Green Synthesis of Biodiesel from Grape Seed Oil using a Carbon-Based Solid Catalyst

FRANCISCO DAVID ÁVILA OROZCO; CLAUDIA E. DOMINI; BEATRIZ S. FERNÁNDEZ BAND

Golden, CO

Encuentro; 10th Annual ACS Summer School on Green Chemistry and Sustainable Energy; 2012

American Chemical Society

Background In Argentina, the production of grape is centered in the provinces of Mendoza and San Juan. An important amount of this fruit is used in the production of wine. Since the early ‘90s, this industry has experienced a steady increase as a result of the making of fine wines.  The main national wineries have made important investments for the conversion of strains and to improve the use of technology in winemaking processes. These actions have positioned the domestic industry as one of the best in the world. As a result of its activity, the wine industry generates a large amount of waste, which has to be properly handled to avoid possible environmental damage. However, this situation also offers the possibility of recovering some substances of commercial value. One of these substances is grape seed oil. The production of this oil involves the separation of skins and stones of grapes, the drying and grinding of seeds, and the final extraction and refining of the oil. In order to obtain 1 Ton of oil, 15 Tons of grape seeds are required. Given that grape seed oil is a byproduct, its production is conditioned by the production of grape. Therefore, the increase in production levels depends on the increase in the number of vineyards. The most important Argentine factories of grape seed oil are Olivi Hermanos and ICI Argentina [1].  Introduction Due to global warming and to the decline in the world oil reserves, biodiesel has gained over the last years an increasing importance as an alternative fuel. One of the most relevant aspects of biodiesel is the fact that it is obtained from biomass feedstock and it is for this reason considered a renewable source of energy. Besides being biodegradable, this biofuel contributes far less than fossil fuels to global warming because the carbon that composes it comes mostly from the carbon dioxide in the air. Besides, its emissions are essentially free of aromatic compounds, heavy metals such as Cd, Co, Cu, Pb, V and Ni and other pollutants, such as NOx and SOx which affect the quality of air [2]. Biodiesel is usually obtained by the transesterification between a triglyceride and an alcohol in the presence of an alkaline catalyst to produce fatty acid esters (FAME) and glycerol. An alkaline-catalyzed transesterification process is commonly adopted given that alkaline catalysts are more effective than acid ones. However, the use of an alkaline catalyst in the transesterification reaction presents certain disadvantages, such as the formation of soaps which could originate the emulsification of FAME and glycerol. A number of researchers have demonstrated the importance of the selectivity of the catalyst for the transesterification [3,4]. Moreover, the use of solid acid catalysts in the production of biodiesel has allowed the development of simple and economical processes. Zeolites, MCM-41, tungstated zirconia and silica-supported zirconium sulfate are among the most widely studied heterogeneous acid catalysts [5]. Recently, carbon nanotubes (CNTs) have emerged as an attractive material because of many interesting properties which are intimately related to their small size, cylindrical structure and length-diameter high aspect ratio [6]. Commonly, Multiwalled carbon nanotubes (MWCTNs) are massively produced because of their low price, and they could be used as effective precursors to generate a solid acid catalyst given that the sulfuric acid can be intercalated among the layers of the graphite [7].  Objetives The aim of this work is to develop an effective and green process for the synthesis of biodiesel from grape seed oil using functionalized MWCNTs as a carbon-based solid catalyst. To this purpose, MWCNTs should be functionalized by means of the treatment with sodium hypochlorite, nitric acid and sulfuric acid. Furthermore, the efficiency of the functionalized MWCNTs in the triglycerides conversion will be evaluated by the biodiesel percentage recovery. The different variables involved in the transesterification reaction, such as the type of catalyst and alcohol, catalyst concentration, oil/alcohol molar ratio, time and temperature of reaction, and the stirring mechanism will be optimized by means of the basis of experimental design.  Experimental procedure The procedure developed by Qing Shu et al. [8] was adapted and applied to the synthesis of biodiesel from grape seed oil using functionalized MWCNTs. The experimental procedure and the experimental variables are respectively shown in the scheme and table below. Sulfonated MWCNTs (s- MWCNTs) were used as carbon-based solid acid catalyst and they were prepared as follows: 2 g MWCNTs were merged in 50 mL concentrated sulfuric acid (96%) solution at 200 ºC under reflux and stirred for 10 h. After that, the suspension was filtered and the s- MWCNTs were washed and dried at 115 ºC for 2 h.  Conclusion The synthesis of biodiesel from grape seed oil using sulfonated multi-walled carbon nanotubes as a solid-based acid catalyst was achieved. The highest percentage of recovery (90% wt.) was achieved when the transesterification reaction was assisted by an ultrasonics bath. Given that the materials, reagents and equipment required for the process could be easily implemented, the experimental procedure proved to be an effective, economical and green alternative for the synthesis of biodiesel.  Acknowledgements The authors of this work would like to thank the financial support from Universidad Nacional and Proyecto Grupo de Investigación (PGI) granted by Secretaría General de Ciencia y Tecnología (Argentina). B.S. Fernández and F. D. Avila Orozco, wishes to thank Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET, Argentina).