NAMS 2002 Workshop - ICOM 2008

Pervaporation and Vapor Permeation III – 5
Friday July 18, 4:30 PM-5:00 PM, Kaua’i
Treatment of Gas Containing Hydrophobic VOCs by a Hybrid Absorption-
Pervaporation Process: The Case of Toluene
F. Heymes, LGEI, Ecole des Mines d'Ales, Ales, France
P. Manno-Demoustier, LGEI, Ecole des Mines d'Ales, Ales, France
J. Fanlo, LGEI, Ecole des Mines d'Ales, Ales, France
E. Carretier (Speaker), Université Paul Cézanne Aix Marseille, Provence, France -
emilie.carretier@univ-cezanne.fr
P. Moulin, Université Paul Cézanne Aix Marseille, Provence, France
Recent legislation encourages industrialists to set up equipment for treating their
VOC-loaded gaseous effluents. For hydrophobic components such as toluene,
poor solubility in water requires specific absorbent. This work contributes to the
development of a hybrid absorption-pervaporation process to treat gases
containing hydrophobic compounds by coupling absorption and in-situ
membrane-based regeneration. The approach can be split into several parts. The
first part aimed to review hydrophobic absorption knowledge to determine an
efficient absorbent. Four chemical classes were tested (i) polyethylene glycols,
(ii) phthalates (iii) adipates and (iv) silicon oil. Experiments were performed to
check gas-liquid partitioning and viscosity. All missing experimental data were
determined, and this allowed selection of di(2- ethylhexyl) adipate (DEHA) as the
most attractive absorbent. Influence of temperature was correlated in the range
(20 to 70) °C. DEHA was shown to be efficient in other aromatic and chlorinated
VOCs. The second part examined the hydrodynamics and mass transfer of a
packed column fed with DEHA to eliminate the toluene from a medium-
concentration gaseous effluent (0.5-5g.m -3 ). The hydrodynamic study showed
that the viscosity of DEHA was not a technical obstacle to its implementation in
an industrial column. The absorption of toluene by DEHA showed the efficiency
of this process. But, this efficiency decreases quickly when the washing liquid
becomes loaded with toluene. From the point of view of mass transfer modelling,
we showed that mass transfer is limited by liquid-side resistance, which seems
logical since DEHA is a viscous absorbent. Our experimental results showed that
the kLa of the system depends on the liquid speed but also on the gas speed.
This behaviour has also been observed by the few authors who have used
viscous fluids in their experiments, but runs counter to all the authors who have
work on low-viscosity fluids: generally, they do not take into account the gas
speed. During the third pervaporation part, bibliographical research and a
preliminary theoretical evaluation led to the choice of PDMS for separating the
toluene / absorbent mixture, whatever the absorbent. PDMS has a high affinity
for toluene and a lower affinity for the different absorbents. The permeability of
the toluene was evaluated at 25°C and confirmed the potential of PDMS for
recovering toluene. Experiments led with the various pure absorbents showed