The production of bio-fertilisers and bio-composts is an environmentally friendly way of overcoming the disposal problems of organic wastes especially OPW which are in abundance. The innate fabric of the fibres of OPW is tough and hence very difficult to decompose. However, recent researches have come out with different effective ways of composting and preparing bio-fertilisers from these wastes via enzymatic and chemical means. Most often, PKC is used to enhance the fibres’ decomposability due to their good nutrient contents for making fertiliser. PKCs consist of 6.0% P2O2, 11.0% K2O, 13.5% CaO, 3.5% MgO and 7.5% SO2 (Mohammad et al. 2012). An experiment to investigate the growth of palm oil seed­lings using the same quantities of bio-fertiliser from PKC, normal chemical fertiliser and a control (no fertiliser application) gave frond lengths of 62.03 cm, 53.42 cm, and 28.85 cm, respectively. The petiole dry weights recorded were 0.30 g, 0.25 g, and 0.28 g, respectively (Henson and Dolmat 2003). This clearly shows the high prefer­ence of bio-fertiliser from PKC for healthy plant growth. The overall nutrient con­tents of OPW fibres and PKC make them appropriate for the preparation of bio-fertilisers and bio-composts which many studies have reported (Mohammad et al. 2012; Baharuddin et al. 2009).

POME is also commonly blended with other OPW fibres for composting and fertilisers. Kala et al. (2009) have tested the potency of blending OPT, EFB and OPF with POME for compost to be highly effective. OPT (with POME 4:1 w/w) was found to exhibit properties of a very good compost as potting media for ornamental plants. However, POME alone has been efficiently used for making fertilisers or composts (Siregar et al. 2002) through optimised solid-state fermentation with ther­mophilic fungus, Chaetomium sp. (Yaser et al. 2007).

The fibres from OPW have also been used individually for making composts. EFB is bulky; thus, in order to reduce its bulkiness and make it easier to handle, they are compressed into mats usually called Ecomat (Sung et al. 2010). Ecomat is also found to improve the decomposition rate of the wastes hence producing efficient compost. EFB has fertiliser contents (expressed in kg/ton EFB) of 3.8 kg urea, 3.9 kg rock phosphate, 18.0 kg muriate of potash and 9.2 kg kieserite (Singh et al. 1999) whilst OPF contains 4.4 kg of kieserite, 19.3 kg of muriate, 2.8 kg of rock phosphate and 7 kg of urea/ton (Sung et al. 2010). Compost made from EFB with Trichoderma sp. and supplemented with nitrogen has proven to be of same nutrient values and biode­gradability as compared to chicken manure when they were tested on tomato plants (Mukhlis 2006). Pruned OPFs that are used as mulch as well as for soil conservation in the plantation are found to contribute directly to the supply of phosphates and indirectly by reducing the phosphate sorption capacity in soils (Fairhurst 1996).

Nowadays, the efforts on finding new catalysts for biodiesel production are pro­gressing intensively. Different types of catalysts are produced and studied in order to maximize biodiesel yield and at the same time minimize catalyst use without sacrificing their catalytic performance.

The research and development on catalysis are expanding at an extensive rate, mainly to ensure that the process can achieve high productivity in shorter time. Traditional raw materials that are commonly used at industrial scale consist of edi­ble sources that are valuable as food supply, such as soybean and canola.

Further implementation of these sources for biodiesel industry can lead to competi­tion in food sector, which may result in deficiencies of food supply for human con­sumption. Nonedible oils from alternative feedstocks are being recognized as a feasible solution to this matter. However, the process involving nonedible sources requires additional steps for refining purpose. Furthermore, the feedstock can account for up to 85% of the cost for biodiesel production (Canakci and Sanli 2008). It is essential to choose feedstock with lower price when considering the competitiveness of biodiesel with petroleum-based diesel fuel. Waste cooking oil is an attractive feed­stock as it can be acquired at low cost, but it contains FFA and water that are undesir­able for the reaction, especially for the process involving base catalyst.

