Transesterification of non edible feedstock with lithium

Fuel Processing Technology 122 (2014) 72–78

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Transesterification of non edible feedstock with lithium incorporated egg shell derived CaO for biodiesel production Jutika Boro ⁎,1, Lakhya Jyoti Konwar 1, Dhanapati Deka Biomass Conversion Laboratory, Department of Energy, Tezpur University, Napaam, Tezpur 784028, India

a r t i c l e

i n f o

Article history: Received 11 December 2011 Received in revised form 25 September 2013 Accepted 20 January 2014 Available online 11 February 2014 Keywords: Egg shell Doped catalyst Biodiesel Transesterification Characterization

a b s t r a c t A series of Li doped egg shell derived CaO is prepared for biodiesel production from nonedible oil feedstock. The catalyst is characterized by X-ray diffraction (XRD), Fourier transform infrared spectrometer (FT-IR), Brunauer– Emmett–Teller (BET) surface area measurements and their basic strengths were measured by Hammett indicators. Maximum conversion of 94% is observed with 5% of catalyst amount and 2% of Li loading is observed to be optimum for better conversions. Though the catalyst is not reusable its catalytic activity can be improved by activating it at appropriate temperature and reloading it with Li. NMR studies showed that the final product separated after transesterification is biodiesel. © 2014 Elsevier B.V. All rights reserved.

1. Introduction Alternative fuels for diesel engines have gain importance because of diminishing petroleum reserves and the environmental consequences of exhaust gases from petroleum fueled engines [1]. In this respect, biodiesel is an emerging alternative to diesel fuel derived from renewable and locally available resources which is biodegradable, nontoxic and environmentally friendly. It is mainly produced via transesterification of vegetable oil, which is a renewable and sustainable source [2]. In the transesterification reaction, a triglyceride reacts with an alcohol in the presence of a catalyst, producing a mixture of fatty acids alkyl esters and glycerol [3]. Currently, biodiesel is produced by performing a transesterification reaction with homogeneous base catalysts such as KOH or NaOH dissolved in methanol. This production process can provide high FAME yields under mild conditions — atmospheric pressure, a temperature of 60 °C, and a reaction time of approximately 1 h [4]. The major disadvantage of homogeneous catalysts is that they cannot be reused or regenerated, because the catalyst is consumed in the reaction. Moreover the separation of catalyst from products is difficult and requires more equipment which results in higher production costs [5]. Based on these drawbacks, the use of heterogeneous catalysts could be an attractive solution. Heterogeneous catalysts can be separated more easily from reaction products and undesired saponification reactions can be avoided by using heterogeneous acid catalysts [6]. Bio-diesel synthesis using solid catalysts could also lead to cheaper production costs because of reuse of

⁎ Corresponding author. Tel.: +91 9864664257; fax: +91 3712 267005 6. E-mail address: [email protected] (J. Boro). 1 Jutika Boro and Lakhya Jyoti Konwar have contributed equally to this research work. 0378-3820/$ – see front matter © 2014 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.fuproc.2014.01.022

the catalyst and the possibility for carrying out both transesterification and esterification simultaneously [7]. Currently, heterogeneous catalysts including supported catalysts [8], alkali earth oxides [9], hydrotalcites catalyst [10], Eu2O3/Al2O3 [11], and a resin-supported azidoproazaphosphatrane catalyst [12] have been reported to be utilized extensively for biodiesel production. Experiments have been carried out by using CaO as base catalyst in biodiesel production. Recently researchers have utilized waste egg shells and mollusk shells [13–15] as heterogeneous catalysts to make biodiesel production more sustainable. It is reported that the catalyst prepared from the waste shells could be reused without much loss in activity and the preparation method for such catalyst was found to be simple. Based on the work reported by Watkins et al. [16], many researchers prepared Li doped CaO catalyst for producing biodiesel from different feedstocks [17,18]. But, very little work is reported for preparing similar catalyst in which the support CaO is synthesized from renewable sources. In this investigation, Li incorporated egg shell derived CaO is used as catalyst for the transesterification of Nahor oil (Mesua ferrea Linn), a nonedible feedstock having high acid value. The possibility of reusing the catalyst for minimizing the cost of biodiesel production with an environmentally benign process is also explored. 2. Material and method 2.1. Materials Mesua ferrea Linn or locally known as Nahor oil was mechanically extracted from the seeds (collected in the locality) using a screw press in the mechanical expeller and then settled until impurities were precipitated. Synthesis-grade methanol (99% assay and 0.2% water content),

