HomeMy WebLinkAboutAppendix E- CAVITATION AS A NOVEL TOOL FORCAVITATION AS A NOVEL TOOL FOR
PROCESS INTENSIFICATION OF BIODIESEL SYNTHESIS
Mandar A. Kelkar, Parag R. Gogate and Aniruddha B. Pandit*
Chemical Engineering Department,
Institute of Chemical Technology,
University of Mumbai, Matunga, Mumbai – 400 019
* Corresponding author: Email: abp@udct.org Fax +91 22 24145614
Various products derived from vegetable oils have been proposed as an alternative
fuel for diesel engines. Today “bio-diesel” is the term applied to the esters of simple alkyl
fatty acids used as an alternative to petroleum based diesel fuels. Importance of biodiesel in
the recent context increases due to increasing petroleum prices; limited fossil fuel reserves
and environmental benefits of biodiesel (decrease in acid rain and emission of CO2, SOx and
unburnt hydrocarbons during the combustion process). Due to these factors, and due to its
easy biodegradability, production of biodiesel is considered as an advantage over that of fossil
fuels. The conventional techniques for the synthesis of biodiesel refer to a catalysed chemical
reaction involving vegetable oil and an alcohol to yield acid alkali esters and glycerol. Usually
waste vegetable oils as against virgin vegetable oil have been used for the synthesis with an
aim to reduce the cost of production (Zhang et al., 2003). The conventional techniques
typically utilize temperatures in the range of 70 to 200°C, pressures in the range of 6 to 10
atm and reaction times of up to 70 hours for achieving conversions in the range of 90 to 95%
based on the type of raw material used (usually mixtures of fatty acids obtained as waste). The
present work aims at using cavitation as an alternative technique for the synthesis of biodiesel.
Cavitation results in conditions of very high local temperatures and pressures at the same time
releasing free radicals which intensifies many chemical reactions (Gogate et al. 2003).
Esterification of Fatty acid (FA) odour cut (C8-C10) with methanol in the presence of
concentrated H2SO4 as a catalyst has been studied in hydrodynamic cavitation reactor as well
as in the sonochemical reactor.
The hydrodynamic cavitation
reactor consists of a reservoir or
a collecting tank with (10 lit)
capacity that is connected to the
multistage centrifugal pump
with power rating of 1.5 kw. A
schematic representation of the
setup has been shown in the
figure 1. The pipe connected to
the discharge side of the pump
branches into main and bypass
lines. The main line has the
facility to incorporate different
orifice plate to generate
cavitation of different intensities
and characteristics. The main
line and bypass line having the
throttling valves and pressure
P1
Figure 1: Schematic representation of the experimental
setup for hydrodynamic cavitation reactor
gauges for the adjusting the pressure. The operating temperature of the reactor was
maintained by circulating water within the jacket surrounding the tank as the energy
dissipated by the pump can increase the temperature of the mixture. The sonochemical reactor
used in the present work is a conventional cleaning tank type reactor equipped with 3
transducers at the bottom of the tank in triangular pitch and operates at an irradiating
frequency of 20 kHz and power dissipation of 120kW. Few experiments have also been
carried out with other acid/alcohol combination viz. coconut fatty acids with methanol and
ethanol and FA odour cut with fatty alcohols with an aim of investigating the efficacy of
cavitation for giving the desired yields and also to quantify the degree of process
intensification that can be achieved using the same.
The different reaction operating parameters such as molar ratio of acid to alcohol,
catalyst quantity have been optimized under acoustic as well as hydrodynamic cavitating
conditions in addition to the optimization of the geometry of the orifice plate in the case of
hydrodynamic cavitation reactors. It has been observed that ambient operating conditions of
temperature and pressure and reaction times of less than 3 hours, for all the different
combinations of acid/alcohol studied in the present work, was sufficient for giving more than
90% conversion. This clearly establishes the efficacy of cavitation as an excellent way to
achieve process intensification of the bio-diesel synthesis process. To cite a specific
illustration as regards to the degree of process intensification achieved in the present work,
with an operating ratio of FA cut (waste fatty acids) to methanol as 1:10, 0.1% by weight
loading of the catalyst and at operating temperature of 300C, 92% conversion was achieved
using hydrodynamic cavitation in only 90 minutes of reaction time whereas conventional
method for the esterification of waste cooking oil using methanol required about 69h to obtain
more than 90% oil conversion to methyl esters at 650C operating temperature and a molar
ratio of methanol to oil as 30:1 (Freedman et al., 1986).
Comparison of energy efficiencies of hydrodynamic cavitation reactors with
sonochemical reactors indicated that hydrodynamic cavitation is more energy efficient as
compared to acoustic cavitation. Depending on the type of acid/alcohol combination used in
the present work the energy efficiency for hydrodynamic cavitation varied in the range of 1 ×
10-4 to 2 × 10-4 g/J whereas for acoustic cavitation it was order of magnitude lower i.e. in the
range of 5 × 10-6 to 2 × 10-5 g/J. The obtained results are quite similar to those obtained in our
earlier works for cell disruption, hydrolysis of fatty acids and degradation of colored dye
effluents (Save et al. 1997, Pandit & Joshi, 1993 and Sivakumar & Pandit, 2002) clearly
establishing the superiority of the hydrodynamic mode for generation of cavities.
The present work has clearly illustrated the efficacy of cavitation as a novel tool for
process intensification of synthesis of bio-diesel which has been looked at an affordable
alternative to conventional petroleum based fuels.
References:
Freedman, B., Butterfield, R.O., Pryde, E.H., J. Am. Oil. Chem. Soc., 63 (1986), 1375
Gogate, P.R., Mujumdar, S., Pandit, A.B., J. Chem. Tech. Biotech., 78 (2003), 685
Pandit, A.B., Joshi, J.B., Chem. Eng. Sci., 48 (1993), 3440
Save, S.S., Joshi, J.B., Pandit, A.B., Chem. Engg. Res., Des., 75 (1997), 41
Sivakumar, M., Pandit, A.B., Ultras. Sonochem., 9 (2002), 123
Zhang, Y., Dube, M.A., Mclean, D.D., Kates, M., Bioresource Technology, 89 (2003), 1