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Oxygen transport enhancement by functionalized magnetic nanoparticles (FMP) in bioprocesses
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The enhancement of fluid properties, namely thermal conductivity and mass diffusivity
for a wide range of applications, through the use of nanosized particles’ suspensions
has been gathering increasing interest in the scientific community. In previous studies,
Olle et al. (2006) showed an enhancement in oxygen absorption to aqueous solutions of
up to 6-fold through the use of functionalized nanosized magnetic particles with oleic acid
coating. Krishnamurthy et al. (2006) showed a remarkable 26-fold enhancement in dye
diffusion in water. These two publications are landmarks in mass transfer enhancement
in chemical systems through the use of nanoparticles.
The central goal of this Ph.D. thesis was to develop functionalized magnetic nanoparticles
to enhance oxygen transport in bioprocesses. The experimental protocol for magnetic
nanoparticles synthesis and purification adopted in this thesis is a modification of
that reported by Olle et al. (2006). This is facilitated by employing twice the quantity
of ammonia, added at a slower rate, and by filtering the final nanoparticle solution in a
cross-flow filtration modulus against 55 volumes of distilled water. This modification in
the protocol resulted in improved magnetic nanoparticles with measurably higher mass
transfer enhancement. Magnetic nanoparticles with oleic acid and Hitenol-BC coating
were screened for oxygen transfer enhancement, since these particles are relatively
inexpensive and easy to synthesize. A glass 0.5-liter reactor was custom manufactured specifically for oxygen transport studies in magnetic nanoparticles suspensions. The
reactor geometry, baffles and Rushton impeller are of standard dimensions. Mass transfer
tests were conducted through the use of the sulphite oxidation method, applying
iodometric back-titration. A 3-factor central composite circumscribed design (CCD)
was adopted for design of experiments in order to generate sufficiently informative data
to model the effect of magnetic nanoparticles on interfacial area and mass transfer
coefficient. The parameters ranges used were: 250-750 rpm for stirring speed, 0-2 vvm
for aeration and 0-0.00120 g g−1 magnetic nanoparticles mass fraction.
It was found that 36 nm-sized nanoparticles produced during the course of this
dissertation enhanced the volumetric mass transfer coefficient up to 3.3-fold and the
interfacial area up to 3.3-fold in relation to gas-liquid dispersions without nanoparticles.
These results are concordant with previously published enhancement data (kLa enhancement
by 7.1-fold and a enhancement by 4.1-fold) (Olle et al. 2006). The magnetic
nanoparticles synthesized in this thesis were stable (constant diameter) over a 1wide
pH range (2-9). Statistical regression models showed that both kLa and a have high
sensitivity to the nanoparticles loading. Empirical correlation models were derived for
kLa and for interfacial area, a, as function of physical properties and nanoparticles loading.
These correlations lay out a methodology that can help the scientific community to
design and scale-up oxygen transfer systems that are based on nanoparticle suspensions.
Descrição
Palavras-chave
Oxygen mass transfer enhancement Magnetic nanoparticles Fe3O4 Oleate Hitenol-BC Sulfite oxidation