Biodiesel Review

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Adeyemi N.A., 1Mohiuddin A.K.M., 2Ahmed Tarig Jameel, 2 Suleyman Muyib 3Badmus Ganiyu A. 1

Mechanical Engineering Department, International Islamic University, Malaysia 2 Biotechnology Engineering Department, International Islamic University, Malaysia 3 Agricultural Engineering Division, Nigerian Institute for Oil Palm Research, Benin City, Nigeria Biodiesel Production: A Comparative Review ABSTRACT Increasingly, biodiesel production from some of the major edible, non edible and waste cooking oils feature prominently in addressing renewable energy discuss. Plant sources bearing similar physical and chemical properties as petrol diesel remain a veritable alternative for renewable energy in reducing dependence on fossil fuel. Factors affecting transesterification of vegetable oil continues to be modified using competitive alternatives for improve production of biodiesel production for industrial and automotive uses. Process improvement using catalyst, co-solvent, ultrasonication, enzymes has revolutionized the biodiesel production industry. While the process feasibility has been proven, sustainability remains a force that is driving the biodiesel research for optimization. Some of these processes and challenges are discussed in view of current resources available and the present process limitations highlighted. Considering the level of research thrust in establishing a 'renewable energy culture' amongst major global energy consumers with biodiesel, process alternative are suggested for a sustainable biodiesel production. Keywords; biodiesel, vegetable oil, transesterification

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INTRODUCTION Vegetable oil has been the preferred start-up material (Freedman et al, 1984,1986; Knothe, 2001; Eevara et al, 2009) for biodiesel production because its rheology is analogous, when chemically modified, to petro-diesel commonly by transesterification, in presence of an acid/ alkaline catalysts (homogeneous and heterogeneous catalysis) to give the an ester and glycerol (Tan et al, 1999). Viscosity, degree of saturation, iodine value (IV), moisture content, energy yield are amongst the characteristics which makes the vegetable oil an ideal feedstock for biodiesel production (Geller and Goodrum, 2000; Monteiroa et al, 2008). Also its portability, availability, renewability, higher combustion efficiency, lower sulfur and aromatic content (Knothe, 2006). Esters are common derivatives of triglycerides (TGs) or fatty acids by either by pyrolysis (Knothe at al, 2009), micro-emulsion (Schwab, 1998) and transesterification (Ma and Hanna, 1999). The first account of what we know as biodiesel today can be traced back to a patent of the University of Brussels (Belgium) describing the alcoholysis (often referred to as transesterification) of vegetable oils using ethanol (EtOH) (and mentions methanol (MeOH) in order to separate the fatty acids from the glycerol by replacing the glycerol with short linear alcohols (Darnoko et al, 2000). Since then biodiesel production, feedstock & fuel properties, standard have been extensively studied, documented and critically reviewed (Ma & Hanna, 1999, Meher et al, 2006; Chisti, 2007; Canakci and Sanli, 2008; Demirbas, 2009). Estimated 90% of vehicular fuel needs are met by crude oil, which industry; represent the single largest industry in terms of dollar value on earth (Laughton, 2003) which is widely seen objectionable because it is polluting, causes damage to life and to value buildings, emits radiation or generates more heavy goods traffic. Biodiesel are now regarded as renewables, capable of supplying a significant proportion of energy in the long-term future as regarding environmental concern arising from fossil fuel use. Even though cost, overall energy balance between crop growth and use are considerations that are challenging biodiesel production from vegetable oils (Cockerill and Martin, 2000,) in particular, the type of feedstock for biodiesel production. Most vegetable oil, the palm oil in particular, is ideal (Lam et al, 2009) for biodiesel but with the food verse fuel debate and a caveat of an ‘eco-nightmare’ (Cockerill and Martin, 2000) been issued with continued use of food material for biodiesel production, a rethink to use of food-grade oil is been reconsidered as the highlighted negative

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consequences of using food crop for biofuel, risked raising food prices and the push to expand the use of biofuels could result in clearing of forests (Srinivasan, 2009). Since availability of feedstock, technical feasibility has been central to the biodiesel industry discuss, the focus of this paper is to highlight progress of the biodiesel processing, material alternatives as alternative energy source using palm oil and other lipid sources and to highlight technical gray-areas in the industrial application of use of some the laboratory based solution. Suggestions at overcoming some of the technical barriers are also made. FEED STOCK PROPERTIES Most vegetable oil and animal fat feed-stocks are Monoglycerides (MGs), Diglycerides (DGs) and TGs with long-chain (C16– C18) fatty acid groups attached by ester linkages to a glycerol backbone. Table1. Their highly viscosity caused from their molecular weights (Knothe, 2001) and chemical structures (Georing et al, 1982) makes them quite unsuitable for direct inject (DI) engine (Wenze et al, 1980). The chemical structures of vegetable oils are significantly different from that of diesel fuel but modifiable. Other considerations include properties like viscosity, degree of saturation, iodine value, moisture content, energy yield, combustion efficiency, sulfur and aromatic content (Ma & Hanna, 1999; Vicente et al, 2007; Encair et al, 2007) does not favor vegetable oils for automotive uses as a result of clogging and choking. The properties of the triglyceride and the biodiesel fuel are determined by the amounts of each fatty acid that are present in the molecules. Chain length and number of double bonds determine the physical characteristics of both fatty acids and triglycerides (Abramovic and Klofuta, 1998). Studied influence of TG composition in the biodiesel qualities correlates to cetane number, Iodine Value (IV), oxidation stability and Cold Flow Pour Point (CFPP) of biodiesel to the Free fatty acid (FFA) of TG (Ramos, 2009) and rheological properties of the final products could be used to predict viscosity values of the individual components (Knothe, 2006). Similarly algae, waste cooking oil, non edible oil and industrial waste stock (Wang et al, 2007) from the oleochemIcal industries have been identified as a veritable source of biodiesel feed-stock. Some of the transesterification methods are highlighted below. BIODIESEL PRODUCTION METHOD

