CHAPTER 6. IN-SITU TRANSESTERIFICATION OF P. americana SEEDS FOR BIODIESEL PRODUCTION

Transcription

1 129 CHAPTER 6 IN-SITU TRANSESTERIFICATION OF P. americana SEEDS FOR BIODIESEL PRODUCTION 6.1 INTRODUCTION The supply of petroleum based fuels is decreasing and one day the people will run out of it. The trend of the high demand is increasing and supply greatly affects the environment. The search for new fuel sources could be a vital part of leaving this world in the best shape possible with at least some natural resources intact. One popular alternative fuel is biodiesel, which is a diesel like product extracted from plant matter. It can be burnt in existing engine. Biodiesel, an exact alternative to petroleum diesel fuel contains no petroleum. Since it is derived from vegetable oils and other organic matter, it is a renewable fuel. Biodiesel can be burnt in most diesel engines, either undiluted or mixed with petroleum diesel in any ratio with little required engine modifications. The main drawback for the commercialization is the high cost of pure vegetable or seed oils, which constitutes between 70 to 85% of the overall biodiesel production cost (Revellame et al 2010, Haas and Foglia 2005, Mondala et al 2009). Use of waste cooking oil for biodiesel production results in other challenges of wide-ranging properties that may affect the biodiesel production reliability (Revellame et al 2010, Vyas et al 2010, Diaz-Felix et al 2009). The plants yielding non-edible oils, such as karanja, jatropha, castor, neem, pongamia and algae may play an important role in providing new alternative source of feedstock (Dorado

2 , Korbitz 2009, Miao and Wu 2006). But development of these alternative raw materials requires vast land and technology. Thus, in order to reduce the cost per gallon of biodiesel, alternative feedstock those are required, as waste and having less commercial value must be considered. Transesterification is the reaction of a fat or oil with an alcohol (with or without catalyst) to form esters and glycerol. Because of the reaction is reversible, excess alcohol is used to shift the equilibrium to the products side (Ma and Hanna 1999). Transesterification reaction can be catalyzed by both homogeneous (alkalies and acids) and heterogeneous catalysts. The most commonly used alkali catalysts are NaOH, CH 3 ONa, and KOH (Vicente et al 2004). Recently, the production of simple alkyl FA esters by direct alkali-catalyzed in-situ transesterification of commercially produced soy flakes by mild agitation of the flakes with alcoholic sodium hydroxide at 60 C was reported (Haas et al 2004). Mondala et al (2009) conducted the experiment with an in-situ transesterification procedure, which was applied on dried primary and secondary sludge samples. The in-situ process eliminated the need to extract and separate the lipids and fatty acids contained in the sludge since the fatty acid containing lipids are simultaneously extracted and transesterified. Thus the reaction time and the amount of solvent and samples required are reduced compared to a separate lipid extraction and transesterification process. In a previous study, Haas et al (2004) performed an alkali-catalyzed in-situ transesterification on soy flakes for biodiesel production Description of the Plant The P. americana tree has shiny evergreen and elliptic leaves 4-8 in (10-20 cm) long. It is a much-branched and medium-sized tree of 60 ft (18 m) or more in height. This practically insures that the flower will not be self-pollinated. The P. americana tree is cultivated for its delicious and highly nutritious fruit. P. americana fruits contain up to 30% oil and have the highest protein. Fruits may be

3 131 pear shaped to round and smaller than a golf ball to almost as big as a football, depending on the variety. There are three principal groups of P. americana: Mexican, Guatemalan and West Indian, named for the areas where they were originally cultivated. Mexican P. americana have foliage with an anise scent and small fruits about the size of a plum, with black or purple smooth skin. Guatemalan P. americana have larger, blackish-green and rough-skinned fruits. The West Indian P. americana has the largest fruits, up to 1 kg, with smooth light green skin. Mexican P. americana has the highest oil content and West Indian has the lowest. The important cultivars now in commercial production are mostly hybrids between these three original groups. There are at least 500 named cultivars. One of the most popular cultivars is Fuerte, a Mexican-Guatemalan hybrid with smooth skinned, shiny green and pear shaped fruits. 'Hass', a Guatemala type, has rough skinned fruits that turn purple when fully ripe. Most of the commercially grown hybrids are self-fertile. P. americana, which is a semitropical fruit variety that is a plant from Central America, is grown in five continents and almost 50 countries around the world (Knight 2002). It has an olive-green peel and thick pale yellow pulp that is rich in vegetable oils and appreciated for its sensory attributes. There is a global increase in consumption per day by day due to its rich nutritious content attracted towards fruit processing and industrial processes once the edible pulp is separated, seed are left as residues and these byproducts from industrialization can cause ecological problems like increased numbers of insects and rodents. In addition, there are economic losses due to the high cost of transporting these byproducts to disposal areas (Ferrari et al 2004). P. americana s seeds are a potential starch source due to their content around 30%, thus the extracted P. americana seed product can be acceptable for using as food (Olaeta et al 2007, Kahn 1987). Thus, studies to investigate the benefits of these byproducts as sources of fuel and fuel additive will gain more importance

