2091r 2010 American Chemical Society pubs.acs.org/EF

Energy Fuels 2010, 24, 2091–2097 : DOI:10.1021/ef901318sPublished on Web 02/12/2010

Nanocrystalline Lithium Ion Impregnated Calcium Oxide As Heterogeneous Catalyst

for Transesterification of High Moisture Containing Cotton Seed Oil

Dinesh Kumar and Amjad Ali*

School of Chemistry and Biochemistry, Thapar University, Patiala 147004 India

Received November 9, 2009. Revised Manuscript Received January 16, 2010

The present work demonstrates the application of nanocrystalline Liþ impregnated CaO as a heterogeneouscatalyst for transesterification of used cottonseed oil with a higher amount of moisture. Catalysts with differentalkali metal ions were prepared by the wet impregnation method, and their basic strengths were measured byHammett indicators and a maximum was found in the case of lithium carbonate impregnated CaO. Furthercharacterization of the lithium impregnated catalyst by powder X-ray diffraction and transmission electronmicroscopy studies supports the formation of a nanosized catalyst with a particle size of about 50 nm. The samecatalyst has been chosen for studying the transesterification reaction of used cotton seed oil withmethanol. Thevariables used for the transesterification were impregnated alkali metal ion, percentage of Liþ impregnation,catalyst concentration, reaction temperature (35-65 �C), oil to methanol molar ratio, reaction time (0.5-8 h),free fatty acid content (up to 6 wt %), moisture content (up to 15 wt %), and mixture of free fatty acid andmoisture content. Reaction parameters have been optimized to achieve the least reaction period for thecompletionof the reaction.Complete transesterificationofused cotton seedoilwithmethanol required45min inthe presence of lithium carbonate impregnated CaO nanocatalyst at 65 �C when moisture and free fatty acidcontents present in oil were 0.26 and 0.31 wt%, respectively. The same catalyst was found to be effective for thetransesterification of cotton seed oil even in the presence of 15 wt % water though it took 2.5 h for thecompletion of the reaction.

1. Introduction

Depleting fossil fuel reserves and increasing environmentalconcerns are the main cause for the search of renewable fuels,such as biodiesel, in the recent past. Combustion of fossil fuelscauses the emissionof air pollutants viz.,NOx, SOx,CO,CO2,particulate matter, and volatile organic compounds (VOCs),out of which CO2 is the main culprit for global warming.1

Hence, there is a need to substitute the fossil based fuels withrenewable and eco-friendly one. Vegetable oils have long beenconsidered a potential diesel fuel substitute although their usehas been hindered by economic and technical difficulties.High viscosity and high molecular weight of vegetable oilsleads to the poor fuel atomization, incomplete combustion,carbon deposition on the injector, and fuel build up in thelubricant oils causing serious engine fouling.2-4

Transesterification of vegetable oils with short carbonchain alcohols in the presence of catalyst (acid or base)leads to the formation of glycerol and fatty acid alkyl esters,commonly known as biodiesel.5 Viscosity of biodiesel(4-6 cSt) is less than vegetable oil (35-40 cSt) and hencecould overcome most of the problems associated with the

use of vegetable oil.6 Biodiesel can be prepared from avariety of triglycerides including vegetable oils, animalfats, and waste greases in the presence of homogeneousor heterogeneous catalyst.7-11 Homogenous alkali cata-lyst has been used frequently at the industrial scale forbiodiesel production as it catalyzes the reaction at fasterrate and requires mild reaction conditions. However, thesame catalyst yielded biodiesel and glycerol contami-nated with catalyst and leads to the formation of soap iffree fatty acids (FFAs) and moisture contents are greaterthan 0.5% and 0.3% (w/w), respectively.12,13 More re-cently, there has been an increased research activity directedtoward the development of heterogeneous catalysts whichhas several advantages, viz., formation of uncontaminatedproducts, is recyclable, has low sensitivity toward FFAsand moisture content, and does not corrode the reactionvessel.14,15

A variety of heterogeneous catalysts for transesterifica-tion reactions were reported in the literature, including

*To whom correspondence should be addressed. Tel: +91-175-2393832. Fax: þ91-175-2364498, 2393005. E-mail: amjadali@thapar.edu, amjad_2kin@yahoo.com.(1) Klass, L. D. Biomass for Renewable Energy, Fuels, and Chemicals;

