Development of relationships between the inherent properties of raw coconut shells and the adsorption characteristics of coconut shell-based activated carbons

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Certain mineral elements are known to catalyze the carbonization and activation processes of activated carbon manufacture. This facility has been variously harnessed to shape the properties of activated carbons. In the past this has been done by applying the mineral elements externally on the precursor materials to influence the properties of activated carbons. It is known however, that some of the mineral elements affecting the properties of activated carbons are inherent to the raw material. If this were so then it would be possible to take advantage of their presence to affect the properties of activated carbons. In this case the additional time, resources and cost needed to externally apply these elements would be obviated. The extent to which this is possible has not yet been examined. In this work an attempt has been made to address this issue by first investigating if the relevant mineral elements occur in significant concentrations in precursor materials of plant origin to influence the carbonization and activation processes of activated carbon manufacture. It is further investigated if for a given precursor material variations in the concentrations of the mineral elements borne as a result of differences in the origin are significant enough to engender differences in the properties of activated carbons made from them. The work also sought to identify relationships, if any, that exist between the concentrations of the inherent mineral elements in the raw material and the properties of the activated carbons made from the precursor materials. For this study coconut shells from five different geographical locations of Ghana were selected. Subsequently the presence and the distribution of the elements potassium, zinc, copper, calcium, iron and lead were examined using Atomic Absorption Spectroscopy (AAS) and related to the iodine numbers of activated carbons made from the shells. An analysis of the adsorption characteristics of the activated carbons prepared in the setup built specifically for this work showed that the samples behaved in a manner anticipated of activated carbons. Thus, the set-up functioned successfully. Scanning electron micrographs (SEM’s) of the samples revealed that the earlier theories held about the mode of pore formation of activated carbons during their preparation is valid. Further results showed that the concentration of the mineral elements vary depending on the origin of the shells. It was established that the shells with lower potassium concentrations exhibited higher iodine numbers. Due to the very low inherent concentrations of the other elements studied, their individual influences were not immediately clear. Additional investigations conducted by externally influencing the mineral elements’ concentrations in the shells by soaking them in solutions of salts of the elements show that the elements, all to varying degrees, affect the iodine numbers of activated carbons. The results of this work show that it is possible to take advantage of the inherent concentration of potassium and other mineral elements in raw coconut shells to influence the adsorption properties of coconut shell-based activated carbons. Thus, the objectives set out for this work were to a very large extent achieved. It is recommended that further investigations be carried out to see if similar conclusions can arrived at for precursor materials other than coconut shells. It is further recommended that the effect of other mineral elements beyond those specifically investigated in this work be studied.
A Thesis Submitted to the Department of Chemical Engineering in conformity with the requirements for the Degree of Doctor of Philosophy, 2004