ACETYLATION OF CORN COB AND MANGO KERNEL KINETICS AND APPLICATION FOR NON -AQUEOUS ADSORPTION PROCESS

1.0INTRODUCTION

Oil is the life blood of any modern industrial society. It fuels the machineries and lubricates the wheels of the world’s production. It is one of the most important energies and raw material sources for synthetic polymers and chemicals worldwide (Hussein et al., 2008; Annunciado et al., 2005).

Whenever oil is explored, transported and stored and its derivatives are used, there is risk of spillage with potential to cause significant environmental impact (Hussein et al., 2008). Due to its destructive properties, once an area has been contaminated with oil, the whole character of the place is damaged and when it encounters something to cling to, whether it be a beach, a rock, the feathers of a duck or a bathers hair, it does not readily let go (Aynechi, 2004). Hence, pollution by petroleum oils affects sea life, economy, tourism and leisure activities because of the coating properties of these materials (Hussein et al., 2008). The adverse impact to ecosystems and the long term effect of environmental pollution call for an urgent need to develop a wide range of materials for cleaning-up oil from oil impacted areas especially as the effectiveness of oil treatment varies with time, the type of oil and spill, the location and weather conditions (Adebajo et al., 2003).

Huge amounts of agricultural wastes (corn cob and mango kernel) are produced in many countries of the world. However, only a fraction of these materials are reused. One of the features of these organic materials is that it can absorb by capillary forces an amount of oil and/or water greater than its own weight (Bodirlau and Teaca, 2009). In addition this natural material can be completely degraded in nature by biological, physical, chemical and

photochemical processes (Tronc et al., 2006). In the past two decades, the reuse of agricultural byproducts as oil sorbents has received growing attention due to their low cost and biodegradability (Adebajo et al., 2003). Most agricultural byproducts derived from plants such as bagasse, coir, kenaf, rice straw, sisal and saw dust have been investigated for oil spill cleanup application (Choi and Cloud, 1992). The main drawbacks of these plant- derived sorbents are a relatively low oil sorption capacity, low hydrophobicity and poor buoyancy compared to synthetic sorbents such as polypropylene (Bayat et al., 2005; Anunciado et al.,2005).

Once plant-derived sorbents are applied to saturated environments, preferential water sorption is favoured over the sorption of oil because the sorbents are generally hydrophilic in nature. A better understanding of the chemical composition of these natural fibers is necessary for developing natural fiber sorbents. Agricultural byproducts can be considered polymeric composites made up primarily of cellulose, hemicellulose and lignin (Kumar, 1994; Homan et al., 2000). These polymers make up the cell wall and are responsible for most of the physical and chemical properties exhibited by these materials (Bodirlau and Teaca, 2009). Agricultural byproducts have a well-documented problem of water sorption and lack of dimensional stability, due to associated hydroxyl functionality. These groups are abundantly available in all the three major chemical components of plant based materials and are responsible for their hydrophilicity (Bodirlau and Teaca, 2009).

Hydrophobicity (oleophilicity) is one of the major determinants of sorbents properties influencing the effectiveness of oil sorption in the presence of water. The effectiveness of the sorbents in saturated environments would be enhanced if the density of the hydroxyl functionality is decreased (Bodirlau and Teaca, 2009). This functional group (hydroxyls) is

the most reactive and abundant site in the cell wall polymers of the lignicellulosic materials. The hydroxyl functionality of these fibers can be reduced by chemical modification such as acetylation, methylation, cyanoethylation, benzoylation, acrylation and acylation (Hofle et al., 1978; Sun et al., 2004; Breitenbeck et al., 2007).

The acetylation reaction is one of the most common techniques used for hydrophobic treatment of lignocellulosic materials (eg. wood) by a substitution reaction of a hydroxyl group (hydrophilic) into an acetyl group (hydrophobic) as shown in Figure 1.1. This reaction is usually carried out by heating lignocellulosic material in the presence of acetic anhydride with or without catalyst (Rowel et al., 1994). Various catalysts have been used for enhancing the efficiency of acetylation reactions. Pyridine and 4-dimethyl amino pyridine (DMAP) have been commonly applied for acetylation for many years (Hofle et al., 1978). However, they are too toxic and/or expensive for commercial use. Sun et al., (2004), recently reported that acetylation of sugarcane bagasse with N- bromosuccinimide (NBS) as catalyst in a solvent-free system was a convenient and effective method. In addition, they claimed modified bagasse applied in oil-water system presented an enhanced oil sorption capacity exceeding that of commercial synthetic sorbents.

 

 

 

 

Source: Bodirlau and Teaca, 2009