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Transesterification Several reviews (Pryde, 1983; Vasudevan et al, 2008; Pereda et al 2009) have highlighted and discussed biodiesel production by transesterification using various feed-stocks and their current state of the art production. Mole ratio of alcohol: oil, concentration, temperature FFA level, moisture and reaction time constitute the most considered factors in nearly all the literatures presented. Alkali and acid catalyzed transesterification of TG are more suitable to make automotive fuel and this has spurned a variety of industries globally (Licht, 2007) which generates high yields of Methyl esters (MEs) in short reaction times and the reaction conditions are moderated with vegetable Oil of low FFA (Dunn, 2005). Oil/ alcohol ratio between 1:3 to 1:45 depending on water and FFA content, catalyst (0.2-3% w/w) in single and two stage transesterification for soybean oil (Wenze et al, 2006), palm oil, rape seed oil (van Kasteren, 2007; Umer & Rashid, 2008), sunflower (Widyan & al-Shouyhk, 2001), palm oil (Darnoko & Cheryan, 2000). A summary of some optimized transesterification with mole ratio of alcohol:oil is listed in table 2. However, acid catalysis is preferred if there are significant quantities of FFA in the feed stock as with animal fat and waste oil, as the reaction time is very slow and high levels of alcohols are needed to force the reaction equilibrium toward the transesterified products (Freedman et al, 1984; Al-Widyan & Al-Shyoukh, 2002). Ester conversions of 95.1 and 99.7% have been reported in the presence of a lipase (Watanabe et al, 1999). The FFA content in the Palm fatty acid distillate (PFAD) was reduced from 93% to less than 1.5%wt by optimum esterification and esterified product had to be neutralized with 10.24%wt of 3M sodium hydroxide (NaOH) in water solution at a reaction temperature of 80°C for 20 min to reduce the residual FFA and glycerides. Transesterified waste palm oil using sulfuric acid (H2SO4) concentrations (1.5–2.25 M) and different concentrations of hydrochloric acid (HCl) and EtOH at different excess levels gave the best process combination at 2.25M H2SO4 with 100% excess EtOH which reduced c from an initial value of 0.916 to a final value of 0.8737 in about 3 hr of reaction time. To circumvent the mass transfer limitation observed in earlier studies (Ma et al, 1997, Freedman et al, 1984) in situ alkali-catalyzed transesterification was 4

identified as an alternate protocol, to take place directly within the oil bearing material during incubation in alkaline alcohol. The oilseed is not isolated prior to transesterification to Fatty acid methyl ester (FAME) directly in its raw agricultural material exploiting the advantages of simultaneous easy extraction of neutral lipids. Haas et al (2005) reported that by drying the soybean flake a marked reduction in the reagent requirements was achieved. This approach to FAME synthesis eliminates the need for isolation, and possibly refining, of the oilseed lipid, the process could reduce biodiesel production costs (Haas & Scotts, 2007). Oil was recovered from largely hydrolytically degraded oil (PV, 25–26; FFA, 25– 26%) from the pulp of oil palm fruits (Jude et al, 2002; 2003). This acid-catalyzed conversions of the oil into alkyl esters were 96–97% for both MeOH and EtOH with accompanying low concentrations of FFA, TG, DG, and MG. Yields of alkyl esters from in situ transesterification were significantly greater up to 17.5% than those obtained from the conventional reaction which may be partially due to the fact that the residual oil usually retained in pressed fibre of the pre-extraction process was transesterified in situ. Investigation of in situ transesterification of Sunflower seed Oil (Zeng et al, 2009) for the effects of moisture content of sunflower seeds, at the molar ratio of catalyst/oil of 0.5:1, the molar ratio of MeOH/oil of 101.39:1, the molar ratio of DEM/oil of 57.85:1, the agitation speed of 150 rpm, and reaction temperature of 20°C gave a product containing 97.7% FAME and 0.74% FFA was obtained within 13 min. The inclusion of DEMassisted rapid in situ transesterification by shortening reaction time and reducing the addition amounts of catalyst and MeOH. The moisture content of sunflower seeds, the catalyst category, and the agitation speed showed very limited influence on the rapid in situ transesterification, while the molar ratio of catalyst/oil, the molar ratio of MeOH/oil, the molar ratio of DEM/oil, and the reaction time were the important factors affecting the biodiesel yield, the FFA content, and the FAME purity.

Enzyme Catalysis Recent studies suggest that microorganism that act on lipids hold several advantages (Cherry and Fidantsef, 2003) in esterification (Wenze et al, 2006), transesterification (Nagayama et al, 2002) and enantioselective hydrolysis 5

(Steenkamp & Brady, 2003; Kobayashi & Adachi, 2004; Perez-Victoria & Morales, 2007) can catalyze to 98.4% conversion of biodiesel esters to overcome the kinetic related limitation. In a recent review, Szczesna Antczak et al, 2009 listed 12 microbial producers of lipases in studies of biodiesel production systems in organic or non-organic solvent. Similar to the factors considered in transesterification enzyme activities, pH of the environment, substrate interaction with products are crucial parameters affecting the yield on enzymatic synthesizes of biodiesel. It has to be noted that one of the advantages is that extracellular and intercellular lipases effectively catalyze the transesterification of TGs without the associated problems of waste-water alkaline treatment, FFA and water interference, energy intensivity and glycerol recovery (Fukuda et al, 2001 & Burkert et al, 2004). The dynamics and equilibrium of enzymatic reaction reported (Al-Zuhair et al, 2007; Zheng et al, 2009; Ibrahim, 2008) with experimental and computer simulation using the Ping Pong Bi Bi model, accounting for all reactant species, shows that increasing the initial EtOH concentration produces an increase in the initial production rate and yield of fatty acid ethyl ester and lowers the final concentration of free fatty acid whereas lower EtOH concentration led to a higher final concentration of free fatty acid (Xiaolong & Qingyu, 2006). Watanabe et al 2000 compared the effectiveness of enzymatic transesterification of various soybean oil and reported unchanged activity of the lipase C. antartica. The versatility of this method is also cited in waste oil and industrial, oil-rich bleached earth (Park et al, 2004) using Ashbya gossypii. At present, however biodiesel from lipase (enzymes) is not competitive with conventional fuels in the whole world (Garcia et al, 2000) and can only be used for a small fraction of existing demand for transport fuels (Kusdiana & Saka, 2001) because of cost, recoverability, reusability. Many commercially available enzymes are too costly for the intended applications, even if they can be recovered and reused by immobilization. Therefore, reduced enzyme prices may dramatically increase the number of applications and even enable large-scale processes such as the production of biodiesel from lipids (van Beilen and Li, 2002). Self regeneration during immobilization of the enzymes in inert support

