Production of biodiesel using the microwave technique

Biodiesel production is worthy of continued study and optimization of production procedures because of its environmentally beneficial attributes and its renewable nature. Non-edible vegetable oils such as Jatropha oil, produced by seed-bearing shrubs, can provide an alternative and do not have competing food uses. However, these oils are characterized by their high free fatty acid contents. Using the conventional transesterification technique for the production of biodiesel is well established. In this study an alternative energy stimulant, ‘‘microwave irradiation’’, was used for the production of the alternative energy source, biodiesel. The optimum parametric conditions obtained from the conventional technique were applied using microwave irradiation in order to compare the systems. The study showed that the application of radio frequency microwave energy offers a fast, easy route to this valuable biofuel with the advantages of enhancing the reaction rate (2 min instead of 150 min) and of improving the separation process. The methodology allows for the use of high free fatty acid content feedstock, including Jatropha oil. However, this emerging technology needs to be further investigated for possible scale-up for industrial application.

Journal of Advanced Research (2010) 1, 309–314 Cairo University Journal of Advanced Research ORIGINAL ARTICLE Production of biodiesel using the microwave technique Shakinaz A El Sherbiny, Ahmed A Refaat, Shakinaz T El Sheltawy * Department of Chemical Engineering, Faculty of Engineering, Cairo University, Egypt Received 30 October 2009; revised 28 January 2010; accepted March 2010 Available online 15 September 2010 KEYWORDS Microwave; Biodiesel; Transesterification; Non-edible oil Abstract Biodiesel production is worthy of continued study and optimization of production procedures because of its environmentally beneficial attributes and its renewable nature Non-edible vegetable oils such as Jatropha oil, produced by seed-bearing shrubs, can provide an alternative and not have competing food uses However, these oils are characterized by their high free fatty acid contents Using the conventional transesterification technique for the production of biodiesel is well established In this study an alternative energy stimulant, ‘‘microwave irradiation’’, was used for the production of the alternative energy source, biodiesel The optimum parametric conditions obtained from the conventional technique were applied using microwave irradiation in order to compare the systems The study showed that the application of radio frequency microwave energy offers a fast, easy route to this valuable biofuel with the advantages of enhancing the reaction rate (2 instead of 150 min) and of improving the separation process The methodology allows for the use of high free fatty acid content feedstock, including Jatropha oil However, this emerging technology needs to be further investigated for possible scale-up for industrial application ª 2010 Cairo University Production and hosting by Elsevier B.V All rights reserved Introduction Biodiesel has many merits as a renewable energy resource including being derived from a renewable domestic resource, thereby relieving the reliance on petroleum fuel, and being bio* Corresponding author Tel.: +20 10 6044605 E-mail address: chakinaz@hotmail.com (S.T El Sheltawy) 2090-1232 ª 2010 Cairo University Production and hosting by Elsevier B.V All rights reserved Peer review under responsibility of Cairo University doi:10.1016/j.jare.2010.07.003 Production and hosting by Elsevier degradable and non-toxic Further, compared to petroleumbased diesel, biodiesel has a more favorable combustion emission profile, such as low emissions of carbon monoxide, particulate matter and unburned hydrocarbons [1] Fuels derived from vegetable oils, due to their agricultural origin, are able to reduce net CO2 emissions to the atmosphere along with import substitution of petroleum products [2] They present a very promising alternative to diesel oil since they are renewable and have similar properties [3] The use of non-edible vegetable oils compared to edible oils is very significant because of the tremendous demand for edible oils as food Moreover, edible oils are far too expensive to be used as fuel at present [4] The interest in using Jatropha curcas as a feedstock for the production of biodiesel is rapidly growing The properties of the crop and its oil have persuaded investors, policy makers and clean development mechanism (CDM) project