J. Boro et al. / Fuel Processing Technology 122 (2014) 72–78

calcium oxide (99.9%) and lithium carbonate (99.8%) were procured from Merck, India Ltd. and are used as received. Waste egg shells are collected from Dhansiri Women's Hostel, Tezpur University, Assam, India. 2.2. Catalyst preparation Collected egg shells were washed thoroughly and dried at 120 °C for 1 h. It is then grinded and allowed to pass through a 0.8 mm sieve mesh. As reported previously, CaO is formed when the egg shells are calcined at 800 °C [14–16], we have calcined the collected waste shells for 2 h at 800 °C. It is then stored in a dessicator for further use. A series of Li doped egg shell derived CaO catalyst in the range of 1–5% was prepared by wet impregnation as reported by Kumar et al. [17].

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Transesterification was carried out in laboratory scale in a 250 mL round bottom two neck flask equipped with a water cooled condenser and a constant temperature magnetic stirrer with hot plate. Catalyst was activated by dispersing it with methanol at 40 °C under magnetic stirring. After 1 h of the catalyst activation pretreated oil was added to the mixture and then the mixture was vigorously stirred and refluxed at 65 °C for 6 h under stirring at 900 rpm. After the reaction, the catalyst was separated from the biodiesel product by centrifugation and the excessive amount of methanol was evaporated under reduced pressure in a rotary evaporator. 4. Results and discussions 4.1. Characterization

2.3. Instruments The powder X-ray diffractograms of calcined samples were recorded on a Philips X’Pert X—ray diffractometer (Cu—Kα radiation, λ = 1.5406 Å) in 2θ range 10—70° at a scanning rate of 2° min−1. The XRD phases were identified using the powder diffraction file (PDF) database (JCPDS, International Center for Diffraction Data). IR spectra were recorded in KBr pallets on a Nicolet (Impact 410) FT-IR spectrophotometer. The Brunauer–Emmett–Teller (BET) surface areas of the prepared catalysts were measured using a SMART-SORB-92/93 surface area analyzer. Hammett indicator method was used to determine the basic strength of the catalyst. The method of Hammett indicator-benzene carboxylic acid (0.02 mol/L anhydrous methanol solution) titration was used to measure the basicity of the catalysts. Approximately 300 mg of a sample was shaken with 1 mL solution of Hammett indicator diluted in benzene and methanol and left to equilibrate for 2 h. The color of the medium (catalyst) was then noted. The Hammett indicators used in our study are bromothymol blue (H_ = 7.2), phenolphthalein (H_ =9.8), 2, 4-dinitroaniline (H− = 15.0) and 4-nitroaniline (H− = 18.4). The 13C NMR spectra were recorded on a Jeol JNM-ECS400 spectrometer at a carbon frequency of 100.5 MHz, 32768×-resolution points, number of scans 1000, 1.04 s acquisition time and 2.0 s relaxation delay. All 1H NMR analyses were done at 25.5 °C with acetone-d6 and TMS as solvent and internal standard respectively. 3. Experimental 3.1. Feedstock analysis

4.1.1. XRD analysis Powder X-ray diffraction patterns for CaO (inset) and 1–5% Li loaded CaO are presented in Fig. 1. It was observed that the XRD patterns of CaO were altered with increasing Li loading. Initially the XRD peaks that were observed for 1% and 2% of Li loading on CaO consists of CaO (JCPDS 21-0155) peaks and Li2O (JCPDS 09-0355) peaks along with new peaks at 2θ ~18.48°, 34.28°, 47.37°, 51.07° and 72.22° which correspond to crystalline Li–Ca phase (JCPDS 65-0763). The peaks of Li2O are observed for Li-2% onwards. The fact that Li2O appears in the XRD pattern of the catalyst is probably due to the reason that Li+ attract electrons of O2− strongly since it has a high electronegativity (Pauling scale 0.98 kJ·mol−1) [19]. In addition the small radius of Li+ (90 pm) allows its incorporation into the lattice structure of CaO easily. The new phases might also have formed during the interaction between Li with the support (CaO). However the peak for CaO is replaced by new peaks as the Li % loading is increased indicating that the crystal structure of CaO is compressed by Li incorporation. It was observed that in the XRD pattern for 5% Li loading diffraction peaks of Li–Ca were the dominant one suggesting that CaO could not retain its structure with increasing Li loading resulting in the formation of Li containing phase. 4.1.2. FT-IR analysis The Fourier transform infrared (FTIR) spectra of different Li loadings on CaO are presented in Fig. 2. The spectra clearly shows that the CaO structure was altered after the introduction of Li as new peaks were observed in the FTIR spectra of Li loaded CaO catalysts. In the low energy region of egg shell derived CaO, weak bands corresponding to C\O

