Bio De Reactores
Enviado por azulita_chii • 13 de Abril de 2014 • 2.885 Palabras (12 Páginas) • 211 Visitas
D. Moutafchieva, D. Popova, M. Dimitrova, S. 4, 2013, 351-356Journal of Chemical Technology and Metallurgy, 48,Tchaoushev
EXPERIMENTAL DETERMINATION
OF THE VOLUMETRIC MASS TRANSFER COEFFICIENT
D. Moutafchieva, D. Popova, M. Dimitrova, S. Tchaoushev
University of Chemical Technology and Metallurgy
8 Kl. Ohridski, 1756 Sofia, Bulgaria
E-mail: dmoutaf@uctm.edu
Received 16 April 2013
Accepted 15 May 2013
ABSTRACT
The volumetric mass transfer coefficient (kLa) is often used in order to compare the efficiency of bioreactors
and as an important scale-up factor. In bioreactors, a number of methods are available for estimation the overall
volumetric oxygen mass transfer coefficient: the dynamic method, the steady-state method based on a preliminary
determination of the oxygen uptake rate, the gaseous oxygen balance, the carbon dioxide balance. Each method
provides a different estimation of the value of kLa. We examined the sensitivity of the various methods and compare
the kLa values obtained in order to select the most suitable method as a function of the type of bioreactor used. In
this work we applied dynamic gassing-out method for measuring the volumetric mass transfer coefficient kLa in
three type gas-liquid reactors (stirred tanks, bubble columns and airlift). Тhe aim of this work is on the basis of our
experimental data to obtain several correlations for evaluation of kLa.
Keywords: volumetric oxygen transfer coefficient, bubble columns, CSTR, airlift reactors.
INTRODUCTION
Aeration and agitation are important variables to
provide effective oxygen transfer rate during aerobic
bioprocesses. Hence, the knowledge of the volumetric
mass transfer coefficient (kLa) is required. The deter�
mination of kLa in a bioreactor is essential in order to
establish its aeration efficiency and to quantify the effects
of operating variables on oxygen supply.
Oxygen transfer in aerobic bioprocesses is essential
and any shortage of oxygen vastly affects the process
performance. Therefore, oxygen mass transfer is one
of the most important phenomena in the design and
operation of mixing�sparging equipment for bioreactors
[4]. It can be described and analyzed by means of the
volumetric mass transfer coefficient, kLa. The values of
kLa are affected by many factors, such as geometrical and
operating characteristics of the reactor (type of impeller,
the geometry of the bioreactor, the agitation speed and
the air flow rate), media composition and properties,
concentration and microorganism’s morphology and
biocatalyst’s properties [3].
In aerated systems the critical limiting factor in pro�
viding the optimal environment is the oxygen transfer
rate (OTR). The mass balance for the dissolved oxygen
in the well�mixed liquid phase can be written as:
dC L∗= k L a (C L − C L ) − rO2 = OTR − OUR
dt
(1)
When oxygen uptake rate, OUR = 0, the oxygen
mass balance in the liquid phase can be simplified to:
dCL∗= k L a (CL − CL= OTR)
dt
or
(2)
the oxygen mass transfer rate can be described as
proportional to the concentration gradient. For aerobic
fermentation the maximum value of the concentration
gradient is limited due to the low solubility of oxygen.
Therefore, the maximum mass transfer rate from the gas
to the liquid in the bioreactor can be estimated by kL a.CL
,
∗
351
Journal of Chemical Technology and Metallurgy, 48, 4, 2013
as CL is the saturation concentration in the liquid phase.
Integrating:
CL 2
CL1
∗
Hence a plot of of
∗ CL − CL1
ln ∗
CL − CL 2
vs. t should result in a straight line of slope kL a .
∫(
1
dC = kL a ∫ dt∗CL − CL0
t
)
(3)
∗ CL − CL1
ln ∗ = kL a.t
CL − CL 2
(4)
METHODS
...