Microwave Assisted Continuous Conversion Of Karanja Oil Tobiodiesel Biology Essay


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In the last century, industrialization and fast growth of the world population have resulted in energy consumption 10 times larger than the rest of the history. In fact, major part of the energy was consumed in transportation activities resulted in by travel and trade activities and the main fuel used in transportation is gasoline and diesel; both are petroleum derivatives. It is a known fact that the rapid increase in the demand will result in price surge in petroleum. Although fossil fuels seem to be the primary source of energy for the next several decades, such price increase makes them insufficient for sustainable economical growth of countries (developed and developing) in the long term (Zachariadis 2003).

In addition to petroleum price increases, another important effect of using petroleum derivatives is environmental pollution, such as air, water and soil. Among them, air pollution is major concern due to densely populated urban areas and that transportation is responsible for 28% of total CO2 emission; in fact, the road transport alone currently is responsible for 84% of all transport related CO2 emissions (Zachariadis 2003). To reduce the toxic exhaust gases and also evaporative emissions from vehicles, reformulated gasoline is considered to be an alternative solution by focusing on high energy content and low toxic gases, such as NOx and SOx emission but it is not very much effective in directly reducing CO2 emission (Heather 2003). Another fossil fuel alternative is liquefied petroleum gas (LPG), which results in low CO2 emission but its storage and bulk transportation make the use of LPG potentially hazardous (Heather 2003). With the Kyoto Protocol agreement submitted to the United Nations Framework Convention on Climate Change (UNFCCC), the use of renewable energy sources is encouraged and supported throughout the world. In this regard, renewable energy sources are considered to be much more effective solution to reduce CO2 emission and to achieve a sustainable economic growth than fossil fuels.

Electricity and hydrogen are energy carriers. Since they are not freely available in nature, they need to be produced from an energy source, such as thermal, nuclear or renewable energy sources. When they are produced from a carbon-free energy source, they eliminate the net carbon dioxide emission to the atmosphere. However, technical and economical problems limit the usage of renewable sources to produce electricity and hydrogen in a large scale, such as power plant

For the transient period between hydrogen and petroleum based economies, the use of renewable feedstock to produce renewable fuels, such as biodiesel and bio-alcohols, seems to be promising to support sustainable economic growth and also to reduce the carbon dioxide and related toxic gases emissions. For example, the alcohols, especially ethanol and methanol, produced from biological sources could be used as fuel or fuel additives. When ethanol is used in a higher compression ratio, shorter burn time and lean burn internal combustion engine, much better fuel usage efficiency than gasoline could be achieved. In contrast to these advantages, the drawback of ethanol is its low energy content. Methanol has more limitations than ethanol because it is corrosive, highly toxic, colourless, odourless, and its flame when burned is almost invisible in daylight. Similar to ethanol, its energy density is lower than that of gasoline. Although alcohols seem to be inefficient as fuel sources, their usage as fuel additives are considered to be better approach to decrease pollutant emissions (Heather 2003).

Alternatively, vegetable oils are estimated to be promising renewable fuels. They could be used directly or indirectly. Direct usage of them in the internal combustion engines leads to the lubricating problems, coke formation, high viscosity and low volatility. Therefore, when they are converted into better fuels, such as methyl esters, known as biodiesel, the drawbacks related to the direct usage could be eliminated. In addition to vegetable oils, animal fats and waste cooking oils could be used to produce biodiesel.

In general, diesel fuels have high-energy density and biodiesel has further advantage because its usage lowers green house gases (GHG) emission (Heather 2003). Also, it contributes much less to global warming than fossil fuels since carbon in the biodiesel are reused by the plants; hence resulting in a near net zero carbon dioxide (CO2) emission. Biodiesel has high cetane number, better lubricating properties and safer handling. Although there are many advantages of biodiesel, it is reported that the NOx emission from the vehicle using biodiesel is slightly higher than that of using petro-diesel.