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and in situ regeneration are areas that need to be explored. Sequential multienzymatic reactions can be employed to direct patternwise consecutive reaction where it is evident that some enzymes promote mass-transfer limitations at relatively low flow rates but absent at higher flow rates Algae Xeng et al, 2009 cited single cell organisms (SCO) having 20% lipid as a veritable source of material for biodiesel production. Theoretically, this is a more efficient source of lipids. These sun-light driven factories convert CO2 to biofuels based on a higher photosynthetic efficiency compared to other energy crops and as most of the accumulated oils in microalgae are TGs (Cheirsilpa et al, 2008) and algae can sequester up to 50 % of their dry body mass in oil (Scwab, 2009) They are the fastest growing photosynthesizing organisms completing an entire growing cycle every few days (Meng et al, 2009). Microalgae as an alternative material for biodiesel production has not been popular even though approximately 46 tons of oil/hectare/year can be produced from diatom algae and between 1-3% of the total cropping area would be needed to producing algal biomass that satisfies 50% of the transport fuel needs in US land, with some algae produce up to 50% oil by weight (Cherry & Fidantsef, 2003). This method is species-dependent (Chisti, 2007). The technical feasibility has been demonstrated employing raceway ponds and Photobioreactors. The production of algae to harvest oil for biodiesel has not been undertaken on a commercial scale, however working feasibility studies have been conducted to arrive at the above number (Sheehan, 1998). CURRENT STATE OF THE ART AND CHALLENGES The transesterification reaction is a cascade reaction where the triglyceride (oil) is stripped of fatty acid chains in stages until only glycerol remains. Reported poor conversion (Freedman et al, 1984; Umer et al, 2008, Bautista et el, 2009) means that MG, DG and TGs will remain in the biodiesel as impurities. There is concordance amongst researchers that oil/ alcohol ratio, temperature, stirring rate, pressure, time, concentration including unavailable

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thermodynamic properties affects the kinetics of alcoholysis (Ma et al, 1998; Schuchardt et al, 1998; Fukuda et al, 2001; Encinar et al, 2007; Stamenkovic et al, 2007) and has posed challenges to researchers. Initial transesterification progress is fast with 85% conversion occurring in the first 5 min and the rate drops to almost nothing making it difficult to reach 96.5% (Stamenkovic, et al 2005) and remains unsatisfactorily explained (Mjalli et al, 2009). However, the slow dispersion of reactants has shown to be reduced by agitation (Stamenkovic et al 2007). The initial phase of the reaction results in a slow reaction rate, the reaction being mass transfer controlled (Noureddini & Zhu, 1997). Beside this, the low solubility of MeOH in the vegetable oil affects final product quality. Earlier work (Ma et al, 1999) showed that agitation effect is most significant during the initial slow rate region of the reaction and as shown to be critical during a continuous process for the glycerolysis of soybean oil (Espinosa da Cunha et al, 2009) and beef tallow (Noureddini et al, 2004). At two agitation speeds (300 and 600 rpm) a higher conversion of the oil in a shorter reaction time was reached at higher speed. bubble size mean drop diameter and the drop size distribution at different agitation speeds in a batch stirred reactor studied (Stamenkovic et al, 2007) from measurements of drop size, drop size distribution and the conversion degree that, the autocatalytic behavior of the methanolysis reaction can be explained by this ‘‘self-enhancement’’ of the interfacial area, due to intensive drop breakage process. Final phase of methanolysis became slower; approaching the state of equilibrium, despite the increased interfacial area is due to the decrease of MeOH concentration and the increase of glycerol and FAME concentrations. Investigation into the phase distribution of alcohol in transesterified soybean oil (Chiu et al, 2005) revealed that as chain length of alcohol increase, more alcohol were found in the final ester phase and the glycerol-rich phase had dissolved most of the catalyst. The presence of MeOH in the biodiesel glycerine system tends to increase the distribution of catalyst in the biodiesel phase (Zhou & Boocock, 2006). The phase studies of alcohol and oil concluded that difference in the distribution of MG, DG and TG in the glycerol-rich and ester-rich phase revealed ethanol was a better solvent but MeOH was better at pushing the reaction to the required direction suggested a mixture of alcohol to optimize the

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phase behaviors. This is also corroborated by Wahlen et al, 2009 during the synthesis of biodiesel using mixed feedstock and longer chain alcohol. Noted shortcomings of using short chain alcohol reported that these reactions take very long times (>69 h) with low conversion efficiencies (Freedman et al, 1986). Transesterification in n-butanol, increasing the reaction temperature from 80 to 110 °C was reported to have significantly increased the kinetics of the reaction, with greater than 95% conversion at the higher temperature within 8 min compared to 50% conversion after 16 min at 80 °C. Issariyakul et al, 2006 obtained 90% ester yield in a MeOH/ EtOH mixture with a two stage method using fryer grease. Dias et al, 2008 simultaneously compared the different homogeneous catalyst on the waste and virgin oil with CH3OH, NaOH, KOH. As discussed above, several alternatives are been employed to increase the conversion rates and the yields of esters in order to lower production costs and improve biodiesel product quality. The model of the three consecutive, reversible reaction in transesterification proposed variously (Mjalli et al, 2009; Samios et al, 2009) though creates an understanding of the kinetics and dynamic of transesterification, narrowed the complexity and yet to incisively look into the phase equilibrium mechanism where the immiscible alcohol-oil phase emulsify and truncate the reaction. Because of the density differences between the two phases and their interfacial energy, CH3OH/ soybean oil dispersions are unstable and coalesce in the absence of agitation. The rate of coalescence is important both during biodiesel synthesis and downstream separation of the reaction products. Recently Ataya et al, 2007; 2008 proposed addition of FAMEs to the reaction mixture as a strategy to decrease the TG induction period which decreased with a decrease in the water concentration, increase in the methanol (MeOH)-to-oil molar ratio for a dispersed nonpolar-TG phase and continuous polar-MeOH phase, increase in the alcohol carbon chain length, and increased with an increase in the FFA concentration. To reduce the mass transfer limitation related to transesterification, efficient mixing energy-intensive methods have been successfully employed to at

