PRODUCTION OF BIODIESEL AND ITS OPTIMIZATION

Transcription

1 CHAPTER III PRODUCTION OF BIODIESEL AND ITS OPTIMIZATION 1. Introduction There is increasing interest in developing alternative energy resources. An immediately applicable option is replacement of diesel fuel by biodiesel, which consists of the simple alkyl esters of fatty acids. With little modification, diesel engine vehicles can use biodiesel fuels. Biodiesel has been defined as the fatty acid methyl esters (FAME) or FA ethyl esters derived from vegetable oils or animal fats (Triglyserides, TG) by transesterification with methanol or ethanol. Its main advantages over fossil fuel are that it is renewable, biodegradable, and nontoxic. Its contribution to greenhouse gases is minimal, since the emitted CO 2 is equal to the CO 2 absorbed by the plants to create the TG. They can also be used as heating oil. Conversely, they do present other technical challenges, such as low cloud points and elevated NOx emissions. Currently, there are no modifications needed in the existing diesel engines to use biodiesel as a blend with petroleum diesel fuel. The use of biodiesel is encouraged by governments across the world to improve energy supply security, reduce greenhouse gas emissions, and boost rural incomes and employments [1, 2]. US green fuel production yielded 16.2 billion liters of ethanol in Ethanol has a 2.8% share of the US automobile fuel market. Substantial tax credits of about $2 billion per year has enabled this technology to develop necessary infrastructure for product delivery at a fast pace. There have been several attempts to evaluate the ethanol production schemes to determine how much energy is consumed in the process. Ethanol as fuel was found to reduce greenhouse emissions by 18%. Cellulosic ethanol from poplar or switch grass was found to reduce greenhouse gas emissions by more than 90%. Biodiesel looks promising but more research is called for in all of these different alternative fuel categories [3]. Biodiesel (BD) is a biodegradable and environmentally benign alternative fuel that is used in diesel engines and heating systems. BD also reduces carbon monoxide and hydrocarbon particulates from diesel engine emissions [1]. In contrast to fossil fuels, BD does not significantly contribute to a net increase in carbon dioxide because, for the most part, the 95

2 fatty acid sources from which it is made are photo synthetically derived. In comparison to fuel ethanol, BD production results in a lower release of nitrogen, phosphorus, and pesticide pollutants per net energy gain and is estimated to have a higher energy yield. Typically, the triglycerides (TG) in the feedstock are directly transesterified with methanol in the presence of an acid, base, or enzyme (lipase) catalyst to afford fatty acid methyl esters (FAME) and glycerol [2, 4-6]. Currently, the most common commercial process for BD production is by base-catalyzed transesterification of a refined vegetable oil with methanol [7]. Figure. 3.1: Transesterification reaction of Pongamia and Jatropha oil and methanol in the presence of alkali catalyst. The transesterification reaction may be performed through several methods such as acidic, alkali, or enzyme catalysis, the first two taking place at higher temperatures than the last one. Zeolite and metal catalysis also have been proposed. All of the proposed methods have disadvantages such as long reaction times, formation of soap, and a high cost of consumables or infrastructure. The application of low-frequency ultrasound recently has been suggested for fast, cost-efficient alkali-catalyzed transesterification of TG to FAME [8]. The transesterification of natural triglycerides (eg; oils and fats), which serve as key reagents to vital products in the chemical industry, is a highly desired goal. These are employed to obtain lots of products used in a wide variety of industrial processes. The most significant products obtained by transesterification, which involve the use of millions of tons of fats and oils a year, are soaps, long chain carboxylic acids, detergents, mono and diglycerides, methyl esters of fatty acids, additives for foods, cosmetics, pharmaceuticals and alternative fuels for diesel engines Several processes are normally 96

3 employed for catalytic transesterification, but these reactions must be carried out at high temperatures and pressures which reduce selectivity, are energy demanding and suffer from the presence of by-products [9 11]. One of the objectives of this work was to use microwave irradiation as an easy and fast method for Bio Diesel synthesis through triglycerides transesterification with methanol. The reactions were carried out either at atmospheric or under pressure, in order to compare their results with the ones conducted with conventional heating [12]. Currently, the most common commercial process for BD production is by base-catalysed transesterification of a refined vegetable oil with methanol [13, 14]. Many reports of transesterification have come in literature using different vegetable oils for biodiesel preparation such as palm oil [15] Jatropha oil [16], Pongamia oil [17], Soy bean, cotton seed, castor oil [18] rape seed [19], chicken feather [20], used cooking oil, canola and hazelnut [21]. This chapter discusses various methods of biodiesel preparation such as homogeneous catalysis transesterification (NaOH as catalyst), heterogeneous catalysis transesterification (Mg - Al Hydrotalacite (MAH) and calcium hydroxyapatite as catalyst), conventional heating method of transesterification, microwave and ultrasonic assisted transesterification. 2. Results and Discussion 2.1. Homogeneous catalyst for Transesterification Preparation of Bio-diesel using NaOH as catalyst The physical properties of the commercial grade Pongamia oil is as given in Table 1. The average molecular weight calculated for the Pongamia oil was 870 g/mol. A 500 ml three necked glass flask with a water cooled condenser at the top was charged with 50 g of oil, with different volume of anhydrous methanol and varied amounts of catalyst. Each mixture was vigorously stirred and refluxed for the required reaction time. After several hours, the reaction mixture was cooled and separated by filtration. The filtrate was allowed to settle down to separate into two layers. The oil phase consisted of methyl esters and unreacted triglycerides, while the aqueous phase primarily contained methanol and glycerol. The residual methanol was separated from the liquid phase by distillation. Experiments were carried out by changing different parameters like methanol/oil molar ratio, reaction time, catalyst amount, temperature and mixing intensity. Glycerol formed after the reaction was weighed and mole value was calculated. This mole value of 97