Academic Press: New York. 1998; pp 1-2.(2) Pryde, E. H. Vegetable oil fuel standards. Vegetable Oil Fuels:

Proceedings of the International Conference on Plant and Vegetable OilsFuels; ASAE: Fargo, ND, 1982; pp 101-105.(3) Sridharan, R.; Mathai, I. M. J. Sci. Ind. Res. 1974, 33, 178–187.(4) Encinar, J. M.; Gonzalez, J. F.; Rodriguez, J.; Tejedor, A. Energy

Fuels 2002, 16, 443–450.(5) Wagner, L. E. Master’s Thesis, Kansas State University,

Manhattan, KS, 1983.

(6) Allen, C. A. W.; Watts, K. C.; Ackman, R. C.; Pegg, M. J. Fuel1999, 78, 1329–1336.

(7) Ma, F.; Hanna, M. F. Bioresour. Technol. 1999, 70, 1–15.(8) De, B. K.; Bhattacharya, D. K. Lipid-Fett 1999, 101, 404–406.(9) Alcantara, R.; Amores, J.; Canoira, L.; Fidalgo, E.; Franco,M. J.;

Navarro, A. Biomass Bioenergy 2000, 18, 515–527.(10) Meher, L. C.; Vidya Sagar, D.; Naik, S. N. Renewable Sustain-

able Energy Rev. 2006, 10, 248–268.(11) Vicente,G.;Martinez,M.;Aracil, J.Bioresour. Technol. 2004, 92,

297–305.(12) Haas, M. J. Lipid Technol. 2004, 16, 7–11.(13) Canakci, M.; Gerpen, J. V. Trans. ASAE 1999, 42, 1203–1210.(14) Clark, J. H.; Macquarrie, D. J. Chem. Soc. Rev. 1996, 25, 303–

310.(15) Tanabe, K.; Misono, M.; Ono, Y.; Hattori, H. Stud. Surf. Sci.

Catal. 1989, 51, 27–213.

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immobilized enzymes,16-23 calcium carbonate,24 alkali-earth-metal compounds,25 sulphated zirconia,26 tin compoundssupported in ion-exchange resins,27,28 alkylguanidines hetero-genized onorganic polymers,29,30 zeolites,31,32 alumina loadedwith alkali-metal salt,33,34 and calcium oxide loaded withlithium.35-37 Recent studies have also found functionalizedmesoporous silica, such as tin-oxide-modified mesoporousSBA-15,38,39 titanium-grafted mesoporous silica,40-43 andmagnesium supported MCM-4144,45 effective for catalyzingtransesterification reactions using a variety of triglycerides.However, for complete (>98%) biodiesel conversion fromvegetable oils, most of the heterogeneous catalyst requireshigh temperature and pressure conditions and a longer dura-tion of reaction. All these factors lead to an increase in theproduction cost of biodiesel.20,46

A major problem for the commercialization of biodiesel isits production cost which should be at par withmineral diesel.Production cost can be reduced by using low-quality cheap

feedstock, using heterogeneous catalyst, and by reducing thetime period of the transesterification reaction in order toreduce the energy consumption during the reaction. Withthese objectives kept in mind, the present work demonstratesthe preparation of Liþ impregnated calcium oxide as ananocrystalline heterogeneous catalyst for biodiesel produc-tion from used cottonseed oil. The reaction parameters havebeen optimized to obtain the complete transesterification ofoil in the minimum possible time to reduce the energyconsumption for the reaction.

2. Experimental Section

2.1. Materials and Methods. Used cooking oil was collectedfrom local restaurants located in Patiala. NaOH,KOH, LiNO3,KNO3, NaNO3, Li2CO3, K2CO3, Na2CO3, CaO, palmitic acid,and silica gel for thin layer chromatography (TLC), of reagentgrade quality, were purchased from Loba Chemie, India, andused as such without further purification. Methanol (99.8%)used in the present study was obtained from Merck, India, andmethyl oleate (99%) used as a biodiesel standard was procuredfrom Sigma-Aldrich.

Free fatty acid value, saponification, and the iodine value ofthe used cottonseed seed oil were determined by following themethods as reported in the literature,47 and values were found tobe 0.31% (w/w), 190.4 mg of KOH/g, and 94.72, respectively.The moisture content was determined by the Karl Fisher titri-metric method and was found to be 0.26% (w/w).