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addressing the interphase dispersion, increase interfacial contract and presented as follows; Ultrasonication An ultrasonic field is known to produce unique chemical and physical effects that arise from the collapse of the cavitation bubbles (Bondy & Sollner, 1935). Their uses have been cited in synthesis of nanostructured materials, processing of biomass, sonofusion, sonodynamic therapy, and sonochemical degradation of pollutants (Hanh et al, 2009) and hazardous chemicals (Schuchardt et al, 1998; Okitsu et al, 2002; Taleyarkhan et al, 2004; Stavarache et al, 2005). A low frequency ultrasonic irradiation can be used to produce emulsions from immiscibility liquids and help generate small droplets and large interfacial areas if the ultrasonication device is placed near the liquid–liquid interface in a two phase reaction system (Bondy C, Sollner, 1935; Peng et al, 2007; Sivakumar et al, 2002). Disselkamp et al, 2007 contrasted differences in a heterogeneous catalytic reaction for cavitating and non cavitating ultrasound incorporating an inert dopant, which does not partake in solution chemistry to enable facile transition from high power non cavitating to cavitating condition as not all liquid readily cavitate. The mechanism for discriminating between physical and chemical effects of ultrasound with different conditions have been coupled to a bubble dynamics mode (Kalva et al, 2009) and the result is attributed to the difference in intensity of microturbulence produced by cavitation bubbles in oil and MeOH. This effect is a low intensity of microturbulence generated by cavitation bubbles in oil, which restrict an intimate dispersion of oil in MeOH for high alcohol to oil molar ratios. The optimum alcohol to oil molar ratio for the experimental system used in this study is 12:1. Transesterification of triglyceride with various alcohols has been shown (Vasudevan et al, 2008), under the low frequency ultrasonic irradiation (24KHz), stirring conditions (600 rpm) to be higher than those under the conventional stirring condition and that an optimal reaction condition was obtained with an alcohol to TG ratio of 6:1 (Hanh et al, 2007) low frequency ultrasonication (24 KHz) and mechanical stirring (600 rpm) with MeOH gave high yields of methyl esters (95%) after a short reaction time

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(20 min) similar to those using mechanical stirring. Use of ultrasonication in conventional transesterification with EtOH gave similar yields to those using mechanical stirring but significantly lower than respective yields using MeOH. This also showed the alcohol-dependency of the operation. Gogate's review presented this method as very efficient for intensification of chemical processing and that analysis & fabrication and design of Cavitational reactors would offer realistic solution to conventional transesterification. . Supercritical Fluid Extraction (SFE) TG utilization in the presence of a acid/ alkali catalyst is affected by high level of water content and FFA (Jeong and Park, 2006) with undesirable saponified products, hence the study to reduce catalyst has attracted interest in wateradded supercritical method with a feature of easier product separation, since glycerol, a co-product of transesterification, is more soluble in water than in MeOH (Kusdiana and Saka, 2001; Georgogiannia et al, 2008). Single phase medium using SCF due to the creation of a single phase environment has some unique advantages including increased species mixing, heat and mass transfer, fast reaction typically at a few minutes level, are environmentally benign, and have good scalability, as well as being simple and easy for continuous production (Wenze et al, 2006) and make SCFs ideal for separation and extraction of useful products and for oxidation of organic materials (Wen et al, 2009). For most of the supercritical methods of biodiesel production, the reaction requires temperatures of 340– 400°C and pressures of 20–70 MPa, Rapeseed oil was treated at 250350°C, 43 MPa and 240 s with a molar ratio of 42 in MeOH for transesterification to biodiesel fuel. By this MeOH approach, crude vegetable oil as well as its wastes could be readily used for biodiesel fuel production in a simple preparation. Regardless of the content of water supercritical MeOH method does not require a catalyst and the FFA in the oils are esterified at once (Kusdiana and Saka, 2004). Co-solventing Enhancing solubility, thru addition of a co-solvent (Royon et al, 2006; Jarnefeld, 2006; Guan et al, 2009) to create a single phase greatly accelerated the reaction

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so that it reached substantial completion in a few minutes. The technique is applicable for use with other alcohols and for acid-catalyzed pretreatment of high free fatty acid feed stocks (Arjun et al, 2008). Comparison of various co-solvent dimethyl ether (DME), diethyl ether DEE, tert-butyl methyl ether TBME and tetrahydrofuran (THF) (Guan et al, 2009) to synthesize BDF from sunflower oil by using a KOH catalyst at 25°C in a closed batch reactor was reported (Wen et al 2009). Addition of a co-solvent enhanced the transesterification rate at the MeOH/oil molar ratio of 6 at 25°C, and sunflower oil was almost completely converted into BDF after 20 min reaction while only approximately 78% conversion was reached in the absence of a cosolvent. The oil conversion was influenced by the cosolvent/ MeOH molar ratio, MeOH/oil molar ratio, and catalyst concentration. However, the homogeneous flow was broken with the formation of immiscible glycerol, and transformed to a dispersed flow of fine glycerol droplets. The problem of immiscibility of MeOH and vegetable oil leading to a mass-transfer resistance in the transesterification of vegetable oil (Kusdiana and Saka, 2004) can be overcome by this method amongst many other techniques being developed like membrane separation (Dube, 2007) and Inert Dopant (Disselkamp et al, 2007)