Homogeneous catalyst can drive the reaction forward in a short period as the cata­lyst is in homogeneity with other reactants. The cheaper price also contributes to the broad use of liquid catalyst for biodiesel synthesis. However, the nature of the catalyst makes the separation of biodiesel from reactants harder. Separation of catalyst proceeds by washing with water, which generated wastewater during the purification step. Also, the catalyst is seldom recovered and recycled. Heterogeneous catalyst requires harsher operating conditions, such as elevated temperature, high alcohol to oil molar ratio, and extended reaction time to increase the biodiesel output. This type of catalyst faces mass transfer limitation of oil-alcohol-heterogeneous catalyst (three-phase system) in the initial stage of the reaction. Another problem related to heterogeneous catalyst is leaching of catalyst into reactants, which will then affect its catalytic activity. Regardless of that, solid catalyst is recovered easier at the end of the process and more suitable for continuous process as it can be placed in fixed bed reactor.

Alkaline catalyst such as NaOH and KOH is excellent for catalyzing conversion of triglycerides into biodiesel. The reaction proceeds at faster rates with high FAME yield compared to acid catalyst. A drawback associated with alkaline catalyst is its intolerability towards high FFA and water content, especially involving nonedible feedstocks. The contact between the catalyst and FFA leads to formation of soap, while hydrolysis of FAME generates more FFA during the process. Acid catalyst can put up with feedstock of high FFA content, as esterification takes place and produced alkyl esters. This benefits the production of biodiesel from low-cost lipid sources, and acid catalysts can simultaneously catalyze esterification and transesterification.

Despite its resistance towards high amount of FFA, the acid catalyst is less pref­erable to alkaline catalyst because of its inferiority in terms of reaction times due to the difference in the chemical pathway of the reaction, where alkaline catalyst fol­lows a more direct route for nucleophilic substitution (Lotero et al. 2005). Furthermore, its corrosiveness behavior towards equipments and pipelines at ele­vated temperature is also problematic.

Ionic liquids combine the benefits of homogeneous catalyst (i. e., same phase with the reactants) and heterogeneous catalyst (i. e., easier recyclability) for bio­diesel synthesis. High yield and conversion can be achieved by manipulating the combinations of cations and anions to produce suitable catalysts. They are excellent in catalyzing the reaction, especially Brqrnsted acidic ionic liquids, and the perfor­mance is also up to par when compared with conventional homogeneous catalysts. A gap that must be addressed to enable the deployment of ionic liquids for industrial scale biodiesel production is its cost, which is too expensive and several times higher than conventional homogeneous catalyst. Efficient methods for reclaiming ionic liquids have to be identified in order to overcome the barrier related to its cost. Separation involving thermal application is quite unsustainable when the amount of energy required to generate heat is taken into consideration, while supercritical extraction using carbon dioxide needs to be operated at high pressure to enhance the separation efficiency. There is lack of study on alkaline ionic liquids for the trans­esterification process at the moment, and also the mechanism on how cations and anions react with triglyceride source to catalyze the conversion is still deficient.

The ability of ionic solids in catalyzing chemical synthesis is promising, particu­larly for biodiesel-related process. The hybridization between cations of ionic liq­uids and anions of Keggin-POM heteropolyacids produced solid catalysts that are able to enhance the transesterification reaction, owing to functional ions that can be modified according to the specific processes. They also have high thermal resistance due to the strong ionic bond between the ions. In-depth study on ionic solids as cata­lyst for transesterification or esterification reactions is required to verify its viability in the process. The optimum operating conditions are yet to be determined, and information on the leaching of the catalyst into the reactants is also missing.

To overcome the drawbacks on conventional method in producing biodiesel, the advancement in novel process is progressing rapidly. The introduction of technolo­gies such as ultrasonic irradiation, microwave irradiation, and reactive distillation allows the reaction to reach completion in shorter time. The application of microwave — assisted transesterification is faster than conventional transesterifica­tion, but the scale-up of this technology is difficult.

