Biofuel From Oil Palm and Palm Oil Residues
Biofuel From Oil Palm and Palm Oil Residues
|Biofuel from Oil Palm and Palm Oil Residues|
By: Professor Dr. Nor Aishah Saidina Amin, Mailin Misson, Wan Nor Nadyaini Wan Omar, Siti Eda Eliana Misi, Roslindawati Haron, Mohd Fadhzir Ahmad Kamaruddin.
Concerns over environmental problem and diminishing supply of fossil fuels have intensified the search for alternative source of energy (Je-Lu et al., 2008, 2004; Sensoz and Angin, 2008; Aho et al., 2008). In the current situation, oil prices are volatile while supplies are unstable. Besides its vulnerability in energy supply and demand, the world is still depending on petroleum for the main source of energy. An alternative and renewable energy source is eminent to solve the current issues of over dependence on fossil fuels for energy. One such solution is to process agricultural residues as an energy source as it produces energy with lower greenhouse emissions than fossil fuel sources (Dermibas, 2008).
The term biofuel is referred to liquid or gaseous fuels for the transport sector that are produced from renewable sources such as vegetable oil and biomass (Dermibas, 2007). The interests in the biofuels production are due to energy security reasons, environmental concerns, foreign exchange savings, and socioeconomic issues related to the rural sector. Biofuel offers several advantages to the environment and sustainability (Pupan, 2002).
Over the last few decades, the Malaysian palm oil industry has grown to become a very important agriculture-based industry. The oil palm, (Elaeis guineensis) originated from West Africa is able to grow up to 20m tall (Sumathi et al., 2007). Currently, Malaysia has become the world’s largest producer and exporter of palm oil, replacing Nigeria as the chief producer since 1971 (Yusoff, 2006). Its production accounts approximately 40-60% of the total world palm oil production over the last 25 years. As a result, Malaysia generates a huge quantity of residues in the form of palm oil and oil palm biomass.
They are three potential feedstocks for biofuel production including crude palm oil (CPO), waste cooking oil (WCO) and palm oil-based fatty acid mixture (FAM) (Chew and Bhatia, 2008). As shown in Figure 3.1, there are two methods to convert palm oil into biofuels: (1) transesterification of palm oil to produce methyl or ethyl esters (biodiesel), and (2) catalytic cracking of palm oil to lower molecular hydrocarbon products (Twaiq et al., 1999; Yean-Sang, 2004). The hydrocarbons produced from palm oil are low in nitrogen and free from sulfur (Tamunaidu, 2006). However, only WCO and FAM are appropriate for energy production to avoid the controversial issue involving energy production from food sources.
Besides, Malaysia also generates huge quantity of oil palm biomass including oil palm trunks, oil palm fronds, empty palm fruit bunches (EPFB), shells and fibers. It was reported the oil palm industry generate 9.66, 5.20 and 17.08 million tons of fibre, shell and empty fruit bunches, respectively, in the year 2005 (Chew and Bhatia, 2008). Biomass forms about 90% of the whole palm tree, while the remaining 10% would be the palm oil. There are several available processes which can convert biomass to the higher-value commodity chemicals and fuels as summarized in Figure 3.1. It includes biomass gasification, pyrolysis and liquefaction followed by catalytic upgrading.
Figure 3.1 Processing steps in converting palm oil and oil palm biomass to biofuels
The production of biofuel from biomass such as cotton stalk (Je-Lu et al., 2008), wheat grass, beech wood (Dermibas, 2007), EPFB (Mansor et al., 2008, Ani et al., 2000) has been widely reported. Being the largest oil palm producer, EPFB is produced in huge quantities in the oil palm industries. The EPFB can be converted into biofuel via pyrolysis technology before being upgraded to higher quality oil. The steps for the production of higher value-added products from EPFB are illustrated in Figure 3.2.
Figure 3.2 Process for conversion of EPFB to value-added chemicals.
EPFB consists of three major components, namely cellulose, hemicellulose, and lignin (Runcang et al., 1999). Due to the crosslinking, lignocellulosic materials are insoluble in all solvents and are hardly degraded at typical biomass pyrolysis temperature (300-500 °C) (Aguado et al., 2006, Boateng et al., 2006, Lappas et al., 2007). One of the most promising alternatives is for the raw materials to be chemically or biologically pretreated before thermo-chemical conversion or pyrolysis takes place. The pretreatment of EPFB is able to degrade the lignin structure and cleave the chains to produce important chemicals during pyrolysis.
Pyrolysis is generally a thermal degradation process in the absence of an externally oxiding agent. Pyrolysis products consist of bio-oil (condensable gas), synthetic gas (non-condensable gas), and char (Boateng et al., 2006). Modern pyrolysis process uses zeolite catalysts which have shown excellent performance as solid acid cracking catalysts due to their higher selectivity (Tamunaidu and Bhatia, 2007; Leng et al., 1999). Zeolite catalysts, due to their shape selectivity, thermal stability and easy separation from the products and possibility of regeneration of deactivated catalysts have been widely used in the field of petrochemistry (Chaube, 2004).
The use of vegetable oils (i.e. WCO, FAM, palm, soybean, peanut and olive oil) and animal oils (i.e. beef tallow) however, would facilitate the production of biodiesel. Transesterification is the most common way to produce biodiesel as shown in Scheme 1 (Marchetti et al., 2007). However, when the amount of free fatty acid in the feedstock exceeds 0.5%, side reaction of direct esterification will inherently take place (Scheme 2).
Scheme 1 Transestrification reaction
Scheme 2 Esterification reaction
Esterification can be homogenously or heterogeneously catalyzed to improve the yield. Heterogeneous catalysts are present in different phases from the reactants, usually in solid forms and the reactants are in liquid or gaseous phases whereas homogeneous catalysts are in the same phase with the reactant. In heterogeneous production, several type of heterogeneous catalyts such as earth metal oxides, various alkaline metal compunds supported on alumina or zeolite can catalyze transesterification reactions (Liu etal., 2007). Previous studies reported that these catalysts have been found to be efficient heterogeneous catalysts for transesterification of vegetable oil. Alkali metal compounds supported on alumina or zeolite are found to be expensive catalyst and complicated to prepare, which limited their industrial application (Xie et al., 2007). Conversely, the metal oxide is a good solid base catalyst for high biodiesel yield (Jittputti et al., 2006).
The activity among alkaline earth oxide catalysts is in the order of: BaO > SrO > CaO > MgO. Based on this order of activity the better catalyst is BaO. However, BaO is not suitable for this process since it is noxious and can be dissolved by methanol. Hence, SrO is the more probable choice for the heterogeneous biofuel process. Super acid catalyst such as sulphated zirconia, SO42-/ZrO2 has also been used as heterogeneous catalyst. It is capable of producing high yield of alkyl esters (Furuta et al., 2004), and can be easily separated from the product (Liu et al., 2007). According to Kiss et al. (2006), SO42-/ZrO2 also has great environmental advantage including low corrosion and no acid waste problems.
The objective of this chapter is to investigate the potential of oil palm and palm oil wastes in the production of biofuel. Empty palm fruit bunch (EPFB), waste cooking oil (WCO) and palm oil-based fatty acid mixture (FAM) were used as a feedstock. In short, this study presents methods to utilize palm oil wastes as a source of renewable energy to reduce green house gas emission and ultimately, global warming.