4 glycerol was compared with the theoretical value and based on this difference the conversion of triglyceride was estimated [8, 9, 11, 22]. The preliminary studies to determine the optimum quantity of methanol, catalyst (NaOH), reaction temperature and reaction time required for the transesterification of Pongamia oil were conducted by varying the concentration of methanol from 8 to 25 (w/v), NaOH concentration from 0.5 to 1.5%, the reaction temperature from 30 to 60ºC and the reaction time from 60 to 140 min Effect of NaOH concentration The catalyst concentration was varied from 0.5% to 1.5%. Methanol concentration of 11(w/v) gave the best ester yield. A constant reaction temperature of 60ºC and a reaction time of 90 min was employed with variations in NaOH concentration. The results of this study are presented in Figure: 2a. The results clearly indicate that the optimum concentration of NaOH required for effective transesterification was 1.0%. It was observed that if the NaOH concentration was reduced below or increased above the optimum, there was no significant increase in the biodiesel production, but there was increased formation of glycerol and emulsion. The variation in the NaOH concentration versus the ester yield percentage is shown in Figure 2a. It is seen clearly from Figure 2a that a maximum ester yield of 91% was obtained using 1.0% NaOH concentration Effect of methanol quantity The molar requirement of methanol was found to be nearly 11 (w/v). Hence, to optimize the amount of methanol required for the reaction, experiments were conducted with 8, 10, 15 and 25 (w/v)% of methanol. The concentration of NaOH, reaction temperature and reaction time used with the methanol variations were constant at 1.0%, 60ºC and 90 min respectively. The results clearly indicate that the optimum concentration of methanol required for effective transesterification of Pongamia oil was 11(w/v)%. Moreover, it was found that when the concentration of methanol was increased above or reduced below the optimum, there was no significant increase in the biodiesel production, but the excess or shortfall in the concentration of methanol only contributed to the increased formation of glycerol and emulsion. The variation in methanol concentration versus ester yield percentage is shown in 98

5 Figure 2b. Figure 2b clearly shows that a maximum ester yield of 88% was obtained using 11 (w/v)% of methanol. Figure. 3.2 : The conventional method of preparation of Pongamia biodiesel 2a) effect of catalyst, 2b) effect of temperature, 2c) effect of methanol, 2d) effect of time Effect of reaction temperature The temperature variations adopted in this study were 30, 45, 60 and 90ºC. A constant reaction time of 90 min and constant methanol and NaOH concentrations of 11(w/v) and 1.0% respectively, gave the best ester yield. The temperature alone was varied for the production of biodiesel from Pongamia oil. The results clearly indicate that the maximum ester yield was obtained at a temperature of 60ºC. The variation in reaction temperature versus ester yield percentage is shown in Figure 2c. It clearly shows that the ester yield proportionately increased with the increase in the reaction temperature. Since the 99

6 reaction temperature has to be below the boiling point (65ºC) of methanol, the reaction temperature was fixed at 60ºC. A maximum ester yield of 91.7% was obtained at 60ºC as shown in Figure 2c Effect of reaction time Reaction times of 30, 60, 90 and 120 min were selected in order to optimize the reaction time. A constant methanol concentration of 11(w/v), constant NaOH concentration of 1.0% and constant temperature of 60ºC were maintained. The results of this study are given in Figure 2d. The results clearly indicate that the biodiesel yield increased with reaction time. The biodiesel yield was found to be more or less the same at 90 and 120 min of reaction time. The variation in the reaction time versus the ester yield percentage is shown in Figure 2d and it clearly shows that the maximum ester yield of 92% was obtained when the reaction time was 90 min Heterogeneous catalyst for transesterification The transesterification process can be catalyzed by both acids and bases. Base catalysts like sodium or potassium hydroxide are used in a majority of transesterification reactions. Base catalysts are preferred to acid catalysts because they have better activity and do not facilitate corrosion. Base catalysis poses emulsification and separation difficulties, and side reactions like decomposition and polymerization may also occur during distillation after the reaction. To overcome these difficulties researchers have focused their attention on developing heterogeneous catalysts. The employment of heterogeneous catalysts helps to separate the products easily [3, 16]. Solid acid catalysts such as zeolites, clays and ion exchange resins have been tried but their reaction rates are found to be very low. Solid base catalysts such as simple metal oxides, mixed oxides and ion exchange resins have also been tried for the transesterification process. Conventional homogeneous catalysts are expected to be replaced in the near future by environmentally friendly heterogeneous catalysts mainly because of environmental constraints and simplifications in the existing processes. At the laboratory scale, many different heterogeneous catalysts have been developed to catalyze the transesterification of vegetable oils with methanol. Hydrotalcites, Mg 6 Al 2 (OH)16SO 4.4H 2 O, have been used as precursors of catalysts and have attracted much attention during the development of new environmentally friendly catalysts. The structure of hydrotalcite resembles that of brucite, 100