Reactive distillation allows the reaction and separation of reactants in the same distillation column and can potentially reduce the capital and investment cost if implemented at a larger scale. Further studies need to be conducted to identify new novel processes that have the capability to produce biodiesel effectively at moderate operating conditions without sacrificing the yield and conversion.

The enzyme leakage of alginate/K-carrageenan beads containing cross-linked lipase was compared to that of lipase entrapped in same hybrid matrix without cross­linking by modifying the method of Wu et al. (2007). Both the types of beads were incubated at 25°C, 200 rpm in 0.01 M phosphate buffer of pH 7 soon after bead formation. The enzyme leakage was done by withdrawing the buffer every 1 h and recording the absorbance at 280 nm using a UV-vis spectrophotometer.

The enzyme leakage from immobilized lipase with and without glutaraldehyde cross-linking is plotted against time and is shown in Fig. 12.5a. It was observed that 65.76% reduction in enzyme leakage was observed from the hybrid beads after cross-linking as compared to that from non-cross-linked beads. Thus, it is under­stood that cross-linking with glutaraldehyde followed by entrapment in hybrid matrix can significantly reduce enzyme leakage. The reasons for the reduced enzyme leakage can be attributed to the increased molecular weight of the cross — linked enzyme and efficient interaction of enzyme moieties with the polymers of alginate and K-carrageenan.

Biomass can be gasified at high temperatures or low temperatures. The biomass undergoes partial oxidation resulting in gas and charcoal production. Then, the charcoal is finally converted into H2, CO, CO2, and CH4. This conversion process can be expressed as

Biomass + heat + steam ^ H2 + CO + CO2 + CH4 + hydrocarbons + char + etc. (4.4)

Hydrothermal gasification processes have currently been investigated both for waste treatments process and production of energy and valuable materials from bio­mass and organic wastes. The supercritical water gasification (SCWG) process has advantages compared over conventional gasification processes such that higher gas­ification efficiencies are achieved at much lower temperatures of ~400°C (Calzavara et al. 2005; Youjun et al. 2012). At supercritical conditions, a fluid is neither liquid nor gas as it cannot be made to boil by decreasing the pressure at constant tempera­ture, and it would not condense by cooling under a constant pressure (Saka et al. 2006). Under supercritical condition, with temperature and pressure above its criti­cal point (T> 374°C and P > 22.06 MP), water acts as a reactive medium due to its specific transport and solubilization properties. In these conditions, water of liquid state undergoes significant changes in its physical properties: decreasing in the dielectric constant, thermal conductivity, and viscosity while the density only decreases a little. Thus, supercritical water acts as a nonpolar solvent of high diffu — sivity and high transport properties and able to dissolve many organic compounds and gases.

Study area. The study area is comprised of the palm oil mills at Sabah, Malaysia. Availability of oil palm biomass (EFB, empty fruit bunch) at Sabah is 943,401 ton/ year (dry weight).

Sample collection. The study was conducted during the year 2011-2014, and the EFB is to be collected in round the year from the outlet of some selected palm oil industries located in Sabah industrial zone, Malaysia. During the research, the fol­lowing physical and chemical methods can be done to produce the desire ethanol production for palm oil.

Method. Thorough literature survey has revealed that the biomass(EFB) from palm can be transformed into bioethanol by three main methods: (1) chemical (2) semi­chemical, and (3) purely biochemical/enzymatic transformations (Fig. 7.1). In the literatures, it has already been proved that the adopted methods for bioethanol pro­duction are not free from restraints. Some methods are polluting the environment and the products, some are high cost and less productive, and some are proved to be inconvenient technologically. However, we have to search a newer method that can

Fig. 7.1 Flow chart of physical-chemical treatment process

minimize the production cost, keep the environment fresh, and above all make the yields of biofuels higher.

