(386g) Mixing Effects on the Reaction Kinetics and Dynamics of Saccharomyces Cerevisiae Mediated Glucose Fermentation to Bioethanol

Mixing
Effects on the Reaction Kinetics and Dynamics of Saccharomyces Cerevisiae Mediated
Glucose Fermentation to Bioethanol

Ashwin Gaikwad,
Department of Chemical Engineering, Visvesvaraya National
Institute of Technology, Nagpur-440010, India

Saikat Chakraborty,
 Department
of Chemical Engineering, Indian Institute of Technology Kharagpur, Kharagpur-
721302, India

Abstract

Conversion
of lignocellulosic biomaterials to valuable fuels and chemicals is seen to be
highly attractive because of the abundantly available lignocellulosic biomass.
To convert these biomaterials into fuels, enzymatic hydrolysis and fermentation
are proved to be most promising and environmentally benign processes. This work
explores the effects of mixing on the reaction kinetics and dynamics of Saccharomyces
cerevisiae-mediated fermentation of glucose to bioethanol at four different
mixing conditions, i.e., 0 rpm (no mixing), 40, 80 and 150 rpm (high mixing).
Based on the idea that mixing is one of the important process parameters to
influence bioethanol yield in fermentation, we explore the effect of mixing on
the reaction kinetics and dynamics of fermentation process using a coupled
experimental and modeling approach. The growth kinetics of S. cerevisiae was shown to be influenced by the mass
transfer mechanism and µ_Max and K_s were both increases
consistently with increase in the mixing speed. As the domination of ethanol
formation was seen only for the first 12 hours and after that ethanol
consumption by S. cerevisiae, attributes to the metabolic and
biomass structured model of glucose metabolism via
catabolic and anabolic pathways. The kinetic constant for ethanol formation (k₁)
increases with the mixing speed and attains a constant value at 80 rpm whereas
the kinetic constant for ethanol consumption (k₂)
increases monotonically up to 100 rpm and attains constant value
thereafter.  At a mixing speed of
80 rpm, the reactor operates in the intermediate regime, where both
mass-transfer and reaction kinetics govern the product yield, and we obtain the
maximum ethanol yield (4.32 mg/ml), which is 89% of the theoretical value. Thus, it was discovered that the
maximum ethanol yield was achieved in neither of the two asymptotic limits of
mass transfer limited asymptote (no mixing) or reaction limited asymptote
(complete mixing), but at moderate mixing conditions (in the intermediate
regime where both mass-transfer and reaction play determining roles). A mathematical model developed for the
proposed reaction scheme for the determination of ethanol yield at different
mixing conditions matches well with the experimental data confirms the validity
of our model for the batch reactor configuration.

Keywords:  Lignocellulose,
Mixing, Fermentation, Glucose, Mass Transfer, Ethanol