Piotr M. Machniewski

Gas-phase oxidation of volatile organic compounds (VOCs) with the aid of ozone can be an attractive, energy-efficient way of treating exhaust gas streams in a low-temperature process, enabling the sustainable operation of industrial installations in a natural environment. This work is focused on the efficiency and kinetics of toluene oxidation with ozone towards CO₂ and H₂O in the presence of a SiO₂-supported cobalt catalyst. A kinetic model is proposed based on a simplified reaction mechanism, with the parameters determined from measurements carried out in a fixed-bed reactor at 40–65 °C under conditions ensuring negligible mass transfer resistance. The proposed model provided satisfactory agreement between the predicted and measured toluene and ozone conversion rates and the formation rate of CO₂, as well as in conditions when mass transfer resistance due to internal diffusion in the catalyst pellet was necessary to consider. The discussed results provide an assessment of the space velocity and ozone usage necessary to achieve a given degree of toluene conversion and mineralization to CO₂. The proposed model can be used for the design of a sustainable, low-temperature ozone-assisted catalytic process of VOC abatement.

The results of experimental study on effectiveness of gas phase total oxidation of toluene towards carbon dioxide and water with the aid of ozone over Co(II)/ SiO₂ catalyst are presented in this work. The main objective of the work was to determine ozone demand necessary for total mineralisation of toluene at the temperature range of 40 -100 °C chosen to minimise catalyst poisoning by water.Completemineralisation of toluene was possible if sufficient ozone/toluene ratio was maintained in the gas supplied to the reactor. For ozone/toluene molar ratios less than 20 the extent of toluene mineralization increased with temperature up to a plateau starting at approximately 60°C,which was caused by ozone shortage. Stoichiometry of the total oxidation of toluene with ozone indicates that only one oxygen atom in theozone molecule is used for the oxidation of toluene, to achieve complete mineralisation. Experimentally determined ozone/toluene ratio (20-25) necessary for the total oxidation of toluene was larger than the theoretical one mostly due to ozone losses resulting from its “unproductive” decomposition. At the range of lower values of mineralisation ratethe toluene oxidation proceeds according toa more efficient mechanism, indicating less ozone demand being between 6 and 18 moles of ozone per mole of toluene. A possible mechanism of toluene oxidation was suggested. The mechanism involves the formation of ^•OH radicals, which may explain the effectiveness of Co(II)/ SiO₂ catalyst in combination with ozone for the oxidation of toluene andother aromatic VOCsin a low-temperature process.

A mathematical model of waste tyre pyrolysis process is developed in this work. Tyre material decomposition based on a simplified reaction mechanism leads to main product lumps: noncondensable (gas), condensable (pyrolytic oil) and solid (char). The model takes into account kinetics of heat and mass transfer in the grain of the shredded rubber material as well as surrounding gas phase. The main reaction routes were modelled as the pseudo-first order reactions with a rate constant calculated from the Arrhenius type equation using literature values of activation energy determined for main tyre constituents based on TG/DTG measurements and tuned pre-exponential parameter values obtained by fitting theoretical predictions to the experimental results obtained in our laboratory reactor. The model was implemented within the CFD software (ANSYS Fluent). The results of numerical simulation of the pyrolysis process revealed non-uniformity of sample’s porosity and temperature. The simulation predictions were in satisfactory agreement with the experimentally measured mass loss of the tyre sample during pyrolysis process investigated in a laboratory reactor.

Electroflotation is used in the water treatment industry for the recovery of suspended particles. In this study the bubble formation and release of hydrogen bubbles generated electrolytically from a platinum cathode was investigated. Previously, it was found that both the growth rate and detachment diameter increased with increasing wire diameter. Conversely, current density had little effect on the released bubble size. It was also found that the detached bubbles rapidly increased in volume as they rose through the liquid as a result of decreasing hydrostatic pressure and high levels of dissolved hydrogen gas in the surrounding liquid. The experimental system was computationally modelled using a Lagrangian-Eulerian Discrete Particle approach. It was revealed that desorption of gaseous solutes from the electrolyte solution, other than hydrogen, may have a significant impact on the diameter variation of the formed bubbles. The simulation confirmed that liquid circulation, either forced or induced by the rising bubble plume, influences both the hydrogen supersaturation (concentration) in the neighbourhood of the electrode and the size of the resulting bubbles.

Ozonation of benzaldehyde in its aqueous solutions based on mechanistic approach and incorporating ozone decomposition model is presented in this work. As the basis the modified and extended HSB model of ozone decomposition with phosphates and carbonates reactions included has been applied. It was then tuned with the literature data and the results of our own measurements on ozone decay in aqueous solutions. The model was extended to model benzaldehyde oxidation reactions in the aqueous solutions. Model predictions compare favorably against experimental data obtained in the range of pH 2.3 to 8 with or without radical scavenger (t-butanol).

Measurements of the absorption rate of carbon dioxide into aqueous solutions of N-methyldiethanoloamine (MDEA) and 2-ethylaminoethanol (EAE) have been carried out. On this basis a mathematical model of the performance of an absorption column operated with aqueous solution of a blend of the above amines at elevated temperatures and pressures have been proposed. The results of simulations obtained by means of this model are described. The work is a part of a wider program, aimed at the development of a new process.

In this study the bubble size distribution and energy dissipation rate are measured in a plunging liquid jet bubble column. The maximum stable bubble diameter in the mixing zone was successfully predicted based on Weber number analysis. A Pareto analysis indicated that the coalescence of bubbles principally occurred as a binary process. The bubble number flux was modeled based on the bubble number concentration, collision frequency of two bubbles of the same diameter, and the probability of coalescence taking place. In general, the predictions were in good agreement with the measurements for both the mixing and pipe flow zones.