In order to do that, sample should be pretreated by some physical methods to remove the unwanted materials from the EFB. In this stage, care should be taken so that the cellulosic materials remain unaltered; its constituents and fungal deteriora­tion should be avoided. Breaking down the pure cellulosic materials into sugar chain could be done by the diluted H2SO4. This diluted H2SO4 could repeatedly be used by making its pH suitable after removal of water by evaporation. Biotransformation or enzymatic degradation will be costly and time consuming in this stage, so this process is not encouraging. Other known discrepancies to conduct the enzymatic method may make this step handicapped.

After treatment with dil. acid, sugar-containing mass could be treated by two methods into biofuels: (1) chemical treatment by non-pollutant and reuseable cata­lyst like Pd or Rh with some mild oxident or hydroforming agent. So, the catalyst could work in increasing the cetane number of the biofuels and at the same time convert the sugar unit successfully into biofuels. In this case, we have to keep sharp eyes on Pd catalyst that may contain some water-soluble ligands so that its activity in water will increase. Using of palladium metal to different chemical transforma­tions has already been proved effective in the era of cost, mildness toward the envi­ronment, and above all its reuseability with 100% efficacy. So, this method deserves a rigorous trial to make it standard for this valuable transformation.

Another important method could be implied on the sugar-containing mass by solid-supported enzymes/microorganisms. Although this method is very tough in selecting the microorganisms, it still deserves huge demand in making contaminant — free biofuels. Because immediate transformation of sugars into ethanol could be separated from the solid-containing microorganisms by modern equipped sieves. With rigorous trial and right choice of the microorganisms or enzymes/yeasts, the project could be successful. But selection of the best microorganisms or enzymes, preservation of the enzymes alive or effective throughout the reaction, is very diffi­cult task in this method. Owing to these drawbacks, this method still keeps huge demand in the research of renewable energy source from biomass.

7.2 Conclusion

Bioethanol can be obtained from different vegetable oils. The most common ones are soybean oil, rapeseed oil, and sunflower oil. Vegetable oil represents 95% of the raw material utilized in the process. This project is based on the production of bioethanol-used EFB of palm oil in Malaysia.

Malaysia can be a pioneer in lignocellulose-ethanol technology using EFB as a resource by integrating a bioethanol plant near palm oil mills. This new industry can generate various spin-offs beneficial to the country. Independent palm oil processing mills would be expected to be the main contributors of EFB as they do not have plan­tation to decompose the EFB residues generated from their mills. The development of a bioethanol demonstration plant has to overcome barriers related to the supply chain. This can be done through educational campaigns on the benefits of a renew­able energy industry.

There are two main advantages of locating the production plant in Malaysia. Firstly is that Malaysia is the world’s largest producer and exporter of palm oil. This represents an enormous advantage in terms of availability or raw material. Malaysia’ neighbor, Indonesia, with growing plantation acreage, enhances the availability of feedstock. The second advantage is the palm oil price compared to other vegetable oil price, such as soybean and rapeseed oil, is historically and statistically lower by an average of 20%. Since 90% raw material utilized in the process is vegetable oil, a 20% advantage in the price translates directly into an advantage of the same pro­portion in the cost of production of the finished products. Moreover, overhead cost, in particular personnel cost, is substantially lower in Malaysia compared to Europe and USA, where the main production and consumption of bioethanol take place.

The utilization of palm oil (EFB) for bioethanol production is to be undoubtedly a sustainable and eco-friendly approach for renewable biofuel production. As the importance of bioethanol production is growing, an equal or more attention is needed for the efficient use of this easily cultivable feedstock to generate the green fuel bioethanol.

Advantages of Bioethanol

• The price of bioethanol-petrol fuels will be kept reasonably low due to govern­ment subsidies and lower taxes in order to encourage the use of a cleaner petrol alternative, assuming public interest is sufficient to create a significant market in the UK for bioethanol- and alcohol-fuelled cars.

• Bioethanol produces only carbon dioxide and water as the waste products on burning, and the carbon dioxide released during fermentation and combustion equals the amount removed from the atmosphere while the crop is growing.

• It is a renewable source.

• Can be used as an additive with petrol and water.

• Has a greater thermal efficiency due to a higher octane rating allowing greater compression ratios.