Biodiesel is the mixture of monoalkyl esters formed by a catalyzed reaction of the triglycerides found in the vegetable oils or animal fats with a simple monohydric alcohol. According to reaction stoichiometry, three moles of alcohol are needed for one mole of trialcylglycerol to produce methyl esters. In practice, at least 1.6 times more alcohol is needed for a complete reaction because of that transesterification is a reversible reaction. Methanol and NaOH or KOH are commonly used in biodiesel production because of their low cost and high reactivity.

While transesterification is well-established, and becoming increasingly important, there remains considerable inefficiencies in existing transesterification processes. In conventional heating of transesterification process (batch, continuous, and super critical methanol process), heat energy is transferred to the raw material through convection, conduction, and radiation from surfaces of the raw material. Thus, the conventional heating consumes more energy and take long preheat and reaction time, Optimally 1 hour [4], to produce over 95 percent conversion yield biodiesel product. An alternative energy stimulant, ''microwave irradiation'' can be used for the production of the alternative energy source, biodiesel. In the electromagnetic radiation spectrum, the microwave radiation region is located between infrared radiation and radio waves. Microwaves have wavelengths of 1mm - 1 m, corresponding to frequencies between 0.3 - 300 GHz. In general, in order to avoid interference, industrial and domestic microwave apparatus are regulated to 12.2 cm, corresponding to a frequency of 2.45 GHz, but other frequency allocations do exist [6]. Microwaves, a non-ionizing radiation incapable of breaking bonds, are a form of energy and not heat and are manifested as heat through their interaction with the medium or materials wherein they can be reflected (metals), transmitted (good insulators that will not heat) or absorbed (decreasing the available microwave energy and rapidly heating the sample) [7]. Microwaves, representing a non-ionizing radiation, influence molecular motions such as ion migration or dipole rotations, but not altering the molecular structure. Polar solvents of low molecular weight and high dielectric constant irradiated by microwaves increase their temperature very rapidly, reaching boiling point in a short time

There are two mechanisms by which microwave energy can interact with a sample. If a molecule possesses a dipole moment, then, when it is exposed to microwave irradiation, the dipole tries to align with the applied electric field. Because the electric field is oscillating, the dipoles constantly try to realign to follow this. At 2.45 GHz, molecules have time to align with the electric field but not to follow the oscillating field exactly. This continual reorientation of the molecules results in friction and thus heat. If a molecule is charged, then the electric field component of the microwave irradiation moves the ions back and forth through the sample while also colliding them into each other. This movement again generates heat. Because the mixture of vegetable oil, methanol, and potassium hydroxide contains both polar and ionic components, rapid heating is observed upon microwave irradiation, and because the energy interacts with the sample on a molecular level, very efficient heating can be obtained. In addition, because the energy is interacting with the molecules at a very fast rate, the molecules do not have time to relax and the heat generated can be, for short times, much greater than the overall recorded temperature of the bulk reaction mixture. In essence, there will be instantaneous localized superheating. Thus, the bulk temperature may not be an accurate measure of the temperature at which the actual reaction is taking place [9]. Microwave heating compares very favorably over conventional methods, where heating can be relatively slow and inefficient because transferring energy into a sample depends upon convection currents and the thermal conductivity of the reaction mixture [10]. Our objective of the present work is to analyze how the conversion varies when the reactor is scale up interms of reactor length and to observe how the increase in the residence time will effect on conversion of different reaction mixtures having different methanol concentrations and to see whether the obtained product is meeting the required standards to be called as biodiesel or not.


Biodiesel (defined by the Association for Standards and Testing of Materials as mono - alkyl esters of long chain fatty acids) is usually produced by

(i) Direct use/blending,

(ii) Micro-emulsion,

(iii) Pyrolysis, and

(iv) Transesterifcation.

Direct Use/Blending

Vegetable oil can be directly used as diesel fuel without any changes to engine. The very firstengine (by Rudolf Diesel) was tested using vegetable oil as fuel. The primary concernwith vegetable oil as fuel is its high viscosity (atomization of vegetable oil is difficult), which leads to problems in the long run: Advantages of vegetable oil as diesel fuel are

(i) Liquid nature and portability,

(ii) High heat content (80 per cent of diesel fuel),

(iii) Ready availability, and

(iv) Renewability.