Microwave assisted reaction Microwave irradiation is a well-established methodology to improve extraction and accelerate chemical reactions such as those of hydrolysis (Ipsita & Gupta, 2003) and esterification (Fini & Breccia, 1997) because of its convenience, rapidity, and economy advances in equipment design, trends in electrical energy costs, and research on food properties have provided a basis for modeling microwave heating patterns that should stimulate the development of new and improved commercial food processes (Tan et al, 2001). In conventional heating of transesterification process (batch, continuous, and super critical MeOH process), heat energy is transferred to the raw material through convection, conduction, and radiation from surfaces of the raw material as shown when TGs in soaked soybeans were already hydrolyzed into DGs and free fatty acids during soaking and were further hydrolyzed by microwaves (Yoshida et al, 1995).

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Satisfactory transesterification was achieved in a short time (30s), with alcohol to oil molar ratio 12:1 and the continuous conversion of waste frying palm oil to ethyl ester was over 97%. Although, the mechanism of the microwave effect on a chemical reaction, whether thermal or non-thermal, is debatable (Saifuddin and Chua), however the transesterification results clearly establish that there is considerable enhancement in reaction rates. This brings about considerable time saving as well as cost (Kusdiana & Saka, 2001) 100% biodiesel yield by applying microwave irradiation for two minutes compared to one hour with the conventional technique, with adjusted temperature to 65°C, a MeOH/oil molar ratio of 6:1and potassium hydroxide (1%) used as a catalyst has been reported (Refaat & El Sheltawy, 2008) and showed that microwave-enhanced biodiesel is not, at least, inferior to that produced by the conventional technique (Yoshida & Takagi, 1997) Catalytic Conversion The problems associated with the homogeneous catalysts are the high consumption of energy and expensive separation of the homogeneous catalyst from the reaction mixture (Sree et al, 2009). Alternative heterogeneous catalysts have been successfully explored (Di Serio et al, 2005; Ma et al, 2008) to circumvent the difficulties with homogeneous catalysts for transesterification of high FFA-containing oils. Heterogeneous catalyst developed to eliminate the need for aqueous quenching and elimination metal salts (Zhou & Boocock, 2006) (soaps) but the conversion for most of the heterogeneous are not high enough to be used for industrial based production (Xie et al, 2006) and relatively prolonged reaction period (Guan et al, 2009). There have also been experiments aimed at replacing the sodium and potassium compounds with basic ammonium compounds as catalysts or reactants. Such as Amines, aminoguanidines, nitroguanidines; and triamino(imino)phosphoranes. The guanidines are the more active catalysts, the activity following their relative basicity. At a concentration of 3 mol % was similar to that of potassium carbonate at the same concentration. The saturated aqueous solution of guanidine carbonate has a pH of 11 to 11.5. The aqueous solution of free guanidine, on the other hand, gives just as strong an alkaline reaction as lyes. KOH loaded on Al2O3 and Naγ zeolite supported as 13

heterogeneous catalysts, though leaching of potassium species in both spent catalysts was observed, biodiesel yield of 91.07% was reported (Noiroj et al, 2009) at temperatures below 70C within 2–3 h at a 1:15 molar ratio of palm oil to MeOH and a catalyst amount of 3–6 wt%. Table 4 shows various conditions of solid homogeneous and heterogeneous catalysts use in transesterification of various feed-stocks. TECHNICAL SUCCESSES / LIMITATION Some other technical details such as reaction equilibrium (Zhou & Boocock, 2006), reaction kinetic (Mjalli et al, 2009) investigated of transesterification provides parameters that predict the extent of the reaction at any time under particular conditions and been used to understand why a reaction does not proceed to the theoretically determined point (Boocock et al 1998). Yet as the single-step transesterification is economically impractical to reach the standard 96.5% purity, the alternative acid pre-esterification to convert the fatty acids to biodiesel significantly increase the yield when using high fatty acid oils with fatty acids >10%, It does not significantly increase the ester content of the fuel (Jarnefeld, 2006; Obibuzor et al, 2003). In earlier kinetic studies (Noureddini & Zhu, 1997) identified two phase nature of vegetable oil/MeOH mixture that requires vigorous stirring to proceed in the transesterification reaction and the products purification from residual catalyst which is left in the reaction product due to unreacted MeOH and saponified products (Fukuda et al, 2001). Observed drop size distributions narrowed and shifted to smaller sizes with increasing agitation speed as well as with the progress of the methanolysis reaction at a constant agitation speed in both nonreaction (MeOH/sunflower oil) and reaction (MeOH/KOH/sunflower oil) systems (Slinn & Kendall, 2009) that due to the fact that the interfacial area increases, hence the rate of reaction occurring at the interface will also be enhanced progressively (Stamenkovic et al 2005). The two-phase base-catalyzed reaction can be explained to be affected by the distribution of MeOH, catalyst glycerol and alcohol in the biodiesel and glycerine phase (Chiu et al, 2005; Mjalli et al 2009). Droplet size has a major influence on reaction end point and that the reaction was mass-transfer limited. The droplet size was observed to initially decrease