• The price of bioethanol should be kept relatively low as governments encourage the use of more eco-friendly fuels.

Zhu et al. (2006) reported the high catalytic activity of heterogeneous solid super base CaO catalyst in the production of biodiesel from Jatropha oil. By using solid base catalyst, 93% of oil conversion was obtained within 2.5 h at 70°C, catalyst dos­age of 1.5% and methanol/oil molar ratio of 9:1. However, extra purification step was performed by using decalcifying agents (citric acid) to eliminate the remaining calcium species in biodiesel.

Besides, similar study using CaO was done by Taufiq-Yap et al. (2011a). The stability between single metal CaO and bimetal calcium-based oxides was inves­tigated via methanolysis of Jatropha oil. He and his co-researchers found that calcium-based mixed oxides catalysts (CaMgO and CaZnO) are able to produced high yield of biodiesel under mild condition with stronger stability. In optimum environment, more than 80% of biodiesel content was yielded at 65°C, catalyst amount of 4 wt%, methanol/oil ratio of 15 and 6 h reaction time. The result revealed that calcium-based mixed oxides rendered more feasible reaction than bulk CaO, this was due the drop of CaO catalytic activity throughout six cycles. This phenomenon was due to the leaching of active Ca2+ into the reaction medium and reacted with FFA content and resulted soap formation. Furthermore, the study was furthered by examining the optimum stoichiometric ratio between bimetal (Ca:Mg) catalysts in order to achieve maximum transesterification activity Taufiq — Yap et al. (2011b). A reaction model was design by using response surface meth­odology (RSM) to search for optimum condition in biodiesel mass production (Lee et al. 2011).

Endalew et al. (2011) tested the mixture of metal oxide catalysts in the simulta­neous esterification and transesterification of high FFA Jatropha oil in single-step reactions. According to Bender (1960), transition metal oxide catalysts are found to tolerate with high acid and water content, which are able to perform esterification and transesterification simultaneously. On the other hand, the presence of Lewis base and acid catalytic sites in amphoteric metal oxide catalyst is able to perform single-step esterification and transesterification reaction. Thus, the rare earth metal oxide catalysts loaded on transition metal oxide (La2O3-ZnO), amphoteric oxide (La2O3-Al2O3), and perovskite catalyst (La0 jCa0 9MnO3) were prepared for the cata­lytic test. However, the results showed a low transesterification activity due to the presence of weak base and acid strength. This indicated the catalysts required harsh reaction condition with longer reaction time, higher temperature, and pressure. Besides, alkaline earth metal oxide (CaO), alkali doped alkaline earth metal oxide (Li-CaO), and mixture of solid base (CaO or Li-CaO) with solid acid catalyst (Fe2(SO4)3) were studied in single-step simultaneous esterification and transesterifi­cation process. Soap formation was found in the CaO and Li-CaO catalyzed reac­tion in which FFA in the oil neutralized the Ca2+ on the surface of the catalyst. However, both CaO+Fe2(SO4)3 and Li-CaO+Fe2(SO4)3 showed complete conver­sion to biodiesel in single step process under mild condition. The presence of Lewis acid from Fe3 + promoted the esterification reaction for FFA reduction, and high basicity of CaO and Li-CaO transesterifies the oil to biodiesel.

The biodiesel production by transesterification of Jatropha oil with methanol using alumina-supported potassium nitrate (KNO2/Al2O3) was performed. Although the solid base catalyst gave high oil conversion (>84%) under mild condition of 70°C, 6% catalyst amount, 12:1 methanol/oil molar ratio for 6 h, the reusability for this catalyst was low. The results showed that conversion was less than 80% after third run (Vyas et al. 2009).

