VOC Treatment using an hybrid process based on Adsorption-Ozonation

Among the many pollutants identified in air pollution problems are volatile organic compounds (VOCs). These are compounds that occur naturally in a gaseous state, or that evaporate easily at ambient temperature and pressure. Thirty-six percent of VOC emissions come from manufacturing industry, mainly due to the use of solvents, degreasers, preservatives...

The nuisance caused by these emissions can be direct (toxicological risks) or indirect (photochemical pollution). To combat this pollution, a number of protocols, directives and laws have been put in place at international, European and national level. Players in the various industrial sectors concerned have made major efforts to reduce solvent use and promote VOC recycling operations. However, the "clean technology" approach is not always enough, and it is often necessary to capture and treat these emissions.

Conventional treatment techniques available on the market fall into two categories:

• recuperative" processes, including absorption, adsorption, condensation and membrane processes;

• destructive" processes, including thermal and catalytic oxidation, biological treatment, photocatalytic processes and absorption with chemical reaction.

The choice of an appropriate treatment depends on many factors: the flow rate and VOC concentration, the nature of the molecules, the complexity of the mixture and, of course, the cost of its implementation and use. As these processes often come up against technological or economic limitations, new ones are emerging. Advanced oxidation processes (AOPs), for example, have been the focus of increasing research in recent years. Their aim is to create oxidizing species (atomic oxygen, hydroxyl radicals, etc.) that are highly reactive and not very selective in relation to the nature of the VOCs. Ozone can be a source of these oxidizing species.

The process developed here is a hybrid one, combining two techniques – adsorption on zeolites and ozone oxidation – in a single reactor, at ambient pressure and temperature. Zeolites were chosen as the adsorbent because of their chemical and thermal stability. More specifically, hydrophobic zeolites were chosen to overcome the problem of humidity in the effluents to be treated. During the adsorption phase, VOCs are continuously trapped in the porous zeolite matrix. A stream of ozonated air is sent sequentially through the reactor to oxidize the adsorbed VOCs and regenerate the material. Since oxidation takes place at room temperature, the formation of toxic by-products such as nitrogen oxides and dioxins can be avoided. All types of volatile organic compounds can a priori be treated by this process. The...