7 Mg(OH) 2, where the magnesium cations are octahedrally coordinated by hydroxyl ions, resulting in stacks of edge-shared layers of the octahedral. In the hydrotalcite structure, part of the Mg 2+ ions are replaced by Al 3+ ions forming positively charged layers. Chargebalancing anions (usually SO 2 4 ) and water molecules are situated in the inter layers between the stacked brucite like cation layers. Calcinations at high temperature decomposes the hydrotalcite into interactive, high surface area and well-dispersed mixed Mg Al oxides which present basic sites that are associated with structural hydroxyl groups as well as strong Lewis basic sites associated with O 2 Mn + acid base pairs [23-25] Catalyst preparation Mg-Al-SO 4 hydrotalcite was synthesized by the co-precipitation of Mg 2+ and Al 3+ ions in an alkaline solution containing NaOH. 1.0 M solution of Mg 2 (SO 4 )6H 2 O (0.3M) and Al 2 (SO 4 ).9H 2 O (0.1M) were drop wise mixed in 3:1 ratio with 1 M NaOH. The reaction time ph was maintained between 9 and 11 and the reaction was carried out under nitrogen atmosphere. The resultant mixture was aged at 90 0 C for 72 hours. The hydrotalcite was separated by high speed centrifugation and washed with DI water. The hydrotalcite sample was dried at 100 C and then calcined at 400 C [26]. The prepared hydrotalcite was analyzed by XRD, FT-IR, SEM, Surface analysis, and TGA techniques Transesterification of Pongamia Oil Pongamia oil and an appropriate volume of methanol with calcined Mg Al hydrotalcite catalyst (0.5 1%) were placed into a 500 ml three necked flask equipped with reflux condenser and Teflon stirrer ( rpm). The reaction mixture was blended for a period of time at 65 C temperature under atmospheric pressure. The molar ratio of methanol to oil was taken as 6:1. After the reaction, the hydrotalcite catalyst was separated by filtration. Subsequently, the methanol was recovered by a rotary evaporator in vacuum at 45 C and the ester layer was separated from the glycerol layer using a separating funnel. The fined ester layer was dried over sodium sulfate and analyzed by gas chromatography on a Shimadzu GC chromatograph with FID detector. The oven temperature program consisted of start at 40 C and end at 360 C. The internal 101

8 standard used was C 4 to C 24 FAME (Fatty Acid Methyl Ester) mix (Sigma Aldrich, USA) (Sigma Aldrich, USA) Characterization of catalyst XRD analysis revealed prominent 2θ peaks at 11.8, 23.8, 35.2, 62.4, and On comparison (JCPDS card no #: ) the formation of Mg-Al hydrotalcite was understood. A few other peaks were due to intermediate compounds. The basal spacing was calculated to be nm. The sharp peak (003) indicates the formation of highly crystalline materials. Indexing of the diffraction peaks was done using a standard JCPDS file. The reflections were indexed in a hexagonal lattice with an R 3 m rhombohedral symmetry. The parameter of hydrotalcite corresponding to the cation-cation distance within the brucite-like layer can be calculated as follows: a = 2 d (110). On the other hand, the c parameter is related to the thickness of the brucite-like layer and the interlayer distance and can be obtained from the equation c = 3 d (003) [27, 28]. Figure. 3.3: XRD pattern of Mg-Al Hydrotalcite As shown in Figure 3.3 the basal reflections from the (003), (006), and from (110) planes in XRD patterns are indicative of Mg-Al-SO 4, proving hydrotalcite formation with an interlayer spacing of nm [28]. Sharp X-ray diffraction lines were detected in the precursor with r = 0.75, which has the composition of the stoichiometric hydrotalcite, Mg 6 Al 2 (OH).16SO 4 4H 2 O. All the other hydrotalcite containing precursors showed broader XRD lines, corresponding to smaller crystallites or less ordered structures [29, 30]. The values of the unit cell parameters, assuming rhombohedral symmetry, with the c parameter corresponding to three times the thickness of the expanded brucite like layer, are presented in Table 3.1. The a and c parameters decreased with increasing aluminum content, which can be explained by the substitution of larger Mg2+ ions by smaller Al3+ ions [31]. 102

9 Using Scherrers formula, one can find the size of the crystal or particle size. Where K is the shape factor, λ is the X-ray wavelength, typically 1.54 Å, β is the line broadening at half the maximum intensity (FWHM) in radians, and θ is the Bragg angle; τ is the mean size of the orderedd (crystalline) domains, which may be smaller or equal to the grain size. The dimensionless shape factor has a typical value of about 0.9, but varies with the actual shape of the crystallite. The Scherrer equation is limited to nano-scal le particles. It is not applicable to grains larger than about 0.1 µm, which precludes those observed in most metallographic and ceramographic microstructures. Using the Scherrer formula the crystal size was found to be within 4.66 nm to 21.2 nm [29, 31]. Mg-Al Hydtotalcite d (003) d (110) d (003) crystal basal space (003) 2θ d 003 (Å) d & c & Basal spacing C= a = nm Table 3.1: XRD calculation of interlayer distance Figure 3.4 shows the FT-IR spectrum of Mg-Al hydrotalcite. The spectrum was characterized with asymmetric and symmetric stretching vibrations of carboxyl group at 1425 cm -1, along with the O-H stretching of the hydroxyl group and deformation vibration of H 2 O at cm -1. The spectrum is skewed on the right hand side and the net small peak at 2952 cm -1 is due to the hydrogen bonding of H 2 O and interlayer of SO 2-4 anions. In the lower frequencies, the peak at 1637 cm -1 in all the samples can be attributed to the bending mode of the interlayer water. The main absorption band of the sulphate anions was observed at 1370 cm -1. In the low energy ranges of the spectra ( cm -1 ), peaks around 469 cm -1 are attributed to the presence of Mg-O and Al-O bonds. 103

10 Figure 3.4: FT-IR spectrum of Mg-Al Hydrotalcite The hydrotalcite formation by this preparative route was analyzed by SEM. Figure.3.5 shows hows the Rose Petals morphology characteristic of hydrotalcite materials which was observed for all the samples. Figure 3.5: SEM picture of Mg-Al Hydrotalcite Figure 3.6 shows the TGA-DTA TGA DTA curves of both the samples which may be divided into two well differentiated main regions. In the first one, ranging from 120 C to 220 C, there is an endothermic peak eak related to the dehydration of the sample, which is accompanied by a mass loss of 7.78%. The second region, ranging from 270 C C to 600 C corresponds to 104