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and then increase which correlated with the creation of surface active intermediary’s and then the consumption and evaporation of MeOH. This observation explained the slow-fast-slow nature which limits the biodiesel reaction by developing a mass-transfer based reaction model using the data from the batch reactor. Recent kinetic models that have incorporated drop size, interfacial area, dispersion (Stamenkovic et al, 2007) and agitation (Mjalli et al, 2009) to improve the kinetic models for their transesterification. Of great significance is realigned transesterification mechanism incorporating all the significant reaction species (Samios et al, 2009) where a deviation from the tradition transesterification technique using what he called a TDSP process was applied. With an increased alcohol:oil ratio of 10:1 in presence of acid-basic catalyst of sunflower and linseed oil conversion to FAME of 97% was reported. However, the two-step protocol exploited has produced significant result (Saimos, 2009). Notable is the BIOX process in that it uses inert reclaimable cosolvents in a single-pass reaction taking only seconds at ambient temperature and pressure (Demibras, 2008). Chew and Bhatia (2008) noted that the challenges of successfully finding a catalytic technology include (1) economic barrier, (2) selectivity and (3) design, operation and control of catalytic reactor. As the performance of anion heterogeneous catalysts is still unfavorable compared to the alkali homogeneous catalysts and it is dependent upon the pH value of the reaction medium, some of the alkali metal ions are easily dissolved in the reaction media. Catalytic recovery and reuse has cost operation implication as reported that resin ion-exchange activity depends heavily on density of the base sites and basic site density (the number of basic sites per square meter) of pure metals are much higher than that of their mixed oxides whose catalytic activities have demonstrated promising result (Kim et al, 2008). Leaching of solid acid catalyst (Granados, et al, 2009) and efficient reuse (Kouzu et al 2009) features prominently in the reports. Process type has high impact on product purity; however purification remains a difficult area from the paucity of literature data available. The membrane method (Dube et al, 2007), resin (Berrios & Skelton, 20087), silica gels, water and phosphoric acid washing (Predojevic, 2008) are summarized on

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Table 4. As noted by Demibras, 2009, the most important aspects of biodiesel production to ensure trouble-free operation in diesel engines are: (i) complete transesterification reaction (ii) removal of glycerine (iii) removal of catalyst (iv) removal of alcohol (v) removal of free fatty acids. At the moment technical details about the use of some of these absorbent are not detailed and needs to be worked out for various feed stocks. See table 5 The conditions that have provided beneficial effects of ultrasound on bioprocesses are case-specific and are therefore not widely available in the literature (Rokhina et al, 2009). It is noted also that the non thermal effects increases reaction rates by 2-5 folds at all water activity level. So far ultrasonication has been demonstrated to provide sufficient and effective mixing for production of biodiesel for various sources. Degradation of feedstock and products have not been report hence it looks as if the technology will continue to enjoy patronage in the instance to overcome mass transfer limitation. CONCLUSION In conclusion, transesterification by the conventional alkali-based method is still the preferred alternative for biodiesel production. Input properties of catalyst (basic or acid), oil/ alcohol ratio, and temperature have been confirmed to be critical and their instability results to impurities and hence reducing quality of biodiesel leading to fuel deterioration during storage as well as to significant operational

problems

such

as

engine

deposits.

The

improvement

in

transesterification must go beyond the aim of lowering viscosity of vegetable oil. Visualization of the reaction is critical in revealing the inter-phase interaction needs further development in this field, incorporating particle dynamics. Undoubtedly, the single bubble/drop studies provided useful insights into the interphase transport phenomenon, but it is readily acknowledged that one encounters ensembles of bubbles and drops in most applications rather than isolated bubbles or drops. In spite of the overwhelming pragmatic importance of these systems, particularly in biotechnological processes, very little is known about the interphase mass transfer between ensembles of fluid spheres and a non-Newtonian continuous phase (Chiu et al, 2005).

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Further kinetic study will provide insight at understand and predicting transesterification in conventional and sonic reactors. Other critical but overlooked physical parameter in the reaction, such as droplet size, dispersion rate, settling time etc, will give more accurate model with a view to improve the efficiency of model in this process design. As it is obvious that catalytic intervention can not be circumvented in biodiesel production, feasibility evaluation needs to consider alternative catalyst away from the traditional acid/ alkali method. Material alternative using hydrotalcite, spinel and other impregnated inert monolith supporting catalysts (Centi & Perathoner, 2003) can revolutionize the biodiesel industry because of their comparative advantage in producing environmentally benign waste and price

is

competitive.

Marchetti

et

al,

2008

presented

an

alternative

heterogeneous catalyst scenario amongst two others to be a more positive and possible future technology as a result of the above suggested. While the extent of catalyst can be limited by the ability to ‘create’ them, recourse to naturally occurring material (egg shell and oyster shell) have shown interesting outcome, possibly opening an area to reduce cost. Production of low-cost microbial diesel primarily requires improvements of biotechnology if it is to compete with petro-diesel. Unlike in the use of inorganic material, microalgae will pose new challenges as the factor controlling its growth will call for robust methods of control. While gene manipulation can produce microalgae strains that will surpass naturally existing ones, long term feasibility is questionable compared to other low-cost biodiesel production. The extension of in situ transesterification to other feedstock WVO, soap stock, microalgae lipids could reduce energy input, however substantial quantities of reagents are required to achieve high efficiency transesterification and inadequate thermodynamic data may delay its application (Van Gerpen et al, 2005, Antoni et al; 2007). The establishment of a single phase transesterification process warrants greater attention as the phase problems (reactant/ product) usually encountered is eliminated through co-solventing, supercritical methods, microwave/ ultrasonication although at the expense of higher pressure and temperature (Zhou et al, 2003). The primary concerns with these methods are

17

the additional complexity of recovering and recycling the co-solvent, if there are not inert, although this can be simplified by choosing a co-solvent with a boiling point near that of the alcohol being used. However these results are still yet to be translated for industrial use. Micro-reactors been used to overcome reactions limited by some physical properties of liquids which could be also applied for biodiesel production for oils. Immediate scalability may not be in view using present reaction data. A new reaction dynamics may have to be explored. A general fiat approach to transesterification will entail combination of some of the methods mentioned as non food raw material is becoming readily available.

