AREAS OF EXPERTIES - DEPARTMENT OF ENVIRONMENTAL CHEMISTRY

Laboratory of Thermal Studies

Biomass Investigations

The thermal decomposition and temperature – controlled combustion of various plant materials and solid biomass fuels are studied. The formed volatiles and the time and temperature dependence of the processes are investigated at various temperature programs (temperature – time functions) under laboratory conditions. We also study the gasification of biomass materials.

We can contribute to biomass R&D projects by the following activities:

• Obtaining detailed information on the partial processes of the combustion, gasification, charcoal formation and pyrolysis
• Exploring and characterizing the differences and/or similarities of the various biomass raw materials
• Determining the thermal properties of solid byproducts and intermediate productss of various biomass utilization technologies. This type of information is helpful in the understanding and optimization of the processes

Besides, we can

• Test the efficiency of the catalysts used to improve pyrolysis oils by fast, micro-scale experiments
• Determine self-ignition and other data in relation to the storage and transport possibilities of industrial charcoals and torrefied woods

Thermal decomposition of polymers, and waste plastic recycling

During decades of research activity we have accumulated a detailed knowledge on the thermal and catalytic decomposition of plastics and on the issues of environmental protection in plastic waste handling. From 1998 to 2005 we have been working in cooperation with partners from Belgium, Czech Republic, Finland, France, Germaly and Italy in two EU K&F projects that realised the construction of a pilot plant pyrolyser for recycling waste electric and electronic equipments and the dehalogenation of the oil products. Our main task has been in these projects the analysis of products for the optimization of the working parameters of the equipment.

We may assist K&F projects or provide cooperation based on our competence in the fields, as follows:

• chemical and thermal analysis of the waste to be recycled
• selection of adequate and feasible recycling technology according to the size of a planned plant
• laboratory scale experiments
• chemical analysis of the products of a pilot plant for the optimization of process conditions
• chemical analysis of the products of a recycling plant for the optimization of process conditions

Studies related to the combustion of solid fuels

We investigate two basic processes of the combustion of solid fuels in the kinetic regime:

• the formation of flammable gases and volatiles by pyrolsis
• the burn-off of the chars

In this way we obtain fundamental information on these processes and on the fuels studied. The results can aid the planning and optimization of combustors for fuels with irregular properties.

Equipment and special software:

• Thermobalance – mass spectrometer system (TG-MS). The sample is heated by various temperature programs. The changing sample mass is measured with high precisions during the experiments. The formed volatiles are analyzed simultaneously by a coupled mass spectrometer
• Pirolysis-gas chromatography-mass spectrometry (Py-GC-MS). Fast heating is applied to the set pyrolysis temperature and held for 10-30 s isothermal pyrolysis. The volatile products are purged on-line to CG-MS for separation and identification
• Software for the reaction kinetic analysis of TG and TG-MS data. Series of experiments are carried out at different experimental conditions, including different temperature – time functions and different oxygen concentrations in the ambient gas. The experiments are evaluated simultaneously, by the method of least squares, assuming multistep mechanisms

Atmospheric Chemistry Laboratory

The main research area of our group is the study of the kinetics and molecular mechanism of elementary chemical and photochemical reactions. For the most part, we investigate such processes and phenomena that play an important role in the complex interplay between climate change and the chemistry of the environment. A better understanding of such chemical and photochemical processes may help influence the environmental changes in a positive direction by providing scientific basis for judicious environmental legislative decisions.

We apply mainly the so-called direct experimental methods that we have implemented through several years of technical development in our group. Accordingly, the atoms, free radicals and electronically excited molecules under study are produced either by pulsed-laser photolysis or microwave-discharge dissociation of molecules in a fast flow of inert gas, and the processes are monitored by recording time-resolved spectra. The experimental results are interpreted and extended by quantum chemical and theoretical reaction kinetic computations. The kinetic and photochemical data determined experimentally are used as input parameters in the different atmospheric chemistry and combustion models through international co-operation.

The two main areas of our research are the following:

Kinetics of gas phase elementary reactions

We determine kinetic parameters, product branching ratios and structure-activity relationships for key uni- and bimolecular elementary reactions with relevance to the formation and further fate of reactive greenhouse gases in the atmosphere, the combustion chemistry of atmospheric fires and alternative fuels. With the study of these model reactions of practical importance, we address also fundamental questions in chemical kinetics, such as the temperature- and pressure dependence and the product yields for multichannel radical-radical reactions and the role of H-bonded "pre-reaction complexes" in the kinetics and mechanism of gas phase elementary reactions. Accurate enthalpy and entropy values for free radicals are determined experimentally by using the so-called "bromination-equilibrium" kinetic method.