Alkali metal ion concentrations in CaO were determined byESICO microprocessor flame photometer model 1382E. X-raydiffraction (XRD) data for powder samples were collected onPanalytical’s X’Pert Pro with CuKR radiation. The samples werescanned in the range of 2θ = 5-70� at the scanning speed of 2�/min. The surface areas of the catalyst were determined by usingthe adsorption/desorption method at 77 K by the standardBrunauer-Emmett-Teller (BET) method using MicromeriticsTristar 3000 equipment.All sampleswere degassed at 473K for 90min under nitrogen atmosphere to remove the physisorbedmoist-ure from the catalysts. Field emission scanning electron micro-scopy (FESEM) was performed on TECNAI G220, S-TWIN tocollect the SEM images of the catalysts, and transmission electronmicroscopy (TEM) was performed on QUANTA 200 FEG torecord TEM images. Fourier transform-nuclear magnetic reso-nance (FT-NMR) spectra of biodiesel and vegetable oil wererecorded on a Bruker Avance-II (400 MHz) spectrophotometer.The basic strengths of the catalysts (H_) were determined by usingHammett indicators: neutral red (H_ = 6.8), bromthymol blue(H_= 7.2), phenolphthalein (H_= 9.3), Nile blue (H_ = 10.1),tropaeolin-O (H_ = 11.1), 2,4-dinitroaniline (H_ = 15.0), and4-nitroaniline (H_ = 18.4).

2.2. Preparation of Catalyst. The nanocrystalline alkali metalion impregnated CaO catalyst was prepared by the wet impregna-tion method as reported in the literature36 with a slight modifica-tion. In a typical preparation, 10 g of calciumoxide was suspendedin 40 mL of deionized water, and to this 10 mL of aqueous alkalimetal salt solution of appropriate concentration was added, e.g.,while preparing 1.5 wt % lithium ion impregnated calcium oxide,0.798 g of Li2CO3 was used. The slurry was stirred for 2 h, thenevaporated to dryness, and heated at 120 �C for 24 h. A series ofalkali metal ions (Liþ, Naþ, and Kþ) impregnated catalysts usingdifferent salts of alkali metal ions (K2CO3, Na2CO3, Li2CO3,KNO3, NaNO3, and LiNO3) with varying metal concentrations(wt %) ranging from 0.5 to 5.0 wt % (metal ion/CaO) wereprepared and characterized by flame photometry, X-ray powderdiffraction (XRD), BET surface area measurement, a Hammettindicator test, and FESEM and TEM techniques.

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The catalysts prepared in such a manner were designated asMA-CaO-XX, where MA represent the impregnated alkalimetal salt and XX represent the percentage of impregnation inCaO, e.g., LiC-CaO-1.5 and LiN-CaO-1.5 represent CaO cata-lysts formed by impregnation of 1.5% (wt %) of Liþ usingLi2CO3 and LiNO3 salts, respectively.

2.3. Transesterification of Used Cottonseed Oil. In a typicaltransesterification reaction, used cottonseed oil andmethanol ina 1:12 molar ratio and 5 wt % of catalyst were taken in a twoneck round-bottom flask. The reactionmixturewas heated up to65 �C with continuous stirring until the completion of thereaction. The samples have been withdrawn from the reactionmixture after every 5 min with the help of a glass capillary anddiluted with hexane to perform thin layer chromatographic(TLC) studies.

The completion of the reaction and primary characterizationof the product was done by the TLC technique using hexane/ethyl acetate/acetic acid (90:9:1) as the mobile phase and silicagel as the stationary phase. Biodiesel shows a higher mobilitythan vegetable oil with the selected solvent system, and completeconversion of vegetable oil to biodiesel was supported by thedisappearance of the vegetable oil spot on the TLC plate.Further biodiesel so produced was characterized by 1H and13C NMR spectroscopy, and the 1H NMR technique was alsoused for the quantification of biodiesel as described in theliterature.48,49

3. Results and Discussion

3.1. Catalyst Characterization. The basic strength of thealkaline earth metal oxides and hydroxides increase in theorder of Mg<Ca< Sr< Ba,36 and CaO has been chosenfor the present work becasue it is inexpensive and lesstoxic. Further, the basic strength of CaO can be enhancedby impregnating it with alkali metal ions. The actualimpregnated amount of alkali metal ions was determinedby the flame photometric method. The surface areaof Li, Na, and K carbonate impregnated (1.5 wt %) cal-cium oxide catalysts were measured by the Brunauer-Emmett-Teller (BET) method. Alkali metal ion impreg-nated CaO catalysts show high surface area in compari-son with pure CaO, and the highest surface area wasfound in the case of lithium impregnated CaO as shownin Figure 1.