developers to consider Jatropha as a substitute for fossil fuels to tackle the 310 challenges of energy supply and GHG emission reduction [5] The oil produced by this crop can be easily converted to liquid biofuel that meets the American and European standards [6] Additionally, the press cake can be used as a fertilizer and the organic waste products can be digested to produce biogas (CH4) [5] The plant itself is believed to prevent and control soil erosion or can be used as a living fence or to reclaim wasteland [7] Microwave irradiation, an unconventional energy source, has been used for a variety of applications including organic synthesis, wherein chemical reactions are accelerated because of selective absorption of MW energy by polar molecules, non-polar molecules being inert to the MW dielectric loss [8] Microwaves, representing a non-ionizing radiation, influence molecular motions such as ion migration or dipole rotations without altering the molecular structure 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 Microwave heating compares very favourably with 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 [9] To allow for a strict comparison between microwave irradiation and conventional heating under similar conditions (reaction medium, temperature and pressure), a monomode microwave reactor should be used This ensures wave focusing (reliable homogeneity in the electric field) and accurate control of the temperature (using an optical fibre or infrared detection) throughout the reaction [10] Reflux systems have been developed in an effort to use solvents in microwave assisted organic synthesis without the risk of explosion Reflux systems are at minimal risk of explosion because they are operating at atmospheric pressure and because flammable vapors cannot be released into the microwave cavity Several examples of microwave irradiated transesterification methods have been reported incorporating adapted domestic ovens for use as flow systems [11] or batch laboratory ovens [12] but only moderate conversions were obtained A more recent study used homogeneous catalysis, both in a batch and in a flow system [13] Leadbeater and Stencel reported the use of microwave heating as a fast, simple way to prepare biodiesel in a batch mode [14] This was followed by a continuous flow approach allowing for the reaction to be run under atmospheric conditions and performed at flow rates of up to 7.2 L/ using a L reaction vessel [15] Experimental Materials The main oil treated in this investigation is Jatropha oil The fatty acid composition of the Jatropha oil used as a feedstock for biodiesel production is given in Table and the oil characteristics are given in Table Determination of the composition of the oil was by gas chromatograph (Auto system XL, PerkinElmer type) using fused silica capillary column 60 m · 0.32 mm (ID) at the split ratio 1:5 The oven temperature was planned to remain at 150 °C for one min, then heated at 30 °C/min up to 240 °C S.A El Sherbiny et al Table Fatty acid profile of feedstock Fatty acid Composition (wt.%) Palmitic (16:0) Stearic (18:0) Oleic (18:1) Linoleic (18:2) 18.22 5.14 28.46 48.18 Table Main characteristics of feedstock Parameter Unit Value Viscosity Pour point Cloud point Flash point Acid value Iodine value Calorific value mm2/s °C °C °C mg KOH gÀ1 mg iodine gÀ1 MJ kgÀ1 46.6 À3 235 6.2 101 39.54 Helium was used as the carrier gas with a flow rate mL/ and also as an auxiliary gas for FID One micrometer of each diluted sample with analytical grade dichloromethane from BDH (England) was injected The viscosity of the original oil and the produced biodiesel was measured using the Brookfield viscometer model DV-II As evident from the tables, the fatty acid composition of the oil is dominated by oleic acid (29%) and linoleic acid (48%) i.e., the oil contains about 77% unsaturated fatty acid, which is reflected on its pour and cloud points (À3 and °C, respectively) Methanol (Analytical) El-Nasr Pharmaceutical Chemicals Co (ADWIC) Mwt 32.04 Assay 99.8% was used KOH was used in this study: KOH pellets purified Thann-Fransu Production methodology Biodiesel production was performed in two-step reaction mechanisms:  Acid-catalyzed esterification  Base-catalyzed transesterification Acid-catalyzed pretreatment The Jatropha oil used had an initial acid value of 6.2 mg KOH/g corresponding to a free fatty acid (FFA) level of 3.1%, which is above the 1% limit for a satisfactory transesterification reaction using an alkaline catalyst [16] Therefore, FFAs were first converted to esters in a pretreatment process with methanol (molar ratio methanol/oil = 6.5:1) using H2SO4 as catalyst (0.3%) in 90 reaction time at 60 °C [6] Base-catalyzed transesterification using the conventional technique The method applied for the production of biodiesel from Jatropha oil in this research is base-catalyzed transesterification in a laboratory-scale setup The reaction was performed using methanol as alcohol and KOH as catalyst The transeste- Microwave biodiesel rification process was studied at two catalyst loadings (1 and 1.5 wt.