11 the weight loss due to the dehydroxylation and de-carbonation reactions, which resulted in a mass loss of 8.96%. The third endothermic region, ranging from 780 C to 900 C, has a weight loss of 5.06%. The weight loss corresponds to the decomposition of interlayer anion present in the brucite layer and the dehydroxylation of vicinal OH groups in the hydrotalcite [27, 32]. Figure. 3.6: TGA-DTA curve of Mg-Al-Hydrotalcite Application of catalyst for transesterification of Pongamia Oil The molar ratio of methanol to vegetable oil was one of the most important variables that affect ester formation because the conversion and the viscosity of the produced ester depended on it. The stoichiometric molar ratio of methanol to oil is 3:1 However, when mass transfer is limited due to problems of mixing, the mass transfer rate appears to be much slower than the reaction rate, so the conversion can be elevated by introducing an extra amount of the reactant methanol to shift the equilibrium to the right-hand side. Higher molar ratios result in greater ester conversions in a shorter time [33, 34]. From Figure 7a it is evident that the optimum molar ratio of methanol to Pongamia oil is 6.0. Beyond the molar ratio of 6.0, the added methanol does not significantly enhance the ester conversion. In addition, the 105

12 conversion increased sharply with reaction time, then reached a plateau representative of a near equilibrium conversion after a 4 h reaction. A near maximum conversion of 90.8% was obtained after a 4 h reaction time. Figure 3.7: Transesterification reaction using Mg-Al-Hydrotalcite with Pongamia oil. 7a) effect of methanol molar ratio, 7b) effect of catalyst, 7c) effect of RPM, 7d) effect of temperature. Increasing the amount of catalyst caused the slurry (mixture of catalyst and reactants) to become too viscous giving rise to a problem of mixing and a demand for higher power consumption for adequate stirring. On the other hand, when the catalyst amount is not sufficient, maximum conversion cannot be reached. In most cases, sodium hydroxide or potassium hydroxide have been used in the process of alkaline methanolysis, both in concentrations ranging from 0.5% to 1.5% w/w of oil. In our work, the reaction profiles indicate 106

13 that the ester conversion increased with the increase of catalyst amount from 0.5% to 1.5% (0.5% w/w of oil: 68.2%, 1.0: 79.5%, and 1.5: 90.5%). However, Figure 7b shows that the conversion to biodiesel decreased with increase in catalyst amount beyond 1.5% (2.0: 85.0%, 2.5: 83.7%), which may possibly be due to the mixing problem of reactants, products and solid catalyst. The maximum ester conversion reached 90.5% when 1.5% catalyst was added. Mixing is very important for the transesterification of Pongamia oil, because the oil and methanol are immiscible and the reactants and the solid catalyst are separated in the heterogeneous system. Generally, a more vigorous stirring causes better contact among the reactants and solid catalyst, resulting in the increase in reaction rate. Figure 7c clearly shows that the reaction progressed only upon stirring and that the stirring of the reactants had a significant effect on the transesterification of the oil (100 rpm: 19.5%, 200: 60.2%, 300: 90.2%, 400: 90.2%, and 500: 90.3%). Adding solid catalyst to the reactants while stirring facilitated the chemical reaction, and the reaction started quickly. It also established a very stable emulsion of oil, MeOH and catalyst. The ester conversion increased rapidly with an increase of stirring speeds from 100 to 500 rpm. Increasing the stirring speed over 300 rpm did not result in further enhancement in the conversions (above 90.2%). The effect of reaction temperature on the ester conversion was studied at six different temperatures, i.e. 50, 55, 60, 65, 70 and 75 C. Figure 7d shows the variation of ester conversion with reaction temperature. Transesterification proceeded slowly at 50 C, where the conversion was 19.6% in a 4 h reaction. Lower temperatures resulted in a drop of the ester conversion because only a small amount of molecules were able to get over the required energy barrier. The ester conversion increased up to 90.4% in a 4 h reaction on increasing the reaction temperature to 65 C (55 C: 31.8%, 60 C: 70.2%). Thus, the optimum temperature for the preparation of the ester was found to be 65 C, which was near the boiling point of anhydrous methanol. The conversion fell to about 80.0% in the temperature range of C (70 C: 80.9%, 75 C: 80.0%), probably because the molar rate of methanol to oil decreased when the methanol reactant volatilized into gas phase above 65 C, the boiling point of pure methanol. The catalytic transesterification of Pongamia oil with methanol to form biodiesel was investigated using the Mg/Al Hydrotalcite. The conversion of biodiesel was 90.8%. The obtained biodiesel was analyzed by a Shimadzu GC 2010 using C 4 C 24 FAME MIX., as standard. All relative percentages determined by GC for 107

14 each fatty acid methyl ester sample are the means of triplicate runs. This method was used for the methyl esters reported in Tab S.No FAME Profile Pongamia Biodiesel Using Mg-Al 1 16: :1-3 18: :1 58: : : : : : : Table 3.2: Gas chromatography result of Pongamia biodiesel. From Table 3.2, the% composition of the five important fatty acid methyl esters (FAMEs), found in the biodiesel samples such as palmitic (C16:0), stearic (C18:0), oleic (C18:1), linoleic (C18:2), and linolenic (C18:3) acid methyl esters were determined and reported. The Table also shows that linoleic and oleic acid methyl esters are the major components in the synthesized biodiesel samples. The GC study shows clearly that the catalyst Mg - Al hydrotalcite is efficient in transesterification of Pongamia oil to biodiesel Hydroxyapatite as a catylyst from waste animal bones CaO is an environmental friendly material useful as a basic oxide catalyst. Ca(NO 3 ) 2, CaCO 3, CaPO 4 and Ca(OH) 2 are raw materials to produce CaO, but natural sources such as 108