Kumar et al. (2010) investigated the catalytic activity of mesoporous Na supported on SiO2 catalyst (Na/SiO2) in the transesterification of Jatropha oil with methanol using ultrasonic irradiation. The optimum conditions to produce 98.53% of bio­diesel yield were 9:1 methanol/oil ratio, 3 wt% catalyst amount, and 50% ultrasonic wave amplitude for 15 min. The results showed that ultrasonic transesterification showed conversion rate that was similar to conventional method with shorter reac­tion time without mechanical stirring. The high stability of Na/SiO2 catalyst is capa­ble of maintaining biodiesel yield at above 90% for five consecutive cycles.

The effect of stirring rate (0-300 rpm) on transesterification of Jatropha oil using immobilized lipase is shown in the Fig. 12.7e. As is clear from the figure, there was an increase in ethyl ester formation with increase in mixing intensity. At 300 rpm (rotations per minute), the ethyl ester formation reached 100%. Mixing intensity plays a major role in biodiesel production using immobilized enzyme systems with respect to diffusion and reaction rate. The diffusion problems when using immobilized enzyme systems can be overcome either by reducing the size of immobilized enzymes or by increasing high degree of turbulence around the particle (Shuler and Kargi 1992). However, higher mixing intensity can lead to immobilized enzyme rupture.

To convert oil palm biomass to liquid biofuels, several technologies in the pipeline that can be considered are pyrolysis (bio-oil), catalytic depolymerisation (synthetic diesel), microbial fermentation (bioethanol) and hydrotreating (hydrocarbon fuel). In all endeavour, the most important stage is oil palm biomass pretreatment as it has been well documented as one of the most tedious and energy intensive processes due to difficulty in breaking the complicated cell wall of oil palm biomass.

Pyrolysis of oil palm biomass generates bio-oils and other coproducts such as biochar and gas in different concentration at varying temperature ranges. MPOB has set up a pyrolysis experimental rig for small-scale slow pyrolysis (Sukiran et al. 2010,2011) and a Biomass Experimental Kit (BEK) for larger scale biochar produc­tion as the targeted product. The biochar produced has potential for soil remedy and GHG emissions reduction (carbon sequestration). Other emerging pyrolysis tech­nology is microwave-induced pyrolysis (Salema and Ani 2011; Omar et al. 2011).

Under the National Key Economic Area (NKEA), one attempt is to set up com­mercial pyrolysis plant to produce bio-oil from EFB. The bio-oil produced will be used to replace fossil-based fuels.

The bioethanol production from EFB involves three processes, i. e. thermo — mechanical/chemical fractionation, sugar hydrolysis and extraction followed by microbial fermentation (Malaysia-Danish Environmental Cooperation Programme 2008; Politov et al. 2009; Mohd Asyraf et al. 2011a, b; Ria et al. 2011). The poten­tial bioethanol production is about 388 L of ethanol per tonne of EFB (Malaysia — Danish Environmental Cooperation Programme 2008). Two forms of oil palm biomass, i. e. EFB and oil palm trunk (OPT), can be used in fermentation to produce bioethanol (Yamada et al. 2010). The biomass samples must be subjected to a pre­treatment via delignification with 1% NaOH, acid hydrolysis and enzymatic sac­charification prior to fermentation process and then fermented using Saccharomyces cerevisiae to produce fermentation broth which yields a mixture of bioethanol and water coproducts after distillation.

Although there is an active pursuit on pilot and commercial scale production of bioethanol from oil palm biomass, the bioethanol plant is far from reaching on the ground. However, with the penetration of more promising technologies, there is plan to set up pilot and commercial biorefinery plant side by side at palm oil mills to produce various products from oil palm biomass (The Star 2011).

With the current market trends and demand towards sustainable development and climate change mitigation, it is envisaged that the future trend in bioenergy deployment is probably to convert oil palm biomass into aviation fuel. Research has shown that a few palm esters can be used as potential aviation fuel. Besides, a trial is ongoing to produce aviation fuel via hydrotreating process (MPOB in collabora­tion with UOP).

