Optimization of the transesterification reaction in biodiesel production F. Ferel la a, * , G. Mazziotti Di Celso b , I. De Michelis a , V. Stanisci c , F. Vegliò a a Department of Chemistry, Chemical Engineering and Materials, University of L’Aquila, Monteluco di Roio, 67040 L’Aquila, Italy b Department of Food Science, University of Teramo, Via C.R. Lerici 1, 64023 Mosciano Sant’Angelo (TE), Italy c Fox Petroli S.p.A., Via Osca 74, 66054 Vasto (CH), Italy a r t i c l e i n f o Article history: Received 7 December 2008 Received in revised form 21 January 2009 Accepted 23 January 2009 Available online 14 February 2009 Keywords: Biodiesel Rapeseed oil Transesterification ANOVA a b s t r a c t In this paper response surface methodology (RSM) was used to study the transesterification reaction ofrapeseed oil for biodiesel production. The three main factors that drive the conversion of triglycerides into fatty acid methyl esters (FAME) were studied according to a full factorial design at two levels. These factors were catalyst concentration (KOH), temperature and reaction time. The range investigated for ea ch fa cto r was sel ect ed tak inginto ac cou nt the process of FoxPetro li S.p.A. An aly sis of va ria nc e (AN OVA) was used to determine the significance of the factors and their interactions which primarily affect the fir st of thetwo tra nsesteri fica tio n sta ge s. This analy sis ev ide nc ed thebest ope ra tin g con dit ion s of thefirst transesterification reaction performed at Fox’s plant: KOH concentration 0.6% w/w, temperature 50 C and reac tion time 90 min wit h a CH 3 OH to KOH ratio equal to 60. Three empirical models were derived to correlate the experim ental results, suitable to predict the behavior of triglyceride , diglyceride and monog lyceride concentration . These models showed a good agreement with the experimental results, demonstrating that this methodology may be useful for industrial process optimization. 2009 Elsevier Ltd. All rights reserved. 1. Introduction The problems that nowadays affect fossil fuels are well known: incr easi ng pric e tha t mak es petr oleu m no lon ger econ omi call y sus- tainable, emission of very dangerous pollutants for human health, emission of carbon dioxide that is the main reason of the global warming. Moreover fossil fuels are non-renew able resources, so they wi ll last for a lim ite d period of tim e. In th is scenari o ve ge table oils are more attr acti ve, beca use of the ir ren ewa ble nat ure and environmental benefits. Biodiesel is said to be carbon neutral, as biodiesel yiel din g pla nts absorb more carbon dioxide than tha t added to the atmosphere when used as fuel [1–4]. It is highly bio- deg rad able in fresh water as wel l as in soil. The best par t of biod ie- sel (9 0– 98 %) is mineralized in 21–28 da ys un de r aerobic or anaerobic conditions [5–7]. Furthermore, the use of biodiesel in diesel eng ines red uces the emi ssions of hyd roca rbo ns, carbon monoxide, particulate matter and sulphur dioxide. Only nitrogen oxides emission increases: this behavior is due to the oxygen con- tent of biodiesel [8–14]. However, vegetable oils have some disad- vantages. First of all, the direct use in internal combustion engines is problem atic . Due to the ir high visc osit y (about 11–17 times greater than diesel fuel) and low volatility, they do not burn com- plet ely and form deposits in the fuel inje ctor s of diesel eng ine [15,16] . An impr ovement on visco sit y can be ob tai ne d wi th tra ns e- sterification, which seems to be the process that assures best re- sult s in te rms of lo we ri ng vi scos it y an d impr ov in g ot he r characteristics [3] . Besides these tech nica l diffi cult ies, the re are som e so cia l pr ob lem s to be co ns ide red , as the extensiv e use of ve g- etable oils may cause starvation in poor and developing countries. As regards cataly st, potassium hydrox ide has been success ful in produ cing biodiesel at indust rial level [17]. Never theless, potas- sium hydroxide produces soaps by neutralizing the free fatty acid in the oil or by tr igl yce ri de sap onificati on . Th us, bio di ese l and gl yc- erine have to be purified by washing with hot distilled water two or three times, resulting in a high consumption of both time and water [3] . Unf ortunat ely, due to the ir pol arit y, soap s diss olv e in glycerol phase during the separation stage after the reaction, but they ma y be sep arated by me ans of a sim pl e cen trifuga tion. Fo rma- tion of soaps decreases biodiesel yield obtained after the clarifica- tio n and sep aration sta ge s. In ad dition, the dis sol ved so aps increase the meth yl ester solubilit y in glycero l, an additional cau se of yield loss[4] . Several types of vegetable oils can be used for the biodiesel production. In this paper rapeseed oil was studied, but there are no technical restrictions to the use of other kinds of veg- etable oils, although biodiesels coming from some vegetable oils may not fulfil quality standards [18–22] . In Italy diesel fuel consumption was about 26 million tons in 2007[23]. Considering that from every hectare of rape is possible to obtain around 1.1–1.2 tons of oil [24], the possibility of total substitu tion of diesel fuel with biodiesel is unlikely . However, veg- etables oil can represent a small contribution, if biodiesel and die- 0016-2361/$ - see front matter 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.fuel.2009.01.025 *Corresponding author. Tel.: +39 0862 43 4265; fax: +39 0862 43 4203. E-mail address: francesco.ferella@un ivaq.it(F. Ferella). Fuel 89 (2010) 36–42 Contents lists available at ScienceDirect Fuel journal homepage: www.elsevier.com/locate/fuel
