Dipartimento di Chimica Fisica ed Elettrochimica
Messrs
GranitiFiandre S.p.A.
Via Radici Nord, 112
42014 Castellarano (RE)
Italy
REPORT
Gaseous phase NOx removal tests on samples of
Orosei Active
- tests with plants in continual operation -
Prof. C.L. Bianchi, Dr C. Pirola
Milan, 14 February 2012
Prof. Claudia L. Bianchi
Docente di Chimica Industriale e Impianti Chimici
[email protected]
Introduction
GranitiFiandre S.p.A. (Castellarano, Reggio Emilia) commissioned a series of tests to assess and
quantify the photocatalytic activity of some of its products (ceramic tiles) towards the
photodegradation of the nitrogen oxides in the air in reactors operating in continuous flow
conditions. The test was performed by the team headed by Prof. C.L. Bianchi in the laboratories
of the University of Milan, Department of Physical Chemistry and Electrochemistry.
Continuous-Flow Test System
The test system used, illustrated in Fig.1, was designed in accordance with the ISO 22197-1
standard: “Fine Ceramics – Test method for air-purification performance of semiconducting
photocatalytic materials. Part 1: Removal of nitric oxide”. This system allows to investigate the
efficiency of a photocatalytic material in the removal of a specific pollutant. It consists of a
pollutant gas source, a photoreactor, an ultraviolet light source and a pollutant analysis device.
Fig 1: Experimental equipment
Key:
1
2
3
4
5
6
7
8
9
10
UV lamp
Reactor with optical window
Specimen slot
NOx gas cylinders
Compressor and filter
Mass flow meters
Gas mixer
Humidifier
Analyser
Pump
Key:
The supply of gas assures the continuous flow of air containing the required pollutant at a
specific concentration, temperature and humidity to the system.
The flow of each gas is controlled by means of mass flow meters, so to obtain the required
pollutant concentration and flow rate at the photoreactor intake.
The photoreactor is provided with a compartment where to lodge a flat sample 50 mm wide and
100 mm long, with the surface parallel disposed with regard to the optical window.
There is a gap of 5 mm between the sample and the optical window, through which the test gas
flows. In this way, it just has to pass through the space between the specimen and the window.
The window is specifically made in quartz, a material that absorbs a minimal amount of light in
Prof. Claudia L. Bianchi
Docente di Chimica Industriale e Impianti Chimici
[email protected]
the near-ultraviolet wavelengths.
The sample has to be 49.5 mm wide and 99.5 mm long to be inserted in this system.
Ambient light is simulated by a lamp above the reactor, which emits light in the UV-A region
with a power of 20 W/cm2. The nitrogen oxides, supplied by a gas cylinder in an initial amount of
500 ± 10 ppb (0.5 ± 0.01 ppm), are continually monitored, after the lamp is switched on, by
means of a chemiluminescence instrument (Teledyne) capable of exactly measuring the NO and
NO2 and the sum of these two compounds, defined as NOx.
Operating Procedure
Once the gas supply has been set at a concentration of 500 ppb, the sample is placed in the
compartment and the photoreactor with the quartz window is closed.
At this point the test gas is allowed to flow through an external circuit, bypassing the reactor, to
check the incoming NOx concentration. The gas is then fed through the reactor without
irradiation (dark condition) for about two minutes and the NOx concentration is recorded. If the
outgoing NOx value is lower than the 90% of the incoming concentration, the system is
maintained in dark conditions until the value returns within the set limits, so to allow the
complete physical adsorption of the pollutant on the sample and prevent downstream
adsorption, which might reduce the accuracy of the test.
At the end of the test, the irradiation is stopped and the flow of pollutant is turned off, leaving
the air flow in operation and measuring any NOx desorbed by the sample during the next thirty
minutes.
The analysed tile sample, Iris Ceramica Orosei Active, referred to below as Orosei Active, was
sampled and cut to the necessary sizes (as described above) from an original tile randomly
withdrawn from a new, completely intact pack.
In this test, the sample’s photocatalytic efficiency was measured using 4 different gas flow
rates, 32.4, 21, 9 and 4.4 l/h respectively, leaving the sample in a continuous flow of pollutant
for one hour (1 h) for each flow rate and monitoring the relative conversion.
The photoreactor intake flow rates were selected in order to maintain the same dynamic flow
conditions within the reactor at all the times. Reynolds number was specifically calculated for
each flow rate (see values in Tab.1) and laminar gas flows were confirmed in all cases.
Data Obtained
The table below (Tab.1) contains the Reynolds number calculated and the contact time
(reciprocal to spatial velocity) for each flow rate tested, allowing the assessment of the time for
which the pollutant remained in contact with the sample.
The final column contains the NOx conversion values.
Prof. Claudia L. Bianchi
Docente di Chimica Industriale e Impianti Chimici
[email protected]
Flow rate
NOx
conversion
Contact time
(l/h)
Reynolds
number
32.4
20
2.8
74.2
21.0
13
4.3
78.1
9.0
5.7
10.0
82.6
5.4
3.4
16.7
83.7
(s)
(%)
The obtained data reveal that the sample Orosei Active is always photocatalytically active in the
degradation of NOx in the gaseous phase. Its efficiency is increased if the pollutant gas flow is
reduced, allowing a longer contact time between the photo-active part of the material and the
NOx.
Conclusions
The sample OROSEI ACTIVE was found to be active in the photocatalytic degradation of nitrogen
oxides in the air.
Prof. Claudia L. Bianchi
Principal Investigator
Prof. Claudia L. Bianchi
Docente di Chimica Industriale e Impianti Chimici
[email protected]