Table 1 shows the characteristics of M. ferrea Linn (Nahor oil) used in our study. The crude oil extracted was dark reddish colored in appearance with a high acid value of 15.7 mg KOH/g. This indicates that a two-step transesterification process is required for biodiesel production for effective base catalyzed transesterification.

Intensity

XRD pattern for egg shell derived CaO

3.2. Reaction procedures

10

20

30

40

Fuel properties

ASTM method used

Mesua ferrea Linn oil

ASTM D 664 ASTM D464 ASTM D5768-02

15.7 196.3 88.5

10

60

70

Li-1% Li-2% Li-3% Li-4% Li-5%

Table 1 Properties of Mesua ferrea Linn oil.

Acid value (mg KOH/g) Saponification value (mg/g) Iodine value (g/100 g)

50

2θ

Intensity

To reduce the acid value of the feedstock acid esterification of 25 g of M. ferrea Linn (Nahor oil) was performed with conc. H2SO4 acid (1.0% based on the oil weight) as a catalyst. The molar ratio of methanol to oil was maintained at 6:1 and the reaction was carried out for 3 h at 60 °C. Samples were collected at regular intervals and acid values were determined. The process was continued till the acid value reduced to b1. The pretreated oil with low acid value was than transesterified with the catalyst prepared.

20

30

40

50

60

70

80

90

2θ Fig. 1. XRD patterns of egg shell derived CaO (inset) and Li impregnated catalysts.

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J. Boro et al. / Fuel Processing Technology 122 (2014) 72–78 Table 3 Surface area of Li impregnated egg shell derived CaO.

Li-1% Li-2% Li-3%

Transmittance (%)

Li-4% Li-5% Egg shell derived CaO

Catalyst

Surface area (m2/g)

Manufactured CaO Egg shell derived CaO Li-1% Li-2% Li-3% Li-4% Li-5%

20.4 6.88 4.73 4.12 3.05 1.56 1.15

5. Effect of different parameters 5.1. Effect of Li loading on egg shell derived CaO

wavenumber cm-1 Fig. 2. FT-IR pattern for Li (1–5%) loaded catalysts.

stretching mode (ν3) of carbonate ion are observed at 875.77 cm−1 and the peaks around 1450 cm−1 correspond to the bending vibration (ν4) of O\Ca\O group. Their intensity increases after the introduction of lithium carbonate (Li2CO3) which suggests that the sample after the loading contains significant amount of carbonate phase and successful incorporation of Li into CaO structure. Moreover these bands are also characteristic bands of Li2CO3 [20]. The IR band observed in the region 3424.87 and 1636.27 cm−1 is due to O\H stretching and bending (νOH) respectively. However with increasing Li loading the intensity of the O\H vibrational band decreases significantly which may be due to the incorporation of Li+ ions into the CaO defect sites. In the Li loaded catalysts, the peaks near 700 cm−1 are probably due to the Li\O stretching mode whereas the weak bands around 420 cm−1 are assigned to the Li\O asymmetric stretching [21]. This peak becomes more prominent with increasing Li loading. New peaks corresponding to Li2O are also observed in the IR spectra of Li loaded samples at around 687 cm−1. The FTIR spectra of catalysts with increasing Li show the formation of new peaks at around 2513.41, 2932.43 and 1787.33 cm−1 which might be due to the formation of a new single phase Li–Ca compound. 4.1.3. Basicity and BET surface area analysis On the basis of the method previously described in Section 2.3 basicity of the catalysts was determined using Hammett indicators followed by titration. Table 2 depicts the different Li loaded catalyst with their basicity values. It was found that all the catalysts prepared were basic in nature and the basicity of the egg shell derived CaO is lesser than the Li loaded catalyst. Comparison of BET surface area of manufactured CaO, egg shell derived CaO and Li doped catalyst is shown in Table 3. Compared to the egg shell derived CaO smaller surface area was observed for Li loaded samples. It is already reported in the literature [16,22] that this decrease in BET surface area is due to the micropore plugging of CaO upon Li loading. However it has been observed that the basicity affects the catalytic activity more than surface area. Similar observations were made by Meher et al. [23]. Table 2 Basic strengths of Li impregnated egg shell derived CaO. Catalyst

