Utilization of Crab Shells As Heterogeneous Catalyst in the Synthesis of Methyl and Ethyl Biodiesel

INTRODUCTION

Biodiesel is biodegradable and renewable fuel obtained through a chemical process called transesterification in which vegetable oil or animal fat (triglycerides) is reacted with an alcohol in the presence of a catalyst, and glycerin as a major co-product (Figure 1) is removed by decantation. Biodiesel has emerged as an alternative to replacing diesel oil by presenting similar combustion properties1 and minimize environmental pollution.2

Fig. 1. Transesterification reaction for biodiesel production. R1, R2 and R3 are a mixture of several fatty acid chains.

Among the catalysts, the mostly used in homogeneous phase is alkaline due to faster reaction and higher yields, requiring lower pressures, temperatures and molar ratio alcohol: oil.3 Nevertheless, the presence of free fatty acid (over 1.0 mg KOH/g) and water in the oil feedstock implies in soap formation, reducing the ester yield and inhibiting the biodiesel purification.3

As an alternative method of biodiesel production, the use of heterogeneous catalysts presents some advantages, such as easy separation from the reaction medium and reusability. The heterogeneous catalyst is separated by a filtration process instead of exhaustive washing, when homogeneous catalysis is used, reducing the volume of residual water and environmental impact.4 Nevertheless, heterogeneous catalysts have been proposed as a high operating cost.3, 5 Due to that, the biggest challenge in this area is to search for catalyst with a high performance and lower costs.

High interest has been shown regarding the use of CaO due to its economic advantages, high alkalinity, low solubility and easy handling.6 Despite recent and few numbers of papers published in this area, some of them presents as sources of CaO, the waste of natural products such as egg shells, bones, oyster shells of molluscs,7-9 resulted

from a calcination process since the bark of these species are composed of about 40-55% of CaCO3.10

Another challenge given to the productive sector of biodiesel takes place regarding the use of alcohol used in the transesterification reaction. On an industrial scale, methanol is the alcohol used for presenting a lower cost, and improved handling of the final product because of its low homogeneity biodiesel, thus allowing easy separation by settling.3 However it is a toxic alcohol, lethal, non-renewable, offers high risk of explosion and needs to be handled with great caution. Alternatively, ethanol has been studied as a promising possibility for not presenting these unwanted properties of methanol, furthermore ethanol is a renewable, providing greater environmental benefit to biodiesel.11

According to that, in this work we propose an environmentally friendly alternative for biodiesel production sector, studying the use of CaO obtained from food residue from crab shell as heterogeneous catalyst. A study of the kinetic of the reaction while using this catalyst in the synthesis of biodiesel, is done comparing both methyl and ethyl alcohol.

EXPERIMENTAL PROCEDURE

To obtain the catalyst, waste from crab shells obtained from local restaurants were used. The samples were previously washed, dried at 100 °C and ground in a blender resulting in a fine powder. Powder X-ray diffraction (PXRD) analyses of the samples were carried out on a Shimadzu XRD-6000, using a graphite crystal monochromator to select the Cu-Kα1 radiation source at λ = 1.5406 Å, with a step size of 0.02 s-1.

The transesterification reaction was carried out with 100 g of soybean oil, 5% (m/m) of the catalyst, a molar ratio alcohol/oil ratio of 12/1 (methanol or ethanol), magnetic stirrer and reflux temperature. Every hour during 8 hours, aliquots (6 mL) were picked and processed with a centrifugation up to remove the catalyst and formed glycerol, followed by evaporation of excess solvent emissions. The percentage of methyl and ethyl esters (% w/w) of the samples dissolved in CDCl3 was obtained by 1H NMR, using a 300 MHz Varian Unity Plus 300 spectrometer, as a relation between the converted esters and their respective triglycerides.

RESULTADOS E DISCUSSÕES: After calcination, the crab shells resulted in a white powder with a yield of around 41% (m/m). Analysis of diffraction patterns indicated that the crab shells before calcination has CaCO3 as the main constituent, while the crab shell after calcination at 900 ° C resulted in the CaO of high purity.

