Cyclodextrins: a potential absorbent for VOC abatement

The capacity of cyclodextrins in trapping VOCs is studied. Cyclodextrins (CDs) are a family of
cyclic oligosaccharides that are composed of α-1,4-linked glucopyranose subunits. The most
notable feature of cyclodextrins is their ability to form inclusion complexes (host–guest
complexes) in solution with a very wide range of solid, liquid and gaseous compounds by a
phenomenon of molecular complexation. Inclusion in cyclodextrins exerts a profound effect on
the physicochemical properties of guest molecules as they are temporarily locked within the
host cavity giving rise to beneficial modifications of guest molecules. Cyclodextrins are non
toxic compounds.
Volatile Organic Compounds (VOCs) are among the most common air pollutants emitted from
chemical, petrochemical, and allied industries. VOCs are one of the main sources of
photochemical reaction in the atmosphere leading to various environmental hazards; on the
other hand, these VOCs have good commercial value. There are many techniques available
to control VOCs emission (destruction based and recovery based) with many advantages and
limitations. Absorption is one of the recovery techniques with a removal efficiency of 95 to
98% but its applications are limited to hydrosoluble VOCs.
The measurements of vapour liquid equilibrium (VLE) data in absence or in the presence of
cyclodextrins were done. These data are needed to perform the design of an absorber for
process application. The determination of Henry’s law constant (Hc) was achieved with a
static headspace coupled with a gas chromatography (HS-GC). Moreover this technique
permits us to calculate the association constant in the aqueous medium between the volatile
solute and different cyclodextrins. The use of cyclodextrins may lead to a reduction of 95% of
the Henry’s law constant for some VOCs.
Dynamical studies were done by using impinger filled with an aqueous solution of
cyclodextrin. By contacting a contaminated air with this solution, we observed the transfer of
the VOCs from the gaseous phase to the liquid phase. These results show that by using
cyclodextrins as liquid solvent, absorption can be used for the removal of a large variety of
VOCs from gaseous effluents. The test in an absorber tower are also performed.