Porosity development in carbons derived from olive oil mill residue under steam pyrolysis

Activated carbons were obtained from olive oil mill wastes (OMW) by a single-step steam pyrolysis process, under different conditions of heat treatment temperature (HTT = 873-1073 K) and duration of reaction (15-120 min). Porosity characteristics were determined from N-2 adsorption isotherms and subsequent analysis by the BET-and alpha(s)-methods. Development in the texture parameters was found to depend on both experimental variables. A two- step rate process of reaction is proposed to govern carbon activation: a slow external steam-carbon reaction (under mild conditions) removing disorganized material and is associated with considerable weight loss but with low generation of porosity. A second bulk gasification process dominates at high temperature, and/or prolonged duration, and leads to considerable evolution of porosity with minor change in burn-off. Pyrolysis/carbonization under the flow of steam is suggested to enhance removal of low molecular volatiles, retards decomposition of high molecular products, initiates controlled gasification at lower temperatures, and prevents shrinkage of the produced carbon skeleton. OMW seems to need severe conditions of temperature and duration to obtain good adsorbing carbons, or requires pretreatment to remove skin, flesh and seed contaminants.