SOURCE:

Faculty: Physical Sciences
Department: Pure And Industrial Chemistry

CONTRIBUTORS:

Nwadiogbu, J.O
Ajiwe, V.I.E
Okoye, P.A.C

ABSTRACT:

Oil spills have caused significant environmental and ecological problems. Effective decontamination and cleanups are necessary after the spill for the protection of the environment and human health. Although there are currently many cleanup technologies, such as in situ burning and the use of chemical dispersants and sorbents (such as booms and skimmers), the development of environmentally friendly sorbents that have less logistic burden in usage and biodegradable are needed. In the past two decades, the reuse of agricultural byproducts as oil sorbents has received growing attention due to their low cost and biodegradability. The main drawbacks of plant-derived sorbents are: relatively low oil sorption capacities, low hydrophobicities, and poor buoyancy compared to synthetic sorbents such as polypropylene and polyurethane. In line with this, corn cob and mango kernel were modified by acetylation to increase their hydrophobic properties, thereby increasing their oil sorption capacities in aqueous environment. The amount of substrate and reactant were combined in the ratio 1:20 (g dried sorbent/ mL of acetic anhydride). The reaction temperature, time and amount of catalyst were varied between (303 and 403 K, 60 and 180 min and 1 and 4 %g/mL respectively) to optimize the process. Fourier Transform Infrared Spectroscopy (FTIR) was used to investigate the acetylation of corn cob and mango kernel such that the effects of time, temperature and catalyst were significant for corn cob and mango kernel acetylation. Kinetic analysis suggests surface and intra-particle diffusion mechanisms for corn cob acetylation at 30oC and 100oC and also 100oC for mango kernel acetylation. Thermodynamic models used enabled the evaluation of the following; heat of acetylation (0.029 Jmol-1) for corn cob and (0.8696 Jmol-1) for mango kernel, critical temperature (0.814 Kel) for corn cob and (0.016 Kel) for mango kernel, critical degree of acetylation (1.037) for corn cob and (1.977) for mango kernel, heat capacity (4.157 x 10-4 Jmol-1 K-1) for corn cob and (1.242 X 10-2 Jmol-1 K-1) for mango kernel, entropy changes (5.005 x 10-4 Jmol-1) for corn cob and (1.495 x 10-2 Jmol-1 K-1) for mango kernel. At studied temperature conditions values of Gibbs free energy were -0.123 Jmol-1 (303 Kel), -0.138 Jmol-1 (333 Kel) and -0.158 Jmol-1 (373 Kel) for corn cob acetylation while values for mango kernel acetylation were -3.66 Jmol 1 (303 Kel), -4.11 (333 Kel) and -4.71 Jmol-1(373 Kel). The optimum acetylation conditions in this study were found to be at 100oC for 180minutes using 1% catalyst for mango kernel and 100oC for 60minutes using 3% catalyst for corn cob. Characterization by X-ray diffraction indicated a slight reduction in crystallinity, suggesting that the structure of the materials have been transformed to amorphous structure after acetylation, as a result of the substitution of acetyl groups for hydroxyl groups, thereby reducing the hydrogen density of the materials. The water absorption capacity (WAC) studies gave the maximum values (3.28 and 2.86) for raw and acetylated corn cob respectively and (2.50 and 2.04) for raw and acetylated mango kernel respectively. These values confirmed that raw corn cob and mango kernel had their WAC reduced after acetylation indicating a considerable increase in hydrophobicity. The maximum oil sorption capacity for raw and acetylated corn cob were 2.03 g/g and 2.50 g/g respectively while sorption capacity for raw and acetylated mango kernel were 1.13 g/g and 1.34 g/g respectively. These results suggest that the treated materials are more effective in oil removal from aqueous environment suggesting that the application in non-aqueous adsorption processes like oil sorption and oil remediation in aqueous environments is promising.