4 METHODOLOGY P. americana seeds were obtained as a waste-product from a fruit processing industry (Chennai, India) with an average moisture content of the seed was 47 wt%. The collected seed were identified and authenticated by Centre for Advanced Studies in Botany, University of Madras, Chennai, Tamil Nadu, India Co solvent Selection for in-situ Transesterification Selection of an appropriate solvent is important for in-situ transesterification. A preliminary extraction experiment was done with different solvents such as MTBE, carbon tetra chloride, chloroform, THF and n-hexane to find out suitable solvent for maximum yield of oil extracted. Fresh seeds were cut into pieces, air-dried, pulverized and sieved through a 120 mesh size. It was then finally dried in an oven at 105 C until a moisture content reaches below 0.10 wt% using an auto-titration 701 Karl Fisher Tritino Metrohm. Complete drying helps in the appreciable reduction of reagent requirement in extraction (Haas and Scott 2007). The grounded seed was mixed with equal weight of filter aid (diatoms earth) for easy penetration of solvent when packed in a thimble in a Soxhlet apparatus. P. americana seed oil was extracted from 30 g of P. americana seed with 250 ml of solvent by Soxhlet s method. The extraction time was maintained for a maximum of 16 hours at the rate of 8 cycles per hour. Then, the solvent was removed with a help of rotary evaporator. The oil yield obtained was expressed in terms of mass percentage of the samples and calculated. The unsaponifiable matter content is the quantity, expressed as a percentage of matter other than which does not under go esterification or transesterification under the present condition (Sorho et al 2006, Hautfenne 1982). The percentage of oil extracted, unsaponifiable matter percentage and FFA content were used as parameters to evaluate the selection of solvent used for in-situ production of

5 133 biodiesel. FFA content of the crude P. americana extract was determined by standard volumetric titration (Lin and Sue 1995) Analysis Gas chromatography was used to analyze various fatty acid profiles present in P. americana seed oil. Fatty acids were initially transformed in to their respective methyl esters that follows the methods as prescribed by Hartman and Lago (1973). The FAME profile of the P. americana was measured using GC Preparation of Catalyst The KOH was preferred as alkali catalyst for catalyzing transesterification reaction because KOH is readily soluble and the reaction rate was slightly higher when compared to equimolecular weight of NaOH (Vicente et al 2004). Preparation of the catalyst was estabilished by dissolution of potassium hydroxide with excess methanol. A stock of catalyst solution was prepared by dissolving 15 g of KOH in 100 ml of methanol under cold condition. The dissolution of KOH in methanol produces the methoxide and water. The solution was dried by the addition of 5 g of previously dried anhydrous sodium sulphate. The weight percentage of the catalyst required for the reaction was added from the stock based on their weight proportions In-situ Transesterification In in-situ transesterification, the oil was not extracted from the seed and reacted with the alcohol in the presence of catalyst. The extraction and transesterification occurred simultaneously (Ozgül and Türkay 1993, Kildiran et al 1996, Harrington and D'Arcy-Evans 1985). In-situ alkali catalyst transesterification method was preferred for low acidity oils. The feedstock was prepared as in extraction step apart from that extra care was taken for complete drying in hot air oven at 105 C until the moisture content reaches as low as possible ( 0.01 wt%),

6 134 because the water considerably decrease the yield of alkali catalyzed transesterification (Ma et al 1998). The reaction was carried out in a wide mouth triple neck flat bottom round flask. The reaction was performed in batch where the reactor was placed in a heating mantle controlled by temperature controller. The temperature can be raised up to 65 C with an accuracy of ±1 C. The powdered, dried seeds were charged into reactor along with co solvent. When a required temperature was attained, the catalyst already dissolved in methanol was added. The stirring was performed with a mechanical stirrer through wide neck and a water-cooled condenser was fixed to other neck. The reaction was performed at different catalyst concentration, weight of methanol, temperature, strring speed and weight of co-solvent Downstream Process After the reaction was completed under prescribed condition solid cake and mother liquor were separated by vacuum filtration followed by a solvent rinse. After separation the filtrate was washed with water and extracted with petroleum ether to remove residual co-solvent, unreacted methanol and catalyst. This was then dried under vacuum. The biodiesel yield from P. americana seed was calculated as shown below in Equation (6.1) (6.1) The biodiesel properties were determined as per the standard test and compared with ASTM D6751 standard.

