Effect of carbonization temperature on characterization and water vapor adsorption of coffee-shell activated carbon

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.

Surface Modification of Porous Carbon Nanomaterials for Water Vapor Adsorption

“…Water molecules begin to fill micropores of carbon nanomaterial. This result is consistent with the finite simplification model of the Do-Do adsorption model …”

“…Figure (b–d) shows the surface microstructure of carbon nanomaterials modified by SDBS. The results showed that the pore nanostructure of CCNMs is reduced by the modification process, compared with that in our previous work . The element composition and content of carbon nanomaterials obtained by EDS are shown in Figure S3.…”

“…The water vapor adsorption process of CCNMs is not only affected by surface functional groups and porous nanostructure, but also by adsorption temperature. The water vapor adsorption isotherms and finite simplified model fitting results of CCNM and SDBS-CCNMs at different adsorption temperatures are shown in Figure . It can be seen that the simplified model can fit the water vapor adsorption isotherm well.…”

“…Water vapor adsorption isotherms were calculated by breakthrough curve and adsorption capacity calculation formula of samples under different relative pressures. And water vapor adsorption isotherms were fitted by the finite simplification model of the Do-Do adsorption model . Furthermore, water vapor adsorption kinetic curve was calculated by measuring the breakthrough curve of the samples at a relative humidity of 70%.…”

“…Water vapor adsorption equilibrium data of SDBS-CCNMs was tested in a dynamic adsorption experimental system. The water vapor adsorption isotherm was simulated by the finite simplification model of the Do-Do adsorption model . The Clausius–Clapeyron equation was used to calculate adsorption thermodynamics of different samples.…”