Abstract
The production of activated carbons (ACs) from rapeseed cake and raspberry seed cake using slow pyrolysis followed by physical activation of the obtained solid residues is the topic of this study. The effect of activation temperature (850, 900 and 950 °C), activation time (30, 60, 90 and 120 min) and agent (steam and CO2) on the textural characteristics of the ACs is investigated by N2 adsorption. In general, higher activation temperatures and longer activation times increase the BET specific surface area and the porosity of the ACs, regardless of the activation agent or raw material. Steam is more reactive than CO2 in terms of pore development, especially in the case of raspberry seed cake. The performance of the ACs in liquid adsorption is evaluated by batch phenol adsorption tests. Experimental data are best fitted by the Freundlich isotherm model. Based on total yield, textural characteristics and phenol adsorption, steam activation at 900 °C for 90 min and CO2 activation at 900 °C for 120 min are found as the best activation conditions. Raspberry seed cake turns out to be a better raw material than rapeseed cake. Moreover, AC from raspberry seed cake produced by steam activation at 900 °C for 90 min performs as well as commercial AC (Norit GAC 1240) in phenol adsorption. The adsorption kinetics of the selected ACs are best fitted by the pseudo-second-order model.
Highlights
Activated carbons (ACs) are widely used as adsorbents in the purification of waste streams.Phenols, acid dyes, pesticides and heavy metals are common pollutants in liquid waste streams, while the removal of VOCs, NOx and SOx is frequently the objective of air pollution control
Each solid residue was further converted to AC using physical activation
The burn-off, ash content and total AC yield are shown in Table 1 for the various activation conditions
Summary
Activated carbons (ACs) are widely used as adsorbents in the purification of waste streams.Phenols, acid dyes, pesticides and heavy metals are common pollutants in liquid waste streams, while the removal of VOCs, NOx and SOx is frequently the objective of air pollution control. Carbonization (pyrolysis) is usually performed between 400 and 850 ̋ C in order to remove considerable amounts of tar and volatile matter from the raw material, resulting in a solid residue with a relatively high carbon content and a preliminary porosity [2,3]. This raw porosity, is usually not developed enough for most AC applications, and additional activation to create new pores and/or to unclog and to widen existing ones is required
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