15 egg [35, 36], shrimp [37], oyster [38], and crab and cockle shells [39] have also been employed. Animal bone can also be used as raw material. Calcium phosphate is the main component of bone and can be transformed to hydroxyapatite which has relatively high catalytic activity, good thermal and chemical stability, and can make the production of biodiesel environmentally friendly. In the present investigation, the bone-derived catalysts were characterized and utilized in the production of biodiesel using palm oil and methanol. Performance of the prepared catalyst was compared with that of laboratory grade CaO normally employed for base catalyzed transesterification. Reusability of the catalyst was also tested Catalyst Preparation Bone powder referred to as milled animal bone'' was prepared directly from bone without digestion/reprecipitation steps by crushing bone from sheep in a hydraulic press at 100 psi followed by pressure cooking in water at 15 psi and 1000 C for 4 h with a water change halfway through to remove tissue and fat. The clean bone chips were subsequently dried for 16 h in an oven set at 105 C before being ground finely to a <2mm particle size powder using a hammer mill [40, 41]. The bones were calcined in a high-temperature muffle furnace (Toshibha, India) at different temperatures ranging from 200 C to 1000 C under static air to observe the influence of the calcinations process on transformation of calcium species into hydroxyl apatite. Crushed and powdered catalysts were sieved and stored in a air-tight container before use Characterization Scanning electron microscopy (SEM) analysis was done to study the morphology and the size of the catalysts using a JEOL JSM-6390 microscope. X-Ray powder diffraction analysis (XRD 6000 SHIMADZU model) coupled with Cu Kα radiation was done to study the structure transformation of the catalysts on calcination. FT-IR spectra were obtained with a FTIR Excalibur FTS 3000 MX SHIMADZU in the range of 400 to 1000 cm -1. The elemental composition was determined by energy dispersive X-ray fluorescence spectroscopy (EDXRF; EDX-720, Shimadzu, Japan) under vacuum mode and the surface area analysis was performed using surface area analyser (Nova, United Kingdom). 109

16 Transesterification Palm oil and methanol were taken in suitable molar ratios. Calcined bone was added at levels of 5 to 25 wt%, the mixture was stirred vigorously in a mechanical stirrer at 150 rpm at 65 C for 4 h using a reflux condenser. The same reaction was also carried out with commercial CaO. After completion of the transesterification, the catalyst was recovered by filtration through Whatman filter paper (size 42). The resultant mixture was allowed to separate, the upper layer was subjected to rotary evaporation (40 C to 45 C) to recover excess methanol and the product obtained was dried over sodium sulphate before subjecting to gas chromatography (GC). The sample peaks were compared with C 4 C 24 FAME standards. A FID detector was used and the oven temperature was set to 340 C. The characteristic property of palm oil and palm biodiesel are shown in Table 3.3. Properties Palm Oil Palm biodiesel Standard method Standard value Iodine value g iodine/100 g g iodine/100 g EN max Peroxide value meq/kg - - Kinematic viscosity mm 2 /S 3.68 mm 2 /S ASTM-D mm 2 /S Acid value 0.58 mg KOH/g mg KOH/g ASTM- D max Calorific value MJ/kg MJ/kg - - Free Glycerol % mass ASTM D %,max. Total Glycerol % mass ASTM D % max. 110

17 Properties Palm Oil Palm biodiesel Standard method Standard value Ester content % EN % C16:0 9.47% - - C18: % - - C18: % - - C18: % - - C18:3 3.49% - - C20:0 1.18% - - C22:0 0.86% - - Table 3.3. Comparison of the properties of palm oil and palm biodiesel and composition of biodiesel. The reusability of the catalyst was investigated by carrying out repeated transesterification cycles. The catalysts was separated after 4 h from the reaction mixture and washed with double distilled water and finally washed with acetone and dried in an oven at 50 C Characterization of waste animal bone derived catalysts The XRD pattern with respect to calcinations is shown in Figure 3.8. The prominent 2θ peaks obtained for uncalcined, 200 C calcined and 400 C calcined samples are 32.1, 25.8, 49.8 and Indexing of the diffraction peaks was done using a standard JCPDS (Joint Committee on Powder Diffraction Standards) file and the conformation of calcium phosphate (JCPDS card no #: ) was understood. The catalyst calcined above 600 to 1000 C shows a different XRD pattern and the prominent 2θ peaks obtained and h,k,l values are 21.8 (200), 25.8 (002), 28.1 (102), 28.9 (210), 31.8 (211), 32.2 (112), (300), 40.4 (221), 40.8 (103), 46.8 (222), 48.1 (132), 48.7 (230), 49.5 (213), 50.5 (321), 51.3 (140), 52.1 (402), 53.3 (004), 59.9 (240), 60.5 (331), 61.6 (241), 63.1 (502). Indexing of the diffraction peaks was done using a standard JCPDS file and the confirmation of calcium hydroxyapatite (JCPDS card no #: ) was understood. 111

18 Figure. 3.8: XRD patterns of the animal bone derived catalysts prepared at the different temperatures. Microstructural changes with respect to calcinations are shown in Figure 3.9. The morphology of the uncalcined sample appeared like mass of aggregates, having less surface area. Whereas the catalysts which were calcined at 200 C and 400 C showed some change in its morphology but still their particle size reduction seem to be minimum, whereas catalysts calcined at 600 C to 1000 C were rod like crystal particles. Their particle size reduction was maximum, exhibiting higher surface area, an important characteristic of a heterogeneous catalyst. 112

19 Figure 3.9. SEM image of the animal bone derived catalysts prepared at different temperatures: (a) uncalcined (b) 200 C (c) 400 C (d) 600 C (e) 800 C (f) 1000 C. The BET studies confirmed that the particle size decreased as the calcination temperature increased leading to an increase in surface area. The uncalcined catalyst had a surface area of only m2/g whereas that of catalyst calcined at 1000 C was m 2 /g (Table 3.4). 113