Basic strength (H_)

Total basicity (mmol/g)

Manufactured CaO Egg shell derived CaO Li-1% Li-2% Li-3% Li-4% Li-5%

9.8 b H_ b 10.1 7.2 b H_ b 9.8 15.0 b H_ b 18.4 15.0 b H_ b 18.4 15.0 b H_ b 18.4 15.0 b H_ b 18.4 15.0 b H_ b 18.4

0.51 0.47 0.9 1.3 1.5 1.4 1.6

All samples were activated at 800 °C prior to measurements.

Fig. 3 shows the conversion obtained with the different Li loadings on egg shell derived CaO activated at 120 °C for 2 h. It was observed that the conversion increased up to 2% of Li loading (95 b) beyond which it decreased. Therefore 2% Li loading is considered to be the optimum amount. The initial increasing conversion is probably due to the incorporation of Li+ ion into the CaO framework which may have improved the basicity of CaO or may be due to the combine effect of CaO, Li2O and Li–Ca phase. However when the loading is increased up to 5% catalytic activity drops indicating that Li–Ca alone doesn't take active part during reaction. The other possible reason behind this decrease in conversion may have caused due to overloading of Li. 5.2. Effect of catalyst amount Different literatures have suggested that the conversion is also affected by the amount of catalyst used for the reaction. In our study the effect of catalyst amount was investigated at a 10:1 methanol to oil molar ratio at 65 °C (Fig. 4). The catalyst amount was varied in the range of 1–8 wt.%. It was observed that the conversion increased with the increasing catalyst amount from 1 to 5 wt.% attaining a maximum conversion of 94.0%. Beyond 5 wt.% the conversion became nearly constant and drop in conversion was observed for 8 wt.% catalyst amounts. Hence in our study we have taken 5 wt.% as the optimum catalyst amount. 5.3. Effect of methanol:oil ratio Apart from catalyst amount the other factor that highly influences the transesterification reaction is the methanol to oil molar ratio. It has already been established that an optimal methanol to oil molar 100

90

Conversion (%)

3500 3000 2500 2000 1500 1000 500

80

70

60

50

40 0

1

2

3

4

Li loading(%) Fig. 3. FAME yield with Li loading on CaO derived from egg shell.

5

95 90 85 80 75 70 65 60 55 50 45 40 35 30 25

75

95 90 85

0% Li-1% Li-2% Li-3% Li-4% Li-5%

Conversion (%)

Conversion (%)


80 75 70 65 60 55

0

1

2

3

4

5

6

7

8

9

50

Catalyst amount 45 60

Fig. 4. Effect of catalyst amount.

65

70

75

80

Reaction Temperature (oC) ratio sets the reaction towards forward direction and helps in achieving maximum yield [24]. Fig. 5 represents the effect of methanol to oil molar ratio. It can be seen from the fig. that the conversion increases for methanol to oil molar ratio till 10:1 after which it either remains constant for all the Li loaded catalysts or the conversion decreases (as observed for 5% Li loaded sample). Therefore methanol to oil molar ratio of 10:1 was considered as optimal ratio in this study. It should also be noted that the excess methanol could be recovered and reused for another set of experiment.

Fig. 6 shows the effect of reaction time on methyl ester conversion. The reaction is carried out with 10:1 methanol to oil molar

100

80

Conversion

5.4. Effect of reaction time and temperature

Fig. 7. Effect of reaction temperature on conversion.