The samples collected during the reactions were analysed by 1H NMR and the percentage of fatty acid methyl esters (FAME) and fatty acid ethyl esters (FAEE) (% w/w) was determined as described at literature by Gelbard12 and Ghesti13, respectively.

From the analysis of the 1H NMR spectra of each sample was drawn a comparative curve of evolution of the levels of esters along the reaction when processed in methanol and ethanol (Figure 3). The content of the FAME reached 95% after 7 hours of reaction, while the level of FAEE even after 8 hours of reaction reached only 13%.

Fig. 3: Comparative kinetic study of the transesterification of soybean oil using CaO obtained from crab shell, producing the FAME and FAEE.

The minimum ester content proposed by EN 14214 is 96.5%. The results showed that the FAME obtained with the crab shell almost meet this standard specifications reaching 95% after 7 hours of reaction. Otherwise, the FAEE obtained with the same conditions, apart from the reflux temperature, presented an ester content of only 13% after 8 h of reaction. This result can be attributed to the lower reactivity of ethyl alcohol due to its lower acidity compared with methanol, and its greater steric hindrance.14, 15 However it can be seen that the kinetic reaction curve did not reach a threshold reaction time analysis, indicating that probably higher reaction time or in larger proportions of the catalyst, it is possible to obtain a better yield in the production of FAEE.

CONCLUSIONS

It was observed that CaO obtained through residue from crab shells has high purity after its calcination at 900 oC and revealed to be very efficient as heterogeneous catalyst at the transesterification reaction at the production of FAME. While used in a proportion of 5% led to a methyl ester content of 95% after 7 h of reflux. Nevertheless, the catalyst did not show the same performance in the production of FAEE, resulting in a conversion of only 13% after 8 h of reflux. These results indicate that the use of promising waste crab and probably several other crustaceans such as eco-friendly and sustainable alternative source for biodiesel production.

REFERENCES

1. Thaiyasuit P., Pianthong K., Worapun I., J. Oil Sci. 2012, 61, 81-88.

2. Hoekman S.K., Broch A., Robbins C., Ceniceros E., Natarajan M., Renew. Sustain. Energy Rev. 2012, 16, 143-169.

3. Lam M. K., Lee K. T., Mohamed A. R., Biotechnol. Adv. 2010, 28, 500-518.

4. Kawashima A., Matsubara, K., Honda K., Bioresour. Technol. 2008, 99, 3439-3443.

5. Refaat A. A., Int. J. Environ. Sci. Technol. 2009, 6, 677-694.

6. Kouzo M., Hidaka J., Fuel 2012, 93, 1-12.

7. Viriya-Empikul N., Krasae P., Puttasawat B., Yoosuk B., Chollacoop N., Faungnawakij K., Biores. Techonol. 2010, 101, 3765-3767.

8. Nakatani N., Takamori H., Takeda K., Sakugawa H., Bioresour. Technol. 2009, 100, 1510-1513.

9. Wei Z., Xu C., Li B., Bioresour. Technol. 2009, 100, 2883-2885.

10. Campana-Filho S. P., Britto D. D., Curti, E., Abreu F. R., Cardoso M. B., Battisti M. V., Sim P. C., Goy R. C., Signini R., Lavall R. L. Quím. Nova 2007, 30, 644-650. 11. Cavalcante K. S. B., Penha M. N. C., Mendonça K. K. M., Louzeiro H. C., Vasconcelos A. C. S., Maciel A. P., Souza A. G., Silva, F. C. Fuel 2010, 89, 1172.

12. Gelbard G., Brès O., Vargas R. M., Vielfaure F., Schuchardt U. E. J Am Oil Chem Soc. 1995, 72, 1239-1241.

13. Ghesti G. F., Macedo J. L., Resck I. S., Dias J. A., Dias S. C. L. Energy Fuels 2007, 21, 2475-2480.

14. Lang X., Dalai A. K., Bakhshi N. N., Reaney M. J., Hertz P. B. Bioresour. Technol. 2001, 80, 53-62.

15. Chemat F., Poux M., Galema S. A. J Chem Soc Perkin Trans 2, 1997, 2371-2374.