7 RESULTS AND DISCUSSION Selection of Solvent The co-solvent plays an important role in both extractions, as a reaction promoter in the process and to accelerate the in-situ transesterification. Five cosolvent were investigated and their yield on the extracted oil by MTBE, carbon tetra chloride, chloroform, THF and n-hexane were found to be 9.2%, 6.5%, 8.1%, 9.4% and 9.3% respectively (Table 6.1). The oil content of P. americana seed is lower than many other vegetable seeds such as palm (40%), soybeans (18 22%), rape seed (41%) and sunflower (40%) respectively (Lidefelt 2007). The P. americana yield by Soxhlets method was lower (9.4%) than expected (15%) from the findings of Rachimoellah et al, 2009, this may be happened due to the geography and seasons of origin (Haas 1951, Weatherby 1934). Table 6.1 P. americana oil yield, Unsaponifiable matter and FFA for different solvents extracted using Soxhlets method Solvent used Weight of oil extracted a (g) Extracted weight % Unsaponifiable matter content % FFA (%) MTBE Carbon tetra chloride Chloroform THF n-hexane a Per 30 gram of seed by Soxhlets extraction

8 136 From the Table 6.1 it was observed that the oil extracted by THF and n- hexane yields high, without a much significant difference in FFA and unsoponifiable matter content. Since THF had proved to be good in extraction and the same can form a single phase to improve the mass transfer of oil and methanol to intensify the transesterification of oil and aliphatic alcohols (Boocock et al 1998, Mao et al 2004, Zhou et al 2003). From these above considerations, THF is selected as co-solvent for in-situ transesterification Characterization of P. americana seed oil The quantitative analyses of fatty acids composition of P. americana seed oil were presented in Table 6.2. About eleven different types of fatty acids were identified. Linoleic acid (40.93 wt%) was the principle fatty acid. The other major fatty acids in the seed were Oleic acid (21.37 wt%), Palmitic acid (21.20 wt%), Linolenic acid (7.87 wt%). Other fatty acids present in trace concentration were miristic acid, palmitoleic acid, stearic acid, arachidic acid, behenic acid and eliosenic acid varying from 0.32 to 2.20%. P. americana seed oil contains high concentration of polyunsaturated acids of 48.8 wt%. The saturated fatty acid content of P. americana was about wt%. The fatty acids in the seed have higher levels of polyunsaturated acids. 2.36% was undetectable. This last undetermined part may consist of Sterols, triterpenes phenols, tannins and perseit, which are of higher alcohol and hydrocarbons (Leite et al 2009, Olaeta et al 2007).

9 137 Table 6.2 Fatty acid compositions of P. americana Fatty acid Carbon number Weight percentage Miristic C14: Palmitic acid C16: Palmitoleic acid C16: Stearic acid C18: Oleic acid C18: Linoleic acid C18: Linolenic acid C18: Arachidic acid C20: Eliosenic acid C20: Behenic acid C22: Lingnoceric acid C24: From the Table 6.2, the average molecular weights of fatty acid and triglyceride were calculated from the fatty acid compositions were and respectively. Table 6.3 shows the physical and chemical properties of extracted P. americana seed oil. The acid value was 1.53 mg KOH g -1, which requires no pretreatment with acid (Ghadge and Raheman 2006) and enables the use of alkali catalyst KOH for this study. Table 6.3 Physical and chemical properties of the extracted P. americana seed oil Parameters Values Specific gravity Saponification value (mg KOH g -1 ) 187 Iodine value 131 Acid value (mg KOH g -1 ) 1.53 Average Molecular wt of oil (g mol -1 ) Average molecular wt of FAME (g mol -1 )