60

40

90 20

Conversion (%)

80

Egg shell derived CaO Li-1% Li-2% Li-3% Li-4% Li-5%

70 60 50

0 1

2

3

4

Run Fig. 8. Reusability study of Li-2% loaded catalysts.

40 30 6:1

8:1

10:1

12:1

14:1

100

Recycled Catalyst

methanol:oil molar ratio 90

100 95 90 85 80 75 70 65 60 55 50 45 40 35 30

Egg shell derived CaO

Li-1% Li-2% Li-3% Li-4% Li-5%

1

2

3

4

5

6

Reaction Time (in h) Fig. 6. Effect of reaction time on methyl ester conversion.

Transmittance (%)

Conversion (%)

Fig. 5. Effect of methanol/oil ratio.

80

70

60

50

40 4000

3000

2000

Wavelength (cm-1) Fig. 9. FTIR pattern of recovered catalyst.

1000

76


6. Catalyst reusability

Table 4 Physical and fuel properties of Mesua ferrea Linn biodiesel. Fuel properties

ASTM method used

ASTM D6751 (biodiesel)

Mesua ferrea Linn biodiesel

Acid value (mg KOH−1) Calorific value (kJ/g) Flash point (°C) Cloud point (°C)

D664 D5865 D 93 D 2500

0.5 33–40 100–170 −3.0 to 12

0.14 39.71 135b 4.3

ratio for 6 h in the presence of 5 wt.% catalyst amount and conversion is monitored in an interval of 1 h. It can be seen from the fig. that the conversion became almost constant after 4 h of reaction time. Therefore we have considered the optimum reaction time of 4 h for complete reaction. Transesterification of Nahor oil was carried out at different temperatures with optimum methanol to oil ratio, reaction time and catalyst amount. It was observed that maximum methyl ester conversion was obtained for the reaction temperature of 65 °C beyond which it decreased (Fig. 7). This decrease in conversion beyond 70 °C might have been cause by the loss of methanol at higher temperature.

One of the most important advantages of a heterogeneous catalyst over a homogeneous catalyst is its reusability. As the best activity was observed for Li-2% catalyst, reusability tests were carried out for Li-2% loaded catalysts only. The appearance of the catalyst was observed to be changed from white to dark brown after separating it from the reaction mixture. The recovered catalyst was washed with hot methanol to remove the organic impurity attached to it during reaction (unreacted oil, glycerol). The washed catalyst was dried followed by activation at 120 °C. It was observed that the catalytic activity decreased drastically in consecutive runs (Fig. 8). The possible reason for this loss in activity is derived from the fact that there must have been some catalyst loss during filtration and methanol wash or due to the pore blockage of the catalyst with reactant and product. It was expected that the recovered-methanol washed-catalysts were Li was loaded again and activated the initial activity could be regained. In order to investigate the reasons elaborately behind this decrease in activity infrared spectra study was used to characterize the recovered methanol-washed catalyst. FT-IR pattern for the recycled catalyst is shown in Fig. 9. From the figure, it can be seen that, recovered catalyst

Fig. 10. 1H NMR spectrum of (a) Nahor oil feedstock (b) Nahor oil biodiesel.


showed broad peaks around 3404.92 cm−1, which belonged to the OH group of glycerol. Moreover the important peaks observed at 2925.08 and 2856.05 cm−1 correspond to asymmetrical stretching and symmetric stretching of CH2 group respectively. The asymmetrical bending vibration of methyl group (δ as CH3) is found to overlap the scissoring vibration of methylene groups (δs CH2) at 1433 cm−1 whereas the strong and broad peak at 1116.44 cm− 1 corresponds to the C\O group of methyl ester. This indicates that the catalyst is totally covered with the product which in turn reduces the contact opportunity of the methanol and catalyst. Hence drop in catalytic activity is observed [25]. 7. Biodiesel analysis 7.1. Physical and fuel properties The fuel properties of synthesized Nahor oil biodiesel were determined according to the American Society for Testing and Materials (ASTM) and the results are presented in Table 4 along with the recommended values for biodiesel (ASTM-D6751). It can be seen from the table that the Nahor oil biodiesel produced in the presence of Li loaded