20 Contents Chemical composition of the catalysts in weight (%) Uncalcined 200 C 400 C 600 C 800 C 1000 C C O Na Mg P Ca Surface area (m 2 /g) Table 3.4. Chemical composition and surface area of animal bone derived catalyst prepared at different temperatures. FTIR patterns with respect to calcinations were recorded as in Figure The FT-IR spectra of the calcination products exhibited only the characteristic absorption peaks of hydroxyapatite [41, 42]. The peaks around 1047 to 1095 cm -1 correspond to asymmetric stretching vibrations of P-O bonds. The bands around 570 to 632 cm -1 correspond to the vibrations of O-P-O bonds in calcium phosphate. The peak of carbonate at 870 to 875 cm -1 is seen in the uncalcined sample at 200 to 600 C very clearly, whereas only a trace is present at 800 C and is completely absent at 1000 C. 114

21 Figure 3.10 : IR spectra of animal bone derived catalysts prepared at different temperatures. The inorganic composition (C/O/Na/Mg/P/Ca) of the different catalysts were determined by OXFORD INCA EDS (Table 3.4). EDS analyses revealed that the content of inorganic phases of bones consisted mainly of calcium and phosphorus with some minor components such as C, Na, and Mg. The result in Table 3.4 also indicates that the calcium, oxygen and phosphorous contents increase as the temperature is increased and reach a maximum at 800 C, suggesting that the activity will also increase due to the formation of hydroxyapatite. As shown in Figure 3.11, the mechanism of hydroxyapatite in transesterification reaction starts with disassociation of Ca 5 (PO 4 ) 3 (OH) 2 and methanol (steps i, ii and iii). Next, 115

22 the formation of methoxide anion results from the reaction between methanol and hydroxide ion. The anion then attacks the carbonyl carbon of the triglyceride to form a tetrahedral intermediate. Subsequently, the rearrangement of the intermediate molecule results in the formation of a mole of methyl ester and diglyceride, (step iv). The methoxide then attacks another carbonyl carbon atom in the diglyceride, forming another mole of methyl ester and monoglyceride. Finally another methoxide attacks the monoglyceride producing a total of three moles of methyl ester and a mole of glycerol [43]. Figure Proposed mechanism of FAME preparation using hydroxylapatite catalyst Optimization of transesterification over waste animal bone-derived catalysts Effect of calcinations temperature for catalyst The calcinations at higher temperatures led to desorption of carbon dioxide from the animal bone catalyst, producing basic sites that catalyzed transesterification of palm oil with methanol. Calcining at 200, 400 and 600 C was not enough to produce highly active catalysts. However calcinating at 800 C gave a yield of 96.78% after a reaction time of 4 h at 65 C. Additionally, the transesterification activity agreed well with the Ca content in the catalyst samples; namely, a higher Ca content in the form of CaO resulted in higher activity. The conversion was comparable to commercial CaO, which exhibited a conversion of 99%. Further increase in temperature suppressed the catalytic activity of the catalyst due to the high sintering rate of the catalyst and high energy consumption [37]. The descending order of the conversion rate over the catalysts at different temperature is ranked as follows: 800 C > 600 C > 1000 C > 400 C> 200 C > uncalcined. Therefore, the optimum calcination temperature was 800 C. 116

23 Figure 3.12 : Effect of calcination temperature on FAME conversion Effect of oil to methanol ratio The FAME content increased significantly when the oil/methanol ratio was changed from 1:1 to 1:18, but was lower at methanol ratios above 18 (Figure a). 117

24 Figure.3.13 : Effect of different parameters on FAME conversion: (a) molar ratio of methanol (b) catalyst concentration (wt%) (c) reaction temperature ( C) (d) reaction time ( h) (e) stirring rate (rpm) (f) reusability. The high amount of methanol (oil to methanol ratio of 1:18) promoted the formation of methoxy species on the CaO surface, leading to a shift in the equilibrium in the forward direction, thus increasing the rate of conversion up to 96.78%. However, further increases in the oil to methanol ratio did not promote the reaction. It is understood that the glycerol would largely dissolve in excessive methanol and subsequently inhibit the reaction of methanol to the reactants and catalyst, thus interfering with the separation of glycerin, which in turn 118

25 lowers the conversion by shifting the equilibrium in the reverse direction [43]. Therefore, the optimum ratio of oil to methanol was 1:18, which is more than double the practical oil to methanol ratio for homogeneous transesterification of 6: Effect of catalyst loading The effect of catalyst loading on FAME conversion over animal bone derived catalyst was investigated (Figure 3.13b). When a small amount of catalyst (<1 wt%) was used, the maximum product yield could not be reached. The maximum conversion of 96.78% was obtained with a catalyst loading of 20 wt%. However, the yield did not increase when the catalyst loading was above 20 wt% which led to the formation of a slurry too viscous to enable adequate stirring. Thus, getting the reactants to and from the catalyst becomes the rate determining step (mass transport limitation) which is why adding more catalyst does not exhibit any effect. Therefore it is evident that the optimum catalyst loading is 20 wt% in the present study Effect of reaction temperature The effect of reaction temperature on FAME yield over animal bone derived catalyst was investigated (Figure 3.13c). There was a steady increase in the conversion on rising the reaction temperature and a maximum conversion of 96.78% was obtained at 65 C. On increasing the temperature above 65 C there was a decline in the conversion as the temperature reaches above the boiling point of methanol since methanol bubbles inhibit the mass transfer on the interface of the phases [44]. Therefore, the optimum reaction temperature was found to be 65 C with the catalyst in the present study Effect of Reaction time The effect of reaction time on FAME yield in this transesterification was investigated and is shown in Figure 3.13d. The FAME content increased significantly on increasing the reaction time from 1 hour to 6 hours and a maximum yield of 96.78% was obtained after 4 h. On further increase of the reaction time the yield remained the same till the end of 6 h and started to decline due to equilibrium shift in the reverse direction and also due to the 119

