The ozone-initiated oxidation of m-xylene and 2-chloroethanol under solvent-free conditions was studied as a function of time. Gas chromatographic analysis of ozonated m-xylene showed an increase in the conversion of substrate from ca. 1% after 3 hours to approx. 14% after 24 hours. The presence of acetic acid, ethyl acetate or acetone during ozonation significantly improved the percentage conversion of m-xylene compared to similar products obtained under solvent-free conditions.
The presence of activated carbon during ozonation of m-xylene showed marginal improvement in percent conversion compared to ozonation without solvent. It was also found that ozonation of 2-chloroethanol gave quantitative amounts of chloride ions. The percentage conversion of 2-chloroethanol in the presence of acetic acid and ethyl acetate was higher than that under solvent-free conditions.
2-Chloroethanol in the presence of 5% hydrogen peroxide in water at pH levels 4 and 7 showed marginal changes in percent conversion compared to ozonation alone, however, percent conversion and product yield improved significantly when the pH of the solution was increased to 10 Where where use has been made of the work of others, it is duly acknowledged in the text.
CONCLUSIONS
70 : 30 ratio acetone : water versus ozonation time 88 Figure 4.0 Percentage conversion of 2-CE and product selectivity versus ozonation.
LIST OF TABLES
LIST OF SCHEMES
Introduction
Economic considerations continue to keep landfills as the most attractive option for disposal of household and industrial waste.1 Alternative waste disposal methods such as incineration and composting produce ash and slag fractions that must ultimately be disposed of.2,3 Despite the development of landfill technology since from open uncontrolled landfills to high-rise buildings designed to eliminate or reduce the potential harmful impact of waste on our environment, the generation of toxic contaminated leachate remains an inevitable consequence of the practice of landfilling waste. Leachate occurs when the moisture content of the waste exceeds its field capacity, which is defined as the maximum moisture that can be held in a porous medium without percolating downward.4 There are many factors such as seasonal weather fluctuations, disposal techniques, phase sequence, accumulation and compression methods etc. Leachate from industrial landfills is highly contaminated with volatile and non-volatile organic compounds and is characterized by the presence of significant amounts of difficult-to-treat compounds and "solid" COD (chemical oxygen demand).
Some of these are miscible, while a few contaminants are immiscible.9 Studies from developed countries have confirmed the presence of hazardous organic contaminants such as phthalates, phenols, pesticides, volatile compounds such as benzene, toluene, ethylene and xylene (BTEX), polyaromatics . hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) in leachate from municipal landfills.10,11,12 These hazardous organic compounds are primarily leached from the waste material sent to the landfill. Most of these compounds find their way into nearby streams, rivers and dams and pose a threat to aquatic life and humans. In this study, m-xylene and 2-chloroethanol were chosen as models, respectively PAH and organochlorine compounds.
Occurrence and uses of xylene
Properties of xylene
1,2-dimethylbenzene
- Xylene in the environment
- Transformation of xylene
- Biodegradation of xylenes
- Biofiltration
- Occurrence of halogenated organic compounds
- Properties of 2-chloroethanol
- Transformation of 2-chloroethanol
- Oxidation of organic compounds
- Properties of ozone
- History of ozone-organic chemistry
- Types of ozone attack
Since xylenes are only slightly soluble in water, only a very small proportion of xylene in the atmosphere is likely to be removed by precipitation. In the first case, the first step in the decomposition appears to be oxidation to the corresponding methylbenzyl alcohol. In the mixed culture, degradation of p-xylene occurred, although a long lag period was observed before degradation began.
In the experiments with Arthrobacter sp. decomposition of p-xylene was found to occur only in the presence of benzene and at a slow rate.89. In contrast, the concentrations of oxylene and p-xylene were only slightly reduced in the experiment. The biofiltration proved to be highly effective for removing xylene at a gas flow rate of 0.4 m3 h-1, corresponding to a gas residence time of 157 s.
The reaction of ozone with natural organic matter (NOM) can result in the formation of numerous byproducts. A very important period in the history of ozone chemistry began with Harry's first paper in 1903.
R 2 CHNH 2
Aqueous ozonation chemistry
This involves the decomposition of the ozone by means of a chain reaction mechanism that leads to the production of hydroxyl free radical species. The initiators of the free radical reaction are those compounds capable of inducing the formation of superoxide radical ions, O2 ∙ −, from an ozone molecule. The scheme shows that reaction of the hydroxyl ions with ozone produces one hydroperoxide radical (HO2·) and one superoxide radical ion (O2∙).
Hydroxyl radicals react with functional groups of organic solutes to form organic radicals that add O2 and then remove HO2∙ / O2·. Staechlin and Hoigne147 believe that the production of the highly ozone-selective O2· − ion promotes a chain reaction for the formation of free hydroxyl radicals OH·. The promoters of the free radical reaction are organic and inorganic molecules capable of regenerating the anion of the superoxide radical from the hydroxyl radical.
