensive theoretical and experimental work has shown that the application of carbon adsorbents for heat storage can be used in adsorptive cooling systems/adsorptive refrigerators utilizing closed thermodynamic cycles (Meunier 2001). The most interesting system is methyl alcohol and microporous carbon material pair (Leite et al. 2005; Wang et al. 2003). Because of its ability to selectively adsorb vapours and gases, extended internal porosity and large specific surface area, active carbon is a good solid adsorbent for storage of mass and energy (Marsh and RodriguezReinoso 2006). It is a significantly cheaper than, for instance, zeolites working in water vapour pairs. In addition, methanol is a very good adsorbate because it can work at temperatures considerably lower than 0 °C (melting point for CH3 OH = −94 °C) and its molecules are sufficiently small and easily adsorbed in microporous carbon systems. Methanol is more easily desorbed and its working pressure is always lower than atmospheric pressure, which allows for a rapid identification of any faults in a cooling system. The temperature of desorption of methanol from an adsorbent is considerably lower than for water vapour systems. For all these reasons the methanol-active carbon pair can be used for storage of food and medicines, ice production, in air conditioning systems and heat pumps (Wolak and Buczek 2005). Performance of an adsorbent in a thermodynamic system depends upon properties such as specific area, type and number of pores, adsorbent form and adsorption enthalpy of the adsorbat
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