The basic strengths of the catalysts were determined byusing the Hammett indicators50 and summarized in Table 1.The basic strength of LiC-CaO-1.5 was found to be max-imum, 15.0 < H_ < 18.4, among the prepared catalysts,probably due to the formation of strong basic sites on theCaO surface. Hence, the LiC-CaO-1.5 catalyst is expected toshow the highest catalytic activity toward the transesterifica-tion reaction of vegetable oil.

Powder X-ray diffraction studies of CaO and Li, Na, andK carbonate impregnated (1.5 wt %) CaO have been per-formed, and comparisons of XRD patterns are given inFigure 2. The intense peaks at 2θ ∼ 37.34, 53.93, and 32.23correspond to the d-values of 2.39, 1.69, and 2.75, respec-tively, of calciumoxide, while peaks at 2θ∼ 34.18, 18.16, and47.18 correspond to d-values of 2.63, 4.92, and 1.92, respec-tively, of calcium hydroxide as shown in Figure 2. Theparticle size of the LiC-CaO-1.5 catalyst was determinedby the Debye-Scherrer method51 using powder XRD dataand found to be about 70 nm.

Scanning electron microscopic images of pure CaO showsthat it has clusters of∼5 μm sized particles. Impregnation ofthe same with Liþ (1.5 wt %) using Li2CO3 leads to theformation of impregnated CaO particles in hexagonal andoval shapes as shown in Figure 3. The average size ofparticles by FESEM studies were found to be ∼4 μm.TEManalysis of the same particles shows that these particlesare the clusters of further smaller particles with an averagesize of∼50 nm and hence supports the presence of catalyst inthe nanoparticle form as shown in Figure 4.

The characterization of impregnated CaO catalysts re-veals that lithium carbonate impregnated CaO possesses the

Figure 1. Comparison of BET surface areas of pure CaO with thatof Li, Na, and K ion impregnated CaO.

Table 1. Comparison of the Basic Strengths of Alkali Metal Ion

Impregnated CaO with That of Pure CaO

catalyst type basic strength (H_)

CaO 9.8 < H_ < 10.1LiC-CaO-1.5 15.0 < H_ < 18.4LiN-CaO-1.5 11.1 < H_ < 15.0NaC-CaO-1.5 10.1 < H_ < 11.1NaN-CaO-1.5 10.1 < H_ < 11.1KC-CaO-1.5 10.1 < H_ < 11.1KN-CaO-1.5 10.1 < H_ < 11.1

Figure 2. Comparison of powder XRD patterns of commerciallyavailable CaOwith LiC-CaO-1.5, NaC-CaO-1.5, andKC-CaO-1.5.

(48) Gelbard, G.; Bres, O.; Vargas, R. M.; Vielfaure, F.; Schuchardt,U. F. J. Am. Oil Chem. Soc. 1995, 72, 1239–1241.(49) Knothe, G. J. Am. Oil Chem. Soc. 2001, 78, 1025–1028.

(50) Wan, T.; Yu, P.; Wang, S.; Luo, Y. Energy Fuels 2009, 23, 1089–1092.

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highest surface area and basic strength and is expected toshow highest activity toward the transesterification reaction.When transesterification reactions were performed in thepresence of Liþ, Naþ, andKþ impregnated CaO, the lithiumion impregnated CaO took the least time for the completionof the reaction and hence chosen for further studies.

3.2. Transesterification Reactions and Biodiesel Character-

ization. Transesterification reactions of used cotton seed oilwith methanol (1:12 molar ratio) were performed in thepresence of prepared catalysts (5 wt %, catalyst/oil) at65 �C. Prepared catalysts were used to carry out the trans-esterification reactions of used cotton seed oil in order todetermine the least reaction time for the completion of thetransesterification reaction. During the course of study, thefollowing parameters have been varied (i) impregnated alkalimetal ion, (ii) impregnated lithium ion concentration, (iii)catalyst concentration, (iv) reaction temperature, (v) oil/methanol molar ratio, (vi) moisture content (1-15 wt %),(vii) free fatty acid content (0.5-6 wt %), and (viii) mixtureof moisture and free fatty acid contents.

