Catalytic conversion of non-food oilseeds into methyl esters : traditional and ultrasound assisted techniques

Introduction The most recent challenge concerning the biodiesel production deals with the processing of non-food, raw oils to make them suitable to be used as biofuels. For these oils several standardization processes are often required. The search for high efficiency transformation methods is therefore a key issue in this context. In this work, different kinds of non-edible oilseeds from crops such as Brassica juncea, Nicotiana tabacum and Cartamus tinctorius have been selected to be processed processed using traditional and ultrasound (US)-assisted methods. Experimental The oilseeds were deacified by free fatty acids (FFA) esterification and then wholly converted into methyl esters (ME) by transesterification. Sulphonic ion exchange resins Amberlyst®46 (A46) and Purolite®D5081 were used as esterification catalysts. Homemade catalysts of the kind SO4 =/TiO2-SnO2 (TiO2 loadings from 5 to 20%) and prepared by impregnation were also tested in the esterification. Both the reactions were carried out in slurry modality using the conditions reported in the Table 1. US experiments were performed using a tip-type sonicator at 20 kHz. ME yields were monitored through acid base titrations and GC analyses [1,2]. Software PROII (Simsci Esscor-Invensys) was used to perform process simulations. Results/Discussion FFA conversions close to 90% were achieved for all the oils deacidified on A46 and D5081, as already observed by the authors for other kinds of feedstock [3]. These catalysts were recycled for several times showing practically no deactivation This stable behaviour is due their peculiarity of being sulphonated only the external surface. This confers absence to mass transfer limitations and minimization of side products formation [4]. For these catalysts, a kinetic pseudohomogenous model [5] was used as for comparison with the experimental data: a very good correlation for different kinds of oils characterized by different initial acidities was achieved. This represent an important results for the esterification process scalability. The catalysts of composition SO4 =/TiO2-SnO2 resulted in less satisfactory performances than the ones obtained with the ion exchange resins. Moreover, they deactivated after few uses, probably due to the leaching of the active sulphate groups [6]. In Table 1 the results of both the esterification and transesterification reactions are displayed for traditional and US-assisted methods. Table 1. Conversion of an acid rapeseed oil: operative conditions and achieved results. Esterification catalyst: D5081, transesterification catalyst: NaOCH3. Reaction Method T (K) MeOH:Oil (%wt) Cat:Oil (%wt) Time (min) Conv. to ME (%) Est. Traditional 313a 338b 16:100 10:100 360 52.8a 71.2b US 313a 338b 16:100 10:100 360 77.3a 76.1b Trans. Traditional (2 steps) 333step1 333step2 20:100step1 5:100step2 1:100step1 0.5:100step2 90 step1 60step2 96.9 US (1 step) 293 20:100 1:100 30 86.6 The use of US allows to achieve higher ME conversions in the esterification at lower temperatures and in the transesterification. In the latter case shorter times and lower amount of reagents are required. For the different oils it was in general observed that the positive effect of US is more pronounced at lower temperatures, whereas at higher temperatures it does not seems to bring any advantage with respect to the traditional method. This suggests that at lower temperatures the acoustic cavitation effects are enhanced: it has in fact already been reported the existence of an optimum temperature for the occurrence of the acoustic cavitation in different reactive systems, oilseeds included [7]. In the US-promoted FFA esterification, these effects may be described in terms of the mechanical events enabled by the US waves inside the liquid reaction medium and in particular in the proximity of the catalyst’s surface. In the case of the homogeneously catalyzed transesterification, the high reactivity observed with the use of US may be ascribable to the effects caused by the acoustic cavitation in an homogenous medium, which generates very high local temperatures and pressures [8]. References 1. C. L. Bianchi, D. C. Boffito, C. Pirola, S. Vitali, G. Carvoli., D. Barnabè and A. Rispoli, Biodiesel/Book 1. ISBN 978-953-307-713-0, 2011. 2. C. Pirola, D. C. Boffito, G. Carvoli, A. Di Fronzo, V. Ragaini and C. L. Bianchi, Soybean/Book 2, ISBN 978-953-307-533-4, 2011. 3. C. L. Bianchi, C. Pirola, D. C. Boffito and V. Ragaini, Catal. Lett.., 134, 179 (2010) 4. C. Pirola, C. L. Bianchi, D. C. Boffito, G. Carvoli and V. Ragaini, Ind. Eng. Chem. Res., 49, 4601 (2010) 5. T. Pöpken, T. Götze and J. Gmehling, Ind. Eng. Chem, Res., 39, 2601 (2000) 6. D. C. Boffito, C. Pirola, and C. L. Bianchi, Chem. Today., 30, 42 (2012) 7. H. Lu, Y. Liu, H. Zhou, Y. Yang, M. Chen, B. Liang, Comput. Chem. Eng., 33, 1091 (2009) 8. K. S. Suslick, Science, 247, 1439 (1990)