ACETYLATION OF SELECTED AGRICULTURAL WASTES KINETICS AND APPLICATION FOR OIL SPILL CLEAN UP

 

1.1Background of the study

Energy is the prime mover for all developed and developing nations. Crude oil is the major global source of energy. However, its exploration has resulted in serious environmental pollution ranging from air, water and soil pollutions. One of the main sources of water pollution is crude oil spill. The result of crude oil activities leaves most of our surface water heavily contaminated with several pollutants including dissolved and dispersed oils. These pollutants pose threats to aquatic animals and make our soil infertile. Oil spill over the oceans and seas requires prompt attention due to their environmental and economic impacts (Annunciado et al., 2005).

Whenever oil is produced, stored, transported, and used, there is a risk of spillage with the potential to cause adverse environmental impact (Hussein et al., 2008). The spilt oil eventually contaminates the food chain and affects our health. Therefore, spilled oil causes enormous environmental problems unless it is removed as quickly as possible (Sayed and Zayed, 2006).

Oil pollution, particularly of sea and navigable water has elicited more public concern than other waste or spilt material. Oil pollution of the sea has steadily increased with the increased oil production. The total annual influx of petroleum hydrocarbon is about

10 million metric tonnes. The bulk of this influx is due to transportation related activities, spillage from tanker uploading operation, pipeline rupture which may be due to industrial waste as leakage from engines, incorrect operation of valves and

discharge of oily waste (Hussein et al., 2009). Oil pollution of the shorelines in addition to the reduction of amenity, also affects marine, shore life and vegetation.

Crude oil consists of different hydrocarbons that range from a light gas to heavy solid. When oil spills on water, the physical and chemical properties of oil change progressively i.e. these physico-chemical changes enhance oil dissolution in sea water (She et al., 2010). This process is referred to as weathering which includes evaporation, dissolution, adsorption onto suspended materials, agglomeration e.t.c (Alade et al., 2011). The adverse impact of oil spill on the ecosystem and the long term effect of environmental pollution calls 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).

Large amount of agricultural waste (corn cob, corn husk, plantain peel, plantain pseudostem, bread fruit seed husk, borassus coir e.t.c) are produced in many countries of the world. However, many of these waste materials are not 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 it’ s own weight (Bodirlau and Teaca, 2009).

Furthermore, these natural materials can be completely degraded in nature by biological, physical, chemical and photochemical processes. (Tronc et al., 2006).

In small scale spills, oil can be removed with a sorbent. The sorbent in use today can be classified as either polymers, natural materials, or treated cellulosic materials. (Deschamps et al., 2003). Adebajo et al., (2003) recently reviewed the porous materials used for spill cleanup, and several studies of different natural, synthetic and

mineral sorbents have also been conducted (e.g Choi and Cloud, 1992; Deschamps

et al., 2003; Tease et al., 2001). Most recently used commercial sorbents are synthetic sorbents made of polypropylene or polyurethane (Tease et al., 2001). They have good hydrophobic and oleophilic properties, but their non-biodegradability is a major disadvantage (Choi and Cloud, 1992, Deschamps et al., 2003).

Since most oil products are biodegradable, oil could be disposed of for example by composting. A biodegradable material with excellent absorption properties would be advantageous in this respect. A number of natural sorbents have been studied for use in oil-spill clean-up e.g cotton (Choi and Cloud, 1992; Choi et al., 1993; Choi, 1996), wool (Choi and Moreau, 1993; Choi, 1996; Radetic et al., 2003), bark (Haussard et al., 2003, Saito et al., 2003), milkweek (Choi and Cloud, 1992, Choi , 1996) kapok,(Choi, 1996, Hori et al., 2000) kenaf (Choi and Cloud, 1992, Choi; 1996) barley straw (Ibrahim et al., 2009) olive waste (El-hamouz et al., 2007), rice straw (Sun et al., 2002). (Srinivasen and Viaraghvan, 2008), Most of them have better absorption capacities than synthetic ones, but they often sorb water well which is a disadvantage when used in marine environments (Wei et al., 2005).

Nwadiogbu et al. (2015) studied the equilibrium and kinetic studies of the removal of crude oil from aqueous medium by sorption on hydrophobic corncobs. They observed that the sorption process occurred via a surface reaction and intra-particle diffusion mechanism. They further reported that the maximum monolayer sorption capacities were 0.0768 mg/g and 0.0043 mg/g for the acetylated and raw corn cobs respectively.

Sun et al. (2004) esterified sugar bagasse with acetic anhydride using N- bromosuccinimide as a catalyst under mild condition. The acetylation increased hydrophobic properties of the bagasse obtained at 800C for 6 hours and was found to be 1.9 times better than the commercial synthetic sorbent.

Once plant derived sorbent are applied to saturated environments, preferential water sorption is naturally favored over the sorption of oil because the sorbents are typically hydrophilic in nature. Agricultural by-products have well documented problems with water sorption and lack of dimensional stability due to their associated hydroxyl functionality. These groups are abundantly available in all the major chemical components of plant-base materials are responsible for the hydrophilicity (Bordilau and Teaca, 2009).

The use of sorbents to clean-up oil spill presents many advantages due to simplicity of approach and the inexpensive nature of the materials (Chung and Vennosa, 2008). In addition, plant derived organic sorbents are biodegradable thus leaves no permanent residue. Agricultural by products can be considered polymeric composites made up primarily of cellulose, hemicelluloses 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 (Bordilau and Teaca, 2009).

Hydrophobicity (oleophilicity) is one of the major determinants of sorbent properties influencing the effectiveness of oil sorption in the presence of water. The effectiveness of the sorbents in natural environments would be enhanced if the density of the hydroxyl functionality is decreased (Bordilau and Teace, 2009). 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; Breitenbeck et al., 1997; Sun et al., 2004).

Acetylation reaction is one of the most common techniques employed for hydrophobic treatment of lignocellulosic materials (like wood) which involves a substitution reaction

 

of a hydroxyl group (hydrophilic) into an acetyl group(hydrophobic) as shown in figure 1.1.

 

 

O

 

R C

OH +

 

 

 

O   O

 

 

 

C

R + R-COOH

 

R C

O

 

lignocellulose anhydride modified lignocellulose acid

 

 

 

 

O O

O

OH + C O C       O C R COOH R

 

lignocellulose anhydride modified lignocellulose