Biodiesel produced in the transesterification reaction wascharacterized by 1Hand 13CNMRspectroscopy. The protonNMR spectrum of used cottonseed oil shows a multiplet at4.1 and 5.2 ppm due to the presence of glyceridic protons

along with other hydrocarbon-proton peaks at their normalpositions.52 The appearance of a new peak at 3.6 ppm due to-OCH3 protons and disappearance of the glyceridic protonssupport the formation of biodiesel as shown in Figure 5. Theproton NMR spectra has also been used to confirm thecompletion of the reaction (>98% conversion of vegetableoil to biodiesel) by following the methods as reported in theliterature.48,49

The carbon-13 NMR spectrum of cottonseed oil showstwo peaks at 62.2 and 69.0 ppm due to the glyceridic carbonatoms along with other hydrocarbon-carbons peaks at theirnormal positions. Disappearance of these two peaks andappearance of a new peak at 51.5 ppm due to the -OCH3

carbon supports the formation of the methyl ester of cottonseed oil as shown in Figure 6.

3.2.1. Effect of Alkali Metal Ion on Catalyst Activity. Inorder to test the effect of impregnated alkalimetal ions on theactivity of the catalyst, six different catalysts, viz., LiC-CaO-1.5, LiN-CaO-1.5, KN-CaO-1.5, KC-CaO-1.5, NaN-CaO-1.5, andNaC-CaO-1.5 were prepared. The basic strengths ofthe prepared catalysts were determined by Hammett indica-tors and found to be maximum (15.0-18.4) for nanocrystal-line LiC-CaO-1.5. The basic strength of the alkali metal ionimpregnated catalysts decreases with the increase of alkalimetal ion size. Smaller size ions are expected to insert easily

Figure 3. Comparison of SEM images of (a) CaO with (b) LiC-CaO-1.5.

Figure 4. TEM image of LiC-CaO-1.5.Figure 5. Comparison of the 1H NMR spectra of (a) cotton seed oilwith that of (b) biodiesel.

(52) Vigli, G.; Philipidis, A.; Spyros, A.; Dais, P. J. Agric. FoodChem.2003, 51, 5715–5722.

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in the framework of CaO to create oxygen gaps, which areresponsible for the strong basic strength.53 Thus, with anincrease in the size of the alkali metal ion in CaO, the basicstrength as well as the catalytic activity toward transester-ification decreases. Thus, the reaction proceeds at a fasterrate in the case of LiC-CaO-1.5 while other catalyst showsrelatively lower activity toward transesterification of usedcottonseed oil as summarized in Figure 7. LiC-CaO-1.5 wasselected for further studies because it was the highest inactivity toward the transesterification reaction.

3.2.2. Effect of Impregnated Lithium IonConcentration.Todetermine the optimum amount of lithium ion impregnationin CaO, a series of catalysts by varying the amount of lithiumion from 0.5 to 5 wt % (metal ion/CaO) in CaO wereprepared. Transesterification of used cottonseed oil wasperformed with methanol (1:12 molar ratio) at 65 �C in thepresence of prepared catalysts. The reaction time requiredfor the complete transesterification was found to decrease

from 3 h to 45 min as the amount of lithium ion in CaO wasincreased from 0.5 to 1.5 wt %. However, a further increasein Liþ ion concentration does not reduce the reaction time asshown in Figure 8, and hence, LiC-CaO-1.5 catalyst was usedfor transesterification reactions to optimize other parametersfor achieving the minimum time for the completion of thetransesterification reaction.

3.2.3. Effect of Catalyst Concentration. A series of trans-esterification reactions of used cotton seed oil with methanol(1:12 molar ratio) at 65 �C was performed in the presence ofnanocrystalline LiC-CaO-1.5 by varying its concentration from1 to 8 wt % (catalyst/oil) in order to find the optimum catalystconcentration. Time required for the complete conversion ofvegetable oil to biodiesel decreases from 7 h to 45 min as thecatalyst concentrationwas increased from1 to5wt%.Afurtherincrease in the catalyst concentration does not reduce thereaction time significantly as shown in Figure 9. The transester-ification reactions were further studied with a catalyst concen-trationof 5wt%ofoil for optimizationof theother parameters.