Environmental photochemistry and photophysics

Our investigations are aimed at answering fundamental questions in photochemistry and photophysics, which, at the same time, are related also to practical environmental chemistry problems; experiments are carried out in both gas- and liquid phases. Comparison of the results obtained in gas- and liquid phases provides the possibility to a more general description of the specific solvent effects (polarity, viscosity, ion-strength, etc.) on photochemical and photophysical processes. A great part of the gas-phase studies are related to the atmospheric photochemistry of carbonyl molecules: the temperature and pressure dependence of photodissociation quantum yields are determined, the role of the first-excited singlet and triplet states are investigated in the photochemical mechanisms (contribution to the EU's atmospheric chemistry project SCOUT-O3). In the liquid phase, the main research subjects are the study of the relaxation kinetics of electronically excited molecules, photo-induced electron transfer processes and the effect of hydrogen bonding on photochemical and photophysical processes. The model systems selected for liquid-phase investigations have relevance for the aquatic environment and the photo-transformation of airborne organic aerosols.

Instrumentation

The most important instruments of our group are the different laser units: exciplex lasers (equipped also with vacuum-UV and IR optics), Nd:YAG lasers (equipped with 532-, 355- and 266 nm optics ) and dye lasers (tuneable range: 210-850 nm), as well as the other special light sources: mercury lamps, flash- and high-power Xe lamps and resonance fluorescence lamps. These light sources are operated as part of the reaction kinetics and photochemical measuring systems employed in basic research, but they have been used also for the purpose of applied studies and in industrial research contracts. The latter studies include, for example, the followings: qualification of the environmental acceptability of freon-substitutes and alternative fuels; water purification; flame-diagnostics, diagnostics of halogen lamps; photochemical synthesis of fine chemicals, industrial photochlorination and photo-oxidation; cosmetology. Further potential applications include: photodynamic therapy; laser ablation, polymer degradation, preparation of special surface layers; flow diagnostics; "field" atmospheric measurements; "green-chemistry" applications.

Expertise

Special knowledge and capabilities represented by members of our group are, for example, the following:

• Atmospheric chemistry, combustion chemistry, reaction kinetics, photochemistry, photophysics, spectroscopy
• Determination of kinetic parameters by using direct experimental methods, pulsed-laser photolysis and discharge flow
• Quantum chemical and theoretical reaction kinetic computation; development and testing of the mechanism of complex reaction systems
• Laser spectroscopy of atoms, free radicals and electronically excited molecules: luminescence, laser-induced fluorescence, UV-VIS transient absorption
• Photophysical kinetics of organic molecules displaying dual luminescence
• Thermodynamics and kinetics of hydrogen-bonded complexes
• Kinetics of photoreduction systems
• Photo-oxidation and relative-rate kinetic measurements in environmental photoreactors
• Development of instrumentation and methods for the analysis of atmospheric organics
• Organic photochemical synthesis and industrial photochemistry
• Purification of water applying photochemical and photocatalytic methods

Electrochemistry laboratory

In general, we are involved in electrochemistry projects of environmental protection significance: in particular, we study electrochemical processes being promising for removal of certain pollutants from groundwater. To this end we perform electrochemical kinetics measurement on various electrodes of electrocatalytic activity. Our related skills are as follows:

Electrochemical impedance spectroscopy (EIS) and related methods

• Dielectric spectroscopy, Faraday-distortion methods
• EIS for the study of various electrochemical kinetics problems (examples of the past five years: characterization of the electrochemical double layer and adsorption processes on the platinum-group metals; corrosion properties of metals; inhibitors; conversion layers; polymer coatings)

Theories on electrochemical kinetics:

• Noise analysis and its application in electrochemical kinetics
• Relation of electrode geometry and electrode kinetics; calculation of current density distributions and diffusion fields at various geometries

Electrocatalysis and corrosion:

• Developing metallic and bimetallic catalists along with their
• characterization by electrochemical means; catalytic oxidation of chlorinated hydrocarbons
• Bimetallic corrosion; cathodic corrosion protection; connection between corrosion and catalytic properties of metals; metal adsorption and its role in soldering and welding technologies

Development of instruments:

• Developing electrochemical instruments (examples of the past five years: bipotentiostat of femtoampere sensitivity for nanoelectrochemistry studies; development of various current meters for electrochemical scanning tunnelling microscopes, data aquisition systems)
• Construction of various industrial and/or laboratory measurement systems (examples of the past five years: measurement systems for electrical, optical, and spectroscopical quality control tests of metal-halide discharge lamps, for the GE Hungary)