5.2.2.1 Empty Fruit Bunches

EFB is a nonwood lignocellulosic material which forms about 23% of the total mass (or weight) of the FFB (Schmidt 2007). EFBs are the wastes (i. e. solid residue pro­duced in largest quantity in the oil mill) obtained after stripping off the fresh palm fruitlets from the whole FFB. An EFB is made up of a main stalk (about 20-25% of the total weight of EFB) and numerous spikelets (about 75-80% of the total weight of the EFB) with sharp spines at their tips (Ahmad et al. 2009). The production of 1 tonne of CPO generates nearly 1.3 tonnes of EFB. Globally, about 42.3 million tonnes of EFB is generated by the palm oil industry annually (Kelly-Yong et al. 2007; Ahmad et al. 2009).

EFB vascular strands contain about 41.3-46.5% cellulose, 25.3-33.8% hemicel — lulose and 27.6-32.5% lignin (Sudiyani 2009; Piarpuzan et al. 2011). EFB sugar contents are about 2.5% galactose and 33.1% glucose (Abdul Khalil et al. 2006). Current research on the proximate and ultimate analysis of EFB by Mohammed et al. (2012) shows about 55.6% moisture content (by wet weight), 3.45% ash, 8.97% fixed carbon, 82.58% volatile matter, 46.62% carbon, 6.45% hydrogen, 1.21% nitrogen, 0.035% sulphur, 0.18% magnesium, 0.06% phosphorus and 45.66% oxygen in the EFB (Elbersen et al. 2005). The fatty acid content in EFB is <2% with its extractives and crude protein also constituting approximately 7.8% and 1-3.8%, respectively. Though the calorific value of EFB is between 17 and 19 MJ/kg (Ma and Yusoff 2005; Mohammed et al. 2012), a value slightly lower (due to high moisture and oxygen contents) than that for wood and coal (Demirbas 2004; Yang et al. 2006), it serves as a potential source of biofuel.

The inorganic contents (expressed in % ash, moisture free) of EFB have been analysed by Lahijani and Zainal (2011) , Omar et al. (2011) and Mohammed et al. (2012) to consist of Si2O (10.83-27.0), K2O (34.7-53.73), CaO (1.9-12.5), MgO (4.8-8.75), Cl (3.6-5.3), Fe2O3 (1.28-3.6), Al2O3 (0.46-1.22), Na2O (0.55­1.54) and P2O5 (1.12-3.6). EFB fuel density is about 1,420 kg/m3 (Mohammed et al. 2012).

At present, commonly used homogeneous base catalysts are sodium hydroxide (NaOH), potassium hydroxide (KOH), and sodium methoxide (CH3ONa).

They are usually employed for catalyzing the conversion of triglycerides into biodiesel because of their high catalytic activity, which resulted in a relatively fast reaction (Hoda 2009). Besides, they are also preferred over acid catalysts in terms of their economical usage and available at cheaper price. Homogeneous base cata­lysts are proven to be appropriate choice for biodiesel synthesis, owing to the mild reaction conditions required for achieving high methyl ester yield (Phan and Phan 2008).

Although these catalysts are outstanding in terms of operating conditions, they also have some drawbacks. One of them is that they cannot tolerate feedstock

Fig. 9.2 Reactions between free fatty acid and basic catalysts to produce soap

containing high free fatty acid (FFA) content, especially when nonedible oils are used as the feedstock. FFA reacts with the basic catalyst and produces soap. The formation of soap is shown in Fig. 9.2. FFA reacts with the catalyst to form soap and water through saponification process when an alkali catalyst is added to oil or fat having significant amounts of FFA. This reaction is undesirable as it complicates the separation between products further downstream. Moreover, the saponification consumes alkali catalysts, decreasing transesterification rate and resulted in lower biodiesel yield.

Water is another element in oils or fats that is undesirable for producing bio­diesel. Hydrolysis of triglycerides and alkyl esters may occur if water is present. This leads to the formation of FFA, and thus produced undesired soap when an alkali catalyst is used. As water catalyzes the hydrolysis reaction, the substrates should have minimum water content, or nearly anhydrous.

Hydrolysis of esters not only reduced biodiesel yield, but it also contributes to increased soap formation as more fatty acids are produced (Leung and Guo 2006).