estudio y caracterización de un plasma de microondas a presión ...

Destrucción de VOCs con plasma de Aire
of trichloroethylene. On the other hand, the uniformity of the C-Cl bonds in carbon
tetrachloride facilitates rupture and limits recombination.
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Concentration curves of carbon tetrachloride and trichloroethylene show an
exponential decline that ends at the same concentration; thus, the decomposition of
trichloroethylene is more efficient than the decomposition of carbon tetrachloride
because the decline in the C2HCl3 curve is more pronounced. To analyse this behaviour,
the parameter of decline, , can be calculated from the outlet concentration and the
amount of energy dissipated in the plasma [28, 29]:
where X is the VOC concentration after reaction and E is the deposited energy density
(applied microwave power/gas flow rate; J/L). β represents the energy density required
to reduce the concentration of trichloroethylene or carbon tetrachloride to 1/e of X0
(extrapolated zero Watts of microwave power) and is an indicator of the ease of
destruction.
Similar exponential behaviour was observed by Yan et al. [30] in a corona
plasma. These authors suggested that a linear recombination of the active species
produced VOC destruction. Thus, X0 corresponded to the initial concentration of
contaminant. However, in our case, X0 is several orders of magnitude lower (653 ppbv
for C2HCl3 and 1059 ppbv for CCl4) than the initial concentration (1000 ppmv for both
compounds), as shown in Figure 5.3. Thus, to fully explain the observed concentration
of contaminants, other destruction mechanisms that are independent of the power supply
must be relevant. One possibility is that chlorine released from the contaminants reacts
with Cu (I), which is introduced into the plasma from the tip of the torch.
The β parameter obtained for CCl4 and C2HCl3 was 9420 and 9397 J/L,
respectively; thus, β does not depend strongly on the concentration of the compound.
Rather, β is affected by the configuration of the plasma torch such as the flow rate,
microwave power and initial concentration, which makes the proposed device incredibly
versatile.