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Catalytic conversion of non-food oilseeds into methyl esters : traditional and ultrasound assisted techniques
No full textIntroduction
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
Learning distillation by a combined experimental and simulation approach in a three steps laboratory : Vapor pressure, vapor-liquid equilibria and distillation column
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No full textKinetic of esterification of diluted acetic acid with pure 2-ethyl-1-hexanol
No full textThe esterification of diluted acetic acid with pure 2-ethyl-1-hexanol is a purification process, involving a liquid-liquid-solid catalyst system, where streams of water containing small amount of acid are purified and the acetic acid is converted to a high commercial value ester at the same time. This process has been studied in a wide range of acetic acid (AA) concentration (6-15%, w/w). A maximum final conversion of 67% can be reached at 372 K. A mathematical model is here proposed: this takes into account all the diffusional and reactive steps between the aqueous and organic phases and from the latter into the pores of the solid catalyst. The relative importance of the different steps is fully discussed
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