10 Effect of Catalyst The catalyst is an important reactant used in the process of transesterification of the fatty acids. Catalyst aims at speeding up the process by aiding the rapid breaking of triglyceride bonds. The effect of catalyst s concentration (0.02, 0.03, 0.04, 0.05 and 0.06 wt% of catalyst with respect to weight of P. americana seed) on the biodiesel yield is shown in Figure 6.1. The other parameters such as 10 g of P. americana seed, 1.0 g methanol, 55 C reaction temperature, 400 rpm agitation rate, 20 g of co solvent and 40 min reaction time were kept constant. It was clearly observed that using a lower concentration (0.02 wt%) led to an incomplete reaction and resulted in a lower yield of methyl esters. The yield was found to be increased and reached as optimum level at a catalyst amount of 0.05 wt% with a yield of 89% (Figure 6.1). With higher catalyst concentrations, the yield was slightly decreasing, this may be due to formation of soap or favoring the reverse reaction Catalyst (wt%) Figure 6.1 Effect of catalyst on biodiesel production at 1.0 g methanol, 55 C reaction temperature, 400 rpm agitation rate, 20 g of co solvent and 40 min reaction time

11 Effect of Methanol to Feedstock In order to know the appropriate amount of methanol for P. americana insitu transesterification, series of methanol amount (0.5, 1.0, 1.5, 2.0 g) was selected for biodiesel production with 10 g of P. americana seed, temperature at 55 C, agitation speed at 400 rpm, reaction time at 40 min, and 20 ml co-solvent. The catalyst was kept as 0.05 wt% that was optimized previously. For complete transesterification 3:1 stoichiometric proportion of alcohol is needed. However higher concentration of methanol is used to ensure the equilibrium to attain a maximum ester yield (Ma and Hanna 1999). The graph of methanol to biodiesel yield shows that the maximum yield of biodiesel was observed under experimental conditions with 1.5 g of methanol. The yield in biodiesel was found to be low as 86% when 0.5 g of methanol was used but there was considerable increase in the yield up to 91.1 % on increasing the methanol weight to 1.5 g. On further increasing the methanol weight there was no shift in biodiesel yield (Figure 6.2). But increase in methanol amount may interfere with glycerol drives the equilibrium back to the left side (Lin et al 2009) Methanol(g) Figure 6.2 Effect of methanol on biodiesel production at 0.05 g of catalyst, 55 C reaction temperature, 400 rpm agitation rate, 20 g of co solvent and 40 min reaction time

12 Effect of Temperature Temperature facilitates a reaction by weakening the chemical bonds and thus ineases the formation of new product bonds. In studying the effect of reaction temperature, the experiments were conducted using the obtained optimal conditions of catalyst concentration, methanol, reaction time, co solvent amount and agitation speed were maintained at 40 min, 20 ml and 400 rpm, respectively. The biodiesel yield was calculated for varying temperatures (45 to 65 C). The maximum temperature was set at 65 C boiling point of methanol. Varying the temperature from 45 to 65 C showed an increase in the methyl esters yield with the optimum yield being observed at 65 C. At the end of 40 th min the reaction set with temperature of 65 C showed a maximum biodiesel yield of 92.2 wt%. Figure 6.3 shows increasing trends in biodiesel yield from 87.3 wt% at 45 C to 92.2 wt% at 65 C Temperature ( C) Figure 6.3 Effect of temperature on biodiesel production at 0.05 g of catalyst, 1.5 g methanol, 400 rpm agitation rate, 20 g of co solvent and 40 min reaction time

13 Effect of Time The effect of reaction time was investigated as shown in the Figure 6.4 using the optimal parameters obtained as 0.05 g of catalyst, 1.5 g methanol, 65 C reaction temperature, 400 rpm agitation rate, and 20 g of co solvent. The time was varied as 30, 40, 50 and 60. With the optimal conditions obtained, it was observed that the yield was found to be increased with increase in reaction time. The yield was lower at shorter times and increased as the time was lengthened to 50 min with and yield of 92.8 wt%. The optimal yield was observed at the reaction time of 50 min. The effect of the reaction time on the conversion efficiency of methyl esters is shown in Figure Time (mins) Figure 6.4 Effect of reaction time on biodiesel production at 0.05 g of catalyst, 1.5 g methanol, 65 C reaction temperature, 400 rpm agitation rate, and 20 g of co solvent Effect of rpm The agitation speed enhances the contact of the reactants during the transesterification process and causes the reaction to be initiated. The stirring speed was varied from 300 rpm to 700 rpm at intervals of 100 rpm while other parameters

