Chemical and Biomolecular Engineering - Theses
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ItemAqueous-phase oxidation of brown-coal dewatering effluent using phenol as a model( 1982)Victorian-brown-coal dewatering effluent has been shown to contain quantities of phenol which would prevent its direct discharge to any water course. A proposal to oxidize this effluent, using oxygen, to less toxic compounds or more readily biodegradable material, has been investigated. A rapid-mixing stopped-flow apparatus, capable of examining the reaction between dissolved oxygen and aqueous phenol solutions under conditions of elevated temperature and pressure, has been designed and constructed. The phenol/oxygen reaction has been investigated at temperatures between 150°C and 225°C and under conditions of excess oxygen, excess phenol and near the stoichiometric ratio. An analytical system comprising a High-Performance Liquid Chromatograph has been developed and some reaction products not previously isolated from the phenol/oxygen reaction system have been identified. The experimental results have led to the development of a reaction pathway for phenol oxidation by oxygen. Reaction steps in the mechanism which are critical in determining the reaction product distributions and those that can be considered as rate limiting have been determined. The reaction pathway for oxidation of phenol by oxygen and published information for oxidation of phenol by ozone are used to develop a reaction pathway for ozone oxidation. The phenol/oxygen pathway is also used to propose several strategies for the operation of a brown-coal dewatering effluent treatment plant.
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ItemCarbon monoxide attack on brown coal( 1981)The attack of carbon monoxide on a Loy Yang brown coal of medium-light lithotype in the presence of water and sodium carbonate as a catalyst was investigated. The equipment used was a one-litre magnetically stirred stainless steel autoclave. The operating parameters studied were reaction temperatures ranging from 300 to 3750 C, initial carbon monoxide pressures from 500 to 1200 psig, sodium carbonate level from 1 to 15 gm and reaction time from 0 to 3 hours.* Separations of the oil yields into further fractions, i.e. pre-asphaltenes, asphaltenes and maltenes were carried out and their properties in terms of elemental compositions, molecular weights and structural parameters were determined. The results show that a relationship exists between oil yield and conversion and between hydrogen consumption and conversion. The theoretical maximum oil yield possible, assuming a hypothetical 100% conversion is postulated to be 64% of d.a.f. coal. Within the operating range studied, the maximum oil yield achieved is 51.3% ± 3.4% of d.a.f. coal and the corresponding hydrogen consumption is 0.76 ± 0.05 moles per 60 gm of d.a.f. coal; the optimum process conditions being: reaction temperature 350-375°C, reaction time 2 hours, initial carbon monoxide pressure 1000 psig and sodium carbonate level 10 gm. However, conversion is found to increase with severity of process conditions. Hence, for this series of runs, the maximum conversion achieved is 83.6% ± 0.4% and the corresponding hydrogen consumption is 0.80 ± 0.04 moles per 60 gm of d.a.f. coal; the process conditions being: reaction temperature 375°C, reaction time 3 hours, initial carbon monoxide pressure ~50 psig and sodium carbonate level 10 gm. Increasing the reaction temperature, especially from 350 to 375°C and to a lesser extent reaction time appear to reduce the degree of substitution of the aromatics and increase the aromaticity, hence the number of fused rings in the pre-asphaltenes, asphaltenes and maltenes are increased correspondingly. More maltenes are formed at the expense of pre-asphaltenes and asphaluenes, indicating that these conditions tend to promote dehydrogenation and hydrocracking activities. Increasing the carbon monoxide pressure and catalyst level on the other hand, have the opposite effect, as they favour the hydrogenation of the aromatic rings and the formation of more hydroaromatic structures. Furthermore, they tend to promote the formation of more phenols and phenolic acids. The study of the kinetics has shown that the coal liquefaction process can be satisfactorily represented by a pseudo third-order reaction model for temperatures at 325, 3~0 and 3750 C. except that mass transfer or incomplete decomposition interferes at 3250 C. Mathematical models representing these reaction kinetics at 350 and 3750C have been developed accordingly, resulting in a reasonably good agreement between the models and the experimental data. Finally the results obtained have led to a better understanding of the mechanism of the carbon monoxide-water liquefaction process. It has been found that sodium catalyses the water-gas shift reaction which in turn produces the activated hydrogen required for the stabilization of the reactive fragments. Since the shift reaction is catalytic and the sodium is chemisorbed by the coal particles.the stabilization of the reactive fragments by the activated hydrogen is believed to be taking place intimately and efficiently at the coal surface. It is estimated that this reaction accounts for most of the liquefaction process. The other less significant mechanisms which/are also bel1ieved to be relevant are the formate and hydride-transfer reactions, Kolbe-Schmitt synthesis and carbonization. © 1981 Dr. Chia Nien Bien