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egg shell derived catalyst has fuel properties within the limits of ASTM D6751for biodiesel. 7.2. NMR studies 7.2.1. 1H NMR analysis Biodiesel produced in the transesterification of Nahor oil was characterized by 1H NMR spectroscopy (Fig. 10). The frequency range between δ = 3 and 5 ppm (where δ is chemical shift) represents the resonances of the molecules containing oxygenates or the methoxy groups of FAME. The major difference between the 1H NMR spectra of the feedstock and resulting methyl ester formation is the disappearance of glyceride protons around 4.0–4.3 ppm and appearance of methyl ester protons around 3.6 ppm. As can be seen from Fig. 10(b) a single peak appears near 3.57 ppm and a multiplet peak corresponding to α-CH2 protons at 2.28 ppm appears which is related to methoxy group. These peaks confirm the presence of fatty acid methyl ester (FAME) in biodiesel. Biodiesel production is also confirmed from the decreasing peaks at 4.0–4.3 ppm which is due to the glyceride protons, Fig. 10(b). A triplet near 0.8 ppm in the spectrum appears for the

Fig. 11. 13C NMR spectrum of (a) Nahor oil feedstock and (b) Nahor oil biodiesel.

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terminal methyl protons, a strong signal at 1.2 ppm is related to the methylene protons of carbon chain, multiplet around 1.6 is due to the β-carbonyl methylene protons and the peaks around 5.3 ppm are assigned to the olefinic hydrogens respectively [26–30]. 7.2.2. 13C NMR analysis Fig. 11(a and b) represents the spectrum of 13C NMR of the Nahor oil and Nahor oil biodiesel respectively. The peaks at 61.94 and 69.09 ppm in the NMR spectrum of the Nahor oil were attributed to the \O\CH\ and \O\CH2\ functional groups of TAG. These two peaks disappear when methyl esters are formed and a new peak at 50.68 ppm appears which is associated with \OCH3 carbon Fig. 11(b). Characteristic peak of ester carbonyl (\COO\) appears at 173.33 ppm while the peaks around 131.02 and 126.46 ppm indicate the presence of unsaturated fatty acids in the 13C NMR spectrum of biodiesel. In the spectral region from (35–11 ppm) the peak from 28.88 to 29.40 ppm is related to \CH2\CH2\ group of FAME. Signal at 13.59 ppm was ascribed to the CH3 group of the methyl ester formed [27,29,31]. 8. Conclusion Investigation on Li doped egg shell derived CaO is carried out for the transesterification of M. ferrea Linn (Nahor oil) which is a nonedible feedstock. Under the optimum reaction condition of 2% Li loading, 5 wt.% catalyst amount, 10:1 methanol to oil ratio, 4 h reaction time and 65 °C reaction temperature, maximum biodiesel conversion was achieved. The catalyst was reusable and the drop in activity is attributed to the coverage of the catalyst surface by the product formed during the reaction. The initial catalytic activity is attributed to the formation mixed Li–Ca phase along with the presence of Li2O and CaO. Acknowledgment One of the authors, Jutika Boro is highly grateful to the University Grant Commission, Government of India for providing financial assistance in the form of Rajiv Gandhi National Fellowship. References [1] W. Xie, Z. Yang, H. Chun, Catalytic properties of lithium-doped ZnO catalysts used for biodiesel preparations, Industrial and Engineering Chemistry Research 46 (2007) 7942–7949. [2] J. Kansedo, T.K. Lee, S. Bhatia, Biodiesel production from palm oil via heterogeneous transesterification, Biomass and Bioenergy 33 (2009) 271–276. [3] U. Schuchardta, R. Serchelia, M.R. Vargas, Transesterification of vegetable oils: a review, Journal of the Brazilian Chemical Society 9 (1) (1998) 199–210. [4] A. Kawashima, K. Matsubara, K. Honda, Acceleration of catalytic activity of calcium oxide for biodiesel production, Bioresource Technology 100 (2009) 696–700. [5] B. Freedman, E.H. Pryde, T.L. Mounts, Variables affecting the yields of fatty esters from transesterified vegetable oils, Journal of American Oil Chemists' Society 61 (1984) 1638–1643. [6] S. Martino Di, T. Riccardo, P. Lu, S. Elio, Heterogeneous catalysts for biodiesel production, Energy and Fuels 22 (2008) 207–217.

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