Document Type

Theses, Ph.D

Rights

Available under a Creative Commons Attribution Non-Commercial Share Alike 4.0 International Licence

Disciplines

1.4 CHEMICAL SCIENCES

Publication Details

Successfully submitted for the award of Master of Philosophy to the Technological University Dublin in 2002.

Abstract

Rate constants (in units of 10-11 cm3 molecule-1s-1) were measured for the following reactions at 298+-2K and 1 atmosphere pressure using a relative rate technique. k(OH+Benzene)= 1.42+-0.1; k(OH+p-Xylene)= 15.9 +-2.5 k(OH+Toluene)=6.30+-0.15; k(OH+o-Ethyltoluene)=14.1+-1.1; k(OH+Ethylbenzene)=7.50+-0.72:k(OH+m-Ethyltoluene)=23.0+-1.5; k(OH+o-Xylene)=14.5+-3.1; k(OH+p-Ethyltoluene)=14.2+-1.0; k(OH+m-Xylene=23.1+-2.2: k(OH+1,3,5-Rimethylbenzene= 69.7+-4.3 The increase in reactivity with increasing degree of alkyl substitution on the aromatic ring supports the conclusions of previous studies that the dominant reaction pathway at room temperature for reaction of hydroxyl radicals with aromatic compounds is addition to the benzene rig. The rate data are compared with previous measurements and discusses in terms of structure-activity relationships The Photochemical Ozone Creation Potentials (POCPs) of selected aromatic compounds were investigated under simulated atmospheric conditions. The results show that the number of NO molecules oxidised per substrate molecule reacted varies for each aromatic but in all cases is great then two. The rate of NO oxidation and the time corresponding to the maximum O3 concentration correlates well with the reactivity of the aromatic towards OH radicals. These results have implications when implementing control strategies for VOCS. Rate constants (in units of 10-22 cm3 molecule-1s-1) were measured for the following reactions at 298+-2K and 1 atmospheric pressure using an absolute rate technique: k(03+Benzene) = 0.189+-0.027 k(03+Ethylbenzene)=1.05+-0.45 k(O3+Toluene)= 2.40+-0.51 k(O3+0-Xylene)=2.12+-0.13 Rate data were obtained by monitoring the decay of aromatic in the presence of excess O3. The observed decrease in the decay of aromatic with the addition of a radical trap (cyclohexane) provided indirect evidence for the occurrence of secondary reactions leading to enhanced aromatic consumption. By monitoring the relative rates of decay of pairs of aromatics it was shown that the reactive species was most likely the OH radical. Comparison of atmospheric lifetimes for reaction with O3 OH and NO3 radicals shows that ozonolysis of aromatics is insignificant under atmospheric conditions compared to reaction with OH

DOI

https://doi.org/10.21427/D7860R

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