% KOH) and three alcohol to oil molar ratios (4.5:1, 6:1, and 7.5:1) One of the most important variables affecting the yield of an ester is the molar ratio of alcohol to triglyceride The stoichiometric ratio for transesterification requires three moles of alcohol and one mole of triglyceride to yield three moles of fatty acid alkyl esters and one mole of glycerol However, transesterification is an equilibrium reaction in which an excess of alcohol is required to drive the reaction to the right [17] However, an excessive amount of alcohol makes the recovery of the glycerol difficult, so that the ideal alcohol/oil ratio has to be established empirically [18] Most of the studies on the base-catalyzed transesterification of WVO reported that maximum conversion to the ester occurred with a molar ratio of 6:1 [19–22] Transesterification of pretreated waste rapeseed oil carried out by Yuan and co-workers showed a maximum conversion at 6.5:1 of methanol to oil ratio [23], whereas an earlier study by Leung and Guo found a maximum conversion at a ratio of 7:1 [24] Catalyst concentration is closely related to the free acidity of the oil When there is a large free fatty acid content, the addition of more potassium hydroxide, or any other alkaline catalyst, compensates this acidity and avoids catalyst deactivation [16] The addition of an excessive amount of catalyst, however, gives rise to the formation of an emulsion, which increases the viscosity and leads to the formation of gels These hinder the glycerol separation and, hence, reduce the apparent ester yield The result of these two opposing effects is an optimal catalyst concentration of about 1.0–1.5% Reviewing the literature indicated that it was most efficient to fix the reaction temperature at 65 °C, which is slightly above the boiling point of methanol (64.7 °C) When the reaction temperature exceeds the boiling point of methanol, the methanol will vaporize and form a large number of bubbles which may inhibit the reaction [22,25,26] The agitation rate was kept at 400 rpm Since this reaction can only occur in the interfacial region between the liquids and also due to the fact that fats and alcohols are not totally miscible, transesterification is a relatively slow process As a result, vigorous mixing is required to increase the area of contact between the two immiscible phases [27] Stamenkovic´ and co-workers studied the effect of agitation intensity on methanolysis of sunflower oil and reported that by using the microphotographic technique, drop size distributions were found to become narrower and shift to smaller sizes with increasing agitation speed as well as with the progress of the methanolysis reaction at a constant agitation speed [28] Berchmans and Hirata used an agitation intensity of 400 rpm for the two-step methanolysis of Jatropha oil [25] All the reactions were carried out in the reaction conical flasks, which were immersed at 65 °C in a thermostatic water bath equipped with a magnetic stirrer at 400 rpm Potassium methoxide solution was freshly prepared by dissolving the fresh KOH pellets in the predetermined amount of methanol Mixing was performed by continuous stirring for 5– 10 Warm oil was then added to the catalyst/alcohol mixture and the reaction mix was kept at 65 °C throughout the reaction time Once the reaction was completed, the reaction mixture was poured into a 200 mL separating funnel and the solution was allowed to settle overnight before the glycerol layer was removed from the bottom of the separating funnel to get the ester layer (biodiesel) to the top In practice, the separated biodiesel layer should have been water-washed to re- 311 move the excess catalyst, alcohol and other impurities However, due to the small size of the oil samples used in the glass reaction tubes, the refinement stage on this experiment was omitted The experiments were run in triplicate; each set of operation conditions was conducted three times and the average was recorded Microwave-assisted technique The optimum parametric conditions that were obtained