Species such as ·OOCH2COO∙ and CO32− “scavenge” the hydroxyl radicals produced, preventing the interaction between the OH· radical and ozone, leading to. Some of the most common inhibitors are bicarbonate ions, alkyl groups, tertiary alcohols and humic substances.
- Motivation for the study
- Hypothesis
- Objectives of the study
- Introduction
- Ozonation experiments
- Ozonation of m-xylene and 2-chloroethanol
- Ozonation of m-xylene and 2-chloroethanol in the presence of organic solvents
- Ozonation of m-xylene and 2-chloroethanol in the presence of acetic acid and ethyl acetate
- Ozonation of m-xylene in the presence of acetic acid in an aqueous medium
- Ozonation of 1 % m-xylene in the presence of acetic acid and acetone
- Ozonation of 1 % m-xylene in acetic acid and acetone in the presence of water
- Ozonation of m-xylene in the presence of activated carbon
- GC-MS analysis
- Gas chromatography analysis
- Extraction of carboxylic acids from product mixture
- FTIR analysis
- Calculation of conversion of substrate molecule after ozonation
- Calculation of selectivity and yield of products after ozonation
- Introduction
- Calibration of ozone generator
- Oxidation of m-xylene under solvent free conditions
- Product characterization for ozonation of pure m-xylene
- GC-MS analysis of m-xylene and product mixture
- FTIR analysis of product mixture
- Analysis of isolated products by 1 H NMR
- Ozonation of m-xylene in the presence of organic solvents
- Effect of acetic acid on ozonation of m-xylene
- Comparison of data for ozone initiated oxidation of m-xylene in acetic acid
- Effect of ethyl acetate on ozonation of m-xylene
- Comparison of data for ozone initiated oxidation of m-xylene in ethyl acetate
- Ozonation of 1% m-xylene in ethyl acetate
- Effect of activated charcoal on ozonation of m-xylene
- Comparison of data for ozone initiated oxidation of m-xylene in the presence of activated charcoal
- Ozonation of 1% m-xylene in the presence of water
- Reaction sequence for m-xylene ozonation
- Introduction
- Product identification for ozonation of 2-chloroethanol
- Chloride and Conductivity analysis of product mixture
- Analysis of the product mixture by 1 H NMR
- Analysis of the product mixture by GC-MS
- Analysis of the product mixture by FTIR
- Oxidation of 2-chloroethanol under solvent free conditions
- Ozone initiated oxidation of 2-chloroethanol in the presence of organic solvents
- Effect of acetic acid on ozonation of 2-chloroethanol
- Comparison of data for ozonation of 2-chloroethanol in the presence of acetic acid
- Effect of ethyl acetate on ozonation of 2-chloroethanol
- Comparison of data for ozonation of 2-chloroethanol in the presence of ethyl acetate
- Effect of activated charcoal on ozonation of 2-chloroethanol
- Comparison of data for ozonation of 2-chloroethanol in the presence of activated charcoal
- Ozone initiated oxidation of 2-chloroethanol in aqueous medium
- Effect of pH on the ozonation of 2-chloroethanol
- Comparison of data for ozonation of 2-chloroethanol at different pH levels
- Effect of activated charcoal on the ozonation of 2-chloroethanol in water
- Comparison of data for ozone initiated oxidation of an aqueous solution of 2-chloroethanol in the presence of activated charcoal
- Effect of hydrogen peroxide on ozonation of 2-chloroethanol in water
- Comparison of data for ozone initiated oxidation of an aqueous solution of 2-chloroethanol in the presence of hydrogen peroxide
- Reaction pathway for ozonation of 2-chloroethanol
- Conclusions
- Ozonation of m-xylene
- Ozonation of 2-chloroethanol
- Future work
No new product peaks were observed during the ozonation of 2-chloroethanol in the presence of 5 % acetic acid. The specific conductivity of the ozonated mixture in the presence of acetic acid was slightly higher. It is clear that the percentage conversion of 2-chloroethanol in the presence of 5 % ethyl acetate increases as the ozonation time increases.
It is clear from Table 4.8 that the percentage conversion of 2-chloroethanol in the presence of 20% ethyl acetate increases as the ozonation time increases. In this study, the ozone-initiated oxidation of 2-chloroethanol in the presence of activated carbon was investigated. The yield of the main products AcAlde and AA obtained in the presence of activated.
The ozonation of 2-chloroethanol in the presence of hydrogen peroxide in water at different pH levels showed interesting observations.
Hoigne J., “Aqueous ozone chemistry and pollutant transformation by ozonation and advanced oxidation processes. Jans U., Hoigne J., Activated carbon and carbon black-catalyzed transformation of aqueous ozone to OH radicals, Ozone Sci. Gomes M., Razumovskii S.D., Zaikov G.E., Effect of solvent polarity on the reaction rate of ozone with unsaturated compounds, Int.