The problems appear only after long period. Some of common problems are:

(i) Coking and trumpet formation on the injectors to such an extent that fuel atomization becomes difficult,

(ii) Carbon deposits,

(iii) Oil ring sticking, and

(iv) Thickening and gelling.


Micro emulsion is defined as colloidal dispersion of fluid microstructures (1-150 nm) in solvent forming two immiscible phases. The common solvents used are methanol and ethanol. Micro-emulsions is the probable solution to high viscosity of vegetable oil. Their atomization is relatively easy because of lower viscosity.


Pyrolysis means conversion of one substance to another by application of heat. Catalysts are used to speed up the process. Different products can be obtained from the same material depending on different path of reaction and this makes pyrolytic chemistry difficult. Pyrolysis of vegetable oil gives different lower hydrocarbons that can be used as fuel.


Transesterfication is a kind of organic reaction where alcohol group in ester is substituted. Itcan also be reaction of vegetable oil/fat with alcohol to give ester and glycerol. The applicability of transesteri-fication is not restricted to laboratory. Several relevant industrial processes use this reaction to produce different types of compounds. An example is the production of PET (polyethyleneterephthalate), which involves a step where dimethylterephthalate is transesterified with ethylene glycol in the presence of zinc acetate ascatalyst. Furthermore, a large number of acrylic acid derivatives are produced by transesterification of methyl acrylate with different alcohols, in the presence of acid catalysts.

Transesterification of Vegetable Oils

In transesterification of vegetable oils, a triglyceride reacts with three molecules of alcohol in the presence of catalyst, producing a mixture of fatty acids alkyl esters and glycerol (Figure 1). The overall process is a sequence of three consecutive reactions, in which die- and monoglycerides are formed as intermediates. Transesterification is a reversible reaction thus; excess alcohol is used to increase the yields of the alkyl esters and to allow its phase separation from the glycerol formed. Conversion of vegetable oil to biodiesel is effected by several parameters namely

(i) Time of reaction,

(ii) Reactant ratio (Molar ratio of alcohol to vegetable oil),

(iii) Type of catalyst,

(iv) Amount of catalyst, and

(v) Temperature of reaction.

Transesterification can be alkali-, acid- or enzyme-catalyzed; however, enzyme catalysts are rarely used, as they are less effective (Ma and Hanna 1999). The reaction can also take place without the use of a catalyst under conditions in which the alcohol is in a supercritical state (Saka and Kusdiana 2001; Demirbas 2002). Biodiesel can also be produced by esterification of fatty acid molecules.

Transesterification reaction can be represented as

where R1, R2, and R3 are long hydrocarbon chains. This reaction is reversible and hence, to shift the equilibrium towards right (i.e. the formation of methyl esters), excess alcohol is used (Naik 2006). Transesterification can be catalyzed by both acidic and basiccatalysts. Acid catalyzed transesterification is slow and needs temperatures higher than 100 oC whereas base catalyzed reaction is known to be fast even at room temperature buthighly sensitive to the presence of free fatty acid content. Free fatty acid and moistureadversely affect the transesterification reaction. For example, the production of methylesters using base catalysts decreases in the presence of as low as 3% free fatty acidcontent. In fact, free fatty acids and alkali catalysts forms alkali soaps; hence decreasing the catalyst amount is needed for transesterification reaction. Furthermore, soap could causeemulsion, and this result in difficulties in the downstream recovery and biodiesel purification steps (McLean 2003). Basically, soap formation occurs through the followingreaction;

R-OH + X-OH → R-OX + H2O (R = alkyl; X = Na or K)

If there is some water, hydrolysis of alkyl esters happen and free fatty acids produced with the following reaction path;

R-OCH3 + H2O → R-OH + CH3OH (R = alkyl)

Water can also react with triacylglycerols to form free fatty esters. Higher alcohols are particularly sensitive to water contamination. Thus, for a complete reaction, alcohol must be free of water and free fatty acid content in the oil must be lower than 0.5% (International Energy Outlook 2007). Thus, free fatty acids in feedstock like beef tallow or fryer grease needs to be treated to eliminate the possible side reactions listed above.