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Catalysis. A, Chemical. 246, (1-2),24--32, 2006 128.Xin Meng a, Jianming Yang a, Xin Xu a, Lei Zhang a, Qingjuan Nie b, Mo Xian. BIODIESEL production from oleaginous microorganisms. Renewable Energy. Volume 34, Issue 1, January 2009, Pages 1-5 129.Yan Zheng, Jing Quan, Xin Ning, Li-Min Zhu, Bo Jiang, Zhi-Yan He. Lipasecatalyzed transesterification of soybean oil for biodiesel production in tertamyl alcohol. World J Microbiol Biotechnol (2009) 25:41–46 130.Yanchang Wang, Fazhi Zhang, Sailong Xu, Lan Yang, Dianqing Li, David G. Evans, Xue Duan. Preparation of macrospherical magnesia-rich magnesium aluminate spinel catalysts for methanolysis of soybean oil. Chemical Engineering Science 63 (2008) 4306 -- 4312 131.Yoshida Hiromi and Sachiko Takagi. Microwave Roasting and Positional Distribution of Fatty Acids of Phospholipids in Soybeans (Glycine max L.). JAOCS 74, 915–921 (1997) 132.Yusuf

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Leaching and homogeneous contribution in liquid phase reaction catalysed by solids: The case of triglycerides methanolysis using CaO. Applied Catalysis B: Environmental. (2009), doi:10.1016/j.apcatb.2009.02.014

31

Table 1: Fatty Acid Composition of Some Vegetable Oil Oil VS320 Captex 355 SF

C6:0 C8:0 C10:0 C12:0 C14:0 C16:0 C16:1 C18:0 C18:1 C18:2 C18:3 C20:0 C20:1 C22:0 C24:0 Author 4.19 40.24 36.9 4.18 6.84 3.33 0.15 1.37 2.05 0.13 Geller & Goodrum, 2000 0.4 58.5 40.2 11.5 1

11.5 45

4 3.8

24.5 33.3

53.0 7.7

7 0.3

SBO Frying Oil Sunflower seed oil

1

11.5

4

24.5

53.0

7

6.6

5.1

19.6

68.7

SFO Unused Spent WFO

0.1

0.2

0.3

6.3 8.2

0.1 0.2

3.6 3.6

28.5 27.7

60.3 58.4

0.1 0.5

0.2 0.2

0.2 0.2

0.7 0.6

0.2

8.4

0.2

3.7

34.6

50.5

0.6

0.4

0.4

0.8

0.3

11.3

0.1

3.6

24.9

53

6.1

0.3

0.3

0.3

0.1

0.1

6.6

46.1

8.6

0.3

0.4

0.2

0.1

0.1

3 14.2 19.4

6.9 44.2 42.4

2.2 10.7 2.9

0 0.4 0.9

Soybean Oil Palm oil

0.1

0.7

36.7

Coconut Lard Tallow

46.5 0.1 0.1

19.2 1.4 1.4

9.8 23.6 23.6

Zeng, 2009 Georgogianni et al 2009 Georgogianni et al 2009 Georgogianni et al 2008 insitu Hancsok et al, 2004 Dias et al 2008 Ramos et al, 2009 Ramos et al, 2009 Kincs, 1985

Table 2: Some Optimized Transesterification Using Homogeneous Liquid Catalyst on Various Feedstock Oil Catalyst Alcohol Alcohol:oil Time Temp Ester type ratio Yield (%) WVO H2SO4 2.25M EtOH 3 hr Ambient 90% PO SF seed oil H2SO4 2.25M MeOH 200:1 4hr 64.5°C 300:1 1 hr Used FO KOH 1% MeOH 6:1 30 min Crude PKO NaOH 1% wt of oil MeOH 1:3 120 Ambient 92.77% min SBO NaOH 0.3% wt MeOH 12:1 60 min 70°C 97.2% KOH 0.1 % wt 12:1 95.6% (Magnesol aided separation) Raphanus NaOH 0.6 % wt of oil EtOH 11.7:1 60 min 38°C 99.10% Sativus (Magnesol aided separation) Virgin oil NaMethoxide 0.6% MeOH 6:1 60 min 60°C 97% Sunflower NaOH 0.6% SBO NaMethoxide/ NaOH 0.8% 92% WVO NaOH 0.8% SF seed oil NaOH 2% MeOH 7:1 2h EtOH Lard 1.26% MeOH 7.5:1 20min 65°C 97.8 ± 0.6% PFAD H2SO4 5% MeOH 8.8:1 60 min 93%

References Widyan & al_Shouykh, 2001 Siler-Marinkovic & Tomasevic, 1998, 2003 Attanathos et al, 2004 Kalva et al, 2007

Domingos et al, 2008 Dias et al 2008

Georgoganni et al, 2008 Jeong et al, 2009 Chongkhong et al, 2009

Table 3: Various Conditions of Solid Homogeneous and Heterogeneous Catalysts Use In Transesterification of Various Feedstock Catalyst Na/NaOH/ γ-Al2O3 KF- γ-Al2O3 zeolite loaded with mixed metal Combined acidic/ alkali in presence of co-solvent THF and dioxane Ion exchange resin, Amberlyst 15, 31, 35 & 36

Remark Soybean oil Soybean oil

References Kim et al, 2004 Suppes et al, 2004

Pre-esterification with dioxane was more effective than THF

Hancsok et al, 2004

Babassu coconut, corn, palm, palm kernel, and soybean, Higher yield of ester in shorter chain Fatty acid. catalytic activity of the resin depends on the FA composition of the vegetable oil employed MeOH, EtOH and mixed alcohol at WCO, with two-stage method yield > 90% FAME compared to 50% 6:1 alcohol:oil ratio with single stage Mg-Al hydrotalcite Soybean methanolysis Acid catalyst Fe +3 vanadayl 473K 3h, MeOH:oil ratio 30:1. Not sufficient as industrial catalyst phosphate KF/Hydrotalcite Solid Catalyst Palm oil transesterification at 338K, MeOH:oil ratio 12:1 for 3 hr Iron doped HTC SBO yield 100% FAME, Dopant cations incorporated into HTC lattice, after 80 min Mg-La Oxide (3:1) oil:catalyst ration Easy and inexpensive method to prepare catalyst. At 65°C for 0.3 h and Reaction time for 2.2 h FAME yield 100% edible and non edible oil Porous Zirconia, titanic and alumina Reaction time 5.4 s with over 15 cycle reuse with feedstock of high micro-particle at high pressure 2500 FFA. Scale up study at a factor of 49 times gave 87.5% conversion. psi and temp (300-450°C) Acidic ion exchange resin WCO, 50-60°C, catalyst at 1-2wt%

dos Reis et al, 2005

Longer chain alcohol/ acid base Mixed feedstock FAME yield in 40 mins catalyst in microwave reactor

