Tedlar

The subjects involved in the study breathed through a facemask connected to a valve of a resistance-free 1L plastic bag (Tedlar bag, SKC Ltd, Dorset, UK). One hour before sampling, eating and exercise were not allowed. The use of inhaled corticosteroids was stopped four weeks before the measurements except in 7 patients due to severe asthma symptoms. Children participated in the study were sampled randomly without division on healthy controls and children with wheezing. All samples from subjects taking part in this study were collected in the same room in order to prevent the appearance of a background bias. The plastic bags were emptied via pump with constant flow over a stainless-steel two-bed sorption tube, filled with carbograph 1TD/Carbopack X (Markes International, Llantrisant, Wales, UK) within 1 h after collection. The air-tight capped tubes were kept at room temperature until analysis (in average for three weeks). The capped tubes can be kept at room temperature up to six months without significant changes of VOCs profile. The bags were cleaned by filling and empting 2 times with nitrogen and reused for next measurements. In this study 1L of mixed breath (end-tidal and dead space air) was collected. Dead-space air comprises only a small part (30 ml) of the total sample of exhaled air collected and we have shown that the contribution of dead-space air to the total volume of whole breath does not lead to sensitivity issues in measuring VOCs by GC-tof-MS [28] (link).
The exhaled air samples were measured by means of GC-tof-MS [35] . All collected samples were measured randomly, i.e. the batch of 26 samples a random set of breath samples obtained from healthy controls and children with wheezing. The GC-tof-MS method applied here is a non-targeted GC-tof-MS method, i.e. no prior identification of the compounds was performed. All chromatographic conditions were optimized by us previously [28] (link) and consequently in consultation with the producer of our instrument and based on common chromatographic experience we chose a column and the temperature programming that were suitable to detect many different classes of volatile compounds and at the same time keep the best possible separation of the compounds at a high sensitivity and a high dynamic range. The detailed parameters of GC-tof-MS measurements are listed in Table 2.

The changes in resistance caused by the influence of CO gas and experimental conditions were measured using a home-made dynamic gas sensing setup. The gas chamber was crafted using a glass of 8-cc volume with inlet and outlet gas ports. Additionally, the calibrated concentration of testing gas kept in Tedlar bags was utilized to inject CO gas, maintaining a flow rate of 200 sccm. A program-controlled script was run using Alicat Mass Flow Controllers (MFCs) to achieve the target concentrations, while dry air was used as reference gas for sensing measurement. The sensors were sustained under the steady flow of dry air for 5 min before the target gas with various concentrations was exposed to the sensor chip for the script duration. Chemisensing measurements were characterized using a Keithley 4200A semiconductor parameter analyzer.

Figure 1 shows a schematic diagram
of the three-stage (i) pyrolysis, (ii) catalytic steam reformer, (iii)
and water gas shift reactor system used to produce hydrogen from waste
polypropylene. The first-stage (i) pyrolysis took place in a stainless
steel reactor, 30 cm in length and 2.5 cm in diameter, and heated
externally by a temperature-controlled electrically heated furnace.
The polypropylene (1.00 g) was loaded into a stainless steel crucible,
which was held in place in the center of the pyrolysis reactor. The
pyrolysis heating regime consisted of heating the reactor from 20
to 500 °C at 20 °C min^–1 and held at that
temperature for 20 min. The evolved pyrolysis hydrocarbons derived
from the thermal degradation of the polypropylene pyrolysis were passed
directly to the reforming reactor where catalytic steam reforming
took place in the presence of the 10 wt % Ni/Al₂O₃ catalyst (1.00 g). The reforming reactor was also constructed of
stainless steel (length 30 cm, 2.5 cm diameter) heated with a temperature-controlled
electrical furnace. The steam required for reforming was supplied
to the second-stage reactor via a water syringe pump (WPI SPLG100
syringe pump) to give a controlled input of steam. The temperature
of the second-stage (ii) reforming catalytic reactor was maintained
at 850 °C throughout the experiments.
The product gases from the second-stage (ii) reforming
reactor
were passed directly to the third-stage stainless steel (iii) water
gas shift reactor, of length 14.5 cm and 2 cm diameter, heated by
a temperature-controlled furnace. The product gases from the reforming
reactor consist of mainly hydrogen and carbon monoxide undergoing
catalytic water gas shift reaction in the presence of the metal–alumina
catalysts (0.50 g). Steam was generated from water added via a second
WPI SPLG100 syringe pump. The temperature of the water gas shift catalytic
reactor was an investigated process parameter, and temperatures between
250 and 650 °C were examined using each of the different metal–alumina
(Fe, Zn, Mn, Cu, Co) catalysts. Thermocouples monitored the temperatures
of the pyrolysis, catalytic steam reforming, and catalytic water gas
shift processes throughout the experiments. The three-stage reactor
system was continually purged with nitrogen at 100 mL min^–1, producing a nominal gas residence time of 88 s in the second-stage
(ii) reforming reactor and 26 s in the third-stage (iii) water gas
shift reactor. The gases leaving the reactor system were passed through
a series of water and dry-ice-cooled glass condensers to remove condensable
products, which consisted of mostly unreacted water (condensed steam).
The final product gases were collected in a 25 L Tedlar gas sample
bag.
The experimental procedure for the operation of the three-stage
reactor system involved initially heating the (ii) second- and (iii)
third-stage catalytic reactors to the desired temperature, 850 °C
for the (ii) second stage and investigated temperatures between 250
and 650 °C for the (iii) third stage. Once the catalyst reactor
temperature had been stabilized, the pyrolysis reactor was heated
to 500 °C at 20 °C min^–1 and held at that
temperature for 20 min. The heating of the first-stage (i) pyrolysis
coincided with the injection of steam into the (ii) reformer reactor
and the third-stage (iii) water gas shift reactor. The reactor system
was tested via many baseline experiments to determine repeatability
and reproducibility, and only negligible differences occurred between
experiments. Data reported here were the average of at least two repeat
experiments.