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7/17/2019 Fuel Volume 89 Issue 1 2010 [Doi 10.1016_j.fuel.2009.01.025] F. Ferella; G. Mazziotti Di Celso; I. de Michelis; V. S…
Optimization of the transesterification reaction in biodiesel production
F. Ferella a,*, G. Mazziotti Di Celso b, I. De Michelis a, V. Stanisci c, F. Vegliò a
a Department of Chemistry, Chemical Engineering and Materials, University of L’Aquila, Monteluco di Roio, 67040 L’Aquila, Italyb Department of Food Science, University of Teramo, Via C.R. Lerici 1, 64023 Mosciano Sant’Angelo (TE), Italyc Fox Petroli S.p.A., Via Osca 74, 66054 Vasto (CH), Italy
a r t i c l e i n f o
Article history:
Received 7 December 2008Received in revised form 21 January 2009
Accepted 23 January 2009
Available online 14 February 2009
Keywords:
Biodiesel
Rapeseed oil
Transesterification
ANOVA
a b s t r a c t
In this paper response surface methodology (RSM) was used to study the transesterification reaction of
rapeseed oil for biodiesel production. The three main factors that drive the conversion of triglycerides
into fatty acid methyl esters (FAME) were studied according to a full factorial design at two levels. These
factors were catalyst concentration (KOH), temperature and reaction time. The range investigated for
each factor was selected takinginto account the process of FoxPetroli S.p.A. Analysis of variance (ANOVA)
was used to determine the significance of the factors and their interactions which primarily affect the
first of thetwo transesterification stages. This analysis evidenced thebest operating conditions of thefirst
transesterification reaction performed at Fox’s plant: KOH concentration 0.6% w/w, temperature 50 C
and reaction time 90 min with a CH3OH to KOH ratio equal to 60. Three empirical models were derived
to correlate the experimental results, suitable to predict the behavior of triglyceride, diglyceride and
monoglyceride concentration. These models showed a good agreement with the experimental results,
demonstrating that this methodology may be useful for industrial process optimization.
2009 Elsevier Ltd. All rights reserved.
1. Introduction
The problems that nowadays affect fossil fuels are well known:
increasing price that makes petroleum no longer economically sus-
tainable, emission of very dangerous pollutants for human health,
emission of carbon dioxide that is the main reason of the global
warming. Moreover fossil fuels are non-renewable resources, so
they will last for a limited period of time. In this scenario vegetable
oils are more attractive, because of their renewable nature and
environmental benefits. Biodiesel is said to be carbon neutral, as
biodiesel yielding plants absorb more carbon dioxide than that
added to the atmosphere when used as fuel [1–4]. It is highly bio-
degradable in fresh water as well as in soil. The best part of biodie-
sel (90–98%) is mineralized in 21–28 days under aerobic or
anaerobic conditions [5–7]. Furthermore, the use of biodiesel indiesel engines reduces the emissions of hydrocarbons, carbon
monoxide, particulate matter and sulphur dioxide. Only nitrogen
oxides emission increases: this behavior is due to the oxygen con-
tent of biodiesel [8–14]. However, vegetable oils have some disad-
vantages. First of all, the direct use in internal combustion engines
is problematic. Due to their high viscosity (about 11–17 times
greater than diesel fuel) and low volatility, they do not burn com-
pletely and form deposits in the fuel injectors of diesel engine
[15,16]. An improvement on viscosity can be obtained with transe-
sterification, which seems to be the process that assures best re-sults in terms of lowering viscosity and improving other
characteristics [3]. Besides these technical difficulties, there are
some social problems to be considered, as the extensive use of veg-
etable oils may cause starvation in poor and developing countries.
As regards catalyst, potassium hydroxide has been successful in
producing biodiesel at industrial level [17]. Nevertheless, potas-
sium hydroxide produces soaps by neutralizing the free fatty acid
in the oil or by triglyceride saponification. Thus, biodiesel and glyc-
erine have to be purified by washing with hot distilled water two
or three times, resulting in a high consumption of both time and
water [3]. Unfortunately, due to their polarity, soaps dissolve in
glycerol phase during the separation stage after the reaction, but
they may be separated by means of a simple centrifugation. Forma-
tion of soaps decreases biodiesel yield obtained after the clarifica-tion and separation stages. In addition, the dissolved soaps
increase the methyl ester solubility in glycerol, an additional cause
of yield loss [4]. Several types of vegetable oils can be used for the
biodiesel production. In this paper rapeseed oil was studied, but
there are no technical restrictions to the use of other kinds of veg-
etable oils, although biodiesels coming from some vegetable oils
may not fulfil quality standards [18–22].
In Italy diesel fuel consumption was about 26 million tons in
2007 [23]. Considering that from every hectare of rape is possible
to obtain around 1.1–1.2 tons of oil [24], the possibility of total
substitution of diesel fuel with biodiesel is unlikely. However, veg-
etables oil can represent a small contribution, if biodiesel and die-
0016-2361/$ - see front matter 2009 Elsevier Ltd. All rights reserved.doi:10.1016/j.fuel.2009.01.025