Abstract
Coffee shells, which are abundant in cellulose and lignin, are good raw materials to prepare activated carbon. In this paper, coffee shells were selected as raw materials for activated carbon preparation by KOH chemical activation. Influence of carbonization temperature on adsorption capacity of water vapor over activated carbon was researched. Thermogravimetric analysis was employed to select the scope of carbonization temperature. Activation energies of coffee shells pyrolyzed at different heating rates were calculated. Nitrogen adsorption/desorption isotherm and scanning electron microscopy (SEM) were adopted to characterize the activated carbon. And water vapor adsorption isotherms were simulated by the finite simplification model of Do-Do adsorption model. The results show that activation energies of coffee shells pyrolysis process with heating rates of 5, 10 and 20 K/min are 17.21, 18.01 and 57.52 kJ/mol, respectively. The optimal carbonization temperature of coffee shells is 923 K. The adsorption amount of water vapor can reach about 702.3 mg/g under experiment temperature of 298 K and relative humidity of 70%. The highest total pore volume and Brunauer–Emmett–Teller (BET) specific surface area are 1.41 cm3/g and 2817 m2/g, respectively. The simulation results of the finite simplification model are consistent well with water vapor adsorption experiment results. The results show that activated carbon prepared at the optimal condition would be the potential candidate for solar drying system.
Highlights
Water vapor is one of the most common substances in nature, and its chemical classification belongs to inorganic substances composed of hydrogen and oxygen elements (Robert, 2001)
The coffee shells are mainly composed of cellulose, hemicellulose and lignin
It is known that pyrolysis temperature ranges of hemicellulose, cellulose and lignin are 493–598 K, 583–673 K and 373–1173 K, respectively (Yang et al, 2007)
Summary
Water vapor is one of the most common substances in nature, and its chemical classification belongs to inorganic substances composed of hydrogen and oxygen elements (Robert, 2001). Solid drying dehumidification which mainly depends on choice of adsorption materials is one of solar drying methods (Wang et al, 2013; Zheng et al, 2014). Used adsorbents are silica gel (Liu et al, 2017), molecular sieve (Wei et al, 2013) and activated carbon (Tso and Chao, 2012). Silica gel is utilized diffusely in thermal energy storage (Yu et al, 2014), extraction of water from air (Bar, 2004; Wang et al, 2017), adsorption heat transformation (Gordeeva et al, 2013) and solid desiccant cooling systems (Wang et al, 2009; Zheng et al, 2014). Its physical and chemical stability is strong and activated carbon is insoluble in water and most other solvents, which make it suitable for solar energy drying system
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