Acid Catalyzed Transesterification

Transesterification is catalyzed by Bronsted acids. These catalysts give very high yields in alkyl esters, but the rate of reaction is slow, requiring, typically, temperatures above 100 °C and more than 3h to reach complete conversion. H2SO4 is a commonly used acid catalyst. the mechanism of an acid catalyzed process.

Base Catalyzed Transesterification

The base-catalyzed transesterification of vegetable oils proceeds faster than the acid catalyzed reaction. Because of above reason, together with fact that the bases are less corrosive than acidic catalyst, industrial processes usually use base catalysts such as, alkaline metal alkoxides and hydroxides as well as sodium or potassium carbonates. The mechanism of the base-catalyzed transesterification of vegetable oils is shown in Figure Alkaline metal alkoxides (for the trans-esterfication) are the most active catalysts,since they give very high yields in short reaction times even if they are applied at low molar concentrations. However, they require absence of water, which makes them inappropriate for typical industrial processes. Alkaline metal hydroxides (KOH and NaOH) are cheaper than metal alkoxides, but less active. Undesirable side reaction (saponification) reduces the ester yields and makes the recovery of the glycerol difficult due to the formation of emulsions. For this study, base (KOH, Base catalyzed process) has been used as catalyst.

Influence of Free Fatty Acids on Biodiesel Production

Feedstock quality in large part dictateswhat type of catalyst or process is needed to produce FAAE that satisfies relevant biodiesel fuel standards such as ASTM D6751 or EN14214. If the feedstock contains a significant percentage of FFA (>3 wt.%), typical homogenous base catalysts such as sodium or potassium hydroxide or methoxide will not be effective as a result of an unwanted side reaction in which the catalyst will react with FFA to form soap (sodium salt of fatty acid) and water (or methanol in the case of sodium methoxide), thus irreversibly quenching the catalyst and resulting in an undesirable mixture of FFA, un reacted TAG, soap, DAG, MAG, biodiesel, glycerol, water, and/or methanol (Lotero et al. 2005). In fact, the base-catalyzed transesterification reaction will not occur or will be significantly retarded if the FFA content of the feedstock is 3 wt.% or greater (Canakci and Van Gerpen1999, 2001). For instance, nearly quantitative yields of biodiesel are achieved with homogenous base catalysts in cases where the FFA content of the feedstock is 0.5 wt. % or less (Naik et al. 2008). However, the yield of biodiesel plummets to 6% with an increase in FFA content to 5.3 wt. %( Naik et al.2008). A further complicating factor of high FFA content is the production of water upon reaction with homogenous base catalysts (reaction [1], Fig. 2). Water is particularly problematic because, in the presence of any remaining catalyst, it can participate in hydrolysis with biodiesel to produce additional FFA and methanol (reaction[2],

A common approach in cases where the FFA content of a feedstock is in excess of 1.0 wt.%(Freedman et al. 1984;Mbaraka et al. 2003; Zhang et al. 2003; Wang et al. 2005)is a two step process in which acid pretreatment of the feedstock to lower its FFA content is followed by trans-esterification with homogenous base catalysts to produce biodiesel. In a typical acid pretreatment procedure, FFA areesterified to the corresponding FAME in the presence of heat, excess methanol, and acid catalyst, normally sulfuricacid (Ramadhas et al.2005; Nebel and Mittelbach 2006;Veljkovic et al. 2006; Issariyakul et al. 2007; Kumartiwarietal. 2007; Sahoo et al. 2007; Meng et al. 2008; Naik et al.2008; Rashid et al.2008a). The two-step procedure readily accommodates high FFA-containing low-cost feedstocks for the preparation of biodiesel (Canakci and Van Gerpen1999, 2001, 2003a).