26 formation of emulsions. Comparatively lesser yield at lower (1 hr) reaction time is due to the absence of calcium methoxide, which is the driving force for the transesterification reaction. Therefore, the optimum reaction time was found to be 4 h over the catalyst in the present study Effect of stirring rate The effect of stirring rate (50 to 250 rpm) on FAME yield in the biodiesel production was investigated and is shown in Figure 3.13e. The immiscible phases of methanol, oil and the catalyst surface need a certain stirring speed to increase the yield. The FAME yield increases as the stirring rate is increased and reached a maximum yield of 96.78% at a stirring rate of 200 rpm. There was no significant change on increasing the stirring rate. Therefore, the optimum stirring rate was fixed as 200 rpm Reusability of waste animal bone-derived catalyst The reusability of the catalyst animal bone derived was investigated by carrying out the transesterification in subsequent reaction cycles and is shown in Figure 3.13f. The catalyst was separated after 4 h from the reaction mixture and washed with double distilled water and finally washed with acetone and dried in an oven set at 50 C. Subsequent reaction cycles were performed under the same operating conditions using catalyst recycled after each cycle. After 5 th cycle of the transesterification conversion is 83.7%. The catalyst derived from animal bones had excellent activity in heterogeneous transesterification of palm oil for biodiesel production. Calcination of the catalyst derived from the animal bones resulted in an increase in surface area, leading to better catalytic activity. Among the calcined catalysts, the catalyst calcined at 800 C gave the highest biodiesel yield. The comparison of the performance of animal bone-derived catalyst with synthetic CaO normally employed proves that irrespective of the origin of CaO, the basic CaO acts as catalyst in the transesterification. Since the waste bone catalyst shows high catalytic activity and ecologically friendly properties, it is a potential catalyst for biodiesel production. 120

27 2.4. Conventional heating, microwave and ultrasonic methods Vegetable oils have not been accepted as a diesel engine fuel for two reasons. They are more expensive than petroleum fuels and too viscous to be atomized efficiently in a diesel engine. Among the various attempts to reduce their viscosity, their conversion to corresponding fatty ester appears to be the most promising solution [4]. Different technologies are currently available and are used in the industrial production of transesterified oil for use as biodiesel. The alkali catalyzed method is the most developed method among biodiesel production processes. The controlling parameters which affect the conversion rate using this technology are the molar ratio of alcohol to oil, the temperature, and the pressure. Industrial application of such technology is sure to be successful if it is carried out under optimum conditions [5, 6]. Sonochemistry is the application of ultrasound to chemical reactions and processes. The origin of sonochemistry stems from acoustic cavitation: the growth and highly energetic collapse of microscopic bubbles in a liquid. The chemical effects of ultrasound include the formation of radicals and the enhancement of apparent reaction rates at ambient temperatures. Ultrasonic waves are above the normal human hearing range (18-20 khz) [7]. In general, the conversion of vegetable oil to biodiesel occurs during a transesterification process in the presence of a catalyst and heat. Recently, ultrasonic wave assisted synthesis of biodiesel has been found to be an attractive technique because it gave a higher yield of pure products in less conversion time. When ultrasonic waves are passed through a mixture of immiscible liquids, such as vegetable oil and methanol, extremely fine emulsions can be generated. These emulsions have large interfacial areas which provide more reaction sites for catalytic action and, thus, increasing the rate of transesterification reaction [8-11]. In the present work the transesterification of Pongamia pinnata (L.) Pierre oil was carried out by sonochemical method using pulse and continuous modes. The results of transesterification were compared to the results obtained using conventional method. Ultrasonic energy increased the reaction rate by several fold, reducing the reaction time from approximately min to less than 1 min. 121

28 Preparation of bio-diesel by conventional method Biodiesel from Pongamia pinnata (L.) Pierre was prepared by following previously reported methods [12,13]. Physical properties of Pongamia pinnata (L.) Pierre oil determined in this study are listed in Table 3.5. Properties Pongamia Oil Pongamia biodiesel Standard method Standard Value Iodine Value g iodine/100 g oil g iodine/100 g oil EN max. Peroxide Value (meq/kg) - - Kinematic Viscosity (@ 40 0 C) cp 5.96 cst or 7.46 Cp ASTM D cst Acid value 9.35 (mg KOH/g) (mg KOH/g) ASTM D max. Saponification Value mg KOH/g oil mg KOH/g Oil - - Water Content 0.5% 0.12% ASTM D 2709 Max. 0.05% Carbon Residue Value 0.095% 0.049% ASTM D 4530 Max. 0.05% Cloud Point 8 to 9 4 to 6 Pour Point 2 to 1-3 to 0 ASTM D 2500 ASTM D Calorific Value MJ/kg - - Table 3.5 : Physical properties of crude Pongamia pinnata (L.) Pierre Oil and Pongamia pinnata (L.) Pierre biodiesel. 122

29 Preliminary studies to determine the optimum quantity of methanol, the catalyst NaOH, the reaction temperature and the reaction time required for the transesterification of Pongamia pinnata (L.) Pierre oil were conducted by varying the concentration of methanol from 8 to 25 (w/v), NaOH concentration from 0.5 to 1.5%, the reaction temperature from 30 to 90 C and the reaction time from 30 to 130 min. Figure 3.14: The conventional method of preparation of Pongamia pinnata (L.) Pierre biodiesel. Effects of a) catalyst, b) methanol, c) temperature, and d) time In order to find out the effect of NaOH as catalyst, concentrations of 0.5%, 1% and 1.5% NaOH were used and evaluated (Figure 3.14a). 1% NaOH yielded the maximum quantity of product (85% (w/v)) and was used as the optimum concentration for subsequent experiments. An increased formation of emulsion was noticed with increase in NaOH concentration above the optimum level, whereas biodiesel conversion remained incomplete at lower concentrations. 123