Figure 6. Comparison of 13C NMR spectra of (a) cotton seed oilwith that of (b) biodiesel.

Figure 7. Effect of impregnated alkali metal ion on reaction timerequired for the complete conversion of used cottonseed oil tobiodiesel.

Figure 8. Effect of lithium ion concentration in CaO on the timerequired for complete transesterification of used cottonseed oil tobiodiesel.

Figure 9. Effect of catalyst concentration on the time required forcomplete transesterification of used cottonseed oil to biodiesel.

(53) Barrault, J.; Pouilloux, Y.; Clacens, J. M.; Vanhove, C.;Bancquart, S. Catal. Today 2002, 75, 177–181.

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3.2.4. Effect of Reaction Temperature. A series of transes-terification reactions was conducted in the presence of 5 wt% (catalyst/oil) nanocrystalline LiC-CaO-1.5 to find theoptimum temperature for the transesterification reaction.The time required for the complete transesterification ofvegetable oil to biodiesel decreases from 6 h to 45 min as thetemperature of the reaction was increased from 35 to 65 �C.A further increase in the reaction temperature does notreduce the reaction time significantly as shown in Figure 10.

3.2.5. Effect ofMethanol/OilMolarRatio.The effect of themethanol/oil molar ratio on the transesterification reaction isone of the important parameters which affects themethyl esteryield aswell as cost of the biodiesel production. The theoreticalminimum oil to methanol molar ratio should be 1:3 for thecomplete conversion of vegetable oil to biodiesel. However,with transesterification being a reversible reaction, usuallysuch reactions performed with an excess of methanol shiftsthe equilibrium in the forward direction to achieve amaximummethyl ester yield. Heterogeneous catalysts usually catalyzedthe transesterification reaction at a slower rate and took moretime for the completion of the reaction. The use of highermolar ratios of oil to alcohol (viz., 1:15, 1:40, andeven1:275) toimprove the yield of transesterified product in less time havebeen reported in the literature54-56 when reactions werecatalyzed by heterogeneous catalysts.

To determine the optimum oil/methanol molar ratio, thereactions were performed with 1:3 to 1:18 molar ratios at65 �C using 5 wt % of LiC-CaO-1.5 catalyst. The rate oftransesterification reaction increases as the oil/methanolratio was increased from 1:3 to 1:12, and the reaction wasfound to be completed in 45minwhen a 1:12 ratio was taken.A further increase in the oil/methanol ratio does not increasethe reaction rate significantly, and complete conversion stilltakes 45 min as shown in Figure 11.

3.2.6. Effect of Moisture Content. The presence of water(>0.3%) in vegetable oil, used for the transesterificationreaction, leads to the formation of soap instead of biodiesel

in the presence of homogeneous catalyst.13 Used cotton seedoil taken for the present studies was found to have 0.26%moisture content, and the transesterification reaction of thesame using NaOH or KOH as a catalyst leads to the sapo-nification reaction. However, the same reaction when cata-lyzed by nanocrystalline LiC-CaO-1.5 yielded the completeconversion of oil to biodiesel. In order to determine the highestmoisture resistance of LiC-CaO-1.5 catalyst, transesterifica-tion reactions were performed in the presence of 1-35 wt %(water/oil) water. The same catalyst was found to be effectivefor the complete transesterification of cotton seed oil in 2.5 heven when 15 wt % of moisture content was present in thereaction mixture as shown in Figure12. Further addition ofwater (>15%) to the reaction mixture decreases the productyield and leads to saponification of the oil.

3.2.7. Effect of Free Fatty Acid Contents. The presence offree fatty acid contents (>0.5 wt % of oil) leads to thesaponification instead of the transesterification in the pre-sence of homogeneous catalyst.12 Used cottonseed oil taken

Figure 10. Effect of reaction temperature on the time required forcomplete transesterification of used cottonseed oil to biodiesel.

Figure 11. Effect of the oil/methanol molar ratio on the timerequired for complete transesterification of used cottonseed oil tobiodiesel.

Figure 12. Effect of moisture content on the time required forcomplete transesterification of used cottonseed oil to biodiesel.