14 142 were kept at their optimal values. The phase changes were observed to be different at different stirring speeds. At lower stirring speeds, the formation of the phase changes was found to be slower than at higher speeds. Figure 6.5 illustrates the effect of agitation speed on the biodiesel yield. The optimal conversion efficiency is observed at the stirring speed of 600 rpm with a yield of 93.2 wt% Stirrer Speed(rpm) Figure 6.5 Effect of rpm on biodiesel production at 0.05 g of catalyst, 1.5 g methanol, 65 C reaction temperature, 20 g of co solvent and 50 min reaction time Effect of Co-Solvent The effect of co-solvent was performed. The results show that by increasing the co-solvent, the biodiesel yield was found to be improved. The significant increase in production of biodiesel indicate, the influences of solvent on oil extraction and could improve the mass transfer of oil and methanol and intensifies the transesterification of oil and aliphatic alcohols. The amount of co-solvent (THF) is varied from 20 g to 40 g with a regular increase of 10 g. Other parameters influencing the reaction and yield were kept at optimum. Figure 6.6 illustrates the effect of co solvent on yield. No significant change was observed in yield on varying the amount of co solvent used above 30 g. The difference in yield was very less with an optimum yield of 94.1 wt% when 30 g of co solvent was used.

15 Co Solvent (g) Figure 6.6 Effect of co-solvent on biodiesel production at 0.05 g of catalyst, 1.5 g methanol, 65 C reaction temperature, 600 rpm agitation rate and 50 min reaction time 6.4 PROPERTIES OF P. americana SEED BIODIESEL The product biodiesel was analyzed according to ASTM test methods and the results of the in-situ transesterification were presented in Table 6.4. The specific gravity of the product biodiesel was found to be decreased sharply from to Lower value of the specific gravity of the final biodiesel is an indication of completion of reaction and removal of heavy glycerin (Miao and Wu 2006). Two of the main excellent parameters for P. americana methyl esters were the oxidation stability and the low temperature properties. The cold soak filterability was measured according to ASTM D7501. The cold soak filtration time of crude biodiesel was s, and was significantly lower than ASTM biodiesel limit of 360 s. Cloud point is an important parameter for determining the cold weather performance of biodiesel (Dunn 2009). The saturated fatty acids of P. americana seed oil is accounted as 23.2 wt%. P. americana biodiesel generally has

16 144 a better cloud point than soy biodiesel because of its lower level of total saturated fatty acids (Knothe 2008, Canakci and Sanli 2008). Properties Table 6.4 Properties of P. americana biodiesel Units Test methods ASTM D6751 Limits P. americana Biodiesel Specific gravity --- ASTM D Flash point C ASTM D min 172 Cloud point Pour point o C ASTM D2500 Report -2 o C ASTM D 2500 Report -8 Oxidation Stability h EN min >7 Cold Soak Filtration Time second ASTM D Max 147 Viscosity@40 o C mm 2 s -1 ASTM D Acid number mg KOH g - 1 ASTM D Max Cetane number --- ASTM D min 49.3 Water & sediments vol% ASTM D Max Copper strip corrosion --- ASTM D130 Number 3 Max 1a Sulphated ash wt% ASTM D Max Phosphorous content wt% ASTM D Max Na & K combined ppm EN Max 4 Ca & Mg combined ppm EN Max 3 Low temperature operability of biodiesel fuel is an important aspect from the engine performance standpoint in cold weather conditions. Thus, a high content of unsaturated FAME improves the low-temperature properties of biodiesel. However, it is reported that oxidation stability decreases with the increase of polyunsaturated methyl esters such as linoleic and linolenic esters (Knothe 2006, McCormick et al 2007). But P. americana biodiesel resembles a quite high oxidation stability greater than 7 h was obtained. P. americana seed contains natural antioxidant (Fernández et

17 145 al 2010, Nagaraj et al 2010). For this reason, the biodiesel product could be employed as direct or as an additive to improve cold flow property and the oxidation stability of those biodiesel that do not meet the standard. Its clears that the properties of biodiesel depend very much on the nature of its raw material as well as the process used for its production. Inherent properties from P. americana biodiesel that have an effect on the performance of biodiesel as diesel substitute, such as density, viscosity, cetane number, copper strip corrosion, FAME profile and phosphorus content, flash point and the acid value. They have been included in Table 6.4 and their fuel properties were with in ASTM D6751 standard specification for biodiesel fuel (B100) 6.5 CONCLUSION In regions where a large cultivation and P. americana fruit processing, the usage of P. americana seed to make biodiesel can generate benefits. In-situ Transesterification had produced a biodiesel of good quality. The best solvent for in-situ process to produce biodiesel was THF, which showed good cold flow properties. Finally, the product obtained by in-situ transesterification can be employed as a direct fuel or can be blend with other conventional biodiesel to improve cold flow property and oxidation stability. As a conclusion, production of biodiesel from a cheap raw material such P. americana seed by in-situ transesterification method would increase economical importance of P. americana and these FAME form a clean and alternative energy source.