from the conventional technique were applied using the microwave-assisted technique in order to compare the systems In order to verify the advantages of microwave irradiation, the technique was applied on the oil without pretreatment A scientific microwave with advanced vessel technology was used This allowed fast vessel heating with homogeneous microwave distribution throughout the cavity The oven used was the Start S (Milestone), manufactured by Milestone Inc., USA A normal pressure glass reactor is equipped with a 500 mL flask and a reflux condenser The oven is supplied with a colour touch screen controller that enables the creation, storage and use of time vs temperature or time vs power reaction profiles The output microwave power is variable up to 1200 watts, controlled via a microprocessor The optimum parametric conditions obtained from the conventional technique were applied again using microwave irradiation in order to compare the systems The temperature was adjusted to 65 °C, and the oil was preheated to the desired temperature of 65 °C using the microwave unit The alcohol– catalyst mixture was then fed into the flask through the condenser, and the mixture was irradiated under reflux for different reaction times of 1, and Results and discussion Results obtained by using the mechanical conventional technique The effect of process variables on biodiesel yield The base-catalyzed transesterification result of Jatropha oil was investigated by changing catalyst (KOH) to oil ratios (% w/w) and alcohol to oil ratios (% w/w) The highest conversion was obtained with 1.5% of catalyst (KOH) to oil ratio and 7.5:1 of methanol to oil molar ratio for 60 min, and under these condition, the Jatropha oil methyl ester (JOME) yield was 99.8% Figs and show biodiesel yield% with time for KOH 1% and KOH 1.5% at different alcohol/oil molar ratios One of the most important variables affecting the yield of ester is the molar ratio of alcohol to triglyceride In this study, a molar ratio of 7.5:1 has given a yield of over 98% Biodiesel with the best properties was obtained using potassium hydroxide as the catalyst in many studies [29–32] Methanolysis with wt.% KOH catalyst resulted in successful conversion giving the best yields and viscosities of the esters in most of the literature reviewed However, using a concentration of 1.5% showed better results in this study Results obtained by using the microwave-assisted technique Applying the microwave technique as previously described in the Experimental section showed that the application of radio 312 Fig Effect of alcohol/oil molar ratios on biodiesel yield using KOH 1% as catalyst S.A El Sherbiny et al Fig Effect of time on biodiesel yields from Jatropha oil using microwave irradiation Table Quality assessment of biodiesel production from Jatropha oil Fig Effect of alcohol/oil molar ratios on biodiesel yield using KOH 1.5% as catalyst frequency microwave energy enhances the reaction rate for the conversion of Jatropha oil to biodiesel, and drives the reaction equilibrium toward the production of biodiesel Highest biodiesel yield (97.4%) was obtained by applying microwave irradiation for two minutes compared to h with the conventional technique The results are depicted in Fig It should be pointed out, however, that these results were achieved by using Jatropha oil without pretreatment It was also evident that exceeding the optimum reaction time will lead to deterioration of biodiesel yield The interpretation of these results requires further investigation The most accepted interpretation is that the exceeded time favours the equilibrium in the reverse direction Attributing the decrease in yield after exceeding the optimum time to cracking followed by oxidizing of the formed fatty acid methyl esters to aldehydes, ketones and lower chained organic fractions could be excluded because the GC results not show peaks of oxygenated compounds [33] Property JOME ASTM D 6751 EN 14214 Viscosity (mm2/s) Flash point (°C) 5.8 185 1.9–6.0 P130 3.5–5.0 P120 component triacylglycerols of vegetable oils and their corresponding methyl esters resulting from transesterification is approximately one order of magnitude [34] Kinematic viscosity has been included in biodiesel standards (1.9–6.0 mm2/s in ASTM D6751 and 3.5–5.0 mm2/s in EN 14214) [35] The viscosity of the produced biodiesel was calculated using the Brookfield viscometer Model DV-II and was found to be 5.8 mm2/s The result obtained is compatible with the reports from other studies on biodiesel from Jatropha oil Kumar and Sharma reported a value