Wahlen et al, 2008

0.6% NaMethoxide 0.6% NaOH for SF 0.8% NaOH for WFO

Dias et al, 2008

Virgin Oil FAME of 99.4% purity yield

Issariyakul et al, 2006 Xie et al, 2006 Li & Xie, 2008 Lijing et al, 2008 Macala et al, 2008 Seshu 2008

Babu

et

McNeff et al, 2008 Ozbay et al, 2008

al,

0.8% NaoH for WFO macrospherical magnesia-rich magnesium aluminate spinel catalysts (MgO · Mg Al2O4) Calcium methoxide catalyst:oil ratio 4%

Degree of methanolysis not stated. higher catalytic activity in the Wang, et al 2008 methanolysis of soybean oil compared with an MgO/MgAl2O4/_Al2O3 90% FAME at 65°C in 2 h with MeOH:oil ratio 1:1. activity slightly Liu et al, 2008 decreased after 20 cycle reuse

Mg, MCM-41, Mg-Al hydrotalcite, K impregnated Zirconia (1) 24 KHz ultrasonication (U), (2) 600 rpm mechnical stirring (M) KOH/Al2O3 (25%), KOH/Naγ (10%)

ZrO activity increased with more K. Ultrasonication significantly Georgogianni et increased reaction compared with mechanical stirring 2009 Mg-Al HT, MCM-41, ZrO yield - 97%, 85%, 89% at 24 h mechanical stirring and 96%, 89%, 83% at 5 h ultrasonication respectively Palm Oil yields 91.7% FAME at <70°C, 2-3hrs MeOH:oil ratio 15:1, Noiroj et al, 2009 catalyst 3-6 wt%

Mg-Zr (2:1 wt/wt%)

SFO, JO transesterified at 65°C for 30-45 min. marginal decrease yield after 4th cycle reuse of 5%

Sree et al, 2009

Ferric Sulphate / active carbon MeOH:Oil ratio of 18:1, at 368.15K catalyst mass concentration powder 3.5%. loss of activity ater 1st reuse

Gan et al, 2009

Heterogenous KF loaded nano-Y Canola oil yield 97.7% FAME during 338K, 15:1 MeOH:Oil raio at 3 Boz et al, 2009 Al2O3 Calcinated at 773K for 8 h wt% . Observed leaching lead too 30-40% activity loss Calcinated egg shells at 1000°C KNO3/ Al2O3 solid catalyst

SBO yield > 95%. FAME at MeOH:oil ratio 9:1 for 3 h at 65°C. Wei et al, 2009 Reused 13 times with no loss in activity.

Jatropha oil yield over 84% FAME under the conditions of 70°C, Amish et al, 2009 methanol/oil mole ratio of 12:1, reaction time 6 h, agitation speed 600 rpm and catalyst amount (catalyst/oil) of 6% (w). Al2O3 supported CaO and MgO Lipid of yellow green microalgae, Nannochloropsis oculata at 50 C. Emin et al 2009 catalysts 97.5% biodiesel yield over 80 wt.% CaO/Al2O3 catalyst increased to 97.5% from 23% when methanol/lipid molar ratio was 30. Al2O3 supported CaO and MgO catalysts were more active than pure CaO

al

and MgO in the production of biodiesel from the microalgae Nannochloropsis oculata. CaO/ Al2O3could be reused twice. Tri-potassium phosphate, triNaPO3, SBO, 97.3% ester yield at 60°C , 12o min. catalyst regenerated in Guan et al, 2009a diKHPO4, THF KOH. Yield FAME at 88% co-solvent reduce yield KF/ ZnO (5.52 wt%)

PO transesterification yield 89.23% at 9.72 h, methnoal: oil ratio Hameed et al, 2009 11.43, 65°C

Table 4: Biodiesel Purification methods Material

Method of purification

pure glycerol

Addition of pure glycerol to upper layer of product and hot water washing to remove Issariyakul catalyst , with mixed alcohol & tannic acid 2006

Water Wash

Reference et

al,

Membrane

Phase separates at room temperature into a FAME. permeate consistently separated to yield a FAME-rich non-polar phase containing a minimum of 85 wt.% FAME

Dube et al, 2007, Cao et al, 2008

Absorbent (900µm)

BD10 All method demonstrated removal of glycerol & soap only. Water washing has real effect on MeOH and none on glycerides, OSI, AV and water content

Berrios & Skelton, 2008

Purolite (600µm)

PD206

Magensol (60µm) Silica gel, phosphoric water

5% two-step alkali transesterification of waste sunflower oils (WFOs) results showed that acid, silica gel and phosphoric acid treatments gave the highest (~92%), while the hot water treatment the lowest yields (~89%),

Predojevic, 2008

Table 5: Purification of Biodiesel to EN 14214 Standard using water wash, Resin and Magnesol, Water content

Acid value

OS I

Water wash







√











Resin



















Magnesol



















MeOH Glycerol TG DG MG

Soap

 - not effectively reduced to EN 14214 standard  - effectively reduced to EN 14214 standard Berrisos & Skelton, 2008

Abbreviations Mono glyceride Di glyceride Triglyceride dimethyl ether diethyl ether tert-butyl methyl ether tetrahydrofuran Palmitic Fatty Acid Distillate biodiesel fuel diacylglycerols Waste vegetable Oil Supercritical Fluid Supercritical methanol Supercritical Extraction Sunflower seed oil Jatropha Oil

MG DG TG DME DEE TBME THF PFAD BDF DGs WVO SCF SCM SCE SFO JO

Soybean Oil Palm Kernel Oil Palm Oil Crude Palm Oil Oxidative Stability Index

SBO PKO PO CPO OSI