Global NEST Journal

The work deals with coal combustion in a pilot-plant fluidised bed (7 cm i.d.) under atmospheric conditions.
The aims are to capture and analyse qualitatively as well as quantitatively the volatile polycyclic
hydrocarbons emitted by using coal as energy source under various combustion conditions. After establishing
the sampling procedure, the emissions are caught in five different traps (two cyclones, nylon and
teflon filters, and XAD-2). The contribution of each of the sixteen polycyclic aromatic hydrocarbons
(PAH) listed by the US Environmental Protection Agency (EPA) as priority pollutants is analysed, and
their emissions as a function of the combustion variables (combustion temperature, percentage of
excess oxygen, air flow and fluidising agent) are reported. Synchronous Fluorescence Spectroscopy is
the analytical tool used for identification and quantification of the PAH emissions.

The present work investigates the hydrotreating process of a diesel in order to achieve lower sulphur and
aromatics content. The entire work was performed in a Hydrodesulphurization (HDS) pilot plant unit
located in Chemical Process Engineering Research Institute (CPERI). For the tests, a commercial HDS
catalyst (CoMo) was used while the feed was provided by the deep desulphurization unit of a Greek
refinery (Motor-Oil refinery). For the determination of diesel aromatics, a method based on the ASTM D-
2549-85 was applied. The objective of the work was to investigate the ability of a typical HDS catalyst for
aromatics saturation. The effect of the main hydrotreating operating parameters (T, P, WHSV, H2/Oil
ratio) on sulphur and aromatics removal was also investigated. In general, the data showed that the product
density and the aromatic and sulphur content of diesel decreased as the temperature or pressure increased
or space velocity decreased. It was concluded that with the present catalyst an aromatics saturation
degree of up to 40% could be achieved, giving a diesel product with aromatics content of about 20-25%
wt. However, high temperatures (>370°C) were required in order to achieve 500 ppmw sulphur in this
feedstock.

The soil adsorption behaviour of atrazine and its photodegradation intermediate 4,6-diamino-2-chloro-1,3,5-
s-triazine (I), was evaluated by measuring partition coefficients on five representative European topsoils using
classical batch experiments. From this study, (I) appears to be less immobilised than atrazine itself, especially
for typical agricultural soils. Consequently, (I) has a higher tendency to reach the saturated zones, and
hence, the groundwater. In order to remove atrazine and its degradation products from groundwater prior
to making it drinkable, photocatalytic degradation onto membranes immobilizing 30±3 wt.% TiO2 has been
investigated as a possible technology to mineralize these waters satisfactorily. For this purpose, experiments
have been carried out using a pilot-plant facility, with 0.02 - 0.10 mmol L-1 solutions of atrazine, as well as
of compound (I) and of 2,4,6-trihydroxy-1,3,5-s-triazine (II). When employing an excess of hydrogen peroxide
as the oxidizing agent, the monitoring of chemical oxygen demand (COD), as well as control by HPLC,
showed that (II) was a photostable degradation product, owing to its resistance to attack by hydroxyl radicals.
On the other hand, when kinetic runs were carried out onto membranes in the presence of dissolved
oxygen only or of sub-stoichiometric quantities of H2O2, (II) could be quantitatively mineralized. A mechanism
has been proposed, based on the possible direct involvement of holes in the irradiated semiconductor
surface, together with superoxide anions, these latter being produced by the reaction of conduction band
electrons with dissolved oxygen. This mechanism, which is inhibited by an excess of hydrogen peroxide,
owing to its reaction yielding hydroxyl radicals by any route, is also substantiated by previous experiments,
carried out in the presence of ozone, with and without photocatalytic promoters.

Estimates of the amount of secondary organic aerosol formed in the atmosphere from the degradation of
traffic C6-C12 hydrocarbon emissions in the city of Athens are presented. Around 1.26 tn of organic aerosol
is estimated to be produced during a six hours air pollution episode from the aromatic hydrocarbons,
the other NMHC groups contributing an additional 0.2 tn. The main contributor to the SOA production is
m-xylene. It accounts, together with toluene, for around 50% of the produced organic aerosol. The main
aerosol products that are expected to form from the Athens NMHC traffic mixture are nitrophenols. Due
to predominant wind flow to the S-SE direction in the area, a portion of these aerosols is likely to contribute
to the SOA burden of the marine atmosphere over SE Mediterranean. These results are also relevant to
ozone abatement strategies involving species-specific NMHC reductions and affecting fine particulate
composition and concentrations.