Guillaume Bastien Baur
Contamination of the environment by anthropogenic volatile organic compounds (VOC) became of major concern during the last decades. Present in gas streams of many industrial exhausts, they are harmful and detrimental for both human health and environment even at low concentration. Several techniques have been developed and applied for VOC abatement, e.g.: absorption, condensation, bio-filtration, photo-, thermal or catalytic oxidation. Although good performances were reported, they suffer from different drawbacks such as low efficiency at diluted concentration, difficult handling or low throughput. In this sense adsorption appears to be the most efficient method for complete removal of VOC from diluted streams. Various adsorbents were developed for VOC abatement such as activated carbon (AC), zeolites, silica or polymers. Although their efficiencies for certain VOC was shown, their abatement capacities can be reduced due to the lack of specific interactions. The approach taken in this thesis is based on the development of specific adsorbents towards VOC. The surface of commercial adsorbents is functionalized depending on the VOC physical properties aiming to create specific interactions. Activated carbon is a widely used adsorbent and received great attention for VOC removal due to their low cost and versatility. Because of their well-developed microporosity AC show large abatement capacity for non-polar VOC such as benzene or toluene even at low concentration. Generally used in the form of granules, powder or pellets, AC can present mass transfer limitations and flow mal-distribution (preferential gas passage or bypass through the adsorbent bed). To circumvent these drawbacks, activated carbon fibers (ACFs) consisting of arranged microfilaments are used in this work. First, the adsorption of toluene, as a model of non-polar high boiling point VOC, was studied over ACFs. The influence of the ACFs microporosity on the toluene adsorption capacity was addressed using two samples with different microporosity but similar surface chemistry. The influence of the pore size on the enthalpy of adsorption was evaluated through the modelling of adsorption isotherms measured experimentally. The adsorption enthalpy was also evaluated using simulation of toluene temperature-programmed desorption (TPD). The values obtained were then compared. Besides morphology, surface chemistry is known to influence the VOC adsorption capacity of ACFs. The influence of the surface oxygen content on the toluene and the acetaldehyde removal capacity was then evaluated. The increased concentration of O-containing groups affects toluene adsorption whereas it promotes the acetaldehyde removal. Specific functionalization of the ACFs surface was performed for the removal of polar VOC represented by formaldehyde and acetaldehyde. Taking advantage of their large specific surface area, ACFs were functionalized by diethylene triamine (DETA) via liquid layer deposition. ACFs with different DETA loading were synthesized and their adsorption capacity towards formaldehyde was evaluated. The influence of DETA loading on the adsorption capacity was measured and an adsorption mechanism was suggested. The deposition of nano-particles (NPs) of basic metal oxide on the ACFs surface was used for increased acetaldehyde abatement. By combining the high intrinsic adsorption capacities of metal oxide NPs and the large specific surface area of ACFs, an effective acetaldehyde adsorbent was
EPFL2015