of 5.65 mm2/s [36] The flash point of the produced biodiesel was estimated to be 185 °C This flash point is quite high compared to diesel Hence, biodiesel is extremely safe to handle The high flash point was referred to in many previous literature; Agarwal and Agarwal reported a flash point of 191 °C compared to 71 °C for mineral diesel [2], and Kumar and Sharma reported a flash point of 170 °C for Jatropha oil methyl ester (JOME) [36] The calorific value (MJ/Kg) for the produced Jatropha biodiesel is 39.632 compared to 45.343 for mineral diesel Comparing the results with those obtained from neat and waste edible oils The results obtained from this study on Jatropha-based biodiesel are confirming the results obtained in a previous study conducted by Refaat and co-workers on neat and waste edible vegetable oils [33] which also showed that no substantial differences were obtained from different oil origins Hence, it can be concluded that biodiesel produced from Jatropha oil is at least not inferior to that produced from edible oils Quality assessment of produced biodiesel Quality assessment was performed using physical parameters such as viscosity, flash point and calorific value, as shown in Table The viscosity difference forms the basis of an analytical method, viscometry, applied to determine the conversion of vegetable oil to methyl ester The viscosity difference between Conclusion From the obtained results, using the conventional technique, the best yield % for the production of biodiesel from Jatropha oil was obtained using a methanol/oil molar ratio of 7.5:1, potassium hydroxide as catalyst (1.5%), and a reaction time Microwave biodiesel of one hour with the reaction temperature maintained at 65 °C The study also showed that the quality of the produced biodiesel satisfies the international American and European standards; hence, inedible vegetable oils such as Jatropha oil, produced by seed-bearing shrubs, can provide an alternative, and they not have competing food uses The results showed that application of radio frequency microwave energy offers a fast, easy route to this valuable biofuel with advantages of enhancing the reaction rate and improving the separation process The reaction time was reduced to instead of 150 minutes (90 for the pretreatment process and 60 for transesterification), because, by using the microwave technique, no pretreatment is required The methodology also allows for the use of high free fatty acid content feedstock, including Jatropha oil However, this will need time control, otherwise the yield may be affected Acknowledgements Sincere thanks are due to both Prof Dr Guzine El-Diwani and Dr Nahed Kamal of the Chemical Engineering Department – National Research Center – Dokki – Egypt, for generously offering the oil and equipment Thanks are also due to M.A Refaat, A.M Hanafy, M.M Hassen and M.S Sakr, the undergraduate students in the Department of Chemical Engineering, Cairo University, for their efforts References [1] Al Zuhair S Production of biodiesel: possibilities and challenges Biofuels Bioprod Bioref 2007;1(1):57–66 [2] Agarwal D, Agarwal AK Performance and emissions characteristics of Jatropha oil (preheated and blends) in a direct injection compression ignition engine Appl Therm Eng 2007;27(13):2314–23 [3] Banapurmath NR, Tewari PG, Hosmath RS Performance and emission characteristics of a DI compression ignition engine operated on Honge, Jatropha and sesame oil methyl esters 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production and fuel quality assessment of biodiesel Trans Am Soc Agric Eng 2001;44(2):193–200 [35] Knothe G, Steidley KR Kinematic viscosity of biodiesel fuel components and related compounds Influence of compound S.A El Sherbiny et al structure and comparison to petrodiesel fuel components Fuel 2005;84(9):1059–65 [36] Kumar A, Sharma S An evaluation of multipurpose oil seed crop for industrial uses (Jatropha curcas L): a review Ind Crop Prod 2008;28(1):1–10  ... technique were applied using the microwave- assisted technique in order to compare the systems In order to verify the advantages of microwave irradiation, the technique was applied on the oil without... to 65 °C, and the oil was preheated to the desired temperature of 65 °C using the microwave unit The alcohol– catalyst mixture was then fed into the flask through the condenser, and the mixture... most of the literature reviewed However, using a concentration of 1.5% showed better results in this study Results obtained by using the microwave- assisted technique Applying the microwave technique