On the Dynamic Measurement of Dissolved Oxygen Concentration during
Liquid Phase Glycerol Catalytic Oxidation
R. Ducoulombier, P. Fongarland*, M. Capron and F. Dumeignil
Unité de catalyse et de chimie du solide, bâtiment C3, cité scientifique, 59655 Villeneuve d’Ascq, France
*pascal.fongarland@ec-lille.fr
Normalized Pressure or
Dissolved Concentration
Introduction. The progressive rarefaction of fossil resources has increased the interest on
renewable raw resources. Glycerol is a by-product of the reaction of transesterification of
triglycerides used for producing biodiesels. It can be valorized by liquid phase oxidation,
which yields added value compounds such as dihydroxyaceton or hydroxypyruvic acid. The
aim of this work is to enable more reliable kinetics studies of the liquid phase catalytic
oxidation of glycerol. In situ direct determination of the concentration in dissolved oxygen
using a specific probe at the reaction practical temperature (60-80 °C) and pressure (0.5 –
5 MPa of O2) is very useful for kinetic and external mass transfer coupling studies. This
paper deals with the interest of using a unique commercial probe for studying the liquid phase
glycerol oxidation reaction. Experimental. The measurements were performed in a 300 mL
stirred tank reactor in batch mode. The gas-liquid mass transfer coefficient (kLa) of oxygen in
glycerol-water mixture as well as the Henry coefficient (He) in the absence of chemical
reaction were first determined using the conventional physical absorption method (dynamic
pressure steps). The influence of liquid composition, temperature and pressure on the value of
kLa was studied. Subsequently, a Fugatron® probe (OXY-100 from LPD company) was
adapted to the reactor and successfully used for measuring the quantity of dissolved oxygen
with a calibrated mass spectrometer. Results. The Henry coefficient obtained for the O2-water
system (101.8 kPa at 25 °C and 0.5 MPa) was in good agreement with Gourich et al.
(101.6 kPa).1 He varied from 101 to
1,0
196 kPa with the water-glycerol mixture
0,8
composition. The kLa in the absence of a
chemical reaction was measured for
0,6
several mixture compositions, impeller
 O2 Pressure Response
rotation
rates,
temperatures
and
0,4
+ O2 Fugatron Response
pressures, which led values within the
0,2
range of 10-4 to 0.39 s-1. The Fugatron®
probe efficiency for measuring the
T90% = 38 s
0,0
oxygen dissolution extent was then
0
10
20
30
40
50
60
70
validated. Indeed, the results were similar
Time (s)
to those obtained by the dynamic pressure method, even if the response time t90%
(corresponding to 90 % of the saturation) for the probe was delayed at 38 s compared to 6 s
for the pressure response (Figure 1). However, this is much less than previous studies on H2
solubilization2,3 with a similar probe. Note that the presence of a slurry and gas bubbles had
no influence on the oxygen liquid concentration measurement. Conclusion. Direct in-situ
measurement of oxygen concentration in the liquid phase during glycerol oxidation reaction
in a slurry reactor containing gas bubbles is made possible by the use of the Fugatron® probe.
However, response time can be a limit especially for dynamic systems when the characteristic
time is lower than 30 s (typical reaction startup or kLa > 0.03 s-1).
1
Gourich, B; Vial, Ch.; El Azher, N.; Soulami, M.B.; Ziyad, M.; Biochemical Engineering J. 39, 1-14 (2008).
Meyberg, M.; Roessler, F.;. Ind. Eng. Chem. Res. 44, 9705-9711 (2005).
3
Schärringer, P.; Müller, T.E.; Kaltner, W.; Lercher, J.A;. Ind. Eng. Chem. Res. 44, 9770-9775 (2005).
2