Cleaning with catalysts

On repeated occasions we have read that volatile organic compounds are danaging for the atmosphere and to our health. This is why a group of researchers at the Leioa campus of the University of the Basque Country have put forward a process for “cleaning” these compounds before they are emitted into the atmosphere. Industry was chosen, amongst all the sources of these compounds, as the object for study.

To eliminate these compounds, they used catalytic oxidation, i.e. using oxygen from the atmosphere and, with the help of a catalyst, burning off the prejudicial compounds.

Catalysts, in this process, provide a number of advantages. On the one hand, they reduce the energy necessary for burning the contaminant compounds and, on the other, each type of contaminant gas has its specific catalyst. Nevertheless, for the combustion process to be effective, the catalysts have to comply with a series of requirements.

Where and when?

Catalysts usually have two basic components: the base and the active phase. The base usually involves a porous solid (in order to achieve the maximum surface for reaction). As regards the active phase, this is the compound that initiates the reaction, normally a metal such as platinum or palladium or, as in the case of the Leioa research, a zeolite.

In the process of catalysis, the contaminant gas enters the pores of the catalyst and it is there that it reacts with the active phase. Water, carbon dioxide and a halogenated compound are produced as a result of this reaction. This last product is subsequently neutralised in a shower of caustic soda. Thus, only H20 and CO2 are liberated into the atmosphere.

In this case the researchers worked with zeolite catalysts and the results obtained showed that the canals present within the structure of the zeolites are of great importance in the reaction.

Zeolites may have parallel or intercrossing; and it would seem that the zeolites with the second structure are better for this type of reaction. This is because an obstacle in a zeolite structure of parallel canals will prevent the gas passing through while this does not happen in the case of zeolites with a structure of intercrossing canals.

The kinetics of the reaction

But apart from the type of canal there are other characteristics that influence the reaction. Very important, for example, is the amount of contaminant gas, the quantity of catalyst used and the temperature of combustion. Two more factors are the kinetics of the reaction and its evolution.

Temperature, in fact, is one of the most important parameters. The lower the temperature of combustion, the less will be the energy spent.

The researchers are currently trying to establish the durability of the catalysts, i.e. to ascertain when active phase compound has to be replaced or renewed so that the “cleaning” of the volatile organic compounds continues to operate.