Catalysts for Biodiesel Production

Biodiesel is produced commercially using homogenous basic catalysts such as sodium (or potassium) hydroxide or methoxide because the transesterification reaction is generally faster, less expensive, and more complete with these materials than with acid catalysts(Boocock et al 1996a). The biodiesel industry currently uses sodium methoxide, since methoxide cannot form water upon reaction with alcohol such as with hydroxides (Zhou and Boocock 2006a). Other alkoxides, such as calcium ethoxide, have also effectively catalyzed biodiesel production, albeit with higher methanol and catalyst requirements (Liu et al. 2008). The homogenous base-catalyzed transesterification reaction is about 4,000times faster than the corresponding acid-catalyzed process (Reid 1911; Srivastava and Prasad 2000).Furthermore, base-catalyzed reactions are performed at generally lower temperatures, pressures, and reaction times and are less corrosive to industrial equipment than acid-catalyzed methods. Therefore, fewer capital and operating costs are incurred by biodiesel production facilities in the case of the base-catalyzed transesterification method (Freedman et al. 1986; Demirbas 2008).However, the homogenous acid-catalyzed reaction holds an important advantage over the base-catalyzed method in that the performance of acid catalysts is not adversely influenced by the presence of FFA. In fact, acids can simultaneously catalyze both esterification and trans-esterification (Haas et al. 2003; Lotero et al. 2005; Miaoand Wu 2006; Demirbas 2008; Zhangand Jiang 2008).For instance, FAME were prepared from acid oil, which consisted of 59.3 wt.% FFA, by acid-catalyzed trans-esterification at 65°C for 26 h with H2SO4(1.5:1 molar ratio of catalyst to oil) and methanol (15:1 molar ratio of methanol to oil) in 95 wt.% purity. The remaining products consisted of FFA (3.2 wt. %), TAG (1.3 wt.%),and DAG (0.2wt.%) (Haas et al. 2003).A wide range of catalysts may be used for biodiesel production, such as homogenous and heterogeneous acids and bases, sugars, lipases, ion exchange resins, zeolites, and other heterogeneous materials. A recent exotic example is that of KF/Eu2O3, which was used to prepare rapeseed oil methyl esters with92.5% conversion efficiency (Sun et al. 2008). In general, acids are more appropriate for feedstocks high in FFA content. Homogenously catalyzed reactions generally require less alcohol, shorter reaction times, and more complicated purification procedures than heterogeneously catalyzed transesterification reactions. Heterogeneous lipases are generally not tolerant of methanol, so production of ethyl or higher esters is more common with enzymatic methods. For a recent comprehensive review on catalysts used for biodiesel preparation, (2007).Non catalytic transesterification of biodiesel may be accomplished in supercritical fluids such as methanol, butanol very high pressure (45-65 bar), temperature (350°C),and amount of alcohol (42:1 molar ratio) are required(Saka and Kusdiana 2001; Demirbas 2003, 2005, 2006;Kusdiana and Saka 2004). Advantages of supercritical transesterification versus various catalytic methods are that only very short reaction times (4 min, for instance) are needed, and product purification is simplified because there is no need to remove a catalyst. Disadvantages of this approach include limitation to a batch-wise process, elevated energy and alcohol requirements during production, and increased capital expenses and maintenance associated with pressurized reaction vessels (Saka andKusdiana 2001; Demirbas2003,2005,2006;Kusdianaand Saka 2004).

Different types of feedstock available

Desirable characteristics of alternative oilseed feed stocks for biodiesel production include adaptability to local growing conditions (rainfall, soil type, latitude, etc.),regional availability, high oil content, favorable fatty acid composition, compatibility with existing farm infrastructure, low agricultural inputs (water, fertilizer, pesticides),definable growth season, uniform seed maturation rates, potential markets for agricultural by-products, and the ability to grow in agriculturally undesirable lands and/or in the off-season from conventional commodity crops. Biodiesel fuels prepared from feedstocks that meet at least a majority of the above criteria will hold the most promiseasalternatives to petrodiesel. In general, there are four major biodiesel feedstock categories: algae, oilseeds, animal fats, and various low-value materials such as used cooking oils, greases, and soap stocks


