1. Analysis of oxygen transport enhancement
by functionalised magnetic nanoparticles (FMP)
in biopolymer production processes
Filipe Ataíde, Filomena Freitas, Maria Ascensão Miranda Reis, Rui Oliveira∗
CQFB/REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia,
Universidade Nova de Lisboa, P-2829-516 Caparica, Portugal
Introduction
Magnetic nanoparticles are usually found as suspensions of
nanosized particles composed by:
◮ a magnetic core (in many cases, an iron oxide) which
provides an easy recovery from different media (using
the HGMS technique as suggested by [1]
)
◮ a hydrophobic coating (usually surfactants or polymers)
confering colloidal stability to the particle.
(a) (b)
Figure 1: Sample of FMP’s in (a) an homogenous state and (b) under the influence of
a magnet.
Using different coatings, it is possible to provide further
properties to the magnetic nanoparticles and consequently
the fluid in which FMP’s are dispersed in, such as:
◮ Oxygen carriers
◮ Biomolecules scaffolds, etc.
FMP’s proved to be gas-liquid mass transfer enhancers[2,3]
not solely using oxygen soluble coatings such as oleic acid
but also with polymers not known to be oxygen carriers.
The potential transfer enhancements for which FMP’s are
becoming a popular tool in liquid-gas mass transfer en-
hancement experiments are:
◮ Random (Brownian) motion of the particles which leads
to microconvection in the surrounding fluid (kL)
◮ Coalescence inhibition (a)
◮ Facilitation of bubble break-up due to surface tension (a)
Application to biopolymers production
In fermentations, when the biopolymer is extracellular, the
broth apparent viscosity increases exponentially with the ac-
cumulation of polymer in the liquid phase. The more sen-
sitive parameters in fed-batch runs that are analysed in this
work and show the impact of FMP’s on mass transfer are:
◮ EPS concentration
◮ Aeration rate
◮ Stirrer speed
◮ Particles loading
Application to biopolymers production
(continuation)
Figure 2: Bioreactor during a fermentation – the milky aspect of the fermentation
broth is due to the high viscosity attained at the end of the batch.
Glycerol(g.L-1
)
5
10
15
20
25
30
35
40
45
Ammonium(g.L-1
)
0
0.2
0.4
0.6
0.8
1
1.2
Biomass,EPS
(g.L-1
)
0
2
4
6
8
10
12 pO2(%)
0
20
40
60
80
100
Time (days)
0 1 2 3 4 5 6 7 8
Figure 3: Profiles of a fermentation fed-batch run of Pseudomonas oleovorans:
glycerol – square, ammonium – circle, pO2 – dashed line, biomass – triangle and EPS
– diamond.
Figure 4: Viscosity of fermentation broth during fermentations
Transfer enhancement experiments
A chemical method can be used to perform preliminary ex-
periments for mass tansfer determination[2,4,5]
. This method
uses the sodium sulfite oxidation reaction in the presence
of Cu2+
or Co2+
catalyst, which is oxidised following the
reaction:
Na2SO3 + 0.5 O2
Cu2+
or Co2+
−−−−−−−→ Na2SO4
According to [5]
, it is possible to determine the absorption of
oxygen into a sulfite solution caused by a pseudo-nth
-order
reaction with the sulfite ions:
OUR = a C∗
O2
− CO2,bulk
2
n + 1
knC∗
O2
n−1
DO2,L + k2
L
(1)
The rationale to determine the volumetric mass transfer co-
efficient is to, firstly, garantee 3 conditions:
CO2,bulk = 0; Ha < 0.3; Ha ≪
CSO2−
3
zC∗
O2
(2)
If the concentration of Co2+
(catalyst) is under 1 × 10−5
M
(reaction not chemically enhanced[2]
), it is possible to as-
sume that the reaction rate is much slower than mass trans-
fer rate but still fast enough to consume all the oxygen in
the bulk solution. Thus, the 1 can be rewritten as
OUR = kLa · C∗
O2
= kLa · H · pO2,G (3)
For online monitoring of the sodium sulfite concentration a
recent approach suggested by [6]
was used which changes
the quantification method from iodometric titration to a UV
spectrophotometer absorption at 260 nm.
Sodiumsulfiteconcentration,CSO3
2-
(M)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Time (h)
0 0.5 1 1.5
Figure 5: Sodium sulfite oxidation batch runs for different stirrer speeds: black –
500 rpm, red – 300 rpm and blue – 0 rpm
Conclusions and future works
Nanoparticules may provide a window of opportunity on
productivity by decreasing the viscosity of fermentation
broth.
References
[1] A. Ditsch et al., 2005, High-gradient magnetic separation of magnetic nanoclusters, Industrial & Engineering Chemistry Research, 44 (17), 6824–6836.
[2] B. Olle et al., 2006, Enhancement of oxygen mass transfer using functionalized magnetic nanoparticles, Industrial & Engineering Chemistry Research, 45 (12), 4355–4363.
[3] S. Krishnamurthy et al., 2006, Enhanced mass transport in nanofluids, Nano Letters, 6 (3), 419–423.
[4] V. Linek and V. Vacek, 1981, Chemical-engineering use of catalyzed sulfite oxidation-kinetics for the determination of mass-transfer characteristics of gas-liquid contactors, Chemical Engineering Science, 36 (11), 1747–1768.
[5] P. Danckwerts, 1970, Gas-Liquid Reactions, Chemical Engineering Series, McGraw-Hill.
[6] A. Lewis and D. Roberts, 2005, New techniques for following the oxidation of sodium sulfite in mass-transfer studies, Industrial & Engineering Chemistry Research, 44 (1), 183–185.
Acknowledgements
This work was supported by the Portuguese Fundação para a Ciência e Tecnologia through a Ph.D. grant SFRH/BD/43956/2008.
rui.oliveira@dq.fct.unl.pt