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721–723.(56) Leclercq, E.; Finiels, A.; Moreau, C. J. Am. Oil Chem. Soc. 2001,

11, 1161–1165.

2097

Energy Fuels 2010, 24, 2091–2097 : DOI:10.1021/ef901318s Kumar and Ali

for the present studies was found to have 0.31% free fattyacid content, and the transesterification reaction of the sameusingNaOHorKOHas a homogeneous catalyst leads to theformation of soap instead of biodiesel. However, the samereaction when catalyzed by nanocrystalline LiC-CaO-1.5yielded the complete conversion of oil to biodiesel in 45min. In order to determine the maximum tolerance of pre-pared catalyst for free fatty acid contents, FFAs (1-6 wt %of oil) in the form of palmitic acid were added in the reactionmixture while performing the transesterification reaction ofused cotton seed oil. Catalyst LiC-CaO-1.5 was found to beeffective for the complete transesterification of cottonseedoil in 2.5 h even when 6 wt % of free fatty acid content waspresent in the reaction mixture as shown in Figure 13.Further addition of free fatty acid content (>6%) to oilleads to the saponification of oil.

3.2.8. Effect ofMixture ofMoisture Content and Free FattyAcid. Most of the low-quality feedstock contains a highamount of moisture and free fatty acid content. To studythe combined effect of moisture and free fatty acid contenton the activity of prepared catalyst (LiC-CaO-1.5), bothwere added together during the transesterification reactionof used cottonseed oil. When 2 wt % moisture and the freefatty acid content of each were added together, LiC-CaO-1.5nanocatalyst took 2.5 h for the completion of the transester-ification reaction. The moisture content when increased upto 5 wt% in the presence of 2 wt% of free fatty acid took 4 hfor the completion of the reaction as shown in Table 2. Afurther increase of either the moisture or FFA content in the

reactionmixture leads to the formation of soap instead of thetransesterified product.

4. Conclusions

The present work demonstrates the preparation of a seriesof alkali metal ion (Li, Na, andK) impregnatedCaO catalystsand investigation of their catalytic activities toward transes-terification of used cottonseed oil (with 0.26, 0.31, wt %moisture and FFA contents, respectively). Calcium oxideimpregnated with Li2CO3 was found to have the highest basicstrength as supported by Hammett indicator tests andexist in the nanocrystalline form as supported by TEM andpowder XRD studies. The same catalyst (LiC-CaO-1.5) took45min for the complete transesterification of used cottonseedoil with methanol (1:12 molar ratio) at 65 �C and 6 h at roomtemperature (35 �C). Further, the prepared catalyst wasfound to be effective for the complete transesterification ofused cottonseed oil at 65 �C with the oil/methanol molarratio being 1:12 even in the presence of (i) 15 wt % moisturein 2.5 h, (ii) 6 wt % of free fatty acid in 2.5 h, (iii) 5 wt %moisture and 2wt% free fatty acid content in 4 h. In short, theprepared nanocatalyst has the potential to convert the cheapfeedstock, having a higher amount of moisture and FFAs,into biodiesel to reduce its production cost. Presently, studiesare focused in our lab to test the efficiency of the same cata-lyst for the transesterification of other vegetable oils andanimal fats.

Acknowledgment. A.A. acknowledges the financial supportfrom theDST,NewDelhi (GrantNo. SR/FTP/CS-30/2007), andSCBC, Thapar University for providing the necessary researchfacility. D.K. acknowledges the JRF fellowship from DST. WeacknowledgeSAIF (PunjabUniversity) for the powderXRDandNMR, IIC (IITRoorkee) for theFESEMandTEM, andKunashInstruments for the surface area studies.

Figure 13. Effect of free fatty acid content on the time required forcomplete transesterification of used cottonseed oil to biodiesel.

Table 2. Effect of Moisture and Free Fatty Acid Content When

Present Together on the Reaction Time Required for the Complete

Transesterification of Cottonseed Oil in the Presence of the LiC-

CaO-1.5 Catalyst

wt %

S. no. moisture FFAs reaction time (h) conversiona

1 1 1 2 complete2 2 2 2.5 complete3 3 3 8 saponification4 5 3 8 saponification5 5 2 4 complete6 6 2 8 saponification

aComplete conversion of cottonseed oil to biodiesel was determinedby TLC and proton NMR spectroscopy, and saponification was visua-lized due to the formation of solid soap.