Traditional oilseed feed stocks for biodiesel production predominately include soybean, rapeseed/canola, palm, corn, sunflower, cottonseed, peanut, and coconut oils. Non edible oils include Jatropha curcas, Pongamia pinnata (Karanja or Honge), Madhuca indica, commonly known as Mahua, Melia azedarach, commonly referred to as syringa or Persian lilac, Moringa oleifera, commonly known as Moringa, Nicotiana tabacum, commonly referred to as tobacco, Balanites aegyptiaca, commonly known as desert date, Terminalia catappa, commonly known in Brazil as castanhola, Hevea brasiliensis, commonly referred to as the rubber tree, Vernicia fordii, commonly known as tung, Asclepias syriaca, commonly referred to as common milkweed, Zanthoxylum bungeanum, Rice bran, Raphanus sativus, commonly known as radish, Brassica carinata, commonly known as Ethiopian or Abyssinian mustard, Camelina sativa, commonly known as false flax or goldof-pleasure, Calophyllum inophyllum, commonly known as Polanga, Cynara cardunculus, commonly known as cardoon, Carthamus tinctorius, commonly known as safflower,

Animal fats

Animal fats may include materials from a variety of domesticated animals, such as cows, chickens, pigs, and other animals such as fish and insects. Animal fats are normally characterized by a greater percentage of saturated fatty acids in comparison to oils obtained from the plant kingdom. Animal fats are generally considered as waste products, so they are normally less expensive than commodity vegetable oils, which make them attractive as feed stocks for biodiesel production.

Other waste oils.

Waste oils may include a variety of low value materials such as used cooking or frying oils, vegetable oil soap stocks, acid oils, tall oil, and other waste materials. Waste oils are normally characterized by relatively high FFA and water contents and potentially the presence of various solid materials that must be removed by filtration prior to conversion to biodiesel. In the case of used cooking or frying oils, hydrogenation to increase the useful cooking lifetime of the oil may result in the introduction of relatively high melting trans constituents, which influence the physical properties of the resultant biodiesel fuel.

Biodiesel production by using microwave irradiation

The important fact about the microwave irradiation is,it is capable of reducing the reaction times significantly as well as improve product yields.(Azcan and Danishman 2008).the main advantages of using microwave irradiation in the production of biofuels are short reaction times, a low oil to methanol ratio,an ease of operation and reduction in the quantity of byproducts and with lesser energy consumption(saifuddin and chua 2004). Several examples of producing biodiesel by using microwavr irradiation have been reported using both homogeneous and heterogeneous catalysts Azcan et al.(2008) reports 93.7%(for 1 wt%KOH) and 92.2%(for 1wt%NaOH) yield of biodiesel at 313K temperature with in 1 minunder microwave heating. Barnard et al.(2007) reported that continuous flow microwave method for the transesterification reaction is more efficient than using a conventional heated apparatus.

Biodiesel analysis

Biodiesel analysis includes to find out the ester or FAME content. The obtained should meet the specifications given by the various authorizing institutions like ASTM, EN, IS etc. by using several methods like GC, HPLC, TCL and FTIR spectroscopy.Determination of products by GC is not easy and it is time consuming and difficult because of the use of special column. TLV can be simple but it will give a number of results on the otherhand Thermogravimetric analyzer ,an instrument which measures the weight changes with respect to temperature, with the integration of ceric ammonium nitrate test it can be used for %FAME analysis instead of GC and TLC

Materials and Methods

Pongamia pinnata (Karanja or Honge)

