Rezultaty
A plasma catalytic test bench at the laboratory scale (1 to 3 L/min) was built. This test bench allows to precisely controlling the composition of the reactant flow (air, toluene, humidity). Analysis of the gas flow rate composition is made on-line by gas chromatography, specific ozone and NOx analyzers.
Plasma reactor is a packed bed DBD type of cylindrical design.
Four different catalysts [porous alumina (Al2O3), manganese oxide supported over porous alumina (MnO2/Al2O3; Mn=8.8 wt%), gold supported over zinc oxide (Au/ZnO; Au=0.3wt%) and N150 (Industrial catalyst, Süd Chemie)] have been tested in ozone and VOC (toluene) removal from air.
The catalysts were located downstream to the plasma reactor. The best results in toluene removal were obtained with MnO2/Al2O3. The best results in ozone removal were obtained with Au/ZnO. This catalyst is also the best one regarding the carbon balance in toluene removal (more than 90% of the toluene removed from the gas phase is transformed into CO2)
Regarding these results, the final catalysts would have to contain two kinds of active phase:
- Gold (nanodispersed gold particles) for CO2 selectivity and ozone removal
- Manganese oxide for toluene conversion.
The study carried out makes the inventory of pollutants and their impact on health. This first part of the document is based on a bibliographic work.
In a second part an inventory of pollutants already observed in vehicles is done. It addresses substances, which occur in vehicle environment. Three sources of contaminants are analysed:
- Outdoor pollution
- Materials
- Human activities
The study allows to aware citizen about in-vehicle environment and health impact. Results presented allow giving an overview of the substances observed in order to define specifications of the technical development.
The performance studies of commercially available cabin air filters were supplemented with laboratory studies on various electrostatic air cleaning techniques. Measurements were made with
- electrified fibrous filters
- electret filters (together with a corona charger)
- electrostatic precipitators
The experiments with the electrified fibrous filter (i.e. a fibrous filter exposed to an external electric field) indicated that an improvement of efficiency can be achieved in dry conditions. However, the combination of a contaminated filter material and high air humidity causes a significant degradation of efficiency. Thus, this technique was excluded from the further considerations.
The combination of the corona charger and an electret filter was found to provide quite good filtration performance. This system seemed to perform quite well also in the laboratory loading test, i.e. efficiency of the filter exposed to simulated test aerosol (diesel fume and ISO Coarse test dust) remained at a reasonable level. Laboratory experiments may, however, produce too optimistic picture about the performance, because the high concentration of electrically charged loading test aerosol generates strong electric fields, which will not occur in normal operation conditions. It seems that determining the true performance of corona charger & electret filter requires extensive field studies.
The experiments with cigarette smoke indicated that a significant degradation of electret filter efficiency took place, i.e. relatively low amounts of cigarette smoke caused a strong efficiency decrease. Thus, it seems that electret filters are unsuitable for conditions where filter becomes exposed to cigarette smoke. There is also some evidence that similar behaviour is observed when electret filter is exposed to fine combustion aerosol. Thus, it is very questionable if the good efficiency of the corona charger & electret air cleaning system could be maintained at all operation conditions.
The properties of the electrostatic precipitators were studied by using two commercially available devices and with two-miniature laboratory prototypes prepared for CLEANRCAB purposes. The results indicated that high efficiency for fine particles could be achieved with moderate pressure drop level. Also, it was observed that good efficiency could be achieved with the compact or miniature electrostatic collectors.
A plasma catalytic test bench, including a Valeo climate module was built, allowing testing flow rates in the 100 to 400 m3/h range. The plasma module and the electrical generator was provided by IUT (Institut für Umwelttechnologien Gmbh).
The COV (toluene) concentration can be varied from 1 to 100 ppmv.
The air-toluene flow passes first in the plasma module and then through the catalyst bed.
Analytical devices (gas chromatograph, ozone analyzer and NOx analyzer) allow to measure the gas composition before and after the plasma-catalytic module.
The VOC removal efficiency of the plasma-catalyst reactor was tested at the laboratory and real scale (HVAC test bench).
At the laboratory scale, 1 g of catalyst was used at a flow rate of 315 mL/min. The catalyst is located downstream to the plasma zone. The energy density used in plasma was maintained at 35 Wh/m3. The toluene concentration was 240 ppm.
Four catalysts formed by gold nanoparticles supported on active carbon were tested and compared to the effect of the plasma alone. The catalyst are:
- pure active carbon used without pretreatment (AC)
- Au (0.5 wt%) supported on active carbon (0.5Au/AC)
- active carbon without gold but after the same treatment than 0.5Au/AC
- Au(0.8 wt%) supported on active carbon supplied by World Gold Council (0.8AuWGC)
Compared to the plasma alone (toluene removal=45%), the use of a catalyst increases the toluene removal to more than 90%. Simultaneously, an increase in the CO2 selectivity was observed. The residual ozone concentration was less than 1 ppb for 0.5Au/AC (1.7 ppm without catalyst).
At real scale (120 m3/h; 1 ppm of toluene, 0.15Wh/m3, 20W, 25°C, RH=19%, 140 g of catalyst), the initial efficiency of the system plasma-catalyst (0.1Au/AC) was not higher than the performances of the AC filter alone (toluene removal=80%), but after more than 300 min in stream, the plasma-catalyst system presents stabilized efficiency at >70%, whereas the efficiency of the active carbon filter alone (less than 50%) continuously decreases with time on stream.
According to the fact that more energy than in car is available in heavy vehicle we have investigated the efficiency of the plasma-catalyst module in toluene removal until an energy density of 15 J/L (420W for 100 m3/h). We have shown that by increasing the energy density delivered in the plasma module a better efficiency in toluene removal of the plasma alone was observed, and by adding a specific catalyst (manganese oxide supported on active carbon), as high as 7 ppm of toluene can be totally removed with only a energy density of 15 J/L (420 W for 100 m3/h).
The value of 7 ppm of toluene is much higher than the highest possible VOC concentration in open polluted area. According to our experiments that have shown that the plasma efficiency in VOC removal increases when the VOC concentration decreases, we can expect that energy requested in real conditions will be lower. For example, for 100 ppb of toluene (0.1 ppm), and according to our predicting model, the same efficiency of the plasma module (50%), requests only 2 J/L (56 W for 100 m3/h). Concerning the catalyst, the amount deduced from the experimental data (0.3 g for 1.5 L/min) leads to 334 g for 100 m3/h.
These power and catalyst weight show that the plasma catalyst system could be used for largest vehicles than cars (trucks, buses, trains...) in which the constraints regarding the size and the energy consumption of the system are less severe than for cars.
There are no standards up to now for the in-vehicle environment. It is our understanding that in-vehicle air quality should meet the strictest ambient air quality standards set for the general population, which includes susceptible people.
The study provides recommendations for in-vehicle pollutant limits and pollutants to measure in order to obtain critical information for air quality in vehicles. The study is already finished.
Experimental results with plasma treatment in various conditions in order to evaluate performances on VOC destruction. The results have shown that the performances of the plasma module increase with the decrease of the pollutant concentrations. Nevertheless, plasma needs to be combined with an active catalyst to improve the process.
By combining the well-admitted conversion law:
1-X=exp(-Ed/b) and a kinetical approach of the reaction rate: r=k.[Tol]^a an euristic model can be deduced from experimental data.
This model allows to roughly predict the toluene conversion in function of the energy density and the initial toluene conversion.
For example, for an energy density of 2 J/L, the model predicts that the conversion of 1ppm of toluene will be 18%, whereas for an initial toluene concentration of 50 ppb, the conversion will reach 62%.
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