30 The molar requirement of methanol was found to be 11 (w/v). In order to optimize the amount of methanol required for the reaction, experiments were conducted with 8, 10, 15 and 25 (w/v)% of methanol. The concentration of NaOH, reaction temperature and reaction time used with the methanol variations were kept constant at 1.0%, 60 C and 90 min respectively. The optimum concentration of methanol required for effective transesterification of Pongamia pinnata (L.) Pierre oil was 11% (w/v) providing an ester yield of 85% (Figure 3.14b). Moreover, when the concentration of methanol was increased above or reduced below the optimum, there was significant decrease in biodiesel production, with excess methanol only contributing to an increased formation of glycerol and emulsion. The temperature variations attempted in this study were 30, 45, 60 and 90 C. A constant reaction time of 90 min and an optimum methanol and NaOH concentrations of 11 (w/v) and 1.0% respectively, were used. The ester yield proportionately increased with an increase in reaction temperature (Figure 3.14c). The reaction temperature was maintained at 60ºC, since it had to be below the boiling point of methanol (65ºC). A maximum ester yield of 85% was obtained at 60 C. In order to find the reaction time required for optimum yeild, time intervals of 30, 60, 90 and 120 min were selected. Methanol concentration was maintained at 11% (w/v), NaOH at 1.0% and temperature at 60 C. The average results of this study are given in Figure 3.14d. A maximum ester yield of 85% was obtained at a time point of 90 min. Extending the reaction time above 90 min resulted in reduced yield due to backward reaction and emulsion formation Sonochemical synthesis of biodiesel About 50 g of Pongamia pinnata (L.) Pierre oil was added to sodium methoxide solution prepared by reacting 8 ml (4 w/v) methanol with 0.5 g (1%) sodium hydroxide. The sample size was scaled to match the available reaction chamber size for the ultrasonic horn ( 60 ml). Ultrasonic energy was applied in two different modes: the pulse and the continuous modes. In the pulse mode, ultrasonic energy was applied for every 5 sec., and the samples were collected at the end of 30 th, 60 th, 90 th, 120 th, and 150 th sec., time intervals. The pulse mode allowed relatively high amplititudes (high intermediate dissipated power) without causing excessive heating. In short, the pulse mode allowed for generation of intense 124

31 ultrasonic fields while maintaining a moderate average of the dissipated power level. The reaction was studied in three amplititude levels, namely: 40, 60, and 120 Hz. In the continuous sonication mode, the reactants were sonicated continuously for 15 sec., at 120 Hz. A total of 10 reaction mixtures were prepared and each was sonicated for 1, 2, 3, etc., up to 15 sec., time intervals. The reaction was quenched every time by adding water (50 ml) and hexane (50 ml) immediately after the ultrasonic treatment. The mixture of Pongamia pinnata (L.) Pierre oil and biodiesel was separated as detailed in the previous section. For accuracy, all the experiments described were repeated 4 times. It is important to note that external heating was not used in any of the ultrasonication experiments [8, 9, 11] Ultrasonication pulse method Figure 3.15 shows the transesterification of Pongamia pinnata (L.) Pierre oil as a function of time with ultrasonic treatment in the pulse mode at three different amplititudes. The highest yield of 96% was obtained after a time interval of 120 sec., at 120 Hz. At a frequency of 60 Hz, the highest yield was 92% in 250 seconds, and at a frequency of 40 Hz the highest yield of 91% was obtained in 300 sec. Yields as high as 96% were obtained within 120 sec., at a frequency of 120 Hz (Figure 3.15a). 125

32 Figure 3.15: Comparison of biodiesel conversion obtained in pulse mode. Effects of different ultrasonication frequencies against various a) time points, b) catalyst concentrations, and c) methanol concentrations. In the ultrasonic assisted reaction, parameters like concentration of catalyst and methanol were varied. The catalyst content was varied from 0.2% to 1.8% and the methanol content was varied from 2% (w/v) to 18% (w/v). The best yield was obtained when the concentration of NaOH was 1%. The yield was between 96 and 98%. When the concentration of catalyst was reduced below 1% the transesterification remained incomplete and the yield was very poor. However, when the concentration of catalyst exceeded 1%, the oil was saponified and the biodiesel yield was almost zero. Figure 3.15b reveals that at 60 Hz, a catalyst concentration of 1% gave the best yield. At 40 Hz the yield obtained was 60% and at 120 Hz the yield obtained was 83%. The results obtained using various 126

33 concentrations of methanol at different frequencies in the sonochemical methods is shown in Figure 3.15c. A methanol concentration of 4% (w/v) gave the best yield. At a lower concentration more of mono and diglycerides are formed and at higher concentration there was no observed effect. Transesterification under different ultrasonication frequencies and time intervals were studied. Figure 3.15c clearly shows that the best yield was obtained at 120 Hz in a time of 120 seconds. Increasing the time did not affect the yield. At 40 Hz and 60 Hz transesterification was low compared to that observed at 120 Hz. Transesterification at 60 Hz for 250 sec., resulted in 92% conversion of biodiesel. Lowering the frequency to 40 Hz and increasing the time duration to 300 sec., resulted in no change in biodiesel conversion. Temperature variations could not be carried out since sonication itself generated lot of heat Ultrasonication continuous method Figure 3.16a shows the biodiesel production as a function of time with ultrasonic irradiation in the continuous mode at three different frequencies. The highest yield obtained after 15 sec., was 83% at 120 Hz. At 60 Hz, the highest yield achieved was 86% in 15 sec., and at 40 Hz the highest yield obtained was 68% in 15 sec. 127