Karanja belongs to the family Leguminaceae. It is a medium sized glabrous tree that generally attains a height of about 18 m and a trunk diam > 50 cm. It can grow under a wide range of agroclimatic condition and is a common sight around coastal areas, riverbanks tidal forests and roadsides. Karanja is a native to humid and subtropical environments having annual rainfall between 500-2500 mm in its natural habitat, the maximum temperature ranges from 27-38°C and the minimum 1-16°C. It can grow on most soil type's rangingfrom stony to sandy to clayey, including verticals. It does not do well in dry sands. It is highly tolerant of salinity and can be propagated either by seeds or by root suckers1.The fruits and sprouts are used in folk remedies for abdominal remedies in India, the seeds for keloid tumors in Sri Lanka, and a powder derived from plants for tumors in Vietnam. In India, seeds were used for skin ailments and the oil is used as an ointment for rheumatism. Leaves are active against Micrococcus and their juice is used for colds, coughs, diarrhea, etc. Juices from the plant as well as the oil are antiseptic. It is said to be an excellentremedy for itch and herpes. Flowers are used for diabetes. The bark is known to bethe remedy for beriberi. The oil has been known for its curative effect for skin problems such as, leucoderma, scabies and skin itches1. The tree bears green pods, which after 10 to 11 months gets matured and changes to a tan colour in the month of May-June. Thepods are flat to elliptic, 5-7 cm long and contain one to two kidney shaped brownish red kernels. The dried pods usually split with a hammer and the kernels are obtained. The seed collection is basically a rural activity. The oil is extracted from kernels in small oil mills or village ghanis. The yield of kernels per tree is between 8-24 kg. The fresh extracted oil is yellowish orange to brown and rapidly darkens on storage. It has a disagreeable odour and bitter taste. The oil contains several furanoflavones such as, karanjin, pongapin, kanjone and pongaglabrin. Karanja oil is mainly used as a raw material for soap, but the mainconstraints for its more usage are the colour and odour. The oil is used as lubricant, water-paint binder, and also as a fuel for cooking and lamps in rural areas of India.

Properties of Karanja oil



Kinematic viscosity(mm2/s)


Acid value(mg KOH/g)


Free fatty acid(%)


Iodine value(gI2/100g)


Saponification number(mgKOH/g)


Fatty acid composition of Crude karanja oil(AZAM ET AL.2005)

Fatty acid




































Experimental setup

A domestic microwave oven 800W,2450MHz was used with modification for all the microwave mediated experiments. Oven can be operated at specific levels of power and the temperature can not be measured and we are unable to control the temperature. The output microwave power levels are fixed in microwave oven viz. 800, 600, 450, 300, 180 and 100W. Irradiation time can be fixed in increments of 10s. a Teflon tubing of 13m length and 4mm ID was used as reactor. Liquid hold up of the reactor was . The Teflon tubing enter from top, coils flat from periphery towards the centre, and exits from top. The reactants were premixed outside the microwave chamber and pumped through a FMI pump and Peristaltic pump. A 3 bladed agitator was used to mix the reactants so as to aid uniform mixingthrough out the premixing tank. The pumps were controlled by a manual controller for adjusting flow rate.The coiled Teflon assembly was supported over thermocol base.Biodiesel from Karanja oil was synthesized in this manner

Pretreatment step

The karanja oil obtained from tumkur, it was fresh and had an initial FFA of 5.2% but it is not suitable for the direct transesterification. The %FFA of the oil should be reduced for that the oil is pretreated in a Teflon tubular reactor in continuous mode . sulfuric acid (4%w/w) was used as catalyst and methanol(35%w/w) were mixed in the premixing tank with karanja oil. Final FFa of the oil is reduced to 1.3% and it is further used for transesterification step

Transesterification step

Biodiesel was synthesized using a Teflon tubular reactor in continuous mode from karanja oil. KOH pellets (1.2%w/w) were dissolved in methanol 30%w/w, 40%w/w, 45%w/w, 50%w/w separately and mixed wwith karanja oil in premixing tank. A pre mixing tank was used to mix the reactants at an agitation speed of 1200 rpmand the mixture was pumped in to reactor using variable flow rate FMI pump for redidence times 2min,3min, 4min, 5min and Peristaltic pump for residence times 6min, 7min, 8min, 9min, 10min. The microwave oven was operated for 10 to 15 minutes at 100w and 180w power levels. The product stream was mixed with methanolic oxalic acid (0.5N, 1ml/100ml product) and allowed for phase separation.

The lower glycerol phase was discarded. The upper layer was washed with warm water(3-5 times). The unreacted reactants,FFA, soap and otherwater soluble components were washed out. The ceric ammonium nitrate test was conducted to test the presence of glycerin. The product having no glycerin was then passed over silica gel and sodium sulfate. The product was filtered to obtain purified biodiesel. The properties of biodiesel such as density, viscosity, saponification number, iodine value, cetane index, acid value and %FFA were determined as per standard procedure.The quality of biodiesel and hence FAME yield was calculated using thermogravimetric technique

The procedure followed to calculate quality or FAME in biodiesel using TG/DTA is as follows

The platinum crucible weights are made to zero

About 5-10mg of biodiesel sample , undiluted, was loaded to sample crucible and accurate weight was measured by the TG/DTA to an accuracy of 0.001mg. This value is set to 100% TG in software

The temperature program was run and TG and differential TG(DTG) curves as a function of temperature are obtained

ADTG peak, observed around 2330C, shows the presence of FAME in biodiesel. The area under the curve of DTG or the % mass loss at 2330C gives the % weight of FAME in biodiesel.

Using this data FAME yield can be calculated using the equation shon below

%yield = ( %purity of biodiesel X mass of biodiesel layer)/(% triglyceride in karanja oil X weight of oil)X100

Results and Discussion

Time vs conversion plot at different methanol concentrations

Flow rate vs conversion at different methanol concentrations

Effect of Residence time on conversion:

Residence time in the reactor is varied from 2 minutes to 10 minutes by fixing the corresponding flow rate and for different concentrations of oil to methanol ratio. The conversion goes on increasing as the residence time is increased and it is giving good conversion at 40%(w/w).The reason may be as the reaction mixture is allowed for the prolonged time to get exposure to the micro wave radiation the bulk temperature is increasing for longer residence time

Effect of methanol concentration:

As the methanol concentration is varied from 30%(w/w) ratio to 50%(w/w) ratio the conversion profile is increasing in the 30%(w/w) ratio to 40%(w/w) ratio but as the concentration of methanol is further increased there is a down fall in the conversion the reasons may be for the low conversions are presence of impurities, presence of free fatty acid in karanja oil,side reaction saponification, also limits the conversion by consuming the catalyst, Conversion keeps on increasing with the weight ratio as we go on increasing the weight ratio the density difference between upper and lower layer keeps decreasing and hence leads to problems in separating the two. As we further increase the weight ratio a third separate layer containing pure exces alcohol is formed. At higher weight ratio a large amount of alcohol is present in the transesterified products i.e. biodiesel and glycerin.

Effect of power:

As the power is varied 100w and 180w the conversion increased with increase in the power the reason is as the power increased the bulk temperature of the system is further increased on comparison with the 100w

Effect of flow rate:

Flow rate is varied in the range 16 ml/min to 82 ml/min. As the flow rate is high the reaction mixture is not having the sufficient time to attain the fruitful temperature to shift the equilibrium towards right, that is product side.On the otherhand when the flow rate is decreased it is having the sufficient time to attain the temperature to give the good conversion

Properties of karanja biodiesel synthesized through continuous microwave assisted two step technique


Karanja biodiesel

ASTM D6751-08




Kinematic viscosity(mm2/s)



Acid value(mg KOH/g)



Iodine value(gI2/100g)



Saponification number(mgKOH/g)



Ctane index



% Ester conten




Karanja biodiesel was synthesized using teflon tubular reactor in continuous mode. Parameters like residence time,power level and methanol concentration were varied to obtain high yield of biodiesel. The oil was first pretreated in continuous reactor where FFA was reduced from 5.2% to 1.3%. in the second step at 180W power, 40%methanol, 1.2% KOH, for a retention time of 10min 92% FAME was achieved. The properties of biodiesel synthesized were measured and compared with ASTM standards.

The future work includes scale up of the reactor in terms of reactor dimensions like changing the diameter of the reactor pipe, thickness of the reactor pipe, and if possible changing reactor type from plug flow reactor to mixed flow reactor and to observe the effects with these when the parameters like methanol concentration, catalyst concentration, power level ,residence time are varied.

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